Patent GB-1192840-A (GB)
Title: Tubing Irradiation apparatus and process
Inventor: SPILLERS FRANK WAYNE
IPC: B29C71/04
Filed: 1968-04-18
Abstract: 1,192,840. Tubing irradiation. DOW CHEMICAL CO. 18 April, 1968 [18 April, 1967], No. 18426/68. Heading B5B. A process for the irradiation of plastics tubing, comprises passing the tubing through a flattening zone and alternately irradiating the tubing on opposite sides a plurality of times while it is still in the flattened state (i.e., the top section of the tubing is in actual contact with the lower half). Apparatus comprises feeding means for continuously feeding plastics tubing to means for flattening the tubing, the said flattening means being disposed so that the tubing is alternately irradiated, on opposite sides thereof, a plurality of times, said flattened tubing being irradiated by irradiation means while flattened by said flattening means, and further comprising means for continuously withdrawing the irradiated flattened tubing from the flattening means. The flattening means is suitably a primary roller having a smooth outer surface, and desirably comprises also a secondary roller mounted in operative relationship with the primary roller, and arranged so that the plastics tubing is passed over and flattened by said primary roller, and then inverted by the secondary roller and conducted back over a second primary roller, the tubing being irradiated as it passes over the primary rollers. Preferably, a plurality of the primary and secondary rollers are arranged so that the tubing is alternately irradiated on one side and inverted by the secondary rollers. An alternative apparatus to accomplish the desired flattening comprises a plurality of pairs of vertically spaced horizontally arranged flat plates disposed directly underneath the irradiation means so as to receive the irradiation. These plates are spaced a predetermined vertical distance apart so that when the tubing passes therethrough, it is completely flattened. These plates are somewhat wider than the flattened tubing and have an opening or a series of openings in the plate which is uppermost, as wide as the width of the flattened tubing so as to permit full and direct irradiation of the tubing as it passes through the irradiation zone in a flattened state. A further alternative method to accomplish the desired flattening is to create a vacuum inside the plastic tubing by compressing it against a stationary plate by means of a pair of idle rollers mounted on opposite ends of an arm rotating about a powered shaft at the middle of the arm in a direction opposite to the feed of the tubing. The irradiation means may be an electron beam generator, and specified materials include polyethylene, polypropylene; copolymers of ethylene with propylene, isobutylene, amylene, acetylene, butadiene, and butene-1 and butene- 2; and terpolymers of ethylene, propylene and vinyl esters as, e.g. the acetate, propionate and butyrate. In Fig. 1, a relatively thick (30 mils.) tubing 20 is cooled in a water bath or spray (not shown) and conveyed by the driven nip rollers 15 to radiation cubicle 19, in which an electron beam gun 10 is arranged so that several passes of tubing 20 are irradiated and ionized as they are flattened on the primary rollers 12 mounted directly under the gun 10. Tubing 20 is passed over the primary rollers 12 and under the irradiation means 10 a plurality of times. The number of passes is preferably an even number so that opposite sides of the tubing are exposed to the electron beam the same number of times. Tubing 20 is then guided around the inverting wheels 16 and back to primary roller 12 and irradiation means 10 a plurality of times as desired. Guide rollers 14 may be included for positioning the tubing but are not essential. After leaving cubicle 19, irradiated tubing 20 is passed between driven nip rolls 23, 22 and then into oven 21 where it is heated and inflated in known manner, and then withdrawn via nip rolls 24 so as to effect both longitudinal and radial stretching in known manner. Fig. 2 shows an expanded view of the radiation conveyer. Rolls 12 are mounted closely together directly under gun 10 and guide rollers 14 are mounted below and on either side of shaft 13. Inverting wheels 16 are independently mounted below guide rollers 14 on shaft 17 which are not parallel to the axes of the guide rollers but diverge horizontally at an acute angle to the centre line of the guide rollers 14 so that the tubing is received from one smooth roller 12, inverted, and diverted slightly so that it will feed on to the next adjacent smooth roller. The last inverting wheel 18 feeds the irradiated tubing from the last smooth roller 12 up and out of the cubicle. The rollers and wheels of the irradiation conveyer are not powered but driven by the friction of the tubing passing over them. Film irradiated by the process of the invention shows a greater uniformity of thickness than film irradiated in conventional manner.