Drying processes for composite films comprising polyvinyl acetal and polyvinyl ethylene acetal resins

A process for the manufacture of a composite film, said composite film comprising:

• i) a film A comprising a polyvinyl acetal and/or a polyvinyl ethylene acetal and, optionally, a plasticiser, and
• ii) a carrier film,
• said process comprising the following steps, in that order:
• a) providing a carrier film;
• b) coating one surface of the carrier film with a solution comprising a solvent, the polyvinyl acetal and/or polyvinyl ethylene acetal, and the optional plasticizer;
• c1) drying the composite film on roll support at a temperature from 25 to 90° C.;
• and
• d) performing one or more drying steps selected from a list consisting of the following steps:
• IR drying, UV drying, microwave drying, vacuum drying, roll supported drying at a temperature of more than 130° C. and less than 180° C., air floatation drying at a temperature of more than 130° C. and less than 180° C.;
• to obtain the composite film, wherein the film A has a surface roughness Rz of 0.1 μm to 3.0 μm, and wherein the carrier film has a surface roughness Rz of 1.0 μm to 10 μm on a surface in contact with the film A.