Method for producing coating liquid and method for producing thermal insulating material

Abstract

A method for producing a coating liquid, comprising: a preparation step of preparing an emulsion containing a polymer emulsifier, a binder resin, and a liquid medium, and aerogel particles; and a mixing step of mixing the emulsion and the aerogel particles prepared in the preparation step, and causing at least a part of the aerogel particles to coagulate, thereby obtaining a coating liquid containing coagula of the aerogel particles, the polymer emulsifier, the binder resin, and the liquid medium.

Description

TECHNICAL FIELD

[0001] The present application relates to a method for producing a coating liquid and a method for producing an insulating material. BACKGROUND

[0002] As a material having excellent insulating properties, aerogel is known. Further, a method for processing aerogel into a particulate form and using it as a constituent material of an insulating material is proposed (for example, Patent Documents 1 and 2). In Patent Document 1, a particulate aerogel is proposed to be used as a filler between resin plates and the like constituting an insulating window. In Patent Document 2, a method is shown in which, after preparing an aqueous dispersion liquid containing aerogel particles and organic fibers, water is evaporated, and the thus obtained intermediate product is further press-molded, thereby producing an insulating material (molded product).

[0003] PRIOR ART DOCUMENTS

[0004] PATENT DOCUMENTS

[0005] Patent Document 1: Japanese Patent Application Publication No. 2012-91943

[0006] Patent Document 2: Japanese Patent Application Publication No. 2014-35044 SUMMARY

[0007] PROBLEMS TO BE SOLVED BY THE INVENTION

[0008] A composite material in which aerogel particles are dispersed in a resin component is expected to have excellent heat resistance. However, when such a composite material is liquidized, there is a problem in that the resin component penetrates into the pores of the aerogel particles and loses the pore structure, thereby decreasing the insulating properties, and the strength of the coating film is not sufficiently obtained, and cracks are easily generated.

[0009] Therefore, an object of the present application is to provide a method for producing an insulating material, which can obtain an insulating material having high insulating properties and high film-forming properties, in which penetration of a resin component into the pores of aerogel particles is suppressed. Further, an object of the present application is to provide a coating liquid for forming the above-described insulating material and a method for producing the same.

[0010] MEANS FOR SOLVING THE PROBLEMS

[0011] One aspect of the present application relates to a method for producing a coating liquid, comprising: a preparation step of preparing an emulsion containing a high molecular emulsifier, a binder resin, and a liquid medium, and aerogel particles; and a mixing step of mixing the emulsion and the aerogel particles prepared in the above preparation step, so that at least a part of the aerogel particles are aggregated, thereby obtaining a coating liquid containing the aggregates of the aerogel particles, the high molecular emulsifier, the binder resin, and the liquid medium.

[0012] The coating liquid obtained in the production method described above is obtained by agglomerating the aerogel particles, and the contact interface between the aerogel particles and the resin component is reduced, and the penetration of the resin component into the pores of the aerogel particles is suppressed. Also, the coating liquid obtained in the production method described above is obtained by agglomerating the aerogel particles and other components when mixed, and not by mixing the agglomerates of the aerogel particles prepared in advance, and thus the aerogel particles and the agglomerates thereof are uniformly dispersed, and the unevenness, cracking, and the like of the coating film caused by the segregation of the aerogel particles can be suppressed. Also, in the production method described above, the binder resin emulsified by the polymeric emulsifier is mixed in advance, and thus the penetration of the resin component into the pores of the aerogel particles is further suppressed. Therefore, according to the coating liquid obtained in the production method described above, an aerogel material having high thermal insulation and high film-forming properties can be obtained.

[0013] Also, in the production method described above, the binder resin in the emulsion is covered with the polymeric emulsifier by using the polymeric emulsifier, and thus the agglomerates of the fine particles of the binder resin and the aerogel particles are less likely to come into contact, the binder resin is less likely to enter the gaps in the agglomerates of the aerogel particles, and the agglomerates of the aerogel particles are less likely to disintegrate. Therefore, the coating film obtained in the production method described above is less likely to disintegrate the agglomerates of the aerogel particles even when a certain degree of pressure is applied at the time of coating, and for example, a coating method such as airless spraying, in which high pressure is applied, can be preferably used.

[0014] In one embodiment, the average diameter of the agglomerates described above can be 2 to 40 times the average diameter of the aerogel particles prepared in the preparation step described above. By forming such agglomerates, the effects described above can be more significantly exhibited.

[0015] In one embodiment, when a dilute solution obtained by diluting the coating liquid described above is observed with an optical microscope, the area occupied by the agglomerates having a diameter of 20 μm or more among the area occupied by the aerogel particles and the agglomerates in the field of view of the observation can be 50% or more. Thereby, the effects described above can be more significantly exhibited.

[0016] In one embodiment, the total content of the aerogel particles and the agglomerates in the coating liquid described above can be 70% or more by volume based on the total volume of the solid components. Thereby, an aerogel material having further excellent thermal insulation can be formed.

