JP2010070603A - Aqueous rust-preventive coating composition - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an aqueous rust-preventive coating composition composed mainly of a vinylidene chloride copolymer latex exhibiting good storage stability, sufficient rust-preventive properties and excellent water-resistant adhesive properties to a topcoating in rust-preventive coating applications for various metal members of construction and building materials. <P>SOLUTION: The aqueous rust-preventive coating composition includes 100 pts.mass of solid contents of a latex composed of a vinylidene chloride copolymer resin comprised of (meth)acrylic acid and the like, and 0.05-3 pts.mass of a specific silane coupling agent. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention is a vinylidene chloride type which has good storage stability of coating compositions, sufficient rust prevention, and excellent water resistance adhesion to top coating in various anti-corrosive coating applications such as construction and building materials. The present invention relates to a water-based anticorrosive coating composition mainly comprising a copolymer latex.

  In recent years, interest in the protection of the global environment has increased, and there has been an active shift from solvent-based paints to water-based paints due to the stricter regulations on solvents and heavy metals. There is a strong demand for water-based paints having excellent antirust and moisture resistance. Among various water-based paint resins, the vinylidene chloride copolymer latex resin is particularly suitable as a resin for rust-proof paint because of its excellent barrier properties such as low water vapor transmission rate and low oxygen transmission rate. Yes.

As a rust preventive paint, Patent Document 1 discloses a rust preventive paint composition obtained by mixing tannic acid with a vinylidene chloride copolymer resin latex. This rust preventive coating composition exhibits excellent rust preventive performance due to the synergistic effect of the barrier action of vinylidene chloride resin and the chelate reaction of tannic acid and iron oxide. However, this coating composition has problems such as changes occurring during storage at a temperature of 20 ° C. or more, the effect of tannin gradually diminishing, and rust prevention properties gradually decreasing. Further, Patent Document 2 discloses a rust preventive coating composition in which aluminum tripolyphosphate and a polyhydric alcohol compound, which are rust preventive pigments, are mixed with a vinylidene chloride copolymer resin latex. However, when this water-based anticorrosive coating composition is applied as an undercoat, and various types of paint are applied to the topcoat, poor adhesion due to a large difference in elastic modulus between the undercoat and the topcoat occurs. There was a problem. On the other hand, Patent Document 3 discloses an aqueous coating composition in which a vinylidene chloride copolymer resin latex is mixed with a silicone resin leveling agent for the purpose of improving adhesion to the top coat film. However, when the coating film coated with the top coating is immersed in water on the coating film coated with the water-based anticorrosive coating composition, the difference in water absorption between the top coating film and the undercoating film is too large. There is a problem that a difference in volume expansion occurs, and an adhesive force sufficient to absorb strain generated from the difference in volume expansion is not sufficient, so that swelling occurs between the undercoat and the top coat.
JP-A 63-105073 Japanese Patent Laid-Open No. 5-140501 JP-A-5-156199

  The object of the present invention is mainly composed of a latex composed of a vinylidene chloride copolymer resin capable of forming a coating film having good storage stability of the coating composition, sufficient rust prevention property, and excellent water resistance adhesion to the top coat. It is in providing the water-system antirust coating composition made into.

As a result of intensive studies in order to solve the above-mentioned problems, the present inventors have found that a water-based anticorrosive paint using a specific silane coupling agent in a latex made of a specific vinylidene chloride copolymer resin. Only in the composition, it was found that the storage stability was good, the rust prevention property and the water-resistant adhesion to the top coat were excellent, and the present invention was completed.
That is, the first of the present invention is a chlorine-containing vinyl monomer (A) comprising 80 to 95% by mass of at least one kind selected from vinylidene chloride and vinyl chloride, a carboxylic acid group-containing vinyl monomer ( B) Chloride formed by emulsion polymerization of a mixture containing 0.5 to 5% by mass and one or more other vinyl monomers (C) 3 to 15% by mass copolymerizable therewith. A composition comprising a latex comprising a vinylidene-based copolymer resin and a silane coupling agent, wherein the silane coupling agent is added to the solid content of 100 parts by mass of the latex comprising the vinylidene chloride-based copolymer resin. It is an aqueous rust preventive coating composition characterized by containing 05-3 mass parts.
The second aspect of the present invention is characterized in that the ratio of vinyl chloride in the chlorine-containing vinyl monomer (A) composed of at least one selected from vinylidene chloride and vinyl chloride is 0 to 25% by mass. The water-based rust preventive coating composition according to the first aspect.
In the third aspect of the present invention, the aqueous carboxylic acid group-containing vinyl monomer (B) is at least one selected from acrylic acid and methacrylic acid. It is a rust preventive coating composition.
A fourth aspect of the present invention is a silane coupling agent having an epoxy group as a silane coupling agent, a silane coupling agent having a chloropropyl group, a silane coupling agent having an isocyanate group, or a silane coupling agent having a mercapto group. It is at least 1 sort (s) chosen from these, The water-based antirust coating composition as described in any one of said 1st-3rd characterized by the above-mentioned.

