Surface-treated aluminum sheet, resin-coated surface-treated aluminum sheet, and molded body

Abstract

To provide a surface-treated aluminum sheet having corrosion resistivity, machining followability, and resin adhesiveness.SOLUTION: A surface-treated aluminum sheet includes: an aluminum base material; and an amorphous layer formed on at least one surface of the aluminum base material. The aluminum base material is an aluminum sheet or an aluminum alloy sheet. The amorphous layer includes aluminum hydroxide, in which the ratio (O / Al) of oxygen element and aluminum element is in the range of 1.7-3.0, and the thickness is 1 nm or more.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a surface-treated aluminum plate, a resin-coated surface-treated aluminum plate, and a molded body.

Background Art

[0002] Conventionally, as a surface-treated aluminum plate applied to food cans, beverage cans, etc., a surface-treated aluminum plate by chromate phosphate treatment has been manufactured. Further, as a surface-treated aluminum plate applied to home appliance parts, building structural members, etc., a surface-treated aluminum plate by chromic acid chromate treatment has been manufactured. And in view of recent regulations on hexavalent chromium, a so-called chromium-free surface-treated aluminum plate is known.

[0003] For example, in Patent Documents 1 to 5 below, as a chromium-free surface treatment, a treatment for forming aluminum hydroxide called boehmite on the surface of an aluminum base material is disclosed.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Patent Document 5

Summary of the Invention

Problems to be Solved by the Invention

[0005] For chromium-free surface-treated aluminum sheets, performance equivalent to or better than that of chromate phosphate treatment or chromate chromate treatment is required. Specifically, corrosion resistance, conformability to molding processes (processing conformability), and adhesion between the surface treatment layer and the resin layer or coating (hereinafter also referred to as "resin adhesion") are required.

[0006] Generally, the boehmite mentioned above is used for sealing pores in anodized aluminum coatings and is known as a corrosion-resistant material. Furthermore, boehmite is known for its needle-like structure with uneven surfaces. It is believed that this needle-like structure provides an anchoring effect to resin layers such as coatings and films, thereby improving resin adhesion.

[0007] On the other hand, coatings containing aluminum hydroxide, such as boehmite, are generally obtained by immersing an aluminum substrate in hot water or exposing it to steam or superheated steam. However, obtaining the aforementioned needle-like structure requires a long processing time, and therefore, it has not been applicable to manufacturing lines that require short processing times and continuously process sheets. Furthermore, due to the aforementioned processing time, cost reduction has not been achieved.

[0008] Furthermore, because the aforementioned needle-like structure is brittle, surface-treated aluminum sheets having such a needle-like structure have the problem of not being able to adequately follow metal press working processes such as drawing and ironing.

[0009] This invention was made in view of solving such problems, and aims to provide a surface-treated aluminum sheet that combines corrosion resistance, processability, and resin adhesion. It also aims to provide a resin-coated surface-treated aluminum sheet and a molded article using the surface-treated aluminum sheet. [Means for solving the problem]

[0010] To solve the problems illustrated above, the surface-treated aluminum plate in one embodiment of the present invention comprises (1) an aluminum substrate and an amorphous layer formed on at least one surface of the aluminum substrate, wherein the aluminum substrate is an aluminum plate or an aluminum alloy plate, and the amorphous layer contains aluminum hydroxide, has an oxygen-to-aluminum ratio (O / Al) in the range of 1.7 to 3.0, and has a thickness of 1 nm or more.

[0011] In (1) above, (2) preferably further comprises a crystalline layer formed on the amorphous layer, wherein the crystalline layer contains aluminum hydroxide, the ratio of oxygen to aluminum (O / Al) is in the range of 1.7 to 3.0, and the thickness is 5 nm or more.

[0012] In (2) above, (3) it is preferable that the thickness of the crystalline layer is 20 times or less the thickness of the amorphous layer.

[0013] To solve the problems illustrated above, the resin-coated surface-treated aluminum plate in one embodiment of the present invention further has a resin layer on any of the surface-treated aluminum plates described in (1) to (3) above, wherein the resin layer is a thermoplastic resin layer or a thermosetting resin layer.

[0014] To solve the problems illustrated above, it is preferable that the molded article in one embodiment of the present invention consists of (5) a surface-treated aluminum plate according to any of (1) to (3) above, or (4) a resin-coated surface-treated aluminum plate.

[0015] In (5) above, (6) it is preferable that the molded body is one of a container, a lid, and a structural member. [Effects of the Invention]

[0016] According to the present invention, it is possible to provide a surface-treated aluminum sheet that combines corrosion resistance, processability, and resin adhesion. [Brief explanation of the drawing]

[0017] [Figure 1] This is a diagram schematically showing the surface-treated aluminum plate of the first embodiment of the present invention. [Figure 2] This is a diagram schematically showing the surface-treated aluminum plate of the second embodiment of the present invention. [Figure 3] This is a diagram schematically showing the resin-coated surface-treated aluminum plate of an embodiment of the present invention. [Figure 4] This is a diagram showing a cross-sectional image of the surface-treated aluminum plate of the second embodiment of the present invention by TEM (transmission electron microscope). [Figure 5] This is a schematic diagram for explaining the test evaluation method in an embodiment of the present invention.

Embodiments for Carrying Out the Invention

[0018] <Surface-treated aluminum plate 100> Hereinafter, embodiments for implementing the surface-treated aluminum plate of the present invention will be described. FIG. 1 is a diagram schematically showing an embodiment of the surface-treated aluminum plate of the present invention.

[0019] The surface-treated aluminum plate 100 of this embodiment includes an aluminum base material 10 and an amorphous layer 20 formed on at least one surface of the aluminum base material 10. Although the surface-treated aluminum plate 100 shown in FIG. 1 has the amorphous layer 20 on one of its sides, it is not limited thereto, and the amorphous layer 20 may be provided on both sides of the aluminum base material 10.

