JP2001049456A - Production of chromate treated steel sheet excellent in adhesion with organic film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a chromate treated steel sheet by which a chromate film excellent in adhesion with an organic film is formed on a galvanized steel sheet. SOLUTION: The surface of a galvanized or galvannealed alloy steel sheet contg., by weight, >=30% zinc is coated with a chromate treating soln. contg. chronic acid and a chromic acid reduced product in the range of 30 to 70% as a Cr reducing ratio, moreover contg. one or >= two kinds selected from a silica sol, an alumina sol and a titania sol of 1 to 30 nm primary average particle size, also, in which, in the case the total weight in which the weight of the above chromic acid and chromic acid reduced product is expressed in terms of CrO3 is defined (IS A, and the total weight in which the weight of the silica sol, alumina sol and titania sol is respectively expressed in terms of SiO2, Al2O3 and TiO2 is defined as B, 0.83>=B/(A+B)>=0.40 is satisfied, and next, induction heating is executed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing a chromate-treated steel sheet, and more particularly, to a method for producing a chromate-treated zinc-based alloy-plated steel sheet having excellent adhesion to an organic film.

[0002]

2. Description of the Related Art In recent years, in order to enhance the plating surface function containing 30% by weight or more of zinc, such as a Zn, Zn-Al-based alloy-coated steel sheet, an alloyed hot-dip galvanized steel sheet, a conventional chromate treatment for the purpose of corrosion protection only Therefore, the necessity of a chromate treatment having multiple functions is increasing.

Under these circumstances, Japanese Patent Laid-Open Publication No.
There is known a technique of adding fumed silica to a chromate solution as disclosed in JP-A-17340. But,
On the contrary, when the amount of the additive increases, the basic function as the chromate film may be hindered. That is, by adding the additive in a certain amount or more, the adhesion between the chromate film and the plating is reduced, and peeling is likely to occur at the interface between the chromate film and the plating. As a result, the function of the chromate film at the peeled portion cannot be exhibited, and the basic function of corrosion resistance is reduced. As a result, sufficient adhesion to the organic film has not been obtained.

As a countermeasure, Japanese Patent Publication No. 56-36869
As shown in Japanese Patent Application Publication No. H10-163, there is a means for adhering a metal noble than zinc such as cobalt or nickel before chromate treatment, improving adhesion between zinc plating and a chromate film, and improving paint adhesion. Proposed. However, these methods increase the number of processing steps and are not desirable from the viewpoint of manufacturing cost. In addition, there is a problem that the corrosion resistance of the plating is reduced by attaching a metal which is more noble than zinc.

[0005]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and provides a chromate treatment technique for forming a chromate film having excellent adhesion to an organic film on a zinc-based alloy-plated steel sheet. The purpose is to provide.

[0006]

The present inventors have conducted detailed studies to solve these problems in the prior art, and as a result, have found that chromic acid and chromic acid reduction products and metal oxides By applying induction heating to the chromate treatment technology using the chromate treatment solution contained in the compounding ratio,
The inventors have found that the above-mentioned problems can be solved and have excellent adhesion to an organic film, which has led to the present invention. According to the present invention, it is possible to obtain a chromate-treated steel sheet having excellent adhesion to an organic film without adhering cobalt, nickel, or the like to zinc or a zinc-based alloy-plated steel sheet before chromate treatment.

[0007] That is, the present invention relates to a method in which zinc is added in a weight ratio of 30.
% Or more of chromic acid and a chromate reduction product in the range of 30% to 70% in terms of Cr reduction ratio, and a primary average particle diameter of 1 nm to 30 nm , Alumina sol and titania sol, wherein the total weight of the chromic acid and the chromate reduction product in terms of CrO ₃ is A, , The weight of the titania sol
When the total weight in terms of O ₂ , Al ₂ O ₃ , and TiO ₂ is B, a chromate treatment liquid satisfying 0.83 ≧ B / (A + B) ≧ 0.40 is applied. The present invention provides a method for producing a chromate-treated steel sheet having excellent adhesion to an organic film, characterized in that the steel sheet is heated to 80 ° C./sec.

