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T E C H N I C A L M A N U A L
index 1
CONTENTS PAGE
DTM/E/2Ed/Nov01
INTRODUCTION ..............................................................................................01
Chemical Structure ......................................................................................01
General Characteristics of Standard Lucite Diakon Grades ........................01
General Characteristics of Toughened Lucite Diakon ST Grades ................02
The Lucite Diakon Grade Range ..................................................................03
DATA FOR DESIGN ..........................................................................................06
Mechanical Properties ..................................................................................06
Thermal Properties ......................................................................................14
Flammability ..................................................................................................14
Electrical Properties ......................................................................................15
Optical Properties ........................................................................................15
Chemical Resistance ....................................................................................21
Permeability ..................................................................................................23
Melt Flow Behaviour ....................................................................................23
Sound Insulation ..........................................................................................27
Water Absorption ..........................................................................................27
INJECTION MOULDING ..................................................................................29
The Injection Moulding Process....................................................................29
Design of Components for Moulding ............................................................31
Multi-Coloured Mouldings ............................................................................32
Mould Design ................................................................................................33
Moulding Technique ......................................................................................41
Distortion ......................................................................................................48
Mouldflow Simulation ....................................................................................49
Moulding Fault Remedies ............................................................................56
index 2
CONTENTS PAGE
DTM/E/2Ed/Nov01
EXTRUSION ......................................................................................................58
Extruder ........................................................................................................58
Sheet Extrusion ............................................................................................59
Co-Extrusion ................................................................................................60
Production of Extruded Sheet ......................................................................61
Lighting Diffuser Profile Extrusion ................................................................62
Tube Extrusion ..............................................................................................65
Fabrication of Sheet Extruded from Lucite Diakon ......................................66
Extrusion Fault Remedies ............................................................................67
FINISHING, COLOURING AND DECORATING ..............................................68
Machining......................................................................................................68
Cements and Adhesives ..............................................................................69
Ultrasonic Assembly......................................................................................70
Hot Surface Welding ....................................................................................72
Stresses and Molecular Orientation in Lucite Diakon Components ............72
Cleaning........................................................................................................76
Antistatic Treatment ......................................................................................76
Automotive Signal Lamp Lens Colours ........................................................76
Decoration of Lucite Diakon..........................................................................80
HEALTH, SAFETY AND ENVIRONMENTAL ASPECTS OF LUCITE DIAKON ....82
APPENDICES....................................................................................................83
APPENDIX I ACRYLIC SPECIFICATIONS ..............................................83
APPENDIX II ADDRESSES ......................................................................84
APPENDIX III VOLATILE CHEMICALS EVOLVED DURING
PROCESSING OF LUCITE DIAKON ..................................85
EUROPEAN SALES OFFICES ........................................................................86
page 1
INTRODUCTION
Lucite Diakon is the trade mark for the range of
acrylic moulding and extrusion polymers made by
Lucite International based on poly methyl
methacrylate (PMMA).
CHEMICAL STRUCTURE
Poly methyl methacrylate is an atactic polymer and
since the methyl and the ester groups are incapable
of being interchanged in a crystal lattice these
polymers are therefore amorphous and transparent.
Since the substituents on the α-carbon atom restrict
chain flexibility, and since the side groups are polar
and relatively small, there is fairly substantial inter-
chain attraction. The polymer is therefore hard and
rigid with a glass transition temperature of 110°C.
The ST grades of Lucite Diakon have properties
modified to give greater toughness and resistance
to environmental stress cracking and crazing
compared with the basic grades. At the same time
the excellent transparency of the basic range has
been largely retained.
Methyl methacrylate monomer is produced by
several manufacturing processes, the most
common of which involves the following stages:
1 Acetone is reacted with hydrogen cyanide to
form acetone cyanhydrin:
GENERAL CHARACTERISTICS OF STANDARD
LUCITE DIAKON GRADES
Clarity
Lucite Diakon mouldings are transparent, crystal
clear and completely colourless even in thick
sections.
As the base polymer is ‘water white’ in colour, a
complete range of colours - transparent, translucent
and opaque - can be produced from Lucite Diakon.
The light transmission is at the theoretical maximum
of 92%, enabling wide use where optical properties
are critical. Indeed acrylics often represent a very
satisfactory replacement for glass, with their
advantages of light weight, ease of shaping into
complicated designs and greater resistance to
breakage.
Resistance To Outdoor Exposure And
Ultra-Violet Light
The weathering properties of acrylics are excellent.
Lighting fittings exposed outdoors in both temperate
and tropical climates for many years show no
changes in colour or physical properties.
Surface Gloss And Hardness
The surface hardness of Lucite Diakon and its
resistance to scratching are exceptionally high for a
plastics material, being approximately the same as
for aluminium. Lighting fittings, after many years’
service in heavily industrialised districts, show no
deterioration in efficiency although they have
inevitably been subjected to abrasion by windborne
dust and by repeated cleaning.
Other Properties
Lucite Diakon components are rigid, dimensionally
stable, odourless, resistant to many common
chemicals, have low water absorption and are easy
to decorate. Lucite Diakon, as with other PMMA
materials, is capable of being fully recycled.
DTM/E/2Ed/Nov01
2 Acetone cyanhydrin is treated with sulphuric acid
and methyl alcohol to give methyl methacrylate
monomer:
Lucite Diakon polymer is produced from
monomer by a free radical vinyl polymerisation
process, ie free radicals are formed and react
with monomer molecules to form long chains
which are substantially unbranched:
page 2
GENERAL CHARACTERISTICS OF TOUGHENED
LUCITE DIAKON ST GRADES
Clarity
Lucite Diakon ST has a refractive index and
standard transmission comparable with the grades
of Lucite Diakon, while the level of haze is greater.
The haze level increases with temperature,
becoming most apparent during the extrusion
process or when removing hot mouldings from the
mould, and will disappear gradually as the
component cools to ambient temperature.
Resistance To Outdoor Exposure And
Ultra-Violet Light
Although the weathering properties of impact
acrylics are not as good as basic Lucite Diakon, the
ST grades resist yellowing and retain excellent
surface gloss and physical properties.
Impact Strength And Craze Resistance
The higher impact strength, elongation and the
lower flexural modulus of ST grades increase the
range of applications open to acrylic material. The
designer is offered greater freedom and the user
greater flexibility by minimising cracking problems
during processing and subsequent handling,
transportation, assembly and service.
The excellent craze resistance is beneficial where
mouldings or extrudates require a greater craze
resistance than conventional acrylic materials,
especially for articles which come into contact with
aqueous detergents and soap solutions.
By careful examination of component requirements,
namely degree of impact improvement, ease of
processability and flow, and resistance to outdoor
exposure, the designer or user will be able to select
the most appropriate grade of Lucite Diakon ST.
DTM/E/2Ed/Nov01
LUCITE DIAKON ASTM DIN DESCRIPTION
GRADE D788 7745
TYPE % TYPE
CMG302/MG102* 8 108-53 General purpose moulding and extrusion grade with high heat resistance.
Used mainly for optical parts, display items, tube and profile extrusion.
CMG314V 8 116-53 Injection moulding grade with improved heat resistance. Used primarily
for automotive rearlights and dashboard lenses.
CMH454L 8 116-73 High molecular weight grade used for injection moulding with improved heat
and chemical resistance. Used mainly for automotive rearlights.
CMH454/MH254* 8 108-73 High molecular weight grade for extrusion. Used mainly for extruded sheet.
CLG902/LG702* 8 100-53 Injection moulding grade with good melt flow properties and medium heat
resistance. Versatile grade used in many diverse applications such as
telecommunications, copying equipment and lighting diffusers.
CLH952/LH752* 8 108-73 Extrusion grade with improved melt flow and medium heat resistance. Used
mainly for sheet, tube and profile extrusion.
6 92-53 Injection moulding grades with excellent melt flow. Used for large area and thin
wall mouldings or where a long flow length is required.
STANDARD LUCITE DIAKON GRADE RANGE, RELATED TO ACRYLIC MOULDING POWDER SPECIFICATIONS
The Lucite Diakon range of acrylic polymers,
related to acrylic moulding powder specifications, is
shown in the table above.
The standard grades of Lucite Diakon are available
as approximately 2.5 mm cylindrical compound
granules. Certain grades, as indicated above, are
available as free flowing spherical bead polymer
with weight average particle size of 600 microns.
Acrylic materials are hygroscopic but the special
precautions taken during manufacture and
packaging mean that Lucite Diakon polymer does
not normally require drying before processing.
*Denotes grade coding for 600 micron bead polymer
CLG340CLG356/LG156*CLG960
DTM/E/2Ed/Nov01
page 3
TOUGHENED LUCITE DIAKON ST GRADE RANGE
LUCITE DIAKON ST G8 SERIES
The G8 Series provides the best combination of
impact resistance, rigidity, heat resistance and
surface hardness. They can be processed by
injection moulding or extrusion.
ST15G8 8* Has been developed to minimise cracking
on ejection problems.
ST25G8 8* Has medium impact resistant properties giving
a good balance between heat resistance,
impact strength and processability.
ST35G8 8* Offers high impact strength and good
chemical resistance.
ST45G8 8* Is a very high impact material.
ST15G6 6* Offers very easy melt processing coupled
with adequate impact resistance to overcome
minor cracking problems.
ST25G6 6* Is a medium impact resistant material with
excellent melt flow for large area or
complicated mouldings.
ST35G6 6* Offers high impact resistance with good
chemical resistance and processability.
ST45G6 6* Is a very high impact resistant material while
still processing excellent processing
characteristics.
ST25G7 6* Offers medium impact performance with
good moulding properties.
LUCITE DIAKON ST G6 SERIES
The G6 series is suitable for injection moulding
applications where ease of melt flow is important.
There is some loss in heat resistance compared
with the G8 series.
LUCITE DIAKON ST G7 SERIES
This series offers a balance of properties between
impact strength, heat resistance and surface
hardness and is designed primarily for injection
moulding.
ST25N8 8* Has an excellent combination of impact
resistance and temperature resistance.
LUCITE DIAKON ST N8 SERIES
This series is designed to be used where
temperature resistance coupled with impact
properties are important. The melt characteristics
are also suitable for the extrusion process.
ST25H8 8* Has the best combination of impact
strength, chemical resistance and
heat resistance.
LUCITE DIAKON ST H8 SERIES
The H8 series offers a unique combination of high
impact strength coupled with excellent heat,
chemical, surface scratch resistance and rigidity.
The series is suitable for injection moulding and
extrusion.
*Classification as defined in ASTM D 788 if basic
PMMA materials
DTM/E/2Ed/Dec02
page 4
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page 5
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DTM/E/2Ed/Nov01
page 6
Figure 1 Creep in tension at 23°C (10 MN/m2)
DATA FOR DESIGN
MECHANICAL PROPERTIES
Many of the standard mechanical tests give
information based on short-term loading at
arbitrarily chosen temperatures and strain rates.
The short-term properties, as measured by ISO,
ASTM or Lucite international standard methods are
given in the preceding section but most of these
results should not be used in the design of load-
bearing articles, because many of the properties of
Lucite Diakon, like those of other thermoplastics,
depend markedly upon temperature and time under
load.
The mechanical properties relevant to design
include the following:
Creep;
Long term strength and fatigue;
Impact strength
Except where otherwise stated, all data have been
obtained from unannealed specimens tested in air,
but some general comments on the effects of
chemical environment are made in a separate
section. If the article is to operate in an environment
other than air, care should always be exercised in
the selection of the appropriate data for design.
Creep
The load-bearing behaviour of an article made from
Lucite Diakon cannot be calculated simply by taking
a value of flexural modulus from a standard test
and applying it to, for example, a standard beam
formula because, in common with all other plastics,
the properties of Lucite Diakon vary appreciably
over a narrow temperature range and, under
constant load, the strain in articles made from
Lucite Diakon increases with time, ie the material
creeps under load.
Hence load-bearing calculations should involve the
use of creep data. Creep is defined as the total
strain, which is time-dependent, resulting from an
applied load, and creep data are often presented in
the form of strain/log time curves at 23°C as shown
in Figures 1 and 2.
DTM/E/2Ed/Nov01
page 7
Figure 2 Creep in tension at 23°C (20 MN/m2)
Figure 3 100-second isochronous stress/strain curves at 23°C
DTM/E/2Ed/Nov01
page 8
Figure 4 100-second apparent flexural modulus vs temperature (°C)
By taking cross-sections of the creep curves at
constant time, it is possible to generate isochronous
stress/strain curves, and Figure 3 represents short-
term data in this form.
Creep behaviour is temperature-dependent: an
increase in temperature decreases the modulus and
increases the strain at constant stress, as shown by
the 100-second apparent flexural modulus data
shown in Figure 4.
The effect of moisture on creep in Lucite Diakon is
comparatively small at constant strains, the total
decrease in stress corresponding to a change in
material from a dry to a wet state is approximately 12%.
Given an appropriate ‘family’ of creep curves of the
kind shown in Figures 1 and 2, it is possible to
calculate the load-bearing behaviour. The design
brief should include details of the function of the
article, the service conditions, estimated lifetime of
the component under load, and the maximum
service temperature. It is then normally assumed
that the component is subjected to a load which is
maintained constant throughout the lifetime at the
maximum service temperature. Working to a
maximum strain of 0.5%, the stress at the maximum
service temperature and lifetime, which cuts the
0.5% strain axis, is multiplied by 200 to give the
appropriate value of creep modulus. This value of
creep modulus may then be used in standard
strength-of-materials formulae, in order to predict
the likely long-term deformation or deflection.
Long Term Strength and Fatigue
The strength of Lucite Diakon also depends upon
time and temperature. Failure data are presented
as curves of stress against log (time to failure) and
typical curves for compression moulded Lucite
Diakon CMG302 tested in air at 23°C under a
constant load, are shown in Figure 5.
Crazing (localised structural breakdown) in standard
Lucite Diakon grades can occur at stresses
considerably below those required to produce
complete failure; the onset of crazing is also shown
in Figure 5. In most articles made from Lucite Diakon
it is necessary to avoid the appearance of crazing for
aesthetic reasons. Thus the crazing data in Figure 5
- normally represent the upper limit to which the
article can be stressed at any given time. A value of
design stress is obtained by dividing the crazing
stress at a given time and temperature by a suitable
safety factor, eg 1.5 to 2.0.
DTM/E/2Ed/Nov01
page 9
Figure 5 Static fatigue characteristics at 23°C, 65% rh
The value of design stress should be used in
strength-of-materials formulae to estimate the
minimum part thickness required to avoid mechanical
failure. The failure stress at any time decreases with
increase in temperature.
Failure resulting from a repeatedly applied load is
generally called ‘fatigue’. The failure stress under
dynamic load conditions is generally lower than that
resulting from a static load, at the same time and
temperature. The effect on load-bearing capability
of applying a fully reversed square wave load
pattern at 30 cycles/min to injection moulded Lucite
Diakon CMG302 is shown in Figure 6.
Long term strength also depends on the nature of
the environment. When Lucite Diakon is stressed in
an active environment its strength may decrease as
the result of, for example, solvent stress cracking.
The basic grades of Lucite Diakon are prone to
crazing after repeated immersion in detergent
solutions if the surface of the moulding is stressed
in tension as the result of initial fabrication or
subsequent conditions of use.
One of the significant advantages of ST grades of
Lucite Diakon is much improved resistance to
crazing by solvents and detergent solutions.
Unpolymerised acrylic cements can also be a stress
cracking hazard. When mouldings have to be
cemented together, the risk of cracking and crazing
can be minimised by annealing and by ensuring
that there are no interference fits between mating
surfaces. Wherever possible, holes and slots should
be moulded-in, because any subsequent machining
operations create stresses which in some
applications need to be removed by annealing.
(See page 74 for details of annealing).
Impact Strength
When articles moulded or extruded from standard
grades of Lucite Diakon break in service under
impact conditions, the fractures are almost always
brittle. There are three principle factors which
promote the likelihood of brittle failure:
A decrease in service temperature;
An increase in stress concentration;
Orientation resulting from fabrication.
DTM/E/2Ed/Nov01
page 10
Charpy-type specimens of different notch geometry
are tested across the material flow direction over
the range of temperatures of practical importance,
using a pendulum impact machine.
Figure 6 Dynamic fatigue characteristic in flexure at 23°C, 65% rh
Figure 7 Charpy impact strength vs notch tip radius
Impact data at 23°C, presented as energy to break
per unit area, are plotted against notch tip radius in
Figure 7.
DTM/E/2Ed/Nov01
page 11
-20 -10 0 10 20 30 40 50 600
4
8
12
16
20
24
Un-notched
2 mm notch tip radius
0.25 mm notch tip radius
CMG302
Test temperature ˚C
Imp
act
stre
ng
th K
J/m
2
Figure 8 Charpy impact strength of CMG302 vs test temperatures
As the notch tip decreases, the stress concentration
increases, the impact energy required to break
specimens decreases. The designer should therefore
conform to the principle of sound design and radius
corners as generously as possible.
Lucite Diakon ST grades show a significant
improvement in impact strength over basic grades. It
should be noted also that Lucite Diakon H grades (eg
CMH) are slightly tougher than G grades (eg CMG).
Figures 8 and 9 present impact strength data on
Lucite Diakon for unnotched, bluntly notched (2mm
notch tip radius) and sharply notched (0.25 mm
notch tip radius) specimens as a function of test
temperature.
As the stress concentration becomes more severe,
i.e. as the notch becomes sharper, the impact
strength at any temperature drops, and the tough-
brittle transition occurs at a higher temperature.
Figure 9 Charpy impact strength of ST45G8 vs test temperatures
DTM/E/2Ed/Nov01
page 12
The processing conditions, specifically melt temperature
and factors influencing orientation in the mould can
affect impact behaviour. The effects of different melt
temperatures on the impact strength of the Lucite
Diakon grades are shown in Figures 10 and 11.
Un-notched - along flow
Un - notched - across flow
Notch tip radius - 0.25 mm
220 230 240 250 260 270 2800
2
4
6
8
12
14
16
18
10
Melt temperature ˚C
Imp
act
stre
ng
th K
J/m
2
CMG302
Figure 10 Charpy impact strength of CMG302 vs melt temperature
Figure 11 Charpy impact strength of ST45G8 vs melt temperature
DTM/E/2Ed/Nov01
page 13
For standard grades of Lucite Diakon, with a sharp
notch, impact strength is independent of cylinder
temperature and direction of test relative to the flow
direction. In contrast, the behaviour of unnotched
specimens depends on both cylinder temperature
and direction of tests; in the ‘weak’ across-flow
direction the impact strength increases slightly as
the cylinder temperature is increased, whereas it
decreases somewhat in the ‘strong’ along-flow
direction. Melt viscosity decreases with increase in
cylinder temperature and therefore residual
orientation decreases as the cylinder temperature
increases.
Mouldings showing the most severe strains and
highest degree of orientation will have lower impact
strengths - these conditions result from the use of
low melt and low mould temperatures and slow
injection rates. The most robust mouldings are
produced using high mould and melt temperatures,
maximum injection rates and medium injection
pressures.
These general comments apply equally to both
Standard and ST grades of Lucite Diakon.
Figure 12 Force/Time curves on instrumented
fallingweight impact test
Impact Strength of ST Grades
When a specimen of plastic is subjected to an
impact force, two factors in particular influence the
energy required to break the specimen. These are:
The energy required to initiate a crack;
The energy required to propagate the crack.
The energy required to break the specimen is the
sum of these two components.
Standard grades of Lucite Diakon break by a brittle
mechanism which means in effect that once a crack
has been initiated there is no significant resistance
to crack propagation.
Lucite Diakon ST grades on the other hand have
been specially modified to build in resistance to
crack propagation and provide a substantial
increase in toughness.
Most standard impact tests do not distinguish
between the two components of the breaking
energy but an instrumental falling weight impact test
enables the two energies to be separated during a
single impact test.
