JPH0925581A - White chromate treatment method with excellent chromium elution resistance, corrosion resistance and coating performance - Google Patents

Abstract

(57) Abstract: [PROBLEMS] To provide a chromate treatment method that improves corrosion resistance and coating performance of a non-ferrous metal-plated steel sheet or a non-ferrous metal material and has a beautiful appearance after treatment and excellent chromium elution resistance. SOLUTION: Reduced chromic acid having a Cr ³⁺ / Cr ⁶⁺ composition ratio of 3/7 to 7/3 is converted to chromic anhydride in an amount of 7.5 to 100 g / on a surface of a non-ferrous metal-plated steel sheet or a non-ferrous metal material. l
And a phosphoric acid compound in a weight ratio of 0.5 to 3.0 based on the reduced chromic acid equivalent of chromic anhydride, and a weight ratio of 0.5 to 5 in terms of the reduced chromic acid equivalent of chromic anhydride. 0.0 silica and / or colloidal silica of silicate, and at least one selected from phosphonic acid or its salt compound 1.0 to 20 g / l, water-soluble or water-dispersible organic polymer compound A method for treating a white chromate film having a beautiful appearance after treatment, which is excellent in chromium elution resistance, corrosion resistance and coating performance, by applying a chromate treatment liquid containing more than 30 g / l and heating and drying.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to aluminum (hereinafter referred to as aluminum) or aluminum alloy-plated steel sheet, zinc or zinc alloy-plated steel sheet, tin or tin alloy plating, and aluminum or aluminum alloy material, zinc or zinc alloy material. The present invention relates to a chromium-dissolving white chromate treatment method which is excellent in corrosion resistance of a non-ferrous metal-plated steel sheet or a non-ferrous metal material such as a material, tin or a tin alloy-based material, and appearance quality after coating performance treatment.

[0002]

2. Description of the Related Art Chromate treatment has been used for a long time as a simple anticorrosion treatment for metal surfaces, and is roughly classified into electrolytic chromate and reactive chromate whose main component is trivalent chromium.
There is a coating chromate which contains hexavalent chromium and is dried after coating without washing with water. In recent years, chromate treatment has come to be widely used in home appliances, building materials, automobiles, etc.,
Consumers have come to demand various performances. For example, uniformity of appearance, appearance quality such as fingerprint resistance, paint adhesion, corrosion resistance when used naked, poor solubility of chromium in alkali degreasing (chromium elution resistance), etc. are examples. Among these performances, for example, corrosion resistance, particularly corrosion resistance in the worked part and resistance to dissolution of chromium, which are difficult to achieve at the same time, are included, and it is technically not easy to express all the performances in a well-balanced manner. From the viewpoint of consumer protection and global environmental protection, it is considered that the insolubility of chromium is an important issue to be solved in the responsibility of the material supplier, not only from the demand of consumers, but especially hexavalent chromium. Countermeasures are urgently needed for coating chromate containing a large amount of.

As a known technique for making chromate insoluble, for example, as described in JP-A-3-215683, a method of heating the chromate film at a relatively high temperature of 300 ° C. is known. However, it is not economical considering the cost of the drying equipment. In addition, Japanese Unexamined Patent Publication No.
As seen in JP 358082 A and JP 5-287548 A, a resin such as polyacrylic acid or a reducing agent such as alcohol is added to a chromate treatment bath, hexavalent chromium is fixed by reduction, and trivalent chromium is resin. A method of crosslinking in the inside is also known. According to this method, the corrosion resistance of the chromate film is improved by helping the barrier effect of the resin, but if the film breaks in the processed part, the self-healing action of hexavalent chromium does not work, so that the corrosion resistance of the processed part is not sufficient. The difficulty remains. Also, since a large amount of reducing components are present in the treatment bath,
Poor bath stability. Japanese Patent Application Laid-Open No. 61-23767 discloses that a mixture of a water-dispersible organic polymer containing no hydroxyl group and chromate has excellent bath stability. However, the obtained chromate-treated plate has a significantly high chromium elution amount.

JP-A-63-145785 discloses a composition comprising an acrylic polymer emulsion obtained by emulsion polymerization using a polyoxyethylene-polyoxypropylene block polymer emulsifier and a hexavalent chromium compound. It is disclosed. This composition is 40 ℃ due to the effect of emulsifier
However, it is stable for 3 weeks or more, but since the emulsifier remains in the resin chromate film after drying, water resistance and bare corrosion resistance are not sufficient. In addition, the present inventors have filed Japanese Patent Application No. 6-30289.
No. 0 discloses a chromate treatment bath containing reduced chromic acid, phosphonic acid and a water-soluble organic polymer. In this case, a chromate film excellent in corrosion resistance, paint adhesion and treated appearance can be obtained, but the organic compound used is 30 g.
/ L or less, the poor solubility of chromium (chromium elution resistance) was not sufficient, and further improvement was required in this respect.

[0005]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a white chromate treatment method which is excellent in corrosion resistance and paint adhesion even though it has a low chromium elution. .

[0006]

Means for Solving the Problems In the chromate treatment bath containing reduced chromic acid, phosphonic acid and an organic polymer compound as a main component, the present inventors have improved the corrosion resistance by increasing the addition concentration of the organic polymer compound. We have succeeded in the development by discovering that a white chromate treatment liquid with excellent chromium elution resistance can be obtained without deteriorating paint adhesion and appearance after treatment. That is, the gist of the present invention is to convert the reduced chromic acid having a composition ratio of Cr ³⁺ / Cr ⁶⁺ of 3/7 to 7/3 on the surface of a non-ferrous metal-plated steel sheet or a non-ferrous metal material into chromic anhydride. 7.5-100 g / l, (b) a phosphoric acid compound in a weight ratio of 0.5 to 3.0 with respect to the chromic anhydride equivalent of the reduced chromic acid, and (c) an anhydride of the reduced chromic acid. Colloidal silica of silica and / or silicate in a weight ratio of 0.5 to 5.0 with respect to chromic acid, and (di) phosphonic acid or phosphonate compound 1.0 to 20 g / l, and (E)
Water-soluble or water-dispersible organic polymer compound 30 g / l
A chromate treatment liquid containing super and is applied, dried by heating, and converted to a Cr amount of 7.5 to 100 mg / m ² per side.
The method is a white chromate treatment method which is excellent in chromium elution resistance, corrosion resistance, and coating performance of a nonferrous metal-plated steel sheet or a nonferrous metal material characterized by forming a chromate film.

The features and effects of each component constituting the hardly soluble chromate treatment liquid excellent in corrosion resistance, coating performance and appearance after treatment, which are the objects of the present invention, will be described in detail below. (I)
As the reduced chromic acid, the chromic acid aqueous solution prepared by reacting an aqueous solution of chromic anhydride with a reducing agent to adjust the composition ratio of Cr ³⁺ / Cr ⁶⁺ to 3/7 to 7/3 is used. Further, the concentration of reduced chromic acid in the chromate treatment solution is 7.5 with chromic anhydride.
The concentration is regulated in the range of up to 100 g / l, and the concentration to be used is determined depending on the coating method and conditions. Reduced chromic acid in which Cr ⁶⁺ is partially reduced to Cr ³⁺ is prepared by the following method. That is, an inorganic anion (for example, phosphate ion) is added to a high-concentration aqueous solution of chromic anhydride to prepare an organic reducing agent,
Adding inorganic reducing agent, Cr ³⁺ by reduction reaction Cr ⁶⁺
Change As the reducing agent, organic compounds such as starch, sugars and alcohols, or inorganic compounds such as hydrazine and hypophosphorous acid are used.

When the composition ratio of Cr ³⁺ / Cr ⁶⁺ is less than 3/7, a large amount of soluble Cr ⁶⁺ is contained in the chromate film formed, so that the film is colored and the corrosive environment after coating is affected. The paint adhesion when exposed, the so-called secondary paint adhesion and the corrosion resistance after painting deteriorate. On the other hand, Cr ³⁺ / C
When the composition ratio of r ⁶⁺ exceeds 7/3, the chromate treatment bath is apt to gel with time and the corrosion resistance deteriorates. Therefore, the composition ratio of Cr ³⁺ / Cr ⁶⁺ in the reduced chromic acid of (a) is regulated in the range of 3/7 to 7/3, and preferably in the range of 5/5 to 6/4.

When the concentration of reduced chromic acid in the chromate treatment liquid is less than 7.5 g / l, it is difficult to form a chromate film satisfying the corrosion resistance and the coating performance, and when the concentration exceeds 100 g / l. In particular, there is an increased tendency for the chromate treatment bath to gel over time. Therefore, the concentration of the reduced chromic acid in (a) is 7.5 to 100 g / l in terms of chromic anhydride, and preferably 10 to 60 g / l.
The range is l.

Further, the chromate-treating liquid of the present invention has the purpose of improving the uniformity of the phosphoric acid compound (b) and the chromate-treating liquid for the purpose of improving the whiteness of the chromate film and the corrosion resistance, and the coating performance. (C) Silica and / or silicate colloidal silica is added. (B) Examples of the phosphoric acid compound include phosphoric acid (H ₃ PO ₄ ) and polyphosphoric acid (H
_{2 P 2 O 7, H 5} P 3 O 10, H 6 P 4 O 13), and its ammonium salts, Al salts, Mg salts. You may use these individually or in mixture of 2 or more types.

(B) The addition amount of the phosphoric acid compound is 0.5 to 1 based on 1 of the reduced chromic acid of (a) converted to chromic anhydride.
It is regulated within the range of 3.0. (B) When the addition amount of the phosphoric acid compound is less than 0.5 with respect to (a) reduced chromic acid, a white chromate film is difficult to be formed, and the addition amount is 3.0 with respect to reduced chromic acid. If it exceeds the range, the chromate film is likely to dissolve in water and the corrosion resistance deteriorates. Therefore, the addition amount of the (b) phosphate compound is
(B) It is 0.5 to 3.0, preferably 0.75 to 2.0 with respect to the reduced chromic acid.

The silica (c) and / or the colloidal silica silicate is added in a range of 0.5 to 5.0 with respect to (b) 1 of reduced chromic acid converted to chromic anhydride. (C) When the amount of colloidal silica added is less than 0.5 with respect to (A) reduced chromic acid, the uniform coating property deteriorates, so that the appearance performance and corrosion resistance targeted by the present invention,
It is difficult to secure painting performance. On the other hand, the addition amount of (c) colloidal silica is (b) 5.
If it exceeds 0, the work adhesion of the chromate film is deteriorated, and the appearance is deteriorated due to interference color. Therefore, the addition amount of (c) colloidal silica is 0.5 to 5.0, and preferably 1.5 to 3.5 with respect to (a) reduced chromic acid.

The (c) colloidal silica used in the present invention is mainly used as a fine particle colloid having an average particle size of 1 to 100 mμ, and the primary or secondary average particle size is 500 to 3, depending on the intended appearance. The colloidal silica having a relatively large particle size of 000 mμ may be added in combination. Further, in the present invention, in order to form a white chromate film excellent in desired corrosion resistance and coating performance, phosphonic acid or its salt compound shown below is 1.0
~ 20 g / l is added. Phosphonic acid is represented by the following formula (I):
(IV).

[0014]

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[0015]

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[0016]

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[0017]

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[0018]

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Also, one or more compounds selected from these water-soluble salts may be used. The phosphonic acid or its salt compound selected from the above is added singly or in combination of two or more kinds to the chromate bath. Among the phosphonic acids, particularly hydroxyalkyldiphosphonic acid, aminoalkylphosphonic acid and its salt compounds are easily dissolved in the chromic acid solution, and the solution preparation and handling on an industrial scale are relatively easy, which is preferable in practice. .

