JP2002146550A - Chromate treatment solution and treatment method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a chromate treatment solution and a treatment method by which a chromate film having excellent adhesion of a coating film and corrosion resistance can be deposited even when aqueous cleaning is performed in a chromate treatment solution using an oxycarboxylic compound as a reducing agent. SOLUTION: An oxycarboxylic compound is added in 0.3 to 1.1 by molar ratio to the total Cr. Further, ammonia is added thereto in 0.01 to 3.0 by molar ratio to the total Cr. When phosphoric acid or a phosphoric compound is added to the chromate treatment solution in the ratio of P/total Cr of 0.01 to 2.0, or, water dispersible organic resin is added thereto in 20 to 500 g/L, the corrosion resistance of the film further improves. The chromate treatment solution is applied on the material to be treatment such as a metallic material. After that, drying is performed without water washing to deposit the chromate film.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention provides a coating film excellent in adhesion and corrosion resistance even when subjected to aqueous cleaning such as alkali degreasing or weak acid degreasing during the pretreatment of coating after the formation of a chromate film. The present invention relates to a chromate treatment solution and a treatment method capable of forming a chromate film without elution of chromium ions and having excellent storage stability.

[0002]

2. Description of the Related Art Chromate treatment has been widely used as a temporary rust preventive treatment or a pre-coating treatment for metal materials such as zinc-plated steel, copper-plated steel plate, aluminum plate, and the like. As a chromate treatment solution, a part of hexavalent chromium ions in the treatment solution is reduced to insoluble trivalent chromium ions in advance, so that less harmful hexavalent chromium ions are eluted. Are widely used to form a thin chromate film having a yellow appearance. In addition, there is also a solution in which silica sol, phosphoric acid, and an organic resin are further added to a chromat treatment solution in which a part of the hexavalent chromium ion is reduced to a trivalent chromium ion to improve corrosion resistance and coating film adhesion. It is used.
For example, a chromate treatment solution containing a silica sol, a carboxylic acid and / or a carboxylic acid derivative at a reduction ratio of trivalent chromium ions of 25 to 60% (JP-A-6-41)
765) reducing the reduction rate to trivalent chromium ions from 40 to
Chromium containing 65% phosphoric acid and organic resin
And a treating solution (JP-A-9-165686).

However, since a large amount of hexavalent chromium ions still remain in such a chromate treatment solution, the chromate film does not contain hexavalent chromium ions at the stage of forming the chromate film. It has also been proposed to do so. For example, a method of reducing hexavalent chromium ions by utilizing an oxidation-reduction reaction accompanying metal elution when applied to a metal material and heat energy during drying. However, such a method requires a drying facility capable of high-temperature drying, and when a metal material is continuously treated, the pH may be increased due to elution of metal ions into the chromate treatment solution or contamination may occur. There is a problem that the treatment liquid easily gels.

[0004] Therefore, a method has been proposed in which, from the stage of the chromate treatment liquid, hexavalent chromium ions are scarcely contained, and trivalent chromium ions are stabilized even by a pH change by forming a complex. For example, epoxy resin, acrylic resin,
A method in which a polyol resin obtained by adding a polyol to a polyester resin or the like is added to a chromate treatment solution (Japanese Patent Laid-Open Publication No.
-9746), and a Cr concentration of 1 to 20 g /
Chromium (VI) is added to the chromatized solution L, and an oxycarboxylic acid compound such as tartaric acid, malonic acid, citric acid, lactic acid, gluconic acid, glyceric acid, tropic acid, benzylic acid or hydroxyvaleric acid is added to the hexavalent chromium A method of reducing the ions to trivalent chromium ions and reducing the hexavalent chromium ions to a Cr ⁶⁺ / total Cr ratio of 0.1 or less (Japanese Patent Application Laid-Open No. 10-81977). Here, the total Cr is the sum of trivalent and hexavalent chromium ions. The chromate film formed by these chromate treatment solutions has excellent hexavalent chromium elution resistance, good corrosion resistance, and good coating film adhesion even if the amount of chromium is increased without drying at high temperature.

However, when a metal material is treated with these chromate treatment liquids, and then the metal material is processed and painted, if an aqueous cleaning such as alkali degreasing or weak acid degreasing is performed before painting, There was a problem that the water-resistant secondary adhesion was reduced. Such a problem does not occur if a solvent-based cleaning liquid such as methylene chloride is used for cleaning. However, it is not used in recent years because there is a great possibility of adversely affecting the environment and the human body.