[0017] In one embodiment, the mixing step described above can be a step of further mixing a water-soluble polymer having a hydrophobic group, and the coating liquid described above can further contain the water-soluble polymer described above. Thereby, the dispersibility of the aerogel particles is further improved, and even when the packing rate of the aerogel particles is increased, a coating liquid in which the aerogel particles and the agglomerates thereof are uniformly dispersed can be more easily obtained.

[0018] Another aspect of the present application relates to a method for producing a thermal insulating material, including: a coating step of coating a coating liquid produced in the above-mentioned method on a support to obtain a coating film; and a removing step of removing at least a part of the liquid medium from the coating film to obtain a thermal insulating material. According to this method, penetration of the resin component into the pores of the aerogel particles can be suppressed, and a thermal insulating material having high thermal insulation and high film-forming property can be easily obtained.

[0019] In one embodiment, the pore volume of the thermal insulating material can be 0.15 cm 3 / g or more.

[0020] In one embodiment, the coating step is a step of coating the coating liquid by a coating method in which the pressure applied to the coating liquid exceeds 1.5 MPa.

[0021] Still another aspect of the present application relates to a coating liquid containing an aggregate of aerogel particles, a polymeric emulsifier, a binder resin, and a liquid medium, wherein, when a diluted liquid obtained by diluting the coating liquid is observed with an optical microscope, the area occupied by the aggregate having a diameter of 20 μm or more in the area occupied by the aerogel particles and the aggregate in the field of view is 50% or more.

[0022] Effects of the Invention

[0023] According to the present application, a method for producing a thermal insulating material that can obtain a thermal insulating material having high thermal insulation and high film-forming property with suppressed penetration of the resin component into the pores of the aerogel particles can be provided. Furthermore, according to the present application, a coating liquid for forming the thermal insulating material and a method for producing the same can be provided. DETAILED DESCRIPTION

[0024] Hereinafter, a preferred embodiment of the present application will be described in detail. However, the present application is not limited to the following embodiment. In the present specification, a numerical range represented by "~" indicates a range including the values recited before and after "~" as the minimum value and the maximum value, respectively. "A or B" includes either one of A and B, and can include both. The materials exemplified in the present embodiment can be used alone or in combination of two or more, unless otherwise specified.

[0025] The method for producing the coating liquid of the present embodiment includes: a preparation step of preparing an emulsion containing a polymeric emulsifier, a binder resin, and a liquid medium, and aerogel particles; and a mixing step of mixing the emulsion and the aerogel particles prepared in the preparation step, and allowing at least a part of the aerogel particles to aggregate, thereby obtaining a coating liquid containing an aggregate of aerogel particles, a polymeric emulsifier, a binder resin, and a liquid medium.

[0026] The coating liquid obtained by the production method of the present embodiment is obtained by agglomeration of the aerogel particles, and the contact interface between the aerogel particles and the resin component is reduced, and the penetration of the resin component into the pores of the aerogel particles is inhibited. In addition, in order to reduce the contact interface, it is possible to consider preparing agglomerates of the aerogel particles in advance, but in this case, it is difficult to disperse the agglomerates in the coating liquid, and the agglomerates can be disintegrated by stirring operation or the like for dispersion. In the present embodiment, the aerogel particles are agglomerated when mixed with other components, and thus the aerogel particles and the agglomerates thereof are uniformly dispersed, and the unevenness, cracking, or the like of the coating film due to the segregation of the aerogel particles is inhibited. In addition, in the present embodiment, the binder resin emulsified by the polymeric emulsifier is mixed in advance, and thus the penetration of the resin component into the pores of the aerogel particles is further inhibited. Therefore, the production method of the present embodiment can obtain a coating liquid that can form an aerogel material having high thermal insulation and high film-forming properties.

[0027] In addition, in the production method of the present embodiment, the binder resin in the emulsion is covered with the polymeric emulsifier, and thus the agglomerates of the fine particles of the binder resin and the aerogel particles are less likely to contact, the binder resin is less likely to enter the gaps in the agglomerates of the aerogel particles, and the agglomerates of the aerogel particles are less likely to disintegrate. Therefore, the coating film obtained by the production method of the present embodiment is less likely to disintegrate the agglomerates of the aerogel particles even when a certain degree of pressure is applied at the time of coating, and for example, a coating method such as airless spraying that applies high pressure can be preferably used.

[0028] The production method of the aerogel material of the present embodiment includes a coating step of coating the coating liquid produced by the above-described method on a support to obtain a coating film, and a removal step of removing at least a part of the liquid medium from the coating film to obtain an aerogel material. The production method of the aerogel material of the present embodiment can further include a coating liquid production step of producing the coating liquid by the above-described method.

[0029] According to the production method of the present embodiment, the penetration of the resin component into the pores of the aerogel particles is inhibited, and an aerogel material having high thermal insulation and high film-forming properties can be easily obtained.

