| 摘要 |
982,036. Net or ornamented film of polypropylene. FMC CORPORATION. April 6, 1962 [June 2, 1961], No. 13414/62. Heading B5B. A net of polypropylene having uniaxially drawn ribs connected by undrawn junctures is produced by hot or cold drawing a perforated film. The perforations may be round, eliptical, rectangular with rounded corners, or clover leaflike, and may be produced by punching or, drilling a perforated film or during casting. Drawing may be uniaxially or biaxial. In the latter case, drawing may be effected simultaneously or in series along its longitudinal and transverse axes. The draw ratios in the longitudinal and transverse directions may be the same or different, and may be 1.5-20 to 1. The ratio of widest/narrowest width of rib is preferably equal to the ratio of yield/draw load. Stretching in each direction may be effected in two stages. As shown in Fig. 9, stretching is first effected in direction 47 and then in direction 45 to produce the configuration shown in Fig. 10 with drawn ribs 53 and undrawn junctures 55. An ornamental film may be similarly produced by hot drawing a film having discrete coated areas of heat absorbent material instead of holes and/or complementary areas of heat reflecting material. A second coating step is preferably carried out between longitudinal and transverse stretching. |
