Water-repellent coating film, coating composition, and water-absorbent material

Abstract

The water-repellent coating is formed on the surface of the water-absorbent substrate that is permeated with oil. , nothing Nanoparticles and Water- and oil-repellent resin are contained in a mass ratio of 50:50 to 90:10.

Description

Water-repellent coating, coating composition and water-absorbent material

[0001] The present disclosure relates to a water-repellent coating, a coating composition, and a water-absorbent material having water repellency.

[0002] Water-repellent coatings with water-repellent properties have been known. When highly water-absorbent substrates, such as wood, mortar, or ceramics, which are often used for building materials or exterior walls, absorb water, the substrate expands and contracts due to the absorption of water, resulting in cracks or even fractures. For this reason, highly water-absorbent substrates must be prevented from invading the interior while allowing the invaded moisture to escape to the exterior. Generally, such highly water-absorbent substrates are covered with a coating film formed from a urethane resin composition or a photocurable resin composition to protect the surface. Patent Document 1 discloses a water- and oil-repellent wooden building material using a fluorine-containing acrylic ester compound, finely divided silica, a photopolymerizable oligomer, a reactive monomer, and a photopolymerization initiator. Patent Document 2 also discloses a Michael-curable water-repellent coating composition containing a silicone acrylic block polymer and an α,β-unsaturated carbonyl group-containing material.

[0003] Japanese Patent No. 4985560 Japanese Patent Laid-Open No. 2004-359858

[0004] However, since Patent Document 1 uses a photocurable resin composition, curing with electron beams or ultraviolet light is required to form a water- and oil-repellent coating, which makes the formation of the water- and oil-repellent coating time-consuming and labor-intensive. Furthermore, although the coating of Patent Document 2 does not require curing with electron beams or ultraviolet light, it takes a long time to cure at room temperature and requires heating to shorten the curing time, making it unsuitable for large substrates. Furthermore, the formed coating is impermeable to water, so it cannot be dried when the substrate is wet.

[0005] The present disclosure has been made to solve the above-mentioned problems, and aims to provide a water-repellent coating, a coating composition, and a water-absorbent material that can easily exhibit moisture permeability without requiring curing by electron beams or ultraviolet rays or curing by heating.

[0006] [Correction based on Rule 91 04.07.2023] The water-repellent coating according to the present disclosure is formed on the surface of a water-absorbent substrate that has been permeated with oil, and contains inorganic nanoparticles and a water- and oil-repellent resin in a mass ratio of 50:50 to 90:10.

[0007] [Correction based on Rule 91 04.07.2023] According to the present disclosure, oil is impregnated into a water-absorbent substrate, and inorganic nanoparticles and a water- and oil-repellent resin are contained on the surface of the water-absorbent substrate in a mass ratio of 50:50 to 90:10. This makes it possible to easily form a water-repellent coating with moisture permeability on the water-absorbent substrate.

[0008] Fig. 1 is a cross-sectional view showing an article according to embodiment 1. Fig. 2 is a cross-sectional view showing an article immediately after a water-repellent coating according to embodiment 1 has been applied. Fig. 3 is a cross-sectional view showing an article after oil has penetrated according to embodiment 1. Fig. 4 is a cross-sectional view showing an article immediately after a water-repellent coating according to embodiment 2 has been applied. Fig. 5 is a cross-sectional view showing an article after oil has penetrated according to embodiment 2.

[0009] Hereinafter, embodiments of the water-repellent coating, coating composition, and water-absorbing material of the present disclosure will be described with reference to the drawings. Note that the present disclosure is not limited to the embodiments described below. Furthermore, the dimensional relationships between the components in the drawings may differ from those in reality. Furthermore, in the following description, terms indicating directions will be used as appropriate to facilitate understanding of the present disclosure, but these terms are for the purpose of explaining the present disclosure and do not limit the present disclosure. Examples of terms indicating directions include "up," "down," "right," "left," "front," and "rear."

