GB281316A - Improvements in proofed paper and method of producing same - Google Patents

Abstract

281,316. Scutan Co., (Assignees of Reid, J.). Nov. 26, 1926, [Convention date]. Waterproofing; proofing processes and compositions. - A proofed flexible sheet of paper is produced by passing a thin sheet of close-grained fibrous cellulosic material through or in contact with a bath of bituminous proofing material of relatively high melting point and heated to a temperature substantially above 250‹ F., removing the sheet before it is saturated with proofing material, and cooling rapidly the proofed surface. A preferable proofing material comprises a mixture containing a bituminous product known as mineral rubber 100 parts, scale wax 10 parts, and Montan wax 2 parts. The mixed bath has a melting point of above 250‹ F., and is heated preferably to a temperature of 450‹ F., at which it is liquid but still very viscous. A web of paper is passed through the heated bath, remaining in it only about five seconds. Air and moisture are driven from the web, which becomes impregnated on both surfaces, as shown at a on the Figure, but with little permeation toward the centre b of the sheet. Surplus proofing material is stripped from the web as it leaves the bath to allow of rapid cooling, which may be accelerated by passage over a chilled roll, to avoid carbonization of the dry middle fibres of the sheet. From 15 per cent to 35 per cent by weight of proofing material is preferably incorporated with the paper, which will give a product with about one third or one quarter of its thickness not infused. The web may be proofed similarly on one side only by passing it over a roll dipping in a bath of the proofing agent, the web again being cooled quickly.