Coating liquid, method for manufacturing the coating liquid, and coating film

Abstract

To provide a coating liquid or the like which is improved in dispersibility of an aerogel and can form a coating film capable of preventing occurrence of powder falling and excellent in heat insulation performance.SOLUTION: The coating liquid contains a water-soluble polymer having a siloxane bond-containing hydrophobic group, an aerogel, and a liquid medium. The siloxane bond-containing hydrophobic group is represented by the following general formula (1). The water-soluble polymer contains at least one selected from polyvinyl alcohol, polyacrylic acid, cellulose, chitosan, and alginic acid. (In the general formula (1), R1-R7 each represent an alkyl group, a halogenated alkyl group, an aromatic hydrocarbon group, or a trialkylsiloxy group; n represents an integer of 0-10; m represents an integer of 0-10; and l represents an integer of 10 or more.)SELECTED DRAWING: None

Description

[Technical Field]

[0001] This invention relates to a coating liquid, a method for producing a coating liquid, and a coating film. [Background technology]

[0002] Aerogels are known as materials with excellent thermal insulation properties. However, attempts to disperse hydrophobic aerogels in water-soluble polymer solutions such as polyvinyl alcohol result in poor compatibility and difficulty in dispersion. Insufficient dispersion of aerogels significantly affects the physical properties of the coating film after application, leading to problems such as reduced film strength and uneven thermal insulation performance due to the uneven distribution of aerogels.

[0003] Therefore, in order to improve the dispersibility of hydrophobic aerogels and enhance the strength of the coating film, a coating solution has been proposed in which hydrophobic silica aerogel particles are dispersed in a water-soluble polymer obtained by introducing alkyl groups into the hydroxyl groups of cellulose (see, for example, Patent Document 1). [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2020-172590 [Overview of the project] [Problems that the invention aims to solve]

[0005] However, in water-soluble polymers that have been hydrophobized by introducing alkyl groups, as in the prior art described above, the dispersion of hydrophobic silica aerogel particles is insufficient, resulting in uneven heat insulation performance and problems such as powder shedding when the coating film made using the coating solution is touched.

[0006] The present invention aims to solve the aforementioned problems in the conventional era and achieve the following objectives. Specifically, the present invention aims to provide a coating liquid, a method for producing the coating liquid, and a coating film that can form a coating film with improved aerogel dispersibility, prevention of powder fallout, and excellent heat insulation performance. [Means for solving the problem]

[0007] The means to solve the aforementioned problem are as follows: <1> The coating solution is characterized by containing a water-soluble polymer having hydrophobic groups including siloxane bonds, an aerogel, and a liquid medium. <2> The hydrophobic group containing the siloxane bond is represented by either of the following general formulas (1) and (2), <1> This is the coating liquid described in [the relevant document]. [ka] [ka] However, in the above general formulas (1) and (2), R 1 ~R 7 represents an alkyl group, a halogenated alkyl group, an aromatic hydrocarbon group, or a trialkylsiloxy group, where n is between 0 and 10, m is between 0 and 10, and l is an integer of 10 or more. <3> The water-soluble polymer comprises at least one selected from polyvinyl alcohol, polyacrylic acid, cellulose, chitosan, and alginic acid. <1> from <2> It is a coating liquid as described in any of the following. <4> The number average molecular weight of the water-soluble polymer having hydrophobic groups containing siloxane bonds is 5,000 or more. <1> from <3> It is a coating liquid as described in any of the following. <5> The aerogel is a silica aerogel. <1> from <4> It is a coating liquid as described in any of the following. <6> The aerogel content is 50% by mass or more based on the total mass of solids in the coating solution, <1> from <5> It is a coating liquid as described in any of the following. <7> The coating liquid according to any one of <1> to <6> above, wherein the degree of hydrophobicity of the water-soluble polymer having a hydrophobic group containing a siloxane bond is 5% by mass or less with respect to the amount of hydroxyl groups of the water-soluble polymer. <8> The coating liquid according to any one of <1> to <7> above, which is for a heat insulating material. <9> A method for producing the coating liquid according to any one of <1> to <8> above, The method for producing a coating liquid, characterized by including a step of reacting a water-soluble polymer with a compound represented by the following general formula (3) to synthesize a water-soluble polymer having a hydrophobic group containing a siloxane bond.

