WO1996011138A2

WO1996011138A2 - Manufacture and filling of plastics bags

Info

Publication number: WO1996011138A2
Application number: PCT/GB1995/002406
Authority: WO
Inventors: Michael Anthony Cowan
Original assignee: Hanlex Limited
Priority date: 1994-10-11
Filing date: 1995-10-11
Publication date: 1996-04-18
Also published as: GB9420456D0; WO1996011138A3

Abstract

A form and fill machine for resealable plastics bags having reclosable fastening strip adjacent the mouth thereof, the machine comprising a filling tube (60) around which the bags are formed on a continuous tube from sheet material upon which the fastening strip is attached, means (66, 68) for advancing the continuous tube over the filling tube in bag-width steps, sealing means (76) for forming side seams and at least partially severing successive bags at bag width intervals, and means (78, 80) for spreading the lower end of the continuous tube prior to forming a side seam, characterized in that the spreading means comprises at least one means (80) for externally engaging a portion of the continuous tube so as to position the portion of the tube whereat the fastening strip is disposed relative to the sealing means.

Description

MANUFACTURE AND FILUNG OF PLASTICS BAGS

This invention relates to the manufacture and filling of plastics bags.

A problem encountered in form and fill operations involving reclosable bags is that of avoiding creases or wrinkles in the seams of the bag, particularly the side seams, either before the bag is first opened or when it is reclosed. Bags with this defect are unsightly and encounter consumer resistance at the point of sale. The applicant has discovered that these creases or wrinkles are often due to the fastening strip being incorrectly oriented relative to the heat- sealing apparatus by which the seams are produced on the form and fill machine.

Therefore the invention provides a form and fill machine for resealable plastics bags having a reclosable fastening strip adjacent the mouth thereof, the machine comprising a filling tube around which the bags are formed as a continuous tube from sheet material upon which the fastening strip is attached, means for advancing the continuous tube over the filling tube in bag-width steps, sealing means for forming side seams and at least partially severing successive bags at bag width intervals, and means for spreading the lower end of the continuous tube prior to forming a side seam, characterised in that the spreading means comprises at least one means of externally engaging a portion of the continuous tube so as to position the portion of the tube whereat the fastening strip is disposed relative to the sealing means.

The spreading means may also include a spreader opposite to the external engaging means for pushing the tube wall away from the external engaging means from within the tube.

The external engaging means may be a gripper.

The machine may have a drawdown device for pulling the tube of material over the filling tube, the drawdown device comprising first and second traction means for engaging the material, the traction means being closely spaced from each other so that in operation a folded portion of the tube material whereat the fastening strip is located passes between them.

The first and second traction means may be a pair of belts. Another problem addressed by the invention is that encountered in machines such as that shown in UK patent specification 2.254.038A, the disclosure of which is incorporated herein by reference.

Specification 2.254.038 describes a method and apparatus for the application of a zipper fastening strip to a web of sheet material to be formed into reclosable plastics bags on a form and fill machine. The method involves inter alia heat-sealing the fastening strip in its closed condition to a folded portion of the sheet material and subsequently fusing the fastening strip at bag- width intervals so that when the bags are subsequently heat-sealed to provide side seams and are separated from each other at said intervals the ends of the two fastening strip portions are securely fixed to each other and cannot become separated. The web of sheet material is stationary whilst the fusing operation is performed, and thus the movement of the material through the machine, and in particular through the station whereat the fastening strip is attached to the web, is intermittent. This is a significant limitation on the speed of operation of the process because care must be taken not to overheat the fastening strip or the sheet material when the strip is attached. Overheating could damage the sheet material or inadvertently fuse parts of the fastening strip together. This may occur if the material is advanced slightly less than the correct distance, so that a small portion is heated twice at the strip-attaching station. Conversely, if the web advance is slightly greater than intended, a short portion of the strip may fail to be attached to the web leading to defective re-closing when the bag is in use.

It is an object of at least the preferred embodiment of the invention to address these problems.

Thus in a further aspect the invention provides a method of making resealable thermoplastic bags having fastening strips for selectively closing the bags, comprising supplying sheet material and fastening strip, fixing the fastening strip to the sheet material at a first station, locally fusing the strip at a second station downstream of the first station at bag-width intervals at which the bags will subsequently be separated, maintaining a quantity of sheet material between the first and second stations, whereby the sheet material is moved intermittently through the second station to advance it by said bag-width interval between successive fusing operations and is moved continuously through the first station, the speed of the sheet material through the first station being controlled in response to the quantity of material maintained between the first and second stations.

In another aspect the invention provides apparatus for making resealable thermoplastic bags having fastening strips for selectively closing the bags, comprising means for supplying sheet material, means for providing fastening strip, means for fixing the fastening strip to the sheet material, means for locally fusing the strip at bag-width intervals at which the bags will subsequently be separated from each other, material accommodation means between the heat- sealing means and the fusing means whereby in operation the sheet material moves intermittently through the fusing means whilst moving continuously through the heat-sealing means, and means for controlling the speed of continuous movement of the material in response to the quantity of material in the material accommodation means.

