JP5457611B1 - Surface-treated galvanized steel sheet excellent in scratch and end face corrosion resistance and method for producing the same - Google Patents

Abstract

An object of the present invention is to use a zinc-based plated steel sheet without containing chromium, corrosion resistance, chemical resistance, heat-resistant yellowing, molding processability, fingerprint resistance, conductivity of any flat part, after alkaline degreasing, and processed part. Providing chromium-free surface-treated galvanized steel sheets with excellent balance of performance such as paint adhesion.
A galvanized layer is provided on both surfaces of a steel sheet, and a two-layer coating comprising a specific acidic inorganic coating layer and a specific alkaline organic-inorganic composite coating layer is further provided on the surface of the galvanized layer. A surface-treated galvanized steel sheet in which the coating weight of the coating layer is 0.01 to 0.5 g / m ² and the coating weight of the alkaline organic inorganic composite coating layer is 0.5 to 3 g / m ² .
[Selection figure] None

Description

The present invention relates to a chromium-free surface-treated steel sheet that is excellent in corrosion resistance, solvent resistance, and paintability in a zinc-based plated steel sheet that has a smaller amount of zinc per unit area. The surface-treated steel sheet of the present invention is excellent in corrosion resistance of the flat part, after alkaline degreasing, and in the processed part, and excellent in chemical resistance, heat yellowing, molding processability, fingerprint resistance, conductivity, and paint adhesion. . In particular, the present invention is used for an electrogalvanized steel sheet. Generally, zinc-based plated steel sheets have a zinc basis weight of about 20 g / m ^{2 on} one side. When the amount of zinc is reduced, the anticorrosion period of zinc is shortened and corrosion progresses in the long term. The present invention is particularly excellent in inhibiting corrosion of exposed iron parts such as scratches and end faces, and exhibits a scratch and end face corrosion resistance equal to or higher than that of the conventional one even if the amount of zinc is small, and it also generates red rust over a long period of time. The present invention also relates to a chromium-free surface-treated steel sheet that also suppresses

  Conventionally, galvanized steel sheets have been widely used in the fields of home appliances and building materials. Since zinc-based plated steel sheets are insufficient in corrosion resistance and paintability (post-coating for design) as they are, products subjected to chemical conversion treatment such as chromate and zinc phosphate are manufactured. Among these products, chromate-treated products may be used without coating depending on the application. In that case, since fingerprints adhere to the surface of the steel sheet and the appearance is impaired, a product called a fingerprint-resistant steel sheet coated with a resin as a main component has been put to practical use. Further, in recent years, various chromium-free fingerprint-resistant steel plates mainly made of resin without using hexavalent chromium have been put into practical use in accordance with European RoHS regulations.

This fingerprint-resistant steel sheet, particularly in the field of home appliances, has been improved in recent years, with corrosion resistance, heat-resistant yellowing, molding processability, fingerprint resistance, electrical conductivity, paintability, etc. of flat parts, after alkaline degreasing and processed parts, etc. It is necessary to have various performance requirements.
As a conventional surface treatment, chromate treatment or phosphate treatment is performed, and after that, it is often coated on a molded product through a molding process such as bending, extrusion, or sliding. Moreover, depending on a use, it may use as it is, without painting.
When molding a fingerprint-resistant steel plate, non-volatile or volatile press oil is used to reduce wear on the mold. If the oil or dirt adheres to it, coating failure will occur, and cleaning is performed to remove it. In this cleaning, a cleaning agent mainly composed of alkali or acid is often used. This cleaning agent shortens the processing time in order to increase production efficiency, and the cleaning agent is often used at a higher concentration or higher temperature than in the past. Furthermore, in the subsequent painting process, spray coating is the mainstream, and when the anti-fingerprint film is peeled off or partially damaged during cleaning, the surface of the film is uneven. For this reason, poor appearance occurs when the paint is applied. Further, the solvent is volatilized at the time of coating, and baking is performed at a high temperature. However, in the case of single-sided coating, the non-coated surface is exposed to a high-temperature atmosphere. Alternatively, there is a step of volatilizing the press oil at a high temperature after the molding process when the volatile press oil is used, even when it is not painted. At this time, the film containing the resin component and the color developing component is yellowed as described above. This thermal yellowing impairs the product value from the viewpoint of design.
In addition, even in home appliances, information devices such as OA and AV require conductivity and electromagnetic wave shielding. Particularly in recent years, the frequency of communication has been increased, and it is important to provide conductivity for the purpose of preventing charging. In order to develop excellent corrosion resistance and chemical resistance, if the anti-fingerprint film is applied thick, the performance inevitably deteriorates. Therefore, it is a technical problem to make it compatible with conductivity.

In recent years, the economic growth of emerging countries such as China and India has been remarkable, and the consumption of resources has also accelerated rapidly. Zinc, which is a kind of base metal, is also a target substance, and there is concern over the long-term depletion of zinc. Attempts to conserve resources have begun due to concerns over supply insecurity over the past few years.
For example, a conventional electrogalvanized steel sheet has 20 g / m ² or more of zinc plated on one side. The reduction in the zinc basis weight of the electrogalvanized steel sheet makes it difficult to suppress long-term corrosion of iron, particularly in exposed portions of iron, and cannot maintain the conventional quality.

A galvanized steel sheet having a zinc basis weight of less than 20 g / m ² on one side is generally inferior in rust prevention ability when exposed to a corrosive environment for a long period of time due to a small amount of zinc basis weight. Conventionally, chromate and phosphate are used to impart rust prevention. As described above, it is not preferable to use the chromate treatment due to environmental considerations such as recent RoHS regulations. In the case of phosphating, it is difficult to reduce the film thickness, and a coating amount of ² g / m ² or more is usually attached. By increasing the film thickness, it is possible to compensate for the insufficient corrosion resistance, but on the other hand, it is not possible to impart conductivity that has been regarded as important in recent years, such as extremely poor conductivity.

  In addition to not containing hexavalent chromium due to environmental regulations, fingerprint-resistant steel plates are used in various ways as described above. Until now, several techniques for chromium-free surface-treated steel sheets have been proposed.

For example, Patent Document 1 discloses a treatment liquid containing any one of a water-soluble resin having a specific structure, a silane coupling agent, a titanium compound, and a zirconium compound on the surface of a zinc-based plated steel sheet, and drying obtained therefrom. A lower layer of the film, and further a urethane resin having a specific structure having a glass transition temperature in the range of −40 ° C. to 0 ° C., a water-soluble epoxy resin, colloidal silica, a polyethylene wax having a specific particle diameter, a water-soluble organic solvent and water. And a two-layer galvanized steel sheet having a dry film obtained therefrom as an upper layer. In this technology, a zinc-plated steel sheet having a zinc basis weight of 20 g / m ² or more has excellent corrosion resistance, but when used for a zinc-based steel sheet having a weight of less than 20 g / m ² , the corrosion resistance is extremely lowered, and the performance balance Can not be satisfied. In particular, corrosion is remarkably easy to occur at the exposed portions of iron such as scratches and end surfaces, and sufficient corrosion resistance cannot be obtained.

Patent Document 2 includes a treatment liquid containing a cationic polyurethane resin, a cationic phenol resin, a silane coupling agent, a manganese compound, a zirconium compound, a vanadium compound, and a Fischer-Tropsch wax having specific physical properties in a specific ratio. A zinc-based plated steel sheet on which a treatment film is formed is disclosed. However, this technique is not always satisfactory from the viewpoints of corrosion resistance, chemical resistance after heat treatment and alkali treatment, and durability in heat-resistant yellowing. Since it is a single-layer treatment, if the film is thickened to satisfy the above performance, the conductivity is lowered, and all the items required for the fingerprint-resistant steel sheet cannot be satisfied.
In addition, when used for a zinc-based plated steel sheet having a zinc basis weight of less than 20 g / m ^{2 due to} the single-layer treatment, the scratched portion and end surface corrosion resistance are significantly impaired.

Patent Document 3 discloses a surface-treated metal plate covered with a film made of an alkali metal silicate, an organic resin, a solid water-dispersible wax, and a silane coupling agent. However, even in this case, sufficient corrosion resistance cannot be obtained at exposed portions of iron such as scratches and end surfaces in a galvanized steel sheet having a zinc basis weight of less than 20 g / m ² .

  In Patent Document 4, a zirconium film formed by a chemical conversion treatment solution made of hexafluorozirconic acid and an inorganic acid and an upper layer are made of a water-dispersible polyurethane resin, a water-soluble polycarbodiimide resin, an organic titanium compound, colloidal silica, and polyethylene wax. A surface-treated steel sheet coated with a film is disclosed. With this technique, although relatively excellent corrosion resistance can be obtained, the paint adhesion is poor and the performance balance cannot be satisfied.

Patent Document 5 discloses a surface-treated metal plate covered with an organic-inorganic composite film containing an aqueous resin, a silicate compound, a polyolefin wax, and colloidal silica. However, with this technique, not only does not sufficient corrosion resistance be obtained at the exposed portions of iron such as scratches and end surfaces in a galvanized steel sheet having a zinc basis weight of less than 20 g / m ^2, but also flat, after alkaline degreasing, and processing Satisfactory corrosion resistance cannot be obtained even in parts.

Patent Document 6 discloses a film containing one or more selected from phosphoric acid, phosphate, silica, silane coupling agent, Ca, Mn, Mg, Ni, Co, Fe, and Ca-based compounds. In addition, a surface-treated steel sheet coated with a film containing an organic resin on the upper layer is disclosed. Also in this case, in the galvanized steel sheet having a zinc basis weight of less than 20 g / m ² , not only the flat surface, after alkaline degreasing, and the processed portion, but also the scratched portion and the end surface corrosion resistance cannot be satisfied.

Patent Document 7 discloses an aqueous resin composition comprising an alkali silicate and a water-soluble resin. Even with this technology, zinc-coated steel sheets with a basis weight of less than 20 g / m ² are not only able to obtain sufficient corrosion resistance at exposed portions of iron such as scratches and end faces, but also after flat, alkaline degreasing In addition, satisfactory corrosion resistance cannot be obtained even in the processed part.

In Patent Document 8, the first layer is formed by a film made of an oxide or hydroxide selected from Si, Zr, Ti, and Hf, and the upper layer is formed by a film made of an organic resin consisting of a carboxyl group and a hydroxyl group and a crosslinking agent. A galvanized steel sheet is disclosed. With this technology, not only the corrosion resistance is not obtained at the exposed portions of iron such as scratches and end faces in a galvanized steel sheet having a zinc basis weight of less than 20 g / m ^2, but also satisfied with recent required quality. I can't say that.

In Patent Document 9, the outermost layer is coated with an organic resin having an anionic functional group, a cationic metal element selected from Li, Na, K, Mg, Ca, and Sr and a crosslinking agent, and the undercoat is further coated with a silane cup. A galvanized steel sheet coated with a ring agent and an organic resin is disclosed. Even in this case, when a galvanized steel sheet having a zinc basis weight of less than 20 g / m ² is used, not only sufficient corrosion resistance cannot be obtained at the exposed portions of iron such as scratches and end surfaces, but also flat portions, alkaline degreasing The basic corrosion resistance of the rear and processed parts cannot be satisfied.

Patent Document 10 discloses a galvanized steel sheet coated with a film formed of an organic resin, a crosslinking agent such as an isocyanate compound or a carbodiimide compound, an organic rust inhibitor, silica, phosphoric acid, niobium and zirconium compounds, a guanidine compound, and a wax. Is disclosed. Even in this case, when a galvanized steel sheet having a zinc basis weight of less than 20 g / m ² is used, sufficient corrosion resistance cannot be obtained at the exposed portions of iron such as scratches and end faces, flat surfaces, alkali The basic corrosion resistance after degreasing and processed parts cannot be satisfied. Furthermore, red rust is likely to occur at locations where iron is exposed, and the corrosion resistance over a long period is insufficient.

In Patent Document 11, a first layer is coated with an epoxy resin, an organic resin composed of a hydrazine derivative, a silane coupling agent, a phosphoric acid, a film composed of hexafluorometal acid, and a second layer is coated with an epoxy resin, a urethane resin, and an organic resin. A galvanized steel sheet coated with a film containing one or more organometallic compounds selected from titanium compounds, organozirconium compounds, and organoaluminum compounds is disclosed. Even in this case, when a zinc-based plated steel sheet having a basis weight of zinc of less than 20 g / m ² is used, the corrosion resistance of the scratched part and the end face part is insufficient, and the appearance color such as yellowing of the steel material surface after heating is obtained. Change.

