COMPOSITES | TECHNOLOGY


Polymer-metal hybrid composites are proliferating in automotive applications.Peter Mapleston surveys the latest developments in over- moulding and other processes


Seeking a bond between plastics and metal


Engineering plastics are making a major contribu- tion to weight reduction in automotive, electronic and numerous industrial products by being used in place of metals. In most cases, the replacement is total, but there is also a growing trend to create over-moulded hybrid metal-plastics composites in which the best is made of both materials. The trend is not new – car front-ends built using hybrid technology developed by Bayer (now Lanxess) first appeared in the mid-1990s – but it does appear to be gathering pace. Current development efforts are leading to


improved bond strength between the two materials, and also towards more cost-effective production systems that lend themselves to lower batch sizes. Polyplastics is one materials company tackling the interfacial issue. Technologies developed during this century have improved bonding force and airtightness at the joint by giving the metal surface physical texture and chemical affinity to the thermoplastic, it notes. “However, since many factors (metal parts, resin materials, mould structure,


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injection moulding 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.” Polyplastics emphasises the importance of using the right polymer. For instance, it points to the fact that when there are changes in the local environ- ment after moulding (heat, humidity, for example), bonding capability can decline due to differences between the linear expansion of the metal and the resin, and other factors. Some compounds offered by Polyplastics


incorporate what it calls an “affinity improvement agent” to improve adhesion to metal surfaces. The company offers various grades of PPS and PBT with enhanced metal adhesion. “We are also currently developing even more metal adhesion grades with new functionalities in order to cater to new de- mands,” it says. Turning to metal surface treatment, Polyplastics points to new developments, like its Quick-10 technology, which uses rapid heating and cooling


Main image: Evonik


developed Vestamelt Hylink


copolyamide- based adhe- sion promoter to support production of plastic-metal hybrid


components


January/February 2019 | INJECTION WORLD 41


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