FR2825350A1 - MULTILAYER GASKET, PLUG OR CONTAINER NECK COMPRISING SUCH GASKET, AND METHODS OF MAKING IT - Google Patents

Abstract

The invention concerns a cap liner (9) comprising: a middle layer made of a plastic material with gas barrier effect; first and second outer layers comprising each a polyolefin resin and arranged on either side of the middle layer; an intermediate polyethylene layer, placed between the middle layer and each of the outer layers, the intermediate layers being designed to protect the middle layer against moisture and to prevent degradation of said middle layer gas barrier properties. The cap liner can be placed in a cap near its transverse wall or towards the free end of its skirt or on a container neck. It can be planar or thermoformed. The invention also concerns methods for producing a neck-joint cap assembly.

Description

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 The invention relates to a composite seal suitable for being placed in a stopper or on a container neck, a stopper comprising such a seal, a neck comprising such a seal and an assembly comprising a stopper, a container and such a seal, the container being empty or at least partially filled with a certain content.

 The invention also relates to a method of plugging a container with a stopper provided with such a seal, and a method of making and sealing a neck provided with such a thermoformed seal.

 The invention applies more particularly to the case of containers intended to contain carbonated drinks, the seal according to the invention ensuring liquid tightness and gas impermeability between the inside and the outside of the container closed by the said cap.

Such seals are already known, in particular described in patent FR 2 704 805 issued by the applicant.

Such seals generally comprise a middle layer made of a material having gas barrier properties, as well as additional layers, arranged on either side of the middle layer, intended in particular to impart a certain flexibility to the seal.

The gas barrier properties of the middle layer of the seal placed in a stopper make it possible to seal the containers so that there is no entry of oxygen inside the container, nor exit of carbon dioxide from the container, in the case of carbonated drinks for example.

In this way, the alteration of the products contained in these containers is avoided, in particular their taste qualities when it comes to drinks.

However, the material of which the middle layer is made is very porous and easily absorbs water. However, this material loses its gas barrier properties when it has absorbed water.

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 Consequently, seals of the prior art, sensitive to humidity, can undergo a degradation of their gas barrier properties, and no longer play their role when they are placed in a cap on a container neck.

US Patent 6,139,931 describes a seal comprising a middle layer having gas barrier properties, on either side of which are arranged layers of polyolefin resin.

These polyolefin resin layers are preferably made of recycled material, or of poor quality, this in order to reduce the cost of producing the joint.

According to one possible embodiment, the seal also comprises two outer layers made of good quality polyolefin resin, and suitable for contact with food.

One of the functions of these outer layers is to prevent the entry of water into the joint, which could affect the gas barrier properties of the middle layer.

However, the fact that these layers are located on either side of the joint, and not inside it, has a number of drawbacks.

On the one hand, the outer layers of the joint are subjected to attacks which can damage them and thus affect their integrity. Let us cite in particular the contact of the seal with the end wall of the plug in which the seal is intended to be placed, as well as the contact with the rim of the neck of the container intended to cooperate with said plug. The seal can also be damaged, even unintentionally, by the user. The protection of the middle layer against humidity is no longer ensured.

On the other hand, it has been found that the protection against humidity of the middle layer is not optimal when the protective layers are arranged at a distance from said middle layer, on either side of the joint.

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 The invention aims to solve these problems. The invention also aims to provide a simple method of fitting a plug comprising such a seal on a container neck or a plug on a container neck provided with such a seal.

To this end, and according to a first aspect, the invention relates to a composite seal suitable for being placed on a container neck or in a cap comprising an annular skirt provided with an internal thread intended to cooperate with the external thread of a container neck for screw cap mounting on said neck, said seal comprising on the one hand a middle layer made of a plastic material with gas barrier effect and on the other hand a first and a second outer layer comprising each a polyolefin resin, and arranged on either side of said middle layer.

According to the invention, the joint also comprises, between the middle layer and each of the outer layers, an intermediate layer of polyethylene, said intermediate layers being intended to protect the middle layer from moisture and thus to prevent the degradation of the properties. gas barrier of said middle layer.

According to one possible embodiment, the intermediate layers are made of low or medium density polyethylene. They have a thickness of between 80 and 150 μm, in particular close to 115 μm.

