Patent GB-1174313-A (GB)
Title: Process for Uniaxially Orienting Polypropylene Films.
Inventor: CHILL LEONARD
IPC: B29C55/06
Filed: 1967-05-24
Abstract: 1,174,313. Uni-axial orientation of polypropylene films. CHEVRON RESEARCH CO. 24 May, 1967 [24 May, 1966], No. 24251/67. Heading B5B. A process for orienting stereoregular polypropylene film uniaxially in the longitudinal direction to an ultimate draw ratio in the range of from 6 1 to below fibrillation in two or more successive orientation stages, comprises, passing in a first orientation stage cast propylene film of thickness 2-0 to 20 mils between a nip roll and a feed roll having a temperature of from 200 to 280‹ F., the contact time of the film and feed roll being sufficient to heat the film to within at least 10‹ F. of the feed roll temperature, and drawing the film through a 0-2 to 3 inches long linear path defined by the minimum tangential gap between the feed roll and a first draw roll having a peripheral speed of from 2 to 5 times that of the feed roll and a temperature of from 50‹ to 200‹ F., and in at least one additional orientation stage drawing the film to said ultimate draw ratio over a heated roll and between said heated roll and a following stage draw roll so as to effect drawing over a partially arcuate path defined by the arc over which the film stretches in contact with the heated roll and the minimum tangential gap between the heated roll and the following stage draw roll, the major portion of said drawing occurring over said arc, the heated roll having a temperature of from 260‹ to 320‹ F. and a peripheral speed substantially equal to that of the draw roll of the preceding orientation stage, said following stage draw roll having a temperature of from 50‹ to 200‹ F. and a peripheral speed greater than that of the heated roll and the contact time of the film and heated roll being sufficient to heat the film to within at least 10‹ F. of the heated roll temperature. There may be only one additional orientation stage and the peripheral speed of the draw roll in said additional orientation stage may be from 1-2 to 5 times that of the heated roll. In such a process, the peripheral speed of the first draw. roll may be about 4 times that of the feed roll and the peripheral speed of the draw roll of the additional orientation stage is suitably. about 2 times that of the heated roll. In general,; the temperature of the feed roll may be between 260‹ and 280‹ F. and that of the heated roll between 260‹ and 305‹ F. The polypropylene used is generally at least 85% stereoregular, and more usually at least 95% stereoregular, which polypropylene is essentially insoluble in refluxing heptane. In apparatus as shown, film 1 is passed between nip roll 2 and heated feed roll 3, and is stretched in the tangential gap between roll 3 and draw roll 5, the ratio of the peripheral speeds of roll 5 to roll 3 being 2 : 1 to 5 : 1. Nip roll 4 is optional and is used with high casting speeds. By contact with roll 5 film 1 is cooled and stretching terminated. From roll 5 film 1 passes to the second stage, in which it is heated as it moves in contact with heated roll 7. Nip roll 6 is optional and is used with high casting speeds. The film is drawn by the combined effect of drawn roll 9 and nip roll 10. Draw roll 9 has a peripheral speed about 1 - 2 to 5 times that of roll 7. Nip roll 10 anchors the film against roll 9 so that it stretches the film. Nip roll 8 is optional and is engaged for high speed operation. Drawing occurs over the periphery of roll 7 as well as and between roll 7 and roll 9. Film velocity measurements indicate that the majority of stretching in the second stage occurs while the film is in contact with roll 7. At high casting speeds it may be difficult to get enough heat transfer from the roll to the film to bring the film to within 10‹ F. of the feed roll temperature; and under such conditions auxiliary heating means may be used to partially heat the film before it reaches the heated roll. This may be accomplished by passing the film over preheat rolls or through a heated zone. Similarly preheat means may be used in conjunction with the following stage heated roll. The draw roll diameters of the first and subsequent stages are not critical, .but the diameters of the heated rolls may be varied according to the film velocity and path length required.