effects of coating formulation on coating thermal ... · pdf fileeffects of coating...

8
Effects of coating formulation on coating thermal properties and coated paper print quality in xerography Chong Liang, Ning Yan, David Vidal, and Xuejun Zou KEYWORDS: Paper coating, Thermal conductivity, Thermal diffusivity, Xerography SUMMARY: The effects of coating formulation on thermal characteristics of coating layers (namely thermal diffusivity, specific heat capacity and heat conductivity) were systematically studied and their impact on xerography print quality was evaluated. Model coatings were prepared using ground calcium carbonate or kaolin pigment mixed with styrene butadiene latex binder in various proportions (from 6 to 25 pph). As expected, porosity was shown to be a key parameter for thermal conductivity of the coating layers, and is mainly determined by the latex concentration. Particle size distribution (PSD) and pigment morphology also affected the thermal characteristics of the coating layers. It was found that the bulk thermal conductivity of the coating layers can be accurately predicted by a geometric mean model based on the pigment, latex and air contents. Print quality on model coated papers was evaluated in terms of print gloss, toner adhesion and pair- wise visual ranking. It was demonstrated that print gloss is improved by decreasing the bulk thermal conductivity of the coatings. The coating formulated with the pigments with the steepest PSD and 10 pph of latex had a relatively low thermal conductivity and the best print quality. ADDRESSES OF THE AUTHORS: Chong Liang ([email protected]), Mascoma Canada Inc., Mississauga, Ontario, Canada, Ning Yan ([email protected]), Faculty of Forestry, University of Toronto, Toronto, Ontario, Canada, David Vidal ([email protected]), Xuejun Zou ([email protected]), FPInnovations, Pointe-Claire, Quebec, Canada Corresponding author: Ning Yan In recent years, digital printing has seen the largest growth in the printing industry. This is mainly due to the development of a new generation of large-scale high-speed digital xerography press. Xerography is an electrostatic dry- ink printing technology which involves six steps (Duke, et al., 2002): (1) Charging a photoconductive belt; (2) Generating a latent image on the photoconductive belt by image-wise light/laser exposure; (3) Developing the latent image by brushing charged pigment powders (toner) onto the image area; (4) Transferring the toner from the photoconductive belt to substrate (paper); (5) Fusing the toner on the paper in a fuser; (6) Discharging the photoconductive belt and cleaning the residual toner. In xerography process, toner fusion consumes the largest amount of energy and is one of the key steps in determining print quality. When toner and paper pass through the fuser nip formed between a heating roll and a pressure roll, the toner powders absorb the thermal energy from the heating roll and then melt and coalesce with each other before being fixed onto the paper surface. Typically, un-fused toners on the paper are at room temperature at the entrance of the fusing nip, but have to reach their melting temperature (could be around 110 -120C depending on the type and manufacturer) before the nip exit. Since fusing only takes several milliseconds in a xerography printing press, an adequate heat transfer at the fuser nip is of great importance. In many applications, paper is coated with inorganic pigments and latex binders to obtain higher smoothness, whiteness, and gloss. Comprehensive studies on toner fusion in xerography printing and related heat transfer, detailing the effects of toner properties, paper properties, fuser roll configurations, and fusing process conditions have been conducted by several researchers (Mitsuya, Kumasaka, 1992; Sanders, Rutland, 1996; Bandyopadhay et al., 2001; Maijala et al., 2004; Vernhes et al., 2006; Gane et al., 2007; Gerstner et al., 2009; Gerstner, 2010). However, the contributions of the coating layer to heat transfer, toner fusion and resulting print quality have not been fully understood. In fact, the thermal and surface properties of paper can be altered significantly with the addition of a coating layer. Recent studies have shown that the coating layer affects the effective heat transfer area for toner, and its thermal properties have an inverse effect on the toner temperature at the toner-coating interface (Azadi, 2007). Air gaps may also form at this interface due to a “heat sink” effect introduced by the coating structure (Cormier, Zou, 2008). These problems may result in insufficient toner fusion and thus a decrease in print quality. Therefore, it is necessary to investigate the effects of coating compositions on the thermal properties of coated paper and link them to print quality Past studies (Parker et al., 1961; Morikawa, Hashimoto, 1998; Simula, Niskanen, 1998; Salazer, 2003) have shown how, by measuring the thermal diffusivity D, specific heat capacity C p , and apparent (effective) density ρ of a material, its thermal conductivity K can be experimentally determined through Eq 1: K = D · ρ · C p [1] With a systematic experimental approach, this study provides a good understanding on the effects of coating compositions on the above thermal properties of coating layers. The relationship between the latter and the quality of PAPER PHYSICS Nordic Pulp and Paper Research Journal Vol 27 no.2/2012 451

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Page 1: Effects of coating formulation on coating thermal ... · PDF fileEffects of coating formulation on coating thermal properties and coated paper ... KEYWORDS: Paper coating ... “heat

Effects of coating formulation on coating thermal properties and coated paper print quality in xerography Chong Liang Ning Yan David Vidal and Xuejun Zou

KEYWORDS Paper coating Thermal conductivity

Thermal diffusivity Xerography

SUMMARY The effects of coating formulation on

thermal characteristics of coating layers (namely thermal

diffusivity specific heat capacity and heat conductivity)

were systematically studied and their impact on xerography

print quality was evaluated Model coatings were prepared

using ground calcium carbonate or kaolin pigment mixed

with styrene butadiene latex binder in various proportions

(from 6 to 25 pph) As expected porosity was shown to be

a key parameter for thermal conductivity of the coating

layers and is mainly determined by the latex concentration

Particle size distribution (PSD) and pigment morphology

also affected the thermal characteristics of the coating

layers It was found that the bulk thermal conductivity of

the coating layers can be accurately predicted by a

geometric mean model based on the pigment latex and air

contents Print quality on model coated papers was

evaluated in terms of print gloss toner adhesion and pair-

wise visual ranking It was demonstrated that print gloss is

improved by decreasing the bulk thermal conductivity of

the coatings The coating formulated with the pigments

with the steepest PSD and 10 pph of latex had a relatively

low thermal conductivity and the best print quality

ADDRESSES OF THE AUTHORS Chong Liang (cliangmascomacom) Mascoma Canada

Inc Mississauga Ontario Canada

Ning Yan (ningyanutorontoca) Faculty of Forestry

University of Toronto Toronto Ontario Canada

David Vidal (davidvidalfpinnovationsca)

Xuejun Zou (Xuejunzoufpinnovationsca) FPInnovations

Pointe-Claire Quebec Canada

Corresponding author Ning Yan

In recent years digital printing has seen the largest growth

in the printing industry This is mainly due to the

development of a new generation of large-scale high-speed

digital xerography press Xerography is an electrostatic dry-

ink printing technology which involves six steps (Duke et

al 2002)

(1) Charging a photoconductive belt

(2) Generating a latent image on the photoconductive

belt by image-wise lightlaser exposure

(3) Developing the latent image by brushing charged

pigment powders (toner) onto the image area

(4) Transferring the toner from the photoconductive belt

to substrate (paper)

(5) Fusing the toner on the paper in a fuser

(6) Discharging the photoconductive belt and cleaning

the residual toner

In xerography process toner fusion consumes the largest

amount of energy and is one of the key steps in determining

print quality When toner and paper pass through the fuser

nip formed between a heating roll and a pressure roll the

toner powders absorb the thermal energy from the heating

roll and then melt and coalesce with each other before

being fixed onto the paper surface Typically un-fused

toners on the paper are at room temperature at the entrance

of the fusing nip but have to reach their melting

temperature (could be around 110 -120C depending on the

type and manufacturer) before the nip exit Since fusing

only takes several milliseconds in a xerography printing

press an adequate heat transfer at the fuser nip is of great

importance

In many applications paper is coated with inorganic

pigments and latex binders to obtain higher smoothness

whiteness and gloss Comprehensive studies on toner

fusion in xerography printing and related heat transfer

detailing the effects of toner properties paper properties

fuser roll configurations and fusing process conditions

have been conducted by several researchers (Mitsuya

Kumasaka 1992 Sanders Rutland 1996 Bandyopadhay

et al 2001 Maijala et al 2004 Vernhes et al 2006 Gane

et al 2007 Gerstner et al 2009 Gerstner 2010)

However the contributions of the coating layer to heat

transfer toner fusion and resulting print quality have not

been fully understood In fact the thermal and surface

properties of paper can be altered significantly with the

addition of a coating layer Recent studies have shown that

the coating layer affects the effective heat transfer area for

toner and its thermal properties have an inverse effect on

the toner temperature at the toner-coating interface (Azadi

2007) Air gaps may also form at this interface due to a

ldquoheat sinkrdquo effect introduced by the coating structure

(Cormier Zou 2008) These problems may result in

insufficient toner fusion and thus a decrease in print quality

Therefore it is necessary to investigate the effects of

coating compositions on the thermal properties of coated

paper and link them to print quality

Past studies (Parker et al 1961 Morikawa Hashimoto

1998 Simula Niskanen 1998 Salazer 2003) have shown

how by measuring the thermal diffusivity D specific heat

capacity Cp and apparent (effective) density ρ of a material

its thermal conductivity K can be experimentally

determined through Eq 1

K = D ρ Cp [1]

With a systematic experimental approach this study

provides a good understanding on the effects of coating

compositions on the above thermal properties of coating

layers The relationship between the latter and the quality of

PAPER PHYSICS

Nordic Pulp and Paper Research Journal Vol 27 no22012 451

Table 1 Characteristics of Pigments

Note a Median is defined as D50 (50 percentile) b Distribution is defined as either i Percentage of particles with diameter less than 2 microm ii Width of PSD defined as (D70 ndash D30)D50

toner fusion is also studied by evaluating print quality of

coated papers This work will help papermakers engineer

optimum coatings from better raw material selection and

develop advanced coated papers to better suit high-speed

digital xerography press

Materials and Methods Materials

Three types of ground calcium carbonate (GCC) namely

Hydrocarb 90 Hydrocarb 60 and Covercarb HP and one

type of kaolin clay pigments namely Capim DG were used

in this study and their characteristics are summarized in

Table 1 (the particle size distributions were determined by

SedigraphTM

particle size analyzer) Sixteen different

coating formulations were prepared by mixing 100 pph of

one of the four pigments with 6 10 18 or 25 pph of

styrene-butadiene (SB) latex (Tg = -23C commercial

grade) with the solid content adjusted to 60 ww These

formulations are referred hereafter by their abbreviated

brand name of the pigment followed by the amount of latex

expressed in pph (eg CCHP-18 referring to a formulation

of Covercarb HP mixed with 18 pph of latex)

Formation of Standalone Coating Layers

Standalone coating layers were formed by casting model

coating colours in standard polystyrene Petri dishes which

were pre-treated by wiping a thin layer of silicone release

oil on the inner walls Approximately 40 g of coating

colour was dozed into each Petri dish and was dried under

ambient condition The resulted coating layer had a

thickness of 10 plusmn 008 mm

Measurements of Coating Layer Properties

Coating Structure Characterization by Mercury Intrusion Porosimetry

The model coating layers were characterized by mercury

intrusion porosimetry for both porosity and pore-size

distribution using an AutoPore IV 9500 mercury

porosimeter developed by Micromeritics Instrument Corp

USA The maximum applied pressure of mercury was

31000 psi (214 MPa) The mercury-intrusion measure-

ments were corrected for the compression of liquid mercury

and the expansion of the penetrometer (sample holder)

Detailed working mechanism of the mercury porosimeter

can be obtained from Micromeritics Instrument Corp

(Webb 2001)

After performing mercury intrusion porosimetry the

porosity of each coating layer was used in the calculations

for the apparent density Apparent density was obtained by

using the sample weight divided by the sample volume as

opposed to skeletal density which is defined as the sample

weight divided by the volume of the solid components only

Thermal Diffusivity Measurement

The effective thermal diffusivity of model coating layers

was measured using an LFA447 NanoFlashreg Xenon flash

apparatus developed by Netzsch Instrument Inc Germany

The working principle of this instrument was explained in

(Zhao Schabel 2006) For sample preparation coating

layers were cut into discs with a diameter of 05 inch

(127 cm) The specimens were then sprayed with 3ndash5

layers of liquid graphite The dried graphite layer ensured

consistent light energy absorption for each specimen and

the effect of its thickness was adjusted for by an internal

correction factor provided by the instrument software

(Liang 2009)

Specific Heat Capacity Measurement

The specific heat capacity of model coating layers was

measured by a Q1000 differential scanning calorimeter

from TA Instruments USA using air as a reference

material The instrument was operated under the ramp

mode for the temperature range of 10 ndash 100˚C with a steady

heating rate of 10˚Cmin

Print Quality Evaluation

For print quality evaluations 6 selected model coating

colours HC90-10 HC90-18 HC90-25 HC60-10 CCHP-

10 and CPDG-10 were applied on Xerox Digital Color

Elite Silk Cover Paper with a coat weight of 20 plusmn 07 gm2

(close to industrial standard) by a bench-top rod coating

technique The coated paper samples were dried under

ambient conditions as a low Tg latex was used and then

printed with a 100 solid black area of 8 inch x 10 inch by

a Xerox Workcentre 7345 Multifunction Copier under a

high resolution mode (with pre-set printing speed and

amount of toner used) The same solid black area was also

printed on original Xerox cover paper as control

Print Gloss Measurement

Print gloss of the coated paper samples was measured using

a RhopointTM

Novo-GlossTM

Statistical Glossmeter

developed by Rhopoint Instrumentation Ltd England The

instrument was calibrated against a standard black glass tile

with gloss units (GU) of 899 938 and 990 for the

measurement angel of 20˚ 60˚ and 75˚ respectively The

specular gloss of the 100 black print on the samples was

measured at 75˚ according to the TAPPI Test Methods T

480

Name

Particle Size Distributionb

Morphology Mediana

(microm) lt 2 microm

Width

Hydrocarb 90 (HC90)

061 951 101 Spherical

Hydrocarb 60 (HC60)

138 638 116 Spherical

Covercarb HP (CCHP)

064 977 073 Spherical

Capim DG (CPDG)

071 885 106 Platy

PAPER PHYSICS

452 Nordic Pulp and Paper Research Journal Vol 27 no22012

Toner Adhesion Test

Toner adhesion on the coated paper samples was measured

using an IGT AIC2 Printability Tester from IGT Testing

Systems Netherlands The printed coated paper specimens

were cut into strips of 15 cm wide A piece of 3M Scotch

Magic Tape 810D green tape was attached on the printed

surface of each strip and was peeled off by the IGT tester

at a constant angle with a force of 650 N and speeds from

05 to 5 ms After peeling the strips were scanned using an

Epson 4990 scanner and the images were converted to

binary black and white images to quantify the number of

white pixels (representing the quantity of toners removed)

The percentage of white pixels over the total number of

pixels on the scanned image was calculated and used to

compare how well toners adhered on each specimen

Pair-wise Visual Ranking

From the printed coated paper samples 2 areas (11 cm x 7

cm) of the solid black print were cut and mounted

individually on white card papers creating 2 batches of

samples for visual evaluation on their print quality 15

participants 6 males and 9 females with normal or

corrected to normal visions and with minimal to plentiful

visual ranking experience participated in this exercise in a

laboratory under controlled environment with a constant

light source Pair-wise method was used to visually rank the

sample prints within the same batch based on the

participantsrsquo perceptions of good print quality For each

pair of samples the number of the one with better print

quality was entered in a score matrix until all the possible

combinations of samples were compared For each sample

the number of entries on the score matrix was counted and

the sample with most entries (ie best print quality) was

given the highest ranking

Results and discussions

Effects of Coating Compositions on Coating Layer Properties

Porosity and Pore Size

Fig 1 shows that the Hydrocarb 90 (HC90) and Hydrocarb

60 (HC60) coating layers have similar porosity of ca 28

vv at 6 pph of latex and ca 3 vv at 25 pph This is

consistent with the porosity obtained by Azadi in the recent

study on coating layer compression (Azadi et al 2009)

Comparing with the Covercarb HP (CCHP) and Capim DG

(CPDG) coating layers the latter two have higher porosity

under the same latex concentration

Overall with the addition of 25 pph of latex the reduction

in porosity for all GCC coating layers (HC90 HC60 and

CCHP) is around 25 vv but is only 16 vv for clay

(CPDG) as compared to the lowest addition level of 6 pph

of latex These data suggest that as the latex concentration

in a coating layer increases its porosity decreases but the

reduction in porosity depends on the type of pigments with

the pore space between platy particles being more difficult

to fill in On the other hand Fig 2 shows that the median

Fig 1 Effect of Latex Concentration on Porosity

Fig 2 Effect of Latex Concentration on Pore Size

pore diameter of all GCC coating layers decreases only for

latex concentration greater than 10 pph This suggests that

before the latex concentration reaches 10 pph adding latex

only reduces the number of pores in the coating layer when

the latex concentration exceeds 10 pph the additional latex

starts to reduce both the number and the diameter of coating

pores This qualitatively agrees with the SEM image

analysis results given in Stroumlm et al (2010) The pore sizes

of CPDG (kaolin) coating layers remain roughly constant

indicating a different internal pore structure

Fig 1 also shows that at the same latex concentration the

HC90 and HC60 coating layers have the same porosity in

spite of their different median pigment particle sizes This

suggests that the pigment particle size has no significant

effect on the porosity of a coating layer This agrees with

the finding from Di Risio (Di Risio Yan 2006) that for

pigments with size around or below 1 microm the variation in

coating porosity due to change in pigment size is not

significant (as long as PSD width is similar) However

pigment particle size has an influence on the size of pores

formed in a coating layer Fig 2 shows that the median pore

size of HC60 coating layers is approximately twice as large

as that of HC90 corresponding to the size ratio between

HC60 and HC90 pigments This is reasonable since larger

voids will form among the larger pigment particles if the

two types of pigments have the same morphology and PSD

width Both Di Risio (2006) and Watanabe

et al (1980)

reported a similar trend on kaolin coating layers

PAPER PHYSICS

Nordic Pulp and Paper Research Journal Vol 27 no22012 453

Fig 3 Effect of Latex Concentration on Density (Descending skeletal density Ascending apparent density)

The CCHP coating layers have significantly larger

porosity than the HC90 ones due to the narrower (or steeper)

particle size distribution of CCHP The median diameter of

pores in CCHP coating layers is also larger than that of

HC90 These results are in agreement with Di Risio (2006)

Malla et al (1999) and Okomori et al

(1998) As the PSD

width decreases less fine particles are available to fill the

voids among the coarse particles thus increasing the

porosity and median pore size in a coating layer

A comparison on porosity between CPDG and HC90

coating layers shows that the former has a larger porosity

than the latter at the same latex concentration This is in

agreement with the packing simulation findings by

Vidal et

al (2004) which showed that pigment particles with larger

aspect ratio (ie kaolin) create a bulkier coating structure

Apparent Density

Since adding latex reduces the porosity of coating layers

(Fig 1) an increase in apparent density is thus obtained

(See ascending curves in Fig 3) Also as expected we

observe that pigments with a wider particle size distribution

or with a lower aspect ratio produce significantly denser

coating layers

Thermal Diffusivity

Air has a larger thermal diffusivity (ca 20 mm2s)

