JP2000119864A - Production of chromate treatment hot dip coated steel sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for forming multi-purpose chromate film on a hot dip coated steel sheet containing >=30% Cr without impairing an original chromate function. SOLUTION: When conducting a chromate treatment on the surface of a steel sheet containing >=30 wt.% Cr applied to hot dip plating, a component in a chromate treatment solution contains chromic acid and a chromic acid reduction product, the treatment solution has pH 1-4 and further, contains one kind, two kinds or more selected from a group of a silica sol, an alumina sol, a titania sol, a water soluble resin, a water dispersion resin and an emulsion resin, further, the treatment solution satisfying formula, 0.99>=B/(A+B)>=0.4, is coated on a steel sheet and then, the steel sheet is heated at a temp. rising speed of >=25 deg.C/sec and to a reaching sheet temp. of 80-280 deg.C by induction heating. Where, A is the total weight of the chromic acid weight expressed in terms of CrO3, B is the total weight of the silica sol, alumina sol, titania sol or organic resin expressed in terms of SiO2, Al2O3, TiO2 or CH2.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates in particular to the use of Z
The present invention relates to a method for producing a steel sheet in which a surface of a hot-dip plating containing 30% or more of n is subjected to a chromate treatment.

[0002]

2. Description of the Related Art In recent years, in order to enhance the plating surface function of Zn, Zn-Al-based alloy-coated steel sheet, alloyed hot-dip galvanized steel sheet, etc. containing 30% or more of Zn, conventional chromate treatment only for corrosion protection has been carried out. There is an increasing need for a chromate treatment having multiple functions. For example, Japanese Patent Application Laid-Open No.
In the case where fumed silica is added to a chromate solution as shown in JP-A-17340, etc., and for the purpose of preventing abrasion during processing, a resin is added to a chromate solution as shown in JP-B-4-2672. In some cases.
These enhance the functionality of the chromate film by adding inorganic oxides or organic resins to the chromate solution to supplement the properties that cannot be expected with chromic acid by the properties of the additive.

However, as the amount of additives increases,
Conversely, the basic function as a chromate film may be hindered. That is, by adding an additive over a certain amount, the adhesion between the chromate film and the plating is reduced,
Peeling is likely to occur at the interface between the chromate film and the plating. As a result, the function of the chromate film cannot be exhibited at the peeled portion, and the basic function of corrosion resistance is reduced. In our study, this phenomenon is one or two selected from silica sol, alumina sol, titania sol, water-soluble resin, water-dispersible resin, and emulsion resin.
And the total weight of chromic acid in terms of CrO ₃ is A, and the weights of silica sol, alumina sol, titania sol, and organic resin are SiO ₂ , Al ₂ O ₃ ,
The total weight in terms of TiO ₂ and CH ₂ is B, and B / (A
+ B) It occurs remarkably in the processing solution satisfying ≧ 0.4. In particular,
In a hot-dip coated steel sheet, the plating surface is microscopically smooth as compared with the electroplating, and the anchoring effect cannot be expected. As a means of making peeling less likely to occur in our investigations, it is effective to increase the ratio of chromate reduction products to chromate in the chromate, and usually a chromate treatment solution having a Cr reduction ratio of 25 to 70%. It is effective to improve the effect by using Pb, but a sufficient effect cannot be obtained in hot-dip plating, particularly in hot-dip plating in which Pb, Sn or the like during plating is 100 ppm or less.

As a countermeasure, Japanese Patent Publication No. 56-36869
As disclosed in Japanese Patent Application Laid-Open Publication No. H10-207, a means has been proposed in which a metal noble than Zn such as Co or Ni is attached before chromate to improve the adhesion between Zn and the chromate and to improve the paint adhesion. I have.

