Coating composition, coating film, and method for producing same

Abstract

Provided is a coating composition with which a coating film having excellent insulation properties can be formed.　This coating composition contains an alkali metal silicate and fibrous inorganic particles, the alkali metal silicate is constituted by a mixture of lithium silicate, potassium silicate, and sodium silicate, and the molar ratio (lithium silicate / (potassium silicate + sodium silicate)) of the molar amount of the lithium silicate to the total molar amount of the potassium silicate and the sodium silicate is 0.05-5.

Description

Paint composition, paint film, and method for manufacturing the same

[0001] The present invention relates to a paint composition, a coating film formed by the paint composition, and a method for manufacturing the coating film.

[0002] Metal components are widely used in various fields such as automobiles and electrical equipment. Among these metal components, when dissimilar metal components with different ionization tendencies come into contact in environments with water or humidity, the metal component that easily conducts leakage current is prone to corrosion. To prevent such corrosion (electrolytic corrosion), an insulating coating is sometimes applied to the surface of the metal component.

[0003] For example, Patent Document 1 discloses a paint composition containing a bisphenol A type epoxy resin modified with methoxysilane. Patent Document 1 states that if such a paint composition is applied to the surface of a light metal alloy, an insulating and corrosion-preventive coating film can be formed.

[0004] Furthermore, in recent years, methods for forming coating films using inorganic paints mainly composed of water-soluble alkali metal silicates, known as water glass, have been investigated. For example, Patent Document 2 discloses an inorganic composition mainly composed of water-soluble alkali metal silicates as a coating composition that can form a coating film with excellent heat resistance.

[0005] Japanese Patent Publication No. 2011-195751 Japanese Patent Publication No. 2004-002813

[0006] However, coatings formed by organic coating compositions such as those in Patent Document 1 may not have sufficient heat resistance and are unsuitable for use at high temperatures. On the other hand, coatings formed by inorganic coating compositions such as those in Patent Document 2 have excellent heat resistance and are also environmentally friendly because they do not use organic solvents. However, when coatings formed by coating compositions containing alkali metal silicates, as in Patent Document 2, are applied to the surface of metal components that are particularly prone to leakage current, sufficient insulation may not be obtained.

[0007] The present invention has been made in view of the above circumstances, and aims to provide a coating composition that can form a coating film with excellent insulating properties, a coating film formed by the coating composition, and a method for manufacturing the coating film.

[0008] The present invention provides the following paint composition, a coating film formed by the paint composition, and a method for manufacturing the coating film.

[0009] Item 1 A paint composition comprising an alkali metal silicate and fibrous inorganic particles, wherein the alkali metal silicate is composed of a mixture of lithium silicate, potassium silicate, and sodium silicate, and the molar ratio of the molar amount of lithium silicate to the total molar amount of potassium silicate and sodium silicate (lithium silicate / (potassium silicate + sodium silicate)) is 0.05 to 5.

[0010] Item 2 The paint composition according to Item 1, wherein the content of the alkali metal silicate is 10% to 95% by mass of the total solid content of the paint composition by 100% by mass.

[0011] Item 3 The coating composition according to item 1 or 2, wherein the fibrous inorganic particles are one or more selected from the group consisting of potassium titanate fibers, wollastonite fibers, and titanium oxide fibers.

[0012] Item 4 The paint composition according to any one of items 1 to 3, wherein the content of the fibrous inorganic particles is 5% by mass to 90% by mass of 100% by mass of the total solid content of the paint composition.

[0013] Item 5 The paint composition according to any one of items 1 to 4, wherein the average fiber length of the fibrous inorganic particles is 3 μm to 20 μm, and the average aspect ratio of the fibrous inorganic particles is 10 to 100.

[0014] Item 6 A paint composition according to any one of items 1 to 5, which is substantially free of a hardening agent.

[0015] Item 7 A coating composition according to any one of items 1 to 6, which is substantially free of conductive particles.

[0016] Item 8 A coating film provided on the surface of a substrate, comprising a cured product of a coating composition described in any one of items 1 to 7.

[0017] Item 9 The coating film according to item 8, wherein the substrate is made of a metal material.

[0018] Item 10 A method for manufacturing a coating film according to item 8 or 9, comprising the steps of: applying the coating composition onto the surface of a substrate; and heat-treating the coating composition applied to the surface of the substrate at 50°C to 200°C to form a coating film.

[0019] According to the present invention, it is possible to provide a coating composition that can form a coating film with excellent insulating properties, a coating film formed by the coating composition, and a method for manufacturing the coating film.