[0010] Embodiment 1. Figure 1 is a cross-sectional view showing an article according to embodiment 1. In this embodiment 1, the article is constructed by applying a water-repellent coating 2 to the surface of a water-absorbent substrate 1. The water-repellent coating 2 contains inorganic nanoparticles 3 and a water- and oil-repellent resin 4. The water-repellent coating 2 may also contain oil 5. Although the water- and oil-repellent resin 4 exhibits water repellency even when used alone, when the inorganic nanoparticles 3 are mixed in, minute irregularities are formed on the surface. This improves water repellency and results in ultra-water repellency.

[0011] Furthermore, by appropriately adjusting the amount of inorganic nanoparticles 3 mixed, the water-repellent coating 2 becomes porous, containing fine pores, and exhibits moisture permeability, allowing water vapor to pass through. Because the water-repellent coating 2 is ultra-water-repellent, even when liquid water comes into contact with the coating, water does not penetrate or adhere to the coating, preventing the water-absorbent substrate 1 from getting wet. Furthermore, because the water-repellent coating 2 is moisture-permeable, it does not prevent water vapor from entering or leaving the water-absorbent substrate 1. When a typical water-repellent paint is applied, it prevents the water-absorbent substrate 1 from getting wet, but inhibits the entry and exit of water vapor. The water-repellent coating 2 of the first embodiment inhibits water from adhering to or wetting the surface of the water-absorbent substrate 1, while maintaining functions that utilize the moisture absorption of the water-absorbent substrate 1, such as controlling indoor air humidity.

[0012] By appropriately adding inorganic nanoparticles 3 to the water-repellent coating 2, dust adhesion to the water-repellent coating 2 is also suppressed. If the water- and oil-repellent resin 4 does not contain a sufficient amount of inorganic nanoparticles 3, when the water-absorbent substrate 1 has surface irregularities or pores exceeding 10 μm, the water-repellent coating 2 will simply cover the surface of the irregularities or pores with a thin film, without significantly changing the shape of the irregularities or pores. In this state, even if the water-absorbent substrate 1 is coated with the water-repellent coating 2, water droplets will penetrate the pores and wet the water-absorbent substrate 1. Furthermore, dust and other particles can easily become trapped or get trapped in the irregularities or pores of the water-repellent coating 2, resulting in the adhesion of dust and other particles. In the present embodiment 1, because the inorganic nanoparticles 3 are appropriately mixed into the water-repellent coating 2, even when the water-repellent coating 2 is applied to a water-absorbent substrate 1 with irregularities or pores, the water-repellent coating 2 will be formed on the surface of the water-absorbent substrate 1, reducing the irregularities and blocking the pores. This achieves a dust adhesion suppression effect.

[0013] (Water-absorbent substrate 1) As the water-absorbent substrate 1, a highly water-absorbent substrate such as wood, tile, brick, stone, mortar, concrete, soil, clay, plaster, gypsum, gypsum board, rock wool sound-absorbing board, fabric, nonwoven fabric, paper, etc. is used. In particular, it is highly effective if the surface of the water-absorbent substrate 1 is not a smooth surface with a gloss, but has irregularities with an arithmetic mean roughness Ra of several μm or more. Furthermore, the irregularities on the surface have an anchoring effect, which improves adhesion to the water-repellent coating 2, resulting in a durable water-repellent coating 2. As such, the water-absorbent substrate 1 may be made of either an inorganic material or an organic material.

[0014] (Inorganic Nanoparticles 3) The average particle size of the primary particles of the inorganic nanoparticles 3 is 2 nm or more and 20 nm or less, and preferably 5 nm or more and 15 nm or less. If the average particle size of the primary particles of the inorganic nanoparticles 3 is less than 2 nm, it becomes difficult to prepare the coating composition, and the water repellency or moisture permeability of the water-repellent coating 2 becomes insufficient. On the other hand, if the average particle size of the primary particles of the inorganic nanoparticles 3 exceeds 20 nm, appropriate fine irregularities are not formed on the surface of the water-repellent coating 2, resulting in insufficient water repellency, and the surface irregularities of the water-repellent coating 2 become too large, making it easy for dust to adhere. The average particle size of the primary particles of the inorganic nanoparticles 3 is a value measured by observation with an electron microscope.

