KR100312404B1 - Method for forming molyphosphate coating having superior coating adhesiveness and corrosion resistance on zinc coated steel sheet - Google Patents

Abstract

PURPOSE: A method for forming molyphosphate coating having superior coating adhesiveness and corrosion resistance on zinc coated steel sheet is provided. CONSTITUTION: The method is characterized in that after treating a zinc coated steel sheet with molyphosphate, the zinc coated steel sheet is washed with either a washing solution containing 3-methyl-5-pyrazoline 10-100g per 1L water at a temperature range of 25 to 70deg.C or a washing solution with a sodium molybdate concentration of 5.0 to 100g/L at a temperature range of 40 to 60deg.C at pH4-8.

Description

Method for producing molybdate film excellent in resin adhesiveness and corrosion resistance

The present invention relates to a method for producing a molybdate film having excellent resin adhesion and corrosion resistance, and more particularly, after washing with galvanized molybdate film, or washing with a solution in which 3 methyl 5 pyrazoline is added to the washing step, or the molybdate film treatment. The present invention relates to a method for producing a molten phosphate coating of a galvanized steel sheet which can improve resin adhesion and corrosion resistance by subjecting a sodium molybdate solution to an immersion treatment.

Conventionally, in order to improve the corrosion resistance of galvanized steel sheet, the conventional chromate treatment method is a well-known technique, but chromate drug itself has been attempted to develop an alternative substance by subjecting to environmental regulations as a carcinogenic substance. It is reported that the molybdate material system can replace the existing chromate treatment during this effort. It is a technical limitation that corrosion resistance is inferior to existing chromate treatment materials. Kobe, Japan, has obtained a patent on the formation of molybdate film from the results of the experiments on the addition of phosphate, sulfuric acid and acetic acid to the solution of kalium molybdate (K ₂ MoO ₄ : 10-200 g / L). It claims to expose technical limitations without mention of surface appearance (whiteness). (GB 2B 2070073) Bech-Nielsen provides Mole with applying an oxidation current of -2.5 to +5.0 V (vs SHE) at a Mo concentration of 2.9 to 9.9 g / L and a Mo / P ratio of 0.2 to 0.8. Although a patent (WO 93/10278) claims a manufacturing technique for forming a phosphate film, it is recognized that the technical limitation is that the reaction time takes more than 2 minutes. In addition, in order to use for home appliances or construction, the acrylic resin or vinyl-based resin is roll-coated to 1 ~ 2μm thickness on the morphic phosphate film, it is recognized as a technical limitation that the poor adhesion of the morphophosphate film and resin.

The present invention is to solve the above-mentioned problems, the molybdate excellent in resin adhesiveness to improve the resin adhesiveness of the molybdate film by washing with a solution in which 3 methyl 5 pyrozoline was added to the washing step after the galvanized molybdate film treatment It aims at the film manufacturing method.

In addition, an object of the present invention is to improve the corrosion resistance of the molybdate coating by shielding the function of the coating with a molybdate component by performing an immersion treatment in the sodium molybdate solution after galvanized molybdate.

In order to achieve the above object, the present invention is to find a method for improving the adhesion between the molybphosphate film and the resin bar 3 Ml 5 pyrozoline in the washing step after molybdate treatment is preferably 10 to 100g / L Invented that the resin adhesiveness is improved. Insoluble 3 methyl5 pyrozoline is an insoluble organic substance that becomes suspended in a flush solution. This material preferentially adsorbs to the molybdate film pores during the washing process, thereby lowering the activation energy of the van der Waals bond when the hydroxyl bond of the resin film and the hydroxyl group of the molybdate film are combined during the roll coating of the resin film. It is achieved by improving the adhesiveness of a film.

In another aspect, the present invention is to prepare a molybdate film of excellent corrosion resistance, characterized in that the molybdate film of the galvanized steel sheet is treated with a solution of sodium molybdate concentration of 5.0 to 100g / L, pH 4 to 8, treatment temperature of 40 to 60 ℃ It is characterized by providing a method.

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a schematic cross-sectional view of a molybdate film according to Example 1 of the present invention.

Figure 2 is a schematic cross-sectional view of the molybdate film according to Example 2 of the present invention.

Hereinafter, the present invention will be described in detail through examples.

First, the first embodiment of the present invention, in the galvanizing, molybdate film treatment and resin coating process of the continuous process, it is composed of the injection of 3 methyl 5 pyrazoline in the washing solution after the molybdate film treatment process and each The detailed technical action of the process is as follows.

The molybdate film is formed by immersing or spraying a galvanized steel sheet in a solution composed of molybdate, phosphoric acid group, sulfuric acid group and nitrate group, thereby forming a hydroxide of Mo-P-OH amorphous. This hydroxide coating improves the corrosion resistance of the galvanized steel sheet by consuming the dissolved oxygen by the effect of shielding the surface of the zinc plated steel sheet from the external corrosion factor and reducing the Mo ⁶⁺ → Mo ^{4+ in} the coating. 3 Methyl 5 pyrozoline is an additive used for the purpose of improving the corrosion resistance of lubricating agents, rust preventives, etc., and is a semi-stable substance having strong acid hydrophobicity. The resin film is an acrylic resin, which is applied to the molybdate film by a roll coating method, and the corrosion resistance and the powder resistance are improved.

