Twist-crown cap seals with improved gas barrier

Abstract

The invention relates to a twist-crown bottle closure which can be released by rotation and has a sealing insert consisting substantially or entirely of a polymer compound, wherein the polymer compound comprises: - at least one styrene-based copolymer; - at least one barrier polymer in a amount of at most 40 wt.%, based on the total amount of polymer compound; - at least one polyolefinic polymer or copolymer; - at least one component which is liquid at 20°C, in particular a mineral oil, and also customary auxiliaries.

Description

[0001] 06.08.24

[0002] AC 1307

[0003] Seals for twist crown caps with improved gas barrier

[0004] Description

[0005] The invention relates to twist-off crown caps and similar closures that can be removed from the sealed container by twisting, in particular closures for bottles, especially beer bottles. More specifically, the invention relates to PVC-free sealing elements for such closures.

[0006] Twist crown caps, also referred to as twist crown caps, are called "twist crowns" in English.

[0007] Twist-off crown caps offer consumers an advantage over standard crown caps ("pry-off") because they can be opened without tools. In some countries, twist-off crown caps have become the standard over the years, making it unthinkable to buy bottled beer without them, and they have long been a basic consumer expectation. The ease of opening the twist-off crown cap without tools is a significant advantage over conventional crown caps.

[0008] In industry, seals for twist-off crown caps are still frequently manufactured using PVC-containing compounds. These seals for twist-off crown caps are usually made of PVC in general, and flexible PVC in particular, as this ensures compliance with the stringent requirements for both tightness and opening force. The tightness of the twist-off crown cap must, on the one hand, prevent leakage (i.e., spillage) of the contents, which is a particularly challenging task with pressurized liquids such as beer, and on the other hand, prevent contamination of the contents. Additionally, as already mentioned, the seal must also withstand the opening forces. It must therefore be ensured that the container can be opened by twisting the twist-off crown cap, but does not open on its own. However, the use of flexible PVC-containing compounds in seals for container closures is undesirable.The conventional incineration of household waste from halogenated plastics produces acidic gases, the release of which into the atmosphere is harmful. Furthermore, even small amounts of PVC interfere with the material recycling of plastic waste, as well as the recycling of tinplate, the standard material for the metallic part of twist-off crown caps. In addition, such PVC-based sealing elements require the use of plasticizers, which are also considered health concerns.

[0009] Globally, PVC still dominates as a sealing insert in twist crown caps, although proposals for replacing PVC have already been made in the prior art (e.g. in WO 2011 / 060804 and WO 2011 / 069520).

[0010] PVC-free seals for such twist-off crown corks are already known from our earlier patent application on this topic, published as W02011 / 060804.

[0011] The seal then contains compounds based on thermoplastic elastomers (TPE) of styrene-ethylene-butylene-styrene (SEBS) and additionally contain linear low-density polyethylene (LLDPE), low-density polyethylene (LDPE) and / or a polypropylene / polyethylene copolymer as well as significant amounts of white oil.

[0012] WO 02 / 14171 discloses vessel seals based on TPE, polybutene and polyisobutylene, which are intended for conventional screw caps (for vessels with larger opening diameters than bottles).

[0013] US patent 7,056,971 discloses compounds that can also be used to manufacture seals for twist-off crown caps. The compound comprises a TPE, in particular a TPV or an SBS containing polyisobutylene.

[0014] From US 9,969,913, vessel seals are known that are based on compounds with a vinyl-based block copolymer, a polyolefin and an isobutylene-based (co)polymer.

[0015] These compounds contain special ester-based, biocompatible processing aids, particularly natural oils, and are supposed to be free of white oil, as this allegedly increases oxygen permeability. The known compounds contain significant amounts (above 40 wt%) of PIB-based barrier polymers to reduce oxygen permeability.

[0016] US 9,969,913 does not specifically apply to twist crown caps.

[0017] There is therefore still a need for twist-off crown cork closures that feature a polymer-based sealing insert, not PVC-based. In addition to all these characteristics, the seals must also comply with legal requirements regarding the potential migration of chemical components.

[0018] It is therefore an essential object of the invention to provide twist-off crown cork closures with a sealing insert which makes it possible to provide the container closure with a polymer-based sealing element that does not contain PVC and complies with the legal requirements regarding the migration of packaging components.

