KR20030054471A - Zn-co-w electrolyte for preventing anode passive film - Google Patents

Abstract

PURPOSE: A Zn-Co-W electrolyte for preventing deposition of anode passive film on the surface zinc anode is provided. CONSTITUTION: The Zn-Co-W electrolyte comprises 60 to 200g/L of zinc chloride; 0.1 to 6 g/L of cobalt chloride; W 0.1 to 4g/L; citric acid 0.1 to 10g/L; 30 to 400 g/L of at least one auxiliary conductive agent selected from potassium chloride, ammonium chloride and sodium chloride; 0.1 to 2mL/L of polyethylene glycol having a molecular weight of 100 to 2000: 0.5 to 5g/L of ethylenediaminetetraacetate or their salt. In above method, W is derived from at least one material selected from the group consisting of sodium tungstate, ammonium tungstate and potassium tungstate; citric acid is derived at least one material selected from the group consisting of sodium citrate, ammonium citrate and potassium citrate; and EDTA is selected from the group consisting of C10H14O8Na2, C10H12O8Na4, C10H14O8(NH4)2 and C10H12O8(NH4)4.

Description

Zn-Co-W Electrolyte For Preventing Anode Passive Film}

The present invention relates to a plating solution that can prevent the formation of a passivation film on the surface of a zinc anode when manufacturing a zinc-cobalt-tungsten alloy electroplated steel sheet, and more specifically, using a soluble anode, a zinc-cobalt-tungsten alloy electroplating. The present invention relates to a zinc-cobalt-tungsten alloy electroplating solution capable of preventing the formation of a passivation film on the surface of a zinc anode in producing a coated steel sheet.

Galvanized steel sheet among rust-proof surface treated steel sheets is widely used for automobiles, home appliances, and building materials because of its excellent corrosion resistance. However, in recent years, new galvanized steel sheets are required to secure high corrosion resistance with thin plating in terms of energy and resource saving. . In response to these demands, Zn-Fe alloy plated steel sheets, Zn-Ni alloy plated steel sheets, and the like have been developed and put into practical use.

Recently, Zn-Co-W alloy-coated steel sheet has been developed by alloying a small amount of Co and W on a galvanized steel sheet with excellent economic and corrosion resistance. In the case of Zn-Co-W alloy-coated steel sheet, W eluted from the plating layer in a corrosive environment forms tungsten oxide on the surface of the steel sheet, acting as a barrier against corrosion, thereby increasing corrosion resistance. However, zinc anodes are used to manufacture Zn-Co-W alloy plated steel sheets in plating facilities using soluble anodes. At this time, tungsten oxide is attached to the surface of zinc anodes to form a passivation film. Will be suppressed. In plating facilities using soluble anodes, as the plating time elapses, the anodes are consumed and the thickness becomes thinner and the distance from the steel sheet is farther away. Therefore, in order to make the gap between the steel sheet and the anode constant, the anode should be in close contact with the steel sheet by compensating for the thinning of the anode thickness as the plating time elapses. However, if a passivation occurs on the anode surface, the anode does not dissolve uniformly, which causes severe irregularities on the surface of the anode. In this state, when the anode is brought into close contact with the steel sheet by a certain depth, the uneven portion generated by the passivation film is brought into contact with the steel sheet, causing scratches on the steel sheet, thereby degrading the quality of the plated steel sheet. In addition, some of the passivation films formed on the surface of the anode may fall out in the form of agglomeration and float in the plating solution, blocking the holes of various nozzles, thereby preventing normal solution flow.

As a method for preventing the formation of a passive film on the surface of the zinc anode in the electroplating solution, there is a method disclosed in Korean Laid-Open Patent Publication 1999-037268. This method is to suppress the passivation film by alloying 3 ~ 10% of aluminum during the production of zinc anode to prevent the formation of passivation film by the nickel plating on the surface of zinc anode in Zn-Ni alloy electroplating solution. to be. When the zinc anode alloyed with aluminum is used for Zn-Ni alloy plating, aluminum contained in the anode is dissolved in the plating solution. In the Zn-Ni alloy plating, even if aluminum is present in the plating solution, the Zn-Al alloy anode may be used because it does not significantly affect the plating reaction. However, when the zinc anode alloyed with aluminium is used for the production of Zn-Co-W alloy-coated steel sheet, the aluminum dissolved in the anode is not plated on the steel sheet, so that the concentration of aluminum in the plating solution increases as the plating time increases. In addition, there is a problem that the aluminum present in the plating solution interferes with the electrodeposition of W and greatly reduces the amount of W alloy.

