WO2006130923A1

WO2006130923A1 - A stopper with a foamed core and an outer skin

Info

Publication number: WO2006130923A1
Application number: PCT/AU2006/000798
Authority: WO
Inventors: Adrian Raymond Vom Berg; Frantisek Tkac
Original assignee: Advanced Beverage Closures Pty Ltd
Priority date: 2005-06-10
Filing date: 2006-06-09
Publication date: 2006-12-14
Also published as: AU2006255496A1

Abstract

A stopper (10) for a container includes a core (12) of foamed polymeric material and an outer skin (14). The polymeric material comprising the core is foamed with a foaming agent prior to injection of the foamed polymeric material into the injection cavity (26). The core is fully encapsulated by the outer skin by simultaneously injecting the outer skin with foamed polymeric material via a sequenced injection technique. A liner wad (100) for a threaded closure includes a wad (112) of foamed polymeric material and an outer skin (114). The outer skin comprises a plurality of layered polymeric films (116) bonded to the wad via a tie resin, and having a thickness of 100-500 microns.

Description

CLOSURE FOR A CONTAINER

Field of the Invention

The present invention relates to a closure for a container and a method for its manufacture. In particular, the invention relates to stoppers for narrow-necked containers, such as bottles for still and sparkling wine, and liner wads for screw- thread closures .

Background of the Invention

Wine bottle stoppers have historically been produced from the bark of the tree Qercus Suber, otherwise known as cork. The use of cork has been based on traditional practice and the physical properties of this material such as its density, compressive force and elastic modulus which make it suitable for this use. However, stoppers formed from cork demonstrate a number of disadvantages, including but not limited to crumbling, deterioration in wet and dry environments, an ability to support microbial growth if untreated, and the occurrence of taint causing chemicals such as trichloroanisole (TCA) . Additionally, there is a limited availability of cork for manufacture of wine bottle stoppers .

Consequently, there has been a trend toward the production of synthetic stoppers. In the main, many of the current synthetic stoppers have been unable to fully satisfy the physical and functional requirements for maintaining the integrity of the contents of containers, and satisfy the requirements for use by the end customer. Specific concerns include the inability of synthetic stoppers to be effectively retained in the neck of the bottle over extended time periods, wine taint and flavour scalping caused by contact of the wine with the synthetic material, and a tendency to allow air to enter the bottle either through or past the synthetic stopper.

These faults and drawbacks arise as a consequence of the characteristics of the polymer (s) selected to comprise the synthetic stoppers, inconsistency in the cellular structure obtained therein, and inherent variations in the manufacturing process itself. A consistent, uniform, fine cell structure contributes to the ability of a stopper to maintain even compression during insertion of the stopper into a narrow- necked container, and also to suitable reduction in stopper to corkscrew contact, for ready removal of the corkscrew from the stopper after extraction of the stopper from the narrow-necked container .

The present invention seeks to overcome at least some of the aforementioned disadvantages.

It is to be understood that although prior art use and publications may be referred to herein, such reference does not constitute an admission that any of these form a part of the common general knowledge in the art, in Australia or any other country. Summary of the Invention

In a first aspect of the invention there is provided a stopper for a container comprising a core of foamed polymeric material and an outer skin.

In one embodiment of the invention the outer skin adheres to the core of foamed polymeric material .

In another embodiment of the invention the outer skin substantially encapsulates the core.

The foamed polymeric material is selected to provide the core with desirable compressive recovery and compression set properties, whereas the outer skin affords the stopper with desirable release and gas permeability properties. In one embodiment of the invention the core of foamed polymeric material has a compressive recovery of less than 20 seconds. In another embodiment of the invention the core of foamed polymeric material has a compression set of no more than 30%.

In one embodiment of the invention the polymeric material (s) comprising the core are selected from one or more thermoplastic elastomers (TPE) , one or more thermoplastic vulcanisates (TPV) , or a homogenous blend thereof . In one embodiment of the invention the core contains a ratio by weight percent of thermoplastic elastomers : thermoplastic vulcanisates of about 30:70 to 75:25. - A -

In an alternative embodiment of the invention the polymeric material (s) comprising the core also contains a metallocene catalysed (co) polymer, preferably a metallocene catalysed polyalkylene copolymer, such as an ethylene octane copolymer, or a metallocene catalysed polypropylene copolymer. In one embodiment of the invention the core contains 20% to 30% by weight of metallocene catalysed (co) polymer.

Typically, the selection of polymeric material (s) comprising the core is governed by a consideration of whether the stopper is used for short or long term storage purposes. For short- term beverage storage, for example, the polymeric material preferably comprises a metallocene catalysed polyalkylene copolymer, such as an ethylene octane copolymer, or a metallocene catalysed polypropylene copolymer, optionally blended with one or more TPVs. For long-term beverage storage, the polymeric material preferably comprises one or more thermoplastic vulcanisates .

