JP7099424B2 - Zinc-based plated steel sheet with surface treatment film and its manufacturing method - Google Patents

Description

The present invention relates to a galvanized steel sheet with a surface-treated film and a method for producing the same.

Galvanized steel sheets are widely used in fields such as automobiles, home appliances, and building materials. Conventionally, for the purpose of improving corrosion resistance, a surface-treated steel sheet in which the surface of a zinc-based plated steel sheet is chromated with a treatment liquid containing chromic acid, dichromic acid or salts thereof as a main component has been widely used. However, due to recent global environmental problems, there is an increasing demand for the adoption of galvanized steel sheets with chromate-free surface treatment (hereinafter referred to as "chromate-free treated steel sheets"), and various chromates are used. Free-treated steel sheets have been developed and put into practical use.

It is essential that the chromate-free treated steel sheet has excellent corrosion resistance on a flat surface, but it also needs to satisfy various other performances. One of them is heat resistant cracking. Chromate-free treated steel sheets are often used by welding, and the types of welding are gas welding using the heat generated from combustion gas, arc welding using the electric discharge phenomenon, and electric resistance heat. Examples include spot welding and seam welding. In any of the above-mentioned welding methods, the welded portion is exposed to a temperature exceeding the melting point of the steel of about 2,000 ° C., and even in the vicinity of the welded portion, the temperature exceeds the melting point of the plating layer of about 500 ° C. There is a place. When the surface temperature of the chromate-free treated steel sheet exceeds 500 ° C. by welding, the plating layer melts and the shape of the surface of the plating layer changes due to the thermal expansion of the plating layer. Along with this, the shape of the surface-treated film on the plating layer also changes, and especially in the case of a film mainly composed of inorganic components whose thermal expansion rate is lower than that of the plating layer, it cannot follow the shape change due to the thermal expansion of the plating and the subsequent cooling shrinkage. , There was a problem that a tortoiseshell-shaped crack (hereinafter referred to as "crack") was generated after welding. In particular, the larger the amount of film adhered, the more remarkable cracks occur.

In the case of a film containing an organic resin, the organic resin is thermally decomposed by heating by welding, and the surface of the film may turn yellow depending on the type of organic resin such as phenol resin. There is a problem that the appearance is remarkably inferior, that is, the heat-resistant discoloration property is inferior.

Therefore, there is a demand for a chromate-free treated steel sheet that suppresses the above-mentioned phenomenon and has excellent corrosion resistance, heat-resistant discoloration, and heat-resistant cracking resistance on a flat surface. Furthermore, considering that chromate-free treated steel sheets are used in various applications such as automobiles, home appliances, and building materials, in addition to these, corrosion resistance of bent parts, corrosion resistance after alkaline degreasing, blackening resistance, paintability, and after alkaline degreasing. It is also required to have excellent coating properties and storage stability of the surface treatment liquid, and a chromate-free treated steel sheet that satisfies all of them is required.

Patent Document 1 describes a surface treatment using a surface treatment liquid containing a phenol resin having a specific skeleton, a cationic urethane resin, a silane coupling agent, an organic titanium compound, and a vanadium compound in a specific ratio. A technique for forming a film and imparting excellent corrosion resistance to a zinc-based plated steel sheet is disclosed. Further, Patent Document 2 further contains a molybdic acid compound, and Patent Document 3 discloses a technique using a surface treatment liquid further containing a molybdic acid compound and a fluorine compound.

Patent Document 4 describes a silane coupling agent having a glycidyl group on the surface of a hot-dip zinc-plated steel plate having an Al oxide layer formed on its surface, a tetraalkoxysilane, and a silane having a hydrolyzable group obtained from a phosphonic acid. A surface treatment liquid containing a compound, a zirconium carbonate compound, a vanadic acid compound, and water is applied to form a surface treatment film, and an organic polymer resin having an OH group and / or a COOH group on the upper layer is prevented. A technique for forming a second layer film containing a rust-added component to obtain a surface-treated steel plate having excellent corrosion resistance is disclosed.

Patent Document 5 describes a specific ratio of an organic phosphoric acid compound, a vanadic acid compound, a zirconium carbonate compound and a silane coupling agent to a titanium-containing aqueous solution obtained by mixing a specific titanium compound with a hydrogen peroxide solution. Disclosed is a surface-treated steel sheet in which a first-layer film is formed by a surface-treating liquid to which the compound is added in the above, and a second-layer film is formed by a surface-treatment solution containing an organic resin on the upper layer.

Japanese Unexamined Patent Publication No. 2010-236074 Japanese Unexamined Patent Publication No. 2011-179057 Japanese Unexamined Patent Publication No. 2012-067369 Japanese Unexamined Patent Publication No. 2017-066446 Japanese Unexamined Patent Publication No. 2011-195941

The techniques of Patent Documents 1 to 3 are excellent in heat-resistant discoloration resistance, corrosion resistance of flat surface portions, corrosion resistance of bent portions, blackening resistance, coating property after alkaline degreasing, and storage stability of surface treatment liquid. However, the surface-treated film formed on the zinc-based plated steel sheets of Patent Documents 1 to 3 has a polysiloxane bond formed by a condensation reaction of a silane compound as a main skeleton, and the amount of the film adhered is large. It is relatively high at 0.2 to 1.8 g / m ² . Therefore, when heated at a high temperature exceeding 500 ° C., cracks that can be visually confirmed are likely to occur due to the thermal decomposition of the polysiloxane bond, and the heat-resistant cracking property is insufficient. Further, when the phenol resin, the organic titanium compound, and the fluorine compound are contained, the yellowing after heating becomes remarkable as the heating time becomes longer. In Patent Documents 1 to 3, the heat-resistant discoloration property after heating the surface-treated steel sheet to 500 ° C. in 30 seconds and holding it for 30 seconds is evaluated, but the holding time is 5 minutes as in the present embodiment described later. However, the heat-resistant discoloration property is not sufficient when evaluated under the condition that the heating time is longer.

Since the surface-treated film formed in Patent Document 4 also has a polysiloxane bond formed by a condensation reaction of a silane compound as a main skeleton, the polysiloxane bond is thermally decomposed when heated at a high temperature exceeding 500 ° C. As a result, cracks that can be visually confirmed are likely to occur, and the heat-resistant cracking property is insufficient. In addition, since there are many hard components derived from the zirconium carbonate compound, sufficient coatability cannot be ensured. Furthermore, the corrosion resistance is not sufficient.

The technique of Patent Document 7 is excellent in corrosion resistance and coating property of a flat surface portion. However, heat-resistant cracking resistance, heat-resistant discoloration resistance, corrosion resistance of bent parts, blackening resistance, and the like are not taken into consideration, and their levels are not sufficient.

Therefore, in view of the above problems, the present invention does not contain a chromium compound in the surface treatment film, and has heat-resistant cracking resistance, heat-resistant discoloration resistance, corrosion resistance on flat surfaces, corrosion resistance on bent parts, corrosion resistance after alkaline degreasing, blackening resistance, and coating property. A method for manufacturing a zinc-based plated steel sheet with a surface-treated film, which can produce a zinc-based plated steel sheet with a surface-treated film that has excellent paintability after alkaline degreasing and has excellent storage stability of the surface-treated liquid. The purpose is to provide.

As a result of diligent studies, the present inventors have found a resin compound having a specific bisphenol skeleton, a cationic urethane resin emulsion, a silane coupling agent having a specific reactive functional group, and an organic titanium chelate compound. A first surface treatment liquid containing a tetravalent vanadium compound, a molybdic acid compound, and water is applied to the surface of a zinc-based plated steel plate, and then heat-dried at a predetermined temperature to adhere to one side. A first film having an amount of 0.02 to 0.19 g / m ² is formed, and then a second surface treatment liquid containing at least one organic resin selected from urethane resin and acrylic resin and water is applied. The above problem is solved by applying to the surface of the first film and then heating and drying at a predetermined temperature to form a second film having an adhesion amount of 0.4 to 3.0 g / m ² per side. I found that it could be solved.

