JPH10152626A - Water-repellent member and water-repellent coating composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a water-repellent member showing persistent surface repellency for a long term by forming a surface layer containing photocatalyst particles, a water-repellent silicone and a substance which prevents the silicone from being hydrophilized by photoexcitation on the surface of a substrate or immobilizing a substance which prevents the water-repellent silicone from being hydrophilized on at least part of the surface layer. SOLUTION: Examples of the photocatalysts include anatase titanium oxide, zinc oxide, tin oxide and strontium titanate. The silicone is a resin represented by the average compositional formula: Rp SiO(4-p)/2 (wherein R is a functional group comprising at least one monovalent organic group or a functional group comprising at least two members selected among monovalent organic groups and hydrogen groups; X is an alkoxyl or a halogen; and p is a number in the range: 0<<2. Examples of the substances which inhibit the water-repellent silicone from being hydrophilized by the photoexcitation by the photocatalyst include cobalt alloys, cobalt oxides, cobalt chlorides and cobalt sulfates.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a member and a substrate capable of maintaining the surface water repellency of a water repellent silicone for a long period of time while exhibiting oxidative decomposability by a photocatalyst such as antibacterial, deodorizing and antifouling. The present invention relates to a water-repellent coating composition capable of imparting the same properties as the above-mentioned members to a coated film surface when a coating film is formed on the surface.

[0002]

2. Description of the Related Art In recent years, it has been widely proposed to carry out antibacterial, deodorizing, antifouling, etc. utilizing the oxidative decomposability of a photocatalyst. The present inventors have also found that, besides the conventionally known oxidative decomposability, the photocatalyst has a property of making the surface superhydrophilic in response to photoexcitation, and utilizing this property, a transparent member or the like can be used. It is also possible to prevent fogging of mirrors, improve visibility in rainy weather, improve rainfall cleaning of various members such as buildings, and secure cleaning possibility only with water.
No. 5 is proposed.

[0003] In one embodiment of WO 96/29375, there is a member in which a surface layer made of a photocatalyst and silicone is formed on the surface of a substrate. This member is made of silicon
It exhibits water repellency of about 90 ° due to its water repellency, but at least part of the organic groups bonded to the silicon atoms in the silicone molecules are replaced with hydroxyl groups by photoexcitation of the photocatalyst to exhibit hydrophilicity. In addition, the amount of physically adsorbed water adsorbed on the surface increases according to the photoexcitation of the photocatalyst,
It becomes super hydrophilic. As a result, it is possible to prevent fogging of the transparent member and the mirror, improve visibility in rainy weather, improve rainfall washability of various members such as a building, and ensure washability only with water.

[0004]

However, on the other hand, there are applications in which water repellency is more preferable than hydrophilicity.
For example, members installed outdoors, such as power lines, antennas, and roofs, are susceptible to rain, snow, and ice. If water droplets adhere to the transmission line, the shape of the water droplets becomes a downward conical shape, so that discharge becomes easy, which leads to power transmission loss. In this case, in winter, the water droplets hang down in an icy manner, the tip is sharpened, and the discharge amount further increases. In addition, if snow and ice adhere to the antenna, the electric field intensity decreases, which deteriorates the quality of communication or causes communication failure. Furthermore, if ice or snow adheres to members installed outdoors, such as power transmission lines, antennas, and roofs, if left unattended, depending on the weight, for example, cutting of power transmission lines, collapse of steel towers, bending of antennas, deformation of roofs, etc. Etc. may occur. Therefore, these members installed outdoors require frequent snow removal in a snowfall area, and have required a great deal of cost and labor.

For example, in order to prevent the icing and snow,
It is preferable to impart water repellency to the member surface. When water repellency is imparted to the member surface, water droplets move around on the member surface. As a result, water droplets are less likely to adhere, and snow and ice are less likely to adhere because water droplets do not adhere.

As one method for solving the above problems, there is a method of forming a surface layer made of a water-repellent silicone on the surface of a substrate. However, in this configuration, the dirt adheres with time, and the contact angle with water is reduced to about 70 °.
The effect of water repellency does not last. Therefore, as another method for solving the above-mentioned problem, a photocatalyst and a water-repellent silica-
There is a method of forming a surface layer comprising According to this method, it is possible to decompose the adhered dirt over time based on the oxidative decomposability of the photocatalyst. However, in this configuration, when exposed to sunlight outdoors, the silicone is hydrophilized by photoexcitation of the photocatalyst, so that the water repellency of the surface cannot be maintained. In view of the above circumstances, an object of the present invention is to provide a member capable of maintaining the surface water repellency for a long period of time.

