JP2820584B2 - Electrolytic coloring method of aluminum material - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming a colored film on the surface of aluminum or an aluminum alloy (hereinafter collectively referred to as aluminum material) by utilizing light interference.

[0002]

2. Description of the Related Art As a method of electrolytically coloring an aluminum material, after forming an anodic oxide film on the aluminum material,
A secondary electrolytic coloring method has been put to practical use in which a metal or a metal compound is electrolytically deposited in micropores of an anodic oxide film in a metal salt-containing solution to form a color. The color tone obtained by this method is limited from a light brownish color to black. As a method for obtaining a multicolor, Japanese Patent Publication No. 54-13860 discloses that after an anodic oxide film is formed, an intermediate treatment for expanding micropores in an electrolytic bath containing phosphoric acid is performed, and then a solution containing a metal salt is formed. There is proposed a tertiary electrolytic coloring method in which AC electrolysis is performed. Light incident on the colored film formed by this method is reflected on the interface between the anodic oxide film and the aluminum material and on the surface of the electrolytic colored precipitate. Colors are generated by the interference effect in which interference occurs between these reflected lights. However, the range of the hue is narrow, and only light colors are obtained. Also, the coloring uniformity is poor.

[0003]

In the secondary electrolytic coloring, the lightness can be changed from a light color to a black color. In this case, as shown in FIG. 1, electrolytic deposits 4 are filled in micropores 3 of anodized film 2 formed on the surface of aluminum material 1. The height of the electrolytic deposit 4 is not uniform due to the influence of impurities in the aluminum material 1 and variations in the electric resistance of the barrier layer 5, and the like. Therefore, scattering and absorption of light here are remarkable, and the obtained hue is limited to brown. In the tertiary electrolysis method, an enlarged portion 6 is formed at the bottom of the fine hole 3 as shown in FIG.
Is filled with the electrolytic deposit 4. In this case, the principle of color development is as follows: the reflected light 7 on the upper surface of the electrolytic deposit 4 and the anodic oxide film 2
And the reflected light 8 at the interface of the aluminum material 1. The appearing interference color corresponds to the optical path difference between the reflected light 7 and the reflected light 8. The electrolytic deposit 4 is formed in an enlarged portion 6 of the micropore 3.
Therefore, compared to the case of the secondary electrolytic coloring, variations in individual heights are small, and the upper surface of the electrolytic deposit 4 forms one plane.

However, the height of the electrolytic deposit 4 is regulated by the enlarged portion 6 because the enlarged portion 6 formed at the bottom of the fine hole 3 by the intermediate treatment is low. Therefore, the optical path difference between the reflected light 7 and the reflected light 8 is limited, and the range of the hue to interfere is narrowed. In order to obtain a wide range of color tones, it is required to deposit electrolytic deposit 4 at a high level as shown in FIG. In this case, the electrolytic deposit 4 fills the small-diameter fine holes 3 beyond the enlarged portion 6. As a result, the height of each of the electrolytic deposits 4 becomes non-uniform, and the color changes to a brownish color without interference of light. In particular, when electrolytically coloring an aluminum material having a complicated shape, the height of the electrolytic deposit 4 is not uniform due to the influence of the potential distribution of the electrolytic cell, and different colors are formed in the same material. Color unevenness occurs.

As described above, it has been difficult to obtain a wide range of hues and obtain a uniform coloring property by the conventional electrolytic coloring. Japanese Patent Application Laid-Open No. 3-33802 also discloses an aluminum material which is similarly colored by light interference. However, it is possible to obtain a film having an excellent color uniformity and an arbitrary color tone with a high degree of freedom. Can not. The present invention has been devised in order to solve such a problem, and by devising the shape of the micropores formed in the anodic oxide film and the shape of the electrolytic deposit, the blue, green, and blue colors are improved. An object of the present invention is to form a film having a wide range of colors such as yellow and red and having a uniform color on the surface of an aluminum material.

