Heat-resistant coated article and method for producing the same

Abstract

Provided is a heat-resistant coated article excellent in both heat resistance and water resistance.　A heat-resistant coated article 1 comprises: a base material 2; a first coating film 3 provided on a surface 2a of the base material 2; and a second coating film 4 provided on the first coating film 3. The first coating film 3 is a heat-cured product of a composition containing an alkali metal silicate and inorganic particles. The second coating film 4 is a cured product formed by an alkali metal silicate and an acidic curing agent.

Description

Heat-resistant coated object and manufacturing method thereof

[0001] The present invention relates to a heat-resistant coated article and a method for producing the heat-resistant coated article.

[0002] Paints are used in a wide range of fields, including automobiles, electrical machinery, metal parts, and buildings. Among these, organic paints such as acrylic resins and urethane resins are typically used for paints intended to protect and beautify objects. Organic paints have excellent coating film adhesion, impact resistance, and water resistance, but their low heat resistance makes them unsuitable for painting parts used at high temperatures around the engine of automobiles and other vehicles.

[0003] Therefore, in recent years, a method of forming a coating film from an inorganic coating material mainly composed of a water-soluble alkali metal silicate known as water glass has been studied. For example, Patent Document 1 proposes the use of an inorganic coating material mainly composed of a water-soluble alkali metal silicate as a coating material capable of forming a coating film having excellent properties such as heat resistance and heat dissipation. Furthermore, Patent Document 2 proposes the use of an inorganic coating material mainly composed of a water-soluble alkali metal silicate as a coating material to be applied to the inner wall surface of a combustion chamber.

[0004] Japanese Patent Publication No. 2004-002813

[0005] The paints of Patent Documents 1 and 2 are excellent in heat resistance and are also environmentally friendly because they do not use organic solvents. However, glassy coating films formed from water glass inherently have problems with water resistance, such as being water-soluble and not resistant to moisture, and the paints of Patent Documents 1 and 2 also have the problem of insufficient water resistance.

[0006] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a heat-resistant coated article that is excellent in both heat resistance and water resistance, and a method for producing the heat-resistant coated article.

[0007] The present invention provides the following heat-resistant coated article and method for producing the heat-resistant coated article.

[0008] Item 1. A heat-resistant coated article comprising a substrate, a first coating film provided on the surface of the substrate, and a second coating film provided on the first coating film, wherein the first coating film is a thermoset product of a composition containing alkali metal silicates and inorganic particles, and the second coating film is a cured product formed from alkali metal silicates and an acidic curing agent.

[0009] Item 2: SiO contained in the alkali metal silicate constituting the first coating film ２ and M ２ O (M is one or a mixture of two or more selected from alkali metals) ２ / M ２ O) is 1.5 to 8.5, and SiO contained in the alkali metal silicates constituting the second coating film ２ and M ２ O (M is one or a mixture of two or more selected from alkali metals) ２ / M ２ Item 3. The heat-resistant coated article according to item 1, wherein O) is 1.5 to 8.5.

[0010] Item 3. The heat-resistant coated article according to Item 1 or 2, wherein the alkali metal silicates constituting the first coating film are one or more selected from the group consisting of sodium silicate, potassium silicate, and lithium silicate.

[0011] Item 4. The heat-resistant coated article according to any one of Items 1 to 3, wherein the alkali metal silicates constituting the second coating film are one or more selected from the group consisting of sodium silicate, potassium silicate, and lithium silicate.

[0012] Item 5. The heat-resistant coated article according to any one of Items 1 to 4, wherein the acidic curing agent has an acid dissociation constant in water at 25° C. of 4 or less.

[0013] Item 6. The heat-resistant coated article according to any one of Items 1 to 5, wherein the inorganic particles are fibrous particles and / or non-fibrous particles.

[0014] Item 7. The heat-resistant coated article according to any one of Items 1 to 6, wherein the second coating film is a cured product formed by applying an aqueous composition (2A) containing an alkali metal silicate to the surface of the first coating film to form an uncured coating film, applying an aqueous composition (2B) containing an acidic curing agent to the uncured coating film, and then heat-treating the uncured coating film at 40°C to 600°C.

[0015] Item 8. The heat-resistant coated article according to any one of Items 1 to 7, wherein the first coating film is a thermoset product formed by applying an aqueous composition (1) containing alkali metal silicates and inorganic particles to the surface of the substrate and then heat-treating the applied composition at 40°C to 600°C.

[0016] Item 9. The heat-resistant coated article according to any one of items 1 to 8, wherein the substrate is made of a metal material.

[0017] Item 10. A method for producing a heat-resistant coated article according to any one of Items 1 to 9, comprising the steps of: applying an aqueous composition (1) containing alkali metal silicates and inorganic particles onto the surface of a substrate, and heat-treating the composition at 40°C to 600°C to form a first coating film; and applying an aqueous composition (2A) containing alkali metal silicates onto the surface of the first coating film to form an uncured coating film, applying an aqueous composition (2B) containing an acidic curing agent to the uncured coating film, and heat-treating the composition at 40°C to 600°C to form a second coating film.

[0018] Item 11. The method for producing a heat-resistant coated article according to Item 10, wherein the content of the alkali metal silicates is 10% by mass to 80% by mass in 100% by mass of the total solids content in the aqueous composition (1).

[0019] Item 12. The method for producing a heat-resistant coated article according to Item 10 or 11, wherein the aqueous composition (1) is substantially free of an acidic curing agent.

[0020] Item 13. The method for producing a heat-resistant coated article according to any one of Items 10 to 12, wherein the acidic curing agent in the aqueous composition (2B) has an acid dissociation constant in water at 25°C of -5 to 4.

