KR101144536B1 - Phosphate-treated electrogalvanized steel sheet with high anti-corrosion and method of manufacturing the same - Google Patents

Abstract

A zinc phosphate-treated galvanized steel sheet capable of securing high corrosion resistance by adding magnesium (Mg) to a phosphate treatment, and a process for producing the same.

The high corrosion-resistant phosphate-treated zinc electroplated steel sheet according to the present invention comprises: a base steel sheet; An electrogalvanized layer formed on the base steel sheet; And a phosphate layer comprising two or more kinds of phosphates and formed on the electrogalvanized layer, wherein the two or more kinds of phosphates include phosphates containing zinc (Zn) and phosphates containing magnesium (Mg) .

Description

TECHNICAL FIELD [0001] The present invention relates to a zinc-coated galvanized steel sheet having high corrosion resistance, and a method of manufacturing the same. BACKGROUND ART [0002]

The present invention relates to an electrogalvanized steel sheet (EG), and more particularly, to an electrogalvanized steel sheet (EG) comprising magnesium (Mg) in an aqueous phosphate solution for treatment of a phosphate film for the purpose of improving the quality of a steel sheet in the process of manufacturing an electrogalvanized steel sheet, To a high corrosion resistant phosphate-treated electrogalvanized steel sheet capable of omitting a chromate post-treatment process for ensuring high corrosion resistance, and a method for manufacturing the same.

Electro galvanized steel sheet (EG) is a kind of galvanized steel sheet, which is a steel sheet on which a zinc coating is formed on the surface of a cold rolled steel sheet by an electrolytic method.

The electro-galvanized steel sheet can reduce the amount of zinc adhered as compared with the hot-dip galvanized steel sheet (GA), and has the advantage of uniformly adhering zinc over the entire steel sheet. Due to these advantages, the electro-galvanized steel sheet is widely used as a material for household electric appliances, and recently its application range has been extended to applications such as a bottom chassis such as an LCD (Liquid Crystal Display) TV and a monitor.

Fig. 1 schematically shows a general galvanized steel sheet production line.

Referring to FIG. 1, an electrogalvanized steel sheet is generally manufactured through a pre-treatment step (S110), an electro-galvanizing step (S120), and a post-treatment step (S130).

In the pretreatment step (S110), the cold rolled steel sheet is pickled and degreased. In the electro-galvanizing step (S120), a zinc coating is formed on the surface of the cold-rolled steel sheet by an electrolytic method. In the post-treatment step (S130), the phosphate treatment (S132) and the chromate treatment (S134) are performed.

At this time, the phosphate treatment (S132) is carried out so as to form a phosphate coating on the surface of the steel sheet in order to improve the quality of the steel sheet in terms of corrosion resistance, weatherability and the like during the process of manufacturing the galvanized steel sheet.

Conventional aqueous solutions for treating phosphates used in galvanized steel sheets were prepared by dissolving a zinc or zinc compound in an aqueous solution of phosphoric acid and nitric acid and dissolving a small amount of a manganese compound and a nickel compound in one or both of them.

However, sufficient corrosion resistance can not be ensured by only the phosphate treatment (S132) using the above-described aqueous solution for treating phosphates.

Therefore, the corrosion resistance of the phosphate coating is improved by a method of post-treatment (S134) with a chromate salt after the phosphate treatment (S132), or a method of coating a corrosion-resistant water-soluble resin with a thin film.

However, in the chromate post-treatment (S134), there is a problem that chromium, which is a harmful component, adversely affects the human body or the environment. In the case of the corrosion-resistant water-soluble resin, .

It is an object of the present invention to provide a highly corrosion-resistant phosphate-treated electrogalvanized steel sheet capable of securing sufficient corrosion resistance by containing magnesium in a phosphate coating.

Another object of the present invention is to provide an aqueous solution for phosphating to form a phosphate film in a phosphate treatment process for improving quality after electro-galvanizing, thereby omitting a separate step such as chromate post-treatment or corrosion-resistant water-soluble resin thin film coating And a method for manufacturing a galvanized steel sheet with high corrosion resistance and corrosion resistance.

