| 摘要 |
Polyvinyl acetals are manufactured by acting on an aqueous emulsion of a polyvinyl ester containing a polyvinyl alcohol or a water-soluble derivative thereof as emulsifying agent, in the presence of a mineral acid or a strong organic acid, with a quantity of a carbonyl compound sufficient to convert at least part of the polyvinyl ester to a polyvinyl acetal. Specified materials are: water-soluble derivatives of polyvinyl alcohol-polyvinyl alcohols partly esterified with an organic acid, e.g. acetic, propionic, or butyric acid, or partly acetalized with an aldehyde, e.g. formaldehyde, acetaldehyde, butyraldehyde, octyraldehyde, or. benzaldehyde; polyvinyl esters-the formate, acetate, propionate, and butyrate; acid catalysts-mineral acids, e.g. sulphuric, hydrochloric, nitric, phosphoric, hydrofluoboric acids, and strong sulphonic acids, e.g. toluene sulphonic acids; carbonyl compounds-formaldehyde, acetaldehyde, propionaldehyde, butyraldehyde, octyraldehyde, benzaldehyde, cyclohexanone and methylcyclohexanone. There may also be present an alcohol, e.g. methyl, ethyl or propyl alcohol. In examples (1), (2), (4), an emulsion of polyvinyl acetate in aqueous polyvinyl alcohol is acetalized by acetaldehyde in the presence of methyl alcohol and sulphuric acid, by butyraldehyde in the presence of ethyl alcohol and p-toluene sulphonic acid, or by octyraldehyde in the presence of ethyl alcohol and phosphoric acid; (3) an emulsion of polyvinyl butyrate in aqueous-alcoholic polyvinyl alcohol is acetalized by acetaldehyde in the presence of methyl alcohol and hydrochloric acid. The product of example 2 may be worked up as threads. Specifications 466,173 and 469,319 are referred to. |
