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COATING COATING RHEOLOGYRHEOLOGY

Werner Blank, R. Berndlmaier &D. MillerKing Industries &Ray Fernando Air Products

wblank@kingindustries.comwww.wernerblank.com

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What is RheologyHow to Measure Rheology Importance of Rheology on Paint ApplicationsLimitations of Rheology Measurements

Rheology

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Coating Rheology - OutlineCoating Rheology - Outline Rheological Properties of Rheological Properties of

CoatingsCoatings Effect of Rheological Effect of Rheological

Properties on Coating ProcessProperties on Coating Process Effect of Coating Variables on Effect of Coating Variables on

RheologyRheology Limitations of Rheology Limitations of Rheology

MeasurementsMeasurements How to modify RheologyHow to modify Rheology

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Why is Rheology Important for a PaintMixing

Pigment DispersionPumping

Storage Settling

ApplicationSprayDipFlow coatRoller coatBrush

Film formationFlow and levelingCoalescence

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What is Rheology ?

Flow of Liquids - Viscosity - Resistance to flow

Science of Deformation and Flow

Shear Rate is Velocity Gradient = (V

1

-V

0

)/d [ s

-

1

]Shear Stress = F/A [N cm

-2

]

Velocity = V

0

dVelocity = V

1

A - Area

F - Force

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Newtonian FluidsNewtonian FluidsSh

ear S

tress

, Pa

Visc

osity

, Pa s

Shear Rate, s

-1

Shear Rate, s

-1

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Non-Newtonian Viscosity Non-Newtonian Viscosity BehaviorBehavior

Bingham

Plastic

PseudoplasticNewtonianDilatant

Shear Thinning

Shear Thickening

"Yield"

YieldStress

Shear Rate, s

-1

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Shear Rates for Various Sub-ProcessesShear Rates for Various Sub-Processes

10

-2

10

-1

10

0

10

+1

10

+2

10

+3

10

+4

10

+5

10

+6

log

(Vis

cosi

ty)

log (Shear Rate (s

-1

))

Settling

WickingMixing

(Slurries) RollCoating

SprayCoating

Sag & Leveling

Brush/RollPick Up

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pigment anti-settling

spray applications, sag

roll, dip, flow and brush applications

flow and press applications

Vis

cosi

ty η

Shear Rate s-1

RHEOLOGY PROFILE

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Common Viscosity Measurement Common Viscosity Measurement MethodsMethods

Cup Methods [Zahn]Spindle Methods

[Brookfield]

Paddle Methods[Stormer]

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Rotational RheometersRotational Rheometers

ParallelPlate

ConcentricCylinder

Cone andPlate

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Viscosity Units

Name Test Methods UnitsGardner-Holdt Bubble ArbitraryZahn, Ford Cup SecondsBrookfield Spindle PoiseStormer Paddle Krebbs KUCapillary Flow Stokes, Sec.

ICI Cone-Plate PoiseRheometer Cone-Plate Poise

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Viscosity: UnitsThe units of Viscosity are: Pascal.second [Pa.s] in SI, Poise in CGS

1 poise = 100 centipoise (cps) 1 poise = 0.1 Pa·sec 1 poise = 0.0671969 lb/(ft·sec) 1 poise = 4.031814 lb/(ft·min)

Pa = Pascal = N·m

-2

pressure, stress

N = Newton = m ·kg ·s

-2

force

η (poise)stoke = ρ (g/cm

3

)

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Non-Newtonian Viscosity BehaviorNon-Newtonian Viscosity Behavior

RPM Viscosity (cps) Spindle #0.5 8000 41 5000 "

2.5 2560 "5 1520 "10 1000 "20 550 250 316 "100 227 "

Brookfield Viscosities @ Different RPMsWaterborne Coating

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Limitation in Single-Point Viscosity Limitation in Single-Point Viscosity MeasurementsMeasurements

log

(Vis

cosi

ty)

log (Shear Rate)

Brookfield Single RPM Viscosity

In Formula Development this behavior must be knownIn Formula Development this behavior must be knownbefore defining production viscosity specsbefore defining production viscosity specs

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Flow PatternsFlow Patterns

Velocity = 0

Velocity = V

Laminar Flow Laminar Flow

Turbulent FlowTurbulent Flow

EddiesEddies

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Impact of Rheology on Flow PatternImpact of Rheology on Flow Pattern

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Orifice Viscometers (Viscosity Cups)Orifice Viscometers (Viscosity Cups)

η (poise)ν (stoke) = ρ (g/cm

3

)

For low viscosity (<10cps)Kinetic Energy Correctioncan be as high as 90%

Not Suitable for non-Newtonian Fluids

Temperature !

