JPH0941168A - Zinc-inorganic based surface treated steel sheet excellent in flaw resistance and corrosion resistance - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce an economical zinc plated or zinc alloy plated steel sheet having high rust preventive property. SOLUTION: An inorganic based rust preventive coating composition is applied to a zinc or zinc alloy plated steel sheet. This composition contains, when [component A] represents the partial hydrolytic condensation product of organic silicate represented by the chemical formula Si(OR)4 (where R is a substitutional or nonsubstitutional alkyl group), an alkali group-containing slag [component B] or a pH8-13 powdery basic compound [component C] and a zinc powder [component D] by 300-10000 pts.wt. in total based on 100 pts.wt. of silica (expressed in terms of SiO2 contained in the [component A]. By this method, the zinc plated or zinc alloy plated steel sheet, excellent in external appearance of coated film and adhesion, free from the occurrence of white rust, and having superior rust preventive property, can be produced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface-treated steel sheet on which a zinc-plated steel sheet which is resistant to flaws and has excellent corrosion resistance is used as a base.

[0002]

2. Description of the Related Art In recent years, the excellent corrosion resistance of zinc- or zinc-based alloy-plated steel sheets has come to the forefront with the demand for improved performance of durable consumer products such as automobiles, buildings, and home appliances. The demand is growing remarkably, especially in Japan. However, the standards for the requirements for better products have become more sophisticated year by year, and as surface-treated steel sheets are required to have even better corrosion resistance, coated steel sheets with plated steel surfaces further coated with resin are being used. It's coming. However, the plated zinc and zinc-based alloys are easily dissolved in water in the acidic region of pH 8 or less and the basic region of pH 13 or more, and the elution rate becomes fast, so the coating resin is also easily deteriorated and white rust is generated. There was a problem that was likely to occur.

Therefore, in the conventional galvanized or zinc-based alloy plated steel sheet, after forming a plating layer on the base steel sheet,
A chromate film or a phosphate film layer is formed, and an organic film layer is laminated to prevent the intrusion of water from the outside and suppress the occurrence of white rust, thus improving the corrosion resistance. . The chemical conversion coatings on zinc-plated or zinc-based alloy-plated steel sheets are mainly phosphate coatings and chromate coatings, which are intended to prevent white rust and improve the coating base. It was not enough as a countermeasure.

Therefore, in order to improve the corrosion resistance of the coated steel sheet, a means for incorporating zinc powder or zinc-based alloy powder into the resin coating has been proposed (Japanese Patent Laid-Open Nos. 58-174582 and 62-234576). JP-A-63-270131
In the organic film-plated steel sheet by these means, the zinc dust and zinc-based alloy powder contained in the resin film have a high elution rate, and there is no countermeasure for preventing the occurrence of white rust in the paint. In addition, the resin in the surface layer had a small hardness and was damaged by a small external force, and rust progressed from that portion.

[0005]

SUMMARY OF THE INVENTION It is an object of the present invention to prevent the occurrence of white rust, which is pointed out in a conventional coated steel sheet obtained by coating a resin on a galvanized or zinc alloy plated steel sheet, and to improve the corrosion resistance. Further, the strength of the resin is improved so that the resin is not easily scratched by an external force and partial rust is prevented from occurring.

[0006]

According to the present invention, zinc has a pH of 8
In the weakly alkaline range of ~ 13, the corrosion rate is extremely slow,
Focusing on stability, blast furnace and converter slag (pH 9 to 12.6) or pH 8 to 1 containing an alkali group
It was found that the powdery basic compound of 3 and zinc powder are used in combination to keep the surface of zinc-plated or zinc-based alloy-plated steel sheet alkaline and to provide rust-preventing properties, thereby exhibiting the galvanic protection property of zinc. It has been completed. Also, since the slag contains a large amount of Al ₂ O ₃ and SiO _{2, the} average hardness is about Hv 700 to 900, which is extremely high. An inorganic rust preventive coating composition film is formed to protect the surface of a zinc or zinc alloy plated steel sheet.