The middle layer may consist of an EVOH sheet and its thickness between 35 and 65 μm.

The first outer layer can be made of EVA comprising between 7 and 15% of VA, and its thickness can be between 90 and 160 μm.

The second outer layer may comprise polyethylene or EVA, as well as a compound with an oxygen-absorbing effect, comprising sodium ascorbate and / or sodium sulfite. The thickness of the second outer layer can be between 130 and 230 µm.

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 According to a second aspect, the invention relates to a plug comprising on the one hand a transverse end wall and on the other hand an annular skirt projecting substantially perpendicularly from said transverse wall and comprising an internal thread intended to cooperate with the thread outer of a container neck for screw mounting the cap on said neck, the cap further comprising a substantially discoidal seal as previously described, said seal being placed inside the cap, substantially perpendicular to the axis of said plug, and being intended to ensure liquid tightness and impermeability to gases between the interior and exterior of the container closed by said plug.

The seal is placed inside the cap so that the first outer layer is located opposite the transverse end wall.

According to a first embodiment, the seal is substantially planar and is located near the transverse wall.

According to a second embodiment, the seal is thermoformed, so that it has a shape complementary on the one hand to that of the container neck with which the stopper is intended to be associated and on the other hand to that of the inner face from the transverse end wall of the plug, the said seal being located, before the fitting of the plug on the container neck, towards the free end of the skirt opposite the transverse wall and, after the fitting of the cap on the container neck, near the transverse wall.

The stopper may also include a tamper-evident band comprising means for holding the seal before the stopper is placed on the container neck.

According to a possible embodiment, the stopper comprises a substantially annular lip projecting from the transverse wall in the same direction as the skirt, said lip being intended to cooperate with the internal face of the neck of the container, the seal being thermoformed so as to present a recess forming a housing adapted to receive said lip.

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bouchon et l'ergot, la divergence de la lèvre assurant le maintien du joint au fond du bouchon. The stopper may also have a lug projecting substantially radially from the annular skirt towards the axis of the stopper, the said lug being located towards the end part of the skirt linked to the transverse wall of the stopper, the lip being slightly diverging from the outside in the trunk of cone from its base towards its free end, so that, after the cap has been placed on the container neck, the seal is placed between the transverse wall of the

plug and lug, the divergence of the lip ensuring the maintenance of the seal at the bottom of the plug.

According to a third aspect, the invention relates to a container neck or a container having a neck, the said neck being provided with an external thread intended to cooperate with the internal thread of a plug, and comprising a substantially discoidal seal such as previously described, said seal covering the neck opening and being thermoformed, so that it has a shape complementary on the one hand to that of the container neck and on the other hand to that of the inner face of the transverse wall end of the cap intended to be associated with the neck.

Preferably, the seal is placed on the neck so that the second outer layer is located opposite the inside of the neck.

According to a fourth aspect, the invention relates to an assembly comprising a plug, a container and such a seal.

When the stopper is screwed onto the neck, the seal is compressed, towards its peripheral zone, between the rim of the neck of the container and the transverse end wall of the stopper, so as to ensure liquid tightness and impermeability to gas between the inside and the outside of the container.

Finally, according to a fifth aspect, the invention relates to methods of plugging a neck with a plug provided with a seal or methods of plugging a neck provided with a seal using a plug.

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l'invention ; , - la figure 8 est une vue en coupe radiale partielle d'un ensemble bouchon- col-joint, obtenu après mise en place du bouchon de la figure 5 sur un col de récipient, ou après mise en place d'un bouchon sur le col de la figure 7 ; The other characteristics of the invention result from the following description of embodiments, description made with reference to the appended figures in which: - Figure 1 is a greatly enlarged cross section of a sheet of composite material constituting a joint according to the invention; - Figure 2 is a partial radial sectional view of a plug having a seal made from the sheet of Figure 1, according to a first variant of a first embodiment; - Figure 3 is a partial radial sectional view of a plug having a seal made from the sheet of Figure 1, according to a second variant of a first embodiment; - Figure 4 is a radial sectional view of the cap of Figure 2, mounted on a container neck, in the fully screwed position, before first opening; - Figure 5 is a partial radial sectional view of a stopper comprising a thermoformed seal produced from the sheet of Figure 1, according to a second embodiment; - Figure 6 is a partial radial sectional view of the cap of Figure 5, provided with a seal, when mounting the cap on the neck of a container; FIG. 7 is a view in partial radial section of a container neck provided with a thermoformed seal, according to a third embodiment of

the invention; , - Figure 8 is a partial radial sectional view of a cap-neck-seal assembly, obtained after placing the cap of Figure 5 on a container neck, or after placing a cap on the neck of Figure 7;

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 - Figure 9 is a partial radial sectional view of the plug of Figure 8 after unscrewing.

