AUTOMOTIVE PAINTS 1-17 @ Standard acrylic urethane Commonly referred to as just "urethane" or "acrylic urethane," this is a dual-component type top coat material mainly consisting of acrylic resins. It becomes hard when mixed with an isocyanate hardener. It has an outstanding coat performance but dries very slowly (over 12 hours at 20°C) resulting in a lower workability level than lacquer type materials. Drying can be accelerated to only one hour by using hot air (60°C). Its coating performance is as good as the paint on new vehicles and it does not require extra polishing to produce a iuster after drying.
For these reasons, standard acrylic urethane is used commonly for total coating and coating over relatively large areas. @ Acrylic urethane lacquer This is a paint designed to improve the coating performance of an air-drying acrylic lacquer without affecting its quick-drying property. It mainly consists of nitrocellulose and acrylic resin and becomes hard when mixed with an isocyanate hardener. It looks as quick-drying as 1 an acrylic lacquer because, when the solvent evaporates, the nitrocellulose component increases the initial hardness of the coat.
At the same time, since the acrylic resin reacts with isocyanate and forms a netted structure, it yields a better coating performance than the acrylic lacquer. But this material must be used very carefully because some parts in the coat are dissolved by a solvent while some other parts are not. This tends to cause defects in secondary repairs or in places where two-tone colors are overlapping. In addition, the increased apparent hard- ness of the coat tends to make the paintwork personnel think as if drying is completed and remove the masking tape. This damages the coat because it is still wet.
The acrylic urethane lacquer is often used in bodywork stations without modern facilities (booths, driers), but is gradually being replaced by the quick-drying acrylic urethane (see below). @ Quick-drying acrylic urethane This material is often referred to as a quick-drying urethane. It is designed to shorten the dry- ing time without affecting the coat performance of the standard acrylic urethane. It is made mainly of acrylic resins and becomes hard when mixed with an isocyanate hardener. The quick-drying acrylic urethane is used commonly for repainting purposes because of its quick- drying property and outstanding coat performance.
®Baked type These are single-component type paints that become hard when heated (about 140°C). Baked type paints that are used in car production lines are also used for repainting. @ Thermosetting amino alkyd Also called melamine baked paint, this is a solid type paint mainly consisting of melamine and alkyd resins. ® Thermosetting acrylic This is a metallic paint mainly consisting of melamine and acrylic resins. - 19-