Patent GB-968156-A (GB)
Title: Thermoplastic film making
IPC: B29C48/08
Filed: 1962-04-26
Abstract: 968,156. Making thermoplastic films; laminates and laminating. UNITED STATES RUBBER CO. April 26, 1962 [June 1, 1961], No. 15897/62. Headings B5B and B5N. An apparatus for producing films of thermoplastic organic materials, e.g. P.V.C., comprises a hollow drum 10 rotatably journalled by means of horizontal shafts 10a and 10b (Figs. 1 and 2) in bearings 11 and 12 and comprising a cylindrical steel body 15 the opposite ends of which are closed by plates 16 and 17. The body 15 has a smooth-surfaced coating 18 of a material having a low thermal conductivity. Water or other cooling liquid is circulated through the drum by means of pipes 19 and 20 extending through shafts 10a and 10b and the lower half of the drum is occupied by this liquid. The drum is driven by means of a motor through speed reducer 26, sprocket 25, chain 24 and sprocket 23 mounted on shaft 10b. Above the drum 10 is an adjustable doctor blade 27 positioned to provide a trough in which a mass 28 of the plastisol to be formed into the film may be accumulated. The plastisol is fed into the trough from the tank 29 through the pipe 31 provided with a control valve 32. The mass of plastisol 28 is protected from heat escaping from the heated portion of the drum by a water-cooled baffle 58. Located at one side of the drum 10 and downstream from the doctor blade 27 is a heating unit 33 for fusing the plastisol layer 28a deposited on the outer surface of the drum coating 18 as the result of rotation of the drum in the direction of the arrow A. The heating unit 33 comprises an outer enclosure or heating box 34 closed on all sides except at the end immediately adjacent to the drum 10 and containing a nozzle member 35 the top and bottom of which carry wheels or rollers 36 engaging the top and bottom walls of the box 34. The member 35 is provided at its front end with a curve and perforated orifice plate 37 through which a heating gas can be directed on to a portion of the peripheral surface of the drum 10. The position of the member 35 within the box 34 and hence the distance of the perforated plate 37 from the drum 10 can be adjusted by means of a hand wheel 47 which controls a double-acting pneumatic motor whose piston 40 is connected by a rod 39 to the member 35. The nozzle member 35 is provided in the side wall 35d thereof with a slot 48 through which projects the outlet end 49a of a conduit 49 stationarily extending through the side wall 34d of the box 34. The conduit 49 communicates at its inlet end 49b via a blower 52 with the outlet end of a combustion chamber 50 in which is arranged an open flame gas burner 51 to which air and a combustible gas are fed at controllable rates. The inlet end of the chamber 50 communicates via a duct 53a, 53 and 53b with the interior of the box 34 near to the rear end of the latter. There is thus provided a circulation system by means of which air heated in the chamber 50 and containing gaseous combustion products is fed into the nozzle member 35 and discharged therefrom through the perforated plate 37 to impinge on the plastisol layer supported on the drum 10. The hot air is then drawn past the top and bottom of the nozzle member 35 to the rear of the box 34 from which it is exhausted via the conduit 53 and returned by the blower 52 to the chamber 50 for reheating. The side walls of the nozzle member 35 are a close sliding fit with those of the box 34 so that no leakage of hot air from the slot 48 into the box 34 can occur. The small amounts of heated air escaping through the gaps 54 between the front end of the box 34 and the drum 10 are drawn into the suction chambers 55 by a suction fan 57 via the conduit 56 so that heated air containing products of combustion formed by the burner 51 does not escape into the atmosphere surrounding the apparatus. After being carried past the heating zone and then solidified by the cooling liquid in the drum 10 the cured film 28b is stripped from the drum over a stripping roller 60 and collected on the driven drum 61. The low thermal conductivity material coating 18 on the peripheral surface of the drum 10 may consist of a ceramic substance, a polyfluorohydrocarbon or a heat resistant phenolic synthetic resin of the high-frequency insulation type capable of withstanding tem. peratures in excess of 450 F. The temperature of the air discharged from the nozzle 35 may be about 650 F. to about 800 F. and its velocity about 4,000 to about 10,000 feet per minute. The cooling water in the lower half of the drum 10 may be maintained at about 50 to 100 F. The viscosity of the plastisol at the doctor blade 27 is preferably 6,000 to 100,000 centipoises. As shown in Fig. 5, a web of fabric or other sheet material 65 may be bonded with a thermoplastic film to form a laminate by feeding it from a supply spool to between the drum and the rollers 63 and 64 positioned near the exit part of the heating zone 33 and the exit part of the cooling zone respectively. When the web 65 passes between the drum 10 and the roller 63 it contacts the still soft and adhesive outer surface of the film 28a and as the film and the fabric or other sheet material thereafter move with the drum towards the roller 64, a strong bond is effected between the film and the fabric or sheet material enabling the resulting laminate to be stripped from the drum at the roller 64. The rate of production of the laminate is thereby as high as that of the film and exposure of the fabric or other sheet material to the high temperatures required for curing the film at its plastisol stage is avoided. The insulated coating 18 applied to the drum 10 may be a paper such as ordinary Kraft paper 103 (Fig. 8) let off from roll 101 and travelling round and with the drum to the take-up roll 102. The film 104 formed in the same manner as previously described is continuously stripped from the drum and wound over a take-up roll 105. The paper collected on the roll 102 may be reused.