WO1999037541A1

WO1999037541A1 - Bag closing method and apparatus

Info

Publication number: WO1999037541A1
Application number: PCT/GB1999/000217
Authority: WO
Inventors: Paul Utz; Paul Wollmershäuser; Gerald Schubert; David John Wilkinson
Original assignee: Tetley Gb Ltd.
Priority date: 1998-01-22
Filing date: 1999-01-22
Publication date: 1999-07-29
Also published as: GB0018015D0; DE19982636T1; GB2348862A; GB2348862B; AU2177699A

Abstract

A method of and an apparatus for closing flexible bags made e.g. of paper, plastics or metal foil. The open-topped flexible bag (1) is held in a cassette (2) configured closely to surround the outer walls of the bag. A pair of closing jaws (3) can engage and then pivot to fold the vertical sides of the bag (1). Each jaw (3) includes a flat perforated vacuum plate (5) which can grip the sides of the bag during the closing operation and a heat sealing strip (6) for sealing the bag once closed. A pair of triangular closing plates (4) fold the other sides of the bag inwardly. Each triangular plate (4) includes a perforated vacuum plate (8) for holding the side of the bag below the closing plate (4) during the closing operation. A pair of spring plates (9) are inserted into the open top of the bag during the closing process to help hold the bag sides and form the corner creases during the closing operation.

Description

- 1 -

BAG CLOSING METHOD AND APPARATUS

The present invention relates to a method of and apparatus for closing bags, and in particular to a method of and apparatus for closing flexible bags containing a product which in itself has low structural strength and dimensional stability. Many fast moving consumer goods are packaged in flexible bags made from, for example, flexible plastics film, paper, coated paper, metal foil, or laminates composed of some or all of these materials. One known such packaging process is the form/fill/seal process. One difficulty with packing product into such flexible bags is that with the known bag closing processes there can be a tendency for the bag's contents to be disturbed during the closing process. This can interfere with the closing and subsequent sealing processes and also distort the shape and reduce the stability (e.g. for stacking purposes) of the closed bag. Any disturbance of the bag or its contents can also be undesirable from a consumer aesthetics standpoint . According to a first aspect of the present invention, there is provided a method for closing an open topped flexible bag, comprising folding the sides of the bag projecting beyond the bag's contents inwardly to close the bag, and constraining the sides of the bag below the level of the fold lines that will form in the top of the bag as it is folded to remain substantially planar throughout the folding operation.

According to a second aspect of the present invention, there is provided an apparatus for closing an open topped flexible bag, comprising means for folding the sides of the bag projecting beyond the bag's contents inwardly to close the top of - 2 - the bag; and means for constraining the sides of the bag below the level of the fold lines that will form in the top of the bag as it is folded to remain substantially planar throughout the folding operation.

In these aspects of the present invention, the bag sides below the fold lines that form the closed top of the bag (i.e. typically the horizontal fold lines that will form to close the top of the bag) are constrained to remain substantially planar during the folding operation. The Applicants have recognised that a particular cause of disturbance to the bag's contents during the closing process is movement or distortion of the sides of the bag as it is closed. This can happen readily because the sides of the bag themselves have no or little rigidity. By restraining this movement of the sides of the bag during bag closing, this source of disturbance to the bag's contents is reduced or alleviated. Constraining each of the bag's sides in this manner can also help to ensure that the desired final bag shape is achieved because it reduces any tendency of the bag's sides to distort (e.g. bow) during the closing operation. It can additionally help to ensure that flat surfaces, e.g. for the bag's base, can be reliably achieved. This can be particularly desirable, for example, where the closed bags are to be stacked and as a result can reduce the amount of support that is required from secondary packaging and hence reduce the quantity and costs of secondary packaging.

The bag's sides are preferably constrained to remain substantially planar by the appropriate arrangement of planar surfaces, for example, walls, closely adjacent one or more, or most preferably all, of the outer sides of the bag, against which the bag's side or sides will abut if it or they distort outwardly from a substantially planar configuration during the closing process .

