JP2016094640A - Method for manufacturing electrogalvanized steel sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing an electrogalvanized steel sheet, capable of: manufacturing an electrogalvanized steel sheet having a high degree of whiteness without degrading characteristics of an electrogalvanized layer and without reducing a current efficiency when electrogalvanized; and stably maintaining a high degree of whiteness even when continuously operated.SOLUTION: The method for manufacturing an electrogalvanized steel sheet comprises steps of: forming an electrogalvanized layer on a steel sheet by an electrogalvanizing method; contacting the steel sheet having the electrogalvanized layer for 0.5 seconds or more with an acidic aqueous solution including 0.002-0.05 mol/L of at least one kind of a nitrate ion, an iodate ion, a bromate ion and a chlorate ion in total, including a zinc ion of 0.3-1.5 mol/L and having a pH of 1-3; and forming a chemical conversion coating on the surface of the electrogalvanized layer.SELECTED DRAWING: Figure 1

Description

  The present invention mainly relates to a method for producing an electrogalvanized steel sheet used for home appliances and the like, and more particularly to a method for producing an electrogalvanized steel sheet having high whiteness by treating the plated surface. .

Electrogalvanized steel sheets subjected to chemical conversion treatment are currently used in many applications because they have good corrosion resistance and cost. In addition, such a plated steel sheet is generally required to have a high degree of whiteness because the appearance of the product is good. Therefore, various techniques for improving the whiteness have been developed.
Here, although the whiteness of the steel sheet is reduced by the chemical conversion treatment after plating, it largely depends on the surface state of the plating layer before chemical conversion treatment, so the whiteness is improved by optimizing the electrogalvanizing conditions. Many technologies have been developed. In addition, as an index of whiteness of the electrogalvanized steel sheet, brightness (L value) is usually used.

  As a method for producing an electrogalvanized steel sheet having high whiteness, for example, as disclosed in Patent Document 1, an inorganic ion (Tl) is contained in a sulfuric acid-based zinc plating bath, and electrogalvanization is performed. There is a manufacturing method of applying. If this manufacturing method is used, high whiteness (brightness) can be obtained by the effect of Tl.

  As another method, there is a method of improving the whiteness of the electrogalvanized steel sheet by using an electrogalvanizing bath to which a predetermined organic substance is added. For example, Patent Document 2 uses a sulfuric acid galvanizing bath containing at least one selected from the group of glycine, aspartic acid, carboxylic acid having two or more carboxylic acid groups or salts thereof having a predetermined concentration. In Patent Document 3, an electrogalvanizing bath to which a predetermined amount of at least one selected from the group consisting of a metal salt of naphthenic acid, an aniline derivative, a lower alkanoyl compound, and an organic peroxide is added is used.

However, as disclosed in Patent Document 1, the electrogalvanized steel sheet produced using a plating bath containing an inorganic substance is co-deposited in the plating layer, so that the corrosion resistance of the plating layer is deteriorated or the hardness is low. There is a problem that the characteristics of the galvanized layer are lost, such as an increase.
In addition, as in Patent Documents 2 and 3, the production method using a plating bath to which an organic substance has been added has a problem that current efficiency is lowered during electrogalvanization and a problem that the life of the insoluble anode is shortened. In addition, the manufactured electrogalvanized steel sheet has a problem that the characteristics of the galvanized layer are lost, for example, the hardness of the plated layer is increased because the organic matter added to the plating bath is co-deposited in the plated layer. It was.

  In order to solve the above problems, the present inventors, as shown in Patent Document 4, form a plating layer on a steel sheet by electrogalvanizing, and then nitrate, iodate, bromate and chlorate ions. The technology which optimizes about the surface shape of the formed plating layer was developed by making it contact with the specific acidic aqueous solution containing at least 1 type of these for a fixed time. According to this technique, the obtained electrogalvanized steel sheet has high whiteness, and since it is not necessary to add an inorganic substance or an organic substance to the plating bath at the time of manufacture, the plating layer resulting from the eutectoid of the inorganic substance or the organic substance There is an effect that it is possible to effectively suppress deterioration of characteristics and a decrease in current efficiency during electroplating.

