JP6943232B2 - Surface treatment liquid, manufacturing method of surface treatment steel sheet, and surface treatment steel sheet - Google Patents

Description

The present invention relates to a surface treatment liquid for a molten Zn-Al-Mg based alloy plated steel sheet, and more particularly to a surface treatment liquid capable of obtaining a surface treatment steel sheet having excellent corrosion resistance, blackening resistance, and sweat resistance. The present invention also relates to a method for producing a surface-treated steel sheet using the surface-treated liquid. Furthermore, the present invention relates to a surface-treated steel sheet, and more particularly to a surface-treated steel sheet having excellent corrosion resistance, sweat resistance, and blackening resistance.

A Zn-based plated steel sheet having a Zn-based plated layer provided on the surface of the steel sheet is used in an extremely wide range of fields because it has high corrosion resistance due to the sacrificial anticorrosion action of Zn. Above all, for the purpose of improving white rust resistance and red rust resistance, a chromate-treated steel sheet in which a Zn-based plating layer is subjected to chromate treatment with a treatment liquid containing chromic acid, dichromic acid or salts thereof as a main component. However, it has been generally used in the past. However, in recent years, from the viewpoint of global environmental problems, there is an increasing demand for non-polluting surface-treated steel sheets that are not chromate-treated, so-called chrome-free treated steel sheets.

Therefore, many chromate-free treatment techniques for suppressing zinc corrosion (white rust) in galvanized steel sheets have been proposed without using chromate treatment. Examples of the chromate-free processing technique include the following techniques (1) to (4) and techniques in which they are combined.
(1) A technique for utilizing the passivation action of molybdic acid, tungstic acid, etc., which are compounds of Mo or W belonging to the same Group 6 (Group IVA in the former IUPAC formula) as Cr.
(2) A technique using a transition metal such as Ti, Zr, V, Mn, Ni, Co or a metal salt of a rare earth element such as La or Ce.
(3) A technique based on a chelating agent such as a polyvalent phenol carboxylic acid such as tannic acid or a compound containing S and N.
(4) A technique for forming a polysiloxane film using a silane coupling agent.

On the other hand, there are various types of Zn-based galvanized steel sheets. Among them, molten Zn-Al alloy-plated steel sheets have better corrosion resistance than hot-dip Zn-plated steel sheets, so they are mainly used for home appliances, civil engineering, and building materials. Widely used in. This hot-dip Zn-Al alloy-plated steel sheet exhibits excellent corrosion resistance even in a harsh environment with a large amount of flying salt, such as a coastal area, but in recent years, Zn has been added to contain Mg to further improve appearance uniformity and corrosion resistance. The application of −Al—Mg-based alloy-plated steel sheets is expanding.

Therefore, in recent years, there has been an increasing demand for chromate-free surface treatment coatings for Zn—Al—Mg-based alloy-plated steel sheets. However, since blackening is remarkable in the Zn-Al-Mg-based alloy-plated steel plate containing Al and Mg in the plating layer, the surface-treated film provided with the Zn-Al-Mg-based alloy plating layer has excellent corrosion resistance. In addition, it is required to have excellent blackening resistance.

Here, blackening is a phenomenon in which the surface of the plating layer turns black in a moist environment or the like, and is considered to be caused by the change of zinc oxide generated on the outermost surface of the plating layer to oxygen-deficient zinc oxide. There is. In a Zn-Al-Mg alloy plated steel sheet, elements such as Al and Mg, which are more easily oxidized than Zn, diffuse to the outermost surface of the plating layer, deprive zinc oxide of a part of oxygen, and oxygen-deficient zinc oxide. Since it is changed to, blackening becomes remarkable.

Regarding the chromate-free treatment applied to such a Zn-Al-Mg-based alloy-plated steel sheet, various techniques have been proposed from the viewpoints of corrosion resistance and blackening resistance, for example, as in Patent Documents 1 to 9. There is.

Patent Document 1 proposes a technique for forming a composite film mainly composed of a sparingly soluble compound of Ti and V on the surface of a Zn—Al alloy plating layer via an Al—F reaction layer.

Patent Document 2 proposes a surface treatment film containing an oxide or hydroxide of a valve metal and a fluoride of a valve metal.

Patent Document 3 proposes a technique for forming a two-layer film on the surface of a galvanized steel sheet. The two-layer coating is composed of a first layer made of silica or alumina and a second layer provided on the surface of the first layer and containing an oxide or hydroxide of a valve metal and a fluoride of a valve metal. ..

Patent Document 4 proposes a technique for forming a surface treatment film containing a valve metal compound as a main component on the surface of an Mg-containing Zn alloy plating layer via an interface reaction layer containing a Mg compound derived from the plating layer. Has been done.

Patent Document 5 proposes a surface treatment liquid for a Zn—Al alloy plated steel sheet containing V, Mo, P, Zr, Si, amine, and an organic resin. The surface treatment film formed by the surface treatment liquid includes a first chemical conversion treatment layer containing V, Mo and P formed on the plating layer and other components formed on the first chemical conversion treatment layer. It is a composite film composed of.

Patent Document 6 proposes a surface treatment liquid containing a Ti compound containing fluorine, phosphoric acid, and an oxidizing agent that polymerizes the Ti compound.

In Patent Documents 7 and 8, a surface treatment agent containing an organic resin in addition to an inorganic compound, a Zr compound, a V compound, a fluorocomplex of Ti, and an inorganic phosphorus compound, on the surface of a Zn—Al—Mg alloy plated steel sheet. A method has been proposed in which the above is applied and dried to form an inorganic-organic composite film.

In Patent Document 9, a Zn-Al-Mg-Si alloy plated steel sheet, a layer of an insulating material formed on the surface of the plated steel sheet, and a film containing Al formed on the surface of the layer of the insulating material are provided. A surface-treated steel sheet having a surface-treated steel sheet has been proposed.

Japanese Unexamined Patent Publication No. 2003-306777 JP-A-2002-194558 Japanese Unexamined Patent Publication No. 2004-232020 JP-A-2007-0233009 Japanese Unexamined Patent Publication No. 2015-117433 Japanese Unexamined Patent Publication No. 2004-143549 JP 2015-0105404 Japanese Unexamined Patent Publication No. 2016-089232 Japanese Patent No. 5655981

However, the conventional techniques such as the above-mentioned Patent Documents 1 to 9 have the following problems.

In the techniques proposed in Patent Documents 1 to 5, (A) the first layer of the surface-treated film composed of two layers forms a reaction layer between the plating layer and the surface-treated film, or (B). ) Although it is a single-layer film, it has a film structure like a two-layer film by forming a reaction layer at the interface between the plating layer and the surface-treated film. In these techniques, the adhesion between the surface treatment film and the plating layer can be improved by forming the reaction layer, and as a result, corrosion of the plated steel sheet, particularly generation of white rust can be suppressed. However, fluoride is used to form the reaction layer, and the surface of the plating layer is activated by the etching action of the fluoride, so that the plating surface layer is oxidized in a moist environment and the blackening resistance is reduced. There's a problem.

On the other hand, in the technique proposed in Patent Document 6, since a reaction layer is not formed without using fluoride in the first layer, blackening is less likely to occur as compared with the method using fluoride, but the plating layer and surface treatment The adhesion of the film becomes insufficient, and the corrosion resistance is lowered.

Further, in the techniques proposed in Patent Documents 7 and 8, the film can be made dense by combining various inorganic components and organic components, and the corrosion resistance can be improved even with a single-layer film. However, since fluoride is used in the above technique, it is unavoidable that the blackening resistance is lowered by the fluoride.

Although the technique proposed in Patent Document 9 can improve the blackening resistance to some extent, the effect of suppressing the permeation of corrosion factors such as water and salt is small, and the corrosion resistance is inferior.

By the way, all of the above-mentioned conventional techniques aim to delay the start of corrosion of the underlying steel sheet by providing a surface treatment film on the plating layer to suppress corrosion of the plating layer. Since the base steel sheet is protected only by the plating layer, corrosion of the base steel sheet is suppressed in the exposed part of the base steel sheet, for example, the part where the plating or film is damaged by press molding or bending, or the cut end face. Can't.