[0020] Figure 1 is a schematic cross-sectional view showing a coating film according to one embodiment of the present invention.

[0021] The following describes an example of a preferred embodiment of the present invention. However, the following embodiments are merely illustrative. The present invention is not limited in any way to the following embodiments.

[0022] In this specification, when "X to Y" (where X and Y are any numbers) is written, it means "greater than or equal to X and less than or equal to Y". Furthermore, when "greater than or equal to X" (where X is any number) is written, it includes the meaning of "X or greater than X", and when "less than or equal to Y" (where Y is any number) is written, it includes the meaning of "Y or less than Y". In addition, when "X and / or Y (where X and Y are any combination)" is written, it means "at least one of X and Y", and can mean "X only", "Y only", or "X and Y".

[0023] In this specification, the term "aqueous system" is used to distinguish it from solvent systems, and refers to systems that use an aqueous medium, preferably water, as the medium. This does not preclude the use of systems that contain some organic solvents in their components.

[0024] <Paint Composition> The paint composition of the present invention comprises alkali metal silicate and fibrous inorganic particles. The paint composition of the present invention is preferably an aqueous composition, and more preferably does not contain organic solvents in its components. The alkali metal silicate is composed of a mixture of lithium silicate, potassium silicate, and sodium silicate. In the paint composition of the present invention, the molar ratio of the molar amount of lithium silicate to the total molar amount of potassium silicate and sodium silicate (lithium silicate / (potassium silicate + sodium silicate)) is 0.05 to 5. In this specification, the molar amounts of lithium silicate, potassium silicate, and sodium silicate refer to the molar amounts of solids excluding water.

[0025] Conventionally, inorganic paint compositions containing alkali metal silicates have excellent heat resistance when formed into a coating film, but when applied to the surface of metal components where leakage currents are likely to flow, they sometimes fail to provide sufficient insulation.

[0026] In response to this, the present inventors focused on the molar ratio of the molar amount of lithium silicate to the total molar amount of potassium silicate and sodium silicate (lithium silicate / (potassium silicate + sodium silicate)) in a coating composition containing alkali metal silicate and fibrous inorganic particles, and found that by setting the above molar ratio to 0.05 to 5, a coating film with excellent insulating properties can be formed.

[0027] Therefore, the coating composition of the present invention makes it possible to form a coating film that has high heat resistance while also having excellent insulating properties. Furthermore, the coating composition of the present invention also makes it possible to achieve high film hardness in the resulting coating film.

[0028] Incidentally, the paint composition of the present invention only needs to have its composition when the paint composition is applied. For example, a solution containing an alkali metal silicate and a solution containing fibrous inorganic particles may be prepared, and the solutions may be mixed with each other during application. Alternatively, a solution containing two types of alkali metal silicates and fibrous inorganic particles and a solution containing one type of alkali metal silicate may be prepared, and the solutions may be mixed with each other during application. Of course, a solution containing an alkali metal silicate and fibrous inorganic particles may be prepared in advance.

[0029] Hereinafter, the details of each component in the paint composition of the present invention will be described.

[0030] Alkali metal silicate; The paint composition of the present invention contains an alkali metal silicate composed of a mixture of lithium silicate, potassium silicate, and sodium silicate. Further, the molar ratio of the molar amount of lithium silicate contained in the paint composition to the total molar amount of potassium silicate and sodium silicate (lithium silicate / (potassium silicate + sodium silicate)) is 0.05 to 5.

[0031] By including all three types of alkali metal silicates, lithium silicate, potassium silicate, and sodium silicate, in the paint composition in the above-mentioned specific molar ratio, the insulation property is improved, the curing reaction is promoted, and a strong paint film can be obtained even at low temperatures.

[0032] Lithium silicate can be represented, for example, by the compositional formula of Li ２ O·nSiO ２ (where n is the molar ratio). The molar ratio n of SiO ２ / Li ２ O in lithium silicate may be any value as long as lithium silicate is water-soluble, preferably 2.5 to 8.5, more preferably 3.0 to 5.0. Incidentally, lithium silicate may be used as an aqueous solution of lithium silicate.

[0033] Potassium silicate can be represented, for example, by the compositional formula of K ２ O·nSiO ２ (where n is the molar ratio). The molar ratio of SiO ２ / K ２The molar ratio n of O may be any value as long as potassium silicate becomes water-soluble, preferably 1.5 to 5.0, more preferably 3.0 to 4.0. Potassium silicate may be used as an aqueous potassium silicate solution.

