KR940000282B1 - Manufacturing Method of Zinc Electroplated Steel Sheet with Excellent Gloss and White - Google Patents

Abstract

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Description

Manufacturing Method of Zinc Electroplated Steel Sheet with Excellent Gloss and White

FIG. 1 is a photograph showing the plated layer microstructure of the plated specimen and the plated specimen with the additive added without addition of the additive to the plating bath.

The present invention relates to a method of manufacturing a zinc electroplated steel sheet, and more particularly, to a method of manufacturing a zinc electroplated steel sheet having excellent whiteness and glossiness of the surface appearance of pure zinc plating in a chloride bath and having a fine plating structure of the plating layer. It is about.

Plating has been developed to improve the corrosion resistance of steel sheet, and zinc electroplating steel sheet is widely used in automobiles and home appliances. Acidic baths used for electrogalvanizing include sulfuric acid baths mainly composed of zinc sulfate and chloride baths mainly composed of zinc chloride. Conventionally, sulfur-based water baths are mainly used, but sulfur-like water baths have lower electric conductivity than chloride baths, and thus high voltages are required to obtain a predetermined plating current, which leads to high power cost and low allowable current density. Is difficult. However, while the chloride bath has good electrical conductivity and low power cost and is advantageous for high-speed plating, the surface gloss and white of the obtained plating layer are deteriorated and the microstructure of the plating layer is large, resulting in a rough surface. In this case, not only the surface appearance of the plated surface, but also the surface such as phosphate treatment, chromate treatment, and anti-fingerprint process, which is a post-plating process, is not good, and even after coating, the sunscreen is adversely affected.

As a method for improving the gloss of a zinc chloride bath product, a method of adding a polyethylene oxide alkylate sulfone compound (Japanese Patent Publication No. 42-8764) and a method of containing cadmium ions in a chloride bath (Japanese Patent) Publication No. 46-40402) is known, but there is a problem that strict control of concentration is difficult to apply to the actual plating process.

In addition, Japanese Patent Publication No. 58-48635 discloses a method of imparting glossiness by deposition before plating, but in this case, plating solution is contaminated and expensive to install deposition equipment. , The deposition solution is easily contaminated due to the elution of the iron of the plating disc, there is a problem in use.

Accordingly, the present inventors have conducted research and experiments to improve the above problems, and based on the results, the present invention proposes the present invention, before the plating or during the plating, and the additive formaldehyde and By adding a predetermined amount by mixing ethylene glycol is to provide a method for producing a zinc electroplated steel sheet excellent in the whiteness and gloss of the surface appearance and fine plating structure of the plating layer, the purpose.

Hereinafter, the present invention will be described.

The present invention is a plating liquid composition composed of a molar concentration of zinc: 0.7 to 2.0, and a chlorine concentration of 5.0 to 9.0, pH of the plating liquid: 2.0 to 5.5, temperature of the plating liquid 40 to 75 ℃, flow rate: 0.5 to 2.5 m sec. And Current density: In the method of producing a galvanized steel sheet by electroplating under the plating conditions of 30 ~ 180 A / dm², 0.1ml / l or more of the additive formaldehyde and ethylene glycol in the plating solution, respectively, and the sum 8.0 The present invention relates to a method for producing a galvanized steel sheet having excellent gloss and white color by electroplating by adding in a range of ml / l or less.

Hereinafter, the numerical limitation reason and the like will be described in detail.

When the molar concentration of zinc in the plating solution is 0.7 or less, the surface appearance is black and streaks in the flow direction are severe and the powder is plated on the surface, and when the molar concentration of zinc is 2.0 or more, the surface is rough and the cost increases. Therefore, the zinc molar concentration in the plating liquid is preferably limited to 0.7 to 2.0.

The concentration of chlorine is added to improve the conductivity in electroplating, but the content of the above chlorine causes a delamination of the plating surface due to supersaturation at a predetermined temperature above 9.0 molar concentration, and the conductivity of the chlorine is lower than 5.0 molar concentration, resulting in an increase in plating voltage. Since the surface appearance causes a blackened shape, it is preferable to limit the concentration of chlorine to 5.0 to 9.0 molar concentration.

