Coating composition, coating method, and coated body

Abstract

To provide a coating composition capable of forming a coating film excellent in blocking resistance and anticorrosion properties.SOLUTION: The coating composition contains: (A-1) at least one pigment having an aspect ratio of 1 or more and less than 5 and selected from barium sulfate, silica, and calcium carbonate; and (A-2) a scaly pigment having an average particle diameter of 2-30 μm and an aspect ratio of 5 or more and less than 30. The mass ratio of (A-1):(A-2) is within the range of 90:10-70:30.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a coating composition, a coating method using said coating composition, and a coated body, and in particular to a coating composition capable of forming a coating film having excellent blocking resistance and corrosion prevention properties. [Background technology]

[0002] In recent years, the coating industry has been shifting from solvent-based materials that use organic solvents to water-based materials, and various studies are being conducted on water-based paints for metals as well.When forming a coating on a metal substrate, a coating specification that combines a primer paint with excellent corrosion resistance and a top coat paint with excellent weather resistance is widely used for structural applications.

[0003] JP 2021-1314 A (Patent Document 1) describes an invention for an aqueous coating material comprising a film-forming component and a powder component, wherein the film-forming component comprises an aqueous epoxy resin emulsion as a resin component, and the gel fraction of the formed coating is 10% or more, the powder component comprises an anti-rust pigment and calcium carbonate, and the powder component contains 50 to 300 parts by weight of the powder component per 100 parts by weight of the resin component, and the powder component contains 30 to 90% by weight of the calcium carbonate, and it describes that the configuration of this invention allows for the production of an aqueous coating material with excellent coating film strength, adhesion, rust prevention, etc.

[0004] JP 2021-195500 A (Patent Document 2) describes an invention of a paint composition containing a resin, a flake-like aluminum pigment or stainless steel flakes, and a flake-like pigment other than the aluminum pigment or stainless steel flakes, wherein the flake-like aluminum pigment or stainless steel flakes are non-leafing aluminum pigments or stainless steel flakes with an average particle diameter of 20 to 60 μm, and the flake-like pigment other than the aluminum pigment or stainless steel flakes has an average particle diameter of 5 to 50 μm and an aspect ratio of 10 to 100, and the mass ratio (A / B) of the flake-like aluminum pigment or stainless steel flakes (A) to the flake-like pigment other than the aluminum pigment or stainless steel flakes (B) is 1 / 2 to 1 / 18. The invention describes that the configuration of this invention makes it possible to form a coating film that has excellent environmental barrier properties and good corrosion resistance, even when applied in a thick film.

[0005] WO 2020 / 026743 (Patent Document 3) describes an invention for an aqueous coating composition comprising acrylic resin particles (A) and a rust inhibitor (B), wherein the acrylic resin particles (A) have an acid value of 10 to 100 mgKOH / g and 80% by weight or more of all copolymerization components are polymerizable unsaturated monomers having a solubility parameter value of 9.5 or less, and the rust inhibitor (B) contains an aminosilane (b1), an azole compound (b2), and at least one compound (b3) selected from the group consisting of fatty acids, aromatic acids, and aliphatic amines. The invention states that the configuration of this invention makes it possible to provide an aqueous coating composition that is excellent in all of corrosion prevention, adhesion, and water resistance.

[0006] The aqueous coating material described in Patent Document 1, the paint composition described in Patent Document 2, and the water-based paint composition described in Patent Document 3 are all capable of forming coating films with excellent corrosion resistance and are recognized as suitable water-based paints for metals. On the other hand, in factory coating of structural steel and the like, in addition to the corrosion resistance obtained by applying the same paint once or multiple times, blocking resistance is required to prevent the coating film from fusing or being damaged when coated metal materials are stacked. Factory coating refers to coating using factory equipment for the purpose of mass production. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Patent Publication No. 2021-1314 [Patent Document 2] Patent Publication No. 2021-195500 [Patent Document 3] International Publication No. 2020 / 026743 Summary of the Invention [Problem to be solved by the invention]

[0008] The present inventors have examined the coating compositions described in Patent Documents 1 to 3 and found that they have problems with blocking resistance when applied to metal substrates in factory coating, and there is room for improvement when used in factory coating of structural steel and the like.

