Thermosetting coating composition, substrate with cured coating film, and method for producing same

Abstract

To provide a thermosetting coating composition that can form a cured coating layer with excellent transparency, substrate adhesion, long-term hydrophilicity, and long-term condensation resistance.SOLUTION: A thermosetting coating composition includes (A) amino resin and (B) colloidal silicas. The content of (A) amino resin is 45 pts.mass or more and 100 pts.mass or less relative to 100 pts.mass of the solid content of the resin component. The content of the (B) colloidal silicas is 150 pts.mass or more relative to 100 pts.mass of the solid content of the resin component.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a thermosetting coating composition. The present invention also relates to a cured coating film formed from the thermosetting coating composition, a substrate with the cured coating film, and a method for producing the substrate with the cured coating film. [Background technology]

[0002] Conventionally, hydrophilicity has been imparted to cured coating films of industrial products. For example, in the case of industrial products such as automobile parts and wet-related products such as bathrooms and kitchens, hydrophilicity must be maintained for a long period of time, approximately 3 to 10 years. Common methods for imparting hydrophilicity to cured coating films of industrial products include blending a surfactant into the curable composition or blending a compound having an organic hydrophilic group, such as polyethylene glycol. However, when blending a non-reactive surfactant to impart hydrophilicity, there is a problem in that the non-reactive surfactant is washed away when the cured coating film is washed with water, making it impossible to maintain hydrophilicity. Furthermore, when blending a polyethylene glycol or the like to impart hydrophilicity, there is a problem in that hydrophilicity cannot be maintained once the water absorption capacity of the polyethylene glycol or the like reaches its upper limit. In other words, conventional methods have made it difficult to maintain hydrophilicity in industrial products for a long period of time.

[0003] To improve hydrophilicity, it has been proposed to form a cured coating film using an active energy ray-curable organic-inorganic hybrid resin composition containing (A) silica fine particles with a chain structure, (B) an organic compound having a (meth)acryloyl group or a (meth)acrylamide group, and (C) a photopolymerization initiator (see Patent Document 1). Also, to improve hydrophilicity, a hydrophilic coating agent has been proposed that contains (A) colloidal silica sol, (B) an acrylic polymer having an active hydrogen and a weight-average molecular weight (Mw) of 5,000 to 200,000, (C) a reactive silane coupling agent, and (D) a curing agent for the acrylic polymer (B), with the contents of components (A) to (C) adjusted (see Patent Document 2). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2004-083846 [Patent Document 2] International Publication No. 2009 / 044912 Summary of the Invention [Problem to be solved by the invention]

[0005] The present inventors have found that even when the active energy ray-curable organic-inorganic hybrid resin composition described in Patent Document 1 is used, silica fine particles leak out of the cured coating film after a long period of time, making it difficult to maintain hydrophilicity for a long period of time. Furthermore, the active energy ray-curable organic-inorganic hybrid resin composition described in Patent Document 1 has a problem in that it requires UV irradiation equipment because the curing mechanism is an ultraviolet curing system, and it cannot be applied to substrates with complex surface shapes. Furthermore, the present inventors have found that even when the hydrophilic coating agent described in Patent Document 2, whose resin component is composed solely of a polyol resin, is used, it is difficult to maintain hydrophilicity for a long period of time.

[0006] The present invention has been made in view of the above-mentioned background art and problems, and an object of the present invention is to provide a thermosetting coating composition capable of forming a cured coating film that is excellent in transparency, substrate adhesion, long-term hydrophilicity, and long-term condensation resistance. [Means for solving the problem]

[0007] The present inventors have conducted extensive research to solve the above problems and have found that the above problems can be solved by using a thermosetting coating composition containing (A) an amino resin and (B) colloidal silica, with the contents of (A) the amino resin and (B) the colloidal silica adjusted. The present invention was completed based on this finding.