The gist of the invention is as follows: (1) A portion of an organic silicate represented by the chemical formula Si (OR) ₄ (R is a substituted or unsubstituted alkyl group) on the surface of a zinc- or zinc-based alloy-plated steel sheet. The hydrolysis condensate is referred to as [A component], and silica (SiO 2) contained in [A component] is used.
₂ conversion value) One part or two kinds of slag [B component] containing an alkali group and powdery basic compound [C component] having a pH of 8 to 13 per 100 parts by weight in total is 300 to 1000.
Zinc excellent in flaw resistance and corrosion resistance, characterized in that an inorganic rust preventive coating composition film containing 0 part by weight is formed.
Inorganic surface treated steel sheet.

(2) A partial hydrolysis-condensation product of an organic silicate represented by the chemical formula Si (OR) ₄ (R is a substituted or unsubstituted alkyl group) is [A component] on the surface of a zinc- or zinc-based alloy-plated steel sheet. And one kind of slag [B component] containing an alkali group and powdery basic compound [C component] having a pH of 8 to 13 with respect to 100 parts by weight of silica (SiO ₂ conversion value) contained in [A component]. Or two kinds and zinc powder [D
[Ingredients] in a total amount of 300 to 10,000 parts by weight to form an inorganic rust-preventive coating composition film. A zinc / inorganic surface-treated steel sheet excellent in flaw resistance and corrosion resistance.

(3) 1 of a slag [B component] containing an alkali group and a powdery basic compound [C component] having a pH of 8 to 13
The total amount of one kind or two kinds is 100 to 10 parts by weight, and the zinc powder [D component] is contained in a ratio of 0 to 90 parts by weight, and the resistance according to (1) or (2) above. Zinc / inorganic surface treated steel sheet with excellent scratch resistance and corrosion resistance. (4) A chromate film or a phosphoric acid film is formed on the surface of a zinc or zinc alloy-based plated steel sheet, and an inorganic anticorrosive coating composition film is formed on the surface thereof (1) to (3) ) The zinc-inorganic surface-treated steel sheet having excellent scratch resistance and corrosion resistance as described above.

[0010]

In the present invention, slag containing an alkali group or a powdery basic compound having a pH of 8 to 13 is used in combination with zinc powder to keep the surface of galvanized or zinc-based alloy plated steel sheet alkaline and prevent rust. Is given to exert the anticorrosive property of zinc. Blast furnace and converter slag have a pH of 9
The range is from ˜12.6. Zinc has a very slow corrosion rate and is stable in the pH range of 9 to 12.6. The surface of the zinc-plated or zinc-based alloy-plated steel sheet coated with this coating has a slow corrosion rate due to its alkaline atmosphere, and the amount of anticorrosion current is small, so zinc elution is small, and excessive elution of zinc is suppressed. It Therefore, when the inorganic rust-preventive coating composition of the present invention is applied to the surface of a galvanized or zinc-alloy plated steel sheet, the zinc consumption is small, while exhibiting the rust preventive function sufficiently. Good anti-corrosion performance is maintained.

Furthermore, the slag containing an alkaline group as a corrosion product of zinc powder or the alkaline group of the powdery basic compound having a pH of 8 to 13 facilitates the formation of zinc hydroxide and keeps the coating more alkaline. What is particularly noteworthy is that not only white rust does not occur but also red rust on the steel sheet decreases, and good corrosion resistance can be obtained. Since the slag contains a large amount of Al ₂ O ₃ and SiO _{2, the} average hardness is about Hv 700 to 900, which is an extremely high level. Therefore, a coating film containing slag has a strong protective power against external force, and has a property that the coating film is hardly damaged. Examples of the slag containing an alkali group include blast furnace slowly cooled slag, blast furnace granulated slag, converter slag, electric furnace slag, and SUS slag.

