JP3149761B2 - Manufacturing method of galvanized steel sheet with excellent white rust resistance - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a galvanized steel sheet having a surface capable of suppressing the generation of white rust on the surface of a galvanized steel sheet.

[0002]

2. Description of the Related Art Galvanized steel sheets have been widely used because they have been conventionally produced by electroplating or hot-dip galvanizing, and the corrosion resistance of ground iron can be largely suppressed by the sacrificial corrosion resistance of the plating film.

[0003] However, zinc-plated steel sheets generate white zinc rust during the corrosion process, and thus the appearance quality is greatly reduced.

Therefore, post-treatment for suppressing the white rust is widely performed. A typical method of this post-treatment is a chromate treatment mainly using chromic acid, dichromic acid or salts thereof.

[0005] This chromate treatment is an economical treatment method which has excellent corrosion resistance and can be performed relatively easily.

However, the chromate treatment uses hexavalent chromium, which is a pollution-controlling substance. In the treatment process, chromate salts have an adverse effect on the human body, and it is difficult to dispose of chromium sludge after wastewater treatment. In addition, there are various problems such as the possibility that hexavalent chromium may be eluted from the product after the chromate treatment. Therefore, the use control standards for chromic acids are becoming stricter, and at the same time, problems such as the management of chromate treatment plants, wastewater treatment, and secondary contamination by chromate treatment products are advancing. Measures are taken to prevent the emission of ash to the public, but these require enormous equipment and costs. In addition, when an alkaline degreasing solution is used in the degreasing step of the rust-preventive oil and the press oil of the chromate-treated steel sheet, chromium in particular is considerably eluted.

[0007] In view of the above, a number of pollution-free treatment techniques that do not rely on chromate treatment to prevent the generation of white rust on zinc-based plated steel sheets have been proposed. For example, there is a method in which a thin film is formed by a method such as immersion, coating, or electrolytic treatment using an inorganic compound, an organic compound, an organic polymer material, or a solution in which these are combined.

Specifically, (1) a method using an oxide of a polymetal such as molybdenum and tungsten (for example, JP-A-57-5875); and (2) a method using tannic acid (for example, JP-A-51-5875). −
(No. 71233) (3) A pollution-free chromate treatment method that does not contain hexavalent chromium and is composed of trivalent chromium (for example, JP-A-61-587) is known.

[0009]

However, in the above method (1), the stable region against corrosion of oxides of polymetals such as molybdenum and tungsten is narrower than that of chromium, and the same corrosion resistance as chromate is obtained. Is impossible.

In the method (2), if sufficient corrosion resistance is to be obtained, coloring by tannic acid occurs.

Furthermore, the method (3) does not fundamentally meet the need for chromium-free because soluble chromium is used.

The present invention has been made in view of such circumstances, and has a galvanized steel sheet having a chemical conversion treatment film which is safe and harmless in the manufacturing process and further in the use process, and which is excellent in white rust resistance. An object of the present invention is to provide a method for producing the same.

[0013]

According to the present invention, in order to solve the above-mentioned problems, a silicate ester and an inorganic salt of aluminum have a molar ratio of Al / (Al + Si) of 0.025 to 0.2.
75, and one or more of inorganic salts of nickel, cobalt, and magnesium
A solution containing a molar ratio of 0.01 or more to 1 and the same molar number or less as Al is applied to a zinc-plated steel sheet, and then dried by heating. An object of the present invention is to provide an excellent method for producing a galvanized steel sheet.

Further, the present invention provides that the treatment liquid contains a wet type colloidal silica in a range of 0.025 to 1.0 times the number of moles of silicate added. An object of the present invention is to provide a method for producing a zinc-coated steel sheet having excellent white rust resistance.

Further, the present invention provides a method for producing a galvanized steel sheet having excellent white rust resistance, wherein aluminum nitrate is used as an inorganic salt of aluminum.

Further, the present invention provides a method for producing a zinc-coated steel sheet having excellent white rust resistance, wherein the temperature of the heating and drying is less than 200 ° C.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described specifically.

In the present invention, a silicate ester and an inorganic salt of aluminum are contained so that the molar ratio of Al / (Al + Si) is in the range of 0.025 to 0.75. One or more inorganic salts are present in a molar ratio to Al of at least 0.01,
A solution containing the same mole number or less as 1 is applied to a steel plate on which zinc-based plating has been performed, and then heated and dried.

In the present invention, a coating excellent in corrosion resistance can be obtained by applying a solution obtained by mixing a silicate ester and an inorganic salt of aluminum. Although the reason is not necessarily clear, the use of a silicate ester forms a siloxane bond in the hydrolysis / condensation process, and the siloxane bond is formed into a thin film, which is capable of suppressing white rust. It is considered that the uniformity and the denseness of the steel are improved, and the corrosion resistance is improved.