In one embodiment of the invention the polymeric material (s) forming the core are foamed with foaming agents. Examples of foaming agents include, but are not limited to, expandable fillers, chemical foaming agents, and inert gasses such as nitrogen and carbon dioxide. The expandable filler is preferably a polymeric shell containing a liquid hydrocarbon. The core preferably contains about 5% to 10% of the expandable filler based on the total polymeric material content.

The polymeric materials are foamed with a foaming agent to afford a density to the core of about 0.35 to about 0.65 g.cπf³, preferably about 0.4 to 0.6 g.cm^"3. In the preferred embodiment, the outer skin is formed from one or more thermoplastic elastomers. The thermoplastic elastomer or blend thereof comprising the outer skin may be the same as, or may differ from, the thermoplastic elastomers comprising the core, depending on the desired properties of the outer skin. Preferably, the outer skin is comprised of one or more thermoplastic elastomers which affords adhesion between the outer skin and the core .

In one embodiment of the invention, the one or more thermoplastic elastomers comprising the outer skin is also blended with colour-providing pigments, release agents, and other additives known to the person skilled in the art to afford desirable characteristics to the outer skin.

The stopper is configured for insertion with an interference fit into an opening of a container. In one embodiment of the invention the stopper is substantially cylindrical. The stopper has a uniform outer diameter and opposing axial ends provided with tapered bands or fillets.

In a further embodiment of the invention, respective surfaces of the opposing axial ends of the stopper are provided with a film. The film further reduces the gas permeability of the stopper. Preferably, the film comprises a single layer of polyvinylidene chloride (PVDC) . Suitable examples of polyvinylidene chloride films include but are not limited to L801 and L810A PVDC latex from Asahi Kasei Chemicals. The thickness of the film is about 10-30 microns. In a second aspect of the invention there is provided a method of producing a stopper for containers comprising injecting a foamed polymeric material into an injection cavity and forming a core of foamed polymeric material and co-injecting an outer skin encapsulating the core.

In one embodiment the polymeric material comprising the core is foamed with a foaming agent prior to injection of the foamed polymeric material into an injection cavity. The core is fully encapsulated by the outer skin by simultaneously injecting one or more thermoplastic elastomers, optionally blended with colour-providing pigments and release agents, with the foamed polymeric material via a sequenced injection technique. In this way, the core is substantially encapsulated by the outer skin in a single process step, and adhesion between the outer skin and the core is effected.

In a further embodiment of the invention the method further comprises applying a film to respective surfaces of the opposing axial ends of the stopper. In one particular embodiment of the invention the film is applied as a water- based emulsion of polyvinylidene chloride (PVDC) to respective surfaces of opposing axial ends of the stopper.

It is also an object of the present invention to provide a closure for a container comprising a threaded closure means having a liner wad disposed therein with desirable compressibility and permeability properties.

In a third aspect of the invention there is provided a liner wad for a threaded closure means, wherein the liner wad comprises a wad of foamed polymeric material and an outer skin. Preferably, the outer skin is bonded to one or more surfaces of the wad of foamed polymeric material .

Typically, the polymeric material (s) are selected from one or more thermoplastic elastomers (TPE) , one or more thermoplastic vulcanisates (TPV) , or a combination thereof.

In the preferred embodiment, the polymeric material is comprised of TPV. Preferably, the TPV has a high degree of cross-linked ethylene-propylene-diene-monomer (EPDM) . A typical example thereof is Santoprene 271-64 from Advanced Elastomer Systems.

In the preferred embodiment the polymeric material (s) forming the wad are foamed with foaming agents. The foaming agents may be physical, chemical, or inert gases. Examples of foaming agents include, but are not limited to, expandable fillers such as Expancel 92MB120 for Akzo Nobel, chemical foaming agents such as Hydracerol BIH70 from Clariant, and inert gasses such as nitrogen and carbon dioxide. The wad preferably contains about 5% to 10% of the foaming agent based on the total polymeric material content .

The polymeric materials are foamed with a foaming agent, either a physical, chemical or gaseous foaming agent, to afford a density thereto of about 0.4 and 0.6 g.cm^"3, preferably 0.35-0.50 g.cm^"3.

In one embodiment, the wad has a thickness of about 2 ± 0.2 mm. In the preferred embodiment, the outer skin comprises a plurality of layered polymeric films. The layered polymeric films are bonded to surface (s) of the wad via a tie resin. Advantageously, the outer skin provides a low permeability barrier to gasses such as oxygen, carbon dioxide and sulphur dioxide. One embodiment of the invention, for example, affords an oxygen permeability of approximately 1.7 cc.20u.m^" ².day^"1.atm^'1, which exceeds acceptable oxygen permeability standards for long term storage of wine.

In one embodiment, the layered polymeric films have a total thickness of about 100-500 microns. In a preferred embodiment, the outermost polymeric film comprises a polyalkylene film, preferably a linear low density polyethylene (LLDPE) film of about 50 microns thickness.

