| 摘要 |
PROBLEM TO BE SOLVED: To provide a biaxially stretched resin film excellent in flatness by preventing the deterioration of flatness generated not only immediately after production but also after a time is elasped from the point of time of production. SOLUTION: In a resin film stretched in a biaxially direction to be subjected to heat treatment, the heat distortion ratio of the film in the longitudinal direction thereof is within a range of -10×10<-5> -5×10<-5> (l/ deg.C) and the defference between the max. and min. values of the heat distortion ratio is 4×10<-5> (1/ deg.C) or less and the difference Y between the max. and min. values of double refraction at the arbitrary point of the film in the lateral direction thereof satisfies Y<=20×10<-3> X with respect to the width X of the film and, when the thickness of the resin film is set to Z(μm), thickness irregularity T(%) satisfies T<=(130/Z)+1.5. |