Chemical formula

Advantages of the Invention

[0008] According to the present invention, the above-mentioned various problems in the prior art can be solved, the above-mentioned object can be achieved, the dispersibility of the aerogel can be improved, the occurrence of powder falling can be prevented, and a coating liquid, a method for producing a coating liquid, and a coating film having excellent heat insulation performance can be provided.

Embodiments for Carrying Out the Invention

[0009] (Coating Liquid) The coating liquid of the present invention contains a water-soluble polymer having a hydrophobic group containing a siloxane bond, an aerogel, and a liquid medium, and further contains other components as necessary.

[0010] In this invention, the dispersibility of the aerogel is greatly improved by including a water-soluble polymer having hydrophobic groups containing siloxane bonds. As a result, the uneven distribution of the aerogel is reduced, and a coating film with excellent heat insulation performance can be formed without powder shedding.

[0011] <Water-soluble polymer containing hydrophobic groups with siloxane bonds> In water-soluble polymers having hydrophobic groups containing siloxane bonds, there are no particular restrictions on the water-soluble polymer as long as it has hydroxyl groups, and it can be appropriately selected depending on the purpose. For example, water-soluble polymers obtained from synthetic products, plants and animals, fish and shellfish, seaweed, tree sap, microbial products, etc., can be used. Among these, polyvinyl alcohol, polyacrylic acid, cellulose, chitosan, and alginic acid are preferred, with polyvinyl alcohol and cellulose being particularly preferred.

[0012] The aforementioned polyvinyl alcohol is a resin containing alcoholic hydroxyl groups in the polymer structure. Polyvinyl alcohol is usually obtained by saponifying vinyl ester polymers. The polyvinyl alcohol may be one in which some of the vinyl alcohol units have been modified by reactions such as acetalization, etherification, acetoacetylation, or cationization. The aforementioned polyvinyl alcohol may be synthesized as appropriate, or a commercially available product may be used. An example of such a commercially available product is the product name: Kuraray Poval 5-88 (manufactured by Kuraray Co., Ltd.).

[0013] Examples of the cellulose include methylcellulose, carboxymethylcellulose, hydroxyethylcellulose, hydroxypropylmethylcellulose, or modified cellulose obtained by further modifying these. The cellulose may be synthesized as appropriate, or a commercially available product may be used. An example of such a commercially available product is Metroze 60SH-10000 (manufactured by Shin-Etsu Chemical Co., Ltd.).

[0014] The hydrophobic group containing the siloxane bond is preferably one represented by either general formula (1) or general formula (2) below. By introducing a hydrophobic group containing a siloxane bond into the side chain of a water-soluble polymer, compatibility with hydrophobic silica aerogel can be improved.

[0015] [ka]

[0016] [ka] However, in the above general formulas (1) and (2), R 1 ~R 7 represents an alkyl group, a halogenated alkyl group, an aromatic hydrocarbon group, or a trialkylsiloxy group, where n is between 0 and 10, m is between 0 and 10, and l is an integer of 10 or more. R 1 ~R 7 The alkyl group and halogenated alkyl group are preferably linear, branched, or cyclic with 1 to 18 carbon atoms. Examples of aromatic hydrocarbon groups include phenyl groups. Phenyl groups may have substituents such as alkyl groups or hydroxyl groups. The alkyl group in the trialkylsiloxy group preferably has 1 to 10 carbon atoms. Examples of trialkylsiloxy groups include the trimethylsiloxy group. From the standpoint of improving the compatibility of the aerogel, l is preferably an integer of 10 or more, and more preferably an integer between 10 and 70.

