KR100343009B1 - Preparation of the high corrosion resistant and anti-black patina chromate solution and its film on hot dip galvanized steel - Google Patents

Abstract

In the present invention, the white rust generation time is secured over 240 hours on the basis of SST at 50 ° C to 60 ° C, which is the drying temperature of the coated chromate treatment of the hot dip galvanizing facility. The present invention relates to a chromate solution having high corrosion resistance and high blackening resistance, and a chromate coating method using the same.

In the case of conventional hot dip galvanized chromate solution, it is known that the corrosion resistance blackening resistance increases as the drying temperature is higher, but it is difficult to secure a high drying temperature in actual facilities. Therefore, the subject of the present invention is to develop a high corrosion resistant high blackening chromate solution and a chromate film prepared using this solution, which can ensure corrosion resistance blackening resistance even at low chromate drying temperature.

Description

Chromate solution for high corrosion-resistant black zinc-plated hot dip galvanized steel sheet and its coating method {Preparation of the high corrosion resistant and anti-black patina chromate solution and its film on hot dip galvanized steel}

According to the present invention, the white rust generation time is secured 240 hours on the basis of SST at 50 ~ 60 ℃, which is the coated chromate drying temperature of the hot dip galvanizing facility, and has high blackening resistance even after 240 hours test in the constant temperature and humidity test at 50 ℃ and 90% H. The present invention relates to a chromate solution having corrosion resistance and high blackening resistance and a method for producing a chromate film using the same.

Hot-dip galvanized steel sheets are subjected to chromate treatment as a post-treatment in almost all products except for some coating materials. This chromate treatment is used for temporary rust prevention to prevent the occurrence of white rust occurring during the production of galvanized steel sheets and during storage in warehouses or transportation to demand. The chromate solution consists of an etching agent for promoting the reaction mainly based on the chromic acid compound supplying Cr ⁶⁺ , a reducing agent for controlling chromium hexavalent and trivalent in the solution, and an additive for improving corrosion resistance. Inadequate selection of components, inadequate addition or insufficient drying temperature could not ensure sufficient corrosion resistance.

The chromate solutions developed to date require a drying temperature of 70 ° C. or higher in order to obtain excellent corrosion resistance black wall resistance. Namely, Korean Patent Application No. 97-72740: 70 to 120 ° C. in a drying furnace,. 97-072740 (application number): drying furnace temperature 70-120 ° C, 96-039091 (application number): steel plate temperature 120-180 ° C, 97-073554 (application number): drying furnace temperature 80-180 ° C, 94- 040088 (application number): drying furnace temperature 100-200 degreeC, 93-029945 (application number): steel plate temperature 120-200 degreeC, 92-026486 (application number): drying furnace temperature 80-200 degreeC.

However, when the drying temperature is higher than a certain temperature, the manufacturing cost is increased, and if the drying temperature is not sufficiently secured, corrosion resistance and blackening resistance are lowered. Therefore, the present inventors have come to think of the development of a low temperature hardening type chromate solution having, for example, a hot-dip galvanizing facility sufficiently securing the length of a drying furnace and having a corrosion resistance blackening resistance while lowering the drying temperature to around 50 to 60 ° C. Accordingly, as a result of the research, it is possible to secure the characteristics of chromate film even at low temperature below 70 ℃, to increase the thermal efficiency on the equipment, and to prevent unevenness or unevenness of the surface due to the rolling phenomenon caused by the hot air during the formation of low temperature drying on the equipment. The invention relates to the production of chromate solution through prevention and the effect of corrosion and blackening resistance of the film according to the solution. The low temperature is added to the chromium solution containing silica and phosphoric acid to improve the corrosion resistance and blackening resistance of the chromate solution of the prior art. The main solution was prepared by adding the metal salt in the range that can show the film characteristics in the well and the concentration range of the best corrosion resistance and blackening resistance, and developed the chromate solution of the present invention in which the subsidiary solution was added. It was early. In other words, the present invention is amino silane containing 1 to 2 or more of volatile organic compounds of low boiling point in polyethylene glycol, methanol, dimethyl ketone, methylene chloride in order to lower the chromate drying temperature than the conventional solution, and acts as adhesion and curing agent A chromate solution composed of a subsidiary solution prepared by the addition of a main solution containing chromium trivalent, phosphate, silica sol, cobalt, titanium, and molybdenum, and dried at a temperature of 50 ° C. to 60 ° C. has excellent corrosion resistance and blackening resistance. It relates to a chromate solution having a chromate coating method using the same.