[0006]

DISCLOSURE OF THE INVENTION The present invention provides excellent coating film adhesion and corrosion resistance, and dissolution of hexavalent chromium ions, even when an aqueous cleaning such as alkali degreasing or weak acid degreasing is performed during pretreatment for coating. An object of the present invention is to provide a chromate treating solution and a treating method which can form a uniform chromate film and have excellent storage stability.

[0007]

According to a first aspect of the present invention, there is provided C
The r concentration is 1 to 40 g / L in total Cr, hexavalent chromium ions are reduced to trivalent chromium ions by addition of an oxycarboxylic acid compound, and hexavalent chromium ions are reduced to a ratio of ^{Cr6 +} / total Cr of 0.1. In the chromate treatment solution described below, the addition amount of the oxycarboxylic acid compound is added in a molar ratio of 0.3 to 1.1 with respect to the total Cr, and ammonia is added in the molar ratio of 0.01 to 3.0 with respect to the total Cr. A second aspect of the present invention is a chromat treatment solution characterized by adding phosphoric acid or a phosphoric acid compound to the chromate treatment solution of the first invention.
A chromate treatment liquid characterized by being added at a ratio of r = 0.01 to 2.0. Further, the third and fourth inventions are the chromate treatment liquids of the first or second invention. A chromate treatment liquid characterized in that 20 to 500 g / L of a water-dispersible organic resin is added to the solution. Here, the water-dispersible organic resin is a nonionic ionic resin alone or a mixture of a nonionic ionic resin having three kinds of hydrophilic components of anionic ionic, cationic ionic, and nonionic ionic types. It is preferable that the ratio of (anionic type + cationic type + nonionic type) is 0.9 or more. A fifth invention is a chromate treatment method comprising applying the chromate treatment liquid according to any one of the first to fourth inventions to a material to be treated, and then drying the material without washing with water.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The present inventors have formed a chromate treatment solution in which most or all of hexavalent chromium ions have been reduced to trivalent chromium ions by adding a polyol resin or an oxycarboxylic acid compound. Investigations were made on whether the chromate film was vulnerable to water-based cleaning. As a result, alkali metal ions such as sodium ions and potassium ions and surfactants were adsorbed to the chromate film during cleaning, and the hydrophilicity was enhanced. Turned out to be. And when we further investigated the cause of adsorption of this alkali metal ion and surfactant,
Phosphate ions that have not been used in the reduction of hexavalent chromium ions and have not reacted with the metal material remain in the chromate film, or are formed by decomposition of the oxycarboxylic acid compounds or the polyol resin. , A compound having a functional group such as a carboxyl group, a carbonyl group, or a hydroxyl group.

Therefore, the present inventors have proposed that when an oxycarboxylic acid compound is used as a reducing agent, the oxycarboxylic acid compound and its decomposition products are not left in the chromate film in order to prevent the unreacted oxycarboxylic acid compound and its decomposition products from remaining in the chromate film. Examination of the suitable amount of carboxylic acid added revealed that simply reducing the amount of carboxylic acid impaired the stability of trivalent chromium ions and reduced the stability of the chromate treatment solution. For example, when a plated steel sheet having a temperature of 40 ° C. is continuously treated assuming work in the summer, the chromate treatment liquid is likely to gel. Therefore, when the amount of the oxycarboxylic acid compound to be added is reduced, it is necessary to add a complexing agent for trivalent chromium ion as an auxiliary complexing agent. As a result of various studies on the auxiliary complexing agent, it was found that ammonia was preferable. When ammonia is added, the trivalent chromium ion forms an amine complex, and is stable in the processing solution.