We first refer to Figure 1 which shows in cross section a sheet 1 of composite material comprising several juxtaposed layers.

The sheet 1 firstly comprises a middle layer 2, made of a plastic material with a gas barrier effect. The middle layer 2 can for example consist of a sheet of EVOH (ethyl vinyl alcohol copolymer), with a thickness of between 35 and 65 μm, in particular 50 μm, the EVOH having a modulus of rigidity of between 1500 and 2500 MPa, for example 2000 MPa.

The sheet 1 then comprises two intermediate layers 3,4, arranged on either side of the middle layer 2 and linked to said intermediate layer 2 by a layer of glue 5,6.

Each of the two intermediate layers 3,4 is made of low or medium density polyethylene, with a modulus of rigidity of between 250 and 500 MPa. The thickness of each of the two intermediate layers 3,4 is between 80 and 150 μm, in particular close to 115 μm.

The role of these intermediate layers 3,4 is to protect the middle layer 2 against moisture, so that the latter retains its gas barrier properties. Polyethylene provides much better performance than EVA (copolymer of ethylene and vinyl acetate) used in the prior art.

The sheet 1 finally comprises two outer layers 7,8, each linked to one of the intermediate layers 3,4. The materials making up the outer layers 7,8 have a stiffness modulus of between 50 and 100 MPa.

A first outer layer 7 is made of EVA comprising between 7 and 15% of VA (vinyl acetate), in particular 9.4% of VA. The thickness of the

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 first outer layer 7 is between 90 and 160 µm. It can for example be of the order of 125 μm.

A second outer layer 8 comprises a polyolefin, polyethylene or EVA, as well as a compound with an oxygen-absorbing effect, such as a mixture of sodium ascorbate and sodium sulfite.

The thickness of the second outer layer 8 is between 130 and 230 μm, and in particular close to 180 μm.

The production of sheet 1 is carried out by coextrusion. The middle and middle layers are assembled by gluing.

A seal 9, generally in the form of a disc, is then cut from the sheet 1, for example using a punch of the desired diameter, the said seal 9 being able to be placed in a stopper intended to close a container, or on a container neck.

We now describe three embodiments of the invention, making it possible to obtain a cap-container-seal assembly with very good liquid tightness and very good gas impermeability.

First of all, a plug 10 comprising such a seal 9, according to a first embodiment of the invention, is described with reference to FIGS. 2, 3 and 4.

The plug 10, of axis 11, is for example made of plastic.

The plug 10 firstly comprises a transverse end wall 12, from which protrudes an annular skirt 13, substantially perpendicular to said transverse end wall 12.

The annular skirt 13 has, on its inner face 14, a thread 15, for mounting by screwing the plug 10 on the neck of a container, the said neck

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 comprising an external thread complementary to the thread 15 of the plug 10, as will be described later.

 The skirt 13 further comprises a knurling 16 on its outer face 17, this knurling 16 being intended to facilitate the screwing and unscrewing of the plug 10 by a user, by offering a better grip and by limiting the sliding of the fingers of the user on the outer face 17 of the skirt 13.

 The plug 10 then comprises a tamper-evident band 18, connected to the free end portion 19 of the annular skirt 13 by frangible bridges 20 or a line of lower resistance. The tamper-evident band 18 has an annular hooking projection 18a, projecting substantially radially towards the axis 11 of the plug 10, and intended to cooperate with an external projection of a container neck to prevent the tamper-evident band 18 is not released from said pass.

The plug 10 also includes a seal 9, substantially discoidal, cut from the sheet 1 previously described. The diameter of the seal 9 is substantially equal to the inside diameter of the skirt 13 of the plug 10.