Patent Document 12 discloses a galvanized steel sheet coated with a film made of one or more compounds selected from polyurethane resin, silicon oxide, polyolefin resin, phosphoric acid, carbodiimide group-containing compound, oxazoline group-containing compound and titanium compound. ing. Even in this case, when a galvanized steel sheet having a zinc basis weight of less than 20 g / m ² is used, not only the scratched portion and end face portion corrosion resistance but also the performance satisfying the corrosion resistance of the flat portion, after alkaline degreasing and the processed portion can be obtained. Absent. In addition, red rust is likely to occur at locations where iron is exposed, and long-term corrosion resistance cannot be satisfied.

JP 2004-2958 A JP 2008-194839 A Japanese Patent No. 2998790 JP 2011-17082 A JP 2002-221754 A JP 2003-213396 A JP 7-316443 A JP 2010-47796 A JP 2009-248460 A JP 2005-281863 A JP 2008-910 A JP 2008-25023 A

The chrome-free surface-treated zinc-based plated steel sheet that has been proposed so far is more efficient than the conventional surface-treated zinc-based plated steel sheet in which an organic resin is coated on the chromate film. Is economical, but the performance balance regarding required properties such as corrosion resistance, heat-resistant yellowing, molding processability, fingerprint resistance, conductivity, and paintability of the flat portion, after alkaline degreasing and in the processed portion is still insufficient.
Also in the technique formed by two layers, since the resin component is contained in the lower layer, the heat yellowing resistance and conductivity are inferior, and similarly, the performance balance regarding the required characteristics is insufficient. Even when no resin is used for the lower layer, the performance balance is insufficient. Moreover, all of these techniques are cases where a surface-treated galvanized steel sheet having a zinc basis weight on one side of 20 g / m ² or more is used. In the case of using a zinc-based plated steel sheet having a zinc basis weight of 1 to 15 g / m ^{2 on} one side, the above-described technique cannot provide more satisfactory corrosion resistance. In particular, it is extremely inferior at the scratched part and the end face part. Reduction of the zinc basis weight of the galvanized steel sheet contributes to the suppression of the depletion of zinc, which is a resource, and the price increase. As a result, long-term stable supply of galvanized steel sheet is possible.
The present invention uses a zinc-based plated steel sheet, and has various performances such as corrosion resistance, chemical resistance, heat-resistant yellowing, molding processability, fingerprint resistance, conductivity, and paint adhesion of a flat portion, after alkaline degreasing, and a processed portion. In addition to providing a surface-treated galvanized steel sheet with an excellent balance of zinc, especially when using a galvanized steel sheet having a reduced zinc basis weight of 1 to 15 g / m ² , the surface area of zinc can also be reduced in terms of scratches and end surface corrosion resistance. It aims at providing the outstanding surface treatment steel plate which shows the corrosion resistance equivalent to the zinc-plated steel plate whose quantity is 20 g / m < ² > or more.

The present inventors diligently studied the means for solving the problems of the prior art, and repeated studies to ensure various properties required for the surface-treated galvanized steel sheet without using any chromium. As a result, the corrosion resistance, solvent resistance, molding processability, conductivity, and paintability of the flat part, after alkaline degreasing and in the processed part are good, and the top scratched part and end face corrosion resistance is excellent, and red rust is observed over a long period of time. The present inventors have found a surface-treated zinc-based plated steel sheet that is excellent in a performance balance that hardly occurs, and have completed the present invention. Specifically, it has a zinc-based plating layer on both surfaces of a steel plate, and further has a two-layer coating comprising an acidic inorganic coating layer and an alkaline organic-inorganic composite coating layer on the surface of the galvanized layer. A surface-treated zinc-based plated steel sheet having a coating weight of 0.01 to 0.5 g / m ² and a coating weight of the alkaline organic inorganic composite coating layer of 0.5 to 3 g / m ² ,
Acidic inorganic coating layer having an acidic inorganic coating layer having a pH of 2 to 5, comprising at least a zirconium compound (A), a water-dispersible silica (B), a magnesium compound (C), a vanadium compound (D) and a fluorine compound (E). It is a layer formed by applying the agent (L),
An anionic organic / inorganic composite coating layer comprising an anionic urethane resin (U) having a weight average molecular weight of 100,000 to 200,000, an alkali silicate (V), a titanium alkoxide (W), a polycarbodiimide resin (X), and a silane cup It is a surface-treated zinc-based plated steel sheet that is a layer formed by applying an alkaline organic-inorganic composite coating agent (M) having a pH of 9 to 12 to which at least a ring agent (Y) is added. In addition, the term “zinc plating” and “zinc-based plating” in the claims and in this specification means plating containing zinc as a main component (50% by weight or more), and components constituting the plating (plating metal) Is a concept including not only an embodiment in which zinc is alone but also an embodiment (so-called alloy plating) in which a plurality of metals including other metals (for example, Ni and the like) are included.

That is, the present invention
(1) The steel sheet has a galvanized layer on both surfaces thereof, and further has a two-layer coating comprising an acidic inorganic coating layer and an alkaline organic-inorganic composite coating layer on the surface of the galvanized layer. A surface-treated galvanized steel sheet having a weight of 0.01 to 0.5 g / m ² and a coating weight of the alkaline organic inorganic composite coating layer of 0.5 to 3 g / m ² ,
The acidic inorganic coating layer is formed by adding at least a zirconium compound (A), a water-dispersible silica (B), a magnesium compound (C), a vanadium compound (D), and a fluorine compound (E), and has an acidic inorganic pH of 2 to 5. A layer formed by applying a coating (L);
The alkaline organic-inorganic composite coating layer has an anionic urethane resin (U), alkali silicate (V), titanium alkoxide (W), polycarbodiimide resin (X) and silane having a weight average molecular weight of 100,000 to 200,000. The present invention relates to a surface-treated zinc-based plated steel sheet, which is a layer formed by applying an alkaline organic inorganic composite coating agent (M) having a pH of 9 to 12 to which at least a coupling agent (Y) is added.
(2) The surface-treated zinc-based plated steel sheet according to (1), wherein the zinc basis weight on one side of the zinc-based plated steel sheet is 1 to 15 g / m ² .
(3) The alkaline organic inorganic coating layer includes a water-dispersible wax (Z), and relates to the surface-treated zinc-based plated steel sheet according to (1) or (2).
(4) The surface-treated zinc system according to any one of (1) to (3), wherein the anionic urethane resin (U) contained in the alkaline organic-inorganic composite coating layer has a carboxyl group or a salt thereof. It relates to a plated steel sheet.
(5) The solid content mass ratio of the metal (a) containing the zirconium compound (A) and the anionic urethane resin (U) contained in the alkaline organic inorganic composite coating layer is (a) / (U) = 0.001 to 0. .4, the solid content mass ratio of the water-dispersible silica (B) and the anionic urethane resin (U) is (B) / (U) = 0.001 to 1, and the metal (c) contained in the magnesium compound (C) The solid content mass ratio of the alkali silicate (V) is (c) / (V) = 0.001 to 0.5, the vanadium compound (D) -containing metal (d) and the solid of the alkali silicate (V) The mass ratio is (d) / (V) = 0.001 to 0.5, and the mass ratio of solid content of the fluorine element (e) of the fluorine compound (E) and the metal (c) contained in the magnesium compound (C) is ( e) / (c) = 0.1-30, titanium alkoxide (W) containing metal (w) and alk The solid content mass ratio of the silicate (V) is (w) / (V) = 0.01 to 1, and the solid content mass ratio of the polycarbodiimide (X) and the anionic urethane resin (U) is (X) / ( U) = 0.001 to 0.5, solid content mass ratio of silane coupling agent (Y) and anionic urethane resin (U) is (Y) / (U) = 0.001 to 0.5, water dispersion (3) or (4), wherein the solid content mass ratio of the conductive wax (Z) and the anionic urethane resin (U) is (Z) / (U) = 0.01 to 0.2 This relates to a surface-treated zinc-based plated steel sheet.
(6) The surface-treated zinc-based plated steel sheet according to any one of (1) to (5), wherein the alkaline organic-inorganic composite coating layer has a glass transition temperature exceeding 100 ° C.
(7) The surface-treated zinc-based plated steel sheet according to any one of (1) to (6), wherein the zinc-based plated steel sheet is an electrogalvanized steel sheet.
(8) Two-layer film formation for forming the acidic inorganic coating layer and alkaline organic-inorganic composite coating layer according to any one of (1) to (6) on the surface of a zinc-based plated steel plate having a galvanized layer on the surface of the steel plate The two-layer coating forming step includes forming an acidic inorganic coating layer by applying an acidic inorganic coating agent (L) on the galvanized steel sheet and drying at 50 ° C. or higher and 100 ° C. or lower. A step of forming an alkaline organic-inorganic composite coating layer by applying an alkaline organic-inorganic composite coating agent (M) to the upper layer of the acidic inorganic coating layer and coating it, followed by drying at an ultimate temperature of 100 ° C. or higher and lower than 200 ° C. The present invention relates to a method for producing a surface-treated zinc-based plated steel sheet.
(9) It relates to the surface-treated zinc-based plated steel sheet obtained by (8).

The surface-treated zinc-based plated steel sheet of the present invention has no corrosion resistance and resistance to any of the flat part, after alkaline degreasing, and processed part without using chromium, even if the zinc basis weight on one side is 1 to 15 g / m ^2. Excellent performance balance with respect to chemical properties, heat-resistant yellowing, molding processability, fingerprint resistance, conductivity, and paintability. In addition, it has excellent scratch and end face corrosion resistance equivalent to or better than a conventional surface-treated zinc-based plated steel sheet having a zinc weight per side of 20 g / m ² or more. The surface-treated zinc-based plated steel sheet of the present invention can be used without being painted or painted. Accordingly, the present invention has a very large industrial utility value in order to overcome environmental problems, reduce the risk of zinc resource depletion, and satisfy the performance balance of the above characteristics.

  Hereinafter, an embodiment of the present invention will be described in detail. However, the technical scope of the present invention is not limited to the embodiment.

≪Surface-treated zinc-plated steel sheet≫
The surface-treated galvanized steel sheet according to this embodiment has a galvanized layer on both surfaces of the steel sheet, and further has a two-layer coating comprising an acidic inorganic coating layer and an alkaline organic-inorganic composite coating layer on the surface of the galvanized layer. A surface-treated zinc-based plated steel sheet in which the coating weight of the acidic inorganic coating layer is 0.01 to 0.5 g / m ² and the coating weight of the alkaline organic inorganic composite coating layer is 0.5 to 3 g / m ^2. is there. Here, the acidic inorganic coating layer has an acidic pH of 2 to 5 comprising a zirconium compound (A), a water-dispersible silica (B), a magnesium compound (C), a vanadium compound (D) and a fluorine compound (E). It is a layer formed by applying an inorganic coating agent (L), an alkaline organic inorganic composite coating layer comprising an anionic urethane resin (U) having a weight average molecular weight of 100,000 to 200,000, and an alkali silicate (V) , An alkaline organic-inorganic composite coating agent (M) having a pH of 9 to 12 consisting of titanium alkoxide (W), polycarbodiimide resin (X), and silane coupling agent (Y). Here, the two-layer coating according to this embodiment has an acidic inorganic coating layer as a lower layer (layer formed on a galvanized layer) and an alkaline organic-inorganic composite coating as an upper layer (layer formed on an acidic inorganic coating layer). Has a layer. Hereinafter, first, a method for producing a surface-treated zinc-based plated steel sheet (hereinafter, also simply referred to as “surface-treated steel sheet”) according to this embodiment will be described.

≪Method for producing surface-treated galvanized steel sheet≫
Next, the manufacturing method of the surface treatment steel plate concerning this form is explained. The surface-treated steel sheet according to the present embodiment includes a step of forming an acidic inorganic coating layer by applying an acidic inorganic coating (L) to a zinc-based plated steel sheet as a base material, and an alkaline organic-inorganic composite coating (M ) And then drying to form an alkaline organic-inorganic composite coating layer. Hereinafter, details, roles, addition amounts, and the like of each component of the chemicals used in the production method will be described.

<Acid inorganic coating agent (L)>
The acidic inorganic coating agent (L) comprises at least a zirconium compound (A), a water-dispersible silica (B), a magnesium compound (C), a vanadium compound (D), and a fluorine compound (E). Hereinafter, each raw material component will be described in detail.

(Component A: zirconium compound)
In the acidic inorganic coating agent (L) according to this embodiment, it is assumed that a part of the zirconium compound (A) reacts with the fluorine compound (E) in the coating agent (L) to partially ionize fluorine. Is done.
2 H ⁺ + ZrF ₆ ^{2 −} → 2 H ⁺ + ZrF ₄ +2 F ⁻ etc. Fluorine ions (F ⁻ ) have good etching ability. In particular, it has good etching ability under acidic conditions. Therefore, when the acidic inorganic coating agent of this embodiment is brought into contact with the surface of a metal material (in this embodiment, a zinc-based plated steel sheet that is a base material of the surface-treated zinc-plated steel sheet), a treatment film is formed. It is considered that the fluorine ions in the acidic inorganic coating material moderately dissolve the surface and form a reaction layer at the boundary between the treatment film and the surface of the metal material. For this reason, the coating adhesion of the treated film to the surface of the galvanized steel sheet is improved in each step. By improving the adhesion, the planar portion, alkali degreasing and processed portion corrosion resistance are also improved.