式（Ｉ）中、ベンゼン環に結合しているＹ₁及びＹ₂は、それぞれ互いに独立に、水素原子、又は、以下の一般式（ＩＩ）若しくは（ＩＩＩ）により表されるＺ基であり、１ベンゼン環当たりのＺ基の置換数の平均値は０．２～１．０であり、ｎは２～５０の整数を表す。

式（ＩＩ）及び（ＩＩＩ）中、Ｒ₁、Ｒ₂、Ｒ₃、Ｒ₄及びＲ₅は、それぞれ互いに独立に、水素原子、炭素数１～１０のアルキル基、又は炭素数１～１０のヒドロキシアルキル基であり、Ａ^-は水酸イオン又は酸イオンを表す。 The present invention has been made based on such findings, and its gist structure is as follows.
[1] A resin compound (A) having a bisphenol skeleton represented by the following general formula (I) and a cation having at least one cationic functional group selected from a first to third amino groups and a quaternary ammonium base. A silane coupling agent (C) having at least one reactive functional group selected from an active hydrogen-containing amino group, an epoxy group, a mercapto group and a methacryloxy group, and an organic titanium chelate compound (D). ), The tetravalent vanadium compound (E), the molybdic acid compound (F), and water in a range satisfying the following conditions (1) to (5), the first surface treatment liquid (α). ) Is applied to the surface of a zinc-based plated steel plate, and then heated and dried at a plate temperature of 50 to 180 ° C. to form a first film having an adhesion amount of 0.02 to 0.19 g / m ² per side. The process of forming and
After that, a second organic resin (G) selected from a urethane resin and an acrylic resin and water are contained, and the solid content mass (G _s ) of the organic resin (G) is 50% or more. The surface treatment liquid (β) was applied to the surface of the first film, and then heated and dried at a plate temperature of 50 to 300 ° C., and the adhesion amount per side was 0.4 to 3.0 g / m ² . The process of forming the second film and
A method for manufacturing a galvanized steel sheet with a surface-treated film, which comprises.
(1) Solid mass (A _s ) of the resin compound (A), solid content mass (B _s ) of the cationic urethane resin emulsion (B), and solid content mass of the silane coupling agent (C). Ratio of solid content mass (B _s ) of the cationic urethane resin emulsion (B) to the total of (C _s ) [(B _s ) / {(A _s ) + (B _s ) + (C _s )}] Is 0.10 to 0.30
(2) The solid content mass (As) of the resin compound (A), the solid content mass (B _s ) of the cationic urethane resin emulsion ( _B ), and the solid content mass (C) of the silane coupling agent (C). The ratio of the solid content mass (C _s ) of the silane coupling agent (C) to the total of C _s ) [(C _s ) / {(As) + (B _s ) + (C _s )}] is ₀ . .60 to 0.85
(3) Ratio of solid content mass (C _s ) of the silane coupling agent (C) to titanium reduced mass (D _Ti ) of the organic titanium chelate compound (D) {(C _s ) / (D _Ti )} Is 50-70
(4) The ratio of the vanadium-equivalent mass (EV) of the _tetravalent vanadium compound (E) to the titanium-equivalent mass (D _Ti ) of the organic titanium chelate compound (D) {( _EV ) / (D _Ti ). } Is 0.30 to 0.50
(5) The solid content mass (As) of the resin compound (A), the solid content mass (B _s ) of the cationic urethane resin emulsion ( _B ), and the solid content mass (C) of the silane coupling agent (C). The ratio of the molybdenum-equivalent mass (F _Mo ) of the molybdenum acid compound (F) to the total of C _s ) [(F _Mo ) / {(As) + (B _s ) + (C _s )}] is ₀ . 003 to 0.030

In formula (I), Y ₁ and Y ₂ bonded to the benzene ring are hydrogen atoms independently of each other, or Z groups represented by the following general formulas (II) or (III). The average value of the number of Z group substitutions per benzene ring is 0.2 to 1.0, and n represents an integer of 2 to 50.

In formulas (II) and (III), R ₁ , R ₂ , R ₃ , R ₄ and R ₅ are independent of each other and have a hydrogen atom, an alkyl group having 1 to 10 carbon atoms, or an alkyl group having 1 to 10 carbon atoms, respectively. It is a hydroxyalkyl group, ^and A- represents a hydroxide ion or an acid ion.

[2] The first surface treatment liquid (α) further contains an acid component (I), and the first surface treatment liquid (α) further contains an acid component (I).
The solid content mass (As) of the resin compound (A), the solid content mass (B _s ) of the cationic urethane resin emulsion (B), and the solid content mass (C _s ) of the silane coupling agent (C) _. The ratio [(I _g ) / {( _{As) + (B s) + (C s ) }} ] of the mass (I _g ) of the acid component (I) to the total of the above is 0.10 or less. The method for manufacturing a zinc-based plated steel sheet with a surface-treated film according to [1].

[3] The first surface treatment liquid (α) further contains an aluminum dihydrogen dihydrogen rust preventive pigment (H ₁ ).
The ratio of the solid content mass (H _s 1) of the _{tripolyhydrohydric} acid dihydrogen aluminum-based rust preventive pigment (H ₁ ) to the vanadium-equivalent mass (EV) of the tetravalent vanadium compound (E) {(H _s 1) / ( The method for producing a zinc-based plated steel plate with a surface-treated film according to the above [1] or [2], wherein _EV )} is 3 to 300.

[4] The second surface treatment liquid (β) further contains an aluminum dihydrogen dihydrogen rust preventive pigment (H ₂ ).
The ratio of the solid content mass (H s 2) of the _{tripolyhydric} acid dihydrogen dihydrogen rust preventive pigment (H ₂ ) to the solid content mass (G _s ) of the organic resin (G) {(H _s 2) / (G _s ) } Is 0.05 to 1.00, the method for producing a zinc-based plated steel sheet with a surface-treated film according to any one of the above [1] to [3].

[5] At least one of the aluminum dihydrogen dihydrogen rust preventive pigments (H ₁ ) and (H ₂ ) tripolyphosphate is selected from aluminum dihydrogen tripolyphosphate and Zn, Mg, Si, and Ca. Including the additive elements of
The ratio of the total mass ( _HE ) of the added elements to the mass (HP) of phosphorus in each ( _{H 1} ) and ( _{H 2} ) {( _HE ) / (HP)} is 0.1 to 10. The method for producing a zinc-based plated steel sheet with a surface-treated film according to the above [3] or [4], which is 0.0.

[6] The second surface treatment liquid (β) further contains wax (W), and the second surface treatment liquid (β) further contains wax (W).
The ratio of the solid content mass (W _s ) of the wax (W) to the solid content mass (G _s ) of the organic resin (G) {(W _s ) / (G _s )} is 0.002 to 0.100. The method for manufacturing a zinc-based plated steel sheet with a surface-treated film according to any one of the above [1] to [5].

[7] A galvanized steel sheet with a surface-treated film manufactured by the method for producing a galvanized steel sheet with a surface-treated film according to any one of the above [1] to [6].

The method for producing a zinc-based plated steel plate with a surface-treated film of the present invention does not contain a chromium compound in the surface-treated film, and has heat-resistant cracking resistance, heat-resistant discoloration resistance, corrosion resistance on flat surfaces, corrosion resistance on bent parts, corrosion resistance after alkaline degreasing, and corrosion resistance. It is possible to manufacture a zinc-based plated steel plate with a surface treatment film that is excellent in blackening, paintability, and paintability after alkaline degreasing, and is also excellent in storage stability of the surface treatment liquid.

[Galvanized steel sheet]
The zinc-based plated steel sheet used in the present invention is an electric Zn plated steel sheet, a hot-dip Zn plated steel sheet, a Zn-Al plated steel sheet, a Zn-Al-Mg plated steel sheet, a Zn-Mg plated steel sheet, and a Zn- Fe-plated steel sheets, Zn—Ni-plated steel sheets and the like can be used. The plating method may be either electroplating or hot-dip plating. Further, in the above zinc-based plated steel sheet, for the purpose of improving the blackening resistance of the zinc-based plated steel sheet, a small amount of Ni or Co is added to the plating, or an acid or alkaline aqueous solution containing Ni, Co, Fe is used. , These metals may be deposited on the surface of a zinc-based plated steel plate. It is desirable that the plating adhesion amount of the above-mentioned galvanized steel sheet is 10 g / m ² or more per side from the viewpoint of ensuring corrosion resistance.

[First surface treatment liquid (α)]
The first surface treatment liquid (α) used in the present invention is a resin compound (A) having a specific bisphenol skeleton, a cationic urethane resin emulsion (B), and a silane coupling having a specific reactive functional group. It contains an agent (C), an organic titanium chelate compound (D), a tetravalent vanadium compound (E), a molybdic acid compound (F), and water, and optionally the acid component (I) and It may contain at least one of the aluminum dihydrogen dihydrogen rust preventive pigments (H ₁ ).

式（Ｉ）中、ベンゼン環に結合しているＹ₁及びＹ₂は、それぞれ互いに独立に、水素原子、又は、以下の一般式（ＩＩ）若しくは（ＩＩＩ）により表されるＺ基であり、１ベンゼン環当たりのＺ基の置換数の平均値は０．２～１．０であり、ｎは２～５０の整数を表す。 <Resin compound (A)>
The resin compound (A) contained in the first surface treatment liquid (α) has a bisphenol skeleton represented by the following general formula (I).

In formula (I), Y ₁ and Y ₂ bonded to the benzene ring are hydrogen atoms independently of each other, or Z groups represented by the following general formulas (II) or (III). The average value of the number of Z group substitutions per benzene ring is 0.2 to 1.0, and n represents an integer of 2 to 50.

Here, the average value of the number of substitutions of Z groups is a value obtained by dividing the total number of Z groups introduced by the total number of benzene rings (that is, 2n). In the present invention, when the Z group is selected as at least one of Y1 and Y2, the resin compound (A) is at least one cationic functional group selected from the first to third amino groups and the quaternary ammonium base. Since it has, it can be more stably dissolved in the first surface treatment liquid (α), and storage stability can be obtained. Further, in the present invention, the average degree of polymerization n is set to 2 to 50. If n is less than 2, the effect of imparting corrosion resistance is insufficient. On the other hand, when n exceeds 50, the stability of the resin compound (A) in the first surface treatment liquid (α) is lowered due to the decrease in water solubility, thickening, etc., and the storage stability is insufficient. Become. Preferably n is 2-8.

