JPH09195062A - Production of hot dip galvanized steel sheet excellent in corrosion resistance, blackening resistance and scratching resistance - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a steel excellent in scratching resistance in addition to both characteristics of corrosion resistance and blackening resistance without executing special treatment such as pretreatment by treating the surface of a galvanized steel sheet by a chromate soln. contg. the organic acid salt of Co and or Ni. SOLUTION: The surface of a hot dip galvanized steel sheet is treated by a chromate soln. contg. one or more kinds among the organic acid salt of Co and/or Ni. Thus, its corrosion resistance and blackening resistance can be improved over a long period without executing pretreatment before the chromate treatment to obtain the improvement of the production efficiency, and furthermore, the effect of improving its scratching resistance can be obtd. Moreover, it is recommended that Al is incorporated by >=4 mass% into the plating layer of the galvanized steel from the viewpoint of obtaining excellent corrosion resistance. It is recommended that the chromate treating soln. contains one or more kinds among the organic acid salt of Co and/or Ni together with chromic acid and a chromic acid-reduced substance as the main components, and oxalic acid, formic acid or acetic acid used as the organic acid.

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 hot dip galvanized steel sheet, and more particularly, to corrosion resistance, blackening resistance and flaw resistance without any special treatment such as pretreatment. The present invention relates to a method capable of efficiently producing a hot-dip galvanized steel sheet excellent in heat resistance.

[0002]

2. Description of the Related Art Among hot-dip galvanized steel sheets, especially A
Although the zinc-based plated steel sheet containing 1% by mass or more of 4 has a relatively short history, it has been widely used in the fields of construction, home appliances, etc. because of its excellent corrosion resistance, and its applications are diversifying. Then, for the purpose of further improving the corrosion resistance, a method of applying chemical conversion treatment such as chromate treatment to the surface of the hot-dip galvanized steel sheet is adopted. However, when the chromate-treated hot-dip galvanized steel sheet is stored under high temperature and high humidity for a certain period of time, a phenomenon in which the steel sheet discolors black in a spotty manner is observed. This phenomenon is usually observed when the hot dip galvanized steel sheet is subjected to chromate treatment, but is particularly noticeable when the Al content in the plating layer is high, and the appearance of the plated steel sheet is It is known to change color significantly and turn black.

In the use of the hot-dip galvanized steel sheet, until now, the steel sheet had been further coated, but with the expansion of applications, it is increasingly used without coating without coating. It's starting. Therefore, quality requirements for corrosion resistance and blackening resistance under unpainted have become more severe.

Among these, as a method for increasing the blackening resistance,
For example, the following many technologies have been proposed. Hot-dip galvanized steel sheet, Ni ions and / or Co
A method of pre-treating with a solution containing ions and then performing chromate treatment (JP-A-59-177381). A method of treating a surface of zinc or a zinc-based alloy with a solution having a pH of 5 to 9 containing at least one of Fe ion, Ni ion and Co ion prior to the chromate treatment (Japanese Patent Publication No. 7-74461). A method of subjecting a hot-dip galvanized steel sheet to mechanical treatment such as skin pass rolling, heat treatment, and then chromate treatment (JP-A-55-131178). A method in which the surface of the hot-dip galvanized coating is washed with an alkaline aqueous solution, treated with an aqueous solution containing Ni ions, and then subjected to a chromate treatment (JP-A 61-110777). A method of subjecting a hot-dip galvanized steel sheet to a blast treatment and then a chromate treatment (JP-A-63-166974).

However, in any of these methods, in order to enhance the blackening resistance, before the chromate treatment,
Pretreatment such as treatment with a predetermined solution, heat treatment or blast treatment is required. Therefore, during the manufacturing process of the plated steel sheet, equipment for performing such a pretreatment is newly required, and the manufacturing efficiency is extremely poor.

Further, the above-mentioned method is intended to improve the blackening resistance by adding Ni, Co or the like to the pretreatment solution before the chromate treatment. The effect of improving the blackening resistance by the addition of these metals is as described in the above-mentioned publication, but in short, Co or Ni is deposited in the form of a metal or an oxide at the active sites generated on the plating surface. By doing so, it is considered that the activity of the plating surface is lowered, and as a result, the progress of corrosion due to the local battery can be suppressed. However, when pretreatment with a Ni / Co-containing solution under strongly acidic conditions (pH 1 to 4) or strongly alkaline conditions (pH 11 to 13.5) recommended by this method, the oxide film on the outermost layer is severely etched, It was found that even if the blackening resistance was improved, the corrosion resistance was significantly deteriorated.

