JPH0219477A - Surface treatment of metal - Google Patents

Abstract

PURPOSE:To easily obtain a coating film having high corrosion resistance by coating the surface of a metal with zinc by an improved blast coating method, immersing the coated metal in an aq. chromating soln. not contg. any mineral acid, pulling up and drying the metal. CONSTITUTION:An aggregate of multilayer coated particles obtd. by sticking zinc (alloy) to the peripheries of iron (alloy) nuclei is prepd. as a blasting material. This blasting material is projected on the surface of a metal to form a zinc (alloy) coating film. This coating film is chromated with an aq. chromating soln. contg. chromic anhydride and trivalent Cr ions but not contg. any mineral acid and the chromated coating film is dried. An insoluble chromate film is formed on the zinc (alloy) coating film without damaging the coating film even when the chromating soln. intrudes into the film and a coating film having high corrosion resistance is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to anticorrosion treatment of metal surfaces. As an anticorrosion treatment for metal surfaces, it is well known to hot dip or electroplate zinc and then chromate treatment. A blast galvanizing method is also known. Recently, an improved blasting material consisting of an aggregate of multiple independent particles made of iron or iron alloy particles as a core and a zinc or zinc alloy layer coated around it through an iron-zinc alloy layer has been developed. An improved method of blasting zinc coating was developed (Japanese Patent Publication No. 59-9312), which consisted of projecting the surface of the alloy. This process is referred to herein as the modified blast zinc coating process.

This method uses a paper storage facility and is an innovative method that consumes less energy and has fewer environmental pollution elements. However, the zinc coating formed by this method still has insufficient corrosion resistance, and has an adhesion of 100 mg/d rd. red rust occurs within 24 hours in a salt spray test. This is believed to be due to the porous nature of the zinc coating formed by this method, which is an iron-zinc alloy.

Therefore, the improved blast zinc coating method alone cannot provide a sufficient anticorrosion effect, and some treatment must be performed in combination with this method.

A relatively simple method for this is chromate treatment,
There are several methods for chromate treatment of objects to be treated using the conventional improved blast zinc coating method. In other words, non-aqueous chromate treatment, mold chromate treatment for baking,
Aqueous chromate treatment is known.

Among these, non-aqueous chromate treatment, which is applied to objects to be treated using the improved blast zinc coating method, has the advantage of being able to use a closed solvent system and not discharging waste water. Although the disclosed method is particularly advantageous and the applicant's company has successfully combined this method with the modified blast zinc coating method described above, environmental regulations regarding halogenated hydrocarbon solvents (vapors) have recently become stricter. Because of the long history and the high cost of the solvent,
Once again, a combination with water-based treatment was detected.

Conventional aqueous treatment solutions include those that contain mineral acids and those that do not, and those that do not contain mineral acids are not widely used because they are considered to be less effective. While reconsidering combinations with plating methods, we unexpectedly discovered that an aqueous chromate treatment solution that does not contain mineral acids is more effective than one that contains mineral acids.

[Structure of the invention]

The present invention involves projecting onto a metal surface a blasting material consisting of an aggregate of multi-layer coated particles made of iron or iron alloy as a core and zinc or zinc alloy coated around the core through an iron-zinc alloy layer. This process consists of forming a coating film of zinc or zinc alloy, and treating the thus formed surface with an aqueous chromate treatment solution containing chromic anhydride and trivalent chromium ions but not containing mineral acids. Provides metal surface treatment methods.

Conventionally used chromate treatment solutions contain so-called mineral acids such as sulfuric acid or nitric acid, and these acids penetrate into the inside of the specially structured blasted zinc coating made of porous zinc or zinc alloy. Penetration and inclusion damage the coating, leading to a decrease in corrosion resistance, and use has been avoided for materials such as springs, which generate hydrogen and are prone to hydrogen embrittlement. The combination of the treatment liquid of the method of the invention and the improved blasted zinc coating exhibits a completely unexpected and excellent effect in this respect. due to the extremely large specific surface area of the porous film.

It exhibits sufficient reactivity, forms a chromate film with almost no water solubility without hydrogen embrittlement, and can provide a coating film with high corrosion resistance.

The improved blast zinc coating method used in the method of the present invention is disclosed in detail in the aforementioned Japanese Patent Publication No. 59-9312, and will not be reproduced here.

The chromic anhydride used in the chromate treatment solution used in the method of the present invention is a compound also called chromium trioxide, and its concentration is 0.0 parts per 100 parts of water.
5 to 10 parts is preferred. If the amount is less than 0.05 part by weight, the formation of a chromate film is somewhat insufficient. Moreover, if 10 parts by weight is added, the coating may become thick, which may cause problems.

Trivalent chromium ion sources include chromium sulfate, chromium nitrate, chromium chloride, chromium fluoride, chromium phosphate, chromium oxalate,
Chromium acetate, etc. or a mixture thereof, the concentration of which is 0 as trivalent chromium ions per 100 parts by weight of water.
．． 0.005 to 5 parts by weight is preferred.

If it is less than 0.05 parts by weight, it will not contribute to promoting the reaction, and if it exceeds 5 parts by weight, the reaction will be promoted too much and the formed film may become powdery.

The chromate treatment in the method of the invention is preferably carried out at a temperature of 5°C to 90°C. The treatment time is 0.1 seconds to 30 minutes, preferably 5 seconds to 5 minutes. 5℃
At lower temperatures, the chromate reaction does not proceed at a practical rate, and at temperatures above 90° C., the reaction proceeds too quickly, resulting in non-uniform formation of the chromate film. Regarding the contact time, at least 0.1 second is required to form a film of effective thickness, but if it exceeds 30 minutes, the formed film becomes non-uniform and is disadvantageous in terms of productivity.

After the chromate treatment, it may be allowed to dry naturally, but from the viewpoint of productivity, forced drying may be performed using warm air. The preferred temperature in this case is 30°C to 120°C. At temperatures below 30°C, the effect of forced drying is poor, and at temperatures above 120°C, the corrosion resistance of the chromate coating deteriorates.

In the chromate treatment according to the method of the present invention, the process is completed by simply immersing the object to be treated in the treatment solution and then pulling it up and drying it (naturally or forcedly), and substantially no cleaning waste water is generated. This reduces the size of treatment equipment and eliminates the need for solvent vapor and disposal measures, such as those used in non-aqueous chromate treatment.

[Specific disclosure of the invention]

The present invention will be specifically disclosed below using Examples and Comparative Examples. The present invention is not limited to these examples.

For the test, 100X50X2. Omm mild steel test panels were used. After vapor degreasing this test panel with trichloroethane, a zinc-iron blasting material described in Japanese Patent Publication No. 59-5312 was projected for 30 minutes on the surface, and a basis weight of 100 mg/drd was obtained by the amount of zinc-iron. An alloy coating was produced. This test panel was subjected to various chromate treatments of Examples and Comparative Examples. The amount of chromium deposited on this test panel was confirmed by the method described below, and the panel was further subjected to the corrosion resistance test described below.

The chromate coating on the treated object is removed using diluted hydrochloric acid.
The chromium concentration in the stripping solution was measured using an atomic absorption spectrophotometer, and the value was converted to the weight of the chromate film deposited.

Cycle test Salt spray test specified in JIS-Z-2371 for 4 hours, drying at 60°C for 2 hours, 50°C, 98%
The above wet test was repeated for 2 hours as one cycle.

In the above examples, "1 part" means "parts by weight."
It is about.

Example 1 0.5 parts of chromic anhydride to 100 parts of deionized water.

A treatment solution was prepared by uniformly dissolving 0.25 parts of chromium sulfate 18 hydrate to give a trivalent chromium concentration. The test panel subjected to the blast zinc coating treatment was immersed in this treatment solution for 15 seconds and allowed to air dry. The samples thus prepared were subjected to measurement of the amount of chromium deposited and a corrosion resistance performance test. The results are shown in Table 1.

Example 2 A treatment solution was prepared by uniformly dissolving 2.0 parts of chromic acid anhydride and 1.0 parts of chromium sulfate 18 hydrate at a trivalent ROM concentration in 100 parts of deionized water. The test panel subjected to the blast zinc coating treatment was immersed in this treatment solution for 30 seconds and dried with warm air at 50°C.

The results are shown in Table 1.

Example 3 To 100 parts of deionized water, 5 parts of chromic anhydride and chromium sulfate 18 hydrate were added at a trivalent chromium ion concentration of 0.01.
A test panel subjected to the blast zinc coating treatment was immersed in the treatment solution for 5 minutes and dried with warm air at 50°C.