[0020] <Aluminum base material 10> In the surface-treated aluminum plate 100 of this embodiment, pure aluminum plates and aluminum alloy plates can be used as the aluminum base material 10. The alloy type of the aluminum base material is selected according to the application. For example, for materials used for containers and lids, JIS standard 3000 series or 5000 series aluminum alloy plates are used from the viewpoint of processability, strength, and corrosion resistance. In addition, 6000 series or 7000 series aluminum alloy plates are used for structural members of automobiles, etc., depending on the application.

[0021] <Amorphous layer 20> In the surface-treated aluminum plate 100 of this embodiment, the amorphous layer 20 contains aluminum hydroxide, has an oxygen-to-aluminum ratio (O / Al) in the range of 1.7 to 3.0, and has a thickness of 1 nm or more.

[0022] The amorphous layer 20 in this embodiment contains aluminum hydroxide. In this embodiment, it is preferable that the aluminum hydroxide contained in the amorphous layer 20 contains alumina monohydrate (AlO(OH)) or alumina trihydrate (Al(OH)3). By including alumina monohydrate or alumina trihydrate as aluminum hydroxide, the corrosion resistance, processability, and resin adhesion of the amorphous layer 20 can be improved. The method for forming the amorphous layer 20 is not particularly limited, but for example, it can be formed by immersing an aluminum substrate in an alkaline solution with a pH of 8 to 13 heated to 30 to 100°C for 0.1 to 20 seconds, and then washing it with water at 5 to 100°C. Further details on the method for forming the amorphous layer 20 will be described later.

[0023] Furthermore, the aluminum hydroxide-containing film in the amorphous layer 20 of this embodiment has an amorphous structure. In this embodiment, an amorphous structure refers to a state in which no lattice fringes are observed in a cross-sectional image obtained by TEM (transmission electron microscope). These lattice fringes appear when two waves are imaged: the transmitted wave of an electron beam emitted from a crystal and the diffracted wave from a certain lattice plane of the crystal. They are light and dark fringes corresponding to the interplanar spacing of the crystal lattice. When the film has a crystalline structure, these lattice fringes are observed in a cross-sectional image obtained by TEM in minute regions of the film that satisfy the above-mentioned diffraction conditions. However, when the film has an amorphous structure, the above-mentioned diffraction conditions are not met, and therefore no lattice fringes are observed in the film.

[0024] Generally, coatings containing aluminum hydroxide, such as boehmite, formed on the surface of aluminum or aluminum alloys by immersion in hot water or exposure to steam or superheated steam, have a film thickness of approximately 500 to 3,000 nm, and a structure with needle-like or feather-like irregularities is observed in cross-sectional images obtained by TEM. This needle-like structure has a crystalline structure, and the aforementioned lattice fringes are observed in cross-sectional images obtained by TEM. On the other hand, this needle-like structure is not observed in the amorphous layer 20 in this embodiment, and the amorphous layer 20 has an amorphous structure, so the aforementioned lattice fringes are not observed in cross-sectional images obtained by TEM.

[0025] In this embodiment, a thickness of 1 nm or more for the amorphous layer 20 improves corrosion resistance, processability, and resin adhesion, but is more preferably 3 nm or more, and even more preferably 6 nm or more. On the other hand, there is no particular upper limit to the thickness of the amorphous layer 20, but from the viewpoint of processing time and the like, it is preferably 1,000 nm or less, and even more preferably 500 nm or less.

[0026] Traditionally, the resin adhesion of aluminum hydroxide, such as boehmite, has been thought to be due to the anchoring effect of needle-like or feather-like irregularities. While it is true that the anchoring effect improves resin adhesion, further detailed research has revealed that the fact that aluminum hydroxide is insoluble or poorly soluble in water also contributes significantly to resin adhesion. If the surface layer of the aluminum substrate is a naturally formed water-soluble film, when moisture reaches the adhesive interface with the resin, the film on the surface of the aluminum substrate dissolves, causing the resin layer to easily peel off the substrate. This is especially pronounced in beverage cans and food containers, where heat sterilization with hot water or steam is performed during the filling process. Similar peeling phenomena also occur in structural members used in high-temperature and high-humidity environments. As a countermeasure, by making the surface layer of the aluminum substrate a film containing insoluble or poorly soluble aluminum hydroxide, the adhesive interface can be maintained, and resin adhesion can be significantly improved.

[0027] Conventionally, in processes that form aluminum hydroxide, such as boehmite treatment, it has been thought that a needle-like structure of aluminum hydroxide is essential to improve resin adhesion. Therefore, the process took about 30 to 120 seconds to allow the needle-like structure to grow sufficiently. The inventors focused on the property that aluminum hydroxide is insoluble or poorly soluble in water and hypothesized that resin adhesion could be improved even with an extremely thin film of about 1 to 10 nm that is formed in a very short time of about 0.1 to 2 seconds during the initial formation of a film containing aluminum hydroxide. When they actually conducted tests to confirm this, they obtained the results they had hypothesized, and discovered that resin adhesion was greatly improved even with a 1 to 10 nm aluminum hydroxide film in the initial stage of film formation. The aluminum hydroxide film obtained at this time was an amorphous layer without a needle-like structure, and it was found that it had excellent processability due to being an amorphous layer. Through this mechanism, good results were also obtained in terms of resin adhesion after processing.

[0028] In this embodiment, the ratio of oxygen to aluminum (O / Al) in the amorphous layer 20 is in the range of 1.7 to 3.0. The ratio (O / Al) is determined by identifying the amorphous layer from a cross-sectional image obtained by TEM and performing energy-dispersive X-ray analysis (EDS) on the central portion of that layer.