式（ＩＩ）及び（ＩＩＩ）中、Ｒ₁、Ｒ₂、Ｒ₃、Ｒ₄及びＲ₅は、それぞれ互いに独立に、水素原子、炭素数１～１０のアルキル基、又は炭素数１～１０のヒドロキシアルキル基である。アルキル基又はヒドロキシアルキル基の炭素数が１０を超えると、樹脂化合物（Ａ）を十分に水溶化することができず、第１の表面処理液中で不安定となる。Ｒ₁、Ｒ₂、Ｒ₃、Ｒ₄及びＲ₅の具体例としては、メチル、エチル、プロピル、ブチル、ヒドロキシエチル、２－ヒドロキシプロピル、ヒドロキシイソブチルなどを挙げることができる。Ａ^-は水酸イオン又は酸イオンを表す。酸イオンの具体例としては、酢酸イオン、リン酸イオン、蟻酸イオンなどを挙げることができる。

In formulas (II) and (III), R ₁ , R ₂ , R ₃ , R ₄ and R ₅ are independent of each other and have a hydrogen atom, an alkyl group having 1 to 10 carbon atoms, or an alkyl group having 1 to 10 carbon atoms, respectively. It is a hydroxyalkyl group. If the number of carbon atoms of the alkyl group or the hydroxyalkyl group exceeds 10, the resin compound (A) cannot be sufficiently solubilized and becomes unstable in the first surface treatment liquid. Specific examples of R ₁ , R ₂ , R ₃ , R ₄ and R ₅ include methyl, ethyl, propyl, butyl, hydroxyethyl, 2-hydroxypropyl, hydroxyisobutyl and the like. A ^- represents a hydroxide ion or an acid ion. Specific examples of the acid ion include acetate ion, phosphate ion, formic acid ion and the like.

The resin compound (A) represented by the general formula (I) is a bisphenol-formalin condensate, and the synthesis method thereof is not limited, but for example, formalin and amine are allowed to act on bisphenol A in the presence of an alkaline catalyst. It can be obtained by letting it.

<Cationic urethane resin emulsion (B)>
As long as the cationic urethane resin emulsion (B) contained in the first surface treatment liquid (α) has at least one cationic functional group selected from the first to third amino groups and the quaternary ammonium base. , The polyol component which is a constituent monomer component, the isocyanate component, and the polymerization method are not particularly limited. Examples of the cationic functional group include an amino group, a methylamino group, an ethylamino group, a dimethylamino group, a diethylamino group, a trimethylamino group, a triethylamino group and the like, and the first to third amino groups or the fourth. If it is a secondary ammonium base, it is not particularly limited. In addition to the cationic urethane resin emulsion (B), an anionic or nonionic urethane resin emulsion may be used in combination. In this case, in order to prevent the resin from agglomerating, the content of the cationic urethane resin emulsion (B) in the urethane resin emulsion is preferably 50% by mass or more.

<Silane coupling agent (C)>
The silane coupling agent (C) contained in the first surface treatment liquid (α) may have at least one reactive functional group selected from an active hydrogen-containing amino group, an epoxy group, a mercapto group and a methacryloxy group. There is no particular limitation. Particularly, a trialkoxysilane having three alkoxy groups is preferable. Specific examples include N- (2-aminoethyl) 3-aminopropyltrimethoxysilane, 3-aminopropyltrimethoxysilane, 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropylmethyldimethoxysilane, 3-methacryloxypropyltrimethoxysilane, 2- (3,4 epoxycyclohexyl) ethyltriethoxysilane, 3-mercaptopropyltrimethoxysilane, and the like can be used. By having at least one reactive functional group selected from an active hydrogen-containing amino group, an epoxy group, a mercapto group and a methacryloxy group, it firmly binds to the resin compound (A) and the cationic urethane resin (B) and has corrosion resistance. In particular, it has the effect of improving the corrosion resistance of the bent portion. On the contrary, when a silane coupling agent having no of these functional groups is used, the corrosion resistance of the bent portion becomes insufficient.

<Organic Titanium Chelate Compound (D)>
The organic titanium chelate compound (D) contained in the first surface treatment liquid (α) is not particularly limited, and examples thereof include titanium acetylacetonate, titanium octylene glycolate, titanium tetraacetylacetonate, and titanium ethylacetacetate. be able to. Inorganic salts such as titanium nitrate, titanium sulfate, titanium acetate, titanium phosphate, and titanium carbonate are not preferable because they do not exhibit the effect of improving corrosion resistance. When the organic titanium chelate compound (D) is dissolved in water and used, titanium is dissolved as a chelate complex, so a highly polar water-soluble solvent or peroxide that affects this complex is not added. Is preferable.

<Tetravalent vanadium compound (E)>
The tetravalent vanadium compound (E) contained in the first surface treatment liquid (α) is not particularly limited, and examples thereof include vanadyl sulfate, vanadyl dichloride, vanadyl phosphate, vanadyl oxalate, and vanadyl acetylacetonate. Can be done. The tetravalent vanadium compound (E) has an effect of improving the corrosion resistance of the flat surface portion. From the viewpoint of obtaining the highest effect, the vanadium compound (E) that produces VO ²⁺ (vanadyl) ions is preferable as the tetravalent vanadium compound (E). A pentavalent vanadium compound (for example, ammonium metavanadate) is not used in the present invention because it is too water-soluble, so that it has high elution from the film and is inferior in flat surface corrosion resistance and corrosion resistance after alkaline degreasing.

<Molybdic acid compound (F)>
The molybdic acid compound (F) contained in the first surface treatment liquid (α) is not particularly limited, and examples thereof include molybdenic acid, ammonium molybtensate, sodium molybdenate, potassium molybdenate, magnesium molybdenate, zinc molybdenate and the like. It can also be mentioned, such as phosphoribtenic acid, ammonium phospholibtenate, sodium phospholibtenate and the like. In the present invention, it is preferable to use one or more selected from these.

[(B _s ) / {(A _s ) + (B _s ) + (C _s )}]: 0.10 to 0.30
In the first surface treatment liquid (α), the solid content mass (As) of the resin compound (A), the solid content mass (B _s ) of the cationic urethane resin emulsion (B), and the silane coupling agent (C) _. ) To the total solid content mass (C _s ) of the cationic urethane resin emulsion (B) as a ratio of the solid content mass (B _s ) [(B _s ) / {(A _s ) + (B _s ) + (C) _s )}] needs to be 0.10 to 0.30. If the mass ratio is less than 0.10, the proportion of the urethane resin is too small, and the corrosion resistance of the bent portion deteriorates. Therefore, the mass ratio is 0.10 or more, preferably 0.12 or more. On the other hand, when the mass ratio exceeds 0.30, the corrosion resistance of the flat surface portion and the corrosion resistance after alkaline degreasing are inferior. Therefore, the mass ratio is 0.30 or less, preferably 0.28 or less.

[(C _s ) / {(A _s ) + (B _s ) + (C _s )}]: 0.60 to 0.85
In the first surface treatment liquid (α), the solid content mass (As) of the resin compound (A), the solid content mass (B _s ) of the cationic urethane resin emulsion (B), and the silane coupling agent (C) _. The ratio of the solid content mass (C _s ) of the silane coupling agent (C) to the total solid content mass (C _s ) of) [(C _s ) / {(As) + (B _s ) + (C _{s )} )}] It is necessary that it is 0.60 to 0.85. If the mass ratio is less than 0.60, the proportion of the silane coupling agent is too small, and the corrosion resistance of the flat surface portion, the corrosion resistance of the bent portion, and the corrosion resistance after alkaline degreasing are inferior. Therefore, the mass ratio is set to 0.60 or more, preferably 0.65 or more. On the other hand, when the mass ratio exceeds 0.85, the corrosion resistance of the bent portion and the storage stability of the first surface treatment liquid deteriorate. Therefore, the mass ratio is 0.85 or less, preferably 0.80 or less.

{(C _s ) / (D _Ti )}: 50-70
In the first surface treatment liquid (α), the ratio of the solid content mass (C _s ) of the silane coupling agent (C) to the titanium reduced mass (D _Ti ) of the organic titanium chelate compound (D) {(C _s ). ) / (D _Ti )} needs to be 50-70. When the mass ratio is less than 50, the corrosion resistance of the flat surface portion, the corrosion resistance of the bent portion, the corrosion resistance after alkaline degreasing, and the storage stability of the first surface treatment liquid are deteriorated. Therefore, the mass ratio is 50 or more, preferably 55 or more. On the other hand, when the mass ratio exceeds 70, the corrosion resistance of the flat surface portion and the corrosion resistance after alkaline degreasing are lowered. Therefore, the mass ratio is 70 or less, preferably 65 or less.

In calculating various mass ratios in the present invention, the solid content mass (C _s ) of the silane coupling agent (C) is hydrolyzed by alkoxysilane (R-Si (-OR ₁ ) ₃ ) and silanol. It is the mass in the state of (R-Si (-OH) ₃ ). This is because when the silane coupling agent is dissolved in water, most of it is hydrolyzed, and the alcohol generated by the hydrolysis is coated with the first surface treatment liquid (α) and dried to form the first film. This is because it volatilizes and does not act as an active ingredient.

{( _EV ) / (D _Ti )}: 0.30 to 0.50
In the first surface treatment liquid (α), the ratio of the vanadium-equivalent mass (EV) of the _tetravalent vanadium compound (E) to the titanium-equivalent mass (D _Ti ) of the organic titanium chelate compound (D) {(E). _V ) / (D _Ti )} needs to be 0.30 to 0.50. If the mass ratio is less than 0.30, the corrosion resistance of the flat surface portion deteriorates. Therefore, the mass ratio is 0.30 or more, preferably 0.35 or more. On the other hand, when the mass ratio exceeds 0.50, the corrosion resistance of the flat surface portion, the corrosion resistance of the bent portion, and the corrosion resistance after alkaline degreasing are lowered. Therefore, the mass ratio is 0.50 or less, preferably 0.48 or less.