[0007]

According to the present invention, in order to solve the above-mentioned problems, photocatalytic particles, water-repellent silicone, and hydrophilicity of the water-repellent silicone by photoexcitation of the photocatalyst are provided on a substrate surface. Or a layer containing photocatalyst particles and a water-repellent silicone is formed on the surface of the base material, and is further formed on at least a part of the surface of the layer. The present invention provides a water-repellent member to which a substance for preventing the water-repellent silicone from becoming hydrophilic by photoexcitation of the photocatalyst is fixed.
Preventing the silicon from becoming hydrophilic by photoexcitation of the photocatalyst by making the surface layer contain a substance such as cobalt or a cobalt compound for preventing the photocatalyst from becoming hydrophilic by photoexcitation. Can be.
In addition, since the photocatalyst is contained, it is possible to decompose the dirt adhering with time based on the oxidative decomposability of the photocatalyst. Therefore, the water repellency of the surface can be maintained, and it is possible to prevent ice and snow from adhering to members installed outdoors, such as power transmission lines, antennas, and roofs.

[0008]

Next, a specific configuration of the present invention will be described. In one embodiment of the present invention, as shown in FIG. 1, a surface containing a photocatalyst particle, a silicone, and a substance for preventing photo-catalyzed hydrophilicity of photocatalyst such as cobalt or a cobalt compound on the surface of a substrate. A layer is formed. In another embodiment of the present invention, as shown in FIG.
A layer containing photocatalyst particles and a water-repellent silicone is formed on the surface of the substrate, and at least a part of the surface of the layer is hydrophilic by photoexcitation of a photocatalyst of a water-repellent silicone such as cobalt or a cobalt compound. The substance to prevent the conversion is fixed.

A photocatalyst has an energy greater than the energy gap between the conduction band and the valence band of the crystal.
A substance capable of generating conduction electrons and holes by excitation of electrons in the valence band (photoexcitation) when irradiated with light (excitation light) having a short wavelength (excitation light).
Oxides such as zeta-type titanium oxide, zinc oxide, tin oxide, ferric oxide, bismuth trioxide, tungsten trioxide and strontium titanate can be suitably used. When the photocatalytic oxide is an anatase type titanium oxide, zinc oxide, or strontium titanate, the light source used for photoexcitation of the photocatalyst is sunlight, indoor lighting, fluorescent lamp, mercury lamp, incandescent lamp, xenon. Lamps, high-pressure sodium lamps, metal halide lamps, BLB lamps and the like can be suitably used. When the photocatalytic oxide is tin oxide, a germicidal lamp, a BLB lamp, or the like can be suitably used.

The silicone has an average composition formula R _p SiO _{(4-p) / 2} (where R is a functional group comprising one or more monovalent organic groups, or a monovalent organic group) A resin represented by the following formula: X is an alkoxy group or a halogen atom, and p is a number satisfying 0 <p <2. Is available.

As the cobalt compound, a cobalt alloy, cobalt oxide, cobalt chloride, cobalt sulfate, cobalt iodide, cobalt bromide, cobalt acetate, cobalt chlorate, cobalt nitrate and the like can be suitably used.

The thickness of the surface layer is preferably set to 0.4 μm or less. Then, cloudiness due to irregular reflection of light can be prevented, and the surface layer becomes substantially transparent. Further, it is more preferable that the thickness of the surface layer be 0.2 μm or less. Then, it is possible to prevent the surface layer from being colored by light interference. Also, the thinner the surface layer, the better its transparency. Further, when the film thickness is reduced, the wear resistance of the surface layer is improved.

A metal such as Ag, Cu and Zn can be added to the surface layer. The surface layer to which the metal is added can kill bacteria and fungi attached to the surface even in a dark place.

Pt, Pd, Ru, Rh, I
A platinum group metal such as r or Os can be added.
The surface layer to which the metal is added can enhance the redox activity of the photocatalyst, and can improve the decomposability of organic contaminants and the decomposability of harmful gases and odors.

