a body of oriented thermoplastic material is converted through heating in an area adjoining one boundary surface of the material portion to a layer of substantially non - oriented material . a film is fixed to the fixing layer by pressing the film with a compression and heating element and the necessary heat is supplied so that the film will be fixed to the fixing layer . since the film is bonded to substantially non - oriented plastic material , the desired detachability in the bond between the film and the material portion is achieved .