[0006]

The electrolytic coloring method according to the present invention includes the following steps. First step: Anodizing step of forming an anodic oxide film on the surface of aluminum material Second step: Intermediate processing step of enlarging the bottom of fine pores of the anodic oxide film Third step: In a solution containing a metal salt and a barrier-type film forming agent Step of Adjusting Barrier Layer Thickness by Fourth Step: Continuously depositing electrolytic deposits in the microporous enlarged portions so that the upper surface of electrolytic deposits is maintained in the range of the microporous enlarged portions in the same solution. Electrolytic coloring step 5th step: immersing the aluminum material in the noble metal solution,
A step of substituting a part or all of the electrolytic deposit with a noble metal; a sixth step: applying a current density of 0.1 to 5 A / dm ^{2 to the} aluminum material in an inorganic acid, an organic acid or a mixed solution thereof;
Re-anodizing treatment by supplying a positive direct current in the step, and growing a porous anodic oxide film having a thickness corresponding to the target interference color below the layer substituted with the noble metal.

Hereinafter, each step will be described in detail. The various solutions used in each step do not dissolve aluminum and its alloy elements at the time of building bath, but become solutions in which aluminum and alloy elements are dissolved according to the transition of operation. Therefore, it is preferable to perform the treatment while controlling the amounts of aluminum and alloy elements dissolved in the solution.

First step: (anodic oxidation) An anodic oxide film is formed in a usual manner on an aluminum material whose surface has been cleaned by degreasing, etching or the like. As the electrolytic solution at this time, an inorganic acid such as sulfuric acid, phosphoric acid, and chromic acid, an organic acid such as oxalic acid and tartaric acid, or a mixed solution thereof is used. An alkaline aqueous solution such as sodium hydroxide and sodium carbonate can also be used. Anodization is performed by applying a positive direct current, a positive pulse voltage, or an AC / DC superimposed voltage to an aluminum material in an electrolytic solution. The anodic oxide film 2 formed on the surface of the aluminum material 1 by anodic oxidation has a structure in which a large number of fine holes 3 are distributed via a barrier layer 5, as shown in FIG. The thickness of the anodic oxide film 2 is arbitrarily adjusted according to the application. For example, for a building material, a thickness of about 10 to 25 μm may be sufficient in consideration of corrosion resistance.

Second step: (intermediate treatment) Anodized aluminum material 1 is immersed in a solution mainly containing an organic acid such as phosphoric acid or oxalic acid or tartaric acid, and is subjected to alternating current, positive direct current or positive pulse voltage. Figure 3
As shown in (b), an enlarged portion 6 is formed at the bottom of the fine hole 3. Third step: (adjustment of barrier layer) This step has a close relationship with the next fourth step (electrolytic coloring), in which the height of electrolytic deposits is made uniform during electrolytic coloring and uniform coloring is achieved. This is an important step in obtaining. The electrolyte used is Ni, Sn, Co, Fe, Cu, Se, P
one or more metal salts such as b, Mo, Ti, and Mn;
It contains one or more barrier-type film-forming agents such as boric acid, ammonium borate, tartaric acid, ammonium tartrate, citric acid and the like. The thickness of the barrier layer 5 is adjusted by immersing the aluminum material in the electrolyte and applying a positive direct current or a positive pulse voltage. As specific electrolysis conditions, the thickness of the barrier layer 5 after adjustment is about 20 to 15
0 nm, an electrolysis voltage of 20 to 150 V, 10
Electrolysis time and current density of 0.1 to 1 A / dm for seconds to 10 minutes
² is adopted.

