MANUFACTURE OF BAGS

Abstract: In the manufacture of bags with handles, an extruded plastics tube is extruded, folded inwardly by a first folding device (21) to form gusseted side portions (4) and flattened. A transverse heat seal is formed by a sealing device (22) and a cutting device (23) removes a central section of the tubing to form handle portions (10). The gusseted side portions (4) are folded in turn onto a medial tubing portion (3) by a second folding device (24) having arcuate folding ramps and a further transverse heat seal and a transverse perforation line are applied to the base of the bag.

Description: MANUFACTURE OF BAGS This invention relates to a method of and apparatus for the manufacture of plastic bags, e.g. for use as bin liners. It is well known to manufacture plastic bags from a continuous tube of extruded polyethylene. The extruded tubing is expanded to reduce the thickness of the polyethylene film, flattened, heat sealed and severed across the width of the tubing, such that the heat seals form the bottoms of the bags. Handles can be foπned by removing an upper central section of the bags, and by providing a series of transverse perforation lines rather than severing the tubing, a series of bags which can be wound into a roll may be produced. In order to reduce the width of the roils of bags, and to reduce the size of the machinery required for the bag manufacture, it is known to fold the sides of die tubing inwardly to form gussets prior to sealing. It is also known to fold the gusseted tubing prior to sealing, as described in GB-A- 1584746, which enables an especially strong seal to be produced. However, this folding metiiod is not suitable for the manufacture of rolls of interconnected bags formed with handles, as the folding operation superimposes the handles at the same side of the folded tube, and the resulting string of bags cannot be satisfactorily wound into a roll. Handles at the open end of a bag are often desirable for tying closed the bag after it has been filled, e.g. wid refuse, or to facilitate carrying the bag. The present invention seeks to overcome this drawback of the prior art and accordingly provides a method of manufacturing a bag from iay lat tubing comprising steps of first folding the longitudinal edges of the tubing to form inwardly extending gussets, further folding die flattened gusseted tubing to reduce die tubing's widtii. and transversely sealing the folded and gusseted, tubing to form a base seal, characterised in that handles are formed between the folding operations by removing a central section of the gusseted tubing and by transversely sealing the tubing at a position corresponding to the ends of the handles. Preferably, the tubing is folded to form gusseted tubing portions with gussets extending inwardly to a depth substantially one third the widtii of the gusseted tubing, and the gusseted portions are folded about respective -longitudinal fold lines to lie against opposite sides of a medial portion of the tubing between the gusseted portions. A bag produced according to the claim method allows the combination of advantages associated with a strong base seal and the aforementioned benefits which stem from the provision of handles in a bag that, in its folded form, is considerably narrower than previously known bags with handles. Further, the handles on the folded bag are located at laterally opposed sides of the bag allowing a string of bags to be wound evenly into a roll. In the preferred method the gusseted portions are each folded by passing d e flattened tubing over a discrete arcuate folding ramp having a lateral edge around which the gusseted portion is folded, nips are provided upstream of and downstream of each folding ramp, the tension of the tubing as it passes over the folding ramp is controlled by adjusting die relative speed of the nips, and die orientation of the nips is adjusted to maintain a substantially uniform tension across me widdi of the tubing as it passes over the folding ramp. The adjustment of the orientation of the nips allows satisfactory folds to be achieved despite the asymmetry of the two stage second folding operation. Although the order in which steps of removing the central section of the gusseted tubing and sealing the tubing at the position corresponding to the ends of the handles are preformed is readily interchangeable, it has been found tiiat the bag manufacturing process is easier to control when the tubing is transversely sealed at the position corresponding to the ends of die handles before the central section of the gusseted tubing is removed. Further, in die preferred method, a series of bags are formed from a continuous length of layflat tubing, the handles of one bag being connected to die base of die next bag, and a transverse line of weakness is formed between adjacent base and handle seals to facilitate separation of individual bags, said line of weakness being produced after folding of die two bags joined at d e line of weakness has been completed. By providing the transverse line of weakness, e.g. a row of perforations, after the tubing is folded, die tubing can be subjected to a greater