| 摘要 |
<p>A recording sheet material comprises a white, black or otherwise coloured base sheet coated with an obscuring film capable of becoming transparent by the application of localized pressure and composed of minute agglomerates of polyethylene or polypropylene bound to each other and adhered to the base sheet by a polymeric binder, e.g. unvulcanized rubber, polyisobutylene, polystyrene. The film, which is microscopically heterogeneous, fissured and microporous, and preferably 5 to 100 microns thick, is formed by applying to the base sheet a dispersion or solution comprising the polymeric binder and the polyolefine, e.g. 1 to 5% by weight of polyethylene of molecular weight 3000 to 150,000, a preferably water-immiscible solvent, e.g. xylene halogenated hydrocarbon being used with elevated temperature if necessary. Alternatively, separately prepared polymeric binder and polyolefine solutions may be admixed, the same or miscible solvents being used. A solution of a dyestuff may be incorporated in the polymer solution. If desired a coat of transparent varnish can be applied over the polymer film to protect it. Specification 705,417 is referred to.</p> |
