WO2017026683A1 - Zinc flash plating solution for galvanized steel sheet having excellent surface appearance, method for manufacturing galvanized steel sheet using same, and galvanized steel sheet - Google Patents

Abstract

The present invention relates to a zinc flash plating solution which can provide a galvanized steel sheet having an excellent surface appearance, a method for manufacturing a galvanized steel sheet using the same, and a galvanized steel sheet manufactured thereby.

Description

Zinc Flash Plating Solution for Electro Zinc Plated Steel Sheet with Excellent Surface Appearance, Manufacturing Method of Electro Zinc Plated Steel Sheet Using the Same and Electro Zinc Plated Steel Sheet

The present invention relates to a zinc flash plating solution which can provide an electrogalvanized steel sheet having an excellent surface appearance, and a method of manufacturing an electrogalvanized steel sheet using the same and an electrogalvanized steel sheet prepared therefrom.

Electro-galvanized steel sheet has a beautiful appearance, excellent paintability, and easy to control the amount of galvanized coating, so it is widely applied to high-end home appliances and automobile exterior plates. In particular, domestic electro-galvanized steel sheet is mainly used chromium-free or anti-fingerprint products of about 1㎛.

The whiteness and unevenness of these galvanized steel sheets directly determine the appearance quality of the final product.

Recently, automakers have made efforts to reduce the thickness of coatings or reduce the number of coatings in order to reduce costs. However, when the coating thickness decreases, the surface defects of the coated steel sheet tend to be transferred to the painted surface and appear as defects, so that the surface quality of the coated steel sheet needs to be more strictly managed.

Therefore, in the related art, various methods have been proposed to reduce the surface quality of the galvanized steel sheet, in particular, the unevenness of the plating surface and to improve the whiteness.

For example, Patent Literature 1 discloses a method of pickling a steel sheet with an acidic aqueous solution containing 50 to 3,000 ppm of nitrogen organic compound, which is adsorbed on the surface of the steel sheet to uniformize the plating stain. To alleviate this. In addition, Patent Document 2 discloses a method of improving whiteness and gloss by pickling with an aqueous sulfuric acid solution containing colloidal silica having an average particle diameter of 4 to 200 nm to reduce irregularities on the surface of the steel sheet.

However, even if the surface of the cold rolled steel sheet before acid plating is pickled and modified by using an acid solution, the cold rolled steel pole surface state cannot be made exactly the same according to the components contained in the cold rolled steel or the heat treatment history. After the difference occurs in the structure and orientation of the plating layer, as a result of the color difference of the electrogalvanized steel sheet. In addition, in the case where a composition variation due to the structure of the cold rolled steel sheet or the concentration of components occurs, it is difficult to homogenize the cold rolled steel sheet surface by pickling, so there is a problem of spots locally on the galvanized layer.

Accordingly, a method of controlling the components of the electro-zinc plating solution or the electroplating conditions to remove stains caused by local deviation of the surface of the cold rolled steel sheet and to have a uniform plating appearance irrespective of the components or surface state of the cold rolled steel sheet is proposed. It became.

For example, Patent Document 3 proposes a hydrochloric acid-based electrogalvanized solution containing polyethylene glycol, vanillin, and Mg, and Patent Document 4 proposes Cu, In, Sn, Pb, to suppress epitaxial growth of zinc in the electroplating solution. The present invention proposes a method for miniaturizing the plating structure and removing stains by adding and vacancy by adding elements such as Ge, Sb, Cd, and Ag.

However, high molecular weight polyether-based organic molecules, such as polyethylene glycol, are electrochemically decomposed on the surface of the anode during electroplating using an insoluble anode, or the efficiency of the insoluble anode is reduced. As a result, the viscosity of the solution may increase, which may inhibit high flow operation. In addition, when vaccinating the plating layer by adding metal ions other than zinc to the electrogalvanizing solution, the precipitation ratio of zinc and the added trace metal is different from the concentration ratio in the solution, and thus the component ratio of the metal in the solution is continuously changed during the continuous plating process. It is difficult to manufacture a galvanized steel sheet of a high quality, and it is difficult to constantly control the composition of the plating solution. In addition, when metal other than zinc is vacant in the plating layer, there is a problem of decreasing whiteness in the steel sheet for home appliances or inhibiting the phosphate treatment property of automotive galvanized steel sheet and causing staining.

On the other hand, as the most effective method of suppressing the non-uniformity of the electro-galvanized layer due to the difference in the material of the cold-rolled steel sheet or localized component thickening, etc., an ultra-thin metal layer, that is, a method of flash treatment has been proposed.

Patent Literatures 5, 6, and 7 are electro-galvanized when electro-galvanizing is performed after plating metals such as Ni, Co, Fe, Ti, Mn, Cu, Cr, Mo, and W up to several hundred mg / m ² or less. It is disclosed that the stain of the steel sheet can be removed and homogenized.

Among them, Ni flash treatment is the best in terms of plating adhesion, economical efficiency, manageability, and effect, but due to human health of Ni, it is not suitable as a base treatment for electroplating, and wastewater treatment problems are seriously taken. In addition, Co is a very expensive metal, it is not economical, Fe is oxidized during the electroplating process sludge is generated, it is very difficult to manage the solution. In addition, since Cu is substituted plating with Fe of the cold rolled steel sheet even if electricity is not applied, it is very difficult to manage the adhesion amount, and the zinc and the standard reduction potential difference are very large, thereby deteriorating the corrosion resistance of the galvanized steel sheet. Even in the case of other metals, it is not economical by flash treatment for electro zinc plating in terms of human health and plating efficiency.

