METHOD FOR PRODUCING FILMS BASED ON PLASTICIZED POLYVINYL ACETAL HAVING A PREDEFINED VISCOSITY

摘要

The invention is directed to a process to extrude a melt stream at 150 - 250°C comprising at least one polyvinyl acetal and at least one plasticizer having a predefined melt viscosity at 60 - 170°C characterized by a) providing a first melt stream comprising at least a first plasticizer and a first polyvinyl acetal resin and measuring online its melt viscosity at 60 - 170°C; b) 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.