Table 1 shows the results of measuring the amount of chromium deposited and performing a corrosion resistance test on the samples thus prepared.

Example 4 1.0 parts of chromic anhydride to 100 parts of deionized water,
A treatment solution was prepared by uniformly dissolving 0.5 part of chromium nitrate nonahydrate as a trivalent chromium ion, and the test panel subjected to the blast zinc coating treatment was immersed in this treatment solution for 5 seconds, and allowed to air dry. I let it happen. The amount of chromium deposited and a corrosion resistance test were conducted on the samples thus prepared. The results are shown in Table 1.

Example 5 To 100 parts of deionized water, 2.0 parts of chromic acid anhydride, 0.1 part of chromium nitrate nonahydrate as trivalent chromium ion concentration, 2.0 parts of chromic anhydride, and chromium nitrate nonahydrate were added. A treatment solution in which a trivalent chromium ion concentration of 0.1 part was uniformly dissolved was prepared and dried. The amount of chromium deposited and a corrosion resistance test were conducted on the samples thus prepared. The results are shown in Table 1.

Example 6 0.2 parts of chromic anhydride to 100 parts of deionized water,
The trivalent chromium ion concentration of chromium chloride hexahydrate is 0.
A treatment solution was prepared by uniformly dissolving 0.05 parts, and the test panel subjected to the blast zinc coating treatment was immersed in this solution for 2 minutes, and then dried with warm air at 80°C. Table 1 shows the results of measuring the amount of chromium deposited and performing a corrosion resistance test on the samples thus prepared.

Example 7 1.0 parts of chromic anhydride to 100 parts of deionized water.

The trivalent chromium ion concentration of chromium chloride hexahydrate is 0.
A treatment solution was prepared by uniformly dissolving two parts of the treatment solution, and the test panel subjected to the blast zinc coating treatment was immersed in the solution for 15 seconds, and then dried with warm air at 50°C. The amount of chromium deposited and a corrosion resistance test were conducted on the samples thus prepared. The results are shown in Table 1.

Example 8 1.0 part of chromic anhydride to 100 parts of deionized water.

Trivalent chromium ion concentration of chromium acetate hexahydrate is 0.2
A treatment solution was prepared in which the above-described zinc-blasted coating was uniformly dissolved, and the test panel was immersed in it for 4 parts, followed by air drying. The amount of chromium deposited and a corrosion resistance test were conducted on the samples thus prepared. The results are shown in Table 1.

Comparative Example 1 (Example containing sulfuric acid, nitric acid, borofluoric acid) Chromic anhydride Log, sulfuric acid 5 mQ, nitric acid 2 + aQ borofluoric acid 20
A treatment solution was prepared by adding 1000 g of deionized water to homogeneously dissolve 1000 g of deionized water. The test panel with the blast zinc coating was immersed in this for 30 seconds.

The soaking machine was left in the air, washed with water, and dried with warm air.

The amount of chromium deposited and a corrosion resistance test were conducted on the samples thus prepared. The results are shown in Table 1.

Comparative Example 2 (Example containing sulfuric acid and nitric acid) A treatment solution was prepared by uniformly dissolving 1.0 part of chromic anhydride, 0.1 part of sulfuric acid, and 0.1 part of nitric acid in 100 parts of deionized water. The test panel with the blast zinc coating was immersed in this for 4 seconds. After leaving the soaking machine in the air, it was washed with water and dried with warm air. The amount of chromium deposited and a corrosion resistance test were conducted on the samples thus prepared. The results are shown in Table 1.

Comparative Example 3 The blasted zinc coated test panel was immersed in the solution of Comparative Example 2 for 3 seconds. It was allowed to dry naturally by leaving it in the air in a soaking machine. The amount of chromium deposited and a corrosion resistance test were conducted on the samples thus prepared. The results are shown in Table 1.

Comparative Example 4 A sample prepared in the same manner as in Comparative Example 3 except that immersion was performed for 20 seconds was subjected to measurement of the amount of chromium deposited and a corrosion resistance performance test. The results are shown in Table 1.

Comparative Example 5 For 100 parts of trichlorotrifluoroethane, t-
Butanol 15 parts, chromic anhydride 2 parts, oxalic acid 0.0
A processing solution containing 1 part of the above was prepared by uniformly dissolving it. This was boiled in a tank having a condensation device at the top, and the condensate at the top was refluxed into the tank.

The processing liquid was maintained in this state. Test panels with blasted zinc coatings were immersed for 1 minute.

The test panel was force dried in fresh air at 40° C. for 3 minutes, washed in a solution of trichlorotrifluoroethane and t-butanol, and then dried.

The amount of chromium deposited and a corrosion resistance test were conducted on the samples thus prepared. The results are shown in Table 1.

Comparative Example 6 Corrosion resistance performance tests were conducted on test panels that had been subjected to blast zinc coating treatment but not chromate treatment.

The results are shown in Table 1.

Example 9 After heating the treated panel of Example 7 in an electric furnace at 120° C. for 30 minutes, a corrosion resistance test was conducted together with the unheated treated panel. The results are shown in Table 2.

Comparative Example 7 A test panel electrogalvanized with a plating thickness of 8 μm was subjected to the chromate treatment of Example 7.

After heating in an electric furnace at 120° C. for 30 minutes, a corrosion resistance test was conducted together with the unheated treated panel. The results are shown in Table 2.

Comparative Example 8 Hot dip galvanized test panel (fabric weight 150
A corrosion resistance test was conducted on a sample treated in the same manner as in the comparative example using 1,500 mg/m2 (1,500 mg/dg"). The results are shown in Table 2.

Comparative Example 9 In place of the test panel coated with blast zinc in Comparative Example 1, a similar test was conducted using a test panel coated with electrogalvanized coating having a plating thickness of 8 μI. Table 2 shows the results.
Shown below.

Comparative Example 1O Table 2 shows the test results of 8 μm electrolytic galvanized plate subjected to the treatment of Comparative Example 4 (method of JP-A-62-93383).

Table 2 These results show that the method of the present invention is much more effective than the chromate treatment using a chromate treatment solution containing hexavalent chromium and sulfuric acid, which is generally used for electroplated steel sheets (Comparative Example 7). It can be seen that it is excellent. A chromate treatment solution that does not contain sulfuric acid but contains trivalent chromium ions has hardly been used so far.

Comparing the product (1) obtained by the method of the present invention, the hot-dip galvanized product (II), and the product (III) obtained by applying the aqueous chromate treatment used in the present invention to the hot-dip galvanized steel sheet product (III), the corrosion resistance is ( I) is the best, followed by (m), and (II) is the worst. However, in terms of processing cost, (1) is the cheapest.

(II) is approximately 3.5 times as large as (1). The processing costs for bars are (I) (n) (III).

13 yen/kg 45 yen/kg 49 yen/kg What is particularly noteworthy is that the products heat-treated by the method of the present invention have even better corrosion resistance. In contrast to conventional galvanized products, which deteriorate significantly when heated, it is well known that hydrogen chromate coatings on conventional zinc plating are extremely weak against heat of 80°C or higher, resulting in a decrease in corrosion resistance. It is.

Therefore, it is clear that the combination of the modified zinc blasting process and an aqueous chromate treatment solution that does not contain sulfuric acid and contains trivalent ions had an unexpected effect.

Claims (1)

[Claims] 1. A blasting material consisting of an aggregate of multi-layer coated particles made of iron or iron alloy as a core and zinc or zinc alloy coated around this core via iron-zinc alloy metal. Forming a coating film of zinc or zinc alloy by spraying onto the surface; treating the surface thus formed with an aqueous chromate treatment solution containing chromic anhydride and trivalent chromium ions and no mineral acids. A metal surface treatment method consisting of: 2. The method according to claim 1, wherein the chromate treatment solution contains trivalent chromium ions and hexavalent chromium ions. 3. The trivalent chromium ion is at least one ion selected from the group consisting of chromium sulfate, chromium nitrate, chromium chloride, chromium acetate, chromium fluoride, chromium phosphate, and chromium oxalate. the method of. 4. A claim in which the chromate treatment solution contains trivalent chromium salt in a trivalent chromium ion concentration of 0.005 to 5 parts by weight and 0.05 to 10 parts by weight of chromic anhydride per 100 parts by weight of water. Methods described in 1 to 3.