GB1398311A - Moulding of polyester film - Google Patents

Abstract

1398311 Moulding polyester film; sheet forming YARSLEY RESEARCH LABORATORIES Ltd 26 April 1973 [8 May 1972] 21367/72 Headings B5B and B5A A method of moulding biaxially oriented polyester film comprises forcing a pre-heated male mould 14 having a shape which is consistent with that of the desired moulded film into a preheated flat film (12a) (Fig. 1, not shown) until from 42 to 62À5% of the desired final draw is obtained, the edges of the film around the base area of the moulding being supported, but not clamped (as by lead clamp ring 13 which acts through its own weight), so that the film is able to move inwardly around the base area of the moulding during advance of the male mould, and cooling the film on the male mould whereby film pre-form 12b is obtained and then vacuum forming the preform under a vacuum of not more than 6 in. Hg, while heating the pre-form, to obtain the desired final shape 12c, stopping heating, and cooling the moulded film while not allowing the vacuum to rise above 6 in. Hg. Substantially 50% of the required final draw of the moulded film may be obtained in the prodrawing stage. The assembly of cup mould 10, film blank 12a and clamp ring 13 is heated in an infra-red oven, preferably to 160‹ C., while the pre-forming male mould 14 is similarly heated preferably to 100‹ C., and then forced down into the cup mould to the position shown in Fig. 2. After cooling, film pre-form 12b is placed over vacuum-forming cup 15. Gasket 18 is interposed between preform 12b and flange 17, followed by top gasket 19, clamp ring 20, and clamps 21. Vacuum is applied at 16 and increased while the film is heated by a bank of infra-red heaters above the assembly, until the desired depth of draw is obtained Heating is then discontinued, and after some cooling the vacuum is reduced from 6 in. to 2 in. Hg and maintained at this level until cooling is complete.