| 摘要 |
PURPOSE:To obtain a polyester film whose adhesive force is particularly excellent, by performing longitudinal orientation so that an index of birefringence after the longitudinal orientation becomes less than a specific value. CONSTITUTION:An unoriented film is oriented in a longitudinal direction so that an index of birefringence DELTAn of the film becomes less than 0.08, to begin with. Then activation treatment is performed prior to entering into a lateral orientation process, the film is oriented 2.5-4.5 times laterally at the temperature of 90 deg.C-150 deg.C within a tenter, biaxially oriented film is manufactured and fixed thermally after an undercoating agnet, for example, water-soluble resin or water-soluble emulsion has been applied to the film according to necessity. When a magnetic layer s applied to the film after corona discharge treatment has been applied to the film prior to application of the magnetic layer after biaxial orientation and thermal fixation, adhesion which is by no means inferior to the film, whose index of refraction nalpha is more than 1.499 even if the index of refraction nalpha of the film in a thickness direction is less than 1.499, is displayed. As an effect, however, improving the adhesion is little with the index of refraction nalpha of less than 1.4900, it is desirable that the same is more than 1.4900. |
