Title of the invention: Coating composition of galvanized steel sheet containing magnesium and steel sheet coated therewith
Technical field
[One]
The present invention relates to a coating composition for a magnesium-containing galvanized steel sheet and a magnesium-containing galvanized steel sheet coated therewith. More specifically, the present invention relates to a coating composition for preventing the occurrence of black spots and black spots when exposed to a high temperature and high humidity environment of a galvanized steel sheet containing Mg, and to a galvanized steel sheet including Mg coated therewith.
Background
[2]
A patent for a water-soluble coating composition containing olefin resin, organic silane, blackening inhibitor, inorganic metal rust inhibitor, etc., as a technology for improving corrosion resistance and blackening resistance of alloy-plated steel sheets containing Mg in the plating layer (Korean Patent No. 10- 1586840 B1, Korean Patent No. 10-1262497 B1, etc.), but the olefin resin, which occupies most of the constituent materials of the coating layer, has a high moisture and/or oxygen permeability, so it is not possible to fundamentally suppress the occurrence of blackening and black spots. Further, the patent does not mention the oxygen and/or moisture permeability of the coating layer.
[3]
In addition, as a technology for preventing blackening due to moisture of the Mg metal plate, an inorganic coating layer is formed by coating a composition containing a siloxane precursor with atmospheric plasma, and a composition containing a polyvinylidene polymer is coated on the inorganic coating layer. There is a technology for forming an organic coating layer (Korean Patent No. 10-1758474). However, since the coating layer is composed of only polyvinylidene-based polymers that are not cross-linked, it has high moisture and oxygen permeability compared to the coating layer composed of cross-linked polyvinylidene-based polymers. There is a disadvantage in that an organic solvent is inevitably used to prepare the den-based polymer as a fluid coating solution.
[4]
Patents mentioning a polyvinylidene resin containing a carboxyl group are US Patent US 6037124 A (Carboxylated polyvinylidene fluoride solid supports for the immobilization of biomolecules and methods of use thereof), US Patent Publication US 2013-0231428 A1 (FAST FILM FORMATION WATER BASED BARRIER COATING), etc., but there is no blackening prevention application and crosslinking of plated steel sheets containing Mg.
[5]
In addition, in the past, polyvinylidene-based polymers were dissolved in an organic solvent and coated on a steel sheet containing Mg in order to prevent moisture and oxygen permeation. As it is not, chemical resistance is insufficient and there is a limit to lowering the moisture and oxygen permeability. In addition, an emulsifier is used for the synthesis of polyvinylidene polymer (copolymer) through emulsion (co) polymerization. Due to the emulsifier containing a salt of molecular weight, it is vulnerable to moisture, and when exposed to a high temperature and high humidity environment for a long time, yellowing occurs. (ref. Emulsion Polymerization and Emulsion Polymers, by Peter A. Lovell (Editor), Mohamed S. El-Aasser (Editor), March 1997)
[6]
[Prior technical literature]
[7]
[Patent Literature]
[8]
(Patent Document 1) Korean Patent No. 10-1586840
[9]
(Patent Document 2) Korean Patent No. 10-1262497
[10]
(Patent Document 3) Korean Patent No. 10-1758474
[11]
(Patent Document 4) US Patent No. 6037124 A
[12]
(Patent Document 5) US Patent Publication No. 2013-0231428 A1
[13]
[Non-patent literature]
[14]
(Non-Patent Document 1) Emulsion Polymerization and Emulsion Polymers, by Peter A. Lovell (Editor), Mohamed S. El-Aasser (Editor), March 1997
Detailed description of the invention
Technical challenge
[15]
The present invention is to solve the above problems, to provide a coating composition for a magnesium-containing plated steel plate and a magnesium-containing plated steel plate coated therewith. In addition, the present invention provides a coating composition for a galvanized steel sheet containing magnesium for suppressing the occurrence of black spots and black spots in a plated steel sheet containing Mg in a plating layer, and a magnesium-containing galvanized steel sheet coated therewith.
Means of solving the task
[16]
According to one aspect of the present invention, a steel sheet coating composition comprising 10 to 20% by weight of a carboxylated vinylidene copolymer, 1 to 5% by weight of a water-dispersible crosslinking agent and the balance water based on the weight of the carboxylated vinylidene copolymer Is provided.
[17]
The carboxylated vinylidene copolymer may be prepared by emulsion-free emulsion copolymerization with a vinylidene-based monomer and a monomer including a carboxyl group as main components.
