JPH10152792A - Production of electrogalvanized steel sheet excellent in appearance - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an electrogalvanized steel sheet having a uniform surface appearance without affecting to the original characteristic excellent in the coating stickiness and the corrosive resistance in the galvanized steel sheet by using pickling liquid containing pickling loss reducer to executing the pickling treatment of the steel sheet just before galvanizing and further, applying water washing treatment. SOLUTION: The steel sheet to be galvanized, passing the ordinary processes of a hot-rolling process, pickling process, cold-rolling process, annealing process, etc., is galvanized to produce the electrogalvanized steel sheet. In this electrogalvanizing process, degreasing treatment and the water-washing for cleaning the surface of the steel sheet to be galvanized and further, the pickling treatment and the water-washing for activating the surface of the steel sheet are ordinarily executed and successively, the galvanizing is executed. Therein, in order to activate the surface of the steel sheet, the pickling treatment is executed to the steel sheet by using the pickling liquid containing desirably 0.001-50g/l pickling loss reducer just before galvanizing and further, after applying the water-washing treatment, the electrogalvanization is executed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing an electrogalvanized steel sheet, and more particularly to a method for producing an electrogalvanized steel sheet, which has excellent plating adhesion and corrosion resistance and a uniform surface appearance. The present invention relates to a method for obtaining an excellent galvanized steel sheet.

[0002]

2. Description of the Related Art Electrogalvanized steel sheets have excellent adhesion and corrosion resistance, and are therefore widely used mainly for applications such as materials for home appliances. In recent years, in response to demands from customers to omit the coating process, chromate treatment and further resin coating have been applied to the upper layer of electrogalvanized,
BACKGROUND ART Steel sheets having not only improved corrosion resistance but also fingerprint resistance and lubricity have been developed, and their use in home appliances has been rapidly increasing. However, electrogalvanized steel sheets used in these applications are often used without painting, so the color and appearance did not pose a major problem in the case of coated steel sheets that were used with conventional painting. The demands have become very strict.

[0003] By the way, electrogalvanized steel sheets were originally
It is known that it is difficult to obtain a uniform appearance such as streak patterns due to the influence of various factors such as dirt on the surface of the steel plate, unevenness of oxide film thickness, segregation of components, texture distribution, etc. I have. However, in many cases, the cause cannot be specified, and even if the cause can be specified, the cause cannot often be removed from operational constraints.

[0004] Therefore, as a method for producing an electrogalvanized steel sheet to obtain a uniform appearance without being affected by the material,
(1) A method of uniformizing nucleation of Zn crystals by performing Zn plating at a high current density in an initial stage of plating (for example, JP-A-7-3167878), (2) Before applying Zn plating, A method of performing pre-plating such as Ni plating (for example, JP-A-7-76793), and (3) a method of adding an organic compound to a plating bath (for example, JP-A-8-158)
090), and (4) a method in which the amount of pickling loss before plating is regulated to a specific amount or more (for example, JP-A-8-104995).

[0005]

However, the method (1) described above does not sufficiently solve the above problem because the effect of eliminating the influence of the material and making the appearance uniform is extremely small. In the method (2), although the effect of making the appearance uniform is slightly observed, the good plating adhesion inherent in the electrogalvanized steel sheet is lost. Therefore, conventionally,
There has been a problem that electrogalvanized steel sheets cannot be used in applications where they have been used. In the method (3), the appearance was slightly uniform, but both the plating adhesion and the corrosion resistance were remarkably deteriorated, and only those which could not be used were obtained. Further, in the method (4), in addition to obtaining a uniform appearance, in some cases, the influence of the material may be amplified, and the above problem cannot be solved at all.

Accordingly, an object of the present invention is to solve the above-mentioned problems, and to provide an electrogalvanized steel sheet having a uniform surface appearance without affecting the inherently excellent properties such as plating adhesion and corrosion resistance. It is another object of the present invention to provide a method capable of manufacturing an electrogalvanized steel sheet having excellent appearance.

[0007]

Means for Solving the Problems The present inventors have intensively studied the causes of the appearance of electrogalvanized steel sheets being non-uniform due to the material. As a result, poor appearance of the electrogalvanized steel sheet is caused by unevenness of the surface state of the base steel sheet due to contamination of the steel sheet surface, uneven oxide film thickness, segregation of components, texture distribution, and the like. It was found that most of the non-uniformity of the surface state existed before the annealing step before entering the electroplating line. Furthermore, it has been found that it is extremely difficult to make the uneven surface of the steel sheet uniform by a degreasing treatment or an acid pickling treatment by a usual method performed in an electroplating line.

