JP2001181855A - Surface treating solution for plated steel sheet and treating method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a non-chromic acid based surface treating solution capable of depositing a resin film excellent in corrosion resistance and film adhesion and to provide a treating method therefor. SOLUTION: The first surface treating solution is obtained by adding a water soluble urethane resin and an oxycarboxylic compound to a treating solution of the phosphate of one or more kinds of metals selected from manganese, magnesium, molybdenum, zinc, calcium and zirconium. The second surface treating solution is obtained by mixing a silane coupling agent and a silica sol to the first surface treating solution. In this treating method, the first and second surface treating solutions are applied on the surface of a plated steel sheet so as to control the film quantity to 0.1 to 5.0 g/m2, and after that, without executing water washing, the same is dried at a sheet temperature of 80 to 250 deg.C.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface treating solution for a plated steel sheet capable of forming a film excellent in corrosion resistance, adhesion after painting and resistance welding, and a treating method.

[0002]

2. Description of the Related Art Zinc, aluminum, copper or alloys of these metals are used for post-treatment and painting pre-treatment of plated steel sheets.
Conventionally, chromate treatment has been widely used. However, since the formed chromate film contains a trace amount of hexavalent chromium ions harmful to the human body, its safety has conventionally been a problem. For example, if the coating material of the plated steel sheet is used in applications where the human body frequently comes into contact, such as home appliances and office equipment, the coating will wear and the chromate film will be exposed,
Contact with the chromate coating is conceivable. For this reason, the post-treatment and the pre-coating treatment of the plated steel sheet have been attempted to enhance the safety of the plated steel sheet by applying a non-chromic acid-based surface treatment, and various surface treatment solutions have been developed conventionally. .

As one type of the non-chromic acid-based treatment liquid, a phosphate treatment in which a phosphate of one or more metals selected from manganese, magnesium, molybdenum, zinc, calcium or zirconium is dissolved in water. There is liquid,
When the phosphate metal is as described above, the solubility in water is low, and the stability of the processing solution is poor. For this reason, it was difficult to form a phosphate film having high corrosion resistance by using a treatment solution having a high concentration for treating a plated steel sheet. To increase the solubility of phosphate, add inorganic or organic acids,
It is possible if the treatment liquid is made strongly acidic, but if the treatment liquid is made strongly acidic, the reactivity with the plated steel sheet is too strong, so that a uniform phosphate film cannot be obtained, and the treatment liquid deteriorates quickly. There was a problem. Further, the formed phosphate film was inferior in corrosion resistance and film adhesion to a conventional chromate film and a resin film formed thereon.

As a method for improving the corrosion resistance of a phosphate film, it is known that silica sol is added to a phosphating solution so that the phosphate film contains silica. If so, the adhesion of the coating film will be reduced. As a method for improving the adhesion of the phosphate film, it is known to add a silane coupling agent to the phosphating solution and perform the treatment. When the ring agent is added, the silane coupling agent undergoes hydrolysis and dehydration condensation, so that the adhesion of the coating film varies depending on the degree thereof, and the treatment liquid thickens and gels. Furthermore, if the film is crystalline, such as a phosphate film, the ductility is poor, so that the film and the plating layer are apt to form galling during press molding, and the corrosion resistance of the processed portion is reduced. When an organic resin film is formed on the phosphate film, press formability is improved, but the number of processing steps is two.

[0005]

SUMMARY OF THE INVENTION The present invention provides a surface treatment solution for a non-chromic acid-based plated steel sheet which is excellent in corrosion resistance and coating film adhesion in one-step treatment, and a method for treating the same.

[0006]

The first surface treating solution of the present invention is a solution for treating a phosphate of one or more metals selected from manganese, magnesium, molybdenum, zinc, calcium or zirconium. An aqueous urethane resin and an oxycarboxylic acid compound are added, and the phosphate concentration is 2.0 to 100 g / L as P, the aqueous urethane resin concentration is 5 to 400 g / L, and the oxycarboxylic acid compound concentration is phosphate. The molar ratio of the oxycarboxylic acid compound / P to the amount of P is 0.20 to 3.0. The second surface treatment liquid is obtained by mixing silica sol with a silane coupling agent to form a silane coupling agent. By bonding a part of the agent to the silica surface of the silica sol, ²⁹ Si (−) due to the silane coupling agent not reacting with the silica sol was obtained.
O-) ₃ and silica sol ²⁹ due to Si (-O-) ₄ nuclear magnetic resonance analysis (NMR) peak - click intensity ratio R = ²⁹ Si (-O
^{_{-) 3/29 Si (-O-}} ) 4 is added silica sol-containing silane coupling agent was adjusted to a range of 0.16 to 1.85 in the first surface-treatment liquid, a silane coupling agent amount S is a molar ratio of S / P = 0.0 to the P amount of the phosphate.
02 to 2.0. The treatment method is such that the first and second surface treatment liquids are applied to the surface of the plated steel sheet so that the coating amount becomes 0.1 to 5.0 g / m ^2, and then, without washing with water, at a sheet temperature of 80 to 250 ° C. It is characterized by drying.

