US20130112688A1

US20130112688A1 - Hydrogen generating, oxygen scavenging closure cap

Info

Publication number: US20130112688A1
Application number: US13/704,159
Authority: US
Inventors: Hilde Krikor; Luc Verheyen
Original assignee: La Seda de Barcelona SA
Current assignee: Plastipak BAWT SARL
Priority date: 2010-06-18
Filing date: 2011-06-14
Publication date: 2013-05-09
Also published as: JP5946225B2; EP2397419A1; EP2397419B9; JP2013534884A; ES2530678T3; WO2011157695A1; ES2530678T9; EP2397419B1

Abstract

The closure cap (1) is capable of generating molecular hydrogen from a chemical reaction with water, and can be used for closing a container and for scavenging oxygen. The cap (1) comprises a shell (10), an active layer (11) that is capable of chemically reacting with water and generating molecular hydrogen, and a liner (12) that is permeable to water vapour and to molecular hydrogen; said active layer (11) has an inner face (11 a), an outer face (11 b) and a circumferential edge (11 c); the shell (10) comprises an housing and the active layer (11) is entirely contained in said housing; the outer face (11 b) and the circumferential edge (11 c) of the active layer (11) are in contact with the shell (10) and are bonded to the shell (10); the liner (12) is closing said housing (H) and is bonded to the shell (10) on the whole periphery of the active layer (11) and to the inner face (11 a) of the active layer (11).

Description

TECHNICAL FIELD

The invention relates to a novel closure cap that is capable of generating molecular hydrogen from a chemical reaction with water, and that can be used for closing a container and for scavenging oxygen. The container can be used for storing any oxygen-sensitive substance that can be altered by oxygen, and in particular a food substance or a beverage such as for example juice, beer, wine, . . .

PRIOR ART

Aromatic polyester resins, and in particular polyethylene terephthalate (PET), are widely used in the packaging industry for making various types containers for storing any substance, and in particular for storing food substance or a beverage.
PET has a number of valuable properties for packaging, but lacks sufficient gas barrier properties for many applications. In particular because of its oxygen permeability, PET alone is not appropriate for packaging oxygen-sensitive food and beverage products such as beer, fruit juices, some carbonated soft drinks, etc. . . . PET is also permeable to carbon dioxide, which in turn leads to a short shelf life for carbonated products, such as carbonated soft drinks, stored in PET containers.
In order to improve the gas barrier properties of packaging articles, in particular oxygen and/or carbon dioxide barrier properties, it is now common to use multilayered packaging articles, and in particular multilayered containers, that include at least one barrier layer. For example, in the field of bottle packaging, a typical and common multilayered wall structure for a hollow rigid container is a three-layer wall: two internal and external layers made of PET, and one intermediate gas barrier layer sandwiched between the two PET layers.
A first known type of barrier layer is made of, or comprises, polymers that have excellent gas-barrier properties, in particular to O₂and/or CO₂, and is generally referred as “passive barrier layer”. Among the polymers used for making passive barrier layers, homo- or copolymers of polyamides are commonly used. Among these polyamides, the so-called “MXD6” or “MXD6 nylon” (specific polyamide material manufactured by Mitsubishi Gas Chemical Company, Japan) is preferably used, i.e. a poly(m-xylyleneadipamide) produced by the polycondensation of a diamine component composed mainly of m-xylylenediamine and a dicarboxylic acid component composed mainly of adipic acid.
A second known type of barrier layer, which has been more recently developed, is made of, or comprises, polymeric composition that has oxygen-scavenging properties, and is generally referred as “active barrier layer”. Generally speaking, an active barrier layer reacts with the oxygen and “captures” the oxygen when the oxygen penetrates into the layer. Such active barrier layer is thus progressively “consumed” in use.
Examples of polymeric compositions used for making active barrier layer are described notably in European patent application EP-A-0 301 719 or in European patent application EP-A-0 507 207. Said polymeric compositions generally comprise an oxidizable polymer and a transition metal catalyst. In EP-A-0 301 719, the preferred oxidizable polymers are polyamides, and especially MXD6. In EP-0 507 207, one preferred oxidizable polymer is polybutadiene. In both cases, preferred transition metal catalysts are transition metal salts, an in particular cobalt stearate. Other known metal salts used for making such composition are rhodium, manganese, copper, iron.
With multilayered packaging articles having at least one gas barrier layer comprising a polyamide (e.g. MXD6) and a polyester (e.g. PET), very good results can be achieved in terms of shelf life of the packaged products. More especially when the barrier layer comprises a polyamide (e.g. MXD6), polyester (e.g. PET), and a catalyst such as a cobalt salt, the multilayered packaging article can be used for storing oxygen-sensitive products, such as beer, fruit juice, or the like. The shelf life of the packaged product widely depends of the amount of polyamide in the packaging article and of the thickness of the barrier layer.
In return, the use of gas barrier polymer, like polyamide in the container wall renders the recycling of the container more difficult. In addition, when polyamide is used, in particular for making a monolayer container, there is a risk of formation of haze in the container wall due to the orientation of the polyamide during the process for making the container. Said haze formation in the container wall is obviously detrimental for all the applications where it is important to have a transparent container, —i.e. a container whose wall has no eye-visible whitening or haze, in order to have a better appearance of the packaged product.
In order to improve the O₂scavenging performance of a plastic container, it is also known to close the container with a closure cap comprising a layer having O₂scavenging properties.
Another recent route for making a container having oxygen scavenging properties is described in PCT application WO 2008/090354. The O₂scavenging properties are obtained by using an active substance, such as for example a hydride, that is capable of chemically reacting with water and generating molecular hydrogen, and by making said molecular hydrogen react with oxygen which may ingress the container. In the variant of FIG. 4 of s PCT application WO 2008/090354, said active substance is incorporated in a plug that is positioned in a cap. In such a variant, the active substance can however prejudicially contaminate the product stored in the container.

