JP2006312754A - Treatment method for surface of anodized aluminum - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a treatment method for attaining the improvement of the corrosion preventability for the surface of anodized aluminum, the improvement of the elution properties from the coated anodized aluminum or the like, i.e., a coating method. <P>SOLUTION: In the treatment method for the surface of an aluminum forming material, an aluminum forming material is anodized, and thereafter, fluorinated resin emulsion is mixed with a cationic or anionic surfactant so as to make an electrodeposition coating material, which is electrodeposited to stick a fluorinated resin coating film, and next, the fluorinated resin coating film is heat-treated. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a treatment method aimed at improving the anticorrosion property of the surface of anodized aluminum and improving the elution from the coated anodized aluminum, that is, a coating method.

Aluminum is lightweight and is used in ship engine parts such as outboard motor cases, automobile parts such as chassis, outdoor structures such as building panels, and various aerospace equipment. However, the anticorrosion is usually anodized and has a large number of micropores, so that it is sealed, but the anticorrosion effect is still insufficient, and therefore there are proposals to apply various plastic paints.
An example of a method for applying a fluororesin to a metal is to obtain a densified and highly anticorrosive material by coating the fluororesin with a binder and attaching it to the metal, followed by heat treatment at a high temperature. Further, there is known a method in which a modified fluororesin and a grafted acrylic acid are used and applied to a metal as a solvent adhesion type. In addition, when a fluororesin is applied to an aluminum member, a method is known in which a chromic acid chromate treatment or an anodizing treatment is applied and a paint containing a fluororesin is applied. However, in this method, the film thickness of the fluororesin is large, and the adhesion to aluminum is small and an adhesive layer such as chromic acid is provided, or a primer layer such as epoxy resin, acrylic resin or polyester resin is provided. (Japanese Patent Laid-Open No. 2003-71381). Also known is an electrodepositable resin composition in which a copolymer of acrylic acid and a fluorinated alkyl ester of acrylic acid imparting cationic properties is used together with a crosslinking material, and a fluororesin powder is also added (Japanese Patent Laid-Open No. 2002-38078). Publication) This resin film is inferior in mechanical strength and chemical properties as compared with a fluororesin alone, and inferior in heat resistance.
Each of the above methods has a problem in that the chemical and mechanical strength of the film is insufficient, and there is a limitation in the field of application for parts having a large opportunity for impact and wear.

There is also a proposal to electrodeposit an emulsion obtained by mixing acrylic acid or methacrylic acid with isocyanate, polysiloxane and fluororesin fine powder with organic acid, but it is not a fluororesin alone. And mechanical weaknesses (Japanese Patent Laid-Open No. 2001-19897). There are also electrodeposition paints consisting of acrylic resin, fluororesin and amino resin, but this is also inferior in corrosion resistance, inferior in mechanical strength such as wear resistance, and inferior in heat resistance. JP 2002-249702 A).
Each of the above methods has a problem in that the chemical and mechanical strength of the film is insufficient, and there is a limitation in the field of application for parts having a large opportunity for impact and wear.
This electrodeposition coating method includes an anionic electrodeposition paint that is electrolyzed using an anodic deposition electrodeposition paint with the product as an anode, and a cationic electrode that is electrolyzed with a cathodic deposition electrodeposition paint using the product as a cathode. There is a wearing method.
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JP 2001-19897 A JP 2002-249702 A JP 2002-38078 A JP 2003-71381 A

  The problem to be solved by the invention is that an aluminum product that has only been anodized is insufficient in its anticorrosive effect, and even if a fluororesin is directly coated on the aluminum product or its anodized product, it is temporarily anticorrosive. Although effective, equipment used under severe conditions is required to have better anticorrosion properties and less ion elution.

  The present invention has been made in order to solve the above-mentioned problems. The invention of claim 1 is directed to anodizing an aluminum molding material, and then subjecting a fluorine-containing resin emulsion paint to a secondary solution together with an anionic or cationic surfactant. A method of treating the surface of an aluminum molding material, characterized by electrolyzing and electrodepositing a fluorine-containing resin film, and then heat-treating the fluorine-containing resin film. The surface treatment method for an aluminum molding material according to claim 1, wherein is selected from an aluminum alloy for drawing and an aluminum alloy for casting.

  The aluminum substrate used here may be pure aluminum as well as aluminum alloy for drawing and aluminum alloy for casting. First, degreasing and cleaning are performed, and etching and acid cleaning are performed as necessary. Next, the aluminum alloy is used as an anode, and lead or graphite is used as a cathode, and electrolysis is performed with a direct current or a pulse waveform. Thus, an anodic oxide film having a large number of holes or micropores called bores is formed.