[18]
The vinylidene-based monomer is vinylidene fluoride, vinylidene chloride, vinylidene fluoride-co-hexafluoropropylene, vinylidene chloride-co-acryl Vinylidene chloride-co-acrylonitrile, vinylidene chloride-co-acrylonitrile-co-methyl methacrylate, vinylidene chloride-co-vinyl It may be at least one selected from the group consisting of chloride (vinylidene chloride-co-vinyl chloride) and vinylidene chloride-co-methyl acrylate.
[19]
The monomers containing the carboxy group are acrylic acid, methacrylic acid, crotonic acid, 2-ethylacrylic acid, 2-Pentenic acid, 4-pentenoic acid, 2 -Propylacrylic acid, 2-Octenoic acid, 3-vinylbenzoic acid, 4-vinylbenzoic acid, 2-carboxyethyl acrylate trans-3-benzoylacrylic acid, 2-bromoacrylic acid and It may be at least one selected from the group consisting of 2-bromomethyl-acrylic acid.
[20]
In the emulsion-free emulsion copolymerization of the vinylidene-based monomer and the monomer containing the carboxy group as a main component, based on the total weight of the emulsion polymerized material, the vinylidene-based monomer is 10 to 15 wt% based on the total weight of the emulsion polymerization material, the It may be a non-emulsifying agent emulsion copolymerization of an emulsion polymerization material including 0.5 to 1.5 wt% of a monomer containing a carboxy group and the balance water based on the vinylidene monomer.
[21]
The water-dispersible crosslinking agent may be at least one selected from the group consisting of aziridine, isocyanate compounds, and carbodoomide compounds.
[22]
Further, according to another aspect of the present invention, there is provided a plated steel sheet containing magnesium in a plating layer having a coating film layer formed of the steel sheet coating composition of the present invention.
[23]
The steel sheet coating composition may be applied on a plated steel sheet containing magnesium such that a dry film adhesion amount is 500 to 800 mg/m 2 to form a coating film layer.
Effects of the Invention
[24]
The coating composition according to the present invention is coated on the surface of a plated steel sheet and is cross-linked during drying to form a three-dimensional dense molecular structure. Accordingly, compared to a coating agent formed of a non-crosslinked polyvinylidene-based polymer, moisture and/or oxygen permeability can be lowered, and thus blackening and/or black spots can be prevented when exposed for a long time in a high temperature and high humidity environment. In addition, it is environmentally friendly because no organic solvent is used in the coating composition. Therefore, the plated steel sheet on which the coating film is formed with the coating composition according to the present invention is prevented from blackening and/or black spots. In particular, even when exposed to a high temperature and high humidity environment, it exhibits excellent physical properties to prevent the occurrence of blackening and/or black spots.
Brief description of the drawing
[25]
1 is a photograph of evaluating the blackness of a steel sheet after being left for 120 hours at 50° C., 95% relative humidity by coating an existing material with the coating composition of the present invention. (a) shows a comparative example, and (b) shows an invention example.
Best mode for carrying out the invention
[26]
Hereinafter, preferred embodiments of the present invention will be described. However, embodiments of the present invention may be modified in various other forms, and the scope of the present invention is not limited to the embodiments described below.
[27]
According to one aspect of the present invention, a steel sheet coating composition comprising 10 to 20% by weight of a carboxylated vinylidene copolymer, 1 to 5% by weight of a water-dispersible crosslinking agent and the balance water based on the weight of the carboxylated vinylidene copolymer Is provided.
[28]
The steel sheet coating composition of the present invention described above is a water-dispersible polyvinylidene polymer (including a carboxyl group in the molecular structure) having low moisture and/or oxygen permeability, that is, water dispersibility that can react with a carboxylated vinylidene copolymer and a carboxyl group. It contains a crosslinking agent (curing agent), and does not contain an emulsifying agent or dispersing agent.
[29]
Therefore, there are no defects such as holes in the coating film formed on the steel plate, and moisture and/or oxygen permeability is minimized by sufficient crosslinking. Therefore, when the plated steel sheet containing Mg is exposed to a high temperature and high humidity environment, it exhibits the effect of minimizing the occurrence of blackening and black spots.
