| 摘要 |
The viscosity and/or stability to water of polyvinyl alcohols or their partial esters, acetals or ethers, or of moulded objects, other than printing surfaces, of such materials is increased by treatment with a solution of a chromium or an iron compound, with the application of other influences if desired, such as a thermal or photo-chemical treatment, the conditions of treatment being such that the mechanical properties of the polyvinyl compound are not damaged. Suitable iron or chromium compounds include ferric chloride, chromates and chromic acid. In examples: (1) a film made from polyvinyl alcohol or a water - soluble derivative thereof is treated with a potassium bichromate solution, washed and exposed to sunlight; (2) a hose pipe made of a material containing 25 per cent of polyvinyl alcohol is immersed in boiling water and then treated with aqueous chromic acid; (3) an aqueous solution of polyvinyl alcohol is thickened by treatment with aqueous ferric chloride. Specification 451,009 is referred to. p The Specification as open to inspection under Sect. 91 refers to treatment with metal compounds in general. This subject-matter does not appear in the Specification as accepted.
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