[(F _Mo ) / {( _{As) + (B s) + (C s ) }} ]: 0.003 to 0.030
In the first surface treatment liquid (α), the solid content mass (As) of the resin compound (A), the solid content mass (B _s ) of the cationic urethane resin emulsion (B), and the silane coupling agent (C) _. ) To the total mass (C _s ) of the solid content of the molybdenum acid compound (F) in terms of molybdenum (F _Mo ) ratio [(F _Mo ) / {(A _s ) + (B _s ) + (C _s ) }] Is required to be 0.003 to 0.030. If the mass ratio is less than 0.003, the blackening resistance deteriorates. Therefore, the mass ratio is 0.003 or more, preferably 0.006 or more. On the other hand, when the mass ratio exceeds 0.030, the storage stability of the first surface treatment liquid is lowered. Therefore, the mass ratio is 0.030 or less.

<Acid component (I)>
The acid component (I) can be optionally added to the first surface treatment liquid (α) for the purpose of further improving the corrosion resistance. The acid component (I) improves the corrosion resistance, particularly the corrosion resistance of the bent portion, by etching and inactivating the plated surface. As the acid component (I), it is preferable to use a weak acid from the viewpoint of preventing pH shock (local and rapid pH change) at the time of addition, suppressing elution of cationic phenol and cationic urethane, and ensuring corrosion resistance. As the weak acid, for example, phosphoric acid, acetic acid, formic acid, hydrofluoric acid, fluoride and the like are preferable, and orthophosphoric acid is particularly preferable.

[(I _g ) / {( _{As) + (B s) + (C s ) }} ]: 0.10 or less When the acid component (I) is added to the first surface treatment liquid (α), the resin compound _Acid with respect to the total of the solid content mass (As) of (A), the solid content mass (B _s ) of the cationic urethane resin emulsion (B), and the solid content mass (C _s ) of the silane coupling agent (C). The ratio of the mass (I _g ) of the component (I) [(I _g ) / {(As) + (B _s ) + (C _s )}] is _preferably 0.10 or less. This is because if the mass ratio exceeds 0.10, the storage stability of the first surface treatment liquid is lowered. The mass (I _g ) of the acid component (I) in the present invention is the mass of the pure acid component (I). When the acid component (I) diluted with water or the like is used, the mass (I _g ) of the acid component (I) is the specific gravity (g / mL) of the acid component solution x 1000 (mL) x the acid component solution. It is determined by the purity (w / w%) of. The lower limit of the mass ratio is not particularly limited, but is preferably about 0.05 in order to obtain better corrosion resistance.

<Aluminum dihydrogen tripolyphosphate rust preventive pigment (H ₁ )>
An aluminum dihydrogen tripolyphosphate rust preventive pigment (H ₁ ) can be optionally added to the first surface treatment liquid (α) for the purpose of further improving the corrosion resistance of the scratched portion. The aluminum dihydrogen dihydrogen tripolyphosphate rust preventive pigment (H ₁ ) may be pure aluminum dihydrogen dihydrogen phosphate, but in order to further improve the corrosion resistance of scratches, aluminum dihydrogen tripolyphosphate and Zn, Mg, Si , And at least one additive element selected from Ca, and the total mass of the additive elements ( _HE ) with respect to the mass (HP) of phosphorus in the _{tripolyhydrohydric} dihydrogen aluminum-based rust preventive pigment (H ₁ ). ) With a ratio of {( _HE ) / ( _HP )} of 0.1 to 10.0 is more preferable.

{(H _s1 ) / ( _EV )}: 3 to 300
When an aluminum dihydrogen tripolyphosphate rust preventive pigment (H ₁ ) is added to the first surface treatment liquid (α), dihydrogen tripolyphosphate with respect to the vanadium-equivalent mass (EV) of the _tetravalent vanadium compound (E). The ratio of the solid content mass (H _s 1) of the aluminum-based rust preventive pigment (H ₁ ) {(H _s 1) / ( _EV )} is preferably 3 to 300. When the mass ratio is 3 or more, the effect of improving the corrosion resistance of the scratched portion can be sufficiently obtained, and it is preferably 20 or more. When the mass ratio is 300 or less, the corrosion resistance of the flat surface portion is not impaired, and it is preferably 200 or less.

<Water>
The water contained in the first surface treatment liquid (α) is used as a component of the resin compound (A), the cationic urethane resin emulsion (B), the silane coupling agent (C), and the organic titanium chelate compound (D). On the other hand, those having less influence are preferable. When Na, Cl, etc. contained as impurities in water remain in the film, the corrosion resistance may be lowered or the coatability may be lowered. Therefore, the water used is preferably one having few impurities, and for example, its electric conductivity is preferably less than 100 μS / cm. It is more preferably 50 μS / cm or less, still more preferably 10 μS / cm or less.

<Solid content concentration>
The solid content concentration of the first surface treatment liquid (α) is preferably 4 to 20% by mass as the solid content concentration when dried at 110 ° C. for 2 hours. This is because when the solid content concentration is in the range of 4 to 20% by mass, it becomes easy to secure the amount of adhesion of the first film, which will be described later, and the storage stability of the first surface treatment liquid is also excellent.

<Other ingredients>
A defoaming agent or a wettability improving agent may be added to the first surface treatment liquid (α), if necessary. The type of defoaming agent is not particularly limited, and for example, a silicone-based or fatty acid-based emulsion type can be used. The wettability improving agent lowers the surface tension of the surface treatment liquid, improves the wettability of the zinc-based plated steel sheet, and improves the appearance uniformity. Examples of the wettability improving agent include, but are not limited to, water-soluble solvents such as ethanol, butanol, and butyl cellosolve. Further, a wettability improving agent containing acetylene is suitable because it also has a defoaming effect.

Nitrate such as nickel nitrate and ammonium nitrate may be added to the first surface treatment liquid (α) for the purpose of further improving the blackening resistance. As mentioned above, nitric acid gives a pH shock, but nitrate does not give a pH shock.

The solid content mass of the other components is preferably 5% or less of the solid content of the first surface treatment liquid (α). This is because when the solid content mass of the other components exceeds 5%, the corrosion resistance of the flat surface portion deteriorates.

[Second surface treatment liquid (β)]
The second surface treatment liquid (β) used in the present invention contains at least one organic resin (G) selected from urethane resin and acrylic resin, water, and optionally aluminum dihydrogen dihydrogen tripolyphosphate. It may contain at least one of the anticorrosive pigment (H ₂ ) and the wax (W).

<Organic resin (G)>
The organic resin (G) contained in the second surface treatment liquid (β) is one or both of the urethane resin and the acrylic resin. By using at least one organic resin (G) selected from urethane resin and acrylic resin, it is possible to obtain excellent corrosion resistance and coating property of a flat surface portion while having excellent heat cracking resistance and heat discoloration property.

As the urethane-based resin, for example, an oil-modified polyurethane resin, a polyester-based polyurethane resin, a polyether-based urethane resin, a polycarbonate-based polyurethane resin, or the like can be used.

As the acrylic resin, for example, acrylic (co) obtained by (co) polymerizing one or more acrylic monomers among acrylic monomers such as acrylic acid, methacrylic acid, acrylic acid ester, methacrylic acid ester, and styrene. Polymers can be mentioned. Further, the acrylic (co) polymer may be urethane-modified and / or polyester-modified.

Further, a mixture of two or more of the urethane resin and the acrylic resin described above, an addition polymer, or the like can also be used.

As the organic resin (G), resins other than the above, such as epoxy resin and alkyd resin, have the effect of improving corrosion resistance like urethane resin and acrylic resin, but are not used because they deteriorate heat cracking resistance and thermal discoloration. ..

The solid content mass (G _s ) of the organic resin (G) is 50% or more with respect to the solid content of the second surface treatment liquid (β). When the solid content mass (G _s ) of the organic resin (G) is less than 50%, the effect of barriering corrosion factors is reduced, and the corrosion resistance of the flat surface portion, the corrosion resistance of the bent portion, and the corrosion resistance after alkaline degreasing are deteriorated. be. The upper limit of the solid content mass (G _s ) of the organic resin (G) is not particularly limited, but is 100% when the second surface treatment liquid (β) does not contain the following optional components or other components. ..

<Aluminum dihydrogen tripolyphosphate rust preventive pigment (H ₂ )>
An aluminum dihydrogen dihydrogen rust preventive pigment (H ₂ ) tripolypolyphosphate can be optionally added to the second surface treatment liquid (β) for the purpose of further improving the corrosion resistance of the flat surface portion and the corrosion resistance of the bent portion. As the rust-preventive pigment (H ₂ ) based on aluminum dihydrogen tripolyphosphate, pure aluminum dihydrogen dihydrogen phosphate may be used, but in order to further improve the corrosion resistance of the flat surface portion and the corrosion resistance of the bent portion, aluminum dihydrogen dihydrogen tripolyphosphate is used. It contains at least one additive element selected from Zn, Mg, Si, and Ca, and is an additive element with respect to the mass (HP) of phosphorus in the _{tripolyhydrohydric} dihydrogen aluminum-based rust preventive pigment (H ₂ ). It is more preferable to use one having a total mass ( _HE ) ratio {( _HE ) / ( _HP )} of 0.1 to 10.0.