[0017] A water-soluble polymer having a hydrophobic group represented by either general formula (1) or general formula (2) above can be synthesized, for example, by reacting a water-soluble polymer with a compound represented by general formula (3) below. By reacting the hydroxyl group of the water-soluble polymer with the epoxy group of the compound represented by general formula (3), a hydrophobic group containing a siloxane bond represented by general formula (1) or (2) above is introduced into the side chain of the water-soluble polymer.

[0018]

Chem.

[0019] As the compound represented by the general formula (3), those synthesized as appropriate may be used, or commercially available products may be used. Examples of the commercially available products include epoxy silicone (trade name X-22-173BX, trade name X-22-173DX, manufactured by Shin-Etsu Chemical Co., Ltd.). The inventor has analyzed the product named "X-22-173BX" (manufactured by Shin-Etsu Chemical Co., Ltd.) by NMR and IR, and confirmed that in the general formula (3), R 1 ~R 3 is a methyl group, R 4 is a butyl group, R 5 ~R 7 is a methyl group, n = 1, m = 3, and l = 32. Also, the product named "X-22-173DX" (manufactured by Shin-Etsu Chemical Co., Ltd.) has been analyzed by NMR and IR, and it has been confirmed that in the general formula (3), R 1 ~R 3 is a methyl group, R 4 is a butyl group, R 5 ~R 7 is a methyl group, n = 1, m = 3, and l = 63.

[0020] The number average molecular weight (Mn) of the water-soluble polymer having a hydrophobic group containing a siloxane bond is preferably 5,000 or more, more preferably 5,000 or more and 5,000,000 or less, and even more preferably 10,000 or more and 100,000 or less. The number average molecular weight (Mn) of the water-soluble polymer can be measured in terms of polystyrene using gel permeation chromatography (GPC).

[0021] The degree of hydrophobicity of a water-soluble polymer having hydrophobic groups containing siloxane bonds is preferably 5% by mass or less, more preferably 1% by mass or less, and even more preferably 0.5% by mass or less, relative to the amount of hydroxyl groups. The degree of hydrophobicity is, for example, 1 This can be measured by comparing the integral ratio of the methyl group bonded to silicon, which originates from the hydrophobic group, with that of the methyl group using 1H NMR.

[0022] The content of the water-soluble polymer having hydrophobic groups containing siloxane bonds is preferably 1% by mass or more, more preferably 5% by mass or more, and even more preferably 10% by mass or more, based on the total mass of solids in the coating solution.

[0023] <Aerogel> In a narrow sense, a dry gel obtained by supercritical drying of a wet gel is called an aerogel, a dry gel obtained by drying under atmospheric pressure is called a xerogel, and a dry gel obtained by freeze-drying is called a cryogel. However, in this embodiment, a low-density dry gel obtained by any of these drying methods of a wet gel is called an "aerogel." That is, in the present invention, "aerogel" means a broad aerogel, which is "a gel comprised of a microporous solid in which the dispersed phase is a gas." Generally, the interior of an aerogel has a mesh-like microstructure and has a cluster structure in which particulate aerogel components of about 2 nm to 20 nm are bound together. There are pores less than 100 nm in size between the frameworks formed by this cluster structure. As a result, an aerogel has a three-dimensionally fine porous structure.

[0024] The aerogel is preferably a silica aerogel, for example, a silica aerogel with silica as the main component. To suppress the deterioration of the aerogel's performance due to moisture absorption, a hydrophobic silica aerogel having hydrophobic groups on its surface is more preferable. Specifically, the silica aerogel is hydrophobic because a trisubstituted silyl group represented by the following formula is bonded to its surface. In the formula, R1 , R 2 , R 3 These may be the same or different, and are selected from alkyl groups having 1 to 18 carbon atoms, or aryl groups having 6 to 18 carbon atoms, preferably methyl, ethyl, cyclohexyl, or phenyl groups.

