| 摘要 |
Water-soluble transparent films consisting of a mixture of dextrin and polyvinyl alcohol are made by (a) heating to 80-90 DEG C. for 2-3 hours a suspension of a white dextrin (not more than 90% of which is soluble in water) in an aqueous solution of an emulsifying agent and a polyvinyl alcohol gelling agent (which is an alkali metal borate, sulphate or carbonate or an azo dye) until the dextrin dissolves in the aqueous solution, the proportions of emulsifying agent and gelling agent used being such as to constitute 1 to 5% and 0.05 to 5% by weight respectively of the sum of the weights of dextrin and polyvinyl alcohol in the final film and the proportion of dextrin used being such that its concentration in the solution is 10 to 70% by weight; (b) mixing the dextrin solution with a polyvinyl alcohol solution of 10 to 20% concentration in such proportions that the concentration of dextrin in the mixed solution is up to twice that of the polyvinyl alcohol, dissolving in the mixed solution a proportion of a polyhydric alcohol or of a polyglycol constituting 10 to 50% of the total solids (P.V.A. plus dextrin) in the mixed solutions at a temperature of 80 DEG to 90 DEG C. for 2 to 3 hours; (c) forming a film from the solution and (d) spraying the film with a 0.5 to 1% solution in a volatile organic solvent of a water-soluble glyceride or sucroglyceride of a higher fatty acid. The white detrin may be the partial degradation product of corn, wheat, potato, tapioca or sago starches. The polyvinyl alcohol may be a hydrolysis product of a polyvinyl acetate of a desired molecular weight such as, for example, a mixture of 85 to nearly 100% of polyvinyl alcohol and 15 to just over 0% of unhydrolysed polyvinyl acetate ranging in viscosity from 5 to 60 c.p.s. at 20 DEG C. |