[0029] Generally, the ratio (O / Al) of aluminum oxide (Al2O3) is known to be around 1.5, the ratio (O / Al) of alumina trihydrate (Al(OH)3) is around 3.0, and the ratio (O / Al) of alumina monohydrate (AlO(OH)) is around 2.0. In this embodiment, in order to obtain the required corrosion resistance, processability, and resin adhesion, the ratio (O / Al) of the amorphous layer 20 needs to be in the range of 1.7 to 3.0.

[0030] The amorphous layer 20 of this embodiment is substantially free of phosphorus or chromium. On the other hand, the amorphous layer 20 of this embodiment contains alumina monohydrate or alumina trihydrate as aluminum hydroxide. It may also contain other compounds such as the aforementioned aluminum oxide (Al2O3). It may also contain trace amounts of compounds present in the treatment solution, such as silicon dioxide (SiO2) or magnesium oxide (MgO). What is important in this embodiment is to set the ratio (O / Al) of the amorphous layer 20 in the range of 1.7 to 3.0.

[0031] As described above, the important thing in this embodiment is to make the surface coating of the surface-treated aluminum plate insoluble or sparingly soluble in water. Aluminum hydroxide is thought to be formed when water and active metallic aluminum come into contact, and the formed coating becomes extremely stable in water. Therefore, the resulting coating is insoluble or sparingly soluble in water. When the formed aluminum hydroxide-containing coating contains a large amount of alumina trihydrate, the ratio (O / Al) will be close to 3.0. Also, when the formed aluminum hydroxide-containing coating contains a large amount of alumina monohydrate, the ratio (O / Al) will be close to 2.0. On the other hand, when aluminum oxide (Al2O3), which has a ratio (O / Al) of around 1.5, is included, the higher the proportion of aluminum oxide in the coating, the smaller the overall ratio (O / Al) of the coating becomes. When the proportion of aluminum oxide in the coating increases, even a coating containing aluminum hydroxide becomes more soluble in water, and the required corrosion resistance and resin adhesion cannot be obtained. The same applies when a large amount of compounds of other elements are included.

[0032] Based on the results of tests conducted by the present inventors, it is preferable to set the ratio (O / Al) of the entire amorphous layer 20 coating to a range of 1.7 to 3.0 in order to obtain sufficient corrosion resistance and resin adhesion. Furthermore, as the proportion of alumina monohydrate to alumina trihydrate in the aluminum hydroxide contained in the coating increases, corrosion resistance and resin adhesion improve. Therefore, it is more preferable to set the ratio (O / Al) to a range of 1.8 to 2.6, and even more preferable to a range of 1.9 to 2.2. This is because alumina monohydrate is more thermally stable than alumina trihydrate, and its insoluble properties are stably maintained even in high-temperature water.

[0033] <Surface-treated aluminum sheet 200> Next, the surface-treated aluminum plate of the present invention will be further described with reference to the following second embodiment. Figure 2 is a schematic diagram showing the surface-treated aluminum plate 200 according to the second embodiment. The surface-treated aluminum plate 200 according to the second embodiment differs from the first embodiment mainly in that a crystalline layer 30 is formed on an amorphous layer 20. Therefore, the same reference numerals are used for common components and their descriptions are omitted.

[0034] In Figure 2, an amorphous layer 20 and a crystalline layer 30 are formed on one side of the aluminum substrate 10, but this is not the only possible configuration. For example, the amorphous layer 20 and the crystalline layer 30 may be formed on both sides of the aluminum substrate. Alternatively, both the amorphous layer 20 and the crystalline layer 30 may be formed on one side of the aluminum substrate 10, while only the amorphous layer 20 is formed on the other side. Furthermore, the amorphous layer 20 and the crystalline layer 30 may be formed on one side of the aluminum substrate 10, while a known metal layer or resin layer may be formed on the other side.

[0035] <Crystalline layer 30> In this embodiment, the surface-treated aluminum plate 200 has a crystalline layer 30 formed on an amorphous layer 20. The crystalline layer 30 is formed as a coating containing aluminum hydroxide, similar to the amorphous layer 20. The form of aluminum hydroxide is alumina monohydrate or alumina trihydrate, and the ratio of oxygen and aluminum elements (O / Al) in the crystalline layer 30 is in the range of 1.7 to 3.0.

[0036] The crystalline layer 30 of this embodiment is substantially free of phosphorus or chromium. On the other hand, the crystalline layer 30 of this embodiment may contain aluminum oxide (Al2O3) in addition to alumina monohydrate and alumina trihydrate. It may also contain trace amounts of compounds present in the treatment solution, such as silicon dioxide (SiO2) and magnesium oxide (MgO). What is important in this embodiment is to set the ratio (O / Al) of the crystalline layer 30 in the range of 1.7 to 3.0.

[0037] When the crystalline layer 30 is observed in a magnified cross-section using a TEM or SEM (scanning electron microscope), needle-like or feather-like irregularities are observed. Figure 4 is a TEM cross-sectional image showing an example of the amorphous layer 20 and crystalline layer 30 in this embodiment. The amorphous layer 20 formed on the aluminum substrate 10 has a dense structure, and the crystalline layer 30, which has a needle-like structure, is formed on top of it. Thus, the aluminum hydroxide-containing film in the crystalline layer 30 has a needle-like structure, and a clearly different structure from the amorphous layer 20 is observed in the cross-sectional image. Note that the lines between the aluminum substrate 10 and the amorphous layer 20, and between the amorphous layer 20 and the crystalline layer 30 in Figure 4 are lines added to make their respective boundaries clearer.

