JP3107883B2 - Pretreatment method for painting aluminum or aluminum alloy products - 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 pre-painting an aluminum molded article or an aluminum alloy molded article.

[0002]

2. Description of the Related Art Aluminum molded articles and aluminum alloy molded articles are used in many fields such as transportation machinery, building materials, home electric appliances and the like. As surface treatment methods for aluminum molded articles or aluminum alloy molded articles, anodic oxidation (alumite method), coloring treatment, and chemical film treatment (reaction chromate method, MBV method, boehmite method, etc.) are generally known.

[0003] When an aluminum molded product or an aluminum alloy molded product is used without being painted, it is generally subjected to a reaction chromate treatment. However, when the corrosion resistance of the film is required, the amount of chromium adhering increases and coloring occurs. It cannot be used when a colorless appearance is required.

[0004] When coating an aluminum molded article or an aluminum alloy molded article, an anodic oxide film treatment, a boehmite treatment, and a reaction chromate treatment are applied as pre-coating treatments to improve corrosion resistance and coating adhesion. Considering the pretreatment for clear coating utilizing the brilliancy of the material of aluminum molded products or aluminum alloy molded products, the corrosion resistance is insufficient for aluminum hydrated oxide film by boehmite treatment, and the amount of film for anodic oxide film is insufficient. Since it loses much gloss, it is unsuitable as a pretreatment for clear coating that emphasizes the appearance of the material surface. The reaction chromate film has excellent corrosion resistance, but if a colorless film appearance is required, the amount of chromium is limited to 10 mg / m ² or less, so that rust (water is Penetrates the metal surface and locally causes electrolytic corrosion, resulting in a width of 0.1 to 0.5 mm
Rust in a state where some degree of earthworm-like rust progresses with time is insufficient in corrosion resistance.

[0005]

As described above, no pretreatment method has yet been found which retains the appearance of the material surface of an aluminum molded article or an aluminum alloy molded article and which satisfies the corrosion resistance and adhesion after coating. . An object of the present invention is to maintain the appearance of the material surface of an aluminum molded article or an aluminum alloy molded article, before forming a pretreatment film having excellent corrosion resistance after nakedness, corrosion resistance after coating (particularly rust corrosion resistance), and adhesion. It is to provide a processing method.

[0006]

Means for Solving the Problems As a result of intensive studies to achieve the above object, the present inventors have found that aluminum molded articles or aluminum alloy molded articles contain hexavalent chromium ions and sulfate ions, It was found that a colorless chromate film could be obtained by performing cathodic electrolysis in a prepared acidic aqueous solution, and that this film was excellent in film corrosion resistance, post-coating rust corrosion resistance, and paint adhesion. Thus, the first invention has been completed. In the first invention, the surface of an aluminum molded article or an aluminum alloy molded article contains hexavalent chromium ions of 2 g / l or more and sulfate ions of 0.02 to 2.0 g / l, and has a pH of 0.5 to 2.0.
Using an acidic solution adjusted to a current density of 0.5 to 20 A / dm ² for at least 30 seconds to form a colorless chromate film having a chromium deposition amount of 30 to 250 mg / m ^2. The present invention provides a method for pre-coating an aluminum molded article or an aluminum alloy molded article.

The present inventors have conducted research following the above-mentioned first invention. As a result, the acidic aqueous solution used in the first invention contains at least one compound selected from colloidal silica, fumed silica and alkali metal silicate. It has been found that by containing the specified amount, the coloring of the chromate film can be suppressed and a colorless and relatively thick chromate film can be formed, and the second invention has been completed. The second invention is
The surface of an aluminum molded product or an aluminum alloy molded product is hexavalent chromium ion 2 g / l or more, sulfate ion 0.02
~ 2.0 g / l, and colloidal silica, fumed silica,
PH 0.5 containing one or more silica sols of alkali metal silicates at a solid content of less than 5 g / l
0.5 to 20 A using an acidic aqueous solution adjusted to 2.0
Pre-coating of an aluminum or aluminum alloy molded article characterized by forming a colorless chromate film having a chromium deposition amount of 50 to 300 mg / m ² by performing cathodic electrolysis at a current density of / dm ² for 30 seconds or more. Provide a way.

