Container closures comprising only one polymer

Abstract

A container closure, in particular a vacuum screw closure, having a sealing insert which comprises or consists of a polymer material (except for PVC), the sealing insert comprising essentially only one type of copolymer, preferably only one copolymer and in addition to this only conventional additives.

Description

[0001] Single-polymer vessel closures

[0002] The invention generally relates to container closures with a polymer-based sealing insert for bottles and other containers for holding beverages and food. The container closures are free of halogen-containing substances and are suitable even for demanding applications.

[0003] Beverages and foodstuffs are filled into various types of containers for transport, storage, and preservation. These containers often need to be sealable to prevent leakage and to protect them from unwanted substances that could contaminate or damage the contents. In many applications, these contaminants are not limited to solid or liquid contaminants. If the contents are sensitive to gaseous substances, these must also be prevented from entering. This is achieved by an appropriately designed container closure.

[0004] Metal and / or plastic vessel closures have been around for a long time. They are used in the form of screw caps, twist locks, and crown corks, for example, to tightly seal vessels such as bottles, jars, and the like. Such vessels have a mouth that must be sealed by the vessel closure. A sufficiently tight closure of the vessel must be ensured, on the one hand, to prevent the vessel contents from leaking out and, on the other hand, to protect the vessel contents from the entry of unwanted substances, including gaseous substances such as oxygen, trichloroanisole, and others.

[0005] The necessary tightness is usually achieved by a sealing insert made of a material that is both sufficiently strong and elastic and is arranged in the vessel closure so that it contacts the vessel mouth when the vessel closure is attached to the vessel. The sealing insert is usually disc-shaped or ring-shaped and arranged on the inside of the vessel closure. When the vessel is closed, it rests against the vessel mouth and is pressed against the mouth by the vessel closure, with its hardness combined with its elasticity creating the seal. A good sealing insert compensates for the unevenness that is always present in the vessel mouth. Therefore, the more uneven the vessel mouth is, the higher the demands placed on the sealing insert.

[0006] Sealing with a sealant can be further optimized if the sealant is foamed. Chemical blowing agents such as citric acid salts, bicarbonates, or solvent-filled microspheres (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. Previously used chemical blowing agents based on semicarbazides or dicarbonamides are undesirable, as the byproducts formed during their decomposition pose a toxicological risk when in contact with food.

[0007] A key factor in meeting such higher requirements is the appropriate choice of gasket material. Many common materials are well-suited for relatively simple applications, but less so, or not at all, for more demanding seals.

[0008] The sealing insert must also meet additional requirements, such as being pasteurizable or even sterilizable for many applications. It must withstand considerable internal pressure (e.g., in carbonated beverages) but release in a controlled manner if this pressure is exceeded (overpressure valve effect).

[0009] If the vessel closure is a twist-lock closure, the sealing insert must not offer excessive resistance to the twisting of the vessel closure on the mouth when opening.

[0010] In addition, the sealing insert must be as easy to manufacture and install as possible in the vessel closure. It is known to cut disc-shaped sealing inserts from sheets or films and then attach them to the vessel closure ("out-shell molding") or, as is often preferred, to insert them in a flowable form into the vessel closure, where they are formed and solidified ("in-shell molding"). In-shell molding also allows the production of sealing inserts that are not disc-shaped, but rather ring-shaped.

[0011] In the case of polymer-based gasket inserts, this is conventionally done by introduction as a liquid plastisol with subsequent shaping (optional) and drying at temperatures generally above 190°C, or in the case of thermoplastic materials by introduction in a heated, flowable state, subsequent shaping and cooling.

[0012] While PVC-based gasket inserts were once widely used, PVC and other halogen-containing materials now raise significant concerns. They are considered potentially harmful to health and are not easily disposed of. In many countries, the use of such halogen-containing materials is regulated or even prohibited by law or regulation.

[0013] There is therefore a significant need for vessel closures that do not require halogen-containing materials, without having to forego the advantages that, for example, PVC-containing sealing inserts have in terms of processing, sealing properties, costs, and the like.

[0014] Common gasket inserts usually consist of mixtures (also called "compounds") of various, often dissimilar, polymers. In the following, we will refer to different polymers based on the same or homologous monomers as "different," but not as "dissimilar." For example, all copolypropylenes containing only propylene and another olefin are different, but not "dissimilar," whereas PP copolymers and SEBS are different.

[0015] Common gasket inserts usually consist of a base material, often a polyolefin, which inherently approximates the required properties. The properties of the gasket insert are then specifically adjusted by blending in other polymers to further optimize its properties in terms of elasticity or temperature resistance for the intended application.

[0016] Most compounds with only one polymer (besides lubricant, stabilizer, and the like), however, are unsuitable for the purposes of the invention. Compounds with a non-elastomeric thermoplastic (e.g., most PP types) as the only polymer in the gasket insert are consistently too hard and not elastic enough. Compounds with only one elastomeric thermoplastic or thermoplastic elastomer, on the other hand, are generally too soft. An exception are certain PP-based copolymers, which, with contents of conventional lubricants, etc., can be processed into a gasket insert according to the invention. Such compounds are defined in the patent claims.

