GB754860A - Process for vulcanizing sheet rubber - Google Patents

Abstract

A process for vulcanizing sheet rubber comprises forming a roll of alternate layers of sheet rubber containing vulcanizing ingredients and a sheet of dielectric material which is different from the rubber and which is incorporated into the roll under a tension of at least 0.1 lbs. per inch of width, dielectrically heating the roll to the vulcanizing temperature by placing in a high frequency electric field, e.g. of 1 to 50 megacycles per second, maintaining around the roll an atmosphere, preferably of an inert gas such as carbon dioxide or nitrogen, of at least 5 lbs. per square inch pressure which is raised in temperature simultaneously with the rubber by means independent of said field terminating the dielectric heating when the vulcanizing temperature has been reached, and thereafter utilizing only said independent heating means to maintain the rubber in the roll at its vulcanizing temperature for a period requisite to achieve vulcanization. A vulcanizing apparatus is described, which is the same as that described in Specification 754,859. In one example a rubber sheet 2500 yards long, 0.008 inch thick, and 5 feet wide, comprising 100 parts Wild Para Rubber 7 parts sulphur, 1 part Sym. Dibeta Naphthyl para Phenylene Diamine is incorporated in a roll with alternate layers of a highly polished sulphite paper and subjected simultaneously to a high frequency electric field of 21 megacycles per second and to heating by steam coils for 90 minutes, when the vulcanizing temperature of 300 DEG F. is reached. The dielectric heating is then stopped and the heating by steam coils continued to maintain the temperature at 300 DEG F. for a further 75 minutes. On completion of the vulcanization the sheet rubber is rapidly removed from the roll and cooled on cooling rollers with the simultaneous application of talc or of a solution of silane such as octadecyl or hexadecyl trichlorosilane which forms a silicone coating on the rubber surface. Other examples refer to the vulcanization of crepe rubber, chloroprene, and smoked sheet.