Models for the Rheology of ClayModels for the Rheology of Clay--GCC Coating ColorsGCC Coating Colors

Saeid SavarmandSaeid Savarmand**

Pierre J. CarreauPierre J. CarreauFranFranççois Bertrandois BertrandDavid J.David J.--E. VidalE. Vidal

2008 TAPPI 10th Advanced 2008 TAPPI 10th Advanced Coating Fundamentals Coating Fundamentals

SymposiumSymposium

**Presently at Sun Chemical Corp., Carlstadt, NJ 07072, USA.Presently at Sun Chemical Corp., Carlstadt, NJ 07072, USA.

11

Rheology Controls Runnability and Quality

Wet streaks

High shearviscosity

Misting

High extensional viscosity

/ Yield Stress

Orange peel

Low shear viscosity/ Yield stress

Blade Coating Metering size press

22

•• Replacement ofReplacement of CLAY with GCC•• Partial replacement ofPartial replacement of LATEX with STARCH

Gain new insights into how pigments and Gain new insights into how pigments and binders affect coating rheologybinders affect coating rheology

Objectives

33

2

,

1m

Coating Viscosity: Correlations with Solids Content at Fixed Shearing Condition

Maron-Pierce(1956)

1

0

m

2

0

,0

1m

Low shear

High shear

(m - ) determinesthe viscosity level

21

m

: suspension viscosity

: medium viscosity

: volume solids content

m : maximum packing fraction

SolidLiquid

Mat

eria

l Res

ista

nce

(Dim

ensi

onle

ss)

44

,0[ ]

0

,0

1m

m

Combined Impact of Shearing Condition and Solids Content on Coating Rheology

0 11 ( / )n

c

Shear Rate or

Shea

r Vis

cosi

tySuspension Rheology of Non-Interacting Particles

,[ ]

,

1m

m

(Krieger & Dougherty, 1959)

Shear Stress

01( , )

02 2( , )

1( , ) 2 2( , )

55

Combined Impact of Shearing Condition and Solids Content on Coating Rheology (II)

Shea

r Vis

cosi

tyHigh Solids Content or Interacting Particles

,[ ]

,

1m

m

Shear Stress

Modified K-D Correlation

New 3-parameter model ( )y

1( , ) 2 2( , )

*

,0

1 1y

y m

1( , )y

2 2( , )y

6

Maximum Packing Fraction (m

)

Rheology of Coating

Suspensions

?

Coating Structure

77

Experiment: Material & Apparatus

Pigment

Clay Premier (Imerys)

Ground Calcium Carbonate (GCC) Hydrocarb 90 (Omya)

Ground Calcium Carbonate (GCC) Carbitol 60 (Imerys)

Latex: SBR CP 692NA (Dow Chemical)

Starch

Staley ICB-3000

CMC: Finnfix 10 (Noviant)

Dispersant: Dispex N40V (Ciba)

Apparatus

Rheometer: CVO 120 (Malvern)

Mixer: Cowles disperser (Premier Dispersator)

88

10-1 100 101 102 103100

101

102

103

104

105

0

1

2

3

4

5

0 50 100 150 200

I

II III

Solid-like behavior

Liquid-like behavior

Shear Strain, Time, t (s)

Cre

ep C

omp

lian

ce, J

(Pa-1

)

Liquid- like behavior

Viscoelastic behavior

Solid- like behavior

( )( ; ) tJ t

1( ; )t

J tt

7.27.06.86.56.05.55.04.5

Shear Stress,

(Pa)

Yielding(A Transition)

Creep Compliance, J Transient Shear Viscosity, t

Perception of Yield Phenomenon

Tra

nsi

ent S

hea

r V

isco

sity

, t

(Pa

s)

99

Proposed Model Fitted to a Clay-Based Coating Color

Clay Coating Color: 47.3 vol.%; 12pph Latex; 0.5pph CMC; pH8

1.E-01

1.E+01

1.E+03

1.E+05

1.E+07

0 10 20 30 40 50 60 70 80

Shear Stress (Pa)

Shea

r Vis

cosi

ty (P

a s)

Exp

( )y

Data from Steady Shear Test

Data from Creep Test

1010

Proposed Model Fitted to a GCC-Based Coating Color

GCC Coating Color: 45.8 vol.%; 9 pph Latex; 4.3 pph Starch; 0.5pph CMC; pH8

1.E-01

1.E+01

1.E+03

1.E+05

0 10 20 30 40 50 60

Shear Stress (Pa)

Shea

r Vis

cosi

ty (P

a s)

Exp

( )y

Measurement artifact due to the uneven shear stress within the gap of Couette geometry

11

Experimental Results

Impact of replacing Clay by GCC

in pure pigment suspensions

1212

10-2

10-1

68%

100

(s-1).