Accordingly, an object of the present invention is to produce a Zn-Co-W alloy electroplated steel sheet in an acid plating solution using a soluble anode, which can prevent the formation of a passivation film on the surface of the zinc anode without affecting the plating reaction. It is to provide a Co-W alloy electroplating solution.

According to the invention,

Zinc Chloride 60 ~ 200g / l, Cobalt Chloride 0.1 ~ 6g / l, Tungsten 0.1 ~ 4g / l, Citric Acid 0.1 to 10 g / l, at least one conducting aid 30 to 400 g / l selected from the group consisting of potassium chloride, ammonium chloride and sodium chloride, 0.1 to 2 ml / l polyethylene glycol with a molecular weight of 100 to 2000, ethylenediaminetetraacetic acid or A zinc-cobalt-tungsten alloy electroplating solution consisting of salts of 0.5 to 5 g / l and having a pH of 3 to 6 is provided.

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

By using the water-soluble zinc-cobalt-tungsten alloy electroplating solution of the present invention, the formation of the passivation film on the surface of the zinc anode in the plating facility using the zinc anode is prevented.

The reason why zinc chloride is limited to 60 to 200 g / l in the plating solution used in the production of zinc-cobalt-tungsten alloy plated steel sheet of the present invention is that when zinc chloride is less than 60 g / l, high-speed plating is not possible by the continuous plating method. If added more than 200g / l, the solubility of zinc will be exceeded and it will be precipitated as zinc salt.

The reason for limiting the concentration of cobalt chloride and tungsten in the plating solution to 0.1 to 6 g / l and 0.1 to 4 g / l, respectively, is sufficient to produce a steel sheet having excellent corrosion resistance at low price, even if it is added beyond the range. The passivation effect produced on the surface of the anode, which is the purpose of the same, is the same. Tungsten may be added with at least one or two or more components selected from the group consisting of sodium tungstate, ammonium tungstate and potassium tungstate.

Citric acid forms a complex ion with tungsten ions in the plating solution to prevent precipitation as tungsten oxide, less effective at less than 0.1 g / l, there is no problem even if it exceeds 10 g / l, but it is uneconomical. Citric acid may be added with at least one or two or more components selected from the group consisting of sodium citrate, ammonium citrate and potassium citrate.

Potassium chloride, ammonium chloride, sodium chloride, etc., in the plating solution play a role of conduction aid to improve the electrical conductivity of the plating solution.In the continuous plating equipment for high current density plating, the concentration of the conduction aid should be added at least 30g / l. It is possible to produce products stably, and if the concentration of the conductive additive exceeds 400g / l, the conductive additive may be precipitated when the temperature of the plating solution is low, so that the conductive additives such as potassium chloride, ammonium chloride and sodium chloride may be used alone or mixed. It is preferably added to limit the concentration to 30-400 g / l.

The polyethylene glycol in the plating solution is added for the purpose of improving the flatness of the plating layer. If the concentration is less than 0.1 ml / l, the plating layer becomes rough. Even if the concentration of polyethylene glycol is 2ml / l or more, there is no problem in the quality of plating and steel plate, but since only 2ml / l is sufficient, the concentration of polyethylene glycol is limited to 0.1 ~ 2ml / l in consideration of economic efficiency. desirable. As the polyethylene glycol, polyethylene glycol having a molecular weight of 100 to 2000 is used. If the molecular weight is less than 100, the effect is insignificant, and even if the molecular weight exceeds 2000, further improvement in physical properties cannot be expected.

Plating the ether diamine tetraacetic acid (C ₁₀ H ₁₆ O _8, one people EDTA) or its salt is added in solution. EDTA is believed to be chemically adsorbed on the zinc anode surface to prevent cobalt and tungsten from being plated with zinc on the anode surface to form a passivation film. If EDTA is added less than 0.5g / l, it is not economical or weak to prevent the passivation film formed on the surface of the zinc anode during the continuous plating process. In consideration, it is preferable to limit the amount to 0.5 to 5 g / l. Examples of such EDTA salts include ₁₀ H ₁₄ O ₈ Na ₂ , C ₁₀ H ₁₂ O ₈ Na ₄ , C ₁₀ H ₁₄ O ₈ (NH ₄ ) ₂ and C ₁₀ H ₁₂ O ₈ (NH ₄ ) ₄ .

If the pH of the plating solution is less than 3, the plating efficiency is low. If the pH of the plating solution is higher than 6, zinc ions and cobalt ions may precipitate into the hydroxide, and the limitation is limited to 3 to 6 because the hydroxide accumulates on the anode surface and interferes with the current flow. desirable.

