Patent GB-943681-A (GB)
Title: Thermal copying sheet
Inventor: WEEL WALTER H VANDER
IPC: B41M5/26
Filed: 1959-04-03
Abstract: 943, 681. Thermographic copying materials. LABELON TAPE CO. Inc. Nov. 3,1959, No. 37307/59. Drawings to Specification. Heading G2C. A thermographic copying sheet insensitive to stylus pressure and having surfaces containing not more than 3% by weight of materials which would impart tackiness and waxiness comprises a support having two coatings both on the same side, one being a coating of a heatsensitive fusible material which is solid and non-tacky below 165‹F. and melts to a viscous liquid at a temperature between 165 and 210‹F. and the other coating being of a cloudy lightcoloured lacquer film ("blush coat") devoid of tackiness and insensitive to stylus pressure which is opaque below a temperature of 215‹F. but is adapted to be made at least translucent upon resolidification of the first coating to provide a visible record and which has a non-greasy and non-waxy surface before, during and after being made translucent, and in the case where the heat-sensitive fusible material layer is uppermost and waxy, a thin flexible heat-resistant organic polymeric film is provided as an outer stylus pressure resistant layer. The support is preferably heat-transparent but opaque to light with a rough surface e.g. paper, greaseproof paper but may be transparent to light, e.g. regenerated cellulose, cellulose ester, polyester, resin-impregnated fibre glass, starch or resin impregnated fabric (tracing paper). For the production of engineering templates the support may be of aluminium, steel, or other metal sheet. The fusible material coating preferably comprises a mixture of high and low melting point waxes, e.g. one or more natural waxes such as carnauba wax mixed with montan, ceresin, or a low melting paraffin wax, and may contain 1-5% of an oil such as castor oil, red oil, petrolatum, or a long chain fatty acid. Instead of waxes there may be employed rosin esters, polyterpenes waxy polyethylene glycols or polythenes, vinyl resins, halogenated polyethylene, natural or synthetic rubbers, all with plasticomers if required or a high-melting carrier such as cellulose ester or ether or ethyl acrylate resin containing dispersed discrete fusible particles such as stearic acid, potassium stearate, solid animal fat, triphenyl phosphate and toluene sulphonamides. The blush coat is a solution in water of an acetone solution of cellulose acetate, pyroxylin, or ethyl cellulose. To improve adhesion between the coats, either may contain 1 to 3% of a synthetic wax, rosin or a rosin ester, a matting agent such as talc, bentonite, diatomaceous earth, powdered silicon or rice starch. Dyes or less desirably pigments may be included in either of the coats and the support may be light or dark in colour as required to give the desired contrast between the image and background. Over the blush coat may be applied by coating or laminating an outer layer of polyethyl or polymethyl methacrylate or a cellulose ester or regenerated cellulose to provide greater rigidity in the sheet, reduce the tendency of the sheet to curl, improve storing quality and produce a glossy appearance. To enable pencil marks to be made on this layer it may be abraded or etched or embossed. Indicia may be applied to the sheet, e.g. along the margin, by means of a heated wheel or other marking tool or ink printing either before or after cutting a web of the sheet material. To further reduce sheet curl a non- waxy fusible coating may be applied to the rear of the support, e.g. a coating of cellulose acetate or pyroxylin. Only part of the sheet may be thermographic.