An aqueous solution of sulfuric acid, oxalic acid, phosphoric acid, chromic acid, aromatic sulfonic acid or the like is used as the electrolytic bath for the anodic oxidation electrolytic bath.
The thickness of the anodized film is 2 to 50 μm, more preferably 5 to 10 μm. When the film is thinner than 2 μm, the film is too thin, and the depth of the hole (bore) formed in the resin film to be applied later is anodized. Is too shallow, it is not preferable because the fluorine-containing resin film produced later is less cast. On the other hand, when the thickness is larger than 50 μm, a deeper bore than necessary is generated, so that the anodic oxidation costs too much, and there are problems in heat resistance, heat dissipation, and dimensional stability.
A fluorine-containing resin film is electrodeposited on the aluminum base material having the anodized film as described above by secondarily electrolyzing a fluorine-containing resin emulsion paint together with an anionic or cationic surfactant. The resin used here is a fluororesin such as tetrafluoroethylene resin, tetrafluoroethylene / hexafluoropropylene, polychlorotrifluoroethylene, polyvinylidene fluoride, polyvinylethylene fluoride / tetrafluoroethylene, ethylene / chlorotrifluoroethylene, etc. Is mentioned. It is to be noted that tetrafluoroethylene resin is most preferable because it is most excellent in corrosion resistance, wear resistance, etc., and perfluoroalkyl compounds are not preferable because of the influence of alkyl groups, but are limited to the above-mentioned fluorine-containing resins depending on applications. is not.

In electrodeposition, the resin is used together with a cationic surfactant, and an organic acid such as lactic acid or acetic acid is added to water and mixed well with a mixer such as a disper or a homomixer to perform electrodeposition coating. .
A perfluoroalkyl quaternary amine salt is used as the fluorine-based cationic surfactant.
The blending amount of the fluorine-containing resin is preferably 5 to 100 parts by weight with respect to 100 parts by weight of the ionic aqueous solution.
When a cationic surfactant is used, the object to be coated serves as a cathode, so that there is no elution of metal ions, so no discoloration occurs in aluminum.
The electrodeposition-coated resin film is formed to have a thickness of 1 to 100 μm, preferably 5 to 50 μm, while being cast in an anodized aluminum bore. If the film thickness is less than 1μ, the resin holding effect by throwing into the bore is insufficient, and the properties such as impact and wear are not sufficient, and the anticorrosion effect does not increase. If it exceeds 100μ, the product is more than necessary. Since the resin protective film is formed, the cost is high, and it is not preferable for precise component design.

  According to the method of the present invention, as a result of the secondary electrolysis and electrodeposition of a fluorine-containing resin emulsion paint together with a cationic surfactant on the outside of the anodized surface of aluminum, the resin is porous (bore) in the anodized film. Since a fluorine-containing resin film is formed with a penetration effect by entering part of the entrance, the resin film is firmly bonded even if it is thin, and fluorine is incorporated into the molecular structure, as is apparent from the salt spray crosscut test. By having it, the thing excellent in heat resistance and corrosion resistance is obtained. Furthermore, the electrodeposition film of the fluorine-containing resin can be completely integrated with the resin particles by sintering or firing to form a stronger film, thereby ensuring corrosion resistance. In addition, as seen from the state of change in conductivity and sulfate ion elution amount during the elution test, according to the present invention, the electroconductivity of the fluorine-containing resin film has low conductivity, and the sulfate ion elution amount is also extremely low. It turns out that the effect is remarkable. Furthermore, it can be seen that the hot water resistance, acid resistance, and alkali resistance are very high. Therefore, by providing a corrosion-resistant coating on such a lightweight aluminum material, it is effective as a component that requires corrosion resistance, such as marine engine parts, automotive parts, outdoor structures, and aerospace equipment. As a result, it is possible to provide a component suitable for a chemical instrument having a high purity.

After anodizing the aluminum molding material, the fluorine-containing resin emulsion is subjected to secondary electrolysis with a cationic surfactant to electrodeposit the fluorine-containing resin film, and then the fluorine-containing resin film is sintered or fired. Although it is characterized, the temperature varies depending on the resin, but is preferably above the curing point. FIG. 1 is an enlarged cross-sectional view of a product obtained by the present invention, in which a fluororesin film 3 that is partially penetrated into an aperture 2 by anodization of an aluminum base 1 and cast is formed. Next, the fine pores of the resin film can be completely solidified and densified by sintering or firing at 180 ° C. to 200 ° C.
The present invention eliminates the technical common sense that sealing treatment is usually performed with hot water or the like, which is usually performed on aluminum materials, and also without directly filling the pores with a secondary electrolytic material such as molybdenum. By electrodeposition, it completely retains the properties inherent to fluorine-containing resins, such as heat resistance, chemical resistance, and abrasion resistance, which were not previously thought of, and it is also possible to apply fluorine-containing resins to powder coating and melt coating. Since a film strongly bonded to an aluminum material can be obtained as compared with the above-described one, a product having a surface far superior to that of a conventional aluminum material can be provided.

