JPH0781193B2 - Metal surface treatment method - Google Patents

Description

TECHNICAL FIELD The present invention relates to anticorrosion treatment of a metal surface. As the anticorrosion treatment of the metal surface, it is well known that zinc is subjected to hot dipping or electroplating and then chromate treatment. A blast galvanizing method is also known. Recently, an improved blast material consisting of an aggregate of independent particles formed by depositing zinc or a zinc alloy layer around the iron or iron alloy particle as a core through an iron-zinc alloy layer is used as the iron or iron. An improved blast zinc coating method has been developed which consists of projecting onto the alloy surface (Japanese Patent Publication No. 59-9312). This method is referred to herein as the improved blast zinc coating method.

This method is an epoch-making method with low equipment cost, low energy consumption and few decontamination factors, but the zinc coating formed by this method is still insufficient in corrosion resistance, and the adhesion amount of 100 mg / dm ² In the salt spray test, red rust occurs within 24 hours. This is believed to be due to the zinc coating formed by this method being an iron-zinc alloy and being porous.

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

A relatively simple method for that is chromate treatment,
There are several conventional chromate treatments for an object to be treated by the improved blast zinc coating method. That is, non-aqueous chromate treatment, baking type chromate treatment,
Aqueous chromate treatment is known.

Among them, as a chromate treatment to be applied to an object to be treated by the improved blast zinc coating method, a non-aqueous chromate treatment has an advantage that a closed system of a solvent can be used and waste water is not discharged, and so on, JP-A-61-67773. The disclosed method is particularly advantageous, and the Applicant Company has succeeded in combining this method with the improved blast zinc coating method, but recently the environmental regulations for halogenated hydrocarbon solvents (steam) have become stricter. Since it has been used and the solvent is expensive, the combination with the aqueous treatment was examined again.

Conventional aqueous treatment solutions include those containing mineral acids and those containing no mineral acids, and those containing no mineral acids are considered to be less effective and have not been used much. While reexamining the combination with the plating method, it was surprisingly discovered that the aqueous chromate treatment liquid containing no mineral acid is superior to the one containing mineral acid.

[Structure of Invention]

The present invention uses a core of iron or an iron alloy, and projects a blast material composed of an aggregate of multi-layer coated particles obtained by depositing zinc or a zinc alloy around the core through an iron-zinc alloy layer onto a metal surface. By forming a coating film of zinc or a zinc alloy on the surface, and treating the surface thus formed with an aqueous chromate treatment liquid containing chromic anhydride and trivalent chromium ions and containing no mineral acid. Provide a surface treatment method.

Conventionally used chromate treatment liquid contains so-called mineral acids such as sulfuric acid or nitric acid, and these acids are contained even in the blast zinc coating film of special structure made of porous zinc or zinc alloy. It has been avoided to be used for a material such as a spring, which is permeable and contained and damages the coating, resulting in a decrease in corrosion resistance, and also hydrogen, which easily causes hydrogen embrittlement. The combination of the treatment liquid of the method of the present invention and the improved blast zinc coating exhibits a very unexpected effect in this respect. Even if a large amount of treatment liquid is included in the blast zinc coating, it does not damage the coating, and due to the extremely large specific surface area of the porous coating, it exhibits sufficient reactivity and does not cause hydrogen embrittlement and is water-soluble. It is possible to form a chromate film having almost no content and obtain a coating film having high corrosion resistance.

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

Although the chromic anhydride used in the chromate treatment liquid used in the method of the present invention is a compound also called chromium trioxide, its concentration is 0.05-10 with respect to 100 parts by weight of water.
Parts are preferred. If it is less than 0.05 part by weight, the formation of the chromate film is slightly insufficient. On the other hand, if it exceeds 10 parts by weight, the coating may be thick and may cause inconvenience.

