WO2012049131A1

WO2012049131A1 - Package with shrinkable film lid

Info

Publication number: WO2012049131A1
Application number: PCT/EP2011/067663
Authority: WO
Inventors: Stefano Capitani; Lino Cosaro; Bertrand Gaillard; Riccardo Palumbo; Jvanohe Rizzi
Original assignee: Cryovac, Inc.
Priority date: 2010-10-11
Filing date: 2011-10-10
Publication date: 2012-04-19
Also published as: EP2627583A1

Abstract

A tray lidded package comprising a tray with two peripheral flanges separated by a groove, and at least one heat-shrinkable film lid sealed onto at least one of said flanges is described. The tray is useful as a support for packaging products, particularly food products.

Description

PACKAGE WITH SHRINKABLE FILM LID

DESCRIPTION

The present invention relates to packages for products, preferably food products, in particular packages for food products comprising a tray and at least a shrinkable film lid sealing it.

It is common practice in packaging products to use a product support member, often in the form of a tray and to cover it with a heat-shrinkable film. In particular, in tray lidding applications, the heat shrinkable film is sealed to the edges of the lower support, i.e. along a peripheral flange, or to a film which, in turn, is sealed to the edges of the lower support. In the art , tray lidded packages are clearly distinguished from vacuum skin (VSP) packages, in that in the latter the sealing area of the film is not limited to the flange surface but extends to the whole surface of the tray not occupied by the product

The resultant tray lidded package has a neat, clean appearance which is more actractive to the final consumer.

Commercially sold packages usually have a product support member with a cavity formed therein, and a flange around the perimeter of the member, the product is placed in the cavity of the product support member and a heat-shrinkable film is placed over the product and sealed all along the flange of the product support member.

One of the main drawbacks of this kind of tray lidded package is the risk of distorsion of the product support member due to the shrink force imparted to the sidewalls of the product support member by the shrinkable film. The distortion of the support member is even more evident in case the lidding film is a composite in which both films are heat shrinkable.

One possible approach to this technical problem consists in modulating the shrink properties of the lidding film(s) as described for example in WO 2011029950.

In alternative, in order to minimize the problem, the product support member is given a rigid structure of a suitable thickness to withstand the shrinkable film force.

However, the need of a suitable thickness of the product support member increases the amount of material used for the manufacturing of the tray lidded packages with a resultant increase of production costs. Moreover, food trays are usually thrown-away items and their volume, weight and cost should be kept as lowest as possible to reduce the environmental impact or the re-cycling costs for their disposal.

There is the need to have a tray lidded package with a tray of reduced thickness but suitable rigidity/robustness to withstand shrinkable film force with no deformation.

WO 94/27868 discloses some packaging systems for increased food product shelf life. The tray lidded packages are trays with a peripheral flange with one or more raised ledges to secure a pair of membranes to enclose the tray. The lower membrane is attached to a first ledge of the flange and the upper membrane is attached to a second ledge or to a recessed lip of the flange. The two attachment surfaces are separated by a trough or by being positioned on different levels. Function of this trough is to facilitate trimming of the lower membrane - once sealed - without damaging the integrity of the package.

Such tray lidded packages are useful for food products which need to be maintained in one condition under certain circumstances and then converted to another conditions, for example fresh meat that needs to be "bloomed" when exposed for sale.

We have now found that one of the trays disclosed in WO 94/27868 is particularly useful in packaging systems with at least one heat-shrinkable film sealing it. In particular, a tray comprising two peripheral flanges separated by a groove has a suitable rigidity/robustness to withstand shrinkable film force with no deformation even with a significant reduction of thickness over conventional tray used for packaging products, in particular food products.

Therefore, a first object of the present invention is a tray lidded package comprising a tray with two peripheral flanges separated by a groove, and at least one heat-shrinkable film lid sealed onto at least one of said flanges.

In a preferred embodiment, object of the present invention is a tray lidded package comprising a tray with two peripheral substantially coplanar flanges separated by a groove, and at least one heat-shrinkable film lid sealed onto at least one of said flanges.

In another preferred embodiment, object of the present invention is a tray lidded package for food products comprising a tray with two flanges, still more preferably two peripheral substantially coplanar flanges, separated by a groove, and at least one heat-shrinkable film lid sealed onto at least one of said flanges .