As the inorganic salt of aluminum used here, various ones such as aluminum nitrate, aluminum chloride and aluminum sulfate can be used. Among them, aluminum nitrate is preferable. The reason may be that nitrate groups having relatively high volatility volatilize from the film in the heating step and do not adversely affect the growth of the network of the film.

As the silicate ester, Si (OC _n H)
_{2n + 1} ) A compound having a structure represented by ₄ can be used. For example, methyl silicate, ethyl silicate, n
-Butyl silicate and the like. From the viewpoint of cost, it is desirable to use relatively inexpensive ethyl silicate, but the present invention is not limited to this.

The ratio between the silicate ester and the inorganic salt of aluminum is expressed as Al / (Al + Si) in a molar ratio of 0.025.
When the molar ratio is lower than 0.025 and when the molar ratio is higher than 0.75, the corrosion resistance is greatly reduced as compared with the case where the molar ratio is within the above range. This is because it was confirmed that the rust suppressing ability was insufficient. Here, the mechanism by which the corrosion resistance is changed by Al / (Al + Si) is not clear at present, but it is considered that the mechanism depends on the film structure of the obtained Al-Si-based film.

In the present invention, in addition to the inorganic salts of silicate and aluminum, one or more of inorganic salts of nickel, cobalt, and magnesium are used in a molar ratio of 0.01 or more with respect to Al. It is contained in the solution within the same molar number or less. By adding the inorganic salt of nickel, cobalt, and magnesium, the corrosion resistance of the Al—Si-based coating in a defective portion (including both a defect generated during film formation and a relatively small defect generated during forming of a steel sheet) is reduced. It can be significantly reduced.

Here, the content is set to 0.01 or more in terms of molar ratio with respect to Al, because if it is less than this, there is almost no effect of suppressing the decrease in the corrosion resistance of the film defect portion. The reason why the number of moles is equal to or less than that of Al is that if the molar ratio is exceeded, the proportion of Al and Si in the coating decreases, and nickel, cobalt, and magnesium reduce the proportion of Al.
This is because they hinder the film-forming action of the -Si-based film, resulting in a film having a poor coverage and deteriorating the corrosion resistance.

The inorganic salts of nickel, cobalt and magnesium to be added include nitrates, sulfates and chlorides, and are not particularly limited.

Further, the colloidal silica of the wet type is used in an amount of from 0.025 to 1.25 times the number of moles of the silicate ester added.
By containing it in a range of 0 times, the corrosion resistance can be further improved. Here, if the addition amount is less than 0.025 times, the effect due to the addition of colloidal silica is hardly observed, and if it exceeds 1.0 time, the effect of suppressing white rust is not observed. This is presumably because excess colloidal silica hinders the formation of the network structure of the film. Although the mechanism of the effect is not clear at present, the colloidal silica enhances the Al-Si network structure and suppresses corrosion by forming a dense corrosion product (basic zinc chloride) during corrosion. The effect can be considered.

The organic solvent used in the above solution is not particularly limited. For example, methanol, ethanol, butanol, propanol, methylcellosolve, ethylcellosolve, ethylcellosolve, butylcellosolve, ethylene glycol, diglycol A solvent capable of dissolving a silicate ester, an aluminum salt, a nickel salt, a cobalt salt, a magnesium salt such as formaldehyde methoxyethanol can be used, and a non-polar solvent such as 1,4 dioxane can be used, such as alcohol. Can be used in combination with various polar solvents. Water can also be used in combination with alcohol and the like.

The method of applying the solution is not particularly limited, and examples thereof include a method using a roll coater, a method of dipping in a treatment liquid, and a method of spraying.

After the solution is applied as described above, it is heated and dried to form a film.
It affects the corrosion resistance of the Al-Si based coating. Even when this temperature is 200 ° C. or more, the ability to inhibit white rust is sufficiently high. However, when the heating temperature is increased to a temperature higher than this temperature, the corrosion resistance tends to decrease. Therefore, the heating temperature is preferably less than 200 ° C. The decrease in corrosion resistance when the heating temperature is increased in this way is presumed to be due to an increase in the number of pinballs caused by rapid evaporation of the organic solvent and an increase in the film peeling area in the processed part due to the hardening of the film. You. In any case, since the treatment of the present invention is a chemical conversion treatment on zinc-based plating, the upper limit of the treatment temperature is defined by the temperature at which the thermal diffusion of the zinc plating and the steel sheet as the substrate occurs rapidly, and is about 350 ° C. Is considered to be the upper limit.

Examples of the galvanized steel sheet of the present invention include a galvanized steel sheet by electroplating, a zinc-nickel alloy-coated steel sheet, a galvanized steel sheet by hot-dip coating, an alloyed galvanized steel sheet, and an aluminum-galvanized steel sheet. However, the present invention is not limited to this.