Furthermore, in the above method, since the pretreatment is carried out at pH 5 to 9, the problem of etching seen in the above method does not occur, but as described above, the new equipment for performing the pretreatment is used. There is a problem that is required separately.

On the other hand, for the purpose of improving the corrosion resistance of hot-dip galvanized steel sheets, Japanese Patent Laid-Open No. 57-174469 discloses
Chromic anhydride, Co salt of inorganic acid, silica sol, phosphoric acid,
A method of surface-treating a plated steel sheet with a chromate treatment liquid containing a fluorine compound has been proposed. However,
The fluorine compound added to the chromate treatment solution violently etches the oxide layer formed on the outermost layer of the plating,
Even if the corrosion resistance is improved, there is a problem that the blackening resistance is reduced.

Similarly, in JP-A-56-69377, the zinc surface is treated with an acidic aqueous solution containing at least one of Ni, Co and Fe in advance, and then chromate treatment is performed to adhere the coating film. Have been proposed to improve the corrosion resistance and the corrosion resistance of molded articles after coating. Although this method can improve the corrosion resistance, it requires a separate treatment with an acidic aqueous solution before the chromate treatment, which causes problems in production efficiency and equipment. Furthermore, no blackening resistance is considered in this method.

As described above, none of the above methods is a method for efficiently producing a plated steel sheet having both corrosion resistance and blackening resistance. Further, in the above-mentioned conventional technique, while either corrosion resistance or blackening resistance is improved, there is a drawback that the oxide layer on the surface of the plating layer is severely etched, but it is also possible to avoid such inconvenience. There is a long-felt need for a way to do it.

[0011]

DISCLOSURE OF THE INVENTION The present invention has been made in view of the above circumstances, and its purpose is to provide a melt having excellent corrosion resistance and blackening resistance as well as excellent scratch resistance. It is an object of the present invention to provide a method capable of efficiently producing a zinc-based plated steel sheet without performing a special treatment such as a pretreatment.

[0012]

The manufacturing method of the present invention which has solved the above-mentioned problems is a method for manufacturing a plated steel sheet in which a chromate film is applied on a hot-dip galvanized steel sheet. By treating the surface of the steel sheet with a chromate solution containing at least one organic acid salt of Co and / or Ni, it is possible to produce a plated steel sheet having excellent corrosion resistance, blackening resistance and scratch resistance. I have.

In order to further improve these various characteristics, it is preferable to satisfy the following requirements. 4 mass% or more of Al is contained in the plating layer. Metal Cr in the chromate film: 10 to 150 mg / m
² and the total amount of Cr deposited in the chromate coating (metal Cr
Conversion): Amount of metallic Co and / or amount of metallic Ni = 1: 0.0
The mass ratio is 1 to 0.5. The organic acid in the organic acid salt is oxalic acid, formic acid or acetic acid. Chromic acid reduced product in the chromate solution is 10 to 50 mass% with respect to the total amount of chromic acid and the chromic acid reduced product.
Is included in the ratio. The organic acid salt concentration in the chromate solution is 0.1 to 25 g /
Let it be liters. Further, the chromate solution contains at least one metal oxide sol as a solid content in a mass ratio of the metal oxide sol: chromic acid and chromic acid reduced product = 0.5 to 5.0: 1. Furthermore, phosphoric acid was added to the chromate solution:
Chromic acid and chromic acid reduced product = 0.01 to 0.5: 1
It is contained in the mass ratio of.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION As a result of intensive studies to solve the above problems, the present inventors have found that if a plated steel sheet is treated with a chromate solution containing at least one organic acid salt of Co and / or Ni, chromate It is possible to improve corrosion resistance and blackening resistance over a long period of time without pretreatment before applying treatment, resulting in improved production efficiency and scratch resistance that was not expected at all from conventional technology. The inventors have found that an improvement effect can be obtained and completed the present invention.