[0009] Therefore, an object of the present invention is to provide a coating composition capable of forming a coating film having excellent blocking resistance and corrosion resistance. Another object of the present invention is to provide a coating method and a coated body using such a coating composition. [Means for solving the problem]

[0010] As a result of intensive research into achieving the above-mentioned object, the present inventors have found that a coating composition capable of forming a coating film having excellent blocking resistance and corrosion prevention properties can be provided by combining at least one pigment having a specific aspect ratio and selected from barium sulfate, silica, and calcium carbonate with a scaly pigment having a specific average particle size and aspect ratio in a specific mass ratio, and have thus completed the present invention.

[0011] Therefore, the coating composition of the present invention is (A-1) at least one pigment having an aspect ratio of 1 or more and less than 5 and selected from barium sulfate, silica, and calcium carbonate; and (A-2) a scale-like pigment having an average particle size of 2 to 30 μm and an aspect ratio of 5 to 100, and the mass ratio of (A-1):(A-2) is within the range of 90:10 to 70:30.

[0012] In a preferred embodiment of the coating composition of the present invention, the average particle size of (A-1) is smaller than the average particle size of (A-2).

[0013] The coating method of the present invention is a coating method in which the coating composition of the present invention described above is applied to a metal substrate.

[0014] The coated body of the present invention is a coated body obtained by applying the above-mentioned coating composition of the present invention to a metal substrate. [Effects of the Invention]

[0015] The coating composition of the present invention can provide a coating film that is excellent in blocking resistance and corrosion resistance. Furthermore, the coating method and coated article of the present invention can provide a coating method and coated article that use such a coating composition. DETAILED DESCRIPTION OF THE INVENTION

[0016] The present invention relates to a coating composition, a coating method, and a coated body.

[0017] The coating composition of the present invention contains two pigments corresponding to the following (A-1) and (A-2). (A-1) At least one pigment having an aspect ratio of 1 or more but less than 5, selected from barium sulfate, silica, and calcium carbonate (A-2) A scaly pigment having an average particle size of 2 to 30 μm and an aspect ratio of 5 to 100

[0018] In this specification, the pigment corresponding to (A-1) is also referred to as (A-1), (A-1) pigment, etc. Furthermore, the pigment corresponding to (A-2) is also referred to as (A-2), (A-2) pigment, (A-2) scaly pigment, etc.

[0019] In addition, in the coating composition of the present invention, the mass ratio of the (A-1) pigment to the (A-2) pigment is within the range of 90:10 to 70:30, preferably within the range of 90:10 to 75:25, and more preferably within the range of 90:10 to 80:20.

[0020] The (A-1) pigment contributes to blocking resistance, while the (A-2) pigment contributes to corrosion prevention. Furthermore, the combined use of the (A-1) pigment and the (A-2) pigment provides better blocking resistance than that achieved when the (A-1) pigment is used alone. The inventors believe that this phenomenon occurs because, when the scale-shaped (A-2) pigments are arranged in parallel within the coating film, the presence of the hard (A-1) pigment between the (A-2) pigments provides a bridging effect and disperses the pressure applied from above within the coating film, resulting in high blocking resistance. In particular, when the average particle size of the (A-1) pigment is smaller than that of the (A-2) pigment, the combined use of the (A-1) pigment and the (A-2) pigment provides a significant improvement in blocking resistance. By adjusting the mass ratio of the (A-1) pigment to the (A-2) pigment within the range of 90:10 to 70:30, it is possible to form a coating film that is excellent in both blocking resistance and corrosion prevention.

[0021] (A-1) At least one pigment selected from barium sulfate, silica, and calcium carbonate The pigment (A-1) is a pigment selected from barium sulfate, silica, and calcium carbonate, and preferably has a Mohs hardness of 3 or more, more preferably 3 to 7, and even more preferably 3 to 4.

[0022] The Mohs scale is a numerical representation of hardness based on how well an object scratches against a standard material. Standard materials are designated on the Mohs scale, ranging from 1 to 10, in order of softest to softest. Specific standard materials are: 1 for talc, 2 for gypsum, 3 for calcite, 4 for fluorite, 5 for apatite, 6 for orthoclase, 7 for quartz, 8 for topaz, 9 for corundum, and 10 for diamond. Mohs hardness can be measured using a Mohs scale in the usual way.

