| 摘要 |
A process which combines a calender with a stretching system and a set of heating rolls is provided in this invention to produce films of polypropylene resin of wide thickness range. The polypropylene films which have cavities distributed in the film and on the surfaces are suitable for writing or printing and have a low density. The films have surface qualities of each side of surface within +/-2x10-6 inch of the average depth of the cavities, +/-2% of the average of the gloss at 45 DEG angle and +/-0.02 of the average of coefficient of friction. Such a film is obtained by passing the molded film from the calender through a set of heating rolls at temperatures revealed in this invention before entering the stretching system. The obtained polypropylene film has superior printability, low density and high stiffness, and thus is suitable for use as a paper substitute.
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