Polyvinylbutyral of reduced tackiness and improved tensile strength

Claim 1

A process for preparing polyvinylbutyral of reduced tackiness and improved tensile strength by acetalization of polyvinyl alcohol with n-butryaldehyde in aqueous phase in the presence of an acid catalyst, which comprises: acetalizing polyvinyl alcohol; the polyvinyl alcohol having less than 0.5% by weight of vinyl acetate units and being in the form of an aqueous solution cooled to a temperature below 20° C.; the acetalizing in said cooled aqueous polyvinyl alcohol solution starting at a temperature below 20° C., which temperature is raised to above 40° C. during the course of the reaction; the resulting polyvinylbutyral having a residual vinyl alcohol content of from 14 to 28% and a viscosity (measured according to DIN 53015 at 23° C. on a 5% by weight solution in ethanol) of between 10 and 200 mPa·s; subjecting said resulting polyvinylbutyral, under acetalization conditions, to an aftertreatment of from 50° to 70° C. in the presence of up to 1% by weight (based on the weight of the resulting polyvinylbutyral) of an organic sulfonic acid or a salt thereof, the sulfonic acid having from 8 to 30 carbon atoms and an emulsifying action.