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Type of ViscosityShear Rate (γ ) sec-1

0.01 0.1 1.0 10 100 1000 10,000 Sag, Leveling Pumping, Mixing,

Pouring Dispersing

Particle Suspension

Dipping, Flow Coating

Roller

Spraying and

Brushing

Brookfield Stormer ICI Efflux Cup

Controlled Stress Rheometer

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Viscosities of Common MaterialsViscosities of Common Materials

Viscosity (cps) ConsistencyAir 1.00E-03 Gaseous

Water 1.00E+00 FluidOlive Oil 1.00E+02 LiquidGlycerine 1.00E+03 Liquid

Golden Syrup 1.00E+05 Thick FluidPolymer Melts 1.0E+05 - 1.0E09 Toffee-Like

Pitch 1.00E+12 StiffGlass 1.00E+24 Rigid

1000 cps = 10 poise = 1 Pa s

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GRINDING & DISPERSION

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GRINDING-DISPERSION EQUIPMENT

THREE ROLLER MILL

BALL MILL

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SAND MILL DISPERSER

4000 ft/min.2000 ft/min

V/U ratio Fractional pigment vol./ultimate pigment vol.

MILLBASE FORMULATION

0.1

1

10

100

0 0.2 0.4 0.6 0.8 1V/U

VIS

CO

SIT

Y M

ILLB

AS

E, P

OIS

E

Three roll mill High speed disperser Ball millSand mill Kinetic dispersion

PIGMENT PARTICLES

Flocculation

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PIGMENT PARTICLES

Dispersed

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0.001

0.01

0.1

1

10

100

cm

0.1 1 10 PARTICLE SIZE, micron

1 10 100

PIGMENT SETTLING24 hours

POISE

Pigment 3.0 g/cm3

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APPLICATION PROCESSBRUSHSPRAY

AIRLESSELECTROSTATIC, BELL, DISKHVLP GunsPOWDER

DIP - FLOW COATINGFLUIDICED BED

CURTAIN COATINGROLLER COATING

DIRECT - REVERSEKNIFE COATINGELECTROCOATING

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Brush Application

Shear thinning-easy brushinglow resistance

Flow and Leveling - recoverySagging - high low shear viscosityOpen time - lapping Settling - thixotropic

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Brush Applications

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Viscosity - DefinitionViscosity - Definition

Shear Rate is Velocity Gradient = (V

1

-V

0

)/d [ s

-

1

]Shear Stress = F/A [N cm

-2

]

Velocity = V

0

dVelocity = V

1

A - Area

F - Force

Viscosity = Shear Stress / Shear Rate [Pa s]

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What Effects Spray PerformanceWhat Effects Spray Performance

Paint Viscosity (Elongational)Surface tension

Shear thinning ThixotropyPseudo plastic flow

Solvent evaporationThixotropySaggingFlow and Leveling

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Application SprayFormation of droplets by surface tension

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Application Spray

Extension of the coating film

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SpraySpray RheologyRheology Primary Mode of Deformation in Spray is Extensional,

not Shear Coating Ligaments are stretched and disintegrated

in to droplets in the spray process

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Shear & Extensional ViscositiesShear & Extensional Viscosities

V

0

dV

1

A - AreaA - Area

F - ForceF - Force

Shear Viscosity[Pa s]= Shear Stress Shear Rate

A - AreaA - Area

F - ForceF - ForceV

0

Extensional Viscosity = Extensional Stress Extension Rate

For Simple (Newtonian) Fluids,Extensional Viscosity (EV) = 3 x Shear Viscosity(SV)For Complex Fluids, EV can be as high as 10000 x SV

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Vacuum

ELONGATIONAL VISCOSITY

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ELONGATIONAL VISCOSITY

Contraction Flow

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ROLLER COATING

Direct Roller CoatingReverse Roller Coating

Roller pick upRibbon FormationMisting and Spattering Flow-Out and Leveling

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Cavitation

Misting

Application Roll

Substrate

Coating ApplicationCoating Application

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43

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Higher Viscosity Hinders Flow and LevelingHigher Viscosity Hinders Flow and Leveling

