JP5160866B2 - Surface-treated molten Zn-Al alloy-plated steel sheet - Google Patents

Description

  The present invention relates to a surface-treated molten Zn-Al alloy-plated steel sheet that is optimal for automobiles, home appliances, and building materials, and in particular, the surface treatment composition and the surface treatment film formed thereby completely contain hexavalent chromium. The present invention relates to an environment-adaptive surface-treated plated steel sheet.

Conventionally, in the fields of automobiles, architecture, civil engineering, home appliances, etc., hot-dip Zn-Al alloy-plated steel sheets have been widely used. As this hot-dip Zn—Al-based alloy-plated steel sheet, a hot-dip Zn-plated steel sheet (hereinafter referred to as GI) whose Al content in the plating layer is 0.2% by mass or less is mainly about 5% by mass. Galvanium steel sheet (hereinafter referred to as GF) and a galvalume steel sheet (hereinafter referred to as GL) having an Al content of about 55% by mass are used. Among these, GF has a lower cost than GL and has higher corrosion resistance than GI, and therefore is in high demand particularly in the field of construction. In the future, as the price of Zn rises, demand for home appliances is expected to increase as a substitute for thick-coated Zn-plated steel sheets.
However, GF generally has the following problems.
Tortoise-patterned spangles are formed in GF, but this spangle has different forms depending on plating conditions (for example, annealing before plating, bath components), cooling conditions after plating (for example, cooling rate), etc. Appearance may be impaired when used naked. In addition, when a colored steel plate is applied, spangles may float on the painted surface and impair the appearance after painting. For this reason, in recent years, the demand for GF having a beautiful plating layer having a metallic luster without spangle has increased.

In addition, when a plating layer containing elements such as Mg and Al that are more easily oxidized than Zn is present, a blackening phenomenon that the plating surface turns black is likely to occur when exposed to a corrosive atmosphere for a long time. There are drawbacks. For this reason, the surface treatment which can reduce black discoloration is needed for the surface of a hot-dip Zn-Al type alloy plating steel plate.
As a method for suppressing black discoloration, there is a method in which the surface of a plated steel sheet is replaced with an aqueous solution containing ions of Fe, Ni, Co, etc., and Fe, Ni, Co, etc. are deposited on the surface of the plating layer (for example, Patent Documents). 1). However, this method necessitates a replacement process, which complicates the manufacturing process. Therefore, a technique for simultaneously improving blackening resistance in a chemical conversion treatment step performed for the purpose of imparting corrosion resistance is required.
Further, post-coating may be applied in the fields of automobiles, architecture, civil engineering, home appliances, etc., and paint adhesion is required. For coating adhesion, the adhesion at the plating film / chemical conversion film interface and the adhesion at the chemical conversion film / coating film interface are important. If the adhesion at each interface is insufficient, the coating film peels off. Arise.

Many chemical conversion treatment techniques for imparting corrosion resistance to hot-dip Zn-Al alloy-plated steel sheets have been proposed. Conventionally, chromate treatment with a treatment liquid containing chromic acid, dichromic acid or a salt thereof as a main component has been performed. However, chromate treatment uses hexavalent chromium, which is a pollution-controlling substance, and because of the environmental considerations and the waste liquid treatment of chromate treatment liquid requires a great deal of labor and expense, chromate-free technology that does not contain chromium. Is being considered. For example, Patent Documents 2 to 4 propose titanium-zirconium-based chromate-free treated metal plates.
JP 59-177381 A JP 2004-2950 A International Publication No. 2003/93533 Pamphlet JP 2003-306777 A

However, these conventional chromate-free treatments cannot satisfy all of the corrosion resistance, blackening resistance and paint adhesion.
Therefore, the object of the present invention is to solve such problems of the prior art, and does not contain hexavalent chromium in the surface treatment composition or film, has excellent blackening resistance, corrosion resistance and paint adhesion, and has a plating appearance. An object of the present invention is to provide a surface-treated hot-dip Zn—Al-based alloy-plated steel sheet having excellent properties.

In order to solve the above-mentioned problems, the present inventors have studied from both the plating composition and surface treatment composition of a hot-dip Zn—Al alloy-plated steel sheet, and as a result, have obtained the following findings.
(I) The plating composition has a metallic luster with no spangles or very fine spangles formed by adding appropriate amounts of Mg and Ni based on a general Al concentration of GF. A hot-dip Zn-Al alloy-plated steel sheet having a beautiful plated appearance and improved blackening resistance is obtained.

(Ii) Regarding surface treatment, first, as a result of examining the addition of various metal salts to the treatment liquid in order to improve blackening resistance, Ni salts and / or Co salts should be added to the treatment liquid. Was found to be effective. However, if Ni salt, Co salt or the like is added to the treatment liquid as it is, the corrosion resistance is lowered. In order to improve the blackening resistance without reducing the corrosion resistance, it is necessary to add a Ni salt, a Co salt or the like to the treatment liquid and form a dense reaction layer on the surface of the plating film by the treatment. However, since a strong Al oxide film is formed on the Zn-Al-based plating surface, if the processing reactivity is low, a dense reaction layer is not formed between the plating surface and the processing film. Corrosion resistance cannot be expressed. As a result of the investigation, the above (i) is obtained by treating with a treatment liquid (surface treatment composition) containing a specific titanium-containing aqueous liquid, a nickel compound or / and a cobalt compound, and a fluorine-containing compound in a predetermined ratio. In addition to optimizing the plating composition, excellent blackening resistance is obtained, and the reactivity is enhanced by the fluorine-containing compound. As a result, a dense reaction layer is formed on the plating surface. It was found that excellent corrosion resistance comparable to that of the chromate film can be obtained while being chromate-free because high barrier properties are imparted. Furthermore, it was found that high paint adhesion is imparted by adding a water-soluble organic resin and / or a water-dispersible organic resin in a specific ratio to the treatment liquid.

The present invention has been made on the basis of such knowledge and has the following gist.
[1] On at least one surface of the steel sheet, Al: 1.0 to 10% by mass, Mg: 0.2 to 1.0% by mass, Ni: 0.005 to 0.1% by mass, and the balance On the surface of a molten Zn-Al alloy-plated steel sheet having a molten Zn-Al-based alloy plating layer composed of Zn and inevitable impurities,
Titanium obtained by mixing at least one titanium compound selected from hydrolyzable titanium compounds, low-condensates of hydrolyzable titanium compounds, titanium hydroxide, and low-condensates of titanium hydroxide with hydrogen peroxide water Containing aqueous liquid (A) in a solid content ratio of 5 to 60 mass%, nickel compound and / or cobalt compound (B) in a solid content ratio of 0.01 to 1 mass%, and fluorine-containing compound (C) in solid form The surface treatment composition (H) containing 1 to 40% by mass of a water-soluble organic resin and / or water-dispersible organic resin (D) in a proportion of solids of 31 to 85% by mass is applied and dried. A surface-treated hot-dip Zn—Al-based alloy-plated steel sheet, comprising a surface-treated film having a film adhesion amount of 0.5 to 3.0 g / m ² formed by the treatment.
[2] In the surface-treated molten Zn-Al alloy-plated steel sheet of [1], the fluorine-containing compound (C) is at least one selected from zircon ammonium fluoride and zircon hydrofluoric acid. A surface-treated hot-dip Zn-Al alloy-plated steel sheet.

[3] In the surface-treated molten Zn-Al alloy-plated steel sheet according to [1] or [2], the surface treatment composition (H) further contains an organic phosphate compound (E) in a solid content ratio of 5 to 5. A surface-treated hot-dip Zn—Al-based alloy-plated steel sheet containing 60% by mass.
[4] In the surface-treated molten Zn-Al alloy-plated steel sheet according to any one of [1] to [3], the surface treatment composition (H) further contains the vanadic acid compound (F) in a solid content ratio. A surface-treated hot-dip Zn—Al-based alloy-plated steel sheet containing 0.1 to 30% by mass.
[5] In the surface-treated molten Zn-Al alloy-plated steel sheet according to any one of [1] to [4], the surface treatment composition (H) further contains a zirconium carbonate compound (G) in a solid content ratio. A surface-treated hot-dip Zn—Al-based alloy-plated steel sheet characterized by containing 0.1 to 20% by mass.
[6] In the surface-treated molten Zn-Al alloy-plated steel sheet according to any one of [1] to [5], the water-soluble organic resin and / or the water-dispersible organic resin (D) is a water-dispersible acrylic resin. A surface-treated hot-dip Zn-Al alloy-plated steel sheet, characterized in that there is.

  The surface-treated molten Zn-Al alloy-plated steel sheet of the present invention comprises a specific titanium-containing aqueous liquid, a nickel compound or / and a cobalt compound, a fluorine-containing compound, a water-soluble organic resin or / and a water-dispersible organic resin. In combination with the optimization of the plating composition, excellent blackening resistance can be obtained and the reaction with the fluorine-containing compound in the surface treatment composition. As a result, a dense reaction layer is formed on the plating surface, and a high barrier property is imparted by the surface treatment film itself, so that excellent corrosion resistance comparable to that of the chromate film can be obtained while being chromate-free. Further, high paint adhesion can be obtained by the water-soluble organic resin and / or the water-dispersible organic resin. Further, by optimizing the plating composition, it has a beautiful plating appearance with a metallic luster in which spangles are not formed or very fine spangles are formed.

