JPH07330468A - Composition for coating - Google Patents

Abstract

PURPOSE:To obtain a compsn. for coating which forms cured coating films having an excellent adhesion property and high hardness on the surfaces of various base materials by combining an organoalkoxysilane and thermosetting resin varnish and further, combining alumina therewith. CONSTITUTION:This compsn. for coating contains the total 100 pts.wt. of components (a) to (e) as shown below and additives when desired. The non- volatile content thereof in an acidic region where the pH of the liquid compsn. is <=7 is 8 to 55 pts.wt. (a) 10 to 45 pts.wt. organoalkoxysilane expressed by R<1>Si(OR2)3 (R<1> is 1 to 8C org. group; R<2> is 1 to 5C alkyl group and/or 1 to 4C acyl group), the hydrolyzate of this silane, its partial condensate and/or complete condensate (in terms of organoalkoxysilane), (b) 2 to 20 pts.wt. thermosetting resin, (c) 1 to 14 pts.wt. colloidal and/or superfine particulate alumina (in terms of alumina), (d) 1 to 70 pts.wt. hydrophilic org. solvent, (e) 3 to 60 pts.wt. water.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION This invention relates to coating compositions and more particularly to iron, stainless steel, aluminum and other metals, ceramics, cement, concrete, glass, plastics, paper, fibers, wood and other products. , Or organic or inorganic coating surface and cured at room temperature or under heating, weather resistance, heat resistance, alkali resistance, acid resistance, organic solvent resistance, chemical resistance,
Coating for forming a highly hard coating film with excellent corrosion resistance, stain resistance, abrasion resistance, impact resistance, flexibility, electrical insulation, antistatic property, workability and repairability and good adhesion. Composition.

[0002]

2. Description of the Related Art Conventionally, the hardness of the surface of a base material, chemical resistance,
Various coating compositions have been proposed for forming a cured coating film on the surface of a substrate for the purpose of improving heat resistance, electric insulation and the like.

For example, the following (a) and (b) are known as organoalkoxysilane-based coating compositions. (A) An organoalkoxysilane represented by RSi (OR ') ₃ (wherein R and R'represent an alkyl group or an aryl group) or a hydrolyzate thereof, and Si (OR ") ₄
(Wherein R ″ represents an alkyl group) and a composition thereof with a tetraalkoxylane or a hydrolyzate thereof (Japanese Patent Publication Nos. 55-4148, 55-40631, and 55-41273). (B) A composition containing an organoalkoxysilane represented by RSi (OR ') ₃ (wherein R and R'represent an alkyl group or an aryl group) or a hydrolyzate thereof and colloidal silica. (Japanese Patent Application Laid-Open No. 55-94971, Japanese Patent Application Laid-Open No. 5
9-68377, etc.).

However, with these coating compositions, a transparent coating film having relatively good adhesion can be obtained on the surface of a glass substrate or an inorganic substrate, but on the surface of other organic substrates, etc. And the resulting coating film is insufficient in alkali resistance, corrosion resistance, impact resistance, flexibility, electric insulation and the like.

On the other hand, as a thermosetting resin-based coating composition, it is needless to mention that no reference is given to the composition containing a thermosetting resin which is liquid at room temperature as a main component, or an organic solvent containing a thermosetting resin. Dissolved varnish is widely known.

The cured coating films of these thermosetting resins have excellent adhesion to the surface of the organic base material, but lack sufficient adhesion to the surface of the metal or the inorganic base material, and The weather resistance, antifouling property, antistatic property, heat resistance and hardness of the film are insufficient.

[0007]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention In the present invention, alkali resistance, corrosion resistance, impact resistance, which are problems of the organoalkoxysilane coating composition and the thermosetting resin coating composition, For coatings that can form cured coatings that have excellent adhesion to a wide range of various substrate surfaces, which solves flexibility, electrical insulation, weather resistance, stain resistance, antistatic properties, heat resistance, hardness, etc. It is intended to provide a composition.

