GB2062573A - Shrink wrapping process and shrink wrapped package - Google Patents

Abstract

An article, e.g. a lamb carcass, having a re-entrant, e.g. at the base of the carcass rib cage, is shrinkwrapped by applying a flexible shrinkable sheet material to the article so as to leave an overlap, e.g. a pleat(s) of adjacent portions of the body of the sheet over the re-entrant. The sheet is then shrunk, the amount of overlap and degree of shrinking being sufficient to leave slack film over the re-entrant. Handling of the article is thus facilitated, since it can be gripped in the region of the re-entrant.

Description

SPECIFICATION Shrink wrapping process and shrink wrapped packages The present invention relates to a method of packaging articles having a re-entrant.

The shrink wrapping of articles with shrinkable sheet material, initially in flat, tubular or bag form, for example, is well known in the art. It is sometimes desirable to be able to shrink-wrap articles which have a re-entrant. The usual shrink wrapping process produces a package in which the sheet material used for the shrink wrapping is in its final form stretched taut across the reentrant. This may be undesirable because it causes difficulty in handling the packaged articles.

Thus it is not possible to grip the article by the reentrant because of the shrink wrap sheet stretched across the re-entrant. Further, the packaged articles may be more likely to slide relative to one another in a container in which they are placed, which may produce a safety hazard.

A specific problem arises in connection with the packaging of animal carcasses e.g. lamb carcasses.

The carcasses are traditionally packed in muslin which is unhygienic and permits leaks. Current and impending regulations in many countries require plastic packaging. However carcass unloading is achieved by grasping the carcass in the region of the base of the rib cage which is the approximate centre of gravity, and this is not possible with the conventional shrink wrapped packaging because the shrunk film is taut over the cavity of the base of the rib cage.

US patent specification 3 756 395 discloses the use of heat shrinkable plastics film for packaging clusters of container such as cylindrical beverage cans. The plastic packaging is reinforced by laminations, which may be provided by pleats.

There is a reference to the use of localised heatshielding during the heat shrinking process. This is used to provide localised bonding of overlapping flaps. In packages consisting of clusters of containers as described in US 3 756 395 it is important for the containers to be held firmly together as movement of the containers relative to one another is likely to lead to damage to the plastics film around the containers, general instability of the packages and consequential difficulties in handling. It will be apparent to persons skilled in the packaging art that although the disclosure of US 3 756 395 may mention the formation of pleats, the final package must not have unshrunk loose portions of film.

US 3 756 395 is not concerned with the problem solved by the present invention.

GB 879 201 and GB 879 203 disclose the wrapping of bottles e.g. for soft drinks with a film of material e.g. a cellulose film. The film is pleated and then twisted to provide a closure at either end of the bottle. Reference is made to shrinking the film by subjecting it to water spray. This appears to be done to obtain a neater wrapping fitting more closely around the bottle. The wrapped articles of the above British patents, namely the bottle, does not have a re-entrant into which a hand is inserted to grip the article, and in general there is no problem in gripping film wrapped soft drink bottles.

According to the present invention there is provided a process for packaging an article having a or re-entrant which comprises applying a flexible shrinkable sheet material to the article so as to enclose the article and to leave an overlap of adjacent portions of the body of the sheet materia! over a re-entrant, subjecting the enclosed article to a shrinking step so as to shrink the flexible shrinkable sheet material onto the article, the amount of overlap and the degree of shrinking being so selected that when the shrinking step has been completed there is a sufficient slack portion of the sheet material over at least part of the reentrant to facilitate gripping by its re-entrant.

The present invention is concerned with wrapping a single article and not with wrapping clusters of individual articles. When packaging groups of articles in a single shrink-wrapped package it is undesirable, as already explained, to have slack portions of the film, such as are required by the present invention. The article wrapped in accordance with the present invention is one having a re-entrant. An article has a reentrant for the purposes of this specification if there are first and second points spaced apart on the article which can be joined by a first line which does not touch the article between the first and second points and which can be joined to a third point on the article between the first and second points by second and third straight lines respectively which do not cut through the article and which make an angle of not more than 90 degrees with one another.