Although in the present context the tray lidded package of the invention will be described in more details in its preferred application for the packaging of food products, all features are intended to be suitable for their application in packaging any products.

The tray of the tray lidded package object of the present invention, characterized by the presence of two peripheral flanges, preferably two peripheral substantially coplanar flanges, shows an increased rigidity in comparison with a similar tray with a single peripheral flange and therefore is particularly useful to reduce the thickness of trays in tray lidded packages with a heat-shrinkable film to be sealed on it.

The resultant tray lidded package in fact is able to withstand shrinkable film force with no deformation with a tray thickness which is significantly downgauged in comparison with conventional trays in tray lidding.

Neither the rigidity/robustness of the tray having two coplanar flanges separated by a groove nor its advantageous use in combination with heat-shrinkable films is specifically mentioned in WO 94/27868.

In fact, according to WO 94/27868, the rigidity of the tray is conferred by the material used for its preparation and the two covering membranes may advantageously be under slight resilient tension, that is may be slightly stretched before sealing. In the art, stretchable films are clearly distinguishable from shrinkable films as they have not been previously oriented according to the process described below.

As said, the present invention relates to tray lidded packages comprising at least a shrinkable film covering it.

The heat-shrinkability is imparted to the film by solid-state orientation or stretching of the film, either mono-axially or bi-axially, during film manufacture. In a typical process, the thick structure which is extruded through either a round or a flat extrusion die is quickly quenched, then it is heated to a suitable temperature, called the orientation temperature, which is higher than the glass transition temperature (Tg) of the resins used in the film itself but lower than the melting temperature (Tm) of at least one of said resins, and stretched in either or both of the machine longitudinal and transverse directions.

Upon exposure of the resultant film to heat, such a feature will allow the film to shrink or, if restrained, to create shrink tension.

Therefore, a shrinkable film is a film characterized by a free shrink at 120°C in at least one direction of at least 4%, preferably at least 10%, more preferably at least 15%. The free shrink is measured according to ASTM D2732.

Therefore, a tray lidded package with one or more heat-shrinkable films must have a tray with a suitable robustness to withstand the above shrink force.

The tray of the tray lidded package according to the present invention is preferably rigid with a base or bottom portion of any desired shape, for example rectangular, squared, circular, oval, etc., and with side-walls extending upwardly and optionally also outwardly from the periphery of said base or bottom portion, and ending with two substantially coplanar flanges separated by a groove.

The tray can be a mono-layer or a multi-layer structure, either foamed, partially foamed or solid and can be made of any suitable material. The tray may be also provided with a suitable liner, completely or partially covering the internal surface.

Examples of suitable materials for the tray of the invention are styrene-based polymers, such as polystyrene and high impact polystyrene, polypropylene, high density polyethylene, polyesters, such as polylactate, polyethyleneterephthalate and polyethylenenaphthalenate homo- and co-polymers, polyvinylchloride, acrylic polymers, polycarbonates and the like.

Preferred materials are polyethyleneterephtalate (PET), polypropylene (PP), polyethyleneterephtalate-polypropylene (PET-PP), polypropylene-polyethylene (PP-PE), polylactic acid (PLA) derived polymers.

As said, the tray of the tray lidded package according to the present invention has reduced thickness which allows to significantly decrease the amount of material used for its preparation.

It is clear to the expert in the field that the thickness of a tray depends on several factors, such as the material forming the tray, the overall dimensions of the tray and the kind of heat- shrinkable film which is used for the packaging.

A tray made of polypropylene has a thickness generally ranging from 400 μιη to 700 μιη while a PET tray has a thickness generally ranging from 200 μιη to 500 μιη.

For example, a rectangular tray with dimensions 145 x 230 mm and a depth of 30 mm in PP has a thickness around 650 μιη when to be used with a film having a high shrinkability. The thickness of the tray according to the present invention can be reduced of at least 10%, preferably from 20% to 40% with respect to single flanged conventional trays

Especially in medium- and large-sized tray lidded packages, this thickness reduction corresponds to a very significant reduction of the weight of the tray.

A preferred embodiment of the present invention is a tray lidded package for food products comprising a tray made of polypropylene with two peripheral, preferably substantially coplanar, flanges separated by a groove, said tray having a thickness ranging from 200 μιη to 1200 μιη, preferably from 240 μιη to 630 μιη, and at least one heat-shrinkable film lid sealed onto at least one of said flanges .

