Patent GB-1028357-A (GB)
Title: Process for the preparation of polymer films
Inventor: NYBERG DAVID DOLPH
IPC: C08L53/02
Filed: 1964-11-04
Abstract: 1,028,357. Films. SHELL INTERNATIONALE RESEARCH MAATSCHAPPIJ N.V. Nov. 4, 1964 [Nov. 6, 1963], No. 44947/64. Heading B5B. Polymer films having improved tensile strength are made by laying down as a film a latex comprising a block copolymer having the formula A-B-A in which each A is an independently selected non-elastomeric polymer block having an average molecular weight in the range of 2,000 to 100,000 and a glass transition temperature above 25 C., the total polymer block A content being at least 5% by weight of the polymer and B is an elastomeric polymer block having an average molecular weight in the range of 25,000-1,000,000 and a glass transition temperature below 10 C., removing water from the latex and annealing the resulting film for 1-120 mins. at 50-160. In the block copolymer the elastomeric block B may be a polymer of an aliphatic conjugated diene, e.g. isoprene, methyl-isoprene, butadiene, copolymers of styrene-butadiene and of butadiene-acrylonitrile. The non-elastomeric blocks A comprising preferably 15-30% of the polymer, may comprise homopolymers of the lower olefins or of alkenyl aromatic hydrocarbons, e.g. styrene, vinyl toluene, methyl styrene, or methyl methacrylate. Suitable block polymers are the systems polystyrenepolyisoprene-polystyrene and polystyrene-polybutadiene-polystyrene. Hydrogenated derivatives of these block polymers may be used as well. Desirably, the average molecular weight of the A blocks is 8,000-45,000 and that of the B blocks is 35,000-150,000. One of the blocks may be " tapered," i.e. contain an increasing proportion from one end to the other of units of a monomer promoting either elastomeric or non-elastomeric properties in the blocks. The block copolymer may be extended with an extending oil, the proportion thereof being up to 100 parts by weight per 100 parts by weight of the block copolymer and the average molecular weight of the polymer block B being 350Y to 1500Y, Y being a number between 100 and 100 plus the number of parts by weight of the extending oil. Suitably, in the oil-extended block co-polymer the average molecular weight of the blocks A is from 10,000 to 33,000 and the average molecular weight of block B is 500Y to 1250Y. The latices may be modified by the presence of pigments, e.g. carbon black, titanium dioxide and other known pigments. The latices from which the films are formed are made by emulsifying block polymer cements with water and an emulsifying agent and then removing the cement solvent, either by flashing or by creating and collapsing a foam. The resulting latex desirably contains 25-70% by weight of polymer based on the total latex weight. After formation of the latex, a film thereof is laid down on any suitable surface and water removed therefrom, either by evaporation at ambient temperature or by heating, e.g. while the film, cast on a moving belt, passes through a tunnel drier. Subsequently, the film is annealed, either while still attached to the belt or after separation therefrom, suitably for 5 to 60 mins. at 90 to 120 C.