| 摘要 |
PURPOSE:To prevent the breakage of a superthin film when peeled off by improving the separating strength of the film by a method in which a laminate sheet consisting of polyester-propylene copolymer having a specific melting point is consecutively biaxially stretched and then concurrently biaxially stretched, the laminate film is heat-treated at a specific temperature and cooled, and the polyester film is peeled off. CONSTITUTION:Polyester-propylene (having 100-150 deg.C melting points) copolymer (PPC) is extruded through a nozzle into a laminate sheet. The sheet is stretched 3.0 times or more in the longitudinal direction and then subjected to a consecutive biaxial stretching of 3.0 times or more for bilateral direction. The laminate sheet is further concurrently stretched biaxially with 1.3-2.5 times' draw ratios for both longitudinal and bilateral directions. The film so stretched is heat-treated at temperatures above the melting point of PPC but below the melting point of polyester and gradually cooled to room temperature. The polyester film is then separated from the laminate film to obtain a superthin polyester film. By the concurrent biaxial stretching after the consecutive biaxial stretching, the orientation of the film is promoted and the polyester film becomes easily separable. The breakage of the film when separated can thus be prevented due to its high strength. |