The seal 9 is placed at the bottom of the plug 10, near the transverse end wall 12. When it is placed at the bottom of the plug 10, the seal 9 is substantially flat, or slightly curved, the concavity being for example directed towards the free end part 19 of the annular skirt 13, as illustrated in the figures.

According to a first alternative embodiment, illustrated in FIG. 2, the seal 9 is held at the bottom of the plug 10 by the thread 15 of the inner face 14 of the annular skirt 13.

According to a second alternative embodiment, illustrated in FIG. 3, the seal 9 is held at the bottom of the plug 10 by notches 21 projecting radially from the annular skirt 13 towards the axis 11 of the plug 10, the said notches 21 being located towards the end part 22 of the skirt 13 linked to the transverse wall 12 of the

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 plug 10 so that the seal 9 can be placed between the said notches 21 and the transverse wall 12.

When it is placed at the bottom of the plug 10, the seal 9 is therefore prevented from leaving said plug 10, but is however free to be rotated about the axis 11 of said plug 10.

Furthermore, the seal 9 is kept at a distance from the transverse wall 12 of the plug 10 by a projection 23, situated on the inner face 14 of the skirt 13, towards the end part 22 of the skirt 13 linked to the transverse wall 12.

The seal 9 is placed inside the plug 10 so that the first outer layer 7 is located opposite the transverse end wall 12.

Reference is made to FIG. 4 which represents a neck 24 of container 25 on which a plug 10 having a seal 9 is mounted by screwing.

The neck 24 is substantially cylindrical, of axis 26, has an annular rim 27 and defines an opening 28.

The neck 24 has, on its outer face 29, a thread 30 complementary to the internal thread 15 of the plug 10, as well as a seat 31. The neck 24 also has an annular projection 29a, projecting substantially radially from the outer face 29, towards outside of said pass 24.

When the plug 10 has been placed on the neck 24, the annular projection 29a of the neck 24 forms a stop for the annular hooking projection 18a of the plug 10, and prevents the axial movement of the tamper-evident band 18 towards the outside of the container 25, so as to prevent the tamper-evident band 18 from escaping from the neck 24-before or after first use.

When the plug 10 is completely screwed onto the neck 24, as illustrated in FIG. 4, the seal 9 covers the opening 28 of the neck 24, the peripheral zone 32 of said seal 9 being in contact with the flange 27 of the neck 24.

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 The peripheral zone 32 of the seal 9 is thus compressed between the rim 27 of the neck 24 of the container 25 and the transverse wall 12 of the plug 10, so that a good seal is ensured between the inside and the outside of the closed container 25 through plug 10.

 When the plug 10 is completely screwed onto the neck 24, the seal 9 is curved, its concavity being directed towards the transverse wall 12 of the plug 10.

 The middle layer 2 of the seal 9 acts as a gas barrier. Thus, there can be no penetration of gas (in particular of oxygen) inside the container 25, nor outlet of gas (in particular of carbon dioxide) out of the container 25. The quality of the content of the container 25 is therefore preserved , even after several months of storage.

The intermediate layers 3, 4 placed on either side and in the immediate vicinity of the middle layer 2, guarantee the preservation of the gas barrier properties of the middle layer 2 by protecting it from humidity. The middle layer 2 is thus protected on the one hand from the humidity of the ambient air, outside the container 25, and on the other hand from contact with the content - for example liquid - of the container 25.

The second outer layer 8, located towards the inside of the container 25, makes it possible to absorb the oxygen contained in the container 25, between the level of the content of the said container 25 and the rim 27 of the neck 24, preserving even better, this fact, the qualities of the contents of the container 25.

The seal 9 according to the invention therefore guarantees very good conservation of the content of the container 25, and this for a long storage time.

Referring now to Figure 5, which shows a plug 10 provided with a seal 9, according to a second embodiment of the invention, before mounting on a container neck.

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The stopper 10 is generally similar to the stopper of FIG. 2, and is intended to be associated with a container neck 25 similar to the neck of FIG. 4.

 The plug 10 further comprises a substantially annular lip 33, projecting from the transverse wall 12 of the plug 10 in the same direction as the skirt 13. The lip 33 is intended to cooperate with the internal face 34 of the neck 24 of the container 25, for sealing. The lip 33 is slightly diverging externally in a truncated cone from its base towards its free end 35.

