Aluminium Strip with Antibacterial Coating

Abstract

An aluminium strip for manufacturing a package of a solid, liquid or gaseous product consisting of an aluminium alloy. The aluminium strip has at least a one-sided or two-sided antibacterial coating. The object of proposing an aluminium strip consisting of an aluminium alloy with at least a one-sided or two-sided antibacterial coating, which can be more easily produced with very good antibacterial effect of the coating and can already provide very good antibacterial properties at extremely low concentrations of the antibacterial substance, is achieved by the antibacterial coating containing ZnMoO.sub.4 as the antibacterial substance.

Claims

1. An aluminium strip for manufacturing a package of a solid, liquid or gaseous product consisting of an aluminium alloy, wherein the aluminium strip has at least a one-sided or two-sided antibacterial coating, wherein the antibacterial coating contains exclusively ZnMoO.sub.4 as an antibacterial substance and the antibacterial coating of the aluminium strip has a dry weight of 0.5 g/m.sup.2 to 15 g/m.sup.2.

2. The aluminium strip according to claim 1, wherein the concentration of ZnMoO.sub.4 in the antibacterial coating is at least 0.1% by weight to a maximum of 4% by weight, preferably 0.2% by weight to 2% by weight, preferably 0.25% by weight to 1% by weight, further preferably 0.5% by weight to 1% by weight.

3. The aluminium strip according to claim 1, wherein the one-sided or two-sided antibacterial coating of the aluminium strip has a dry weight of 2 g/m.sup.2 to 12 g/m.sup.2, preferably 3 g/m.sup.2 to 6 g/m.sup.2, further preferably 3.5 g/m.sup.2 to 5 g/m.sup.2.

4. The aluminium strip according to any one of claim 1, wherein the aluminium strip has a thickness of 0.1 mm to 0.3 mm, preferably 0.15 mm to 0.25 mm.

5. The aluminium strip according to claim 1, wherein the aluminium strip is an aluminium strip for manufacturing a can, preferably an aluminium strip for manufacturing a beverage can, in particular an aluminium can lid strip.

6. The aluminium strip according to claim 1, wherein the aluminium strip consists of an aluminium alloy of type AA5xxx or AA3xxx, preferably AA5182 or AA3104.

7. The aluminium strip according to any one of claim 1, wherein the antibacterial coating is formed as an antibacterial varnish layer, which contains at least one binder and ZnMoO.sub.4 as an antibacterial substance.

8. The aluminium strip according to any one of claim 1, wherein the aluminium strip has at least a one-sided or two-sided chromium-free passivation layer.

9. The aluminium strip according to any one of claim 1, wherein the antibacterial coating is resistant to pasteurisation and/or sterilisation.

10. The aluminium strip according to any one of claim 1, wherein the antibacterial coating is a varnish layer on a solvent epoxy resin basis, on a solvent polyester basis, based on an epoxy resin water dispersion, a polyester water dispersion or based on a polyolefin water dispersion.

11. A method for manufacturing an aluminium strip according to claim 1, in which a rolling ingot or a casting strip is cast from an aluminium alloy, the rolling ingot or optionally the casting strip is homogenised, the rolling ingot or the casting strip is hot-rolled to form a hot strip, the hot strip is cold-rolled to an optional end thickness of 0.1 mm to 0.3 mm with at least one intermediate annealing or without intermediate annealing and optionally subjected to a final heat treatment, wherein the aluminium strip is coated on one or both sides with at least one antibacterial coating, wherein the antibacterial coating contains exclusively ZnMoO.sub.4 as an antibacterial substance and the antibacterial coating of the aluminium strip has a dry weight of from 0.5 g/m.sup.2 to 15 g/m.sup.2.

12. The method according to claim 11, wherein the aluminium strip is subjected to a one-sided or two-sided chromium-free surface passivation after cold rolling at the end thickness.

13. The method according to claim 12, wherein the antibacterial coating is applied to the aluminium strip by a one-sided or two-sided coil coating process, preferably using a roll coating process.

14. The method according to any one of claim 11, wherein the antibacterial coating is baked at a maximum metal temperature of 180 C. to 300 C., preferably at 230 C. to 260 C., wherein the baking time is between 5 s and 45 s, preferably between 8 s and 30 s.