tension during folding man would otiierwise be possible, and hence the speed of die tubing and die rate of production of bags can be increased. The present invention also provides apparatus for manufacturing a series of bags from layflat tubing comprising: first folding means for folding die longitudinal edges of the tubing to form inwardly extending gussets, second folding means for further folding die gusseted tubing to reduce die tubing's widtii; means for transversely sealing die folded and gusseted tubing to thereby form a base seal; and means for producing a transverse line of weakness extending across the tubing to facilitate separation of individual bags; characterised in tiiat between die first and second folding means are provided cutting means for removing a central section of the tubing for forming handles, and sealing means to seal the tubing transversely at a position corresponding to die ends of the handles. A clear understanding of the invention will be gained from the following description of the preferred embodiment, which is given with reference to the accompanying drawings, wherein: Figure 1 is a cross-section through the tubing after the gussets are formed; Figure 3 is a similar schematic view showing the upper end of d e finished bag when folded: Figure 4 is a plan view of die upper end of die folded bag shown in Figure 3: Figure 5 is a similar view to Figure 3 showing die bag unfolded and ready to be opened; Figure 6 shows die steps involved in forming die finished bag; Figure 7 shows the initial steps involved in forming a plurality of parallel production lines from a single extruder: Figure 8 is a schematic side view of a folding device: and Figures 9 and 10 are taken along die lines A- A' and B-B', respectively in Figure 8. In Figures 1-5 of die drawings, die layers of plastic film which make up a bag are shown separated, but tiiis is for ease of illustration only and it will be understood diat in practice tiiey lie flat against each odier. The tubing shown in Figure 1 has equal gussets 2 having a depdi w substantially equal to one tiiird the widtii of die gusseted tubing, tiiereby leaving a medial tubing portion 3 of widtii w between the two gusseted side portions 4, also of width w. The gusseted side portions 4 are folded over about respective longitudinal fold lines 5 to lie against the opposite side faces of the medial portion 3. as indicated by the arrows 6 in Figure I. so that the folded tubing assumes the configuration illustrated in Figure 2. A weided seal 7 is produced across die full widtii of the folded tubing by applying a heated blade, wire or bar against die folded tubing in well known manner, and as will be seen from Figure 2 ten iayers of film become welded together over essentially the complete length of die seai. Alternanvely, a heated blade wire or bar may be Figure 2 ten layers of film become welded togetiier over essentially the complete length of the seal. Alternatively, a heated blade wire or bar may be applied contemporaneously to each side of the tubing. A very strong seal is obtainable as a result of either metiiod. Tests have shown die seal does not have any identifiable weak points. Figures 3, 4 and 5 show die upper end of die bag which is open and has handles 10 provided by removal of a bag segment, for example, by an appropriate cutting operation. The handles 10 are formed at opposite sides of the gusseted tubing 1 and have a widtii less than die gusset widtii. Preferably, the widtii of each handle is between i w and %w so that when die bag is folded die handles overlap in die central region of die folded bag. A welded seal 11 is produced across die upper ends of die handles, by applying a heated blade wire or bar, in a similar manner to the production of die welded seal 7, to connect die layers of plastic film forming the handles. A continuous tube of gusseted plastic film can be formed into a continuous series of bags witii die handles of one bag connected to the base of die next bag and, by providing suitable perforations between die base seal 7 of one bag and the handle seals 11 of me next bag, single bags can be easily separated for use by tearing bags apart at the perforations. Figure 5 shows the upper end of die bag unfolded ready for use with die handles 10 to the sides of the mouth of the bag 12. After the bag has been used, the mouth 12 can be closed by tying die handles 10 togetiier, if desired. Figure 6 shows the steps involved in forming a series of bags according to this invention from a expanded polyethylene tube 1. The polyediylene tubing 1 is extruded continuously from an extruder 20 and expanded to form an upright cylindrical column in a known manner. The expanded tubing is drawn upward by a speed reference nip dirough a first folding device 21 which contemporaneously forces the sides of die tubing inwardly to form the gussets 2 as described above and flattens die cylindrical column of tubing. The flattened and gusseted tubing tiien passes to a cutting device 21. Alternatively, the extruded tubing could be flattened and tiien gusseted in a manner known per se. Furthermore according to a modification shown in Figure 7 a larger column of