Decorative Platingon Plastic POP

Since the 1950s, plastics have been substituted for metals in a multitude of applications and for a variety of reasons, including weight advantages, cost advantages, and the relative ease of creating complexly shaped substrates through molding. These factors prompted the development of suitable decorative finishing processes, specifically plating processes, starting in the early 1960s. Electroless metal deposition as a base for a thicker, decorative electrolytic deposit has proven extremely reliable and commercially successful. For lower-performance applications, electroless nickel is a suitable choice. However, ever since the demonstration in the 1970s that electroless copper provides better resistance to environmental exposure (Ref 29, 30), it has become the material of choice in the majority of higher-performance applications, especially automotive. The molded substrate is chemically treated to improve adhesion of the copper film (see the section "Processes" in this article), then about 0.5 to 0.75 pm of electroless copper is applied. Typically an electrolytic copper or Watts nickel strike follows, and then a thicker (12 to 25 pm) electrolytic bright acid copper deposit. Finishing coats of electrolytic nickel and/or chromium plating are then applied.

Substrate materials (Ref 28) for decorative plating-on plastic include acrylonitrile-butadiene-styrene (ABS), ABS/polycarbonate, polyphenylene oxide, polycarbonate, polysulfone, polyester, nylon, and so on. There are many grades for any given plastic, and these may differ considerably in plateability. Certain grades of foamed plastics may also be used. For decorative POP, ABS is by far the most commonly used plastic. ABS is a thermoplastic alloy with an acrylonitrile-styrene matrix that has butadiene rubber dispersed throughout. The butadiene is selectively etched by the pretreatment chemistry, creating a uniformly roughened surface suitable for plating.

In all POP applications, control of the molding process is critical. Care must be taken to avoid introducing stresses or strains, to avoid troublesome mold-release agents, to limit use of "regrind" resin, to ensure a resin-rich surface (in cases where fillers are used), and so on. The use of complexly shaped parts necessitates close attention to such details as mold design and maintenance, melt and mold temperatures, fill speed, and many other parameters. In designing or troubleshooting a plating-on-plastic process, it is critical to use molded parts of the exact grade and design to be used, as there is high interdependence between molding and plating processes.

0 0

Post a comment