KR960011017B1 - Chromate solution with an excellent corrosion resistance and plating adhesivity, and method for making a chromate film to use the same - Google Patents

Abstract

The chromate treatment is applied to galvanized steel sheet for automobile and household electric appliances. The chromate coating of treatment solution for chromate steel sheet comprises the total concentration of chromium of the concentration of PO43- 80 to 150g/L, 30 to 80g/L, the concentration of colloidal silica 50 to 200g/L, the concentration of acrylic emulsion 1 to 8g/L, and 0.2 to 0.6 the ratio of Cr3+/total Cr. The chromate film on the surface of zinc and zinc system alloy coating steel sheet is produced by coating of chromate solution having the same composition as mentioned above, and drying at 80 to 200deg.C without washing treatment.

Description

Chromate solution excellent in corrosion resistance and paint adhesion, and chromate coating method using the same

1 is a graph showing the coating adhesion state of a chromate coating different from the amount of phosphoric acid added in the chromate solution.

The present invention relates to a chromate solution having excellent corrosion resistance and coating adhesion, and a method for producing a chromate coating using the same. More specifically, the coated chromate coating solution for chromate steel sheet having a uniform surface appearance and excellent corrosion resistance and coating adhesion, and using the solution It relates to a method for producing a chromate coating.

In general, plating is performed with zinc, zinc-based alloys, or the like as a method for improving the corrosion resistance of steel sheets, and phosphate treatment and chromate treatment are performed to prevent the occurrence of white rust in the plating layer by the plating.

The phosphate treatment is mainly carried out as a base treatment for the purpose of painting, and the chromate treatment is performed for the purpose of temporary rust prevention. Recently, the phosphate treatment has been pursued at the same time to secure the corrosion resistance and the coating adhesion effect by the chromate treatment.

The chromate coating function is imparted by the self-healing function by the soluble chromium component in the coating, the compactness of the coating, and the corrosion barrier effect by the chromium trivalent compound in the coating.

The chromate coating method is divided into electrolytic, reactive, and coating by treatment methods according to the solution composition, and shows a difference in characteristics according to each treatment method.

That is, in the case of electrolytic chromate, the amount of chromium adhesion can be precisely controlled by controlling the amount of electricity, but there is a disadvantage in that corrosion resistance is poor due to the occurrence of microcracks and the like. As the treatment time increases, the lifetime of the solution decreases due to solution aging, such as the dissolution of metal ions on the surface of the workpiece and the free acidity in the solution, thereby making it difficult to control the amount of chromium deposits. Due to the discharge of the chromium-containing solution by water washing after chromate treatment, not only there is a problem in pollution, but also the self-repair function according to the chromate coating component is weak, so that the corrosion resistance of the coating is not sufficient.

In contrast, the coated chromate forms a film by simply applying a solution on a steel plate rather than a reaction between the solution and the material to be formed in the film formation. There is no pollution problem according to the emission.

However, the coated chromate has excellent self-repairing effect but relatively low corrosion barrier effect, so it is required to select and control various additives to compensate for this, and to uniformize the surface appearance according to the increase of chromium adhesion. Is required.

Accordingly, the present invention provides a chromate solution and a method of forming a chromate film using the solution for forming a chromate film having excellent corrosion resistance and surface appearance as well as excellent coating adhesion by controlling the appropriate component and content of the coated chromate treatment solution. Its purpose is to provide it.

Hereinafter, the present invention will be described.

The present invention is a chromate solution for chromate steel sheet, the total chromium concentration: 80-150g / ι, Concentration: 30-80g / ι, colloidal silica concentration: 50-200g / ι, acrylic emulsion concentration: 1-8g / ι and the trivalent chromium ratio to the total chromium is 0.2-0.6. The present invention relates to a chromate solution having excellent paint adhesion.

In addition, the present invention is a method for producing a chromate coating on zinc and zinc-based alloy-plated steel sheet, the coating of the chromate solution according to the present invention to the steel sheet and then drying at 80-200 ℃ without washing with water The present invention relates to a chromate coating method having excellent corrosion resistance and paint adhesion.

Hereinafter, the chromate solution by this invention is demonstrated in detail.

The chromate solution according to the present invention is composed of a solution in which an appropriate amount of Cr ³⁺ ions is present as a reducing agent on the basis of chromic acid and phosphoric acid, colloidal silica and acrylic emulsion are added thereto.

Compounds composed of chromium 6 components such as CrO ₃ , Na ₂ , Cr ₂ , O ₇ , K ₂ , CrO ₄ , (NH ₄ ) ₂ , Cr ₂ , O ₇ such that the total Cr concentration is 80-150g / ι It is preferable to add one or two or more of them. The reason is that when the total Cr concentration is 80g / ι or less, the amount of chromate coating is small, so that the corrosion resistance effect is extremely low. This is because the appearance of the coating becomes poor.

In this case, the total Cr is preferably reduced to a portion of chromium hexavalent by using a reducing agent, and the trivalent chromium ratio (hereinafter referred to as chromium circle ratio) to the total chromium is preferably 0.2-0.6, because the solution by adding a reducing agent If the chromium reduction ratio is less than 0.2, the self-healing effect of soluble chromium in the film is expected, but the anti-corrosion effect is lowered due to low corrosion barrier efficiency. This is because a problem of easy gelation of the solution occurs.

Phosphoric acid in the solution not only improves the corrosion resistance but also affects the surface color and film adhesion. The phosphoric acid is one kind of PO ₄ ^{-3 mixtures} such as H ₃ PO ₄ , NaH ₂ PO ₄ , Na ₂ HPO ₄ It is preferable to mix and add two or more types. At this time, when the concentration of phosphoric acid is less than 30g / ι solution stability is lowered, if more than 80g / ι has the effect of improving the corrosion resistance, but the coating adhesion is rapidly deteriorated, so that the concentration of phosphoric acid is 30-80g / ι It is desirable to.