The manufacturing method of the present invention will be described below in accordance with the manufacturing process. First, the hot-dip galvanized steel sheet as the original plate may be either a galvanized steel sheet or a galvanized steel sheet, but from the viewpoint of obtaining particularly excellent corrosion resistance, 4% by mass or more of Al is contained in the plating layer. Use of zinc-based plated steel sheet containing is recommended. The elements other than Al are not particularly limited, and include Pb, M
Examples thereof include g and Nb. The total amount of these elements added is preferably 0.1% by mass or less, and if it is within this range, it does not adversely affect the corrosion resistance and blackening resistance, which are the objectives of the present invention. Specific examples of the hot-dip galvanized steel sheet used in the present invention include galfan containing 5% by mass of Al and galvalume containing 55% by mass of Al.

Next, a chromate treatment liquid is applied to the surface of the plated steel sheet. This chromate treatment liquid is particularly useful for improving the corrosion resistance of the plated steel sheet, the blackening resistance and the scratch resistance, and in the present invention, from the viewpoint of production efficiency, the surface of the plated steel sheet is directly treated with the chromate treatment liquid. It has the greatest characteristic in that the composition is specified so that the above-mentioned various properties can be obtained even if it is applied.

The chromate treatment liquid used in the present invention is
It contains chromic acid and a chromic acid reduced product as main components, and at least one organic acid salt of Co and / or Ni.
Contains seeds.

Of these, the chromic acid reduced product is 10 to 50 with respect to the total amount of chromic acid and the chromic acid reduced product (hereinafter, these may be collectively referred to as a chromic acid compound).
It is preferably contained in a mass% ratio. The content of the chromic acid reduced product has a great influence on the elution property and corrosion resistance of Cr, and if the ratio is less than 10% by mass, most of the Cr present in the chromate film becomes soluble Cr, which results in high humidity. Below, the soluble Cr elutes to cause uneven chromate and the like, which adversely affects the appearance. More preferably, it is 20 mass% or more. On the other hand, when the content of the chromic acid reduced product exceeds 50% by mass, a large amount of stable Cr ₂ O ₃ is generated in the chromate film, and the proportion of soluble Cr having a self-repairing effect is reduced, resulting in deterioration of corrosion resistance. To do. It is more preferably 40% by mass or less.

In the present invention, C is added to the chromate treatment liquid.
It has the greatest feature in adding an organic acid salt of o and / or Ni, which dramatically improves the corrosion resistance of the hot-dip galvanized steel sheet and also improves the blackening resistance, and at the same time, improves the scratch resistance. The stickiness can also be improved.

As described above, in the present invention, Co and / or Ni are used.
The feature is that the organic acid salts of are used, and when these inorganic acid salts are used, a sufficient effect cannot be obtained. The reason is not clear, but considering, for example, the case of corrosion resistance,
If an inorganic acid salt is used, the above-mentioned chromic acid compound added to the chromate treatment liquid, the bond of the metal oxide sol and phosphoric acid (described later), which is added as necessary, or the bonds between them are cleaved. Therefore, it is considered that the corrosion resistance improving effect is significantly reduced. On the other hand, when the organic acid salt of the above metal is used as in the present invention, it is considered that the corrosion resistance can be remarkably improved because these bonds are further strengthened.

The reason why the blackening resistance is improved by adding an organic acid salt of Co and / or Ni is that the inorganic acid salt has too strong an etching action, and therefore even the oxide layer of the outermost surface of the plating layer is formed. While the blackening resistance is reduced due to etching, the organic acid salt has a weaker etching action than the inorganic acid salt. Therefore, it is possible to prevent a reduction in the blackening resistance due to an excessive etching action, and It is considered that the scratch resistance can be remarkably improved.

Further, in the present invention, Co or Ni is particularly selected from the heavy metals which have been conventionally recognized to have an effect on corrosion resistance and the like. It is considered that these ions are adsorbed to the active sites existing on the plating surface to suppress the activation, and therefore the reaction due to the chromate treatment can be uniformly promoted throughout the plating layer. The elements with the greatest adsorption are Co and N
i, and using other metal elements is inferior in terms of corrosion resistance and blackening resistance.

The above Co capable of effectively exhibiting such an action
And / or the organic acid concentration of Ni, in the chromate treatment liquid,
It is preferably 0.1 to 25 g / liter. If the organic acid concentration is less than 0.1 g / liter, sufficient effects on corrosion resistance and blackening resistance cannot be obtained. A more preferable lower limit value is 0.5 g / liter. On the other hand, if the upper limit exceeds 25 g / liter, the effect is saturated and it is economically wasteful. The optimum upper limit value in consideration of the above effects and economy is 15 g / liter.