[0030] Aerogel

[0031] In a narrow sense, a dried gel obtained by using a supercritical drying method for a wet gel is called an aerogel, a dried gel obtained by drying at atmospheric pressure is called a xerogel, and a dried gel obtained by freeze drying is called a cryogel, but in the present embodiment, the low-density dried gel obtained is called an "aerogel" regardless of the drying method of the wet gel. That is, in the present embodiment, the "aerogel" refers to the aerogel in a broad sense, i.e., "Gel comprised of a microporous solid in which the dispersed phase is a gas (aerogel comprised of a microporous solid in which the dispersed phase is a gas)". Generally, the aerogel has a network-like fine structure in the inside thereof, and has a cluster structure in which particle-like aerogel components of about 2 to 20 nm are combined. Between the frameworks formed by the clusters, there are fine pores of less than 100 nm. Thus, the aerogel is three-dimensionally formed with a fine porous structure.

[0032] The aerogel according to the present embodiment is, for example, a silica aerogel in which silica is the main component. As the silica aerogel, for example, a so-called organic-inorganic hybrid silica aerogel in which an organic group (methyl group or the like) or an organic chain is introduced can be given.

[0033] As the aerogel according to the present embodiment, for example, the following forms can be given. By adopting these forms, it is easy to obtain an aerogel excellent in thermal insulation, flame retardancy, heat resistance, and softness. By adopting each form, it is possible to obtain an aerogel having thermal insulation, flame retardancy, heat resistance, and softness corresponding to each form.

[0034] (Form 1)

[0035] The aerogel according to the present embodiment can have a structure represented by the following general formula (1). The aerogel according to the present embodiment can have a structure represented by the following general formula (1a) as a structure including the structure represented by formula (1).

[0036]

[0037] In formula (1) and formula (1a), R 1 and R 2 independently represent an alkyl group or an aryl group, R 3 and R 4 independently represent an alkylene group. Here, as the aryl group, a phenyl group, a substituted phenyl group, or the like can be given. In addition, as the substituent of the substituted phenyl group, an alkyl group, a vinyl group, a mercapto group, an amino group, a nitro group, a cyano group, or the like can be given. p represents an integer of 1 to 50. In formula (1a), two or more R 1each of which can be the same or different, and likewise, 2 or more of R 2 each of which can be the same or different. In formula (1a), 2 R 3 each of which can be the same or different, and likewise, 2 or more of R 4 each of which can be the same or different.

[0038] By introducing the structure represented by the above formula (1) or formula (1a) as a component of an aerogel into the skeleton of the aerogel, an aerogel having low thermal conductivity and being soft is obtained. From this viewpoint, in formula (1) and formula (1a), as R 1 and R 2 , an alkyl group having 1 to 6 carbon atoms, a phenyl group, and the like can be respectively and independently mentioned, and as the alkyl group, a methyl group, and the like can be mentioned. Also, in formula (1) and formula (1a), as R 3 and R 4 , an alkylene group having 1 to 6 carbon atoms, and the like can be respectively and independently mentioned, and as the alkylene group, an ethylene group, a propylene group, and the like can be mentioned. In formula (1a), p can be set to 2 to 30, and can also be 5 to 20.

[0039] (Second Mode)

[0040] The aerogel according to the present embodiment has a ladder structure having a strut portion and a bridge portion, and the bridge portion can have a structure represented by the following general formula (2). By introducing this ladder structure as a component of an aerogel into the skeleton of the aerogel, it is possible to improve the heat resistance and mechanical strength. In the present embodiment, the "ladder structure" is a structure having two strut portions and bridge portions connecting the strut portions to each other (a structure in the form of a so-called "ladder"). In the present mode, the skeleton of the aerogel can be formed of a ladder structure, but can also be a structure in which the aerogel has a ladder structure in part.

[0041]

[0042] In formula (2), R 5 and R 6 independently represent an alkyl group or an aryl group, and b represents an integer of 1 to 50. Here, as the aryl group, a phenyl group, a substituted phenyl group, and the like can be mentioned. Also, as the substituent of the substituted phenyl group, an alkyl group, a vinyl group, a mercapto group, an amino group, a nitro group, a cyano group, and the like can be mentioned. In addition, in formula (2), when b is an integer of 2 or more, 2 or more of R 5 each of which can be the same or different, and likewise, 2 or more of R 6 each of which can be the same or different.

[0043] By introducing the above structure as an aerogel component into the skeleton of the aerogel, for example, an aerogel having superior softness to a conventional aerogel having a structure derived from ladder-type silsesquioxane (i.e., having a structure represented by the following general formula (X)) is obtained. Silsesquioxane is a polysiloxane having a composition formula: (RSiO 1.5 ) n has various skeleton structures such as a cage type, a ladder type, and a random type. In addition, in the conventional aerogel having a structure derived from ladder-type silsesquioxane, the structure of the bridging portion is -O-, but in the aerogel according to the present embodiment, the structure of the bridging portion is the structure represented by the above general formula (2) (polysiloxane structure). However, the aerogel of the present form can have a structure derived from silsesquioxane in addition to the structure represented by general formula (2).