[0034] Sodium silicate can be represented, for example, by the compositional formula of Na ２ O·nSiO ２ (where n is the molar ratio). In sodium silicate, the molar ratio n of SiO ２ / Na ２ O may be any value as long as sodium silicate becomes water-soluble, preferably 1.5 to 4.5, more preferably 1.5 to 3.0. Sodium silicate may be used as an aqueous sodium silicate solution.

[0035] The molar ratio of the molar amount of lithium silicate contained in the coating composition to the total molar amount of potassium silicate and sodium silicate (lithium silicate / (potassium silicate + sodium silicate)) is 0.05 to 5, preferably 0.08 to 3, more preferably 0.1 to 2, still more preferably 0.2 to 1.5, even more preferably 0.2 to 1.0, and particularly preferably 0.25 to 0.7. By setting the molar ratio (lithium silicate / (potassium silicate + sodium silicate)) within the above range, a coating film with excellent insulation properties can be formed.

[0036] The molar ratio of each alkali metal of sodium silicate, potassium silicate, and lithium silicate contained in the coating composition (Na:K:Li) is preferably 0.1:0.1:1 to 9.5:4.8:1, more preferably 0.3:0.15:1 to 5:3:1, and still more preferably 0.5:0.2:1 to 4.5:2.5:1.

[0037] In the coating composition of the present invention, the content of alkali metal silicate (total content of lithium silicate, potassium silicate, and sodium silicate) is preferably 10% to 95% by mass, more preferably 20% to 90% by mass, still more preferably 40% to 85% by mass, and particularly preferably 60% to 80% by mass in 100% by mass of the total solid content of the coating composition.

[0038] Fibrous inorganic particles; The coating composition of the present invention contains fibrous inorganic particles. By including fibrous inorganic particles in the coating composition, the film-forming properties are improved, the strength of the resulting coating film can be improved, and the thickness of the coating film can be easily maintained.

[0039] Fibrous inorganic particles are defined as particles in which, when the longest side of the smallest rectangular parallelepiped (circumscribed rectangular parallelepiped) circumscribing the particle 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), both L / B and L / T are 5 or greater, with the major axis L corresponding to the fiber length and the minor axis B corresponding to the fiber diameter.

[0040] From the viewpoint of further improving the reinforcing properties of the resulting coating film, the fibrous inorganic particles are preferably solid inorganic particles.

[0041] The true specific gravity of the fibrous inorganic particles is preferably 2.0 g / cm³, from the viewpoint of making the viscosity of the paint composition suitable for application and making sedimentation of the paint composition less likely to occur during storage. ３ The above is preferable, preferably 6.0 g / cm³. ３ More preferably, 4.0 g / cm³ ３ The following applies:

[0042] Examples of fibrous inorganic particles include potassium titanate fibers, wollastonite fibers, titanium oxide fibers, or glass milled fibers. Preferably, the fibrous inorganic particles are potassium titanate fibers, wollastonite fibers, or titanium oxide fibers, and more preferably potassium titanate fibers. One of these may be used alone, or two or more may be used in combination.

[0043] Potassium titanate fibers can be broadly used from those that are conventionally known, such as potassium hexatinate fibers or potassium octatinate fibers.

[0044] The average fiber length of the fibrous inorganic particles is preferably 3 μm to 20 μm, more preferably 4 μm to 15 μm, even more preferably 4.5 μm to 10 μm, and particularly preferably 5 μm to 9 μm. By setting the average fiber length of the fibrous inorganic particles within the above range, the strength of the resulting coating film can be further improved.

[0045] The average fiber diameter of the fibrous inorganic 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.

[0046] The average aspect ratio of the fibrous inorganic particles is preferably 10 or more, more preferably 10 to 100, and even more preferably 15 to 35.

[0047] The average fiber length and average fiber diameter of fibrous inorganic particles can be measured by observation with a scanning electron microscope. For example, multiple fibrous inorganic particles are photographed with a scanning electron microscope, and 300 fibrous inorganic particles are arbitrarily selected from the observed images. Their fiber lengths and fiber diameters are then measured. The average fiber length is calculated by summing the lengths of all the particles and dividing by the number of particles, and the average fiber diameter is calculated by summing the diameters of all the particles and dividing by the number of particles. The average aspect ratio (average fiber length / average fiber diameter) can be calculated from the average fiber length and average fiber diameter measured using the above method.

[0048] The Mohs hardness of the fibrous inorganic particles is preferably 1 to 6, more preferably 2 to 5. When the Mohs hardness of the fibrous inorganic particles is within the above range, the hardness of the coating film is further improved. In addition, fibrous inorganic particles with appropriate hardness improve the toughness of the coating film, making it possible to suppress the occurrence of cracks. Mohs hardness is an index that represents the hardness of a substance; substances that are scratched when minerals are rubbed together have lower hardness.

