Heat-seal-capable aluminium alloy strip for beverage can lids

Abstract

The present invention relates, inter alia, to an aluminium alloy strip for producing a beverage can lid, the aluminium alloy strip having an aluminium alloy of type AA5xxx. The problem of specifying an aluminium alloy strip made of an aluminium alloy of type AA5xxx for producing a beverage can lid which enables plastic elements to be fastened to the produced beverage can lids in a reliable and cost-effective manner is solved in that the aluminium alloy strip has, on one side or on both sides, a heat-seal-capable coating which contains polyolefin, wherein the polyolefin is cross-linked at least partially via a hydroxyalkyl amide and the heat-seal-capable coating contains wax.

Description

[0001] Heat sealable aluminum alloy tape for beverage can ends

[0002] The present invention relates to an aluminum alloy strip for producing a beverage can end, wherein the aluminum alloy strip comprises an aluminum alloy of type AA5xxx. Furthermore, the invention relates to a method for producing an aluminum alloy strip, wherein the method comprises: casting a rolling ingot or a cast strip made of an aluminum alloy of type AA5xxx; homogenizing the rolling ingot or the cast strip; hot rolling the rolling ingot or the cast strip into a hot strip; and cold rolling the hot strip to final thickness with at least one intermediate annealing or without intermediate annealing. Finally, the invention relates to a use of an aluminum alloy strip, a resealable beverage can end, and a beverage can with a resealable beverage can end.

[0003] Beverage cans are an important type of packaging for beverages. A beverage can usually consists of a beverage can body and a beverage can end, which are hermetically connected to one another, for example by a flange. The beverage can body primarily serves to contain the beverage and can also be made up of several parts. The beverage can end serves, on the one hand, to securely close the cavity formed by the beverage can body, thus preventing the beverage from leaking out, for example during storage or transport of the unopened beverage can. On the other hand, the beverage can end is typically designed in such a way that an opening can be created in the beverage can end for the intended removal of the beverage by the consumer.

[0004] In addition to tinplate, aluminum alloys are primarily used as materials for the production of beverage cans. Due to the different requirements placed on the respective materials, the beverage can body and the beverage can end are typically made of different aluminum alloys. While AA3xxx aluminum alloys have prevailed for beverage can bodies due to their good forming properties, AA5xxx aluminum alloys are typically used for beverage can ends. These alloys have improved mechanical properties due to their higher magnesium content. This allows for greater internal pressure stability of the beverage can end, thus preventing unwanted bulging of the beverage can end, for example, in the case of carbonated beverages.

[0005] Most beverage can ends in use today have a mechanism that irreversibly creates an opening for dispensing the beverage. For example, the opening is created by pressing in a section of the beverage can end defined by a pre-punched predetermined breaking line. Such a mechanism does not provide for resealing the created opening, which has a number of disadvantages: Firstly, the beverage is relatively unprotected from environmental influences such as dirt, dust, and insects. Secondly, the beverage is not protected against leakage if, for example, the beverage can is shaken violently or falls over. Thirdly, carbon dioxide can easily escape from the beverage.

[0006] A mechanism for creating a resealable opening in a beverage can lid is known, for example, from German utility model DE 29812116 U1. This mechanism features an additional, rotating lid made of sheet metal to close the opening and reopen it as needed. However, sheet metal has the disadvantage that it can have sharp edges, which poses a significant risk of injury to the consumer when operating the resealable mechanism. Therefore, considerations are being given to creating a resealable opening in a beverage can lid by attaching plastic elements to the beverage can lid.According to this approach, the plastic elements are intended to ensure that the opening created for dispensing the beverage can be closed and reopened if necessary, without posing a significant risk of injury to the consumer from sharp metal edges. One problem with implementing this approach, however, is the secure and cost-effective attachment of the plastic elements to the beverage can end. This as yet unsolved problem is currently hindering the further development and market launch of resealable openings in beverage can ends based on plastic elements. For example, if the connection between the plastic elements and the beverage can end is insufficiently strong, the plastic elements could become detached, rendering the mechanism for reclosing the beverage can end inoperable.

[0007] Against this background, the present invention aims to provide an aluminum alloy strip made of an AA5xxx aluminum alloy for producing a beverage can end, which enables the secure and cost-effective attachment of plastic elements to the produced beverage can ends. Furthermore, the invention aims to provide a method for producing such an aluminum alloy strip and to provide an advantageous use of the aluminum alloy strip. Finally, the invention aims to provide a resealable beverage can end, to which plastic elements can be securely and cost-effectively attached, as well as a corresponding beverage can.

[0008] According to a first teaching of the invention, the above-mentioned object is achieved for an aluminum alloy strip for producing a beverage can end, wherein the aluminum alloy strip comprises an aluminum alloy of the type AA5xxx, in that the aluminum alloy strip has on one side or on both sides a heat-sealable coating which contains polyolefin.

[0009] Within the scope of the invention, it has been found that a heat-sealable coating containing polyolefin enables the secure and cost-effective attachment of plastic elements to an aluminum alloy strip comprising an aluminum alloy of the AA5xxx type. Because the coating of the aluminum alloy strip according to the invention is heat-sealable, the plastic elements can be attached to beverage can lids made from the aluminum alloy strip according to the invention using the simple and proven process of heat sealing. Generally, plastic parts are joined together during heat sealing by heating the joining surfaces of the parts to be joined and pressing them together, resulting in a melting.The heat-sealable coating of the aluminum alloy strip according to the invention can also provide corresponding joining surfaces, so that plastic elements can be connected to the aluminum alloy strip according to the invention by means of the heat-sealable coating. As was further demonstrated within the scope of the invention, a connection produced by heat-sealing between the heat-sealable coating of the aluminum alloy strip and the plastic elements of a resealable beverage can end attached thereto is capable of permanently providing the adhesive forces necessary for a secure connection. The heat-sealable coating serves as an adhesion promoter between the aluminum alloy of the beverage can end and the plastic elements. Since the heat-sealing process also enables efficient high-volume production, cost-effective attachment of the plastic elements is also achieved.

[0010] Because the heat-sealable coating of the aluminum alloy strip according to the invention contains polyolefin, the coating also exhibits a high level of health compatibility, thus meeting applicable food safety regulations in this regard. In particular, the heat-sealable coating of the aluminum alloy strip according to the invention is free of formaldehyde, bisphenol A (BPA), melamine, polytetrafluoroethylene [PTFE], and styrene. Due to the harmful effects of these substances on health, their use in the food sector is either restricted in many countries to strict limits or even completely prohibited.However, the heat-sealable coating of the aluminum alloy strip according to the invention is based on polyolefin, which is unproblematic in this respect, and does not contain any of the substances mentioned, so that the coating accordingly has a high level of health compatibility and food law requirements are met.

[0011] It has also been found that the heat-sealable coating of the aluminum alloy strip according to the invention is also readily suitable for the manufacturing processes of beverage can lids, in particular for the forming processes required for this purpose.