Fourth step: (Electrolytic coloring) This is a treatment for depositing the electrolytic deposit 4 in the fine pores 3 of the anodic oxide film 2 in which the thickness of the barrier layer 5 is adjusted, and the same metal salt-containing solution as in the third step. Alternatively, it is electrolyzed in a solution having the same composition. The electrolysis is performed by applying alternating current, rectangular wave alternating current, negative direct current or negative pulse voltage to the aluminum material 1 immersed in the metal-containing solution. The electrolysis voltage is adjusted in a range of 20 to 50V. The electrolysis time ranges from 15 to 90 seconds,
As shown in (c), the time is set so that the upper surface of the precipitate 4 does not exceed the enlarged portion 6 of the fine hole 3. At this time, when the height of the electrolytic precipitate 4 reaches the micropores 3 beyond the enlarged portion 6, the amount of the electrolytic precipitates 4 in the individual micropores 3 decreases as described with reference to FIG. Due to the variation, when the pores are filled up to the fine pores 3 having a smaller diameter, the variation in the amount appears as a difference in the height of the electrolytic deposit 4. As a result, the upper surface of the electrolytic deposit 4 does not become flat, and a brown color tone without light interference is obtained. In the present invention, by adjusting the electrolysis conditions such as current density and time, the height of the electrolytic deposit 4 does not exceed the enlarged portion 6 of the micropores 3.

Fifth step: (substitution of noble metal) An electrolytically colored aluminum material is immersed in a solution containing one or two or more noble metal salts such as Au, Ag, Pt, Pd, Ru, Rh, Os, and Ir. Then, part or all of the electrolytic deposit 4 is replaced with a noble metal or a noble metal salt. As shown in FIG. 3D, the cross-sectional structure of the film subjected to the substitution treatment is such that the electrolytic deposit 4 is dissolved in the noble metal solution and is replaced by the noble metal layer 9 at the same time. The noble metal layer 9 is maintained at a constant height without being dissolved in the subsequent sixth step (re-anodizing). FIG. 3D shows a state in which the entire amount of the electrolytic deposit 4 is replaced with a noble metal. However, a two-layer structure in which only a part of the electrolytic deposit 4 is replaced with a noble metal can be used. . The thickness of each layer when forming a two-layer structure is determined in the fourth step (electrolytic coloring).
And the immersion time of the fifth step (precious metal substitution). Further, by changing the combination of the types of the electrolytic deposit 4 and the noble metal 9 and the thickness of these layers, it is possible to delicately change the color tone to be developed.

Sixth step: (re-anodizing treatment) This is a step of growing a re-anodized film layer 10 under the electrolytic deposit 4 and the noble metal layer 9 formed up to the fifth step. As the electrolyte, an inorganic acid such as sulfuric acid, an organic acid such as oxalic acid, or a mixed solution thereof is used, and the temperature is maintained in a temperature range of 10 to 30 ° C. By the re-anodizing treatment, an anodic oxide film having lower micropores 11 extending vertically downward from the electrolytic deposit 4 or the noble metal layer 9 is formed. In the present invention, a positive direct current is supplied at the time of re-anodizing, and the thickness of the re-anodizing film 10 is controlled. The thickness of the re-anodized film 10 is most important in determining the hue of the interference color, and the current density is set in the range of 0.1 to 5 A / dm ² to accurately control the film thickness. When the current density is less than 0.1 A / dm ² , the growth of the re-anodized film is slow, and when the current density exceeds 5 A / dm ² , the potential distribution in the electrolytic cell deteriorates due to an increase in the electrolytic voltage. The coloring uniformity due to the thickness variation is deteriorated.

Further, when the current density is lowered by a specified amount immediately before the end of the re-anodizing treatment, as shown in FIG. Irregularities 13 are also formed at the interface with oxide film 2. The irregularities 12 and 13 promote scattering of light at the interface to make the interference color opaque, so that a new color tone is obtained. The irregularities 12, 13 effective for imparting opacity are
Immediately before the end of the re-anodizing treatment, the current density is reduced from 1/100 to 1
/ 10 and formed by continuing the electrolysis. For example, as shown in FIG. 4, at time T ₁ lowering the current I abruptly 1 / 100-1 / 10, the voltage V
Gradually decreases until time T _2,, a constant voltage time T _2, or later. The time (T _{1 to} T ₂ ) varies depending on the composition of the electrolytic solution used, but is usually 10 seconds to 10 minutes. At time (T _{1 to} T ₂ ), as shown in FIG. 3 (f), the bottom of some lower micropores 11 spreads like a tree root,
At the interface between the anodic oxide film 2 and the aluminum material 1, irregularities become severe. By utilizing this phenomenon, an opaque color tone can be obtained.

