Water-based coating composition

Abstract

This invention provides a water-based paint composition that exhibits rust-preventive properties on hot-dip galvanized surfaces even in harsh environments such as salt spray tests. [Solution] An aqueous paint composition comprising the following components (A) to (C). (A) Ingredients: (meth)acrylic emulsion (B) Ingredients: Phosphate-based rust inhibitor (C) Component: Particles having silanol groups on their surface

Description

Technical Field

[0001] The present invention is an aqueous paint composition having rust preventive properties, particularly for hot dip galvanized coatings.

Background Art

[0002] Hot dip galvanized coatings are used in the chassis of vehicle bodies and already have a certain degree of rust preventive properties. However, a paint is applied to further improve the rust preventive properties. Paints called semi-dry paints or wax-based paints have a chemically stable wax as the main component and improve the rust preventive properties against hot dip galvanized coatings. However, since the coating film components are not polymerized (crosslinked), it is known that the coating film is brittle and difficult to peel off. In particular, in vehicles, the chipping resistance is low, where the coating film is damaged by impacts such as small stones on the coating film, and corrosion occurs from the damage.

[0003] In the case of paints of the type that cure by a chemical reaction (polymerization) such as Patent Document 1, the rust preventive properties can be maintained, but it is necessary to heat the entire chassis. On the other hand, in the case of paints that form a coating film by fusion or polymerization such as an emulsion, the coating film is formed at room temperature, so the workability is excellent. However, in a severe environmental test such as a salt spray test, the rust preventive properties of the coating film deteriorate and rust occurs. In particular, in hot dip galvanized coatings, rust occurs significantly, so a paint having a strong coating film strength and rust preventive properties for hot dip galvanized coatings is required. Furthermore, an aqueous paint that takes environmental considerations is required."

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] Conventionally, with water-based paint compositions, it has been difficult to improve the rust prevention properties of the paint film in harsh environments such as salt spray tests when used in paints for hot-dip galvanizing. [Means for solving the problem]

[0006] As a result of diligent research to achieve the above objective, the inventors have completed the present invention, which is an aqueous coating composition having rust-preventive properties for hot-dip galvanized surfaces.

[0007] The gist of the present invention is described below. The first embodiment of the present invention is an aqueous coating composition comprising the following components (A) to (C). (A) Ingredients: (meth)acrylic emulsion (B) Ingredients: Phosphate-based rust inhibitor (C) Component: Particles having silanol groups on their surface

[0008] A second embodiment of the present invention is an aqueous paint composition according to the first embodiment, wherein component (B) is a phosphate-based rust inhibitor containing magnesium and / or aluminum.

[0009] A third embodiment of the present invention is an aqueous coating composition according to the first embodiment, wherein component (B) is magnesium phosphate and / or aluminum dihydrogen tripolyphosphate.

[0010] A fourth embodiment of the present invention is an aqueous coating composition according to the first embodiment, wherein component (C) is silicon dioxide particles and / or silicone resin particles.

[0011] A fifth embodiment of the present invention is a hot-dip galvanized member coated with the aqueous coating composition described in any of the first to fourth embodiments.

[0012] A sixth embodiment of the present invention is an aqueous coating composition according to any of the first to fourth embodiments, used for a vehicle chassis. [Effects of the Invention]

[0013] This invention enables the creation of an aqueous coating composition that provides corrosion prevention properties for hot-dip galvanized surfaces even in harsh environments such as salt spray tests. [Modes for carrying out the invention]

[0014] The details of the present invention will now be described. The component (A) that can be used in the present invention is a (meth)acrylic emulsion. For example, an emulsion is a polymer particle that is stably dispersed in water or the like, produced by emulsion polymerization of a compound (monomer) containing a (meth)acrylic group as a polymerizable monomer, with a surfactant and a polymerization initiator, and dried. The component (A) forms a film when the aqueous paint composition is dried. Other monomers besides compounds containing a (meth)acrylic group, such as styrene, may also be included. In the drying process of the present invention, when water or the like evaporates, the polymer particles gather together and fuse. Here, a self-crosslinking type is also possible, in which a crosslinking reaction occurs between polymers when the polymers, which are insoluble in water or the like in droplet form, fuse together during the drying process. Hereinafter, emulsion refers to polymer particles dispersed in a medium, and a medium containing 30 to 80% by mass of polymer particles can be used.

