Formulating High-Performance Waterborne Epoxy Coatings

Presented at a meeting of the Thermoset Resin Formulators Association

Hyatt Regency MontréalSeptember 11-12, 2006

M.J. Watkins, D.J. Weinmann, J.D. Elmore

Mythbusters

“Waterborne epoxy coatings can never match theperformance of solvent based systems”

Myth #1

Myth #2

“I know how to formulate other waterborne systems,So I can use all my current tricks and additives to formulate waterborne epoxies”

“Devil is in the Details”(and the details are in the paper)

This presentation will

1. Define achievable high performance

2. Outline general formulation techniques

Please see paper for specific recommendations

Topics

• Waterborne epoxy types

• Type 5 waterborne epoxy performance

• Stoichiometry effects

• Pot life issues

• Components (cosolvents, pigments, additives, etc.)

• Dispersing pigments

• Pigment selection

Waterborne Epoxy Types

Best Performance Non-ionic aqueous dispersions Solid resin dispersions

Primers and topcoats

Amine dispersionSolid epoxy dispersion

5

Flooring, masonry coatings

Amine dispersionLiquid or liquid

emulsion4

Low yellowing topcoats

Carboxy-functional acrylic dispersion

Liquid or solid emulsion

3

Light – to medium-duty metal primers

Water soluble amine

Solid dispersion2

Flooring, masonry coatings

Water soluble amine

Liquid or liquid emulsion

1

Typical ApplicationCuring Agent FormResin FormType

Primers and topcoats

Amine dispersionSolid epoxy dispersion

5

Flooring, masonry coatings

Amine dispersionLiquid or liquid

emulsion4

Low yellowing topcoats

Carboxy-functional acrylic dispersion

Liquid or solid emulsion

3

Light – to medium-duty metal primers

Water soluble amine

Solid dispersion2

Flooring, masonry coatings

Water soluble amine

Liquid or liquid emulsion

1

Typical ApplicationCuring Agent FormResin FormType

Type 5 Epoxy Resin DispersionType 5 Epoxy Resin Dispersion

* Brookfield, #5 spindle, 20 rpm, 25 °C.

Name:Name: EPI-REZ 6520-EPI-REZ 6520-WH-53WH-53Description: Modified 1001-Description: Modified 1001-typetypeEEW, g/eq, solids:EEW, g/eq, solids: 550 550Viscosity, cP*:Viscosity, cP*: << 3000 3000Solids, % weight:Solids, % weight: 53.0 53.0Lb./Gal:Lb./Gal: 9.0 9.0VOC Cosolvent:VOC Cosolvent: PM (<4%) PM (<4%)

Type 5 Curing Agent Type 5 Curing Agent DispersionDispersion

* Brookfield, #5 spindle, 20 rpm, 25 °C.

Name:Name: EPIKURE 6870-W-53EPIKURE 6870-W-53Description: Description: Modified polyamine Modified polyamine adductadductAHEW, g/eq, solids:AHEW, g/eq, solids: 225 225Viscosity, cP*:Viscosity, cP*: 8,000 8,000Solids, % weight:Solids, % weight: 53 53Lb./Gal:Lb./Gal: 9.1 9.1VOC Solvent:VOC Solvent: None None

Performance of White Enamels

Discernable End Discernable End PotlifePotlife

20

30

40

50

60

70

80

90

100

110

120

0 1 2 3 4 5 6Time, hours, After Mixing A + B

Vis

cosi

ty,

KU

/ 6

0° G

loss

Val

ue

60° Gloss

Viscosity

Semi-Gel

2000 Hour Salt Spray

3 mils DFT on cold-rolled steel

SB epoxy / polyamide Type 5 WB system

Epoxy / Amine Ratio Effects on Performance(Stoichiometry)

Higher epoxy level gave improved:

Higher curing agent level gave improved:

Pot life Cure rate

Acid resistance Gloss

Alkali resistance Adhesion

Water resistance Abrasion resistance

Humidity resistance Solvent resistance

Corrosion resistance Stain resistance

Wat

er I

mm

ers

ion

, hrs

.

