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Adhesives and Potting Compounds for High Service Temperature in Automotive Applications

Adhesives and Potting Compounds for High Service Temperature in Automotive Applications

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Adhesives and Potting Compounds for High Service Temperature in Automotive Applications

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  1. Adhesives and Potting Compounds for High Service Temperature in Automotive Applications Presented at The Thermoset Resin Formulators Association Meeting Boston, MA October 3-4, 2004 Liz Walker liz.walker@nstarch.com Michel Ruyters michel.ruyters@nstarch.com Page 1 TRFA Oct 3-4, 2004

  2. Presentation Outline • Introduction • Automotive Electronics Evolution - New Demands on Adhesives & Protective Materials • New Materials Development Program -Target Properties & Test Matrix • Epoxy Materials • Anhydride Cured • Improved Resin & Compounds • Imidazole Cured • Summary of Material Properties • Alternative High Performance Thermoset Technology • Possible Candidate Materials • Cyanate Ester Adhesive • Next Generation – Improve Thermal Shock Performance • Combine Toughening with Thermal Stability • Summary Page 2 TRFA Oct 3-4, 2004

  3. Harsh Environments for Automotive Electronics Motor Management -40°C to +180°C High service temperature (180°C) Fuels, Oils, Vibration On Transmission -40°C to +180°C ATF, Vibration Page 3 TRFA Oct 3-4, 2004

  4. Conseqences for Polymeric Materials • Polymeric materials used for the assembly and protection of electronics must survive higher service temperatures, temperature extremes, fluid exposure and vibration. • Critical Properties • High Temperature Resistance – 150°C - 200°C • Adhesion to Metals and Engineered Plastics • Adhesion Retention at High Temperature • Chemical Resistance • Operate in Wide Temperature Range Page 4 TRFA Oct 3-4, 2004

  5. New Product Development - Target Properties • Thermal Stability • High crosslink density – High Tg above use temperature • Low thermal degradation – Low weight loss • Adhesion • High values at 180°C to aluminum and plastics (PBT, PPS, ...) • Minimal decrease during service life @ -40°C to + 180°C • Easy to Process • 1 Component Compound, no mixing required • Low temperature, minimal cure time post cure in operation only • Long working time, shelf life • Low viscosity for potting, easy air release Page 5 TRFA Oct 3-4, 2004

  6. New Product Development - Testing • Thermal Stability – • TMA - Glass Transition & Coefficient of thermal expansion • TGA - Report Temperature at 1% weight loss • Fluid Immersion – weight change at temperature • Oil SAE 10W-40- 24 hr @ 150°C, Water 1 hr @ 100°C • Adhesion – Maximize values, minimize loss • Tensile Lap Shear Strength (TLSS) ASTM D-1002 • Test at room temperature (RT) and 180°C • Initial and after exposure to 180°C • Aluminum ( acid etch), untreated PPS, 30%GF PBT • Easy to Process • Viscosity over time for pot life/working time and shelf life • 3 days minimum at RT with no increase in viscosity • 25°C and 40°C conditions Page 6 TRFA Oct 3-4, 2004

  7. High Temperature Performance Epoxies • 1st Generation Epoxy materials - multifunctional resins cured with anhydrides • Advantage • High adhesion • Thermally stable • Good chemical resistance • Low exotherm • Disadvantage • Two component • Moisture sensitive • Slow to react, long multi-step cure schedules Page 7 TRFA Oct 3-4, 2004

  8. High Temperature Performance Epoxies Example - Compound 1 • 2nd Generation novel multifunctional epoxy resin blend • High crosslink density possible • Low viscosity : fillers can be used • Good reactivity at high temperature • Low reactivity at room temperature • Novel accelerated anhydride • Good latency at room temperature • Highly efficient cure at 120-150°C • 1 Component formulated products Page 8 TRFA Oct 3-4, 2004

  9. Long Cure/ Post Cure – Maximize Tg, Minimize CTE Example - Compound 1 Page 9 TRFA Oct 3-4, 2004

  10. Thermal Stability – Low Weight Loss (TGA) Example – Compound 1 TGA Test atmosphere : 20% O2, 80% N2 50 ml/min 1 % weight loss @ 297 °C Page 10 TRFA Oct 3-4, 2004

  11. Adhesion – Aluminum to Aluminum Tensile Lap Shear Strength - Example Compound 1 84% retention tested@ 25°C 93% retention tested @ 180°C CompareTesting Temperature and Aging Effects Page 11 TRFA Oct 3-4, 2004

  12. Adhesion PPS to PPS Tensile Lap Shear Strength Example - Compound 1 81% retention tested @ 25°C 88% retention tested @ 180°C Compare Testing Temperature and Aging Effects Page 12 TRFA Oct 3-4, 2004

  13. High Temperature Performance Epoxies Example - Compound 2 • Proprietary solid imidazole hardener • Moderate Tg, still maintains good chemical resistance • Faster Cure, higher reactivity than Compound 1 • Various cure temps./ timesfull cure at 150°C/30min • Improved stability as a 1 Component Product • Long potlife1 wk at RT • Longer Shelf Life 3 mos@ 6°C (2 X Compound 1) • Much Improved adhesion • 2X to 3X TLLS vs.Compound 1 at 25°C and 180°C • Increased polarity, resulting in better wetting of substrate Page 13 TRFA Oct 3-4, 2004

