Heres a good write-up on the evolution of automotive paints for someones future reference. From tripod.com:
7. Automotive Paint
7.1. WHAT TYPE OF PAINTS ARE USED ON AUTOMOBILES?
Japanese Varnish: In the early years, between 1900 and the 1920's, Japanese varnishes were used. The varnish was applied by brush. Nitrocellulose Lacquer: in the 1920's, several paint manufacturers were involved in the development of nitrocellulose lacquers. This paint had rapid drying and low viscosity properties, and was applied with air pressure through a spray gun leaving a hard dry finish in approximately one hour. When rubbed, polished, and waxed, it far surpassed in durability and appearance the qualities of the Japanese lacquers. Synthetic Enamel: In the mid 1930's, a new and completely different type of paint was developed, the alkyd or synthetic enamels. It proved to have superior qualities in film strength, adhesion, luster, flexibility and durability over all previous paints. The resin base was developed from the reaction between phthalic anhydride and glycerin, with gums, oils and plasticizers added during the manufacturing process a drying oil such as linseed, a polyhydric alcohol, such as glycerine, and a dibasic acid, such as Phthalic Anhydride. It dries by solvent evaporation, like the lacquer paints, but the resin remains soft and sticky when no solvents are present. It cures to a hard finish by absorption of oxygen from the air. The curing process can be accelerated by heat, and several methods of baking enamel were developed. Unlike lacquer, when dry, it needs no polishing to produce a high luster finish. Acrylic Lacquer: As time passed, chemists developed a substitute for nitrocellulose lacquer, using an acrylic resin as a base. The resins used in acrylic lacquer tend to be slightly brittle. This deficiency is overcome by the use of a plasticizer ( a liquid that is a solvent for these resins and softens them slightly). A cellulosic resin is any resin derived from cellulose (pure cotton). Acrylic lacquer was used extensively by General Motors. Acrylic Enamel: During the late 1960's and early 1970's, technology brought on the development of acrylic enamel, which was harder and more durable. Chemically, it is a cousin to synthetic enamel, but is modified with acrylic resin, and is not soft and sticky with no solvents present. It cures further with the absorption of oxygen from the air. Unlike the lacquers, which remain soluble in solvents, the enamel family is insoluble in solvent when cured. An acrylic resin is chemically any polymer whose basic monomers are chemical derivatives of acrylic acid. Polyurethane Enamel: In the mid 1970's, polyurethane enamel was developed to withstand the severe stress of high speed airplane surfaces, which are subject to rapid temperature changes and flexing. This paint was much more durable than the acrylic enamels. Acrylic Urethane Enamel: Acrylic urethane enamels were developed to withstand environmental elements, such as acid rain and ultra violet rays. It is the most durable paint to date.