[0015] The following mechanisms of self-crosslinking can be considered. For example, a polymer having a functional group (e.g., a pendant functional group) and a crosslinking agent substance having two or more functional groups are added to water. During the drying process, as the water evaporates, the functional groups of the polymer and the functional groups of the crosslinking agent react, causing self-crosslinking. For example, a polymer having a carbonyl group as a pendant functional group reacts with a crosslinking agent component having two or more functional groups (e.g., a polyhydrazide), causing self-crosslinking. Alternatively, for example, a polymer having a functional group (e.g., a pendant functional group) is added to water. However, the water does not contain a crosslinking agent substance. During the drying process, as the water evaporates, the functional groups pendanted on the polymer react with functional groups pendanted on another polymer, causing self-crosslinking. Or, during the drying process, as the water evaporates, the functional groups pendanted on the polymer react with reactive groups that may be present on the adhesion surface (e.g., hydroxyl groups), causing crosslinking. More specifically, examples include reactions between polymers pendanted with hydrolyzable silanes, and reactions between polymers pendanted with hydrolyzable silanes and hydroxyl groups on the adherend. While self-crosslinking aqueous emulsions include these types, they are not limited to these.

[0016] (A) The component may be a compound (monomer) containing a (meth)acrylic group, and it may be a homopolymer or copolymer. Examples of compounds containing a (meth)acrylic group include (meth)acrylic acid, (meth)acrylate compounds, and (meth)acrylamide compounds, but it is not limited to these. Furthermore, it may contain monomers different from the compound (monomer) containing a (meth)acrylic group, such as styrene, maleic acid, and fumaric acid, and it may also contain silicone or urethane in part of the backbone.

[0017] (A) Examples of components include (meth)acrylic, (meth)acrylic-styrene, (meth)acrylic-silicone, and (meth)acrylic-urethane. Specific examples of components include the ULTRASOL series from Aica Kogyo Co., Ltd., the Polysol series from Resonac Co., Ltd., the VONCOAT series from DIC Corporation, the ACRONAL series from BASF Japan Ltd., the Aron series from Toagosei Co., Ltd., UW-600 and UW-550CS from Taisei Fine Chemical Co., Ltd., and Neocryl XK-12 and Neocryl XK-16 from Kusumoto Kasei Co., Ltd., but are not limited to these.

[0018] Component (B) that can be used in the present invention includes phosphate-based rust inhibitors. Here, "phosphate-based" includes derivatives having a phosphate or tripolyphosphate skeleton, but does not include derivatives of phosphite. A derivative is a compound in which the side chain of a specific compound skeleton is substituted.

[0019] Component (B) is preferably a metal salt phosphate-based rust inhibitor, and preferably a salt containing a metal such as magnesium or aluminum along with phosphoric acid or tripolyphosphate. For reasons that are not entirely clear, when used in combination with component (C) described later, it effectively improves rust prevention, and is particularly effective in preventing rust on hot-dip galvanized surfaces.

[0020] Specific examples of component (B) include magnesium phosphate, magnesium monohydrogen phosphate, magnesium dihydrogen phosphate, aluminum dihydrogen tripolyphosphate, and magnesium oxide treated products of zinc dihydrogen tripolyphosphate. Alternatively, component (B) may be pre-mixed with component (C) described later, such as silica-modified magnesium phosphate. Particularly preferred components (B) are magnesium phosphate or aluminum dihydrogen tripolyphosphate.

[0021] (B) components include, but are not limited to, LF Bousei PM-308, PM-303W, MZP-500, PMG manufactured by Kikuchi Color Co., Ltd., and K-WHITE #105, CZ140W, G105 manufactured by Teika Co., Ltd. Also, examples of those containing (B) component and the following (C) component include, but are not limited to, LF Bousei CRF-62 manufactured by Kikuchi Color Co., Ltd., and K-WHITE #82, #84, #84S, #450H manufactured by Teika Co., Ltd.

