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Introduction to Waterborne Paints & Coatings Rheology
Presentation from Coatex at Chinacoat 2014
Add a drop of rheology to your paints and coatings
Introduction to Waterborne
Paints & Coatings Rheology
3
Rheology is part of our daily life!
We look at honey flowing out of the jar, we eat yoghurt with pieces of fruit suspended in it
We squeeze toothpaste tube and wait for shower gel coming out of the bottle
Rheology is simply one way of describing those sensations!
What is…Rheology?
4
World leading designer and producer of waterborne Rheology Additives
Entirely dedicated to water based processes and formulations with minerals
More than 40 years of experience in Rheology
Coatex and Rheology
5
Summary
From Paint to Rheology
• In-can properties
• Paint texture
• Application properties
• Film properties
From Rheology to Paint
• Mechanisms
• Viscosity - Definition
• Rheology profiles
• Shear rates and Paint Properties
• Shear rates and Viscosimeters
• Conclusion
6
From Paint to Rheology
In-can properties
7
From Paint to Rheology: In-can properties
No re-agglomeration of particles
Optimized dispersion of pigments and fillers
Use a suitable and effective dispersant
Coadis™ and Ecodis™
good dispersion of fillers and
pigments
facilitation of the dispersibility
prevention of re-agglomeration
throughout storage
good stability and shelf life of the
paint
good optical properties of the film
2- Dispersing
agent
3- Fillers
Stirr ing
1- Water
Dispersion of Ca CO3 into water
100
200
300
400
500
20 30 40 50 60 70 80 90
Without dispersing agent
Solids content of the slurry
With dispersing agent
Vis
co
sit
y o
f th
e s
lurr
y
8
From Paint to Rheology: In-can properties
The right dispersing agent with the right dosage
Solids content increase
While maintaining viscosities low
Significant improvement in stability during storage at high temperature with Ecodis™ P 90
0 0.3
% dispersing Agent (dry/dry)
Vis
co
sit
y (
mP
a.s
)
Ecodis™ P 90
70% CaCO3
0.5 0.7 0.9
With
Polyphosphates
With
Ecodis™ P 90
9
From Paint to Rheology: In-can properties
Paint stability
No sedimentation of particles
Low shear viscosity control
Gravity on mineral particles sedimentation
Thickeners generating high viscosities at low shear prevention of dense mineral particles
sinking
Acrylic thickeners Viscoatex™ 46 and 730 with a pseudoplastic type rheology prevent sedimentation
10
From Paint to Rheology: In-can properties
No liquid phase floating
Control of syneresis
Hydrophobically modified, associative thickeners
Associative interaction network/bridging
between
•particles of binder
•thickeners hydrophobic end groups
•aqueous phase
•pigments
Hydrophobically modified thickeners, HASE or HEUR
Rheotech™ 2000/2800
Coapur ™ XS 71
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From Paint to Rheology
Paint texture
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From Paint to Rheology: Paint texture
Feel of consistency & smoothness Mid-shear viscosity (about 100 s-1) Rheotech™ 2800 for semi-gloss or one coat matt paints Rheotech™ 3800 for matt or semi-matt paints Rheotech™ 4800 for matt paints or fillers
Paint texture
Medium shear viscosity
KU or Stormer viscosity
Rheological Behaviour of Acrylic Thickeners Rheotech™ X800 series
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From Paint to Rheology: Paint texture
Optimized behaviour after tinting stability after color addition No viscosity drop upon tinting & no color float associative acrylic rheology
modifiers: Rheotech™ range
Tinting system
Color acceptance
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From Paint to Rheology