15. A can lid of a can, in particular a beverage can manufactured from an aluminium strip according to claim 1, wherein the can lid has a one-sided or two-sided antibacterial coating, wherein the antibacterial coating contains exclusively ZnMoO.sub.4 as an antibacterial substance and the antibacterial coating of the can lid has a dry weight of 0.5 g/m.sup.2 to 15 g/m.sup.2.

16. Can lid of a can according to claim 15, wherein the antibacterial coating of the can lid has a dry weight of 2 g/m.sup.2 to 12 g/m.sup.2 or preferably 3 g/m.sup.2 to 6 g/m.sup.2.

17. Can body of a can, in particular a beverage can manufactured from an aluminium strip, wherein the can body has a one-sided or two-sided antibacterial coating, wherein the antibacterial coating contains exclusively ZnMoO.sub.4 as an antibacterial substance and the antibacterial coating of the can body has a dry weight of 0.5 g/m.sup.2 to 15 g/m.sup.2.

18. Can body of a can according to claim 17, wherein the antibacterial coating of the can body has a dry weight of 2 g/m.sup.2 to 12 g/m.sup.2 or preferably 3 g/m.sup.2 to 6 g/m.sup.2.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0038] The invention will be explained in greater detail below by describing exemplary embodiments in connection with the drawing. The drawing shows in:

[0039] FIG. 1a and FIG. 1b are embodiments of aluminium strips according to the invention with a one-sided or two-sided antibacterial coating in a schematic sectional view;

[0040] FIG. 2 in a perspective representation an exemplary embodiment of a package of a liquid product in the form of a beverage can;

[0041] FIG. 3 in a schematic representation an exemplary embodiment according to the method for manufacturing the aluminium strip up to cold rolling the aluminium strip to end thickness and;

[0042] FIG. 4 the optional passivation with subsequent coating of the aluminium strip with an antibacterial coating according to an exemplary embodiment in a schematic representation.

DETAILED DESCRIPTION OF THE INVENTION

[0043] The FIGS. 1a and 1b show exemplary embodiments of aluminium strips 1, 2 in a schematic sectional view in the form of a one-sided coated aluminium strip 1 and a two-sided coated aluminium strip 2. The one-sided or two-sided coating 3 is designed as an antibacterial coating. It contains at least ZnMoO.sub.4 as an antibacterial substance. Preferably, the antibacterial coating contains exclusively ZnMoO.sub.4 as the antibacterial substance. It has been found that even the exclusive use of ZnMoO.sub.4 as an antibacterial substance in the antibacterial coating is sufficient to provide very good antibacterial properties of the surface of the aluminium strip. At the same time, it was found that the metal salt ZnMoO.sub.4 incorporated in the varnish layer of the coating has only very low tendencies to migrate into liquids in contact with the antibacterial coating.

[0044] Preferably, the antibacterial coating 3 has concentrations of 0.1% by weight to a maximum of 4% by weight, preferably 0.2% by weight to 2% by weight, preferably 0.25% by weight to 1.0% by weight and further preferably 0.5% by weight to 1.0% by weight of ZnMoO.sub.4. It has been shown that good to very good antibacterial effects can be achieved at these concentrations.

[0045] The dry weight of the one-sided or two-sided antibacterial coating of the aluminium strip corresponds to an indication of the thickness of the coating. Exemplary embodiments of the antibacterial coating according to the invention have a dry weight of 0.5 g/m.sup.2 to 15 g/m.sup.2, preferably 2 g/m.sup.2 to 12 g/m.sup.2, preferably 3 g/m.sup.2 to 6 g/m.sup.2, further preferably 3.5 g/m.sup.2 to 5 g/m.sup.2. The corresponding dry weights are adapted to the various applications of the aluminium strip in relation to the provision of packages of solid, liquid or gaseous substances, in particular beverage cans. A two-sided antibacterial coating is shown in FIG. 1b.

[0046] The aluminium strip 1, 2 of the exemplary embodiments represented in FIGS. 1a and 1b exhibit a thickness of 0.1 mm to 0.3 mm, preferably 0.15 mm to 0.25 mm. Aluminium strips with corresponding thicknesses can be used particularly preferably for the manufacture of beverage cans. Alternatively, however, other packages of solid, liquid or gaseous products can also be manufactured from them.