  The hot-dip Zn—Al-based alloy-plated steel sheet used as the base of the surface-treated hot-dip Zn—Al-based alloy-plated steel sheet (hereinafter referred to as “surface-treated plated steel sheet” for convenience) of the present invention has Al: 1 on at least one surface of the steel sheet. 0.0-10 mass%, Mg: 0.2-1.0 mass%, Ni: 0.005-0.1 mass%, with the balance being molten Zn-Al alloy plating consisting of Zn and inevitable impurities It has a layer. The reason for limiting the plating composition of the hot-dip Zn—Al-based alloy-plated steel sheet and preferable manufacturing conditions will be described in detail later.

  In the surface-treated plated steel sheet of the present invention, the surface-treated film formed on the surface of the molten Zn-Al alloy plating layer is a hydrolyzable titanium compound, a low condensate of hydrolyzable titanium compound, titanium hydroxide, titanium hydroxide. A titanium-containing aqueous liquid (A) obtained by mixing at least one titanium compound selected from low-condensates with hydrogen peroxide water, a nickel compound or / and a cobalt compound (B), and a fluorine-containing compound (C) and a water-soluble organic resin or / and water-dispersible organic resin (D) are contained in a predetermined ratio, and if necessary, an organic phosphate compound (E), a vanadic acid compound (F), It is formed by applying and drying a surface treatment composition (H) containing at least one kind of zirconium carbonate compound (G) in a predetermined ratio. This surface treatment film does not contain hexavalent chromium (however, excluding chromium as an inevitable impurity).

The titanium-containing aqueous liquid (A) contains at least one titanium compound selected from hydrolyzable titanium compounds, hydrolyzable titanium compound low condensates, titanium hydroxide and titanium hydroxide low condensates. It is an aqueous liquid containing titanium obtained by mixing with hydrogen oxide water.
The hydrolyzable titanium compound is a titanium compound having a hydrolyzable group directly bonded to titanium, and generates titanium hydroxide by reacting with water such as water or water vapor. The hydrolyzable titanium compound may be one in which all of the groups bonded to titanium are hydrolyzable groups, or a part of the groups bonded to titanium may be hydrolyzable groups.
The hydrolyzable group is not particularly limited as long as it generates titanium hydroxide by reacting with moisture as described above. For example, a lower alkoxyl group or a group that forms a salt with titanium (for example, Halogen atoms such as chlorine, hydrogen atoms, sulfate ions, etc.).

The hydrolyzable titanium compound containing a lower alkoxyl group as the hydrolyzable group is particularly represented by the general formula Ti (OR) ₄ (wherein R represents the same or different alkyl groups having 1 to 5 carbon atoms). Tetraalkoxy titanium is preferred. Examples of the alkyl group having 1 to 5 carbon atoms include a methyl group, an ethyl group, an n-propyl group, an iso-propyl group, an n-butyl group, an iso-butyl group, a sec-butyl group, and a tert-butyl group. Can be mentioned.
Typical examples of the hydrolyzable titanium compound having a group capable of forming a salt with titanium as a hydrolyzable group include titanium chloride and titanium sulfate.

Moreover, the low condensate of a hydrolysable titanium compound is a low condensate of the above-mentioned hydrolysable titanium compounds. The low condensate may be one in which all of the groups bonded to titanium are hydrolyzable groups, or a part of the groups bonded to titanium may be hydrolyzable.
For hydrolyzable titanium compounds whose hydrolyzable group forms a salt with titanium (for example, titanium chloride, titanium sulfate, etc.), an aqueous solution of the hydrolyzable titanium compound and an alkaline solution such as ammonia or caustic soda are used. Orthotitanic acid (titanium hydroxide gel) obtained by the reaction can also be used as a low condensate.

As the low condensate of the hydrolyzable titanium compound and the low condensate of titanium hydroxide, a compound having a condensation degree of 2 to 30 can be used, and a compound having a condensation degree of 2 to 10 is particularly preferable. When the condensation degree exceeds 30, a white precipitate is formed when mixed with hydrogen peroxide, and a stable titanium-containing aqueous liquid cannot be obtained.
The hydrolyzable titanium compounds, low condensates of hydrolysable titanium compounds, titanium hydroxide, and low condensates of titanium hydroxide can be used alone or in combination of two or more thereof. Tetraalkoxy titanium which is a hydrolyzable titanium compound represented by the formula is particularly preferable.

As the titanium-containing aqueous liquid (A), any conventionally known liquid can be used without particular limitation as long as it is an aqueous liquid containing titanium obtained by mixing the above-described titanium compound and hydrogen peroxide solution. Specifically, the following can be mentioned.
(I) A titanyl ion hydrogen peroxide complex or an aqueous solution of titanic acid (peroxotitanium hydrate) obtained by adding hydrogen peroxide to a hydrous titanium oxide gel or sol (JP-A 63-35419, JP-A 1-2224220 gazette).

(Ii) A liquid for forming a titania film obtained by synthesizing a titanium hydroxide gel produced from an aqueous solution of titanium chloride or titanium sulfate and a basic solution with a hydrogen peroxide solution (Japanese Patent Laid-Open No. 9-71418, (See Kaihei 10-67516).
When obtaining this titania film-forming liquid, titanium hydroxide gel called orthotitanic acid is precipitated by reacting an aqueous solution of titanium chloride or titanium sulfate having a salt-forming group with titanium and an alkaline solution such as ammonia or caustic soda. Let Next, the titanium hydroxide gel is separated by decantation with water, washed thoroughly with water, further added with hydrogen peroxide water, and excess hydrogen peroxide is decomposed and removed, whereby a yellow transparent viscous liquid can be obtained.

The precipitated orthotitanic acid is in a gel state polymerized by polymerization of OH or hydrogen bonds, and cannot be used as an aqueous liquid containing titanium as it is. When hydrogen peroxide solution is added to this gel, a part of OH is in a peroxidized state, dissolved as a peroxotitanate ion or in a kind of sol state in which the polymer chain is divided into low molecules, and excess hydrogen peroxide Is decomposed into water and oxygen, and can be used as an aqueous liquid containing titanium for forming an inorganic film.
Since this sol contains only oxygen and hydrogen atoms in addition to titanium atoms, when it is changed to titanium oxide by drying or firing, only water and oxygen are generated, so carbon components necessary for thermal decomposition such as sol-gel method and sulfate Further, it is not necessary to remove the halogen component, and a titanium oxide film having a relatively high density can be formed even at a low temperature.

(Iii) Hydrogen peroxide is added to an aqueous solution of an inorganic titanium compound such as titanium chloride or titanium sulfate to form peroxotitanium hydrate, and then the solution obtained by adding a basic substance is allowed to stand or be heated. A titanium oxide forming solution obtained by forming a precipitate of a titanium hydrate polymer, and then removing hydrogen and other dissolved components derived from at least a titanium-containing raw material solution (Japanese Patent Application Laid-Open 2000-247638, JP-A-2000-247639).

The titanium-containing aqueous liquid (A) using a hydrolyzable titanium compound and / or a low condensate thereof as a titanium compound (hereinafter referred to as “hydrolyzable titanium compound a” for convenience of explanation) contains hydrolyzable titanium compound a. It can be obtained by reacting with hydrogen oxide water at a reaction temperature of 1 to 70 ° C. for about 10 minutes to 20 hours.
In the titanium-containing aqueous liquid (A) using the hydrolyzable titanium compound a, the hydrolyzable titanium compound a is hydrolyzed with water by reacting the hydrolyzable titanium compound a with hydrogen peroxide. A product obtained by producing a hydroxyl group-containing titanium compound and then coordinating hydrogen peroxide to this hydroxyl group-containing titanium compound, and this hydrolysis reaction and coordination by hydrogen peroxide occur simultaneously. It produces a chelate solution that is extremely stable at room temperature and can withstand long-term storage. The titanium hydroxide gel used in the conventional manufacturing method is partially three-dimensionalized by Ti—O—Ti bonds, and the titanium-containing aqueous liquid (A) obtained by reacting this gel with hydrogen peroxide is composition and stable. Sex is essentially different.

  Further, when the titanium-containing aqueous liquid (A) using the hydrolyzable titanium compound a is heated or autoclaved at 80 ° C. or higher, a titanium oxide dispersion containing ultrafine particles of crystallized titanium oxide is obtained. When the heat treatment or autoclave treatment is less than 80 ° C., crystallization of titanium oxide does not proceed sufficiently. The titanium oxide dispersion thus produced has an average particle diameter of titanium oxide ultrafine particles of 10 nm or less, preferably about 1 to 6 nm. When the average particle diameter of the titanium oxide ultrafine particles is larger than 10 nm, the film forming property is deteriorated (when the film is dried after coating to form a film, cracking occurs at a film thickness of 1 μm or more), which is not preferable. The appearance of this titanium oxide dispersion is translucent. Such a titanium oxide dispersion can also be used as the titanium-containing aqueous liquid (A).

