GB2163698A

GB2163698A - Paper sack

Info

Publication number: GB2163698A
Application number: GB08420795A
Authority: GB
Inventors: Ian Wilson
Original assignee: Henry & Co Ltd A & S
Current assignee: Henry & Co Ltd A & S
Priority date: 1984-08-16
Filing date: 1984-08-16
Publication date: 1986-03-05
Also published as: GB8420795D0; GB2163698B

Abstract

In a method and apparatus for forming a self seal closure on a paper sack (10) having a flattened tubular body which is permanently closed at one end and whose opposite end is open and carries a longitudinally projecting flap, a pressure sensitive hot melt adhesive is applied to an elongate strip of tape (28) and the tape is then pressed against the sack (10) so that the adhesive is applied to the sack (10) adjacent its open mouth. The material of the tape (28) is selected such that the tape can be peeled off the adhesive to leave the adhesive on the sack (10), whereby the flap can then be folded onto the adhesive to close the sack.

Description

SPECIFICATION Paper sack The present invention is concerned with paper sacks and in particular with paper sacks of the type used for carrying mail order goods.

A high proportion of the paper sacks which are currently used for the carrying of mail order goods comprise a paper tube whose one end is pre-closed using a crepe paper overtape and string stitching and whose other end is closed using metal staples, when the goods have been duly inserted.

Stapled sacks have a number of disadvantages, however. Merchandise within the sack can be inadvertently damaged by the staples.

There is a risk of injury from the staples to those persons who have to handle the sacks during filling, in transit and when being opened. Such injuries have caused problems with the postal authorities in the past. The closure of sacks by stapling is relatively slow.

Furthermore, the sacks are not tamper proof, in that the staples can be carefully removed and reinserted without it being visibly evident that the sack has been opened.

Another traditional method of closing paper sacks uses string stitching. This is, however, a relatively expensive operation, and requires the sacks to be passed through a stitching machine after filling. It is thus necessary for there to be a stitching machine available at the point where the goods are inserted in the sack.

In order to eliminate the need for special apparatus, such as staplers or stitchers, at the filling location, there have been several attempts to date to produce a seif-sealing sack which requires no special machinery to effect sack closure.

Attempts have been made to apply not melt adhesives directly to the sack itself from a hot melt applicator. However, because the loose sacks were not under tension and tend to have an uneven surface, such attempts have been unsuccessful.

Attempts have also been made to use a pressure sensitive latex adhesive. This, however, is a waterbased emulsion product and has to be dried after application. Running speeds were thus extremely low and fouling of machine parts by the adhesive was a problem. Furthermore, the self sealing properties of latex adhesives are badly affected by dust and daylight (U.V) and the shelf life of the sacks has been extremely low.

It is an object of the present invention to provide a method and apparatus for producing self scaling paper sacks which avoid the problems of the known techniques described above.

In accordance with a first aspect of the present invention, there is provided a method of forming a self seal paper sack comprising: (a) forming an open sack comprising a flattened tubular body which is permanently closed at one end and whose opposite end is open and carries a longitudinally projecting flap, the base of the flap being pre-creased in order to facilitate easy and accurate folding during the sealing operation; (b) applying pressure sensitive adhesive to an elongate strip of tape; and (c) pressing the adhesive-carrying tape against the sack so that the adhesive is applied to the sack adjacent its open mouth; (d) the material of the tape being selected such that the tape can be peeled off the adhesive to leave the adhesive on the sack, whereby the flap can then be folded onto the adhesive to close the sack.

In accordance with a second aspect of the present invention, there is provided an apparatus for forming a self seal closure on a sack which has a flattened tubular body which is permanently closed at one end and whose opposite end is open and carries a longitudinally projecting flap, the apparatus comprising an adhesive applicator adapted to apply a pressure sensitive adhesive to an elongate strip of tape and means for pressing the adhesive carrying tape against the sack so that the adhesive is applied to the sack adjacent its open mouth, the tape material being such that the tape can be peeled off the adhesive to leave the adhesive on the sack.

In accordance with a third aspect of the present invention there is provided an apparatus for forming a self seal sack comprising means for forming an open sack having a flattened tubular body which is permanently closed at one end and whose opposite end is open and carries a longitudinally projecting flap, an adhesive applicator for applying a pressure sensitive adhesive to an elongate strip of tape, and means for pressing the adhesive-carrying tape against the sack so that the adhesive is applied to the sack adjacent its open mouth, the tape material being selected such that the tape can be peeled off the adhesive to leave the adhesive on the sack.

Preferably, the adhesive is a hot melt, pressure sensitive adhesive.

The invention also embraces a self sealsack when produced by the aforegoing apparatus or method.