[0044]

[0045] In formula (X), R represents a hydroxyl group, an alkyl group, or an aryl group.

[0046] The structure and the chain length of the strut portion, and the interval of the structure of the bridging portion are not particularly limited, but from the viewpoint of further improving heat resistance and mechanical strength, as the ladder structure, a ladder structure represented by the following general formula (3) can be possessed.

[0047]

[0048] In formula (3), R 5 , R 6 , R 7 , and R 8 each independently represent an alkyl group or an aryl group, a and c each independently represent an integer of 1 to 3000, and b represents an integer of 1 to 50. Here, as the aryl group, a phenyl group, a substituted phenyl group, and the like can be given. Also, as the substituent of the substituted phenyl group, an alkyl group, a vinyl group, a mercapto group, an amino group, a nitro group, a cyano group, and the like can be given. In addition, in formula (3), when b is an integer of 2 or more, 2 or more of R 5 each can be the same or different, and similarly, 2 or more of R 6 each can be the same or different. Also, in formula (3), when a is an integer of 2 or more, 2 or more of R 7 each can be the same or different, and similarly, when c is an integer of 2 or more, 2 or more of R 8 each can be the same or different.

[0049] In addition, from the viewpoint of obtaining more superior softness, in formulae (2) and (3), as R 5 , R 6 , R7 and R 8 (wherein, R 7 and R 8 exist only in formula (3)), an alkyl group having 1 to 6 carbon atoms, a phenyl group, and the like can be respectively and independently exemplified, and as the alkyl group, a methyl group, and the like can be exemplified. Also, in formula (3), a and c can be respectively and independently set to 6 to 2000, but can also be 10 to 1000. Also, in formulae (2) and (3), b can be set to 2 to 30, but can also be 5 to 20.

[0050] (third aspect)

[0051] The aerogel according to the present embodiment can be a dried product of a wet gel that is a condensate of a sol (dried product of a wet gel derived from a sol), the wet sol containing at least one selected from the group consisting of a silicon compound having a hydrolyzable functional group or a condensable functional group and a hydrolysis product of a silicon compound having a hydrolyzable functional group. Also, the aerogel described so far can also be an aerogel thus obtained by drying a wet gel generated from a sol containing a silicon compound or the like.

[0052] As the silicon compound having a hydrolyzable functional group or a condensable functional group, a polysiloxane compound can be used. That is, the above sol can contain at least one compound selected from the group consisting of a polysiloxane compound having a hydrolyzable functional group or a condensable functional group and a hydrolysis product of a polysiloxane compound having a hydrolyzable functional group (hereinafter, referred to as "polysiloxane compound group" according to the case).

[0053] The functional group in the polysiloxane compound is not particularly limited and can be set to a group that reacts with the same functional group or with another functional group. As the hydrolyzable functional group, an alkoxy group can be given. As the condensable functional group, a hydroxyl group, a silanol group, a carboxyl group, a phenolic hydroxyl group, and the like can be given. The hydroxyl group can be included in a hydroxyalkyl group or the like that contains a hydroxyl group. In addition, the polysiloxane compound having a hydrolyzable functional group or a condensable functional group can further have a reactive group (a functional group other than the hydrolyzable functional group and the condensable functional group) different from the hydrolyzable functional group and the condensable functional group. As the reactive group, an epoxy group, a mercapto group, a glycidyloxy group, a vinyl group, an acryloyl group, a methacryloyl group, an amino group, and the like can be given. The epoxy group can be included in a glycidyloxy group or the like that contains an epoxy group. The polysiloxane compound having these functional groups and reactive groups can be used alone or two or more kinds thereof can be used in combination. Among these functional groups and reactive groups, for example, as a group that improves the softness of the aerogel, an alkoxy group, a silanol group, a hydroxyalkyl group, and the like can be given, and among these, the alkoxy group and the hydroxyalkyl group can further improve the solubility of the sol. Also, from the viewpoint of improving the reactivity of the polysiloxane compound and reducing the thermal conductivity of the aerogel, the number of carbon atoms of the alkoxy group and the hydroxyalkyl group can be set to 1 to 6, but from the viewpoint of further improving the softness of the aerogel, it can be 2 to 5, and it can be 2 to 4.

[0054] As the polysiloxane compound having a hydroxyalkyl group in the molecule, a polysiloxane compound having a structure represented by the following general formula (A) can be given. By using the polysiloxane compound having a structure represented by the following general formula (A), a structure represented by general formula (1) and formula (1a) can be introduced into the skeleton of the aerogel.

[0055]

[0056] In formula (A), R 1a represents a hydroxyalkyl group, R 2a represents an alkylene group, R 3a represents a hydroxyalkyl group, and R 4a each independently represents an alkyl group or an aryl group, and n represents an integer of 1 to 50. Here, as the aryl group, a phenyl group, a substituted phenyl group, and the like can be given. Also, as the substituent of the substituted phenyl group, an alkyl group, a vinyl group, a mercapto group, an amino group, a nitro group, a cyano group, and the like can be given. In addition, in formula (A), 2 R 1a each can be the same or different, and similarly, 2 R 2a each can be the same or different. Also, in formula (A), 2 or more R 3a each can be the same or different, and similarly, 2 or more R 4a each can be the same or different.

