Patent GB-754957-A (GB)
Title: Improvements in or relating to manufacture of rubber latex articles
IPC: B29C41/14
Filed: 1954-04-07
Abstract: 754,957. Making porous rubber articles. INTERNATIONAL LATEX CORPORATION. April 7, 1954 [April 22, 1953], No. 10190/54. Class 87(2) Seamless, porous rubber articles, especially underwear garments, are produced by dipping into rubber latex a former with its surface covered by small depressions and inductively heating a metallic member comprised in the former to drive out from the depressions air entrapped during the dipping process so that it ruptures the film which bridges them, thereby creating a multitude of pores in the film. The dipping former 43, Fig. 9, may be a hollow glass casing with the top sealed and the cavities may be formed in its surface by using photo-sensitive glass, masking it with a perforated screen and subjecting it to ultra-violet light, then heat-treating it and dipping it in acid, which eats away the areas previous exposed to the light and forms the required cavities in the surface. The mask may be a photographic negative prepared from a representation of the desired surface, and-the shape of the depressions may be controlled by varying the trarismittancy of the negative. Magnetic steel wool 63, or plates or sheets, are placed inside the glass casing and the interior filled with. liquid to promote heat transfer, suitable liquids being chlorinated or fluorinated hydrocarbons, silicones and high boiling -ethers. As the former emerges from the dipping bath the steel wool 63 is heated by a high frequency magnetic field generated by alterating current in a coil 64 which preferably is of water cooled copper tubing, this heating causing the entrapped air to rupture, the film. Drying as partial or complete curing of the film can be effected by induction heating by means of a second coil encompassing the whole former. Alternate dipping and blowing are continued until a porous film of the desired thickness has been built up. Alternatively, the dipping former may be a hollow magnetic metal casing with a vitreous covering, e.g. porcelain, which has been fired on it. The cavities are made by placing a tool 69 with projections 71 on a machine which oscillates at very high frequency, bathing the porcelain in a liquid containing a fine abrasive, and bringing the oscillating tool into contact with the surface. On leaving the bath the hollow casing is inductively heated as before. The former may comprise curved tubes bent to the required shape and joined to a sheet of magnetic metal, with a porcelain coating on both sides of the sheet with the cavities in its surface. In other modifications the cavities may be formed in the surface of a sheet of rubber stretched over a metallic former, or of nylon or polystyrene shaped and fitted on the former in one or more pieces. Such a sheet may be made by a dipping- process as in the present invention. The holes are blocked by omitting the blowing step in the last few dips. When the sheet is placed on the metallic former it is turned inside out and then vulcanized or cured to harden its surface. If the cavities extend right through the sleeve it should be cemented to the backing to prevent communication between these and consequent unsatisfactory blowing. The cavities may be in the surface of the metallic member itself, which may be fabricated in the required form by assembling perforated metal sheets on the former and bonding the whole together with a synthetic resin. Alternatively metal may be sprayed on a reverse replica of the cavitied surface and a sheet of the sprayed metal placed on a rigid backing. U.S.A. Specifications 2,015,632, 2,086,481 and 2,360,736 are referred to.