JP3241170B2 - Pretreatment method for cationic electrodeposition coating of aluminum-based metal materials - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pretreatment method for applying a cationic electrodeposition coating to an aluminum-based metal material. More specifically, by performing cathodic electrolysis treatment on the surface of the metal material in an acidic aqueous solution containing hexavalent chromium ions and / or trivalent chromium ions, the performance after cationic electrodeposition coating, that is, coating film adhesion The present invention relates to a novel coating pretreatment method having extremely good corrosion resistance after painting.

Here, the aluminum-based metal material refers to a pure aluminum material, an aluminum alloy material, or a material in which the surface of another material is plated with these aluminum-based metals.

[0003]

2. Description of the Related Art Conventionally, iron-based metallic materials such as cold-rolled steel sheets, various types of galvanized steel sheets, and surface-treated steel sheets have been mainly used in industrial production activities such as the automobile industry and home appliance manufacturing industry. The use of aluminum-based metallic materials, which are beneficial in many respects, has increased. For example, in automobiles, iron-based metallic materials such as cold-rolled steel sheets, various types of galvanized steel sheets, and surface-treated steel sheets are generally used for each part of a vehicle body according to required performance. However, on the other hand, reduction of fuel consumption of automobiles is required as one of environmental measures in recent years, and the use of aluminum-based metal materials is increasing for the purpose of reducing the weight of automobiles as one of the methods. Further, in response to such a trend, there are cases in which the entire body of an automobile has already been made of aluminum.

[0004] In the case of coating such an aluminum-based metal material, chromate treatment has been mainly used since ancient times as a pre-coating treatment for imparting good coating film adhesion and corrosion resistance after coating. . However, in the case of cationic electrodeposition coating, which is currently the mainstream of primers in the field of automotive coating, the conventional chromate treatment cannot be said to be an optimal coating pretreatment method. The reason for this is that the cationic electrodeposition coated aluminum material with the chromate treatment as the coating base is the cationic electrodeposition coated cold rolled steel sheet or the zinc-based steel sheet with the phosphate treatment as the coating base (currently, these are mainly Is poorer in corrosion resistance and adhesion after coating, and the chromate-treated film is not chemically stable enough. This is because phenomena such as a remarkable deterioration of the adhesion of the coating film due to a slight reception are observed.

[0005]

In view of the above, the present invention solves the problem of poor adhesion of the coating film, which is present in the conventional chromate treatment method, as a pre-treatment when performing cationic electrodeposition coating on an aluminum-based metal material. It is another object of the present invention to provide a novel pretreatment method for coating, which is more suitable for cationic electrodeposition coating and has more excellent post-coating corrosion resistance.

[0006]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to solve the above-mentioned problems, and as a result, it has been found that cathodic electrolysis of an aluminum-based metal material in an acidic aqueous solution containing chromium is performed by cationic electrodeposition coating. The present inventors have concluded that this is the most suitable pretreatment, and have completed the present invention.

That is, according to the present invention, in the pretreatment for cationic electrodeposition coating of an aluminum-based metal material, the metal material is treated with 6
Provided is a method for pre-treatment of cationic electrodeposition coating of an aluminum-based metal material, comprising performing cathodic electrolysis in an acidic aqueous solution containing valent chromium ions and / or trivalent chromium ions.

Hereinafter, the configuration of the present invention will be described in detail. The catholyte treatment solution containing chromium ions in the present invention is roughly classified into two cases, namely, a case using hexavalent chromium ions and a case using trivalent chromium ions.

First, the case of performing cathodic electrolytic treatment with a solution containing hexavalent chromium ions will be described. With such an electrolytic solution, if the treatment is continued, a part of the chromate film mainly composed of trivalent chromium formed as a film is dissolved and trivalent chromium ions accumulate in the bath.
The case where both trivalent and trivalent chromium ions coexist will be discussed at the same time. First, when a hexavalent chromium ion is contained as a cathodic electrolysis solution, the supply source is not particularly limited, but it is more preferable to use chromic anhydride,
Its concentration is 4 to 300 g / l as chromium, pH
It is preferable to use an acidic solution of 2.0 or less. further,
In order to improve the electrolysis efficiency, it is more preferable to add an inorganic acid such as sulfuric acid or hydrogen fluoride, or a complex fluoride such as hydrosilicofluoric acid, borofluoric acid, zircon hydrofluoric acid, or titanium hydrofluoric acid.