[0023] Generally, the Mohs hardness of barium sulfate is in the range of 3.0 to 3.5, the Mohs hardness of silica is in the range of 6.5 to 7.0, and the Mohs hardness of calcium carbonate is in the range of 3.0 to 4.0.

[0024] The (A-1) pigment has an aspect ratio of 1 or more and less than 5, preferably 1-3.

[0025] In the present invention, the aspect ratio of a pigment is a value determined from the pigment in an image obtained by SEM (scanning electron microscope) and refers to the ratio (D / T) of the average particle diameter (D) to the average thickness (T) of the pigment. The average particle diameter (D) and average thickness (T) of the pigment refer to the average particle diameter and thickness of 100 or more pigment particles in an image obtained by SEM (scanning electron microscope). Here, the pigment particle diameter refers to the maximum length of the pigment in the image obtained by SEM (scanning electron microscope) and is also referred to as the long side of the pigment. The pigment thickness refers to the maximum length of the pigment in the direction perpendicular to the long side of the pigment in the image obtained by SEM (scanning electron microscope) and is also referred to as the short side of the pigment. However, for circular pigments in an SEM image, the pigment particle diameter (long side) and pigment thickness (short side) have the same value.

[0026] The pigment (A-1) preferably has an average particle size of 0.5 to 30 μm, more preferably 0.5 to 10 μm, and even more preferably 0.5 to 5 μm.

[0027] The average particle size of a pigment is the average particle size that can be determined from the particle size distribution measured using a laser diffraction / scattering particle size analyzer (e.g., SALD-7500nano, manufactured by Shimadzu Corporation). The particle size is expressed as the spherical equivalent diameter determined by the laser diffraction / scattering method. Note that the term "average particle size of a pigment" used in this specification refers to the average particle size that can be determined from the particle size distribution measured using a laser diffraction / scattering particle size analyzer, excluding the "average particle size (D) of a pigment" used to determine the aspect ratio. Specifically, the average particle size here is the average value based on a logarithmic scale (geometric mean diameter).

number

number

[0028] The average particle size of the (A-1) pigment is preferably smaller than that of the (A-2) pigment, more preferably at least 0.5 μm smaller than that of the (A-2) pigment, and even more preferably 0.5 to 1 μm smaller than that of the (A-2) pigment. By making the average particle size of the (A-1) pigment smaller than that of the (A-2) pigment, the (A-2) pigment is more easily aligned parallel to one another in the coating film, resulting in better corrosion resistance and blocking resistance.

[0029] The specific gravity of the (A-1) pigment is preferably 2 to 5. In the present invention, the substance that serves as the standard for specific gravity is water.

[0030] The pigment (A-1) is at least one pigment selected from barium sulfate, silica, and calcium carbonate, and two or more of these may be used in combination. Silica also includes cristobalite and white carbon. From the viewpoint of excellent water resistance, coating appearance, and corrosion resistance, the pigment (A-1) preferably contains precipitated barium sulfate.

[0031] The pigment (A-1) may be used alone or in combination of two or more kinds.

[0032] The amount of the pigment (A-1) contained in the coating composition of the present invention is preferably 9 to 100 parts by mass, and particularly preferably 10 to 80 parts by mass, per 100 parts by mass of the resin.

[0033] (A-2) A scaly pigment having an average particle size of 2 to 30 μm and an aspect ratio of 5 or more but less than 30 The (A-2) pigment is a scaly pigment. A scaly pigment is a pigment with a thin, flat, foil-like shape. Specific examples include metal pigments such as zinc, nickel, chromium, tin, copper, silver, platinum, gold, and aluminum, as well as glass flakes, talc, mica, kaolin clay, and micaceous iron oxide. Metal pigments also include alloy pigments such as stainless steel. Furthermore, scaly pigments, such as talc and mica, may be surface-treated with a metal oxide such as titanium oxide.

[0034] The pigment (A-2) has an average particle size of 2 to 30 μm, preferably 2 to 20 μm, and more preferably 2 to 10 μm.

[0035] The (A-2) pigment has an aspect ratio of 5 to 100, preferably 5 to 60, from the viewpoint of improving environmental barrier properties, and more preferably 5 to 30, from the viewpoint of the appearance of the coating film.