[0008] That is, according to the present invention, the following inventions are provided. [1] A thermosetting coating composition comprising (A) an amino resin and (B) colloidal silica, the content of the (A) amino resin is 45 parts by mass or more and 100 parts by mass or less per 100 parts by mass of the resin component in terms of solid content, A thermosetting coating composition, wherein the content of the (B) colloidal silica is 150 parts by mass or more per 100 parts by mass of the resin component in terms of solid content. [2] The thermosetting coating composition according to [1], wherein the colloidal silica (B) contains chain silica. [3] The thermosetting coating composition according to [1] or [2], wherein the thermosetting coating composition contains, as the resin component, a polyol resin (C) in addition to the amino resin (A). [4] The thermosetting coating composition according to [3], wherein the (C) polyol resin contains a (meth)acrylic polyol. [5] The thermosetting coating composition according to any one of [1] to [4], wherein the amino resin (A) contains a melamine resin. [6] A cured coating film formed from the thermosetting coating composition according to any one of [1] to [5]. [7] A substrate having a cured coating film formed from the thermosetting coating composition according to any one of [1] to [5] on at least a portion of the surface of the substrate. [8] A coating step of coating at least one surface of a substrate with the thermosetting coating composition according to any one of [1] to [5]; a curing step of curing the thermosetting coating composition by heating to form a cured coating film after the coating step; A method for producing a substrate with a cured coating film, comprising: [Effects of the Invention]

[0009] According to the present invention, it is possible to provide a thermosetting coating composition capable of forming a cured coating film that is excellent in transparency, substrate adhesion, long-term hydrophilicity, and long-term condensation resistance. Furthermore, according to the present invention, it is also possible to provide a cured coating film formed from such a thermosetting coating composition, a substrate with the cured coating film, and a method for producing a substrate with the cured coating film. DETAILED DESCRIPTION OF THE INVENTION

[0010] The present invention will now be described in more detail. In this specification, the term "solid content" refers to the components remaining after excluding volatile components such as organic solvents from the thermosetting coating composition, and which constitute the cured coating film when cured.

[0011] <Thermosetting paint composition> The thermosetting coating composition according to the present invention comprises (A) an amino resin and (B) colloidal silica. The thermosetting coating composition may further comprise (C) a polyol resin in addition to the (A) amino resin as a resin component. In the present invention, the thermosetting coating composition comprises (A) an amino resin and (B) colloidal silica, and by adjusting the contents of the (A) amino resin and (B) colloidal silica, it is possible to form a cured coating film that is excellent in transparency, substrate adhesion, long-term hydrophilicity, and long-term condensation resistance.

[0012] The thermosetting coating composition of the present invention can be suitably used as a coating material. Cured coating films formed from such thermosetting coating compositions can be applied to a variety of fields requiring transparency, substrate adhesion, long-term hydrophilicity, and long-term condensation resistance. In particular, the thermosetting coating composition of the present invention does not require UV irradiation equipment for curing, and can therefore be widely used on substrates with complex surface shapes. Examples of such substrates include bathroom and kitchen plumbing products, eyeglasses, goggles, show windows, and complexly shaped headlamps, rear lamps, and face shields. The components constituting the thermosetting coating composition are described in detail below.

[0013] ((A) Amino resin) The (A) amino resin is not particularly limited, but examples thereof include melamine resin, guanamine resin, glycoluril resin, and urea resin. Among these, melamine resin is preferred from the viewpoint of hydrophilicity and curability. The melamine resin may be either a condensation product of a monomer or a polymer of dimer or higher, or a mixture thereof.

[0014] The melamine resin is preferably alkyl-etherified. Examples of lower alcohols that can be used for alkyl-etherification include methyl alcohol, ethyl alcohol, isopropyl alcohol, n-butanol, and isobutanol. Among these, methylated melamine resin, butylated melamine resin, and mixed methyl-butyl etherified melamine resin are particularly preferred.

[0015] Examples of methylated melamine resins include MW-30M, NW-30, NW-22, MS-21, MS-11, NM-24X, MS-001, MX-002, MX-035, MX-042, MX-706, MX-708, MX-730, and MX-750 manufactured by Sanwa Chemical Co., Ltd., and Amidair L-105-60 manufactured by DIC Corporation. Examples of butylated melamine resins include Melan 2220, 22, 221, 282B, 28, 265B-2, 2650LS, 268A, and 803A manufactured by Showa Denko Materials Co., Ltd. Examples of methyl-butyl mixed etherified melamine resins include MX-43, 45, 410, and 417 manufactured by Sanwa Chemical Co., Ltd.

[0016] Among the alkyl etherified melamine resins mentioned above, those containing a methylol group, an imino group, or both a methylol group and an imino group in the molecule as functional groups are particularly preferred from the viewpoint of low-temperature curing properties when the substrate to be coated is a plastic substrate. These may be used alone or in combination of two or more.