Using this test force/time curves represented in
Figure 12 for CMG302 and ST45G8 indicate the
process of breaking 3 mm thick injection mould
discs.
In both traces the area under the curve AB
represents the energy required to initiate a crack
and the area under the curve BC represents the
energy required to propagate the crack. The higher
resistance offered by ST45G8 to both crack
initiation and propagation can be clearly seen and
accounts for the fact that ST45G8 is about 10 times
as tough as CMG302 on this test.
The energy required to initiate a crack is dependent
upon the grade chosen and sample thickness. The
crack propagation energy on the other hand is also
influenced by the sample dimensions. If the sample
is too small for the propagation energy to be
absorbed or dissipated then the crack will reach the
sample boundary and complete failure will occur. If
however the sample in question is large, then an
initiated crack will cease to grow before reaching
the sample boundary and although the article may
crack, it will not disintegrate. This is an important
consideration for applications such as vandal-
resistant lighting fittings.
DTM/E/2Ed/Nov01
page 14
THERMAL PROPERTIES
Typical values of the thermal properties of Lucite
Diakon relevant to design, such as thermal
expansion coefficient and specific heat, are given in
the tables on pages 4-5. There are slight differences
between the thermal expansion characteristics of
Lucite Diakon grades, as shown in Table 1.
Lucite Diakon Grade cm/cm°C x 10-5
Standard grades 7.1
Medium Impact ST 10.0
High Impact ST 11.5
Table 1 Linear thermal coefficient of expansion -
average results from -10°C to +50°C
The thermal expansion of basic grades over the range
-70°C to +70°C can be represented by the formula: %
expansion = 0.0068t + 0.000015t2, where t is the
temperature rise in degrees C. It is recommended that
designers avoid using moulded-in metal inserts
because the difference in expansion coefficients
between Lucite Diakon and metals can give rise to
stress cracking in the Lucite Diakon. If moulded-in
metal inserts are essential, it is recommended that
Lucite Diakon ST grades are used.
It should be noted that although grades of Lucite
Diakon may be described in terms of their softening
point or deflection temperature under load, these
quantities refer to specific conditions described in
the appropriate test. As a general working guide a
temperature 10°C below the ISO heat deflection
temperature for the grade can be used as the
maximum continuous working temperature for a
well-moulded article which is not under load, as
shown in Table 2.
To assess the maximum service temperature for a
load-bearing application, the designer needs to
assess the load on the article, the environment, the
expected service life and the tolerable maximum
deflection or deformation. In addition, the maximum
service temperature will be affected by the level of
stress during processing or fabrication.
The maximum service temperature range has been
extended by the introduction of the HS (High
Softening) grades of Lucite Diakon for which data is
available on request.
FLAMMABILITY
Although Lucite Diakon is combustible, it burns
slowly without normally producing undue quantities
of smoke, and the main products of combustion are
H20, CO2 and CO; as in the combustion of all
organic materials including paper and wood.
The flammability characteristics of some grades of
Lucite Diakon are shown in Table 3.
Lucite Diakon Grade °C
CLG356,LG156,CLG960,ST25G6,ST45G6 70
CLG340,CLG902,LG702,LH752,CLH952 75
ST25G8,ST45G8 80
MG102,CMG302,MH254,CMH454,CMG314V,CMH454L 85
Table 2 Maximum continuous working
temperatures for the Lucite Diakon
grades
TEST METHOD/ UNITS LUCITE DIAKON LUCITE DIAKON
PROPERTY STANDARD ST GRADES
GRADES
Flammability cm/min 2.8-3.8 4.0-6.5
ASTM D635-96
Burning rate
[Sample Thickness 1.6mm]
BS2752 cm/min 3.5 6.5
Method 508A
Burning rate
DIN 4102 Class B2 B2
Federal Motor Vehicle cm/min 3.1 6.1
Safety Standard
ISO 3795
Burning rate
Underwriters
Laboratories Inc Class HB HB
UL94
Glow Wire Test deg C 650 650
IEC 695-2-1
Smoke density % ‘M’ Grades 5 Medium
Impact ST 7-16
ASTM D2843-93 ‘L’ Grades <5 High
[Sample Thickness 3.2mm] Impact ST 23-30
Table 3 Flammability Characteristics of
Lucite Diakon
DTM/E/2Ed/Nov01
page 15
The flammability characteristics of the Lucite Diakon
range have been extended by the introduction of
the MGW grades; data for a grade with an 850 glow
wire rating is available on request.
ELECTRICAL PROPERTIES
The electrical properties of Lucite Diakon depend
on many factors such as the electrical frequency (or
time) and temperature, the quantity of absorbed
moisture, and the grade.
The frequency dependence of permittivity (dielectric
constant) and dissipation factor for some grades of
Lucite Diakon at 23C are shown in detail in Table 4.
An increase in absorbed moisture increases all
these values. In the audio frequency range, the
dielectric properties of the Lucite Diakon grades are
similar. There is, however, some difference between
the values of volume resistivity for the standard
grades of Lucite Diakon at very low frequencies, as
shown in Table 4.
Property Units CMG302 CMG314V CMH454 CLG356 CLG902 CLH952
MG102 MH254 LG156 LG702 LH752
CMH454L
Volume resitivity at
23°C and 60% rh
Polarisation time 60 sec ohm m 7x1015 7x1015 7.5x1015 1x1016 8x1015 7x1015
Polarisation time 1000 sec ohm m 2x1017 3x1017 4x1017 5x1016 3x1016 3x1016
Dissipation factor
23°C and 60% rh 50 Hz 0.050 0.050 0.051 0.064 0.066 0.062
23°C and 60% rh 103 Hz 0.034 0.034 0.034 0.034 0.034 0.035
40°C and 60% rh 103 Hz 0.055 0.055 0.056 0.048 0.052 0.050
60°C and 60% rh 103 Hz 0.075 0.076 0.077 0.064 0.067 0.068
90°C and 60% rh 103 Hz 0.085 0.084 0.083 0.078 0.080 0.081
23°C and 95% rh 103 Hz 0.047 0.050 0.053 0.040 0.044 0.046
Permittivity
23°C 50% rh 50 Hz 3.9 4.0 4.2 3.7 3.8 3.9
23°C 60% rh 103 Hz 3.3 3.4 3.6 3.1 3.4 3.6
23°C 95% rh 103 Hz 3.6 3.5 3.4 3.0 3.3 3.5
Breakdown voltage k V/mm 16 15 15 14 15 16
Table 4 Electrical properties of Lucite Diakon
OPTICAL PROPERTIES
The exceptional clarity of Lucite Diakon has made
the material suitable for many optical applications,
and some of the more important optical properties
are presented below.
Refraction
Values of some primary optical constants at 23°C for
basic Lucite Diakon grades are summarised below.
As the refractive index (nd) depends on the
wavelength of light, the value below is that
measured at 587.6 nm (Sodium line). The critical
angle, Xd is defined by the refractive index
where nf is the refractive index measured at 486.1
nm and nc at 656.3 nm. Also shown in the table is
the variation of refractive index with temperature,
again measured at 587.6 nm.
(sin Xd = 1/n). The variation of refractive index with
wavelength of visible light is shown in Figure 13.
This variation is simplified in the table by the use of
the relative dispersion,
DTM/E/2Ed/Nov01
page 16
Figure 13 Refractive index vs wavelength
When carefully compression moulded, Lucite
Diakon is optically isotropic. When Lucite Diakon is
extruded or injection moulded some orientation of
the material occurs causing the moulding to
Figure 14 Dependence of haze level on
temperature for Lucite Diakon ST grades
become optically anisotropic. Different values are
obtained for the refractive index when measured in
different directions, this being related to the extent
and direction of molecular orientation. The
maximum difference between the principal refractive
indices measured parallel with and at right angles to
the main direction of orientation, called the
birefringence, is about 10-3. However, such a large
difference is achieved only by considerable
stretching, and the maximum birefringence in
normal highly oriented mouldings is about 10-4.
See page 72 for further comments on orientation
and stress.
ST grades of Lucite Diakon are toughened by the
inclusion of a specially manufactured impact
modifier which is matched in refractive index to
standard grades of Lucite Diakon at 20°C. The
refractive indices of the modifier and standard
grade Lucite Diakon vary with temperature in
different ways so that as the temperature deviates
from 20°C, the refractive index difference between
the two components becomes great enough to
introduce haze.
The dependence of haze upon temperature is
shown in Figure 14.
Light Transmission
When a parallel beam of light falls normally on to a
polished surface of a material, some light is
reflected as a consequence of the change in
refractive index at the interface with air. In the case
of basic grade Lucite Diakon, about 4% is reflected
at each surface. As the angle of incidence
increases from zero (normal incidence), this
reflection loss increases, slowly at first and then,
beyond 60°, very rapidly as shown in Figure 15.
DTM/E/2Ed/Nov01
page 17
Figure 15 Reflection of light at Lucite Diakon/air interface
Thus for a sheet of Lucite Diakon, having two
surfaces, reflections limit the direct transmission
factor to about 92%. If light falls on the sheet
equally from all angles (as from a sky of uniform
brightness), the resultant integrated transmission of
the sheet is reduced to about 85%.
Light may also be absorbed by a material, or
scattered. In the case of basic Lucite Diakon
grades, very little light is scattered from the bulk of
the pure material but scattering may occur at the
surface due to imperfections such as scratches, or
from internal impurities. Such scattering can
adversely affect the resolution of an image seen
through the material (reduce its clarity), and will
cause a deterioration of the contrast in the image
(haziness).
As mentioned above, the two components in Lucite
Diakon ST grades have their refractive indices
matched at 20°C and the greater the deviation from
this temperature, the greater will be the haze level
observed, and the lower light transmission as
shown in Figure 16.
The absorption of light by standard Lucite Diakon
grades in the visible region is extremely low, and is
almost independent of wavelength. Outside this
range of wavelengths significant absorption does
occur and this reduces the transmission factor and
makes it dependent on sheet thickness. The
transmission curve is shown in Figure 17. Whilst the
normal standard Lucite Diakon grades have a high
transmission of UV light some special ultra-violet
(UV) stabilised grades are produced, and their
transmission curves are shown in Figure 18.
The special UV grades of Lucite Diakon are only
recommended for use in particularly critical
applications, for example, with high intensity mercury
vapour lamps having high UV emission characteristics,
or for applications such as camera lenses where UV
transmission similar to glass is required.
Comparative transmissions for Lucite Diakon ST
are given in Figures 19 and 20, pages 19-20.
DTM/E/2Ed/Nov01
page 18
Figure 17 Transmission curve for standard Lucite Diakon grades (3.2 mm sample)
Figure 16 Light transmission versus temperature for ST grades
DTM/E/2Ed/Nov01
page 19
Figure 18 Comparative transmission curves for normal and uv stabilised Lucite Diakon standard grades
(3.2 mm samples)
Figure 19 Transmission curve for Lucite Diakon ST 45G8 (3.2mm sample)
DTM/E/2Ed/Nov01
page 20
Piping of Light
Because of its optical characteristics, and particularly
its low absorption, standard Lucite Diakon grades
lend themselves to the exploitation of the
phenomenon of total internal reflection. In particular, a
beam of light can be efficiently ‘piped’ round bends
and through great lengths of material. The critical
angle for an interface with air is 42°, so that provided
the ‘light-pipe’ end face is perpendicular to its axis,
light incident at any angle on the end face will be
accepted and transmitted, subject to losses due to
reflection from the end face itself. To prevent
excessive loss when light is ‘piped’ around curves, the
radius of curvature should not be less than three
times the diameter of the ‘pipe’. Since optical defects
in a boundary cause scattering of light and reduce the
efficiency of the system, it is important that all
cemented junctions are free from irregularities, and
that all exterior surfaces are highly polished and free
from scratches or other imperfections.
Optical Fibres
The science of fibre optics involves transmittance of
light in a transparent fibre from one end to the other
by total internal reflection, which is made possible
by coating the optical fibre with a material of lower
refractive index.
Acrylic fibre diameters typically range from 0.25 mm
up to 3.0 mm with a fluorinated methacrylate
polymer coating (Refractive Index 1.394) to a
thickness of 8 micrometers. Acrylic fibres have
attenuation losses of 470 decibels/kilometre or
greater compared with 50 dB/Km or lower for silica
optical fibres and are therefore not generally
suitable for distances more than 20 metres.
However acrylic fibres do offer greater flexibility,
toughness and lightness together with lower costs
when compared with silica fibres.
Figure 20 Comparative transmission curves for normal and uv stabilised Lucite Diakon ST45G8 (3.2mm samples)
DTM/E/2Ed/Nov01
page 21
CHEMICAL RESISTANCE
All standard grades of Lucite Diakon give mouldings
which are resistant to water and have good
dimensional stability under conditions of changing
humidity. No staining or whitening occurs on
exposure to high temperatures or high humidities.
Articles made from Lucite Diakon are resistant, at
temperatures up to 60°C, to dilute mineral and
organic acids, and dilute and concentrated solutions
of most alkalis. At room temperature, Lucite Diakon
mouldings are unaffected by aqueous solutions of
inorganic salts, aliphatic hydrocarbons, fats and
oils, and most of the common gases. They are
attacked by chlorinated aliphatic hydrocarbons,
aromatic hydrocarbons, ketones, alcohols, ethers
and esters, including those esters which are used
as plasticisers for other plastics. Care should
therefore be taken to ascertain the effect of organic
liquids in prolonged contact with Lucite Diakon.
Table 5 indicates the chemical resistance of Lucite
Diakon grades to a range of common chemicals, as
judged by visual examination of small, unstressed
samples immersed in various liquids at 23°C.
The performance of articles in service will, however,
depend on the presence of internal and external
stresses and orientation in the manufactured article.
It is recommended that appropriate tests be carried
out to simulate the actual conditions of the
application.
In general, Lucite Diakon ST grades are more
resistant to attack than standard grades of Lucite
Diakon upon which they are based, but even they
will be attacked upon prolonged exposure to
chemicals which attack standard grades.
The following symbols are used:
A - Satisfactory
B - Some attack but only slight reduction in
mechanical properties
C - Unsatisfactory
Chemical Concentration Category
Acetaldehyde 100% C
Acetic acid 10% A
100% C
glacial C
Acetic anhydride B
Acetone 100% C
Acetonitrile C
Acetophenone C
Alcohol, allyl C
amyl C
benzyl C
n-butyl C
ethyl 10% A+
50% B
100% C
isopropyl 10% B
50% B
100% B
methyl 10% A
50% B
100% C
Aluminium potassium sulphate Saturated solution A
Ammonia 0.88 relative
density solution A
Liquid C
Ammonium chloride Saturated solution A
Amyl acetate C
Aniline C
Anthracene Solution in paraffin A
Benzaldehyde C
Benzene C
Benzoyl chloride C
Butyl acetate C
Butyl acetyle ricinoleate B
n-Butyle chloride C
Butyl stearate B
Butyraldehyde C
n-Butyric acid Concentrated C
Calcium chloride Saturated solution A
Carbon disulphide C
Carbon tetrachloride C
‘Cetavlon’* 1% aqueous solution A
10% aqueous solution A
1% ‘Cetavlon’ in 5% ethyl A
alcohol/aqueous solution
Chlorine 2% aqueous solution B
Chloroform C
Chromic acid 10% A
Saturated solution C
Citric acid Saturated solution A
Meta-cresol C
Cyclohexane C
Cyclohexanol C
Cyclohexanone C
Cyclohexene C
Decahydronaphthalene C
(Decalin*)
Dialkyl phthalate B
Dibutyl phthalate B
Dinonyl phthalate B
Dioctyl phthalate B
Dialkyl sebacate B
Dibutyl sebacate B
Dioctyl sebacate B
Diethyl ether C
DTM/E/2Ed/Nov01
page 22
Chemical Concentration Category
Epichlorhydrin C
Ethylene dibromide C
Ethyl acetate C
Ethylene dichloride C
Ethylene glycol A
Ethylene oxide dry A
moist B
Ferric chloride 10% aq A
Formaldehyde 40% aq A
Formic acid 10% A
90% C
Glycerol A
Hexane A
Hydrochloric acid 10% A
Concentrated A
Hydrocyanic acid C
Hydrofluric acid Concentrated C
Hydrofluoroboric acid B
Hydrogen peroxide 10 vols A
90% C
Iranoline * A
Iron perchloride B
Lactic acid A
Lanoline A
Mercury A
Metol quinone A
Methylamine A
Methyl benzoate C
Methyl cyclohexanol C
Methylene dichloride C
Methyl naphthalene C
Methyl salicylate C
Monochlorobenzene C
Naptha Crystals C
Napthalene Saturated solution B
Naphthalene crystals in paraffin
10% B
Nitic acid A
Nitrobenzene C
n-Octane B
100 octane aviation fuel B
Oils: diesel A
olive A
transformer Saturated solution A
Oxalic acid A
Chemical Concentration Category
Paraffin, medicinal A
Perchloroethylene C
Petroleum ether (100-120°C) A
Phenol C
Phosphoric acid 10% A
95% C
Piperidine C
Potassium chlorate Saturated solution A
Potassium dichromate 10% A
potassium hydroxide Saturated solution A
Potassium permanganate 0.1 N solution A
Polypropylene adipate A
Polypropylene laurate A
Polypropylene sebacate A
Sebacic acid A
Silicones R220 B
F130 B
M441 C
F110 B
Sodium carbonate Saturated solution A
Sodium chlorate Saturated solution A
Sodium hydroxide Saturated solution A
Sodium hypochlorite (105 chlorine) A
Sodium thiosulphate 40% aqueous solution A
Sulphuric acid 10% A
30% A
98% C
Tartaric acid Saturated solution A
Tetrahydrofuran C
Tetrahydronaphthalene
(Tetraline*) C
Toluene C
Trichloroethane C
Trichloroethylene C
Tricresyl phosphate C
Trixylenyl phosphate C
Water A
White spirit A
Xylene C
+ Short term contact is satisfactory, but Lucite Diakon is not
recommended for prolonged contact with alcoholic liquids
*Trade mark
Table 5 Chemical resistance of Lucite Diakon
at 23 C.
The chemical resistance table refers only to the
effects on Lucite Diakon resulting from contact with
the substances listed. Information on compliance
with particular requirements for contact with
foodstuffs, potable water, cosmetics or
pharmaceutical products should be requested from
Lucite international Sales Offices or Agents, giving
details of the application and country for which
regulatory approval is required.
DTM/E/2Ed/Nov01
page 23
PERMEABILITY
The permeability of standard grade Lucite Diakon
mouldings to oxygen, nitrogen, and carbon dioxide
is given below.
The values are expressed as the number of cubic
centimetres of gas passing at standard temperature
and pressure per square metre per day per
atmosphere excess pressure through a film 25 μm
thick.
Permeant cm3 (STP)/m2/d/atmosphere
Nitrogen 60
Oxygen 230
Carbon dioxide 1700
For a film 25 μm thick, a temperature of 25°C and a
relative humidity of 75%, the amount of water
vapour transmitted by Lucite Diakon is 68 g/m2/d.
MELT FLOW BEHAVIOUR
Lucite Diakon produces a highly elastic melt whose
flow behaviour differs considerably from that of
‘Newtonian’ fluids.
All the measurements of melt behaviour were
made with a capillary rheometer. The shear rate
η in a circular die of radius R and length
L is related to the volume flow rate of melt Q by
η = 4QπR3 The shear stress τ at the wall of the
die resulting from a pressure drop ΔP is given by
τ = R.ΔP/2L.
The relationship between shear rate and shear
stress is obtained experimentally, and data are
presented in Figures 21 to 23 where apparent shear
viscosity is defined as the ratio of shear stress to
shear rate.
