Plating on plastic | decoration
Electroplated plastic parts can match the appearance of metal while offering cost and weight savings and increased design fl exibility. David Coombes provides some expert tips on designing components for electroplating
Bright ideas: Avoiding the pitfalls of plating plastics
Bright chrome plating is a classic fi nish for many metal products, providing corrosion resistance and increased hardness in addition to a superb high quality decorative appearance. The same decorative benefi ts can also be achieved on plastics, with the added advantages of weight-saving and improved design fl exibility - surface treatments applied to the moulding tool can, for example, extend options beyond traditional bright chrome to include a mix of mirror and textured fi nishes on the same component. There are two routes to achieving a real metal
coating on plastic – vacuum deposition or electroplat- ing. Vacuum deposition can be very cost effective. However, vacuum deposited metal is not that durable - moderate abrasion will quickly remove the fi nish as will many organic solvents. In addition, the required protective lacquer can leave an undesirable ‘orange peel’ effect on the surface. Where durability is required, such as for automotive applications, the metal must be integrated with the plastic surface and this is best achieved by electroplating. Electroplating chemically and physically bonds the
metal to the polymer substrate by electrolytic deposi- tion. To do this, an electric current is passed through the metal to be deposited and then through the
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workpiece, removing atoms from the coating material and attaching them to the surface of the part. As most plastics are electrically insulating, the fi rst step in the plating process is to make the part electrically conduc- tive, which is achieved by depositing a layer of nickel in a chemical dipping process over a catalytic palladium layer. This layer must be integral with the surface of the part for the bonding to be effective, which is one of the biggest restrictions on plating plastic. These base layers also allow different fi nal surface
fi nishes to be achieved. Bright nickel is used to achieve the traditional mirror chrome fi nish while satin nickel is employed for today’s fashionable slightly-dulled satin chrome effect. Although polyamide (PA) and polypropylene (PP) can
be successfully plated, some 90% of plastic plated components are manufactured from acrylonitrile butadiene styrene (ABS). ABS lends itself to plating because the butadiene molecules at the surface can be relatively easily removed using chemicals to leave spherical undercuts, which act as an excellent key for the palladium/nickel layer. Over the years, specifi c grades of ABS have been
developed for plating applications. Low thermal expansion grades, for instance, have overcome the
November/December 2014 | INJECTION WORLD 53
Main image: Optimising part designs for
electroplating will result in fi nished
components with a high
surface quality and long
service lifetime
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