[0021] Item 14. The method for producing a heat-resistant coated article according to any one of Items 10 to 13, wherein the content of the acidic curing agent in the aqueous composition (2B) is 0.01 mol / L or more.

[0022] According to the present invention, it is possible to provide a heat-resistant coated article that is excellent in both heat resistance and water resistance, and a method for producing the heat-resistant coated article.

[0023] FIG. 1 is a schematic cross-sectional view showing a heat-resistant coated article according to one embodiment of the present invention.

[0024] Hereinafter, an example of a preferred embodiment of the present invention will be described. However, the following embodiment is merely an example, and the present invention is not limited to the following embodiment.

[0025] In this specification, when it is stated that "X to Y" (X and Y are any numbers), it means "X or more, Y or less." Furthermore, when it is stated that "X or more" (X is any number), it includes the meaning of "X or more than X," and when it is stated that "Y or less" (Y is any number), it also includes the meaning of "Y or less than Y." Furthermore, "X and / or Y (X and Y are any configurations)" means "at least one of X and Y," and can mean three things: "X only," "Y only," and "X and Y."

[0026] In this specification, the term "water-based" is used to distinguish it from a solvent-based system, and means that an aqueous medium, preferably water, is used as the medium, and does not exclude the use of a system that contains a certain amount of organic solvent among its components.

[0027] In this specification, "fibrous particles" refer to particles in which, when the longest side of the rectangular parallelepiped circumscribing the particle and having the smallest volume (circumscribing rectangular parallelepiped) is defined as the major axis L, the next longest side as the minor axis B, and the shortest side as the thickness T (B>T), L / B and L / T are both 5 or more, and the major axis L corresponds to the fiber length and the minor axis B corresponds to the fiber diameter. "Non-fibrous particles" refer to particles in which L / B is less than 5.

[0028] <Heat-Resistant Coated Article> Fig. 1 is a schematic cross-sectional view showing a heat-resistant coated article according to one embodiment of the present invention. As shown in Fig. 1, the heat-resistant coated article 1 includes a substrate 2, a first coating film 3, and a second coating film 4. The substrate 2 has a first main surface 2a and a second main surface 2b that face each other. The first coating film 3 is provided on the first main surface 2a of the substrate 2. Furthermore, the second coating film 4 is provided on the first coating film 3.

[0029] Note that FIG. 1 is merely a diagram showing one example of the structure of the heat-resistant coated article of the present invention, and the structure of the heat-resistant coated article of the present invention is not limited thereto. The first coating film may be provided on at least a portion of the surface of the substrate. For example, as shown in FIG. 1, the first coating film 3 may be provided on the entire first main surface 2a of the substrate 2, or may be provided on only a portion of the first main surface 2a. The first coating film may be disposed in an appropriate position depending on the intended use. Note that, although another film may be provided between the substrate and the first coating film, from the viewpoint of further improving adhesion between the substrate and the first coating film, it is preferable that the first coating film be provided directly on the substrate.

[0030] The second coating film may be provided on at least a portion of the surface of the first coating film. For example, as shown in FIG. 1 , the second coating film 4 may be provided so as to cover the entire surface 3 a of the first coating film 3, or may be provided so as to cover only a portion of the surface 3 a of the first coating film 3, as long as the effects of the present invention can be achieved. The second coating film may be provided so that at least a portion thereof extends into the first coating film. Furthermore, the second coating film may be a very thin film, as long as the effects of the present invention can be achieved. Although another film may be provided between the first coating film and the second coating film, it is preferable that the second coating film be provided directly on the first coating film.

[0031] In addition, in FIG. 1 , the first coating film 3 and the second coating film 4 are provided only on the first main surface 2 a of the substrate 2, but the first coating film 3 and the second coating film 4 may be provided on both the first main surface 2 a and the second main surface 2 b of the substrate 2.

[0032] In the present invention, the first coating film is a thermosetting product of a composition containing an alkali metal silicate and inorganic particles, and the second coating film is a cured product formed from an alkali metal silicate and an acidic curing agent.

[0033] The alkali metal silicates include, for example, M ２ O.nSiO ２ (M is an alkali metal, n is a molar ratio). Examples of alkali metal silicates include sodium silicate (Na ２ O.nSiO ２ ), potassium silicate (K ２ O.nSiO ２ ), or lithium silicate (Li ２ O.nSiO ２ ) etc.

[0034] Examples of the acidic curing agent include organic acids and inorganic acids that exhibit acidity in the form of an aqueous composition.

[0035] Conventionally, glassy coating films formed from water glass have not been sufficiently water resistant, and in particular, water glass containing inorganic particles to impart various properties has had the problem of being prone to microcracks when formed into a coating film, resulting in insufficient water resistance.

[0036] The present inventors have discovered that by providing a second coating film, which is a cured product formed from an alkali metal silicate and an acidic curing agent as described above, on top of a first coating film, which is a thermosetting product of a composition containing alkali metal silicates and inorganic particles and is provided on the surface of a substrate, it is possible to improve the water resistance while maintaining the heat resistance of a heat-resistant coated product.

[0037] Such heat-resistant coated articles can be used for vehicle parts, aircraft parts, building materials, cooking utensils, etc., and are particularly suitable for use on vehicle parts such as rolling bearings, sliding bearings, brake rotors, brake calipers, and mufflers.

[0038] Hereinafter, each component of the heat-resistant coated article of the present invention will be described in detail.

[0039] (Substrate) Examples of the material of the substrate include metallic materials such as simple metals such as iron, aluminum, copper, or titanium, and alloys thereof; and non-metallic materials such as resin, glass, concrete, or ceramics. One of these may be used alone, or two or more may be used in combination. From the viewpoint of further improving the adhesion and heat resistance of the first coating film, it is preferable that the material of the substrate is a metallic material. The substrate may be subjected to a known surface treatment. Examples of the surface treatment include metal coating treatment or chemical conversion treatment. Examples of the metal coating treatment include electroplating, hot-dip plating, or vapor deposition plating. Examples of the chemical conversion treatment include chromate treatment or phosphate treatment.

