KR100782720B1 - Coating composition for galvannealed steel sheet, method for forming coating layer and steel sheet having the coating layer formed thereof - Google Patents

Abstract

Coating composition for a galvannealed steel sheet, a method for forming a coating layer and a steel sheet having the coating layer are provided to form a phosphate coating having good adhesion and lubrication performance on a surface of a GA steel plate. Coating composition for a galvannealed steel sheet includes a zinc oxide. When 10ml of the coating composition is neutralized by 0.1N NaOH, an amount of NaOH consumed by neutralization titration is 0.5ml or less. When content of zinc oxide is 3 to 3.5wt%, 0.5ml or less of the coating composition 10ml can be neutralization-titrated by 0.1N NaOH. More specifically, zinc oxide can be added such that when the coating composition 10ml is neutralization-titrated by 0.1N NaOH, an amount of NaOH consumed by neutralization titration is 0.5ml or less, preferably, 0.3 to 0.5ml.

Description

Coating composition for alloyed hot-dip galvanized steel sheet, method for forming film using same, and steel sheet having film formed according to it {Coating Composition for Galvannealed Steel Sheet, Method for Forming Coating Layer and Steel Sheet Having the Coating Layer Formed Thereof}

1 is a graph showing the shear adhesion strength according to the change in the concentration of the free acid in the coating solution,

2 is a graph showing a change in the friction coefficient according to the change in the coating amount.

The present invention relates to a coating composition for alloying hot-dip galvanized steel sheet to form a phosphate coating on an alloyed hot-dip galvanized steel sheet (hereinafter referred to as 'GA steel sheet' Galvannealed), a film forming method using the same and a steel sheet having a film formed accordingly. More specifically, the present invention relates to a coating composition for alloyed hot-dip galvanized steel sheet in which adhesion and lubricity to the GA steel sheet form a phosphate film, a method for forming a film using the same, and an alloyed hot-dip galvanized steel sheet having a film formed accordingly. .

GA steel sheet is different depending on alloying degree, but in case of 9 ~ 12wt.% Fe, standard electrode potential is base than iron (-0.44V), so when zinc plated layer is formed on steel sheet, Large quantities are used in automotive steel sheets because of their excellent protection, low cost and ease of manufacture. However, GA steel plate has a disadvantage in that the plating layer is very rough and brittle, so that the contact area with the die is large and the adhesion is easy when machining. Therefore, when the plated steel sheet is press-molded, the steel sheet itself is cracked due to high frictional load, which causes a decrease in productivity and workability in the automobile manufacturing process. On the other hand, in automobiles, adhesives are used to bond the inner and outer panels, which prevents noise while driving the body, improves the dent resistance of the outer panels, and prevents the penetration of contaminants such as water or salt into the hamming. It also improves.

In order to improve such a problem, an alloy such as iron-zinc (Fe-Zn) or phosphorus-zinc (P-Zn) is 3000-5000 mg / m ^{2 by} electroplating so that iron or phosphorus is contained over 95 wt.% On the GA steel sheet. Thinly plated flash steel has been used, but the cost of manufacturing steel sheet is high, so automakers have avoided the use of flash steel in terms of cost reduction. In addition, the Korean Patent Application Nos. 2001-71291 and 2001-84492 presented by the present inventors have very good friction characteristics, but have a disadvantage in that the resin adheres to the welding electrode, thereby reducing weldability and difficult to form phosphate crystals. In addition, the Republic of Korea Patent Application No. 2003-95244 has the disadvantages of excellent processability and phosphate treatment, but iron oxide is poor adhesive adhesion and expensive nickel component in the coating layer. In addition, alloy electroplated steel sheets such as zinc-iron or zinc-nickel are inferior in workability due to high coefficient of friction and expensive to manufacture compared to GA steel sheets.

On the other hand, by applying a phosphate solution containing nickel, manganese, zinc binary or ternary metal ions of low-cost and excellent workability to the GA steel sheet, it is possible to manufacture a phosphate-based automotive lubricating steel sheet excellent in workability. However, since phosphoric acid is a weak acid, it is impossible to reduce the free acid in a solution more than a certain limit, and thus, a large amount of free phosphoric acid remains in the coating, which degrades adhesion to the adhesive and has a very inferior adhesiveness. Accordingly, the coated phosphate-based lubricated steel sheet which does not wash with water after coating has a problem in that weldability, paintability and corrosion resistance including workability are good, but adhesive adhesion is very poor due to the large amount of free phosphoric acid in the coating.

