WO2007023317A2

WO2007023317A2 - Absorbing system in a container

Info

Publication number: WO2007023317A2
Application number: PCT/GB2006/050258
Authority: WO
Inventors: Michael Alan John Feast; John Hirst; Brenton John Zebedee
Original assignee: Stanelco Rf Technologies Limited; Emco Packaging Systems Limited
Priority date: 2005-08-25
Filing date: 2006-08-24
Publication date: 2007-03-01
Also published as: GB0517347D0; GB2429451A; WO2007023317A3; GB2429451B

Abstract

A polymeric container, for example for food or drink, contains a compartment containing an absorber (20, 38) for scavenging a selected gas or vapour from within the polymeric container. The compartment is formed by welding a polymeric membrane (18, 42) which is permeable to the selected gas or vapour to an internal surface of the polymeric container (30) or its polymeric closure (12, 16, 34) prior to the filling and closure of the container. The polymeric materials comprising the compartment are hence different in nature, and are dielectrically welded together to obtain secure closure of the compartment.

Description

Absorbing system in a container

This invention relates to a method of manufacturing an absorbing system comprising a compartment for removing gases or vapours from a sealed container and an absorbing system so manufactured.

Published patent applications such as WO 99/05922 and WO 02/11566 described products and processes for the removal of oxygen from within sealed containers. In the packaging of food and drink in sealed containers, and in the packaging of pharmaceuticals and other materials, it is often beneficial to remove certain gases from the inside of the sealed package so that the gas does not affect the contents in a deleterious fashion during storage. Oxygen is one such gas which can cause such effects. Such problems may be avoided by purging oxygen from the package before it is sealed and replacing it with a gas such as nitrogen which is effectively inert, but it is not easy to ensure complete removal of oxygen, and oxygen may subsequently be generated by the contents of the package during storage or may diffuse into the package through its walls during storage. Oxygen can be removed from within the sealed container by providing a scavenger within the container, which may for example be a material such as metallic iron powder which reacts with oxygen in the presence of water vapour, or a material such as palladium or derivatives thereof which catalyses a reaction of oxygen in the presence of hydrogen to form water Similar issues arise with other gases, for example carbon dioxide or ethylene, and in some contexts it may be desired to remove vapours such as water vapour or odours, and in these cases a range of different scavenger materials is required.

According to the present invention, there is provided a polymeric container containing a compartment, the compartment containing an absorber for scavenging a selected gas or vapour from within the polymeric container, the compartment being formed by welding a polymeric membrane which is permeable to the selected gas or vapour to an internal surface of the polymeric container or its polymeric closure prior to the filling and closure of the container, wherein the two polymeric materials comprising the compartment are different in nature and are dielectrically welded together to obtain secure closure of the compartment.

The present invention also provides a method of forming a polymeric container containing a compartment, the compartment containing an absorber for scavenging a selected gas or vapour from within the polymeric container, wherein the method comprises welding a polymeric membrane which is permeable to the selected gas or vapour to an internal surface of the polymeric container or its polymeric closure prior to the filling and closure of the container, the two polymeric materials comprising the compartment being different in nature and being dielectrically welded to obtain secure closure of the compartment .

In this application, the term "sealed container" should be understood to include small and large sealed containers, particularly but not exclusively sealed food and drink packages, and in particular, sealed food packages containing for example vegetables or sliced cooked meats, and sealed drink bottles containing for example wine, beer or fruit juice.

The material within the compartment would conventionally be referred to as a scavenging element.

The term scavenging element in this specification should be construed as encompassing any material which absorbs or removes a selected gas or vapour. For example the scavenging element may be an absorber for oxygen, for carbon dioxide, for ethylene, for moisture (such as silica gel, or a zeolite), or for an odour.

The permeable polymeric membrane is bonded to other parts to form the compartment, and those other parts may be impermeable. For example the permeable polymeric membrane may be bonded to an impermeable flexible polymeric material, to form a flexible compartment, or may be bonded to a rigid element, for example a lid of a container or a part of a lid, or to a board or other structure which may be of foam or of other materials, and which may be coated with a polymeric material, such that the scavenging element is effectively exposed to the atmosphere within the sealed container by virtue of the permeable polymeric material.

For the avoidance of doubt, the impermeable material may or may not form part of the wall of the sealed package. The compartment may be manufactured as a discrete entity enclosing the scavenging element and then located within the package (before or after the contents to be protected by the scavenging process) , for example as part of or within the cap of a bottle. But in many cases the compartment is formed in part by a wall of the sealed package.

Thus the compartment is preferably manufactured as part of the sealed package using a component, or part of a component, of the sealed package as the impermeable material. In the case of a drinks container with a screw cap, the impermeable material of the compartment can be the cap liner, or in the case of a food container, one of the walls of the container can be used as the impermeable material of the compartment.