Hereinafter, the contents of the present invention will be described in detail.
The total amount of the chlorine-containing vinyl monomer (A) composed of at least one selected from vinylidene chloride and vinyl chloride of the present invention is 80 to 95% by mass, preferably 85 to 93% by mass. When it is 80% by mass or more, the barrier property is improved, and sufficient antirust property can be exhibited. On the other hand, the adhesiveness with a topcoat can be improved by setting it as 95 mass% or less. The proportion of vinyl chloride in the chlorine-containing vinyl monomer (A) composed of at least one selected from vinylidene chloride and vinyl chloride is 0 to 25% by mass, preferably 5 to 20% by mass. It is. Increasing the proportion of vinyl chloride reduces the crystallinity in the vinylidene chloride copolymer resin and contributes to improved adhesion. However, if the proportion of vinyl chloride is 25% by mass or more, the barrier property decreases and, as a result, rust prevention. Decreases.

  The latex composed of the vinylidene chloride copolymer resin of the present invention is copolymerized with a carboxylic acid group-containing vinyl monomer (B). By using the carboxylic acid group vinyl monomer, the dispersibility with the pigment is improved, the rust prevention is improved, and the adhesion to the object to be coated and the top coat film is also improved. Examples of the carboxylic acid group-containing vinyl monomer (B) include acrylic acid, methacrylic acid, itaconic acid, maleic acid, and fumaric acid. Among these, acrylic acid and methacrylic acid are preferable.

  The amount of the carboxylic acid group-containing vinyl monomer (B) is 0.5 to 5% by mass, preferably 1 to 3% by mass. When the content is 0.5% by mass or more, dispersibility with the pigment is improved, adhesion is improved, and sufficient rust prevention can be exhibited. On the other hand, when the content is 5% by mass or less, the hydrophilic substance in the coating film becomes a preferable amount, and the water-resistant adhesion aimed by the present invention can be expressed.

  Examples of the other vinyl monomers (C) copolymerizable with the chlorine vinyl monomer (A) and the carboxylic acid group-containing vinyl monomer (B) include, for example, methyl acrylate, propyl acrylate, Examples thereof include alkyl ester monomers of ethylene-based α, β-unsaturated carboxylic acids such as butyl acrylate and methyl methacrylate. Moreover, the monomer which has nitrile groups, such as acrylonitrile or methacrylonitrile, is mentioned similarly, for example. Also, ethylene-based α, β-unsaturated carboxylic acid hydroxyalkyl esters, acrylamide and other ethylene α, β-unsaturated carboxylic acid acrylamide compounds, vinyl acetate and other vinyl esters, allyl acetate and other allyl esters, allyl methyl Examples include allyl ethers such as ethers, and also styrene compounds.

  The amount of the other vinyl monomer (C) copolymerizable with the chlorine vinyl monomer (A) and the carboxylic acid group-containing vinyl monomer (B) is 3 to 15% by mass, preferably It is the range of 5-10 mass%. When the content is 3% by mass or more, the crystallinity of the vinylidene chloride copolymer resin is lowered and the film formability is improved, and the elastic modulus of the resin itself is lowered and the adhesion is improved. On the other hand, when the content is 15% by mass or less, the amount of vinylidene chloride in the vinylidene chloride copolymer resin is a preferable amount without decreasing, and sufficient rust prevention properties can be exhibited.

  The vinylidene chloride copolymer resin latex is obtained by mixing each of the above monomers within the above range and adding a polymerization initiator, a surfactant and the like and emulsion polymerization to obtain a polymerization initiator, a surfactant. The type of the agent is not particularly limited. This emulsion polymerization can be carried out in the same manner as before.

