JP2001115273A - HOT DIP Zn-Al SERIES PLATED STEEL SHEET EXCELLENT IN SECULAR BLACKENING RESISTANCE - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a hot dip Zn-Al series plated steel sheet excellent in secular blackening resistance. SOLUTION: As to this hot dip Zn-Al series plated steel sheet excellent in secular blackening resistance, in a hot dip Zn-Al series plated steel sheet having a plating layer containing, by weight, 0.1 to 70% Al, and the balance Zn with inevitable impurities, the surface of the plating layer is provided with a film layer containing one or two or more kinds among boric acid and borate compounds by 0.01 to 5 g/m2.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hot-dip Zn-Al alloy-plated steel sheet having excellent resistance to blackening over time.

[0002]

2. Description of the Related Art Recently, in the field of building materials and civil engineering, hot-dip galvanized steel sheets which have been unpainted or coated after processing are used. Most of these steel sheets are subjected to chromate treatment in the form of coils or cut sheets. After being packed as it is and stored in a warehouse or the like for a certain period of time, it is processed into various members and used. During storage, the occurrence of white rust is significantly prevented by the chromate treatment. However, during the rainy season when the humidity is high, the chromate-treated material may undergo blackening over time (black rust), significantly increasing the commercial value. There is a high demand for improvement of blackening resistance over time because of lowering. The hot-dip Zn-Al coated steel sheet is a steel sheet having better corrosion resistance than the hot-dip Zn-coated steel sheet. However, the resistance to blackening regardless of the presence or absence of the chromate treatment is not much different from that of the normal hot-dip Zn-coated steel sheet, and improvement is desired. .

As a measure for suppressing blackening with time, for example, a zinc-based alloy-coated steel sheet disclosed in Japanese Patent Publication No. 3-49982 is immersed or sprayed with a solution of Ni ions or Co ions or a mixed solution of both. Processing N
The method of attaching i or Co, the hydroxide of Co disclosed in Japanese Patent Publication No. 5-33311, the hydroxide of Fe, or an aqueous solution containing both is sprayed on the plating surface at 100 ° C. or more to form an oxide film. A method for forming the film is known. In each case, after treatment with these solutions, blackening over time of the plated surface was slightly suppressed, but the effect was not always sufficient.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems of the prior art and to provide a hot-dip Zn-Al alloy-plated steel sheet having excellent resistance to blackening over time.

[0005]

Means for Solving the Problems The inventors of the present invention have developed a Zn-Al alloy plated steel sheet which exhibits excellent anti-aging blackening by uniformly distributing a small amount of a blackening preventing component on the plating surface. Various studies were made. As a result, it has been found that good temporal blackening resistance can be obtained by forming a thin film containing boric acid and a borate compound as a temporal blackening inhibiting component on a plating surface in a post-treatment step of a steel sheet, and completed the present invention. Therefore, the gist of the invention is as follows: (1) By weight%, Al: 0.1 to 70% by weight,
A hot-dip Zn—Al-based plated steel sheet having a plating layer composed of a balance of Zn and unavoidable impurities, wherein a coating layer containing one or more of boric acid and a borate compound on a surface of the plating layer is 0.01 to 0.01%. A hot-dip Zn-Al-based plated steel sheet excellent in blackening resistance over time, characterized by having 5 g / m ² .

(2) When the plating layer is composed of Mg: 0.1% by weight.
1 to 30%, one or two kinds of Si: 0.1 to 5%,
The hot-dip Zn-Al-based plated steel sheet according to the above (1), further comprising: (3) The plating layer is, by weight%, Sn: 0.5 to 10%,
One or more of Sb: 0.05 to 1% and Pb: 0.05 to 1% are further contained. Excellent hot-dip Zn-Al plated steel sheet. (4) The coating layer is formed of an inorganic compound, an organic resin, or both an inorganic compound and an organic resin, containing one or more of Cr, Si, Ni, Co, and Zn. The hot-dip Zn—Al-based plated steel sheet according to any one of the above (1) to (3), which is excellent in blackening resistance over time.

[0007]

Embodiments of the present invention will be described below in detail. The gist of the present invention is to form a film containing boric acid and a borate compound on a hot-dip Zn-Al-based plating surface using an inorganic compound or an organic resin having a film forming ability, so that plating appearance, that is, in a wet atmosphere To provide a hot-dip Zn-Al-plated steel sheet having excellent resistance to blackening over time of the plating surface.

