PLANT FOR THE CONTINUOUS MANUFACTURE OF BAGS USING POLYPROPYLENE, POLYTHENE, PVC AND SIMILAR PLASTICS

Abstract: Plastic bags are fashioned by sealing two layers of polypropylene, polythene or PVC film along two, three or four sides, often with holes punched along one of the longitudinal edges, the continuous film being uncoiled from a bulk supply turned out by chill-roll extrusion methods. The plant disclosed comprises a folding station (5), then in sequence, a heat-seal station (11), a cooling stage and a cutting station (40), and turns out the bags in an entirely continuous process.

Description: The present invention relates to plant for the continuous cycle manufacture of bags fashioned in polypropylene, polythene, PVC and similar plastic materials. The prior art embraces a variety of systems for the formation of plastic bags by heat-sealing, all of which are intermittent in operation insofar as they involve indexing previously cut and folded sheets of plastic film, generally on a conveyor belt, into a heat-seal station that consists in a vertically reciprocating plate disposed transversely to the path of the conveyor, the film material being held motionless at the station until such time as two, three or four sides have been fused together to form the bag. Thus, given of necessity that the sheet must remain static at the heat-seal station, plastic bags of the type in question are costly to manufacture, and there is no way in which this aspect of production can be speeded up. A further drawback experienced with indexing type systems is that waste is generated, as a transverse strip of the film has to be trimmed away in order to provide an opening for the bag and ensure a tidy finish. US-A-2 866 392 shows means to manufacture pouches of cellophane or the like, comprising a folding station, at least a sealing station having electrically heated roller-carried sealing irons, and a cutting station having a roller-carried blade cooperable with a fixed blade. A problem of the sealing station is that the plastic film has a direct contact with the heated irons and, moreover, there is not an efficient device for cooling the heat-sealed film. US-A-4 599 926 discloses a die-cutting roll to cut holes in traveling web materials and to drive the fragments or the waste inwardly under vacuum through an axial passage inside the roll. The document does not disclose cooling means nor an application of the roll to a plant for the continuous production of bags or the like. The object of the present invention is to provide plant for the continuous cycle manufacture of bags using one or more reels of film, or alternatively, and by virtue of this same capacity for continuous production, operating in combination with a chill-(or ( cast-) roll facility of the type which produces film by continuous extrusion. A further object of the invention is to step up the number of bags turned but per hour by the plant, without jeopardizing quality. Another object of the invention is to reduce the quantity of waste generated in manufacture. Utilizing plant according to the present invention, moreover, it becomes possible to turn out bags, in continuous cycle, with stiffening ribs, and with holes if appropriate, either by adding a further layer of film or by direct extrusion. The stated objects are comprehensively realized in plant according to the present invention, having the characterizing features according to claim 1. The invention will now be described in detail, by way of example, with the aid of the accompanying drawings, in which: fig 1 is a schematic representation of the plant disclosed, viewed in plan; fig 2 is a further schematic of the plant, viewed in side elevation; fig 3 illustrates a heat-seal station, in side elevation; fig 4 shows the sectional view of the heat-seal station taken through III-III in fig 3; fig 5 is a side elevation of the cut and punch station; fig 6 is the sectional view of the punch station, taken through IV-IV in fig 5; fig 7 is the sectional view of the cutter station taken through V-V in fig 5. With reference to figs 1 and 2, it will be observed that the plant described is of the type utilizing a continuous film of plastic material (polypropylene) folded into two thicknesses. 1 denotes the supply roll, supported by a holder 2, from which the film 3 is uncoiled, passed between two guide rollers 4 and fed to a folding device 5 of conventional embodiment, shown schematically in the drawings. The folding device 5 serves to double up the film into two identical sandwiched layers, denoted 6, which are fed between two guide rollers 7 and then passed around a roller denoted 8, this in its turn flanked by a pressure roller 8a the purpose of which is to flatten the fold and align the running film in readiness for its passage through a set of units, or stations, to which the present invention effectively relates. 9 denotes a drive unit consisting in two power driven pinch rolls 10 by which the film is drawn from the supply roll and fed into the successive stations. 11 denotes a heat seal station, in its entirety, located following and in alignment with the drive unit. With reference now to figs 3 and 4, the heat-seal station 11 comprises a top roll 12 and a bottom roll 13, both of which are driven by a belt 14 looped around two pulleys 15 and 16 keyed to the respective shafts 17 and 18 of the rolls 12 and 13. The belt 14 is kept taut by a tensioner 19, and turned by a pulley 20 set in rotation by a bevel gear pair 21 in receipt of drive from a shaft 22 coupled to a geared motor 23 (see fig 2). The roll shafts 17 and 18 are embodied hollow in order to accommodate wires 24 supplying electrical power to resistances 25 by which the rolls 12 and 13 are heated. In the example illustrated, the resistances 25 are arranged in two parallel and laterally positioned circumferential elements 26 and 27 by means of which to produce a pair of continuous longitudinal seams along the folded outer edges of the running film, and one transverse element 28 by means of which to produce a seam across the film. The shafts 17 and 18 are supported by bearings 29 and 29a carried in journal blocks 30 and 31 made fast to two respective rails 32 and 33 which are mounted slidably to columns 34. Each column 34 is part-threaded in such a way as to accept two lock nuts 37 which impinge on relative sleeves denoted 38; in effect, it is these sleeves that are mounted slidably to the columns and permit of adjusting the position of the roll shafts. 39 denotes one of four pneumatic cylinders located between the two rails 32 and 33, by which the two heated rolls are urged together elastically during operation and separated in the event of a stoppage. 35 denotes a belt looped around the bottom heated roll 13, the purpose of which is to isolate the folded film entirely from the surface of the roll, thereby preventing direct contact between the two; the belt 35 is set in motion by the roll 13 itself, and tensioned by means denoted 36. Plant according to the present invention comprises a cut and punch station located following the heat seal station. As discernible from figs 5, 6 and 7, the station in question, denoted 40 in its entirety, comprises two distinct devices: a transverse cutter 40a by which the continuous film is separated into single bags, and a punch 40b designed to produce a plurality of holes along one longitudinal edge of each bag. The cutter device 40a comprises a top roll 41a and a bottom roll 41b, of which the top roll 41a is urged elastically into contact with the bottom roll by spring means embodied in rubber 42. 43 denotes a transversely disposed blade carried by the bottom roll 41b, which operates in conjunction with a striker 44 set into the top roll 41a. The blade and the striker are clamped and adjusted for position by way of means denoted 43a and 44a, respectively. The shafts 45 and 46 of the cutter device 40a are embodied hollow in order to permit of ducting a coolant to and from the rolls by way of relative manifolds 47, and are driven utilizing a system identical to that previously described for the heat seal rolls. The punch device 40b similarly comprises two rolls, of which the top roll 51 affords a plurality of holes 52, arranged in a circular formation and accommodating relative balls 53 each of which is held in place by a retaining ring 54 and urged against the ring by a setscrew 55. The bottom roll 56 of the device is fitted with a plurality of hollow cylindrical cutting edges 57 positioned in such a way as to register with the balls 53 of the top roll, and thus puncture each bag with circular holes. The bottom roll is carried by a shaft 60 that will be embodied hollow to permit of connection to an extractor system 61 for removal of the punchings which accumulate during the course of production. Like the rolls of the cutter device, the two punch rolls 51 and 56 are urged together elastically by rubber spring means 62. The runout from the final station coincides with a conveyor belt 63 by which the finished bags are gathered up and counted. Alternative embodiments of the invention might well be contemplated, without prejudice to the scope of the appended claims; for example, the number and position of the resistances in the heat seal rolls could be varied to suit different types and sizes of bags.

