M4. decorating plastic parts with processes that are also common to non-plastics – Silk screening, roll coating, electroplating, labeling (except in-mold labeling described below), laser marking, flocking, dyeing, vacuum metalizing, sputtering, polishing and buffing are all described in Chapter 8 of this handbook. Printing (various processes) is described in chapter 9. Polishing and buffing operations for thermoplastics must be carried out with softer wheels, slower speeds and lighter pressures than with metal parts, to avoid overheating the surface of the workpiece.

M4a. electroplating of plastics - A number of plastics can be electroplated by being treated to make the surface conductive before the plating operation. One way to do this is to plate the part by the electroless method with a thin layer; electroless plating can be used with non-conductive materials. Another approach is to add carbon to the plastic when the part is molded. A third method is to coat the workpiece with a conductive paint. The electroless method involves several steps: 1) acid etching to create a microporous surface, 2) a neutralizer bath to reduce any residual acid, 3) a catalyst bath to deposit palladium in the surface micropores, 4) an accelerator bath to prepare the palladium for electroless plating and, 5) electroless plating with either copper or a nickel-phosphorous alloy. The conductive part is then plated by conventional methods. ABS and PEC (polyphenylene ether copolymer) are the most frequently plated plastics, but polystyrene, ABS/polycarbonate, nylon and polysulfone are also processed. Automotive hardware and trim are often made from plated plastic moldings. A major application is the plating of the circuit paths on printed circuit boards. Epoxy/glass, polyimide, phenolic and Teflon/glass are common substrates. The plating of household faucets, knobs, marine hardware, hospital equipment and kitchenware are other uses.

M5. in-mold decorating - It is quite feasible to place decorative or other material in a mold so that the item, after molding, is integral with the molded part. Several alternative methods are possible: 1) The mold cavity walls can be coated with another material prior to molding to provide a surface finish on the molded part different from that which would otherwise be achieved. Both liquid and powder coatings are used. 2) product labels can be inserted in a mold before the molding operation and, 3) decorative foils or other objects can also be placed in the mold so that they become part of the finished product. This approach is feasible with injection molding, compression molding, RIM and other molding processes, including those carried out with reinforced plastics. The advantage with coatings is that they eliminate surface porosity, and provide a durable, smooth surface for the part. The advantage with inserted foils and labels is that the inserted object is securely held and, in some cases, increases the strength  of the finished part while reducing the amount of material required. The need for later finishing operations is often reduced. Foils with a brushed aluminum or wood grained appearance are common inserts. The inserting operation at the molding machine can be manual or, in many cases, robotic. One early and still common in-mold decorating operation is the use of preprinted, resin-impregnated paper in the molding of melamine dishes and urea and phenolic products. Thermoplastics can also be processed with decorative inserts. Polypropylene, polyethylene, polystyrene, polycarbonate, ABS and acrylics are suitable for in-mold label and foil decorating.

M6. sheet and film embossing - Several methods are used to produce textures in the surfaces of plastic film and sheet. Such textures change the appearance of the sheet, provide a different feel and can hide other imperfections. One common example of a changed surface of sheet plastic is the modification of flexible vinyl sheets to provide a leather-like appearance. The common method for producing this effect is to run the heated sheet through a pair of cooled forming rolls. At least one of the rolls is engraved with the reverse of the pattern desired on the plastic sheet. When passed through the rollers, the sheet is formed and then cooled so that the texture becomes permanent. Depending on the results wanted, the roll used to back up the engraved roll can be rubber or another resilient material. It can be flat steel or can be engraved to better emboss the sheet or provide some other pattern on the reverse side. Although it is most common to have a heated sheet and cool rolls, sometimes, the sheet is initially cool and is formed by rolls that are heated. Still another method uses formed paper, with a release agent on its surface, in a film casting operation so that the film or sheet as initially made has the texture in it. Sometimes, when deep embossing is desired, the roll is porous and a vacuum is drawn in it. Other methods involve dielectric or frictional heating in small areas of the sheet to aid in forming.

Forming or embossing is sometimes combined with printing a pattern on the surface to enhance the appearance of the texture. Valley printing , that is, printing in the depressed parts of the surface, is illustrated in Fig. 4M6 which shows equipment that embosses and prints the surface in the same operation. This approach is useful in imparting wood grain, textile or leather effects on vinyl, urethane or

other plastic sheets.

Fig. 4M6 Valley embossing and printing of film or sheet. 2 a) Valley printing - printing in the depressed areas of an embossed sheet. b) Schematic view of combination embossing and valley printing equipment: A - patterned applicator rolls, B - analox rolls, C - doctor blade to remove excess ink, D - ink pan, E – furnisher roll.