[0007]

When a water-based urethane resin is added to a phosphating solution to treat a plated steel sheet, a urethane resin film in which phosphate crystals are dispersed is formed. The urethane resin of this resin film is excellent in ductility and coating film adhesion, so that it follows the deformation of the plated steel sheet, and it is difficult for the resin film and the plating layer to generate galling during press working, and the corrosion resistance of the processed part does not decrease . The phosphate is contained in an amount of 2.0 to 100 g / L as a P amount, and the added amount of the aqueous urethane resin is 5 to 4 g.
00 g / L. Here, the P amount of the phosphate is a numerical value calculated by the weight of the contained phosphate × (the amount of phosphorus contained in the chemical formula of the phosphate / the molecular weight of the phosphate). When the P content is less than 2.0 g / L, the corrosion resistance of the resin film is insufficient, and when it is more than 100 g / L, the adhesion of the coating film tends to decrease. On the other hand, aqueous urethane resin has a concentration of 5
If it is lower than g / L, the galling resistance during press working is insufficient, and the corrosion resistance of the processed part is inferior. If it is higher than 400 g / L, the stability of the processing solution is inferior and gelation is likely to occur.

As the phosphate, a phosphate of one or more metals selected from manganese, magnesium, molybdenum, zinc, calcium or zirconium is used as in the prior art. Sufficient corrosion resistance cannot be obtained with phosphates other than these, and when carbonates, nitrates, sulfates, acetates, fluorides, chlorides, etc. other than phosphates are added, the stability of the treatment solution and The corrosion resistance of the resin film decreases. Phosphate normal salt _{^{M 1 3 PO 4, M 2}} 3 (PO 4) 2, dihydrogenphosphate M ^{1
_{H 2 PO 4, M 2 (}} H 2 PO 4) 2, monohydrogen M ¹ ₂ HPO _4,
Any of M ² HPO ₄ may be used, and two or more of these may be used (M ¹ and M ² are monovalent and divalent metals, respectively).

The aqueous urethane resin is a water-soluble or water-dispersible resin obtained by reacting an organic polyisocyanate compound with a polyol compound, and is particularly preferably a self-emulsifying resin. Here, the organic polyisocyanate
The aromatic compounds include aromatic diisocyanates such as phenylene diisocyanate, tolylene diisocyanate, diphenylmethane diisocyanate, naphthalene diisocyanate, hexamethylene diisocyanate, and lysine diisocyanate. Aliphatic diisocyanate such as isocyanate, cyclohexane diisocyanate, isophorone diisocyanate
And alicyclic diisocyanates such as norbornane diisocyanate, xylylene diisocyanate and tetramethyl xylylene diisocyanate. Polyol compounds include polyester polyols, polyether polyols, polycarbonate polyols, polyacetal polyols, and polyacrylate polyols.
And polyolefin polyols such as polyesteramidepolyol and polybutadiene. To obtain a self-emulsifying type, a hydrophilic component such as a carboxylic acid-containing compound may be introduced into the molecule.

When the urethane resin is of a self-emulsifying type, the ionicity becomes anionic, cationic or nonionic depending on the introduced hydrophilic component. When an acid or silane coupling agent is added, if the ionicity is an anion or cation, the urethane resin particles aggregate,
Gelation may occur. On the other hand, it has been found that such a phenomenon does not occur when the ionicity is that of nonionic. Therefore, the urethane resin uses only nonionic urethane resin, or when nonionic or cationic urethane resin is mixed, nonionic ionic resin /
(Anionic + Cationic +
The ratio of nonionic) is 0.5 or more,
Avoid gelling of the processing solution. To make the ionicity of the urethane resin nonionic, polyethylene glycol, isocyanate, or the like may be introduced into the polymer skeleton. A hydroxyl group is used as an anion, and a sulfonic acid (salt) group is used as cation. , A carboxyl (salt) group or the like may be introduced.