[0012] The aluminum alloy strip according to the invention has a heat-sealable coating containing polyolefin on one side or on both sides. In the case of a single-sided coating, the heat-sealable coating is preferably applied to that side of the aluminum alloy strip which corresponds to the outside of a beverage can end and is not intended to come into contact with a beverage contained therein before the beverage can is opened. In this way, the plastic elements for a resealable beverage can end can be attached to the outside. In the case of a double-sided coating, the heat-sealable coating is preferably also applied to that side of the aluminum alloy strip which corresponds to the inside of a beverage can end and is intended to come into contact with a beverage contained therein before the beverage can is opened.In this context, it has been shown that the heat-sealable coating of the aluminum alloy strip according to the invention also acts as a highly functional barrier between the aluminum alloy of the beverage can end and the beverage. In particular, the heat-sealable coating, on the one hand, protects the beverage against the migration of aluminum from the can end material. On the other hand, the aluminum alloy of the beverage can end is also protected from attack by the beverage, for example, when the beverage is carbonated. Furthermore, the heat-sealable coating of the aluminum alloy strip according to the invention also fulfills the function of a highly functional barrier on an outer side of a beverage can end, for example, when the beverage comes into contact with the outer side of the beverage can end during or as a result of drinking.

[0013] In a preferred embodiment of the aluminum alloy strip according to the invention, the polyolefin is polyethylene or polypropylene, or a blend of both. Polyethylene (PE) and polypropylene (PP) are the two most widely used polyolefins and are particularly cost-effective. The heat-sealable coating of the aluminum alloy strip according to the invention preferably contains the same polyolefin from which the plastic elements to be fastened are made, since in this case, the fusion during heat sealing is particularly reliable, thus creating a particularly secure connection.

[0014] In a preferred embodiment of the aluminum alloy strip according to the invention, the polyolefin is at least partially crosslinked. During the crosslinking of a polyolefin, and of a polymer in general, the chain-like macromolecules of the polymer are linked through chemical reactions to form a three-dimensional network. Among other things, the crosslinking results in an increase in the hardness and toughness of the polymer and a decrease in its solubility. This is advantageous for the production of beverage can ends, as it improves both the mechanical and chemical resistance of the heat-sealable coating.

[0015] In a preferred embodiment of the aluminum alloy strip according to the invention, the polyolefin is at least partially crosslinked by a hydroxyalkylamide. The hydroxyalkylamide is preferably N,N,N',N'-tetrakis(2-hydroxyethyl)adipamide. Hydroxyalkylamides, and in particular the aforementioned N,N,N',N'-tetrakis(2-hydroxyethyl)adipamide, are well suited for crosslinking polyolefins due to their chemical properties, resulting in effective crosslinking. N,N,N',N'-tetrakis(2-hydroxyethyl)adipamide as a crosslinking agent also offers the advantages of being suitable for use in the food industry, and the resulting crosslinked polyolefin exhibits high resistance to weathering influences such as ultraviolet radiation.

[0016] In a preferred embodiment of the aluminum alloy strip according to the invention, the heat-sealable coating contains wax. This is preferably a PTFE-free wax such as carnauba wax, polyethylene wax, polypropylene wax, polyamide wax, or a mixture of the aforementioned waxes. Because the heat-sealable coating of the aluminum alloy strip according to the invention contains wax, the surface smoothness and surface hardness of the heat-sealable coating can be increased. This has a beneficial effect on the handling of the aluminum alloy strip and beverage can ends made from it in manufacturing processes, for example, during transport within a production line, and also improves the punchability of the aluminum alloy strip. Furthermore, PTFE-free wax is generally unproblematic with regard to health compatibility and food safety regulations.In a preferred embodiment of the aluminum alloy strip according to the invention, the heat-sealable coating has a basis weight of 1.0 g / m. 2 up to 20.0 g / m 2 The heat-sealable coating preferably has a basis weight of 2.0 g / m 2 up to 14.0 g / m 2 The heat-sealable coating particularly preferably has a basis weight of 3.0 g / m 2 up to 5.0 g / m 2 or 6.0 g / m 2 up to 12.5 g / m 2 Most preferably, the heat-sealable coating has a basis weight of 3.5 g / m 2 up to 4.5 g / m 2 or 6.5 g / m 2 up to 12.0 g / m 2 The basis weights stated are dry weights. For a given mass density, the basis weight of the heat-sealable coating correlates with the thickness of the heat-sealable coating. Because the heat-sealable coating has a basis weight in the range of 1.0 g / m2 up to 20.0 g / m 2 A good compromise between sufficient seal strength and low material usage can be achieved. A particularly good compromise is found in the preferred range of 2.0 g / m 2 up to 14.0 g / m 2 A lower basis weight, especially in the particularly preferred range of 3.0 g / m 2 up to 5.0 g / m 2 or most preferably 3.5 g / m 2 up to 4.5 g / m 2 , leads to lower material usage and thus to cost reduction. A higher basis weight, especially in the particularly preferred range of 6.0 g / m 2 up to 12.5 g / m 2 or most preferably 6.5 g / m 2 up to 12.0 g / m 2 , leads to a higher seal seam strength and thus to a more secure fastening of the plastic elements.

[0017] In a preferred embodiment of the aluminum alloy strip according to the invention, the heat-sealable coating, after heat-sealing against a polypropylene film with a sealing force of 90 N, a sealing time of 1 s, and a sealing temperature of 180°C, has a seal seam strength of at least 35 N with a seal seam width of 15 mm. Preferably, the heat-sealable coating, after heat-sealing against a polypropylene film with the stated parameters of sealing force, sealing time, sealing temperature, and seal seam width, has a seal seam strength of at least 39 N. Particularly preferably, the heat-sealable coating, after heat-sealing against a polypropylene film with the stated parameters, has a seal seam strength of at least 42 N. The seal seam strength can be determined, for example, according to DIN 55529.The term "seal seam strength" is synonymous with the term "release force" used in DIN 55529, which is always specified as an arithmetic mean. When heat-sealing a polypropylene film, it is important to ensure that a sufficiently thick polypropylene film is used to prevent the polypropylene film from tearing during the determination of the seal seam strength due to the comparatively high sealing forces. In this context, the thickness of the polypropylene film should be 200 μm or more, for example.Because the heat-sealable coating of the aluminum alloy strip according to the invention has a seal seam strength of at least 35 N under the conditions mentioned, it is possible to ensure that the adhesive forces required for a secure connection between the heat-sealable coating and the plastic elements to be fastened are provided to a sufficient degree. Consequently, a sufficiently secure fastening is achieved. A higher seal seam strength, preferably of at least 39 N or more preferably at least 42 N, can provide correspondingly higher adhesive forces, thus achieving an even more secure fastening.

