Using step cure to reduce stress
Curing high temperature epoxy systems can be challenging, especially when used as a potting compound or encapsulant. Curing at extremely high temperatures from the very beginning of the curing process can result in a highly stressed polymer and a higher linear shrinkage. Linear shrinkage occurs as the epoxy cures and high linear shrinkage can result in the epoxy pulling away from the substrate preventing a tight bond. Highly stressed polymers are more prone to cracking under thermal cycling. It is important to cure epoxy systems using step cure methods to reduce internal stress of epoxy and limit linear shrinkage. Step cure method simply means using multiple cure temperatures and times starting at a low temperature, then increasing to a higher temperature, then back down to a lower temperature.
EB-115 is a high temperature epoxy adhesive that benefits from a step cure profile. Instead of curing for 1 hour at 150°C which will result in a full cure but may be highly stressed, curing for 1 hour at 100°C + 1 hour at 150°C will result in a low stress, high temperature resistant polymer with lower crack resistance. This is a prime example of a step cure profile used by aerospace guidance control manufacturers for high strength screw reinforcement. EB-115 is also used in fiber optic application to pot fiber terminal in ferrules.
|Mix Ratio by Weight||100/15|
|Mixed Viscosity @RT(cps)||6000-7000|
|Pot Life @25°C(100 gram)||90 min|
|Recommended Cure||2 hrs @ 100°C + 2 hrs @ 175°C|
|Alternate Cure||2-4 hrs @ 150°C|
|Lap Shear Strength @25°C(psi)||1900|
|Service Temp.Range||-55°C to 230°C|
|Volume Resistivity(500 V)||8 x 10^15|