Container closure with only one polymer

Abstract

A container closure, in particular a vacuum rotary closure, has a sealing gasket which comprises or consists of a polymeric material (except PVC), where the sealing gasket substantially comprises a unique kind of copolymer, preferably a unique copolymer, and in addition only common additives.

Description

Technical Field

[0001] The present invention generally relates to a container closure for bottles and other containers for holding beverages and foods, which container closure has a polymer-based sealing liner. The container closure is free of halogen-containing substances and is also suitable for demanding applications. Background Art

[0002] Beverages and foods are filled into various containers for transport and for storage or preservation. Usually, the containers must be closable so that the contents cannot escape and also prevent the ingress of unwanted substances that could contaminate or damage the contents. In many applications, this is not only about solid or liquid contaminants. If the contents are sensitive to gaseous substances, the ingress of these must also be prevented. This is achieved by correspondingly designed container closures.

[0003] Container closures made of metal and / or plastic have long been known. They are used, for example, in the form of screw caps, twist closures and crown caps to tightly close containers such as bottles, glasses and the like. Such containers have openings that must be closed by the container closures. In this case, a sufficiently tight closure of the container must be ensured in order to prevent the container contents from flowing out and to protect the container contents from the ingress of undesirable substances, including gaseous substances such as oxygen, trichloroanisole and the like.

[0004] The necessary tightness is usually achieved by a sealing liner which consists of a sufficiently strong but also elastic material on the one hand and is arranged in the container closure in such a way that it contacts the opening of the container when the container closure is arranged on the container. The sealing liner is usually arranged in a disk-shaped or annular manner on the inner side of the container closure. In the closed state of the container, the sealing liner rests on the container opening and is pressed against the opening by the container closure, wherein its hardness together with its elasticity brings about a seal. A good sealing liner hereby compensates for any unevenness of the container opening which is always present.

[0005] The more uneven the container opening is, the higher the requirements placed on the sealing gasket.

[0006] The sealing by means of the sealing compound can optionally be further optimized if it is present in foamed form. Chemical blowing agents such as citrates, bicarbonates or expandable microspheres filled with solvents (e.g. "Expancel") can be used for foaming, as can physical blowing agents such as CO2 or nitrogen (N2), which are introduced into the melt under high pressure during melting in the extruder. In contrast, the chemical blowing agents based on semicarbazide or diformamide used previously are undesirable because the by-products produced during their decomposition are toxicologically problematic in contact with foods.

[0007] An important factor in meeting such high demands is the appropriate selection of the material of the sealing gasket. Many known materials are well suited for relatively simple applications, but are less suitable or not suitable at all for demanding seals.

[0008] The sealing liner must also meet other requirements here, so it should be pasteurizable or even sterilizable for many purposes of use. The sealing liner should withstand significant internal pressures (for example in carbonated beverages), but also yield in a controlled manner when the internal pressure is exceeded (overpressure valve effect).

[0009] If the container closure is a twist closure, the sealing liner does not oppose the rotation of the container closure at the opening with excessive resistance during opening.

[0010] Furthermore, the sealing liner must be as easy to produce as possible and must be able to be placed in the container closure. It is known to cut a disk-shaped sealing liner out of a web or film and subsequently fix it in the container closure ("out-shell molding") or, as is often preferred, to inject it into the container closure in a flowable form, to mold it there and to solidify it ("in-shell molding"). In-shell molding also allows the production of sealing liners that are not disk-shaped but rather ring-shaped.

[0011] In polymer-based sealing liners, this is usually achieved by injection as a liquid plastisol, followed by molding (optional) and drying at temperatures typically above 190°C, or in the case of thermoplastic materials, by injection in a heated, flowable state, followed by molding and cooling.

[0012] Previously, PVC-containing sealing liners were widely used, but PVC and other halogen-containing materials are now facing great opposition. They are considered to be potentially harmful to health and cannot be removed without problems. In many countries, the use of such halogen-containing materials is regulated or even prohibited by laws or regulations.

[0013] There is therefore a considerable need for container closures which can also function without halogen-containing materials, without having to give up the advantages of sealing liners containing PVC, for example, with regard to processing, sealing properties, costs etc.

[0014] Known sealing liners usually consist of mixtures (also referred to as "compounds") of different, often also heterogeneous polymers. In the following, different polymers based on the same or homologous monomers are referred to as "different" but not "heterogeneous". Thus, all copolymers of polypropylene containing only propylene and another olefin are different but not "heterogeneous", whereas PP copolymers and SEBS are heterogeneous.

[0015] Known sealing gaskets usually consist of a base material, usually a polyolefin, which itself already approaches the required property category. The properties of the sealing gasket are then specifically set by admixing other polymers in order to further optimize its properties with regard to elasticity or temperature resistance for the intended use.

[0016] In contrast, most compounds with only one polymer (in addition to lubricants, stabilizers, etc.) are not suitable for the purposes of the present invention. Compounds with non-elastomeric thermoplastics (e.g., typically PP types) as the only polymer in the sealing liner are always too hard and not very elastic. In contrast, compounds with only one elastomer thermoplastic or thermoplastic elastomer are usually too soft.