  14. Thermal Stability – Low Weight Loss (TGA) Example - Compound 2 1% Weight Loss @ 322°C Page 14 TRFA Oct 3-4, 2004

  15. Adhesion - Aluminum to Aluminum Tensile Lap Shear Strength Example – Compound 2 60% retention tested @ 25°C 46% retention tested @ 180°C Compare Testing Temperature & Aging Effects Page 15 TRFA Oct 3-4, 2004

  16. Adhesion PPS to PPS Tensile Lap Shear Strength Example – Compound 2 88% retention tested @ 25°C 84.5% retention tested @ 180°C Compare Testing Temperature & Aging Effects Page 16 TRFA Oct 3-4, 2004

  17. Compare Properties - Compounds 1 & 2 Page 17 TRFA Oct 3-4, 2004

  18. Performance of Anhydride & Imidazole Cured Epoxy Materials Summary • Imidazole Cured Epoxy • Stable 1-Part with +25°C Storage • Higher Reactivity, Higher Exotherm • Good for adhesive bonds • Moderate Tg , high thermal stability • Maintains good chemical resistance • Higher initial Adhesive strength • Higher loss after aging on Al Anhydride Cured Epoxy • Stable 1-Part with -40°C Storage • Low Viscosity, Low Exotherm • Good for potting • Very High Tg, Low CTE possible • With post cure • Moisture sensitive, respiratory sensitizer • Lower than desired adhesive strength on plastics • Both can be brittle at -40°C limiting thermal shock performance Page 18 TRFA Oct 3-4, 2004

  19. Alternative High Performance Thermoset Materials • Chemisties Considered • Polyimid • Mainly solids, two-step imidisation, water by-product, voids • Bismaleimide • Mainly solids, high processing temperatures • Chemistry Tested • Cyanate Ester • Liquid monomer available • Possibility to blend for improved properties Page 19 TRFA Oct 3-4, 2004

  20. Cyanate Ester Epoxy Blend Adhesion Al to Al- TLSS 89.7% retention tested @ 25°C 76.4% retention tested @ 180°C Compare Testing Temperature and Aging Effects Page 20 TRFA Oct 3-4, 2004

  21. Cyanate Ester Epoxy Blend Adhesion PPS to PPS - TLSS 85.7% retention tested @ 25°C 79.4% retention tested @ 180°C Compare Testing Temperature and Aging Effects Page 21 TRFA Oct 3-4, 2004

  22. Cyanate Ester Epoxy Blend - Thermal Stability TGA – Thermal Stability 0.5 % weight loss at 300°C Page 22 TRFA Oct 3-4, 2004

  23. Cyanate Ester • Advantages • 1 Component, low viscosity possible • Very high thermal stability, high Tg • High initial adhesion like epoxy imidazole on Al and PPS • retention @ 180°C better on aluminum • Less susceptible to moisture after cure • Can be modified/blended to improve performance or cure • Limitations • Current formulas require very high temperature cure • or multi-step cure at lower temperatures • Uncured liquid is moisture sensitive Page 23 TRFA Oct 3-4, 2004

  24. Challenge to Improve Polymeric Materials Combine Low and High Temperature Performance High Temperature Resistance • Poor Performance in thermal shock • Eliminating micro-cracking • Toughened thermosets can control micro-cracking, but cause • reduced Tg & thermal stability High Chemical Resistance High crosslink density Reduced modulus Temperature Shock Resistant Page 24 TRFA Oct 3-4, 2004

  25. Improve Thermal Shock Performance-40°C to 180°C • Micro-cracking • Understand micro-cracking physics • Model changes during thermal shock • Improve Testing • Perform fatigue and fracture analysis • Develop optical methods to verify modeling • Reduce micro-cracking while retaining high temperature performance • Toughening that does not compromise thermal stability Page 25 TRFA Oct 3-4, 2004

  26. Toughening Thermosets Improve Thermal Shock Performance • Co-Reaction with Elastomers - • Low Tg, soft segments chemically bound to high Tg hard segments • Co-Polymer blend with phase separation - during cure • Large low Tg soft domain clusters form between high Tg rigid segments, driven by polarity differences • Elastomeric particles • Hard rigid high Tg matrix with low Tg cushions throughout • absorb impact and stress Page 26 TRFA Oct 3-4, 2004

  27. Co-polymer Blend with Phase Separation Example Compounds 3 & 4 Page 27 TRFA Oct 3-4, 2004

  28. Summary - High Service Temperature Adhesives and Potting Compounds • Demonstrated • 1 Component Epoxies • High Tg, low viscosity, low CTE Potting Compound , high service temperature (when post cured) • Moderate Tg Adhesive for 180°C - maintains adhesion after heat exposure • Cyanate ester blend with High Adhesion • Slightly higher thermal stability than Epoxies • Adhesion equal to imidizole/ epoxy, better high-adhesion retention on Al • Future Goals for New Product Development • Maintain high temperature stability & adhesion AND • Improve Adhesion to Engineering Plastics • Improve Thermal Shock Performance Page 28 TRFA Oct 3-4, 2004

  29. Industry Robert Bosch GmbH Epcos Wabash Emerson & Cuming G. Van Wuytswinkel C. Bosmans C. Van Der Borght ICI G. Smyth R. Bailey P. Dooling References High Performance Thermosets Lin/Pearce Polymer Toughening C. Arends Cyanate Ester Technology I. Hamerton Appreciation, Acknowledgements & References Page 29 TRFA Oct 3-4, 2004