JP2010077357A - Paint composition - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a composition for paint, causing little staining of a coating film surface by adsorption of dust and oily substances in air in the case of exposing the coating film comprising a water-based paint outdoors, enabling stain prevention especially immediately after forming the coating film, keeping a persistent stain proofing property to resist formation of residual raindrop mark after rain and having good storage stability of the coating liquid. <P>SOLUTION: The paint composition includes (A) an aqueous resin dispersion obtained by polymerizing an α,β-ethylenic unsaturated monomer, (B) a water-soluble resin composition comprising an amphiphilic polymer having at least one functional groups selected from amido, amino and hydroxyl groups as a hydrophilic part and having a hydrophobic part, and (C) a water-dispersed colloidal silica. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a coating composition used for building interior materials, exterior materials and the like. Specifically, the surface of the paint film is made hydrophilic immediately after the paint film is formed to improve water wettability, and the function of washing rainwater into the interface between the paint film and the pollutant to wash out the pollutant can be expressed. It is related with the coating composition which can form the coating film excellent in the property and its effect sustainability.

  Paint is applied to protect the building and improve its appearance. Conventionally, organic solvent dilution type paints have been widely used. However, environmental problems such as the release of organic solvents into the atmosphere such as sick house syndrome and VOC regulations have been raised, and the conversion to water-based paints has accelerated. Progressing. On the other hand, consumer needs are also increasing expectations for the long-term durability and high functionality of these products.

  If non-polar pollutants such as dust and oily substances in the atmosphere and carbon contained in exhaust gas adhere to and accumulate on the coating film of building materials, etc., it accumulates without being washed away by rainwater, and the state of dirt is It becomes uneven and easily noticeable. Usually, in order to prevent this rain streak contamination, a technique is employed in which rainwater is intervened at the interface between the pollutant and the coating surface by increasing the hydrophilicity of the coating surface, and the pollutant is washed away. In solvent-based paints, a technique has been proposed in which alkoxysilane is coordinated on the surface of the coating film and hydrolyzed with time to make the surface of the coating film hydrophilic. The problem with this technology is that the degree of hydrolysis depends on the weather conditions for about one month immediately after the formation of the coating film, so that the hydrolysis is delayed especially when the dry condition continues, and the coating film becomes dirty. Is a point.

  In water-based paints, a method of reducing the water contact angle of a coating film by adding a specific solvent to an aqueous emulsion has been proposed (Patent Document 1), but the effect is not sufficient, and over a long period of time. It was difficult to maintain the effect.

  Patent Document 2 proposes that a specific block copolymer cross-linking agent and dihydrazide compound cross-linking agent may be used together to reduce contamination by forming a cross-linked coating film with a polycarbonyl compound. However, water resistance is not sufficient. It was inferior in sustainability.

  Patent Document 3 proposes a method of overcoating a mixture of an acrylic resin and colloidal silica on a coating film of a colloidal silica aqueous dispersion inorganic coating containing an inorganic filler, but sufficient contamination is not obtained. It was.

  In patent document 4, although the method of hydrophilizing the coating-film surface by cold-blending colloidal silica to an emulsion is proposed, it is required with respect to 30-400 weight part of solid content of an acrylic resin emulsion. The amount of colloidal silica was as large as 100 parts by weight, and the durability of the effect was inferior.

  Patent Document 5 also proposes a method of forming a coating film having excellent decontamination property using fluorine-containing polymer particles, colloidal silica, and organoalkoxysilane, but the solid content of the fluorine-containing polymer particles is 100. A very large amount of colloidal silica of 50 to 300 parts by weight with respect to parts by weight was required.

Patent Document 6 proposes a method of forming an emulsion in which colloidal silica is covered with a vinyl polymer to form a coating film having a high solid content concentration and excellent film formability. Since it was covered with a vinyl polymer, it was inferior in the ability to prevent contamination.
Japanese Patent Laid-Open No. 10-46099 Japanese Patent Laid-Open No. 10-298489 JP 54-139938 A Japanese Patent Application Laid-Open No. 11-116885 Japanese Patent Laid-Open No. 11-124534 JP 2000-290464 A

  The object of the present invention is to solve the above-mentioned problems, and when exposed to the outdoors in a paint film composed of a water-based paint, there is little contamination of the paint film surface due to adsorption of dust and oily substances in the atmosphere, In particular, it is possible to provide a coating composition that can prevent contamination immediately after the formation of a coating film, has no trace of rain traces after rain, has good stain resistance over a long period of time, and has good storage stability of the coating liquid. .

According to the present invention, (A) an aqueous resin dispersion obtained by polymerizing an α, β-ethylenically unsaturated monomer and (B) at least one functional group selected from an amide group, an amino group, and a hydroxyl group are hydrophilic. A coating composition comprising a water-soluble resin composition comprising an amphiphilic polymer having a hydrophobic part and a water-dispersed colloidal silica is provided.

  As described above, according to the present invention, by using a water-based paint, it is possible to provide a low-fouling paint composition capable of forming a coating film having good stain resistance and excellent water resistance over a long period of time. became.

  Hereinafter, embodiments of the present invention will be described in detail.

  As a result of various researches to achieve the above object, the present inventors have (A) an aqueous resin dispersion obtained by polymerizing an α, β-ethylenically unsaturated monomer and (B) an amide. A water-soluble resin composition comprising an amphiphilic polymer having at least one functional group selected from a group, an amino group and a hydroxyl group as a hydrophilic part and having a hydrophobic part, and (C) water-dispersed colloidal silica It has been found that when a coating composition characterized by the above is used for a coating material or the like, it is possible to form a coating film having good stain resistance and excellent water resistance over a long period of time.

  Although the detailed mechanism of the present invention has not yet been elucidated, the present inventors consider as follows. (B) A water-soluble resin composition comprising an amphiphilic polymer having at least one functional group selected from an amide group, an amino group and a hydroxyl group as a hydrophilic part and having a hydrophobic part has a hydrophobic part (A) It is considered that the water-dispersed colloidal silica (C) is adsorbed on the hydrophobic part of the surface of the aqueous resin dispersion and the hydrophilic part (C). That is, the water-soluble resin composition (B) functions to connect the aqueous resin dispersion (A) and the water-dispersed colloidal silica (C) to the surface of the aqueous resin dispersion (A). The water-dispersed colloidal silica was adsorbed, and it was possible to form a structure in which the water-dispersed colloidal silica was effectively oriented on the outermost surface of the coating film even after the coating film was formed.

