| 摘要 |
1,223,967. Heat-recoverable sheet of polymeric material. RAYCHEM CORP. 20 March 1969 [22 March, 1968], No. 14640/69. Heading B5B. [Also in Division F2] A process for expanding a sheet or strip of a polymeric material capable of having the property of heat-recoverability imparted in it, which comprises applying a force to the sheet or strip in a direction perpendicular to the sheet or strip, the force being sufficient to reduce the thickness and increase at least one of the other dimensions of the sheet or strip, in the absence of tension in the sheet or strip, the temperature of the sheet or strip while the force is applied being, for a crystalline material in the range of from 60‹ C. to the crystalline melting point of the material or a temperature not exceeding the upper limit of the crystalline melting range of the material or, for a non-crystalline material, in the range of from 60‹ C. to the softening point of the material. The force is preferably sufficient to reduce the thickness and increase only one of the other dimensions of the sheet or strip. The "softening point" of the material is measured as specified in ASTM 648 using the 264 p.s.i. stress. As shown in the drawing, polymeric sheet material 3 to be treated is withdrawn from the supply reel 1 (which is provided with a let-off braking mechanism in the form of a roller 2) over an idler roll 4 by a slowly rotating driven steam-heated roller 5 and is expanded in the longitudinal direction at a nip 6 between roller 5 and steam-heated roller 7 which is driven at a higher peripheral speed than roller 5 to accommodate the expanded sheet. The expanded sheet 3 is then passed over a fast-moving cooling roll 9 and the sheet 3 is then passed over an idler roll 10 and on to wind up roll 11 having a constant torque wind-up drive 12. In an example, a 6-inch wide strip, 0À050 inch thick, of high-density polyethylene is irradiated by passing it under a 1 MEV high energy electron beam and then passed through a steam-heated triple roll mill. The first two rollers are maintained at 104‹ C. and the third roller, which has the highest peripheral speed, is water cooled. The selective speeds of the strip on the input and output sides of the mill are in the ratio 1: 1À35 giving a longitudinal expansion of 35%. A 69 inch length of the strip is coated with mastic and wrapped around a 20-inch diameter pipe, fastened and recovered by heating with infra-red rays from a catalytic heater. The width of the recovered sleeve is 5¥ inches. |