The organic acid in the organic acid salt is not particularly limited, and examples thereof include formic acid, gluconic acid, acetic acid, oxalic acid and benzoic acid. Among them, formic acid, acetic acid, and oxalic acid are recommended for the purpose of improving corrosion resistance, blackening resistance, and scratch resistance. Such organic acid salts may be used alone or in combination of two or more kinds.

The amount of Co and / or Ni added is such that the total amount of Cr deposited in the chromate film (calculated as metallic Cr): metallic Co in order to effectively exert the effects of improving corrosion resistance, blackening resistance and scratch resistance. Amount and / or metallic Ni amount = 1: 0.01
It is preferable to use the above mass ratio. More preferably, it is 1: 0.05 or more. On the other hand, the ratio is 1: 0.5
If it is added in excess, the effect of improving the above-mentioned various characteristics will be saturated, and the cost will be high, which is economically wasteful.
It is more preferably 1: 0.2 or less.

The Cr content in the chromate film is
It is preferably 10 to 150 mg / m ² in terms of metal Cr. When the Cr content is less than 10 mg / m ² , corrosion resistance is poor and white rust is easily generated, which is not preferable. It is more preferably 20 mg / m ² or more. On the other hand, the Cr content is 1
Even if it is added in excess of 50 mg / m ² , its effect is saturated, resulting in cost increase and other problems such as the need to reduce the production line speed in order to obtain the desired Cr content. It is more preferably 50 mg / m ² or less.

In the present invention, since the chromate treatment liquid having such a composition is applied to the surface of the plated steel sheet, organic salts of Co and Ni are present in the entire chromate layer, and as a result, after the production of the plated steel sheet, Even after a lapse of time, Co and Ni can diffuse into the chromate film, so that various properties such as blackening resistance can be maintained for a long period of time. On the other hand, in the conventional method in which the Co / Ni-containing solution is pretreated before the chromate treatment, Co and Ni, which are effective in improving the blackening resistance, are only present near the interface between the outermost surface of the plating layer and the chromate layer. Since it exists, it is easily consumed and it is impossible to maintain characteristics such as blackening resistance over a long period of time. The present invention basically uses a chromate treatment liquid having the above composition, but it is preferable to further contain the following components in order to obtain more excellent performance.

The chromate solution contains at least one metal oxide sol as a solid content in a mass ratio of the metal oxide sol: chromic acid and chromic acid reduced product = 0.5 to 5.0: 1. . When the chromate treatment liquid contains a metal oxide sol, it has the effect of increasing the thickness of the chromate film and further improving the corrosion resistance, as well as the damage that the chromate film receives when subjected to physical impact during processing. Can be reduced, so that the corrosion resistance after molding can be further improved. In order to effectively exhibit such an action, it is preferable to contain the solid content in the oxide sol at a ratio of 0.5 parts by mass or more with respect to 1 part by mass of the chromic acid compound. It is more preferably 1.0 part by mass or more. However, if added excessively, it becomes difficult to uniformly apply the chromate treatment liquid and the workability deteriorates. Therefore, the solid content in the oxide sol is 5.0 parts by mass or less relative to 1 part by mass of the chromic acid compound. Preferably. It is more preferably 3.0 parts by mass or less.

The type of metal oxide sol used in the present invention is not particularly limited, and commercially available metal oxide sols such as Al, Si, Ti, Sb and Zr can be used. These oxide sols may be used alone or 2
It is also possible to use any combination of two or more species. Among these, Al, Si, and Ti oxide sols are most recommended in terms of the effect of improving blackening resistance.

Phosphoric acid was added to the chromate solution as phosphoric acid: chromic acid and chromic acid reduced product = 0.01 to 0.
It is contained in a mass ratio of 5: 1. Phosphoric acid has the effect of etching the plating surface, and also has the effect of improving the adhesion between the chromate film and the plating layer and improving the corrosion resistance. In order to effectively exhibit such an action, it is preferable to contain phosphoric acid in a proportion of 0.01 parts by mass or more based on 1 part by mass of the chromic acid compound. More preferably 0.05
It is at least part by mass. However, if the addition amount of phosphoric acid exceeds 0.5 parts by mass with respect to 1 part by mass of the chromic acid compound, the blackening resistance and the scratch resistance are deteriorated and the commercial value is lowered.
The reason for this is considered to be that the etching effect of phosphoric acid becomes excessive, which adversely affects blackening resistance and scratch resistance. It is more preferably 0.1 part by mass or less.