The surface treatment composition (H) containing the titanium-containing aqueous liquid (A) using the hydrolyzable titanium compound a is applied to the surface of the plated steel plate and dried (for example, heat-dried at a low temperature), thereby adhering to itself. A dense titanium oxide-containing film (surface treatment film) having excellent properties can be formed.
The heating temperature after applying the surface treatment composition (H) is, for example, 200 ° C. or less, particularly preferably 150 ° C. or less. By heating and drying at such a temperature, an amorphous material containing some hydroxyl groups (amorphous) A titanium oxide-containing film can be formed.
In addition, when the titanium oxide dispersion obtained through the heat treatment or autoclave treatment as described above at 80 ° C. or more is used as the titanium-containing aqueous liquid (A), the crystal can be obtained by simply applying the surface treatment composition (H). It is useful as a coating material for materials that cannot be heat-treated.

Further, as the titanium-containing aqueous liquid (A), a titanium-containing aqueous liquid (A1) obtained by reacting the hydrolyzable titanium compound a with hydrogen peroxide in the presence of a titanium oxide sol can also be used. .
The titanium oxide sol is a sol in which amorphous titania fine particles and / or anatase type titania fine particles are dispersed in water (for example, an aqueous organic solvent such as an alcohol or alcohol ether may be added if necessary). As this titanium oxide sol, conventionally known ones can be used. For example, (i) a titanium oxide aggregate obtained by hydrolyzing a titanium-containing solution such as titanium sulfate or titanyl sulfate, (ii) titanium alkoxide, etc. Titanium oxide aggregates obtained by hydrolyzing organic titanium compounds of the above, (iii) Titanium oxide aggregates obtained by hydrolyzing or neutralizing titanium halide solutions such as titanium tetrachloride, etc. An amorphous titania sol dispersed in water, or a sol in which the titanium oxide aggregates are calcined to form anatase-type titanium fine particles and this is dispersed in water can be used.

In the firing of the amorphous titania, the amorphous titania can be converted into anatase titania by firing at a temperature at least higher than the crystallization temperature of anatase, for example, 400 ° C. to 500 ° C. or more. Examples of the aqueous sol of titanium oxide include, for example, TKS-201 (trade name, manufactured by TEIKA CORPORATION, anatase crystal form, average particle diameter 6 nm), TA-15 (trade name, manufactured by NISSAN CHEMICAL CO., LTD., Anatase crystal form). STS-11 (trade name, manufactured by Ishihara Sangyo Co., Ltd., anatase type crystal form) and the like.
In the titanium-containing aqueous liquid (A1), the mass ratio x / y between the titanium oxide sol x and the titanium hydrogen peroxide reactant y (reaction product of the hydrolyzable titanium compound a and hydrogen peroxide solution) is 1 / A range of 99 to 99/1, preferably about 10/90 to 90/10 is suitable. If the mass ratio x / y is less than 1/99, the effect of adding the titanium oxide sol cannot be sufficiently obtained in terms of stability, photoreactivity, etc. On the other hand, if it exceeds 99/1, the film forming property is inferior. Absent.

The titanium-containing aqueous liquid (A1) can be obtained by reacting the hydrolyzable titanium compound a with hydrogen peroxide at a reaction temperature of 1 to 70 ° C. for about 10 minutes to 20 hours in the presence of a titanium oxide sol.
The production form and characteristics of the titanium-containing aqueous liquid (A1) are the same as those of the titanium-containing aqueous liquid (A) using the hydrolyzable titanium compound a described above, but in particular, by using a titanium oxide sol. , It is possible to suppress a partial condensation reaction during the synthesis to increase the viscosity. The reason is considered to be that the condensation reaction product is adsorbed on the surface of the titanium oxide sol, and polymerization in a solution state is suppressed.

  Further, when the titanium-containing aqueous liquid (A1) is heated or autoclaved at 80 ° C. or higher, a titanium oxide dispersion containing ultrafine particles of crystallized titanium oxide is obtained. The titanium-containing aqueous liquid (A) using the hydrolyzable titanium compound a described above also describes the temperature conditions for obtaining this titanium oxide dispersion, the particle diameter of the crystallized titanium oxide ultrafine particles, the appearance of the dispersion, etc. It is the same. Such a titanium oxide dispersion can also be used as the titanium-containing aqueous liquid (A1).

Similar to the titanium-containing aqueous liquid (A) using the hydrolyzable titanium compound a described above, the surface treatment composition (H) containing the titanium-containing aqueous liquid (A1) is applied to the surface of the plated steel sheet and dried (for example, By heating and drying at a low temperature, it is possible to form a dense titanium oxide-containing film (surface-treated film) having excellent adhesion by itself.
The heating temperature after applying the surface treatment composition (H) is, for example, 200 ° C. or less, particularly preferably 150 ° C. or less. By heating and drying at such a temperature, anatase-type titanium oxide containing some hydroxyl groups is contained. A film can be formed.
As described above, of the titanium-containing aqueous liquid (A), the titanium-containing aqueous liquid (A) and the titanium-containing aqueous liquid (A1) using the hydrolyzable titanium compound a are excellent in storage stability, corrosion resistance, and the like. It is particularly preferable to use these in the present invention.

  The compounding ratio of hydrogen peroxide water to at least one titanium compound selected from hydrolyzable titanium compounds, hydrolyzable titanium compound low condensates, titanium hydroxide, titanium hydroxide low condensates is titanium compounds 0.1 to 100 parts by mass, preferably 1 to 20 parts by mass in terms of hydrogen peroxide, with respect to 10 parts by mass. If the blending ratio of the hydrogen peroxide solution is less than 0.1 parts by mass in terms of hydrogen peroxide, chelate formation is not sufficient and white turbid precipitation occurs. On the other hand, if it exceeds 100 parts by mass, unreacted hydrogen peroxide tends to remain, and dangerous active oxygen is released during storage, which is not preferable.

The hydrogen peroxide concentration of the hydrogen peroxide solution is not particularly limited, but it is preferably about 3 to 30% by mass from the viewpoint of ease of handling and the solid content of the product liquid related to coating workability.
Other sols and pigments can be added and dispersed in the titanium-containing aqueous liquid (A) as necessary. Examples of the additive include commercially available titanium oxide sol, titanium oxide powder, mica, talc, silica, barita, clay, and the like, and one or more of these can be added.
The addition amount of the titanium-containing aqueous liquid (A) in the surface treatment composition (H) is 5 to 60% by mass, preferably 8 to 40% by mass, in terms of the solid content, from the viewpoint of the stability of the treatment liquid. . The treatment liquid stability is inferior in both cases where the addition amount (solid content ratio) of the titanium-containing aqueous liquid (A) is less than 5 mass% or more than 60 mass%.

The nickel compound and / or cobalt compound (B) is blended for improving blackening resistance. Examples of the nickel compound include nickel acetate, nickel nitrate, nickel sulfate, and the cobalt compound. , Cobalt acetate, cobalt nitrate, cobalt sulfate and the like, and one or more of these can be used. Among these, nickel acetate and cobalt acetate are preferable from the viewpoint of both blackening resistance and corrosion resistance.
The addition amount of the nickel compound and / or cobalt compound (B) in the surface treatment composition (H) is 0.01 to 1% by mass in terms of solid content from the viewpoint of achieving both blackening resistance and corrosion resistance. Preferably it is 0.05-0.7 mass%. If the addition amount of the nickel compound and / or cobalt compound (B) is less than 0.01% by mass, the effect of improving blackening resistance cannot be sufficiently obtained, while if it exceeds 1% by mass, the corrosion resistance is lowered.

The fluorine-containing compound (C) is blended in order to enhance the reactivity between the treatment liquid (surface treatment composition) and the plating surface and form a dense reaction layer from the viewpoint of improving the corrosion resistance. Examples of the fluorine-containing compound (C) include zircon ammonium fluoride, zircon potassium fluoride, zircon hydrofluoric acid, titanium ammonium fluoride, hydrofluoric acid, and ammonium hydrofluoride. Species or two or more can be used. Among these, from the viewpoint of achieving both corrosion resistance and blackening resistance, it is preferable to use at least one selected from zircon ammonium fluoride and zircon hydrofluoric acid.
The addition amount of the fluorine-containing compound (C) in the surface treatment composition (H) is 1 to 40% by mass, preferably 2 to 30% by mass in terms of solid content. When the addition amount of the fluorine-containing compound (C) is less than 1% by mass, the reactivity between the treatment liquid and the plating surface is poor, so that sufficient corrosion resistance cannot be obtained and blackening resistance is not improved. On the other hand, if it exceeds 40% by mass, the etching property of the treatment liquid becomes high. As a result, the plating surface is excessively etched, and the corrosion resistance is deteriorated.

  The water-soluble organic resin and / or water-dispersible organic resin (D) is an organic resin that can be dissolved or dispersed in water, and a conventionally known method for water-solubilizing or dispersing the organic resin in water. The method can be applied. Specifically, for example, the organic resin contains a functional group (for example, a hydroxyl group, a polyoxyalkylene group, a carboxyl group, an amino (imino) group, a sulfide group, a phosphine group, etc.) that can be water-soluble or water-dispersed independently. If necessary, some or all of these functional groups can be converted to acidic compounds (such as carboxyl group-containing resins) with amine compounds such as ethanolamine and triethylamine; aqueous ammonia; lithium hydroxide, hydroxylated Neutralized with alkali metal hydroxides such as sodium and potassium hydroxide, and basic resins (such as amino group-containing resins), neutralized with fatty acids such as acetic acid and lactic acid; mineral acids such as phosphoric acid For example, a method for dissolving or dispersing the prepared resin in water, a method for dispersing the organic resin in water using an emulsifier, and the like.

Examples of organic resins include epoxy resins, phenol resins, acrylic resins, urethane resins, olefin-carboxylic acid resins, nylon resins, resins having a polyoxyalkylene chain, polyvinyl alcohol, polyglycerin, carboxymethyl cellulose. , Hydroxymethyl cellulose, hydroxyethyl cellulose and the like. The said organic resin can use 1 type (s) or 2 or more types.
Among these, the use of at least one organic resin selected from water-soluble or water-dispersible acrylic resins, urethane resins, and epoxy resins from the viewpoint of storage stability of the surface treatment composition. preferable. In particular, the use of a water-dispersible acrylic resin in a water-soluble organic resin and / or water-dispersible organic resin (D) in a solid content ratio of 50% by mass or more, preferably 70% by mass or more is a surface treatment. It is preferable from the viewpoint of the balance between the storage stability of the composition and the performance of the coating film.

The water-dispersible acrylic resin is prepared by a conventionally known method, for example, an emulsion polymerization method, a suspension polymerization method, a polymer having a hydrophilic group by solution polymerization, and neutralized and dispersed in water as necessary. The surface treatment composition (H) can be obtained by using an acrylic emulsion obtained by an emulsion polymerization method using only a nonionic emulsifier without using an ionic emulsifier as an emulsifier. It is preferable from the viewpoint of long-term storage stability. The emulsion polymerization method may be single-stage polymerization or multi-stage polymerization, but preferably, the multi-stage polymerization method is used to form hydrophilic groups such as carboxyl groups, amino groups, hydroxyl groups, polyoxyalkylene groups on the outermost surface side of the aqueous dispersion particles. Long-term storage stability can be further improved by orienting many sex groups.
Specifically, for example, in the multistage polymerization method, in the initial polymerization, the ratio of unsaturated monomers having a hydrophilic group such as a carboxyl group, an amino group, a hydroxyl group, or a polyoxyalkylene group is reduced, and the final polymerization is performed. Can be obtained by increasing the ratio of the unsaturated monomer having a hydrophilic group.
In addition, the glass transition temperature of the resin in the water-dispersible acrylic resin is 25 to 80 ° C., preferably 28 to 75 ° C., and the corrosion resistance and blackening resistance of the film formed by the surface treatment composition (H). It is suitable from the point of.

Here, the glass transition temperature (° C.) of the copolymer can be calculated by the following equation.
1 / Tg (° K) = (W1 / T1) + (W2 / T2) +
Tg (° C.) = Tg (° K) -273
In each formula, W1, W2,... Represent the mass% of each monomer used for copolymerization, and T1, T2,... Represent the Tg (° K) of the monomer homopolymer, respectively. T1, T2,... Are values according to Polymer Hand Book (Second Edition, edited by J. Brandup / EHImmergut) III-139-179. The glass transition temperature (° C.) when the Tg of the homopolymer of the monomer is not clear is a static glass transition temperature. For example, a differential scanning calorimeter “DSC-220U” (manufactured by Seiko Instruments Inc.) is used. Take the sample in a measuring cup, remove the solvent completely by vacuum suction, measure the change in calorie in the range of -20 ° C to + 200 ° C at a rate of temperature rise of 3 ° C / min. The change point is the static glass transition temperature.

Examples of the carboxyl group-containing unsaturated monomer include acrylic acid, methacrylic acid, maleic acid, maleic anhydride, crotonic acid, and itaconic acid.
Examples of the nitrogen-containing unsaturated monomer such as the amino group-containing unsaturated monomer include N, N-dimethylaminoethyl (meth) acrylate, N, N-diethylaminoethyl (meth) acrylate, Nt- Nitrogen-containing alkyl (meth) acrylates such as butylaminoethyl (meth) acrylate; acrylamide, methacrylamide, N-methyl (meth) acrylamide, N-ethyl (meth) acrylamide, N-methylol (meth) acrylamide, N-methoxymethyl Polymerization of (meth) acrylamide, N-butoxymethyl (meth) acrylamide, N, N-dimethyl (meth) acrylamide, N, N-dimethylaminopropyl (meth) acrylamide, N, N-dimethylaminoethyl (meth) acrylamide, etc. Amides; 2-vinylpyridine, - vinyl-2-pyrrolidone, aromatic nitrogen-containing monomers such as 4-vinylpyridine; and allylamine and the like.

Examples of the unsaturated monomer containing a hydroxyl group or a polyoxyalkylene group include 2-hydroxyethyl (meth) acrylate, hydroxypropyl (meth) acrylate, 2,3-dihydroxybutyl (meth) acrylate, and 4-hydroxybutyl (meth). Monoesterified product of polyhydric alcohol such as acrylate, polyethylene glycol mono (meth) acrylate, polypropylene glycol mono (meth) acrylate and acrylic acid or methacrylic acid; monoesterified product of polyhydric alcohol and acrylic acid or methacrylic acid Examples thereof include compounds obtained by ring-opening polymerization of ε-caprolactone.
Examples of the unsaturated monomer copolymerizable with the unsaturated monomer having a hydrophilic group include methyl (meth) acrylate, ethyl (meth) acrylate, n-propyl (meth) acrylate, and isopropyl (meth) acrylate. , N-butyl (meth) acrylate, isobutyl (meth) acrylate, tert-butyl (meth) acrylate, 2-ethylhexyl acrylate, n-octyl (meth) acrylate, lauryl (meth) acrylate, tridecyl (meth) acrylate, octadecyl ( Examples thereof include alkyl (meth) acrylates having 1 to 24 carbon atoms such as (meth) acrylate and isostearyl (meth) acrylate; vinyl acetate and the like.
The unsaturated monomer mentioned above can use 1 type (s) or 2 or more types. In the description of the present application, “(meth) acrylate” means “acrylate or methacrylate”.

  Examples of the urethane-based resin include a chain extender which is a low molecular weight compound having two or more active hydrogens such as a diol and a diamine as needed, and a polyurethane composed of a polyol and a diisocyanate such as polyester polyol and polyether polyol. Those which are chain-extended in the presence and stably dispersed or dissolved in water can be suitably used, and conventionally known ones can be widely used (for example, Japanese Patent Publication No. 42-24192, Japanese Patent Publication No. 42-24194, (See JP-B-42-5118, JP-B-49-986, JP-B-49-33104, JP-B-50-15027, JP-B-53-29175).

As a method for stably dispersing or dissolving the polyurethane resin in water, for example, the following method can be used.
(1) A method of imparting hydrophilicity by introducing an ionic group such as a hydroxyl group, an amino group or a carboxyl group into the side chain or terminal of a polyurethane polymer, and dispersing or dissolving in water by self-emulsification.
(2) A polyurethane polymer whose reaction has been completed or a polyurethane polymer whose terminal isocyanate group has been blocked with a blocking agent such as oxime, alcohol, phenol, mercaptan, amine, sodium bisulfite, etc. is forcibly submerged in water using an emulsifier and mechanical shearing force. How to disperse. Further, a method in which a urethane polymer having a terminal isocyanate group is mixed with water, an emulsifier and a chain extender, and dispersion and high molecular weight are simultaneously performed using mechanical shearing force.
(3) A method in which a water-soluble polyol such as polyethylene glycol is used as a polyol as a main polyurethane material, and is dispersed or dissolved in water as a water-soluble polyurethane.
In addition, what was obtained by the different method among the dispersion | distribution or melt | dissolution methods mentioned above can also mix and use a polyurethane-type resin.

Examples of the diisocyanate that can be used for the synthesis of the polyurethane resin include aromatic, alicyclic or aliphatic diisocyanates. Specifically, hexamethylene diisocyanate, tetramethylene diisocyanate, 3,3′-dimethoxy-4, 4'-biphenylene diisocyanate, p-xylylene diisocyanate, m-xylylene diisocyanate, 1,3- (diisocyanatomethyl) cyclohexanone, 1,4- (diisocyanatomethyl) cyclohexanone, 4,4'-diisocyanato Cyclohexanone, 4,4'-methylenebis (cyclohexyl isocyanate), isophorone diisocyanate, 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, p-phenylene diisocyanate, diphenylmethane di Isocyanate, m- phenylene diisocyanate, 2,4-naphthalene diisocyanate, 3,3'-dimethyl-4,4'-biphenylene diisocyanate, 4,4'-biphenylene diisocyanate and the like. Among these, 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, hexamethylene diisocyanate, and isophorone diisocyanate are particularly preferable.
Examples of commercially available polyurethane resins include Hydran HW-330, HW-340, HW-350 (both trade names, manufactured by Dainippon Ink and Chemicals), Superflex 100, 150, E-2500, F-3438D (all are trade names, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.).

  As the epoxy resin, a cationic epoxy resin obtained by adding an amine to an epoxy resin; a modified epoxy resin such as an acrylic modification or a urethane modification can be preferably used. Examples of cationic epoxy resins include adducts of epoxy compounds with primary mono- or polyamines, secondary mono- or polyamines, and primary and secondary mixed polyamines (see, for example, US Pat. No. 3,984,299). An adduct of an epoxy compound and a secondary mono- or polyamine having a ketiminated primary amino group (see, for example, US Pat. No. 4,017,438); an epoxy compound having a ketiminated primary amino group Examples include etherification reaction products with hydroxyl compounds (see, for example, JP-A-59-43013).

  As the epoxy resin, those having a number average molecular weight of 400 to 4000, particularly 800 to 2000, and an epoxy equivalent of 190 to 2000, particularly 400 to 1000 are preferable. Such an epoxy resin can be obtained, for example, by a reaction between a polyphenol compound and epirulhydrin, and examples of the polyphenol compound include bis (4-hydroxyphenyl) -2,2-propane, 4,4. -Dihydroxybenzophenone, bis (4-hydroxyphenyl) -1,1-ethane, bis (4-hydroxyphenyl) -1,1-isobutane, bis (4-hydroxy-tert-butylphenyl) -2,2-propane, Bis (2-hydroxynaphthyl) methane, 1,5-dihydroxynaphthalene, bis (2,4-dihydroxyphenyl) methane, tetra (4-hydroxyphenyl) -1,1,2,2-ethane, 4,4-dihydroxy Diphenylsulfone, phenol novolak, cresol novolak, etc. That.

  The addition amount of the water-soluble organic resin and / or water-dispersible organic resin (D) in the surface treatment composition (H) is 31 to 85% by mass in terms of solid content, preferably from the viewpoint of paint adhesion. 32 to 80% by mass. If the addition amount of the water-soluble organic resin and / or water-dispersible organic resin (D) is less than 31% by mass, the chemical film cannot follow deformation such as processing, and the film peels off at the plating film / chemical film interface. The paint adhesion is poor. On the other hand, when it exceeds 85 mass%, the reactivity with the plating by an inorganic component becomes insufficient, and sufficient corrosion resistance and blackening resistance cannot be imparted.

The surface treatment composition (H) used in the present invention comprises a titanium-containing aqueous liquid (A), a nickel compound or / and a cobalt compound (B), a fluorine-containing compound (C) and a water-soluble organic resin or / And water-dispersible organic resin (D) are essential, and if necessary, one of organic phosphoric acid compound (E), vanadic acid compound (F), and zirconium carbonate compound (G). The above can be contained.
Examples of the organic phosphoric acid compound (E) include 1-hydroxymethane-1,1-diphosphonic acid, 1-hydroxyethane-1,1-diphosphonic acid, 1-hydroxypropane-1,1-diphosphonic acid and the like. Suitable examples include hydroxyl group-containing organic phosphorous acid; carboxyl group-containing organic phosphorous acid such as 2-hydroxyphosphonoacetic acid, 2-phosphonobutane-1,2,4-tricarboxylic acid, and salts thereof. These 1 type (s) or 2 or more types can be used.

The organic phosphoric acid compound (E) has an effect of improving the storage stability of the titanium-containing aqueous liquid (A). Among them, 1-hydroxyethane-1,1-diphosphonic acid has a particularly large effect. It is particularly preferred to use this.
The addition amount of the organic phosphoric acid compound (E) in the surface treatment composition (H) is 5 to 60% by mass in terms of the solid content, and the storage stability and water resistance of the titanium-containing aqueous liquid (A). It is preferable from the viewpoint of adhesion. When the amount of the organic phosphoric acid compound (E) added is less than 5% by mass, the effect of improving the storage stability of the titanium-containing aqueous liquid (A) is small. On the other hand, when it exceeds 60 mass%, phosphoric acid exists excessively, resulting in deterioration of water resistance. The more preferable addition amount of the organic phosphoric acid compound (E) is 8 to 50% by mass.

Examples of the vanadic acid compound (F) include lithium metavanadate, potassium metavanadate, sodium metavanadate, ammonium metavanadate, and anhydrous vanadate, and one or more of these can be used. Of these, ammonium metavanadate is preferable from the viewpoint of water adhesion resistance.
The addition amount of the vanadic acid compound (F) in the surface treatment composition (H) is preferably 0.1 to 30% by mass in terms of solid content from the viewpoint of corrosion resistance after alkaline degreasing. If the amount of vanadate compound (F) added is less than 0.1% by mass, the effect of improving the corrosion resistance after alkaline degreasing is insufficient. On the other hand, when it exceeds 30 mass%, since V exists excessively, sufficient corrosion resistance cannot be expressed. A more preferable addition amount of the vanadic acid compound (F) is 0.5 to 20% by mass.

Examples of the zirconium carbonate compound (G) include salts of zirconium carbonate such as sodium, potassium, lithium, and ammonium, and one or more of these can be used. Of these, ammonium zirconium carbonate is preferable from the viewpoint of water-resistant adhesion.
The addition amount of the zirconium carbonate compound (G) in the surface treatment composition (H) is preferably 0.1 to 20% by mass in terms of solid content from the viewpoint of corrosion resistance and the like. When the added amount of the zirconium carbonate compound (G) is less than 0.1% by mass, the effect of improving the corrosion resistance is insufficient. On the other hand, when it exceeds 20% by mass, Zr is excessively present, so that sufficient corrosion resistance cannot be exhibited. A more preferable addition amount of the zirconium carbonate compound (G) is 0.2 to 15% by mass.

In the surface treatment composition (H), if necessary, for example, etching agents such as silane coupling agents, resin fine particles, inorganic phosphate compounds, heavy metal compounds other than the components specified by the present invention, thickeners, A surfactant, a lubricity-imparting agent (polyethylene wax, fluorine-based wax, carnauba wax, etc.), a rust inhibitor, a color pigment, an extender pigment, a rust preventive pigment, and a dye can be contained.
Further, the surface treatment composition (H) can be used as diluted with a hydrophilic solvent such as methanol, ethanol, isopropyl alcohol, an ethylene glycol solvent, or a propylene glycol solvent, if necessary.
The adhesion amount of the surface treatment film formed by the surface treatment composition (H) is 0.5 to 3.0 g / m ² , preferably 0.5 to 2.0 g / m ² . When the coating amount is less than 0.5 g / m ² , the corrosion resistance is inferior. On the other hand, when it exceeds 3.0 g / m ² , the coating adheres to the roll or mold during roll forming or pressing, and the appearance after pressing is inferior. .

  Next, the hot-dip Zn—Al-based alloy-plated steel sheet that serves as the base of the surface-treated plated steel sheet of the present invention will be described. Mg added to the molten Zn-A1 alloy-plated layer of this hot-dip Zn-Al alloy-plated steel sheet mainly obtains a beautiful plating appearance with a metallic luster with no spangles or very fine spangles formed. Similarly, Ni added to the plating layer is aimed mainly at improving blackening resistance, but an appropriate amount of Mg is required to improve blackening resistance by adding Ni. By coexisting, it is necessary that Ni is concentrated in the outermost layer portion of the plating layer. Moreover, Ni concentration in a plating layer outermost layer part can be more appropriately produced by controlling the cooling rate after plating to an appropriate range.

Hereinafter, the reason for limiting the component composition of the molten Zn—Al-based alloy plating layer (hereinafter simply referred to as “plating layer”) will be described.
When the Al content in the plating layer is less than 1.0% by mass, an Fe—Zn alloy layer is formed thick at the plating layer-substrate interface, and the workability deteriorates. On the other hand, if the Al content exceeds 10% by mass, a eutectic structure of Zn and Al cannot be obtained, and the Al-rich layer increases and the sacrificial anticorrosive action decreases, so that the corrosion resistance of the end face portion is inferior. Moreover, when it is going to obtain the plating layer in which Al exceeds 10 mass%, the top dross which has Al as a main component will generate | occur | produce easily in a plating bath, and the problem that a plating external appearance is impaired also arises. For these reasons, the Al content in the plating layer is 1.0 to 10% by mass, preferably 3 to 7% by mass.

One of the aims of limiting the plating composition in the present invention is to eliminate spangles (zero spangled) peculiar to hot-dip Zn-Al alloy plating with a GF composition, or to form very fine spangles, and no plating. In order to obtain a beautiful plating appearance with metallic luster, the present inventors conducted the following experiment in order to investigate the relationship between the plating composition and the plating appearance.
Mg and Ni were added individually to a hot-dip Zn-Al alloy plating bath containing Al (4 to 5% by mass) of GF composition, and a steel plate was hot-dip Zn-Al alloy plated in these plating baths. The plated appearance (particularly spangle size, degree of dross adhesion, color tone, gloss) of the plated steel sheet was visually observed. As a result, the plating layer to which Ni was added showed no change in the plating appearance within the experimental range of the present inventors, and showed a plating appearance almost equivalent to that of normal GF, but the plating layer to which Mg was added was The spangle size, color tone, gloss, etc. changed depending on the added amount.