Still more preferred is a tray lidded package for food products comprising a tray made of polypropylene with two peripheral substantially coplanar flanges separated by a groove, said tray having a thickness ranging from 220 μιη to 1100 μιη , preferably from 240 μιη to 590 μιη, and at least one heat-shrinkable film lid sealed onto at least one of said flanges .

Another preferred embodiment of the present invention is a tray lidded package for food products comprising a tray made of polyethyeleneterephtalate with two peripheral, preferably substantially coplanar, flanges separated by a groove, said tray having a thickness ranging from 100 μιη to 1000 μιη, preferably from 120 μιη to 450 μιη, and at least one heat- shrinkable film lid sealed onto at least one of said flanges .

The heat-shrinkable film covering the tray containing the food product can be a mono-layer or a multi-layer film of any known conventional material for shrinkable films.

At least one heat-shrinkable film covers the tray in the tray lidded package according to the present invention, but one or more further films, either shrinkable or not, can be optionally present. For example, the heat-shrinkable film can be a mono- or multi-layer oxygen-permeable film generally containing polyolefins or modified polyolefin resins or any suitable non-barrier resin.

The heat-shrinkable film can be also a multi-layered oxygen-impermeable film comprising at least an oxygen-barrier layer and a heat sealable layer. Suitable polymers for the oxygen- barrier layer are PVDC, EVOH, polyamides, PET and blends thereof.

In case of one heat-shrinkable film covering the tray according to the present invention, the film can be sealed on one or both flanges.

In case of two or more films covering the tray, one of the film can be sealed on one flange and the remaining can be sealed on the other flange. Alternatively, all the films can be sealed on one flange or on both flanges.

Preferably, the heat-shrinkable film is sealed on both flanges; in case of sealing on only one flange, the sealing on the internal flange is preferred.

The sealing of the film is carried out according to conventional techniques.

The portion of the film extending beyond the perimeter of the tray can be cut or used to peel off the film when needed.

A preferred embodiment of the present invention is a tray lidded package for food products, in particular fresh meat products, comprising a tray with two peripheral substantially coplanar flanges separated by a groove, a product loaded onto the tray, an inner oxygen- permeable film over the product and the tray and sealed onto at least one of said flanges, and an outer oxygen-impermeable film over the inner oxygen-permeable film and in close proximity thereto sealed onto at least one of said flanges. The space between the two films comprises a minimum discrete free volume containing the amount of oxygen necessary to inhibit discoloration of the packaged meat product during its shelf-life.

The inner oxygen-permeable film and the outer oxygen-impermeable film can be sealed independently onto one or both the flanges of the tray, preferably they are both sealed on both flanges of the tray, optionally with a stronger sealing on the internal flange and with a weaker sealing on the external flange. Preferably both the inner oxygen-permeable film and the outer oxygen-impermeable film are heat-shrinkable.

These tray lidded packages can be prepared according to one of the procedures described in EP 0 690 012 or in WO 2006/087125 by using two different supply rolls, one for the oxygen-permeable film and one for the oxygen-impermeable film, or a single supply roll with a composite of the two lidding films for the lidding machine.

Preferably, the tray lidded package for fresh meat products is manufactured following a process comprising the use of a twin lidding film with an inner oxygen-permeable film and an outer oxygen-impermeable film, wherein said twin lidding film is used as a composite wound up on a single supply roll and wherein, following unwinding and before entering into the lidding station, the inner oxygen-permeable film and the outer oxygen-impermeable film of the twin lidding film are separated and then superposed again one over the other before the heat-sealing step, as described in EP 1848635.

The manufacturing of the tray according to the present invention can be carried out following conventional thermoforming techniques, for example starting from a flat sheet or a pre-made billet, or starting from the resin, i.e. as pellets, by molding techniques.

The groove separating the two peripheral flanges of the tray of the present invention can be of any suitable shape/design, for example U-shape or V-shape, and of any suitable depth and width.

Mainly for manufacturing reasons, a U-shaped groove is particularly preferred.

Preferably, the depth and width of the groove, independently each other, range from 3 mm to

30 mm.

The selection of a specific shape as well as of a specific depth/width within the above range mainly depends on the optional additional functions of the groove of the tray of the present invention. As a general rule, the depth and width will be at minimum values when the groove has the only structural function of separating the two peripheral flanges of the tray, generally between 3 and 10 mm, preferably between 3 and 5 mm.