The electrolysis conditions are not particularly limited, except that the electrolysis is performed using an aluminum-based metal material to be treated as a cathode, but the bath temperature during electrolysis is set to 40 ° C. to 60 ° C.
More preferably, the current density is set in the range of 0.5 to 60 A / dm ² . The electrolysis time is determined by the amount of chromium deposited on the surface of the aluminum-based metal material, and the amount of chromium deposited is preferably from ²⁰ to 300 mg / m ^2.
When a valent chromium bath is used, the current density is 1-2 A / dm ²
In the case of (1), it is possible to obtain a predetermined chromium deposition amount in an electrolysis time of 30 to 120 seconds.

The counter electrode (anode) in the cathodic electrolytic treatment
It is preferable to use a lead-based electrode used in chromium plating. However, it is also possible to use an insoluble electrode such as iron, stainless steel or carbon. When iron or stainless steel is used, ions such as iron and nickel elute, but it is acceptable if these ions are mixed into the electrolyte up to several g / l. Further, in the case of stainless steel, elution of trivalent chromium ions may occur, but trivalent chromium ions are generated during the process of chromium precipitation on the surface of the aluminum-based metal material serving as the cathode and are accumulated in the bath. Therefore, even in the case of a hexavalent chromium bath, trivalent chromium ions coexist in an actual operating state, and it is acceptable that trivalent chromium ions are mixed in the electrolyte up to several g / l. However, as impurities, phosphate ions having a small solubility product with nitric acid ions or trivalent chromium ions having strong oxidizing properties should be avoided from mixing in order to reduce the efficiency of film formation.

Next, the trivalent chromium bath will be described. In a trivalent chromium bath, chromium sulfate (Cr ₂ (SO ₄ ) ₃ ) or chromium chloride (CrCl ₃ ) is used as a chromium supply source, and these are used with an organic complexing agent such as oxalic acid, formic acid, glycine, oxycarboxylic acid, or the like. Use a complexed bath. By appropriately controlling the electrolysis current density and the electrolysis time, it is possible to obtain a film similar to a hexavalent chromium bath. However, a long electrolysis time is required when the treatment is performed at the same current density due to poor deposition efficiency. Also, in a bath using trivalent chromium, if a lead-based electrode is used as a counter electrode, trivalent chromium ions in the bath will be oxidized to hexavalent chromium ions, so it is necessary to use an insoluble electrode such as carbon. is there.

The aluminum-based metal material subjected to cathodic electrolysis using the acidic aqueous solution containing chromium of the present invention exhibits extremely good coating film adhesion and post-coating corrosion resistance by the subsequent cationic electrodeposition coating. The method according to the present invention may be carried out at any stage before the cationic electrodeposition coating, but is more preferably carried out at the material production stage in order to simplify the equipment because of the electrolytic treatment. For example, if the process is performed after the rolling process in a light pressure maker, since the aluminum-based metal material is flat, equipment for uniformizing the chromium adhering by the cathodic electrolysis treatment is simpler, and the shape of the target material is simpler. This is because the carry-out of the electrolytic treatment solution to the next step is reduced, and the burden on the wastewater treatment equipment is reduced. In addition, the surface-treated aluminum-based metal material of high added value by such a method can be coated as it is, so that the burden on the coating process of the material user (automobile, home appliance manufacturer, etc.) can be remarkably reduced. Further, since the film formed by the cathodic electrolysis method of the present invention is chemically stable, a phosphate treatment step (alkali degreasing → water washing → phosphoric acid) which is widely used as a conventional pretreatment for coating iron-based metallic materials. (Salt treatment → washing with water) has no effect on the effect, and the user can simultaneously paint with a combination of conventional iron-based metal materials. There is no need to add a new one.

[0014]

EXAMPLES Hereinafter, the present invention will be described in detail with reference to examples of the present invention and comparative examples, but the present invention is not limited to these examples. In this example, a test was performed in the following manner, and the results are shown in Table 2. (A) Test aluminum alloy material A5052 (JIS standard) 70 mm (length) x 150 mm (width) x 1.0 mm (thickness)

(B) Cathodic electrolytic treatment A5052 material is alkali-degreased (for example, a 2% aqueous solution of fine cleaner 4327 manufactured by Nippon Parkerizing Co., Ltd.
After heating and immersion for 5 minutes), the surface was cleaned and then subjected to a cathodic electrolysis treatment under the following conditions, followed by water washing and deionized water washing, followed by hot air drying at 100 ° C. . -Electrolyte composition: Refer to Table 1.-Electrolysis conditions: Electrolyte No. in Table 1. In Examples 1 and 2, a lead electrode was used as an anode, For No. 3, a carbon electrode was used as an anode, and the amount of chromium deposited was adjusted by the electrolysis time. Bath temperature 40 ° C Current density 2A / dm ²

