Patent GB-718422-A (GB)
Title: Preparation of molecularly oriented coated films
IPC: C08J7/056
Filed: 1951-02-13
Abstract: Coated film suitable as a base for the manufacture of photographic film (see Group XX), is produced by casting into the form of a film a highly polymeric linear polyester of a dicarboxylic acid with a dihydric alcohol (e.g. as described in Specification 522,161), coating one or both surfaces of the film with an aqueous dispersion of a hydrophobic copolymer containing at least 35 per cent. by weight of vinylidene chloride, drying and thereafter molecularly orienting the coated film by stretching it at elevated temperature (e.g. 70 DEG -120 DEG C.), both laterally and longitudinally in either order or simultaneously.  The stretching may be effected in two stages at 70 DEG -120 DEG C., the temperature in the second stage being 5-30 DEG C. higher than in the first stage. The vinylidene chloride copolymer may contain 4-65 per cent. of one or more vinyl compounds or polymerizable vinylidene compounds other than vinylidene chloride. The vinyl and vinylidene compounds may have the general formula CH2=CRX where R represents a hydrogen atom, an alkyl radical (e.g. methyl or ethyl) or a halogen atom and X represents a hydrocarbon radical (e.g. methyl, phenyl or naphthyl) or a negative atom or group (e.g. a halogen atom, -NO, -NO2, -CN, -COOH, -SO3H, -CONH2, -CONHR1, -CONR2, (-CO)R1, (-CO).OR1, -CHO, -OOCR and ether radicals, e.g. -OR11, wherein R and R1 represent alkyl radicals and R11 represents an alkyl or aryl radical.  In the preparation of the copolymer (see for example, Specifications 504,958 and 617,129), there may be used vinyl acetate, propionate, chloracetate, chloride or bromide; methyl or butyl acrylates; methyl, isobutyl, methoxy-ethyl, chlorethyl or 2-nitro-2-methylpropyl methacrylates; methyl or octyl alphachloro-acrylates; methyl vinyl or methyl isopropenyl ketone; itaconic acid, acrylonitrile or methacrylonitrile; styrene or isobutylene; vinyl naphthalene; ethyl or butyl vinyl ether; N-vinyl phthalimide, N-vinyl succinimide or N-vinyl carbazole; methylene diethyl malonate. Preferred copolymers are prepared from reaction mixtures initially containing 35-96 per cent. (preferably 75-95 per cent.) of vinylidene chloride, 3.5-64.5 (preferably 4-20) of acrylic ester and 0.5-25 (preferably 1-5) of itaconic acid.  The acrylic esters may be alkyl esters of acrylic and methacrylic acids having 1-18 carbon atoms in the alkyl group.  The coated film base may be provided with a superimposed coating of a water-permeable colloid, e.g. gelatin or a polyvinyl alcohol, which may contain a light-sensitive material.  In an example a molten ethylene glycol/terephthalic acid polyester melting at 200-300 DEG C. made from terephthalic acid and a polymethylene glycol containing 2-10 carbon atoms as described in Specification 578,079 is run into a reservoir maintained at 265-275 DEG C. and 0.5-10 mm. mercury pressure and led either directly or through a barometric column at 265-275 DEG C. to a metering pump.  The molten polyester is then pumped at 50-200 p.s.i. and 265-300 DEG C. to an extrusion hopper at 265-300 DEG C. and extruded through a long narrow slot on to a casting wheel at 15-85 DEG C.  The film of solidified polyester is passed successively through a water bath at 18-25 DEG C. a bath of a 10-25 per cent. aqueous dispersion of a copolymer of vinylidene chloride, methyl acrylate and itaconic acid and a drying zone at about 90-100 DEG C., laterally stretched to 1.5-5 times its original width on tenter belts or rolls at 70 DEG -120 DEG C., longitudinally stretched to 1.5 to 5 times its original length at about 100-105 DEG C., heat set at 115-150 DEG C. while under such tension that no substantial shrinkage occurs, cooled to below 100 DEG C., passed through a 2 per cent. aqueous gelatine solution and dried at 100-105 DEG C. under substantially no tension.  In some examples the stretched coated film is further coated with a gelatine sub-layer by passing it through a dispersion of gelatine in a mixture of organic solvents, e.g. acetic acid, acetone and methanol or aqueous methanol. Since gelatine substrata are ineffective for anchoring emulsions of the hydrophilic hydroxyl polymer silver-halide type to the coated films of the invention, polyvinyl alcohol substrata may be used instead.  Additional synthetic colloids which can be anchored by these methods include polyvinyl alcohols and their water-soluble derivatives, e.g. partially hydrolised polyvinyl acetates and mixed polyvinyl-chloride-acetates, hydrolised inter-polymers of vinyl acetate with unsaturated compounds such as maleic anhydride and acrylic acid esters (see Specifications 542,703, 542,704, [both in Group XX], and 600,023); and low substituted cellulose ethers, e.g. methyl-and ethyl-cellulose.  Natural colloids which may be anchored include casein, albumen, gum arabic, agar agar and polyglycuronic acid.  An example is given of the preparation of a photographic film using a film base of the invention (see Group XX).  Examples are furnished of the copolymerization by known methods in aqueous emulsions containing a mixture of the monomers, a catalyst, an activator and an emulsifying and/or dispersing agent of vinylidene chloride, methyl acrylate, and itaconic acid in the proportions 90 : 10 : 2 and 188 : 12 : 4 parts by weight respectively; of vinylidene chloride, ethyl acrylate and itaconic acid in the proportions 60 : 40 : 2, and of vinylidene chloride and acrylonitrile in the proportions 93 and 7.