Other synthetic resins, such as those of the alkyd, petroleum, urea, and vinyl types, are sometimes incorporated with the phenolics in the same surface coating to obtain some desired property. The addition of a plasticizer, such as tricresyl phosphate or dibutyl phthalate, improves the flexibility of the film.
Spirit varnishes, in which the synthetic resin is dissolved in a solvent, are also available. In this type the soluble fusible resin (form A) is dissolved in an organic solvent such as acetone or the various alcohols, and conversion of the resin to the insoluble, infusible state (form C) is effected by baking the film.
Coatings made from tar-acid resins are widely used in so-called 4-hour enamels and varnishes, for both interior and exterior application. They are also used in the manufacture of linoleum, artificial leather, adhesives, and printing inks. When incorporated with nitrocellulose or cellulose acetate lacquers they improve the adhesion, luster, and resistance to alkalies.
Production in the United States.
In 1937 the output of tar-acid resins for surface coatings exceeded 20 million pounds (net resin). Those from phenol and the substituted phenols accounted for a very large part of the total. They were followed by resins from cresylic acids and the xylenols in that order.
In 1937 there were about 20 domestic makers of this type of synthetic resin, with factories located in California, Connecticut, Illinois, Indiana, New Jersey, New York, Massachusetts, Michigan, Missouri, Ohio, Pennsylvania, and Rhode Island.
Imports into and exports from the United States.
Imports of oil-soluble phenolic resins have been negligible. This is due, in part, to licenses and agreements between certain domestic and foreign makers, to the remarkable advancement and pioneering work done in this country, to the holding of many basic patents by Americans, and to the relatively high duty on imports.
Exports of these products, usually in the form of enamels, varnishes, and lacquers, have been appreciable and are probably increasing each year. Official statistics are not reported separately.