  Furthermore, the vinylidene chloride copolymer resin latex for water-based anticorrosive paints of the present invention can be used as it is to form a clear film as a coating agent, and various kinds of commonly used as required. In addition, for example, antifoaming agents, rheology modifiers, thickeners, dispersants, surfactants and other stabilizers, wetting agents, plasticizers, colorants, waxes, silicone oils, etc. Good. Moreover, if necessary, it is also possible to mix and use a color pigment, an extender pigment, and a rust preventive pigment.

  By coating the vinylidene chloride copolymer resin latex of the present invention with a silane coupling agent, the coating film using the water-based anticorrosive paint composition mainly composed of the vinylidene chloride copolymer resin latex as the undercoat is a top coat. It greatly contributes to the improvement of water-resistant adhesion with paint.

  The silane coupling agent is not particularly limited as long as it is a compound having an alkoxysilane at the terminal, but at the same time vinyl group, epoxy group, stil group, methacryloxy group, acryloxy group, amino group, ureido group, chloropropyl group, mercapto group. Those having a group, a sulfide group, an isocyanate group, a ketimino group and the like are used. In particular, a silane coupling agent having an epoxy group, a chloropropyl group, an isocyanate group, or a mercapto group is selected from the viewpoint of maintaining the storage stability of the coating composition and improving the water-resistant adhesion between the undercoat film and the topcoat film. Examples of the silane coupling agent having an epoxy group include 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropyltriethoxysilane, 3-glycidoxypropylmethyldimethoxysilane, and 3-glycidoxypropylmethyl. Examples include diethoxysilane, 2- (3,4-epoxycyclohexyl) ethyltrimethoxysilane, and the like, in particular, 3-glycidoxypropyltrimethoxysilane, 2- (3,4-epoxycyclohexyl) ethyltrimethoxysilane, and the like. Is mentioned. Examples of the silane coupling agent having a chloropropyl group include 3-chloropropyltrimethoxysilane. Examples of the silane coupling agent having an isocyanate group include 3-isocyanatopropyltriethoxysilane. Examples of the silane coupling agent having a mercapto group include 3-mercaptopropyltrimethoxysilane, 3-mercaptopropylmethyldimethoxysilane, and 3-mercaptopropyltriethoxysilane.

  The amount of the silane coupling agent is 0.05 to 3 parts by weight, preferably 0.1 to 2 parts by weight, based on 100 parts by weight of the solid content of the latex composed of the vinylidene chloride copolymer resin. When the amount is 0.05 parts by mass or more, the water-resistant adhesion with the top coating material, which is the object of the present invention, can be sufficiently exerted, and when the amount is 3 parts by mass or less, the storage stability of the coating composition can be maintained.

  As a method for applying the water-based anticorrosive coating composition of the present invention, known methods such as air spray, airless, roll coater, curtain flow coat, roll coat, and immersion can be used on the surface of the article to be coated. Is dried at room temperature or under heating for a predetermined time.

  The aqueous rust preventive paint composition of the present invention can be used as it is as a rust preventive paint film, but it is also possible to apply a top coat onto the water rust preventive paint film for the purpose of maintaining the appearance and weather resistance. It is. The top coating is not particularly limited, and examples thereof include solvent-based and water-based top coatings such as acrylic resin, urethane resin, silicon resin, and vinyl chloride resin.

By using it as an undercoat film of a water-based anti-corrosion paint composition mainly composed of a latex composed of the vinylidene chloride copolymer resin of the present invention, a paint film having excellent water-resistant adhesion with a top coat paint can be formed.
The aqueous rust preventive coating composition comprising the vinylidene chloride copolymer resin latex of the present invention and a silane coupling agent has good storage stability of the coating composition, sufficient rust prevention, and water-resistant adhesion to various top coats. It is very useful as a rust preventive paint for various objects.

  Hereinafter, the present invention will be described more specifically with reference to examples and the like, but the present invention is not limited to these examples and the like. In addition, the part and% in an Example and a comparative example show a mass part and the mass%, respectively.

