| 摘要 |
1,028,053. Making polypropylene films. MONTECATINI SOC. GENERALE PER L'INDUSTRIA MINERARIA E CHIMICA. May 27, 1963 [May 28, 1962], No. 21096/63. Heading B5B. A film of crystalline polypropylene consisting essentially of isotactic macro-molecules is produced by melt extruding the polymer to form a film, quenching the film to between 0‹ and 20‹ C, and, without stretching, heating it under free-shrinking conditions at 50‹ to 150‹ C. The quenching of the freshly extruded film may be effected by causing it to pass over and in contact with a cooled rotating roll which is maintained at a temperature within the range 0‹ to 20‹ C. inclusive. The temperature of the film during the heating stage may be maintained for a period from a fraction of a second to 60 minutes, and may be effected by a continuous or discontinuous process, the time and temperature of the heating step of the process being approximately inversely proportional. In an example, a polypropylene having an intrinsic viscosity of 1À7 and a residue of 95% after heptane extraction is melt extruded at 260‹ C. extruder head temperature to form a film which is stretched while still plastic and quenched by passing over and in contact with a cooled rotating roll which is maintained at a temperature of 18‹ to 20‹ C. and is spaced 5-6 cm. from the extrusion die. The quenched film is then removed from the roll and maintained for 60 minutes at a temperature of 60‹ C. while being free to shrink. Films produced according to the invention are glossy and substantially free from haze in spite of having a considerable degree of crystallinity. |