[0017] The weight-average degree of polymerization of the melamine resin is not particularly limited, but is preferably 1.5 to 10.0, more preferably 2.0 to 9.0. If the weight-average degree of polymerization of the melamine resin is within the above range, a coating film with a good balance of hardness and flexibility can be obtained, and defects such as cracks are less likely to occur. The weight-average degree of polymerization can be calculated based on the weight-average molecular weight determined by gel permeation chromatography (GPC) in terms of standard polystyrene.

[0018] The content of (A) amino resin is 45 to 100 parts by mass, preferably 47 to 100 parts by mass, and more preferably 50 to 100 parts by mass, per 100 parts by mass of the resin component in the thermosetting coating composition in terms of solid content. When the content of amino resin is within the above range, the main reaction mechanism is a self-condensation reaction between amino resins, and by taking advantage of the hydrophilicity of the amino resin itself, a cured coating film with excellent hydrophilicity for a long period of time can be obtained.

[0019] ((B) Colloidal Silica) (B) Colloidal silica is a colloidal solution of silicon dioxide (silica, SiO2) or its hydrate. Depending on the properties of the dispersion medium (solvent), colloidal solutions can be divided into aqueous colloidal silica and organic solvent-based organosilica sols, and either can be used. The colloidal silica is preferably in a dispersed state. The dispersed state refers to a state in which silica is suspended as fine particles in a medium (e.g., water) due to electrostatic repulsion between silica particles with positively or negatively charged surfaces. Dispersed colloidal silica is preferred because it can form a coating film with higher transparency.

[0020] Examples of organic solvents used as dispersion media for colloidal silica include methanol, ethanol, normal propanol, isopropanol, normal butanol, isobutanol, t-butanol, ethylene glycol, propylene glycol, trimethylene glycol, butanediol, ethylene glycol monopropyl ether, propylene glycol monomethyl ether, methyl ethyl ketone, and methyl isobutyl ketone.

[0021] It is preferable to use chain silica as the silica forming the colloidal silica. Chain silica is silica in which silica particles are bonded in a chain to form an elongated shape, and more preferably silica in which silica particles are bonded in a chain to form an elongated shape extending only in one plane. In addition to the basic structure described above, the chain silica may partially have at least one microstructure selected from the group consisting of a branched structure, a cyclic structure, a crosslinked structure, a spherical structure, a rod-like structure, a flat structure, and a scale-like structure. By incorporating chain silica, the surface area of ​​the silica is improved, thereby increasing the number of silanol groups exposed on the surface of the cured coating film, and the formation of fine irregularities on the surface of the cured coating film makes the structural hydrophilic effect more pronounced. Therefore, the use of chain silica can achieve greater hydrophilicity than the use of spherical silica.

[0022] It is preferable that the chain silica is not subjected to a hydrophobic treatment so that it can easily maintain its hydrophilicity for a long period of time. On the other hand, to further improve the hydrophilicity of the chain silica, a hydrophilic treatment may be performed to introduce hydrophilic groups onto the surface. The hydrophilic treatment method is not particularly limited, and can be performed by a conventionally known method. Examples of hydrophilic groups to be introduced include hydroxyl groups, alkali metal salts thereof, silanol groups, alkali metal salts thereof, carboxylic acid groups, alkali metal salts thereof, sulfonic acid groups, alkali metal salts thereof, phosphate groups, alkali metal salts thereof, polyalkylene oxide groups, their adducts and inclusion complexes with alkali metal compounds, quaternary ammonium bases, and quaternary phosphonium bases. Among these, polyalkylene oxide groups and silicate groups having a high concentration of hydroxyl groups or silanol groups are particularly preferred, and these hydrophilic groups are preferably introduced by chemically bonding them to the silica surface via an appropriate functional group. From the perspective of long-term hydrophilicity, surface-untreated silica having a high concentration of silanol groups is particularly preferred.

[0023] The average primary particle size of the silica particles is preferably 1 nm to 300 nm, more preferably 3 to 100 nm, and even more preferably 5 to 50 nm. As long as the average primary particle size of the silica particles is within the above range, the shape of each individual silica particle unit may be spherical or rod-like. The chain structure of the silica is preferably formed by bonding 3 to 20 silica particle units, more preferably 4 to 10 silica particle units. The average length of the chain structure of the silica is preferably 10 nm to 500 nm, more preferably 30 to 300 nm, and even more preferably 40 to 200 nm. The average primary particle size of the silica can be measured by the BET method, dynamic light scattering, electron microscope observation, etc. If the average primary particle size of the silica particles and the average length of the chain structure are within the above ranges, long-term hydrophilicity can be further improved.

