Full definition
Primers are thin chemical coatings applied to substrates to enhance the adhesion of adhesives. They serve multiple purposes, including promoting the wetting of the adhesive, creating chemical bonds with the substrate, and providing a protective layer against re-oxidation of metal surfaces. The selection of a primer must be tailored to the specific substrate-adhesive combination, as using an inappropriate primer can lead to weakened bonds. Common primer systems include rubber-to-metal primers like Chemlok/Chemosil 205/211 from LORD Corp, which use a two-coat system where 205 bonds to metal and 211 bonds to rubber during vulcanization. Silane primers are effective for glass and ceramics, improving moisture resistance, while polyolefin primers facilitate bonding with low-energy plastics such as polyethylene and polypropylene. Metal primers, including chromate-based options, provide high-performance adhesion but are subject to regulatory restrictions under REACH and EPA guidelines. Primers are typically applied via spray, brush, or dip methods and must dry to a specified thickness, usually between 5-15 μm, before adhesive application. The timing of adhesive application is also crucial, as it must occur within the primer's open time window, generally ranging from 4 to 72 hours post-drying, depending on the manufacturer's specifications.