(C) Electrocoating Coating was carried out under the following electrodeposition conditions using a cationic electrocoating paint ELEKRON 2000 manufactured by Kansai Paint. Electrodeposition conditions: The coating film thickness was targeted at 20 μm. Bath temperature: 29 ° C. Voltage: 220 V Energizing time: 120 seconds Rinsing: Tap water was sprayed for 20 seconds. Baking: The temperature was kept at 170 ° C. in an oven and kept for 20 minutes.

(D) Intermediate and Top Coating Assuming an automobile outer panel, after the cationic electrodeposition coating, the following middle and top coatings were further performed.・ Intermediate coating: Kansai Paint TP-37, target thickness 30μ
Spray painting with m. -Top coat: Spray-painted with Kanami Paint's Neo Amilac 6000 with a target film thickness of 30 µm.

An evaluation test was performed by the following method. (1) Measurement of Chromium Adhesion on Cathode Electrolytic Treatment Film It was measured by a fluorescent X-ray analysis method. (2) Salt Spray Test (Evaluation of Corrosion Resistance of Cathodic Electrodeposition Only) After cross-scratching the sample surface after cationic electrodeposition coating so as to reach a sharp cutter body, a salt spray test (JIS-Z2731) was performed for 1000 hours. The result of measuring the maximum swelling width (mm) on one side from the cross scratches in the case of was evaluated according to the following criteria. ：: 1.5 mm or less Δ: 1.6 to less than 4 mm ×: 4 mm or more

(3) Composite Cycle Test (Evaluation of Corrosion Resistance of Three Coats) After the cationic electrodeposition coating, a sample subjected to the middle / overcoat coating was cross-scratched with a sharp cutter so as to reach the substrate, and the following a → b The cycle of → c → was repeated 12 cycles, and the result of measuring the maximum swelling width on one side (mm) from the cross scratch after the cycle was evaluated according to the following criteria. a. Salt spray test (JIS-Z2371): 24 hours ← c b. Wetting test (40 ° C., 85% RH): 120 hours c. Indoor: 24 hours → a ○: 1.5 mm or less △: 1.6 to less than 4 mm ×: 4 mm or more

(4) Water-resistant secondary adhesion test The 3-coat paint sample used in the evaluation test of (3) was immersed in deionized water at 40 ° C. for 240 hours, and was then moved to a base using a sharp cutter. 0.0mm square gobang eyes 10
The number of strips obtained after cutting into 0 pieces and performing cellophane tape peeling was evaluated according to the following criteria. ○: Number of peeled pieces 0 △: Number of peeled pieces 1 to 5 ×: Number of peeled pieces 6 or more

Example 1 Electrolyte No. 1 in Table 1 After subjecting the aluminum material to cathodic electrolytic treatment with a target of 50 mg / m ² of chromium attached to the aluminum material using No. 1, it was subjected to a coating test. The electrolysis time at this time was 15 seconds.

Example 2 Electrolyte No. 1 in Table 1 After subjecting the aluminum material to cathodic electrolytic treatment with a target of a chromium deposition amount of 150 mg / m ² using No. 1, the coating material was subjected to a coating test. The electrolysis time at this time was 30 seconds.

Example 3 Electrolyte No. 1 in Table 1 After subjecting the aluminum material to cathodic electrolytic treatment with a target of a chromium adhesion amount of 300 mg / m ² using No. 1, the aluminum material was subjected to a coating test. The electrolysis time at this time was 60 seconds.

Example 4 The electrolyte solution no. After subjecting the aluminum material to cathodic electrolytic treatment with a target of a chromium adhesion amount of 150 mg / m ² using the aluminum material 2, the aluminum material was subjected to a coating test. The electrolysis time at this time was 30 seconds.

Example 5 The electrolyte solution No. 1 shown in Table 1 was used. After subjecting the aluminum material to cathodic electrolytic treatment with the target of chromium adhesion of 100 mg / m ² using No. 3, the aluminum material was subjected to a coating test. The electrolysis time at this time is 300
Seconds.