[0008] Further, it has been found that by adding titanium as a fluorine and a metal ion to the acidic aqueous solution used in the first invention, the rust resistance after coating can be further improved, and the third invention has been found. Was completed. According to a third aspect of the present invention, the surface of an aluminum molded product or an aluminum alloy molded product is hexavalent chromium ion 2 g / 1 or more,
0.02-2.0 g / l of sulfate ion, 0.4 g of fluorine
/ Less than, containing less than 1.0 g / l of titanium ions,
Use an acidic aqueous solution adjusted to pH 0.5 to 2.0,
Cathode electrolytic treatment at a current density of 5 to 20 A / dm ² for 30 seconds or more to form a colorless chromate film having a chromium deposition amount of 30 to 250 mg / m ² . Provide coating pretreatment method.

The present invention is a method for forming a colorless chromate film by subjecting an aluminum molded article or an aluminum alloy molded article to a cathodic electrolysis treatment in an acidic aqueous solution containing hexavalent chromium ions and sulfate ions. The configuration of the present invention will be specifically described.

First, each component of the acidic aqueous solution will be described. Hexavalent chromium ions include chromic anhydride, dichromic acid, and alkali metal salts of dichromic acid, and one or more of them can be used in combination.
Its concentration range is 2 to 50 g / l. If the hexavalent chromium ion concentration is less than 2 g / l, a chromate film having sufficient corrosion resistance cannot be obtained, and if it exceeds 50 g / l, there is no problem in performance, but the burden of drainage treatment and the like is uneconomical.
Further, as the electrolytic treatment is performed, trivalent chromium ions increase. However, in practicing the present invention, the trivalent chromium ions are not affected by the increase or decrease of the trivalent chromium ions. Is not provided.

As the sulfate ion, sulfuric acid and alkali metal salts of sulfuric acid can be used.
0 g / l. If the concentration is less than 0.02 g / l,
No colorless chromate film is formed. 2.0g /
If it exceeds 1, the amount of chromium adhering decreases and the corrosion resistance decreases, which is not preferable.

The pH of the acidic aqueous solution is adjusted to a value of 0.5 to 2.
Limited to the range of 0. In order to control the pH, it can be arbitrarily selected from ammonium hydroxide, alkali metal hydroxide, alkali metal carbonate, chromic acid, sulfuric acid, nitric acid and the like and added to the aqueous solution. pH is 0.
Although there is no problem in performance even if it is less than 5, since the pH of the processing solution is increased by performing the cathodic electrolytic treatment, p is always required for industrial production.
H adjustment is required and difficult to maintain and control. When the pH exceeds 2.0, the amount of the attached chromate film decreases rapidly, and it becomes difficult to obtain an appropriate amount of attached chromium.

Although the temperature of the processing solution is not specified,
More preferably, it is 30 ° C to 60 ° C. If the temperature is lower than 30 ° C., heat is generated by electrolysis, and cooling is required to maintain the temperature, which is uneconomical for industrial production. Even if the temperature is higher than 60 ° C., there is no significant change in the characteristics of the formed film. However, after the electrolytic treatment, the processing liquid adheres to the object to be processed and dries while moving to the next washing step. It is not preferable because the washing property is deteriorated.

Next, in the electrolytic treatment, an object to be treated is used as a cathode, and the anode is subjected to electrolytic treatment using stainless steel, carbon, titanium platinum, lead, lead oxide (a catalyst electrode in which lead oxide is formed on titanium) or the like. . The conditions for the electrolytic treatment are such that the electrolytic current density at the cathode is in the range of 0.5 to 20 A / dm ² . When the current density is lower than 0.5 A / dm ^2, it is difficult to form a chromate film. On the other hand, when the current density is higher than 20 A / dm ² , the film is colored and the film is redissolved. A colorless chromate film cannot be obtained.

[0015] The electrolytic treatment time is required to be 30 seconds or more.
The electrolysis time is controlled so that the amount of the formed film (the amount of chromium adhered) falls within a desired range. There are various factors that change the amount of formed film (the amount of chromium adhered),
In the method of the present invention, the concentration of each component of the processing solution, p
Even if H, temperature, current density, and the like are fixed to the preferable conditions of the present invention, the desired amount of chromium can be controlled according to the metal to be treated by changing the electrolysis time. Conversely, the amount of chromium deposited can be controlled by fixing the electrolysis time and changing the current density.