Example 1
AC4CH casting aluminum alloy 50mm long, 25mm wide, 3.5mm thick Plate was alkali degreased, washed and dried, then anodized for 30 minutes at 27% sulfuric acid, temperature 3 ° C, current density 3A / dm ² Processing was performed to obtain an anodized film having a thickness of 10 μm. Next, after neutralizing by washing with water, a product with a resin film thickness of 10 μm is obtained by electrodeposition with a treatment voltage of 80 V and an electrolysis time of 90 seconds using a tetrafluoroethylene resin dispersion as a fluorine-containing resin together with a cationic surfactant. Got. This is subjected to primary baking at 100 ° C. for 10 minutes, secondary baking at 180 ° C. for 4 minutes to thermally cure the fluorine-containing resin film to eliminate micropores, and anodization having the fluorine-containing resin film according to the present invention Aluminum was obtained.

Example 2
A pipe having a diameter of 100 mm and a thickness of 10 mm made of an aluminum alloy for extension of JIS A symbol 5052 is prepared, degreased, washed with alkali, washed with water, dried with sulfuric acid 27%, temperature 15 ° C., current density 2.5 A / dm ² Was anodized for 15 minutes to obtain an anodized film having a thickness of 10 μm. Next, after neutralization by washing with water, a cationic fluorosurfactant and a tetrafluoroethylene resin dispersion are used as a fluorine-containing resin, and electrodeposition is performed at a treatment voltage of 80 V and an electrolysis time of 90 seconds. Obtained.
Next, after washing with water to neutrality, this was washed with water and dried, then subjected to primary heat treatment at 100 ° C. for 10 minutes, and then subjected to secondary heat treatment at 180 ° C. for 40 minutes to thermally cure the fluorine-containing resin film and fine The pores were extinguished to obtain anodized aluminum having a fluororesin film according to the present invention.

Example 3
JIS A2024 expansion aluminum alloy, length 100mm, width 100mm, thickness 1.0mm prepared, degreased, washed with alkali, washed with water, dried with sulfuric acid 25%, temperature 10 ± 1 ° C, current density in 3A / dm ^2, the anodic oxidation treatment for 15 minutes to obtain those anodic oxide film thickness 15.mu.. Next, after neutralization by washing with water, a cationic fluorosurfactant and a tetrafluoroethylene resin dispersion are used as a fluorine-containing resin, and electrodeposition is performed at a treatment voltage of 80 V and an electrolysis time of 90 seconds. Obtained.
Next, after washing with water to neutrality, this was washed with water and dried, then subjected to primary heat treatment at 100 ° C. for 10 minutes, and then subjected to secondary heat treatment at 180 ° C. for 40 minutes to thermally cure the fluorine-containing resin film and fine The pores were extinguished to obtain anodized aluminum having a fluorine-containing resin film according to the present invention.
A plate material having a length of 50 mm, a width of 25 mm, and a thickness of 10 mm, which is the same as that of Example 2, is prepared, and a dispersion of polychlorotrifluoroethylene resin is used as the fluorine-containing resin. An electrolytic treatment was carried out from degreasing under conditions to obtain a product having a film thickness of 10 μm.

Comparative Example 1
The same material as shown in Example 1 was anodized by the same method, degreased, washed, washed with water and dried, and then the same fluorine-containing resin coating was applied to obtain a product with a resin film thickness of 10 μm. This was subjected to a primary heat treatment at 100 ° C. for 10 minutes, and then subjected to a secondary heat treatment at 250 ° C. for 30 minutes to obtain an anodized aluminum having a fluorine-containing resin film for comparison.

Comparative Example 2
After degreasing, washing, washing with water and drying with the same materials as those shown in Example 2, the same fluorine-containing resin paint as that shown in Example 2 was electrodeposited in the same manner as in Example 2, Primary heat treatment was performed at 100 ° C. for 10 minutes, and secondary heat treatment was performed at 180 ° C. for 40 minutes to obtain an aluminum plate having a comparative fluorine-containing resin film.

Comparative Example 3
The same material as shown in Example 3, anodized by the same method, degreased, washed, washed with water and dried, then coated with acrylic resin paint, heat treated at 145 ° C. for 30 minutes, and comparative acrylic resin An anodized aluminum having a coating was obtained.

