JPH0931666A - Pretreatment for coating of stainless steel sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To form a coating film excellent in coating film adhesion and corrosion resistance after coating by treating a stainless steel sheet with an acidic treating solution contg. metal ions and sulfate ions and thereafter, subjecting the resulting treated stainless steel sheet to coating type chromating. SOLUTION: In this pretreatment, the surface of a stainless steel sheet is brought into contact with an acidic treating solution which contains metal ions and sulfate ions and has a pH of 0.5 to 4.5 and then washed with water and thereafter, the resulting surface is coated with a coating type chromating solution contg. hexavalent and trivalent chromium ions and then dried to form a chromate coating film having a 5 to 150mg/m<2> coating weight expressed in terms of metal chromium on the surface. As the metal ions contained in the acidic treating solution, those of one kind selected from among divalent or higher valent metal ions other than alkaline earth metal ions, preferably selected from among Fe, Ni and Co ions can be used and in particular, those of one kind selected from between ions of Ni and Co which are nobler than Fe are more desirable. Preferably, this acidic treating solution also contains ions of one kind selected from among fluoride ion and fluorinated ions and further contains phosphate ion.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pretreatment method for coating stainless steel sheets. More specifically, the present invention relates to a novel pretreatment method for coating, which forms a coating film having excellent coating film adhesion and corrosion resistance after coating on the surface of a stainless steel plate.

[0002]

2. Description of the Related Art Generally, stainless steel sheets have much better corrosion resistance than ordinary steel sheets, and therefore have a wide range of applications as high-grade durable materials such as building materials, vehicles, equipment,
It is used in various fields such as kitchen supplies. However, when the stainless steel plate is used unpainted, dirt easily adheres to the surface, and the dirty part becomes the starting point of corrosion, or when used on the coast of the coast, pitting corrosion caused by chlorine Therefore, there is a problem that not only the design property is deteriorated, but also the functionality is deteriorated. Therefore, in order to solve these problems, a coated stainless steel plate obtained by coating a stainless steel plate is used as a building material or the like.

The surface of a stainless steel plate is generally covered with a stable metal oxide, and it is known that the adhesion between the surface and the coating film is low. In order to solve this problem, solvent cleaning, alkali cleaning, nitric hydrofluoric acid treatment, and phosphate treatment have been applied as pretreatments for coating stainless steel sheets. It is chromated.

However, these conventional coating pretreatment methods have the following problems.

The conventional pretreatment using solvent cleaning has only the effect of removing oils and fats adhering to the surface, has no effect of improving the adhesion of the coating film, and does not improve the water wettability of the surface of the stainless steel sheet. The coating type chromate treatment liquid cannot be applied to the treated surface. Further, the working environment is inevitably deteriorated by the solvent used.

The conventional pretreatment by alkali cleaning is effective for removing oils and fats on the surface, but the metal oxide on the surface of the stainless steel plate cannot be removed, so that the adhesion of the coating film is not improved and the surface is wet with water. Sex is not improved. Therefore, it may not be possible to perform chromate treatment on the obtained pretreated surface. Further, since the adhered alkaline components are not sufficiently removed by washing with water, there arises a problem that the adhesiveness of the coating film is significantly deteriorated with time.

The above-mentioned pretreatment with nitric hydrofluoric acid has the effect of improving the adhesiveness of the coating film, but the working environment due to hydrofluoric acid tends to deteriorate, and the cost of wastewater treatment is high, which is economically disadvantageous. is there. Further, it is not possible to avoid deterioration of coating film adhesion with time only by the nitric hydrofluoric acid treatment.

Similarly, the pretreatment with phosphate has the effect of improving the adhesion of the coating film, but it causes a problem in the line operation because it produces sludge. That is, when the generated sludge adheres to the stainless steel plate, the steel plate itself or the roll surface may be scratched, or the coating film after coating may have a so-called "butsu" defect, and the coating film may peel off at that portion. There is a problem such as causing. Also, phosphate treatment is usually 4
Since it is carried out at 0 to 70 ° C., phosphate may be deposited in the vicinity of the heater of the treatment liquid tank, the heating efficiency may be lowered, and an economic disadvantage may occur. In addition, the phosphating solution must be regularly discarded to remove sludge,
The maintenance cost will be quite high. Incidentally, as a pretreatment method for coating the stainless steel plate, Japanese Patent Publication No. 63-663.
There is a method disclosed in Japanese Patent Laid-Open No. 93. According to this method, a stainless steel plate is subjected to a phosphate treatment, subjected to roll squeezing, and further coated with a coating type chromate treatment solution in a chromium amount of ² to 60 mg / m ² . In this method, the initial and aging adhesion between the stainless steel plate and the coating film is good, but the phosphate waste liquid treatment step is required, and the above problems cannot be solved.