(Niskanen Simula 1999) than polymers (with a magnitude

of 01 mm2s) (Salazer 2003) it was shown theoretically

that the effective thermal conductivity of the coating layers

increased with the binder content up to the critical pigment

volume concentration (Vidal Zou 2004) However Fig 4

shows that the experimental thermal diffusivity values of

the HC90 HC60 and CPDG coating layers remain roughly

constant when the latex concentration exceeds 10 pph One

explanation as suggested by Salazar (2003) is that air and

latex can be very compatible in terms of diffusing heat to

each other since they might have similar thermal effusivity

a measure of a materialrsquos ability to exchange thermal

energy with its surroundings Therefore even if there are

less air pores in the coating layers when the latex content

increases heat can still diffuse through the coating layers

Fig 4 Effect of Latex Concentration on Thermal Diffusivity

effectively due to the higher amount of latex surrounding

the pigment particles

It can be seen that the thermal diffusivity of the HC90

coating layer is larger than that of HC60 when the latex

concentration is less than 10 pph but when the latex

concentration exceeds 10 pph the two have approximately

the same thermal diffusivity This might be a combined

effect due to the pigment particle size and the thermal

coupling between air and latex As the median particle size

of HC60 is twice as large as that of HC90 at a low latex

concentration it takes a longer distance for heat to

propagate through the HC60 pigment particles which has a

relatively low thermal diffusivity value (ca 2 mm2s)

(Niskanen Simula 1999) Once the latex concentration

exceeds 10 pph the effect due to the thermal coupling

between air and latex might be so strong that the obstacle

on heat propagation due to pigment particle size becomes

insignificant

Fig 4 also shows that the thermal diffusivity of the HC90

coating layer is larger than that of CCHP and CPDG

samples under the same latex concentration up to 25 pph

This can be due to the lower densities (or higher porosity)

of CCHP or CPDG samples affected by the narrower

particle size distribution or higher aspect ratio of pigments

The lower intrinsic thermal diffusivity value of clay (ca

05 mm2s) (Niskanen Simula 1999) than GCC also

contributes to this result

Specific Heat Capacity

Fig 5 shows that as the latex concentration rises the

specific heat capacity Cp of coating layers increases in a

linear fashion (represented by the solid trend lines) This

increase with additional latex can be explained by the

higher intrinsic Cp value of latex (ca 19 Jg˚C) than those

of pigment (ca 08 Jg˚C) and air (ca 10 Jg˚C) The

linearity of the trend lines is supported by the calculation of

Cp for the coating layers using the simplified 1st order

parallel model shown in Eq 2 (assuming the mass of air

pores is negligible)

latexlatexppigmentpigmentpeffp mCmCC

[2]

PAPER PHYSICS

454 Nordic Pulp and Paper Research Journal Vol 27 no22012

Fig 5 Effect of Latex Concentration on Specific Heat Capacity

where m represents the mass fraction of each coating

component and m=1 The calculated results (the dashed

lines) were found to be in close agreement with the trend

lines of the experimental data This confirms with Salazar

(2003) that the effective specific heat capacity Ceff of a

composite always follows the mixture rule

Therefore it is reasonable that the specific heat capacity

values of HC90 and HC60 coating layers at the same latex

concentration are the same as they have same porosity and

density Hence the pigment particle size is not expected to

have a significant effect on the bulk specific heat capacity

The differences in experimental data shown in Fig 5 might

be due to the sensitivity of the DSC instrument

The Cp of CCHP and CPDG coating layers is also very

close to those of HC90 ones Since the mass fraction of air

is negligible the effects of pigment particle size distribution

or morphology on the specific heat capacity are

insignificant as expected

Bulk (Effective) Thermal Conductivity

Fig 6 shows that as the latex concentration increases up to

25 pph the bulk thermal conductivity of all coating layers

increases As explained earlier adding latex in a coating

layer results in two effects on a coating structure (1)

increasing the volume fraction of latex and thus reducing

the volume fraction of air and (2) breaking the air pores

down to smaller sizes Both latex and air have much lower

intrinsic thermal conductivity values (ca 020 WmK

(Saxaner et al 1999) and 0026 WmK (CRC 2009)

respectively) than pigments (2ndash5 WmK) (Bouguerra

1997) but the reduction in the pore volume (ie porosity) is

more significant than the increase in the latex volume In

addition having smaller pores in the coating layer means

that the pigment particles have a higher chance to be

connected creating a better channel for heat transfer

Changing the median pigment particle size between

HC90 and HC60 coating layers does not result in a change

in the apparent density specific heat capacity or thermal

diffusivity (when the latex concentration exceeds 10 pph)

of the coating layers formed Therefore the bulk thermal

Fig 6 Effect of Latex Concentration on Thermal Conductivity

conductivity of the two groups of coating layers are the

same meaning that pigment particle size alone does not

have a significant effect

Between HC90 and CCHP coating layers using pigments

with a wider particle size distribution (HC90) results in an

increased apparent density an unchanged specific heat

capacity and a higher thermal diffusivity value for the

coating layers formed Therefore the bulk thermal

conductivity of HC90 samples is higher than that of CCHP

Lastly a CPDG coating layer has lower apparent density

and thermal diffusivity but higher specific heat capacity

than a HC90 coating layer at the same latex concentration

The intrinsic thermal properties of clay (CPDG) contribute

greatly to these results However the higher aspect ratio of

the CPDG pigment does contribute to a bulkier coating

structure and therefore affects the thermal diffusivity of

the structure The combined effect is a bulk thermal

conductivity of the CPDG coating layers lower than that of

HC90

Modelling Thermal Conductivity by Geometric Mean

The theoretical bulk thermal conductivity of each coating

layer sample was modeled by calculating the geometric

mean of the K values of pigment latex and air based on

their volume fraction v as Eq 3

airlatexpigment v

air

v

latex

v

pigmenteff KKKK [3]

where Kpigment = 26 WmK for GCC or 16 WmK for

kaolin

Klatex = 020 WmK

Kair = 0026 WmK

vpigment and vlatex are derived from the porosity (vair)

and the pigment to latex mass ratio with their

individual density given 1v

Fig 7 shows that the geometric mean model provides very

good fittings of the experimental data points for the

different pigments and latex concentrations studied This

shows that the bulk thermal conductivity of the coatings

can be well predicted by the geometric mean model

Furthermore it shows that the thermal conductivity only

PAPER PHYSICS

Nordic Pulp and Paper Research Journal Vol 27 no22012 455

Fig 7 Modelling Thermal Conductivity by the Geometric Mean Model

depends on the intrinsic thermal conductivities of the

coating constituents and their respectively volume fractions

(the latter being affected by the PSD and the shape of the

pigment used) In fact this model constitutes a much

simpler model than the Lumped Parameter model proposed

recently by Gerstner (2010) while resembling the empirical

model suggested by Azadi et al (2010)

Print Quality Test Results

Print Gloss

Fig 8 shows that the average print gloss of the model

coated paper was significantly reduced as the bulk thermal

conductivity of the corresponding type of coating layer

increases This suggests that the bulk thermal conductivity

of the coating layers affect the fusing process of toner

which includes toner coalescence melting and spreading

similar to what is concluded by Azadi et al (2008) One

possible explanation is that when the coating bulk thermal

conductivity is lower the coating plays the role of a heat

barrier (dissipating less heat to the base paper) This helps

the toner layer to reach uniformly its melting temperature

and allows the toner layer to level off evenly As a result a

ldquomirror-likerdquo surface is thus created and a high print gloss

is obtained

Interestingly thermal diffusivity of the coating layer gave

a weaker correlation to print gloss with R2 around 052 It

might be due to the fact that thermal diffusivity deals

mostly with the heat flow in the coating layer itself while

print gloss is mostly determined by the heat flow at the

tonercoating interface which thermal conductivity might

be more important However this remains to be confirmed

by further studies

Toner Adhesion

The results of the toner adhesion test show that the amount

of toner removed is affected by the peeling speed of the

Scotch tape Therefore the minimum percentages of toner

remained (adhered) on the coated paper samples at all

peeling speeds were taken for the study These data are

listed in Table 2 and plotted in Fig 9 It shows no

correlation between the percentage of toners remained on

Fig 8 Effect of Bulk Thermal Conductivity of the Coating Layers on Average Print Gloss (in ) of the Coated Papers

Fig 9 Effect of Bulk Thermal Conductivity of the Coating Layers on Toner Adhesion on the Coated Papers

Table 2 Minimum Toner Adhesion on Coated Papers

the coated paper and the bulk thermal conductivity of the

corresponding type of coating layer A similar comparison

was done by Gerstner et al

(2009) and no definite

correlation was found either As explained by Kianercy

(2004) and Sipi (2001) only three factors have been found

to have significant impacts on toner adhesion which are

surface tension of paper toner viscosity at the tonerpaper

interface and fusing speed

Pair-wise Visual Ranking

The result of the visual ranking test shows that for coating

layers with 10 pph of latex the CCHP-10 coating provides

the best print quality and the CPDG-10 coating provides

the worst print quality Among the HC90 coating layers

with different latex concentrations the HC90-10 and

Sample Minimum Toner Remained ()

HC90-10 987 HC90-18 946 HC90-25 872 HC60-10 218 CCHP-10 999 CPDG-10 811

PAPER PHYSICS

456 Nordic Pulp and Paper Research Journal Vol 27 no22012

Fig 10 Effect of Bulk Thermal Conductivity of the Coating Layers on Average Ranking Score of the Printed Coated Papers

Table 3 Summary of the Print Quality Test Results

HC90-18 coating provide significantly better print quality

than the one made with 25 pph of latex However no

correlation was found between print quality (quantified by

the average ranking score) of a sample with the bulk

thermal conductivity of the coating layers see Fig 10

These findings suggest that there are other factors which

have a more significant effect on the print quality of coated

paper However this is beyond the scope of this study

A summary of the print quality test results (Table 3)

reveals that the coating layer formulated with Covercarb

HP pigment and 10 pph of latex has the best ranking in all

three tests Therefore with its relatively low thermal

conductivity this coating formulation is the best candidate

among the ones studied for use in xerography printing

Conclusions The effects of coating formulations on thermal

characteristics of the coating layers were systematically

studied for assessing their impact on xerographic toner

fusion onto the coated papers It was shown that porosity is

a key parameter in the design of a coating layer for heat

transfer applications The latex concentration in the coating

formulation plays a significant role as it determines the

overall porosity of the coating layers Therefore in order

for the coating layer to act as a heat barrier (and provide

sufficient uniform heat transfer to the toner layer) it needs

to have an acceptably high porosity or a low latex

concentration The particle size distribution (narrow PSD)

and morphology (high shape factor) of pigments also affect

positively the porosity and thus the overall thermal

characteristics of the coating layers However the median

particle size of pigments did not show any significant

effect It was also found that the bulk thermal conductivity

of the coating layers can be accurately predicted by a

simple geometric mean model based on the pigment latex

and air volume contents

A 75˚ TAPPI print gloss measurement a toner adhesion

test using an IGT printability tester and a pair-wise visual

ranking test were performed on paper samples coated with

model coating colours and printed with 100 solid black

by xerography The print gloss of coated papers was

significantly improved when the coating bulk thermal

conductivity was low This is attributed to the insulating

effect of the coating thus providing a more uniform toner

fusion No other correlation was found between the print

quality and thermal properties of the samples

Lastly it was found that the coating made of Covercarb

HP a narrow PSD pigment and 10 pph of latex gave a

relatively low thermal conductivity and the best ranking in

all three print quality tests Therefore among all the

formulations tested this coating is the best candidate for

coated paper applications in xerography

Acknowledgements The financial and technical supports from NSERC IPS Scholarship FPInnovations Xerox Research Center of Canada and Surface Science Consortium at the Pulp and Paper Centre University of Toronto are gratefully acknowledged

Literature

Azadi P (2007) Modeling of mechanical and thermal responses of paper coatings under compression using discrete element method Thesis for the Degree of Master of Applied Science University of Toronto Toronto Canada

Azadi P Yan N Farnood R (2008) Discrete Element Modeling of the Transient Heat Transfer and Toner Fusing Process in the Xerographic Printing of Coated Papers Computers amp Chemical Engineering 32(12) 3238-3245

Azadi P Nunnari S Farnood R Kortschot M Yan N (2009) High speed compression of highly filled thin composites effect of binder content and stiffness Progress in Organic Coatings 64(4) 356-360

Azadi P Farnood R Yan N (2010) FEM-DEM Modeling of Thermal Conductivity of Porous Pigmented Coatings Computational Materials Science 49(2) 392-399

Bandyopadhay A Ramarao BV Shih EC (2001) Transient response of a paper sheet subjected to a traveling thermal pulse evolution of temperature moisture and pressure fields Journal of Imaging Science and Technology 45(6) 598-608

Bouguerra A Laurent JP Goual M Queneudec M (1997) The measurement of the thermal conductivity of solid aggregates using the transient plane source technique Journal of Physics D Applied Physics 30 2900-2904

Ranking (Best to Worst)

Print Gloss

Toner Adhesion

Visual Ranking

1 CCHP-10 CCHP-10 CCHP-10 2 CPDG-10 HC90-10 HC90-10 3 HC90-10 HC90-18 HC90-18 4 HC90-18 HC90-25 HC60-10 5 HC60-10 CPDG-10 CPDG-10 6 HC90-25 HC60-10 HC90-25

PAPER PHYSICS

Nordic Pulp and Paper Research Journal Vol 27 no22012 457

Cormier L Zou X (2008) Toner fusion in electrophotographic printing ndash issues from Papricanrsquos perspectives FPInnovations Paprican Division Pointe-Claire QC February 8 2008

CRC Handbook of Chemistry and Physics (2009) 89th ed Taylor amp Francis Group

Di Risio S Yan N (2006) Characterizing Coating Pore Structures of Paper Using Scanning Probe Microscopyrdquo TAPPI Journal 5(3) 9-14

Di Risio S Yan N (2006) Characterizing Coating Layer Z-directional Binder Distribution in Paper Using Atomic Force Microscopy Colloids and Surfaces A Physicochemical and Engineering Aspects 289(1-3) 65-74

Duke CB Noolandi J Thieret T (2002) The surface science of xerography Surface Science 500 1005-1023

Gane PAC Ridgeway CJ Schoelkopf J Bousfield DW (2007) Heat transfer through calcium carbonate-based coating structures observation and model for a thermal fusing process Journal of Pulp and Paper Science 33(2) 60-70

Gerstner P Gane PAC (2009) Considerations for thermally engineered coated printing papers focus on electrophotography Journal of Pulp and Paper Science 35(3-4) 108-117

Gerstner P Paltakari J Gane PAC (2009) Measurement and modeling of heat transfer in paper coating structures Journal of Material Science 44 (2) 483-491

Gerstner P (2010) Heat Transfer Through Porous Multiphase Systems Measurement Modelling and Application in Printing of Coated Papers PhD Thesis Aalto university Helsinki Finland

Kianercy A (2004) Characterizing toner-paper adhesion in xerography Thesis for the Degree of Master of Applied Science University of Toronto Toronto Canada

Liang C (2009) Effect of coating formulations on thermal properties of coating layers Thesis for the Degree of Master of Applied Science University of Toronto Toronto Canada

Maijala J Putkisto K Pietikaumlinen R Groumln J (2004) Heat transfer during fixation of coating layers in dry surface treatment Nordic Pulp and Paper Research Journal 19(3) 291-299

Malla PB Starr RE Werkin TJ (1999) The effects of kaolin particle size structure clay loading and binder level on glossing and offset print properties ndash A CLC coating study 1999 TAPPI Coating Conference Proceedings Toronto Ontario Canada TAPPI Press

Mitsuya T Kumasaka T (1992) Heat transfer and toner melting in an electrophotographic fuser system Journal of Imaging Science and Technology 36 88-92

Morikawa J Hashimoto T (1998) Thermal diffusivity measurement of papers by an AC joule heating method Polymer International 45(2) 207-210

Niskanen K Simula S (1999) Thermal diffusivity of paper Nordic Pulp and Paper Research Journal 14(3) 236-242

Okomori K Lepoutre P (1998) Effect of pigment size and shape distribution on the cohesion of pigmented coatings 1998 TAPPI CoatingPapermakers Conference New Orleans LA USA TAPPI Atlanta GA USA 819 ndash 835

Parker WJ Jenkins RJ Butler CP Abbott GL (1961) Flash method of determining thermal diffusivity heat capacity and thermal conductivity Journal of Applied Physics 32(9) 1679-1684

Salazer A (2003) On thermal diffusivity European Journal of Physics 24(3) 351-358

Sanders DJ Rutland DF (1996) Effect of paper properties on fusing fix Journal of Imaging Science and Technology 40(2) 175-179

Saxaner NS et al (1999) Thermal conductivity of styrene butadiene rubber compounds with natural rubber prophylactics waste as filler European Polymer Journal 35 1687-1693

Simula S Niskanen K (1998) Thermal diffusivity measurement of non-impact printing paper Journal of Imaging Science and Technology 42(6) 550-553

Sipi KM (2001) Toner layer structure and toner adhesion on coated paper NIP17 International Conference on Digital Printing Technologies Fort Lauderdale FL USA 145-150

Stroumlm G Hornatowska J Changhong X Terasaki O (2010) A novel SEM cross-section analysis of paper coating for separation of latex from void volume Nordic Pulp and Paper Research Journal 25(1) 107-113

Vernhes P Blayo A Bloch J-F Pineaux B (2006) Influence of the thermal field on the fusing step in electrophotographic printing Proceedings of the Technical Association of the Graphic Arts 465-485

Vidal D Zou X Uesaka T (2004) Modeling coating structure development Monte-Carlo deposition of particles with irregular shapes Nordic Pulp and Paper Research Journal 19(4) 420ndash427

Wantanabe J Kohara Y Takahashi S (1980) Effects of clay properties on paper coating structure Tappi 63(1) 43 ndash 46

Webb PA (2001) An introduction to the physical characterization of materials by mercury intrusion porosimetry with emphasis on reduction and presentation of experimental data Micromeritics Instrument Corp January 2001 Retrieved on January 14 2009

httpwwwmicromeriticscomapplicationsarticlesaspx

Zhao S Schabel S (2006) Measurement of thermal properties of paper by a light flash method Das Papier T65 34-39

PAPER PHYSICS

458 Nordic Pulp and Paper Research Journal Vol 27 no22012

Page 2: Effects of coating formulation on coating thermal ... · PDF fileEffects of coating formulation on coating thermal properties and coated paper ... KEYWORDS: Paper coating ... “heat

