Sealing inserts for crown corks with reduced metal-sheet thickness

Abstract

Crown cork for a vessel for holding beverages or foods that has a mouth to be closed with the crown cork, having a sealing insert arranged in the crown cork such that it sealingly closes the mouth when the crown cork is mounted on the vessel, where the crown cork including the sealing insert contains no halogen-containing materials, where the sheet metal used for the crown cork has a thickness of 0.10-0.19 mm, wherein the sealing insert contains at least twenty per cent by weight, based on the total weight of the sealing insert, of at least one, preferably fully hydrogenated, styrene triblock copolymer, especially styrene-ethylene-butadiene-styrene copolymer (SEBS), SEEPS and / or SEPS, or a mixture of two or more of these copolymers.

Description

[0001] Sealing insert for crown caps with reduced sheet thickness

[0002] The invention generally relates to vessel closures made of metal and / or plastic, in particular crown caps, with a polymer-based sealing insert for bottles and other containers for holding beverages and food. More specifically, the invention relates to such vessel closures, in particular crown caps, provided with a sealing insert. The vessel closures are free of halogen-containing substances and are also suitable for demanding applications, especially for crown caps with reduced sheet thickness.

[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 take 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, both to prevent the contents from leaking out and to protect the 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] A key factor in meeting such 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.

[0007] 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).

[0008] If the container closure is a twist-off closure (e.g. a twist-off crown cap, also known as a “twist crown”), the sealing insert must not offer too much resistance to the twisting of the container closure on the mouth when opening.

[0009] 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.

[0010] In the case of polymer-based gasket inserts, this is conventionally done by introduction as a plastisol followed by shaping and drying, or in the case of thermoplastic materials by introduction in a heated, flowable state, followed by shaping and cooling.

[0011] 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.

[0012] 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.

[0013] There are already a number of proposals for this in the state of the art.

[0014] For decades, it has been known to produce sealing inserts (both for screw caps and for lever-type closures such as conventional crown caps) based on polymers that do not contain halogens. These sealing inserts are generally "compounds," i.e., mixtures of one or (usually) several polymers with additives that adapt the properties of the sealing insert to the intended application, facilitate its processing or use, and so on.

[0015] Typical polymers in such compounds are thermoplastics, especially polyolefins, thermoplastic elastomers, elastic thermoplastics, and synthetic rubbers. Typical additives include plasticizers, oils, lubricants, antioxidants, stabilizers, pigments, fillers, and the like.

[0016] Polymer-based sealing inserts vary in their permeability to foreign substances depending on the choice of their components. Such foreign substances can, for example, penetrate between the sealing insert and the vessel mouth if the sealing insert does not fit optimally against the mouth. They can also be soluble in the sealing insert material and diffuse into the vessel. The sealing insert must therefore be optimized in terms of its mechanical properties (especially hardness and elasticity) and its chemical properties (solubility of foreign substances).

[0017] It is already known to add one or more substances to the material of a gasket insert that chemically bind and thus "capture" penetrating oxygen—hence the term "scavenger." One example is sodium sulfite, which is incorporated into the gasket insert in the form of solid particles of a suitable size.

[0018] However, there is still a need for sealing inserts without halogen-containing materials that enable improved sealing performance, especially in problematic and demanding applications, particularly in the applications explained in more detail below:

[0019] A more specific problem that can be solved by means of the invention arises with vessel closures that can be levered off or twisted off, in particular with crown corks.

[0020] The usual containers, typically beer bottles and bottles for carbonated soft drinks and mineral water, are mass-produced products with varying quality of the finish area in terms of unevenness, hairline cracks, and the like. Beverages such as beer, soft drinks, and mineral water are susceptible to flavor changes, which may be caused by oxidation after exposure to oxygen and / or by the penetration of flavor-altering substances such as trichloroanisole.

[0021] However, storage times are usually short.

[0022] There are state-of-the-art sealing inserts that ensure adequate sealing in conventional crown caps. However, there is a growing need for manufacturers to use thinner tinplate for such crown caps.

[0023] While conventional crown caps in Europe have a sheet thickness of 0.20 to 0.23 mm, the company wants to work with sheet thicknesses of 0.19 mm and below, down to 0.15 mm, in order to save material.

[0024] However, a crown cap made of thinner tinplate with the same yield strength cannot reliably press the sealing insert against the vessel mouth with the same force as a conventional crown cap made of thicker sheet metal.