[0025] [ka]

[0026] As the porosity of the aerogel increases, the number of air pores of several tens of nanometers that obstruct the mean free path increases, resulting in lower thermal conductivity. Because the aerogel surface has hydrophobic groups, even when dispersed in an aqueous medium, water seeps into or penetrates the pores. This means that the aerogel can maintain its inherently high porosity in the state of the coating liquid and even in the state of the coating film after application, and consequently exhibit excellent heat insulation performance.

[0027] The silica aerogel is particulate, and its average particle size is preferably 1 μm to 50 μm, more preferably 1 μm to 25 μm, and even more preferably 1 μm to 10 μm. If the average particle size is too small, the overall ratio of interparticle voids increases, which is undesirable because it reduces the proportion of nano-sized pores in the silica aerogel, thus reducing its thermal insulation and sound absorption properties. On the other hand, if the average particle size is too large, the size of the interparticle voids increases, which may cause air convection between the large voids and reduce the thermal insulation and sound absorption effects, which is also undesirable.

[0028] The silica aerogel may be synthesized as appropriate, or a commercially available product may be used. Examples of such commercially available products include the product name MT-1100 (manufactured by Cabot Corporation).

[0029] The aerogel content is preferably 70% by mass or more, based on the total mass of solids in the coating solution. When the aerogel content is 70% by mass or more, excellent heat insulation performance can be achieved.

[0030] <Liquid media> As the liquid medium, an aqueous solvent containing water is preferred. As water, pure water such as ion-exchanged water, ultrafiltered water, reverse osmosis water, or distilled water, or ultrapure water can be used. The aqueous solvent may contain an organic solvent in addition to water. The organic solvent can be any solvent that is compatible with water, and examples include alcohols such as methanol, ethanol, isopropanol, butanol, ethylene glycol, and propylene glycol; ethers such as diethyl ether, tetrahydrofuran, and 1,4-dioxane; ketones such as acetone and methyl ethyl ketone; carboxylic acids such as acetic acid and propionic acid; and nitrogen-containing compounds such as acetonitrile, dimethylformamide, and triethylamine. In the coating solution of the present invention, the content of the liquid medium is not particularly limited and can be appropriately changed according to the viscosity of the desired coating solution.

[0031] <Other ingredients> Other ingredients include, for example, surfactants, thickeners, pigments, and leveling agents.

[0032] (Method of manufacturing the coating solution) The method for producing the coating liquid of the present invention includes a step of synthesizing a water-soluble polymer having hydrophobic groups containing siloxane bonds, preferably including a mixing step, and further including other steps as necessary.

[0033] Water-soluble polymers having hydrophobic groups containing siloxane bonds can be synthesized by the synthesis method described above. In the mixing step, a water-soluble polymer having hydrophobic groups containing siloxane bonds, an aerogel, and other components as needed are mixed in a liquid medium. There are no particular restrictions on the mixing method, and it can be appropriately selected depending on the purpose. Examples include shaking, magnetic stirrer stirring, mechanical stirring, vibration stirring, and ultrasonic stirring.

[0034] (coating film) The coating film of the present invention contains a water-soluble polymer having hydrophobic groups containing siloxane bonds, an aerogel, and further contains other components as needed. The aforementioned coating film may be obtained by removing the liquid medium from the coating solution of the present invention described above. That is, the components in the coating film may be the same as the components in the coating solution described above, and the content of each component in the coating film may be the same as the solid content of each component in the coating solution described above.

[0035] There are no particular restrictions on the method of applying the coating liquid to the object, and it can be appropriately selected according to the purpose. Examples include dip coating, spray coating, spin coating, and roll coating.

[0036] The object to which the coating liquid is applied is not particularly limited. The material constituting the object may be, for example, metal, ceramic, glass, resin, or a composite material thereof. Furthermore, the form of the object can be appropriately selected according to the purpose of use, material, etc., and examples include block shape, sheet shape, powder shape, fibrous shape, etc.

[0037] The average thickness of the coating film is not particularly limited and can be appropriately selected depending on the purpose, but is preferably 0.01 mm or more and 30 mm or less, and more preferably 0.1 mm or more and 20 mm or less.

