Patent GB-1295690-A (GB)
IPC: B29C65/00
Filed: 1970-07-24
Abstract: 1295690 Seaming non-metallic sheet material IMPERIAL CHEMICAL INDUSTRIES Ltd 16 July 1971 [24 July 1970] 35983/70 Heading B5K A web of a porous aliphatic polyolefine material having a porosity to air of at least 0À5 x 10<SP>-2</SP> ml.(cm.<SP>2</SP> sec. cm. and a thickness of less than 1À5 mm. is bonded to a substrate by interposing between the porous polyolefine material and the substrate a liquid composition that (a) wets the porous polyolefine material and the substrate, (b) is free of heat-activatable adhesive, and (c) has a conductivity of at least 1 Î 10<SP>-4</SP> mhos. cm.<SP>-1</SP>, contacting the porous polyolefine and the substrate and subjecting them to radio frequency heating at a frequency of at least 25 MHz, whereby the porous polyolefine material is heated at its interface with the liquid composition to a temperature above the boiling point of the liquid composition and above the melting point of the polyolefine material so that the polyolefine material bonds to the substrate and the liquid vaporizes, the substrate either having a similar melting point to the porous polyolefine whereby the substrate and the porous polyolefine fuse together during the welding operation or having an open structure whereby the porous polyolefine flows through, and mechanically interlocks with, the interstices of the substrate during the welding operation. Specified polyolefines are homopolymers of ethylene, copolymers of ethylene with minor amounts, e.g. up to 25% by weight, of comonomers of propylene or vinyl acetate, homopolymers of propylene or copolymers of propylene with minor amounts, e.g. up to 25% by weight, of comonomers such as ethylene and homopolymers and copolymers of 4-methylpentene-1, e.g. up to 25% by weight. Blends of such polymers may be used. A preferred polyolefine is an open cell foam made from low density (specific gravity less than 0À94) polyethylene. The substrate may be the same material as the web or another thermoplastic material, a perforated film, or a porous woven or non-woven fibrous web, e.g. a cotton fabric web. Preferably, the boiling point of the liquid composition is not greater than the melting point of the polyolefine material. The liquid composition may be an aqueous surfactant solution containing 0À5 to 5% by weight, based on the weight of the liquid composition, of a surfactant which is solid at the boiling point of the liquid composition. Specified surfactants include anionic alkali metal salt surfactants, e.g. sodium alkyl benzene sulphonates, sodium alkyl sulphates, sodium dialkyl sulphosuccinates, sodium (alkyl substituted diphenyl ether) sulphonates, particularly sodium docecyl benzene sulphonate, sodium di-isobutyl sulphosuccinate, sodium dioctyl sulphosuccinate, and sodium lauryl sulphate. A mixture of an anionic surfactant that is solid at the boiling point and a non-ionic surfactant that is liquid at the boiling point of the solvent may be used. Sufficient conductivity of the liquid can be ensured by the use of a suitable electrolyte dissolved in the liquid composition. For porous polyethylene, an aqueous solution containing at least 0À3%, preferably 0À5 to 5%, by weight based on the weight of the aqueous solution, of an electrolyte, such as sodium chloride, may be used. For porous polypropylene or poly-4-methyl pentene- 1, an aqueous solution containing 10-30% by weight of sodium chloride, may be used. The aqueous solution may contain 0À5-3% by weight of a thickener, e.g. hydroxy methyl cellulose, hydroxy ethyl cellulose, hydroxypropyl methyl cellulose, methyl cellulose, sodium carboxy methyl cellulose, etherified cellulose and salts thereof, vegetable gums, e.g. gum arabic or gum tragacanth, starch ethers, soluble starches, dextrins, alginates, casein, gelatin, polyvinyl alcohol, polyvinyl acetate. Preferably, the amount of liquid interposed between the polyolefine and the substrate is 5-50 gm.<SP>-2</SP>. The radio frequency current is at a frequency of 27-70 MHz. The invention is applicable to seaming two sheets together to form containers, e.g. sacks, bed-linen, e.g. pillow cases, and garments, e.g. inspection gowns and overalls.