Often adhesives are not considered suitable for joining structural assemblies that need to go through a paint-bake or stoving process. This is due to the brief exposure to high temperature (around 200°C / 390°F for 10-15 minutes). However, there are many temperature resistant adhesives that can resist these conditions for this brief duration – providing the joint is not unduly stressed and upon returning to normal room temperature, the bonded joint will regain the vast majority of its original strength.
Although two-part epoxies normally quote an upper service temperature limit of 80°C, this doesn’t mean that for brief periods they can’t go higher. We have seen excellent results with two part epoxies such as Permabond ET538, for structural bonding. The adhesive joint is easily powder coated, and then the joint is supported during the stoving process. The bond regains strength upon cooling.
Single-part epoxy adhesives, on the whole, offer higher temperature resistance than regular two-part epoxies. So they are ideal if you want greater loadbearing during the stoving process or where supporting a joint is not feasible.
Structural acrylic – recent testing suggests MMA-based structural acrylic, Permabond TA4210 is performing exceptionally well at temperatures in excess of 180 deg C, making it capable of withstanding a paint-bake cycle or powder coating process. MMA adhesives offer a fast room temperature cure – as well as a very high bond strength with good resistance to peel, impact and vibration stress.
The graph above shows lap shear strength retention of Permabond TA4210 MMA-based structural acrylic adhesive after high temperature exposure.
Conclusion: After paint baking at 180 deg C, very high bond strength return after cooling to room temperature. Thus indicating minimal damage to the adhesive bond from the heat exposure. For customers in the US, the closest similar product would be Permabond TA4810.
For further help and advice on selecting temperature resistant adhesives, please contact our Permabond technical team, and we would be happy to assist.