The present invention has been proposed to solve the above problems,

An object of the present invention is to provide a film-forming composition used to form a phosphate film having excellent adhesive adhesion and lubricity on the surface of the GA steel sheet.

Another object of the present invention is to provide a method for forming a phosphate coating having excellent adhesion and lubricity on the surface of a GA steel sheet.

Still another object of the present invention is to provide a GA steel sheet having a phosphate coating having excellent adhesion and lubricity.

According to one aspect of the invention,

The coating composition is provided with a coating composition for alloying hot-dip galvanized steel sheet comprising 15 to 25% by weight of hypophosphorous acid, 0.1-1% by weight of manganese, 3-5.5% by weight of zinc oxide and the balance.

According to another aspect of the present invention,

Coating the coating-forming composition of the present invention on an alloyed hot-dip galvanized steel sheet so that the coating amount is 200-400 mg / m 2; And

After coating, drying to a steel sheet temperature of 70 ~ 100 ℃;

Provided is a method for forming a phosphate film on an alloyed hot dip galvanized steel sheet comprising a.

According to another aspect of the present invention,

An alloyed hot-dip galvanized steel sheet having a film having a dry coating amount of 200 to 400 mg / m 2 per one side of the film-forming composition of the present invention is provided.

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

The film-forming composition according to the present invention used to form a phosphate coating, specifically, a phosphorus-zinc-manganese coating, on an alloyed hot-dip galvanized steel sheet is composed of hypophosphorous acid having a very high oxidizing power as a main component, and the content of free acid is controlled. The film formed on the GA steel sheet using the film forming composition of the present invention exhibits excellent adhesion.

The film-forming composition (coating composition) according to the present invention comprises hypophosphorous acid, manganese, zinc oxide and the balance water, the concentration of the free acid is controlled. Furthermore, the coating composition of the present invention may include components that can be optionally added to the phosphate film forming composition such as wax, lubricant, etc. as needed in the art.

In the film-forming composition of the present invention, hypophosphorous acid and manganese are 15-25 wt%, preferably 18 wt% and manganese 0.1-1 wt%, preferably 0.5 wt%, in the composition. It is formulated with.

If the content of hypophosphorous acid is less than 15% by weight, the processability is poor, and if it exceeds 25% by weight, solution management is difficult and the amount of zinc oxide to reduce the free acid concentration is very uneconomical. If the manganese content is less than 0.1% by weight, the processability is poor, and if the manganese content is more than 1% by weight, it is difficult to completely dissolve manganese and it is uneconomical.

On the other hand, as a method of securing manganese in the composition, the metal manganese may be dissolved directly in the composition, and the amount of manganese carbonate or potassium permanganate may be converted into the amount of manganese to be dissolved.

Zinc oxide is added to minimize the content of free acid in the composition, zinc oxide in the coating composition may be blended at 3-5.5% by weight. The content of zinc oxide varies depending on the content of hypophosphorous acid, and when the zinc oxide is blended at 3-5.5% by weight, the content of free acid in the coating composition can be controlled to be below the level intended by the present invention.

That is, in the coating composition according to the present invention, when neutralizing titrating 10 ml of the coating composition containing hypophosphorous acid and manganese in the above-mentioned range with 0.1 N NaOH, the amount of NaOH consumed for neutralization titration is 0.5 ml or less. When the zinc oxide content is 3-5.5% by weight, the free acid content of the coating composition may be neutralized with 0.1 N NaOH of 0.5 ml or less of 10 ml of the coating composition.

More specifically, in the coating composition according to the present invention, when zinc titrates 10 ml of the coating composition with 0.1 N NaOH, the amount of NaOH consumed for neutralization titration is 0.5 ml, preferably 0.3-0.5 ml. It may be added in an amount to.

Therefore, the concentration of free acid in the coating composition according to the present invention is 0.5 ml, preferably 0.3-0.5 ml of 0.1 N NaOH consumed for neutralization titration when 10 ml of the coating composition is neutralized with 0.1 N NaOH. The amount is controlled so as to be as good as possible. 1 shows a graph showing the adhesive strength according to the change in concentration of the free acid in the coating composition. The horizontal axis of the graph shows the amount of 0.1 N NaOH used for neutralization titration of 10 ml of the coating composition. As shown in FIG. 1, the higher the content of the free acid in the coating solution, the lower the adhesive strength.

