IE940760A1 - A plastic bag production process - Google Patents

Abstract

Flattened tubular thermoplastic film is lead from a supply reel 11 to a spreading station 25 at which the film 14 is tensioned transversely to remove creases. Upper and lower layers 31,32 of the film 14 are separated by means of an air bubble 30 formed between the spreading station 25 and a bubble collapsing means 35 having a set of three in-line spaced-apart rollers 36 around which the film 14 is led to gradually bring the upper and lower layers 31,32 of the film together in a controlled manner. The film 14 is then delivered to sealing stations 40 at which transverse seals across the width of the film 14 are formed by heat sealing bars which clamp the film 14 therebetween. Downstream of the sealing stations 40 the film 14 passes through coolers 46,48 for cooling the seals. Both film layers are cut longitudinally to provide a bag inlet opening in the film 40 extending between each adjacent pair of seal prior to delivering the film 14 to a guillotine 53. At the quillotine 53 the film is cut transversely across each seal to part individual bags away from a leading end of the film 14 <Fig.1>.

Description

A Plastic Bag Production Process This invention relates to a plastic bag production process and apparatus for carrying out the process.

The invention particularly relates to producing plastic bags from a flattened tubular thermoplastic film by sealing and cutting the flattened tubular film across its width. Difficulties arise in handling such tubular films leading to wastage and production process downtime. It is an object of the present invention to provide an improved plastic bag production process which minimises these problems.

According to the invention there is provided a plastic bag production process comprising the steps ; leading a flattened tubular thermoplastic film from a supply reel to a spreading station; passing the film around a spreader roller at the spreading station, the spirally wound grooves surface of the roller spreader roller having in an outer resilient extending outwardly in opposite directions from a centre of the roller for transversely tensioning the film for crease removal; separating upper and lower layers of the film by means of an air bubble formed within the film; collapsing the inflated film by bringing the upper and lower layers of the film together in a controlled manner at a downstream end of the bubble; ftUU ίΤ/θΰί OPEN TO PUBLIC INSPECTION UNDER SECTION 28 AND RI O 23 JNL. N0.../.W........OF ZlfaW ^940760 - 2 feeding the film incrementally to an associated pair of sealing stations in turn downstream of the air bubble; at each sealing station passing the film between a pair of pneumatically operated heat sealing bars which are movable together and apart, stopping the film and clamping the film between the heat sealing bars fusing the film layers together forming a transverse seal across the width of the film; releasing the clamping bars and delivering the film to an air cooler, directing a stream of cooling air at each seal as it locates at the air cooler; leading the film to each of a pair of spaced-apart water cooled seal clamps in turn, at each clamp passing the film between a pair of water cooled clamping bars, stopping the film with a seal located between the clamping bars and clamping the seal between the clamping bars for a preset desirable seal cooling period and subsequently releasing the film; cutting both of the film layers longitudinally at a cutting station by means of a cutter blade at the cutting station to provide a bag inlet opening in the film extending between each adjacent pair of seals; feeding the film to a guillotine and cutting the film transversely across the width of the film along each seal intermediate side edges of the - 3 seal to part individual bags away from a leading end of the film; discharging bags from the guillotine and collecting and packing said bags.

In one embodiment of the invention the process includes the step of collapsing the inflated film by delivering the film to bubble collapsing means having two or more spacedapart rollers mounted on a roller support, leading the film around the rollers for gradually bringing the upper and lower layers of the film together in a controlled manner.

In another embodiment the process includes the step of applying a braking force to each roller.

In a further embodiment the process includes the step of forming the air bubble between the bubble collapsing means and an associated roller spaced-apart from the bubble collapsing means around which the film is led, the bubble collapsing means being movable relative to said associated roller for adjusting the size of the air bubble formed between the bubble collapsing means and said associated roller.

In another embodiment the bubble collapsing means is located downstream of the spreader roller, the bubble being formed between the spreader roller and the bubble collapsing means.

In a further embodiment the bubble collapsing means is mounted upstream of the spreader roller.

In another embodiment the process includes the step of delivering the film to a first set of draw rollers mounted Γ9407«π - 4 between the spreading station and the first heat sealing station and an associated second set of draw rollers mounted downstream of the coolers, each set of draw rollers engaging the film for incrementally feeding the film through the sealing stations and coolers, the bubble collapsing means being mounted between the first set of draw rollers and the first sealing station for forming the air bubble downstream of the first set of draw rollers between the first set of draw rollers and the bubble collapsing means.

In a further embodiment the process includes the step of setting the sealing stations a pre-set distance apart corresponding to one or more bag widths and locking the sealing stations together by means of a spacer rod fixed on one of the sealing stations and slidably engaging and releasably lockable on the other sealing station.