[0036] The Mohs hardness of the pigment (A-2) is not particularly limited, but is, for example, 1 to 3. In the present invention, by blending a certain amount of the pigment (A-1) having a Mohs hardness of 3 or more, high blocking resistance can be obtained even when a scaly pigment (A-2) having a low Mohs hardness is blended.

[0037] The specific gravity of the pigment (A-2) is preferably 2.0 to 3.5.

[0038] The pigment (A-2) is preferably selected from talc, mica, glass flakes, and aluminum, and is most preferably talc from the viewpoint of dispersion stability.

[0039] The pigment (A-2) may be used alone or in combination of two or more.

[0040] The amount of the pigment (A-2) contained in the coating composition of the present invention is preferably 1 to 40 parts by mass, and particularly preferably 1 to 20 parts by mass, per 100 parts by mass of the resin.

[0041] (A-3) Pigments that do not fall under (A-1) pigments or (A-2) pigments The coating composition of the present invention may contain a pigment other than pigment (A-1) or pigment (A-2). In this specification, a pigment other than pigment (A-1) or pigment (A-2) is also referred to as pigment (A-3), pigment (A-3), etc.

[0042] (A-3) Pigments include anti-rust pigments, extender pigments, coloring pigments, and the like.

[0043] Examples of anti-rust pigments include zinc powder, zinc oxide, barium metaborate, calcium silicate, aluminum phosphate, condensed aluminum phosphate, aluminum tripolyphosphate, zinc phosphate, zinc phosphite, potassium phosphite, calcium phosphite, aluminum phosphite, calcium zinc phosphate, zinc aluminum phosphate, zinc phosphomolybdate, aluminum phosphomolybdate, magnesium phosphate, and vanadate / phosphate mixed pigments.

[0044] Examples of color pigments include titanium oxide, iron oxide (e.g., red iron oxide), carbon black, yellow lead, molybdate orange, ultramarine, Prussian blue, phthalocyanine blue, phthalocyanine green, quinacridone red, naphthol red, benzimidazolone yellow, Hansa yellow, benzimidazolone orange, and dioxazine violet.

[0045] The pigment (A-3) may be used alone or in combination of two or more.

[0046] The coating composition of the present invention preferably has a pigment volume concentration (PVC) of 10 to 50%, more preferably 15 to 30%, and from the viewpoint of orientation of the scaly pigment, particularly preferably 15 to 25%.

[0047] In the present invention, the pigment volume concentration (PVC) is the ratio of the total volume of the pigment to the total volume of the film-forming components in the paint composition, and can be calculated from the composition and specific gravity of each component that makes up the film-forming components.

[0048] The coating composition of the present invention contains a resin. The resin preferably contains a water-dispersible resin. In the present invention, a "water-dispersible resin" refers to a resin that can be distributed in water to form a heterogeneous system (e.g., an emulsion or suspension). When the coating composition of the present invention contains a water-dispersible resin, the water-dispersible resin is dispersed in the coating composition of the present invention. The inclusion of a water-dispersible resin facilitates the use of high-molecular-weight resins, which facilitates improving the corrosion resistance of the coating film and improves the dispersibility of the (A-1) pigment and (A-2) pigment of the present invention in the coating film, making it easier to achieve the blocking resistance and corrosion resistance that are the effects of the present invention.

[0049] The water-dispersible resin can be prepared, for example, by emulsifying the water-dispersible resin in water, or by emulsion polymerization of the monomer components, using a surfactant as needed, while applying forced shear force using a high-speed agitator or the like. Alternatively, an aqueous resin dispersion can be prepared by adding a surfactant as needed to a water-dispersible resin polymerized in an organic solvent medium and then subjecting the resin to phase inversion into water, and the organic solvent contained in the aqueous resin dispersion can be removed by distillation or the like as needed. Alternatively, an aqueous resin dispersion can be prepared by polymerization in water using water as the medium.

[0050] Water-dispersible resins can be classified into emulsion resins and dispersion resins. Emulsion resins refer to water-dispersible resins obtained by emulsion polymerization. Dispersion resins refer to self-water-dispersible resins. Resins that dissolve in water are water-soluble resins. In the present invention, it is preferable to include an emulsion resin, and emulsion resins can also be used in appropriate combination with dispersion resins or water-soluble resins.