In the present invention, a preferable chromium deposition amount range is 30 to 250 mg / m ² . Chromium adhesion 3
If the amount is less than 0 mg / m ² , the corrosion resistance after coating, especially the rust resistance, is poor. If the amount exceeds 250 mg / m ² , the appearance of the chromate film is colored and is not suitable for clear coating. However,
In the case of a colored coating, 250 mg / m ² or more can be used.

The aluminum molded article or the aluminum alloy molded article which has been subjected to the cathodic electrolytic treatment according to the present invention is washed with water and then dried to be applied as a base for coating or for anticorrosion.
Further, if necessary, a post-treatment with a generally used chromate aqueous solution, an organic compound, or the like can be performed.

The second invention provides an aluminum molded article or an aluminum alloy molded article containing hexavalent chromium ion, sulfate ion and at least one compound selected from colloidal silica, dry silica and alkali metal silicate. In this method, a colorless and relatively thick chromate film is formed, and each method will be specifically described.

First, each component of the acidic aqueous solution will be described. Hexavalent chromium ions and sulfate ions are the same as in the first invention. Examples of the silica sol include one or two of colloidal silica, fumed silica, and a silicate of an alkali metal.
Any mixture of more than two species can be applied arbitrarily, and the solid content concentration is 5
g / l. The addition of the silica sol has an effect of suppressing coloring of the film even if the amount of chromium adhered is large. However, when the solids concentration of the silica sol exceeds 5 g / l, the coloring of the film is suppressed, but the corrosion resistance after coating is poor. The pH range of the acidic aqueous solution, the temperature of the treatment solution, and the conditions of the electrolytic treatment are the same as in the first invention.

The preferred range of the amount of chromium deposited in the second invention is 50 to 300 mg / m ² . In the first invention, the chromate film appearance was colored when the chromium adhesion amount exceeded 250 mg / m ² , but according to the present invention, the chromium adhesion amount was 300 mg / m ² and the corrosion resistance after coating was good. Naturally, in the case of colored coating, 300 mg / m ² or more can be used.

Furthermore, the present inventors have found that a film excellent in filiform rust resistance after coating can be formed by adding a specified amount of fluorine and titanium to the acidic electrolyte used in the first invention. The third invention has been achieved. First, each component of the acidic aqueous solution will be described. 6
The chromium ions and sulfate ions are the same as in the first invention. As the fluorine, one or a mixture of two or more of hydrofluoric acid, hydrofluoric acid, and titanium hydrofluoric acid can be arbitrarily applied. The concentration as fluorine is 0.4 g / l
Is less than. By adding fluorine, the etching of the material can be accelerated and the reactivity can be increased.
If it exceeds / l, the formation of a chromate film by electrolysis is suppressed, making it difficult to obtain the desired amount of chromium deposited, and the obtained chromate film is colored, which is unsuitable for clear coating.

Examples of titanium include titanium hydrofluoric acid and salts of sodium, potassium, ammonium and the like, and titanyl sulfate. The concentration of titanium used in the present invention is less than 1.0 g / l. Although the corrosion resistance of the coating obtained by the first invention after coating is as described above, it has been found that the addition of titanium further improves the rust resistance. The effect does not change even if the added amount of titanium exceeds 1.0 g / l. The pH range of the acidic aqueous solution, the temperature of the treatment solution, and the conditions of the electrolytic treatment are the same as in the first invention.

[0023]

Next, the present invention will be specifically described with reference to examples and comparative examples.

(Examples 1 to 4) The test plate was prepared by grinding the surface of an aluminum alloy (JIS code AC4C) plate, cleaning the surface by alkali degreasing, and then subjecting the plate to electrolytic treatment. The acidic aqueous solution contains hexavalent chromium ions of 20 g / l with chromic anhydride and sulfate ions of 0.4 g / l with sulfuric acid.
The pH was adjusted to the conditions shown in Table 1 (Example 1 pH 0.6 to Example 4 pH 1.8) using ammonium hydroxide. The test plate was immersed in the acidic aqueous solution to serve as a cathode, and a current density of 2 A / dm ² was applied for 60 seconds. During this time, the temperature of the aqueous solution was maintained while circulating at 40 ° C. After energization, the test plate was taken out, washed with water, and dried in a drying oven at 100 ° C. for 5 minutes. Next, a thermosetting acrylic resin clear was applied to the test plate (thickness: 30 μm), baked and dried at 140 ° C. for 30 minutes, and then subjected to a corrosion resistance test (fiber rust test, salt spray test). Table 1 shows the results.

