IE42745B1 - Packaging method - Google Patents

Abstract

1508126 Packaging BRITISH VISQUEEN Ltd 25 March 1975 [30 April 1974] 18875/74 Addition to 1335304 Heading B8C A method of wrapping an article comprises advancing the article, 3, against a curtain formed by a web 9 of heat-shrinkable plastics film and a web 7 of a tear-tape material drawn from supply means 8, 6 respectively on opposite sides of the path of the article and transversely heat-sealed together at 10 to form the curtain across the path of the article. The article is then further advanced into the curtain, with further withdrawal of the material from the web supply means, until the curtain extends around the article to beyond its trailing end, the tear-tape material 7 being withdrawn non-continuously from its supply means so that a predetermined length not greater than “ of the length of the perimeter of the article in the direction of its advancement is withdrawn. The two webs are then transversely heat sealed together and severed behind the article to leave on one side the article 3a enveloped or partially enveloped in a sleeve formed from the two webs, and on the other side the two webs sealed together to form again a curtain. As described, the article 3 is advanced by a pusher 2 into the curtain and on to a conveyer 4 which, after sealing and severing of the webs by heated jaws 11, 12 and knife 13, carries the package into a shrink tunnel 5. The supply roller 6 for the tear-tape material is braked intermittently so that the tear-tape extends over 1/ 9 to 1/ 11 of the article perimeter. Preferably the brake is released as the jaws 11, 12 open and is applied when a stud 19 on a roller 17 actuates a micro-switch 18. Alternative actuating means, e.g. photo-electric, pneumatic, or magnetic, or marks on the tear-tape web, or a controlled dancer roll may be used to control the length of material fed. The curtain may be narrower or wider than the article fed and its end edges may be heatsealed. The tear-tape web may be wider than the other. Two webs of the heat-shrinkable material may be supplied to form a double layer. The webs may be of similar materials, e.g. polyethylene, polypropylene, or copolymers thereof.

Description

This invention relates to a method of shrink-wrapping articles in plastics film, which is a modification of a method claimed in Patent Specification No. 38957 which describes and claims a plastics-film wrapper provided with a tear-tape heat-sealed along each edge to the film by an edge-to-edge seam, the strength of the heat-seals, and/or the longitudinal tensile strength of the tear-tape relative to the tensile strength of the film in the direction parallel thereto, being such that the wrapper will tear along the heat-seals, or along the film adjacent to the heat-seals, when a peeling force is applied to an end of the tape.

Also described and claimed in Patent Specification No. 38957 is a method of forming a package provided with such a wrapper. This method is a modification of a method previously well-known and used for packaging articles by shrink-wrapping, in which an article to be wrapped is advanced into a curtain formed by two webs of heat-shrinkable plastics film drawn at substantially the same rates from opposite sources and transversely heat-sealed together to form a continuous curtain across the path of the article, is then further advanced, with withdrawal of the webs from their sources, until the curtain extends round the article to beyond its trailing end, and the two webs are then transversely heat-sealed together and severed behind the article so as to leave, on one side of the line of severance, the article enveloped or partially enveloped in a sleeve formed from the webs, and on the other side the two webs sealed together to form again a curtain. Finally, the sleeve is subjected to heat sufficient to shrink it upon the article. In accordance with Patent Specification No. 38957 this method is modified by substituting a web of tear-tape material for one of the webs of heat-shrinkable plasties film, and arranging for the tear-tape material to be withdrawn from its source at a linear speed not exceeding 1/4, and preferably equal to about 1/10, of the linear speed of withdrawal of the heat-shrinkable plastics film, so that it forms only a relatively narrow strip in the wrapper. In the method particularly described, supply reels for the webs are carried by interconnected gear wheels such that the tear-tape material may be withdrawn continuously during the formation of the wrapping, at a predetermined fraction of the speed of withdrawal of the heat-shrinkable web.

We have now found that there are substantial advantages to be had in providing the tear-tape in such a method by supplying a predetermined length of the tear-tape material discontinuously during the formation of the wrapping, rather than by supplying both materials concurrently but at different rates. Thus, the average liner speed of supply of the teartape material is still only a fraction of that of the heatshrinkable film, but the complications of providing and adjusting a continuous supply of the two webs at the rates required are avoided.

In accordance with the present invention, therefore a method of forming a package in which an article is wrapped in a heat-shrinkable plastics film wrapper provided with a teartape which is heat-sealed along each edge to the film by an edge to edge seam, the strength of the heafseals and/or the longitudinal tensile strength of the tear-tape relative to the tensile strength of the film in the direction parallel thereto being such that the wrapper will tear adjacent to the heat-seals when a peeling force is applied to an end of the tape, comprises advancing the article against a curtain formed by a web of the heat-shrinkable plastics film and a web of the tear-tape material drawn from supply means on 437 45 opposite sides of the path of the article and transversely heat-sealed together to form the curtain across the path of the article; further advancing the article into the curtain, witli withdrawal of material from the web supply means, until the curtain extends around the article to beyond its trailing end, the tear-tape material being withdrawn non-continuously from its supply means and in such manner that its withdrawn length is not greater than 1/4 of the total length withdrawn from the two supply means; and transversely heat-sealing together and severing the two webs behind the article to leave, on one side, the article enveloped or partially enveloped in a sleeve formed from the webs, and on the other side the two webs sealed together to form again a curtain, and subjecting the sleeve to heat sufficient to shrink it around the article.