(A) The aqueous resin dispersion may be a resin composition obtained by polymerizing an α, β-ethylenically unsaturated monomer using water as a medium, and preferably has the following (1) uniform structure. An aqueous resin dispersion containing one or both of an emulsion and an emulsion having a heterogeneous structure obtained by a multistage emulsion polymerization method,
(2) Aqueous resin dispersion obtained by phase inversion and forced emulsification of acrylic resin, alkyd resin, epoxy resin, polyester, polyurethane, etc. polymerized and / or condensed in an organic solvent medium,
Is mentioned.

  Emulsions with a uniform structure enable the formation of dense coatings and provide coatings with excellent water permeation resistance and clearness, and heterophasic emulsions can be formed by combining monomers with different glass transition temperatures. By using these emulsions, such as being able to obtain a coating film with excellent film properties and excellent non-adhesiveness, the range of coating film properties formed can be expanded.

  Aqueous resin dispersions obtained by phase inversion and forced emulsification of acrylic resins, alkyd resins, epoxy resins, polyesters, polyurethanes, etc. polymerized and / or condensed in organic solvent media with water It is possible to form a coating film having excellent properties.

(A) Examples of the α, β-ethylenically unsaturated monomer that can be used in the aqueous resin dispersion include the following monomers. Methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, sec-butyl acrylate, t-butyl acrylate, hexyl acrylate, 2-ethylhexyl acrylate, octyl acrylate, nonyl acrylate, decyl acrylate, dodecyl Acrylate, n-amyl acrylate, isoamyl acrylate, lauryl acrylate, stearyl acrylate, methyl (meth) acrylate, ethyl (meth) acrylate, n-propyl (meth) acrylate, isopropyl (meth) acrylate, n-butyl (meth) acrylate, Isobutyl (meth) acrylate, sec-butyl (meth) acrylate, t-butyl (meth) Acrylate, hexyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, octyl (meth) acrylate, nonyl (meth) acrylate, decyl (meth) acrylate, dodecyl (meth) acrylate, n-amyl (meth) acrylate, isoamyl ( (Meth) acrylate, lauryl (meth) acrylate, stearyl (meth) acrylate, behenyl (meth) acrylate, cyclohexyl (meth) acrylate, phenyl (meth) acrylate, benzyl (meth) acrylate, methoxyethyl (meth) acrylate, ethoxyethyl ( (Meth) acrylate monomers such as (meth) acrylate, methoxypropyl (meth) acrylate, and ethoxypropyl (meth) acrylate;
Styrene derivatives such as styrene, α-methylstyrene, chlorostyrene, vinyltoluene, methoxystyrene;
Carboxyl group-containing monomers such as (meth) acrylic acid, fumaric acid, maleic acid, maleic anhydride, itaconic acid, itaconic anhydride, and crotonic acid;
(Meth) acrylic acid, crotonic acid, itaconic acid; 2-hydroxyethyl (meth) acrylate, 2 (3) -hydroxypropyl (meth) acrylate, 4-hydroxybutyl acrylate, 2-hydroxybutyl (meth) acrylate Hydroxyl group-containing monomers such as allyl alcohol, mono (meth) acrylic acid ester of polyhydric alcohol, polyethylene glycol (meth) acrylate, polypropylene glycol (meth) acrylate;
(Meth) acrylamide, maleamide, N-methyl (meth) acrylamide, N-ethyl (meth) acrylamide, N, N-dimethyl (meth) acrylamide, N-isopropylacrylamide, N, N-dimethylaminopropyl (meth) Amide group-containing monomers such as acrylamide and N-vinyl-2-pyrrolidone;
Amino group-containing monomers such as 2-aminoethyl (meth) acrylate, dimethylaminoethyl (meth) acrylate, 3-aminopropyl (meth) acrylate, 2-butylaminoethyl (meth) acrylate, and vinylpyridine;
Epoxy group-containing monomers and oligomers obtained by reaction of glycidyl (meth) acrylate, allyl glycidyl ether, an epoxy compound having two or more glycidyl groups and an ethylenically unsaturated monomer having an active hydrogen atom;
Vinyltrimethoxysilane, vinyltriethoxysilane, vinylmethyldimethoxysilane, vinylmethyldiethoxysilane, 3- (meth) acryloxypropyltrimethoxysilane, 3- (meth) acryloxypropyltriethoxysilane, 2- (meth) Acryloxyethyltrimethoxysilane, 2- (meth) acryloxyethyltriethoxysilane, 3- (meth) acryloxypropylmethyldimethoxysilane, 3- (meth) acryloxypropylmethyldiethoxysilane, 3- (meth) acryl Alcohols such as loxypropylmethyldipropoxysilane, 3- (meth) acryloxybutylphenyldimethoxysilane, 3- (meth) acryloxypropyldimethylmethoxysilane, and 3- (meth) acryloxypropyldiethylmethoxysilane Shishiriru group-containing monomer;
Other representative examples include vinyl acetate, vinyl chloride, and ethylene, butadiene, acrylonitrile, dialkyl fumarate, and the like.

  Furthermore, in order to improve the function of the obtained coating film, it is also possible to introduce a crosslinked structure. In general, the crosslinked structure is roughly classified into two types: “intraparticle crosslinked structure” and “interparticle crosslinked structure”.

  By incorporating this “intraparticle cross-linking structure” and “interparticle cross-linking structure” into the emulsion particles, the coating performance such as toughness, blocking resistance, non-adhesiveness, and solvent resistance can be greatly improved. Can be improved.

  Examples of monomers for obtaining the intra-particle / inter-crosslinked structure are listed as follows.

Intraparticle crosslinking: A monomer having two or more polymerizable unsaturated double bonds in the molecule.
A method using divinylbenzene, ethylene glycol di (meth) acrylate, trimethylolpropane tri (meth) acrylate, allyl (meth) acrylate or the like;
Combining monomers having functional groups that react with each other at temperature during the emulsion polymerization reaction, for example, ethylenically unsaturated monomers having a functional group in combination such as a carboxyl group and a glycidyl group, or a hydroxyl group and an isocyanate group A method using a monomer mixture selectively containing; hydrolyzable condensation reaction, (meth) acryloxypropyltrimethoxysilane, (meth) acryloxypropylmethyldimethoxysilane, etc. It can be produced by a method such as a method using a monomer mixture containing a saturated monomer.