In a particularly preferred embodiment, this is achieved by holding the open bag in an open topped cassette configured closely to surround the bag's sides during the folding operation. The side walls of the cassette will then constrain unwanted outward movement of the bag's sides. The cassette's sides should extend to a position below the fold lines and reach an appropriate height relative to the intended fold lines (the approximate positions of which at least should be predetermined and thus known) to ensure appropriate constraining. Thus preferably, where the bag to be closed has a rectangular cross-section, one pair of opposing sides of the cassette reach substantially the height to which the bag is filled with its contents and are most preferably of a height just below the horizontal fold lines in the top of the bag in order to maximise their constraining action. The other pair of opposing sides could be of similar height, but preferably are lower to facilitate the closing process. Thus, according to a third aspect of the present invention, there is provided a method of closing an open-topped flexible bag, comprising: folding the sides of the bag projecting above the bag's contents inwardly to close the top of the bag; and holding the bag in a open-topped cassette configured closely to surround the bag throughout the folding process.

In these arrangements, the bag can be held securely in the cassette, rather than being simply placed therein. A vacuum can be induced at the base of the cassette to pull the bag against the base of the cassette for this purpose.

In a particularly preferred such embodiment, successive open bags are placed in successive cassettes on a moving conveyor and are moved successively to and through a closing station where they are closed. The cassettes provide a particularly convenient way of - 4 - transporting the bags to and holding them at the closing station. The bags can also be held in the cassettes for other parts of the packaging process, e.g. filling the bags, if desired and preferably a succession of bags are transported in successive cassettes on a conveyor through spaced apart bag-filling and bag-closing stations. This latter arrangement permits the bag- filling and closing operations to be physically separated which can be advantageous . One or more sides of the bag or parts thereof can alternatively or additionally be constrained by pulling or retaining them against a planar surface during the folding operation. This may be appropriate in certain folding arrangements, for example if there would be a tendency for sides of the bag to bow or pull inwards during the folding process . Where such an arrangement is required, one or more of the sides of the bag are preferably held against a planar surface by a vacuum or suction means. Most preferably, sides or parts thereof of the bag are engaged against flat perforated plates behind which vacuum is induced to hold the bag sides against the flat plates.

The top of the bag can be folded closed in any desired manner. Preferably the folding is carried out by means of folding jaws or plates having substantially planar surfaces which engage the bag's sides. Most preferably the arrangement is such that the bag's sides are substantially prevented from sliding across the bag engaging surfaces of the folding means, as this helps to form more precise and sharper folds. This can be achieved by the appropriate use and arrangement of vacuum or suction means to hold the bag's sides against such sliding.

In a particularly preferred embodiment, where the bag has a rectangular cross-section, one pair of opposing side walls of the bag are folded inwardly from their initially vertical position such that they meet or overlap and thus form a closed top of the bag.

This can conveniently be achieved by means of folding jaws having flat faces which can be engaged against opposing sides of the bag and pivoted inwardly to fold those sides of the bag in this manner. Most preferably, each jaw is arranged to grip the sides of the bag which it engages as it pivots so that the bag's side is restrained substantially from sliding over the surface of the jaw as the folding proceeds. The surface of each jaw which initially engages the bag's side preferably therefore comprises a flat vacuum plate which can be actuated to pull the bag's side against the plate as it is folded. This restraining of the bag's sides from sliding over the bag engaging faces of the jaws as the jaws pivot to close the bag reduces further any tendency of the bag's sides to distort as the bag is closed. In combination with the restraining of the bag sides below the fold lines, for example by the cassette walls, it can ensure that these sides of the bag are held flat right up to the desired fold lines at the top of the bag. This permits a sharper fold to be achieved, and without reliance on support from the bag or its contents during the folding operation.

In this embodiment, the other pair of opposing side walls of the bag should be folded inwards appropriately during the closing operation. Thus, the other opposing side walls of the bag are preferably folded inwardly substantially simultaneously with the first two side walls as the bag is closed. Typically, the other opposing side walls would be folded so as to form a gable-like transition region at their ends. This can be achieved by engaging the two other opposing sides of the bag with appropriately, e.g. substantially triangularly, shaped plates which can be pivoted to fold these sides inwardly as the bag is closed, to form triangular folds at these sides of the bag.