In a further aspect of the invention there is provided a threaded closure for a container having a liner wad disposed therein, wherein the liner wad comprises a wad of foamed polymeric material and an outer skin.

In the description and claims of the invention, except where the context requires otherwise due to express language or necessary implication, the words "comprise" or variations such as "comprises" or "comprising" are used in an inclusive sense, i.e. to specify the presence of the stated features, but not to preclude the presence or addition of further features in various embodiments of the invention. Brief Description of the Drawings

Preferred embodiments, incorporating all aspects of the invention, will now be described by way of example only with reference to the accompanying drawings, in which:

Figures l(a), 1 (b) , and l(c), show side, plan, and cross- sectional views, respectively, of a stopper for a container in accordance with a first aspect of the present invention; Figure 2 shows a flow chart describing a method of manufacturing the stopper of Figure 1; and,

Figures 3 (a) , 3 (b) and 3 (c) show plan, side, and cross- sectional views, respectively, of a liner wad of a threaded closure for a container in accordance with an alternative aspect means of the present invention.

Detailed Description of the Preferred Embodiments of the Invention

Before the preferred embodiment of the present apparatus is described, it is understood that this invention is not limited to the particular materials described, as these may vary. It is also to be understood that the terminology used herein is for the purpose of describing the particular embodiment only, and is not intended to limit the scope of the present invention in any way. It must be noted that as used herein, the singular forms "a", "an", and "the" include plural reference unless the context clearly dictates otherwise. Unless defined otherwise, all technical and scientific terms used herein have the same meanings as commonly understood by one of ordinary skill in the art to which this invention belongs .

Referring to Figures 1 (a) - (c) , there is shown a stopper 10 for a container (not shown) having a core 12 of foamed polymeric material and an outer skin 14. The outer skin 14 substantially encapsulates the core 12. Preferably, the outer skin 14 adheres to the core 12 of foamed polymeric material .

The stopper 10 is configured for insertion with an inteference fit into an opening of a container. In particular, it is envisaged that the stopper 10 will be typically used to plug an opening in a narrow necked bottle, such as narrow-necked bottles for still and sparkling wine.

In this particular embodiment, the stopper 10 is substantially cylindrical having a central portion 16 of uniform outer diameter and opposing axial ends 18. In one embodiment, the central portion 16 has a diameter of about 21.0 ± 0.2 mm, and one or both axial ands 18 are provided with circumferential tapered bands or fillets 17, having a length of up to 3 mm and reducing to an outer diameter of about 19.8 ± 0.2 mm in a direction away from the central portion 16. The length of the stopper 10 is nominally about 38 mm.

In an alternate embodiment the central portion 16 of the stopper 10 has a diameter of about 29 ± 0.2 mm, and the one or both axial ends 18 are provided with circumferential tapered bands or fillets 17 with a length of up to 3 mm, reducing to an outer diameter of about 26.0 ± 0.2 mm in a direction away from the central portion 16. The length of the stopper 10 is nominally 38 mm.

Typically, the thickness of the skin 14 is about 1.5 +/- 0.5 mm at the opposing axial ends 18, and about 0.8 +/- 0.2 mm along the central portion 16 of the stopper 10.

The foamed polymeric material is selected to provide the core 12 with desirable compressive recovery and compression set properties, whereas the outer skin 14 affords the stopper 10 with desirable release and gas permeability properties.

The term "compressive recovery" as used herein refers to the time taken for a material to substantially revert to its original shape after undergoing a compressive force, and in respect of the present invention relates to the ability of the material to obtain sealing pressure in an opening of a container after inserting the material in the opening of the container to form an interference fit therein. One test to measure compressive recovery in respect of the present invention is to measure the time taken to substantially obtain sealing pressure in the neck of a bottle of 19 mm diameter after insertion and compression of a stopper through an insertion diameter of 16 mm. A short period of time indicates a good compressive recovery which is important for maintaining a vacuum applied to the neck of the bottle at the time of bottling to reduce the oxygen level in the headspace. This in turn also has a significant bearing on the rate of sulfur dioxide loss on storage. In one embodiment of the invention the core of foamed polymeric material has a compressive recovery of less than 20 seconds. The term "compression set" as used herein refers to the ability of a material to resist permanent deformation under load, and in respect to the present invention relates to the ability of a stopper to provide ongoing sealing pressure by maintaining its original dimensions. In a standard test to measure compression set, a 50% compression is applied to the material, across the diameter thereof, for 70 hours at ambient temperature. The loss of original diameter is measured when the load is removed and a recovery time of 30 minutes has elapsed. In another embodiment of the invention the core of foamed polymeric material has a compression set of no more than 30% under the above test conditions.