OBJECTIVE OF THE INVENTION

A general and main objective of the invention is to propose a novel closure cap that includes an active substance capable of chemically reacting with water and generating molecular hydrogen into a container.
A more particular objective of the invention is to propose a novel closure cap, that includes an active substance capable of chemically reacting with water and generating molecular hydrogen into a container, and that can be in contact with the content of the container without any risk of contamination of the said substance by the active substance.
A more particular objective of the invention is to propose a novel closure cap, that includes an active substance capable of chemically reacting with water and generating molecular hydrogen into a container, and that can be easily manufactured.
A more particular objective of the invention is to propose a novel active closure cap for a container, said cap being suitable for scavenging oxygen that may penetrate inside the container, notably through the permeable wall of the container, or oxygen that is present in the head space of the container.

SUMMARY OF THE INVENTION

These objectives are achieved by the closure cap of claim 1. This closure cap of the invention comprises a shell that can be fitted onto a container for closing an opening of said container, an active layer that is capable of chemically reacting with water and generating molecular hydrogen, and a liner that is permeable to water vapour and to molecular hydrogen; said active layer has an inner face, an outer face and a circumferential edge; the shell comprises an housing and the active layer is entirely contained in said housing; the outer face and the circumferential edge of the active layer are in contact with the shell and are bonded to the shell; the liner is closing said housing and is bonded to the shell on the whole periphery of the active layer and to the inner face of the active layer.

BRIEF DESCRIPTION OF THE DRAWINGS

Other characteristics and advantages of the invention will appear more clearly on reading the following description of several closure cap embodiments, which description is given by way of non-limiting example and with reference to the accompanying drawings, in which:

FIG. 1 is a view in cross-section of a first variant of closure cap fitted onto a container neck,

FIGS. 2 to 6 are partial views in cross-section of five other variants of closure cap.

DETAILED DESCRIPTION

In reference to FIG. 1, a closure cap 1 of the invention is fitted onto a standard neck 2 of a plastic container C comprising a top opening (container mouth), like for example a bottle neck. This top opening of the neck 2 is knowingly used for filling the container with a product and/or for pouring the product outside the container. In this particular embodiment, the closure cap 1 is screwed on the container neck 2. In another variant, the closure cap 1 could be snapped on the container neck 2.
The material and the shape of the container are not important. In particular the container can be for example any plastic container or any cardboard container; the container can be for example a bottle-shaped container, a flask, a jar, a tube, a bag, a pouch. Within the scope of the invention, the container can be rigid, semi rigid or flexible. The containers contemplated in the present invention may be either of a monolayer or a multilayer construction. Suitable materials which may be used as a layer or part of one or more layers in either monolayer or multilayer containers include polyester (including but not limited to PET), polyetheresters, polyesteramides, polyurethanes, polyimides, polyureas, polyamideimides, polyamides, polyphenyleneoxide, phenoxy resins, epoxy resins, polyolefins (including but not limited to polypropylene and polyethylene), polyacrylates, polystyrene, polyvinyls (including but not limited to polyvinyl chloride)) and combinations thereof. All of the aforementioned polymers may be in any desired combination thereof.
The container C can be manufactured by using any method known in the art, including but not limited to injection moulding, injection blow moulding (IBM), injection stretch-blow moulding (ISBM), extrusion blow moulding, thermoforming, rotational moulding, folding.
This closure cap 1 comprises three main components: a closure shell 10, an active layer 11, and a liner 12.