[0057] By using a wet gel (generated from a sol) that is a condensate of a sol containing the above-described polysiloxane compound, a low-thermal-conductivity and soft aerogel is further easily obtained. From this viewpoint, in formula (A), as R 1a may be mentioned, and as the hydroxyalkyl group, a hydroxyethyl group, a hydroxypropyl group, and the like can be mentioned. Also, in formula (A), as R 2a may be mentioned, and as the alkylene group, an ethylene group, a propylene group, and the like can be mentioned. Also, in formula (A), as R 3a and R 4a may each independently be mentioned, and as the alkyl group, a methyl group, and the like can be mentioned. Also, in formula (A), n can be set to 2 to 30, but can also be 5 to 20.

[0058] As the polysiloxane compound having the structure represented by the above-described general formula (A), commercially available products can be used, and compounds such as X-22-160AS, KF-6001, KF-6002, KF-6003, and the like (all manufactured by Shin-Etsu Chemical Co., Ltd.), XF42-B0970, Fluid OFOH 702-4%, and the like (all manufactured by Momentive) can be mentioned.

[0059] As the polysiloxane compound having an alkoxy group in the molecule, a polysiloxane compound having a structure represented by the following general formula (B) can be mentioned. By using a polysiloxane compound having a structure represented by the following general formula (B), a ladder structure having a bridging portion represented by general formula (2) or (3) can be introduced into the skeleton of the aerogel.

[0060]

[0061] In formula (B), R 1b represents an alkyl group, an alkoxy group, or an aryl group, R 2b and R 3b each independently represent an alkoxy group, R 4b and R 5b each independently represent an alkyl group or an aryl group, and m represents an integer of 1 to 50. Here, as the aryl group, a phenyl group, a substituted phenyl group, and the like can be mentioned. Also, as the substituent of the substituted phenyl group, an alkyl group, a vinyl group, a mercapto group, an amino group, a nitro group, a cyano group, and the like can be mentioned. Also, in formula (B), the 2 R 1b may each be the same or different, and the 2 R 2b may each be the same or different, and likewise, the 2 R 3beach of which can be the same or different. Also, in formula (B), when m is an integer of 2 or more, 2 or more of R 4b each of which can be the same or different. Also, 2 or more of R 5b each of which can be the same or different.

[0062] By using a (wet) gel (formed from a sol) that is a condensate of a sol containing the above-described polysiloxane compound or a hydrolysis product thereof, a low-thermal-conductivity and soft aerogel is further easily obtained. From this viewpoint, in formula (B), as R 1b , an alkyl group having 1 to 6 carbon atoms, an alkoxy group having 1 to 6 carbon atoms, and the like can be given, and as the alkyl group or the alkoxy group, a methyl group, a methoxy group, an ethoxy group, and the like can be given. Also, in formula (B), as R 2b , an alkyl group having 1 to 6 carbon atoms, an alkoxy group having 1 to 6 carbon atoms, and the like can be given, and as the alkyl group or the alkoxy group, a methyl group, a methoxy group, an ethoxy group, and the like can be given. Also, in formula (B), as R 3b , an alkyl group having 1 to 6 carbon atoms, an alkoxy group having 1 to 6 carbon atoms, and the like can be given, and as the alkyl group or the alkoxy group, a methyl group, a methoxy group, an ethoxy group, and the like can be given. Also, in formula (B), as R 4b , an alkyl group having 1 to 6 carbon atoms, an alkoxy group having 1 to 6 carbon atoms, and the like can be given, and as the alkyl group or the alkoxy group, a methyl group, a methoxy group, an ethoxy group, and the like can be given. Also, in formula (B), as R 5b , an alkyl group having 1 to 6 carbon atoms, an alkoxy group having 1 to 6 carbon atoms, and the like can be given, and as the alkyl group or the alkoxy group, a methyl group, a methoxy group, an ethoxy group, and the like can be given. Also, in formula (B), m can be set to 2 to 30, but can also be 3 to 35, or 5 to 20.

[0063] The polysiloxane compound having the structure represented by the above-described general formula (B) can be obtained by appropriately referring to the production method reported in Japanese Patent Application Publication No. 2000-26609, Japanese Patent Application Publication No. 2012-233110, and the like. Also, as the polysiloxane compound, XR31-B1410 (manufactured by Momentive) can also be used.

[0064] In addition, since the alkoxy group undergoes hydrolysis, the polysiloxane compound having the alkoxy group can exist in the sol in the form of a hydrolysis product, and the polysiloxane compound having the alkoxy group and the hydrolysis product thereof can be mixedly present. Also, in the polysiloxane compound having the alkoxy group, the alkoxy group in the molecule can be all hydrolyzed, or can be partially hydrolyzed.

