GB705417A - Improvements in and relating to coated paper suitable for stylus inscription and method of making the same - Google Patents

Abstract

705,417. Record sheets. NASHUA GUMMED & COATED PAPER CO. June 28,1951 [June 29, 1950], No. 15399/51. Drawings to Specification. Classes 96 and 140 A record sheet, especially paper suitable for receiving inscriptions from a stylus, having a supporting layer of paper with a dark surface and an obscuring film covering the dark surface is prepared by emulsifying in a solution of a thermoplastic resinous material a volatile liquid, which is a non-solvent for the resinous material and is substantially insoluble in the solution solvent, to form an emulsion of which the solution is the continuous phase and multitudinous droplets of the volatile liquid are the disperse phase, coating the paper with a film'of the emulsion, and drying the film to effect solidification of the resin and to evaporate the dispersed droplets by diffusion, so that the film has a cellular structure consisting of a multiplicity of discrete microscopic voids beneath the surface. The film is normally opaque owing to its heterogeneous structure of voids distributed throughout the homogenous resinous material, but is adapted by local coalescence, due to release of air from the voids by heat, pressure, or both by the stylus, to form a transparent area disclosing'the dark paper surface. Suitable resinous materials are ethyl cellulose with or without compatible resins, e.g. chlorinated diphenyl resins or coumarone-indene resins, polystyrene resins, polyvinyl resins, e.g. vinylacetatevinyl chloride copolymer, polymers of esters of methacrylic acid, e.g. polymethyl methacrylate, or cellulose ester resins, e.g. nitrocellulose or cellulose acetate in, say, benzene, toluene, 'xylene, chloroform, propylene or methylene dichlorides, or n-butyl acetate as solvent. The properties of the film may be modified by plasticizers, e.g. tricresyl phosphate, dioctyl phthalate, and castor oil, and emulsifying agents, e.g. stearyl dimethyl benzyl ammonium chloride, aromatic polyglycol ethers, or sorbitan trioleate, may be added to the solution. The stability of the emulsion is improved by homogenisation. The volatile liquid may be water, a water-miscible liquid, or diluted with water, or a water solution of a solid, which may have an ingredient added to reduce the vapour pressure, when less volatile solvents are used for the resin, e.g. sodium acetate, lead acetate, ethylene glycol,. or glycerol.