tubing is expanded from an extruder 40 and flattened without gussets. The tubing is slit sealed longitudinally to form a plurality, e.g. tiiree, flattened tubings of equal widtii. The tubings are separated ~ by a series of guiding rollers 41 and delivered to folding devices 42. Each tubing is re-inflated and gusseted in a similar manner to die first described alternative by folding devices 42. In diis manner a plurality of parallel production lines can be fed from a single extruder 40. The extruder 40 and extruder 20 differ only in scale. In each embodiment the following description of die bag forming process and apparatus applies equally to the single production line of Figure 6 and each of the parallel production lines of Figure 7. The handles 10 of individual bags to be made from die continuous tubing are formed by first heat sealing the tubing across its widtii in a sealing device 22 which, in a manner itself well known, applies a heated blade so tiiat the layers of film are welded togetiier. The transverse seals are formed at regular intervals along the tubing corresponding to die length of bags being produced. A central section of the gusseted tubing adjacent to each seal is tiien removed by an appropriate cutting device 23 to form the handles at eitiier side of die gusseted tubing. It will be appreciated tiiat the removed central tubing section includes the medial part of the transverse seal between the handles. The sealing and cutting devices, 22 and 23, could be combined into one device and/or their order reversed. The tubing is next folded by a second folding device 24, described in more detail below. A base seal 7 is provided across the widtii of the folded bag as described above by a heat sealing device 25, and a series of perforations made across die widtii of die tubing between the base seal 7 of one bag and die handle seal 11 of the next bag by a perforating device 26. Sealing and perforating devices, 25 and 26, could also be combined into a single device and/or tiieir order reversed. Finally the tubing is wound into a roll by a winding device 27. The individual bags may be separated before rolling, and rolled such that the individual bags overlap. The roll of bags may or may not have a separate core element, e.g. a cardboard tube, depending on the particular requirements of the user. Advantageously, in the preferred order of operations, die perforations are provided after the folding has been completed, i.e. downstream of die second folding means 24 along die tubing patii, which allows die tubing to be drawn dirough the folding devices and otiier apparatus upstream of die perforation device at a greater speed than otiierwise would be possible. A line speed reference signal (A) can be sent from die speed reference nip to a controller 28 which co-ordinates die speed of die sealing, cutting and folding devices 22,23 and 24 in the single production line of Figure 6 or each of the parallel production lines of Figure 7. The sealing and cutting devices 22 and 23 are co-ordinated by a co-ordination reference signal (B) generated in die first device after die first folding device 21. Sensing of the hole created by the removed bag segment formed by cutting device 23 triggers the operation of the sealing and perforating devices 25.26. Preferably an optical sensor is used to sense the hole, but any other suitable sensor may be used. Winding device 27 is coordinated by sensing the perforations formed by perforating device 26. Optionally the number of bags wound into rolls by the winding device 27 can be counted using the co-ordination reference signal (B), or direct from devices 25 or 26 using reference signal (C). In the preferred embodiment die speed control for sealing, perforating and winding devices 25,26 and 27 is discrete from me speed reference signal (A), but devices 25,26 and 27 may alternatively be controlled using signal (A). Figures 8-10 show schematically the second folding device which has first and second nips 30, 31 witii a first arcuate folding ramp or plate 33 therebetween, and a second arcuate folding ramp or plate 34 located between die second nip 31 and a third nip 32. The ramps have lateral edges around which die tubing is folded. The tubing 1 passes under tension between die two nips, 30 and 31, which guide die tubing over the first ramp 33, such tiiat one outer side portion 4 of the flat tubing is folded by the ramp 33 onto the medial portion 3 of the tubing. The tubing then passes, under tension, over the ramp 34 between the second and third nips, 31 and 32, which folds die otiier side portion of die tubing 4 onto the opposite side of the medial portion, thereby sandwiching the medial portion between the two outer portions. The tension of the tubing passing across the folding ramps 33,34 is controlled by varying the speed of the nip 30-32, and by adjusting die orientation of the nips an even tension can be maintained across the widtii of die tubing as it passes across die ramps 33,34. The maintenance of an even tension across the width of the tubing allows a satisfactory fold to be achieved as each of the two side portions 4 is successively folded onto die medial portion 3.