[0040] The shape of the substrate is not particularly limited, and may be, for example, a sheet, plate, sphere, film, large structure, assembly or molded article with a complex shape.

[0041] The lower limit of the thickness of the substrate is not particularly limited and is, for example, 10 μm or more. The upper limit of the thickness of the substrate is not particularly limited and can be appropriately selected depending on the application of the heat-resistant coated article of the present invention and the shape of the part to which the heat-resistant coated article is to be used.

[0042] (First Coating Film) The first coating film is a thermoset product obtained by thermally curing a composition containing an alkali metal silicate and inorganic particles. The first coating film may further contain other materials as necessary.

[0043] The film thickness of the first coating film is preferably 1 μm to 500 μm, more preferably 3 μm to 30 μm. By setting the film thickness of the first coating film to the above upper limit or less, errors in the coating film properties are less likely to occur under various cyclic environments such as high temperature, high compression, and high-frequency vibration. By setting the film thickness of the first coating film to the above lower limit or more, a smooth coating film surface is more easily obtained.

[0044] Alkali metal silicates; SiO of alkali metal silicates used to form the first coating film ２ and M ２ O (M is one or a mixture of two or more selected from alkali metals) ２ / M ２O) is preferably 1.5 to 8.5, more preferably 2.0 to 6.0, and even more preferably 2.0 to 5.0. ２ / M ２ By setting the content of O) within the above range, it is possible to further improve the film-forming properties of the first coating film and the heat resistance and water resistance of the heat-resistant coated product.

[0045] The alkali metal silicates used to form the first coating film are preferably one or more selected from the group consisting of sodium silicate, potassium silicate, and lithium silicate. From the viewpoint of further improving the heat resistance of the heat-resistant coated article and further suppressing microcracks in the heat-resistant coated article, the alkali metal silicates are more preferably sodium silicate and potassium silicate.

[0046] In the case of a mixed system in which sodium silicate and potassium silicate are used in combination as alkali metal silicates, the molar ratio of potassium silicate to sodium silicate (potassium silicate / sodium silicate) is preferably 0.1 to 50, more preferably 0.2 to 5.0. By setting the molar ratio (potassium silicate / sodium silicate) within the above range, it becomes easier to form a second coating film on the surface of the first coating film.

[0047] The sodium silicate used to form the first coating film is, for example, Na ２ O.nSiO ２ (n is the molar ratio) ２ / Na ２ The molar ratio of O may be any value that makes sodium silicate water-soluble, and is preferably 1.5 to 4.5, more preferably 1.5 to 3.0.

[0048] The potassium silicate used to form the first coating film is, for example, K ２ O.nSiO ２ (n is the molar ratio) ２ / K ２ The molar ratio of O may be any value that makes potassium silicate water-soluble, and is preferably 1.5 to 5.0, more preferably 3.0 to 4.0.

[0049] The lithium silicate used to form the first coating film is, for example, Li ２ O.nSiO ２ (n is the molar ratio) ２ / Li ２ The molar ratio of O may be any value that makes the lithium silicate water-soluble, and is preferably 2.5 to 8.5, more preferably 7.0 to 8.0.

[0050] Inorganic Particles: The inorganic particles used to form the first coating film may be fibrous particles and / or non-fibrous particles.

[0051] The fibrous particles are preferably solid inorganic particles from the viewpoint of further improving the reinforcing properties of the first coating film.

[0052] The true specific gravity of the fibrous particles is preferably 2.0 g / cm from the viewpoint of making the viscosity of the composition that forms the first coating film suitable for application and making it less likely for sedimentation to occur during storage. ３ or more, preferably 6.0 g / cm ３ or less, more preferably 4.0 g / cm ３ The following is the result.

[0053] Examples of the fibrous particles include potassium titanate fibers, wollastonite fibers, titanium oxide fibers, milled glass fibers, and milled carbon fibers, and potassium titanate fibers are preferred. One of these may be used alone, or two or more may be used in combination.

[0054] As the potassium titanate fiber, a wide variety of conventionally known fibers can be used, and examples thereof include potassium hexatitanate fiber and potassium octatitanate fiber.

[0055] The average fiber length of the fibrous particles is preferably 1 μm to 50 μm, more preferably 3 μm to 30 μm, and even more preferably 3 μm to 20 μm. The average fiber diameter of the fibrous particles is preferably 0.01 μm to 1 μm, more preferably 0.05 μm to 0.8 μm, and even more preferably 0.1 μm to 0.7 μm. The average aspect ratio of the fibrous particles is preferably 10 or more, more preferably 10 to 100, and even more preferably 15 to 35.

[0056] The average fiber length and average fiber diameter of the fibrous particles can be measured by observation with a scanning electron microscope, and the average aspect ratio (average fiber length / average fiber diameter) can be calculated from the average fiber length and average fiber diameter. For example, a plurality of fibrous particles are photographed with a scanning electron microscope, 300 fibrous particles are arbitrarily selected from the observation image, and their fiber lengths and fiber diameters are measured. The average fiber length can be calculated by integrating all the fiber lengths and dividing by the number of particles, and the average fiber diameter can be calculated by integrating all the fiber diameters and dividing by the number of particles.

[0057] By using fibrous particles as the inorganic particles, the inorganic particles are arranged in three dimensions in the first coating film, and the strength of the first coating film is further increased.

[0058] The non-fibrous particles include solid inorganic particles and hollow inorganic particles, and can be appropriately selected depending on the desired physical properties of the first coating film.

