Aluminium Foil with Improved Barrier Property

Abstract

An aluminium alloy foil with a thickness of maximum 12 μm, maximum 9 μm or less than 8 μm. The aluminium alloy foil is an AA1xxx or A8xxx aluminium alloy in the annealed state. In addition, a method for manufacturing an aluminium alloy foil and its use. The object of proposing an aluminium alloy foil with improved barrier properties, a method for its manufacture and a use of the aluminium alloy foil is achieved in that the aluminium alloy foil has a maximum number of pores with a pore size of 1 μm to 200 μm of maximum 12 per dm.sup.2, maximum 8 per dm.sup.2 or maximum 6 per dm.sup.2. In addition, a method is specified for how this aluminium alloy foil can be manufactured.

Claims

1. An aluminium alloy foil with a thickness of maximum 12 inn, maximum 9 μm or less than 8 μm, wherein the aluminium alloy foil has an AA1xxx or AA8xxx aluminium alloy in the material state H2x or O, wherein the aluminium alloy foil has a maximum number of pores with a pore size of 1 μm to 200 μm of maximum 12 per dm.sup.2, maximum 8 per dm.sup.2 or maximum 6 per dm.sup.2.

2. The aluminium alloy foil according to claim 1, wherein the aluminium alloy foil has an oxide layer thickness of 3 to 6 nm measured along the entire width of the aluminium alloy foil, wherein the oxide layer thickness of the aluminium alloy foil at the edge region of the aluminium alloy foil is at most 30% greater than in the middle of the aluminium alloy foil.

3. The aluminium alloy foil according to any one of claim 1, wherein the oxide layer thickness is maximally 5 nm on both the matt and gloss side of the aluminium alloy foil.

4. The aluminium alloy foil according to claim 1, wherein the aluminium alloy foil has an aluminium alloy with the following alloy constituents in % by weight: 0.05%≤Si≤0.30%, Fe:0.7≤Fe≤1.3%, Cu≤0.05%, Mn≤0.05%, Mg≤0.05%, Cr≤0.05%, Zn≤0.10%, Ti≤0.025%, the remainder Al and unavoidable impurities individually at most 0.05%, in total at most 0.15%.

5. The aluminium alloy foil according to claim 4, wherein the aluminium alloy of the aluminium alloy foil has at least one of the further restrictions of the alloy constituents in % by weight: 0.05%≤Si≤0.30%, 0.8≤Fe≤1.15%, Cu≤0.05%, 0.01%≤Mn≤0.04%, preferably 0.015%≤Mn≤0.035%, particularly preferably 0.018%≤Mn≤0.025%, Mg≤0.01%, preferably Mg≤0.005%, particularly preferably Mg≤0.0035%, Cr≤0.02%, Zn≤0.07% and/or 0.005%≤Ti≤0.025%.

6. The aluminium alloy foil according to claim 4, wherein the aluminium alloy foil in the material state O has a yield strength Rp0.2 in accordance with DIN EN 546-2 of at least 55 MPa, preferably at least 58 MPa, measured transversely, longitudinally or diagonally to the rolling direction.

7. The aluminium alloy foil according to claim 3, wherein the aluminium alloy foil has a tensile strength Rm in accordance with DIN EN 546-2 of at least 80 MPa in the material state H2x or O, measured transversely, longitudinally and/or diagonally to the rolling direction.

8. The aluminium alloy foil according to claim 3, wherein the elongation at break A.sub.100mm in accordance with DIN EN 546-2 of the aluminium alloy foil is at least 6.2%, preferably at least 6.5%, measured diagonally to the rolling direction.

9. A method for manufacturing an aluminium alloy foil according to claim 1, wherein the method comprises the following steps: manufacturing an aluminium alloy strip for cold rolling by casting a rolling ingot from an aluminium alloy of an AA1xxx or AA8xxx aluminium alloy, wherein the aluminium alloy melt is filtered before and/or during the casting of the rolling ingot, homogenising the cast rolling ingot and hot rolling of the rolling ingot into a hot strip or continuous casting of a casting strip from a melt of a filtered aluminium alloy of type AA8xxx or AA1xxx with a subsequent, optional hot rolling of the casting strip, cold rolling of the aluminium alloy strip to a first intermediate thickness, recrystallisation annealing of the cold-rolled aluminium alloy strip at this intermediate thickness, cold rolling of the aluminium alloy strip to a second intermediate thickness, doubling the aluminium alloy strip and carrying out an intermediate annealing, foil rolling of the doubled aluminium alloy strip to the final thickness of the doubled foil, separating and winding up the layers at a final thickness of the individual layers of maximum 12, maximum 9 μm or less than 8 wherein optionally the aluminium alloy foil is assembled in a plurality of rolls and carrying out a final annealing of the coil or the assembled rolls for at least 150 h at 200 to 245° C. furnace air temperature with a final cooling phase for at least 3 h, preferably at least 7 h, at 100° C. furnace air temperature.