[0018] In a preferred embodiment of the aluminum alloy strip according to the invention, the heat-sealable coating has a porosity with which the current intensity measured in the “Enamel Rater” porosity measurement at a basis weight of the heat-sealable coating in the range of 8 g / m 2 up to 12 g / m 2is at most 5 mA, wherein the “Enamel Rater” porosity measurement is carried out with a direct voltage of 6.3 V and the current is determined after a measuring time of 4 s. Preferably, the heat-sealable coating has a porosity with which the current measured under these conditions is at most 2 mA. Particularly preferably, the heat-sealable coating has a porosity with which the measured current is at most 1 mA. Preferably, the “Enamel Rater” porosity measurement is carried out on a beverage can end shell made from the aluminum alloy strip. The “Enamel Rater” porosity measurement is a measurement method commonly used in the packaging industry for testing electrically non-conductive coatings on metallic materials, which is carried out on test pieces of the coated metallic material.In connection with beverage can ends, so-called beverage can end shells are used as test pieces. A beverage can end shell or shell refers to a precursor product of a beverage can end that has already been punched out and formed, but does not yet have the final shape of a beverage can end and also does not have a pull tab for opening the beverage can end. To carry out the "Enamel Rater" porosity measurement, a test setup is selected in which the test piece comes into contact with an electrolyte solution on the coated side. The electrolyte solution is electrically contacted via a first electrode. A second electrode is connected to the metal layer of the test piece. A direct voltage, usually 6.3 V, is then applied between the electrodes.Since the coating of the test piece is an electrical insulator, current flow between the electrodes via the electrolyte can only occur due to unpainted areas or pores in the coating of the test piece. The measured current is therefore a measure of the area of ​​unpainted areas or pores in the coating of the test piece. The higher the measured current, the greater the porosity. Since the measured current does not usually assume a steady-state value immediately, the current is usually determined after a measurement time of 4 s, during which a steady-state value is usually present. The measured current also depends on the thickness and thus on the basis weight of the coating, since unpainted areas or pores are more likely to occur at lower thicknesses than at higher thicknesses. In the context of beverage can ends, a coating weight of around 8 g / m² can occur. 2up to 12 g / m 2 It can be assumed that a current of no more than 5 mA measured in the “Enamel Rater” porosity measurement corresponds to a sufficiently low porosity of the coating.

[0019] In particular, a measured current of no more than 5 mA for the heat-sealable coating of the aluminum alloy strip according to the invention can ensure that the heat-sealable coating, due to its sufficiently low porosity, adequately fulfills its function as a highly functional barrier and also as an adhesion promoter. With a measured current of preferably no more than 2 mA, and particularly preferably no more than 1 mA, a coating with correspondingly lower porosity and thus improved properties as a highly functional barrier or adhesion promoter can be provided.

[0020] In a preferred embodiment of the aluminum alloy strip according to the invention, the aluminum alloy strip comprises an aluminum alloy of the type AA5052 or AA5182. These aluminum alloys are particularly well suited for the production of beverage can ends due to their high magnesium content and the associated mechanical properties. Furthermore, they are readily suitable for being provided with the heat-sealable coating.

[0021] In a preferred embodiment of the aluminum alloy strip according to the invention, the aluminum alloy strip has a metal thickness of 0.1 mm to 0.3 mm, preferably 0.15 mm to 0.25 mm. The metal thickness does not include the thickness of the heat-sealable coating or other coatings. Because the aluminum alloy strip has a metal thickness of 0.1 mm to 0.3 mm, a good compromise can be achieved between sufficient mechanical strength on the one hand and low material usage and low weight on the other. A lower metal thickness leads, on the one hand, to lower material usage and thus to a reduction in costs. On the other hand, a lower metal thickness also leads to a lower weight of the beverage can end, which is particularly advantageous for transporting the beverage cans.A higher metal thickness, on the other hand, leads to better mechanical strength and thus, in particular, greater internal pressure stability of the beverage can end. The preferred metal thickness range of 0.15 mm to 0.25 mm achieves a particularly good compromise between sufficient mechanical strength on the one hand and low material usage and low weight on the other.

[0022] In a preferred embodiment of the aluminum alloy strip according to the invention, the aluminum alloy strip additionally has a chromium-free conversion layer on one side or on both sides. The one-sided or double-sided chromium-free conversion layer is preferably arranged directly on the metal layer of the aluminum alloy strip and is covered by a heat-sealable coating. The fact that the aluminum alloy strip according to the invention has a conversion layer makes it possible to achieve, on the one hand, improved corrosion protection and, on the other hand, improved adhesion of the heat-sealable coating. A chromium-free conversion layer is more suitable for contact with food than a chromium-containing conversion layer. The chromium-free conversion layer preferably contains zirconium phosphate. This allows particularly good adhesion properties to be achieved compared to the polyolefin-containing heat-sealable coating.In principle, however, the aluminum alloy strip according to the invention can also be realized with conversion layers containing other metal phosphates such as titanium phosphate or chromium phosphate.

[0023] In a preferred embodiment of the aluminum alloy strip according to the invention, the aluminum alloy strip has at least one further layer on one side or on both sides. For example, the aluminum alloy strip according to the invention can have a further polymer layer on one side or on both sides, preferably a film consisting of polyolefin, preferably a polyethylene film or polypropylene film, or a film consisting of a blend of both polymers. The mechanical properties of the aluminum alloy strip can be improved with such a polymer layer, both on the side of the aluminum alloy strip which corresponds to the inside of a beverage can end and on the side which corresponds to the outside. This can, in particular, improve the internal pressure stability of a beverage can end produced from the aluminum alloy strip according to the invention.A polymer layer on the inside can also provide better protection for the beverage against the migration of aluminum from the can end material, while also protecting the aluminum alloy of the beverage can end from attack by the beverage. A polymer layer on the outside can also provide protection against external influences such as mechanical stress.

[0024] According to a second teaching of the invention, the above-mentioned object is achieved by a method for producing an aluminum alloy strip, the method comprising:

[0025] Casting of a rolled ingot or cast strip from an aluminium alloy of type AA5xxx;

[0026] Homogenization of the rolling ingot or the cast strip;

[0027] Hot rolling of the rolling ingot or the cast strip into a hot strip; cold rolling of the hot strip to the final thickness with at least one intermediate annealing or without intermediate annealing; achieved in that the method further comprises:

[0028] Producing a heat-sealable coating on one side or both sides of the cold-rolled aluminum alloy strip to final thickness, wherein the heat-sealable coating contains polyolefin.

[0029] Through the process steps of casting a rolling ingot or cast strip from an AA5xxx aluminum alloy, homogenizing the rolling ingot or cast strip, hot rolling the rolling ingot or cast strip into a hot strip, and cold rolling the hot strip to final thickness with or without intermediate annealing, an aluminum alloy strip from an AA5xxx aluminum alloy can be produced reliably and efficiently. If the process is carried out with at least one intermediate annealing, work hardening that occurs during cold rolling can be eliminated, so that lower strengths in the as-rolled state are possible at the final thickness. In principle, however, the process can also be carried out without intermediate annealing. Optionally, the aluminum alloy strip can also be subjected to a final heat treatment after cold rolling, which can also eliminate work hardening.

[0030] Because the method according to the invention comprises, as an additional method step, the production of a heat-sealable coating on one or both sides of the aluminum alloy strip cold-rolled to its final thickness, wherein the heat-sealable coating contains polyolefin, a corresponding heat-sealable coating with the advantages already explained in connection with the first teaching can be provided on the aluminum alloy strip. In particular, therefore, an aluminum alloy strip according to the first teaching of the invention is produced using the method according to the second teaching of the invention.

[0031] In a preferred embodiment of the process according to the invention, the heat-sealable coating is produced by applying and baking a lacquer. This allows the heat-sealable coating to be provided in a cost-effective and process-reliable manner. In principle, however, the heat-sealable coating can also be produced by other suitable processes, such as extrusion coating or lamination, on the aluminum alloy strip cold-rolled to its final thickness.

[0032] In a preferred embodiment of the process according to the invention, the coating is a water-based coating. Compared to conventional solvent-based coatings, a water-based coating has greater environmental compatibility. Furthermore, a water-based coating is less problematic with regard to health compatibility and food safety regulations, as it does not contain aminoplasts such as melamine or benzoguamine as reactants.