The trivalent chromium ion source is chromium sulfate, chromium nitrate, chromium chloride, chromium fluoride, chromium phosphate, chromium oxalate,
Chromium acetate, etc., or a mixture thereof, whose concentration is 0.005 as trivalent chromium ion per 100 parts by weight of water.
-5 parts by weight is preferred. If it is less than 0.005 parts by weight, it does not contribute to the promotion of the reaction, and if it exceeds 5 parts by weight, the reaction is promoted too much and the formed coating film may become powdery.

The chromate treatment in the method of the present invention is preferably carried out at a temperature of 5 ° C to 90 ° C. Processing time is 0.1 seconds to 3
It is 0 minutes, preferably 5 seconds to 5 minutes. At temperatures below 5 ° C, the chromate reaction does not proceed at a practical rate and
If the temperature exceeds ℃, the reaction proceeds too much and the formation of the chromate film becomes non-uniform. It takes at least 0.1 seconds to form a coating having an effective contact time, but if it exceeds 30 minutes, the formed coating becomes non-uniform and it is disadvantageous in terms of productivity.

After the chromate treatment, it may be naturally dried, but from the viewpoint of productivity, it may be forcedly dried with warm air. The preferable 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 film returns and deteriorates.

The chromate treatment in the method of the present invention is completed by simply immersing the object to be treated in the treatment liquid, pulling it up and drying (natural or forced), and substantially no washing wastewater is generated. This reduces the size of the processing equipment and eliminates the need for solvent vapor and disposal measures such as non-aqueous chromate treatment.

[Specific disclosure of invention]

Hereinafter, the present invention will be specifically disclosed with reference to Examples and Comparative Examples. The invention is not limited by these examples.

A 100 × 50 × 2.0 mm mild steel test panel was used for the test.
After steam degreasing this test panel with trichloroethane, the zinc-iron blast material described in Japanese Patent Publication No. 59-9312 was projected for 30 minutes, and a zinc-iron alloy with a basis weight of 100 mg / dm ² was applied to the surface. A film was formed. 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 following method, and further subjected to the following corrosion resistance performance test.

Chromium adhesion of the object to be treated Remove the chromate film of the object to be treated with diluted hydrochloric acid,
The chromium concentration in the stripping solution was measured by an atomic absorption spectrophotometer, and the value was converted to the weight of the chromate film adhesion amount.

Corrosion resistance test (cycle test) The salt spray test specified in JIS-Z-2371 is performed for 4 hours, the drying at 60 ° C for 2 hours, and the wet test at 50 ° C for 98% or more for 2 hours is defined as one cycle. , This was repeated.

In the above examples, "part" is simply referred to as "part by weight".
That is.

Example 1 A treatment solution was prepared by uniformly dissolving 0.25 parts of chromic anhydride and 0.25 parts of chromium sulfate 18-hydrate as a trivalent chromium concentration in 100 parts of deionized water. The test panel which had been subjected to the blast zinc coating treatment was dipped in this treatment liquid for 15 seconds and naturally dried. For the sample created in this way,
The amount of chromium deposited and the corrosion resistance performance test were conducted. The results are shown in Table 1.

Example 2 A treatment solution was prepared by uniformly dissolving 1.0 part of chromic anhydride in 2.0 parts and chromium sulfate 18-hydrate as trivalent chromium concentration in 100 parts of deionized water. The test panel subjected to the blast zinc coating treatment was dipped in this treatment liquid for 30 seconds and dried with warm air at 50 ° C. The results are shown in Table 1.

Example 3 A treatment solution was prepared by uniformly dissolving 5 parts of chromic acid anhydride and 0.01 part of chromium sulfate 18-hydrate as a trivalent chromium ion concentration in 100 parts of deionized water, and coating the blasted zinc with the above solution. The treated test panel was dipped for 5 minutes and dried with warm air at 50 ° C. Table 1 shows the results of the measurement of the chromium deposition amount and the corrosion resistance performance test of the sample thus prepared.