The polymeric material (s) comprising the core 12 are selected from one or more thermoplastic elastomers (TPE) , one or more thermoplastic vulcanisates (TPV), or a combination thereof. Blends of TPEs with TPVs in various ratios will afford a range of compressive recovery and compression set properties. It is envisaged that a person skilled in the art will be able to readily select one or more TPEs and TPVs, and be able to formulate a suitable blend ratio thereof to obtain the desired compressive recovery and compression set properties of the stopper of the present invention. In one embodiment of the invention the core contains a ratio by weight percent of thermoplastic elastomers : thermoplastic vulcanisates of about 30:70 to 75:25.

The polymeric material (s) comprising the core can also contain a metallocene catalysed (co) polymer, preferably a metallocene catalysed polyalkylene copolymer, such as an ethylene octane copolymer, or a metallocene catalysed polypropylene copolymer. In this particular embodiment of the invention the core contains 20% to 30% by weight of metallocene catalysed (co) polymer.

Typically, the selection of polymeric material (s) or homogenous blend thereof comprising the core is governed by a consideration of whether the stopper is used for short or long term storage purposes. For short-term beverage storage, for example, the polymeric material preferably comprises a metallocene catalysed polyalkylene copolymer, such as an ethylene octane copolymer, or a metallocene catalysed polypropylene copolymer, blended with one or more TPVs. A suitable example of the metallocene catalysed polyethylene copolymer is Exact 0201 from Dex Plastomers, although alternatives such as Engage using the Dupont-Dow Insight technology are acceptable alternatives for the purpose of the present invention.

Alternatively, if faster compressive recovery characteristics are desired for the core, the metallocene catalysed polyalkylene copolymer may be a metallocene catalysed polypropylene copolymer, optionally blended with one or more TPVs. Vistamaxx from ExxonMobil is a typical example of a preferred metallocene catalysed polypropylene copolymer.

For longer term beverage storage, for example timeframes greater than 2 years, the core is preferably formed substantially from one or more foamed TPVs. In this particular embodiment, the TPVs are alloys of a rubber phase and a plastic phase in which the rubber copolymer phase is cross-linked and the plastic phase is polypropylene. The rubber copolymers are preferably of the type ethylene- propylene (EPDM) . Suitable examples of TPVs are Santoprene 271-73EU and Vyram, both from Advanced Elastomer Systems.

The polymeric material (s) forming the core are foamed with foaming agents. The term "foaming agent" as used herein refers to a physical agent, chemical agent, or gas, which is blended with the polymeric materials, and achieves a substantially even cellular structure throughout the matrix of the foamed polymeric material by a controlled release (or incorporation) of gaseous materials therein under treatment by heat. Examples of foaming agents include, but are not limited to, expandable fillers, chemical foaming agents, and inert gasses such as nitrogen and carbon dioxide. The expandable filler is preferably a polymeric shell containing a liquid hydrocarbon. When the liquid hydrocarbon inside the shell is heated its pressure increases and the polymeric shell softens resulting in the filler expanding. Suitable expandable fillers include Expancel 92MB120 from Akzo Nobel which are microspheres comprising a polymer shell encapsulating a liquid hydrocarbon. Utilising an expandable filler of this type assists in improving compatibilisation and dispersion in the matrix of the foamed polymeric material . Suitable examples of a chemical foaming agent includes Hydracerol BIH70 from Clariant .

A ratio of the polymeric material to the foaming agent, and the processing conditions for foaming the polymeric material must be optimised, these being techniques readily understood or known to those versed in the art. The core preferably contains about 5% to 10% of the expandable filler based on the total polymeric material content .

The polymeric material is foamed with a foaming agent to afford widespread and substantially even porosity throughout the core, so as to absorb and repel the compressive action required to insert the stopper into the container neck. The polymeric materials are foamed with a foaming agent to afford a density to the core of about 0.35 to about 0.65 g.cm^"3, preferably about 0.4 to 0.6 g.cm^"3.

The outer skin is formed from one or more TPEs, one or more TPVs, or homogenous blend thereof. The TPEs and/or TPVs comprising the outer skin may be the same as, or may differ from, the polymeric materials comprising the core, depending on the desired properties of the outer skin. Preferably, the outer skin is comprised of one or more TPEs, TPVs which affords adhesion between the outer skin and the core.

Preferably, the outer skin is a thermoplastic vulcanisate

(TPV) , with a cross-linked rubber phase comprising an isobutylene-isoprene co-polymer. The preferred TPV affords very low gas permeability properties to the outer skin, coupled with suitable hysteresis properties for the stopper insertion process. Preferably, the outer skin has a base hardness of about 65 - 85 Shore A. A typical example is Trefsin 3271-65W308 and 3271-85W308 from Advanced Elastomer Systems. A suitable alternative to this material is an EVA copolymer, with a VA content of between 8 and 10%. An example of this resin is Escorene FL00209 from ExxonMobil. Although the oxygen permeability is not as good as that of Trefsin, it does allow for desired adhesion to the foamed core .