[0033] In a preferred embodiment of the process according to the invention, the coating contains a polyolefin dispersion. Due to the fine distribution of the polyolefin in the dispersion, a homogeneous, heat-sealable coating can be produced during application and baking of the coating.

[0034] In a preferred embodiment of the process according to the invention, the polyolefin dispersion is a polyethylene dispersion or a polypropylene dispersion, or a mixture of both. Accordingly, the polyolefin contained in the heat-sealable coating produced is polyethylene or polypropylene, or a corresponding blend. Polyethylene (PE) and polypropylene (PP) are the two most widely used polyolefins and are therefore particularly cost-effective. The polyolefin dispersion is preferably a dispersion of the same polyolefin from which the plastic elements of the resealable beverage can lid to be attached are made. In this case, the fusion during heat-sealing is particularly reliable, resulting in a particularly secure bond.

[0035] In a preferred embodiment of the process according to the invention, the lacquer contains a crosslinking agent. This can result in the polyolefin being at least partially crosslinked, thus improving both the mechanical and chemical resistance of the heat-sealable coating, as already explained in connection with the first teaching.

[0036] In a preferred embodiment of the process according to the invention, the varnish contains a hydroxyalkylamide as a crosslinking agent. The hydroxyalkylamide is preferably N,N,N',N'-tetrakis(2-hydroxyethyl)adipamide. By using a hydroxyalkylamide as a crosslinking agent, and in particular by using N,N,N',N'-tetrakis(2-hydroxyethyl)adipamide, effective crosslinking of the polyolefin, suitability for use in the food industry, and high weather resistance can be achieved, as already explained in connection with the first teaching.

[0037] In a preferred embodiment of the process according to the invention, the varnish contains wax. This is preferably a PTFE-free wax such as carnauba wax, polyethylene wax, polypropylene wax, polyamide wax, or a mixture of the aforementioned waxes. Because the varnish contains wax, the surface smoothness and surface hardness of the heat-sealable coating can be increased, thus improving, among other things, the punchability of the aluminum alloy strip. Furthermore, PTFE-free wax is generally unproblematic with regard to health compatibility and food safety regulations.

[0038] In a preferred embodiment of the process according to the invention, the water-based varnish contains 1 to 15 wt.%, preferably 2 to 6 wt.%, of an aqueous solution of a hydroxyalkylamide, 1 to 20 wt.%, preferably 5 to 11 wt.%, of PTFE-free wax, and the remainder an aqueous polyolefin dispersion. The aqueous polyolefin dispersion can have a solids content of up to 60 wt.%, preferably 40 to 50 wt.%. Furthermore, the aqueous polyolefin dispersion can preferably be an aqueous polyethylene dispersion or an aqueous polypropylene dispersion. The aqueous solution of a hydroxyalkylamide may preferably be a solution of 10 to 90 wt.%, preferably 20 to 40 wt.% of N,N,N',N'-tetrakis(2-hydroxyethyl)adipamide in deionized water or in weakly basic water containing 0.1 to 0.5 wt.% of N,N-dimethylethanolamine (DMEA).The PTFE-free wax can be, for example, carnauba wax, polyethylene wax, polypropylene wax, polyamide wax, or a mixture of the aforementioned waxes. The specified composition of the water-based varnish allows for the heat-sealable coating to be produced cost-effectively, while also ensuring the advantageous properties of the heat-sealable coating are achieved reliably.

[0039] In a preferred embodiment of the method according to the invention, the coating is applied using a single-sided or double-sided coil-coating process. In a coil-coating process, the aluminum alloy strip to be coated is unwound from one coil, coated, and rewound onto another coil. This allows for easy handling of the aluminum alloy strip for coating purposes. In principle, however, the method according to the invention can also be implemented using other methods for handling the aluminum alloy strip.

[0040] In a preferred embodiment of the method according to the invention, the coating is applied using a one-sided or two-sided roll-coating process. In a roll-coating process, the coating is applied to one or both sides of the aluminum alloy strip by rollers. This allows the thickness or basis weight of the coating to be adjusted very precisely, even at high coating speeds, so that a reliable coating can be achieved. In principle, however, the method according to the invention can also be implemented using other coating methods. For example, the coating can also be applied by spraying, preferably by electrostatic spraying.

[0041] In a preferred embodiment of the method according to the invention, the lacquer is baked such that a maximum metal temperature in the range of 200°C to 300°C, preferably in the range of 220°C to 260°C, is reached. With the stated maximum metal temperature ranges, reliable curing of the heat-sealable coating can be achieved without any noticeable softening of the aluminum alloy strip. The baking time, i.e., the duration of a heating process at the end of which the maximum metal temperature is reached, can be, for example, in the range of 5 s to 35 s, preferably in the range of 8 s to 25 s.

[0042] According to a further preferred embodiment of the method, after the heat-sealable coating has been applied and baked, a further polymer layer in the form of a heat-sealable film consisting of polyolefin, preferably a polyethylene or polypropylene film, is applied. Especially in the strip-shaped state, a particularly economical way of coating the strip with a polyolefin film, preferably a polyethylene or polypropylene film, or a film made of a blend of the two polymers, can be achieved by applying a suitable polyolefin film, for example by lamination or hot-lamination.

[0043] In a preferred embodiment of the method according to the invention, the rolling ingot or cast strip is cast from an aluminum alloy of the type AA5052 or AA5182. These aluminum alloys exhibit particularly advantageous mechanical properties, as already explained in connection with the first teaching.

[0044] In a preferred embodiment of the method according to the invention, the hot-rolled strip is cold-rolled to a final metal thickness of 0.1 mm to 0.3 mm, preferably 0.15 mm to 0.25 mm. The metal thickness does not include the thickness of the heat-sealable coating or other coatings. These metal thickness ranges allow a good compromise between sufficient mechanical strength and low material usage, as well as low weight, to be achieved, as already explained in connection with the first teaching.

[0045] In a preferred embodiment of the method according to the invention, the aluminum alloy strip is subjected to a chromium-free phosphating treatment on one or both sides. The chromium-free phosphating is preferably carried out using zirconium phosphate. By means of a chromium-free phosphating treatment, preferably using zirconium phosphate, a chromium-free conversion layer, preferably containing zirconium phosphate, can be produced on one or both sides of the aluminum alloy strip. The advantages of this conversion layer have already been explained in connection with the first teaching. In principle, however, other metal phosphates, such as titanium phosphate or chromium phosphate, can also be used for the phosphating treatment instead of zirconium phosphate.Phosphating is preferably carried out in such a way that the conversion layer, produced on one or both sides, is arranged directly on the metal layer of the aluminum alloy strip and is subsequently covered by a heat-sealable coating. Phosphating can particularly preferably be carried out in conjunction with the coil-coating process for applying the coating, i.e., "in line." This eliminates the need for winding and unwinding the aluminum alloy strip, thus achieving greater process efficiency. Phosphating is preferably carried out using a no-rinse process, which does not require a rinsing step, since the phosphating agent is applied to the aluminum alloy strip and dried. Compared to phosphating processes with rinsing steps, no-rinse processes are more economical and environmentally friendly.