[0024] Commercially available chain silica products can also be used, such as those manufactured by Nissan Chemical Industries, Ltd. under the trade names MA-ST-UP, IPA-ST-UP, PGM-ST-UP, and MEK-ST-UP. Similarly, commercially available spherical silica products can be used, such as those manufactured by Nissan Chemical Industries, Ltd. under the trade names MA-ST, EG-ST, IPA-ST, PGM-ST, and MEK-ST.

[0025] The content of (B) colloidal silica is 150 parts by mass or more, preferably 150 parts by mass or more and 1000 parts by mass or less, more preferably 170 parts by mass or more and 700 parts by mass or less, more preferably 190 parts by mass or more and 600 parts by mass or less, and even more preferably 200 parts by mass or more and 500 parts by mass or less, per 100 parts by mass of the resin component solid content in the thermosetting coating composition. If the content of colloidal silica is within the above range, a cured coating film having excellent long-term condensation resistance can be obtained.

[0026] ((C) Polyol resin) The polyol resin (C) is not particularly limited, but examples thereof include (meth)acrylic polyol, polyester polyol, polyether polyol, polycarbonate polyol, etc. Among these, it is preferable to use (meth)acrylic polyol. These may be used alone or in combination of two or more.

[0027] The (meth)acrylic polyol is not particularly limited, and for example, a polymer of a (meth)acrylic compound containing a (meth)acrylic compound having a hydroxyl group can be used. As the (meth)acrylic compound having a hydroxyl group, for example, 2-hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, hydroxybutyl (meth)acrylate, etc. can be used. These compounds may be used alone or in combination of two or more. Among these, it is preferable to use 2-hydroxyethyl (meth)acrylate.

[0028] Examples of other compounds copolymerizable with a (meth)acrylic compound having a hydroxyl group include unsaturated carboxylic acid compounds such as (meth)acrylic acid, maleic acid, and fumaric acid; methyl (meth)acrylate, ethyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, tert-butyl (meth)acrylate, neopentyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, octyl (meth)acrylate, stearyl (meth)acrylate, and isostearyl (Meth)acrylic acid alkyl esters such as (meth)acrylate, cetyl (meth)acrylate, and lauryl (meth)acrylate; (meth)acrylic compounds having a fluorine atom such as 2,2,2-trifluoroethyl (meth)acrylate, 2,2,3,3-tetrafluoropropyl (meth)acrylate, 1H,1H,5H-octafluoropentyl (meth)acrylate, and 2-(perfluorooctyl)ethyl (meth)acrylate; isobornyl (meth)acrylate, cyclohexyl (meth)acrylate (Meth)acrylic compounds having an alicyclic structure such as cyclopentanyl (meth)acrylate, dicyclopentenyloxyethyl (meth)acrylate; (meth)acrylic compounds having an ether group such as polyethylene glycol mono(meth)acrylate, methoxyethyl (meth)acrylate, methoxybutyl (meth)acrylate, methoxytriethylene glycol (meth)acrylate, and methoxypolyethylene glycol (meth)acrylate; benzyl (meth)acrylate, 2-ethyl-2-methyl-[1,3]-dioxolan-4-yl-methyl (meth)acrylate, and dimethylaminoethyl (meth)acrylate; unsaturated carboxylic acid ester compounds such as diethyl maleate and diethyl phthalate; vinyl compounds such as styrene, α-methylstyrene, vinyl acetate, vinyl benzoate, vinyltoluene, acrylonitrile, vinylpyridine, vinylpyrrolidone, and vinyl chloride; and acrylamide compounds such as N,N-dimethyl (meth)acrylamide and N,N-diethyl (meth)acrylamide. These compounds may be used alone or in combination of two or more.Among these, it is preferable to use (meth)acrylic acid, methyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, tert-butyl (meth)acrylate, and methoxyethyl (meth)acrylate.

[0029] The weight average molecular weight (Mw) of the (meth)acrylic polyol is 500 to 100,000, more preferably 1,000 to 50,000, and even more preferably 2,000 to 20,000. The weight average molecular weight (Mw) can be measured using gel permeation chromatography (GPC).

