WO2023089824A1 - Aluminum member and method for producing same - Google Patents

Abstract

An aluminum member (1) is provided with a base material (10) that is formed of aluminum or an aluminum alloy. The aluminum member (1) is provided with an anodic oxide coating film (20) that comprises: a barrier layer (21) which is in contact with a surface (11) of the base material (10); a first porous layer (22) which is in contact with a surface of the barrier layer (21), the surface being on the reverse side from the base material (10); and a second porous layer (23) which is in contact with a surface of the first porous layer (22), the surface being on the reverse side from the barrier layer (21), and which has a plurality of pores that are arrayed so as to linearly extend from the surface that is in contact with the first porous layer (22) toward an exposed front surface (24). The first porous layer (22) has at least either a plurality of branched pores or a plurality of pores that have a larger average pore diameter than the pores of the second porous layer (23). The anodic oxide coating film (20) incorporates white pigment particles.

Description

Aluminum member and its manufacturing method

The present disclosure relates to an aluminum member and a manufacturing method thereof.

In recent years, there has been an increasing demand for mobile devices and personal computer housings, for example, to have a paper-like white appearance. In order to meet such demands, attempts have been made to make the appearance of aluminum members white by forming an anodized film on the surface of a substrate made of aluminum or an aluminum alloy.

In Patent Document 1, the arithmetic mean height Sa of the surface of the substrate is 0.1 μm to 0.5 μm, the maximum height Sz is 0.2 μm to 5 μm, and the average length RSm of the roughness curve element is Aluminum members are disclosed that are between 0.5 μm and 10 μm.

Japanese Patent No. 6525035

According to the aluminum member of Patent Document 1, the arithmetic mean height Sa of the base material, the maximum height Sz, and the average length RSm of the roughness curve element are set within predetermined ranges, whereby the aluminum member has a white appearance. is obtained. However, there is a demand for an aluminum member that has improved whiteness when viewed obliquely and that has an appearance similar to that of paper.

The present disclosure has been made in view of such problems of the conventional technology. An object of the present disclosure is to provide an aluminum member with low angular dependence and a method of manufacturing the same.

The aluminum member according to the first aspect of the present disclosure includes a base material made of aluminum or an aluminum alloy. The aluminum member includes a barrier layer in contact with the surface of the base material, a first porous layer in contact with the surface of the barrier layer opposite to the base material, and a first porous layer in contact with the surface of the first porous layer opposite to the barrier layer. An anodic oxide film including a porous layer and a second porous layer having a plurality of linearly aligned pores extending from the surface in contact with the surface to the exposed surface. The first porous layer has at least one of a plurality of branched pores and a plurality of pores having an average pore size larger than that of the second porous layer. The anodized film incorporates white pigment particles.

A method for manufacturing an aluminum member according to a second aspect of the present disclosure first anodizes a substrate made of aluminum or an aluminum alloy with an electrolytic solution capable of forming a plurality of aligned linearly extending holes. A first anodizing step is included. The method includes a second anodizing step of second anodizing the first anodized substrate with an electrolyte. The method includes incorporating white pigment particles into the anodized film obtained by the first anodization and the second anodization. The electrolytic solution for the second anodization is an electrolytic solution capable of forming at least one of a plurality of pores having an average pore diameter larger than that of the plurality of branching pores and the plurality of linearly extending pores.

According to the present disclosure, it is possible to provide an aluminum member with low angle dependence and a method for manufacturing the same.

FIG. 1 is a cross-sectional view showing an example of an aluminum member according to this embodiment. FIG. 2 is a diagram showing an example of a method for manufacturing an aluminum member according to this embodiment. FIG. 3 is a diagram illustrating a method of evaluating angle dependence of whiteness using a goniophotometer. FIG. 4 is a graph showing the angle dependence of Example 1, Comparative Examples 1 to 3, and Reference Example. FIG. 5 is a graph showing the angle dependence of Example 2, Comparative Examples 4 to 6, and Reference Example. FIG. 6 is a graph showing the angle dependence of Example 3, Comparative Examples 7 to 9, and Reference Example. FIG. 7 is a graph showing the angle dependence of Example 4, Comparative Examples 10 to 12, and Reference Example. FIG. 8 is an image obtained by FIB (focused ion beam) processing of the cross section of the aluminum member of Example 6 and magnifying it by 2,550 times with a TEM (transmission electron microscope). FIG. 9 is an image obtained by FIB-processing the cross section of the aluminum member of Example 6 and enlarging it 19,500 times with a TEM. FIG. 10 is an image obtained by FIB-processing the cross section of the aluminum member of Example 6 and enlarging it 43,000 times with a TEM. FIG. 11 is an image obtained by FIB-processing the cross section of the aluminum member of Comparative Example 14 and enlarging it 2,550 times with a TEM. FIG. 12 is an image obtained by FIB-processing the cross section of the aluminum member of Comparative Example 14 and enlarging it 19,500 times with a TEM. FIG. 13 is an image obtained by FIB-processing the cross section of the aluminum member of Comparative Example 14 and enlarging it 43,000 times with a TEM. FIG. 14 is an image obtained by FIB-processing the cross section of the aluminum member of Comparative Example 15 and enlarging it 2,550 times with a TEM. FIG. 15 is an image obtained by FIB-processing the cross section of the aluminum member of Comparative Example 15 and enlarging it 19,500 times with a TEM. FIG. 16 is an image obtained by FIB-processing the cross section of the aluminum member of Comparative Example 15 and enlarging it 43,000 times with a TEM. FIG. 17 is an image obtained by FIB-processing the cross section of the aluminum member of Example 7 and enlarging it 2,550 times with a TEM. FIG. 18 is an image obtained by FIB-processing the cross section of the aluminum member of Example 7 and enlarging it 19,500 times with a TEM. FIG. 19A is the result of line analysis of the aluminum member of Example 7 by EDS (energy dispersive X-ray spectroscopy). FIG. 19B is the result of line analysis of the aluminum member of Example 7 by EDS (energy dispersive X-ray spectroscopy).

Hereinafter, the aluminum member and the method for manufacturing the aluminum member according to the present embodiment will be described in detail with reference to the drawings. Note that the dimensional ratios in the drawings are exaggerated for convenience of explanation, and may differ from the actual ratios.

[Aluminum member]
As shown in FIG. 1 , an aluminum member 1 of this embodiment includes a base material 10 and an anodized film 20 . These components are described below.

(Base material 10)
The base material 10 is made of aluminum or an aluminum alloy. The substrate 10 may be made of, for example, a 1000 series alloy, a 3000 series alloy, a 5000 series alloy, a 6000 series alloy, or a 7000 series alloy. The base material 10 contains 0% by mass to 10% by mass of magnesium, 0.1% by mass or less of iron, and 0.1% by mass or less of silicon, and the balance is aluminum and inevitable impurities aluminum or aluminum It may be made of an alloy. The base material 10 contains 0% to 10% by mass of magnesium, 0.1% by mass or less of iron, 0.1% by mass or less of silicon, 10% by mass or less of zinc, and the balance being aluminum. and aluminum or an aluminum alloy that is an inevitable impurity.

Although magnesium does not necessarily need to be contained in the base material 10, if the base material 10 contains magnesium, aluminum and magnesium form a solid solution, and the strength of the base material 10 can be improved. Moreover, by setting the content of magnesium to 10% by mass or less, the strength of the base material 10 can be improved while suppressing the deterioration of the corrosion resistance of the base material 10 . The content of magnesium may be 0.5% by mass or more, or may be 1% by mass or more. Also, the content of magnesium may be 8% by mass or less, or may be 5% by mass or less.

