Copolyamide Promotes Bonding of Metal to Plastic In Hybrid Overmolding Process

Adhesive coating enables one-step in-mold forming and overmolding of sheet metal.

At the recent K 2016 show in Dusseldorf, a new one-step process for forming, overmolding, and bonding nylon to sheet metal was demonstrated at the booth of Wittmann Battenfeld (U.S. office in Torrington, Conn.). The key to the process is a copolyamide hot-melt adhesive called Vestamelt Hylink from Evonik High-Performance Polymers (Parsippany, N.J.). It promotes chemical bonding between metals and various nylons. In so-called hybrid parts where plastic is overmolded onto sheet metal, this bonding agent—applied to the metal sheet via coil coating or spraying —can avoid the need to design “mechanical locks” between the two materials. Vestamelt Hylink was introduced at K 2010 but was used for the first time in production in 2013.

Originally, forming the coated metal sheet was a separate operation from overmolding and bonding. But R&D at the German Institute for Plastics Processing (IKV) in Aachen developed a method of forming the coated metal in the injection mold during the same cycle as overmolding. This was demonstrated at K with a cup-shaped part overmolded with Evonik’s Vestamid Terra HS1850, a biobased nylon 610 with 30% glass fiber..

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