[0046] According to a third teaching of the invention, the above-mentioned object for the use of an aluminum alloy strip is achieved by using the aluminum alloy strip according to the first teaching for producing a resealable beverage can end. In this context, the aluminum alloy strip according to the first teaching, in particular due to the heat-sealable coating containing polyolefin, enables secure and cost-effective fastening of the plastic elements of the resealable beverage can end to the aluminum alloy strip by means of the simple and proven heat-sealing process. Regarding further embodiments and advantages of the use according to the invention, reference is additionally made to the explanations in connection with the first teaching.According to a fourth and fifth teaching of the invention, the above-mentioned object for a resealable beverage can end and for a beverage can with a resealable beverage can end is achieved in that the beverage can end is produced from an aluminum alloy strip according to the first teaching. Here, too, the aluminum alloy strip according to the first teaching enables secure and cost-effective fastening of the plastic elements of the resealable beverage can end. Regarding further embodiments and advantages of the resealable beverage can end according to the invention and the beverage can according to the invention, reference is made in addition to the explanations in connection with the first teaching.

[0047] The invention will be explained in more detail below by the description of exemplary embodiments in conjunction with the drawing. The drawing shows in

[0048] Fig. 1a, 1b show embodiments of aluminum alloy strips according to the invention according to the first teaching in a schematic sectional view;

[0049] Fig. 2a, 2b an embodiment of a method according to the invention according to the second teaching in a schematic representation;

[0050] Fig. 3 shows an example of a beverage can according to the invention according to the fifth

[0051] Teaching with a beverage can lid according to the invention according to the fourth teaching in a schematic representation.

[0052] Figs. 1a and 1b each show an embodiment of an aluminum alloy strip 10, 11 according to the invention in a schematic sectional view. Fig. 1a first shows an aluminum alloy strip 10 with a metal layer 12 and a heat-sealable coating 13 applied on one side. Using the heat-sealing method, plastic elements for creating a resealable beverage can end can be securely and cost-effectively attached to the heat-sealable coating 13, making the aluminum alloy strip 10 particularly suitable for producing a sealable beverage can end. Furthermore, the polyolefin-containing heat-sealable coating 13 is also highly compatible with health and unproblematic with regard to currently applicable food regulations.

[0053] The metal layer 12 of the aluminum alloy strip 10 is made of an aluminum alloy of type AA5xxx, here, for example, type AA5182, which, due to its high magnesium content, exhibits high strength and is therefore well suited for the production of beverage can ends. Furthermore, the metal layer 12 has a thickness of, for example, 0.2 mm. This thickness ensures, among other things, sufficient internal pressure stability of the beverage can end. At the same time, the weight of the beverage can end and the material used in its production are limited to a reasonable level.

[0054] The heat-sealable coating 13 of the aluminum alloy strip 10 contains, for example, polypropylene as a polyolefin, as well as PTFE-free wax. The polypropylene is cross-linked using a hydroxyalkylamide, here, for example, using N,N,N',N'-tetrakis(2-hydroxyethyl)adipamide. As a result of the cross-linking, the mechanical and chemical resistance of the heat-sealable coating 13 is improved. In this context, hydroxyalkylamides are well suited as cross-linking agents for polyolefins due to their chemical properties. Furthermore, the N,N,N',N'-tetrakis(2-hydroxyethyl)adipamide used here as an example is unproblematic with regard to use in the food sector. The PTFE-free wax also contained in the heat-sealable coating 13 increases the surface smoothness and surface hardness of the heat-sealable coating 13 and thus, among other things, improves the punchability of the aluminum alloy strip 10.The basis weight of the heat-sealable coating 13 is in the range of 1.0 g / m. 2 up to 20.0 g / m 2 , preferably in the range of 2.0 g / m 2 up to 14.0 g / m 2 , which allows a good compromise to be achieved between sufficiently secure fastening of the plastic elements and low material usage. Furthermore, the seal seam strength of the heat-sealable coating 13 after heat sealing against a polypropylene film with a sealing force of 90 N, a sealing time of 1 s and a sealing temperature of 180 °C is at least 35 N with a seal seam width of 15 mm. This enables a sufficiently secure fastening of the plastic elements. Finally, the heat-sealable coating has a porosity with which the current intensity measured in the "Enamel Rater" porosity measurement at a basis weight of the heat-sealable coating in the range of 8 g / m 2 up to 12 g / m 2is a maximum of 5 mA, whereby the "Enamel Rater" porosity measurement is carried out with a direct voltage of 6.3 V, and the current is determined after a measurement time of 4 s. This ensures that the porosity of the heat-sealable coating 13 is sufficiently low so that the heat-sealable coating 13 adequately fulfills its properties as an adhesion promoter and as a highly functional barrier.

[0055] Another embodiment of an aluminum alloy strip 11 according to the invention is shown in Fig. 1b, also in a schematic sectional view. This aluminum alloy strip 11 also has a metal layer 12 and, adjacent thereto, a heat-sealable coating 13 on each side. With regard to the metal layer 12 and the heat-sealable coatings 13 of the aluminum alloy strip 11, the above statements apply analogously to the aluminum alloy strip 10 shown in Fig. 1a.

[0056] Unlike the aluminum alloy strip 10 from Fig. 1a, however, the aluminum alloy strip 11 shown in Fig. 1b is provided on both sides with a heat-sealable coating 13. In a beverage can end made from the aluminum alloy strip 11, the heat-sealable coating 13 on the upper side primarily serves the purpose of securing the plastic elements to create a resealable beverage can end. In contrast, the heat-sealable coating 13 on the underside functions primarily as a highly functional barrier. In this function, the heat-sealable coating 13 protects the beverage against the migration of aluminum from the can end material, on the one hand, and the aluminum alloy of the beverage can end from attack by the beverage, on the other.

[0057] Furthermore, the aluminum alloy strip 11 shown in Fig. 1b has, in addition to the metal layer 12 and the double-sided heat-sealable coatings 13, a conversion layer 14 on each side. The exemplary conversion layers 14 shown are chromium-free, preferably contain zirconium phosphate, and are arranged directly on the metal layer 12 so that they are each covered by the heat-sealable coatings 13. In addition to providing protection against corrosion, the conversion layers 14 particularly improve the adhesion of the heat-sealable coatings 13. Because the conversion layers 14 do not contain harmful chromium, they are well suited for contact with food. Furthermore, the zirconium phosphate, which is preferably present, achieves particularly good adhesion of the polyolefin-containing heat-sealable coatings 13.

[0058] In principle, further layers can also be present on the aluminum alloy strips 10, 11 shown in Fig. 1a and 1b. For example, the aluminum alloy strip 11 from Fig. 1b could have a polymer layer on a side corresponding to an inner side of a beverage can lid as a barrier layer and / or to improve the internal pressure stability of the beverage can lid. Additionally or alternatively, the aluminum alloy strip 11 could have a polymer layer on a side corresponding to an outer side of a beverage can lid as protection against external influences and / or also to improve the internal pressure stability of the beverage can lid. Figs. 2a and 2b now show, in a schematic view, an embodiment of a method according to the invention for producing an aluminum alloy strip, in particular for producing an aluminum alloy strip according to the invention. Fig.Figure 2a shows the process steps 20a, from casting the rolling ingot up to and including cold rolling the hot strip to final thickness. Figure 2b shows the process steps 20b for coating the aluminum alloy strip following cold rolling.

