EP0299643A1

EP0299643A1 - Improvements in or relating to packaging

Info

Publication number: EP0299643A1
Application number: EP88305885A
Authority: EP
Inventors: Anthony Thomas Baden Fuller; Arthur Neville Jones
Original assignee: Koninklijke Emballage Industrie Van Leer BV
Current assignee: Greif International Holding BV
Priority date: 1987-07-02
Filing date: 1988-06-29
Publication date: 1989-01-18
Also published as: GB8715532D0

Abstract

A method of packaging a heat transformation product, such as popcorn (6), in a rigid container is described. The mouth of a bag (4) portion formed from a film of heat-extensible plastics material is contacted with the mouth of the container in which the product is situated. The bag portion is collapsed into the container by a pressure differential so that the bag substantially follows the interior contour of the container and the product. The interior volume of the container and the bag portion are at least sufficient to contain the product in its heat-transformed state. Packages produced by the method are also described.

Description

This invention relates to packaging and is concerned with a method of packaging a heat transformation product, that is to say a product which changes in shape, size, texture or other physical attribute on heating. Preferred heat transformation products are those food products which change in shape, size, texture and colour or release flavour on heating. A prime example of a food transformation product is grains of corn (maize) which upon heating, produce "popcorn" while another is poppadoms. The present invention will be described mainly with reference to grains of corn although it is applicable to other heat transformation products. For ease of reference, such grains of corn, whether in the "popped" or "unpopped" condition will hereinafter be referred to as "popcorn". The invention also relates to packages produced by the method.
There has been increasing interest in providing popcorn in packages which can be placed in an oven or microwave oven and heated to pop the corn while still in the package, so that on heating, the resulting popcorn is retained in the package and does not fly all around the oven and so that the resulting atmosphere generated in the package does not escape or rupture the package explosively or other than in a controlled manner. A problem with such packages is that in the unpopped state the popcorn occupies relatively little room but expands greatly in volume on heating. The package therefore has to be big enough to contain the popped popcorn which means that when the corn is in the unpopped state there is a large amount of empty package which can flop about and become damaged or which has to be carefully held in position before heating.
It is an object of the invention to provide a package for a food transformation product which takes up relatively little volume before heating but can expand on heating to contain the product.
According to one aspect of the present invention there is provided a method of packaging a food transformation product, comprising the steps of forming a bag portion from a film of heat-extensible plastics material bringing the mouth of said bag portion into contact with the mouth of a rigid container having untransformed food product therein, collapsing said bag portion by drawing a vacuum between the interiors of said container and said bag portion or by external pressure thereon to cause the bag portion substantially to follow the interior contour of the container and food product therein and sealing the mouth of said bag portion to the mouth of said container. The method is preferably carried out continuously and use may be made of a conventional thermoforming vacuum packaging machine.
In one embodiment of the present invention, the method is carried out by forming the bag portion, as by deep-drawing the film of heat extensible plastics material, and then placing over the mouth of the bag portion an inverted rigid container which has the untransformed food product adhered, as by an edible adhesive, such as sugary or toffee-like mixture, to what would normally be the base of the container. After the bag portion has been invaginated into the rigid container the container can be turned up the normal way.
In another embodiment of the present invention, the bag portion is formed and then allowed to collapse or forced by pressure or vacuum into a collapsed state in which it is placed over the mouth of the rigid container in which the untransformed food product can be held in a loose condition.
In either case, when the resulting package is stood on its base and heated in an oven/hot plate or microwave oven, the bag portion will stretch and form a dome under the influence of the heat and will contain the food product, e.g. popcorn, as it increases in volume during heating the lined fibre tray and the bag portion being capable of extensive expansion to relieve any excess pressure. However, the seal between the bag portion and the container may be a broken or intermittent seal to allow the escape of air and/or moisture during heating. A preferred safety release is the inclusion of a strip of paper at one or more points in the seal.
The plastics material of which the bag portion of the package is made is a heat-extensible material which is heat-resistant in that it can withstand the temperatures in an oven or microwave oven at which the food product undergoes transformation. For use in a microwave oven the plastics material should have low dielectric loss properties. Suitable plastics materials for the bag portion include cast polyesters such as polyethylene terephthalate or polybutylene terephthalate, polycarbonates, and polypropylene, but other suitable materials may be employed. The plastics material may have a thickness of 25 to 200 microns, but preferably has a thickness of 25 to 100 microns.