Japanese Patent Laid-Open No. 9-195082 JP-A-8-74089 Japanese Patent Laid-Open No. 10-287992 JP 2011-038167 A

  However, although the electrogalvanized steel sheet manufactured by the technique of Patent Document 4 has high whiteness at the initial stage of operation, it is caused by a change in the composition of the acidic aqueous solution when operated continuously for a long period of time. In some cases, the whiteness of the electrogalvanized steel sheet gradually decreased. This decrease in whiteness is an event that can occur even when the operation is controlled so that the concentration and pH of the nitrate, iodate, bromate, and chlorate ions in the acidic aqueous solution are constant. Further improvement is desired.

  The purpose of the present invention is to produce an electrogalvanized steel sheet having a high whiteness without deterioration of the properties of the plating layer, without reducing the current efficiency during electrogalvanization, and even when continuously operated, An object of the present invention is to provide a method for producing an electrogalvanized steel sheet that can stably maintain high whiteness.

As a result of repeated investigations to solve the above-mentioned problems, the inventors of the present invention have reduced the whiteness described above. The cause was thought to be the increase in the concentration of zinc ions that were not contained in the acidic aqueous solution at the start of operation.
By bringing a steel sheet on which galvanization is formed into contact with the acidic aqueous solution, the surface of the plating layer having fine irregularities is dissolved and flattened, thereby increasing the whiteness. However, when zinc ions are mixed in the acidic aqueous solution and the zinc ion concentration is increased, the reactivity of the acidic aqueous solution is lowered, and the flattening effect is reduced. As a result, it is estimated that a decrease in whiteness occurs.

Furthermore, as a result of intensive studies, the inventors of the present invention have found that when the zinc concentration in the acidic solution is extremely low, the whiteness (L value) of the surface-treated steel sheet changes greatly due to the change in the zinc concentration, but the zinc concentration In the specific range, attention was paid to the fact that even if the zinc concentration changes, the influence on the change in whiteness is small.
And by adjusting the zinc concentration in the acidic solution in advance to a specific range (specifically, 0.3 to 1.5 mol / L) before operation, the zinc in the plating layer is eluted into the acidic aqueous solution by continuous operation. Even when the zinc ion concentration changes, it is possible to minimize the change in the whiteness (L value) of the surface-treated steel sheet, and to stably manufacture an electrogalvanized steel sheet having high whiteness. I found it.

The present invention has been made based on such findings, and the gist thereof is as follows.
(1) forming a plating layer having a zinc content of 97% by mass or more on a steel sheet by electrogalvanizing;
The steel plate on which the plating layer is formed contains 0.002 to 0.05 mol / L in total of at least one of nitrate ions, iodate ions, bromate ions and chlorate ions, and 0.3 to 1.5 mol / L of zinc ions. A step of contacting an acidic aqueous solution containing L and having a pH of 1 to 3 for 0.5 seconds or more;
A method for producing an electrogalvanized steel sheet, comprising: forming a chemical conversion film on the plating layer.

(2) The method further comprising the step of bringing the steel sheet on which the plating layer is formed into contact with the acidic aqueous solution and then contacting the basic solution having a pH of 8.5 to 12 for 0.5 seconds or longer (1) ) The method for producing an electrogalvanized steel sheet as described above.

(3) The method for producing an electrogalvanized steel sheet according to the above (1) or (2), wherein an adhesion amount per one side of the chemical conversion film is 0.05 to 1 g / m ² .

  According to the present invention, there is no deterioration of the properties of the plating layer, and an electrogalvanized steel sheet having high whiteness can be produced without reducing the current efficiency during electrogalvanization, and even when continuously operated, It is possible to provide a method for producing an electrogalvanized steel sheet that can stably maintain high whiteness.

It is the graph which showed the change of L value of an electrogalvanized steel plate when changing only zinc ion content (mol / L).