[0038] The coating film of the present invention can prevent powder shedding and has excellent heat insulation properties derived from aerogel, so it can be widely applied as a heat insulating material in applications such as portable information terminals, in-vehicle batteries, in-vehicle interior components, cryogenic containers, space, construction, automotive, home appliances, semiconductors, and industrial equipment. In addition to its use as a heat insulating material, the coating film can also be used as a water repellent, sound absorbing material, vibration damping material, catalyst support material, etc. [Examples]

[0039] The following describes embodiments of the present invention, but the present invention is not limited in any way to these embodiments.

[0040] (Synthesis Example 1) <Synthesis of Polyvinyl Alcohol 2 Having Hydrophobic Groups Including Siloxane Bonds> In a 200 mL three-necked flask equipped with a stirring bar, condenser, thermometer, and dropping funnel, 100 g of 10% aqueous polyvinyl alcohol (polyvinyl alcohol 1) (product name: Kuraray Poval 5-88, manufactured by Kuraray Co., Ltd., number average molecular weight: approximately 2,4000), 0.1 g of caustic soda (sodium hydroxide, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was added, and 2 g of epoxy silicone (product name: X-22-173BX, manufactured by Shin-Etsu Chemical Co., Ltd.) was added and the mixture was stirred at 70°C for 5 hours. After the reaction was complete, the mixture was neutralized and the product was precipitated with acetone. After washing, the mixture was dried under reduced pressure at 80°C for 24 hours to obtain 8.3 g of polyvinyl alcohol 2 containing siloxane bonds, as in Synthesis Example 1. Analysis by NMR revealed that the degree of hydrophobicity of polyvinyl alcohol 2 containing siloxane bonds, as in Synthesis Example 1, was 0.2% by mass.

[0041] (Synthesis Example 2) <Synthesis of Cellulose 2 containing hydrophobic groups with siloxane bonds> In Synthesis Example 1, cellulose 2 containing hydrophobic groups with siloxane bonds was obtained in the same manner as in Synthesis Example 1, except that cellulose 1 (product name: Metroze 60SH-10000, manufactured by Shin-Etsu Chemical Co., Ltd.) was substituted for a 10% aqueous polyvinyl alcohol solution. NMR analysis revealed that the degree of hydrophobicity of cellulose 2 containing hydrophobic groups with siloxane bonds in Synthesis Example 2 was 0.2% by mass.

[0042] (Synthesis Example 3) <Synthesis of Cellulose 3 Having an Alkyl (Stearyl) Group> In a 200 mL three-necked flask equipped with a stirring bar, condenser, thermometer, and dropping funnel, 100 g of a 10% aqueous solution of hydroxypropyl methylcellulose (product name: Metroze 60SH-10000, manufactured by Shin-Etsu Chemical Co., Ltd.) and 0.5 g of caustic soda (sodium hydroxide, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) were added. 5 g of stearyl glycidyl ether (manufactured by Yokkaichi Synthetic Co., Ltd.) was then added, and the mixture was stirred at 70°C for 3 hours. The temperature was then raised to 90°C and stirred for 2 hours. After the reaction was complete, the mixture was neutralized, the product was washed with hot water, and then dried under reduced pressure at 80°C for 24 hours to obtain 9.1 g of hydroxypropyl methylcellulose 3 having stearyl groups. Analysis using NMR confirmed that the introduction rate (degree of hydrophobicity) of cellulose 3 having alkyl groups (stearyl groups) was approximately 0.5% by mass.

[0043] (Example 1) Polyvinyl alcohol 2 having hydrophobic groups containing siloxane bonds, as in Synthesis Example 1, was dissolved in 24 g of distilled water. 5 g of silica aerogel (product name: MT-1100, manufactured by Cabot Corporation) was added, and the mixture was stirred at 2,000 rpm for 10 minutes using an Awatori Rentaro AR-100 (manufactured by Thinky Co., Ltd.) to obtain the coating solution of Example 1.