[0008] Therefore, as a result of intensive studies on a method of preventing the appearance defect of electrogalvanized by making the steel sheet surface before plating uniform, the pickling solution having an action of reducing the pickling loss in the pickling solution was obtained. The present inventors have found that it is extremely effective to include a weight loss reducing agent, and have reached the present invention.

That is, the present invention comprises a step of, immediately before plating, subjecting a steel sheet to a pickling treatment using a pickling solution containing a pickling loss reducing agent, performing a water washing treatment, and then performing electrogalvanizing. An object of the present invention is to provide a method for producing an electrogalvanized steel sheet having an excellent appearance.

It is preferable that the pickling liquid contains 0.001 to 50 g / l of a pickling loss reducing agent.

Hereinafter, the method for producing an electrogalvanized steel sheet of the present invention (hereinafter, referred to as “method of the present invention”) will be described in detail.

In the method of the present invention, a steel sheet which has been subjected to common steps such as a hot rolling step, a pickling step, a cold rolling step, and an annealing step is used as a material to be plated. This is a method of producing an electrogalvanized steel sheet by performing galvanization. In this electrogalvanizing step, usually, a degreasing treatment and a water washing for cleaning the surface of the steel plate as a material to be plated, and a pickling treatment and a water washing for activating the steel plate surface are performed. Subsequently, electrogalvanizing is performed. Here, the pickling treatment performed in the present invention refers to a pickling treatment performed for the purpose of activating the steel sheet surface immediately before electrogalvanizing, and after hot rolling, in order to remove so-called black scale. This is different from the pickling step to be performed.

In the method of the present invention, the pickling treatment performed immediately before electrogalvanizing is a treatment of a material to be plated with a pickling solution containing a pickling loss reducing agent as an essential component. The pickling weight loss reducing agent used is an organic compound having an action of reducing pickling weight loss.

The acid component used as a component of the pickling solution is as follows:
There is no particular limitation, and conventional ones can be used. For example, sulfuric acid, hydrochloric acid, phosphoric acid, nitric acid, hydrofluoric acid and the like can be mentioned. Further, the acid concentration in the pickling solution may be in a usual range, and is not particularly limited. For example, a pure acid concentration of 5 to 500 g
/ L. The temperature of the pickling solution may be in a normal range, and is not particularly limited, and may be, for example, in a range from normal temperature to 95 ° C. The time of the pickling treatment is the time required for the surface of the steel sheet before plating to be uniform, the type of the pickling solution, the concentration of the acid, the temperature, the type of the pickling loss reducing agent contained in the pickling solution, the content, etc. Is appropriately selected according to the conditions. For example, one second to one hour. Further, the pickling liquid generally contains iron ions and impurities, but the pickling liquid used in the present invention may also contain these, and the amount is not particularly limited.

In the present invention, whether or not the organic compound used as the pickling weight loss reducing agent has the action of reducing the pickling weight loss can be easily confirmed, for example, by the following method. That is, the type of pickling solution,
The steel sheet manufactured under the same conditions is immersed for a certain period of time while the concentration and the temperature are kept constant, and the pickling loss (g / m ² ) is measured from the weight change before and after the immersion. If the weight loss of the pickling is smaller in the case where the organic compound is added than in the case where the organic compound is not added, the organic compound has an action of reducing the weight loss in the pickling.

In the present invention, the reason why an electrogalvanized steel sheet having a uniform appearance can be obtained by performing a pickling treatment by using a pickling solution containing a pickling weight loss reducing agent in the pickling solution is completely explained. Although it was not clarified, it can be inferred as follows. That is, when the surface of the steel sheet before the pickling was uneven, if the pickling treatment was performed with a pickling solution containing no pickling weight loss reducing agent, the pickling was performed between the active part and the inactive part of the steel sheet. A difference is generated in the speed, and as a result, the difference in the etching state of the steel sheet surface, the difference in the amount of the element enriched in the surface, and the difference in the amount of the pickling smut generated by the pickling treatment become more remarkable. Therefore, when plating is performed, the shape, size, orientation, and the like of the formed plating crystal become non-uniform, resulting in poor appearance. On the other hand, when an organic compound is contained in a pickling solution as a pickling weight loss reducing agent, it is presumed that this organic compound is adsorbed to a specific portion of the steel sheet surface during pickling, so that the pickling weight loss is reduced, and It is considered that the surface of the subsequent steel sheet is made uniform, and as a result, a uniform plating crystal is obtained. Therefore,
In the present invention, the pickling weight loss reducing agent contained in the pickling solution is essential to be an organic compound having an action of reducing pickling weight loss, but the purpose is to reduce pickling weight loss. Instead, the purpose is to make the steel sheet surface after pickling uniform.