[0022] From the viewpoint of maintaining rust prevention properties, the (B) component is preferably contained at 0.01 to 15.0% by mass based on the whole composition.

[0023] The (C) component that can be used in the present invention is particles having a silanol group on the surface. Although the exact reason is unknown, it has been confirmed that the rust prevention property against hot-dip galvanizing is exhibited by using in combination hydrophilic particles having a silanol group (Si-OH) remaining on the particle surface and the (B) component. Also, the (C) component may be used in a state of being contained in the (B) component in advance.

[0024] The (C) component is preferably silicon dioxide (silica) particles or silicone resin particles. A mixture of multiple types with different average particle sizes may also be used. In the present invention, commercially available known silicon dioxide particles can be used. Specifically, AEROSIL series manufactured by Nippon Aerosil Co., Ltd., CAB-O-SIL series manufactured by Cabot Corporation, Reolosil manufactured by Tokuyama Corporation, Nipsil series manufactured by Tosoh Silica Corporation, etc. are known, but are not limited thereto. Also, as silicone resin particles, X-52-8432 manufactured by Shin-Etsu Chemical Co., Ltd. etc. are known, but are not limited thereto.

[0025] The particle size of component (C) is not limited, but is preferably in the range of 1 nm to 100 μm, more preferably in the range of 1 nm to 10 μm, and even more preferably in the range of 1 to 50 nm. For (C) components on the order of nm, the particle size may be the primary particle diameter measured by observation with an electron microscope, etc., and for particles on the order of μm, it may be the 50% average particle size measured with a laser particle size analyzer. The 50% average particle size measured with a laser particle size analyzer is the particle size at a cumulative volume ratio of 50% in the particle size distribution obtained by the laser diffraction scattering method (D50).

[0026] From the viewpoint of exhibiting rust prevention properties against hot-dip galvanized steel, the total amount of components (B) and (C) is 0.01 to 15.0% by mass of the entire composition. Furthermore, it is preferable that component (C) is present in an amount of 0.01 to 15.0% by mass of the entire composition.

[0027] In the aqueous coating composition of the present invention, "aqueous" refers to a composition containing water. As water, deionized water, pure water, tap water, or natural water can be used alone or in mixtures. Of these, deionized water and pure water are preferred because they do not contain impurities and are easy to control in terms of quality, and deionized water is even more preferred because it is inexpensive. Furthermore, pH-adjusting water may be used in combination. pH-adjusting water can be water with a pH greater than 7 and serves to adjust the overall pH of the aqueous coating composition. Specific examples of pH-adjusting water include, but are not limited to, 28% by mass ammonia water, alkaline electrolyzed water, sodium hydroxide aqueous solution, and potassium hydroxide aqueous solution.

[0028] In an aqueous paint composition, the water content can be adjusted to 30-60% by mass of the total composition, preferably 40-50% by mass. When the water content is within this range, good applicability and drying properties can be maintained, and the paint film thickness after drying can exhibit optimal rust prevention.

[0029] The aqueous coating composition of the present invention may contain appropriate amounts of additives such as film-forming aids, plasticizers, pigments (except for component (C)), surfactants, thickeners, and solvents, as long as they do not impair the properties of the present invention. These additives can be used to adjust the workability, drying properties, and film-forming properties.