In another embodiment the cutting station is located downstream of the cooling station and the film layers are cut by engaging a cutter blade with the film intermediate the sides of the film for longitudinally parting the film.

In a further embodiment at the cutting station the film layers are cut by engaging a cutter blade with a side edge of the film, the film being drawn over the cutter blade to part the upper and lower layers of the film.

The invention will be more clearly understood by the following description of some embodiments thereof, given by way of example only, with reference to the accompanying drawings, in which : Fig. 1 is a diagrammatic side sectional elevational view of apparatus used for carrying out a plastic bag production process according to the invention; Fig. 2 is a perspective view of portion of the apparatus; Fig. 3 is a perspective view of a further portion of the apparatus; Fig. 4 is a detail schematic perspective view of portion of the apparatus; Fig. 5 is a view similar to Fig. 1 showing apparatus for carrying out another embodiment of the invention; Fig. 6 is a view similar to Fig. 1 showing apparatus for carrying out a third embodiment of the invention; and Fig. 7 is a view similar to Fig. 1 showing apparatus for carrying out a fourth embodiment of the invention.

Referring to the drawings, and initially to Figs. 1 to 4 thereof, a process and apparatus according to the invention for producing plastic bags will be described.

Apparatus for carrying out the bag production process is indicated generally by the reference numeral 10. A supply reel 11 of flattened tubular thermoplastic film is rotatably mounted on a support 12 at an inlet of the apparatus 10. Film 14 is led via guide rollers to a film feeder 15. The film feeder 15 comprises two spaced-apart sets of rollers, namely upper fixed rollers 16 and lower movable rollers 17 about which the film 14 is led. The movable rollers 17 are mounted on a pivot arm 18 biased by a spring 19 away from the fixed rollers 16. Spring tension can be adjusted to suit the particular film 14 being processed. Front draw rollers 22 and rear draw t 9 4 0 V 6 0 - 6 rollers 23 draw the film 14 incrementally through the apparatus 10. When the draw rollers 22,23 are in drive mode they pull film 14 from the film feeder 15, the arm 18 pivoting upwardly against spring bias to release film 14 on demand to the draw rollers 22,23. When the draw rollers 22,23 cut out in between each stepped feed of film 14, the arm 18 pivots downwardly under spring bias moving the rollers 17 away from the fixed rollers 16 storing up film 14 from the supply reel 11 for feeding out on demand to the draw rollers 22,23.

Downstream of the film feeder 15 there is provided a spreading station 25 comprising a spreader roller 26 having spirally wound grooves in an outer rubber surface of the roller 26 extending outwardly in opposite directions from a centre of the roller 26. The film 14 passes between the spreader roller 26 and an associated smooth surfaced roller 27, the spiral grooves transversely tensioning the film to remove creases from the film.

An air bubble 30 is formed within the film 14 immediately downstream of the spreading station 25 to separate upper and lower layers 31,32 respectively of the film 14. Spaced-apart from the spreading station 25 is a bubble collapsing means 35 having three spaced-apart rollers 36 around which the film is led passing between adjacent rollers 36 to gradually bring the upper and lower layers 31,32 of the film 14 together in a controlled manner to prevent creasing of the overlying upper and lower film layers 31,32. It will be noted that the bubble collapsing means 35 is movable on a support frame 38 of the apparatus 10 for adjusting the distance between the bubble collapsing means 35 and the spreader roller 26 to allow alteration of the bubble size for different types of film 14. This facilitates controlled handling of films of different sizes. The rollers 36 are rotatably mounted in94 07« *) - 7 line between end supports 37 which are movable between a number of spaced-apart set positions on the frame 38. The end supports 37 could alternatively be slidably mounted on the frame 38.

The rollers 36 are individually braked by air pressure pads to control their speed at various machine feeds and draw lengths. This braking also advantageously minimises or eliminates slippage of the film relative to the rollers 36 each time film feed stops which can cause marking on the film 14.

Downstream of the rear draw roller 23 there is provided a pair of spaced-apart sealing stations 40. Each of the sealing stations 40 is slidably adjustable on the frame 38 for alteration of the relative spacing of the sealing stations 40. Thus the sealing stations 40 can be spaced apart appropriately for any desired bag width. It will be noted that during operation of the apparatus 10 due to the tension applied to the film 14 by the draw rollers 22,23, a certain amount of slippage can occur and it may be necessary to adjust the positions of the sealing stations 40 on the frame 38. To facilitate easy and quick adjustment, the sealing stations 40 are interconnected by a spacer rod 42 fixed on one of the sealing stations 40 and slidable in a clamp 43 on the other sealing station 40 for setting the sealing stations 40 a preset distance apart. Thus conveniently when locked together at their desired spacing the sealing stations 40 can be adjusted together on the frame 38. A measuring scale is provided on the rod 42 for setting the spacing between the sealing stations 40.