[0059] The true specific gravity of the non-fibrous solid inorganic particles is preferably 2.0 g / cm from the viewpoint of making the viscosity of the composition that forms the first coating film suitable for application and making it less susceptible to settling during storage. ３ or more, preferably 6.0 g / cm ３ or less, more preferably 4.0 g / cm ３ The following is the result.

[0060] Examples of solid inorganic particles that are non-fibrous particles include silicon carbide, silicon nitride, aluminum nitride, boron nitride, magnesium oxide, alumina, potassium titanate, sodium titanate, magnesium potassium titanate, lithium potassium titanate, cristobalite, kaolin, talc, amorphous silica, cordierite, steatite, mica, forsterite, vermiculite, sepiolite, glass flakes, graphite, molybdenum disulfide, etc. One of these may be used alone, or two or more may be used in combination.

[0061] The average particle size of the non-fibrous solid inorganic particles is preferably 0.5 μm to 15 μm, more preferably 0.5 μm to 7 μm. When the average particle size of the solid inorganic particles is equal to or greater than the lower limit, the function of the aggregate supporting the cured coating film is more effectively exhibited. When the average particle size of the solid inorganic particles is equal to or less than the upper limit, the solid inorganic particles are further prevented from settling in the liquid phase.

[0062] In this specification, unless otherwise specified, the average particle size refers to the particle size at 50% cumulative volume in the particle size distribution measured by laser diffraction (D ５０ ) This D ５０ is the particle size at which the cumulative value reaches 50% when the particle size distribution is calculated on a volume basis and the number of particles is counted from the smallest particle size on a cumulative curve with the total volume set to 100%.

[0063] The true specific gravity of the non-fibrous hollow inorganic particles is preferably 0.5 g / cm from the viewpoint of making the viscosity of the composition that forms the first coating film suitable for application and making it less likely for sedimentation to occur during storage. ３ or more, preferably 1.0 g / cm ３ or less, more preferably 0.8 g / cm ３ The following is the result.

[0064] Examples of hollow inorganic particles that are non-fibrous particles include silicon dioxide compounds, etc. Here, "silicon dioxide compounds" refers to compounds containing 50 mass % or more of silicon dioxide, and "hollow" refers to particles that are porous or have a single spherical void.

[0065] Examples of hollow inorganic particles made of silicon dioxide compounds include shirasu balloons, fly ash balloons, and borosilicate glass balloons, and borosilicate glass balloons are preferred. One of these may be used alone, or two or more may be used in combination.

[0066] The average particle size of the non-fibrous hollow inorganic particles is preferably 5 μm to 40 μm, more preferably 5 μm to 25 μm. Although this varies depending on the composition and shell thickness of the hollow inorganic particles, an average particle size of the hollow inorganic particles equal to or greater than the lower limit described above is preferred because the proportion of the internal space volume is relatively large, resulting in more sufficient insulating efficiency due to the hollow structure. Furthermore, an average particle size of the hollow inorganic particles equal to or less than the upper limit described above is preferred because it is less likely to affect the surface smoothness of the first coating film.

[0067] The pressure resistance strength of the non-fibrous hollow inorganic particles is preferably 10 MPa or more, more preferably 20 MPa or more. If the pressure resistance strength is equal to or greater than the above lower limit, a cured product having higher surface strength can be obtained. The upper limit of the pressure resistance strength of the non-fibrous hollow inorganic particles is not particularly limited. The upper limit of the pressure resistance strength of the non-fibrous hollow inorganic particles is usually about 180 MPa.

[0068] (Second Coating Film) The second coating film is a cured product formed from an alkali metal silicate and an acidic curing agent. The second coating film may further contain other materials as necessary. The film thickness of the second coating film is preferably 0.1 μm to 15 μm, more preferably 0.3 μm to 12 μm, and even more preferably 0.5 μm to 9 μm. By setting the film thickness of the second coating film within the above range, the heat resistance and water resistance of the heat-resistant coated product can be further improved.

[0069] Alkali metal silicates; SiO of alkali metal silicates used to form the second coating film ２ and M ２ O (M is one or a mixture of two or more selected from alkali metals) ２ / M ２ O) is preferably 1.5 to 8.5, more preferably 3.0 to 8.3, and even more preferably 5.0 to 8.0. ２ / M ２ By setting the content of O) within the above range, the heat resistance and water resistance of the heat-resistant coated article can be further improved.

[0070] The alkali metal silicate used to form the second coating film is preferably one or more selected from the group consisting of sodium silicate, potassium silicate, and lithium silicate. From the viewpoint of further improving the heat resistance and water resistance of the heat-resistant coated article, the alkali metal silicate is more preferably potassium silicate or lithium silicate.

[0071] The sodium silicate used to form the second coating film is, for example, Na ２ O.nSiO ２ (n is the molar ratio) ２ / Na ２ The molar ratio of O may be any value that makes sodium silicate water-soluble, and is preferably 1.5 to 4.5, more preferably 1.5 to 3.0.

[0072] The potassium silicate used to form the second coating film is, for example, K ２ O.nSiO ２ (n is the molar ratio) ２ / K ２ The molar ratio of O may be any value that makes potassium silicate water-soluble, and is preferably 1.5 to 5.0, more preferably 3.0 to 4.0.

[0073] The lithium silicate used to form the second coating film is, for example, Li ２ O.nSiO ２ (n is the molar ratio) ２ / Li ２ The molar ratio of O may be any value that makes the lithium silicate water-soluble, and is preferably 2.5 to 8.5, more preferably 7.0 to 8.0.

[0074] Acidic curing agent: The curing reaction of alkali metal silicates is accelerated in the presence of an acidic curing agent. Therefore, in the present invention, the acidic curing agent may be any acid catalyst that exhibits either Bronsted acidity or Lewis acidity in the curing reaction of alkali metal silicates.