The use of dielectric welding for performing the bond offers the only method that we have found for bonding polymerically dissimilar permeable membranes and impermeable materials and providing a robust assembly process, greater seal reliability, and an attractive appearance .

The permeability of the permeable polymeric material may be obtained either by selecting materials which have very low gas barrier properties or by perforating the polymeric material for example by passing a polymeric sheet over any type of perforating roller. In either case, the permeable polymeric membrane may comprise a single layer such as low density polyethylene having a thickness between 10 and 150 microns, or may be of laminated construction in which one or more layers of permeable polymeric material are laminated together. An example of a second permeable material which may be laminated in this way is a compressed very fine polymeric fibrous material such as Tyvek (RTM) .

The permeability of a material to a particular gas is typically defined by the volume of that particular gas which passes through one square metre of the material during a 24 hour interval. The pressure difference across the material whilst its permeability is being measured varies from one method to another and it is therefore important to describe the method that has been employed as well as the numerical result. Thus a typical figure for permeability is given in cubic centimetres per square metre per day. As an example, in this application, we are describing as permeable to oxygen a material that has a permeability of at least 1000 cm³/m²/day when subjected to a pressure difference of 100 millibars .

It is important to understand that the permeable material must allow the passage not only of the gas, water vapour, or odour which is to be removed by means of the scavenging element within the compartment but also of any other material which is necessary for catalysing or activating the process of scavenging or absorption. Thus, in the particular case of oxygen scavenging for example, where palladium and/or other platinum group metals or derivatives thereof are present within the compartment, both oxygen and hydrogen must be able to pass through the permeable polymeric membrane in order to allow any oxygen present within the compartment to be transformed into water. In the case where metallic iron dust is present as the scavenging element within the compartment, a relative humidity of around 75% is required within the compartment in order to allow the oxidation of the metallic iron dust, thereby eliminating any oxygen present.

The selection of the permeable polymeric membrane and the impermeable material between which the absorbent material is to be sealed is determined by the application in which the absorbing or scavenging compartment is being used. For every application, the materials should be selected to provide optimal performance of the absorbing compartment. However, it is essential that the permeable polymeric membrane and the impermeable material are reliably sealed together in order to prevent the scavenger or absorbent material from escaping through a leaking seal into the sealed container. In order to achieve optimal performance of the absorbing compartment in each specific application, the permeable polymeric membrane and the impermeable material (together the enclosing materials) are selected according to their respective physical and chemical properties. The enclosing materials must then be reliably sealed together in order to make the compartment. It has been found that dielectric welding allows enclosing polymeric materials of widely differing natures, compositions and thicknesses to be so sealed, and indeed, enclosing materials which cannot be reliably sealed together by other means can be so sealed by the use of controlled dielectric welding.

As is known, the dielectric welding is carried out by compressing the materials that are to be bonded together between opposed electrodes of electrically conducting material, and applying a suitable RF signal between the electrodes.

Preferably the electrically conducting material of each electrode is separated from the materials to be bonded by one or more layers of electrically insulating material. This insulation acts as a dielectric barrier, and also suppresses heat loss from the material being welded. The electrically insulating material is preferably one that is not dielectrically heated, for example PFA (perfluoro alkoxyalkane) , or polytetra- fluoroethylene (PTFE) . As another example, the electrodes may be of aluminium, and be coated with a layer of alumina (by anodising) which is impregnated with PTFE. Alternatively or additionally, a sheet of insulating material such as silicone rubber, providing good thermal and electrical insulation, may be interposed between the electrodes and the material to be bonded. The layer of electrically insulating material is preferably no more than 2 mm thick, and may be between 20 and 50 μm.

The radio frequency supply may in principle be at a frequency between 1 MHz and 200 MHz, usually between 10 MHz and 100 MHz, but stringent limits are imposed on any emitted radio waves. In practice therefore the choice of frequency may be more limited. For example the supply frequency may be 27.12 MHz, or 40.68 MHz.

Preferably the radio-frequency signal generator is a solid-state device, and the signals are supplied via a matching network. The matching network incorporates an inductor and at least one variable capacitor controlled by a servo motor; it monitors the radio frequency current and voltage, and adjusts the value of the (or each) variable capacitor so that the impedance presented to the generator remains at a constant value such as 50 Ω.