In the present invention, the Cr concentration of the chromate treatment solution is 1 to 40 in total Cr (total of trivalent and hexavalent chromium ions).
g / L. If the total Cr concentration is lower than 1 g / L, the corrosion resistance is insufficient, and if the total Cr concentration is higher than 40 g / L, the treatment liquid tends to gel. An oxycarboxylic acid compound is added to the chromatized solution so that the molar ratio to the total Cr becomes 0.3 to 1.1, and ammonia is added to the total C
It is added so that the molar ratio with respect to r becomes 0.01 to 3.0. The total amount of the oxycarboxylic acid compound added is C
If the molar ratio to r is less than 0.3, the reduction of hexavalent chromium ions cannot be reduced to 0.1 or less in the ratio of Cr ⁶⁺ / total Cr, so that the obtained chromate film has a resistance to 6%.
The elution of chromium (IV) ions decreases, and if it is more than 1.1, the adhesion of the coating film decreases with aqueous washing. Here, the oxycarboxylic acid compound is the same as the conventional one, for example, tartaric acid, malonic acid, citric acid, lactic acid, gluconic acid, glyceric acid, tropic acid, benzylic acid, hydroxyvaleric acid, etc., which can be used alone or in combination. . On the other hand, the amount of added ammonia is
When the molar ratio to the total Cr is less than 0.01, the stability of the chromate treatment liquid is not sufficiently improved when the metal material is continuously treated. When the molar ratio is more than 3.0, the p of the chromate treatment liquid is insufficient.
Since H becomes too high, hydrogen ions indispensable for the reduction reaction become insufficient, and it takes time for the reduction treatment. The reduction by the oxycarboxylic acid compound is accelerated by heating the chromate treatment liquid, and a reduction treatment in a short time becomes possible.
Although it is industrially advantageous, if the temperature is too high, the stability of the complexed trivalent chromium ion is impaired and the treatment liquid gels. Therefore, it is preferable to perform the treatment at a liquid temperature of 90 ° C. or lower.

When a phosphoric acid or a phosphoric acid compound is added to the chromate treatment solution, the chromate film can be made into a hardly soluble chromium phosphate film. As the phosphoric acid compound, a water-soluble compound such as ammonium dihydrogen phosphate is used, and the amount of P added is adjusted so that P / total Cr = 0.01 to 2.0. If it is less than 0.01, the effect of improving corrosion resistance due to insolubilization of the film is small, and if it exceeds 2.0, unreacted phosphoric acid with the metal material may remain in the chromate film. When water-based cleaning is applied to the chromate film,
Coating adhesion decreases.

When a water-dispersible organic resin is added to the chromate treatment solution without or with phosphoric acid or a phosphoric acid compound added, the barrier effect of the chromate film is increased in any case. And the corrosion resistance of the processed part can be improved. The addition of the water-dispersible organic resin is from 20 to
Adjust to 500 g / L. If it is less than 20 g / L, the effect of improving the corrosion resistance of the processed portion is small, and if it is more than 500 g / L, the viscosity of the treatment liquid becomes high and application becomes difficult.

The water-dispersible organic resin has an anion, a cation, or a nonion depending on the hydrophilic component introduced. In addition, the elution of metal ions from the plated steel sheet may disturb the charge balance of the water-dispersible organic resin, resulting in an increase in the average particle diameter and gelation of the treatment liquid. However, if the ionicity is nonionic, such a phenomenon does not occur. Therefore, it is preferable to use nonionic ones. On the other hand, when the organic resin is a mixture of an anionic resin and a cationic resin, the ratio of nonionic resin / (anionic resin + cationic resin + nonionic resin) is set to 0.1. 9 or more to prevent the treatment liquid from gelling.
In order to make the ionicity of the water-dispersible organic resin nonionic, polyethylene glycol, isocyanate, etc. may be introduced into the polymer skeleton.
In order to make the cation, a sulfonic acid (salt) group, a carboxyl (salt) group or the like may be introduced.

It has been conventionally practiced to add a polymer resin powder having a melting point of 100 ° C. or higher as a lubricant to the chromate treatment liquid to enhance the lubricity of the chromate film at the time of press working. However, in the case of this chromate treatment liquid, an olefin resin such as polyethylene or polypropylene or a fluorine resin having a melting point of 100 ° C. or more may be added.

The application of the chromate treatment liquid to the material to be treated such as a metal material is carried out in the same manner as in the case of the conventional coating type chromate treatment, by a known method, for example, a roll coating method, an air car. When the method is carried out by a ten method, an electrostatic atomization method, a squeeze roll coating method or the like, and is carried out by a method of drying without washing with water, a chromate film excellent in water-resistant secondary adhesion of a coating film can be formed. As the material to be treated, a Zn-based plated steel sheet, for example, Zn, Zn-
Al-based alloy, Zn-Ni-based alloy, Zn-Mn-based alloy, Z
Examples of a plated steel sheet such as an n-Mg-based alloy and a Zn-Al-Mg-based alloy and an Al-based plated steel sheet include plated steel sheets such as an Al, Al-Zn-based alloy, and an Al-Si-based alloy. Furthermore, treatment of a Cu-based plated steel sheet, a Ni-based plated steel sheet, or the like is also possible.