Table 1 Characteristics of Pigments

Note a Median is defined as D50 (50 percentile) b Distribution is defined as either i Percentage of particles with diameter less than 2 microm ii Width of PSD defined as (D70 ndash D30)D50

toner fusion is also studied by evaluating print quality of

coated papers This work will help papermakers engineer

optimum coatings from better raw material selection and

develop advanced coated papers to better suit high-speed

digital xerography press

Materials and Methods Materials

Three types of ground calcium carbonate (GCC) namely

Hydrocarb 90 Hydrocarb 60 and Covercarb HP and one

type of kaolin clay pigments namely Capim DG were used

in this study and their characteristics are summarized in

Table 1 (the particle size distributions were determined by

SedigraphTM

particle size analyzer) Sixteen different

coating formulations were prepared by mixing 100 pph of

one of the four pigments with 6 10 18 or 25 pph of

styrene-butadiene (SB) latex (Tg = -23C commercial

grade) with the solid content adjusted to 60 ww These

formulations are referred hereafter by their abbreviated

brand name of the pigment followed by the amount of latex

expressed in pph (eg CCHP-18 referring to a formulation

of Covercarb HP mixed with 18 pph of latex)

Formation of Standalone Coating Layers

Standalone coating layers were formed by casting model

coating colours in standard polystyrene Petri dishes which

were pre-treated by wiping a thin layer of silicone release

oil on the inner walls Approximately 40 g of coating

colour was dozed into each Petri dish and was dried under

ambient condition The resulted coating layer had a

thickness of 10 plusmn 008 mm

Measurements of Coating Layer Properties

Coating Structure Characterization by Mercury Intrusion Porosimetry

The model coating layers were characterized by mercury

intrusion porosimetry for both porosity and pore-size

distribution using an AutoPore IV 9500 mercury

porosimeter developed by Micromeritics Instrument Corp

USA The maximum applied pressure of mercury was

31000 psi (214 MPa) The mercury-intrusion measure-

ments were corrected for the compression of liquid mercury

and the expansion of the penetrometer (sample holder)

Detailed working mechanism of the mercury porosimeter

can be obtained from Micromeritics Instrument Corp

(Webb 2001)

After performing mercury intrusion porosimetry the

porosity of each coating layer was used in the calculations

for the apparent density Apparent density was obtained by

using the sample weight divided by the sample volume as

opposed to skeletal density which is defined as the sample

weight divided by the volume of the solid components only

Thermal Diffusivity Measurement

The effective thermal diffusivity of model coating layers

was measured using an LFA447 NanoFlashreg Xenon flash

apparatus developed by Netzsch Instrument Inc Germany

The working principle of this instrument was explained in

(Zhao Schabel 2006) For sample preparation coating

layers were cut into discs with a diameter of 05 inch

(127 cm) The specimens were then sprayed with 3ndash5

layers of liquid graphite The dried graphite layer ensured

consistent light energy absorption for each specimen and

the effect of its thickness was adjusted for by an internal

correction factor provided by the instrument software

(Liang 2009)

Specific Heat Capacity Measurement

The specific heat capacity of model coating layers was

measured by a Q1000 differential scanning calorimeter

from TA Instruments USA using air as a reference

material The instrument was operated under the ramp

mode for the temperature range of 10 ndash 100˚C with a steady

heating rate of 10˚Cmin

Print Quality Evaluation

For print quality evaluations 6 selected model coating

colours HC90-10 HC90-18 HC90-25 HC60-10 CCHP-

10 and CPDG-10 were applied on Xerox Digital Color

Elite Silk Cover Paper with a coat weight of 20 plusmn 07 gm2

(close to industrial standard) by a bench-top rod coating

technique The coated paper samples were dried under

ambient conditions as a low Tg latex was used and then

printed with a 100 solid black area of 8 inch x 10 inch by

a Xerox Workcentre 7345 Multifunction Copier under a

high resolution mode (with pre-set printing speed and

amount of toner used) The same solid black area was also

printed on original Xerox cover paper as control

Print Gloss Measurement

Print gloss of the coated paper samples was measured using

a RhopointTM

Novo-GlossTM

Statistical Glossmeter

developed by Rhopoint Instrumentation Ltd England The

instrument was calibrated against a standard black glass tile

with gloss units (GU) of 899 938 and 990 for the

measurement angel of 20˚ 60˚ and 75˚ respectively The

specular gloss of the 100 black print on the samples was

measured at 75˚ according to the TAPPI Test Methods T

480

Name

Particle Size Distributionb

Morphology Mediana

(microm) lt 2 microm

Width

Hydrocarb 90 (HC90)

061 951 101 Spherical

Hydrocarb 60 (HC60)

138 638 116 Spherical

Covercarb HP (CCHP)

064 977 073 Spherical

Capim DG (CPDG)

071 885 106 Platy

PAPER PHYSICS

452 Nordic Pulp and Paper Research Journal Vol 27 no22012

Toner Adhesion Test

Toner adhesion on the coated paper samples was measured

using an IGT AIC2 Printability Tester from IGT Testing

Systems Netherlands The printed coated paper specimens

were cut into strips of 15 cm wide A piece of 3M Scotch

Magic Tape 810D green tape was attached on the printed

surface of each strip and was peeled off by the IGT tester

at a constant angle with a force of 650 N and speeds from

05 to 5 ms After peeling the strips were scanned using an

Epson 4990 scanner and the images were converted to

binary black and white images to quantify the number of

white pixels (representing the quantity of toners removed)

The percentage of white pixels over the total number of

pixels on the scanned image was calculated and used to

compare how well toners adhered on each specimen

Pair-wise Visual Ranking

From the printed coated paper samples 2 areas (11 cm x 7

cm) of the solid black print were cut and mounted

individually on white card papers creating 2 batches of

samples for visual evaluation on their print quality 15

participants 6 males and 9 females with normal or

corrected to normal visions and with minimal to plentiful

visual ranking experience participated in this exercise in a

laboratory under controlled environment with a constant

light source Pair-wise method was used to visually rank the

sample prints within the same batch based on the

participantsrsquo perceptions of good print quality For each

pair of samples the number of the one with better print

quality was entered in a score matrix until all the possible

combinations of samples were compared For each sample

the number of entries on the score matrix was counted and

the sample with most entries (ie best print quality) was

given the highest ranking

Results and discussions

Effects of Coating Compositions on Coating Layer Properties

Porosity and Pore Size

Fig 1 shows that the Hydrocarb 90 (HC90) and Hydrocarb

60 (HC60) coating layers have similar porosity of ca 28

vv at 6 pph of latex and ca 3 vv at 25 pph This is

consistent with the porosity obtained by Azadi in the recent

study on coating layer compression (Azadi et al 2009)

Comparing with the Covercarb HP (CCHP) and Capim DG

(CPDG) coating layers the latter two have higher porosity

under the same latex concentration

Overall with the addition of 25 pph of latex the reduction

in porosity for all GCC coating layers (HC90 HC60 and

CCHP) is around 25 vv but is only 16 vv for clay

(CPDG) as compared to the lowest addition level of 6 pph

of latex These data suggest that as the latex concentration

in a coating layer increases its porosity decreases but the

reduction in porosity depends on the type of pigments with

the pore space between platy particles being more difficult

to fill in On the other hand Fig 2 shows that the median

Fig 1 Effect of Latex Concentration on Porosity

Fig 2 Effect of Latex Concentration on Pore Size

pore diameter of all GCC coating layers decreases only for

latex concentration greater than 10 pph This suggests that

before the latex concentration reaches 10 pph adding latex

only reduces the number of pores in the coating layer when

the latex concentration exceeds 10 pph the additional latex

starts to reduce both the number and the diameter of coating

pores This qualitatively agrees with the SEM image

analysis results given in Stroumlm et al (2010) The pore sizes

of CPDG (kaolin) coating layers remain roughly constant

indicating a different internal pore structure

Fig 1 also shows that at the same latex concentration the

HC90 and HC60 coating layers have the same porosity in

spite of their different median pigment particle sizes This

suggests that the pigment particle size has no significant

effect on the porosity of a coating layer This agrees with

the finding from Di Risio (Di Risio Yan 2006) that for

pigments with size around or below 1 microm the variation in

coating porosity due to change in pigment size is not

significant (as long as PSD width is similar) However

pigment particle size has an influence on the size of pores

formed in a coating layer Fig 2 shows that the median pore

size of HC60 coating layers is approximately twice as large

as that of HC90 corresponding to the size ratio between

HC60 and HC90 pigments This is reasonable since larger

voids will form among the larger pigment particles if the

two types of pigments have the same morphology and PSD

width Both Di Risio (2006) and Watanabe

et al (1980)

reported a similar trend on kaolin coating layers

PAPER PHYSICS

Nordic Pulp and Paper Research Journal Vol 27 no22012 453

Fig 3 Effect of Latex Concentration on Density (Descending skeletal density Ascending apparent density)

The CCHP coating layers have significantly larger

porosity than the HC90 ones due to the narrower (or steeper)

particle size distribution of CCHP The median diameter of

pores in CCHP coating layers is also larger than that of

HC90 These results are in agreement with Di Risio (2006)

Malla et al (1999) and Okomori et al

(1998) As the PSD

width decreases less fine particles are available to fill the

voids among the coarse particles thus increasing the

porosity and median pore size in a coating layer

A comparison on porosity between CPDG and HC90

coating layers shows that the former has a larger porosity

than the latter at the same latex concentration This is in

agreement with the packing simulation findings by

Vidal et

al (2004) which showed that pigment particles with larger

aspect ratio (ie kaolin) create a bulkier coating structure

Apparent Density

Since adding latex reduces the porosity of coating layers

(Fig 1) an increase in apparent density is thus obtained

(See ascending curves in Fig 3) Also as expected we

observe that pigments with a wider particle size distribution

or with a lower aspect ratio produce significantly denser

coating layers

Thermal Diffusivity

Air has a larger thermal diffusivity (ca 20 mm2s)

(Niskanen Simula 1999) than polymers (with a magnitude

of 01 mm2s) (Salazer 2003) it was shown theoretically

that the effective thermal conductivity of the coating layers

increased with the binder content up to the critical pigment

volume concentration (Vidal Zou 2004) However Fig 4

shows that the experimental thermal diffusivity values of

the HC90 HC60 and CPDG coating layers remain roughly

constant when the latex concentration exceeds 10 pph One

explanation as suggested by Salazar (2003) is that air and

latex can be very compatible in terms of diffusing heat to

each other since they might have similar thermal effusivity

a measure of a materialrsquos ability to exchange thermal

energy with its surroundings Therefore even if there are

less air pores in the coating layers when the latex content

increases heat can still diffuse through the coating layers

Fig 4 Effect of Latex Concentration on Thermal Diffusivity

effectively due to the higher amount of latex surrounding

the pigment particles

It can be seen that the thermal diffusivity of the HC90

coating layer is larger than that of HC60 when the latex

concentration is less than 10 pph but when the latex

concentration exceeds 10 pph the two have approximately

the same thermal diffusivity This might be a combined

effect due to the pigment particle size and the thermal

coupling between air and latex As the median particle size

of HC60 is twice as large as that of HC90 at a low latex

concentration it takes a longer distance for heat to

propagate through the HC60 pigment particles which has a

relatively low thermal diffusivity value (ca 2 mm2s)

(Niskanen Simula 1999) Once the latex concentration

exceeds 10 pph the effect due to the thermal coupling

between air and latex might be so strong that the obstacle

on heat propagation due to pigment particle size becomes

insignificant

Fig 4 also shows that the thermal diffusivity of the HC90

coating layer is larger than that of CCHP and CPDG

samples under the same latex concentration up to 25 pph

This can be due to the lower densities (or higher porosity)

of CCHP or CPDG samples affected by the narrower

particle size distribution or higher aspect ratio of pigments

The lower intrinsic thermal diffusivity value of clay (ca

05 mm2s) (Niskanen Simula 1999) than GCC also

contributes to this result

Specific Heat Capacity

Fig 5 shows that as the latex concentration rises the

specific heat capacity Cp of coating layers increases in a

linear fashion (represented by the solid trend lines) This

increase with additional latex can be explained by the

higher intrinsic Cp value of latex (ca 19 Jg˚C) than those

of pigment (ca 08 Jg˚C) and air (ca 10 Jg˚C) The

linearity of the trend lines is supported by the calculation of

Cp for the coating layers using the simplified 1st order

parallel model shown in Eq 2 (assuming the mass of air

pores is negligible)

latexlatexppigmentpigmentpeffp mCmCC

[2]

PAPER PHYSICS

454 Nordic Pulp and Paper Research Journal Vol 27 no22012

Fig 5 Effect of Latex Concentration on Specific Heat Capacity

where m represents the mass fraction of each coating

component and m=1 The calculated results (the dashed

lines) were found to be in close agreement with the trend

lines of the experimental data This confirms with Salazar

(2003) that the effective specific heat capacity Ceff of a

composite always follows the mixture rule

Therefore it is reasonable that the specific heat capacity

values of HC90 and HC60 coating layers at the same latex

concentration are the same as they have same porosity and

density Hence the pigment particle size is not expected to

have a significant effect on the bulk specific heat capacity

The differences in experimental data shown in Fig 5 might

be due to the sensitivity of the DSC instrument

The Cp of CCHP and CPDG coating layers is also very

close to those of HC90 ones Since the mass fraction of air

is negligible the effects of pigment particle size distribution

or morphology on the specific heat capacity are

insignificant as expected

Bulk (Effective) Thermal Conductivity

Fig 6 shows that as the latex concentration increases up to

25 pph the bulk thermal conductivity of all coating layers

increases As explained earlier adding latex in a coating

layer results in two effects on a coating structure (1)

increasing the volume fraction of latex and thus reducing

the volume fraction of air and (2) breaking the air pores

down to smaller sizes Both latex and air have much lower

intrinsic thermal conductivity values (ca 020 WmK

(Saxaner et al 1999) and 0026 WmK (CRC 2009)

respectively) than pigments (2ndash5 WmK) (Bouguerra

1997) but the reduction in the pore volume (ie porosity) is

more significant than the increase in the latex volume In

addition having smaller pores in the coating layer means

that the pigment particles have a higher chance to be

connected creating a better channel for heat transfer

Changing the median pigment particle size between

HC90 and HC60 coating layers does not result in a change

in the apparent density specific heat capacity or thermal

diffusivity (when the latex concentration exceeds 10 pph)

of the coating layers formed Therefore the bulk thermal

Fig 6 Effect of Latex Concentration on Thermal Conductivity

conductivity of the two groups of coating layers are the

same meaning that pigment particle size alone does not

have a significant effect

Between HC90 and CCHP coating layers using pigments

with a wider particle size distribution (HC90) results in an

increased apparent density an unchanged specific heat

capacity and a higher thermal diffusivity value for the

coating layers formed Therefore the bulk thermal

conductivity of HC90 samples is higher than that of CCHP

Lastly a CPDG coating layer has lower apparent density

and thermal diffusivity but higher specific heat capacity

than a HC90 coating layer at the same latex concentration

The intrinsic thermal properties of clay (CPDG) contribute

greatly to these results However the higher aspect ratio of

the CPDG pigment does contribute to a bulkier coating

structure and therefore affects the thermal diffusivity of

the structure The combined effect is a bulk thermal

conductivity of the CPDG coating layers lower than that of

HC90

Modelling Thermal Conductivity by Geometric Mean

The theoretical bulk thermal conductivity of each coating

layer sample was modeled by calculating the geometric

mean of the K values of pigment latex and air based on

their volume fraction v as Eq 3

airlatexpigment v

air

v

latex

v

pigmenteff KKKK [3]

where Kpigment = 26 WmK for GCC or 16 WmK for

kaolin

Klatex = 020 WmK

Kair = 0026 WmK

vpigment and vlatex are derived from the porosity (vair)

and the pigment to latex mass ratio with their

individual density given 1v

Fig 7 shows that the geometric mean model provides very

good fittings of the experimental data points for the

different pigments and latex concentrations studied This

shows that the bulk thermal conductivity of the coatings

can be well predicted by the geometric mean model

Furthermore it shows that the thermal conductivity only

PAPER PHYSICS

Nordic Pulp and Paper Research Journal Vol 27 no22012 455

Fig 7 Modelling Thermal Conductivity by the Geometric Mean Model

depends on the intrinsic thermal conductivities of the

coating constituents and their respectively volume fractions

(the latter being affected by the PSD and the shape of the

pigment used) In fact this model constitutes a much

simpler model than the Lumped Parameter model proposed

recently by Gerstner (2010) while resembling the empirical

model suggested by Azadi et al (2010)

Print Quality Test Results

Print Gloss

Fig 8 shows that the average print gloss of the model

coated paper was significantly reduced as the bulk thermal

conductivity of the corresponding type of coating layer

increases This suggests that the bulk thermal conductivity

of the coating layers affect the fusing process of toner

which includes toner coalescence melting and spreading

similar to what is concluded by Azadi et al (2008) One

possible explanation is that when the coating bulk thermal

conductivity is lower the coating plays the role of a heat

barrier (dissipating less heat to the base paper) This helps

the toner layer to reach uniformly its melting temperature

and allows the toner layer to level off evenly As a result a

ldquomirror-likerdquo surface is thus created and a high print gloss

is obtained

Interestingly thermal diffusivity of the coating layer gave

a weaker correlation to print gloss with R2 around 052 It

might be due to the fact that thermal diffusivity deals

mostly with the heat flow in the coating layer itself while

print gloss is mostly determined by the heat flow at the

tonercoating interface which thermal conductivity might

be more important However this remains to be confirmed

by further studies

Toner Adhesion

The results of the toner adhesion test show that the amount

of toner removed is affected by the peeling speed of the

Scotch tape Therefore the minimum percentages of toner

remained (adhered) on the coated paper samples at all

peeling speeds were taken for the study These data are

listed in Table 2 and plotted in Fig 9 It shows no

correlation between the percentage of toners remained on

Fig 8 Effect of Bulk Thermal Conductivity of the Coating Layers on Average Print Gloss (in ) of the Coated Papers

Fig 9 Effect of Bulk Thermal Conductivity of the Coating Layers on Toner Adhesion on the Coated Papers

Table 2 Minimum Toner Adhesion on Coated Papers

the coated paper and the bulk thermal conductivity of the

corresponding type of coating layer A similar comparison

was done by Gerstner et al

(2009) and no definite

correlation was found either As explained by Kianercy

(2004) and Sipi (2001) only three factors have been found

to have significant impacts on toner adhesion which are

surface tension of paper toner viscosity at the tonerpaper

interface and fusing speed

Pair-wise Visual Ranking

The result of the visual ranking test shows that for coating

layers with 10 pph of latex the CCHP-10 coating provides

the best print quality and the CPDG-10 coating provides

the worst print quality Among the HC90 coating layers

with different latex concentrations the HC90-10 and

Sample Minimum Toner Remained ()

HC90-10 987 HC90-18 946 HC90-25 872 HC60-10 218 CCHP-10 999 CPDG-10 811

PAPER PHYSICS

456 Nordic Pulp and Paper Research Journal Vol 27 no22012

Fig 10 Effect of Bulk Thermal Conductivity of the Coating Layers on Average Ranking Score of the Printed Coated Papers

