JP3149770B2 - Manufacturing method of galvanized steel sheet with excellent white rust resistance - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to the production of a zinc-coated steel sheet which forms a coating on the surface of a zinc-based coating capable of greatly suppressing the generation of white rust, and hexavalent chromium is contained in the coating and in a treatment solution thereof. The present invention relates to a method for producing a galvanized steel sheet having no white rust and excellent in white rust resistance.

[0002]

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

[0003] However, zinc-coated galvanized steel sheet is corroded in the course of its use, resulting in white zinc rust, which greatly reduces the appearance quality. In order to suppress this white rust, various post-treatments are widely performed after zinc-based plating.
As a typical method of the post-treatment, there is a chromate treatment method in which chromic acid or a salt thereof is a main component and various other additives are added. This chromate treatment is an economical treatment which has excellent corrosion resistance and can be performed relatively easily.

[0004]

However, the chromate treatment uses highly toxic hexavalent chromium. In the treatment process, there are problems such as the adverse effect of chromate on the human body and the disposal of chromium sludge after wastewater treatment. In addition, there are various problems such as elution of hexavalent chromium from the product after the chromate treatment.

[0005] In view of the above, in order to prevent the generation of white rust on galvanized steel sheets, a number of pollution-free treatment techniques that do not rely on chromate treatment have been proposed.

For example, there is a method in which a thin film is formed by immersion, coating, electrolytic treatment, or the like using an inorganic compound, an organic compound, an organic polymer, or a solution in which these are combined. Specifically, the following techniques have been proposed.

(1) A method using a polymetal oxide such as molybdenum and tungsten (for example, Japanese Patent Application Laid-Open No. 57-587)
No. 5) (2) A method using tannic acid (see, for example,
(3) A pollution-free chromate treatment method using a treatment solution containing trivalent chromium and containing no hexavalent chromium (for example, JP-A-61-587). According to the method, the stable area against corrosion of polymetal oxides such as molybdenum and tungsten is narrower than that of chromium, and it is impossible to obtain the same corrosion resistance as chromate.

In the method (2), there is a problem that coloring by tannic acid occurs when sufficient corrosion resistance is to be obtained.

Furthermore, in the method (3), the treatment time (reaction time) needs to be relatively long, and its corrosion resistance is not sufficiently high.

The present invention has been made in view of such circumstances, and forms a safe and harmless chemical conversion coating film on a zinc-based plating in a manufacturing process and a use process, thereby having excellent white rust resistance. An object of the present invention is to provide a method capable of manufacturing a zinc-based plated steel sheet.

[0011]

According to the present invention, in order to solve the above-mentioned problems, first, a silicate ester and an aluminum inorganic salt are used in an Al / (Al + Si) molar ratio of 0.0
A solution containing 15 to 0.75 or less, and further containing a trivalent chromium compound in the range of 0.1 to 3 times the total number of moles of aluminum and silicate as the number of moles of chromium metal. After coating on a steel plate on which zinc-based plating is formed, it is heated and dried, and the adhesion amount is (Al + Si +
A method for producing a galvanized steel sheet having excellent white rust resistance, characterized by forming a coating of 50 mg / m ² or more in terms of Cr) metal.

Second, in the above method, the treatment liquid contains the wet-type colloidal silica in an amount of 0.025 to 1.0 times the number of moles of the silicate ester added. Provided is a method for producing a zinc-coated steel sheet having excellent white rust resistance.

Thirdly, there is provided a method for producing a galvanized steel sheet having excellent white rust resistance according to any one of the above methods, wherein aluminum nitrate is used as an aluminum inorganic salt.

Fourthly, there is provided a method for producing a galvanized steel sheet excellent in white rust resistance, wherein the heating and drying temperature is less than 200 ° C. in any of the above methods.

[0015]

DETAILED DESCRIPTION OF THE INVENTION As described above, in the present invention, a solution containing a silicate ester, an inorganic salt of aluminum, and a trivalent chromium compound is applied to a steel sheet on which zinc-based plating has been formed, so that corrosion resistance is reduced. An excellent film can be formed. Although the reason is not necessarily clear, it is considered that silicic acid, aluminum oxide, and chromium oxide form a network structure, form a dense composite oxide thin film, and obtain the ability to suppress white rust.

As the aluminum inorganic salt, aluminum nitrate, aluminum chloride, aluminum sulfate and the like can be used. Among them, aluminum nitrate is preferable. The reason is not always clear at the moment,
It is conceivable that nitrate promotes the formation of the network structure of the film or does not hinder the formation of such a network structure.

As the silicate ester, for example, methyl silicate, ethyl silicate and n-butyl silicate can be used. From the viewpoint of cost, it is preferable to use inexpensive ethyl silicate,
There is no particular limitation.

Examples of the trivalent chromium compound include, but are not limited to, chromium nitrate, chromium chloride, chromium sulfate, chromium acetate, and the like.

