GB2164919A - Plastic bags suitable for automatic packaging - Google Patents

Abstract

An end weld plastic wicket bag suitable for automatic packaging is held on the wicket by one face 12 of the bag but the other face 10 is not retained because it has a cut or cut-out 22 which is at least as long as the distance between the wicket-receiving apertures 20 in the first face but not as long as the width of the bag. The bags may be produced continuously from a length of layflat tubing. <IMAGE>

Description

SPECIFICATION Plastic bags suitable for automatic packaging This invention relates to plastic bags and the production thereof, in particular plastic bags collated in packs on a retaining wicket. Such collated plastic bags can be used for automatic packing operations.

Plastic bags can be made from layflat tubing by welding two thicknesses of the plastic film together and the welds may extend down the sides of the bag to form a so-called sideweld bag. Alternatively, the bottom end of the bag can be formed by a weld across layflat tubing giving a so-called endweld bag.

It is conventional for sideweld bags to be collated in packs of say two hundred by means of a metal wicket. This holds the lower face of the top bag and all the bags beneath it while the top bag is blown open to receive its contents. When the bag has been filled it is pulled away from the wicket and the next bag blows open. This well-known practice requires each bag to have a lip projecting beyond the top opening, but at one face only of the bag. The metal wicket then passes through the projecting lips of the collated bags.

These bags are a simple pouch having two flat faces joined by welds at the sides and a fold at the bottom. The manufacture of these bags from layflat tubing is dependent on the fact that the welds extend down each side, whereas the projecting lip where there must be only one thickness of the plastic material, projects from the top end of the bag.

However, for many products, e.g. chickens or sugar, the requirement is for a square section bag which necessitates providing gussets in the side of the bag. This in its turn necessitates the bag being an endweld bag for which the conventional lip to receive a wicket cannot readily be achieved. This is because such a bag must necessarily be made with the bag travelling end first and it is difficult to take away part of one face during manufacture, There is, therefore, no automatic packing using endweld bags although there is a demand for this.

Broadly, the present invention provides an endweld bag which is wicketed or at any rate is suitable for placing on a wicket. The endweld bag may have side gussets.

In one aspect this invention provides a plastic bag having a bottom end formed by a weld across the width of the bag, at least one aperture in one face of the bag proximate its upper extremity to be threaded onto a retaining element, and at least one cut or cut-out in the second, opposite face of the bag adjacent the upper extremity which cut(s) or cut-out(s) (i) are dimensioned and positioned such that the said second face is not retained by the retaining element, but (ii) extend less than the full width of the bag.

Such a bag has no need for the lip which is conventional for a wicketed sideweld bag, and can readily be provided with side gussets.

Preferably the second face of the bag, which is the face with the cut(s) or cut-out(s), also has aperture(s) positioned to allow through passage of each retaining element (but not retained by reason of the cut(s) or cutout(s)). Alternatively the cut-out(s) may overlie the aperture(s) in the first mentioned face and in this way allow through passage of the retaining element(s) without distortion of the said second face.

One specific possibility is a cut-out which is large enouth to extend over both the said apertures in the first mentioned face of the bag, which cut-out however, does not extend to the upper extremity of the face of the bag from which it is cut.

Another specific form is for the said aperture(s) to extend through both faces, but be joined on the second face by a slit cut in that face only.

It is conventional for a metal retaining wicket to have a pair of spaced uprights and a cross-piece joining them. It is preferred to use such an arrangement, in which case there has to be a pair of the said apertures in the first face of the bag, spaced apart to correspond to the pair of uprights.

The general effect achieved is that both faces of the bag can continue to a common upper extremity, retaining element(s) which can be a conventional metal wicket extend through both faces of the bag adjacent the extremity but only the first mentioned face is retained by the wicket.

In another aspect, this invention provides a plurality of identical plastic bags as set forth above collated together on at least one retaining element having an upright extending through the said apertures in the first mentioned faces of the bags and also having at least one laterally extending portion extending laterally from the said upright to overlie a portion of each bag and thereby retain the bags collated together. preferably the laterally extending portion is a cross piece extending between a pair of uprights.

