Patent GB-466598-A (GB)
Title: Improvements in and relating to the production of polyvinyl resins
IPC: D01F6/14
Filed: 1935-09-26
Abstract: Relates to the production of substantially colourless polyvinyl acetal resins from a polyvinyl ester other than formate, or from a hydrolysis product thereof, and a saturated aliphatic aldehyde other than formaldehyde.  Specifications 351,082*, 436,072, and 454,691 are referred to.  The products of the invention give a colour value less than 2,0 units on the Lovibond scale in a 15 per cent solution.  In one form of the process the ester and the aldehyde are reacted in the presence of a hydrolyzing and acetalizing catalyst, an organic solvent other than an alcohol, and water (or water and an alcohol) in amount small enough to secure that at least 80 per cent of the hydroxyl groups formed are acetalized, but large enough to give a colourless product. Instead of free aldehydes, substances which liberate aldehydes may be used.  Catalysts specified are sulphonic acids, strong carboxylic acids, e.g. trichlor acetic acid, and strong mineral acids, e.g. sulphuric acid.  In the other form of the process the aldehyde and a partially or completely hydrolyzed polyvinyl ester (which may be partially acetalized) are reacted in the presence of an acetalizing catalyst under the conditions set out above. Catalysts specified are those mentioned above and in addition metal chlorides, and sulphates, such as zinc chloride, calcium chloride, acid sodium sulphate.  In both forms of the process solvents specified are esters of carboxylic acids, e.g. an ester of the acid of the polyvinyl ester, lower aliphatic acids, e.g. acetic acid, dioxane and acetone. The alcohol may be that corresponding with the ester used as solvent. The resin may be precipitated by water, or separated by steam distillation of the solvents, or the reaction mixture may be extruded as a film or thread into air or into a precipitation bath (the catalyst being first neutralized or not), washed and dried.  The polyvinyl ester used may have a viscosity of 10 centipoises measured as described in Specification 436,072.  The resin may be exposed to thevapour of formaldehyde, phenyl isocyanate, ketone &c., in order to reduce the percentage of free hydroxyl groups.  The resins may be used for the purposes specified in Specification 436,072.  In examples, the materials and solvents used are as follows, with sulphuric acid as catalyst and with water in each case: (1) polyvinyl acetate, paraldehyde, ethyl acetate, ethyl alcohol; (2) polyvinyl acetate, paraldehyde, butyl acetate, butyl alcohol; (3) polyvinyl acetate, paraldehyde or acetaldehyde, ethyl acetate, ethyl alcohol; (4) polyvinyl acetate hydrolyzed to 50 per cent, paraldehyde or acetaldehyde, ethyl acetate, ethyl alcohol; (5) polyvinyl acetate, butyric aldehyde, ethyl acetate, ethyl alcohol; (6) polyvinyl acetate, propionic aldehyde, ethyl acetate, ethyl alcohol; (7) polyvinyl acetate, paraldehyde, aqueous acetic acid (strength 50 per cent).  In the products of these examples, the percentages of acyl groups removed from the polyvinyl ester are 69, 72, 98, 52, 80, 80 and 73,4 and the percentage replacement of these by aldehyde is 90, 87, 89, 87, 88, 88 and 92 respectively.  In connection with the examples, the permissible variations in the proportions of solvent, aldehyde, alcohol, water, and catalyst, and in the temperature, are discussed.  A sample furnished under Sect. 2 (5) was prepared as follows: polyvinyl acetate was dissolved in ethyl alcohol and ethyl acetate, there being added octyl aldehyde and water.  The mixture was reacted in the presence of sulphuric acid.  The hydrolysis was 62 per cent complete and the acetal reaction 85,4 per cent complete.