  A vinylidene chloride copolymer resin latex was produced by the following method. In a pressure-resistant reactor with glass lining, 82 parts of pure water, 0.2 part of sodium alkyldiphenyl ether disulfonate and 0.1 part of sodium persulfate were charged, and after deaeration with stirring, the temperature of the contents was adjusted. Maintained at 50 ° C. In a separate container, 73 parts of vinylidene chloride (VDC), 17 parts of vinyl chloride (VC), 2 parts of acrylic acid (AA) and 8 parts of butyl acrylate (BA) were weighed and mixed to prepare a monomer mixture. 10 parts of the monomer mixture was added all at once into the pressure-resistant reactor and polymerized until the internal pressure dropped. Subsequently, 90 parts of the remaining monomer mixture was continuously quantified and injected over 15 hours. In parallel, 0.8 parts of sodium alkyldiphenyl ether disulfonate was continuously metered in over 10 hours. During this time, the contents were kept at 50 ° C. while stirring, and the reaction was allowed to proceed until the internal pressure sufficiently decreased. The polymerization yield was 99.9%. Since the polymerization yield is almost 100%, the composition of the copolymer is almost equal to the charge ratio. After removing the unreacted monomer from the latex thus obtained by steam stripping, the solid content was adjusted to 60%.

Using the vinylidene chloride copolymer resin latex thus obtained, an aqueous rust preventive paint was prepared with the following composition.
<Production of water-based rust preventive paint>
16.35 parts of pure water, 1.89 parts of butyl glycol (film-forming auxiliary: manufactured by Wako Pure Chemical Industries, Ltd.), 0.13 part of Benton LT (thickener: manufactured by NL. Industries Inc.), SN deformer H2 (antifoaming agent: manufactured by San Nopco Co., Ltd.) 0.20 part, Synperonic PE / F87 30% aqueous solution (stabilizer: manufactured by ICI Chem. & Ply.) 3.43 parts, Surfynol 104E (wetting agent: Manufactured by Nissin Chemical Industry Co., Ltd.) 0.30 parts, Proxel BD (preservative: manufactured by Avecia) 0.05 parts, BYK154 (dispersant: manufactured by BYK Chemie GmbH), 0.50 parts, K-white84 (antirust pigment) : Teika Co., Ltd.) 5.96 parts, Toda Color 120ED (Colored Pigment: Toda Kogyo Co., Ltd.) 3.28 parts, Talc MS (External Pigment: Nihon Talc Co., Ltd.) 2 Charged .37 parts to the vessel to prepare a pigment dispersion was stirred min 10,000 revolutions for 20 minutes at VMA GETZMANN GmbH Co. DISPERMAT GMBH-D-51580. Subsequently, 45.40 parts of the vinylidene chloride copolymer resin latex previously adjusted to pH 4 with 10% ammonia water, KBM-703 (silane coupling agent: 3-chloro, manufactured by Shin-Etsu Chemical Co., Ltd.) were added to this pigment dispersion. Pyrtrimethoxysilane) 0.16 parts (solid content ratio of vinylidene chloride copolymer resin 0.5%), 10% sodium nitrite (flash rust inhibitor: Wako Pure Chemical Industries, Ltd.) 1.14 parts and 1.00 parts of CS-12 (film forming aid: manufactured by Chisso Corporation) were added and stirred until uniform to obtain an aqueous rust-proof paint.

Subsequently, the top coat used for top coat adhesion evaluation was prepared with the following composition.
<Preparation of top coat>
Propylene glycol (film-forming aid: manufactured by Wako Pure Chemical Industries, Ltd.) 2.1 parts, water 3 parts, AMP95 (pH adjuster: Angus Chemical Company) 0.2 parts, Dehydran 1293 (antifoaming agent: Cognis Company) 0 .5 parts, Surfinol 104E (wetting agent: manufactured by Nissin Chemical Industry Co., Ltd.) 0.4%, Orotan 165A (dispersing agent: manufactured by Rohm and Haas Japan Co., Ltd.) 6.2 parts, And stirred for 10 minutes at 10,000 rpm with a DISPERMAT GMBH-D-51580 manufactured by VMA GETZMANN GmbH to prepare a pigment dispersion. Subsequently, 53.7 parts of Polytron F830 (binder: Asahi Kasei Chemicals Co., Ltd. acrylic latex), 5 parts of methoxybutanol (film forming aid: Wako Pure Chemical Industries, Ltd.), butyl diglycol (Nippon Chemical Co., Ltd.) were added to this pigment dispersion. Membrane auxiliary: Wako Pure Chemical Industries, Ltd. 5 parts, Dehydran 1293 (antifoaming agent: Cognis Company) 0.8 part, Coatex BR100P (thickener: Cognis Company) 5 parts are added and stirred until uniform. A top coat was obtained.