Table 3 Summary of the Print Quality Test Results

HC90-18 coating provide significantly better print quality

than the one made with 25 pph of latex However no

correlation was found between print quality (quantified by

the average ranking score) of a sample with the bulk

thermal conductivity of the coating layers see Fig 10

These findings suggest that there are other factors which

have a more significant effect on the print quality of coated

paper However this is beyond the scope of this study

A summary of the print quality test results (Table 3)

reveals that the coating layer formulated with Covercarb

HP pigment and 10 pph of latex has the best ranking in all

three tests Therefore with its relatively low thermal

conductivity this coating formulation is the best candidate

among the ones studied for use in xerography printing

Conclusions The effects of coating formulations on thermal

characteristics of the coating layers were systematically

studied for assessing their impact on xerographic toner

fusion onto the coated papers It was shown that porosity is

a key parameter in the design of a coating layer for heat

transfer applications The latex concentration in the coating

formulation plays a significant role as it determines the

overall porosity of the coating layers Therefore in order

for the coating layer to act as a heat barrier (and provide

sufficient uniform heat transfer to the toner layer) it needs

to have an acceptably high porosity or a low latex

concentration The particle size distribution (narrow PSD)

and morphology (high shape factor) of pigments also affect

positively the porosity and thus the overall thermal

characteristics of the coating layers However the median

particle size of pigments did not show any significant

effect It was also found that the bulk thermal conductivity

of the coating layers can be accurately predicted by a

simple geometric mean model based on the pigment latex

and air volume contents

A 75˚ TAPPI print gloss measurement a toner adhesion

test using an IGT printability tester and a pair-wise visual

ranking test were performed on paper samples coated with

model coating colours and printed with 100 solid black

by xerography The print gloss of coated papers was

significantly improved when the coating bulk thermal

conductivity was low This is attributed to the insulating

effect of the coating thus providing a more uniform toner

fusion No other correlation was found between the print

quality and thermal properties of the samples

Lastly it was found that the coating made of Covercarb

HP a narrow PSD pigment and 10 pph of latex gave a

relatively low thermal conductivity and the best ranking in

all three print quality tests Therefore among all the

formulations tested this coating is the best candidate for

coated paper applications in xerography

Acknowledgements The financial and technical supports from NSERC IPS Scholarship FPInnovations Xerox Research Center of Canada and Surface Science Consortium at the Pulp and Paper Centre University of Toronto are gratefully acknowledged

Literature

Azadi P (2007) Modeling of mechanical and thermal responses of paper coatings under compression using discrete element method Thesis for the Degree of Master of Applied Science University of Toronto Toronto Canada

Azadi P Yan N Farnood R (2008) Discrete Element Modeling of the Transient Heat Transfer and Toner Fusing Process in the Xerographic Printing of Coated Papers Computers amp Chemical Engineering 32(12) 3238-3245

Azadi P Nunnari S Farnood R Kortschot M Yan N (2009) High speed compression of highly filled thin composites effect of binder content and stiffness Progress in Organic Coatings 64(4) 356-360

Azadi P Farnood R Yan N (2010) FEM-DEM Modeling of Thermal Conductivity of Porous Pigmented Coatings Computational Materials Science 49(2) 392-399

Bandyopadhay A Ramarao BV Shih EC (2001) Transient response of a paper sheet subjected to a traveling thermal pulse evolution of temperature moisture and pressure fields Journal of Imaging Science and Technology 45(6) 598-608

Bouguerra A Laurent JP Goual M Queneudec M (1997) The measurement of the thermal conductivity of solid aggregates using the transient plane source technique Journal of Physics D Applied Physics 30 2900-2904

Ranking (Best to Worst)

Print Gloss

Toner Adhesion

Visual Ranking

1 CCHP-10 CCHP-10 CCHP-10 2 CPDG-10 HC90-10 HC90-10 3 HC90-10 HC90-18 HC90-18 4 HC90-18 HC90-25 HC60-10 5 HC60-10 CPDG-10 CPDG-10 6 HC90-25 HC60-10 HC90-25

PAPER PHYSICS

Nordic Pulp and Paper Research Journal Vol 27 no22012 457

Cormier L Zou X (2008) Toner fusion in electrophotographic printing ndash issues from Papricanrsquos perspectives FPInnovations Paprican Division Pointe-Claire QC February 8 2008

CRC Handbook of Chemistry and Physics (2009) 89th ed Taylor amp Francis Group

Di Risio S Yan N (2006) Characterizing Coating Pore Structures of Paper Using Scanning Probe Microscopyrdquo TAPPI Journal 5(3) 9-14

Di Risio S Yan N (2006) Characterizing Coating Layer Z-directional Binder Distribution in Paper Using Atomic Force Microscopy Colloids and Surfaces A Physicochemical and Engineering Aspects 289(1-3) 65-74

Duke CB Noolandi J Thieret T (2002) The surface science of xerography Surface Science 500 1005-1023

Gane PAC Ridgeway CJ Schoelkopf J Bousfield DW (2007) Heat transfer through calcium carbonate-based coating structures observation and model for a thermal fusing process Journal of Pulp and Paper Science 33(2) 60-70

Gerstner P Gane PAC (2009) Considerations for thermally engineered coated printing papers focus on electrophotography Journal of Pulp and Paper Science 35(3-4) 108-117

Gerstner P Paltakari J Gane PAC (2009) Measurement and modeling of heat transfer in paper coating structures Journal of Material Science 44 (2) 483-491

Gerstner P (2010) Heat Transfer Through Porous Multiphase Systems Measurement Modelling and Application in Printing of Coated Papers PhD Thesis Aalto university Helsinki Finland

Kianercy A (2004) Characterizing toner-paper adhesion in xerography Thesis for the Degree of Master of Applied Science University of Toronto Toronto Canada

Liang C (2009) Effect of coating formulations on thermal properties of coating layers Thesis for the Degree of Master of Applied Science University of Toronto Toronto Canada

Maijala J Putkisto K Pietikaumlinen R Groumln J (2004) Heat transfer during fixation of coating layers in dry surface treatment Nordic Pulp and Paper Research Journal 19(3) 291-299

Malla PB Starr RE Werkin TJ (1999) The effects of kaolin particle size structure clay loading and binder level on glossing and offset print properties ndash A CLC coating study 1999 TAPPI Coating Conference Proceedings Toronto Ontario Canada TAPPI Press

Mitsuya T Kumasaka T (1992) Heat transfer and toner melting in an electrophotographic fuser system Journal of Imaging Science and Technology 36 88-92

Morikawa J Hashimoto T (1998) Thermal diffusivity measurement of papers by an AC joule heating method Polymer International 45(2) 207-210

Niskanen K Simula S (1999) Thermal diffusivity of paper Nordic Pulp and Paper Research Journal 14(3) 236-242

Okomori K Lepoutre P (1998) Effect of pigment size and shape distribution on the cohesion of pigmented coatings 1998 TAPPI CoatingPapermakers Conference New Orleans LA USA TAPPI Atlanta GA USA 819 ndash 835

Parker WJ Jenkins RJ Butler CP Abbott GL (1961) Flash method of determining thermal diffusivity heat capacity and thermal conductivity Journal of Applied Physics 32(9) 1679-1684

Salazer A (2003) On thermal diffusivity European Journal of Physics 24(3) 351-358

Sanders DJ Rutland DF (1996) Effect of paper properties on fusing fix Journal of Imaging Science and Technology 40(2) 175-179

Saxaner NS et al (1999) Thermal conductivity of styrene butadiene rubber compounds with natural rubber prophylactics waste as filler European Polymer Journal 35 1687-1693

Simula S Niskanen K (1998) Thermal diffusivity measurement of non-impact printing paper Journal of Imaging Science and Technology 42(6) 550-553

Sipi KM (2001) Toner layer structure and toner adhesion on coated paper NIP17 International Conference on Digital Printing Technologies Fort Lauderdale FL USA 145-150

Stroumlm G Hornatowska J Changhong X Terasaki O (2010) A novel SEM cross-section analysis of paper coating for separation of latex from void volume Nordic Pulp and Paper Research Journal 25(1) 107-113

Vernhes P Blayo A Bloch J-F Pineaux B (2006) Influence of the thermal field on the fusing step in electrophotographic printing Proceedings of the Technical Association of the Graphic Arts 465-485

Vidal D Zou X Uesaka T (2004) Modeling coating structure development Monte-Carlo deposition of particles with irregular shapes Nordic Pulp and Paper Research Journal 19(4) 420ndash427

Wantanabe J Kohara Y Takahashi S (1980) Effects of clay properties on paper coating structure Tappi 63(1) 43 ndash 46

Webb PA (2001) An introduction to the physical characterization of materials by mercury intrusion porosimetry with emphasis on reduction and presentation of experimental data Micromeritics Instrument Corp January 2001 Retrieved on January 14 2009

httpwwwmicromeriticscomapplicationsarticlesaspx

Zhao S Schabel S (2006) Measurement of thermal properties of paper by a light flash method Das Papier T65 34-39

PAPER PHYSICS

458 Nordic Pulp and Paper Research Journal Vol 27 no22012

Page 3: Effects of coating formulation on coating thermal ... · PDF fileEffects of coating formulation on coating thermal properties and coated paper ... KEYWORDS: Paper coating ... “heat

Toner Adhesion Test

Toner adhesion on the coated paper samples was measured

using an IGT AIC2 Printability Tester from IGT Testing

Systems Netherlands The printed coated paper specimens

were cut into strips of 15 cm wide A piece of 3M Scotch

Magic Tape 810D green tape was attached on the printed

surface of each strip and was peeled off by the IGT tester

at a constant angle with a force of 650 N and speeds from

05 to 5 ms After peeling the strips were scanned using an

Epson 4990 scanner and the images were converted to

binary black and white images to quantify the number of

white pixels (representing the quantity of toners removed)

The percentage of white pixels over the total number of

pixels on the scanned image was calculated and used to

compare how well toners adhered on each specimen

Pair-wise Visual Ranking

From the printed coated paper samples 2 areas (11 cm x 7

cm) of the solid black print were cut and mounted

individually on white card papers creating 2 batches of

samples for visual evaluation on their print quality 15

participants 6 males and 9 females with normal or

corrected to normal visions and with minimal to plentiful

visual ranking experience participated in this exercise in a

laboratory under controlled environment with a constant

light source Pair-wise method was used to visually rank the

sample prints within the same batch based on the

participantsrsquo perceptions of good print quality For each

pair of samples the number of the one with better print

quality was entered in a score matrix until all the possible

combinations of samples were compared For each sample

the number of entries on the score matrix was counted and

the sample with most entries (ie best print quality) was

given the highest ranking

Results and discussions

Effects of Coating Compositions on Coating Layer Properties

Porosity and Pore Size

Fig 1 shows that the Hydrocarb 90 (HC90) and Hydrocarb

60 (HC60) coating layers have similar porosity of ca 28

vv at 6 pph of latex and ca 3 vv at 25 pph This is

consistent with the porosity obtained by Azadi in the recent

study on coating layer compression (Azadi et al 2009)

Comparing with the Covercarb HP (CCHP) and Capim DG

(CPDG) coating layers the latter two have higher porosity

under the same latex concentration

Overall with the addition of 25 pph of latex the reduction

in porosity for all GCC coating layers (HC90 HC60 and

CCHP) is around 25 vv but is only 16 vv for clay

(CPDG) as compared to the lowest addition level of 6 pph

of latex These data suggest that as the latex concentration

in a coating layer increases its porosity decreases but the

reduction in porosity depends on the type of pigments with

the pore space between platy particles being more difficult

to fill in On the other hand Fig 2 shows that the median

Fig 1 Effect of Latex Concentration on Porosity

Fig 2 Effect of Latex Concentration on Pore Size

pore diameter of all GCC coating layers decreases only for

latex concentration greater than 10 pph This suggests that

before the latex concentration reaches 10 pph adding latex

only reduces the number of pores in the coating layer when

the latex concentration exceeds 10 pph the additional latex

starts to reduce both the number and the diameter of coating

pores This qualitatively agrees with the SEM image

analysis results given in Stroumlm et al (2010) The pore sizes

of CPDG (kaolin) coating layers remain roughly constant

indicating a different internal pore structure

Fig 1 also shows that at the same latex concentration the

HC90 and HC60 coating layers have the same porosity in

spite of their different median pigment particle sizes This

suggests that the pigment particle size has no significant

effect on the porosity of a coating layer This agrees with

the finding from Di Risio (Di Risio Yan 2006) that for

pigments with size around or below 1 microm the variation in

coating porosity due to change in pigment size is not

significant (as long as PSD width is similar) However

pigment particle size has an influence on the size of pores

formed in a coating layer Fig 2 shows that the median pore

size of HC60 coating layers is approximately twice as large

as that of HC90 corresponding to the size ratio between

HC60 and HC90 pigments This is reasonable since larger

voids will form among the larger pigment particles if the

two types of pigments have the same morphology and PSD

width Both Di Risio (2006) and Watanabe

et al (1980)

reported a similar trend on kaolin coating layers

PAPER PHYSICS

Nordic Pulp and Paper Research Journal Vol 27 no22012 453

Fig 3 Effect of Latex Concentration on Density (Descending skeletal density Ascending apparent density)

The CCHP coating layers have significantly larger

porosity than the HC90 ones due to the narrower (or steeper)

particle size distribution of CCHP The median diameter of

pores in CCHP coating layers is also larger than that of

HC90 These results are in agreement with Di Risio (2006)

Malla et al (1999) and Okomori et al

(1998) As the PSD

width decreases less fine particles are available to fill the

voids among the coarse particles thus increasing the

porosity and median pore size in a coating layer

A comparison on porosity between CPDG and HC90

coating layers shows that the former has a larger porosity

than the latter at the same latex concentration This is in

agreement with the packing simulation findings by

Vidal et

al (2004) which showed that pigment particles with larger

aspect ratio (ie kaolin) create a bulkier coating structure

Apparent Density

Since adding latex reduces the porosity of coating layers

(Fig 1) an increase in apparent density is thus obtained

(See ascending curves in Fig 3) Also as expected we

observe that pigments with a wider particle size distribution

or with a lower aspect ratio produce significantly denser

coating layers

Thermal Diffusivity

Air has a larger thermal diffusivity (ca 20 mm2s)

(Niskanen Simula 1999) than polymers (with a magnitude

of 01 mm2s) (Salazer 2003) it was shown theoretically

that the effective thermal conductivity of the coating layers

increased with the binder content up to the critical pigment

volume concentration (Vidal Zou 2004) However Fig 4

shows that the experimental thermal diffusivity values of

the HC90 HC60 and CPDG coating layers remain roughly

constant when the latex concentration exceeds 10 pph One

explanation as suggested by Salazar (2003) is that air and

latex can be very compatible in terms of diffusing heat to

each other since they might have similar thermal effusivity

a measure of a materialrsquos ability to exchange thermal

energy with its surroundings Therefore even if there are

less air pores in the coating layers when the latex content

increases heat can still diffuse through the coating layers

Fig 4 Effect of Latex Concentration on Thermal Diffusivity

effectively due to the higher amount of latex surrounding

the pigment particles

It can be seen that the thermal diffusivity of the HC90

coating layer is larger than that of HC60 when the latex

concentration is less than 10 pph but when the latex

concentration exceeds 10 pph the two have approximately

the same thermal diffusivity This might be a combined

effect due to the pigment particle size and the thermal

coupling between air and latex As the median particle size

of HC60 is twice as large as that of HC90 at a low latex

concentration it takes a longer distance for heat to

propagate through the HC60 pigment particles which has a

relatively low thermal diffusivity value (ca 2 mm2s)

(Niskanen Simula 1999) Once the latex concentration

exceeds 10 pph the effect due to the thermal coupling

between air and latex might be so strong that the obstacle

on heat propagation due to pigment particle size becomes

insignificant

Fig 4 also shows that the thermal diffusivity of the HC90

coating layer is larger than that of CCHP and CPDG

samples under the same latex concentration up to 25 pph

This can be due to the lower densities (or higher porosity)

of CCHP or CPDG samples affected by the narrower

particle size distribution or higher aspect ratio of pigments

The lower intrinsic thermal diffusivity value of clay (ca

05 mm2s) (Niskanen Simula 1999) than GCC also

contributes to this result

Specific Heat Capacity

Fig 5 shows that as the latex concentration rises the

specific heat capacity Cp of coating layers increases in a

linear fashion (represented by the solid trend lines) This

increase with additional latex can be explained by the

higher intrinsic Cp value of latex (ca 19 Jg˚C) than those

of pigment (ca 08 Jg˚C) and air (ca 10 Jg˚C) The

linearity of the trend lines is supported by the calculation of

Cp for the coating layers using the simplified 1st order

parallel model shown in Eq 2 (assuming the mass of air

pores is negligible)

latexlatexppigmentpigmentpeffp mCmCC

[2]