Further, in the Zn-Al-Mg based alloy plated steel sheet, in addition to the above-mentioned blackening phenomenon in a wet environment, it is known that when a person comes into direct contact with the plated steel sheet, the touched portion turns black with time. There is. This is because human sweat, which is weakly acidic, adheres to the steel sheet and the sweat component permeates into the film, causing easily oxidizable elements such as Al and Mg present on the plating surface to oxidize over time and turn black. It is a phenomenon that occurs. The conventional surface-treated film as described above can suppress the blackening due to human sweat to some extent, but the sweat resistance is still inadequate.

As described above, the conventional Zn-Al-Mg-based alloy-plated steel sheet with a chromate film is insufficient in any or all of corrosion resistance, blackening resistance, and sweat resistance, and has excellent corrosion resistance and blackening resistance. , Zn-Al-Mg based alloy plated steel sheet having sweat resistance is required.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a surface-treated steel sheet having excellent corrosion resistance, blackening resistance, and sweat resistance.

As a result of repeated studies to solve the above problems, the inventors have obtained the following findings.

(1) A surface-treated film containing a specific component is formed on the Zn-Al-Mg-based alloy plating layer, and the surface-treated film is specified on the side in contact with the molten Zn-Al-Mg-based alloy plating layer. By forming an interfacially concentrated layer in which the components of the above are concentrated, in addition to suppressing corrosion of the plating layer, it is possible to improve the corrosion resistance of the exposed portion of the base steel plate by the combined effect with the plating layer.

(2) Furthermore, the components of the interfacial concentrated layer function as a barrier against moisture and salt that have entered the surface treatment film, and delay the arrival at the plating surface, so that not only blackening in a moist environment but also sweat It is possible to suppress black discoloration over time after adhesion, and improve blackening resistance and sweat resistance.

The present invention has been made based on the above findings, and its gist structure is as follows.

1. 1. A surface treatment liquid for molten Zn-Al-Mg alloy plated steel sheets.
(1) As the P compound, one or two or more selected from the group consisting of inorganic phosphoric acid, organic phosphoric acid, and salts thereof.
(2) As N compounds, one or both of inorganic N compounds and amines,
(3) As the Si compound, one or two or more selected from the group consisting of silica, tetraalkoxysilane, and a silane coupling agent.
(4) One or both of the inorganic Co compound and the inorganic Ni compound,
Contains (5) organic resin and (6) water,
The concentration of the P compound is 0.25% by mass to 5% by mass.
The total concentration of the inorganic Co compound and the inorganic Ni compound is 0.25% by mass to 5% by mass.
_{The mass ratio r N / P} of the N compound to the P compound is 0.10 to 10.
_{A surface treatment liquid having a mass ratio r Si / C} of the Si compound to the organic resin of 0.05 to 1.5.

2. (7) The surface treatment liquid according to 1 above, further containing 1 or 2 or more selected from the group consisting of Zn compounds, Al compounds, and Mg compounds.

3. 3. (8) The surface treatment liquid according to 1 or 2 above, which further contains a V compound.

4. (9) The surface treatment liquid according to any one of 1 to 3 above, further containing one or both of molybdic acid and molybdate as a Mo compound.

5. (10) The surface treatment liquid according to any one of 1 to 4 above, further containing one or both of a Zr compound and a Ti compound.

6. The surface treatment liquid according to any one of 1 to 5 above is applied to at least one surface of a molten Zn-Al-Mg-based alloy-plated steel sheet having a temperature of 25 ° C. or higher.
A method for producing a surface-treated steel sheet, in which the temperature is raised at a rate of 20 ° C./sec or more after 1.0 second or more has elapsed after the coating.

7. A surface-treated steel sheet obtained by the method for producing a surface-treated steel sheet according to 6 above.

According to the present invention, it is possible to obtain a surface-treated steel sheet having corrosion resistance, blackening resistance, and sweat resistance.

Next, the method of carrying out the present invention will be specifically described.

[Surface treatment liquid]
The surface treatment liquid according to the embodiment of the present invention is a surface treatment liquid for a molten Zn-Al-Mg-based alloy-plated steel sheet, and contains the following (1) to (6) as essential components, and optionally the following. It can contain 1 or 2 or more selected from (7) to (10). Hereinafter, each component will be described.
(1) One or two or more selected from the group consisting of inorganic phosphoric acid, organic phosphoric acid, and salts thereof as P compound (2) One or both of inorganic N compound and amine as N compound (3) Si As the compound, one or two or more selected from the group consisting of silica, tetraalkoxysilane, and a silane coupling agent (4) One or both of an inorganic Co compound and an inorganic Ni compound (5) Organic resin (6) Water (7) ) One or more selected from the group consisting of Zn compounds, Al compounds, and Mg compounds (8) V compounds (9) As Mo compounds, one or both of molybdic acid and molybdenate (10) Zr compounds and Ti One or both of the compounds

(1) P compound By containing P in the surface treatment film, corrosion resistance and sweat resistance can be improved. Therefore, the surface treatment liquid of the present invention contains 1 or 2 or more selected from the group consisting of inorganic phosphoric acid, organic phosphoric acid, and salts thereof as the P compound.

Any compound can be used as the inorganic phosphoric acid, the organic phosphoric acid, and salts thereof, without particular limitation. Examples of the inorganic phosphoric acid include phosphoric acid, primary phosphate, secondary phosphate, tertiary phosphate, pyrophosphate, pyrophosphate, tripolyphosphate, tripolyphosphate, phosphite, and phosphite. , Hypophosphoric acid, and hypophosphate, it is preferable to use 1 or 2 or more selected from the group consisting of hypophosphite. As the organic phosphoric acid, it is preferable to use phosphonic acid (phosphonic acid compound). As the phosphonic acid, for example, it is preferable to use one or two or more selected from the group consisting of nitrilotrismethylenephosphonic acid, phosphonobtantricarboxylic acid, methyldiphosphonic acid, methylenephosphonic acid, and ethylidendiphosphonic acid. .. When the P compound is a salt, the salt is preferably a salt of Group 1 to Group 13 elements in the periodic table, more preferably a metal salt, and an alkali metal salt and alkaline earth. It is preferably 1 or 2 or more selected from the group consisting of metal salts.

When the surface treatment liquid containing the P compound is applied to the plating layer, the surface of the plating layer is etched by the action of the P compound, and the interfacial concentrated layer in which Zn, Al, and Mg which are the constituent elements of the plating layer are incorporated is formed. It is formed on the plating layer side of the surface treatment film. By forming the interface-concentrated layer, the bond between the surface-treated film and the surface of the plating layer is strengthened, and the adhesion of the surface-treated film is improved.

(Preferable range of concentration of P compound)
The concentration of the P compound in the surface treatment liquid is 0.25% by mass to 5% by mass. If it is less than 0.25% by mass, the etching effect is insufficient and the adhesion to the plating interface is lowered, not only the corrosion resistance of the flat surface is lowered, but also the plating and the film are damaged due to defects, cut end faces, processing, etc. The corrosion resistance and sweat resistance of the part are also reduced. It is preferably 0.35% by mass or more, more preferably 0.50% by mass or more. On the other hand, if it exceeds 5% by mass, not only the life of the surface treatment liquid is shortened, but also the appearance when the film is formed tends to be uneven. In addition, the amount of P eluted from the surface treatment film increases, and the blackening resistance deteriorates. It is preferably 3.5% by mass or less, more preferably 2.5% by mass or less.

(2) N compound The surface treatment liquid of the present invention contains one or more of an inorganic N compound and an amine as an N compound. Like the P compound described above, the N compound has an action of activating the surface of the plating layer by an etching action and an action of adsorbing to the plating surface. By the above action, the surface treatment film and the surface of the plating layer can be firmly bonded.