That is, as described above, the conventional pretreatment method cannot stably impart sufficient coating film adhesion to the stainless steel plate, and particularly when it is used as a building material for exteriors, which is severely deteriorated with time. Was prone to problems and could not be processed at a low cost using industrial equipment.

[0010]

DISCLOSURE OF THE INVENTION The present invention solves the above-mentioned problems of the prior art, and provides a stainless steel sheet with a coating film having excellent coating film adhesion and corrosion resistance after coating, stably and at low cost. It is an object of the present invention to provide a novel pretreatment method for coating a formed stainless steel plate.

[0011]

Means for Solving the Problems As a result of intensive investigations by the present inventors regarding means for solving the above-mentioned problems, after treating a stainless steel sheet with an acidic treatment liquid containing metal ions and sulfate ions, It was newly found that the above problems can be solved by further applying a coating type chromate treatment to the above.

That is, in the pretreatment method for coating a stainless steel sheet according to the present invention, the surface of the stainless steel sheet is brought into contact with an acidic treatment liquid having a pH of 0.5 to 4.5 containing metal ions and sulfate ions and washed with water. After that, a coating type chromate treatment liquid containing hexavalent chromium ions and trivalent chromium ions was applied onto this surface and dried, and the surface was chromated with 5 to 150 mg / m ² in terms of metallic chromium. It is characterized by forming a film.

The metal ion contained in the acidic treatment liquid of the present invention is preferably an ion of a metal having a valence of 2 or more excluding an alkali metal, and is an ion of at least one metal selected from Fe, Ni and Co. Is more preferable,
More preferably, it is an ion of at least one kind of metal selected from Ni and Co, which are metals that are more noble than Fe.

The acidic treatment liquid of the present invention preferably further contains at least one selected from fluoride ions and fluoride ions.

The acidic treatment liquid of the present invention preferably further contains phosphate ions.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION The method of the present invention is not limited to a stainless steel plate, but can be applied to a molded product produced by processing a stainless steel plate. Applicable to all.
In addition, the pretreatment method for coating of the present invention is applied to clear coating using a resin such as fluorine-based or silicone-based, colored coating using a resin such as polyester-based, polyurethane-based, and acrylic-based, powder coating, and electrodeposition coating. It can be used as a pretreatment for various coatings including the above.

The structures of the acidic treatment liquid and the chromate treatment liquid of the present invention will be described in detail below. First, the acidic treatment liquid of the present invention will be described. The acidic treatment liquid of the present invention is an aqueous treatment liquid containing metal ions and sulfate ions and having a pH of 0.5 to 4.5.

The type of metal ion used in the acid treatment liquid of the method of the present invention includes divalent or higher valent metal ions excluding alkali metals, and at least one metal ion selected from Fe, Ni and Co. Are preferred, and more preferably Ni and Co, which are metals that are nobler than Fe.
At least one metal ion selected from the above is used. Use of an alkali metal is not preferable because the adhesion of the coating film may be deteriorated with time. In order to supply the metal ions to the acidic treatment liquid, sulfate, carbonate, phosphate, nitrate, oxide, hydroxide or organic acid salt of the metal can be used. Metal chlorides are not preferable because there is a risk that chlorine ions generated from them will corrode equipment such as a treatment tank with an acidic treatment liquid. Further, the sulfate ions in the acidic treatment liquid are supplied from sulfuric acid, the sulfate salt of the metal ion, and / or other sulfate salt.

In the method of the present invention, the concentration of the metal ion contained in the acidic treatment liquid is not particularly limited, but it is preferably in the range of 0.2 to 30 g / liter in terms of metal atom, More preferably, it is within the range of 0.5 to 20 g / liter. The metal ion concentration is 0.
If it is less than 2 g / liter, the pH of the acidic treatment liquid is 0.5 to
When adjusted to 4.5, sufficient performance may not be obtained in some cases. On the other hand, if the metal ion concentration exceeds 30 g / liter, the treatment effect is saturated and the economical loss due to the consumption of the acidic treatment liquid becomes large, which is disadvantageous.