[0005]

However, the method disclosed in JP-B-56-36869 increases the number of processing steps and is not desirable from the viewpoint of manufacturing cost. Also, Zn
There is a problem that the corrosion resistance of plating is reduced by attaching a more noble metal. In view of such circumstances, an object of the present invention is to form a multifunctional chromate film at low cost on a hot-dip coated steel sheet containing 30% or more of Zn without performing chromate pretreatment and without impairing the original function of chromate. It is to provide a method.

[0006]

In order to solve the above problems and achieve the object, the present invention uses the following means. (1) In the production method of the present invention, a chromate treatment is performed on a surface of a hot-dip coated steel sheet containing 30% by weight or more of Zn by weight, and the chromate treatment is performed by a chromate treatment. As a component in the liquid, it contains chromic acid and a chromic acid reduction product, and further contains one or more selected from the group consisting of silica sol, alumina sol, titania sol, water-soluble resin, water-dispersible resin, and emulsion resin. And applying a treatment liquid satisfying the following formula (1) and having a pH of 1 to 4 to the hot-dip coated steel sheet, and raising the hot-dip coated steel sheet coated with the chromate treatment liquid by induction heating. A step of heating at a temperature rate of 25 ° C./sec or more and a reached plate temperature of 80 to 280 ° C., characterized by having excellent adhesion of a chromate film. Formate process is a method for producing a hot dip plated steel sheet.

0.99 ≧ B / (A + B) ≧ 0.4 (1) where A is the total weight of chromic acid in terms of CrO ₃ ,
B: The weights of silica sol, alumina sol, titania sol, and organic resin were respectively SiO ₂ , Al ₂ O ₃ , TiO ₂ ,
Total weight converted to CH ₂ . (2) The production method of the present invention is characterized in that, in the treatment liquid application step, the amount of water in the chromate treatment liquid applied to the steel sheet is ² to ²⁰ g / m ^2. 5. A method for producing a chromate-treated hot-dip coated steel sheet having excellent chromate film adhesion as described in 1. above.

(3) The manufacturing method of the present invention is characterized in that, in the treatment liquid applying step, the temperature of the plate invading the applying step is set to 50 ° C. or less, and the uniform appearance as described in (1) or (2) above. This is a method for producing a chromate-treated hot-dip coated steel sheet having excellent properties and adhesion of a chromate film.

(4) The method according to any one of (1) to (3), wherein the steel sheet induction-heated in the steel sheet heating step is cooled by an air-cooled or water-cooled roll. This is a method for producing a chromate-treated hot-dip coated steel sheet having excellent appearance uniformity and excellent adhesion of a chromate film.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present inventors have developed a multifunctional chromate film without impairing the original function of chromate.
In order to obtain an inexpensive method for forming on a hot-dip coated steel sheet containing 30% or more of n, intensive studies have been made. As a result, in order to form a multifunctional chromate film having excellent adhesion with plating on a plated steel sheet without performing chromate pretreatment, a chromate treatment solution to which an inorganic oxide or an organic resin was added was applied. Hot-dip steel sheet is heated by induction heating.
The finding that heating from a plate was effective was obtained.

[0011] Based on this finding, the present inventors have developed a composition, pH, and coating composition of a treatment solution obtained by adding an inorganic oxide and / or an organic resin to a chromate solution on a hot-dip coated steel sheet containing 30% or more of Zn. Apply a chromate treatment solution with the water content adjusted within a certain range, and heat it from the plate by induction heating.Without chromate pretreatment, a multifunctional chromate film can be formed without impairing the original function of chromate. And found a method of inexpensively forming it on a hot-dip coated steel sheet containing 30% or more of Zn, and completed the present invention.

That is, according to the present invention, a coating and a manufacturing condition of a chromate-treated hot-dip coated steel sheet are limited to the following ranges, whereby a chromate-processed hot-dip coated steel sheet having excellent adhesion and uniform appearance of a chromate film is manufactured at low cost. be able to.