[0049] In the coating composition of the present invention, the content of fibrous inorganic particles is preferably 5% to 90% by mass, more preferably 10% to 80% by mass, even more preferably 15% to 60% by mass, and particularly preferably 20% to 40% by mass, based on 100% by mass of the total solid content of the coating composition.

[0050] Other Additives; The coating composition of the present invention may contain other additives besides the alkali metal silicate and fibrous inorganic particles described above. Other additives can be appropriately selected and used depending on the purpose. Examples of other additives include non-fibrous inorganic particles, solid lubricants, dispersants, defoamers, wetting agents, colorants, sealing agents, surface modifiers, viscoelastic modifiers, and thickeners.

[0051] Examples of non-fibrous inorganic particles include solid inorganic particles and hollow inorganic particles. Non-fibrous inorganic particles can be appropriately selected and used depending on the purpose.

[0052] Examples of solid inorganic particles that are non-fibrous inorganic 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, calcium carbonate, or molybdenum disulfide. One of these may be used alone, or two or more may be used in combination.

[0053] The average particle size of the solid inorganic particles, which are non-fibrous inorganic particles, is preferably 0.05 μm to 15 μm, more preferably 0.1 μm to 7 μm. When the average particle size of the solid inorganic particles is above the lower limit, they can exhibit an even greater function as aggregate supporting the resulting coating film. Furthermore, when the average particle size of the solid inorganic particles is below the upper limit, the solid inorganic particles can be made less likely to settle in the liquid phase.

[0054] In this specification, unless otherwise specified, the average particle diameter refers to the particle diameter at the point where the cumulative value reaches 50% when the particle size distribution is determined on a volume basis using a laser diffraction method, with the total volume set to 100%, and the number of particles is counted from smallest to largest.

[0055] On the other hand, examples of non-fibrous inorganic particles, such as hollow inorganic particles, include silicon dioxide-based compounds. Here, "silicon dioxide-based compound" means a compound containing 50% by mass or more of silicon dioxide. Furthermore, "hollow" may be composed of porous material or of a single spherical void.

[0056] Examples of hollow inorganic particles made from silicon dioxide-based compounds include volcanic ash balloons, fly ash balloons, silica aerogel, or borosilicate glass balloons. Preferably, the hollow inorganic particles made from silicon dioxide-based compounds are silica aerogel and borosilicate glass balloons. These may be used individually or in combination of two or more.

[0057] The true specific gravity of hollow inorganic particles, which are non-fibrous inorganic particles, is preferably 0.01 g / cm³, from the viewpoint of making the viscosity of the paint composition suitable for application and making sedimentation of the paint composition less likely to occur during storage. ３ The above is a more preferable 0.5 g / cm³. ３ The above is preferable, preferably 1.0 g / cm³. ３ More preferably, 0.8 g / cm³ ３ The following applies:

[0058] The average particle size of the hollow inorganic particles, which are non-fibrous inorganic particles, is preferably 3 μm to 100 μm, more preferably 5 μm to 40 μm, and even more preferably 5 μm to 25 μm. Although it varies depending on the composition and outer shell thickness of the hollow inorganic particles, when the average particle size of the hollow inorganic particles is above the lower limit, the proportion of the internal space volume becomes relatively larger, and the thermal insulation efficiency relying on the hollow structure can be further enhanced. Also, when the average particle size of the hollow inorganic particles is below the upper limit, it can be made less likely to affect the surface smoothness of the resulting coating film.

[0059] The pressure resistance strength of the hollow inorganic particles, which are non-fibrous inorganic particles, is preferably 10 MPa or more, more preferably 20 MPa or more. When the pressure resistance strength of the hollow inorganic particles is equal to or greater than the lower limit mentioned above, a coating film with higher surface strength can be formed. The upper limit of the pressure resistance strength of the hollow inorganic particles, which are non-fibrous inorganic particles, is not particularly limited. The upper limit of the pressure resistance strength of the hollow inorganic particles, which are non-fibrous inorganic particles, is usually around 180 MPa.

[0060] In the coating composition of the present invention, the content of non-fibrous inorganic particles is preferably 0% to 85% by mass, more preferably 0% to 70% by mass, even more preferably 0% to 45% by mass, and particularly preferably 0% to 20% by mass, based on 100% by mass of the total solid content of the coating composition.

[0061] In the paint composition of the present invention, the total content of fibrous inorganic particles and non-fibrous inorganic particles is preferably 5% to 95% by mass, more preferably 10% to 80% by mass, even more preferably 15% to 60% by mass, and particularly preferably 20% to 40% by mass, based on 100% by mass of the total solid content of the paint composition.

