JPH09184093A - Aluminum material and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the adhesion of a coated film at the time of coating of an Al product and the corrosion resistance after coating by forming a synthetic film, composed of nonporous anodic oxide film and boehmite film, on the surface of an Al product. SOLUTION: The surface of a stock, such as sheet and casting, or press formed part, etc., of pure Al or Al-type metal such as Al-Mn alloy is degreased with an alkalescent degreasing solution and successively pickled to undergo cleaning. Subsequently, boehmite treatment is performed to form a boehmite film of 700-3000Å thickness, and further, an electric current is applied by using the Al material as anode in an electrolyte in which boric acid, adipate, phthalate, etc., are dissolved to form a nonporous anodic oxide film of 70-2000Å thickness as an undercoat layer for boehmite film. At the time of coating the Al material, this synthetic film is previously baked to undergo heating and drying, by which moisture content is regulated to <=5wt.%. A thermoplastic acrylic resin type coating material is applied to the surface of this Al material.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to electric appliances, articles,
Related to the aluminum material or aluminum alloy product used for decorative products, building materials, automobile parts, fin materials, etc., which has been subjected to the coating base treatment and its manufacturing method, the adhesion of the coating film and the corrosion resistance after coating. It is a heightened one.

[0002]

2. Description of the Related Art Generally, when applying a coating to an aluminum plate or an aluminum alloy plate, a coating base treatment is carried out in order to enhance the adhesion of the coating film. Examples of conventional coating base treatments include chemical film treatments such as chromate treatment and boehmite treatment, and porous anodizing treatment. Properties required for these coating base treatments are coating film adhesion and post-coating corrosion resistance.

However, the conventional coating substrate treatment has the following problems. In the boehmite treatment, if the thickness of the coating is reduced, the corrosion resistance deteriorates,
Usually, a film with a thickness of 10,000 Å or more is generally formed. Also, since the surface has feather-like irregularities, an anchor effect is obtained and the adhesion with the coating tends to be high, but the water content of the coating is high. Is usually as high as 15 to 30% by weight, and particularly when baking coating is performed, the adhesion of the coating film may be significantly deteriorated due to evaporation of water from the coating film.

In the above-mentioned porous anodizing treatment, when baking is applied, the adhesion of the coating film may be deteriorated due to the evaporation of water from the coating film as in the case of the boehmite treatment described above. Measures such as not performing hole treatment are taken, but in this case, corrosion resistance may be insufficient. Further, in the porous anodizing treatment, a plurality of treatments such as degreasing, etching, desmutting, electrolysis and sealing are required in order to form an oxide film uniformly, resulting in high cost. Further, it is general to form an oxide film having a thickness of about 10 μm, but it takes 30 minutes or more for electrolytic treatment to form a film having such a thickness. Inferior. Further, in the sealing treatment, it is necessary to perform the treatment at a high temperature of about 90 ° C., so that heating requires cost. Also, thickness 1
Since it is difficult to uniformly form a thin film having a thickness of μm or less, a thick film is inevitably formed, and if the film is treated before the forming process, the formability is deteriorated.

In the chromate treatment, the coating film adhesion and corrosion resistance are excellent, but there is a drawback that the chromium-containing wastewater at the time of applying the chromate film leads to environmental pollution and the wastewater treatment is expensive. In addition, since chromium in the film is harmful to the human body for food-related applications, there is an increasing demand for dechromization.

In order to solve the above-mentioned problems, the inventor of the present invention immerses an aluminum plate or an aluminum alloy plate in an aqueous solution of boric acid, borate, phosphate, adipate, etc. We have found that a method of forming a non-porous anodic oxide film by electrolysis is effective, and have applied for a patent (Japanese Patent Application No. 7-88497, Japanese Patent Application No. 7-88497).
88498). However, in such a non-porous anodized film, the non-porous anodized film is excellent in coating adhesion and corrosion resistance after coating because the water content and anion content are small. Adhesion may remain unsatisfactory depending on the paint to be applied on top, which limits the paint used.

[0007]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and has a high degree of freedom in selecting a coating material to be used, good moldability and productivity, and low cost. To provide an aluminum material having excellent properties and corrosion resistance after coating, and a method for producing the same.

