JP2020066793A - Surface treatment liquid and manufacturing method of surface-treated steel plate and surface-treated steel plate - Google Patents

Abstract

To provide a surface-treated steel plate having an excellence in corrosion resistance, blackening resistance, and perspiration resistance.SOLUTION: A surface treatment liquid for hot dip Zn-Al-Mg based alloy coated steel sheet includes (1) one or more P compounds selected from a group consisting of an inorganic phosphoric acid, an organic phosphorus acid, and their salts, (2) either or both of an inorganic N compound and an amine, as a N compound (3) one or more Si compounds selected from a group consisting of silica, tetraalkoxysilane, and silane coupling agent, (4) either or both of an inorganic Co compound and an inorganic Ni compound, (5) an organic resin, and (6) water, wherein concentration of the P compound is 0.25 mass% to 5 mass%, total concentration of the inorganic Co compound and the inorganic Ni compound is 0.25 mass% to 5 mass%, r, a mass ratio of the N compound to the P compound, is 0.10 to 10, and r, a mass ratio of the Si compound to the organic resin, is 0.05 to 1.5.SELECTED DRAWING: None

Description

  The present invention relates to a surface treatment solution for hot dip Zn-Al-Mg alloy plated steel sheet, and more particularly to a surface treatment solution capable of obtaining a surface treated steel sheet excellent in 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 treatment liquid. Furthermore, the present invention relates to a surface-treated steel sheet, and particularly to a surface-treated steel sheet excellent in corrosion resistance, sweat resistance, and blackening resistance.

  A Zn-based plated steel sheet having a Zn-based plating layer provided on the surface of the steel sheet has high corrosion resistance due to the sacrificial anticorrosive action of Zn, and is therefore used in an extremely wide range of fields. Among them, for the purpose of improving white rust resistance and red rust resistance, a chromate-treated steel sheet obtained by subjecting a Zn-based plating layer to a chromate treatment with a treatment liquid containing chromic acid, dichromic acid or a salt thereof as a main component. However, it has been generally used conventionally. However, in recent years, from the viewpoint of global environmental problems and the like, there is an increasing demand for pollution-free surface-treated steel sheets that do not rely on chromate treatment, so-called chromium-free treated steel sheets.

Therefore, many chromate-free treatment techniques have been proposed which suppress corrosion of zinc (white rust) in zinc-based plated steel sheets without using chromate treatment. Examples of the chromate-free processing technique include the following techniques (1) to (4) and techniques combining them.
(1) A technique that utilizes a passivation action of molybdic acid, tungstic acid, or the like, which is a compound of Mo or W belonging to the same Group 6 (group IVA in the old IUPAC formula) as Cr.
(2) A technique using a transition metal such as Ti, Zr, V, Mn, Ni, or Co, or a metal salt of a rare earth element such as La or Ce.
(3) A technology based on a chelating agent such as a polyhydric phenolcarboxylic acid such as tannic acid or a compound containing S or N.
(4) A technique of forming a polysiloxane film using a silane coupling agent.

  On the other hand, there are various types of Zn-based plated steel sheets, but among them, hot-dip Zn-Al alloy-plated steel sheets are superior in corrosion resistance to hot-dip Zn-plated steel sheets, so they are mainly used in home appliances, civil engineering, and construction materials. Widely used in. This hot-dip Zn-Al alloy-plated steel sheet shows excellent corrosion resistance even in a severe environment with a large amount of incoming salts, such as at the coast, but in recent years Zn was added to improve the appearance uniformity and corrosion resistance. The application of -Al-Mg-based alloy plated steel sheet is expanding.

  Therefore, in recent years, even in Zn-Al-Mg alloy plated steel sheets, there is an increasing demand for chromate-free surface treatment films. However, in a Zn-Al-Mg-based alloy-plated steel sheet in which the plating layer contains Al and Mg, blackening is remarkable, so that the surface-treated coating including the Zn-Al-Mg-based alloy plating layer has excellent corrosion resistance. In addition, it is required to have excellent blackening resistance.

  Here, the black discoloration is a phenomenon in which the plating layer surface is discolored black in a wet environment, and is considered to be caused by the change of zinc oxide formed 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, depriving zinc oxide of a part of oxygen and oxygen-deficient zinc oxide. The blackening becomes noticeable because it changes to.

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

  Patent Document 1 proposes a technique of 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 valve metal and a fluoride of valve metal.

  Patent Document 3 proposes a technique for forming a two-layer coating on the surface of a zinc-based plated steel sheet. The two-layer coating includes a first layer made of silica or alumina, and a second layer provided on the surface of the first layer and containing a valve metal oxide or hydroxide and a valve metal fluoride. .

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

  In patent document 5, the surface treatment liquid for Zn-Al type alloy plating steel plate containing V, Mo, P, Zr, Si and amine, and an organic resin is proposed. The surface treatment film formed by the surface treatment solution 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 consisting of.