Closure Shell 10

The closure shell 10 is a plastic piece that comprises a top wall 100 and a lateral wall 101. The top wall 100 forms a disc and comprises an outer face 100 a and an inner face 100 b that is intended in use to be oriented toward the inside (IN) of the container (FIG. 1). The lateral wall 101 is substantially perpendicular to the top wall and forms a substantially cylindrical lateral skirt 101. The inner face 101 a of this skirt 101 comprises a screwing thread 101 b that can cooperate with the screwing thread 20 of the neck 2 for securing the closure cap 1 onto the neck 2.
The closure shell 10 also comprises sealing means for substantially hermetically closing the top opening of the container neck 2, and avoiding any leakage of the product contained in the container. In this particular example, these sealing means comprise an inner cylindrical sealing lip 102 a and an outer cylindrical sealing lip 102 b, that extend both from the inner face 100 b of the top wall 100. The outer sealing lip 102 b is positioned between the inner sealing lip 102 a and the skirt 101. These sealing lips 102 a and 102 b can be replaced by any sealing element that cooperates with the container neck for sealing the top opening of the neck 2, once the closure cap 1 is fitted onto the neck 2.
The inner face 100 b of the top wall 100 comprises a central recess 103 that is made in the thickness of the top wall. This recess 103 is delimited by a bottom wall 103 a and a peripheral lateral wall 103 b. The lateral wall 103 b extends downwardly from the bottom wall 103 a and surrounds the bottom wall 103 a. This recess 103 forms a housing H for the active layer 11.
The closure shell 10 further comprises a shoulder portion 104 that surrounds the recess 103. Said shoulder portion 104 joins the lateral wall 103 b of the recess 103 to the internal sealing lip 102 a.
The material of the closure shell 10 can be any known thermoplastic material that can be moulded in a mould, and more particularly any known thermoplastic material that can be processed by injection moulding. Preferably, the closure shell is made from a polyolefin, like for example polypropylene, polyethylene, polyethylene terephthalate or a blend thereof. A good candidate for making the closure shell 10 is HDPE (High Density Polyethylene).

