| 摘要 |
The invention relates to less shear-thinning polyvinyl acetals that are characterized in that their solution viscosity in a 30 % by weight solution in methyl ethyl ketone changes by not more than 10 % in a shear rate range of 1 to 100 s<SUP>-1</SUP>. The invention also relates to a method for producing less shear-thinning polyvinyl acetals by acetalizing partly or completely saponified vinyl ester polymers with = 50 mole % of vinyl alcohol units with one or more aldehydes, optionally in the form of the hydrates, hemiacetals or acetals thereof. The inventive method is characterized in that the aldehyde is provided to 0 to 60 % by weight, based on the total of aldehyde, within the first one to ten minutes of acetalization and is prereacted during 1 to 30 minutes, and the remainder is then continuously metered to the solution within at least 20 minutes. |