[0008]

Means for Solving the Problems As a result of intensive studies to achieve the above-mentioned object, the inventors of the present invention have found that by combining an organoalkoxysilane and a thermosetting resin varnish, and further by compounding alumina, an inorganic system Being able to form a cured coating film with excellent adhesion on the surface of various substrates regardless of organic type,
The inventors have found that the surface hardness and antistatic property of a cured coating film can be improved, and completed the present invention.

The present invention comprises the following components (a) to (e) and optionally added additives.
Total of (e) [= (a) + (b) + (c) + (d) +
(E)] in an amount of 100 parts by weight and the nonvolatile content of the liquid composition in the acidic region of pH 7 or less is 8 to 55 parts by weight. (A) R ¹ Si (OR ² ) ₃ (In the formula, R ¹ has 1 to ¹ carbon atoms.
8 organic group, R ² is an alkyl group having 1 to 5 carbon atoms and /
Or an organoalkoxysilane represented by a C1-4 acyl group), a hydrolyzate of the organoalkoxysilane, a partial condensate and / or a complete condensate thereof (calculated as organoalkoxysilane) 10 to 45 parts by weight. (B) 2 to 20 parts by weight of thermosetting resin (c) 1 to 14 parts by weight of colloidal and / or ultrafine alumina (alumina equivalent) (d) 1 to 70 parts by weight of hydrophilic organic solvent (e) water 3 to 60 parts by weight

Regarding the coating composition of the present invention,
Hereinafter, each component will be described. Component (a) Organoa represented by R ¹ Si (OR ² ) ₃
Lucoxysilane, water content of the organoalkoxysilane
Degradation product, partial condensate and / or complete condensate thereof The organoalkoxylane used in the present invention is one which is hydrolyzed and polycondensed in the presence or absence of an acid or an alkali in the presence of water to give a high molecular weight. The coating film is cured under heating or at room temperature. Further, in the coating composition of the present invention, a coupling agent for improving the affinity between the organic component (b) thermosetting resin and the inorganic component (c) colloidal and / or ultrafine particle-like alumina and It acts as a dispersant for uniformly dispersing the alumina in the composition.

In the above organoalkoxysilane, R ¹ in the above formula is an organic group having 1 to 8 carbon atoms, for example, a methyl group,
Alkyl groups such as ethyl group and n-propyl group, as well as γ-chloropropyl group, vinyl group, 3,3,3-trifluoropropyl group, γ-glycidoxypropyl group, γ-methacryloxypropyl group, γ- A mercaptopropyl group, a phenyl group, a 3,4-epoxycyclohexylethyl group, a γ-aminopropyl group and the like, and R in the formula
² is an alkyl group having 1 to 5 carbon atoms and / or an acyl group having 1 to 4 carbon atoms, for example, methyl group, ethyl group, n-propyl group, i-propyl group, n-butyl group, sec-butyl group, An organic silane compound having a t-butyl group, an acetyl group, or the like.

Specific examples of these organoalkoxysilanes include methyltrimethoxysilane, methyltriethoxysilane, ethyltrimethoxysilane, ethyltriethoxysilane, n-propyltrimethoxysilane, and n-propyltrimethoxysilane.
Propyltriethoxysilane, i-propyltrimethoxysilane, i-propyltriethoxysilane, γ-chloropropyltrimethoxysilane, γ-chloropropyltriethoxysilane, vinyltrimethoxysilane, vinyltriethoxysilane, 3,3,3 -Trifluoropropyltrimethoxysilane, 3,3,3-trifluoropropyltriethoxysilane, γ-glycidoxypropyltrimethoxysilane, γ-glycidoxypropyltriethoxysilane, γ-methacryloxypropyltrimethoxysilane, γ-methacryloxypropyltriethoxysilane, γ-mercaptopropyltrimethoxysilane, γ-
Mercaptopropyltriethoxysilane, phenyltrimethoxysilane, phenyltriethoxysilane, 3,4
-Epoxycyclohexylethylmethoxysilane, 3,
4-epoxycyclohexylethylethoxysilane, γ
Examples include -aminopropylmethoxysilane and γ-aminopropylethoxysilane.

