Low shear-thinning polyvinyl acetals having a solution viscosity in 30% strength by weight solution in methyl ethyl ketone which changes by not more than 10% in a shear rate range from 1 to 100 s−1. The preparation of the low shear-thinning polyvinyl acetals involves acetalation of 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 the hydrates, hemiacetals or full acetals, wherein from 0 to 60% by weight of the aldehyde, based on the total amount of the aldehyde, is initially introduced over the course of the first one to ten minutes of the acetalation and is prereacted over the course of from 1 to 30 minutes, and the remaining proportion is then metered in continuously over the course of at least 20 minutes.