[0059] First, in step 22, a rolling slab 21a is produced from a type 5xxx aluminum alloy. The rolling slab 21a is produced, as schematically shown here, for example using a discontinuous direct chill (DC) casting process. Alternatively, however, other casting processes, such as continuous strip casting (not shown), can also be used. After casting, the rolling slab 21a is homogenized in step 23 using a homogenization furnace 28a. Subsequently, in step 24, the rolling slab 21a is hot-rolled into a hot strip 21b. Hot rolling 24 can take place in reversing stands (as shown) and / or in tandem stands with multiple passes (not shown). Thereafter, in step 25a, the hot strip 21b is cold-rolled to the final thickness into a cold strip 21c.During cold rolling 25a, at least one optional intermediate annealing step 25b can be performed, here by way of example using a batch furnace 28b, or alternatively by way of example using a continuous furnace (not shown). The at least one optional intermediate annealing step 25b softens the cold strip 21c. Consequently, following the at least one optional intermediate annealing step 25b, further cold rolling steps 25a can be performed until the cold strip 21c has reached its final thickness, which is, here, by way of example, 0.2 mm. A final heat treatment is also possible, which likewise serves to soften the cold strip 21c in order to facilitate further processing if necessary. For this purpose, the cold strip with its final thickness, for example in the coil, is subjected to a heat treatment, for example in a batch furnace. The process steps 20b, which are performed following cold rolling 25a, are shown in Fig. 2b.The starting point for this is the cold-rolled and optionally finally heat-treated cold strip 21c. This is first provided with an optional conversion layer and then with a heat-sealable coating, as described below. In this example, the optional conversion layer and the heat-sealable coating are applied on one side, but this is only an example. Conversion layers and / or heat-sealable coatings could also be applied on both sides of the cold strip 21c. Likewise, the application of the conversion layer is to be understood as an example, and in principle, the conversion layer can be omitted on one or both sides.

[0060] To create the conversion layer, the cold strip 21c is unwound from a coil and fed, for example, to a phosphating step 26, which is designed here as a one-sided roll-coating process. Alternatively, the phosphating solution can also be sprayed on, for example, by electrostatic spraying 26a. Furthermore, the phosphating can also be carried out by the cold strip 21c passing through a bath containing the phosphating solution (not shown). However, the roll-coating process has the advantage that the application of the phosphating solution can be precisely adjusted even at high throughput speeds. Phosphating 26 is a preferred no-rinse process in which the phosphating agent, here zirconium phosphate, remains on the cold strip 21c, so that in particular no rinsing step is required.For this purpose, the cold-rolled strip 21c coated with the phosphating solution is passed through the drying oven 28c so that the phosphating agent dries. As already described above, the phosphating step 26 is not absolutely necessary for the implementation of a method according to the invention. However, a single-sided or double-sided phosphating step 26 can produce a conversion layer on one or both sides of the cold-rolled strip 21d, which not only protects against corrosion but, in particular, improves the adhesion of the subsequently applied heat-sealable coating. Preferably, a chromium-free phosphating 26 is carried out, so that the conversion layer produced on one or both sides does not contain harmful chromium and is more suitable for contact with food.

[0061] Finally, in process step 27, a polyolefin-containing heat-sealable coating is produced on the cold-rolled strip 2 Id, which here, by way of example, is already provided with a conversion layer. The heat-sealable coating is produced here, for example, by applying a water-based lacquer to the cold-rolled strip 2 Id and then baking it. The lacquer contains, for example, a polypropylene dispersion as a polyolefin dispersion. In addition, the lacquer contains, for example, N,N,N',N'-tetrakis(2-hydroxyethyl)adipamide as a crosslinking agent and PTFE-free wax. The lacquer is applied, like the phosphating 26, using a one-sided roll-coating process. Here, too, spraying, in particular electrostatic spraying 27a of the lacquer, or, as a further alternative, passing it through a lacquer bath (not shown) is possible.For curing, the cold-rolled strip 21d, coated on one side with the lacquer, is fed into a curing furnace 28d. The curing process is carried out in such a way that a maximum metal temperature in the range of 200 °C to 300 °C is reached. The curing time is typically in the range of 5 s to 35 s. The result of the curing process is the cold-rolled strip 2le, which has a heat-sealable coating on one side. This strip is then wound onto a coil for easier storage and transport.

[0062] The aluminum alloy strip according to the invention, which was produced, for example, using the inventive method just described, can now be used in particular for the production of a resealable beverage can end. Since plastic elements for realizing a resealable beverage can end can be securely and cost-effectively attached to the heat-sealable coating of the aluminum alloy strip according to the invention by heat sealing, the aluminum alloy strip according to the invention is particularly suitable for this purpose. The production of at least one resealable beverage can end is achieved, for example, by punching at least one beverage can end out of the aluminum alloy strip according to the invention using suitable tools and subsequently, if necessary, forming it.The plastic elements for realizing the resealable mechanism can then be attached to the at least one punched-out beverage can lid by means of heat sealing.

[0063] Fig. 3 shows, by way of example, a schematic representation of a beverage can 30 according to the invention with a beverage can end 32 according to the invention, which was produced by the just-described inventive use of the aluminum alloy strip according to the invention. In addition to the beverage can end 32, the beverage can 30 also has a beverage can body 31, which is hermetically connected to the beverage can end 32 by means of a flange. Instead of the flange, other suitable connection methods, such as an adhesive connection, are also conceivable. While the beverage can body 31 is designed as a single piece in this example, the beverage can body 31 can in principle also be designed as multiple pieces, in particular as two pieces. An element 33 for implementing a resealable mechanism, which is only indicated schematically, can be provided on the beverage can end 32.The element 33 can then be heat-sealed onto the heat-sealable coating on the outside of the beverage can end 32. In this example, the beverage can end 32 also has a heat-sealable coating on its inside, which acts as a highly functional barrier and protects both the beverage against the migration of aluminum from the beverage can end 32 and the aluminum alloy of the beverage can end 32 from attack by the beverage. Within the scope of the invention, laboratory tests were also conducted to investigate, among other things, how the seal seam strength of the heat-sealable coating of the aluminum alloy strip according to the invention depends on various influencing parameters, in particular the basis weight of the coating. For this purpose, two test specimens, each measuring 290 mm x 210 mm, were cut from an aluminum alloy strip of type AA5182.The aluminum alloy strip was produced by performing the process steps described in connection with Fig. 2a, namely casting a rolling ingot, homogenizing the rolling ingot, hot rolling the rolling ingot into a hot strip, and cold rolling the hot strip to final thickness with optional intermediate annealing. In addition, the aluminum alloy strip was pretreated with a double-sided chromium-free phosphating using zirconium phosphate to create corresponding conversion layers on the aluminum alloy strip. The metal thickness of the aluminum alloy strip was 0.224 mm.

[0064] A heat-sealable coating containing polyolefin was then produced on one side of each of the two test specimens just described in the laboratory. For this purpose, a water-based varnish was first applied to one side of the test specimens. The water-based varnish contained 2 to 6 wt.% of an aqueous solution of a hydroxyalkylamide, 5 to 11 wt.% of PTFE-free wax, and the remainder an aqueous polyolefin dispersion. The aqueous polyolefin dispersion, for example, was an aqueous polypropylene dispersion with a solids content of 40 to 50 wt.%. The aqueous solution of a hydroxyalkylamide was a solution of 30 wt.% N,N,N',N'-tetrakis(2-hydroxyethyl)adipamide in weakly basic water containing 0.3 wt.% DMEA. When applying the water-based varnish to the two test specimens, the target basis weight of the resulting heat-sealable coating for the first test specimen was 4 g / m². 2and for the second test specimen 12 g / m 2 The applied coating was then baked in a laboratory oven. The oven was heated to a temperature of 295 °C, and the two coated test pieces were each placed in the oven for 21 seconds. The test pieces heated up, and at the end of each heating process, a maximum metal temperature of 243 °C was reached.

