JP2943681B2 - White chromate treated steel sheet with excellent corrosion resistance and appearance - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a chromate-treated steel sheet in which a zinc or zinc alloy-plated steel sheet is formed with a chromate film having excellent corrosion resistance and a beautiful white appearance. The present invention relates to a chromate-treated steel sheet that can be used as an interior / exterior member of an electric appliance or an outer plate material of steel furniture or the like.

[0002]

2. Description of the Related Art Conventionally, zinc or zinc alloy (hereinafter referred to as a zinc-based) coated steel sheet has been widely used for automobiles, household electric appliances, building materials and the like. These galvanized steel sheets are inferior in corrosion resistance as they are, and have insufficient adhesion with a resin coating film formed for the purpose of adjusting the appearance, and are often subjected to chromate treatment on the plating layer. . However, recently, so-called “naked use”, which is used without coating with a resin coating, has been increasing. For this reason, it is necessary to further improve the corrosion resistance of a chromate-treated film, which has conventionally only had to fulfill the role of primary rust prevention.
No. 14050 and Japanese Patent Publication No. 52-2851 propose a technique for improving corrosion resistance by adding silica sol or trivalent chromium ion to a chromate treatment solution.

However, since the chromate-treated steel sheet to which the above-described technology is applied has a lot of yellow color and uneven appearance, the demand for the chromate-treated steel sheet for bare use is becoming severer with the increase in demand. It is not possible to satisfy the requirement, that is, both the improvement of corrosion resistance and the enhancement of appearance quality.

Therefore, a method for producing a chromate-treated steel sheet having a white appearance with improved color tone and uneven coating has been proposed. For example, Japanese Patent Publication No. 3-68115 discloses a method of using a chromate treatment solution in which the mixing ratio of chromic acid, silica sol, and phosphoric acid is specified.
In JP-A No. 11-115, there is disclosed a method of performing a baking treatment at a temperature of 150 ° C. or more using a chromate treatment solution containing a carboxylic acid and / or a derivative of a carboxylic acid together with chromic acid and silica sol.

However, while the white chromate-treated films obtained by the methods disclosed in these publications are becoming severer, the color tone satisfying the user's requirements has not been obtained, and the latter method has a high baking temperature during production. However, there is a problem in that the production efficiency is low and the cost burden is large because high-temperature drying equipment is required.

[0006]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a chromate treated steel sheet having excellent corrosion resistance and exhibiting a beautiful and high-grade white appearance.

[0007]

Means for Solving the Problems The white chromate-treated steel sheet having excellent corrosion resistance and appearance according to the present invention which can solve the above-mentioned problems is a chromate-treated steel sheet having a chromate film formed on the surface of a zinc or zinc alloy plated steel sheet. And
The chromate film is coated with a chromate treatment solution containing colloidal silica and a silane coupling agent having three methoxy groups on the surface of a zinc or zinc alloy-plated steel sheet and dried to reduce the amount of the deposited metal Cr. It is formed so as to be ⁵ to 100 mg / m ² per side in terms of conversion. The zinc or zinc alloy plated steel sheet before chromate treatment has a 60 ° specular gloss of G ₀ , and the 60 ° specular gloss of a steel sheet after chromate treatment. Is defined as G _{1, the point} is that G ₀ and G ₁ satisfy the following expressions (1) and (2). 40.0 ≦ G ₀ ≦ 150.0 (1) 0.4G ₀ ≦ G ₁ (2)

In the present invention, the average particle diameter of the colloidal silica is 10 to 50 nm, and the amount of the colloidal silica and the silane coupling agent in the chromate treatment solution is 1.0 with respect to the chromic acid conversion value of 1. ~
10.0, 0.5 to 5.0 of the silane coupling agent is contained, and the reduction ratio of chromium in the chromate treatment liquid is:
Cr ³⁺ / (Cr ³⁺ + Cr ⁶⁺ ) is 0.1 to 0.5, and the chromate treatment solution further comprises a phosphoric acid compound of 0.05 to 0.50 with respect to a chromic acid conversion value of 1. Is a preferred embodiment.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION The inventors of the present invention have conducted intensive studies in order to meet stricter user requirements, and as a result, the appearance of a chromate-treated steel sheet is closely related to the glossiness of an original sheet (galvanized steel sheet). I found that. Then, using a base plate having a specific glossiness, if the glossiness of the base plate is maintained at least 40% of the glossiness after the chromate treatment, the appearance of the steel plate after the chromate treatment becomes excellent, and The inventors have found that the combined use of colloidal silica and a silane coupling agent in the above is effective in forming a white film having excellent corrosion resistance and beautiful appearance, and completed the present invention. Hereinafter, the present invention will be described in detail.