In this arrangement, flat vacuum plates which can - 6 - engage and grip the sides of the bag are preferably arranged below these pivoting plates and are arranged not to pivot when these plates are pivoted. The vacuum plates can be used to hold open and planar the bag's sides below the fold lines induced by these plates. This helps to prevent these parts of the bag's sides from bowing inwardly as these plates fold the bag sides, and also the bag's sides from sliding over the surface of these plates during the folding process. Preferably the, e.g. triangular, plate and vacuum plate arrangements (if provided) are arranged to be retractable from their bag folding position to a position in which they would not overlap a bag in a position to be folded. This permits this folding plate arrangement to be moved away to permit, for example, indexing of successive bags to be closed through the closing station.

In a particularly preferred folding arrangement, a pair of plates is introduced into the neck of the bag during the folding operation and the plates, preferably resiliently, engaged against opposing inner surfaces of the bag. The plates can be pushed outwards against opposing sides of the bag but allowed to move, preferably resiliently, towards each other as the bag's sides are pushed together during the closing process. These plates help to hold the bag's sides in position while it is folded and can in particular aid the formation of corner creases of the top of the bag. For this latter purpose, they are preferably initially prevented from moving inwardly as the bag is closed so as to form sharper corner creases . These plates should preferably be introduced to a level just above where the folding jaws initially engage the bag's sides.

The plates preferably remain substantially vertical throughout their lateral movement as the bag is closed. Thus in one preferred embodiment the plates are suspended independently of each other and moved - 7 - laterally by moving their suspension points (e.g. by means of an air cylinder) appropriately during the folding operation. The individual plates can conveniently be suspended from different points on and driven along, a rail in this arrangement. This embodiment is preferred where larger lateral movement of the plates is required, e.g. for closing larger bags. Where less lateral movement is required the plates can be suspended from the same point (e.g. arranged in a "wishbone" type fashion) , and moved laterally by driving their free ends together and apart without moving their suspension points.

Preferably, the bag is folded such that it has a substantially flat or planar, preferably horizontal, top (except for a fin, if provided (see below) ) . Thus the bag's sides are preferably folded from their initially vertical positions to substantially horizontal positions (except for any material upstanding in a fin, if provided) . The folding operation is preferably such that the bag is formed with a fin upstanding from the closed top of the bag. The fin can then be folded over and secured to or laid on the closed top of the bag as is known in the art. In a particularly preferred such arrangement, the fin is folded only once (through 180°) , and then the folded fin rotated through 90° to lay it against the flat top of the bag. This helps to avoid the fin forming a prominent ridge on the flat top of the bag. Preferably the fin is trimmed to a predetermined height above the top of the closed bag before it is folded. This can be achieved, as is known in the art, using optical sensors and cutting blades. This trimming of the fin to a uniform height helps the subsequent fin folding operations as they are then performed on a standardised fin. It also helps to standardise the appearance of the top of the finished pack.

Where a fin is formed, formation of the fin can be - 8 - further aided by introducing a pair of, e.g. spring plates into the open top of the bag, as discussed above. In a particularly preferred embodiment where a fin is formed and laid against the top of the bag, the side of the fin which is or will be in view or on the outside is arranged to be wider than the inner, concealed side of the fin. This arrangement permits the wider visible fin side to conceal and overlap the narrower inner fin side, thereby providing a neater finished product which is desirable from a consumer aesthetics standpoint. One side of the fin can particularly conveniently be made wider than the other by making the plates introduced into the neck of the bag (where used) of appropriate, different widths. In this latter arrangement the e.g. substantially triangular, folding plates are preferably appropriately offset from the bag's centre line to take account of the differing widths of the plates on the folding operation.

The bag is preferably sealed immediately after it is closed and while the closed bag is still held in position by the folding means. This helps to stop the bag from relaxing after the closing operation before it is sealed and to prevent the resilience of the bag from causing it to try to reopen. The sealing itself can be achieved in any suitable manner, e.g. by heat-sealing or the use of ultrasound. The bag or at least its inner surface should be of an appropriately sealable, e.g. heat-sealable, material.

This immediate sealing can conveniently be achieved by using the folding or closing jaws to also seal the bag top once they have folded it closed. The jaws preferably therefore each include a heat-sealing strip on a surface that engages the closed bag (for example along the side of the jaws that abut the fin formed in the closing process) . The bag can then be sealed by increasing the pressure on the jaws in a direction pushing the bag sides together. This can be achieved by - 9 - pushing the jaws together to push these strips towards each other substantially immediately the closing operation is finished.

