Surface Decoration

Consumer tastes and publicity needs are not always fully met by the pigmentation of plastics or by two-color injection molded parts.  There is also demand for plastic products with a decorative (or informative) surface. Printing, painting, and hot stamping are frequently used to finish and/or imprint molded surfaces.  As results achieved depend on material grades, modifications, coloring, and reinforcement media, special grades have been developed for some methods.

Printing:
Offset printing, silk screening, pad, or tampon printing are among the methods adapted to plastics.  Special printer's colors are offered by the established manufacturers of tampon printing colors.  Two-component systems such as epoxies or polyurethanes are best suited to improve adhesive strength and scratch resistance of decoration on Ticona’s engineering resins.  Cleaning, or thermal or physical surface preparation, may be required for good adhesion.

Sublimation Printing:
In sublimation (diffusion) printing, color in dry dye crystals is transferred from a release film to a plastic substrate under heat and pressure.  The dye crystals vaporize and the vapor penetrates the plastic part, yielding a durable, wear-resistant decoration.  This process is cost competitive with other processes, such as two-stage injection molding or silk screening.  It is, however, limited to polyesters and polyester-based alloys by currently available dyes intended for textile applications.  New dyes are under development for applications with other than polyester-based thermoplastics.

Painting:
Although most plastics can be painted, some, such as polyethylene, polypropylene, and polyacetal, are very resistant to solvents and can be difficult to paint.  They require special primers or pretreatments (cleaning, acid etching, or primers) for satisfactory adhesion.  Many amorphous plastics easily accept a wide variety of coatings.

Although rolling and dipping are sometimes used, power spray painting is the usual method of paint application.  Among the coatings used for plastics are polyurethane-, epoxy-, acrylic-, alkyd-, and vinyl-based paints.  When choosing a paint system, the processor should be sure the substrate can withstand any required oven curing.

Hot Stamping:
In this one-step, economical process, pressure from a heated die transfers a high-quality image from a transfer tape to a flat plastic surface.  Designs can be transferred in pigmented, woodgrain, or metallic finishes.  Stamping temperatures over 170 °C should be used to obtain higher adhesive strength and scratch resistance.  Although an aftertreatment is not required, the parts may require cleaning, or a flame or corona pretreatment.

Decals and Labels:
These are usually self-adhesive, precut, printed patterns on a substrate that simply adhere to the surface of a part.  Decals generally use a transparent plastic film, while labels normally use an opaque plastic, metallic, multilayer sandwich base.