[0015] The use of inorganic nanoparticles 3, particularly those in which primary particles are moderately aggregated or bonded, can provide the effects of improving water repellency, improving moisture permeability, and suppressing dust adhesion. The average particle size of the aggregated or bonded inorganic nanoparticles 3 is preferably from 2 to 50 times the average particle size of the primary particles. More preferably, the average particle size of the aggregated or bonded inorganic nanoparticles 3 is from 5 to 20 times the average particle size of the primary particles. If the average particle size of the aggregated or bonded inorganic nanoparticles 3 is less than twice the average particle size of the primary particles, the water-repellent coating 2 formed will have high water repellency, but will not provide the effects of improving moisture permeability and suppressing dust adhesion. If the average particle size of the aggregated or bonded inorganic nanoparticles 3 is more than 50 times the average particle size of the primary particles, the water-repellent coating 2 formed will be brittle and easily breakable, and will lose its water repellency in a short period of time when exposed to rain, etc. The average particle size of the aggregated or bonded inorganic nanoparticles 3 here is a value obtained by mixing them in an amount of 5 mass % or less into a solvent used to prepare the coating composition, performing a dispersion treatment equivalent to the method used to prepare the coating composition, and measuring by a laser diffraction / scattering method.

[0016] Examples of inorganic nanoparticles 3 include silica, alumina, zirconia, and titania. Because the surfaces of inorganic nanoparticles 3 are generally hydrophilic, it is preferable to use inorganic nanoparticles that have been subjected to a hydrophobic treatment. Examples of hydrophobic treatment methods include reacting inorganic nanoparticles 3 with a silylating agent such as hexamethyldisilazane, a silane coupling agent, or the like, and mixing inorganic nanoparticles 3 with a low-molecular-weight silicone compound or a fluorocarbon compound and adsorbing them to the surface. The former method is preferred because it results in highly stable hydrophobicity. Instead of hydrophobizing inorganic nanoparticles 3, a method of reducing their hydrophilicity by heat treatment is also preferred. Heating inorganic nanoparticles 3 to 150°C or higher, preferably 300°C or higher, reduces their hydrophilicity and facilitates the development of water-repellent properties in the water-repellent coating 2. In terms of the shape of inorganic nanoparticles 3, non-spherical nanoparticles such as non-spherical silica, fumed silica, and fumed alumina prepared by precipitation or liquid-phase synthesis are particularly preferred, as their original particle shape is such that primary particles are appropriately bonded.

[0017] [Correction based on Rule 91 04.07.2023] (Water- and Oil-Repellent Resin 4) The water- and oil-repellent resin 4 may be a fluororesin, or a resin such as silicone resin, acrylic resin, urethane resin, or epoxy resin, whose surface is rendered water-repellent by adding a fluorine-containing side chain or by mixing in a fluorine-based additive. Among these, fluororesins and silicone resins are preferred due to their excellent durability and water repellency. The mixing ratio of inorganic nanoparticles 3 to water- and oil-repellent resin 4 is preferably 50:50 to 90:10 by mass in the dry state. More preferably, the mixing ratio of inorganic nanoparticles 3 to water- and oil-repellent resin 4 is 60:40 to 80:20. If the inorganic nanoparticles 3 are too low, even if water repellency is achieved, the effects of improving moisture permeability and suppressing dust adhesion cannot be achieved. If the inorganic nanoparticles 3 are too high, the water-repellent coating 2 becomes brittle and peels off after a short period of time when exposed to outdoor conditions.

[0018] (Oil 5) Silicone oil or fluorine oil is preferably used as oil 5. Examples of silicone oil that can be used include dimethyl silicone oil, amino-modified silicone oil, alkyl-modified silicone oil, epoxy-modified silicone oil, and higher fatty acid-modified silicone oil. Examples of fluorine oil include hydrofluoroether, perfluoropolyether, and chlorotrifluoroethylene. The boiling point of oil 5 is preferably 120°C or higher. These oils 5 are highly chemically stable and have high water repellency, and are therefore preferably used in this embodiment 1.

