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High-Temperature Adhesives for Automotive Applications

This presentation discusses the development of adhesives and potting compounds with high service temperature for automotive electronics, focusing on their thermal stability, adhesion, and performance in harsh environments.

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High-Temperature Adhesives for 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

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