Apparatus and method for the manufacture of easy-to-open shrink sleeve wrap packages

Abstract

 The invention concerns a method of manufacturing an easy-to-open shrink sleeve wrapped package comprising wrapping up one or more products in a shrink thermoplastic film and submitting the obtained sleeve to a heat shrinking step to give a tight package, wherein the package comprises a tear strip defined by perforations to facilitate opening of the package, said method being characterized in that a) the tear strip is defined by a close sequence of pairs of mutually diverging weakness segments, having the same or substantially the same shape and size, and diverging in the same direction, and b) said sequence of pairs of mutually diverging weakness segments is created by perforating across the film width before the wrapping step.
The invention also concerns a unit for perforating a film.

Description

Technical field

[0001] The present invention relates to an apparatus and method for producing new shrink sleeve wrap packages comprising an easy-to-open tear strip defined by a peculiar pattern of perforations created across the width of the thermoplastic packaging material.

Background of the invention

[0002] Typically in shrink sleeve wrapping, an article to be packaged or a plurality of articles that are to be formed into a unit for distribution or transportation, are conveyed by an automatic in-feed conveyor to a sleeve wrapping machine, wrapped up in a shrink film which is then transversely sealed into a tubular form and conveyed to a heat tunnel where the wrapping film will shrink to conform to the packaged article or plurality of articles, in the latter case holding them together in a tightly packed condition.

[0003] Shrink sleeve wrapping can be used to individually package a single article, such as for instance any yarn holder in textile, such as bobbins, tubes and the like, or to combine two or more different articles that however need to be sold or at least distributed together, or to collate a plurality of the same article in a single unit. Since this last one is the most interesting application of shrink sleeve wrapping, in the following the apparatus and method of the present invention will be discussed in relation therewith, but this should not be interpreted as a limitation to the scope of the appended claims.

[0004] There are essentially two main processes for shrink sleeve wrapping, i.e. a single roll shrink sleeve wrapping process, which can be considered a discontinuous process, and a two-rolls shrink sleeve wrapping process, which is a continuous process.

[0005] In the former method a single sheet of shrink wrap film of suitable size is cut from a roll of film and is wrapped around the articles to be packaged, that are grouped together, with or without a supporting tray, to form a desired external configuration, thus forming a tube that covers the top, bottom and the leading and trailing sides of the collation, with the longitudinal edges of the film projecting beyond the other two side edges thereof. The leading edge of the sheet will then be overlapped by the trailing edge, typically on the bottom of the package, i.e., underneath the collation, and be sealed thereto. This occurs before the collated package enters into the heated shrink tunnel or preferably at the same time. In the former case any sealing system and preferably any heat-sealing system can suitably be employed, while in the latter case it will be the pressure created by the weight of the products in combination with the high temperature reached in the heated shrink tunnel to give the overlapped transverse seal. In the heated shrink tunnel, the film will shrink tightly around the collated products with the projecting longitudinal edges collapsing against the side edges of the collation thus creating, in a film thickened area, the so-called " bullseyes" , i.e. openings that are typically used for gripping, sufficiently large to allow introduction of the fingers of one hand and sufficiently resistant to allow raising the collated package and moving it without any rupturing.

[0006] In the two-rolls process, the shrink film is fed from two different rolls, an upper roll and a lower roll. A first transverse seal joins the leading edges of said two films, a collation of products is then pushed against said transverse seal pulling both films to wrap up the collation and a second transverse seal is then created behind the collation at the same time as a transverse cut to severe the sealed package from the film webs and the front transverse seal between the leading edges of the next package. The loosely wrapped up package is then conveyed to a heated shrink tunnel to complete the packaging process as seen for the single roll system.

[0007] In both processes one of the main problems is to obtain a package that besides keeping the articles together in a tightly manner as a self-contained unit may also make them easily accessible and removable from the package, if and when desired, by the application of an appropriate force, in a relatively simple, effective, and non time consuming manner without requiring the use of cutting devices that may adversely affect the packaged articles and/or create a safety problem if not used correctly.

[0008] In most of the applications furthermore it would be highly preferable to have an easy-to-open package that may make the packaged products selectively accessible and removable by the application of an appropriate force, while the remainder of the package still may be treated as a self-contained unit. This would in fact allow selective removal of only some of the packaged articles, e.g., a number sufficient to fill in the shelves of a shop, while the package containing the others can still be moved as a single unit.

