| 摘要 |
PURPOSE:To improve the durability of spring property by letting a film for lifter, made from uniaxially oriented polyethylene-2,6-naphthalenedicarboxylate holding the Young's modulus and the retention of the Young's modulus at specific temperature and humidity at specific values. CONSTITUTION:When a polyethylene-2,6-naphthalenedicarboxylate (PEN) film is used for a lifter, the one whose ultimate viscosity number is 0.50-0.70 extent is used and uniaxial-oriented at least by a melting extrusion process or the like. Then, the PEN film is left in the atmosphere of temperature 70 deg.C and humidity 80%RH under no tension for 72hr, and the retention of a Young's modulus is kept at 80%. It is achieved by making a drawing magnification more than 4.0 times and executing a heat treatment at 230-250 deg.C. Besides, the Young's modulus is kept at 400kg/mm<2> at least temperature of 80 deg.C or less. Thus, the durability of spring property is improved. |