As the N compound, any compound can be used without particular limitation. As the inorganic N compound, it is preferable to use 1 or 2 or more selected from the group consisting of N oxo acid, N oxo acid salt, ammonia and ammonium salt, and nitric acid, nitrate, nitrite, nitrite and ammonia. , And one or more selected from the group consisting of ammonium salts are more preferred. As the amine, it is preferable to use at least one selected from the group consisting of primary amines, secondary amines, and tertiary amines. Further, as the amine, any amine such as an aliphatic amine, an aromatic amine, or a heterocyclic amine can be used, but it is preferable to use an aliphatic amine. In particular, amines having one or more primary amino groups such as diethylenetriamine, hydroxyethylaminoethylamine, ethylaminoethylamine, methylaminopropylamine; secondary such as diethylamine, diethanolamine, N-methylethanolamine, N-ethylethanolamine and the like. Secondary amines; it is preferable to use one or more selected from tertiary amines such as trimethylamine.

(Preferable range of concentration of N compound)
The concentration of the N compound in the surface treatment liquid is not particularly limited, but is preferably 0.1% by mass to 10% by mass. When the concentration of the N compound is 0.1% by mass or more, the adhesion between the surface treatment film and the plating layer is further improved. As a result, in addition to the corrosion resistance of the flat surface portion, the corrosion resistance of the defective portion, the cut portion, and the damaged portion caused by processing and the like, and the sweat resistance are further improved. Further, when the concentration of the N compound is 10% by mass or less, the life of the surface treatment liquid can be further extended.

(3) Si compound The Si compound is a component that forms a skeleton that forms a surface treatment film together with an organic resin described later. The surface treatment liquid of the present invention contains, as a Si compound, one or two or more selected from the group consisting of silica, tetraalkoxysilane, and a silane coupling agent.

The silica is not particularly limited and any silica can be used. As the silica, for example, one or both of colloidal silica and dry silica can be used. As the colloidal silica, for example, Snowtex O, C, N, S, 20, OS, OXS, NS and the like manufactured by Nissan Chemical Industries, Ltd. can be preferably used. Further, as the dry silica, for example, AEROSIL 50, 130, 200, 300, 380 manufactured by Nippon Aerosil Co., Ltd. can be preferably used.

As the tetraalkoxysilane, any one can be used without particular limitation, but the general formula Si (OR) ₄ (in the formula, R represents the same or different alkyl groups having 1 to 5 carbon atoms). ) Is preferably used. As the tetraalkoxysilane, for example, it is preferable to use one or two or more selected from the group consisting of tetramethoxysilane, tetraethoxysilane, and tetrapropoxysilane.

Any silane coupling agent can be used without particular limitation. Examples of the silane coupling agent include γ-glycidoxypropyltrimethoxysilane, γ-glycidoxypropylmethyldiethoxysilane, γ-glycidoxypropyltriethoxysilane, γ-mercaptopropylmethyldimethoxysilane, and the like. It is preferable to use 1 or 2 or more selected from the group consisting of γ-mercaptopropyltrimethoxysilane.

By incorporating the above Si compound into the surface treatment film, the Si compound is dehydrated and condensed to form an amorphous film having a siloxane bond having a high barrier effect that shields corrosion factors. Further, by combining with an organic resin or the like described later, a film having a higher barrier property is formed. Further, in a corroded environment, a dense and stable corrosion product is formed in a defective portion or a damaged portion of a plating or a film generated by processing, and has an effect of suppressing corrosion of a base steel sheet by a combined effect with plating. From the viewpoint of high effect of forming a stable corrosion product, it is preferable to use one or both of colloidal silica and dry silica as the Si compound.

(Preferable range of concentration of Si compound)
The concentration of the Si compound in the surface treatment liquid is preferably 0.2% by mass to 9.5% by mass. When the concentration of the Si compound is 0.2% by mass or more, the barrier effect due to the siloxane bond is further enhanced, and as a result, in addition to the corrosion resistance of the flat surface portion, the corrosion resistance of the defective portion, the cut portion, and the damaged portion caused by processing and the like. , And sweat resistance is further improved. Further, when the concentration of the Si compound is 9.5% by mass or less, the life of the surface treatment liquid can be further extended.

(4) Inorganic Co Compound, Inorganic Ni Compound By containing at least one of Co and Ni in the surface treatment film, blackening resistance can be improved. It is considered that this is because Co and Ni have the effect of delaying the elution of the water-soluble component from the film in a corrosive environment. Further, Co and Ni are elements that are less likely to be oxidized than Zn, Al, and Mg. Therefore, it is considered that by concentrating at least one of Co and Ni at the interface with the plating layer, the interfacial concentrated layer acts as a barrier against corrosion, and as a result, blackening resistance is improved. Therefore, in the present invention, one or both of the inorganic Co compound and the inorganic Ni compound are added to the surface treatment liquid.

-Inorganic Co compound By using a surface treatment liquid containing an inorganic Co compound, Co can be contained in the film and incorporated into the interfacial concentrated layer. It is preferable to use a cobalt salt as the inorganic Co compound. As the cobalt salt, it is more preferable to use 1 or 2 or more selected from the group consisting of cobalt sulfate, cobalt carbonate, and cobalt chloride.

-Inorganic Ni compound By using a surface treatment liquid containing an inorganic Ni compound, Ni can be contained in the film and incorporated into the interfacial concentrated layer. It is preferable to use a nickel salt as the inorganic Ni compound. As the nickel salt, it is more preferable to use 1 or 2 or more selected from the group consisting of nickel sulfate, nickel carbonate, and nickel chloride.

(Concentration of Co compound and Ni compound)
The total concentration of the inorganic Co compound and the inorganic Ni compound in the surface treatment liquid is 0.25% by mass to 5% by mass. If it is less than 0.25% by mass, the interfacial concentrated layer becomes non-uniform, and not only the corrosion resistance of the flat surface portion is lowered, but also the corrosion resistance of the defective portion, the cut end face portion, the damaged part of the plating or the film caused by processing, etc. is also lowered. .. It is preferably 0.5% by mass or more, more preferably 0.75% by mass or more. On the other hand, if it exceeds 5% by mass, the appearance when the film is formed tends to be non-uniform, and the corrosion resistance is lowered. It is preferably 4.0% by mass or less, more preferably 0.30% by mass or less.

(5) Organic Resin The organic resin is a component that forms a skeleton that forms a surface treatment film together with the above-mentioned Si compound. As the organic resin, any one or two or more can be used without particular limitation, but all of epoxy resin, urethane resin, acrylic resin, acrylic silicon resin, acrylic-ethylene copolymer, and acrylic-styrene can be used. It is preferable to use 1 or 2 or more selected from the group consisting of polymers, alkyd resins, polyester resins, ethylene resins, and fluororesins.

Above all, from the viewpoint of corrosion resistance, it is preferable to use an organic resin having one or both of an OH group and a COOH group. Examples of the organic resin having one or both of the OH group and the COOH group include epoxy resin, acrylic copolymer resin, ethylene-acrylic acid copolymer resin, alkyd resin, polybutadiene resin, phenol resin, and polyurethane resin. One or two or more selected from the group consisting of polyamine resins, polyphenylene resins, and mixtures or addition polymers of two or more of these resins can be used.

Examples of the epoxy resin include an epoxy resin obtained by glycidyl etherification of bisphenol A, bisphenol F, novolak and the like, an epoxy resin obtained by adding propylene oxide, ethylene oxide or polyalkylene glycol to bisphenol A and glycidyl etherification, and further an aliphatic epoxy. Resins, alicyclic epoxy resins, polyether epoxy resins and the like can be used.

Examples of the urethane resin include oil-modified polyurethane resin, alkyd-based polyurethane resin, polyester-based polyurethane resin, polyether-based urethane resin, and polycarbonate-based polyurethane resin.

Examples of the acrylic resin include polyacrylic acid and its copolymer, polyacrylic acid ester and its copolymer, polymethacrylic acid and its copolymer, polymethacrylic acid ester and its copolymer, and urethane-acrylic acid. Examples thereof include copolymers (or urethane-modified acrylic resins) and styrene-acrylic acid copolymers, and resins obtained by modifying these resins with other alkyd resins, epoxy resins, phenol resins, or the like may be used.

