Process for the heat treatment of biaxially stretched thermoplastic resin films

Abstract

Abstract 1,216,176. Heat treating biaxially stretched synthetic resin films. KOBUNSHI KAKO KENKYUJO K.K. 5 March, 1969 [5 March, 1968], No. 11764/69. Heading B5B. Biaxially stretched thermoplastic synthetic resin films are heat treated by passing a pair of such films, one of which is superimposed on and in contact with the other, in a sinuous path around a series of heating rolls in successive groups, the heating rolls in each of said successive groups being at a higher temperature than that of the rolls of the preceding groups and being rotated at a peripheral speed which is equal to or lower than that of the rolls of the immediately preceding group and is lower than that of the rolls of at least one preceding group to carry out successive heat-treatment steps under such conditions that the film webs are contracted or relaxed in the longitudinal and transverse directions to give a relaxation or a contraction in area of less than 25%. The pair of film webs may be prepared from a biaxially stretched tubular film of the synthetic resin. The two film webs may be separated after the heat treatment or may be laminated to one another under pressure after the heat treatment. The synthetic resin may be polypropylene, high density polyethylene, polystyrene, a polyester or polyvinyl chloride. When the synthetic resin is polystyrene, five groups of heat-treatment rolls may be employed, maintained at about 80‹ C., about 100‹ C., about 115‹ C., about 135‹ C. and about 145‹ C. respectively. When it is high density polyethylene, four groups of rolls at about 80‹ C., about 100‹ C., about 115‹ C. and about 124‹ C. respectively may be employed. Each group of heat-treatment rolls may comprise two heat-treatment rolls.

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