JPH10219494A - Chromate treated electrogalvanized steel sheet having excellent blackening resistance and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve blackening resistance and appearance of chromate treated materials and to prevent deterioration of appearance of phosphate treated materials, etc., as well exclusive of these chromate treated materials in a production line capable of producing not only the electrogalvanized steel sheets which are subjected to the remedy for prevention of the blackening suitable for the electrogalvanized steel sheets and are subjected to a post treatment but the electrogalvanized steel sheets not subjected to the post treatment as well. SOLUTION: The electrogalvanized steel sheets are brought into contact with a weakly alkaline soln. which is added with at least either of Ni ions and Co ions at a ratio of >=0.001 to <=10g/l and has a pH value of >=8 to <=11, by which at least either of the Ni and Co are deposited at the ratio within the range of >=0.01 to <=0.01g/l on the surfaces of the electrogalvanizing layers to form metallic layers on the surfaces of the electrogalvanizing layers. The steel sheets are then subjected to the chromate treatment.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a chromate-treated galvanized steel sheet having excellent resistance to blackening and a method for producing the same.

[0002]

2. Description of the Related Art When an electrogalvanized steel sheet is used without painting, a chromate film is usually formed on the electrogalvanized layer by a chromate treatment. Although the corrosion resistance of the chromate-treated electrogalvanized steel sheet having such a chromate film formed thereon is remarkably improved, a part or all of the surface of the chromate-treated electrogalvanized steel sheet turns grayish brown or brown during storage in a high-temperature and humid environment. Phenomenon (hereinafter referred to as "blackening phenomenon")
May occur. A chromate-treated electrogalvanized steel sheet having a blackening phenomenon significantly reduces its commercial value.

Although the details of the blackening phenomenon are not always clear, blackening is a corrosion phenomenon on the zinc surface. Pb in the plating film promotes blackening, and Ni has the effect of suppressing blackening. There is a report that there is. Various studies have been made on the means for preventing the occurrence of such a blackening phenomenon.
For example, Japanese Patent Application Laid-Open No. 60-77988 discloses that Ni ions in a galvanizing bath are mixed in a range of 5 to 500 times the amount of Pb ions contained as impurities, and 1/100 of the amount of Zn ions.
Using an electrogalvanizing bath containing not more than 25 and not more than 10 g / l, the steel sheet is electrogalvanized by such an electrogalvanizing bath, and then subjected to chromate treatment to improve blackening resistance. A method (hereinafter referred to as Prior Art 1) is disclosed.

[0004] Japanese Patent Application Laid-Open No. 2-8374 discloses N
i ions are contained in an amount within the range of 100 to 300 ppm, and the content of Pb ions contained as impurities is 0.5%.
By using an electrogalvanizing bath having a Ni ion / Pb ion ratio of 500 ppm or less and a Ni ion / Pb ion ratio in the plating bath exceeding 500, the steel sheet is electrogalvanized by such an electrogalvanizing bath, and then subjected to a chromate treatment. A method for improving blackening resistance (hereinafter referred to as Prior Art 2) is disclosed.

According to the prior arts 1 and 2 described above, although the blackening resistance of the chromate-treated electrogalvanized steel sheet is improved, the appearance of the surface of the electrogalvanized steel sheet is reduced due to the inclusion of Ni in the plating film. In particular, whiteness decreases.

Regarding such a problem, Japanese Patent Application Laid-Open No. 63-4 / 1988
No. 099 discloses that 30 ions of Ni are contained in a galvanizing bath.
If it is present in an amount of 0 ppm or more, the whiteness of the galvanized steel sheet subjected to the phosphate treatment is reduced to 50 or less. Therefore, it is necessary to maintain the Ni ion concentration in the galvanizing bath as low as possible. Ni using powder
A method for removing ions (hereinafter referred to as Prior Art 3) is disclosed.

Japanese Patent Application Laid-Open No. 1-129991 discloses a method of controlling the concentration of Ni ions in a zinc plating bath to 10 ppm or less in order to keep the color tone of a galvanized steel sheet white after the phosphate treatment. (Hereinafter referred to as Prior Art 4).