Active Layer

11

The active layer 11 is for example a disk-shaped layer, with an inner face 11 a, an outer face 11 b, and a circumferential edge 11 c. The active layer 11 is positioned inside the recess 103 of the closure shell 10 and is entirely contained in the recess 103. More especially, the active layer 11 completely fills the recess 103 without protruding outside the recess 103, the thickness E of the active layer 11 being substantially equal to the depth of the recess 103. The inner face 11 a of the active layer 11 (i.e. face 11 a oriented towards the inside IN of the container) is thus flush with the inner face 104 a of the shoulder portion 104, and there is no overlap of the active layer 11 outside the recess 103, and in particular no overlap of the material of the active layer 11 onto the inner face 104 a of the shoulder portion 104.
The outer face 11 b and the circumferential edge 11 c of the active layer 11 are in contact with, and are bonded to, respectively the bottom wall 103 a and lateral wall 103 b of the recess 103 of the shell 10. The active layer 11 is preferably only thermal bonded to the shell 10, i.e. without using an additional adhesive layer in-between.
The active layer 11 is capable of chemically reacting with water and generating molecular hydrogen from this reaction with water. The material of the active layer 11 can be made of or can comprise any active substance forming such a hydrogen source. Preferably, but not only, said active substance suitable for the release of molecular hydrogen as a result of contact with water is one of the active substances described in PCT application WO2008/090354.
In one preferred embodiment, the material of the active layer 11 comprises a polymeric matrix containing the active substance which is incorporated in the polymer matrix and which is capable of chemically reacting with water and generating molecular hydrogen from this reaction with water.
Suitable polymeric matrix materials include but are not limited to low density polyethylene, in particular linear low density polyethylene, high density polyethylene, polypropylene, ethylene vinyl acetate, thermoplastic elastomers (TPEs), like styrenic block copolymers, polyolefin blends, elastomeric alloys, thermoplasticpolyurethanes, thermoplastic copolyester, and thermoplastic polyamides, or blend thereof. In particular a good candidate among thermoplastic elastomer materials is a material comprising styrenic block copolymers consisting of polystyrene blocks and rubber blocks, such as for example SEBS, SEPS, SBS, SBC.
The ratio of the weight of active substance to matrix material may be at least 0.01, preferably at least 0.02. The matrix may be a polymeric matrix and said active substance may be dispersed therein. In general, once an active material is dispersed into a polymer, the rate of release of hydrogen is limited by either the permeation rate of water into the polymeric matrix and/or by the solubility of water in the chosen matrix. Thus, selection of polymeric materials based on the permeability or solubility of water in the polymer allows one to readily control the rate of release of molecular hydrogen from any number of active substances.
The polymeric matrix may include at least 1 wt % of active substance, preferably at least 2 wt %. The polymeric matrix may include less than 20 wt % of active substance. Suitably, the polymeric matrix includes 1-16 wt %, preferably 4-12 wt % of active substance. The balance of material in the polymeric matrix may predominantly comprise a said polymeric material.
Active substances suitable for the release of molecular hydrogen as a result of contact with water are preferably the ones described in PCT application WO2008/090354. In particular, said active substance may comprise a metal and/or a hydride. Said metal may be selected from sodium, lithium, potassium, magnesium, zinc or aluminum. A hydride may be inorganic, for example it may comprise a metal hydride or borohydride; or it may be organic.
More particularly, active substances include but are not limited to: sodium metal, lithium metal, potassium metal, calcium metal, sodium hydride, lithium hydride, potassium hydride, calcium hydride, magnesium hydride, sodium borohydride, and lithium borohydride.
Where the rate of reaction between the active substance and water is too slow, the addition of hydrolysis catalysts and/or agents in the polymeric matrix can be used. For example, the rate of hydrolysis of silicon hydrides may be enhanced by the use of hydroxide or fluoride ions, transition metal salts, or noble metal catalysts.
The active substance may also be the polymeric matrix. For example, polymeric silicon hydrides such as poly(methylhydro)siloxane provide both a polymeric matrix and an active substance capable of releasing molecular hydrogen when in contact with moisture.

Liner

12

The liner 12 is closing the recess 103 of the shell 10. The liner 12 is in contact with and is bonded to the inner face 11 a of the active layer 11 and to the shoulder portion 104 of the shell 10 on the whole periphery of the active layer 11.
In this particular variant of FIG. 1, the liner 12 is also in contact with and is bonded on its whole periphery to the internal sealing lip 102 a of the closure shell 10. This characteristic is however not mandatory.
When the closure cap 1 is fitted onto a container C, this liner 12 is facing the inside IN of the container C, and forms a protective barrier that prevents the product stored in the container from contacting the active layer 11 and that prevents the active substance (H₂generator) of the active layer 11 from migrating into the container. This liner 12 also to limit the ingress of water in contact with the active layer 11, and thereby enables to obtain a controlled release of molecular hydrogen by the active layer 11 over a prolonged period of time.
Preferably, the liner 12 is only thermal bonded to the active layer 11 and to the shell 10, i.e. without using an additional adhesive layer.
The liner 12 can be a monolayer or a multilayer component. The material of the liner 12 is preferably selected in order to obtain a liner 12 that:

- (i) is heat bondable to the closure shell and to the active layer 11, and
- (ii) is permeable to water vapour and to molecular hydrogen.