[0044] (Example 2) In Example 1, the coating solution of Example 2 was obtained in the same manner as in Example 1, except that the polyvinyl alcohol 2 having hydrophobic groups containing siloxane bonds in Synthesis Example 1 was replaced with the cellulose 2 having hydrophobic groups containing siloxane bonds in Synthesis Example 2.

[0045] (Example 3) The coating solution for Example 3 was obtained in the same manner as in Example 1, except that 26 g of distilled water and 3 g of silica aerogel (product name: MT-1100, manufactured by Cabot Corporation) were replaced.

[0046] (Example 4) The coating solution for Example 4 was obtained in the same manner as in Example 1, except that 28 g of distilled water and 1 g of silica aerogel (product name: MT-1100, manufactured by Cabot Corporation) were replaced.

[0047] (Comparative Example 1) Comparative Example 1 was obtained in the same manner as in Example 1, except that the polyvinyl alcohol 2 having hydrophobic groups containing siloxane bonds in Synthesis Example 1 was replaced with a 10% aqueous solution of polyvinyl alcohol (polyvinyl alcohol 1) (product name: Kuraray Poval 5-88, manufactured by Kuraray Co., Ltd., number average molecular weight: approximately 24,000).

[0048] (Comparative Example 2) Comparative Example 2 was obtained in the same manner as in Example 1, except that Cellulose 2, which has hydrophobic groups containing siloxane bonds in Synthesis Example 2, was replaced with Cellulose 1 (product name: Metroze 60SH-10000, manufactured by Shin-Etsu Chemical Co., Ltd.).

[0049] (Comparative Example 3) Comparative Example 3's coating solution was obtained in the same manner as in Example 1, except that the polyvinyl alcohol 2 having hydrophobic groups containing siloxane bonds from Synthesis Example 1 was not added, and 25 g of distilled water was used.

[0050] (Comparative Example 4) In Example 1, the coating solution of Comparative Example 4 was obtained in the same manner as in Example 1, except that the polyvinyl alcohol 2 having a hydrophobic group containing a siloxane bond in Synthesis Example 1 was replaced with cellulose 3 having an alkyl group (stearyl group) in Synthesis Example 3. Furthermore, the cellulose 3 having an alkyl group (stearyl group) in Synthesis Example 3 is a reproduction of Sanjelose 90L (manufactured by Daido Chemical Industries, Ltd.) used in Example 1 of Japanese Patent Application Publication No. 2020-172580. According to Daido Chemical Industries, Ltd.'s product catalog (http: / / www.daido-chem.co.jp / topics / view / 2, accessed February 9, 2022), the alkyl group (stearyl group) introduction rate (degree of hydrophobicity) of Sanjelose 90L is 0.3% by mass to 0.6% by mass.

[0051] Next, the various properties were evaluated as follows. The results are shown in Tables 1 and 2. Note that the content of each component in Tables 1 and 2 is based on mass.

[0052] <Dispersibility> Using the Awatori Rentaro AR-100 (manufactured by Thinky Co., Ltd.), the dispersion state was observed immediately after stirring at 2,000 rpm for 10 minutes, and the dispersibility was evaluated based on the following criteria. A level of A or higher is considered a feasible level. [Evaluation Criteria] A: It is liquid and free of lumps. B: It is liquid but has clumps. C: Regardless of whether there are lumps or not, the volume increases and it becomes whipped. D: Not distributed

[0053] <Powder fallout> The obtained coating solution was dried at 100°C for 3 hours and formed into sheets with a thickness of 300 μm. The amount of aerogel powder that fell off each sheet after drying was evaluated according to the following criteria. A or higher is considered a feasible level. [Evaluation Criteria] A: No powder fallout. B: Powder falls off when the sheet is touched. C: Powder falls out just by moving the sheet. D: Sheet cannot be formed

[0054] <Thermal conductivity> Using each of the obtained coating solutions, coating films measuring 200 mm × 200 mm × 0.3 mm were prepared. A thermal conductivity measuring device (HFM-446, manufactured by NETZSCH) was used to measure the thermal conductivity of the coating film when it was placed between two plates (a heating plate and a cooling plate) while the heating plate was heated.