[30]
The carboxylated vinylidene copolymer used in the steel sheet coating composition of the present invention is water-dispersible. This is to ensure that an organic solvent is not used in the steel plate coating composition of the present invention, and thus, an eco-friendly steel plate coating composition. In addition, the carboxylated vinylidene copolymer may be prepared by a surfactant-free emulsion copolymerization reaction using a vinylidene-based monomer and a monomer containing a carboxyl group as main components. This is to prevent defects due to residual emulsifiers, etc., when forming a coating film on a steel sheet using the coating composition of the present invention.
[31]
The vinylidene-based monomer is not limited thereto, but, for example, vinylidene fluoride, vinylidene chloride, vinylidene fluoride-co-hexafluoropropylene (vinylidene fluoride- co-hexafluoropropylene), vinylidene chloride-co-acrylonitrile, vinylidene chloride-co-acrylonitrile-co-methyl methacrylate (vinylidene chloride-co-acrylonitrile-co) -methyl methacrylate), vinylidene chloride-co-vinyl chloride and vinylidene chloride-co-methyl acrylate It can be more than that. These may be used alone or in combination of two or more, if necessary. The polymer film synthesized from the above vinylidene-based monomer has low oxygen and moisture permeability.
[32]
In the emulsion-free emulsion copolymerization of the vinylidene-based monomer and a monomer containing a carboxy group, the vinylidene-based monomer is preferably contained in an amount of 10 to 15 wt% of the total weight of the emulsion polymerization material. If the content of the vinylidene-based monomer is less than 10 wt%, the content of the polymer material contained in the coating composition is low, so a material containing a large amount of water must be coated to obtain the desired film thickness. Since holes are formed in the coating film, blackening of the plating layer existing under the coating cannot be prevented. In addition, oxygen and/or moisture barrier properties by the polymer film may be insufficient, and/or the content of a monomer containing a carboxyl group is relatively high, so that a large amount of polymer electrolyte is formed in the aqueous phase in the process of forming a copolymer. This may result in poor water dispersion stability. When the content of the vinylidene-based monomer exceeds 15 wt%, since it does not contain an emulsifier for emulsion polymerization, there is a problem in that the carboxylated vinylidene copolymer has poor water dispersion stability and is easily gelled.
[33]
The monomer containing the carboxy group is not limited thereto, but examples include acrylic acid, methacrylic acid, crotonic acid, 2-ethylacrylic acid, and 2-pentenoic acid ( 2-Pentenic acid), 4-pentenic acid, 2-propylacrylic acid, 2-Octenoic acid, 3-vinylbenzoic acid, 4-vinylbenzoic acid, 2-carboxyethyl acrylate trans At least one or more selected from the group consisting of -3-benzoylacrylic acid, 2-bromoacrylic acid and 2-bromomethyl-acrylic acid may be used. These may be used alone or in combination of two or more, if necessary.
[34]
A monomer containing a carboxy group is emulsion-copolymerized with a vinylidene-based monomer to improve the water dispersion stability of the carboxylated vinylidene copolymer, and the effect of forming a dense film of a network structure by reacting with a crosslinking agent during drying and curing. There is.
[35]
In the emulsion copolymerization of the vinylidene-based monomer and a monomer containing a carboxyl group with an emulsifier-free agent, the monomer containing a carboxy group is preferably contained in an amount of 0.5 to 1.5 wt% compared to the vinylidene monomer. If the content of the monomer containing a carboxyl group is less than 0.5 wt%, the water dispersion stability of the carboxylated vinylidene copolymer decreases, and there are few sites capable of reacting with the crosslinking agent, forming a coating film with a dense network structure. It is difficult to do. If it exceeds 1.5 wt%, there is a problem in that a large amount of polymer electrolyte is formed in the aqueous phase in the process of forming the carboxylated vinylidene copolymer, resulting in poor water dispersion stability.
[36]
In the emulsion polymerized material, the balance other than the vinylidene-based monomer and the monomer including a carboxyl group is water. Water generally used for preparing the copolymer may be used, but is not limited thereto, but distilled water, tap water, deionized water, pure water, ultrapure water, and the like may be used. In addition, the emulsion polymerization material may include other additives generally used in an emulsifying agent-free emulsion copolymerization reaction, for example, a polymerization initiator or the like, if necessary. These other additives are common in the art and are not described in detail herein.
[37]
A method for producing a carboxylated vinylidene copolymer by an emulsifying agent-free emulsion copolymerization reaction is generally known in the art, and can be performed by any known emulsifying agent-free emulsion copolymerization method. Accordingly, the conditions of the emulsification-free emulsion copolymerization method, for example, conditions including temperature and time conditions, and other additives used therein are not separately described in the present specification, and the present invention is not limited thereto. A carboxylated vinylidene copolymer prepared by any method known in the art can be used in the coating composition of the present invention.