The material of the liner 12 can be any polymeric material that enables to obtain characteristics (i) and (ii). The materials of the liner 12 include but are not limited to low density polyethylene, in particular linear low density polyethylene, high density polyethylene, polypropylene, ethylene vinyl acetate, thermoplastic elastomers (TPEs), like styrenic block copolymers, polyolefin blends, elastomeric alloys, thermoplasticpolyurethanes, thermoplastic copolyester, and thermoplastic polyamides, or blend thereof. In particular a good candidate among thermoplastic elastomer materials is a material comprising styrenic block copolymers consisting of polystyrene blocks and rubber blocks, such as for example SEBS, SEPS, SBS, SBC.
Bonding of the Liner 12 with the Closure Shell 10
An efficient bonding between the liner 12 and the closure shell 10 is very important, in order to avoid delamination problems that would detrimentally lead to a risk of leakage and contact of the active layer 11 with the product stored in the container, and thereby to a risk of contamination of the product.
This efficient bonding is preferably obtained by using materials for the closure shell 10 and the liner 12 that are compatible in terms of thermal bonding, and that enable to achieve a very good thermal bonding of the liner 12 with the shell 10. To this end, the material of the liner 12 and the material of the closure shell 10 comprise, or are made of, at least one identical polymer. The material of the liner 12 can however be a polymeric material that differs from the material of the closure shell 10. In a preferred embodiment, the closure shell 10 was for example in HDPE and the liner 12 was a monolayer liner made of EVA or LLDPE or a thermoplastic elastomer comprising polyolefin blends or SEBS blends.
This efficient bonding is also improved by the particular structure of the closure cap with a recess 103 containing the active layer 11 and with a shoulder peripheral bonding portion 104. Thanks to the recess 103, the active layer 11 does not exert onto the liner 12 a mechanical action that would contribute to delaminate the liner 12 from the closure shell 10. The width (I) of the shoulder bonding portion 104 (FIG. 1) will be selected by one skilled in the art in order to obtain a sufficient bonding area between the liner 12 and the shell 10, and to avoid any risk of delamination during normal use.
FIGS. 2 to 6 show other variants for the closure cap.
In the variant of FIG. 3, the top wall 100 of the shell 10 comprises a recess 103, but in contrast with the variant of FIGS. 1, 2, 4, 5 and 6, does not comprise a shoulder bonding portion 104 for bonding the liner 12 to the shell 10. In this variant, the liner 12 is bonded to the shell only on its circumferential edge 12 a.
When the liner 12 is in contact with the internal sealing lip 102 a (like for example in the variants of FIGS. 1 and 2), there is a risk that the liner 12 exerts a mechanical constraint on the lips that leads to a deformation of the lip 102 a. Such a deformation can provoke leakage problems when the cap is fitted onto a container. To avoid this problem, in the variants of FIGS. 4 to 6, the liner 12 is advantageously not in contact with the internal sealing lip 102 a, and there is a gap G between the circumferential edge 12 a of the liner 12 and the internal sealing lip 102 a.

Manufacturing Process

The closure 1 can be for easily and quickly manufactured by using an over injection technique.
In a first step, the closure shell 10 is injection moulded in a mould. In a second step, the active layer 11 is over injected onto the closure shell. Then in a third step, the liner 12 is over injected onto the closure shell 10 and active layer 11.
During injection, the active layer 11 is compressed in the injection mould. When this mould is opened, a decompression of the active layer 11 can occur. In such a case the active layer 11 exerts on the liner 12 a pressure that pushes the liner 12 away from the shell 10. The bonding of the liner 12 is thus less strong, which can lead to detrimental delamination problems. To solve this problem, especially (but not only) when the active layer 11 comprises a thermoplastic elastomer, it is preferable that the hardness of the active layer 11, for example measured with a durometer according to ASTM D2240, is not less than Shore A hardness 40.

O₂Scavenging

In use, when the container C is containing a product, in particular an oxygen-sensitive product, and is closed by the closure cap 1, the liner 12 avoids any contact between the active layer 11 and the product stored in the container C. The water vapour contained in the head space of container penetrates through the liner 12 and enters in contact with the active layer 11.
As a result, the active substance of the active layer 11 produces molecular hydrogen that migrates through the liner 12 and penetrates in the container head space. This molecular hydrogen combines with oxygen which may have entered in the container through its permeable wall. As a result a reaction between hydrogen and oxygen takes place, and water is produced. This oxygen scavenging reaction can be catalysed by a catalyst incorporated in the closure cap 1 and/or in the container wall and/or in the container neck.
A large number of catalysts are known to catalyze the reaction of hydrogen with oxygen, including many transition metals, metal borides (such as nickel boride), metal carbides (such as titanium carbide), metal nitrides (such as titanium nitride), and transition metal salts and complexes. Group VIII metals are particularly efficacious. Of the Group VIII metals, palladium and platinum are especially preferred because of their low toxicity and extreme efficiency in catalyzing the conversion of hydrogen and oxygen to water with little or no byproduct formation. The catalyst is preferably a redox catalyst.
Preferably, but not necessarily, for facilitating the recycling of the closure 1, the closure cap 1 has a density less than 1, and the closure shell 10, the active layer 11, and the liner 12, have respectively three different colours in order to visually differentiate them. This is obtained for example by adding a first colorant (for example red) to the polymeric material of the active layer 11, and by adding a different colorant (for example blue) to the polymeric material of the liner 12, the shell 10 containing for example no colorant and being substantially white. The addition of colorant can be performed prior to injection or during the injection of closure cap components. In a variant, a third colorant (for example green) can be also added to the polymeric material of the shell 10.