The reasons for limiting the coating of the chromate-treated hot-dip coated steel sheet of the present invention and the reasons for limiting the manufacturing conditions will be described below. (1) Coating of hot-dip coated steel sheet with chromate treatment a. The steel sheet to be coated The present invention is effective for a hot-dip coated steel sheet containing 30% or more by weight of Zn, for example, a hot-dip zinc-coated steel sheet, commonly called a 5% Al-Zn alloy plated steel sheet, commonly called 55% A
Examples include l-Zn plated steel sheet and alloyed hot-dip Zn coated steel sheet. However, application to an electrical Zn-plated steel sheet, an electrical Zn-Ni plated steel sheet, etc. is also possible.

The reason for limiting to hot-dip plating containing 30% or more of Zn is as follows. 1) Zn 30% or more Cr ^{6+ in the} chromate treatment solution reacts with Zn to form a layer mainly composed of Cr ³⁺ at the chromate film-plating interface, and this layer is considered to contribute as a binder layer for plating and the chromate film. If Zn is less than 30%, a reaction hardly occurs even when induction heating is used, and it is difficult to form a film having excellent adhesion.

2) Hot-dip galvanizing In electrogalvanizing, the oxide on the surface of the plating is thin and fine irregularities are formed, so that the chromate film can be adhered to the surface. Since it is coated with a stable oxide (such as Al ₂ O ₃ ) and is smooth, even if a chromate film is formed by an ordinary method, the film will have poor adhesion.

B. Chromate coating In the present invention, the surface of the steel sheet contains chromic acid and a chromate reduction product as components in a chromate treatment solution, and further contains silica sol, alumina sol, titania sol, a water-soluble resin, a water-dispersible resin, And a treatment liquid containing one or more selected from the group of emulsion resins, satisfying the following formula (1), having a pH of 1 to 4, and a coating water content of ² to 20 g / m ^2. Is used to form a chromate film.

0.99 ≧ B / (A + B) ≧ 0.4 (1) where A: total weight of chromic acid in terms of CrO ₃ ,
B: Total weight of silica sol, alumina sol, titania sol, and organic resin in terms of SiO ₂ , Al ₂ O ₃ , TiO ₂ , and CH ₂ . As described above, the inorganic oxide (silica sol, alumina sol, titania sol) or /
In addition, by adding an organic resin (a water-soluble resin, a water-dispersible resin, an emulsion resin) to a chromate solution within a range satisfying the above formula (1), characteristics that cannot be expected with chromic acid (that is, chromate with a coated steel sheet) The characteristics of the additive, which are also excellent in the adhesion and appearance uniformity of the film, can be supplemented by the characteristics of the additive, and as a result, the functionality of the chromate film can be enhanced.

On the other hand, in the case of a chromate treatment solution containing the above additive, the adhesion between the chromate film and the plating is reduced as described above in the prior art, and the function of the chromate film cannot be exhibited. Although there is a problem that the corrosion resistance, which is a function, is reduced, in the present invention, by limiting to the production conditions using induction heating described below, the chromate pretreatment is not performed, and the original function of chromate is not impaired. It is possible to form a functional chromate film on the hot-dip coated steel sheet at low cost.

The preferred range of the chromium reduction rate of the chromic acid reduction product of the present invention is 5% or more and less than 70%. If it is less than 5%, the solubility of chromium is poor, and if it is more than 70%, the liquid stability is poor. Desirably 25-50%
It is.

The preferred range of the amount of chromium deposited in the present invention is 4 to 200 mg / m ² in terms of chromium metal. 4
At less than mg / m ² , there is almost no effect of improving corrosion resistance.
If it exceeds 00 mg / m ² , remarkable coloring occurs and the amount of chromium dissolved increases. Preferably 7-80 mg
/ M ² .

