JPH09296279A - Production of galvanized steel sheet excellent in resistance to zinc white rust and resistance to scratching - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method capable of forming a safe and harmless chemical conversion film at a production stage and a use process and capable of producing a steel sheet excellent in resistances to zinc white rust and scratching. SOLUTION: After applying a soln. in which silicate and aluminum inorg. salt are kept in a molar ratio, Al/(Al+Si) of >=0.015 and <=0.75 and moreover resin is mixed so that its solid content is kept between >=0.1 and <=20 by wt. ratio per total amount of an Al amount in the aluminum inorg. salt and an Si amount in the silicate on the steel sheet, the sheet is heated and dried to form the film having a coverage of >=50mg/m<2> expressed in terms of (Al+Si) metal.

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 zinc-plated steel sheet which is excellent in white rust resistance and scratch resistance and has a coating containing no hexavalent chromium.

[0002]

2. Description of the Related Art Conventionally, zinc-based plated steel sheets have been widely used because they are manufactured by electroplating and hot dip plating, and the sacrificial anticorrosion property of the plating film can significantly suppress the corrosion of base steel. .

[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 method has excellent corrosion resistance and is an economical treatment method that can be performed relatively easily.

[0004]

However, the chromate treatment uses hexavalent chromium, which is highly toxic, and in the treatment process there is a problem of adverse effects of chromate on the human body and waste treatment of chromium sludge after wastewater treatment. In addition, there are various problems such as elution of hexavalent chromium from the product after chromate treatment.

Therefore, in order to prevent the occurrence of white rust on the zinc-based plated steel sheet, many pollution-free treatment techniques have been proposed that do not rely on chromate treatment.

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

(1) A method using a polymetal oxide such as molybdenum or tungsten (see, for example, JP-A-57-587).
No. 5) (2) Method using tannic acid (for example, JP-A-51-
No. 71233) (3) A non-polluting chromate treatment method using a treatment liquid containing trivalent chromium and containing no hexavalent chromium (for example, Japanese Patent Laid-Open No. 61-587). In the method, the stable region against corrosion of polymetal oxides such as molybdenum and tungsten is narrower than that of chromium, and it is impossible to obtain corrosion resistance comparable to that of chromate.

Further, the above method (2) has a problem that coloring with tannic acid occurs when trying to obtain sufficient corrosion resistance.

Further, in the above method (3), it is necessary to take a relatively long treatment time (reaction time), and the corrosion resistance thereof cannot be said to be sufficiently high.

In addition to corrosion resistance, it is desirable that the film has scratch resistance. In recent years, home appliance manufacturers are increasingly using unpainted chemical conversion treated steel plates as final products. If the coating film is inferior in scratch resistance, the surface of the steel plate will be scratched during work and assembly work, and the commercial value will be greatly reduced.

The present invention has been made in view of the above circumstances, and forms a safe and harmless chemical conversion treatment film in the manufacturing process and the use process, and thus has excellent white rust resistance and scratch resistance. An object of the present invention is to provide a method capable of producing a system-plated steel sheet.

[0012]

In order to solve the above-mentioned problems, the present invention firstly requires that a silicate ester and an aluminum inorganic salt have an Al / (Al + Si) molar ratio of 0.01.
5 or more and 0.75 or less, and further, the amount of solid content of the resin is 0.1 or more and 20 or less by weight ratio with respect to the total amount of Al in the aluminum inorganic salt and Si in the silicate ester. After coating the mixed solution on a steel plate, it is heated and dried, and the adhesion amount is 50 mg / m in terms of (Al + Si) metal.
Provided is a method for producing a zinc-based plated steel sheet having excellent white rust resistance and scratch resistance, which is characterized by forming ^two or more films.

Secondly, there is provided a method for producing a zinc-based plated steel sheet having excellent white rust resistance and scratch resistance, which is characterized in that aluminum nitrate is used as an aluminum inorganic salt in the above method.

Thirdly, there is provided a method for producing a zinc-based plated steel sheet excellent in white rust resistance and scratch resistance, which is characterized in that the heating and drying temperature is less than 200 ° C. in any one of the above methods.

Fourthly, in any one of the above methods, the solution contains one or more inorganic salts of nickel, cobalt and magnesium in a molar ratio to Al of 0.01.
As described above, there is provided a method for producing a zinc-based plated steel sheet having excellent white rust resistance and scratch resistance, which is characterized by containing not more than the same number of moles as Al.

Fifth, in the method according to any one of the first to third methods, the solution contains phosphoric acid or a phosphoric acid compound as the number of moles of phosphoric acid relative to the total number of moles of aluminum and silicate ester. Provided is a method for producing a zinc-based plated steel sheet having excellent white rust resistance and scratch resistance, which is characterized by being contained in a range of 5% to 200%.