According to an aspect of the present invention, there is provided a galvanized steel sheet having a high corrosion resistance, An electrogalvanized layer formed on the base steel sheet; And a phosphate layer comprising at least two kinds of phosphates and formed on the electrogalvanized layer, wherein the two or more kinds of phosphates include phosphates containing zinc (Zn) and phosphates containing magnesium (Mg) do.

According to another aspect of the present invention, there is provided a method for manufacturing a galvanized steel sheet having a high corrosion resistance and a high corrosion resistance, the method comprising: coating a surface of an electro galvanized steel sheet with an aqueous phosphate solution containing zinc ions and magnesium ions, And a phosphate layer containing zinc-containing phosphate and magnesium-containing phosphate is formed on the surface of the electro-galvanized steel sheet.

The high corrosion-resistant phosphate-treated electrogalvanized steel sheet according to the present invention and the method for manufacturing the same provide a corrosion-resistant phosphate coating containing magnesium-containing phosphate on the surface of an electrogalvanized steel sheet, There is an advantage that sufficient corrosion resistance can be secured even without application of a water-soluble resin.

Therefore, the produced steel sheet can prevent the rust generated during transportation and storage for a long period of time, and also can effectively prevent the rust generated at the damaged area from being transferred to the entire surface of the steel sheet.

In addition, the zinc-plated steel sheet and the method of manufacturing the same according to the present invention have the advantage of minimizing the impact on the human body and the environment by not using chromium (Cr).

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will now be described in detail with reference to the accompanying drawings, wherein like reference numerals refer to like elements throughout.

BRIEF DESCRIPTION OF THE DRAWINGS The advantages and features of the present invention, and the manner of achieving them, will be apparent from and elucidated with reference to the embodiments described hereinafter in conjunction with the accompanying drawings. It should be understood, however, that the invention is not limited to the disclosed embodiments, but is capable of many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, To fully disclose the scope of the invention to those skilled in the art, and the invention is only defined by the scope of the claims. Like reference numerals refer to like elements throughout the specification.

FIG. 2 shows a galvanized steel sheet with a high corrosion resistant phosphate treatment according to an embodiment of the present invention.

2, the electro-galvanized steel sheet includes a base steel sheet 210, an electro-galvanized layer 220, and a phosphate layer 230.

The base steel sheet 210 may be a normal cold rolled steel sheet.

An electro-galvanized layer 220 is formed on the surface of the base steel sheet 210. The electro-galvanized layer 220 is formed by depositing a zinc coating on the surface of the base steel sheet 210 by an electrolytic process in which a base steel sheet 210 is put into a sulfuric acid plating bath or the like.

The electro-galvanized layer 220 may be formed in a state in which the surface of the base steel sheet 210 is cleanly processed through a process such as pickling or degreasing.

The phosphate layer 230 is formed on the surface of the electro-galvanized layer 220. The phosphate layer 230 may be formed on one side or both sides of the base steel sheet 210 as a reference.

The phosphate layer 230 comprises two or more phosphates. At this time, the phosphate layer 230 includes phosphate containing zinc (Zn) and phosphate containing magnesium (Mg). Phosphoric acid can also react with iron (Fe) to form iron-containing phosphates.

The zinc-containing phosphate may be Zn ₃ PO ₄ ? 4H ₂ O, Zn ₃ (PO ₄ ) ₂ , and the magnesium-containing phosphate may be MgPO ₄ (strictly Mg ₃ (PO ₄ ) ₂ ).

That is, in the present invention, the phosphate layer 230 contains Zn ₃ PO ₄ ? 4H ₂ O and MgPO ₄ .

FIG. 3A is a SEM photograph showing the crystal structure of Zn ₃ PO ₄ ? 4H ₂ O, and FIG. 3B is a SEM photograph showing the crystal structure of Zn ₃ PO ₄ ? 4H ₂ O + MgPO ₄ .

When FIG. 3a and FIG. 3b, Zn ₃ PO _4? If the Zn ₃ PO _4? Complex phosphate of 4H ₂ O + MgPO ₄ compared to the crystal structure of the 4H ₂ O is formed it can be seen that the crystal structure much finer.