[0062] The paint composition of the present invention may contain an appropriate amount of water, a thickener, etc., from the viewpoint of adjusting the viscosity during film formation.

[0063] Examples of thickening agents include inorganic thickening agents such as montmorillonite, synthetic hectorite, and smectite; polyacrylic acid-based thickening agents; urethane-based thickening agents; polyether-based thickening agents; cellulose-based thickening agents such as methylcellulose and carboxymethylcellulose; and organic thickening agents such as gum arabic. One of these may be used alone, or two or more may be used in combination.

[0064] In the paint composition of the present invention, the content of other additives is not particularly limited as long as it does not hinder the effects of the present invention, but is preferably 50% by mass or less, more preferably 30% by mass or less, and even more preferably 10% by mass or less, of 100% by mass of the paint composition.

[0065] Furthermore, it is preferable that the paint composition of the present invention substantially does not contain conductive particles. Conductive particles refer to particles that have conductivity, and specifically, particles with an conductivity of 1.0 × 10⁻⁶ ２ This refers to a conductivity of S / cm or higher. In this case, a coating with superior insulating properties can be obtained. Specific examples of conductive particles include, for example, iron powder, silver powder, gold powder, and nickel powder. "Substantially free of conductive particles" means that conductive particles are not intentionally incorporated into the paint composition, and that the paint composition does not contain conductive particles except in cases where conductive particles are mixed in as trace impurities. In particular, the content of conductive particles per 100% by mass of the total amount of the paint composition is preferably less than 1% by mass, and more preferably less than 0.5% by mass. Among these, it is even more preferable that the paint composition contains no conductive particles at all.

[0066] Furthermore, the paint composition of the present invention does not necessarily have to contain substantially no magnetic powder. Specific examples of magnetic powder include, for example, iron powder, iron-silicon alloy powder, iron-nickel alloy powder, and iron oxide. "Substantially free of magnetic powder" means that magnetic powder is not intentionally incorporated into the paint composition, and that the paint composition does not contain magnetic powder except in cases where trace amounts of magnetic powder are mixed in as impurities. In particular, the content of magnetic powder relative to 100% by mass of the total amount of the paint composition is preferably less than 1% by mass, and more preferably less than 0.5% by mass. Even more preferably, the paint composition contains no magnetic powder at all. However, the paint composition of the present invention may contain magnetic powder depending on its use and purpose, and is not particularly limited.

[0067] (Method for producing the paint composition) The paint composition of the present invention can be produced by mixing lithium silicate, potassium silicate, sodium silicate, fibrous inorganic particles, and other additives as described above, in an appropriate amount of a medium such as an aqueous medium.

[0068] The order in which the materials are mixed is not particularly limited. For example, lithium silicate, potassium silicate, and sodium silicate may be mixed first, and then fibrous inorganic particles and other additives may be added to the mixture and mixed. Alternatively, lithium silicate, potassium silicate, sodium silicate, fibrous inorganic particles, and other additives may be mixed simultaneously.

[0069] The mixing method and conditions for each material are not particularly limited and should be any method and conditions that allow for sufficient dispersion of fibrous inorganic particles in the composition. For example, mixing can be done using a disperser, roll mill, homomixer, bead mill, etc., under room temperature (25°C).

[0070] <Coating Film> The coating film of the present invention is a coating film provided on the surface of a substrate and having insulating properties. Furthermore, the coating film of the present invention is composed of a cured product of the above-described coating composition.

[0071] Since the coating film of the present invention is composed of a cured product of the above-described coating composition, it has high heat resistance and excellent insulating properties. Therefore, by applying such a coating film to the surface of a substrate, a coated product with excellent heat resistance and insulating properties can be obtained.

[0072] The coating film of the present invention only needs to be applied to at least a portion of the surface of the substrate. For example, as shown in Figure 1, if the substrate 2 has opposing first main surface 2a and second main surface 2b, the coating film 1 may be applied to the entire surface of the first main surface 2a of the substrate 2. Of course, the coating film 1 may be applied to only a portion of the first main surface 2a of the substrate 2.

[0073] Furthermore, although Figure 1 shows the coating 1 applied only to the first main surface 2a of the substrate 2, the coating 1 may also be applied to both the first main surface 2a and the second main surface 2b of the substrate 2. Alternatively, the coating 1 may be applied to the entire surface of the substrate 2.