[0019] Reactive oils are also preferably used as the oil 5. Examples of oils known as drying oils that solidify through air oxidation include linseed oil, tung oil, mustard oil, perilla oil, walnut oil, perilla oil, safflower oil, and sunflower oil. If a non-reactive oil 5 is used, the oil 5 that penetrates the water-absorbent substrate 1 gradually diffuses from the surface to the interior of the water-absorbent substrate 1, potentially reducing the water-repellent effect of the oil 5. If an oil 5 that undergoes air oxidation is used, the oil 5 solidifies after the water-repellent coating 2 is formed, thereby suppressing subsequent diffusion of the oil 5. Furthermore, in addition to making the water-absorbent substrate 1 water-repellent, if the water-absorbent substrate 1 is made of a flexible material such as wood, the solidification also has the effect of improving its strength. These effects enable the realization of a water-repellent coating 2 that is stable over a long period of time.

[0020] The mass ratio of oil 5 to water- and oil-repellent resin 4 in the coating composition for forming water-repellent coating 2 is preferably from 0% to 250% by mass, and more preferably from 0.5% to 100% by mass. If the mass ratio of oil 5 is too large, oil 5 may remain in water-repellent coating 2, reducing the effects of improving water repellency and inhibiting dust adhesion, or may result in excessive voids in water-repellent coating 2 after migration of oil 5, reducing the effects of improving coating strength and inhibiting dust adhesion.

[0021] (Water-repellent coating 2) The water-repellent coating 2 is formed by applying a coating composition consisting of inorganic nanoparticles 3, a water-repellent and oil-repellent resin 4, and a solvent to the water-absorbent substrate 1. The total amount of the inorganic nanoparticles 3 and the water-repellent and oil-repellent resin 4 is preferably 0.1% by mass or more and 10% by mass or less, and more preferably 0.5% by mass or more and 5% by mass or less, relative to the coating composition. If the total amount of the inorganic nanoparticles 3 and the water-repellent and oil-repellent resin 4 is less than 0.1% by mass, when applied to the water-absorbent substrate 1, a water-repellent coating 2 of sufficient thickness may not be formed on the surface of the water-absorbent substrate 1, and sufficient water repellency may not be obtained. On the other hand, if the total amount of the inorganic nanoparticles 3 and the water-repellent and oil-repellent resin 4 exceeds 10% by mass, adhesion to the water-absorbent substrate 1 decreases, and the water-repellent coating 2 is likely to peel off. Furthermore, cracks may occur, making it easier for water to penetrate and dust to adhere.

[0022] The coating composition here has a lower concentration than general paints that are applied to surfaces other than the water-absorbent substrate 1. As a result, even though the coating composition contains a large amount of inorganic nanoparticles 3, the water- and oil-repellent resin 4 can sufficiently penetrate into the water-absorbent substrate 1, ensuring the adhesion of the water-repellent coating 2.

[0023] (Solvent) In the present embodiment 1, a solvent capable of dissolving the water- and oil-repellent resin 4 is required. For example, fluorine-based solvents such as hydrofluoroether (HFE), hydrofluorocarbon (HFC), and perfluoropolyether (PFPE), ketone-based solvents such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and diisobutyl ketone, ester-based solvents such as ethyl acetate and butyl acetate, carbonate-based solvents such as dimethyl carbonate and diethyl carbonate, ether-based solvents such as diisopropyl ether, methyl cellosolve, and ethyl cellosolve, and glyme-based solvents such as monoglyme and ethyl glyme are preferably used. As a dilution solvent, alcohol-based solvents such as ethanol, 2-propanol, and butanol, and hydrocarbon-based solvents such as toluene and xylene may also be used.

[0024] A solvent capable of dissolving the inorganic nanoparticles 3 and the water- and oil-repellent resin 4 is mixed, and the mixture is dispersed using a disperser such as a homogenizer, dissolver, or high-pressure disperser. After a certain period of time has passed, the dispersion of the inorganic nanoparticles 3 is mixed with a solution of the water- and oil-repellent resin 4 and oil 5 and stirred to form a homogeneous liquid. This results in the preparation of a coating composition. Another preferred method involves mixing the inorganic nanoparticles 3, a portion of the water- and oil-repellent resin 4, and a solvent capable of dissolving the water- and oil-repellent resin 4 and dispersing them, and after a certain period of time, the remaining solution of the water- and oil-repellent resin 4 is mixed with oil 5 and stirred to form a homogeneous liquid. The coating composition prepared in this manner, when used to form a water-repellent coating 2, can achieve particularly good effects of improving moisture permeability and suppressing dust adhesion.