[0008]

Generally, the production of an electrogalvanized steel sheet is carried out by the same equipment and the same plating bath without chromate treatment, phosphate treatment and post-treatment. Therefore, as in Prior Art 3 and Prior Art 4, when Ni is added to the plating bath in order to improve the blackening resistance of the electrogalvanized steel sheet, not only the chromate-treated material but also the appearance of other plated steel sheets Will also deteriorate. Therefore, there has conventionally been a problem with the addition of Ni to the plating bath.

On the other hand, blackening resistance of hot-dip galvanized steel sheet is as follows:
It is known to be significantly inferior to electrogalvanized steel sheets. The reason is that a thick and uneven Zn oxide film is generated on the surface of the hot-dip galvanized steel sheet compared to the electro-galvanized steel sheet, and Al in the plating bath exists as an oxide on the surface of the galvanized steel sheet. This is because the blackening phenomenon easily proceeds.

As a countermeasure against blackening of the hot-dip galvanized steel sheet, for example, Japanese Patent Publication No. 3-49982 discloses a technique of electrogalvanizing the surface of a hot-dip galvanized steel sheet (hereinafter referred to as Prior Art 5). It is disclosed that the blackening resistance of the electrogalvanized steel sheet is better than that of the galvanized steel sheet. Further, in prior art 5, a hot-dip galvanized steel sheet after hot-dip galvanizing is
pH 1 containing 1 to 20 g / l of i ion or Co ion
A method is disclosed in which the substrate is immersed in a solution having a pH of ４4 or pH 11 to 13.5 to deposit Ni or Co in an amount of 0.3 to 15 mg / m ² .

Japanese Unexamined Patent Publication (Kokai) No. 2-267279 also discloses that a hot-dip galvanized steel sheet is made of Na gluconate and E
A method for improving the resistance to blackening by contacting with a Ni or Co treatment solution containing a complexing agent such as DTA, NTA, citrate (hereinafter referred to as Prior Art 6) is disclosed.

According to the prior arts 5 and 6, the blackening resistance of a galvanized steel sheet is improved. However, the blackening resistance of the electrogalvanized steel sheet is not improved. The reason is that, as described above, since the surface of the electrogalvanized layer does not have a thick oxide film or Al oxide such as a hot-dip galvanized layer, an acid or alkaline solution such as a Ni or Co treatment solution is used. This is considered to be because a non-uniform oxide film is formed on the surface of the electrogalvanized layer as a result of excessive activation of the plating surface due to excessive erosion.

As described above, since the electrogalvanized steel sheet and the hot-dip galvanized steel sheet have different surface states, particularly oxidation states, slight oxidation phenomena such as blackening on the surface of the galvanized layer are suppressed. The means are considered to be different, and there is a need for blackening prevention measures suitable for electrogalvanized steel sheets. However, blackening prevention measures suitable for electrogalvanized steel sheets have not yet been established.

[0014] Accordingly, an object of the present invention is to solve the above-mentioned problems, take measures to prevent blackening suitable for electrogalvanized steel sheets, and perform chromate treatment in the same equipment and the same plating bath.
When manufacturing electrogalvanized steel sheets without phosphating or post-treatment, the blackening resistance of chromate-treated material is remarkably improved, and the appearance of phosphate-treated materials other than chromate-treated material deteriorates. An object of the present invention is to provide an electrogalvanized steel sheet having excellent resistance to blackening and a method for producing the same.

[0015]

A chromate-treated electrogalvanized steel sheet according to the first aspect of the present invention includes a steel sheet, an electrogalvanized layer formed on a surface of the steel sheet, and a surface of the electrogalvanized layer. A metal layer formed by depositing at least one of Ni and Co in an amount within a range of 0.01 mg / m ² or more and 10 mg / m ² or less, and a metal layer formed on the metal layer. It is characterized by being composed of a chromate film.