The substrate to which the present invention can be applied includes metals, ceramics, glass, plastic, wood, stone, cement, concrete, fiber, cloth, combinations thereof, and laminates thereof. It can be suitably used. Speaking of applicable base materials, roofing materials, building materials such as wall materials,
Building exteriors, building interiors, window frames, window glass, structural members, power lines, antennas, vehicle exteriors and paintings, exteriors of machinery and articles, dustproof covers and paintings, traffic signs, various display devices,
Advertising towers, noise barriers for roads, noise barriers for railways, bridges, exterior and coating of garages, tunnel interiors and coatings, insulators, solar battery covers, solar water heater collector covers, vinyl houses, vehicle lighting Light covers, housing equipment, toilets, bathtubs, washbasins, lighting fixtures, lighting covers, kitchen utensils, dishes, dishwashers, dish dryers, sinks, cooking ranges, kitchen hoods
And a film to be attached to the article.

Next, a surface layer containing photocatalyst particles, water-repellent silicone, and a substance for preventing the water-repellent silicone from becoming hydrophilic by photoexcitation of the photocatalyst is formed on the surface of the substrate. The method of manufacturing the water-repellent member described above will be described. The production method in this case is basically based on applying a coating composition on the surface of a substrate and curing the coating composition.

Here, the coating composition contains a precursor of silicon as an essential component of a substance for preventing the photocatalyst particles, cobalt or a cobalt compound or the like from becoming hydrophilic due to photoexcitation of the photocatalyst. Solvents such as ethanol and propanol, catalysts that promote hydrolysis of silicone precursors such as hydrochloric acid, nitric acid, sulfuric acid, acetic acid and maleic acid, and basic compounds such as tributylamine and hexylamine Silicon compounds such as acidic compounds such as aluminum, aluminum triisopropoxide and tetraisopropyl titanate;
And a surfactant for improving the dispersibility of the coating liquid such as a silane coupling agent.

As cobalt or a cobalt compound, a water-soluble cobalt compound is preferably used. As the water-soluble cobalt compound, for example, cobalt chloride, cobalt sulfate, cobalt iodide, cobalt bromide, cobalt acetate, cobalt chlorate, cobalt nitrate and the like can be suitably used.

[0019] Here silicone - The precursor emissions in the average composition formula _{R p SiX q O (4-} pq) / 2 ( wherein, R consists of one or more organic groups monovalent functional X or a functional group comprising two or more selected from a monovalent organic group and a hydrogen group, X is an alkoxy group or a halogen atom, and p and q are 0 <p <2, 0 <
a film-forming element composed of a siloxane represented by the following formula: q <4) or a general formula R _p SiX _4-p (where R is one or more monovalent organic groups) Wherein X is an alkoxy group or a halogen atom, and p is 1 or 2. A film-forming element comprising a hydrolyzable silane derivative to be
Can be suitably used.

Here, as the coating film forming element comprising the hydrolyzable silane derivative, methyltrimethoxysilane,
Methyltriethoxysilane, methyltripropoxysilane, methyltributoxysilane, ethyltrimethoxysilane, ethyltriethoxysilane, ethyltripropoxysilane, ethyltributoxysilane, phenyltrimethoxysilane, phenyltriethoxysilane, phenyltripropoxysilane, Phenyltributoxysilane,
Dimethyldimethoxysilane, dimethyldiethoxysilane, dimethyldipropoxysilane, dimethyldibutoxysilane, diethyldimethoxysilane, diethyldiethoxysilane, diethyldipropoxysilane, diethyldibutoxysilane, phenylmethyldimethoxysilane, phenylmethyldiethoxysilane, phenyl Methyldipropoxysilane, phenylmethyldibutoxysilane, n-propyltrimethoxysilane, n-propyltriethoxysilane, n-propyltripropoxysilane, n-propyltributoxysilane, γ-glycoxydoxypropyltrimethoxysilane, γ -Acryloxypropyltrimethoxysilane and the like can be suitably used.

The film-forming element composed of the siloxane includes partial hydrolysis and dehydration-condensation polymerization of the hydrolyzable silane derivative, or partial hydrolyzate of the hydrolyzable silane derivative, tetramethoxysilane, tetramethoxysilane and tetramethoxysilane. It can be produced by dehydration polycondensation with a partial hydrolyzate such as ethoxysilane, tetrapropoxysilane, tetrabutoxysilane, diethoxydimethoxysilane and the like.