  Interparticle cross-linking: The most typical example is a method in which an ethylenically unsaturated monomer having a carbonyl group is copolymerized and then a compound having two or more hydrazide groups is mixed in the molecule.

  Examples of the carbonyl group-containing ethylenically unsaturated monomer include acrolein, diacetone (meth) acrylamide, formylstyrene, (meth) acryloxyalkylpropanal, diacetone (meth) acrylate, acetonyl (meth) acrylate, acetoacetoxy Examples include ethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate-acetyl acetate, butanediol-1,4-acrylate-acetyl acrylate, vinyl ethyl ketone, and vinyl isobutyl ketone. In particular, acrolein, diacetone acrylamide and vinyl methyl ketone are preferable.

  Examples of the compound having two or more hydrazide groups in the molecule as a pair of the carbonyl group include carbohydrazide, oxalic acid dihydrazide, malonic acid dihydrazide, succinic acid dihydrazide, glutaric acid dihydrazide, adipic acid dihydrazide, and sebacic acid. Examples include dihydrazide, dodecanoic acid dihydrazide, isophthalic acid dihydrazide, citric acid trihydrazide, 1,2,4-benzenetrihydrazide, and thiocarbodihydrazide. Among these, carbohydrazide, adipic acid dihydrazide, and succinic acid dihydrazide are preferable from the viewpoint of dispersibility in the emulsion and water resistance.

  In addition, by using a water-soluble resin containing polyvinyl alcohol, polyacrylamide, polyacrylic acid, polyacrylate, or a copolymer thereof, it is possible to design a paint with excellent coating workability or to apply a coating with higher hydrophilicity. By forming the film, a coating film having excellent contamination resistance can be obtained. The water-soluble resins preferably have a weight average molecular weight of 5,000 to 100,000. When the weight average molecular weight is less than 5,000, the toughness and weather resistance of the coating film tend to be poor. On the other hand, when the weight average molecular weight exceeds 100,000, the viscosity becomes high and the coating workability is deteriorated.

  In addition to (A) an aqueous resin dispersion obtained by polymerizing an α, β-ethylenically unsaturated monomer, an aqueous resin dispersion such as a urethane dispersion is used, so that the water resistance and blocking properties of the coating film are increased. Can be improved. Thereby, the maintenance of the stain resistance after the coating film is formed becomes better.

  Furthermore, in order to improve the weather resistance and light resistance of the resulting coating film, it is possible to incorporate a polymerizable light-stable monomer or a polymerizable UV-absorbing monomer.

Specific examples of the polymerizable light-stable monomer include:
4- (meth) acryloyloxy-2,2,6,6-tetramethylpiperidine,
4- (meth) acryloylamino-2,2,6,6-tetramethylpiperidine,
4- (meth) acryloyloxy-1,2,2,6,6-pentamethylpiperidine,
4- (meth) acryloylamino-1,2,2,6,6-pentamethylpiperidine,
4-cyano-4- (meth) acryloylamino-2,2,6,6-tetramethylpiperidine,
4-crotonoyloxy-2,2,6,6-tetramethylpiperidine,
4-crotonoylamino-2,2,6,6-tetramethylpiperidine,
1- (meth) acryloyl-4- (meth) acryloylamino-2,2,6,6-tetramethylpiperidine,
1- (meth) acryloyl-4-cyano-4- (meth) acryloylamino-2,2,6,6-tetramethylpiperidine, and 1-crotonoyl-4-crotonoyloxy-2,2,6,6- Tetramethylpiperidine and the like can be mentioned.

As the polymerizable ultraviolet absorbing monomer, specifically, for example,
2- [2′-hydroxy-5 ′-(methacryloyloxymethyl) phenyl] -2H-benzotriazole,
2- [2′-hydroxy-5 ′-(methacryloyloxyethyl) phenyl] -2H-benzotriazole,
2- [2′-hydroxy-5 ′-(methacryloyloxypropyl) phenyl] -2H-benzotriazole,
2- [2′-hydroxy-5 ′-(methacryloyloxyhexyl) phenyl] -2H-benzotriazole,
2- [2′-hydroxy-3′-t-butyl-5 ′-(methacryloyloxyethyl) phenyl] -2H-benzotriazole,
2- [2′-hydroxy-5′-t-butyl-3 ′-(methacryloyloxyethyl) phenyl] -2H-benzotriazole,
2- [2′-hydroxy-5 ′-(methacryloyloxyethyl) phenyl] -5-chloro-2H-benzotriazole,
2- [2′-hydroxy-5 ′-(methacryloyloxyethyl) phenyl] -5-methoxy-2H-benzotriazole,
2- [2′-hydroxy-5 ′-(methacryloyloxyethyl) phenyl] -5-cyano-2H-benzotriazole,
2- [2′-hydroxy-5 ′-(methacryloyloxyethyl) phenyl] -5-tert-butyl-2H-benzotriazole, and 2- [2′-hydroxy-5 ′-(methacryloyloxyethyl) phenyl]- 5-nitro-2H-benzotriazole and the like can be mentioned.

  Of course, it is also possible to use a non-reactive light stabilizer or ultraviolet absorber together during the polymerization.

  In the resin composition of the present invention, as a polymerization initiator used when polymerizing the α, β-ethylenically unsaturated monomer, those conventionally used for radical polymerization can be used. is there. For example, persulfates such as potassium persulfate and ammonium persulfate; 2,2′-azobis (2-aminodipropane) hydrochloride, 4,4′-azobis-cyanovaleric acid, 2,2′-azobis ( 2-methylbutanamide oxime) azo compounds such as dihydrochloride tetrahydrate; peroxides such as hydrogen peroxide and t-butyl hydroperoxide. Furthermore, a redox system in which a reducing agent such as L-ascorbic acid or sodium thiosulfate is combined with ferrous sulfate or the like can also be used.

  Also, alkyl mercaptans such as lauryl mercaptan, n-butyl mercaptan, t-butyl mercaptan, octyl mercaptan, n-dodecyl mercaptan, thioglycolic acid-2-ethylhexyl, 2-methyl-t-butylthiophenol, carbon tetrabromide , And chain transfer agents such as α-methylstyrene dimer can also be used. By appropriately using these, the gloss, film formability, and non-adhesiveness of the coating film can be controlled.