The bag folding and closing arrangement described above is believed to be advantageous in its own right. Thus, according to a fourth aspect of the present invention, there is provided an apparatus for closing an open-topped flexible bag having a rectangular cross- section, comprising: a pair of opposing folding jaws, each jaw having a substantially planar surface for engaging the side of the open bag in use, the jaws being arranged to be pivotable inwardly and towards each other to fold a pair of opposing sides of the bag together, each jaw further including vacuum means for holding the bag's side against the planar surface of the jaw during its folding movement ; a pair of opposing substantially triangular plates for engaging the remaining pair of opposing sides of the open bag, the triangular plates arranged to be pivotable inwardly and towards each other to fold these opposing sides of the bag towards each other; and a pair of vacuum plates, each being mounted substantially immediately below a respective triangular plate for gripping the bag's side below the triangular plate, which vacuum plates do not pivot with the triangular plates during the folding operation. According to a fifth aspect of the present invention, there is provided a method for closing an open-topped flexible bag having a rectangular cross- section comprising: holding opposing sides of the bag against planar surfaces of an opposing pair of pivotable folding jaws by means of a vacuum; holding each of the remaining pair of opposing sides of the bag against a respective planar vacuum plate arranged adjacent that surface and below a - 10 - pivotable substantially triangular plate; and pivoting the opposing jaws and triangular plates inwardly and towards each other to close the top of the bag while maintaining the vacuums that hold the bag's sides against the jaw's surfaces and vacuum plates. The above aspects of the invention can and preferably do include any or all of the preferred features of the invention described above, such as the pair of plates to be introduced into the neck of the bag during the folding process.

The present invention is particularly suited to closing flexible bags of paper, coated paper, plastics, metal foil or laminates composed of some or all of these materials. The bags can be filled with any desired product, although the closing process of the present invention is particularly suited for closing flexible bags filled with flexible products, or products of low inherent structural strength and stability, such as stacks of infusion packages (e.g. tea or coffee bags) . Thus according to a further aspect of the present invention, there is provided a closed flexible bag containing stacks of infusion packages, said bag having been closed by a method or with an apparatus in accordance with the present invention. A preferred embodiment of the present invention will now be described by way of example only, and with reference to the accompanying drawings, in which: Figure 1 shows an end view of a bag closing arrangement in accordance with the present invention prior to commencing the closing operation;

Figure 2 shows an end view of the bag closing arrangement during the closing operation;

Figure 3 shows an end view of the bag closing arrangement at the end of the closing operation; Figure 4 shows an end view of the bag closing arrangement after a bag has been closed;

Figure 5 shows a closed bag in its cassette; and - 11 -

Figure 6 shows a pack of infusion packages closed in accordance with the invention.

A bag closing operation in accordance with the present invention is shown in Figures 1 to 4. The closing of a flexible bag containing a single stack of infusion packages is shown in this example, but it is equally applicable to other sizes of bags and bags filled with other contents.

Plural flat-bottomed rectangular cross-section, flexible bags 1 made of paper, coated paper, plastics film, metal foil or a laminate of some or all of these materials, are successively formed on a form/fill/ seal machine, as is known in the art but left open-topped and not filled at this machine. They are then placed in successive cassettes 2 on a conveyor (not shown) . The cassettes may be conveniently made from moulded or machined plastics, and are configured closely to surround the bags .

The flexible bags are carried along the conveyor in the cassettes 2 to a filling station where the bags are filled with their contents, in this example a stack of tea bags . This can be done in any manner known in the art. The filled bags 1 are then transported successively in their cassettes 2 on the conveyor to and indexed through a closing station.

The closing station includes folding and sealing jaws 3 and closing plates 4, which can be operated to fold and close the top of the bags above their contents to provide a flat horizontal top with an upstanding fin. Figure 1 shows an end view of the arrangement prior to commencing the closing operation. A bag 1 is moved in its cassette 2 to a position between the jaws 3. The jaws 3 can engage and then pivot to fold horizontal the vertical sides of the bag 1. The jaws 3 each include a flat perforated vacuum plate 5 (behind which vacuum can be induced) which can grip securely the sides of the bag 1 during the closing operation. A heat -sealing strip 6 - 12 - is provided on the top of each of the jaws 3 to seal the bag once closed.