[0011] Even if phosphate is simply dissolved in water, its solubility is low, so the saturated aqueous solution is unstable, and the amount of P is 100 g.
/ L is also difficult to increase the concentration. However, when the oxycarboxylic acid compound is added to the aqueous phosphate solution, the aqueous solution is stable even when the amount of P is 100 g / L. The reason why the aqueous solution is stabilized by the addition of the oxycarboxylic acid compound is not clear, but the metal of the phosphate is chelated with the hydroxyl group and the carboxyl group oxygen of the oxycarboxylic acid to prevent precipitation of the phosphate. It is estimated that Since the oxycarboxylic acid compound generates a phosphate ion and a phosphate ester, the addition of the oxycarboxylic acid compound also has an effect of increasing the rust prevention effect of the resin film. Here, examples of the oxycarboxylic acid compound include tartaric acid, malonic acid, citric acid, lactic acid, gluconic acid, glyceric acid, tropic acid, benzylic acid, and hydroxyvaleric acid. These may be used alone or in combination.

The amount of the oxycarboxylic acid compound to be added is a molar ratio of the oxycarboxylic acid compound /
Set P = 0.20 to 3.0. When this ratio is smaller than 0.20, the stability of the aqueous solution is poor, and when this ratio is larger than 3.0,
Since many unreacted oxycarboxylic acid compounds are present in the resin film, the water resistance of the resin film is weakened, and the corrosion resistance and the water-resistant secondary adhesion after coating are reduced.

When a silica sol is added to the phosphating solution containing the aqueous urethane resin and the oxycarboxylic acid compound, the corrosion resistance is further improved.
As described above, the adhesion of the coating film is reduced. When a silane coupling agent is added to prevent the coating film adhesion from lowering, the hydrolyzate, silanol, is thickened and gelled by dehydration condensation. For this reason, the silane coupling agent cannot be added indefinitely in order to recover the decrease in coating film adhesion due to the addition of the silica sol, and the silane coupling agent does not need to be added until the dehydration condensation of silanol proceeds. Thus, it was necessary to limit the amount of silica sol to be added in advance.

As a method for reducing the concentration of silanol to a concentration at which dehydration condensation does not occur, a method of mixing the silane coupling agent and silica sol in advance and reacting the silane coupling agent with the silica sol to reduce the silanol concentration. It has been known. By using this method, the mixing amount of the silane coupling agent and the silica sol can be adjusted so that the concentration of the silanol does not cause dehydration condensation. However, there has been no means for grasping and managing the degree of the reaction. The present invention makes it possible to provide such a control means, and to provide a surface treatment liquid in which both are added to a phosphate aqueous solution.

That is, the silica sol and the silane coupling agent have a low concentration even if they are directly added to the phosphating solution to a concentration at which the effect of improving the corrosion resistance of the resin film and the adhesiveness of the coating film are recognized. Does not react, but reacts when both are directly mixed. Here, as the silane coupling agent, an organotrialkoxysilane R ¹ Si (O
R ² ) ₃ [R ¹ is an alkyl group, an epoxy group, a vinyl group,
(Meth) acrylic group, amino group, R ² is hydrogen or alkyl group], the structure of silanol is R ¹ S
i (OH) ₃ . The silanol to the silica sol surface - reaction about Le is ²⁹ Si (-O-) ₄ of peak attributable to silica sol in the nuclear magnetic resonance analysis (NMR) - due to click the silane coupling agent does not react to silica sol Do ²⁹
The peak of Si (-O-) ₃ is measured, and it can be grasped from the peak intensity ratio. Therefore, if the peak strength ratio can be measured, it becomes possible to control the storage stability of the treatment liquid, the corrosion resistance of the resin film and the adhesion of the coating film.