10. The method according to claim 9, wherein the aluminium alloy has the following alloy constituents in % by weight: 0.05%≤Si≤0.30%, 0.7≤Fe≤1.3%, Cu≤0.05%, Mn≤0.05%, Mg≤0.05%, Cr≤0.05%, Zn:≤0.10%, Ti:≤0.025%, the remainder Al and unavoidable impurities individually 0.05% by weight, in total at most 0.15% by weight, and the recrystallisation annealing of the cold-rolled strip is carried out at furnace air temperature of 450° C. to 550° C. for at least 5 h and the intermediate annealing after doubling the strip is carried out at a furnace air temperature of 240° C. to 320° C. for 0.5 h.

11. The method according to claim 10, wherein the aluminium alloy foil has at least one of the following restrictions of the alloy constituents in % by weight: 0.05%≤Si≤0.30%, 0.8%≤Fe≤1.15%, Cu≤0.05%, 0.01%≤Mn≤0.04%, preferably 0.015%≤Mn≤0.035%, particularly preferably 0.018%≤Mn≤0.025%, Mg≤0.01%, preferably Mg≤0.005%, particularly preferably Mg≤0.0035%, Cr≤0.02%, Zn≤0.07% and/or 0.005%≤Ti≤0.025%.

12. The method according to claim 9, wherein the homogenising of the rolling ingot is carried out at 420 to 600° C. for at least 7 h.

13. The method according to any one of claim 9, wherein the rolling ingot is hot rolled to a hot rolling final thickness of 2 mm to 4 mm during hot rolling and the hot rolling final temperature is between 300° C. and 350° C.

14. The method according to claim 9, wherein the final annealing is carried out for at least 150 h at 200° C. to 225° C.

15. Use of an aluminium alloy foil according to claim 1, in a multi-layer composite material, in particular packages with barrier requirements for the aluminium foil.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0092] The invention is described in greater detail below using exemplary embodiments in connection with the drawing, in which is shown:

[0093] FIG. 1a a SEM image of a roll pore of a foil, which is recorded with DIN EN 546-4,

[0094] FIG. 1b a SEM image of a section of a package of aluminium alloy foils charged with micropores,

[0095] FIG. 2 a schematic sectional view of a device for measuring the maximum number of pores per 1 dm.sup.2 across the foil width,

[0096] FIG. 3 a schematic plan view of the measuring surfaces for determining the maximum number of pores per dm.sup.2 and

[0097] FIG. 4a), b), c) digital photographs of foil samples according to the invention and not according to the invention.

DETAILED DESCRIPTION

[0098] FIG. 1a first shows a SEM image of an aluminium alloy foil in the material state O with a thickness of 6 μm, which has a rolling pore with a diameter of approximately 30 μm. The previously known DIN EN 546-4 covers corresponding pores in aluminium alloy foils, as pores with a size of 20 μm upwards to 200 μm must be taken into account in accordance with this standard.

[0099] FIG. 1b, on the other hand, shows a SEM image of a section of a foil package charged with micropores, which has been prepared using Cross Section Polisher (CSP). The middle foil shows an indentation of approx. 1 μm and a micropore channel. It is assumed that micropores are three-dimensional structures which create a connection from one side of the foil to the other side of the foil that is not always straight.

[0100] It is easily conceivable that a high number of micropores with a size of significantly less than 20 μm, for example 1 to 5 μm, can also lead to the barrier effect of the aluminium alloy foil being negatively affected. For this reason, aluminium alloy foils, which have a low pore count per dm.sup.2 in accordance with DIN EN 546-6, do not necessarily also have a very good barrier effect. This applies to all aluminium alloy types mentioned here, i.e. to alloys of type AA1xxx or AA8xxx.

[0101] The aluminium alloy foils according to the invention from the aforementioned aluminium alloy types AA8xxx and AA1xxx with a thickness of maximum 12 inn, maximum 9 μm or less than 8 μm, on the other hand, have a maximum number of pores with a pore size of 1 μm to 200 μm of maximum 12 per dm.sup.2, maximum 8 or maximum 6 per dm.sup.2 in the material state H2x or O. Thus, pores with a size of 1 μm to 20 μm, which are not taken into account in accordance with DIN EN 546-6, are also taken into account. By the aluminium alloy foils according to the invention having a particularly low maximum number of pores with a pore size of 1 μm to 200 μm and thus also of the smallest pores starting with 1 μm pore size, improved barrier properties of the aluminium alloy foil can be provided.