The said article to be packaged by the method may be a number of individual articles to be collectively packaged. The article may be advanced against and into the curtain from any direction, the supply means and heat20 sealing means for the webs being appropriately located.

In the methods of this type normally used for shrink-wrapping, the article is advanced horizontally from a position on one side of the curtain to a position on the opposite side; but it may alternatively be advanced upwards, or dropped, into a curtain formed horizontally.

The tear-tape material is preferably withdrawn during a single phase of the wrapping operation only, and it will generally be convenient to arrange for this to take place at the beginning of the operation. The tear-tape preferably forms about 1/10, say from 1/11 to 1/9, of the total length withdrawn from the two supply means.

Some particular forms of the method of the invention will now be. more particularly described by way of example with reference to the accompanying drawings, of which: Figure 1 is a diagrammatic side view, partly in section, of a packaging line, and 43745 Figure 2 is a perspective view of a finished package.

In Figure 1: 1 is a table for supporting successive articles to be wrapped? 2 is a pusher for pushing an article, 3, from the table 1 on to a conveyor, 4, which conveys it through a shrink tunnel, 5; 6 is a reel from which is drawn a first web, 7, of sheet material, which is a heat-sealable tear-tape material; 8 is a reel from which is drawn the second web, 9, which is of heat-shrinkable, heat-sealable plastics film; 10 is a transverse heat-seal between the two webs, forming them into a continuous curtain across the path of the article, 3; and 11, 12 are the gripping jaws of a heat-sealer for forming a double bead seal, the jaw 11 having mounted thereon, between two gripping blocks, a heated knife, 13, extending along the length of the jaw, and the jaw 12 being recessed at 14 to receive the knife.

The reel 8 is driven by roller 15 at a constant rate adjusted in accordance with the rate of use of the web 9 during the wrapping, the web 9 being withdrawn through a web accumulator, 16. The reel 6 is rotatable, and is arrested by a ratchet coupled to its shaft and worked by signals generated through a microswitch, 18, activated by projecting studs, 19, mounted on one end of a roller 17.

The ratchet release mechanism is activated by the release of the heat-sealer jaws, 11, 12, from the heat-sealing position. 20 is a friction roller provided to prevent excessive slackening of the web 7 upon roller 17 when its withdrawal is arrested. The studs 19 are arranged at intervals appropriate to the predetermined length of the tear-tape desired for the wrapping.

In operation of the method, with the heat-sealer jaws in the open position the article 3 (which in the embodiment shown is a pair of cartons) is pushed by the pusher 2 into contact with the curtain formed by webs 7 and 9, which are of substantially equal widths, and on to the conveyor, 4.

The curtain and the lower jaw of the heat-sealer partially support the package as it crosses the gap, and during the advancement of the article the predetermined length of web is withdrawn, usually at the start of the wrapping, and 4374S at the same time web 9 is withdrawn from the web accumulator and continues to be withdrawn, slipping across the surface of the article, until it envelopes the article, the teartape web 7 being held back as the article advances. After the trailing end of the article has passed the heat-sealer, the heat-sealer is brought into operation to seal together and sever the webs transversely, leaving on one side a continuous curtain of web, freshly seamed as at 10, and on the other the advancing article, 3a, loosely wrapped in a sleeve, 21, of the shrinkable film, the sleeve being provided with a tear-tape, 22, seamed into the wrapper by the first and second heat-seals, 10b and 10a. By passage through the shrink tunnel 5, the sleeve is shrunk around the article and over the ends thereof into close contact with the article, to form a package as shown in Figure 2, an aperture, 23, being left at each end and a tab, 24, being formed by each end of the tear-tape, 7, through shrinkage of the film at each side thereof. The tear-tape may be readily grasped by the tab for opening the package. The length of the tear-tape web, 7, metered for the wrapping of each article, and hence the width of the tear-tape in the package, is not critical, provided that the tape is sufficiently strong in relation to the tear strength of the other web, and to the size of - the package, to provide for efficient opening of the package. Moreover, some variation in the length of tear-tape web segment can usually be tolerated, to allow for such factors as, for example, the travel of roller 17 to the first stop position after the arresting mechanism has been brought into operation.

If desired, the tear-tape web may be somewhat wider than the web forming the main part of the wrapper, to provide a longer tab at one or both ends of the tape in the finished package.

