JPH02267277A - Method for chromating zinc or zinc alloy plated steel sheet - Google Patents

Abstract

PURPOSE:To form a coating film having superior uniform coatability and corrosion resistance by adding a specified amt. of a silane coupling agent to an aq. chromating soln. contg. hexavalent Cr, trivalent Cr, phosphate ions and an org. solvent under specified conditions and coating the surface of a Zn or Zn alloy plated steel sheet with the chromating soln. CONSTITUTION:A silane coupling agent is added to an aq. chromating soln. contg. 3.0-50g/l Cr<6+>, 2.0-40g/l Cr<3+>, 1.0-100g/l PO4<3-> and 3-50g/l at least one kind of org. solvent selected among 4-8C tert. alcohols and acetonitrile in 0.25-1.5 weight ratio of Cr<3+> to Cr<6+> and 0.1-1.2 weight ratio of PO4<3-> to (Cr<6+>+Cr<3+>) The coupling agent is added to the chromating soln. in 0.05-0.3 molar ratio to Cr<6+> and mixed. The surface of a Zn or Zn alloy plated steel sheet is coated with the chromating soln. and dried to form a chromate coating film by 10-200mg/m<2> (expressed in terms of Cr). This coating film has superior alkali resistance, welding resistance and coatability.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to electrogalvanized steel sheets, electrogalvanized steel sheets, and galvannealed steel sheets (these steel sheets are hereinafter collectively referred to as zinc-based galvanized steel sheets). The present invention relates to a chromate treatment method capable of forming a chromate film with excellent uniform coating properties and excellent corrosion resistance, alkali resistance, welding resistance, and paintability (coating film adhesion and corrosion resistance after painting) on the surface of

[Prior art] Chromate treatment solutions used to consist of chromic acid or dichromic acid aqueous solutions, but various methods have been proposed to form a film that is hardly soluble when treated with acid or alkali after forming a chromate film. has been done. These conventional techniques and their advantages and disadvantages will be explained below.

As a method for forming a hardly soluble chromate film on the surface of a zinc-based plated steel sheet, the invention disclosed in JP-A-50-158535 discloses a method of forming a hardly soluble chromate film on the surface of a zinc-based plated steel sheet using a chromate anhydride-phosphoric acid-water-soluble or water-dispersible polymer compound-based chromate solution. Cr6+ in the treatment solution is reduced to 70% or more (r3+) with a reducing agent such as ethylene glycol. However, the chromate film formed by implementing this invention contains polymers. Although it has excellent properties such as poor solubility, corrosion resistance, and paintability, it has the disadvantage of poor weldability.

Next, the chromate solution disclosed in Japanese Patent Publication No. 61-58522 specifies the components of chromic acid-chromic acid reduction product-silica sol system. However, when processing and painting a surface-treated steel sheet on which a chromate film has been formed using the method of this invention, mainly hexavalent chromium in the chromate film is likely to be eluted by alkali cleaning before painting, that is, the alkali resistance is poor. There are problems in that the corrosion resistance of the coating is reduced and that welding, for example spot weldability, is poor because the coating contains silica.

Next, JP-A-58-22383 and JP-A-62-1 disclose the use of a silane coupling agent as a hexavalent chromium reducing agent in a chromate treatment solution.
No. 83478 is mentioned. Although the films formed by the methods of these inventions all have excellent paint film adhesion,
The chromate film formed by the method of the former invention has poor alkali resistance because it does not contain silica or organic polymer, and the latter invention has problems such as insufficient spot weldability because it contains colloidal silica. We have it. Examining the performance of each component in the prior art in the above-mentioned chromate treatment method, organic polymers and silica sol improve corrosion resistance, etc., but tend to deteriorate weldability. Furthermore, since the silane coupling agent tends to reduce Cr'+, it tends to make the corrosion resistance of the chromate film unstable.

[Problems to be Solved by the Invention] Therefore, the present invention solves the problems of the prior art in the chromate treatment method for zinc-plated steel sheets, and provides a method that has excellent uniform coating properties, corrosion resistance, alkali resistance, welding resistance, and workability. It is also an object of the present invention to provide a method for forming a chromate film with excellent paintability.

