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Formulating High-Performance Waterborne Epoxy Coatings Presented at a meeting of the Thermoset Resin Formulators Association Hyatt Regency Montréal September.

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Presentation on theme: "Formulating High-Performance Waterborne Epoxy Coatings Presented at a meeting of the Thermoset Resin Formulators Association Hyatt Regency Montréal September."— Presentation transcript:

1 Formulating High-Performance Waterborne Epoxy Coatings Presented at a meeting of the Thermoset Resin Formulators Association Hyatt Regency Montréal September 11-12, 2006 M.J. Watkins,D.J. Weinmann, J.D. Elmore

2 Mythbusters “Waterborne epoxy coatings can never match the performance 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”

3 “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

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 * Brookfield, #5 spindle, 20 rpm, 25 °C. Name: EPI-REZ 6520-WH-53 Description: Modified 1001-type EEW, g/eq, solids: 550 Viscosity, cP*: < 3000 Solids, % weight: 53.0 Lb./Gal: 9.0 VOC Cosolvent: PM (<4%)

7 Type 5 Curing Agent Dispersion * Brookfield, #5 spindle, 20 rpm, 25 °C. Name:EPIKURE 6870-W-53 Description: Modified polyamine adduct AHEW, g/eq, solids: 225 Viscosity, cP*: 8,000 Solids, % weight: 53 Lb./Gal: 9.1 VOC Solvent: None

8 Performance of White Enamels

9 Discernable End Potlife 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 / polyamideType 5 WB system

11 Epoxy / Amine Ratio Effects on Performance (Stoichiometry) Higher epoxy level gave improved: Higher curing agent level gave improved: Pot lifeCure rate Acid resistanceGloss Alkali resistanceAdhesion Water resistanceAbrasion resistance Humidity resistanceSolvent resistance Corrosion resistanceStain resistance

12 Effects of Epoxy/Curing Agent Ratio

13

14 Pot Life Characterization End of Pot Life ÀViscosity Increase Above Application Limit ÁSignificant Change in Gloss (10 Units Lower at 60°) ÂDecrease 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 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

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

19 Cosolvent Selection (based on results with Type 5) MnAK DAA

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 Suppress Foam Generation During Manufacturing, Filling, Tinting, and Application Selection Considerations 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 Useful Generic Types  Silicone Based  Oil Based Possible Problems Due to Improper Choice or High Use Levels 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 Positive functions –Decrease time to achieve desired hardness –Improves early solvent resistance Negative functions Negative functions –Shortens pot life –Decrease water & acid resistance Most effective Most effective –Tertiary Amines such as 2,4,6- Tris(Dimethylaminoethyl)Phenol Effect of an Accelerator on the Hardness Development Effect of an Accelerator on the Hardness Development J J JJ B B B B <6B 5B 3B B F 2H Time, Hours, After Coating J Accelerated Control B Control Pencil Hardness

26 Flash Rust Inhibitors Occurs on ferrous substrates under high relative humidityOccurs on ferrous substrates under high relative humidity Effectiveness depends on % solids. Adding water canEffectiveness 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 incompatible  lead naphthanate  chromates or dichromates  tertiary aminesSeveral common inhibitors ineffective or incompatible  lead naphthanate  chromates or dichromates  tertiary amines Use in curing component for stabilityUse in curing component for stability Minimize levels to avoid water sensitivityMinimize levels to avoid water sensitivity

27 Adhesion Promoters Benefits Benefits –Improved substrate wetting and adhesion Especially galvanized steel, cold rolled steel, and aluminum Especially galvanized steel, cold rolled steel, and aluminum Less effective on blasted or phosphated steel Less effective on blasted or phosphated steel –Faster cure & hardness development –Incorporate in epoxy during pigment grind –Improved corrosion resistance Chemical Structure is Important 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 May Improve Abrasion Resistance and Early Water Resistance Useful Types 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 NH 3 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 Oil and Water Absorption Low Soluble Salt Content Low Soluble Salt Content Low Ionic Character Low Ionic Character Extender Pigments Extender Pigments –Variety of Shapes and Sizes Anti-Corrosive Pigments Anti-Corrosive Pigments –Acceptable Water Solubility –pH >6

35 + recommended - not recommended Extender Pigments

36 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

37 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 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

41 June, 2005 What is HEXION? Thermoset Resins


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