Examples of the acrylic silicon resin include those containing a hydrolyzable alkoxysilyl group in the side chain or the terminal of an acrylic copolymer as a main agent and a curing agent added thereto. When these acrylic silicone resins are used, excellent weather resistance can be expected.

Examples of the alkyd resin include oil-modified alkyd resin, rosin-modified alkyd resin, phenol-modified alkyd resin, styrene-modified alkyd resin, silicon-modified alkyd resin, acrylic-modified alkyd resin, oil-free alkyd resin, high-molecular-weight oil-free alkyd resin, and the like. Can be mentioned.

Examples of the ethylene resin include ethylene-acrylic acid copolymers, ethylene-methacrylic acid copolymers, ethylene-based copolymers such as carboxyl-modified polyolefin resins, ethylene-unsaturated carboxylic acid copolymers, and ethylene-based ionomers. Further, a resin obtained by modifying these resins with another alkyd resin, epoxy resin, phenol resin or the like may be used.

Examples of the fluororesin include fluoroolefin-based copolymers, which include, for example, alkyl vinyl ethers, synchroalkyl vinyl ethers, carboxylic acid-modified vinyl esters, hydroxyalkyl allyl ethers, tetrafluoropropyl vinyl ethers and the like as monomers, and fluorine monomers ( There is a copolymer obtained by copolymerizing with fluoroolefin). When these fluororesins are used, excellent weather resistance and excellent hydrophobicity can be expected.

Further, from the viewpoint of corrosion resistance and processability, the organic resin is preferably a thermosetting resin. When a thermosetting resin is used, it is preferable that the surface treatment liquid further contains a curing agent. Examples of the curing agent include urea resins (butylized urea resins, etc.), melamine resins (butylated melamine resins), butylated urea / melamine resins, amino resins such as benzoguanamine resins, blocked isocyanates, oxazoline compounds, and phenol resins. One or two or more selected from the group can be used.

(Preferable range of organic resin concentration)
The concentration of the organic resin in the surface treatment liquid is preferably 1% by mass to 30% by mass. When the concentration of the organic resin is 1% by mass or more, the skeleton of the film can be formed more sufficiently. Therefore, in addition to the corrosion resistance of the flat surface portion, the corrosion resistance of the defective portion, the cut portion, and the damaged portion caused by processing, and the sweat resistance. The sex is further improved. Further, when the concentration of the organic resin is 30% by mass or less, the life of the surface treatment liquid can be further extended.

(6) Water The surface treatment liquid contains water as a solvent.

A solvent other than water can be further added to the surface treatment liquid in order to improve wettability and impart a defoaming effect. It is preferable to use an organic solvent as the solvent other than the water. As the organic solvent, for example, one or two or more selected from the group consisting of ethanol, t-butanol, and butyl cellosolve can be used.

The above (1) to (6) are essential components of the surface treatment liquid of the present invention. The surface treatment liquid in one embodiment of the present invention may have a composition composed of the above components (1) to (6).

From the viewpoint of environmental compatibility, it is preferable that the surface treatment liquid does not contain Cr. In other words, the surface treatment liquid according to the embodiment of the present invention can be a chromium-free surface treatment liquid containing no Cr. By using a surface treatment liquid that does not contain Cr, a surface treatment film that does not contain Cr (chromium-free surface treatment film) can be formed.

Further, from the viewpoint of further improving the blackening resistance, it is preferable that the surface treatment liquid does not contain an inorganic fluorine compound. By using a surface treatment liquid that does not contain an inorganic fluorine compound, it is possible to prevent activation of the surface of the plating layer due to etching by the inorganic fluorine compound and further improve blackening resistance. The inorganic fluorine compound also includes an ionic fluorine compound (for example, fluoride ion, hexafluorotitate ion, etc.) generated by dissociation of the inorganic fluorine compound. Of these, it is preferable that it does not contain a fluoride salt. Here, the fluoride salt includes a salt of a fluorometallic acid such as hexafluorotitanic acid. The surface treatment liquid of the present invention is allowed to contain a fluororesin.

Further, the surface treatment liquid in the other embodiment may further contain 1 or 2 or more arbitrarily selected from the following (7) to (10).

(7) Zn compound, Al compound, Mg compound When a surface treatment film is formed on a molten Zn-Al-Mg based alloy plated steel plate using the surface treatment liquid of the present invention, the etching effect of the surface treatment liquid causes Zn, Al, and Mg contained in the plating layer are inevitably incorporated into the surface treatment film. As a result, as will be described later, an interface-enriched layer containing Zn, Al, and Mg is formed on the plating layer side of the surface treatment film. However, not only these elements can be taken in from the plating layer, but also one or two or more selected from the group consisting of Zn compounds, Al compounds, and Mg compounds can be contained in the surface treatment liquid.

The Zn compound, Al compound, and Mg compound are not particularly limited, but are preferably inorganic compounds, and are 1 or 2 or more selected from the group consisting of salts, chlorides, oxides, and hydroxides. Is preferable.

Suitable Zn compounds include, for example, one or more selected from the group consisting of zinc sulfate, zinc carbonate, zinc chloride, zinc oxide, and zinc hydroxide. Moreover, as a suitable Al compound, for example, 1 or 2 or more selected from the group consisting of aluminum sulfate, aluminum carbonate, aluminum chloride, aluminum oxide, and aluminum hydroxide can be mentioned. Suitable Mg compounds include, for example, one or more selected from the group consisting of magnesium sulfate, magnesium carbonate, magnesium chloride, magnesium oxide, and magnesium hydroxide. Nitrate is included in the N compound. Further, the phosphorus salt shall be contained in the P compound.

(Preferable concentration range)
The total concentration of the Zn compound, Al compound, and Mg compound in the surface treatment liquid is preferably 0.25% by mass to 5% by mass. The interfacial concentrated layer can be formed more effectively at 0.25% by mass or more, and the corrosion resistance can be further improved. On the other hand, if it exceeds 5% by mass, the appearance when the film is formed tends to be non-uniform, and the corrosion resistance of the flat portion, the defective portion, the damaged portion of the plating or the film generated by processing, etc. may be lowered.

(8) V compound In order to contain V in the surface treatment film, the V compound can be added to the surface treatment liquid. V in the surface treatment film usually exists evenly dispersed, but it elutes moderately in a corrosive environment, and the plating component that also elutes in a corrosive environment combines with zinc ions and the like, resulting in a dense protective film. To form. As a result, it is possible to further enhance the corrosion resistance not only to the flat surface portion but also to the defective portion, the damaged portion of the plating or film caused by processing, and the corrosion progressing from the cut end face to the flat surface portion.

Suitable V compounds include, for example, one or more selected from the group consisting of sodium metavanadate, vanadyl sulfate, and vanadium acetylacetonate.

(Preferable concentration range of V compound)
The concentration of the V compound in the surface treatment liquid is preferably 0.05% by mass to 4% by mass. If it is 0.05% by mass or more, it becomes easy to form a protective film by elution in a corrosive environment, and the corrosion resistance of defective parts, cut end face parts, damaged parts of plating and film caused by processing, etc. is improved. On the other hand, if it exceeds 4% by mass, the appearance when the film is formed tends to be non-uniform, and the blackening resistance is also lowered.

(9) Mo compound In order to contain Mo in the surface treatment film, one or both of molybdic acid and molybdate can be added as the Mo compound to the surface treatment liquid. By adding one or both of molybdic acid and molybdate to the surface treatment liquid, the blackening resistance of the obtained surface treatment steel sheet can be further improved.

Examples of the molybdate include one or more selected from the group consisting of sodium molybdate, potassium molybdate, magnesium molybdate, and zinc molybdate.

(Preferable concentration range of Mo compound)
The total concentration of the Mo compound in the surface treatment liquid is preferably 0.01% by mass to 3% by mass. When it is 0.01% by mass or more, the production of oxygen-deficient zinc oxide is further suppressed, and the blackening resistance is further improved. Further, when it is 3% by mass or less, the life of the chemical solution is further extended and the corrosion resistance is further improved.