[0065] These polysiloxane compounds having a hydrolyzable functional group or a condensable functional group and the hydrolysis product of the polysiloxane compound having a hydrolyzable functional group can be used alone or two or more kinds can be used in mixture.

[0066] When the aerogel according to the present embodiment is produced, as the silicon compound having a hydrolyzable functional group or a condensable functional group, a silicon compound other than the polysiloxane compound described above can be used. That is, the sol containing the silicon compound described above can contain at least one selected from the group consisting of a silicon compound (other than a polysiloxane compound) having a hydrolyzable functional group or a condensable functional group and a hydrolysis product of the silicon compound having a hydrolyzable functional group, in addition to the above-described polysiloxane compound group, or instead of the above-described polysiloxane compound group (hereinafter, referred to as "silicon compound group" as the case can be). The number of silicon atoms in the molecule of the silicon compound can be 1 or 2.

[0067] As the silicon compound having a hydrolyzable functional group in the molecule, there are no particular limitations, and examples include alkylsilicon alcoholates and the like. From the viewpoint of improving water resistance, the number of hydrolyzable functional groups of the alkylsilicon alcoholate can be 3 or less. As such alkylsilicon alcoholates, monalkyltrialkoxysilane, monoalkyldialkoxysilane, dialkyldialkoxysilane, monoalkylmonoalkoxysilane, dialkylmonoalkoxysilane, trialkylmonoalkoxysilane, and the like can be given, and specifically, methyltrimethoxysilane, methyldimethoxysilane, dimethyldiethoxysilane, dimethyldimethoxysilane, ethyltrimethoxysilane, hexyltrimethoxysilane, and the like can be given. Here, as the hydrolyzable functional group, an alkoxy group such as a methoxy group, an ethoxy group, and the like can be given.

[0068] As the silicon compound having a condensable functional group, there are no particular limitations, and examples include silanetetrol, methylsilanetriol, dimethylsilanediol, phenylsilanetriol, phenylmethylsilanediol, diphenylsilanediol, n-propylsilanetriol, hexylsilanetriol, octylsilanetriol, decylsilanetriol, trifluoropropylsilanetriol, and the like.

[0069] The silicon compound having a hydrolyzable functional group or a condensable functional group can also have the above-described reactive group (functional group other than the hydrolyzable functional group and the condensable functional group) other than the hydrolyzable functional group and the condensable functional group.

[0070] As the silicon compound having a number of hydrolyzable functional groups of 3 or less and having a reactive group, vinyltrimethoxysilane, 3-glycidyloxypropyltrimethoxysilane, 3-glycidyloxypropylmethyldimethoxysilane, 3-methacryloyloxypropyltrimethoxysilane, 3-methacryloyloxypropylmethyldimethoxysilane, 3-acryloyloxypropyltrimethoxysilane, 3-mercaptopropyltrimethoxysilane, 3-mercaptopropylmethyldimethoxysilane, N-phenyl-3-aminopropyltrimethoxysilane, N-2-(aminoethyl)-3-aminopropylmethyldimethoxysilane, and the like can also be used.

[0071] Also, as the silicon compound having a condensation functional group and having a reactive group, vinylsilanetriol, 3-glycidyloxypropylsilanetriol, 3-glycidyloxypropylmethylsilandiol, 3-methacryloyloxypropylsilanetriol, 3-methacryloyloxypropylmethylsilandiol, 3-acryloyloxypropylsilanetriol, 3-mercaptopropylsilanetriol, 3-mercaptopropylmethylsilandiol, N-phenyl-3-aminopropylsilanetriol, N-2-(aminoethyl)-3-aminopropylmethylsilandiol, and the like can be used.

[0072] In addition, as the silicon compound having 3 or less hydrolyzable functional groups at the molecular terminals, bistrimethoxysilylmethane, bistrimethoxysilyl ethane, bistrimethoxysilylhexane, ethyltrimethoxysilane, vinyltrimethoxysilane, and the like can be used.

[0073] The silicon compound having a hydrolyzable functional group or a condensation functional group (excluding polysiloxane compounds) and the hydrolysis product of the silicon compound having a hydrolyzable functional group can be used alone or two or more kinds thereof can be used in mixture.

[0074] By using the above-described silicon compound (excluding polysiloxane compounds), the structures represented by the following general formulas (4) to (6) can be introduced into the skeleton of the aerogel. The aerogel according to the present embodiment can have any one of these structures alone or two or more kinds of these structures.

[0075]

[0076] In formula (4), R 9 represents an alkyl group. Here, as the alkyl group, an alkyl group having 1 to 6 carbon atoms or the like can be mentioned, and as the alkyl group, a methyl group or the like can be mentioned.

[0077]

[0078] In formula (5), R 10 and R 11 each independently represent an alkyl group. Here, as the alkyl group, an alkyl group having 1 to 6 carbon atoms or the like can be mentioned, and as the alkyl group, a methyl group or the like can be mentioned.