[0047] The aluminium strips 1, 2 preferably consist of an aluminium alloy for packages, in particular beverage cans of type AA5xxx or of type AA3xxx, preferably AA5182 or AA3104, AA3105 or AA3004. The aluminium alloy types mentioned have particularly high strengths and particularly good forming properties. The aluminium alloys of type A3xxx, in particular AA3104, are thereby used for the necessarily less solid regions of a beverage can, i.e. for example for the can body, while the variants of type AA 5xxx, in particular AA5182, are used for the aluminium strip of the can lid.

[0048] According to the exemplary embodiment of FIG. 1b, a two-sided antibacterial coating 3 and additionally a passivation layer 4 are provided, which significantly increases the adhesion of the antibacterial coating 3 again. This passivation layer can also be applied only on one side, for example if an antibacterial coating is used on only one side of the aluminium strip. The passivation layer is thereby preferably chromium-free in order to be better suited for contact with foodstuffs. For example, a zirconium phosphating is preferably provided as a passivation layer.

[0049] Preferably, the antibacterial coating is formed as an antibacterial varnish layer, which contains at least one binder and ZnMoO.sub.4 as an antibacterial substance. Varnishes are liquid, paste or powder coating materials that contain binders as well as organic solvents and/or water. The binder should thereby form the subsequent coating on the aluminium strip surface. If the binder is mixed with the antibacterial substance ZnMoO.sub.4, the antibacterial substance can be distributed particularly evenly over a large surface of the aluminium strip via the varnish layer. Preferably, the antibacterial substance ZnMoO.sub.4 thereby has a particle size of 0.1 m to 20 m, preferably 0.5 m to 5 m, further preferably 0.5 m to 2 m. Due to the small particle sizes, a very good and homogeneous distribution of the antibacterial substance in the coating can be achieved. As mentioned above, all particle size information is mean particle sizes.

[0050] It has been found that the antibacterial substance ZnMoO.sub.4 makes it possible to provide antibacterial varnish layers that are resistant to pasteurisation, as binders that have already been tested can be used here. The pasteurisation resistance was tested for the coatings according to the invention by heating to 85 C. for 30 minutes. After this treatment, the coating should exhibit no or almost no yellowing, also known as blushing. The pasteurisation of foodstuffs is usually much shorter in order to keep the ingredients of the foodstuffs unchanged as much as possible.

[0051] The same applies to sterilisation resistance, which has been tested by contact with hot steam at 130 C. for 45 minutes. Here, too, the antibacterial substance did not show any negative effects on sterilisation-resistant varnish systems. It is therefore possible to provide antibacterial and sterilisation-resistant aluminium strips.

[0052] Preferably, the antibacterial coating 3 consists of a varnish layer on a solvent epoxy resin basis, solvent polyester basis, on the basis of an epoxy resin water dispersion or on the basis of a polyolefin water dispersion.

[0053] Epoxy resin-based coatings in particular often have very good temperature resistance and do not show any blushing during pasteurisation at 85 C. for 30 minutes at a concentration of up to 4% by weight ZnMoO.sub.4. Blushing was also not detected for coatings with 0.5% by weight of ZnMoO.sub.4 under sterilisation conditions in contact with hot steam at 130 C. for 45 minutes.

[0054] FIG. 2 now shows an exemplary embodiment of a package in the form of a beverage can 5 with a can lid 6 and a can body 7. The can body 7 can also be formed in two parts such that the can is composed of a total of 3 sheet metal parts. According to one exemplary embodiment, the antibacterial coating of the can lid has a dry weight of 0.5 g/m.sup.2 to 15 g/m.sup.2, preferably 2 g/m.sup.2 to 12 g/m.sup.2 or preferably 3 g/m.sup.2 to 6 g/m.sup.2. The can body can also have a dry weight of 0.5 g/m.sup.2 to 15 g/m.sup.2, preferably 2 g/m.sup.2 to 12 g/m.sup.2 or preferably 3 g/m.sup.2 to 6 g/m.sup.2 as an antibacterial coating. Due to the preferred use of the antibacterial coating with exclusively ZnMoO.sub.4, it is possible to further improve hygiene during drinking of beverage cans if, for example, the aluminium can lid strip has a corresponding one-sided or two-sided antibacterial coating. The colonisation of the surface of the beverage can is significantly inhibited even at low concentrations of the antibacterial substance ZnMoO.sub.4 and the number of germs present is significantly reduced within 24 hours.

