new ideas and strategies for titanium dioxide extension by

New ideas and strategies for titanium dioxide extension by mineral pigments

David Skelhorn

Technical Service Manager

Paint and Coatings

Titanium Dioxide is the premium

material for producing WHITE

How do we create a WHITE material?

Understanding that helps to

duplicate how TiO2 works.

Light Scattering

Water and Air, we all know, are transparent.

The whiteness we see comes from light scattering

between air and water in a) Foam and b) Clouds

Physical form creates light scattering.

WHAT DO YOU SEE HERE?

Calcium Carbonate Crystal

Crystals are transparent. The whiteness we see

comes from light scattering between mineral and the

environment in which it is located and is highly

dependent on particle size.

Calcite is strongly

Bi-refringent,

(2 refractive indices)

Splits light into two

directions

CALCITE

Mechanisms which create scattering.

Complete opacity is achieved when all incident light is

scattered (reflected back) - or absorbed.

Light scatter occurs when light energy changes direction

a) Refraction b) Diffraction

Index of Refraction Particle size effect

Too Small “JUST RIGHT”

Too Big 0.2-0.4 μm

380nm

740nm

Refractive Indices of Common Paint Components

Minerals and Resins have similar Refractive Indices

Minerals do NOT scatter light so develop

either CLEAR or HAZY appearance.

White Pigments Refractive Index Vehicles or Media Refractive Index

Titanium Dioxide 2.73 Vacuum 1.00

Kaolin 1.64 Air 1.00

Calcium Carbonate (Calcite)

1.49+1.63 Water 1.33

Ground Silica 1.49 Vinyl resin 1.48

Diatomaceous Earth

1.45 Acrylic resin 1.49

Refractive Indices of Common Paint Components

White Pigments Refractive Index Vehicles or Media Refractive Index

Titanium Dioxide 2.73 Vacuum 1.00

Kaolin 1.64 Air 1.00

Calcium Carbonate (Calcite)

1.49+1.63 Water 1.33

Ground Silica 1.49 Vinyl resin 1.48

Diatomaceous Earth

1.45 Acrylic resin 1.49

Materials with DIFFERENT RI’s scatter light and appear

WHITE. TiO2 is different to the resins – and so is AIR

Note TiO2/Water is bigger than TiO2/resin

Fresnel Reflectivity

0.00

0.02

0.04

0.06

0.08

0.10

0.12

0.14

1.0 1.5 2.0 2.5 3.0 Particle Refractive Index

Fresnel equation prediction of Refractive Index differences on Light Scattering

R.I. of

AIR

R.I. of

Resins

R.I. of

Rutile

Particle R.I. – Binder R.I.

Binder R.I. + Particle R.I.

2

R.I. of

Water

For a typical paint resin AIR is as effective as TiO2 for light scattering.

Mie Theory Prediction of particle diameter on Light Scattering

30

5

25

20

15

10

0

S (

μm

-1)

0 .2 .4 .6 .8 1

Sphere Diameter (Microns)

Conclusion:

Use particles 0.2 - 0.3

microns to maximize

diffraction-based

scattering.

Source: Erik S. Theile & Roger H. French, DuPont.

Mie Theory Prediction of interparticle separation on Light Scattering

Source: Erik S. Theile & Roger H. French, DuPont.

J. Ceram. Soc, 81 [3] 469-79 (1998)

Scattering Coefficient S for two morphological rutile

particles as a function of interparticle separation.

Results show >0.5 microns required to be efficient.

21

22

23

24

25

0 0.1 0.2 0.3 0.4 0.5

Separation (um)

S (

um

)

-1

The physics is well known.

We have the information required to engineer

light scattering:

Particle size effects

Refractive index effects

Spacing effects

Conclusions from the Physics

Light Scattering Mechanisms and PVC

CPVC λ <1.0 λ >1.0

Light Scattering through

R.I. difference, and particle

size effects.

Industrial minerals with Low

R.I. only contribute light

scatter from size effects.

However they can make a

significant contribution to

enhancing TiO2 through

“spacing effects”

Light Scattering through

R.I. difference (TiO2 & Air),

and particle size of

scattering sites.