At each sealing station 40 the film 14 is passed between a pair of pneumatically operated heat sealing bars 44 which are movable together and apart. The film is stopped 0 7 « Π - 8 and the bars 44 operated to clamp the film layers 31,32 together for fusing the layers together forming a transverse seal across the width of the film. The temperature of the sealing bars and seal time are adjustable to accommodate different films 14. Advantageously with a pair of sealing stations 40 the sealing time is effectively halved by carrying out the sealing in two stages.

Downstream of the sealing stations 40 the film 14 is delivered to an air blast cooler 46 which directs a stream of cooling air at each seal as it locates at the air blast cooler 46 for preliminary cooling of each seal. The film 14 is then led through a pair of water cooled seal clamps 48. At each clamp cooler 48 the film 14 is passed between a pair of pneumatically operated water cooled clamping bars 49 which are movable together and apart. The film 14 is stopped with a seal located between the clamping bars 49. The clamping bars 49 are operable to clamp the seal between the clamping bars for a preset seal cooling time and then subsequently release the film 14.

Film leaving the clamp coolers 48 is led to a cutting station 50 at which the film is cut longitudinally intermediate its edges to separate the film into two parts. At the cutting station 50 a blade 51 is slidably mounted on a crossbar 52 for positioning the blade 51 relative to the film 14. Each of the film parts are fed through a guillotine 53 downstream of the front draw roller 22 for cutting the film parts centrally along each seal transversely across the width of the film for dividing each film into individual bags. The bags discharged from the guillotine 53 are then collected on a table 54 and packaged.

P9407t - 9 Referring to Fig. 3, a second cutting station 55 is provided on the apparatus 10, in this case immediately downstream of the rear draw rollers 23, for use instead of the cutting station 50. A cutter blade 56 is slidably mounted by a carriage 57 on a cross bar 58. A locking screw 59 is operable to allow sliding of the carriage 57 on the cross bar 58 and locking of the carriage 57 on the cross bar 58. In use, the cutter blade 56 is engaged with a side edge 13 of the film 14, the film 14 being drawn over the cutting blade 56 to part the upper and lower layers 31,32 of the film 14 providing an opening along one side edge 13 of the film 14.

Fig. 4 shows a film 14 with spaced-apart transverse seals 61 being delivered to the guillotine 53 for cutting the film 14 along the seals 61 to form individual bags 62. In this case, the bags extend the full width of the film 14 an edge 13 of the film 14 having been previously cut open at the cutting station 55.

Referring now to Fig. 5 the apparatus 10 is shown in another arrangement for use. In this case the bubble 30 is located upstream of the film feeder 15 by means of an alternative type bubble collapsing means 70. The bubble collapsing means 70 is also shown in Figs. 1 to 3 where it is not being used for collapsing the bubble but merely to assist in delivering the film 14 to the film feeder 15. Best shown in Fig. 2, the bubble collapsing means 70 comprises a stand 71 having a pair of spaced-apart uprights 72 upon which a pair of vertically spaced-apart rollers 73 are rotatably mounted. Each of the rollers 72 is height adjustable on the uprights 72 for controlling the size of the bubble to be formed and the film angle. Spaced-apart slots 74 are provided on the uprights 72 for height adjustment of the rollers 73 on the uprights 72. The stand 71 can be mounted at a number of positions on - 10 the frame 38 of the apparatus 10 for positioning the bubble at different locations appropriate for optimum handling of different types of film. In Fig. 5 the bubble 30 is formed between the rollers 73 on the stand 71 and a film guide roller 78 on the frame 38. It will be noted that by passing around and between the rollers 73 the film layers 31, 32 are gradually brought together for overlying the layers 31,32 without creasing the film material. This bubble handling arrangement is particularly suitable for handling relatively thick films.

Referring now to Fig. 6, the bubble collapsing means 70 is shown mounted in this case immediately downstream of the film feeder 15. This position is particularly advantageous for handling wider widths of film as it allows improved control of side to side movement of the film to be achieved.

Referring now to Fig. 7 the bubble collapsing means 70 is shown mounted immediately downstream of the rear draw rollers 23. This position can provide improved control of film advance through the apparatus 10 as both layers of the film are retained together for the major portion of the travel to the sealing stations 40. Further, there is no crushing of the material as it passes through the rear draw roller 23.