Further, the phosphate layer may further contain nickel (Ni), a compound thereof, manganese (Mn) or a compound thereof.

Nickel exists in the phosphate layer in the form of Ni, Zn ₂ Ni (PO ₄ ) ₂ and Ni ₃ (PO ₄ ) ₂ , improving the corrosion resistance and forming a high quality phosphate layer _.

Manganese is present in the form of Mn, Zn ₂ Mn (PO ₄ ) _2, (MnFe) ₅ H ₂ (PO ₄ ) _{2 in} the phosphate layer and plays a role in improving the adhesion.

Referring to FIG. 2, an inner fingerprint coating layer 240 may be further included on the surface of the phosphate layer.

A method of manufacturing a galvanized steel sheet with a high corrosion-resistant phosphate treatment according to the present invention is as follows.

First, an electro-galvanized steel sheet on which an electro-galvanized layer is formed on a base steel sheet and an aqueous solution for phosphating treatment for forming a phosphate layer are prepared.

In an electro-galvanized steel sheet, the thickness of the electro-galvanized layer may be about 2 to 3 mu m. The adhesion amount of zinc can be approximately 20 g / m ² .

The aqueous solution for phosphate treatment contains zinc ions and magnesium ions in an aqueous solution containing phosphoric acid and nitric acid.

In the present invention, the zinc ion is a main component constituting the phosphate layer.

The zinc ions are preferably contained in an aqueous solution for treating phosphates at a concentration of 1,000 to 3,000 ppm. When the zinc ion concentration exceeds 3,000 ppm, the adhesion to the zinc plated layer is lowered due to the increase in the weight of the coating. If the zinc ion concentration is less than 1,000 ppm, the coating itself is not formed, or the coating amount is low and the corrosion resistance is reduced, and the appearance of the material becomes uneven.

Next, the magnesium ion serves to improve the corrosion resistance of the phosphate layer by making the crystal of the coating finer.

Such magnesium ions are preferably contained in an aqueous solution for treating phosphates at a concentration of 500 to 2,000 ppm. When the magnesium ion is added at a concentration of less than 500 ppm, there is a problem that the corrosion resistance and the black degeneration are reduced. When the magnesium ion exceeds 2,000 ppm, the corrosion resistance is slightly increased, but it causes yellowing in terms of heat resistance.

The aqueous solution for phosphate treatment may further contain nickel ions or manganese ions as well as zinc ions and magnesium ions.

Nickel ion promotes the film forming reaction and forms a dense phosphate layer. Further, the nickel ion serves to improve the adhesion between the coating and the coating or coating and the inner fingerprint coating layer.

The nickel ions are preferably contained in an aqueous solution for treating phosphates at a concentration of 50 to 300 ppm. When the concentration of the nickel ion exceeds 300 ppm, the compactibility of the coating film is lowered, and the outer appearance of the coating film becomes dark, thereby deteriorating the film quality. When the concentration of nickel ions is less than 50 ppm, particles of the phosphate layer become coarse and the adhesion of the paint or the like is deteriorated.

The manganese ion improves the mechanical properties by improving the durability of the coating.

The manganese ions are preferably contained in an aqueous solution for treating phosphates at a concentration of 100 to 700 ppm. When the concentration of manganese ions is less than 100 ppm, it is difficult to expect improvement in the durability of the phosphate layer. When the concentration of manganese ions exceeds 700 ppm, the appearance of the coating becomes bright, but the solution stability of the aqueous solution for phosphate treatment is impaired, .

In addition, the aqueous solution for phosphate treatment may further contain other metal ions such as iron ions at a concentration of 2 to 30 ppm in order to improve the solution stability and to increase the uniformity of the phosphate layer. When the concentration of the other metal ions is less than 2 ppm, the effect of improving the uniformity of the phosphate layer can not be obtained and the corrosion resistance is lowered. When the concentration of the other metal ions exceeds 30 ppm, the sludge of the aqueous solution for phosphate treatment is promoted.

