Engineering plastics have contributed to weight reduction in automotive parts, electronics and electrical products, and many other industrial products, by being used in place of metal materials. Today rather than simply replacing metal materials, many metal- resin composite materials are manufactured which still have some metal materials, and replace the rest with engineering plastics. Metal- resin composite materials deliver the advantage of simultaneously using both the properties of metal materials (such as high rigidity, electrical conductivity, etc.) and the properties of engineering plastics (such as low density, electrical insulation, etc.). However, since there is a bond interface between the two materials, it presents a higher level of technical difficulty when bonding force and airtightness are required.
Past methods used to produce metal-resin composite materials
include simple insert molding, as well as physical joining through caulking or screw tightening, bonding with adhesives, and sealing with potting agent. However, simple insert molding, caulking and screw tightening often did not provide enough functionality because they provide poor airtightness. Bonding with adhesives and sealing with potting agent involve large numbers of parts and extensive procedures, making high costs inevitable.
In order to resolve this problem, technologies appeared from the year 2000 onward which give the bond interface of the metal and resin properties of bonding force and airtightness with injection molding alone by giving the metal surface physical texture and chemical affinity in advance and making it into insert molding. However, since many factors (metal parts, resin materials, mold structure, injection molding conditions, etc.) in this method have an effect on bonding, it does not provide stable bonding. As a result, there are still not many examples of this going into mass production. Thus here we will introduce some points to keep in mind to get metal-resin bonding capability with injection molding alone.