CA2569303A1

CA2569303A1 - Self-venting cover for heatable food package

Info

Publication number: CA2569303A1
Application number: CA002569303A
Authority: CA
Inventors: Gary Tee
Original assignee: Ffp Packaging Solutions Limited; Gary Tee
Current assignee: FFP Packaging Solutions Ltd
Priority date: 2005-03-03
Filing date: 2006-02-24
Publication date: 2006-09-08
Also published as: EP1861322B1; EP1861322A1; WO2006092562A1; AU2006219770A1; US20080251518A1; GB2423758A; GB0504418D0; GB0603762D0; DE602006001860D1; ATE401258T1; ZA200609410B; AU2006219770A2; AU2006219770B2

Abstract

A self-venting cover for a heatable food package comprises a sheet of film having a slit formed therein to permit the passage of steam therethrough. A label is secured to the film for controlling the flow of steam through the opening. The label includes a sheet of material having a first region secured to the film in an area remote from the slit and having a second elongated region covering the slit. The elongated region is only partially secured to the film and forms a vent passage between the unsecured portion of the elongated region and the film itself, which vent passage extends from the slit towards the periphery of the label to permit controlled venting of steam from the opening. The elongated region of the label is relatively narrow and the first region is relatively wide and is located spaced from the opening.

Description

SELF-TENTING COTTER F~R EATABLE F~4~ PACKAGE
This iilvention relates to a self venthlg cover for a heatable food paclcage, and in the preferred embodiment provides cover particularly suitable for a food package intended for mice owave heatilzg.
Food products, pax-ticularly pre-coolced food products, are conunonly sold hl packages which are intended for re-heathlg either in a conventional oven or in a microwave oven. Such paclcages commonly comprise a relatively rigid tray which contains the food product in question and a film cover which is secured to the tray around the top edge thereof.
Heating the paclcage results hl the generation of steam within the paclcage and if no steps are taken to vent the steam, pressur a generated in the pack is liable to "explode". This is highly undesirable. The traditional solution to this problem was to instruct users of the pacl~
to pierce the film cover prior to heating of the paclL. This proceduare is effective provided that the customer does as instructed and pierces the film. However, if the user fails to pierce the film the problem of pack explosion remains.
With a view to alleviating the problem outlined above packages have been proposed which include vent systems which automatically vent the package in the event of elevated temperature and/or elevated pressure within the pack. Such systems are shown, for example, in EP-A-0174188 and US-A-5989608. Whilst the prior art proposals appear to offer solutions to the problem outlined above, they are in themselves deficient in various respects. In particular, the automatic venting systems of the prior art may iulder certain circiunstances not be effective to provide the required venting with the result that excessive pressure builds up within the pack, and also suffer from the disadvantage that the venting aperture will be re-sealed in the event that pressure within the pack falls below the pressure on the exterior of the pack. This can result in implosion of the pack.
In addition to the problems with prior art arrangements as described above, it is now perceived that the presence of some excess pressure withilz a pack is desirable during the heating process. Accordingly, whilst venting of a package to prevent explosion is desirable, that ventiilg should ideally be canied out in a controlled manner, at least during the early phases of heating, so as to derive benefit from a super-ambient steam pressure generated within the package.
With a view to obviating the disadvantages outlizied above and providhig a controlled and reliable venting arr angement there is provided, in accordance with the present invention, a self venting cover for a heatable food package comprising: a sheet of fihn having at least one opening formed therein to permit the passage of steam therethrough; and a label secured to the fihn for controlling the flow of steam through the opening, the label comprising a sheet of material having a first region secured to the film in an area remote from the opel~ing and having a second elongated region covering the opening, wherein the elongated region is ol~ly pal-tially secured to the film and a vent passage is defined between the unsecured portion of the elongated region and the film itself, the vent passage extending from the opening towards the periphery of the label to permit controlled venting of steam from the openitag.
Preferably, the label includes a strip which is 11011-adheSlVe alld which, in one embodiment, extends the full length of the label, in particular all the way to the opposing edges of the label to provide two vent passages and which, in total, extends the full length of the cover to pr ovide two vent passages from the aperture. Such an arrangement is particularly easy to mass-produce because the non-adhesive strip and adjacent adhesive areas can be produced in the machine direction of the machine which is fabricating the cover.
In an alternative embodiment, however, the non-adhesive portion of the label is surrounded by adhesive, at least one side of which is relatively narrow compared with the adhesive bounding at least one other side of the non-adhesive portion. IN this embodiment, then, the passage does not extend all the way to the edge of the label and instead the relatively narr ow region of adhesive bordering the non-adhesive portion will lift as pressure within the passage increases to a pre-defined level so as to allow venting to atmosphere.
Preferably, the label includes a relatively narrow region adjacent the aperture and a relatively wide region located spaced from the aperture. The r elatively wide region provides a large area for adhesive bonding or welding of the cover to the film. By this means, complete detachment of the cover from the film is avoided. The relatively narrow region allows the portion of the label which overlies the aperttu a to become detached from the film during heating, then eby providing a free and unrestrictive passage through the opening in the later stages of package heating.