[38]
The carboxylated vinylidene copolymer is blended in an amount of 10 to 20 wt% in the steel sheet coating composition of the present invention. If the content of the carboxylated vinylidene copolymer contained in the steel sheet coating composition is less than 10 wt%, the content of the polymer material contained in the coating composition is low, so that the desired thickness of the film is reduced, and a material containing a large amount of water is coated. Therefore, when the coating layer is dried, a hole is formed in the coating layer due to a boiling phenomenon, so that blackening of the plating layer existing under the coating layer cannot be prevented. When the content of the carboxylated vinylidene copolymer exceeds 20 wt%, there is a problem in that the water dispersion stability is poor, and thus gelation is easily formed.
[39]
The steel sheet coating composition of the present invention also contains a water-dispersible crosslinking agent (curing agent). The water-dispersible crosslinking agent usable in the steel sheet coating composition of the present invention is not limited thereto, but is, for example, selected from the group consisting of aziridine, isocyanate compounds, and carbodiimide compounds. It can be used at least some kind. Although not limited thereto, as a specific example of aziridine, CROSSLINKER CX100 (DSM Chemical), as a specific example of an isocyanate compound Bayhydur (covestro chemical), and a specific example of carbodiimide, STAHL EVO Permutex (Stahl) ).
[40]
The water-dispersible crosslinking agent is contained in an amount of 1% to 5% by weight, preferably 1% to 3% by weight (based on the weight of the carboxylated vinylidene copolymer) relative to the carboxylated vinylidene copolymer. desirable. The water-dispersible cross-linking agent reacts with carboxyl groups present on the carboxylated vinylidene copolymer surface during the process of coating material coated on a plated steel sheet containing Mg and drying and curing to form a dense three-dimensional film to form a moisture content. And it serves to block oxygen. If it is less than 1% by weight, crosslinking becomes insufficient due to insufficient amount of the crosslinking agent required for the curing reaction, and if it exceeds 5% by weight, components that do not participate in crosslinking other than the amount required for crosslinking are present as impurities in the film. As a result, a defect occurs, and the moisture barrier effect decreases.
[41]
In the steel sheet coating composition of the present invention, portions other than the carboxylated vinylidene copolymer and the water-dispersible crosslinking agent are water. The water is not limited thereto, but may be, for example, tap water, pure water, ultrapure water, distilled water, deionized water, or the like.
[42]
The steel sheet coating composition of the present invention may consist essentially of or consist of the carboxylated vinylidene copolymer, a water-dispersible crosslinking agent, and water. If necessary, the steel plate coating composition of the present invention may contain additives such as adhesion promoters, rust inhibitors, lubricants, etc. that may be generally blended in the steel plate surface treatment composition in the art.
[43]
The steel sheet coating composition of the present invention is prepared by mixing the carboxylated vinylidene copolymer, a water-dispersible crosslinking agent, and water, and the manufacturing method is not particularly limited.
[44]
After coating the steel plate coating composition of the present invention on a plated steel plate having a plated layer containing Mg and drying to form a coating layer on the surface of the plated steel plate, moisture and/or oxygen permeability to the steel plate is lowered, and black spots and/or black spots Occurrence is prevented.
[45]
In order to improve the corrosion resistance of the steel sheet, the plating layer generally contains Mg. In general, a plating layer containing 0.5% to 5% by weight of Mg is used in terms of improving the corrosion resistance of the steel sheet. However, in the plating layer containing Mg, Mg concentrates as oxide on the top layer of the plating layer (the surface directly in contact with air), and when it is easily contacted with oxygen and/or moisture in the atmosphere, blackening and/or black spots are caused by incomplete oxidation and corrosion reaction. There is a problem that arises. Therefore, by blocking the plating layer with a coating layer having a small amount of moisture and/or oxygen permeation, and preventing oxygen and/or moisture from passing through the coating layer, corrosion of the Mg oxide present in the uppermost layer of the plating layer is prevented. Expression can be suppressed by the phenomenon of sunspots. Therefore, in the present invention, in order to prevent the occurrence of black spots and/or black spots in the plated layer containing Mg as described above, a coating layer is formed by applying the steel plate coating composition of the present invention to the plated layer containing Mg.