[0019] It is also one of the tasks of the invention to define corresponding vessel closures.

[0020] It has now surprisingly turned out that certain compounds with a suitable Shore A hardness, and preferably based on TPE, polyolefin and white oil, sustainably meet these requirements.

[0021] The formulation according to the invention also enables the production of seals for twist-off crown corks that meet the specified requirements for (gas) tightness and opening forces without containing PVC-containing compounds.

[0022] To solve the problem of using a PVC-free polymer compound as a sealing insert for twist-off crown corks, a sealing insert for twist-off crown corks according to the invention is equipped with the features defined in claim 1.

[0023] Furthermore, the invention includes the use of particularly suitable polymer compounds for the production of such vessel closures.

[0024] In the twist-lock crown cap closures according to the invention, the sealing element is designed in a similar way as an insert on the inner surface of the container closure, as is the case with the known PVC-containing twist-lock crown caps.

[0025] More specifically, the invention relates to container closures made of metal, such as tinplate or aluminum, for holding beverages, which must be protected from the migration of packaging components in accordance with legal regulations.

[0026] In principle, the manufacturing process according to the invention starts with a metal container closure blank, which is preferably first pretreated on its inside with a suitable adhesive lacquer. PVC-free lacquer systems, such as those from ACTEGA Rhenania (e.g., ACTEbond HLD 79-3 or ACTEbond HLD 305), are particularly suitable for this purpose, as the compounds most preferred according to the invention adhere especially well to them. Bisphenol-A-free lacquers are preferred.

[0027] Alternatively, a suitable adhesion promoter layer can be applied by lamination, coating or possibly also by co-extrusion.

[0028] To ensure a tight closure of the vessel, the vessel closures according to the invention have a sealing insert made of a compound that meets the aforementioned requirements regarding processability on the one hand and sealing properties on the other, and that also meets the legal requirements regarding the migration of packaging components.

[0029] In particularly preferred embodiments of the invention, the vessel closure is suitable for sterilization.

[0030] Twist crown caps are subject to special requirements that do not apply to other twist closures, or not with the same significance.

[0031] The design of the glass external thread of twist bottle openings results in a significantly narrower contact surface for the sealing element, as shown in Fig. 1. The contact surface for the sealing element is shown in bold in Fig. 1; it lies at the edge of the bottle opening.

[0032] Due to the smaller contact surface with the sealant, the gas barrier tends to be significantly weaker, which considerably reduces shelf life compared to PryOff systems (classic crown caps). The available contact surface is also small compared to conventional screw caps, such as cam-type screw caps.

[0033] In contrast, the invention discloses significantly improved materials that, in the case of twist-off crown caps and similar screw caps, guarantee a very good seal of the bottle and significantly reduce the loss of carbon dioxide from the contents and / or the ingress of oxygen into the bottle. The specific neck geometry of bottles designed for twist-off crown cap closures necessitates very soft and elastic sealing materials, but also materials that, due to the small contact area between the sealing material and the bottle neck, must meet special, often very high, requirements regarding carbon dioxide permeability and oxygen barrier properties.

[0034] The available material selection is significantly narrower than, for example, for closures for conventional wide-necked containers (>28mm diameter), such as cam-type rotary closures.

[0035] Highly crystalline barrier raw materials significantly reduce internal compressive strengths, and also reduce lateral impact strength and greatly increase the risk of leakage, whereas soft barrier polymers (Shore A<60) can greatly increase opening torques.

[0036] An important objective of the invention is to achieve a balance with regard to the aforementioned factors, so that, for example, beer does not suffer any significant loss of quality until the end of its minimum shelf life of often 12 months, and the bottle can be easily opened at any time during this period, even when chilled.

[0037] Conventionally, this type of closure requires large proportions of highly elastic polymers with high resilience.

[0038] In practice, however, these polymer types exhibit very high permeation for gases (O2, CO2, Volatile Organic Compounds VOCs).

[0039] It was therefore surprising to find that even small to moderate amounts of special soft barrier raw materials such as HR (“butyl rubber”), styrene-isobutylene / butylene-styrene block copolymer (SIBS) and / or PiB (also partially cross-linked in so-called TPVs) in the formulation lead to a significant reduction in CO2 permeation.

[0040] Furthermore, this effect also provides better protection for the contents against negative olfactory changes caused by gases such as VOCs. Protection against oxidative changes to the contents is also significantly improved, without the need for chemical reducing agents (so-called oxygen scavengers).

