KR890003813B1 - Chromate solution with an excellant corrosion resistance - Google Patents

Abstract

The Cr concentration is made to 0.01-1 mol./l by mixing one, or two above species among Na2CrO4, Na2Cr2O7, K2CrO4, K2Cr2O7, or CrO3 and the PO4-3 concentration is made to 0.4-0.75 mol/l by mixing one, or two above species among H3PO4, NaH2PO4, Na2HPO4, (NH4)H2PO4, or (NH4) 2HPO4. The Cr3+ concentration ratio to the total Cr is made to 0.1- 0.5 by adding reducing agent, so the chromate solution is made by adding water soluble Cu compound for the Cu2+ concentration to be 0.004-0.012 mol/l. Chromate treated steel plate with good corrosion resistance and good surface figure can be manufactured by using this chromate solution.

Description

Chromate solution with excellent corrosion resistance

It is a graph which shows the change of corrosion resistance with addition of Cu ion.

The present invention relates to a chromate treatment solution for improving the corrosion resistance of the galvanized steel sheet and to give a beautiful surface appearance, and more particularly to a coated chromate solution without gelation of the solution. Conventionally, steel plates coated with zinc or aluminum are used without coating or painting.However, in order to improve rust resistance and paint adhesion and corrosion resistance, surface treatment is performed by using a solution containing mainly chromateic acid on the surface of the coated steel sheet. The function of the chromate coating on the type of material to be treated is largely divided into two functions, a self-healing function and a corrosion barrier. The embroidery function is based on soluble chromium ions in the coating. The function is that it depends on the density and continuity of the coating. Common chromate treatment methods include electrolytic chromate, reactive chromate and coated chromate. However, in the electrolytic chromate treatment, chromium coating uniformity is deteriorated and microcracks are generated on the coating itself, resulting in a decrease in corrosion resistance, and a reaction of forming a chromate coating by the reaction between the surface of the workpiece and the chromate treatment solution. In the case of the type chromate treatment, the free acidity in the liquid decreases depending on the amount of the material to be treated, which makes the film formation difficult.

In the case of the reactive chromate treatment, there is a method of increasing the chromium concentration in a solution and adding an etchant to improve the corrosion resistance, but when the chromium concentration is increased, the chromium film is easily dissolved in water, colored, and the chromium coating uniformity is increased. In addition, it is difficult to obtain a good appearance and a large amount of addition is required in order to obtain sufficient corrosion resistance when the etchant is added to promote the reaction. In this case, the reaction between the chromate treatment solution and the surface of the plated steel sheet to be treated rapidly progresses. Due to shortening of the service life and surface coloration and chromic acid contamination, the amount of the etchant is limited. Therefore, it is difficult to improve the life of the treatment liquid by proper concentration management and the corrosion resistance of the film is not sufficient.

On the other hand, in the case of the coated chromate treatment, the film formation method is a method of drying the film immediately without applying water after application on a steel sheet rather than directly reacting the solution with the treated material. Since there is little dissolution of the substrate to be treated, there is almost no aging of the treatment liquid, and there is almost no discharge of chromium ions out of the factory by washing with water after treatment.

However, the chromate treatment has a problem in that the coating is formed by coating, which results in a lack of discontinuity of the coating due to volume shrinkage during drying and lack of adhesion between the coating and the workpiece.

In order to solve this problem, a method of adding an appropriate amount of a titanium compound to a chromate solution and a method of adding a resin have been developed. The addition of titanium compounds aims to improve the corrosion resistance due to the reduction effect and metal ion effect, but there are disadvantages of coloration of the surface of the material and the occurrence of precipitates in the solution, and the addition of resin and the adhesion between the chromate film and the substrate to be treated when the resin is added. Density is improved, but the difference depending on the type and amount of resin, but the gradation of the gel (gel) phenomenon is inevitable and will be subject to restrictions on use after a certain time.

Accordingly, an object of the present invention is to provide a coated chromate solution without gelation of the solution in order to obtain a chromate-treated steel sheet excellent in corrosion resistance and surface appearance.

The chromate solution according to the present invention contains Cr ³⁺ ions as a reducing agent based on chromic acid and phosphoric acid, and a small amount of water-soluble Cu compound is added thereto.