These organoalkoxysilanes have 1
They may be used alone or in combination of two or more. Preferably, methyltrimethoxysilane or methyltriethoxysilane is used. Further, a hydrolyzate obtained by previously hydrolyzing such an organoalkoxysilane in the presence or absence of an acid or an alkali, and a partial condensate obtained by further aging the hydrolyzate and polycondensating it, and / or
Alternatively, an organopolysiloxane compound which is a complete condensate can be used.

The proportion of the component (a) in the total 100 parts by weight of the coating compositions (a) to (e) is 10 to 45 parts by weight, preferably 15 to 40 parts by weight in terms of organoalkoxysilane. . When the blending ratio of the component (a) is less than 10 parts by weight, the hardness of the cured coating film is insufficient, while 4
If the amount exceeds 5 parts by weight, the hardness of the coating film increases, but the impact resistance, bending resistance, etc. are significantly reduced, which is not preferable.

Component (b) Thermosetting Resin The thermosetting resin has at least two functional groups in the molecular chain and is three-dimensionally crosslinked and polymerized by heating to be cured, and the cured product exhibits thermoplasticity. It is a resin that is not shown, and is a resin that cures when heated or left at room temperature in the presence or absence of a curing agent. In the present invention, it is copolymerized with an organopolysiloxane produced by polycondensation of the organoalkoxylane of the component (a) to form a cured coating film having high hardness and flexibility, and an organic group of the cured coating film. Improves adhesion to the agent surface.

Examples of such thermosetting resins include phenol resins, amino resins such as urea resins and melamine resins, epoxy resins such as bisphenol A type epoxy resins and bisphenol F type epoxy resins, alkyd resins, unsaturated polyester resins, and the like. For example, maleic acid type unsaturated polyester, diallyl phthalate type unsaturated polyester and the like, acrylic resin, polyamide resin and urethane resin can be exemplified, and in the present invention, among these, those soluble in the hydrophilic organic solvent of the component (d) are used. The product is used as a varnish dissolved in the solvent.

These thermosetting resins may be used alone or in combination of two or more. Preferably, at least one selected from the group consisting of amino resin, phenol resin, epoxy resin, acrylic resin and polyamide resin is used.

The mixing ratio of the component (b) in the total 100 parts by weight of the coating compositions (a) to (e) is 2
-20 parts by weight, preferably 4-15 parts by weight. When the mixing ratio of the component (b) is less than 2 parts by weight, sufficient impact resistance of the coating film cannot be obtained, while when it exceeds 20 parts by weight, the surface hardness of the coating film is significantly reduced, which is not preferable.

Component (c) Colloidal or ultrafine particles
Alumina colloidal alumina is an alumina sol having a pH of 2.5 to 6 in which water and / or lower alcohols are used as a dispersion medium, contains 5 to 25% by weight of alumina, and contains an acid such as nitric acid, hydrochloric acid or acetic acid as a stabilizer. The ultrafine particulate alumina used here is alumina produced by a high temperature hydrolysis method of a purified aluminum salt (a specific example; manufactured by Degussa).

In the present invention, since such alumina has a high positive charge, the antistatic property of the coating film is improved,
As a result, the antifouling property of the coating film is improved. Alumina also improves the adhesion and heat emissivity of the coating film. In addition, it is possible to prevent the formation of spots on the coating film.