The container is preferably in the form of a flanged tray or dish which may be round or substantially rectangular in plan view. It is most desirable that the tray is substantially square in plan view although other constraints may favour a somewhat oblong plan view. It is desirable for the container to have a depth at least one third of the diagonal/width or diameter in order to achieve optimum results. The container is preferably made of fibrous material, such as moulded fibre pulp, paper, cardboard or fibre board made in conventional manner by moulding fibres deposited by paper-making techniques. Alternatively, the container may be made from bonded wood chips or bonded fibre material provided that the bonding material can withstand subsequent heating. All these containers are lined with a lining of heat-resistant plastics material which is compatible with the material of which the bag portion is made and which can be sealed to the bag portion by processes such as heat-sealing, thermal bonding or even by adhesive means.
The container may also be made of plastics material provided that the material can withstand the subsequent heating and can be sealed to the bag portion.
If the package is to be heated in a microwave oven to effect the transformation of the food product, it is desirable that the container should be provided with susceptor material to enhance the heating effect of the microwave radiation. The susceptor material, of which ferrites, metal particles. e.g. aluminium particles, and various argillaceous materials, e.g. bentonite, are examples, may be incorporated in the container in various ways. Thus, for example, a pad of susceptor material may be incorporated between the interior of the base of a container made of fibrous material and the heat-resistant plastics lining of the container or a pad of susceptor material may be present externally. Alternatively, the container may be sprayed or otherwise treated with susceptor material, either internally before lining, or externally. For example, the container may have a metalised film thereon of e.g. aluminium particles at an optical density of 0.18 to 0.3. However, with some containers, such as those made of moulded fibre pulp, the pulp from which the container is made will normally contain clays, such as bentonite, or other fillers which may then become incorporated in the pulp from which the container is moulded in sufficient quantities to act as susceptor materials in conjunction with the inherent moisture content of the normal moulded fibre containers available in commerce, which moisture content is usually 10% but may range from 5 to 15%, so that there is no need for the addition of further susceptor material, as the package will perform satisfactorily as a result of its self-suscepting properties.
If the container is made of plastics, then the plastics may contain susceptor material as a filler.
It will thus be appreciated that the susceptibility of the package or the container can be selected both in degree and position in accordance with the requirements of the transformation product. To this end, it may in some cases be desirable to provide the base of the container with ribs or feet so as to position, for example, a pad of susceptor material at an appropriate distance from the turntable of a microwave oven.
The first embodiment of the present method is particularly useful for packaging popcorn which is present in a sweet form, since in this case the individual grains are covered with a sugary or toffee-like mixture.
Such a sugary or toffee-like mixture provides a convenient adhesive for holding the popcorn to the base of the container when the latter is inverted over the deep drawn bag portion. However, other suitable edible materials may be used in an adhesive capacity if appropriate.
In accordance with another aspect of the present invention there is provided a package of a food transformation product, comprising a container having untransformed product therein and a bag portion of heat extensible plastics material lying within the container and substantially following the interior contour of the container and food product therein, the bag portion being sealed to the mouth of the container, preferably by a broken or intermittent seal. When the package of food transformation product is placed in an oven or microwave oven, the product expands and extends the bag portion above the container to form a bag full of the product which is retained in the bag.
In order to enable the package to be opened readily, especially when the package is hot after the transformation of the food product, a tear-strip or opening strip may be incorporated in the side of the package. The tear strip may comprise a strip of material which is different from the material of which the lining of the container or of the container itself is made and which is also different from the material of which the bag portion is made, but which can be adhered as by heat-sealing, adhesively or otherwise both to the container or its linining and the bag. A suitable material for such a tear-strip is that sold under the Registered Trade Mark "Melinex" 850, which is a co-extruded plastics film comprising a layer of polyester and a layer of a heat-seal material which is present at a rate of 4 to 5g/m²; the tear-strip is conveniently about 30 microns thick.
If the package of food transformation product is to be stored then it is desirable to place the package in an outer or secondary package as it is possible to provide a desired and controlled atmosphere within such a secondary package thereby prolonging the shelf life of the food transformation product as the secondary package can be made with a very low gas and moisture vapour transmission rate. The primary package containing the food product can be placed in a thermo-formed outer container and covered with a lidding material which is sealed to the outer container in a controlled atmosphere packaging machine by means of so-called easy peel seal, that is to say a seal in which two compatible polymer materials are united by heat, but one of the polymers contains a differentially soluble polymer additive which settles out on cooling to form a line of weakness along which the polymers can be separated. Alternatively, the primary package of food transformation product can be flow wrapped in conventional manner.
In order to enable the invention to be more readily understood reference will now be made to the accompanying drawings which illustrate diagrammatically and by way of example some embodiments thereof, and in which:-