Recently, as in Patent Documents 8 and 9, a method of improving the surface appearance of an electrogalvanized steel sheet by flash treatment with a Zn-based alloy electroplating solution has been proposed. Although this method has the effect of improving the whiteness and surface appearance to a certain level than without the flash treatment, the unevenness and staining of the epitaxial growth of the galvanized layer caused by the component thickening of the surface of the cold rolled steel sheet and the nonuniformity of the oxidation level. There is a disadvantage that can not be removed completely. In addition, it is difficult to manage the constant concentration of the alloy component ions in the solution, it is difficult to manage the solution in the continuous electroplating process.

(Patent Document 1) JP1997-059788

(Patent Document 2) Japanese Laid-Open Patent Publication JP2003-306790

(Patent Document 3) Korean Patent Publication No. KR2003-0049811

(Patent Document 4) Japanese Laid-Open Patent Publication JP2001-040494

(Patent Document 5) Japanese Laid-Open Patent Publication JP1996-165593

(Patent Document 6) Japanese Laid-Open Patent Publication JP1996-049091

(Patent Document 7) JP1997-202993

(Patent Document 8) Korean Patent Application No. KR2012-0151505

(Patent Document 9) Korean Application Patent KR2012-0112818

One aspect of the present invention is the non-uniformity of the plating structure, color, plating thickness, etc. of the electro-zinc plated steel sheet generated due to the local component difference, the oxidation degree difference of the surface of the cold-rolled steel sheet used as the base steel sheet of the galvanized steel sheet It is to provide a zinc flash plating solution for an electrogalvanized steel sheet capable of removing the electroplated steel sheet, a method for producing an electrogalvanized steel sheet using the same and an electrogalvanized steel sheet prepared therefrom.

One aspect of the present invention provides a zinc flash plating solution for an electrogalvanized steel sheet having an excellent surface appearance including zinc (Zn) ions, amine organic compounds and other unavoidable impurities.

Another aspect of the invention, the step of degreasing and pickling the steel sheet; Performing zinc flash plating on the base steel sheet using a zinc flash plating solution; And electro-galvanizing the zinc flash-plated base steel sheet, wherein the zinc flash plating solution uses the above-described plating solution. Provide galvanized steel sheet.

When performing zinc coating after zinc flash treatment using the zinc flash plating solution according to the present invention, localized nonuniformity of zinc plated structure and zinc due to the component thickening of the surface of the cold-rolled steel sheet, the nonuniformity of the oxide layer, and zinc By eliminating the thickness variation of the plating layer, it is possible to provide an electrogalvanized steel sheet having excellent surface appearance.

In addition, the electro-galvanized steel sheet produced by the present invention, when used in automobiles, home appliances, etc., has the effect of reducing the irregularities and stains generated after coating.

In addition, the zinc flash plating solution according to the present invention has a high plating efficiency and is suitable for application to a continuous electroplating process for mass production.

Figure 1 shows the results of observing the surface of the invention example 1-1 in the embodiment of the present invention.

Figure 2 shows the results of observing the surface of Comparative Example 1-1 in the embodiment of the present invention (where 1 represents a stain generated on the surface).

Recently, with the development of steel manufacturing equipment and technology, the surface of the cold rolled steel sheet is manufactured very clean and the surface quality is strictly controlled. There is a problem that the shape of the spots and defects occur.

Therefore, the present inventors have identified the cause of unevenness of plating and plating structure on the surface of the galvanized steel when degreasing and pickling in a conventional manner without flash treatment before plating, and the method for solving the problem Studied.

Cold rolled steel sheet, which is used as a base steel sheet of electro-zinc plating, is manufactured through a number of heat treatment, pickling, and rolling processes. In this manufacturing process, trace alloy components contained in the steel are locally concentrated on the surface of the steel sheet, or the oxide layer thickness of the steel sheet surface. There is a slight deviation in.

Electro zinc plating process is carried out on the base steel sheet such as cold rolled steel sheet is a process in which the zinc ions contained in the plating solution is reduced and precipitated on the surface of the base steel sheet when electricity is applied using the base steel sheet as a cathode. It is the process of rearranging crystalline metal on the surface of steel sheet. When zinc atoms are re-arranged on the surface of the steel sheet in the galvanizing, the direction of the galvanized particles is determined by the arrangement of iron atoms in the pole surface layer of the steel sheet and the components and the oxidation level of the surface. Therefore, the lower the oxidation level of the surface of the steel sheet, the more clean steel sheet in the form of exposed iron atoms, the greater the tendency of epitaxy growth when zinc is deposited on the surface. Therefore, the minute difference of the pole surface of the steel plate directly affects the orientation and grain size of the galvanized structure, so that the difference is insignificant in the plated steel sheet before plating, so that the galvanized structure is obviously different. Unevenness may lead to thickness variation of the plating layer.

In order to fundamentally solve the above problems, the inventors of the present invention, when the zinc flash plating prior to the electro-galvanizing of the base steel sheet, even if the electro-galvanization of ordinary galvanized steel sheet having a uniform appearance It was confirmed that it can be provided.