(Comparative Examples 1 to 3) 20 g / l of hexavalent chromium ion with chromic anhydride and 0.4 g / l of sulfate ion with sulfuric acid
The pH of the added acidic aqueous solution was adjusted using ammonium hydroxide to the conditions shown in Table 1 (Comparative Example 1 pH 2.2 to Comparative Example 3).
(pH 3.0), the same electrolytic treatment and coating as in Example 1 were performed, and a corrosion resistance test was performed. Table 1 shows the results.

Example 5 The pH of an acidic aqueous solution in which hexavalent chromium ions were added with chromic anhydride at 5 g / l and sulfate ions at 0.05 g / l with sulfuric acid was adjusted to 1.0 using ammonium hydroxide. The same electrolytic treatment and painting as in Example 1 were performed, and a corrosion resistance test was performed. Table 1 shows the results.

Example 6 The pH of an acidic aqueous solution containing 50 g / l of hexavalent chromium ion added with chromic anhydride and 1.5 g / l of sulfate ion with sulfuric acid was adjusted to 1.0 using ammonium hydroxide. The same electrolytic treatment and painting as in Example 1 were performed, and a corrosion resistance test was performed. Table 1 shows the results.

Example 7 The pH of an acidic aqueous solution in which hexavalent chromium ions were added with chromic anhydride at 20 g / l and sulfate ions at 0.4 g / l with sulfuric acid was adjusted to 1.0 using ammonium hydroxide. . . The test plate was immersed in the acidic aqueous solution to serve as a cathode, and a current density of 15 A / dm ² was supplied for 30 seconds. The same coating as in Example 1 was performed, and a corrosion resistance test was performed. Table 1 shows the results.

Comparative Example 4 The pH of an acidic aqueous solution containing 20 g / l of hexavalent chromium ion with chromic anhydride and 0.4 g / l of sulfate ion with sulfuric acid was adjusted to 1.0 using ammonium hydroxide. . . The test plate was immersed in the acidic aqueous solution to serve as a cathode, and current was supplied at a current density of 30 A / dm ² for 30 seconds. The same coating as in Example 1 was performed, and a corrosion resistance test was performed. Table 1 shows the results.

Example 8 Hexavalent chromium ions were 20 g / l with chromic anhydride and sulfate ions were 0.4 g / l with sulfuric acid.
The pH of an acidic aqueous solution obtained by adding 2 g / l of silica sol to dry silica (Aerosil 300, Nippon Aerosil Co., Ltd.) was adjusted to 1.0 using ammonium hydroxide. A test plate was immersed in the acidic aqueous solution to serve as a cathode, and the current density was set to 2 A / dm ²
For 60 seconds. The same coating as in Example 1 was performed, and a corrosion resistance test was performed. Table 2 shows the results.

Example 9 Hexavalent chromium ions were 20 g / l with chromic anhydride and sulfate ions were 0.4 g / l with sulfuric acid.
The pH of an acidic aqueous solution obtained by adding 2 g / l of silica sol to dry silica (Aerosil 300, Nippon Aerosil Co., Ltd.) was adjusted to 1.0 using ammonium hydroxide. The test plate was immersed in the acidic aqueous solution to serve as a cathode, and the current density was set to 10 A / dm.
² for 30 seconds. Perform the same coating as in Example 1,
A corrosion resistance test was performed. Table 2 shows the results.

