WO2000064775A1

WO2000064775A1 - Container closure with gas scavenging seal

Info

Publication number: WO2000064775A1
Application number: PCT/GB2000/001460
Authority: WO
Inventors: Andrew Huckstep
Original assignee: Crown Cork & Seal Technologies Corporation; Carnaudmetalbox Plc
Priority date: 1999-04-21
Filing date: 2000-04-17
Publication date: 2000-11-02
Also published as: GB9909083D0; AU4581600A

Abstract

A lid (10) for closing the neck (2) of a packaging container has an oxygen scavenging sealing material (42) disposed around its periphery, and is designed such that when it is attached to the container a free region of sealing material (42) having a substantial area is in contact with the headspace gas within the container. The sealing material is preferably constrained within a peripheral channel (18), having a width such that the free region is in the range 3 to 10mm. The channel also includes a strengthening bead (38) formed above and around the free region, and extending above the height of the centre panel of the lid.

Description

CONTAINER CLOSUREWITH GAS SCAVENGING SEAL

This invention relates to closures for containers intended for packaging a product which is susceptible to deterioration by virtue of a gas in the container headspace . One particular combination of product and gas is beer, with oxygen which may occur in the container headspace as a residue of the filling operation or by virtue of inward permeation through the package wall. Beer is oxygen-sensitive, and for long shelf life of the package the oxygen concentration in the headspace gas should therefore be as low as possible and preferably zero .

It is already well known to use metal lids for closing glass or other containers onto a food product. The lids may form the whole closure as with conventional Twist-Off or PT (Press-on, Twist-off) caps, or they may be associated with plastic rings which serve to attach the closure in place on the container and/or to provide mechanical - tamperevidence for the closure. Such metal lids, with or without an associated plastics ring, usually have sealing material formed on their undersurface around their periphery. The sealing material may be a plastisol which is flowed into a shallow peripheral channel around the lid when in liquid form, and subsequently cured to a rubbery consistency so as to be capable of making an hermetic seal with the container neck when the closure is fitted.

In addition to the long-established use of metal lids for food products, it has more recently been proposed to use them for beers and other carbonated drinks held in wide-mouthed flask-like containers made from PET (Polyethylene Terephthalate) . Our copending patent application PCT/GB98/03013 (Agents Ref : W0058 O) represents one proposal of this kind. However, the lids which are described in that specification have no provision for removing oxygen from the container headspace; as previously indicated, this may restrict the shelf life of the package to an undesirable degree.

The present invention seeks in a technically and cost-effective way to provide a lid forming part or all of a container closure with the capability of removing oxygen or other gas from the container headspace . In accordance, therefore, with the invention there is provided a lid for closing the neck of a packaging container, the lid having sealing material disposed around its periphery for forming a hermetic seal with the container neck, characterised in that the sealing material is capable of scavenging a predetermined gas which may exist in the container headspace, and when the lid is fitted to the container a free region of the sealing material having a substantial area exists within the confines of the container neck and in contact with the headspace gas .

The area of the free region of sealing material may be varied in dependance upon various factors. The free region is typically annular, its radial thickness lying within the range 3 - 10mm, typically 6 mm.

As previously mentioned, an important application of the invention is for carbonated beverages such as beer. Preferably for such an application the lid has a downwardly facing peripheral channel in which the sealing material is received, the width of the channel providing the free region of the sealing material . Preferably the channel further includes a bead formed above and around the free region of the sealing material to strengthen the channel against the carbonation pressure. Typically, the bead extends above the height of the centre panel of the lid.

In order that the invention may be more fully understood an embodiment of the invention and a modification thereof will now be described by way of example and with reference to the accompanying drawings. In the drawings : -

Fig.l shows a closure in accordance with the invention, as seen in part on a radial section and before fitting to a container; and

Pig.2 similarly shows the closure when fitted to the container, and a modification thereof.

Referring now to Figs. 1 and 2, a closure 10 is provided for closing the neck 12 (Fig.2) of a wide- mouthed container which is moulded from PET (polyethylene terephthalate) . The container holds a carbonated product (not shown) , and is therefore subject to an internal pressure which is above ambient pressure. Typically the product is a 2.7 volume (C0 ) beer, and the superatmospheric pressure is about 2.5 bar at 20°C.

The closure 10 is composite and formed essentially of two parts, namely a closure lid in the form of a substantially plane disc 14, and an open ended ring 16 in which the lid is held captive. The lid is shown only in part, and should be understood to be circular and stamped from tinplate or other metal having protective varnish or decoration on its upper and lower faces as required. When the closure is in use the lower face is directed towards the container interior and the upper face faces outwardly .