　Iron and silicon are difficult to form a solid solution with aluminum. Therefore, when the base material 10 contains these elements, these elements tend to precipitate as a second phase containing iron or silicon in the anodized film 20 . When the anodized film 20 contains such a second phase, part of the light transmitted through the anodized film 20 is absorbed by the second phase, so that the aluminum member 1 appears yellowish. Sometimes it looks like The base material 10 may contain 0.05% by mass or less of iron. Also, the base material 10 may contain 0.05% by mass or less of silicon.

Zinc does not necessarily have to be contained in the base material 10, but if the base material 10 contains zinc, the strength of the base material 10 can be maintained. Moreover, by setting the zinc content to 10% by mass or less, the strength of the base material 10 is maintained while the appearance of the aluminum member 1 is not impaired. The content of zinc may be 8% by mass or less.

The base material 10 may contain inevitable impurities. In the present embodiment, unavoidable impurities mean those that are present in raw materials or that are unavoidably mixed in during the manufacturing process. Unavoidable impurities are essentially unnecessary impurities, but they are allowable impurities because they are trace amounts and do not affect the properties in aluminum or aluminum alloys. Unavoidable impurities that can be contained in aluminum or aluminum alloys are elements other than aluminum, magnesium, iron, and silicon. Examples of unavoidable impurities that may be contained in aluminum or aluminum alloys include copper, manganese, chromium, zinc, titanium, gallium, boron, vanadium, zirconium, lead, calcium and cobalt. The total amount of inevitable impurities in the aluminum or aluminum alloy is preferably 0.5% by mass or less, more preferably 0.2% by mass or less, further preferably 0.15% by mass or less, and 0 0.10 mass % or less is particularly preferred. In addition, the content of each element contained as inevitable impurities is preferably 0.05% by mass or less, more preferably 0.03% by mass or less, and further preferably 0.01% by mass or less. preferable.

The substrate 10 may have unevenness on the surface 11 on the anodized film 20 side. The unevenness formed on the surface 11 of the aluminum member 1 can diffusely reflect light passing through the anodized film 20 . The unevenness of the surface 11 can be formed by a roughening treatment described later. The arithmetic mean height Sa of the surface 11 of the substrate 10 may be between 0.3 μm and 0.5 μm. Also, the maximum height Sz of the surface 11 of the substrate 10 may be 3 μm to 5 μm. Also, the average length RSm of the roughness curve element of the surface 11 of the substrate 10 may be 6 μm to 10 μm. The arithmetic mean height Sa of the surface 11 of the substrate 10 is 0.3 μm to 0.5 μm, the maximum height Sz is 3 μm to 5 μm, and the average length RSm of the roughness curvilinear element is 6 μm to 10 μm. There may be.

By setting the arithmetic mean height Sa to 0.3 μm or more, the light transmitted through the anodized film 20 is diffusely reflected on the surface 11 of the substrate 10, so that the whiteness when the aluminum member 1 is viewed from an angle is further improved. can be higher. In addition, by setting the arithmetic mean height Sa to 0.5 μm or less, it is possible to suppress the light transmitted through the anodized film 20 from being trapped between the unevenness of the surface 11 of the base material 10. 1 can be suppressed from becoming gray in appearance. The arithmetic mean height Sa may be 0.4 μm or less. The arithmetic mean height Sa can be measured according to ISO25178.

By setting the maximum height Sz to 3 μm or more, the light transmitted through the anodized film 20 is diffusely reflected by the surface 11 of the substrate 10, so that the whiteness of the aluminum member 1 when viewed obliquely can be further increased. can be done. In addition, by setting the maximum height Sz to 5 μm or less, it is possible to suppress the light transmitted through the anodized film 20 from being trapped between the unevenness of the surface 11 of the base material 10, so that the appearance of the aluminum member 1 can be reduced. can be suppressed from turning gray. The maximum height Sz may be 4.7 μm or less. The maximum height Sz can be measured according to ISO25178.

By setting the average length RSm of the roughness curve element to 6 μm or more, the pitch of the irregularities on the surface 11 of the base material 10 does not become too small, so that the light transmitted through the anodized film 20 reaches the surface 11 of the base material 10. It is possible to suppress trapping between unevenness. Therefore, it is possible to prevent the appearance of the aluminum member 1 from becoming gray. Further, by setting the average length RSm of the roughness curve element to 10 μm or less, the pitch of the irregularities on the surface 11 of the substrate 10 does not become too large. Therefore, the light transmitted through the anodized film 20 is diffusely reflected by the surface 11 of the base material 10, and the whiteness of the aluminum member 1 when viewed obliquely can be further increased. The average length RSm of the roughness curvilinear element may be 7 μm or more and may be 9.5 μm or less. The average length RSm of roughness curve elements can be measured according to JIS B0601:2013 (ISO 4287:1997, Amd.1:2009).

The arithmetic mean height Sa, the maximum height Sz, and the average length RSm of the roughness curve element of the surface 11 of the base material 10 can be measured by removing the anodized film 20 from the base material 10 . Since the unevenness of the surface 11 of the substrate 10 is smoothed by the anodization, the unevenness of the surface 11 of the substrate 10 before anodization and the unevenness of the surface 11 of the substrate 10 after anodization are different in shape. There is a risk that Therefore, in this embodiment, the shape of the surface 11 of the substrate 10 after the anodized film 20 is removed is measured. A method for removing the anodized film 20 from the substrate 10 is not particularly limited. For example, according to JIS H8688:2013 (a method of measuring the mass per unit area of anodized films of aluminum and aluminum alloys), the aluminum member 1 is immersed in a chromic acid (VI) phosphate solution to dissolve and remove the anodized film 20. can do.

The shape and thickness of the base material 10 are not particularly limited, and can be appropriately changed according to the application. Further, the base material 10 may be processed or heat treated.

(Anodized film 20)
Anodized film 20 is provided on surface 11 of substrate 10 . Such an anodized film 20 can improve corrosion resistance, wear resistance, and the like. Anodized film 20 includes barrier layer 21 , first porous layer 22 , and second porous layer 23 . The second porous layer 23 may be the outermost layer of the anodized film 20 .

The barrier layer 21 is in contact with the surface 11 of the substrate 10. Barrier layer 21 is a dense, non-porous layer. Although the thickness of the barrier layer 21 is not particularly limited, it may be, for example, 1 nm or more, or 10 nm or more. Also, the thickness of the barrier layer 21 may be 500 nm or less, or may be 300 nm or less.

The barrier layer 21 contains aluminum oxide. In addition to aluminum and oxygen, the barrier layer 21 includes sulfur, carbon, sodium, potassium, phosphorus, silicon, nitrogen, which is an element derived from the components of the solution of the electrolytic solution used in the anodization, and nitrogen, which is a constituent element of ammonia. It may contain elements such as In the barrier layer 21 and the first porous layer 22 produced by the two-stage electrolysis method in which the porous type electrolytic solution is combined, the whiteness of the aluminum member 1 is adjusted by the color tone of the film itself obtained by the electrolytic solution components and the refraction of incident light. can be even higher.