The third point lies between the first and second points if a perpendicular from the third point to the line joining the first and second points cuts that line at a point between said first and second points.

The second and third lines do not cut through the article. The lines may run along a planar surface of an article, but not cut through the surface between the third point and the first and second points respectively. Preferably the lines do not touch the article between the third point and the first and second points respectively.

The third point preferably lies in the plane of minimum cross-section. The plane of minimum cross section is the plane through the first and second points in which the area between the line joining the first and second points and the surface of the article is a minimum. In the case of a reentrant constituted by two planar surfaces at right angles the plane of minimum cross-section will be perpendicular to the two surfaces.

Preferably the re-entrant is provided by a recess. For the purposes of this specification a recess is a cavity communicating with the outer surface of the article wherein a section through the cavity has a minimum distance between points on opposed sides of the cavity spaced above the base of this section. The minimum distance may be the same at various heights above the base as in the case of a cavity having straight parallel sides. Preferably the shortest distance between points on opposed sides below the points connected by the line of minimum distance is greater than the said minimum distance as in the case of a cross-section through an animal carcass in the region of the rib cage.

The existence of a re-entrant provides a means for providing a space into which a hand or some other means for gripping the article can be inserted.

The overlap is provided over the re-entrant. The overlap may be formed inside a notional line joining the extremities of the re-entrant in which case the overlap can be regarded as being formed within the re-entrant or can be formed outside the said notional line. In both case the overlap will be over the re-entrant surface. The overlap may be within the recess or outside it.

By requiring the overlap to be in adjacent portions of the body of the sheet material, the formation of the required overlap by overlapping the edges of the sheet is excluded.

The overlap of the adjacent portions of the body of the sheet may be any conventient form. It is particularly preferred to provide the overlap in the form of one or more pleats in the sheet material.

Thus the overlap may be provided by one or more single pleats or, preferably, by one or more double pleats. In the case of a double pleat the pleated portion may extend inwardly into the package or outwardly from it. In the latter case it may act as a handle or grip by which the package may be held.

The ove;iapping portion, e.g. the pleat, may extend substantially over the entire length or breadth of the package.

The amount of sheet material in the overlap is sufficient to enable the sheet material to be depressed so as to enter the re-entrant sufficiently to facilitate a good grip on the re-entrant in the case of a package which is to be moved manually.

The amount of the overlap of the flexible sheet material may be such that even when the entire area of overlap material is subjected to the shrinking step the sheet over at least part of the re-entrant is not shrunk taut in at least one direction but is slack, so facilitating for example gripping the article by the re-entrant. However it is preferable to carry out the shrinking step in such a way that at least a part of the overlap is protected from the shrinking step. Thus in the case of the preferred shrinking step namely heat shrinking, a portion of the overlap may be protected from shrinkage by the action of a heat shield.

A person skilled in the art of shrink wrapping will realise that the necessary slack in the relevant part of the shrink wrapped package would not be obtained if the overlapping portions of the sheet are bonded together over the entire area of the overlap e.g. as a result of heat sealing taking place during heat shrinking. He will therefore carry out the shrinking step in such a way as to avoid any undesirable bonding together of the overlap in the portion where slack is desired.

Further, a person skilled in the art of shrink wrapping will realise that in sealing a package prior to subjecting it to a shrinkage step, allowance is normally made for air otherwise trapped in the package, to escape during the shrinkage process by not completely sealing the package at this stage. Further sealing may be effected during and/or after the shrinkage step.

The shrinking step is preferably carried out in such a way that the flexible sheet does not adhere to the base of the re-entrant as this may impair ease of gripping the article. However adhesion of the flexible sheet to the base of the recess or reentrant is not usually a problem in the preferred application of the invention to packaging carcasses.

The process of the present invention may be applied to the shrink wrapping of any article having a re-entrant. It is particularly suitable however for the shrink wrapping of carcasses, in particular lamb carcasses. In such carcasses the area where it is particularly important to avoid having a taut shrunk film is in the region of the base of the rib cage.

In packaging carcasses it is particularly desirable to wrap the carcass with the flexible shrinkable sheet material in such a way that each rear leg is wrapped in sheet material so that bridging of taut film across the legs does not take place on shrinking.