The amount of sulfate ion is not particularly limited, and may be any amount capable of adjusting the pH of the acidic treatment liquid of the present invention between 0.5 and 4.5, for example, 10 to 200 g / liter.

The acidic treatment liquid used in the method of the present invention preferably contains, in addition to the above components, at least one selected from fluoride ions and fluoride ions.
The fluorine concentration (g / liter) of these is preferably lower than that of sulfate ion, and generally, it is preferably 0.01 to 5 g / liter as fluorine (calculated as fluorine ion). If the fluorine concentration is less than 0.01 g / liter, the effect of improving the etching action on the resulting acidic treatment liquid may be insufficient, and if the fluorine concentration is higher than the sulfate ion concentration, or it exceeds 5 g / liter. If so, the processing tank may be corroded, or the working environment may be deteriorated by a volatile acid such as hydrofluoric acid. Examples of sources of fluorine ions and fluoride ions include, but are not limited to, hydrofluoric acid, hydrofluoric acid, zircon hydrofluoric acid, and titanium hydrofluoric acid.

The acidic treatment liquid of the present invention preferably further contains phosphate ions. The concentration of phosphate ions in the acidic treatment liquid is preferably lower than the concentration of sulfate ions, more preferably 0.01 to 10 g / liter. If the concentration of phosphoric acid is less than 0.01 g / liter, sufficient phosphate ion addition effect may not be obtained, and it may be higher than the concentration of sulfate ion, or 10
If it exceeds g / liter, sludge of phosphate may be generated. The phosphate ion is preferably supplied to the acidic treatment liquid as orthophosphoric acid or a salt thereof.

The pH of the acidic treatment liquid of the present invention is 0.5 to 4.5.
Is adjusted within the range of, and preferably adjusted to 1 to 3.5. When the pH is less than 0.5, it is not preferable because the working environment is deteriorated due to the corrosion or acid mist of the tank or the pipe into which the acidic treatment liquid of the present invention is put, and when the pH exceeds 4.5,
It is not preferable because the resulting acidic treatment liquid has a reduced etching effect on the stainless steel plate and metal ions are precipitated.

In addition to the above inorganic ions, the acidic treatment liquid used in the method of the present invention is an organic acid such as glycolic acid, lactic acid, malic acid, tartaric acid, citric acid, gluconic acid, heptgluconic acid, and ascorbic acid. Alternatively, these salts may be contained. These organic compounds have a pH adjusting action and a metal complexing action with respect to the acidic treatment liquid.

The acidic treatment liquid used in the method of the present invention includes:
In addition to the above metal ions and acid components, a surfactant may be added in order to remove oil adhering to the surface of the stainless steel plate. As the surfactant used for this purpose,
Examples include nonionic surfactants, cationic surfactants, anionic surfactants, and amphoteric surfactants.
For example, as the nonionic surfactant, polyethylene glycol such as polyoxyethylene alkylphenyl ether, polyoxyethylene alkyl ether, polyoxyethylene fatty acid ester, polyoxyethylene sorbitan fatty acid ester, polyoxyethylene / polyoxypropylene / block polymer, etc. Type, polyhydric alcohol type such as sorbitan fatty acid ester, and fatty acid alkylolamide type. Examples of the cationic surfactant include amine salts such as higher alkyl amine salts and polyoxyethylene higher alkyl amines, and quaternary ammonium salts such as alkyl trimethyl ammonium salts. As anionic surfactants, their solubility is generally low in the acidic region, so many of them are difficult to use,
Any type such as polyoxyethylene higher alkyl ether sulfate and polyoxyethylene alkylphenyl ether sulfate to which ethylene oxide is added can be used. Examples of the amphoteric surfactant include amino acid type such as methyl alkylaminopropionate and betaine type such as alkyl dimethyl betaine. At least one selected from these surfactants can be added to the acidic treatment liquid, but it should be noted that the combined use of a cationic surfactant and an anionic surfactant may cause problems in liquid stability. Is. Further, the addition concentration of the surfactant is appropriately 10 g / liter or less, but it is important to appropriately select the type and concentration of the surfactant depending on the type and concentration of oil to be mixed.

