Patent GB-1100650-A (GB)
Title: Induction heating process and apparatus-system for bonding web materials
IPC: B31B50/64
Filed: 1965-06-01
Abstract: 1,100,650. Seaming non-metallic sheet material; laminates. A. L. JAMES, and W. C. HELLIS. 1 June, 1965 [11 June, 1964], No. 23306/65. Headings B5K and B5N. A process of heat-sealing plies of sheet material together by rendering thermoplastic material fusible at certain predetermined areas, comprises positioning, contiguous to these areas, a stratum of fine mesh particles of a nature to become quickly heated when subjected to a high frequency electrical induction field, subjecting the particles in the stratum to a high frequency electrical induction field to thereby concentrate the heating effect upon substantially only the thermoplastic material immediately contiguous to the particles and applying pressure to the plies with the thermoplastic material interposed therebetween to effect heat sealing. The particles preferably comprise metallic oxides, e.g. black or brown iron oxide, but may be iron, aluminium, copper or a comminuted metal alloy. The particles may be applied to the plies in a solvent or carrier applied by printing, painting or a screen process either over a heat-sealable plastic surface or upon the interface surface of a substrate web with a superposed plastic surface of another web. Alternatively, a separate small stratum such as a tape or filament may be interposed between the plies to be sealed together, this stratum being composed of a thermoplastic carrier medium containing the particles. Preferably, the pattern of the particles is such that voids or interstices are left between dots or stripes of the particles, Fig. 17 (not shown). The electrical induction field is applied by coils of the air-core type which are tubular and are cooled, in operation, by the passage therethrough of a coolant, e.g. water. In one embodiment, Figs. 1-5 (all not shown), zones y, z of the particles are laid on a web of paper or film and these zones or the entire web are then imprinted with a thermoplastic material, e.g. polyethylene or other polyolefin, polyester or a vinylic polymer. A second similarly prepared web is positioned on the first web with the coated surfaces in faceto-face contact. The induction field is applied by a flattened helical coil C of the air-core type. Pressure is applied by rollers R-1, R-2 and a knife K may cut off individual containers. To form a longitudinal seam in a paperboard web to form a circular- or rectangular-section container, Figs. 6-10 (all not shown), a tape T, containing the particles, is folded during continuous travel of the web into S-shaped section around the edge portions to be joined and then sealing is effected using two air-core coils C-1, C-2. In a further embodiment, Figs. 13 and 14 (both not shown), the inductive heating step and the pressure step are carried out simultaneously by hollow rotating rollers 20, 21 in which air-core coils 23, 24 are non-rotatably mounted. In another embodiment, Figs. 15 and 16 (both not shown), the invention is applied to a packaging machine in which thermoplastic tubular stock is formed and sealed along longitudinal edges from a plastic film web W-5 and simultaneously filled with materials. Thereafter, the web is formed into separate containers. Suitable designs and arrangements of aircore coils are illustrated in Figs. 19 and 20 (both not shown).