| 摘要 |
PROBLEM TO BE SOLVED: To stably produce a surface roughened biaxially stretched polyester film uniform in cloudiness over the lateral direction of the film. SOLUTION: In a method for producing a biaxially stretched film using a raw material being a resin compsn. consisting of 90-96wt.% of a thermoplastic polyester resin, and 10-4wt.% of a thermoplastic resin having a glass transition temp. higher than that of the polyester resin and critical surface tension different from that of the resin by 0.1 dyne/cm or more and having melt viscosity of 500-50,000 poise at 280 deg.C and at a shearing speed of 10<2> sec<-1> , when the max. value of cloudiness in the lateral direction in the stretched film is set to Hmax and cloudiness at other position in the lateral direction other than Hmax is set to H, the temp. at the stretching start point (the boundary point of the preheating zone and the stretching zone) of the film corresponding to the position of cloudiness H is regulated so as to become higher than the temp. at the stretching start point of the film corresponding to the position of Hmax to perform simultaneous stretching to uniformize the cloudiness in the lateral direction of the stretched film. |
