Insights into how pigments and binders affect coating rheology by replacement of clay with GCC and partial replacement of latex with starch

1. Models for the Rheology of Clay-GCC Coating Colors
Saeid Savarmand*
Pierre J. Carreau
François Bertrand
David J.-E. Vidal
2008 TAPPI 10th Advanced
Coating Fundamentals
Symposium
*Presently at Sun Chemical Corp., Carlstadt, NJ 07072, USA.

2. Rheology Controls Runnability and Quality
Blade Coating Metering size press
Wet streaks Orange peel Misting
High shear Low shear viscosity High extensional
viscosity / Yield stress viscosity
/ Yield Stress
1

3. Objectives
Gain new insights into how pigments and
binders affect coating rheology
• Replacement of CLAY with GCC
• Partial replacement of LATEX with STARCH
2

4. Coating Viscosity:
Correlations with Solids Content at Fixed Shearing Condition
2
0   
 1 
     
Low shear m ,0 
Maron-Pierce
(1956) 2
   
High shear
 1 
   m ,  

(m- ) determines 
the viscosity level
Material Resistance
(Dimensionless)
Liquid Solid
0  2
 : suspension viscosity   
   1 
 : medium viscosity  m 
 : volume solids content
m : maximum packing fraction
1 m 
3

5. Combined Impact of Shearing Condition and
Solids Content on Coating Rheology
Suspension Rheology of Non-Interacting Particles
[ ]m ,0
0   
 1 
      (Krieger & Dougherty, 1959)
m ,0 
(01,  )
Shear Viscosity
(02 , 2 )   0 1

   1  ( / c ) n [ ]m ,
   
 1  
  m ,  
 
(1,  )
( 2 , 2 )
Shear Rate or Shear Stress
4

6. Combined Impact of Shearing Condition and Solids
Content on Coating Rheology (II)
High Solids Content or Interacting Particles
Modified K-D Correlation
 
( y1,  ) y   
 1  1
y 
*    
m ,0 
Shear Viscosity
( y 2 ,  2 )
New 3-parameter model
    (  )
y
 [ ]m ,
   
 1 
   m ,  


(1,  )
( 2 , 2 )
Shear Stress
5

7. Rheology of Coating
Coating Structure
Suspensions
?
Maximum Packing Fraction (m)
6

8. 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)
7

9. Perception of Yield Phenomenon
Creep Compliance, J Transient Shear Viscosity, t
 (t ) 1
J (t ; )   J (t ; ) 
t   
  t 
Yielding
(A Transition)
Transient Shear Viscosity, t (Pa s)
5 105
Solid-like behavior
Creep Compliance, J (Pa-1)
Shear Stress,
4 Solid- II III
104  (Pa)
7.2
like 7.0
I
3
behavior 103
6.8
6.5
Liquid- 6.0
like 5.5
102 5.0
2
behavior 4.5
Viscoelastic
101
1 behavior
Liquid-like behavior
0
0 10
0 50 100 150 200 10-1 100 101 102 103
Time, t (s) Shear Strain, 
8

10. Proposed Model Fitted to a Clay-Based Coating Color
Clay Coating Color: 47.3 vol.%; 12pph Latex; 0.5pph CMC; pH8
1.E+07
Data from
Creep Test
Exp
1.E+05 
Shear Viscosity (Pa s)
    (  )
y

1.E+03
Data from Steady
1.E+01 Shear Test
1.E-01
0 10 20 30 40 50 60 70 80
Shear Stress (Pa)
9

11. 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+05
Exp

Shear Viscosity (Pa s)
1.E+03
    (  )
y

Measurement
artifact due to
the uneven
shear stress
1.E+01
within the
gap of
Couette
geometry
1.E-01
0 10 20 30 40 50 60
Shear Stress (Pa)
10

12. Experimental Results
Impact of replacing Clay by GCC
in pure pigment suspensions
11

13. How blending GCC with clay affects
pigment suspension viscosity?
..
60% 68% (s ))
68% (s-1
-1
100
100
Shear viscosity (Pa s)
310
10-1
10-1 500
10-2
10-2
0 25 50 75 100 % GCC
% Clay 100 75 50 25 0
Non-linear relationship between coating viscosity and blend ratio
12

14. How blending GCC with clay affects m?
– Pigment Suspensions
68
High viscosity
m (High Shear)
64
60
56
52
0 25 50 75 100 % GCC
% Clay 100 75 50 25 0
Adding a small amount of GCC to clay suspension
significantly decreases m
13

15. Coating Color Viscosity
Clay/GCC Blend, 12 pph latex, 0.5 pph CMC
106
105
104
Shear viscosity (Pa s)
103
102
101
100
10-1
47 vol.%
35 vol.%
41 vol.%
10-2
0.5 1 2 5 10 20 40 60 100
Shear stress (Pa) GCC 100%
Clay/GCC 75/25%
Clay 100%
14

16. Impact of replacement of latex by starch
Without Starch With Starch
12 pph latex 9 pph latex
0.5 CMC 4.3 pph starch
0.5 CMC
15

17. Impact of Binder Replacement on Coating Color Viscosity
– Clay-Based Coating Color
105
104
Shear viscosity (Pa s)
103
102
101
100
10-1
10-2
37 vol.%
40 vol.%
1 2 6 10 20 40
Shear stress (Pa)
12 pph latex, 0.5 pph CMC 42%
9 pph latex, 4.3 pph starch, , 0.5 pph CMC 43%
Similar Viscosity and Yield Stress
16

18. Impact of Binder Replacement on Coating Color Viscosity
– GCC-Based Coating Color
105
104
Shear viscosity (Pa s)
103
102
101
100
10-1
10-2
46 vol.%
34 vol.%
40 vol.%
1 2 5 10 20 40 60 100
Shear stress (Pa)
12 pph latex, 0.5 pph CMC
9 pph latex, 4.3 pph starch, , 0.5 pph CMC
Reduction of Viscosity and Yield Stress
17

19. Impact of Binder Replacement on Coating Color Viscosity
– 75/25% Clay/GCC-Based Coating Color
105
Shear viscosity (Pa s)
104
103
102
101
100
10-1
10-2
35 vol.%
41 vol.%
47 vol.%
1 2 5 10 20 40 60 100
Shear stress (Pa)
12 pph latex, 0.5 pph CMC
9 pph latex, 4.3 pph starch, , 0.5 pph CMC
Reduction of Viscosity and Yield Stress
18

20. The starch replacement does not affect
the microstructure so much as
the pigment does.
19

21. Determination of Maximum Packing Fraction
(m)
Clay–GCC Blend
Maximum Packing Fraction
0.52
0.50
m,0 m,
With starch
0.48 No starch
0.46
0.44
0.42
0 % GCC 25 50 75 100
100 % Clay 75 50 25 0
100% Clay Volume Blend Ratio 100% GCC
20

22. Yield Stress Results
Clay–GCC Blend
75/25% Clay/GCC
102
100% GCC
100% Clay
100% Clay-based, no starch
100% GCC-based, no starch
75/25% Clay/GCC-based, no starch
Yield Stress (Pa)
With Starch
101
No Starch
Yield Stress 0% 45% 45%
Viscosity  0% 10% 25%
100% Clay-based, with starch at 100 s-1
100 100% GCC-based, with starch (not shown)
75/25% Clay/GCC-based, with starch
0.30 0.35 0.40 0.45 0.50
Volume Fraction, 
21

23. 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 model

  2    2


      
   * 1 
y    1     1 
  
    
  m ,0     m , 
   

  
22

24. Thank you!
Questions?
23