Typically, the thermoplastic elastomer (s) , thermoplastic vulcanisate(s) , or blend thereof comprising the outer skin is also blended with colour providing pigments, release agents, and other additives known to the person skilled in the art to afford desirable characteristics to the outer skin. Incorporation of a poly-siloxane master-batch (such as supplied by Dow-Corning MB50-001) to provide reduction in surface friction is preferred.

Additionally, respective surfaces of one or both axial ends 18 of the stopper 10 can be provided with a film 19. The film 19 further reduces the gas permeability of the stopper 10. The term "gas permeability" as used herein refers to the ability of a matrix of a material to allow or restrict passage of gas therethrough. Preferably, the film 19 comprises a single layer of polyvinylidene chloride (PYDC) . Suitable examples of polyvinylidene chloride films include but are not limited to L801 and L810A PVDC latex from Asahi Kasei Chemicals. The thickness of the film 19 is 10-30 microns. Typically, the film 19 reduces the gas permeability of the stopper 10 to 0.00004cc/day.atm which is comparable to the gas permeability of tinfoil liners on standard screw cap closures (0.00002cc/day.atm.) .

Figure 2 illustrates the process of manufacture of the stopper

10. The polymeric material (s) comprising the core and optionally the foaming agents, are blended 22 in a first conventional mixing apparatus (not shown) . The blended polymeric material (s) are/is foamed with a foaming agent prior to injection of the polymeric material into an injection cavity 26. The components of the outer skin, comprising a blend of TPEs, TPVs, colour providing pigments, and release agents, and other additives are blended 24 in a second conventional mixing apparatus (not shown) and then the outer skin is co-injected with the foamed polymeric material via the action of a multi-material injection moulding press equipped with a two-channel nozzle 28. In this way, adhesion between the outer skin and the core is achieved, together with total encapsulation of the core by the outer skin, in a single process step .

Upon completion of the injection moulding step 28, it is preferable to remove residual materials which would normally taint a beverage contained in the container. Typically, the residual materials are anti-oxidants and heat stabilizers, which have been added to the polymeric materials of the core or the outer skin to provide consistent performance under high processing temperatures. The removal of residual materials, as described below, is similar to a treatment step that is common in the manufacture of medical bottle closures, and said removal step has been adapted to the specific requirements of a beverage container stopper .

The stoppers are placed in wire mesh trays in an appropriately designed washing unit, and subjected to treatment 30 with a warm ethanol/water solution applied under pressure via fine sprays for a predetermined period of time. A film can then be applied to respective surfaces of the opposing axial ends of the stopper 10.

The surface of the outer skin 14 of the stopper 10 is cleaned 30 via the action of ethanol as previously described, followed by a further washing with hexane 32, to activate the polymeric surface to facilitate the adhesion of the PVDC during the drying process. A water based of PVDC emulsion is applied 34 via techniques currently employed in the current coating of packaging materials, and dried using warm air of approximately 40C. The dry film build should be in the order of 10-20 microns thick to obtain required barrier properties, whilst ensuring that film cracking does not occur during compression and insertion of the closure to the narrow necked bottle. Upon complete drying, the Oxygen Transmission Rate (OTR) has been found to fall between 2-8 cc/m2/atm/day, which is most suitable for long term storage of oxygen sensitive beverages.

After allowing the stoppers to drain, the stoppers are further washed 36 with hot water applied under pressure via fine sprays for a predetermined period of time. The stoppers are then subjected to a stream of hot air to effect drying prior to removal of the stoppers from the washing unit .

The stopper can optionally be passed through a conventional rotational pad printer 38 if it is desired to apply trademarks/branding or other insignia or indicia to the stopper. To ensure optimal adhesion between the outer skin and the printing medium, it is preferred that the stopper is subjected to a pass of corona discharge (plasma treatment) to provide sufficient surface activation. After printing, any remaining volatile materials, in particular odour-forming materials are removed from the stoppers by the applying a vacuum thereto 40. The stoppers are transferred to a hot water jacketed vacuum oven, and subjected to pressures of around 5 mbar at 50 deg C for a predetermined period of time. When removed and cooled to ambient temperature, the stoppers are ready for packing and dispatch 42.

Referring to Figures 3 (a) to 3 (c) , there is shown a liner wad 100 for use in a threaded closure means (not shown) . The threaded closure means is of a type used with beverage containers for storing wine, alcoholic beverages such as beer, pre-mixed alcoholic beverages, cider, spirits, and liqueurs, still water, sparkling water, fruit and/or vegetable juices, fruit-based drinks, milk-based drinks, syrups, cordials, soy- based drinks, tea-flavoured beverages, coffee-flavoured beverages, and effervescent drinks or screw top jars and containers for storing foodstuffs, pharmaceuticals and substances which require storage in a closed, dry environment. Typically, the threaded closure means is formed from plastic or metals.