Example 4 1.0 part of chromic anhydride and 0.5 part of chromium nitrate nonahydrate as trivalent chromium ions were uniformly dissolved in 100 parts of deionized water to prepare a treatment solution, and the blast zinc described above was added to the treatment solution. The coated test panel was dipped for 5 seconds and allowed to air dry. The chromium deposition amount and the corrosion resistance performance test were performed on the sample thus prepared. The results are shown in Table 1.
Shown in.

Example 5 Chromic anhydride of 2.0 parts, chromium nitrate nonahydrate of 0.1 part as trivalent chromium ion concentration of 0.1 part, chromic anhydride of 2.0 parts of chromium nitrate nonahydrate of trivalent chromium ion concentration of 100 parts of deionized water. A treatment solution in which 0.1 part was uniformly dissolved was prepared, and the test panel subjected to the blast zinc coating treatment was immersed in this treatment solution for 5 seconds and naturally dried. The chromium deposition amount and the corrosion resistance performance test were performed on the sample thus prepared. The results are shown in Table 1.

Example 6 A treatment solution was prepared by uniformly dissolving 0.05 parts of chromic anhydride in an amount of 0.2 parts and chromium chloride hexahydrate as a trivalent chromium ion concentration in 100 parts of deionized water. Immerse the coated test panel for 2 minutes at 80 ℃
Dried with warm air. Table 1 shows the results of the measurement of the chromium deposition amount and the corrosion resistance performance test of the sample thus prepared.

Example 7 A treatment liquid was prepared by uniformly dissolving 0.2 parts of chromic anhydride and 1.0 part of chromium chloride hexahydrate as trivalent chromium ion concentration in 100 parts of deionized water. Immerse the coated test panel for 15 seconds at 50 ℃
Dried with warm air. The chromium deposition amount and the corrosion resistance performance test were performed on the sample thus prepared. The results are shown in Table 1.

Example 8 A treatment solution was prepared by uniformly dissolving 1.0 part of chromic acid anhydride and 0.2 part of chromium acetate hexahydrate as a trivalent chromium ion concentration in 100 parts of deionized water. The test panel was treated, immersed for 4 minutes and allowed to air dry. The chromium deposition amount and the corrosion resistance performance test were performed on the sample thus prepared. The results are shown in Table 1.

Comparative Example 1 (Example containing sulfuric acid, nitric acid, borofluoric acid) 10 g of chromic anhydride, 5 ml of sulfuric acid, 2 ml of nitric acid, 20 g of borofluoric acid
A treatment liquid was prepared by adding it uniformly to 00 g of deionized water and dissolving it uniformly. The blast zinc-coated test panel was immersed in this for 30 seconds. After immersion, leave it in the air and wash it with water.
Dried with warm air. The chromium deposition amount and the corrosion resistance performance test were performed on the sample thus prepared. The results are shown in Table 1.

Comparative Example 2 (example containing sulfuric acid and nitric acid) 1.0 part of chromic anhydride, 0.1 part of sulfuric acid to 100 parts of deionized water
Solution and 0.1 part of nitric acid were uniformly dissolved to prepare a treatment liquid. The test panel coated with the blast zinc was immersed in this for 4 seconds. After the immersion, it was left in the air, washed with water, and dried with warm air. The chromium deposition amount and the corrosion resistance performance test were performed on the sample thus prepared. The results are shown in Table 1.
Shown in.

Comparative Example 3 The test panel coated with the blast zinc was dipped in the liquid of Comparative Example 2 for 3 seconds. After the immersion, it was left in the air to be naturally dried. The chromium deposition amount and the corrosion resistance performance test were performed on the sample 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 the immersion was performed for 20 seconds was subjected to measurement of the chromium deposition amount and corrosion resistance performance test. The results are shown in Table 1.

Comparative Example 5 A treating solution containing 15 parts of t-butanol, 2 parts of chromic anhydride and 0.01 part of oxalic acid uniformly dissolved in 100 parts of trichlorotrifluoroethane was prepared. This was boiled in a tank having a condenser in the upper part, and the condensate in the upper part was refluxed in the tank.