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

  In Patent Documents 7 and 8, a surface treatment agent containing an organic resin in addition to an inorganic compound such as a Zr compound, a V compound, a fluoro complex of Ti, and an inorganic phosphorus compound on the surface of a Zn-Al-Mg alloy plated steel sheet. A method of forming an inorganic-organic composite film by applying and drying is proposed.

  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 is proposed.

JP, 2003-306777, A JP 2002-194558 A JP, 2004-232020, A JP, 2007-023309, A JP, 2005-117433, A JP, 2004-143549, A [Patent Document 1] Japanese Unexamined Patent Publication No. JP, 2016-088922, A Japanese Patent No. 5655981

  However, the conventional techniques including the above Patent Documents 1 to 9 have the following problems.

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

  On the other hand, in the technique proposed in Patent Document 6, since the first layer does not use a fluoride and a reaction layer is not formed, blackening is less likely to occur as compared with the method using a fluoride, but the plating layer and the surface treatment The adhesion of the coating becomes insufficient and the corrosion resistance decreases.

  Further, in the techniques proposed in Patent Document 7 and Patent Document 8, it is possible to make the film dense by combining various inorganic components and organic components, and to improve the corrosion resistance even with a single-layer film. However, in the above technique, since fluoride is used, it is unavoidable that the reduction in blackening resistance due to fluoride is reduced.

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

  By the way, the above-mentioned conventional techniques aim to delay the start of corrosion of the base steel sheet as a result 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, the corrosion of the base steel sheet is suppressed at the exposed part of the base steel sheet, for example, the part where the plating or coating is damaged by press forming or bending, or the cut end surface. I can't.

  In addition, in the Zn-Al-Mg alloy-plated steel sheet, in addition to the above-described phenomenon of blackening in a wet environment, when a person directly contacts the plated steel sheet, a phenomenon in which a touched portion is blackened with time is known. There is. This is because weakly acidic human sweat adheres to the steel plate and permeates the sweat component into the film, causing easily oxidized elements such as Al and Mg on the plating surface to oxidize with time and turn black. It is a phenomenon. The conventional surface-treated coating as described above can suppress blackening due to human sweat to some extent, but its sweat resistance is still at an insufficient level.

  As described above, the conventional chromate film-coated Zn-Al-Mg alloy plated steel sheet is insufficient in any or all of corrosion resistance, blackening resistance, sweat resistance, and has excellent corrosion resistance and blackening resistance. A 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 thereof 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 treatment film containing a specific component is formed on a Zn-Al-Mg alloy alloy plating layer, and the surface treatment film is specified on the side in contact with the molten Zn-Al-Mg alloy alloy plating layer. By forming the interface-enriched layer in which the component is concentrated, corrosion of the plating layer is suppressed, and the corrosion resistance of the exposed portion of the base steel sheet can be improved by the combined effect with the plating layer.

(2) Furthermore, the component of the interface thickening layer functions as a barrier against water and salt that have penetrated into the surface treatment film, and delays the arrival at the plating surface, so that not only blackening in a wet environment but also sweat It is possible to suppress black discoloration with time after adhesion and improve blackening resistance and sweat resistance.

  The present invention has been made on the basis of the above findings, and its gist configuration is as follows.

1. A surface treatment liquid for hot dip Zn-Al-Mg alloy plated steel sheet, comprising:
(1) As the P compound, one or more selected from the group consisting of inorganic phosphoric acid, organic phosphoric acid, and salts thereof,
(2) As the N compound, one or both of an inorganic N compound and an amine,
(3) As the Si compound, one 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) contains an 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,
The surface treatment liquid, wherein the mass ratio r _{Si / C} of the Si compound to the organic resin is 0.05 to 1.5.

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

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

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

5. (10) The surface treatment liquid according to any one of the above 1 to 4, 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 hot dip Zn-Al-Mg alloy-plated steel sheet at a temperature of 25 ° C or higher,
A method for producing a surface-treated steel sheet, comprising heating at a rate of 20 ° C./second 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 as described in 6 above.

  According to the present invention, a surface-treated steel sheet having both corrosion resistance, blackening resistance, and sweat resistance can be obtained.

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

[Surface treatment liquid]
The surface treatment liquid in one embodiment of the present invention is a surface treatment liquid for hot-dip Zn-Al-Mg alloy-plated steel sheet, contains the following (1) to (6) as essential components, and optionally the following. One or two or more selected from (7) to (10) can be contained. 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 a P compound (2) One or both of an inorganic N compound and an amine as an N compound (3) Si As the compound, one 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) Mo compounds as one or both of molybdic acid and molybdate (10) Zr compounds and Ti One or both of the compounds

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

  The inorganic phosphoric acid, organic phosphoric acid, and salts thereof are not particularly limited, and any compound can be used. As the inorganic phosphoric acid, phosphoric acid, primary phosphate, secondary phosphate, tertiary phosphate, pyrophosphate, pyrophosphate, tripolyphosphate, tripolyphosphate, phosphorous acid, phosphite , One or more selected from the group consisting of hypophosphorous acid and hypophosphite are preferably used. As the organic phosphoric acid, it is preferable to use phosphonic acid (phosphonic acid compound). As the phosphonic acid, it is preferable to use, for example, one or more selected from the group consisting of nitrilotrismethylenephosphonic acid, phosphonobutanetricarboxylic acid, methyldiphosphonic acid, methylenephosphonic acid, and ethylidenediphosphonic acid. . When the P compound is a salt, the salt is preferably a salt of a Group 1 to Group 13 element in the periodic table, more preferably a metal salt, and an alkali metal salt or an alkaline earth salt. 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 an interface 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. The formation of the interface concentrated layer strengthens the bond between the surface treatment film and the surface of the plating layer, and improves the adhesion of the surface treatment film.