The liner wad 100 is configured for insertion into a base of a threaded closure means, and is adapted to compress and form a seal between the base of the threaded closure means and a rim of an open neck of the container when borne down upon by the rim. Typically, the liner wad 100 is disc-like. The liner wad 100 includes a wad 112 of foamed polymeric material and an outer skin 114. Preferably, the outer skin 114 is bonded to one or more surfaces of the wad 112 of foamed polymeric material. The wad 112 provides a compressible substrate for attachment of the outer skin 114 which restricts ingress and/or egress of gasses into the container. It is important that the wad 112 is compressible to ensure that any contours in the mouth or rim of the container are accommodated by the threaded closure means. In this way, it is envisaged that a long term sealing pressure is able to be applied to the substance contained in the container thereby enhancing its storage life. Furthermore, the outer skin 114 is arranged to afford a very low permeability barrier to gasses such as oxygen, carbon dioxide and sulphur dioxide, all of which feature prominently in concerns for storage life of beverages in particular.

Typically, the polymeric material (s) of the wad are selected from one or more thermoplastic elastomers (TPE) , one or more thermoplastic vulcanisates (TPV) , or a combination thereof, as described above in respect of the core 12 of the stopper 10.

In the preferred embodiment, the polymeric material is comprised of TPV. Preferably, the TPV has a high degree of cross-linked ethylene-propylene-diene-monomer (EPDM) . A typical example thereof is Santoprene 3251 from Advanced Elastomer Systems. If material costs are an issue, a metallocene PP from ExxonMobil (Vistamaxx VMXIlOO) , or an SEBS based resin may also be effectively utilised. In an alternative embodiment, the polymeric material is comprised of a thermoplastic elastomer, preferably Styrene- Ethylene-Butylene-Styrene (SEBS) . Preferably, the SEBS displays a high degree of cross-linking. Typically, cross- linking in the SEBS takes place after the polymeric material has been foamed and during extrusion of the foamed SEBS.

The polymeric material (s) forming the wad 112 are foamed with foaming agents. The foaming agents may be physical, chemical, or inert gases. Examples of foaming agents include, but are not limited to, expandable fillers such as Expancel 92MB120 for Akzo Nobel, chemical foaming agent such as Hydracerol BIH70 from Clariant, and inert gasses such as nitrogen and carbon dioxide. The wad 112 preferably contains about 5% to 10% of the foaming agent based on the polymeric material content .

The polymeric materials are foamed with a foaming agent, either a physical, chemical or gaseous foaming agent, to afford a density thereto of about 0.4 and 0.6 g.cπf³, preferably 0.35-0.50 g.cm^"3.

Typically, the foamed polymeric materials are extruded into a sheet of predetermined width at a thickness of about 2 ± 0.2 mm.

The outer skin 114 includes a plurality of layered polymeric films 116. The layered polymeric films 116 are bonded to surface (s) of the wad 112 via a tie resin 118 which is activated by heat and/or pressure. Advantageously, the outer skin 114 provides a low permeability barrier to gasses such as oxygen, carbon dioxide and sulphur dioxide. One embodiment of the invention, for example, affords an oxygen permeability of approximately 1.7 cc^Ou.m^.day^.atπf¹, which exceeds acceptable oxygen permeability standards for long term storage of wine .

Typically, the layered polymeric films 116 have a total thickness of about 100-500 microns.

In a preferred embodiment, an outermost polymeric film 118 comprises a polyalkylene film, preferably a linear low density polyethylene (LLDPE) film of about 50 microns thickness. Where the container is arranged to store beverages containing ethanol (otherwise known as alcohol) , it is preferable to use a polyethylene film as the outermost polymeric film 118 to protect the wad 112 from contact with the beverage, as in some cases the foamed polymeric materials used in the wad 112 will have limited resistance to ethanol, such as for example ethyl vinyl alcohol (EVOH) .

Alternatively, the outermost polymeric film may be provided with an inert inorganic coating. Suitable examples of such inert inorganic coatings include, but are not limited to, Al₂O₃ and SiO_x, applied via plasma deposition techniques.

It will be understood that the thickness of the outer skin 114, the number of layers of polymeric films 116 from which it is made, and the specific characteristics of the polymeric films 116 can all be manipulated to achieve variations in the overall permeability features of the outer skin 114. For example, a 0.5 mm thick layer of Trefsin can be applied to the wad 112 in a less complicated manufacturing process, while still providing a line wad 100 for a threaded closure means suitable for mid term storage of beverages.

For example, in one embodiment of the liner wad 100, the outer skin 114 consists of an outermost polymeric film 118 of LLDPE of about 50 microns thickness, the LLDPE film being in contiguous communication with a 10 micron thick layer of

Novatec 270L (or equivalent) , which in turn is in contiguous communication with a 25 micron thick layer of Soarnol A4412

(or equivalent) , which in turn is in contiguous communication with a 10 micron thick layer of Novatec 240H which is tie bonded to the wad 112.

The extrusion and application of the outer skin 114 to the wad 112 is achieved via standard technologies familiar to those skilled in the art. The outer skin 114 may be applied to one or both sides of the wad 112 depending on the permeability and cost requirements .