[Means for Solving the Problems] In the present invention, in order to solve the problems faced by the conventional technology in the chromate treatment method for zinc-based plated steel sheets,
First, the following measures were taken for the water-based chromate solution to be applied. That is, a. In order to effectively exert the action of the silane coupling agent, the contents of hexavalent chromium and trivalent chromium are specified, and the chromium ratio (Cr3+/Cr
6 + weight 1 ratio) was also identified.

b. In order to improve the uniform application of the chromate solution, the chromate solution should contain a specific amount of an organic solvent selected from C4 to C8 tertiary alcohols and acetonitrile; Since it can exist relatively stably in the chromate film, it maintains the above-mentioned effect and does not adversely affect the quality of the chromate film.

C. Containing a specific amount of phosphate ions in the chromate solution to contribute to improving the alkali resistance and corrosion resistance of the film;
Therefore, the value of the ratio of PO437/Cr6++Cr'' was also specified.

d. Before applying the chromate solution, add and mix a silane coupling agent to the chromate solution at a specific molar ratio to the Cr'+ concentration in the solution, and then apply the mixed solution to the surface of the zinc-based plated steel sheet. By this means, Cr in the chromate solution applied to the plating surface was
'+' means that during the drying process of the chromate coating solution, the chromate coating solution undergoes the reducing action of the silane coupling agent and solvent, and the bonding action of the silanol groups progresses the network bonding, forming a chromate film with excellent corrosion resistance and alkali resistance. .

e. In order to prevent the formed film from impairing weldability, the aqueous chromate solution does not contain silica or organic polymers that increase the glabellar insulation resistance of the film.

The present inventor was able to complete the present invention by applying the above-mentioned ingenuity to the aqueous chromate solution. That is, the present invention provides 3.0 to 50 g/j2 of hexavalent chromium, 2.0 to 40 g/2 of trivalent chromium, and phosphate ions (P
o, 3-) 1.0 to 100 g/I2, and 3 to 50 g/(l) of at least one organic solvent selected from a tertiary alcohol having 4 to 8 carbon atoms and acetonitrile, and a chromium ratio of (Cr3+/Cr6+ weight ratio)
is 0.25 to 1.5, and furthermore, the weight ratio of phosphate ions to total chromium (PO43-/Cr"+Cr"
) is 0.1 to 1.2, a silane coupling agent is added and mixed in a molar ratio of 0.05 to 0.30 to the hexavalent chromium concentration in the chromate solution, and then A chromate solution is applied to the surface of a zinc-based plated steel sheet, and then dried, leaving 10 to 20 chrome deposits on the surface.
The present invention relates to a method for chromate treatment of galvanized steel sheets, which is characterized by forming a chromate film of 0 mg/m''.

First, the composition of the aqueous chromate solution used in the method of the present invention will be explained. This chromate solution uses water as a solvent, and contains 3.0 to 50 g/l of Cr'+ and 2.0 to 50 g/l of Cr'+.
Contains 40g# of Cr3+ as a basic component. 3.0
g/l Cr" and less than 2.0 g/l Cr'+
If the amount of Cr'+ exceeds 50 g/l or 40 g/l, it becomes difficult to form a chromate film showing satisfactory corrosion resistance, and the viscosity of the chromate solution increases and the stability of the chromate solution increases. This results in poor properties and makes it difficult to control the amount of chromium deposited. Also, the important thing about the amount of chromium is Cr
'+ and Cr'+ content ratio, chromium ratio (Cr"
/Cr") is required to be within the range of 0.25 to 1.5. If the chromium ratio is less than 0.25, the Cr'+ concentration in the chromate solution increases accordingly, so silane is added to the solution. When a coupling agent is added, the reduction reaction of Cr'+ in the chromate solution by the silane coupling agent becomes more likely to occur.As a result, the chromate solution is heated, and as a result, the Cr'+ is reduced by the solvent in the chromate solution. This tends to occur as the reaction progresses and the solvent evaporates, leading to a deterioration in the quality of the chromate solution.On the other hand, if the chromium ratio exceeds 1.5, the chromate solution tends to gel and the corrosion resistance of the chromate film formed decreases. The chromium ratio is controlled by adding a reducing agent such as ethanol, methanol, oxalic acid, starch, or sucrose, if necessary.

As other components, the chromate solution of the present invention has a content of 1.0 to 10
Contains 0 g/(l of PO43-).