[0030] The aforementioned film-forming aid is preferably a compound with a high boiling point and low volatility, such as glycols including ethylene glycol, ethylene glycol monoisobutyl ether, diethylene glycol propylene glycol, hexylene glycol, and polymethyl glycol; propylene glycol methyl ether, dipropylene glycol methyl ether, tripropylene glycol methyl ether, propylene glycol methyl ether acetate, dipropylene glycol methyl ether acetate, propylene glycol n-propyl ether, dipropylene glycol n-propyl ether, tripropylene glycol n-propyl ether, propylene glycol n-butyl ether, and dipropylene glycol Examples of ethers include, but are not limited to, ethyl carbitol n-butyl ether, tripropylene glycol n-butyl ether, propylene glycol phenyl ether, dipropylene glycol dimethyl ether, mixtures of dipropylene glycol methyl ether and propylene glycol phenyl ether, mixtures of tetrapropylene glycol methyl ether and higher alkyl ether, ethyl carbitol, butyl carbitol, butyl carbitol acetate, ethyl cellosolve, butyl cellosolve, butyl cellosolve acetate, benzyl acetate, 2,2,4-trimethyl-1,3-pentanediol monoisobutyrate, benzyl alcohol, petroleum hydrocarbons, etc.

[0031] Examples of the aforementioned plasticizers include dibutyl phthalate, diisononyl phthalate, diheptyl phthalate, di(2-ethylhexyl) phthalate, butyl benzyl phthalate, butyl oleate, diethylene glycol dibenzoate, triethylene glycol dibenzoate, pentaerythritol ester, polyethylene glycol, polypropylene glycol, and polytetramethylene glycol. Other examples include, but are not limited to, polyester-based plasticizers obtained from dibasic acids such as sebaciic acid, adipic acid, azelaic acid, and phthalic acid, and dihydric alcohols such as ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, and dipropylene glycol.

[0032] Suitable pigments include organic pigments and inorganic pigments, excluding component (C). Examples of organic pigments include isoindolinone, isoindoline, azomethine, perylene, anthraquinone, dioxazine, and phthalocyanine. Examples of inorganic pigments include, but are not limited to, carbon black, ultramarine blue, prussian blue, iron oxide red, zinc oxide, zinc phosphite, titanium dioxide, and lithopone.

[0033] Examples of the surfactants include anionic surfactants having -SO3Na and -SO3NH4 in their molecules, nonionic surfactants that do not contain ions in their molecules, cationic surfactants that contain a quaternary ammonium salt in their molecules, and amphoteric surfactants that contain both anions and cations in their molecules. In the present invention, nonionic surfactants are preferred as the surfactant, and higher alcohol-based nonionic surfactants are more preferred. It is preferable to add 0.1 to 1.0 parts by mass per 100 parts by mass of component (A).

[0034] The aforementioned thickening agent can be, but is not limited to, aqueous solutions or emulsions of polymers such as sodium polyacrylate, polyacrylic acid, ammonium polyacrylate, carboxylic acid copolymers, or sodium salts of carboxylic acid copolymers that are compatible with water. However, component (A) is excluded. The thickening agent does not form a film after drying, unlike component (A).

[0035] Examples of the aforementioned solvents include, but are not limited to, ethyl acetate, butyl acetate, ethylcyclohexane, cyclohexane, hexane, isohexane, methanol, ethanol, isopropyl alcohol, and acetone.

[0036] For the drying process, the ambient temperature is preferably -10 to 80°C, and more preferably -5 to 60°C. The drying time is preferably 30 minutes to 72 hours, and more preferably 1 to 12 hours.

[0037] The coating can be applied using conventionally known coating methods. Specifically, it can be obtained by adjusting the viscosity and resin solid content to ensure a predetermined film thickness on the substrate, applying it to the substrate using a spray gun, and then drying it. For example, the film thickness after drying that can be formed by a single spray application is 10 μm to 1 mm, but it is also possible to apply multiple coats to increase the film thickness.

[0038] This invention can be used as a rust-preventive coating for vehicle chassis and other parts that use hot-dip galvanizing. [Examples]

[0039] The present invention will now be described in more detail with reference to examples, but the present invention is not limited to these examples. (Hereinafter, the aqueous coating composition will also be simply referred to as the composition.)