[0038] Whether or not the aluminum hydroxide-containing coating in the crystalline layer 30 of this embodiment has a crystalline structure can be determined by whether or not lattice fringes are observed in the TEM cross-sectional image. If it is a crystalline layer, lattice fringes will be observed. These lattice fringes appear when two waves are imaged: the transmitted wave of an electron beam emitted from the crystal and the diffracted wave from a certain lattice plane of the crystal. They are a pattern of light and dark fringes corresponding to the interplanar spacing of the crystal lattice. When the coating has a crystalline structure, these lattice fringes are observed in the TEM cross-sectional image in minute regions of the coating that satisfy the above-mentioned diffraction conditions. However, when the coating has an amorphous structure, the above-mentioned diffraction conditions are not met, and therefore, lattice fringes are not observed in the coating. Note that the TEM cross-sectional image in Figure 4 was observed at 1 million times magnification, but the presence or absence of the lattice fringes mentioned above cannot be determined at this magnification. Observation of lattice fringes, which is necessary to determine the presence or absence of a crystalline structure in the coating, needs to be performed at a magnification of 2 million times or more.

[0039] In this embodiment, the thickness of the crystalline layer 30 is 5 nm or more, preferably 25 nm or more, and more preferably 50 nm or more. On the other hand, there is no particular upper limit to the thickness of the crystalline layer 30, but from the viewpoint of processing time and cost, it is preferably 400 nm or less, and more preferably 200 nm or less.

[0040] The role of this crystalline layer 30 is to improve resin adhesion through an anchoring effect caused by needle-like or feather-like irregularities. This anchoring effect does not depend on the thickness of the coating, but on the roughness of the coating surface, so it does not need to be thicker than necessary. Making the crystalline layer 30 thicker than necessary increases processing time, thus reducing productivity and increasing costs. In the range confirmed by the inventors through testing, an anchoring effect is obtained and resin adhesion is improved when the thickness of the crystalline layer 30 is 5 nm or more, but the improvement in resin adhesion saturates around 200 nm and does not improve beyond 400 nm. Furthermore, if the thickness is made more than 500 nm, the crystalline layer 30 cannot follow the processing, resulting in cohesive failure during processing, which conversely leads to a decrease in resin adhesion.

[0041] In this embodiment, the ratio of amorphous layer 20 to crystalline layer 30 is preferably such that the thickness of the crystalline layer 30 is 20 times or less the thickness of the amorphous layer 20. As described above, the amorphous layer has excellent workability, so even when large deformations are applied by processes such as drawing and ironing, the amorphous layer 20 follows the processing and can uniformly cover the surface of the processed area. On the other hand, the needle-like structure of the crystalline layer 30 cannot follow the processing because it is crystalline, and is processed while causing film cracking. When the surface of the aluminum plate after drawing and ironing was observed, it was found that the crystalline layer 30 was partially broken up, and when the cross-section was observed, it was found that there was a large step difference between the part where the crystalline layer 30 remained and the part where it did not.

[0042] Further investigation of this phenomenon revealed that when the thickness of the crystalline layer 30 exceeds 20 times the thickness of the amorphous layer 20, the resin layer peels off due to the step difference between the amorphous layer 20 and the crystalline layer 30 that occurs after processing, resulting in reduced resin adhesion. Therefore, it is preferable to keep the ratio of the amorphous layer 20 to the crystalline layer 30 below the above value from the viewpoint of ensuring resin adhesion to the processed area. More preferably, the above thickness ratio should be 15 times or less. Note that this problem only occurs when the crystalline layer 30 is extremely thick compared to the amorphous layer 20, so there is no lower limit to the above thickness ratio.

[0043] Furthermore, if the amorphous layer 20 is absent, that is, if only the crystalline layer 30 is formed on the aluminum substrate, there is no layer that can follow the processing, and the corrosion resistance and resin adhesion of the processed area will be significantly reduced. Therefore, the amorphous layer 20 is essential in this embodiment, and the presence of this layer on the aluminum substrate provides good processing followability, corrosion resistance of the processed area, and resin adhesion.

[0044] <Resin-coated surface-treated aluminum plate 300> Next, the resin-coated surface-treated aluminum plate of the present invention will be described. Figure 3 is a schematic diagram showing the resin-coated surface-treated aluminum plate 300 according to this embodiment. The resin-coated surface-treated aluminum plate 300 according to this embodiment differs from the surface-treated aluminum plate of the first or second embodiment in that the resin layer 40 is formed on the amorphous layer 20 or on the crystalline layer 30. Therefore, the same reference numerals are used for common components and their descriptions are omitted.

[0045] In Figure 3, the resin layer 40 is formed on the amorphous layer 20 via the crystalline layer 30, but this is not the only possible configuration. In other words, in this embodiment, the resin layer 40 may be formed directly on the amorphous layer 20. Also, in this embodiment, the amorphous layer 20 and the resin layer 40 may be formed on both sides of the aluminum substrate.

[0046] In this embodiment, the material of the resin layer 40 can be a known resin used to coat a metal substrate, and among these, thermoplastic resins or thermosetting resins are preferably used. Examples of thermoplastic resins include one or more resins such as polyolefin resins, polyester resins, polycarbonate resins, acrylic resins, polystyrene resins, ABS resins, polyamide resins, fluororesins, and polyvinyl chloride resins. Examples of thermosetting resins include one or more resins such as acrylic resins, unsaturated polyester resins, phenolic resins, urea resins, polyurethane resins, silicone resins, polyimide resins, melamine resins, and epoxy resins.

