GB834243A - Non-blocking film and process for manufacturing the same - Google Patents

Abstract

Transparent non-blocking films having microscopic protuberances on both surfaces are prepared by casting a film-forming solution having microscopic particles of a chemically inert inorganic substance dispersed therein on to a film-casting surface having microscopic pits therein, as prepared by the method of Specification 737,032. "Blocking" is defined as the adhesion of one film surface to another due either to an electrostatic charge on the surfaces, to the condition of the surfaces, to the surfaces being pressed together or to their having been rendered slightly tacky by heating. After the cast film has been dried it has microscopic protuberances on the surface which was not in contact with the casting base because, when the film dries, it shrinks about the particles at the surface and leaves them partly protruding above the general level of the surface. The film-forming material may be a polyethylene, a polyvinyl chloride, a cellulose ester such as a nitrate or acetate, rubber hydrochloride or a chlorinated rubber. The particulate inorganic substance may be silica aerogel, diatomaceous silica, bentonite, calcium carbonate, talc, soapstone, titanium pigments, mica, magnesium or calcium silicate or glass. The inorganic powder is preferably added to the film-forming composition in the form of a dispersion in an organic solvent such as benzene, methyl ethyl ketone or toluene, or in a plasticizer such as dioctyl phthalate, dibutyl sebacate or dioctyl sebacate or in a mixture of a solvent and a plasticizer. In an example, a mixture of 70 parts of a dispersion of 12.5 parts by weight of silica aerogel (of 1 to 10 microns radius particle size) in 100 parts of methyl ethyl ketone and 62.5 parts of toluene, and 840 parts of a solution of 100 parts of polyvinyl chloride in 500 parts of methyl ethyl ketone, 207 parts of toluene, 18 parts of dioctyl sebacate and 15 parts of dibutyl sebacate, is cast on to a polyvinyl alcohol casting surface having 100 to 2,000 pits (of radius 1 to 10 microns) per square centimetre, prepared by the method of Specification 737,032.