The first porous layer 22 is in contact with the surface of the barrier layer 21 opposite to the substrate 10 . The first porous layer 22 may have a plurality of branched holes. Each hole of the first porous layer 22 has a dendritic structure, and the first porous layer 22 is provided with a plurality of holes extending while branching from the surface of the barrier layer 21 toward the second porous layer 23 . good too. The first porous layer 22 is provided with linear holes extending from the surface of the barrier layer 21 toward the second porous layer 23, and holes branching from the linear holes may be provided. The average pore diameter of the plurality of pores of the first porous layer 22 is, for example, within the range of 5 nm to 350 nm. The average pore size of the first porous layer 22 may be 10 nm or more, or may be 20 nm or more. Also, the average pore size of the first porous layer 22 may be 300 nm or less. The average pore diameter of the plurality of pores in the first porous layer 22 may be larger than the average pore diameter of the plurality of pores in the second porous layer 23 .

The thickness of the first porous layer 22 is not particularly limited, but may be 10 nm or more and 5000 nm or less. By setting the thickness of the first porous layer 22 to 10 nm or more, the whiteness of the aluminum member 1 can be further improved. By setting the thickness of the first porous layer 22 to 5000 nm or less, it is possible to maintain a high degree of whiteness when the anodized film 20 is formed. The thickness of the first porous layer 22 may be 50 nm or more, or may be 100 nm or more. The thickness of the first porous layer 22 may be 4000 nm or less, or may be 3500 nm or less.

The first porous layer 22 contains aluminum oxide. In addition to aluminum and oxygen, the first porous layer 22 contains carboxyl groups such as sulfuric acid, phosphoric acid and their salts, oxalic acid, salicylic acid, citric acid, maleic acid and tartaric acid derived from the electrolytic solution for anodization. Acids and salts thereof, as well as compounds such as silicates and ammonium salts may also be included. Salts include sodium and potassium salts. Since the first porous layer 22 contains the above elements, the first porous layer 22 becomes white, so that the aluminum member 1 with a higher degree of whiteness can be obtained.

The second porous layer 23 is in contact with the surface of the first porous layer 22 opposite to the barrier layer 21 . The second porous layer 23 is arranged as the outermost layer of the aluminum member 1 and may be exposed. The second porous layer 23 has a plurality of holes aligned and linearly extending from the surface in contact with the first porous layer 22 toward the exposed surface 24 . The pores of the second porous layer 23 may be connected to the pores of the first porous layer 22 . The average pore diameter of the plurality of pores of the second porous layer 23 is, for example, within the range of 5 nm to 200 nm. The average pore diameter of the second porous layer 23 may be 8 nm or more, or may be 10 nm or more. Also, the average pore size of the second porous layer 23 may be 100 nm or less, 50 nm or less, or 30 nm or less.

The thickness of the second porous layer 23 is not particularly limited, but may be 2 μm or more and 50 μm or less. By setting the thickness of the second porous layer 23 to 2 μm or more, the interference color of the anodized film 20 formed on the base material 10 can be suppressed, and the L ^* value of the aluminum member 1 can be improved. can be done. By setting the thickness of the second porous layer 23 to 50 μm or less, dissolution during the formation of the anodized film 20 can be reduced. The thickness of the second porous layer 23 may be 5 μm or more, or may be 8 μm or more. Also, the thickness of the second porous layer 23 may be 25 μm or less, or may be 15 μm or less.

The second porous layer 23 contains aluminum oxide. In addition to aluminum oxide, the second porous layer 23 contains a carboxylic acid such as sulfuric acid, amidosulfuric acid, phosphoric acid and their salts, oxalic acid, salicylic acid, citric acid, maleic acid and tartaric acid derived from the electrolytic solution for anodization. Acids containing groups and salts thereof, as well as compounds such as silicates and ammonium salts may be included. Salts include sodium and potassium salts. Since the second porous layer 23 contains the above compound, the transparency of the second porous layer 23 is increased, so that the light diffused by the first porous layer 22 is easily transmitted, and the whiteness is maintained at a high level. The aluminum member 1 is obtained.

The first porous layer 22 has at least one of a plurality of branched pores and a plurality of pores with an average pore size larger than that of the second porous layer 23 . That is, the first porous layer 22 may have a plurality of branched pores, may have a plurality of pores with an average pore diameter larger than that of the second porous layer 23, and may have a plurality of pores with an average pore diameter larger than that of the second porous layer 23. may have a plurality of branched pores with a larger average pore size. Thereby, the diffuse reflection in the first porous layer 22 can be promoted, and the angle dependence of the whiteness can be reduced. In this specification, the average pore diameter is the average value obtained by observing the cross section of the aluminum member 1 with a transmission electron microscope and measuring 10 or more pores.

The anodized film 20 incorporates white pigment particles. The white pigment particles may be arranged in at least one of the pores of the first porous layer 22 and the pores of the second porous layer 23 . By incorporating the white pigment particles into the anodized film 20, angle dependence can be improved.

The white pigment particles may contain at least one of organic pigment particles and inorganic pigment particles, but preferably contain inorganic pigment particles. The inorganic pigment particles may contain at least one selected from the group consisting of titanium oxide, aluminum oxide, zinc oxide and zinc sulfide. The white pigment particles may be spherical, elliptical, polygonal, plate-like, scale-like, needle-like, amorphous and mixtures thereof.

The average particle size of the white pigment particles may be smaller than the average pore size of the first porous layer 22 . Also, the average particle size of the white pigment particles may be smaller than the average pore size of the second porous layer 23 . The average particle size of the white pigment particles may be, for example, 10 nm or more and 200 nm or less. By setting the average particle size of the white pigment particles to 10 nm or more, the angle dependence can be sufficiently reduced. In addition, by setting the average particle diameter of the white pigment particles to 200 nm or less, the white pigment particles can easily enter the pores of the first porous layer 22 and the pores of the second porous layer 23. Many white pigment particles can be efficiently incorporated. The average particle size of the white pigment particles may be 13 nm or more, or 15 nm or more. Also, the average particle size of the white pigment particles may be 150 nm or less, or may be 100 nm or less. As used herein, the average particle size is the average value of particle sizes actually measured using a microscope such as a SEM (scanning electron microscope).

The plurality of pores of the first porous layer 22 and the plurality of pores of the second porous layer 23 may have a sealant containing aluminum hydrate in which aluminum is hydrated. You don't have to. The sealant may contain a nickel compound. Also, instead of the sealing treatment, it may be coated with a transparent organic material, inorganic material, or composite material, or it may not be coated. Examples of organic material coatings include resin coatings such as acrylic resins, urethane resins, and fluorine resins. Examples of inorganic material coatings include DLC (Diamond-like Carbon), sputtered films of metals such as silicon, and Permeate (registered trademark) series manufactured by D&D Co., Ltd. Examples include inorganic coating films containing inorganic components. Examples of composite coatings include coatings that include resins and inorganic materials.

The arithmetic mean height Sa of the exposed surface 24 of the anodized film 20 may be 0 μm to 0.45 μm. By setting the arithmetic mean height Sa of the surface 24 to 0.45 μm or less, part of the light is reflected on the surface 24 of the anodized film 20, so that the whiteness of the aluminum member 1 can be further improved. The arithmetic mean height Sa can be measured according to ISO25178. Further, the arithmetic mean height Sa of the surface 24 of the anodized film 20 can be adjusted by polishing the surface 24 or the like.

The L ^* value in the L ^* a ^* b ^* color system of the aluminum member 1 measured from the anodized film 20 side is 82.5 to 100, the a ^* value is −1 to +1, and the b ^* value is − It may be from 1.5 to +1.5. The L ^* value, a ^* value and b ^* value in the L ^* a*b ^* color system conform to JIS Z8781-4:2013 ( ^Colorimetry -Part 4: CIE 1976 L*a*b* color space). can be asked for. The L ^* value, a ^* value and b ^* value can be measured using a color difference meter or the like, and are measured under conditions such as a diffuse illumination vertical light receiving method (D/0), a viewing angle of 2°, and a C light source. be able to.

