Patent GB-483223-A (GB)
Title: Polyvinyl acetal resins
IPC: C08F8/28
Filed: 1936-07-08
Abstract: Polyvinyl acetal resins are prepared by treating a partially or substantially completely hydrolyzed polyvinyl ester (other than formate) or polyvinyl alcohol, preferably in the presence of an acid acetalysis catalyst, with a cyclic aldehyde, e.g. benzaldehyde or furfural, and one or more of the bodies formaldehyde, acetaldehyde, propionaldehyde, butyraldehyde, and cyclohexanone and its derivatives either simultaneously or successively, the proportion of cyclic aldehyde being such that the acetal portion of the product contains not more than 25 per cent by mols. of cyclic aldehyde acetal.  The carbonyl-containing bodies may be replaced by substances yielding them, e.g. paraldehyde, acetaldehyde diethyl acetal, trioxymethylene. When cyclohexanone is used, the reaction medium is preferably anhydrous.  When polyvinyl alcohol is used as starting material it may be suspended in a solvent for the product, e.g. isopropyl or other lower fatty alcohol, benzene or heptane, there being then added the aldehyde mixture together with the acetalysis catalyst which may be a non-oxidizing strong acid, e.g. hydrochloric acid, sulphuric acid, phosphoric acid, alkyl sulphuric acids, sulphonic acids, chlorinated aliphatic acids such as mono-, di-, and tri-chloracetic acids, oxalic acid, formic acid, or an acid-reacting salt such as ferric, aluminium or zinc chloride. Preferably, a polyvinyl ester is used as starting material and the p  reaction carried out in the presence of a de-esterifying agent. The ester may be dispersed in a medium comprising the de-esterifying agent, which may be an aqueous or anhydrous primary or secondary alcohol, e.g. methyl, ethyl, or propyl alcohol or ethylene glycol, with or without additional solvents, e.g. benzene, heptane, nitroethane, ethyl acetate, methyl propionate or dibutyl ether, and the aldehydes added together with an acid de-esterification and acetalysis catalyst which may be any of those listed above.  Suitable esters include polyvinyl acetate, propionate, butyrate and benzoate, and interpolymers of vinyl esters and other polymerizable bodies, e.g. of vinyl acetate and propionate, of vinyl acetate and oleate, of vinyl acetate and chloracetate, of vinyl acetate and vinyl ethyl ether and of vinyl acetate and maleic anhydride.  In either case the resulting resin may be separated by precipitation or steam distillation, which may be followed by re-precipitation and washing.  The product may be de-hydroxylated by esterification (e.g. in suspension in pyridine by the action of organic acid chlorides or anhydrides) or etherification or may be de-esterified (e.g. by a basic de-esterifying agent).  The resins may be plasticized, e.g. with tricresyl and tributyl phosphates, dibutyl and diamyl phthalates, tribromphenol, diacetin, triacetin, monochlornaphthalene.  The resins may be pressed into blocks and skived to lamin  for preparing laminated glass, cellulose nitrate or acetate, or wood; made into films by coating a solution of the resin on to a glass or metal plate or a revolving drum, evaporating, stripping, and curing by heating with warm air; or into threads or films by extrusion; they may be used as lacquers or varnishes; to impregnate fabrics or wood; to insulate electric conductors; as antihalation, antistatic and anticurling backings for photographic films; as over-coatings for photographic film; as carriers for photographic emulsion; as adhesives; or as wetting, dispersing, and sizing agents.  Resin solvents specified are acetone, ethylene dichloride, dioxane, methyl and iso-propyl alcohols, benzene, heptane, and acetone-methanol, and methylene chloride-alcohol mixtures.  Detailed examples are given of resins prepared from polyvinyl acetate by acetalization with benzaldehyde and paraldehyde, acetaldehyde, or butyraldehyde, with 2 : 4-dimethoxybenzaldehyde and paraldehyde, or with furfural and trioxymethylene simultaneously; or with trioxymethylene, and benzaldehyde successively; or from polyvinyl alcohol by acetalization with benzaldehyde and paraldehyde or butyraldehyde simultaneously.  The treatment in pyridine solution of a polyvinyl benzaldehyde butyraldehyde acetal resin with acetic anhydride is also described.  Specifications 351,082*, 383,764, 430,136, 445,565, and 477,446 are referred to.