The colored aluminum material exhibits an interference color having a hue determined by the total thickness of the electrolytic deposit 4 or the noble metal layer 9 and the re-anodized film 10. Here, the electrolytic deposit 4 or the noble metal layer 9 has a limited thickness because it is within the range of the enlarged portion 6 at the bottom of the fine hole 3. Therefore, the hue of the interference color is mainly determined by the thickness of the re-anodized film 10. For example, thickness 3
Table 1 shows the relationship between the interference color and the re-anodized oxide film 10 when the 0 nm-thick electrolytic precipitate 4 was formed, as viewed from a direction perpendicular to the surface of the colored aluminum material. Although the thickness of the re-anodized film 10 is not particularly limited, the region with a rich color is about 50 to 500 nm. In the re-anodized film 10 having a thickness outside this range, a grayish color tends to be formed.

[0015]

When going through the first to sixth steps, finally, FIG.
A film having a novel cross-sectional structure shown in (e) or (f) is formed. In order to obtain such a cross-sectional structure, it is essential to carry out all the steps sequentially from the first step. The interference color that appears due to this cross-sectional structure provides an aluminum material having a wide range of hues and excellent coloring uniformity. The electrolytically colored aluminum material is sealed by boiling, high pressure steam contact, spray coating, electrodeposition coating, or the like.

[0017]

EXAMPLES Example 1 A test piece having a length of 100 mm and a width of 200 mm cut out of an A1100P-H14 plate having a thickness of 2 mm was used.
As shown in FIG. 5, the test piece 20 was set to a width L = 350 mm,
Electrolyzer 21 with vertical W = 120 mm and depth D = 120 mm
And placed in a positional relationship orthogonal to the graphite counter electrode 22. Then, the test piece 20 and the counter electrode 22 are connected via the power source 23.
And the test piece 20 was electrolytically colored under the following conditions. First step: In a 150 g / l sulfuric acid electrolytic bath maintained at a temperature of 20 ° C., a positive direct current having a current density of 1.5 A / dm ² was supplied for 45 minutes, and a 20 μm-thick anodic oxide film was formed on the test piece 20. Formed on the surface. Second step: In a 100 g / l phosphoric acid bath maintained at 25 ° C, a positive DC voltage of 20 V was applied to the anodized test piece 20 for 10 minutes.

Third step: In a solution containing the following metal salt and barrier type film forming agent,
A positive direct current of 0.5 A / dm ² was supplied to the test piece 20 for 80 seconds to adjust the barrier layer. Electrolyte composition: nickel sulfate _{NiSO 4 · 6H 2 O 50g /} l Magnesium MgSO ₄ · 7H ₂ sulfate O 50 g / l boric acid H ₃ BO ₃ 30g / l water balance

Fourth step: The following rectangular wave alternating current was supplied to the test piece in an electrolytic bath having the same composition as in the third step, and the test piece was electrolytically colored. Frequency 10 Hz Anode / cathode time ratio 1/10 Anode current density 0.4 A / dm ² Cathode current density 0.4 A / dm ² Electrolysis time 15 seconds

[0020] Step _{5: H 2 PtCl 6 · 6H 2} O: 5g / l and H ₂ SO _{4: 2}
The test piece 20 was immersed in a solution containing 0 g / l for 2 minutes to perform a noble metal replacement treatment. Sixth step: In a 150 g / l sulfuric acid electrolytic bath maintained at a temperature of 20 ° C,
A voltage of 15 V was applied to the test piece 20 with a positive direct current, and electricity was supplied (coulomb / dm ² ) shown in Table 2. As shown in Table 2, the obtained hue changed according to the quantity of electricity, in other words, the thickness of the re-anodized film. Each hue has excellent coloring uniformity, regardless of the distance from the counter electrode 22 to the test piece 20.
A uniform film of the same color was formed on the surface of the test piece 20.

