GB436072A - Improvements in the manufacture of films, threads, sheets or the like and the manufacture of resins therefor - Google Patents

Abstract

Polyvinyl resins are manufactured by reacting together a polyvinyl ester (other than formate), a body (other than acetaldehyde) containing an active carbonyl group capable of combining with free hydroxyl groups of a hydrolysis product of the polyvinyl ester, and water in the presence of a hydrolysing and acetalizing catalyst and an organic solvent (other than an alcohol), and, if desired, in the presence of an alcohol, the amount of water or of water and alcohol together being, under the conditions of reaction, sufficiently small to give homogeneous reaction conditions such that the acetal reaction may attain or exceed 87 per cent of completion. When the carbonyl compound is formaldehyde or a body yielding it in the reaction, the amount of water or of water and alcohol together is preferably also sufficiently large to secure the production of a substantially colourless resin. In a modification of the process, a hydrolysis product (partial or complete), of a polyvinyl ester (other than formate), formed in absence of a carbonyl compound, is reacted with a carbonyl compound (other than acetaldehyde), in the presence of an acetalizing catalyst and an organic solvent (other than an alcohol), and, if desired, in the presence of water or an alcohol or both in an amount sufficiently small to permit of obtaining homogeneous reaction conditions such that the acetal reaction may attain or exceed 87 per cent of completion. When the carbonyl compound is formaldehyde or a body yielding it, the reaction is preferably performed in the presence of water or an alcohol or both in an amount sufficiently large to secure the production of a substantially colourless resin. For either hydrolysis or acetal reaction alone or for both simultaneously, suitable catalysts are sulphonic acids, strongly dissociated organic carboxylic acids, e.g. trichloracetic acid, and mineral acids, particularly sulphuric acid. When the acetal reaction is performed subsequently to the hydrolysis there may also be used certain metal chlorides or sulphates, e.g. zinc chloride, calcium chloride or sodium acid sulphate. In the latter modification of the process, the acetal reaction may immediately follow the hydrolysis, using the same reaction-medium, with or without first neutralizing the hydrolysis catalyst and replacing it by a milder catalyst, or the acetal reaction may be quite distinct from the hydrolysis as regards time, place and conditions. The polyvinyl ester employed should preferably have a viscosity (as a solution in benzene containing the simple molecular weight, in grams, per litre) of 10 centipoises or more and should be 80 per cent or more hydrolysed. Films or threads are manufactured by extruding the reaction mixture into air or into a precipitation bath, with or without previous neutralization of the catalyst. The products are also suitable for the production of sheets, rods or tubes from which formed articles may be made by cutting, stamping or pressing, safety glass, coating compositions, e.g. for liners for bottle caps or for insulating electric wires, and mouldings, e.g. dentures or electrical insulating parts. The resins in film, thread or granule form may be treated for reduction of the percentage of free hydroxyl groups by exposing them to vapours of formaldehyde, phenyl isocyanate, ketene or other bodies capable of replacing the hydrogen in hydroxyl groups. In examples: (1) polyvinyl acetate having a viscosity of 15 centipoises is heated to 70 DEG C. with water and paraformaldehyde in the presence of sulphuric acid, butyl acetate and butyl alcohol; (2)--(4) the butyl acetate and butyl alcohol are replaced by ethyl acetate and ethyl alcohol; (5) polyvinyl acetate of 30 centipoises viscosity is treated as in (4); (6) polyvinyl acetate of 50 or 60 centipoises viscosity is employed; (7) a hydrolysis product of polyvinyl acetate (prepared by 50 per cent hydrolysis of polyvinyl acetate of 2.5 centipoises viscosity, in ethyl alcohol containing sulphuric acid) is isolated and heated to 70 DEG C. with aqueous formaldehyde and sulphuric acid in the presence of ethyl acetate and ethyl alcohol. Details are given of the limiting conditions in respect of the amounts of water, alcohol, catalyst and aldehyde, and of temperature, which must be observed in order to effect a high percentage acetal reaction, with or without substantial absence of colour. The formaldehyde or body yielding it may be replaced by propionaldehyde, butyraldehyde, benzaldehyde, furfurol, crotonaldehyde or a ketone, and the polyvinyl acetate by the propionate or butyrate. In the latter case the ester used as solvent should preferably correspond to the polyvinyl ester, whilst the alcohol, if any, should correspond to the ester solvent. Instead of the ester solvents there may be used solvents which permit the addition of considerable amounts of water, e.g. dioxane or acetone, in which case the alcohol may be dispensed with and replaced by an additional amount of water. Specifications 351,082 and 383,764 are referred to. The first Provisional Specification describes the preparation of the starting materials of examples (5) and (6) above, by polymerizing vinyl acetate containing some acetaldehyde, in benzene solution by means of the catalyst of example (1) of Specification 387,323. Acrolein is additionally specified as a suitable aldehyde. Specifications 387,353 and 405,986 also are referred to.