| 摘要 |
PURPOSE:To obtain the titled film excellent in mechanical properties, heat resistance and moisture absorption characteristics and being anisotropic in these properties, by passing a solvent-containing film of a specified aromatic polyamic acid through a heating furnace along the lengthwise direction so as not to change its crosswise dimension. CONSTITUTION:A solution formed by dissolving a polyamic acid based on repeating units of formula I in an organic solvent such as N-methyl-2-pyrrolidone is cast on a flat metallic belt or the like to form a liquid film. This liquid film is fed to a heating furnace to remove the solvent to thereby form a solvent-containing film. While the crosswise dimension of this film is being kept constant by clamping both edges of the film, it is fed too a heating furnace along the lengthwise direction, heated to 10-200 deg.c for about 20-300min to remove the remaining solvent and further heated to 200-450 deg.C for 20-300min. In this way, the titled film based on repeating units of formula II, excelling in heat resistance, suited as, e.g., a base film for high-density magnetic recording media and characterized in that the difference between the lengthwise and crosswise tensile strengths, elongations, tensile moduli and glass transition points are each within 5%, and the differences between the coefficients of lengthwise and crosswise expansion and between the coefficients of lengthwise and crosswise moisture expansion are each within 10% can be obtained. |