According to a second aspect of the present invention, there is provided a method for producing a chromate-treated electrogalvanized steel sheet, comprising: applying an electrogalvanized steel sheet to an electrogalvanized steel sheet having an electrogalvanized layer formed on at least one surface. The electrogalvanized steel sheet is prepared by adding at least one of Ni ions and Co ions in an amount of not less than 0.001 g / l and not more than 10 g / l to a weak alkaline solution having a pH value of 8 or more and less than 11. By contacting, 0.01 mg of at least one of Ni and Co was applied to the surface of the electrogalvanized layer.
/ m ² or more and 10 mg / m ² to form a metal layer on the surface of the electrogalvanized layer by depositing in an amount within the range of
It is characterized by performing chromate treatment.

According to a third aspect of the present invention, in the method according to the second aspect, the weak alkaline solution is a sodium pyrophosphate solution or a sodium tripolyphosphate solution, or the sodium pyrophosphate solution and the tripolyphosphate are combined. It is characterized by being a mixture with a sodium-based solution.

[0018]

Next, a galvanized steel sheet having excellent blackening resistance according to the present invention will be described below. The electrogalvanized steel sheet having excellent blackening resistance according to the present invention includes a steel sheet, an electrogalvanized layer formed on the surface of the steel sheet, a metal layer formed on the electrogalvanized layer, and a metal layer formed on the electrogalvanized layer. And a chromate film formed on the substrate.

In the basic structure described above, the present invention is characterized in that at least one of Ni and Co is deposited on the surface of the electrogalvanized layer in an amount of 0.01 mg / m ² or more and 10 mg / m ² or less. In this case, the metal layer is formed on the surface of the electrogalvanized layer.

That is, at least one of Ni and Co is applied on the surface of the electrogalvanized layer in an amount of 0.01 mg / m ² or more,
By precipitating in an amount of 0 mg / m ² or less and forming a metal layer on the surface of the electrogalvanized layer, the blackening resistance of the chromate-treated material can be improved, and the whiteness can be improved. A galvanized steel sheet is obtained.

If the precipitation amount of at least one of Ni and Co is less than 0.01 mg / m ² , the blackening resistance of the chromate-treated material cannot be remarkably improved. On the other hand, when the precipitation amount of at least one of Ni and Co exceeds 10 mg / m ² , the appearance deteriorates such as a decrease in whiteness and unevenness. Therefore, Ni and C on the surface of the electrogalvanized layer
The amount of at least one of o is 0.01 mg / m ² or more,
0 mg / m ² or less, thereby improving the blackening resistance of the chromate-treated material.
And / or the effect of Co is fully exhibited,
Deterioration of appearance due to the above components can be suppressed to a substantially negligible degree.

Ni and C on the surface of electrogalvanized layer
At least one, more preferred deposition amount of o is 0.0
It is in the range of 1 mg / m ² or more and 1 mg / m ² or less, and more preferably in the range of 0.01 mg / m ² or more and 0.2 mg / m ² or less.

As described above, in the electrogalvanized steel sheet having excellent blackening resistance according to the present invention, at least one of Ni and Co is deposited on the surface of the electrogalvanized layer in the above-mentioned predetermined amounts, and It is the same as a conventional electrogalvanized steel sheet except that a metal layer is formed on the surface. Therefore, description of the other components will be omitted.

Next, a method for producing an electrogalvanized steel sheet having excellent blackening resistance according to the present invention will be described below. The blackening phenomenon is considered to be a phenomenon caused by oxidation of the zinc surface. Therefore, it is determined that the blackening phenomenon can be suppressed by modifying the surface of the zinc plating layer. That is, since the addition of Ni to the galvanized coating has a favorable effect on the blackening resistance, it is determined that the blackening resistance can be improved by depositing Ni on the surface of the zinc plating layer.

According to any of the treatment methods, Ni cannot be precipitated on the surface of the electrogalvanized layer to improve the blackening resistance.
By depositing Ni on the surface of the electrogalvanized layer, blackening resistance can be improved. The method will be described in detail below.

The present inventors have conducted intensive studies on a method of depositing Ni on the surface of an electrogalvanized layer, and as a result,
It has been found that precipitation of Ni effective for preventing the blackening phenomenon can be achieved only by a sodium pyrophosphate-based solution or a sodium tripolyphosphate solution or a mixture of both.

As is well known, Ni is an amphoteric metal and N
i-ions in acidic and alkaline solutions
Has greater solubility. Then, the precipitation treatment of Ni was performed using both the acidic solution and the alkaline solution.