In particular, the inventors of the present invention optimize the components of the plating solution used in the zinc flash plating, and by performing zinc flash plating using them, the localization of the galvanized structure caused by the concentration of components on the surface of the cold-rolled steel sheet, non-uniformity of the oxide layer By resolving the phosphorous nonuniformity and the thickness of the galvanized layer, it was confirmed that an electrogalvanized steel sheet having excellent surface appearance was obtained, and thus the present invention was completed.

EMBODIMENT OF THE INVENTION Hereinafter, this invention is demonstrated in detail.

Zinc flash plating solution for an electrogalvanized steel sheet according to an aspect of the present invention preferably comprises zinc (Zn) ions, amine-based organic compounds and other unavoidable impurities.

More specifically, the zinc (Zn) ions are sulfuric acid (SO ₄ ) -based or hydrochloric acid (HCl) -based, preferably contained at a concentration of 1 ~ 150g / L.

When the concentration of zinc (Zn) ions is less than 1 g / L, the plating efficiency is lowered, and the limit current density, which is the maximum current density that can be plated, is lowered, thereby making it difficult to operate high-speed electroplating. On the other hand, if the concentration exceeds 150g / L, the zinc content in the plating solution is high, the raw material price is increased, there is a problem that Zn waste due to the solution loss is increased.

The present inventors have tried to add various types of organic and inorganic compounds to the plating solution containing zinc (Zn) ions, but the added compound bonds too strongly to the surface of the steel sheet and the surface of the plating layer, or the content is appropriate. Exceeding the above resulted in the precipitation of zinc in the subsequent electro zinc plating is suppressed, the burning phenomenon occurs, the plating quality was deteriorated. On the other hand, if the bonding strength is too weak, or the content is insufficient, the appearance is good after electro zinc plating. It was confirmed that it could not be obtained.

On the other hand, in the case of the amine-based organic compound, the lone pair of electrons included in the nitrogen atom forms a bond with the metal, and the electron density of the nitrogen varies depending on the number of hydrocarbons, the chain length, and the end group bonded to the nitrogen atom. For example, when alcohols are bonded to nitrogen rather than the same number of alkyls of the same length, the amine group has a stronger adsorption force with the metal surface because the OH group acts to push electrons toward the nitrogen atom. However, when the number of hydrocarbons combined with nitrogen increases, the electron density of nitrogen may increase, but the adsorption force may be weakened because carbon hydrogen interferes with the bonding of nitrogen and the metal surface.

Therefore, in the present invention, it is preferable that the zinc flash plating solution contains an amine-based organic compound having the property of easily adsorbing on the surface of the base steel sheet and the zinc plated layer, in addition to the zinc (Zn) ions. You can get it.

The difference in oxidation degree localized on the surface of the cold rolled steel and the nonuniform concentration of the components contained in the steel cause a difference between the rate of precipitation of zinc (Zn) ions and the rate of epitaxy growth in the early stage of electrogalvanization. In the amine-based compound is adsorbed on the surface of the steel sheet irrespective of the state of the cold-rolled steel sheet surface it is possible to uniformly control the nucleation rate of the initial electroplating.

In addition, when electro-galvanizing the cold rolled steel sheet, the nuclei of zinc plating are formed only at the beginning of the plating, and during the plating, zinc tends to grow only without nucleation. That is, in order to generate secondary nucleation in the electro-zinc plating process, a sufficient overvoltage than a normal level is applied, or zinc plating is sufficiently progressed so that the growth rate of zinc is slowed down compared to the applied overvoltage. Therefore, the structure and orientation of the electro-galvanized layer formed under ordinary electro-zinc plating conditions have a certain relationship with the orientation of the cold-rolled steel sheet, and are directly affected by the orientation of the cold-rolled steel sheet during ultra-thin galvanizing at the level of flash plating. .

However, when an organic compound that is easily adsorbed on the zinc plating surface is added, the growth of the zinc plating is suppressed during the initial galvanization, and nucleation is continuously performed. Therefore, by using a plating solution containing an amine-based organic compound, it is possible to form a uniform and fine zinc flash plating layer irrespective of the surface state of the cold rolled steel sheet. This uniform galvanized steel sheet can be produced.

Therefore, the zinc flash plating solution for electrogalvanized steel sheet of the present invention has a technical significance in that it contains an amine organic compound in addition to zinc (Zn) ions.

In the present invention, it is advantageous to use a primary to tertiary amine organic compound as the amine organic compound, more preferably an aliphatic containing at least one nitrogen atom in the compound molecule and having a chain length of 1 to 5 carbon atoms. It is preferable that the hydrocarbon per 1 nitrogen atom of an aliphatics structure is 1 type, or 2 or more types of mixtures chosen from the compound which has 1-3 bonds.

In order for an amine to maintain a bond with the surface of a metal (steel plate), it is preferable to have a lone pair of electrons at a nitrogen atom. However, when four hydrocarbons per nitrogen atom, like quaternary amines, are bonded, there are no lone pairs of nitrogen and they have a cation, which is relatively electrostatically repulsive with the cation-forming metal surface. Disadvantages. In addition, the quaternary amine compound bonded with a hydrocarbon having an aliphatic structure has a problem in that the solubility in the aqueous solution decreases as the molecular weight increases, so that dissolution is impossible or precipitation occurs.

In addition, when the length of the hydrocarbon contained in the above-mentioned primary to tertiary amine organic compounds exceeds 5 carbon atoms, the ratio of nitrogen in the molecule is low, so that the effect of the adsorption is weak on the metal surface.