One closing plate 4 arrangement is shown in Figure 1. There is a corresponding opposing closing plate arrangement on the opposite side of the closing means to close the opposing end side of the bag 1. Each closing plate 4 has a triangular configuration and is pivotable about its base edge towards the bag (i.e. into the plane of Figure 1 for the closing plate shown) to fold the end of the bag inwards and horizontal. Each closing plate 4 is reciprocal horizontally on an arm 7 between the positions shown in Figures 1 (not in use) and 2 (the closing position) to permit bags to be brought past its position to or from the closing means on the conveyor. Each closing plate arrangement also includes a perforated vacuum plate 8 which includes feather-edged flexible rubber vacuum suckers, and which can grip and hold the end side of the bag below the closing plate 4 as the plate moves during the closing operation. Two spring plates 9 are also provided which can move vertically and can be inserted inside the open top of the bag 1 to help hold the bag sides and form the corner creases during the closing operation. The plates are resiliently biassed inwardly into the position shown, but can be driven apart horizontally at their free ends by a suitable driving means or arrangement . Alternatively separate plates could be suspended independently from and powered (e.g. by an air cylinder or other motor means) along a horizontal rail mounted above the closing station to move them laterally during the closing operation, the rail being vertically moveable .

It should be noted that the vertical sides of the cassette 2 come up the sides of the bag relatively close to where the horizontal folds forming the top of the bag will be. The cassette is sized such that there is little or no gap between the sides of the filled bag - 13 -

(whose basal area will be known) and the cassette sides. In the closing operation, the closing plates 4 are moved on the arms 7 to their closing positions overlapping the end sides of the bag. The vacuum plates 5 on the jaws 3 and the vacuum plates 8 below the closing plates 4 are then actuated to grip securely the sides of the bag that they are immediately adjacent to. A vacuum may also be induced below the cassette 2 (which has a hole in its base for this purpose) to hold the base of the bag 1, if desired.

The effect of these vacuum gripping arrangements is to constrain the bag surfaces that they hold to remain substantially planar and against the vacuum plates as the bag is closed so as to reduce any tendency for the surfaces to bow or collapse, or slip or slide across the folding jaw and plate surfaces, which may hinder the closing operation and in particular the stability and structure of the final closed bag, but without the need to rely on the bag's contents (in this example the stacks of infusion packages) to provide any support during the closing operation. It should be noted that the sides of the cassette 2 also help to constrain undesired movement of the bag's sides during the closing operation, due to their close fit with the bag's sides (which is important for this reason) . For example the sides 10 resist the bag's sides bowing outwards as the top of the bag is pushed inwards and down to close it.

Once the bag's sides have been gripped by the vacuum arrangements, the plates 9 are introduced into the top of the bag. They are then forced apart horizontally to engage the sides of the bag. Simultaneously, or thereafter, the jaws 3 and closing plates 4 are pivoted inwardly and down to fold the sides of the bag down over the stacks of infusion packages. As noted above, the vacuum arrangement and cassette 2 resist any undesired movement of the bag sides during the closing operation. Part way through the folding - 14 - process, once the plates 9 have established where the corner creases will form, the plates are allowed to move (or moved, if they are driven) together to correspond with the inwards pushing of the folding jaws 3. The triangular closing plates 4 are also withdrawn at an appropriate moment once the end gable-like regions have been properly formed. Figure 2 shows the closing operation part way through and Figure 3 the positions when the top is finally formed. As the bag is completely closed, the last part of the motion together of the plates is effected by the folding jaws, as can be seen from Figure 3. (The jaws 3 have rebates 11 to allow the plates 9 to remain in position until the jaw motion is completed. The rebates are deep enough that the plates 9 are not actually gripped.) As can be seen from the Figures, the bag is formed with a vertical fin 12.