The effect | action by adding this component A is demonstrated in detail. A film in which zirconium and fluorine coexist is formed by the action of the zirconium compound (A) and the fluorine compound (E) added to the acidic inorganic coating agent, and an extremely excellent effect is exhibited in the exposed end face part of the iron part. In general, a battery of iron and zinc is formed in the exposed part of the iron part to promote zinc anodic dissolution. On the other hand, alkali concentration occurs due to the reduction of dissolved oxygen at the cathode, and excessive sacrificial corrosion protection of zinc proceeds. When exposed to a long-term corrosive environment, the sacrificial corrosion protection of zinc is insufficient and corrosion of the iron surface also proceeds. I will let you. The surface-treated zinc-based plated steel sheet according to the present embodiment plays a role of buffering the pH that can rise in the cathode portion by the release of fluoride because of the coating in which zirconium and fluorine coexist. That is, excessive sacrificial corrosion protection in the anode part is suppressed, and sacrificial corrosion protection is kept moderate. Therefore, the coexistence film derived from the zirconium compound (A) and the fluorine compound (E) exhibits excellent corrosion resistance at the end face portion. In the surface-treated zinc-based plated steel sheet according to the present embodiment, excessive sacrificial corrosion protection is suppressed by the presence of fluoride ions on the surface of the zinc-based plated steel sheet having a zinc basis weight of 1 to 15 g / m ² on one side. It has end face corrosion resistance equal to or higher than that of a surface-treated zinc-based plated steel sheet having a basis weight of 20 g / m ² or more treated with the surface treatment agent, and can suppress the occurrence of red rust.

  Examples of the zirconium compound (A) according to this embodiment include zirconium hydrofluoric acid, zirconium ammonium fluoride, basic zirconium carbonate, zirconium nitrate, zirconium acetate, zirconium hydroxide, and zirconium oxide. These may be used alone or in combination of two or more.

  Here, when determining the addition amount of the component (A) in the acidic inorganic coating material, it is preferable to consider the addition amount of the component (U) in the alkaline organic inorganic composite coating material. Specifically, the contained metal (a) contained in the component (A), that is, the solid content mass ratio (a) / (U) = 0.001 to 0.4 of the zirconium element (a) and the component (U). Preferably there is. More preferably, (a) / (U) = 0.005 to 0.3, and still more preferably (a) / (U) = 0.01 to 0.1. When (a) / (U) is less than 0.001, the overall corrosion resistance including scratch corrosion resistance and end surface corrosion resistance is inferior, and when it exceeds 0.4, not only the scratch corrosion resistance is inferior, but also the coating adhesion is reduced. . Even if it is an acidic inorganic coating layer, it mix | blends with the same solid content mass ratio.

(Component B: water-dispersible silica)
Next, as the water-dispersible silica (B) according to the present embodiment, (1) a part of the water-dispersible silica (B) may be dissolved in the acidic inorganic coating, but the entire amount is not completely dissolved. In the treatment film formed on the surface of the metal material using the acidic inorganic coating agent, it remains as a solid substance, and (2) is mainly composed of oxide (may be powder or liquid). If there is no particular limitation. Here, as the water-dispersible silica (B), those having an average particle diameter in the air of about 0.001 to 100 μm are preferable, and fine particles of about 0.001 to 1 μm are more preferable. Excessively large particles protrude from the film (acidic inorganic coating layer) and become a kind of film defect, which tends to be a starting point of corrosion. Therefore, it is necessary to have an appropriate particle size, and when the particle size is small, there is an advantage that adhesion is easily obtained. The surface coating agent of this embodiment preferably contains water-dispersible silica (B) in a colloidal state.

More specifically, examples of the water-dispersible silica include liquid phase silica synthesized from a liquid phase and gas phase silica synthesized from a gas phase.
Examples of the liquid phase silica include Snowtex C, Snowtex O, Snowtex N, Snowtex S, Snowtex UP, Snowtex PS-M, Snowtex ST-OL, Snowtex 20, Snowtex 30, Snowtex 40. (Both manufactured by Nissan Chemical Industries, Ltd.).
Examples of the vapor phase silica include Aerosil 50, Aerosil 130, Aerosil 200, Aerosil 300, Aerosil 380, Aerosil TT600, Aerosil MOX80, Aerosil MOX170 (all manufactured by Nippon Aerosil Co., Ltd.).
Only one of these liquid phase silica and gas phase silica may be used as the water-dispersible silica, or a plurality may be used in combination.

  Water-dispersible silica (B) functions as a binder during film formation and has a role of continuous film formation. In particular, the blending of zirconium hydrofluoric acid (A1) and water-dispersible silica (B) is effective in uniformly arranging fluoride ions in the film, and as a regulator of excess fluoride ions. Have a role. When fluoride ion exists excessively, it is disadvantageous in terms of scratch corrosion resistance and paint adhesion. It is preferable that fluoride ion is 0.05-0.5 as solid content mass ratio (e) / (B) with water-dispersible silica (B). More preferably, it is 0.1-0.4. More preferably, it is 0.15-0.35. Within such a range, excellent end face corrosion resistance and scratch corrosion resistance are good, and coating adhesion can also be provided.

  Here, when determining the addition amount of the component (B) in the acidic inorganic coating material, it is preferable to consider the addition amount of the component (U) in the alkaline organic inorganic composite coating material as well as the component (A). is there. Specifically, it is preferable that the solid content mass ratio (B) / (U) = 0.001 to 1 of the water-dispersible silica (B) and the component (U). More preferably, (B) / (U) = 0.005 to 0.5, and still more preferably (B) / (U) = 0.01 to 0.3. When (B) / (U) is less than 0.001, the overall corrosion resistance including scratch corrosion resistance and end surface corrosion resistance is inferior, and when it exceeds 1, not only the scratch corrosion resistance is inferior, but also the coating adhesion decreases.

(Component C: Magnesium compound)
Moreover, the acidic inorganic coating agent which concerns on this form uses a magnesium compound (C) as one raw material. The acidic inorganic coating agent obtained by adding the components (A), (B), and (E) increases in solution viscosity with time and gels. This originates from the product produced by the reaction between zirconium fluoride and silica. The acidic inorganic coating agent obtained by adding the components (A), (B) and (E) can stably coexist in an aqueous solution, particularly in an acidic aqueous solution having a pH of about 2.0 to 5.0. It is difficult, and the viscosity of the aqueous solution increases with time and tends to gel.
On the other hand, such a phenomenon hardly occurs in the acidic inorganic coating material obtained by adding the components (A) to (E). Even after a certain time (for example, several weeks to several months) has elapsed after production, the viscosity is maintained at a low level (that is, the coating material stability is good) and it can withstand industrial use. The present inventors presume that the presence of this magnesium compound (C) has an influence on this property. This point is as follows.

In acidic inorganic coating agent in the present embodiment, the magnesium compound (C) F ^- Since the reaction (catch) easily, F present in free in an acidic inorganic coating agent according to the present embodiment ^- is there is substantially no It is considered a thing.
On the other hand, when such a magnesium compound (C) is not added, the fluorine ion (F ⁻ ) dissolves the solid surface of the water-dispersible silica (B), and the water-dispersible silica (B) is bonded to each other. It is considered that a three-dimensional network is gradually formed by fusion and viscosity increases and gelation occurs.

Since the acidic inorganic coating agent according to the present embodiment contains the magnesium compound (C), it is considered that there is almost no F ⁻ that exists free. Therefore, it is considered that the zirconium compound (A) and the water-dispersible silica (B) can coexist stably.
Further, it is considered that the magnesium compound (C) not only has the ability to catch F ⁻ but also acts as an inhibitor against corrosion inhibition and contributes to the improvement of corrosion resistance.
This is because these are considered to have a higher ability to catch F ^−, and the stability of the coating agent according to the present embodiment is further increased. This point will be described in further detail. Although the effect due to the magnesium compound (C) present in the coating layer is not clear, it contributes to the stabilization of the corrosion products generated in the corrosive environment. Corrosion of metals can be considered as destruction of corrosion products that protect the zinc surface as the pH rises due to elution of zinc and exposure to dissolved oxygen due to exposure to corrosive environments. However, the magnesium compound (C) can contribute to corrosion resistance in that it produces a stable corrosion product while being exposed to a high pH environment.

  In the acidic inorganic coating material according to the present embodiment, the magnesium element (c) is contained in the following form (compound), and such a form (compound) contributes to an improvement in corrosion resistance. Is preferable.

Examples of the magnesium compound (C) include magnesium nitrate, magnesium sulfate, magnesium carbonate, magnesium hydroxide, magnesium fluoride, ammonium magnesium phosphate, magnesium hydrogen phosphate, magnesium oxide, and the like.
These may be used alone or in combination of two or more. Moreover, in the acidic inorganic coating material which concerns on this form, magnesium element (c) may be contained as a magnesium metal single-piece | unit.

Of these forms (compounds), the magnesium compound (C) is particularly preferably an oxide or a hydroxide. The reason is that the corrosion resistance of the coated metal material having the treated film formed using the coating agent of this embodiment as a base is further improved. Of these, only one component or a plurality of components may be added.
The components derived from the magnesium compound (C) are considered to be dissolved in the coating agent of this embodiment and exist in a molecular or ionic state.

  In the acidic inorganic coating material according to this embodiment, the magnesium compound (C) contains a magnesium element (c) in a molar amount (γ) (mol / L) and a fluorine element in a molar amount (α) (mol / L) (γ / α) is preferably 0.001 to 1.7, more preferably 0.005 to 1.4, and most preferably 0.01 to 1.0. preferable. Within such a range, the stability of the acidic inorganic coating material according to this embodiment is good, and the corrosion resistance of the coating film formed on the surface of the metal material using the acidic inorganic coating material according to this embodiment is more Since it increases, it is preferable.

Here, when determining the addition amount of the component (C) in the acidic inorganic coating material, it is preferable to consider the addition amount of the component (V) in the alkaline organic inorganic composite coating material. Specifically, in the acidic inorganic coating material according to this embodiment, the metal content of the magnesium compound (C), that is, the solid content mass ratio (c) / (V) of the magnesium element (c) to the component (V) is 0. 0.001 to 0.5 is preferable. More preferably (c) / (V) = 0.005 to 0.3, and still more preferably (c) / (V) = 0.01 to 0.1.
When (c) / (V) is less than 0.001, sufficient drug stability cannot be obtained, and corrosion resistance is also inferior. On the other hand, when (c) / (V) exceeds 0.5, the drug stability is also poor. Even if it is an acidic inorganic coating layer, it mix | blends with the same solid content mass ratio.

(Component D: Vanadium compound)
Moreover, it is preferable that the acidic inorganic coating material which concerns on this form uses a vanadium compound (D) as one raw material. This vanadium compound (D) acts as a corrosion inhibitor and is effective for raising the corrosion resistance. Further, when the vanadium compound (D) is used, the stability of the acidic inorganic coating material according to the present embodiment becomes better. This effect is significant especially in acidic inorganic coatings, and contributes to stability improvement.
This is presumably because the vanadium compound (D) is coordinated to the fluorine compound (E) or the zirconium compound (A) which has partially released F ⁻ in the acidic inorganic coating material according to this embodiment.

  Further, this vanadium compound (D) also acts as an inhibitor against corrosion and is considered to contribute to the improvement of corrosion resistance. This point will be described in further detail. In a corrosive environment, with the elution of zinc and vanadium compound (D), the vanadium compound (D) is reduced, changes to a state that is relatively difficult to elute into water, and exhibits corrosion resistance by being present on the surface of the galvanized surface. Is.

  This vanadium compound (D) is particularly preferably a compound having the ability to form a chelate complex. The vanadium compound (D) is not particularly limited as long as it is a chelate complex vanadium compound. For example, one or more compounds of propionic acid, oxalic acid, gluconic acid, tartaric acid, malic acid, ascorbic acid, acetylacetone, and sulfuric acid are used. Is mentioned.

  Such a vanadium compound (D) is an acidic inorganic coating agent according to this embodiment, wherein the metal content of the vanadium compound (D) relative to the alkali silicate (V), that is, the solid content mass ratio of the vanadium element (d) ( d) / (V) = 0.001 to 0.5, more preferably 0.005 to 0.3, and particularly preferably 0.01 to 0.1. Such a range is preferable because the storage stability and running property (operation stability) of the acidic inorganic coating material according to the present embodiment are further improved.