(Preferable concentration range 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, not only the etching effect is insufficient, the adhesion with the plating interface is reduced, the corrosion resistance of the flat surface portion is deteriorated, and also the damage of the plating or film caused by the defective portion, the cut end surface portion, the processing, etc. Corrosion resistance and sweat resistance of the part are also reduced. It is preferably 0.35 mass% or more, and more preferably 0.50 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 of the formed film tends to be non-uniform. Further, the amount of P eluted from the surface-treated film increases, and the blackening resistance decreases. 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, as the N compound, one or more of an inorganic N compound and an amine. Like the above-mentioned P compound, 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 one or more selected from the group consisting of N oxo acid, N oxo acid salt, ammonia and ammonium salt. Nitric acid, nitrate, nitrous acid, nitrite, ammonia , And one or more selected from the group consisting of ammonium salts are more preferably used. As the amine, it is preferable to use at least one selected from the group consisting of primary amine, secondary amine, and tertiary amine. As the amine, any amine such as aliphatic amine, aromatic amine, or heterocyclic amine can be used, but aliphatic amine is preferably used. In particular, amines having one or more primary amino groups such as diethylenetriamine, hydroxyethylaminoethylamine, ethylaminoethylamine, methylaminopropylamine; secondary amines such as diethylamine, diethanolamine, N-methylethanolamine, N-ethylethanolamine. Primary amine; It is preferable to use one or two or more selected from tertiary amines such as trimethylamine.

(Preferable range of N compound concentration)
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 and the sweat resistance of the defective portion, the cut portion, and the damaged portion caused by processing are further improved. If 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 serves as 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 the Si compound, one or more selected from the group consisting of silica, tetraalkoxysilane, and a silane coupling agent.

  The silica is not particularly limited and any one 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 manufactured by Nissan Kagaku Co., 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 tetraalkoxysilane can be used without any particular limitation, but the general formula Si (OR) ₄ (wherein R represents the same or different alkyl groups having 1 to 5 carbon atoms) It is preferable to use the one represented by (4). As the tetraalkoxysilane, it is preferable to use, for example, one or more selected from the group consisting of tetramethoxysilane, tetraethoxysilane, and tetrapropoxysilane.

  The silane coupling agent is not particularly limited and any one can be used. Examples of the silane coupling agent include γ-glycidoxypropyltrimethoxysilane, γ-glycidoxypropylmethyldiethoxysilane, γ-glycidoxypropyltriethoxysilane, γ-mercaptopropylmethyldimethoxysilane, and It is preferable to use one or two or more selected from the group consisting of γ-mercaptopropyltrimethoxysilane.

  By including the above Si compound in the surface-treated film, the Si compound is dehydrated and condensed to form an amorphous film having a siloxane bond having a high barrier effect for shielding a corrosion factor. In addition, a film having a higher barrier property is formed by combining with an organic resin described later. Further, in a corrosive environment, a dense and stable corrosion product is formed in a defective portion or a damaged portion of the coating or film caused by processing, and also has an effect of suppressing the corrosion of the base steel sheet by a combined effect with the 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 Si compound concentration)
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 in the flat portion, the corrosion resistance in the defective portion, the cut portion, and the damaged portion caused by processing or the like. , And sweat resistance is further improved. Further, when the concentration of the Si compound is 9.5 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-treated film, it is possible to improve blackening resistance. This is considered to be because Co and Ni have the effect of delaying the elution of the water-soluble component from the film in a corrosive environment. Co and Ni are elements that are less likely to be oxidized than Zn, Al, and Mg. Therefore, by concentrating at least one of Co and Ni at the interface with the plating layer, the interface concentration layer serves as a barrier against corrosion, and as a result, blackening resistance is considered to be 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 incorporated into the film and taken into the interface concentrated layer. A cobalt salt is preferably used as the inorganic Co compound. As the cobalt salt, it is preferable to use one 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 taken into the interface concentrated layer. A nickel salt is preferably used as the inorganic Ni compound. As the nickel salt, it is more preferable to use one 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 mass%, not only the interface concentrated layer becomes non-uniform and the corrosion resistance of the flat surface portion lowers, but also the corrosion resistance of the defective portion, the cut end surface portion, the damaged portion of the plating or coating generated by processing, etc., lowers. . It is preferably 0.5% by mass or more, and more preferably 0.75% by mass or more. On the other hand, if it exceeds 5% by mass, the appearance of the formed film tends to be non-uniform, and the corrosion resistance decreases. It is preferably 4.0% by mass or less, and more preferably 0.30% by mass or less.

