Pintura de peças plásticas

501-36-49 Paint - General Information 501-36-49 DESCRIPTION AND OPERATION Painting Plastic Parts General Although these days plastics can be produced in all colors and with a matt or gloss surface, painting is often necessary. NOTE: Manufacturer's limitations concerning the feasibility of painting certain components must always be observed. Reasons in favor of applying paint to plastic are: ‡ Individual coloring, matching the body paint. ‡ More gloss and color brilliance through painting. ‡ Removal of production imperfections. ‡ Protection from atmospheric exposure. Nowadays painting plastic presents no problems because the materials are known and matched to the paint. In order that the painter can use the correct painting materials, the type of plastic must first be correctly determined. To allow this, plastics are marked on the rear in accordance with the recommendations of the Association of Vehicle Manufacturers. Once the type of plastic is determined it is an easy matter to assign special paint recommendations, matched to that particular plastic. Unmarked plastics require knowledge of materials so that a correct choice of paint materials can be made and the component can be reliably painted. Plastic groups Thermoplastics When warmed these undergo a reversible transformation into a plastic deformable state and once cooled they maintain their shape. They consist of string-like (linear) or only slightly branched molecular chains. Thermosets Thermosets are hard and have the form of a close-meshed network in all directions. They do not undergo plastic deformation, are especially resistant to chemicals, are difficult to swell and are insoluble. At normal temperatures they are hard to brittle. At first the material does not undergo any change when heated, but when it reaches a critical point, the thermoset is totally destroyed. Elastomers Elastomers are characterized by high elasticity over a wide temperature range. They have properties like rubber or a sponge and after compression or distension they return to their original state. Types of plastic The plastics used in the automotive area: ‡ ABS - Acrylonitrile butadiene styrene (polymer) ‡ PA - Polyamide ‡ PC - Polycarbonate ‡ PE - Polyethylene ‡ PP - Polypropylene ‡ PP/EPDM - Polypropylene/ethylene propylene diene copolymer ‡ PC/PBT - Polycarbonate/Polybutylene terephthalate ‡ PBT/PC - Polybutylene terephthalate/Polycarbonate ‡ PUR - Polyurethane ‡ GRP - Glass reinforced plastic NOTE: PE and PP are plastics which cannot be painted, or can only be painted using special techniques. As well as the pure plastics, so-called 'blends' are also used. This means combinations of different plastics. If we were dealing with metals they would be called alloys. Plastic identification Normally the identifier is marked on the plastic components used in vehicle construction. One method to determine the plastic group is the sanding test. In this a place is chosen which will not be visible later, and the finger belt sander is used to sand the plastic. The plastic group can be determined using the pattern left by the sanding and the dust: ‡ Thermosets produce a white dust. ‡ Thermoplastics smear and do not produce dust. The plastic group can be determined by a sound test: