JPH11350161A - Conversion treatment agent for zinc or zinc alloy plating and conversion treatment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To ensure corrosion resistance for a zinc or zinc alloy plating film by using a treating agent contg. a basic aluminum but not contg. chromium and fluorine as a conversion treatment agent for zinc or zinc alloy plating. SOLUTION: A conversion treatment soln. contg. basic aluminum is applied to the conversion treatment of zinc or zinc alloy. A pH adjusting agent, a complexing agent, etc., may be added if necessary. Since the treating agent does not essentially contain chromium and fluorine, only drying is required and water washing is not required at the time of forming a chemical coating. The basic aluminum is represented by the formula [Al(OH)n A(6-n)/a ]m , wherein A is a chlorine atom, a nitrate group, a sulfate group or the like and (a), (n) and (m) are each an integer. The basic aluminum is preferably aluminum chloride or aluminum polychloride and the concn. of the basic aluminum in the treating soln. is preferably about 0.5-5 g/1 (expressed in terms of aluminum).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a chemical conversion treatment agent and a chemical conversion treatment method for zinc or a zinc alloy, and more particularly to a chemical conversion treatment agent and a chemical conversion treatment method containing no chromium and fluorine.

[0002]

2. Description of the Related Art Conventionally, zinc plating or zinc alloy plating (hereinafter sometimes simply referred to as zinc plating) has been used relatively frequently as a method for preventing corrosion of metal surfaces. In order to further improve the corrosion resistance of the steel, a chromate treatment is generally performed. This chromate film further improves the corrosion resistance.

Conventionally, most chromate treatments are gloss chromate treatments. Recently, however, colored chromate treatments such as black chromate treatment from the appearance and green chromate treatment from the viewpoint of corrosion resistance have been used relatively frequently. I have.

[0004] In such a chromate treatment widely used, the basic bath composition is composed of chromic anhydride and mineral acid (H ₂ SO ₄ , HN
O ₃ , HF, H ₂ SiF ₆ , H ₃ PO ₄ , HCl) aqueous solution, which is generally classified into a coating type, a reaction type, and an electrolytic type,
By converting hexavalent chromium in the chromic anhydride-containing liquid into trivalent chromium, a film is formed. For example, the coating composition of this _{time, xCr 2 O 3 · yCrO 3} · zH 2 O , and the coating type, reaction type, in any of the electrolytic also residual hexavalent chromium unreduced Some generation film Is inevitable.

[0005] As described above, the purpose of the chromate treatment for the galvanized film is chemical polishing and chemical conversion film formation. For the former chemical polishing, a fluorine compound is added, and for the film formation, 6 times. It deals with reduction of chromium (VI).

However, in recent years, since hexavalent chromium is contained in a chromate-treated film, that is, a chromate film, there is a concern that the hexavalent chromium may have an adverse effect on the skin of the human body. There is a problem that it is eluted from the film and remains in the natural world. Conventionally, various processing methods have been studied in order to solve such a problem, but a sufficient solution has not been found yet.

[0007]

SUMMARY OF THE INVENTION Accordingly, a general object of the present invention is to develop a chemical conversion treatment agent and a chemical conversion treatment method using the same to ensure further corrosion resistance of a zinc or zinc alloy plating film. is there.

Conventionally, chromate treatment has been performed for such a purpose, but there is a problem of elution of hexavalent chromium as described above, and there is a need for a solution. Therefore, a specific object of the present invention is to develop a technique for solving the problem of elution of hexavalent chromium remaining in a chromate film.

In order to achieve such an object, a treatment method using trivalent chromium, in which only a trivalent chromium is initially contained in a chromate treatment solution, is promising. From the beginning, it has been found that the method using trivalent chromium does not form a sufficient film and the corrosion resistance is considerably inferior to the conventional method in which the film formation is promoted by reducing the trivalent chromium to trivalent chromium.

Therefore, another object of the present invention is to develop a technique for forming a chemical conversion film having excellent corrosion resistance by surface treatment using a treatment solution containing no chromium. In addition, as described above, the chromate treatment liquid may contain a fluorine compound, and the presence of the fluorine compound is effective for chemical polishing of the surface of the article to be treated, and to obtain excellent film adhesion and corrosion resistance. The use of fluoride is desirable. However, the use of fluoride is not preferable because it has an adverse effect on human bones and is an environmentally regulated substance.

Therefore, still another object of the present invention is to provide:
It is an object of the present invention to develop a technology for forming a chemical conversion coating film having more excellent corrosion resistance by performing a chemical conversion treatment using a surface treatment solution that does not use chromium and fluoride.

[0012]

Means for Solving the Problems The present inventors have completely changed the idea without sticking to the conventional chromate treatment, and have made basic aluminum such as polyaluminum chloride which has not been used for the formation of a chemical conversion film. It has been found that a kind of chemical conversion treatment with a solution containing a zinc or zinc alloy plating film forms a chemical conversion coating film comparable to the conventional chromate coating film, and completed the present invention.

Here, the present invention is as follows. (1) A chemical conversion treating agent for zinc or zinc alloy plating, comprising basic aluminum. (2) Above that does not contain chromium compounds and fluorine compounds
The chemical conversion treating agent for zinc or zinc alloy plating according to (1).

(3) A chemical conversion treatment method for zinc or a zinc alloy, wherein the chemical conversion treatment agent according to the above (1) or (2) is applied to a zinc or zinc alloy plating film to form a chemical conversion treatment film. (4) The chemical conversion treatment method according to the above (3), wherein the chemical conversion treatment film is formed without performing water washing after applying the chemical conversion treatment agent.

As described above, the present invention has been found to provide excellent corrosion resistance by performing a treatment using a chemical conversion treatment solution containing basic aluminum (hereinafter, also referred to as "basic aluminum treatment"). It is a completed product, and other additional components such as a pH adjuster and a complexing agent are optional.

In a preferred embodiment of the present invention, the chemical conversion treating agent contains essentially no chromium or fluorine.
Also, when forming the chemical conversion film, it is only necessary to dry without performing washing with water, so that the load of wastewater treatment can be reduced.

[0017]

Next, the present invention will be described more specifically with reference to the accompanying drawings. FIG. 1 is a process chart when the present invention is applied to a galvanized or zinc alloy-plated article.

In the figure, the articles targeted in the present invention are those in which the chemical conversion treating agent according to the present invention has been developed in place of the conventional chromate treating agent, and is generally applied to articles which have been conventionally subjected to chromate treatment. It is possible. But,
From a practical point of view, it is a zinc-plated or zinc-alloy-plated article that has been pre-plated by electroplating of a so-called secondary molded product, for example, a home appliance part, an automobile part, and the like.

After such an article is washed with water, the article is generally immersed in a nitric acid solution, if necessary, a sulfuric acid or hydrochloric acid solution, subjected to an acid activation treatment, and washed with water. in this way,
After performing the acid activation treatment, the chemical conversion treatment, that is, the basic aluminum treatment is performed using the chemical conversion treatment agent according to the present invention. The treatment conditions at that time are as follows.

Range of treatment conditions for chemical conversion treatment pH range: 1.0 to 3.4, preferably 1.5 to 3.4 Temperature range: 10 to 60 ° C, preferably 15 to 25 ° C Time range: 5 to 180 seconds, preferably 15 to 180 seconds Preferred composition examples of the chemical conversion treating agent according to the present invention are as follows.

Basic aluminum: 0.1 to 5 g / L pH adjuster, complexing agent: Appropriate amount Water: Remaining Examples of the pH adjuster include hydrochloric acid, sulfuric acid, and nitric acid.
Lactic acid is exemplified as a complexing agent.

The chemical conversion treatment is carried out by applying the chemical conversion treatment agent to a zinc or zinc alloy plating film, and specific examples thereof include immersion in an aqueous solution containing the chemical conversion treatment agent, application and spraying of the aqueous solution. . When the chemical conversion treatment is performed and then dried, a corrosion-resistant chemical conversion film is formed on the surface of the article.

Then, if desired, a resin such as water-soluble or water-dispersible acrylic, urethane, silicone, melamine or the like can be coated to further secure corrosion resistance.

Here, the basic aluminum used in the present invention refers to aluminum forming [Al (H ₂ O) ₆ ] ³⁺ , and specifically, aluminum chloride, aluminum nitrate, aluminum sulfate, lactic acid Aluminum, their double salts, for example, aluminum as alum.

Further, when the above-mentioned aluminum compound or its double salt is dissolved in water, it is polymerized to form a polynuclear complex having the following composition formula, and these are called polyaluminum chloride, polyaluminum nitrate, polyaluminum sulfate and the like. However, it is apparent that these are also included in the “basic aluminum” referred to in the present invention. [Al (OH) _n A _{(6-n) / a} ] m where A represents a chlorine atom, a nitrate group, a sulfate group, etc.
n and m are integers.

The basic aluminum used in the present invention is preferably aluminum as aluminum chloride or polyaluminum chloride. The concentration range of the basic aluminum in the present invention is preferably 0.5 to 5 g / L as aluminum in the treatment liquid, and more preferably.
1.5 to 3.0 g / L.

The formation mechanism of the chemical conversion film formed by using the chemical conversion treating agent according to the present invention is still largely unknown, but up to now, it is presumed as follows. As shown in the following formula (1) by the action of a local battery in an acidic solution, the zinc or zinc alloy-plated surface is simultaneously dissolved in zinc and simultaneously in the presence of water and dissolved oxygen as a solvent, (1)
Receiving the emitted electrons by the formula, forms a hydroxyl ion by the formula (2).

[0028] The anode reaction ^{(anode): Zn → Zn 2+ + 2e} - ··· (1) cathode reaction _{(cathode): H 2 O +1/2 O 2} + 2e - → 2 OH - ·· (2) an oxidation-reduction reaction The hydroxyl group generated by the occurrence of, acts on the proton generated by the ligand dissociation of aluminum aquo ion derived from basic aluminum,
Promotes the formation of hydroxo aquo ions coordinated with OH groups.

[Al (H ₂ O) ₆ ] ³⁺ ← → [Al (OH) (H ₂ O) ₆ ] ²⁺ + H ⁺ ... (3) [Al (OH) (H ₂ O) ₆ ] ²⁺ ← → [Al (OH) ₂ (H ₂ O) ₄ ] ⁺ + H ⁺ ... (4) The hydrogen ions H ⁺ generated in formulas (3) and (4) are calculated by the formula (2) of hydroxide ion OH ^- and neutralize.

The hydroxo aquo ion coordinated with an OH group is
Hydrogen bond to each other to form a mu-hydroxo polynuclear complex. This is expected to be promoted by an increase in the hydroxoacion generated in the above formulas (3) and (4), and to be polymerized.

In this way, when the polymerization proceeds and the molecular diameter becomes 0.001 to 0.1 μm, it exists in the liquid as a hydrophobic colloid having a high positron valence and a high adsorptivity. This hydrophobic colloid is considered to be adsorbed on the galvanized film because of its high adsorption activity. This forms a rust preventive film containing aluminum as a main component by drying.

A chemical conversion film mainly composed of aluminum is formed on the surface of the article by such a chemical conversion treatment. However, depending on the use, corrosion resistance may be insufficient. In such a case, the organic resin film may be further coated by conventional means. Perform processing.

That is, the article on which the above-mentioned chemical conversion film is formed, washed and dried is immersed in a bath of a coating agent as appropriate. As described above, examples of the coating agent include water-soluble or water-dispersible resins such as acrylic, urethane, silicone, and melamine. After coating, dry the product. Thus, according to the present invention, without containing chromium, fluorine (fluoride),
A corrosion resistant film is formed, and the corrosion resistance can be improved.

Japanese Patent Publication No. 59-13595 discloses the use of aluminum chloride or the like as a corrosion inhibitor to be added to water in order to protect portions of iron or iron alloy that come into contact with water from corrosion. Has been disclosed. In this case, too, a thin film of aluminum hydroxide having good adhesion and insolubility is formed, and the anticorrosion effect is exhibited.
5.5 Since the aluminum content is as small as 5 to 50 ppm, the formation of the above-mentioned chemical conversion film on the zinc or zinc alloy plating film is not expected.

[0035]

[Example] [Example 1] Galvanizing a cold-rolled steel sheet (8 μm)
After rinsing with water, the plate was immersed in an acid active solution of 67.5% nitric acid (2 mL / L) at room temperature for 5 seconds and then washed with water. Then, at 25 ° C in the following formulation aqueous solution
After subjecting to a basic aluminum treatment by rocking immersion for 60 seconds, it was dried at 60 ° C. for 15 minutes without washing with water to form a chemical conversion film. Basic aluminum treatment solution Polyaluminum chloride: 10 g / L (0.5 g / L as Al) 35% hydrochloric acid (pH adjuster): 5 g / L Water: Remaining The same applies hereinafter.

Example 2 Galvanizing (8 μm) was applied to a cold-rolled steel sheet.
m) and washed with water, immersed in a 67.5% nitric acid 2 mL / L acid activation solution at room temperature for 5 seconds, and then washed with water. Then, at 25 ℃
After shaking for 60 seconds to perform basic aluminum treatment,
The coating was dried at 60 ° C. for 15 minutes to form a chemical conversion film. (Note) Aluminum polylactate: Trade name TAXERAM G-17P
[Manufactured by Taki Chemical Co., Ltd.] The same applies hereinafter.

[Comparative Example 1] Galvanizing (8 μm)
m) and washed with water, immersed in a 67.5% nitric acid 2 mL / L acid activation solution at room temperature for 5 seconds, and then washed with water. Then, at 25 ℃
After shaking for 60 seconds to perform basic aluminum treatment,
It was dried at 60 ° C. for 15 minutes without washing with water. Basic aluminum treatment solution Polyaluminum chloride: 0.1 g / L (0.005 g / L as Al) 35% hydrochloric acid (pH adjuster): 5 g / L Water: The remainder.

[Comparative Example 2] Galvanizing (8 μm)
m) and washed with water, immersed in a 67.5% nitric acid 2 mL / L acid activation solution at room temperature for 5 seconds, and then washed with water. Then, at 25 ℃
After shaking for 60 seconds to perform basic aluminum treatment,
It was dried at 60 ° C. for 15 minutes without washing with water. Basic aluminum treatment liquid Polyaluminum chloride: 1.0 g / L (0.050 g / L as Al) 35% hydrochloric acid (pH adjuster): 5 g / L Water: The remainder.

Comparative Example 3 Galvanizing (8 μm)
m) and washed with water, immersed in 67.5% nitric acid (2 mL / L) at room temperature for 5 seconds, and washed with water. Then, add 25
After immersing in rocking at 60 ° C for 60 seconds to perform zinc phosphate treatment, it was dried at 60 ° C for 15 minutes.

Example 3 A cold-rolled steel sheet was zinc-iron alloy plated (8 μm: iron eutectoid rate 0.4%), washed with water, and then treated with an acid active solution of 67.5% nitric acid 2 mL / L at room temperature for 5 seconds. After immersion, it was washed with water. Thereafter, the substrate was subjected to a basic aluminum treatment by rocking and immersing in the following formulation at 25 ° C. for 60 seconds, and then dried at 60 ° C. for 15 minutes without washing with water. Basic aluminum treatment solution Polyaluminum chloride: 10 g / L (0.5 g / L as Al) 35% hydrochloric acid (pH adjuster): 5 g / L Water: The remainder.

Example 4 A cold-rolled steel sheet was zinc-iron alloy plated (8 μm: iron eutectoid rate 0.4%), washed with water, and then treated with a 67.5% nitric acid 2 mL / L acid active solution at room temperature for 5 seconds. After immersion, it was washed with water. Thereafter, the substrate was subjected to a basic aluminum treatment by rocking and immersing in the following formulation at 25 ° C. for 60 seconds, and then dried at 60 ° C. for 15 minutes without washing with water.

[Comparative Example 4] A cold-rolled steel sheet was plated with zinc-iron alloy (8 µm: iron eutectoid rate 0.4%), washed with water, and then treated with a 67.5% nitric acid 2 mL / L acid active solution at room temperature for 5 seconds. After immersion, it was washed with water. Thereafter, the substrate was subjected to a basic aluminum treatment by rocking and immersing in the following formulation at 25 ° C. for 60 seconds, and then dried at 60 ° C. for 15 minutes without washing with water. Basic aluminum treatment solution Polyaluminum chloride: 0.10 g / L (0.005 g / L as Al) 35% hydrochloric acid (pH adjuster): 5 g / L Water: The remainder.

Comparative Example 5 A cold-rolled steel sheet was zinc-iron alloy plated (8 μm: iron eutectoid rate 0.4%), washed with water, and then treated with an acid active solution of 67.5% nitric acid 2 mL / L at room temperature for 5 seconds. After immersion, it was washed with water. Thereafter, the substrate was subjected to a basic aluminum treatment by rocking and immersing in the following formulation at 25 ° C. for 60 seconds, and then dried at 60 ° C. for 15 minutes without washing with water. Basic aluminum treatment liquid Polyaluminum chloride: 1.0 g / L (0.050 g / L as Al) 35% hydrochloric acid (pH adjuster): 5 g / L Water: The remainder.

[Comparative Example 6] A cold-rolled steel sheet was plated with zinc-iron alloy (8 µm: iron eutectoid rate 0.4%), washed with water, and then treated with an acid active solution of 67.5% nitric acid 2mL / L at room temperature for 5 seconds. After immersion, it was washed with water. Thereafter, the substrate was rock-immersed in the following formulation at 25 ° C. for 60 seconds to perform zinc phosphate treatment, and then dried at 60 ° C. for 15 minutes.

The results are shown in Table 1 below.
As can be seen from these, according to the present invention, a remarkable effect of improving corrosion resistance is observed as compared with the conventional zinc phosphate chemical conversion treatment.

[0046]

[Table 1]

[0047]

As described above, according to the present invention, by treating with a chemical conversion treatment solution containing neither chromium nor fluorine, excellent corrosion resistance equivalent to or higher than that of a conventional chromate film can be obtained. The obtained film can be obtained, and can easily deal with environmental problems and health problems that are a problem today, and its practical significance is great.

[Brief description of the drawings]

FIG. 1 is a process chart of one embodiment when a chemical conversion treating agent according to the present invention is used.

Claims (4)

[Claims] 1. A chemical conversion treating agent for zinc or zinc alloy plating comprising basic aluminum. 2. The chemical conversion treating agent for zinc or zinc alloy plating according to claim 1, which does not contain a chromium compound and a fluorine compound. 3. A chemical conversion treatment method for zinc or a zinc alloy, wherein the chemical conversion treatment agent according to claim 1 or 2 is applied to a zinc or zinc alloy plating film to form a chemical conversion treatment film. 4. The chemical conversion treatment method according to claim 3, wherein after applying the chemical conversion treatment agent, the chemical conversion treatment film is formed without washing with water.