[0055] [Table 1]

[0056] [Table 2] [Industrial applicability]

[0057] The coating film of the present invention can prevent powder shedding and has excellent heat insulation properties derived from aerogel, so it can be widely applied as a heat insulating material in applications such as portable information terminals, in-vehicle batteries, in-vehicle interior components, cryogenic containers, space, construction, automotive, home appliances, semiconductors, and industrial equipment.

Claims

1. It contains a water-soluble polymer having hydrophobic groups including siloxane bonds, an aerogel, and a liquid medium. A coating solution characterized in that the hydrophobic group containing the siloxane bond is represented by either of the following general formulas (1) and (2). 【Chemistry 1】 【Chemistry 2】 However, in the general formulas (1) and (2) above, R1 to R7 represent an alkyl group, a halogenated alkyl group, an aromatic hydrocarbon group, or a trialkylsiloxy group, n is 0 to 10, m is 0 to 10, and l is an integer of 10 or more.

2. A water-soluble polymer having hydrophobic groups containing siloxane bonds, an aerogel, and a liquid medium, A coating solution characterized in that the number-average molecular weight of the water-soluble polymer having hydrophobic groups containing siloxane bonds is 5,000 or more.

3. A water-soluble polymer having hydrophobic groups containing siloxane bonds, an aerogel, and a liquid medium, A coating liquid characterized in that the aerogel content is 50% by mass or more based on the total mass of solids in the coating liquid.

4. A water-soluble polymer having hydrophobic groups containing siloxane bonds, an aerogel, and a liquid medium, A coating solution characterized in that the degree of hydrophobicity of the water-soluble polymer having hydrophobic groups containing siloxane bonds is 5% by mass or less relative to the amount of hydroxyl groups in the water-soluble polymer.

5. The coating liquid according to any one of claims 1 to 4, wherein the water-soluble polymer comprises at least one selected from polyvinyl alcohol, polyacrylic acid, cellulose, chitosan, and alginic acid.

6. The coating liquid according to any one of claims 1 to 4, wherein the aerogel is silica aerogel.

7. A coating liquid according to any one of claims 1 to 4, for use as an insulating material.

8. A method for producing a coating liquid according to any one of claims 1 to 4, A method for producing a coating solution, characterized by comprising the step of reacting a water-soluble polymer with a compound represented by the following general formula (3) to synthesize a water-soluble polymer having a hydrophobic group containing a siloxane bond. 【Transformation 3】 However, in the general formula (3) above, R1 to R7 represent an alkyl group, a halogenated alkyl group, an aromatic hydrocarbon group, or a trialkylsiloxy group, n is 0 to 10, m is 0 to 10, and l is an integer of 10 or more.

9. A water-soluble polymer having a hydrophobic group containing a siloxane bond, It contains aerogel and A coating film characterized in that the hydrophobic group containing the siloxane bond is represented by either of the following general formulas (1) and (2). 【Chemistry 4】 【Transformation 5】 However, in the general formulas (1) and (2) above, R1 to R7 represent an alkyl group, a halogenated alkyl group, an aromatic hydrocarbon group, or a trialkylsiloxy group, n is 0 to 10, m is 0 to 10, and l is an integer of 10 or more.

10. A water-soluble polymer having a hydrophobic group containing a siloxane bond, It contains aerogel and A coating film characterized in that the number-average molecular weight of the water-soluble polymer having hydrophobic groups containing siloxane bonds is 5,000 or more.

11. A water-soluble polymer having hydrophobic groups containing siloxane bonds, It contains aerogel and A coating film characterized in that the degree of hydrophobicity of the water-soluble polymer having hydrophobic groups containing siloxane bonds is 5% by mass or less relative to the amount of hydroxyl groups in the water-soluble polymer.

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