[0065] After baking the lacquer, the basis weight of the heat-sealable coating was determined for each of the two test specimens. For this purpose, a circular sample piece was punched out of each coated specimen, which had a radius of 39.9 mm and a corresponding area of ​​50.0 cm 2The coated samples were weighed using a laboratory precision balance. The heat-sealable coating was then removed from the samples by burning. For this purpose, the samples were each placed in a laboratory oven at a temperature of 550 °C for 15 minutes, which thermally decomposed the heat-sealable coating. After burning, the samples were kept in water to cool and then rubbed with a solvent-soaked cloth to remove any remaining paint residue from the surface. Finally, the uncoated samples were weighed again, and the basis weight of the heat-sealable coating was determined by calculating the difference between the weight of the coated sample and the weight of the uncoated sample and dividing it by the area of ​​the sample. This resulted in a basis weight of 4.1 g / m² for the first test sample.2 For the second test specimen, a value of 11.7 g / m 2 determined.

[0066] Finally, the seal seam strength of the heat-sealable coating was determined for each of the two test specimens. For this purpose, three test strips with a width of 15 mm were cut from each of the two test specimens using a metal strip cutting machine. Subsequently, a strip of polypropylene film, also 15 mm wide, was heat-sealed to one side of each of the six test strips. The thickness of the polypropylene film was 200 μm. Heat sealing was carried out using a heat-sealing device with a sealing force of 90 N, a sealing time of 1 s, and a sealing temperature of 180 °C. The seal seam strength was then determined for each of the six test strips according to DIN 55529, but with a peel angle of 180 °C instead of the 90 °C specified in DIN 55529.Finally, for each of the two test specimens, an average seal strength was calculated as the average value from the three test strips. The determined values ​​are shown in Table 1 below.

[0067] Table 1:

[0068] As the table shows, the seal seam strengths for both test specimens exceed a value of 35 N, which is sufficient to provide a sufficiently secure bond between the heat-sealable coating and the plastic elements to be attached to a resealable beverage can end. The seal seam strengths for both test specimens even exceed a value of 39 N, thus enabling an even more secure bond. Unlike the first test specimen, the second test specimen even achieves a value exceeding 42 N, resulting in a particularly secure bond. In the case of the second test specimen, the higher seal seam strength can be attributed in particular to the higher basis weight of the heat-sealable coating.

[0069] Finally, within the scope of the invention, laboratory tests were also conducted to investigate the porosity of the heat-sealable coating of the aluminum alloy strip according to the invention. For this purpose, two additional test specimens 3 and 4 were cut from an aluminum alloy strip of type AA5182, analogous to the two test specimens 1 and 2 described above, and provided with a heat-sealable coating on one side by baking a water-based varnish. The two additional test specimens differed from the two test specimens described above only with regard to the basis weight of the heat-sealable coating and were otherwise identical. The basis weight of the heat-sealable coating was 8.0 g / m 2 for the third test specimen and 12.0 g / m 2 for the fourth candidate.

[0070] To investigate the porosity, at least three beverage can end shells were produced from test specimens 3 and 4 by punching and forming. A porosity measurement was then carried out on the coated inside of the shells using an “Enamel Rater”. For this purpose, an electrolyte solution was filled into a cylindrical test vessel, which was mounted horizontally and rotatable, until approximately one third of the test vessel volume was filled. The electrolyte solution consisted of 98.8 wt.% deionized water, 1.0 wt.% NaCl and 0.2 wt.% dioctyl sodium sulfosuccinate, the latter serving to reduce the interfacial tension so that any existing pores were better filled by the electrolyte solution. After the electrolyte solution had been poured into the test vessel, the shell, in which the porosity of the heat-sealable coating was to be measured, was placed on the test vessel.The diameter of the test vessel was matched to the diameter of the shells so that the shells could be fitted precisely. The test vessel was then evacuated through an opening located on its outer surface approximately halfway up, so that the shell was pressed onto the test vessel due to the resulting excess pressure from the laboratory environment, thus fixing it in place. The test vessel was then rotated horizontally by 180° so that the shell fixed to it faced downwards. In this position, the electrolyte solution in the test vessel came into contact with the coated interior of the shell. Furthermore, a first electrode, which was located inside the test vessel and was contacted from the outside via a cable, was immersed in the electrolyte solution in this position. Finally, the metal layer of the shell was contacted using a metal pin, which acted as the second electrode.To actually perform the "Enamel Rater" porosity measurement, a DC voltage of 6.3 V was applied to the two electrodes. After a measurement time of 4 s, the strength of the current flowing between the two electrodes was measured. This determined the current strength for each of the shells produced from test pieces 3 and 4. Finally, the mean current strength of the porosity measurement was calculated for each test piece as an average value across at least three individual shells produced from it. The determined values ​​are shown in Table 2 below.

[0071] Table 2:

[0072] As the table shows, the measured average currents for both test specimens are not only below 5 mA, but also below 2 mA, and for the fourth test specimen even below 1 mA. Based on these values, it can be assumed that the respective heat-sealable coatings, whose basis weight is in the range of 8 g / m 2 up to 12 g / m 2 have sufficiently low porosity for use in beverage can ends. Therefore, it can be achieved in particular that the heat-sealable coating of the aluminum alloy strip according to the invention sufficiently fulfills its properties as an adhesion promoter and as a highly functional barrier for a resealable beverage can end.

[0073] The further embodiments also form part of the disclosure. 1. Aluminum alloy strip for producing a beverage can end, wherein the aluminum alloy strip comprises an aluminum alloy of the type AA5xxx, characterized in that the aluminum alloy strip has a heat-sealable coating containing polyolefin on one side or on both sides.

[0074] 2. Aluminum alloy strip according to embodiment 1, characterized in that the polyolefin is at least partially crosslinked by a hydroxyalkylamide, preferably by N,N,N',N'-tetrakis(2-hydroxyethyl)adipamide.

[0075] 3. Aluminum alloy strip according to embodiment 1 or 2, characterized in that the heat-sealable coating contains wax.

[0076] 4. Aluminium alloy strip according to one of embodiments 1 to 3, characterized in that the heat-sealable coating has a basis weight of 1.0 g / m 2 up to 20.0 g / m 2 , preferably 2.0 g / m 2 up to 14.0 g / m 2 , particularly preferably 3.0 g / m 2 up to 5.0 g / m 2 or 6.0 g / m 2 up to 12.5 g / m 2 , most preferably 3.5 g / m 2 up to 4.5 g / m 2 or 6.5 g / m 2 up to 12.0 g / m 2 , has.