According to a further aspect of this invention there is provided a method of making plastic bags as set forth above which comprises advancing layflat tubing to a first station or set of stations whereat the aforesaid apertures and cut(s) or cut-out(s) are formed in the tubing, and thereafter at a subsequent station or stations forming a weld across the width of the tubing and severing the tubing to form a plastic bag.

At least one cut or cut-out may be formed as the layflat tubing passes over an internal dolly where the faces are separated, in which case the said aperture(s) may extend through both faces of the tubing and be formed at a subsequent or previous station to the internal dolly. Alternatively to the foregoing, cut-out(s) may be formed fully through both faces of the tubing, and thereafter closed on the first face of the bag by the application of adhesive tape to that face over the cut-out(s). Subsequently the aperture(s) are punched through the adhesive tape.

Preferably the manufacturing operations include the step (conventional in itself) of forming gussets at each side of the tubing. Gusseting may precede, follow or be more or less simultaneous with formation of the aperture(s) and cut(s) or cut-out(s).

The invention will be further explained and exemplified by the following detailed description of a bag embodying the invention, and manufacturing operations to make such bags, both with reference to the accompanying diagrammatic drawings. In the drawings: Figure 1 shows a plastic bag embodying the invention; Figure 2 is a side view of a pack of such bags collated on a wicket; Figure 3 shows a conventional wicket; Figure 4 diagrammatically shows a first sequence of manufacturing operations; Figure 5 shows the station where slots are cut, seen in vertical section on the centre line of the tubing; Figure 6 is a large scale detail showing superimposed, the outlines of the holes and cut out, and the perforations; Figure 7 diagrammatically shows a second sequence of manufacturing operations.

Referring to Fig. 1 of the drawings a plastic bag has a face 10 which as shown is the upper face, and a lower face 12. They each have an upper extremity 14 at the same distance from the bottom of the bag. Down each side of the bag a portion is folded in to form a side gusset 16. The bottom end of the bag is formed by a strip 1 8 where both faces and the infolded gussets 16 are all welded together.

Because of the side gussets the regions of the bag spaced from the bottom weld 18 can be opened out to give a rectangular section.

Near to its upper extremity 14 but slightly spaced from it, the lower face 12 of the bag has a pair of apertures viz round holes 20 spaced apart from each other. Lines of perforation 21 extend from these holes 20 to the upper extremity 14 of the lower face 10. The upper face 10 has an oval cut-out 22 which, when the bag is laid flat, overlies the two holes 20 in the lower face 12 and also a band extending across between them.

As shown by the side view of Fig. 2 a stack of these bags collated together are held by a metal wicket (itself illustrated by Fig. 3).

This has a pair of spaced-apart uprights 24 and a cross bar 26 which extends between the tops of the uprights. The uprights 24 extend through the apertures 20 and cut-outs 22 in the bags on the stack and thereby hold the entire collated pack together. However, the upper face 10 of the topmost bag is not held by the cross bar. The oval out-out 22 is larger than the cross bar 26, and allows the face 10 to lift off the wicket while the lower face 12 is held down by the cross bar extending over the inside of the lower face 12 between the holes 20. For automatic packaging an air flow is supplied in the direction of the arrow A to blow open the bag 41 lifting the face 10 off the wicket. The bag is filled in this condition.Then the filled bag is removed from the wicket by forcing it in the direction of the arrow A, whereupon the lower face 12 rips from the round holes 20 to the upper extremity 14 roughly along the chain-dotted lines 21, which are preferably perforations, indicated in Fig. 1.

The automatic opening of the topmost bag, filling, and removing from the wicket is directly analogous to present practice with sideweld bags. Different, however, is that those bags are held by the wicket passing through holes in a projecting lip whereas here there is no such lip and the face 10 of the topmost bag is free to come off the wicket because of the cut out 22.