PAPER PHYSICS

454 Nordic Pulp and Paper Research Journal Vol 27 no22012

Fig 5 Effect of Latex Concentration on Specific Heat Capacity

where m represents the mass fraction of each coating

component and m=1 The calculated results (the dashed

lines) were found to be in close agreement with the trend

lines of the experimental data This confirms with Salazar

(2003) that the effective specific heat capacity Ceff of a

composite always follows the mixture rule

Therefore it is reasonable that the specific heat capacity

values of HC90 and HC60 coating layers at the same latex

concentration are the same as they have same porosity and

density Hence the pigment particle size is not expected to

have a significant effect on the bulk specific heat capacity

The differences in experimental data shown in Fig 5 might

be due to the sensitivity of the DSC instrument

The Cp of CCHP and CPDG coating layers is also very

close to those of HC90 ones Since the mass fraction of air

is negligible the effects of pigment particle size distribution

or morphology on the specific heat capacity are

insignificant as expected

Bulk (Effective) Thermal Conductivity

Fig 6 shows that as the latex concentration increases up to

25 pph the bulk thermal conductivity of all coating layers

increases As explained earlier adding latex in a coating

layer results in two effects on a coating structure (1)

increasing the volume fraction of latex and thus reducing

the volume fraction of air and (2) breaking the air pores

down to smaller sizes Both latex and air have much lower

intrinsic thermal conductivity values (ca 020 WmK

(Saxaner et al 1999) and 0026 WmK (CRC 2009)

respectively) than pigments (2ndash5 WmK) (Bouguerra

1997) but the reduction in the pore volume (ie porosity) is

more significant than the increase in the latex volume In

addition having smaller pores in the coating layer means

that the pigment particles have a higher chance to be

connected creating a better channel for heat transfer

Changing the median pigment particle size between

HC90 and HC60 coating layers does not result in a change

in the apparent density specific heat capacity or thermal

diffusivity (when the latex concentration exceeds 10 pph)

of the coating layers formed Therefore the bulk thermal

Fig 6 Effect of Latex Concentration on Thermal Conductivity

conductivity of the two groups of coating layers are the

same meaning that pigment particle size alone does not

have a significant effect

Between HC90 and CCHP coating layers using pigments

with a wider particle size distribution (HC90) results in an

increased apparent density an unchanged specific heat

capacity and a higher thermal diffusivity value for the

coating layers formed Therefore the bulk thermal

conductivity of HC90 samples is higher than that of CCHP

Lastly a CPDG coating layer has lower apparent density

and thermal diffusivity but higher specific heat capacity

than a HC90 coating layer at the same latex concentration

The intrinsic thermal properties of clay (CPDG) contribute

greatly to these results However the higher aspect ratio of

the CPDG pigment does contribute to a bulkier coating

structure and therefore affects the thermal diffusivity of

the structure The combined effect is a bulk thermal

conductivity of the CPDG coating layers lower than that of

HC90

Modelling Thermal Conductivity by Geometric Mean

The theoretical bulk thermal conductivity of each coating

layer sample was modeled by calculating the geometric

mean of the K values of pigment latex and air based on

their volume fraction v as Eq 3

airlatexpigment v

air

v

latex

v

pigmenteff KKKK [3]

where Kpigment = 26 WmK for GCC or 16 WmK for

kaolin

Klatex = 020 WmK

Kair = 0026 WmK

vpigment and vlatex are derived from the porosity (vair)

and the pigment to latex mass ratio with their

individual density given 1v

Fig 7 shows that the geometric mean model provides very

good fittings of the experimental data points for the

different pigments and latex concentrations studied This

shows that the bulk thermal conductivity of the coatings

can be well predicted by the geometric mean model

Furthermore it shows that the thermal conductivity only

PAPER PHYSICS

Nordic Pulp and Paper Research Journal Vol 27 no22012 455

Fig 7 Modelling Thermal Conductivity by the Geometric Mean Model

depends on the intrinsic thermal conductivities of the

coating constituents and their respectively volume fractions

(the latter being affected by the PSD and the shape of the

pigment used) In fact this model constitutes a much

simpler model than the Lumped Parameter model proposed

recently by Gerstner (2010) while resembling the empirical

model suggested by Azadi et al (2010)

Print Quality Test Results

Print Gloss

Fig 8 shows that the average print gloss of the model

coated paper was significantly reduced as the bulk thermal

conductivity of the corresponding type of coating layer

increases This suggests that the bulk thermal conductivity

of the coating layers affect the fusing process of toner

which includes toner coalescence melting and spreading

similar to what is concluded by Azadi et al (2008) One

possible explanation is that when the coating bulk thermal

conductivity is lower the coating plays the role of a heat

barrier (dissipating less heat to the base paper) This helps

the toner layer to reach uniformly its melting temperature

and allows the toner layer to level off evenly As a result a

ldquomirror-likerdquo surface is thus created and a high print gloss

is obtained

Interestingly thermal diffusivity of the coating layer gave

a weaker correlation to print gloss with R2 around 052 It

might be due to the fact that thermal diffusivity deals

mostly with the heat flow in the coating layer itself while

print gloss is mostly determined by the heat flow at the

tonercoating interface which thermal conductivity might

be more important However this remains to be confirmed

by further studies

Toner Adhesion

The results of the toner adhesion test show that the amount

of toner removed is affected by the peeling speed of the

Scotch tape Therefore the minimum percentages of toner

remained (adhered) on the coated paper samples at all

peeling speeds were taken for the study These data are

listed in Table 2 and plotted in Fig 9 It shows no

correlation between the percentage of toners remained on

Fig 8 Effect of Bulk Thermal Conductivity of the Coating Layers on Average Print Gloss (in ) of the Coated Papers

Fig 9 Effect of Bulk Thermal Conductivity of the Coating Layers on Toner Adhesion on the Coated Papers

Table 2 Minimum Toner Adhesion on Coated Papers

the coated paper and the bulk thermal conductivity of the

corresponding type of coating layer A similar comparison

was done by Gerstner et al

(2009) and no definite

correlation was found either As explained by Kianercy

(2004) and Sipi (2001) only three factors have been found

to have significant impacts on toner adhesion which are

surface tension of paper toner viscosity at the tonerpaper

interface and fusing speed

Pair-wise Visual Ranking

The result of the visual ranking test shows that for coating

layers with 10 pph of latex the CCHP-10 coating provides

the best print quality and the CPDG-10 coating provides

the worst print quality Among the HC90 coating layers

with different latex concentrations the HC90-10 and

Sample Minimum Toner Remained ()

HC90-10 987 HC90-18 946 HC90-25 872 HC60-10 218 CCHP-10 999 CPDG-10 811

PAPER PHYSICS

456 Nordic Pulp and Paper Research Journal Vol 27 no22012

Fig 10 Effect of Bulk Thermal Conductivity of the Coating Layers on Average Ranking Score of the Printed Coated Papers

Table 3 Summary of the Print Quality Test Results

HC90-18 coating provide significantly better print quality

than the one made with 25 pph of latex However no

correlation was found between print quality (quantified by

the average ranking score) of a sample with the bulk

thermal conductivity of the coating layers see Fig 10

These findings suggest that there are other factors which

have a more significant effect on the print quality of coated

paper However this is beyond the scope of this study

A summary of the print quality test results (Table 3)

reveals that the coating layer formulated with Covercarb

HP pigment and 10 pph of latex has the best ranking in all

three tests Therefore with its relatively low thermal

conductivity this coating formulation is the best candidate

among the ones studied for use in xerography printing

Conclusions The effects of coating formulations on thermal

characteristics of the coating layers were systematically

studied for assessing their impact on xerographic toner

fusion onto the coated papers It was shown that porosity is

a key parameter in the design of a coating layer for heat

transfer applications The latex concentration in the coating

formulation plays a significant role as it determines the

overall porosity of the coating layers Therefore in order

for the coating layer to act as a heat barrier (and provide

sufficient uniform heat transfer to the toner layer) it needs

to have an acceptably high porosity or a low latex

concentration The particle size distribution (narrow PSD)

and morphology (high shape factor) of pigments also affect

positively the porosity and thus the overall thermal

characteristics of the coating layers However the median

particle size of pigments did not show any significant

effect It was also found that the bulk thermal conductivity

of the coating layers can be accurately predicted by a

simple geometric mean model based on the pigment latex

and air volume contents

A 75˚ TAPPI print gloss measurement a toner adhesion

test using an IGT printability tester and a pair-wise visual

ranking test were performed on paper samples coated with

model coating colours and printed with 100 solid black

by xerography The print gloss of coated papers was

significantly improved when the coating bulk thermal

conductivity was low This is attributed to the insulating

effect of the coating thus providing a more uniform toner

fusion No other correlation was found between the print

quality and thermal properties of the samples

Lastly it was found that the coating made of Covercarb

HP a narrow PSD pigment and 10 pph of latex gave a

relatively low thermal conductivity and the best ranking in

all three print quality tests Therefore among all the

formulations tested this coating is the best candidate for

coated paper applications in xerography

Acknowledgements The financial and technical supports from NSERC IPS Scholarship FPInnovations Xerox Research Center of Canada and Surface Science Consortium at the Pulp and Paper Centre University of Toronto are gratefully acknowledged

Literature

Azadi P (2007) Modeling of mechanical and thermal responses of paper coatings under compression using discrete element method Thesis for the Degree of Master of Applied Science University of Toronto Toronto Canada

Azadi P Yan N Farnood R (2008) Discrete Element Modeling of the Transient Heat Transfer and Toner Fusing Process in the Xerographic Printing of Coated Papers Computers amp Chemical Engineering 32(12) 3238-3245

Azadi P Nunnari S Farnood R Kortschot M Yan N (2009) High speed compression of highly filled thin composites effect of binder content and stiffness Progress in Organic Coatings 64(4) 356-360

Azadi P Farnood R Yan N (2010) FEM-DEM Modeling of Thermal Conductivity of Porous Pigmented Coatings Computational Materials Science 49(2) 392-399

Bandyopadhay A Ramarao BV Shih EC (2001) Transient response of a paper sheet subjected to a traveling thermal pulse evolution of temperature moisture and pressure fields Journal of Imaging Science and Technology 45(6) 598-608

Bouguerra A Laurent JP Goual M Queneudec M (1997) The measurement of the thermal conductivity of solid aggregates using the transient plane source technique Journal of Physics D Applied Physics 30 2900-2904

Ranking (Best to Worst)

Print Gloss

Toner Adhesion

Visual Ranking

1 CCHP-10 CCHP-10 CCHP-10 2 CPDG-10 HC90-10 HC90-10 3 HC90-10 HC90-18 HC90-18 4 HC90-18 HC90-25 HC60-10 5 HC60-10 CPDG-10 CPDG-10 6 HC90-25 HC60-10 HC90-25

PAPER PHYSICS

Nordic Pulp and Paper Research Journal Vol 27 no22012 457

Cormier L Zou X (2008) Toner fusion in electrophotographic printing ndash issues from Papricanrsquos perspectives FPInnovations Paprican Division Pointe-Claire QC February 8 2008

CRC Handbook of Chemistry and Physics (2009) 89th ed Taylor amp Francis Group

Di Risio S Yan N (2006) Characterizing Coating Pore Structures of Paper Using Scanning Probe Microscopyrdquo TAPPI Journal 5(3) 9-14

Di Risio S Yan N (2006) Characterizing Coating Layer Z-directional Binder Distribution in Paper Using Atomic Force Microscopy Colloids and Surfaces A Physicochemical and Engineering Aspects 289(1-3) 65-74

Duke CB Noolandi J Thieret T (2002) The surface science of xerography Surface Science 500 1005-1023

Gane PAC Ridgeway CJ Schoelkopf J Bousfield DW (2007) Heat transfer through calcium carbonate-based coating structures observation and model for a thermal fusing process Journal of Pulp and Paper Science 33(2) 60-70

Gerstner P Gane PAC (2009) Considerations for thermally engineered coated printing papers focus on electrophotography Journal of Pulp and Paper Science 35(3-4) 108-117

Gerstner P Paltakari J Gane PAC (2009) Measurement and modeling of heat transfer in paper coating structures Journal of Material Science 44 (2) 483-491

Gerstner P (2010) Heat Transfer Through Porous Multiphase Systems Measurement Modelling and Application in Printing of Coated Papers PhD Thesis Aalto university Helsinki Finland

Kianercy A (2004) Characterizing toner-paper adhesion in xerography Thesis for the Degree of Master of Applied Science University of Toronto Toronto Canada

Liang C (2009) Effect of coating formulations on thermal properties of coating layers Thesis for the Degree of Master of Applied Science University of Toronto Toronto Canada

Maijala J Putkisto K Pietikaumlinen R Groumln J (2004) Heat transfer during fixation of coating layers in dry surface treatment Nordic Pulp and Paper Research Journal 19(3) 291-299

Malla PB Starr RE Werkin TJ (1999) The effects of kaolin particle size structure clay loading and binder level on glossing and offset print properties ndash A CLC coating study 1999 TAPPI Coating Conference Proceedings Toronto Ontario Canada TAPPI Press

Mitsuya T Kumasaka T (1992) Heat transfer and toner melting in an electrophotographic fuser system Journal of Imaging Science and Technology 36 88-92

Morikawa J Hashimoto T (1998) Thermal diffusivity measurement of papers by an AC joule heating method Polymer International 45(2) 207-210

Niskanen K Simula S (1999) Thermal diffusivity of paper Nordic Pulp and Paper Research Journal 14(3) 236-242

Okomori K Lepoutre P (1998) Effect of pigment size and shape distribution on the cohesion of pigmented coatings 1998 TAPPI CoatingPapermakers Conference New Orleans LA USA TAPPI Atlanta GA USA 819 ndash 835

Parker WJ Jenkins RJ Butler CP Abbott GL (1961) Flash method of determining thermal diffusivity heat capacity and thermal conductivity Journal of Applied Physics 32(9) 1679-1684

Salazer A (2003) On thermal diffusivity European Journal of Physics 24(3) 351-358

Sanders DJ Rutland DF (1996) Effect of paper properties on fusing fix Journal of Imaging Science and Technology 40(2) 175-179

Saxaner NS et al (1999) Thermal conductivity of styrene butadiene rubber compounds with natural rubber prophylactics waste as filler European Polymer Journal 35 1687-1693

Simula S Niskanen K (1998) Thermal diffusivity measurement of non-impact printing paper Journal of Imaging Science and Technology 42(6) 550-553

Sipi KM (2001) Toner layer structure and toner adhesion on coated paper NIP17 International Conference on Digital Printing Technologies Fort Lauderdale FL USA 145-150

Stroumlm G Hornatowska J Changhong X Terasaki O (2010) A novel SEM cross-section analysis of paper coating for separation of latex from void volume Nordic Pulp and Paper Research Journal 25(1) 107-113

Vernhes P Blayo A Bloch J-F Pineaux B (2006) Influence of the thermal field on the fusing step in electrophotographic printing Proceedings of the Technical Association of the Graphic Arts 465-485

Vidal D Zou X Uesaka T (2004) Modeling coating structure development Monte-Carlo deposition of particles with irregular shapes Nordic Pulp and Paper Research Journal 19(4) 420ndash427

Wantanabe J Kohara Y Takahashi S (1980) Effects of clay properties on paper coating structure Tappi 63(1) 43 ndash 46

Webb PA (2001) An introduction to the physical characterization of materials by mercury intrusion porosimetry with emphasis on reduction and presentation of experimental data Micromeritics Instrument Corp January 2001 Retrieved on January 14 2009

httpwwwmicromeriticscomapplicationsarticlesaspx

Zhao S Schabel S (2006) Measurement of thermal properties of paper by a light flash method Das Papier T65 34-39

PAPER PHYSICS

458 Nordic Pulp and Paper Research Journal Vol 27 no22012

Page 4: Effects of coating formulation on coating thermal ... · PDF fileEffects of coating formulation on coating thermal properties and coated paper ... KEYWORDS: Paper coating ... “heat

Fig 3 Effect of Latex Concentration on Density (Descending skeletal density Ascending apparent density)

The CCHP coating layers have significantly larger

porosity than the HC90 ones due to the narrower (or steeper)

particle size distribution of CCHP The median diameter of

pores in CCHP coating layers is also larger than that of

HC90 These results are in agreement with Di Risio (2006)

Malla et al (1999) and Okomori et al

(1998) As the PSD

width decreases less fine particles are available to fill the

voids among the coarse particles thus increasing the

porosity and median pore size in a coating layer

A comparison on porosity between CPDG and HC90

coating layers shows that the former has a larger porosity

than the latter at the same latex concentration This is in

agreement with the packing simulation findings by

Vidal et

al (2004) which showed that pigment particles with larger

aspect ratio (ie kaolin) create a bulkier coating structure

Apparent Density

Since adding latex reduces the porosity of coating layers

(Fig 1) an increase in apparent density is thus obtained

(See ascending curves in Fig 3) Also as expected we

observe that pigments with a wider particle size distribution

or with a lower aspect ratio produce significantly denser

coating layers

Thermal Diffusivity

Air has a larger thermal diffusivity (ca 20 mm2s)

(Niskanen Simula 1999) than polymers (with a magnitude

of 01 mm2s) (Salazer 2003) it was shown theoretically

that the effective thermal conductivity of the coating layers

increased with the binder content up to the critical pigment

volume concentration (Vidal Zou 2004) However Fig 4

shows that the experimental thermal diffusivity values of

the HC90 HC60 and CPDG coating layers remain roughly

constant when the latex concentration exceeds 10 pph One

explanation as suggested by Salazar (2003) is that air and

latex can be very compatible in terms of diffusing heat to

each other since they might have similar thermal effusivity

a measure of a materialrsquos ability to exchange thermal

energy with its surroundings Therefore even if there are

less air pores in the coating layers when the latex content

increases heat can still diffuse through the coating layers

Fig 4 Effect of Latex Concentration on Thermal Diffusivity

effectively due to the higher amount of latex surrounding

the pigment particles

It can be seen that the thermal diffusivity of the HC90

coating layer is larger than that of HC60 when the latex

concentration is less than 10 pph but when the latex

concentration exceeds 10 pph the two have approximately

the same thermal diffusivity This might be a combined

effect due to the pigment particle size and the thermal

coupling between air and latex As the median particle size

of HC60 is twice as large as that of HC90 at a low latex

concentration it takes a longer distance for heat to

propagate through the HC60 pigment particles which has a

relatively low thermal diffusivity value (ca 2 mm2s)

(Niskanen Simula 1999) Once the latex concentration

exceeds 10 pph the effect due to the thermal coupling

between air and latex might be so strong that the obstacle

on heat propagation due to pigment particle size becomes

insignificant

Fig 4 also shows that the thermal diffusivity of the HC90

coating layer is larger than that of CCHP and CPDG

samples under the same latex concentration up to 25 pph

This can be due to the lower densities (or higher porosity)

of CCHP or CPDG samples affected by the narrower

particle size distribution or higher aspect ratio of pigments

The lower intrinsic thermal diffusivity value of clay (ca

05 mm2s) (Niskanen Simula 1999) than GCC also

contributes to this result

Specific Heat Capacity

Fig 5 shows that as the latex concentration rises the

specific heat capacity Cp of coating layers increases in a

linear fashion (represented by the solid trend lines) This

increase with additional latex can be explained by the

higher intrinsic Cp value of latex (ca 19 Jg˚C) than those

of pigment (ca 08 Jg˚C) and air (ca 10 Jg˚C) The

linearity of the trend lines is supported by the calculation of

Cp for the coating layers using the simplified 1st order

parallel model shown in Eq 2 (assuming the mass of air

pores is negligible)

latexlatexppigmentpigmentpeffp mCmCC

[2]