[46]
As described above, the present invention prevents the occurrence of black spots and/or black spots due to Mg contained in the plating layer, and can be applied to any plated steel sheet containing the Mg in the plating layer. In order to improve the corrosion resistance of the steel sheet, as described above, the plating layer generally contains about 0.5% by weight to 5% by weight, preferably about 1.5% by weight to 3% by weight of Mg. This makes it impossible to manufacture a plating bath due to oxidation of the surface of the plating bath when the Mg content in the plating layer exceeds 5% by weight, and when Mg is less than 0.5% by weight, the effect of improving corrosion resistance is insignificant.
[47]
Therefore, the present invention can be applied to a plated steel sheet having a plating layer containing 0.5% to 5% by weight of Mg, preferably 1.5% to 3% by weight. At this time, the balance of the plating layer may be any composition known in the art, but is not limited thereto, but, for example, the balance of the plating layer may be Zn or Al.
[48]
The plated steel sheet containing Mg in the plating layer may be specifically a galvanized steel sheet, more specifically, a ternary galvanized steel sheet in which the plating layer is composed of Mg/Al/Zn. More specifically, the plating layer may be Mg 0.5% to 5% by weight, preferably 1.5% to 3% by weight, Al may be 1.5% to 11% by weight and the balance Zn.
[49]
The steel plate coating composition of the present invention may be applied to a plated steel plate containing Mg in a plated layer by any coating method known in the art, and the coating method is not limited. For example, it can be applied by any coating method such as dip coating, bar coating, roll coating, spray coating.
[50]
The film adhesion amount was set so that the dry film adhesion amount was 500 to 800 mg/m 2 . The dry film coating weight 500 mg / m 2 is not enough is less than the moisture and oxygen barrier effect blackening are undesirable can be generated easily 800mg / m 2 preferably in that the machining resin eliminated or welding, etc. Tube Mill decrease if it exceeds the Not.
[51]
The steel sheet coating composition of the present invention may be applied to one side or both sides of a plated steel sheet containing Mg in the plating layer.
[52]
After coating the steel plate coating composition of the present invention on a plated steel plate containing Mg in a plated layer, it is dried. Drying can also be performed by any drying method and/or condition known in the art, and is not particularly limited. For example, by drying at a temperature of 100° C. to 200° C. for 5 to 30 seconds, a coating layer may be formed on the plated steel sheet. By drying in the above temperature and time range, the steel plate coating composition is crosslinked and dried to form a three-dimensional dense molecular structure.
[53]
In the coating and drying process, a water-dispersible carboxylated polyvinylidene-based copolymer containing a carboxyl group in the molecular structure according to the present invention and a water-dispersible crosslinking agent (curing agent) capable of reacting with the carboxyl group are crosslinked to form a three-dimensional To form a dense molecular structure. Accordingly, moisture and/or oxygen permeability is lowered, and generation of black spots and/or black spots is prevented even when exposed for a long time in a high temperature and high humidity environment. In addition, it is eco-friendly because organic solvents are not used among the coating materials.
Mode for carrying out the invention
[54]
Hereinafter, the present invention will be described in more detail through examples. However, it should be noted that the following examples are for illustrative purposes only and are not intended to limit the scope of the present invention. This is because the scope of the present invention is determined by matters described in the claims and matters reasonably inferred therefrom.
[55]
(Example)
[56]
1. Preparation of carboxylated polyvinylidene emulsion copolymer
[57]
After adding 12 g of vinyllidiene and 0.1 g of acrylic acid to 100 g of distilled water, and raising the temperature to about 30°C, while stirring at a speed of 200 rpm with a stirrer, 0.02 g of potassium peroxysulfate, sodium bisulfite ) 0.01 g was added to proceed with the emulsion polymerization for about 5 hours to prepare a carboxylated polyvinylidene emulsion copolymer dispersion having a conversion ratio of 99.5% or more . At this time, the size of the prepared polymer particles was 0.1 ~ 0.5㎛.
[58]
2. Manufacture of coating material to prevent blackening of plated steel sheet including Mg
[59]
Prepare a coating material by mixing 0.1 g of azidiline crosslinking agent (brand name CX-100, DSM) in a dispersion in which 10 g of the carboxylated polyvinylidene emulsion copolymer prepared in item 1 is dispersed in 85 g of distilled water at room temperature. I did.