First, Ni was deposited on the surface of the electrogalvanized layer using an acidic bath, and as a result, it was confirmed that the above-mentioned Ni deposition was possible. However, when Ni was precipitated using an acidic bath, the amount of chromate adhering in the subsequent chromate treatment was extremely reduced, and the effect of improving blackening resistance was insufficient. On the other hand, Ni was deposited on the surface of the electrogalvanized layer using a strong alkaline bath, for example, a sodium hydroxide solution, but a sufficient amount of Ni could be deposited on the surface of the galvanized layer. Did not.

The present inventors have studied on a method for depositing Ni using a neutral or weakly alkaline processing solution. As described above, prior art 7 (Japanese Unexamined Patent Application Publication No.
No. 267279 discloses that a hot-dip galvanized steel sheet is contacted with a Ni or Co treatment liquid containing a complexing agent such as Na gluconate and EDTA, NTA, citrate, etc. to improve blackening resistance. Although a method is disclosed, this method cannot improve the blackening resistance of an electrogalvanized steel sheet even if the blackening resistance of a galvanized steel sheet is improved.

The reason is that for the electrogalvanized steel sheet, the components of the processing solution used and the pH which greatly affects the state of the presence of these components are not appropriate, and thus the deposited Ni and / or Co This is considered to be because the presence state and the surface state of the electrogalvanized layer were inappropriate for preventing blackening of the electrogalvanized steel sheet.

Therefore, the study of the component system and the pH value of the treatment solution most suitable for the electrogalvanized steel sheet was advanced. As a result, it has been found that when a sodium pyrophosphate-based solution or a sodium tripolyphosphate-based solution having a pH of 8 or more and less than 11 or a mixture thereof is used, a considerably high concentration of Ni ions is dissolved.

When such a solution is brought into contact with an electrogalvanized steel sheet, a sufficient amount of Ni and / or Co can be precipitated on the surface of the electrogalvanized layer, and Ni and Co are uniformly deposited. It was confirmed that they had precipitated. Further, the chromate film was also formed uniformly. Thereby, even in the case of the electrogalvanized steel sheet, it was confirmed that the blackening resistance after the chromate treatment was remarkably improved.

Further, like Ni, Co ions can be dissolved in a weakly alkaline sodium pyrophosphate-based solution or a sodium tripolyphosphate-based solution having a pH of 8 or more and less than 11 or a mixture thereof, and an electrogalvanized steel sheet is brought into contact with this solution. By doing so, it was confirmed that metal Co was precipitated, and the blackening resistance after chromate treatment could be greatly improved.

As described above, Ni and / or Co
Must be kept within the range of 0.01 mg / m ² or more and 10 mg / m ² or less. In order to maintain the precipitation amount of Ni and / or Co within this range, the pH value must be maintained. In a sodium pyrophosphate-based solution or sodium tripolyphosphate-based solution or a mixture thereof, which is a weakly alkaline solution having a pH of 8 to less than 11,
g / l or less of Ni ions and / or Co ions may be added.

If the amount of Ni ions and / or Co ions added to the weakly alkaline solution, sodium pyrophosphate-based solution or sodium tripolyphosphate-based solution, or a mixture thereof, is less than 0.001 g / l, sufficient black resistance is obtained. On the other hand, when the amount of addition exceeds 10 g / l, the corrosion resistance of the steel sheet is reduced.

[0036] Ni and / or Co are deposited on the surface of the electrogalvanized layer in the range of 0.01 mg / m ² or more and 1 mg / m ² or less, which is the more preferred amount of precipitation described above, and still more preferably. 0.01 mg / m ² or more.
In order to precipitate within a range of ² mg / m ² or less, a pH value of 8
The addition amount of Ni ions and / or Co ions to a sodium pyrophosphate-based solution or a sodium tripolyphosphate-based solution or a mixed solution thereof, which is a weak alkaline solution of not less than 11, is 0.005 g / l or more,
It is preferably set to 1 or less.