A test panel coated with blast zinc and holding the treatment liquid in such a state was 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 chromium deposition amount and the corrosion resistance performance test were performed on the sample thus prepared. The results are shown in Table 1.

Comparative Example 6 A corrosion resistant performance test was performed on a test panel that had been subjected to blast zinc coating treatment and not subjected to chromate treatment.
The results are shown in Table 1.

Example 9 The treated panel of Example 7 was heated in an electric furnace at 120 ° C. for 30 minutes and then subjected to a corrosion resistance performance test together with the unheated treated panel. The results are shown in Table 2.

Comparative Example 7 A chromate treatment of Example 7 was applied to a test panel plated with an electrogalvanized film having a plating thickness of 8 μm, heated for 30 minutes in an electric furnace at 120 ° C., and then subjected to a corrosion resistance test with a non-heated treated panel. went. The results are shown in Table 2.

Comparative Example 8 Hot dip galvanized test panel (Basis weight 150g / m
² (1,500 mg / dm ² )) was used to perform a corrosion resistance test on a sample treated in the same manner as in Comparative Example 7. The results are shown in Table 2.

Comparative Example 9 Instead of the blast zinc coated test panel in Comparative Example 1, an electrogalvanized test panel having a plating film thickness of 8 μm was used to perform the same test. The results are shown in Table 2.
Shown in.

Comparative Example 10 Similarly, Table 2 shows the test results of 8 μm electrogalvanized plate which was subjected to the treatment of Comparative Example 4 (method of JP-A-62-93383).

Note) The number of cycles indicates the number of cycles of occurrence of red rust.
The number in () shows the number of cycles that generated a large amount of white rust.

These results show that the method of the present invention is far superior to the electroplated steel sheet that has been chromate-treated with a chromate treatment liquid containing hexavalent chromium and sulfuric acid, which is generally used (Comparative Example 7). You can see that Chromate treatment liquids containing trivalent chromium ions without containing sulfuric acid have been hardly used so far.

Comparing the product (I) obtained by the method of the present invention with the hot dip galvanized product (II) and the hot dip galvanized steel plate product subjected to the aqueous chromate treatment used in the present invention (III), the corrosion resistance is (I) is the best
(III) follows this, and (II) is the worst. However, in terms of processing cost, (I) is the cheapest, and (II) is about the same as (I).
It will be 3.5 times. If the processing cost for the bar is increased, it will be (I) 13 yen / kg (II) 45 yen / kg (III) 49 yen / kg.

What is particularly noticeable is that the product of the method of the present invention that has been heat-treated is much more excellent in corrosion resistance. This is in contrast to conventional galvanized products, which are significantly degraded by heating. It has been well known that an aqueous chromate coating for ordinary zinc plating is extremely weak against heat of 80 ° C. or higher and causes deterioration of corrosion resistance.

Therefore, it is clear that the combination of the improved blast zinc method and the aqueous chromate treatment solution containing no sulfuric acid and containing trivalent ions had an unexpected effect.

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Claims (4)

[Claims] 1. A blasting material consisting of an aggregate of multi-layer coated particles obtained by depositing zinc or a zinc alloy around the nucleus with an iron or iron alloy as a nucleus through an iron-zinc alloy layer, and projecting it onto a metal surface. To form a coating film of zinc or a zinc alloy by treating the metal thus formed with an aqueous chromate treatment solution containing chromic anhydride and trivalent chromium ions and containing no mineral acid. Surface treatment method. 2. A chromate treatment liquid containing trivalent chromium ions and 6
The method of claim 1 containing valent 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 described in 2. 4. The chromate treatment solution contains 0.005 to 5 parts by weight of trivalent chromium salt and 0.05 to 10 parts by weight of chromic anhydride with respect to 100 parts by weight of water in terms of trivalent chromium ion concentration. The method according to any one of 3 to 3.