Bookbinding and the Conservation of Books
A Dictionary of Descriptive Terminology

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hot-melt adhesive

A resinous adhesive which achieves a solid state and resultant strength by cooling, as contrasted with other adhesives which achieve the same results through evaporation or removal of the solvents. Before heating, a hot-melt adhesive is a thermoplastic, 100% solid material, and is all adhesive. Upon the application of heat, the usual operating temperature being in the range of 175 to 205° C. (350 to 400° F.), the material changes to a fluid state. Subsequent to the removal of heat, it sets by simple cooling.

When a hot-melt adhesive comes into close contact with the surface to be bonded, a molecular layer of film at the surface of this substrate immediately attains a temperature approaching that of the hot melt. In addition a high degree of wetting, almost coalescence. of the hot melt and the material occurs. Immediately thereafter, the adhesive loses heat to the film over the entire area and temperature equilibrium is attained. Since the adhesive is in contact with a mass much larger than itself, the temperature of the entire system drops to the point at which the hot melt sets to a solid state with sufficient cohesive strength to bond the films together. Thus the uniqueness of hot-melt adhesives stems from the speed with which they produce a bond, which is almost instantaneously.

Although the use of hot-melt adhesives eliminates the cost of solvents required by some other adhesives, the principal cost reduction results from the time saved in their application. In addition, a lesser quantity of the hot melt can usually be utilized to produce an equivalent bond.

Hot-melt adhesives are used extensively in binding books made of loose sheets, especially those that are not rounded and backed, e.g., paperback books, telephone and other directories, etc. For books that are to be rounded and backed, however, the so-called DRYING MEMORY of the hot-melt adhesives causes problems. In addition, hot-melt adhesives alone do not lend themselves well to the binding of heavily loaded or coated paper, from which all particulate matter must be removed before application of the adhesive. See also: ADHESIVE BINDING ;ONE-SHOT METHOD (1) ;TWO-SHOT METHOD .

(81 , 89 , 179 , 219 , 309 )

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