[0025] The following method is also preferred as a method for preparing a coating composition. A high-concentration mixture of inorganic nanoparticles 3, a water- and oil-repellent resin 4, a solvent capable of dissolving the water- and oil-repellent resin 4, and oil 5 is prepared at a concentration at least twice that of the liquid used for coating. This mixture is then dispersed using the aforementioned disperser and diluted with the solvent to form a coating composition. The coating composition prepared in this manner provides particularly excellent super-water repellency and durability when formed into a water-repellent coating 2. While the oil 5 is preferably dissolved in the solvent in the coating composition, it may also be present as fine oil droplets. By being present as oil droplets, the oil 5 can efficiently penetrate the water-absorbent substrate 1 during application, and fine pores are formed in the formed water-repellent coating 2.

[0026] The coating composition is applied by spray coating, brush coating, roller bucket coating, etc. The thickness of the water-repellent coating 2 is 100 cm ２ It is preferable to adjust the adhesion weight of the water- and oil-repellent resin 4 and the inorganic nanoparticles 3 after drying to 0.03 g or more and 1.2 g or less per coating. If the adhesion weight of the water- and oil-repellent resin 4 and the inorganic nanoparticles 3 is less than 0.03 g, sufficient water repellency may not be obtained. On the other hand, if the adhesion weight of the water- and oil-repellent resin 4 and the inorganic nanoparticles 3 exceeds 1.2 g, the water repellency may decrease due to friction, or the water-repellent coating 2 may be easily peeled off.

[0027] The water-repellent coating 2 thus formed exhibits high water repellency, with a water contact angle exceeding 140°. When a large amount of oil 5 is used, the water contact angle may be approximately 120° immediately after application, but after several hours, it becomes ultra-water-repellent, exceeding 140°. As the oil 5 migrates to the water-absorbent substrate 1 over time, the contact angle changes, resulting in high water repellency. Here, the water contact angle is measured by the following method. A water droplet of approximately 5 μL is dropped onto the surface of the water-repellent coating 2 from the tip of a PTFE (polytetrafluorethylene)-coated needle with an inner diameter of 0.1 mm, and the contact angle is measured using a contact angle meter (CX-150 model, manufactured by Kyowa Interface Science Co., Ltd.).

[0028] When the water-absorbent substrate 1 is an inorganic material such as brick or mortar, the oil 5 covers the surfaces of the inorganic fine particles that make up the substrate and fills in gaps, thereby suppressing the hydrophilicity of the water-absorbent substrate 1. The water- and oil-repellent resin 4 has a similar function, but the oil 5 can exert a greater effect by acting on deeper parts of the water-absorbent substrate 1.

[0029] When the water-absorbent substrate 1 is an organic material such as wood or paper, the oil 5 has the same effect as when the substrate is made of an inorganic material, covering the surface of the material constituting the substrate and filling in gaps. For organic materials, the oil 5 also has the effect of penetrating into the material. Organic materials often swell when they absorb moisture, causing a decrease in strength and a change in shape, but the penetration of the oil 5 can suppress this decrease in strength and change in shape.

[0030] FIG. 2 is a cross-sectional view showing an article immediately after application of the water-repellent coating 2 according to the first embodiment. Next, the function of the oil 5 will be described in detail. As shown in FIG. 2, immediately after application of the water-repellent coating 2, the oil 5 does not dissolve in the water-repellent and oil-repellent resin 4 and forms oil droplets. Note that a trace amount of oil 5 may also be contained in the inorganic nanoparticles 3 or the water-repellent and oil-repellent resin 4. The oil 5 has a high affinity for the water-absorbent substrate 1, which has a higher surface energy than the water-repellent and oil-repellent resin 4 and the inorganic nanoparticles 3. Therefore, even if the oil 5 is contained in the water-repellent coating 2 immediately after application, as shown in FIG. 2, a large portion of the oil 5 will migrate from the water-repellent coating 2 to the water-absorbent substrate 1 over time.