As an example of the amine-based organic compound, the primary amine-based organic compound containing one nitrogen atom in the compound molecule has a high boiling point and is soluble in aqueous solution, such as ethanolamine or amino propanol. It can be selected from alcohols. In addition, as a secondary amine organic compound containing one nitrogen atom in the molecule, it can be selected from diethanolamine, methylethanolamine, etc., and tertiary amine system containing one nitrogen atom in the molecule. The organic compound may be selected from triethylamine, diethylaminoethanol, diethanolethylamine, triethanolamine, and the like. In addition, linear structures such as ethylenediamine, diethylenetriamine, triethylenetetramine, diaminopropane, spermidine, and spermine Cyclic or steric structures such as polyamine, cyclen (1,4,7,10-tetraazacyclododecane), cyclam (1,4,8,11-tetraazacyclotetradecane), hexamethylenetetramine (hexamethylentetramine) It can be selected from a water-soluble polyamine and a water-soluble amine polymer.

Of these, three-dimensional water-soluble polyamines and water-soluble amine-based polymers have a large number of nitrogen atoms, and the non-covalent electron pairs of nitrogen atoms are exposed to the outside of the molecule, and thus have a high possibility of bonding with metal, thereby facilitating adsorption. There is a more beneficial effect on improving the surface of the steel sheet.

The amine organic compound of the present invention is not limited to the amine compound described above, and may be used alone or in combination of two or more amine organic compounds.

Such an amine organic compound is preferably contained in the plating solution at 0.05 ~ 10g / L.

If the concentration of the amine organic compound is less than 0.05 g per 1 L of the plating solution, the amount of the organic compound adsorbed on the metal surface is small, and the adsorption reaction of the organic compound during the plating process is less than that of the zinc precipitation reaction, thereby improving the appearance after galvanizing. Is not big. On the other hand, if the content exceeds 10g, the adsorption of the organic compound is excessive and the zinc precipitation reaction is suppressed, thereby causing a burning phenomenon.

As described above, the zinc flash plating solution for electro-galvanized steel sheet of the present invention containing zinc (Zn) ions and an amine organic compound preferably has a pH of 1.0 to 5.0.

If the pH of the zinc flash plating solution is less than 1.0, the rate of reduction of hydrogen in the solution increases during electro-galvanizing of the base steel sheet as a cathode, thereby decreasing the amount of deposition of zinc plating. A problem that does not precipitate occurs. On the other hand, when the pH exceeds 5.0, there is a problem that precipitation occurs while inevitable impurities such as iron form hydroxides from zinc ions or steel sheets.

Meanwhile, the zinc flash plating solution of the present invention may further include a supporting salt such as sodium sulfate, potassium sulfate, ammonium sulfate, potassium chloride or sodium chloride for the purpose of improving conductivity.

At this time, the supporting salt is preferably contained in less than 200g / L, even if the supporting salt in the above range, the electro-galvanized steel sheet produced by electro-galvanizing after zinc flash plating may have a uniform plating appearance.

In addition, a complexing agent may be further included to suppress precipitation of iron, nickel, manganese and other impurity ions eluted from the steel sheet and inevitably contained in the zinc flash plating solution.

As the complexing agent, for example, citric acid, sodium citrate, sodium heptonate and the like can be used, and the content thereof is preferably 30 g / L or less. Even if the complexing agent is included in the above range, the galvanized steel sheet prepared by zinc plating after electroplating may have a uniform plating appearance.

The supporting salts and the complexing agents may be selectively added to the zinc flash plating solution of the present invention, and even if these components are not added, they do not significantly affect the appearance of the galvanized steel sheet produced.

Hereinafter, a method of manufacturing an electrogalvanized steel sheet using the zinc flash plating solution of the present invention described above will be described in detail.

First, after the cold rolled steel sheet is degreased and pickled in a conventional manner, it is preferable to sequentially perform zinc flash plating and electro zinc plating.

Here, the steel sheet that can be used as the base steel sheet is not particularly limited, any steel sheet for the electro-galvanized steel sheet is possible, but preferably may be a cold-rolled steel sheet.

It is preferable to use the plating solution of the present invention when the zinc flash plating, and the plating amount in the state in which the temperature of the plating solution is adjusted to room temperature (approximately 25 ° C.) to 80 ° C. and the current density is applied at 1 to 100 A / dm ² . It is preferable to carry out so that it may become 10-2000 mg / m <^2> .

At this time, when the temperature of the zinc flash plating solution exceeds 80 ℃, the amount of solution evaporation is excessive, the management of the plating solution is difficult, there is a risk of causing corrosion in the working environment. Although the plating effect is excellent even if the temperature of the zinc flash plating solution is kept at room temperature, it is more preferable to maintain at 40 to 65 ° C because the plating efficiency is good and the management is good.

In addition, when the current density is less than 1A / dm ^{2, the} plating efficiency is low, and in order to obtain an appropriate level of zinc flash plating amount, there is a problem that the plating takes a long time, which is not suitable in the continuous plating process. On the other hand, if it exceeds 100A / dm ² there is a problem that burning occurs in the zinc flash plating process, causing stains, or poor adhesion of the plating layer formed after the subsequent electro-galvanization.