Figure 1 is a schematic view of plant for packaging popcorn,
Figure 2 is a schematic view of another plant for packaging popcorn,
Figure 3 is a schematic view of a plant for packaging the package produced by the plant shown in Figure 1 or Figure 2,
Figure 4 is a view of a package prepared by the plant shown in Figures 2 and 3,
Figure 5 is a perspective view of a flow wrapped package, and,
Figure 6 is a view of the package after it has been heated in an oven.

Referring now to Figure 1 of the drawings, a film 1 of polybutylene terephthalate 100 microns thick is unwound from a reel 2 and fed to a deep-drawing station 3 in which the film is deep-drawn in conventional manner make a forming 4 which for convenience will be referred to as a bag.
Moulded fibre trays 5, lined with a film of polyethylene terephthalate 36 microns thick and containing unpopped popcorn 6 adhered to the bases thereof by a toffee-like mixture, are fed along a conveyor 7 to a loading wheel 8. The loading wheel has a number of arms 9 each fitted with holding means 10 to hold a tray 5 firmly in position, either by means of grippers (not shown) or by suction. The loading wheel 8 is mounted above the film 1 and positioned so as to place the mouth of a tray 5 over the mouth of a bag 4, the peripheries of the mouths of the tray and bag being of the same shape. As the popcorn is adhered to the tray 5 by the toffee-like mixture, the popcorn does not fall into the bag. The bag 4 and inverted tray 5 are then are passed to a conventional vacuum/gas packaging machine 11 connected via a pipe 12 to a source of vacuum, where a vacuum is drawn between the bag 4 and the inverted tray 5 so that, as shown, the bag 4 is drawn into the tray 5 so as to lie closely adjacent the popcorn and substantially follow the interior contour of the container. Alternatively, the bag could merely occupy the head space of the tray in a collapsed state. The resulting package is then passed to a heat-sealing and cutting station 14 where the mouth of the bag 4 is heat-sealed to the lining at the mouth of the tray 5 and the package is severed from the surrounding film 1. The seal between the bag and the tray lining may be a broken or intermittent seal for a reason to be explained hereinafter. The sealed packages 15 are then removed by a conveyor 16.
When a package 15 of popcorn prepared in the manner described above, is placed in an oven or microwave oven and heated, the grains of corn expand many-fold and generate steam pressure and this expansion causes the grains to push out the bag 4 back to its original shape so that the bag 4 and the tray 5 are filled with a mass of expanded popcorn 17. Should it be desired for reasons of safety or function, during the heating of the package in the oven heated air and moisture generated by the heat can escape at the intermittent seal between the mouth of the bag and the mouth of the tray, if such a seal is provided.
Referring now to Figure 2, there is shown another plant for packaging a food transformation product which is not adhered to the base of a container. In this plant preformed containers in the form of deep flanged trays or tubs 20 of moulded fibre material are taken from a stock 21 of trays by destacking apparatus indicated by arrow 22 and placed in rows across a conveyor 23 so as to form a closely spaced array of trays on the conveyor. The trays 20 are fed beneath a loading device 24 which deposits a disc 25 of susceptor material at the bottom of each tray. The trays 20 are then fed to a thermoforming station 26. A reel 27 of polyethylene terephthalate film 28 which has a thickness of 36 microns is mounted above the conveyor 23 and the film is united with the trays 20 at the thermoforming station and serves to hold the discs 25 of susceptor material in the trays. The film is coherently bonded to the trays and discs by being heated by a heater 29 and by being drawn downwardly by a vacuum applied at a vacuum outlet 30.
After leaving the thermoforming station 26, the trays pass to a station 31 at which a tear strip 64 (c.f. Figure 4) is added. At this station 31 which is not shown in detail a strip of "Melinex" 850 is fed to each tray in a direction transverse to the conveyor so as to lie over the flange of the tray and is heat-sealed to the lining of the tray inside the tray and at the flange by means of a heated wheel or block (not shown).
After leaving the tear-strip station 31, the trays pass to a loading station 32 where the food transformation product 33, e.g. grains of corn, is placed in the tray. The trays then pass to an invaginating station 34.
A reel 35 of a film 36 of polybutylene terephthalate 100 microns thick is mounted above the conveyor 23 and above another thermoforming station 37 at which the film 36 is thermoformed into a forming or bag portion 38 using a heater 39 and a vacuum applied at a vacuum outlet 40. The bag portion 38 is shown as being of substantially the same shape as a tray 20 but it may be of any convenient shape bearing in mind its eventual purpose to hold the transformed food product.