[0010] First, zinc or zinc alloy plated steel sheet used as the original plate in the present invention, the 60 ° specular gloss G ₀ must satisfy the following formula (1). 40.0 ≦ G ₀ ≦ 150.0 (1) The colloidal silica diffuses and reflects light incident on the surface of the chromate-treated steel sheet to whiten the film. At this time, the gloss G _{0 of the} original sheet is 150. If it exceeds 0, the original plate itself looks blackish, so even if a white chromate film is formed on the original plate, the whitening effect is canceled out, and a high-quality white appearance cannot be obtained. . In the case glossiness G ₀ is less than 40.0, more noticeable is uneven coating of the chromate film can not be prevented the coating unevenness increases the amount of the colloidal silica. The use of an original plate having a gloss in the above-mentioned range makes it possible to make use of the white color of the chromate film and also effectively exerts the action of reducing uneven coating.

The zinc or galvanized steel sheet can be used without any particular limitation as long as it satisfies the above condition of glossiness. Pure zinc plating, zinc-nickel alloy plating, zinc-iron alloy plating, zinc-chromium alloy plating, or the like, which is applied to a steel sheet, may be used as appropriate.

The gloss after the chromate treatment is 60
° Specular gloss is G ₀ , 60 ° of steel plate after chromate treatment
The specular gloss is taken as G _1, the following (2) must satisfy the equation. 0.4G ₀ ≦ G ₁ (2) If the amount of coating film is increased or the amount of colloidal silica is excessively increased in consideration of the improvement of the corrosion resistance of the chromate-treated steel sheet, the gloss G ₁ after the processing becomes lower than that of the original sheet. The gloss G ₀ is less than 40%, but in this case, the unevenness of application of the chromate-treated steel sheet is conspicuous and a high-grade feeling is lost. Therefore, the gloss after the chromate film is formed is maintained at least 40% of the original sheet. It is necessary to.

[0013] In order to balance the degree of glossiness retention after the above-mentioned chromate treatment with the corrosion resistance, the amount of the chromate-treated film to be applied is 5 to 100 mg / m ² per one side of the steel sheet.
(In terms of metal Cr). If the amount is less than 5 mg / m ² , the corrosion resistance is not exhibited, and if it exceeds 100 mg / m ² , the above requirement (2) cannot be satisfied, and only a steel sheet with inconspicuous coating unevenness and a strong yellowish color and poor appearance can be obtained. Because there is no.

Next, the composition of the chromate treatment liquid will be described. The chromate treatment liquid is usually an aqueous solution mainly composed of chromic anhydride, but in the present invention, colloidal silica and a silane coupling agent must coexist in the chromate treatment liquid. It is known that the colloidal silica contained in the chromate film improves the corrosion resistance of the chromate film. Has been found to have the effect of whitening the color tone and making the color tone unevenness less noticeable, and thus is indispensable. The amount of colloidal silica in the treatment liquid is 1.0 to 1 with respect to the chromic acid conversion value of 1.
It is preferably set to 0.0. If the amount is too small, the whitening effect and the effect of making color tone unevenness inconspicuous will not be exhibited.
However, if added in excess of 10.0, the alkali resistance of the resulting film may be reduced, which may adversely affect corrosion resistance. The average particle size of colloidal silica is 10 to 50 nm.
It is preferred that This is because the use of colloidal silica having a particle size in this range provides the best whitening effect and corrosion resistance of the film.