As soon as the bag is closed and the fin formed, the sealing strips 6 are pressed inwardly to seal the bag (the strips are left hot during the closing process but extra pressure is applied at this stage to seal the bag) while the closing pressure is maintained. This is because the resilience of the bag material can tend to reopen it if it is not sealed immediately. This sealing arrangement also permits easy and ready control of sealing pressures, temperatures, times, etc. The seal should be peelable, as this facilitates opening of the bag. To achieve this, the area of the sealing zone may be coated during the manufacture of the material with a heat sealing peelable lacquer or a peelable thermoplastic (of lower melting point than that of the inner surface of the bag material if this surface is thermoplastic) .

The jaws 3 away from the heat sealing strips 6 are made of a low thermal conductivity, e.g. plastic, material so that they do not heat up apart from in the region of the heat sealing strips 6. This helps to - 15 - avoid unwanted heating of the bag 1, which could lead to undesirable effects such as welding of the inside surface of the bag to its contents. For this reason the plastic jaw extends around the heat sealing strip 6 to prevent direct contact between the strip 6 and the horizontal top surface of the closed bag.

After the bag 1 is closed and sealed, the jaws 3 and plates 9 are withdrawn, and the vacuums released, as shown in Figure 4. The closed bag at this stage appears as shown in Figure 5.

It should be noted that the closed height of the bag can be adjusted by moving the jaws 3 and plates 4 vertically relative to the cassettes 2. This should preferably be done to ensure that the bags are always closed closely over the bag's contents (stacks of infusion packages) with little or no head space in the closed pack. The flexible nature of the bag walls means that they can easily be folded at slightly different heights. Because nominally identical stacks of infusion packages vary in height over relatively long periods

(e.g. due to variations in tea density), preferably the height of each bag's contents is measured before it is closed and the height measurements used to adjust automatically the closed height of the bag to ensure minimum headspace (e.g. in a control loop) if there is a longer term trend towards a different stack height. Height adjustment could also be done manually, if desired.

The closing operation is preferably provided with an appropriate dust extraction arrangement (not shown) as the closing process can expel infusion dust from the stacks of infusion packages as the bags are closed.

The closed bags 1 can then be transported to further finishing stations, where, for example, the fins can be trimmed to a uniform height. This can be useful to ensure that any subsequent fin folding stations are presented with standardised bags upon which to perform - 16 - their respective operations and to help standardise the appearance of the tops of the closed bags. The fins can also be folded over and optionally adhered to the tops of the bags to provide a flat top. These processes can also be automatically height adjusted on the basis of the height measurement of the bag's contents discussed above, if desired.

Releasable resealable adhesive labels can be secured over the bags if desired. Such labels can perform reclosure and/or tamper-evincing functions. The label could, for example, comprise an elongate strip having adhesive regions at each of its ends which can be separated by removing a tear out strip provided in the label when it is desired to open the bag. The label can also include a readherable adhesive portion to allow it to be used repeatedly to reclose the bag after it has been first opened, if desired. A label can also be used to hold the fin flat against the top of the pack. This can conceal the cut edges of the fin from view (which is better from a consumer aesthetics standpoint) and help to render the pack flatter (which is advantageous if the bags are to be stacked) . The techniques for these processes can be any suitable techniques known in the art . The operation of the various components of the apparatus may be controlled using a programmable control which will allow the proper coordination of the various operations, or indeed by any other suitable process control . Figure 6 shows a bag of tea bags closed in accordance with the invention. The bag 20 has a sealed flat, block-bottom 21 which receives two stacks 22 of tea bags, and is packed and closed as described above. The bag is sealed with a peelable heat-seal at its upper end, and the elongate fin 12, formed when the bag is first closed, is folded over and held against the top of the pack to form a flatter top 23 by a releasable - 17 - tamper-evident resealable label 24. The label 24 has an adhesive anchoring pad 25 at each end and a tear-off strip 26 which can be readily removed to release the label material linking the anchoring pads 25, thereby allowing the bag to be opened. The part 27 of the label is provided with a repeatably adherable adhesive strip which can be used to reclose the bag once it has been opened.

Once the bag is opened, as tea bags are removed, the fin can be further folded or rolled down, and retained in a closed position by the part 27 of label 24. This will help to reclose the pack thereby keeping the contents fresher.