[0017] An exception is a specific PP copolymer which can be processed into a sealing liner according to the invention by containing common lubricants etc. Such a compound is defined in the claims.

[0018] The copolymer based on PP forms the main component of the sealing compound, which preferably has no content of other polymers (or only contains other polymers very slightly). In other words, (except for the usual additives) the only polymer forming the sealing element is actually completely or completely responsible for its properties. Summary of the invention

[0019] According to the invention, a container closure, in particular a vacuum rotary closure, is therefore provided with a sealing element which comprises or consists of a polymer material, wherein the sealing element substantially comprises a single type of copolymer, preferably a single copolymer and also conventional additives.

[0020] In a preferred embodiment, the polymer material comprises a PP-based copolymer or is a PP-based copolymer, in particular a binary copolymer or a ternary copolymer.

[0021] Particularly preferably, the sealing liner comprises at least one PP / PE dipolymer (a copolymer consisting of propylene and ethylene). Alternatively, it can comprise a PP / PE / BU terpolymer (a copolymer consisting of propylene, ethylene and butene).

[0022] In a preferred embodiment of the invention, the container closure has a sealing liner in which the copolymer has an MFR (ASTM D 2240) of less than 10 g / 10 min, preferably less than 8 g / 10 min and particularly preferably ≤6 g / 10 min at 230° C. and a support weight of 2.16 kg.

[0023] A preferred embodiment of the invention also has a container closure in which the copolymer has a Shore A hardness (ISO 868) of less than 80 and preferably greater than 60.

[0024] In a further or identical embodiment, container closures are provided in which the copolymer has a melting point between 140° C. and 190° C., preferably between 160° C. and 180° C. and particularly preferably a maximum of 165° C. (ISO 11357-3).

[0025] In a preferred embodiment of the invention, the container closure comprises a copolymer having a molecular weight of 0.8 to 1.0, preferably 0.86 to 0.9 g / cm 3 and specifically about 0.88 g / cm 3 Density (DIN EN ISO 1183-1).

[0026] In addition to the polymer, the sealing gasket according to the invention is preferably provided with conventional additives selected from the group consisting of lubricants, antioxidants, dyes and / or fillers.

[0027] Polymers suitable for practicing the present invention are available from the Mitsui Chemicals Group and LyondellBasell Industries.

[0028] Sealing gaskets made of the material can be used for oil-containing packings and are suitable for PT caps. The sealing gaskets are also sterilizable. The suitability for sterilizability can be determined at the sealing material by corresponding tests.

[0029] The prerequisites for suitability can be met with the aid of the known dynamic mechanical thermal analysis (DMTA). In principle, a heating curve is determined for the phase angle (tan δ), the inflection point of which should be sufficiently (usually at least 10° C.) above the set sterilization temperature.

[0030] The test validation is carried out by manufacturing the closure and testing it under corresponding application parameters, such as the maximum sterilization temperature, the duration of the sterilization (=time at the maximum sterilization temperature) and the counterpressure.

Claims

1. A container closure, in particular a vacuum rotary closure, having a sealing liner which comprises or consists of a polymer material (other than PVC), wherein the sealing liner essentially comprises a single type of copolymer, preferably a single copolymer and otherwise comprises only conventional additives.

2. The container closure according to claim 1, The polymer material includes a PP-based copolymer or a PP-based copolymer.

3. A container closure according to claim 1 or 2, The polymer material comprises a binary copolymer or a ternary copolymer or a binary copolymer or a ternary copolymer.

4. A container closure according to any one of the preceding claims, The container closure comprises at least one PP / PE copolymer (a copolymer of propylene and ethylene).

5. A container closure according to any one of the preceding claims, The container closure comprises a PP / PE / BU terpolymer (a copolymer composed of propylene, ethylene and butene).

6. A container closure according to any one of the preceding claims, The copolymers therein have an MFR (DIN EN ISO 1133) of less than 10 g / 10 min, preferably less than 8 g / 10 min and particularly preferably ≤6 g / 10 min at 230° C. and a support weight of 2.16 kg.

7. A container closure according to any one of the preceding claims, The copolymers therein have a Shore A hardness of less than 80 and preferably greater than 70 (determined in accordance with DIN ISO 7619-1).

8. A container closure according to any one of the preceding claims, The copolymers here have a melting point between 140° C. and 190° C., preferably between 160° C. and 180° C. and particularly preferably at most 165° C. (DIN EN ISO 11357-3).

9. A container closure according to any one of the preceding claims, The copolymer has a 0.8 g / cm 3 Up to 1.0g / cm 3 , preferably 0.86g / cm 3 Up to 0.9g / cm 3 And especially about 0.88g / cm 3 Density (DIN EN ISO 1183-1).

10. A container closure according to any one of the preceding claims, The additive is selected from lubricants, antioxidants, dyes and / or fillers.

11. A container closure according to any one of the preceding claims, The sealing material is present in the form of a closed-cell foam, so that the density according to DIN EN ISO 1183-1 is lower than the initial density of the sealing material, but still reaches at least 50%, preferably at least 70%, of the initial density.