The material accommodation means may comprise at least one dancer roll.

The control means may sense the position of the at least one dancer roll as indicative of the said quantity of material.

There may be a further material accommodation means downstream of the fusing means, and means for advancing the material through the fusing means by one bag width interval upon detection of movement of the further accommodation means.

The invention will now be described by way of example with reference to the accompanying drawings, wherein:

Figure 1 shows diagrammatically in side elevation apparatus according to one aspect of the invention;

Figure 2 shows part of a form and fill machine according to another aspect of the invention;

Figure 3 is a view on arrow 3 in Figure 2; and

Figure 4 is a perspective view of part of the machine of Figure 2. Referring to Figure 1 there is shown a fastener or zipper insertion machine which in many respects is similar to that shown in Figure 1 of specification 2.254.038.

A web of sheet material 8 is stored as a roll or unwind 10, and is fed via a dancer 12 to a conventional V-board 14 at which the web is folded.

A string of fastener strip 16 is provided from unwind 18. This strip is of two-part form, respective parts being attached to opposite sides of a bag at the mouth thereof so that it is reclosable. A suitable fastener or zipper strip is that shown in our co-pending European application number 93304909.0 and sold under our registered trade mark ZIPTITE.

The fastener strip 16 passes over a tensioning roller 20, around guides 22,24 and is introduced in to the folded portion of the web 8 at 26.

The folded web and fastener strip then pass through a first station 29 at which the strip is heat sealed to the folded web, one half of the strip to each side of the fold. The station 29 is as generally described in specification 2.254.038 (or in more detail in related specification 2.251.404), and therefore will not be described here further. However, an important difference is that the web and fastener strip pass continuously through station 29, whereas in the prior art device the movement is intermittent. The rate of heat transfer at the station 29 to the web is chosen so that the web fuses to the fastener strip without degradation and without loss of dimensional stability.

The web with its attached fastener strip is unfolded at 30, save where it is held folded by the closed fastener, and then passes through drive-rollers 32 continuously driven by motor 34.

The web then passes around dancer rolls 36 and through a second station constituted by ultrasonic welder 38. It then travels around an adjustable tensioning roller 40, through an indexing drive 2 and around an output dancer 44. It then passes to a form and fill machine (not shown).

Downstream of the dancer 36 the movement of the web is intermittent. It advances in steps equal to the width of the filled bags issuing from the form and fill machine. The advance of the web is controlled by a photoelectric sensor 46 which senses movement of the dancer 4 and causes the indexing drive 42 to advance the web by one bag-width interval.

The ultrasonic welding station 38 compresses and fuses together a short portion of the fastening strip each time the web stops. The flattened (compressed) portions are thus at bag-width intervals. The side seam forming jaws of the form and fill machine are operated so as to form the side seams in line with the flattened portions, and to sever the bags from each other so that at each side of the bag there is part of the flattened portion. The end of the fastener strip of each bag thus are securely fixed together.

The welding station 38 is similar to that described in specification 2.254.038, and referenced 30 in the drawings thereof. It therefore will not be further described here, except to note that its removal from a position immediately following the heat-sealing station 29 in '038 to the position downstream of dancer 36 is an important feature of this embodiment.

The dancer 36 accommodates sufficient web material to permit the downstream web to move intermittently whilst allowing the upstream web to move continuously. The dancer 36 is pivotally mounted about an axis 48. Any drift in its mean angular position implies a mismatch between the average rate of withdrawal of the web by the indexing drive 42 and the rate at which it is continuously supplied by the drive rolls 32.

The drift is sensed by a position sensor 50 which supplies a feedback signal (diagrammatically shown at 52) to the control circuit of motor 34, thereby enabling the speed of the web through the upstream part of the apparatus to be adjusted to match the output demand. This is essentially a fine adjustment control; major changes eg. if there is a change in the bag size required, and the bag width interval is altered, are achieved by a range-change facility.

The amount of power (heat rate) supplied to the heat sealing station 29 may if necessary be adjusted to reflect substantial changes in web speed through that station, or of course changes in material.

Referring now to Figure 2, part of the form and fill machine is illustrated. The machine comprises a filling tube 60 through which product is delivered to fill bags formed on the machine. Web 8 from the Figure 1 apparatus is delivered around the top of the tube 60 where a shoulder 61 guides it to wrap around the outside of the filling tube 60. The now-tubular web 63 is drawn down over the filling tube by two traction devices 62,64. Referring to Figure 3 it can be seen that the traction devices 62 consists of two parallel belts 66,68 driven in synchronism around pulleys 69 and disposed with a small parallel gap 70 between them. The now tube-shaped web 8 has a flange-like portion 72 projecting radially of the tube 60, due to the closed fastener strip 16 maintaining a portion of the web in a folded state. This projecting flange passes through the gap 76 between the belts 66,68. The traction device 64 may be similarly configured to the device 62, but need only be a single belt.