[0025] A reduction in tinplate thickness leads to an overall decrease in sealing performance (internal pressure strength).

[0026] This effect can be counteracted by using optimized seals in terms of hardness and elasticity or mechanically improved tinplate with a higher yield strength.

[0027] Seals with an optimized ratio of hardness to elasticity are just one important component for the use of thinner tinplate for crown corks. In addition, tinplate with a higher yield strength should be used.

[0028] While tinplate alloys with a maximum yield strength of 415 MPa are used for standard crown corks, tinplate with a yield strength of 415 to 620 MPa should be used for crown corks with a thickness of 0.18 mm and tinplate with a yield strength of >620 MPa should be used for crown corks with a thickness of 0.15 mm.

[0029] The maximum possible yield strength, or stiffness, of a tinplate is determined by the forming process during the deep drawing of the crown cork. To achieve an optimal ratio of ductility to strength, thinner (<0.20 mm) tinplates should preferably be manufactured using the so-called "double reduction" process; otherwise, the risk of damage during the forming of the crown cork (premature tearing) is significantly increased.

[0030] For the production of packaging steels, especially tinplate, this process uses so-called hot-rolled strips with a thickness of approximately 1.5 - 4.0 mm.

[0031] First, the hot strip is pickled and then cold rolled.

[0032] During cold rolling, the first thickness reduction of the tinplate takes place.

[0033] In order to achieve the high deformations resulting from the thickness reduction, the roll gap is lubricated with a mixture of water and rolling oil.

[0034] In addition, the tinplate must be cooled with water because the rolling process generates heat.

[0035] The work hardening must then be removed by an annealing process, as the significant reduction in thickness causes the tinplate to become very hard and brittle, making it unsuitable as a packaging material.

[0036] However, before annealing can be carried out, the cold-rolled tinplate must be degreased.

[0037] Annealing the tinplate ensures that its malleability is restored.

[0038] The tinplate is then further reduced in thickness by dry re-rolling, entirely without lubrication or cooling. The resulting "double-reduced" material enables the production of tinplates that compensate for lower thicknesses with higher strength.

[0039] The tinplate is then tinned or chrome-plated to protect it from corrosion before being finally conditioned in various packaging sizes.

[0040] Tinplate for packaging steels and crown corks made from them are specified according to DIN EN 10202 or ENI 7177.

[0041] There is therefore a need for improved vascular closures.

[0042] The invention aims to create improved closures that can be used not only generally but also for the particularly demanding applications discussed here.

[0043] Against this background, it is an important object of the invention to propose improved crown caps without halogen-containing materials with a sealing insert, which can be designed both as screw caps and as lever-off caps and are easier and therefore more cost-effective to produce.

[0044] A further important object of the invention is to provide such crown caps with improved tightness, in particular against leaks, even in mass-produced containers such as beer bottles and the like.

[0045] The good barrier effect of the well-known sealing insert should be maintained.

[0046] One of the objects of the invention is to provide such vessel closures with a sealing insert that can be produced by means of in-shell molding.

[0047] The sealing insert should be designed to be very soft in order to reliably seal the bottle even in the presence of hairline cracks and similar mouth defects. Further objects and advantages of the invention will become apparent from the following description, including the exemplary embodiments.

[0048] The invention solves these and other problems with the feature combinations of the independent patent claims.

[0049] Advantageous embodiments are defined in the subclaims.

[0050] The following detailed description of the invention will first address definitions and features that are of general importance for the invention and its optional embodiments, regardless of individual embodiments. The definitions already given above should be taken into account and do not contradict the following explanations. Unless otherwise stated in the description, technical terms have their usual meaning.

[0051] The invention is then illustrated using individual embodiments.

[0052] Definitions and measurement methods:

[0053] A vessel closure within the meaning of this application is a crown cap, preferably designed as a conventional lever-off crown cap or as a twist crown cap of standard dimensions. It consists of a body made of metal and / or plastic and a sealing insert arranged therein. The vessel closure can be a twist-off closure (with threaded elements including cams and the like) or a removable, usually pry-off closure (without twisting the vessel closure), including a crown cap, snap-on lid, and the like. A plug is not a vessel closure in this sense.

[0054] A sealing insert in the sense of the invention is a basically disc-shaped or ring-shaped (optionally provided with a profile) molded part, which either consists entirely of a homogeneous polymer compound, or comprises at least two different, each homogeneous materials, of which at least one is a homogeneous polymer compound.

