KR20030056671A - Alternatives for conversion coating solution and it's film for hot dip galvanized steel sheet has a good apperance and anti-corrosion - Google Patents

Abstract

The present invention relates to a galvanized steel sheet using a chromate replacement treatment solution for chromium-free hot dip galvanized steel sheet excellent in corrosion resistance even if the chromate treatment is omitted on the surface of the hot-dip galvanized steel sheet and a method of manufacturing the same. That is, the present invention relates to the production of a solution for a surface-treated steel sheet having a corrosion resistance after applying the present invention to a hot-dip galvanized steel sheet by a roll coating (Roll Coating), the reactivity is excellent in the pH range of 0.5 to 2.5 and low temperature and solution stability It is excellent and provides a film formed after the reaction with the galvanized layer has a good corrosion resistance and beautiful appearance steel sheet manufacturing method.

Description

Galvanized steel sheet using chromate alternative treatment solution for hot-dip galvanized steel sheet with excellent surface appearance and corrosion resistance and its manufacturing method {Alternatives for conversion coating solution and it's film for hot dip galvanized steel sheet has a good apperance and anti-corrosion}

The present invention relates to a galvanized steel sheet using a chromate replacement treatment solution for chromium-free hot-dip galvanized steel sheet excellent in corrosion resistance even if the chromate treatment is omitted on the surface of the hot-dip galvanized steel sheet and a manufacturing method thereof. That is, the present invention provides a surface-treated steel sheet having a corrosion resistance after applying the present invention to a hot-dip galvanized steel sheet by a roll coating (Roll Coating), and has a low pH as well as excellent reactivity in the range of pH 0.5 ~ 2.5 and solution stability The steel sheet and its manufacturing method are characterized by excellent corrosion resistance and excellent surface appearance of the film formed after the reaction with the zinc plated layer.

The demand for hot-dip galvanized steel is increasing for building materials and home appliances, and in developed countries for automobiles. Domestic and foreign cold-rolled product producers and other steel-based SMEs that produce this hot-dip galvanized steel sheet produce products by chemical treatment such as chromate treatment and phosphate treatment as final post-treatment. Double chromate coating is an inexpensive treatment that gives galvanized steel a good coating adhesion and corrosion resistance.

However, since chromium is a representative pollutant and causes serious damage to workers and the environment, regulatory laws have been enacted and are expected to be implemented in developed countries. In addition, in the case of chromate-treated steel sheets, hexavalent chromium (Cr ⁺⁶ ) is generated as wastewater in the process, and thus, wastewater treatment is costly and time-consuming, and its use will soon be banned in accordance with international chrome usage regulations. As it is known, research on chromate has not been carried out until now, and researches to develop materials to replace chromium are being actively conducted worldwide.

To date, research has been conducted to reduce chromium hexavalent and to develop 100% chromium trivalent solution since hexavalent chromium is more toxic than trivalent chromium, but this is basically to remove chromium. Also, 100% chromium trivalent solution did not have the advantage of replacing the existing chromate solution in terms of corrosion resistance and price. Therefore, research has already begun to replace chromium fundamentally, and new types of chemicals composed of Mo, W, Ti, Zr, Co, Ce, etc. based on inorganic elements as chromium substitutes are currently non-toxic. It is being studied as a substitute. And recently, according to US Pat. No. 5,607,521, a new molybdate process was developed to replace chromium for the treatment of galvanized steel sheets. The so-called "Molyphos" uses molybdate and orthophosphoric acid. Molyphos 33 and 66, which have a molar ratio of Mo / P of 0.33 and 0.66, are immersed at 60 ° C for 2 minutes.

However, the corrosion resistance of Molyphos passivated galvanized steel sheet has the same characteristics as the existing chromate solution in low PH and outdoor exposure test, but the corrosion resistance is poorly observed in salt spray test. The disadvantage is that it is usually more than seven times more expensive. In addition, many research institutes are working to develop chromium substitutes using molybdate.

On the other hand, according to a recent research paper, there is an attempt to convert the steel sheet using organic materials other than inorganic materials, and as organic materials, alkoxysilane has recently emerged as a substitute for chromate and phosphate.