Coating Viscosity Decreases

Leveling

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Coating LevelingCoating Levelingλ

γ = dynes/cm

χ

∆t =log (α0/αt)λ

4η

226γχ3

α

46

0

10

20

30

40

50

60

SE

CO

ND

S

0

10

20

30

40

50

60

MIN

UT

ES

1E0 1E1 1E2 1E3 1E4 1E5POISE

LEVELING TIMEVISCOSITY

α

γ= 0.5 µ

= 30dyn/cm χ = 50 µ

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0

10

20

30

40

50

60

MIN

UT

ES

0

10

20

30

40

50

60

SE

CO

ND

S

1E0 1E1 1E2 1E3FILM THICKNESS, micron

LEVELING TIMEVISCOSITY

η = 100 POISE

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SAGGING

ρgχ2

2ηυ =

υg = 980 cm/sec2

χ

ρ = g/cm3

η = Poise

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1E-4

1E-3

1E-2

1E-1

1E0

1E1

1E2

1E3S

AG

GIN

G c

m/1

0 m

in.

1 10 100 1000 10000 VISCOSITY, POISE

25 50 100 200 500

SAGGING

micron

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Effect of Coating Variables on Rheology Effect of Coating Variables on Rheology (Structure / Property Relationships)(Structure / Property Relationships)

Effect of Coating Ingredients Binders (Solutions Vs Dispersions) Pigments & Fillers Dispersants & Surfactants Rheology Modifiers

Coating Rheology Customization Criteria for Rheology Modifier

Selection Criteria for Other Additives Selection

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1

10

100 V

ISC

OS

ITY

, P

OIS

E

1E0 1E1 1E2 1E3 1E4 1E5 1E6SHEAR RATE sec-¹

VISCOSITY POLYMER SOLUTION

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log η T =13 - 17.44(T-Tg)

51.6+(T-Tg)

WLF Equation

Tgs = Co - C1 x Ws

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1E-1

1E0

1E1

1E2

1E3

1E4

1E5

1E6

VIS

CO

SIT

Y,

PO

ISE

0 20 40 60 80 100 TEMPERATURE C

VISCOSITY as a FUNCTION OF TgWILLIAMS,LANDEL,FERRY EQUATION

Tg of polymer17

7

-13

-33-53

-73

SL1513bw

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-1

1

3

5 V

ISC

OS

ITY

, L

OG

PO

ISE

, 2

5°C

0 0.1 0.2 0.3 0.4 WEIGHT FRACTION OF SOLVENT

METHANOL WATER ACETONE BU ACETATE

VISCOSITY OF K-FLEX UD-320-100

SL1507

Tgs = C0 - C1 x WsC0 = 243.9C1 = 365 MethanolC1 = 339 WaterC1 = 320 AcetoneC1 =239 Bu-acetate

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PACKING OF SPHERES

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Effect of Dispersed Coating Effect of Dispersed Coating IngredientsIngredients

“Vis

cosi

ty”

% Volume Solids 66

For Random Packing, For Random Packing, Critical Volume Fraction - Critical Volume Fraction -

0.660.66

Cubic PackingCritical Volume

Fraction - 0.5236

Tetrahedral Packing

Critical VolumeFraction - 0.7405

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1E-1

1E0

1E1

1E2

1E3

VIS

CO

SIT

Y

0 0.1 0.2 0.3 0.4 0.5 VOLUME FRACTION

SPHERE SPH SW SPH FLOC

VISCOSITY OF DISPERSION

SL2094

Continous phase

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1

10

100

VIS

CO

SIT

Y,

PO

ISE

1E0 1E1 1E2 1E3 1E4 1E5 1E6SHEAR RATE sec-¹

45 % 47 % 50 %

VISCOSITY DISPERSIONShear thickening

PHASE VOLUME

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RHEOLOGY CONTROL SOLVENT BORNE COATINGS