In order to improve the above problems, the present invention mainly uses an chromic acid compound for supplying Cr ⁶⁺ to promote the reaction, a reducing agent for controlling chromium hexavalent and trivalent in solution, and a low boiling point in addition to additives for improving corrosion resistance. And a non-corrosive organic compound to develop a high corrosion resistance and high black sintered hot dip galvanized chromate steel sheet having a beautiful surface appearance, uniformity, and excellent corrosion resistance and blackening resistance even at low drying temperatures as described above.

1 is a graph showing the results of the corrosion resistance test of the coating according to the concentration of the metal salt.

2 is a graph showing the white degree difference of the coating according to the concentration of the metal salt.

3 is a graph showing the time of occurrence of initial white rust by drying temperature.

Hereinafter, the present invention will be described in detail.

The chromate solution according to the present invention is classified into two types, a main solution and a subsidiary solution.

First, the subject solution is explained as follows.

Trivalent chromium having a total chromium concentration of 50 to 120 g / l and a Cr ³⁺ / total chromium ratio of 0.3 to 0.7, silica sol 5 to 30 g / l, and phosphoric acid 5 to 0.1-5 g / l of amino silane in main solution and polyethylene glycol containing 40 g / l, one or more of Co, Mo, and Ti added in the form of metal salt so that the total amount thereof is 0.1-1 g / l, and methanol, dimethyl It consists of a subsidiary solution containing one or two or more of ketones and methane dichloride, and the pH of the whole chromate solution is adjusted to between 1 and 5 by adding the amount of the subsidiary solution in the range of 0.1 to 7% relative to the main solution. To chromate solution. Here, in the case of the ratio of trivalent chromium to the total chromium, that is, the ratio of Cr ³⁺ / tatol Cr, the CrO ₃ powder is present in the form of Cr ⁶⁺ when hydrolyzed in water, but is an alcohol-based reducing agent. When added, a portion of the hexavalent chromium is reduced to Cr ³⁺ in the form of Cr ₂ O ₃ , in the present invention, the amount of chromium reduced to trivalent from the total amount of chromium is in the range of 30% to 70%.

In addition, the present invention is applied to the chromate solution prepared as described above on a hot-dip galvanized steel sheet 20 to 100mg / ㎡ on the basis of the dry film adhesion amount and then hot-dip galvanized characterized in that dried at a steel plate temperature of 40 ~ 120 ℃ A method for producing a chromate coating of a steel sheet. That is, the hot dip galvanized steel sheet having a coating weight of 20 to 100 g / m 2 is degreased, washed with water, dried and coated with a roll coater so that the amount of chromium deposited is about 50 mg / m 2, and then heated at 40 ° C. to 120 ° C. using hot air. Drying is performed in the temperature range of. In this case, the drying temperature may be set to 40 ° C. or higher to achieve a predetermined drying effect. However, in the case of 120 ° C., the hot air drying temperature is preferably in the range of 40 ° C. to 100 ° C., as it may cause problems in corrosion resistance.

As described above, the materials constituting the chromate solution and the reason for limiting the amount thereof are as follows.

The reason for limiting the total chromium concentration in the water-based chromate solution to 50 to 120 g / l is that when the chromium concentration is low, the chromate adhesion amount becomes smaller, and the corrosion resistance becomes worse. Since the appearance of the chromate treated film becomes poor, the total chromium concentration was limited to 50 to 120 g / L having good corrosion resistance and surface appearance.