{(H _s2 ) / (G _s )}: 0.05 to 1.00
When the aluminum dihydrogen dihydrogen tripolyphosphate rust preventive pigment (H ₂ ) is added to the second surface treatment liquid (β), the aluminum dihydrogen tripolyphosphate rust preventive against the solid content mass (G _s ) of the organic resin (G). The ratio of the solid content mass (H s 2) of the _rust pigment (H ₂ ) {(H _s 2) / (G _s )} is preferably 0.05 to 1.00. When the mass ratio is 0.05 or more, the corrosion resistance of the flat surface portion and the corrosion resistance of the bent portion can be further improved. When the mass ratio is 1.00 or less, the content of the organic resin (G) is ensured and the corrosion resistance is not impaired.

<Wax (W)>
Wax (W) can be optionally added to the second surface treatment liquid (β) for the purpose of ensuring lubricity. As the wax (W), it is preferable to use at least one selected from those having a melting point: 70 to 120 ° C., and specific examples thereof include polyethylene wax, polyethylene oxide wax, polypropylene wax, microcrystalline wax and the like. Be done. Lubricity can be obtained when the melting point is 70 ° C. or higher, and when the melting point is 120 ° C. or lower, lubricity can be obtained without being too hard.

The wax (W) is preferably an emulsion that is stably dispersed in water with an emulsifier, and preferably has a particle size of 0.08 to 0.30 μm. When the particle size is 0.08 μm or more, the desired lubricity effect can be obtained, and since the amount of the emulsifier used does not increase, the alkali resistance and coatability do not deteriorate. On the other hand, when the particle size is 0.30 μm or less, the specific gravity of the wax (W) does not decrease and floating separation in the second surface treatment liquid does not occur, so that the storage stability is excellent.

{(W _s ) / (G _s )}: 0.002 to 0.100
When the wax (W) is added to the second surface treatment liquid (β), the ratio of the solid content mass (W _s ) of the wax (W) to the solid content mass (G _s ) of the organic resin (G) {( W _s ) / (G _s )} is preferably 0.002 to 0.100. When the mass ratio is 0.002 or more, the effect of improving the lubricity can be sufficiently obtained, and from this viewpoint, 0.010 or more is more preferable. On the other hand, if the mass ratio is 0.100 or less, it is economically advantageous and does not further reduce the corrosion resistance, and from these viewpoints, 0.080 or less is more preferable.

<Water>
The water contained in the second surface treatment liquid (β) preferably has little effect on the organic resin (G). When Na, Cl, etc. contained as impurities in water remain in the film, the corrosion resistance may be lowered or the coatability may be lowered. Therefore, the water used is preferably one having few impurities, and for example, its electric conductivity is preferably less than 100 μS / cm. It is more preferably 50 μS / cm or less, still more preferably 10 μS / cm or less.

<Solid content concentration>
The solid content concentration of the second surface treatment liquid (β) is preferably 4 to 20% by mass as the solid content concentration when dried at 110 ° C. for 2 hours. This is because when the solid content concentration is in the range of 4 to 20% by mass, it becomes easy to secure the amount of adhesion of the second film, which will be described later, and the storage stability of the second surface treatment liquid is also excellent.

<Other ingredients>
A defoaming agent or a wettability improving agent may be added to the second surface treatment liquid (β), if necessary. The type of defoaming agent is not particularly limited, and for example, a silicone-based or fatty acid-based emulsion type can be used. The wettability improving agent lowers the surface tension of the surface treatment liquid, improves the wettability with respect to the first film, and improves the appearance uniformity. Examples of the wettability improving agent include, but are not limited to, water-soluble solvents such as ethanol, butanol, and butyl cellosolve. Further, a wettability improving agent containing acetylene is suitable because it also has a defoaming effect. Further, a rust preventive pigment such as Ca exchange silica or silicon oxide may be added to the second surface treatment liquid (β) for the purpose of further improving the corrosion resistance. The other components shall be added within a range in which the solid content mass (G _s ) of the organic resin (G) is 50% or more.

[Manufacturing method of galvanized steel sheet with surface treatment film]
In the method for producing a zinc-based plated steel plate with a surface-treated film of the present invention, the above-mentioned first surface-treated liquid (α) is applied to the surface of the zinc-based plated steel plate, and then heat-dried at a plate temperature of 50 to 180 ° C. Then, a step of forming a first film having an adhesion amount of 0.02 to 0.19 g / m ² per side, and then applying the above-mentioned second surface treatment liquid (β) to the first film. It comprises a step of applying to the surface and then heating and drying at a plate temperature of 50 to 300 ° C. to form a second film having an adhesion amount of 0.4 to 3.0 g / m ² per side.

As a method of applying the first surface treatment liquid (α) to the surface of the galvanized steel sheet, any of a coating method, a dipping method and a spraying method may be used. As the coating method, any method such as a roll coater (3-roll method, 2-roll method, etc.), a squeeze coater, a die coater, a bar coater, or the like may be used. Further, after the application of the first surface treatment liquid (α), it is also possible to adjust the coating amount, make the appearance uniform, and make the film thickness uniform by the air knife method or the roll drawing method.

Reach plate temperature: 50-180 ° C
After applying the first surface treatment liquid (α), heat drying is usually performed without washing with water. As the heating / drying means, a dryer, a hot air furnace, a high frequency induction heating furnace, an infrared furnace, or the like can be used. It is desirable to perform heat drying so that the ultimate plate temperature is 50 to 180 ° C. When the reaching plate temperature is lower than 50 ° C., a large amount of water remains in the first film, and the corrosion resistance becomes insufficient. Further, if the reaching plate temperature is higher than 180 ° C., defects may occur in the first film during drying, and the corrosion resistance may decrease.

Adhesion amount per side of the first film: 0.02 to 0.19 g / m ²
In the present invention, the amount of adhesion of the first film per surface needs to be 0.02 to 0.19 g / m ² . When the adhesion amount is less than 0.02 g / m ² , the corrosion resistance of the flat surface portion and the corrosion resistance after alkaline degreasing are deteriorated, and the blackening resistance is further deteriorated. Therefore, the adhesion amount is 0.02 g / m ² or more, preferably 0.03 g / m ² or more. On the other hand, if the adhesion amount exceeds 0.19 g / m ² , the heat-resistant cracking property and the heat-resistant discoloration property deteriorate. Therefore, the adhesion amount is 0.19 g / m ² or less, preferably 0.15 g / m ² or less.

In the present invention, in order to obtain excellent heat-resistant cracking resistance and heat-resistant discoloration, the amount of the first film adhered is reduced, but on the other hand, this works disadvantageously with respect to corrosion resistance. Therefore, in the present invention, in order to obtain excellent corrosion resistance in addition to heat cracking resistance and heat discoloration resistance, a second film is formed on the first film.

The method of applying the second surface treatment liquid (β) to the surface of the first film is the same as the application of the first surface treatment liquid (α).

Reach plate temperature: 50-300 ° C
After applying the second surface treatment liquid (β), heat drying is usually performed without washing with water. As the heating / drying means, a dryer, a hot air furnace, a high frequency induction heating furnace, an infrared furnace, or the like can be used. It is desirable to perform heat drying so that the ultimate plate temperature is 50 to 300 ° C. When the temperature of the reaching plate is lower than 50 ° C., a large amount of solvent such as water remains in the second film, and the corrosion resistance and the coatability after alkaline degreasing become insufficient. Further, if the reaching plate temperature is higher than 300 ° C., there may be a problem of deterioration of corrosion resistance due to denaturation of the organic resin (G) or the like.

Adhesion amount per side of the second film: 0.4 to 3.0 g / m ²
In the present invention, the adhesion amount of the second film per one side needs to be 0.4 to 3.0 g / m ² . If the adhesion amount is less than 0.4 g / m ² , the corrosion resistance becomes insufficient. Therefore, the adhesion amount is 0.4 g / m ² or more, preferably 0.6 g / m ² or more. On the other hand, if the adhesion amount exceeds 3.0 g / m ² , the paintability becomes insufficient. Therefore, the adhesion amount is set to 3.0 g / m ² or less, preferably 2.0 g / m ² or less.

Further, the optimum heating time in each step is appropriately selected depending on the type of galvanized steel sheet used and the like. From the viewpoint of productivity and the like, about 0.1 to 60 seconds is preferable, and about 1 to 30 seconds is more preferable.

The present invention includes a galvanized steel sheet having the first film and the second film as described above on both sides or one side. Therefore, as the form of the present invention, for example, there are the following.
(1) One side: Plating layer-First film-2nd film, One side: Plating layer (2) One side: Plating layer-First film-2nd film, One side: Plating layer-Known phosphate-treated film, etc. 3) Both sides: Plating layer-1st film-2nd film (4) One side: Plating layer-1st film-2nd film, 1st side: Plating layer-1st film (5) 1st side: Plating layer-1st film- Second film, one side: Plating layer-Second film

[Action of the present invention]
In the first and second surface treatment liquids of the present invention, it is presumed that each component has the following actions, but the present invention is not limited by these speculations.