The colloidal or ultrafine particles of alumina have an average particle size or average thickness of 5 to 50 mμ.
Granules or feathers are preferred. The mixing ratio of the component (c) in the total 100 parts by weight of the coating compositions (a) to (e) is 1 to 14 parts by weight, preferably 3 to 12 parts by weight, in terms of alumina. When the blending ratio of the component (c) is less than 1 part by weight, a sufficient antistatic effect cannot be obtained, while when it exceeds 14 parts by weight, the coating composition thickens, which is not preferable.

Component (d) Hydrophilic Organic Solvent The hydrophilic organic solvent used in the present invention is an organic solvent that dissolves the thermosetting resin of the component (b) and is compatible with water. In addition to dissolving the above, it is used as a regulator for the solid content concentration and viscosity of the coating composition, and as a hydrolysis regulator for the alkylalkoxysilane of component (a).

The hydrophilic organic solvent used in the present invention includes alcohols, glycols, esters, ethers and ketones. Alcohols having 1 to 1 carbon atoms
8 aliphatic alcohols such as methanol, ethanol, n-propanol, i-propanol, n-butanol, sec-butanol, t-butanol, n-pentanol, n-hexanol, 4-methyl-2-pentanol, 4 -Methyl-n-pentanol, methyl carbitol and the like can be mentioned. Examples of glycols include ethylene glycol and propylene glycol. As the esters, formic acid of the alcohols and glycols, acetic acid, esters such as propionic acid,
Specific examples include methyl formate, ethyl formate, butyl formate, methyl acetate, ethyl acetate, butyl acetate, ethyl propionate and the like.

As the ethers, alkyl ethers of alcohols and glycols, such as dimethyl ether, diethyl ether, dibutyl ether, methyl ethyl ether, ethyl butyl ether, ethylene glycol monobutyl ether, ethylene glycol monoethyl ether acetate, propylene. Examples thereof include glycol monoethyl ether. As the ketones, acetone, diethyl ketone, methyl ethyl ketone,
Examples include acetophenone.

The hydrophilic organic solvent may be used alone or as a mixed solvent of two or more kinds. In the present invention, i-propanol, methyl carbitol and methyl ethyl ketone are used singly or in a mixed solvent of two or more kinds thereof. Is preferably used.

The compounding ratio of the component (d) in the total 100 parts by weight of the coating compositions (a) to (e) is 1
˜70 parts by weight, preferably 10 to 50 parts by weight. When the colloidal alumina of the component (c) is alcoholic, this alcohol is also included in the hydrophilic organic solvent. When the compounding ratio of the component (d) is less than 1 part by weight, the viscosity of the coating composition is excessively increased and the storage stability is lowered, while when it exceeds 70 parts by weight, the storage stability is improved, but the coating composition. This is not preferable because the solid content concentration in the inside becomes small, the drying rate and the hydrolysis rate of the obtained coating film decrease, and it takes a long time to cure.

[0027] In the component (e) water present invention, water is an essential component as a hydrolysis agent of the alkyl alkoxy silane component (a). As this water, tap water, distilled water, or ion-exchanged water can be used.
Also included are water produced by hydrolysis of the alkylalkoxysilane of the component (a) and water contained as a dispersion medium of the colloidal alumina of the component (c).

The compounding ratio of the component (e) in 100 parts by weight of the coating compositions (a) to (e) is 3 parts by weight.
-60 parts by weight, preferably 10-40 parts by weight. When the blending ratio of the component (e) is less than 3 parts by weight, hydrolysis of the alkylalkoxysilane of the component (a) is difficult to sufficiently occur, while when it exceeds 60 parts by weight, the stability of the coating composition decreases, In addition, the drying speed of the coating film decreases, which is not preferable.

The coating composition of the present invention contains, in addition to the components (a) to (e), a surfactant, if necessary.
Additives such as acids, aluminum acetylacetonate, pigments, ultrafine silica and curing agents for thermosetting resins can be included.