Application properties
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From Paint to Rheology: Application properties
Ease of application
Easy to load paint (brush or roller)
Viscosity control at low to medium shear
With standard thickeners
With Coapur™ 975 W
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From Paint to Rheology: Application properties
Ease of application
Low spatter ability
Viscosity control at medium to high shear With cellulosic
thickeners
With Rheotech™ 2800
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From Paint to Rheology: Application properties
Good covering power
Good film build & brushability
Viscosity control at high shear
With cellulosic thickeners
With Coapur™ 3025
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From Paint to Rheology
Film properties
19
From Paint to Rheology: Film properties
Good film build, brushability & flow/leveling
Fine tuned viscosity at high & low shear
With cellulosic thickeners
With accurate control of viscosity
Newtonian to balanced polyurethane thickeners offer optimized flow and leveling:
Coapur™ 830 W for medium PVC Coapur™ 2025 for low PVC
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From Paint to Rheology: Film properties
Water & Weather resistance
Wet scrub resistance
Hydrophobic thickeners
In medium and high PVC paints,
hydrophobic characteristics of
polyurethane thickeners (HEUR) improve
water resistance
Coapur™ 830 W (for medium/high PVC) Coapur™ 975 W (for high/medium PVC)
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From Paint to Rheology: Film properties
Water & Weather resistance
Wet scrub resistance
Dispersant showing a strong hydrophobic character
Very high PVC Paints
binder not sufficient to encircle mineral particles
hydrophobic dispersant increase the water resistance
2 000 cycles 10 000 cycles
Matt paint PVC = 77%
with Coadis™ 123K
22
From Rheology to Paint
Mechanisms
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From Rheology to Paint: Mechanisms - Dispersion
Repulsive energy between particles prevents agglomeration and sedimentation
d
E
dc
In can long term pigment stabilization Prevents flocculation and
acceleration of settling
Stabilization by adsorption of a polyelectrolyte dispersant
24
From Rheology to Paint: Mechanisms - Thickening
ASE (Alkali Swellable Emulsion) acrylic polymers in water emulsion
Neutralization of the acid groups using an alkali to get the polymer soluble in water
Resulting anionic groups trap water molecules in hydrodynamic volumes of entangled polymers by hydrogen bonds, generating a gel
Low shear viscosity get increased
Carboxylate groups
Acrylic chain
C O-
O
O H
H Hydrogen bonds
25
From Rheology to Paint: Mechanisms - Thickening
HASE (Hydrophobically modified Alkali Swellable Emulsion) acrylic polymers with hydrophobic monomers in water emulsion
Interaction with the binder + gelling effect : both increase viscosities
Add increased response at medium and high shear rates
Carboxylate groups
Acrylic chain
O H
H
C O-
O
Hydrogen bonds
Hydrophobic monomer
Binder Associative interaction
26
From Rheology to Paint: Mechanisms - Thickening
HEUR (Hydrophobic Ethoxylated URethane) polymers with a hydrophilic core grafted at both ends with hydrophobic groups of well selected size/shape by a urethane bond
Thickening is obtained at:
• high shear rates through the associative mechanism
• low shear rates through the association mechanism
Hydrophilic backbone
PEG
Urethane link
Linear hydrophobic end group
Branched hydrophobic end group
27
From Rheology to Paint: Mechanisms - Thickening
ASSOCIATIVE HASE or HEUR
viscosity at high shear rate.