The liner wads 100 are punched out of the extruded sheet as described above in diameters appropriate for insertion to the threaded closure means, preferably a plastic or metal threaded closure, which provides the locking mechanism to the beverage container. The insertion of the liner wad 100 to the threaded closure means is usually achieved via, but not limited to, compressed air, to avoid the application of mechanical methods which can distort the liner wad 100 in such a way as to compromise the sealing performance that can be achieved if no such distortion is evident. Examples

Example 1: Formulation for Stopper for still wine bottle

1) Core - 92% Santoprene 271-73 (or Uniprene 7010- 73) and 8% (by weight) Expancel 92MB120

2) Outer skin - 98% Escorene EVA Ultra FL00909. Pigment is HDPE from Clarient

3) Coating on respective surfaces of opposing axial ends of stopper - Asahi Kasei PVDC latex L801 or L810A, applied to a dry film thickness of between 15 and 30 micron .

Example 2 : Formulation for Liner wad for screw thread closure

1) Wad - 95% Santoprene 271-73, or Uniprene 7010-73 , or Microflex SEBS and 5% by weight of Expancel 92MB120.

2) Outer skin - LLDPE film (50 microns) bonded to Novatec 270L (or equivalent) (10 micron) , which in turn is bonded to Soarnol A4412 (or equivalent) (25 micron) , which in turn is bonded to Novatec 240H (10 micron) which is tie bonded to the wad 112.

Example 3 : Formulation for Liner wad for screw thread closure

2) Outer Skin - Al₂O₃ plasma treated PET/CPP film (Toppan GX-P12u/CPP30u) applied with the cast PP layer in contact with the wad 112. Example 4 : Formulation for Liner wad for screw thread closure

1) Wad - 95% Santoprene 271-73, or Uniprene 7010-73

, or Microflex SEBS and 5% by weight of Expancel 92MB120. 2) Outer Skin - SiO_x plasma treated PE film applied with the cast PE layer in contact with the wad 112.

Numerous variations and modifications will suggest themselves to persons skilled in the relevant art, in addition to those already described, without departing from the basic inventive concepts. All such variations and modifications are to be considered within the scope of the present invention, the nature of which is to be determined from the foregoing description.

Claims

1. A stopper for a container comprising a core of foamed polymeric material and an outer skin.

2. The stopper according to claim 1 , wherein the outer skin adheres to the core of foamed polymeric material .

3. The stopper according to claim 1 or claim 2, wherein the outer skin substantially encapsulates the core.

4. The stopper according to any one of the preceding claims , wherein the polymeric material (s) are selected from one or more thermoplastic elastomers (TPE) , one or more thermoplastic vulcanisates (TPV) , or a homogenous blend thereof .

5. The stopper according to claim 4 , wherein the core contains a ratio by weight percent of thermoplastic elastomers: thermoplastic vulcanisates of about 30:70 to 75:25.

6. The stopper according to claim 4 or claim 5, wherein the polymeric material (s) further comprise a metallocene catalysed (co) polymer.

7. The stopper according to claim 6, wherein the metallocene catalysed (co) polymer is a metallocene catalysed polyalkylene copolymer .

8. The stopper according to claim 7, wherein the metallocene catalysed polyalkylene copolymer is an ethylene octane copolymer or a metallocene catalysed polypropylene copolymer.

9. The stopper according to any one of claims 6 to 8 , wherein the core contains 20 % to 30 % by weight of metallocene catalysed (co) polymer.

10. The stopper according to any one of claims 6 to 9, wherein for short term beverage storage the polymeric material comprises a metallocene catalysed polyalkylene copolymer blended with one or more TPVs.

11. The stopper according to any one of claims 6 to 9, wherein for long term beverage storage the polymeric material comprises one or more TPVs.

12. The stopper according to any one of the preceding claims , wherein the polymeric material (s) are foamed with foaming agents.

13. The stopper according to claim 12, wherein the foaming agents comprise expandable fillers, chemical foaming agents, or inert gases.

14. The stopper according to claim 13 , wherein the expandable filler is a polymeric shell containing a liquid hydrocarbon.

15. The stopper according to claim 13 or claim 14, wherein the core contains about 5 % to 10 % of the expandable filler based on the total polymeric material content.

16. The stopper according to any one of claims 12 to 15, wherein the density of the core is about 0.35 to about 0.65

17. The stopper according to any one of the preceding claims, wherein the outer skin is formed from one or more thermoplastic elastomers, one or more thermoplastic vulcanisates, or homogenous blends thereof.

18. The stopper according to claim 17, wherein the one or more thermoplastic elastomers, one or more thermoplastic vulcanisates, or homogenous blends thereof is blended with colour-providing pigments, release agents, and other additives known to the person skilled in the art to afford desirable characteristics to the outer skin.

19. The stopper according to any one of the preceding claims, wherein the stopper is substantially cylindrical, having a uniform outer diameter and opposing axial ends provided with tapered bands or fillets.

