| 摘要 |
1,214,395. Making polypropylene films and sheets. MITSUBISHI PETROCHEMICAL CO. Ltd. 28 Oct., 1968 [27 Oct., 1967], No. 50965/68. Heading B5B. Polypropylene films and sheets are made by melt extruding a crystallizable substantially isotactic polypropylene through a slot die to form a flat molten sheet at least one surface of which is caused to pass over and in contact with a quenching roller, the temperature of the peripheral surface of the roller and the period of contact of any point on the surface of the sheet with the roller being such that the surface of the sheet is cooled to a temperature below the melting point of the polymer while the inner portion of the sheet remains in the molten state. Both surfaces of the sheet are then contacted with quenching water (as by passing through a bath of quenching water) maintained at a temperature not exceeding 40‹ C. Prior to being contacted with the quenching roll the film, after leaving the quenching roll, may be passed over a second quenching roll in such a manner that the other surface of the film is also cooled to below the melting point of the polymer, the inner portion of the film still remaining in a molten state. The molten polypropylene sheet may have a thickness exceeding 0À5 mm., e.g. 1À5 mm. In the examples, a sheet having a thickness of 1À5 mm made according to the process of the invention, may be biaxially stretched at a stretch ratio of 5 in the longitudinal and 7 in the transverse direction to obtain a biaxially stretched film having a thickness of 35 microns. The period of contact of the molten polypropylene sheet with the quenching roller may be in accordance with the expression:- in which:- # = the contact time in seconds; L = the thickness of the sheet in cm.; t 0 = the temperature of the molten polymer in ‹C.; t, = the surface temperature of the quenching roller in ‹C. Quenching water may be ejected from nozzles on to both surfaces of the sheet while it is passed through the quenching bath. |