[0030] The polyester polyol is not particularly limited, but may be obtained by a known method, such as by polycondensation of a diol with a dicarboxylic acid or a dicarboxylic acid chloride, or by esterifying a diol or a dicarboxylic acid and then subjecting it to an ester exchange reaction. The diol used in the synthesis of the polyester polyol is not particularly limited, but examples thereof include ethylene glycol, propylene glycol, 1,4-butanediol, 1,6-hexanediol, diethylene glycol, dipropylene glycol, triethylene glycol, tripropylene glycol, tetraethylene glycol, and tetrapropylene glycol. The dicarboxylic acid used in the synthesis of the polyester polyol is not particularly limited, but examples thereof include adipic acid, succinic acid, glutaric acid, pimelic acid, sebacic acid, azelaic acid, dimaleic acid, terephthalic acid, isophthalic acid, and phthalic acid.

[0031] The polyether polyol is not particularly limited, but examples thereof include polyethylene oxide, polypropylene oxide, and ethylene oxide-propylene oxide random copolymers.

[0032] The polycarbonate polyol is not particularly limited, but examples thereof include reaction products obtained by polycondensation of the following components A and B. Component A is not particularly limited, but examples thereof include diols such as 1,4-butanediol, 1,6-hexanediol, neopentyl glycol, 1,8-octanediol, 1,9-nonanediol, 1,4-cyclohexanedimethanol, 2-methylpropanediol, dipropylene glycol, and diethylene glycol, as well as reaction products of these diols with dicarboxylic acids such as oxalic acid, malonic acid, succinic acid, adipic acid, azelaic acid, and hexahydrophthalic acid. Component B is not particularly limited, but examples thereof include aromatic carbonates or aliphatic carbonates such as diphenyl carbonate, bis(chlorophenyl) carbonate, dinaphthyl carbonate, phenyltoluyl carbonate, phenylchlorophenyl carbonate, 2-tolyl-4-tolyl carbonate, dimethyl carbonate, diethyl carbonate, diethylene carbonate, and ethylene carbonate.

[0033] The content of (C) polyol resin is preferably less than 55 parts by mass, and more preferably less than 50 parts by mass, per 100 parts by mass of the resin component in the thermosetting coating composition converted to solids. In the present invention, the content of polyol resin as a resin component is low, which prevents stress relaxation and increases cure shrinkage of the coating film, but by incorporating a large amount of colloidal silica, cure shrinkage can be suppressed.

[0034] (Other ingredients) The thermosetting coating composition of the present invention may contain other components in addition to the above components (A) to (C) as long as the object of the present invention is not impaired. Such other components may include leveling agents, polymerization inhibitors, antistatic agents, antioxidants, non-reactive diluents, matting agents, antifoaming agents, dispersants, anti-settling agents, dispersants, heat stabilizers, adhesion improvers, silane coupling agents, plasticizers, etc., as needed.

[0035] <Method for preparing thermosetting coating composition> The thermosetting coating composition of the present invention can be obtained by mixing and stirring the above-mentioned components using a conventionally known device such as a mixer, disperser, stirrer, etc. Examples of such device include a mixing and dispersion mill, a homodisper, a mortar mixer, a roll, a paint shaker, a homogenizer, etc.

[0036] In the present invention, the thermosetting coating composition can be diluted with a solvent as needed, for example, to adjust the viscosity to a coating composition suitable for use as such. The solvent is not particularly limited as long as it dissolves the resin component of the resin composition. Specific examples include aromatic hydrocarbons (e.g., toluene, xylene, and ethylbenzene), esters or ether esters (e.g., ethyl acetate, butyl acetate, and methoxybutyl acetate), ethers (e.g., diethyl ether, tetrahydrofuran, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, propylene glycol monomethyl ether, and diethylene glycol monoethyl ether), ketones (e.g., acetone, methyl ethyl ketone, methyl isobutyl ketone, di-n-butyl ketone, and cyclohexanone), alcohols (e.g., methanol, ethanol, n- or i-propanol, n-, i-, sec-, or t-butanol, 2-ethylhexyl alcohol, and benzyl alcohol), amides (e.g., dimethylformamide, dimethylacetamide, N-methylpyrrolidone, etc.), sulfoxides (e.g., dimethyl sulfoxide), water, and mixtures of two or more of these solvents.