By setting the L ^* value to 82.5 or more, the brightness is improved, so that the whiteness of the aluminum member 1 can be further improved. Also, the upper limit of the L ^* value is not particularly limited, and is 100, which is the maximum value of L ^* . The L ^* value may be 85 or greater, or may be 87.5 or greater.

In addition, by setting the a ^* value to −1 to +1 and the b ^* value to −1.5 to +1.5, the saturation becomes close to 0, so that the aluminum member 1 can be red, yellow, green, blue, etc. can be suppressed, and the whiteness of the aluminum member 1 can be further improved. The a ^* value may be −0.8 to +0.8, and the b ^* value may be −0.8 to +0.8.

When the reflection intensity on the anodized film 20 side is measured using a goniophotometer at a detector angle of -80 degrees to +20 degrees, the ratio of the maximum reflection intensity to the minimum reflection intensity may be 18 or less. When the above ratio is 18 or less, the aluminum member 1 looks white even when viewed from various angles, so the angle dependence of the whiteness degree can be further reduced. The lower limit of the ratio is 1 because the smaller the ratio, the lower the angle dependence.

As described above, the aluminum member 1 according to this embodiment includes the base material 10 made of aluminum or an aluminum alloy and the anodized film 20 . The anodized film 20 includes a barrier layer 21 in contact with the surface 11 of the substrate 10 and a first porous layer 22 in contact with the surface of the barrier layer 21 opposite to the substrate 10 . The anodic oxide film 20 is in contact with the surface of the first porous layer 22 opposite to the barrier layer 21 and has a plurality of holes extending linearly in alignment toward the surface 24 exposed from the surface in contact with the first porous layer 22 . It includes a second porous layer 23 having a The first porous layer 22 has at least one of a plurality of branched pores and a plurality of pores having an average pore size larger than that of the second porous layer 23 . The anodized film 20 incorporates white pigment particles.

The second porous layer 23 has a plurality of linearly extending holes and thus has high translucency, and most of the incident light reaches the first porous layer 22 without being absorbed by the second porous layer 23 . The first porous layer 22 has at least one of a plurality of branched pores and a plurality of pores having an average pore size larger than that of the second porous layer 23 . Therefore, the light passing through the first porous layer 22 is diffusely reflected by the first porous layer 22 . The light reflected by the surface 11 of the substrate 10 is further diffusely reflected by the first porous layer 22 and passes through the second porous layer 23 . Therefore, the aluminum member 1 of the present embodiment is presumed to have low angle dependence of whiteness. In addition, as described above, the second porous layer 23 has high translucency, and a large amount of light is reflected on the surface 11 of the base material 10 without being absorbed by the second porous layer 23. Therefore, the aluminum member having a high degree of whiteness can be used. 1 is obtained. Furthermore, since the anodized film 20 incorporates white pigment particles, the angle dependence is further improved. Since the aluminum member 1 has a paper-like white appearance, it can be preferably used for housings such as smartphones and personal computers.

[Manufacturing method of aluminum member]
As shown in FIG. 2, the method for manufacturing the aluminum member 1 includes a roughening treatment step S1, an etching step S2, a first anodization step S3, a second anodization step S4, and a pigment incorporation step S5. , and a sealing step S6. Each step will be described in detail below.

(Roughening treatment step S1)
In the roughening treatment step S1, irregularities are formed on the surface 11 of the base material 10 made of aluminum or an aluminum alloy. Although the roughening treatment step S1 is not an essential step, it can make the appearance of the aluminum member 1 whiter. The substrate 10 forming the unevenness may be produced by, for example, preparing a molten metal containing a predetermined element, casting, extruding, rolling, heat treating, or the like. Further, the base material 10 forming unevenness may be used as it is after casting, after rolling, or after heat treatment, without performing any particular surface treatment. Further, the substrate 10 forming the irregularities may be used by grinding with a milling machine, polishing the surface 11 with emery paper, buffing, chemical polishing, electropolishing, or the like. The surface 11 of the base material 10 forming irregularities may be polished so that the arithmetic mean height Sa is approximately less than 100 nm. By setting the arithmetic mean height Sa of the surface 11 of the substrate 10 to less than 100 nm, the brightness of the substrate 10 is increased. Therefore, it is possible to obtain the aluminum member 1 having a paper-like white appearance even after the unevenness formation of the surface 11, the etching step S2, the first anodization step S3, and the second anodization step S4.

The unevenness of the surface 11 of the base material 10 may be formed by, for example, blasting. In the blasting process, particles can collide with the surface 11 of the substrate 10 to form unevenness. The blasting method is not particularly limited, and for example, at least one of wet blasting and dry blasting can be used. In the roughening treatment step S1, unevenness may be formed by colliding particles having an average particle diameter of 20 μm or less against the surface 11 of the substrate 10 . By setting the average particle size to 20 μm or less, it is possible to suppress absorption of the light passing through the anodized film 20 by the unevenness of the surface 11 of the substrate 10, thereby making the appearance of the aluminum member 1 whiter. be able to.

The average particle size of the blasted particles may be 10.5 μm or less. On the other hand, the lower limit of the average particle size is not particularly limited, but may be 2 μm or more. By setting the average particle size to 2 μm or more, the unevenness is appropriately formed on the surface 11 of the substrate 10 , so that the light passing through the anodized film 20 can be diffusely reflected. Therefore, even when viewed obliquely from different angles, the aluminum member 1 looks white, so that the aluminum member 1 can be made white like paper. The average particle size represents the particle size when the cumulative value of the particle size distribution on a volume basis is 50%, and can be measured by, for example, a laser diffraction/scattering method.

Examples of particles used for blasting include ceramic beads containing silicon carbide, boron carbide, boron nitride, alumina, zirconia, etc., metal beads containing stainless steel, steel, etc., resin beads containing nylon, polyester, melamine resins, etc. Examples include glass beads including glass and the like. In the case of wet blasting, the particles can be mixed with a liquid such as water and sprayed onto the substrate 10 . Conditions such as the injection pressure and the total number of particles in the blasting process are not particularly limited, and can be appropriately changed according to the state of the substrate 10 and the like. In the blasting process, the particles may collide with the surface of the substrate 10 so that the incident angle is less than or equal to a predetermined value. The incident angle may be 60 degrees or less, 45 degrees or less, 30 degrees or less, 15 degrees or less, or 5 degrees or less.

The method of forming unevenness on the surface 11 of the base material 10 is not limited to blasting, and may be formed by other methods such as laser processing and etching using a surface-roughening agent. In laser processing, unevenness is formed by irradiating the surface 11 of the base material 10 with laser light. The diameter, depth and pitch of the recesses and protrusions on the surface 11 of the base material 10 can be adjusted by adjusting the spot diameter, wavelength, output, frequency and pulse width of the laser light, the moving speed of the laser light with respect to the base material 10, and the like. can be changed by In the roughening treatment by etching, for example, unevenness may be formed by etching with a chemical containing fluoride such as Arsatin (registered trademark) OL-25 manufactured by Okuno Chemical Industries Co., Ltd. The depth of the recesses and the height of the protrusions on the surface 11 of the substrate 10 can be changed by adjusting the temperature, concentration and time of the etchant.