The addition amount of these (d) phosphonic acids is 1.0
If it is less than g / l, the action and effect of phosphonic acid, which is the object of the present invention, that is, the surface cleaning due to the etching action on the surface of the material to be treated and the accompanying uniform formation of the chromate film and the anticorrosion effect due to inclusion in the film are unsatisfactory. Since it is sufficient, the desired excellent corrosion resistance and coating performance cannot be obtained. Also (d)
When the amount of phosphonic acid added exceeds 20 g / l, the effect of addition is saturated and the stability of the treatment bath is deteriorated by promoting the reduction of Cr ^{6+ in} the chromate treatment bath, which is not preferable. Therefore, (d) the addition amount of the phosphonic acid to the chromate treatment bath is 1.0 to 20 g /
It is regulated in the range of 1, preferably 1.5 to 10 g / l.

Further, in the present invention, in order to suppress the elution of chromium from the chromate film, the water-soluble or water-dispersible organic polymer compound (e) is added. Addition of organic polymer not only improves chromium elution resistance, but also
It also has the effect of improving coating performance and corrosion resistance. As the organic polymer compound, anionic polyacrylic acid having a carboxyl group and its co-polymer compound, maleic acid-co-polymer compound, vinyl acetate-co-polymer compound are used. These organic polymer compounds are mainly added and used alone, but two or more kinds of them may be added in combination.

The amount of this organic polymer compound added is 30 g.
It is necessary to control it to over 1 / l. It is presumed that this is because when the amount exceeds 30 g / l, the sealing effect by the organic polymer compound remarkably appears, and as a result, the chromium elution amount decreases. When the amount added is 30 g / l or less, as shown in FIG. 1, it is difficult to obtain the hardly soluble chromate film which is the object of the present invention. However, there is a concern that the long-term stability of the treatment liquid may be impaired as the amount of the organic polymer compound added increases, but the amount of the organic compound added may be controlled according to the required chromate film characteristics. Therefore, the addition amount of the organic polymer compound is regulated in the range of more than 30 g / l, preferably in the range of more than 30 to 180 g / l.

The relationship between the amount of organic polymer compound added and the amount of chromium elution shown in FIG.
It is measured by the following treatment liquid composition and chromium elution test using a galvanized steel sheet of g / m ² . (1) Treatment liquid composition-Chromic acid concentration 20 g / l (Cr ³⁺ 55%)-Phosphoric acid 20 g / l-Silica colloid 60 g / l-Phosphonic acid 10 g / l-Organic polymer compound 0-220 g / l (2 ) Chromium elution test Measure the amount of chromium on the steel sheet before and after immersion in boiling water for 30 minutes by fluorescent X-ray method

The present invention is configured as described above.
(A) Reduced chromic acid- (b) phosphoric acid compound- (c) roller
Idal silica- (ni) phosphonic acid or one of its salt compounds
More than one type- (e) Water-soluble or water-dispersible organic polymer
A chromate treatment liquid consisting of a compound is applied to the surface of the material to be treated.
Then, in terms of Cr, 7.5-100 mg / m per side ^Two 
And heat dried. The method of applying the chromate solution is
It is possible to use a method which is generally used in the past. For example,
Apply by dipping or spraying method, squeeze roll
Method, air knife method to remove excess chromate treatment liquid
Method to wipe and adjust chromate film amount, roll coater
Method is used to adjust the amount of chromate film.
It is. Next, after applying the chromate treatment liquid, heat drying
Although it is treated, the heating and drying method has also been
The known method of is adopted. For example, hot air drying, gas
Typically, electric heating, infrared heating, etc. are used, and the plate temperature is 4
In the temperature range of 0 to 200 ° C, preferably 60 to 150 ° C
Heat dried.