[0031]

【Example】

(First Example) Electrogalvanized steel sheet having a thickness of 0.7 mm and a coating weight of 20 g / m ² per side, and a thickness of 0.7
20g / m ² per side of electroplated zinc-nickel alloy plated steel sheet (nickel content 13%)
Plate thickness is 0.7mm and coating weight is 60g / m per side
² , hot-dip galvanized steel sheet having a thickness of 0.7 mm and a coating weight of 45 g / m ² per side of an alloyed hot-dip galvanized steel sheet having a thickness of 0.7 mm and a coating weight of 80 g per side
/ M ² of hot-dip aluminum-galvanized steel sheet (aluminum content 55%) was prepared, and an ethanol solution in which ethyl silicate, aluminum nitrate, and magnesium nitrate having the compositions shown in Table 1 were dissolved was applied thereto using a roll coater. After that, a heating drying process was performed while changing the heating temperature by a hot-air drying furnace to form films of Examples 1 to 25 and Comparative Examples 1 to 7. The heating temperature at that time is also shown in Table 1. At this time, the amount of the chemical conversion film deposited can be changed depending on the solid components of the treatment liquid or the application conditions of the roll coater. The amount of the sample prepared here is as shown in Examples 1 to 17, 20 to 25, For Examples 1 to 7, 120 mg in terms of the total amount of S, Al, and Mg
/ M ² . In Example 18, 60 mg /
m ² , and about 160 mg / m ^{2 in} Example 19. Regarding the steel sheet, among the above-mentioned steel sheets, Examples 1 to 19 and all the comparative examples were electrogalvanized steel sheets, Examples 20 to 22.
Is a hot-dip galvanized steel sheet, Example 23 was an electrogalvanized nickel-plated steel sheet, Example 24 was a hot-dip aluminum-galvanized steel sheet, and Example 25 was a galvannealed steel sheet.

Of the above steel sheets, Examples 23 to 25 used galvanized steel sheets, and others used electrogalvanized steel sheets.

The samples were subjected to a salt spray test (JIS-Z-2371), and the area ratio of white rust occurrence after 48 hours and 72 hours was examined, whereby the white rust resistance was evaluated. Further, in order to evaluate the corrosion resistance of the cut portion, the surface of the sample after the chemical conversion treatment was scratched to reach the base iron with a cutter knife, and the degree of white rust generation after 24 hours of the salt spray test was examined. Table 1 shows the results.

The white rust resistance in Table 1 was evaluated according to the following criteria.

White rust generation area rate Evaluation point 0 to 5% ◎ 5 to 25% ○ 25 to 50% △ 50 to 80% × 80 to 100% XX Further, the corrosion resistance of the cut portion was evaluated according to the following criteria. .

Evaluation of rust on cut part Evaluation point No white rust occurred ◎ Part of cut part ○ White rust generation Part of cut part △ White rust started to flow △ Part of cut part occurred × white A large amount of rust flows As shown in Table 1, Examples 1-2 which are within the scope of the present invention
No. 5 was confirmed to have both good white rust resistance and excellent corrosion resistance at the cut portion. Among the comparative examples, those in which either ethyl silicate or aluminum nitrate is low have poor white rust resistance, and those in which magnesium nitrate is not contained even in an appropriate range or in which the amount is low are white rust resistance. Even if the properties were good, the corrosion resistance of the cut portion was poor. Further, those containing too much magnesium nitrate were inferior in both white rust resistance and corrosion resistance of cut portions.

[0037]

[Table 1]

(Second embodiment) Ethyl silicate, aluminum nitrate and magnesium nitrate were fixed on an electrogalvanized steel sheet having a thickness of 0.7 mm and a coating weight of 20 g / m ² per side, as shown in Table 2. Contained in proportions
After applying a solution using various solvents shown in Table 2 by a roll coater as a solvent, a heating drying process was performed by changing a heating temperature in a hot air drying furnace, and Examples 26 to 3 were applied.
5 was formed. The heating temperature at that time is also shown in Table 2. In the chemical conversion treatment of the sample prepared here, the adhesion amount of the film was 120 mg / in terms of the total amount of Si, Al, and Mg.
m ² .

The samples were subjected to a salt spray test (JIS-Z-2371) in the same manner as in the first embodiment, and the area ratio of white rust generation after 48 hours and 72 hours was examined. Was evaluated. Further, the corrosion resistance of the cut portion was also evaluated in the same manner as in the first example. Table 2 shows the results. The evaluation criteria were the same as in the first embodiment.

As shown in Table 2, it was confirmed that, within the range of the present invention, good corrosion resistance was exhibited in both the sound part and the cut part of the chemical conversion film without being largely affected by the type of the solvent.