[0075] Examples of the acidic curing agent include inorganic acids, organic acids, and solid acids. In the present invention, the acidic curing agent is preferably at least one acid selected from the group consisting of inorganic acids, organic acids, and solid acids, and more preferably an inorganic acid or an organic acid.

[0076] Examples of inorganic acids include mineral acids such as phosphoric acid, sulfuric acid, hydrochloric acid, nitric acid, and boric acid, sulfates, hydrochlorides, nitrates, etc. The inorganic acid is preferably a mineral acid.

[0077] Examples of the organic acid include organic carboxylic acids such as formic acid, acetic acid, gluconic acid, lactic acid, succinic acid, phthalic acid, and citric acid; and organic sulfonic acids such as methanesulfonic acid, paratoluenesulfonic acid, and paraaminobenzenesulfonic acid.

[0078] A solid acid is a compound that exhibits acidity on the surface of a solid. The solid acid may be a compound that has an acidic active site on the surface of the solid. Examples of solid acids include metal oxides and solid phosphoric acid.

[0079] The acidic curing agent may be one of the above-exemplified acidic curing agents, or a mixture of any two or more of the above-exemplified acidic curing agents, or a complex of two or more of the above-exemplified acidic curing agents chemically combined.

[0080] From the viewpoint of further accelerating the curing reaction of alkali metal silicates, the acidic curing agent preferably has an acid dissociation constant (pKa) of 4 or less, more preferably from -5 to 4, even more preferably from -3 to 4, and particularly preferably from 1.5 to 4. In the present invention, the acid dissociation constant (pKa) is the value in water at 25°C. When the acidic curing agent is a polyvalent acid, the first dissociation constant (pKa １ ) is defined as the acid dissociation constant (pKa) in the present invention.

[0081] <Method for producing heat-resistant coated article> The method for producing a heat-resistant coated article of the present invention comprises the steps of: (I) applying an aqueous composition (1) containing alkali metal silicates and inorganic particles onto the surface of a substrate, followed by heat treatment at 40°C to 600°C to form a first coating film; and (II) applying an aqueous composition (2A) containing alkali metal silicates onto the surface of the first coating film to form an uncured coating film, applying an aqueous composition (2B) containing an acidic curing agent to the uncured coating film, and then heat treating the uncured coating film at 40°C to 600°C to form a second coating film.

[0082] Specifically, the heat-resistant coated article of the present invention can be produced as follows.

[0083] (Step (I)) Step (I) is a step of applying an aqueous composition (1) containing the alkali metal silicate and the inorganic particles to the surface of the substrate, followed by heat treatment at 40°C to 600°C to form a first coating film.

[0084] The content of alkali metal silicates in the aqueous composition (1) is preferably 10% by mass to 80% by mass, more preferably 15% by mass to 40% by mass, based on 100% by mass of the total solids content in the aqueous composition (1). When the content of alkali metal silicates is equal to or greater than the above-mentioned lower limit, the adhesion between the obtained first coating film and the substrate can be further improved. When the content of alkali metal silicates is equal to or less than the above-mentioned upper limit, the heat resistance and water resistance of the obtained heat-resistant coating can be further improved.

[0085] The content of inorganic particles in the aqueous composition (1) is preferably 20% by mass to 90% by mass, more preferably 60% by mass to 85% by mass, based on 100% by mass of the total solids content in the aqueous composition (1). When the content of inorganic particles is equal to or greater than the above-mentioned lower limit, the effect of imparting functionality by the inorganic particles is easily obtained. When the content of inorganic particles is equal to or less than the above-mentioned upper limit, the adhesion between the obtained first coating film and the substrate can be further improved.

[0086] The aqueous composition (1) preferably uses water as a medium. The alkali metal silicate used in the aqueous composition (1) is preferably an aqueous solution raw material (aqueous alkali metal silicate solution), and is preferably present in the composition mainly in the form of an aqueous solution.

[0087] The aqueous composition (1) can be produced by mixing an appropriate amount of water with alkali metal silicates, inorganic particles, and, if necessary, other materials such as dispersants, antifoaming agents, wetting agents, colorants, solid lubricants, or sealants. The solids concentration of the aqueous composition (1) is preferably 10% to 80% by mass. Adjusting the solids concentration within the above range makes it easier to adjust the film thickness of the resulting first coating film. It is desirable that the aqueous composition (1) is substantially free of an acidic curing agent. In this specification, "substantially free of a material" means that the content of that material in the composition is 0.1% by mass or less, and it is also possible that the material may not be contained at all in the composition.

[0088] As described above, the aqueous composition (1) can be used as a single liquid containing all of the constituent components. However, if it is desired to maintain a long usable life after the preparation of the liquid formulation, an aqueous dispersion of only the components excluding the alkali metal silicates can be prepared as a first liquid. Then, before using the aqueous composition (1), the alkali metal silicates can be prepared as a second liquid, which can be mixed with the first liquid. By using a two-liquid system, the usable life of the composition can be further extended. In the two-liquid system, a portion of a component that does not exhibit a curing reaction with alkali metal silicates may be dispersed in the second liquid. Alternatively, a portion of the alkali metal silicates may be dispersed in the first liquid.

[0089] The first coating film is formed from a thermoset product of an alkali metal silicate prepared by mixing an aqueous composition (1) with inorganic particles and applying the composition to the surface of a substrate, and then subjecting the composition to heat treatment while the inorganic particles are incorporated into the matrix of the alkali metal silicate. The amount of aqueous composition (1) applied should be such that the film thickness after heat treatment is preferably 1 μm to 500 μm, more preferably 3 μm to 30 μm.