Sixthly, in the method according to any one of the first to third methods, the solution has a trivalent chromium compound as a chromium metal mole number of 0.1 relative to a total mole number of aluminum and a silicate ester. Provided is a method for producing a zinc-based plated steel sheet having excellent white rust resistance and scratch resistance, which is characterized in that the content thereof is in the range of 2 to 3 times.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, as described above, a solution containing a silicate ester, an inorganic salt of aluminum, and a resin is applied onto a steel sheet to form a film excellent in corrosion resistance and scratch resistance. can do. Although the reason for this is not clear, it is considered that silicic acid and aluminum oxide form a network structure, form a dense complex oxide thin film, and obtain white rust inhibiting ability. Further, it is considered that the addition of the resin into the coating reduces the sliding resistance on the coating surface and improves the scratch resistance.

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

As the silicic acid ester, for example, methyl silicate, ethyl silicate, n-butyl silicate can be used. Considering the cost, it is preferable to use inexpensive ethyl silicate,
There is no particular limitation.

As the resin, for example, polyester-based, urethane-based, polyolefin-based, acrylic-based, alkyd-based, vinyl-based, silicon-based, and latex-based resins can be used, but they are stably dispersed in a solution. It is only necessary to be able to do so, and there is no particular limitation.

The ratio of the silicate ester to the aluminum inorganic salt is in the range of 0.015 to 0.75 in terms of 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 to cause a problem in the white rust inhibiting ability, and if it exceeds 0.75, the white rust inhibiting ability is similarly insufficient. Here, like this
The reason why the corrosion resistance changes depending on the / (Al + Si) molar ratio is considered to be that the corrosion resistance depends on the denseness of the obtained film structure.

Further, the resin is mixed such that the solid content thereof is 0.1 to 20 in weight ratio with respect to the total amount of Al in the aluminum inorganic salt and Si in the silicate ester. This is because when the addition ratio is less than 0.1, the effect of improving the scratch resistance is hardly seen, and conversely, when the addition ratio is 20
This is because even if it exceeds, no further effect can be obtained.

In the present invention, the above-mentioned silicate ester,
In addition to aluminum inorganic salts and organic solid lubricants, one or more inorganic salts of nickel, cobalt, and magnesium are used in a solution in a molar ratio to Al of 0.01 or more and the same number of moles or less as Al. Preferably contained in
By adding the inorganic salts of nickel, cobalt, and magnesium in this manner, the corrosion resistance in the defect portion of the Al-Si-based film (including both defects that occur during film formation and relatively small defects that occur during forming of the steel sheet) is improved. The reduction can be significantly reduced.

Here, the content of one or more of these is set to 0.01 or more in terms of the molar ratio to Al. If the content is less than this, the effect of suppressing the deterioration of the corrosion resistance of the film defects is almost the same. This is because it is not seen, and the reason why the number of moles is the same as or less than that of Al is
This is because the ratio of Si and Si decreases, and nickel, cobalt, and magnesium interfere with the film-forming action of the Al-Si-based film, resulting in a film with a poor coverage and deteriorating corrosion resistance.

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

Further, in the present invention, phosphoric acid or a phosphoric acid compound is contained in the solution in the range of 5% to 200% as the number of moles of phosphoric acid, based on the total number of moles of aluminum and silicate ester. Is preferred. Thereby, the white rust resistance can be further improved.

Here, the content of 5% or more and 200% or less is that when the content is less than 5%, the effect of the addition of the phosphoric acid compound is hardly seen, and when it exceeds 200%, the white rust suppressing effect is obtained. This is because you can no longer see. The reason for this is 2
It is presumed that when the content exceeds 00%, phosphate ions inhibit the growth of a dense Al-Si network structure and cause film defects. Further, the mechanism by which the effect is exerted by the addition of the phosphoric acid compound is not necessarily clear at present, but it is considered that the plating surface is inactivated by the phosphoric acid compound and the Al-Si network structure is strengthened by the phosphoric acid compound. To be

Examples of the phosphoric acid compound include primary ammonium phosphate, secondary ammonium phosphate, and tertiary phosphate.
It is possible to use ammonium, sodium phosphate, etc., but not limited to these.

Furthermore, in the present invention, the trivalent chromium compound (trivalent chromium ion) is defined as the number of moles of chromium metal, and the total number of moles of aluminum and silicate ester is
It is preferably contained in the solution in the range of 0.1 to 3 times. This can further improve the white rust resistance.

