Description:
This invention relates to a plastics-film wrapper provided with a tear-tape, for packages and the like. It also relates to methods of forming such wrappers, especially in shrink-packaging, and to apparatus for use in such methods.
Tear-tapes for plastics-film wrappers have previously been attached to a surface of the film by a bond that is of greater strength than the tear strength of the film in the direction parallel to the tape, or have been provided by weakening the film along parallel lines, for example by lines of perforations.
In accordance with the present invention, a plastics-film wrapper is provided with a tear-tape heat-sealed along each edge to the film by an edge-to-edge seam, the longitudinal tensile strength of the tear-tape relative to the tensile strength of the film in the direction parallel thereto, and/or the strength of the heat-seals, being such that the wrapper will tear along the film adjacent to the heat-seals, or along the heat-seals, when a peeling force is applied to an end of the tape.
The present invention also provides a package formed by enclosing an article or articles in a plastics-film wrapper as just described.
The invention in its broadest scope will now be more particularly described by way of example with reference to FIGS. 1, 2 and 3 of the accompanying drawings, of which:
FIG. 1 is a perspective view of a package provided with a plastics-film wrapper of the invention; and
FIGS. 2 is a section through the tear-tape and the adjacent film.
FIG. 3 illustrates an apparatus and method of wrapping the article.
In FIG. 1 : 1 indicates the contents of the package, in this case two cartons; 2 is a plastics-film wrapper; and 3 is the tear-tape, sealed to the film along each of its edges by a bead seal, as at 4. It will be seen that, unlike applied tear-tapes previously known in the art, the plastics film of the wrapper is not continuous beneath (or over) the tear-tape, but is heat-sealed to the tear-tape by edge-to-edge seams. The wrapper shown in the drawings is a heat-shrink wrapper which has been applied to the package as an open-ended sleeve, and the ends of the wrapper, which initially extended beyond the ends of the cartons, have shrunk around the ends of the pack into contact with the ends of the cartons, the end edges of the shrunk wrapper being shown at 5. The tear-tape may readily be removed by holding an end, 6 thereof and peeling it off the package.
In the package shown in the drawings, it will be seen that the tear-tape is thicker than the film even after shrinkage of the film; and in a preferred form of the invention the tear-tape is made of essentially the same plastics material as the film, but is of a thicker gauge. The invention is used with particular advantage in shrink-packaging, and in such case it is preferred that the tear-tape be less shrinkable than the plastics film of the wrapper; it is generally preferred that the tear-tape 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. It is thus particularly preferred that, for shrink-wrappers, the tear-tape be of film of essentially the same plastics material as the wrapper, but of thicker gauge, and that it be substantially non-shrinkable at the shrinkage temperature of the wrapper.
One preferred method of forming packages according to the present invention is a modification of a known method of shrink-packaging in which articles are enclosed by heat-sealing between two webs of heat-shrinkable plastics film drawn from separate sources. Thus, the present invention further provides a method of forming the package that comprises: advancing an article to be wrapped into a curtain formed by a web of the heat-shrinkable plastics film and a web of the tear-tape material drawn from opposite sources and transversely heat-sealed together to form a continuous curtain across the path of the article; further advancing the article, with withdrawal of said webs from their sources, until the curtain extends round the article to beyond its trailing end, the tear-tape material being withdrawn from its source at a linear speed not exceeding one-fourth of the linear speed of withdrawl of the heat-shrinkable plastics film; transversely heat-sealing and severing the two webs together 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; and subjecting the sleeve to heat sufficient to shrink it upon the article.
The transverse heat-seals formed in this preferred method may be double linear seals, with the line of severance lying between the individual seals; or the webs may be simultaneously severed and sealed together, on each side of the line of severance, for example by means of a hot knife or wire. The sleeve containing the article to be wrapped may conveniently be heat-shrunk upon the article by passing the enveloped article through a shrink tunnel. Meanwhile, the process of applying the sleeve may be repeated for the next article.
The invention further provides, for operating this preferred method, an apparatus that includes means for advancing the articles to be wrapped along a predetermined path; means for supplying a first web and a second web of sheet material from opposite sides of said path, for withdrawal from their supply means around an article on its advancement; a heat sealer for transversely sealing the webs together to form a continuous curtain extending across said path; means for severing said webs along the length of the heat-seal; and control means associated with the web supply means for controlling the relative linear speeds of withdrawal of the webs, such that the first web may be withdrawn from its source of supply at a linear speed not greater than one-fourth of the linear speed of withdrawal of the second web.
This embodiment of the invention will now be more particularly described with reference to FIG. 3 of the accompanying drawings, which is a diagrammatic side view, partly in section, of the apparatus in use.
In FIG. 3 : 7 is a table for supporting successive articles to be wrapped; 8 is a pusher for pushing an article, 9, from the table 7 on to a conveyor, 10, which conveys it through a shrink tunnel, 11; 12 is a reel from which is supplied a first web, 13, of sheet material, which is a heat-sealable tear-tape material; 14 is a reel from which is supplied to the second web, 15, which is of heat-shrinkable, heat-sealable plastics film; 16 is a transverse heat-seal between the two webs, forming them into a continuous curtain across the path of the article, 9; and 17, 18 are the gripping jaws of a heat-sealer for forming a double bead seal, the jaw 17 having mounted thereon, between the two gripping blocks, a heated knife, 19, extending along the length of the jaw, and the jaw 18 being recessed at 20 to receive the knife. The reels 12 and 14 are carried by interconnected gear wheels selected according to the rates required, so that the web 13 may be withdrawn at a linear speed only a predetermined fraction of the speed of withdrawal of the web 15. For example, a ratio of about one-tenth will give a wrapper with a tear tape as shown in FIG. 1.