Furthermore, the plug 10 comprises a lug 36 projecting substantially radially from the annular skirt 13 towards the axis 11 of the plug 10, the said lug 36 being located towards the end part 22 of the skirt 13 linked to the transverse wall 12 of the plug. 10. The role of lug 36 will be described later.

The plug 10 also includes a seal 9, substantially discoidal, cut from the sheet 1 previously described.

The seal 9 is placed inside the plug 10 and is located, before the first mounting of the plug 10 on the neck 24 of the container 25, towards the free end 19 of the skirt 13 of the plug 10, or towards the strip d tamper-evident 18, as illustrated in FIG. 5. For this purpose, the tamper-evident band 18 comprises a substantially annular bead 18b, located near the hooking projection 18a, towards the transverse wall 12 of the plug 10. A space 37 is thus formed towards the tamper-evident band between the attachment projection 18a and the bead 18b, this space 37 being able to receive part of the seal 9 in order to ensure its retention in the plug 10 before the first mounting of the plug. 10 on the neck 24 of container 25.

The seal 9 has a particular shape, obtained for example by thermoforming, this shape being complementary both to that of the neck 24 of container 25 with which the cap 10 is intended to be associated, and that of the inner face 38 of the wall transverse 12 of the plug 10.

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Thus, starting from the center of the joint 9 and traversing a radius of said joint 9, there are successively: - a central part 39 substantially flat and parallel to the transverse wall
12 of plug 10; a recess 40 situated substantially in line with the lip 33, formed by moving away from the transverse wall 12 and having, in radial section, the general shape of a U, the bottom 41 of which is substantially parallel to the transverse wall 12, said recess forming a housing 42 capable of receiving said lip 33, as described below; - A peripheral zone 32 located substantially in the same plane as the central part 39; an end 43 intended to be engaged in the space 37 formed in the tamper-evident band 18 of the plug 10.

The diameter of the thermoformed joint 9 is substantially equal to the inside diameter of the skirt 13 or of the tamper-evident band 18 of the plug 10.

Similarly to the first embodiment, the seal 9 is placed inside the plug 10 so that the first outer layer 7 is located opposite the transverse end wall 12.

We now refer to Figures 6,8 and 9.

When the plug 10 is first mounted on the neck 24 (FIG. 6), the rim 27 of the neck 24 comes into contact with the peripheral zone 32 of the seal 9. The plug 10 is given an axial movement directed towards the interior of the container 25 , then a helical movement, so that the thread 15 of the plug 10 and the thread 30 of the neck 24 come into mutual engagement. Consequently, the seal 9 is moved axially by the rim 27 of the neck 24, towards the transverse wall 12 of the plug 10, the end 43 of the seal being disengaged from the space 37 in which it was initially held.

When the plug 10 is completely screwed onto the neck 24 (FIG. 8), the central part 39 of the seal 9 is substantially in contact with the transverse wall 12

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 of the plug 10, the lip 33 is engaged in the housing 42, the peripheral zone 32 of the seal 9 is compressed between the flange 27 of the neck 24 and the transverse wall 12 of the plug 10, and the end 43 of the seal 9 is located between the transverse wall 12 and the lug 36.

In addition, an area of the recess 40 of the seal 9 is compressed between the lip 33 and the inner face 34 of the neck 24.

Thus, a good seal is ensured between the inside and the outside of the container 25 closed by the plug 10.

This embodiment makes it possible, due to the position of the seal 9 towards the tamper-evident band 18, to limit the introduction of oxygen into the container 25 via the plug 10 during the fitting of said plug 10 on the neck 24, thus making any nitrogen blanketing performed before mounting the plug 10 more efficient.

When the thread 15 of the plug 10 and the thread 30 of the neck 24 are at the start of mutual engagement, and before the plug 10 is completely screwed onto the neck 24, it is possible to clean the outer face 29 of the neck 24 by a water jet in order to eliminate any traces of product contained in the container 25 on the said neck 24. This cleaning operation does not in any way affect the properties of the content of the container 25, since the seal 9 covers the opening 28 of the neck 24.

