GB790200A - Improvements in or relating to the production of semi-moistureproof sheet wrapping material - Google Patents

Abstract

790,200. Semi-moistureproof sheet materials. BRITISH CELLOPHANE, Ltd. June 7,1956 [June 10, 1955], No. 16710/55. Class 140. Semi-moistureproof sheet wrapping material comprises a regenerated cellulose base film, e.g. in gel form, coated on one side or on both sides with a non-semi-moistureproof water-repellent coating and having a coating on the uncoated side or one of the coated sides of a semi-moistureproof substance. A " semi-moistureproof coating " is defined as a uniform coating on one side of a regenerated cellulose film 0.0009 inch thick resulting in a degree of impermeability of the film of 700 to 7000 gm. per 100 square metres per hour over a 24 hour period at 39.5Œ0.5‹ C. at a humidity differential of at least 95 per cent. The term " non-semi-moistureproof coating " is defined as one resulting in a degree of impermeability in excess of 7000 gm. per hour under the same conditions. The term " waterrepellent surface " is a surface which when at 45 degrees to the horizontal and a drop of water is placed thereon, the drop rolls off the surface leaving no continuous trail. The non-semimoistureproof water-repellent coating which may be present in a proportion of less than 1 per cent by weight of product may be applied from a solution in a volatile solvent or solvent mixture, or an aqueous colloidal dispersion, emulsion or solution which may be cationic or non-ionic and which may contain a softening agent, e.g. glycerine. Suitable water-repellent coatings have bases selected from polymers and copolymers of vinyl halides and esters, vinylidene halides, acrylic and methacrylic acid and their derivatives, styrene and its derivatives, acrylonitrile and methacrylonitrile, butadiene, isobutylene, ethylene and its homologues, nitrocelluloses, artificial and synthetic rubber latices, polyamide resins, silicones, waxes, watersoluble complex compounds of the Werner type containing a trivalent nuclear chromium atom co-ordinated with a carboxylic acid group having at least 10 carbon atoms, chlorinated polyvinyl halides, aliphatic methyl pyridinium salts, chlorinated polyethylene. Prior to coating with the semi-moistureproof substance the uncoated side or one of the coated sides of the film may be coated with an anchoring agent, e.g. polyethylene imine, partially condensed products of melamine or urea and formaldehyde, the colloidal particles of which, in aqueous dispersion, may be treated according to Specification 675,477, [Group IV (a)], to carry a positive electric charge. The semi-moistureproof coating, which renders the film heat-sealable, may comprise (i) a cellulose derivative filmforming agent and a mono-, di-, tri- or tetraester of pentaerythritol and a saturated aliphatic monocarboxylic acid having 12 to 35 carbon atoms, as described in Specification 664,248; (ii) a film-forming agent and a waxy polymerization product of monomeric long-chain nalkyl ether of vinyl alcohol, the allyl group of which contains 12 to 34 carbon atoms, as described in Specification 756,346, (iii) an organic solvent soluble cellulose derivative film-forming agent, paraffin or candelilla wax or a waxy polymer as in (ii) and a polysiloxane in which long chains of siloxane units are terminated in methyl or hydroxyl groups as described in Specification 768,571, or (iv) the polymerization product of monomeric vinyl chloride (79 per cent), monomeric vinylidene chloride (20 per cent) and itaconic acid (1 per cent). Specification 790,201 also is referred to.