The organic compound used as the pickling weight loss reducing agent may be a low molecular weight compound or a high molecular weight compound as long as it has an action of reducing the pickling weight loss and making the surface of the steel sheet after pickling uniform. Is not particularly limited. For example, aldehydes, oxygen-containing organic compounds such as acetylenic alcohols, pyridines, quinolines, nitrogen-containing organic compounds such as aliphatic amines, organic sulfides,
Sulfur-containing organic compounds such as sulfonium compounds,
Oxygen, nitrogen, containing two or more such as sulfur, quinolinols, cyclic ketoamines, alkyl sulfoxides, sulfonic acids, thioureas, organic thiocyanates, thiazoles, thiomorpholine derivatives, sulfonated imidazolines, Alternatively, a phosphorus-containing organic compound, an alkyne having a triple bond, and the like can be given.

As the pickling weight loss reducing agent, a commercially available organic corrosion inhibitor can be suitably used. For example, Hivilon Y-30, Hivilon Y-32, Hivilon Y-32L, Hivilon Y-32L manufactured by Sugimura Chemical Industry Co., Ltd.
K, Hibiron Y-36, Hibiron Y-31L1, Hibiron Y-3100, Hibiron A-6, Hibiron A-8, Hibiron P-2, Hibiron YS-7, Hibiron YN-3,
Hivilon AI-1, Hivilon A-5, Hivilon A-50
2. Ebit 105, Ebit 155, Ebit 530, Ebit S600, Ebit S600A, Ebit S600B, Ebit 600L, manufactured by Asahi Chemical Industry Co., Ltd.
EBIT 600LAC, EBIT 600LSC, EBIT 600 LPC, EBIT 700, EBIT 700A,
Ebit 700BK, Evint 710N, Ebit 80
0 and the like. Furthermore, the present invention is not limited to this as long as it has an action of reducing the amount of pickling loss and making the surface of the steel sheet uniform after pickling. In the present invention, the pickling weight loss reducing agent may be used alone or may be used alone.
A combination of more than one species may be used.

In the method of the present invention, the combined amount of the pickling loss reducing agent in the pickling solution is preferably 0.001 to 50.
g / l, particularly preferably 0.002 to 10 g / l
It is. If the pickling weight loss reducing agent is less than 0.001 g / l, a uniform plating appearance cannot be obtained, and if it exceeds 50 g / l, the effect is saturated, which is not only uneconomical but also causes plating unevenness or pickling. Problems such as deterioration of the stability of the liquid may occur.

Further, the pickling solution used in the method of the present invention can improve the dispersibility of an organic compound used as a pickling weight reducing agent, improve the stability of the pickling solution, suppress foaming, and improve the wettability with a steel sheet. For the purpose of the above, a surfactant, an antifoaming agent, an organic solvent and the like may be further contained as necessary.

In the method of the present invention, after the pickling treatment, the electrolytic zinc plating is performed through a water washing treatment. In this washing treatment, part or all of the pickling loss reducing agent adsorbed on the steel sheet surface in the pickling liquid is removed. In the present invention, as described above, the action of the pickling weight loss reducing agent is to make the surface of the steel sheet after pickling uniform, and therefore, as long as this object is achieved, the pickling weight loss reducing agent can be completely removed by the water washing treatment. Alternatively, the plating may be carried out while a part of the steel sheet is not completely removed but adsorbed on the surface of the steel sheet. However, if excessive pickling weight loss reducing agent remains adsorbed on the steel sheet surface,
Since the remaining organic compound may cause plating unevenness, in such a case, it is necessary to reduce the amount of the remaining organic compound by strengthening the washing and using a brush roll.

