Patent GB-1217634-A (GB)
Title: A process for manufacturing a porous sheet material
IPC: B29C71/02
Filed: 1969-03-21
Abstract: 1,217,634. Finishing fabrics, yarns and threads; knitting machines; knitted fabrics. FORD MOTOR CO. Ltd. 21 March, 1969 [1 April, 1968], No. 14871/69. Headings D1C, D1K, D1S and D1W. A porous sheet material is made by knitting or weaving tapes of a polymeric material, fastening the longitudinal edges of the material to a tenter frame, and directing heated air at the upper and lower surfaces of the knitted or woven material at an angle essentially perpendicular to the plane of the material. In the embodiment described, the polymeric material comprises a polyvinyl chloride resin having an inherent viscosity of 1.28-1.35, preferably 1.30-1.33, blended with a plasticizer, stabilizer, fillers and pigments; is fused into a mass in a mixer; and is hot worked in a steam heated mill 10, Fig. 2, which comprises two heated rolls 12, 14, the roll 14 rotating faster than the roll 12. A band 18 of the plastics mass forms around the roll 14. A suitable portion of the band 18 is directed by a knife 19 onto a belt 20 and passes between calender rolls 22, 24 and around rolls 26, 28 to form a thin film 30 from 0.003-0.008, preferably 0.005, inch thick. The cooled film 30 is wound on a roll and sliced into a plurality of narrow rolls 32, e.g. five inches wides. The film 30, Fig. 3, passes from a roll 32 around drive rolls 34, 36 and between arbors 38, 40 which slit the film into thin tapes 42 which are drawn by rollers 44, 45 across a lubricating roll 46 positioned between guide combs 47, 48. Each tape 42 entering a circular knitting machine 50 passes through a stop motion device 52 comprising a spring 54 which, upon breakage of a tape, returns to a neutral position to trip a switch (not shown) to stop the slitting and knitting machine. Each tape passes through guides 56, 58 to a folding mechanism 59 comprising a plate 60 having a spring steel arm 61 with a hole 62. As the tape passes through the hole 62 the edges thereof are folded towards each other and around a nylon reinforcing yam 66 which also passes through the hole 62. The folded and reinforced tapes are then knitted on the circular knitting machine. The knitted material is wound into a roll which is positioned at the entrance of a tenter frame. As the material is unwound it is slit longitudinally and opened out. The edges of the material are pinned onto the tenter frame, e.g. as shown in U.S.A. Specifications 2,429,177 and 2,473,404, which transports the material into an oven. Hot air is directed onto the material by spaced tubes, Fig. 4 (not shown), located above and below the material which preferably reaches a temperature of 275‹F. The ends of the tubes located above the material are spaced three inches therefrom and heated air issues from these tubes at a velocity of 6,000 feet per minute. The ends of the tubes located below the material are spaced eight inches therefrom and heated air issues from these tubes at a velocity of 7,000 feet per minute. Succeeding rows of tubes are laterally displaced from the tubes in the preceding row by an amount approximately equalling the inside diameter of the tubes. Lateral stretching continues in a dormant zone and then the material passes into a cooling zone in which the tenter-frame sides move parallel to each other. The material is smoothed and pressed by passage between a rubber roll (74) and a steam heated drum (76), Fig. 5 (not shown), around two steam heated polyetetrafluoroethylenecoated rolls (78), (80), between a water-cooled steel pressing roll (82) and a rubber roll (84), around an idler roll (86) and into a cooling chamber. The material leaving the roll (80) has a face temperature of 300‹F and the rolls (82), (84) exert sufficient pressure to smooth the fuse by flowing the polyvinyl chloride. A protective coating is applied to the material 68 by an applicator roll 94, Fig. 6, comprising a wool felt sleeve 96 on a steel core 98 and dipping into a solution 102 of polyvinyl chloride and polymethyl methacrylate with methyl ethyl ketone as solvent. A doctor blade 104 is provided. The coated material passes into a drying oven 106.