In the present invention, the amount of water in the chromate treatment solution applied on the surface of the zinc or zinc-based alloy-plated steel sheet is preferably in the range of ² g / m ^{2 to} 20 g / m ² . Further, in the step of applying the chromate treatment liquid, it is preferable that the temperature of the plate entering the application step be 50 ° C. or less. Further, in the case where cooling is performed after heating by induction heating, it is preferable to perform cooling by air cooling or a water-cooled roll.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS As described above, the present invention applies induction heating to chromate treatment using a predetermined chromate treatment solution. Hereinafter, the present invention will be described in more detail. As the material for the steel sheet of the present invention, a zinc or zinc-based alloy-plated steel sheet (hereinafter abbreviated as a zinc-based alloy-plated steel sheet) is used. The present invention particularly relates to a zinc-based alloy-plated steel sheet containing 30% or more by weight of zinc, for example, so-called 5
% Al-Zn alloy-plated steel sheet, so-called 55% Al-Zn-plated steel sheet, etc., and these plating layers are applied by a known plating method such as a hot-dip plating method or an electroplating method.

[0010] Chromate treatment is performed on these galvanized steel sheets. As a result of a detailed study of the chromate treatment solution used in the present invention, the treatment solution containing chromic acid and a chromate reduction product, and a metal oxide is effective for improving the adhesion to an organic film, and the present invention It turned out that it can be used suitably in.

In the present invention, the chromic acid and the chromic acid reduction product are preferably added so that the Cr reduction ratio is 30% to 70%. Here, the Cr reduction rate is determined by C
r ^{6 +} concentration ([Cr ⁶⁺ ] g / l), total Cr concentration ([C
r] g / l), and the Cr reduction rate = ([Cr]-[Cr
^{6 +} ]) × 100 / [Cr]. If the Cr reduction ratio is less than 30%, sufficient paint adhesion cannot be obtained.
Particularly, from the viewpoint of corrosion resistance, when the amount of Cr attached is preferably 20 g / m ² or more, or when the thickness of the organic film to be coated is large (for example, 50 μm or more), it is more preferably 35% or more. On the other hand, the Cr reduction rate is 70%
If it exceeds 300, bending workability will be reduced, and it will be particularly remarkable when bent at a low temperature. It is more preferably at most 60%.

Further, as the metal oxide, silica, alumina or titania can be suitably used, and if necessary, two or more of these may be added. The primary average particle diameter of these particles is preferably in the range of 1 nm to 30 nm. When the primary average particle size exceeds 30 nm, the adhesion decreases. When the thickness of the organic film to be coated exceeds 100 μm, it is more preferably in the range of 1 nm to 14 nm. The method for producing the metal oxide used in the present invention is not particularly limited, and for example, silica, alumina, and titania produced by a gas phase method can be used. However, silica produced by a gas phase method is preferred.

In the present invention, from the viewpoint of adhesion, the mixing ratio of the chromic acid and the chromic acid reduction product to the metal oxide is preferably such that the weight of the chromic acid and the chromic acid reduction product is expressed in terms of CrO _3. Let the total weight obtained be A, and the weights of silica sol, alumina sol, and titania sol are SiO ₂ ,
When the total weight in terms of Al ₂ O ₃ and TiO ₂ is B, preferably 0.83 ≧ B / (A + B) ≧ 0.40, more preferably 0.68 ≧ B / (A + B) ≧ 0.5. Range.

The amount of water in the chromate treatment liquid applied on the steel sheet should be in the range of ² g / m ^{2 to} 20 g / m ² .
If the water content is less than 2 g / m ² , plating and Cr ⁶⁺ do not sufficiently react even if induction heating described later is used, and the intended effect cannot be obtained. Even if the water content exceeds 20 g / m ² , the chromate adheres unevenly, and the functionality of the chromate decreases. More preferably 3 g / m ^{2 to} 15 g / m ² , most preferably 5 g / m ^{2 to} 12 g / m ²
g / m ² .

