| abstract |
The invention relates to a process for making an opaque and glossy film from a thermoplastic polyester composition, comprising the steps of a) extruding the polyester composition through a slot die, and quenching to form a substantially amorphous film having a crystallinity of at most 5%; b) rapidly heating the amorphous film to a drawing temperature in the range from T g to (T g +50)° C. while applying a draw ratio in the range of from λ initiation to λ max. in longitudinal direction, and a drawing rate of at least 1 m/min to form an oriented film showing stress-whitening, wherein λ initiation is the draw ratio at which a transfer from a transparent product to a stress-whitened product occurs and λ max. is the draw ratio at which failure of the stress whitened film occurs; and c) heat-setting the oriented stress-whitened film; the thermoplastic polyester composition substantially consisting of at least one crystallizable polyester derived from at least one aliphatic diol and at least one aromatic dicarboxylic acid. n With this process it is possible to make a unitary, glossy, opaque film from a polyester composition that does not contain void-forming additives like high amounts of fine pigment particles or dispersed non-miscible polymer particles. The film obtained also has very good mechanical properties. It is a further advantage that the process can be performed continuously on conventional extrusion and stretching equipment used for making transparent film from polyesters. n The invention also relates to an opaque polyester film obtainable by said process. |