[0102] FIG. 2 now shows a schematic sectional view of a device for measuring the maximum number of pores per dm.sup.2 over the entire foil width. FIG. 2 shows the aluminium alloy foil 1, a light source 2, for example an overhead projector and a photo camera 3, which is to photograph the measuring surface 3A for evaluation. The device must be positioned in a darkened room so that no scattered light affects the measurement. The remaining luminance in the darkened room is preferably less than 0.25 lux. The aluminium alloy foil 1 is fixed in the measuring range by a frame 5, which completely surrounds the measuring surface, such that the aluminium alloy foil 1 is positioned as flat as possible in the measuring surface 3A.

[0103] The light source 2 illuminates the aluminium alloy foil 1 through a transparent glass plate, which is not shown in FIG. 2. However, it is indicated by the expansion of the light source 2 that the illumination of the aluminium alloy foil 1 from below should be as homogeneous as possible. The distance of camera 3 must be selected depending on the size of the measuring area to be captured and the objective used. An objective with the smallest possible focal length should be selected such that the minimum distance can be selected in order to cover the measuring area with the best possible resolution.

[0104] The light source 2 is completely darkened with the aluminium alloy foil and the frame 5 such that only light which has penetrated the aluminium alloy foil 1 through pores within the measuring surface 3A can reach the camera. The aluminium alloy foil 1 is divided along the entire width 4 into preferably at least three or at least five measuring surfaces and thus the entire foil width is captured with the measurement. Since after foil rolling the aluminium alloy foils are often assembled to certain widths into so-called rolls and then annealed, the width 4 of the aluminium alloy foil 1 refers to the width of the foil roll or, without assembling, the entire width of the foil coil. The division into different measuring surfaces 3A, preferably at least five measuring surfaces 3A along the entire width of the aluminium alloy foil, also enables the detection of locally occurring populations of pores with sizes from 1 μm to 20 μm. These pores are not taken into account in the known porosity measurement according to DIN EN 546-4.

[0105] The following test setup was used for the foils measured in the following: The light source was an overhead projector from the company Andreas+Kern with an optical halogen lamp 36 V and 400 W with a luminous flux of up to 6000 lumens. The foil to be examined was placed on the projector and fixed via a metal frame of a defined size so that the foil laid flat on the projector and was sealed on the side. The camera used was a Sony Alpha 6000 with 6000×4000 pixels with an objective of the type Minolta MD Rokkor 50 mm f1.4. An aperture with a value of 2 with an ISO value of 800 at an exposure time of 30 seconds was used for the recordings. The distance from the camera sensor to the foil was 700 mm. The software Image Analyzer was used for image analysis. As FIG. 4 shows, the measuring surfaces 3A were arranged next to one another without gaps across the width 4 perpendicular to the longitudinal direction 7 of the aluminium alloy foil 1, so that the entire width of the aluminium alloy foil 1 is measured. The size of the measuring surface was 183 mm×276 mm and thus 5.0508 dm.sup.2. From the measuring surface with the highest number of pores, the number of pores with a size of 1 μm to 200 μm was then determined by software and normalised to 1 dm.sup.2 by dividing the measured number of pores in the worst measuring surface by the total area of the measuring surface in dm.sup.2. The result was rounded to a whole number. With this measuring method, in particular the locally occurring smallest pores with a size of less than 20 μm, in particular 5 μm to 1 μm, can be recorded and counted.

[0106] As exemplary embodiment A, an aluminium alloy with an alloy composition according to Table 1 was cast into a rolling ingot. The aluminium alloy melt was thereby treated with flushing gases before and/or during the casting of the rolling ingot and filtered via degassers and a deep bed filter. As already mentioned, this filtration serves to prevent non-metallic impurities from the melt in the subsequent rolling ingot. The rolling ingot was then subjected to homogenisation, which was carried out in the temperature range of 420-600° C. for at least 5 hours for the present aluminium alloy, in order to bring as many casting phases as possible back into solution.

[0107] The rolling ingot was then hot rolled during hot rolling to a hot rolling final thickness of 2 mm to 4 mm and wound into a hot strip at a hot strip final temperature between 300° C. and 350° C. The hot strip was cold rolled in several cold rolling passes to an intermediate thickness of for example 0.60 mm to a maximum of 0.80 mm. Recrystallisation annealing was then carried out at a furnace air temperature of 450° C. to 550° C. for at least 5 hours. The aluminium strip thus recrystallised was subjected to further cold rolling steps to a second intermediate thickness between 11 μm and 20 μm and doubled for foil rolling. After doubling, intermediate annealing was carried out for half an hour at a furnace air temperature of 240° C. to 320° C. The foil rolling of the doubled strip was then carried out.