The present invention provides an improved bag closing process and apparatus . By providing flat surfaces to restrain those parts of the bag which bulge or push outwards, and using vacuum plates to restrain those parts of the bag which want to pull inwards and to prevent unwanted sliding of the bag's sides, during the closing process, the bag is held substantially flat right up to the desired crease lines and the closing action and folding of the bag is prevented from disturbing or deforming the bag's contents (and the bag itself - except where desired) . This permits the closing process not to rely on the contents of the bag as a former about which to fold the bag and to prevent inward movement of the bag sides as the bag is folded, and to fold the bag effectively as if it had preformed creases where it is to be folded. Thus the process can close an empty flexible bag just as well as a full one and achieve a flat top with a flexible bag. It also prevents disturbance of the bag's contents which could move the contents into, for example, the fin or seal region of the bag and thus interfere with the sealing operation or the appearance of the closed bag.

Thus the invention is particularly applicable to closing flexible bags containing infusion packages, such - 18 - as tea bags, coffee bags and the like (where the infusion is tea leaves, coffee grounds, chamomile, etc . ) . The infusion packages may be of any shape and may include tags, if desired. A further advantage of the closing process of the present invention is that it provides a very precise closing process which can close a flexible bag closely around the bag's contents. This permits the size of the closed bag to be reduced. As is know in the art, space saving in the context of, for example, fast moving consumer goods, is extremely desirable, as it, for example, permits transport and shelf space savings. The closing operation also permits the headspace above the bag's contents to be reduced and even minimised. This saves space but is also particularly advantageous because it permits the bag's contents to be used to perform a load bearing function for the finished pack, and without significant distortion of the top of the bag (which could lead to uneven bag heights over a series of bags) when so doing. This permits such bags to be readily stacked one on top of the other, without the need for extensive secondary packaging.

Claims

- 19 - Claims

1. A method of closing an open topped flexible bag, comprising: folding the sides of the bag projecting beyond the bag's contents inwardly to close the bag, and constraining the sides of the bag below the level of the fold lines that will form in the top of the bag as it is folded to remain substantially planar throughout the folding operation.

2. The method of claim 1, comprising arranging planar surfaces closely adjacent one or more of the outer sides of the bag, against which surfaces the bag's side or sides will abut if it or they distort outwardly from a substantially planar configuration during the folding operation, so as to constrain those bag sides to remain substantially planar during the folding operation.

3. The method of claim 1 or 2 , further comprising holding the open bag in an open topped cassette configured closely to surround the bag's sides during the folding operation.

4. A method of closing an open-topped flexible bag, comprising: folding the sides of the bag projecting above the bag's contents inwardly to close the top of the bag; and holding the bag in a open-topped cassette configured closely to surround the bag throughout the folding process.

5. The method of claim 3 or 4 , further comprising placing successive open bags in successive cassettes on a moving conveyor and moving the cassettes successively to and through a closing station where the bags are closed. - 20 -

6. The method of claim 5, wherein a succession of bags are transported in successive cassettes on a conveyor through spaced apart bag-filling and bag-closing stations .

7. The method of any one of the preceding claims, comprising retaining one or more sides of the bag or one or more parts of the bag against a planar surface during the folding operation to constrain its or their movement.

8. The method of any one of the preceding claims, comprising folding the top of the bag closed using folding jaws or plates having substantially planar surfaces which engage the bag's sides.

9. The method of any one of the preceding claims, further comprising restraining the bag's sides from sliding across the bag engaging surfaces of the folding means used to fold the bag closed during the folding operation.

10. The method of any one of the preceding claims, wherein the bag has a rectangular basal cross-section, and one pair of opposing side walls of the bag are folded inwardly from their initially vertical position such that they meet or overlap to form the closed top of the bag.

11. The method of claim 10, wherein the other opposing side walls of the bag are folded inwardly substantially simultaneously with the first two side walls as the bag is closed.

12. The method of any one of the preceding claims, further comprising introducing a pair of plates into the neck of the bag during the folding operation, engaging - 21 - the plates against opposing inner surfaces of the bag, and allowing the plates to move towards each other as the bag's sides are pushed together during the closing process .

13. The method of claim 12, wherein the plates initially prevented from moving inwardly as the bag is closed so as to form sharper corner creases.