In the preferred articles for wrapping in accordance with the present invention an overlap may be formed over the re-entrant constituted by the carcass legs. Preferably it is formed at least over the re-entrant formed by the recess at the base of the rib cage.

The flexible shrinkable sheet material used in the present invention may be initially in flat, tubular or bag form for example, and may be a film or net. It is possible to carry out shrinking of certain films by the reaction of solvents. It is preferred however to use a heat shrinkable thermoplastics sheet material. The preferred sheet materials are any heat shrinkable film of low-, medium- or high-density polyethylene, ethylene copolymer such as copolymers of ethylene with vinyl acetate, butene, hexene, propylene, butyl acrylate or ethyl acrylate, ionomer resin, polyvinyl chloride, polypropylene or polyvinylidene chloride.

Preferably the film should be chosen to facilitate heat welding of the film to itself where required in the process for preparing the completed package.

While closure of the completed package by heat sealing is preferred, other means such as bundle tying may be employed. The film is preferably of the kind having shrinkage capacity of 5060% in a principal shrinkage direction which in the case of the preferred packages is normally aligned transversely of the carcass. It preferably also has a shrinkage capacity of from 40-50% in the direction approximately at right angles to the principal shrinkage direction. Thus the film maybe a polyethylene film of the type designated SDX in PFMS 4/68 as amended in August 1970 (issued by Packaging Films Manufacturers Association).

The film may be of an extra low slip type designated "EL" the extra low slip being achieved by the incorporation of slip reducing additives in the film or by causing the film to have a ribbed or otherwise roughened surface by extrusion moulding, embossing or laminating techniques or by applying an anti-skid lacquer.

Films having reduced slip at low temperatures are particularly preferred when this invention is to be used for the packaging of articles to be stored at low temperatures e.g. meat carcasses.

An example of such a film is one comprising a matrix of a thermoplastic polymer containing a uniformly distributed particulate organic solid, formed by introducing particulate organic solid comprising particles with a maximum dimension in the range 50 to 2000 microns and a minimum dimension of not less than 50 microns into the thermoplastic polymer forming the matrix before the film is formed. The particulate organic solid may for example be a high molecular weight high density polyethylene. The matrix may be low density polyethylene.

Copending United Kingdom patent application 8021 642 (Case 4984) is directed to a frozen package wrapped in such a film.

A preferred film of the above type containing the specified organic solid has a matrix of ethylene copolymer preferably a copolymer containing 2 to 30% by weight of units derived from vinyl acetate, ethyl acrylate, or butyl acrylate. United Kingdom patent application 8021641 (Case 4985) is directed to such a film.

As mentioned above the flexible sheet may be heat-welded to itself in the formation of the final package, so as to give a package in which parts of the flexible sheet material are heat-welded together.

It is preferred to carry out this heat-welding in such a way as to give a package in which at least one end of the package is heat-sealed such that the seal extends across and through the overlap.

It is preferred that the packages are formed by employing a flat film initially as opposed to a tubular film and by employing a process in which the sheet envelope is formed, filled and sealed in a substantially continuous manner.

In one such process, which is often referred to as the "form and fill" process, flat sheet material, preferably a thermoplastics material, is supplied from a reei and formed into a back-seamed tube by drawing it around a vertically arranged hollow former or cylinder and bonding the longitudinal edges of the material, for example by heat sealing, to form the back seam. The tube thus formed is advanced through the apparatus by pulling on the tube and a transverse seal is made to seal the forward end of the tube. The product which is to be packaged is dropped through the hollow cylinder into the tube below and the tube is then sealed above the product to enclose it in a sealed bag which, simultaneously with the sealing operation, is cut from the formed tube.This latter sealing operation not only seals the top of the bag but also seals the bottom of the next bag to be produced. The material is normally progressed intermittently through the apparatus by the transverse sealing jaws to which a reciprocating action is applied.

In another such process, a flat sheet material, preferably a thermoplastics material, is fed to a conveyor machine and the product to be packaged is placed on the material which is then formed into a tube around the product and the longitudinal edges of the material heat sealed together above the product. The leading edge of the tube thus formed is then transversely sealed and the tube behind the product is also similarly transversely sealed. The seal also serves to seal the tube ahead of the next product and should therefore be sufficiently broad to allow it to be cut through without destroying the seal on the completed pack or the new leading end of the tube.

