TAR-ACID RESINS IN ADHESIVES
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.