Al: 4 to 5 mass%, Ni: 0.03 mass% containing molten Zn-Al alloy plating bath (total content of Ce and La as misch metal: 0.008 mass%) 3% by mass was added, and a steel sheet was plated using this molten Zn-Al alloy plating bath, and the relationship between the Mg content in the plating layer and the plating appearance (spangle size, degree of dross adhesion, color tone) was examined. . The result is shown in FIG. According to this, when the Mg content is 0.1% by mass or more, the spangle starts to become finer, and when it is 0.2% by mass or more, the spangle almost disappears and the color tone shows a white taste with a metallic luster. Further, when the Mg content is less than 0.2% by mass, the blackening resistance is also lowered. As will be described later, if Mg coexisting with Ni in the plating layer is less than 0.2% by mass, the concentration of Ni in the outermost layer portion of the plating layer is eliminated, resulting in a decrease in blackening resistance. It is. On the other hand, when the Mg content exceeds 1.0% by mass, the color tone changes from grayish white to gray and the dross adhesion increases. Moreover, when Mg content exceeds 1.0 mass%, it will become easy to produce a crack in a plating layer and the problem that workability falls also arises. Moreover, when there is too much Mg, blackening-proof property is also inferior.
Therefore, the Mg content in the plating layer has a lower limit of 0.2% by mass in order to obtain a beautiful plating appearance and excellent blackening resistance, preventing dross adhesion and color tone deterioration, and further preventing deterioration of workability. Therefore, the upper limit is set to 1.0% by mass.

  In the plating composition, it has been described that Mg mainly contributes to the improvement of the plating appearance and Ni mainly contributes to the improvement of the blackening resistance. As a result of the examination by the present inventors, Ni improves the blackening resistance. It was found that coexistence with Mg is indispensable for exerting the effect. That is, it has been found that Mg has an effect of forming a beautiful plating appearance and indirectly promotes the effect of improving the blackening resistance by Ni by coexisting with Ni. This was clarified by analyzing the plating layer in the depth direction by glow discharge luminescent surface analysis (GDS) for the plated steel sheets having different blackening resistance. An example of the analysis result is shown below.

Regarding the hot-dip Zn-Al alloy-plated steel sheet having the following three types of GF compositions (1) to (3) (all are cooled to 250 ° C. after plating at 5 ° C./second), the depth from the plating layer surface The concentrated form of each element of Al, Zn, Mg, and Ni was investigated in the vertical direction.
(1) Plated steel sheet containing only Mg in the plating layer and poor in blackening resistance (2) Plated steel sheet containing only Ni in the plating layer and inferior blackening resistance (3 ) Plated steel sheet containing Mg and Ni in the plating layer and excellent in blackening resistance Since blackening is considered to be a problem of the plating surface, the samples (plated steel sheets) of (1) to (3) above From the outermost surface, a depth of about 200 nm (2000 mm) was intensively analyzed. The result is shown in FIG. In the analysis of the plating component elements, a GDS analyzer was used to discharge for 30 seconds in the depth direction at an anode diameter of 4 mmφ and a current of 20 mA for analysis.

According to FIG. 2, the concentration peak of each plating component element is observed in the vicinity of the plating surface in any of the above samples (1) to (3), but the concentration form of each element is slightly different in each sample. I understand that.
First, in the plating layer of sample (1) containing only Mg, which has poor blackening resistance, an Mg concentration peak is observed at almost the same position as Zn in the outermost layer (outermost surface), and the concentration of Al is increased. The enrichment peak is on the inner side (substrate side) of the Zn and Mg concentration peaks.
Moreover, the concentration peak of the plating layer of the sample (2) containing only Ni having poor blackening resistance is Al, followed by Zn at the outermost layer portion, and the Ni concentration peak is the Al concentration peak. On the inside (base side).

On the other hand, the plating layer of the sample (3) containing Mg and Ni, which has excellent blackening resistance, has a Ni concentration peak in the same outermost layer as Zn, and each concentration peak of Mg and Al is Ni. It is inside the concentration peak (base side).
Although not shown in FIG. 2, the same amount of Mg and Ni as in the sample (3) coexist in the plating layer, and the plating obtained at a cooling rate of up to 250 ° C. after plating was 30 ° C./second. A steel plate that did not show a significant effect on blackening resistance was analyzed in the same manner, but it was found that the concentration of Ni in the outermost layer portion of the plating layer was less than that of the sample (3).
From the above analysis results, Ni is concentrated in the outermost layer portion of the plating layer excellent in blackening resistance, and it is necessary for the Ni concentration in the outermost layer portion to coexist with Mg. understood. It has also been found that the cooling rate after plating affects the Ni concentration.
In addition, from the analysis result by the fluorescent X-ray mentioned above, it is estimated that Ni concentration of a plating layer outermost layer part exists in the depth of about 30 nm (300 kg) from the plating outermost surface.

  In general, in terms of standard energy for oxide generation, Al and Mg are elements that have a stronger oxidization action than Zn, and conversely, Ni is an element that has a low oxidization action. Blackening is due to oxygen deficiency by diffusing (moving and concentrating) the plating component element with strong oxidization action to the outermost surface of the plating layer, and taking some oxygen from the zinc oxide generated on the outermost surface of the plating layer. If it occurs due to the conversion to zinc oxide, the plating layer of sample (1) with inferior blackening resistance shows that Mg concentrated in the outermost layer deprives oxygen of zinc oxide, and also has inferior blackening resistance. Since the plating layer of sample (2) was concentrated with Al on the surface layer side than Ni, Al, which is also highly oxidizable, took oxygen from zinc oxide and converted it into oxygen-deficient zinc oxide. Can be considered.

In contrast, the outermost layer portion of the plating layer of the sample (3) excellent in blackening resistance is enriched with Ni, which is weakly oxidizable, and the outermost layer portion of Mg and Al coexisting as a barrier layer. It is considered that the diffusion (migration / concentration) to the surface is suppressed and the blackening resistance is improved.
That is, in order to improve blackening resistance, it is necessary that Ni is concentrated in the outermost layer portion of the plating layer, so that it plays a role as a barrier layer. This is thought to be caused by the coexistence of However, the mechanism by which Ni moves and concentrates in the outermost layer portion of the plating layer by coexisting with Mg is not always clear at present.

When the Ni content in the plating layer is less than 0.005 mass%, even if Mg coexists, the concentration of Ni on the outermost layer of the plating layer is small, and the effect of improving blackening resistance cannot be obtained. On the contrary, even if Ni is 0.005 mass% or more, if Mg is less than 0.2 mass%, concentration of Ni in the outermost layer is not observed.
In addition, when the Ni content exceeds 0.1% by mass, although there is an effect of improving blackening resistance, Al—Mg-based dross containing Ni is generated in the plating bath, and the plating appearance due to dross adhesion is impaired. It is not preferable.
For the above reasons, in the present invention, the Ni content in the plating layer is set to 0.005 to 0.1% by mass, and the Mg content is set to 0.2 to 1.0% by mass as described above. .

In the plated steel sheet of the present invention, a misch metal containing Ce and / or La can be contained in the plating layer. Although this misch metal containing Ce and / or La has no effect on zero spangle formation, it increases the fluidity of the plating bath, prevents the occurrence of fine unplated pinholes, and smoothes the plating surface. Works.
If the content of misch metal is less than 0.005 mass% in terms of the total amount of Ce and La, the effect of suppressing pinholes cannot be sufficiently obtained, and the effect of smoothing the surface is lost. On the other hand, if the total amount of Ce and La exceeds 0.05% by mass, it will be present as an undissolved suspended matter in the plating bath, which will adhere to the plated surface and impair the plating appearance. For this reason, the misch metal containing Ce and / or La is preferably 0.005 to 0.05% by mass, and preferably 0.007 to 0.02% by mass in terms of the total amount of Ce and La.
As described above, an appropriate amount of Mg and Ni is contained in the plating layer having a GF composition, and if necessary, an appropriate amount of misch metal containing Ce and / or La is contained, so that there is no spangle or very fine spangle. Is formed, and a hot-dip Zn-Al alloy-plated steel sheet having a metallic appearance and a beautiful plating appearance free from unplating such as minute pinholes and excellent blackening resistance can be obtained.

The above hot-dip Zn—Al-based alloy-plated steel sheet can be obtained, for example, under the following production conditions.
The steel plate to be used as the base steel plate may be appropriately selected from known steel plates depending on the application, and is not particularly limited. For example, using a low carbon aluminum killed steel plate or an extremely low carbon steel plate is a viewpoint of the plating work. To preferred. This steel plate (underlying steel plate) is immersed in a hot-dip Zn-Al alloy plating bath and subjected to hot-dip (hot) plating, and then pulled up from the plating bath and cooled, and a hot-dip Zn-Al-based alloy plating layer is formed on the steel plate surface. Form. This plating layer contains Al: 1.0 to 10% by mass, Mg: 0.2 to 1.0% by mass, Ni: 0.005 to 0.1% by mass, and, if necessary, Ce and / or Or the misch metal containing La is 0.005-0.05 mass% in the total amount of Ce and La, and the remainder consists of Zn and an unavoidable impurity. Therefore, it is preferable to adjust the bath composition of the molten Zn—Al-based alloy plating bath to be substantially the same as the alloy plating layer composition.
Further, as described above, Ni is concentrated in the outermost layer portion of the molten Zn—Al-based alloy plating layer.