[0090] The aqueous composition (1) can be applied by well-known methods such as spray coating, spin coating, dipping, or brush coating. Of these, spray coating is preferred as the application method. Furthermore, it is preferable to roughen the application surface of the substrate in advance by physical roughening such as grit blasting or chemical roughening such as wet etching, since this facilitates the formation of a uniform film of the aqueous composition (1) on the application surface. Since the composition to be applied is the aqueous composition (1), it is desirable that no oil is attached to the application surface of the substrate. Therefore, it is preferable to degrease and clean the application surface of the substrate before applying the aqueous composition (1).

[0091] The heat treatment temperature is preferably 40°C to 600°C, more preferably 100°C to 300°C. However, if the aqueous composition (1) contains water and is immediately subjected to heat treatment, the surface may harden first, trapping the water inside, resulting in a so-called "skinning" phenomenon, and the water may later evaporate, causing voids or peeling at the interface. To prevent this, it is preferable to evaporate (dry) the water before performing the heat treatment.

[0092] The heat treatment time is not particularly limited as long as the alkali metal silicate is thermally cured, but is preferably 0.5 to 4 hours.

[0093] The first coating film may have a two-layer structure with different contents of alkali metal silicates. For example, a first coating film A may be formed in direct contact with the substrate, and then a first coating film B may be formed on top of this first coating film A. In this case, the solid volume fraction of the alkali metal silicates contained in first coating film B is preferably in the range of 1.05 to 2.0 times the solid volume fraction of the alkali metal silicates contained in first coating film A.

[0094] (Step (II)) Step (II) is a step of applying an aqueous composition (2A) containing an alkali metal silicate onto the surface of the first coating film to form an uncured coating film, applying an aqueous composition (2B) containing an acidic curing agent to the uncured coating film, and heat-treating the resulting film at 40°C to 600°C to form a second coating film.

[0095] The content of alkali metal silicates in the aqueous composition (2A) is preferably 10% by mass to 100% by mass, more preferably 20% by mass to 100% by mass, and even more preferably 50% by mass to 100% by mass, based on 100% by mass of the total solids content in the aqueous composition (2A). When the content of alkali metal silicates is within the above range, the adhesion between the first coating film and the second coating film is further improved.

[0096] The aqueous composition (2A) preferably uses water as a medium. The alkali metal silicate used in the aqueous composition (2A) is preferably an aqueous solution raw material (aqueous alkali metal silicate solution), and is preferably present in the composition mainly in the form of an aqueous solution.

[0097] The aqueous composition (2A) can be produced by mixing an appropriate amount of water with alkali metal silicates and, if necessary, other materials such as dispersants, antifoaming agents, wetting agents, colorants, or solid lubricants. The solids concentration of the aqueous composition (2A) is preferably 5% to 80% by mass. By adjusting the solids concentration of the aqueous composition (2A) within the above range, it becomes even easier to adjust the film thickness of the second coating film.

[0098] The coating amount of the aqueous composition (2A) is preferably 1 g / m ２ ~100g / m ２ and more preferably 5 g / m ２ ~20g / m ２ By setting the coating amount of the aqueous composition (2A) within the above range, it is possible to seal microcracks in the first coating film, and to further improve the water resistance of the first coating film while maintaining its excellent heat resistance.

[0099] Examples of the method for applying the aqueous composition (2A) include well-known methods such as spray coating, spin coating, dipping, brush coating, etc. Among these, spray coating is preferred as the method for applying the aqueous composition (2A).

[0100] The uncured coating film is formed by applying the aqueous composition (2A) onto the surface of the first coating film. If the uncured coating film is in an uncured state, the uncured coating film may have a two-layer structure in which uncured coating film A is formed directly on the surface of the first coating film, and then uncured coating film B is formed on uncured coating film A.

[0101] The aqueous composition (2B) may be applied to the uncured coating film after water has been evaporated (dried) to the extent that the applied alkali metal silicates do not harden, or the aqueous composition (2B) may be applied to the uncured coating film while it is still wet and not dried.

[0102] The aqueous composition (2B) preferably uses water as a medium, that is, the aqueous composition (2B) is preferably an aqueous solution of an acidic curing agent.

[0103] The lower limit of the content of the acidic curing agent in the aqueous composition (2B) may be any concentration that allows the uncured alkali metal silicates of the aqueous composition (2A) to gel quickly after application of the aqueous composition (2B), and is preferably 0.01 mol / L, more preferably 0.1 mol / L.

[0104] A more preferred lower limit of the content of the acidic curing agent in the aqueous composition (2B) can be appropriately determined depending on the acid dissociation constant (pKa) of the acidic curing agent, and when the acidic curing agent is a weak acid, i.e., an acid exhibiting a pKa ≥ 0, it is not particularly limited, but can be, for example, 0.2 mol / L, preferably 0.5 mol / L. Furthermore, a more preferred lower limit of the content of the acidic curing agent in the aqueous composition (2B) when the acidic curing agent is a strong acid, i.e., an acid exhibiting a pKa < 0, is not particularly limited, but can be, for example, 0.2 mol / L, preferably 0.3 mol / L.

[0105] By adjusting the content of the acidic curing agent in the aqueous composition (2B) to the above lower limit or more, the water resistance of the heat-resistant coated article can be further improved.

[0106] The upper limit of the content of the acidic curing agent in the aqueous composition (2B) can be appropriately determined depending on the acid dissociation constant (pKa) of the acidic curing agent, and from the viewpoint of further improving the heat resistance and workability of the heat-resistant coated product, for example, when the acidic curing agent is a weak acid, that is, an acid showing a pKa ≧ 0, the upper limit can be, but is not particularly limited to, 15 mol / L. Furthermore, when the acidic curing agent is a strong acid, that is, an acid showing a pKa < 0, an excessively high concentration is undesirable due to the influence of corrosion, and the upper limit of the content of the acidic curing agent in the aqueous composition (2B) can be, for example, 1.0 mol / L, preferably 0.7 mol / L.