Po, 3- is preferably orthophosphoric acid (H, PC), )
It is added in the form of If the amount of PO43- is less than 1.0 g/l, the corrosion resistance and alkali resistance of the chromate film will decrease, while if it exceeds 100 g/g, the reduction of Cr'+ in the chromate solution by the silane coupling agent will proceed rapidly. Decrease the quality of the liquid. Regarding the amount of PO43, what is particularly important is the total chromium (Cr) in the chromate solution.
"+Cr") is the ratio to the amount. The ratio of PO43-/total Cr is preferably in the range of 0°1 to 1.2. If this ratio is less than 0.1, the alkali resistance and corrosion resistance of the chromate film tend to decrease, while if it exceeds 1.2, the chromate film tends to deteriorate. The reduction effect of Cr← in the solution by the silane coupling agent becomes extremely easy to proceed, and the C in the chromate solution is
Since r'+ is reduced to a large extent or almost to Cr 3+ , the quality of the chromate solution deteriorates and it becomes difficult to form a film that meets the purpose of the present invention.

Furthermore, as another component, at least one type of solvent selected from C4 to C8 tertiary alcohol and acetonitrile is used as a wettability improver to improve the coating properties of the chromate solution, and in some cases, a mixture of multiple of the above-mentioned solvents is used. Add 3 to 50 g/l to Kurome-1 liquid. All of the above-mentioned solvents contain C in the chromate solution within about 35°C.
It has relatively high stability against r'+ and has the effect of improving the wettability of the chromate solution to the plating surface without having the same adverse effect on the quality of the chromate film.

Therefore, the improved wettability contributes to improving the uniform application of the chromate solution during high-speed operation. If the amount of solvent is less than 3g/12, it will be difficult to confirm the effect;
If it exceeds g/l, no improvement in effectiveness can be expected by adding more, and it is not favorable from an economical or working environment standpoint.
Generally, the above-mentioned solvent is added in proportion to the total chromium concentration in the chromate solution or the coating speed.

Specifically, the C4 to C8 tertiary alcohol is t-
Examples include butanol and t-amyl alcohol.

In addition, 0.2 to 10 g/
Alkali resistance can be further improved by blending 1 of zinc ions. If the amount of zinc ions is less than 0.2 g/l, it is difficult to confirm the improvement effect, and conversely, if the amount of zinc ions is less than 0.2 g/l,
Zn ions are added to the chromate solution in the form of zinc white, zinc carbonate, zinc phosphate, or zinc hydroxide. Furthermore, a complex fluoride can be added to the chromate solution alone or together with zinc, if necessary.

The amount added is preferably within the range of 0.2 to 8 g/l in terms of F. Preferred specific examples of the fin fluoride are fluorozirconic acid, fluorotitanic acid, fluorosilicic acid, or fluoroboric acid, and these are By adding the same amount to the chromate solution, etching of the zinc-based plating surface by the chromate solution progresses, and the eluted metal ions,
Alternatively, the metal ion and the zinc ion added to the chromate solution are complexed by the complex fluoride, and the metal or zinc ion is added to the chromate solution.
The complex becomes a purifying component of the chromate film and contributes to improving the corrosion resistance and coatability of the film. If the F equivalent amount is less than 0.2 g/l, it is difficult to confirm the effect of adding fluoride, while if it exceeds 8 g/l, the corrosion resistance of the chromate film will decrease.

After adding the silane coupling agent to the aqueous chromate solution as described above, it is desirable to maintain the temperature at about 35° C. or lower, preferably about 25° C. or lower, and to use it as soon as possible after adjustment. When coating, add a silane coupling agent to the chromate solution in advance at a molar ratio (silane coupling agent/Cr) to the molar concentration of CI-6+ in the chromate solution.
' + molar ratio) within the range of 0.05 to 0.30 and mixed. Although the silane coupling agent is not specified, preferred examples include those shown in [I] and n1 below.

[I]YRSiX [II[]YSiX R... Alkyl group X... Methoxy group or ethoxy group Y... Vinyl group, mercapto group, glycidoxy group or methacryloxy group Specifically, as a silane coupling agent, Vinyltrimethoxysilane, vinyltriethoxysilane, γ-mercaptopropyltrimethoxysilane, γ-glycidoxypropyltrimethoxysilane, γ-glycidoxypropylmethyldimethoxysilane, γ-methacryloxypropyltrimethoxysilane, γ -methacryloxypropylmethyldimethoxysilane and the like.

As mentioned above, the type of silane coupling agent is not specified in the present invention, but the one represented by formula -8 has good solubility in the aqueous chromate solution and improves the corrosion resistance of the chromate film. These are particularly preferred because they make a large contribution to the future.

If the molar ratio of the silane coupling agent added is less than 0.05, it becomes difficult to confirm the effect of improving the alkali resistance of the chromate film, and conversely, if it exceeds 0.3, the stability of the chromate solution tends to gradually decrease. Cr'+ increases in the content and tends to gel more easily. More preferably, they are mixed in a molar ratio of 0.1 to 0.2.