After thermoforming and cooling of the resulting bag 38 at the thermoforming station 37, the bag 38 in a collapsed condition is then brought into contact with a tray with the mouths of the bag 38 and tray 20 in register with one another and the tray and bag are passed to the invaginating station 34 where by means of compressed air introduced through an inlet 41 the bag 38 is invaginated so that the bag substantially follows the interior contour of the tray and the grains of corn 33 in the tray. The tray 20 with the invaginated bag then passes to a vacuum sealing station 42 where a vacuum is applied via a vacuum outlet 43 to the space between the interior of the tray and the bag so that the bag is now forced closely to follow the interior contour of the tray and the grains of corn. At the same time the mouth of the bag is heat-sealed to the lining of the tray at the flange thereof. The seal is preferably an intermittent seal as indicated above. After leaving the station 42, the filled and sealed packages are separated by a knife or cutting means 44 into individual packages 45 which are either passed for sale or are passed for packaging in the plant shown in Figure 3 in which the packages 45 are packaged in secondary or outer containers. The necessity for packaging the packages 45 in outer containers may arise not merely for presentation but in order to extend the shelf-life of the food transformation product by packing it in a desired or controlled atmosphere.
Referring now to Figure 3, a film 50 of thermoplastic material comprising a layer of polyvinylidene chloride sandwiched between two layers of ionomeric polymer such as that sold under the Registered Trade Mark "SURLYN" and having a total thickness of 125 microns is unwound from a reel 51 and passed to a thermoforming station 52 where the film is thermoformed to produce an outer container 53 shaped to receive a package 45 leaving the plant shown in Figure 2 or a package 15 leaving the plant shown in Figure 1. The outer container 53 then passes to a loading station in which a package 45 (or 15) is placed in the container 53.
A lidding material 54 comprising a film of thermoplastic material comprising a layer of polyvinylidene chloride sandwiched between a layer of ionomeric polymer and a layer of polyethylene terephthalate and having a total thickness of 60 microns is unwound from a reel 55 and is brought to cover the container 53 with the ionomer layer of the lidding material in contact with a flange of the outer container. The lidding material is then united with the flange of the container 53 in a vacuum/gas flush controlled atmosphere packaging machine 56 of conventional kind in which the space between the lidding material 54 and the interior of the container 53 is filled with carbon dioxide or nitrogen and the lidding material is heat-sealed to the flange of the container. Finally, the containers are separated by cutting means 57 to provide the finished package 58.
Referring now to Figure 4, there is shown a cross-section through the package 58 showing the outer container 53 sealed by a lid 60 around a flange 61 of the container 53. The container 53 is formed with an internal shoulder 62 on which rests the outer flange of the tray 20 with its lining 63 secured to the wall of the tray and holding the disc 25 of susceptor material in place. The grains of corn 33 are closely covered by the invaginated bag 38 which is sealed to the mouth of the tray. In addition, a tear strip 64 is shown lying between the bag 38 and the tray lining 63.
Figure 5 shows an alternative wrapping in which the package 45 or 15 has been flow-wrapped in an envelope of material similar to the lidding material 54 using a convential flow-wrapping machine.
When the package shown in Figure 4 is to be used, the lid 60 is removed and to this end a tear strip similar to the tear strip 64 may be present at the edge or across the lid. The package 45 is then removed from the container 53 and placed in a microwave oven and heated in accordance with instructions present on the lid, on the package 45 or on the container 53. Heat generated causes the grains of corn to "pop" to produce popcorn and causes the bag 38 to be pushed out of the tray firstly to the position indicated at 65 in Figure 6 but due to the heat generated, the expansion of the atmosphere within the tray and the fact that the bag is made of heat-extensible plastics, the bag eventually takes up the position shown at 66. It will be appreciated that as the bag expands from the position shown at 65 to the position shown at 66, there is a thinning of the bag material. Accordingly, the thickness of the bag material, the shape to which the bag is thermoformed and the amount of food transformation product are chosen so that when the bag takes up the position shown at 66, the transformed product is contained wholly within the bag without any risk that the bag might burst. Thus it is possible to influence the final volume of the bag by controlling the thickness of the bag material.
Instead of providing the lid 60 of the package 58 with a tear strip similar to the tear strip 64 it could be provided with so-called "easy peel" seal but in this case the outer package 53 and the lidding material 54 would be made of different polymers such as a nylon, polyvinylidene chloride, polythene composite or a polypropylene, polyvinylidene chloride, polythene composite for the outer package and a polyester, polyvinylidene chloride, polythene composite for the lidding material. In an easy peel seal a differentially soluble polymer additive, such as polybutylene is incorporated in the lidding material. After heat sealing the lidding material to the flange 61 of the outer package 53, the polymer additive, which has become incorporated in the lidding material during the melting of the latter, settles out on cooling as a line of weakness permitting easy opening of the outer package. This can be assisted by the provision of a tab of the lidding material, if desired.
It will be appreciated that many modifications of the present packages are possible depending upon the materials used, the food transformation product and the temperature at which the transformation is to take place.

