AUTOMOTIVE PAINTS 1 -13 (1) PRIMER Primer is applied directly onto the bare metal to prevent rust and give adhering power for the next coat. It is generally applied in a very thin coat and does not require sanding. There are several kinds of primer. However, a primer is less often used today in repainting because a new product, primer- surfacer, has been developed to replace it. CD Wash primer Also called an etching primer, wash primer mainly consists of vinyl butyrai resins and zinc chro- mate (rust preventive pigments). Wash primer is available in two types, a single-component type and a dual-component type.
The dual-component type wash primer provides better rust preven- tive and adhesive power. Wash primer must be applied very carefully as the designed adhesion power is lost when the coat is too thick or left to dry more than necessary. ® Lacquer primer Ill Lacquer primer mainly consists of nitrocellulose and alkyd resins. It dries very fast and the next coat can be applied quickly. But it is less rust preventive than other types of primers. @ Urethane primer This is a dual-component type primer mainly consisting of alkyd resins. It becomes hard when mixed with isocyanate (hardener).
Urethane primer has outstanding rust preventive and adhesive power, but requires hot air (around 60°C) for drying because drying under normal temperature (20°C or below) is a very slow process. @ Epoxy primer This is a dual-component type primer mainly consisting of epoxy resins. It becomes hard when mixed with an amine family hardener. Epoxy primer also has outstanding rust preventive and adhesive power, but requires hot air (around 60°C) for drying because drying under normal tem- perature (20°C or below) is a very slow process.
In an automobile production line, a water-based epoxy resin paint is electrically deposited (ED) on the bare metal bodyshell, and is dried at a high temperature over 150°C. Primer which is applied to areas other than the bare metal, such as aluminum or resin compo- nents, is called a bonding primer because its sole purpose is not prevention of rust but to ensure good adhesion between the material and the next coat of paint. (2) PUTTY Putty is a paste-like paint used to fill deep dents that cannot be filled by other types of undercoat or second coats.
Three types of putty, namely metal putty, polyester putty and lacquer putty, are used selectively depending on the depth of the dent to be filled. Putty is normally applied thickly by a spatula to fill the dent, and smoothed later by sanding. CD Metal putty Metal putty is a dual-component paint mainly consisting of an unsaturated polyester resin. It becomes hard when mixed with organic peroxides (hardener). This putty is used mainly to cor- rect surface irregularities on the base metal in sheet meta! working. !t is very f!exib!e and can be applied to form a very thick coat (up to around 30 mm), but contains many pores and is hard to sand. - 15-