Many other modifications may be made in the apparatus and method particularly described with reference to the drawings. For example, instead of the stud-and-microswitch arrangement described for activating the arresting mechanism for roller 6, other means of signalling may be used to - 7 arrest the supply of tear-tape web after a desired amount has been provided . Thus, for example, signals generated by a photoelectric beam passing through holes in a disc or drum attached to the roller 17, or by a pneumatic sensing of such holes, may be used, as may signals generated by the sensing of magnetic studs or implants on or associated with the roller, or by proximity detectors, such as inductance probes, sensing projections on the roller. Alternatively, calibrating devices on the tear-tape web, such as printed lines for activating photoelectric switches, or perforations activating pneumatic switches, may be used to bring the arresting mechanism into operation at the desired intervals.

In another method of metering the tear-tape material, a three-roll (or multiple-roll) accumulator, such as that shown for the second web in Figure 1, may be used, but in this case the dancer roll is mechanically displaced by an amount calculated to give the desired length of tear-tape material. For the downward (lengthening) movement of the dancer roller, the output roller from the accumulator is arrested and the input roller released; for the upward (shortening) movement of the dancer roller, by which the tear-tape length is fed to the wrapping operation, the input roller to the accumulator is arrested and the output roller released.

The invention is used with particular advantage in the shrink-wrapping of articles in open-ended sleeves as illustrated by the drawings. The sleeve may initially extend beyond the edges of the article or articles, as shown, or the wrapper may be used merely to form a band round the article or articles, in which case the sleeve will be initially of a length not substantially exceeding the corresponding dimension of the article or articles, so that it will not be drawn around the ends thereof. Alternatively however, the sleeve may extend beyond the ends of the article and Its end edges may be joined by heat-sealing, so that in the finished package the article is wholly enclosed in the wrapper.

In a preferred form of the method of the invention the tear-tape is made of essentially the same plastics material as the film, but is of a thicker gauge, and in such case it is preferred that the tear-tape be less shrinkable than the plastics film of the wrapper, and especially that it be substantially non-shrinkable. The use of a tape that will not shrink, or will shrink only slightly, at the shrinkage temperature of the wrapper, gives the advantage that a legend or decoration may be printed on the tape, and the print will not become distorted on shrinkage of the wrapper. The tear-tape may be of a plastics material different from that of the wrapper film, provided that it be readily heat-sealable to the film.

The method of the invention may be used to wrap articles in a double layer of plastics film, by providing a web of doubled film, or two webs supplied Prom separate reels, at the side opposite the tear-tape material, and heat-sealing the tear-tape and the two layers together s imultaneously.

The invention provides a simple and economical method of providing tear-tapes for wrappers of plastics films that may be readily heat-sealed, particularly by means of a hot knife or hot wire as hereinbefore described. Such materials include the polyolefines, especially polyethylene, polypropylene, copolymers of ethylene and propylene, and copolymers of ethylene or propylene with other ethylenically unsaturated monomers. These plastics materials can be formed into both shrinkable and non-shrinkable films, by suitable modification of the film-forming methods, and are thus equally suitable for making the teartape webs. The invention may be used for packaging articles irrespective of the size of the articles. Thus, it may be used for overwrapping relatively small articles, such as boxes of confectionery, or for wrapping very large ones, as, for example, in the shrink-wrapping of loaded pallets.

Claims (5)

1. CLAIMS:1. A method of forming a package in which an article is wrapped in a heat-shrinkable plastics film wrapper provided with a tear-tape which is heat-sealed along each edge to the film by an edge to edge seam, the strength of the heat - seals and/or the longitudinal tensile strength of the tear-tape relative to the tensile strength of the film in the direction parallel thereto being such that the wrapper will tear adjacent to the heatseals when a peeling force is applied to an end of the tape, the method comprising advancing the article against a curtain formed by a web of the heatshrinkable plastics film and a web of the tear-tape material drawn from supply means on opposite sides of the path of the article and transversely heat-sealed together to form the curtain across the path of the article; further advancing the article into the curtain, with withdrawal of material from the web supply means, until the curtain extends around the article to beyond its trailing end, the tear-tape material being withdrawn non-continuously from its supply means and in such manner that its withdrawn length is not greater than 1/4 of the total length withdrawn from the two supply means; and transversely heat-sealing together and severing the two webs behind the article to leave, on one side, the article enveloped or partially enveloped in a sleeve formed from the webs, and on the other side the two webs sealed together to form again a curtain, and subjecting the sleeve to heat sufficient to shrink it around the article.

2. A method as claimed in Claim 1 in which the tear-tape material is withdrawn during a single phase of the packaging operation only.

3. A method as claimed in Claim 1 or Claim 2 in which the web of heat-shrinkable film comprises two layers of film.

4. A method as claimed in anyone of the preceding claims in which the tear-tape material forms from 1/11 to 1/9 of the total length withdrawn from the two supply means.

5. A method as claimed in Claim 1 and substantially as