AUTOMOTIVE PAINTS 1 -15 CD Lacquer primer-surfacer This paint mainly consists of nitrocellulose and alkyd or acrylic resin, and is used very commonly because of its quick-drying and high workability. But it is not as good as other reaction type primer-surfacers in terms of resistance against rust and absorption and adhesive power. ®Urethane primer-surfacer This is a dual-component reaction type paint consisting mainly of nitrocellulose and acrylic or alkyd resin. It becomes hard when mixed with isocyanate (hardener). It has outstanding rust pre- ventive, smoothing and adhering capacity as well as resistance against absorption. But it requires hot air (around 60°C) for faster drying.
Several types of urethane primer-surfacer are available commercially. Some dry more quickly but are less outstanding in performance than other types. They should be used selectively according to the type of work. @Thermosetting amino alkyd primer-surfacer II This is a primer-surfacer designed for repainting using baking paints. It requires baking at a tem- perature 90 to 120°C for 20 to 30 minutes, but gives the same coating performance as paint- work on production lines. (4) SURFACER Surfacer is a second coat paint that is applied over a primer, putty or other undercoats, and has the following properties:
·Smoothing · Prevention of absorption ·Adhesion Several types of surfacers are available commercially and they fall in either the lacquer, urethane or baking paint family. But they have been replaced by the primer-surfacer and, therefore, are rarely used for repainting. (5) SEALERS Several types of sealers are used selectively to prevent a variety of defects that may occur in old coating, or improve its properties. · Prevent bleeding · Prevent shrinkage · Prevent absorption · Improve adhesion But use of sealer has become rare today because defects such as bleeding, shrinkage and absorption can be prevented by the urethane primer-surfacer.
Sealer is applied on the hidden areas of doors, hinges, etc., that cannot be accessed easily when sanding. When selected carelessly, however, the sealer may affect the adhesive power of the top coat. Therefore, it is important to test adhesion prior to application and to use only the minimum amount of sealer needed. Sealer is sometimes applied over the primer-surfacer when the top coat (Super White, Super Red, Pearl Mica, etc.) only has a low hiding power. Sealer, applied over primer-sUifacer to improve its hid~ ing power, is called a color sealer or color base. - 17-