models for the rheology of clay-gcc coating colors
DESCRIPTION
Insights into how pigments and binders affect coating rheology by replacement of clay with GCC and partial replacement of latex with starchTRANSCRIPT
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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.
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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
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•• 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
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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)
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,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( , )
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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
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6
Maximum Packing Fraction (m
)
Rheology of Coating
Suspensions
?
Coating Structure
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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)
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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)
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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
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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
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Experimental Results
Impact of replacing Clay by GCC
in pure pigment suspensions
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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
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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
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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.%
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Impact of replacement of latex by starch
12 pph latex0.5 CMC
9 pph latex4.3 pph starch0.5 CMC
Without Starch With Starch
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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
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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
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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
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The starch replacement does not affect
the microstructure so much as
the pigment does.
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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
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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%
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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
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Thank you!Thank you!
Questions?Questions?