Next, the effect of the water content of the applied chromate treatment liquid will be described. If the water content of the liquid applied to the steel sheet surface is less than 2 g / m ² , plating and Cr ⁶⁺
Does not react sufficiently, and a sufficient effect cannot be obtained. Preferably, it should be at least 3 g / m ² , most preferably at least 5 g / m ² . On the other hand, if it exceeds 20 g / m ² , the chromate adheres unevenly, and the functionality of the chromate decreases. Preferably not more than 15 g / m ² , most preferably 12 g / m ²
You should: Therefore, the water content of the liquid to be applied is in the range of ^{2 to 20} g / m ² , and more preferably 3 to ²⁰ g / m ^2.
To 15 g / m ^2, and most preferably it is necessary to the range of 5~12g / m ^2.

The pH of the processing solution should be 1 to 4. If the pH is less than 1, the inorganic oxide or resin added for functionalization becomes unstable and cannot perform its function sufficiently, or plating and chromate react violently at the time of coating, and excess Zn is contained in the chromate treatment solution. Mixing, causing deterioration of the processing solution. When the pH of the processing solution exceeds 4, the reactivity between the plating and the chromate is remarkably reduced,
Since the pH rises, it is difficult to keep the pH below 1 in continuous operation, and it is necessary to add or replace a new treatment liquid, which is not preferable in operation.

The treatment liquid contains mineral acids such as phosphoric acid, nitric acid and sulfuric acid, or salts thereof, ammonia,
It is possible to add a basic compound such as sodium hydroxide or a reducing agent for reducing Cr ⁶⁺ in the chromate, and the present invention basically does not restrict the addition. However, the pH of the processing solution needs to be within the above range. By forming a film using a chromate treatment solution adjusted to the above ranges of component composition, pH, and amount of applied moisture, the chromate film adheres without chromate pretreatment and without impairing the original function of chromate. It is possible to obtain a chromate-treated hot-dip coated steel sheet having excellent properties and uniformity in appearance at low cost.

A steel sheet having such characteristics can be manufactured by the following manufacturing method. (2) Chromate-treated hot-dip coated steel sheet manufacturing process (Manufacturing method) A chromate-treated solution adjusted to the above-described composition, pH, and applied moisture range is applied to the hot-dip coated steel sheet surface at a penetration plate temperature of 50 ° C. The composition is applied to a steel sheet prepared as follows, and heated by induction heating at a heating rate of 25 ° C./sec or more and a reached sheet temperature of 80 to 280 ° C. Next, the heat-dried steel sheet is cooled by an air-cooled or water-cooled roll.

A. Heating temperature: 80 to 280 ° C (attained sheet temperature), heating rate: 25 ° C / sec or more Conventionally, a chromate treatment liquid applied to the surface of a steel sheet has been heated and dried from the surface of the steel sheet by hot air drying. In the present invention, the first feature is that the plate is heated by induction heating, whereby an effect can be obtained without performing a chromate pretreatment with Ni or Co or the like. However,
If the heating rate is less than 25 ° C./sec, a sufficient effect cannot be obtained.
Therefore, a heating rate of 25 ° C./sec or more is required.

If the reached plate temperature is less than 80 ° C., drying becomes poor, and chromate adheres to rolls and the like of the production line that are touched after drying, so that the desired steel plate cannot be obtained and the load on the operation increases. The reason for setting the temperature to 280 ° C. or lower is that even if heating is performed at a temperature higher than that, there is a case where a significant effect cannot be obtained in characteristics, and Cr ^{6+ in} the chromate is reduced to Cr ³⁺ and the original function may not be exhibited. This is because, unless a considerably large cooling facility is installed after heating, the properties of the steel sheet may be adversely affected. Therefore, the ultimate plate temperature is 80 to 280 ° C, preferably 100 to 220 ° C.
Should be ° C. The upper limit of the heating rate is not particularly specified, but if it is too fast, it will be difficult to control the target sheet temperature, and it will be difficult to operate, so it is necessary to set it according to the capacity of the line. is there.

Therefore, in the present invention, it is necessary to heat the chromate treatment solution applied to the steel sheet surface by induction heating to a heating rate of 25 ° C./sec or more and a reached sheet temperature of 80 ° C. or more and 280 ° C. or less. is there. Although this mechanism is not clear, it is presumed that the reaction between the plating and Cr ⁶⁺ easily proceeds because the steel sheet is heated by induction heating, and that the effect of water greatly contributes to this reaction. However, it is conceivable that the temperature of the plating surface is increased by heating from the steel sheet before the moisture evaporates, so that a reaction is easily caused.