[0008]

The aluminum material according to claim 1, wherein a boehmite film having a thickness of 700 to 3000 Å and a nonporous anode having a thickness of 70 to 2000 Å are formed on the surface of aluminum or an aluminum alloy. A composite coating comprising an oxide coating and having a water content of 5% by weight or less is formed, and the non-porous anodic oxide coating is provided as an underlayer of the boehmite coating. Further, the aluminum material according to claim 2 is characterized by a coated aluminum material obtained by coating the surface of the aluminum material according to claim 1 or 2.

According to a third aspect of the method for producing an aluminum material, after boehmite treatment is applied to the surface of aluminum or aluminum alloy to form a boehmite film, boric acid, borate, phosphate, adipate, A non-porous anodic oxide film is formed as an underlayer of the boehmite film by anodizing with an aqueous electrolyte solution containing one or more selected from the group consisting of phthalates, benzoates, tartrates and citrates. The method is characterized by comprising a step of forming a composite film and a step of subjecting the surface of the composite film to a baking treatment at 250 ° C. or higher to reduce the water content of the composite film to 5% by weight or less.

In the method for producing an aluminum material according to claim 4, in the method for producing an aluminum material according to claim 3, the step of forming a composite film on the surface of aluminum or an aluminum alloy is performed before or after forming. It is characterized by including a step of performing.

According to a fifth aspect of the present invention, there is provided a method of producing an aluminum material according to the third or fourth aspect of the present invention, after which the surface of the aluminum material is coated. A method of manufacturing a painted aluminum material, comprising:

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the aluminum material and the coated aluminum material of the present invention will be described in detail by the manufacturing method thereof. The aluminum or aluminum alloy used as the material of the aluminum material of the present invention is not particularly limited, and is a pure aluminum 1000 series alloy, Al-Cu series alloy, A
2000-based alloy of 1-Cu-Mg system, 3 of Al-Mn system
000 series alloy, Al-Si series 4000 series alloy, Al-
Mg-based 5000-based alloy, Al-Mg-Si-based 600
0-based alloy, Al-Zn-Mg-Cu-based, Al-Zn-M
g-based 7000 series alloy, Al-Fe-Mn-based 8000
A system alloy or the like is used, and a molding alloy, a structural alloy, an electric alloy, or a casting alloy such as AC1A, AC2A, AC3A, or AC4B is used.

Further, those alloys that have undergone various heat treatments such as solution treatment and aging treatment are also used. Further, a clad material obtained by cladding the surface of these aluminum alloys can also be used. Further, the aluminum or aluminum alloy may be a processed material that has been subjected to press molding or the like in advance, an unprocessed plate material, extruded material,
It may be a cast product. In the present invention, among these alloy systems, 1000 series, 3000 series, 5000 series,
6000 series and the like are preferable, and 1000 series is particularly preferable.

Pretreatment is applied to such a material. The pretreatment is not particularly limited as long as it can remove the oil and fat adhering to the surface of the material and remove the heterogeneous oxide film on the material surface. For example, after performing degreasing treatment with a weak alkaline degreasing solution, alkali etching with an aqueous sodium hydroxide solution, then performing desmutting treatment in a nitric acid aqueous solution, a method of performing acid cleaning after the degreasing treatment, etc. are appropriately selected. Used.

Then, the pretreated material is subjected to a boehmite treatment in building bath water to form a boehmite film on the surface of the material. High-temperature water can be used as the bath water, but ion-exchanged water with an electric conductivity of 0.1 μS or less is particularly useful because it prevents blackening of the surface of the material and easily forms a boehmite film. Is preferred.

The temperature of the bath water is 90 ° C to the boiling point (100
° C). The boehmite treatment in the present invention is 1 to
About 2 minutes is enough. Conventional boehmite treatment time is 3
Although it is 0 minutes or more, in the present invention, in order to form a thin boehmite film, the treatment is performed in a short time of about 1 to 2 minutes. To the construction bath water, it is preferable to use an alkaline additive such as ammonia, amine, alcohol amine, amide, triethanol amine, etc. in that the production rate of the boehmite film becomes faster, and in that case, the boehmite film In order to prevent the film thickness from becoming too thick, the boehmite treatment time needs to be further shortened to about 1 minute or less.