Therefore, in the present invention, by applying the technical action of lowering the activation energy of the resin and hydroxyl bond by 3 methyl 5 pyrozoline to adsorb 3 methyl 5 pyrozoline to the molybdate film pores to improve the adhesion between the molybdate film and the resin Main action.

In addition, referring to Fig. 2 of the present invention, a cross-sectional schematic diagram of the phosphate film according to the second embodiment of the present invention is described. Molyphosphate coating Mo-P-OH serves to protect the zinc plated layer from corrosion factors by the corrosion barrier effect of the coating formed mainly as a coating system and the reduction reaction of Mo component to Mo ⁶⁺ ⇒ Mo ⁴⁺ . However, these coatings do not have a dense structure, and there are pores in which the zinc plating layer and the external corrosion environment are directly exposed. As the external corrosion factors (H ₂ O, O ₂ ) penetrate into the pores, oxidation of the galvanized steel sheet proceeds. In order to improve the corrosion resistance of the molybphosphate coating, it is a technical challenge to shield these pores.

In the present invention, the molybdate has developed a technology to shield the pores by immersion in Mo solution to shield the pores of molybdate. Molybdate shielding the pores is mainly in the state of Mo6 + and improves the corrosion resistance of the zinc plated steel sheet by inhibiting the penetration of external corrosion factors by the reduction reaction to Mo ^{6 +} ⇒ Mo ^{4 +} .

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

Example 1

In the present invention, a galvanized steel sheet is produced with a molybdenum concentration of 4.0 to 16 g / L, a phosphoric acid concentration of 7.0 to 14 g / L, and a nitric acid group of 8.0 to 50 g / L (55 to 60 ° C.). Was prepared as a specimen, the acrylic resin was applied to a thickness of 1 ~ 2μm by a roll coding method.

The resin adhesiveness evaluation was performed by crushing the coating film of the specimen at intervals of 1 mm, and then performing a scotch tape peeling test and immersing in the water for 30 minutes, and then performing a scotch paper peeling test. The adhesive evaluation was carried out by the following five-point method based on a conventional method.

5: good (no peeling and cracking), 4: good (within 5% peeling and cracking)

3: Normal (within 5% of peeling and cracking) 2: Deterioration (within 35% of peeling and cracking)

1: severe (35% or more peeling and cracking)

Table 1 below describes the experimental results performed in the present invention. When 3 methyl 5 pyrozoline was not added to the molybdate film as in Comparative Example 1, after washing at 25 ° C. with a washing solution, the resin adhesiveness was evaluated. As a result, primary adhesiveness 3 and secondary adhesiveness were very poor. Was evaluated. On the other hand, when 3 methyl5 pyrozoline is added to the washing solution as in Inventive Example 1, it can be seen that the primary adhesion and the secondary adhesion are improved to 5. As mentioned above, the 3methyl5-pyrazoline component is adsorbed to the pores of the molybphosphate film to reduce the activation energy between the hydroxyl group and the resin component of the molybphosphate film, thereby improving the resin adhesiveness. A schematic diagram of this consideration is shown in FIG. 1. As shown in FIG. 1, it is determined that the 3 methyl5 pyrozoline component adsorbed on the molybphosphate film increases the adhesion between the hydroxyl group and the resin of the molybphosphate film.

3 methyl 5 pyrazoline (g / L) Temperature ℃ Primary adhesion 2nd adhesion Comparative example One 0 25 3 2 Inventive Example One 10 25 4 4 2 50 25 4 5 3 100 25 5 5 Comparative example 2 120 25 5 5 3 100 20 4 3 Inventive Example 4 100 30 5 5 5 100 60 5 5 6 100 70 3 3

In the present invention, the amount of 3 methyl 5-pyrazoline added to the washing solution was limited to 10 to 100 g / L. The reason is as follows.

As shown in Inventive Example 1 to Inventive Example 3, 3-methyl 5-pyrazoline has improved adhesion when it is increased from 10 g / L to 100 g / L, and when it is increased to 120 g / L as in Comparative Example 1, it does not increase any more. Indicated. For this reason, when 100 g / L or more is added, it is judged that the adhesion is no longer improved even when the amount of 3 methyl 5 pyrozoline is increased due to saturation of the pores of the molybphosphate film. 100g / L is put.

In addition, in the present invention, the treatment temperature of the washing water was limited to 25 to 60 ℃, the reason is as follows. As shown in Comparative Example 3, when treated at a water wash temperature of 20 ° C. under 100 g / L of 3 methyl 5 pyrozoline, primary adhesion 4 and secondary adhesion 3 were evaluated. It can be seen that there is a minimum treatment temperature for the adsorption of 3 methyl5 pyrazoline. As in Inventive Example 4 and Inventive Example 5, when the temperature of the washing water is increased, the adhesion is measured as 5 or more, and when the temperature is 70 ° C. as in Inventive Example 6, the adhesion is reduced again. It is believed that dissolution occurs. Therefore, the preferable washing temperature range is 25-60 degreeC.