It will be appreciated that the controlled bubble handling of the process facilitates high quality bag production at speed with minimum wastage. Smooth and efficient handling of a wide range of films can be achieved with reliable operation of the process and apparatus promoting high throughput of film and minimising down time, interruption and stoppages to the process. Conveniently the apparatus is readily easily set up for optimum handling of different sizes and thicknesses of film. Even film of relatively - 11 low quality can be processed thus avoiding delays in replacing films, this being particularly important where film stock is ordered on a justin time basis . The invention is not limited to the embodiments 5 hereinbefore described which may be varied in both construction and detail.

Claims (11)

CLAIMS - 12 1.
1. A plastic bag production process comprising the steps : leading a flattened tubular thermoplastic film from a supply reel to a spreading station; passing the film around a spreader roller at the spreading station, the spreader roller having spirally wound grooves in an outer resilient surface of the roller extending outwardly in opposite directions from a centre of the roller for transversely tensioning the film for crease removal; separating upper and lower layers of the film by means of an air bubble formed within the film; collapsing the inflated film by bringing the upper and lower layers of the film together in a controlled manner at a downstream end of the bubble; feeding the film incrementally to an associated pair of sealing stations in turn downstream of the air bubble; at each sealing station passing the film between a pair of pneumatically operated heat sealing bars which are movable together and apart, stopping the film and clamping the film between the heat sealing bars fusing the film layers together forming a transverse seal across the width of the film; - 13 releasing the clamping bars and delivering the film to an air cooler, directing a stream of cooling air at each seal as it locates at the air cooler; leading the film to each of a pair of spaced-apart water cooled seal clamps in turn, at each clamp passing the film between a pair of water cooled clamping bars, stopping the film with a seal located between the clamping bars and clamping the seal between the clamping bars for a preset desirable seal cooling period and subsequently releasing the film; cutting both of the film layers longitudinally at a cutting station by means of a cutter blade at the cutting station to provide a bag inlet opening in the film extending between each adjacent pair of seals; feeding the film to a guillotine and cutting the film transversely across the width of the film along each seal intermediate side edges of the seal to part individual bags away from a leading end of the film; discharging bags from the guillotine and collecting and packing said bags.
2. 2. . A process as claimed in claim 1 including the step of collapsing the inflated film by delivering the film to bubble collapsing means having two or more spaced-apart rollers mounted on a roller support, leading the film around the rollers for gradually bringing the upper and lower layers of the film together in a controlled manner. - 14
3. 3. A process as claimed in claim 2 including the step of applying a braking force to each roller.
4. 4. A process as claimed in claim 2 or 3 including the step of forming the air bubble between the bubble 5. Collapsing means and an associated roller spacedapart from the bubble collapsing means around which the film is led, the bubble collapsing means being movable relative to said associated roller for adjusting the size of the air bubble formed 10 between the bubble collapsing means and said associated roller.
5. 5. A process as claimed in any of claims 2 to 4 wherein the bubble collapsing means is located downstream of the spreader roller, the bubble 15 being formed between the spreader roller and the bubble collapsing means. 20 7 A process as claimed in any of claims 1 to 4 wherein the bubble collapsing means is mounted upstream of the spreader roller. A process as claimed in any of claims 1 to 4 wherein the process includes the step of delivering the film to a first set of draw rollers mounted between the spreading station and the first heat sealing station and an associated second set of draw rollers mounted downstream of the coolers, each set of draw rollers engaging the film for incrementally feeding the film through the sealing stations and coolers, the bubble collapsing means being mounted between the first set of draw rollers and the first sealing station for forming the air bubble downstream of the first 940761 - 15 set of draw rollers between the first set of draw rollers and the bubble collapsing means.
6. 6. 8. A process as claimed in any preceding claim including the step of setting the sealing stations a pre-set distance apart corresponding to one or more bag widths and locking the sealing stations together by means of a spacer rod fixed on one of the sealing stations and slidably engaging and releasably lockable on the other sealing station.
7. 7. 9. A process as claimed in any preceding claim wherein the cutting station is located downstream of the cooling station and the film layers are cut by engaging a cutter blade with the film intermediate the sides of the film for longitudinally parting the film.
8. 8. 10. A process as claimed in any of claims 1 to 8 wherein at the cutting station the film layers are cut by engaging a cutter blade with a side edge of the film, the film being drawn over the cutter blade to part the upper and lower layers of the film.
9. 9. 11. A plastic bag production process substantially as hereinbefore described with reference to the accompanying drawings.
10. 10. 12. Plastic bags whenever produced by a process as claimed in any preceding claim.
11. 11. 13. Apparatus for carrying out the plastic bag production process as claimed in any of claims 1 to 11 substantially as hereinbefore described with reference to the accompanying drawings.