| 摘要 |
A process for preparing polyvinyl acetals in an aqueous medium by reacting an aqueous solution of polyvinyl alcohol containing an acid catalyst with an aldehyde in the presence of an emulsifier, neutralizing the mixture and recovering the polyvinyl acetal is characterized in that the emulsifier is introduced into the reaction mixture in an amount of 0,04 to 0,2% by weight of the polyvinyl alcohol after at least 60% of the polyvinyl alcohol and at least 50% of the aldehyde have been added to the reaction medium and the temperature of the reactants has been raised to between 50 DEG and 100 DEG C., the temperature being maintained within the said range while the mixture is agitated until the rate of reaction of the aldehyde with the alcohol is substantially reduced. Preferably the emulsifier is added after the other ingredients have been completely added. The emulsifier may be sodium or ammonium lauryl sulphate, dioctyl sodium sulphosuccinate, ammonium perfluorocarboxylates, sodium aryl sulphonates, adducts of chlorinated cyclopentadiene and maleic anhydride, partially neutralized polymethacrylic acid, alkylaryl sulphonates, sodium N-oleyl-N-methyl taurate, sodium alkylaryl polyether sulphonates, triethanolamine lauryl sulphate, di-ethylcyclohexyl ammonium lauryl sulphate, sodium secondary alkyl sulphates, sulphated fatty acid esters and sulphated aryl alcohols. Specified aldehydes are acetaldehyde, butyraldehyde and heptaldehyde. The acid catalyst may be sulphuric acid or para-toluene sulphonic acid. The products may be compounded with plasticizers, e.g. triethylene glycol di-2-ethyl butyrate, dibutoxyethyl adipate and dibutyl sebacate, and used in the preparation of safety glass laminates. Specification 566,004 is referred to. |