PAPER PHYSICS

454 Nordic Pulp and Paper Research Journal Vol 27 no22012

Fig 5 Effect of Latex Concentration on Specific Heat Capacity

where m represents the mass fraction of each coating

component and m=1 The calculated results (the dashed

lines) were found to be in close agreement with the trend

lines of the experimental data This confirms with Salazar

(2003) that the effective specific heat capacity Ceff of a

composite always follows the mixture rule

Therefore it is reasonable that the specific heat capacity

values of HC90 and HC60 coating layers at the same latex

concentration are the same as they have same porosity and

density Hence the pigment particle size is not expected to

have a significant effect on the bulk specific heat capacity

The differences in experimental data shown in Fig 5 might

be due to the sensitivity of the DSC instrument

The Cp of CCHP and CPDG coating layers is also very

close to those of HC90 ones Since the mass fraction of air

is negligible the effects of pigment particle size distribution

or morphology on the specific heat capacity are

insignificant as expected

Bulk (Effective) Thermal Conductivity

Fig 6 shows that as the latex concentration increases up to

25 pph the bulk thermal conductivity of all coating layers

increases As explained earlier adding latex in a coating

layer results in two effects on a coating structure (1)

increasing the volume fraction of latex and thus reducing

the volume fraction of air and (2) breaking the air pores

down to smaller sizes Both latex and air have much lower

intrinsic thermal conductivity values (ca 020 WmK

(Saxaner et al 1999) and 0026 WmK (CRC 2009)

respectively) than pigments (2ndash5 WmK) (Bouguerra

1997) but the reduction in the pore volume (ie porosity) is

more significant than the increase in the latex volume In

addition having smaller pores in the coating layer means

that the pigment particles have a higher chance to be

connected creating a better channel for heat transfer

Changing the median pigment particle size between

HC90 and HC60 coating layers does not result in a change

in the apparent density specific heat capacity or thermal

diffusivity (when the latex concentration exceeds 10 pph)

of the coating layers formed Therefore the bulk thermal

Fig 6 Effect of Latex Concentration on Thermal Conductivity

conductivity of the two groups of coating layers are the

same meaning that pigment particle size alone does not

have a significant effect

Between HC90 and CCHP coating layers using pigments

with a wider particle size distribution (HC90) results in an

increased apparent density an unchanged specific heat

capacity and a higher thermal diffusivity value for the

coating layers formed Therefore the bulk thermal

conductivity of HC90 samples is higher than that of CCHP

Lastly a CPDG coating layer has lower apparent density

and thermal diffusivity but higher specific heat capacity

than a HC90 coating layer at the same latex concentration

The intrinsic thermal properties of clay (CPDG) contribute

greatly to these results However the higher aspect ratio of

the CPDG pigment does contribute to a bulkier coating

structure and therefore affects the thermal diffusivity of

the structure The combined effect is a bulk thermal

conductivity of the CPDG coating layers lower than that of

HC90

Modelling Thermal Conductivity by Geometric Mean

The theoretical bulk thermal conductivity of each coating

layer sample was modeled by calculating the geometric

mean of the K values of pigment latex and air based on

their volume fraction v as Eq 3

airlatexpigment v

air

v

latex

v

pigmenteff KKKK [3]

where Kpigment = 26 WmK for GCC or 16 WmK for

kaolin

Klatex = 020 WmK

Kair = 0026 WmK

vpigment and vlatex are derived from the porosity (vair)

and the pigment to latex mass ratio with their

individual density given 1v

Fig 7 shows that the geometric mean model provides very

good fittings of the experimental data points for the

different pigments and latex concentrations studied This

shows that the bulk thermal conductivity of the coatings

can be well predicted by the geometric mean model

Furthermore it shows that the thermal conductivity only

PAPER PHYSICS

Nordic Pulp and Paper Research Journal Vol 27 no22012 455

Fig 7 Modelling Thermal Conductivity by the Geometric Mean Model

depends on the intrinsic thermal conductivities of the

coating constituents and their respectively volume fractions

(the latter being affected by the PSD and the shape of the

pigment used) In fact this model constitutes a much

simpler model than the Lumped Parameter model proposed

recently by Gerstner (2010) while resembling the empirical

model suggested by Azadi et al (2010)

Print Quality Test Results

Print Gloss

Fig 8 shows that the average print gloss of the model

coated paper was significantly reduced as the bulk thermal

conductivity of the corresponding type of coating layer

increases This suggests that the bulk thermal conductivity

of the coating layers affect the fusing process of toner

which includes toner coalescence melting and spreading

similar to what is concluded by Azadi et al (2008) One

possible explanation is that when the coating bulk thermal

conductivity is lower the coating plays the role of a heat

barrier (dissipating less heat to the base paper) This helps

the toner layer to reach uniformly its melting temperature

and allows the toner layer to level off evenly As a result a

ldquomirror-likerdquo surface is thus created and a high print gloss

is obtained

Interestingly thermal diffusivity of the coating layer gave

a weaker correlation to print gloss with R2 around 052 It

might be due to the fact that thermal diffusivity deals

mostly with the heat flow in the coating layer itself while

print gloss is mostly determined by the heat flow at the

tonercoating interface which thermal conductivity might

be more important However this remains to be confirmed

by further studies

Toner Adhesion

The results of the toner adhesion test show that the amount

of toner removed is affected by the peeling speed of the

Scotch tape Therefore the minimum percentages of toner

remained (adhered) on the coated paper samples at all

peeling speeds were taken for the study These data are

listed in Table 2 and plotted in Fig 9 It shows no

correlation between the percentage of toners remained on

Fig 8 Effect of Bulk Thermal Conductivity of the Coating Layers on Average Print Gloss (in ) of the Coated Papers

Fig 9 Effect of Bulk Thermal Conductivity of the Coating Layers on Toner Adhesion on the Coated Papers

Table 2 Minimum Toner Adhesion on Coated Papers

the coated paper and the bulk thermal conductivity of the

corresponding type of coating layer A similar comparison

was done by Gerstner et al

(2009) and no definite

correlation was found either As explained by Kianercy

(2004) and Sipi (2001) only three factors have been found

to have significant impacts on toner adhesion which are

surface tension of paper toner viscosity at the tonerpaper

interface and fusing speed

Pair-wise Visual Ranking

The result of the visual ranking test shows that for coating

layers with 10 pph of latex the CCHP-10 coating provides

the best print quality and the CPDG-10 coating provides

the worst print quality Among the HC90 coating layers

with different latex concentrations the HC90-10 and

Sample Minimum Toner Remained ()

HC90-10 987 HC90-18 946 HC90-25 872 HC60-10 218 CCHP-10 999 CPDG-10 811

PAPER PHYSICS

456 Nordic Pulp and Paper Research Journal Vol 27 no22012

Fig 10 Effect of Bulk Thermal Conductivity of the Coating Layers on Average Ranking Score of the Printed Coated Papers

Table 3 Summary of the Print Quality Test Results

HC90-18 coating provide significantly better print quality

than the one made with 25 pph of latex However no

correlation was found between print quality (quantified by

the average ranking score) of a sample with the bulk

thermal conductivity of the coating layers see Fig 10

These findings suggest that there are other factors which

have a more significant effect on the print quality of coated

paper However this is beyond the scope of this study

A summary of the print quality test results (Table 3)

reveals that the coating layer formulated with Covercarb

HP pigment and 10 pph of latex has the best ranking in all

three tests Therefore with its relatively low thermal

conductivity this coating formulation is the best candidate

among the ones studied for use in xerography printing

Conclusions The effects of coating formulations on thermal

characteristics of the coating layers were systematically

studied for assessing their impact on xerographic toner

fusion onto the coated papers It was shown that porosity is

a key parameter in the design of a coating layer for heat

transfer applications The latex concentration in the coating

formulation plays a significant role as it determines the

overall porosity of the coating layers Therefore in order

for the coating layer to act as a heat barrier (and provide

sufficient uniform heat transfer to the toner layer) it needs

to have an acceptably high porosity or a low latex

concentration The particle size distribution (narrow PSD)

and morphology (high shape factor) of pigments also affect

positively the porosity and thus the overall thermal

characteristics of the coating layers However the median

particle size of pigments did not show any significant

effect It was also found that the bulk thermal conductivity

of the coating layers can be accurately predicted by a

simple geometric mean model based on the pigment latex

and air volume contents

A 75˚ TAPPI print gloss measurement a toner adhesion

test using an IGT printability tester and a pair-wise visual

ranking test were performed on paper samples coated with

model coating colours and printed with 100 solid black

by xerography The print gloss of coated papers was

significantly improved when the coating bulk thermal

conductivity was low This is attributed to the insulating

effect of the coating thus providing a more uniform toner

fusion No other correlation was found between the print

quality and thermal properties of the samples

Lastly it was found that the coating made of Covercarb

HP a narrow PSD pigment and 10 pph of latex gave a

relatively low thermal conductivity and the best ranking in

all three print quality tests Therefore among all the

formulations tested this coating is the best candidate for

coated paper applications in xerography

Acknowledgements The financial and technical supports from NSERC IPS Scholarship FPInnovations Xerox Research Center of Canada and Surface Science Consortium at the Pulp and Paper Centre University of Toronto are gratefully acknowledged

Literature

Azadi P (2007) Modeling of mechanical and thermal responses of paper coatings under compression using discrete element method Thesis for the Degree of Master of Applied Science University of Toronto Toronto Canada

Azadi P Yan N Farnood R (2008) Discrete Element Modeling of the Transient Heat Transfer and Toner Fusing Process in the Xerographic Printing of Coated Papers Computers amp Chemical Engineering 32(12) 3238-3245

Azadi P Nunnari S Farnood R Kortschot M Yan N (2009) High speed compression of highly filled thin composites effect of binder content and stiffness Progress in Organic Coatings 64(4) 356-360

Azadi P Farnood R Yan N (2010) FEM-DEM Modeling of Thermal Conductivity of Porous Pigmented Coatings Computational Materials Science 49(2) 392-399

Bandyopadhay A Ramarao BV Shih EC (2001) Transient response of a paper sheet subjected to a traveling thermal pulse evolution of temperature moisture and pressure fields Journal of Imaging Science and Technology 45(6) 598-608

Bouguerra A Laurent JP Goual M Queneudec M (1997) The measurement of the thermal conductivity of solid aggregates using the transient plane source technique Journal of Physics D Applied Physics 30 2900-2904

Ranking (Best to Worst)

Print Gloss

Toner Adhesion

Visual Ranking

1 CCHP-10 CCHP-10 CCHP-10 2 CPDG-10 HC90-10 HC90-10 3 HC90-10 HC90-18 HC90-18 4 HC90-18 HC90-25 HC60-10 5 HC60-10 CPDG-10 CPDG-10 6 HC90-25 HC60-10 HC90-25

PAPER PHYSICS

Nordic Pulp and Paper Research Journal Vol 27 no22012 457

Cormier L Zou X (2008) Toner fusion in electrophotographic printing ndash issues from Papricanrsquos perspectives FPInnovations Paprican Division Pointe-Claire QC February 8 2008

CRC Handbook of Chemistry and Physics (2009) 89th ed Taylor amp Francis Group

Di Risio S Yan N (2006) Characterizing Coating Pore Structures of Paper Using Scanning Probe Microscopyrdquo TAPPI Journal 5(3) 9-14

Di Risio S Yan N (2006) Characterizing Coating Layer Z-directional Binder Distribution in Paper Using Atomic Force Microscopy Colloids and Surfaces A Physicochemical and Engineering Aspects 289(1-3) 65-74

Duke CB Noolandi J Thieret T (2002) The surface science of xerography Surface Science 500 1005-1023

Gane PAC Ridgeway CJ Schoelkopf J Bousfield DW (2007) Heat transfer through calcium carbonate-based coating structures observation and model for a thermal fusing process Journal of Pulp and Paper Science 33(2) 60-70

Gerstner P Gane PAC (2009) Considerations for thermally engineered coated printing papers focus on electrophotography Journal of Pulp and Paper Science 35(3-4) 108-117

Gerstner P Paltakari J Gane PAC (2009) Measurement and modeling of heat transfer in paper coating structures Journal of Material Science 44 (2) 483-491

Gerstner P (2010) Heat Transfer Through Porous Multiphase Systems Measurement Modelling and Application in Printing of Coated Papers PhD Thesis Aalto university Helsinki Finland

Kianercy A (2004) Characterizing toner-paper adhesion in xerography Thesis for the Degree of Master of Applied Science University of Toronto Toronto Canada

Liang C (2009) Effect of coating formulations on thermal properties of coating layers Thesis for the Degree of Master of Applied Science University of Toronto Toronto Canada

Maijala J Putkisto K Pietikaumlinen R Groumln J (2004) Heat transfer during fixation of coating layers in dry surface treatment Nordic Pulp and Paper Research Journal 19(3) 291-299

Malla PB Starr RE Werkin TJ (1999) The effects of kaolin particle size structure clay loading and binder level on glossing and offset print properties ndash A CLC coating study 1999 TAPPI Coating Conference Proceedings Toronto Ontario Canada TAPPI Press

Mitsuya T Kumasaka T (1992) Heat transfer and toner melting in an electrophotographic fuser system Journal of Imaging Science and Technology 36 88-92

Morikawa J Hashimoto T (1998) Thermal diffusivity measurement of papers by an AC joule heating method Polymer International 45(2) 207-210

Niskanen K Simula S (1999) Thermal diffusivity of paper Nordic Pulp and Paper Research Journal 14(3) 236-242

Okomori K Lepoutre P (1998) Effect of pigment size and shape distribution on the cohesion of pigmented coatings 1998 TAPPI CoatingPapermakers Conference New Orleans LA USA TAPPI Atlanta GA USA 819 ndash 835

Parker WJ Jenkins RJ Butler CP Abbott GL (1961) Flash method of determining thermal diffusivity heat capacity and thermal conductivity Journal of Applied Physics 32(9) 1679-1684

Salazer A (2003) On thermal diffusivity European Journal of Physics 24(3) 351-358

Sanders DJ Rutland DF (1996) Effect of paper properties on fusing fix Journal of Imaging Science and Technology 40(2) 175-179

Saxaner NS et al (1999) Thermal conductivity of styrene butadiene rubber compounds with natural rubber prophylactics waste as filler European Polymer Journal 35 1687-1693

Simula S Niskanen K (1998) Thermal diffusivity measurement of non-impact printing paper Journal of Imaging Science and Technology 42(6) 550-553

Sipi KM (2001) Toner layer structure and toner adhesion on coated paper NIP17 International Conference on Digital Printing Technologies Fort Lauderdale FL USA 145-150

Stroumlm G Hornatowska J Changhong X Terasaki O (2010) A novel SEM cross-section analysis of paper coating for separation of latex from void volume Nordic Pulp and Paper Research Journal 25(1) 107-113

Vernhes P Blayo A Bloch J-F Pineaux B (2006) Influence of the thermal field on the fusing step in electrophotographic printing Proceedings of the Technical Association of the Graphic Arts 465-485

Vidal D Zou X Uesaka T (2004) Modeling coating structure development Monte-Carlo deposition of particles with irregular shapes Nordic Pulp and Paper Research Journal 19(4) 420ndash427

Wantanabe J Kohara Y Takahashi S (1980) Effects of clay properties on paper coating structure Tappi 63(1) 43 ndash 46

Webb PA (2001) An introduction to the physical characterization of materials by mercury intrusion porosimetry with emphasis on reduction and presentation of experimental data Micromeritics Instrument Corp January 2001 Retrieved on January 14 2009

httpwwwmicromeriticscomapplicationsarticlesaspx

Zhao S Schabel S (2006) Measurement of thermal properties of paper by a light flash method Das Papier T65 34-39

PAPER PHYSICS

458 Nordic Pulp and Paper Research Journal Vol 27 no22012

Page 5: Effects of coating formulation on coating thermal ... · PDF fileEffects of coating formulation on coating thermal properties and coated paper ... KEYWORDS: Paper coating ... “heat

Fig 5 Effect of Latex Concentration on Specific Heat Capacity

where m represents the mass fraction of each coating

component and m=1 The calculated results (the dashed

lines) were found to be in close agreement with the trend

lines of the experimental data This confirms with Salazar

(2003) that the effective specific heat capacity Ceff of a

composite always follows the mixture rule

Therefore it is reasonable that the specific heat capacity

values of HC90 and HC60 coating layers at the same latex

concentration are the same as they have same porosity and

density Hence the pigment particle size is not expected to

have a significant effect on the bulk specific heat capacity

The differences in experimental data shown in Fig 5 might

be due to the sensitivity of the DSC instrument

The Cp of CCHP and CPDG coating layers is also very

close to those of HC90 ones Since the mass fraction of air

is negligible the effects of pigment particle size distribution

or morphology on the specific heat capacity are

insignificant as expected

Bulk (Effective) Thermal Conductivity

Fig 6 shows that as the latex concentration increases up to

25 pph the bulk thermal conductivity of all coating layers

increases As explained earlier adding latex in a coating

layer results in two effects on a coating structure (1)

increasing the volume fraction of latex and thus reducing

the volume fraction of air and (2) breaking the air pores

down to smaller sizes Both latex and air have much lower

intrinsic thermal conductivity values (ca 020 WmK

(Saxaner et al 1999) and 0026 WmK (CRC 2009)

respectively) than pigments (2ndash5 WmK) (Bouguerra

1997) but the reduction in the pore volume (ie porosity) is

more significant than the increase in the latex volume In

addition having smaller pores in the coating layer means

that the pigment particles have a higher chance to be

connected creating a better channel for heat transfer

Changing the median pigment particle size between

HC90 and HC60 coating layers does not result in a change

in the apparent density specific heat capacity or thermal

diffusivity (when the latex concentration exceeds 10 pph)

of the coating layers formed Therefore the bulk thermal

Fig 6 Effect of Latex Concentration on Thermal Conductivity

conductivity of the two groups of coating layers are the

same meaning that pigment particle size alone does not

have a significant effect

Between HC90 and CCHP coating layers using pigments

with a wider particle size distribution (HC90) results in an

increased apparent density an unchanged specific heat

capacity and a higher thermal diffusivity value for the

coating layers formed Therefore the bulk thermal

conductivity of HC90 samples is higher than that of CCHP

Lastly a CPDG coating layer has lower apparent density

and thermal diffusivity but higher specific heat capacity

than a HC90 coating layer at the same latex concentration

The intrinsic thermal properties of clay (CPDG) contribute

greatly to these results However the higher aspect ratio of

the CPDG pigment does contribute to a bulkier coating

structure and therefore affects the thermal diffusivity of

the structure The combined effect is a bulk thermal

conductivity of the CPDG coating layers lower than that of

HC90

Modelling Thermal Conductivity by Geometric Mean

The theoretical bulk thermal conductivity of each coating

layer sample was modeled by calculating the geometric

mean of the K values of pigment latex and air based on

their volume fraction v as Eq 3

airlatexpigment v

air

v

latex

v

pigmenteff KKKK [3]

where Kpigment = 26 WmK for GCC or 16 WmK for

kaolin

Klatex = 020 WmK

Kair = 0026 WmK

vpigment and vlatex are derived from the porosity (vair)

and the pigment to latex mass ratio with their

individual density given 1v

Fig 7 shows that the geometric mean model provides very

good fittings of the experimental data points for the

different pigments and latex concentrations studied This

shows that the bulk thermal conductivity of the coatings

can be well predicted by the geometric mean model

Furthermore it shows that the thermal conductivity only

PAPER PHYSICS

Nordic Pulp and Paper Research Journal Vol 27 no22012 455

Fig 7 Modelling Thermal Conductivity by the Geometric Mean Model

depends on the intrinsic thermal conductivities of the

coating constituents and their respectively volume fractions

(the latter being affected by the PSD and the shape of the

pigment used) In fact this model constitutes a much

simpler model than the Lumped Parameter model proposed

recently by Gerstner (2010) while resembling the empirical

model suggested by Azadi et al (2010)