Preferably, at least the portion of the label which overlies the opening is of a material which tends to shrink when heated. Such shrilllcage assists in detaclW g the label from the film in the region of the opelung and ensures that the label will not re-close the opening ill the event that pressure within the package temporarily falls to a sub-ambient level.
In one embodiment, the opening is in the form of a slit cut in the material of the film.
The slit may be a simple linear slit running in the machine direction of the machine used for forming the cover. Such an anallgement is particularly easy ~to implement in practice.
In an altenlative embodiment, however, the opening is iu the form of a hole punched in the material of the film. More particularly, the two concentric, circtunferentially spcaed circular ar cs axe cut iii the film so as to form two selmi-circular flaps which are comlected to the f1h11 by a pair of common, radial tabs which separate the arcuate cuts. It will, of course, be uilderstood that other hole shapes inay be used, such as square, but appropriate shaping of the slits which form the two flaps.
The invention inay be embodied as a cover which is secur ed by appropriate means to a relatively rigid tray. In the preferred embodnnent, the cover is securable to a tray by way of a peelable bond facilitating easy removal of the cover in order to seine the product contained within the tray. In the alternative, the cover may be used in association with other film material to form a paclcage i11 another form such as a flexible bag or pouch.
In practice, the material of the label can be relatively thin material, for example 50 microns thiclc PVC. Such an arrangement is particularly desirable because the covers cail be pre-formed in a packaging factory environment and reeled for delivery to a food packaging factory for ultimate use. This is a considerable advantage over relatively complex arrangements using multi-layer materials which are not susceptible to reel delivery.
The above and further features and advantages of the invention will become clear fiom the following description of embodiments thereof, reference being made to the accompanying drawings, in which Figure 1 is a top plan view of a food paclcage provided with a cover in accordaalce with a first embodiment of the present invention; and Figure 2 is a top plan view of a label in accordance with a second einbodilnent of the ll1Ve11t10I1.
Referring first to Figure l, the package 1 illustrated comprises a cover 2 which is bonded to the upper edge of a tray contaiiling a food product. The cover 2 comprises a sheet of fihn material 3 and a label 4 secured to the film material by adhesive. The film 3 is formed with a slit 5 rui111ii1g ll1 the machine direction A of the machirla which was used to form the cover. The slit 5 may be a through slit or maybe a line of weakness which, when pressure begins to build withizl the package, will open to provide an opening. The position ofthe slit 5 is such that it is covered by an elongate portion 6 of the label 4.
The label 4 includes, in addition to the elongate portion 6, a generally circular pol-tion 7. The label 4 is secured to the film 3 by two areas of adhesive 8, 9. The ar eas of adhesive are separated by a central strip 10 which is not adhesively secured to the fihln.
As illustrated, the strip 10 runs the entire length of the label 4 in the machine direction A.
In this embodiment of the invention, the strips 8, 9 and 10 are formed by laying down two spaced apart strips of adhesive on the material of the label 4 before the label is secured to the fihn. It is to be noted, however, that other arrangements are possible such as other pattern coatings, or in particular if desired the entire surface of the label 4 facing the film may be coated with adhesive, and a central strip of that adhesive may be treated in some way to prevent adhesion to the underlying film 3. Alternatively, it may be possible to secure tlne label 4 to the film by means other than adhesive, for example a welding process.
In the illustrated preferred embodinents of the invention the fihn 3 is a polyester/polypropylene lamilate comprising a layer of approximately 12 microns of polyester laminated to a layer of 50-70 microns of cast polypropylene. The label is formed from a shrinlc grade PVC fihn, for example 50 IlllCIOIIS thick and is secured to the film by a suitable food grade adhesive, for example an acrylic based adhesive.
The effect of the arrangement described above is that vent passages 11,12 are defined between the material of the film 3 and the material of the label 4, the vent passages connecting the opening formed by the slit 5 to the exterior of the package.
VJlnen a paclcage fonned as described above is heated, for example in a microwave oven, steam will be liberated from the food product contained in the package and this will elevate the pressure within the package. Initially, there will be little leakage of steam from the package. However, as the pressure and temperature of the paclcage ilcreases the slit 5 will eventually open to define an opemilg which connects the interior of the package to the passages 11, 12. Steam may thereafter vent in a contr olled manner through the passages 1 l, 12 to prevent explosion of the pack but to maintain a super-ambient steam pressure withil the package.
Preferably, the material of the label will tend to shrink under the influence of heat.
Accordingly, as heating of the package continues the elongate region 6 of the label will tend to detach itself from the underlying film and shrink baclc towards the round portion 7. The round portion 7 will be less liable to detach from the fihn 3 because of the larger area of contact of adhesive between the round portion 7 and the film 3. The sluinl~ing of the label material means that after a certain period of heating the label will not be able to re-adhere to the film material in the region of the slot and accordingly implosion of the paclcage will be prevented.