The reason for limiting the Cr ³⁺ / total chromium ratio to 0.3 to 0.7 is that when the Cr ³⁺ / Cr ⁶⁺ ratio becomes higher than 0.7 due to the increase in the chromium trivalent concentration by adding a reducing agent, the corrosion barrier effect becomes large but the self-repair effect becomes difficult. On the contrary, if the chromium hexavalent component is less than 0.3, the corrosion resistance due to the self-healing effect is improved, but the corrosion barrier effect is decreased, and the chromium elution amount is increased, thereby deteriorating the overall rust resistance.

If the amount of phosphoric acid is insufficient, the reactivity with the surface is difficult to secure the amount of adhesion, and if the amount is increased, the blackening resistance decreases, so that the amount of phosphoric acid is limited to 5 to 40 g / l in consideration of the appropriate adhesion amount and the blackening resistance.

Silica sol plays a role of forming crosslinking during drying process and has a barrier effect against corrosion by generating zinc ions and insoluble salts by Lewis acid behavior and alcoholic behavior of Si-O and Si-OH groups. . In addition, it has hydrophobicity, which reduces the adsorption of moisture in a corrosive environment, thereby improving corrosion resistance and increasing film adhesion. Therefore, if the amount of silica sol is small, corrosion resistance and film adhesion cannot be improved. If the amount of silica sol is too high, the amount of precipitated precipitates decreases the stability of the solution. Therefore, the amount of silica sol is limited to 5 to 30 g / l in order to obtain optimal coating properties. .

When metal salts of Mo, Co, and Ti are added to a solution consisting of chromic acid-phosphate-silica sol, they are formed on the surface in the form of Co ₃ O ₄ and TiO _2, etc. It has the effect of improving black stools.

Next, the subsidiary solution in the chromate solution of the present invention will be described.

The subsidiary solution was prepared by adding amino silane containing 1 to 2 or more of volatile organic compounds having low boiling point to polyethylene glycol, methanol, dimethyl ketone, and methylene chloride, and acting as an adhesive and a curing agent. Methanol, dimethyl ketone and methyl glolide are very low volatiles with a boiling point of 50-70 ° C. and have high solubility in polyethylene glycol. Therefore, the addition of methanol, dimethyl ketone, dichloromethane, etc. to polyethylene glycol increases the composite condensation rate of the polymer even at low temperatures and has compatibility with components such as molybdenum, titanium, and cobalt to increase the reaction rate and thus have the above effects at low temperatures. The film will be formed.

In addition, it can prevent the chromate film on the surface of the steel sheet from being pushed due to the flow rate of hot air in the drying furnace during low temperature drying, and acts as a curing agent to prevent corrosion deterioration by more uniform and shrinkage or non-uniform etching. Addable aminosilane.

Hereinafter, the effects of the present invention will be described through Examples.

Example

The hot dip galvanized steel sheet having a plating deposition amount of 40 g / m 2 was degreased, washed with water and dried, coated with a chromium deposition amount of 50 mg / m 2, and then hot air dried at 60 ° C. Specimens of this hot-dip galvanized steel sheet were subjected to a salt spray test at 35 ° C and 5 wt% NaCl solution, and the rust area was visually observed to determine the initial 5% white rust development time. The blackness resistance evaluation was evaluated by measuring the white degree difference using a color difference meter after a test for 240 hours in a constant temperature and humidity test of 50 ℃, 90% H.