(Component E: Fluorine compound)
Examples of the fluorine compound (E) include hydrofluoric acid, ammonium fluoride, sodium fluoride, zirconium hydrofluoric acid, titanium hydrofluoric acid, silicohydrofluoric acid, zirconium ammonium fluoride, titanium ammonium fluoride, and potassium silicofluoride. And ammonium silicofluoride.
These may be used alone or in combination of two or more. When the zirconium compound (A) is a fluorine compound, the fluorine compound (E) may not be mixed.

As described above, the fluorine compound (E) has a role of buffering an alkali generated in a corrosive environment by dissociation of fluoride ions and suppressing an excessive increase in pH. Therefore, the sacrificial anticorrosive ability of zinc is sufficiently exhibited, contributes to stabilization of the generated corrosion product, and is effective in corrosion of zinc and iron.
It is preferable that the solid content mass ratio (e) / (c) of the fluorine element (e) of the fluorine compound (E) and the metal (c) contained in the magnesium compound (C) is 0.1 to 30. The lower limit of (e) / (c) is more preferably 0.3, still more preferably 1, particularly preferably 2, and most preferably 3. On the other hand, the upper limit of (e) / (c) is more preferably 20, more preferably 10, even more preferably 8, and most preferably 6. When the addition amount of the fluorine compound (E) is (e) / (c) less than 0.1 in terms of solid content mass ratio, the scratch resistance and end face portion corrosion resistance are poor without exhibiting sufficient pH buffering ability. When (e) / (c) exceeds 30, the amount of dissociated fluoride ions increases excessively, resulting in poor scratch corrosion resistance.

(Ingredients: other optional ingredients)
As optional components of the acidic inorganic coating agent according to the present embodiment, there are a filler, a surfactant, an antifoaming agent, a leveling agent, an antibacterial agent, a coloring agent, and the like, which can be added within a range not impairing the performance of the film. .

(Ingredient: Liquid medium)
The acidic inorganic coating material according to this embodiment is aqueous. The aqueous system means that the solvent is a main component containing 60% or more of water. The solvent may be water alone, but one or more water-soluble organic solvents such as monohydric or polyhydric alcohols, ketones, cellosolves and the like are used for the purpose of adjusting the drying property of the film and the viscosity of the coating agent. You may use together.

(Total concentration)
Total concentration in the acidic inorganic coating according to this embodiment {zirconium compound (A), water-dispersible silica (B), magnesium compound (C), vanadium compound (D), fluorine compound (E), other components (conductivity The concentration of all substances other than the solvent contained in the acidic inorganic coating material according to this embodiment of the substance, coloring pigment, etc.) is preferably 1 to 50% by mass. The total concentration is more preferably 2 to 40% by mass, and most preferably 3 to 20% by mass. Such a range is preferable in terms of the liquid stability of the coating agent and the practical use. The total concentration referred to here is a concentration calculated from the solid content mass. More specifically, the concentration is calculated from the mass of the solid content remaining after drying the acidic inorganic coating material according to this embodiment at about 100 ° C.

(liquid)
The acidic inorganic coating agent according to this embodiment is an aqueous solution obtained by adding the above components, and its pH is preferably 2.0 to 5.0, and preferably 2.5 to 4.5. Is more preferable. Such a range is preferable because the etching on the surface of the metal material is suppressed and the running performance is further improved.

  Thus, since the acidic inorganic coating material which concerns on this form uses a component (A)-(E) as a raw material in a suitable quantity and is moderate acidity, it brings the following effect. The surface-treated zinc-based plated steel sheet having fingerprint resistance may be used without being painted. Therefore, it is necessary and desirable to maintain the appearance of the steel material itself even after the surface treatment. The cause of the change in the appearance color of the steel material is a change in surface roughness and refractive index. Under such circumstances, when the acidic inorganic coating material according to this embodiment is used, an appropriate steel surface is etched because it is moderately acidic. Therefore, even if the steel material is coated with a component having a refractive index different from that of the steel material, the unevenness on the surface of the steel material is increased, which has the effect of increasing the diffuse reflection of light and suppressing the change in appearance color.

  When it is necessary to adjust the pH of the acidic inorganic coating material according to this embodiment, an appropriate acid (for example, acetic acid, nitric acid, phosphoric acid and salts thereof) or alkali (for example, ammonia, organic amine and salts thereof) is used. It can be performed by adding.

<Alkaline organic-inorganic composite coating agent (M)>
The alkaline organic-inorganic composite coating agent according to the present embodiment includes an anionic urethane resin (U) having a weight average molecular weight of 100,000 to 200,000, an alkali silicate (V), a titanium alkoxide (W), a polycarbodiimide resin (X ), A silane coupling agent (Y) is added at least. The alkaline organic inorganic composite coating layer can further contain a water-dispersible wax (Z). By adjusting the solid content mass ratio of the components within the range described below, the agent is prepared as an alkaline organic-inorganic composite coating agent, and the agent is applied to the surface of the acidic inorganic coating layer or the galvanized steel sheet and dried. An alkaline organic-inorganic composite coating layer is formed. The alkaline organic-inorganic composite coating layer formed on the acidic inorganic coating layer is flat, after alkaline degreasing, and processed part of any corrosion resistance than when formed alone without forming the acidic inorganic coating layer on the galvanized steel sheet. Scratch and end face corrosion resistance, chemical resistance, and molding processability are improved. Furthermore, the best effects including heat-resistant yellowing, fingerprint resistance, conductivity, and paintability can be exhibited. In particular, it has a great effect on the scratched part and the end face part, contributing to the suppression of the occurrence of red rust. The details of the role and amount of each component will be described below.

(Component U: Anionic urethane resin)
The anionic urethane resin (U) used in the alkaline organic-inorganic composite coating agent according to the present embodiment is a main component that forms the coating layer according to the present embodiment, and has corrosion resistance, chemical resistance, molding processability, heat-resistant yellowing, and coating. It bears the basic characteristics of sex. Here, the anionic urethane resin (U) is water dispersible.
Urethane resin has high adhesion to the undercoat layer (referred to here as interlayer adhesion) and can form a dense film, so that it can corrode zinc-based plating, such as water, oxygen, acid and alkali-containing inorganic salts It has the effect of blocking external factors and has the effect of developing corrosion resistance and chemical resistance. By making the polyol species forming the skeleton of the urethane resin a polyether type or a polyester type, it is possible to obtain a urethane resin in which a balance between flexibility and elasticity can be obtained, and adhesion can be improved. In addition, a dense film can be formed by appropriately branching and imparting toughness. By these combined actions, entanglement between polymer chains, interaction between urethane groups, etc. are effectively expressed, and corrosion resistance, chemical resistance, paintability, etc. are exhibited. The polyol species of the urethane resin are generally roughly classified into polyether, polyester, and polycarbonate. Since polyester and polycarbonate have polar groups, they have strong intermolecular interaction and are suitable as tough films. On the other hand, since polyether does not have a polar group, it is a film in which the intermolecular interaction is inferior in mechanical strength compared to polyester and polycarbonate. However, since it has a chemically stable ether group, it is effective for chemical resistance. On the other hand, polycarbonate polyols are advantageous in terms of chemical and mechanical stability, but have the disadvantage of being somewhat expensive. As mentioned above, it is suitable that the water-dispersed urethane resin of this embodiment is a polyether type or a polyester type. Here, the polyether type and polyester type of the polyol species that form the skeleton of the urethane resin are those in which the repeating component of each ether and the repeating unit component of the ester are mainly used as the polyol component. Here, “main” means 50% by mass or more based on the total mass of the polyol.

  The weight average molecular weight of the anionic urethane resin (U) used for the alkaline organic-inorganic composite coating agent is preferably 100,000 to 200,000. The molecular weight of the urethane resin greatly affects the film properties. The low molecular weight substance acts as a plasticizer in the film and causes low Tg and low mechanical properties. As a result, various film performances such as corrosion resistance, solvent resistance and chemical resistance are lowered. Furthermore, the weight average molecular weight affects the volume of the urethane resin in the alkaline organic / inorganic composite coating layer, and the volume of the urethane resin in the alkaline organic / inorganic composite coating layer increases as the weight average molecular weight of the urethane resin increases. As a result, high Tg and high physical properties are achieved, and good film performance is exhibited.

  Here, the weight average molecular weight described in the present specification, including the weight average molecular weight of the anionic urethane resin (U) according to the present embodiment and the raw material described below, is specified in JIS-K7252-4. It is a measured value by a method by size exclusion chromatography.

  Anionic urethane resins (U) are polyisocyanates (especially diisocyanates); polyols (especially diols); carboxylic acids or sulfonic acids having two or more, preferably two hydroxyl groups, or reactive derivatives thereof; and polyamines (especially Diamine) is obtained by a general synthesis method. More specifically, although not limitedly interpreted, for example, a urethane prepolymer having an isocyanate group at both ends is produced from a diisocyanate and a diol, and a carboxylic acid having two hydroxyl groups or a reactivity thereof. A derivative is reacted to form a derivative having isocyanato groups at both ends, and then a tertiary amine such as triethanolamine is added to form an ionomer (triethanolamine salt), which is then added to water to form an emulsion, and further a diamine is added to extend the chain. By performing, an anionic urethane resin (U) can be obtained.

  Examples of the polyisocyanate used when producing the anionic urethane resin (U) include aliphatic, alicyclic and aromatic polyisocyanates, and any of them can be used. Specifically, for example, tetramethylene diisocyanate, hexamethylene diisocyanate, lysine diisocyanate, hydrogenated xylylene diisocyanate, 1,4-cyclohexylene diisocyanate, 4,4′-dicyclohexylmethane diisocyanate, 2,4′-dicyclohexylmethane diisocyanate, Isophorone diisocyanate, 3,3′-dimethoxy-4,4′-biphenylene diisocyanate, 1,5-naphthalene diisocyanate, 1,5-tetrahydronaphthalene diisocyanate, 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, 4, , 4'-diphenylmethane diisocyanate, 2,4'-diphenylmethane diisocyanate, phenylene diisocyanate, xylylene diisocyanate Tetramethylxylylene diisocyanate and the like. Among these, tetramethylene diisocyanate, hexamethylene diisocyanate, lysine diisocyanate, hydrogenated xylylene diisocyanate, 1,4-cyclohexylene diisocyanate, 4,4'-dicyclohexylmethane diisocyanate, 2,4'-dicyclohexylmethane diisocyanate, isophorone diisocyanate When an aliphatic or alicyclic polyisocyanate such as 1,6-hexane diisocyanurate (trimer) or carbodiimidized diisocyanate is used, a film excellent in corrosion resistance, heat yellowing, molding processability and the like is obtained. Since it is obtained, it is preferable.

  As the polyol species used when producing the anionic urethane resin (U), it is preferable to use a polyether polyol or a polyester polyol. The polyether or polyester skeleton is not easily broken even when it comes into contact with a strong alkaline or strongly acidic aqueous solution, and is important for obtaining chemical resistance and corrosion resistance after alkaline degreasing.

  Examples of glycol components used in the production of polyether polyol and polyester polyol include ethylene glycol, 1,2-propanediol, 1,3-propanediol, 2-methyl-1,3-propanediol, and 2-butyl- 2-ethyl-1,3-propanediol, 1,4-butanediol, neopentyl glycol, 3-methyl-2,4-pentanediol, 2,4-pentanediol, 1,5-pentanediol, 3- Methyl-1,5-pentanediol, 2-methyl-2,4-pentanediol, 2,4-diethyl-1,5-pentanediol, 1,6-hexanediol, 1,7-heptanediol, 3,5 -Heptanediol, 1,8-octanediol, 2-methyl-1,8-octanediol, 1,9-nona Diols, aliphatic diols such as 1,10-decanediol, cycloaliphatic diols such as cyclohexanedimethanol and cyclohexanediol, trimethylolethane, trimethylolpropane, hexitols, pentitols, glycerin, polyglycerin, pentaerythritol, Examples include trivalent or higher polyols such as dipentaerythritol and tetramethylolpropane.

  Examples of polyether polyols include 1,2-propanediol, 1,3-propanediol; amines such as bisphenol A and ethylenediamine in addition to the low molecular polyols such as trimethylolpropane, glycerin, polyglycerin, and pentaerythritol. Examples include ethylene oxide and / or propylene oxide adducts to compounds and the like; polytetramethylene ether glycol and the like. The polyether polyols used in this embodiment preferably have a weight average molecular weight of 300 to 5,000, particularly preferably 1,000 to 3,000.