The type of phosphoric acid used in the present invention is not particularly limited, and examples thereof include orthophosphoric acid, pyrophosphoric acid, metaphosphoric acid and condensed phosphoric acid. These may be used alone or in combination of two or more, and the combination is not particularly limited.

The method for treating the surface of the plated steel sheet with the above chromate treatment liquid is not particularly limited, and a commonly used method such as a method of applying a roll squeeze after spraying or dipping, a method of applying with a roll coater, a method of drying after spraying, etc. Can be adopted. Further, an organic and / or inorganic resin film may be further formed on the chromate film for the purpose of further improving performance such as corrosion resistance and reducing elution Cr.

The method of the present invention is characterized in that the pretreatment which has been conventionally performed prior to the chromate treatment can be omitted from the viewpoint of production efficiency, but a superior performance is obtained. Therefore, as long as the action of the present invention is not impaired, heavy metal (Ni,
It may be pretreated with a solution containing an organic acid salt or an inorganic acid salt of Fe, Co, etc.). Specifically, for example, after pretreatment with an organic acid salt-containing solution of Ni, then Co
When treated with the organic acid salt-containing chromate treatment solution, the properties such as blackening resistance can be further improved.

The present invention will be described in detail below based on examples.
However, the following examples do not limit the present invention,
All modifications and alterations without departing from the spirit of the preceding and following descriptions are included in the technical scope of the present invention.

[0035]

EXAMPLES After manufacturing various samples shown in Tables 1 to 4 under the following conditions, the following measurement items were evaluated. The amount of elements attached to the steel sheet is 220 x 300 mm.
After the surface of the plate having the size was dissolved, ICP analysis (using SPS1500VR manufactured by Seiko Instruments Inc.) was performed to determine the mass ratio of each element. (1) Original plate: 5% Al-containing hot dip galvanized steel sheet (Zn adhesion amount: 60 g / m ² ) (2) Chromate treatment: 10 to 50 g / liter CrO
After immersing in a _3- containing chromate solution, it was rolled and dried.

(3) Test Method: Corrosion Resistance Test After cutting each sample into a size of 70 × 150 mm square, a salt spray test was conducted according to JIS Z2371. The evaluation of the corrosion resistance test was performed by measuring the white rust generation rate at the time when 120 hours had elapsed after the start of the test. ◯: White rust generation 1% or less △: White rust generation 1% to 5% or less ×: White rust generation 5% or more Black discoloration resistance test After cutting a sample into the same size as in the above corrosion resistance test, 50 ° C, The sample was kept for 96 hours under the condition of relative humidity of 98%. The color tone of this sample was visually compared with the color tone of a sample stored in a dryer for 96 hours, and evaluated according to the following criteria. ◯: No black discoloration is observed Δ: Black discoloration is slightly recognized ×: Black discoloration is recognized

Scratch resistance test A sample cut into a size of 40 × 250 mm was cut into 50 pieces.
A tool having a contact area of × 100 mm was used for pinching with a load of 1.5 tons. Then, after moving the sample in that state, the glossiness and the degree of flaw on the surface of the sample were visually observed and evaluated according to the following criteria. ◯: Slightly scratched (less than 30% of scratches on the sample surface) ×: Highly scratched (30% or more of scratches on the sample surface) Cr elution test Manufacture plated steel sheet After 72 hours, the sample was used and immersed in boiling water for 1 minute. C before and after immersion
The eluted Cr rate was calculated by measuring the amount of r, and evaluated according to the following criteria. ○: Cr elution rate of 30% or less ×: Cr elution rate of more than 30%

The results are also shown in Tables 1 to 4. First, Table 1 shows the results of examining the usefulness of the organic acid salt of Co and / or Ni added to the chromate solution and the optimum addition amount thereof.

[0039]

[Table 1]

Nos. 1 to 13 are examples in which an optimum amount of organic acid salt of Co and / or Ni was added, and good results were obtained in all measurement items. In contrast, N
o.14 is an example in which the organic acid salt of Co and / or Ni is not contained in the chromate solution, and the corrosion resistance is poor. No.15 is
This is an example in which the content of the organic acid salt of Co and / or Ni is small, and the corrosion resistance and the blackening resistance are poor.

