| 摘要 |
1,096,127. Biaxially orienting tubular films. UNION CARBIDE CORPORATION. March 7, 1966 [March 12, 1965], No. 9811/66. Heading B5B. A preformed flattoned tubular film 20 (Fig. 3) passes through the nip of squeeze rolls 28 and is reinflated to form a secondary bubble which is drawn vertically upwards through a cylindrical radiant heater system 30 comprising cylindrical radiant heaters 42, 44, 46 and 48 spaced apart from each other and having a longitudinal central passage for the tubular film therein. Each of the heaters includes a series of electrical resistance elements 65 equally spaced about the circumference of the heater and controlled by a known transformer type of control. The internal wall of each heater is preferably provided with screening 63 and the diameter of the central passage of each heater is sufficiently large to allow the tubular film in its radially distended condition to pass through the passage with ample clearance. A high velocity stream of a cooling gas, such as air, is introduced adjacent to the upwardly moving column of tubular film, so as to cause the gas to impinge upon the tubing being heated and is also introduced in the vicinity of the draw zone, by means of an air ring 50 between the heaters 44, 46 and a blower 51. The air ring has a slot orifice which directs the stream of air upwards and as the tubular film 20 advances towards the squeeze rolls 34 it is surrounded by an upwardly moving stream of air composed partly of ambient air drawn up the heater passage by the upward movement of the tubing, by the chimney effect of the heaters and by the induction effect of the high velocity air stream from the air ring 50. The heaters are situated and adjusted so that the air stream initially at room temperature always remains at a temperature below that of the tubular film in the draw zone, thus serving to control the temperature of the film and to prevent overheating of the film in the draw zone. It is preferred to rapidly cool the expanded tubular film after the expansion is completed to prevent the annealing of the film and thereby to produce film having maximum heat shrinkage for packaging purposes. For this purpose an air ring 53 may be provided to rapidly cool the expanded tubular film. In addition an exhaust ring 54 having iris diaphragm controlled openings 56 and 58 may be provided. The inflated tubular film 20 is drawn through the heater system 30 and is flattened by the squeeze rolls 34 which are driven at a peripheral speed higher than that of squeeze rolls 28 either to pick up slack formed during biaxial stretching or to impart additional machine direction stretch. The film may, if desired, be annealed by reinflation and heating in the apparatus 72, 74, 76. |