[0016]

EXAMPLES Example 1 Various amounts of ammonia were first added to an aqueous solution of chromic anhydride, and then different oxycarboxylic acid compounds were added to prepare chromate treatment solutions of various compositions. Then, this treatment liquid is applied to an electrogalvanized steel sheet (sheet thickness 0.8 m).
m, the amount of Zn plating on one side is 20 g / m ² ).
It was applied by a tar and dried at an ultimate plate temperature of 100 ° C. Table 1
2 shows the composition of the chromate treatment solution and the amount of chromium adhering to the chromate film.

[0017]

[Table 1]

Next, the following performance tests were performed on the chromate-treated steel sheet. Table 2 shows the results. (1) Stability test of treatment liquid A treatment liquid at 40 ° C was set on a roll coater and continuously applied to a steel sheet. Then, even after the application of 3,000 m ² in surface area, the treatment liquid was evaluated by the symbol を where no gelation or precipitate was observed, and the observed liquid was evaluated with the symbol ×. (2) Cr ⁶⁺ elution resistance test A test piece of a chromate-treated steel sheet was immersed in hot water at 90 ° C. for 3 minutes, the amount of Cr ⁶⁺ eluted was measured, and the elution amount was 1 mg / m ^2.
Less than 1 mg / m ² and 5 mg / m ²
Those with less than 5 mg / m ² were evaluated with the symbol x and those with 5 mg / m ² or more were evaluated with the symbol x.

(3) Adhesion test of coating film After the test piece was subjected to alkali degreasing, washed with water and dried, an organic solvent-based acrylic paint was applied to a thickness of 25 µm on a dry coating film and dried. Next, the coated steel sheet was exposed to hot water of 90 ° C for 2 hours.
After immersion for a time, a coating film adhesion test based on the grid method of JIS K 5400 was performed. And the coating film remaining rate is 8
Those with 0% or more were evaluated with the symbol 、, those with 60% or more and less than 80% were evaluated with the symbol 、, and those with less than 60% were evaluated with the symbol x. The degreasing was performed using Surfcleaner-SD270 (manufactured by Nippon Paint Co., Ltd.) at pH 12 and at a liquid temperature of 40 ° C.
It was degreased for 0 seconds. Nippon Paint Co., Ltd. for acrylic paint
Manufactured by Super Luck F-50. (4) Corrosion resistance test of unprocessed portion A salt spray test (JIS Z 2371) was carried out for 100 hours, and those having a white rust occurrence rate of less than 5% of the entire area were indicated by a symbol ◎.
, Those of 5% or more and less than 10% were evaluated with the symbol で, those of 10% or more and less than 30% were evaluated with the symbol 、, and those of 30% or more were evaluated with the symbol x.

[0020]

[Table 2]

As shown in Comparative Examples 1 of Tables 1 and 2, when the concentration of ammonia with respect to the total Cr in the chromate treatment liquid is lower than 0.01, stabilization of trivalent chromium ions during continuous treatment of the steel sheet. Is insufficient, gelation of the treatment liquid is observed. Further, as shown in Comparative Example 2, if the amount of the oxycarboxylic acid compound added to the chromatized solution was excessive,
Oxycarboxylic acid compounds that do not contribute to the reduction reaction remain in the chromate film, and the adhesion of the chromate film after alkali degreasing decreases. On the other hand, the chromate film formed by the chromate treatment solution of the present invention shows good coating adhesion even after alkali degreasing, has no elution of hexavalent chromium ions, and has good corrosion resistance in unprocessed portions.