[60]
3. Step of forming a crosslinked thin film to prevent blackening
[61]
Coating the coating material prepared in item 2 above with a bar coater on a three-way plated steel sheet containing Al-Mg-Zn in the plating layer (plating layer composition: Mg 3.0wt%, Al 1.5wt%, the balance Zn) and then dried with hot air Made it. Hot air drying was performed at 200°C for 10 seconds. The dry film adhesion amount was adjusted to 500 to 800 mg/m 2 .
[62]
In the drying process, the carboxylated polyvinylidene-based copolymer and the crosslinking agent in the coating composition were crosslinked as shown in Scheme 1 below to form a coating layer having a three-dimensional dense molecular structure.
[63]
[Scheme 1]
[64]

[65]
(R: alkyl group)
[66]
4. Evaluation of blackness prevention ability
[67]
The blackening prevention performance of the plated steel sheet was evaluated.
[68]
In the evaluation, the plated steel sheet (inventive example) on which the coating layer of item 3 was formed and the ternary plated steel sheet (steel sheet of item 3, comparative example) containing Al-Mg-Zn without coating treatment were used at an atmosphere temperature of 50°C and 95 After 120 hours after loading into a constant temperature and humidity unit of% (left under high temperature and high humidity conditions), the presence /absence of black stools was evaluated with the naked eye and a color difference meter. In addition, pictures of the surfaces of Comparative Example (a) and Inventive Example (b) after being allowed to stand in high temperature and high humidity conditions are shown in FIG. 1. As for the color difference meter, the invention example was 1.5 and the comparative example was 10 units based on delta E.
[69]
As can be seen from FIG. 1, the plated steel sheet of Inventive Example (b) in which a coating layer was formed with the coating composition according to the present invention did not generate red rust, and exhibited good results in appearance as there was no surface discoloration.
Claims
[Claim 1]
A steel sheet coating composition comprising 10 to 20% by weight of a carboxylated vinylidene copolymer, 1 to 5% by weight of a water-dispersible crosslinking agent and the remainder based on the weight of the carboxylated vinylidene copolymer.
[Claim 2]
The steel sheet coating composition according to claim 1, wherein the carboxylated vinylidene copolymer is prepared by emulsifying a non-emulsifying agent based on a vinylidene-based monomer and a monomer including a carboxyl group as a main component.
[Claim 3]
The method of claim 2, wherein the vinylidene-based monomer is vinylidene fluoride, vinylidene chloride, vinylidene fluoride-co-hexafluoropropylene, vinyl Lidene chloride-co-acrylonitrile, vinylidene chloride-co-acrylonitrile-co-methyl methacrylate, vinyl A steel plate coating composition, which is at least one member selected from the group consisting of leadene chloride-co-vinyl chloride and vinylidene chloride-co-methyl acrylate.
[Claim 4]
The method of claim 2, wherein the monomer containing a carboxy group is acrylic acid, methacrylic acid, crotonic acid, 2-ethylacrylic acid, 2-pentenoic acid, 4-pentenoic acid, 2-propylacrylic acid, 2-Octenoic acid, 3-vinylbenzoic acid, 4-vinylbenzoic acid, 2-carboxyethyl acrylate trans-3-benzoylacrylic acid, At least one member selected from the group consisting of 2-bromoacrylic acid and 2-bromomethyl-acrylic acid, a steel sheet coating composition.
[Claim 5]
The method of claim 2, wherein the non-emulsifying agent emulsion copolymerization comprising the vinylidene-based monomer and the monomer containing the carboxyl group as a main component is based on the total weight of the emulsion-polymerized material, and the vinylidene-based monomer is 10 based on the total weight of the emulsion-polymerized material. ~15 wt%, a non-emulsifying agent emulsion copolymerization of an emulsion polymerized material containing 0.5 to 1.5 wt% and the balance water with respect to the vinylidene monomer of the monomer containing the carboxy group, steel sheet coating composition.
[Claim 6]
The steel sheet coating composition according to claim 1, wherein the water-dispersible crosslinking agent is at least one selected from the group consisting of aziridine, isocyanate compounds, and carbodoomide compounds.
[Claim 7]
A plated steel sheet containing magnesium in a plated layer having a coating film layer formed of the steel sheet coating composition of claim 1.
[Claim 8]
The plated steel sheet containing magnesium according to claim 7, wherein the steel sheet coating composition is applied on a plated steel sheet containing magnesium so that a dry film adhesion amount is 500 to 800 mg/m 2 to form a coating film layer.