(10) Zr compound, Ti compound In order to contain one or both of Zr and Ti in the surface treatment film, one or both of the Zr compound and the Ti compound can be added to the surface treatment liquid. Zr and Ti have the effect of preventing the surface treatment film from becoming porous and densifying the film. Therefore, by adding the Zr compound and / or the Ti compound, it becomes difficult for the corrosive factor to permeate the surface treatment film, and as a result, the corrosion resistance is further improved.

-Ti compound As the Ti compound, one or two or more selected from the group consisting of titanium sulfate, titanium chloride, titanium hydroxide, titanium acetylacetonate, titanium octylene glycolate, and titanium ethylacetacetate may be used. preferable. Among them, the organic titanium chelate compound is more preferable from the viewpoint of having a high effect of densifying the film when the surface treatment liquid is dried to form the film. Nitrate is included in the N compound.

-Zr compound As the Zr compound, it is preferable to use 1 or 2 or more selected from the group consisting of zirconyl acetate, zirconyl sulfate, potassium zirconyl carbonate, and sodium zirconyl carbonate. Nitrate and ammonium salt are included in the N compound.

(Preferable concentration range of Zr compound and Ti compound)
The total concentration of the Zr compound and the Ti compound in the surface treatment liquid is preferably 0.2% by mass to 20% by mass. When it is 0.2% by mass or more, the effect of suppressing permeation of corrosion factors is enhanced, and not only the corrosion resistance of the flat surface portion but also the corrosion resistance of the defective portion, the cut end face portion, the damaged portion of the plating or the film caused by processing, etc. is improved. On the other hand, the life of the chemical solution can be further extended by setting the content to 20% by mass or less.

r _{N / P} : 0.10 to 10
_{When the mass ratio r N / P} of the N compound to the P compound in the surface treatment liquid is less than 0.10, the corrosion resistance and blackening resistance of the flat surface portion, the defective portion, the cut end face portion, and the processed portion are lowered. Therefore, the r _{N / P is set} to 0.10 or more, preferably 0.30 or more, and more preferably 0.60 or more. On the other hand, when the r _{N / P} is higher than 10, not only the adhesion between the surface treatment film and the plating is insufficient and the corrosion resistance of the flat surface portion is lowered, but also the plating or film formed in the defective portion, the cut end face portion, the processing, etc. Corrosion resistance and sweat resistance of damaged parts are also reduced. Therefore, r _{N / P is set} to 10 or less, preferably 7 or less, and more preferably 5 or less.

r _{Si / C} : 0.05 to 1.5
_{The mass ratio r Si / C} of the Si compound to the organic resin in the surface treatment liquid is 0.05 to 1.5. If it is less than 0.05, stable corrosion products are less likely to be formed, so that the corrosion resistance of the defective portion, the damaged portion of the plating or film caused by processing, and the cut end face portion is lowered. Therefore, r _{Si / C} is set to 0.05 or more, preferably 0.1 or more, and more preferably 0.2 or more. On the other hand, when r _{Si / C} exceeds 1.5, the denseness of the film is lowered, so that corrosion factors easily invade the film, and the corrosion resistance, blackening resistance, and sweat resistance of the flat surface are lowered. Therefore, r _{Si / C} is 1.5 or less, preferably 1.2 or less, and more preferably 1.0 or less.

_{When the total mass ratio r (Co + Ni) / P} of the inorganic Co compound and the inorganic Ni compound to the P compound in the surface treatment liquid is 0.1 or more, it is formed on the plating layer side of the surface treatment film. The number of interfacial concentrated layers is increased, and in addition to the corrosion resistance of the flat surface portion, the corrosion resistance of the defective portion, the cut end face portion, the damaged portion of the plating or the film caused by processing, etc. is further improved. Therefore, r _{(Co + Ni) / P} is preferably 0.1 or more, more preferably 0.25 or more, and further preferably 0.8 or more. Further, when r _{(Co + Ni) / P} is 10 or less, the corrosion resistance is further improved. Therefore, r _{(Co + Ni) / P} is preferably less than 10, more preferably 6 or less, and even more preferably 2.4 or less.

[Production method]
Next, a method for manufacturing a surface-treated steel sheet according to an embodiment of the present invention will be described. The method for producing a surface-treated steel sheet in the present embodiment includes the following steps (I) and (II).
(I) Coating step of applying a surface treatment liquid to at least one surface of a molten Zn-Al-Mg-based alloy plated steel sheet at 25 ° C. or higher (II) After 1.0 seconds or more have elapsed after the coating, 20 ° C. Raising process to raise the temperature at a rate of / sec or more

-Fused Zn-Al-Mg-based alloy-plated steel sheet The molten Zn-Al-Mg-based alloy-plated steel sheet is not particularly limited, and any molten Zn-Al-Mg-based alloy-plated steel sheet can be used. The hot-dip Zn-Al-Mg-based alloy-plated steel sheet includes a hot-dip Zn-Al-Mg-based alloy-plated layer on at least one surface of the base steel sheet. Details of the base steel plate and the molten Zn-Al-Mg-based alloy plating layer will be described later.

-Coating The surface treatment liquid is applied to the surface of the molten Zn-Al-Mg alloy plated steel sheet. The coating can be carried out by any method without particular limitation. The coating can be performed by, for example, one or two or more selected from the group consisting of coating by a coater, coating by a dipping method, and coating by a spray. As the coater, for example, one or two or more selected from the group consisting of a roll coater (3-roll method, 2-roll method, etc.) and a squeeze coater can be used.

After the coating, the coating amount can be adjusted arbitrarily. The coating amount adjustment can be performed by, for example, one or both of the air knife method and the roll drawing method. By adjusting the coating amount, not only the coating amount of the surface treatment liquid can be controlled more accurately, but also the appearance and the film thickness can be made uniform.

The temperature of the molten Zn-Al-Mg based alloy plated steel sheet at the time of performing the coating is 25 ° C. or higher. When the temperature of the molten Zn-Al-Mg-based alloy-plated steel sheet to be coated is less than 25 ° C., the molten Zn-Al-Mg-based alloy-plated steel sheet may be heated to 25 ° C. or higher prior to the coating. Further, when the temperature of the molten Zn-Al-Mg based alloy plated steel sheet is already 25 ° C. or higher, the coating can be performed as it is (without heating). For example, the temperature of a steel sheet during hot-dip plating is generally about 400 ° C. Therefore, in the case of continuous coating after hot-dip plating, it is preferable to carry out the coating before the temperature of the steel sheet after hot-dip plating becomes less than 25 ° C. On the other hand, the upper limit of the temperature of the molten Zn-Al-Mg-based alloy-plated steel sheet at the time of performing the coating is not limited, but it is preferably 65 ° C. or lower in consideration of using an aqueous surface treatment liquid.

-Raising temperature After 1.0 seconds or more have passed after the coating, the temperature is raised at a rate of 20 ° C./sec or more. As a result, the applied surface treatment liquid is dried and a surface treatment film is formed. If the above conditions are not satisfied, the formation of the interfacial concentrated layer becomes insufficient, and as a result, corrosion resistance, blackening resistance, and sweat resistance are lowered.

The heating temperature (reaching plate temperature) in the temperature rise is not particularly limited. However, from the viewpoint of forming a film having excellent barrier properties, the heating temperature is preferably 60 ° C. or higher. Further, from the viewpoint of reducing the energy required for raising the temperature and preventing the occurrence of film defects due to excessive heating, the heating temperature is preferably 200 ° C. or lower. The heating temperature is more preferably 80 to 180 ° C., and even more preferably 100 to 160 ° C.

[Surface-treated steel sheet]
The surface-treated steel sheet of the present invention can be obtained by applying the above-mentioned surface treatment liquid to the surface of a molten Zn-Al-Mg-based alloy-plated steel sheet under the above-mentioned conditions, heating the temperature and drying. The surface-treated steel sheet thus obtained has an interface-concentrated layer in which a specific component is concentrated on the side of the surface-treated film in contact with the molten Zn-Al-Mg-based alloy plating layer. Therefore, in addition to suppressing corrosion of the plating layer, the synergistic effect of the interface-concentrated layer and the plating layer improves the corrosion resistance of the exposed portion of the base steel plate. Furthermore, the components of the interfacial concentrated layer function as a barrier against moisture and salt that have entered the surface treatment film, and delay the arrival at the plating surface, so that not only blackening in a moist environment but also after sweat adhesion occurs. It is possible to suppress blackening over time and improve blackening resistance and sweat resistance.