  Examples of the polyester polyol include a polyol such as a low molecular weight polyol; an ester-forming derivative such as a polycarboxylic acid whose amount is less than the stoichiometric amount, its ester, its anhydride and / or its carboxylic acid halide, and / or Alternatively, lactones such as γ-caprolactone, δ-caprolactone, ε-caprolactone, dimethyl-ε-caprolactone, δ-valerolactone, γ-valerolactone, γ-butyrolactone and / or hydroxy obtained by hydrolysis ring-opening reaction thereof. Examples thereof include those obtained by direct esterification with carboxylic acid and / or transesterification. Examples of the polyvalent carboxylic acid or its ester-forming derivative include oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, dodecanedioic acid, 2-methylsuccinic acid. Acid, 2-methyladipic acid, 3-methyladipic acid, 3-methylpentanedioic acid, 2-methyloctanedioic acid, 3,8-dimethyldecanedioic acid, 3,7-dimethyldecanedioic acid, hydrogenated dimer acid Aliphatic dicarboxylic acids such as dimer acid; aromatic dicarboxylic acids such as phthalic acid, terephthalic acid, isophthalic acid and naphthalenedicarboxylic acid; cycloaliphatic dicarboxylic acids such as cyclohexanedicarboxylic acid; trimellitic acid, trimesic acid, castor oil fatty acid Tricarboxylic acids such as monomer; Polyvalent carboxylic acids such as tetracarboxylic acids such as pyromellitic acid And the like. Examples of ester-forming derivatives of these polyvalent carboxylic acids include these acid anhydrides, chlorides of the polyvalent carboxylic acids, carboxylic acid halides such as bromides, methyl esters, ethyl esters, propyl esters of the polyvalent carboxylic acids, Examples include lower aliphatic esters such as isopropyl ester, butyl ester, isobutyl ester, and amyl ester.

  Since the carboxylic acid and / or sulfonic acid used when producing the anionic urethane resin (U) having a carboxyl group or a salt thereof, and their reactive derivatives introduce an acidic group into the anionic urethane resin (U), And an anionic urethane resin (U) is used for water dispersibility. The purpose of neutralizing these anionic groups with a neutralizing agent is to impart water dispersibility. Illustrate organic acids having a polyalkanol group such as dimethylolpropionic acid, dimethylolbutanoic acid, dimethylolpentanoic acid, dimethylolhexanoic acid, 1,4-butanediol-2-sulfonic acid (eg, dimethylolalkanoic acid) (Eg, carboxylic acids, sulfonic acids). Examples of the reactive derivative include hydrolyzable esters such as acid anhydrides. Thus, by making the anionic urethane resin (U) self-dispersible and not using an emulsifier or as much as possible, a film having excellent corrosion resistance can be obtained. Of these, dimethylolpropionic acid and dimethylolbutanoic acid are preferred. These carboxylic acids and sulfonic acids can be used alone or in combination.

  In producing the anionic urethane resin (U), polyamine, water or the like is used. These polyamines, water, and the like are used as adjusted prepolymer chain extenders. These polyamines are appropriately selected from commonly used polyamines. Examples of the polyamine used include low-molecular diamines such as ethylenediamine, propylenediamine, hexamethylenediamine, tolylenediamine, piperazine, and 2-methylpiperazine; polyether diamines such as polyoxypropylenediamine and polyoxyethylenediamine; , Isophoronediamine, norbornenediamine, bis (4-amino-3-methyldicyclohexyl) methane, diaminodicyclohexylmethane, bis (aminomethyl) cyclohexane, 3,9-bis (3-aminopropyl) -2,4,8,10 -Alicyclic diamines such as tetraoxaspiro (5,5) undecane; m-xylenediamine, α- (m / paminophenyl) ethylamine, m-phenylenediamine, diaminodiphenylmethane, diami Polyamines such as diphenylsulfone, diaminodiethyldimethyldiphenylmethane, diaminodiethyldiphenylmethane, dimethylthiotoluenediamine, diethyltoluenediamine, α, α'-bis (4-aminophenyl) -p-diisopropylbenzene; Succinic acid dihydrazide, adipic acid dihydrazide, sebacic acid dihydrazide, phthalic acid dihydrazide, hydrazine hydrate, 1,6-hexamethylenebis (N, N-dimethylsemicarbazide), 1,1,1 ′, 1′-tetramethyl- And hydrazines such as 4,4 ′-(methylene-di-para-phenylene) disemicarbazide. These chain extenders can be used alone or in combination of several kinds.

  The anionic urethane resin (U) may be silane-modified with a hydrolyzable silane compound at the stage of synthesis. There are no particular restrictions on the type of silane compound and the amount of modification when silane modification is performed. As the silane compound, a known silane coupling agent can be used. By modifying the silane, the adhesion between the anionic urethane resin (U) and the reaction undercoat film layer (interlayer adhesion) is improved, and further, the denseness of the overcoat film is improved. Thereby, the corrosion resistance after molding part and alkali degreasing, and moldability improve.

  The anionic urethane resin (U) is preferably blended with a film-forming aid in order to enhance the stability of the resin during synthesis and the film-forming property when the surrounding environment during film-forming is under low temperature drying. . Examples of the film forming aid include butyl cellosolve, N-methyl-2-pyrrolidone, butyl carbitol, and texanol, and N-methyl-2-pyrrolidone is more preferable.

(Component V: alkali silicate)
The alkaline organic-inorganic composite coating material according to this embodiment uses alkali silicate (V) as one raw material. Generally, alkali silicate (V) is a component having extremely high water solubility. However, when in contact with metal ions other than alkali metals, water-insoluble salts are formed. For example, water-insoluble salts can be formed with metal ions such as Mg and Ca, which are alkaline earth metals. In addition, a water-insoluble salt is similarly formed by contact with the above-described organic titanium compound. In other words, it forms a salt that is insoluble in water by contacting zirconium hydrofluoric acid and magnesium compound contained in the lower acidic inorganic coating layer, and organic titanium compound contained in the upper alkaline organic inorganic composite coating layer. Therefore, the surface-treated galvanized steel sheet according to the present embodiment exhibits excellent corrosion resistance.
When the test piece is exposed to a corrosive environment, the reduction reaction of dissolved oxygen proceeds under the coating and exhibits strong alkalinity. However, since the surface-treated zinc-based plated steel sheet according to this embodiment is maintained at a relatively high alkalinity under the coating by the added alkali silicate, an excessive increase in pH is suppressed by its buffering action. Therefore, when the surface treating agent according to the present embodiment is used, even if the amount of zinc per side on the one side is 1 to 15 g / m ² which is smaller than conventional, excellent corrosion resistance can be obtained at the scratched portion and the end surface portion, and for a long time. It suppresses the occurrence of red rust equivalent to or greater than that of the surface-treated galvanized steel sheet having a basis weight of 20 g / m ² or more.

Alkali silicates used in this embodiment (V) is preferably in the range of _SiO 2 / Na ₂ O 4-1. More _preferably, SiO 2 / _Na 2 O is 4-2. When SiO ₂ / Na ₂ O exceeds 4, the viscosity becomes extremely high and workability is deteriorated. When SiO ₂ / Na ₂ O is less than 1, sufficient scratch corrosion resistance and end surface corrosion resistance cannot be obtained.

  As for the alkali silicate (V) used by this form, it is preferable that solid content mass ratio (V) / (U) of a component (U) and a component (V) is 0.01-1. More preferably, (V) / (U) is 0.02 to 0.5. More preferably, it is 0.05-0.3. Most preferably, (V) / (U) is 0.1 to 0.2. When (V) / (U) exceeds 1, the alkaline organic / inorganic composite coating layer becomes brittle, and sufficient processed portion corrosion resistance and molding processability deteriorate. If it is less than 0.01, sufficient scratches and end face corrosion resistance cannot be obtained. Even when an alkaline organic-inorganic composite coating layer is used, it is configured with the solid content mass ratio.

(Component W: Titanium alkoxide)
The alkaline organic-inorganic composite coating material according to this embodiment uses titanium alkoxide (W) as one raw material. By using titanium alkoxide (W), alkaline organic-inorganic composite coating by metal crosslinking with carboxylic acid present in the skeleton of anionic urethane resin (U) and carbodiimide group present in the skeleton of water-soluble carbodiimide resin (X) The layer can be dense. Thereby, a precise | minute film | membrane can be formed and the corrosion resistance after alkali degreasing | defatting and chemical resistance improve. Further, the corrosion resistance of the processed part is improved by the rust prevention effect derived from the titanium alkoxide (W) itself. Further, an insoluble salt is formed in the alkali silicate (V) and water to form a coating layer having a higher barrier property.

  Titanium alkoxide (W) has a structure in which an alkoxy group is coordinated around a titanium atom. Such compounds readily hydrolyze and condense in water. Therefore, it is estimated that the titanium alkoxide (W) forms an oligomer or polymer condensed in water. The titanium alkoxide (W) used in this application is preferably a coexistence of an alkoxy group and a chelating agent. Specifically, titanium tetraisopropoxide, titanium tetranormal butoxide, titanium butoxide dimer, titanium tetra-2-ethylhexoxide, titanium diisopropoxybis (acetylacetonate), titanium tetraacetylacetonate, titanium dioctyloxybis (Octylene glycolate), titanium diisopropoxybis (ethyl acetoacetate), titanium diisopropoxybis (triethanolaminate), titanium lactate ammonium salt, titanium lactate, polyhydroxy titanium stearate and the like. Particularly preferred are titanium diisopropoxybis (ethyl acetoacetate), titanium diisopropoxybis (triethanolaminate), and the like.

  In the alkaline organic inorganic composite coating agent according to this embodiment, the contained metal contained in the component (W), that is, 0.01% as the solid content mass ratio (w) / (V) of the titanium (w) and the component (V). ~ 1 is preferred. More preferably, (w) / (V) is 0.03 to 0.8. More preferably, (w) / (V) is 0.06 to 0.6. Most preferably (w) / (V) is 0.1 to 0.5. When (w) / (V) exceeds 1, sufficient corrosion resistance after alkaline degreasing, solvent resistance, and coating adhesion cannot be obtained, and sufficient stability of the alkaline organic-inorganic composite coating agent cannot be obtained. . When (w) / (V) is less than 0.01, the effect of improving the corrosion resistance, solvent resistance, and processed portion corrosion resistance after alkali degreasing cannot be sufficiently obtained.

(Component X: polycarbodiimide resin)
The alkaline organic-inorganic composite coating agent according to this embodiment uses a water-soluble carbodiimide resin (X) as one raw material. Here, the water-soluble carbodiimide resin (X) plays a role of organic crosslinking with the carboxylic acid present in the skeleton of the anionic urethane resin (U). Thereby, a precise | minute film | membrane can be formed and the corrosion resistance after alkali degreasing | defatting and chemical resistance improve. Furthermore, since a carbodiimide group having a relatively high polarity is introduced into the top coat layer, it greatly contributes to coating adhesion.

  The carbodiimide resin in the polycarbodiimide resin (X) is a polymer having —N═C═N— group in the molecule, and can be produced, for example, by decarboxylation condensation reaction of diisocyanate in the presence of a carbodiimidization catalyst. Here, examples of the carbodiimidization catalyst include tin, magnesium oxide, potassium ion, 18-crown-6, a combination with 3-methyl-1-phenyl-2-phospholene oxide, and the like. As diisocyanate, the diisocyanate in what was illustrated as a polyisocyanate used for manufacture of anionic urethane resin (U) can be illustrated.

  The polycarbodiimide resin (X) is a water-based polycarbodiimide resin and is not particularly limited, but is dispersed or dissolved in water. The water-dispersed polycarbodiimide resin is particles that are clearly detected by a particle size distribution analyzer (trade name PAR-III, manufactured by Otsuka Electronics Co., Ltd.). On the other hand, the water-soluble polycarbodiimide resin is extremely small particles that are detected to the detection limit by a particle size distribution measuring device.

  The carbodiimide equivalent of the polycarbodiimide resin (X) (the chemical formula amount of the carbodiimide resin per mol of carbodiimide groups, in other words, the value obtained by dividing the molecular weight of the carbodiimide resin by the number of carbodiimide groups contained in the carbodiimide resin) is not particularly limited. However, it is preferably in the range of 100 to 1,000, and more preferably in the range of 300 to 700.

  In the alkaline organic inorganic composite coating agent according to this embodiment, the solid content mass ratio of the component (X) and the component (U) is preferably (X) / (U) = 0.001 to 0.5. More preferably, (X) / (U) is 0.005 to 0.4. More preferably, (X) / (U) is 0.01 to 0.3. Most preferably, it is 0.02-0.2. If (X) / (U) exceeds 0.5, the corrosion resistance is rather deteriorated. When (X) / (U) is less than 0.001, sufficient paint adhesion cannot be obtained. The alkaline organic / inorganic composite coating layer is also blended in the above-described solid content mass ratio.