Claims

1. A closure cap (1) comprising a shell (10) that can be fitted onto a container for closing an opening of said container, an active layer (11) that is capable of chemically reacting with water and generating molecular hydrogen, and a liner (12) that is permeable to water vapour and to molecular hydrogen, wherein said active layer (11) has an inner face (11 a), an outer face (11 b) and a circumferential edge (11 c), wherein the shell (10) comprises an housing (H) and the active layer (11) is entirely contained in said housing (H), wherein the outer face (11 b) and the circumferential edge (11 c) of the active layer (11) are in contact with the shell (10) and are bonded to the shell (10), and wherein the liner (12) is closing said housing (H) and is bonded to the shell (10) on the whole periphery of the active layer (11) and to the inner face (11 a) of the active layer (11).

2. The closure of claim 1, wherein the shell (10) comprises a top wall (100) having a recess (103) that forms the said housing (H), and wherein the liner (12) is closing the said recess (103) and is bonded to the shell (10) on the whole periphery of the said recess (103).

3. The closure of claim 1, wherein the shell (10) comprises a shoulder portion (104) that surrounds the recess (103), and the liner (12) is bonded to the shoulder portion (104) on the whole periphery of the recess (103).

4. The closure of claim 3, wherein the active layer (11) is flush with said shoulder portion (104).

5. The closure of claim 2, wherein the active layer (11) completely fills the recess (103) without protruding outside the recess (103).

6. The closure of claim 1, wherein the shell (10) comprises an inner cylindrical sealing lip (102 a) and wherein the liner (12) is not in contact with the inner cylindrical sealing lip (102 a).

7. The closure of claim 1, wherein the active layer (11) and the liner (12) are over injected onto a moulded shell (10).

8. The closure of claim 1, wherein the active layer (11) comprises an active substance that is capable of chemically reacting with water and generating molecular hydrogen.

9. The closure of claim 8, wherein the active substance is selected from the group comprising Group I, II, and III metals, Group I, II, and III metal hydrides, rare earth metals, rare earth hydrides, alkali metal borohydrides, alkaline earth metal borohydrides, alkali metal aluminum hydrides, silicon hydrides, tin hydrides, and combinations thereof.

10. The closure of claim 8, wherein the active substance is selected from the group comprising sodium hydride, lithium hydride, sodium borohydride, sodium metal, lithium metal, potassium metal, calcium hydride, magnesium hydride, lithium aluminum hydride, and combinations thereof.

11. The closure of claim 1, wherein the active layer (11) comprises a polymeric matrix.

12. The closure of claim 11, wherein the polymeric matrix comprises a polyethylene.

13. The closure of claim 11, wherein the polymeric matrix comprises an ethylene vinyl acetate copolymer.

14. The closure of claim 11, wherein the polymeric matrix comprises a thermoplastic elastomer.

15. The closure of claim 14, wherein the thermoplastic elastomer comprises a polyolefin blend.

16. The closure of claim 14, wherein the thermoplastic elastomer comprises SEBS.

17. The closure of claim 1, wherein the hardness of the active layer (11) is not less than Shore A hardness 40.

18. The closure of claim 1, wherein the liner (12) comprises a polyethylene.

19. The closure of claim 1, wherein the liner (12) comprises a thermoplastic elastomer.

20. The closure of claim 19, wherein the thermoplastic elastomer comprises a polyolefin blend.

21. The closure of claim 19, wherein the thermoplastic elastomer comprises SEBS.

22. The closure of claim 1, wherein the liner (12) comprises an ethylene vinyl acetate copolymer.

23. The closure of claim 1, wherein the shell (10) is made of a polymeric material comprising a polyolefin.

24. The closure of claim 1, wherein the material of the liner (12) and the material of the closure shell (10) comprise, or are made of, at least one identical polymer.

25. The closure of claim 1, wherein the liner (12) is only thermal bonded to the closure shell (10) and to the active layer (11).

26. The closure of claim 1, wherein the shell (10), the active layer (11), and the liner (12) have respectively three different colours in order to visually differentiate them.

27. The closure of claim 1, having a density less than 1.

28. An assembly comprising a plastic container and a closure cap, wherein the closure cap (1) is defined by claim 1.

29. The assembly of claim 28, wherein the plastic container and/or the closure cap (1) comprises a catalyst for promoting a reaction between molecular hydrogen and molecular oxygen.