| 摘要 |
PROBLEM TO BE SOLVED: To obtain a magnetic recording card which has very high reliability by using polyester film which has a heat shrinkage factor that is in a specific range and has the coefficient of thermal expansion which is in a specific range. SOLUTION: The heat shrinkage factor of polyester film to be used at 50 deg.C for 120 minutes is -0.05 to 0.05%, preferably 0 to 0.1%. The heat shrinkage factor at 70 deg.C for 120 minutes is -0.1 to 0.1%, preferably 0 to 0.1%. Also, the coefficient of thermal expansion is in the range of 6×10<-6> to 26×10<-6> (1/ deg.C), and the anisotropy of the coefficient of thermal expansion is preferably below 10×10<-6> (1/ deg.C). Polyester which constitutes polyester film is virtually linear polyester. Its main acid component and glycol component are aromatic dicarboxylic acid and aliphatic glycol respectively. As an aromatic dicarboxylic acid component, e.g. terephthalic acid, etc., are used, and as aliphatic glycol, e.g. ethylene glycol, etc., are used. |