On the other hand, it is preferable that the ratio of the free acid to the total acidity of the aqueous solution for phosphate treatment is 0.01 to 0.15. If the ratio of the free acidity to the total acidity is more than 0.15, the etching property to the zinc plating becomes high, and the surface condition of the zinc plating layer may become uneven, so that the phosphate layer may also be heterogeneous.

In order to adjust the pH and acidity of the aqueous solution for phosphate treatment, other additives such as phosphoric acid and nitric acid may be added at a content ratio of 3.7% by weight or less based on the total weight of the aqueous solution. If the amount of the other additives exceeds 3.7% by weight, there is a problem that the uniformity of the appearance is lowered and the crystal structure of the phosphate becomes coarse.

The aqueous phosphate solution may be coated on the surface of the galvanized steel sheet by spraying. At this time, the spraying is preferably carried out in a temperature range of 50 to 62 ° C. When the spray temperature is lower than 50 ° C, there is a problem that the crystal growth is weak in the phosphate layer and the surface properties of the phosphate layer are deteriorated. If the spray temperature exceeds 62 ° C, the unreacted solution becomes excessively sludge- have.

The coating amount of the aqueous phosphate solution is preferably 1.0 to 1.8 g / m ² . If the coating amount of the aqueous solution for phosphate treatment is less than 1.0 g / m ² , the corrosion resistance can not be sufficiently exhibited. If the coating amount exceeds 1.8 g / m ² , the work peelability is lowered and uniform phosphate layer is hardly formed as a whole.

Drying may proceed at a temperature of about 50 ° C after coating of the aqueous solution for phosphate treatment.

Through the coating and drying of the aqueous solution for phosphate treatment, a phosphate layer containing zinc-containing phosphate and magnesium-containing phosphate is formed on the surface of the galvanized steel sheet.

On the other hand, the coating of the aqueous solution for the phosphate treatment can be carried out in a state where the surface of the galvanized steel sheet is pretreated in advance. At this time, the surface of the electro-galvanized steel sheet can be treated with a surface conditioner, and as the surface conditioner, Gardolene 6513 / M1 (manufactured by Samyang Chemical Co., Ltd.) or the like can be used.

Further, after the phosphate layer is formed, the inner fingerprint coating may be further performed to improve the worker's fingerprint or contamination resistance during the manufacturing process of the manufactured steel sheet.

The phosphate layer formed using the magnesium-containing aqueous solution for phosphate treatment according to the present invention has higher corrosion resistance than the conventional phosphate film, thereby preventing corrosion during long-term transportation and storage of the material, It is possible to omit the post-treatment process of the chromate which is carried out for the purpose, thereby reducing the cost and the influence on the environment and the human body.

In addition, the phosphate layer formed by using the aqueous solution for the treatment of phosphates according to the present invention is excellent in adhesion to the inner fingerprint coating layer and the paint to improve the workability and appearance of the material, Thereby effectively improving the quality of the entire steel plate.

Example

Hereinafter, the configuration and operation of the present invention will be described in more detail with reference to preferred embodiments of the present invention. It is to be understood, however, that the same is by way of illustration and example only and is not to be construed in a limiting sense.

The contents not described here are sufficiently technically inferior to those skilled in the art, and a description thereof will be omitted.

1. Phosphate treatment Of galvanized steel sheet  Produce

A cold-rolled steel sheet having a steel sheet thickness of 0.8 mm was degreased, washed with hydrochloric acid, and subjected to electro-galvanizing at an adhesion amount of 20 g / m ² . The electro-galvanized steel sheet thus prepared was pretreated with a surface conditioner (manufactured by Samyang Chemical Co., Ltd., product name: Gardolene 6513 / M1) after washing with water.

Thereafter, the surface of the electro-galvanized steel sheet was coated with an aqueous solution for treating phosphates having the conditions shown in Table 1 by a spraying method, followed by drying to form a phosphate coating.

In Table 1, the concentrations of zinc ions, nickel ions, manganese ions and magnesium ions, other metal ions and other additives are 1/1000 ppm.

[Table 1]

2. Property evaluation method

(1) Appearance uniformity: The degree of surface uniformity after the phosphate treatment was visually observed and evaluated.

