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a variety of paper that differs from ordinary paper in its greater quantity of paper pulp per unit area. There is no uniform international classification that makes a sharp distinction between paper and cardboard. For example, in the USSR, cardboard is the term for paper matter with more than 250 g of pulp per sq m; in the German Democratic Republic, more than 150 g/m2; and in Poland, more than 180 g/m2.
The operations in the production of cardboard are beating, molding, pressing, and drying; they do not differ in principle from similar operations for making paper, although material with coarser and stiffer fibers (such as brown wood pulp, hemi-cellulose, sulfate pulp, and waste paper) is more frequently used as raw material to make cardboard.
Types of cardboard include packing, printing, footwear, electric-insulation, and millboard. Packing cardboard is used to make boxes and cartons. Types of printing cardboard are binder’s board (for making book bindings and clean products), matrix board (for making matrices for molding stereotypes), and ticket cardboard. Types of millboard include facing board (for facing dry gypsum plaster) and wallboard (for covering building walls). Types of industrial cardboard are fitting board (for making sealing gaskets), sound-deadening and thermal-insulation cardboard, and waterproof and filter board.
Cardboard is made on cardboard machines. A distinction is made between single-ply and multi-ply cardboard. The layers of multi-ply cardboard are usually prepared from fibers. The inner layers are molded from cheaper compositions; the outer layers are molded from more durable and expensive fiber (for example, the inner layers of most types of box cardboard are molded from white pulp with a small amount of cellulose added, from waste paper, or from other cheap fibrous materials; the outer layers are made of bleached or unbleached sulfate pulp).
The properties of cardboard are evaluated by a series of general and special technical parameters. The general parameters include mass per square meter, thickness, and moisture content. The special parameters include absorbent capacity, electric-insulation properties, and deformation upon moistening and drying. The required properties for each type of cardboard are provided by the selection of the proper intermediate products, by their treatment, and by the introduction of adhesives, binders, fillers, and dyes into the cardboard, and by the application of polymer films and metal foil to the surface of the cardboard.
REFERENCESLapinski, J. KartonodelateVnye mashiny. Moscow, 1966. (Translated from Polish.)
Legman, G. Osnovy tekhnologii pererabotki bumagi i kartona. Moscow, 1968. (Translated from German.)
M. M. KOTIK