J

J

J

J

0

200

400

600

800

1000

1200

IncreasingAmine:Epoxy Weight Ratio

(Solids Basis)

JJ

J

J

0

200

400

600

800

1000

1200

Sal

t S

pra

y, h

rs.

IncreasingAmine:Epoxy Weight Ratio

(Solids Basis)

Wat

er I

mm

ers

ion

, hrs

.

J

J

J

J

0

200

400

600

800

1000

1200

IncreasingAmine:Epoxy Weight Ratio

(Solids Basis)

JJ

J

J

0

200

400

600

800

1000

1200

Sal

t S

pra

y, h

rs.

IncreasingAmine:Epoxy Weight Ratio

(Solids Basis)

Effects of Epoxy/Curing Agent Effects of Epoxy/Curing Agent RatioRatio

Pen

cil

Har

dn

ess

ME

K D

ou

ble

Ru

bs

J

J

J J

B

B

BB

<6B

5B

3B

B

F

2H

J 2 Week Cure

B 24 Hour CureJ

J

J

J

0

40

80

120

160

200

240

IncreasingAmine:Epoxy Weight Ratio

(Solids Basis)

IncreasingAmine:Epoxy Weight Ratio

(Solids Basis)

Pen

cil

Har

dn

ess

ME

K D

ou

ble

Ru

bs

J

J

J J

B

B

BB

<6B

5B

3B

B

F

2H

J 2 Week Cure

B 24 Hour CureJ

J

J

J

0

40

80

120

160

200

240

IncreasingAmine:Epoxy Weight Ratio

(Solids Basis)

IncreasingAmine:Epoxy Weight Ratio

(Solids Basis)

Effects of Epoxy/Curing Agent Effects of Epoxy/Curing Agent RatioRatio

Pot Life Pot Life CharacterizationCharacterization

End of Pot LifeEnd of Pot LifeViscosity Increase Above Application LimitViscosity Increase Above Application LimitSignificant Change in Gloss (10 Units Lower at Significant Change in Gloss (10 Units Lower at

60°)60°)Decrease or Loss of Cure (Hardness)Decrease or Loss of Cure (Hardness)

Factors Affecting Pot LifeFactors Affecting Pot Life

Cosolvents

Functions• Coalescing aids• Freeze-thaw stabilizers• Leveling agents• Pigment wetters• Foam control

Performance Effects• Dry time• Gloss• Hardness development• Final film properties

• Glycol ethers are most versatile

- Ethylene glycol ethers are suitable

- Propylene glycol ethers are preferred for non-HAP status

• Diacetone alcohol can be useful

• Partition between water and resin phases- Slow and dynamic process

Cosolvents

Cosolvents

Others – see paper for details

• Alcohols

• Aromatics

• Ketones

• Glycol ether acetates

Cosolvent Cosolvent SelectionSelection(based on results with Type 5)(based on results with Type 5)

8

8.5

9

9.5

10

10.5

11

11.5

12

12.5

100 125 150 175 200 225 250 275 300

To

tal H

anse

n S

olu

bili

ty P

aram

eter

, cg

s u

nit

s

DPNP

DPTB

EM

EE

EH

EEH

DM DE

DPDB

Boiling Point, °C

DPNBTPNB

PPh

PM

PE

PNP

PTB PNB

DPMEB

EP

Poor Coalescing

Good Coalescing

TPM

MnAK

DAA

Freeze-Thaw Resistance

Adding glycol ethers and/or alcohols

• Reduces freezing point

• Promotes recovery of frozen material

• 25-30%v of total volatiles provides

resistance to 1-3 Cycles

• Examples: ethylene glycol monopropyl

ether (EP), or methanol

• 1:1 blend of DAA / PnB (Type 5 )

Liquid Resins as Alternative Coalescing Aids

• Increase solids

• Decrease VOC

• Increase gloss

• Liquid aromatic epoxy resin (e.g. EPON™ 828)

• Liquid aliphatic epoxy resin (e.g EPONEX™ 1510)