In more detail, the solution according to the present invention is Na ₂ CrO ₄ , Na ₂ Cr ₂ O ₇ , K ₂ CrO ₄ , K ₂ Cr ₂ O ₇ , CrO ₃ Cr Cr concentration by mixing one or two or more To 0.01-1 mol / l, and one or two PO ₄ ^-3 compounds such as H ₃ PO ₄ NaH ₂ PO ₄ , Na ₂ HPO ₄ (NH ₄ ) H ₂ PO ₄ , (NH ₄ ) ₂ HPO _4, and the like. After mixing on paper to make the concentration of PO ₄ ^-3 0.4-0.75 mol / l, and then reducing agents such as CH ₃ OH, C ₂ H ₅ OH, C ₂ H ₆ O ₂ , C ₃ H ₈ O ₂ By reducing the Cr ions in the solution, the ratio of the trivalent chromium concentration to the total chromium (hereinafter referred to as "chromium concentration ratio") is set to 0.1-0.5, and the water soluble so that the Cu ⁺⁺ concentration is 0.004-0.012 mol / l. It is characterized by adding a Cu compound.

When the concentration of chromium ions is less than 0.01 mol / l, the corrosion resistance of the film is extremely low. When the concentration of chromium ions is more than 1 mol / l, the color of the surface is severely damaged and the appearance is impaired. It was set as.

When the concentration of PO ₄ ^-3 is less than 0.4 mol / l, the effect of adding PO ₄ ^-3 ions does not appear, resulting in yellow spots on the appearance of the film. Therefore, the surface appearance is poor and the adhesion between the film itself and the material to be treated is reduced. If the concentration of PO ₄ ^-3 is more than 0.75 mol / l, dark spots appear on the surface, which damages the appearance of the film.

When the chromium concentration ratio in the urine solution is reduced to 0.1 or less due to the addition of a reducing agent, the anti-rust effect only by the soluble chromium concentration itself in the film is extremely low.

Cu ⁺⁺ in solution contributes to the formation of a chromate film and itself as a constituent of the film itself, contributing to the formation of a dense and firm film. Contribution to the above effect when the concentration of Cu ⁺⁺ is less than 0.004 mol / l If the corrosion resistance is very low and 0.012 mol / l or more is less than the chromic acid adhesion is inhibited by the anticorrosive effect is reduced and the corrosion resistance is greatly reduced.

EXAMPLE

After chromic solution was applied to the plated steel sheet by dipping or spraying, it was squeezed using a solid roll. After squeezing the solution, it was dried for 4 seconds in a hot air at 100 ° C and left in the air for a certain period of time (24 hours). .

Table 1 shows the corrosion resistance evaluation by salt spray after the treatment with the conventional coated chromate solution and the chromate solution according to the present invention, and the changes in the surface appearance of the steel sheet before and after the chromate treatment. The figure shows the corrosion resistance by the salt spray test for the effect on the addition of Cu ions in chromate solution.

The chemicals used in the examples were CuSO ₄ as H ₃ PO ₄ , NaH ₂ PO ₄ , Cu ⁺⁺ for CrO ₃ , Na ₂ CrO ₄ , and PO ₄ ^-3 for Cr ions and Cr in solution. The ratio of ⁺³ / Cr ⁺⁶ was adjusted by adding an alcoholic organic solvent.

Compared with the conventional chromate solutions (samples A, B, C, D) and comparative examples (samples E, F, G, H) according to Table 1, the chromate solutions (samples I, J, K, L) of the present invention As a result of the increase in corrosion resistance, no surface gelation was observed.

의 조건에서 구리이온첨가에 따른 내식성의 변화를 나타내고 있는바 이에 의하면 구리이온 농도가 0.004-0.012mol/l에서 백청(white rust)발생면적이 가장 적은 것으로 나타났다.Figure _{CrO 3: 0.2mol / l, PO} 4 -3: 0.63mol / l chromium concentration ratio

The corrosion resistance of copper ions was increased under the conditions of, and the copper ions concentration showed the smallest white rust generation area at 0.004-0.012 mol / l.

As described above, as a result of using the chromate treatment solution according to the present invention, it was possible to produce a chromate treatment steel sheet excellent in corrosion resistance and steel sheet appearance.

TABLE 1

Claims (1)

Na ₂ CrO ₄ , Na ₂ Cr ₂ O ₇ , K ₂ CrO ₄ , K ₂ Cr ₂ O ₇ , CrO ₃ , or a mixture of two or more thereof, the Cr ion concentration is 0.01-1 mol / l, and H ₃ PO _{4, NaH 2 PO 4, Na} 2 HPO 4, (NH 4) H 2 PO 4, (NH 4) 2 HPO u of a mixture of PO ₄ ^-3 or more compounds one or two or the concentration of PO ₄ ^-3 0.4-0.75 mol / l, by addition of reducing agent, the ratio of trivalent chromium concentration to total chromium (chromium concentration ratio) is set to 0.1-0.5 and water soluble copper so that the Cu ⁺⁺ concentration is 0.004-0.012 mol / l. A chromate solution characterized in that the composition is added by adding a compound.

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