[0055] "In-shell molding" refers not only to the known processes in which a thermally flowable polymer compound is introduced into the closure body and stamped there to form a disc-shaped sealing insert (SACMI or Zapata processes), but also to processes in which the polymer compound is introduced by injection, possibly only in the edge area of ​​the sealing surface, and formed into an annular sealing insert.

[0056] Polymer compounds within the meaning of the invention are mixtures of one or (usually) several polymers with additives (e.g. plasticizers, anti-blocking agents, lubricants, antioxidants, stabilizers, fillers, pigments...) which adapt the properties of the compound to the intended application, facilitate its processing or use, etc.

[0057] A thermoplastic elastomer is an industrially produced polymer with elastic properties based on its molecular structure. Typical thermoplastic elastomers are (block) copolymers of styrene and butadiene, sometimes with the addition of other monomers (ethylene, isoprene, etc.).

[0058] Percentages in this description are percentages by weight based on the total weight, provided they relate to the proportions of components in a product consisting of several components.

[0059] The melt flow rate (MFR) indicates the flowability of a substance or mixture at 190°C and a 5 kg load. It is determined according to DIN EN ISO 1133-1 and expressed in g / 10 min using standard commercial melt flow testing instruments, e.g., from ZwickRoell. The Shore D hardness indicates the hardness of a substance or mixture. It is determined in accordance with ASTM D 2240 on pressed plates at least 6 mm thick. The measurement time is 5 s. The corresponding test specimens were produced at 180°C by melting under pressure and subsequent cooling to 23°C (holding time 30 min).

[0060] The Shore A hardness is determined analogously to the Shore D hardness according to ASTM D 2240. Here, too, the measurement time is 5 seconds.

[0061] Compression set (DPR) is a measure of the recovery behavior (permanent deformation) of a substance or mixture of substances. The test specimens are manufactured analogously to those for Shore hardness measurements at temperatures between 170 and 230 °C. The test specimens have a diameter of 13 mm and a thickness of 6.3 mm. The design tolerances correspond to DIN ISO 815-1. The test specimens are conditioned and siliconized according to the same standard. For compression set, the respective test specimen is subjected to a compression of 25% for 22 hours at a specified temperature. After a loading period of 22 hours, the test specimen is released, and after 30 minutes, the thickness of the test specimen is measured again, or the permanent deformation is determined. This is also measured according to DIN ISO 815-1 at the specified temperature after a loading period of 22 hours and is expressed as a percentage of the permanent compression, based on the specimen before compression.

[0062] A DVR of 25% corresponds to a permanent "compression" of the specimen by a quarter of its original height (thickness).

[0063] A compound is processable within the meaning of the invention if it can be processed in a conventional manner on a standard system for the production of container closures with polymer-based sealing inserts. A material according to the invention is pasteurizable if it allows a gas-tight closure in an industrial pasteurization process at 60°C to 85°C and does not lose its performance properties for the intended application.

[0064] The following parameters were chosen for closure tests with crown caps, including those according to the invention:

[0065] The bottle mouths are made of glass according to DIN EN ISO 12821 CC 26 H180.

[0066] The locking ring had a corresponding inner diameter of 28.25 mm and 28.3 mm (if steel muzzles are taken into account).

[0067] The closing force was 300 kg. The closing speed was 15 mm / s. Pasteurization was carried out at 68 °C for 20 minutes (holding time) in a spray pasteurizer.

[0068] The figures provide an overview of the experiments conducted and their results:

[0069] Fig. 1 is a summary of parameters of the sealing compounds and crown cap blanks used.

[0070] Fig. 2 shows schematically the closing technique used.

[0071] Fig. 3 shows the pressure testing device used.

[0072] Fig. 4 shows the results of sealing tests with different sealing compounds.

[0073] Fig. 5 shows results analogous to Fig. 4.

[0074] Fig. 6 shows results of lateral impact strength tests.

[0075] Fig. 7 shows results on the tightness of various crown caps, only material C is according to the invention.

[0076] Fig. 8 shows results analogous to Fig. 7, in detail.

[0077] Fig. 9 is an overview of study results.

[0078] Fig. 10 shows results for internal pressure resistance of various materials. It can be seen that crown caps according to the invention exhibit superior technical properties compared to crown caps with a lower SEBS content.