Here, the content is set in the range of 0.1 to 3 times because when it is less than 0.1 times, the effect of adding the chromium compound is hardly seen, and when it exceeds 3 times, the white content is increased. This is because the rust suppressing effect cannot be seen. It is presumed that the reason for this is that if the amount exceeds 3 times, the chromium ions inhibit the growth of a dense Al-Si network structure and cause film defects. The mechanism by which the addition of the trivalent chromium compound exerts its effect is not always clear at present, but the inactivation of the plating surface by the chromium compound,
It can be considered to strengthen the Al-Si network structure with chromium oxide.

As the trivalent chromium compound, for example, chromium nitrate, chromium chloride, chromium sulfate, chromium acetate and the like can be used, but the trivalent chromium compound is not limited to these.

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,
An organic solvent capable of dissolving a silicate ester, an aluminum salt, a resin such as diformaldehyde methoxyethanol can be used, and a non-polar solution such as 1,4 dioxane can be used in combination with a polar solvent 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 solution to the steel sheet, a method using a roll coater, a method of dipping the steel sheet in the solution or a method of spraying the solution onto a plated steel sheet, and then removing an excessive solution by a roll are used. Can be applied.

After applying the solution in this manner, heat drying is carried out, and the temperature at that time is preferably lower than 200.degree. The heat treatment temperature after application to the steel sheet affects the corrosion resistance of the Al-Si-based film, and white rust suppression ability can be obtained even at 200 ° C or higher, but the corrosion resistance tends to decrease with increasing heat treatment temperature. It is in. It is presumed that this is due to an increase in the number of pinholes caused by the rapid evaporation of the organic solvent and an increase in cracks due to the hardening of the film. There is no problem with the heating temperature as long as the solvent used can be volatilized, and its lower limit is determined by the volatility of the solvent.

In the present invention, such a coating is applied to a zinc-based plated steel sheet, but the treatment temperature must be a temperature at which the galvanization and the heat diffusion of the steel sheet as the substrate do not occur rapidly. It is considered that about 350 ° C. is a practical upper limit.

The adhesion amount of the film formed after heating and drying is
It is 50 mg / m ² or more in terms of (Al + Si) metal.
This is because if it is less than 50 mg / m ² , the corrosion resistance is insufficient. There is no upper limit of the amount of adhesion, but if the amount of adhesion is too large, flexibility deteriorates and cracks and peeling easily occur. Therefore, the film thickness is about 1.0 μm and 1.0 g / m ² or less. Is preferred.

As the steel plate applied in the present invention, various zinc-based plated steel plates can be used and are not particularly limited. Examples thereof include a galvanized steel sheet by an electroplating method, a zinc-nickel alloy plated steel sheet, a galvanized steel sheet by a hot dip coating method, and an aluminum-zinc alloy plated steel sheet.

[0039]

【Example】

(First embodiment) Adhesion amount with a plate thickness of 0.7 mm 20 per side
g / m ² electrogalvanized steel sheet, 0.7 mm thick adhesion amount per side 20 g / m ² electrozinc-nickel alloy plated steel sheet (nickel content 13%), 0.7 mm thick adhesion amount per side 60 g / m ² hot-dip galvanized steel sheet,
45 mm / m ² alloyed hot-dip galvanized steel sheet with a plate thickness of 0.7 mm and 80 g / m ² hot-dip aluminum-zinc alloy plated steel sheet with a plate thickness of 0.7 mm (aluminum content 55%) ) Is prepared, and a methyl cellosolve solution in which the silicic acid ester, aluminum salt, and resin shown in Table 1 are dissolved by the composition shown in Table 2 is applied by a roll coater, and then the heating temperature is changed by a hot air drying oven to perform heat treatment. Application, Examples 1-36 and Comparative Example 1
A film of ~ 8 was formed. The heating temperature at that time is also shown in Table 2. The amount of the chemical conversion coating deposited at this time can be changed depending on the amount of solid components in the treatment liquid or the coating conditions such as a roll coater.

Regarding the steel plate, of the above steel plates, Examples 1 to 30 and Comparative Examples 1 to 8 are electrogalvanized steel plates, Examples 31 to 33 are hot dip galvanized steel plates, and Example 34 is electrozinc-nickel alloy plating. Steel sheet, Example 35 was a hot dip galvanized steel sheet, and Example 36 was an alloyed hot dip galvanized steel sheet.

Next, the corrosion resistance and scratch resistance of the samples thus prepared were evaluated by the following methods, and also shown in Table 2.

(1) Corrosion resistance For each sample, a salt spray test (JIS-Z-23
71) was carried out and the white rust generation area ratio after 24 hours and 48 hours was examined, and the white rust resistance was evaluated by this.