[0074] The coating film of the present invention may be placed in an appropriate position depending on the intended application. Although other films may be provided between the substrate and the coating film, it is preferable that the coating film be directly applied to the surface of the substrate in order to further improve the adhesion between the substrate and the coating film.

[0075] (Substrate) The substrate material may be a metallic material such as iron, aluminum, copper, or titanium, or alloys thereof; or a non-metallic material 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 coating film, the substrate material is preferably a metallic material. The substrate may be subjected to known surface treatments. Surface treatments include metal coating treatment or chemical conversion treatment. Metal coating treatments include electroplating, hot-dip plating, or vapor deposition plating. Chemical conversion treatments include chromate treatment or phosphate treatment.

[0076] The shape of the substrate is not particularly limited. The substrate may be, for example, a sheet, a plate, a sphere, a film, a large structure, an assembly with a complex shape, or a molded product.

[0077] The lower limit of the substrate thickness is not particularly limited, for example, 10 μm or more. The upper limit of the substrate thickness is also not particularly limited and can be appropriately selected depending on the intended use and shape of the coated object.

[0078] (Coating Film) The coating film of the present invention is a cured product of a paint composition containing alkali metal silicate and fibrous inorganic particles, and has insulating properties. Furthermore, because lithium silicate is contained in the paint composition that constitutes the coating film, the curing reaction is easily accelerated, and a strong coating film can be formed even at low temperatures.

[0079] Therefore, it is preferable that the coating composition constituting the coating film of the present invention substantially does not contain a curing agent. "Substantially contained no curing agent" means that a curing agent is intentionally not included in the coating composition, and that the coating composition does not contain a curing agent except in cases where a trace amount of curing agent is mixed in as an impurity. In particular, it is preferable that the curing agent content is less than 5% by mass per 100% by mass of the total amount of the coating composition, more preferably less than 0.5% by mass, and even more preferably that the coating composition contains no curing agent at all.

[0080] The thickness of the coating film is not particularly limited, but is preferably 0.5 μm or more, more preferably 1 μm or more, even more preferably 5 μm or more, particularly preferably 10 μm or more, preferably 500 μm or less, more preferably 100 μm or less, even more preferably 50 μm or less, and particularly preferably 30 μm or less. The thickness of the coating film can be appropriately selected depending on the intended use and shape of the coated object.

[0081] The hardness of the coating film is not particularly limited, but the hardness measured according to the scratch hardness (pencil method) of JIS K 5600-5-4 is preferably 3H or higher, more preferably 6H or higher, and even more preferably exceeding 8H. The hardness of the coating film can be appropriately selected depending on the intended use and shape of the coated object.

[0082] The resistance of the coating film of the present invention is, for example, 300 MΩ to 10,000 MΩ under measurement conditions of a temperature of 25°C and an applied voltage of 250 V. In this specification, "having insulating properties" means that the resistance of the coating film measured under the above measurement conditions is 300 MΩ or more.

[0083] <Method for manufacturing a coating film> The method for manufacturing a coating film of the present invention comprises the steps of applying the above-described coating composition onto the surface of a substrate (hereinafter sometimes referred to as the "coating step") and heat-treating the coating composition applied to the surface of the substrate at 50°C to 200°C to form a coating film (hereinafter sometimes referred to as the "heat treatment step").

[0084] (Coating process) Before applying the above-mentioned coating composition to the surface of the substrate, it is preferable to degas the coating composition or pass it through a filter. This is to prevent the formation of pinholes after coating film formation and to prevent the coating film from becoming convex due to the inclusion of foreign matter.

[0085] Furthermore, it is preferable to pre-roughen the surface of the substrate (coated surface) by physical roughening such as grid blasting or chemical roughening such as wet etching. In this case, the coating film can be formed more uniformly on the coated surface of the substrate. It is also preferable that no oil adheres to the coated surface of the substrate. Therefore, it is preferable to degrease and clean the coated surface of the substrate before applying the coating composition to it.

[0086] The method of applying the paint composition is not particularly limited and can be done by well-known methods such as spray coating, spin coating, dipping, or brush application. Among these, spray coating is preferred as the method of applying the paint composition.

[0087] The amount of paint composition applied should be set so that the thickness of the paint film after the heat treatment process is preferably 0.5 μm to 500 μm, more preferably 1 μm to 100 μm, even more preferably 5 μm to 50 μm, and particularly preferably 10 μm to 30 μm. The thickness of the paint film can be appropriately selected depending on the intended use and shape of the object to be painted.