The invention is described further hereinafter, by way of example only, with reference to the accompanying drawings, in which: Fig. la is a plan view of a "pinch bottomed" sack prior to application of an adhesive-bearing strip in accordance with the present method; Fig. ib is a diagrammatic section on the line A-A in Fig. la; Fig. ic is a plan view corresponding to Fig.

1 a when the adhesive-bearing strip has been applied to the sack; Fig. id shows the bag of Fig. ic when the strip has been removed to leave the adhesive on the sack; Fig. le shows the sack of Fig. id when the open flap has been folded over and applied to the adhesive to close the sack; and Fig. 2 is a diagrammatic side view showing one embodiment of an apparatus in accordance with this invention for applying the adhesive-bearing strip to the sacks.

With reference first to Figs. 1 a to 1 e, Figs.

la and 1b show a so-called "pinch bottomed" sack 1 a which comprises a flattened tube portion 12 having flaps 14a, 14b at its two ends, respectively. The flap 14b has already been folded over (see Fig. 1 b) and permanently glued by an adhesive 16 to the wall of the tube to close the right-hand end of the tube 12, as viewed in the drawings. Such a sack is produced by a machine known as a "pinch-bottomer". The tube 12 for pinch bottom sacks has a stepped end configuration created by perforating a special pattern during formation of the tube in a tubing machine and then snatching the tube apart. This produces the tube 12 with flaps 14a, 14b at its two ends, one of which is creased, glued and folded as described above to produce the sack of Figs. 1a and 1b.Conventional "pinchbottomed" sacks have the top flap (14a) trimmed off to produce a "flush cut" open mouthed sack which would normally be closed by the stapling or stitching techniques described initially.

In the present technique, the top flap 14a is retained. As indicated in Fig. 1c, a strip 18 of silicone coated release paper, carrying on its one side a layer of pressure-sensitive hot melt adhesive, is applied to the tube 12 adjacent the open end thereof. When the strip 18 is subsequently removed, an adhesive stripe 20 remains on the tube, as shown in Fig. 1d.

After filling the sack can then be closed by folding over the flap 14a and adhering this same to the tube 12 by the adhesive 20.

With reference now to Fig. 2, pinch bottom sacks 1 a (already having the configuration of Figs. la and 1b) are carried into the apparatus on a conveyor 22, travelling from right to left as indicated by the arrow F. The sacks are orientated so as to travel sideways with their open mouths and flaps 14a facing forwards (towards an operator side of the apparatus).

Disposed above a downstream portion of the conveyor 22 is a pressure belt 24 which is urged downwardly against the upper run of the belt 22 by means of a plurality of springloaded pressure rollers 26. Where the sacks 1a enter the pressure belt section, a strip 28 (preferably about 3a mm wide) of silicone coated release paper is fed in with the sacks from a reel 3a mounted on a support 32. Just prior to its entry to the pressure belt section 24, the strip 28 of silicone-coated release paper is passed over a hot melt jetting head 34.

Sacks travelling on the conveyor 22, spaced laterally apart with a predetermined gap therebetween, are sensed by two photocells 36a, 36b which are arranged to detect the leading and trailing edges of the sacks to derive signals for controlling the release of hot melt to the silicone release paper strip 28 by the jetting head 34. When a sack has passed these photocells, the hot melt jetting head shuts off until the arrival of the next sack is detected by the photocells 36. Thus a series of adhesive stripes separated by gaps is produced on the silicone coated release paper 28.The stripe length is arranged to be slightly less than the sack width, as shown in Fig. id. By suitable adjustment of the timing and position of the photocells 36, the stripe of adhesiveon the silicone strip 28 is timed to coincide with a sack on entry of that sack and the strip 28 into the pressure section 24, the gaps in the adhesive coinciding with the spaces between the sacks 10.

The feed position of the release paper strip 28 is disposed such that the strip 28 is applied to the sacks 10 at a position parallel to but spaced slightly from the open mouth of the sack 10 (see Fig. inc).

When pressure is applied in the pressure belt selection 24 to the silicone paper strip 28 and the sacks disposed therebeneath, adhesive transfer takes place from the silicone paper strip 28 to the sacks 10. The silicone paper strip acts thereafter merely as a masking tape for the adhesive.

Adjacent the downstream end of the pressure belt section 24, the sacks are sensed by further photocells 38a, 38b which detect the leading and trailing edges of the sacks and activate a pneumatically operated cutting mechanism 40 so as to cut the silicone paper strip 28 centrally between adjacent sacks 10 into individual strips 18. This thus leaves a small tab of the strip projecting from each side of the sack.

The finished sacks 10 are then counted and collated into bundles in a conventional fashion.