Further, the pH of the chromate treatment solution is preferably in the range of 1-4. If the pH of the treatment liquid is less than 1, the metal oxide added for functionalization becomes unstable and cannot exhibit sufficient adhesiveness, or plating and chromate react violently when applied to a plated steel sheet, and excess zinc is removed. It is mixed into the chromate treatment liquid and causes deterioration of the treatment liquid. On the other hand, if the pH of the treatment liquid exceeds 4, the reactivity between the plating and the chromate is remarkably reduced, and the target film properties cannot be obtained. Further, within the above-mentioned range of the pH, reducing mineral acids such as phosphoric acid, nitric acid, and sulfuric acid or salts thereof, basic compounds such as ammonia and sodium hydroxide, and Cr ⁶⁺ in the chromate treatment liquid, within the above pH range. A reducing agent and an organic resin for the purpose may be added.

As the chromate treatment for forming the chromate treatment layer in the present invention, a known method such as a coating type, a reaction type and an electrolytic type can be used. For the coating type chromate treatment, an anhydrous washing type is used. Here, the temperature at which the steel sheet enters the coating step greatly affects the reactivity between the steel sheet and the chromate. In the present invention, the temperature at which the steel sheet enters is preferably 50 ° C. or lower, more preferably 45 ° C. or lower. Intrusion plate temperature is 50
When the temperature exceeds ℃, the temperature of the chromate treatment solution gradually increases,
Evaporation is likely to occur, and even if induction heating is performed, a sufficient effect cannot be obtained. On the other hand, if the intruding plate temperature is too low, the surface may condense before the steel plate enters the coating process, and in such a case, water may inhibit the reaction between plating and chromate, so the steel plate will condense It is better not to lower the temperature until.

Further, the amount of metal oxide adhering on the steel sheet is as follows:
Preferably in the range of ^{40mg / m 2 ~300mg / m 2} . If the amount of the metal oxide is less than 40 mg / m ² , sufficient adhesion cannot be obtained. If it exceeds 300 mg / m ² , bending workability is particularly lowered. More preferably ^{60mg / m 2 ~250mg / m 2} , most preferably ^{80mg / m 2 ~220mg / m 2} . As the chromate deposition amount deposited on the steel sheet preferably with Cr terms in the range of ^{5mg / m 2 ~100mg / m 2} . In order for the metal oxide to be fixed on the steel plate, Cr is required. However, when the amount of Cr attached is less than 5 mg / m 2, it cannot be fixed. If the amount of Cr attached exceeds 100 mg / m ² , the adhesion will be reduced. More preferably 20 mg / m ^{2 to} 70 mg / m ² , most preferably 30 mg / m ²
a ^{mg / m 2 ~55mg / m 2} .

Next, the chromate treatment liquid applied to the steel sheet surface is heated and dried by induction heating. By the induction heating, the adhesion between the chromate film and the plating does not decrease as compared with the conventional hot-air drying, and as a result, the adhesion with the organic film formed on the chromate film can be improved. Although this mechanism is not clear, unlike conventional hot air drying in which heating and drying is performed from the surface of a steel sheet, in induction heating, the reaction between plating and Cr ⁶⁺ easily proceeds because heating is performed from the steel sheet. In this reaction, the influence of water greatly affects the temperature of the plating surface before the water in the chromate treatment liquid evaporates due to the heating from the steel sheet, and without performing a chromate pretreatment such as nickel or cobalt. It is estimated that the chromate and the plating easily react.

The heating rate in induction heating is 25 ° C.
/ Sec or more. If the heating rate is less than 25 ° C./sec, sufficient adhesion to the organic film cannot be obtained. If the heating rate is excessively high, it is difficult to control the target sheet temperature and the operation becomes difficult. Therefore, it is necessary to set the temperature according to the capacity of the line. Further, the reached plate temperature is preferably in the range of 80 ° C to 280 ° C. 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 burden on the operation increases. On the other hand, if the ultimate plate temperature exceeds 280 ° C., not only a large effect is not obtained in characteristics, but also Cr ^{6+ in} the chromate may be 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. The ultimate plate temperature is
The temperature is more preferably in the range of 100 ° C to 220 ° C.