[0041] Nevertheless, the system offers the possibility of delaying the effects of oxidative changes in the product even longer, especially in the case of biologically active products such as unpasteurized beer, by using such oxygen scavengers.

[0042] The adhesion behavior to the adhesive lacquer systems commonly used in crown caps is also positively influenced according to the invention.

[0043] This improvement allows storage times (best before date) to be significantly extended, and the risk of transport-related influences to be significantly reduced.

[0044] The invention can be advantageously used with various types of twist locks, e.g.

[0045] Twist crown caps, especially for sheet thicknesses < 0.22mm, specifically < 0.20mm, particularly preferred 0.18mm (each + / - 0.01mm) aluminium roll-on closures

[0046] Seals in 2-piece plastic caps.

[0047] According to the invention, the sealing element consists essentially, preferably entirely, of a polymer compound. A polymer compound, or simply compound, is understood to be a mixture of at least one polymer (e.g., SEBS) with additives, for example, for adjusting the hardness and elasticity of the sealing element, for processing the compound, for example, during the manufacture of the sealing element, and / or for other purposes.

[0048] All weight percentages in this disclosure refer to the total weight of the polymer compound of the sealing element. Percentages are weight percentages (wt.%) unless otherwise stated.

[0049] According to the invention, the polymer compound of the sealing element comprises several components, in particular at least: a styrene-based polymer; a barrier polymer in a content not exceeding 40%; a polyolefinic polymer, which may be a copolymer; a component that is liquid at 20°C, in particular a mineral oil, and conventional additives.

[0050] In preferred embodiments of the invention, the compound comprises, as a styrene-based polymer, at least one styrene-based block copolymer (SBC), in particular SEBS, SEEPS, or SEPS. In particularly preferred embodiments, the compound comprises 7-40% SEBS, SEEPS, and / or SEPS, specifically with a styrene content of 30-35 wt% and a solution viscosity in toluene at 10 wt% of >1500 mm². 2 In particularly preferred embodiments of the invention, the content of SEBS, SEEPS and / or SEPS does not exceed 35 wt.%.

[0051] In these or other preferred embodiments of the invention, the compound comprises, as a component liquid at 20°C, at least one mineral or synthetic oil, preferably white oil, and / or at least one poly-alpha-olefin liquid at 20°C (kinematic viscosity at 40°C between 60 and 300 mm²). 2 / s, determined according to ASTM D 445, preferably at approximately 70 mm 2 / s). The amount of this component is preferably 5 - 30 wt.%.

[0052] The ratio of styrene-based block copolymer (SBC), in particular SEBS, to the component that is liquid at 20°C, in particular oil, is advantageously >0.7:1.

[0053] When using olefin block copolymers (OBCs) instead of SBCs, a ratio of >2:1 OBC to liquid component is advantageous, especially for white oil.

[0054] Preferred OBCs according to the invention are those with ethylene as the main monomer and C4, C6 and / or C8 as the secondary monomer. Ethylene-octene block copolymers, such as those available from Dow as infuse types, are particularly preferred. Those with a density between 0.868 g / cm³ and 0.868 g / cm³ are especially suitable. 3 and 0.880 g / cm² 3 and exhibit a compression set at 70°C (DIN ISO 815-1, specimen type B) between 40 and 60%.

[0055] In these or other preferred embodiments of the invention, the compound comprises, as a barrier polymer, a barrier polymer that is solid at 20°C and ambient pressure (approx. 1 bar) and has a hardness of ShA <60, containing isobutylene units (preferably 11R (=butyl rubber) and / or styrene-isobutylene-styrene copolymer (SIBS)).

[0056] The amount of barrier polymer in the compound is preferably 5-40%, more preferably 5-35% and particularly preferably 10-25%.

[0057] In these or other preferred embodiments of the invention, the compound comprises PE (co)polymers, e.g. LDPE and / or, more specifically, 30-80% of at least one such polyolefinic (co)polymer, preferably with an ethylene content of >5%. A content of 5-20% of such coPPs is particularly preferred.

[0058] In particularly preferred embodiments, the polyolefinic (co-)polymer has a Shore D hardness between 25 and 48; a melting point of max. 150°C; and / or a density of 0.86-0.90 g / cm³. 3 . Such materials are commercially available from Exxonmobil (Vistamaxx) or LyondellBasell (Adflex).