[0047] Among thermoplastic resins, polyolefin resins, polyester resins, and mixtures thereof are more preferably applicable. Examples of polyolefin resins include one or more resins such as polyethylene resin, polypropylene resin, ethylene-propylene copolymer resin, ethylene-acrylic acid ester copolymer resin, and ionomer resin. Examples of polyester resins include one or more resins such as polyethylene terephthalate resin, polybutylene terephthalate resin, polyethylene terephthalate resin copolymerized with polyethylene isophthalate, and polybutylene terephthalate resin copolymerized with polybutylene isophthalate. Polyester resin is more preferably applied as the resin layer 40.

[0048] The resin layer 40 may be a multilayer resin layer, for example, two polyethylene terephthalate resin layers copolymerized in different proportions of polyethylene isophthalate can be used. Furthermore, the resin layer 40 may be a resin layer blended with multiple different resins, for example, a resin layer blended with polyethylene terephthalate resin and ionomer resin or ethylene-propylene copolymer resin, or a resin layer blended with polyethylene terephthalate resin and polybutylene terephthalate resin can be applied.

[0049] The resin layer 40 can be compounded with known resin compounding agents, such as antiblocking agents like amorphous silica, inorganic fillers like calcium carbonate, magnesium carbonate, talc, and glass, various fibers like glass fibers, carbon fibers, and aramid fibers, antistatic agents, antioxidants like tocopherol, and ultraviolet absorbers, according to known methods.

[0050] The thickness of the resin layer 40 is not particularly limited, but for thermoplastic resins, it is preferably in the range of 3 to 300 μm, and more preferably in the range of 5 to 230 μm. For thermosetting resins, it is preferably in the range of 0.5 to 100 μm, and more preferably in the range of 1 to 50 μm. Generally, corrosion resistance improves as the resin layer becomes thicker, but resin adhesion and processability decrease, so there is an optimal thickness range depending on the application. The method for forming the resin layer 40 will be described later.

[0051] <Manufacturing method for surface-treated aluminum sheets> Next, the method for manufacturing the surface-treated aluminum sheet in this embodiment will be described below. Note that the manufacturing method shown here is merely one example in this embodiment and is not limited to this method.

[0052] The manufacturing method for the surface-treated aluminum plate in this embodiment includes methods such as immersing the aluminum substrate in an alkaline solution at 30°C to 100°C and pH 8 to 13 for 0.1 to 20 seconds, performing cathodic electrolysis in an alkaline solution at 30°C to 100°C and pH 8 to 13 for 0.1 to 10 seconds, or performing anodic electrolysis in the same alkaline solution for 0.1 to 10 seconds. These processing methods make it possible to form an amorphous layer on the aluminum substrate containing aluminum hydroxide, with an oxygen-to-aluminum ratio (O / Al) in the range of 1.7 to 3.0 and a thickness of 1 nm or more.

[0053] The treatment solution (alkaline solution) used in the above processing step is preferably an aqueous solution of sodium carbonate, an aqueous solution of sodium aluminate, an aqueous solution of sodium hydroxide, or an aqueous solution of potassium hydroxide. Pure water is preferred for the alkaline solution, and generally, ion-exchanged water with an electrical conductivity of 1 μS / cm or less is used, but tap water with an electrical conductivity of 300 μS / cm or less can also be used. Since the presence of calcium carbonate or silicon dioxide as impurities in the solution acts as an inhibitor of aluminum hydroxide film formation, it is preferable to use water from which these impurities have been removed.

[0054] The pH of the treatment solution (alkaline solution) used in the above processing step is preferably 8 to 13, more preferably 8 to 12, and even more preferably 8 to 11. Aluminum hydroxide is hardly formed in acidic solutions with a pH of 6 or lower, and stable film formation is possible in water or alkaline solutions with a pH of 7 or higher. The reason why a pH of 8 or higher is preferable is to dissolve the naturally formed oxide film present on the surface of the aluminum substrate before treatment in a very short time. Generally, the naturally formed oxide film on an aluminum substrate is a film mainly composed of aluminum oxide, which can be dissolved in an alkaline solution in a very short time. Since water and the active metallic aluminum surface need to come into contact in order to form aluminum hydroxide, it is necessary to dissolve the naturally formed oxide film in a very short time in order to shorten the processing time. On the other hand, if the pH exceeds 13, the metallic aluminum surface dissolves excessively, making it difficult to form a homogeneous and stable film containing aluminum hydroxide with minimal unevenness. Also, if the pH exceeds 11, the formed aluminum hydroxide will mainly consist of alumina trihydrate, making it difficult to form alumina monohydrate, which is more stable in high-temperature water. Therefore, from the viewpoint of ensuring excellent resin adhesion, a pH of 11 or lower is more preferable.

[0055] The temperature of the treatment solution (alkaline solution) used in the above processing step is preferably 30°C to 100°C, more preferably 50°C to 100°C, and even more preferably 60°C to 100°C. The higher the temperature of the treatment solution, the faster the native oxide film present on the surface of the aluminum substrate before processing can be dissolved.

[0056] In the above processing step, contact between the aluminum substrate and the alkaline solution is preferably performed by cathodic electrolysis rather than immersion. Cathodic electrolysis suppresses localized dissolution of the aluminum substrate, allowing for the formation of a more homogeneous aluminum hydroxide-containing coating. Furthermore, the current density for the cathodic electrolysis in this processing step is, for example, 1 to 10 A / dm². 2 It can be done in this way. Furthermore, anodic electrolysis can be used as a method to form a homogeneous and thick aluminum hydroxide coating in the above processing step. The current density for the anodic electrolysis in this processing step is, for example, 1 to 10 A / dm². 2 It can be done in this way.

[0057] <Manufacturing method for resin-coated surface-treated aluminum plates> Next, the method for manufacturing the resin-coated surface-treated aluminum plate in this embodiment will be described below. Note that the manufacturing method shown here is merely one example in this embodiment and is not limited to this method.

