Patent GB-1496384-A (GB)
Title: Laminated structure
IPC: H05B3/38
Filed: 1975-02-14
Abstract: 1496384 Laminates E I DU PONT DE NEMOURS & CO 14 Feb 1975 [15 Feb 1974] 6404/75 Heading B5N [Also in Division H5] A laminated heating element comprises a film of polymeric insulating material 10, a discontinuous layer 11 of electrically conductive elastomeric material containing carbon black dispersed in a heat resistant elastomer adhered to film 10 and covering all of the film 10 except for spacing areas 12 which are longitudinally spaced along the length of the film 10 and extend the full width of the film 10 whereby the layer 11 is divided into a series of spaced coated areas 13, at least two spaced apart supply conductor wires 14 in intimate contact with the layer 11 and extending the entire length of the element, and a film of polymeric insulating material in contact with layer 11 and the spacing areas 12. The elastomeric material comprises acetylene black or high structure furnace black dispersed in a fluorocarbon elastomer, e.g. a copolymer of vinylidene fluoride and one other fluorine containing monomer, for example an ethylenically unsaturated monomer containing one fluorine atom substituent on each double bonded carbon atom, examples of which are given, in a silicone elastomer, EPDM elastomers or polychloroprene elastomers. The polymeric films 10, 15, which may be identical, may be made of polythene terephthalate, polyimides, fluorocarbon plastics (polyvinyl fluoride) polythene, or polypropylene. The polymeric films may be adhered to fabric or fibrous sheets, e.g. fibre glass fabric sheets. One or both films may have an external coating of reflective or heat-absorbing material. The supply wires 14 are made of copper, brass or aluminium and are preferably coated with a conductive adhesive, e.g. carbon black mixed in a linear copolyester and a volatile solvent. The elastomeric conducting layer 11 may be applied to film 10 as a water dispersion or in a solvent by a gravure printing roll, by silk screen printing, by a spray or by a brush. The layers of the laminate are preferably united by heat and pressure but the top films 15 can be secured to the elastomeric layer 11 and bottom film 10 by tacks or staples through the uncoated edges 16 and spacing areas 12 when the heater is secured in operative position. The Specification describes a method of continuously providing discrete areas 14 of elastomer on a polymeric film 10, using a gravure printing roll, passing the coated film 10 through a forced air drying tunnel and winding the film on a storage roll. The film 15 is then continuously coated with a polyester adhesive using a gravure printing roll, the coated film is dried and finally stored on a roll. The conductor wires 14 are prepared from aluminium sheet which is initially coated with conductive adhesive by means of a gravure printing roll, is dried and then slitted to provide ¥-inch wide conductor strips. The wires are then continuously fed between the previously prepared polymeric films through heated nip rollers to unite the films together. The laminate may be cut to length along any of the spacing areas 12 and the resultant element will not need its cut edges to be bound. It may be secured in position, e.g. in walls, floors or ceilings by staples through the spacing areas. The laminated elements may be used as contact heaters for pipes and tanks.