When the Zn-Co-W alloy plated steel sheet is manufactured using the water-soluble plating solution formed in the composition range defined by the present invention as described above, there is almost no change in the alloy composition of the plating layer and no passivation film is formed on the surface of the zinc anode. It is possible to manufacture zinc-cobalt-tungsten alloy electroplating steel sheet because there is no problem that the surface of the steel sheet is scratched by the passivation film and the passivation film is suspended in the plating solution to block various nozzles.

Hereinafter, the present invention will be described in more detail with reference to Examples.

Example 1

To prepare a water-soluble zinc-cobalt-tungsten alloy electroplating solution to have a composition as shown in Table 1, put in a plating bath, put a zinc anode having a width of 50mm, length 100mm, thickness 10mm for 4 hours, after the plating is finished The zinc anode was taken out, washed with water and dried to separate the porous passivation film attached to the surface of the anode.

In addition, the plated solution was dried by washing with water by filtration of a passive film floating in the plating solution using a filtration device. The final passivation amount was measured by adding the passivation film formed on the zinc anode and the film present in the plating solution and weighing the resultant. In the plating process, the plated steel sheet was changed every 1 minute using a cold rolled steel sheet having a thickness of 0.8 mm equal to the anode size. The plating current density was 60 A / dm ² , and polyethylene glycol added for the purpose of flattening the coating layer had a molecular weight of 600, 1 ml / l, the same for each plating solution, and the temperature was 60 ° C.

EDTA was added as a sodium salt (C ₁₀ H ₁₄ O ₈ Na ₂ ). In addition, 0.5 g / l of citric acid added to prevent the deposition of tungsten ions in the plating solution was added.

TABLE 1

As shown in Table 1 above, as in the case of Inventive Examples (1 to 10) according to the present invention, 80 to 200 g / l of zinc chloride, 0.1 to 6 g / l of cobalt chloride, and 0.1 to tungsten when preparing a plating solution 4g / l, potassium chloride alone, potassium chloride and ammonium chloride as a conduction aid, or mixed with potassium chloride and sodium chloride, 100 ~ 400g / l and EDTA 0.5 ~ 5g / l and plated for 4 hours at pH3 ~ 6 The amount of film generation was very small, 0.21 g or less.

In the case of Comparative Examples 1 and 2, the other plating bath conditions were the same as those of Examples 1 and 4 of the present invention, respectively, but EDTA was not added in the solution, and the amount of passivation coating was relatively high, at 3.16 g and 7.88 g, respectively.

On the other hand, in the case of Comparative Example 3, the other plating bath conditions were the same as in Inventive Example 4, but the amount of EDTA added in the plating solution was lower than the range defined in the present invention, and the passivation film suppressing effect was not sufficient. In the case of Comparative Examples 4, 5, and 6, the other plating bath conditions were the same as those of Examples 7, 8, and 9, respectively, but the EDTA was not added in the solution, and the passivation amount was relatively 8.39g, 13.27, and 22.82g, respectively. Large amount occurred.

Even in the plating equipment using soluble zinc anode, it prevents the formation of non-coated film on the surface of zinc anode without causing problems such as scratching on the surface of the plated steel plate and also solves the problem that the passive film floats in the plating solution and blocks various nozzles. It is possible to stably produce Zn-Co-W alloy coated steel sheet with excellent surface quality.

Claims (4)

At least one conduction aid selected from the group consisting of 60 to 200 g / l zinc chloride, 0.1 to 6 g / l cobalt chloride, 0.1 to 4 g / l tungsten, 0.1 to 10 g / l citric acid, potassium chloride, ammonium chloride and sodium chloride 30 Zinc-cobalt-tungsten alloy electroplating solution composed of ~ 400g / l, polyethylene glycol 0.1-2ml / l, molecular weight 100-2000, ethylenediaminetetraacetic acid or its salt 0.5-5g / l and pH 3-6. 2. The electroplating solution of claim 1, wherein the tungsten is added with at least one component selected from the group consisting of sodium tungstate, ammonium tungstate and potassium tungstate. The electroplating solution of claim 1, wherein the citric acid is added with at least one component selected from the group consisting of sodium citrate, ammonium citrate and potassium citrate. The method according to claim 1, wherein the EDTA salt is C ₁₀ H ₁₄ O ₈ Na ₂ , C ₁₀ H ₁₂ O ₈ Na ₄ , C ₁₀ H ₁₄ O ₈ (NH ₄ ) ₂ and C ₁₀ H ₁₂ O ₈ (NH ₄ ) Electroplating solution, characterized in that selected from the group consisting of _four .