[0079]

[0080] In formula (6), R 12 represents an alkylene group. Here, as the alkylene group, an alkylene group having 1 to 10 carbon atoms or the like can be mentioned, and as the alkylene group, an ethylene group, a hexylene group, or the like can be mentioned.

[0081] (Fourth Aspect)

[0082] From the viewpoint of further toughening and achieving further excellent thermal insulation and flexibility, the aerogel according to the present embodiment can contain silica particles in addition to the aerogel component. The aerogel containing the aerogel component and the silica particles can also be referred to as an aerogel composite. In the aerogel composite, although the aerogel component and the silica particles are complexed, it is considered that the cluster structure characteristic of the aerogel is maintained, and a fine porous structure is three-dimensionally provided.

[0083] The aerogel containing the aerogel component and the silica particles can be referred to as a dried product of a wet gel that is a condensate of a sol containing at least one selected from the group consisting of the above-described silicon compound having a hydrolyzable functional group or a condensable functional group and a hydrolysis product of a silicon compound having a hydrolyzable functional group and the silica particles. Therefore, the description relating to the first to third modes can also be appropriately applied to the aerogel according to the present embodiment.

[0084] The silica particles can be used without particular limitation, and examples include amorphous silica particles and the like. Examples of the amorphous silica particles include fused silica particles, fumed silica particles, colloidal silica particles, and the like. Among these, the colloidal silica particles have high monodispersity and are easy to inhibit aggregation in the sol. In addition, the silica particles can be silica particles having a hollow structure, a porous structure, or the like.

[0085] The shape of the silica particles is not particularly limited, and examples include spherical, cocoon-type, and associated-type. Among these, by using spherical particles as the silica particles, aggregation in the sol is easily inhibited. From the viewpoint of easily imparting appropriate strength and flexibility to the aerogel and easily obtaining an aerogel excellent in resistance to shrinkage upon drying, the average primary particle diameter of the silica particles can be 1 nm or more, 5 nm or more, or 20 nm or more. From the viewpoint of easily inhibiting solid thermal conduction of the silica particles and easily obtaining an aerogel excellent in thermal insulation, the average primary particle diameter of the silica particles can be 500 nm or less, 300 nm or less, or 100 nm or less. From these viewpoints, the average primary particle diameter of the silica particles can be 1 to 500 nm, 5 to 300 nm, or 20 to 100 nm.

[0086] In the present embodiment, the average particle diameter of the aerogel component and the average primary particle diameter of the silica particles can be obtained by directly observing the aerogel using a scanning electron microscope (hereinafter, referred to as "SEM"). The "diameter" as used herein means the diameter of a circle when the cross section of a particle exposed on the cross section of the aerogel is regarded as a circle. Further, the "diameter of a circle when the cross section is regarded as a circle" means the diameter of a true circle when the area of the cross section is replaced by the area of the true circle. In addition, in calculating the average particle diameter, the diameters of 100 particles are measured and averaged.

[0087] Further, the average particle diameter of the silica particles can also be measured from the raw material. For example, the average primary particle diameter of the biaxial silica particles is calculated from the results obtained by observing 20 arbitrary particles using SEM in the following manner. That is, taking as an example the case of colloidal silica particles having a solid component concentration of generally 5 to 40 mass% or so and dispersed in water, a chip obtained by cutting a wafer having a pattern wiring into a square of 2 cm is immersed for about 30 seconds, and then the chip is washed with pure water for about 30 seconds and subjected to nitrogen blowing drying. Then, the chip is placed on a sample stage for SEM observation, and the silica particles are observed at a magnification of 100,000 times at an acceleration voltage of 10 kV, and an image is taken. From the obtained image, 20 arbitrary silica particles are selected, and the average of the particle diameters of these particles is taken as the average particle diameter.

[0088] From the viewpoint of easily obtaining an aerogel having excellent shrinkage resistance, the number of silanol groups per 1 g of silica particles can be 10 x 10 18 or more, 50 x 10 18 or more, or 100 x 10 18 or more. From the viewpoint of easily obtaining a homogeneous aerogel, the number of silanol groups per 1 g of silica particles can be 1000 x 10 18 or less, 800 x 10 18 or less, or 700 x 10 18 or less. From these viewpoints, the number of silanol groups per 1 g of silica particles can be 10 x 10 18 to 1000 x 10 18 or less, 50 x 10 18 to 800 x 10 18 or less, or 100 x 10 18 to 700 x 10 18 or less.

[0089] From the viewpoint of further easily obtaining good reactivity, the content of the polysiloxane compound group (the sum of the content of the polysiloxane compound having a hydrolyzable functional group or a condensable functional group and the content of the hydrolysis product of the polysiloxane compound having a hydrolyzable functional group) in the above-described sol can be 5 parts by mass or more, or 10 parts by mass or more, relative to 100 parts by mass of the total amount of the sol. From the viewpoint of further easily obtaining good compatibility, the content of the polysiloxane compound group in the above-described sol can be 50 parts by mass or less, or 30 parts by mass or less, relative to 100 parts by mass of the total amount of the sol. From these viewpoints, the content of the polysiloxane compound group in the above-described sol can be 5 to 50 parts by mass, or 10 to 30 parts by mass, relative to 100 parts by mass of the total amount of the sol.