10-2

10-1

68%

100310

(s-1).

10-2

10-1

68%60%

100310500

(s-1).

10-2

10-1

68%60%

100310500

(s-1).

How blending GCC with clay affects pigment suspension viscosity?

Non-linear relationship between coating viscosity and blend ratio

Shea

r vis

cosi

ty (P

a s)

0100

2575

5050

7525

1000% Clay

% GCC

1313

How blending GCC with clay affects m ? –

Pigment Suspensions

52

56

60

64

68 m

(Hig

h Sh

ear) High viscosity

0100

2575

5050

7525

1000% Clay

% GCC

Adding a small amount of GCC to clay suspension significantly decreases m

1414

Coating Color Viscosity

Clay/GCC Blend, 12 pph latex, 0.5 pph CMC

Shear stress (Pa)

Shea

r vi

scos

ity

(Pa

s)

10-2

10-1

100

101

102

103

104

105

106

0.5 1 2 5 10 20 40 60 100

GCC 100%Clay/GCC 75/25%

Clay 100%

47 v

ol.%

41 v

ol.%

35 v

ol.%

15

Impact of replacement of latex by starch

12 pph latex0.5 CMC

9 pph latex4.3 pph starch0.5 CMC

Without Starch With Starch

1616

Impact of Binder Replacement on Coating Color Viscosity –

Clay-Based Coating Color

Shear stress (Pa)

Shea

r vi

scos

ity

(Pa

s)

10-2

10-1

100

101

102

103

104

105

1 2 6 10 20 40

9 pph latex, 4.3 pph starch, , 0.5 pph CMC12 pph latex, 0.5 pph CMC 42%

43%

40 v

ol.%

37 v

ol.%

Similar Viscosity and Yield Stress

1717

Impact of Binder Replacement on Coating Color Viscosity –

GCC-Based Coating Color

Shear stress (Pa)

Shea

r vi

scos

ity

(Pa

s)

10-2

10-1

100

101

102

103

104

105

1 2 5 10 20 40 60 100

9 pph latex, 4.3 pph starch, , 0.5 pph CMC12 pph latex, 0.5 pph CMC

46 v

ol.%

40 v

ol.%

34 v

ol.%

Reduction of Viscosity and Yield Stress

1818

Impact of Binder Replacement on Coating Color Viscosity –

75/25% Clay/GCC-Based Coating Color

Shear stress (Pa)

Shea

r vi

scos

ity

(Pa

s)

10-2

10-1

100

101

102

103

104

105

1 2 5 10 20 40 60 100

9 pph latex, 4.3 pph starch, , 0.5 pph CMC12 pph latex, 0.5 pph CMC

47 v

ol.%

41 v

ol.%

35 v

ol.%

Reduction of Viscosity and Yield Stress

19

The starch replacement does not affect

the microstructure so much as

the pigment does.

2020

Determination of Maximum Packing Fraction (m )

Clay–GCC BlendM

axim

um P

acki

ng F

ract

ion

100% Clay 100% GCCVolume Blend Ratio

0 25 50 75 1000.42

0.44

0.46

0.48

0.50

0.52

% GCC

2575 50 0100 % Clay

m,0 m,With starch

No starch

2121

0.30 0.35 0.40 0.45 0.50

100

101

102

100% Clay-based, no starch100% GCC-based, no starch75/25% Clay/GCC-based, no starch

100% Clay-based, with starch100% GCC-based, with starch75/25% Clay/GCC-based, with starch

Yield Stress Results

No Starch

With Starch

100%

Cla

y

100%

GC

C

75/2

5% C

lay/

GC

C

Volume Fraction,

Clay–GCC Blend

Yiel

d St

ress

(Pa)

Yield Stress

Viscosityat 100 s-1

(not shown)

0% 45% 45%

10% 25%

0%

2222

Summary

Focus on the impact of binder addition

Investigated modifications on coating formulations by– Replacement of clay by GCC

Pure clay coating colors behave quite differently than GCC-based blends, even if we have 75% clay in them

Observed viscosity synergy at ~ 75/25% clay/GCC blend

– Partial replacement of latex by starch

Starch replacement did not modify yield stress and viscosity of clay-based coating color

Observed 45% reduction in yield stress when GCC is present

Observed 10 to 25% reduction in high shear viscosity when GCC is present

Introduced a new Casson-type 3-parameter model2

,0 ,

2* 1 1 1y

m m

23

Thank you!Thank you!

Questions?Questions?