Procédé pour le scellement à chaud au moyen de matières thermoplastiques et installation pour la mise en oeuvre de ce procédé

摘要

742,130. Seaming non-metallic sheet material. BERGHRACHT, M. May 7, 1953 [May 7, 1952], No. 12799/53. Class 42 (1). [Also in Group XVII] In a method of hot sealing material coated with thermoplastic material or articles produced therefrom, pressure is exerted on the surfaces to be sealed after heating of those surfaces and is effected with progressively increasing pressure in the course of subsequent cooling. Preferably, the surfaces to be united are preheated to softening temperature of the thermoplastic material without pressure thereon ; at this temperature, the surfaces are pressed lightly together to cause the thermoplastic coatings to interpenetrate ; the material is then allowed to cool while the surfaces are pressed together with progressively increasing pressure, such pressure being removed only when the thermoplastic material has negligable plasticity. As shown, Fig. 2, pre-formed tubes 1 of thermoplastic-coated sheet are fed between rollers 2, 3, 4 to a pre-heating roller 7 whereon the thermoplastic material is heated to softening point and an end of each tube is folded by blades 5, 6 to form the bottom seam of a bag. This seam is gripped lightly by heated grippers 8 on a cylinder 9, and then strongly gripped with progressively increasing pressure by unheated grippers 11 on a cylinder 10 which is unheated and may be cooled. The formed bags are stacked at 12. The tops of filled bags are sealed as the bags pass along a guideway 14, Fig. 3. The faces 15, 151 to be sealed are pre-coated with thermoplastic material which is pre-heated to softening point in a heating zone 16 wherein a positive temperature gradient is provided in the direction of feed of the bags by means of electric resistance or steam heaters or infra-red lamps. The surfaces 15, 151 are then lightly pressed together by reciprocating heated grippers 17, 171 and the seal thus formed, while cooling gradually, is clamped between rollers 21, 211, 22, 221, 23, 231, &c., the pressure between successive pairs of rollers increasing progressively. The rollers are adjustable vertically and the spring loadings of the rollers and of grippers 17, 171 are individually adjustable.