Claims: Plant for the continuous production of bags using polypropylene, polythene, PVC and similar plastic film, comprising: a drive unit (9) by means of which to uncoil a continuous film from one or more supply rolls; continuously operating rotary heat-seal means (11) consisting in power driven rolls (12, 13) disposed with axes parallel and normal to the path followed by the film, and with which to produce fused seams along longitudinal parallel edges of the film, and in the transverse direction; rotary means (40) by which to cut and divide the filmtransversely and/or longitudinally into single bags, characterized in that the power driven rolls (12, 13), are provided with external surfaces affording electrical resistances coinciding with circumferential and straight line generators of the roll geometry, and the bottom roll (13) is enveloped by a belt loop (35) serving to prevent direct contact between the roll and the running film. Plant as in claim 1, comprising rotary heat-seal means (11) that consist in two power driven rolls (12, 13) keyed to respective hollow shafts (17, 18) through which power supply conductors are routed to the electrical resistances, wherein the roll shafts are carried between rails (32, 33) adjustable for height, in such a way that the relative positions of the shafts can be altered, and interconnected by pneumatic cylinders in such a way that the rolls can be urged together elastically during operation and separated one from the other in the event of a stoppage occurring. Plant as in claim 1, characterized in that it comprises rotary cutting means or cut-and-punch means to punch one longitudinal edge of the bags, comprising a cutter device (40a) consisting in two rolls (41a, 41b) disposed with axes parallel and normal to the path followed by the film, the surfaces of which respectively afford at least one blade and at least one striker plate coinciding with cylindrical and/or straight line generators of the roll geometry. Plant as in claim 1, characterized in that it comprises rotary cut-and-punch means comprising a punch device (40b) consisting in a top roll (51) that affords a plurality of holes (52) arranged in a circumferential formation and accommodating relative balls (53) each of which retained by a ring (54), and a bottom roll (56) that is fitted with a plurality of cylindrical cutting edges (57) positioned in such a way as to interact with the balls (53) of the top roll. Plant as in claim 4, wherein the cylindrical cutting edges (57) are hollow, and connect by way of the hollow interior of the bottom roll (56) with an extractor system (61) that is connected likewise to the hollow interior of the roll (56) by way of a hollow shaft on which the roll itself is carried. Plant as in claim 1, characterized in that the belt (35) is set in motion by the roll (13) itself and is provided with tensioning means (36).

Inventors: BRAGAGLIA, GIORGIO, OLLARI, ERMES
Applicants: GENERATORI ELETTRONICI ALTA FREQUENZA  G.E.A.F. S.R.L.
Application year: 1989
Main classification: B31B23
IPC codes: B31B23