[0021]

Example 2 Using the same electrolytic cell 21 and test piece 20 as in Example 1, the following treatment was performed. First to fourth steps: Same conditions as in Example 1. Fifth step: HAuCl ₄ .3H ₂ O: 10 g / l and H ₂ SO ₄ : 1
The test piece 20 was immersed in a solution containing 0 g / l for 10 minutes. Sixth step: A positive direct current was supplied at a current density of 1 A / dm ² for 65 seconds.
The color tone that appeared after the re-anodizing treatment is shown in Table 3 by test number 4
, And was uniformly colored over the entire surface of the test piece.

Comparative Example 1 The following treatment was performed using the same electrolytic cell 21 and test piece 20 as in Example 2. Steps 1 to 5: Same as in Example 2 Step 6: A positive direct current was supplied at a current density of 0.05 A / dm ² for 1300 seconds (test number 5) and at a current density of 8 A / dm ² for 8 seconds (test number 6). In Test No. 5, the coating deteriorated due to the re-anodizing treatment, and in Test No. 6, a markedly uneven colored coating was formed.

[0024]

Example 3 Using the same electrolytic cell 21 and test piece 20 as in Example 1, the following treatment was performed. First to fourth steps: Same conditions as in Example 1 Fifth step: Ag ₂ SO ₄ : 10 g / l and H ₂ SO ₄ : 10 g / l
The test piece 20 was immersed in the solution containing for 10 minutes. Sixth Step: The test piece 20 was immersed in a 150 g / l sulfuric acid solution maintained at a temperature of 20 ° C., a positive direct current was supplied at a constant current density of 1 A / dm ² , and re-anodized for 55 seconds. The formed re-anodized film had a thickness of 220 nm. Immediately before the end of the re-anodizing treatment, the current density was reduced to 1/20 by 0.05 A /
dm ² and electrolyzed for 30 seconds in this state. Table 4 shows the color tone of the obtained colored film corresponding to the conditions of the re-anodizing treatment. In Table 4, the values of the lightness L ^* measured in the L ^* a ^* b ^* color system are shown. The lightness L ^* is
The larger the value, the brighter the color. Test number 7
In the film of No. 3, the brightness was lower than that of Test No. 3 in which no current drop was performed, and an opaque blue color was obtained.

Comparative Example 2 The following treatment was performed using the same electrolytic cell 21 and test piece 20 as in Example 1. Steps 1 to 5: The same conditions as in Example 3 Step 6: The test piece was immersed in a 150 g / l sulfuric acid solution maintained at a temperature of 20 ° C., and a positive direct current was supplied at a constant current density of 1 A / dm ² . Re-anodizing treatment was performed for 55 seconds. Immediately before the end of the re-anodizing treatment, electrolysis (test number 8) for 3 seconds with ^1/2 current density reduced to 0.5 A / dm ² and 1/200
Was electrolyzed for 300 seconds (test number 9) with the current density lowered to 0.005 A / dm ² . In this case, in both of Test Nos. 8 and 9, as shown in Table 4, the decrease in lightness L ^* was small, and only a transparent color was obtained.