[0055] Corresponding test results show tests of different exemplary embodiments of the invention in comparison with an uncoated zero sample No. 11. The results of the tests are represented in Table 1.

[0056] All exemplary embodiments represented in Table 1 have a dry weight of the antibacterial coating of 3.5 g/m.sup.2 to 4.5 g/m.sup.2, with the concentration of ZnMoO.sub.4 varying from 0.25% by weight to 2% by weight. As an antibacterial coating, a varnish layer on a solvent epoxy resin basis was used.

[0057] The antibacterial effect was tested in accordance with JIS Z2801 and ISO 22196 respectively. Deviating from these standards, the bacterial count of the samples was determined as a double determination with partly different contact times.

[0058] 4 cm4 cm coated test surfaces consisting of an aluminium strip according to the invention were previously cleaned with 70% ethanol and then inoculated with a test germ, here Escherichia coli, with an amount of 400 l/test piece. Some of the samples were rinsed with neutral solution immediately after inoculation and the bacterial count was determined. The other part of the samples was rinsed with neutral solution after specific periods of 2 h, 4 h, 6 h or 24 h in a climatic chamber at 36 +/1 C. at a relative humidity of more than 90%. The reduction in bacterial count was determined in comparison to the initial bacterial count of untreated test areas.

[0059] It has been shown that with an antibacterial coating with 0.25% by weight ZnMoO.sub.4, the number of bacteria could be reduced by more than 99% within 24 hours after a 24-hour test in accordance with JIS Z2801 or ISO 22196. From a content of 0.5% by weight of ZnMoO.sub.4 in the coating, no improvement in the antibacterial effect or reduction of germs could be achieved after 24 hours. The addition of additives, for example polyether-modified polydimethylsiloxane, did not improve the result, as point 4 shows, for example.

[0060] An accelerated reduction in the bacterial count was observed when the concentration of ZnMoO.sub.4 was increased after 2 h, 4 h or 6 h. In particular, at 0.5% by weight of ZnMoO.sub.4, the bacterial count was reduced by 92.51% after 6 hours. However, there was a reduction of 97.22% at 1% by weight ZnMoO.sub.4 after 6 h, as shown in sample No. 2 of Table 1.

[0061] Sample No. 3 was additionally subjected to a foodstuff regulatory migration test, where a total migration of less than 10 mg/dm.sup.2 is considered acceptable. Sample number 3 reached 0.16 mg/dm.sup.2 for zinc and 0.01 mg/dm.sup.2 for molybdenum after 10 days in contact with 3% acetic acid at a temperature of 60 C. The test conditions were carried out taking into account the requirement in accordance with EU Regulation Number 10/2011 (OM2). Apart from the corrosion of the aluminium strip, only an extremely low migration of zinc and molybdenum of 0.16 mg/dm.sup.2 or 0.01 mg/dm.sup.2 for molybdenum could be measured. The antibacterial coating is therefore particularly suitable for contact with foodstuffs.

[0062] The non-antibacterial coated sample No. 11 (zero sample) clearly shows that no significant reduction in bacterial count could be achieved after 24 hours. Sample No. 15, containing 0.5% by weight of ZnMoO.sub.4, pasteurised at 85 C. for 30 minutes, showed the highest bacterial reduction count within 24 hours according to ISO 22196. At the same time, no yellowing of the varnish layer (blushing) was found.

[0063] FIG. 3 now shows in a schematic view the individual method steps for manufacturing an exemplary embodiment of the aluminium strip up to the cold rolling of the aluminium strip at end thickness.

