Process for production of embossed films based on plasticized polyvinyl acetal

The invention is directed to a process for embossing a film comprising plasticized polyvinyl acetal with a roughness Rz on at least one surfaces of 20 to 100 (mu)m by the process steps of a. extrusion of plasticised polyvinyl acetal to a film with a stochastic roughness of the surfaces of Rz = 1 to 70 (mu)m, b. embossing of at least one surface of the film obtained in step a) with channels having a depth of 5 - 50 (mu)m, a width of 10 - 200 (mu)m and a pitch of 50 - 2500 (mu)m, wherein c. the surface roughness of the elevations between the channels is at most 20% lower as obtained in step a).