| 摘要 |
1,040,366. Polypropylene yarn. HERCULES POWDER CO. June 12, 1964 [June 12, 1963], No. 24490/64. Heading B5B. An elastic polypropylene yarn having a recovery of at least 90%, preferably 95%, after being stretched at least 10 times to an elongation of not more than 50% is made by heat treating a polypropylene yarn which has been drawn not more than 150% at 135-155‹ C. Polypropylene yarn may be so heat treated for from 3-30 mins. and thereafter cold drawn 40-80%. The yarn may be in a relaxed state during heat treatment. In an alternative method polypropylene yarn which has been drawn 20-30% at a temperature of 145- 155‹ C. is heat-treated at 145-15o‹ C. under tension. Thus polypropylene yarn may be drawn 20-30% while passing around a roller heated to a temperature of 145-155‹ C. and then heat treated while passing around a second roller heated to 145-155‹ C. rotating at a higher peripheral speed, the yarn being wrapped several times around each roll to give sufficient residence time to bring the yarn to substantially the same temperature as the roll. Yarn having a recovery of at least 95% after being stretched at least 10 times to an elongation of not more than 50% may be made by subjecting a yarn which has been cold-drawn 90-125% to heattreatment at 150‹ C. and thereafter cold-drawing by 75%.
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