The amount of the chromate film formed on the surface of the material to be treated by these methods is regulated within the range of 7.5 to 100 mg / m ² per one side in terms of Cr. When the amount of deposited Cr is less than 7.5 mg / m ² , the white appearance of the present invention, which is the object of the present invention, can be obtained, but the corrosion resistance and the corrosion resistance after coating are insufficient, which is not preferable.
On the other hand, if the amount of deposited Cr exceeds 100 mg / m ² , the adhesion workability of the chromate film is deteriorated and the processing adhesion after coating is also deteriorated, which is not preferable. Therefore, the amount of chromate film in the present invention is in the range of 7.5 to 100 mg / m ² , preferably 10 to 60 mg / m ² per one surface in terms of Cr amount.

The material to be treated which is the subject of the present invention is an Al-plated steel sheet by a hot dipping method, an Al-Si alloy plated steel sheet, a Zn plated steel sheet, a Zn-Al alloy plated steel sheet, a Zn-Al-Si alloy. System alloy plated steel sheet, Zn-
Al-Mg alloy plated steel sheet, Zn-Fe alloy plated steel sheet, Zn-plated steel sheet by electroplating method, Zn-Ni
Type alloy plated steel sheet, Zn-Cr type alloy plated steel sheet, Zn
-Ni-Cr based alloy plated steel sheet, Zn-Fe based alloy plated steel sheet, Sn based alloy plated steel sheet and other various non-ferrous metal plated steel sheets and Al materials, Al-Mg-Si, Al-Mg-Si
-Cu, Al-Mg-Si-Cu-Mn alloy-based material, Z
Examples include non-ferrous metal materials such as n-material, Zn-Al, Zn-Mg, and Zn-Al-Mg alloy materials.

In particular, in the application of the method of the present invention, compared to the conventional method, the material to be treated, in which the action and effect of (di) phosphonic acid or its salt compound is remarkably obtained, that is, a stable oxide film is formed. A very effective performance improving effect can be obtained for an aluminum-plated steel sheet, an aluminum alloy-plated steel sheet, a Zn-plated steel sheet, a Zn-alloy plated steel sheet and an aluminum material, an aluminum alloy material, a Zn alloy material and the like by the hot dipping method. Furthermore, when the method of the present invention is applied, generally, the material to be treated to which the oil and fat content is not adhered is left as it is, and the material to which the oil and fat content is adhered is surface-treated with a degreasing solution containing an alkali builder. Chromate treatment is applied after cleaning, but not limited to this. For example, when the surface of the material to be treated is not significantly discolored by the degreasing treatment, the method of the present invention may be applied after degreasing and washing treatment of the material to which the oil and fat content is not attached with a degreasing agent containing an alkali builder or the like. No problem.

[0028]

EXAMPLES In order to clarify the effects of the present invention, some examples and comparative examples will be specifically described. Examples A to G and Comparative Examples a to e Table 1 shows the composition of the chromate treatment liquid constituted by the method of the present invention as an example. Table 2 shows the composition of the chromate treatment liquid used as a comparative example. Next, Table 3 shows the performance evaluation results of the chromate-treated materials against the test materials of the chromate-treated solution according to the method of the present invention and the comparative chromate-treated solution, using typical examples of various non-ferrous metal materials as test materials. In addition, in the chromate treatment, the non-ferrous metal material having oil and fat adhered thereto was subjected to chromate treatment after degreasing with an alkaline degreasing agent containing 10 g / l NaOH and 5 g / l Na ₂ CO ₃ as main components. In addition, the material without oil and fat content was directly subjected to chromate treatment and subjected to an evaluation test.

