Abstract: Polyvinyl acetals are obtained in a cost-effective and environmentally advantageous manner by employing as at least a portion of the aqueous acetalization medium, the mother liquor from a previous acetalization reaction.

Abstract: The invention relates to a method for producing polyvinylacetals that can be obtained by saponifying a vinylester polymer and subsequently acetalizing the polyvinyl alcohol, which is obtained therewith, with one or more aldehydes selected from the group consisting of aliphatic and aromatic aldehydes having 1 to 15 C atoms, whereby: a) the polyvinyl alcohol is present in an aqueous medium; b) a pH value of <1 is set optionally by adding acid; c) the acetalization is initiated by adding the aldehyde constituent, and; d) the precipitated polyvinylacetal is separated from the filtrate by filtration. The inventive method is characterized in that 10 to 100% by weight of the aqueous medium consists of the filtrate of a previous preparation, and the filtrate produced in d) is optionally reused in another preparation.