[0058] The manufacturing method for the resin-coated surface-treated aluminum plate in this embodiment includes a method of forming a resin layer on the surface-treated aluminum plate obtained as described above. The resin layer can be formed by any method; for example, in the case of thermoplastic resins, methods include directly laminating the molten resin onto the surface-treated aluminum plate, or processing the resin into a film on a separate line and then heat-pressing it onto the surface-treated aluminum plate heated on a lamination line. Furthermore, as a method to further improve resin adhesion, a thermoplastic resin film with an adhesive layer of thermosetting resin laminated on the bonding surface can also be used. In the case of thermosetting resins, methods include coating with a roll coater and then drying in an oven, or coating with a spray and then drying in an oven.

[0059] <Molded products (containers, container lids, etc.) and methods for manufacturing the same> Next, the molded article and its manufacturing method in this embodiment will be described below. The molded body in this embodiment is a molded body formed by processing the above-mentioned surface-treated aluminum plate or resin-coated surface-treated aluminum plate, and specifically includes containers, lids, structural members, etc.

[0060] Examples of containers include beverage cans, food containers, rectangular cans, drums, spray cans, and battery cases. These containers can be manufactured using the surface-treated aluminum sheet or resin-coated surface-treated aluminum sheet described above, using known molding methods. As an example, the surface-treated aluminum sheet or resin-coated surface-treated aluminum sheet is punched out to a predetermined shape and dimensions, and then molded into various containers using a press die. Conventional known processing methods such as deep drawing, deep drawing and re-drawing, deep drawing and ironing can be applied as molding methods. By forming a thermoplastic resin layer or thermosetting resin layer on the surface of the surface-treated aluminum sheet in advance, the coefficient of friction of the surface against processing tools can be reduced, allowing for thinner side walls of the container and weight reduction of the container. Furthermore, it is possible to reduce the amount of washing water used in the container manufacturing process and omit painting and baking processes performed after container molding, thus realizing container manufacturing with a low environmental impact.

[0061] Examples of lids include stay-on-tab (SOT) type easy-open lids, fully-open type easy-open (EOE) lids, easy-peel lids using aluminum foil, bottom lids for 3-piece cans such as welded cans, crown-type lids, screw caps, and slip-on lids. One example of a molding method for SOT and EOE lids is to first punch out a surface-treated aluminum sheet or a resin-coated surface-treated aluminum sheet into a predetermined shape and dimensions, and then, or simultaneously, mold it into a can lid using a press die. Next, scoring and riveting are performed on the outer surface of the can lid to create a partial opening or a fully opening, and opening tabs are attached. The opening edge is then curled for double crimping, and sealing compound is applied to the inner surface of the curl and dried to produce the can lid. In addition, bottom lids for 3-piece cans such as welded cans may be manufactured using a method that omits the scoring, riveting, and tab attachment processes described above.

[0062] Examples of structural members include structural members for automobiles, ships, aircraft, home appliances, and building structural members such as doors, shutters, ducts, and aluminum sashes. All of these structural members can be manufactured using the aforementioned surface-treated aluminum sheets or resin-coated surface-treated aluminum sheets by known methods such as press working.

[0063] <Examples> The present invention will be described in more detail below with reference to examples. First, the measurement method used in the examples will be described.

[0064] [Measurement of the ratio of oxygen to aluminum (O / Al)] After forming an amorphous layer containing aluminum hydroxide, or an amorphous and crystalline layer, on an aluminum substrate, samples were cut out using a microsampling method and fixed onto a copper support. Subsequently, cross-sectional TEM samples with a thickness of approximately 100 nm were prepared by FIB (focused ion beam) processing, and TEM observation and EDS analysis were performed to calculate the ratio of oxygen to aluminum elements (O / Al). In this analysis, in order to obtain accurate information, the process from FIB processing to TEM analysis was carried out in a cooling environment (cryo-processing and observation). <TEM (Transmission Electron Microscope)> Analysis equipment: H-9500 manufactured by Hitachi High-Technologies Observation conditions: Acceleration voltage: 200 kV Magnification accuracy: ±10% <EDS (Energy Dispersive X-ray Spectroscopy)> Analysis equipment: HD-2700 (Transmission Electron Microscope) manufactured by Hitachi High-Technologies Acceleration voltage: 200 kV Beam diameter: Approximately 0.2 nm in diameter Elemental analysis equipment: Manufactured by Oxford Instruments Ultim Max TLE X-ray detector: Si drift detector Energy resolution: Approximately 130 eV X-ray extraction angle: 24.8° Solid angle: Approximately 1.1 sr Integration time: 10 seconds

[0065] [180° Peel Test and Evaluation] After can manufacturing, the adhesion between the resin layer and the surface treatment layer was tested and evaluated as follows. First, a resin layer was formed on the surface-treated aluminum plate to produce a resin laminate plate. Specifically, on both sides of the surface-treated aluminum plate heated at 280°C for 10 seconds, an unstretched two-layer PET film (thickness 20 μm) was laminated, and then it was put into water and rapidly cooled to obtain a resin laminate plate. Note that the two-layer PET film used was a film in which two layers, a PET resin copolymerized with 2 mol% isophthalic acid (IA) as the surface layer and a PET resin copolymerized with 15 mol% isophthalic acid (IA) as the lower layer, were laminated at a layer ratio of 4 / 1. Next, a beverage can was produced using the obtained resin laminate plate. Specifically, 50 mg / m was applied to both sides of the resin laminate plate 2A paraffin wax was applied, and a blank with a diameter of 142 mm was punched out to produce the first cup. Next, this first cup was processed into a 350 mL can with a reduction ratio of 65% using a known can-making machine (Body Maker). At this time, the evaluation surface was the outer surface of the can. After cutting a T-shape from the side wall of the molded can at the position and dimensions shown in Figure 5(a), the 180° peel strength of a 15 mm wide film was measured using the 180° peel test shown in Figure 5(b). A tensile testing machine was used for the measurement, and the tensile speed was 20 mm / min at room temperature. The resin adhesion after can manufacturing was evaluated as follows. Passing: Maximum tensile strength of 0.8 N / 15 mm or higher as measured by a tensile testing machine. Failure: Maximum tensile strength measured by the tensile testing machine is less than 0.8 N / 15 mm.