[0059] The usual excipients include, for example, antioxidants, lubricants (unsaturated fatty acid amides, polydimethylsiloxanes, etc.), pigments and fillers such as CaCOs, talc.

[0060] The content of excipients can reach or even exceed 20% by weight. For example, the filler content can be 20% by weight.

[0061] The sealing element may also contain oxygen-absorbing compounds (so-called scavengers), e.g. up to 20 wt.% sodium sulfite.

[0062] The oxygen-absorbing compounds are preferably incorporated into the sealing material during compounding in particle sizes smaller than 20 pm (D5O). The particle size is preferably determined by laser diffractometry on a Sympatec Helos device, and D5O is calculated volumetrically.

[0063] The mechanical characteristics of the aforementioned and other preferred embodiments of the invention include:

[0064] Preferred Shore hardness A = 50-80, particularly preferred A = 55-75 (determined according to DIN ISO 7619-1); compression set (CSR) after 22h at 23°C storage temperature = 18-25% (determined according to DIN ISO 815-1, specimen type B); compression set (CSR) after 22h at 70°C storage temperature = 30-60% (determined according to DIN ISO 815-1, specimen type B)

[0065] COj loss in the twist crown cap is <0.lcm 3 / d (Measurement with Carbopack device, manufacturer: ExtraSolution (Italy); Measuring principle: The entire container (bottle plus crown cap) is hermetically sealed and the escaping CO2 is determined over 24h by IR detection at a wavelength of 43 pm in accordance with ASTM F2476.) Oxygen permeability OTR film <10,000 cm 3 .100pm / m 2 .d: <10,000 at 23°C and 90% rel.

[0066] Humidity (ASTM D3985). Measurement with device: OX TRAN Model 2 / 22, Manufacturer: Mocon

[0067] The other physical quantities are determined according to the following methods: - Shore D hardness according to DIN ISO 7619-1

[0068] Density according to ASTM D792-13

[0069] Melting points are determined by Dynamic Differential Scanning (DSC) according to DIN EN ISO 11357-3 and are to be understood as the peak melting temperature, which is determined from the second heating curve. Kinematic viscosity is determined according to ASTM D445.

[0070] Preferred embodiments of the invention yield the following values:

[0071] Example recipes The closures according to the invention can be used under cold-filling, hot-filling, and subsequent pasteurization conditions up to 90°C. Special embodiments can be pasteurized at temperatures between 60 and 70°C for up to 60 minutes.

Claims

Patent claims 1. Twist-removable crown-cap-type bottle closure (“twist crown”) with a sealing insert consisting substantially or entirely of a polymer compound, wherein the polymer compound comprises: - at least one styrene-based copolymer; - at least one barrier polymer in a content of no more than 40 wt.%, based on the total amount of polymer compound; - at least one polyolefinic polymer or copolymer; - at least one component that is liquid at 20°C, in particular a mineral oil, as well as usual auxiliary materials.

2. Closure according to claim 1, comprising as a styrene-based copolymer at least one styrene-based block copolymer, in particular styrene-ethylene-butylene-styrene (SEBS, hydrogenated styrene-butadiene-styrene block copolymer), styrene-ethylene-ethylene-propylene-styrene (SEEPS, hydrogenated styrene-isoprene / butadiene-styrene block copolymer) or styrene-ethylene-propylene-styrene (SEPS, hydrogenated styrene-isoprene-styrene block copolymer).

3. Closure according to claim 1 or 2, wherein the compound is 5-40 wt.% SEBS, SEEPS or SEPS, specifically with 30-35 mol% styrene content and a solution viscosity in toluene at 10 wt.% of 1500 - 3000 mm². 2 / s (measured at 25°C using a Brookfield LVT viscometer) contains.

4. Closure according to one of the preceding claims, wherein the ratio of styrene-based copolymer, in particular SEBS, to the component liquid at 20°C, in particular mineral oil, is >0.7:

1.

5. Closure according to one of the preceding claims, wherein the compound comprises as a barrier polymer a barrier polymer solid at 20°C and ambient pressure (approx. 1 bar), preferably with a hardness of ShA <60, which contains isobutylene units.