Extending axially along the filling tube 60 (behind it in Figure 2) is a conventional heat sealing device which welds the free edges of the web together to form a tube with a longitudinal seam 74. When the bags are separated this seam forms a transverse seam across the back of the bag.

Below the end of the tube 60 is a pair of lateral heat sealing and severing jaws 76 of conventional form. These jaws grasp and flatten and weld the tube, producing side seams aligned with the intermittent flattened portion of the strip 16 as already described. The tube 63 is held by the jaws whilst filled with a measured quantity of product via filling tube 60, and the last previously-filled bag is simultaneously severed by the jaws. Alternatively, the jaws may provide a line of perforations if it is preferred that the bags remain connected but detachable.

Pivotally mounted inside and at the base of the tube 60 is a spring- loaded spreader bar 78. This is biased outwardly so as to tension the tube towards a flattened shape. At 180° to the spreader 78 is a gripper device 80, the gripper and the spreader being aligned parallel to and directly above the jaws 76. The gripper 80 grasps the tube 63 in the region of the fastener strip 16 and the flange 72 and pulls it in opposition to the spreader 78. The gripper 80 is able consistently to grasp the tube 63 and together with the spreader 78 present it accurately and in a wrinkle- and crease-free state to the jaws 76. This enables the side seams of the bag to be formed without creases or other distortions which would reduce the attractiveness of the package. The use of two internal spreaders such as 78 as found in the prior art is not effective in that regard, because they do not accurately locate the strip 16 and flange 72 relative to the sealing jaws 76. The spreader 78 may itself be replaced by another gripper similar to gripper 80, and disposed at 180° thereto.

Figure 4 shows the gripper 80 in more detail. It consists of a pair of pneumatically-operated jaws 82 driven by actuator 84 supplied with compressed air supplied to port 84. The jaws can be advanced to grasp the flange 72 by a double-piston pneumatic cylinder 88 supplied with compressed air via ports 90. The cylinder 88 is mounted via clamp 92 upon pedestal 94 which is provided with a slotted fixing plate 96. This enables it to be adjustably mounted on the support structure of sealing jaws 76.

Each feature disclosed in this specification (which term includes the claims) and/or shown in the drawings may be incorporated in the invention independently of other disclosed and/or illustrated features.

The appended abstract as filed herewith is included in the specification by reference.

Claims

CLAIMS:

1. A form and fill machine for resealable plastics bags having reclosable fastening strip adjacent the mouth thereof, the machine comprising a filling tube around which the bags are formed on a continuous tube from sheet material upon which the fastening strip is attached, means for advancing the continuous tube over the filling tube in bag-width steps, sealing means for forming side seams and at least partially severing successive bags at bag width intervals, and means for spreading the lower end of the continuous tube prior to forming a side seam, characterised in that the spreading means comprises at least one means for externally engaging a portion of the continuous tube so as to position the portion of the tube whereat the fastening strip is disposed relative to the sealing means.

2. A machine as claimed in Claim 1 , wherein the spreading means also includes a spreader opposite to the external engaging means for pushing the tube wall away from the external engaging means from within the tube.

3. A machine as claimed in Claim 1 or Claim 2, wherein the external engaging means is a gripper.

4. A machine as claimed in Claim 1 , 2 or 3, in which a drawdown device for pulling the tube of material over the filling tube, the drawdown device comprises first and second traction means for engaging the material, the traction means being closely spaced from each other so that in operation a folded portion of the tube material whereat the fastening strip is located passes between them.

5. A machine as claimed in Claim 4, wherein the first and second traction means are a pair of belts.

6. A method of making resealable thermoplastic bags having fastening strips for selectively closing the bags, comprising supplying sheet material and fastening strip, fixing the fastening strip to the sheet material at a first station, locally fusing the strip at a second station downstream of the first station, at bag-width intervals at which the bags will subsequently be separated, maintaining a quantity of sheet material between the first and second stations, whereby the sheet material is moved intermittently through the second station to advance it by said bag-width interval between successive fusing operations and is moved continuously through the first station, the speed of the sheet material through the first station being controlled in response to the quantity of material maintained between the first and second stations.

7. Apparatus for making resealable thermoplastic bags having fastening strips for selectively closing the bags, comprising means for supplying sheet material, means for providing fastening strip, means for fixing the fastening strip to the sheet material, means for locally fusing the strip at bag- width intervals at which the bags will subsequently be separated from each other, material accommodation means between the heat-sealing means and the fusing means whereby in operation the sheet material moves intermittently through the fusing means whilst moving continuously through the heat-sealing means, and means for controlling the speed of continuous movement of the material in response to the quantity of material in the material accommodation means.

8. Apparatus as claimed in Claim 7, wherein the material accommodation means comprises at least one dancer roll.

9. Apparatus as claimed in Claim 7 or Claim 8, wherein the control means senses the position of the at least one dancer roll as indicative of the said quantity of material.

10. Apparatus as claimed in any preceding claim, comprising a further accommodation means downstream of the fusing means, and means for advancing the material through the fusing means by one bag width interval upon detection of movement of the further accommodation means.