The coating composition of the present invention contains the above-mentioned components (a) to (e) and, if necessary, additives and has a nonvolatile content of 8 to 55 parts by weight, preferably 8 to 55 parts by weight, in the acidic region of pH 7 or less. It is a liquid composition of 20 to 45 parts by weight.
If the non-volatile content is less than 8 parts by weight, a coating film having a sufficient thickness cannot be obtained by one application, resulting in poor workability. On the other hand, if it exceeds 55 parts by weight, it becomes difficult to obtain a coating film having a uniform thickness. Not preferable.

The coating composition of the present invention is prepared by dissolving the thermosetting resin of the component (b) in the hydrophilic organic solvent of the component (d) to prepare a varnish, and adding the colloidal or varnish of the component (c) to the varnish. Ultrafine particulate alumina, water of component (e) and, if necessary, additives are added to sufficiently disperse the alumina by using a roll mill or a ladle machine. It can be prepared by adding the organoalkoxysilane of the component (a) to this and stirring sufficiently.

Substrates to be coated with the coating composition of the present invention include metals such as iron, stainless steel and aluminum, inorganic substrates such as cement, concrete, glass and ceramics, plastic, paper and wood. In addition to the organic base materials, the surface of organic and inorganic coating films.

For coating the substrate with the coating composition, coating means such as brush coating, spraying, dipping, roll coating, spin coating and printing can be used. A coating film having a dry film thickness of 0.1 to 20 μm can be formed by coating once, and the coating can be repeated about 2 to 5 times. Further, in the case of multiple coating, the curing treatment may be performed once.

When the coating composition of the present invention is coated on a substrate, the organoalkoxysilane component (a) is hydrolyzed at a temperature of room temperature to 60 ° C. and, at the same time, a polycondensation reaction is caused to form a sol. The reaction proceeds further to form a gel, that is, an organopolysiloxane compound. Leave it at room temperature for 1-10 days or 8
By heating at 0 to 200 ° C. for 3 to 60 minutes, the organopolysiloxane compound and the thermosetting resin of the component (b) are copolymerized with the evaporation of the solvent, and the component (c) is further added.
To form a composite coating film of alumina. However, the reaction temperature and the standing time or the heating time are not limited to the above, because they depend on the type and mixing ratio of each component used.

[0035]

The cured coating film formed by the coating composition of the present invention has organopolysiloxane for metal substrates and inorganic substrates, and thermosetting resin for organic substrates. Adhesion to various base materials is extremely excellent by leading the property.

Further, the surface hardness of the cured coating film is high, which is close to that of an inorganic substance due to the composite of organopolysiloxane and alumina, and the thermosetting resin serves as a cushioning material to reduce the impact and flexibility due to the high hardness. The mechanical properties such as impact resistance and bending resistance are also extremely excellent because they are interpolated.

Further, the composite of alumina not only improves the thermal emissivity but also prevents the chargeability of the thermosetting resin due to the positive charge of the alumina, and as a result, improves the pollution preventive property and the heat dissipation. A cured coating film having excellent properties, antistatic properties and antifouling properties can be obtained.

In addition to the above, the organopolysiloxane and the thermosetting resin interpolate with each other, and weather resistance, heat resistance, acid resistance, alkali resistance, organic chemical resistance, corrosion resistance, abrasion resistance,
A cured coating film having excellent electric insulation can be obtained. The coating composition of the present invention is extremely excellent in workability because various coating means can be adopted, and is also excellent in repairability because it can be repeatedly coated.

[0039]

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to the following examples. In addition, "part" and "%" in the examples are based on weight unless otherwise specified.

Examples 1 to 7 and Comparative Example 1 (1) Preparation of Coating Composition A varnish prepared by dissolving the component (b) in the component (d) was prepared by using the following components, and the components (c) and (e) were added. ) And additives, with or without addition, is stirred for 60 minutes using a stirrer, then component (a) is added and further stirred for 30 minutes, and this is dispersed and blended by a roll mill, and coating at the blending ratio shown in Table 1 is performed. Compositions A to G (Examples 1 to 7) and coating composition H (Comparative Example 1) were prepared.