(Component Y: Silane coupling agent)
The alkaline organic-inorganic composite coating agent according to this embodiment uses a silane coupling agent (Y) as one raw material. The silane coupling agent (Y) has an alkoxy group and an organic functional group with a silicon atom at the center. Alkoxy groups bonded directly to silicon atoms are easily hydrolyzed in water to give silanol groups. Since the silanol group is an unstable functional group, dehydration condensation occurs because the silanol group changes to a thermodynamically stable siloxane bond. The polymerized siloxane and the remaining silanol groups can form a tough and excellent adhesive film by the adsorption to the substrate and the interaction with the constituent components of the alkaline organic / inorganic composite coating layer. Thus, the silane coupling agent (Y) used by this form contributes to the adhesiveness with the acidic inorganic coating layer by a silanol group. In addition, a dense film is formed by interacting with the components derived from the anionic urethane resin (U) and the alkali silicate (V) added to the alkaline organic-inorganic composite coating agent. Therefore, it exhibits excellent corrosion resistance.

  Although it does not specifically limit as a silane coupling agent (Y) used by this form, The following are mentioned. Vinyltrimethoxysilane, vinyltriethoxysilane, γ-aminopropyltrimethoxysilane, γ-aminopropylethoxysilane, N- [2- (vinylbenzylamino) ethyl] -3-aminopropyltrimethoxysilane, γ-methacryloxy Propylmethyldimethoxysilane, γ-methacryloxypropyltrimethoxysilane, γ-methacryloxypropylmethyldiethoxysilane, γ-methacryloxypropyltriethoxysilane, γ-glycidoxypropyltriethoxysilane, γ-glycidoxypropylmethyl Diethoxysilane, γ-glycidoxypropyltrimethoxysilane, 2- (3,4-epoxycyclohexyl) ethyltrimethoxysilane, N-β (aminoethyl) γ-aminopropyltrimethoxysilane, N-β- (amino Til) -γ-aminopropyltriethoxysilane, N-β- (aminoethyl) -γ-aminopropylmethyldimethoxysilane, N-phenyl-γ-aminopropyltrimethoxysilane, γ-mercaptopropyltrimethoxysilane, etc. Can be mentioned. The said silane coupling agent (Y) may be used independently and may use 2 or more types together.

  In the alkaline organic inorganic composite coating agent according to this embodiment, the solid content mass ratio between the silane coupling agent (Y) and the component (U) is preferably (Y) / (U) = 0.001 to 0.5. . More preferably, (Y) / (U) is 0.005 to 0.3. More preferably, (Y) / (U) is 0.01 to 0.2. Most preferably, it is 0.02-0.1. When (Y) / (U) exceeds 0.5, the stability of the coating agent decreases. When (Y) / (U) is less than 0.001, the effect of the silane coupling agent (Y) is not exhibited, and any film performance such as corrosion resistance, chemical resistance, solvent resistance, and coating adhesion is deteriorated. To do.

(Component Z: Water dispersible wax)
The water-dispersible wax (Z) used in the present embodiment is contained for imparting slipperiness to the coating layer and improving molding processability. The average particle size is preferably in the range of 0.05 to 1.0 μm, more preferably 0.1 to 0.6 μm. When the average particle diameter of the water dispersible wax exceeds 1.0 μm, the dispersion stability of the wax is deteriorated. When the average particle diameter of the water dispersible wax is less than 0.05 μm, sufficient moldability cannot be obtained. Here, the particle size of polyethylene wax refers to the average particle size measured using a particle size distribution measuring device.

  The molecular weight and melting point of the water dispersible wax (Z) are not particularly limited, but the acid value is preferably in the range of 5 to 50, more preferably in the range of 10 to 30. When the acid value is less than 5, since the wax and the resin are almost incompatible, the wax is perfectly oriented on the surface of the film during the film formation, and is easily detached from the top coat layer, resulting in a decrease in molding processability. It is not preferable. On the other hand, when the acid value exceeds 50, the hydrophilicity of the wax becomes strong, so that the slipperiness of the wax itself is lowered and the scratch resistance is lowered, which is not preferable. As the water dispersible wax (Z), an aqueous dispersion prepared using a surfactant as a dispersant is usually used. There is no particular limitation on the method of dispersing the water-dispersible wax, and a method used industrially may be used.

The acid value of the water dispersible wax (Z) is determined by the following method. A predetermined amount of sample is taken and dissolved in an organic solvent. A phenolphthalein indicator is added to a solution diluted with an organic solvent, and titrated with a 0.1N KOH ethanol solution. The acid value is determined by the following formula.
Acid value = 56.11 × Normality × Titration / sample weight

  In the alkaline organic-inorganic composite coating material according to this embodiment, (Z) / (U) is preferably 0.01 to 0.2 as the solid content mass ratio of component (Z) to component (U). More preferably, (Z) / (U) is 0.02 to 0.1. When (Z) / (U) exceeds 0.2, the corrosion resistance decreases due to the influence of the surfactant used in the water-dispersible wax. When (Z) / (U) is less than 0.01, sufficient moldability cannot be obtained.

(Ingredients: Colloidal silica)
The alkaline organic-inorganic composite coating material comprising the components (U) to (Z) may use colloidal silica as one raw material. Colloidal silica plays a role of adjusting fingerprint resistance and molding processability. Colloidal silica is an aqueous dispersion in which silanol groups are present on the surface, but the particle size, shape, and type are not particularly limited, but the particle size is preferably in the range of 20 to 200 nm. More preferably, it is ˜100 nm. Here, the particle size of silica refers to the average particle size measured using a particle size distribution measuring device.

(Ingredients: other optional ingredients)
As optional components of the alkaline organic-inorganic composite coating agent according to the present embodiment, there are a filler, a surfactant, an antifoaming agent, a leveling agent, an antibacterial agent, a coloring agent, etc., which should be added as long as the performance of the film is not impaired. Can do.

(Ingredient: Liquid medium)
The alkaline organic-inorganic composite coating material according to this embodiment is water-based. The aqueous system means that the solvent is a main component containing 60% or more of water. The solvent may be water alone, but one or more water-soluble organic solvents such as monohydric or polyhydric alcohols, ketones, cellosolves and the like are used for the purpose of adjusting the drying property of the film and the viscosity of the coating agent. You may use together.

(Total concentration)
The solid content concentration of the alkaline organic inorganic composite coating material according to the present embodiment is preferably in the range of 5 to 30% by mass, more preferably in the range of 10 to 25% by mass in total of the solid content of each component. In addition, solid content concentration here is a density | concentration computed from the mass of the solid content which remains after drying the alkaline organic inorganic composite coating material which concerns on this form at about 100 degreeC.

(liquid)
The pH of the alkaline organic-inorganic composite coating material according to this embodiment is preferably in the range of 9-12. When pH adjustment is necessary, an alkaline substance such as ammonia, dimethylamine, or triethylamine, or an acidic substance such as acetic acid, nitric acid, or phosphoric acid can be added as long as the effects of the present embodiment are not impaired. Further, the pH of the alkaline organic-inorganic composite coating material can be adjusted by adding a metal salt such as Mg, Al, Zn or the like.

<Method for preparing both agents>
The preparation method of both coating agents (an acidic inorganic coating agent and an alkaline organic-inorganic composite coating agent) according to this embodiment is not particularly limited, and both can be produced by a conventionally known method. Here, the suitable example of the preparation method of acidic inorganic coating material (L) is demonstrated first. First, an aqueous solution to which an arbitrary amount of the zirconium compound (A) is added is prepared. In this case, as the zirconium compound (A), one containing fluorine (zirconium fluoride or the like) may be used, or one not containing fluorine may be used. When the zirconium compound (A) not containing fluorine is used, a fluorine compound (E) (HF or the like) is further added as described later. Next, an arbitrary amount of the magnesium compound (C) is added and mixed here. Then, an arbitrary amount of water-dispersible silica (B), vanadium compound (D), and a compound containing a fluorine compound (E) as required is added to the aqueous solution and mixed. In this way, it is possible to prepare an agent having a solid content concentration of a predetermined value in which these components are dissolved or dispersed. Next, the suitable example of the adjustment method of an alkaline organic inorganic composite coating material (M) is demonstrated. First, an arbitrary amount of component (U) is added to deionized water, and an arbitrary amount of component (V) is further added and mixed. Next, an arbitrary amount of the component (W) is added and mixed. Arbitrary amount of component (X) is added and mixed, arbitrary amount of component (Y) is added and mixed, and arbitrary amount of component (Z) is added and mixed so that the final solid content concentration is obtained. adjust. In this way, it is possible to prepare an agent having a solid content concentration of a predetermined value in which these components are dissolved or dispersed.

<Base material>
As a base material used in the manufacturing method of this embodiment, a zinc-based plated steel sheet is preferable from the application. Examples of the plating method for the galvanized steel sheet include hot dip plating, electroplating, vapor deposition plating, and the like. Although not particularly specified, zinc plating is more preferably processed by electroplating.

<Application order of both agents>
The two-layer surface treatment layer (acidic inorganic coating layer and alkaline organic inorganic composite coating layer) of this embodiment is dried after contacting the acidic inorganic coating agent on the surface of the galvanized surface, and further the alkaline organic inorganic composite is formed thereon. It is obtained by bringing the coating material into contact and drying. Hereinafter, each process is explained in full detail.

<Acid inorganic coating layer forming step>
First, the process of forming an acidic inorganic coating layer will be described.
(Cleaning process)
When oil or dirt adheres to the surface of the galvanized steel sheet, after solvent degreasing, alkali degreasing, and acid degreasing, the surface condition is cleaned by washing with water, and then the coating is contacted with an acidic inorganic coating. Better. If necessary, it may be dried after washing with water.
(Contact process)
In the manufacturing method of the present embodiment, the acidic inorganic coating agent of the present embodiment as described above is brought into contact with the surface of the galvanized steel sheet after the cleaning step as described above.
The method of contacting is not particularly limited, and for example, a conventionally known method can be applied. For example, roll coating, curtain flow coating, air spraying, airless spraying, dipping, bar coating, and brush coating methods can be applied. In addition, before bringing the acidic inorganic coating agent of this embodiment into contact with the surface of the zinc-based plated steel sheet in this way, in other lines, the zinc-based plated steel sheet may be subjected to hot water washing, alkaline degreasing, surface, as necessary. Ordinary pre-processing such as adjustment may be applied.
(Drying process)
In the manufacturing method of the present embodiment, the acidic inorganic coating agent of the present embodiment is brought into contact with the surface of the galvanized steel sheet by the method as described above and then dried. The drying method is not particularly limited, and for example, a conventionally known method can be applied. Examples thereof include an air blow method and a method using a dryer (an oven or the like). If it is the method of drying using a dryer, a drying temperature and drying time will not be restrict | limited in particular, For example, the highest ultimate temperature of the surface of the said zinc-plated steel plate shall be 60-120 degreeC, and it will dry for about 1 to 120 second. be able to.

<Alkaline organic-inorganic composite coating layer forming step>
Next, the process of forming an alkaline organic inorganic composite coating layer will be described.
(Contact process)
In the production method of this embodiment, the alkaline organic inorganic composite coating agent of this embodiment as described above is brought into contact with the surface of the acidic inorganic coating layer formed as described above.
The method of contacting is not particularly limited, and for example, a conventionally known method can be applied. For example, roll coating, curtain flow coating, air spraying, airless spraying, dipping, bar coating, and brush coating methods can be applied.
(Drying process)
In the production method of the present embodiment, the alkaline organic inorganic composite coating material of the present embodiment is brought into contact with the surface of the acidic inorganic coating layer by the method as described above and then dried. The drying method is not particularly limited, and for example, a conventionally known method can be applied. If it is a method of drying using a dryer, the drying temperature and the drying time are not particularly limited, for example, the highest reached temperature of the surface of the galvanized steel sheet on which the acidic inorganic coating layer is formed is 100 to 180 ° C., It can be dried for about 1 to 120 seconds. A more preferable maximum temperature is 120 to 150 ° C.

≪Structure and properties of surface-treated galvanized steel sheet≫
<Layer structure>
The surface-treated zinc-based plated steel sheet according to the present embodiment has a two-layer film of an acidic inorganic coating layer and an alkaline organic inorganic composite coating layer. Here, in this embodiment, from the viewpoint of performance balance, it is a two-layer coating-treated galvanized steel sheet formed by coating a two-layer coating in which the acidic inorganic coating layer is the lower layer and the alkaline organic-inorganic composite coating layer is the upper layer. preferable. The alkaline organic-inorganic composite coating layer preferably contains a water-dispersible wax (Z).