Example 6 The electrolyte No. 1 shown in Table 1 was used. After subjecting the aluminum material to cathodic electrolysis with a target of chromium deposition of 150 mg / m ² (electrolysis time: 30 seconds) using the sample No. 1, the aluminum material was further subjected to a phosphate treatment in the following steps and subjected to a coating test. This example is based on the premise that the aluminum material subjected to the cathodic electrolysis according to the present invention passes through the phosphating step together with the iron-based material, and in this case, the phosphating of the film formed by the cathodic electrolysis is performed. It is for investigating the influence of the process (degreasing, chemical conversion). (1) Degreasing: Fine cleaner L4480
(Nippon Parkerizing alkaline degreasing agent) Temperature 42 ° C
For 120 seconds. (2) Rinse: tap water was sprayed at room temperature for 30 seconds. (3) Surface adjustment: Preparen-ZTH (a surface conditioner manufactured by Nippon Parkerizing Co., Ltd.) was sprayed at room temperature for 20 seconds. (4) Phosphate treatment: Palbond L3080 (Zinc phosphate treating agent manufactured by Nippon Parkerizing) 12 at 42 ° C
An immersion treatment was performed for 0 seconds. (5) Rinse: tap water was sprayed at room temperature for 30 seconds. (6) Deionized water washing: Deionized water was sprayed at room temperature for 20 seconds. (7) Draining drying: 18 in an oven at a temperature of 110 ° C
Left for 0 seconds.

Comparative Example 1 After the aluminum material was degreased, it was directly coated without performing cathodic electrolytic treatment to prepare a sample.

Comparative Example 2 Instead of performing the cathodic electrolysis treatment on the aluminum material, the following chromate treatment was performed with the target amount of chromium attached being 50 mg / m ² , and then the sample was prepared by painting. In the chromate treatment, after the surface of the material is cleaned by alkali degreasing, a bath containing Alchrom 713, a reaction chromate treatment agent manufactured by Nippon Parkerizing Co., Ltd. is used at a concentration of 7%.
The immersion treatment was performed for 0 second. After the treatment, it was washed with tap water and deionized water and dried with warm air.

Comparative Example 3 An aluminum material was subjected to chromate treatment with a target chromium deposition amount of 150 mg / m ² instead of the cathodic electrolytic treatment, followed by painting to prepare a sample. The chromate treatment was the same as in Comparative Example 2, but the treatment time was 120 seconds.

The following can be said from the results in Table 2. As shown in Examples 1 to 5, those subjected to the cathodic electrolysis treatment according to the present invention impart extremely good coating performance to cationic electrodeposition coating. Moreover, as shown in Example 6, even after passing through the phosphating step which has been performed as a pretreatment for coating a conventional iron-based material after the cathodic electrolytic treatment, the effect is not changed at all. On the other hand, as shown in Comparative Example 1, those without the pre-coating treatment showed extremely poor results in the combined cycle test assuming the actual use environment. Further, as shown in Comparative Examples 2 and 3, those subjected to the chromate treatment, which is a conventional technique, have a slight difference depending on the amount of chromium adhering. The result was not satisfactory enough.

[0031]

By performing the cathodic electrolysis treatment of the present invention as a pre-coating treatment in the case of performing cationic electrodeposition coating on aluminum-based metal materials, it is possible to obtain extremely good coating performance. The advantages of dressing can be fully exhibited. Moreover, by preliminarily subjecting the aluminum-based metal material to the cathodic electrolysis treatment of the present invention, the material user can not only directly coat the metal material, but also perform the cathodic electrolysis to form the aluminum film. Since the system material does not affect the performance of the coating even if the system material is further passed through a pre-coating process of iron-based material, that is, a phosphating process, the aluminum-based metal material processed according to the present invention is made of iron-based material. Phosphate treatment and painting can be performed simultaneously in combination with the system material, which brings advantages such as the necessity of a new coating pretreatment process dedicated to aluminum, which is necessary for chromate treatment.

[0032]

[Table 1]

[0033]

[Table 2]

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) C25D 11/38

Claims (1)

(57) [Claims] 1. A cationic electrodeposition coating pretreatment of an aluminum-based metallic material, the metallic material surface hexavalent chromium ions and / or contains trivalent chromium ions, phosphate ions
Cathodic electrolytic treatment in an acidic aqueous solution having a pH of 2.0 or less and containing no cations.
A pretreatment method for cationic electrodeposition coating of an aluminum-based metal material having excellent secondary adhesion and corrosion resistance after coating.