Patent GB-632995-A (GB)
Title: Improvements in or relating to method of making a film of thermoplastic material
IPC: B29C48/08
Filed: 1946-10-11
Abstract: A solution of a plasticized polyvinyl chloride, or copolymer of vinyl chloride with a lower proportion of a copolymerizable monomer or monomers, in a volatile solvent, is deposited upon a casting surface to form a film and during at least the initial stages of evaporation of the solvent the temperature is maintained below the boiling point of the solvent; the temperature is then increased and the film is heated in contact with the casting surface to an extent which permits residual strains in the film to be relieved.  The film is cooled and then stripped from the casting surface.  The heating to remove strain is carried out at a temperature approaching or exceeding the fusion temperature of the film.  Examples of monomers which may be polymerized with the vinyl chloride are vinylidene chloride, vinyl acetate or other vinyl carboxylate, methyl or ethyl acrylate or methacrylate, vinyl methyl ketone, and styrene.  The solution may contain plasticizers, fillers, pigments, waxes, resins, and stabilizers. The volatile solvent may be benzene, toluene, chlorbenzene, chlortoluene, ethylene dichloride, acetone, methyl ethyl ketone, or cyclopentanone.  Heating to evaporate the solvent may be effected by a stream of hot air.  The second heating operation may be effected by radiation from infra-red lamps.  Cooling may be carried out with a stream of cold air or a spray of cold water. In an example, a solution of polyvinyl chloride in methyl ethyl ketone, containing dioctyl phthalate as plasticizer and a small proportion of wax, is spread on a metal belt and dried to form a solid film by a counter-current of hot air during which the temperature of the layer rises from 60 DEG  to 100 DEG  C.  The dried film on the metal belt then passes a bank of infra-red lamps which heat it to about 190 DEG C. for a few minutes and render it almost liquid. The film is then cooled to about 40 DEG  C. by means of a cold-water spray on the reverse side of the carrier and is stripped from the belt.  The Specification as open to inspection under Sect. 91 comprises also the production of films from thermoplastic materials in general, including cellulose esters and ethers, corn proteins; polymers and copolymers of vinylidene chloride, vinyl carboxylic esters, acrylic and methacrylic compounds, vinyl methyl ketone, and styrene; hydrolyzed polyvinyl esters, and polyvinyl acetals. This subject-matter does not appear in the Specification as accepted.ALSO:The Specification as open to inspection under Sect. 91 comprises the production of rubber hydrochloride films.  A solution of rubber hydrochloride in a volatile solvent is deposited upon a casting surface, and during at least the initial stages of evaporation of the solvent the temperature is maintained below the boiling point of the solvent.  The temperature is then increased and the film is heated in contact with the casting surface until residual strains in the film have been relieved. The film is then cooled and stripped.  Heating to remove strains is effected at a temperature approaching or exceeding the fusion temperature of the film.  The solution may contain plasticizers, fillers, pigments, waxes, resins, and stabilizers.  The volatile solvent may be or may include benzene, toluene, chlorbenzine, chlortoluene, ethylene dichloride, acetone, methyl ethyl ketone, or cyclopentanone.  Heating to evaporate solvent may be effected by a stream of hot air.  The second heating may be effected by radiation from infra-red lamps.  Cooling may be carried out with a stream or spray of cold water or air.  This subject-matter does not appear in the Specification as accepted.