In the present specification, for the sake of convenience, the content of the free acid in the coating composition is represented as an amount consumed when titrating with 0.1 N NaOH, but the present invention is not limited thereto, and also includes a case where the same acid concentration is obtained by titration with another alkaline solution. will be.

When the content of the free acid in 10 ml of the coating composition exceeds a concentration corresponding to 0.5 ml of 0.1 N NaOH, the adhesion of the phosphate coating to the GA steel sheet, that is, the phosphorus-zinc-manganese coating, is poor. In addition, the lower the concentration of free acid in the composition is more preferable, but the lower limit is not limited. However, if the content of free acid in 10 ml of the coating composition is less than the concentration corresponding to 0.3 ml of 0.1N NaOH, the coating composition and the GA steel sheet Because of its lack of reactivity, the adhesion of the lubricating film is weakened and precipitates are formed in the solution.

Roughly, zinc oxide is used in the composition in a nearly saturated solubility in the coating composition so that the free acid content in 10 ml of the coating composition is below the concentration corresponding to 0.5 ml of 0.1 N NaOH. Although not limited to this, for example, when 5 wt% of zinc oxide is added when hypophosphorous acid is 18 wt% in the film-forming composition (coating composition) according to the present invention, the content of free acid in 10 ml of the coating composition is 0.1. It can be managed at concentrations corresponding to 0.5 ml of N NaOH.

On the other hand, although it is irrelevant to adhesion, the addition of alcohol to the film-forming composition of the present invention has the advantage that the surface tension of the solution is increased to improve the spreadability and wettability to obtain a uniform lubricating film without stains. Accordingly, alcohol may optionally be added to the encapsulation composition of the present invention optionally at up to 3% by weight, preferably 1 to 3% by weight. An alcohol content above 3% by weight is undesirable since it promotes aging of the composition. The alcohol is optionally added as necessary, and the lower limit is not limited, but in order to exhibit sufficient surface tension increase effect due to the addition of alcohol, it is preferable to add 1% by weight or more. Ethyl alcohol may be generally used as the alcohol.

Although not limited thereto, the coating composition of the present invention may include, for example, 18% by weight of chirophosphoric acid, 5% by weight of zinc oxide, 0.5% by weight of manganese, 2% by weight of ethyl alcohol, and the balance of water. When the content of free acid in 10 ml of the coating composition neutralizes 10 ml of the coating composition with 0.1 N NaOH, the GA steel sheet is controlled by using a coating composition in which the amount of NaOH consumed for the neutralization titration is 0.5 ml or less. The phosphate film excellent in adhesive force can be formed.

The film-forming composition of the present invention is coated on a steel sheet, specifically, a hot-dip galvanized steel sheet and dried to form a phosphate film, specifically, a phosphorus-zinc-manganese film, on the hot-dip galvanized steel sheet.

The film-forming composition of the present invention is applied to the alloyed hot-dip galvanized steel sheet so that the amount of one-side coating is 200-400 mg / m 2. The coating composition of the present invention may be coated on one or both sides of the GA steel sheet. If the coating amount is less than 200 mg / m 2, the workability, which is the original purpose of the lubricated steel sheet, is deteriorated. 2 is a graph showing a change in the friction coefficient according to the change in the coating amount, as can be seen in Figure 2, it can be seen that the low coefficient of friction in the one-side coating amount range of the present invention.

On the other hand, the coating is not limited to this, but may be performed, for example, by using a roll coater or by spraying the composition on the surface of the steel sheet. In no case, however, should it be washed after coating. Coating can generally be carried out at room temperature. After coating, drying can be performed at the steel plate temperature of 70-100 degreeC. If the steel sheet temperature is less than 70 ℃, the film is not completely dried, if it exceeds 100 ℃ it is uneconomical.

The alloyed hot-dip galvanized steel sheet having a dry film adhesion amount of 200 to 400 mg / m < 2 > coating of the film forming composition of the present invention is excellent in adhesiveness and lubricity.

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

Example  One

The GA steel sheet having a thickness of 0.8 mm was cut to 100x150 mm, degreased, and coated on one surface of the GA steel sheet with the adhesion amount of Table 1 below of the film-forming composition (coating composition) blended with the composition of Table 1 with the bar coater No. 3 It was dried at 70 ℃ to form a phosphate film to prepare a specimen. In Table 1, the content of free acid in the coating composition is expressed as the amount of 0.1N NaOH used for titration of 10ml of the coating composition. Zinc oxide was formulated into the coating composition in an amount such that the content of 10 mL free acid in the coating composition was the amount shown in Table 1 below.

