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Formulating High-Performance Waterborne Epoxy Coatings

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Presentation on theme: "Formulating High-Performance Waterborne Epoxy Coatings"— Presentation transcript:

1 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

2 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”

3 “Devil is in the Details”
(and the details are in the paper) This presentation will Define achievable high performance Outline general formulation techniques Please see paper for specific recommendations

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

5 Waterborne Epoxy Types
Best Performance Non-ionic aqueous dispersions Solid resin dispersions

6 Type 5 Epoxy Resin Dispersion
Name: EPI-REZ 6520-WH-53 Description: Modified 1001-type EEW, g/eq, solids: Viscosity, cP*: < 3000 Solids, % weight: Lb./Gal: VOC Cosolvent: PM (<4%) * Brookfield, #5 spindle, 20 rpm, 25 °C.

7 Type 5 Curing Agent Dispersion
Name: EPIKURE 6870-W-53 Description: Modified polyamine adduct AHEW, g/eq, solids: Viscosity, cP*: ,000 Solids, % weight: Lb./Gal: VOC Solvent: None * Brookfield, #5 spindle, 20 rpm, 25 °C.

8 Performance of White Enamels

9 Discernable End Potlife
20 30 40 50 60 70 80 90 100 110 120 1 2 3 4 5 6 Time, hours, After Mixing A + B Viscosity, KU / 60° Gloss Value 60° Gloss Viscosity Semi-Gel

10 2000 Hour Salt Spray 3 mils DFT on cold-rolled steel
SB epoxy / polyamide Type 5 WB system 3 mils DFT on cold-rolled steel

11 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

12 Effects of Epoxy/Curing Agent Ratio

13 Effects of Epoxy/Curing Agent Ratio

14 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)

15 Factors Affecting Pot Life

16 Cosolvents Functions Coalescing aids Freeze-thaw stabilizers
Leveling agents Pigment wetters Foam control Performance Effects Dry time Gloss Hardness development Final film properties

17 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

18 Cosolvents Others – see paper for details Alcohols Aromatics Ketones
Glycol ether acetates

19 Total Hansen Solubility Parameter, cgs units
Cosolvent Selection (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 Total Hansen Solubility Parameter, cgs units DPNP DPTB EM EE EH EEH DM DE DP DB Boiling Point, °C DPNB TPNB PPh PM PE PNP PTB PNB DPM EB EP Poor Coalescing Good Coalescing TPM DAA MnAK

20 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 )

21 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

22 Coalescence Properties
2 µm Type 2 System Avg. surface roughness = 25X Type 5 System Avg. surface roughness = 1.25X SB Epoxy Avg. surface roughness = 1X

23 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

24 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

25 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(Dimethylaminoethyl)Phenol Effect of an Accelerator on the Hardness Development 2H J B J F B J B B Pencil Hardness J 3B B 5B J Accelerated Control B Control <6B 24 48 72 Time, Hours, After Coating

26 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

27 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

28 Mar and Slip Agents May Improve Abrasion Resistance and Early Water Resistance Useful Types Polydimethylsiloxanes Wax Dispersions Micronized Polyethylene Dispersions Silicones

29 Fungicides and Mildewcides
Generally not required for waterborne epoxy systems Can cause instability

30 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

31 Thixotropes / Thickeners
Used for component stability and sag resistance Modified hydroxyethyl cellulosics Modified clays HEUR thickeners for component stability and grind viscosity

32 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

33 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

34 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 >6

35 Extender Pigments + recommended not recommended

36 Corrosion Inhibitors Zn-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

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

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

39 Corrosion Inhibitors in Type 5 Epoxy
Blank Calcium Phosphate Ca Phosphate + organic Information provided by Halox®

40 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

41 What is HEXION? Thermoset Resins June, 2005

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