By such a boehmite treatment, a boehmite film having feather-like irregularities is formed on the surface of aluminum or an aluminum alloy. The thickness of the boehmite film is 700 to 3000Å, preferably 1500 to
It is about 2500Å. If the film thickness is less than 700Å,
The formation of feather-like irregularities is insufficient, the anchor effect cannot be obtained, and sufficient coating film adhesion cannot be obtained. On the other hand, if the film thickness exceeds 3000 Å, it will be difficult to sufficiently remove the water contained in the boehmite film, and the adhesion after coating will decrease. Therefore, the thickness of the boehmite coating may be the minimum thickness necessary for the feather-like irregularities to produce the anchor effect. The water content of the boehmite film before the baking treatment described below is usually as high as 15 to 30% by weight.

Then, the boehmite-treated material is subjected to anodization treatment in which it is electrolyzed in an electrolytic bath to form a non-porous anodic oxide coating as an underlayer of the boehmite coating. As an electrolytic bath, boric acid, borate, phosphate, adipate, phthalate, benzoic acid, which is an electrolyte that hardly dissolves the non-porous anodic oxide film that forms, and forms a non-porous anodic oxide film An electrolyte aqueous solution in which one or more selected from the group consisting of acid salts, tartrate salts, citrate salts and the like are dissolved is used. Among these electrolytes, boric acid, adipic acid salt, and phthalic acid salt are preferable in terms of the properties of the oxide film, cost, and the like. The electrolyte concentration in the aqueous electrolyte solution is selected from the range of 2% by weight to the saturation concentration of the electrolyte.
The bath temperature of the electrolytic bath is in the range of 20 ° C to 90 ° C.

In this electrolytic bath, the aluminum or aluminum alloy material is electrolyzed by being connected to a power source so as to become an anode even if it is continuous or intermittent. An insoluble conductive material is used for the cathode. A direct current is used as the electrolysis current. In the direct current electrolysis, electrolysis is performed with a direct current density of about 1 to 30 A / dm ² and an electrolysis time of about several seconds to 3 minutes.

The applied voltage is about 5 to 142 V, preferably about 20 to 50 V, since the thickness of the oxide film formed is about 14 Å for a voltage of 1 V under direct current.
Range. From the standpoint of a power supply device, it is preferably 50 V or less, and excellent electrocoat adhesion and post-coating corrosion resistance can be obtained even by electrolysis at such a low voltage. By such anodizing treatment, a non-porous anodized film having a uniform thickness is formed as a base layer of the boehmite film. The film thickness of the non-porous anodic oxide film is 70 to 2000Å, preferably 3
It is about 00 to 700Å. If the film thickness is less than 70Å, the thickness is too thin to obtain sufficient corrosion resistance. On the other hand, the upper limit of the film thickness can be up to 7,000 Å, but even if the thickness exceeds 2000 Å, the effect cannot be expected to increase anymore, and the electrolysis time is increased and the cost of the electrolysis equipment is increased, which is economically economical. It is disadvantageous, the moldability is lowered, and the film is cracked. Therefore, 2000 Å or less is sufficient.

The anodized film thus obtained is non-porous, and its porosity is about 5% or less at the maximum, and usually about 2% or less. Further, the water content of the anodic oxide film before the baking treatment described later is about 1 to 5% by weight, usually about 1 to 3% by weight, which is a very low value. Furthermore, the anion content of the oxide film is 0.1.
It is a low value of about 7 to 7% by weight, usually about 1 to 5% by weight. On the other hand, the porous anodic oxide film obtained by a normal sulfuric acid bath or oxalic acid bath has a very high porosity of 5 to 60%, the water content is about 15% by weight after the sealing treatment, and the anion content is included. The amount is about 12 to 15% by weight.

Therefore, in the anodic oxide coating of the present invention, moisture and anions volatilized from the coating become remarkably small, and peeling of the coating due to release of moisture and anions during baking coating becomes small. Further, the baking treatment described below further reduces the amount of water and anions. Also,
The coating film thus obtained is non-porous and therefore has good corrosion resistance after coating.

Further, in the formation of the non-porous anodic oxide film according to the present invention, the bath temperature of the electrolytic bath has a wide range of 20 ° C. to 90 ° C., so that the bath management becomes easy. Furthermore, since the applied voltage may be 142 V or less, usually 50 V or less, it is also advantageous in terms of equipment such as a power supply device. Further, since an electrolyte having a low oxide film solubility is used, the film is less likely to be dissolved during electrolysis and current efficiency is improved. The above anodic oxidation treatment can be performed on unprocessed aluminum or aluminum alloy such as a coil, or can be performed on the aluminum or aluminum alloy after being subjected to processing such as pressing.