Around its periphery the lid 14 is formed with two contiguous and concentric annular channels the outer one 18 of which is downwardly facing and holds a sealing material 42 for the closure, as will be more fully discussed later in the specification. The inner channel 20 is upwardly facing, the two channels sharing a common, generally downwardly and inwardly extending, wall 22. Within this wall the inner channel 20 extends inwardly via a base radius 24 to an upwardly and inwardly inclined generally frustoconical wall 26. The wall 26 is of lesser axial height then the common wall 22 and merges at its top end with a large flat panel 28 which occupies the centre of the closure. Typically the closure has an overall diameter of 68mm, the diameter of the central panel being 60mm.

The outer channel 18 is flanked by the common wall 22 on its inside and, on its outside, by a downturned cylindrical margin 30 which forms the outer periphery of the lid 14. The margin 30 extends downwardly to the lid free edge which is denoted by the reference numeral 32.

In the radially inward direction of the closure the outer channel 18 continues from the top end of its margin 30 and through an outer radius 33 to a flat annular panel 34 which is destined to overlie the container neck 12 as shown in Fig.2. In its turn the flat panel is joined to the base of the outer flank 36 of a continuous upstanding bead 38 of substantially semicircular cross-section. The inner flank of this bead merges with the common wall 22 When viewed in radial section, i.e. as shown in the drawings, the wall 22 has generally the form of a shallow S so as to join the bead 38 and radius 24 steplessly together.

The plastics ring 16 of the closure 10 is essentially cylindrical and has a relatively thick tubular wall 50 having a thickness, typically, of

2.5mm. In use the ring has to hold the lid 14 securely against substantial pressure which may exist in the associated container; it is therefore moulded from a relatively hard, creep-resistant polymeric material, polypropylene filled with 20% talc being preferred.

The ring 16 has a generally cylindrical exterior surface which is ribbed at 52 to assist gripping. The interior surface 54 of the ring is generally cylindrical, but an interrupted multi-start thread formed of three identical and regularly spaced segments 56 each occupying 110° of subtended angle projects inwardly from it.

Around its upper end as shown, the ring 16 is formed with an inwardly projecting flange 60 having an annular lower face 62 which is spaced from the thread segments 56 by a substantial axial spacing.

Fig.2 shows the closure 10 as assembled and as subsequently fitted to a container neck 12 which has three thread segments 82 complementary to the thread segments 56 of the closure. The ring 16 is formed by injection-moulding using a collapsible mould core so that, in particular, the upper flanks 72 of the thread segments 56 can be closely toleranced and steeply angled as required.

For assembly the lid is forced into the ring through its bottom end, past the thread segments 56. The rounded undersurfaces of the thread segments assist this movement, which continues until the lid is located and held loosely captive in the axial spacing between the undersurface 62 of the flange 60 and the thread segments 56. In this condition the closure is ready for application to the container neck 12. The closure is fitted to the container in a conventional way by downward pressure and rotational torque (in the screwing-up direction) which are applied to the ring 16 after the closure has been presented to the container neck. Fig.2 shows the closure and container when the screw thread segments 56, 82 of the ring and container neck have been fully engaged. The container neck rim then deeply indents the sealing material 42 in the lid channel 18, the ring flange 60 bearing resiliently down upon the lid periphery to maintain a secure gas and liquid-tight seal by the sealing material despite the lifting action of product pressure on the underside of the lid.

The closed package is intended for a pop concert or other such occasion at which beer (or other carbonated product) must be dispensed from the packages to individual consumers in a quick and safe manner. Opening is simply achieved by a server who twists the ring 16 in the normal anti-clockwise direction, manually or otherwise. The ring is accordingly allowed to rise on the container neck, driven by product pressure the effect of which is transmitted to the ring by the engagement of its flange 60 with the lid periphery.

Although it makes firm engagement with the flange 60 substantially at all times, the lid is able to rotate relatively freely in relation to the ring. This freedom of the ring to rotate independantly of the lid substantially reduces the torque which must be applied at the beginning of the unscrewing operation, when substantial stiction (static friction) still exists between the lid and the container at the sealing material 42. As unscrewing proceeds the gas-tight seal between the lid and the container neck is broken, and gas is able to escape between the lid and the neck in a generally downward direction between the thread segments 56, 82 and down any vent slots (not shown) which may be formed in the thread segments. In this way the risk that the closure will "missile" in a dangerous manner is prevented. Eventually the closure is free for removal, and the container can be passed to a consumer for consumption of the beer product. An important feature of the invention is illustrated in Fig.2, in which the radial disposition of the container neck 12 in relation to the channel 18 and the sealing material 42 is clearly visible.