Print Quality Test Results

Print Gloss

Fig 8 shows that the average print gloss of the model

coated paper was significantly reduced as the bulk thermal

conductivity of the corresponding type of coating layer

increases This suggests that the bulk thermal conductivity

of the coating layers affect the fusing process of toner

which includes toner coalescence melting and spreading

similar to what is concluded by Azadi et al (2008) One

possible explanation is that when the coating bulk thermal

conductivity is lower the coating plays the role of a heat

barrier (dissipating less heat to the base paper) This helps

the toner layer to reach uniformly its melting temperature

and allows the toner layer to level off evenly As a result a

ldquomirror-likerdquo surface is thus created and a high print gloss

is obtained

Interestingly thermal diffusivity of the coating layer gave

a weaker correlation to print gloss with R2 around 052 It

might be due to the fact that thermal diffusivity deals

mostly with the heat flow in the coating layer itself while

print gloss is mostly determined by the heat flow at the

tonercoating interface which thermal conductivity might

be more important However this remains to be confirmed

by further studies

Toner Adhesion

The results of the toner adhesion test show that the amount

of toner removed is affected by the peeling speed of the

Scotch tape Therefore the minimum percentages of toner

remained (adhered) on the coated paper samples at all

peeling speeds were taken for the study These data are

listed in Table 2 and plotted in Fig 9 It shows no

correlation between the percentage of toners remained on

Fig 8 Effect of Bulk Thermal Conductivity of the Coating Layers on Average Print Gloss (in ) of the Coated Papers

Fig 9 Effect of Bulk Thermal Conductivity of the Coating Layers on Toner Adhesion on the Coated Papers

Table 2 Minimum Toner Adhesion on Coated Papers

the coated paper and the bulk thermal conductivity of the

corresponding type of coating layer A similar comparison

was done by Gerstner et al

(2009) and no definite

correlation was found either As explained by Kianercy

(2004) and Sipi (2001) only three factors have been found

to have significant impacts on toner adhesion which are

surface tension of paper toner viscosity at the tonerpaper

interface and fusing speed

Pair-wise Visual Ranking

The result of the visual ranking test shows that for coating

layers with 10 pph of latex the CCHP-10 coating provides

the best print quality and the CPDG-10 coating provides

the worst print quality Among the HC90 coating layers

with different latex concentrations the HC90-10 and

Sample Minimum Toner Remained ()

HC90-10 987 HC90-18 946 HC90-25 872 HC60-10 218 CCHP-10 999 CPDG-10 811

PAPER PHYSICS

456 Nordic Pulp and Paper Research Journal Vol 27 no22012

Fig 10 Effect of Bulk Thermal Conductivity of the Coating Layers on Average Ranking Score of the Printed Coated Papers

Table 3 Summary of the Print Quality Test Results

HC90-18 coating provide significantly better print quality

than the one made with 25 pph of latex However no

correlation was found between print quality (quantified by

the average ranking score) of a sample with the bulk

thermal conductivity of the coating layers see Fig 10

These findings suggest that there are other factors which

have a more significant effect on the print quality of coated

paper However this is beyond the scope of this study

A summary of the print quality test results (Table 3)

reveals that the coating layer formulated with Covercarb

HP pigment and 10 pph of latex has the best ranking in all

three tests Therefore with its relatively low thermal

conductivity this coating formulation is the best candidate

among the ones studied for use in xerography printing

Conclusions The effects of coating formulations on thermal

characteristics of the coating layers were systematically

studied for assessing their impact on xerographic toner

fusion onto the coated papers It was shown that porosity is

a key parameter in the design of a coating layer for heat

transfer applications The latex concentration in the coating

formulation plays a significant role as it determines the

overall porosity of the coating layers Therefore in order

for the coating layer to act as a heat barrier (and provide

sufficient uniform heat transfer to the toner layer) it needs

to have an acceptably high porosity or a low latex

concentration The particle size distribution (narrow PSD)

and morphology (high shape factor) of pigments also affect

positively the porosity and thus the overall thermal

characteristics of the coating layers However the median

particle size of pigments did not show any significant

effect It was also found that the bulk thermal conductivity

of the coating layers can be accurately predicted by a

simple geometric mean model based on the pigment latex

and air volume contents

A 75˚ TAPPI print gloss measurement a toner adhesion

test using an IGT printability tester and a pair-wise visual

ranking test were performed on paper samples coated with

model coating colours and printed with 100 solid black

by xerography The print gloss of coated papers was

significantly improved when the coating bulk thermal

conductivity was low This is attributed to the insulating

effect of the coating thus providing a more uniform toner

fusion No other correlation was found between the print

quality and thermal properties of the samples

Lastly it was found that the coating made of Covercarb

HP a narrow PSD pigment and 10 pph of latex gave a

relatively low thermal conductivity and the best ranking in

all three print quality tests Therefore among all the

formulations tested this coating is the best candidate for

coated paper applications in xerography

Acknowledgements The financial and technical supports from NSERC IPS Scholarship FPInnovations Xerox Research Center of Canada and Surface Science Consortium at the Pulp and Paper Centre University of Toronto are gratefully acknowledged

Literature

Azadi P (2007) Modeling of mechanical and thermal responses of paper coatings under compression using discrete element method Thesis for the Degree of Master of Applied Science University of Toronto Toronto Canada

Azadi P Yan N Farnood R (2008) Discrete Element Modeling of the Transient Heat Transfer and Toner Fusing Process in the Xerographic Printing of Coated Papers Computers amp Chemical Engineering 32(12) 3238-3245

Azadi P Nunnari S Farnood R Kortschot M Yan N (2009) High speed compression of highly filled thin composites effect of binder content and stiffness Progress in Organic Coatings 64(4) 356-360

Azadi P Farnood R Yan N (2010) FEM-DEM Modeling of Thermal Conductivity of Porous Pigmented Coatings Computational Materials Science 49(2) 392-399

Bandyopadhay A Ramarao BV Shih EC (2001) Transient response of a paper sheet subjected to a traveling thermal pulse evolution of temperature moisture and pressure fields Journal of Imaging Science and Technology 45(6) 598-608

Bouguerra A Laurent JP Goual M Queneudec M (1997) The measurement of the thermal conductivity of solid aggregates using the transient plane source technique Journal of Physics D Applied Physics 30 2900-2904

Ranking (Best to Worst)

Print Gloss

Toner Adhesion

Visual Ranking

1 CCHP-10 CCHP-10 CCHP-10 2 CPDG-10 HC90-10 HC90-10 3 HC90-10 HC90-18 HC90-18 4 HC90-18 HC90-25 HC60-10 5 HC60-10 CPDG-10 CPDG-10 6 HC90-25 HC60-10 HC90-25

PAPER PHYSICS

Nordic Pulp and Paper Research Journal Vol 27 no22012 457

Cormier L Zou X (2008) Toner fusion in electrophotographic printing ndash issues from Papricanrsquos perspectives FPInnovations Paprican Division Pointe-Claire QC February 8 2008

CRC Handbook of Chemistry and Physics (2009) 89th ed Taylor amp Francis Group

Di Risio S Yan N (2006) Characterizing Coating Pore Structures of Paper Using Scanning Probe Microscopyrdquo TAPPI Journal 5(3) 9-14

Di Risio S Yan N (2006) Characterizing Coating Layer Z-directional Binder Distribution in Paper Using Atomic Force Microscopy Colloids and Surfaces A Physicochemical and Engineering Aspects 289(1-3) 65-74

Duke CB Noolandi J Thieret T (2002) The surface science of xerography Surface Science 500 1005-1023

Gane PAC Ridgeway CJ Schoelkopf J Bousfield DW (2007) Heat transfer through calcium carbonate-based coating structures observation and model for a thermal fusing process Journal of Pulp and Paper Science 33(2) 60-70

Gerstner P Gane PAC (2009) Considerations for thermally engineered coated printing papers focus on electrophotography Journal of Pulp and Paper Science 35(3-4) 108-117

Gerstner P Paltakari J Gane PAC (2009) Measurement and modeling of heat transfer in paper coating structures Journal of Material Science 44 (2) 483-491

Gerstner P (2010) Heat Transfer Through Porous Multiphase Systems Measurement Modelling and Application in Printing of Coated Papers PhD Thesis Aalto university Helsinki Finland

Kianercy A (2004) Characterizing toner-paper adhesion in xerography Thesis for the Degree of Master of Applied Science University of Toronto Toronto Canada

Liang C (2009) Effect of coating formulations on thermal properties of coating layers Thesis for the Degree of Master of Applied Science University of Toronto Toronto Canada

Maijala J Putkisto K Pietikaumlinen R Groumln J (2004) Heat transfer during fixation of coating layers in dry surface treatment Nordic Pulp and Paper Research Journal 19(3) 291-299

Malla PB Starr RE Werkin TJ (1999) The effects of kaolin particle size structure clay loading and binder level on glossing and offset print properties ndash A CLC coating study 1999 TAPPI Coating Conference Proceedings Toronto Ontario Canada TAPPI Press

Mitsuya T Kumasaka T (1992) Heat transfer and toner melting in an electrophotographic fuser system Journal of Imaging Science and Technology 36 88-92

Morikawa J Hashimoto T (1998) Thermal diffusivity measurement of papers by an AC joule heating method Polymer International 45(2) 207-210

Niskanen K Simula S (1999) Thermal diffusivity of paper Nordic Pulp and Paper Research Journal 14(3) 236-242

Okomori K Lepoutre P (1998) Effect of pigment size and shape distribution on the cohesion of pigmented coatings 1998 TAPPI CoatingPapermakers Conference New Orleans LA USA TAPPI Atlanta GA USA 819 ndash 835

Parker WJ Jenkins RJ Butler CP Abbott GL (1961) Flash method of determining thermal diffusivity heat capacity and thermal conductivity Journal of Applied Physics 32(9) 1679-1684

Salazer A (2003) On thermal diffusivity European Journal of Physics 24(3) 351-358

Sanders DJ Rutland DF (1996) Effect of paper properties on fusing fix Journal of Imaging Science and Technology 40(2) 175-179

Saxaner NS et al (1999) Thermal conductivity of styrene butadiene rubber compounds with natural rubber prophylactics waste as filler European Polymer Journal 35 1687-1693

Simula S Niskanen K (1998) Thermal diffusivity measurement of non-impact printing paper Journal of Imaging Science and Technology 42(6) 550-553

Sipi KM (2001) Toner layer structure and toner adhesion on coated paper NIP17 International Conference on Digital Printing Technologies Fort Lauderdale FL USA 145-150

Stroumlm G Hornatowska J Changhong X Terasaki O (2010) A novel SEM cross-section analysis of paper coating for separation of latex from void volume Nordic Pulp and Paper Research Journal 25(1) 107-113

Vernhes P Blayo A Bloch J-F Pineaux B (2006) Influence of the thermal field on the fusing step in electrophotographic printing Proceedings of the Technical Association of the Graphic Arts 465-485

Vidal D Zou X Uesaka T (2004) Modeling coating structure development Monte-Carlo deposition of particles with irregular shapes Nordic Pulp and Paper Research Journal 19(4) 420ndash427

Wantanabe J Kohara Y Takahashi S (1980) Effects of clay properties on paper coating structure Tappi 63(1) 43 ndash 46

Webb PA (2001) An introduction to the physical characterization of materials by mercury intrusion porosimetry with emphasis on reduction and presentation of experimental data Micromeritics Instrument Corp January 2001 Retrieved on January 14 2009

httpwwwmicromeriticscomapplicationsarticlesaspx

Zhao S Schabel S (2006) Measurement of thermal properties of paper by a light flash method Das Papier T65 34-39

PAPER PHYSICS

458 Nordic Pulp and Paper Research Journal Vol 27 no22012

Page 6: Effects of coating formulation on coating thermal ... · PDF fileEffects of coating formulation on coating thermal properties and coated paper ... KEYWORDS: Paper coating ... “heat

Fig 7 Modelling Thermal Conductivity by the Geometric Mean Model

depends on the intrinsic thermal conductivities of the

coating constituents and their respectively volume fractions

(the latter being affected by the PSD and the shape of the

pigment used) In fact this model constitutes a much

simpler model than the Lumped Parameter model proposed

recently by Gerstner (2010) while resembling the empirical

model suggested by Azadi et al (2010)

Print Quality Test Results

Print Gloss

Fig 8 shows that the average print gloss of the model

coated paper was significantly reduced as the bulk thermal

conductivity of the corresponding type of coating layer

increases This suggests that the bulk thermal conductivity

of the coating layers affect the fusing process of toner

which includes toner coalescence melting and spreading

similar to what is concluded by Azadi et al (2008) One

possible explanation is that when the coating bulk thermal

conductivity is lower the coating plays the role of a heat

barrier (dissipating less heat to the base paper) This helps

the toner layer to reach uniformly its melting temperature

and allows the toner layer to level off evenly As a result a

ldquomirror-likerdquo surface is thus created and a high print gloss

is obtained

Interestingly thermal diffusivity of the coating layer gave

a weaker correlation to print gloss with R2 around 052 It

might be due to the fact that thermal diffusivity deals

mostly with the heat flow in the coating layer itself while

print gloss is mostly determined by the heat flow at the

tonercoating interface which thermal conductivity might

be more important However this remains to be confirmed

by further studies

Toner Adhesion

The results of the toner adhesion test show that the amount

of toner removed is affected by the peeling speed of the

Scotch tape Therefore the minimum percentages of toner

remained (adhered) on the coated paper samples at all

peeling speeds were taken for the study These data are

listed in Table 2 and plotted in Fig 9 It shows no

correlation between the percentage of toners remained on

Fig 8 Effect of Bulk Thermal Conductivity of the Coating Layers on Average Print Gloss (in ) of the Coated Papers

Fig 9 Effect of Bulk Thermal Conductivity of the Coating Layers on Toner Adhesion on the Coated Papers

Table 2 Minimum Toner Adhesion on Coated Papers

the coated paper and the bulk thermal conductivity of the

corresponding type of coating layer A similar comparison

was done by Gerstner et al

(2009) and no definite

correlation was found either As explained by Kianercy

(2004) and Sipi (2001) only three factors have been found

to have significant impacts on toner adhesion which are

surface tension of paper toner viscosity at the tonerpaper

interface and fusing speed

Pair-wise Visual Ranking

The result of the visual ranking test shows that for coating

layers with 10 pph of latex the CCHP-10 coating provides

the best print quality and the CPDG-10 coating provides

the worst print quality Among the HC90 coating layers

with different latex concentrations the HC90-10 and

Sample Minimum Toner Remained ()

HC90-10 987 HC90-18 946 HC90-25 872 HC60-10 218 CCHP-10 999 CPDG-10 811

PAPER PHYSICS

456 Nordic Pulp and Paper Research Journal Vol 27 no22012

Fig 10 Effect of Bulk Thermal Conductivity of the Coating Layers on Average Ranking Score of the Printed Coated Papers

Table 3 Summary of the Print Quality Test Results

HC90-18 coating provide significantly better print quality

than the one made with 25 pph of latex However no

correlation was found between print quality (quantified by

the average ranking score) of a sample with the bulk

thermal conductivity of the coating layers see Fig 10

These findings suggest that there are other factors which

have a more significant effect on the print quality of coated

paper However this is beyond the scope of this study

A summary of the print quality test results (Table 3)

reveals that the coating layer formulated with Covercarb

HP pigment and 10 pph of latex has the best ranking in all

three tests Therefore with its relatively low thermal

conductivity this coating formulation is the best candidate

among the ones studied for use in xerography printing

Conclusions The effects of coating formulations on thermal

characteristics of the coating layers were systematically

studied for assessing their impact on xerographic toner

fusion onto the coated papers It was shown that porosity is

a key parameter in the design of a coating layer for heat

transfer applications The latex concentration in the coating

formulation plays a significant role as it determines the

overall porosity of the coating layers Therefore in order

for the coating layer to act as a heat barrier (and provide

sufficient uniform heat transfer to the toner layer) it needs

to have an acceptably high porosity or a low latex

concentration The particle size distribution (narrow PSD)

and morphology (high shape factor) of pigments also affect

positively the porosity and thus the overall thermal

characteristics of the coating layers However the median

particle size of pigments did not show any significant

effect It was also found that the bulk thermal conductivity

of the coating layers can be accurately predicted by a

simple geometric mean model based on the pigment latex

and air volume contents

A 75˚ TAPPI print gloss measurement a toner adhesion

test using an IGT printability tester and a pair-wise visual

ranking test were performed on paper samples coated with

model coating colours and printed with 100 solid black

by xerography The print gloss of coated papers was

significantly improved when the coating bulk thermal

conductivity was low This is attributed to the insulating

effect of the coating thus providing a more uniform toner

fusion No other correlation was found between the print

quality and thermal properties of the samples

Lastly it was found that the coating made of Covercarb

HP a narrow PSD pigment and 10 pph of latex gave a

relatively low thermal conductivity and the best ranking in

all three print quality tests Therefore among all the

formulations tested this coating is the best candidate for

coated paper applications in xerography

Acknowledgements The financial and technical supports from NSERC IPS Scholarship FPInnovations Xerox Research Center of Canada and Surface Science Consortium at the Pulp and Paper Centre University of Toronto are gratefully acknowledged

Literature

Azadi P (2007) Modeling of mechanical and thermal responses of paper coatings under compression using discrete element method Thesis for the Degree of Master of Applied Science University of Toronto Toronto Canada

Azadi P Yan N Farnood R (2008) Discrete Element Modeling of the Transient Heat Transfer and Toner Fusing Process in the Xerographic Printing of Coated Papers Computers amp Chemical Engineering 32(12) 3238-3245

Azadi P Nunnari S Farnood R Kortschot M Yan N (2009) High speed compression of highly filled thin composites effect of binder content and stiffness Progress in Organic Coatings 64(4) 356-360

Azadi P Farnood R Yan N (2010) FEM-DEM Modeling of Thermal Conductivity of Porous Pigmented Coatings Computational Materials Science 49(2) 392-399

Bandyopadhay A Ramarao BV Shih EC (2001) Transient response of a paper sheet subjected to a traveling thermal pulse evolution of temperature moisture and pressure fields Journal of Imaging Science and Technology 45(6) 598-608

Bouguerra A Laurent JP Goual M Queneudec M (1997) The measurement of the thermal conductivity of solid aggregates using the transient plane source technique Journal of Physics D Applied Physics 30 2900-2904

Ranking (Best to Worst)

Print Gloss

Toner Adhesion

Visual Ranking

1 CCHP-10 CCHP-10 CCHP-10 2 CPDG-10 HC90-10 HC90-10 3 HC90-10 HC90-18 HC90-18 4 HC90-18 HC90-25 HC60-10 5 HC60-10 CPDG-10 CPDG-10 6 HC90-25 HC60-10 HC90-25

PAPER PHYSICS

Nordic Pulp and Paper Research Journal Vol 27 no22012 457

Cormier L Zou X (2008) Toner fusion in electrophotographic printing ndash issues from Papricanrsquos perspectives FPInnovations Paprican Division Pointe-Claire QC February 8 2008

CRC Handbook of Chemistry and Physics (2009) 89th ed Taylor amp Francis Group

Di Risio S Yan N (2006) Characterizing Coating Pore Structures of Paper Using Scanning Probe Microscopyrdquo TAPPI Journal 5(3) 9-14