[0031] Figure 3 is a cross-sectional view showing the article according to embodiment 1 after penetration of oil 5. As shown in Figure 3, when oil 5 is absorbed into the water-absorbent substrate 1, the portion of the water-absorbent substrate 1 in contact with the water-repellent coating 2 contains oil component 6. As the oil 5 is absorbed into the water-absorbent substrate 1, voids remain in the water-repellent coating 2 where the oil 5 was present. When the oil 5 contained in the inorganic nanoparticles 3 or the water- and oil-repellent resin 4 migrates to the water-absorbent substrate 1, microvoids are generated in those portions.

[0032] As described above, the water-repellent coating 2 of the first embodiment has a micro-irregular surface and is porous due to the inorganic nanoparticles 3 and the water- and oil-repellent resin 4. Even when dust comes into contact with the coating, it does not adhere to the coating, and the intermolecular forces acting on the dust are weak, making it difficult for the dust to adhere. This, combined with the fact that large protrusions or recesses are unlikely to form, results in dust-resistant properties. The micro-pores created by the migration of the oil 5 have the effect of improving the super-water-repellent properties. Furthermore, the micro-pores created by the migration of the oil 5 in the water-repellent coating 2 improve the water vapor permeability of the water-repellent coating 2, improving its moisture permeability. Furthermore, the micro-irregularities improve the super-water-repellent properties and the effect of suppressing dust adhesion. When applied to a non-water-absorbent substrate, the water-repellent coating 2 retains the oil 5, which can make it easier for dust and other particles to adhere. However, in the first embodiment, the water-repellent coating 2 is applied to a water-absorbent substrate 1, so this problem does not occur.

[0033] When oil 5 migrates to the water-absorbent substrate 1, it can prevent the water-absorbent substrate 1 from absorbing water and swelling when in contact with water or in a high-humidity environment, which can cause peeling of the water-repellent coating 2. Even in the absence of oil 5, the water-absorbent substrate 1 has super water-repellency and is therefore effective in preventing water from penetrating into the water-absorbent substrate 1, but the inclusion of oil 5 can further prevent water from penetrating.

[0034] [Correction based on Rule 91 04.07.2023] According to the present embodiment 1, oil 5 is permeated into water-absorbent substrate 1, and inorganic nanoparticles 3 and water- and oil-repellent resin 4 are contained on the surface of water-absorbent substrate 1 at a mass ratio of 50:50 to 90:10. Therefore, water-repellent coating 2 having moisture permeability can be easily formed on water-absorbent substrate 1.

[0035] Conventionally, water- and oil-repellent wood building materials have been known that use fluorine-containing acrylic ester compounds, fine silica particles, photopolymerizable oligomers, reactive monomers, and photopolymerization initiators. However, because these are photocurable resin compositions, they require curing with electron beams or ultraviolet light to form a water- and oil-repellent coating, which makes the formation of the water- and oil-repellent coating time-consuming and labor-intensive. Also known are Michael-cured water-repellent coating compositions containing silicone-acrylic block polymers and α,β-unsaturated carbonyl group-containing compounds. However, while these coatings do not require curing with electron beams or ultraviolet light, they require long curing times at room temperature and require heating to shorten the curing time, making them unsuitable for large substrates. Neither coating provides a stain-resistant effect, such as suppressing the adhesion of dust and other particles, and may even promote the adhesion of dust and other particles. In contrast, the present embodiment 1 provides a water-repellent coating 2 that is easily moisture-permeable and does not require curing with electron beams or ultraviolet light or heating, and also combines waterproofness, stain resistance, and moisture permeability.

[0036] Embodiment 2. Figure 4 is a cross-sectional view showing an article immediately after application of a water-repellent coating 2 according to embodiment 2, and Figure 5 is a cross-sectional view showing an article after penetration of oil 5 according to embodiment 2. This embodiment 2 differs from embodiment 1 in that the water-absorbent substrate 7 is porous. In this embodiment 2, parts that are common to embodiment 1 are given the same reference numerals and their description will be omitted, and the following description will focus on the differences from embodiment 1.