Therefore, the silica sol and the silane coupling agent are preliminarily mixed before being added to the phosphating solution, and the silica sol is reacted with the silane coupling agent. If it is confirmed and added to the processing solution, the corrosion resistance of the processing solution and the storage stability of the processing solution can be harmonized. ²⁹ Confirmation of the silane coupling agent concentration which does not react to silica sol by nuclear magnetic resonance analysis Si (-O-) ₃ and ²⁹ Si (-O-) ₄
The peak - click intensity ratio _{^{R = 29 Si (-O-) 3}} /29 Si (-O
−) According to ₄ . As a result of the experiment, it was found that when R was smaller than 0.16, the corrosion resistance of the resin film was insufficient, and when it was larger than 1.85, the storage stability was lowered when added to the treatment liquid. For this reason, the peak intensity ratio R is 0.1.
It was necessary to set it to 6 to 1.85.

When the mixture of the silica sol and the silane coupling agent is added to the treatment liquid, the addition amount S of the silane coupling agent is S / P = 0.00 in molar ratio to the P amount of the phosphate.
Perform so as to be 2 to 2.0. When S / P is less than 0.002, the effect of improving the adhesion of the resin film to the coating film is small, and S / P is small.
If P is larger than 2.0, the silane coupling agents tend to cause a dehydration condensation reaction between the silane coupling agents, so that the stability of the treatment liquid is reduced.

The type of the silane coupling agent is not particularly limited, and may be, for example, one or two of an amino-based, ureido-based, vinyl-based, methacryl-based, epoxy-based, mercapto-based, and isocyanate-based alkoxysilane. The above may be used. Specifically, as an amino group, γ-
Aminopropyltriethoxysilane, γ-aminopropyltrimethoxysilane, N- (β-aminoethyl) -γ
-Aminopropyltrimethoxysilane, γ-phenylaminopropyltrimethoxysilane, etc., and ureido-based ureidopropyltriethoxysilane; vinyl-based vinyltriethoxysilane, vinyltrimethoxysilane, vinyltris (β- (Methoxyethoxy) silane. Also, methacryl-based γ-methacryloxypropyltrimethoxysilane and γ-methacryloxypropylmethyldimethoxysilane, and epoxy-based β- (3,4-epoxycyclohexyl) ethyltrimethoxysilane and γ-glycid Xypropyltrimethoxysilane.
Further, as a mercapto type, γ-mercaptopropyltrimethoxysilane is used, and as an isocyanate type,
γ-isocyanatopropyltriethoxysilane and the like.

If necessary, a solid lubricant, for example, an olefin such as a fluororesin or a high-pressure polyethylene, may be added to the treatment liquid in order to enhance the lubricity and workability of the resin film and improve the galling resistance during press molding. It is also possible to add a resin or a powder of a polyester resin such as polyethylene terephthalate. In this case, the addition amount is preferably 20% by weight or less of the urethane resin in order to stabilize the processing solution. Further, an epoxy-based or oxazoline-based crosslinking agent may be added to enhance the film quality. It is preferable that the amount of addition be 20% by weight or less from the viewpoint of stability of the processing solution.

It is preferable that the pH of the treatment liquid is 1.5 to 6.0. If the pH is less than 1.5, the reactivity with the plated steel sheet is too strong, so that the resin film is not uniform, the plating metal dissolution in the processing solution increases, and the deterioration of the processing solution is accelerated. On the other hand, when the pH is more than 6.0, the reactivity of the treatment liquid tends to be low, and the corrosion resistance tends to decrease. The pH can be adjusted by the addition amount of a phosphate or an oxycarboxylic acid compound, but a pH adjuster may be used if necessary. For example, when raising the pH, ammonia water or a hydroxide salt is used, and when lowering the pH, an inorganic acid such as phosphoric acid is used.

The resin film has a coating amount of 0.1 to 5.0 g / m.
^{Make 2} If it is less than 0.1 g / m ² , sufficient corrosion resistance, fingerprint resistance and galling resistance cannot be obtained, and if it exceeds 5.0 g / m ² , the resistance weldability decreases.

The treatment liquid may be applied to the plated steel sheet by a known method, for example, a roll coating method, an air curtain method, an electrostatic atomization method, a squeeze rolling method, etc. After that, dry without washing with water. Drying at a plate temperature of 80 to 250 ° C
Do with. If the temperature is lower than 80 ° C., the resin film cannot be dried sufficiently and the film cannot be formed. Drying at a temperature higher than 250 ° C. lowers the corrosion resistance of the resin film.

As the plated steel sheet, Zn-based plated steel sheet,
For example, Zn, Zn-Al alloy, Zn-Ni alloy,
Zn-Mn alloy, Zn-Mg alloy, Zn-Al-M
Examples of a plated steel sheet such as a g-based alloy and an Al-based plated steel sheet include plated steel sheets such as Al, an Al-Zn-based alloy, and an Al-Si-based alloy. Furthermore, Cu-based plated steel sheets,
It is also possible to treat Ni-based plated steel sheets.