Being of an oxygen-sensitive nature, over a period of months following the container filling and closing operations the beer in the container will deteriorate if a substantial concentration of oxygen exists in the container headspace. This relatively high oxygen concentration may remain from the filling operation, and/or it may occur subsequently by virtue of oxygen permeation through the package wall.

In order to reduce the oxygen concentration of the headspace or, as appropriate, maintain it at a desired low level, the sealing material 42 of the closure 10 has an oxygen scavenger in suitable form incorporated into it. In addition to the presence of this oxygen scavenger in the sealing material 42, the closure 10 is further modified by extending the channel 18 in the radially inward direction so that a substantial free region of the sealing material and, correspondingly, of the oxygen scavenger is presented to the container headspace. In Fig.2 this area is provided by an annulus of radial thickness T which extends around the closure periphery. Also shown in Fig.2 is a radial clearance D by which the container neck 12 may be separated from the outer margin 30 of the lid 14. In order to resist gas ingress into the sealing material 42, this clearance is made as small as possible, with due allowance being made for the manufacturing tolerances of the container and the lid. A typical value of the distance D is 1.5mm, although clearances of up to 2mm may occur. The thickness T may be varied in dependance upon such factors as the activity of the oxygen scavenger, the volume of the container headspace, the oxygen permeability of the container wall and of the sealing material, the temperature at which the beer will be held in storage, and the shelf life required for the beer. A typical value of the thickness T is 6mm, although thicknesses within the range 3 - 10mm are contemplated. In any event, the thickness T will usually be substantially larger than the clearance D, ratios of between 3:1 and 6:1 being typical. In this respect it should be noted that in order to minimise oxygen permeation into the container headspace, conventional practice would dictate that the thickness T should be made as small as possible, and likewise within the 0 to 2mm range of the clearance D.

The sealing material 42 is a blend of a conventional PVC plastisol sealing compound with a reducing agent such as sodium ascorbate or sodium sulphite which is dispersed in the plastisol liquid in find particulate form with a particle size of, preferably, less than 0.5mm. The material is flowed into the outer channel and subsequently cured in the usual way for plastisol sealing compounds. A blowing agent may be used if desired to provide increased resilience and permeability of the sealing material to oxygen. In that respect, Applicants believe that a substantial permeability of the sealing material for oxygen may be beneficial because it allows the oxygen access to the scavenging sites within it.

The bead 38 forms a pressure-resistant connection between the annular panel 34 and the inner channel 20. It is provided in order to strengthen the outer channel 18 against high superatmospheric pressures of the order of 5 bar and above which may exist in the container headspace for some products. A possible modification of the lid for lower pressure applications is shown in Fig.2 (only) and indicated by dashed lines. A gently domed but downwardly and inwardly sloping panel 64 now joins the inside periphery of the annular panel 34 to the radius 24 at the base of the inner channel 20, so as to form the common wall separating the channels 18 and 20. The panel can therefore be considered to replace the bead 38 and wall 22 which have previously been described.

Whilst it has been specifically described above for the packaging of beer, the invention may have application to the packaging of other products, whether pressurised or otherwise. The closure may be formed entirely of plastics or metal (rather than from a combination of the two) , and the scavenger incorporated in the sealing material may be capable of scavenging gases other than oxygen .

The incorporation of scavenger into the sealing material gives particular cost benefits, particularly if the sealing material can be deposited and cured by conventional methods despite the presence of the scavenger. A wide variety of sealing compounds and scavengers may be used.

Claims

C AIMS :

1. A lid for closing the neck of a packaging container, the lid having sealing material disposed around its periphery for forming a hermetic seal with the container neck, characterised in that the sealing material is capable of scavenging a predetermined gas which may exist in the container headspace, and when the lid is fitted to the container a free region of the sealing material having a substantial area exists within the confines of the container neck and in contact with the headspace gas.

2. A lid according to claim 1, characterised in that the free region of the sealing material is annular.

3. A lid according to claim 2, characterised in that the radial thickness of the free region of sealing material is in the range 3 to 10mm.

4. A lid according to claim 2, or claim 3, characterised in that there is a downwardly facing peripheral channel in which the sealing material is received, the width of the channel providing the free region of the sealing material.

5. A lid according to claim 4, characterised in that the channel includes a bead formed above and around the free region of the sealing material, the bead strengthening the channel against any pressure from within the packaging container.

6. A lid according to claim 5, characterised in that the lid has a horizontal centre panel, and that the bead extends above the height of the centre panel.