Component (a) Organoalkoxysilane (a) -1: Methyltrimethoxysilane (a) -2: Methyltriethoxysilane Component (b) Thermosetting resin (b) -1: Amino resin (urea melamine ) Nonvolatile content 60% (b) -2: Amino resin (melamine) Nonvolatile content 60% (b) -3: Epoxy / polyamide resin Nonvolatile content 40% (b) -4: Phenolic resin Nonvolatile content 58% (b)- 5: Acrylic resin 50% non-volatile content

Component (c) Colloidal or Ultrafine Particle Alumina (c) -1: Aqueous Colloidal Alumina 20% Alumina, pH 4.0 (c) -2: Ultrafine Particle Alumina Average Particle Size 15 mμ Component (d) Hydrophilic Organic solvent (d) -1: i-propanol (d) -2: butylcarbitol (d) -3: methyl ethyl ketone component (e) water

Component (f) (additive ) (f) -1: nonionic surfactant (f) -2: aluminum acetylacetonate (f) -3: acetic acid (f) -4: pigment titanium oxide (f) ) -5: Pigment Iron oxide (f) -6: Ultrafine particulate silica Average particle size 1
5 mμ

[0044]

[Table 1]

(2) Preparation of test piece for evaluation test Test composition for evaluation test was prepared by applying the coating composition shown in Table 1 prepared in (1) above to various substrates shown in Table 2 and curing the composition. TP1-17 were prepared. Among the substrates to be coated, steel plates, steel containers and stainless steel containers are alkali degreased, aluminum plates are degreased with toluene,
In other cases, the cleaning treatment was performed as a base treatment before the coating composition was applied. An air spray gun was used for applying the coating composition, and an electric oven was used for heating. The coating compositions were used within 8 hours after preparation. Table 3 shows the number of times the coating composition was applied and the curing conditions.

[0046]

[Table 2]

*) Portland cement and river sand (5 mm or less), mortar of cement / water / sand = 1 / 0.65 / 2.5 (weight ratio) was aged in water at 20 ° C. for 28 days.

[0048]

[Table 3]

(3) Evaluation test The following evaluation test was conducted on the test piece prepared in the above item (2). Adhesion JIS K-5400-6.15 Conforms to cross-cut test Hardness JIS K-5400-6.14 Conforms to pencil scratch test Impact resistance Conforms to JIS K-5400-6.13.2

After holding the test piece at 300 ° C. for 24 hours in a heat resistant electric furnace,
Cool and allowed to cool after the test piece 8 hours kept in observation boiling water resistance boiling water the appearance of the coating film, which 1
After repeating 0 times, observing the appearance of the coating film After observing the test piece for 20 days in warm water with a water resistance of 60 ° C, observe the appearance of the coating film.

Salt water resistance After maintaining the test piece in 4% saline solution for 20 days, the appearance of the coating film was observed. Salt sprayability 4% saline solution was continuously sprayed on the test piece for 480 hours, then the appearance of the coating film was observed . After immersing the test piece for 20 days in a mixed solvent of acetone / cellosolve / ethyl acetate / hydrous alcohol for industrial use / toluene = 3/2/2/1/2 (weight ratio), observe the appearance of the coating film

[0052]Alkali resistance  Keep test pieces in 10% caustic soda solution for 20 days
After holding, observe the appearance of the coating filmAlkali resistance Keep test pieces in 5% caustic soda solution for 20 days
After that, observe the appearance of the coating film

After keeping the test piece in 20% acid- resistant hydrochloric acid for 20 days, observing the appearance of the coating film After keeping the test piece in 20% acid- resistant sulfuric acid for 20 days, observing the appearance of the coating film Antistatic property JIS L1094 According to the method A half-life measurement method of the -1980 electrostatic measurement method. As the measuring method, a test piece was set in a half-life measuring device, an applied voltage of +10 kV was applied for 30 seconds, the voltage after the applied voltage was cut off was measured with time, and the half-life was obtained. The unit is seconds.

