| 摘要 |
1,028,945. Making polypropylene film. EASTMAN KODAK CO. Jan. 29, 1963 [April 26, 1962], No. 3550/63. Heading B5B. In the making of polypropylene film by melt extruding a crystalline polypropylene to form a film 1À3 mm. or more thick, quenching the film to retain it in an amorphous form and then stretching the film widthwise and lengthwise at a temperature above the second order transition temperature but below the melting point to orient the film biaxially and reduce its thickness to the required value, the film just before stretching is subjected to a heating step at a temperature 15‹ to 20‹ C. above the tenter temperature sufficiently to heat the quenched film throughout its thickness. The widthwise stretch ratio may be 6 to 8 and the lengthwise stretch ratio 4 to 6. The polypropylene may be at least 95% crystalline and may have a melting point of 165‹ to 170‹ C. The stretching operation may be performed at 130‹ to 155‹ C. and the preheating at 154‹ to 170‹ C. The melt extrusion temperature may be 190‹ to 230‹ C. and the quenching temperature 5‹ to 15‹ C. |