[0037] As shown in Figure 4, immediately after the water-repellent coating 2 is applied, the oil 5 does not dissolve in the water- and oil-repellent resin 4 and forms oil droplets. Then, as shown in Figure 5, when the oil 5 is absorbed into the water-absorbent substrate 7, the portion of the water-absorbent substrate 7 in contact with the water-repellent coating 2 contains oil components 8. Here, since the coating composition contains inorganic nanoparticles 3, it forms the water-repellent coating 2 on the surface without penetrating into the porous surface during application. In the second embodiment, as in the first embodiment, effects such as improved water repellency of the water-repellent coating 2, improved moisture permeability, improved adhesion in contact with water or in a high-humidity environment, and prevention of moisture penetration into the water-absorbent substrate 7 are obtained.

[0038] Hereinafter, the embodiment will be specifically described with reference to examples and comparative examples, but the embodiment is not limited to the following examples.

[0039] [Example 1] Silica nanoparticles hydrophobized with dimethyldichlorosilane (AEROSIL R 976, manufactured by Nippon Aerosil Co., Ltd., average particle size in solvent: 12 nm) were used as inorganic nanoparticles 3, Fluorosurf FS1610TH (Fluorotechnology) was used as water- and oil-repellent resin 4, and the fluorine-based solvent Asahiklin (manufactured by AGC Chemical Co., Ltd.) was used as the solvent. The mass ratio of inorganic nanoparticles 3 to water- and oil-repellent resin 4 was 2:1, and the coating composition was adjusted so that the total of inorganic nanoparticles 3 and water- and oil-repellent resin 4 was 2 mass%. Dimethyl silicone oil was added to this coating composition as oil component 6 so that it was 0.5 mass% of the water- and oil-repellent resin 4. A coating composition was obtained by passing these through an atomization device.

[0040] Example 2 The same procedure as in Example 1 was carried out except that Oil 5 was added so that the ratio was 1 mass %.

[0041] Example 3 The same procedure as in Example 1 was carried out except that Oil 5 was added so that the ratio was 5%.

[0042] Example 4 The same procedure as in Example 1 was carried out except that Oil 5 was added so that the ratio was 10%.

[0043] Example 5 The same procedure as in Example 1 was carried out except that Oil 5 was added so that the ratio was 20%.

[0044] Example 6 The same procedure as in Example 1 was carried out except that Oil 5 was added so that the ratio was 50%.

[0045] Example 7 The same procedure as in Example 1 was carried out except that Oil 5 was added so that the ratio was 80%.

[0046] Example 8 To the composition of Example 1, hardened oil (boiled linseed oil) was added as oil 5 so that the amount was 1% of the water- and oil-repellent resin 4.

[0047] Example 9 The same procedure as in Example 1 was carried out except that the proportion of Oil 5 was changed to 0%.

[0048] Comparative Example 1 Only the water- and oil-repellent resin 4 was used as the coating composition.

[0049] Comparative Example 2 The coating composition consisted of only Oil 5, dimethyl silicone oil.

[0050] [Evaluation substrate and coating formation method] The coating compositions of Examples 1 to 9 and Comparative Example 1 were applied with a brush to a water-absorbent substrate 7 made of wood (plain cedar wood) and dried at room temperature for 10 minutes to obtain a water-repellent coating 2. In Comparative Example 2, the coating was obtained by applying the coating with a brush and then drying for 20 minutes with hot air from a dryer.

[0051] [Sliding Angle] Examples 1 to 9 were super water-repellent, with water contact angles exceeding 140°. The water-repellency evaluation here was performed by dropping 15 μL of water onto the coated surface using a micropipette, tilting the substrate at 5° increments of 1°, 5°, 10°, and 15° to measure the tilt angle at which the water began to slide, and evaluating the sliding angle as the average value of three measurements.

[0052] [Stain resistance] Stain resistance was evaluated by observing dust adhesion using Kanto loam, a JIS test powder. The stain resistance of uncoated wood that had not absorbed water was rated as 5, and the direction with more Kanto loam dust adhesion was rated as 6 to 9, and the direction with less Kanto loam dust adhesion was rated as 1 to 4, giving a rating of 10.