[0107] Thus, the content of the acidic curing agent in the aqueous composition (2B) is preferably 0.1 mol / L to 15 mol / L, more preferably 0.5 mol / L to 15 mol / L, when the acidic curing agent is a weak acid, i.e., an acid exhibiting a pKa of 0 or greater. Furthermore, the content of the acidic curing agent in the aqueous composition (2B) is preferably 0.1 mol / L to 1.0 mol / L, more preferably 0.2 mol / L to 0.7 mol / L, when the acidic curing agent is a strong acid, i.e., an acid exhibiting a pKa of less than 0.

[0108] The curing reaction of the uncured alkali metal silicates in the aqueous composition (2A) is thought to proceed due to the catalytic action of the excess acidic curing agent at the contact interface between the uncured alkali metal silicates and the aqueous composition (2B), and therefore, the amount of the aqueous composition (2B) to be applied is not particularly limited, but it is preferable that the amount is such that all of the applied aqueous composition (2B) penetrates into the uncured coating film. The aqueous composition (2B) may be applied so that the acidic curing agent in the aqueous composition (2B) comes into contact with at least the first coating film.

[0109] The aqueous composition (2B) can be applied by known methods such as spray coating, spin coating, dipping, or brush coating. Among these, the method of applying the aqueous composition (2B) is preferably spray coating. Furthermore, since the uncured alkali metal silicates of the aqueous composition (2A) react quickly at the contact interface after application of the aqueous composition (2B), there is no particular limitation on the time until the heat treatment described below. However, if the coating film is not dried after application of the aqueous composition (2B), it is preferable to perform the heat treatment within 1 hour after application of the aqueous composition (2B).

[0110] The heat treatment temperature in step (II) is preferably 40°C to 600°C, more preferably 150°C to 550°C. The heat treatment sufficiently hardens the alkali metal silicates that have been partially condensed and hardened by the acidic curing agent. However, if the aqueous composition (2A) and the aqueous composition (2B) contain water, immediately subjecting them to heat treatment may result in the surface hardening first and trapping water inside, a phenomenon known as "skinning." The water may then evaporate, resulting in the formation of voids or peeling at the interface. To prevent this, it is preferable to evaporate (dry) the water before performing the heat treatment.

[0111] The heat treatment time is not particularly limited as long as the alkali metal silicate is thermally cured, but is preferably 0.5 to 4 hours.

[0112] In the present invention, the aqueous composition (2B) is applied to an uncured coating film on a sufficiently cured coating film (first coating film), and a high concentration of acid is allowed to penetrate into the uncured coating film, which is thought to be able to withstand condensation promotion by strong acid, and by subsequent heat treatment, a second coating film can be formed on the first coating film, which has excellent adhesion to the first coating film and also functions as a sealing layer for the first coating film.

[0113] The present invention will be described in more detail below with reference to specific examples. The present invention is not limited to the following examples, and can be practiced with appropriate modifications within the scope of the present invention.

[0114] The inorganic particles used in the production examples are specifically as follows:

[0115] Fibrous particles 1:8 potassium titanate fiber, solid particles, average fiber length 15 μm, average fiber diameter 0.5 μm, true specific gravity 3.4 g / cm ３ Non-fibrous particles 2: silicon carbide, solid particles, average particle diameter 3 μm, true specific gravity 3.2 g / cm ３ Non-fibrous particles 3: magnesium potassium titanate, solid particles, average particle diameter 4 μm, true specific gravity 3.4 g / cm ３

[0116] The average fiber length, average fiber diameter, and aspect ratio of the fibrous particles 1 were determined from the average values ​​of 300 randomly selected particles measured by observation with a scanning electron microscope (manufactured by Hitachi High-Technologies Corporation, trade name "S-4800"). The average particle diameter of the non-fibrous particles 2 was measured with a laser diffraction particle size distribution analyzer (manufactured by Shimadzu Corporation, trade name "SALD-2300").

[0117] <Formation of First Coating Film> (Production Example 1) An aqueous alkali metal silicate solution was prepared by mixing purified water and alkali metal silicates in the compositions and amounts shown in Table 1. Inorganic particles in the compositions and amounts shown in Table 1 were mixed with the prepared aqueous alkali metal silicate solution while stirring, to obtain an aqueous composition (1).

[0118] Next, the obtained aqueous composition (1) was applied using a spray onto the surface of the substrate shown in Table 1 so that the film thickness after heat curing would be as shown in Table 1, and then heat treatment was carried out under the heat treatment conditions shown in Table 1 to form a first coating film No. 1.

[0119] (Production Example 2) A first coating film No. 2 was formed in the same manner as in Production Example 1, except that the substrate was changed to that shown in Table 1.

[0120] (Production Example 3) A first coating film No. 3 was formed in the same manner as in Production Example 2, except that the inorganic particles were changed to those shown in Table 1.

[0121]

[0122] <Formation of Second Coating Film> (Examples 1 to 27 and Comparative Examples 1 to 5) Onto the surface of the first coating film obtained above, aqueous composition (2A) was applied using a spray in the amount shown in Table 2 to form an uncured coating film. Onto the surface of the obtained uncured coating film, aqueous composition (2B) was applied using a spray, and excess water on the surface was wiped off. Thereafter, the resultant was allowed to stand for 30 minutes and then heat-treated under the heat-treatment conditions shown in Table 2 to obtain a coated product.