Additional scattering can be

developed from engineering

around micro-void size (0.2-

0.4um is ideal).

We will review the various aspects

associated with use of these techniques.

Film surfaces above/below CPVC

40% PVC

Structured Pigment

20% PVC

Structured Pigment

20 microns

Part 1: Above CPVC

Involves engineering the inherent porosity associated with these films.

Single Pigment Formulation:

Raw Material Pounds

Water 266.56

KTPP 1.80

Dispersant 8.00

Dispersant 4.00

Defoamer 3.00

Pigment

Modified Hydroxyethylcellulose 4.50

Vinyl Acrylic Latex (55% solids) 227.50

Water 13.66

Ethylene Glycol 24.99

Coalescent #2 10.00

Water 121.20

Variable

0 – 60 PVC

TiO2 0 - 631 lb/100g

OR

Calcium Carbonate 0 - 450 lb/100g

OR

Calcined Clay 0 - 432 lb/100g

OR

Structured Pigment 0 - 432 lb/100g

Contrast Ratios of Single Pigment Paints

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.70

0.80

0.90

1.00

0% 10% 20% 30% 40% 50% 60%

Pigment Volume Concentration (%)

Co

ntr

as

t R

ati

o

12um CaCO3

3um CaCO3

Calcined Clay

Structured Pigment

Titanium Dioxide

0.7um CaCO3


0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.70

0.80

0.90

1.00

0% 10% 20% 30% 40% 50% 60%


Co

ntr

as

t R

ati

o

Titanium Dioxide

TiO2 has a very high

Refractive Index.

Particle size is small

(particle count is high)

Note: TiO2 experiences

Crowding Effects.

Peaks followed by

Reduction of light scattering

Titanium Dioxide is Engineered

for light Scattering:

ΔR.I. = 1.45

Mean diameter = 0.2-0.4um

NeoGen 2000 Structured

Pigment is also Engineered for

light scattering:

ΔR.I. = 0.16(mineral) + 0.48(air)

Mean pore diam. = ~0.3um (air)

Micro-void structure for light scattering


0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.70

0.80

0.90

1.00

0% 10% 20% 30% 40% 50% 60%


Co

ntr

as

t R

ati

o

Calcined Clay

Structured Pigment

Titanium Dioxide

2xR.I. Air (1.0)/Mineral(1.64)

Larger Pore structure

Higher Oil Absorption of Structured

Pigment means its CPVC is lower than

that of Calcined Clays

2xR.I. Air(1.0)/Mineral(1.64)

Smaller pore structure

No Crowding effects


0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.70

0.80

0.90

1.00

0% 10% 20% 30% 40% 50% 60%

Pigment Volume Concentration (% PVC)

Co

ntr

as

t R

ati

o

Calcined Clay

Structured Pigment

Titanium Dioxide

No Crowding with Structured Pigment or Calcined Clay!

Comparison of calcined clays

92.0

92.5

93.0

93.5

94.0

94.5

95.0

95.5

96.0

96.5

97.0

CIE

L*

Structured Pigment

Calcined Clay

0% 10% 20% 30% 40% 50%

PVC (%)

Lower volume

requirement of EITHER:

Structured Pigment – OR

Titanium Dioxide

These differences in response change

Tint Strength in Pigmented systems

Higher Whiteness

(Tint) at same

volume loading

Structured Calcined

Pigment Clay

Response of Calcined Clays – L*

Wet Opacity

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

0% 10% 20% 30% 40% 50%

% PVC

Co

ntr

as

t R

ati

o

Structured Pigment

Calcined Clay

TiO2

At lower TiO2 levels Structured Pigment

use increases and compensates for opacity

reduction. Effect appears additive.

Lost from TiO2

Gained from Structured Pigment

Structured Pigment provides

Higher WET OPACITY than

other extenders.