(5) Organic resin The organic resin is a component that serves as a skeleton for forming 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 any particular limitation, but an epoxy resin, a urethane resin, an acrylic resin, an acrylic silicon resin, an acrylic-ethylene copolymer, an acrylic-styrene copolymer is used. It is preferable to use one 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 an epoxy resin, an acrylic copolymer resin, an ethylene-acrylic acid copolymer resin, an alkyd resin, a polybutadiene resin, a phenol resin, a polyurethane resin, One 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 bisphenol A, bisphenol F, novolac, and the like, glycidyl etherified epoxy resin, bisphenol A added with propylene oxide, ethylene oxide, or polyalkylene glycol, and glycidyl etherified epoxy resin, and further aliphatic epoxy. Resins, alicyclic epoxy resins, polyether epoxy resins, etc. can be used.

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

  Examples of the acrylic resin include polyacrylic acid and copolymers thereof, polyacrylic acid esters and copolymers thereof, polymethacrylic acid and copolymers thereof, polymethacrylic acid esters and copolymers thereof, 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 and the like may be used.

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

  As the alkyd resin, for example, oil-modified alkyd resin, rosin-modified alkyd resin, phenol-modified alkyd resin, styrenated alkyd resin, silicon-modified alkyd resin, acrylic modified alkyd resin, oil-free alkyd resin, high molecular weight oil-free alkyd resin, etc. Can be mentioned.

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

  As the fluororesin, there is a fluoroolefin copolymer, for example, alkyl vinyl ether, synchroalkyl vinyl ether, carboxylic acid modified vinyl ester, hydroxyalkyl allyl ether, tetrafluoropropyl vinyl ether, etc. There is a copolymer obtained by copolymerizing with a fluoroolefin). When these fluororesins are used, excellent weather resistance and excellent hydrophobicity can be expected.

  Furthermore, from the viewpoint of corrosion resistance and workability, the organic resin is preferably a thermosetting resin. When using a thermosetting resin, it is preferable that the surface treatment liquid further contains a curing agent. Examples of the curing agent include urea resins (butylated 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 more selected from the group consisting of 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. If the concentration of the organic resin is 1% by mass or more, the skeleton of the film can be formed more sufficiently, so that in addition to corrosion resistance on the flat surface portion, corrosion resistance on defective portions, cut portions, and damaged portions caused by processing, and sweat resistance. The property 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.

  In addition, a solvent other than water may be further added to the surface treatment liquid in order to improve wettability and provide 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 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 comprising 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 containing no Cr, a surface treatment film containing no Cr (chrome-free surface treatment film) can be formed.

  Further, from the viewpoint of further improving blackening resistance, it is preferable that the surface treatment liquid does not contain an inorganic fluorine compound. By using the surface treatment liquid containing no inorganic fluorine compound, activation of the surface of the plating layer due to etching with the inorganic fluorine compound can be prevented, and blackening resistance can be further improved. It should be noted that the inorganic fluorine compound also includes an ionic fluorine compound (for example, fluoride ion, hexafluorotitanate ion, etc.) generated by dissociation of the inorganic fluorine compound. Above all, it is preferable not to contain a fluoride salt. Here, the fluoride salt also includes a salt of a fluorometal acid such as hexafluorotitanic acid. The surface treatment liquid of the present invention is allowed to contain a fluororesin.

  Moreover, the surface treatment liquid in another embodiment may further optionally contain one or more selected from the following (7) to (10).

(7) Zn compound, Al compound, Mg compound When a surface treatment film is formed on a hot dip Zn-Al-Mg alloy plated steel sheet using the surface treatment solution of the present invention, due to the etching effect of the surface treatment solution, Zn, Al, and Mg contained in the plating layer are inevitably incorporated into the surface treatment film. As a result, as described later, an interface concentrated layer containing Zn, Al, and Mg is formed on the plating layer side of the surface treatment film. However, in addition to incorporating these elements from the plating layer, one 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 one or more selected from the group consisting of salts, chlorides, oxides, and hydroxides. It 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. Examples of suitable Al compounds include one or more selected from the group consisting of aluminum sulfate, aluminum carbonate, aluminum chloride, aluminum oxide, and aluminum hydroxide. 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. The nitrate is included in the N compound. The phosphorus salt is included in the P compound.

(Suitable concentration range)
The total concentration of Zn compound, Al compound, and Mg compound in the surface treatment liquid is preferably 0.25% by mass to 5% by mass. When the content is 0.25% by mass or more, the interface concentrated layer can be formed more effectively and the corrosion resistance can be further improved. On the other hand, if it exceeds 5% by mass, the appearance of the formed film tends to be non-uniform, and the corrosion resistance of the flat part, the defective part, the plating or the damaged part of the film caused by processing may be deteriorated.