[0015] The silane coupling agent has been added for the purpose of improving the adhesion between the chromate-treated film and the resin film further applied thereto, but the chance of use without coating increases. It is considered unnecessary. However, the silane coupling agent has the effect of reducing Cr ⁶⁺ in the processing solution to Cr ³⁺ to reduce yellowish tint, and is dense and strong due to the interaction between the silane coupling agent and colloidal silica. The present inventors have found that a chromate-treated film is formed and contribute to the improvement of corrosion resistance, so that it was an essential component.

The silane coupling agent is a compound in which a methoxy group or an ethoxy group and a functional group such as a vinyl group, a glycidoxy group, a methacryloxy group, an amino group, and a mercapto group are bonded to Si with or without an alkyl group. is there. In the present invention, in particular, when a silane coupling agent having three methoxy groups is used, both the effect of improving the yellow tint and the effect of improving the corrosion resistance can be formed in a well-balanced manner. Among the coupling agents, a silane coupling agent in which three methoxy groups are bonded to Si is used. Specific examples include vinyltrimethoxysilane, γ- (methacryloxypropyl) trimethoxysilane, γ-glycidoxypropyltrimethoxysilane, N-β (aminoethyl) γ-aminopropyltrimethoxysilane, γ-mercaptopropyl Trimethoxysilane and the like can be mentioned, and these can be used alone or in combination of two or more.

The silane coupling agent is preferably used in the chromate treatment solution in a range of 0.5 to 5.0 with respect to a chromic acid conversion value of 1. If the amount is too small, the effect of reducing yellowness and the effect of improving corrosion resistance do not appear. Further, even if added in excess of 5.0, these effects will be saturated. Therefore, from the viewpoint of economy, it is preferable to set the content to 5.0 or less.

By using a silane coupling agent and colloidal silica in combination as described above, a chromate-treated steel sheet having excellent corrosion resistance and a high-quality appearance with a beautiful white appearance can be obtained. In order to obtain a free coating, the reduction rate of chromium in the chromate treatment solution:
It is preferable to adjust Cr ³⁺ / (Cr ³⁺ + Cr ⁶⁺ ) to 0.1 to 0.5. When the content of Cr ³⁺ is less than 0.1, it is difficult to reduce the yellow tint of the film because the content of Cr ³⁺ is small even if the effect of reducing the Cr ⁶⁺ → Cr ³⁺ by the silane coupling agent is added. However, when the content of Cr ³⁺ exceeds 0.5, the stability of the processing solution decreases, so that it is desired to adjust the treatment solution to the above range. The method of adjusting Cr ³⁺ to the above range is not particularly limited, but may be performed by adding a known reducing agent such as ethanol, methanol, oxalic acid, starch, and sucrose.

In a preferred embodiment of the present invention, the chromate treatment solution further contains a phosphoric acid compound in an amount of 0.05 to 0.50 with respect to a chromic acid conversion value of 1. This is because the phosphate compound is effective in improving the corrosion resistance of the chromate-treated film, particularly the alkali resistance. 0.0
If it is less than 5, the effect of improving the corrosion resistance will not be exhibited, and if it exceeds 0.50, the hygroscopicity of the film will increase and the corrosion resistance may be adversely affected, so it is recommended to add an amount within the above range. You. As the phosphate compound, orthophosphoric acid, various condensed phosphoric acids, or ammonium salts or alkaline earth metal salts thereof can be used.

The chromate-treated steel sheet of the present invention can be produced by applying a chromate treatment solution having the composition described above to a zinc-based plated steel sheet and drying it.
The coating method is not particularly limited, and may be appropriately selected from known roll coater methods, bar coater methods, air knife methods, spray mist methods, curtain coater methods, and the like. The drying conditions after the application are preferably 40 to 150 ° C. at the reached plate temperature. When the temperature is lower than 40 ° C., whitening of the film may be insufficient. If the temperature exceeds 150 ° C., the corrosion resistance of the film deteriorates and the production cost increases, which is not preferable.

[0021]

EXAMPLES The present invention will be described in more detail with reference to the following Examples, which do not limit the present invention.
Modifications and alterations that do not depart from the spirit described below are all included in the technical scope of the present invention.