(Etching step S2)
The etching step S2 is not an essential step, but can remove the corners of the unevenness of the surface 11 of the base material 10 formed in the roughening treatment step S1 and smooth the unevenness. Etching conditions are not particularly limited as long as an aluminum member 1 having a high degree of whiteness can be obtained.

In the etching step S2, the roughened base material 10 may be etched with at least one of an acidic solution and an alkaline solution. As the acidic solution, for example, an aqueous solution of hydrochloric acid, sulfuric acid, nitric acid, or the like can be used. Moreover, as an alkaline solution, aqueous solutions, such as sodium hydroxide, potassium hydroxide, and sodium carbonate, can be used, for example. The concentrations of the acidic solution and the alkaline solution are not particularly limited, but when using an aqueous sodium hydroxide solution, it may be, for example, 10 g/L to 100 g/L.

The etching time and etching temperature are also not particularly limited, and can be appropriately adjusted according to the state of the substrate 10 and the etching solution. For example, the etching time is 5 seconds to 90 seconds and the etching temperature is 40.degree. C. to 60.degree.

(First anodizing step S3)
In the first anodizing step S3, the substrate 10 having the unevenness is first anodized with an electrolytic solution capable of forming a plurality of linearly aligned holes. The electrolytic solution used in the first anodization is not particularly limited as long as it can form a plurality of straight holes in the second porous layer 23 . The electrolytic solution may be, for example, an aqueous solution containing at least one electrolyte selected from the group consisting of sulfuric acid, amidosulfuric acid, phosphoric acid and salts thereof, acids containing carboxyl groups, and salts thereof. Acids containing a carboxyl group include at least one acid selected from the group consisting of oxalic acid, salicylic acid, citric acid, maleic acid and tartaric acid. Among these, the electrolytic solution for the first anodization preferably contains at least one selected from the group consisting of sulfuric acid, amidosulfuric acid and compounds having a carboxyl group. The electrolytic solution for the first anodization is preferably an acidic electrolytic solution, and the pH of the electrolytic solution is, for example, 0-2. The concentration of the electrolyte in the electrolytic solution is, for example, 1 g/L to 600 g/L.

The conditions for the first anodization are not particularly limited, and can be appropriately adjusted according to the state of the substrate 10 and the like. The temperature of the electrolyte may be, for example, 0°C to 30°C. Current densities may be, for example, between 1 mA/cm ² and 50 mA/cm ² . The electrolysis time may be, for example, 10 minutes to 50 minutes.

(Second anodizing step S4)
In the second anodizing step S4, the first anodized substrate 10 is second anodized with an electrolytic solution. The electrolytic solution for the second anodization is an electrolytic solution capable of forming at least one of a plurality of branching pores and a plurality of pores having an average pore diameter larger than that of the plurality of linearly extending pores. The electrolytic solution used in the second anodizing step S4 forms at least one of the plurality of branched pores in the first porous layer 22 and the plurality of pores having an average pore diameter larger than the plurality of linearly extending pores. It is not particularly limited as long as it can be formed. The electrolytic solution may be an aqueous solution containing at least one electrolyte selected from the group consisting of compounds having a carboxyl group such as tartaric acid, phosphoric acid, chromic acid, boric acid, and salts thereof. Among these, the electrolytic solution for the second anodization preferably contains at least one selected from the group consisting of a compound having a carboxyl group, phosphoric acid, and salts thereof. Specifically, the electrolytic solution for the second anodization is preferably an aqueous tartrate solution. The aqueous tartrate solution can form at least a plurality of branching pores. Also, the electrolytic solution for the second anodization is preferably an aqueous solution of phosphoric acid. The phosphoric acid aqueous solution can form a plurality of pores having a larger average pore diameter than the plurality of linearly extending pores. The electrolytic solution for the second anodization may contain at least one selected from the group consisting of sodium, potassium and ammonia. The electrolyte for the second anodization may be an acidic or alkaline electrolyte. When the electrolyte for the second anodization is an alkaline electrolyte, the pH of the electrolyte is, for example, 9-14. In order to make the electrolyte alkaline, the electrolyte may be mixed with sodium hydroxide or the like. The concentration of the electrolyte in the electrolytic solution is, for example, 0.5 g/L to 300 g/L.

The conditions for the second anodization are not particularly limited, and can be appropriately adjusted according to the state of the substrate 10 and the like. By way of example, the temperature of the electrolyte may be, for example, 0°C to 40°C. The voltage may be, for example, 2V to 500V. The amount of electricity per unit area may be, for example, 0.05 C/cm ² to 40 C/cm ² . The electrolysis time may be, for example, 0.1 minutes to 180 minutes.

(Pigment incorporation step S5)
In the pigment incorporation step S5, white pigment particles are incorporated into the anodized film 20 obtained by the first anodization and the second anodization. The anodized film 20 includes a barrier layer 21 , a first porous layer 22 and a second porous layer 23 .

The white pigment particles may be incorporated into the anodized film 20 by electrophoresis, or may be incorporated by a method such as an immersion method that does not involve electrophoresis. In the electrophoresis method, electrodes are immersed in a suspension containing white pigment particles and a dispersion medium for dispersing the white pigment particles, and a voltage is applied between the electrodes. When a voltage is applied, an electrophoresis phenomenon causes the white pigment particles to migrate in the dispersion medium toward the electrodes. For example, white pigment particles can be incorporated into the anodized film 20 by using a member including the substrate 10 and the anodized film 20 as an anode or a cathode.

The white pigment particles may be negatively charged or positively charged. When the white pigment particles are negatively charged, a member including the base material 10 and the anodized film 20 is installed at the anode, and when the white pigment particles are positively charged, the base material 10 and the anodized film A member with a coating 20 is placed on the cathode. Carbon may be placed on the electrode on the opposite side of the electrode on which the member is placed.

The positive and negative charges of the white pigment particles can be adjusted by the type of white pigment particles and the pH of the suspension. A direct current is normally passed between the electrodes from a power source. The dispersion medium may be an electrolyte, such as an aqueous solution. The pH of the dispersion may be, for example, 8 or more and 11 or less. The applied voltage in electrophoresis may be, for example, 100 V or more and 200 V or less. Also, the voltage application time in electrophoresis may be 1 minute or more and 60 minutes or less. The temperature of the electrolyte in electrophoresis may be, for example, 0°C to 40°C. As for the material and average particle size of the white pigment particles, those described above can be employed.

In the immersion method, the first anodized and second anodized members are immersed in a suspension containing white pigment particles and a dispersion medium for dispersing the white pigment particles. Thereby, the white pigment particles can be incorporated into the anodized film 20 . A suspension similar to that used in electrophoresis may be used.

The content of white pigment particles in the suspension may be 1% by mass or more and 50% by mass or less. The suspension may contain additives including a dispersant for dispersing the white pigment particles in addition to the white pigment particles and the dispersion medium.

(Sealing treatment step S6)
Although the sealing step S6 is not an essential step, by sealing the pores of the first porous layer 22 and the pores of the second porous layer 23, the corrosion resistance of the aluminum member 1 can be improved. The pore-sealing treatment can be performed by a known method, such as hot water, hot steam, aqueous nickel acetate solution, nickel fluoride, silicate, and combinations thereof. By the pore-sealing treatment, an aluminum hydrate in which aluminum is hydrated is produced in the pores.