[0123] In Comparative Examples 1 and 2, coated articles were obtained by performing only heat treatment on the surface of the first coating film without applying the aqueous composition (2A) or the aqueous composition (2B). In Comparative Examples 3 and 4, coated articles were obtained by performing heat treatment on the surface of the first coating film without applying the aqueous composition (2A). In Comparative Example 5, a second coating film was formed directly on the surface of an SPCC plate (50 mm x 50 mm x 1 mm thick, not blasted) without using the first coating film, to obtain a coated article.

[0124]

[0125] <Evaluation of Coated Articles> (Film Formability) The appearance of the coated articles obtained in the Examples and Comparative Examples was visually evaluated on a scale of 6 shown in Table 3, and the results are shown in Table 4.

[0126] (Thermal Shock Resistance Test) The coated articles obtained in the Examples and Comparative Examples were preheated in a radiant furnace at 500°C for 10 minutes, and then immersed in purified water at 25°C within 5 seconds to apply a thermal shock. The state of the coating film after the thermal shock was visually evaluated using the six-point scale shown in Table 3, and the results are shown in Table 4.

[0127] (Water Resistance Test) The coated articles obtained in the Examples and Comparative Examples were immersed in purified water at 98°C for 120 minutes, and the state of the coating film after immersion was visually evaluated using the six-point scale shown in Table 3. The results are shown in Table 4.

[0128]

[0129]

[0130] In Examples 1 to 27, by having the first coating film and the second coating film, there was no problem with film-forming properties, and both heat resistance and water resistance were achieved.

[0131] Comparative Examples 1 and 2 are comparative examples in which only the heat treatment was additionally performed without forming the second coating film, which shows that the water resistance cannot be improved by simply performing the heat treatment for a long time or at a high temperature when forming the first coating film.

[0132] Comparative Examples 3 and 4 are comparative examples in which the aqueous composition (2A) was not applied, and the film-forming properties were reduced compared to Comparative Examples 1 and 2 in which only the first coating film was applied. This shows that unless the aqueous composition (2A) is applied in advance, the film-forming properties of the first coating film are deteriorated by the aqueous composition (2B). It is also clear that increasing the heat treatment temperature improves water resistance but reduces heat resistance.

[0133] Comparative Example 5 is a comparative example in which a second coating film was formed directly on the surface of the substrate without forming a first coating film, and the film-forming properties of the coating film were not obtained, and major defects including peeling occurred even after heat treatment.

[0134] REFERENCE SIGNS LIST 1... heat-resistant coated object 2... substrate 2a... first main surface 2b... second main surface 3... first coating film 3a... surface 4... second coating film

Claims

1. A heat-resistant coating comprising a substrate, a first coating film provided on the surface of the substrate, and a second coating film provided on the first coating film, wherein the first coating film is a heat-cured product of a composition containing an alkali metal silicate and inorganic particles, and the second coating film is a cured product formed from an alkali metal silicate and an acidic curing agent.

2. SiO contained in the alkali metal silicate constituting the first coating film ２ and M. ２ O (M is one or a mixture of two or more selected from alkali metals) ２ / M ２ O) is 1.5 to 8.5, and SiO contained in the alkali metal silicate constituting the second coating film ２ and M. ２ O (M is one or a mixture of two or more selected from alkali metals) ２ / M ２ The heat-resistant coating according to claim 1, wherein O) is 1.5 to 8.

5.

3. A heat-resistant coating as described in claim 1 or claim 2, wherein the alkali metal silicates constituting the first coating film are one or more types selected from the group consisting of sodium silicate, potassium silicate, and lithium silicate.

4. A heat-resistant coating as described in claim 1 or claim 2, wherein the alkali metal silicates constituting the second coating film are one or more types selected from the group consisting of sodium silicate, potassium silicate, and lithium silicate.

5. A heat-resistant coated article according to claim 1 or 2, wherein the acidic curing agent has an acid dissociation constant in water at 25°C of 4 or less.

6. A heat-resistant coating according to claim 1 or 2, wherein the inorganic particles are fibrous particles and / or non-fibrous particles.

7. A heat-resistant coated product according to claim 1 or 2, wherein the second coating film is a cured product formed by applying an aqueous composition (2A) containing an alkali metal silicate on the surface of the first coating film to form an uncured coating film, applying an aqueous composition (2B) containing an acidic curing agent to the uncured coating film, and then heat-treating the uncured coating film at 40°C to 600°C.

8. A heat-resistant coated product according to claim 1 or 2, wherein the first coating film is a thermoset product formed by applying an aqueous composition (1) containing alkali metal silicates and inorganic particles onto the surface of the substrate, followed by heat treatment at 40°C to 600°C.

9. The heat-resistant coated article according to claim 1 or 2, wherein the substrate is made of a metal material.

10. A method for producing a heat-resistant coated article according to claim 1 or 2, comprising the steps of: (I) applying an aqueous composition (1) containing alkali metal silicates and inorganic particles onto a surface of a substrate, and heat-treating the composition at 40°C to 600°C to form a first coating film; and (II) applying an aqueous composition (2A) containing alkali metal silicates onto the surface of the first coating film to form an uncured coating film, applying an aqueous composition (2B) containing an acidic curing agent to the uncured coating film, and heat-treating the composition at 40°C to 600°C to form a second coating film.

11. A method for producing a heat-resistant coated article according to claim 10, wherein the content of the alkali metal silicates is 10% by mass to 80% by mass, relative to 100% by mass of the total solids content in the aqueous composition (1).

12. The method for producing a heat-resistant coated article according to claim 10, wherein the aqueous composition (1) is substantially free of an acidic curing agent.

13. The method for producing a heat-resistant coated article according to claim 10, wherein the acid dissociation constant of the acidic curing agent in the aqueous composition (2B) in water at 25° C. is −5 to 4.

14. A method for producing a heat-resistant coated article according to claim 10, wherein the content of the acidic curing agent in the aqueous composition (2B) is 0.01 mol / L or more.

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