Claims: CLAIMS: 1. A method of manufacturing a bag from layflat tubing comprising steps of first folding die longitudinal edges of the tubing to form inwardly extending gussets, further folding die flattened gusseted tubing to reduce die tubing's widtii, and transversely sealing die folded and gusseted tubing to form a base seal, characterised in that handles are formed between the folding operations by removing a central section of the gusseted tubing and by transversely sealing die tubing at a position corresponding to die ends of die handles. 2. A metiiod according to claim 1, wherein the tubing is folded to form gusseted tubing portions with gussets extending inwardly to a depth substantially one third the width of the gusseted tubing. 3. A metiiod according to claim 2, wherein the gusseted portions are folded about respective longitudinal fold lines to lie against opposite sides of a medial portion of die tubing between the gusseted portions. 4. A method according to claim 3, wherein the gusseted portions are folded successively onto the medial portion. 5. A metiiod according to claim 4, wherein the gusseted portions are each folded by passing the flattened tubing over a discrete arcuate folding ramp having a lateral edge around which the gusseted portion is folded. 6. A metiiod according to claim 5, wherein nips are provided upstream of and downstream of each folding ramp, and the tension of the ttibing as it passes over the folding ramp is controlled by adjusting the speed of the nips. 7. A method according to claim 6, wherein the orientation of the nips is adjusted to maintain a substantially uniform tension across the widtii of die tubing as it passes over the folding ramp. 8. A method according to any one of die preceding claims, wherein die tubing is transversely sealed at die position corresponding to die ends of die handles before the central section of die gusseted tubing is removed. 9. A metiiod according to any one of the preceding claims, wherein die speed of die tubing between the first folding of the tubing and die transverse sealing of the folded and gusseted tubing is conttolled using a signal generated according to die speed after the tubing is first folded. 10. A method according to any one of die preceding claims, wherein a series of bags are formed from a continuous length of layflat tubing, the handles of one bag being connected to the base of die next bag, and a ttansverse line of weakness is formed between adjacent base and handle seals to facilitate separation of individual bags, said line of weakness being produced after folding of die two bags joined at the line of weakness has been completed. 11. A bag manufactured in accordance with any one of the preceding claims. 12. Apparatus for manufacturing a series of bags from layflat tubing comprising: first folding means for folding the longitudinal edges of die tubing to form inwardly extending gussets, second folding means for further folding the gusseted tubing to reduce the tubing's widtii; means for transversely sealing the folded and gusseted tubing thereby to form a base seal; and means for producing a transverse line of weakness extending across the mbing to facilitate separation of individual bags; characterised in that between the first and second folding means are provided cutting means for removing a central section of die tubing for forming handles, and sealing means to seal the tubing transversely at a position corresponding to the ends of die handles. 13. Apparatus according to claim 12, wherein the first folding means is arranged to fold die longitudinal edges of the tubing to substantially one third die widtii of the gusseted tubing to form gusseted portions of the tubing. 14. Apparatus according to claim 13, wherein the second folding means is arranged to fold die gusseted portions about respective longitudinal fold lines to lie against opposite sides of a medial portion of the tubing between die gusseted portions. 15. Apparatus according to claim 14, wherein the second folding means comprises two arcuate folding ramps, arranged in succession for folding die respective portions onto the medial portion and means for guiding die flattened tubing over the folding ramps. 16. Apparatus according to claim 15, wherein the guiding means comprise nips upstream of and downstteam of each folding ramp, the relative speed of die nips being adjustable to control the tension in the tubing as it passes over the ramp. 17. Apparatus according to claim 16, wherein die nips are adjustable in position to maintain a substantially uniform tension across the widtii of die tubing as it passes over the ramps. 18. Apparatus according to any one of claims 12 to 17. wherein the sealing means is arranged to seal across die full widtii of the gusseted tubing, and the cutting means is positioned downstream of the sealing means and is arranged to remove with a central section of the tubing a portion of the seal produced by die sealing means. 19. Apparatus according to any one of claims 12 to 18, wherein a controller s provided to sense the speed of die gusseted tubing and generate a signal for co-ordinating the operating speed of die cutting means, the sealing means and die second folding means. 20. Apparatus according to any one of claims 12 to 19, wherein die means for producing a transverse line of weakness are downstream of die second folding means. 21. A roll of bags made by die metiiod according to claims 1 to 10 or by the apparatus of claims 12 to 20.

Inventors: ANGLESS DAVID MICHAEL, ANGLESS, DAVID, MICHAEL
Applicants: ANGLESS DAVID MICHAEL, POLY LINA LTD, ANGLESS, DAVID, MICHAEL, POLY-LINA LIMITED
Application year: 1996
Main classification: B31B23
IPC codes: B23B23, B31B1, B31B19, B31B23, B65D30