Patent ID: 7776962
Filing Date: 2010-08-17
Classification: C08F,C09D

Abstract:
1. A process for the preparation of low shear-thinning polyvinyl acetals, the solution viscosity thereof, measured using a cone-and-plate measuring system in 30% strength by weight solution in methyl ethyl ketone, varying by not more than 10% in a shear rate range from 1 to 100 s −1 , comprising acetalizing partly hydrolyzed or completely hydrolyzed vinyl ester polymers comprising ≧50 mol % of vinyl alcohol units with one or more aldehydes, optionally in the form of their hydrates, hemiacetals or full acetals, wherein from 0.1 to 60% by weight of the aldehyde, based on the total amount of aldehyde, is initially introduced over the course of the first one to ten minutes of the acetalizing and is prereacted for from 1 to 30 minutes, and the remaining proportion is then metered in continuously over the course of at least 20 minutes, wherein acetalization takes place at a temperature of from −10° C. to 30° C.