Container closure

Abstract: A preformed container closure element, preferably a cap, is formed of a polymeric matrix containing an ethylene vinyl alcohol polymer to reduce oxygen permeability of the cap. The cap is of special value for sealing filled jars or bottles, especially of glass, wherein the filling is beer.

Description: This invention relates to container closures that can be used to improve the shelf life of packaged materials, such as bottled beer. It is known to form packages for food and other materials by use of laminated polymeric material, generally including a barrier layer of low permeability to oxygen, and that may be formed of, for instance, a blend of polypropylene and ethylene vinyl alcohol (see for instance EP-A-0,142,183). EP-A-0044484 describes films of polyamide having saponified ethylene vinylacetate copolymers incorporated for the purpose of reducing oxygen transmission. These packages are generally flexible. Jars and bottles are much more rigid. They can be made of relatively thick and relatively impermeable polymeric material, for instance a polymeric material that includes a barrier layer. It is known from US-A-3,857,754 and US-A-3,975,463 to form articles such as bottles from certain compositions that include certain saponified ethylene-vinyl acetate copolymers. Often, however, the jar or bottle is made of glass. The jar or bottle is provided with a closure. Traditionally the closure was of metal but there is a trend now towards forming the closure of polymeric material. A gasket of polymeric material can be provided between the polymeric closure and the jar or bottle. GB-A-2,040,889 describes synthetic cork stoppers formed from foamed ethylene vinyl acetate for improved resilience and hence sealing with the neck of the bottle. Oxygen ingress is minimised by incorporating an oxygen scavenger into the foam cells. US-A-4,723,678 describes the use of a cap in accordance with the preamble of claim 1 containing a sealing gasket and, between the gasket and the cap, a disc of a liner material which acts as a barrier to oxygen and carbon dioxide. One example of material for forming the barrier liner is ethylene vinyl alcohol copolymer. Even when the body of the jar or bottle, is wholly impermeable, e.g., of glass, and the polymeric cap makes an airtight fit with the jar or bottle, possibly through a gasket between the cap and the jar or bottle, it is well accepted that some deterioration of fillings such as beer may occur on storage due to the ingress of gases. Although ingress of oxygen is a main cause of deterioration of beer, off-flavours can also arise when the container is exposed to an atmosphere containing other gases that can give an unpleasant flavour. For instance the containers are sometimes packed on pallets or in crates made of wood that has been impregnated with a preservative that may result in the atmosphere being contaminated with chloroanisole and it is necessary to prevent ingress of this. Accordingly it is well accepted that, when using polymeric caps for beer and other bottles, it is generally necessary to restrict the shelf life. It would be very desirable to be able to improve the shelf life significantly whilst continuing to use conventional materials for the formation of the container body, the container closure and the gasket between the body and closure. A closure according to the invention for closing a filled container has a preformed element of a polymeric composition in which the oxygen permeability of the element has been reduced by incorporation of ethylene vinyl alcohol polymer into the composition and the composition contains 2 to 10 percent by weight of a tie resin. The preferred products of the invention are caps formed from the polymeric composition. Preferred uses of the products are to close filled jars or bottles (especially of glass). The filling is normally beer, but can be any other material whose shelf life is restricted due to contamination during storage by oxygen or other gases. The preformed solid element is preformed in the sense that it is applied to the closure or to the container as a previously manufactured solid matrix and is not subsequently altered as by melting or flowing. This is in contrast to the invention described in our copending application EP-A-0,349,305 filed even date herewith in which a fluid or molten composition is applied on to a container closure to form, for instance, a solid gasket on that closure. The solid matrix is usually made by injection moulding in conventional manner and it is surprising that this can lead to good barrier properties. The preformed element may constitute the entire closure or part only of the closure. If it is the entire closure, then the closure is normally a cap and the cap is formed of the polymeric matrix containing the ethylene vinyl alcohol polymer. The cap can be moulded with an integral seal or intended for use with an inserted disc gasket or with a gasket that is lined on to it from a molten or fluid composition. If the element constitutes part only of the closure, it can be in