Patent GB-1006622-A (GB)
Title: Method of improving the surface properties of polypropylene film
IPC: C08J7/052
Filed: 1963-07-12
Abstract: A polypropylene film is stretched biaxially until its planar orientation index is not less than 2 x 10-3 and its axial orientation index is not over 10 x 10-3 and the surface of the film is then subjected to an oxidation treatment prior to coating with a surface-reforming material, e.g. a solution of a thermoplastic resin in an organic solvent, a water-soluble polymer having an amino, hydroxyl, carboxyl, or sulphonic group, a metal, or an alkyl titanate.  Where the refractive index of the film in the direction of its thickness is a  and the refractive indices normal to each other in the plane of the film are b  and g , the axial orientation index is g -b  and the planar orientation index is 1/2 (b +g )-a .  Biaxial stretching in both directions to a draw ratio exceeding 3 and preferably exceeding 4, at about 130  DEG C., is generally sufficient to obtain such orientation indices.  Treatment enhances the adhesive and other surface properties of the film.  Films composed entirely of stereospecific polypropylene, and blends comprising predominantly polypropylene, especially over about 80% by weight thereof, with polyethylene, polystyrene, and polybutadiene, may be used. Copolymers of ethylene and propylene are also usable.  Oxidation may be effected chemically e.g. using potassium dichromate-concentrated sulphuric acid, chlorosulphonic acid and chlorous acid, singly or in combination, or physically using a corona discharge, flame, or ultra-violet treatment.  Preferably the treated surface is washed immediately after the oxidation treatment with a solution of an amino compound or polyethylene imine, as this inhibits fall in surface adhesive activity on standing.  Alkyl titanate treatment may be followed by extrusion lamination of a thermoplastic resin to the film.  Amino compounds used are those having either an amino group and a hydroxy group e.g. monoethanolamine, diethanolamine, aminophenol and aminonaphthol, or an amino group and a carboxyl or sulphonic acid group, dissolved in alcohol, water, or aqueous alcohol.  Aqueous solutions of cationic aminoformaldehyde resins can be used similarly.  Surface-reforming materials may be applied as coatings or by laminating or, in the case of metals, by vacuum deposition.  Specified resins include polyethylene and polypropylene resins, suitably applied by extrusion coating, preferably following pre-treatment with an alkyl titanate.  Polyolefin resins in general improve heat-sealability.  Vinyl resins e.g. polyvinyl acetate, polyvinyl chloride, vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinyl acetate-maleic acid copolymer, vinyl acetate-ethylene copolymer, polyvinyl alcohol and polyvinyl butyral may also be used. Polyvinyl butyral is useful as a primer in the vacuum deposition of metal.  Polyvinyl esters serve to enhance heat-sealabilty, and polyvinyl alcohol to decrease gas-permeability.  Polyvinylidene chloride, vinylidene chlorideacrylonitrile copolymer and vinylidene chloride-vinyl chloride copolymer also decrease gas-permeability and enhance heat-sealability.  Cellulose derivatives, e.g. a mixture of nitrocellulose, dammar and dioctyl phthalate enhance heat-sealability and are useful primers for vacuum deposition of metals.  Polyamides, suitably those derived from an unsaturated aliphatic acid and ethylene diamine, mixtures of polyamides with alkyd and epoxy resins, polyesters, e.g. polyethylene terephthalate-isophthalate, and copolymers of maleic anhydride or phthalic anhydride with propylene glycol, ethylene glycol or reaction products thereof with styrene, polyurethanes, e.g. the reaction product of diphenylmethane diisocyanate and a polyester, and epoxy resins are also useful as primers for vacuum deposition of metals.  For antistatic treatment, water-soluble polymers are useful e.g. alkali alginates, alkali metal salts of carboxy methyl cellulose, polyvinyl alcohol, alkali metal salts of polyacrylic acid and natural materials of high molecular weight e.g. casein, glue, gelatin, gloiopeltis glue, tragacanth gum, gum arabic, gum karaya, starch and Irish moss.  Mixtures of protein and non-protein polymers may be used, and polyethylene imine may be incorporated in the solution to improve film adhesiveness.  