[0040] [Examples 1-17, Comparative Examples 1-15] The following components were prepared to create the composition. (A) Ingredients: (meth)acrylic emulsion • Acrylic-styrene aqueous emulsion (solids content: 50% by mass) (ULTRASOL ULD-50, manufactured by Aica Kogyo Co., Ltd.) • Acrylic-styrene aqueous emulsion (solids content: 55% by mass) (ULTRASOL C-63, manufactured by Aica Kogyo Co., Ltd.) • Acrylic-styrene water-based emulsion (solids content: 42% by mass) (ULTRASOL GP-300, manufactured by Aica Kogyo Co., Ltd.) • Acrylic water-based emulsion (solids content: 48% by mass) (ULTRASOL A-25, Aica Kogyo Co., Ltd.) • Acrylic-silicone aqueous emulsion (solids content: 50% by mass) (Polysol AP-3900, manufactured by Resonaq Corporation) • Urethane-acrylic water-based emulsion (solids content: 50% by mass) (VONCOAT CF-2800, manufactured by DIC Corporation) • Acrylic water-based emulsion (solids content: 45% by mass) (VONCOAT HY-364, manufactured by DIC Corporation) (A') component: Emulsion other than component (A) • Vinyl acetate-based aqueous emulsion (47.5% by mass) (VONCOAT CC-6250, manufactured by DIC Corporation) (B) Components and (C) Components: Components containing phosphorus-based rust inhibitors and silicon dioxide. • Silica-modified magnesium phosphate rust-preventive pigment (LF Bowsei CRF-62, manufactured by Kikuchi Color Co., Ltd.) • Aluminum dihydrogen tripolyphosphate, zinc oxide, silicon dioxide (K-WHITE #82, manufactured by Teika Co., Ltd.) • Aluminum dihydrogen tripolyphosphate, zinc oxide, silicon dioxide (K-WHITE #84, manufactured by Teika Co., Ltd.) • Aluminum dihydrogen tripolyphosphate, zinc oxide, silicon dioxide (K-WHITE #84S, manufactured by Teika Co., Ltd.) • Aluminum dihydrogen tripolyphosphate, inorganic silica / magnesium compound (K-WHITE #450H, manufactured by Teika Co., Ltd.) (B) Ingredients: Phosphate-based rust inhibitor • Aluminum phosphomolybdate-based rust-preventive pigment (LF Bowsei PM-308, manufactured by Kikuchi Color Co., Ltd.) • Aluminum phosphomolybdate-based rust-preventive pigment (LF Bousei PM-303W, manufactured by Kikuchi Color Co., Ltd.) • Magnesium phosphate-based rust-preventive pigment (LF Bowsei MZP-500, manufactured by Kikuchi Color Co., Ltd.) • Magnesium phosphate-based rust-preventive pigment (LF Bowsei PMG, manufactured by Kikuchi Color Co., Ltd.) • Aluminum dihydrogen tripolyphosphate, zinc oxide (K-WHITE #105, manufactured by Teika Co., Ltd.) • Aluminum dihydrogen tripolyphosphate, zinc oxide, ammonia, inorganic calcium compound (K-WHITE CZ140W, manufactured by Teika Co., Ltd.) • Aluminum dihydrogen tripolyphosphate, inorganic magnesium compound (K-WHITE G105, manufactured by Teika Co., Ltd.) (B') component: Rust inhibitor other than component (B) • Zinc phosphate-based rust-preventive pigment (LF Bousei ZP-DL, manufactured by Kikuchi Color Co., Ltd.) • Zinc phosphate-based rust-preventive pigment (LF Bowsei PW-2, manufactured by Kikuchi Color Co., Ltd.) • Zinc phosphite-based rust-preventive pigment (LF Bousei ZP-600, manufactured by Kikuchi Color Co., Ltd.) • Magnesium and calcium aminophosphate salts (Pigmentan EA, manufactured by Banner Chemicals) • Magnesium and calcium aminophosphate salts (Pigmentan MX, manufactured by Banner Chemicals) • Magnesium and calcium aminophosphate salts (Pigmentan MZ, manufactured by Banner Chemicals) (C) Ingredients: Silicon dioxide • Hydrophilic fumed silica powder (Aerosil 50, Aerosil Japan Co., Ltd.) • Silicone resin emulsion (solids content: 44% by mass) (X-52-8432, manufactured by Shin-Etsu Chemical Co., Ltd.) Other ingredients Film-forming aid • Ethylene glycol monoisobutyl ether (Isobutyl glycol, manufactured by Nippon Emulsifier Co., Ltd.) • Petroleum hydrocarbons (A Solvent, manufactured by ENEOS Corporation) • 2,2,4-trimethyl-1,3-pentanediol monoisobutyrate (CS-12, manufactured by JNC Corporation) plasticizer • Diisononyl phthalate (manufactured by DINP CG Ester Co., Ltd.) pH adjusted water • 25% by mass aqueous ammonia solution (hereinafter referred to as ammonia water) pigment • Zinc phosphite pigment (Pollux White PC-7T1075, manufactured by Sumitomo Color Co., Ltd.) Thickening agent • Thickening agent consisting of a carboxylic acid copolymer (solid content: 44% by mass) (Aron B-300K, manufactured by Toagosei Co., Ltd.) water • Ion-exchanged water (prepared using an ion-exchanged water production device)