Larger dimensions will be preferred in case of additional functions of the groove. In fact, the groove can be used also to contain solids, liquids or gasses. Clearly, this additional function of the groove requires the sealing of at least one film covering the tray to both flanges so that the groove is closed to form a tube.

Such a tube can act as an additional container or as a gas reservoir or as a drip retention.

As a container, it can be filled with substances which can help or improve the conservation of the packaged product, for example adsorbants or the like, or it can be filled with some particular ingredients which should be used with but kept separated by the other(s) inside the main cavity of the tray, for example a sauce, vinagraitte, flakes or the like.

Particularly advantageous is the additional function as a gas reservoir. In fact, the packaging process is usually carried out under modified atmosphere, that is under a pressure higher than the atmospheric pressure. When the tube is formed, the gas contained in it is compressed at the operating pressure. At the end of the packaging process, the compressed gas within the tube expands so creating an inflated tube along the perimeter of the tray. Said inflated tube acts as a further reinforcing element of the tray. If needed, this reinforcing effect can be modulated or adjusted by suitably changing the operating pressure during the packaging procedure.

A further advantage of this function of the groove as gas reservoir is that no additional operating step such as air inflation is needed during the conventional packaging process to have an inflated tube.

When the package requires that the gas contained in the tube could flow into the cavity of the tray, the sealing on the inner flange of the tray according to the present invention will have one or more discontinuations to allow the gas flow.

The groove can also be used for drip retention, that is to collect liquids which eventually separate from the product contained in the main cavity of the tray. In this case, the groove is connected in one or more points of its perimeter with the main cavity of the tray. This additional function as drip retention is particularly useful for vertical presentation of the packages.

Additionally, the portion of film covering the groove can be printed or coloured to improve the appearance of the package or for any other practical or commercial reasons without the risk to hide the product contained in the package.

The groove can optionally have one or more radial ribs to further reinforce the tray. These ribs are particularly preferred in case of large-sized tray lidded packages and/or in case of a large groove.

Claims

1) A tray lidded package comprising a tray with two peripheral flanges separated by a groove, a product loaded onto the tray and at least one heat-shrinkable film lid sealed onto at least one of said flanges.

2) The package according to claim 1 for food products.

3) The package according to claim 1 or 2 wherein the tray is made of polypropylene and has a thickness ranging from 200 μιη to 1200 μιη, preferably from 240 μιη to 630 μιη, more preferably from 240 μιη to 590 μιη.

4) The package according to claims 1 or 2 wherein the tray is made of polyethyeleneterephtalate and has a thickness ranging from 100 μιη to 1000 μιη, preferably from 120 μιη to 450 μιη.

5) The package according to anyone of the preceding claims in which said at least one heat-shrinkable film lid is characterized by a free shrink at 120°C in at least one direction of at least 4%, preferably at least 10%, more preferably at least 15% (ASTM D2732).

6) A tray lidded package according to anyone of the preceding claims wherein the heat- shrinkable film is sealed on the internal flange.

7) The package according to anyone of the preceding claims wherein the heat-shrinkable film is sealed on both flanges.

8) The package according to anyone of the preceding claims comprising one or more further films covering it.

9) The package according to anyone of the preceding claims comprising an inner oxygen-permeable film and an outer oxygen-impermeable film.

10) The package according to claim 9 wherein both inner oxygen-permeable film and an outer oxygen-impermeable film are heat- shrinkable.

11) The package according to anyone of the preceding claims wherein the groove is U- shaped.

12) The package according to anyone of the preceding claims wherein the groove has an additional function as container, gas reservoir or drip retention. lS) The package according to claim 12 wherein the portion of the film covering the groove is printed or coloured.

14) A tray lidded package for food products comprising a tray with two peripheral flanges separated by a groove, a product loaded onto the tray, an inner oxygen-permeable film over the product and the tray and sealed onto at least one of said flanges, and an outer oxygen- impermeable film over the inner oxygen-permeable film and in close proximity thereto sealed onto at least one of said flanges.

15) The package according to anyone of the preceding claims wherin said flanges are substantially coplanar.

16) The package according to claims 14 or 15 wherein both films are sealed onto both flanges

17) Use of a tray with two peripheral flanges separated by a groove as a support for tray lidding packaging a product with at least one heat-shrinkable film sealed on at least one of said flanges.