(8) V compound In order to contain V in the surface treatment film, a V compound can be added to the surface treatment liquid. V in the surface-treated film is usually dispersed uniformly, but it elutes moderately in a corrosive environment, and the plating components that also elute in a corrosive environment combine with zinc ions, etc. to form a dense protective film. To form. As a result, not only the flat portion, but also the defective portion, the damaged portion of the plating or the coating caused by processing, etc., and the corrosion resistance to the corrosion progressing from the cut end face to the flat portion can be further enhanced.

  Suitable V compound includes, 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. When the content is 0.05% by mass or more, the protective film is easily formed by elution in a corrosive environment, and the corrosion resistance of the defective portion, the cut end surface portion, the damaged portion of the coating or the coating film caused by processing is improved. On the other hand, if it exceeds 4% by mass, the appearance of the formed film tends to be non-uniform, and the blackening resistance also deteriorates.

(9) Mo Compound In order to contain Mo in the surface treatment film, one or both of molybdic acid and molybdate can be added to the surface treatment liquid as a Mo compound. By adding one or both of molybdic acid and molybdate to the surface treatment solution, the blackening resistance of the obtained surface-treated 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 compounds in the surface treatment liquid is preferably 0.01% by mass to 3% by mass. When it is 0.01% by mass or more, generation of oxygen-deficient zinc oxide is further suppressed, and blackening resistance is further improved. Further, when the content is 3% by mass or less, the life of the chemical liquid is further extended and the corrosion resistance is further improved.

(10) Zr compound, Ti compound In order to make the surface treatment film contain one or both of Zr and Ti, one or both of the Zr compound and 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 corrosion 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 more selected from the group consisting of titanium sulfate, titanium chloride, titanium hydroxide, titanium acetylacetonate, titanium octylene glycolate, and titanium ethyl acetoacetate is used. preferable. Among them, the organic titanium chelate compound is more preferable from the viewpoint that it has a high effect of densifying the coating when the surface treatment liquid is dried to form the coating. The nitrate is included in the N compound.

-Zr compound As said Zr compound, it is preferable to use 1 or 2 or more selected from the group which consists of zirconyl acetate, zirconyl sulfate, potassium zirconyl carbonate, and sodium zirconyl carbonate. The nitrate and ammonium salts 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. If it is 0.2% by mass or more, the effect of suppressing the penetration 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 surface portion, the damaged portion of the plating or the film caused by processing, etc. is improved. On the other hand, when the content is 20% by mass or less, the life of the chemical liquid can be further extended.

r _{N / P} : 0.10-10
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 the blackening resistance of the flat surface portion, the defective portion, the cut end surface portion, the processed portion are deteriorated. 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 above r _{N / P} is higher than 10, the adhesion between the surface treatment film and the plating becomes insufficient and not only the corrosion resistance of the flat surface portion decreases but also the plating and the coating film generated by the defective portion, the cut end surface portion, the processing, etc. Corrosion resistance and perspiration resistance of the damaged part also deteriorate. Therefore, r _{N / P is set} to 10 or less, preferably 7 or less, 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 coating caused by processing or the like, and the cut end face portion is deteriorated. Therefore, r _{Si / C} is set to 0.05 or more, preferably 0.1 or more, 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 a corrosion factor is easily infiltrated into the film, and the flat portion corrosion resistance, blackening resistance and sweat resistance are lowered. Therefore, r _{Si / C} is 1.5 or less, preferably 1.2 or less, 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, the surface treatment film is formed on the plating layer side. The interface concentrated layer is increased, and in addition to the corrosion resistance of the flat surface portion, the corrosion resistance of the defective portion, the cut end surface portion, and the damaged portion of the plating or the coating caused by the processing 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 further preferably 2.4 or less.

[Production method]
Next, a method for manufacturing the surface-treated steel sheet according to the embodiment of the present invention will be described. The method for manufacturing the surface-treated steel sheet according to the present embodiment includes the following steps (I) and (II).
(I) A coating step of coating a surface treatment liquid on at least one surface of a hot-dip Zn-Al-Mg-based alloy-plated steel sheet at 25 ° C or higher (II) 20 seconds after 20 seconds or more after the coating. Heating process to raise the temperature at a speed of at least 1 second

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

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

  After the coating, the coating amount can be arbitrarily adjusted. The coating amount can be adjusted by, for example, one or both of an air knife method and a 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 effect of making the appearance and the film thickness uniform can be obtained.

  The temperature of the hot-dip Zn-Al-Mg-based alloy plated steel sheet at the time of applying the coating is set to 25 ° C or higher. When the temperature of the hot-dip Zn-Al-Mg-based alloy plated steel sheet to be applied is less than 25 ° C, the hot-dip Zn-Al-Mg-based alloy plated steel sheet may be heated to 25 ° C or higher prior to the application. When the temperature of the hot-dip Zn-Al-Mg-based alloy plated steel sheet is already 25 ° C or higher, the coating can be applied as it is (without heating). For example, the temperature of the steel sheet during hot dipping is generally about 400 ° C. Therefore, when the application is continuously performed after the hot dip coating, the application is preferably performed before the temperature of the steel sheet after the hot dip is less than 25 ° C. On the other hand, the upper limit of the temperature of the hot-dip Zn—Al—Mg-based alloy plated steel sheet at the time of applying the coating is not limited, but considering the use of an aqueous surface treatment solution, it is preferably 65 ° C. or lower.