Example 2

The present invention provides a molten phosphate coating of a galvanized steel sheet with a molybdenum concentration of 4.0 to 16 g / L, a phosphoric acid concentration of 7.0 to 14 g / L, and a nitric acid group of 8.0 to 50 g / L (55 to 60 ° C). Was prepared as a specimen, and the experiment was performed to immerse in sodium molybdate solution to improve the corrosion resistance. Corrosion resistance was evaluated by the time required to generate 5% white rust according to ASTM-B117, and the film weight was measured by atomic absorption spectrometry.

Table 2 below shows the results of treatment for 5 seconds at a solution temperature of 40 ℃. As shown in Comparative Example 1, the adhesion amount of the specimen which was not treated with sodium molybdate was measured at 55 mg / m 2, and the corrosion resistance at this time was found to be very poor at 10 hours. As shown in Inventive Example 1, when treated at 1.0 g / L of sodium molybdate concentration, the adhesion amount was 55 mg / m ² , which was similar to that of Comparative Example 1, and the corrosion resistance was not improved to 10 hours. As shown in Inventive Example 2 to Inventive Example 5, when the sodium molybdate concentration was increased, the adhesion was increased and the corrosion resistance was also increased from 15 hours to 40 hours. When the concentration of sodium molybdate is 120 g / L as in Inventive Example 6, the adhesion amount and the corrosion resistance do not increase any more, but are saturated. The increase in the amount of adhesion is believed to be due to the generation of molybdate blocking the pores. From these results, it can be seen that an appropriate concentration range of sodium molybdate exists, and it is preferable that it is preferably 5.0 g / L to 100 g / L. Inventive Examples 7 to 10 were described according to the pH change in sodium molybdate 100g / L. pH loss was adjusted with hydrochloric acid and sodium hydrooxide. Sodium molybdate solution was not expected to improve the corrosion resistance in strong acidity (Comparative Example 2) or strong alkali solution (Comparative Example 3), rather it was shown that the corrosion resistance is reduced from 5 hours to 8 hours. This may be due to the molten phosphate coating eluting in the strongly acidic or strong alkali region. As shown in Example 7 and 8, in the neutral range pH 4.0-8.0, corrosion resistance is measured more than 38 hours, and it turns out that there exists an optimal pH condition for molybdate formation. Table 3 below describes the results of temperature change of sodium molybdate. The measurement result according to the treatment temperature in the conditions of the concentration of sodium molybdate 100g / L, pH 7.2 was described. As described in Comparative Example 4, it was found that the adhesion amount and the corrosion resistance did not improve at a low temperature of 30 ° C. or lower, and the increase in the adhesion amount and the corrosion resistance increased at 40 ° C. or higher (Invention Examples 9 to 11). It can be seen that there exists a minimum concentration range for the formation of molybdate.

Na ₂ MoO ₄ 2H ₂ O pH Amount of adhesion (mg / m ² ) Corrosion resistance (hrs) Comparative Example 1 - - 55 10 Inventive Example One 1.0 7.2 55 10 2 5.0 7.1 55 15 3 10.0 7.1 56 25 4 50 7.2 60 30 5 100 7.3 60 40 6 120 7.4 60 40 Comparative example 2 100 2.0 50 5 Inventive Example 7 100 4.0 60 40 8 100 8.0 61 38 Comparative example 3 100 10.0 51 8

Na ₂ MoO ₄ 2H ₂ O Treatment temperature ℃ Amount of adhesion (mg / m ² ) Corrosion resistance (hrs) Comparative Example 4 100 30 52 10 Inventive Example 9 100 40 60 40 10 100 50 61 40 11 100 60 58 40

As shown in the present invention, when 3 methyl 5 pyrozoline is added to the flushing water solution, it is possible to prepare a molybdate film having excellent resin adhesion, and the sodium molybdate solution concentration of the present invention is 5.0. When immersion treatment of molybdate film under conditions of ~ 100g / L, pH 4 ~ 8, treatment temperature 40 ℃ or more, processing of molybphosphate film is shielded with molybdate, which increases the adhesion amount and manufactures molybdate-treated steel sheet with excellent corrosion resistance. There is an excellent effect that can be done.

Claims (2)

After the molten phosphate (molyphosphate) coating of galvanized steel sheet 10 to 100g / L of 3 methyl 5 pyrazoline in the wash solution and washed with water at 25-70 ℃ the temperature of the wash water, characterized in that the coating also Method for preparing molybdate film. Molyphosphate coating of galvanized steel sheet and then treated with a solution of sodium molybdate concentration of 5.0-100 g / L, pH 4-8, treatment temperature 40-60 ° C. Manufacturing method.

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