As mentioned above, a chromate solution mixed with a silane coupling agent is applied to the surface of a galvanized steel sheet using a roll coater, and then dried.Although the present invention does not specify the drying conditions, it is preferable to Dry for 5 to 10 seconds at a board temperature of 60 to 150°C to form a chromate film with a chromium adhesion amount of 10 to 200 mg/m.However, after adding the silane coupling agent to the aqueous chromate solution, Maintain the liquid temperature at about 35°C, preferably below about 25°C.If the chromium concentration is relatively low, it will be stable enough for about one month, but if the chromium concentration is high, - Must be applied within weeks.

The amount of chromium deposited is not particularly limited, but if it is less than 10 mg/m2, the corrosion resistance of the film and the corrosion resistance after painting will be insufficient.
If it exceeds 200 mg/m2, it will be difficult to control the amount of chromium deposited in the chromate film, and the corrosion resistance improvement effect will be saturated, making it difficult to expect further effects, and part of the chromate film will be easily removed by external force, so the coating film This causes a decrease in adhesion. Note that the pH of the aqueous chromate solution specified in the present invention is not specified, but is preferably 1.0 to 3.
It is 0th place.

[Function] In the process of blending a silane coupling agent into an aqueous chromate solution and applying it to the surface of a galvanized steel sheet and drying it, Cr'', Cr'' and PO43- in the aqueous chromate solution are mainly caused by thermal energy during drying. Each of the components reacts with the plating surface to form a colorless film represented by (a) and (b), a green film represented by (c), and a golden color represented by (d) and (e). The chromate film is a forming component of the chromate film.

(a) Zn (OH)2 (b) Cr (OH)2 (c) CrP04 ・4H20 (d) ZnO-32n (oH>2-cro3゜3Zn
Zinc chromate compound represented by (OH)z.cr03+ 2Zn (OH)z.CrO:s, etc. (e) Cr (OH), -Cr (OH)-Cry.

(chromic chromate) Next, the silane coupling agent will be explained.

22. Taking a silane coupling agent having a trimethoxy group as an example and representing it as YR,S i (OCH3) 3, it undergoes hydrolysis as shown in the following formula (1). That is, (1) YRS i (OCH3) i+38
．． 0→(f) YRSi (OH)3+3CH30H Due to heating energy after application of the chromate solution, the chromic chromate in (d) further undergoes a condensation reaction as illustrated in FIG. 1, and further undergoes a condensation reaction as illustrated in FIG. As shown, the chromic chromate crosslinks with the hydrolyzed component (f) of the silane coupling agent, and methanol reduces the hexavalent chromium in the chromic chromate. It is thus inferred that the chromic chromate and the hydrolyzed product of the silane coupling agent form a complex cross-linking bond to form a pair of network-like polymer structures. Therefore, the above-mentioned (a), (b), (c), and (d) are present in the structure of the network-like polymeric chromium compound shown in FIGS.
It is presumed that each component exists in a sequestered state or in a bound state with the polymeric chromium compound.

The chromate film having a network molecular structure formed in this manner has strong alkali resistance due to the bonding effect of the silanol groups, that is, it becomes a film in which chromium in the film is difficult to be eluted by alkaline cleaning. Moreover, it is presumed that the network molecular structure also contributes to improving corrosion resistance and coating properties.

Furthermore, since this film does not contain silica or organic polymer compounds, it has a relatively low glabellar insulation resistance value, and therefore has excellent welding resistance.

Examples will be given below to further specifically explain the effects of the present invention, and will be shown together with comparative examples.

[Example] (1) Preparation method of chromate coating liquids Chromate coating liquids No. and A shown in Table 1 were prepared by first dissolving 200 g of chromic anhydride in 500 g of water, and adding phosphoric acid (75% aqueous solution) to this aqueous solution. 86g, methanol 18
g was added and heated at 80 to 90°C for 1 hour to form Cr 3 +/
(After reducing and cooling so that the weight ratio of r 6+ becomes 1.0, 26 g of t-butanol and water are added to bring the total amount to 1 kg.
g. Hereinafter, this liquid will be referred to as an aqueous chromate liquid.

Next, add this aqueous chromate solution to the total chromium content (Cr”+C
r") to 40 g/Ω and the amount of t-butanol to Log/l. ) was added and stirred to prepare chromate coating solutions No. and A.