-Raising temperature After 1.0 second or more has passed after the coating, the temperature is raised at a rate of 20 ° C / second 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 thickening layer will be insufficient, and as a result, corrosion resistance, blackening resistance, and sweat resistance will be reduced.

  The heating temperature (achieved 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, further 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 solution to the surface of the hot-dip Zn-Al-Mg alloy-plated steel sheet under the above-mentioned conditions, and heating 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 coating which is in contact with the molten Zn-Al-Mg alloy plating layer. Therefore, in addition to suppressing the 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 sheet. Furthermore, the component of the interface concentrated layer functions as a barrier against water and salt that have penetrated into the surface treatment film, and delays the arrival at the plating surface, so that not only blackening in a wet environment but also after sweat adhesion It is possible to suppress black discoloration 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 according to the present embodiment has at least one surface of a base steel sheet, a molten Zn-Al-Mg-based alloy plating layer formed on both surfaces of the base steel sheet, and the molten Zn-Al-Mg-based alloy plating layer. And a surface treatment film formed on the.

-Base steel plate The base steel plate is not particularly limited, and any steel plate can be used. 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, various materials such as a low carbon or ultra low carbon aluminum killed steel sheet and a high silicon manganese-based high tensile steel sheet can be applied.

-Fused Zn-Al-Mg-based alloy plating layer A fused Zn-Al-Mg-based alloy plating layer is formed on both surfaces of the base steel sheet. The hot-dip Zn-Al-Mg-based alloy plating layer is not particularly limited, and any one can be used. The Al amount in the plating layer is preferably 1 to 20%. The amount of Mg in the plating layer is preferably 0.1-10%. The plating layer may contain Al and Mg, and the balance has a composition of Zn and inevitable impurities, but is optionally selected from the group consisting of Ni, Si, and Fe. Alternatively, it may contain two 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 Fe content is preferably 15% or less. In other words, the molten Zn-Al-Mg-based alloy plating layer has Al: 1 to 20 mass%, Mg: 0.1 to 10 mass%, Ni: 0 to 10 mass%, Si: 0 to 10 mass%, It may be a plating layer containing Fe: 0 to 15 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 at least the structure on the surface of the plating layer preferably contains a Zn-Al-Mg-based ternary eutectic in an area ratio of 1 to 50%. . Further, it is more preferable that the entire structure of the plated layer satisfies the above condition.

-Surface treatment film The surface treatment steel plate in this embodiment equips at least one surface of the above-mentioned fusion Zn-Al-Mg system alloy plating layer with a surface treatment film. The thickness of the surface treatment film is not particularly limited, but from the viewpoint of economy, it is preferably 3.0 μm or less. On the other hand, from the viewpoint of enhancing the barrier properties of the coating, the thickness of the coating is preferably 0.3 μm or more, 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-treated film may further optionally contain one or two or more 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 one 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 poorly water-soluble or insoluble P compound and a water-soluble P compound coexist as phosphates. When the water-soluble P compound coexists in the film, the water-soluble P compound gradually elutes in a corrosive environment. As a result, it is possible to further suppress defects such as pinholes and the like, the damaged portion exposed to the steel sheet due to processing, and the corrosion at the corroded portion starting from the cut end face.

P adhesion amount: 5 to 100 mg / m ²
The amount of P contained in the surface-treated film is not particularly limited, but when the surface-treated film is formed by the method described above, 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 on the flat surface portion, the corrosion resistance and the sweat resistance on the defective portion, the cut end surface portion, the damaged portion of the plating or the film caused by processing and the like are improved. Therefore, the amount of P attached 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 deposited is 100 mg / m ² or less, the amount of P eluted from the surface-treated film is reduced, and the blackening resistance is improved. Therefore, the amount of P attached is preferably 100 mg / m ² or less, more preferably 70 mg / m ² or less, and further preferably 50 mg / m ² or less.

(B) N
N is a component derived from the N compound (inorganic N compound and amine) contained in the surface treatment liquid. It is considered that by using the surface treatment liquid containing one or both of the inorganic N compound and the amine as the N compound, the interface concentrated layer formed on the plating surface can be firmly bonded to the plating surface.

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

(D) Co, Ni
As described above, the blackening resistance can be improved by including at least one of Co and Ni in the surface treatment film. As described above, the surface treatment film containing Co can be obtained by using the surface treatment liquid containing the 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 amount of Co and Ni deposited: 5 to 100 mg / m ²
The contents of Co and Ni in the surface-treated film are not particularly limited, but when the surface-treated film is formed by the method described above, the total amount of Co and Ni deposited 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 on the flat surface portion, the corrosion resistance on the defective portion, the cut end surface portion, and the damaged portion of the plating or the coating 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 adhesion amount is preferably 100 mg / m ² or less, more preferably 80 mg / m ² or less, and further preferably 60 mg / m ² or less.