[0051] The coating composition of the present invention preferably contains at least one water-dispersible resin selected from the group consisting of water-dispersible acrylic resins, water-dispersible urethane resins, water-dispersible epoxy resins, and water-dispersible alkyd resins. These water-dispersible resins may be modified, such as urethane-modified epoxy resins, amine-modified epoxy resins, isocyanate-modified epoxy resins, acrylic-modified epoxy resins, polyester-modified epoxy resins, dimer acid-modified epoxy resins, alkyd-modified acrylic resins, and acrylic-modified alkyd resins. The inclusion of these water-dispersible resins improves the dispersibility of the components (A-1) and (A-2) of the present invention, making it easier to achieve the effects of the present invention and to improve the corrosion resistance of the coating film.

[0052] The glass transition temperature (Tg) of the resin is preferably −20 to 80° C., and from the viewpoint of film-forming properties, more preferably 0 to 60° C. In the present invention, the Tg of the resin is calculated by the following FOX formula. [FOX formula] 1 / Tg=W1 / Tg1+W2 / Tg2+···+Wi / Tgi+···+Wn / Tgn In the FOX formula, Tg written in the denominator on the left side represents the glass transition temperature (unit: K) of the polymer component consisting of N types of monomers, Tg(1, 2, i, N) represents the glass transition temperature (unit: K) of each monomer, W(1, 2, i, N) is the mass fraction of each monomer, and the relationship W1 + W2 +··· + Wi +··· + Wn = 1 holds. Here, the glass transition temperature of a monomer means the glass transition temperature of its homopolymer.

[0053] In the present invention, the resin is preferably dispersed in the coating composition, and the average particle size of the resin dispersed in the coating composition is preferably 0.01 to 500 μm, and more preferably 50 to 500 nm from the viewpoint of particle stability.

[0054] The average particle size of a resin is the average particle size that can be determined from the particle size distribution measured using a laser diffraction / scattering particle size distribution analyzer (e.g., SALD-7500nano, manufactured by Shimadzu Corporation). The particle size here is expressed as the spherical equivalent diameter determined by the laser diffraction / scattering method.

[0055] The resins may be used alone or in combination of two or more.

[0056] The amount of resin contained in the coating composition of the present invention is preferably 15 to 50 mass %, more preferably 20 to 40 mass %.

[0057] The coating composition of the present invention may contain a film-forming aid. The film-forming aid is a component blended for the purpose of imparting film-forming properties, and includes volatile film-forming aids classified as organic solvents, and non-volatile film-forming aids that act as plasticizers. In the present invention, either a volatile film-forming aid or a non-volatile film-forming aid can be used.

[0058] The boiling point of the volatile film-forming aid is preferably in the range of 120 to 240°C, more preferably in the range of 120 to 190°C. In the present invention, boiling point refers to the boiling point at 1 atmosphere. By increasing the boiling point to more than 120°C, the water-dispersible resin is softened and the fusion properties of the resin during coating can be improved, which makes it easier to improve the corrosion resistance of the coating film. Furthermore, by setting the boiling point to 240°C or less, the film-forming aid is more easily volatilized, making it less likely to cause blocking.

[0059] Examples of the film-forming aid include propylene glycol, propylene glycol monomethyl ether (PGMME), propylene glycol monoethyl ether, propylene glycol monopropyl ether, ethylene glycol monoethyl ether, ethylene glycol monopropyl ether, ethylene glycol monoisopropyl ether, ethylene glycol mono-n-butyl ether, ethylene glycol monoisobutyl ether, ethylene glycol mono-tert-butyl ether, diethylene glycol monoethyl ether, diethylene glycol monopropyl ether, diethylene glycol monoisopropyl ether, diethylene glycol mono-n-butyl ether, diethylene glycol monoisobutyl ether, diethylene glycol mono-tert-butyl ether, 2,2,4-trimethyl-1,3-pentanediol monoisobutyrate, diethylene glycol diethyl ether, diethylene glycol dimethyl ether, triethylene glycol monobutyl ether, propylene glycol monomethyl ether, ethylene glycol diethyl ether, ethylene glycol monoethyl ether, ethylene glycol isopropyl ether, polyethylene glycol monomethyl ether, benzyl diglycol, and triethylene glycol.

[0060] The film-forming aids may be used alone or in combination of two or more.