[0066] [Retort sealing test and evaluation] The resin adhesion in a humid environment was tested and evaluated using the beverage can described above by the following method. First, a cut was made in the film on the outer surface of a 350 mL can at a height of 90 mm from the bottom of the can using a cutter. The can was then placed in a retort kettle while immersed in tap water and subjected to retort treatment at 125°C for 45 minutes. The maximum film peel length below the cut made by the cutter on the removed can was measured and evaluated as follows. Furthermore, it is known that the retort adhesion test of the processed area after can manufacturing correlates with corrosion resistance, and this test allows for the evaluation of both the corrosion resistance and resin adhesion of the processed area. Passing criteria: Film peel length 30mm or less Failure: Film peel length exceeds 30mm

[0067] (Example 1) An aluminum substrate of alloy type A3104, temper H19, and thickness 0.27 mm was prepared. After degreasing the aluminum substrate of rolling oil by a known method, it was subjected to cathodic electrolysis for 1 second in a 1% sodium carbonate aqueous solution (treatment solution A-1) at 60°C. Immediately thereafter, it was washed for 0.5 seconds with ion-exchanged water (treatment solution B) at 20°C, the water was removed with a roller, and it was dried with a dryer to obtain a surface-treated aluminum plate with an aluminum hydroxide coating formed on both sides.

[0068] TEM cross-sectional images of the surface-treated aluminum plates revealed an amorphous layer with an average thickness of 2.5 nm on the aluminum substrate. The average thickness of the coating was determined by measuring 10 arbitrary points that evenly included the uneven areas in the TEM cross-sectional image, and using the average value. The determination of whether the layer was amorphous or crystalline was made based on the presence or absence of lattice patterns in the cross-sectional image. Specifically, observations were performed at a high magnification of 2 million times, and the presence or absence of lattice patterns was determined by observing 2 to 3 different arbitrary cross-sectional images. The ratio of oxygen to aluminum (O / Al) in the amorphous layer was determined to be 3.0 by EDS analysis of the film cross-section. This ratio (O / Al) was calculated by selecting five arbitrary points in the center of the target layer from the TEM cross-sectional image, analyzing the EDS results of these five points, and then using the average value of these five points.

[0069] Next, a resin layer was heat-pressed onto the amorphous layer of the surface-treated aluminum plate to produce a resin laminate plate. Specifically, a two-layer PET film (20 μm thick) of unstretched film was laminated to both sides of a surface-treated aluminum plate heated to 280°C, and then rapidly cooled in water to obtain a resin laminate plate. The two-layer PET film used consisted of two layers laminated at a layer ratio of 4 / 1: a surface layer of PET resin copolymerized with 2 mol% isophthalic acid (IA), and a lower layer of PET resin copolymerized with 15 mol% isophthalic acid (IA). 50 mg / m² was applied to both sides of the resin laminate plate. 2A paraffin wax coating was applied, and a blank with a diameter of 142 mm was punched out to produce the first cup. Next, this first cup was processed into a 350 mL can with a reduction ratio of 65% using a can-making machine (BodyMaker). The film peel strength of the outer surface and can wall of the manufactured beverage can was evaluated using a 180° peel test. The evaluation results are shown in Table 3.

[0070] Next, a retort adhesion test was conducted on the outer surface and wall of beverage cans manufactured using the same method. The evaluation results of the retort adhesion test are shown in Table 3.

[0071] (Example 2) The procedure was carried out in the same manner as in Example 1, except that the temperature of the treatment solution and the treatment time were changed as shown in Table 1. The results are shown in Tables 2 and 3.

[0072] (Example 3) The procedure was carried out in the same manner as in Example 1, except that the temperature of the treatment solution, treatment conditions, and treatment time were changed as shown in Table 1. The results are shown in Tables 2 and 3.

[0073] (Example 4) The procedure was carried out in the same manner as in Example 1, except that the processing conditions were changed to anodic electrolysis and the processing time was changed as shown in Table 1. The results are shown in Tables 2 and 3.

[0074] (Example 5) The procedure was carried out in the same manner as in Example 4, except that the processing time was changed as shown in Table 1. The results are shown in Tables 2 and 3.

[0075] (Example 6) An aluminum substrate of alloy type A5021, temper H18, and thickness 0.25 mm was prepared. After degreasing the aluminum substrate of rolling oil by a known method, it was immersed in a 0.004% aqueous sodium carbonate solution (treatment solution A-2) at 98°C for 15 seconds. Without rinsing with water, it was squeezed with rollers and dried with a dryer to obtain a surface-treated aluminum plate with an aluminum hydroxide coating formed on both sides. The obtained surface-treated aluminum plate was evaluated in the same manner as in Example 1. The results are shown in Tables 2-3.

[0076] (Example 7) The procedure was carried out in the same manner as in Example 6, except that the treatment solution was a 0.001% aqueous sodium carbonate solution (treatment solution A-3) and the treatment time was changed as shown in Table 1. The results are shown in Tables 2 and 3.

[0077] (Example 8) The procedure was carried out in the same manner as in Example 3, except that the treatment solution was a 0.1% sodium aluminate aqueous solution (treatment solution C-1), and the temperature and treatment time of the treatment solution were changed as shown in Table 1. The results are shown in Tables 2 and 3.

