Patent GB-703756-A (GB)
Title: Improvements in or relating to the manufacture of bags from thermoplastic sheet material
IPC: B31B23/00
Filed: 1950-11-10
Abstract: 703,756. Making thermoplastic bags. CELLOPHANE SOC. ANON. Nov. 10, 1950 [Nov. 22, 1949] No. 27546/50. Class 94 (2) [Also. in Group VIII] In a process for the manufacture of bags from a thermoplastic material, or other material coated with a thermoplastic, two webs of the material, of a width which is a multiple of the depth or height of the bags to be made. are superimposed edge to edge and united by heat applied along the coincident edges 1, along one or more intermediate longitudinal lines 2, and also along transverse lines 3, the individual bags being obtained by cutting along the centres of the lines 2 and, as shown in Fig. 1, along transverse lines z, z' adjacent to the, transverse welds 3. Alternatively the webs anay be cut along a longitudinally welded line m, m<SP>1</SP>, Fig. 4, and along a line v, v<SP>1</SP> midway between the welded longitudinal edges and the weld line m, m<SP>1</SP> the transverse cuts then being made along the centre lines t, t' of the transverse welds, so that the mouths of the bags thus produced are at the longitudinal cut v, v<SP>1</SP>. - Instead of the cuts v, v<SP>1</SP> a succession of transverse cuts intermediate adjacent pairs of transverse cuts t, t' may be made. The heat-sealing and cutting- apparatus may be arranged following a printing machine which prints designs &c. on one of the thermoplastic webs, after which the webs are superposed and passed over a metal roller covered with a material of low heat conductivity, e.g. fabric or vulcanized fibre, and under narrow heating-rollers which may have a smooth, knurled, or engraved rim, and are formed with a central groove which provides a narrow unwelded stripe. A series of successively arranged heating rollers may be mounted adjacent to the periphery of the under roller to ensure satisfactory longitudinal welds. The webs are next guided around another roller mounted below a heating-bar which bears upon the webs transversely and may be arranged to travel a short distance in contact with the webs. For high speed operation a series of transverse heating bars 20, Fig. 3, may be-mounted between a pair of endless chains 19, the spacing of the bars being equal to the spacing of the bags, and their movement such that they accompany the web while forming the weld. The longitudinal cutting of the webs and subsequent transverse cutting is effected by passing them around rollers associated with slitters and a cutter operating in known manner. Alternatively the several rollers associated with the welding and cutting operations may be replaced by. a single drum of large diameter with the. requisite operating devices mounted.adjacent to its periphery. In a modification, Fig. 6, the transverse welds are formed after the cutting. The longitudinal welds and cuts are effected by devices 21, 15 respectively, and transverse cuts by a rotary knife 23. Simultaneously with the latter cutting operation, the leading edges of the length thus cut are gripped between a pair of heated jaws such as 25, 25' mounted in the periphery of a rotary drum 26. Pairs of similar jaws 27, 28 are spaced equally around the drum. The jaw 25 is fixed, while the co-operating jaw 25<SP>1</SP> is carried by a lever 39-40 pivoted to the drum and operable by a fixed cam 38 in opposition to a tensioned spring 42. Heat-insulating bars 31 confine the heating to the gripped edges of the bags, which are welded while being carried around by the drum until released upon a conveyer 30. The conveyer may comprise an endless felt band 32 moving over a. perforated casing 33 connected to a suction fan. The ends of the heating jaws may be cut away to form narrow non-heating gaps opposite the centres of the longitudinal welds to prevent re-uniting of the longitudinally severed portions of the webs.