[0009] Collated packages containing tear strips defined by perforations that can be torn when the articles are to be removed are known in the prior art. This is typically achieved by applying perforations to the film in its running direction, i.e. parallel with the edges of the film web. However the packages known in the art suffer from certain inadequacies. In most of the cases in fact tearing of the strip produces a weakening of the whole package and usually allows only a few of the packages to be released easily from the shrink sleeve while keeping the remaining articles within the package.

[0010] When more sophisticated systems are devised that could solve this problem, then the apparatuses required and the manufacturing methods involved are quite elaborated and not easily, if at all, retrofittable, making them non-applicable on an industrial scale.

[0011] It is therefore an object of the present invention to address this problem and provide a method and apparatus for the manufacture of an improved easy-to-open shrink package that can be easily applicable on industrial scale. It is another specific object of the present invention to provide a device that can be used to retrofit the existing shrink sleeve wrapping machines with the aim at manufacturing improved easy-to-open shrink sleeve wrapped packages.

Summary of the invention

[0012] The first object of the present invention is a method for the manufacture of an easy-to-open shrink sleeve wrapped package wherein the package contains a tear strip defined by a specific pattern of perforations which is created transversally in the film web, i.e., it is created in a direction that is at 90 degrees to the direction of movement of the film.

[0013] The second object of the present invention is the device that is used for the creation of the transversal tear strip, the third object is the machine for shrink sleeve wrapping that incorporates said device, and the fourth object is said machine for shrink sleeve wrapping that further incorporates an applicator which affixes a lift tab label to the final shrink package.

Brief description of the drawings

[0014] Figure 1is a plan view of the packaging film comprising a tear strip with a specific pattern of perforations created in accordance to the present invention;

[0015] Figure 2 is a prospective view of a shrink sleeve wrapped package with the tear strip according to the embodiment of Figure 1obtained by the process of the invention;

[0016] Figures 3a, 3b, and 3c are plan views of different alternative slits created at the tear strip starting position;

[0017] Figure 4 is a schematic illustration of the two rolls shrink sleeve wrapping process including the step of creating the tear strip;

[0018] Figure 5 is a cross-sectional view of one embodiment of the perforating device which is used in the process of Figure 4 to create the tear strip;

[0019] Figure 6 shows cross-sectional views of an exemplary knife used in the process and device of the invention;

Detailed description of the invention

[0020] With reference to Figure 1, 10 is the film web, the arrow indicates the longitudinal direction in which film 10 is moved, 11 indicates the easy-to open strip which is created and defined by the sequence of pairs of mutually diverging weakness segments, 12,12', across the film web. The film as known in the art is typically made of a mono- or multi-layer thermoplastic material, and is flexible enough to be used in a wrapping process, it is heat-sealable, as in the shrink wrapping process it is normally heat-sealed either to itself, in the single roll process, or to another thermoplastic film, in the two roll process, and it is a shrink film, i.e., it shrinks at least in the longitudinal direction when heated to the temperature reached in a conventional heat shrink tunnel, so as to tightly cling to the packaged articles. Shrink films for shrink sleeve wrapping applications have a thickness generally comprised between about 12 and about 150 µm, depending on the type, weight and number of articles to be packaged. For most of the conventional shrink sleeve wrapping applications, suitable shrink films have a thickness preferably comprised between about 35 and about 120 µm. They might be cold- or solid-state oriented films, i.e., films obtained by extrusion or co-extrusion, followed by a quenching step, a reheating to a temperature below the melting temperature of the thermoplastic material employed and a bi-axial or preferably mono-axial stretching. Preferably and more conveniently however films used for shrink sleeve wrapping applications are obtained by hot blown. In said process the orientation is typically only, or mainly, in the longitudinal direction and is obtained at a temperature very close to the melting temperature of the thermoplastic material employed.