[0079] The recipes used can be found in Table I:

[0080] Table I:

Claims

Patent claims 1. Crown cap for a container for holding beverages or foodstuffs, which has an opening to be closed with the crown cap, comprising a sealing insert arranged in the crown cap in such a way that it seals the opening when the crown cap is attached to the container, wherein the crown cap including the sealing insert does not contain any halogenated materials, wherein the metal sheet used in the crown cap has a thickness of 0.10-0.19 mm, wherein the sealing insert contains at least twenty percent by weight, based on the total weight of the sealing insert, of at least one, preferably fully hydrogenated, styrene triblock copolymer, in particular styrene-ethylene-butadiene-styrene copolymer (SEBS), SEEPS and / or SEPS, or a mixture of several of these copolymers.

2. Crown cap according to claim 1, wherein the metal sheet used has a thickness of a maximum of 0.20 mm, specifically a maximum of 0.19 mm, preferably 0.14 to 0.17 mm and particularly preferably 0.15 to 0.16 mm.

3. Crown cap according to claim 1 or 2, wherein the metal sheet is a tinplate, preferably produced by means of the “double reduced” process, with a thickness of at most 0.19 mm and having a yield strength of at least 415 MPa, preferably above 415 MPa.

4. Crown cap according to claim 3, wherein the metal sheet has a thickness of at most 0.18 mm at a yield strength between 415 and 620 MPa and preferably a thickness of at most 0.15 mm at a yield strength above 620 MPa 5. Crown cap according to one of the preceding claims, wherein the sealing liner comprises between 20 and 50 wt.%, preferably between 25 and 45 wt.%, particularly preferably containing between 30 and 40 wt.% styrene triblock copolymer(s), in particular SEBS.

6. Crown caps according to one of the preceding claims, wherein the sealing liner contains between 33 and 38 wt.%, preferably between 33 and 37 wt.% styrene triblock copolymer, in particular SEBS.

7. Crown cap according to one of the preceding claims wherein the sealing insert contains at least 20 wt.% oil, preferably white oil, wherein the oil content (in wt.%) is preferably as large as the content of styrene triblock copolymer.

8. Crown cap according to one of the preceding claims, wherein the sealing liner contains at least one olefin polymer or copolymer, in particular PE-LD or PP-CoPo.

9. Crown cap according to one of the preceding claims, wherein the sealing insert has a Shore A hardness at room temperature (23°C) of 40 - 75, preferably 50-70, particularly preferably 55-65.

10. Crown cap according to one of the preceding claims, wherein the sealing insert has a compression set determined according to DIN ISO 815-1 of 10 to 25%, preferably 15 to 20% at 23°C and 30 to 50%, preferably 35 to 45% at 70°C.

11. Crown cap according to one of the preceding claims, wherein the SEBS component of the sealing insert has a solution viscosity in toluene (15 wt.%, 25°C) of > 50 mPa.s, preferably > 100 mPa.s and particularly preferably of > 500 mPa.

12. Crown cap according to one of the preceding claims, wherein the sealing insert comprises a SEBS component with a styrene content between 27 and 35 wt.%, preferably 29-33 wt.%.

13. Crown cap according to one of the preceding claims, wherein the oil-to-SEBS ratio of the sealing insert is between 0.7:1 and 1.3:1, preferably between 0.8:1 and 1.2:1, particularly preferably between 0.9:1 and 1.1:

1.

14. Crown cap according to one of the preceding claims, wherein the sealing insert comprises at least 14% plasticizer - white oils with a kinematic viscosity at 40°C between 60 and 350 cSt and / or liquid polyalphaolefins (C2-C20) of the same viscosity.

15. Crown cap according to one of the preceding claims in which the sealing insert comprises 15 to 60 wt.% polyolefins - PE and PP as well as their copolymers with C4-C8, as well as mixtures thereof.

16. Crown cap according to one of the preceding claims, wherein the sealing liner comprises polybutene (and Copos with C2 / C3) or polystyrene up to 20 wt.%.

17. Crown cap according to one of the preceding claims wherein the sealing insert comprises fillers, preferably calcium carbonate, talc and / or sodium sulfite also as scavengers up to 20 wt.%.

18. Crown cap according to one of the preceding claims, which is designed as a twist crown cap.

19. Crown cap according to claim 1, the metal sheet of which consists at least partly of tinplate and / or of steel, in particular stainless steel or aluminium.

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