In both of the above described processes the flat sheet material is drawn off from a supply and is converted into tubular from by means of guides.

In order to form an overlap e.g. as one or more pleats when employing such processes, suitable guides are introduced at appropriate stages of the package production which automatically introduce the overlap, e.g. pleat or pleats, into the material as the material is drawn over the guides.

It will be understood that package blanks sealed at one end may be produced from flat sheet material using apparatus similar to that described above with reference to the "form and fill" process, by operating the transverse severing mechanism only alternately with the conjoint operation of the transverse sealing and severing mechanism.

It will furthermore be understood that pleated tubular sheet may be produced with the use of suitable guides, for example by inflating the tube against such guides. Package blanks may be readily produced from such pleated tubing by applying intermittent transverse seals and severing cuts.

If a line of weakness is made adjacent to transverse seals intermittently made then rolls of tear-off blanks may be produced.

It is preferred that the overlap e.g. as one or more pleats is formed in the sheet in tubular form or in some form which is a precursor to a tubular form, and in either case before applying a transverse heat weld seal to one end of the tube and thereby to one end of the package. The other end of the package is similarly sealed after filling.

The end welds which extend through the material of the overlap serve to retain the overlap such as a pleat or pleats, in position.

It will be appreciated that in some cases it may be desirable to secure the overlap after its formation against undesirable disturbance during subsequent process stages by localised adhesion or sealing of the material of the overlap to itself such as by point- or dab-sealing for example. Such adhesion or sealing should not of course interfere with the provision of the required slack portion of sheet material over at least part of the recess or re-entrant in the completed package.

The shrinking step of the present invention may be carried out by a conventional method. Thus in the case of heat shrinkable flexible sheet materials a conventional heat shrinking oven may be used.

When required, protection of at least a portion of the overlap over the re-entrant may be achieved in heat shrinking, by using a heat source which only applies heat to a portion of the package.

Alternatively a heat insulating or reflecting member may be applied over at least a portion of the overlap before the package is subjected to heat shrinkage. This member, which may have a T-shaped cross-section for example, may also serve to depress the sheet into the re-entrant.

The invention will now be illustrated by reference to the accompanying drawings.

Suitable apparatus for introducing one or more pleats into sheet material in the continuous production of packages in accordance with the invention is described with reference to Figure 1 to 4 of the accompanying drawings, in which: Figure 1 is a front view of the face of a forming member, Figure 2 is a side view of a pleating former, Figure 3 is a front view of the pleating former of Figure 2, Figure 4 is a section taken along the line A-A of Figure 1 but showing the pleating former assembled with the forming member in relation to.

which the direction in which the use of the sheet is moved is indicated by 5, and Figure 5 is a section along the line B-B of Figure 1 showing the double pleat configuration of material between the forming member and the pleating former.

Referring to Figure 1, a forming member 1 for use in the "form and fill" process described above comprises a hollow cylinder having a slot 2 cut in the wall thereof. The slot 2 is on the opposite side of the cylinder to means (not shown) for forming the back seam in the tube formed from the sheet material. A pleating former 3 having a material entry guide 4 is fitted in relation to slot 2 as shown in Figure 4. The material entry guide 4 is uppermost and extends outwardly of the cylinder through slot 2. The pleating former 3 is supported in this position by means of a narrow lug (not shown) projecting through the slot 2 and indirectly attached to a base member (not shown). It will be appreciated that the shape of the pleating former can be modified simply so that a single, as opposed to a double pleat is introduced into the sheet material.

A sheet material of a suitable width, such as low density polyethylene, is fed around and down the forming member 1. The sheet material is caused, during its movement in the direction 5 indicated in Figure 4, by the pleating former 3 to take up the configuration 6 shown in Figure 5.

When this operation has been effected the back seam is formed in the sheet material and the "form and fill" process continues in the manner described above.

The apparatus illustrated in Figures 1 to 5 may also be used in the other process described in detail above. In this case the forming member 1 is flat and situated so that the pleats or pleat are formed in the flat film before the film reaches the conveyor when the product to be packaged is placed on the pleated film.