At a given injection rate, an increase in melt
temperature reduces the pressure required to fill a
given cavity. For example, if the shear rate in a
runner is 1000s-1, then for Lucite Diakon CMG302
(Figure 21) the corresponding shear stress at
220°C is 3.6 x 105 Pa, and the pressure drop in the
runner is related to the length of the runner L by the
equation
ΔP = 2L/R
If the temperature is raised to 260°C, then at
1000s-1 the shear stress is only 1.3 x 105 Pa,
ie a 40°C increase in temperature has reduced the
injection pressure by a factor of about 2.8.
However, this factor is underestimated because no
account has been taken of shear heating. Heat
generation during injection moulding is proportional
to the pressure drop in the process. It should be
borne in mind that the heat is dissipated in the
regions of high shear rate, and that under extreme
conditions, excessive local temperature rises can
lead to degradation, for example as the melt passes
through the gate.
Alternatively, a machine developing a given head of
pressure along a runner can deliver a greater
quantity of material at a high temperature than at a
low temperature.
Where fast filling of a cavity is required, it may not be
possible to raise the temperature beyond a certain
value because of the risk of depolymerisation. It may
then be necessary to use an easier-flow grade to
achieve the necessary injection rate.
Figures 22 and 23 present curves of apparent shear
viscosity against shear stress for the Lucite Diakon
grades, at 210°C and 240°C respectively. Referring
to Figure 23, if the pressure developed along the
runner produced a shear stress of 1.6 x 105 Pa, the
shear rate in Lucite Diakon CMG302 would be
about 500 sec-1 compared with about 160 sec-1 for
Lucite Diakon CMH454. Hence the volume flow rate
of Lucite Diakon CMG302 would be approximately
three times that of Lucite Diakon CMH454.
Viscosity depends on the pressure applied to the
melt. A hydrostatic pressure of 100 Pa has the
same effect on viscosity as a drop in temperature of
33°C.
DTM/E/2Ed/Nov01
page 24
Figure 21 Variation of melt viscosity with stress for Lucite Diakon’ CMG302 at different temperatures
DTM/E/2Ed/Nov01
page 25
Figure 22 Melt viscosity under shear at 210°C by capillary rheometry
(corrected for die entry pressure drop)
DTM/E/2Ed/Nov01
page 26
Figure 23 Melt viscosity under shear at 240°C by capillary rheometry
(corrected for die entry pressure drop)
DTM/E/2Ed/Nov01
page 27
These figures are averages based on the nature
and intensity of airborne noise. The reduction of
resonance in acrylic glazing as compared with glass
will normally be more than adequate to compensate
for the difference in Sound Reduction Index.
Sheet Weight per unit Sound
area (Kg/m2) Reduction
Index (decibels)
3.2 mm acrylic sheet 3.8 18
6.4 mm acrylic sheet 7.5 23
3.2 mm glass 6.8 22
6.4 mm glass 16.6 27
16 mm twin walled sheet 5.0 25
Figure 24 Water absorption - equilibrium values for
Lucite Diakon standard grades at 1.6
mm thickness
Figure 25 Effect of water absorption on dimensions of Lucite Diakon standard grades at 6.4 mm thickness
(23°C)
WATER ABSORPTION
All grades of ‘Lucite Diakon have a low water
absorption as shown in Figure 24. Although the
equilibrium water content is small, its effect on
dimensions may be considerable, as shown in
Figure 25, and absorbed water may have a slight
effect on mechanical properties, acting to some
extent as a plasticiser. The rate of absorption is
slow, and Figure 26 shows the behaviour of
samples stored at 23°C under conditions of 60%,
80% , 100% relative humidity, and total immersion.
SOUND INSULATION
Insulation against airborne noise may be
represented by the material’s Sound Reduction
Index. The Sound Reduction Index is the ratio of
the sound energy incident on the surface, to that
which is transmitted through and beyond the
material, expressed in decibels. As a general guide
to the meaning of Sound Reduction Index in
decibels, the loudness of the noise will be
approximately halved for every ten decibels
reduction in the index. Comparative figures for
acrylic sheet and glass in a single glazing system
under average conditions would be:
DTM/E/2Ed/Nov01
page 28
Figure 26 Amount of water absorbed by Lucite Diakon standard grades at 6.4 mm thickness (23°C)
DTM/E/2Ed/Nov01
page 29
INJECTION MOULDING
THE INJECTION MOULDING PROCESS
The injection moulding process comprises three
stages, each of which must be closely regulated to
obtain good quality mouldings:
Feeding material into a heated cylinder, where it
softens and becomes a plasticised melt;
Injecting the correct amount of plasticised
material under controlled rate and pressure into
an enclosed mould;
Maintaining sufficient pressure on the material to
compensate for the shrinkage of the material on
cooling as it cools to a point at which it can be
ejected without deformation taking place.
Figure 27 Screw Profile for Lucite Diakon
A stable and suitable rate of plasticisation is
required to give a uniform and good quality melt for
consistent shot to shot production of mouldings.
See page 44 for moulding conditions.
The melt viscosity of acrylic is relatively high
compared with, for example, polyolefine and
polystyrene moulding materials, see Figure 47.
Therefore the plasticising capability is important and
the screw design in the majority of modern
machines is adequate for processing Lucite Diakon.
Figure 27 illustrates a suitable screw design for
processing Lucite Diakon.
The moulding machine often has interchangeable
cylinders having varying shot capacities and
different injection pressure maxima. The injection
pressure and shot capacity are varied within the
different cylinders by a change of screw diameter.
The cylinders, which are generally coded A, B and
C, change progressively through the range from
smaller shot capacities at higher injection pressures
to larger shot capacities at lower injection
pressures. The most suitable cylinder for Lucite
Diakon is the compromise B type. It is also good
practice not to consider using more than 70% of the
rated capacity of any given cylinder.
With high viscosity the injection pressures needed
are correspondingly high and the mould must be of
robust construction to resist these pressures and so
prevent deformation under load. In addition the
locking force, which keeps the mould closed during
injection, must be adequate to resist the total thrust
over the projected area of the mould cavity and so
prevent the mould from opening. For this a
minimum locking force of 30MPa of projected area
should be available.
The quality of an injection moulded part is
influenced by the temperature and pressure of
material in the mould cavity at the moment when
the material in the gate solidifies. At that instant the
mould is filled with hot material under pressure. As
DTM/E/2Ed/Nov01
page 30
the temperature of the material in the mould falls
there are two opposing actions taking place:
Thermal contraction - tending to reduce the
volume of the moulding;
Residual pressure in the melt - tending to
expand the moulding slightly.
The two effects occur at the same time and tend
to counterbalance each other.
The use of programmed injection enables moulds to
be filled at different speeds and pressure during the
injection period. The advantage of being able to fill
the major proportion of a mould quickly whilst at
high pressure and speed and then drop to lower
values maintaining follow-up pressure on the
material helps to reduce the risk of flash and the
degree of moulded-in strain. When using this system
for thick acrylic sections, such as lenses and insignia,
it is possible to inject very slowly at a low pressure
and then, towards the end of the mould filling time, to
increase the pressure to help overcome the
shrinkage.
Control of mould temperature is also important if the
quality of the moulded part is to be kept consistent
throughout production. The use of mould
temperature control units allows the mould
temperature to be raised to its optimum value
before start-up, thus avoiding an initial period of
production of more highly strained parts from a cold
mould, and wastage of material due to short shots.
Figure 28 Nozzles
On most of the screw pre-plasticising machines
various types of nozzle can be fitted. Those nozzles
fall into three basic categories
(see Figure 28).
(1) Mechanical shut-off nozzle
(2) Needle valve shut-off nozzle
(3) Open or straight though nozzle
For Lucite Diakon, nozzles (1) and (3) can be used
quite successfully. However, nozzle (3) is usually
preferred because there are no potential hold-up
points where material can stagnate and
decompose. This is very important when producing
high quality clear mouldings. With this type of
nozzle, however, close temperature control is
required by means of a separate, well-positioned
thermo-couple and temperature controller to
prevent dribble or ‘freeze off’. Type (2) nozzles are
not generally recommended because of the
frictional heating which can occur when using high
injection rates.
Figure 29 Design of components - change of section
DTM/E/2Ed/Nov01
page 31
DESIGN OF COMPONENTS FOR MOULDING
Good component design is of great importance in
the injection moulding of Lucite Diakon and the
following points should be considered at the design
stage if later difficulties are to be minimised or
avoided.
If possible, sharp change of section thickness should
be avoided as this creates excessive moulding flow
problems with thicker sections and the possibility of
excessive sinking on cooling if the gating position is
only permissible at the thinner part of the moulding.
To keep the cross-section constant, thick sections
should be cored out wherever possible (Figure 29).
With certain designs, as for example the prismatic
effect in a tap handle, thick and thin sections are
closely alternated. In this instance the rapid change
in section gives attractive optical results, but
differential thicknesses must be kept within certain
limits to avoid problems in moulding or in service.
As a guide, the thickest sections should not exceed
10 mm. Even then, as the mould cavity fills, the melt
will tend to flow into the thick sections first and the
thin ones thereafter, leaving a weld line where the
adjacent flows of melt re-unite. All edges of the core
pin (which forms the hollow in the handle) should be
radiused to ensure that the melt will not drag over
them with consequent formation of flow lines, and to
reduce the possibility of stress cracking by
eliminating sharp corners in the moulding. Different
cooling rates of thick and thin sections can also lead
to stresses in the finished moulding.
To achieve economy, components are often reduced
in section. This practice can be followed provided
the sections are not made so thin as to cause flow
problems during moulding. In addition to the flow
problems, thin sections cool rapidly in the mould and
result in high quenching stresses which make
mouldings more liable to craze and crack. As a
guide, where long flow paths are encountered, wall
sections should not be less than 3 mm.
Problems resulting from uneven filling of the mould
cavity will occur if the component is surrounded by a
rim which is thicker than the internal portion in the
centre (Figure 30). In this instance material will flow
around the rim faster than across the centre and then
give gas entrapment and “Y” weld line problems.
Figure 30 Design of components - thickness of rim
All corners and sections should be radiused as sharp
corners cause stress concentration, brittle moulding
and also pressure drop leading to possible problems in
mould filling. This particularly applies where blind
holes are to be moulded-in to take screw or other
fastening media. Wherever possible all holes and slots
should be moulded-in since post-moulding machining
operations not only increase finished part cost, but
also set up residual stresses which can only be
removed by annealing.
To maintain the benefits arising from increased impact
strength and flexibility with Lucite Diakon ST grades, it
is important, at the initial design stage of components,
to avoid sharp corners and sudden changes in section
thickness, thereby eliminating areas subject to high
tensile stress as with standard grades. All such corners
should have a minimum radius of 1.5-2.0 mm. It is also
important in the design and gating of the components
to pay attention to the avoidance of weld lines as this
effect, common to many impact modified plastics, is
more noticeable than with a similar component in a
standard Lucite Diakon grade.
If inserts are to be moulded-in, sufficient material
should be allowed around the insert to give adequate
keying and to resist stresses which will be set up
during cooling by the differential thermal contraction of
the insert and the Lucite Diakon. High softening point
plastic inserts like glass reinforced nylon are preferable
to metal to minimise the stress. The insert should be
splined on the outside and provided with a
circumferential slot to give a key to the Lucite Diakon
which is moulded over it.
DTM/E/2Ed/Nov01
page 32
When numerals or letters are to be moulded into the
component these should not be more than one third of
the depth of the section thickness in order to minimise
division of the melt leading to weld lines and ‘tails’.
To aid ejection, the draft angle on a component should
be as generous as possible. This especially applies to
thick components where long injection times are often
necessary and consequently increases moulding
packing. In general 1° suffices for most thinner sections
but as much as 3-4° may have to be accepted in
extreme circumstances.
The shape of the component often dictates the
positions of the mould parting line, gate and ejection
points, and these should be taken into account at the
design stage in order to facilitate the moulding of
good quality components without objectionable
appearance defects.
With tap handles or control knobs the use of a splined
spigot is recommended.
With splined spigots the torque is distributed very
evenly and a matching hole may therefore be moulded
into the boss of the tap handle. The crests and valleys
of the splining should be radiused to reduce and
distribute any stresses which might be generated by
excessive pressure.
With a square section spigot, the torque applied is
concentrated at the internal angles of the moulded
square hole, and cracking could occur.
MULTI-COLOURED MOULDINGS
The techniques described below have been highly
successful with Lucite Diakon, particularly in the
automotive industry on rear light assemblies.
Edge-to-Edge Insert Moulding
The process involves moulding part of a complete
assembly in one tool, and transferring this part to a
second tool, where further material is moulded
against this insert. The hot melt fuses with the
inserted moulding producing a bond between the
two components. The strength of the bond is further
increased if some form of mechanical key is
designed into the joint area. The design of this key
depends largely on the shape of the component. A
few examples are given in Figure 31.
Figure 31 Forms of key with edge-to-edge moulding
The second tool must be accurately designed to
accept the inserted moulding which must be held and
supported firmly during the moulding cycle. Accuracy
in both component and mould is also required to
prevent flashing between the two components.
The pressures exerted upon the inserted moulding
during the second moulding cycle are often high
and, to avoid cracking, components must be
designed without sharp corners. The gate should be
positioned to minimise the strain on the inserted
moulding. When moulding Lucite Diakon, it has
been found advantageous to use the higher
molecular weight grade CMH454V or low impact
versions of ST for the moulding to be used as the
insert, using their superior mechanical strengths to
help prevent cracking.
Ideally the two moulding operations should be
carried out consecutively on adjacent machines, the
moulded inserts transferred directly from one
machine to the next. Under these conditions the
inserts are still warm and the risk of cracking is
reduced. If direct transfer is not possible then it is
helpful to warm the mouldings prior to placing them
in the second tool.
DTM/E/2Ed/Nov01
page 33
Skin Insert Moulding
This process is similar to that described above
except that the insert is a thin component with
smooth surfaces, normally in the region of 1.5 mm
thick. Many of the points mentioned above apply to
skin moulding. The final part is produced by
moulding a second layer skin, which will include the
optics, on to the first in a master tool. It has been
found that when required the use of CMH454V for
the insert skin helps to minimise cracking or colour
bleeding problems. Although, due to component
and tooling considerations, both edge-to-edge and
skin moulding techniques are used, it is considered
skin moulded lenses are more robust than edge to
edge ones.
Multi-Colour Machines
Multi-colour moulding may also be carried out on
special machines with two or more cylinders for
those rearlight assemblies where design, size and
number considerations are suitable. The technique
usually consists of a series of moulds where one
platen is rotated through two or more stations
where injection of the different coloured material
takes place.
MOULD DESIGN
Although many factors have to be considered in the
design of moulds for thermoplastic materials there
are three factors which require special attention for
acrylic materials. Due to the relatively high melt
viscosity and its greater temperature dependence
(see Figure 47) it is usually necessary to use
sprues, runners and gates of generous cross
section compared to those used for material with
low viscosities such as nylon and polystyrene.
Standard grades of Lucite Diakon may be considered
as hard brittle materials and allowance should be
made for this.
• Radius all corners
• Adequate and uniform ejection
• No undercuts
• Minimum 1° taper
• Polish in line of draw
• Uniform mould temperature control
The aesthetic appearance together with high gloss
and clarity obtainable with Lucite Diakon mouldings
requires highly polished moulds.
In general nickel-chrome steels are preferred since in
addition to being tough and hard-wearing they will
take a high polish. For optical quality parts, a steel
like ‘Stavex’* ESR has been found satisfactory.
Sprue Design
The sprue is the channel through which the material
is transferred from the machine nozzle to the
runner(s) and gate(s) and into the mould cavity (ies).
Its design, therefore, is of paramount importance. It
must be of adequate dimensions to prevent freezing
prematurely, but not so large as to extend the cooling
time of the moulding. To fulfil these basic
requirements it is thus important to have a sprue of
adequate diameter but to keep it as short as possible.
A length of approximately 60 mm should be aimed for.
To achieve this mould backing plates or bolsters
should be kept as thin as possible without sacrificing
strength in the mould.
Where it is not possible to provide short sprues due to
component geometry, consideration should be given
to the use of extended machine nozzles (see Figure
32) which can be fitted with suitable heaters and
controlling equipment. An extended nozzle can also
be used to advantage on normal type moulds in order
to obtain better mould filling and to reduce material
wastage.
The size of the sprue necessary for any particular
moulding will vary according to the thickness and the
shape of the parts to be made.
* Trademark of Uddeholm
Figure 32 Extended nozzle
DTM/E/2Ed/Nov01
page 34
As a guide the following sprue diameters should be
used:
For thin section moulding, ie 2.5 mm-4 mm, the
machine nozzle should be 4 mm diameter and the
smaller hole in the sprue bush 4.5 mm diameter;
For thick section mouldings, ie 6 mm and upwards,
the machine nozzle should be 7.5 mm diameter
and the sprue accordingly 8.5 mm diameter.
All sprue bushes should have a tapered bore to allow
easy extraction of the sprue. The angle of the taper
should be between 5-7° inclusive. The higher angle is
preferred for thick mouldings because the long
injection times necessary for these mouldings can
cause packing which tends to make the sprue more
difficult to extract. The sprue bush internal surface
should be free from machine and grinding marks and
should preferably be draw-polished. A generous ‘cold
slug-well’ should be positioned opposite the entrance
of the sprue into the mould whenever possible. In
addition to removing the piece of slightly chilled
material left in the nozzle from the previous shot, it
may also be designed with a ‘Z pin or back taper to
aid the removal of the sprue from the sprue-bush.
The cold ‘slug-well’ is ejected with the moulding and
runner system.
Runner Design
To facilitate the production of good quality mouldings,
particular attention should be paid to the design and
layout of the runner system.
Runners, like sprues, should be generous in diameter
and short in length to minimise pressure loss and
permit adequate follow-up pressure in the initial stage
of cooling.
Full-round runners give the best results (see Figure
33) but if these cannot be used trapezoidal runners
can be used satisfactorily. Half-round and flat
runners tend to cause premature freezing of the
melt and should not be used. In multi-cavity moulds
it is necessary to balance the runner layout by
having main and secondary runners to achieve
even pressure transmission into each cavity of the
mould. A cold slug overflow well should be provided
at the end of main runners.
Figure 33 Runners
As a guide to runner design and size the following
should be used:
For thin-section mouldings, ie 2.5 mm-4mm, the
main runner should be 6 to 8 mm in diameter.
For thick-section mouldings, ie 6 mm and
upwards, the main runners should be 10 mm
and above.
The large diameter runners are usually necessary
for items such as lenses, brush backs, insignias,
etc. If secondary runners are to be used they
should not be significantly smaller than the main
runner.
Hot Runner Moulds
The use of the hot-runner technique for feeding
multi-impression and large area mouldings is now
firmly established in the acrylic moulding industry.
The advantages of hot-runner mouldings are:
Melt enters the cavities in a more controlled
condition than with a sprue and runner system,
as temperature control in the hot runner is
adjustable to finer limits;
A possible reduction in post-moulding finishing
operations to remove large sprue gate witness
marks;
The elimination of cold sprues and runners in
multi-impression moulds which would normally
be scrapped or reworked;
DTM/E/2Ed/Nov01
page 35
Hot-runners enable single impression, large area
mouldings to be edge-gated, whilst keeping the
moulding in the centre of the machine platen.
Effective increase in the shot capacity of the
machine as, once the hot-runner is filled, the
injection capacity can be fully concentrated into
the cavities.
In designing hot-runner moulds (Figure 34) the
following important points should be observed:
Provide adequate heating for the hot runner
manifold (1.8 watts/cm3 or 30 watts/in3) and
nozzle (approximately 300 watts);
Make provision for closely controlling the
temperature of the manifold and nozzles with
suitable instruments;
Insulate the hot-runner manifold and nozzles
from the machine platen or mould cavities by air
or compressed temperature-resistant sheeting;
Provide adequate runner channels in the heated
manifold, ie minimum 12 mm diameter;
Make the machine nozzle orifice diameter of
similar size to the channels in the hot-runner
manifold;
Ensure that the runner channels are devoid of
any sharp corners or blind spots where melt
could become trapped and consequently
degraded.