In the case of zinc flash plating under the above conditions, it is preferable to perform plating so that the zinc adhesion amount satisfies the range of 10 to 2000 mg / m ² , and when the zinc adhesion amount is less than 10 mg / m ^2, the appearance improvement effect of the galvanized steel sheet is insignificant. In addition, when the zinc flash-plated base steel sheet is brought into contact with an acidic electrogalvanizing solution for subsequent electrogalvanization, the flash plating layer may be locally eluted to cause staining. On the other hand, when the zinc adhesion amount exceeds 2000 mg / m ² , the appearance improvement effect of the galvanized steel sheet is good, but very high current density is applied when zinc flash plating is applied or flash plating is performed for a long time, so productivity is reduced and economical. Can not do it.

As described above, the base steel sheet after zinc flash plating is completed includes a flash plating layer, and by performing electro zinc plating on the base steel sheet, a general electro galvanized steel sheet having a zinc adhesion amount of 5 to 100 g / m ² can be produced. Can be.

In the present invention, the conditions of the electro-zinc plating are not particularly limited, and may be carried out in conditions which are usually performed, such as sulfuric acid or hydrochloric acid-based electro zinc plating baths.

The electro-galvanized steel sheet of the present invention obtained by completing the above electro-zinc plating comprises an electro-galvanized layer on the base steel sheet, and has excellent surface appearance.

In particular, even if there are defects such as stains on the base steel sheet, when performing zinc flash plating using the zinc flash plating solution proposed in the present invention before electro-galvanizing, it is possible to ensure excellent surface appearance.

Hereinafter, the present invention will be described in more detail with reference to Examples. However, it is necessary to note that the following examples are only intended to illustrate the present invention in more detail, and are not intended to limit the scope of the present invention. This is because the scope of the present invention is determined by the matters described in the claims and the matters reasonably inferred therefrom.

Example 1 Preparation of Electro-Galvanized Steel Sheet

Inventive Example 1

After preparing the cold rolled steel sheet to the base steel sheet, it was subjected to alkali degreasing and pickling treatment in a conventional manner, and then washed with pure water.

After zinc zinc (Zn) ion concentration was dissolved using zinc sulfate so as to be 20-30 g / L, a zinc flash plating solution was prepared by mixing and dissolving an amine-based organic compound ethanolamine and hexamethyltetramine. At this time, the amine-based organic compound was added so that the total amount is 2.5 ~ 3.5g / L by weight per 1L solution. Thereafter, sulfuric acid was added to adjust the pH of the zinc flash plating solution to 1.5 to 2.5, and then heated to 45 to 55 ° C.

Zinc flash plating was performed by immersing the prepared cold-rolled steel sheet in a heated zinc flash plating solution for 1 second. The current density was controlled so that the coating weight was 50 to 2000 mg / m ² , and the current was 1.5 to 75 A / dm ² . Density was applied.

After the zinc-plated cold-rolled steel sheet is subjected to electro-galvanization in a sulfuric acid-based galvanized solution having a zinc (Zn) ion concentration of 50-150 g / L, the zinc plating amount is 20-40 g / m ² . Water was washed with pure water to obtain an electrogalvanized steel sheet.

Inventive Example 2

100 g / L of sodium sulfate as a supporting salt and 10 g / L of citric acid as a complexing agent were added to the same zinc flash plating solution as Inventive Example 1 to prepare a zinc flash plating solution, and then the sulfuric acid was added to adjust the pH to 1.5 to 2.5. After heating, the temperature was raised to 45 to 55 ° C.

After the zinc flash plating solution was heated on the same cold rolled steel sheet as in Inventive Example 1 using the heated zinc flash plating solution, electrogalvanization was performed under the same conditions to obtain an electrogalvanized steel sheet.

Comparative Example 1

After degreasing and pickling in the same manner as in Inventive Example 1, the cold-rolled steel sheet washed with water was subjected to electro-galvanization without zinc flash plating to obtain an electro-galvanized steel sheet.

At this time, the electrogalvanization was carried out in the same manner as in Example 1.

Comparative Example 2

Zinc (Zn) ion concentration was dissolved using zinc sulfate to 20 ~ 30g / L, and then sulfuric acid was added to adjust the pH of the solution to 1.5 ~ 2.5 to prepare a zinc flash plating solution. Then, the zinc flash plating solution was heated to 45 ~ 55 ℃.

After the zinc flash plating solution was heated on the same cold rolled steel sheet as in Inventive Example 1 using the heated zinc flash plating solution, electrogalvanization was performed under the same conditions to obtain an electrogalvanized steel sheet.

Comparative Example 3

Using zinc sulfate, the zinc (Zn) ion was dissolved in a concentration of 20 to 30 g / L, and then one of the nitrogen-containing compound thiourea and the quaternary amine organic compound cetyltrimethylammonium bromide and choline was selected. Mixing and dissolving prepared a zinc flash plating solution. Thereafter, sulfuric acid was added to adjust the pH of the zinc flash plating solution to 1.5 to 2.5, and then heated to 45 to 55 ° C.

After the zinc flash plating solution was heated on the same cold rolled steel sheet as in Inventive Example 1 using the heated zinc flash plating solution, electrogalvanization was performed under the same conditions to obtain an electrogalvanized steel sheet.

Comparative Example 4

After zinc zinc (Zn) ion concentration was dissolved using zinc sulfate so as to be 20-30 g / L, a zinc flash plating solution was prepared by mixing and dissolving an amine-based organic compound ethanolamine and hexamethyltetramine. At this time, the amine-based organic compound was added so that the total amount is 25 ~ 35g / L by weight per 1L solution. Thereafter, sulfuric acid was added to adjust the pH of the zinc flash plating solution to 1.5 to 2.5, and then heated to 45 to 55 ° C.