• Glycidyl neodecanoate (e.g. Cardura™ E10P)- Low viscosity – easy to disperse in W/B epoxy - Best performance- Improved leveling and gloss- Improved mar and early water resistance

Coalescence Coalescence PropertiesProperties

2 µm

Type 2 SystemAvg. surface roughness = 25X

Type 5 SystemAvg. surface roughness = 1.25X

SB EpoxyAvg. surface roughness = 1X

DefoamersDefoamers

Suppress Foam Generation During Suppress Foam Generation During Manufacturing, Filling, Tinting, and ApplicationManufacturing, Filling, Tinting, and Application

Selection ConsiderationsSelection Considerations– Empirically determinedEmpirically determined– Optimize level (avoid stability & application Optimize level (avoid stability & application

problems)problems)– Must remain active for desired shelf life Must remain active for desired shelf life – Most effective if portion added to grind & remainder Most effective if portion added to grind & remainder

to letdownto letdown– Required level is approximately 0.5% of paint volumeRequired level is approximately 0.5% of paint volume

DefoamersDefoamers

Useful Generic TypesUseful Generic TypesSilicone BasedSilicone Based Oil BasedOil Based

Possible Problems Due to Improper Choice Possible Problems Due to Improper Choice or High Use Levelsor High Use Levels

Pigment flocculationPigment flocculation IncompatibilityIncompatibility

Poor Color acceptancePoor Color acceptance Cratering (fish eyes)Cratering (fish eyes)

Poor inter-coat adhesionPoor inter-coat adhesion Water sensitivityWater sensitivity

Cure Catalysts/AcceleratorsCure Catalysts/Accelerators

Positive functionsPositive functions– Decrease time to achieve Decrease time to achieve

desired hardnessdesired hardness– Improves early solvent Improves early solvent

resistanceresistance Negative functionsNegative functions

– Shortens pot lifeShortens pot life– Decrease water & acid Decrease water & acid

resistanceresistance Most effectiveMost effective

– Tertiary Amines such as 2,4,6-Tertiary Amines such as 2,4,6-Tris(Dimethylaminoethyl)PhenTris(Dimethylaminoethyl)Phenolol

Effect of an Accelerator on Effect of an Accelerator on the Hardness Developmentthe Hardness Development

J

J

J J

B

B

B

B

<6B

5B

3B

B

F

2H

0 24 48 72

Time, Hours, After Coating

J Accelerated Control

B Control

Pen

cil H

ard

nes

s

Flash Rust Flash Rust InhibitorsInhibitors

• Occurs on ferrous substrates under high relative humidityOccurs on ferrous substrates under high relative humidity

• Effectiveness depends on % solids. Adding water can Effectiveness depends on % solids. Adding water can

reduce effectiveness.reduce effectiveness.

• Nitrite salts (Ca or K salts preferred). Nitrite salts (Ca or K salts preferred). • Several common inhibitors ineffective or incompatibleSeveral common inhibitors ineffective or incompatible

lead naphthanate lead naphthanate chromates or dichromates chromates or dichromates tertiary amines tertiary amines

• Use in curing component for stabilityUse in curing component for stability

• Minimize levels to avoid water sensitivityMinimize levels to avoid water sensitivity

Adhesion PromotersAdhesion Promoters

BenefitsBenefits– Improved substrate wetting and adhesionImproved substrate wetting and adhesion

Especially galvanized steel, cold rolled steel, and aluminumEspecially galvanized steel, cold rolled steel, and aluminum Less effective on blasted or phosphated steelLess effective on blasted or phosphated steel

– Faster cure & hardness developmentFaster cure & hardness development– Incorporate in epoxy during pigment grindIncorporate in epoxy during pigment grind– Improved corrosion resistanceImproved corrosion resistance

Chemical Structure is ImportantChemical Structure is Important– Use Use EpoxyEpoxy-functional, -functional, triethoxytriethoxy- or - or diethoxymethyldiethoxymethyl- silanes for - silanes for

best shelf stability. best shelf stability. – Aminosilanes contribute to yellowingAminosilanes contribute to yellowing– Methoxysilanes hydrolyze and give poor adhesionMethoxysilanes hydrolyze and give poor adhesion