On the other hand, the induction heating has a disadvantage that moisture evaporated in the furnace is dewed and condensed water falls on the surface of the steel sheet, thereby causing unevenness of chromate. Although the present invention does not prescribe conditions for avoiding dew condensation, it is possible to avoid dew condensation in the induction heating furnace by basically feeding air at a constant wind speed into the induction heating furnace.

B. Invasion plate temperature in coating process: 50 ° C. or less The ingress plate temperature of the steel plate in the treatment liquid coating process greatly affects the reactivity between the steel plate and the chromate. If the invading plate temperature exceeds 50 ° C., the chromate liquid temperature gradually rises and evaporates easily, so that even if induction heating is performed, a sufficient effect cannot be obtained. Therefore, the temperature of the plate entering the coating step should be 50 ° C. or less. If the temperature of the intruding plate is too low, the surface may be dewed before the steel plate enters the coating step. In such a case, water may hinder the reaction between plating and chromate. In the present invention, the minimum penetration sheet temperature is not specified, but the temperature should be reduced until the steel sheet is dewed.

C. Cooling method: cooling by air cooling or water-cooled rolls. After the chromate is finally heated and dried, cooling may be required from the viewpoint of material properties. As a cooling method,
Water cooling, air cooling, a method using a water-cooled roll can be considered,
In the case of cooling with water, the chromate film is not sufficiently insoluble immediately after the heating, so that the chromate film partially dissolves and cannot exhibit its original function. Therefore, in the present invention, it is impossible to perform water cooling. As a cooling method, it is necessary to use a method in which chromate is not dissolved at the time of cooling, that is, air cooling or using a cooling roll.

Although the present invention is an effective technique to be applied to a chromate treatment solution having a function, it can be applied to other chromate solutions or electroplating other than hot-dip plating without any problem. It is. Also,
As an application of this technology, it is also possible to form an organic resin layer of 0.1 to 300 μm after coating and drying a chromate film, or to form an organic resin layer after cooling, and the present invention specifies the treatment of a chromate upper layer. It does not do. Hereinafter, examples of the present invention will be described to demonstrate the effects of the present invention.

[0032]

EXAMPLES (Example 1) 90 g / m of Zn adhesion per side
^2. Low-Pb (Pb; 100 ppm or less) hot-dip galvanized steel sheet minimized spangle material (surface roughness Ra; 0.5)
To 1.5), the compositions (No. 1, 2, 4 to 8:
Example of the present invention, (3, 9, 10: Comparative Example) subjected to chromate treatment was used as a test material. The coating was performed using a roll coater, and the amount of the chromate film deposited was controlled by adjusting the conditions of the coater and the concentration of the processing solution. In order to change the plate temperature at the time of coating, the coated steel sheet was heated to a predetermined sheet temperature under some conditions before being applied by a coater, and immediately heated and dried. For drying, induction heating (IH) in a heating furnace
And a hot air blowing furnace (CD), and each was heated to a predetermined plate temperature by each method. Table 2 shows the conditions for applying the chromate treatment liquid. Table 3 shows the heating and cooling conditions of the steel sheet (No.
1,3,7,9,11,13,15,22-24,26
To 28, 30, 31, 33 to 47: Examples of the present invention,
2,4 to 6,8,10,12,14,16 to 21,
5, 29, 32: Comparative Example).

The adhesiveness of the chromate film was determined by applying a polyester-based adhesive to the surface of the chromate film and then pasting a polyester-based film on the surface. Analyzer). Steel plate side peeled part 3 by EPMA
The detection strength of C as an adhesive component and Cr as a chromate component was measured for cm × 3 cm, and within the range where C was not detected, the strength of Cr became 1/4 or less of the strength shown in the state in which the chromate treatment was performed. Find the area that
The evaluation was made based on the ratio to the total area. The evaluation criteria are shown below.