The inventors of the present invention, in particular, as a result of earnestly examining the content of Mg and Ni in the molten Zn-Al alloy plating layer, the cooling rate after plating, and the concentration behavior of the plating component elements on the outermost layer of the plating layer, As described above, coexistence of Mg and Ni is indispensable for improvement of blackening, that is, Ni concentration on the outermost layer portion of the plating layer, but this Ni concentration requires up to 250 ° C. after plating. It has been found that the cooling rate has a great influence.
It is known that metals such as Al, Mg, and Ni in the molten Zn-Al alloy plating layer gradually diffuse toward the outermost surface of the plating layer during solidification and normal temperature after plating. In particular, it has been found that the concentration of Mg and Ni on the outermost surface of the plating layer, which has been noted in the experiments by the present inventors, is greatly influenced by the cooling rate up to 250 ° C. after plating. On the other hand, the cooling rate in the temperature range below 250 ° C. hardly affected the concentration of Mg and Ni.

Specifically, by controlling the cooling rate of the plated steel sheet pulled up from the molten Zn—Al alloy plating bath to 250 ° C. to 1 to 15 ° C./second, preferably 2 to 10 ° C./second, It has been found that Ni concentration on the surface layer can be more effectively promoted. When the cooling rate of the plated steel sheet pulled up from the plating bath to 250 ° C. is less than 1 ° C./second, although Ni is sufficiently concentrated in the outermost layer of the plated layer, an alloy layer grows in the plated layer, and a tortoiseshell pattern As a result, the appearance deteriorates and the workability deteriorates. On the other hand, if the cooling rate exceeds 15 ° C./second, the Mg content in the plating layer is in the range of 0.2 to 1.0 mass% and the Ni content is in the range of 0.005 to 0.1 mass%. Further, the concentration of Ni in the outermost layer portion of the plating layer is reduced, and the blackening resistance is not significantly affected. Therefore, the cooling rate of the plated steel sheet pulled up from the molten Zn—Al-based alloy plating bath to 250 ° C. is preferably 1 to 15 ° C./second, more preferably 2 to 10 ° C./second.
The plating bath temperature is preferably in the range of 390 to 500 ° C. If the plating bath temperature is less than 390 ° C., the viscosity of the plating bath increases and the plating surface tends to be uneven, while if it exceeds 500 ° C., dross in the plating bath tends to increase.

In order to produce the surface-treated plated steel sheet of the present invention, the titanium-containing aqueous liquid (A) and the nickel compound and / or cobalt compound (B) as described above are formed on the surface of the molten Zn-Al alloy-plated steel sheet. , A fluorine-containing compound (C), a water-soluble organic resin and / or a water-dispersible organic resin (D) as essential components, and if necessary, an organic phosphoric acid compound (E), a vanadate compound (F), carbonic acid After apply | coating the surface treatment composition (H) (treatment liquid) containing 1 or more types of a zirconium compound (G), it dries without washing with water.
Further, the titanium-containing aqueous liquid (A) and the surface treatment composition (H) may further contain other additive components as mentioned above, if necessary.

The method for applying the surface treatment composition (treatment liquid) may be any method that allows the treatment liquid to adhere to the surface of the plated steel sheet, such as spray + roll squeezing, roll coater, or dipping. Also, the drying method after application is arbitrary, for example, a hot air method, an induction heating method, an electric furnace method, or the like.
The drying temperature (steel plate temperature) of the applied surface treatment composition (treatment liquid) is preferably about 40 to 200 ° C. When the drying temperature is less than 40 ° C., the film formation is insufficient and the film has poor corrosion resistance. On the other hand, even if it is dried at a plate temperature exceeding 200 ° C., the effect of improving the performance such as corrosion resistance corresponding to the drying temperature cannot be obtained.

The titanium-containing aqueous liquid (A) and components (B) to (G) used in the surface treatment composition are shown below.
[Production of titanium-containing aqueous liquid (A)]
Production Example 1 (Titanium-containing aqueous liquid T1)
Ammonia water (1: 9) was added dropwise to a solution in which 5 cc of a titanium tetrachloride 60 mass% solution was made 500 cc with distilled water to precipitate titanium hydroxide. After washing with distilled water, 10 cc of a 30% by mass hydrogen peroxide solution was added and stirred to obtain a yellow translucent viscous titanium-containing aqueous liquid T1 containing titanium.
Production Example 2 (Titanium-containing aqueous liquid T2)
A mixture of 10 parts by mass of tetraiso-propoxytitanium and 10 parts by mass of iso-propanol was dropped into a mixture of 30 parts by mass of 10 parts by mass of hydrogen peroxide and 100 parts by mass of deionized water with stirring at 20 ° C. over 1 hour. did. Thereafter, aging was carried out at 25 ° C. for 2 hours to obtain a yellow transparent, slightly viscous titanium-containing aqueous liquid T2.
Production Example 3 (Titanium-containing aqueous liquid T3)
A titanium-containing aqueous liquid T3 was obtained under the same production conditions as in Production Example 2 except that tetra-n-butoxy titanium was used instead of tetraiso-propoxy titanium used in Production Example 2.

Production Example 4 (Titanium-containing aqueous liquid T4)
A titanium-containing aqueous liquid T4 was obtained under the same production conditions as in Production Example 2 except that tetramer of tetraiso-propoxytitanium used in Production Example 2 was used instead of tetraiso-propoxytitanium.
Production Example 5 (Titanium-containing aqueous liquid T5)
A titanium-containing aqueous liquid was produced under the same production conditions as in Production Example 2, except that hydrogen peroxide was used in 3 times the amount of Production Example 2, dropped at 50 ° C over 1 hour, and further aged at 60 ° C for 3 hours. T5 was obtained.
Production Example 6 (Titanium-containing aqueous liquid T6)
The titanium-containing aqueous liquid T3 produced in Production Example 3 was further heat-treated at 95 ° C. for 6 hours to obtain a white yellow translucent titanium-containing aqueous liquid T6.
Production Example 7 (Titanium-containing aqueous liquid T7)
A mixture of 10 parts by mass of tetraiso-propoxytitanium and 10 parts by mass of iso-propanol, 5 parts by mass (solid content) of “TKS-203” (trade name, manufactured by Teika Co., Ltd.), 30% by mass hydrogen peroxide solution The mixture was added dropwise to a mixture of 10 parts by mass and 100 parts by mass of deionized water with stirring at 10 ° C. over 1 hour. Thereafter, the mixture was aged at 10 ° C. for 24 hours to obtain a yellow transparent, slightly viscous titanium-containing aqueous liquid T7.

[Nickel compound or cobalt compound (B)]
B1: Nickel acetate B2: Nickel nitrate B3: Nickel sulfate B4: Cobalt acetate B5: Cobalt nitrate [fluorine-containing compound (C)]
C1: Zircon ammonium fluoride C2: Zircon hydrofluoric acid C3: Zircon sodium fluoride C4: Zircon potassium fluoride

[Water-soluble or water-dispersible organic resin (D)]
Among the water-soluble or water-dispersible organic resins, the water-dispersible acrylic resins D1 to D5 were produced according to Production Examples 8 to 12 shown below, and D6 to D8 were commercially available products. Table 1 shows the monomer composition of the water-dispersible acrylic resins D1 to D5 and the characteristic values of the resin. In the following production examples, “part” and “%” are based on mass.
Production Example 8 (Water-dispersible acrylic resin D1)
265 parts deionized water, 9 parts Aqualon RN-50 (Note 1), Aqualon RN-2025 (Note 2) 87 in a 2-liter four-necked flask equipped with a reflux condenser, stirrer, thermometer, and dropping funnel 5% (28.9 parts) of a pre-emulsion obtained by forcibly emulsifying monomer mixture liquid 1 (first stage) having the following composition was added, and the temperature was increased after nitrogen substitution.
Monomer mixture 1
Deionized water: 166.5 parts Aqualon RN-50: 6.6 parts Aqualon RN-2025: 53 parts Styrene: 35 parts Methyl methacrylate: 163.5 parts 2-Ethylhexyl acrylate: 105 parts 2-Hydroxyethyl methacrylate: 5 parts Methacrylic acid: 3 parts Acrylonitrile: 38.5 parts Tertiary decanethiol: 1 part

When the temperature reaches 55 ° C. or higher, 5% (4.43 parts) of an aqueous oxidizing agent solution obtained by dissolving 5 parts of perbutyl H (Note 3) in 83.5 parts of deionized water and 2.5 parts of sodium formaldehyde sulfoxylate 5% (4.3 parts) of a reducing agent aqueous solution prepared by dissolving 83.5 parts in deionized water was added, and the temperature was further raised and maintained at 60 ° C. 15 minutes after the addition, the remaining pre-emulsion was added dropwise over 1.5 hours, the oxidizing agent aqueous solution for 3.5 hours, and the reducing agent aqueous solution over 3.5 hours. While the dropping of the oxidizing agent aqueous solution and the reducing agent aqueous solution was continued, the monomer mixed solution 2 (second stage) having the following composition was dropped over 1 hour from the end of dropping of the first stage pre-emulsion.
Monomer mixture 2
Styrene: 15 parts Methyl methacrylate: 84.5 parts 2-Ethylhexyl acrylate: 22.5 parts 2-Hydroxyethyl methacrylate: 4.25 parts Methacrylic acid: 6 parts Acrylonitrile: 15 parts γ-methacryloxypropyltrimethoxysilane: 2. 75 copies

