Method for producing polyvinylacetals

A process for preparing polyvinyl acetals by hydrolysis of a vinyl ester polymer and acetalization of the resultant polyvinyl alcohol with one or more aldehydes selected from the group consisting of aliphatic and aromatic aldehydes having 1 to 15 carbon atoms, comprising:

• a) providing a polyvinyl alcohol to form an initial charge in an aqueous medium,
• b) if necessary, adding acid to adjust to a pH of <1,
• c) initiating acetalization by addition of an aldehyde component, and
• d) precipitating polyvinyl acetal and separating polyvinyl acetal via filtration from a filtrate,
• wherein from 10 to 100% by weight of the aqueous medium of a) comprises the filtrate from a preceding batch of polyvinyl acetal production, and, optionally reusing the filtrate produced in d) in a further polyvinyl acetal production batch.