[0064] First, a rolling ingot 8a is manufactured in step 8, for example in the DC casting process. Similarly, a strip casting not shown here can also be used to manufacture a cast strip. The rolling ingot 8a is then subjected to homogenisation in step 9 and then hot-rolled to form a hot strip 10a in step 10. Hot rolling can be carried out in reversing stands and/or in tandem stands with multiple passes. The hot strip is then cold-rolled to an end thickness in step 11 to form a cold strip 11a. During cold rolling, intermediate annealing can take place in the chamber furnace 12 or in the continuous furnace not shown. A final heat treatment is also not excluded, however, preferably in the full-hard H18 or H19 rolling state, the cold-rolled aluminium strips are fed to the next method step of the coating.

[0065] An exemplary embodiment of a coating method is represented in FIG. 4. The cold-rolled aluminium strip 11a is unwound from a coil and fed to a passivation step 13, which is designed here as a roll coating process. Alternatively, the passivation chemical can also be sprayed on, for example electrostatic spraying 13a of the passivation chemical. Alternatively, passivation can also be carried out by passing through a bath with the passivation liquid. However, the roll coating process has proven its worth due to the possible high throughput speeds and the good accuracy of the passivation chemical application. No-rinse processes are preferred for surface passivation, in which the passivation agent, preferably zirconium phosphate, remains on the aluminium strip and does not need to be rinsed off. For this purpose, the aluminium strip 11a is dried in an oven 15a after the passivation chemical has been applied.

[0066] The coating of the antibacterial coating is also preferably carried out using a roll coating process 14. Other methods for applying the antibacterial coating, such as spraying or electrostatic spraying 14a, are also conceivable in principle.

[0067] Lastly, the baking of the antibacterial coating takes place at a maximum temperature of 180 C. to 300 C., preferably 230 C. to 260 C. in a baking oven 15, in which the maximum metal temperature is maintained for the baking period of 5 seconds to 45 seconds, preferably between 8 seconds and 30 seconds. The aluminium strip 11b provided with an antibacterial coating can then be made available to a manufacturing process of can lids or can bodies.

TABLE-US-00001 TABLE 1 Foodstuff regulatory Bacteria migration test (after 24 (EU h in % Bacteria Regulation No. reduction) (% reduction Sam- 10/2011 JIS Z 2801/ in time ple Remark (OM2)) ISO 22196 interval) 1 Coating 99.99 2 h: 76.00 with 0.5% 4 h: 82.44 ZnMoO.sub.4 6 h: 92.51 2 Coating 1st 2 h: 87.33 with 1% Measurement: 99.99 4 h: 82.67 ZnMoO.sub.4 2nd 6 h: 97.22 measurement: 99.98 3 Coating Total: <10 99.99 with 2% mg/dm.sup.2 ZnMoO.sub.4 Zinc: 0.16 mg/dm.sup.2 Molybdenum: 0.01 mg/dm.sup.2 4 Coating 99.99 with 1% ZnMoO.sub.4 and 5% additives 11 Zero none 2 h: 18.67 sample 4 h: 41.56 6 h: 62.89 12 Coating 99.84 with 0.25% ZnMoO.sub.4 15 Coating 99.99 with 0.5% ZnMoO.sub.4 Pasteurised

[0068] All references, including publications, patent applications, and patents cited herein are hereby incorporated by reference to the same extent as if each reference were individually and specifically indicated to be incorporated by reference and were set forth in its entirety herein.

[0069] The use of the terms a and an and the and similar referents in the context of describing the invention (especially in the context of the following claims) is to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. The terms comprising, having, including, and containing are to be construed as open-ended terms (i.e., meaning including, but not limited to,) unless otherwise noted. Recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g., such as) provided herein, is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention unless otherwise claimed. No language in the specification should be construed as indicating any non-claimed element as essential to the practice of the invention.

[0070] Preferred embodiments of this invention are described herein, including the best mode known to the inventors for carrying out the invention. Variations of those preferred embodiments may become apparent to those of ordinary skill in the art upon reading the foregoing description. The inventors expect skilled artisans to employ such variations as appropriate, and the inventors intend for the invention to be practiced otherwise than as specifically described herein. Accordingly, this invention includes all modifications and equivalents of the subject matter recited in the claims appended hereto as permitted by applicable law. Moreover, any combination of the above-described elements in all possible variations thereof is encompassed by the invention unless otherwise indicated herein or otherwise clearly contradicted by context.