In operation of the method, with the heat-sealer jaws in the open position, the article 9 (which in the embodiment shown is a pair of cartons) is pushed by the pusher 8 into contact with the curtain formed by webs 13 and 15, which are of equal width, and on to the conveyor 10. 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 webs are withdrawn from the supply reels, web 15 at a much greater linear speed than that of web 13, so that it is drawn across the surface of the article until it largely envelops the article, the tear-tape strip being held back as the article advances. At a suitable interval 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 16, and on the other the advancing package, 9a, 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, 16a and 16b. By passage through the shrink tunnel 11, 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 FIG. 1, an aperture, 5, being left at each end and a tab 6, being formed by each end of the tear-tape, through shrinkage of the film at each side thereof. The tear-tape may be readily grasped by the tab for opening the package.
Many modifications may be made in the apparatus and method particularly described with reference to FIG. 3. For example, the table, 7, in the apparatus shown may be replaced by a continuously moving conveyor, and the heat-sealer may be automatically operated in response to means for sensing the arrival of an article at a predetermined position. The relative speeds of withdrawal of the tear-tape material and of the shrinkable film, and hence the width of the tear-tape in relation to the finished package, may be varied within wide limits to achieve an optimum width, having regard to the size and nature of the article, or group of articles, to be packed. Generally, the tear-tape will be withdrawn at a linear speed considerably less than one-fourth of that of the shrinkable film, although a ratio as high as one-fourth may be suitable for small packages. In general, since the cost of the tear-tape material will usually be considerably higher than the cost of the shrinkable film, the method will be operated in such manner that the width of the tear-tape in the finished package is as small as is consistent with efficient operation of the method and ease of removal of the tear-tape. The same considerations apply to the selection of the width of the tear-tape when methods other than that illustrated by FIG. 3 are used to make the wrapper.
Although, in the embodiments of the invention illustrated by the drawings, the tear-tape web and the web of heat-shrinkable film are of equal width, the tear-tape web may be somewhat wider than the film, so that a portion of the tear tape projects beyond the adjacent edges of the shrunken sleeve at one or both ends in the finished package. Or the tear-tape web may, if desired, be somewhat narrower than the plastics film. Instead of the sleeve extending beyond the ends of the article, to be shrunk around the ends, the sleeve may be no longer than the corresponding dimension of the article, so that, on shrinkage, it forms only a band round the article.
The wrappers of the present invention, shrinkable or non-shrinkable, and packages provided with such wrappers, may be produced by methods other than that particularly described, especially by sealing the tear-tape into a web from which individual wrappers may subsequently be separated. Thus, for example, a longitudinally folded strip of the tear-tape material may be placed between two sheets of the plastics wrapper film, or between the edges of a folded sheet, with the edges of the tear-tape strip level with those of the film, and the edges sealed together in pairs, for example by radiant heat, or by severing the edges in pairs by means of a hot knife or hot wire. If desired, the four thicknesses may be sealed and severed simultaneously, adhesion between the bead seals of the two pairs of edges being prevented by separating them during heat-sealing by an inserted blade or foil, or, preferably, by coating the outer surface of the tear-tape strip with a seal-inhibiting substance, such as printing ink or a suitable lacquer, so that the four layers may be simultaneously severed, and sealed in pairs.
The invention is used with particular advantage in the shrink-wrapping of articles in open-ended sleeves as illustrated by the drawings. The sleeves may initially extend beyond the edges of the 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 preferably be initially of a length not substantially exceeding the corresponding dimension of the article or articles, so that it will not shrink around the ends thereof. The wrapper will generally shrink from each side of the end of the tear-tape, leaving a tab by which the tape may readily be grasped, but an end or the ends of the tear-tape may initially project from the edges of the wrapper, if desired.
The invention may also be applied in shrink-packaging methods in which the wrapper wholly encloses the article or articles to be packed. It may also be used to provide tear-tapes in non-shrink wrappers of plastics film.
Instead of the tear-tape being of essentially the same plastics material as the wrapper, and preferably of a thicker gauge, the tape may be of a different material, for example a tape of a different plastics material preferably having a greater tensile strength than the wrapper, provided that it may be readily heat-sealed to the plastics film of the wrapper. As indicated hereinbefore, the ease of removability of the tape may result from low strength in the heat seals. However, it is generally preferred that the wrapper will tear before the heat-seals, particularly in shrink-wrappers, where there may otherwise be a risk of the seals separating during shrinkage. Generally the wrapper will tear most easily along lines closely adjacent to the heat-seals, where the film will have been somewhat weakened by heat-sealing. In shrink-wrapping, the amount of shrinkage brought about in the wrapper should not of course be so great as to cause tearing of the wrapper or separation of the heat seals during the shrinking process. The heat seals are preferably bead seals, but other methods of edge-to-edge heat-sealing may be used if desired. For shrink-wrapping applications, the plastics tear-tape is preferably formed of essentially the same plastics material as the shrinkable film, but it is preferably film of a thicker gauge than the film of the wrapper after shrinkage. In general, however, the tear-tape web may be a plastics web of another kind, for example, a woven or spun-bonded web. It may be of a plastics material different from that of the wrapper film, provided that it is readily heat-sealable to the film.
The invention provides a simple and economical method of providing tear-tapes, especially 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 equally suitable for making the tear-tape webs. The invention may be used for packaging articles irrespective of the size of the articles, especially by shrink-wrapping or shrink-banding. 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. If desired, complete coverage of the articles may be obtained by the sleeve-wrapping method particularly described, by applying a second wrapper, or band, at an angle of 90° to the first.