A comparatively new use for tar-acid resins is in the manufacture of wood adhesives. Ordinary vegetable and animal glues have long been used, although their deficiencies in certain characteristics are well known. These include (a) their inability to produce uniform products, (b) the tendency of most alkaline glues to stain wood, (c) the bad effects of moisture on them, and of bacteria and fungi in the case of animal glues. The tar-acid resins have none of these objectionable qualities. Being chemically inert they are free from attack by fungi and bacteria. Moisture does not affect them, and they do not stain wood.
Three types of resins are used as wood adhesives, principally in bonding plywoods and veneers: (1) Hot press liquid, (2) cold press liquid, and (3) resin film. Furniture, radio cabinets, games, and building products constructed from plywoods bonded with resins can be shipped to tropical countries, the bond not being affected by extreme climatic conditions.
These resin adhesives are more expensive than the usual animal and vegetable glues, a factor which has limited their application. Their advantages may, however, open up to resin bonded plywoods uses in which the more ordinary types are not satisfactory.
TAR-ACID RESINS FOR OTHER USES
The application of tar-acid resins in casting, molding, laminating, surface coatings, and adhesives has been described. There are many other uses, but most of them approach the types of application dealt with.
Impregnation of all sorts of materials with tar-acid resins is an increasing use; such applications are in fabrics for aircraft, crease resistant textiles, wood, asbestos, concrete, and electrical coils. Wood with resin forced into the fiber under pressure is used for furniture, flooring, heads for golf clubs, and handles for utensils. Resin is used as a binder in the manufacture of brake linings for automobiles, as well as in the manufacture of abrasive and grinding wheels.
An interesting application is in the construction of corrosion-resistant chemical plant equipment. In 1922 the German firm of Saureschutz Gesellschaft was incorporated to fabricate equipment composed of a special acid-resisting type of phenolic resin and asbestos. Sometime later its manufacture was started in the United States. All sorts of industrial plant equipment is now available, including cylindrical and rectangular tanks up to 9 feet in diameter and 12 feet high, piping for corrosive liquids and gases, valves, pumps, fans and ventilators, filter press plates and frames, buckets, dippers, etc.
Another new use is for making matrices in which to mold rubber printing plates. Such plates are used at present chiefly in printing cotton and paper bags but extensive experimentation promises to broaden their use. The matrix is made of fiber board of very open structure impregnated with tar-acid resin in the process of manufacture.