When a user unscrews the plug 10, the seal 9 remains held at the bottom of the plug 10, substantially against the transverse wall 12, due on the one hand to the lug 36 and on the other hand to the divergence of the lip 33 Furthermore, the tamper-evident band 18 is detached from the skirt 13 towards the frangible bridges 20 or the line of weakest resistance. FIG. 9 represents such a plug 10, after being placed on a neck 24 and unscrewing.

Finally, reference is made to FIG. 7, which illustrates a third embodiment of the invention.

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A container neck 25, similar to the neck in FIG. 4, is intended to receive a plug 10, similar to the plug in FIG. 5, but without a seal.

 The neck 24 is provided with a seal 9, substantially disc-shaped, cut from the sheet 1 described above, the axis of the seal 9 and the axis 26 of the neck 24 being substantially combined. The seal 9 is placed on the neck 24 so as to completely cover the opening 28 of said neck 24, the diameter of the seal 9 must therefore be sufficiently large. The seal 9 is placed on the neck 24 so that the second outer layer 8 is located opposite the inside of the neck 24.

The seal 9 is thermoformed, so that it has a shape complementary both to that of the neck 24 of the container 25 with which it covers the opening 28, and that of the inner face 38 of the transverse wall 12 of the plug 10 intended to be associated with said collar 24.

In the embodiment shown, the gasket 9 has a shape identical to that of FIG. 5, namely a central part 39 which is substantially planar, a recess 40 situated behind, towards the interior of the container 25, relative to the rim 27 of the neck 24 - forming a housing 42 intended to receive the lip 33 of the plug 10-an area of said recess 40 being substantially tangent to the inner face 34 of the neck 24, a peripheral area 32 resting on the rim 27 of the neck 24, and one end 43 protruding outside the neck 24.

The diameter of the thermoformed joint 9 is slightly greater than the outside diameter of the neck 24, and substantially equal to the inside diameter of the skirt 13 of the plug 10 intended to cooperate with said neck 24.

According to a first variant, the seal 9, previously thermoformed, is placed on the neck 24 so that the shapes of the seal 9 and the neck 24 cooperate.

According to a second variant, a substantially flat seal 9 is placed on the neck 24 so as to cover the opening 28, said seal 9 then being shaped by thermoforming to give it the desired shape.

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 As previously described for the second embodiment of the invention, cleaning of the neck 24 is then possible, the seal 9 making it possible to provide the necessary seal.

 The plug 10 can then be put in place by screwing onto the neck 24.

The cap 10 - neck 24 - seal 9 assembly thus formed is similar to that obtained with the second embodiment, and is shown in FIG. 8.

The peripheral zone 32 of the seal 9 is then compressed between the rim 27 of the neck 24 of the container 25 and the transverse wall of the stopper, and a zone of the recess 40 of the seal 9 is compressed between the lip 33 and the inner face 34 of the neck 24 , so that a good seal is ensured between the inside and the outside of the container 25 closed by the plug 10.

Furthermore, the end 43 of the seal 9 is located between the transverse wall 12 and the lug 36. Thus, when the plug 10 is unscrewed, the seal 9 is held at the bottom of the plug 10, and the configuration illustrated on Figure 9.

As for the first and second embodiment, the seal makes it possible: - to avoid the entry and exit of gas into or out of the container 25 (middle layer 2); - to preserve the gas barrier properties of the middle layer (intermediate layers 3,4); - absorb the oxygen contained in the container 25 (outer layer 8) or entering the container 25, due to the permeability of said container 25.

The quality of the content of the container 25 is therefore preserved, even after several months of storage.

Claims (34)