EFFECT OF RHEOLOGY CONTROLSAGGINGPIGMENT SETTLINGFLOW LEVELINGINTERCOAT ADHESION FLOATING AND FLOODINGGLOSSSEEDING

EFFECTIVENESS POLARITY SOLVENTDISPERSION PROCESSTEMPERATURE RESIN COMPOSITION

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1E2

1E3

1E4

1E5

VIS

CO

SIT

Y,

CP

S

0.001 0.01 0.1 1 10 100 TIME, MINUTES

VISCOSITY PROFILESPRAY PAINT

SPRAY FLASH OFFCURE

Sag ResistanceSag Resistance

ATTAPULGITE SMECTITE ORGANO CLAY ORGANO

SULFONATE SILICA TITANATE

POLYOLEFIN ASSOCIATIVE POLYESTER POLYACRYLATE POLYAMIDE CASTOR DERIVATIVE POLYUREA

RHEOLOGY MODIFIERRHEOLOGY MODIFIER

SEPARATE PHASE - ASSOCIATION

Micrographics

Organo Clay - Platelet StructureHydrogen Bonding

Polyamide - 3D Branching

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Inorganic Rheology Modifiers Inorganic Rheology Modifiers (Thickeners)(Thickeners)

Inorganic

Ultra-Fine Clays(Laponites)

Other Inorganics(Bentonite, Attapulgite)

++

_ _ _ _ Positive Edges & NegativePositive Edges & NegativeFacesFaces

Weak Structure, HighlyWeak Structure, HighlyShear ThinningShear Thinning

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SHEAR THINNING

THIXOTROPE PSEUDOPLASTIC

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ThixotropyThixotropyV

isco

sity

Shear RateThixotropy can increase viscosity measurement error

Vis

cosi

ty

Time

Settling at 140°FPolyamide Hydrogenated

Castor

Thixotropes - Incorporation Organo-Clay

Milled with pigments -- Moisture in platelets Fumed Silica

Added during letdown Hydrogenated Castor Wax

Heat activated in mill stage--mix while cooling Polyamide

Heat activated in mill stage--mix while cooling Or -- Preactivated added during letdown

High Solids Epoxy/PolyamideMarine Primer

Polyamide Component Thixotrope 10 Polyamide adduct 300 Polyamide 35 Titanium dioxide 100 Talc 414 Yellow iron oxide 20 Phthalocyanine blue 1 Butyl alcohol 252

Epoxy Component Thixotrope 15 Bis A epoxy 500 Talc 286 Hydrous kaolin clay 150 Naphtha 200

Orientation of Particles

PolyamideOrganoclay

Oil Modified UrethaneSilica Flatting Agent

Silica Agglomerates

Areasof higher gloss!

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RHEOLOGY FOR WATERBORNE COATINGS

CELLULOSE DERIVATIVES Hydroxyethyl celluloseCarboxymethyl celluloseMethyl cellulose

CARBOXYL FUNCTIONAL ACRYLICASSOCIATIVE THICKENER

HEUR (PEO-hydrophob) HASE (Acrylic- Hydrophob) HMHEC

POLYAMIDES

INORGANICSynthetic ClaysColloidal Silica

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Brush Applications

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BRUSH APPLICATION

SETTLING THIXOTROPYLOW RESISTANCE TO BRUSHING HSVGOOD FILM THICKNESS AND HIDING POWER HSV/HSVNOT SAGGING LSVFLOW AND LEVELING LSV

LSV = LOW SHEAR VISCOSITYHSV = HIGH SHEAR VISCOSITY

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Extensional Viscosities of Waterborne Extensional Viscosities of Waterborne Latex PaintsLatex Paints

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Organic Rheology Modifiers Organic Rheology Modifiers (Cellulosics)(Cellulosics)

R = -CH2CH2OH = HydroxyethylR = -CH2COONa = CarboxymethylR = - C2H5, -CH2CH2OH,= Ethyl, HydroxyethylR = - CH3, -CH2CH2OH,= Methyl, Hydroxyethyl

Natrosol 250 HRMS - 2.5; M

v

-715,000;

Average EO Length - 4 (Longest 10)

OCH2

OR

OHO

HOR

H

H

H

( )n

Hydroxyethyl Cellulose

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Effect of Molecular Weight on ThickeningEffect of Molecular Weight on Thickening

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Cellulosics -Thickening MechanismsCellulosics -Thickening Mechanisms