Hereinafter, chromate coating liquids No. B~ were prepared in the same manner as chromate coating liquids No. and A to have the compositions shown in Table 1.

(2) Chromate treatment method The chromate coating solution prepared in this way was applied to the surface of an electrogalvanized steel sheet and an electrolytic zinc-nickel alloy coated steel sheet by the process shown below, and the results obtained by drying are shown in Table 2. It was shown to.

Steel plate to be treated (*1) → Alkaline degreasing (*2) → Water washing → Roll squeezing → Drying (air drying) → Chromate application → Roll squeezing → Drying (*3) → Evaluation test (*1) Galvanized steel sheet (zinc coating amount 20 g/m2/
20 g/m2) and double-sided electrolytic zinc nickel alloy plated steel plate plating amount 20 g/m2/20 g/m",
(contains 11wt% nickel) and its size is 200x3
An oiling material with a plate thickness of 0.8 mm was used.

(*2) Alkaline degreasing was carried out using a 2% aqueous solution of a weakly alkaline degreaser (Bulklean 342, manufactured by Nihon Paru Ising Co., Ltd.) at a temperature of 60° C. for 30 seconds.

(*3) Drying was carried out at a plate temperature of 100° C. and a drying time of 7 seconds.

(3) Painted plate production method Chromate treated steel plate can be used as is or as described in (4) below.
- After the alkali cleaning described in (a), a baking-type melamine alkyd paint (Oguchi Honyo Co., Ltd., Pricon 700 White) was applied and baked and dried at 140°C for 20 minutes to produce a painted board (film thickness 25 μm). did.

(4) Performance evaluation test (a) Alkali resistance test A chromate-treated steel plate was washed with alkali under the following conditions, and the amount of chromium deposited before and after was measured using fluorescent X-rays (mg/m
2) L, alkali resistance was expressed by the following formula. That is, the smaller the % value, the better the alkali resistance, and the value 0 indicates that the test was not affected by alkali at all.

For alkaline cleaning, use an alkaline degreaser whose main ingredient is sodium silicate (Bulklean N364 manufactured by Nippon Baru Ising).
Spray treatment was performed with a 2% aqueous solution of S) at a temperature of 60°C for 2 minutes.

(b) Corrosion resistance ■ Test piece of electrogalvanized steel plate before and after alkaline cleaning (S. size 70 x 15
A salt spray test specified in JIS-Z-2371 was conducted for 150 hours at a thickness of 0 mm), and the corrosion resistance was evaluated based on the state of white rust occurrence over the entire area of the test piece.

◎: White rust occurrence area rate 0% ○: Same as above, less than 10% △: Same as above 10% or more and less than 30% ×: Same as above 30% or more
A composite corrosion test method using a cycle of drying (60°C) for 2 hours and wet (50°C, R895% or higher) for 2 hours] was conducted.
A 0 cycle test was conducted, and the corrosion resistance was evaluated based on the state of red rust occurrence over the entire area of the test piece.

◎: Red rust occurrence area rate 0% O: Same as above, less than 10% Δ: Same as above, 10% or more and less than 30% ×: Same as above, 30% or more (c) Scratches reaching the base metal on the painted plate corrosion-resistant coating are made with a cutter, and salt water is sprayed. The test was carried out for 200 hours for the electrogalvanized steel sheet and for 300 hours for the electrolytic zinc nickel alloy plated steel sheet. After the implementation, the adhesive tape (cellotape) was peeled off, and the judgment was made by measuring the maximum one-sided peeling from the scratch (unit: mm)
).

(d) Paint film adhesion ■ Goban test For test pieces painted without alkaline cleaning, 1
Square mm square squares were cut with a cutter so as to reach the base metal, and adhesive tape (cellotape) was applied to the surface of the test piece and rapidly peeled off to observe the degree of peeling of the coating film.

■ Erichsen extrusion test A test piece coated without alkaline cleaning was extruded to 6 mm using an Erichsen extruder, cellophane tape was applied and rapidly peeled off, and the degree of peeling of the coating film was observed.

The coating film adhesion in the above items was evaluated in the following four grades depending on the degree of peeling of the coating film.

◎: Coating Jll peeling M 0% ○: Same as above, less than 10% Δ; Same as above, 10% or more and less than 30% ×: Same as above
30% or more (e) Welding resistance If spot welding is continuously performed on electrolytic zinc-nickel alloy plated steel sheets under the following conditions, the welding terminal will gradually deteriorate and weldability will deteriorate. can be determined. In other words, for every 100 points, 30X10
Another test piece of 0 mm was welded, and the number of dots until the tensile shear strength of the test piece could be maintained at 400 kg was recorded.