Figs. 4 and 5 show one sequence by which the bag of Fig. 1 can be made. Continuous layflat tubing, in flattened condition, is supplied from the right in the direction indicated by the arrow B. Firstly a pair of gussets are formed at each side of the advancing layflat tubing, in conventional manner (entailing reinflation).

Next the gusseted tubing passes over another internal dolly 36 and as it does so the cut-out slots 22 are cut out from one face by means of a reciprocating cutter working against the dolly 36 to form the cut-outs 22 at an appropriate repeat distance along the advancing tubing. This repeat distance is equal to the length of a finished bag. The cut-out material is removed by suction.

Fig. 5 shows this dolly 36 sectioned on the vertical centre plane, and the vertically reciprocating cutter 38 which cuts the slots 22. The use of a dolly, i.e. a stationary body enclosed within an advancing tube, is known in itself.

As shown by Fig. 5 the dolly is supported by two pairs of horizontal rollers 42. The dolly itself has rollers 40 which rest on the rollers 42 and the lower half of the advancing film passe through the nips between the rollers 40 and 42.

The dolly may be narrow enough not to interfere with the gussets, or the tubing may open slightly to allow the gussets to pass the doily. A further possibility would be for the gussets to be formed at this stage, by external rollers co-operating with grooves in the dolly.

After the two faces of the flattened tubing have come together again the round holes 20 are punched through the lower face of the tubing at a station 44. This station is positioned so that the holes 20 coincide with a slot 22, and indeed the punches for the round holes 20 pass through the previously cut slot 22. As shown they also punch some material from the-upper face of the tubing at the ends of the slot 22, which is acceptable. Lines of perforation 21 are punched through both faces of the tubing at the same time as the round holes 20 are punched. These lines are not seen on the small scale or Fig. 4. Next at a station 46 an endweld 18 is formed fully across the advancing tubing and the bag 48 which has already been formed by the previous weld is cut off.

Fig. 6 shows to a larger scale the outlines of the holes 20 and cut-out 22. Lines of perforation 21 are punched in at the same time as holes 20 extending from the holes 20 to where the upper extremity of the bag will eventually come. These perforation lines 21 necessarily must passs through both layers of the tubing.

In an important variation on this method as just described with reference to Fig. 4, when the tubing passes over dolly 36 the cutter 38 does not cut out a slot 22 from which waste must be removed, but instead cuts a single line slit. Then at the subsequent station 44 the round holes 20 and perforation lines 21 are punched through both the lower and upper faces of the tubing. Consequently, in the upper face (only) of the tubing the round holes are punched through the ends of the slit which thus joins the holes in the upper face.

When the bag is on the retaining wicket the bag's upper face 10 is not retained by the cross bar 26 of the wicket because this cross bar can pass through the cut which joins the round holes in the upper face.

Fig. 7 shows a second method of forming the bags. Once again continuous layflat tubing is gusseted along two sides in conventional manner and then enters from the right as indicated by the arrow C. At a station 50 a pillar press punches an oval cut-out through both faces of the advancing tubing at a repeat spacing corresponding to the length of the eventual bags. At a subsequent station 52 the cut-out in the upper face of the tubing is closed again by the application of a strip of tape 54 which is bought in from the side as indicated by arrow D, and bears adhesive 56 down its side margins but not on a central strip between. The adhesive adheres to the tubing at either side of the oval cut-out. At a subsequent station 58 a pair of round holes 20 are punched through the adhesive tape, with the punches passing through the oval cut-out in the lower face of the tubing.

Thus the net result of the three operations is to form round holes 20 in one face of the tubing (and of course to be more exact these are in a piece of tape resealing that face) while an oval cut-out 22 has been formed in the other face of the tubing. Lines of perforation 21 extending from the holes 20 are punched at the same time as the holes 20, but are not seen on the small scale of Fig. 7.

Then as before at a subsequent station 46 and endweld 18 is formed across the width of the gusseted tubing and the previously formed bag 48 is cut-off.