[0037] (cured coating) A cured coating film is formed from the above-mentioned thermosetting coating composition. The thickness of the cured coating film is not particularly limited, but is generally 1 to 100 μm, preferably 1.5 to 20 μm, and more preferably 2 to 10 μm. From the viewpoints of drying and curing properties, the upper limit is preferably 100 μm, while from the viewpoints of transparency, substrate adhesion, long-term hydrophilicity, and long-term condensation resistance, the lower limit is preferably 1 μm. In the present invention, the film thickness refers to the thickness of the cured coating film when the cross section of the cured coating film is observed with an optical microscope, a scanning electron microscope (SEM), or the like. When forming a coating of such a thickness, the desired thickness may be formed in a single coating, or may be formed in multiple coatings.

[0038] When the cured coating film formed from the above thermosetting coating composition has a thickness of 2 to 4 μm, the haze measured in accordance with JIS K 7136 is preferably 1.0% or less, more preferably 0.9% or less, and even more preferably 0.8% or less. Furthermore, the total light transmittance measured in accordance with JIS K 7361-1 for a cured coating film having a thickness of 2 to 4 μm is preferably 70% or more, more preferably 80% or more, and even more preferably 90% or more. When the haze and total light transmittance are within the above ranges, the transparency is excellent.

[0039] <Substrate with cured coating> The substrate with a cured coating film according to the present invention comprises a cured coating film formed from the above-described thermosetting coating composition on at least a portion of the substrate surface. The substrate is not particularly limited, and various plastic films can be used. Examples of plastic films include films of polyester resin, polycarbonate resin, polystyrene resin, polyolefin resin, polyethersulfone resin, acrylonitrile-styrene copolymer resin, polyamide resin, cellulose resin, polyarylate resin, polymethyl methacrylate resin, and polymethacrylimide resin. The thermosetting coating composition of the present invention is capable of forming a transparent cured coating film with high total light transmittance and low haze, so it is preferable to use a transparent plastic film.

[0040] The thickness of the substrate is not particularly limited, but is usually 10 μm or more and 500 μm or less, and preferably 30 to 400 μm.

[0041] <Method of manufacturing substrate with coating film> The coated substrate according to the present invention comprises a coating step of applying the above-described thermosetting coating composition to at least one surface of the substrate; a curing step of curing the photocurable resin composition by heating to form a cured coating film after the coating step; Each step will be described in detail below.

[0042] (Coating process) The coating step is a step of applying the above-mentioned thermosetting coating composition to one side of a substrate by a conventionally known method. For example, a coating machine such as a bar coater, a gravure coater, a roll coater (such as a natural roll coater or a reverse roll coater), an air knife coater, a spin coater, or a blade coater can be used for coating. Among these, a coating method using a gravure coater is preferred from the viewpoint of workability and productivity.

[0043] The film thickness after curing and drying is preferably within the above range of film thickness of the cured coating film.

[0044] When the resin composition is diluted with a solvent before use, it is preferable to dry it after application. The drying may be carried out simultaneously with the curing step described below.

[0045] (hardening process) The curing step is a step in which the coated surface of the substrate is heated to cure the applied thermosetting coating composition and form a cured coating film. Examples of heating methods include hot air drying (hot air dryer, dryer, etc.). From the viewpoints of coating film smoothness, coating film appearance, and drying speed, the heating temperature is preferably 80 to 150°C, more preferably 90 to 140°C, and even more preferably 100 to 130°C. [Example]

[0046] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples.

[0047] The following materials were used to prepare the thermosetting coating compositions: Amino resin 1 (butylated melamine resin, manufactured by Showa Denko Materials Co., Ltd., product name: Melan 2220) Amino resin 2 (methylated melamine resin, containing methylol and imino groups, weight average degree of polymerization: 5.7, manufactured by Sanwa Chemical Co., Ltd., product name: Nikalac MS-001) Amino resin 3 (methylated melamine resin, containing methylol and imino groups, weight average degree of polymerization: 7.2, manufactured by Sanwa Chemical Co., Ltd., product name: Nikalac MX-002) Amino resin 4 (methylated melamine resin, containing methylol and imino groups, weight average degree of polymerization: 2.7, manufactured by Sanwa Chemical Co., Ltd., product name: Nikalac MX-042) Amino resin 5 (methyl-butyl mixed etherified melamine resin, containing methylol and imino groups, weight average degree of polymerization: 1.8, manufactured by Sanwa Chemical Co., Ltd., product name: Nikalac MX-410) Amino resin 6 (methylated melamine resin, containing methylol and imino groups, weight-average degree of polymerization: 2.6, manufactured by Sanwa Chemical Co., Ltd., product name: Nikalac MX-706) Amino resin 7 (methylated melamine resin, containing imino groups, weight average degree of polymerization: 3.0, manufactured by Sanwa Chemical Co., Ltd., product name: Nikalac MX-708) Amino resin 8 (methylated melamine resin, containing imino groups, weight average degree of polymerization: 2.4, manufactured by Sanwa Chemical Co., Ltd., product name: Nikalac MX-730) Colloidal silica 1 (organosilica sol, spherical silica, average particle size 12 nm, manufactured by Nissan Chemical Industries, Ltd., product name: PGM-ST) Colloidal silica 2 (organosilica sol, chain silica, average particle size 12 nm, manufactured by Nissan Chemical Industries, Ltd., product name: PGM-ST-UP)

