Patent GB-1216516-A (GB)
Title: Heat welding of thermoplastics
Inventor: HELLER WILLIAM C JUNIOR
IPC: B29C65/00
Filed: 1968-02-12
Abstract: 1,216,516. Seaming non-metallic sheet material. W. C. HELLER Jnr. 12 Feb., 1968 [24 March, 1967], No. 6768/68. Heading B5K. A thermoplastic body is heat welded to another thermoplastic body which may be themoplastic by placing a susceptor sealant having a susceptor material disposed in a thermoplastic carrier substance, selected to be of the same chemical family as the thermoplastic bodies and having a density higher than that of the thermoplastic bodies, against the bodies to be welded, and exposing the susceptor sealant to a form of energy which generates heat therein sufficient to soften the carrier and cause the same to intimately weld the bodies. Preferably, the susceptor comprises a plurality of particles capable of being heated dielectrically, by induction or by radiation and which are uniformly distributed in the carrier which is in sheet or strip form. At the time of application, the maximum dimensions of the susceptor particles is preferably equal or less than one-fourth of the thickness of the susceptor sheet. The susceptor may also be used in the form of a continuous strip or wire or in the form of fibres, threads, woven fabric or screening embedded in the carrier, mixed therewith or woven with the carrier. Alternatively, the susceptor and carrier may be in fluid form and sprayed or printed on to one of the bodies to be sealed. The carrier has a heat sealing temperature range at least as high, but preferably higher, than that of the thermoplastic body and, also, preferably, has a density somewhat higher than that of the body. In one embodiment, Fig. 4, using induction heating of the hysteresis type, a sealant sheet 21, containing magnetic iron oxide particles in a high density polyethylene carrier, is positioned between sheets 22, 23 of medium density polyethylene and passed within and through an induction heating coil 25. Pressure may be applied at the coil 25 or subsequent thereto to assist sealing. In another embodiment (not shown), induction heating of the eddy-current type is employed. In a further embodiment, Fig. 5, a susceptor strip 31 containing a susceptor material responsive to dielectric heating, e.g. a polymer or copolymer of vinyl chloride, vinyl fluoride, vinylidene chloride or vinylidene fluoride, or a polycarbonate, polyurethane, polyacetal or a cellulose derivative, is placed between thermoplastic sheets 32, 33 and heated by electrodes 35, 36.  In a still further embodiment, Fig. 6 (not shown), using radiation heating, a susceptor layer (41), comprising carbon black particles in a polyethylene carrier, is placed between two thermoplastic sheets (42), (43) of which at least the sheet (42) is transparent or translucent to allow infra-red radiation focused by a reflector (45) from an electric lamp (44) to reach the layer (41). Other radiant energy sources include lasers, X-rays, ion beams, electron beams, ultrasonic beams and nuclear radiation. In yet another embodiment, Fig. 7, a susceptor sealant 51 is applied to one sheet 52 to be sealed prior to introduction into the radiant energy field formed by a lamp 55 and focused by a reflector 56. The sheet 52 is sealed to a second sheet 53 by pressure rollers 57, 58.