Mar and Slip Mar and Slip AgentsAgents

May Improve Abrasion Resistance and May Improve Abrasion Resistance and Early Water ResistanceEarly Water Resistance

Useful TypesUseful Types– PolydimethylsiloxanesPolydimethylsiloxanes– Wax DispersionsWax Dispersions– Micronized Polyethylene DispersionsMicronized Polyethylene Dispersions– SiliconesSilicones

Fungicides and Mildewcides

• Generally not required for waterborne epoxy systems

• Can cause instability

Viscosity

• Do not over-dilute the curing agent. Can hard settle

• Do not add cosolvent to curing agent. Can destabilize

• For stability, component viscosity >65 KU at 25°C

• DO NOT use latex viscosity control agents- Often neurtalized with NH3 or amines- React with epoxy - Viscosity build, gel or coagulation & pigment kick-out

Thixotropes / Thixotropes / ThickenersThickeners

Used for component stability and sag resistance

• Modified hydroxyethyl cellulosics

• Modified clays

• HEUR thickeners for component stability and

grind viscosity

Dispersing Pigments

• Disperse pigments, modifying resins, & additives directly into the epoxy resin dispersion

• Water-only pigment dispersions may use too much surfactant & give poor performance

• Dispersing pigments in W/B curing agent may lead to poor stability

• Can disperse pigments in low viscosity polyamide. Then let down with W/B curing agent

Pigments Dispersants

• Use in grind for epoxy resin dispersion stability

• Useful Dispersant Types− Non-ionics, e.g. poly(ethylene oxide) types best− Neutralized acid-functional acrylics – risky − Avoid ionic dispersants (cause gel and kick-out)

• Primary Uses− Pre-wetting pigments when grinding in epoxy− Stabilize dispersion during storage

Pigment Selection GuidelinesPigment Selection Guidelines

Low Oil and Water Low Oil and Water AbsorptionAbsorption

Low Soluble Salt ContentLow Soluble Salt Content Low Ionic CharacterLow Ionic Character Extender PigmentsExtender Pigments

– Variety of Shapes and Variety of Shapes and SizesSizes

Anti-Corrosive PigmentsAnti-Corrosive Pigments– Acceptable Water Acceptable Water

SolubilitySolubility– pH >6pH >6

Chemical Class Comments Calcium Metasilicate • Acicular shape for film strength Barium Sulfate • High density can be a problem Muscovite Mica (e.g 325 mesh waterground mica)

• Aid in moisture resistance • High oil absorption

Talc (Magnesium Silicate) • Avoid due to high viscosity Ceramic Silica-Alumina • Very low oil absorption

• Aids in pigment packing • dark color limits use to primers

Calcium Carbonate • Ionic content can be a problem China Clay (Aluminum Silicate) • May use to aid in brushability

+ recommended - not recommended

Extender Extender PigmentsPigments

• Zn-modified Al triphosphate

• Modified Al triphosphate

• Sr phosphosilicate

• Zn phosphate

• Zn phosphate complex

• Ca phosphosilicate

• Ca ion-exchange silica

• Al-Zn phosphate hydrate

• Zn/silicate-modified Al triphosphate

Corrosion Inhibitors

Corrosion Inhibitors

Not Recommended

• Ca or Ba metaborate

• Zn borate

• Zn phospho oxide complexes

High ionic character

Poor stability

Corrosion Inhibitors in Type 5 Corrosion Inhibitors in Type 5 EpoxyEpoxy

Zinc Phosphate Strontium/Zinc Calcium Phosphate Phosphosilicate

Information provided by Halox®

Corrosion Inhibitors in Type 5 EpoxyCorrosion Inhibitors in Type 5 Epoxy

Blank Calcium Phosphate Ca Phosphate + organic

Information provided by Halox®

Realities – Not Myths

High-performance waterborne epoxy coatings can be formulated which match or exceed solvent based coatings at attractively low VOC

In order to achieve high performance, components and formulating techniques specific to waterborne epoxy must be used

Conclusions

June, 2005

What is HEXION?

Thermoset Resins