Next, the coating type chromate treatment liquid used in the method of the present invention will be described. The coating type chromate treatment liquid used in the method of the present invention contains hexavalent chromium ions and trivalent chromium ions. Examples of the hexavalent chromium ion source include chromic anhydride, dichromic acid, and salts thereof. As the trivalent chromium ion source, the hexavalent chromium ion may be converted into a reducing substance such as methanol or hydrazine. Examples thereof include reduced salts and inorganic acid salts such as trivalent chromium sulfates, nitrates, phosphates and carbonates. The compounding ratio of trivalent chromium ions and hexavalent chromium ions in the coating type chromate treatment liquid is preferably 1/10 to 3/1 in terms of molar ratio. This ratio is 1 /
If it is less than 10, the water resistance of the formed film may be insufficient and the secondary adhesion may be reduced. On the other hand, when this ratio exceeds 3/1, the content of hexavalent chromium ions in the obtained chromate treatment liquid becomes small, and thus the corrosion resistance of the obtained coating may be insufficient.

The coating type chromate treatment liquid may further contain at least one selected from silica sol, colloidal silica and fumed silica. By adding these silica components, the coating film adhesion of the film obtained is further improved, and the coin scratch resistance of the coating film formed thereon is also improved. The amount of silica added is preferably such that the weight ratio of silica / (trivalent chromium ion + hexavalent chromium ion) is 6/1 or less. When this ratio exceeds 6/1, the effect of adding silica is saturated, which is economically disadvantageous and may cause precipitation in the chromate treatment liquid, which is not preferable.

The chromate treatment liquid may further contain phosphate ions. Since the chromate film obtained by adding phosphate ions to the chromate treatment liquid becomes colorless, it is effective when a clear coating film is applied on this film. The amount of phosphate ion added is phosphate ion /
The weight ratio of (trivalent chromium ion + hexavalent chromium ion) is 5
It is preferable to adjust it so that it becomes / 1 or less. If this ratio exceeds 5/1, the water resistance of the resulting coating becomes insufficient and the secondary adhesion thereof may be reduced, which is not preferable.

The coating type chromate treatment liquid contains
Water-soluble polymers such as polymers and copolymers of acrylic acid and / or methacrylic acid, acrylic ester copolymer emulsion, styrene, acrylic ester copolymer emulsion, epoxy resin emulsion, ethylene / acrylic acid copolymer You may add at least 1 sort (s), such as a united emulsion and a polyester resin emulsion. By adding these polymer compounds, the coating film adhesion of the obtained film can be further improved.

Next, the pretreatment method for coating according to the present invention will be specifically described. First, the treatment of the stainless steel sheet with the acidic treatment liquid may be performed by bringing the surface and the acidic treatment liquid into contact with each other by a method such as spraying, dipping, or coating.
Wash with water or hot water and dry. In this process,
The treatment conditions for the steel sheet with the acidic treatment liquid are such that the liquid temperature is room temperature to 80.
C. and contact (treatment) time of 60 seconds or less are sufficient. Next, a coating type chromate treatment is applied. That is, the chromate treatment liquid is applied to the surface of the stainless steel plate treated with the acidic treatment liquid by a method such as dipping or showering to form a treatment liquid layer, and chromate is applied thereto by a method such as air blow or roll squeezing. The coating amount of the treatment liquid may be adjusted, or desired coating may be performed by an arbitrary method such as a roll coating method or a spraying method. There is no particular limitation on the amount of the chromate film formed by the method of the present invention, but the total amount of chromium added is 5 to 150 mg / m ² (as metallic chromium equivalent). It is preferably within the range. This adhesion amount is 5 mg
If it is less than / m ² (calculated as metallic chromium), the corrosion resistance of the obtained coating is insufficient, and if it exceeds 150 mg / m ² , the performance of the obtained coating reaches saturation, which is economically disadvantageous.

[0031]

The action and effect of the coating pretreatment by the method of the present invention are considered as follows. Usually, the surface of a stainless steel plate is covered with a stable metal oxide film, and it is described that the corrosion resistance of the stainless steel plate is due to this metal oxide film. On the other hand, it is known that the adhesion force of a coating film such as a paint applied to a metal to a substrate depends on a polar group in the paint.
However, since the surface of the stainless steel plate is covered with a stable metal oxide film, it is difficult for the polar groups in the paint to exhibit adhesion to the surface of the stainless steel plate when coated on it.

