| 摘要 |
PROBLEM TO BE SOLVED: To lessen stain of oligomer in making a film by lessening oozing out of the oligomer on a film surface by a method wherein an extracted oligomer amount on a surface of a polyester film obtained by a melt extrusion method is specified. SOLUTION: An extracted oligomer amount on a surface of a polyester film obtained by a melt extrusion method is made under 2.0mg/m<2> . Further, the polyester film contains 0.6-1.4wt.% of oligomer content, and a ratio of a linear constituent contained in the extracted oligomer on the film surface is under 30%. Therefore, the polyester film is manufactured by a method wherein after heating once polyester resin at a temperature of a melting end temperature or higher to and excluding a thermal decomposition start temperature in a melt part of an extruder, it is cooled so that a surface temperature of a sheet like melt resin at an outlet of a flat die becomes a temperature of under a melting end temperature down to and including descent temperature crystallization start temperature, and the sheet like melt resin is preferably cooled with the flat die or the like. |
