JPH06306632A - Method for treating bright blue color of hot dip zinc-aluminum alloy plated steel sheet - Google Patents

Abstract

PURPOSE:To simply form a bright blue surface at a low temp. in a short period by subjecting the surface of a hot dip Zn-Al alloy plated steel sheet to treatment by a treating soln. of specified pH contg. specified amounts of molybdenum compounds and fluorides. CONSTITUTION:A steel sheet is applied with hot dip plating by a Zn-Al alloy contg. 0.1 to 60wt.% Al. The surface of this hot dip plated steel sheet is treated by a treating soln. of pH 3.5 to 6 contg. Mo compounds and fluorides. As this treating soln., the one contg. soluble Mo compounds by 0.2 to 3.0% expressed in terms of Mo and fluorides such as HF by 0.1 to 2.0% expressed in terms of F and whose pH is adjusted by NaOH or the like is used. Furthermore, the surface of the steel sheet is subjected to degreasing treatment before the same treatment as necessary. In this way, the surface of the hot dip Zn-Al alloy plated steel sheet is efficiently subjected to bluing treatment without deteriorating its own metallic luster.

Description

Detailed Description of the Invention

[0001]

The present invention relates to the surface appearance of a hot dip galvanized aluminum alloy-plated steel sheet, which is widely used as a material for buildings and household electrical appliances, and the bright surface appearance (metallic luster) of the plated steel sheet. The present invention relates to a processing method for making it a blue color tone without impairing the above. More specifically, the present invention provides a molten zinc-containing composition which has excellent stability of a processing liquid, can be processed by simple equipment, and can be processed at a lower temperature and in a shorter time than conventional methods.
The present invention relates to a novel bright blue treatment method for aluminum alloy plated steel sheets.

[0002]

2. Description of the Related Art Generally, as a method of coloring a metal, there are an inorganic chemical coloring method, an organic chemical coloring method, an electrolytic coloring method, painting and the like. Among these, in terms of equipment, cost and workability. From the above, the inorganic chemical coloring method is the most advantageous method. However, for the aluminum plate, the aluminum alloy plate and the galvanized steel sheet, although various inorganic chemical coloring methods have been devised, the inorganic chemical coloring method for the hot dip zinc-aluminum alloy plated steel sheet as a target material is
Not yet established.

As a known inorganic chemical coloring method for aluminum or aluminum alloy, specifically, 10 to 20 g / liter of ammonium molybdate and 5 to 15 g / liter of ammonium chloride are contained.
A method of treating with an aqueous solution at 0 ° C. for 10 minutes to give a deep black color,
Zinc sulfate 8 g / liter, sodium molybdate 3.
It is known to treat with an aqueous solution containing 3 g / liter and 2 g / liter of sodium fluoride at 50 to 70 ° C. for 5 minutes to give a bright Sudan color. The treatment methods of and are described in Nakayama Takakado; Aluminum Surface Treatment (Nikkan Kogyo Shimbun, 1969). In addition, a composition containing molybdic acid and a compound selected from sodium, potassium and ammonium salts of molybdic acid, and hexavalent chromium and fluoride ions to form a protective film on the surface of an aluminum-containing material is disclosed in Japanese Patent Publication. 45-32922.

On the other hand, various coloring methods have been studied for galvanized steel sheets in the past, and in the same manner as in the case of aluminum and aluminum alloys, the inorganic chemical coloring method is used in terms of equipment, cost and workability. Is advantageous and this method is often used. As an inorganic chemical coloring method for a galvanized steel sheet, for example, a method of blackening the galvanized steel sheet with an aqueous solution containing copper ions and nickel ions is disclosed in JP-A-61-253381. Further, in the prior art relating to the method for coloring a zinc-based plated steel sheet, the color tone is often black, brown, or the like, and the appearance having blue, particularly bright blue with metallic luster, has not yet been obtained.

Next, a case where the above-mentioned processing methods 1 to 3 in the prior art are applied to a hot-dip zinc-aluminum alloy plated steel sheet will be described. Even when the treatment methods of and are used, the color tone when applied to aluminum and aluminum alloy materials is not obtained, and almost no change in color tone is observed. Further, since these treatments are premised mainly on application to a molded body, it takes a long time of 5 minutes or more to perform treatment. Since the treatment liquid used in the treatment method is basically a chromate treatment liquid, the deposited film becomes a chromate film mainly composed of chromium oxide and is yellowish. When the pH is raised to 3.5 to 6, the reactivity is lowered, the amount of the chromate film attached is lowered, and coloring is not generated. When the treatment method is used, a matt black appearance can be obtained in a short time, but the adhesion of the black film is low, and it is necessary to perform some post-treatment to improve the adhesion. That is, when using a hot dip galvanized aluminum alloy-plated steel sheet as a target material, it is possible to obtain a bright blue appearance in a short time by the conventional coloring treatment method applied to aluminum, aluminum alloy, or galvanized steel sheet. It was confirmed that it was not possible.

