JPH04131396A - Production of black steel sheet - Google Patents

Abstract

PURPOSE:To produce a black steel sheet having stable quality without deteriorating a blackening soln. by predissolving the baser phase of a Zn-Ni alloy plating layer on a steel sheet before electrolysis. CONSTITUTION:When a black steel sheet is produced, the baser phase of a Zn-Ni alloy plating layer on a steel sheet is predissolved preferably by anodic electrolysis in an electrolyte soln. or contact with an acidic aq. soln. and then the treated steel sheet is blackened by the conventional method. Even in the case where black steel sheets are continuously produced over a long time, a blackening soln. is not deteriorated and black steel sheets having stable quality are obtd.

Description

[Detailed description of the invention] <Industrial application field> The present invention relates to a method for manufacturing a black steel plate.

<Prior Art> Currently, steel sheets with blackened surfaces are widely used in home appliances, copying machines, information communication devices, automobile parts, interior building materials, etc.

The manufacturing method of this black steel plate includes (1) black painting, (
There are 2) chemical treatment methods, (3) black chromate methods, and (4) anodic treatment methods. Among them, the anodizing method is a manufacturing method that can obtain good blackness, and is described in Japanese Patent Publication No. 61-60915, Japanese Patent Publication No. 63-46158, and Japanese Patent Publication No. 63-46159.
It is disclosed in the publication No.

However, the blackening method using anodic treatment has the characteristic that metals are eluted from the thinning layer of the material, and in the case of Zn in particular, the amount of processing increases and it accumulates in high concentration in the treatment solution (hereinafter referred to as blackening solution). If this occurs, this becomes a white corrosion product and adheres to the steel plate during the blackening process, resulting in a problem of impairing the degree of blackness and uniform appearance.

Regarding this, a technique is disclosed in JP-A No. 61-139699 (Japanese Patent Publication No. 61-139699) in which the pH of the treatment solution is adjusted to 8 to 12, the eluted metal is precipitated as hydroxide, and this is continuously removed from the blackening solution. -17920).

<Problem to be solved by the invention> The method of continuously removing metal hydroxides from the blackening solution cannot prevent the hydroxides from adhering to the surface of the steel sheet, which has the fatal effect of worsening the degree of blackness. In addition to having shortcomings,
There were management and cost problems, such as the difficulty of filtering out hydroxides and the need to install new removal equipment.

An object of the present invention is to provide a method for producing a black steel plate that does not cause deterioration of the blackening solution even when the black steel plate is continuously produced over a long period of time, and can produce a black steel plate with stable product sales.

Means for Solving the Problems〉 The present inventors have solved the metal eluted from the material by dissolving and removing the base phase that does not participate in the blackening of the alloy plating layer of the material and then performing the blackening treatment. The inventors came up with the idea that the amount of (Zn) mixed into the blackening solution could be reduced, and completed the present invention.

That is, according to the present invention, in order to achieve the above object,
In a method for producing a black steel plate in which a steel plate having a Zn-Ni alloy plating layer is blackened by electrolytic treatment, prior to the electrolytic treatment, after preliminary melting of the base phase of the Zn-Ni alloy plating layer of the steel sheet, A method for producing a black steel sheet is provided, which is characterized by subjecting it to a blackening treatment.

Here, the preliminary dissolution is preferably performed by anodic electrolytic treatment in an electrolytic X solution.

Further, it is preferable that the preliminary dissolution is performed by contacting with an acidic aqueous solution.

The present invention will be explained in more detail below.

The blackness of a black steel plate is usually evaluated by the L value using a color difference meter. Although this L tl is an effective index for measuring blackness, it cannot manage subtle differences in color tone, so when we attempted a new measurement using a spectrophotometer, we succeeded in identifying it.

Based on the measurement results with this photometer, we investigated the relationship between the Ni content of the material and the color tone, and found that when the Ni content of the Zn-Ni alloy plated steel sheet was 5 to 15%, there was no difference in color tone. It has been found that black color is produced stably.

Therefore, the present inventors investigated how to extend the life of the blackening liquid within this Ni content range, and obtained the following knowledge.

The phase structure of the Zn-Ni alloy plated steel sheet differs depending on the Ni content. Therefore, the present inventors conducted an electrochemical study of constant current anodic melting (hereinafter referred to as anodic melting) on Zn-Ni alloy brushed steel sheets with different Ni contents and their black steel sheets, and determined the timing of anode melting. When we investigated the phase morphology from the potential of the layer and investigated its relationship with blackening, we found the following.

The potential of a Zn-Ni alloy coated steel sheet with a Ni content of more than 15 wt% is a single phase that stagnates around -700 mV-3, C, E, whereas the potential of Zn with a Ni content of 25 wt% or less is -The potential of the Ni alloy plated steel plate is -700mV-
It is classified into two phases: a phase that stagnates near S, C, and E, and a more base phase.

FIG. 1 shows an example of the results of anode melting of a Zn-Ni alloy plated steel sheet with a Ni content of 15w1t%.

Anode dissolution condition solution 2nSO<'7HzSO4227g/1Na
CJZ200 g/It Melting conditions Current density 20mA/cm” Counter electrode
-700 mV-3, in which the platinum phase shows a γ phase. I can see that there are two levels: C, E, and a more base phase.

This base phase is considered to be related to the dissolution of metal Zn, and does not appear as a peak in X-ray diffraction. Also,
-700mV-3,C,E.

The nearby phase corresponds to the γ phase determined by X-ray diffraction.

Since blackening occurs at the same time as the dissolution of the γ phase begins after the base phase dissolves, it is considered effective for the blackening treatment to dissolve only the γ phase. Therefore, if the base phase (-700mV-5, C, E, phase showing a more base potential) is predissolved and then blackened again, the blackening reaction (γ phase dissolution) will occur in the blackening solution. Only that much Zn is dissolved, and the life of the liquid can be extended.