In examples: B.  After stretching and oxidation, a film is coated with polyvinyl acetate having polyethylene imine incorporated therein. The coated film may be laminated or extrusion laminated to polyvinyl chloride, polyvinylidene chloride, nitrocellulose, polyethylene or aluminium.  D. Stretched and oxidized film is coated with a solution of an alkyl titanate, tetrapropyl titanate or tetra-n-butyl titanate in an organic solvent e.g. isopropyl alcohol, toluene, hexane, kerosene, ethyl acetate and chlorinated hydrocarbons, or a titanate derivative e.g. the reaction product of alkyl titanates with acetyl acetone.  Such compounds are hydrolysed by atmospheric moisture and form an amorphous titanium oxide film on the surface of the polypropylene film.  E. Stretched and oxidized films are coated with solutions of various synthetic resins and then metallized by vacuum deposition with e.g. copper, silver, zinc, or aluminium.  2 and 3. Stretched film oxidized by potassium dichromate-sulphuric acid treatment is coated with a solution of a polyvinylidene chloridepolyacrylonitrile copolymer in methyl ethyl ketone.  10. Stretched film oxidized with potassium dichromate-sulphuric acid mixture is coated on both sides with an ethyl acetate solution of a vinyl chloride-vinyl acetate-maleic anhydride copolymer, dried, coated with a sodium alginate solution, and dried.  Some samples are further coated with the vinyl chloride copolymer.  11. Film stretched and oxdized as above is subjected to various composite coating processes. 12. Film coated with a vinyl chloride polymer is further coated with a polyalkylamine modified melamine-form aldehyde resin, then with a solution of a vinyl chloride copolymer in methyl ethyl ketone.  13. Stretched film is oxidized in a solution of chlorosulphonic acid in trichloroethylene, coated with an aqueous solution of a hydrochloric acid modified cationic melamineformaldehyde resin, dried, and laminated to polyethylene. 14. Stretched film oxidized with potassium dichromate-sulphuric acid mixture is coated with a solution of diethanolamine in aqueous methanol, dried, and coated with a vinyl chloride polymer or vinyl chloride copolymer solution in methyl ethyl ketone or ethyl acetate. 15. A sample treated as in 14 is subjected to corona discharge, treated with a diethanolamine solution and coated with a vinyl chloride polymer.  16. A sample treated as in 14 is treated with a solution of p-amino-benzoic acid in ethyl acetate and coated with a vinyl chloride polymer.  17. A sample treated as in 14 is subjected on one side to flame treatment, treated in an alcoholic solution of 4-amino-1-naphthol, and coated with a vinyl chloride polymer.  18. A sample treated as in 14 is coated with a solution of a vinylidene chloride acrylonitrile copolymer in methyl ethyl ketone.  19. A sample treated as in Example 15 is treated in a saturated aqueous solution of m-amino benzene sulphonic acid to enhance its printability.  20. A sample treated as in 15 is coated with a solution containing polyvinyl acetate and polyethylene imine.  21. A sample treated as in 14 is treated as in 20 and then laminated to polyethylene as in 13.  22. As 21, but laminated to paper.  23. Stretched film oxidized with potassium dichromatesulphuric acid mixture is coated with an aqueous solution of polyvinyl alcohol, optionally containing polyethylene imine.  24. A sample treated as in 23 is coated with a vinyl chloridevinyl acetate copolymer solution. 25. A sample oxidized as in 23 is coated with either polyvinyl alcohol solutions or carboxymethyl cellulose solutions, either of which may contain polyethylene imine, and then laminated to paper. 26. A sample is treated as in 25 but glue is added to the treatment solutions.  27. Stretched film is subjected to corona discharge and then some samples are treated with a solution of tetrapropyl titanate and tetrastearyl titanate in hexane.  All samples are then laminated with polyethylene.  29. Stretched film oxidized with potassium dichromate-sulphuric acid mixture is treated with an alcoholic solution of polyvinyl butyral and metallized with aluminium by vapour deposition.  30. Stretched film oxidized by corona discharge is coated with various resins and metallized as in 29.