When an unprocessed material which has not been molded is used as the aluminum or aluminum alloy material, the molding may be performed before the baking treatment described below or after the baking treatment. Processing may be performed.

Then, before coating the aluminum material on which the composite film is formed, the surface of the composite film is baked at 250 ° C. or higher to heat and dry the composite film to obtain a water content of the composite film. Is 5% by weight or less, preferably 3 to 1% by weight. After the baking treatment, the boehmite film has a water content of 5 to 2% by weight, and the non-porous anodic oxide film has a water content of about 2 to 0.5% by weight.

If the baking temperature is lower than 250 ° C., the water of crystallization in the composite film cannot be removed, so that the water content in the composite film cannot be reduced to 5% by weight or less. It is not possible to sufficiently remove the water of crystallization inside, and when drying or baking the coating described below, there is a problem that the adhesion of the coating film is significantly reduced due to the evaporation of water from the boehmite film and the corrosion resistance is also poor. Occurs. The higher the baking temperature is, the more preferable it is. However, since the moisture content can be released to 5% or less up to 350 ° C, even if the baking temperature is further increased, the cost increases and the strength of the aluminum alloy changes. Therefore, the upper limit of the baking temperature is preferably about 350 ° C. A few minutes is sufficient for the baking process in the present invention. To remove water in the composite film,
This is because the temperature condition is dominant over the time. Also,
This is because the thin boehmite film of 700 to 3000 liters facilitates the removal of water.

Then, coating is applied to the surface of the aluminum material on which the above-described composite film is formed. The paint used here for coating is not particularly limited, but in the present invention, the effect is most effectively obtained especially when a baking type is used. As such paints, thermoplastic acrylic resin-based paints, thermosetting acrylic resin-based paints, epoxy resin-based paints, polyurethane resin-based paints, polyester resin-based paints, polyamide resin-based paints and the like are also used.

The coating method is not particularly limited, but a cation electrodeposition coating method, a spray coating method, a roll coater method, an electrostatic coating method and the like are used. Also, if necessary,
It is also possible to apply multi-layer coating such as intermediate coating and top coating. In this way, the intended coated aluminum material can be obtained.

In the aluminum material of the present invention, since the boehmite film having feather-like unevenness is formed on the surface of aluminum or aluminum alloy, an anchoring effect can be obtained. It is possible to improve the adhesion to the coating film.
Also, this boehmite film has a film thickness of 700 to 3000Å
Since it is thin, it is possible to efficiently remove water by baking as compared with the conventional aluminum material on which a boehmite film having a thickness of 10000 Å or more is formed because the thickness is thin. In addition, the thickness of the boehmite film is 700 to 300.
Even if it is as thin as 0Å, it can be used as an underlayer for the boehmite film.
By forming a non-porous anodic oxide film of 0 to 2000 Å, it has excellent corrosion resistance, and since the amount of water and anions in the non-porous anodic oxide film is small, the non-porous boehmite base during baking coating is non-porous. The amount of water and anions volatilized from the high quality anodic oxide film can be reduced, so that the adhesion of the coating film is excellent.

Since the boehmite film is formed on the non-porous anodic oxide film, an anchor effect with the coating film can be obtained, and therefore the coating film adhesion is hardly insufficient depending on the coating material used. As compared with the conventional aluminum material in which only the non-porous anodic oxide film is formed, the degree of freedom in selecting the paint is increased. Further, in the formation of a non-porous anodic oxide film, sealing treatment is not required, and the electrolysis time can be shortened as compared with the case of forming a porous anodic oxide film, so that the base treatment time can be shortened, The productivity can be improved and the cost can be reduced. Further, the forming process of aluminum or aluminum alloy may be performed before or after the formation of the composite film, but the formability is good. Further, the composite coating formed by the boehmite coating and the non-porous anodic oxide coating has a water content of 5% or less by subjecting the composite coating to a baking treatment at 250 ° C. or higher, so that the moisture content from the composite coating during baking coating and Since the effect of reducing the volatilization amount of anions, particularly the effect of reducing the volatilization amount of water and anions from the boehmite film is excellent, the coating film adhesion becomes remarkably excellent.