In use, once a sack 10 has been filled with the required merchandise, it is just a matter of peeling of the silicone strip 18 from the sack, folding over the flap 14a and pressing this against the strip 20 of adhesive. The sack cannot thereafter be opened without destroying the seal.

The sealing operation provided by the present technique is quicker than methods known hitherto and results in speeding up the overall packing operation. No separate sealing equipment is needed. The package is "tamper evident" since fibre tear occurs at the seal when the package is opened, unlike stapled sacks where the staples can be carefully removed and reinserted or plastics film self seal sacks where fibre tear is not outwardly evident.

A further advantage of the sack produced by the present technique is that the seal pro duces a bond which is subjected only to shear forces, unlike self seal plastics film sacks the closures of which are subject to peel forces and are thus weaker and less secure.

A further refinement to the present technique can be obtained by the inclusion of an ink jet printer (not shown) in the region marked in Fig. 2 by the arrow H adjacent the point where the silicone paper tape 28 leaves the roll 30. The ink jet printer is activated and synchronised by the photocells 36 and can print a simple message on the top surface of the silicone paper strip. This can convey information such as current special offers, thanks for the order, seasons greetings and the like to the mail order customer, if the silicone strip (instead of being thrown away during packaging at the warehouse) is placed in the sack with the merchandise after its removal from the sack to expose the adhesive stripe.

Claims

1. A method of forming a self seal closure on a sack which has a flattened tubular body which is permanently closed at one end and whose opposite end is open and carries a longitudinally projecting flap, the method comprising applying pressure sensitive adhesive to an elongate strip of tape, and pressing the adhesive-carrying tape against the sack so that the adhesive is applied to the sack adjacent its open mouth, the material of the tape being selected such that the tape can be peeled off the adhesive to leave the adhesive on the sack, whereby the flap can then be folded onto the adhesive to close the sack.

2. A method of forming a self seal paper sack comprising: (a) forming an open sack comprising a flatened tubular body which is permanently closed at one end and whose opposite end is open and carries a longitudinally projecting flap, the base of the flap being precreased in order to facilitate easy and accurate folding during the sealing operation; (b) applying pressure sensitive adhesive to an elongate strip of tape; and (c) pressing the adhesive-carrying tape against the sack so that the adhesive is applied to the sack adjacent its open mouth; (d) the material of the tape being selected such that the tape can be peeled off the adhesive to leave the adhesive on the sack, whereby the flap can then be folded onto the adhesive to close the sack.

3. An apparatus for forming a self seal closure on a sack which has a flattened tubular body which is permanently closed at one end and whose opposite end is open and carries a longitudinally projecting flap, the apparatus comprising an adhesive applicator adapted to apply a pressure sensitive adhesive to an elongate strip of tape and means for pressing the adhesive carrying tape against the sack so that the adhesive is applied to the sack adjacent its open mouth, the tape material being such that the tape can be peeled off the adhesive to leave the adhesive on the sack.

4. An apparatus as claimed in claim 3, including a conveyor for carrying a plurality of said sacks, laterally spaced apart, along a linear path, a pressure belt disposed above said path and urged downwardly against said conveyor to provide said means for pressing the tape against the sacks, the adhesive-carrying tape being fed into the nip between the conveyor and the pressure belt so as to be applied to a sack on said conveyor concurrently entering the nip.

5. An apparatus as claimed in claim 4, wherein the tape is fed continuously from a tape supply to said nip, pressure sensitive adhesive being arranged to be applied selectively to the tape at a position upstream of the nip so that the tape receives longitudinally spaced strips of adhesive for application to each of the laterally spaced sacks, respectively.

6. An apparatus as claimed in claim 5, including means disposed upstream of said nip for detecting photo-electrically the leading and trailing side edges of the sacks being conveyed on said conveyor, and means responsive to the detected positions of said leading and trailing side edges of the sacks for controlling said adhesive applicator such that the lengths of the strips of adhesive applied to the tape are less than the width of the sacks.

7. An apparatus for forming a self seal sack comprising means for forming an open sack having a flattened tubular body which is permanently closed at one end and whose opposite end is open and carries a longitudinally projecting flap, an adhesive applicator for applying a pressure sensitive adhesive to an elongate strip of tape, and means for pressing the adhesive-carrying tape against the sack so that the adhesive is applied to the sack adjacent its open mouth, the tape material being selected such that the tape can be peeled off the adhesive to leave the adhesive on the sack.

8. An apparatus as claimed in claim 7, wherein the adhesive is a hot melt, pressure sensitive adhesive.

9. A method of forming a self seal paper sack substantially as hereinbefore described with reference to the accompanying drawings.

10. An apparatus for forming a self seal closure on a sack, substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.