6. Closure according to claim 5, wherein the compound comprises HR (i.e., isobutylene isoprene rubber = butyl rubber) and / or styrene isobutylene styrene (SIBS).

7. Closure according to claim 6, wherein the barrier polymer is HR (i.e., isobutylene-isoprene rubber = butyl rubber) or PIB (i.e., polyisobutylene).

8. Closure according to claim 6, wherein the SIBS has a Shore A hardness of 20 to 50 and a specific density between 0.94 and 0.

96.

9. Closure according to one of the preceding claims, wherein the sealing element contains 5-40 wt.%, more preferably 5-35 wt.%, particularly preferably 10-20 wt.% of barrier polymer.

10. Closure according to one of the preceding claims, wherein the compound comprises 30-80 wt% of at least one polyolefinic (co-)polymer, preferably with an ethylene content of >5 mol%.

11. Closure according to one of the preceding claims, comprising a content of 5-20% PP-based copolymer, preferably with a Shore D hardness <40.

12. Closure according to claim 7 or 8, comprising a polyolefinic (co-)polymer with a Shore D hardness between 25 and 48; a melting point of max. 165°C and / or a density of 0.86-0.90g / cm³ 3 .

13. Closure according to any of the preceding claims, wherein the compound contains up to 50% of a polyolefinic copolymer with ethylene as the main monomer.

14. Closure according to claim 13, wherein the compound contains butene, hexene and / or octene as a co-monomer.

15. Closure according to claim 13, wherein the compound is LLDPE with a Shore D hardness between 40 and 53 and a density between 0.92 and 0.94 g / cm³. 3 contains.

16. Closure according to any of the preceding claims, wherein the compound comprises, as a component liquid at 20°C, at least one mineral or synthetic oil, preferably white oil and / or at least one poly-alpha olefin liquid at 20°C.

17. Closure according to claim 16, wherein the liquid component has a kinematic viscosity determined according to ASTM D445 at 40°C between 60 and 300 mm². 2 / s, preferably between 60 and 150 mm 2 / s and especially preferred between 65 and 75mm 2 / s 18. Closure according to one of the preceding claims, wherein the content of the liquid component is 5 - 30 wt.%, based on the total weight of the polymer compound.

19. Closure according to one of the preceding claims, wherein the excipients are selected from antioxidants, lubricants (unsaturated fatty acid amides, polydimethylsiloxanes, etc.), pigments and fillers such as CaCOs, talc.

20. Closure according to one of the preceding claims, wherein the filler content does not reach 25 wt.%.

21. Closure according to one of the preceding claims, comprising a content of at least one oxygen-absorbing compound.

22. Closure according to claim 18 or 21, containing up to 20 wt.% sodium sulfite.

23. Closure according to claim 22, with a content of 4 - 12% sodium sulfite, preferably with a content of 6 - 10% sodium sulfite.

24. Closure according to one of the preceding claims, wherein the sealing element has a Shore A hardness of 50-80, in particular preferably of 55-75.

25. Closure according to one of the preceding claims, wherein the sealing element has a DVR (DIN ISO 815-1, specimen type B) at 23°C of 18-25% and / or a DVR at 70°C of 30-60%.

26. Closure according to one of the preceding claims, wherein the CC loss in the twist crown cap is <0.12cm 3 / d lies (Measurement with device: Carbopack, manufacturer: ExtraSolution (Italy); Measuring principle: The entire container (bottle plus crown cap) is hermetically sealed and the escaping CO2 is determined over 24h by IR detection of the wavelength 43pm in accordance with ASTM F2476.) 27. Closure according to one of the preceding claims, wherein the polymer compound comprises a Oxygen permeability (OTR) of <10,000 cm² 3 .100pm / m 2 exhibits, measured against the film with d: <10,000 at 23°C and 90% relative humidity (ASTM D3985). This is performed on a Mocon OXTRAN model 2 / 22 instrument.

28. Use of a polymer compound according to one of the preceding claims, for a sealing element of a twist crown cap, aluminium roll-on closure or in a Seal of a 2-part plastic cap.

29. Twist crown cap with sealing element according to the preceding claims, made with a sheet thickness of less than 215 pm, preferably less than 200 pm, particularly preferably less than 190 pm and a yield strength above 415 MPa (according to EN10202:2022).

30. Container for holding food and beverages, in particular a beer bottle, with a closure according to one of the preceding claims.

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