The relatively large area of adhesive provided in the rounded pol-tion 7 will ensure that the label does not become completely detached from the fihn 3.
Refen-ing now to Figure 2, there is shown a modified label 14 which is of sinnilar size and shape to the label of Figure 1 and is used in conjunction with a paclaghig cover as described above in connection with Figure 1. In contrast, however, the the label of the first embodiment, label 14 is secured to the film by a single area of adhesive 18 which in particular extends around the entire periphery of alz adhesive free region 15 which is formed on the elongated portion 16 of the label 14 and which, when applied to the cover material, overlies a venting aperture in the film so as to form a venting passage. Ill contract with the Velltlllg slit 5 of the embodiment of Figure l, iu Figure 2, the venting aperture is formed by a pair of arcuate slits , the ends of which ar a separated so as to form a pair of substantially semi.
circular flaps 20a, 20b which remain attached to the film, and through which steam from within the packaging can vent it will, of course, be understood that a linear slit may be used with the embodiment of Figure 2, as lnay arcuate slits with the embodiment of Figure 1.
The relatively narrow width of the adhesive 18a which bounds the adhesive free region 15 on three sides is of lower strength than that of the adhesive 18b provided on the generally circular portion 17 of the label 14, due to the difference in the contact area of the two adhesive regions 18a, 18b. Rather than a slit 5 as in the embodiment of Figure l, a pair of substantially semi-circular and hence, as steam from the paclcaging vents through the slit 5 into the venting passage formed by the adhesive free region 15, the pressure in that region will izlcrease until it is sufficient to overcome the bonding strength of the adhesive 18a, and the elongated portion 16 of the label 14 lifts, allowing venting of the steam to atmospher e.
AS S110Wn 11 Figure 2, the edge of the label 14 also has all adheslVe free region 21 which extends around the entize periphery so as to form a margin around the label which is not bonded to the underlyhlg cover. Such a margnl may also be provided on the label 4 according to Figure 1. Preferably, the margin is l,Slnln wide and the region of adhesive 18a sun oundhlg the adhesive free region 15 is 2 lnln wide.
In all other respects, the malmer of operation of the label 14 of Figur a 2, includhig the preferable materials and material propel-ties such as shri.llkizlg.