[0078] (Example 9) An aluminum substrate of alloy type A3104, temper H19, and thickness 0.27 mm was prepared. After degreasing the aluminum substrate of rolling oil by a known method, it was subjected to cathodic electrolysis for 5 seconds in a 1% sodium carbonate aqueous solution (treatment solution A-1) at 60°C. Immediately thereafter, it was washed for 2 seconds with ion-exchanged water (treatment solution B) at 98°C, the water was removed with a roller, and it was dried with a dryer to obtain a surface-treated aluminum plate with a coating containing aluminum hydroxide formed on both sides. The obtained surface-treated aluminum plate was evaluated in the same manner as in Example 1. The results are shown in Tables 2-3.

[0079] (Example 10) The procedure was carried out in the same manner as in Example 9, except that the rinsing time after treatment was changed as shown in Table 1. The results are shown in Tables 2 and 3.

[0080] (Example 11) The procedure was carried out in the same manner as in Example 8, except that the treatment solution was changed to a 0.5% sodium aluminate aqueous solution (treatment solution C-2). The results are shown in Tables 2 and 3. The pH of processing solution C-2 is 12.3. When the pH exceeds 12, aluminum hydroxide is formed during the immersion process, and at the same time, the aluminum metal surface is excessively etched, resulting in the formation of a rapidly growing needle-like structure that resembles a rough surface. In this case, the thickness of the crystalline layer exceeds 20 times the thickness of the amorphous layer, and the step between the clumps of needle-like structure formed during processing and the amorphous layer causes film delamination. Therefore, although the evaluation of the 180° peel test and the retort adhesion test were passed, the resin adhesion of the processed area was reduced compared to other examples.

[0081] (Comparative Example 1) Aluminum substrates of alloy type A3104, temper H19, and thickness 0.27 mm were prepared. After degreasing the aluminum substrates of rolling oil by a known method, the same evaluation as in Example 1 was performed without surface treatment. The results are shown in Tables 2 and 3. The coating that naturally formed after degreasing was mainly composed of aluminum oxide, with an oxygen-to-aluminum ratio (O / Al) of 1.6. In this case, the coating on the surface of the aluminum plate dissolves in water during retorting, making it impossible to obtain sufficient resin adhesion.

[0082] (Comparative Example 2) An aluminum substrate of alloy type A3104, temper H19, and thickness 0.27 mm was prepared. After degreasing the aluminum substrate of rolling oil by a known method, it was immersed in a 0.5% sulfuric acid aqueous solution (treatment solution D) at 60°C for 2 seconds, immediately washed with ion-exchanged water (treatment solution B) at 20°C for 0.5 seconds, squeezed with a roller, and dried with a dryer to obtain a surface-treated aluminum plate. The obtained surface-treated aluminum plate was evaluated in the same manner as in Example 1. The results are shown in Tables 2-3. Although pickling is commonly performed as a pre-treatment step for processes such as chromate phosphate treatment, immersion in an acidic solution results in almost no formation of a film containing aluminum hydroxide, instead forming a film primarily composed of aluminum oxide. Consequently, the ratio of oxygen to aluminum elements (O / Al) in the film after surface treatment becomes 1.6, and the film on the surface of the aluminum plate dissolves in water during retorting, making it impossible to obtain sufficient resin adhesion.

[0083] [Table 1]

[0084] [Table 2]

[0085] [Table 3]

[0086] The above examples and comparative examples demonstrate that the surface-treated aluminum sheet produced by this embodiment possesses corrosion resistance, processability, and resin adhesion. Furthermore, it was shown that the surface-treated aluminum sheet produced by this embodiment can achieve the above effects even with a short processing time. On the other hand, the untreated or surface-treated aluminum sheets of the comparative examples failed to satisfy any of the required corrosion resistance, processability, and resin adhesion. [Industrial applicability]

[0087] As described above, the surface-treated aluminum sheet of the present invention can be applied to a wide range of industries, including containers and their lids such as food cans, beverage cans, and battery cases, as well as structural components for ships, aircraft, automobiles, and home appliances, building structural components, and heat exchanger components. [Explanation of Symbols]

[0088] 100 Surface-treated aluminum sheet 10 Aluminum base material 20 Amorphous layer 30 Crystalline layer 200 Surface-treated aluminum sheet 300 Resin-coated surface-treated aluminum plate 40 resin layer

Claims

1. Aluminum substrate and The aluminum substrate comprises an amorphous layer formed on at least one surface of the aluminum substrate, The aluminum substrate is an aluminum plate or an aluminum alloy plate. A surface-treated aluminum plate characterized in that the amorphous layer contains aluminum hydroxide, the ratio of oxygen to aluminum elements (O / Al) is in the range of 2.0 to 3.0, and the thickness is 1 nm or more.

2. The material further includes a crystalline layer formed on the amorphous layer, The surface-treated aluminum plate according to claim 1, wherein the crystalline layer contains aluminum hydroxide, the ratio of oxygen to aluminum (O / Al) is in the range of 1.7 to 3.0, and the thickness is 5 nm or more.

3. The surface-treated aluminum plate according to claim 2, wherein the thickness of the crystalline layer is 20 times or less the thickness of the amorphous layer.

4. A resin-coated surface-treated aluminum plate having a resin layer further on the surface-treated aluminum plate according to any one of claims 1 to 3, wherein the resin layer is a thermoplastic resin layer or a thermosetting resin layer.

5. A molded article comprising a surface-treated aluminum plate according to any one of claims 1 to 3, or a resin-coated surface-treated aluminum plate according to claim 4.

6. The molded body according to claim 5, wherein the molded body is one of a container, a lid, and a structural member.

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