In one application, the impermeable material forming part of the absorbing compartment is the cap liner or wad that is placed within the cap, usually a screw cap, which is placed upon the neck or top of a filled container, for example a glass or PET bottle, after the container has been filled. The cap is then tightened to obtain leak- free closure of the container. Typically, the impermeable material is a closed-cell expanded foam with a smooth surface on both sides. The expanded foam can be made from LDPE, HDPE, PP, PET or from more complex materials. The permeable polymeric membrane is sealed to the impermeable material of the cap liner by dielectric welding in such a way that the compartment is fixed to that surface of the cap seal or wad that is exposed to the contents of the container. It should be noted that no part of the compartment should intrude upon the sealing surface between the bottle and the cap but instead, the absorbing compartment should lie entirely within that area circumscribed by the inner perimeter of the sealing surface between the cap and the container. By means of dielectric welding, the permeable polymeric membrane will remain sealed to the cap liner or wad and the resulting compartment will absorb or scavenge the desired gas, water vapour or odour from within the container. In this way, the shelf life and taste of the contents of the container may be enhanced.

This concept may also be applied to creating such compartments by dielectrically welding a permeable polymeric membrane to the inner surface (that which, in use, is exposed to the contents) of polymeric pull tabs, which are finding widespread use for the lidding of metal and plastic cans.

It should be noted that in this case, the contents of the container may be liquid (as in the case of wine or beer) , powder (as in the case of dried milk powder) or solid (as in the case of foodstuffs or pharmaceuticals) .

The invention will now be further and more particularly described, by way of example only, and with reference to the accompanying drawings in which:

Figure 1 shows a sectional view through the neck and cap of a bottle incorporating a compartment of the invention;

Figure 2 shows a sectional view of a sealed food tray incorporating a compartment of the invention; and

Figure 3 shows a modification to the sealed food tray of Figure 2.

Referring now to figure 1, there is shown the neck 10 and screw cap 12 of a glass or polymer (e.g. PET) bottle 14. The cap 12 would be used to seal the bottle 14 after it has been filled, to ensure a leak-free seal. Within the cap 12 is a disk 16 of foam material referred to as a cap liner, whose edge is compressed between the rim of the neck 10 and the underside of the cap 12 to ensure this leak-free seal. Typically this cap liner 16 is of expanded foam with a smooth surface on both sides, and can be made for example from LDPE, HDPE, PP, PET or other polymeric food-grade materials. Bonded to the underside of the cap liner 16 is a gas-permeable polymeric membrane 18 enclosing oxygen-scavenging material 20, so this material 20 is enclosed within an absorbing compartment formed between the liner 16 and the gas-permeable polymeric membrane 18. The gas-permeable polymeric membrane 18 does not extend to the outer annular part of the cap liner 16 which is clamped between the rim of the neck 10 and the underside of the cap 12. The gas-permeable polymeric membrane 18 is bonded to the cap liner 16 by a dielectric welding process, which can be expected to compress the foam around the weld line (as shown) .

The dielectric welding process may be incorporated into either rotary or flat bed machines, broadly as has been described in WO 03/089302 and WO 01/68452 respectively. However, the processes as set out in these patents must be adapted to suit each combination of permeable membrane and impermeable material.

The conventional way to bond polymeric materials is by heat sealing using a variety of means to deliver the heat, or by the use of ultrasonics, but neither of these methods, nor any other method, has been found to produce results that are acceptable in such demanding applications as the food and drink sectors where it is essential that the seal of the compartment is leak-free. It will be obvious to those skilled in the art that the use of dielectric welding allows the use of a wider selection of permeable polymeric membranes and a wider selection of impermeable polymeric materials. This, in turn, is of great importance when such a wide range of scavenging elements is covered by this invention.

In this example, the permeable polymeric membrane 18 may be a thin film of low density polyethylene for example of thickness 50 μm, which is adequately permeable to gases such as oxygen. Alternatively, it may comprise a membrane of perforated PET (polyethylene terephthalate) laminated with a solvent-free adhesive to a non-woven fabric such as Tyvek (RTM) on the side facing the scavenging material 20. The scavenging material 20 is effectively exposed to gases within the headspace of the bottle 14, and scavenges any oxygen from within that space. In this way, the shelf life of the contents of the bottle 14 may be enhanced, as the taste of the contents does not deteriorate. Thus in this case, typically, a laminate membrane of PET and of PE fibres (of the Tyvek layer) requires to be bonded to a foam layer of say HDPE or PET. Such disparate combinations are very difficult to bond by conventional techniques: for example heat sealing of the 50 μm PE membrane could not be achieved, as the membrane melts away before a seal is formed; heat sealing of the laminate membrane needed high temperatures, and did not give reliable results.

Use of adhesives has a significant risk of inhibiting gas permeability, and is not secure in liquid applications.