[0061] When the coating composition of the present invention contains a film-forming aid, the amount of the film-forming aid contained in the coating composition is preferably 0.1 to 50 parts by mass, more preferably 0.2 to 15 parts by mass, and particularly preferably 0.5 to 10 parts by mass, per 100 parts by mass of the resin.

[0062] Other components that can be appropriately blended into the coating composition of the present invention include solvents, surface conditioners, wetting agents, dispersants, emulsifiers, thickeners, anti-settling agents, anti-skinning agents, anti-sagging agents, anti-foaming agents, anti-color separation agents, viscosity modifiers, rheology control agents, leveling agents, drying agents, antifreezing agents, adhesion improvers, plasticizers, rust inhibitors, preservatives, anti-mold agents, antibacterial agents, insecticides, light stabilizers, ultraviolet absorbers, antistatic agents, and conductivity imparting agents, depending on the purpose.

[0063] The coating composition of the present invention can be prepared by mixing various components appropriately selected as needed. The coating composition of the present invention may be either a one-component type in which the various components are premixed and used as is at the time of application, or a multi-component type (e.g., two-component type) in which two or more components (e.g., base resin and curing agent) that have been stored separately are mixed at the time of application.

[0064] The amount of the film-forming component contained in the coating composition of the present invention is preferably 40 to 70 mass %, more preferably 50 to 65 mass %, and particularly preferably 50 to 60 mass %.

[0065] In the present invention, the film-forming components refer to the components excluding volatile components such as water and organic solvents, and are the components that ultimately form a coating film. In the present invention, the components that remain when the coating composition is dried at 130°C for 60 minutes are considered to be the film-forming components. The mass fraction of the components (film-forming components) that remain when the coating composition is dried at 130°C for 60 minutes is referred to as the heating residue (or non-volatile content NV).

[0066] The coating composition of the present invention is preferably an aqueous coating composition. An aqueous coating composition is a coating composition containing water as the main solvent (the solvent with the highest content in the coating). The water that can be used in the coating composition of the present invention is not particularly limited, but examples include tap water, ion-exchanged water, and pure water such as distilled water. Furthermore, when storing the coating composition for a long period of time, water that has been sterilized by ultraviolet irradiation or the like may be used to prevent the growth of mold and bacteria. When the coating composition of the present invention is an aqueous coating composition, the amount of water contained in the coating composition is preferably 25 to 90 mass %, more preferably 30 to 80 mass %.

[0067] The coating composition of the present invention preferably has a viscosity of 0.01 to 10,000 (Pa s, 23°C) at a shear rate of 0.1 (1 / s), and a viscosity of 0.001 to 10 (Pa s, 23°C) at a shear rate of 1,000 (1 / s). In the present invention, the viscosity is measured using a rheometer (for example, ARES rheometer manufactured by TA Instruments) after adjusting the liquid temperature to 23°C.

[0068] The means for applying the coating composition of the present invention is not particularly limited, and known coating means such as brush coating, roller coating, trowel coating, spatula coating, flow coater coating, spray coating (e.g., air spray coating, airless spray coating, etc.), electrostatic coating, dipping, electrodeposition coating, roll coating, etc. can be used.

[0069] The drying method for the coating composition of the present invention is not particularly limited, and examples include natural drying, heat drying, etc. In the case of heat drying, the drying temperature is preferably 40 to 200° C. Heat drying is carried out by combining various conditions such as preheating and afterheating.

[0070] The coating composition of the present invention is capable of forming a coating film that is excellent in blocking resistance and corrosion prevention properties, and is therefore suitable as a coating composition for use in factory painting.

[0071] The coating method of the present invention is a method of coating a substrate with the coating composition of the present invention described above. Also, the coated body of the present invention is a coated body obtained by coating a substrate with the coating composition of the present invention described above.

[0072] A coating film is formed on a substrate by applying the coating composition of the present invention to the substrate. The coating film thickness is preferably 10 to 100 μm, and more preferably 10 to 60 μm. In the present invention, the coating film thickness means the thickness of the coating film after application and drying.