Cooling and heat cycle property The test piece was kept at 300 ° C. for 30 minutes in an electric furnace and naturally cooled. After repeating this operation 8 times, the appearance of the coating film was observed and steel wool with abrasion resistance # 0000 was used. after rubbing strongly test piece, observing the appearance of the coating film, by conforming to the presence or absence of scratches on the determination weatherability JIS K-5701 was sunshine carbon arc燈耐weathering tester, after exposure to the test piece 2000 hours, the coating film Observe the appearance

Volume resistance 50% relative humidity, measured value at 23 ° C. (Ωcm) Dielectric breakdown strength Measured value by short-time breakdown test (KV / mm) The results of the appearance observation of the coating film were evaluated and judged as follows. O mark: No peeling of the coating film was observed and the appearance was not changed. X: Peeling, cracking or melting damage is observed on part or all of the coating film. / Mark: Tables 4 to 5 show the results of non-evaluation tests, and Table 6 shows the results of retests after the weather resistance test.

[0056]

[Table 4]

[0057]

[Table 5]

[0058]

[Table 6]

[0059]

EFFECT OF THE INVENTION By using the coating composition of the present invention, it is possible to obtain a cured coating film of high hardness which is excellent in chemical properties, mechanical properties and electrical properties and is well balanced as shown in the above Examples. It can be formed regardless of base material such as metal base material, inorganic base material, organic base material, and the cured coating film has extremely excellent adhesion to any base material. Further, by adjusting the composition of the coating composition, a cured coating film can be formed according to the material of the base material and the purpose of the coating. Further, when coating, various known coating means can be adopted, so that workability is excellent, and since recoating can be performed, repairability is also excellent. The present invention provides a coating composition capable of forming a high-hardness cured coating film having excellent chemical properties, mechanical properties, and electrical properties and having a good balance, with good adhesion regardless of the substrate material. However, its industrial significance is extremely large.

Claims (5)

[Claims] 1. A total of [(a) + (b) + (c) + (consisting of the following components (a) to (e) and optionally added additives, the components (a) to (e) being the total]: d) + (e)], and the nonvolatile content of the liquid composition in the acidic region of pH 7 or less is 8 to 55 parts by weight. (A) R ¹ Si (OR ² ) ₃ (In the formula, R ¹ has 1 to ¹ carbon atoms.
8 organic group, R ² is an alkyl group having 1 to 5 carbon atoms and /
Or an organoalkoxysilane represented by a C1-4 acyl group), a hydrolyzate of the organoalkoxysilane, a partial condensate and / or a complete condensate thereof (calculated as organoalkoxysilane) 10 to 45 parts by weight. (B) 2 to 20 parts by weight of thermosetting resin (c) 1 to 14 parts by weight of colloidal and / or ultrafine alumina (alumina equivalent) (d) 1 to 70 parts by weight of hydrophilic organic solvent (e) water 3 to 60 parts by weight 2. The coating composition according to claim 1, wherein the organoalkoxylane of the component (a) is methyltrimethoxysilane and / or methyltriethoxysilane. 3. The thermosetting resin of component (b) is selected from the group consisting of amino resins, phenol resins, epoxy resins, acrylic resins and polyamide resins, which is soluble in the hydrophilic organic solvent of component (d). The coating composition according to claim 1, which is at least one kind. 4. The average particle size or average thickness of the component (c) colloidal or ultrafine particle alumina is 5 to 50.
The coating composition according to claim 1, which is mμ. 5. The coating composition according to claim 1, wherein the hydrophilic organic solvent as the component (d) is at least one selected from the group consisting of i-propanol, butyl carbitol and methyl ethyl ketone.