Thereafter, the adhesiveness and coefficient of friction for the prepared composition were measured. Adhesiveness was cut into three pieces of 100 x 25mm per condition, degreased with toluene, and again immersed in BW-90BG rust preventive oil 25mm and left for one day. After 24 hours, the mastic sealer was applied to the 25 x 25mm part only, dried at 170 ° C for 20 minutes, and then shear sheared at 50 mm / min. The resulting strength was used as the shear strength. The reference strength value of the used mastic sealer shall be at least 8kgf / ㎠.

Existing examples used a coating composition containing 13.1 wt% phosphoric acid instead of hypophosphorous acid.

Hypophosphoric acid was used in the comparative example and the invention example.

The friction coefficient was cut to 45x150mm and coated with automotive cleaning oil (P-DBH) .Then, 650kgf load was applied to the 3.5cm x 3.5cm die and drawn at a drawing speed of 1000mm / min. The coefficient of friction was measured by dividing by 650kgf load. The number of friction is measured in three for each specimen and the average value is shown in Table 1 below.

The economic feasibility is not particularly advantageous in terms of quality when the amount of expensive hypophosphorous acid is more than 30wt.% Or more than 1.1wt.% Of manganese.

As shown in Table 1, in the case of the existing example using phosphoric acid, the friction coefficient was low, but it can be seen that the adhesive strength was not secured at all because the free acid in the solution was 1.8 ml. In addition, in the case of 2 to 8 of the comparative example, even if the concentration of hypophosphorus satisfies 15 to 25% by weight of the range of the present invention, when the free acid concentration is large, the adhesive strength is not secured, and the concentration of the free acid is controlled in the range of the present invention. Even if the content of hypophosphorous acid or manganese does not satisfy the conditions set forth in the present invention, the friction coefficient and / or adhesive strength are undesirable.

If the coating amount is also less than 200 mg / m 2, it can be predicted that the workability will be deteriorated due to the high coefficient of friction. However, as in Inventive Examples 1-9, 15-25 wt% of hypophosphorous acid and 0.1-1 wt% of manganese, the concentration of free acid in the composition is 0.03-0.05 mole, and the coating amount is 200-400 mg / m2. The adhesion strength of 8kgf / ㎠ or more and the coefficient of friction of 0.156 or less showed excellent film properties.

Phosphate coating formed using the coating composition according to the present invention shows excellent adhesion and lubricity to GA steel sheet.

Claims (7)

The coating composition is 15-25% by weight hypophosphorous acid, 0.1-1% by weight manganese, 3-5.5% by weight zinc oxide and the remainder of the coating composition for alloying hot-dip galvanized steel sheet. The method of claim 1, wherein the zinc oxide is formulated into the coating composition in an amount such that the amount of NaOH consumed for neutralization titration is 0.5 ml or less when neutralizing titration of 10 ml of the coating composition with 0.1 N NaOH. Coating composition. The method of claim 1, wherein the content of the free acid in the coating composition is controlled so that the amount of NaOH consumed in the neutralization titration is 0.5 ml or less when neutralizing titrating 10 ml of the coating composition with 0.1 N NaOH. Coating composition. The method of claim 1, wherein the content of the free acid in the coating composition is controlled to an amount of 0.3-0.5 ml of NaOH consumed in the neutralization titration when 10 ml of the coating composition is neutralized with 0.1 N NaOH. Coating composition. The coating composition of claim 1, further comprising up to 3% by weight of alcohol relative to the coating composition. Coating the coating-forming composition of claim 1 on an alloyed hot-dip galvanized steel sheet so that the coating amount is 200-400 mg / m 2; And After coating, drying to a steel sheet temperature of 70 ~ 100 ℃; Phosphate film forming method on an alloyed hot-dip galvanized steel sheet comprising a. Dry coating amount per side of 200 ~ 400 mg / m2 of coating composition for alloyed hot-dip galvanized steel sheet comprising 15-25 wt% hypophosphorous acid, 0.1-1 wt% manganese, 3-5.5 wt% zinc oxide and the balance Alloyed hot dip galvanized steel sheet having a phosphate coating.

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