As shown in Table 1, after applying to the steel sheet using the chromate solution prepared from the main solution and the subsidiary solution in the conditions of the present invention, the corrosion resistance and surface appearance were examined, and the drying temperature was higher than that of the chromate-treated steel plate using only the main solution. Even if the low white rust occurred more than 240 hours was able to secure excellent corrosion resistance. In addition, it was also observed from the results of the measurement of white aberration that the blackening resistance increased when the chromate solution prepared from the present invention was applied. That is, by using a subsidiary solution made by adding a low boiling point volatile organic compound and amino silane to polyethylene glycol, it was possible to secure excellent corrosion resistance and blackening resistance even at a drying temperature of 70 ° C. or less. Looking at, the corrosion resistance by the addition of metal salts (Co, Mo, Ti) to the solution consisting of silica, phosphoric acid, chromium can be seen that the higher the concentration of the white salt occurs as the concentration of the metal salt, the high temperature (100 ℃) of Figure 2 The effect of the black side of the chromate coating itself at low temperature (50 ℃) it can be seen that the black resistance is enhanced at high temperature. In addition, it can be seen that as the concentration of the metal salt increases, blackening resistance increases. This is because black chromatic film itself affects black degeneration, so that the coating composition contains components such as Co ₃ O ₄ and TiO ₂ to prevent black stools, and the ratio of trivalent chromium (Cr) is small. Reaction is delayed and blackening resistance improves. However, when the amount of trivalent chromium is small, the corrosion resistance becomes weak (see Fig. 1). In the concentration range of 0.1 to 1.0 g / l, the difference in corrosion resistance and blackening resistance is small according to the temperature difference between the high temperature and the low temperature. The main solution was appropriate in the range of 0.1 ~ 1.0g / l as the concentration range to show the best characteristics and satisfy the corrosion resistance and blackening resistance at the same time. Therefore, Table 2 shows the characteristics evaluation of the chromate film prepared by preparing a subsidiary solution for the main solution and mixing it in the range of 1% to 10% of the main solution. The film properties were the best at 3% (subsidiary solution ratio) over the entire temperature range, and Table 1 shows the characteristics of peak metal temperature (PMT) for the solution containing 3% of the subsidiary solution to the main solution. In addition, FIG. 3 shows that the inventive solution (Solution B) for the main solution (Solution A) has improved corrosion resistance at low temperatures, and the blackness resistance also shows that the whiteness difference decreases near the low temperature. . In the case of the aminosilane in the subsidiary solution component, the curing reaction is accelerated at a lower temperature than that of the existing epoxy silane and the adhesion is increased, so that the uniformity of the chromate coating and the film phenomena due to the hot air on the equipment due to the low temperature drying. It can be seen that it contributes to the prevention and improvement of the film quality.

Table 2 shows the results of the corrosion and blackening test when the amount of the subsidiary solution was changed with respect to the main solution. As the amount of the subsidiary solution increased to 5%, the corrosion resistance and blackening resistance increased, and the time until the occurrence of 5% white rust by the SST test up to 7% was secured more than 200 hours and the blackening resistance was also very good.

When using the chromate solution prepared in the conditions of the present invention from the results of Table 1 and Table 2 above, the corrosion resistance blackening resistance is improved than when using only the main solution, and even if the drying temperature is low it can have excellent corrosion resistance blackening resistance Could know.

Table 1

TABLE 2

As can be seen from the above, when manufacturing the hot-dip galvanized steel sheet using the chromate solution according to the composition of the present invention, the white blue generation time is secured 240 hours on the basis of SST even at a drying temperature of 50 to 60 ℃, 50 ℃, 90% In the constant temperature and humidity test of H, it is possible to produce a high corrosion resistant high blackening hot-dip galvanized steel sheet having a blackening resistance even after 240 hours test can contribute a great quality improvement. In addition, by drying at a low temperature it is possible to increase the thermal efficiency can lead to a reduction in manufacturing costs due to cost reduction.

Claims (2)

The total chromium concentration in the chromate solution based on water is 50 to 120 g / l, and the trivalent ratio of Cr ³⁺ / total chromium, which is the ratio of trivalent chromium in the total chromium, is 0.3 to 0.7. Main solution and polyethylene containing 5 to 30 g / l chromium, 5 to 30 g / l phosphoric acid, 5 to 40 g / l phosphoric acid, and one or more of Co, Mo, and Ti added in the form of metal salt so that the total amount thereof is 0.1 to 1 g / l It is composed of a glycol solution, an auxiliary silane solution containing 0.1 to 5 g / l of aminosilane, and one or two or more of methanol, dimethyl ketone, and methane dichloride, the amount of which is in the range of 0.1 to 7% with respect to the main solution. Chromate solution, added at and adjusted to pH of the total chromate solution between 1 and 5. After applying the chromate solution prepared in claim 1 on a hot-dip galvanized steel sheet based on the dry film adhesion amount of 20 ~ 100mg / ㎡ and dried to a steel sheet temperature of 40 ~ 100 ℃ of the hot dip galvanized steel sheet Chromate coating method.