GB1121859A - Improvements relating to drafting films - Google Patents

Abstract

A drafting film comprises a flexible, biaxially oriented, highly polymeric polyester film composed of the polyesterification product of at least one dicarboxylic acid and at least one dihydric alcohol, having on at least one surface a layer of essentially hydrophobic vinylidene chloride copolymer containing at least 35% of vinylidene chloride, or of a hydrophobic terpolymer comprising 48 to 70% C2-C10 alkyl acrylate, 30 to 48% styrene, acrylonitrile or methyl methacrylate, and 4 to 12% acrylic or methacrylic acid, followed by a hydrophobic, continuous layer of methyl methacrylate -C1 to C2 alkyl acrylate copolymer having a Tukon film hardness above 10 KHN and containing up to 1 part uniformly dispersed, finely-divided, discrete particles of a water-insoluble, translucence-producing solid matting agent. Suitable polyester supports are films of polyethylene terephthalate, polyethylene terephthalate/isophthalates, and the condensates of terephthalic acid or dimethyl terephthalate with propylene glycol, diethylene glycol, tetramethylene glycol or cyclo-hexane-1, 4-dimethanol, and polycarbonates. The Tukon hardness can be adjusted by mixing the methyl methacrylate copolymer with another acrylic polymer of different hardness. The vinylidene chloride copolymer layer may be a vinylidene chloride/acrylic ester/itaconic acid copolymer. A suitable copolymer may be vinylidene chloride/methyl acrylate/itaconic acid copolymer. The matting agent may be silicon dioxide, rice starch particles and materials additionally acting as opacifying pigment or colouring agent e.g. silica, ground glass, chalk, talc, diatomaceous earth, magnesium carbonate, barytes, clay, Monastral Fast Blue, and other pigments and dyes. Methods of applying the vinylidene chloride copolymer layer are those disclosed in Specifications 718,422, and 786,176, the said layer being usually applied to the polyester base prior to orienting it. The methyl methacrylate copolymer layer is applied as an aqueous dispersion, or latex, containing heat-removable coalescent material and the particles of matting agent which is then dried at 60 to 125 DEG C. and cured at 100 to 150 DEG C to remove the coalescent material, or heated for a longer time at a temperature above 60 DEG C. Suitable coalescent materials are glycols, glycol-ethers, glycol-ether esters. The dispersion may contain a hydrosol of silica, dispersants, a thickener such as a copolymer of methyl vinyl ether and maleic anhydride, and surfactants e.g. isooctyl phenoxy polyethoxy ethanol, to act as wetting agents. The dispersion may be treated mechanically say by passing it through a sand mill to disperse the pigments before or after adding the polymer latex. The dispersions can be applied by dip-coating, bead coating or applicator rolls, or supplied from a gravity- or pressure-fed hopper, and the thickness of the coating can be controlled by doctor blades or air streams. The support film may be coated on both sides with the same drafting film composition or with different drafting film compositions e.g. one side with a drafting film containing a hard matting agent such as silicon dioxide, and the other with either no matting agent or a soft matting agent such as rice starch. The drafting film may be overcoated with a substratum comprised of a reaction product prepared by polymerising, in the presence of gelatin, at least one vinyl monomer such as vinylidene chloride, methyl acrylate or ethyl acrylate. At least one surfactant e.g. an amphoteric material such as sodium N-coco-b -aminopropionate, N-tallow-b -imino-dipropionate, N-lauryl-b -aminopionic acid or cetyl or other long chain betaine, compounds of formula RHNn[(CH2)nCOOM]m where R is an unsubstituted alkyl group of 12 to 18 carbon atoms, m and n are 1 or 2, p is 2-m, and M is a cation such as sodium, potassium, lithium, ammonium, hydrogen, may be present in the substratum.