[0073] Examples of substrates include plastic substrates such as epoxy resin, ABS resin, polycarbonate, polyvinyl chloride, polystyrene, acrylic resin, e.g., polymethyl methacrylate (PMMA), polyethylene terephthalate (PET), polyolefin, e.g., polypropylene (PP), metal substrates such as steel, galvanized steel, tinned steel, stainless steel, magnesium alloy, aluminum, aluminum alloy, titanium, titanium alloy, etc., inorganic substrates other than metals such as cement, mortar, concrete, slate, gypsum, calcium silicate, glass, ceramic, calcium carbonate, marble, artificial marble, etc., wood substrates such as wood, paper substrates, and composite substrates combining two or more of these substrates. Examples of composite substrates include composite substrates such as wood fiber-reinforced cement boards, fiber-reinforced cement boards, and fiber-reinforced cement-calcium silicate boards, metal substrates that have been subjected to various surface treatments, such as oxidation treatments, and plastic substrates whose surfaces are coated with inorganic substances (e.g., glass-coated plastic substrates).

[0074] The substrate is preferably a metal substrate, particularly steel materials used in construction applications, particularly lightweight steel, and the coating composition of the present invention can be particularly suitably used as an anti-rust coating for these substrates.

[0075] The substrates come in various shapes, including two-dimensional substrates such as films, sheets, and plates, and three-dimensional substrates that are complex three-dimensional objects. The surface of the substrate may be smooth or may have irregularities. Specific examples of steel materials include C-shaped steel such as lip channel steel, light channel steel, and deformed light channel steel, L-angle steel such as equal leg light angle steel and unequal leg light angle steel, lightweight steel such as square steel pipes and deck plates, etc.

[0076] The surface of the substrate may be subjected to pretreatment such as degreasing, chemical conversion treatment, or polishing, or may be coated with a sealer or primer. [Example]

[0077] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples. In each example, "parts" and "%" are by mass unless otherwise specified. Furthermore, the film thickness of the coating film is based on the applied coating film.

[0078] Production of aqueous coating compositions The aqueous coating compositions of Examples 1 to 10 and Comparative Examples 1 to 6 were prepared by thoroughly mixing the materials according to the formulations shown in Tables 1 and 2 below using a stirrer. Note that in the compositions of Tables 1 and 2, the amount of water indicates the total amount of water used in preparing the aqueous coating composition, and includes the amount of water used in the resin dispersion or aqueous resin solution. On the other hand, the amount of resin does not indicate the amount of resin dispersion or aqueous resin solution, but rather the amount of resin itself contained in the resin dispersion or aqueous resin solution.

[0079] Preparation of test plates A polished cold-rolled steel plate measuring 70 x 150 x 0.8 mm was polished on the surface with water-resistant abrasive paper of 280 grit size, and then degreased with toluene to prepare a test material.

[0080] Preparation of test plate (I) The aqueous coating compositions of Examples 1 to 10 and Comparative Examples 1 to 6 were diluted to 10% by mass with a thinner (a mixture of water and a film-forming agent) in accordance with JIS K5500 and thoroughly stirred, and then brush-painted onto the above substrate to a coating thickness of 30 μm. The resulting coating was then dried for one week in an environment of 23°C and 50% humidity to obtain test panels (I) for Examples 1 to 10 and Comparative Examples 1 to 6.

[0081] Preparation of test plate (II) The aqueous coating compositions of Examples 1 to 10 and Comparative Examples 1 to 6 were spray-coated onto grit-blasted plates (70 x 150 x 2.3 mm) that had been heated to a surface temperature of 100°C, to a coating thickness of 30 μm, and then dried for 5 minutes in an environment of 23°C and 50% humidity to obtain test plates (II) for Examples 1 to 10 and Comparative Examples 1 to 6.

[0082] <Corrosion resistance> The back surface and end (side) surfaces of the test plate (I) were coated with the same aqueous coating composition as the front surface and dried. Then, a cross-cut was made in the coating film formed on the surface of the test plate (I) to prepare a test plate for evaluating corrosion resistance. The test plate thus prepared was subjected to a cyclic corrosion test under cycle D conditions according to the method of JIS K 5600-7-9:2006, and the number of cycles until rust appeared more than 2 mm from the notch in the cut portion was evaluated. The evaluation criteria are shown below. Coating films with a result of ⊚ or ◯ are coating films with excellent corrosion resistance. (Evaluation criteria) ◎: 51 cycles or more ○: 36 to 50 cycles △: 21 cycles to 35 cycles ×: 20 cycles or less