As described above, in the method for manufacturing the aluminum member 1 according to the present embodiment, the substrate 10 made of aluminum or an aluminum alloy is coated with an electrolytic solution capable of forming a plurality of linearly extending holes. A first anodic oxidation step S3 is included. The method includes a second anodizing step S4 of second anodizing the first anodized substrate 10 with an electrolytic solution. The method includes a step of incorporating white pigment particles into the anodized film 20 obtained by the first anodization and the second anodization. The electrolytic solution for the second anodization is an electrolytic solution capable of forming at least one of a plurality of pores having an average pore diameter larger than that of the plurality of branching pores and the plurality of linearly extending pores.

Since the above method includes the first anodizing step S3 and the second anodizing step S4, the anodized film 20 is formed. In the first anodizing step S<b>3 , a plurality of linearly aligned holes are formed in the anodized film 20 . In the second anodizing step S<b>4 , at least one of a plurality of pores having an average pore diameter larger than that of the plurality of branching pores and the plurality of linearly extending pores is formed in the anodized film 20 . Therefore, the anodized film 20 including the barrier layer 21, the first porous layer 22, and the second porous layer 23 is formed by the first anodizing step S3 and the second anodizing step S4. Then, the white pigment particles are taken into the anodized film 20 by the pigment taking-in step S5. Therefore, the aluminum member 1 having low angular dependence can be manufactured by the above method.

Hereinafter, the present embodiment will be described in more detail with examples, comparative examples, and reference examples, but the present embodiment is not limited to these.

[Example 1]
(roughening treatment)
A 50 mm long and 50 mm wide piece was cut from a rolled and annealed 5000-series aluminum alloy plate having a thickness of 3 mm. The 5000 series aluminum alloy contains 4.31% by mass of magnesium, 0.02% by mass of iron and 0.02% by mass of silicon, with the balance being aluminum (Al) and unavoidable impurities.

Particles were made to collide with the base material by dry blasting to form unevenness on the surface of the base material. As the particles, Fujirandom WA particle number 1200 (alumina particles, maximum particle size: 27.0 μm, average particle size: 9.5±0.8 μm) manufactured by Fuji Seisakusho Co., Ltd. was used. After blasting, the substrate was degreased by immersing it in a 200 g/L nitric acid aqueous solution at room temperature (about 20° C.) for 3 minutes.

(etching)
The substrate on which the unevenness is formed is immersed in an aqueous sodium hydroxide solution with a concentration of 100 g/L at a temperature of 60° C. for 60 seconds for etching, and then immersed in an aqueous nitric acid solution with a concentration of 200 g/L for 2 minutes at room temperature (about 20° C.). to remove the smut.

(First anodizing)
The etched substrate was immersed in an acidic aqueous solution of pH 0 containing sulfuric acid at a concentration of 180 g/L, and first anodized under electrolysis conditions of a temperature of 18° C., a current density of 15 mA/cm ² and an electrolysis time of 22 minutes.

(Second anodic oxidation)
The first anodized member was immersed in an alkaline aqueous solution of pH 13 containing disodium tartrate dihydrate at a concentration of 200 g/L and sodium hydroxide at a concentration of 5 g/L. Then, the member was second anodized under the electrolysis conditions of temperature 5° C., voltage 100 V, amount of electricity 1 C/cm ² , pressure rise rate 1 V/sec, and electrolysis time about 3 minutes.

(pigment)
A dispersion liquid in which titanium oxide particles (white pigment particles) having an average particle size of about 60 nm were dispersed was diluted. Then, the second anodized member was immersed in this diluted solution at 50° C. for 10 minutes, thereby depositing titanium oxide particles on the second anodized member.

(Pore sealing treatment)
The member on which the titanium oxide particles were deposited was sealed with a nickel acetate-based sealing material at 95° C. for 20 minutes. Thus, the aluminum member of this example was produced.

[Comparative Example 1]
An aluminum member was produced in the same manner as in Example 1, except that the second anodized member was sealed without depositing titanium oxide particles.

[Comparative Example 2]
An aluminum member was produced in the same manner as in Example 1 except that titanium oxide particles were deposited on the first anodized member to seal the pores without performing the second anodization.

[Comparative Example 3]
An aluminum member was produced in the same manner as in Example 1, except that the first anodized member was sealed without the second anodization and precipitation of titanium oxide particles.

[evaluation]
The surface properties (Sa, Sz and RSm) of the aluminum member obtained in each example, the first porous layer average pore size, the second porous layer average pore size, color tone, gloss and angle dependence were evaluated as follows. The results are shown in Tables 1 and 2.

(Arithmetic mean height Sa and maximum height Sz)
First, according to JIS H8688:2013, the aluminum member obtained as described above was immersed in a chromic acid (VI) phosphate solution to dissolve and remove the anodized film. Next, the arithmetic mean height Sa and the maximum height Sz of the surface of the anodized film side of the substrate are measured using a three-dimensional white interference microscope Contour GT-I manufactured by Bruker AXS Co., Ltd., according to ISO25178. It was measured. The arithmetic mean height Sa and the maximum height Sz were measured under the conditions of a measurement range of 60 μm×79 μm, an objective lens of 115×, and an internal lens of 1×.

(Average length RSm of roughness curve element)
First, according to JIS H8688:2013, the anodized film of the aluminum member obtained as described above was dissolved in a chromic acid (VI) phosphate solution and removed. Next, the average length RSm of the roughness curve element on the surface of the anodized film side of the substrate is measured using a three-dimensional white interference microscope Contour GT-I of Bruker AXS Co., Ltd., to JIS B0601: 2013. Measured according to The average length RSm of the roughness curvilinear element was measured under the conditions of a cutoff λc of 80 μm, an objective lens of 115×, an internal lens of 1×, and a measurement distance of 79 μm.

(average pore diameter)
A cross section of the aluminum member was observed with a transmission electron microscope to measure the average pore size of the porous layer.

(color tone)
Based on JIS Z8722, using a color difference meter CR400 manufactured by Konica Minolta Japan Co., Ltd., the color tone of the aluminum member was measured from the surface of the anodized film to obtain the L ^* value, a ^* value and b ^* value. For color tone, the illumination/light-receiving optical system is a diffuse illumination vertical light-receiving system (D/0), the observation condition is CIE 2° visual field color matching function approximation, the light source is C light source, and the color system is L ^* a ^* b ^* conditions. measured in

(gloss)
Using a gloss meter Gloss Mobile MODEL GM-1 manufactured by Suga Test Instruments Co., Ltd., the gloss of the anodized film side surface of the aluminum member was measured. Gloss was measured at angles of incidence of 20°, 60° and 99.3° when light was incident parallel to and perpendicular to the rolled surface of the substrate, respectively.

(angle dependence)
The angular dependence of the whiteness of the aluminum member was evaluated using a goniophotometer (GP-2 type) manufactured by Nikka Densoku Co., Ltd. Specifically, as shown in FIG. 3, the aluminum member 101 was irradiated with light, and the intensity of the light received by the detector 102 was measured. The detector 102 is rotatably provided with a predetermined distance around the aluminum member 101 . When the detector 102 is arranged at a position where the incident angle of the incident light 103 is 45 degrees and the reflection angle of the reflected light 104 is 45 degrees, the detector angle is 0 degrees. The reflection intensity of the reflected light 104 reflected by the aluminum member 101 on the anodized film side was measured at intervals of 0.5 degrees in the detector angle range of -80 degrees to +40 degrees. Then, the ratio of the maximum reflection intensity to the minimum reflection intensity (maximum reflection intensity/minimum reflection intensity) in the detector angle range of -80 degrees to +20 degrees was calculated.