the form of a panel that defines part of the closure. For instance the closure can be mainly of metal but can have a removable panel of polymeric material that can be torn out or otherwise ruptured in order to open the container. Another closure element of the invention is a liner or other preformed disc that is fitted between the neck of the filled container and the remainder of the closure, which can be of metal. The container body is preferably of metal or glass but can be of polymeric material. In one preferred aspect of the invention, the container body is of glass or polymeric material (especially being a jar or bottle filled with beer) and the preformed solid element is a plastic cap for the jar or bottle. The cap may be metalor may be polymeric. Thus it may be formed by, for instance injection or compression moulding of a suitable thermoplastic composition that may contain, as a thermoplastic polymer, polyethylene, polypropylene, ethylene propylene copolymer, polystyrene, polyacetyl, polyethylene terephthalate or a blend of two or more of these. The composition from which the cap is made may include other conventional ingredients for such compositions, including anti-oxidants, slip aids and fillers, generally all in minor amounts. The oxygen permeability of the cap is often at least 2cc STP/cm/cm 2 /sec/cmHg x 10 10 , often 2 to 5. In its simplest embodiment, a cap formed of such polymeric material and containing the polymer is the closure on a jar or bottle of glass or of polymeric material, such as polyethylene terephthalate or any of the other polymers mentioned above. When the container body is formed of polymeric material, the oxygen permeability of the body may be substantially zero or may be higher, for instance at least 0.07, typically 0.07 to 2cc STP/cm/cm 2 /sec/cmHg x 10 10 . The polymeric cap may be a crown cap, a twist-on cap or a screw cap or any other form of polymeric cap suitable for closing jars and containers. Instead of or in addition to forming the cap of the polymeric matrix containing ethylene vinyl alcohol polymer, the cap or other closure may be provided with an inner liner or other preformed disc or ring of the matrix containing ethylene vinyl alcohol polymer. For instance the cap may be provided with a preformed internal disc of polymeric matrix containing ethylene vinyl alcohol polymer or a polymeric film of such a matrix nay be sealed across the open top of the jar. The disc or ring is introduced in its final form and may be held loosely in the cap or it may be trapped in the cap by appropriate shaping of the inner face of the cap. This preformed disc or ring may, in some instances, serve as a satisfactory gasket between the closure and the container body. For instance it may be a butyl rubber or other polymeric ring of the type used as a gasket in baby-food jars. When the disc or ring is not a gasket, then a gasket of polymeric material may be provided between the cap and container body. This gasket may be of conventional material or, as described in copending application EP-A-0,349,305 the gasket may be formed on the closure from a fluid or meltable composition that comprises polymeric matrix material and ethylene vinyl alcohol polymer. The essential feature of the invention is that the composition from which the cap is formed contains ethylene vinyl alcohol polymer in an amount and form such that the oxygen permeability of the cap is reduced. The reduction can be very significant, e.g., usually at least 5%, often at least 10% and frequently above 15 or 20%, often as much as 50% or more of the oxygen permeability of the same composition but in the absence of ethylene vinyl alcohol polymer. The permability to other contaminating vapours is also reduced. The amount of ethylene vinyl alcohol polymer is usually in the range 5 to 50%, based on the weight of the other polymeric components. Amounts in the range 10 to 35%, preferably 20 to 30%, are often preferred. The ethylene vinyl alcohol polymer preferably has a melt index (in g/10min measured at 190°C, 2160g) in the range 1 to 15, often 4 to 10, most preferably 4 to 7. It typically has an ethylene content of 20 to 60%, generally 30 to 50%. Preferably the ethylene content is above 40%. The melting point of the polymer is generally in the range 150 to 180°C, preferably 160 to 170°C. The degree of hydrolysis of the polymer (from polyvinyl acetate) is generally above 95%. The oxygen transmission rate of the polymer (measured at 35°C, dry, in cc.15µm/m 2 .24hrs.atm) is generally below 10 and preferably below 5. The water vapour transmission rate (measured at 40°C, 90% RH in g.30µm/m 2 .24hrs) is generally below 50, preferably from 10 to 40. These ethylene vinyl alcohol polymer are especially suitable when, as is preferred, the cap is moulded from polypropylene. Although in some instances a composition that gives reduced permeability can be obtained merely by simple melt blending of the matrix polymer and the ethylene vinyl alcohol polymer, it is often found that the blend with polypropylene or other matrix polymer may have increased