Hereinafter, the configuration of the present invention and the reasons for limitation will be described.
The method for producing an electrogalvanized steel sheet according to the present invention includes:
A step of forming a plating layer having a zinc content of 97% by mass or more on a steel plate by electrogalvanizing (plating layer forming step);
The steel plate on which the plating layer is formed contains 0.002 to 0.05 mol / L in total of at least one of nitrate ions, iodate ions, bromate ions and chlorate ions, and 0.3 to 1.5 mol / L of zinc ions. A step of contacting an acidic aqueous solution containing L and having a pH of 1 to 3 for 0.5 seconds or longer (an acidic aqueous solution contacting step);
A step of forming a chemical conversion film on the plating layer (chemical conversion film forming step).

  By contacting a steel sheet with a plating layer in contact with an acidic aqueous solution containing specific ions (at least one of nitrate ion, iodate ion, bromate ion and chlorate ion) and having a specific pH, Since the surface of the plating layer having fine irregularities is flattened by the ions, incident light can be reflected effectively, and as a result, high whiteness (L value) can be obtained. Furthermore, it is not necessary to add eutectoid inorganic or organic substances in the plating bath, so the characteristics of the plating layer (hardness, corrosion resistance, peeling resistance during processing, etc.) and current efficiency during electrogalvanization Can be secured enough. In addition, by containing 0.3 to 1.5 mol / L of zinc ions in the acidic aqueous solution, even when zinc in the plating layer is eluted into the acidic aqueous solution and the zinc ion concentration is changed during continuous operation, A change in whiteness (L value) of the galvanized steel sheet can be minimized.

(Plating layer forming process)
In the method for producing an electrogalvanized steel sheet of the present invention, a plating layer is formed on the steel sheet by an electrogalvanizing method.
Here, the said plating layer says the plating layer containing zinc, and is formed by the electrogalvanization method. The type of bath used in the electrogalvanizing method is not particularly limited, and for example, a sulfuric acid bath, a chloride bath, a zincate bath, a cyan bath, or the like can be used. However, when components contained in the zincate bath or cyan bath are mixed in the acidic aqueous solution, the influence of anions and additives as impurities is inevitable. For this reason, it is preferable to use a sulfuric acid bath or a chloride bath. The plating layer has a zinc content of 97% by mass or more. There is no problem even if the plating layer contains a small amount of intentionally contained components or inevitably contained impurities (steel components eluted from the original plate, Ni, Co, etc. which may be mixed). When the zinc content is less than 97% by mass, the influence of components other than zinc is increased, and there is a possibility that stable performance cannot be exhibited, and the whiteness inherently possessed by the galvanized steel sheet is reduced. The zinc content in the plating layer can be determined by dissolving the plating layer by contact with an acid solution such as dilute hydrochloric acid and performing wet analysis on the dissolved components.

Moreover, it is preferable that the adhesion amount per one side of the said plating layer is 5-30 g / m < ² > from the point which ensures the characteristic and whiteness of an electrogalvanization layer. In addition, after the amount of adhesion of the plating layer grasps the adhesion area of the plating layer, the mass change of the steel sheet before and after dissolving the plating layer by contact with an acid solution such as dilute hydrochloric acid, or the dissolved plating component It can be determined by quantification.
In addition, after the said plating layer formation process, in order to suppress mixing of the plating bath component into the pickling aqueous solution mentioned later, it is preferable to wash with water. However, when the plating bath is a sulfuric acid bath or a chloride bath mainly composed of zinc ions, sulfate ions, and chloride ions, these components will not adversely affect the effects of the present invention even if mixed in an acidic aqueous solution described later. It is not necessary to wash with water. Moreover, when performing water washing, you may dry after the water washing and before the contact process to acidic aqueous solution.

(Acid aqueous solution contact process)
In the method for producing an electrogalvanized steel sheet according to the present invention, the steel sheet on which the plated layer is formed is a total of at least one of nitrate ion, iodate ion, bromate ion and chlorate ion of 0.002 to 0.05 mol / L. And an acidic aqueous solution containing 0.3 to 1.5 mol / L of zinc ions and having a pH of 1 to 3 for 0.5 seconds or longer.

