| 摘要 |
Polyvinyl acetal resins are prepared by reacting a polyvinyl ester at a temperature not above 50 DEG C. with one or more aliphatic aldehydes boiling below 100 DEG C. (other than formaldehyde) in the presence of a de-esterifying agent and of a strong acid catalyst in a quantity from 1-5 per cent of the reactants and not more than 10 per cent of the polyvinyl ester. The aldehydes may be used in monomeric or polymeric form, or there may be used substances which yield them, e.g. paraldehyde or acetaldehyde diethylacetal. In modifications, if the aldehyde present be in 50-200 per cent excess, or if the reactants be dispersed in a medium consisting substantially entirely of one or more alcohols, the quantity of catalyst may be increased up to 20 per cent of the polyvinyl ester; or the reaction is carried out with the addition of formaldehyde, aliphatic aldehydes boiling above 100 DEG C., cyclic aldehydes, cyclic ketones (e.g. cyclohexanone), or mixtures thereof, in such quantity that the acetal portion of the product contains not more than 25 per cent (mols.) of acetal derived therefrom, the catalyst in this case also being present up to 20 per cent of the polyvinyl ester. The reaction is preferably carried out with polyvinyl acetate, and at 35-40 DEG C. Starting materials specified are: aliphatic aldehydes boiling below 100 DEG C.-acetaldehyde, propionaldehyde, butyraldehyde; de-esterifying agents-methyl, ethyl, propyl and iso-propyl alcohols or ethylene glycol, with or without additional solvents such as methyl or ethyl acetate, dibutyl ether, heptane, ethylene dichloride, benzene, nitroethane; catalysts-sulphuric, alkyl sulphuric and sulphonic, trichloracetic, hydrochloric acids. The resins may be made into photographic-film bases by pressing into blocks and skiving or by coating a solution (e.g. in acetone, ethyl, alcohol, ethylene dichloride, or mixtures thereof) on to a glass or metal plate or a revolving drum, stripping, and curing by heating with warm air. Examples illustrate the preparation of resins from polyvinyl acetate and acetaldehyde, butyraldehyde, or acetaldehyde and (a) butyraldehyde, (b) benzaldehyde, or (c) cyclohexanone, under various conditions. Specification 477,446 is referred to. The Provisional Specification refers to the use of polyvinyl formate, propionate, butyrate, interpolymers of vinyl acetate with vinyl propionate, vinyl oleate, vinyl chloride, vinyl ethyl ether, and styrene, and states broadly that the quantity of catalyst does not exceed 20 per cent of the polyvinyl ester.
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