  The test was carried out by the test method shown below using the water-based anti-corrosion paint and the top coat obtained as described above.

<Storage stability test of coating composition>
The water-based anticorrosive paint sealed in a plastic container was stored in a hot air dryer at 40 ° C. for 1 month, and the solidified state of the paint after cooling to 20 ° C. was visually observed. The storage stability was evaluated according to the following criteria.
○: The paint is fluid when the container is tilted ×: The paint is not fluid when the container is tilted

<Rust prevention test>
After applying and applying a water-based anti-corrosion paint to the polished steel sheet processed and adjusted according to JIS K 5600-1-4 using an applicator so that the dry coating film has a thickness of 40 μm, the end and back are the same. Painted with water-based anti-corrosion paint. The coated plate was dried for one week in an atmosphere of 20 ° C. and 55% RH. The coated plate thus obtained was subjected to JIS K 5600-7-1 as a semi-treatment, and a neutral resistance salt spray test was conducted for 240 hours. The evaluation of rust prevention was based on the following criteria.
○: No swelling, rust width from scratch is 1 mm or less. Δ: Swelling is, but rust width from scratch is 1 mm or less. ×: There is swelling, rust width from scratch is 1 mm or more.

<Water resistance adhesion test with top coat>
Apply a water-based anticorrosive paint to a polished coating steel plate (dimensions: 70 × 150 × 1t) processed and adjusted according to JIS K 5600-1-4 using an applicator so that the dry coating film has a thickness of 40 μm, and let it dry. After that, the edge and the back were also painted using the same water-based rust preventive paint. The coated plate was dried for one day in an atmosphere of 20 ° C. and 55% RH. Then, an overcoating was applied onto the dried coating film using an applicator and dried for one week in an atmosphere of 20 ° C. and 55% RH. A total of 90 μm of dry coating films for the undercoat and the topcoat was obtained. The coated plate thus obtained is put into a 1 L plastic container containing about 600 mL of water, the opening is sealed with a moisture-proof wrap film, and then immersed in water at 20 ° C. for 1 week to swell. Observed. Furthermore, after taking out from water, after drying for 1 week in 20 degreeC and 55% RH atmosphere, the adhesiveness of the part immersed in water was measured according to JISK5600-5-6 (cross-cut method). The evaluation of the swelling of water-resistant adhesion was based on the following criteria. Moreover, evaluation of the adhesiveness of a dry coating film followed the classification | category of the test result of JISK5600-5-6.
[Evaluation of swelling]
○: No swelling in water soaked part and non-soaked part △: Swelling in water soaked part but no swelling in non-soaked part ×: Swelled in both water soaked part and non-soaked part [Adhesion of dry paint film Evaluation]
0: The edge of the cut is perfect and smooth, and there is no peeling to the eyes of any grid. 1; Small peeling of the coating film at the intersection of the cut. It is clearly not more than 5% that is affected at the crosscut part 2; the coating is peeled along the edges of the cut and / or at the intersections.
It is clearly more than 5% but not more than 15% that is affected at the cross-cut part 3; the coating is partially or totally exfoliated along the edges of the cut and / or Or various parts of the eye are partially or completely peeled off. The cross-cut part is clearly affected by more than 15% but not more than 35%. 4; The coating is partially or fully peeled along the edges of the cut and / or Or some of the eyes are partially or completely peeled off. The cross-cut portion is clearly affected by more than 35% but not more than 65%. 5: When the degree of peeling exceeds Category 4

  0.27 parts (solid content ratio of vinylidene chloride copolymer resin) of KBM-703 (silane coupling agent: 3-chloropyrtrimethoxysilane manufactured by Shin-Etsu Chemical Co., Ltd.) in the aqueous rust preventive coating composition in Example 1 0.0%).

  KBM-403 (silane coupling agent: manufactured by Shin-Etsu Chemical Co., Ltd.) instead of KBM-703 (silane coupling agent: 3-chloropyrtrimethoxysilane manufactured by Shin-Etsu Chemical Co., Ltd.) in the composition of the water-based anti-corrosion paint in Example 1 The same procedure as in Example 1 except that 3-glycidoxypropyltrimethoxysilane was used.