Referring now to Figure 2, a stiff, generally rectangular, tray 30 has rounded corners and a peripheral rim 32; it is used to pack a foodstuff 33 such as pre^¬ cooked meat. It may for example be of crystalline polyethylene terephthalate (CPET) with no surface bonding layer, and of thickness about 450 μm to ensure that it is stiff and offers an adequate oxygen barrier; and the rim 32 is of width 4 mm. It is sealed by a film 34 which is welded to the rim 32, for example by dielectric welding. The film 34 might comprise a 15 μm thick upper layer of APET; a 3 μm thick oxygen barrier layer of EVOH; and a lower layer 15 μm thick of APET; these layers may be bonded together by thin layers of adhesive.

Alternatively the tray 30 may incorporate a 50 μm thick PE upper surface layer, and the film 34 would typically incorporate a 50 μm thick PE lower layer, an EVOH oxygen barrier layer, and an APET upper surface layer. The two PE layers are surface bonding layers and enable the film 34 to be heat-sealed to the tray 30.

An absorbing compartment 36 containing a scavenging element 38 (such as iron, in the case where oxygen is desired to be absorbed) , is fixed to the tray wall near the top. The compartment 36, typically about 1 cm square and protruding about 4 mm from the wall, consists of a permeable polymeric membrane 42 to ensure that it is adequately permeable to gases such as water vapour and oxygen, welded around its edge to the side wall of the tray 30. The permeable membrane 42 and the wall of the tray 30 are very different in their composition and mechanical properties, and are sealed together around their periphery by dielectric welding.

In a modification shown in Figure 3, the compartment 36 differs from that of Figure 2 only in that the membrane 42 is welded to the inside of the lidding film 34.

Both the compartment formed by the liner 16 and the disk 18 (as in figure 1) and the compartment 36 formed by the membrane 42 (of Figures 2 and 3) are sealed by a dielectric welding process. At least in the first case the welding process preferably takes place between rollers acting as electrodes so that continuous webs of appropriate polymeric materials are formed into compartments filled with the scavenger material on a continuous basis as the rollers rotate, and are subsequently cut out from the continuous webs by means of a punch or other cutting methods.

Claims

1. A polymeric container containing a compartment, the compartment containing an absorber for scavenging a selected gas or vapour from within the polymeric container, the compartment being formed by welding a polymeric membrane which is permeable to the selected gas or vapour to an internal surface of the polymeric container or its polymeric closure prior to the filling and closure of the container wherein the two polymeric materials comprising the compartment are different in nature and are dielectrically welded to obtain secure closure of the compartment.

2. A container according to claim 1 wherein the impermeable body part comprises part of a cap liner for insertion in the cap of a drinks container.

3. A container according to claim 1 or 2 wherein the impermeable body part is a closed cell expanded foam.

4. A container according to claim 1 wherein the impermeable body part comprises part of the polymeric lid of a food or drinks container.

5. A container according to any of claims 1 to 4 wherein the permeable polymeric membrane comprises polyethylene of thickness less than 150 μm.

6. A container according to any of claims 1 to 4 wherein the permeable polymeric membrane comprises a perforated sheet of material.

7. A container according to any of claims 1 to 4 wherein the permeable polymeric membrane comprises a laminate incorporating a non-woven fabric layer.

8. A method of forming a polymeric container with a compartment that contains an absorber for scavenging a selected gas or vapour, comprising: providing a polymeric container;

providing a polymeric membrane permeable to the selected gas or vapour;

providing a scavenging element containing an absorber for the selected gas or vapour;

bonding the polymeric membrane to an impermeable body part of the container of different material to the permeable polymeric membrane to define the compartment enclosing the scavenging element, wherein the bonding is performed by dielectric welding.

9. A method according to claim 8 wherein the dielectric welding is carried out by: compressing the permeable polymeric membrane and impermeable body part together between opposed electrodes of electrically conducting material using electrically insulating material to separate the electrodes from the polymeric membrane and body part, and applying an RF signal between the electrodes at a frequency in the range 10 MHz to 100 MHz.

10. A method according to claim 9 wherein the electrically insulating material used to separate the electrodes is a sheet material.

11. A method according to claim 9 wherein the electrically insulating material used to separate the electrodes is a permanent coating.

12. A method as claimed in claim 11 wherein the coating comprises alumina.

13. A method as claimed in any one of claims 8 to 12 wherein the permeable polymeric membrane comprises polyethylene of thickness less than 75 μm.

14. A method as claimed in any one of claims 8 to 13 wherein the permeable polymeric membrane comprises a perforated sheet of material.

15. A method as claimed in any one of claims 8 to 14 wherein the permeable polymeric membrane comprises a laminate incorporating a non-woven fabric layer.

16. A sealed container within which is a compartment containing a scavenger material according to any of claims 1 to 7 or made by the method of any one of claims 8 to 15.