14. The method of any one of the preceding claims, comprising folding the bag such that it has a substantially flat or planar top and a fin upstanding from the closed top of the bag.

15. The method of claim 14, further comprising folding the fin once through substantially 180┬░, and then rotating the folded fin through substantially 90┬░ to lay it against the flat top of the bag.

16. The method of any one of the preceding claims, further comprising sealing the closed top of the bag while the closed bag is still held in its closed position by the folding means used to fold the bag closed.

17. A method for closing an open-topped flexible bag having a rectangular basal cross-section comprising: retaining opposing sides of the bag against planar surfaces of an opposing pair of pivotable folding jaws by means of a vacuum; retaining each of the remaining pair of opposing sides of the bag against a respective planar vacuum plate arranged adjacent that surface and below a pivotable substantially triangular plate by means of a vacuum; and pivoting the opposing jaws and triangular plates inwardly and towards each other to close the top of the - 22 - bag while maintaining the vacuums that hold the bag's sides against the jaw's surfaces and vacuum plates.

18. An apparatus for closing an open topped flexible bag, comprising means for folding the sides of the bag projecting beyond the bag's contents inwardly to close the top of the bag; and means for constraining the sides of the bag below the level of the fold lines that will form in the top of the bag as it is folded to remain substantially planar throughout the folding operation.

19. The apparatus of claim 18, wherein the constraining means includes one or more planar surfaces against which a side or sides of the bag can abut in use if they distort outwardly during the folding operation.

20. The apparatus of claim 18 or 19, wherein the constraining means includes vacuum or suction means for holding one or more of the sides of the bag.

21. The apparatus of claim 18, 19 or 20, further comprising vacuum or suction means for holding the bag's sides against sliding across the bag engaging surfaces of the folding means during the folding operation.

22. The apparatus of claim 18, 19, 20 or 21, wherein the folding means comprises folding jaws or plates having substantially planar surfaces which can engage the bag's sides in use.

23. The apparatus of claim 22, comprising folding jaws having substantially flat faces which can in use be engaged against opposing sides of a bag and pivoted inwardly to fold those sides of the bag. - 23 -

24. The apparatus of claim 23, wherein each jaw is arranged to grip the sides of the bag which it engages as it pivots such that the bag's side is restrained substantially from sliding over the surface of the jaw as the folding proceeds.

25. The apparatus of claim 24, wherein the surface of each jaw which initially engages the bag's side comprises a perforated plate behind which vacuum can be induced to hold the bag's side against the plate as it is folded.

26. The apparatus of claim 23 and any one of claims 18 to 25, further comprising two substantially triangularly shaped plates which can be pivoted to fold the two other opposing sides of the bag inwardly as the bag is closed.

27. The apparatus of claim 26, further comprising a vacuum plate which can engage and hold the sides of the bag arranged below each triangular pivoting plate and which vacuum plate is arranged not to pivot when the respective triangular plate is pivoted.

28. The apparatus of claim 26 or 27, wherein the triangular plate and vacuum plate arrangements are arranged to be retractable from their bag folding position to a position in which they would not overlap a bag in a position at which it can be folded.

29. The apparatus of any one of claims 18 to 28, wherein the folding means includes a heat -sealing strip on a surface that engages the closed bag in use.

30. An apparatus for closing an open-topped flexible bag having a rectangular cross-section, comprising: a pair of opposing folding jaws, each jaw having a substantially planar surface for engaging the side of - 24 - the open bag in use, the jaws being arranged to be pivotable inwardly and towards each other to fold a pair of opposing sides of the bag together, each jaw further including vacuum means for holding the bag's side against the planar surface of the jaw during its folding movement ; a pair of opposing substantially triangular plates for engaging the remaining pair of opposing sides of the open bag, the triangular plates arranged to be pivotable inwardly and towards each other to fold these opposing sides of the bag towards each other; and a pair of vacuum plates, each being mounted below a respective triangular plate, for holding the bag's side below the triangular plate, which plates can be arranged not to pivot with the triangular plates during the folding operation.

31. A closed flexible bag containing stacks of infusion packages, said bag having been closed by the method of any one of claims 1 to 17 or with the apparatus of any one of claims 18 to 30.