[0041] Examples 1-7 and Comparative Example 1 were prepared. The composition was prepared by weighing component (A), component (B) (or component (B')), component (C) (or component (C')) and other components into a beaker and stirring for 10 minutes. Detailed preparation amounts are shown in Table 1, and all values ​​are expressed in parts by mass.

[0042] [Table 1]

[0043] Adhesion testing and rust formation testing (1) in a salt spray test were performed on Examples 1-7 and Comparative Example 1. The results are summarized in Table 2.

[0044] [Confirmation of adhesion] Initial adhesion is confirmed by a cross-cut test. The composition is applied to a steel plate (SPCC-SB) or hot-dip galvanized steel plate to a dry film thickness of 30 μm. Then, it is left to dry at 25°C for 24 hours to create a test piece. A grid of 1 mm squares is cut into the surface of the coating to create 100 squares. Then, the surface of the coating is peeled off with adhesive tape and the initial "adhesion" is confirmed by visual inspection according to the evaluation criteria below. Detailed test methods follow JIS G3141. Adhesion should preferably be "○". Evaluation Criteria ○: 100 / 100 ×: Not 100 / 100

[0045] [Confirmation of rust formation in salt spray test 1] The composition is applied to a 150mm long x 70mm wide x 0.8mm thick steel plate (SPCC-SB) or hot-dip galvanized steel plate to a dry film thickness of 30μm. Then, it is left to dry at 25°C for 24 hours to form a coating. A test piece is created by superimposing and fixing a colorless, transparent flat plate measuring 80mm long x 60mm wide x 0.2mm thick onto which 100 square grids (rust occurrence measurement plate) with 0.1mm spacing lines are engraved in a 50mm x 50mm measurement area. The "rust occurrence degree" is determined by visually counting the number of grids where one or more rust points have occurred according to the evaluation criteria below. Details were carried out in accordance with JIS K 2246. Evaluation Criteria A: 0% B: 1-10% C: 11-25% D: 26-50% E: 51-100% The test pieces for the rust formation test described above are placed in a salt sprayer, and the SPCC-SB is checked after 24 hours, and the hot-dip galvanized steel sheet after 100 hours. The salt spraying conditions are to continuously spray a 5% by mass saline solution in a sealed state under a 35°C atmosphere. This conforms to JIS Z 2371:2015 neutral salt spray test. It is preferable that the hot-dip galvanized steel sheet is grade "A" after 100 hours.

[0046] [Table 2]

[0047] Comparing Examples 1-7 with Comparative Example 1, the difference is that in the Examples, component (A) is a (meth)acrylic emulsion, while in the Comparative Example, it is a vinyl acetate emulsion. Although there is no difference in adhesion between the Examples and the Comparative Example, it can be seen that the degree of rust formation after 100 hours for the latter half of the hot-dip galvanized coating is "A" in Examples 1-7, while the degree of rust formation in Comparative Example 1 is "B".