The composition of the plating layer in the present invention contains 0.1 to 70% by weight of Al, and the balance consists of Zn and unavoidable impurities. Al improves plating adhesion between the plating layer and the base steel sheet, and improves corrosion resistance. Al
Is less than 0.1% by weight, the plating adhesion decreases. In addition, an Fe-Zn-based intermetallic compound is formed in a hot-dip plating bath, and a large amount of dross is generated in the plating bath, which causes a deterioration in quality. When the content exceeds 70% by weight, the melting point of the plating bath becomes high, so that problems such as erosion of equipment in the plating bath and increase in heating cost occur.

In addition, the following elements may be selectively added. Mg significantly improves the corrosion resistance of the plating layer when added at 0.1% or more. However, even if it is added in excess of 30% by weight, the effect is not only saturated, but also becomes an oxide, and black dross is generated on the plating bath surface, which causes quality deterioration. Si is added in an amount of 0.1% or more to improve the corrosion resistance of the plating layer and to reduce F between the plating layer and the base steel sheet.
This has the effect of suppressing the e-Zn alloying reaction and the Fe-Al alloying reaction. However, even if Si is added in excess of 5% by weight, the effect is not only saturated, but also the amount of dross generated increases, which causes quality deterioration.

[0010] Sn, Sb and Pb are added when it is necessary to form a spangle pattern on the plating surface. Sn
Is effective when added at 0.5% by weight or more.
The effect saturates with the addition exceeding 0% by weight. Sb,
Pb has its effect when added in an amount of 0.05% by weight or more, but its effect is saturated even when it is added in an amount exceeding 1% by weight. Further, Ti has an effect of improving the corrosion resistance of the plating layer and miniaturizing the plating structure, so that 0.01% by weight or more of the effect may be added. However, even if it is added in excess of 5% by weight, the effect is not only saturated, but also the amount of dross generated increases and causes quality deterioration.

Ni and Fe may enter the plating bath as unavoidable impurities, but are preferably adjusted to be less than 0.1% by weight, respectively. As a method for producing a hot-dip Zn-Al-based plated steel sheet, a steel sheet to be plated is subjected to a non-oxidizing furnace.
After annealing and heating in a reduction furnace method or a total reduction furnace method,
A method of continuously hot-dip plating to a predetermined coating weight by gas wiping after dipping and pulling in a hot-dip plating bath, or a method of hot-dip plating with Ni undercoating on the surface of the steel sheet to be plated and then hot-dip similarly Applicable. Further, in order to improve the surface appearance quality of the hot-dip Zn-Al-based plated steel sheet, the steel sheet to be plated may be subjected to alkali degreasing, pickling, washing with hot water, etc. before heating to remove stains on the surface in advance.

In the present invention, a coating containing one or more of boric acid and a borate compound is formed on the surface of the hot-dip Zn—Al plating in an amount of 0.01 to 5 g / m ² . By containing boric acid and a borate compound, oxidation of the plating surface is suppressed, and as a result, an effect of improving blackening resistance over time can be obtained. Here, borate compounds include, for example, zinc borate,
Sodium borate, lithium borate, tetrafluoroborate,
Ammonium borate or the like can be applied. Coating amount is 0.01 ~
5 g / m ^{2 is} formed. If it is less than 0.01 g / m ² , a sufficient effect of improving blackening resistance over time cannot be obtained. If it exceeds 5 g / m ² , the effect is not only saturated, but also the production cost increases, which is not preferable. In addition, the measuring method of the coating amount is a method of measuring a weight change before and after applying and drying boric acid and a borate compound, and dissolving an acid in a plating layer and measuring a boron content by an atomic absorption method, an IPC method, or the like. However, there is a method of measuring the amount of boric acid and borate compound attached.

Further, the coating layer is made of Cr, Si, Ni, C
an inorganic compound containing one or more elements of o and Zn;
It is preferable to be composed of both an organic resin or an inorganic compound and an organic resin. Cr, Si, Ni, Co, Z
The inorganic compound containing one or more elements of n is not particularly limited, but includes oxides, hydroxides, phosphates, acetates, carbonates, sulfates, nitrates, and the like of these elements.
Examples include nitro compounds and silane compounds. For example, chromium oxide generally used for coating type chromate,
Cobalt hydroxide, cobalt phosphate, cobalt acetate, nickel hydroxide, nickel phosphate, nickel acetate, etc., which are used as conventional anti-blackening agents, such as chromium hydroxide and silicate compounds (for example, colloidal silica) are applied. it can.