As described above, the method for producing an electrogalvanized steel sheet having excellent resistance to blackening according to the present invention is characterized in that at least one of Ni and Co is deposited in a predetermined amount on the surface of the electrogalvanized layer. Except for the step of forming a metal layer on the surface of the electrogalvanized layer, it is the same as the conventional method for manufacturing an electrogalvanized steel sheet. Therefore, description of the other steps is omitted.

[0038]

Next, the method for producing an electrogalvanized steel sheet having excellent resistance to blackening according to the present invention will be described in more detail with reference to examples and comparative examples. According to the plating conditions shown in Table 1, the steel sheet was electrogalvanized to prepare an electrogalvanized steel sheet.

[0039]

[Table 1]

Next, the above galvanized steel sheet is subjected to a metal deposition treatment by immersing it in a treatment solution having a component composition and a pH value within the range of the present invention, and thus the surface of the galvanized layer of the galvanized steel sheet is obtained. Then, at least one of Ni and Co was deposited in an amount within the range of the present invention, thereby forming a metal layer on the surface of the electrogalvanized layer. In the metal deposition treatment, the component composition of the treatment liquid,
Table 2 shows the pH value, the treatment time, and the precipitation amount of Ni and / or Co.

[0041]

[Table 2]

Next, the electrogalvanized steel sheet having a metal layer made of at least one of Ni and Co formed on the surface of the electrogalvanized layer is subjected to a chromate treatment in accordance with the chromate conditions shown in Table 4, and thus, Specimens of electrogalvanized steel sheets having a metal layer within the scope of the invention (hereinafter referred to as “specimens of the present invention”) Prepared 1-21. The type of chromate treatment applied and the amount of attached chromate are also shown in Table 2.

For comparison, a galvanized steel sheet prepared according to the above-described conditions was subjected to a metal deposition treatment by immersing it in a treatment solution in which at least one of the component composition and the pH value was out of the range of the present invention. A metal layer is formed on the surface of the electrogalvanized layer by depositing at least one of Ni and Co on the surface of the galvanized layer of the electrogalvanized steel sheet, and then according to the chromate conditions shown in Table 4, Chromate treatment was performed, and thus the specimens of the electrogalvanized steel sheet (hereinafter referred to as “comparative specimens”) No. 1-6 were prepared. Table 4 shows the plating conditions, the component composition of the treatment solution, and the pH.
The values, the treatment time, the amount of Ni and / or Co deposited, the type of chromate treatment and the amount of chromate adhering are also shown.

[0044]

[Table 3]

[0045]

[Table 4]

Incidentally, Ni and Co in the treatment solutions in Tables 2 and 3 were added as sulfates (6,7 hydrate).
The thus-prepared specimen No. 1 of the present invention was prepared. For each of Sample Nos. 1 to 21 and Comparative Specimens Nos. 1 to 6, a blackening test and a change in appearance were inspected by the following methods.

(1) Black discoloration test method: The whiteness of the specimen was determined by JI
The measurement was performed using a Lab system based on SZ8730. Then
With the specimens stacked, a temperature of 50 ° C and 95
% Relative humidity, a wetness test was performed for 60 days, after which the whiteness of the specimen was measured again in the manner described above. Next, the amount of change (ΔL) in the measured whiteness before and after the wet test was determined. Based on the change in whiteness (ΔL) thus obtained, the blackening resistance of each specimen was evaluated according to the following criteria. The evaluation results are also shown in Table 2.

○: ΔL ≧ −2, and excellent blackening resistance. ×: ΔL <−2, and poor blackening resistance. (2) Appearance criterion: The whiteness of the specimen was determined by JI in the same manner as above.
The measurement was performed using a Lab system based on SZ8730. Then
The whiteness of an electrogalvanized steel sheet as a reference specimen not subjected to the above-described metal deposition treatment was measured by the same method. Next, the difference between the measured value of whiteness of each specimen and the measured value of whiteness of the reference specimen was determined. Based on the difference value thus obtained, the appearance of each specimen was evaluated as follows. The evaluation results are also shown in Table 2.

A: The decrease in whiteness due to the metal deposition treatment was less than 1. ：: The decrease in whiteness due to the metal deposition treatment was 1 or more and less than 2. Δ: The decrease in whiteness due to the metal deposition treatment was 2 or more and less than 4.