The preferred method for dissolving the base phase is anodic electrolysis in an aqueous electrolyte solution such as an acid or salt, or a wet treatment such as dipping or spraying into an aqueous acid solution.

When using salt as the electrolyte during anodic electrolysis, the electrolyte solution may be potassium chloride, nickel chloride, zinc chloride, zinc sulfate, ammonium sulfate, sodium sulfate, potassium sulfate, nickel sulfate, or a mixed solution thereof.

The concentration is 50% from the viewpoint of liquid chamber conductivity and electrolyte solubility.
~200g/J2 is good.

Furthermore, when using an acid as an electrolyte during anodic electrolysis or when performing a wet treatment with an acid aqueous solution, less than 1 wt % of sulfuric acid, hydrochloric acid, nitric acid, or a mixed acid thereof can be used.

The reason why the concentration of acid is set to be less than 1 wt % is because if it exceeds this value, the dissolution progresses quickly, making it difficult to control and causing the plating layer to dissolve more than necessary. Although the lower limit is not particularly specified, it is preferably 0.01 wt% or more from the viewpoint of solubility. Since solubility varies depending on the line and manufacturing conditions, it is best to manage it by considering the operating conditions.

The material targeted by the present invention is a plated steel sheet having a Zn-Ni alloy plating layer with a coating weight of 7 g7m2 or more on the outermost surface. Furthermore, various plating layers may be provided below the plating layer.

The blackening liquid is not particularly limited, but any liquid that is degraded by the blackening treatment is within the scope of the present invention. For example, Na,
In addition, one or more of Nf hydroxide, sulfate, and hydrochloride is added at a concentration of 75 to 200 g/u and nitrate ion at a concentration of 2 to 100 g/u.
A blackening solution containing It is also within the scope of the present invention.

In addition, an inhibitor (thiourea, etc.) and a complexing agent (EDTA, etc.) are added to the blackening solution in order to prevent corrosion products generated due to an increase in the amount of Zn in the solution from adhering to the blackened steel sheet. It is also possible to add it to. In this case, the bath life is further extended due to the effects of pre-electrolysis and the additives.

The method for blackening by electrolytic treatment may be either an alternating electrolysis method or an anodic oxidation method.

The alternating electrolysis method is a method of blackening the steel plate while plating melted metal on the steel plate, and the life of the solution is much longer than that of the anodic oxidation method, but by applying the present invention, the life of the solution will be further extended. .

Although the black steel sheet obtained by the present invention can be used as it is, it is preferable to attach a chromate film on the black layer in order to improve corrosion resistance.

The adhesion amount is preferably about 5 to 150 mg/m2 in terms of Cr. If the amount is less than 5 mg 7 m', there will be no chromate treatment effect and corrosion resistance will not improve. Also, 150mg/l1
When it exceeds 12, corrosion resistance becomes saturated.

Further, in order to protect the black layer, carboxylated polyethylene, acrylic, epoxy, polyurethane, melamine, silicate sol, etc. can be applied. The coating amount is 0.3 to 3.0 by dry weight. 0g/rn' is good. There is no effect if it is less than 0.3g/m'; 3.0g
If it exceeds /m2, there will be no problem in appearance, but weldability will deteriorate.

If a resin or silica sol layer is placed on top of the chromate film formed on the black layer within the above range, the depth of the black color will increase and corrosion resistance can also be significantly improved.

Further, similar effects can be obtained by treatment with a mixed type liquid of chromium and resin within the above range.

<Example> The present invention will be specifically described below based on Examples.

(Example 1) Various Zn-Ni alloy coated steel sheets with the Ni content shown in Table 1 were prepared without pre-melting (comparative example) and after pre-melting was performed under the conditions shown in Table 1, blackening treatment was continued. Elution amount of Zn after cutting (invention examples 1 to 26), appearance after blackening (
blackness/uniform appearance) ○...good, △...fair, ×...
・The Zn-Ni alloy plating layers of the steel sheets used in the comparative examples and examples that were evaluated as poor all have phases with a more base potential of -700 mV-S, C, E, and the examples after pre-melting. Zn-Ni steel plate
All alloy plating layers are -700mV-5. C, E, did not have a phase with a more base potential.

In the table, ■ indicates the bath composition of the blackening solution: 150 g/j2 of NaSO4 and 20 g/11 of nitrate ion.

Note that the above processing was carried out by simulating in a laboratory the case where a 1000 ton steel plate was processed on an actual line.

As shown in Table 1, when preliminary melting is performed according to the present invention, the Zn concentration in the blackening solution can be maintained at a low level, so that each steel plate after treatment (examples of the present invention) It was uniformly black.

<Effects of the Invention> Since the present invention is configured as described above, according to the present invention, even when black steel plates are continuously produced over a long period of time, the treatment liquid does not deteriorate and the quality of the black steel plates is stable. It became possible to manufacture.

[Brief explanation of the drawing]

FIG. 1 is a graph showing an example of anode melting results of a Zn-Ni alloy plated steel sheet with a Ni content of 15 wt%. same

Claims (3)

[Claims] (1) In a method for producing a black steel plate in which a steel plate having a Zn-Ni alloy plating layer is blackened by electrolytic treatment, the base phase of the Zn-Ni alloy plating layer of the steel sheet is preliminarily melted prior to the electrolytic treatment. , a method for producing a black steel sheet, characterized by subjecting it to blackening treatment. (2) The method for producing a black steel sheet according to claim 1, wherein the preliminary melting is performed by anodic electrolysis treatment in an electrolyte solution. (3) The method for producing a black steel sheet according to claim 1, wherein the preliminary melting is performed by contacting with an acidic aqueous solution.