Example 10 20 g / l of hexavalent chromium ion with chromic anhydride and 0.4 g / l of sulfate ion with sulfuric acid
1) The pH of an acidic aqueous solution obtained by adding a silica sol to colloidal silica (Snowtex 0 manufactured by Nissan Chemical Industries, Ltd.) at a solid content of 4 g / l was adjusted to 1.0 using ammonium hydroxide. The test plate was immersed in the acidic aqueous solution to serve as a cathode, and a current density of 10 A / dm ² was supplied for 30 seconds. The same coating as in Example 1 was performed, and a corrosion resistance test was performed. Table 2 shows the results
Shown in

Comparative Example 5 20 g / l of hexavalent chromium ion with chromic anhydride and 0.4 g / l of sulfate ion with sulfuric acid
The pH of an acidic aqueous solution obtained by adding a silica sol to colloidal silica (Snowtex 0 manufactured by Nissan Chemical Industries, Ltd.) at a solid concentration of 8 g / l was adjusted to 1.0 using ammonium hydroxide. The test plate was immersed in the acidic aqueous solution to serve as a cathode, and a current density of 10 A / dm ² was supplied for 30 seconds. The same coating as in Example 1 was performed, and a corrosion resistance test was performed. Table 2 shows the results.

(Example 11) Hexavalent chromium ions were added with chromic anhydride at 20 g / l and sulfate ions at 0.4 g / l with sulfuric acid.
1. The pH of an acidic aqueous solution to which 140 ppm of fluorine and 60 ppm of titanium were added using titanium hydrofluoric acid was adjusted to 1.0 using ammonium hydroxide. A test plate was immersed in the acidic aqueous solution to serve as a cathode, and the current density was 60 A at 2 A / dm ² .
Energized for seconds. The same coating as in Example 1 was performed, and a corrosion resistance test was performed. Table 2 shows the results.

(Example 12) Hexavalent chromium ion was 20 g / l with chromic anhydride, 400 ppm of sulfate ion and 200 ppm of fluorine with titanyl sulfate and titanium hydrofluoric acid.
The pH of the acidic aqueous solution to which 290 ppm of titanium was added was adjusted to 1.0 using ammonium hydroxide. A test plate was immersed in the acidic aqueous solution to serve as a cathode, and the current density was 5 A /
It was energized at dm ² for 60 seconds. The same coating as in Example 1 was performed, and a corrosion resistance test was performed. Table 2 shows the results.

Example 13 Hexavalent chromium ions were 10 g / l with chromic anhydride, 100 ppm of sulfate ions and 100 ppm of fluorine with titanyl sulfate and titanium hydrofluoric acid.
The pH of the acidic aqueous solution to which 80 ppm of titanium was added was adjusted to 1.0 using ammonium hydroxide. A test plate was immersed in the acidic aqueous solution to serve as a cathode, and the current density was 10 A /
It was energized at dm ² for 30 seconds. The same coating as in Example 1 was performed, and a corrosion resistance test was performed. Table 2 shows the results.

Comparative Example 6 The pH of an acidic aqueous solution to which hexavalent chromium ion was added at 20 g / l with chromic anhydride, 400 ppm of sulfate ion, 700 ppm of fluorine and 500 ppm of titanium with titanyl sulfate and titanium hydrofluoric acid was adjusted to ammonium hydroxide. Was adjusted to 1.0 using. A test plate was immersed in the acidic aqueous solution to serve as a cathode, and the current density was 10 A /
It was energized at dm ² for 30 seconds. The same coating as in Example 1 was performed, and a corrosion resistance test was performed. Table 2 shows the results.

Comparative Example 7 The pH of an acidic aqueous solution containing 20 g / l of hexavalent chromium ion with chromic anhydride, 400 ppm of sulfate ion, 200 ppm of fluorine, and 290 ppm of titanium with titanyl sulfate and titanium hydrofluoric acid was adjusted to ammonium hydroxide. Was adjusted to 1.0 using. A test plate was immersed in the acidic aqueous solution to serve as a cathode, and the current density was 30 A /
It was energized at dm ² for 30 seconds. The same coating as in Example 1 was performed, and a corrosion resistance test was performed. Table 2 shows the results.

(Comparative Example 8) A test plate was cleaned by alkali degreasing to clean the surface, then subjected to a reactive chromate treatment (using Alchrome 3703 manufactured by Nippon Parkerizing Co., Ltd.), washed with water, and then dried in a drying oven at 100 ° C for 5 minutes. Dried. Next, a thermosetting acrylic resin clear was applied to the test plate (film thickness 30).
μ) After baking and drying at 140 ° C. for 30 minutes, a corrosion resistance test (fiber rust test, salt spray test) was performed. Table 2 shows the results.