Hydrophobic chains react with binder’s particles by adsorption at their surface or by ion-dipole interaction
The created bonds generate a given resistance against higher shear stress
Hydrophobic chains
Binder Associative interaction
28
From Rheology to Paint: Mechanisms - Thickening
ASSOCIATION HASE or HEUR
viscosity at low shear rate
Well selected hydrophobic end groups contribute to form a hydrophobic network
structuring the aqueous system and boost viscosities at low shear rate
This network is intended to break up temporarily under prolonged shear and to form
again after a given rest time, generating a real thixotropic effect
Association mechanism
29
From Rheology to Paint
Viscosity - Definition
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From Rheology to Paint: Viscosity - Definition
Pure substance based liquids show a Newtonian rheological behavior. Formulations are made
of a blend of liquids, organic and mineral solids and do not follow a single or simple rheological model. The viscosity of formulations depends on the applied shear stress or the
resulting shear rate
Viscosity is the measurement of a resistance to flow
η = shear stress / shear rate = (F/A) / (V/d)
The measurement of viscosity for a given paint is therefore determined by setting either a
shear stress value or a shear rate value
The minimum stress needed to initiate flow is called yield point
FilmThickness
A : Area [m2]
Liquid Layer d
Shear stress = F / A [N.m-2]
F : Force[N]
Liquid Layer d
Shear rate = V / d [s-1]
V : Velocity[m.s-1]
31
From Rheology to Paint
Rheology profiles
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From Rheology to Paint: Rheology profiles
Newtonian profile:
Viscosity independent of shear rate
Typically pure substances such as water
Varnishes, lacquers and gloss paints should ideally exhibit a Newtonian-like rheology profile to enhance application properties such as brushability at application and flow & leveling
33
From Rheology to Paint: Rheology profiles
Dilatant or shear thickening profile:
Viscosity increases as the shear rate increases
This behavior should be avoided as it will give problems either at the paint manufacturing or at the paint use
34
From Rheology to Paint: Rheology profiles
Pseudoplastic or shear thinning profile:
Viscosity decreases as the shear rate increases
Waterborne formulations naturally tend to exhibit a pseudoplastic type rheology profile that should be properly tuned with the use of appropriate thickeners
35
From Rheology to Paint: Rheology profiles
Thixotropic behavior:
This behavior depends on shear duration, which induces a temporary decrease in viscosity
Viscosity recovers its initial value once shear has stopped after a period of time that depends on the intensity and duration of shear
36
From Rheology to Paint
Shear rates and Paint Properties
37
From Rheology to Paint: Shear rates and Paint
Properties Many properties are correlated with viscosity measurements at the various shear rates applicable to paint
Good storage stability and good sag resistance viscosity at very low shear rate
Rate of loading of application tools - brush or spatula viscosity at low shear rate
Feeling at hand stirring at can opening viscosity at medium shear rate
Dynamic properties during application - brush, roller, spray gun – spread ability, film build, spatter resistance viscosity at high shear rate
38
From Rheology to Paint
Shear rates and Viscosimeters
39
From Rheology to Paint: Shear rates and
Viscosimeters Viscosity is measured the most simply using a viscosimeter
Rheological properties measurements depend on time, temperature and stress Taking into account these factors can require a rheometer rather than a viscosimeter
Depending on the shear conditions, different types of viscosimeters and different methods will be chosen to measure and interpret the behavior of the system under consideration
Description of the most widely used viscosimeters in the paint and coating industry are below, as well as the shear ranges to which they are best suited
40
From Rheology to Paint: Shear rates and
Viscosimeters
Brookfield viscosimeter:
Typically used in Quality Control
Rheology at low shear rates
Rotation viscosimeter
Measurement is obtained from the rotation of a spindle immersed in a liquid at a given and adjustable speed (“shear rate” controlled)
The spindle is connected by its shaft to a calibrated spring whose torsion rate is proportional to the measured shear stress
The shear potential will vary on the basis of the size of the spindle and the rotation speed UnitsUnits:
mPa.s12000
10rpm
41
From Rheology to Paint: Shear rates and
Viscosimeters
Stormer or Krebs viscosimeter:
Rotational viscosimeter widely used in the paint industry
Viscosity at medium shear rate
The viscosity is determined by measuring the torque needed to achieve a rotation speed of 200 rotations per minute.
Viscosity value expressed in Krebs Unit (KU).
This measurement is used extensively to evaluate paint applied with a brush or a roller.
105105
StormerViscosimeter
Units: Krebs (KU)
StormerViscosimeter
Units: Krebs (KU)
42
From Rheology to Paint: Shear rates and
Viscosimeters
Cone & Plate or ICI viscosimeter:
Viscosity at high shear rate
Easiest method to evaluate film build and spatter resistance
Cone with a 0.5° angle in direct contact with the lower plate
Evaluation of the torque needed to obtain the rotation speed generating a shear rate of 10000 s-1 and covering viscosities ranging from 0 to 0.5 Pa.s
High ICI viscosity values film build spatter resistance ease of application surface covered between two tool loadings
Cone and plate
43
From Rheology to Paint
Conclusion
44
From Rheology to Paint: Key points
45
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