(Evaluation criteria) 5: Chromate component (Cr)
Area is less than 10%,
4; the area of the portion where the chromate component (Cr) is 1/4 or less is 10% or more and less than 20%; 3; the area of the portion where the chromate component (Cr) is 1/4 or less is 20
% To less than 50%, 2; chromate component (Cr) is 1 /
4 or less, the area of the portion is 50% or more and less than 75%, 1; the area of the portion where the chromate component (Cr) is 1/4 or less is 75% or more.

The appearance of the obtained sample was visually evaluated according to the following evaluation criteria. (Evaluation criteria) ；: no unevenness, Δ: partially uneven (10% of processing area)
%), X: clearly uneven (10% or more of the treated area).

Table 3 shows the above evaluation results. Example N
o. Nos. 1 to 20 were dried by IH on steel sheets coated with various chromate treatment solutions (Examples Nos. 1, 3, 7, 9, and 9 of the present invention).
11, 13, 15 and Comparative Example Nos. 5, 17, 19) and C
D (Comparative Example Nos. 2, 4, 6, 8, 10, 1)
2, 14, 16, 18, 20).

Example N using a processing solution (processing solutions No. 1, 2, 4, 5, 6, 7, 8) satisfying the claims of the present invention.
o. In Examples 1 to 4 and 7 to 16, Examples Nos. 1 to 4 of the present invention by IH drying were clearly used. 1,3,7,9,11,13,15
The peel resistance of the chromate film of Comparative Example No. It is superior to 2,4,8,10,12,14,16.

Further, in Example Nos. 5,6,1
Nos. 7 to 20 are comparative examples using treatment liquids outside the range of the present invention, and all have inferior peel resistance as compared with the above-mentioned examples of the present invention. Example No. 21 to 28 (No. 22 to 24,
26 to 28: Examples of the present invention, No. 21, 25: Comparative example)
Is a result of examining the influence of the heating rate, and Comparative Example No. 2 having a heating rate of 20 ° C./sec outside the range of the present invention. In Nos. 21 and 25, sufficient peeling resistance was not obtained.

Example No. 29 to 32 (No. 30, 3
1: Example of the present invention; 29, 32: Comparative Example) are the results of examining the maximum attainable plate temperature. At 70 ° C. (Comparative Example No. 29) outside the range of the present invention, the peel resistance is poor. Further, even when heating to 300 ° C. (Comparative Example No. 32), which is out of the range of the present invention, a large effect on the peeling resistance was not obtained.

Example No. 33 to 39 (Examples of the present invention) are the results of examining the chromate coating conditions (moisture content). When the moisture content is 1 g / m ² (Nos. 33 and 37), the peel resistance is poor, and 25 g / m ^2. (Nos. 36 and 39) are inferior in appearance uniformity. Example No. 40 to 43 (Examples of the present invention) are the results of examining the plate temperature at the time of applying the chromate. When the plate temperature is 55 ° C. (No. 40, 42), the peel resistance is poor.

Example No. 44 to 47 (Examples of the present invention) are the results of examining the cooling method after heating and drying. By performing water cooling (Examples Nos. 44 and 46 of the present invention), the coating film has poor appearance uniformity.

[0042]

[Table 1]

[0043]

[Table 2]

[0044]

[Table 3]

(Example 2) 80 g of coating weight per one side
/ M ² of a 55% Al-Zn-1.6% Si-based hot-dip coated steel sheet subjected to a chromate treatment having a composition shown in Table 1 was used as a test material. Chromate treatment conditions and the evaluation method were the same as in Example 1, and sample preparation and evaluation (peeling evaluation, appearance evaluation) were performed. The evaluation results are shown in Table 4 (N
o. 1,3: Inventive example, No. 2, 4-8: Comparative example).
As a result of examining the effect of the drying method in plating in which the amount of Zn in the plating layer is about 45%, Example No. 1 of the present invention in which heating and drying are performed by IH using a chromate treatment solution satisfying the claims of the present invention. Comparative Examples Nos. 1 and 3 were dried by CD or / and using a treatment solution outside the scope of the present invention.
It was confirmed that a film having peel resistance superior to 2, 4 to 8 was obtained.