The coating method of the coating composition includes spray coating, dip coating, flow coating, spin coating, roll coating, brush coating, and sponge. A method such as coating can be suitably used. As a curing method, it can be carried out by polymerizing by heat treatment, standing at room temperature, ultraviolet irradiation, or the like.

Next, a layer containing photocatalyst particles and water-repellent silicone is formed on the surface of the substrate, and at least a part of the surface of the layer is formed by photoexcitation of the photocatalyst of the water-repellent silicone. A method for manufacturing a water-repellent member to which a substance for preventing hydrophilicity is fixed will be described. The production method in this case is basically based on the photo-excitation of a photocatalyst such as cobalt or a cobalt compound after coating and curing a coating composition containing photocatalyst particles and a water-repellent silicone precursor. By applying a solution containing a substance for preventing hydrophilization and fixing the solution to the surface.

Here, the coating composition has photocatalyst particles and a precursor of a water-repellent silicone as essential components, and in addition, a solvent such as water, ethanol and propanol, hydrochloric acid, nitric acid, and the like. Catalysts that promote the hydrolysis of silica precursors such as sulfuric acid, acetic acid and maleic acid, basic compounds such as tributylamine and hexylamine, and acidic compounds such as aluminum triisopropoxide and tetraisopropyl titanate Such as a catalyst for curing a precursor of silica,
A surfactant such as a silane coupling agent for improving the dispersibility of the coating liquid may be added.

[0025] Here silicone - The precursor emissions in the average composition formula _{R p SiX q O (4-} pq) / 2 ( wherein, R consists of one or more organic groups monovalent functional X or a functional group comprising two or more selected from a monovalent organic group and a hydrogen group, X is an alkoxy group or a halogen atom, and p and q are 0 <p <2, 0 <
a film-forming element composed of a siloxane represented by the following formula: q <4) or a general formula R _p SiX _4-p (where R is one or more monovalent organic groups) Wherein X is an alkoxy group or a halogen atom, and p is 1 or 2. A film-forming element comprising a hydrolyzable silane derivative to be
Can be suitably used.

Here, as the coating film forming element comprising the hydrolyzable silane derivative, methyltrimethoxysilane,
Methyltriethoxysilane, methyltripropoxysilane, methyltributoxysilane, ethyltrimethoxysilane, ethyltriethoxysilane, ethyltripropoxysilane, ethyltributoxysilane, phenyltrimethoxysilane, phenyltriethoxysilane, phenyltripropoxysilane, Phenyltributoxysilane,
Dimethyldimethoxysilane, dimethyldiethoxysilane, dimethyldipropoxysilane, dimethyldibutoxysilane, diethyldimethoxysilane, diethyldiethoxysilane, diethyldipropoxysilane, diethyldibutoxysilane, phenylmethyldimethoxysilane, phenylmethyldiethoxysilane, phenyl Methyldipropoxysilane, phenylmethyldibutoxysilane, n-propyltrimethoxysilane, n-propyltriethoxysilane, n-propyltripropoxysilane, n-propyltributoxysilane, γ-glycoxydoxypropyltrimethoxysilane, γ -Acryloxypropyltrimethoxysilane and the like can be suitably used.

The film-forming element composed of the above-mentioned siloxane includes partial hydrolysis and dehydration-condensation polymerization of the above-mentioned hydrolyzable silane derivative, or partially hydrolyzate of the above-mentioned hydrolyzable silane derivative, tetramethoxysilane and tetramethoxysilane. It can be produced by dehydration polycondensation with a partial hydrolyzate such as ethoxysilane, tetrapropoxysilane, tetrabutoxysilane, diethoxydimethoxysilane and the like.

The coating method of the coating composition includes spray coating, dip coating, flow coating, spin coating, roll coating, brush coating, and sponge. A method such as coating can be suitably used. As a curing method, it can be carried out by polymerizing by heat treatment, standing at room temperature, ultraviolet irradiation, or the like.

