Plasiticized polyvinylacetal films with greater film-to-film uniformity are produced by a process of extruding a melt stream containing a polyvinyl acetal and a plasticizer at 150-250 C., the film having a predefined melt viscosity at 60-170 C., by providing a first melt stream of at least a first plasticizer and a first polyvinyl acetal resin and measuring its melt viscosity at 60-170 C. online; and adjusting the 60-170 C. melt viscosity by adding a second plasticizer and/or a second polyvinyl acetal resin to the first melt stream in an amount to provide a second melt stream with a melt viscosity at 60-170 C. having a difference of at most 20% to the predefined melt viscosity at 60-170 C.

Plasiticized polyvinylacetal films with grater film-to-film uniformity are produced by a process of extruding a melt stream containing a polyvinyl acetal and a plasticizer at 150-250 C., the film having a predefined melt viscosity at 60-170 C., by providing a first melt stream of at least a first plasticizer and a first polyvinyl acetal resin and measuring its melt viscosity at 60-170 C. online; and adjusting the 60-170 C. melt viscosity by adding a second plasticizer and/or a second polyvinyl acetal resin to the first melt stream in an amount to provide a second melt stream with a melt viscosity at 60-170 C. having a difference of at most 20% to the predefined melt viscosity at 60-170 C.