[0048] (Synthesis of polyol resin 1) 158 parts by mass of propylene glycol 1-monomethyl ether (PGM) was placed in a four-neck flask equipped with a stirrer, reflux condenser, and thermometer, and the temperature was raised to 115°C. Next, 50 parts by mass of 2-hydroxyethyl methacrylate (2-HEMA), 50 parts by mass of methoxyethyl methacrylate (MEMA), and 5 parts by mass of t-butylperoxy 2-ethylhexanoate were added dropwise to the flask over one hour. The mixture was then allowed to react for four hours while maintaining the temperature in the flask at 115°C, yielding polyol resin 1 ((meth)acrylic polyol, Mw: 6400).

[0049] (Synthesis of polyol resin 2) Polyol resin 2 (acrylic polyol, Mw: 6600) was obtained in the same manner as in the synthesis of polyol resin 1, except that 30 parts by weight of 2-HEMA and 70 parts by weight of MEMA were used.

[0050] [Examples 1 to 16, Comparative Examples 1 and 2] [Preparation of Thermosetting Coating Composition] According to the formulations set forth in Tables 1 and 2, the components were stirred and mixed to prepare thermosetting coating compositions.

[0051] [Production of substrate with cured coating] The thermosetting coating composition prepared above was applied once to a PET film (thickness: 100 μm, manufactured by Toyobo Co., Ltd., product name: Cosmoshine A4300) using a wire bar coater so that the dry film thickness was approximately 3 μm. The coating was then cured by leaving it to stand for 10 minutes in a hot air dryer set at 110°C to form a cured coating film, and a substrate with a cured coating film was produced.

[0052] [Evaluation of substrate with cured coating] (Coating appearance) The appearance of the substrates with the cured coating film produced above was visually evaluated according to the following criteria. The measurement results are shown in Tables 3 and 4. [Evaluation criteria] ◯: The coating film has no defects in appearance (whitening, bumps, cracks, and other appearance defects) and is colorless and transparent. ×: Defects in the appearance of the coating film.

[0053] (Optical properties) For the substrates with the cured coating film produced above, the haze (HZ) was measured in accordance with JIS K 7136 using a haze meter (manufactured by Nippon Denshoku Industries Co., Ltd., model number: NDH4000), and the total light transmittance (TT) was measured in accordance with JIS K 7361-1. The measurement results are shown in Tables 3 and 4. A haze value of 1% or less was deemed to be acceptable. On the other hand, a haze value of more than 1% was deemed to be unacceptable. A total light transmittance of 90% or more was deemed to be acceptable. On the other hand, a total light transmittance of less than 90% was deemed to be unacceptable.

[0054] (Adhesion to substrate) According to the cross-cut adhesion test method described in JIS K 5600-5-6, 100 squares (10 squares x 10 squares), 1 mm wide, were cut with a cutter into the cured coating film of the substrate with the cured coating film produced above to prepare a test specimen with a cross-cut pattern. Next, Cellotape (registered trademark) (trade name, manufactured by Nichiban Co., Ltd.) was attached to the test specimen. The Cellotape (registered trademark) was then quickly pulled upward at a 45-degree angle relative to the cross-cut pattern to remove it. The number of remaining cross-cut coatings was counted, and this number was used as an index of substrate adhesion and evaluated according to the following criteria. The measurement results are shown in Tables 3 and 4. [Evaluation criteria] ○: No peeling at all (100 / 100 coatings) △: Slight peeling occurred (number of coatings: 90 or more but less than 100 / 100) ×: Peeling was frequent (less than 90 coatings / 100).

