Why is silicone difficult to bond to metal?
Silicone has a stable molecular structure (its backbone is composed of Si-O bonds, resulting in extremely low surface energy). Ordinary silicone lacks reactive groups on its surface, making it unable to form effective chemical bonds with hydroxyl groups (-OH) or metal ions on metal surfaces (such as aluminum, iron, stainless steel, and copper). Direct bonding with ordinary glue can easily lead to problems such as weak adhesion and easy peeling.
The core function of a primer is to introduce reactive groups (such as hydroxyl and amino groups) onto the silicone surface, enhancing the adhesion of the glue to the metal surface. It acts as a "bridge" connecting two incompatible materials.