[0108] After separating the foil layers, optional assembling of the coil into rolls was carried out. The aluminium alloy foil had a final thickness of maximum 12 maximum 9 or less than 8 In the exemplary embodiment, a thickness of the aluminium alloy foil of 6.3 μm was achieved. After optional assembling, i.e. after cutting the foil to roll width and rolling up the rolls, final annealing of the rolls was carried out at 200° C. to 245° C. furnace air temperature for at least 150 hours with a cooling phase of at least 3 hours at 100° C. furnace air temperature. Unlike the exemplary embodiment A according to the invention, the comparative example B was annealed at a temperature of 330° C. for 50 hours and then cooled to room temperature.

[0109] In Table 2, the mechanical parameters of the aluminium alloy foil in accordance with DIN EN 546-2 of the two variants A and B are initially shown. It has been shown that surprisingly, the aluminium alloy A according to the invention, while having higher yield strength values R.sub.p0.2 and tensile strength values R.sub.m, still had similarly high elongation at break values A.sub.100mm measured diagonally to the rolling direction as the variant B annealed at high temperature. Comparison variant B, on the other hand, showed significantly lower yield strength values R.sub.p0.2 and lower tensile strength values R.sub.m.

[0110] The measurement of the oxide layer thickness distribution over the width of the aluminium alloy foil also showed that the variant A according to the invention has a more homogeneous distribution of the oxide layer thickness over the roll width than the variant B not according to the invention.

[0111] Manufacturing variants A and B were now examined regarding the maximum number of pores per dm.sup.2 according to the present invention. At the same time, further aluminium alloy foils were manufactured from alloy 1 and final annealed using different processes. The measurements with the device described in FIG. 2 showed that furnace air temperatures up to 245° C. for 150 hours with a cooling phase at 100° C. furnace air temperature for 7 hours did not significantly influence the maximum number of pores per dm.sup.2. As a maximum number of pores, 10 per dm.sup.2 could be measured.

[0112] From a temperature of 260° C. for 100 hours or 280° C. for 100 hours, and in particular at 330° C. furnace air temperature for 50 hours without cooling phase, the values for the maximum number of pores with a size of 1 μm to 200 μm increased significantly. This is also illustrated by the photo shown in FIG. 4a) of an aluminium alloy foil not according to the invention which has been annealed according to variant B. Compared to the variants annealed according to the invention of FIGS. 4b) and 4c), very many, very small pores, which have a size of less than 20 inn, can be seen. The aluminium alloy foils in FIG. 4b) and c) were annealed at 245° C., or 220° C. respectively, furnace air temperature for 150 h with a cooling phase at 100° C. furnace air temperature for 7 h. As shown in FIGS. 4b) and 4c), the aluminium alloy foils according to the invention showed no populations of micropores and thus a significantly improved barrier property.

TABLE-US-00001 TABLE 1 Alloy composition in % by weight, remainder Al, Alloy Si Fe Cu Mn Mg Cr Zn Ti Ni 1 Inv. 0.074 0.88 0.002 0.019 0.002 0.0007 0.005 0.005 0.004

TABLE-US-00002 TABLE 2 Mechanical parameters in accordance with DIN EN 546-2, state O Final Rp0.2 Rm A.sub.100 mm annealing [MPa] [MPa] [%] Var. [h] @ [° C.] l q d L Q d D A 150 @ 220 + 61 60 59 84 82 80 6.7 7 @ 100 B 50 @ 330 43 42 41 74 69 70 7.4

TABLE-US-00003 TABLE 3 Oxide layer thickness in [nm], state O Oxide layer thickness Increase Oxide layer thickness Increase gloss side [nm] Edge vs. matt side [nm] Edge vs. Var. Edge Middle Edge Middle Edge Middle Edge Middle A 4.0 3.6 4.0 11% 3.2 2.7 3.2 18.5% B 5.5 2.9 5.5 89% 4.5 2.3 4.6 97.8%

TABLE-US-00004 TABLE 4 Maximum number of pores Final annealing Maximum number of pores per dm.sup.2 Var. [h] @ [° C.] [pores/dm.sup.2] A Inv. 150 @ 220 + 6  7 @ 100 B Comp.  50 @ 330 673 C Inv. 150 @245 + 10 7@ 100 E Comp. 100 @ 260 31 F Comp. 100 @ 280 380

[0113] 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.

[0114] 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.

[0115] 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.