Alkoxysilane is represented by the chemical formula of Y-Si (OR), and Y is an organofunctional group such as vinyl, amino, epoxy, mercapto. Penetrates into the paint resin and increases adhesion. OR is an alkoxy group such as -OCH ₃ , -OC ₂ H ₅ and water-soluble SiOH has a chemical bond in the metal layer. Alkoxysilane has an excellent effect on increasing the corrosion resistance and coating adhesion of the film, but is limited in industrial use because the price is several ten times higher than chromate treatment. In addition, because of low productivity, it is difficult to realize in the near future. In addition, many materials are currently being studied as candidates for chromium replacement, but the results are extremely limited.

According to US Pat. No. 5,693,153, a method of imparting corrosion resistance as a method of immersing by adding 1% LINO ₃ , 10% Al (NO ₃ ) ₃ and 10% aluminum silicate to boiling water as a chromium replacement solution, However, this process requires a high temperature of the solution and a long treatment time is not applicable to the continuous hot dip galvanizing line.

Thus, while a cheaper price as chromium (Cr), common and low coating weight (100mg / m ² or less) is also in corrosion resistance, but alternative materials development are actively conducted with good effect, but the chrome coating weight 100mg / m ² similar to the chromium Galvanized steel sheet applying a material having as much corrosion resistance has not been developed yet. Recently, however, new products have been developed that do not use chromium in a relatively high amount as a mixture with organic substances.

Therefore, the present inventors have conducted a lot of research and experiments to solve the above-mentioned problems, thereby suggesting the present invention. That is, the organic resin-based material was used to coat the hot-dip galvanized steel sheet in the low deposition amount (about 100 mg / m ² ) with only the inorganic material to secure corrosion resistance. In addition, for good applicability to the field line, it is a water soluble solution that is well soluble in water, and has a liquid stability, and in order to save energy, the solution itself is coated at room temperature and dried at about PMT 80 ° C. to form a film. . The existing chromium process has a coating process while maintaining the solution temperature around 40 ~ 50 ℃, but there is a problem in roll, storage tank, and process due to sediment, so the solution development is in progress to improve it. It was.

That is, in order to achieve the above object, the present invention is to apply the present invention to the hot-dip galvanized steel sheet by a roll coating (Roll Coating) to produce a surface-treated steel sheet having a corrosion resistance PH 0.5 ~ 2.5 range and low temperature Zinc-coated steel sheet coated with hot-dip galvanized steel, which has excellent reactivity and excellent solution stability and has excellent corrosion resistance and beautiful surface and appearance of the film formed after reaction with zinc plated layer. The purpose is to provide.

1 is a schematic diagram showing a cross section of a hot-dip galvanized steel film having excellent corrosion resistance according to the present invention.

Figure 2 schematically shows the results of testing the solubility of the phosphate-based material to confirm the stability of the chromium-free aqueous solution of the present invention.

Figure 3 is a diagram showing the initial white rust generated time by embodiment number as an embodiment of the present invention.

Figure 4 shows the effect of improving the corrosion resistance according to the addition of molybdenum to the present invention in the area of white rust generated by the salt spray time (%).

That is, the present invention is characterized in that it has an excellent reactivity with zinc at low temperatures when the steel sheet is produced by treating the material of the present invention on a galvanized steel sheet and as a material for improving the corrosion resistance of aluminum, phosphate, molybdenum It is an acid solution in the range of 0.5 ~ 2.5 pH, made by mixing 1 or 2 or more kinds, and the surface of hot-dip galvanized steel sheet with chromium substitute solution whose concentration range is 0.05mg / l ~ 0.2mg / l.

In addition, as a subsidiary additive to be used in this solution, a silicon compound, i.e., one or more of two kinds of silicate-based tetraethylsilicate, polydimethylsiloxane, having a concentration range of 0.02 vol% to 0.10 vol% is used. . In addition, as a liquid stabilizer for the hydrolysis, one or more of three kinds of methanol, isopropyl alcohol (isoprophylalchol), and glycoethylene (glycolethylene) is used, and the concentration range is 0.01 vol% to 0.15 vol%. A hot-dip galvanized steel sheet having excellent surface appearance is produced.