[0046]

[Table 4]

Example 3 80 g of plating adhesion amount per one side
/ M ² of a hot-dip Al-plated steel sheet subjected to a chromate treatment having the composition shown in Table 1 was used as a test material. Chromate treatment conditions and the evaluation method were the same as in Example 1, and sample preparation and evaluation (peeling evaluation, appearance evaluation) were performed. The evaluation results are shown in Table 5 (Comparative Examples Nos. 1 to 4).

[0048]

[Table 5] This is a result of examining the application to an aluminum-plated steel sheet containing no Zn in the plating layer. In this case, the effect of IH on the peeling resistance was not observed.

[0049]

As described above, according to the present invention,
By specifying the coating and manufacturing conditions of the chromate-treated hot-dip coated steel sheet, a multi-functional chromate film can be formed on the hot-dip coated steel sheet containing 30% or more of Zn without performing the chromate pretreatment and without impairing the original function of the chromate. It can be formed inexpensively.

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Masaaki Yamashita 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Nihon Kokan Co., Ltd. (72) Inventor Ichiro Mishima 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Sun (72) Inventor Akihiro Yamamoto 1-2-1, Marunouchi, Chiyoda-ku, Tokyo, Japan Nihon Kokan Co., Ltd. (72) Inventor Toshiyuki Okuma 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Nippon Steel Pipe F term in the company (reference) 4K026 AA02 AA07 AA09 AA13 AA22 BA06 BB01 CA13 CA19 CA21 CA39 CA41 DA02 DA15 EA00 EA17 EB11

Claims (4)

[Claims] 1. A method for producing a chromate-treated hot-dip steel sheet by performing a chromate treatment on a hot-dip steel sheet surface containing 30% or more of Zn by weight, wherein the chromate treatment is performed as a component in a chromate treatment solution. ,
It contains chromic acid and chromic acid reduction products, and further contains one or more selected from the group consisting of silica sol, alumina sol, titania sol, water-soluble resin, water-dispersible resin, and emulsion resin, and Applying a treatment solution satisfying the formula (1) and having a pH of 1 to 4 to the hot-dip coated steel sheet; and heating the hot-dip coated steel sheet coated with the chromate treatment solution by induction heating at a rate of 25 ° C. / In more than seconds, reached plate temperature: 8
A method of producing a chromate-treated hot-dip coated steel sheet having excellent adhesion of a chromate film, comprising: a step of heating to 0 to 280 ° C. 0.99 ≧ B / (A + B) ≧ 0.4 (1) where A is the total weight of chromic acid in terms of CrO ₃ ,
B: The weights of silica sol, alumina sol, titania sol, and organic resin were respectively SiO ₂ , Al ₂ O ₃ , TiO ₂ ,
Total weight converted to CH ₂ . 2. In the treatment liquid applying step, the amount of water in a chromate treatment liquid applied on a steel plate is 2 to 20 g.
/ M ² , wherein the method for producing a chromate-treated hot-dip coated steel sheet having excellent adhesion of a chromate film according to claim 1, wherein: 3. The chromate having excellent uniformity in appearance and adhesion of a chromate film according to claim 1 or 2, wherein in the treatment liquid applying step, the temperature of the plate entering the applying step is set to 50 ° C. or lower. Manufacturing method of treated hot-dip coated steel sheet. 4. The uniformity of appearance and adhesion of a chromate film according to claim 1, wherein the steel sheet induction-heated in the steel sheet heating step is cooled by an air-cooled or water-cooled roll. Method for producing excellent chromate-treated hot-dip coated steel sheet.