As shown in Tables 1 and 2, the aluminum member of Example 1 has an L ^* value of 80 or more, an a ^* value of −1 to +1, and a b ^* value of −1.5 to +1.5. Met. In addition, as shown in FIG. 4, the aluminum member of Example 1, compared with the aluminum members of Comparative Examples 1 to 3, had a lower angle dependence of the light reflection intensity like the copy paper of Reference Example. . In Example 1, since the gloss value measured from an oblique angle such as 20° and 60° is smaller than that in Comparative Examples 1 to 3, it is said that the angle dependency is improved because the light from the oblique direction is diffused. Conceivable.

Next, aluminum members according to Example 2 and Comparative Examples 4 and 6 were produced, and the surface properties, first porous layer average pore diameter, second porous layer average pore diameter, color tone, gloss, and angle dependence were measured in the same manner as above. evaluated to Tables 3 and 4 show the results.

[Example 2]
An aluminum member was produced in the same manner as in Example 1, except that the second anodized member was sealed with water vapor at 130° C. for 30 minutes.

[Comparative Example 4]
An aluminum member was produced in the same manner as in Example 2, except that the second anodized member was sealed without depositing titanium oxide particles.

[Comparative Example 5]
An aluminum member was produced in the same manner as in Example 2, except that titanium oxide particles were deposited on the first anodized member to seal the pores without performing the second anodization.

[Comparative Example 6]
An aluminum member was produced in the same manner as in Example 2, except that the first anodized member was sealed without the second anodization and precipitation of titanium oxide particles.

As shown in Tables 3 and 4, the aluminum member of Example 2 has an L ^* value of 80 or more, an a ^* value of −1 to +1, and a b ^* value of −1.5 to +1.5. Met. Further, as shown in FIG. 5, compared with the aluminum members of Comparative Examples 4 to 6, the aluminum member of Example 2 had lower angle dependence of the light reflection intensity like the copy paper of the reference example. . In Example 2, since the gloss value measured from an oblique angle such as 20° and 60° is smaller than that in Comparative Examples 4 to 6, it is said that angle dependence is improved because light from an oblique direction is diffused. Conceivable.

Next, aluminum members according to Example 3 and Comparative Examples 7 to 9 were produced, and the surface properties, first porous layer average pore diameter, second porous layer average pore diameter, color tone, gloss and angle dependence were measured in the same manner as above. evaluated to Tables 5 and 6 show the results.

[Example 3]
An aluminum member was produced in the same manner as in Example 1, except that the substrate was etched without being blasted.

[Comparative Example 7]
An aluminum member was produced in the same manner as in Example 3, except that the second anodized member was sealed without depositing titanium oxide particles.

[Comparative Example 8]
An aluminum member was produced in the same manner as in Example 3, except that titanium oxide particles were deposited on the first anodized member to seal the pores without performing the second anodization.

[Comparative Example 9]
An aluminum member was produced in the same manner as in Example 3, except that the first anodized member was sealed without the second anodization and precipitation of titanium oxide particles.

As shown in Tables 5 and 6, the aluminum member of Example 3 has an L ^* value of 80 or more, an a ^* value of −1 to +1, and a b ^* value of −1.5 to +1.5. Met. In addition, as shown in FIG. 6, the aluminum member of Example 3, compared with the aluminum members of Comparative Examples 7 to 9, had a lower angular dependence of the light reflection intensity, like the copy paper of the reference example. . In Example 3, since the gloss value measured from an oblique direction such as 20° and 60° is smaller than that in Comparative Examples 7 to 9, it is said that the angle dependency is improved because the light from the oblique direction is diffused. Conceivable.

Next, aluminum members according to Example 4 and Comparative Examples 10 and 12 were produced, and the surface properties, first porous layer average pore diameter, second porous layer average pore diameter, color tone, gloss, and angle dependence were measured in the same manner as above. evaluated to The results are shown in Tables 7 and 8.

[Example 4]
An aluminum member was fabricated in the same manner as in Example 1, except that the substrate was etched without blasting, and the second anodized member was sealed with water vapor at 130° C. for 30 minutes.

[Comparative Example 10]
An aluminum member was produced in the same manner as in Example 4, except that the second anodized member was sealed without depositing titanium oxide particles.

[Comparative Example 11]
An aluminum member was produced in the same manner as in Example 4, except that titanium oxide particles were deposited on the first anodized member to seal the pores without performing the second anodization.

[Comparative Example 12]
An aluminum member was produced in the same manner as in Example 4, except that the first anodized member was sealed without the second anodization and precipitation of titanium oxide particles.

As shown in Tables 7 and 8, the aluminum member of Example 4 has an L ^* value of 80 or more, an a ^* value of −1 to +1, and a b ^* value of −1.5 to +1.5. Met. Further, as shown in FIG. 7, the aluminum member of Example 4, compared with the aluminum members of Comparative Examples 10 to 12, had lower angle dependency of the light reflection intensity like the copy paper of Reference Example. . In Example 4, since the gloss value measured from an oblique angle such as 20° and 60° is smaller than that in Comparative Examples 10 to 12, it is said that angle dependence is improved because light from an oblique direction is diffused. Conceivable.

Next, aluminum members according to Example 5, Comparative Examples 8 to 9, and Comparative Example 13 were produced, and surface characteristics, first porous layer average pore size, second porous layer average pore size, color tone, gloss, and angle dependence was evaluated as above. The results are shown in Tables 9 and 10.

[Example 5]
The first anodized member was immersed in an aqueous phosphoric acid solution (pH 1) with a concentration of 98 g/L. Then, the member was second anodized under the electrolysis conditions of temperature 5° C., voltage 100 V, amount of electricity 1 C/cm ² , pressure increase rate 1 V/sec, and electrolysis time about 4 minutes. An aluminum member was produced in the same manner as in Example 3 except for the above.

[Comparative Example 13]
An aluminum member was produced in the same manner as in Example 5, except that the second anodized member was sealed without depositing titanium oxide particles.

As shown in Tables 9 and 10, the aluminum member of Example 5 has an L ^* value of 80 or more, an a ^* value of −1 to +1, and a b ^* value of −1.5 to +1.5. Met. In addition, the aluminum member of Example 5, compared with the aluminum members of Comparative Examples 8 to 9 and 13, had a lower angle dependence of the light reflection intensity, like the copy paper of Reference Example. In Example 5, since the gloss value measured from an oblique angle such as 20 ° and 60 ° is smaller than in Comparative Examples 8 to 9 and Comparative Example 13, the angle dependence is due to the diffusion of light from an oblique direction. is thought to have improved.

From the results in Tables 1 to 10, the first anodization and the second anodization were performed as in Examples 1 to 4, and titanium oxide particles were added without significantly decreasing the L ^* value. , an aluminum member with low angle dependence can be obtained.

Next, in order to observe the cross section with a transmission electron microscope, an aluminum member was produced as follows.

[Example 6]
(roughening treatment)
A 50 mm long and 50 mm wide piece was cut from a rolled and annealed 5000-series aluminum alloy plate having a thickness of 3 mm. The 5000 series aluminum alloy contains 4.31% by mass of magnesium, 0.02% by mass of iron and 0.02% by mass of silicon, with the balance being aluminum (Al) and unavoidable impurities.

Particles were made to collide with the base material by dry blasting to form unevenness on the surface of the base material. Fujirandom WA particle number 1200 (alumina particles, maximum particle size: 27.0 μm, average particle size: 9.5±0.8 μm) manufactured by Fuji Seisakusho Co., Ltd. was used as the particles. After blasting, the substrate was degreased by immersing it in a 200 g/L nitric acid aqueous solution at room temperature (about 20° C.) for 3 minutes.