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

(F) Zn, Al, Mg
As already described, when the surface treatment film is formed on the hot dip Zn-Al-Mg alloy plated steel sheet using the above-mentioned surface treatment solution, Zn contained in the plating layer due to the etching effect of the surface treatment solution, Al and Mg are inevitably incorporated into the surface treatment film. As a result, as described later, an interface concentrated layer containing Zn, Al, and Mg is formed on the plating layer side of the surface treatment film. When a surface treatment liquid containing one 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 present in the surface-treated film, particularly in the interface thickening layer, as one or more selected from the group consisting of oxides and hydroxides. It is preferable that Zn, Al, and Mg are contained in the surface treatment film as both a poorly soluble or insoluble compound in water and a water-soluble compound.

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

(G) V
V in the surface treatment film is usually dispersed uniformly, but it elutes moderately in a corrosive environment and combines with zinc ions of the plating component that also elutes in a corrosive environment to form a dense protective film. To form. As a result, not only the flat portion, but also the defective portion, the damaged portion of the plating or the coating caused by processing, etc., and the corrosion resistance to the corrosion progressing from the cut end face to the flat portion can be further enhanced. When V is used, the amount of V adhering to the surface-treated film is preferably 0.2 to 40 mg / m ^{2 in} order to enhance the effect.

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

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

[Interface concentrated layer]
The surface-treated film obtained by the method described above has a thickness in which one or both of P, Zn, Al, Mg, N, and Co and Ni are concentrated on the side in contact with the molten Zn-Al-Mg alloy plating layer. And an interface concentrated layer having a thickness of 0.010 to 0.2 μm. The interface thickening layer has a barrier effect for blocking corrosion factors such as water and oxygen. Further, it is considered that the components of the interface concentrated layer are taken into a corrosion product when a flat surface portion, a defective portion or a damaged portion due to processing corrodes in a corrosive environment, and delays the progress of corrosion.

Thickness of interface concentrated layer: 0.010 to 0.2 μm
The thickness of the interface concentrated layer is preferably 0.010 μm to 0.2 μm. When the thickness of the interface concentrated layer is less than 0.010 μm, the barrier effect and the corrosion inhibition effect by the corrosion product are insufficient. Therefore, the thickness of the interface concentrated 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 interface concentrated layer exceeds 0.2 μm, the amount of components eluted from the concentrated layer increases and the blackening resistance decreases. Therefore, the thickness of the interface concentrated layer is 0.2 μm or less, preferably 0.15 μm or less, more preferably 0.12 μm or less.

  Next, the present invention will be described more specifically based on Examples. The following example shows a preferred example of the present invention, and the present invention is not limited to the example.

(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 type of each component used is as described below, and Tables 1 and 2 show the numbers of each component used. Further, the concentrations of the respective components were 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 Co., Ltd.)
2: Snowtex NS (Nissan Chemical Co., 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: Boncoat EC-740EF (DIC Corporation)
3: Superflex 130 (Daiichi Kogyo Seiyaku Co., Ltd.)
4: Aron melt PES-2005A30 (Toa Gosei 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: MgSO 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: potassium zirconium carbonate 2: zirconium sulfate 3: zirconium acetate

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

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

(Base steel sheet)
1: Molten Zn-5% Al-0.5% Mg alloy-plated steel sheet 2: Molten Zn-2.5% Al-3% Mg alloy-plated steel sheet 3: Molten Zn-6% Al-3% Mg-alloy plated steel sheet 4 : Hot-dip Zn-11% Al-3% Mg alloy plated steel sheet

  Next, the surface of the obtained hot dip plated steel sheet was washed with pure water (deionized water) at 60 ° C. to remove the surface dirt. After the washing, the hot dip plated steel sheet was dried to obtain a base steel sheet.

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

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

(P adhesion amount)
The P adhesion amount was determined by quantifying P contained in the surface-treated coating formed on the hot dip Zn-Al-Mg alloy-plated steel sheet with a fluorescent X-ray analyzer (Rigaku Corporation: ZSX100e).

(Thickness of interface concentrated layer)
The surface-treated coating was processed using a focused ion beam (FIB) to expose the cross section of the coating. Then, using a transmission electron microscope (TEM: CM20FEG manufactured by Philips) equipped with an energy dispersive X-ray analyzer, the film cross section is subjected to line analysis in the vertical direction, 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 C and Zn concentration curves was defined as the interface between the plating layer and the surface treatment film. Further, the P concentration at the interface when the P _i, from the interface, up to the position P concentration is 1 / 5P _i in the surface treatment film in a deemed interface concentrated layer. The line analysis was performed at three points, and the thickness of the interface concentrated layer was calculated from the average value.