The main components of the first surface treatment liquid (α) are the resin compound (A), the cationic urethane resin emulsion (B), and the silane coupling agent (C), and the skeleton of the first film is formed by these main components. Will be done. Since the resin compound (A) has bisphenol as the skeleton of phenol, the first film becomes stronger, and the adhesion to the galvanized steel sheet and the corrosion resistance of the flat surface portion are improved. Further, the resin compound (A) becomes insoluble in an alkaline solution by combining with the cationic functional group (the above-mentioned general formula (II) or (III)) of the cationic urethane resin emulsion (B), and has alkali resistance. The first film is obtained.

The resin compound (A) tends to be yellowish by heating (decreased heat-resistant discoloration), and the first film becomes hard, which tends to cause a decrease in corrosion resistance of the bent portion. Therefore, in the present invention, by blending the cationic urethane resin emulsion (B) with the first surface treatment liquid (α), the above-mentioned heat-resistant discoloration property is improved and the corrosion resistance of the bent portion is reduced by alleviating the heat curing. Can be improved.

While the cationic urethane resin emulsion (B) has the above-mentioned effect, the barrier property of the corrosive factor is lowered and the corrosion resistance of the flat surface portion is impaired, particularly when the amount of adhesion of the first film is small. Therefore, in the present invention, the silane coupling agent (C) is added to the first surface treatment liquid (α) for the purpose of ensuring corrosion resistance and heat-resistant discoloration of the flat surface portion. Since the alkoxy group at the terminal of the silane coupling agent (C) is hydrolyzed to generate an active silanol group (Si—OH), it contributes to the improvement of adhesion to a galvanized steel sheet or a topcoat coating film. Further, a part of the silane coupling agent (C) is dehydrated and condensed to form a siloxane bond (Si—O—Si), which is continuously polymerized (polysiloxane formation: —Si—O—Si—O). -Si-). As a result, the structure becomes extremely stable, and excellent corrosion resistance of the flat surface portion can be obtained.

As described above, by blending the resin compound (A), the cationic urethane resin emulsion (B), and the silane coupling agent (C) in a desired ratio, the adhesion to the galvanized steel sheet and the corrosion resistance of the flat surface portion can be improved. It is considered that the corrosion resistance of the bent portion can be improved. However, it cannot be said that the corrosion resistance is still sufficient with the above-mentioned main components alone. Therefore, in the present invention, the organic titanium chelate compound (D) is used as an essential component in addition to the above main components. It is presumed that the organic titanium chelate compound (D) acts as a catalyst for promoting polysiloxane formation when the first surface treatment liquid is dried to form the first film. As a result, the barrier property of the first film is dramatically improved, and the corrosion resistance of the flat surface portion and the corrosion resistance after alkaline degreasing are improved.

In order to obtain the above effects, as described above, a predetermined amount of the organic titanium chelate compound (D) determined according to the amount of the silane coupling agent (C) is required. If the amount is small, the desired effect cannot be obtained, and if the amount is excessive, the amount of polysiloxane increases too much to form a hard and brittle first film, and the corrosion resistance of the bent portion is lowered. Ideally, the polysiloxane formation by the organic titanium chelate compound (D) is promoted during the formation of the first film, but the polysiloxane formation is also promoted during the storage of the first surface treatment liquid. If the content is excessive, thickening and gelation proceed, and a stable first surface treatment liquid cannot be obtained.

Further, in the first surface treatment liquid (α) in the present invention, the tetravalent vanadium compound (E) is also an essential component. In the present invention, the tetravalent vanadium compound (E) acts as an inhibitor of corrosion, such as passivating zinc during plating, and improves corrosion resistance in a flat portion. The tetravalent vanadium compound (E), particularly vanadyl ion [VO ²⁺ ] having one oxygen, is basically difficult to elute even in a moist environment, and exhibits an inhibitory effect while staying in the first film. This provides excellent corrosion resistance. The inventors speculate that such an effect is achieved by a synergistic effect with Ti, which also exists as a cation.

Further, in the first surface treatment liquid (α) in the present invention, the molybdic acid compound (F) is also an essential component. In a galvanized steel sheet, regardless of whether it is an electroplated steel sheet or a hot-dip plated steel sheet, a blackening phenomenon in which the plated surface becomes black in a corrosive environment is likely to occur. Especially in hot-dip zinc-based plated steel sheets, when Mg or Al is added to improve the corrosion resistance or the adhesion between the plating layer and the base steel sheet, these elements are added to the interface between the plating layer and the base steel sheet and the plating layer. It thickens on the surface layer and promotes blackening, making it blacker than pure zinc-plated steel sheets. The cause of the blackening phenomenon in zinc-based plated steel sheets is not yet clear, but zinc oxide generated on the outermost surface of the plated layer is deprived of oxygen and changed to oxygen-deficient zinc oxide, or zinc corrosion (zinc corrosion). It is said that oxygen-deficient zinc oxide is generated on the plating surface due to insufficient supply of oxygen in the process of (oxidation), and these appear black.

In the present invention, excellent blackening resistance can be obtained by introducing the molybdic acid compound (F) into the first film. Molybdenum is a transition metal and combines with oxygen to form molybdenum oxides (MoO ₂ , MoO ₃ ) and molybdenum acid (MoO ₄ ^2- ). In the present invention, a part of molybdenum acid (MoO ₄ ^2- ) is changed to an oxide of molybdenum (MoO ₂ , MoO ₃ ) under high temperature and high humidity or in a corrosive environment, thereby forming the surface of the zinc oxide layer. Since oxygen is appropriately supplied, it is considered that oxygen-deficient zinc oxide is less likely to be formed. The inventors presume that such a mechanism improves the blackening resistance.

Further, in the present invention, by adding the aluminum dihydrogen dihydrogen rust preventive pigment (H ₁ ) to the first surface treatment liquid (α), the corrosion resistance of the scratched portion can be improved. Aluminum dihydrogen tripolyphosphate rust preventive pigment (H ₁ ) is a sparingly soluble substance, but when it comes into contact with corrosion factors such as water, it gradually elutes and forms a chelate with the metal ions eluted by corrosion. It has the effect of forming a non-conductor film of phosphate by combining with the metal eluted by corrosion. In particular, in the vicinity of the scratched part where the base steel plate is exposed, the tripolyhydrohydric acid aluminum dihydrogen rust preventive pigment (H ₁ ) present in the first film also comes into contact with the corrosion factor, so that it gradually elutes and Zn elutes due to corrosion. In combination with such as, a precipitate of phosphate is formed on the exposed part. Further, this aluminum dihydrogen dihydrogen phosphate rust preventive pigment (H ₁ ) is compounded with a part of the tetravalent vanadium compound (E) by compound addition with the tetravalent vanadium compound (E) and eluted together. And a precipitate of vanadium-containing phosphate is formed in the exposed part. Then, the inventors presume that the vanadium-containing phosphate precipitated in the exposed portion improves the corrosion resistance of the scratched portion due to its high corrosion suppressing effect.

The above first surface treatment liquid (α) is applied to the surface of a galvanized steel sheet so that the amount of adhesion per surface is 0.02 to 0.19 g / m ² , and the surface is heated and dried. The first film formed by using the first surface treatment liquid (α) is said to be prone to cracks because the polysiloxane bond is thermally decomposed and the first film shrinks when heated to a high temperature exceeding 500 ° C. by welding or the like. Conceivable. It is considered that by reducing the adhesion amount of the first film to 0.19 g / m ² or less, the shrinkage stress is relaxed, cracks are less likely to occur, and the heat-resistant cracking property is improved. Further, since the amount of adhesion of the first film is reduced, the color of the first film after discoloration becomes lighter, so that the heat-resistant discoloration property is also improved. However, if the adhesion amount of the first film is 0.19 g / m ² or less, the corrosion resistance is insufficient. Therefore, in order to secure corrosion resistance while maintaining heat cracking resistance and heat discoloration resistance, a second film is formed on the first film by using the second surface treatment liquid (β).

The main component of the second surface treatment liquid (β) is at least one organic resin (G) selected from urethane resin and acrylic resin, and the skeleton of the second film is formed by these main components. The organic resin (G) does not crack or discolor even when heated to more than 500 ° C., and has a strong bonding force with the first coating film and the topcoat coating film. Therefore, by using it as the second coating film, heat-resistant discoloration occurs. It is possible to improve the property, heat-resistant cracking property and paintability. Further, in a corrosive environment, the corrosion resistance can be improved by forming a dense second film having an excellent barrier property against corrosion factors and suppressing excessive elution of the components of the first film.

Further, in the present invention, by adding the aluminum dihydrogen dihydrogen rust preventive pigment (H ₂ ) to the second surface treatment liquid (β), the corrosion resistance of the flat surface portion and the corrosion resistance of the bent portion can be further improved. can. The aluminum dihydrogen tripolyphosphate rust preventive pigment (H ₂ ) gradually elutes when it comes into contact with corrosion factors such as water, and has the action of forming a chelate with the metal ions eluted by corrosion and is combined with the metal eluted by corrosion. It has the effect of forming a non-conductor film of phosphate. When an aluminum dihydrogen dihydrogen rust preventive pigment (H ₂ ) tripolyphosphate is added to the second film, it is considered that excellent corrosion resistance of the flat surface portion and corrosion resistance of the bent portion can be obtained by these synergistic actions. However, if the elution rate of the aluminum dihydrogen dihydrogen rust preventive pigment (H ₂ ) tripolyphosphate is too fast, all of it is washed away before it binds to the eluted metal ions, so that the effect of improving corrosion resistance cannot be obtained. On the other hand, if the elution rate of aluminum dihydrogen dihydrogen tripolyphosphate is too slow, corrosion progresses before a chelate or a non-conductor film is formed, so that the effect of improving corrosion resistance cannot be obtained. In the present invention, aluminum dihydrogen tripolyphosphate is added to the silanol group of the silane coupling agent (C) existing on the surface of the first film and the OH group and / or COOH group of the organic resin (G) contained in the second film. It is considered that the corrosion resistance is improved by binding with each other and optimizing the dissolution rate.