[0027]

[0028]

As described above, according to the present invention, the bottom of the fine pores extending vertically in the anodic oxide film is enlarged, and a part or all of the electrolytic deposit deposited on the enlarged part is removed. After the replacement with the noble metal, lower micropores extending to the bottom of the electrolytic deposit or the noble metal layer are formed by re-anodizing. Current density of 0.1 to 5 A / dm during re-anodizing treatment
By supplying a positive direct current at ² , the thickness of the anodic oxide film extending below the electrolytic deposit or the noble metal layer can be freely and appropriately adjusted, and a wide range required according to the thickness of the anodic oxide film An interference color having a color tone is obtained. Furthermore,
If the current density is lowered immediately before the end of the re-anodizing treatment, an opaque color tone is obtained. In this way,
A coloring material is obtained which can provide uniform coloring over the entire surface of the aluminum material and is used in a wide range of fields as an interior material, an exterior material, a surface layer material and the like.

[Brief description of the drawings]

Fig. 1 Cross-sectional structure of the film formed by the secondary electrolytic coloring method

FIG. 2 shows a film (a) exhibiting interference colors and a film (b) exhibiting no interference colors.

FIG. 3 is a process of forming a colored film according to the present invention.

FIG. 4 Changes with time of current and voltage

FIG. 5 is an electrolytic cell used in Examples.

[Explanation of symbols]

1: Aluminum material 2: Anodized film 3: Micropore 4: Electrolyte deposit 5: Barrier layer 6: Enlarged part 7: Reflected light on the upper surface of electrolytic deposit 8: At interface between aluminum material and anodized film Reflected light 9: Noble metal layer 1
0: Re-anodized film layer 11: Lower micropore 12,
13: Unevenness

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Yoshiro Tanaka 3- 13-12 Mita, Minato-ku, Tokyo Inside Nippon Light Metal Co., Ltd. (72) Inventor Yoshiteru Miyasaka 3- 13-12 Mita, Minato-ku, Tokyo Nippon Light Metal Co., Ltd. (72) Inventor Kunio Wakasugi 2-5-8 Hongo, Takaoka City, Toyama Prefecture Nippon Light Metal Corporation Hokuriku Works (72) Inventor Toshihisa Kinoshita 2-5-8 Hongo, Takaoka City, Toyama Prefecture (56) References JP-A-6-116789 (JP, A) JP-A-6-49688 (JP, A) JP-A-6-272082 (JP, A) JP-A-6 -272085 (JP, A) Table 6-6-506985 (JP, A) (58) Fields surveyed (Int. Cl. ⁶ , DB name) C25D 11/22

Claims (2)

(57) [Claims] 1. An electrolytic coloring method for an aluminum material, comprising the following steps (1) to (6). (1) Anodizing treatment step of forming an anodic oxide film in which a large number of micropores extend in the aluminum material in a vertical direction. (2) Alternating the aluminum material in a solution mainly containing phosphoric acid or an organic acid. An intermediate treatment step of applying a direct current or a positive pulse voltage to enlarge the bottom of the micropore. (3) Ni, Sn, Co, Fe, Cu, Se, Pb, M
A positive DC or positive pulse voltage is applied to the aluminum material in a solution containing one or more metal salts such as o, Ti, and Mn and a barrier-type film-forming agent to adjust the thickness of the barrier layer. (4) Subsequently, an alternating current, a negative direct current, or a negative pulse voltage is applied to the aluminum material in a solution having the same composition, and an electrolytic deposit is deposited in the range of the enlarged portion at the bottom of the fine hole. (5) immersing the aluminum material in a solution containing one or more kinds of noble metal salts such as Au, Ag, Pt, and Pd;
A noble metal replacement step in which a part or all of the electrolytic deposit is replaced with a noble metal or a noble metal salt; (6) a current density of 0.1 to 5 A / dm ^{2 in the} aluminum material in an inorganic acid, an organic acid or a mixed solution thereof; Positive
DC supplies treated again anodized, corresponding to the target interference Wataruiro
Re-anodizing treatment step of growing the porous anodic oxide film thickness on the lower layer was replaced with the noble metal 2. The re-anodizing process according to claim 1,
Immediately before the end of the re-anodizing treatment, the current density is reduced from 1/100 to 1
Method for electrolytically coloring an aluminum material in which the electrolysis is continued at a rate of / 10.