Here, the type of the ions is limited to at least one of nitrate ions, iodate ions, bromate ions and chlorate ions because the plating surface layer is removed by removing a certain amount of the plating surface layer. This is because the unevenness can be flattened and the whiteness can be increased. When other ions are used, the same effect cannot be obtained. In addition, the content of the ions is in the range of 0.002 to 0.05 mol / L because if the amount is less than 0.002 mol / L, the amount of ions is too small, the fine unevenness of the plated crystal can be sufficiently flattened. This is because the desired whiteness cannot be obtained. On the other hand, when the content of the ions exceeds 0.05 mol / L, the amount of ions is too large, so that the surface of the plating layer becomes rough and the whiteness is reduced.
The ion source of various ions described above is not particularly limited as long as desired ions can be obtained. For example, each acidic aqueous solution, metal salt, or a mixture thereof can be appropriately selected in consideration of the ion content and the like.

Further, the content of the zinc ion in the acidic aqueous solution is set in the range of 0.3 to 1.5 mol / L. By setting the content in this range, zinc in the plating layer is eluted in the acidic aqueous solution in continuous operation. This is because even when the concentration fluctuates, a decrease in whiteness (L value) of the electrogalvanized steel sheet can be reduced. When the zinc ion content is lower than 0.3 mol / L, the change in the whiteness (L value) of the surface-treated steel sheet due to the fluctuation of the zinc concentration increases, and it is possible to stably maintain a high whiteness. Can not. On the other hand, if the zinc ion content is higher than 1.5 mol / L, the zinc ion concentration in the acidic aqueous solution will decrease due to the mixing of washing water, etc., so that the zinc ion concentration can be maintained. There is a need to continue to supply zinc ions, which is disadvantageous in terms of manufacturing costs.
The ion source of the zinc ions is not particularly defined, but it is desirable to add as zinc sulfate or zinc chloride. This is because sulfate ions or chloride ions can flatten the surface of the electrogalvanized layer and have little influence on the effect of improving the whiteness of the present invention, and can stably achieve high whiteness.

  Here, FIG. 1 shows a case in which zinc sulfate is added to an acidic aqueous solution in the step of bringing the steel sheet on which the plating layer is formed into contact with an acidic aqueous solution containing 0.02 mol / L of nitrate ions and having a pH of 2.0. It is the graph which showed the change of L value of an electrogalvanized steel plate when content (mol / L) was changed. FIG. 1 also shows that the change in the L value of the obtained electrogalvanized steel sheet is reduced by setting the zinc ion content to 0.3 mol / L or more.

In the acidic aqueous solution contact step, the pH of the acidic aqueous solution needs to be 3 or less. This is because if the pH of the acidic aqueous solution exceeds 3, the reactivity of the acidic aqueous solution becomes insufficient, and the surface of the plating layer is not sufficiently flattened, so that the whiteness cannot be improved. In the acidic aqueous solution contact step of the present invention, unlike the acidic aqueous solution described in Cited Document 4, since it contains zinc ions, the surface of the plating layer is sufficiently flattened unless the pH is 3 or less. I can't do it. On the other hand, the lower limit of the pH of the acidic aqueous solution needs to be 1 or more. When the pH of the acidic aqueous solution is less than 1, the whiteness improvement effect can be obtained, but the amount of galvanized layer to be dissolved increases upon contact with the acidic aqueous solution, and there is a need to increase the amount of galvanized adhesion. This is because the cost for forming the layer is increased.
Furthermore, the pH of the acidic aqueous solution is preferably in the range of 2.0 to 3.0 from the viewpoint that a desired whiteness improvement effect can be obtained and the amount of dissolution of the plating layer can be reduced. Regarding the pH adjustment, it is desirable to use sulfuric acid or hydrochloric acid in the sense that the influence on the effect of flattening the surface of the plating layer and increasing the whiteness is small.