20. The stopper according to claim 19, wherein respective surfaces of the opposing axial ends of the stopper are provided with a film.

21. The stopper according to claim 20, wherein the film comprises a single layer of polyvinylidene chloride (PVDC) .

22. The stopper according to claim 19 or claim 20, wherein the thickness of the film is 10-30 microns.

23. The stopper according to any one of the preceding claims, wherein the core of foamed polymeric material has a compressive recovery of less than 20 seconds.

24. The stopper according to any one of the preceding claims, wherein the core of foamed polymeric material has a compression set of no more than 30%.

25. A method of producing a stopper comprising injecting a foamed polymeric material into an injection cavity and forming a core of foamed polymeric material and co-injecting an outer skin encapsulating the core.

26. The method according to claim 25, wherein the polymeric material comprising the core is foamed with a foaming agent prior to injection of the foamed polymeric material into the injection cavity.

27. The method according to claim 25 or claim 26, wherein core is fully encapsulated by the outer skin by simultaneously injecting one or more thermoplastic elastomers, optionally blended with colour-providing pigments and release agents, with the foamed polymeric material via a sequenced injection technique.

28. The method according to any one of claims 25 to 27, further comprising the step of applying a film to respective surfaces of opposing axial ends of the stopper.

29. The method according to claim 28, wherein the film is applied as a water-based emulsion of polyvinylidene chloride (PVDC) to respective surfaces of opposing axial ends of the stopper .

30. A liner wad for a threaded closure means, wherein the liner wad comprises a wad of foamed polymeric material and an outer skin.

31. The liner wad according to claim 30, wherein the outer skin is bonded to one or more surfaces of the wad of foamed polymeric material .

32. The liner wad according to claim 30 or claim 31, wherein the polymeric material (s) are selected from one or more thermoplastic elastomers (TPE) , one or more thermoplastic vulcanisates (TPV) , or a homogenous blend thereof .

33. The liner wad according to any one of claims 32, wherein the wad contains a ratio by weight percent of thermoplastic elastomers : thermoplastic vulcanisates of about 30:70 to 75:25.

34. The liner wad according to claim 32 or claim 33, wherein the polymeric material (s) further comprise a metallocene catalysed (co) polymer.

35. The liner wad according to claim 34, wherein the metallocene catalysed (co) polymer is a metallocene catalysed polyalkylene copolymer.

36. The liner wad according to claim 35, wherein the metallocene catalysed polyalkylene copolymer is an ethylene octane copolymer or a metallocene catalysed polypropylene copolymer .

37. The liner wad according to any one of claims 34 to 36, wherein the wad contains 20 % to 30 % by weight of metallocene catalysed (co) polymer.

38. The liner wad according to claim 32, wherein the polymeric material is comprised of TPV.

39. The liner wad according to claim 38, wherein the TPV has a high degree of cross-linked ethylene-propylene-diene-monomer (EPDM) .

40. The liner wad according to claim 32, wherein the polymeric material is comprised of SEBS.

41. The liner wad according to claim 40, wherein the SEBS displays a high degree of cross-linking.

42. The liner wad according to any one of claims 30 to 41, wherein the polymeric material (s) are foamed with foaming agents.

43. The liner wad according to claim 42, wherein the foaming agents comprise expandable fillers, chemical foaming agents, or inert gases .

44. The liner wad according to claim 43, wherein the expandable filler is a polymeric shell containing a liquid hydrocarbon.

45. The liner wad according to claim 43 or claim 44, wherein the core contains about 5 % to 10 % of the expandable filler based on the total polymeric material content.

46. The liner wad according to any one of claims 30 to 45, wherein the density of the core is about 0.35 to about 0.65 g. cm^"3.

47. The liner wad according to any one of claims 30 to 46, wherein the wad has a thickness of about 2 ± 0.2 mm.

48. The liner wad according to any one of claims 30 to 47, wherein the outer skin comprises a plurality of layered polymeric films.

49. The liner wad according to claim 48, wherein the layered polymeric films are bonded to the wad via a tie resin.

50. The liner wad according to claim 48 or claim 49, wherein the layered polymeric films have a total thickness of about 100-500 microns.

51. The liner wad according to any one of claims 48 to 50, wherein the outermost polymeric film comprises a polyethylene film.

52. The liner wad according to claim 51, wherein the outermost polymeric film comprises a linear low density polyethylene (LLDPE) film.

53. The liner wad according to any one of claims 48 to 52, wherein the outermost polymeric film is about 50 microns thickness .

54. The liner wad according to any one of claims 30 to 53, wherein the outermost polymeric film is provided with an inert inorganic coating.

55. The liner wad according to any one of claims 30 to 54, wherein the gas permeability of the outer skin is about 1.7 cc.20u.m^"2.day^"1.atm^"1.

56. A threaded closure for a container having a liner wad disposed therein, wherein the liner wad is as defined in any one of claims 30 to 55.