[0006] Hot-dip zinc-aluminum alloy-plated steel sheets are currently widely used as materials for buildings and household electric appliances, and their surface appearance has a white metallic luster. However, this appearance is unsatisfactory in terms of design because it has a sense of quality due to metallic luster, but lacks calmness and texture. Therefore, for hot dip zinc-aluminum alloy coated steel sheet, there is a strong demand for establishment of a surface treatment technology for obtaining a bright blue color that is in harmony with the surrounding environment, has a high metallic luster, and has a high-class feeling. Is there.

[0007]

That is, according to the present invention, the surface of the hot-dip zinc-aluminum alloy plated steel sheet is subjected to an inorganic chemical coloring method which does not require large-scale equipment, at a lower temperature and in a shorter time than before, and the plating is performed. An object of the present invention is to provide a surface glittering blue treatment method capable of performing blue treatment on a steel sheet without impairing the metallic luster that the steel sheet originally has.

[0008]

SUMMARY OF THE INVENTION The present inventors have to solve the problems of the above-mentioned prior art by: 1. The constituent components of the blue film, which is the required color tone, It was judged that it was important to elucidate the two points of the treatment liquid composition and the chemical reactivity of the plated steel sheet, and the examination was advanced. As a result, first, a molybdenum compound is most suitable as a treatment liquid component for forming a colored film exhibiting a blue color on a hot-dip zinc-aluminum alloy-plated steel sheet, and the desired colored film is difficult to obtain with other inorganic compounds. I found a thing.

On the other hand, as a result of investigating the chemical reactivity between the treatment liquid and the plated steel sheet, it was found that a strong oxide film on the surface of the hot dip zinc-aluminum alloy plating layer should be removed and the etching reaction of the plating layer should be carried out quickly. Have found that a certain amount of fluoride is required in the treatment liquid. Furthermore, as a result of investigating the relationship between etching reactivity of fluoride and pH,
These compounds do not exert their effects in all pH regions, but only at pH 3.5 to 6, the reaction rate is most suitable for the coloring treatment targeted in the present invention, and only under these conditions, the metallic luster is impaired. The present inventors have completed the present invention by finding that uniform etching that does not occur is possible.

That is, the method for treating the bright blue color of the hot-dip zinc-aluminum alloy plated steel sheet of the present invention is 0.1-6.
The surface of a steel sheet hot-dipped with a zinc-aluminum alloy having an aluminum content of 0% by weight is used to convert a molybdenum compound into 0.2 to 3.0% by weight in terms of molybdenum.
And a fluoride containing 0.1 to 2.0 wt% in terms of fluorine, containing no chromium, and treated with a treatment liquid having a pH of 3.5 to 6.

[0011]

The function of the present invention will be described in detail below. The content of aluminum in the plating layer of the hot-dip zinc-aluminum alloy plated steel sheet to which the method of the present invention is applied is 0.1 to 60.
% By weight. If the aluminum content is out of this range, the desired bright blue appearance cannot be obtained. That is, when the aluminum content is less than 0.1% by weight, the color tone becomes dark and the gloss is lost. On the other hand, if it exceeds 60% by weight, a sufficient coloring reaction is not carried out and the color tone hardly changes.

The content of molybdenum compound in the treatment liquid is
It is preferably 0.2 to 3.0% by weight in terms of molybdenum, and is added in the form of a soluble molybdenum compound. If the content is less than 0.2% by weight, the reaction rate of the coloring reaction will decrease, and if it exceeds 3.0% by weight, the effect will be saturated and the effect will not be improved, which is economically disadvantageous. Is. More preferable molybdenum content is 0.5 to
It is 2.0% by weight. As the soluble molybdenum compound, molybdate, phosphomolybdic acid, molybdenum chloride or the like can be used.