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

White rust occurrence area rate evaluation 0% to less than 5% ◎ 5% to less than 25% ○ 25% to less than 50% △ 50% to less than 80% × 80% to 100% × × (2) Scratch resistance Test Using a draw bead tester (male die tip: 10R, horizontal pressing load: 50 kg / m ² , deformation height: 1 mm), pull out while deforming each sample to check the peeling state of the film and the presence of scratches on the sample. It was examined visually and evaluated according to the following criteria.

Condition evaluation No peeling and no scratches ◎ No peeling and some scratches ○ Slight peeling and scratches on steel plate △ Significant peeling and scratches on steel plate ×

[Table 1]

[0046]

[Table 2]

As shown in Table 2, all of Examples 1 to 36 within the scope of the present invention showed good white rust resistance and scratch resistance, whereas Comparative Examples 1 to 8 all. It was confirmed that white rust resistance and scratch resistance were poor.

(Second Embodiment) Table 3 was prepared on an electrogalvanized steel sheet having a plate thickness of 0.7 mm and an adhesion amount of 20 g / m ² per side.
As shown in Table 1, using a silicate ester, an aluminum salt and a resin, using various solvents shown in Table 3, and as shown in Table 4, the Al / (Al + Si) molar ratio is 0.2, the resin The solid content of A is A in the aluminum inorganic salt.
1 solution and the total amount of Si in the silicate ester were added so that the weight ratio would be a constant value of 3.0, and then the solution was applied by a roll coater, followed by heat treatment by a hot-air drying furnace. The coatings of Examples 37-43 were formed.

A salt spray test (JIS-Z-2371) was carried out on these samples in the same manner as in Example 1, and the white rust occurrence area ratio after 24 hours and 48 hours was examined. evaluated. Furthermore, the scratch resistance of each sample was evaluated in the same manner as in the first example. The results are shown in Table 4. The evaluation criteria were the same as in the first embodiment.

[0050]

[Table 3]

[0051]

[Table 4]

As shown in Table 4, it was confirmed that within the range of the present invention, good white rust resistance and scratch resistance were exhibited, with little effect on the type of solvent.

(Third Example) An electrogalvanized steel sheet having a plate thickness of 0.7 mm and a deposition amount of 20 g / m ^{2 on} one side was prepared.
After dissolving the silicic acid ester, aluminum salt, and resin shown in Table 5 and further dissolving any of the inorganic salts of magnesium, nickel, and cobalt with the composition shown in Table 6 by a roll coater,
The heating temperature was changed in a hot air drying oven to perform heat treatment, and the coatings of Examples 44 to 58 and Comparative Examples 9 to 16 were formed. The heating temperature at that time is also shown in Table 6. The amount of the chemical conversion coating deposited at this time can be changed depending on the amount of solid components in the treatment liquid or the coating conditions such as a roll coater.

Then, each of these samples was evaluated for corrosion resistance and scratch resistance as in the first embodiment. In addition, in order to evaluate the corrosion resistance of the cut portion, the sample surface after the chemical conversion treatment was scratched with a cutter knife to reach the base metal, and the white rust generation degree after 24 hours of the salt spray test was examined. The results are also shown in Table 6. Also described in.

The corrosion resistance of the cut portion was evaluated according to the following criteria.

Evaluation of rust occurrence on the cut part ・ No white rust ◎ ・ White rust on part of the cut ○ ・ White rust on part of the cut △ △ White rust begins to flow ・ Part of the cut White rust is generated on the x

[Table 5]

[0057]

[Table 6]

As shown in Table 6, all of Examples 44 to 58 within the scope of the present invention showed good white rust resistance, cut portion corrosion resistance and good scratch resistance, whereas It was confirmed that Examples 9 to 16 had poor white rust resistance, cut portion corrosion resistance, and scratch resistance.

(Fourth Example) An electrogalvanized steel sheet having a plate thickness of 0.7 mm and a deposition amount of 20 g / m ^{2 on} one side was prepared.
After applying a methyl cellosolve solution obtained by dissolving the silicic acid ester, aluminum salt, resin and phosphoric acid compound shown in Table 7 with the composition shown in Table 8 using a roll coater, heat treatment was performed by changing the heating temperature in a hot air drying oven. The coatings of Examples 59 to 73 and Comparative Examples 17 to 22 were formed.
The heating temperature at that time is also shown in Table 8. The amount of the chemical conversion coating deposited at this time can be changed depending on the amount of solid components in the treatment liquid or the coating conditions such as a roll coater.