[0024]

EXAMPLES Example 1 An aqueous urethane resin emulsion having nonionic ionicity and an oxycarboxylic acid compound were added to various aqueous phosphate solutions to prepare treatment solutions having a pH of 2.8. Then, this treatment liquid was applied to an electrogalvanized steel sheet (plate thickness: 0.5 mm, coating weight on one side of the sheet: 20 g / m ² ), and dried at a sheet temperature of 160 ° C. Table 1 shows the composition of the processing solution and the amount of the coating.

[0025]

[Table 1] (Note 1) The amount of oxycarboxylic acid added is a molar ratio to the amount of P in the phosphate. (Note 2) Comparative Examples Nos. 2 and 5 could not be applied due to poor stability after preparation of the processing solution.

Next, the following performance tests were carried out on electrogalvanized steel sheets treated with the treatment liquids shown in Table 1 having good treatment liquid stability. Table 2 shows the results. (1) Flat part corrosion resistance test A salt spray test (JIS Z 2371) was conducted for 120 hours.
, Those of 3% or more and less than 10% were evaluated with the symbol で, those of 10% or more and less than 30% were evaluated with the symbol 、, and those of 30% or more were evaluated with the symbol x. (2) Galling resistance test A test piece (30 × 250 mm) was subjected to a drop test (pressing force: 1500 N, drawing speed: 8.3 × 10 ^−2).
m / sec), the film whose residual ratio in the test area is 80% or more is marked with a symbol ◎, the one with 60% or more and less than 80% is marked with a symbol ○, and the one with 40% or more and less than 60% is marked with a symbol. △, 2
Those with 0% or more and less than 40% were evaluated with the symbol x, and those with less than 20% were evaluated with the symbol xx.

(3) Corrosion resistance test on processed part The salt spray test similar to the above (1) Corrosion resistance test on flat part was performed on the test piece for which the galling resistance was evaluated, and the white rust generation rate was 10% of the total area. Those with less than 10% and less than 30% were evaluated with the symbol 、, and those with 30% or more were evaluated with the symbol X. (4) Coating film adhesion test An organic solvent-based acrylic paint was applied in a dry coating film thickness of 30 μm, and a coating film adhesion test was performed in accordance with the JIS K 5400 grid method. Signs ◎
And 80% or more and less than 100% with the symbol ○, 40
% Or more and less than 80% were evaluated with the symbol △, and those less than 40% were evaluated with the symbol x. The adhesion of the coating film was determined by the primary adhesion that was applied to the coating film as it was after coating, and the adhesion to warm water at 40 ° C.
The secondary adhesion performed on the sample immersed for 0 hours was examined.

(5) Resistance weldability test Continuous spot welding was performed using a CF-type Cu-Cr electrode (tip diameter: 5 mm). The following were evaluated with the symbol △, and those with 299 dots or less were evaluated with the symbol x. (6) Temporal change test of treatment liquid The treatment liquid one week after the preparation was applied, and the same test as the flat part corrosion resistance test of (1) was performed. , And those that had decreased were evaluated with the symbol x.

[0029]

[Table 2]

Example 2 A treatment liquid was prepared by mixing manganese dihydrogen phosphate, a urethane resin emulsion, and tartaric acid in various ratios. Also,
Separately, silica sol and γ-silane coupling agent
Glycidoxypropyltrimethoxysilane was mixed in various proportions to cause a part of the silane coupling agent to react with the silica surface of the silica sol, and then caused by the silane coupling agent not reacting with the silica sol by nuclear magnetic resonance analysis. Done ²⁹
Si (-O-) ₃ and silica sol ²⁹ due to Si (-O
-) ₄ peak - click intensity ratio _{^{R = 29 Si (-O-) 3}} /29 Si
(-O-) ₄ was determined, and an additive liquid was prepared by a method of confirming the concentration of the silane coupling agent not reacting with the silica sol. Then, this additive solution was added to the above-mentioned treatment solution, and a hot-dip galvanized steel sheet (having a thickness of 0.8 mm and a coating weight of 40
g / m ² ) by the roll coating method, and the ultimate plate temperature is 150
Dried at ° C. Further, a polyethylene resin powder was added to a part of the mixture of the additive liquid and the treatment liquid, and the mixture was similarly coated and dried. Table 3 shows the composition of the treatment solution prepared in this way and the amount of the resin film adhered. Table 4 shows the same test results as in Example 1.