(2) Crystalline state: The phosphate film was observed with an SEM, the crystal was magnified 3000 times, and the average diameter of the crystal was observed.

(3) Corrosion resistance: The area of the white rust was expressed in% after sealing the cut surface and the back surface of the phosphate treated specimen (150 * 80 mm) with a salt spray test for 48 hours. At this time, when the area of occurrence of white rust was 5% or less, it was evaluated to exhibit high corrosion resistance.

(4) Darkness Modification: The color difference (L, a, b) was measured one by one using a spectrophotometer (150 * 80mm) The amount of change ΔE (√ (L'-L) ² + (a'-a) ² + (b'-b) ² ) was evaluated according to the evaluation criteria after 120 hours in a constant temperature and humidity bath. Here, L and L 'are initial lightness and lightness after leaving, a and a' are initial red-green chromaticity indexes, and red and green chromaticity indexes after leaving, b and b 'are initial yellow-blue chromaticity indexes, And evaluated as good when the blue chromaticity index? E <3.

(5) Peel-off property: After the phosphate treatment, the product subjected to the inner fingerprint coating was evaluated with an Ericsson tester. When the adhesive tape was applied with a force of 10 kgf and then peeled off, it was judged to be peelable at a height at which no peeling occurred.

3. Evaluation results

The evaluation results of the physical properties are shown in Table 2.

[Table 2]

Referring to Table 2, in the case of Comparative Example 1 in which the free acidity is 0, the phosphate coating itself was not produced.

In addition, in Comparative Examples 3 to 5 in which 4% by weight or more of other additives were added, appearance uniformity was poor, and the crystal structure of the phosphate was poor, and the corrosion resistance was also poor.

Further, in the case of Comparative Examples 6 to 8 and 9 to 10 in which other metals such as iron were added in an amount of less than 2 ppm, other physical properties were generally good but corrosion resistance was deteriorated.

On the other hand, when the zinc ion concentration is 2,500 ppm, the nickel ion concentration is 80 ppm, the manganese ion concentration is 250 ppm, the magnesium ion concentration is 1,200 ppm, the content ratio of other additives is 3.65%, the other metal ion concentration is 2 ppm, In the case of Example 1 where the ratio of 0.11 was dense and the corrosion resistance was the most excellent.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.

Accordingly, the true scope of protection of the present invention should be defined by the following claims.

Fig. 1 schematically shows a general galvanized steel sheet production line.

FIG. 2 shows a galvanized steel sheet with a high corrosion resistant phosphate treatment according to an embodiment of the present invention.

3A is a SEM photograph showing the crystal structure of Zn ₃ PO ₄ ? 4H ₂ O. FIG.

3B is a SEM photograph showing the crystal structure of Zn ₃ PO ₄ ? 4H ₂ O + MgPO ₄ .

Claims (11)

delete delete delete Treating the surface of the base steel sheet using a surface conditioner; Forming an electro-galvanized layer on the surface of the base steel sheet to a thickness of 2 to 3 탆; The surface of the base steel sheet on which the zinc electroplating layer is formed is coated with an aqueous solution for phosphating treatment containing zinc ions and magnesium ions at a coating amount of 1.0 to 1.8 g / m ² by spraying at 50 to 62 ° C to form a phosphate coating layer step; Drying the phosphate coating layer to form a phosphate layer containing zinc-containing phosphate and magnesium-containing phosphate on the surface of the steel sheet; And Coating a surface of the steel sheet on which the phosphate layer is formed with an inner fingerprint to form an inner fingerprint coating layer, The zinc ion is contained at a concentration of 1,000 to 3,000 ppm in the aqueous solution for phosphate treatment, and the magnesium ion is contained at a concentration of 500 to 2000 ppm, The aqueous solution for phosphate treatment may further contain 50 to 300 ppm of nickel ions, 100 to 700 ppm of manganese ions and 2 to 30 ppm of iron ions, and the manganese ions may improve the durability of the coating to prevent the phosphate layer from being peeled off . Wherein the phosphate aqueous solution has a ratio of free acid to total acid of 0.01 to 0.15. delete delete delete delete delete delete delete

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