Formulating High-Performance

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Formulating High-Performance Waterborne Epoxy
Coatings
M.J. Watkins,
D.J. Weinmann, J.D. Elmore
Presented at a meeting of the Thermoset Resin
Formulators Association Hyatt Regency
Montréal September 11-12, 2006
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Mythbusters
Myth 1
Waterborne epoxy coatings can never match
the performance of solvent based systems
Myth 2
I know how to formulate other waterborne
systems, So I can use all my current tricks and
additives to formulate waterborne epoxies
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Devil is in the Details (and the details are in
the paper)
This presentation will

1. Define achievable high performance

1. Outline general formulation techniques

Please see paper for specific recommendations

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Topics

• Waterborne epoxy types
• Type 5 waterborne epoxy performance
• Stoichiometry effects
• Pot life issues
• Components (cosolvents, pigments, additives,
  etc.)
• Dispersing pigments
• Pigment selection

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Waterborne Epoxy Types

• Best Performance
• Non-ionic aqueous dispersions
• Solid resin dispersions

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Type 5 Epoxy Resin Dispersion
Brookfield, 5 spindle, 20 rpm, 25 C.
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Type 5 Curing Agent Dispersion
Brookfield, 5 spindle, 20 rpm, 25 C.
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Performance of White Enamels
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Discernable End Potlife
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2000 Hour Salt Spray
SB epoxy / polyamide
Type 5 WB system
3 mils DFT on cold-rolled steel
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Epoxy / Amine Ratio Effects on Performance (Stoich
iometry)
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
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Effects of Epoxy/Curing Agent Ratio
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Effects of Epoxy/Curing Agent Ratio
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Pot Life Characterization

• End of Pot Life
• Viscosity Increase Above Application Limit
• Significant Change in Gloss (10 Units Lower at
  60)
• Decrease or Loss of Cure (Hardness)

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Factors Affecting Pot Life
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Cosolvents

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

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

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Cosolvents

• 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

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Cosolvents

• Others see paper for details
• Alcohols
• Aromatics
• Ketones
• Glycol ether acetates

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Cosolvent Selection(based on results with Type 5)
DAA
MnAK
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Freeze-Thaw Resistance

• Adding glycol ethers and/or alcohols
• Reduces freezing point
• Promotes recovery of frozen material
• 25-30v of total volatiles provides resistance
• to 1-3 Cycles
• Examples ethylene glycol monopropyl ether
• (EP), or methanol
• 11 blend of DAA / PnB (Type 5 )

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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

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Coalescence Properties
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Defoamers

• Suppress Foam Generation During Manufacturing,
  Filling, Tinting, and Application
• Selection Considerations
• Empirically determined
• Optimize level (avoid stability application
  problems)
• Must remain active for desired shelf life
• Most effective if portion added to grind
  remainder to letdown
• Required level is approximately 0.5 of paint
  volume

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Defoamers

• Useful Generic Types? Silicone Based ? Oil
  Based
• Possible Problems Due to Improper Choice or High
  Use Levels
• ??Pigment flocculation ??Incompatibility
• ??Poor Color acceptance ??Cratering (fish eyes)
• ??Poor inter-coat adhesion ??Water sensitivity

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Cure Catalysts/Accelerators

• Positive functions
• Decrease time to achieve desired hardness
• Improves early solvent resistance
• Negative functions
• Shortens pot life
• Decrease water acid resistance
• Most effective
• Tertiary Amines such as 2,4,6-Tris(Dimethylaminoet
  hyl)Phenol

Effect of an Accelerator on the Hardness
Development
2H
J
J
B
B
F
J
B
B
Pencil Hardness
J
3B
B
5B
J
Accelerated Control
B
Control
lt6B
0
24
48
72
Time, Hours, After Coating
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Flash Rust Inhibitors

• Occurs on ferrous substrates under high relative
  humidity
• Effectiveness depends on solids. Adding water
  can
• reduce effectiveness.
• Nitrite salts (Ca or K salts preferred).
• Several common inhibitors ineffective or
  incompatible ? lead naphthanate ?
  chromates or dichromates ? tertiary amines
• Use in curing component for stability
• Minimize levels to avoid water sensitivity

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Adhesion Promoters

• Benefits
• Improved substrate wetting and adhesion
• Especially galvanized steel, cold rolled steel,
  and aluminum
• Less effective on blasted or phosphated steel
• Faster cure hardness development
• Incorporate in epoxy during pigment grind
• Improved corrosion resistance
• Chemical Structure is Important
• Use Epoxy-functional, triethoxy- or
  diethoxymethyl- silanes for best shelf stability.
  
• Aminosilanes contribute to yellowing
• Methoxysilanes hydrolyze and give poor adhesion

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Mar and Slip Agents

• May Improve Abrasion Resistance and Early Water
  Resistance
• Useful Types
• Polydimethylsiloxanes
• Wax Dispersions
• Micronized Polyethylene Dispersions
• Silicones

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Fungicides and Mildewcides

• Generally not required for waterborne epoxy
• systems
• Can cause instability

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Viscosity

• Do not over-dilute the curing agent. Can hard
  settle
• Do not add cosolvent to curing agent. Can
  destabilize
• For stability, component viscosity gt65 KU at
  25C
• DO NOT use latex viscosity control agents
• Often neurtalized with NH3 or amines
• React with epoxy
• Viscosity build, gel or coagulation pigment
  kick-out

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Thixotropes / Thickeners

• Used for component stability and sag resistance
• Modified hydroxyethyl cellulosics
• Modified clays
• HEUR thickeners for component stability and
  grind
• viscosity

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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

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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

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Pigment Selection Guidelines

• Low Oil and Water Absorption
• Low Soluble Salt Content
• Low Ionic Character
• Extender Pigments
• Variety of Shapes and Sizes
• Anti-Corrosive Pigments
• Acceptable Water Solubility
• pH gt6

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Extender Pigments
recommended - not recommended
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Corrosion Inhibitors

• 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

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Corrosion Inhibitors

• Not Recommended
• Ca or Ba metaborate
• Zn borate
• Zn phospho oxide complexes
• High ionic character
• Poor stability

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Corrosion Inhibitors in Type 5 Epoxy
Zinc Phosphate Strontium/Zinc
Calcium Phosphate
Phosphosilicate
Information provided by Halox
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Corrosion Inhibitors in Type 5 Epoxy
Blank Calcium Phosphate Ca Phosphate

organic
Information provided by Halox
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Conclusions
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

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What is HEXION?
Thermoset Resins
June, 2005