Examples of the organic resin include acrylic, polyurethane, polyester and epoxy solvent-based and water-based resins. Examples of the water-soluble resin include a resin in which various hydrophilic groups are introduced into a molecular chain so that the resin can be dissolved or dispersed in water, or a resin in which an emulsion is formed by emulsion polymerization or treatment with a surfactant after polymerization. The film in the present invention may contain various organic and inorganic compounds, resins and the like as long as the purpose is not impaired. Examples of these include corrosion inhibitors,
Surfactant, inorganic lubricant, resin wax, pigment, dye,
Crosslinking agents and the like can be mentioned. When both an inorganic compound and an organic resin are used, the inorganic compound and the organic resin may be simply mixed or combined by a reaction.

As a method for forming a film, an aqueous solution of boric acid and a borate compound or a coating solution for forming an inorganic or organic film containing boric acid and a borate compound while the plating surface after hot-dip plating is at a temperature of 100 ° C. or higher. Spray coating and evaporation and drying to form a film. After hot-dip plating, the plating surface is cooled down to 100 ° C or less, spray coating, dip coating, roll coating, etc. are performed on the plating surface, and then heated and dried with hot air or the like. A method of forming a film or the like can be applied. Further, an inorganic or organic film containing boric acid and a borate compound may be formed on the plating surface by one-step treatment, or after an aqueous solution containing one or more boric acid and a borate compound is applied and dried. Alternatively, it may be formed by a two-step process of forming an inorganic and organic film on the upper layer.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be specifically described below with reference to embodiments. The plating adhesion amount is 100 to 130 g / m ² , and Zn, Al, Mg, Si, Sn, S
A hot-dip Zn-Al-based alloy-plated steel sheet shown in Table 1 containing b and Pb at the concentrations shown in Table 1 was produced. Next, an inorganic compound film containing boric acid and a borate compound, an organic resin film or an inorganic compound / organic resin composite film was formed on the plating surface by a one-step treatment method or a two-step treatment method. The prepared sample was exposed for 5 hours in a humid atmosphere (temperature: 98 ° C., RH: 95% or more) sprayed with saturated steam, and the blackening state of the film-formed surface was visually determined. The criterion is

Rating 5 No black discoloration 4 Change whitish 3 About gray 2 Black change from black grey 1 Complete black discoloration, and a score of 3 or more was considered acceptable. For comparison, a material which did not form a boric acid or borate compound film was treated in the same manner to determine a blackened state (Comparative Example No. 22).
~ 32). The results are summarized in Table 1. As is clear from Table 1, Example No. 1 of the present invention. The plated steel sheets obtained in Nos. 1 to 21 have excellent blackening resistance over time. On the other hand, in Comparative Example No. in which a film containing boric acid and a borate compound was not formed on the plating surface. Nos. 22 to 32 are inferior in aging blackening resistance.

[0018]

[Table 1]

[0019]

Conventionally, in the field of building materials, the problem of appearance deterioration due to blackening with time when a hot-dip Zn-Al-based plated steel sheet is used for a long time has been serious. Since the hot-dip Zn—Al-based plated steel sheet of the present invention has excellent blackening resistance with time, it can be said that this problem can be solved and has extremely high value in industry.

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Kazumi Nishimura 20-1 Shintomi, Futtsu-shi, Chiba Nippon Steel Corporation Technology Development Division (72) Inventor Akira Tanaka 1 Kimitsu, Kimitsu-shi, Chiba New Japan F-term in Kimitsu Works (reference) 4K027 AA05 AA22 AB05 AB44 AB48 4K044 AA02 AB02 BA10 BA18 BA21 BB03 BC02 CA11 CA53

Claims (4)

[Claims] 1. A hot-dip Zn—Al-based coated steel sheet containing, by weight%, Al: 0.1 to 70% by weight and having a plating layer consisting of a balance of Zn and unavoidable impurities. boric acid, one or molten Zn-Al-based plated steel sheet excellent in blackening time with lapse, characterized in that a coating layer containing 2 or more with 0.01-5 g / m ² of the borate compound. 2. The plating layer according to claim 1, wherein the plating layer further contains one or two of Mg: 0.1 to 30% and Si: 0.1 to 5% by weight. A hot-dip Zn-Al-based plated steel sheet having excellent blackening resistance over time according to the description. 3. The plating layer further contains one or more of Sn: 0.5 to 10%, Sb: 0.05 to 1%, and Pb: 0.05 to 1% by weight. The hot-dip Zn-Al-based steel sheet according to claim 1 or 2, wherein the steel sheet is excellent in blackening resistance over time. 4. The coating layer is made of Cr, Si, Ni, Co, Z
4. The black according to any one of claims 1 to 3, wherein the black is formed of an inorganic compound, an organic resin, or both an inorganic compound and an organic resin containing one or more elements of n. Hot-dip Zn-Al-based plated steel sheet with excellent modification.