DTM/E/2Ed/Nov01
page 36
Figure 34 General Assembly of Hot Runner Mould
DTM/E/2Ed/Nov01
page 37
Figure 35 General assembly and operation of typical three-plate mould
page 38
Three-Plate Moulds
These are normally used when multi-cavities for small
components are involved and semi- or fully-automatic
working is required. However, as indicated earlier, due
to the brittle nature of acrylic materials, this type of
design has to be used with care.
This type of mould, as it name suggests, has an extra
plate (see Figure 35). This plate (B) usually carries on
one side the gate and the complete runner system,
preferably trapezoidal, and on the opposite side the
plate carries part of the mould form (usually the
female part).
When the mould opens plate (B) is separated by
means of a delayed action mechanism (eg chains or
length bolts), so breaking the restricted gate. The
mouldings are then ejected from one daylight and the
sprue and runner system are ejected from the other.
Successful ejection of mouldings relies on clean
separation of the moulding and gate at the parting line.
With this method of tooling, restricted gates of the
correct design must be used (see Restricted gate,
Figure 37).
Multi-plate moulds are usually more expensive than
two-plate moulds and can be slower in production if
an operator has to remove the sprue and runner
system when the mould is open. This can usually be
avoided by providing automatic ejection of sprue and
runner. Such a mould is shown in Figure 35 where in
addition to plate (B) the runner is stripped out
automatically with a runner stripper plate (C). The
distance travelled by the plates is governed by the
length of the chain or the length of the bolts used to
separate them.
Gate Design
The type and position of the gate is often dictated by
the design of the component and the number of
mouldings to be produced in each cycle. For guidance
the following section provides information on different
gating methods.
Sprue Gate (Figure 36)
This type of gate is the preferred gate and is normally
used for single-impression moulds, especially suitable
when the component is cup shaped and involves a
Restricted Gate (Figure 37)
This type of gating is used for multi-cavity tools.
Finishing operations can often be eliminated
because the small gate is broken off during the
ejection of the moulding. The gate must not be too
small otherwise the filling of the cavity is impaired.
Also, under the effect of high injection pressures
frictional heating of the material passing through the
gate could lead to splash marking and burning on
the finished component. However the gate must not
be made too large otherwise it will not break off
satisfactorily during ejection. As a guide restricted
gates should not be smaller in diameter than 1.0
mm or greater than 1.8 mm. It is also essential to
have a generous runner system to prevent
premature freezing of the melt.
DTM/E/2Ed/Nov01
Figure 36 Sprue Gate
Figure 37 Restricted Gate
To prevent any cracking around the gate during the
ejection of the moulding (particularly where larger
gates are being used) the gate should have a slight
back taper so that it breaks off about 1.5 mm from
the surface of the moulding.
base. Its advantage over a side gate is that the flow
ratio is reduced and the mould will be filled
symmetrically. This system may be extended to multi-
impression moulds in conjunction with a hot-runner
assembly.
page 39
Owing to the notch effect, restricted gates should
be located at a point in the moulding subject to low
mechanical stresses. Also, where a clean finish is
required, the pronounced orientation of the material
in the gate area often hinders the removal of the
gate-mark by milling, due to small cracks occurring
along the lines of orientation. Hence care should be
taken in the removal of any restricted gates.
Side or Edge Gate (Figure 38)
This is the most common type of gate used to
produce components of a flat or shallow nature.
The size of the gate is dependent upon the shape
and thickness of the moulding. For normal 2 to 4
mm thick mouldings the gate thickness should be
two thirds that of the moulding. For thicker sections
the gate thickness should be approximately 75% of
the component thickness and as wide as the
runner. With multi-cavity moulds where the gates
are arranged in series, it is necessary to balance
the filling of the cavities. This is not always easy to
predict at the design stage of a mould and it may
be necessary to complete the balancing operations
by trial runs. Generally the gates furthest from the
sprue are given the greatest cross-section and
those nearest the sprue the smallest.
Flash Gate (Figure 39)
For long flat components of thin section this type of
gate can be used quite successfully. It enables a
large cavity to be filled quickly and consistently.
The length of the gate is dictated by the length and
width of the article and the flow pattern required. In
some instances it is advantageous to have the gate
the full length of the article, though usually a gate
length which is about 50% of the longer side
dimension is sufficient. However, it is important to
retain adequate thickness of the gate and therefore
more complex finishing operations will be required.
DTM/E/2Ed/Nov01
Figure 38 Side or Edge Gate
Figure 39 Flash Gate
Figure 40 Fan Gate
Fan Gate (Figure 40)
For thick section mouldings such as optical lenses,
this type of gating is used. It enables the runner to
be made of adequate size to aid flow and prevent
the material from chilling off when it is injected
slowly as is necessary when making these
components. It also allows sufficient follow-up
pressure to be maintained on the cavity during the
cooling contraction stage.
DTM/E/2Ed/Nov01
Spider Gate (Figure 43)
This is a variation of the diaphragm gate. It is
normally used for moulding large diameter
apertures and helps to reduce material wastage. A
disadvantage is that weld lines are created by the
meeting of the separate flow streams and this factor
needs to be considered at the component and
mould design stages.
page 40
Tab Gate (Figure 41)
This type of gating can be used as an alternative to
side gating to produce articles of a flat or shallow
nature. It has certain advantages over normal side
gates in that the design minimises the jetting of
material into the mould cavity which may lead to
weld lines and flow marks.
Tab gates are normally used to produce elongated
articles such as radio scales and rules. The tab in
these instances is located towards one end so that
the mould cavity is filled evenly down the greater
part of its length. The longitudinal orientation of the
material tends to strengthen the article and,
because the gate is remote from the centre point of
maximum stress, it avoids the risk of cracks
developing at the gate area if the moulding is
subsequently flexed.
Figure 41 Tab Gate
Figure 44
Figure 45
Figure 43 Spider Gate
Figure 42 Diaphragm Gate
Diaphragm Gate (Figure 42)
For single-impression moulds which are to be
produced with a central orifice, this type of gating
can be used to obtain uniform radial mould filling.
The diaphragm gate is removed by a subsequent
machining operation.
Ring Gate (Figures 44 and 45)
For single or multi-impression moulds which are to
produce tubular type articles this type of gate
ensures consistent filling of the moulds. It also
helps to ensure that the core pin is central with the
cavity, whereas using an ordinary side gate the
initial pressure would tend to displace the core pin
and so cause the article to have an uneven wall
section.
page 41
Submarine (Tunnel) Gate (Figure 46)
Although not recommended, this type of gate can
be used on multi-cavity moulds in a similar manner
to the restricted gate. It is normally used for articles
which cannot have a mould mark on the base or for
a tubular type article. The submarine gate differs
from the restricted system in that is below the
parting line of the mould. This means that the gate
will not break off until the moulding is ejected. It is
essential when using submarine gates to have a
sufficient taper on the gating system so that the
portion below the split line of the mould can be
easily removed with the runner system. This system
can be used to advantage with fully automated
moulds.
the material is exposed to the atmosphere for
excessive periods, or if material is kept under damp
storage conditions. Material should not be allowed
to remain in machine hoppers for more than a few
hours. When not in use, bags and containers
should be sealed and re-used as soon as possible.
Stock control should be practised so that material
storage time is kept to a minimum (recommended
maximum 3 months) and the risk of moisture pick-
up, through prolonged storage, reduced.
If material has become wet because of incorrect
storage or handling, splash or mica marks will be
observed on the surface of the moulded article. For
best results wet material should be dried with
dehumidified air driers at a temperature of 80-90°C
for the Lucite Diakon M grades (eg CMG) [type 8]
and 65-75° for the Lucite Diakon L grades (eg CLG)
[type 6] with the residence time in the drier not less
than 4 hours. Temperatures at or below the
minimum will require longer in the drier while
excessive temperature may lead to sintering of the
granules. If the throughput of the moulding
machine is greater than the time capacity of the
drier problems may occur if the moisture is not only
at the surface but has to diffuse from the centre of
the granule.
In those more critical moulding applications it may
be advantageous to pre-dry or pre-heat the material
straight from the bag or container prior to moulding.
Rework Material
There is a tendency for the original water-white
colour of acrylics to deteriorate slightly with
repeated reworking and hence it is recommended
that the amount of added rework material (scrap
moulding, sprues etc ground up for re-use) should
be limited when the moulded colour is critical. For
applications where colour is less critical, a common
addition level is 20%. Up to 100% of good quality
rework may be used with no significant fall-off in
properties but it is not to be recommended.
It is essential to ensure that the grinder is clean and
that dirt contamination is not included during the
grinding process.
DTM/E/2Ed/Nov01
Figure 46
Gating of Thick Sections
To prevent sink marks and voids which must be
absent when moulding lenses and prisms, the
material shrinkage (a few per cent from melt to solid
state) must be compensated by the flow of
additional material into the mould during cooling.
This flow of material can occupy several minutes
depending on the thickness of the moulding.
Hence the cross-section of the runner and gate
must be of adequate size to prevent the gate
freezing-off too soon.
The edges of the components must not be too thin,
as could occur with the edge of a lens, since
insufficient area would be available for the gate. In
producing thick section articles of this type the gate
thickness is more important than the width and
should, in general, be at least three-quarters the
thickness of the edge section. In order to prevent
any flow lines the edge of the gate should be
slightly radiused and the cavity must be filled slowly.
Runner lengths should be kept to a minimum.
MOULDING TECHNIQUE
Care of Raw Material
Lucite Diakon acrylic polymers are normally suitable
for moulding without any preliminary drying
operation. However, moisture will be absorbed if
page 42
The screen size on the grinder should be 3 mm- 6
mm. Larger screens should not be used since
difficulty could be encountered in feeding, melting
and processing larger particles, particularly if rework
material is being blended with coloured material or
used on shallow-flighted screws.
It is usually necessary to dry rework material prior
to moulding if it has been exposed to the
atmosphere for any length of time. The drying
conditions for rework material are the same as used
for virgin material. It is generally possible, by
grinding sprues and runners soon after they have
been moulded and keeping the material protected
from the atmosphere, to mould it without drying.
Contamination
Lucite Diakon is not compatible with other moulding
materials and strict precautions must be taken to
prevent contamination which is immediately visible
because of the high transparency of the material.
Contamination with other clear materials
(polystyrene and polycarbonate) results in white
cloudy streaks due to differences in refractive index.
Because Lucite Diakon is a good electrical
insulator, it will pick up atmospheric dust by
electrostatic attraction. Care must therefor be taken
when loading machine hoppers to prevent
unnecessary exposure.
Purging
Being a clear material, the changeover from other
materials to Lucite Diakon is more difficult than with
opaque plastics, and many moulders keep a
separate cylinder soley for moulding acrylic. Where
a separate cylinder for acrylic is not available the
most convenient way to clean the cylinder, apart
from a complete strip down, is to purge the machine
using rework Lucite Diakon with the nozzle
removed. The nozzle can be ‘burnt out’ separately.
Where black or heavily filled materials are to be
removed from the cylinder it is useful to use scrap
natural unfilled polypropylene as a purging
compound before changing over to rework Lucite
Diakon.
When purging it is recommended that the cylinder
temperatures be raised during the initial stages of
the operation. This assists removal of material from
cylinder walls. Obviously care must be taken not to
disrupt the carbonised layer on the screw and barrel
or use excessive temperatures which could cause
severe decomposition of the material. After a short
while, temperatures should be reduced and the
machine purged with Lucite Diakon at lower
temperatures to remove remaining traces of
unwanted material. Once the purging operation is
complete a clean nozzle should be fitted.
Temperature Control
The melt viscosity of acrylic is more temperature
dependent than that of many other thermoplastic
materials as can be seen in Figures 47,48 and 49.
It follows, therefore, that the moulding conditions
must be accurately controlled.
DTM/E/2Ed/Nov01
Figure 47 Variation of melt viscosity with
temperature for different thermoplastics
(Shear rate 1000 s-1)
DTM/E/2Ed/Nov01
page 43
Figure 48 Variation of melt viscosity with temperature for different grades of standard Lucite Diakon
(shear rate 1000s-1)
Figure 49 Variation of melt viscosity with temperature for different grades of Lucite Diakon ST
(Shear rate 1000 s-1)
DTM/E/2Ed/Nov01
page 44
Position of Thermocouples
Controlling thermocouples should be located as
close as possible to the heaters they control, eg in
a slot directly under the band heaters. This
arrangement eliminates any time lag in the
response of the controllers and minimises cyclic
variations in temperature.
Measurement of cylinder wall temperatures may be
made by a set of deeply recessed thermocouples
connected to a separate recorder. Such facility is not
essential for production purposes but it is a useful
guide for establishing optimum conditions and for
experimental work.
Nozzle Temperature Control
This subject is discussed on page 30 but it is
recommended that wherever possible separate
control of the nozzle temperature should be used.
For long or extended nozzles separate control is
essential to minimise any defects such as matt
patches or splash marking around the sprue which
occur because of the nozzle being too cold or
too hot.
Moulding Conditions
The actual moulding temperatures and pressure
setting required will vary from grade to grade and
from one type of machine to another, depending on
the size of the machine and the shot weight of the
moulding. They will also depend on the design and
section thickness of the component. The material
temperature may be higher or lower than the
indicated cylinder temperature depending on the
amount of frictional heat introduced by the screw. It
is therefore not possible to be specific about the
Figure 50 Variation of melt viscosity with stress for
CMG302 at different temperatures.
exact moulding conditions for Lucite Diakon and
each case must be considered on its own merit and
in the light of experience.
However, remembering that Lucite Diakon has a
high melt viscosity which is very temperature
dependent when compared to many other
thermoplastic materials, the moulding conditions in
table 6 may be used as a guide for all grades, using
the higher end of the melt temperature range for
higher viscosity grades.
Moulding Type
Normal Large Area Thick Section
Melt 230 to 250°C 260 to 270°C As low as 180°C
Mould temperature 60 to 70°C 70°C 70°C
Screw speed Medium Medium Slow
Back pressure Low (to medium) Low (to medium) High (to medium)
Injection speed Medium to fast Medium to fast Slow to very slow
Cycle time 40 seconds 70 seconds > 2 minutes
Table 6 Guide to moulding conditions
DTM/E/2Ed/Nov01
page 45
Gate Size
The influence of gate size on mouldability or flow
ratio of Lucite Diakon cannot be overstressed.
There is a natural desire to use small gates to
minimise both finishing operations and gate witness
marks. However, the quality and ease of producing
Figure 51 Influence of gate size and melt temperature on the approximate flow ratio for Lucite Diakon
CMG302
mouldings are significantly improved by using large
gates with a balanced sprue and runner system.
Figure 51 shows the influence of gate size and melt
temperature on the approximate flow ratio for Lucite
Diakon CMG302.
page 46
Cylinder Temperatures
Due to the many factors influencing material or melt
temperature it should be noted that melt and cylinder
temperatures are unlikely to be identical and in fact
may differ by a significant amount.
The approximate range of melt temperature over which
Lucite Diakon may be moulded is 200 to 270°C. For
average size mouldings the easy flow Lucite Diakon
type 6 grades will be in the low to middle range and the
higher viscosity Lucite Diakon Type 8 grades in the
middle to high range. It is common to optimise
temperature settings by applying a small gradient to the
cylinder temperature; 5 to 10°C lower at the nozzle and
10 to 20°C lower at the rear or feed zone.
In the absence of experience or correlation between
melt and cylinder temperatures then initial cylinder
temperature settings of 240°C are recommended.
Mould Temperature
It is essential when moulding Lucite Diakon to have
adequate provision for controlling the mould
temperature. Both halves of the mould should be cored
for circulating water at a controlled temperature. With
some mould designs and component shapes it may
well be necessary to control the mould halves at
different temperatures to achieve an acceptable
product. A separate circuit should be used to control
the sprue bush temperature.
The recommended mould temperature for the Lucite
Diakon type 8 grades is between 60 and 80°C
depending upon section thickness and flow path, and
for Lucite Diakon type 6 grades 55-70°C.
Machine Start-Up
Injection moulding machines should not be allowed to
stand idle for long times while at moulding
temperatures, since this allows heat to conduct
backwards along the screw and could cause material to
melt on to the feed section of the screw and create an
obstruction. Where a delay is involved, rear temperature
should be temporarily reduced. Controlled water should
be circulated around the feed pocket during the heating
up period to prevent this section from becoming too hot
and causing sticking of prematurely melted material.
When in production the feed throat should be
maintained between 40 and 60°C.
If any mould setting is required on the injection unit this
should be done once the cylinder has attained the
moulding temperature. The machine and mould should
never be ‘set’ when cold, otherwise the expansion of
the injection unit when it reaches moulding
temperatures could cause serious damage.
Before commencing to mould, the machine should be
purged briefly to ensure that the material in the barrel is
clean and at the right temperature.
Screw Back Pressure
When the screw unit is plasticising, a regulated forward
hydraulic pressure is applied to the screw in partial
opposition to the back pressure generated by the
plasticised melt. The regulated pressure is known as
the screw back pressure or screw reaction pressure. If
this back pressure is greater than the pressure
generated by the melt in front of the screw then no
screw retraction will take place. However, by
adjustment of the screw back pressure, the screw may
be made to refill under controlled conditions and
produce a uniform melt.
Some back pressure is desirable to help expel air from
between the polymer particles or granules and so
prevent air from being included in the melt. Otherwise
this may lead to burning of the material in the cylinder
and may show as splash marks or bubbles (generally
with white inclusions) in the moulding, or in the extreme
case as black streaks. Screw back pressure is also
useful with blends or dry coloured material to aid
mixing, particularly where lightly tinted materials are
being processed. An increase in screw back pressure
causes more work to be done on the material and so
enhances mixing. However, excessive use of back
pressure can lead to overheating of the material die to
frictional heat, which will show as splash marks and
could eventually lead to screw slip (see below) due to
overheating of material on the rear section of the screw.
Screw Speed
Because acrylic moulding materials have relatively high
melt viscosities, attention must be paid to the screw
speed to avoid excessive frictional heating and
degradation. The screw speeds to be used vary
according to the size of machine (ie screw diameter)
and type of article being moulded, but in general they
should be kept as low as possible consistent with an
acceptable cycle time. For shot weights up to 250g
screw speeds of 80-100 rpm are used satisfactorily; for
machines with large diameter screws it is necessary to
keep screw speeds low in the range of 30-40 rpm.
DTM/E/2Ed/Nov01
page 47
Where temperature controllers indicate a marked
tendency to override the preferred set temperature
due to frictional heating, then adjustment of screw
speed and back pressure should be considered. If
full correction by this means is not possible, but the
developed temperature can be accepted, then the
temperature controller should be re-set to control
the temperature at a higher level.
Screw Slip
This term is applied when the screw turns but does
not refill. It is generally caused by molten or semi-
molten material, in or close to the feed section,
sticking to the screw flights and so impeding the
entry of fresh material into the cylinder. It can also
be caused by too high a screw back pressure.
Screw slip can occasionally occur during start-up.
This arises because the machine has been allowed
to stand at moulding temperature for too long a
time. Under these conditions, heat from the cylinder
conducts along the screw raising the temperature of
the rear section of the screw which then causes
premature melting of material in the feed flights.
This is especially so if the screw flights are full of
material.
To overcome screw slip, ie remove the blockage
caused by molten or semi-molten material, the
temperatures of the rear zone and feed pocket
should be lowered, insuring cooling water is
circulating around the feed throat and the machine
purged with rework material. In extreme instances
the rework material may have to be force-fed on to
the screw. Purging should be continued until the
rear temperature stabilises and the screw refills
consistently.