[0088] (Heat Treatment Process) The heat treatment temperature of the paint composition is preferably 50°C to 200°C, more preferably 80°C to 200°C, and even more preferably 80°C to 180°C. Since the paint composition contains lithium silicate, by setting the heat treatment temperature within the above range, the curing reaction is promoted, and a strong coating can be obtained even at low temperatures. However, if the paint composition contains water, and heat treatment is performed as is, the surface may harden first, trapping water in the resulting coating, which can cause so-called "skinning." In this case, voids may form or the interface may peel off as the water in the coating evaporates. Therefore, it is preferable to evaporate (dry) the water in the paint composition before heat treatment.

[0089] The heat treatment time for the paint composition should be set so that the paint composition hardens and forms a coating film. The heat treatment time for the paint composition is not particularly limited, but is preferably 0.5 hours to 10 hours.

[0090] <Applications of the coating film> The applications of the coating film of the present invention are not particularly limited. For example, the coating film of the present invention can be used on vehicle parts such as electric vehicles, aircraft parts, building parts, cooking utensils, etc. In particular, the coating film of the present invention can be suitably used on vehicle parts such as brake rotors, brake calipers, and mufflers. Furthermore, the coating film of the present invention can be suitably used in applications such as parts that require insulating properties (prevention of electrolytic corrosion, prevention of electrical corrosion, prevention of leakage current) and heat resistance, and that require coating at low temperatures.

[0091] Furthermore, because the coating film of the present invention contains lithium silicate in the paint composition that constitutes the coating film, the curing reaction is easily accelerated, resulting in a strong coating film with a dense structure. Therefore, in addition to insulating properties, the coating film of the present invention can also exhibit functions such as corrosion resistance, low staining, prevention of foreign matter adhesion, water resistance, and low water permeability. Thus, the coating film of the present invention can be widely applied to, for example, chemical plant coatings, heat-resistant and fire-resistant coatings, heat-insulating coatings, concrete surface protective coatings, machine parts coatings, underwater structure coatings, exterior coatings, and the like.

[0092] The present invention will be described in more detail below based on specific examples. The present invention is not limited in any way to the following examples and can be implemented with appropriate modifications without changing its essence.

[0093] The alkali metal silicates and fibrous inorganic particles used in the examples and comparative examples are as follows:

[0094] Sodium silicate: Manufactured by Nippon Chemical Industrial Co., Ltd., J Sodium Silicate No. 1, SiO ２ / Na ２ O [molar ratio] = 2.2, solid content 54.5% by mass. Potassium silicate: manufactured by Nippon Chemical Industrial Co., Ltd., 2K potassium silicate, SiO ２ / K ２ O [molar ratio] = 3.6, solid content 29.5% by mass. Lithium silicate: manufactured by Nippon Chemical Industrial Co., Ltd., lithium silicate 35, SiO ２ / Li ２ Molar ratio = 3.5, solid content 25.0% by mass. Fibrous inorganic particles 1:8 potassium titanate fibers, solid particles, average fiber length 8 μm, average fiber diameter 0.5 μm, true specific gravity 3.4 g / cm³. ３Mohs hardness 4. Fibrous inorganic particles 2: Titanium oxide fibers, solid particles, average fiber length 5 μm, average fiber diameter 0.3 μm, true specific gravity 4.2 g / cm³. ３ Mohs hardness 6.5 Alumina: Manufactured by Nippon Light Metal Co., Ltd., AHP300, average particle size 1 μm Silica aerogel: Manufactured by Shanxi Yangzhong New Material, average particle size 15 μm Magnesium potassium titanate: Solid particles, average particle size 0.7 μm

[0095] The average fiber length and average fiber diameter of fibrous inorganic particles were determined from the average values ​​of 300 arbitrary samples measured using a scanning electron microscope (Hitachi High-Technologies Corporation, product name "S-4800").

[0096] <Formation of coating film> (Examples 1-11) An alkali metal silicate aqueous solution was prepared by mixing purified water and alkali metal silicate in the compositions and amounts described in Tables 1 and 2. A coating composition was obtained by mixing fibrous inorganic particles in the amounts described in Tables 1 and 2 while stirring the prepared alkali metal silicate aqueous solution.

[0097] Next, the paint composition was applied to the surface of the substrate (material: stainless steel, thickness: 1 mm) using a spray. Then, the paint composition applied to the substrate was heat-treated at 150°C for 1 hour to form a paint film.

[0098] (Example 12) A coating film was formed in the same manner as in Examples 1 to 11, except that the coating composition applied to the substrate was heat-treated at 200°C for 2 hours to form a coating film.

[0099] (Comparative Examples 1-4) The coating film was formed in the same manner as in Example 1, except that the composition and amount of the coating composition were changed as shown in Table 3 below.

