ICMCTF2018 Session TS3: Coating of Synthetic Materials – Engineering for the Future

Vacuum coating of plastic components as an alternative to electroplating already has a long tradition in industrial practice. The applications range from metallization of headlamp reflectors over decorative controls and instruments up to EMC shielding of electronic devices. Predominantly used methods are magnetron sputtering and thermal evaporation.

A particular challenge is the low thermal stability of many engineering plastics in conjunction with the high energy input of PVD processes and the limited possibilities of substrate cooling in vacuum. Furthermore, for most plastics a sufficient adhesion of PVD coatings directly on the substrate material still cannot be achieved, so that primers or lacquers have to be used as sublayers.

A new approach for PVD direct metallization is taken by Fraunhofer FEP. Here, a short-cycle system for the coating of components by high-rate electron beam evaporation is used to coat components made of polycarbonate (PC) and PC/ABS (acrylonitrile butadiene styrene copolymer) blend. After a short treatment in oxygen plasma the parts are coated with an aluminum layer of some microns thickness in less than one minute, without showing thermal deformations or film delamination.

The key to meet these challenges lies in a high evaporation rate already at low power input in combination with a substrate movement adapted to the component geometry. Possibilities and limitations of the method are explained, properties of coated parts are analyzed in comparison with the current state of the art, and further possible applications are discussed.

Plastic products are playing an ever bigger role in our daily life and they draw more and more attention of the market. Reasons for this trend are low cost, ease of producibility, large freedom of design and low weight.

Coatings on plastic products have mainly been produced by electroplating and lacquers.

Since the 1980’s PVD coatings have been used for decorative applications in the watch industry. Nowadays decorative coatings are applied on watches, faucets, door handles, spectacles (both frames and glasses) and mobile phones.

In recent years a new market has emerged for PVD-coatings on plastics driven by the requirement to reduce weight. This occurs because on one side the expectations of a growing market share for electrical cars exists as well as on the other side CO₂ emissions and fuel consumption can be reduced by weight reduction. The consequence is that the use of plastics in the automotive industry as light weight base material for both interior and exterior parts will have an increasing share. Until now electroplating is the major applied technology, but PVD will get an increasing share in this market due to the requirement for replacement of electroplated chromium. Electroplating is a technology requiring the use of carcinogenic hexavalent chromium (in form of trichromate) during several steps of the plating process. This material is on the list of SVHC’s (Substances of Very High Concern) and imposes severe health dangers on personnel working with the plating lines. Besides this plating technology requires intensive efforts to dispose waste materials.

As replacement for electroplating in-line processes where plastic parts are coated with UV-cured lacquer and a subsequent chromium PVD layer have been developed and are available on the market. Mass production for automotive plastic products is already applied.

In this presentation the developments will be discussed beginning from initial applications on watches and faucets by sputter and arc technology in the 1990’s. In the early 2000’s coatings have been introduced on mobile phones, whereas finally in the last decade the application of coatings on plastic parts by hybrid lacquer/PVD-PECVD processes have been developed.

Different aspects of the requirements for coated products and the related processes will be discussed from the point of view of technologies, productivity, performance and sustainability.

Light-weight materials such as polymers and magnesium alloys exhibit tremendous challenges for surface engineering, not only in terms of selecting appropriate coating architectures and processes, and therefore reducing or avoiding issues that can result in premature coating failure at relatively low stress levels compared to more rigid substrates, but also for the development of sophisticated testing methods for quality evaluation and inspection.