A. Contribution to Hydrodynamic Volume

B. Chain Entanglements

Visc

osity

Molecular Weight

LSV

HSV

(Croll & Kleinlein, 1986)

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Cellulosics - Thickening MechanismsCellulosics - Thickening Mechanisms

C. Depletion Flocculation (Asakura & Oosawa, 1958; Sperry et al., 1981)

Lower Entropy Higher EntropyWhen Interparticle Distance Approaches WSP Molecular DimensionsThere is a Loss of Conformational Degrees of Freedom

G = H - T S

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Cellulosics - Advantages & Cellulosics - Advantages & DisadvantagesDisadvantages

Cellulosics Low Cost Thickeners Poor Leveling (High LSV; Yield Stress) Reduction of Gloss (Depletion Flocculation;

Poor Leveling) Roller Spatter (Extensional Viscosity) Water Sensitivity (WSP Hydrophilicity) Bio-degradation (Enzyme Attack on beta 1-4

Linkage) Syneresis (Depletion Flocculation)

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Associative ThickenersAssociative Thickeners

HEUR (Hydrophobically-Modified Ethoxylated Urethanes)

HASE (Hydrophobically-Modified Alkali-Swellable Emulsions)

HEURASE HMHEC (Hydrophobically-Modified HEC)

Several Different Types Currently in the Market

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R-N-C-(O-CH

2

-CH

2

)

x

-[O-C-N-R”-N-C-(O-CH

2

-CH

2

)

x

]

n

-O-C-N-R’

= O

= O = O

= O

----

H H H H

R, R’ = C

12

-C

18

; R” = C

7

-C

36

; x = 90 - 455; n = 1-4

Associative Thickeners - HEUR TypeAssociative Thickeners - HEUR Type

Acrysol QR-708 Acrysol RM-8 Acrysol RM-825(C

12

H

25

Terminal Hydrophobes; 40,000 Approx.. M.W.)

Acrysol RM-2020UCAR SCT-275 Acrysol SCT-275

(Comb-type; 120,000 Approx.. M.W.)

K-STAY 700

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Associative Thickeners - HASE TypeAssociative Thickeners - HASE Type

Acrysol TT-615Alkali-Swellable, Associative

Thickener Dispersion at “High” Concentration (30%)

(-CH

2

-C-) (-CH

2

-CH-) (-CH

2

-C-)CH

3

CH

3

C=O C=O C=OOH OC

2

H

5

OCH

2

CH

2

O (

(

20

C

18

H

37

As pH increases

K-STAY 800

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Associative Thickeners - Associative Thickeners - HEUR Association ModesHEUR Association Modes

Many Association Modes PossibleDepending on Molecular Architecture

Adsorption Hydrophobic Ion-Dipole

Self Association Intra-Molecular Inter-Molecular

Mix Micelle Formation

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Sensitivity of Associative ThickenersSensitivity of Associative Thickeners

Latex Particle Surface Characteristics

Surfactants Dispersants Cosolvents

Performance Sensitivity

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Viscosities of Aqueous Thickener Viscosities of Aqueous Thickener SolutionsSolutions

10 -2 10 -1 100 101 10 2103

10 -1

100

101

102

Rate [s -1]

E

ta (A

)

[P

]

Aqueous Thickener Solutions

Natrosol 250HR 1.0%

HASE TT-935 1.0%

HEUR SCT-275 1.0%

HASE RM2020 4.0%

ACRYLIC EMULSIONLeafing Aluminum Flake Pigment

8 microns 49 DAYS

No additive Polyamide 607 Polyamide 610

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SUMMARY

RHEOLOGY IS IMPORTANTPREPARATIONAPPLICATIONFILM FORMATIONSTORAGE

ADDITIVES CAN CONTROL RHEOLOGY

RHEOLOGY CAN BE MEASURED NOT ALL MEASUREMENTS ARE MEANINGFUL

WE STILL HAVE TO RELY ON APPLICATION TESTS

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REFERENCES:

Paint Flow and Pigment Dispersion T. C. Patton, Wiley Interscience

Dynamics of Polymeric Liquids, Fluid MechanicsR. B. Bird, Wiley Interscience

Fluid Engineering Fundamentals http://www.efm.leeds.ac.uk/

A Handbook of Elementary Rheology Howard A. Barnes

Introduction to Rheology Barnes, Hutton & Walters