After the chromate-treated layer is dried by heating, the steel sheet is cooled if necessary from the viewpoint of material properties. As a method of cooling, generally, a method using water cooling, air cooling or a water cooling roll can be considered.
Immediately after heating, the chromate film is not sufficiently insolubilized and thus partially dissolves and cannot exhibit its original function. As a cooling method in the present invention, a method using air cooling or a cooling roll in which chromate is not dissolved at the time of cooling is preferable.

[0021]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The effects of the present invention will be specifically described below based on embodiments.

(Examples 1 to 5 and Comparative Examples 1 to 5) Low Pb (P) having a Zn adhesion amount of 90 g / m ² per side and a plate thickness of 1 mm
b; 100 ppm or less) Table 1 for minimized spangled hot-dip galvanized steel sheet (Surface roughness Ra: 0.5 to 1.5)
Chromate treatment solutions (treatment solutions No. 1 to 1)
0) was applied, dried and cooled to form a chromate-treated layer. 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. Table 2 shows the application conditions of the chromate treatment liquid. Further, in order to set the sheet temperature at the time of coating to a predetermined temperature, the plated steel sheet was heated to a predetermined sheet temperature prior to the application of the chromate treatment liquid by a roll coater. Thereafter, a chromate treatment solution was applied and immediately heated and dried. Drying is performed by using an induction heating furnace (hereinafter referred to as “I
H ") at a maximum heating temperature of 120 ° C at a predetermined heating rate. Specific conditions are as shown in Table 3.

(Comparative Examples 6 to 15) In these comparative examples, Examples 1 to 5 and Comparative Example 1 were used except that a hot air blowing furnace (hereinafter also referred to as "CD") was used instead of IH as a heating furnace in heating and drying. Chromate-treated steel sheets were produced in the same manner as in Nos. 1 to 5.

(Examples 6 to 8 and Comparative Example 16) Using the treatment liquid No. 2 shown in Table 1 as a chromate treatment liquid, the heating rate in induction heating was changed in the range of 20 ° C./sec to 60 ° C./sec. Other than that, various chromate-treated steel sheets were manufactured in the same manner as in Examples 1 to 5.

(Examples 9 and 10 and Comparative Examples 17 and 1
8) Manufacture various chromate-treated steel sheets in the same manner as in Examples 1 to 5, except that the treatment liquid No. 2 shown in Table 1 was used as the chromate treatment liquid, and the maximum reached plate temperature was changed in the range of 70 ° C to 300 ° C. did.

(Examples 11 to 16) The processing solutions Nos. 2 and 3 shown in Table 1 were used as the chromate processing solutions.
Various chromate-treated steel sheets were manufactured in the same manner as in Examples 1 to 5 except that the amount of applied water was changed based on various application conditions shown in Table 2. In Examples 14 and 15, various chromate-treated steel sheets were manufactured in the same manner as in Examples 1 to 5, except that the sheet temperature at the time of applying the chromate treatment liquid was changed. Further, in Example 16, a chromate-treated steel sheet was manufactured in the same manner as in Examples 1 to 5, except that a water-cooled roll was used instead of air cooling as a cooling method after heating and drying.

The adhesiveness of the chromate film was determined by applying a polyester-based adhesive to the surface at a thickness of 2 μm, heating and drying in a drying oven at 250 ° C. for 40 seconds, and then immediately attaching a polyester-based film (thickness: 100 μm). Using these as test materials, adhesion was evaluated according to the following evaluation criteria.
Table 3 also shows the results.

[Adhesion strength after processing] A draw bead test was conducted under the conditions of a tip R of 2 mm, a deformation height of 5 mm, and a pressing load of 600 kg, and the film peel strength of the deformed portion was determined according to JIS.
It was measured according to K6845.

[Low-temperature bending workability] A 2T bending was performed at room temperature of 0 ° C, and the degree of peeling was visually determined. The evaluation criteria for the low-temperature bending workability are shown below.

5: No peeling at all 4; There is a locally floating portion on the head of the processed portion (less than 10% of the processing area).