Where an extended delay is likely to occur it is a
wise precaution to increase cooling to the feed
throat and reduce the rear zone cylinder
temperature to about 150°C.
Injection Speed
There are contradicting requirements on the rate of
filling the mould with acrylic materials. Fast injection
speed decreases cycle time, prevents premature
freezing of the melt before the mould is full and
improves the strength of weld lines. However, with
fast injection speed there is a strong possibility of
frictional heat and splash marking, especially with
small gates, flow lines may be more obvious and
there is a higher risk of flashing the mould.
Programmed injection allows a balanced rate of fill
to be achieved. Fast to medium for the majority of
the shot and medium to slow for the balance.
Shrinkage of Mouldings
Shrinkage of mouldings is caused by the reduction
in volume which the material undergoes when it
changes from the molten to the solid state in the
mould and continues to cool to room temperature.
The shrinkage expressed as a fraction, or as a
percentage, is based on the difference between the
dimensions of the cold moulding and of the cold
mould. The extent of shrinkage of Lucite Diakon,
like that of other thermoplastics, is dependent on
the component design, gate design, moulding
conditions and the manner in which the melt flows
to conform to the shape of the tool.
It is almost impossible to predict accurately the
exact amount of shrinkage which will take place on
a given article but approximate shrinkage figures
which may be used as a guide can be obtained by
measurements made on specific test pieces. If
accurate dimensions are required on the finished
components, it is necessary first to carry out trials
under controlled moulding conditions and then to
make final adjustments to the mould dimensions.
When doing this it is essential to measure the
component sometime after moulding to ensure that
full contraction has occurred. The moulding must be
kept dry during this time and it is important to
measure all critical dimensions both in line with, and
across, the flow path of the material, since
shrinkage can vary with the direction of melt flow.
Shrinkage can be adjusted to some extent by the
moulding conditions, but it must be emphasised that
the amount of shrinkage which may be controlled in
this way is limited and is not always sufficient to
compensate entirely for a mould which has been
made grossly under or over size. This sort of
practice may also lead to the danger of excessive
residual stress in a moulding.
On average the shrinkage of Lucite Diakon is in the
order of 0.3 to 0.7%, the higher shrinkage applying
to a thicker moulding.
DTM/E/2Ed/Nov01
DTM/E/2Ed/Nov01
page 48
From experiments with various components, the
following conclusions can be drawn:
Shrinkage is inversely proportional to injection
pressure;
Shrinkage is directly proportional to mould
temperature;
Shrinkage is directly proportional to melt
temperature.
It is worth noting that the flow pattern to the
component will tend to determine which is the main
factor in controlling the shrinkage of the moulding.
For example, the shrinkage of long thin mouldings
exhibiting linear flow paths will be dependent more
on changes in injection pressure and speed than on
other variables, while shrinkage of moulding
exhibiting radial flow paths will be more dependent
on changes in melt and/or mould temperature.
DISTORTION
Acrylic materials are amorphous and therefore
significantly less prone to distortion than crystalline
materials. However, distortion or warpage of
mouldings can occur and is the result of differential
cooling rates; the consequence of incorrect
moulding conditions, Figure 52, or component
design, Figure 53.
Figure 52 Influence of mould temperature on
distortion
Figure 53 Influence of Component Design on
Distortion
Strain in Mouldings
Two types of strain can occur in injection mouldings
and these are of consequence in relation to the
subsequent service behaviour of the moulded
component. These strains arise from:
Molecular orientation - introduced during the flow
of the molten polymer in the mould and frozen in
during cooling.
Quenching or cooling stress - resulting from a
differential rate of cooling between the surface
and the interior of the component.
Refer to the section on Stresses and Molecular
Orientation in Lucite Diakon Components on page
72 for information on causes, problems, testing and
remedy.
page 49
MOULDFLOW SIMULATION
Previous sections have described and considered
basic principles on the injection moulding of Lucite
Diakon; including equipment, component design,
mould design and processing conditions. This
information has been gleaned from many years of
practical experience in the injection moulding of
acrylic materials. However significant effort has
been put into the development and use of software
packages to simulate various aspects of the
injection moulding process. Although the initial
component design, method of production and
subsequent mould design still has to be done, these
mouldflow programmes are significant aids to
assessment of component design, tool layout
including feed system, processing conditions and
possible problem areas.
A series of rheology measurements, coefficients
and thermal properties for each specific Lucite
Diakon grade is required as data input for the
software packages. As an illustration, Table 7
provides the information for Lucite Diakon
CMG314V, the standard normal molecular weight
type 8 grade.
DTM/E/2Ed/Nov01
Obs. Shear Rate Exp. Visc. Temp. Calc.Visc. Diff.% Temp. Shift Std Temp
1. 30.00 7116.00 210. 7835.76 -9.19 7.25 218.99
2. 60.00 4864.00 210. 4782.23 1.71 12.06 221.05
3. 100.00 3454.00 210. 3290.69 4.96 14.42 221.75
4. 150.00 2526.00 210. 2437.05 3.65 14.14 221.68
5. 300.00 1465.00 210. 1452.03 .89 13.20 221.41
6. 600.00 880.00 210. 862.40 2.04 14.37 221.74
7. 1000.00 594.00 210. 586.79 1.23 14.23 221.70
8. 1500.00 442.00 210. 432.10 2.29 15.15 221.94
9. 3000.00 259.00 210. 255.98 1.18 14.90 221.88
10. 6000.00 147.50 210. 151.59 -2.70 12.99 221.34
11. 30.00 4157.00 230. 4238.71 -1.93 1.44 231.79
12. 60.00 2826.00 230. 2845.69 -.69 1.68 232.51
13. 100.00 2089.00 230. 2046.82 2.06 2.01 233.37
14. 150.00 1565.00 230. 1552.29 .82 2.06 233.47
15. 300.00 952.00 230. 948.24 .40 2.21 233.80
16 600.00 577.00 230. 570.52 1.14 2.43 234.23
17. 1000.00 395.00 230. 390.25 1.22 2.53 234.41
18. 1500.00 289.00 230. 288.14 .30 2.49 234.35
19. 3000.00 169.00 230. 171.15 -1.26 2.42 234.22
20. 6000.00 93.00 230. 101.49 -8.37 1.82 232.89
21. 30.00 1720.00 250. 1679.00 2.44 .29 243.42
22. 60.00 1377.00 250. 1351.59 1.88 .31 243.75
23. 100.00 1076.00 250. 1087.84 -1.09 .31 243.79
24. 150.00 860.00 250. 885.93 -2.93 .31 243.87
25. 300.00 570.00 250. 589.62 -3.33 .34 244.39
26. 600.00 373.00 250. 372.92 .02 .43 245.62
27. 1000.00 264.00 250. 260.65 1.29 .49 246.27
28. 1500.00 196.00 250. 194.61 .71 .50 246.39
29. 3000.00 120.00 250. 116.93 2.63 .57 247.13
Table 7 Mouldflow rheology measurements for Lucite Diakon CMG314V
CARREAU EQUATION
REFERENCE TEMPERATURE = 230.00
Fitted activation energy = 165714.93108
Fitted E/R = 19931.07581
THE CARREAU EQUATION
COEFF. P1 = 10369.
COEFF. P2 = .75453e-01
COEFF. P3 = .75629
Fit Coeff. = .99928
DTM/E/2Ed/Nov01
page 50
1st Order 2nd Order
Obs. Shear Rate Exp. Visc. Temp. Calc. Visc. Diff.% Calc.Visc. Diff.%
1. 30.00 7116.00 210. 7111.64 .06 7373.77 -3.50
2. 60.00 4864.00 210. 4394.17 10.69 4760.55 2.17
3. 100.00 3454.00 210. 3081.64 12.08 3390.75 1.87
4. 150.00 2526.00 210. 2325.25 8.63 2563.96 -1.48
5. 300.00 1465.00 210. 1436.74 1.97 1557.21 -5.92
6. 600.00 880.00 210. 887.74 -.87 921.21 -4.47
7. 1000.00 594.00 210. 622.57 -4.59 615.21 -3.45
8. 1500.00 442.00 210. 469.76 -5.91 442.01 .00
9. 3000.00 259.00 210. 290.26 -10.77 245.99 5.29
10. 6000.00 147.50 210. 179.35 -17.76 133.34 10.62
11. 30.00 4157.00 230. 4331.19 -4.02 3923.97 5.94
12. 60.00 2826.00 230. 2676.18 5.60 2648.24 6.71
13. 100.00 2089.00 230. 1876.81 11.31 1948.91 7.19
14. 150.00 1565.00 230. 1416.15 10.51 1512.44 3.48
15. 300.00 952.00 230. 875.01 8.80 960.23 -.86
16 600.00 577.00 230. 540.66 6.72 593.82 -2.83
17. 1000.00 395.00 230. 379.16 4.18 409.75 -3.60
18. 1500.00 289.00 230. 286.10 1.01 302.13 -4.35
19. 3000.00 169.00 230. 176.78 -4.40 175.77 -3.85
20. 6000.00 93.00 230. 109.23 -14.86 99.60 -6.63
21. 30.00 1720.00 250. 2637.82 -34.79 1968.00 -12.60
22. 60.00 1377.00 250. 1629.87 -15.51 1388.42 -.82
23. 100.00 1076.00 250. 1143.03 -5.86 1055.73 1.92
24. 150.00 860.00 250. 862.47 -.29 840.83 2.28
25. 300.00 570.00 250. 532.91 6.96 558.05 2.14
26. 600.00 373.00 250. 329.28 13.28 360.75 3.40
27. 1000.00 264.00 250. 230.92 14.32 257.20 2.64
28. 1500.00 196.00 250. 174.24 12.49 194.63 .70
29. 3000.00 120.00 250. 107.66 11.46 118.37 1.38
1st Order (Power Law) Coeff.A = .13781E+08
Coeff.B = -.69459
Coeff.C = -.24794E-01
Fit Coeff. = .98896
2nd Order (Quadratic) Coeff.A1 = 16.003
Coeff.A2 = -1.0980
Coeff.A3 = -.98320E-02
Coeff.A4 = -.27380E-01
Coeff.A5 = .31997E-02
Coeff.A6 = -.74073E-04
Fit Coeff. = .99827
Specific heat capacity 2300 J/kg deg C
Thermal conductivity 0.2 w/m deg C
Melt density 1100 kg/mx3
No flow temperature 160 deg C
Freeze temperature 120 deg C
page 51
A joint exercise between Lucite International and
Plastics Design Solutions Ltd (See Appendix II for
full address) was carried out to illustrate how data
for the mouldflow simulation process may be used
to influence the design optimisation and production
of Lucite Diakon mouldings. The simple component
design representing an instrument panel lens
together with cavity, sprue, runner, gate size and
gate position variations is illustrated in Figures 54
and 55. A matrix of mouldflow data obtained from
these variations together with changes in material
and processing conditions is listed in Table 8.
DTM/E/2Ed/Nov01
Table 8 Summary of conditions and results
LUCITE DIAKON® Cavity Gate Gate Sprue Injection Melt Melt Apparent Maximum Maximum Maximum Average Comment
Grade Thickness Size Position and Time Flow Temp. Bulk Melt Pressure Shear Shear Shear Rate
mm mm Runner seconds Rate °C Temp. Bar Stress at Gate at Gate
cm3sec-1 °C KPa sec-1 sec-1
CMG314V 2.2 1 x 5 B Good 2 65 250 - 1,793 776 47,100 - infuence
CMG314V 2.5 1 x 5 B Good 2 73 250 - 1,505 796 51,600 - of cavity
CMG314V 2.8 1 x 5 B Good 2 81 250 - 1,321 812 56,800 - thickness
CMG314V 2.5 1 x 5 A Good 2 68 250 - 967 750 48,400 - see fig 56
CMG314V 2.5 1 x 5 B Good 2 73 250 - 1,505 796 51,600 -
CMG314V 2.5 1 x 5 C Good 2 81 250 - 1,808 818 56,700 -
CMG314V 2.5 1 x 5 B Good 2 73 250 252 1,505 796 51,600 - see fig 57
CMG314V 2.5 1 x 5 B Poor 2 68 250 283 2,135 746 46,200 -
CMG314V 2.5 1 x 5 B Good 0.5 146 250 - 1,795 1,010 200,900 - see fig 58
CMG314V 2.5 1 x 5 B Good 1.7 86 250 - 1,532 818 60,300 -
CMG314V 2.5 1 x 5 B Good 3 36 250 - 1,725 742 35,800 -
CMG314V 2.5 1 x 5 B Good 2 73 230 - 2,050 994 - - see fig 60
CMG314V 2.5 1 x 5 B Good 2 73 250 - 1,505 796 - -
CMG314V 2.5 1 x 5 B Good 2 73 270 - 1,067 661 - -
CMG314V 2.5 1 x 2 B Good 2 73 250 - 1,604 1,010 204,200 169,400 see fig 59
CMG314V 2.5 1 x 5 B Good 2 73 250 - 1,505 796 51,600 44,500
CMG314V 2.5 2 x 5 B Good 2 73 250 - 1,423 672 18,100 16,400
CMH454 2.5 1 x 5 B Good 2 73 250 - 1,596 816 - - infuence
CMG314V 2.5 1 x 5 B Good 2 73 250 - 1,505 796 - - of Lucite Diakon
CLG356 2.5 1 x 5 B Good 2 73 250 - 502 584 - - grade
Figure 54 Component and mould cavity layout Figure 55 Sprue and runner designs
DTM/E/2Ed/Nov01
page 52
Figure 56 Influence of gate position on injection pressure,
illustrates that cavity layout has a significant
effect on the required injection pressure and
resultant machine size through locking force
requirement. Similar plots are obtained for
filling pattern and material shear stress. These
may indicate possible distortion, air entrapment
or frictional heating problems
DTM/E/2Ed/Nov01
page 53
Figure 57 Influence of sprue and runner design on temperature and shear rate profiles. As indicated in other
sections on design and processing, the comparatively high melt viscosity and shear sensitivity of
acrylic materials may lead to overheating, degradation and monomer splashing. Although the
figures produced in a simulation exercise may not be exactly those obtained in practice, the
results in Figure 57 strongly underline the difference between good and bad design in the feed
system. It also illustrates that it is often the feed system and not the mould cavity that controls and
influences the injection moulding process. There are many occasions where mouldflow exercises
are limited to the actual component cavity but for the purpose of production efficiency it is
recommended that consideration is given to modelling the feed system
DTM/E/2Ed/Nov01
page 54
Figure 58 Influence of injection time on injection
pressure, shows that there is an
optimum fill time to minimise injection
pressure although other factors like
degree of sinking may influence this
Figure 59 Influence of gate size on shear rate at
the gate, aptly illustrates the frictional
shear degradation problems that often
occurs on the injection moulding of
acrylic materials due to the use of small
gates
DTM/E/2Ed/Nov01
page 55
Figure 60 Influence of melt temperature on injection
pressure. This figure is included to
demonstrate how the mouldflow simulation
may be used to influence processing
conditions
DTM/E/2Ed/Nov01
page 56
MOULDING FAULT REMEDIES
The following table lists the main moulding faults
likely to be encountered, their causes and the
procedures to be followed in order to correct the
faults.
Moulding Fault Remedy
Splash or mica marks, surface streaks A Too Hot
These are caused by volatiles (moisture, 1 Reduce cylinder temperature
monomer) in the melt. 2 Reduce hot runner temperature
A major source of degradation and 3 Reduce screw speed
splash marks is excess frictional heat. 4 Reduce back pressure
5 Reduce injection speed
6 Increase size of sprue/runner/gate
B Too cold
1 Raise cylinder temperature
2 Raise nozzle temperature
C Moisture
1 Dry the material (70 to 80°C for 6 to 12 hours)
Burning or entrapment of air in cylinder
This usually appears as splash marks and small bubbles with 1 Increase back pressure
white inclusions. In its severest form as black streaks. 2 Decrease screw speed
Burn marks on moulding 1 Reduce injection speed
Usually appear on extremities of the moulding and 2 Reduce injection pressure
are caused by insufficient venting of the cavities. 3 Reduce mould locking pressure
4 Reduce cylinder temperature
5 Improve venting of cavity
Matt patches on moulding surface 1 Check nozzle seating for dribble
These generally occur in the same position on each moulding, usually 2 If using vacuum suck-back check operation
close to the gate area. Often caused by a cold slug from the nozzle. 3 If nozzle has mechanical shut-off check operation
4 Increase nozzle temperature
5 Incorporate cold slug-well opposite sprue or enlarge
existing one
6 Polish runner and gate
‘Orange peel’ and smudge marks 1 Reduce cylinder temperature
Surface imperfections resembling orange peel that occur in the gate area. 2 Reduce mould temperature
3 Reduce injection time
4 Increase injection speed
5 Reduce injection pressure
6 Examine gate area for roughness, and polish
if necessary
Voids and sink marks 1 Check feed setting
These are usually due to insufficient pressure to counterbalance material 2 Increase injection pressure
shrinkage in thick sections or in sections furthermost from the gate. 3 Increase injection time
4 Increase injection speed
5 Reduce mould temperature
6 Reduce cylinder temperature
7 Enlarge gate, sprue or runner to reduce
pressure loss
DTM/E/2Ed/Nov01
page 57
Moulding Fault Remedy
Short shot (incomplete filling of mould) or rippled surface 1 Check feed setting. Make sure sufficient material available
This usually occurs in an area furthest from the gate. It is usually 2 Increase injection speed
accompanied by a rippled surface in the area surrounding the 3 Increase injection pressure
short, shot. 4 Increase injection forward time
5 Increase mould temperature
6 Increase cylinder temperature
7 Enlarge gate, sprue or runners to reduce pressure loss.
Warping 1 Increase cooling time
Caused by uneven shrinkage in the moulding. Occurs particularly 2 Use even (both sides) mould temperatures for flat mouldings
on flatmouldings or mouldings with long edges. Also found on 3 Use differential mould temperature control over mould
mouldings of uneven section. surfaces, or between mould halves where opposite surface
areas differ.
4 Adjust injection speed.
5 Reduce cylinder temperatures.
6 Use clamping jig in which to cool mouldings.
Weld lines, flow lines 1 Increase injection pressure
These are caused by the melt separating and rejoining in the mould. 2 Reduce injection speed (Occasionally, to eliminate weld
They usually occur around inserts or as tails from raised characters lines, it may be necessary to increase injection speed)
of sections 3 Increase mould temperature
4 Increase cylinder temperature
5 Change location of gate to alter flow pattern
6 Radius corners to improve flow in mould
Jetting or flow line 1 Reduce injection speed
Usually occur in gate area 2 Reduce cylinder temperature
3 Use tab gate
Crazing 1 Clean mould surface
This occurs as minute surface cracks on the moulding, 2 Increase injection speed
usually in line of flow 3 Increase mould temperature
Delamination 1 Check for contamination
This usually occurs in the gate area or as blisters on the moulding
surface
Cracking or breaking of the part on ejection 1 Decrease injection pressure
2 Decrease injection time
3 Mould opening and ejection speed
4 Increase mould temperature
5 Increase draft angle
6 Eliminate sharp corners and undercuts.
page 58
EXTRUSION
The high molecular weight grades of Lucite Diakon
are normally recommended for extrusion and a
range is available to provide combinations of
properties suited to particular applications.
Where increased toughness is required a range of
Lucite Diakon ST grades is available.
Acrylic materials produce melts which are generally
higher in viscosity than many other thermoplastic
materials under normal processing conditions. The
melt viscosities of the individual grades of Lucite
Diakon are shown in Figures 22 and 23, pages 25-
26.
EXTRUDER
Barrel Design
Single screw vented barrel extruders with bi-metallic
or nitrided barrels are recommended for extruding
Lucite Diakon. (See Appendix III, Volatile Chemicals
Evolved During Processing of Lucite Diakon Acrylic
Polymers.)
