Heat sealable film

摘要

A heat-sealable film comprises a layer of stereoregular polypropylene, which has been subjected to a surface oxidative treatment, and an adhering coating layer on at least one of the surfaces of the polypropylene, which coating layer comprises industrial nitrocellulose, defined as having a nitrogen content in the range 10,7-12,2% by weight, and plasticizer therefor, at least 50% by weight of the plasticizer being constituted by normally solid materials. The ratio of nitrocellulose to plasticizer is within the range 10:5 to 10:15 by weight. The surface oxidative treatment may be such as to reduce the angle of contact between water and the polypropylene surface to 80 degrees or less, and may consist in heating the surface by means of a flame, corona discharge, or treatment with ozone, chromic acid or mixtures of sulphuric acid and sodium dichromate. The solid plasticizer may be N-cyclohexyl p-toluene sulphonamide, N-phenyl p-toluene sulphonamide, N-cyclohexyl benzene sulphonamide or dicyclohexyl phthalate, or an aryl-substituted thiourea. The coating layer may comprise a proportion of a liquid plasticizer. The coating layer may comprise a proportion of resinous material, e.g. rosin, rosin esters, reaction product of rosin and its derivatives with maleic anhydride, natural resins and vinyl polymers containing polar groups, which may be present in proportion less than that of nitrocellulose and the ratio of the combined weight of resinous material and nitrocellulose to plasticizer is within the range 10:5 to 10:15. The coating layer may comprise an isocyanate compound defined as being compounds containing free isocyanate groups and compounds having isocyanate groups reacted with other compounds containing active hydrogen atoms, e.g. compounds containing hydroxy, carboxy, amino or imino groups, such as water or an aliphatic alcohol. The coating may be applied as a lacquer prepared by dissolving the constituents of the coating in a solvent, e.g. a mixture of butyl acetate and toluene in the ratio 6:4, and drying off the solvent. The lacquer may be incorporated into an aqueous emulsion and applied in the emulsified form. Specification 715,914 is referred to.