A method for applying a solution containing a substance for preventing the photocatalyst from becoming hydrophilic by photoexcitation such as cobalt or a cobalt compound, and fixing the solution on the surface includes, for example, cobalt chloride, cobalt sulfate, cobalt iodide, bromide, and the like. cobalt,
Spray coating method, dip coating method, flow coating method, spin coating method, roll coating method, brushing water-soluble cobalt compounds such as cobalt acetate, cobalt chlorate and cobalt nitrate Coating, sponge coating, etc., photoreduction, heat treatment, alcohol
This is performed by fixing by a method such as reduction using a sacrificial oxidizing agent such as toluene.

[0030]

【Example】

Reference example. Anatase type titanium oxide sol (Nissan Chemical, TA
-15, nitric acid peptized type, pH = 1), silica sol (Nippon Synthetic Rubber, Glasca A solution, pH = 4), methyltrimethoxysilane (Nippon Synthetic Rubber, Glasca B solution) and ethanol are mixed. The coating liquid obtained by stirring for 2 to 3 hours was applied on a 5 × 10 cm square glazed tile base material (TOTOKIKI, AB02E11) by spray coating.
A heat treatment was performed at 200 ° C. for 15 minutes to obtain a # 1 sample having a surface layer formed of 11 parts by weight of anatase type titanium oxide particles, 6 parts by weight of silica, and 5 parts by weight of silicone. The contact angle of the # 1 sample with water was 92 °. Here, the contact angle with water was evaluated using a contact angle measuring device (Kyowa Interface Science, CA-X150) by the contact angle with water 30 seconds after a water droplet was dropped from the micro syringe. Next, the surface of the # 1 sample was irradiated for one day with an ultraviolet illuminance of 0.3 mW / cm ² using an ultraviolet light source (Sankyo Electric, Black Light Blue (BLB) fluorescent lamp) to obtain a # 2 sample. As a result, the contact angle with water of the # 2 sample was hydrophilized to 0 °. Next, # 1 sample and #
One sample was irradiated with a mercury lamp at an ultraviolet irradiance of 22.8 mW / cm ² for 2 hours, and the surface of each of the # 3 samples obtained was subjected to Raman spectroscopic analysis. As a result, a peak of methyl group observed on the surface of sample # 1 was not observed in sample # 3, but a peak of hydroxyl group was observed instead. From the above,
It can be seen that the organic group bonded to the silicon atom in the silicon molecule on the surface of the film by the photoexcitation of the anatase type titanium oxide which is a photocatalyst is replaced by a hydroxyl group and becomes hydrophilic.

Embodiment 1 Anatase type titanium oxide sol (Nissan Chemical, TA-15, peptized nitrate, pH = 1),
Silica sol (Nippon Synthetic Rubber, Glasca A solution, pH = 4)
And methyltrimethoxysilane (Nippon Synthetic Rubber, Glasca B solution), cobalt chloride hexahydrate, and ethanol, and stirred for 2-3 hours. -Apply on a 5 x 10 cm square glazed tile base material (TOTOKI KIKI, AB02E11) at 200 ° C
And heat-treated for 15 minutes in anatase type titanium oxide particles 11
A # 4 sample was obtained in which a surface layer consisting of 6 parts by weight of silica, 6 parts by weight of silica, 5 parts by weight of silicon, and 0.2 parts by weight of cobalt was formed. The contact angle of the # 4 sample with water was 97 °. Here, the contact angle with water is measured using a contact angle measuring device (Kyowa Interface Science, CA-X).
150), the contact angle with water was evaluated 30 seconds after a water drop was dropped from the micro syringe. Next, an ultraviolet light source (Sankyo Electric, Black Light Blue-
(BLB) fluorescent lamp) for 1 day at an ultraviolet illuminance of 0.3 mW / cm ² to obtain a # 5 sample. As a result, # 5
The contact angle of the sample with water was still 96 °, maintaining water repellency.
Therefore, it can be understood from the above that the hydrophilicity of the silicon on the surface of the coating film due to the photoexcitation of the anatase type titanium oxide as a photocatalyst is inhibited by cobalt. This is considered because the substitution of the hydroxyl group for the organic group bonded to the silicon atom in the silicon molecule on the surface of the coating is inhibited by cobalt.