The content of fluoride in the treatment liquid is preferably 0.1 to 2.0% by weight in terms of fluorine. If it is less than 0.1% by weight, the etching reaction rate decreases and the reaction rate of the coloring reaction decreases. If it exceeds 2.0% by weight, no further effect can be obtained, which is economically disadvantageous. More preferable fluoride content is 0.3 to 1.0
% By weight. Specific examples of the fluoride supply source include hydrofluoric acid, sodium fluoride, potassium fluoride, ammonium fluoride, sodium hydrogen fluoride, hydrosilicofluoric acid, sodium silicofluoride, and ammonium silicofluoride. Borofluoric acid, titanium hydrofluoric acid, zirconium hydrofluoric acid and the like can be used.

Further, the pH of the treatment liquid needs to be adjusted to 3.5 to 6. When it is less than 3.5, the etching reactivity of the fluorine in the fluoride as the etching agent becomes excessive and the amount of the colored film deposited is rather reduced, so that the desired color tone cannot be obtained. On the other hand, if the pH exceeds 6,
On the contrary, the etching reactivity is lowered, and the coloring reaction rate becomes extremely slow. For pH adjustment, an alkali such as sodium hydroxide, sodium carbonate, ammonia, ammonium bicarbonate, potassium hydroxide or the like, or an acid such as sulfuric acid, nitric acid or phosphoric acid can be used. More preferred
The pH range is 3.8-4.5. In addition, the treatment liquid used in the present invention does not require addition of chromic acid, a chromium compound or the like for the purpose of assisting the coloring property.

As a method of applying the above treatment liquid to the plated steel sheet, it is preferable to perform treatment by a spraying or dipping method at a treatment temperature of 30 to 70 ° C. for a treatment time of 1 to 10 seconds. When the treatment temperature is lower than 30 ° C., the reactivity of the treatment liquid is insufficient, and when the treatment temperature is higher than 70 ° C., further reactivity cannot be obtained, which is economically disadvantageous. A more preferable processing time is 2 to 5 seconds. If the treatment time is less than 1 second, the desired colored appearance cannot be obtained due to insufficient reaction,
On the contrary, when it exceeds 10 seconds, the coloring reaction is saturated and there is no further color change. More preferable processing temperature is 45 to
It is 60 ° C.

When impurities such as oil and dust adhere to the plated steel sheet, it is necessary to perform degreasing treatment such as alkali degreasing and solvent degreasing before the treatment of the present invention. In the present invention, washing and drying may be carried out after the film formation, if necessary. Even if post-treatment such as chromate treatment is carried out for the purpose of improving the corrosion resistance of the plated steel sheet after forming the coating film in the present invention, the effect of the present invention is not reduced.

The reaction mechanism when the plated steel sheet is treated with the treatment liquid of the present invention will be described in detail. When a hot dip zinc-aluminum alloy plated steel sheet is treated with the treatment liquid of the present invention, first, the plating layer is etched by the action of fluorine in the fluoride contained in the treatment liquid. This etching reaction is very important because it controls the reaction rate of the colored film forming reaction. The etching property of fluorine in the fluoride contained in the treatment liquid is the pH of the treatment liquid.
It is largely influenced by the temperature, and the suitable etching reactivity can be maintained in the pH range of 3.5 to 6. The strong natural oxide film existing on the surface of the plating layer is efficiently dissolved and removed by the presence of the fluorine component only in the proper pH range, and the coloring reaction is promoted. Moreover, since the etching reaction in the treatment of the present invention is uniformly performed on the plated layer, the metallic luster peculiar to the plated steel sheet is not impaired.

Further, zinc ions and aluminum ions eluted by the etching reaction are reprecipitated in the form of hydrated oxide on the surface of the plating layer. Further, along with elution of zinc and aluminum in the plated steel sheet, that is, oxidation, the molybdenum compound dissolved in the treatment liquid is reduced to a compound having a lower oxidation number, and precipitates and deposits on the plating surface. Therefore, the hot-dip zinc-aluminum alloy-plated steel sheet treated with the treatment liquid of the present invention has a form in which hydrated oxides of zinc and aluminum and oxides of molybdenum are mixed on the surface of the plated layer while maintaining metallic luster. Is formed, and a blue color tone having glitter is obtained.

When chromic acid, a chromium compound or the like is added to the treatment liquid according to the present invention, the chromium component acts as an inhibitor to the etching reaction.
Sufficient etching reaction is not performed, and the deposition of the colored film becomes insufficient. Also, by lowering the pH below 3.5, the etching reaction is promoted, but at such low pH.
In the region, the chromate film deposition reaction occurs preferentially over the molybdenum oxide deposition, and the chromate film color is colored yellow instead of blue due to molybdenum oxide.