×: The decrease in whiteness due to the metal deposition treatment was 4 or more. As is clear from Table 2, the test sample No. of the present invention. 1-21
All of them were excellent in blackening resistance, and a sufficient amount of chromate was secured. In addition, the specimen No. of the present invention having a metal deposition amount in the range of 0.01 to 0.2 mg / m ² .
In Examples 1-4, 9, 11-12, 14-16, 18, 20 and 21, the appearance after the chromate treatment was excellent, and the decrease in whiteness was extremely small at less than 1. The specimen No. of the present invention having a metal deposition amount in the range of 0.5 to 1 mg / m ² .
In 5, 6, 10, 13, 17 and 19, the appearance after the chromate treatment was good, and the decrease in whiteness was as small as 1 or more and less than 2. 4.5-9.4 mg of metal deposition
/ m ² within the range of the present invention. In Nos. 7 and 8, the appearance after chromate treatment was within the allowable range, and the decrease in whiteness was 2 or more and less than 4.

On the other hand, when the pH value of the processing solution was higher than the range of the present invention and the precipitation amount of Ni and Co was 0,
o. In No. 1, the blackening resistance was inferior. PH of processing solution
The value of the comparative sample No. having a value outside the range of the present invention and low. In Nos. 2 and 3, both blackening resistance and appearance were inferior. The pH value of the processing solution is low outside the range of the present invention, and Ni, C
No. o for which the amount of precipitation was 0 or almost 0. 4 and 5 were inferior to blackening resistance. Further, the Ni ion content of the treatment liquid is large beyond the scope of the present invention,
Specimen N for comparison, in which the precipitation amount of N is larger than the range of the present invention.
o. In No. 6, the appearance was inferior.

[0052]

As described above, according to the present invention, the blackening resistance of the chromate-treated material is improved, and the appearance of the phosphate-treated material other than the chromate-treated material is not deteriorated. An electrogalvanized steel sheet with excellent blackening resistance can be obtained, and the steel sheet is subjected to galvanization using a specific plating bath, and then subjected to post-treatments such as chromate treatment and phosphate treatment. Not only the production of the resulting galvanized steel sheet, but also the production of an electrogalvanized steel sheet without post-processing, which is obtained by performing galvanizing treatment on the steel sheet using the same plating bath described above and not performing the above-mentioned post-processing. In a production line where it is possible, the blackening resistance can be improved for chromate-treated materials, and the appearance of phosphate-treated materials other than chromate-treated materials deteriorates. Capable of preventing, it is possible to provide a galvanized steel sheet and a manufacturing method thereof having excellent blackening resistance, thus industrially useful effects are provided.

Claims (3)

[Claims] A steel sheet, an electrogalvanized layer formed on a surface of the steel sheet, and a surface of the electrogalvanized layer,
A metal layer formed by depositing at least one of Ni and Co in an amount in the range of 0.01 mg / m ² or more and 10 mg / m ² or less, and a chromate film formed on the metal layer A chromate-treated electrogalvanized steel sheet having excellent resistance to blackening, characterized by comprising: 2. A steel sheet is electrogalvanized to prepare an electrogalvanized steel sheet having an electrogalvanized layer formed on at least one surface, and the electrogalvanized steel sheet is
When at least one of the Ni ion and the Co ion is in the range of 0.
At least one of Ni and Co is added to the surface of the electrogalvanized layer by contacting the electrogalvanized layer with a weak alkaline solution having a pH value of 8 or more and less than 11 which is added in an amount of 001 g / l or more and 10 g / l or less. 0.01 mg / m ² or more, 10 mg / m
Forming a metal layer on the surface of the electrogalvanized layer by depositing in an amount within the range of ² or less, and then performing a chromate treatment, the chromate-treated electrogalvanized steel sheet having excellent blackening resistance. Production method. 3. The method according to claim 2, wherein the weak alkaline solution is a sodium pyrophosphate-based solution or a sodium tripolyphosphate-based solution, or a mixed solution of the sodium pyrophosphate-based solution and the sodium tripolyphosphate-based solution. the method of.