What is the purpose of an adhesion promoter on plastics?

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The fundamental point is that adhesion promoters create a chemical bridge between the plastic surface and the coating. Plastics often have low surface energy and few polar groups, which makes it hard for primers and paints to wet and bond to them. An adhesion promoter provides functional groups that can react with the coating resin on one side and bond to the plastic on the other, effectively raising surface energy and creating sites for chemical bonding. This improves wetting, bond strength, and overall adhesion of the primer/paint to the plastic, helping prevent peeling or delamination. It’s not about curing speed, changing color, or making the plastic more flexible.