[0020]

EXAMPLES Next, the following examples are shown together with comparative examples in order to explain the present invention more specifically.

1. Test Material Six hot-dip zinc-aluminum alloy-plated steel sheets with a coating weight of 120 g / m ² were prepared from a zinc-aluminum alloy plating bath and used. The content of aluminum in the plating layer is 0.05% by weight, 0.15% by weight, 5% by weight, 1
Six levels of 5% by weight, 55% by weight and 70% by weight were set. In addition, the content rate of aluminum in the plating film of the test plate used in each Example and Comparative Example is from Example 1 to
6, each of Comparative Examples 1-6.

2. Treatment Process The following treatment process was carried out in each of Examples and Comparative Examples.
However, the coloring treatment conditions are described in each Example and each Comparative Example. (1) Degreasing [Fine Cleaner-L4460 (Nippon Parkerizing Alkaline Degreasing Agent)] 43 ° C., 120 seconds, spray (2) Rinsing [tap water] room temperature, 30 seconds, spray (3) Coloring Examples 1 to 6 And Comparative Examples 1 to 6 respectively. The pH was adjusted using sodium hydroxide and sulfuric acid. (4) Washing with water [tap water] Room temperature, 30 seconds, spray (5) Drying 100 ° C, 120 seconds

Example 1 With respect to the test plate having an aluminum content of 5% by weight in the plating layer, ammonium molybdate was 2.0% by weight in terms of molybdenum and ammonium hydrogen fluoride was 0.7% by weight in terms of fluorine. %, And a spraying treatment was carried out at 50 ° C. for 1 second using a treatment liquid having a pH of 4.0.

Example 2 The test plate having an aluminum content of 0.15% by weight in the plating layer was converted into phosphomolybdic acid in terms of molybdenum.
33% in a treatment liquid of pH 5.7 containing 8% by weight, 1.5% by weight of silicofluoric acid in terms of fluorine and 0.3% by weight of hydrofluoric acid in terms of fluorine (total 1.8% by weight as fluorine). ℃
Immersion treatment was carried out for 9 seconds.

Example 3 The test plate having an aluminum content of 55% in the plating layer was converted to 1.5% sodium molybdate in terms of molybdenum.
A dipping treatment was performed at 67 ° C. for 3 seconds in a treatment liquid of pH 3.6 containing 0.5 wt% of hydrofluoric acid and 0.5 wt% of hydrofluoric acid.

Example 4 Phosphomolybdic acid was added to the test plate having an aluminum content of 0.15% in the plating layer in an amount of 0.
3% by weight and sodium fluoride in terms of fluorine of 0.
Using a treatment solution containing 12% by weight and having a pH of 4.0, spray treatment was carried out at 60 ° C. for 5 seconds.

Example 5 The test plate having an aluminum content of 15% in the plating layer was prepared by converting ammonium molybdate to 1.
0% by weight and 0.5% by weight of silica hydrofluoric acid in terms of fluorine
Immersion treatment was carried out for 3 seconds at 50 ° C. in the treatment liquid containing pH 4.0.

Example 6 The test plate containing 5% by weight of aluminum in the plating layer contained 1.0% by weight of ammonium molybdate and 0.7% by weight of ammonium fluoride in terms of fluorine. 60 ℃ in the treatment liquid of pH 4.2
Immersion treatment was carried out for 2 seconds.

Comparative Example 1 The test plate having an aluminum content of 70% in the plating layer was prepared by converting ammonium molybdate to 1.
Immersion treatment was carried out at 27 ° C. for 0.7 seconds in a treatment liquid of pH 5.5 containing 5% by weight and 0.5% by weight of silicofluoric acid in terms of fluorine.

Comparative Example 2 The test plate having an aluminum content of 0.05% in the plating layer contained 1.0% by weight of phosphomolybdic acid in terms of molybdenum and 1.0% by weight of hydrofluoric acid in terms of fluorine. It was immersed in a treatment solution having a pH of 3.3 for 10 seconds at 70 ° C.

Comparative Example 3 The test plate having an aluminum content of 5% in the plating layer was prepared by converting ammonium molybdate to 1.
Spray treatment was carried out at 50 ° C. for 5 seconds using a treatment liquid having a pH of 3.0 containing 0% by weight and 0.5% by weight of hydrofluoric acid in terms of fluorine.