permeability. This indicates that proper distribution of the components of the blend has not been achieved and the blend may be non-homogeneous. Under these circumstances, the desired reduction in permeability can usually be achieved merely by increasing the shear applied during the mixing. Additionally (or in some instances alternatively) the permeability can be reduced by inclusion of a tie resin. Suitable tie resins for this purpose are materials of the type known for promoting bonding of polymeric films, especially a film of ethylene vinyl alcohol with a film of polymeric matrix material. The amount of tie resin typically is 2 to 10%, based on the weight of matrix polymer. Suitable tie resins are often based on ethylene vinyl acetate or modified polypropylene. Accordingly, once it is found that the simple blend gives worse permeability, the materials should not be abandoned but they should be blended further and/or with a tie resin. Routine experimentation within these guidelines will show how to obtain the desired permeability despite the initial contra-indication. By the invention it is possible to greatly prolong the shelf life of the beer or other content of the sealed jar or bottle. For instance the shelf life may be increased by 50% or more. The following are examples. Example 1 A cap-forming composition is formed of polypropylene with 20% ethylene vinyl alcohol blended into it. The ethylene vinyl alcohol polymer has an ethylene content of 44%, melting point 164°C, melt index 5.5, density 1.14, oxygen transmission rate about 3 to 5 and water vapour transmission rate about 15 to 30 (the measurement conditions and units all being as defined above). The permeability of a cap injection moulded from it is 120 cc/sq.m/day when the blending is by conventional melt blending. This is about the same as the permeability of the polypropylene alone. When the degree of shear during the melt blending is increased significantly, the permeability drops to 80. When 6pbw of an ethylene vinyl acetate tie resin are incorporated, the permeability is about 85, both with conventional blending and with high shear blending. Example 2 A cap formed by high shear mixing of polypropylene and ethylene vinyl alcohol, as in Example 1, has a gasket moulded in it from a composition of 85 parts low density polyethylene, 15 parts ethylene propylene elastomer and 20 parts ethylene vinyl alcohol polymer. The cap is used for sealing a beer bottle. The beer has a better shelf life than when the cap and gasket are both free of the ethylene vinyl alcohol.

Claims: A container closure for closing a filled container, comprising a preformed element of a polymeric composition characterised in that the oxygen permeability of the element has been reduced by incorporation of ethylene vinyl alcohol polymer into the composition and in that the composition includes 2 to 10% by weight of a tie resin. A container closure according to claim 1 in which the preformed element is selected from the entire closure, a removable area defining part of the closure, and a preformed disc that can be fitted between the remainder of the closure and filling in the container body. A closure according to claim 1 or claim 2 which is a cap formed by injection or compression moulding of the said polymeric composition. A closure according to any preceding claim in which the composition comprises materials selected from polyethylene terephthalate and polypropylene. A closure according to any preceding claim in which the oxygen transmission rate of the EVOH polymer (measured at 35°C, dry, in cc.15µm/m 2 .24hrs.atm) is below 10 and the water vapour transmission rate of the EVOH polymer (measured at 40°C, 90% RH in g.30µm/m 2 .24hrs) is below 50. A closure according to claim 5 in which the oxygen transmission rate is below 5 and the water vapour transmission rate is from 10 to 40. A closure according to any preceding claim in which the ethylene vinyl alcohol polymer has a melt index (g/10min measured at 190°C, 2160g) in the range 1 to 15. A closure according to any preceding claim in which the ethylene vinyl alcohol polymer has an ethylene content of 30 to 50% and a melting point of 150 to 180°C. A closure according to any preceding claim in which the tie resin is an ethylene vinyl acetate copolymer. A closure according to any preceding claim in which the amount of the ethylene vinyl alcohol polymer is from 5 to 50% by weight of the other polymeric components of the composition. Use of a closure according to any preceding claim by fitting it to a filled container of which the container body is of metal or glass. Use of a closure according to any of claims 1 to 10 by fitting it to a filled container of which the container body is formed of a polymeric material. Use according to claim 11 or claim 12 in which the container is filled with beer.

Inventors: SAMUEL DAVID NUTTALL, WILLIAMS RICHARD STEPHEN, SAMUEL, DAVID NUTTALL, WILLIAMS, RICHARD STEPHEN
Applicants: GRACE W R & CO, W.R. GRACE & CO.-CONN.
Application year: 1989
Main classification: B65D65
IPC codes: C08L29, C08L101, B65D65