Wet Opacity in Paints

Control A B C

TiO2 100 90 80 80

Extenders 125

Calcined Clay 225

NeoGen 2000 - 162 163 132

12um CaCO3 - 199 205 205

Coarse Kaolin - - - 30

Units: Pounds per 100 gallons

A Control B Control C

Wet opacities:

0.979 0.981 0.974 0.981 0.980

Latex Flat formulation – WET OPACITY

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.70

0.80

0.90

1.00

0% 10% 20% 30% 40% 50% 60%


Co

ntr

as

t R

ati

o

12um CaCO3

3um CaCO3

0.7um CaCO3


12 microns

How many

3 microns from

12 microns???

3 microns

0.7 micron 4x4x4=64

64x64=4096x Multiplier

64x Multiplier

4x4x4=64

3 microns

How many

.7 microns from

3 microns???

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.70

0.80

0.90

1.00

0% 10% 20% 30% 40% 50% 60%


Co

ntr

as

t R

ati

o

12um CaCO3

3um CaCO3

Calcined Clay

Structured Pigment

Titanium Dioxide

0.7um CaCO3

Relative position of Pigments

TiO2 is KING in LOW

PVC formulations.

Absence of High/Low

R.I. results in inability

to perform in this region.

Spacing Tools are key!

NeoGen 2000 Structured Pigment

allows extension at lower

PVC’s than Calcined Clay.

Calcium Carbonates

provide a contribution

influenced strongly by

particle size. Often main

function is cost/sheen control.

Also function as TiO2 SPACERS

Calcined Clays: Excellent at

Medium-High PVC.

Influence of Calcium Carbonate size on 65% PVC decorative paint

65% PVC Latex Interior Paint

Pounds Gallons Pounds Gallons

Titanium Dioxide 80.00 2.52 80.00 2.52

12 micron CaCO3 327.00 14.48 249.00 11.02

Fine CaCO3 78.00 3.45

Structured Pigment 125.00 5.76 125.00 5.76

532.00 22.76 532.00 22.75

Pigment system at 65% PVC

12 microns 3 microns 0.7 microns

60 Gloss 2.8 2.9 3.0

85 Sheen 2.2 2.7 3.4

CIE Lab

L* 96.02 96.39 96.75

a* -0.46 -0.47 -0.62

b* 1.97 1.91 2.27

Delta E 0.00 0.37 0.81

Contrast Ratio 0.941 0.958 0.977

Phthalo Blue Tinted @ 11 lb/100Gal

L* 80.31 81.17 81.42

a* -17.60 -17.30 -17.77

b* -20.56 -19.92 -18.99

Delta E 0.00 1.11 1.93

STAIN (K&N Delta E) 7.7 6.4 3.2

Scrub: Cycles to 1st Break 226 212 305

Properties of 65% PVC Paint film

Partial substitution of coarse Calcium Carbonate by a fine and Ultra-fine grades creates a significant improvements in:

Whiteness (L*)

Contrast Ratio

Tint Strength

While maintaining other film properties close to original values.

Calcium Carbonate particle size is the key to obtaining these improved properties

Conclusions

Part 2: Below CPVC

Low PVC Systems require a different approach using spacing and size tools.

Sub-micron particles experience ATOMIC

forces which drive them to aggregate.

TiO2 at 0.25 microns is strongly affected.

TiO2 Spacing - agglomeration

ATOMIC

FORCES

Dispersed Agglomerated

Efficient Light

Scattering

Inefficient Light

Scattering

Sub-micron particles experience ATOMIC

forces which drive them to aggregate.

TiO2 at 0.25 microns is strongly affected.

TiO2 Spacing – Kaolin & CaCO3

ATOMIC

FORCES

Dispersed Agglomerated

+MINERAL

(LOW R.I.)

Efficient Light

Scattering maintained

Efficient Light

Scattering

This is associated strongly with kaolin but is also

relevant to any other sub-micron mineral, e.g. CaCO3

A family of mineral products which have been

modified to produce a hydrophobic surface while

dispersing in conventional latex paint systems.

Hydrophobic

Mineral

Water

Hydrophobic Minerals – New Materials

TWO Surface Modified products have emerged from this Patent Pending Technology: ImerTiX™ 70 for Water based Systems ImerTiX™ 100 for Solvent Systems We will look at the ImerTiX™ 70 product here:

Benchmarking Hydrophobic Mineral in 20% PVC latex Semi-gloss Paint.