Here, as a result of the study of the present inventors, when the concentration of the acidic solution according to the present invention is below pH 0.5, the components of the substance do not exhibit the characteristics, and if the pH is above 2.5, the target amount of adhesion exceeds 100 mg / m 2, and the solution Precipitation not only occurs in terms of stability, but also the reactivity with zinc, in particular, because of the above reasons, it was found that it should be treated with an acid solution in the range of pH 0.5 ~ 2.5 excellent in reactivity with zinc even at room temperature. The solution concentration range in this case is 0.05 mg / L-0.2 mg / L.

Example

Hereinafter, the configuration of the present invention will be described in more detail with reference to the embodiment of the present invention.

The present invention, as described above, to prepare a solution having excellent corrosion resistance even at low temperature reactivity with the film stability and low-temperature reactivity with the galvanized steel sheet and low adhesion, and to produce a galvanized steel sheet using the solution as follows Substances and submaterials are divided into four categories.

As the transition metal material used, molybdenum, alumina, and tetraethyllysilicate, polydimethylsiloxane, which are silicate-based silica compounds, were used.

Table 1 Properties of chromium-free solution (Examples 1 to 4)

Table 2 Chemical Composition of Cr-free Solution

Table 3 Initial white rust outbreak time

In the case of aluminum film, corrosion resistance is about 1/4 of that of chromium, but it can be used as a corrosion inhibitor. Molybdenum (molybdenum) was confirmed to have a corrosion resistance of about 1/5 compared to chromium by the addition of silicate, and the adhesion amount is increased by the addition of PDMS (Polydimethylsiloxane), which is a polymer material, and the corrosion resistance is improved by more than two times. In the case of molybdenum compounds, sodium molybdenum (Ammonium Molybdenum) was better on the zinc surface of the plating layer than sodium molybdenum, but sodium molybdenum (Sodium Molybdenum) in terms of solution stability was found to be better. .

Based on the above four examples, in order to improve physical properties through the synthesis of inert materials composed of transition metal materials and oxo-anions, metal phosphates, ie, phosphate-based materials, were synthesized. In terms of solution safety, the solution was mixed at a ratio of about 9: 1 to the wash water, and the solubility in the aqueous solution after stirring was summarized in Table 4 below.

Table 4 Chrome Free Aqueous Stability

The phosphate-based material was excellent in solution stability of potassium phosphate and sodium phosphate, and a potassium phosphate material having a pH of 4.67 was selected and mixed with borate and alumina molybdenum in a binary system to conduct a hydrolysis reaction experiment. The result was mixed with the transition metal as shown in FIG. 2 to show the state.

Based on the above experiment, the complex solution is summarized in Table 5 below.

Table 5 Properties of chromium replacement solution (Examples 5-9)

Example 9 For the comparative experiments, 5 vol% of chromium was added for comparative experiments, and the effects were compared.

In comparison with Example 9, in which the inorganic metal material molybdenum and alumina and anionic inert material silicate and phosphate were mixed, the Example 9 having about 5% chromium was added in the corrosion resistance. Best. The corrosion resistance of the solution of Example 8, which contains no chromium at all, can be judged to have excellent corrosion resistance even with a deposition amount of about 1/3 that of chromium. As a result of analysis of the surface of the galvanized steel sheet treated with the solution of Example 9 which had the best corrosion resistance by EDS, Cr or Si was almost 1% or less on the surface, and it could not play a role as a film. It is presumed that corrosion protection was achieved by the formation of passivation film by proper synthesis of transition metal and Oxo-anion inert material by peroxide and PO ₄ .

Table 6 Composition of chemical components (wt%) of chromium substitute solution treated film

In order to examine the effect on the corrosion characteristics of aluminum, which is presumed to play a major role, a solution by concentration was prepared and summarized in Table 7 below.

Table 7 Characteristics of chromium replacement solution (Examples 10 to 13)

Four solutions were treated by Roll Coating from Example 10 to Example 13 while gradually increasing the alumina concentration, and then dried at a drying temperature of PMT 80 ° C. Looking at the state of the solution was generally excellent in solution stability, but as shown in Example 10 it can be seen that the precipitation occurs when the alumina and phosphate ratio is approximately 1: 1.

In addition, after performing the salt spray test to observe the effect of the increase and decrease of the alumina component, the degree of corrosion of the surface was observed for 48 hours 72 hours 120 hours, respectively, and the surface state is shown in Table 8.