  (A) When the aqueous resin dispersion is obtained by emulsion polymerization, a surfactant generally used in emulsion polymerization can be used as an emulsifier. For example, alkyl sulfates such as sodium lauryl sulfate, higher alcohol sulfates, alkyl benzene sulfonates such as sodium dodecylbenzene sulfonate, polyethylene oxide alkyl ether sulfate, polyethylene oxide nonyl phenyl ether sulfonate ammonium, polyethylene oxide-polypropylene Anionic surfactants such as so-called reactive emulsifiers that have an oxide glycol ether sulfate, sulfonic acid group or sulfate ester group and a polymerizable carbon-carbon unsaturated double bond in the molecule; polyethylene oxide alkyl ether, polyethylene Oxide nonylphenyl ether, sorbitan fatty acid ester, polyethylene oxide fatty acid ester, or polymerizable carbon-carbon unsaturated double bond with the aforementioned skeleton A nonionic surfactant such as reactive nonionic surfactants having in the molecule; and alkyl amine salts, cationic surfactants such as quaternary ammonium salts.

  As the pH adjuster, various nitrogen-containing basic compounds conventionally known as neutralizers can be used without particular limitation. Specifically, for example, trimethylamine, alkylamines such as triethylamine, tributylamine, triethanolamine, dimethylethanolamine, diethanolamine, monoethanolamine, N-methyldiethanolamine, N, N-dimethylethanolamine, ethylpropanolamine Representative examples include alcohol amines such as volatile nitrogen-containing basic compounds such as morpholine and ammonia. Of these, one or more pH adjusting agents may be used in combination.

  Further, 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, N- (2-aminoethyl) -3-aminopropyltrimethoxysilane, N- (2-aminoethyl) -3-aminopropylmethyl Dimethoxysilane, N- (2-aminoethyl) -3-aminopropylmethyldiethoxysilane, N-cyclohexyl-3-aminopropyltrimethoxysilane, N-cyclohexyl-3-aminopropyltriethoxysilane, 3- ( Amino group-containing alkoxysilanes such as 2-aminoethyl) -aminopropyltrimethoxysilane, 3- (2-aminoethyl) -aminopropylmethyldimethoxysilane, and 3-anilinopropyltrimethoxysilane are also part of the neutralizing agent. Can be used together.

  (B) Water-soluble resin composition comprising an amphiphilic polymer having at least one functional group selected from an amide group, an amino group and a hydroxyl group as a hydrophilic part and having a hydrophobic part in the aqueous resin composition according to the present invention In the product, the hydrophobic part (A) interacts with the surface of the aqueous resin dispersion, and the hydrophilic part (C) interacts with the surface of the water-dispersed colloidal silica. (C) The water-dispersed colloidal silica is contained as an intermediary agent for forming an oriented structure.

  (B) The aqueous resin composition has an α, β-ethylenically unsaturated monomer having an alkyl chain having 4 to 24 carbon atoms and at least one functional group selected from an amino group, an amide group, and a hydroxyl group. A water-soluble resin composition comprising an amphiphilic polymer having a hydrophilic part and a hydrophobic part is preferred, and a water-soluble resin composition comprising a random copolymer or a block copolymer represented by the following general formula.

_{- [CH 2 -CR 1 (COOR} 2)] l - (X) m -
In the formula, R ₁ is a hydrogen atom or a methyl group. R ₂ is C _n H _{2n + 1} (n is an integer of 4 to 24). X is a monomer having at least one functional group of an amide group, an amino group, and a hydroxyl group. l is an integer of 1 to 100, and m is an integer of 1 to 1000.

  As an α, β-ethylenically unsaturated monomer having an alkyl chain having 4 to 24 carbon atoms, an amino group-containing monomer, an amide group-containing monomer, and a hydroxyl group-containing monomer, (A) an aqueous resin The various monomers described above can be used as monomers that can be used in the dispersion.

  (B) The aqueous resin composition can be synthesized by general bulk polymerization or solution polymerization, but a commercially available product may be used.

  Furthermore, an amphiphilic polymer such as poly (N-isopropylacrylamide), poly (N-vinyl-2-pyrrolidone), hydroxyethyl cellulose, and hydroxypropyl cellulose may be used for the aqueous resin composition (B).

  The proportion of the (B) aqueous resin composition is preferably 0.1 to 50% by weight, particularly preferably 0.5 to 20% by weight, based on the solid content with respect to the (A) aqueous resin dispersion. (A) When it is less than 0.1% by weight based on the solid content with respect to the aqueous resin dispersion, (C) there are few places to attract the water-dispersed colloidal silica, so the effect of stain resistance is inferior. In the case of 50% by weight or more based on the solid content with respect to the resin dispersion, the water resistance in the case of forming a coating film is lowered.

  The shape of the (C) water-dispersed colloidal silica used in the present invention includes a spherical shape, a chain shape, a rod shape, a pearl like shape, a different shape, and the like. In the present invention, these can also be used. Yes, preferably in the form of a chain, a rod, or a pearl like shape. (C) The shape and average particle diameter of the water-dispersed colloidal silica can be confirmed by observation with an electron microscope. Moreover, the average particle diameter of (C) water dispersion colloidal silica is although it does not specifically limit, Preferably it is 0.1-100 nm, More preferably, it is 4-30 nm. (C) If the average particle size of the water-dispersed colloidal silica is larger than 100 nm, the water-stable colloidal silica is liable to settle, so that the storage stability is lowered. On the other hand, the lower limit of the average particle diameter was set to 0.1 nm because it indicates an average particle diameter that can be easily obtained at present, and if it is less than 0.1 nm, it becomes very expensive and difficult to obtain, and the usage is narrowed. End up. Moreover, it is preferable that the pH of (C) water dispersion colloidal silica is 8.4-11.5. (C) When the pH of the water-dispersed colloidal silica is less than 8.4, the system becomes unstable with an alkaline coating composition. Moreover, when pH exceeds 11.5, the dispersion stability of the (C) water dispersion colloidal silica in a coating composition is inferior.