In the method of the present invention, pickling treatment and
After washing with water, electrogalvanize according to the usual method,
Electrogalvanized steel sheet can be obtained. Electric zinc
The bath composition and plating conditions are not limited at all.
Instead, all known methods are applicable. example
For example, the plating bath composition includes a sulfuric acid bath, a chloride bath, and a sulfuric acid bath.
And a chloride bath, and Zn in the plating bath.
The ion concentration may be 0.1 to 3 mol / l. Me
The bath is sodium sulfate, potassium sulfate, sodium chloride
, Potassium chloride, etc., Ni ion, Fe ion
Metal ions, such as Pb ions, aluminum sulfate, etc.
Organic brighteners such as inorganic brighteners and polyethylene glycol
May or may not be contained. Me
For example, the pH of the plating bath is 0.5 to
5.0, plating bath temperature 30-70 ° C, plating solution flow
Speed is 0.1-5.0 m / s, current density is 5-300 A /
dm ^Two, The coating weight is 5 to 200 g / m^TwoYou can
No.

The upper layer of the electrogalvanized layer may be subjected to a chemical conversion treatment such as a phosphate treatment or a chromate treatment or a resin coating according to the purpose of improving corrosion resistance and paint adhesion, imparting fingerprint resistance and lubricity. May be applied.

[0024]

EXAMPLES Hereinafter, Examples and Comparative Examples of the present invention will be described.
The present invention will be described more specifically.

(Examples 1 to 62, Comparative Examples 1 to 4) In each of the examples, a hot-rolled coil in which scale was generated over the entire width and the entire length was supplied to an actual operation line, and a pickling process was performed.
The steps up to the cold rolling step and the annealing step were performed in order.
From the obtained annealed coil, a large number of plating base plates made of a semi-ultra low carbon steel plate having a size of 100 mm × 175 mm and a thickness of 1.0 mm were cut out to obtain samples. The electroplated steel sheet was produced by treating the electroplated steel sheet sample in the order of alkaline electrolytic degreasing → water washing → acid washing → water washing → electrogalvanizing.

The alkaline electrolysis treatment and the subsequent water washing treatment were performed under the following conditions. Alkaline electrolytic treatment Bath composition: NaOH 30 g / l Pakuna 25K (manufactured by Yuken Industries Co., Ltd.) 5 g / l Bath temperature: 70 ° C. Current density: 10 A / dm ² (steel plate is used as anode) Treatment time: 5 seconds While spraying tap water for 10 seconds, the surface of the steel plate was rubbed 10 times with a tortoise scrub.

Table 1 shows the type, concentration, and temperature of the pickling solution in the pickling treatment, and the type and content of the pickling loss reducing agent in the pickling solution. The pickling treatment was performed by immersing the steel sheet in a pickling solution, and the immersion time was 5 seconds. Washing with water after pickling
This was done by spraying tap water for 10 seconds. Electrogalvanizing was performed using a fluidized-bed plating cell under the following conditions.

The appearance of the obtained electrogalvanized steel sheet was evaluated based on the appearance defect rate according to the following criteria. Table 1 shows the results. ◎: appearance defect occurrence rate 未 満 5% or less: appearance defect occurrence rate 5% to less than 20% △: appearance defect occurrence rate 20% to less than 40% ×: appearance defect occurrence rate 40% or more４０

Also, except that the pickling treatment was carried out in advance using a plating base plate extracted from the entire width and the entire length of the same annealed coil and using a pickling solution not containing a pickling loss reducing agent.
As a result of electrogalvanizing after the electrolytic degreasing and pickling treatments as described above, it was confirmed that streak-like poor appearance due to the raw material was generated with any of the plated original plates.

[0030]

[Table 1]

[0031]

[Table 2]

[0032]

[Table 3]

[0033]

[Table 4]

As is clear from Table 1, the electrogalvanized steel sheets produced by the production method of the present invention are all excellent in appearance.

[0035]

According to the method for producing an electrogalvanized steel sheet of the present invention, an electrogalvanized steel sheet has excellent plating adhesion and corrosion resistance, and has a uniform surface appearance and excellent appearance. A galvanized steel sheet can be obtained. Therefore, the method of the present invention is extremely valuable industrially.

Claims (2)

[Claims] (1) Immediately before plating, a steel sheet is pickled using a pickling solution containing a pickling loss reducing agent, and then subjected to a water washing treatment, followed by electrogalvanizing. Manufacturing method of electrogalvanized steel sheet. 2. The pickling liquid according to claim 1, wherein the pickling loss reducing agent is 0.001.
The method for producing an electrogalvanized steel sheet according to claim 1, wherein the composition contains 1 to 50 g / l.