Welding surface: Coated surface - Uncoated surface Pressure force: 200 kg Current: 8.5 kA Current application time: 10 cycles Electrode: R40 (radius type) Material: Chromium - Copper (f) Uniform spreadability test of chromate coating liquid 1st Add a water-soluble organic solvent to the chromate coating solutions No. and G shown in the table [
7, and the uniform coating properties of the chromate film in roll coater coating were evaluated. Table 3 also shows the surface tension of the chromate coating solution.

The uniform applicability of the chromate film was classified into the following three levels.

○: Uniform Δ: Slightly repellent ×: Many repellents In the chromate film containing a silane coupling agent, the organic functional group of the silane coupling agent, that is, the vinyl group, mercapto group, glycidoxy group, or methacryloxy group, is the functional group of the top coating resin. Reacts with the base to improve paint adhesion.

Therefore, Examples N011 to 12 within the scope of the present invention have excellent paint adhesion and do not contain a silane coupling agent, Comparative Example N013.5.8 and Comparative Example No. .4.6 has poor paint adhesion.

[Effects of the Invention] As described above, according to the present invention, the surface of a galvanized steel sheet can be coated uniformly and has excellent alkali resistance, corrosion resistance, paintability (paint film adhesion and corrosion resistance after painting), and resistance. A chromate film with excellent weldability can be formed.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the condensation reaction of chromic chromate, and FIG. 2 is a diagram showing the crosslinking reaction of chromic chromate. Patent Applicant: Japan Bar Power Rising Co., Ltd. Patent Application Agent: Patent Attorney Takuo Murai Figure 2

Claims (1)

[Claims] 1. 3.0 to 50 g/l of hexavalent chromium, and 2.
0-40g/l and phosphate ion (PO_4^3^-)
1.0 to 100 g/l, and 3 to 50 g/l of at least one organic solvent selected from a tertiary alcohol having 4 to 8 carbon atoms and acetonitrile, and a chromium ratio (Cr^3^+/Cr ^6^+weight ratio) is 0.25 to 1
．． 5, and the weight ratio of phosphate ions to total chromium (PO_4^3^-/Cr^6+Cr^3^+) is 0.
After adding and mixing a silane coupling agent to an aqueous chromate solution having a concentration of 1 to 1.2 in a molar ratio of 0.05 to 0.30 with respect to the hexavalent chromium concentration in the chromate solution,
The water-based chromate solution is applied to the surface of a zinc-based plated steel sheet and then dried, so that the amount of chromium deposited on the surface is 10 to 200 m.
A method for chromate treatment of zinc-based plated steel sheet, characterized by forming a chromate film of g/m^2. 2. The method for chromate treatment of zinc-based plated steel sheets according to claim 1, wherein the tertiary alcohol having 4 to 8 carbon atoms contained in the aqueous chromate solution is selected from t-butanol or t-amyl alcohol. 3. The method for chromate treatment of zinc-based plated steel sheets according to claim 1 or 2, wherein the silane coupling agent contained in the aqueous chromate solution is selected from those shown in [I] and [II] below. [I] YRSiX [II] YSiX R...Alkyl group After drying, the plated steel sheet is dried at a temperature of 60 to 150°C for 5 to 1
4. The method for chromate treatment of a zinc-based plated steel sheet according to any one of claims 1 to 3, wherein the chromate treatment is carried out for 0 seconds. 5. The aqueous chromate solution further contains 0.2 to 1 zinc ion.
The method for chromate treatment of a zinc-plated steel sheet according to any one of claims 1 to 3, wherein the zinc-plated steel sheet contains 0 g/l. 6. The method for chromate treatment of a zinc-based plated steel sheet according to any one of claims 1 to 5, wherein the zinc ions are supplied from zinc white, zinc carbonate, zinc phosphate, or zinc hydroxide. 7. The aqueous chromate solution further contains complex fluorides.
Chromate treatment method 8 for zinc-based plated steel sheet according to any one of claims 1 to 6, wherein the complex fluoride contains 0.2 to 8 g/l in terms of fluorozirconic acid, fluorotitanic acid, fluoro The method for chromate treatment of a zinc-based plated steel sheet according to any one of claims 1 to 7, wherein the chromate treatment method is supplied from silicic acid or fluoroboric acid.