Therefore, the effect of the present invention is estimated. In the acid treatment liquid treatment, sulfate ions in the acid treatment liquid have a mild corrosive action (etching action) on the stainless steel sheet. Since this etching action is promoted in the low pH range and is proportional to the concentration of sulfate ion, a certain level of sulfate ion concentration is required to obtain a sufficient etching action. Addition of fluorine ions or fluoride ions is effective as an auxiliary agent for this etching reaction.
On the other hand, in view of corrosion of the equipment itself and work environment,
The pH needs to be adjusted to 0.5 to 4.5, but sulfuric acid needs to be neutralized because even a small amount greatly reduces the pH. It is necessary to add a cation as the neutralizing agent, and as the cation, a divalent or higher valent metal ion excluding an alkali metal is preferable, and Fe, Co, or Ni is preferable.
These metal ions play a role of neutralizing sulfuric acid, and particularly Fe
It is presumed that the noble metals Ni and Co have a role of receiving electrons emitted from the surface of the steel sheet during the etching reaction when the steel sheet is treated. Further, it is presumed that a part of metal ions in the acid treatment liquid is substituted and deposited on the surface of the stainless steel plate to further activate the surface of the steel plate. In addition, the addition of phosphoric acid has the effect of adsorbing phosphoric acid on the surface of the steel sheet, improving the water wettability of this surface, and stabilizing the pH of the acidic treatment liquid due to its pH buffering ability. Then, a stable oxide film on the surface of the steel sheet is partially removed by an etching action by sulfuric acid or fluorine, adsorption of a trace amount of metal deposited on the surface of the stainless steel sheet, and adsorption of phosphoric acid, and activation of water on the surface of the stainless steel sheet. The wettability is greatly improved, and as a result, it becomes possible to apply the coating type chromate treatment liquid evenly to the surface of the stainless steel plate, and when the deposited metal comes into contact with the chromate treatment liquid, some interaction It is considered that (interaction) occurs and thereby the adhesion is further improved. Further, sulfuric acid is an acid having a mild corrosive action on stainless steel as described above, but by adjusting the pH of the treatment liquid to 0.5 to 4.5,
It is presumed that the corrosion resistance does not decrease because the damage to the stable metal oxide film exhibiting the high corrosion resistance of the stainless steel plate is minimized. Furthermore, since the solubility of the sulfate added to the acidic treatment liquid is generally high, the risk of sludge generation is extremely low.

[0033]

EXAMPLES The present invention will be specifically described with reference to the following examples, but the present invention is not limited to these examples.

[0034] Examples 1-10, in each of Comparative Examples 1 to 7 Examples 1 to 10 and Comparative Examples 1 to 7 were subjected to processing operations and the following tests. (1) an acidic treatment solution prepared acidic treatment solution (I) is cobalt sulfate (CoSO ₄ · 7H
20 g of ₂ O) was dissolved in 900 g of water and the pH was adjusted to 1.2 with sulfuric acid, and the total amount was adjusted to 1 liter. The acidic treatment liquids (II), (III), (IV), and (V) were prepared so as to have the compositions shown in Table 1 by the same procedure as the treatment liquid (I).

(2) Preparation of coating type chromate treatment liquid Chromate treatment liquid (a) is 100 g of chromic anhydride.
Was dissolved in 300 g of pure water, and methanol was added to this aqueous solution to reduce a part of chromic acid to adjust the molar ratio of trivalent chromium / hexavalent chromium ions to 3/7. Was added to make the total amount 1 kg. Further, the chromate-treated solutions (b), (c), (d), and (e) were prepared so as to have the compositions shown in Table 2 by the same procedure as the chromate-treated solution (a).

(3) Test plate A commercially available stainless steel plate (SUS304) having a thickness of 0.3 mm, a length of 200 mm and a width of 300 mm was used as a test material.

(4) Treatment with Acid Treatment Solution This test material was subjected to pretreatment for coating under the treatment conditions shown in Table 3. All the treatments before the chromate treatment were performed by a spray method, washed with water, drained and dried.

(5) Treatment with Chromate Treatment Liquid Next, various chromate treatment liquids shown in Table 2 were appropriately diluted so that the chromium deposition amount shown in Table 3 at a WET coating amount of 5 ml / m ² was obtained. Was applied by a roll coater and dried for 5 seconds so that the ultimate plate temperature was 70 ° C.