[0041]

[Table 2]

Example 3 Ethyl silicate and inorganic salts of aluminum were used as examples 36 to 45 on electrogalvanized steel sheets having a thickness of 0.7 mm and a coating weight of 20 g / m ² per side. The solution was dissolved within the scope of the invention, and a solution in which any of magnesium, nickel and cobalt inorganic salts were dissolved was applied by a roll coater, and then dried at 150 ° C. in a hot air drying furnace to form a film. For comparison, Comparative Example 8 using Al acetylacetonate as the Al source, Comparative Example 9 adding manganese nitrate, Comparative Example 10 adding zinc nitrate, Comparative Examples 11 and 12 using lithium silicate as the Si source. A film was formed in the same manner as in Comparative Example 13 using sodium silicate. The amount of the film deposited in the chemical conversion treatment of the sample prepared here was about 120 mg / m ² in terms of the total amount of Si, Al, Mg and the like.

A salt spray test (JIS-Z-2371) was performed on these samples in the same manner as in the first example, and the area ratio of white rust generation after 48 hours and 72 hours was examined. Was evaluated. Further, the corrosion resistance of the cut portion was also evaluated in the same manner as in the first example. Table 3 shows the results. The evaluation criteria were the same as in the first embodiment.

As shown in Table 3, in Examples 37 to 45, which are within the scope of the present invention, good corrosion resistance was obtained in both the sound part and the cut part of the chemical conversion coating, but aluminum was used instead of the inorganic salt of aluminum. In the case of using an organic salt of the above, and in the case of using lithium silicate or sodium silicate instead of the silicate ester, almost no white rust suppressing ability was obtained, and white rust was generated on the entire surface of the steel sheet. In addition, when the inorganic salts of manganese and zinc were used instead of the inorganic salts of magnesium, nickel, and cobalt, the corrosion resistance of the cut portion (defect portion) was not obtained.

[Table 3]

(Fourth Embodiment) Ethyl silicate, aluminum nitrate, magnesium nitrate and colloidal silica were prepared on electrogalvanized steel sheets having a thickness of 0.7 mm and a coating weight of 20 g / m ² per side as Examples 46 to 58. Was applied by a roll coater, and then heated and dried at 100 ° C. in a hot-air drying furnace to form a film. The amount of the film deposited in the chemical conversion treatment of the sample prepared here was about 100 mg / m ² in terms of the total amount of Si and Al.

The samples were subjected to a salt spray test (JIS-Z-2371) in the same manner as in the first example, and the area ratio of white rust generation after 48 hours and 72 hours was examined. Was evaluated. Further, the corrosion resistance of the cut portion was also evaluated in the same manner as in the first example. Table 4 shows the results.
The evaluation criteria were the same as in the first embodiment.

As shown in Table 4, it was confirmed that the addition of colloidal silica within the range of the present invention stably exhibited good white rust even in the salt spray test for 72 hours.

[0048]

[Table 4]

[0049]

As described above, according to the present invention, a silicate ester and an inorganic salt of aluminum are contained in a certain range, and one or more of inorganic salts of magnesium, nickel and cobalt are contained. Is applied to a galvanized steel sheet, and then heated and dried to obtain a galvanized steel sheet with excellent white rust resistance in sound portions and defective portions of the film. The chemical conversion coating thus formed has an industrially significant effect that is industrially safe and pollution-free.

──────────────────────────────────────────────────続 き Continuation of front page (56) References JP-A-9-118989 (JP, A) JP-A-59-177377 (JP, A) JP-A-53-102934 (JP, A) JP-A-59-177934 35682 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) C23C 22/00-22/86 C23C 2/06 C23C 2/26 C25D 5/48

Claims (4)

(57) [Claims] 1. A method in which a silicate ester and an inorganic salt of aluminum are used in a molar ratio of Al / (Al + Si) of 0.025 to 0.2.
75, and one or more of inorganic salts of nickel, cobalt, and magnesium
A solution containing a molar ratio of 0.01 or more to 1 and the same molar number or less as Al is applied to a zinc-plated steel sheet, and then dried by heating. An excellent method for producing galvanized steel sheets. 2. The treatment liquid contains a colloidal silica of a wet type in an amount of 0.02 with respect to the number of moles of silicate added.
The method for producing a galvanized steel sheet having excellent white rust resistance according to claim 1, wherein the zinc-containing steel sheet is contained in a range of 5 to 1.0 times. 3. The method for producing a galvanized steel sheet having excellent white rust resistance according to claim 1, wherein aluminum nitrate is used as the inorganic salt of aluminum. 4. The method for producing a galvanized steel sheet having excellent white rust resistance according to claim 1, wherein the temperature of the heating and drying is lower than 200 ° C.