Next, the surface-treated steel sheet according to the embodiment of the present invention will be described more specifically. The surface-treated steel sheet in the present embodiment is the surface of at least one of the base steel sheet, the molten Zn-Al-Mg-based alloy plating layer formed on both sides of the base steel sheet, and the molten Zn-Al-Mg-based alloy plating layer. It is provided with a surface treatment film formed on the surface.

-Underground steel plate As the base steel plate, any steel plate can be used without particular limitation. As the base steel sheet, either a hot-rolled steel sheet or a cold-rolled steel sheet can be used. As the base steel sheet, for example, various steel sheets such as a low-carbon or ultra-low-carbon aluminum killed steel sheet and a high-silicon manganese-based high-strength steel sheet can be applied.

-Fused Zn-Al-Mg-based alloy plating layer A molten Zn-Al-Mg-based alloy plating layer is formed on both sides of the base steel plate. The molten Zn-Al-Mg based alloy plating layer is not particularly limited, and any one can be used. The amount of Al in the plating layer is preferably 1 to 20%. The amount of Mg in the plating layer is preferably 0.1 to 10%. The plating layer may contain Al and Mg, and the balance may have a component composition of Zn and unavoidable impurities, but is optionally selected from the group consisting of Ni, Si, and Fe1 Alternatively, it may contain 2 or more. When Ni is contained, the amount of Ni is preferably 10% or less. When Si is contained, the amount of Si is preferably 10% or less. When Fe is contained, the amount of Fe is preferably 15% or less. In other words, the molten Zn—Al—Mg based alloy plating layer has Al: 1 to 20% by mass, Mg: 0.1 to 10% by mass, Ni: 0 to 10% by mass, Si: 0 to 10% by mass, It may be a plating layer containing Fe: 0 to 15% by mass and having a composition of the balance Zn and unavoidable impurities. In addition, "%" in the description of the composition of the plating layer means "mass%" unless otherwise specified.

The structure of the molten Zn-Al-Mg-based alloy plating layer is not particularly limited, but it is preferable that at least the structure on the surface of the plating layer contains Zn-Al-Mg-based ternary eutectic in an area ratio of 1 to 50%. .. Further, it is more preferable that the structure of the entire plating layer satisfies the above conditions.

-Surface-treated film The surface-treated steel sheet in the present embodiment includes a surface-treated film on at least one surface of the molten Zn-Al-Mg-based alloy plating layer. The thickness of the surface treatment film is not particularly limited, but is preferably 3.0 μm or less from the viewpoint of economy. On the other hand, from the viewpoint of enhancing the barrier property of the film, the thickness of the film is preferably 0.3 μm or more, and more preferably 0.6 μm or more.

The surface treatment film in one embodiment of the present invention can contain the following (a) to (f) as components derived from the surface treatment liquid and the plating layer used. Further, the surface treatment film may further contain 1 or 2 or more arbitrarily selected from the following (g) to (i). Hereinafter, each component will be described.
(A) P
(B) N
(C) Si
(D) One or both of Co and Ni (e) Organic resin (f) Zn, Al, and Mg
(G) V
(H) Mo
(I) One or both of Zr and Ti

(A) P
P is an element having an effect of improving corrosion resistance and sweat resistance. As described above, a surface treatment film containing P is obtained by using a surface treatment liquid containing 1 or 2 or more selected from the group consisting of inorganic phosphoric acid, organic phosphoric acid and salts thereof as the P compound. be able to.

In the surface treatment film, it is preferable that a P compound that is sparingly soluble or insoluble in water and a water-soluble P compound coexist as a phosphate. When a water-soluble P compound coexists in the film, the water-soluble P compound is gradually eluted in a corrosive environment. As a result, it is possible to further suppress corrosion in the damaged portion exposed to the steel plate due to defects such as pinholes and processing, and the corroded portion starting from the cut end face.

P adhesion amount: 5 to 100 mg / m ²
The amount of P adhering to the surface-treated film is not particularly limited, but when the surface-treated film is formed by the above-mentioned method, it is usually 5 to 100 mg / m ² . When the amount of P adhered is 5 mg / m ² or more, in addition to the corrosion resistance of the flat surface portion, the corrosion resistance and the sweat resistance of the defective portion, the cut end face portion, the damaged portion of the plating or the film caused by processing, etc. are improved. Therefore, the amount of P adhered ^{is preferably 5 mg / m 2} or more, more preferably 7 mg / m ² or more, and further preferably 10 mg / m ² or more. On the other hand, when the amount of P adhered is 100 mg / m ² or less, the amount of P eluted from the surface treatment film is reduced and the blackening resistance is improved. Therefore, the amount of P adhered ^{is preferably 100 mg / m 2} or less, more preferably 70 mg / m ² or less, and even more preferably 50 mg / m ² or less.

(B) N
N is a component derived from N compounds (inorganic N compounds and amines) contained in the surface treatment liquid. By using a surface treatment liquid containing one or both of an inorganic N compound and an amine as the N compound, it is considered possible to firmly bond the interfacial concentrated layer formed on the plating surface with the plating surface.

(C) Si
The surface treatment film contains Si. The Si is a component derived from a Si compound (silica, tetraalkoxysilane and silane coupling agent) contained in the surface treatment liquid. The state of existence of the Si is not particularly limited, but for example, it may be present in the surface treatment film as an amorphous compound having a siloxane bond. Si contained as the compound having a siloxane bond can also serve as a skeleton for forming a surface treatment film together with an organic resin described later.

(D) Co, Ni
As described above, the blackening resistance can be improved by containing at least one of Co and Ni in the surface treatment film. As described above, a surface treatment film containing Co can be obtained by using a surface treatment liquid containing an inorganic Co compound. Similarly, by using a surface treatment liquid containing an inorganic Ni compound, a surface treatment film containing Ni can be obtained.

Total adhesion of Co and Ni: 5-100 mg / m ²
The contents of Co and Ni in the surface treatment film are not particularly limited, but when the surface treatment film is formed by the above-mentioned method, the total adhesion amount of Co and Ni is usually 5 to 100 mg / m ² . When the total adhesion amount is 5 mg / m ² or more, in addition to the corrosion resistance of the flat surface portion, the corrosion resistance of the defective portion, the cut end face portion, the damaged portion of the plating or the film caused by processing, etc. is improved. Therefore, the total adhesion amount ^{is preferably 5 mg / m 2} or more, more preferably 10 mg / m ² or more, and further preferably 15 mg / m ² or more. On the other hand, when the total adhesion amount is 100 mg / m ² or less, the corrosion resistance is improved. Therefore, the total amount of adhesion ^{is preferably 100 mg / m 2} or less, more preferably 80 mg / m ² or less, and even more preferably 60 mg / m ² or less.

(E) Organic Resin The organic resin is a component that serves as a skeleton for forming a surface treatment film together with the compound having a siloxane bond. Therefore, it is preferable that the surface-treated film contains the organic resin mentioned in the description of the surface-treated film.

(F) Zn, Al, Mg
As described above, when a surface treatment film is formed on a molten Zn-Al-Mg based alloy plated steel sheet using the above-mentioned surface treatment liquid, the Zn contained in the plating layer due to the etching effect of the surface treatment liquid, Al and Mg are inevitably incorporated into the surface treatment film. As a result, as will be described later, an interface-enriched layer containing Zn, Al, and Mg is formed on the plating layer side of the surface treatment film. Further, when a surface treatment liquid containing 1 or 2 or more selected from the group consisting of Zn compounds, Al compounds, and Mg compounds is used, Zn, Al, and Mg derived from those compounds are contained in the film. It is captured.