[0077] 5. Aluminum alloy strip according to one of embodiments 1 to 4, characterized in that the heat-sealable coating, after heat-sealing against a polypropylene film with a sealing force of 90 N, a sealing time of 1 s, and a sealing temperature of 180°C, has a seal seam strength of at least 35 N, preferably at least 39 N, particularly preferably at least 42 N, with a seal seam width of 15 mm. 6. Aluminum alloy strip according to one of embodiments 1 to 5, characterized in that the heat-sealable coating has a porosity with which the current intensity measured in the "Enamel Rater" porosity measurement at a 10 basis weight of the heat-sealable coating in the range of 8 g / m 2 up to 12 g / m 2at most 5 mA, preferably at most 2 mA, particularly preferably at most 1 mA, wherein the porosity measurement “Enamel Rater” is carried out with a voltage of 6.3 V and the current intensity is determined after a measuring time of 4 s.

[0078] 7. Aluminum alloy strip according to one of embodiments 1 to 6, characterized in that the aluminum alloy strip comprises an aluminum alloy of type AA5052 or AA5182.

[0079] 8. Aluminum alloy strip according to one of embodiments 1 to 7, characterized in that the aluminum alloy strip has a metal thickness of 0.1 mm to 0.3 mm, preferably of 0.15 mm to 0.25 mm.

[0080] 9. Aluminum alloy strip according to one of embodiments 1 to 8, characterized in that the aluminum alloy strip additionally has a chromium-free conversion layer, which preferably contains zirconium phosphate, on one side or on both sides.

[0081] 10. A method for producing an aluminum alloy strip, in particular for producing an aluminum alloy strip according to any one of embodiments 1 to 9, the method comprising:

[0082] - casting of a rolled ingot or a cast strip of an aluminium alloy of type AA5xxx;

[0083] - homogenizing the rolling ingot or cast strip; - hot rolling the rolling ingot or cast strip into a hot strip;

[0084] - cold rolling the hot strip to final thickness with at least one intermediate annealing or without intermediate annealing; characterized in that the process further comprises:

[0085] - Producing a heat-sealable coating on one side or both sides of the cold-rolled aluminum alloy strip to final thickness, wherein the heat-sealable coating contains polyolefin.

[0086] 11. Method according to embodiment 10, characterized in that the heat-sealable coating is produced by applying and baking a lacquer.

[0087] 12. The method according to embodiment 10 or 11, characterized in that the baking of the lacquer is carried out in such a way that a maximum metal temperature in the range from 200 °C to 300 °C, preferably in the range from 220 °C to 260 °C, 25 is reached.

[0088] 13. Use of an aluminum alloy strip according to any one of embodiments 1 to 9 for producing a resealable beverage can lid.

[0089] 14. Resealable beverage can end, characterized in that the beverage can end is made of an aluminum alloy strip according to one of the embodiments 1 to 9.

[0090] 15. A beverage can with a resealable beverage can lid, characterized in that the beverage can lid is made of an aluminum alloy strip according to one of embodiments 1 to 9.

Claims

Patent claims 1. An aluminum alloy strip for producing a beverage can end, wherein the aluminum alloy strip comprises an aluminum alloy of type AA5xxx, characterized in that the aluminum alloy strip has on one side or on both sides a heat-sealable coating containing polyolefin, wherein the polyolefin is at least partially crosslinked by a hydroxyalkylamide, preferably by N,N,N',N'-tetrakis(2-hydroxyethyl)adipamide, and the heat-sealable coating contains wax.

2. Aluminium alloy strip according to one of Claims 1 and 2, characterized in that the heat-sealable coating has a basis weight of 1.0 g / m 2 up to 20.0 g / m 2 , preferably 2.0 g / m 2 up to 14.0 g / m 2 , particularly preferably 3.0 g / m 2 up to 5.0 g / m 2 or 6.0 g / m 2 up to 12.5 g / m 2 , most preferably 3.5 g / m 2 up to 4.5 g / m 2 or 6.5 g / m2 up to 12.0 g / m 2 , has.

3. Aluminum alloy strip according to one of claims 1 or 2, characterized in that the heat-sealable coating, after heat sealing against a polypropylene film with a sealing force of 90 N, a sealing time of 1 s and a sealing temperature of 180 °C, has a seal seam strength of at least 35 N, preferably at least 39 N, particularly preferably at least 42 N, with a seal seam width of 15 mm.

4. Aluminium alloy strip according to one of claims 1 to 3, characterized in that the heat-sealable coating has a porosity with which the current intensity measured in the porosity measurement “Enamel Rater” at a basis weight of the heat-sealable coating in the range of 8 g / m 2 up to 12 g / m 2at most 5 mA, preferably at most 2 mA, particularly preferably at most 1 mA, wherein the porosity measurement “Enamel Rater” is carried out with a voltage of 6.3 V and the current intensity is determined after a measuring time of 4 s.

5. Aluminum alloy strip according to one of claims 1 to 4, characterized in that the aluminum alloy strip comprises an aluminum alloy of the type AA5052 or AA5182.

6. Aluminum alloy strip according to one of claims 1 to 5, characterized in that the aluminum alloy strip has a metal thickness of 0.1 mm to 0.3 mm, preferably of 0.15 mm to 0.25 mm.

7. Aluminum alloy strip according to one of claims 1 to 6, characterized in that the aluminum alloy strip additionally has on one side or on both sides a chromium-free conversion layer, which preferably contains zirconium phosphate.

8. A method for producing an aluminum alloy strip, in particular for producing an aluminum alloy strip according to one of claims 1 to 7, the method comprising: Casting of a rolled ingot or cast strip from an aluminium alloy of type AA5xxx; Homogenization of the rolling ingot or the cast strip; Hot rolling of the rolling ingot or the cast strip into a hot strip; cold rolling of the hot strip to final thickness with or without intermediate annealing; characterized in that the method further comprises: Producing a heat-sealable coating on one side or on both sides of the aluminum alloy strip cold-rolled to final thickness, wherein the heat-sealable coating contains polyolefin, wherein the heat-sealable coating is produced by applying and baking a varnish, wherein the varnish contains a polyolefin dispersion, hydroxyalkylamide, preferably N,N,N',N'-tetrakis(2-hydroxyethyl)adipamide, as crosslinking agent and wax.

9. The method according to claim 8, characterized in that the varnish is a water-based varnish and the varnish contains a polyolefin dispersion, wherein the polyolefin dispersion is preferably a polyethylene dispersion or a polypropylene dispersion or a mixture of both.

10. The method according to claim 8 or 9, characterized in that the wax is preferably a PTFE-free wax, particularly preferably carnauba wax, polyethylene wax, polypropylene wax, polyamide wax or a mixture of the said waxes.

11. The method according to any one of claims 8 to 10, characterized in that the water-based lacquer contains 1 to 15 wt.%, preferably 2 to 6 wt.% of an aqueous solution of a hydroxyalkylamide, 1 to 20 wt.%, preferably 5 to 11 wt.% of PTFE-free wax and the remainder an aqueous polyolefin dispersion wherein the aqueous polyolefin dispersion preferably contains a Solids content of up to 60 wt.%, preferably 40 to 50 wt.%.

12. The method according to claim 10 or 11, characterized in that the baking of the lacquer is carried out in such a way that a maximum metal temperature in the range from 200 °C to 300 °C, preferably in the range from 220 °C to 260 °C, is reached.

13. Use of an aluminum alloy strip according to one of claims 1 to 12 for producing a resealable beverage can lid.

14. Resealable beverage can end, characterized in that the beverage can end is made of an aluminum alloy strip according to one of claims 1 to 7.

15. A beverage can with a resealable beverage can lid, characterized in that the beverage can lid is made of an aluminum alloy strip according to one of claims 1 to 7.

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