After the zinc flash plating solution was heated on the same cold rolled steel sheet as in Inventive Example 1 using the heated zinc flash plating solution, electrogalvanization was performed under the same conditions to obtain an electrogalvanized steel sheet.

(Example 2) Plating appearance and quality evaluation

Evaluation of the product appearance of each of the galvanized steel sheet produced in Example 1, the results are shown in Tables 1 and 2.

The cold rolled steel surface may be provided with a relatively very uniform material depending on the manufacturing method. However, since the surface of the cold rolled steel sheet is difficult to predict whether staining occurs before the electro-galvanizing is performed, the electro-galvanized steel sheet is directly applied to the cold rolled steel sheet subjected to normal degreasing and pickling only without performing zinc flash plating on the cold rolled steel sheet. First, the occurrence of stains was checked first, and the same cold rolled steel was taken and used as a holding steel sheet.

Unevenness of the surface of the galvanized steel sheet due to the nonuniformity of the surface of the cold rolled steel sheet can be visually confirmed. Thus, whether the improvement according to the zinc flash plating was confirmed visually whether the stain after the electro-galvanization. The stain generation level was set based on the following criteria.

○: The stain is clearly seen by the naked eye, and the difference in plating structure is apparent when the microscope is observed.

(Triangle | delta): Although it is finely stained with the naked eye, when a microscope observes, a plated structure difference does not become large

×: Difficult to identify visually

In addition to the local stains generated on the surface of the galvanized steel sheet, the color difference of the electrogalvanized steel sheet may be generated depending on the trace alloy component, manufacturing conditions, and coils of the base steel sheet. In the case of electroplated steel sheet for automotive or PCM steel sheet, the galvanized steel sheet is used for painting, so the color difference of each coil does not affect the quality characteristics, but for home appliance steel plate, the color needs to be kept constant. .

Therefore, four kinds of cold-rolled coils (the other components being the same) containing a sum of Mn and Al content of 600 ppm to 1300 ppm were subjected to zinc flash plating treatment / untreatment under the respective conditions shown in Tables 1 and 2 below. After electroplating, the color was measured under the conditions of D65 light source, light receiving angle 8 ^o , and viewing angle 10 ^o for three samples for each specimen, and the average whiteness of 12 points was calculated.

In addition, since staining is caused by unevenness of color and plating texture in galvanized steel sheet, the color difference is calculated based on the average color of 12 points manufactured and measured under the same conditions in order to quantitatively compare the level of staining. Calculated as color deviation with square root.

division	Zinc flash plating solution				Plating amount		Quality evaluation
	Zn ion (g / L)	pH	Additive Ingredients and Concentrations	Temperature (℃)	Flash plating (mg / m 2)	Electro zinc plating (g / m 2 )	Spotting Level	Average whiteness	Color deviation
Inventive Example 1-1	25	2	Primary and tertiary water-soluble amines 2.5 to 3.5 g / L	50	50	20	×	87.80	0.26
Inventive Example 1-2					500		×	88.23	0.19
Inventive Example 1-3					1000		×	87.49	0.21
Inventive Example 1-4					2000		×	88.14	0.27
Inventive Example 1-5					50	40	×	87.13	0.24
Inventive Example 1-6					500		×	87.37	0.21
Inventive Example 1-7					1000		×	86.97	0.12
Inventive Example 1-8					2000		×	86.68	0.27
Inventive Example 2-1	25	2	Primary and tertiary water-soluble amines 2.5 to 3.5 g / L, sodium sulfate 100 g / L and citric acid 10 g / L	50	50	20	×	86.76	0.48
Inventive Example 2-2					500		×	86.78	0.39
Inventive Example 2-3					1000		×	86.99	0.23
Inventive Example 2-4					2000		×	86.36	0.52
Inventive Example 2-5					50	40	×	86.43	0.44
Inventive Example 2-6					500		×	86.55	0.24
Inventive Example 2-7					1000		×	86.17	0.30
Inventive Example 2-8					2000		×	86.30	0.38

division	Zinc flash plating solution				Plating amount		Quality evaluation
	Zn ion (g / L)	pH	Additive Ingredients and Concentrations	Temperature (℃)	Flash Plating (mg / m 2 )	Electro zinc plating (g / m 2 )	Spotting Level	Average whiteness	Color deviation
Comparative Example 1-1	-	-	-	-	Not carried	20	○	84.49	2.56
Comparative Example 1-2						40	○	83.57	2.57
Comparative Example 2-1	25	2	-	50	50	20	○	85.39	3.75
Comparative Example 2-2					500		○	85.69	3.24
Comparative Example 2-3					1000		○	85.04	3.16
Comparative Example 2-4					2000		○	84.99	2.98
Comparative Example 3-1	25	2	Thiourea3.8g / L	50	50	20	△	84.14	1.52
Comparative Example 3-2					500		△	84.23	1.04
Comparative Example 3-3					1000		×	84.15	0.92
Comparative Example 3-4					2000		×	84.41	0.87
Comparative Example 3-5	25	2	Cetyltrimethylammonium bromide1.8g / L	50	50	20	△	84.48	1.25
Comparative Example 3-6					500		△	83.67	1.73
Comparative Example 3-7					1000		×	84.16	1.11
Comparative Example 3-8					2000		×	84.54	0.94
Comparative Example 3-9	25	2	Choline chloride7.0g / L	50	50	20	○	84.15	1.52
Comparative Example 3-10					500		○	83.99	1.54
Comparative Example 3-11					1000		○	84.40	1.67
Comparative Example 3-12					2000		○	83.75	1.53
Comparative Example 4-1	25	2	Primary and tertiary water-soluble amines 25 to 35 g / L	50	50	20	△	87.61	0.49
Comparative Example 4-2					500		△	87.97	0.48
Comparative Example 4-3					1000		△	87.46	0.23
Comparative Example 4-4					2000		△	87.25	0.28