Figure 6 is a diagrammatic representation of a preferred use of the present invention in wrapping a carcass and shows a packaged carcass immediately after wrapping and before heat shrinking.

The cutting and heat sealing of the plastics film is carried out using V shaped jaws such that V shaped seals are obtained in the package as indicated diagrammatically in Figure 6, such that the neck may extend between the sides of one V shaped seal while the other V shaped seal extends into the space between the rear legs of the carcass.

The plastic sheet material 6 is provided with a double pleat 7. (This is the type of pleat formed by the pleating member 3 mentioned above.) The package is sealed by a back seam (not shown) and by two transverse V shaped seals 8 and 9. The formation of these seals by V shaped sealing and cutting jaws produces the V shaped seals for the previous and succeeding packages 10 and 11.

An area 12 (marked by dotted lines) of the package over the base of the rib cage is shielded from the action of heat during the subsequent heat shrinking process by suitable shielding means e.g. a heat insulating shield.

The package is then subjected to a conventional heat shrinking step in a heat shrinking tunnel.

In this heat shrinking step the V shaped seal extending into the space between the rear legs 13 avoids or reduces the bridging of the space between the legs by taut shrink film. Material of the pleat is pulled out in the part of the package which is not shielded from heat shrinking, but generally a plurality of creases remain which assist in providing additional frictional resistance to packages sliding relative to one another. The portion of the pleat which is shielded from the heat shrinking provides excess film in that area which enables the carcass to be grasped in the traditional way in the region of the base of the rib cage, which is the approximate centre of gravity.

Furthermore the potential hazard which may arise during unloading shipping containers containing large numbers of carcasses wrapped in plastics film due to carcass slippage is reduced by the separated legs of the package and the creases arising from the double pleat.

Claims (17)

1. A process for packaging an article having a re-entrant which comprises applying a flexible shrinkable sheet material to the article so as to enclose the article and to leave an overlap of adjacent portions of the body of the sheet material over a re-entrant, subjecting the enclosed article to a shrinking step so as to shrink the flexible shrinkable sheet material on to the article, the amount of overlap and the degree of shrinking being so selected that when the shrinking step has been completed there is a sufficient slack portion of the sheet material over at least part of the reentrant to facilitate gripping the article by its reentrant.

2. A process according to Claim 1 wherein the shrinking step is carried out in such a way that the material over the re-entrant does not become attached to the base of the re-entrant.

3. A process according to either one of Claims 1 and 2 wherein the overlap is provided in the form of one or more pleats in the sheet material.

4. A process according to Claim 3 wherein the pleats are double pleats.

5. A process according to any one of the preceding claims wherein the shrinking step is carried out in such a way that at least part of the overlap is protected from the shrinking step.

6. A process according to any one of the preceding claims wherein the shrinking step is a heat shrinking step.

7. A process according to Claim 6 wherein at least part of the overlap is protected from the shrinking step by a heat shield.

8. A process according to Claim 7 wherein the heat shield also acts to depress the sheet into the re-entrant.

9. A process according to any one of the preceding claims wherein the article is an animal carcass.

10. A process according to Claim 9 wherein the article is a lamb carcass.

11. A process according to any one of the preceding claims wherein the flexible shrinkable heat sealable material is a heat-shrinkable thermoplastics film.

12. A process according to Claim 11 wherein the flexible shrinkable thermoplastics film is heat sealable.

13. A process according to Claim 12 wherein the flexible shrinkable heat sealable thermoplastics film enclosing the article is heat sealed such that a substantially V-shaped seal extends into the space between projections on the article.

14. A process according to Claim 13 wherein the projections are the rear legs of an animal carcass.

15. A process according to any one of Claims 11, 12, and 14 wherein the film has a shrinkage capacity of 5060% in a principal shrinkage direction and 4050% in a direction substantially at right angles to the principal shrinkage direction, and the film is aligned with the principal shrinkage direction aligned with the length of the carcass.

1 6. A process substantially as herein before described with reference to the drawings.

17. A packaged article made according to any one of the preceding claims.