For the manufacturing sequences mentioned above the punches or cutters which form the round holes 20 and the lines of perforations 21 can pass through both the upper and lower faces of the tubing and so for forming these there is no difficulty arising from the need to separate the faces of the tubing. The dimensions of a cut-out 22 may or may not be arranged so that the punches for the round holes 20 pass through the previously formed cut-out 22 without cutting additional material out of that face of the tubing.

After manufacture by any of the processes mentioned above the bags so produced are collated into bundles of, say 200 and assembled into packs with the collated bags held together by a conventional metal wicket whose uprights pass through the round holes 20 in one face of each bag, which is arranged to be the lower face in the collated pack, with the cut-out 22 or single line cut in the other, upper face towards the crossbar 26 of the wicket.

In every case mentioned above, the plastic material from which the layflat tubing is made may be clear polyethylene. More preferably it is coloured or tinted polyethylene. The polyethylene may be high density, low density or linear low density. Likewise for the method of Fig. 7 the tape by means of which one cutout is closed may itself be clear or coloured or tinted polyethylene. Other plastics which can be made into films and welded can also be used.

It will be appreciated that with both of these methods of manufacture, a cut or cutout of only limited area is formed in that face of the tubing which becomes the upper face of the bag. This limited area of the cut or cutout has the very significant result that the general integrity of the advancing tubing is not destroyed (as it would be if the upper face was to be cut away across the full width of the eventual bag).

Claims (17)

1. A bag formed out of plastic sheet material, which bag has a bottom end formed by a weld across the width of the bag, at least one aperture in one face of the bag proximate its upper extremity to be threaded onto a retaining element, and at least one cut or cutout in the second, opposite face of the bag adjacent the upper extremity which cut(s) or cut-out(s) are dimensioned and positioned such that the said second face is not retained by the retaining element, but extend less than the full width of the bag.

2. A bag according to claim 1 in which said second face of the bag also has apertures positioned to allow through passage of each retaining element, but in which the second face is not retained owing to the cut or cut-out.

3. A bag according to claim 1 in which said cut(s) or cut-out(s) overlie the apertures in said first face.

4. A bag according to any one of the above claims in which the second face has a cut-out which extends over both the apertures in the first mentioned face of the bag, which cut-out does not extend to the upper extremity of the face of the bag from which it is cut.

5. A bag according to claim 2 in which the said apertures extend through both faces and are joined on the second face by a slit cut in that face only.

6. A bag according to any one of the preceding claims wherein the plastic is polyethylene.

7. A bag according to any one of the preceding claims wherein each side of the bag has a gusset.

8. A bag according to any one of the preceding claims wherein a line of perforations extends from each of the apertures on either or both of the bag to the upper extremity of the bag.

9. A plurality of plastic bags according to any one of the preceding claims, collated together on at least one retaining element having an upright extending through the said apertures in the first mentioned faces of the bags and also having at least one laterally extending portion extending laterally from the said upright to overlie a portion of each bag and thereby retain the bags collated together.

10. Plurality of plastic bags according to claim 9 wherein the laterally extending portion is a cross piece extending between a pair of uprights.

11. Method of making bags as set out in any of claims 1 to 8 comprising advancing layflat tubing to a first station or set of stations whereat the apertures and cut(s) or cutout(s) are formed in the tubing and thereafter at a subsequent station or stations forming a weld across the width of the tubing and severing the tubing to form a plastic bag.

12. Method according to claim 11 in which at least one cut or cut-out is formed as the layflat tubing passes over an internal dolly where the faces are separated.

13. Method according to claim 11 wherein the cut(s) or cut-out(s) are formed fully through both faces of the tubing, and thereafter closed on the first face of the bag by the application of adhesive tape to that face over the cut(s) or cut-out(s), the apertures being subsequently punched through the adhesive tape.

14. Method according to claim 11, claim 12 or claim 13 wherein lines of perforations are punched out through the tubing at the same time as the apertures are punched.

15. Method according to any of claims 12 to 15 including a step of forming gussets at each side of the tubing.

16. A bag substantially as any herein described and with reference to the accompanying drawings.

17. Method for producing bags, substantially as any herein described and with reference to the accompanying drawings.