[0100] <Evaluation of coating film> (Film formation ability) The film formation ability of the coating films obtained in the examples and comparative examples was visually evaluated from their appearance on a 6-point scale (0 to 5) as shown in Table 4, and the results are shown in Tables 1 to 3.

[0101] (Film Hardness) The film hardness of the coatings obtained in the examples and comparative examples was measured in accordance with the scratch hardness (pencil method) of JIS K 5600-5-4, and the results are shown in Tables 1 to 3.

[0102] (Insulation) The insulation properties of the coatings obtained in the examples and comparative examples were measured using a resistivity meter (manufactured by Nitto Seiko Analytech Co., Ltd., product name "HighLester UX MCP-HT800") with a URS probe, and the results are shown in Tables 1 to 3. The insulation properties of the coatings were measured under the following conditions: temperature 25°C, relative humidity 60%, and applied voltage 250V.

[0103] (Water Resistance) The coating films obtained in Example 3 and Comparative Example 3 were placed in beakers containing water and left for 24 hours. The film hardness of the coating films after immersion was measured according to the scratch hardness (pencil method) of JIS K 5600-5-4, and the results are shown in Tables 1 and 3. This evaluated the water resistance of the coating films obtained in Example 3 and Comparative Example 3.

[0104]

[0105]

[0106]

[0107]

[0108] As shown in Tables 1 and 2, in Examples 1 to 12, the molar ratio of the molar amount of lithium silicate to the total molar amount of potassium silicate and sodium silicate (lithium silicate / (potassium silicate + sodium silicate)) in the paint composition was 0.05 to 5, and it was confirmed that there were no problems with the film formation of the coating film and that the insulating properties of the coating film were enhanced.

[0109] On the other hand, as shown in Table 3, in Comparative Example 1, the paint composition did not contain lithium silicate, so the insulating properties of the coating film could not be sufficiently improved. Also, in Comparative Examples 2 and 4, the paint composition did not contain fibrous inorganic particles, so the film-forming properties of the coating film were insufficient, and it was not possible to form a coating film with insulating properties.

[0110] Furthermore, in Comparative Example 3, although the paint composition contained lithium silicate, the molar ratio of the molar amount of lithium silicate to the total molar amount of potassium silicate and sodium silicate (lithium silicate / (potassium silicate + sodium silicate)) was outside the range of 0.05 to 5, and therefore it was not possible to form an insulating coating film.

[0111] Furthermore, in the water resistance tests of Example 3 and Comparative Example 3, while there was no change in the hardness of the coating film before and after immersion in water in Example 3, the coating film of Comparative Example 3 swelled after immersion and its hardness decreased. This confirmed that the coating composition also possesses water resistance when the molar ratio of the molar amount of lithium silicate to the total molar amount of potassium silicate and sodium silicate (lithium silicate / (potassium silicate + sodium silicate)) is within the range of 0.05 to 5.

[0112] 1...Coating film 2...Substrate 2a...First main surface 2b...Second main surface

Claims

1. A paint composition comprising an alkali metal silicate and fibrous inorganic particles, wherein the alkali metal silicate is composed of a mixture of lithium silicate, potassium silicate, and sodium silicate, and the molar ratio of the molar amount of lithium silicate to the total molar amount of potassium silicate and sodium silicate (lithium silicate / (potassium silicate + sodium silicate)) is 0.05 to 5.

2. The paint composition according to claim 1, wherein the content of the alkali metal silicate is 10% to 95% by mass of the total solid content of the paint composition.

3. The coating composition according to claim 1 or 2, wherein the fibrous inorganic particles are one or more selected from the group consisting of potassium titanate fibers, wollastonite fibers, and titanium oxide fibers.

4. The paint composition according to claim 1 or 2, wherein the content of the fibrous inorganic particles is 5% by mass to 90% by mass of the total solid content of the paint composition.

5. The paint composition according to claim 1 or 2, wherein the average fiber length of the fibrous inorganic particles is 3 μm to 20 μm, and the average aspect ratio of the fibrous inorganic particles is 10 to 100.

6. The paint composition according to claim 1 or 2, which is substantially free of a curing agent.

7. The coating composition according to claim 1 or 2, which is substantially free of conductive particles.

8. A coating film provided on the surface of a substrate, comprising a cured product of the coating composition described in claim 1 or 2.

9. The coating film according to claim 8, wherein the substrate is made of a metal material.

10. A method for manufacturing a coating film according to claim 8, comprising the steps of: applying the coating composition onto the surface of a substrate; and heat-treating the coating composition applied onto the surface of the substrate at 50°C to 200°C to form a coating film.

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