The ratio between the silicate ester and the aluminum inorganic salt is in the range of 0.015 or more and 0.75 or less in Al / (Al + Si) molar ratio. This is because this value is 0.01
If it is less than 5, the corrosion resistance is greatly reduced, and a problem occurs in the white rust suppressing ability. If it exceeds 0.75, the white rust suppressing ability is similarly insufficient. Here, Al
It is considered that the reason why the corrosion resistance changes depending on the / (Al + Si) molar ratio is that the corrosion resistance depends on the denseness of the obtained film structure.

The trivalent chromium compound (trivalent chromium ion) is contained in a range of 0.1 to 3 times as the number of moles of chromium metal relative to the total number of moles of aluminum and silicate ester. This is because if the content is less than 0.1 times, the effect of adding the chromium compound is hardly observed, and if it is more than 3 times, the effect of suppressing white rust is not observed. This is presumed to be because chromium ions inhibit the growth of a dense Al-Si network structure and cause film defects. Also, the mechanism by which the effect is exhibited by the addition of the trivalent chromium compound is not always clear at present, but inactivation of the plating surface by the chromium compound,
It is considered that the chromium oxide enhances the Al-Si network structure.

The corrosion resistance can be further improved by adding the wet type colloidal silica in the range of 0.025 to 1.0 times the number of moles of the silicate ester added. Here, this addition amount is 0.02
If it is less than 5 times, the effect of the addition of colloidal silica is hardly recognized, while if it exceeds 1.0 times, the effect of suppressing white rust is not exhibited. This is presumably because excess colloidal silica hinders the formation of the network structure of the film. Although the reason why the corrosion resistance is improved by the addition of colloidal silica has not been elucidated at present, the colloidal silica enhances the Al-Si network structure and the formation of a dense corrosion product (basic zinc chloride) during corrosion. The corrosion suppression effect by formation is considered.

The colloidal silica is preferably an organosilica sol in which the dispersion medium is an organic solvent (for example, an organosilica sol IPA-ST manufactured by Nissan Chemical Co., Ltd.), but an aqueous silica sol may be used and is not particularly limited.

The organic solvent used to form the solution is not particularly limited, but for example, methanol, ethanol,
Butanol, propanol, methyl cellosolve, ethyl cellosolve, butyl cellosolve, ethylene glycol,
Organic solvents capable of dissolving silicates, aluminum salts, and chromium compounds, such as diformaldehyde methoxyethanol, can be used, and non-polar solutions such as 1,4 dioxane can be used in combination with polar solvents such as alcohol. Can be used. Water can also be used in combination with alcohol or the like.

As a method for applying the above-mentioned solution containing a silicate ester, an inorganic salt of aluminum and a trivalent chromium compound to a plated steel sheet, a method using a roll coater, a method for applying a plated steel sheet to a solution or a solution for a plated steel sheet. After spraying, a method of removing excess solution by a roll can be applied.

After the solution is applied in this manner, heating and drying are performed, and the temperature at that time is preferably lower than 200 ° C. Although it has the ability to suppress white rust even at a temperature of 200 ° C. or higher, the corrosion resistance of the Al—Si coating tends to decrease when heated to a temperature higher than this temperature. It is presumed that the decrease in the corrosion resistance when the heating temperature is increased is due to an increase in the number of pinholes caused by rapid evaporation of the organic solvent and an increase in the peeled area of the film in the processed portion due to the hardening of the film. The heating and drying temperature is not problematic as long as the solvent used can be volatilized, and the lower limit is determined by the volatility of the solvent.

Since the film forming treatment of the present invention is a chemical conversion treatment on galvanization, the treatment temperature must be a temperature at which thermal diffusion of the galvanization and the steel sheet as the substrate does not occur rapidly. It is believed that about 350 ° C. is a practical upper limit.

The adhesion amount of the film formed after heating and drying is as follows:
(Al + Si + Cr) 50 mg / m ² or more in terms of metal. This is because if it is less than 50 mg / m ² , the corrosion resistance is insufficient. Although there is no particular upper limit on the amount of coating,
Adhesion amount is too flexible to deteriorate much, since cracks and peeling are likely to occur, the film thickness of approximately 1.0 g / m ² approximately less is preferable that the 1.0 .mu.m.

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

The steel sheet of the present invention also has excellent anti-fingerprint properties, and is very advantageous for use in parts where dirt due to fingerprint attachment is avoided.

[0030]

【Example】

(1st Example) Adhesion amount of 0.7 mm plate thickness 20 per side
g / m ² electrogalvanized steel sheet, 0.7 mm thick coated surface 20 g / m ² per galvanized nickel-nickel alloy coated steel sheet (13% nickel content), 0.7 mm thick coated surface 60g / m ² hot-dip galvanized steel sheet,
Alloyed hot-dip galvanized steel sheet with a coating thickness of 0.7 mm per side of 45 g / m ² per side, hot-dip aluminum-zinc alloy coated steel sheet with a coating thickness of 0.7 g per side of 80 g / m ² (aluminum content 55% ) Was prepared, a silicate ester, an aluminum salt and a chromium (III) salt shown in Table 1 were dissolved in a composition shown in Table 2 and a methyl cellosolve solution was applied by a roll coater, and then the heating temperature was changed by a hot air drying oven. To form a film of Examples 1 to 30 and Comparative Examples 1 to 7. The heating temperature at that time is also shown in Table 2. At this time, the amount of the chemical conversion film deposited can be changed depending on the amount of the solid component in the treatment liquid or the application conditions such as a roll coater.