Di Risio S Yan N (2006) Characterizing Coating Layer Z-directional Binder Distribution in Paper Using Atomic Force Microscopy Colloids and Surfaces A Physicochemical and Engineering Aspects 289(1-3) 65-74

Duke CB Noolandi J Thieret T (2002) The surface science of xerography Surface Science 500 1005-1023

Gane PAC Ridgeway CJ Schoelkopf J Bousfield DW (2007) Heat transfer through calcium carbonate-based coating structures observation and model for a thermal fusing process Journal of Pulp and Paper Science 33(2) 60-70

Gerstner P Gane PAC (2009) Considerations for thermally engineered coated printing papers focus on electrophotography Journal of Pulp and Paper Science 35(3-4) 108-117

Gerstner P Paltakari J Gane PAC (2009) Measurement and modeling of heat transfer in paper coating structures Journal of Material Science 44 (2) 483-491

Gerstner P (2010) Heat Transfer Through Porous Multiphase Systems Measurement Modelling and Application in Printing of Coated Papers PhD Thesis Aalto university Helsinki Finland

Kianercy A (2004) Characterizing toner-paper adhesion in xerography Thesis for the Degree of Master of Applied Science University of Toronto Toronto Canada

Liang C (2009) Effect of coating formulations on thermal properties of coating layers Thesis for the Degree of Master of Applied Science University of Toronto Toronto Canada

Maijala J Putkisto K Pietikaumlinen R Groumln J (2004) Heat transfer during fixation of coating layers in dry surface treatment Nordic Pulp and Paper Research Journal 19(3) 291-299

Malla PB Starr RE Werkin TJ (1999) The effects of kaolin particle size structure clay loading and binder level on glossing and offset print properties ndash A CLC coating study 1999 TAPPI Coating Conference Proceedings Toronto Ontario Canada TAPPI Press

Mitsuya T Kumasaka T (1992) Heat transfer and toner melting in an electrophotographic fuser system Journal of Imaging Science and Technology 36 88-92

Morikawa J Hashimoto T (1998) Thermal diffusivity measurement of papers by an AC joule heating method Polymer International 45(2) 207-210

Niskanen K Simula S (1999) Thermal diffusivity of paper Nordic Pulp and Paper Research Journal 14(3) 236-242

Okomori K Lepoutre P (1998) Effect of pigment size and shape distribution on the cohesion of pigmented coatings 1998 TAPPI CoatingPapermakers Conference New Orleans LA USA TAPPI Atlanta GA USA 819 ndash 835

Parker WJ Jenkins RJ Butler CP Abbott GL (1961) Flash method of determining thermal diffusivity heat capacity and thermal conductivity Journal of Applied Physics 32(9) 1679-1684

Salazer A (2003) On thermal diffusivity European Journal of Physics 24(3) 351-358

Sanders DJ Rutland DF (1996) Effect of paper properties on fusing fix Journal of Imaging Science and Technology 40(2) 175-179

Saxaner NS et al (1999) Thermal conductivity of styrene butadiene rubber compounds with natural rubber prophylactics waste as filler European Polymer Journal 35 1687-1693

Simula S Niskanen K (1998) Thermal diffusivity measurement of non-impact printing paper Journal of Imaging Science and Technology 42(6) 550-553

Sipi KM (2001) Toner layer structure and toner adhesion on coated paper NIP17 International Conference on Digital Printing Technologies Fort Lauderdale FL USA 145-150

Stroumlm G Hornatowska J Changhong X Terasaki O (2010) A novel SEM cross-section analysis of paper coating for separation of latex from void volume Nordic Pulp and Paper Research Journal 25(1) 107-113

Vernhes P Blayo A Bloch J-F Pineaux B (2006) Influence of the thermal field on the fusing step in electrophotographic printing Proceedings of the Technical Association of the Graphic Arts 465-485

Vidal D Zou X Uesaka T (2004) Modeling coating structure development Monte-Carlo deposition of particles with irregular shapes Nordic Pulp and Paper Research Journal 19(4) 420ndash427

Wantanabe J Kohara Y Takahashi S (1980) Effects of clay properties on paper coating structure Tappi 63(1) 43 ndash 46

Webb PA (2001) An introduction to the physical characterization of materials by mercury intrusion porosimetry with emphasis on reduction and presentation of experimental data Micromeritics Instrument Corp January 2001 Retrieved on January 14 2009

httpwwwmicromeriticscomapplicationsarticlesaspx

Zhao S Schabel S (2006) Measurement of thermal properties of paper by a light flash method Das Papier T65 34-39

PAPER PHYSICS

458 Nordic Pulp and Paper Research Journal Vol 27 no22012

Page 7: Effects of coating formulation on coating thermal ... · PDF fileEffects of coating formulation on coating thermal properties and coated paper ... KEYWORDS: Paper coating ... “heat

Fig 10 Effect of Bulk Thermal Conductivity of the Coating Layers on Average Ranking Score of the Printed Coated Papers

Table 3 Summary of the Print Quality Test Results

HC90-18 coating provide significantly better print quality

than the one made with 25 pph of latex However no

correlation was found between print quality (quantified by

the average ranking score) of a sample with the bulk

thermal conductivity of the coating layers see Fig 10

These findings suggest that there are other factors which

have a more significant effect on the print quality of coated

paper However this is beyond the scope of this study

A summary of the print quality test results (Table 3)

reveals that the coating layer formulated with Covercarb

HP pigment and 10 pph of latex has the best ranking in all

three tests Therefore with its relatively low thermal

conductivity this coating formulation is the best candidate

among the ones studied for use in xerography printing

Conclusions The effects of coating formulations on thermal

characteristics of the coating layers were systematically

studied for assessing their impact on xerographic toner

fusion onto the coated papers It was shown that porosity is

a key parameter in the design of a coating layer for heat

transfer applications The latex concentration in the coating

formulation plays a significant role as it determines the

overall porosity of the coating layers Therefore in order

for the coating layer to act as a heat barrier (and provide

sufficient uniform heat transfer to the toner layer) it needs

to have an acceptably high porosity or a low latex

concentration The particle size distribution (narrow PSD)

and morphology (high shape factor) of pigments also affect

positively the porosity and thus the overall thermal

characteristics of the coating layers However the median

particle size of pigments did not show any significant

effect It was also found that the bulk thermal conductivity

of the coating layers can be accurately predicted by a

simple geometric mean model based on the pigment latex

and air volume contents

A 75˚ TAPPI print gloss measurement a toner adhesion

test using an IGT printability tester and a pair-wise visual

ranking test were performed on paper samples coated with

model coating colours and printed with 100 solid black

by xerography The print gloss of coated papers was

significantly improved when the coating bulk thermal

conductivity was low This is attributed to the insulating

effect of the coating thus providing a more uniform toner

fusion No other correlation was found between the print

quality and thermal properties of the samples

Lastly it was found that the coating made of Covercarb

HP a narrow PSD pigment and 10 pph of latex gave a

relatively low thermal conductivity and the best ranking in

all three print quality tests Therefore among all the

formulations tested this coating is the best candidate for

coated paper applications in xerography

Acknowledgements The financial and technical supports from NSERC IPS Scholarship FPInnovations Xerox Research Center of Canada and Surface Science Consortium at the Pulp and Paper Centre University of Toronto are gratefully acknowledged

Literature

Azadi P (2007) Modeling of mechanical and thermal responses of paper coatings under compression using discrete element method Thesis for the Degree of Master of Applied Science University of Toronto Toronto Canada

Azadi P Yan N Farnood R (2008) Discrete Element Modeling of the Transient Heat Transfer and Toner Fusing Process in the Xerographic Printing of Coated Papers Computers amp Chemical Engineering 32(12) 3238-3245

Azadi P Nunnari S Farnood R Kortschot M Yan N (2009) High speed compression of highly filled thin composites effect of binder content and stiffness Progress in Organic Coatings 64(4) 356-360

Azadi P Farnood R Yan N (2010) FEM-DEM Modeling of Thermal Conductivity of Porous Pigmented Coatings Computational Materials Science 49(2) 392-399

Bandyopadhay A Ramarao BV Shih EC (2001) Transient response of a paper sheet subjected to a traveling thermal pulse evolution of temperature moisture and pressure fields Journal of Imaging Science and Technology 45(6) 598-608

Bouguerra A Laurent JP Goual M Queneudec M (1997) The measurement of the thermal conductivity of solid aggregates using the transient plane source technique Journal of Physics D Applied Physics 30 2900-2904

Ranking (Best to Worst)

Print Gloss

Toner Adhesion

Visual Ranking

1 CCHP-10 CCHP-10 CCHP-10 2 CPDG-10 HC90-10 HC90-10 3 HC90-10 HC90-18 HC90-18 4 HC90-18 HC90-25 HC60-10 5 HC60-10 CPDG-10 CPDG-10 6 HC90-25 HC60-10 HC90-25

PAPER PHYSICS

Nordic Pulp and Paper Research Journal Vol 27 no22012 457

Cormier L Zou X (2008) Toner fusion in electrophotographic printing ndash issues from Papricanrsquos perspectives FPInnovations Paprican Division Pointe-Claire QC February 8 2008

CRC Handbook of Chemistry and Physics (2009) 89th ed Taylor amp Francis Group

Di Risio S Yan N (2006) Characterizing Coating Pore Structures of Paper Using Scanning Probe Microscopyrdquo TAPPI Journal 5(3) 9-14

Di Risio S Yan N (2006) Characterizing Coating Layer Z-directional Binder Distribution in Paper Using Atomic Force Microscopy Colloids and Surfaces A Physicochemical and Engineering Aspects 289(1-3) 65-74

Duke CB Noolandi J Thieret T (2002) The surface science of xerography Surface Science 500 1005-1023

Gane PAC Ridgeway CJ Schoelkopf J Bousfield DW (2007) Heat transfer through calcium carbonate-based coating structures observation and model for a thermal fusing process Journal of Pulp and Paper Science 33(2) 60-70

Gerstner P Gane PAC (2009) Considerations for thermally engineered coated printing papers focus on electrophotography Journal of Pulp and Paper Science 35(3-4) 108-117

Gerstner P Paltakari J Gane PAC (2009) Measurement and modeling of heat transfer in paper coating structures Journal of Material Science 44 (2) 483-491

Gerstner P (2010) Heat Transfer Through Porous Multiphase Systems Measurement Modelling and Application in Printing of Coated Papers PhD Thesis Aalto university Helsinki Finland

Kianercy A (2004) Characterizing toner-paper adhesion in xerography Thesis for the Degree of Master of Applied Science University of Toronto Toronto Canada

Liang C (2009) Effect of coating formulations on thermal properties of coating layers Thesis for the Degree of Master of Applied Science University of Toronto Toronto Canada

Maijala J Putkisto K Pietikaumlinen R Groumln J (2004) Heat transfer during fixation of coating layers in dry surface treatment Nordic Pulp and Paper Research Journal 19(3) 291-299

Malla PB Starr RE Werkin TJ (1999) The effects of kaolin particle size structure clay loading and binder level on glossing and offset print properties ndash A CLC coating study 1999 TAPPI Coating Conference Proceedings Toronto Ontario Canada TAPPI Press

Mitsuya T Kumasaka T (1992) Heat transfer and toner melting in an electrophotographic fuser system Journal of Imaging Science and Technology 36 88-92

Morikawa J Hashimoto T (1998) Thermal diffusivity measurement of papers by an AC joule heating method Polymer International 45(2) 207-210

Niskanen K Simula S (1999) Thermal diffusivity of paper Nordic Pulp and Paper Research Journal 14(3) 236-242

Okomori K Lepoutre P (1998) Effect of pigment size and shape distribution on the cohesion of pigmented coatings 1998 TAPPI CoatingPapermakers Conference New Orleans LA USA TAPPI Atlanta GA USA 819 ndash 835

Parker WJ Jenkins RJ Butler CP Abbott GL (1961) Flash method of determining thermal diffusivity heat capacity and thermal conductivity Journal of Applied Physics 32(9) 1679-1684

Salazer A (2003) On thermal diffusivity European Journal of Physics 24(3) 351-358

Sanders DJ Rutland DF (1996) Effect of paper properties on fusing fix Journal of Imaging Science and Technology 40(2) 175-179

Saxaner NS et al (1999) Thermal conductivity of styrene butadiene rubber compounds with natural rubber prophylactics waste as filler European Polymer Journal 35 1687-1693

Simula S Niskanen K (1998) Thermal diffusivity measurement of non-impact printing paper Journal of Imaging Science and Technology 42(6) 550-553

Sipi KM (2001) Toner layer structure and toner adhesion on coated paper NIP17 International Conference on Digital Printing Technologies Fort Lauderdale FL USA 145-150

Stroumlm G Hornatowska J Changhong X Terasaki O (2010) A novel SEM cross-section analysis of paper coating for separation of latex from void volume Nordic Pulp and Paper Research Journal 25(1) 107-113

Vernhes P Blayo A Bloch J-F Pineaux B (2006) Influence of the thermal field on the fusing step in electrophotographic printing Proceedings of the Technical Association of the Graphic Arts 465-485

Vidal D Zou X Uesaka T (2004) Modeling coating structure development Monte-Carlo deposition of particles with irregular shapes Nordic Pulp and Paper Research Journal 19(4) 420ndash427

Wantanabe J Kohara Y Takahashi S (1980) Effects of clay properties on paper coating structure Tappi 63(1) 43 ndash 46

Webb PA (2001) An introduction to the physical characterization of materials by mercury intrusion porosimetry with emphasis on reduction and presentation of experimental data Micromeritics Instrument Corp January 2001 Retrieved on January 14 2009

httpwwwmicromeriticscomapplicationsarticlesaspx

Zhao S Schabel S (2006) Measurement of thermal properties of paper by a light flash method Das Papier T65 34-39

PAPER PHYSICS

458 Nordic Pulp and Paper Research Journal Vol 27 no22012

Page 8: Effects of coating formulation on coating thermal ... · PDF fileEffects of coating formulation on coating thermal properties and coated paper ... KEYWORDS: Paper coating ... “heat

Cormier L Zou X (2008) Toner fusion in electrophotographic printing ndash issues from Papricanrsquos perspectives FPInnovations Paprican Division Pointe-Claire QC February 8 2008

CRC Handbook of Chemistry and Physics (2009) 89th ed Taylor amp Francis Group

Di Risio S Yan N (2006) Characterizing Coating Pore Structures of Paper Using Scanning Probe Microscopyrdquo TAPPI Journal 5(3) 9-14

Di Risio S Yan N (2006) Characterizing Coating Layer Z-directional Binder Distribution in Paper Using Atomic Force Microscopy Colloids and Surfaces A Physicochemical and Engineering Aspects 289(1-3) 65-74

Duke CB Noolandi J Thieret T (2002) The surface science of xerography Surface Science 500 1005-1023

Gane PAC Ridgeway CJ Schoelkopf J Bousfield DW (2007) Heat transfer through calcium carbonate-based coating structures observation and model for a thermal fusing process Journal of Pulp and Paper Science 33(2) 60-70

Gerstner P Gane PAC (2009) Considerations for thermally engineered coated printing papers focus on electrophotography Journal of Pulp and Paper Science 35(3-4) 108-117

Gerstner P Paltakari J Gane PAC (2009) Measurement and modeling of heat transfer in paper coating structures Journal of Material Science 44 (2) 483-491

Gerstner P (2010) Heat Transfer Through Porous Multiphase Systems Measurement Modelling and Application in Printing of Coated Papers PhD Thesis Aalto university Helsinki Finland

Kianercy A (2004) Characterizing toner-paper adhesion in xerography Thesis for the Degree of Master of Applied Science University of Toronto Toronto Canada

Liang C (2009) Effect of coating formulations on thermal properties of coating layers Thesis for the Degree of Master of Applied Science University of Toronto Toronto Canada

Maijala J Putkisto K Pietikaumlinen R Groumln J (2004) Heat transfer during fixation of coating layers in dry surface treatment Nordic Pulp and Paper Research Journal 19(3) 291-299

Malla PB Starr RE Werkin TJ (1999) The effects of kaolin particle size structure clay loading and binder level on glossing and offset print properties ndash A CLC coating study 1999 TAPPI Coating Conference Proceedings Toronto Ontario Canada TAPPI Press

Mitsuya T Kumasaka T (1992) Heat transfer and toner melting in an electrophotographic fuser system Journal of Imaging Science and Technology 36 88-92

Morikawa J Hashimoto T (1998) Thermal diffusivity measurement of papers by an AC joule heating method Polymer International 45(2) 207-210

Niskanen K Simula S (1999) Thermal diffusivity of paper Nordic Pulp and Paper Research Journal 14(3) 236-242

Okomori K Lepoutre P (1998) Effect of pigment size and shape distribution on the cohesion of pigmented coatings 1998 TAPPI CoatingPapermakers Conference New Orleans LA USA TAPPI Atlanta GA USA 819 ndash 835

Parker WJ Jenkins RJ Butler CP Abbott GL (1961) Flash method of determining thermal diffusivity heat capacity and thermal conductivity Journal of Applied Physics 32(9) 1679-1684

Salazer A (2003) On thermal diffusivity European Journal of Physics 24(3) 351-358

Sanders DJ Rutland DF (1996) Effect of paper properties on fusing fix Journal of Imaging Science and Technology 40(2) 175-179

Saxaner NS et al (1999) Thermal conductivity of styrene butadiene rubber compounds with natural rubber prophylactics waste as filler European Polymer Journal 35 1687-1693

Simula S Niskanen K (1998) Thermal diffusivity measurement of non-impact printing paper Journal of Imaging Science and Technology 42(6) 550-553

Sipi KM (2001) Toner layer structure and toner adhesion on coated paper NIP17 International Conference on Digital Printing Technologies Fort Lauderdale FL USA 145-150

Stroumlm G Hornatowska J Changhong X Terasaki O (2010) A novel SEM cross-section analysis of paper coating for separation of latex from void volume Nordic Pulp and Paper Research Journal 25(1) 107-113

Vernhes P Blayo A Bloch J-F Pineaux B (2006) Influence of the thermal field on the fusing step in electrophotographic printing Proceedings of the Technical Association of the Graphic Arts 465-485

Vidal D Zou X Uesaka T (2004) Modeling coating structure development Monte-Carlo deposition of particles with irregular shapes Nordic Pulp and Paper Research Journal 19(4) 420ndash427

Wantanabe J Kohara Y Takahashi S (1980) Effects of clay properties on paper coating structure Tappi 63(1) 43 ndash 46

Webb PA (2001) An introduction to the physical characterization of materials by mercury intrusion porosimetry with emphasis on reduction and presentation of experimental data Micromeritics Instrument Corp January 2001 Retrieved on January 14 2009

httpwwwmicromeriticscomapplicationsarticlesaspx

Zhao S Schabel S (2006) Measurement of thermal properties of paper by a light flash method Das Papier T65 34-39

PAPER PHYSICS

458 Nordic Pulp and Paper Research Journal Vol 27 no22012