However, if the amount of the aluminum dihydrogen dihydrogen rust preventive pigment (H ₂ ) to the organic resin (G) is too large, the aluminum dihydrogen tripolyphosphate rust preventive pigment (H ₂ ) will be excessively eluted. Therefore, the effect of improving the corrosion resistance of the flat surface portion and the corrosion resistance of the bent portion cannot be obtained. On the other hand, when the amount of the tripolyhydrohydric acid dihydrogen aluminum-based rust preventive pigment (H ₂ ) is too small with respect to the organic resin (G), the rust preventive effect of the tripolyhydrohydrogen dihydrogen aluminum-based rust preventive pigment (H ₂ ) is sufficient. It is not exhibited, and the effect of improving the corrosion resistance of the flat surface portion and the corrosion resistance of the bent portion cannot be obtained.

Further, the aluminum dihydrogen dihydrogen rust preventive pigment (H ₂ ) containing tripolyline contains at least one additive element selected from Zn, Mg, Si, and Ca in addition to aluminum dihydrogen tripolyphosphate. The ratio of the total mass ( _HE ) of the added elements to the mass (HP) of phosphorus in the aluminum dihydrogen acid rust preventive pigment ( _{H 2} ) is 0.1 to {( _HE ) / ( _HP )}. When using 10.0, (i) the additive element is incorporated into the phosphate film to form a protective film with higher barrier properties, and (2) zinc due to the pH buffering action of the additive element. It is presumed that the corrosion resistance of the flat surface portion and the corrosion resistance of the processed portion are further improved by the two actions of lowering the corrosion rate of the hydrogen.

[Galvanized steel sheet]
Various galvanized steel sheets shown in Table 1 were prepared.

[Preparation of surface treatment liquid]
The components of the first surface treatment liquid (α) include the resin compound (A) shown in Tables 2A and 2B, the urethane resin emulsion (B) shown in Table 3, and the silane coupling agent (C) shown in Table 4. Titanium compound (D) shown in Table 5, vanadium compound (E) shown in Table 6, molybdic acid compound (F) shown in Table 7, acid component (I) shown in Table 8, and aluminum dihydrogen tripolyphosphate shown in Table 10. A rust preventive pigment (H ₁ ) was used. These components were mixed at the blending ratios shown in Table 12, and deionized water was added so that the solid content concentration when dried at 110 ° C. for 2 hours was 10% by mass. A surface treatment solution was prepared. As the deionized water, ion-exchanged water having an electric conductivity of 10 μS / cm was used.

The components of the second surface treatment liquid (β) include the organic resin (G) shown in Table 9, the aluminum dihydrogen dihydrogen rust preventive pigment (H ₂ ) shown in Table 10, and the wax (W) shown in Table 11. ) An emulsion was used. These components were mixed at the blending ratios shown in Table 13, and deionized water was added so that the solid content concentration when dried at 110 ° C. for 2 hours was 10% by mass, and a second of various levels was added. A surface treatment solution was prepared. As the deionized water, ion-exchanged water having an electric conductivity of 10 μS / cm was used.

[Manufacturing of galvanized steel sheet with surface treatment film]
The surface of the galvanized steel sheet shown in Table 1 is subjected to alkaline degreasing treatment, washed with water and dried, and then the first surface treatment liquid (α) shown in Table 12 is applied to one side by a bar coater and dried by heating without washing with water. Then, the first film was formed. Next, the second surface treatment liquid (β) shown in Table 13 was applied onto the first film by a bar coater and dried by heating without washing with water to form the second film. The amount of adhesion of the first film and the second film per surface was adjusted according to the coating conditions (solid content bar count of each treatment liquid, etc.). Table 14 shows the manufacturing conditions of each level. Here, the amount of adhesion of each of the first film and the second film was determined as follows. First, the amount of Si of the silane coupling agent (C) blended in the first film was quantified by a fluorescent X-ray analyzer, and the amount of adhesion of the first film was determined by converting from this amount of Si. Next, the amount of carbon in the first film was converted from the amount of adhesion of the first film. Then, the amount of carbon in the first film and the entire second film is quantified by a fluorescent X-ray analyzer, the amount of carbon in the first film is removed from this, the amount of carbon in the second film is obtained, and converted from this. The amount of adhesion of the second film was determined.

[quality evaluation]
The following evaluations (1) to (9) and (11) were performed on the samples collected from the manufactured galvanized steel sheets with surface treatment film of each level. In addition, the following evaluations (10) were performed on the first and second surface treatment liquids of each level. These results are shown in Table 15. Evaluations Δ and × were rejected due to insufficient performance.

(1) Heat-resistant cracking resistance Each sample was heated to a plate temperature of 500 ° C. in 30 seconds using an infrared image furnace, held for 5 minutes, and then naturally allowed to cool to room temperature, and the surface appearance was visually observed. The evaluation criteria are as follows.
(Evaluation criteria)
◎: No cracks ○: Very slight cracks △: Narrow cracks on the entire surface ×: Wide cracks in addition to narrow cracks on the entire surface

(2) Heat-resistant discoloration Each sample was heated to a plate temperature of 500 ° C. in 30 seconds using an infrared image furnace, held for 5 minutes, and then naturally allowed to cool to room temperature, and the surface appearance was visually observed. The evaluation criteria are as follows.
(Evaluation criteria)
◎: No discoloration ○: Very slightly brownish ○-: Slightly brownish △: Discolored to brown ×: Discolored to brown

(3) Corrosion resistance on flat surface A salt spray test based on JIS-Z-2371-2000 was carried out for each sample. The corrosion resistance of the flat surface was evaluated by the area ratio of white rust after 240 hours. The evaluation criteria are as follows.
(Evaluation criteria)
◎: White rust occurrence area rate 0%
○ +: White rust occurrence area rate less than 5% ○: White rust occurrence area rate 5% or more and less than 10% ○-: White rust occurrence area rate 10% or more, less than 20% △: White rust occurrence area rate 20% or more , Less than 40% ×: White rust occurrence area rate 40% or more

(4) Corrosion resistance of bent portion Each sample was bent 90 ° so as to be sandwiched between rods (made of stainless steel) having a diameter of 3 mm. This bent sample was subjected to a salt spray test according to JIS-Z-2371-2000. The corrosion resistance of the bent portion was evaluated by the area ratio of white rust generated on the outer surface of the bent portion after 120 hours had passed. The evaluation criteria are as follows.
(Evaluation criteria)
◎: Area ratio of white rust generated in the bent part is 0%
○ +: White rust generation area ratio of the bending part is less than 5% ○: White rust generation area ratio of the bending part is 5% or more and less than 10% ○-: White rust generation area ratio of the bending part is 10% or more, 40 % Δ: White rust generation area ratio of bending part 40% or more, less than 80% ×: White rust generation area ratio of bending part 80% or more

(5) Corrosion resistance after alkaline degreasing The alkaline degreasing agent CL-N364S (manufactured by Nihon Parkerizing Co., Ltd.) was dissolved in pure water at a concentration of 20 g / L and heated to 60 ° C. Each sample was immersed in this alkaline solution for 2 minutes, taken out, washed with water and dried. Each sample was subjected to a salt spray test according to JIS-Z-2371-2000. The corrosion resistance after alkaline degreasing was evaluated by the area ratio of white rust generated after 72 hours. The evaluation criteria are as shown in (3) above.

(6) Corrosion resistance to scratches Each sample was cross-cut with an NT cutter (A300 type manufactured by NT Co., Ltd.), and then a salt spray test conforming to JIS-Z-2371-2000 was carried out. The corrosion resistance of the wound was evaluated by the maximum rust width on one side after 120 hours. The evaluation criteria are as follows. If white rust was generated on the entire test piece and the rust width could not be determined, it was marked with x.
(Evaluation criteria)
◎: Rust width less than 1 mm ○ +: Rust width 1 mm or more and less than 2 mm ○: Rust width 2 mm or more and less than 5 mm △: Rust width 5 mm or more and less than 10 mm ×: Rust width 10 mm or more

(7) Blackening resistance Changes in brightness (L value) when each sample was allowed to stand for 24 hours in a constant temperature and humidity controller controlled to an atmosphere of temperature: 80 ° C. and relative humidity: 95% (ΔL = after test) L value-L value before the test) was calculated. The evaluation criteria are as follows. The L value was measured in SCI mode (including specular reflected light) using SR2000 manufactured by Nippon Denshoku Kogyo Co., Ltd.
(Evaluation criteria)
⊚: -6 ≦ △ L
◯: −10 ≦ ΔL <-6
Δ: -14≤ΔL <-10
×: ΔL <-14

(8) Paintability Each sample is coated with Delicon (registered trademark) # 700 (manufactured by Dai Nippon Toryo Co., Ltd.), which is a melamine alkyd paint, and baked at 130 ° C for 30 minutes to form a coating film with a film thickness of 30 μm. Formed. Then, the sample was immersed in boiling water for 2 hours, and immediately cut to reach the base steel plate having a grid pattern (10 × 10 pieces, 1 mm interval) was made. Further, a 5 mm extrusion process was performed using an Eriksen extruder so that the cut portion was on the outer (front) side, and the coating film was attached and peeled off with an adhesive tape, and the peeled area of the coating film was measured. The evaluation criteria are as follows. The Eriksen extrusion conditions were based on JISZ-2247-2006, with a punch diameter of 20 mm, a die diameter of 27 mm, and a drawing width of 27 mm.
(Evaluation criteria)
◎: No peeling ○ +: Peeling area less than 3% ○: Peeling area 3% or more and less than 10% ○-: Peeling area 10% or more and less than 20% Δ: Peeling area 20% or more and less than 50% ×: Peeling area 50% or more

(9) Coating property after alkaline degreasing The same alkaline degreasing as in (5) above was performed, and the same coating property test as in (8) above was performed on the sample. The evaluation criteria are the same as in (8).