Zn, Al, and Mg are preferably 1 or 2 or more selected from the group consisting of oxides and hydroxides, and are preferably present in the surface treatment film, particularly in the interfacial concentrated layer. It is preferable that Zn, Al, and Mg are contained in the surface treatment film as both a compound that is sparingly soluble or insoluble in water and a compound that is water-soluble.

The above (a) to (f) are essential components of the present invention. Further, the surface treatment liquid may further contain 1 or 2 or more arbitrarily selected from the following (g) to (i).

(G) V
V in the surface treatment film usually exists evenly dispersed, but it elutes moderately in a corrosive environment and combines with zinc ions, which are plating components that also elute in a corrosive environment, to form a dense protective film. To form. As a result, it is possible to further enhance the corrosion resistance not only to the flat surface portion but also to the defective portion, the damaged portion of the plating or film caused by processing, and the corrosion progressing from the cut end face to the flat surface portion. When V is used, the amount of V attached to the surface treatment film is preferably ^{0.2 to 40 mg / m 2 in order to enhance the effect.}

(H) Mo
By adding the Mo compound to the surface treatment liquid, Mo can be contained in the surface treatment film. Since the surface-treated film contains Mo, the blackening resistance of the surface-treated steel sheet can be further improved. When Mo is used, the amount of Mo adhered to the surface treatment film ^{is preferably 0.1 mg / m 2} or more in order to enhance the effect. On the other hand, excessive addition of Mo may cause a decrease in corrosion resistance. Therefore, the amount of Mo adhered ^{is preferably 15 mg / m 2} or less.

(I) Zr, Ti
Zr and Ti are components that prevent the surface-treated film from becoming porous and have the effect of densifying the film, and thus have the effect of further improving the corrosion resistance by making it difficult for corrosion factors to permeate. When one or both of Zr and Ti are used, the total amount of Zr and Ti adhered is preferably ^{10 to 200 mg / m 2 in order to obtain the above effects.}

[Interfacial concentrated layer]
The surface treatment film obtained by the above-mentioned method has a thickness in which P, Zn, Al, Mg, N, and one or both of Co and Ni are concentrated on the side in contact with the molten Zn—Al—Mg-based alloy plating layer. It has an interfacially concentrated layer of 0.010 to 0.2 μm. The interfacial concentrated layer has a barrier effect for shielding corrosive factors such as water and oxygen. Further, it is considered that the components of the interface-enriched layer are incorporated into the corrosion product when the flat surface portion, the defective portion, the damaged portion due to processing, and the like are corroded in a corrosive environment, and the progress of the corrosion is delayed.

Interfacial concentrated layer thickness: 0.010 to 0.2 μm
The thickness of the interface-enriched layer is preferably 0.010 μm to 0.2 μm. If the thickness of the interfacial concentrated layer is less than 0.010 μm, the above-mentioned barrier effect and the effect of suppressing corrosion by corrosion products are insufficient. Therefore, the thickness of the interface-enriched layer is set to 0.010 μm or more, preferably 0.030 μm or more, and more preferably 0.050 μm or more. On the other hand, when the thickness of the interfacial concentrated layer exceeds 0.2 μm, the amount of eluted components from the concentrated layer increases, and the blackening resistance deteriorates. Therefore, the thickness of the interface-enriched layer is 0.2 μm or less, preferably 0.15 μm or less, and more preferably 0.12 μm or less.

Next, the present invention will be described in more detail based on Examples. The following examples show a suitable example of the present invention, and the present invention is not limited to the above examples.

(Example 1)
-Adjustment of surface treatment liquid First, each component shown in Tables 1 and 2 was dissolved in water as a solvent to prepare a surface treatment liquid. The types of each component used are as described below, and Tables 1 and 2 show the numbers of each component used. The concentration of each component was as shown in Tables 1 and 2.

(1) P compound 1: H ₃ PO ₄
2: K ₄ P ₂ O ₇
3: NaP ₃ O ₁₀
4: C ₂ H ₈ P ₂ O ₇

(2) N compound 1: diethanolamine 2: trimethylamine 3: nitric acid 4: ammonia

(3) Si Compound 1: Snowtex OS (Nissan Chemical Industries, Ltd.)
2: Snowtex NS (Nissan Chemical Industries, Ltd.)
3: AEROSIL 300 (Japan Aerosil Co., Ltd.)
4: γ-glycidoxypropyltrimethoxysilane 5: Tetraethoxysilane

(4) Inorganic Co compound 1: CoCO ₃
2: CoSO ₄
3: Co (CH ₃ COO) ₂

(4) Inorganic Ni compound 1: NiCO ₃
2: NiSO ₄
3: Ni (CH ₃ COO) ₂

(5) Organic Resin 1: Watersol CD-540P (DIC Corporation)
2: Boncourt EC-740EF (DIC Corporation)
3: Superflex 130 (Daiichi Kogyo Seiyaku Co., Ltd.)
4: Aron Melt PES-2005A30 (Toagosei Co., Ltd.)

(7) Zn compound 1: ZnCO ₃
2: ZnSO ₄
3: Zn (CH ₃ COO) ₂

(7) Al compound 1: Al ₂ (CO ₃ ) ₃
2: Al ₂ (SO ₄ ) ₃
3: Al (CH ₃ COO) ₃

(7) Mg compound 1: MgCO ₃
2: 0035 ₄
3: Mg (CH ₃ COO) ₂

(8) V Compound 1: Sodium metavanadate 2: Vanadyl sulfate 3: Metavanadyl acetylacetonate

(9) Mo compound 1: molybdic acid 2: sodium molybdate

(10) Zr compound 1: Zirconium potassium carbonate 2: Zirconium sulfate 3: Zirconium acetate

(10) Ti compound 1: Titanium acetylacetonate 2: Titanium sulfate

-Preparation of base steel sheet Next, a molten Zn-Al-Mg alloy plated steel sheet used as a base steel sheet (processed original plate) was prepared. Specifically, a hot-dip galvanized steel sheet having a hot-dip Zn-Al-Mg-based alloy plating layer having the composition described below on both sides was prepared. For each hot-dip galvanized steel sheet, the plate thickness was 0.8 mm, and the amount of plating adhesion was 70 g / m ² per side.

(Base steel plate)
1: Fused Zn-5% Al-0.5% Mg alloy plated steel sheet 2: Fused Zn-2.5% Al-3% Mg alloy plated steel sheet 3: Fused Zn-6% Al-3% Mg alloy plated steel sheet 4 : Fused Zn-11% Al-3% Mg alloy galvanized steel sheet

Next, the surface of the obtained hot-dip galvanized steel sheet was washed with pure water (deionized water) at 60 ° C. to remove stains on the surface. After the cleaning, the hot-dip galvanized steel sheet was dried to obtain a base steel sheet.

-Manufacture of surface-treated steel sheet Next, under the conditions shown in Tables 3 and 4, a surface-treated liquid is applied to the surface of the obtained base steel sheet, and then the temperature is raised to a predetermined temperature at a predetermined temperature rise rate. Then, a surface treatment film was formed. The temperature of the steel sheet when the surface treatment liquid was applied, the elapsed time from the application of the surface treatment liquid to the start of temperature rise, the rate of temperature rise, and the reached plate temperature were as shown in Tables 3 and 4. The types of base steel sheets used are also shown by numbers in Tables 3 and 4. The thickness of the surface treatment film was adjusted according to the amount of solid content (heat residue) contained in the surface treatment liquid, the treatment time, and the like.

-Evaluation of composition and film thickness For each of the obtained surface-treated steel sheets, the composition of the surface-treated film, the thickness of the interface-concentrated layer, and the thickness of the surface-treated film were measured by the following methods. The measurement results are shown in Tables 3 and 4.

(P adhesion amount)
The amount of P adhered was determined by quantifying P contained in the surface-treated film formed on the molten Zn—Al—Mg-based alloy-plated steel sheet with a fluorescent X-ray analyzer (manufactured by Rigaku Corporation: ZSX100e).