In addition, when the colloidal silica is less than 50g / ι may not be expected to improve the corrosion resistance, the stability of the solution is deteriorated, the corrosion resistance is expected to increase due to the densification of the film above 200g / ι, but the sludge ( Sludge) is a problem that occurs severely generated and the appearance of the specimen is poor, so it is preferable to add the concentration of the cooidal silica is 50-200g / ι.

On the other hand, the acrylic emulsion is not expected to improve the corrosion resistance when the acrylic emulsion concentration is less than 1g / ι, the problem of deterioration of uniformity of the chromate coating during operation because the foaming tends to appear severely at 8g / ι or more Since it is generated, it is preferable to add the acrylic emulsion so that the concentration is 1-8 g / ι.

Hereinafter, the method of forming a chromate film using the chromate solution of this invention mentioned above is demonstrated in detail.

The process of forming the chromate film using the chromate solution prepared according to the present invention is performed in a simple manner in the order of degreasing, washing, chromate coating and drying the zinc and zinc-based alloy plated steel sheet, excellent work efficiency and continuous There is a feature that can be easily applied to the plating line.

In the chromate coating step, the coating method may be treated using any method such as dipping, spraying, roll coating, etc., and there is an advantage in that drying can be performed immediately without washing with water after coating. .

In the drying step, the drying temperature is preferably 80-200 ° C., because the drying temperature is insufficient at 80 ° C. or lower, and drying at 200 ° C. or higher may cause cracks in the chromate coating.

In the case of forming the chromate coating by the above method, when the chromium adhesion amount is 30 mg / m 2 or less, the corrosion resistance of the plated steel sheet decreases, and when the adhesion is over 100 mg / m 2 or more, the surface appearance of the steel sheet is poor, so the chromium adhesion amount is 30-100 mg / m 2. It is preferable to apply | coat at m <2>, and it is more preferable to apply | coat at 50-80 mg / m <2>.

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

Example

The galvanized nickel-plated alloy was charged with an electric steel sheet having a surface of 30g / m2 on both sides as a steel sheet. The steel sheet was degreased with an alkaline solution, washed with water to remove moisture, and then the amount of chromium adhered to 50 mg / m2 using a roll coater. The chromate urine solution having the composition as shown in Table 1 was applied to the base steel sheet, wherein the concentration of the solution was used as 30 wt% by adding pure water to facilitate the coating workability.

The coated steel sheet was not washed with water, and immediately dried in a drying furnace at a drying temperature as shown in Table 1, followed by a salt spray test and surface appearance evaluation according to JISZ 2371. The results are shown in Table 1 below. The paint adhesion test was performed according to the addition amount, and the result is shown in FIG.

As shown in Table 1, in Comparative Example (5) having a high chromium reduction ratio, the solution itself is gelled, thereby limiting the use of the solution. In Comparative Example (4), which is too low, the corrosion barrier effect of chromium is lowered. It brought about deterioration of corrosion resistance. In addition, in Comparative Example (7) containing a large amount of colloidal silica, the effect of improving the corrosion resistance was obtained, but a decrease in stability in the solution resulted in the production of sludge, and Comparative Example (6) in which colloidal silica was added in a small amount. The anticorrosive effect is difficult to expect, and in Comparative Example (9) in which a large amount of acrylic emulsion was added, the uniformity of the foam was caused by the deterioration of workability, which resulted in a poor surface appearance and an effect of reducing the corrosion resistance. In the case of the comparative example (8) which did not, there exists a tendency for corrosion resistance to fall.

On the other hand, when the phosphoric acid is added in a small amount as in Comparative Example (1), the wettability with the steel sheet is poor, and the workability and solution stability are lowered. When the phosphoric acid is added in a large amount, the coating adhesion is degraded as shown in FIG. do.

In addition, the comparative example (11) in which the drying temperature is low in the drying operation, the film drying is insufficient, the corrosion resistance is inferior, and in the comparative example (10) dried at a high temperature temperature, the corrosion resistance drops sharply due to cracking of the coating film In the case of Comparative Example (3) containing a large amount of chromium component, the corrosion resistance is increased, but it causes damage to the surface appearance such as spots due to nonuniformity of coating, etc. In the case of), the corrosion resistance was significantly reduced.

On the other hand, Inventive Example (1-20) dried at a drying temperature of 80-200 ° C. using a chromate solution formulated in the composition range of the present invention shows excellent surface appearance and corrosion resistance, and also excellent coating mixing property. have.

As described above, the present invention has an effect of producing a chromate steel sheet having excellent surface appearance and excellent corrosion resistance and paint adhesion by controlling the composition and components of the coated chromate treatment solution appropriately.

Claims (2)

In the chromate solution for chromate steel sheet, the total chromium concentration: 80-150g / ι, Concentration: 30-80g / ι, Colloidal Silica Concentration: 50-200g / ι, Acrylic Emulsion Concentration: 1-8g / ι and Trivalent Chromium Ratio to Total Chromium Chromate solution with excellent adhesion. In the method for producing a chromate coating on zinc and zinc-based alloy plated steel sheet, the total chromium concentration: 80-150g / ι, Concentrate: 30-80g / ι, colloidal silica concentration: 50-200g / ι, acrylic emulsion concentration: 1-8g / ι and chromate solution composed of trivalent chromium ratio of 0.2-0.6 with respect to total chromium on the steel sheet A method for producing a chromate coating having excellent corrosion resistance and coating adhesion after drying at 80-200 ° C. without washing with water.