Dr. B, Master Bond’s resident adhesive expert, explains how to enhance thermal stability, electrical properties and chemical resistance by using heat when curing epoxies.
Dr. B: Hi Sam.
Sam: Hi Dr. B.
Dr. B: Can you meet me in the manufacturing facility?
Sam: Sure Doctor B. See you in a minute.
Dr. B: I want to continue our conversation about how adding heat to cure epoxies enhances properties. You asked how much heat is necessary, and for how long it needs to be added. A common way of measuring temperature resistance is with glass transition temperature. If heat is added for one hour at 150°C, Tg will go up maybe 5 to 10 degrees. If you add heat for 4 hours at 150°C, 300°F, the Tg still increases. If you add heat for 12 hours, it will go even further. Realistically, adding heat for a couple of hours is fine.
Sam: What if we wanted to test for electrical insulation? How is that data affected by adding heat?
Dr. B: The main test data for electrical insulation is dielectric constant, dielectric strength, dissipation factors, and volume resistivity. All of these are affected positively by adding additional heat.
Sam: I’m beginning to see a trend here…. Let’s say we’re looking at electrical conductivity. If we take a two part system and let it cure for 2 to 5 days, it's very conductive. If we add heat for a few hours, it's even more conductive.
Dr. B: That’s right Sam! You’re catching on! Other areas in which properties enhancements are seen is chemical resistance. Materials simply won't resist chemicals nearly as well without adding heat.
Sam: And I bet the same goes for physical strength.
Dr. B: Absolutely. So, that’s an overview of the importance of adding heat when curing epoxies…it is not emphasized enough. So go ahead and spread the word to all your engineering friends.
Heat curing leads to more crosslinking and polymerization allowing the epoxy to develop superior characteristics.