(C) As a specific example of water-dispersed colloidal silica, for example,
Snowtex ST-20, ST-O, ST-C, ST-S, ST-N, ST-20L, ST-AK, ST-UP, ST-ZL manufactured by Nissan Chemical Industries,
Adelite AT-20, AT-30, AT-20N, AT-30N, AT-20A, AT-20S, AT-20Q, AT-30A, AT-30S, AT-40, AT-50 manufactured by ADEKA Corporation , AT-300,
Cataloid S-20H, Cataloid S-30, Cataloid S-30H, Cataloid SI-500, Cataloid SN, Cataloid SA, manufactured by Catalytic Chemical Industry Co., Ltd.
Silica Doll 30, Silica Doll 20, Silica Doll 20A, Silica Doll 20B manufactured by Nippon Chemical Industry Co., Ltd.
Clevosol 30R9, Clevosol 30R50, Clevosol 50R50 manufactured by Clariant Japan Co., Ltd.
DuPont Ludox HS-40, Ludox HS-30, Ludox LS, Ludox SM-30, Ludox AS, Ludox AM
Etc. Of these, one or more water-dispersed colloidal silicas may be used in combination.

  (C) The ratio containing the water-dispersed colloidal silica is preferably 0.5 to 20% by weight, particularly preferably 3 to 15% by weight, based on the solid content with respect to the (A) aqueous resin dispersion. (A) When it is less than 0.5% by weight based on the solid content with respect to the aqueous resin dispersion, the effect of stain resistance is inferior, and (A) 20% by weight or more based on the solid content with respect to the aqueous resin dispersion In this case, the coating film becomes hard and brittle, and the inside of the coating film tends to be porous, and the water resistance tends to be inferior.

  Further, when (D) a hydrolyzable silane represented by the following general formula (a) is further contained, the outflow of (C) water-dispersed colloidal silica after the formation of the coating film due to rainwater is suppressed, so that it is resistant to contamination. The maintainability becomes better, the coating film strength is further improved, and the durability, hardness and heat resistance are improved.

_{^{(R 1) n -Si- (R}} 2) 4-n (a)
In the formula (a), n is an integer of 0 to 3, R ¹ is a hydrogen atom, an alkyl group having 1 to 16 carbon atoms, an aryl group having 5 to 10 carbon atoms, a cycloalkyl group having 5 to 6 carbon atoms, It is selected from a vinyl group, an alkyl acrylate group having 1 to 10 carbon atoms, or an alkyl methacrylate group having 1 to 10 carbon atoms. The n R ¹ may be the same or different. R ² is selected from an alkoxy group having 1 to 8 carbon atoms, an acetoxy group, or a hydroxyl group. (4-n) pieces of R ² may be the same or different.

  (D) Specific examples of the hydrolyzable silane include vinyltrimethoxysilane, vinyltriethoxysilane, vinyltris (2-methoxyethoxy) silane, N- (2-aminoethyl) 3-aminopropylmethyldimethoxysilane, N- (2-aminoethyl) 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropylmethyldimethoxysilane, 2- (3,4-epoxy (Cyclohexyl) ethyltrimethoxysilane, 3-chloropropylmethyldimethoxysilane, 3-chloropropyltrimethoxysilane, 3-methacryloxypropyltrimethoxysilane, 3-mercaptopropyltrimethoxysilane and the like.

  (D) The ratio containing the hydrolyzable silane is preferably 0.05 to 5% by weight, particularly 0.1 to 1% by weight, based on the solid content with respect to the (A) aqueous resin dispersion. Is preferred. (A) When it is less than 0.05% by weight based on the solid content with respect to the aqueous resin dispersion, (D) the effect of maintaining the stain resistance obtained by including hydrolyzable silane is reduced, and (A) aqueous When the amount of the resin dispersion is more than 5% by weight based on the solid content, the storage stability of the paint is lowered.

  The coating composition obtained as described above was coated on a glass substrate and dried at a temperature of 10 ° C. to 200 ° C. for 2 minutes to 10 days, and a static surface contact angle meter CA-X type (Kyowa) The contact angle of the coating film surface with pure water measured by Interface Science Co., Ltd. is preferably 75 ° or less because of excellent stain resistance of the coating film, and more preferably 60 ° or less.

  The coating composition of the present invention is preferably used for water-based coatings used for building interior materials and exterior materials. When used as a paint, only the paint composition can be used as a clear paint, but commonly used color pigments such as bengara, carbon black, titanium oxide, calcium carbonate, barium carbonate, talc, clay , Mica, Alumina, Alum, White clay, Magnesium hydroxide, Magnesium oxide, Diatomaceous earth and other extender pigments, Titanium oxide with photocatalytic activity, Frypontite with anti-smudge / adsorption function, Active zinc white, Magnesium silicate, etc. These functional pigments can also be added. In order to impart various functions as a paint, a thickener, a dispersant, an anti-settling agent, an antifungal agent, an antiseptic, an ultraviolet absorber, a light stabilizer, and the like may be added as appropriate.

  The coating composition obtained in this way can be applied to various inorganic materials, metal materials, wood materials, plastic materials, etc., and it can be dried naturally or by forced drying at a temperature of 50 ° C. or higher. It is possible to form. In addition, during film formation, an organic solvent (film forming aid) such as ethylene glycol monobutyl ether or 2,2,4-trimethyl-1,3-pentanediol monoisobutyrate is arbitrarily used for the purpose of lowering the film formation temperature. It is also possible to add to.

  By using the coating composition of the present invention, it is possible to provide a coating having a coating film that has good stain resistance and excellent water resistance over a long period of time.

  Hereinafter, the present invention will be described more specifically based on Examples and Comparative Examples, but the present invention is not limited to these Examples. In the following examples and comparative examples, “parts” and “%” are based on weight unless otherwise specified.

(Production example of aqueous resin dispersion A1)
In a reactor equipped with a stirrer, a thermometer, a cooling pipe and a dropping device, 250 parts of ion exchange water, polyoxyethylene polycyclic phenyl ether sulfate ammonium salt (trade name: New Coal 707SF, non-reactive anionic emulsifier, 10 parts of Nippon Emulsifier Co., Ltd. were charged, respectively, and the temperature was raised to 80 ° C. while replacing the inside of the reactor with nitrogen.

  Next, 1.2 parts of potassium persulfate (polymerization initiator) was added, and 180 parts of methyl methacrylate, 120 parts of butyl acrylate, 92 parts of cyclohexyl methacrylate, 8 parts of methacrylic acid, 16 parts of New Coal 707SF, and 300 parts of water were dispersed. The emulsified mixture obtained by emulsifying and stirring was added dropwise over 4 hours. After completion of dropping, the mixture was aged while continuing stirring at 80 ° C. for 1 hour, cooled to 40 ° C., adjusted to pH 9.0 with 50% dimethylethanolamine, and a solid content of 42% in which emulsion particles having a uniform structure were dispersed. Aqueous resin dispersion A1 was obtained.