As shown in Table 1, when electro-galvanizing after the flash plating using the zinc flash plating solution provided in the present invention, in all cases, stains due to nonuniformity of the surface of the cold rolled steel sheet can be visually identified. There was no average whiteness of 86-89.

In addition, even when the electro-galvanized steel sheet was manufactured using different cold-rolled steel sheets, the color deviation was less than 0.5, and the surface appearance was uniform, which made it difficult to identify.

In addition, it was confirmed that the adhesion amount during zinc flash plating did not have a significant effect on the appearance of the galvanized steel sheet, and even though the zinc flash plating solution further contained supporting salts and complexing agents, the surface quality of the galvanized steel sheet was similar. Could get

This result shows that when the zinc flash plating layer is formed at the beginning of plating, it is formed with a certain level of particle size and orientation irrespective of the surface state of the base steel sheet, and then zinc is deposited on the zinc flash plating layer on the same surface when electrogalvanizing is performed. Precipitation results in the same appearance and structure regardless of the type of coil and the nonuniformity of the surface of the steel sheet.

On the other hand, as shown in Table 2, in the case of Comparative Examples 1-1 to 1-2 where only the electro-zinc plating was performed without zinc flash plating, severe stains in the form of stripes on the surface were easily observed with the naked eye. As a result, it was confirmed that the plating structure was locally nonuniform.

In addition, the average whiteness was 2 to 3 levels lower than the zinc flash treatment, and the color deviation was measured to be 2.5 to 4.0 in the galvanized steel sheets plated from different cold rolled steel sheets. This shows that the minute difference of the surface of the cold rolled steel sheet has a great influence on the color of the surface after electroplating. In general, when the color difference is 2.0 or more, it is known that the difference between the two colors can be easily determined by the naked eye. Since the color deviation is at least 2.5 or more, the color difference becomes easily recognizable, making it difficult to produce a uniform product.

Although zinc flash plating was carried out, in the case of Comparative Examples 2-1 to 2-4 which did not contain any amine organic compound in the plating solution, the whiteness was slightly increased compared to Comparative Examples 1-1 and 1-2, Surface stains were easily discernible.

In addition, the color variation according to the type of cold rolled steel tended to increase more, which is due to the difference in concentration and pH by plating with a flash plating solution having a relatively low zinc concentration and a high pH compared to a conventional electrogalvanizing solution. It seems to have influenced the frequency of nucleation at the initial stage of plating, but the difference or nonuniformity of the surface of cold rolled steel sheet could be considered to be more weighted and transferred during the galvanizing process.

Results of the case of Comparative Examples 3-1 to 3-12 in which zinc flash plating was performed with a plating solution to which various amine-based compounds were added, followed by producing an electrogalvanized steel sheet were as follows.

First, in Comparative Examples 3-9 to 3-12 in which zinc flash plating was performed by adding choline chloride, a quaternary amine compound, color variation was slightly improved, but surface staining was easily confirmed. This is because choline molecules affect the plating overvoltage change and the growth rate of the plated particles, causing small differences in the frequency of nucleation and the particle size.However, the non-uniformity of the surface of the cold rolled steel sheet is transferred until after electro-galvanization. The improvement seems to be minimal.

On the other hand, in the case of Comparative Examples 3-1 to 3-4 using thiourea as an additive, there was an effect that the stain of the surface of the galvanized steel sheet was significantly improved, the gloss also increased. In addition, the color deviation was significantly reduced compared to Comparative Example 1 or 2. However, when urea was used instead of thiourea, the same results as in Comparative Examples 2-1 to 2-4 were obtained. Urea is an amide compound having the same molecular structure as thiourea but consisting of oxygen atoms instead of sulfur atoms of thiourea. Therefore, unlike the amine compound, the amide compound does not have a significant effect on improving the appearance of the electroplated steel sheet, and in the case of a compound containing sulfur such as thiourea, it is believed that the amide compound has an improvement in product appearance due to the surface adsorption effect by sulfur. . However, since sulfur-containing molecules such as thiourea are easily electrolyzed at the anode, a white precipitate occurs as the plating proceeds, which is not suitable for the continuous electrogalvanization process.

Cetyltrimethylammonium bromide is a kind of surfactant and is a quaternary amine compound like choline. For Comparative Examples 3-5 to 3-8 using these compounds as additives, similar effects to thiourea were seen. These results indicate that choline molecules are not surfactants classified as hydrophobic groups and hydrophilic groups, and thus the molecules are weakly adsorbed on the steel sheet or zinc metal surface, whereas cetyltrimethylammonium is a surfactant that distinguishes hydrophobic and hydrophilic regions, so It is because the tendency to arrange | position at the interface of a steel plate is strong, and it is judged that it is not an effect by metal surface adsorption by an amine. In addition, since halide ions such as bromine are contained, there is a high possibility that halide gas is generated during the high-speed electrozinc plating process with high overvoltage.