<Film weight>
The film weight according to the present embodiment is appropriately determined according to the application. However, the range of the dry film weight of the surface-treated galvanized steel sheet having a two-layer structure of the acidic inorganic coating layer and the alkaline organic inorganic composite coating layer that best achieves the effect of the present embodiment is 0.01% for the acidic inorganic coating layer. it is preferably to 0.5 g / ^{m 2,} more preferably from 0.03 to 0.3 g / ^{m 2.} Most preferably, it is 0.05-0.2 g / m < ² >. When the film weight is less than 0.01 g / m ² , it is disadvantageous in terms of corrosion resistance and molding processability. When the film weight exceeds 0.5 g / m ² , not only the cost increases from the viewpoint of productivity, but also the film performance such as coating adhesion and solvent resistance decreases. The alkaline organic inorganic composite coating layer is preferably coating weight is 0.5 to 3 g / ^{m 2,} more preferably from 0.7~2g / ^{m 2.} Most preferably, it is 0.8-1.5 g / m < ² >. When the dry film weight is less than 0.5 g / m ² , the corrosion resistance, scratched and end face corrosion resistance, chemical resistance, molding processability, and fingerprint resistance are lowered. On the other hand, if the coating weight exceeds 3.0 g / m ² , the heat-resistant yellowing, conductivity and paintability are lowered and the cost is increased.

<Properties>
The surface-treated zinc-based plated steel sheet according to this embodiment has good corrosion resistance, solvent resistance, molding processability, conductivity, and paintability of the flat part, after alkaline degreasing, and the processed part. Excellent corrosion resistance and excellent performance balance that prevents red rust from occurring over a long period of time. Moreover, it is preferable that the glass transition temperature of an alkaline organic inorganic composite coating layer is 100 degreeC or more. In the overcoat (upper layer side) film layer having a glass transition temperature lower than 100 ° C., physical property changes are likely to occur in an actual use environment. The reason is that the cohesive force in the film becomes insufficient and sufficient barrier properties cannot be obtained. However, when the glass transition temperature is 100 ° C. or higher, the cohesive force is increased, so that the barrier property of the film is improved. The increase in the Tg of the film is naturally derived from the anionic urethane resin (U). This can be achieved by changing to a short-chain polyol, increasing the amount of branching, and increasing the number of urethane groups.

≪Application of surface-treated zinc-based plated steel sheet≫
The combination of the acidic inorganic coating layer and the alkali organic inorganic composite coating layer according to this embodiment is not particularly limited, but the fingerprint resistance in the zinc-based plated steel sheet having a zinc basis weight of 1 to 15 g / m ² on one side is not limited. It is preferably used for the required steel plate (anti-fingerprint steel plate) application. The surface-treated zinc-based plated steel sheet according to this embodiment is excellent in molding processability while having corrosion resistance, paint adhesion, solvent resistance, and heat yellowing resistance required for a fingerprint-resistant steel sheet. Scratch and end face corrosion resistance equal to or better than conventional surface-treated galvanized steel sheets with a zinc basis weight of 20 g / m ² or more can be maintained, and consideration is given to effective use of the environment and resources without deteriorating film performance. The surface-treated zinc-based plated steel sheet.

≪Other forms of surface-treated galvanized steel sheet≫
(Lamination order of coating layers)
In the surface-treated zinc-based plated steel sheet according to the present invention, the stacking order of the acidic inorganic coating layer and the alkaline organic-inorganic composite coating layer may be different from the above-described form. That is, an alkaline organic-inorganic composite coating layer may be formed as a lower layer on the surface of a zinc-based plated steel sheet, and an acidic inorganic coating layer may be formed as an upper layer. However, in order to more effectively express the various performances of the above-described acidic inorganic coating layer and alkaline organic-inorganic composite coating layer, the lower layer is an acidic inorganic coating layer and the upper layer is an alkaline organic-inorganic composite, as in the above-described form. A coating layer is preferred.

(How to apply both agents)
In addition, the acidic inorganic coating agent and the alkaline organic-inorganic composite coating agent described above are so-called “coating type coating agents”, but different from the above-described forms, they may be “coating agents other than the coating type”. .
In general, the surface coating agent of a general metal material includes a reaction type (self-deposition type, electrolytic deposition type, etc.) and the like in addition to a coating type. For those other than the coating type, after the coating agent is brought into contact with, for example, the surface of the metal material (zinc-based plated steel sheet) which is the base material described above, it is usually washed with water and then dried. This is because the film formed by bringing the coating material into contact with the surface of the metal material contains an unnecessary component (or a component that lowers the performance) in order to achieve the desired performance. This is because it is preferable to remove them. The “coating-type coating agent” such as the coating agent in the above-described form may be subjected to such a water washing treatment, but it is not always necessary, and the desired performance can be obtained by drying without performing the water washing treatment. The film can be formed (however, it may be washed with water before drying). On the other hand, the “coating agent other than the coating type” is preferably subjected to such a water washing treatment, and if the water washing treatment is performed, a film exhibiting desired performance can be formed. Only a film that does not exhibit the desired performance or has reduced performance can be formed.
Therefore, it is preferable that the coating agent of this embodiment does not contain as much as possible components (nitrate radical, sulfate radical, etc.) that may deteriorate the properties of the film.

  The following examples and comparative examples will specifically illustrate the effects of the present invention. An Example is only an illustration of this invention and does not limit this invention at all. In Examples,% represents mass% unless otherwise specified.

[Preparation of test plate]
(1) Test plate An electrogalvanized steel plate with a thickness of 0.8 mm (zinc adhesion amount per side of 10 g / m ² , 20 g / m ² ) was used.

(2) Degreasing In order to remove stains on the test plate, alkali degreasing was performed. Specifically, alkaline degreasing agent Pulclean N364S (manufactured by Nihon Parkerizing Co., Ltd.) was adjusted to a concentration of 20 g / L with deionized water and sprayed at a temperature of 60 ° C. for 10 seconds. Subsequently, after washing with tap water, it was squeezed with a draining roll and dried with hot air at 50 ° C. for 30 seconds.

(3) Preparation of acidic inorganic coating agent and coating method First, an aqueous solution to which an arbitrary amount of the zirconium compound (A) was added was prepared. Next, an arbitrary amount of the magnesium compound (C) is added and mixed here. Then, an arbitrary amount of water-dispersible silica (B), vanadium compound (D), and a compound containing a fluorine compound (E) as required is added to the aqueous solution and mixed. The acidic inorganic coating agent shown in Table 1 was prepared so that it could be obtained by dissolving or dispersing, and finally the solid content concentration was 3%. The dry coating weight of the acidic inorganic coating layer was adjusted to the coating weight shown in Table 1 by adjusting the solid content concentration or changing the type of bar coater by diluting the acidic inorganic coating agent. . It applied to one side of the electrogalvanized steel sheet using a bar coater, and dried by heating in a hot air drying furnace so as to reach a predetermined plate temperature.

(4) Preparation and coating method of alkaline organic-inorganic composite coating agent Anionic urethane resin (U), alkali silicate (V), titanium alkoxide (W), polycarbodiimide resin (X), silane coupling agent (Y) Using the water-dispersible wax (Z), alkaline organic-inorganic composite coating agents shown in Table 2 were prepared. An arbitrary amount of anionic urethane resin (U) was added to deionized water. Further, an arbitrary amount of alkali silicate (V) is added and mixed. Next, an arbitrary amount of titanium alkoxide (W) is added and mixed. An arbitrary amount of polycarbodiimide resin (X) is added and mixed. An arbitrary amount of the silane coupling agent (Y) is added and mixed. An arbitrary amount of water-dispersible wax (Z) was added and mixed to adjust the final solid content concentration to 16%. The dry film weight of the alkaline organic / inorganic composite coating layer can be obtained by adjusting the solid content concentration or changing the type of bar coater by diluting the alkaline organic / inorganic composite coating agent. It was made to become. The test plate on which the acidic inorganic coating layer was formed was coated on one side using a bar coater, and dried by heating in a hot air drying furnace so that the predetermined plate temperature was reached.

(5) Raw material zirconium compound for acidic inorganic coating agent (A)
(A1) Zirconium hydrofluoric acid (Morita Chemical Industries, trade name: Zircon hydrofluoric acid 40%)
(A2) Zirconium carbonate (Nippon Light Metal, trade name: basic zirconium carbonate)
(A3) Zirconium hydroxide (made by Nippon Light Metal, trade name: zirconium hydroxide)
Water dispersible silica (B)
(B1) Colloidal silica, average particle size 20 μm (manufactured by Nissan Chemical Industries, product name Snowtex O)
(B2) Colloidal silica, average particle size 5 μm (manufactured by Nissan Chemical Industries, product name Snowtex NSX)
(B3) Colloidal silica, average particle size 50 μm (manufactured by Nissan Chemical Industries, product name Snowtex L)
Magnesium compound (C)
(C1) Magnesium oxide (Kyowa Chemical Industry, trade name Kyowa Mug 30)
(C2) Magnesium carbonate (Kyowa Chemical Industry, trade name: Industrial magnesium carbonate)
(C3) Magnesium hydroxide (trade name, Kyowasui Mug F, manufactured by Kyowa Chemical Industry Co., Ltd.)
Vanadium compound (D)
(D1) Vanadyl acetylacetonate (manufactured by Shinsei Chemical Industry, trade name: vanadyl acetylacetonate 50D)
(D2) Vanadyl sulfate (manufactured by Shinsei Chemical Industry, trade name: vanadyl sulfate)
(D3) vanadyl oxalate (trade name, vanadium oxalate (IV), manufactured by Mitsuwa Chemicals)
Fluorine compounds excluding zirconium hydrofluoric acid (E)
(E1) Hydrofluoric acid (Morita Chemical Industries, trade name 55% hydrofluoric acid)
(E2) Ammonium fluoride (Morita Chemical Industries, trade name: Zircon ammonium fluoride)
(E3) Titanium hydrofluoric acid (trade name, titanium hydrofluoric acid, manufactured by Morita Chemical Industries)

(6) Raw material anionic urethane resin (U) for alkaline organic-inorganic composite coating agent
(U1) Polyether-based water-dispersible urethane resin: glass transition temperature 90 ° C., acid value 5 (carboxyl group: derived from dimethylolpropionic acid), weight average molecular weight 100,000 (Daiichi Kogyo Seiyaku, trade name Superflex 130) )
(U2) Polyester-based water dispersible urethane resin: glass transition temperature 95 ° C., acid value 15 (carboxyl group: derived from dimethylolpropionic acid), weight average molecular weight 100,000 (manufactured by ADEKA, trade name ADEKA BONTITER HUX-320)
(U3) Polyester-based water-dispersible urethane resin: glass transition temperature 130 ° C., acid value 20 (carboxyl group: derived from dimethylolpropionic acid), weight average molecular weight 150,000 (manufactured by DIC, trade name Hydran WLS-210)
Alkali silicate (V)
(V1) No. 4 sodium silicate (manufactured by Nippon Chemical Industry Co., Ltd., trade name: sodium silicate No. 4)
(V2) No. 3 sodium silicate (manufactured by Nippon Chemical Industry Co., Ltd., trade name: J sodium silicate No. 3)
(V3) Water-dispersible silica (manufactured by Nissan Chemical Industries, trade name Snowtex N) as a comparative component that is not an alkali silicate
Titanium alkoxide (W)
(W1) Diisopropoxide titanium diacetylacetonate (manufactured by Matsumoto Fine Chemical, trade name TC-100)
(W2) Diisopropoxide titanium bistriethanolamate (manufactured by Matsumoto Fine Chemical, trade name TC-400)
(W3) Diisopropoxide titanium dilactate (Made by Matsumoto Fine Chemical, trade name TC-315)
Carbodiimide resin (X)
(X1) Carbodiimide equivalent 430 (manufactured by Nisshinbo, trade name Carbodilite SV-02)
(X2) Carbodiimide equivalent 380 (manufactured by Nisshinbo, trade name Carbodilite V-02-L2)
(X3) As a comparative component that is not a carbodiimide resin, block isocyanate (trade name: ELASTRON BN-04, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.)
Silane coupling agent (Y)
(Y1) γ-glycidoxypropyltrimethoxysilane (manufactured by Shin-Etsu Chemical Co., Ltd., trade name KBM-403)
(Y2) Tetraethoxysilane (manufactured by Shin-Etsu Chemical Co., Ltd., trade name KBE-04)
Wax (Z)
(Z1) Polyolefin wax, particle size 0.2 μm (product name: Chemipearl W950, manufactured by Mitsui Chemicals)
(Z2) Polyolefin wax, particle size 0.3 μm (Mitsui Chemicals, trade name Chemipearl W900)
(Z3) Polyolefin wax, particle size 0.3 μm (Mitsui Chemicals, trade name Chemipearl W401)

(7) Measurement method of physical properties and resin film properties of alkali organic inorganic composite coating layer (A) in the obtained sample material (a) Glass transition temperature (Tg)
It measured using the dynamic-viscoelasticity measuring apparatus (RSAG2 product made from TA Instruments, Inc.). Tanδmax was defined as Tg.