(6) Coating On the pretreated stainless steel plate, in the coating system, a fluorine-based clear paint for stainless steel plate was bar-coated, and baked for 25 seconds so that the reached plate temperature was 220 ° C. The film thickness was 10 μm. Separately, in the coating system, a bar coating was similarly applied to the pretreated stainless steel plate using a colored paint (polyester top coat), and baked for 30 seconds so that the reached plate temperature was 220 ° C., coating film thickness 15 μm And The following performance tests were conducted on the above-mentioned coating system and the coated stainless steel sheets obtained by the above.

(7) Performance test (a) Adhesion of coating film: (i) Primary adhesion: The coated plate was subjected to a bending test according to the test method of the colored zinc iron plate of JIS G 3312. At this time, the inner space of bending is 0 (0T) and 2 (2
The tape peeling test was performed on the bent portion, and the degree of peeling of the coating film was visually determined according to the following evaluation criteria. (Ii) Secondary adhesion: After immersing the coated plate in boiling water for 2 hours, 1
The next adhesion was tested and evaluated in the same manner. <Evaluation Criteria> Excellent ◎ ... No peeling ↑ ○ ... Peeling area ratio less than 10% ↓ △ ... Peeling area ratio 10% or more and less than 30% Poor × ... Peeling area ratio 30% or more

(B) Corrosion resistance after coating: The coating film was scratched with a cutter to reach the base metal, and a salt spray test was conducted for 3000 hours according to JIS Z2371. The judgment was made by visually observing the area of rust generation on the scratched portion and the entire test plate. <Evaluation criteria> Excellent ◎ ... No rust generation ↑ ○ ... Rust generation area ratio less than 10% ↓ △ ... Rust generation area ratio 10% or more and less than 30% Poor × ... Rust generation area ratio 30% or more

(C) Weather resistance: A scratch on the test plate coated with a fluorine-based clear coating by the above-mentioned coating system, which reaches the base metal, is cut with a cutter, and a carbon arc sunshine weathering is performed according to JIS D 0205. The measurement was carried out for 3000 hours with a meter, and the judgment was made visually according to the following evaluation criteria. <Evaluation Criteria> Excellent ◎ ... No coating film peeling ↑ ○ ... Peeling area ratio less than 10% ↓ △ ... Peeling area ratio 10% or more and less than 30% Poor × ... Peeling area ratio 30% or more

Table 4 shows the test results.

[0044]

[Table 1]

[0045]

[Table 2]

[0046]

[Table 3]

[0047]

[Table 4]

As is apparent from Table 4, Examples 1 to 10 using the pretreatment method for coating according to the present invention showed good adhesion to the coating film and excellent corrosion resistance after coating. On the other hand, Comparative Examples 1 to 7 could not obtain sufficient coating film adhesion, and Comparative Examples 1, 2, 6, and 7 were also insufficient in corrosion resistance after coating.

[0049]

As is apparent from the above description, the method of pretreatment for coating a stainless steel sheet according to the present invention provides a chromate coating having excellent coating adhesion and post-coating corrosion resistance on the surface of the stainless steel sheet efficiently and at low cost. Since it can be formed in the above manner, it has a great effect in practical use.

Claims (4)

[Claims] 1. A surface of a stainless steel plate is brought into contact with an acidic treatment liquid having a pH of 0.5 to 4.5 containing metal ions and sulfate ions, which is washed with water, and then hexavalent chromium ions are added on the surface. A stainless steel sheet, characterized in that a coating type chromate treatment liquid containing trivalent chromium ions is applied and dried to form a chromate film of 5 to 150 mg / m ² in terms of metallic chromium on the surface. Pre-treatment method of paint. 2. The pretreatment method for coating a stainless steel sheet according to claim 1, wherein the metal ions contained in the acidic treatment liquid are ions of at least one metal selected from Fe, Ni, and Co. 3. The acidic treatment liquid further contains fluorine ions,
The pretreatment method for coating a stainless steel sheet according to claim 1 or 2, further comprising at least one selected from the group consisting of and fluoride ions. 4. The pretreatment method for coating a stainless steel sheet according to claim 1, wherein the acidic treatment liquid further contains a phosphate ion.