1. Composite seal suitable for being placed on a neck (24) of a container (25) or in a plug (10) comprising an annular skirt (13) provided with an internal thread (15) intended to cooperate with the external thread ( 30) of a neck (24) of container (25) for mounting by screwing the plug (10) on said neck (24), said seal (9) comprising on the one hand a middle layer (2) produced in a plastic material with a gas barrier effect and on the other hand first and second outer layers (7,8) each comprising a polyolefin resin, and arranged on either side of said middle layer (2), characterized in that it further comprises, between the middle layer (2) and each of the outer layers (7,8), an intermediate layer (3,4) of polyethylene, said intermediate layers (3,4) being intended protect the middle layer (2) from humidity and thus prevent the degradation of the gas barrier properties of said neck middle cheek (2). 2. Joint according to claim 1, characterized in that the intermediate layers (3,4) are made of low or medium density polyethylene. 3. Joint according to claim 1 or 2, characterized in that the intermediate layers (3,4) have a thickness between 80 and 150 m, in particular close to 115 µm. 4. Joint according to any one of claims 1 to 3, characterized in that the intermediate layers (3,4) are joined to the middle layer (2) by a layer of glue (5,6). 5. Joint according to any one of claims 1 to 4, characterized in that the polyethylene making up the intermediate layers (3,4) has a modulus of rigidity of between 250 and 500 MPa. <Desc / Clms Page number 18>  6. Joint according to any one of claims 1 to 5, characterized in that the middle layer (2) consists of a sheet of EVOH (ethyl vinyl alcohol copolymer) with a thickness between 35 and 65 µm. 7. Joint according to any one of claims 1 to 6, characterized in that the material making up the middle layer (2) has a modulus of rigidity of between 1500 and 2500 MPa. 8. Joint according to any one of claims 1 to 7, characterized in that the materials making up the outer layers (7,8) have a modulus of rigidity of between 50 and 100 MPa. 9. Joint according to any one of claims 1 to 8, characterized in that the first outer layer (7) is made of EVA (copolymer of ethylene and vinyl acetate) comprising between 7 and 15% of VA ( vinyl acetate). 10. Joint according to any one of claims 1 to 9, characterized in that the first outer layer (7) has a thickness between 90 and 160 µm. 11. Joint according to any one of claims 1 to 10, characterized in that the second outer layer (8) comprises polyethylene or EVA (copolymer of ethylene and vinyl acetate). 12. Joint according to any one of claims 1 to 11, characterized in that the second outer layer (8) comprises a compound with an oxygen-absorbing effect. 13. Joint according to claim 12, characterized in that the compound with oxygen-absorbing effect comprises sodium ascorbate and / or sodium sulfite. <Desc / Clms Page number 19>  14. Joint according to any one of claims 1 to 13, characterized in that the second outer layer (8) has a thickness between 130