[Evaluation test]
A test formed on the surface of the test plate from a two-layer structure of one layer of a component (A) to (E) or component (U) to (Z), an acidic inorganic coating layer and an alkali organic inorganic composite coating layer The performance of the plate was evaluated as follows. Tables 3 and 4 show the evaluation results of Examples and Comparative Examples, respectively.

(7) -1 Plane part corrosion resistance The salt spray test prescribed | regulated to JIS-Z2371: 2000 was implemented for 240 hours, and the white rust generation | occurrence | production area ratio was evaluated visually.
<Evaluation criteria>
◎: White rust generation area ratio less than 5% ○: White rust generation area ratio 5% or more, less than 10% ◯: White rust generation area ratio 10% or more, less than 30% △: White rust generation area ratio 30% or more, Less than 50% x: White rust generation area ratio 50% or more

(7) -2 Corrosion resistance after alkaline degreasing The alkaline degreasing agent Pulclean N364S (manufactured by Nihon Parkerizing Co., Ltd.) is adjusted to a concentration of 20 g / L with deionized water and sprayed at a temperature of 60 ° C. for 2 minutes (spray pressure 0.5 kg / cm ² ). Subsequently, after washing with tap water, the water was squeezed with a draining roll. Then, the salt spray test prescribed | regulated to JIS-Z2371 was implemented for 240 hours, and the white rust generation | occurrence | production area ratio was evaluated visually.
<Evaluation criteria>
◎: White rust generation area ratio less than 5% ○: White rust generation area ratio 5% or more, less than 10% ◯: White rust generation area ratio 10% or more, less than 30% △: White rust generation area ratio 30% or more, Less than 50% x: White rust generation area ratio 50% or more

(7) -3 Processed part corrosion resistance 6 mm extrusion was performed with an Erichsen tester, and then a salt spray test defined in JIS-Z2371 was carried out for 240 hours, and the white rust generation area ratio was visually evaluated.
<Evaluation criteria>
◎: White rust generation area ratio less than 5% ○: White rust generation area ratio 5% or more, less than 10% ◯: White rust generation area ratio 10% or more, less than 30% △: White rust generation area ratio 30% or more, Less than 50% x: White rust generation area ratio 50% or more

(7) -4 Scratch corrosion resistance After performing a cross-cut with an NT cutter (NT 300, manufactured by NT Corporation), the salt spray test specified in JIS-Z2371 is performed for 120 hours, and the maximum rust width on one side is visually evaluated. did.
<Evaluation criteria>
◎: Rust width less than 5 mm ○: Rust width 5 mm or more, less than 7 mm ○ △: Rust width 7 mm or more, less than 8.5 mm Δ: Rust width 8.5 mm or more, less than 10 mm ×: Rust width 10 mm or more

(7) -5 End surface corrosion resistance The salt spray test prescribed in JIS-Z2371 was conducted for 72 hours, and the rust width from the end surface was visually evaluated.
<Evaluation criteria>
◎: Rust width less than 10 mm ○: Rust width 10 mm or more, less than 12 mm ○ △: Rust width 12 mm or more, less than 13.5 mm Δ: Rust width 13.5 mm or more, less than 15 mm ×: Rust width 15 mm or more

(7) -6 Red Rust Resistance A salt spray test defined in JIS-Z2371 was performed for 72 hours, and the red rust generation area generated from the end face was visually evaluated.
<Evaluation criteria>
A: Red rust occurrence area rate 0%
○: Red rust occurrence area ratio 1% or more, less than 5% △: Red rust occurrence area ratio 5% or more, less than 10% △: Red rust occurrence area ratio 10% or more, less than 20% ×: Red rust occurrence area ratio 20% or more

(8) Solvent resistance The gauze was impregnated with methyl ethyl ketone (MEK), ethanol, and hexane, and the surface of the alkaline organic-inorganic composite coating layer of each test plate was subjected to 20 reciprocating rubbing tests, and the surface was observed.
<Evaluation criteria>
◎: No change in appearance ○: Some change △: Some change ×: Change

(9) Molding processability (mold galling resistance)
A test piece (plate thickness 0.8 mm) cut to 30 mm x 150 mm was molded into a U-shape using a 200-ton crank press (dies and punch shoulder R = 5 mm, clearance: -20% of plate thickness). The appearance of the molded product (site subjected to sliding by the mold) was visually evaluated.
<Evaluation criteria>
A: No change at all,
○: Partly discolored slightly (causing galling),
Δ: Partially discolored (galling is noticeable),
X: Discoloration on the entire surface (galling is extremely noticeable)

(10) Conductivity The surface resistance was evaluated using a surface resistance measuring device (SQ meter / manufactured by Yamazaki Seiki Laboratories). The pressing load was 300 g, the contact area was 0.9 mm in diameter, and the operation speed was 10 mm / min.
<Evaluation criteria>
○: Surface resistance is less than 100Ω Δ: Surface resistance is 100Ω or more and less than 300Ω ×: Surface resistance is 300Ω or more

(11) Coating adhesion With reference to the former JIS K5400, spray coating was performed using a melamine alkyd paint (Glymine # 500 manufactured by Shinto Paint Co., Ltd.). Subsequently, baking was performed at 120 ° C. for 20 minutes, and a 25 μm coating film was formed after drying. Thereafter, 100 1 mm grids were applied and the tape was peeled off.
<Evaluation criteria>
○: No peeling △: The number of remaining grids is 80 or more and less than 100 ×: The number of remaining grids is less than 80

(12) Fingerprint resistance After measuring the color tone (L1, a1, b1 in Hunter color system) {ZE2000 (Nippon Denshoku)}, petrolatum was applied to it, and Kimwipe (manufactured by Techjam) was used. Wipe off, re-measure the color tone (L2, a2, b2) of the same part, and evaluate the color difference (ΔE = √ {(L2-L1) ² + (a2-a1) ² + (b2-b1) ² }} did.
<Evaluation criteria>
○: ΔE is 1.5 or less Δ: ΔE is more than 1.5, 2 or less ×: ΔE is more than 2

(13) Stability of coating agent Each of the acidic inorganic coating agent and the alkaline organic inorganic composite coating agent was allowed to stand in a constant temperature bath at 40 ° C for 1 month, and then the appearance was evaluated visually.
<Evaluation criteria>
○: No change in appearance △: Slightly cloudy or trace amount of precipitation ×: Large amount of precipitation or gelation

As can be seen from Table 3, the 2-coated surface-treated galvanized steel sheet of the example exhibited even better performance than the 1-coated surface-treated galvanized steel sheet, and the basis weight of zinc was 20 g / m in all evaluation items. It was equal to or better than ² steel materials. That is, since the surface-treated steel sheet according to the example has a coating performance equal to or higher than that of a conventional zinc-based plated steel sheet having a zinc basis weight, the amount of zinc used can be suppressed while maintaining excellent quality. On the other hand, it can be seen that one of the items is inferior in the comparative example. Specifically, it is as follows. As shown in Table 4, Comparative Examples 1 to 5, Comparative Example 7 and Comparative Example 8 excluded any of the components (A) to (E), and any of the performances was inferior. In Comparative Examples 9 to 12 and Comparative Examples 14 to 16, any of the components (U) to (Z) was excluded, and any of the performances was inferior. Comparative Examples 17 to 22 are cases where the coating amounts of the acidic inorganic coating layer and the alkaline organic inorganic composite coating layer were outside the scope of the invention, and various performances were not satisfactory. Comparative Examples 23 and 24, the zinc basis weight of the steel material by using a conventional 20 g / ^{m 2} and 10 g / ^{m 2} steel, and except for the component (E), be a prior art type of component (V) are different The steel material having a zinc basis weight of 10 g / m ² does not reach the performance of the surface-treated steel sheet of the example. Comparative Examples 25 and 26 are cases where the conventional chemical conversion treatment was applied to the lower layer, and the conductivity is insufficient with phosphate, and the performance of the surface-treated steel sheet of the example does not reach even in Zr chemical conversion. In Comparative Examples 17 and 18, the evaluation of molding processability is improved despite the fact that the coating weight of the acidic inorganic coating layer is less than 0.01 g / m ² for the following reason. Molding processability depends on the coating amount of the upper layer (alkaline organic-inorganic composite coating layer in this embodiment), and when the coating amount is large, the molding processability is improved. This is because the coating amount of the inorganic composite coating layer is large.

Claims (9)

A galvanized layer is provided on both surfaces of the steel sheet, and a two-layer coating comprising an acidic inorganic coating layer and an alkaline organic-inorganic composite coating layer is further provided on the surface of the galvanized layer, and the coating weight of the acidic inorganic coating layer is 0. a 01~0.5g / ^{m 2,} coating weight of the alkaline organic inorganic composite coating layer is a surface treated zinc-based plated steel sheet is 0.5 to 3 g / ^{m 2,}
The acidic inorganic coating layer is formed by adding at least a zirconium compound (A), a water-dispersible silica (B), a magnesium compound (C), a vanadium compound (D), and a fluorine compound (E), and has an acidic inorganic pH of 2 to 5. A layer formed by applying a coating (L);
The alkaline organic-inorganic composite coating layer has an anionic urethane resin (U), alkali silicate (V), titanium alkoxide (W), polycarbodiimide resin (X) and silane having a weight average molecular weight of 100,000 to 200,000. A surface-treated galvanized steel sheet, which is a layer formed by applying an alkaline organic-inorganic composite coating agent (M) having a pH of 9 to 12 to which at least a coupling agent (Y) is added. Surface treated zinc-based plated steel sheet according to claim 1 zinc basis weight of one surface of the galvanized steel sheet is characterized in that it is a 1 to 15 g / m ^2.   The surface-treated zinc-based plated steel sheet according to claim 1 or 2, wherein the alkaline organic inorganic coating layer contains a water-dispersible wax (Z).   The surface-treated zinc-based plated steel sheet according to any one of claims 1 to 3, wherein the anionic urethane resin (U) has a carboxyl group or a salt thereof.   Solid content mass ratio of zirconium compound (A) containing metal (a) and anionic urethane resin (U) is (a) / (U) = 0.001 to 0.4, water dispersible silica (B) and anion The solid content mass ratio of the conductive urethane resin (U) is (B) / (U) = 0.001 to 1, and the solid content mass ratio of the magnesium compound (C) -containing metal (c) and the alkali silicate (V). (C) / (V) = 0.001 to 0.5, the solid content mass ratio of the metal (d) of the vanadium compound (D) and the alkali silicate (V) is (d) / (V) = 0.001 to 0.5, the solid content mass ratio of the fluorine element (e) of the fluorine compound (E) and the metal (c) contained in the magnesium compound (C) is (e) / (c) = 0.1 to 30 The solid content mass ratio of the metal (w) of the titanium alkoxide (W) and the alkali silicate (V) is (w) / (V = 0.01 to 1, the solid content mass ratio of the polycarbodiimide resin (X) and the anionic urethane resin (U) is (X) / (U) = 0.001 to 0.5, the silane coupling agent (Y) The solid content mass ratio of the anionic urethane resin (U) is (Y) / (U) = 0.001 to 0.5, the solid content mass ratio of the water dispersible wax (Z) and the anionic urethane resin (U) (Z) / (U) = 0.01-0.2, The surface-treated galvanized steel sheet according to claim 3 or 4.   The surface-treated zinc-based plated steel sheet according to any one of claims 1 to 5, wherein the alkaline organic-inorganic composite coating layer has a glass transition temperature exceeding 100 ° C.   The surface-treated galvanized steel sheet according to any one of claims 1 to 6, wherein the galvanized steel sheet is an electrogalvanized steel sheet.   Including a two-layer coating forming step of forming the acidic inorganic coating layer and the alkaline organic-inorganic composite coating layer according to any one of claims 1 to 6 on the surface of the galvanized steel plate having galvanized layers on both surfaces of the steel plate. Here, the two-layer film forming step is a step of forming an acidic inorganic coating layer by applying an acidic inorganic coating agent (L) on the zinc-based plated steel sheet and then drying at 50 ° C. or higher and 100 ° C. or lower. Applying an alkaline organic-inorganic composite coating agent (M) to the upper layer of the acidic inorganic coating layer and coating it to form an alkaline organic-inorganic composite coating layer by drying at an ultimate temperature of 100 ° C. or higher and lower than 200 ° C. A method for producing a surface-treated galvanized steel sheet.   A surface-treated galvanized steel sheet obtained by claim 8.