The temperature is maintained at 60 ° C. for 1 hour after the completion of all the droppings, and then the temperature is lowered to 40 ° C. or less. 3.35 parts of 25% aqueous ammonia, 0.35 parts of Sura-off EX (Note 4), 2, 2, 83.5 parts of 4-trimethyl-1,3-pentanediol monoisobutyrate was added to obtain a water-dispersible acrylic resin D1 having a pH of 8.0 and a non-volatile content (solid content) of 31%.
(Note 1) Aqualon RN-50: trade name, manufactured by Daiichi Kogyo Seiyaku Co., Ltd., nonionic emulsifier, solid content 60%
(Note 2) Aqualon RN-2025: trade name, manufactured by Daiichi Kogyo Seiyaku Co., Ltd., nonionic emulsifier, solid content 25%
(Note 3) Perbutyl H: Trade name, manufactured by NOF Corporation, t-butylhydroxyperoxide, 69% active ingredient
(Note 4) Sura-off EX: trade name, manufactured by Nippon Enviro Chemicals, Inc., preservative

Production Examples 9 to 12 (water dispersible acrylic resins D2 to D5)
In Production Example 8, water-dispersible acrylic resins D2 to D5 were obtained in the same manner as in Production Example 8, except that the monomer composition in the first and second stages was changed to the blending ratio shown in Table 1.
D6: Superflex E-2500 (trade name, manufactured by Daiichi Kogyo Seiyaku Co., Ltd., aqueous polyurethane resin)
D7: Bironal MD-1100 (trade name, manufactured by Toyobo Co., Ltd., water-based polyester resin)
D8: Adeka Resin EM-0718 (trade name, manufactured by ADEKA, water-based epoxy resin)

[Organic Phosphate Compound (E)]
E1: 1-hydroxymethane-1,1-diphosphonic acid E2: 1-hydroxyethane-1,1-diphosphonic acid [vanadic acid compound (F)]
F1: ammonium metavanadate F2: sodium metavanadate [zirconium carbonate compound (G)]
G1: Ammonium zirconium carbonate G2: Sodium zirconium carbonate

As the base steel plate of the surface-treated plated steel plate, the plated steel plate shown in Table 2 was used.
A surface treatment composition appropriately blended with the above-described titanium-containing product liquid (A) and components (B) to (G) was applied to the surface of the plated steel sheet and dried at a predetermined drying temperature for 5 to 20 seconds. It was. These test materials were evaluated for corrosion resistance, blackening resistance and paint adhesion by the following test methods. The results are shown in Tables 3 to 6 together with the composition of the surface treatment composition applied to each test material and the coating conditions.

(1) Corrosion resistance A salt water spray test of JIS-Z-2371-2000 was performed on the specimens whose end portions and back surface were tape-sealed, and the test time at which the white rust generation area ratio was 5% was measured. The evaluation criteria are as follows.
◎: 240 hours or more ○: 144 hours or more, less than 240 hours △: 96 hours or more, less than 144 hours ×: less than 96 hours (2) Blackening resistance The test material is controlled to a temperature of 80 ° C. and a relative humidity of 95% RH. The change in whiteness (L value) when left in a constant temperature and humidity chamber for 24 hours was calculated by ΔL (= L value after test−L value before test). The evaluation criteria are as follows.
○: ΔL ≧ −15
×: −15> ΔL

(3) Paint adhesion Melamine alkyd resin (trade name “Delicon # 700”, manufactured by Dainippon Paint Co., Ltd.) was applied to the test material with / without pretreatment so that the dry film thickness was 30 ± 2 μm. And baked at 130 ° C. for 30 minutes to dry. About this test material, the flat-plate part coating-material adhesiveness and the process part coating-material adhesiveness were evaluated. The pretreatment was performed under the following conditions.
Treatment liquid: Pulclean N364S (trade name, manufactured by Nihon Parkerizing Co., Ltd.), concentration 2%, 60 ° C
Treatment method: 2 minutes spray treatment (1 kgf / cm ² )
(3-1) Adhesiveness of flat plate paint Using a cutter knife on the painted surface, 11 lines were drawn vertically and horizontally at intervals of 1 mm, and 100 squares of 1 mm square were produced in a grid pattern. Thereafter, a cellophane adhesive tape (CT24, manufactured by Nichiban Co., Ltd.) was applied to the grid area, and the number of cells peeled when the cellophane adhesive tape was peeled off was evaluated.

(3-2) Adhesion of paint on the processed part Using a cutter knife on the painted surface, 11 lines were drawn vertically and horizontally at intervals of 1 mm, and 100 squares of 1 mm square were produced in a grid pattern. Thereafter, the cross section was extruded 5 mm with an Erichsen test machine, cellophane adhesive tape (CT24, manufactured by Nichiban Co., Ltd.) was applied to the cross section, and the number of cells peeled when the cellophane adhesive tape was peeled off was evaluated. .
(3-3) Evaluation Criteria ◎: No peeling ○: 1 to 5 squares out of 100 squares are peeled (number of remaining squares 99 to 95)
Δ: 6th to 50th cell out of 100th cell is peeled (number of remaining cells is 94 to 50)
X: The 51st-100th cell of the 100th cell peels (number of remaining cells 49-0)

In Tables 3 and 5, * 1 to * 9 indicate the following contents.
* 1 Plated steel plates No. 1 to 5 listed in Table 2
* 2 Titanium-containing aqueous liquids T1 to T7 described in the specification text
* 3 Nickel compounds or cobalt compounds B1 to B5 described in the main text of the specification
* 4 Fluorine-containing compounds C1 to C4 described in the main text of the specification
* 5 Water-soluble or water-dispersible organic resins D1 to D8 described in the main text of the specification
* 6 Organophosphate compounds E1, E2 described in the main text of the specification
* 7 Vanadic acid compounds F1, F2 described in the main text of the specification
* 8 Zirconium carbonate compounds G1 and G2 described in the specification text
* 9 Mass% of solid content in the surface treatment composition

The graph which shows the relationship between Mg content in a plating layer, and a plating external appearance about the hot-dip Zn-Al type alloy plating steel plate which has a plating layer of GF composition containing an appropriate amount of Ni A hot-dip Zn-Al alloy-plated steel sheet having a GF composition, a plated steel sheet containing only Mg in the plating layer, a plated steel sheet containing only Ni in the plating layer, and Mg and Ni in the plating layer The graph which shows the component analysis result of the plating layer depth direction about the plated steel sheet

Claims (6)

At least one surface of the steel sheet contains Al: 1.0 to 10% by mass, Mg: 0.2 to 1.0% by mass, Ni: 0.005 to 0.1% by mass, the balance being Zn and inevitable On the surface of a hot-dip Zn-Al-based alloy-plated steel sheet having a hot-dip Zn-Al-based alloy plating layer made of mechanical impurities,
Titanium obtained by mixing at least one titanium compound selected from hydrolyzable titanium compounds, low-condensates of hydrolyzable titanium compounds, titanium hydroxide, and low-condensates of titanium hydroxide with hydrogen peroxide water Containing aqueous liquid (A) in a solid content ratio of 5 to 60 mass%, nickel compound and / or cobalt compound (B) in a solid content ratio of 0.01 to 1 mass%, and fluorine-containing compound (C) in solid form The surface treatment composition (H) containing 1 to 40% by mass of a water-soluble organic resin and / or water-dispersible organic resin (D) in a proportion of solids of 31 to 85% by mass is applied and dried. A surface-treated hot-dip Zn—Al-based alloy-plated steel sheet, comprising a surface-treated film having a film adhesion amount of 0.5 to 3.0 g / m ² formed by the treatment.   The surface-treated molten Zn-Al alloy-plated steel sheet according to claim 1, wherein the fluorine-containing compound (C) is at least one selected from zircon ammonium fluoride and zircon hydrofluoric acid.   The surface-treated molten Zn-Al according to claim 1 or 2, wherein the surface-treated composition (H) further contains 5 to 60% by mass of the organic phosphoric acid compound (E) in a solid content ratio. Alloy-plated steel sheet.   The surface treatment composition (H) further contains 0.1 to 30% by mass of the vanadic acid compound (F) in a solid content ratio, according to any one of claims 1 to 3. Surface-treated molten Zn-Al alloy-plated steel sheet.   The surface treatment composition (H) further contains 0.1 to 20% by mass of the zirconium carbonate compound (G) in a proportion of solid content, according to any one of claims 1 to 4. Surface-treated molten Zn-Al alloy-plated steel sheet.   The surface-treated molten Zn-Al alloy according to any one of claims 1 to 5, wherein the water-soluble organic resin and / or the water-dispersible organic resin (D) is a water-dispersible acrylic resin. Plated steel sheet.

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