(Production example of aqueous resin dispersion A2)
In a reactor equipped with a stirrer, a thermometer, a condenser, and a dropping device, 250 parts of ion-exchanged water and 10 parts of New Coal 707SF were charged, and the temperature inside the reactor was increased to 80 ° C. while replacing the inside with nitrogen. .

  Subsequently, 1.2 parts of potassium persulfate (polymerization initiator) is added, and an emulsified mixed solution comprising 172 parts of methyl methacrylate, 20 parts of 2-ethylhexyl acrylate, 8 parts of methacrylic acid, 10 parts of New Coal 707SF, and 140 parts of water. Was added dropwise over 2 hours. Next, 50 parts of methyl methacrylate, 90 parts of 2-ethylhexyl acrylate, 50 parts of cyclohexyl methacrylate, 10 parts of 3-methacryloxypropyltrimethoxysilane (trade name: KBM503, manufactured by Shin-Etsu Chemical Co., Ltd.), 10 parts of New Coal 707SF The emulsion mixture consisting of 140 parts of deionized water was added dropwise over 2 hours. After completion of the dropwise addition, the mixture was aged while continuing to stir at 80 ° C. for 2 hours, cooled to 40 ° C., adjusted to pH 9.0 with 50% dimethylethanolamine, and dispersed emulsion phase particles by multistage emulsion polymerization method. An aqueous resin dispersion A2 having a solid content of 43% was obtained.

(Production example of aqueous resin dispersion A3)
In a reactor equipped with a stirrer, a thermometer, a condenser and a dropping device, 250 parts of ion-exchanged water, α-sulfonato-ω- (1- (allyloxymethyl-alkyloxypolyoxyethyleneammonium salt (trade name: 2 parts of Aqualon KH-10, a reactive anionic emulsifier, an average number of moles of ethylene oxide added, 10 moles manufactured by Daiichi Kogyo Seiyaku Co., Ltd. were charged, respectively, and the temperature inside the reactor was increased to 80 ° C. while replacing the interior with nitrogen.

  Then, 1.2 parts of potassium persulfate (polymerization initiator) is added, 115 parts of methyl methacrylate, 45 parts of butyl acrylate, 30 parts of butyl methacrylate, 4 parts of glycidyl methacrylate, 5 parts of acrylic acid, Aqualon KH-10 4 Part and 150 parts of water were added dropwise over 2 hours. Subsequently, an emulsified mixed solution composed of 70 parts of methyl methacrylate, 40 parts of 2-ethylhexyl acrylate, 50 parts of cyclohexyl methacrylate, 40 parts of diacetone acrylamide, 4 parts of Aqualon KH-10, and 150 parts of deionized water is taken over 2 hours. It was dripped. After completion of the dropwise addition, the mixture was aged while continuing stirring at 80 ° C. for 2 hours, cooled to 40 ° C., adjusted to pH 9.0 with 50% dimethylethanolamine, added with 12 parts of adipic acid dihydrazide, and further stirred for 30 minutes. Thus, an aqueous resin dispersion A3 having a solid content of 43% was obtained in which the emulsion particles having different phase structure were dispersed by a multistage emulsion polymerization method.

(Production example of aqueous resin dispersion A4)
In a reactor equipped with a stirrer, a thermometer, a condenser and a dropping device, 250 parts of ion-exchanged water, α-sulfonato-ω- (1- (allyloxymethyl-alkyloxypolyoxyethyleneammonium salt (trade name: Aqualon KH-10, reactive anionic emulsifier, ethylene oxide average addition mole number 10 mol, Daiichi Kogyo Seiyaku Co., Ltd. 2 parts, α- (1- (allyloxy) methyl-2- (nonylphenoxy) ethyl) ω- While charging 4 parts each of hydroxypolyoxyethylene (trade name: Adeka Soap NE-30, reactive nonionic emulsifier, ethylene oxide average addition mole number 30 mol, manufactured by ADEKA Corporation), while replacing the inside of the reactor with nitrogen, The temperature was raised to 80 ° C.

  Next, 1.2 parts of potassium persulfate (polymerization initiator) is added, 100 parts of methyl methacrylate, 40 parts of butyl acrylate, 50 parts of cyclohexyl methacrylate, 5 parts of 2-hydroxyethyl methacrylate, 5 parts of acrylic acid, aqualon An emulsified mixed solution consisting of 4 parts of KH-10 and 150 parts of water was added dropwise over 2 hours. Next, an emulsified mixed solution comprising 71 parts of methyl methacrylate, 75 parts of 2-ethylhexyl acrylate, 50 parts of cyclohexyl methacrylate, 4 parts of 3-methacryloxypropyltrimethoxysilane, 4 parts of Aqualon KH-10, and 150 parts of deionized water. Was added dropwise over 2 hours. After completion of the dropwise addition, the mixture was aged while continuing to stir at 80 ° C. for 2 hours, cooled to 40 ° C., adjusted to pH 9.0 with 50% dimethylethanolamine, and dispersed emulsion phase particles by multistage emulsion polymerization method. An aqueous resin dispersion A4 having a solid content of 43% was obtained.

(Production example of aqueous resin dispersion A5)
In a reactor equipped with a stirrer, a thermometer, a cooling pipe, and a dropping device, 170 parts of isopropanol was charged and heated to 80 ° C. while being replaced with nitrogen. Next, 3 parts of azobisisobutyronitrile (polymerization initiator) is added, and from 148 parts of methyl methacrylate, 90 parts of 2-ethylhexyl acrylate, 80 parts of cyclohexyl methacrylate, 5 parts of hydroxyethyl methacrylate and 17 parts of acrylic acid. The resulting mixture was added dropwise over 4 hours. After completion of the dropwise addition, the mixture was aged while continuing stirring at 80 ° C. for 4 hours. After cooling to 50 ° C., 10 parts of N, N-dimethylethanolamine and 490 parts of deionized water were added. Next, after removing the solvent under reduced pressure [1.3 × 10 ⁴ Pa (100 torr)] using a reactor equipped with a reflux condenser and a stirrer, the solid content was adjusted to 35% with water. Dilution adjustment was performed, and aqueous resin dispersion A5 having a solid content of 40% was obtained by a phase conversion method.