Example The hot-dip galvanized steel sheet having a 60 ° specular gloss in the range of 30.2 to 180.3 was prepared by changing the rolling conditions of the skin pass in various ways, and used as an original sheet. After applying seven types of chromate treatment solutions having the compositions shown in Table 1 with a roll coater,
Drying and baking were performed at an ultimate plate temperature of 80 ° C. The performance of the obtained chromate-treated steel sheet was evaluated by the following methods, and the measurement results are shown in Tables 2 to 4.

[Coating adhesion amount]
Chromium adhering amount in mate film (mg / m^Two ). [Gloss] According to JIS Z8741 and 60 ° mirror-like
The gloss at the angle of incidence was measured using the original plate (G ₀ ) And chromate treatment
Rigo (G₁ ) Using a gloss meter manufactured by Nippon Denshoku Co., Ltd.
And measured. The gloss retention in the table is G₁ / G₀ 
○, G for ≧ 0.4₁/ G₀ <0.4 and ×
Shown.

[Appearance Unevenness] The appearance of the chromate-treated steel sheet was visually observed and evaluated mainly on whether or not the application unevenness of the chromate film was conspicuous. The evaluation criteria are as follows. ◎: Extremely good appearance ：: Relatively good appearance ：: Slightly noticeable unevenness ×: Significantly uneven appearance

[Appearance color tone] The appearance of the chromate-treated steel sheet was visually observed, and the degree of the effect of the chromate film under the white color was evaluated. The evaluation criteria are as follows. ◎: Extremely good appearance ：: Relatively good appearance 黒: Slightly dark or blackish ×: Extremely dark or blackish

[Corrosion Resistance] A salt spray test was carried out according to JIS Z2371 and the white rust occurrence rate after 72 hours was evaluated according to the following criteria. ：: White rust occurrence rate of less than 1% △: White rust occurrence rate of 1% or more and less than 5% ×: White rust occurrence rate of 5% or more

[0027]

[Table 1]

[0028]

[Table 2]

[0029]

[Table 3]

[0030]

[Table 4]

[0031]

The chromate-treated steel sheet of the present invention is excellent in corrosion resistance and has a beautiful white appearance, so it is unpainted and used as it is for interior and exterior members of automobiles and home electric appliances, or for outer plate materials of steel furniture and the like. Can be used for

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-3-146676 (JP, A) JP-A-4-147981 (JP, A) JP-A-60-135579 (JP, A) JP-A-62 83478 (JP, A) JP-A-4-323383 (JP, A) JP-A-3-234527 (JP, A) JP-A-4-377 (JP, A) (58) Fields investigated (Int. ⁶ , DB name) C23C 22/30 C23C 22/33 C23C 28/00

Claims (5)

(57) [Claims] 1. A chromate-treated steel sheet having a chromate film formed on the surface of a zinc or zinc alloy-plated steel sheet, wherein the chromate film contains colloidal silica and a silane coupling agent having three methoxy groups. The chromate treatment liquid is applied to the surface of a zinc or zinc alloy-plated steel sheet and dried so that the amount of the coating becomes ⁵ to 100 mg / m ² per one side in terms of metal Cr. Of zinc or zinc alloy coated steel sheet
0 ° specular gloss is G ₀ , and 60
° when the specular gloss was G _1, white chromate treated steel sheet G _0, G ₁ is excellent in corrosion resistance and appearance and satisfies the following formulas (1) and (2). 40.0 ≦ G ₀ ≦ 150.0 (1) 0.4G ₀ ≦ G ₁ (2) 2. Colloidal silica having an average particle size of 10 to 5
The white chromate-treated steel sheet according to claim 1, which has a thickness of 0 nm. 3. The colloidal silica and the silane coupling agent in the chromate treatment liquid are 1.0 to 10.0 for colloidal silica and 0.5 to 5.0 for the silane coupling agent based on a chromic acid conversion value of 1. The white chromate-treated steel sheet according to claim 1 or 2, which is contained. 4. A reduction ratio of chromium in a chromate treatment solution:
The white chromate-treated steel sheet according to claim 1, wherein Cr ³⁺ / (Cr ³⁺ + Cr ⁶⁺ ) is 0.1 to 0.5. 5. The white chromate according to claim 1, wherein the chromate treatment liquid further contains a phosphoric acid compound in an amount of 0.05 to 0.50 relative to a chromic acid conversion value of 1. Treated steel sheet.