(etching)
After etching the substrate on which the unevenness is formed by immersing it in an aqueous sodium hydroxide solution with a concentration of 50 g/L at a temperature of 60° C. for 60 seconds, it is then immersed in an aqueous nitric acid solution with a concentration of 200 g/L for 2 minutes at room temperature (about 20° C.). to remove the smut.

(First anodizing)
The etched substrate was immersed in an acidic aqueous solution of pH 0 containing sulfuric acid at a concentration of 180 g/L, and first anodized under electrolysis conditions of a temperature of 18° C., a current density of 15 mA/cm ² and an electrolysis time of 11 minutes.

(Second anodic oxidation)
The first anodized member was immersed in an alkaline aqueous solution of pH 13 containing disodium tartrate dihydrate at a concentration of 106 g/L and sodium hydroxide at a concentration of 3 g/L. Then, the member was second anodized under the electrolysis conditions of a temperature of 5° C., a voltage of 160 V, an amount of electricity of 1 C/cm ² , a pressure rise rate of 1 V/sec, and an electrolysis time of 80 seconds. Thus, the aluminum member of this example was produced.

[Comparative Example 14]
An aluminum member of this example was produced in the same manner as in Example 6, except that the second anodization was not performed.

[Comparative Example 15]
An aluminum member was produced in the same manner as in Example 6 except that the first anodization was not performed, the voltage of the second anodization was 110 V, and the electrolysis time was 11 minutes.

Figures 8, 9 and 10 are images of the cross section of the aluminum member of Example 6 which was subjected to FIB processing and magnified by a transmission electron microscope at 2,550 times, 19,500 times and 43,000 times, respectively. 11, 12 and 13 are images obtained by FIB-processing the cross section of the aluminum member of Comparative Example 14 and magnifying the cross-section by a transmission electron microscope at 2,550 times, 19,500 times and 43,000 times, respectively. 14, 15 and 16 are images obtained by FIB-processing the cross section of the aluminum member of Comparative Example 15 and enlarging the cross-section by a transmission electron microscope at 2,550 times, 19,500 times and 43,000 times, respectively. As shown in FIGS. 8 to 16, the first porous layer has a plurality of branched pores, and the second porous layer has a plurality of linearly extending pores. From FIGS. 8 to 16 and the results of elemental analysis by EDS (not shown), the anodized film of Example 6 has a barrier layer and a first porous layer derived from the second anodization formed on the surface of the substrate. I found out. It was also found that a second porous layer derived from the first anodization was formed on the surface of the first porous layer.

Next, in order to confirm the state of the pigment, an aluminum member according to Example 7 was produced.

[Example 7]
An aluminum member was produced in the same manner as in Example 1 except that the electrolysis time of the first anodization was changed to 11 minutes, the sodium hydroxide concentration of the second anodization was changed to 5 g/L, and the sealing time was changed to 10 minutes.

17 and 18 are images obtained by FIB-processing the cross section of the aluminum member of Example 7 and enlarging it by 2,550 times and 19,500 times with a transmission electron microscope, respectively. 17 and 18 show cross-sectional states similar to FIGS. 8 to 10. In the aluminum member of Example 7, the first porous layer has a plurality of branching holes, and the second porous layer has a linear shape. It can be seen that it has a plurality of holes extending to the .

Next, the aluminum member of Example 7 was subjected to line analysis by EDS. Specifically, line analysis was performed on the portion indicated by line 1 in the "HAADF Detector" of FIG. 19A. As shown in FIGS. 19A and 19B, it was found that the titanium element derived from titanium oxide of the pigment was incorporated into the anodized film. In addition, there is a marked difference in contrast in the area indicated by the arrow in the SEM image, and line analysis also detected a high intensity of titanium in that area.

From the above results, it can be seen that the angle dependence is low for the aluminum member having the first porous layer and the second porous layer and having the white pigment particles incorporated in the anodized film.

Although the present embodiment has been described above with examples and comparative examples, the present embodiment is not limited to these, and various modifications are possible within the scope of the gist of the present embodiment.

Reference Signs List 1 aluminum member 10 substrate 11 surface 20 anodized film 21 barrier layer 22 first porous layer 23 second porous layer 24 surface

Claims (13)

1. a base material formed of aluminum or an aluminum alloy;
   a barrier layer in contact with the surface of the substrate; a first porous layer in contact with the surface of the barrier layer opposite to the substrate; an anodic oxide film comprising a second porous layer having a plurality of linearly aligned pores extending from the surface in contact with the first porous layer toward the exposed surface;
   with
   The first porous layer has at least one of a plurality of branched pores and a plurality of pores having an average pore size larger than that of the second porous layer,
   An aluminum member, wherein the anodized film incorporates white pigment particles.
2. The L* value in ^the L ^* a ^* b ^* color system of the aluminum member measured from the anodized film side is 82.5 to 100, the a ^* value is −1 to +1, and the b ^* value is − The aluminum member according to claim 1, which is 1.5 to +1.5.
3. 2. The ratio of the maximum reflection intensity to the minimum reflection intensity is 18 or less when the reflection intensity on the anodized film side is measured using a goniophotometer at a detector angle of −80 degrees to +20 degrees. 3. The aluminum member according to 2.
4. The aluminum member according to any one of claims 1 to 3, wherein the arithmetic mean height Sa of the surface of the base material is 0.3 µm to 0.5 µm.
5. The aluminum member according to any one of claims 1 to 4, wherein the maximum height Sz of the surface of the base material is 3 µm to 5 µm.
6. The aluminum member according to any one of claims 1 to 5, wherein the average length RSm of the roughness curve element on the surface of the base material is 6 µm to 10 µm.
7. a first anodizing step of first anodizing a substrate made of aluminum or an aluminum alloy with an electrolytic solution capable of forming a plurality of linearly aligned pores;
   a second anodizing step of second anodizing the first anodized substrate with an electrolytic solution;
   a step of incorporating white pigment particles into the anodized film obtained by the first anodization and the second anodization;
   including
   The electrolytic solution for the second anodization is an electrolytic solution capable of forming at least one of a plurality of branching holes and a plurality of holes having an average pore diameter larger than that of the plurality of linearly extending holes. manufacturing method.
8. The method for manufacturing an aluminum member according to claim 7, wherein the electrolytic solution for the first anodization is an acidic electrolytic solution, and the electrolytic solution for the second anodization is an acidic or alkaline electrolytic solution.
9. Further comprising a roughening treatment step of forming unevenness on the surface of the base material,
   9. The method for manufacturing an aluminum member according to claim 7, wherein in the first anodizing step, the substrate on which the irregularities are formed is first anodized.
10. The method for manufacturing an aluminum member according to claim 9, wherein in the roughening treatment step, particles having an average particle diameter of 20 µm or less are collided with the surface of the base material to form the unevenness.
11. The method for manufacturing an aluminum member according to any one of claims 7 to 10, wherein the electrolytic solution for the first anodization contains at least one selected from the group consisting of sulfuric acid, amidosulfuric acid and a compound having a carboxyl group.
12. The aluminum member production according to any one of claims 7 to 11, wherein the electrolytic solution for the second anodization contains at least one selected from the group consisting of a compound having a carboxyl group, phosphoric acid, and salts thereof. Method.
13. The method for manufacturing an aluminum member according to any one of claims 7 to 11, wherein the electrolytic solution for the second anodization contains at least one selected from the group consisting of sodium, potassium and ammonia.

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