In addition, the quaternary amine polymer compound was to be added below 1 g / L, but electro zinc coating was not possible because precipitation occurred in the acidic zinc plating solution.

Zinc flash plating was carried out using the same additive as inventive example 1, but in Comparative Examples 4-1 to 4-4 in which the content was too high, the zinc plating layer turned black in the edge region of the specimen where the current was concentrated. Burning phenomenon could be confirmed. Here, the burning phenomenon refers to a phenomenon in which hydroxide is mixed in the plating layer and blackening occurs because smooth plating is not performed when the plating speed exceeds a critical plating speed.

Among them, in the case of Comparative Example 4-1 in which the current density was applied at about 1.5 A / dm ² level to plate the zinc flash plating at 50 mg / m ² level, the burning phenomenon continued at the edge of the specimen. It was possible to produce an electrogalvanized steel sheet having no silver stain and less color variation. Therefore, the surface unevenness observed on the surface of these steel sheets is not due to unevenness of the surface of the cold rolled steel sheet, but shows unevenness due to the burning of the specimen edges generated during the galvanizing process.

In fact, in the manufacturing process of the galvanized steel sheet, if the agitation due to the flow rate is high and the zinc content in the solution is high, an improvement effect on the burning phenomenon can be expected, but since the current concentration at the edge is rather weighted, the edge of the steel sheet is cut out. Trimming operations must be added.

In addition, as the amount of the additive increases, the unit cost of the solution increases and the plating efficiency decreases. Therefore, it is preferable to contain the additive, that is, the amine organic compound as little as possible while maintaining an appropriate level.

Usually, when pure zinc is electroplated on a steel sheet in an electrogalvanized solution containing no additives, the adhesion between the base steel sheet and the plating layer is very excellent. However, when the flash treatment is performed with a zinc flash solution containing an additive before electro-galvanizing, adhesion between the plating layer and the base steel sheet may be degraded. Therefore, in order to evaluate the adhesion between the plated layer and the base steel sheet, the steel sheet was bent to 90 ^° using a mold having a radius of curvature of 0.5 mm, and then the inside of the bent portion was peeled off with a tape to evaluate the adhesion between the base steel and the zinc plated layer.

As a result of evaluation, in the electrogalvanized steel sheets of all the examples (Invention Examples 1 and 2, Comparative Examples 1 to 4), peeling of the base iron and the zinc plated layer did not occur, and adhesion was good.

1 and 2 show the surfaces of the electrogalvanized steel sheets of Inventive Example 1-1 and Comparative Example 1-1, respectively.

As can be seen from the drawings, in the case of the comparative example without performing the zinc flash plating, it can be seen that the stain on the surface of the final product (electro galvanized steel) is clearly visible, but zinc flash plating according to the present invention on the same steel sheet After the galvannealing, the electrogalvanized steel sheet was very excellent in surface appearance.

Claims (10)

1. Zinc flash plating solution for electro-galvanized steel sheet with excellent surface appearance including zinc (Zn) ions, amine organic compounds and other unavoidable impurities.
2. The method of claim 1,

   The zinc (Zn) ions zinc flash plating solution for an electro-zinc plated steel sheet having an excellent surface appearance that contains at a concentration of 1 ~ 150g / L.
3. The method of claim 1,

   The amine-based organic compound includes at least one nitrogen atom in the compound molecule, and an hydrocarbon having an aliphatic structure having a chain length of 1 to 5 carbon atoms has one to three bonds per nitrogen atom. Zinc flash plating solution for electro-galvanized steel sheet excellent in the appearance of the above.
4. The method of claim 3, wherein

   The amine-based organic compound is a zinc flash plating solution for electro-galvanized steel sheet excellent surface appearance that is contained in the plating solution at 0.05 ~ 10g / L.
5. The method of claim 1,

   The plating solution is a zinc flash plating solution for electro-galvanized steel sheet excellent surface appearance that has a pH of 1.0 ~ 5.0.
6. Degreasing and pickling the steel sheet;

   Performing zinc flash plating on the base steel sheet using a zinc flash plating solution; And

   Electro zinc-plating the zinc-plated base steel sheet, and

   Wherein the zinc flash plating solution is a plating solution of any one of claims 1 to 5 excellent surface appearance of the manufacturing method of the electro-galvanized steel sheet.
7. The method of claim 6,

   The zinc flash plating is a method for producing an electro-zinc plated steel sheet having excellent surface appearance that is carried out at a solution temperature of room temperature ~ 80 ℃, current density of 1 ~ 100A / dm ² , zinc adhesion amount 10 ~ 2000mg / m ² .
8. The method of claim 6,

   The electro-zinc plating is a method for producing an electro-zinc plated steel sheet having excellent surface appearance that is carried out with a zinc adhesion amount of 5 ~ 100g / m ² .
9. An electrogalvanized steel sheet having excellent surface appearance, manufactured by the method of claim 6 and comprising a base steel sheet and a zinc flash plating layer formed on the base steel sheet and an electrogalvanized layer sequentially.
10. The method of claim 9,

    The base steel sheet is an electro-galvanized steel sheet having excellent surface appearance that is a cold rolled steel sheet.

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