Regarding the steel sheets, of the above steel sheets, Examples 1 to 24, Comparative Examples 1 to 7 are electrogalvanized steel sheets, Examples 25 to 27 are hot-dip galvanized steel sheets, and Example 28 is electrogalvanized-nickel alloy plating. A steel sheet, Example 29 used a hot-dip aluminum-galvanized steel sheet, and Example 30 used an alloyed hot-dip galvanized steel sheet.

These samples were subjected to a salt spray test (JIS-Z-2371), and the area ratio of white rust occurrence after 48 hours, 72 hours, and 96 hours was examined, thereby evaluating the white rust resistance. Table 2 shows the results.

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

Evaluation of white rust generation area ratio 0 to less than 5% ◎ less than 5 to 25% ○ 25 to less than 50% △ 50 to less than 80% × 80 to 100% xx

[Table 1]

[0035]

[Table 2]

As shown in Table 2, Examples 1 to 30, which are within the scope of the present invention, showed good white rust resistance, whereas Comparative Examples 1 to 7 all showed good white rust resistance. Was found to be bad.

(Second embodiment) An electrogalvanized steel sheet having a thickness of 0.7 mm and an adhesion amount of 20 g / m ² per side was coated on a galvanized steel sheet.
As shown in Table 3, it contains a silicate, an aluminum salt, and a chromium (III) salt, and various solvents shown in Table 3 are used. As shown in Table 4, the Al / (Al + Si) molar ratio is 0. 0.2, the molar ratio of Cr / (Al + Si) is 0.2.
After the solution contained so as to have a constant value of 5 was applied by a roll coater, a heat treatment was performed in a hot-air drying furnace to form films of Examples 31 to 37.

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 occurrence after 48 hours, 72 hours and 96 hours was examined. The white rust was evaluated. Table 4 shows the results.
Shown in The evaluation criteria were the same as in the first embodiment.

[0039]

[Table 3]

[0040]

[Table 4]

As shown in Table 4, it was confirmed that within the range of the present invention, good corrosion resistance was exhibited without being largely affected by the type of the solvent.

(Third Embodiment) An electrogalvanized steel sheet having a thickness of 0.7 mm and an adhesion amount of 20 g / m ² per one side was coated on a steel sheet having a thickness of 0.7 mm.
As shown in the following, a silicate ester, an aluminum salt, a chromium (III) salt, a methyl cellosolve solution in which colloidal silica is dissolved in the composition shown in Table 6 is applied by a roll coater, and then subjected to a heat treatment in a hot air drying oven. The coatings of Examples 38 to 63 were formed.

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 occurrence after 48 hours, 72 hours, and 96 hours was examined. The white rust was evaluated. Table 6 shows the results.
Shown in The evaluation criteria were the same as in the first embodiment.

[0044]

[Table 5]

[0045]

[Table 6]

As shown in Table 6, it was confirmed that by containing colloidal silica within the range of the present invention, a material exhibiting good corrosion resistance even after 96 hours was obtained.

[0047]

As described above, according to the present invention,
A silicate ester, an inorganic salt of aluminum, a trivalent chromium compound, or a solution containing colloidal silica of a wet type within a certain range in addition to the above is applied to a zinc-plated steel sheet, and then heated and dried. Since the chemical conversion coating is formed by the process, it is safe and harmless in the manufacturing process and in the use process, and the chemical conversion coating thus formed is excellent in the ability to suppress white rust in the healthy portion of the coating. Therefore, the present invention is extremely useful industrially.

──────────────────────────────────────────────────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) Fields investigated (Int. Cl. ⁷ , DB name) C23C 22/00-22/86 C23C 28/00

Claims (4)

(57) [Claims] 1. An aluminum / silicate ester having a silicate ester and an aluminum inorganic salt in an Al / (Al + Si) molar ratio of 0.015 or more and 0.75 or less, and a trivalent chromium compound in a chromium metal mole number. Is applied on a steel plate on which zinc-based plating is formed, and then heated and dried, and the amount of adhesion is (Al + Si + Cr) metal. A method for producing a galvanized steel sheet having excellent white rust resistance, characterized by forming a film of 50 mg / m ² or more in terms of conversion. 2. The treatment liquid contains a wet-type colloidal silica in an amount of 0.0
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 an amount of 25 to 1.0 times. 3. The method according to claim 1, wherein aluminum nitrate is used as the aluminum inorganic salt.
2. A method for producing a zinc-coated steel sheet having excellent white rust resistance according to item 1. 4. The method for producing a galvanized steel sheet having excellent white rust resistance according to claim 1, wherein the heating and drying temperature is lower than 200 ° C.