The temperature of the plating liquid is reduced in conductivity below 40 ℃ and cause a scratched state of powder or streaks on the surface of the plating layer, the surface is darkened and the surface is changed to a yellow color above 75 ℃, the temperature of the plating solution is 40 ~ It is preferable to limit to 75 ° C.

The pH of the plating liquid is less than 2.0, causing the corrosion of the device to increase impurities and darken the color of the surface of the plating layer, the color of the surface is changed to yellow above 5.5, the pH of the plating liquid is preferably limited to 2.0 ~ 5.5 rolls .

When the amount of the additive formaldehyde and ethylene glycol added is 0.1ml / l or less or the total addition amount is 0.2ml / l or less, the color of the surface is changed to white and there is no effect of increasing the gloss. In order to secure the surface of the galvanized layer, the sum of the addition amounts of the additive formaldehyde and the ethylene glycol added in the plating solution should be secured at least 0.2 ml / l, and each addition should be at least 0.1 ml / l.

On the other hand, when the sum of the addition amount of the additive formaldehyde and ethylene glycol is 8.0 ml / l or more, the adhesion of the plating layer is poor, so the sum of the addition amount is preferably limited to 8.0 ml / l or less.

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

EXAMPLE

After the cold-rolled steel sheet as a base metal, electroplating was performed under the plating solution composition and plating conditions shown in Table 2, the glossiness and whiteness of the surface appearance of the coated steel sheet were observed, and the results are shown in Table 1 below.

In addition, about the comparative material (B) and the invention material (6) of Table 2, the microstructure of the plating liquid was observed using a scanning electron microscope, and the results are shown in FIG.

The glossiness of Table 2 is a value measured at an incident angle of 60 ° by a Glossor Meter (ERICHSEN), and the whiteness is a value measured by a Color and Color Difference Meter C-5120 (TOKYO DANSHOKY), and the fineness of the plating layer of FIG. Tissues represent tissues in which the plating solution was expanded with a scanning electron microscope of Stereo Scan CAMBRIDGE 25 MK3.

TABLE 1

* Additive: Formaldehyde + Ethylene Glycol

As shown in Table 1 above, the present invention material (1-10) electroplated by adding formaldehyde and ethylene glycol as additives to the plating solution within the scope of the present invention is electroplated without adding formaldehyde and ethylene glycol as additives. It can be seen that it is very excellent in glossiness and whiteness as compared to one comparative material (AD).

On the other hand, as can be seen from FIG. 1 showing the microstructure of the plating layer, the plating layer [In Fig. 1 (b)] of the invention material 6, in which 2.0 ml / l of formaldehyde and ethylene glycol as additives were added to the plating solution, The particles are laminated in a plate shape, and are finer than the plating layer [FIG. 1 (a)] of the comparative material (B) which was electroplated at 100 A / dm 2 without adding any additives of formaldehyde and ethylene glycol. The plating structure is shown.

As described above, the present invention is electroplated by adding a proper amount of formaldehyde and ethylene glycol additives to the plating bath, thereby providing a zinc electroplated steel sheet having excellent whiteness and glossiness of the surface appearance of the plated steel plate and fine plating structure of the plated layer. There is an effect that can be done.

Claims (1)

Plating liquid composition with zinc molarity: 0.7-2.0, and chlorine molarity: 5.0-9.0, pH of the plating liquid: 2.0-5.5, temperature of plating liquid: 40-75 ° C., flow rate: 0.5-2.5 m / sec, And a current density of 30-180 A / dm < 2 > for electroplating zinc plated galvanized steel sheet, wherein the additives formaldehyde and ethylene glycol in an amount of at least 0.1 ml / l and the sum of the added amounts. A method for producing a zinc electroplated steel sheet having excellent gloss and whiteness, which is added in an amount of not more than 8.0 ml / l and electroplated.