A salt spray test (JIS-Z-2371) was carried out on these samples in the same manner as in the first embodiment.
The white rust generation area ratio after 48 hours and 72 hours was examined, and the white rust resistance was evaluated by this. Furthermore, each sample was evaluated for scratch resistance in the same manner as in Example 1. Table 8 shows the results. The evaluation criteria were the same as in the first embodiment.

[0061]

[Table 7]

[0062]

[Table 8]

As shown in Table 8, all of Examples 59 to 73 within the scope of the present invention showed good white rust resistance and scratch resistance. On the other hand, among the comparative examples, Comparative Examples 17 to 19 in which the phosphoric acid compound is out of the proper range have poor white rust resistance, and Comparative Examples 20 to 22 in which the resin is out of the proper range have poor scratch resistance. Was confirmed.

(Fifth Embodiment) An electrogalvanized steel sheet having a plate thickness of 0.7 mm and an adhesion amount of 20 g / m ^{2 on} one side is prepared.
Silicate ester, aluminum salt, resin, 3 shown in Table 9
After applying a methyl cellosolve solution in which a valent chromium compound was dissolved in the composition shown in Table 10 by a roll coater, heat treatment was performed by changing the heating temperature in a hot-air drying oven, and Examples 74 to 87 and Comparative Examples 23 to 28 were used. A film was formed. The heating temperature at that time is also shown in Table 10. The amount of the chemical conversion coating deposited at this time can be changed depending on the amount of solid components in the treatment liquid or the coating conditions such as a roll coater.

A salt spray test (JIS-Z-2371) was carried out on these samples in the same manner as in the first embodiment.
The white rust generation area ratio after 48 hours and 72 hours was examined, and the white rust resistance was evaluated by this. Furthermore, each sample was evaluated for scratch resistance in the same manner as in Example 1. The results are shown in Table 10. The evaluation criteria were the same as in the first embodiment.

[0066]

[Table 9]

[0067]

[Table 10]

As shown in Table 10, all of Examples 74 to 87 within the scope of the present invention showed good white rust resistance and scratch resistance. On the other hand, among Comparative Examples 23 to 25 in which the trivalent chromium compound is out of the proper range, the white rust resistance is poor, and in Comparative Examples 26 to 2 in which the resin is out of the proper range.
It was confirmed that No. 8 had poor scratch resistance.

[0069]

As described above, according to the present invention,
A chemical conversion coating is formed by applying a solution containing silicate ester, aluminum inorganic salt, and resin within a certain range to the steel sheet, and then heating and drying, so it is safe, harmless, and hygienic during the manufacturing process and in the process of use. Target,
Further, the chemical conversion treatment film thus formed is excellent in white rust suppressing ability and scratch resistance in the healthy portion of the film. Therefore, the present invention is extremely useful industrially.

Claims (6)

[Claims] 1. A silicic acid ester and an aluminum inorganic salt having an Al / (Al + Si) molar ratio of 0.015 or more and 0.75 or less, and a resin whose solid content is the amount of Al in the aluminum inorganic salt and silica. A solution mixed so as to have a weight ratio of 0.1 or more and 20 or less with respect to the total amount of Si in the acid ester is applied on a steel sheet, and then dried by heating,
A method for producing a zinc-based plated steel sheet having excellent white rust resistance and scratch resistance, which comprises forming a film having an adhesion amount of 50 mg / m ² or more in terms of (Al + Si) metal. 2. The method for producing a zinc-based plated steel sheet excellent in white rust resistance and scratch resistance according to claim 1, wherein aluminum nitrate is used as the aluminum inorganic salt. 3. The method for producing a zinc-based plated steel sheet having excellent white rust resistance and scratch resistance according to claim 1 or 2, wherein the heating and drying temperature is less than 200 ° C. 4. The solution contains one or more kinds of inorganic salts of nickel, cobalt and magnesium in a molar ratio to Al of 0.01 or more and the same number of moles or less as Al. The method for producing a zinc-based plated steel sheet having excellent white rust resistance and scratch resistance according to any one of claims 1 to 3. 5. The solution contains phosphoric acid or a phosphoric acid compound in a range of 5% to 200% with respect to the total number of moles of aluminum and silicate as the number of moles of phosphoric acid. The method for producing a zinc-based plated steel sheet having excellent white rust resistance and scratch resistance according to any one of claims 1 to 3. 6. The solution contains a trivalent chromium compound as a chromium metal mole number in a range of 0.1 to 3 times the total mole number of aluminum and silicate ester. The method for producing a zinc-based plated steel sheet excellent in white rust resistance and scratch resistance according to any one of claims 1 to 3.