TiO2 Spacing by Fine Minerals

Reduction of TiO2 by up to 25%

MATERIAL GALLONS LBS

WATER 13.38 111.46

COLLOIDS 226 0.81 7.43

IGEPAL CO-630 0.32 2.79

AMP-95 0.46 3.72

COLLIDS 691 0.77 5.57

TiO 2 (R-706) 6.08 to 4.56 202 to 151

Mineral Spacer 0 to 1.52 variable

NATROSOL PLUS 0.30 2.79

GRIND TOTALS 22.11 336.24

AQUAMAC 440 56.16 483.00

ETHYLENE GLYCOL 3.00 27.87

TEXANOL 4.96 36.39

WATER 13.38 111.46

ACRYSOL TT-935 0.16 1.39

AMMONIA 0.22 1.86

TOTAL PAINT 100.00 998.22

SEMI-GLOSS FORMULATION (20% PVC)

Constant volume of

6.08 Gallons


Excellent gloss/sheen retention up to 15% TiO2

replacement with ImerTiX™ 70.

60 degree Gloss

60.0

65.0

70.0

75.0

80.0

0 5 10 15 20 25

TiO 2 Replacement level (%)

Glo

ss

Un

its

0.7um CaCO3

ImerTiX 70

0.25um Kaolin


Classic TiO2 “spacing” with kaolin 7 ImerTiX™ 70 gives

equal or higher contrast ratio up to 25% TiO2 extension.

Conventional CaCO3 just acts as diluent.

Contrast Ratio

94.5

95.0

95.5

96.0

96.5

97.0

97.5

0 5 10 15 20 25


Co

ntr

as

t R

ati

o

0.7um CaCO3

ImerTiX 70

0.25um Kaolin


Fine kaolin extender looses Whiteness as TiO2 is removed but

Calcium Carbonate and ImerTiX™ 70 have better color retention.

Kaolins are known to have a yellow overtone which is reflected in

the more rapid increase in b value.

White calcium carbonate and ImerTiX™ 70 are more “color

neutral” than kaolin making them a simpler TiO2 substitute.

Hunter L

95.3

95.4

95.5

95.6

95.7

95.8

95.9

96.0

96.1

96.2

96.3

0 5 10 15 20 25


Hu

nte

r L

0.7um CaCO3

ImerTiX 70

0.25um Kaolin

Hunter b

0.7

0.9

1.1

1.3

0 5 10 15 20 25


Hu

nte

r b

0.7um CaCO3

ImerTiX 70

0.25um Kaolin

TiO2 Spacing by Fine Kaolin & CaCO3’s

In Phthalo Blue tinted systems we see the following:

Delta E response is significantly better for the Calcium Carbonates

(and particularly the ImerTiX™ 70) than for the Kaolin.

The Calcium Carbonate and ImerTiX™ 70 maintain b value at higher

extensions.

Tinted Delta E

0.0

0.5

1.0

1.5

2.0

0 5 10 15 20 25


0.7um CaCO3

ImerTiX 70

0.25um Kaolin

Tinted Delta Hunter b

-0.5

0.0

0.5

1.0

0 5 10 15 20 25


Hu

nte

r b

0.7um CaCO3

ImerTiX 70

0.25um Kaolin

TiO2 Spacing - Conclusions

• TiO2 Spacing, which has traditionally been

considered in the context of Kaolin is also

applicable to ImerTiX™ 70 modified Mineral.

• Color attributes of the Hydrophobically modified

ImerTiX™ 70 are very positive in that they retain

high whiteness and much lower yellowness than

even Premium Kaolin making reformulation to

original Tinted Color requirement less complex.

Which Products?

Choice is driven largely by position relative to CPVC

Also consider Paint type, particle size (Gloss), product form.

Below CPVC Above CPVC

NEOGEN™ 2000

Structured Pigment

(Latex)

ImerTiX™ 70 (Latex)

ImerTiX™ 70 (Latex)

ImerTiX™ 100

(Solvent, Powder, Latex)

CPVC

TiO2 Spacing tools Microporosity Engineering

new ideas and strategies for titanium dioxide extension by

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