(Production example of water-soluble resin composition B1)
In a reactor equipped with a stirrer, a thermometer, and a cooling tube, 97 parts of N, N-diethylacrylamide, 3 parts of lauryl acrylate, and 0.1 part of 2,2′-azobis (2,4-dimethylvaleronitrile) were added. After charging and replacing with nitrogen, the mixture was heated in a water bath at 65 ° C. and polymerized for 4 hours to obtain a water-soluble resin composition B1.

(Production example of water-soluble resin composition B2)
In a reactor equipped with a stirrer, a thermometer and a condenser, 98 parts of N-vinyl-2-pyrrolidone, 2 parts of lauryl acrylate, 2,2′-azobis (2,4-dimethylvaleronitrile) 0.1 Part was charged and replaced with nitrogen, then heated in a water bath at 65 ° C. and polymerized for 4 hours to obtain water-soluble resin composition B2.

(Production example of water-soluble resin composition B3)
In a reactor equipped with a stirrer, a thermometer, and a condenser, N-vinyl-2-pyrrolidone 93 parts, 2-dimethylaminoethyl methacrylate 5 parts, n-butyl acrylate 2 parts, 2,2′-azobisiso After charging 0.1 part of butyronitrile and replacing with nitrogen, the mixture was heated in a water bath at 65 ° C. and polymerized for 4 hours to obtain a water-soluble resin composition B3.

(Production example of water-soluble resin composition B4)
In a reactor equipped with a stirrer, a thermometer, and a condenser tube, 75 parts of polyethylene glycol monomethacrylate (trade name: Blemmer PE-350, manufactured by NOF Corporation), 15 parts of 2-hydroxyethyl acrylate, 10 decyl methacrylate Part, 2,2′-azobisisobutyronitrile 0.1 part, and after replacing with nitrogen, the mixture was heated in a water bath at 65 ° C. and polymerized for 4 hours to obtain a water-soluble resin composition B4. .

(Production Example of Resin Composition B5)
In a reactor equipped with a stirrer, a thermometer and a condenser tube, 5 parts of N-vinyl-2-pyrrolidone, 95 parts of stearyl acrylate, 0.1 part of 2,2′-azobis (2,4-dimethylvaleronitrile) Was replaced with nitrogen, heated in a water bath at 65 ° C. and polymerized for 4 hours to obtain a water-soluble resin composition B5.

(Examples 1-15 and Comparative Examples 1-5)
As shown in Table 1, test paints of Examples 1 to 15 and Comparative Examples 1 to 4 were produced. 12 parts deionized water, 20 parts titanium oxide (trade name: Taipei CR-90, manufactured by Ishihara Sangyo Co., Ltd.) as a pigment, nonionic surfactant (trade name: Disperbyk-190, Big Chemie Japan) as an additive (A) Aqueous resin dispersion, (B) aqueous resin composition aqueous solution previously diluted with ion-exchanged water to a concentration of 20% by weight, C) Water-dispersed colloidal silica was added, urethane thickener (trade name: Primal RM-8W, manufactured by Rohm & Haas Co., Ltd.), 2 parts, silicone antifoaming agent (trade name: SN deformer 1312, Sannopco Co., Ltd.) (0.4 parts) and ethylene glycol (2 parts) were added to prepare each paint, and various performance evaluations were performed as follows. The results are shown in Tables 1 and 2.

<Contact angle>
Each test paint to which an appropriate amount of film forming aid was added was applied to a glass plate with a 6 mil applicator, dried at 60 ° C. for 2 hours, and then dried at room temperature for 1 day. A static contact angle with pure water was measured using a FACE contact angle meter CA-X manufactured by Kyowa Interface Science.

<Water resistance>
Each test paint to which an appropriate amount of film-forming aid was added was coated on a glass plate with a 6 mil applicator, dried at 50 ° C. for 6 hours, and then cured at room temperature for one day. Thereafter, the test plate was immersed in water at 23 ° C. for 1 week, and the degree of whitening of the coating film after drying was visually determined.
[Evaluation criteria]
A: There is no discoloration of the coating film.
○: The coating film has almost no discoloration or is slightly bluish and transparent.
Δ: The coating film is locally whitened.
X: The coating film is whitened as a whole.

<Hot water whitening resistance>
Each test paint to which an appropriate amount of film forming aid was added was applied on a blackboard with a 6 mil applicator, dried at 50 ° C. for 6 hours, and then cured at room temperature for one day. Thereafter, the test plate was immersed in warm water at 60 ° C. for 24 hours, and the degree of whitening of the coating film after drying was visually determined.
[Evaluation criteria]
A: There is no discoloration of the coating film.
○: The coating film has no discoloration or is slightly bluish and transparent.
Δ: The coating film is locally whitened.
X: The coating film is whitened as a whole.

<Elution properties>
Each test paint was applied to a polytetrafluoroethylene (PTFE) plate with a 6 mil applicator, dried at 70 ° C. for 2 hours, and then dried at room temperature for 1 day. The produced film was peeled off, cut into a 10 cm × 10 cm square, measured for the weight of the film, and then immersed in ion exchange water at 23 ° C. for 24 hours. The taken-out membrane was dried under reduced pressure at 23 ° C., and the elution rate of the coating film into water was calculated according to the following general formula;
Elution rate (%) = {1− (absolute dry weight after immersion) / (absolute dry weight before immersion)} × 100
[Evaluation criteria]
A: Less than 1% elution rate (There is no deterioration of the coating film and the state at the start of the test is maintained)
○: Elution rate of 1% or more and less than 2% (the coating film is hardly deteriorated and the gloss is maintained)
Δ: Elution rate of 2% or more and less than 5% (the surface of the coating film is washed away slightly and the gloss is partially reduced)
X: Elution rate of 5% or more (the surface of the coating film becomes brittle and the gloss decreases overall)

<Rain-stain stain resistance>
A slate plate coated with a white paint (dimensions 10 cm × 30 cm × thickness 5 mm) is spray-coated with the coating materials of Examples 1 to 15 and Comparative Examples 1 to 5 added with a film-forming aid as appropriate, and 60 ° C. And dried for 2 hours. After this was cured for 10 days, the rain that fell on the roof was covered with a coating film that had a roof inclined at 10 degrees with respect to the horizontal plane and having a groove with a length of 30 mm and a depth of 3 mm carved at a pitch of 3 mm. Mounted vertically to the south so as to flow down on the surface, and exposed for 1 month, 6 months, or 12 months in that state, the appearance of the coating film was compared with an untested coating film, and the contamination state was visually observed. .
[Evaluation criteria]
(Double-circle): Dirt has not adhered at all and is maintaining the state equivalent to the time of a test start.
○: Although there is slight dirt, almost no rain streak is confirmed.
(Triangle | delta): There exists a local stain | pollution | contamination and a rain stripe is confirmed slightly.
X: There is considerable dirt on the entire surface, and rain streaks are confirmed firmly.

