RESIN BONDING TERMS & CONSIDERATIONS
All three tooling methods allow molders to combine two or more resins. They can be combined in two general ways—chemical or heat/melt bonding or through a mechanical or interlock bond. Chemical bonds are created when one material molecularly binds to another, in effect creating an adhesive resin skin between first-and second-shot materials. Heat and pressure can create a “melt” bond between some resins—distorting the two surface areas to the point where they adhere to each other. A mechanical or interlock bond uses designed geometry features of the first and second shots to lock resins together.
In the case of a “melt” bond, which is considerably less robust than true chemical bonding, mechanical bonding can be added to increase the life and performance of the mating areas. There are also cases where a permanent bond is not desirable. A weak melt bond can temporarily adhere one component to another, allowing the product’s end-user to tear off a tamper-evident seal and expose a protected surface or orifice. An interlock bond, with two or more non-bonding resins, is used to create in-mold assembled products with built-in functionality such as rotating or sliding actions.
The involvement of resin suppliers is critical during the initial stages of product design. Although largely anecdotal, a substantial amount of history exists with regard to what generally bonds to what and what does not. You certainly do not want to learn the hard way that glass-filled nylons can be challenging substrates or that certain colorants can dramatically impact bond strength.
The article comes from China injection mold manufacturer - Mold Best Assurance Company Limited, website is www.mbamoldanddesign.com