Embodiment 2 FIG. Anatase type titanium oxide sol (Nissan Chemical, TA-15, peptized nitrate, pH = 1),
Silica sol (Nippon Synthetic Rubber, Glasca A solution, pH = 4)
, Methyltrimethoxysilane (Nippon Synthetic Rubber, Glasca B solution) and ethanol were mixed, and the mixture was stirred for 2 to 3 hours to obtain a coating solution by spray coating.
× 10cm square glazed tile base material (TOTOKI, AB02E
11) Coated on top and heat-treated at 200 ° C. for 15 minutes to obtain 11 parts by weight of anatase type titanium oxide particles, 6 parts by weight of silica,
A surface layer consisting of 5 parts by weight of silicone was formed. Further, 0.3 g of an aqueous solution of cobalt chloride hexahydrate having a cobalt metal concentration of 50 μmol / g was applied thereon, and then an ultraviolet illuminance of 0.4 mW / The cobalt was fixed on the substrate by irradiating it with ultraviolet rays of cm ² for 10 minutes to obtain a # 6 sample. #
The contact angle of 6 samples with water was 96 °. Here, the contact angle with water is measured using a contact angle measuring device (Kyowa Interface Science, CA-X15).
0), and after adding a water drop from the micro syringe, 3
Evaluation was made based on the contact angle with water after 0 seconds. Next, an ultraviolet light source (Sankyo Electric, Black Light Blue- (B
(LB) Fluorescent lamp) to irradiate with an ultraviolet illuminance of 0.3 mW / cm ² for 1 day to obtain a # 7 sample. As a result, the contact angle of the # 7 sample with water was still 94 °, maintaining water repellency. Therefore, it can be understood from the above that the hydrophilicity of the silicon on the surface of the coating film due to the photoexcitation of the anatase type titanium oxide as a photocatalyst is inhibited by cobalt. this is,
It is considered that the replacement of the organic group bonded to the silicon atom in the silicon molecule on the surface of the coating film with the hydroxyl group is inhibited by cobalt.

[0033]

According to the present invention, a surface containing a photocatalyst particle, a water-repellent silicone and a substance for preventing the water-repellent silicone from becoming hydrophilic by photoexcitation of the photocatalyst is provided on the surface of the substrate. A layer containing photocatalyst particles and a water-repellent silicone is formed on the surface of the substrate so that a layer is formed, and at least a part of the surface of the layer is coated with the water-repellent silicone. By fixing a substance for preventing the photocatalyst from becoming hydrophilic by photoexcitation, the surface of the member can maintain water repellency for a long period of time.

[Brief description of the drawings]

FIG. 1 is a diagram showing a surface structure of a member according to the present invention.

FIG. 2 is a diagram showing another surface structure of the member according to the present invention.

Claims (5)

[Claims] 1. A surface layer containing photocatalyst particles, water-repellent silicone, and a substance for preventing the water-repellent silicone from becoming hydrophilic by photoexcitation of the photocatalyst is formed on the surface of a substrate. A water-repellent member characterized in that: 2. A layer containing photocatalyst particles and a water-repellent silicone is formed on the surface of a base material, and at least a part of the surface of the layer is made hydrophilic by the photoexcitation of the photocatalyst of the water-repellent silicone. A water-repellent member, on which a substance for preventing the formation of a water-repellent material is fixed. 3. The water repellent member according to claim 1, wherein the substance for preventing the photocatalyst from becoming hydrophilic by photoexcitation is cobalt or a cobalt compound. Wherein (a) the average composition formula _{R p SiX q O (4-} pq) / 2 ( wherein, R is one or of two or more functional groups of the monovalent organic group, or a monovalent X is an alkoxy group or a halogen atom, and p and q are 0 <p <2, 0 <
q <4 which satisfies q <4), which forms a silicone resin film when cured, and (b) dispersed in the film forming element A water-repellent coating composition comprising the photocatalyst particles thus obtained and (c) cobalt or a cobalt compound. 5. A compound of the general formula R _p SiX _4-p (wherein R is a functional group comprising one or more monovalent organic groups, or a monovalent organic group and a hydrogen group. X is an alkoxy group or a halogen atom, and p is 1 or 2), and is a coating film forming element comprising a hydrolyzable silane derivative represented by the following formula: And curing to form a silicone resin film, (b) photocatalyst particles dispersed in the film forming element, and (c) cobalt or a cobalt compound. Water repellent coating composition.