Process for the manufacture of polyester film

Details Process for the manufacture of polyester film Process for the manufacture of polyester film

B - Operations, Transporting

29

C

18/528

B29C 49/64 (2006.01) B29C 47/00 (2006.01) C08J 5/18 (2006.01)

Patent

CA 1225506

Abstract of the Disclosure PROCESS FOR THE MANUFACTURE OF FILM The invention contemplates the manufacture of a wrinkle-free, amorphous, unoriented polyester film which is produced by an extrusion blowing process. The process consists of extruding a bubble of polyester, expanding the bubble, and then collapsing the bubble at a temperature above the polyester's glass transition temperature to prevent the formation of wrinkles. The collapsing step is effected through the use of a shroud which receives the bubble and has a low friction surface. The process is illustrated in Figure 1 wherein a schematic representation of the process is designated by the number 10. The molten polyester is extruded through a circular die 12 having an annulus 13. Positioned immediately above die 12 is an air ring 14 having an annulus 15 through which passes a stream of air to inert gas. The molten polyester is cooled by the air or gas such that its viscosity increases to produce an acceptance melt strength. A stationary fluid bubble 18 or air or inert gas is located above the air ring and within the interior volume of the tubular polyester bubble 16. As the polyester, usually polyethylene terephthalate or a copolymer thereof, is continuously extruded through the die 12, it is expanded by the fluid bubble 18 and then collapsed by means of a shroud 20. The interior angle of the shroud may vary from 10 to 70 degrees with from 15 to 60 degrees preferred. The polyester then passes through a slit 22 located at the apex of the shroud 20 and is thereafter pressed by means of nip rolls 24. The polyester may then be wound.

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