The zinc powder used with the slag containing an alkali group is usually any powder having an average particle size of 1 to 50 μm, preferably 1 to 20 μm, and may be spherical or flaky. If it is as small as less than 1 μm, excessive agglomeration proceeds in the paint, making it difficult to adjust the paint and apply it to a steel sheet. If it exceeds 50 μm, the layer of the coating film becomes thin locally, and the proper elution rate is lost, and sufficient rust preventive performance cannot be exhibited.

Examples of powdery basic compounds having a pH of 8 to 13 include magnesium hydroxide, basic magnesium carbonate, potassium carbonate, calcium oxide, calcium hydroxide, barium hydroxide, barium metaborate, borax, Portland cement and alumina cement. , Blast furnace cement, etc. If the pH is less than 8 or more than 13, the dissolution rate of zinc rapidly increases and the sacrificial anticorrosive action of zinc does not last long.

The particle size of the powder is 0.01 to 100 μm.
The thing of is desirable. If it is less than 0.01 μm, excessive agglomeration progresses in the paint, making it difficult to adjust the paint and apply it to the steel sheet. If it is larger than 100 μm, the layer of the coating film is locally thinned to lower the corrosion resistance. The pH of the alkaline group-containing slag and the powdery basic compound is 100 g of the alkaline group-containing slag and the powdery basic compound in 900 ml of ion-exchanged water and stirred, and after 24 hours at 20 ° C., a glass electrode pH meter. It was measured at. Granulated blast furnace slag (Essent, made by Nippon Steel Chemical) is 1
1.0, barium metaborate (View Sun 11M-1,
Sakai Chemical Industry Co., Ltd.) showed 10.2.

In the present invention, the organic silicate is hydrolyzed by a known method and used as a hydrolyzed condensate. As organic silicates, methyl silicate, ethyl silicate, propyl silicate, butyl silicate,
2-Methoxyethyl silicate and other higher alkyl silicates can be used. Among them, ethyl silicate has a fast reaction and a good drying property as a coating film, but it is slightly inferior in flexibility and tends to be brittle. Further, butyl silicate has good flexibility, but the reaction is rather slow and the curability as a coating film is poor.
Ethyl silicate is preferable because of its dryness and flexibility.

In addition to organic silicates, alkali silicates such as sodium silicate, lithium silicate and calcium silicate, and inorganic substances such as colloidal silica can be used. In addition, vinyltriethoxysilane, γ
A silane coupling agent such as methacryloxypropyltrimethoxysilane, γ-glycidoxypropyltrimethoxysilane, N- (β-aminoethyl) γ-aminopropyltrimethoxysilane can also be added. In addition to organic silicates, alcohol-soluble phenol resins, polyvinyl butyral, epoxy resins, xylene resins, vinyl resins, polybutadiene resins, petroleum resins, alkyd resins, polyester resins, acrylic resins, melamine resins, urea resins, urethane resins, etc. A system resin can also be used.

The mixing ratio of the organic silicate and the slag containing an alkali group or the powdery basic compound having a pH of 8 to 13 and the zinc powder is 100 parts by weight of silica (SiO ₂ conversion value) contained in the organic silicate, The total amount of the slag containing a group or the powdery basic compound having a pH of 8 to 13 and the zinc powder is 300 to 10000 parts by weight, and preferably 500 to 8000 to 100 parts by weight of silica (SiO ₂ conversion value) contained in the organic silicate. Parts by weight. If the total amount of slag containing an alkaline group or powdery basic compound having a pH of 8 to 13 and zinc powder is less than 300 parts by weight, the film forming property of the coating film deteriorates, and zinc or zinc-based alloy plating, zinc spray coating, etc. Adhesion to the surface of the applied steel sheet decreases. In addition, the total amount of the slag containing an alkaline group or the powdery basic compound having a pH of 8 to 13 and the zinc powder is 1
If it exceeds 0000 parts by weight, the coating film becomes brittle and the corrosion resistance decreases.