  KBM-9003 (silane coupling agent: manufactured by Shin-Etsu Chemical Co., Ltd.) instead of KBM-703 (silane coupling agent: 3-chloropyrtrimethoxysilane manufactured by Shin-Etsu Chemical Co., Ltd.) in the aqueous rust preventive coating composition in Example 1 The same procedure as in Example 1 was conducted except that 3-isocyanatopropyltriethoxysilane was used.

  KBM-803 (silane coupling agent: manufactured by Shin-Etsu Chemical Co., Ltd.) instead of KBM-703 (silane coupling agent: 3-chloropyrtrimethoxysilane manufactured by Shin-Etsu Chemical Co., Ltd.) in the aqueous rust preventive coating composition in Example 1 The same procedure as in Example 1 except that 3-mercaptopropyltrimethoxysilane was used.

  The monomer mixture in Example 1 was the same as Example 1 except that 80 parts of vinylidene chloride (VDC), 10 parts of vinyl chloride, 3 parts of acrylic acid (AA), and 7 parts of butyl acrylate (BA) were used.

  The monomer mixture in Example 1 was the same as Example 1 except that 90 parts of vinylidene chloride (VDC), 3 parts of acrylic acid (AA), and 7 parts of butyl acrylate (BA) were used.

<Comparative Example 1>
The same procedure as in Example 1 was carried out except that KBM-703 (silane coupling agent: 3-chloropyrtrimethoxysilane manufactured by Shin-Etsu Chemical Co., Ltd.) in the aqueous rust-proof coating composition in Example 1 was changed to 0 part.

<Comparative example 2>
1.36 parts of KBM-703 (silane coupling agent: 3-chloropyrtrimethoxysilane manufactured by Shin-Etsu Chemical Co., Ltd.) in the aqueous rust preventive coating composition in Example 1 (solid content ratio of vinylidene chloride copolymer resin 5) 0.0%).

<Comparative Example 3>
The monomer mixture in Example 1 was the same as Example 1 except that 55 parts of vinylidene chloride (VDC), 30 parts of vinyl chloride, 5 parts of acrylic acid (AA), and 10 parts of butyl acrylate (BA) were used.

<Comparative example 4>
The monomer mixture in Example 1 was the same as Example 1 except that 90 parts of vinylidene chloride (VDC), 5 parts of vinyl chloride, 0 part of acrylic acid (AA) and 5 parts of butyl acrylate (BA) were used.

  Comparing Examples 1 to 7 and Comparative Examples 1 to 4, the aqueous rust preventive coating composition of the present invention has good storage stability, and is excellent in both rust prevention and water-resistant adhesion properties with the top coat. I understand that.

INDUSTRIAL APPLICABILITY The present invention can provide a water-based rust-preventive coating composition mainly composed of a vinylidene chloride copolymer latex, which has good storage stability, excellent rust-preventive properties, and excellent water-resistant adhesion to a top coat. Therefore, it can be suitably used as a rust preventive paint for various metal members such as buildings and building materials.

Claims (4)

  Chlorine-containing vinyl monomer (A) comprising at least one selected from vinylidene chloride and vinyl chloride 80 to 95% by mass, carboxylic acid group-containing vinyl monomer (B) 0.5 to 5% by mass A latex comprising a vinylidene chloride copolymer resin formed by emulsion polymerization of a mixture containing 3 to 15% by mass of one or more other vinyl monomers (C) copolymerizable with these And a silane coupling agent, wherein the silane coupling agent is contained in an amount of 0.05 to 3 parts by mass with respect to 100 parts by mass of the solid content of the latex comprising the vinylidene chloride copolymer resin. A water-based anti-rust paint composition.   The ratio of vinyl chloride in the chlorine-containing vinyl monomer (A) composed of at least one selected from vinylidene chloride and vinyl chloride is 0 to 25% by mass. Water-based anticorrosive coating composition.   The water-based rust preventive coating composition according to claim 1 or 2, wherein the carboxylic acid group-containing vinyl monomer (B) is at least one selected from acrylic acid and methacrylic acid.   The silane coupling agent is at least one selected from an epoxy group-containing silane coupling agent, a chloropropyl group-containing silane coupling agent, an isocyanate group-containing silane coupling agent, and a mercapto group-containing silane coupling agent. The aqueous rust preventive coating composition according to any one of claims 1 to 3.