Comparative Example 4 The test plate having an aluminum content of 5% in the plating layer was treated with 8 g / liter of zinc sulfate, 3.3 g / liter of sodium molybdate (0.15% by weight in terms of molybdenum) and sodium fluoride. 2 g / liter (0.09
Immersion treatment was carried out for 5 minutes at 60 ° C. using a treatment liquid containing (% by weight). The pH of the treatment liquid was 6.2, and the pH was not adjusted for this. This treatment method is described in Nakayama Takakado; Aluminum Surface Treatment (Nikkan Kogyo Shimbun, 1969) as a treatment method for coloring aluminum in a bright Sudan color.

Comparative Example 5 The above test plate having an aluminum content of 5% in the plating layer was treated with copper ion of 10 g / liter and nickel ion of 1.5.
Immersion treatment was carried out at 30 ° C. for 2 seconds using a treatment liquid of pH 3.0 containing g / liter and potassium chlorate 20 g / liter. This treatment is the treatment method described in Example 7 of JP-A-61-253381.

Comparative Example 6 The test plate having an aluminum content of 15% in the plating layer was used as 0.5% by weight of chromium trioxide, 0.3% by weight of fluoride as HBF _{4 and} sodium molybdate in terms of molybdenum. Immersion treatment was performed at 50 ° C. for 10 seconds using a treatment liquid containing 0.1% by weight. The pH of the treatment liquid is 1.75.
The pH for this was not adjusted. This treatment is the treatment method described in Example 1 of JP-B-45-32922.

[Test] Examples 1 to 6 and Comparative Examples 1 to 6
The appearance of the test plate treated with was represented by the three-attribute display symbols specified in JIS Z8721. Further, the gloss (G1) before the treatment and the gloss (G2) after the treatment were measured under the condition of 60 degrees, and the change rate of the gloss (ΔG = G2 / G1) was calculated. The adhesiveness of the colored film was evaluated by the peeling state of the cellophane tape peeling. The results of these tests are shown in Table 1.

[0036]

[Table 1]

As is clear from Table 1, in Examples 1 to 6, the surface of the hot dip galvanized aluminum alloy-plated steel sheet having an aluminum content of 0.1 to 60% by weight was colored by the coloring treatment of the present invention. A hue centered on blue with a degree of 3 or more (2.5B to 5PB) is obtained, and the brightness is 6
Even though it is colored as follows, the rate of change in gloss is 0.3.
Was kept above. That is, according to the treatment of the present invention, it was confirmed that it was colored blue while maintaining the metallic luster.

On the other hand, in Comparative Example 1, the aluminum content of the plating layer was more than 60% by weight, so that the coloring reaction did not proceed sufficiently. In addition, Comparative Example 2
However, the pH of the treatment liquid was below 3.5 and the aluminum content of the plating layer was below 0.1% by weight, the etching reaction of hydrofluoric acid became excessive, and the deposition of the colored film was hindered. Fell. In Comparative Example 3,
Since the pH of the treatment liquid was as low as 3.0, the etching reaction by fluorine became excessive, the deposition of the colored film was hindered, and the metallic luster was lost. In Comparative Example 4, the content of the soluble molybdenum compound and the content of fluorine were 0.2% by weight in terms of molybdenum and 0.
Since it was less than 1% by weight and the pH of the treatment liquid was more than 6.0, the reactivity was not sufficiently obtained, and despite the treatment for a long time of 5 minutes, the purpose was the same as in Comparative Examples 1 and 2. Was not obtained. Comparative Example 5 is a conventional technique relating to a black treatment method for a zinc-based plating material. Although blackening was performed, the gloss was extremely reduced, and sufficient adhesion was not obtained. In Comparative Example 6, since the treatment liquid contained chromic acid and had a low pH of 1.75, the chromate film was deposited and the appearance was yellow, and the metallic luster was lost. .

[0039]

As described above, the method for blue treatment of hot-dip zinc-aluminum alloy-plated steel sheet of the present invention is an inorganic chemical coloring method having a great cost merit, and thus gives a great added value in terms of designability. It is possible. Further, the stability of the treatment liquid is better than that of the conventional method, and the treatment can be performed at low temperature and in a short time.

Claims (1)

[Claims] 1. A surface of a steel sheet hot-dipped with a zinc-aluminum alloy having an aluminum content of 0.1 to 60% by weight, a molybdenum compound being 0.2 to 3.0% by weight in terms of molybdenum, Contains 0.1 to 2.0% by weight of fluoride in terms of fluorine and does not contain chromium,
3. A method for treating a bright blue color of a hot dip zinc-aluminum alloy plated steel sheet, which comprises treating with a treatment liquid having a pH of 3.5 to 6.