No. 16 and No. 18 are examples using an inorganic acid salt of Ni and are inferior in all the characteristics of corrosion resistance, blackening resistance and scratch resistance. No. 17 is an example using Mn acetate and is inferior in blackening resistance. No. 19 is an example in which the content of the organic acid salt of Co and / or Ni is large, and the effect of improving corrosion resistance, blackening resistance and the like is saturated, resulting in high cost.

Next, Table 2 examines the influence on the corrosion resistance and the like when the Cr deposition amount and the chromic acid reduced product content are changed.

[0043]

[Table 2]

Nos. 1 to 13 shown in Table 1 above are examples satisfying the preferred requirements of the present invention, and in all cases, all evaluation items of corrosion resistance, blackening resistance, scratch resistance and leached Cr were evaluated. Good results have been obtained.

On the other hand, No. 20 is an example in which the amount of deposited Cr is small and the corrosion resistance is poor. No. 21 is an example in which a large amount of Cr is deposited, and effects such as corrosion resistance are saturated, resulting in an increase in cost. No. 22 is an example in which a chromic acid reduced product is not added, and the Cr elution rate increases.

No. 23 is an example in which the amount of reduced chromic acid is small, and Cr is easily eluted, resulting in uneven chromate.
No. 24 is an example in which there are many chromic acid reduced products, and the corrosion resistance is poor. Next, Table 3 shows the results of examining the effect of adding the oxide sol.

[0047]

[Table 3]

Nos. 3 and 5 to 13 shown in Table 1 above are examples in which the addition amount of the oxide sol satisfies the preferred requirements of the present invention, and good results are obtained for all evaluation items.
On the other hand, No. 25 is an example in which the amount of oxide sol added was large, and repelling occurred during the manufacturing process. No.2
No. 6 is an example in which the amount of oxide sol added is small, and the effect of improving corrosion resistance is small. Finally, Table 4 shows the results of examining the effect of adding phosphoric acid.

[0049]

[Table 4]

Nos. 4 to 13 shown in Table 1 above are examples in which the amount of phosphoric acid added satisfies the preferred requirements of the present invention, and good results are obtained for all evaluation items. On the other hand, No. 27 is an example in which the amount of phosphoric acid added is small, and the effect of improving corrosion resistance and the effect of improving blackening resistance are small. No.2
No. 8 is an example in which the addition amount of phosphoric acid is large, and the blackening resistance and the scratch resistance are lowered.

[0051]

EFFECTS OF THE INVENTION Since the method of the present invention is constructed as described above, hot-dip galvanized steel sheet having excellent corrosion resistance and blackening resistance as well as scratch resistance is subjected to pretreatment, etc. It can be efficiently manufactured without any special treatment.

Claims (8)

[Claims] 1. A method for producing a plated steel sheet in which a chromate coating is applied on a hot dip galvanized steel sheet, the surface of the plated steel sheet containing at least one organic acid salt of Co and / or Ni. A method for producing a hot dip galvanized steel sheet, which comprises producing a hot dip galvanized steel sheet excellent in corrosion resistance, blackening resistance and scratch resistance by treating with a chromate solution. 2. The manufacturing method according to claim 1, wherein the plated layer of the hot-dip galvanized steel sheet contains 4 mass% or more of Al. 3. Metal Cr in the chromate film: 10 to 1
The mass ratio of 50 mg / m ² and the total amount of Cr deposited in the chromate film (calculated as metallic Cr): metallic Co amount and / or metallic Ni amount = 1: 0.01 to 0.5 are satisfied. The manufacturing method described in. 4. The organic acid in the organic acid salt is oxalic acid,
The method according to any one of claims 1 to 3, which is formic acid or acetic acid. 5. The chromate solution contains a chromic acid reduced product in a proportion of 10 to 50% by mass with respect to the total amount of chromic acid and the chromic acid reduced product. Manufacturing method. 6. The production method according to claim 1, wherein the concentration of the organic acid salt in the chromate solution is 0.1 to 25 g / liter. 7. Further, in the chromate solution, at least one metal oxide sol is added as a solid content to the metal oxide sol: chromic acid and chromic acid reduced product = 0.5 to 5.
The manufacturing method according to any one of claims 1 to 6, wherein the mass ratio is 0: 1. 8. Further, phosphoric acid is added to the chromate solution as phosphoric acid: chromic acid and chromic acid reduced product = 0.01.
The manufacturing method in any one of Claims 1-7 containing in a mass ratio of -0.5: 1.