Comparative Example 9 A test plate was cleaned by alkali degreasing to clean the surface, and then dried in a drying oven at 100 ° C. for 5 minutes. Next, a thermosetting acrylic resin clear was applied to the test plate (thickness: 30 μm), baked and dried at 140 ° C. for 30 minutes, and then subjected to a corrosion resistance test (fiber rust test, salt spray test). Table 2 shows the results.

(Evaluation test method) 1) Appearance of coating film JIS-Z8 using a color difference meter on the basis of an untreated sample.
The color difference specified in 730 was measured and evaluated according to the following ranks. ◎ Color difference 0 to 3.2 (discoloration is not visually observed) ○ Color difference 3.2 to 6.5 (slight discoloration is observed) △ Color difference 6.5 to 13 (discoloration is clearly observed) × color difference 13 or more (strong discoloration is observed)

2) Chromium adhering amount Measured by a fluorescent X-ray analyzer.

3) Yarn rust test A coated test plate was cut with an NT cutter to reach the substrate, immersed in a corrosive solution (a mixture of 1N hydrochloric acid and 5% hydrogen peroxide solution) for 1 minute, and dried at room temperature. 24 hours have passed.
After performing a wet test (temperature of 50 ° C., humidity of 80%) for 1000 hours, the length of the thread rust generated from the cut scratch is measured. ◎ Maximum rust length 2mm or less ○ 〃 3mm or less △ 以内 5mm or less × ５ 5mm or more

4) Salt Spray Test (SST) After making a cut on the coated test plate to reach the substrate with an NT cutter, the test was performed for 1000 hours in accordance with JIS-Z2371, and rust and swelling from the cut were measured. Measure significant. ◎ Maximum blister rust width 1mm or less ○ 以内 2mm or less △ 以内 3mm or less × ３ 3mm or more

[0045]

According to the present invention, it is possible to form a colorless chromate film which retains the appearance of the aluminum or aluminum alloy material surface and has excellent corrosion resistance and adhesion after coating. It is possible to improve the corrosion resistance, particularly the yarn rust resistance, which has conventionally been a problem.

[0046]

[Table 1]

[0047]

[Table 2]

Continuation of front page (56) References JP-A-54-13431 (JP, A) JP-A-62-278297 (JP, A) JP-A-3-44496 (JP, A) JP-A-5-309331 (JP) , A) JP-A-5-179486 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C25D 11/38

Claims (3)

(57) [Claims] 1. The surface of an aluminum molded article or an aluminum alloy molded article containing hexavalent chromium ions of 2 g / l or more and sulfate ions of 0.02 to 2.0 g / l and a pH of 0.5 to
Using an acidic solution adjusted to 2.0, 0.5 to 20 A / d
a method for pre-coating an aluminum molded article or an aluminum alloy molded article, wherein a colorless chromate film having a chromium adhesion amount of 30 to 250 mg / m ² is formed by performing cathodic electrolysis at a current density of m ² for 30 seconds or more. . 2. The surface of an aluminum molded article or an aluminum alloy molded article is coated with hexavalent chromium ions of 2 g / l or more, sulfate ions of 0.02 to 2.0 g / l, and colloidal silica.
Using an acidic aqueous solution in which one or more silica sols of dry silica and alkali metal silicate are adjusted to a pH of 0.5 to 2.0 containing less than 5 g / l in a solid content concentration,
Cathodic electrolytic treatment at a current density of 0.5 to 20 A / dm ² for 30 seconds or more, and a chromium adhesion amount of 50 to 300 mg / m 2
^2. A method for pre-coating an aluminum molded article or an aluminum alloy molded article, which comprises forming the colorless chromate film of ² . 3. The surface of an aluminum molded article or an aluminum alloy molded article is hexavalent chromium ion 2 g / 1 or more, sulfate ion 0.02 to 2.0 g / l, fluorine less than 0.4 g / l, titanium ion 1.0 g. / L less than pH
Using an acidic aqueous solution adjusted to 0.5 to 2.0,
Before coating an aluminum molded article or an aluminum alloy molded article characterized by forming a colorless chromate film having a chromium deposition amount of 30 to 250 mg / m ² by performing cathodic electrolysis at a current density of 20 A / dm ² for 30 seconds or more. Processing method.