Screw Design for Vented Extruders
In the extrusion process a great deal of the power
input to the screw is converted into heat by the
shearing action of the screw on the material. It
follows that screw profile designs need to be
carefully chosen to obtain maximum output per
revolution coupled with adequate homogenisation
without excessive adiabatic heat evolution.
The minimum length/diameter (L/D) ratio for a
vented barrel extruder screw suitable for acrylic
material is about 27:1 but higher L/D ratios of 33:1
are available and these are preferred since they
give higher and extremely steady outputs. Screws
are generally nitrided or chromium plated, or have
‘flame-protected’ flights.
If surging is to be avoided a long feed section is
desirable in the screw since acrylic material is hard
and must have sufficient time to plasticise before it
is compressed. A compression ratio of between
2.2:1 and 3.0:1 is recommended for the first stage
of the screw and a pump ratio (volume of first
metering section to volume of second metering
section) between 1:1.5 an d 1:2.0. A deep
decompression zone in the second stage of the
screw is recommended in order to accommodate
melt swell.
Feed Throat
Feed throats are usually fitted with surrounding
water temperature control to prevent bridging or
premature melting of material. Where Lucite Diakon
bead polymer is used it is essential always to
operate with water cooling on the feed throat.
Breaker Plate
A breaker plate and filter pack are not absolutely
necessary with virgin Lucite Diakon, but can help
pigment dispersion in coloured material and where
rework is being processed, acting as a safety
precaution. Where used, the filter pack would
consist of one fine mesh (aperture 75-150 micron)
supported by a coarser mesh (250-300 micron) and
a breaker plate. Manual or automatic filter changers
are usually incorporated in extruders having barrel
diameters 90 mm and above.
Vacuum Pump
In order to obtain the full benefit of the vented barrel
a vacuum pump should be connected to the vent
port so that all the volatiles can be removed from
the melt as it passes through the decompression
zone. A vacuum pump is absolutely necessary
when operating at high screw speeds if a clear,
glossy extrudate is required.
It is essential to have an efficient water cooled
condenser between the vent port and the vacuum
pump in order to collect the volatiles emitted and
thus prevent the pump from becoming blocked.
All pipes between the vent port and the vacuum
pump should be of at least 50 mm bore and ideally
should be insulated to prevent premature
condensation of the volatiles. Any sharp bends or
restrictions in the pipework should be avoided since
they could be readily blocked if premature
condensation takes place.
DTM/E/2Ed/Nov01
page 59
SHEET EXTRUSION
Extruder
An adequately powered vented barrel extruder with
suitable screw design is essential since the removal
of volatiles is necessary in order to obtain good
surface finish at high throughputs.
Die
Correct die design is of prime importance. The die
must be:
Robust enough to withstand high internal
pressures;
Capable of easy adjustment to give uniform flow
across the width;
Free of any hold-up areas so that material and
colour changes can rapidly be carried out;
Free from any blemishes, particularly on the die
lips, which could cause die lines.
Various dies have been developed to obtain uniform
flow across the width; the best of these is the
truncated fishtail manifold die sometimes known as
the ‘coathanger’ die as shown in Figure 62.
The finish of the die lips is of great importance
because any imperfection, particularly on the exit
edge, will immediately be transferred to the moving
sheet as it leaves the die causing die lines. Die lips
are usually made of tool steel and are carefully
machined and polished before being hard chromium
finished for protection. The exit edge is normally
radiused very slightly, about 0.25 mm.
If a wide range of sheet thickness is to be
produced, it will be advisable to have three sets of
lips with different parallels in order to maintain
uniform pressure inside the die body.
Recommended die parallels are given in Table 9.
DTM/E/2Ed/Nov01
Figure 61 Sheet extrusion line layout
Sheet thickness (mm) Die parallel (mm)
Up to 2.5 60
2.5 to 5.0 100
5.0 to 10.0 150
Table 9 Recommended die parallels
Three-Roll Polishing Stack
Various methods have been devised to handle and
cool the extruded acrylic sheet as it leaves the die
but the method generally used is that based on a
three-roll polishing stack. The three-roll stack and
ancillary equipment form a versatile unit capable of
handling most thermoplastic sheets and can produce
either a plain or embossed finish. The best system
for acrylic sheet extrusion is the one based on a
separate motor for each roll.
Whilst the sheet is travelling round the rolls it is
cooled uniformly, polished to remove any fine die
lines caused by imperfections in the die lips and
calendered to improve the thickness tolerance
across the width. Sheet produced with a three-roll
stack should have an excellent surface finish, and if
conditions are carefully controlled, will possess low
residual stress and hence exhibit low shrinkage on
reheating before shaping. Thickness tolerances of
±3%, and even less, are possible.
Patterned or embossed sheet can readily be
produced by fitting an embossing roll in the central
position. The operation is then identical to that used
for producing plain sheet.
page 60
The temperature of embossing rolls must be
accurately controlled and is normally slightly lower
than that required for the production of plain sheet.
The actual roll temperatures depend to some extent
on the pattern and are generally within the range 90-
125°C for three-roll operation. To avoid corrosion and
difficulty in cleaning, it is advisable to have embossing
roll patterns protected by a final flash-chroming.
Surface Protection
In some cases it is desirable to protect the surface
of the sheet with polyethylene film. The film should
be approximately 0.05 mm thick and applied to the
sheet while it is still warm by a separate set of
lightly pressurised rubber-coated rolls positioned
after the thickness monitor and just before the roller
table. The film must be surface treated by electronic
discharge techniques up to 900 W/m2 on the side
which is pressed to the sheet in order to give good
adhesion.
CO-EXTRUSION
With co-extrusion, the advantages of Lucite Diakon
acrylic materials; improved UV resistance and
outdoor weathering, colourability, surface gloss and
surface hardness; are obtained by simultaneously
extruding a thin layer of Lucite Diakon onto the
normal thickness plastic substrate; for example
PVC or ABS. The co-extrusion, commonly referred
to as capping, may be carried out on sheet, profile
and tube.
Selection of the appropriate standard grade of
Lucite Diakon or impact modified grade of Lucite
Diakon ST depends upon the substrate and the
capping properties required. Lucite Diakon ST
grades may also be used to improve the detergent
craze resistance for vanity sinks, work tops and
shower cubicles used in caravans, mobile homes
and hotel bathrooms. To prevent shear degradation
during co-extrusion and promote maximum
adhesion it is important to match the rheology of the
Lucite Diakon grade to that of the substrate
material.
ABS based substrates have similar thermal and
rheological properties to those grades of Lucite
Diakon with medium to high temperature resistance
and melt viscosity. Lucite Diakon CLH952 has been
successfully used but advice should be sought on
the selection of a suitable Lucite Diakon ST grade
depending on the required end use performance.
Rigid PVC is shear sensitive with lower thermal
properties and therefore the lower softening point
easier flow grades of Lucite Diakon are
recommended; for example Lucite Diakon CLG902
or the Lucite Diakon STG6 series.
DTM/E/2Ed/Nov01
Figure 62 Truncated fishtail manifold sheet die
page 61
PRODUCTION OF EXTRUDED SHEET
Die gap
Before commencing extrusion, the die gap should
be set to a thickness depending upon the thickness
of the sheet to be produced. A guide is given in
Table 10 but it is stressed that this is only a guide
since it depends upon extrusion temperatures,
throughput and melt viscosity of extrudates.
Experience has shown that on non-vented
extruders a moisture level of less than 0.04% is
necessary to achieve acceptable extrudate. Acrylic
can be dried down to these levels but this can be
difficult and time consuming and for this reason
vented extruders are recommended for the majority
of acrylic extrusion processes.
Rework
Rework material can be used satisfactorily. The
levels will depend on the nature of the application
as a slight deterioration in the colour of the rework
may take place during this operation. Material to be
reworked should be processed as quickly as
possible under clean conditions to minimise
moisture absorption and dirt contamination. The
grid size on the grinder should be 3-6 mm.
Shutting Down the Extruder
As standard Lucite Diakon is a relatively thermally
stable material no special precautions are
necessary when shutting down the extruder. The
barrel of the extruder should be emptied, the screw
speed reduced to a minimum and the motor
stopped. However, after running Lucite Diakon ST
grades it is recommended that the extruder is
purged with a high molecular weight grade of
standard Lucite Diakon to avoid possible die build
up and discolouration of material on subsequent
start-up.
Sheet Shrinkage
Extruded acrylic sheet can have the problem of high
shrinkage when heated prior to shaping unless
particular care is paid to extrusion conditions. If the
sheet is clamped during heating and shaping, as in
vacuum forming, some shrinkage can be tolerated,
but if it is heated freely in ovens in a manner similar
to cast sheet then a low shrinkage is desirable.
Extrusion conditions which increase shrinkage are:
Low linear speed through three-roll stack;
Excessive melt build-up in nips of three-roll
stack;
Excessive tension between three-roll stack and
pull rolls;
Die temperatures too low;
Excessive draw-down between the lips and
three-roll stack arising from incorrect relationship
of die and nip gap settings.
DTM/E/2Ed/Nov01
Sheet thickness (mm) Die parallel (mm)
2.0 1.7
2.5 2.3
3.0 2.9
4.0 4.0
5.0 5.5
6.0 7.0
Table 10 Die gap guide
MH254 LH752 ST35G8
CMH454 CLH952
Extruder Barrel
Feed throat cooled cooled cooled
Feed* 200-220 200-210 205-225
Meter 220-250 220-240 220-250
Decompression 220-240 210-230 220-230
Meter 220-240 220-235 225-235
Adaptor 220-240 220-235 225-235
Die 225-245 220-240 220-235
Polishing Rolls
Top 110-120 110-120 110-120
Middle 100-110 100-110 100-110
Bottom 90-100 90-100 90-100
Table 11 Typical temperatures (°C) for Lucite
Diakon sheet extrusion
Temperature Conditions
The temperature conditions for the extrusion of sheet from
the various grades of Lucite Diakon are given in Table 11.
*When using compound versions of Lucite Diakon
such as CMH454 and CLH952, it may be necessary
to raise the temperatures a further 5-10°C on the
feeding zone in order to achieve melt stability. On
larger extruders of 120 mm and above further
increases in feed zone temperatures may be
necessary to achieve melt stability.
Moisture
As acrylic materials are hygroscopic they should not
be left exposed to the atmosphere for any length of
time.
page 62
With 3 mm thick sheet, experience has shown that
the longer the time the sheet takes to go around the
rolls of the three-roll stack the higher the shrinkage.
Figure 63 shows the effect of line speed on
shrinkage of 3 mm extruded acrylic sheet produced
on a three-roll stack with 250 mm diameter rolls.
LIGHTING DIFFUSER PROFILE EXTRUSION
Lighting diffuser profiles can be produced by two
methods depending upon the complexity of the
design. For relatively simple shapes, containing no
corners with a radius smaller than 3 mm, the post-
forming method from a tube die is probably the
most satisfactory. Where sharp corners are required
and there are projections to the periphery or an
embossed base, a profile die must be used.
Post-Forming from Tube Dies
Post-forming from a tube die offers several
advantages over the use of profile dies. Tube dies
can be made accurately at low cost, their symmetry
facilitating uniform flow and, with the usual die
centering arrangements, control of wall thickness is
relatively simple. A wide variety of profiles can be
produced from standard tube dies by the use of
internal and external metal forming plates. These
plates, which can either be steel or brass
approximately 6 mm thick, have the forming
surfaces radiused and polished to reduce friction.
Internal and external perforated copper air cooling
tube rings are used to promote uniform cooling of
the profiles.
A suggested design for a 100 mm die is shown in
Figure 64. The circumference of the die should
allow a minimum of 15% draw-down, ie the
circumference of the die should be at least 15%
greater than the periphery of the required section.
In practice, draw-downs of 20-25% are sometimes
used but this introduces excessive orientation. The
die may be fitted with interchangeables to produce
reeded or plain surface as required.
DTM/E/2Ed/Nov01
Figure 63 Effect of linear speed on shrinkage of
acrylic sheet
Output Capabilities
As shown in Figure 63 when operating with a three-
roll polishing stack the line sheet speed is critical if
excessive shrinkage is to be avoided. Because of
this there is a limit to the maximum sheet width
which it is advisable to produce on a given extruder.
Taking 3 mm thick sheet, a minimum line speed of
0.75 metre/minute and rolls of 250 mm diameter as
standard, the maximum recommended widths for
30:1 L/D ratio extruders are given in Table 12.
Extruder Output Maximum recommended
size (mm) (Kg/h) sheet width (mm)
60 80 500
90 300 1400
120 500 2000
150 800 2200
Table 12 Maximum recommended widths of 3 mm
extruded Lucite Diakon sheet
DTM/E/2Ed/Nov01
page 63
Figure 64 Die for 100 mm diameter tube with slitting knife
Figure 65 Die and forming box arrangement
DTM/E/2Ed/Nov01
page 64
Operation
When extrusion starts, the emerging tube is slit by
the knife mounted on the die face. The slit tube is
fed through the cooling box containing only the
external formers. Once the extrudate is held by the
haul-off system the internal formers can be inserted,
the positions of the formers adjusted and cooling
regulated until the desired shape is obtained. The
extrudate is cooled by a gentle flow of air from the
cooling rings. To avoid uneven cooling or too rapid
cooling the air should be directed on to the former,
rather than the extrudate.
A suitable arrangement of the die and forming box
is shown in Figure 65.
Units MG102 MH254 LH752 ST35G8
CMG302 CMH454 CLH952
Extruder Barrel
Feed throat °C cooled cooled cooled cooled
Feed °C 190 200 190 200
Metering °C 205 205 205 210
Decompression °C 200 200 200 205
Metering °C 200 205 200 205
Adaptor °C 200 200 195 205
Die body °C 180-200 190-210 190-200 190-205
Table 13 Typical conditions for Lucite Diakon tube and profile extrusion
Typical conditions for producing profiles by this method
for Lucite Diakon grades are given in Table 13.
Profile Dies
No specific recommendations can be given for the
design of profile dies since every shape presents its
own peculiarities. Frictional drag on the material
during its passage through the die must be taken
into consideration and so must the tendency for
preferential flow in the thicker sections. It follows
that the shape of the die orifice often differs
considerably from that of the extrudate obtained
from it.
With complicated profile dies it may be necessary to
incorporate small adjustable restrictor bars in the die
to control the melt flow through certain areas. A
suggested design for a profile die is shown in
Figure 66.
Care is necessary to avoid distortion of the section
and the use of a cooling formers is recommended.
With elaborate profiles, embossing with a light
diffusing pattern may be required on the outer
Figure 66 Profile die for acrylic lighting diffuser.
surface of the base of the profile. This can readily
be done by means of a two-roll system. In order to
move past the embossing mechanism, some
patterns and shapes may require slight outward
displacement of the sides of the profile, while the
material is still hot and pliable near the die. The
sides are then immediately returned to the desired
final position by means of sizing plates.
Two-colour profiles for lighting fittings can also be
produced by using a specially designed die coupled
to two extruders. With this technique, opal and clear
materials are commonly used. Normally a smaller
extruder produces completely opal sides as the
larger machine produces the clear base.
Alternatively the smaller machine can simply lay an
opal film on to the clear sides. Die design is
complicated for two-colour extrusion and it is
advisable that a die be obtained from an
experienced manufacturer of this type of equipment.
DTM/E/2Ed/Nov01
page 65
sizing bush submerged in hot water at 70°C to
which a variable vacuum may be applied. In order
to effect a satisfactory seal at the entrance to the
vacuum bath a die diameter 20-25% greater than
the sizing die diameter has been found necessary.
The diameter of the sizing die should equal the
diameter of the required tube size plus an
allowance for shrinkage on cooling. A typical
shrinkage allowance for a wall thickness of 5 mm
would be 1.7% and for a 1 mm wall 1.2%.
Typical line speeds for tubes produced by this
technique would be 1-2 metres/minute.
Suggested processing temperatures for tube are
similar to those given for lighting diffusers in Table 13.
Die Design
A typical die design for acrylic tube is shown in
Figure 67. The die should be fully streamlined and
should be chrome plated to minimise any tendency
to sticking. Alternatively a hard tool steel,highly
polished, may be used.
The high melt viscosity of acrylic can lead to
memory lines from the arms of the torpedo carrier.
To reduce this tendency die land lengths up to 20
times the wall thickness and compression ratios
(areas between arms of torpedo carrier to die
annulus) up to 15:1 are recommended.
TUBE EXTRUSION
In common with other thermoplastics the sizing
methods used for tube production may also be
successfully used with Lucite Diakon. The two most
common methods use either internal air pressure with
external sizing plates or an externally applied vacuum
through a sizing bush fully immersed in water.
Internal Air Pressure
This technique can be used for tube sizes up to 75
mm diameter. The air pressure, which should be
accurately controlled, is quite low (100-150 mm of
water). To maintain the internal air pressure an end
plug or a floating plug is commonly used. The
external diameter is maintained by sizing plates and
cooling in hot water (70°C) for tube sizes up to 30
mm or gentle air cooling for larger diameters up to
75 mm where excessive buoyancy in water could
lead to uneven cooling. Slow cooling is essential to
eliminate residual stresses which otherwise could
lead to failure in service. Line speeds using this
technique tend to be slower than for the water-
cooled vacuum system.
To allow for the melt swell of material as it leaves
the die it is normal for the diameter of the die to be
approximately 5% less than the diameter of the
sizing system.
Water Cooled Vacuum System
This is a widely used method for tube extrusion up
to 150 mm diameter and utilises a perforated brass Figure 67 Die for acrylic tube
DTM/E/2Ed/Nov01
page 66
FABRICATION OF SHEET EXTRUDED FROM
LUCITE DIAKON
Sheet extruded from Lucite Diakon can be shaped
by vacuum forming and other conventional shaping
techniques.
Shaping temperatures in the range 150-190°C are
normally used. With vacuum forming it is advisable
to heat the sheet on both sides simultaneously. For
conventional shaping the sheet can be heated in
circulating air or infra-red ovens. Sheet extruded
from MH254 is shaped at the higher end of the
temperature range.
In common with other types of extruded sheet
Lucite Diakon extruded sheet will shrink on heating.
The degree of shrinkage depends upon the
processing conditions, thickness and equipment
used. If the sheet is pre-heated in the unclamped
state in an oven before transferring to a clamping
jig for shaping, allowance must be made for
shrinkage but if the sheet is clamped in a
framework before pre-heating, as in vacuum
forming, no shrinkage allowance is generally
necessary.
Extruded acrylic sheet readily absorbs moisture
from the atmosphere. If pre-heated too rapidly
before shaping, absorbed moisture can produce
small bubbles within the sheet resembling those
formed when the material is overheated. In vacuum
forming, heating rates are generally rapid and
consequently it is essential with this process to use
sheet with a low moisture content. Care should
therefore be taken to minimise moisture uptake
before shaping, either by using the sheet
immediately after extrusion or by storing under
conditions which will reduce moisture absorption.
Packing the sheet in polyethylene film will slow
down the rate of moisture absorption but will not act
as a permanent moisture proof barrier.
If surface bubbling occurs when the sheet is heated
and before it is soft enough to give the required
definition, the moisture content is too high or the
heat too intense. The moisture content can be
reduced by pre-drying the sheets in an air
circulating oven at 70-80°C, and this can
conveniently be done overnight. For effective drying
the sheets should be separated to allow the hot air
to circulate between them.