<Storage stability>
The paints of Examples 1 to 15 and Comparative Examples 1 to 5 were each placed in a 100 ml glass sample bottle, stored in a 50 ° C. constant temperature room for one month in a sealed state, and the state was evaluated as follows.
[Evaluation criteria]
○: Same state as before the test, no change.
Δ: Precipitates are not visually confirmed, but there is a difference in appearance when painted.
X: Precipitation was confirmed visually.

* 1 Spherical colloidal silica, manufactured by Nissan Chemical Industries, Ltd., solid content SiO2: 30%, particle size: 8-11 nm, pH 9.5-10.5, Na stable type * 2 Spherical colloidal silica, Nissan Chemical Industries, Ltd. ), Solid content SiO2: 20%, particle size: 10 to 20 nm, pH 9.5 to 10.0, Na stable type * 3 spherical colloidal silica, manufactured by Nissan Chemical Industries, Ltd., solid content SiO2: 20%, particles Diameter: 10-20 nm, pH 8.5-9.0, pH stable * 4 Spherical colloidal silica, manufactured by Nissan Chemical Industries, solid content SiO2: 20%, particle size: 10-20 nm, pH 9.0-10 0.0, Na stable type * 5 chain colloidal silica, manufactured by Nissan Chemical Industries, Ltd., solid content SiO2: 19%, particle size: 10-18 nm particles bound to 80-120 nm, pH 9.5-11.0 , Na cheap Type * 6 Rod-shaped colloidal silica, manufactured by Nissan Chemical Industries, Ltd., solid content SiO2: 20%, particle size: 40 to 100 nm, pH 9.0 to 10.5, Na stable type * 7 Spherical colloidal silica, Nissan Chemical Industries ( Co., Ltd., solid content SiO2: 40%, particle diameter: 200 nm, pH 8.0 to 10.0, Na stable type * 8 Urethane emulsion, Mitsui Takeda Chemical Co., Ltd., NV 35%
* 9 Titanium oxide, manufactured by Ishihara Sangyo Co., Ltd. * 10 Nonionic surfactant, manufactured by Big Chemie Japan Co., Ltd. * 11 Urethane thickener, manufactured by Rohm and Haas Co., Ltd. * 12 Silicone-based antifoaming agent, Made by San Nopco

  As is clear from Tables 1 and 2, the coating composition of the present invention was excellent in stain resistance and its maintainability, and was also excellent in water resistance and warm water whitening resistance. The general acrylic emulsion of Comparative Example 1 had a high contact angle of the coating film and poor wettability, so that contamination was likely to adhere, and the rain resistance stain resistance was the poorest. In the case of not blending the (C) water-dispersed colloidal silica of Comparative Example 2 and in the case of not blending the (B) water-soluble resin composition of Comparative Example 3, the hydrophilicity of the coating film surface is not improved. It was not washed away and was inferior in rain-resistant stain resistance. In Comparative Example 4, the amount of water-dispersed colloidal silica in (C) was large, so that the initial rain-stain stain resistance was relatively good. However, the amount of colloidal silica in the coating film was large, so that the water resistance was poor and the dissolution rate. Became high. In Comparative Example 5, because B5 of the water-soluble resin composition is highly hydrophobic, it does not dissolve in water, and the colloidal silica cannot be oriented on the surface of the aqueous dispersion (A), so the wettability is poor. It was.

  From the results of the examples, it was found that the hydrophobic part of the water-soluble resin composition (B) was water-soluble (A) because it was possible to form a coating film having good stain resistance and excellent water resistance in the present invention over a long period of time. This is due to adsorption to the surface hydrophobic portion of the resin dispersion and adsorption of the water-dispersed colloidal silica (C) to the hydrophilic portion. (B) The water-soluble resin composition makes it possible to effectively dispose water-dispersed colloidal silica on the outermost surface of the coating film even after the coating film is formed, and realizes good wettability and stain resistance. .

Claims (7)

(A) An aqueous resin dispersion obtained by polymerizing an α, β-ethylenically unsaturated monomer and (B) at least one functional group selected from an amide group, an amino group and a hydroxyl group as a hydrophilic part A coating composition comprising: a water-soluble resin composition comprising an amphiphilic polymer having a hydrophobic portion; and (C) colloidal silica dispersed in an aqueous medium. The coating composition according to claim 1, wherein the aqueous resin composition (B) is a water-soluble resin composition made of a random copolymer or a block copolymer represented by the following general formula.
_{- [CH 2 -CR 1 (COOR} 2)] l - (X) m -
(In the formula, R ₁ is a hydrogen atom or a methyl group. R ₂ is C _n H _{2n + 1} (n is an integer of 4 to 24). X is at least one of an amide group, an amino group, and a hydroxyl group. (1 is an integer of 1 to 100, and m is an integer of 1 to 1000.)   The coating composition according to claim 1, wherein the aqueous resin composition (B) is poly N-isopropylacrylamide.   The coating composition according to claim 1, wherein the aqueous resin composition (B) is poly N-vinyl-2-pyrrolidone.   The coating composition according to claim 1, wherein the (B) aqueous resin composition is hydroxypropylcellulose.   The ratio of the (B) aqueous resin composition to the (A) aqueous resin dispersion is in the range of 0.1 to 15% by weight based on the solid content, and the (C) water-dispersed colloidal silica The ratio of the solid content is 0.5% to 20% by weight, and the weight ratio of (C) / (B) is in the range of 0.5 to 200. The coating composition as described in 2.   The silica component of the (C) water-dispersed colloidal silica has a chain, rod-like, or pearl-like shape, and the pH of the (C) water-dispersed colloidal silica is 8.4 to 11.5. A coating composition according to claim 1.