The performance of the chromate treated material was evaluated according to the following method. Evaluation of corrosion resistance The white rust occurrence rate after 240 hours of salt spray test (JIS Z2371) was measured and judged according to the following criteria. ⊚: No white rust occurred ◯: White rust occurrence rate ≦ 5% △: 5% <White rust occurrence rate ≦ 20% ×: 20% <White rust occurrence rate

Chromium elution resistance The amount of chromium deposited before and after immersion in boiling water for 30 minutes was measured by fluorescent X-rays, and the rate of decrease was calculated by the following formula, and judged according to the following criteria. Chromium elution rate (%) = (Cr deposition amount before immersion-Cr deposition amount after immersion) / (Cr deposition amount before immersion) x 100 ◎: Elution rate ≤ 5% ◯: 5% <Elution rate ≤ 10% △: 10 <dissolution rate ≤ 20% x: 20 <dissolution rate

Paint Adhesion A melamine alkyd resin paint is applied to 25 μm, baked and then immersed in boiling water for 30 minutes. Immediately after being taken out, a 2 mm square is processed with a 10 × 10 = 100 mass cutter, and the tape is peeled off. The peeling area ratio of the paint peeled off by tape peeling was measured and judged according to the following criteria. ⊚: No peeling ◯: Peeling rate ≦ 5% △: 5% <Peeling rate ≦ 15% ×: 15% <Peeling rate

Appearance after treatment The yellowness (Y1 value) after chromate treatment was measured with a color computer (model SM-3) manufactured by Kazu Testing Machine Co., Ltd., and evaluated according to the following criteria. ⊚: Y1 ≦ −1.0 ◯: −1.0 <Y1 ≦ 2.0 Δ: 2.0 <Y1 ≦ 5.0 x: 5.0 <Y1 From these results, the white chromate treatment liquid of the present invention is obtained. The nonferrous metal-plated steel sheet or nonferrous metal material treated by
After treatment, it has a beautiful appearance, excellent chromium elution resistance, corrosion resistance and coating performance.

[0033]

[Table 1]

[0034]

[Table 2]

[0035]

[Table 3]

[0036]

EFFECT OF THE INVENTION With the white chromate treatment liquid of the present invention,
Aluminum or aluminum alloy plated steel sheet, zinc or zinc alloy plated steel sheet, non-ferrous metal plated steel sheet such as tin or tin alloy plated steel sheet, and aluminum or aluminum alloy material, zinc or zinc alloy material, tin or tin alloy material, etc. Chromate treatment with excellent corrosion resistance, paint adhesion, appearance quality after treatment and chromium elution resistance is possible for non-ferrous metal materials.

[Brief description of drawings]

FIG. 1 is a diagram showing the relationship with the amount of chromium eluted from a chromate film when the amount of an organic polymer compound added is changed in the chromate treatment liquid of the present invention.

Front Page Continuation (72) Inventor Haruhiko Eguchi 1-1, Toibata-cho, Tobata-ku, Kitakyushu-shi, Fukuoka New Nippon Steel Co., Ltd. Yawata Works

Claims (1)

[Claims] 1. The composition ratio of (a) Cr ³⁺ / Cr ⁶⁺ is 3/7 to 7 / on the surface of a nonferrous metal-plated steel sheet or a nonferrous metal material.
The reduced chromic acid of 3 is 7.5 to 100 in terms of chromic anhydride.
g / l, and (b) a phosphoric acid compound in a weight ratio of 0.5 to 3.0 with respect to the chromic anhydride equivalent of the reduced chromic acid,
(C) 0.5 to 5.0 by weight of reduced chromic acid converted to chromic anhydride, and / or colloidal silica of silicate, and (d) phosphonic acid or phosphonate compound 1 A chromate treatment liquid containing 0 to 20 g / l and (e) a water-soluble or water-dispersible organic polymer compound of more than 30 g / l is applied, dried by heating, and converted to a Cr amount of 7 per surface. A white chromate treatment method excellent in chromium elution resistance, corrosion resistance and coating performance of a non-ferrous metal-plated steel sheet or a non-ferrous metal material, which comprises forming a chromate film of 5 to 100 mg / m ² .