Table 8 White-blue Generation Areas of Examples 10 to 13 According to the Concentration of Aluminate (Al (NO ₃ ) ₃ 9H ₂ O)

As shown in Table 8, as the Al content is increased, the corrosion resistance is improved, and it can be seen that the hydrolyzed Al component reacts with the zinc layer to form a film to serve as a corrosion inhibitor.

Therefore, the salt spray test was carried out with the solution of Example 13 in the four solutions of Table 7 above, and molybdenum was added to 0.05 in a solution having a 0 to 10% area of corrosion after 48 hours after the initial start of corrosion. The effect on the corrosion behavior was examined as Example 14 with the addition of g / ml. The properties of the resulting solution were as shown in Table 9, the corrosion resistance test results were as shown in FIG.

Table 9 Characteristics of chromium substitute solution with molybdenum

Table 10 Properties of Nickel-Added Chromium Substitutes

Table 11 Change in chromaticity of the surface of the film

Table 12 Initial white rust occurrence time

That is, it was found by the above experiment that the case of adding the ammonium molybdenum in Example 11 showed the best characteristics. Particularly, molybdenum was added to the chromium replacement solution, which maintains a stable (no sedimentation) state of aluminum 0.2g / ml, phosphate 0.05g / ml, silicate 0.05vol%, MeOH 0.05vol%, and PH 0.51. The 14 solution had a whiteness of 74.45 and a yellowness of 1.23, showing the best corrosion resistance effect. This is shown in Figure 4 compared with Example 11.

In addition, a solution in which ammonium nickel was added as a chromium substitute was prepared as in Examples 15 to 18, and the solution color, stability, pH, film surface appearance, and salt spray were added according to the Ni addition amount (g / ml). The initial white rust occurred according to the test was tested and observed, and the results are shown in Tables 10 to 12, respectively.

However, the solution in which ammonium nickel was added as a chromium substitute was more stable than the case in which ammonium molybdenum (Mo) was added.

Looking at the graph as described above, the solution from Example 8 to 14 exhibited excellent corrosion resistance even at a somewhat lower adhesion amount than chromium, and in particular, a mixed solution of aluminate and molybdenum to which silicate-based materials were added as in Example 14 This was found to be the best.

As described above, the surface of the galvanized steel sheet according to the present invention is subjected to a thin film coating treatment of about 100 [mg / m ² ], and then manufactured using the solution of the present invention to produce a steel sheet having excellent surface appearance and excellent corrosion resistance. Could. In addition, due to the excellent reactivity at the zinc surface and low temperature, it is possible to produce steel sheet with excellent corrosion resistance by excellent roll-off and drying, and excellent operation efficiency in the field line. The steel sheet manufacturing method of the present invention using the solution prepared to be formed was found to have excellent applicability to the field line of the continuous process.

Claims (3)

In the manufacturing method of chromium-free zinc plated steel sheet having excellent corrosion resistance even if the chromate treatment is omitted on the galvanized steel sheet, the zinc and the steel sheet have excellent reactivity and beautiful appearance even at normal low temperature working temperature. Chromium-free solution (Cr-free soiution), which is an acid solution in the range of 0.5 to 2.5 pH, made of a mixture of two or more kinds of aluminum, phosphate, and molybdenum, and the concentration range is 0.05 mg / l to 0.2 mg / l. Method for producing a hot-dip galvanized steel sheet, characterized in that to form a film having excellent corrosion resistance and beautiful appearance by the reaction between the steel plate and the zinc plated layer using. The method of claim 1, wherein the chromium free solution is a silicate-based tetrasilicate (tetraethylsilicate), polydimethylsiloxane, as a subsidiary additive, and has a concentration range of 0.02 vol% to 0.10 vol%. The concentration range is 0.01 vol% ~ by using at least one of methanol, isopropyl alcohol, and glycol ethylene as a liquid-stable substance for hydrolyzing the solution. Method for producing a hot-dip galvanized steel sheet characterized in that the plating using a solution to be 0.15vol%. A hot-dip galvanized steel sheet, which is produced by the method for producing a hot-dip galvanized steel sheet according to claim 1 and 2.