Patent GB-936398-A (GB)
Title: Improvements relating to films of fluorine-containing polymers
IPC: C08J5/18
Filed: 1960-03-15
Abstract: A biaxially oriented film of polyvinyl or polyvinylidene fluoride is made by continuously elongating in two mutually perpendicular directions such a film containing a latent solvent. In addition to homopolymers of vinyl and vinylidene fluoride, copolymers thereof with other monoethylenically unsaturated monomers, especially those containing at least 75%, preferably at least 80%, by weight of the vinyl or vinylidene fluoride may be used.  Such films may be made by heating a mixture of particulate, high molecular weight, orientable polyvinyl or polyvinylidene fluoride and a latent solvent until the particles of the polymer coalesce and form a single fluid composition, which is then extruded as a film containing up to 80% by weight of the latent solvent, or alternatively by spreading a mixture of the polymer and the latent solvent or a smooth non-adherent surface and heating the mixture sufficiently to cause the polymer particles to coalesce, the resulting film being quenched with cold water and stripped from the smooth surface.  Films containing a higher proportion of latent solvent may be made by casting hot solutions containing a relatively low amount of polymer in a latent solvent, the original solvent content of the film being reduced to any desired level by driving off the excess.  Both flat and tubular films may be treated and pigments and fillers may be incorporated in the latent solvent-containing films at any convenient processing stage.  Specified pigments include basic zinc chromate, titanium dioxide, oxides of iron, phthalocyanine greens and blues, chrome green and chrome yellows.  A latent solvent is defined as an organic liquid, chemically inert to polyvinyl fluoride and having no significant solvent or swelling action thereon at room temperature, but being capable at an elevated temperature below its normal boiling point of solvent action sufficient to cause polyvinyl fluoride particles to coalesce. Specified latent solvents include butadiene cyclic sulphone, tetramethylene sulphone, dimethyl sulpholane, hexamethylenesulphone, dialkylsulphoxide, dimethyl sulphoxide, dicyanobutene, adiponitrile, ethylene carbonate, propylene carbonate, 1,2-butylene carbonate, 2,3-butylene carbonate, isobutylene carbonate, trimethylene carbonate, N,N-diethyl formamide, N,N-dimethyl formamide, N,Ndimethyl-g -hydroxy acetamide, N,N-dimethylg -hydroxy-butyramide, N,N-dimethylacetamide, N,N,-dimethyl methoxy-acetamide, N-methyl acetamide, N-methyl formamide, N,N-dimethyl aniline, N,N-dimethylethanolamine, 2-piperidone, N-methyl-2-piperidone, N-methyl-2pyrrolidone, N-ethyl-2-pyrrolidone, N-isopropyl2-pyrrolidone, 5-methyl-2-pyrrolidone, g -butyrolactone, d -valerolactone, g -valerolactone, a angelicalactone, b -angelicolactone, #x-captrolactone, and a , b -ang g -substituted alkyl derivatives of g -butyrolactone, g -valerolactone and d -valerolactone, as well as d -substituted alkyl derivatives of d -valerolactone, tetramethyl urea, 1-nitropropane, 2-nitropropane, acetonyl acetone, acetophenone, acetyl acetone, cyclohexanone, diacetone alcohol, dibutyl ketone, isophorone, mesityl oxide, methylamyl ketone, 3-methyl cyclohexanone, bis-(methoxymethyl) uron, diethyl phosphate, ethyl acetoacetate, methyl benzoate, methylene diacetate, phenyl acetate, triethyl-phosphate, tri(morpholino) phosphine oxide, N-acetyl morpholine, N-acetyl piperidine, isoquinoline, quinoline, pyridine and tri(dimethylamido) phosphate.  The film may contain at least 20% by weight of latent solvent, preferably 20-80% and especially 35-70% and may be elongated by stretching or drawing at least 50% in each direction at 30 DEG -185 DEG C.  Elongation in the first direction is suitably effected at 30 DEG -120 DEG C. and in the second direction at 60 DEG -185 DEG C.  Film having a substantially higher tensile strength in one direction of stretch, e.g. the longitudinal direction, than the other, may be made by stretching in this direction to a greater extent than is required to produce a film of substantially balanced tensile properties, or alternatively by stretching in each direction to extents producing film of substantially balanced tensile properties, and then subsequently stretching again in the longitudinal direction. During and/or after elongation of the film, latent solvent is removed from the film, e.g. by drying with air at up to 180 DEG C. if the film is not restrained, or at up to 200 DEG C. with restrained film, until at most 0,5% by weight of the latent solvent, based on the total weight of the film, remains in the film.  After one or both stages of the elongation the film may be allowed to shrink by up to 35% of the elongation initially imparted to the film in that direction.  Specification 845,634 is referred to.