[0048] Examples 8-17 and Comparative Examples 2-15 were prepared. The composition consisted of components (A), (B) (or (B')), (C) (or (C')) and other components, which were weighed into a beaker and stirred for 10 minutes. Detailed preparation amounts are shown in Table 3, and all values ​​are expressed in parts by mass.

[0049] [Table 3]

[0050] For Examples 8-17 and Comparative Examples 2-8, the adhesion confirmation and rust formation degree confirmation in the salt spray test 2 were performed as described above. The results are summarized in Table 4.

[0051] [Confirmation of rust formation in salt spray test 2] The composition is applied to a 150mm long x 70mm wide x 0.8mm thick steel plate (SPCC-SB) or hot-dip galvanized steel plate to a dry film thickness of 30μm. Then, it is left to dry at 25°C for 24 hours to form a coating. A test piece is created by superimposing and fixing a colorless, transparent flat plate measuring 80mm long x 60mm wide x 0.2mm thick onto which 100 square grids (rust count measurement plate) with 0.1mm spacing lines are engraved in a 50mm x 50mm measurement area. The number of grids with one or more rust points according to the evaluation criteria below is counted visually and determined as the "rust occurrence degree." Details were carried out in accordance with JIS K 2246. Evaluation Criteria A: 0% B: 1-10% C: 11-25% D: 26-50% E: 51-100% The test pieces for the rust formation test described above are placed in a salt sprayer, and the SPCC-SB is checked after 24 hours and 100 hours, while the hot-dip galvanized steel sheet is checked after 100 hours and 1000 hours. The salt spraying conditions are to continuously spray a 5% by mass saline solution in a sealed state under a 35°C atmosphere. This conforms to JIS Z 2371:2015 Neutral Salt Spray Test. For the hot-dip galvanized steel sheet, it is preferable that the result is "A" after 100 hours, and it is preferable that the result is "A" or "B" after 1000 hours.

[0052] [Table 4]

[0053] Throughout the examples and comparative examples, a general tendency for high rust formation to occur after 100 hours was observed for SPCC-SB. However, in Examples 8-17, the results for hot-dip galvanized steel sheets were "A" after 100 hours and "A" or "B" after 1000 hours, indicating that the present invention has particularly high rust prevention properties against hot-dip galvanized steel. In Examples 8-15, a raw material containing a phosphate-based rust inhibitor as component (B) and silicon dioxide (silica) as component (C) was added to component (A), while in Examples 16 and 17, a phosphate-based rust inhibitor and silicon dioxide or silicone resin emulsion were added as separate raw materials to component (A). On the other hand, Comparative Examples 2-8 used only a phosphate-based rust inhibitor, Comparative Examples 9-14 used only rust inhibitors other than phosphate-based rust inhibitors, and Comparative Example 15 contained only silicon dioxide (silica). It can be seen that Examples 8-17, which contain components (A) to (C) as essential components, are able to maintain long-term rust prevention. [Industrial applicability]

[0054] In recent years, hot-dip galvanized steel sheets have been used in many vehicles as a material with rust-preventive properties. To further enhance the rust-preventive properties of hot-dip galvanized steel sheets, a topcoat is necessary. Furthermore, it is required that the topcoat be water-based and environmentally friendly. This invention provides a water-based paint composition useful for maintaining rust-preventive properties in the harsh environment of salt spray testing.

Claims

1. A water-based paint composition comprising the following components (A) to (C). (A) Ingredients: (meth)acrylic emulsion (B) Component: Phosphate-based rust inhibitor (C) Component: Particles having silanol groups on their surface

2. The aqueous paint composition according to claim 1, wherein the (B) component is a phosphate-based rust inhibitor containing magnesium and / or aluminum.

3. The aqueous paint composition according to claim 1, wherein the (B) component is magnesium phosphate and / or aluminum dihydrogen tripolyphosphate.

4. The aqueous coating composition according to claim 1, wherein the (C) component is silicon dioxide particles and / or silicone resin particles.

5. A hot-dip galvanized member coated with the aqueous coating composition according to any one of claims 1 to 4.

6. An aqueous paint composition according to any one of claims 1 to 4, used for use on the chassis of a vehicle.

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