[0021] Typical thermoplastic materials employed in shrink sleeve wrapping processes are polyolefins, and in particular ethylene homo- or co-polymers and propylene homo- or co-polymers. The tear strip 11 is the area of film surface comprised between the sequence of pairs of weakness segments 12,12'. The two weakness segments making up each pair, are symmetrically positioned with respect to a transverse axis passing between them and are diverging with respect to said axis. The various pairs, still indicated in the drawings with the numerals 12,12', have preferably the same shape and the same size, diverge in the same direction, i.e., the direction of tearing, and are sequenced, one over the other, across the film width. Therefore said tear strip 11 will have a minimum width, given by the minimum distance between each pair (a), and a maximum width, given by the maximum distance (b) between each pair. The value of (a) will be chosen in such a way to give a tear strip that can be easily grasped by hand and is sufficiently resistant not to break during the tearing-off. A typical value for (a) would thus be in the range 1.5 to 4 cm, preferably 2 to 3 cm. As anticipated, the weakness segments of each pair will not be parallel but mutually diverging. Preferably they will be slightly diverging, wherein, as used herein, this will mean that the angle between the two lines of which the segments are part will not be higher than 30°, typically comprised between 5° and 20°. The maximum distance (b) will thus depend, for a given angle, on the length of each pair of segments. Generally the length of segments 12 and 12' is comprised between about 3 and about 7 cm, preferably between about 4 and about 6 cm, and more preferably around 5 cm. The angle between segments 12 and 12' and the length thereof will then dictate the width of the receiving slots for the perforator blades shown in figure 5 (slots 44 and 45 in the stationary backing 43).

[0022] The weakness segments are obtained by perforating the film. The perforations in said segments, after shrinking, can have the shape of circular holes but perforations with an elongated dash-like shape are preferred. They should be arranged in sufficient proximity to one another linearly to permit the shrunk wrap film to open along the perforations upon application of a reasonable manual force. By way of example, dash-shaped perforations, from about 2 to about 5 mm long, separated by a similar length, would generally provide the desired easy tearing of the strip 11.

[0023] Figure 1 illustrates how each pair of weakness segments ends before the beginning of the next pair. The distance (d) between the terminal edge of one pair of weakness segments and the next pair is small enough to allow conjunction between the two as a result of tear extending from the end of the opened pair of weakness segments to the next pair when tearing of the strip is continued. Said distance (d) however should not be too small as in such a case it would be difficult to control the force required to break the desired number of pairs of weakness segments. Typically said distance will thus be comprised between at least about 0.5 and about 3.0 cm, preferably between about 0.6 and about 2.8 cm and more preferably between about 0.7 and about 2.5 cm.

[0024] As illustrated in Figure 1 the perforations do not reach the edges of the web and preferably they are sufficiently distant therefrom that it will be possible to grip and move the end shrunk package by the bullseye openings without risking the inadvertent rupture of the package. In a most preferred embodiment, illustrated in Figure 2, the film web will be perforated in such a way that a tear strip will be present only on one surface of the end shrunk package. Preferably the tear strip will be centered on one surface of the end package, generally the top surface, leaving an area of from about 3 to about 10 % of the package width, on each edge, non perforated.

[0025] In Figure 1,13 represents a typical slit that links the starting edges of the first pair of weakness segments 12,12'. The aim of slit 13 is to create a starting position for the tear strip 11 or even a pull tab that facilitates opening. Once one finger has been inserted into the slit and it is thus possible to grasp the film, it would be sufficient to apply an upwardly and outwardly directed force thereto to cause the desired pairs of weakness lines to break, thus forming a tear strip of the desired length from the starting position, and thus be able to selectively remove only some of the packaged articles while maintaining the remaining ones within the self-contained unit. The shape of the slit is such to ensure that it severs the film transversely between the two starting perforations of the first pair of weakness segments. Figures 3a, 3b, and 3c illustrate different possible shapes of the slit 13. In one embodiment, illustrated in Figure 3a, the slit has the shape of an inverted V while in the embodiment illustrated in Figure 3b the slit is slightly concave. In the preferred embodiment illustrated in Figure 3c, the slit 13 is slightly concave and its edges 13a and 13b extend beyond the transverse weakening segments. This configuration of the slit 13 will facilitate the complete opening of the package when and if this is desired. Other shapes may however be easily envisaged.

[0026] The package illustrated in Figure 2 contains an array of articles indicated by numeral 22. The tear strip is obtained by a sequence, in this example, of five pairs of weakness segments 12,12'. A slit 13 co-joins the two segments of the first or top pair. In said Figure 2 there is also an adhesive label or tape-like member 14. Part of the surface of said label or tape-like member 14 facing the package surface comprises an adhesive, such as a pressure-sensitive adhesive and is indicated in Figure 2 as 14a. Said part is secured to the surface of the package covering and closing the slit 13 that defines the tear strip starting position, while the non adhesive part of the label or tape-like member 14, indicated in Figure 2 as 14b, covers the non perforated edge of the package beyond slit 13. The label or tape-like member 14 provides extension means for pulling the tear strip from the starting position created by slit 13 when desired and also serves the purpose of preventing the slit 13 from being accidentally pulled. It is preferably suitably colored or printed to give to the end user a clear indication of the presence of a tear strip and of the direction of tearing to be applied. In said Figure 2, 17 is the side bullseye opening formed in the end shrunk package 10.