Example 2 A water-dispersible organic resin in which the ratio of phosphoric acid to nonionic ionic is 0.9 in the chromatized solutions Nos. 2, 3, 4, 5, 9 and 10 of Example 1 Was added. Next, these treatment solutions were applied to the same electrogalvanized steel sheet as that used in Example 1 with a roll coater so that the chromium deposition amount of each treatment solution was constant at 40 mg / m ^2. , And reached a plate temperature of 120 ° C. Table 3 shows the composition of the processing solution and the performance test results similar to those in Example 1. In addition, Table 3 also shows the results of the corrosion resistance test of the processed part performed in the following manner. (5) Corrosion resistance test of processed part A test piece (35 mm x 300 mm) was subjected to a drop test by a pressing force of 200 kg and a drawing speed of 500 mm / mi.
n, a salt spray test (JISZ 23
71) was performed for 100 hours. The symbol ◎ indicates that there is no red rust, the symbol を indicates that the area of red rust occurrence is less than 10% of the total area, the symbol を indicates that the area is 10% or more and less than 30%, and the symbol indicates that the area is 30% or more. It evaluated by x.

[0023]

[Table 3]

As shown in Table 3, the addition of phosphoric acid or a water-dispersible organic resin to the chromate treatment solution of the present invention improves the corrosion resistance. However, when the added amount of phosphoric acid is as small as 0.05 in P / total Cr as in No. 15, and when the added amount of organic resin is as small as 10 g / L as in No. 12, the effect of improving the corrosion resistance is small. Furthermore, as in No. 16, when the amount of phosphoric acid added is large, unreacted phosphoric acid remains in the chromate film, and the adhesion of the film after alkali degreasing decreases. In No. 18, since the added amount of the organic resin was excessive, the treatment liquid thickened and gelled, and it was difficult to evaluate the quality characteristics.

[0025]

As described above, the Cr concentration is 1 to 1 for all Cr.
40 g / L, 6 by addition of oxycarboxylic acid compound
The amount of the oxycarboxylic acid compound added to the total Cr in a chromatized solution in which the hexavalent chromium ions are reduced to trivalent chromium ions and the hexavalent chromium ions are reduced to 0.1 or less in the ratio of Cr ⁶⁺ / total Cr. In addition to the addition of 0.3 to 1.1 in a molar ratio, ammonia is added in a molar ratio of 0.3 to the total Cr.
When added to the chromate coating, water-cleaning such as alkali degreasing or weak acid degreasing provides excellent coating adhesion and corrosion resistance and does not elute hexavalent chromium ions. Further, the chromate treatment liquid has excellent storage stability. Phosphoric acid or a phosphoric acid compound is added to this chromatized solution by P / total Cr =
When added at a ratio of 0.01 to 2.0 or when a water-dispersible organic resin is added at 20 to 500 g / L, the corrosion resistance is further improved. When these chromate treatment liquids are applied to a material to be treated such as a metal material and then dried without washing with water,
A chromate film excellent in water-resistant secondary adhesion of a coating film can be formed.

Continued on the front page (72) Inventor Hirofumi Takezu 5th Ishizu Nishimachi, Sakai City, Osaka Pref. CA36 CA38 CA39 DA15

Claims (6)

[Claims] 1. The Cr concentration is 1 to 40 g / L for all Cr.
Then, the addition of an oxycarboxylic acid compound reduces hexavalent chromium ions to trivalent chromium ions, and the hexavalent chromium ions are reduced to 0.1 or less in the ratio of Cr ⁶⁺ / total Cr to 0.1 or less. The total amount of carboxylic acid compound added is C
While 0.3 to 1.1 are added in a molar ratio to r,
Ammonia is used in a molar ratio of 0.01 to 3.0 with respect to total Cr.
A chromate treatment solution characterized by being added. 2. A chromate treatment solution, wherein phosphoric acid or a phosphoric acid compound is added to the chromate treatment solution of claim 1 in a ratio of P / total Cr = 0.01 to 2.0. 3. A chromate treatment liquid, wherein a water-dispersible organic resin is added to the chromate treatment liquid according to claim 1 in an amount of 20 to 500 g / L. 4. A chromate treatment liquid, wherein a water-dispersible organic resin is added to the chromate treatment liquid according to claim 2 in an amount of 20 to 500 g / L. 5. The water-dispersible organic resin is a nonionic ionic resin alone or a mixture of a nonionic ionic resin having three types of hydrophilic components of anionic, cationic and nonionic ionic resins. The chromate treatment liquid according to claim 3 or 4, wherein the ratio of (anionic ionic substance + cationic ionic substance + nonionic ionic substance) is 0.9 or more. 6. A method for chromate treatment, comprising applying the chromate treatment liquid according to any one of claims 1 to 5 to a material to be treated and drying without washing with water.