[0083] <Blocking resistance> Two test plates (II) obtained as described above were prepared and placed one on top of the other so that their coated surfaces were in contact with each other. A constant pressure load was applied to the entire overlapping area for 24 hours at 40°C. After the load application was stopped, the overlapping test plates were peeled off, and the presence or absence of coating peeling was evaluated using the following four-level load rating. The evaluation criteria are shown below. Coatings that received a result of ◎ or ○ were coatings with excellent blocking resistance. (Evaluation criteria) ◎: No peeling of the coating occurs even when a load of 1.5 MPa is applied. ◯: No peeling of the coating occurs even when a load of 1.0 MPa is applied. △: No peeling of the coating occurs even when a load of 0.5 MPa is applied. ×: No peeling of the coating occurs even when a load of 0.1 MPa is applied.

[0084] The evaluation results and measurement results are shown in Tables 1 and 2.

[0085] The pigments, resins and other components shown in Tables 1 and 2 are described below. (A-1) Pigment Barium sulfate A: "Barium sulfate W-1", precipitated barium sulfate, Mohs hardness 3.5, average particle size 1.5 μm, aspect ratio 1, manufactured by Takehara Sangyo Co., Ltd. Barium sulfate B: "Precipitated Barium 100", precipitated barium sulfate, Mohs hardness 3, average particle size 0.6 μm, aspect ratio 1, manufactured by Sakai Chemical Industry Co., Ltd. Silica: "SIPERNAT820A", silica, Mohs hardness 7, average particle size 6 μm, aspect ratio 1, made by EVONIK Calcium carbonate: "Sunlight SL100", calcium carbonate, Mohs hardness 3, average particle size 6 μm, aspect ratio 1, manufactured by Takehara Chemical Industry Co., Ltd. (A-2) Pigment Aluminum flakes: "RFA4000", Mohs hardness 3, average particle size 30 μm, aspect ratio 100, manufactured by Toyo Aluminum Co., Ltd. Talc: "Microace K-1", Mohs hardness 1, average particle size 8 μm, aspect ratio 7, manufactured by Nippon Talc Co., Ltd. Mica: "A-21S", Mohs hardness 2.5, average particle size 12 μm, aspect ratio 10, manufactured by Yamaguchi Mica Co., Ltd. (A-3) Other pigments Titanium oxide: "R-32", white pigment, manufactured by Sakai Chemical Industry Co., Ltd., aspect ratio 1, Carbon black: "Mitsubishi Carbon Black MA100", black pigment, aspect ratio 1, manufactured by Mitsubishi Chemical Corporation Bengala: "Todacolor 120ED", rust-colored pigment, aspect ratio 1, manufactured by Toda Kogyo Co., Ltd. Anti-rust pigment (zinc phosphate): "K-WHITE #140W", aspect ratio 4, manufactured by Teika Co., Ltd. resin Acrylic emulsion-1: "Acryset EX-41", acrylic emulsion, manufactured by Nippon Shokubai Co., Ltd. Acrylic emulsion-2: "Acryset EF-005", acrylic emulsion, manufactured by Nippon Shokubai Co., Ltd. Acrylic emulsion-3: "VIACRYL VSC6254w / 40WA", acrylic emulsion, manufactured by Daicel Allnex Co., Ltd. Epoxy dispersion: "BECKOPOX EP2307w / 45WAMP", manufactured by Daicel Allnex Co., Ltd. Acrylic resin aqueous solution: "Acryset ARL-453", water-soluble resin, manufactured by Nippon Shokubai Co., Ltd. others Film-forming agent: glycol-based solvent Additives: dispersants, rheology control agents, defoamers

[0086] [Table 1]

[0087] [Table 2]

Claims

1. (A-1) at least one pigment having an aspect ratio of 1 or more but less than 5 and selected from barium sulfate, silica, and calcium carbonate; and (A-2) a scaly pigment having an average particle size of 2 to 30 μm and an aspect ratio of 5 to 100, wherein the mass ratio of (A-1):(A-2) is within the range of 90:10 to 70:

30.

2. 2. The coating composition according to claim 1, wherein the average particle size of (A-1) is smaller than the average particle size of (A-2).

3. A coating method comprising coating a metal substrate with the coating composition according to claim 1 or 2.

4. A coated body obtained by applying the coating composition according to claim 1 or 2 to a metal substrate.

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