Furthermore, in the present invention, it is necessary to bring the steel sheet on which the plating layer is formed into contact with the acidic aqueous solution for 0.5 seconds or more. This is because, when the contact time is less than 0.5 seconds, the contact time is too short, and thus the surface of the plating layer cannot be sufficiently flattened, and a desired whiteness cannot be obtained. The upper limit of the contact time is not particularly limited from the viewpoint of obtaining whiteness, but is preferably 5 seconds or less from the viewpoint of productivity. Moreover, it does not specifically limit about a contact method, For example, methods, such as immersion to aqueous solution, application | coating of aqueous solution, and spraying of aqueous solution, can be used.
In addition, after the said acidic aqueous solution contact process, in order to eliminate the bad influence (contamination etc. to a chemical conversion film) to a subsequent process, it is preferable to wash and dry the said steel plate.

  The temperature of the acidic aqueous solution is not particularly limited, but is preferably in the range of 30 to 60 ° C. from the standpoint of constant temperature retention and temperature increase cost. Further, the acidic aqueous solution may contain a pH buffer, and it is considered that unavoidable impurities are contained. In addition, it may contain a small amount of elution components (Zn, Fe, Ni, etc.) from the plating layer and contamination components of the plating bath.

(Basic solution contact process)
In the method for producing an electrogalvanized steel sheet according to the present invention, after the acidic aqueous solution contact step, the step of contacting the steel plate on which the plating layer is formed with a basic solution having a pH of 8.5 to 12 for 0.5 seconds or longer (basic It is preferable to further comprise a solution contact step. Thereby, a favorable coating-material adhesiveness can be provided after chemical conversion film formation.
In the acidic aqueous solution contact step, if zinc ions are contained in the aqueous solution, a reaction layer containing zinc is generated on the surface of the plating layer, and the adhesion between the plating layer and the chemical conversion film is lowered. For this reason, even if the chemical conversion film and the paint are in close contact, sufficient paint adhesion cannot be obtained. However, this reaction layer can be removed by further providing a basic solution contact step, and good paint adhesion (adhesion between the plating layer and the chemical conversion film) can be imparted.

  In the basic solution contact step, it is preferable to wash the steel plate in advance after the acidic aqueous solution contact step in order to remove the acidic aqueous solution. After the basic solution contact step, adverse effects on the subsequent steps (chemical conversion) In order to eliminate contamination and the like on the film, the steel plate is preferably washed and dried.

(Chemical conversion film formation process)
And in the manufacturing method of the electrogalvanized steel sheet of the present invention, the surface of the electrogalvanized steel sheet that has been brought into contact with the acidic aqueous solution, washed with water and dried, preferably further contacted with a basic solution, washed and dried. To form a chemical conversion film. This chemical conversion film is a layer provided on the surface of the steel sheet so as to be provided with corrosion resistance, adhesion, and scratch resistance. From the standpoint of maintaining these required characteristics and preventing a decrease in whiteness, the amount of adhesion is preferably in the range of 0.05 to 1 g / m ² per side.

  The chemical conversion film is not particularly limited, and a conventionally known chemical conversion film can be used. For example, an inorganic film, an organic film, an organic-inorganic composite film, or a multilayer film of these can be used. The type, component, and adhesion amount may be appropriately selected according to the required characteristics, that is, the above-described corrosion resistance, adhesion, and wrinkle resistance.

EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated in detail, this invention is not limited to these.
(Samples 1 to 32)
The following steps (i) to (iii) were performed to produce an electrogalvanized steel sheet as a sample.
(I) After degreasing and pickling treatment on cold-rolled steel sheet, electrogalvanization method (conditions are plating bath: sulfuric acid acidic bath containing 1.5 mol / L of Zn ²⁺ ions (pH 2.0, temperature 50 ° C), relative flow rate: 1.5 m / sec, current density: 50 A / dm ² ), forming a galvanized layer (zinc content of 97% by mass or more) with an adhesion amount per side of 20 g / m ² After that, some samples were washed with water.
(Ii) The produced electrogalvanized steel sheet was brought into contact with an acidic aqueous solution containing ions shown in Table 1. The conditions of the acidic aqueous solution (ion type, total ion concentration (mol / L), ion source, zinc ion concentration (mol / L), zinc ion source, pH of acidic aqueous solution, type of pH adjusting agent, temperature), Details of the treatment conditions (treatment method, contact time) using an acidic aqueous solution are shown in Table 1. In addition, about the sample, the process by the said acidic aqueous solution is not implemented (refer Table 1).
(Iii) Next, the steel sheet subjected to the acidic aqueous solution treatment was washed with water and dried, and then on the surface of the steel sheet, 100 parts by mass of monomanganese phosphate was mixed with silica (average particle diameter: 7 nm). ) Applying a chemical conversion treatment solution containing 70 parts by mass with a roll coater, baking in a hot air oven at 140 ° C, and drying to form a chemical conversion film consisting of an inorganic film with an adhesion amount per side of 0.4 g / m ² Formed.

  Evaluation was performed on samples 1 to 32 of each electrogalvanized steel sheet obtained as described above. The evaluation method is shown below.

(Evaluation method)
(1) Whiteness (L value)
About each sample, the brightness (L value) by SCE (regular reflection light removal) was measured using the color difference meter (SE2000 by Nippon Denshoku Industries Co., Ltd.). Evaluation is performed according to the following criteria, and the measured values and evaluation results are shown in Table 2.
○: L value is 64 or more ×: L value is less than 64

(2) Amount of dissolution of the plating layer in the acidic aqueous solution contact step For each sample after the acidic aqueous solution contact step, all the zinc plating layer was dissolved by contact with dilute hydrochloric acid (room temperature, 10 mass% hydrochloric acid aqueous solution), and dissolved Zn and ICP It quantified using the analyzer and computed the plating adhesion amount after an acidic aqueous solution contact process. Next, the plating adhesion amount after the acidic aqueous solution contact step is subtracted from the plating adhesion amount before the acidic aqueous solution contact step (20 g / m ² ), and the dissolution amount of the plating layer in the acidic aqueous solution contact step (dissolution amount per unit area ( g / m ² )) was calculated. The results are shown in Table 2.

(3) Stability of whiteness (L value) in continuous operation For each sample, change in lightness (L value) when 3 hours of continuous production was performed under the same production conditions (ΔL = manufactured 3 hours after the start of production) The L value of the prepared sample—the L value of the sample manufactured at the start of the production) was calculated, and the stability was evaluated. For the contact treatment with the acidic aqueous solution, 10 liters of the acidic aqueous solution was used, and production was carried out at a rate of 1 m ² per minute. Evaluation was performed according to the following criteria. The L value was measured by SCE (regular reflection light removal) using a color difference meter (SE2000 manufactured by Nippon Denshoku Industries Co., Ltd.). The evaluation results are shown in Table 2.
○: −2 ≦ △ L
Δ: −3.5 ≦ ΔL <−2
×: ΔL <−3.5

From the results in Table 2, it can be seen that each sample of the present invention has excellent whiteness compared to Samples 1, 2, 9, 15, 23, and 32 of Comparative Examples. This is considered due to the difference in the acidic aqueous solution contact process.
Furthermore, it can be seen that each sample of the present invention is superior in L value stability in continuous operation as compared with the samples 24 and 25 of the comparative example. This is considered to be due to the difference in whether or not an appropriate amount of zinc ions is contained in the acidic aqueous solution.

(Samples 3-2 to 8-2, 10-2 to 14-2, 16-2 to 22-2, 26-2 to 31-2)
By performing the following step (iv) between step (ii) and step (iii) for samples 3 to 8, 10 to 14, 16 to 22, and 26 to 31 of Example of the present invention in Example 1. Electrogalvanized steel sheets of new samples 3-2 to 8-2, 10-2 to 14-2, 16-2 to 22-2, and 26-2 to 31-2 were prepared.
(Iv) The steel sheet treated with the acidic aqueous solution in step (iii) was washed with water and brought into contact with the basic aqueous solution under the conditions shown in Table 3.
The conditions of steps (i) to (iii) are the same as those in Example 1 as shown in Table 3.