DTM/E/2Ed/Nov01
page 67
Fault Probable cause Remedy
Bubbled extrudate 1 Wet material Dry material in oven/use vented extruder
2 Blocked vent Clean vent and pipework
3 Output too high for extruder Reduce screw speed
4 Overheating Reduce operating temperatures
Surface streaks 1 Wet material Dry material in oven/use vented extruder
2 Blocked vent Clean vent and pipework
3 Output too high Reduce screw speed
4 Contamination in die Clean die or purge
5 Entrapped air Change extrusion conditions or screw design
Die lines 1 Imperfections on die lips Polish or replace die lips
Rough surface 1 Too low die temperature Increase die temperature
2 Too low polishing roll temperatures Increase polishing roll temperature
3 Too low melt temperature Increase melt temperature
4 Poor roll finish Polish rolls
Surface craters 1 Ineffective polishing Increase roll temperature and pressure
Poor colour of extrudate 1 Hold-up in extruder Ensure no dead spots, particularly in vent region
2 Contamination Ensure material and machine are clean
Variation of shape 1 Temperature fluctuation in Check temperature control
extruder or die Modify die design
2 Uneven flow through die Reduce output rate
3 Irregular extruder output Adjust feed zone temperature
Check voltage supply
4 Irregular haul off Check haul off for slip or speed variation
5 Partially blocked screw Purge through with rework
Fold marks (‘chevron’ marks)1 Uneven flow through die Modify die design or adjust flow through die with restrictor bar
Unpolished areas (‘lakes’) 1 Uneven flow through die Adjust flow through die with restrictor bar
Excessive orientation 1 Linear sheet speed too slow Increase output of complete line
2 Polishing pressure too high Reduce polishing pressure
3 Line tension too high Reduce tension between polishing rolls and pull rolls
4 Draw-down too high Reduce draw-down
5 Roll temperature too low Increase roll temperature
Poor embossing 1 Melt too viscous Increase melt temperature
2 Rolls too cold Increase roll temperatures
3 Insufficient polishing pressure Increase pressure on rolls
4 Excessive tension Reduce tension between polishing rolls and pull rolls.
EXTRUSION FAULT REMEDIES
DTM/E/2Ed/Nov01
page 68
Standard high speed wood working routers are used
for machining Lucite Diakon. Spindle speeds of
15,000-20,000 rpm are recommended and again,
adequate cooling must be applied to both tool and
work.
Grinding
Parts may be ground with an abrasive disc rotating
at about 3,000 rpm for a 25 cm diameter disc. A
sanding belt may also be used at a speed of about
350 m/min.
These are dry sanding operations and the pressure
must be judged so as to avoid overheating.
It should be noted that the above machining
methods will leave a rough machined edge. If more
exact finishing is required then the roughly
machined edges should be removed by a
subsequent buffing operation.
Buffing
After rough machining, the parts may be polished
using a mechanically driven calico buff. These buffs
are usually 15-35 cm in diameter and are
maintained at a running speed of about 1,400 rpm.
Higher speeds are not recommended since they
may cause overheating of the surface.
The polishing operation requires a compromise
between the speed of the buff and pressure applied
and this must be judged by the operator. It is usual
to apply to the mop a wax dressing containing a
mild abrasive such as Kieselgühr or rouge. A final
cleaning may be given on a swansdown mop with
no wax dressing, but this is not always necessary.
Buffing will cause the acrylic surface to become
stressed and it is therefore essential, in applications
where the parts come into contact with active
solvents, eg decorating or cementing, that the
samples are annealed before further use.
FINISHING, COLOURING AND DECORATING
MACHINING
Components produced from Lucite Diakon may be
finished by simple machining operations such as
sawing and drilling.
Band Saw
Fine-toothed band saws, as used for light metals,
operating at a speed of approximately 1500 m/min
are suitable for cutting Lucite Diakon. For
thicknesses up to 3 mm, blades having 6-8 teeth
per cm should be used. Above 3 mm, up to 12 mm,
blades should have 4-5 teeth per cm. Saw blade
guides should be kept as close together as possible
to prevent blade twisting.
Circular Saw
A Tungsten Carbide tipped circular saw blade with 1 to
2 teeth per cm running at 3000 m/min may be used.
Laser Cutting/De-Gating
Sprue and gates can be effectively removed from
mouldings using Carbon Dioxide laser techniques.
Although expensive, the laser can be accurately
programmed to remove gates and sprues from a
wide range of parts from thick section to
complicated shapes. The main benefit of laser de-
gating is that it leaves no witness mark and no extra
finishing or polishing is required.
To maximise the performance benefit of the laser it
requires accurate location and alignment of
components. This is best achieved using a jig in
combination with a pick and place robot. There are
also certain associated SHE requirements to
consider when working with Carbon Dioxide lasers
which are best covered using automative handling
and appropriate guarding.
Milling and Routing
Milling tools with wide pitch, no front rake and
adequate back clearance are recommended. It is
important to clear away swarf from the work and
cool with copious quantities of soluble oil, coolant
mist or air.
page 69
Drilling
For drilling Lucite Diakon components, it is important
to avoid overheating and it is essential that the swarf
is cleared frequently so that binding does not occur.
Full support must be provided on the underside of
the work which should be clamped or suitably jigged.
Drills should be ground as illustrated in Figure 68.
The important requirements are:
No rake;
A clearance angle of about 15°
The margin between the two cutting faces should
be as small as possible;
The included angle should be obtuse
To produce accurate stress-free holes it is vital to use
an efficient cooling system. Cooling may be of the
soluble cutting-oil type but a strong air jet is equally
effective and avoids the need for a subsequent
cleaning operation. Larger holes can be cut with fly
cutters and trepanning tools with no rake and
adequate back clearance.
Hot Knife
This technique may be used when removing edge or
diaphragm gates from injection mouldings. The
apparatus consists of a knife edge or cutting tool
electrically heated and mounted on a drill-press (see
Figure 69). It is usual to mount the cutting tool on a
block of metal, the temperature of which is
maintained by a band or cartridge heater. The
temperature of the knife should be regulated so that
a clean cut is obtained when the gate is trimmed off.
If the knife is too cold the surface of the moulding will
show a smear mark; if the knife is too hot then the
surface of the moulding will show a bubbled
appearance.
DTM/E/2Ed/Nov01
Figure 68 Design of twist drill
Figure 69 De-gating with a hot knife
CEMENTS AND ADHESIVES
Components made from Lucite Diakon can be
bonded to other acrylics using acrylic cements. A
range of ‘Tensol’ cements and ‘Evo-plas’ adhesives
is produced and supplied by Evode Speciality
Adhesives Ltd, to whom all enquiries should be
directed. These acrylic cements can also be used to
join Lucite Diakon to other materials. However,
page 70
alternative adhesive systems are more suitable in certain
cases, see below. The physical strength, and resultant
appearance of the joint will vary with the type of adhesive
used, and careful consideration should be given to
deciding which adhesive is appropriate for a particular
application.
Preparation of Contact Surfaces
Lucite Diakon should be degreased, if necessary, prior to
application of cements, to ensure a good surface bond.
Antistatic agents should not be used prior to cementing
operations. The best bond strengths are obtained if gloss
surfaces have been lightly abraded with fine emery cloth
before application of cement.
Annealing
It is recommended that components to be cemented are
annealed prior to the application of any cements to
reduce strain induced by moulding, extrusion, machining
or forming operations. Such strain may promote crazing
or cracking in the area of the bond.
Please refer to the section on Stresses and Molecular
Orientation in Lucite Diakon Components on page 72 for
information on causes, problems, testing and remedies.
Bonding
The following text has been reproduced by agreement
with Evode Speciality Adhesives Ltd:
“The correct selection of adhesive is vital in order to
produce bonds with good strength, durability and optical
clarity.
Edge Bonding
Solvent welding is the quickest and easiest way of
forming edge bonds. The best results can be easily and
safely achieved when ‘Etru-Fix’/’Tensol’ 12 are applied
using the appropriate ‘Evo-plas’ application kit. Features
of this system - which is intended for indoor applications -
include high clarity and bubble-free bonds. Filled systems
such as ‘Tensol’ 12 offer slightly better gap filling
properties.
For external applications, a highly durable adhesive such
as ‘Tensol’ 70 is required.
Bonding to Other Substrates (metal, wood, glass etc)
The easiest way to bond Lucite Diakon to other
substrates is by using a cyanoacrylate adhesive. ‘Evo-
Plas’ TC 731, with its low bloom and special adhesion
promoter system is suggested. As well as being useful
for bonding small areas of Lucite Diakon to Lucite
Diakon, this system is also suitable for attaching fittings
to Lucite Diakon.
Where there are high mechanical strength requirements,
then a toughened acrylic adhesive, such as ‘Evo-plas’ TA
431, is to be preferred.
Sealing
Joints in Lucite Diakon and a variety of other materials can
be effectively sealed with a suitable, acrylic compatible
silicone sealant. In order to avoid stress-crazing, the
sealant needs to be neutral cure. A low modulus type,
such as ‘Evo-plas’ Low Modulus Silicone Sealant will best
accommodate any movement in/between the components.
The ‘Evo-Plas’ range of adhesives, cleaning solvents and
Antistatic cleaner is available from most ‘Perspex’
stockists and distributors. Alternatively please contact
Evode Speciality Adhesives Ltd directly” (on +44 (0) 116
232 2922) - see Appendix II for full address.
Before cementing, the user should study the Safety Data
Sheets and ensure that the adhesive is suitable for the
intended application.
ULTRASONIC ASSEMBLY
Ultrasonic welding
This technique offers a quick, clean and efficient method
of joining two components produced from the same
material. Dissimilar materials with a few degrees
difference in melting point is sufficient to allow one
material to melt without allowing the other to achieve its
melting point, preventing a good joint between the parts.
Ultrasonic welding may be divided into two basic types of
operation:
Contact or near field welding where the probe is as
near to the joint area as possible.
Transmission, remote or far-field welding. In this
operation the transmission properties of the rigid
material are used to obtain a weld remote from the
probe.
Both techniques may be used with Lucite Diakon
although contact welding is the better of the two. Contact
welding is the only sure method of producing a water-
tight seal,
DTM/E/2Ed/Nov01
DTM/E/2Ed/Nov01
page 71
but here a probe must be used which surrounds the
article so that the complete weld is made at the
same instant. Due to power output limitations, only
small mouldings may be sealed in this manner. For
larger components a ‘spot welding’ principle has to
be adopted and it is not then possible to guarantee
water-tight seals.
It should be noted that during welding there is likely
to be some evidence on the component surface of
the positioning of the probe. Where required the
welding should be carried out on the rear surface of
the component.
Joint Design
Joint design is important with ultrasonic welding.
The main factor to bear in mind is to have a small
contact area which concentrates the applied
vibration energy and permits a rapid development
of melt.
Figures 70 and 71 show the design of joints related
to the strength of the weld.
Figure 70 Joint designs comparing the weld
strengths of different configurations
Figure 72 Ultrasonic staking
Figure 71 Joint designs showing requirements for
improved joint strength.
Figure 73 Ultrasonic insertion
Ultrasonic Staking
Ultrasonic staking or riveting is a technique for either
joining metal plates to a Lucite Diakon component or
a Lucite Diakon component to a metal assembly.
The final shape of the stake head will depend upon
the shape of the horn. Figure 72 illustrates a
conventional stake before and after assembly.
Ultrasonic Insertion
This technique for inserting and encapsulating shaped
metal inserts, commonly brass, into slightly smaller
holes in Lucite Diakon mouldings is an effective
alternative to the conventional method of placing
inserts into the mould before moulding. (Figure 73)
Ultrasonic assembly results in the introduction of
localised stress and it is recommended that
components be annealed if this stress is likely to
have a significant effect on component
performance. Refer to section on Stresses and
Molecular Orientation in Lucite Diakon Components
on page 72.
page 72
HOT SURFACE WELDING
The principle of this method of joining one
component to another is to melt the surfaces to be
mated. It allows dissimilar but melt compatible
materials to be welded. Hot surface welding is
divided into two basic categories:
Hot Plate Welding
Components are placed in tool rests and then
brought into contact with a hot plate which may be
flat or profiled. After a pre-set time the components
withdraw, the plate retracts out of the way and the
components are then brought together under light
pressure and allowed to cool. A typical cycle time is
20 seconds.
Accurate temperature control and time of contact
with the hot plate are important as under or over
heated surfaces will produce poor or untidy welds.
This technique is commonly used for jointing Lucite
Diakon multicoloured rearlight lenses to their ABS
reflector backs where the lens is designed with a
rim to hide the weld.
Hot Punch Welding
The assembled components are positioned under a
heated punch which is lowered on to the top
component. The heat from the punch melts
localised areas of the top component which fuses
itself to the base component. This technique is
commonly used for welding a flange-edged
component and a flat surface together.
Joints made by hot surface welding are usually
highly strained and it is recommended that
components be annealed after welding to improve
component performance. Refer to section following
on Stresses and Molecular Orientation in Lucite
Diakon Components.
STRESSES AND MOLECULAR ORIENTATION IN
LUCITE DIAKON COMPONENTS
Assessment of quenching stress and molecular
orientation in Lucite Diakon articles may be used to
predict their performance in service. Such means of
appraisal give the producer early guidance on
component quality and help to maintain a high
production efficiency of acceptable parts, so as to
avoid problems of crazing or of cracking which
might otherwise arise during subsequent
decoration, or when the parts are in service.
Because of the high transparency of most
components made from Lucite Diakon, a rapid,
visual method of assessing stress can be
conveniently applied to end products. This method
gives a simple, inexpensive technique for a
preliminary assessment of the quality of
components. In addition, immersion testing in an
active liquid can also prove very useful.
During processing a range of molecular
deformations occur. For the sake of simplicity only
two extreme types of deformation, corresponding to
molecular orientation and to quenching stress, are
considered here.
The first, molecular orientation, results from partial
alignment of polymer molecules, when forced, in
the melt state, into the required shape. The regions
where this is chiefly apparent are at the gate on
injection moulding (where melt under pressure
continues to enter the mould while the moulding is
cooling and contracting) and in thin sections.
The second, quenching stress, results from
differential cooling of the polymer melt. Quenching
stress will also result from any subsequent
operation which introduces localised melting as for
example hot plate welding and hot foil stamping.
Quenching stress is also introduced during any
subsequent machining operations due to localised
frictional heating.
Molecular Orientation
Orientation affects the strength of a component.
Components are stronger when flexed
perpendicular to the molecular orientation and
weaker when flexed parallel to this direction. An
unorientated component would be equally strong
when flexed in either direction.
Orientation gives a lower solvent crazing and stress
cracking resistance. This is particularly relevant to
applications involving the cementing, lacquering or
printing of components.
DTM/E/2Ed/Nov01
page 73
Quenching Stress
High quenching stresses give rise to cracking when
the component comes into contact with active
liquids, usually solvents in the case of acrylics. The
cracks occur parallel to the principal orientation
direction and perpendicular to the direction of the
stress in the absence of orientation.
In moulding, if the stresses are high enough,
cracking can occur in the absence of solvents either
on, or some time after, removal from the mould.
Although the effects of stress and of orientation are
referred to separately above, they both act
simultaneously in components.
Assessment of Stress by Simple Methods
Stresses and molecular orientation are
simultaneously introduced during the injection
moulding process. Stresses arise due to restricted
volume contraction and differential cooling between
surface and middle layers, or between different
parts of mouldings, as the melt cools and solidifies
in the mould.
Molecular orientation is produced as material flows
through the gate and through other small cross-
sections in the moulding. The long-chain polymer
molecules become orientated (lined-up) in the flow
direction under the influence of shearing forces.
They are ‘frozen’ in position, particularly in the gate
area, as the moulding cools and solidifies.
This uniaxial type of orientation in the gate area
gradually changes to a more biaxial or planar type
of orientation as polymer flows sideways as well as
forward away from the gate. Corresponding types of
uniaxial and biaxial quenching stresses are also
‘moulded-in’.
The levels of ‘moulded-in’ stresses and orientation
are governed by the moulding conditions used. It
has been found that, in general, mouldings with the
lowest stresses and orientation are produced when
high mould and melt temperatures and fast injection
rates are used. To produce consistent quality
mouldings, once the right conditions have been
established, control of mould temperature is
essential.
‘Moulded-in’ quenching stresses can be largely
removed by annealing (see following section on
annealing procedures). Orientation levels are
substantially unaffected by annealing except at
temperatures very near the softening point of the
material, when large shrinkages and distortions
occur.
A rough guide to the levels of stress and orientation
can be obtained by means of two simple tests.
Observation of Mouldings Under the Strain
Viewer
Transparent moulded parts are viewed between a
pair of crossed ‘Polaroid1* filters, preferably
mounted above an opal light-diffusing background.
Localised colour fringe patterns indicate areas of
high stress and orientation. A completely stress and
orientation-free moulding would appear black when
rotated in the plane of the filters and when tilted.
The level of stress and orientation increases in
order of the colours, black, grey, white, yellow, red,
blue to pink and green. The colour seen also
depends on the thickness of the article, the thicker
the section the higher the colour seen for a given
stress and orientation level. It is only safe to judge
the differences between mouldings of a particular
article made under different conditions, although
broad distinctions can be made between different
articles where a ‘good’ moulding has low levels of
stress and orientation, while a ‘bad’ moulding has
high levels of stress and orientation.
Figure 74 is an example of the effect seen in
practice and shows the patterns in a simple side-
gated disc moulding made under a range of
moulding conditions.
Observations of the patterns before and after
annealing can give some idea of the relative
amounts of ‘moulded-in’ stresses and orientation.
A big change in the order of colour, or extent of
pattern on annealing, shows the presence of high
‘moulded-in’ stresses. A small change (or no
change) shows that the colours are largely due to
molecular orientation.
1* Registered trade mark of Polaroid
DTM/E/2Ed/Dec02
DTM/E/2Ed/Dec02
page 74
Figure 74 The effect of moulding conditions on
‘moulded-in’ stress when viewed through
crossed ‘Polaroid’ filters
Top left: Low cylinder temperature, low mould
temperature
Top right: High cylinder temperature, low mould
temperature
Bottom Low cylinder temperature, high mould
left: temperature
Bottom High cylinder temperature, high mould
right: temperature
Figure 75 Electrical component injection-moulded
from Lucite Diakon and tested by solvent
immersion
Left: Not annealed;
Right: Annealed
Solvent Immersion Test
This is an accelerated crazing test and has the
advantage that coloured and opaque as well as
clear articles can be examined, although the
amount of information obtained is restricted. The
presence of high ‘moulded-in’ stresses is readily
shown by dipping a moulding in a suitable solvent
such as isopropanol and observing any cracking or
crazing which occurs. Immersion in isopropanol for
3 minutes at room temperature followed by draining
and air drying for 60 minutes is a suitable test. An
example is shown in Figure 75. Rapid cracking,
particularly if accompanied by coloured fringes
when viewed through crossed ‘Polaroid’ filters,
should be taken as a warning that improvement in
component quality is desirable in order to ensure
satisfactory, long term performance under normal
use conditions. If the quality of the moulding cannot
be significantly improved by adjustment to moulding
conditions then it is recommended the moulding is
annealed prior to use.
Annealing Procedures
It has been found that annealing temperatures of
82°C for Lucite Diakon type 8 mouldings and 70°C
for Lucite Diakon types 6 and 7 mouldings are
generally sufficient to relax away ‘moulded-in’
stresses without any large changes in orientation or
any significant dimensional changes occurring.
Higher temperatures may be used with shorter
times providing the shape of the article gives
additional dimensional stability and providing that
some shrinkage, particularly in the gate area, can
be permitted in the application. The limits for a
particular article should be found by experiment.
The time required at a particular annealing
temperature will depend on the thickest section
present in the moulding. By setting up an annealed
reference sample for each particular type of
moulding the application of correct annealing
conditions to subsequent mouldings can be
checked.
