| 摘要 |
744,677. Moisture-proof hydrophilic films. BRITISH CELLOPHANE, Ltd. March 4, 1954 [March 9, 1953], No. 6474/53. Addition to 677,926. Class 140. The process of the parent Specification is modified by using an aqueous dispersion of a vinylidene chloride polymer or copolymer, the aqueous phase of which has a pH between 4 and 14, preferably between 4 and 9. In Specification 677,926 moisture-proof film is produced by applying to water-sensitive, non-fibrous organic base film a partially condensed hydrophilic ureaformaldehyde resin from a neutral (pH 5-8) aqueous dispersion, drying the film with curing the applied resin to the hydrophobic state, and then, while the applied resin is still in the hydrophilic state, applying to the dried film an acidic (pH 1-4) aqueous dispersion of vinylidene chloride polymer or copolymer, and finally heating to evaporate the water, to cure the applied resin to the hydrophobic state, and to consolidate the surface coating. The film may be regenerated cellulose, and the electric charge on the urea-formaldehyde colloidal particles should be opposite to that developed by the film in contact with water. The proportions of urea to formaldehyde may be 1 mol. to 2-3 mols. Vinylidene chloride may be copolymerized with acrylonitrile, vinyl chloride, vinyl acetate, styrene, ethyl acrylate, methyl methacrylate, and n-butyl methacrylate or mixtures thereof. Where vinylidene chloride is copolymerized with methyl methacrylate, acrylonitrile, or ethyl acrylate, or mixtures thereof, an acidic compound namely itaconic or citraconic acid or anhydride or mesaconic acid may be included. The vinylidene chloride dispersion may be brought within the required pH range by addition of sodium bicarbonate, ammonia, or caustic soda, and may be applied to the film in a layer of such thinness that the water is wholly absorbed by the film. Specifications 700,619 and 703,010 also are referred to. |