[0017] The PP-based copolymer forms the main component of the sealant, which preferably contains no (or only very minimal) amounts of other polymers. In other words, the only polymer that forms the sealing element (besides conventional additives) is virtually entirely or completely responsible for its properties.

[0018] According to the invention, a vessel closure, in particular a vacuum screw closure, is therefore provided with a sealing element which comprises or consists of a polymer material, wherein the sealing element essentially comprises a single type of copolymer, preferably a single copolymer, and in addition only conventional additives.

[0019] In a preferred embodiment, the polymer material comprises or is a PP-based copolymer, in particular a bipolymer or a terpolymer.

[0020] It is particularly preferred that the sealing insert comprises at least one PP / PE bipolymer (copolymer of propylene and ethylene). Alternatively, it may comprise a PP / PE / BU terpolymer (copolymer of propene, ethene, and butene).

[0021] In preferred embodiments of the invention, the vessel closure has a sealing insert in which the copolymer has an MFR (ASTM D 2240) of less than 10, preferably less than 8 and particularly preferably <6 g / 10 min. at 230°C and 2.16 kg coating weight.

[0022] Also, preferred embodiments of the invention comprise a vessel closure in which the copolymer has a Shore A hardness (ISO 868) of less than 80 and preferably more than 60.

[0023] In other or the same preferred embodiments, a vessel closure is provided in which the copolymer has a melting point (ISO 11357-3) between 140°C and 190°C, preferably between 160°C and 180°C and particularly preferably not more than 165°C.

[0024] In preferred embodiments of the invention, the vessel closure comprises a copolymer having a density (DIN EN ISO 1183-1) of 0.8 to 1.0, preferably 0.86 to 0.9 g / cm, and especially approximately 0.88 g / cm.

[0025] In addition to the polymer, the sealing inserts of the invention are preferably provided with conventional additives selected from lubricants, antioxidants, colorants and / or fillers.

[0026] Polymers suitable for practicing the invention can be obtained from Mitsui Chemicals Group and LyondellBasell.

[0027] Sealing inserts made from the materials described can be used for greasy products and are suitable for PT caps. They are also sterilizable. The suitability for sterilization can be determined on the sealing material through appropriate testing.

[0028] This suitability can be predicted using the well-known Dynamic Mechanical Thermal Analysis (DMTA). This essentially involves determining the heating curve for the phase angle (tan delta), the inflection point of which should be sufficiently (usually at least 10 °C) above the intended sterilization temperature.

[0029] These tests are validated by manufacturing the closure and testing it under the relevant application parameters, such as maximum sterilization temperature, sterilization time (=time at maximum sterilization temperature) and back pressure.

Claims

AMENDED CLAIMS received by the International Bureau on 12 September 2023 (12.09.2023) 1. Vessel closure, in particular a vacuum screw cap, with a sealing insert which comprises or consists of a polymer material (other than PVC), namely a PP-based copolymer, wherein the sealing insert essentially comprises a single type of copolymer, preferably a single copolymer, and in addition only customary additives.

2. A vascular closure according to claim 1 or claim 2, wherein the polymer material comprises or is a bipolymer or a terpolymer.

3. Vascular closure according to one of the preceding claims, which comprises at least one PP / PE bipolymer (copolymer of propene and ethene).

4. Vessel closure according to one of the preceding claims, which comprises a PP / PE / BU terpolymer (copolymer of propene, ethene and butene).

5. Vessel closure according to one of the preceding claims, in which the copolymer has an MFR (DIN EN ISO 1133) of less than 10, preferably less than 8 and particularly preferably <6 g / 10 min. at 230°C and 2.16 kg coating weight.

6. Vessel closure according to one of the preceding claims, in which the copolymer has a Shore A hardness (determined according to DIN ISO 7619-1) of less than 80 and preferably more than 70.

7. Vessel closure according to one of the preceding claims, in which the copolymer has a melting point (DIN EN ISO 11357-3) between 140°C and 190°C, preferably between 160°C and 180°C and particularly preferably not more than 165°C.

8. Vessel closure according to one of the preceding claims, wherein the copolymer has a density (DIN EN ISO 1183-1) of 0.8 to 1.0, preferably 0.86 to 0.9 g / cm 3 , and specifically approximately 0.88 g / cm 3 has. AMENDED SHEET (ARTICLE 19) 9. A vessel closure according to any one of the preceding claims, wherein the additives are selected from lubricants, antioxidants, dyes and / or fillers.

10. Vessel closure according to one of the preceding claims, in which the sealing material is in closed-cell foam form, so that the density according to DIN EN ISO1183-1 is lower than the initial density of the sealing material, but at least 50%, preferably at least 70% of the initial density is still achieved. AMENDED SHEET (ARTICLE 19)