The annealing process should be carried out in an
oven provided with efficient air circulation and care
must be taken to ensure air circulation around each
part. Mouldings to be annealed should be clean and
dry and should be supported so that they are not
under stress during the annealing process.
page 75
As an initial guide to the conditions required for the
annealing, it is suggested that most sections
moulded from Lucite Diakon type 8 materials can
be annealed by heating for 2 hours at 80-84°C
followed by cooling at a rate of 45°C per hour,
ie 11/2 hours cooling time. Thick sections will require
longer annealing and slower cooling, eg a 5 mm
section will require 4 hours annealing followed by
cooling at a rate of 30°C per hour, ie 2 hours
cooling time. For mouldings made from Lucite
Diakon types 6 and 7 the annealing temperature
should be 68-72°C, and the cooling rate about 35°C
per hour for thin mouldings and 25°C for thicker
mouldings. A controlled rate of cooling is important
as shock cooling, hot oven to cold air, will
reintroduce quenching stress. If the oven cannot be
set to a controlled rate of cooling it is common
practice to switch the oven heating off after the heat
treatment stage and to allow the oven plus contents
to cool to just above room temperature before
removing the mouldings.
Effect of Molecular Weight
Where crazing problems arise in moulding, or
subsequent treatment and handling which cannot
be easily overcome using Lucite Diakon CMG and
CLG, the higher molecular weight Lucite Diakon
CMH and CLH grades are recommended. The
improved mechanical properties of Lucite Diakon
CMH and CLH coupled with superior craze
resistance may be utilised to overcome difficulties
with intermediate cementing and decorating
operations, and for applications where some stress
is applied to the moulding in use.
Influence of Moulding Conditions, Mould and
Component Design
Mouldings with the lowest levels of stress and
orientation are produced using high mould
temperatures, high melt temperatures, maximum
injection rates, and low injection pressures.
Mouldings showing the most severe strains and
highest orientation levels are produced using low
mould and melt temperatures, slow injection rates
and high injection pressures.
The service life of Lucite Diakon components can
be greatly improved if care is taken at the
component and mould design stage.
Sharp corners and sudden changes in section
should be avoided because they give rise to stress
concentrations (notches) which can lead to
premature failure. Flow in long thin sections
requiring the use of high injection pressure should
be avoided. Strength and rigidity is improved by
increasing the thickness in areas of high stress
concentration. Moulded-in metal inserts are not
recommended due to the high stress introduced by
shrinkage around the insert. Care should be taken
with moulded-in holes or slots for the same reason
but a slight taper on highly polished pins can
alleviate the problem. Holes or slots produced by
machining operations create stresses which it may
be necessary to remove by annealing. Weld lines
are areas of weakness and should be avoided in
mouldings subject to high stress concentrations in
service. When mouldings have to be cemented
together the mating halves should not be a tight fit
as this will stress the parts leading to crazing and
cracking when cement is applied.
Moulds for Lucite Diakon should have highly
polished cavities, runners and gates to enable the
material to flow smoothly without interruption into
the cavities. The sprue, runners and gates should
also be kept as short as possible and be of
adequate cross-section to enable the cavities to be
filled without having to apply excessive injection or
hold-on pressures, which cause packing stress. Full
round runners generally give the best results. As
maximum levels of stress and orientation usually
occur round the gate area, the position of the gate
and its size are important. Although design of
components often determines where a gate should
be placed, it is good practice to place the gate at
the thickest portion of the moulding wherever
possible and to make it of as large a cross-section
as possible.
Heating and cooling channels incorporated in the
mould should be placed so that constant controlled
mould temperatures can be maintained.
Intelligent anticipation of possible difficulties and
appropriate attention to component design, gate
position and ease of injection are well repaid by
avoidance of stress-induced problems in
subsequent service.
DTM/E/2Ed/Nov01
page 76
CLEANING
Lucite Diakon components may be cleaned by
washing with mild soap or detergent in warm water
using a clean soft cloth or cotton wool. Inaccessible
corners may be cleaned with, or stubborn stains
removed by, the use of a soft brush. Scouring
powders should not be used as they will mar the
surface.
Organic cleaning agents such as acetone and paint
remover must not be used as they attack Lucite
Diakon components.
Light scratches and small surface blemishes may
be removed by hand polishing using proprietary
metal polish with a clean soft cloth or cotton wool.
ANTISTATIC TREATMENT
All grades of Lucite Diakon have good electrical
insulating properties and become electrostatically
charged during fabrication and handling thereby
attracting dust particles to the surface. Normal
dusting with a cloth will only reinforce the charge
and attract more dust.
The solution to this problem is to make the Lucite
Diakon surface conducting so that static electricity
can be discharged. This can be achieved by
washing with water but obviously this dries rapidly
and the effect is not permanent. A surface film of
moisture may however be maintained by the
application to the surface of a substance for which
water has an affinity, ie a suitable antistatic agent.
The most efficient are quaternary ammonium
compounds because they are effective even under
very dry conditions since they are themselves
conducting and can remain effective for some time
if they are undisturbed. However it must be noted
that these compounds and solutions should not be
used in applications involving contact with
foodstuffs.
Lucite Diakon components can be treated with
antistatic solution on removal from the mould, by
dipping in the solution, suspending and allowing to
drain and dry. This can result in runs and tide marks
and where this is unacceptable, for instance with
automotive instrument facia lenses, the antistatic
solution is applied by controlled spraying.
AUTOMOTIVE SIGNAL LAMP LENS COLOURS
The colours of acrylic material used in the production
of automotive signal lamp lenses have to comply with
international colour specifications ie SAE J578. The
various designs and production techniques for signal
lamp lenses has led to the requirement for a range of
amber, red and neutral colours. Table 14 lists the light
transmission (Y) and colour coordinates (x and y) for
the major 3 mm standard Lucite Diakon Amber and
Red colours while figures 76 to 80 give light
transmission and colour co-ordinates against thickness
for the major range of Lucite Diakon amber and red
signal lamp colours. These colours, when used at a
lens thickness falling between the SAE and ECE limits
in relation to each of the colours, are approved in
Lucite Diakon CM grades against SAE J576..
The neutral colours used for styling considerations are
often a mixture of 3 dyes and therefore the range of
colours is quite large. Apart from visual hue acceptance
the main requirement is light transmission. Figure 81
illustrates a series of commonly used neutrals based
on Lucite Diakon Neutral 9321.
DTM/E/2Ed/Nov01
Amber Series Y x y
310 69.2 0.5700 0.4280
311 65.3 0.5795 0.4190
312 63.0 0.5850 0.4135
316 57.8 0.5975 0.4010
319 60.5 0.5910 0.4070
Red 405 Series Y x y
405 22.3 0.6825 0.3165
413 18.2 0.6920 0.3070
415 24.4 0.6780 0.3215
416 18.7 0.6910 0.3085
418 31.1 0.6610 0.3370
419 28.7 0.6675 0.3310
422 20.6 0.6865 0.3130
4088 26.8 0.6720 0.3270
Red 425 Series Y x y
425 22.0 0.6825 0.3165
433 17.7 0.6920 0.3070
435 24.0 0.6780 0.3215
436 18.2 0.6910 0.3085
438 31.1 0.6610 0.3385
439 28.5 0.6675 0.3320
442 20.2 0.6865 0.3130
428 26.6 0.6720 0.3270
Table 14 Light transmission (Y) and colour
coordinates (x,y) for 3 mm standard
Lucite Diakon Amber and Red
Colours. (‘Spectraflash’ 500,
Illuminant A, CIE 1931 2° observer)
DTM/E/2Ed/Nov01
page 77
Figure 76 Lucite Diakon Automotive Colours: Amber 1-5mm: Light transmission versus thickness
Figure 77 Lucite Diakon Automotive Colours: Amber 1-5mm: Chromaticity coordinates
DTM/E/2Ed/Nov01
page 78
Figure 78 Lucite Diakon Automotive Colours: Red 405 series 1-5mm: Light transmission versus thickness
Figure 79 Lucite Diakon Automotive Colours: Red 425 series 1-5mm: Light transmission versus thickness
DTM/E/2Ed/Nov01
page 79
Figure 80 Lucite Diakon Automotive Colours: Red 1-5mm: Chromaticity coordinates
Figure 81 Lucite Diakon neutrals based on Neutral 9321 type formulation
page 80
DECORATION OF LUCITE DIAKON
The combination of high surface gloss, superb clarity,
good abrasion resistance and excellent weatherability
makes Lucite Diakon an ideally suitable material for
the production of decorated components such as
medallions, insignia, metallised bezels, tap handles
and signs.
It is essential that all the precautions advised are
followed because decoration can be an expensive
operation and the recovery of faulty decorated parts is
difficult or impossible.
Preparation
All the decorating processes mentioned in this section
involve the surface treatment of moulded or extruded
parts. It is therefore essential that the parts are
produced under clean, dry, grease-free conditions.
Moulds must be free from oil contamination, especially
around ejector pins and moving cores. Generous
tapers should be allowed on all surfaces in the line of
draw to reduce the need for mould lubricants.
Silicone-based mould release agents must be avoided
since these cause surface blemishes and loss of
adhesion. When handling components, lint-free cotton
gloves should be worn to avoid fingermarks.
Antistatic agents in the form of aqueous solutions may
be used but care must be taken to ensure that the
film of antistatic agent is dry before decorating or poor
results will be obtained. Although antistatic solutions
prevent dust from being attracted to the component,
they will not prevent gravitational deposition of dust.
When mouldings are to be decorated with more than
one colour it is usually necessary to use one or more
masks. In order to obtain fine definition between
colours, the masks have to be made to fine tolerances.
Consequently the dimensions of the moulding must be
controlled to equally fine limits, and all the principal
moulding variables must therefore be controlled
accurately to ensure dimensional consistency.
Many of the lacquers used for decorating Lucite
Diakon components contain active solvents which will
produce surface crazing or cracking if undue levels of
stress are present. Attention should be paid to the
section on Stresses and Molecular Orientation in
Lucite Diakon Components on page 72.
It is recommended that all components subjected to a
decorating process containing active solvents are
annealed before decorating. All machining, polishing,
hot foil stamping and ultrasonic assembly operations
which are likely to introduce stress should be carried
out before annealing.
Decorating Processes
Either a first (front) or second (back) surface coating
technique may be used for Lucite Diakon. Second
surface decoration is more commonly used because
the high transparency of Lucite Diakon makes it
possible to achieve a wide variety of attractive effects.
The coating is protected by the Lucite Diakon against
deterioration from weathering and abrasion.
Lacquering and Spray Painting
These techniques may be used with Lucite Diakon
and are normally associated with the 3-dimensional
decoration of intricate components where silk-screen
printing cannot be used. Typical examples are
medallions, insignia and thermoformed display signs.
Silk-screen Printing
This is a widely practised technique, ideally suited to
flat acrylic sheet although mouldings with flat surfaces
such as radio scales also lend themselves to this
process. It is particularly adaptable for multi-colour
decorating by successive screening operations with a
series of different screens.
Hot Foil Stamping
This process involves the hot blocking of characters
on to the surface of a component. An electrically
heated metal die of the required design is pressed on
to a stamping foil, the coated side of which is in
contact with the object to be decorated. The hot die
melts the coating, releases it from the foil backing,
and bonds it to the object. Thus, light engraving and
colour filling are achieved in one operation.
Raised lettering on mouldings may be foil stamped by
replacing the metal die with a sheet of aluminium
faced with a sheet of silicone rubber. The flexibility of
the silicone rubber allows for the slight change in
thickness which may occur with some mouldings,
such as rulers, when end gated.
With hot foil stamping it is usually unnecessary to
anneal mouldings as no solvent systems are involved.
DTM/E/2Ed/Nov01
DTM/E/2Ed/Nov01
page 81
However localised stress introduced during hot foil
stamping by slight distortion and rapid change in
temperature of the surface may cause cracking or
crazing if any further decoration is carried out by a
solvent-based technique. This can be eliminated by
using the recommended annealing procedure after
the hot foil stamping operation.
Vacuum Metallising
This technique is used to impart a metallic or
mirror-like appearance to the moulded component.
The metal used (commonly aluminium) is deposited
on to the surface by evaporation under high
vacuum using specialised equipment. Gilt and other
coloured metallic effects may be obtained by using
precoloured Lucite Diakon or by spraying the back
of the moulding with a tinted lacquer and then
metallising with aluminium.
Before metallising, it is advisable to spray the
moulding with a base coat. Apart from improving
adhesion between the moulding and the metal
coating, the base coat also acts as a smoothing
coat on those mouldings which do not have a high
surface finish.
First surface coating
The preferred sequence of operation is:
Spraying with base-coat on to the top surface;
Vacuum deposition of the metal coating;
Spraying with a clear top-coat to protect the
metallised coating from damage by abrasion.
Second surface coating
Here the preferred sequence is:
Spraying the reverse side of the moulding with a
clear base coat;
Vacuum deposition of the metal coating;
Spraying with a back-coat to protect the
metallised coating.
DTM/E/2Ed/Nov01
page 82
HEALTH, SAFETY AND ENVIRONMENTAL
ASPECTS OF LUCITE DIAKON
It is advisable during the design stage of a
component and certainly before processing any
Lucite Diakon grade, as it is a legal requirement in
the European Union, to obtain the relevant Material
Safety Data Sheet and to be fully conversant with
its contents before proceeding.
Therefore when purchasing any grade of Lucite
Diakon a Material Safety Data Sheet (MSDS) must
be obtained for each Lucite Diakon grade. These
Material Safety Data Sheets will be supplied by the
local Lucite International sales office or by the local
Lucite International appointed distributor or agent.
The Lucite Diakon Material Safety Data Sheets
(MSDS) do not include advice on the suitability of
the Lucite Diakon grades for applications, nor any
precautions that may be necessary during the use
in service of any product made from Lucite Diakon.
However certain individual statements can be made
available upon request regarding the compositional
compliance of various Lucite Diakon grades with
respect to national regulations, for example those
for food contact.
DTM/E/2Ed/Nov01
page 83
APPENDICES
APPENDIX I
ACRYLIC SPECIFICATIONS
ASTM D 788-96
Acrylic moulding and extrusion materials are
classified according the heat deflection temperature
(HDT) of the material tested to ASTM D 648-96,
sample annealed to ASTM D 788-96.
HDT Type
79°C and below 5
80-86°C 6
87°C and above 8
LUCITE DIAKON GRADE CLASSIFICATION
Specification CLG340 CLG356 CLG960 CLG902 CMG302 CMG314V CLH952 CMH454 CMH454L
LG156 LG702 MG102 LH752 MH254
ASTM D 788 6 6 6 8 8 8 8 8 8
DIN 7745 92-53 92-53 92-53 100-53 108-53 116-53 108-73 108-73 116-73
Code 1 Vicat Softening Point
VST/B/50 (°C)
84 80-88
92 88-96
100 96-104
108 104-112
116 112-120
Code 2 Viscosity Number
(cm3/g)
53 48-58
63 58-68
73 68-78
83 78-88
93 88-98
103 98-108
DIN 7745
This specification classifies acrylic moulding
materials according to Vicat softening point
(VST/D-50) (code 1) and viscosity number (code 2)
DTM/E/2Ed/Nov01
page 84
APPENDIX II
ADDRESSES
Evode Speciality Adhesives Ltd
Anglo House
Scudamore Road
Leicester
LE3 1UQ
Tel: 0116 232 2922
Fax: 0116 232 2933
Plastic Design Solutions Ltd
80 Church Road
Stockton on Tees
TS18 1TW
Tel: 01642 671711
Fax: 01642 671762
DTM/E/2Ed/Nov01
page 85
Equipment (RPE) is used to ensure that worker
exposure is maintained below the relevant
Occupational Exposure Levels. In practice respecting
the Occupational Exposure Level(s) for the
predominant acrylic monomer(s) will provide adequate
protection against the lower levels of other
constituents that are evolved. This is not necessarily
the case when processing at temperatures higher than
those recommended, when the likelihood of releasing
toxic, irritant and flammable vapours is increased.
As it is impossible to be precise about which volatiles
will be evolved, and at what levels, it is equally
impossible to be precise about which substances will
be present in the vent port condensate liquor and
their relative levels. It is generally assumed, however,
that acrylic monomers and water will predominate and
will include some residual chemical compounds from
the polymerisation process. In the absence of detailed
compositional information it is prudent to regard this
liquor as hazardous. Appropriate Personal Protective
Equipment (PPE), such as impermeable gloves and
eye/face protection, should be worn on a case by
case basis. Vent port condensation liquor should be
disposed of by burning in an incinerator suitable for
the disposal of methacrylates in accordance with local
regulations.
It is intended that the guidance provided in this
Appendix should be used in conjunction with the
current Material Safety Data Sheets (MSDS) for the
grade(s) of Lucite Diakon being used.
Appropriate Material Safety Data Sheets (MSDS) can
be readily obtained from the local Lucite International
sales office or the officially appointed Lucite
International distributor/ agent. It is a legal requirement
in the European Union that the relevant (MSDS) data
for each Lucite Diakon grade is obtained and its
contents understood before handling and processing
each Lucite Diakon grade involved.
APPENDIX III
VOLATILE CHEMICALS EVOLVED DURING
PROCESSING OF LUCITE DIAKON
During thermal processing of Lucite Diakon acrylic
polymers volatile organic compounds (VOCs) are
evolved. When such processing involves the use of a
‘vented extruder’ these volatiles are present in the
vicinity of the extruder die and the vent port. In the
latter case, volatiles may be condensed to form a
condensate liquor. This technical section addresses the
toxicological hazard and risk associated with the
volatiles and vent port liquor.
It is recommended that the Lucite Diakon acrylic
polymers can be processed safely at melt
temperatures up to 280 degrees centigrade. The more
rapid depolymerisation of the polymer above this
temperature or excessive dwell times can cause
gaseous pressure to build up, with a resultant risk of
spraying low-viscosity polymer from the nozzle or die
without any planned screw movement.
All polymers degrade to some extent at their
processing temperature, an effect which increases
with increasing temperature. It is not possible to be
precise which substances will be evolved under the
specific conditions of use. At the recommended
processing temperatures the volatiles evolved are
likely to be comprised predominantly of residual acrylic
monomers and water. The identity of the acrylic
monomers will be depend upon the composition of the
polymer(s) being processed, reference should
therefore be made to the relevant Material Safety Data
Sheets and technical literature for the grade(s) of
Lucite Diakon being used. In addition to acrylic
monomers, much lower (trace) levels of residual
constituents from the polymerisation process are likely
to be present.
It is generally recommended that Local Exhaust
Ventilation (LEV) and/or Respiratory Protective
page 86
EUROPEAN SALES OFFICE
Lucite International Holland B.V.
Merseyweg 16
3197 KG Botlek Rt.
Postbus 1222
3180 AE Rozenburg
Nederland
Fax +31 (0)181 233243
FRANCE
Tel +31 (0)181 233273
ITALY, PORTUGAL, SPAIN
Tel +31 (0)181 233274
GERMANY, SWITZERLAND, AUSTRIA,
BENELUX, NORDIC REGION
Tel +31 (0)181 233272
UNITED KINGDOM, THE REPUBLIC OF
IRELAND, EASTERN EUROPE, GREECE,
TURKEY, MIDDLE EAST, AFRICA
Tel +31(0)181 233271
LUCITE DIAKON TECHNICAL SERVICE
Lucite International UK Limited
The Wilton Centre
Wilton
Redcar
TS10 4RF
England
Tel +44 (0)1642 447117/447116
Fax +44 (0)1642 447105
DTM/E/2Ed/Dec02
Information contained in this publication (and
otherwise supplied to users) is based on our
general experience and is given in good faith, but
we are unable to guarantee its accuracy or to
accept responsibility in respect of factors outside
our knowledge or control. Freedom under patent,
copyright and registered designs cannot be
assumed.
Lucite Diakon is a registered trademark of the
Lucite International group of companies.
A member of the Lucite International Group. Lucite
International UK Limited.
Registered in England No. 3830161
Registered Office: Queens Gate, 15-17 Queens
Terrace, Southampton SO14 3BP, United Kingdom.
www.lucitesolutions.com [email protected]
Lucite Diakon and Lucite Elvakon are registered trademarks of the Lucite International group of companies