(Evaluation method)
(1) Whiteness (L value)
About each sample, the brightness (L value) by SCE (regular reflection light removal) was measured using the color difference meter (SE2000 by Nippon Denshoku Industries Co., Ltd.). The evaluation is performed according to the following criteria, and measured values and evaluation results are shown in Table 4.
○: L value is 64 or more ×: L value is less than 64

(2) Stability of whiteness (L value) in continuous operation For each sample, change in lightness (L value) when 3 hours of continuous production was performed under the same production conditions (ΔL = manufactured 3 hours after the start of production) The L value of the prepared sample—the L value of the sample manufactured at the start of the production) was calculated, and the stability was evaluated. For the contact treatment with the acidic aqueous solution, 10 liters of the acidic aqueous solution was used, and production was carried out at a rate of 1 m ² per minute. Evaluation was performed according to the following criteria. The L value was measured by SCE (regular reflection light removal) using a color difference meter (SE2000 manufactured by Nippon Denshoku Industries Co., Ltd.). The evaluation results are shown in Table 2.
○ ： -2 ≦ △ L
Δ: -3.5 ≦ ΔL <−2
×: △ L <-3.5

(3) Paint adhesion The surface of each sample was coated with Delicon (registered trademark) # 700 (Dai Nippon Paint Co., Ltd.), a melamine alkyd paint, and baked at 130 ° C for 30 minutes. A coating film was formed. Then, it was immersed in boiling water for 2 hours, and cuts were made to reach the steel substrate of the grid pattern (10 × 10 pieces, 1 mm interval) immediately. Furthermore, 5 mm extrusion processing was performed with an Erichsen extruder so that the cut part was on the outside (front) side, and adhesion and peeling were performed with an adhesive tape, and the peeling area of the coating film was measured. Evaluation was performed according to the following criteria. The Eriksen extrusion conditions were JIS-Z-2247-2006, and punch diameter: 20 mm, die diameter: 27 mm, and drawing width: 27 mm.
○: Peeling area is less than 3% △: Peeling area is 3% or more, less than 10% ×: Peeling area is 10% or more

From the results of Table 4, each of the present invention samples, like the present invention sample of Example 1, showed good results in terms of whiteness, dissolution amount of the plating layer, and L value stability in continuous operation. I found out.
Furthermore, it can be seen that the inventive sample in Example 2 is also excellent in paint adhesion. On the other hand, this is considered to be due to the basic solution contact step. This is because sufficient paint adhesion could not be obtained when the basic solution contact step was not performed.

  According to the present invention, there is no deterioration of the properties of the plating layer, and an electrogalvanized steel sheet having high whiteness can be produced without reducing the current efficiency during electrogalvanization, and even when continuously operated, It is possible to provide a method for producing an electrogalvanized steel sheet that can stably maintain high whiteness.

Claims (3)

Forming a plating layer having a zinc content of 97% by mass or more on a steel sheet by electrogalvanizing;
The steel plate on which the plating layer is formed contains 0.002 to 0.05 mol / L in total of at least one of nitrate ions, iodate ions, bromate ions and chlorate ions, and 0.3 to 1.5 mol / L of zinc ions. A step of contacting an acidic aqueous solution containing L and having a pH of 1 to 3 for 0.5 seconds or more;
A method for producing an electrogalvanized steel sheet, comprising: forming a chemical conversion film on the plating layer.   2. The electricity according to claim 1, further comprising a step of bringing the steel sheet on which the plating layer is formed into contact with the basic aqueous solution having a pH of 8.5 to 12 after contact with the acidic aqueous solution for 0.5 seconds or more. Manufacturing method of galvanized steel sheet. Method of manufacturing an electro-galvanized steel sheet according to claim 1 or 2, wherein the adhesion amount per one side of the conversion coating is 0.05 to 1 g / m ^2.

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