Claims

1.~A self-venting cover (1) for a heatable food package comprising: a sheet of film (3) having at least one opening (5;19a, 19b) formed therein to permit the passage of steam therethrough; and a label (4;14) secured to the film (3) for controlling the flow of steam through the opening (5;19a, 19b), the label (4; 14b) comprising a sheet of material having a first region (7; 17) secured to the film (3) in an area remote from the opening and having a second elongated region (6; 16) covering the opening (6;19a, 19b), wherein the elongated region (6;16b) is only partially secured to the film (3) and a vent passage (11, 12;15) is defined between the unsecured portion (10;15) of the elongated region (6;16) and the film (3) itself, the vent passage extending from the opening (5;19a, 19b) towards the periphery of the label (4;14) to permit controlled venting of steam from the opening.

2.~A self venting cover according to claim 1 wherein the unsecured portion of the elongated region (6) includes a strip (10)-which is non-adhesive and which extends the full length of the label (4) along both the first region (7) and the elongated region (6) to provide two vent passages (11, 12) from the opening (5) which, in total, extend the full length of the label (4).

3.~A self venting cover according to claim 1, wherein the unsecured region (15) extends only partially along the elongated region (16) and the elongated region (16) is secured to the film (3) around substantially tile entire periphery of the unsecured region (16)

4. ~A self-venting cover according to claim 3, wherein the secured region (18a) of the elongated region (16) is smaller in area that the secured region (18b) of the first region (17) of the label (14), such that secured region of the elongated region of the label has a weaker bond strength than that of the first region of the label.

5. ~A self venting cover according to any of claims 2 to 4, wherein the unsecured portion (10;15) of the elongated region (6;16) extends in the machine direction of the machine on which the cover is fabricated.

6. ~A self venting cover according to any of claims 2 to 5, wherein the label (4;14), other than the unsecured portion (10;15) of the elongated region (6;16), is adhesively secured to the film.

7.~ A self venting cover according to any preceding claim wherein the elongated region (6;16) of the label (4;14) is relatively narrow and the first region (7;17) is relatively wide and is located spaced from the aperture (5;19a, 19b).

8.~ A self venting cover according to claim 7, wherein the relative narrowness of the elongated region (6, 16) allows the elongated region (6, 16) of the label (4, 14) which overlies the opening (5;19a, 19b) to become detached from the film (3) during heating, thereby providing a free and unrestricted passage through the opening (5;19a, 19b) 11 the later stages of package heating.

9. ~A self venting cover according to any preceding claim wherein at least the elongated region (6;16) of the label (4;14) is of a material which tends to shrink when heated.

10. ~A self venting cover according to any preceding claim wherein the opening (5;19a, 19b) is in the form of a slit cut in the material of the film (3).

11.~A self venting cover according to claim 10 wherein the slit (5) is a simple linear slit (5) running in the machine direction of the machine used for forming the cover.

12. ~A self venting cover according to claim 10, wherein the opening comprises a pair of arcuate slits (19a, 19b), the ends of which are spaced apart so as to form a pair of back to back, substantially semi-circular flaps (20a, 20b).

13. ~A self venting cover according to any preceding claim wherein the material of the label is a relatively thin material whereby the covers can be pre-formed in a packaging factory environment and reeled for delivery to a food packaging factory for ultimate use.