| 摘要 |
PURPOSE:To obtain a film or sheet which keeps high crystallinity, does not whiten and does not lose its transparency even in a heated atmosphere by treating a film or sheet formed by melt-molding a specified aromatic copolyester under specified conditions. CONSTITUTION:A film or sheet formed by melt-molding a copolyester resin comprising structural units of formulas I and II, wherein R is group of formula III, IV, V or VI; and the molar fraction to the total structural units [formula II/(formula I + formula II)] is 0.02-0.20, is rapidly cooled to prepare a film or sheet of a low degree of crystallinity. This film or sheet is aged at a temperature <=60 deg.C and heat-treated at a temperature ranging from the glass transition point Tg to the melting point Tm minus 2 deg.C. The obtained resin has high heat resistance, does not lose its transparency even under high-temperature conditions of about 120 deg.C, can keep a haze <=20%, is highly crystalline (>=70%), excels in gas barrier properties and heat shrinkability and is suitable for food package of microwave oven cooking, etc. Because it is rendered transparent without detriment to its mechanical properties, it is excellent in light resistance and can be used as, e.g., a film for protecting a window panel. |