3: There is a clearly floating portion at the head of the processed part (10% or more of the processing area).

2: There is a part where the peeled part reaches further inside from the head of the processed part (less than 10% of the processing area).

1; There is a portion where the peeled portion reaches further inside from the head of the processed portion (10% or more of the processing area).

[Appearance uniformity] Evaluation was made visually based on the following evaluation criteria.

○: No unevenness Δ: Partial unevenness (less than 10% of processing area) ×: Clearly unevenness (10% or more of processing area)

[0036]

[Table 1]

[0037]

[Table 2]

[0038]

[Table 3]

[0039]

[Table 4]

[0040]

[Table 5]

As is clear from Table 3, the use of the chromate treatment liquid according to the present invention (treatment liquid Nos. 1, 24, 7, 8) provides excellent adhesion and workability. It is extremely effective to use induction heating as a drying means, and in the induction heating, it is important to adjust the heating rate and the maximum reached plate temperature within the range according to the present invention. And Comparative Examples 1 to
18 results. Furthermore, in order to further improve the adhesion and workability, it is effective to adjust the temperature of the sheet entering the coating process of the chromate treatment liquid and the amount of water in the chromate treatment liquid on the applied steel sheet within a predetermined range. Yes, and
It was found that it is effective to use air-cooling or water-cooling roll means as the cooling means.

[0042]

According to the present invention, there is provided a method for producing a chromate-treated steel sheet in which a chromate film having excellent adhesion to an organic film is formed on a galvanized steel sheet.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) C23C 22/77 C23C 22/77 (72) Inventor Masaaki Yamashita 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Sun (72) Inventor Ichiro Mishima 1-2-1, Marunouchi, Chiyoda-ku, Tokyo, Japan Nihon Kokan Co., Ltd. (72) Norio Inoue 1-2-1, Marunouchi, Chiyoda-ku, Tokyo, Japan (72) Inventor Toshiyuki Okuma 1-2-1 Marunouchi, Chiyoda-ku, Tokyo F-term (reference) 4D075 AE03 BB18Z BB35Y BB74X BB93Y BB93Z CA13 DA03 DB05 EA02 EA06 EC02 EC03 EC53 EC54 4K026 AA02 AA07 AA13 AA22 BA06 BB01 BB06 BB09 BB10 CA13 CA19 CA21 CA41 DA02 DA11 DA15 EB00

Claims (4)

[Claims] Claims 1. A chromic acid and a chromic acid reduction product in a range of 30% to 70% in terms of Cr reduction ratio on the surface of a zinc or zinc-based alloy plated steel sheet containing 30% or more by weight of zinc. Contains one or more selected from silica sol, alumina sol and titania sol having a primary average particle diameter of 1 nm to 30 nm, and the weight of the chromic acid and the chromic acid reduction product is defined as CrO ₃ . The total weight is A, and the weights of the silica sol, alumina sol, and titania sol are SiO ₂ , Al ₂ O ₃ , and T, respectively.
When the total weight in terms of iO ₂ is B, 0.83 ≧ B /
(A + B) A chromate treatment solution satisfying ≧ 0.40 is applied, and then heated by induction heating at a heating rate of 25 ° C./sec or more and a reached plate temperature of 80 ° C. to 280 ° C. Method for producing chromate treated steel sheet with excellent heat resistance. 2. The water in the chromate treatment liquid applied on the surface of the zinc or galvanized steel sheet is 2 g / m ² to 2 g / m 2.
Method for producing a chromate-treated steel sheet excellent in adhesion with the organic film according to claim 1, characterized in that the 0 g / m ^2. 3. The chromate treatment having excellent adhesion to an organic film according to claim 1, wherein in the step of applying the chromate treatment liquid, the temperature of the plate entering the application step is set to 50 ° C. or less. Steel plate manufacturing method. 4. The method for producing a chromate-treated steel sheet according to claim 1, wherein the steel sheet is heated by induction heating and then cooled by air or water cooling rolls. Method for producing chromate treated steel sheet with excellent heat resistance.