Claims

1. A method of packaging a heat transformation product, in which the product, held within a rigid container, is covered by a film of plastics material which is sealed to the mouth of the container, characterised in that the mouth of a bag portion formed from a film of heat-extensible plastics material is brought into contact with the mouth of the container which contains therein a heat transformation product in an untransformed state, and in that the bag portion is collapsed to cause the bag portion substantially to follow the interior contour of the container and product therein by the application of a pressure differential between the outside of the bag portion and the inside of the bag portion and container, the interior volume of the container and the bag portion being at least sufficient to contain said product when in its transformed state.

2. A method as claimed in Claim 1, wherein the method is carried out continuously by forming the bag portion by forming a film of heat-extensible plastics material unwound from a reel thereof, invaginating the bag portion into the container by vacuum or external pressure and sealing the mouth of the bag portion to the mouth of the container, preferably by an intermittent seal.

3. A method as claimed in Claim l or 2, wherein an inverted rigid container having the untransformed product adhered therein by means of an adhesive, is placed over the mouth of a deep-drawn bag portion which is then invaginated into the container.

4. A method as claimed in any one of Claims 1 to 3, wherein the rigid container is formed of a heat-resistant plastics material or is formed of moulded or bonded fibrous material provided with a lining of heat-resistant plastics material.

5. A method as claimed in any one of Claims 1 to 4, wherein the rigid container incorporates susceptor material or a pad of susceptor material is incorporated in the container between the lining and the fibrous material.

6. A method as claimed in any one of Claims 1 to 5, wherein the heat transformation product is a food transformation product, such as grains of corn (maize) transformable into "popcorn".

7. A method as claimed in 6, wherein the resulting package of food transformation product is packed within a secondary container using a controlled atmosphere packaging technique.

8. A package of heat transformation product, comprising a container, the product held within the container, and a film of plastics material sealed to the mouth of the container, characterised in that the container contains therein a heat transformation product in an untransformed state and the film of plastics material is in the form of a bag portion of heat-extensible plastics material lying within the container and substantially following the interior contour of the container and product therein, the interior volume of the container and the bag portion being at least sufficient to contain said product in its transformed state.

9. A package as claimed in Claim 8, wherein a tear-strip or opening strip is incorporated in the side of the package, the tear-strip preferably comprising a strip of a co-extruded plastics film comprising a layer of polyester and a layer of heat-seal material.

10. A package as claimed in Claim 8 or 9, wherein the heat-extensible plastics film is a film of a cast polyester, such as polyethylene terphthalate or polybutylene terephthalate, or a film of polycarbonate or polypropylene.

11. A package as claimed in any one of Claims 8 to 10 wherein the container is in the form of a flanged tray or dish and is made of a heat-resistant plastics material or of a moulded or bonded fibrous material lined with a heat-resistant plastics and optionally incorporating a susceptor material or a pad of susceptor material between the fibrous material and the lining.

12. A package as claimed in any one of Claims 8 to 11, wherein the heat transformation product is a food transformation product and comprises grains of corn (maize) transformable into "popcorn".