[0031]

EXAMPLES Hereinafter, the present invention will be described specifically with reference to Examples and Comparative Examples, but the present invention is not limited to only these Examples. As an aluminum alloy J
Using ISA1050 alloy, etching is performed with a 10% sodium hydroxide aqueous solution at 50 ° C. for 60 seconds, followed by washing with city water, followed by desmutting with a 30% nitric acid aqueous solution for 60 seconds, followed by washing with city water and pure water. Pretreated. The pretreated alloy was subjected to boehmite treatment in boiling water (ion exchange water). Here, the film thickness of the boehmite film was adjusted by changing the treatment time. Then, in an electrolyte aqueous solution shown in Table 1 below, the bath temperature was 60 ° C. and the current density was 1 A /
dm ² (direct current) was electrolyzed for 5 minutes, washed with water and dried to form an anodized film. Thereafter, the composite coating was baked under the conditions shown in Table 1 below. Then, apply an acrylic-epoxy coating on the surface of this product to a dry film thickness of 20.
After being applied so as to have a thickness of 30 μm, a top coat of 30 μm was applied. After each coating, a baking treatment at 230 ° C. was performed for 60 minutes to form a coating film having a thickness of 50 μm.

The water content of the obtained composite film was measured by thermogravimetric analysis, and the anion content was measured by XPS. The coated sample was cut into 100 2 mm cross-cuts, peeled off with cellophane tape, and the adhesion of the coating was measured by a "goggle test" in which the number of remaining coatings was counted. Further, a cross-cut reaching the substrate was put on the surface of the coated sample, and a combined cycle corrosion test under the following conditions was performed for 35 cycles, and then the maximum corrosion length from the cross-cut was measured to evaluate the corrosion resistance. Those with a maximum corrosion length of more than 1.0 mm were evaluated as poor (x), those having a maximum corrosion length of 0.5 to 1.0 m were evaluated as good (◯), and those having a maximum corrosion length of 0 to 0.5 mm were evaluated as excellent (⊚). Salt spray: 2 hours at 35 ° C. Dry: 4 hours at 60 ° C. Wet: 2 hours at 40 ° C., 95% RH The results are shown in Table 1 below.

[0033]

[Table 1]

The samples in Table 1 which do not have special remarks have boehmite coating as the upper coating and a non-porous anodic oxide coating as the underlying coating.

[0035]

As described above, since the aluminum material of the present invention has the above-mentioned structure, it has a high degree of freedom in selecting a coating material to be used, has good moldability and productivity, and is low in cost. In addition, there is an advantage that the coating film adhesion and the corrosion resistance after coating are excellent. Further, since the coated aluminum material of the present invention is obtained by coating the above-described aluminum material of the present invention, it has an advantage of excellent coating film adhesion and corrosion resistance. Moreover, the manufacturing method of the aluminum material of the present invention can provide the aluminum material of the present invention with high productivity and at low cost because of the above-mentioned configuration. Moreover, the manufacturing method of the coated aluminum material of the present invention can provide the coated aluminum material of the present invention by having the above-mentioned composition. Therefore, according to the present invention, it is possible to provide at low cost an aluminum material that has been subjected to a coating base treatment having excellent coating film adhesion and corrosion resistance. Therefore, electrical products, articles, ornaments, building materials, automobile parts, pre-coated fin materials Can be suitably used for aluminum products or aluminum alloy products.

Claims (5)

[Claims] 1. A composite coating comprising a boehmite coating having a thickness of 700 to 3000Å and a non-porous anodic oxide coating having a thickness of 70 to 2000Å and having a water content of 5% by weight or less on the surface of aluminum or an aluminum alloy. An aluminum material formed, wherein the non-porous anodic oxide film is provided as a base layer of a boehmite film. 2. A coated aluminum material obtained by coating the surface of the aluminum material according to claim 1. 3. Boehmite treatment is applied to the surface of aluminum or aluminum alloy to form a boehmite film, and then boric acid, borate, phosphate, adipate, phthalate, benzoate, tartrate, citric acid. Composite film forming step of forming a non-porous anodic oxide film as an underlayer of the boehmite film by anodizing with an aqueous electrolyte solution consisting of one or more selected from the group of salts, and the surface of the composite film A method for producing an aluminum material, comprising the step of subjecting the composite coating to a baking treatment at 250 ° C. or higher to reduce the water content of the composite coating to 5% by weight or less. 4. The method for producing an aluminum material according to claim 3, further comprising a step of performing a composite film forming step on the surface of aluminum or an aluminum alloy before or after molding. 5. A method for producing a coated aluminum material, which comprises the step of producing an aluminum material by the method for producing an aluminum material according to claim 3 or 4, and then applying a coating to the surface of the aluminum material.