[0055] (Hydrophilicity: initial) For the substrates with cured coating films produced as described above, 1 μL of water was dropped onto the surface of the cured coating film, and the contact angle after 10 seconds was measured using a contact angle meter (manufactured by Kyowa Interface Science Co., Ltd., model number: DM-500). The hydrophilicity of the cured coating film was evaluated according to the following criteria. The measurement results are shown in Tables 3 and 4. [Evaluation criteria] ⊚: The contact angle was 30° or less, and the hydrophilicity was very good. ◯: The contact angle was more than 30° and not more than 40°, and the hydrophilicity was good. ×: The contact angle was more than 40°, and the hydrophilicity was poor.

[0056] (Hydrophilicity: after hot water test) The substrates with the cured coating film prepared above were immersed in hot water at 60°C for 24 hours to conduct a hot water test. Subsequently, 1 μL of water was dropped onto the cured coating surface after the hot water test, and the contact angle was measured 10 seconds later in the same manner as above to evaluate hydrophilicity. The measurement results are shown in Tables 3 and 4.

[0057] (Hydrophilicity: after constant temperature and humidity test) The substrates with the cured coating film prepared above were placed in a thermo-hygrostat set at 85°C and 85% RT for 250 and 500 hours to conduct a constant temperature and humidity test. After each time period, 1 μL of water was dropped onto the cured coating surface, and the contact angle was measured 10 seconds later in the same manner as above to evaluate hydrophilicity. The measurement results are shown in Tables 3 and 4.

[0058] (Condensation resistance: initial) For the substrates with cured coating films produced as described above, water was sprayed onto the surface of the cured coating film using a spray bottle, and it was visually confirmed whether the water droplets spread across the coating film. The condensation resistance of the cured coating film was evaluated according to the following criteria. A rating of "○" or "△" was considered acceptable, and a rating of "×" was considered unacceptable. The evaluation results are shown in Tables 3 and 4. [Evaluation criteria] ○: The water droplet completely wetted and spread over the coating film. △: A few water droplets were generated on the coating film. ×: Water droplets appeared on the coating film.

[0059] (Condensation resistance: repeated) For the substrates with cured coating films produced above, water was sprayed onto the surface of the cured coating film 10 times in the same manner as in the initial evaluation of condensation resistance described above. Then, water was sprayed onto the surface of the cured coating film again with a spray bottle, and visual inspection was performed to determine whether the water droplets spread across the coating film. Condensation resistance was evaluated in the same manner as described above. The evaluation results are shown in Tables 3 and 4.

[0060] (Condensation resistance: after hot water test) The substrates with the cured coating film prepared as described above were subjected to a hot water test in the same manner as described above. Subsequently, water was sprayed onto the surface of the cured coating film after the hot water test using a spray bottle, and it was visually confirmed whether the water droplets spread across the coating film. Condensation resistance was evaluated in the same manner as described above. The evaluation results are shown in Tables 3 and 4.

[0061] (Condensation resistance: after constant temperature and humidity testing) The substrates with the cured coating film prepared above were subjected to a constant temperature and humidity test in the same manner as described above. Subsequently, water was sprayed onto the surface of the cured coating film after the constant temperature and humidity test using a spray bottle, and it was visually confirmed whether the water droplets spread across the coating film. Condensation resistance was evaluated in the same manner as described above. The evaluation results are shown in Tables 3 and 4.

[0062] [Table 1]

[0063] [Table 2]

[0064] [Table 3]

[0065] [Table 4]

Claims

1. A thermosetting coating composition comprising (A) an amino resin, (B) colloidal silica, and (C) a polyol resin, the content of the amino resin (A) is 45 parts by mass or more and 100 parts by mass or less per 100 parts by mass of the resin component in terms of solid content, the content of the (B) colloidal silica is 150 parts by mass or more per 100 parts by mass of the resin component in terms of solid content, A thermosetting coating composition, wherein the (C) polyol resin contains a (meth)acrylic polyol.

2. 2. The thermosetting coating composition according to claim 1, wherein the colloidal silica (B) comprises chain silica.

3. 3. The thermosetting coating composition according to claim 1, wherein the amino resin (A) comprises a melamine resin.

4. A cured coating film formed from the thermosetting coating composition according to any one of claims 1 to 3.

5. A substrate having a cured coating film formed from the thermosetting coating composition according to any one of claims 1 to 3 on at least a portion of the surface of the substrate.

6. A coating step of coating the thermosetting coating composition according to any one of claims 1 to 3 on at least one surface of a substrate; a curing step of curing the thermosetting coating composition by heating to form a cured coating film after the coating step; A method for producing a substrate with a cured coating film, comprising:

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