 and 230 µm. 15. Plug comprising on the one hand an end transverse wall (12) and on the other hand an annular skirt (13) projecting substantially perpendicularly from said transverse wall (12) and comprising an internal thread (15) intended to cooperate with the external thread (30) of a neck (24) of the container (25) for mounting by screwing the plug (10) on said neck (24), characterized in that it further comprises a seal ( 9) substantially discoid according to any one of claims 1 to 14, the said seal (9) being placed inside the plug (10), substantially perpendicular to the axis (11) of said plug (10), and being intended to ensure liquid tightness and impermeability to gases between the interior and exterior of the container (25) closed by said plug (10). 16. Plug according to claim 15, characterized in that the seal (9) is placed inside the plug (10) so that the first outer layer (7) is located opposite the transverse end wall (12). 17. Plug according to claim 15 or 16, characterized in that the seal (9) is substantially planar. 18. Plug according to any one of claims 15 to 17, characterized in that the seal (9) is located near the transverse wall (12). 19. Plug according to any one of claims 15 to 18, characterized in that it further comprises at least one notch (21) projecting radially from the annular skirt (13) towards the axis (11) of the plug (10 ), the said notch (21) being situated towards the end part (22) of the skirt (13) linked to the transverse wall (12) of the plug (10) so that the seal (9) can be placed between the said notch (21) and the transverse wall (12), said notch (21) being intended to hold the seal (9) at the bottom of the plug (10). <Desc / Clms Page number 20> 20. Stopper according to claim 15 or 16, characterized in that the seal (9) is thermoformed, so that it has a shape complementary on the one hand to that of the neck (24) of container (25) to which the stopper (10) is intended to be associated and on the other hand that of the inner face (38) of the transverse end wall (12) of the plug (10), said seal (9) being located, before putting in place of the stopper (10) on the neck (24) of the container (25), towards the free end part (19) of the skirt (13) opposite the transverse wall (12). 21. Cap according to claim 19, characterized in that it further comprises a tamper-evident band (18) comprising means (18a, 18b, 37) for holding the seal (9) towards the said tamper-evident band ( 18) before placing the plug (10) on the neck (24) of the container (25). 22. Plug according to claim 20 or 21, characterized in that it comprises a lip (33) substantially annular projecting from the transverse wall (12) in the same direction as the skirt (13), said lip (33) being intended to cooperate with the inner face (34) of the neck (24) of the container (25), the seal (9) being thermoformed so as to have a recess (40) forming a housing (42) capable of receiving said lip (33). 23. Stopper according to any one of claims 20 to 22, characterized in that, after the establishment of the stopper (10) on the neck (24) of the container (25), the seal (9) is located near of the transverse wall (12). 24. Cap according to claim 23, when dependent on claim 22, characterized in that it comprises a lug (36) projecting substantially radially from the annular skirt (13) towards the axis (11) of the plug (10), the said lug (36) being located towards the end part ( 22) of the skirt (13) linked to the transverse wall (12) of the plug (10) and in that the lip (33) is slightly diverging externally in a truncated cone from its base towards its free end (35) , so that, after fitting the cap (10) on the container neck (24) (25), the seal (9) is placed between the <Desc / Clms Page number 21>  transverse wall (12) of the plug (10) and the lug (36), the divergence of the lip (33) ensuring the maintenance of the seal (9) at the bottom of the plug (10). 25. Container neck or container having a neck, said neck (24) being provided with an external thread (30) intended to cooperate with the internal thread (15) of a plug (10) for mounting by screwing the plug (10) on said neck (24), characterized in that it further comprises a substantially discoidal seal (9) according to any one of claims 1 to 14, said seal (9) covering the opening (28) of the neck (24) and being thermoformed, so that it has a shape complementary on the one hand to that of the neck (24) of container (25) and on the other hand to that of the inner face (38 ) of the transverse end wall (12) of the plug (10) intended to be associated with the neck (24), said container (25) being empty or at least partially filled with a certain content. 26. container neck or container having a neck according to claim 25, characterized in that the seal (9) is placed on the neck (24) so that the second outer layer (8) is located opposite the inside of the neck (24). 27. An assembly comprising a stopper (10) according to any one of claims 15 to 24 and a container neck (24) (25) or a container (25) having a neck (24), said container (25) being empty or at least partially filled with certain content. 28. Assembly according to claim 27, when it depends on the claim 22, characterized in that, when the plug (10) is screwed onto the neck (24), a region of the seal (9) is compressed between the annular lip (33) and the inner face (34) of the neck (24) of the container (25). 29. An assembly comprising a stopper and a neck (24) of a container (25) or a container (25) having a neck (24) according to claim 25 or 26. <Desc / Clms Page number 22> 30. An assembly according to any one of claims 27 to 29, characterized in that, when the plug (10) is screwed onto the neck (24), the seal (9) is compressed, towards its peripheral zone (32), between the rim (27) of the neck (24) of the container (25) and the transverse end wall (12) of the stopper (10), so as to ensure liquid tightness and gas impermeability between the inside and outside of the container (25). 31. Method for plugging a neck (24) of a container (25) or of a container (25) having a neck (24) with a stopper (10) according to any one of claims 20 to 24, characterized in what, when an axial and / or helical screw movement is imparted to the plug (10), so that the thread (15) of the plug (10) and the thread (30) of the neck (24) come into engagement mutual, the seal (9) is moved by the rim (27) of the neck (24) axially towards the transverse wall (12) of the plug (10) until it comes substantially into contact with said transverse wall ( 12). 32. Method for producing a container neck, or a container having a neck, provided with a seal, according to claim 25 or 26, characterized in that a seal (9) previously thermoformed is placed on the said neck (24), the said seal (9) covering the opening (28) of the neck (24). 33. A method of producing a container neck, or a container having a neck, provided with a seal, according to claim 25 or 26, characterized in that it comprises the following steps: - a seal (9) substantially disc-shaped and flat on the neck (24), said seal (9) covering the opening (28) of said neck (24); - The seal (9) is shaped by thermoforming so as to give it a complementary shape on the one hand that of the neck (24) and on the other hand that of the inner face (38) of the transverse end wall (12) of the plug (10) intended to be associated with the neck (24). 34. Method for plugging a neck (24) of a container (25) or a container (25) having a neck (24) according to claim 25 or 26, characterized in that <Desc / Clms Page number 23>  places a plug on said neck (24) provided with the thermoformed seal (9), for example by screwing.