[0031]

[Table 3] (Note) The addition amount of the silane coupling agent is a molar ratio to the P amount of manganese dihydrogen phosphate.

[0032]

[Table 4]

[0033]

As described above, the first surface treating solution of the present invention is a treating solution of a phosphate of one or more metals selected from manganese, magnesium, molybdenum, zinc, calcium or zirconium. , An aqueous urethane resin and an oxycarboxylic acid compound are added to the mixture, and the concentration of the phosphate is 2.0 to 100 g / L as P, the concentration of the aqueous urethane resin is 5 to 400 g / L, and the concentration of the oxycarboxylic acid compound is phosphate. Oxycarboxylic acid compound / P = 0.20-3.0 in molar ratio with respect to the amount of P, but a non-chromic acid-based material having excellent corrosion resistance and coating film adhesion by one-step treatment on a plated steel sheet A resin film can be formed, and the processing solution is stable. Also,
When adding the silane coupling agent to the first surface treatment liquid, the second surface treatment liquid is obtained by mixing silica sol with the silane coupling agent and binding a part of the silane coupling agent to the silica surface of the silica sol. As a result, ²⁹ Si caused by the silane coupling agent not reacting with the silica sol
(-O-) ₃ and silica sol ²⁹ due to Si (-O-) ₄
Nuclear magnetic resonance analysis (NMR) peak - click intensity ratio R = ²⁹ Si
^{_{(-O-) 3/29 Si (}} -O-) 4 is added silica sol-containing silane coupling agent was adjusted to a range of 0.16 to 1.85 in the first surface-treatment liquid, a silane coupling The additive amount S is expressed as S / P =
The treatment liquid prepared by this method has a balance between storage stability, corrosion resistance of the resin film, and coating film adhesion. Further, the first and second surface treatment solutions are coated on the surface of the plated steel sheet with a coating amount of 0.1 to 5.0 g / m ^2.
After applying so that it does not wash with water, plate temperature 80-250
If dried at ℃, a resin film having excellent corrosion resistance and coating film adhesion can be formed by one-step treatment.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Hirofumi Takezu 5th Ishizu Nishimachi, Sakai City, Osaka Nisshin Steel Co., Ltd. F-Terminator, Surface Treatment Research Laboratory, R & D Laboratories 4D075 CA13 CA33 DB02 DB05 DB06 EB01 4K026 AA02 AA12 AA13 AA22 BA03 BA04 BA05 BB06 BB08 BB10 CA16 CA18 CA23 CA37 CA38 CA39 DA02 DA11 DA15

Claims (3)

[Claims] 1. A material selected from manganese, magnesium, molybdenum, zinc, calcium or zirconium.
An aqueous urethane resin and an oxycarboxylic acid compound are added to the treatment solution of the phosphate of one or more metals, and the phosphate concentration is 2.0 to 100 g / L, and the aqueous urethane resin concentration is 5%. A surface treatment solution for a plated steel sheet, wherein the concentration of the oxycarboxylic acid compound is set to a molar ratio of oxycarboxylic acid compound / P = 0.20 to 3.0 with respect to the P amount of the phosphate. . 2. Silica sol is mixed with a silane coupling agent, and a part of the silane coupling agent is bonded to the silica surface of the silica sol, so that ²⁹ Si ( −
O-) ₃ and silica sol ²⁹ due to Si (-O-) ₄ nuclear magnetic resonance analysis (NMR) peak - click intensity ratio R = ²⁹ Si (-O
^{_{-) 3/29 Si (-O-}} ) 4 was added to the surface treatment solution of claim 1 is silica sol containing silane coupling agent was adjusted to a range of 0.16 to 1.85, the silane coupling agent added amount S is a molar ratio of S / P = 0.0 to the P amount of the phosphate.
A surface treating solution for plated steel sheets, wherein the surface treating solution is 02 to 2.0. 3. The surface treatment solution according to claim 1 or 2 is applied to the surface of a plated steel sheet so as to have a coating amount of 0.1 to 5.0 g / m ² , and is not washed with water. A surface treatment method for a plated steel sheet, characterized by drying at 250 ° C.