The mixing ratio of the alkaline group-containing slag or the powdery basic compound having a pH of 8 to 13 and the zinc powder is 100 to 10 parts by weight of the alkaline group-containing slag or the powdery basic compound having a pH of 8 to 13. On the other hand, it is desirable to mix zinc powder in an arbitrary ratio within the range of 0 to 90 parts by weight. Slag containing an alkaline group or pH 8 to
When the powdery basic compound of 13 is less than 10 parts by weight, that is, when the zinc powder exceeds 90 parts by weight, the dissolution rate of zinc is increased, white rust is easily generated, and corrosion resistance is deteriorated. The thickness of the inorganic anticorrosive coating composition is preferably 10 to 100 μm. 10 μm
If it is less than less than 1, there is a problem in corrosion resistance. If it is thicker than 100 μm, the coating film may be cracked or peeled off, which also causes a problem in corrosion resistance. Preferably, the thickness is 30 to 80 μm.

The coated steel sheet according to the present invention is basically a galvanized steel sheet or a zinc alloy plated steel sheet. Examples of the zinc plated steel sheet include a galvanized steel sheet and Zn-
Fe alloy plated steel sheet, Zn-Ni alloy plated steel sheet, Zn
-Mn alloy plated steel sheet, Zn-Al alloy plated steel sheet, Z
There is an n-Co alloy-plated steel sheet or the like, and further, a steel sheet plated with an alloy in which one or more kinds of Ni, Fe, Mn, Co, Al, Cr and the like are added to each of the plating components, and the above-mentioned plated layer A composite plated steel plate that is a composite of one or more types can also be raised. Of course, the material is not limited to these, and a zinc-based plated steel sheet is appropriately selected according to the required corrosion resistance and the like.

Further, the coating amount is not particularly limited, and a coating amount of about ²⁰ to 400 g / m ² which is generally used for automobile steel sheets (per one side) is sufficient. Further, there is no particular limitation on the method of forming the plating layer, and any known plating method such as electroplating or hot dipping may be used. Further, the chromate film may be formed by any means of coating type, reaction type and electrolytic type. The chromate treatment liquid contains a water-soluble chromium compound as a main component, and an appropriate amount of phosphate radicals, anions such as fluorine ions, metal ions such as Zn, Ni and Co, and organic substances such as starch and methanol are added thereto as necessary. .

If the amount of the chromate film deposited is less than 5 g / m ^{2 in} terms of the amount of metal chromium, corrosion resistance cannot be obtained, and if it exceeds 400 g / m ² , the film peels off or weldability deteriorates. 5 to 400 g /
A range of m ² is suitable. Preferably 20-300 g /
It is better to adjust to the range of m ² . Deposition amount of phosphate coating in the case of electro-galvanized steel sheet 2.5 g / m ² or less, preferably in the case 2 g / m ² or less galvanized.
If the coating layer becomes thick, peeling of the coating may occur and weldability may deteriorate.

[0022]

EXAMPLES Examples will be described below. As a sample of galvanized steel sheet, zinc was electroplated at 20 g / m ² on a low carbon cold rolled steel sheet having a plate thickness of 0.7 mm. The chromate treatment was performed by applying a coating type chromate treatment of 50 g / m ^{2 on} the surface using a roll coater and baking at a maximum reaching temperature of 130 ° C. The phosphoric acid treatment was performed by dissolving zinc oxide in phosphoric acid, diluting it in water, adding nitrite, and spraying. The inorganic anticorrosive coating composition was produced as follows. In the examples, unless otherwise specified, parts by weight are shown. First, as the organic silicate hydrolyzate, one prepared with the following composition was used. Ethyl silicate 40 (Nippon Colcoat) 100 parts Isopropyl alcohol 137 parts Deionized water 8 parts 2% hydrochloric acid 5 parts The above composition was reacted with stirring for 2 hours to prepare a hydrolytic condensate of ethyl silicate. The silica (SiO ₂ conversion value) of this hydrolyzate was 16% by weight.