[0027] Figure 4 schematically illustrates the method according to the present invention that provides for the creation of the tear strip with the above indicated pattern by perforating the shrink film, across the film width, before the wrapping step. In said Figure 4, 21 is an in-feed conveyor where the articles to be packaged 22 are grouped together in the desired configuration and moved to face the wrapping films. The upper shrink wrap film 25 is unwound from an upper film roll 24 and delivered through a plurality of dance bars 26 which create film tension to the perforating unit 27, that will be described in detail in connection with Figure 5. The lower shrink wrap film 29 is delivered from the lower film roll 28. A lowering heat-sealing jaw 30 and fixed position sealing jaw pad 31 create the rear transverse seal 15 of one package and the front transverse seal 16 of the next package and severe, by means of a blade or knife positioned in-between the two sealing bars and parallel thereto, the two packages. The array of articles 22 on the edge of conveyor 21 is then pushed by pusher 23 against the sealed films as soon as the sealing jaw 30 opens up, and is transferred to adjacent conveyor 32, pulling with it the upper and the lower films. Conveyor 32 then brings the separated package 18 to a suitably heated shrink tunnel 33 where the loose tube of shrink film wrapping the array of products in package 18 shrinks and tightly clings to the products giving the end shrunk package 10, with the side bullseye openings 17. The end package is then removed through an out-feed conveyor 34 and if desired it is transported on suitable conveyoring 35 to a position where an applicator 36 (schematically represented) applies thereto the pull to open label 14, to complete the process. In such a case it is preferred that the applicator 36 is sufficiently distant from the shrink tunnel 33, e.g. from about 1 to about 4 m, to allow partial cooling of the package to take place before application of the label. Alternatively the applicator 36 could be closer to the shrink tunnel 33 but in such a case a cooling fan or anyway a cooling system should preferably be provided between the two.

[0028] The perforation process that occurs in the perforating unit 27 is an intermittent process (while the unwinding of film 25 from the roll 24 is a continuous process) and coincides with the closing cycle of the sealing jaw 30 to the sealing jaw pad 31 that makes the sleeve wrap around the articles to be packaged. Alternatively it would also be possible to use reciprocating sealing jaws, where both the upper and the lower jaws move one towards the other.

[0029] Figure 5 illustrates in detail perforating unit 27. In said unit the upper film 25 delivered through the dance bars 26 is intermittently clamped between two clamps 40 and 41, where the upper parts 40a and 41 a move downward in a direction perpendicular to the film web against corresponding lower stationary parts 40b and 41 b to trap the film. A perforating device 42 is positioned above the film web between the two upper clamps 40a and 41 a. Once the film has been clamped, the perforating device lowers against a stationary backing 43 and creates the specific pattern of perforations described above. Clamping occurs along the whole width of the film web or at least along that width of the film web that will be perforated. Clamping can occur simultaneously by lowering and pressing both upper clamps at the same time or the upstream clamp 40 may be actioned first and the downstream one 41 immediately after, to further tension the film between the two clamps. The distance between the two upper clamps should be sufficient to allow the easy vertical movement of the perforating device 42 between them but not much larger than that. While pneumatic clamps are typically employed and are generally preferred, any other type of clamps, e.g., hydraulic, oleodynamic, electric, or spring actuated clamps, may be suitably employed.

[0030] In correspondence with at least the perforating device 42, the lower stationary backing 43 will contain cavities positioned in such a way to allow lowering of the knife into the backing to the desired extent thus creating the desired perforation pattern. While said cavities in the lower stationary backing may correspond precisely to the design of the knife, a better flexibility can be obtained by the use of a stationary backing 43 with two separate parallel channels, 44 and 45, positioned at a distance equal to or lower than the minimum distance (a) of each pair of weakness segments, where each of said channels has a suitable depth as well as a width suitable to receive the set of knives that create one of the two sequences of parallel weakness segments of the tear strip.