(Thickness of surface treatment film)
From the weight change of the hot dip Zn-Al-Mg alloy plated steel sheet before forming the surface treatment coating and the surface treatment steel sheet after applying and drying the surface treatment liquid, the coating adhesion amount (weight) per unit area was measured. . Further, the density of the surface-treated film was measured from the weight and volume of the film obtained by drying only the surface-treatment liquid under the same conditions. The thickness of the surface-treated film was calculated from the amount of film attached and the density.

-Evaluation of Performance Next, the surface treatment steel sheet thus obtained was evaluated for flat portion corrosion resistance, bending portion corrosion resistance, cross-cut portion corrosion resistance, blackening resistance, and sweat resistance by the following methods. The evaluation results are also shown in Tables 3 and 4.

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

(Corrosion resistance of bending part)
Each sample was bent by 180 ° so as to be sandwiched between rods (made of stainless steel) having a diameter of 2 mm, and narrowed with 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 °, and the red rust generation state outside the bent portion (front) after 1500 hours was evaluated. The evaluation criteria are as follows.
◎ +: No red rust on the bent part, and no red rust after 2000 hours ◎: No red rust on the bent part ○: Red rust on the bent part less than 10% ○-: Red rust on the bent part Occurrence area ratio is 10% or more and less than 40% △: Red rust occurrence area ratio of the bent part is 40% or more and less than 80% ×: Red rust occurrence area ratio of the bent part is 80% or more

(Corrosion resistance of cross cut part)
A salt water spray test (JIS-Z-2371-2000) was performed using a flat plate test sample (70 mm x 150 mm) in which four sides were sealed with tape and a cutter reached the base steel plate, and 1500 hours had passed. The state of occurrence of red rust in the subsequent cross cut portion was evaluated. The evaluation criteria are as follows.
◎ +: No red rust on the cross-cut part and no red rust after 2000 hours ◎: No red rust on the cross-cut part ○: Red rust area ratio of the cross-cut part is less than 10% ○-: Red rust on the cross-cut part Occurrence area ratio is 10% or more and less than 40% △: Red rust occurrence area ratio in the cross cut portion is 40% or more and less than 80% ×: Red rust occurrence area ratio in the cross cut portion is 80% or more

(Black resistance)
Change in lightness (L value) when each sample was left standing for 24 hours in a thermo-hygrostat controlled in an atmosphere of temperature: 80 ° C. and relative humidity: 95% (ΔL = L value after test−L value before test) ). The evaluation criteria are as follows. For the L value, SQ2000 manufactured by Nippon Denshoku Industries Co., Ltd. was used, and measurement was performed in SCI mode (including specular reflection light).
⊚ +: −10 ≦ ΔL, and after 96 hours, −10 ≦ ΔL
⊚: −10 ≦ ΔL
◯: −15 ≦ ΔL <−10
Δ: −20 ≦ ΔL <−15
×: ΔL <−20

(Sweat resistance)
On the surface of each sample, 10 μL of artificial sweat according to JIS-B7001-1995 was dropped, and a silicone rubber stopper was pressed against the dropping part to prepare a site contaminated with artificial sweat of a certain area. This test piece was allowed to stand for 4 hours in a thermo-hygrostat controlled in an atmosphere of temperature: 40 ° C. and relative humidity: 80%, and then the appearance change of the contaminated site was evaluated. The evaluation criteria are as follows.
◎: No discoloration ○: Very slight discoloration ○-: Slight discoloration △: Some black discoloration ×: Clear black discoloration

(Example 2)
In the above-mentioned Example 1, the surface treatment liquid containing the inorganic Co compound and not containing the inorganic Ni compound was used. In Example 2, the same experiment as in Example 1 was performed using a surface treatment liquid containing no inorganic Co compound but containing an inorganic Ni compound. The compositions of the surface treatment solutions 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)
The same experiment as in Example 1 was conducted using the surface treatment liquid containing both the inorganic Co compound and the inorganic Ni compound. Table 9 shows the composition of the surface treatment liquid used. Table 10 shows 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 corrosion resistance, blackening resistance, and sweat resistance were all excellent evaluations. On the other hand, in Comparative Examples that did not satisfy the conditions of the present invention, at least one of flat surface corrosion resistance, processed area corrosion resistance, cut area corrosion resistance, blackening resistance, and sweat resistance was inferior.

Claims (7)

A surface treatment liquid for hot dip Zn-Al-Mg alloy plated steel sheet, comprising:
(1) As the P compound, one or more selected from the group consisting of inorganic phosphoric acid, organic phosphoric acid, and salts thereof,
(2) As the N compound, one or both of an inorganic N compound and an amine,
(3) As the Si compound, one 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) contains an 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,
The surface treatment liquid, wherein the mass ratio r _{Si / C} of the Si compound to the organic resin is 0.05 to 1.5.   (7) The surface treatment liquid according to claim 1, further containing one or more selected from the group consisting of a Zn compound, an Al compound, and a 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 hot dip Zn-Al-Mg alloy-plated steel sheet at a temperature of 25 ° C or higher,
A method for producing a surface-treated steel sheet, comprising heating at a rate of 20 ° C./second 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.