Take a walk into any craft or hobby store and ask the sales associate for a metal to plastic adhesive, and they’ll say something like… “You’ll find metal to plastic adhesive in aisle 7 on the middle shelf to the right of the popsicle sticks and above the pom poms.” Indeed, if you’re making Christmas ornaments with the grandkids, this may work. However, finding a high-quality adhesive designed for industrial bonding doesn’t happen that quickly. In this case, you’ll likely be asked many more questions.
Formulating a metal to plastic adhesive requires some serious adhesive engineering. It goes without saying that metals and plastics are very different from each other. The surface energy, coefficients of thermal expansion, hardness, etc.… are all vastly different. Adhesive engineering a metal to plastic adhesive generally involves not only addressing the concerns of adhesion of the particular metal and particular plastic involved but also providing a means of absorbing the stresses between the two.
Thus the need for all of the questions. Some are straight forward, such as…
1. What type of metal?
2. What type of plastic?
3. What is the joint design?
4. What is the bond surface area?
Others seem obscure, like…
5. What will the assembly be used for? (This question is loaded – it gives the adhesive engineer a sense of what environmental conditions and stresses the assembly will be exposed to. Note your answers may beget more questions.)
Then there are the process questions
6. How many assemblies will you be making?
7. Automated or manual assembly? This provides the adhesive engineer with a sense of how fast or slow you’d like the set time to be and helps determine the best choice of product.
The difference between what you find in aisle 7 and an industrial adhesive that has been vetted for your bonding application is, simply put, consistent success.
So what are the best metal to plastic adhesives? Well … that depends – do you have a moment for a few questions?