[0031] In Figure 5, 46 indicates a dancing roll that is secured to the perforating unit frame by fixing one or both of its ends in one or respectively two slots 47. The position of said dancing roll 46 can be varied, by raising or lowering it along side slots 47, whenever an adjustement of the positioning of the tear strip on the package surface is required.

[0032] Figure 6a is a cross-sectional view of the knife 50 used for the creation of the pair of weakness segments of Figure 6b, while Figure 6c is a front view of the same knife. The cutting edge of the knife 50 is serrated with narrow teeth of the same size and triangular sharpened shape. The knife will engage with the film in the perforating device and generally penetrate into the film by from about 20 to about 70 % of the teeth height (from the cutting edge to the valley). The size of the teeth is then suitably selected so as to obtain perforations in sufficient proximity to one another linearly to permit the shrunk wrap film to open along the perforations upon tearing. Typically when dash-shaped perforations are used to create the weakness segments, the perforations will preferably be from about 2 mm to about 5 mm long and separated by a similar unperforated length.

[0033] When the single roll shrink sleeve wrapping process is employed, the perforations can be made by using a perforating unit device as described above or alternatively a rotary cutter where a knife capable of providing the desired perforation pattern is slideably mounted thereon or is integral thereto.

Claims

1. A method of manufacturing an easy-to-open shrink sleeve wrapped package comprising wrapping up one or more products in a shrink thermoplastic film and submitting the obtained sleeve to a heat shrinking step to give a tight package, wherein the package comprises a tear strip defined by perforations to facilitate opening of the package, said method being characterized in that

a) the tear strip is defined by a close sequence of pairs of mutually diverging weakness segments, having the same or substantially the same shape and size, and diverging in the same direction, and

b) said sequence of pairs of mutually diverging weakness segments is created by perforating across the film width before the wrapping step.

2. The method of claim 1 wherein the perforation is carried out intermittently while the film web is clamped and kept tensioned.

3. The method of claim 2 wherein the film is clamped on either side of the perforating device and closely thereto.

4. The method of claim 2 wherein the perforation of the film web is synchronized with the sealing cycle of the sleeve wrapping process.

5. The method of any of the preceding claims wherein the perforations are in sufficient proximity to one another linearly to permit the shrunk wrap film to open along said perforations upon application of a reasonable manual force.

6. The method of any of the preceding claims wherein the perforations have an elongated dash-like shape.

7. The method of any of the preceding claims wherein the starting edges of the first pair of mutually diverging weakness segments are joined by a slit to define the tear starting position.

8. The method of claim 7 wherein a partially adhesive label or tape-like member is applied, with the adhesive part, over the slit.

9. The method of claim 8 wherein the partially adhesive label or tape-like member is a linerless label.

10. A unit 27 for perforating a film for shrink sleeve wrapping applications to create therein an easy-to-open tear strip, which unit comprises a perforating device 42, equipped with a knife 50 with teeth arranged to provide for the desired perforation pattern, an opposite stationary backing 43, carved with two channels 44, 45, of suitable size to receive the knife, and, close to the perforating device 42, an upstream clamp 40 and a downstream clamp 41 to block and tension the film web during perforation, so that perforation is carried out intermittently across the film web.

11. The unit of claim 10 wherein the clamps 40 and 41 are pneumatic clamps.

12. The unit of claim 10 wherein the knife of the perforating device is arranged to create a sequence of pairs of mutually diverging weakness segments, having the same or substantially the same shape and size, diverging in the same direction, and being sequenced, one over the other across the film width.

13. The unit of claim 12 wherein the knife of the perforating device does not reach the edges of the film web.

14. A shrink sleeve wrapping machine comprising means for unwinding the packaging film(s), means for wrapping the unwound film(s) loosely around the articles to be packaged, means for transverse sealing and cutting off the loosely wrapped up packages and means for heating them to shrink the loose sleeve around the articles, said machine being characterized in that it further comprises a perforating unit 27 as in any of preceding claims 10 to 13 positioned between the film(s) unwinding means and the wrapping means.

15. The shrink sleeve wrapping machine of claim 14 which further comprises an applicator 36 of a partially adhesive label or tape-like member positioned downstream the heating means.

16. The shrink sleeve wrapping machine of claim 15 wherein the partially adhesive label or tape-like member is a linerless label.

17. The shrink wrapping machine of claim 16 which is a two rolls shrink sleeve wrapping machine.

Drawing