(Thickness of interfacial concentrated layer)
A surface-treated film was processed using a focused ion beam (FIB) to expose a cross section of the film. Next, using a transmission electron microscope (TEM: CM20FEG manufactured by Phillips) equipped with an energy dispersive X-ray analyzer, the cross section of the coating film is vertically line-analyzed, and C, P, Zn, Al, Mg, N. , And changes in the concentrations of Co and Ni components were measured. The concentration of C, which is a component mainly derived from the surface treatment film, decreases as it approaches the plating layer side, and the concentration of Zn, which is a component mainly derived from the plating layer, increases as it approaches the plating layer side. Therefore, the intersection of the measured concentration curves of C and Zn was defined as the interface between the plating layer and the surface-treated film. Further, when the P concentration at the interface was P _i , the area from the interface to the _{position where the P concentration was 1/5 P i} in the surface treatment film was regarded as the interface concentrated layer. The line analysis was performed at three locations, and the thickness of the interfacial concentrated layer was calculated from the average value.

(Thickness of surface treatment film)
The amount of film adhered (weight) per unit area was measured from the weight changes of the molten Zn-Al-Mg alloy-plated steel sheet before forming the surface-treated film and the surface-treated steel sheet after applying and drying the surface-treating liquid. .. Further, the density of the surface treatment film was measured from the weight and volume of the film obtained by drying only the surface treatment solution under the same conditions. The thickness of the surface-treated film was calculated from the amount and density of the film adhered.

-Evaluation of performance Next, the corrosion resistance of the flat surface portion, the corrosion resistance of the bent portion, the corrosion resistance of the cross-cut portion, the blackening resistance, and the sweat resistance of the obtained surface-treated steel sheet were evaluated by the following methods. The evaluation results are also shown in Tables 3 and 4.

(Corrosion resistance of flat surface)
Each surface-treated steel sheet was subjected to a salt spray test (JIS-Z-2371) in a flat state without pressing, and evaluated by the red rust resistant area after 2500 hours. The evaluation criteria are as follows.
◎ +: Red rust area ratio less than 5% and less than 5% even after 3500 hours ◎: Red rust area ratio less than 5% ○: Red rust area ratio 5% or more and less than 10% ○-: Red rust area ratio 10% or more, 25% Less than Δ: Red rust area ratio 25% or more, less than 50% ×: Red rust area ratio 50% or more

(Corrosion resistance of bent part)
Each sample was bent 180 ° so as to be sandwiched between rods (made of stainless steel) having a diameter of 2 mm, and narrowed down using a vise to create a damaged portion due to processing. A salt spray test (JIS-Z-2371-2000) was performed on the sample bent at 180 ° to evaluate the red rust generation state on the outside (front) side of the bending part after 1500 hours had passed. The evaluation criteria were as follows.
◎ +: No red rust is generated in the bent part, and no red rust is generated even after 2000 hours ◎: No red rust is generated in the bent part ○: Red rust generated area ratio in the bent part is less than 10% ○ −: Red rust in the bent part Area ratio of 10% or more and less than 40% Δ: Area ratio of red rust generated in the bent part is 40% or more and less than 80% ×: Area ratio of red rust generated in the bent part is 80% or more

(Cross-cut part corrosion resistance)
A salt spray test (JIS-Z-2371-2000) was performed using a flat plate test sample (70 mm x 150 mm) with cross-cut scratches that reach the base steel plate with a cutter after sealing the four sides with tape, and 1500 hours have passed. The state of red rust generation in the later cross-cut portion was evaluated. The evaluation criteria were as follows.
◎ +: No red rust is generated on the cross-cut part, and no red rust is generated even after 2000 hours. ◎: No red rust is generated on the cross-cut part. Area ratio of 10% or more and less than 40% Δ: Area ratio of red rust generated in cross-cut part is 40% or more and less than 80% ×: Area ratio of red rust generated in cross-cut part is 80% or more

(Black denaturation resistance)
Brightness (L value) change (ΔL = L value after test-L value before test) when each sample is allowed to stand in a constant temperature and humidity chamber controlled at a temperature of 80 ° C. and a relative humidity of 95% for 24 hours. ). The evaluation criteria are as follows. For the L value, SQ2000 manufactured by Nippon Denshoku Kogyo Co., Ltd. was used, and the measurement was performed in the SCI mode (including specular reflected light).
◎ +: -10 ≦ ΔL, and even after 96 hours, -10 ≦ ΔL
◎: -10 ≦ △ L
◯: -15 ≦ ΔL <-10
Δ: −20 ≦ ΔL <-15
X: ΔL <-20

(Sweat resistance)
10 μL of artificial sweat according to JIS-B7001-1995 was dropped on the surface of each sample, and a silicon rubber stopper was pressed against the dropping portion to prepare a portion contaminated with artificial sweat in a certain area. The test piece was allowed to stand in a constant temperature and humidity chamber controlled to an atmosphere of a temperature of 40 ° C. and a relative humidity of 80% for 4 hours, and then the appearance change of the contaminated part was evaluated. The evaluation criteria are as follows.
◎: No discoloration ○: Very slightly discolored ○ −: Slightly discolored △: Slightly blackened ×: Obviously blackened

(Example 2)
In Example 1 above, a surface treatment liquid containing an inorganic Co compound and not containing an inorganic Ni compound was used. In Example 2, the same experiment as in Example 1 was carried out using a surface treatment liquid containing an inorganic Ni compound without containing an inorganic Co compound. The compositions of the surface treatment liquids used are shown in Tables 5 and 6. Tables 7 and 8 show the manufacturing conditions, measurement results, and performance evaluation results. Other conditions were the same as in Example 1.

(Example 3)
An experiment similar to that of Example 1 was carried out using a surface treatment liquid containing both an inorganic Co compound and an inorganic Ni compound. The composition of the surface treatment liquid used is shown in Table 9. Table 10 shows the manufacturing conditions, measurement results, and performance evaluation results. Other conditions were the same as in Example 1.

As can be seen from the results of Examples 1 to 3, in the invention examples satisfying the conditions of the present invention, the performances of corrosion resistance, blackening resistance, and sweat resistance were all excellently evaluated. On the other hand, in the comparative example which does not satisfy the conditions of the present invention, at least one of the flat surface portion corrosion resistance, the processed portion corrosion resistance, the cut portion corrosion resistance, the blackening resistance, and the sweat resistance was inferior.

Claims (7)

A surface treatment liquid for molten Zn-Al-Mg alloy plated steel sheets.
(1) As the P compound, one or two or more selected from the group consisting of inorganic phosphoric acid, organic phosphoric acid, and salts thereof.
(2) As N compounds, one or both of inorganic N compounds and amines,
(3) As the Si compound, one or two or more selected from the group consisting of silica, tetraalkoxysilane, and a silane coupling agent.
(4) One or both of the inorganic Co compound and the inorganic Ni compound,
Contains (5) organic resin and (6) water,
The inorganic N compound is one or more selected from the group consisting of nitric acid, nitrite, nitrite, and ammonia.
The concentration of the P compound is 0.25% by mass to 5% by mass.
The total concentration of the inorganic Co compound and the inorganic Ni compound is 0.25% by mass to 5% by mass.
_{The mass ratio r N / P} of the N compound to the P compound is 0.10 to 10.
_{A surface treatment liquid having a mass ratio r Si / C} of the Si compound to the organic resin of 0.05 to 1.5. (7) The surface treatment liquid according to claim 1, further containing 1 or 2 or more selected from the group consisting of a Zn compound, an Al compound, and an Mg compound. (8) The surface treatment liquid according to claim 1 or 2, further containing a V compound. (9) The surface treatment liquid according to any one of claims 1 to 3, further containing one or both of molybdic acid and molybdate as a Mo compound. (10) The surface treatment liquid according to any one of claims 1 to 4, further containing one or both of a Zr compound and a Ti compound. The surface treatment liquid according to any one of claims 1 to 5 is applied to at least one surface of a molten Zn—Al—Mg-based alloy-plated steel sheet having a temperature of 25 ° C. or higher.
A method for producing a surface-treated steel sheet, in which the temperature is raised at a rate of 20 ° C./sec or more after 1.0 second or more has elapsed after the coating. A surface-treated steel sheet obtained by the method for producing a surface-treated steel sheet according to claim 6.