[0053] [Water Absorption] The coated surface of the wood obtained by the coating method was immersed in water at room temperature for 15 hours, and the water absorption of the substrate was evaluated by visually observing the color change of the wood under the coating. A rating of 5 was used, with 1 being a rating for no water absorption or color change and 5 being a rating for color change in the uncoated area. Note that in Comparative Example 2, the color change occurred due to the penetration of Oil 5, so the water absorption could not be evaluated. The sliding angle and stain resistance were evaluated in the same way after the water absorption evaluation. The evaluation results are shown in Table 1.

[0054]

[0055] All coatings in Examples 1 to 9 exhibited super-water repellency both after application and after immersion in water, with a sliding angle of 1°. In contrast, Comparative Example 1 exhibited initial water repellency but lost this after immersion in water. The stain resistance after application was better than that of uncoated wood in Examples 1 to 9 and Comparative Example 1, except for Comparative Example 2. Examples 1 to 7 and 9 show that the stain resistance after application decreases with increasing amounts of Oil 5. Although Examples 1 to 4 and 8 exhibited good stain resistance after immersion in water, all of Examples 1 to 9 exhibited better stain resistance than uncoated wood. The stain resistance of Comparative Example 1 after immersion in water was unchanged from that of uncoated wood. Comparative Example 2 exhibited worse stain resistance than uncoated wood both after application and after immersion in water. Examples 1 to 7 and 9 show a tendency for water absorption to improve with increasing amounts of Oil Component 6. This is thought to be due to the effect of Oil 5 being absorbed into the wood, preventing water from penetrating into the wood.

[0056] In this way, Examples 1 to 9 of the present embodiment 1 contain inorganic nanoparticles 3, a water- and oil-repellent resin 4, and an oil 5, and thereby it is possible to easily obtain a water-repellent coating 2 on a water-absorbent substrate 1 that is highly water-repellent, stain-resistant, and moisture-permeable.

[0057] 1 Water-absorbing substrate, 2 Water-repellent coating, 3 Inorganic nanoparticles, 4 Water- and oil-repellent resin, 5 Oil, 6 Oil component, 7 Water-absorbing substrate, 8 Oil component.

Claims

1. The inorganic nanoparticles are formed on the surface of a water-absorbent substrate permeated with oil, and contain inorganic nanoparticles and a water- and oil-repellent resin in a mass ratio of 50:50 to 90:10, and the average particle size of the inorganic nanoparticles is 2 nm or more and 20 nm or less. Water-repellent coating.

2. The oil is a drying oil. The water-repellent coating according to claim 1.

3. The oil is a silicone oil or a fluorine oil. The water-repellent coating according to claim 1.

4. The water- and oil-repellent resin is a fluororesin or a silicone resin. The water-repellent coating according to any one of claims 1 to 3.

5. The water-absorbent substrate is an inorganic material. The water-repellent coating according to any one of claims 1 to 3.

6. The water-absorbent substrate is an organic material. The water-repellent coating according to any one of claims 1 to 3.

7. The surface of the water-absorbent substrate has irregularities with an arithmetic mean roughness Ra of 2 μm or more. The water-repellent coating according to any one of claims 1 to 3.

8. The water-absorbent substrate is porous. The water-repellent coating according to any one of claims 1 to 3.

9. A composition comprising inorganic nanoparticles and a water- and oil-repellent resin in a mass ratio of 50:50 to 90:10, the inorganic nanoparticles having an average particle size of 2 nm or more and 20 nm or less, the surfaces of the inorganic nanoparticles being hydrophobized, and the water- and oil-repellent resin having an oil content of 250% by mass or less. Coating composition.

10. The oil is a drying oil. The coating composition of claim 9.

11. The oil is a silicone oil or a fluorine oil. The coating composition of claim 9.

12. The water- and oil-repellent resin is a fluororesin or a silicone resin. The coating composition according to any one of claims 9 to 11.

13. A water-repellent coating is formed on the surface, the water-repellent coating containing inorganic nanoparticles and a water- and oil-repellent resin in a mass ratio of 50:50 to 90:10, and the inorganic nanoparticles have an average particle size of 2 nm to 20 nm. Water absorbent material.

14. In addition, oil is penetrating The water-absorbent material according to claim 13.