The following tests were conducted on the examples and comparative examples.
<Salt spray test>
Prior to spraying the test piece with salt water, knife cutting was performed, and salt water was sprayed for 336 hours according to JIS Z 2371 “Salt water spray test”, and the surface state was examined with a microscope.
According to this, as a representative example, what typically showed the micrograph of the state of knife-cut of the thing of Example 2 and the thing of the comparative example 2 is shown by FIG. 2 and FIG. 3, respectively. .
1 according to the embodiment of the present invention has no abnormality, but the comparative example in FIG. 3 has black spots at seven locations. This black dot indicates the part where the fluororesin film is peeled off.
In FIG. 3, the positions of the black spots are indicated by reference numerals 1 to 7, but (a), (b), (c), and (d) are enlarged views in FIGS. 4, 5, 6, and 7. Show.
As shown in FIG. 2, no black spots were observed in the sample according to the present invention, but in the comparative example, seven black spots were generated as shown in FIG. Reference numerals 1 to 7 are given depending on the positions of the black spots. In addition, for the enlarged view of this part, four squares (b), (b), (c), and (d) are shown by dotted-line squares. , (C) and (d) are enlarged views of FIGS. 4, 5, 6 and 7, respectively. Also, the position and size of the black spot can be read by the measure shown outside the box.
In addition, since what coated resin other than a fluororesin does not perform a test as mentioned above, but has characteristics, such as corrosion resistance, chemical resistance, and water resistance, a comparative test is abbreviate | omitted.

<Conductivity>
The sample was placed in a 500 ml sealed container and immersed at 80 ° C. for 168 hours to measure the conductivity before and after the elution of sulfate ions from the sample was tested. The initial water is 0.00 μS, as shown in Table 1 after 168 hours.
<Abrasion resistance test>
The resin film was treated at the heat treatment temperature for 1 hour, and the appearance and adhesion were examined.
<Conductivity>
Pure water placed in a 500 ml sealed container, and a test piece was placed in the pure water, and the elution amount of sulfate ions after immersion at 80 ° C. for 168 hours was measured.
<Elution amount of sulfate ion>
Pure water placed in a 500 ml sealed container, and a test piece placed in the pure water were immersed in 80 ° C. for 168 hours, and the elution amount of sulfate ions was measured. The initial water is 0.00 ppm.
<Heat resistant water test>
The test piece was immersed in boiling water for 6 hours and examined for appearance and adhesion.
<Sulfuric acid resistance test>
The test piece was immersed in sulfuric acid having a concentration of 1% at room temperature for 24 hours to examine whether there was any abnormality.
<Alkali resistance test>
The test piece was immersed in caustic soda having a concentration of 5 g / l at 20 ° C. for 24 hours to examine whether there was any abnormality.
<Corrosion resistance test>
Based on JIS Z 2371, a salt spray test was conducted for 1000 hours, and before and after that, 100/100 was observed in the cross section test (1 mm square) based on JIS K 5400 8.5.2. is there.

The results of the above tests are as shown in Table 1, and the examples of the present invention were excellent in all test items, but the salt spray test was particularly superior to the comparative example in the salt spray test. The result was obtained. In the comparative example, sulfate ions were eluted more than in the examples.
In the above test, the elution amount of sulfate ion was measured for the sample anodized in sulfuric acid. However, when anodized in phosphoric acid, it is necessary to consider elution of phosphate ion, but it is the same as sulfate ion. You can think of it as a trend.

Expanded sectional view of a fluorine-containing resin-coated product obtained by the method of the present invention Schematic diagram of the micrograph of the state in which the knife-cut test was performed by performing salt spray for 336 hours according to JIS Z 2371 “Salt spray test” of the fluorine-containing resin coating product obtained by the method of the present invention. Schematic diagram of a microphotograph showing a state in which a knife-cut test was performed by spraying salt water for 336 hours according to JIS Z 2371 “Salt spray test” of a product in which a fluorine-containing resin was directly coated on the anodized film of the comparative example Enlarged schematic diagram of (a) in FIG. Enlarged schematic diagram of (b) in FIG. Enlarged schematic diagram of (c) in FIG. Enlarged schematic diagram of (d) in FIG.

Explanation of symbols

1 Aluminum substrate 2 Anodized porous 3 Fluorine-containing resin film

Claims (2)

  After anodizing the aluminum molding material, secondarily electrolyzing the fluorine-containing resin emulsion paint with an anionic or cationic surfactant to electrodeposit the fluorine-containing resin film, and then heat-treating the fluorine-containing resin film A method for treating the surface of an aluminum molding material. 2. The method for treating a surface of an aluminum molding material according to claim 1, wherein the aluminum molding material is selected from a wrought aluminum alloy and a casting aluminum alloy.

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