(10) Storage stability Each of the prepared surface treatment liquids shown in Tables 12 and 13 was stored in a constant temperature bath at 40 ° C. for 30 days, then taken out and stirred. The appearance of each surface treatment liquid was visually inspected and evaluated. The evaluation criteria are as follows.
(Evaluation criteria)
⊚: No change ○: A very small amount of precipitate was observed Δ: A small amount of precipitate was observed or the viscosity became slightly high ×: A large amount of precipitate was observed or gelled.

(11) Lubricity A disk-shaped test piece having a diameter of 100 mm was cut out from each sample and molded into a cup shape under the conditions of a punch diameter: 50 mm, a die diameter: 51.91 mm, and a wrinkle pressing force: 1 ton. The appearance of the drawn surface (outside of the side surface of the cup) of the molded product was visually inspected, and the degree of damage and the degree of blackening were evaluated. The evaluation criteria are as follows.
(Evaluation criteria)
◎: Almost no change over the entire surface, the appearance is uniform ○ +: Very slight blackening occurs, but the appearance is uniform ○: Scratches and blackening occur a little, and the appearance is clearly uneven ○-: Local Scratches and blackening occur, and the appearance is clearly uneven Δ: Severe scratches and blackening occur mainly in the corners ×: Cracked without being able to be molded

As shown in Table 15, in each of the examples of the present invention, excellent heat cracking resistance, heat discoloration resistance, corrosion resistance of flat surface portion, corrosion resistance of bent processed portion, corrosion resistance after alkaline degreasing, blackening resistance, coating property, and after alkaline degreasing. It has paintability and storage stability. On the other hand, in the comparative example, any of the above characteristics cannot be sufficiently obtained. In addition, No. of Comparative Example. Regarding 46 to 48, 55 to 57, 62, 63, since the type of the resin compound (A) or the urethane resin emulsion (B) is out of the scope of the present invention, at the time of preparing the first surface treatment liquid. The test could not be carried out due to a large amount of precipitation.

The galvanized steel sheet with a surface-treated film produced by the production method of the present invention can be widely used in fields such as automobiles, home appliances, and building materials.

Claims (7)

A resin compound (A) having a bisphenol skeleton represented by the following general formula (I) and a cationic urethane resin having at least one cationic functional group selected from a first to third amino groups and a quaternary ammonium base. An emulsion (B), a silane coupling agent (C) having at least one reactive functional group selected from an active hydrogen-containing amino group, an epoxy group, a mercapto group and a methacryloxy group, an organic titanium chelate compound (D), and the like. A first surface treatment liquid (α) containing a tetravalent vanadium compound (E), a molybdic acid compound (F), and water within a range satisfying the following conditions (1) to (5). A step of applying to the surface of a zinc-based plated steel plate and then heating and drying at a plate temperature of 50 to 180 ° C. to form a first film having an adhesion amount of 0.02 to 0.19 g / m ² per side. When,
After that, a second organic resin (G) selected from a urethane resin and an acrylic resin and water are contained, and the solid content mass (G _s ) of the organic resin (G) is 50% or more. The surface treatment liquid (β) was applied to the surface of the first film, and then heated and dried at a plate temperature of 50 to 300 ° C., and the adhesion amount per side was 0.4 to 3.0 g / m ² . The process of forming the second film and
A method for manufacturing a galvanized steel sheet with a surface-treated film, which comprises.
(1) Solid mass (A _s ) of the resin compound (A), solid content mass (B _s ) of the cationic urethane resin emulsion (B), and solid content mass of the silane coupling agent (C). Ratio of solid content mass (B _s ) of the cationic urethane resin emulsion (B) to the total of (C _s ) [(B _s ) / {(A _s ) + (B _s ) + (C _s )}] Is 0.10 to 0.30
(2) The solid content mass (As) of the resin compound (A), the solid content mass (B _s ) of the cationic urethane resin emulsion ( _B ), and the solid content mass (C) of the silane coupling agent (C). The ratio of the solid content mass (C _s ) of the silane coupling agent (C) to the total of C _s ) [(C _s ) / {(As) + (B _s ) + (C _s )}] is ₀ . .60 to 0.85
(3) Ratio of solid content mass (C _s ) of the silane coupling agent (C) to titanium reduced mass (D _Ti ) of the organic titanium chelate compound (D) {(C _s ) / (D _Ti )} Is 50-70
(4) The ratio of the vanadium-equivalent mass (EV) of the _tetravalent vanadium compound (E) to the titanium-equivalent mass (D _Ti ) of the organic titanium chelate compound (D) {( _EV ) / (D _Ti ). } Is 0.30 to 0.50
(5) The solid content mass (As) of the resin compound (A), the solid content mass (B _s ) of the cationic urethane resin emulsion ( _B ), and the solid content mass (C) of the silane coupling agent (C). The ratio of the molybdenum-equivalent mass (F _Mo ) of the molybdenum acid compound (F) to the total of C _s ) [(F _Mo ) / {(As) + (B _s ) + (C _s )}] is ₀ . 003 to 0.030

In formula (I), Y ₁ and Y ₂ bonded to the benzene ring are hydrogen atoms independently of each other, or Z groups represented by the following general formulas (II) or (III). The average value of the number of Z group substitutions per benzene ring is 0.2 to 1.0, and n represents an integer of 2 to 50.

In formulas (II) and (III), R ₁ , R ₂ , R ₃ , R ₄ and R ₅ are independent of each other and have a hydrogen atom, an alkyl group having 1 to 10 carbon atoms, or an alkyl group having 1 to 10 carbon atoms, respectively. It is a hydroxyalkyl group, ^and A- represents a hydroxide ion or an acid ion. The first surface treatment liquid (α) further contains an acid component (I), and the first surface treatment liquid (α) further contains an acid component (I).
The solid content mass (As) of the resin compound (A), the solid content mass (B _s ) of the cationic urethane resin emulsion (B), and the solid content mass (C _s ) of the silane coupling agent (C) _. The ratio of the mass (I _g ) of the acid component (I) to the total of [(I _g ) / {( _{As) + (B s) + (C s ) }} ] is 0.10 or less. Item 2. The method for manufacturing a zinc-based plated steel sheet with a surface-treated film according to Item 1. The first surface treatment liquid (α) further contains an aluminum dihydrogen dihydrogen rust preventive pigment (H ₁ ) tripolypolyphosphate.
The ratio of the solid content mass (H _s 1) of the _{tripolyhydrohydric} acid dihydrogen aluminum-based rust preventive pigment (H ₁ ) to the vanadium-equivalent mass (EV) of the tetravalent vanadium compound (E) {(H _s 1) / ( The method for producing a zinc-based plated steel sheet with a surface-treated film according to claim 1 or 2, wherein _EV )} is 3 to 300. The second surface treatment liquid (β) further contains an aluminum dihydrogen dihydrogen rust preventive pigment (H ₂ ) tripolypolyphosphate.
The ratio of the solid content mass (H s 2) of the _{tripolyhydric} acid dihydrogen dihydrogen rust preventive pigment (H ₂ ) to the solid content mass (G _s ) of the organic resin (G) {(H _s 2) / (G _s ) } Is 0.05 to 1.00. The method for producing a zinc-based plated steel sheet with a surface-treated film according to any one of claims 1 to 3. At least one of the aluminum dihydrogen dihydrogen rust preventive pigments (H ₁ ) and (H ₂ ) tripolyphosphate is aluminum dihydrogen tripolyphosphate and at least one additive element selected from Zn, Mg, Si, and Ca. Including and
The ratio of the total mass ( _HE ) of the added elements to the mass (HP) of phosphorus in each ( _{H 1} ) and ( _{H 2} ) {( _HE ) / (HP)} is 0.1 to 10. The method for producing a zinc-based plated steel sheet with a surface-treated film according to claim 3 or 4, which is 0.0. The second surface treatment liquid (β) further contains a wax (W), and the second surface treatment liquid (β) further contains a wax (W).
The ratio of the solid content mass (W _s ) of the wax (W) to the solid content mass (G _s ) of the organic resin (G) {(W _s ) / (G _s )} is 0.002 to 0.100. The method for manufacturing a zinc-based plated steel sheet with a surface-treated film according to any one of claims 1 to 5. A galvanized steel sheet with a surface-treated film manufactured by the method for manufacturing a galvanized steel sheet with a surface-treated film according to any one of claims 1 to 6.