Chlorinated Polyvinyl Chloride Varnishes

varnishes that are made from chlorinated polyvinyl chloride resins. Mixtures of acetone with toluene or xylene are suitable solvents for chlorinated polyvinyl chloride varnishes; sometimes butyl acetate is added to the solvent mixture. Chlorinated paraffin, which improves the chemical resistance of coatings, and phthalates and phosphates of various alcohols are used as plasticizers with these varnishes. Chlorinated polyvinyl chloride varnishes are usually sprayed and sometimes applied with a brush; a film forms within 1.5–3 hours at room temperature and within 1 hour at 60°-80°C. Complete drying occurs within 5–6 days at room temperature and 2–3 hours at 60°-80°C. At higher drying temperatures, decomposition of the resin, which is accompanied by the loss of HCl, is possible. Films are formed as the solvents evaporate. These films are redissoluble, noncombustible, and resistant to temperatures as low as — 50°C; furthermore, they exhibit low permeability to vapors, have increased stability in water and in dilute acids and bases, and are not decomposed by microorganisms or by occasional contact with gasoline or mineral oils.

The major disadvantages of chlorinated polyvinyl chloride varnishes are low adhesiveness to metals, low resistance to light and heat, and a lackluster finish. Adhesiveness is improved by drying at elevated temperatures and by introducing additional film-forming agents, for example, alkyd resins, although alkyd resins reduce the resistance to chemical corrosion. Stabilizers are used to improve resistance to light and heat, for example, epoxi-dized vegetable oils and benzophenone derivatives. Many inorganic pigments also have stabilizing action. The chlorinated polyvinyl chloride enamels that are obtained by introducing these inorganic pigments into chlorinated polyvinyl chloride varnishes are used to coat metal, wood, and concrete and are extensively used in shipbuilding, machine building, and construction. The protective properties of these enamels are improved by applying one or two layers of chlorinated polyvinyl chloride varnish over several layers of enamel. To improve adhesion to metals, enamels are applied over an alkyd or phosphatized primer. The low adhesiveness of chlorinated polyvinyl chloride varnishes is an advantage when coatings are required to provide only temporary protection during storage and transport of coated items.