As the slag containing an alkali group, the powdery basic compound and the zinc powder in the rust preventive composition, the followings were used. Alkaline-based ground granulated blast furnace slag (Essent, Nippon Steel Chemical Co., Ltd.) Powdery basic compound with pH 8 to 13 Barium metaborate (View Sun 11M-1, Sakai Chemical Industry Co., Ltd.) Zinc powder F1000 (Honjo Chemical Co., Ltd.) The respective components having the blending amounts (parts by weight) shown in Table 1 were mixed and dispersed with a paint mixer to prepare. The coating was applied with a brush and dried at 20 ° C. for 10 days so that the final dry film thickness was 50 ± 5 μm.

[0024]

[Table 1]

The evaluation of each characteristic was performed as follows. Test Items and Evaluation Method (1) Coating Film State The surface state of the coating film was observed according to JIS K5400 7.1. It was visually inspected whether the appearance of the coating film was normal. Observation items are gloss, unevenness,
Wrinkles, dents, repellants, crushes, etc. If it is good, it is indicated by a symbol, and if it has a defect, it is indicated by a symbol. (2) Adhesion test A test was conducted according to JIS K5400 8.5.2. The crosscut method was adopted. The gap between cuts is 2 mm and the number of squares is 25 mm.
A grid-like cut was made with a cutter knife specified in 4401, the adhesive tape was peeled off, and the adhesion of the coating film after peeling was visually observed.

(3) Scratch resistance JIS K5400
The pencil scratch value was calculated according to 8.4. The hardness of the coating film was examined by scratching the coating film with a pencil and represented by the density symbol of the pencil. (4) Salt Spray Test A test was conducted for 1500 hours under the conditions of JIS K5400 9.1. The test piece was tested by inserting a cross cut reaching the substrate with a cutter knife specified in JIS G 4401. The salt spray test was evaluated as shown in Table 2 below. Table 1 shows the evaluation results for each sample.

[0027]

[Table 2]

[0028]

EFFECTS OF THE INVENTION The steel sheet coated with zinc, zinc-based alloy, zinc sprayed coating, etc. of the present invention exhibits stable rust-preventing performance for a long period of time without occurrence of white rust, and is strongly resistant to external forces. Enables the production of surface-treated steel sheets that are difficult to stick.

Claims (4)

[Claims] 1. A partially hydrolyzed condensate of an organic silicate represented by the chemical formula Si (OR) ₄ (R is a substituted or unsubstituted alkyl group) is [A component] on the surface of a zinc or zinc alloy plated steel sheet. , One kind of a slag [B component] containing an alkali group and a powdery basic compound [C component] having a pH of 8 to 13 relative to 100 parts by weight of silica (converted to SiO ₂ ) contained in the [A component], or 300 kinds of two kinds in total
A zinc-inorganic surface-treated steel sheet excellent in flaw resistance and corrosion resistance, which is formed by forming an inorganic rust preventive coating composition film containing 10000 parts by weight. 2. A partially hydrolyzed condensate of an organic silicate represented by the chemical formula Si (OR) ₄ (R is a substituted or unsubstituted alkyl group) is [A component] on the surface of a zinc- or zinc-based alloy-plated steel sheet. , One kind of a slag [B component] containing an alkali group and a powdery basic compound [C component] having a pH of 8 to 13 relative to 100 parts by weight of silica (converted to SiO ₂ ) contained in the [A component], or A zinc / inorganic surface-treated steel sheet excellent in flaw resistance and corrosion resistance, characterized in that an inorganic rust preventive coating composition film containing 300 to 10,000 parts by weight in total of two kinds and zinc powder [D component] is formed. . 3. A slag containing an alkali group [component B]
And a total amount of one or two powdery basic compounds [component C] having a pH of 8 to 13 of 100 to 10 parts by weight, zinc powder [D
Ingredients] is contained in a proportion of 0 to 90 parts by weight, and the zinc-inorganic surface-treated steel sheet excellent in flaw resistance and corrosion resistance according to claim 1 or 2. 4. A chromate film or a phosphoric acid film is formed on the surface of a zinc or zinc alloy-based plated steel sheet, and an inorganic anticorrosive coating composition film is formed on the surface thereof. Item 3. A zinc-inorganic surface-treated steel sheet excellent in flaw resistance and corrosion resistance according to Item 3.