[0090] When the above-described sol contains a silicon compound (other than a polysiloxane compound), from the viewpoint of further easily obtaining good reactivity, the silicon compound group (the sum of the content of the silicon compound having a hydrolyzable functional group or a condensable functional group and the content of the hydrolysis product of the silicon compound having a hydrolyzable functional group) can be 5 parts by mass or more, or 7 parts by mass or more, or 10 parts by mass or more, relative to 100 parts by mass of the total amount of the sol. From the viewpoint of further easily obtaining good compatibility, the content of the silicon compound group in the above-described sol can be 50 parts by mass or less, or 40 parts by mass or less, or 30 parts by mass or less, relative to 100 parts by mass of the total amount of the sol.

[0091] When the sol contains both the polysiloxane compound group and the silicon compound group, from the viewpoint of further easily obtaining good compatibility, the ratio of the content of the polysiloxane compound group to the content of the silicon compound group can be 1:0.5 or more, or 1:0.7 or more, or 1:1 or more. From the viewpoint of further easily suppressing shrinkage of the gel, the ratio of the content of the polysiloxane compound group to the content of the silicon compound group can be 1:4 or less, or 1:3 or less, or 1:2 or less. From these viewpoints, the ratio of the content of the polysiloxane compound group to the content of the silicon compound group can be 1:0.5 to 1:4, or 1:0.7 to 1:3, or 1:1 to 1:2.

[0092] When the silica particles are contained in the above sol, from the viewpoint of easily imparting the aerogel with appropriate strength, easily obtaining an aerogel excellent in shrinkage resistance at drying, the content of the silica particles can be 1 part by mass or more, 2 parts by mass or more, or 4 parts by mass or more, relative to 100 parts by mass of the total amount of the sol. From the viewpoint of easily suppressing the solid thermal conductivity of the silica particles, easily obtaining an aerogel excellent in thermal insulation, the content of the silica particles can be 20 parts by mass or less, 17 parts by mass or less, or 15 parts by mass or less, relative to 100 parts by mass of the total amount of the sol. From these viewpoints, the content of the silica particles can be 1 to 20 parts by mass, 2 to 17 parts by mass, or 4 to 15 parts by mass, relative to 100 parts by mass of the total amount of the sol.

[0093] Aerogel particles

[0094] As described later, the aerogel particles in the present embodiment can be obtained, for example, by pulverizing a bulk aerogel.

[0095] The average particle diameter D50 (also referred to as the average diameter) of the aerogel particles can be 0.1 to 1000 μm, but can also be 0.5 to 700 μm, 1 to 500 μm, 3 to 100 μm, or 5 to 50 μm. If the average particle diameter D50 of the aerogel particles is large, aerogel particles excellent in dispersibility, handleability, and the like are easily obtained. On the other hand, if the average particle diameter D50 is small, aerogel particles excellent in dispersibility are easily obtained. The average particle diameter of the aerogel particles can be appropriately adjusted depending on the pulverizing method and conditions, sieving, classification method, and the like.

[0096] The average particle diameter D50 of the aerogel particles can be measured by a laser diffraction / scattering method. For example, the aerogel particles are dispersed by adding the aerogel particles to a solvent (ethanol) so that the content of the aerogel particles becomes 0.05 to 5% by mass, and vibrating with a 50 W ultrasonic homogenizer for 15 to 30 minutes. Then, about 10 mL or more of the dispersion liquid is injected into a laser diffraction / scattering type particle size distribution measuring device, and the particle size is measured at 25°C with a refractive index of 1.3 and an absorption of 0. Then, the particle diameter at the cumulative value of 50% (volume basis) in the particle size distribution is set as the average particle diameter D50. As the measuring device, for example, a Microtrac MT3000 (manufactured by Nikkiso Co., Ltd., product name) can be used.

[0097] Also, as the aerogel particles, commercially available products can be used. As the commercially available products of the aerogel particles, for example, ENOVA MT1100 (manufactured by CABOT CORPORATION), AeroVa (manufactured by JIOS AEROGEL CORPORATION), and the like can be given.

[0098] In the present embodiment, the amount of the aerogel particles is preferably an amount in which the total content of the aerogel particles and the agglomerates in the coating liquid becomes 70% by volume or more, more preferably 75% by volume or more, and further preferably 80% by volume or more, based on the total volume of the solid components. Also, the amount of the aerogel particles can be, for example, an amount in which the total content of the aerogel particles and the agglomerates in the coating liquid becomes 99% by volume or less, based on the total volume of the solid components, and can be an amount in which the total content becomes 95% by volume or less, or an amount in which the total content becomes 90% by volume or less.

[0099] <Method for producing aerogel particles>

[0100] The method for producing the aerogel particles is not particularly limited, and for example, can be produced by the following method.

[0101] The aerogel particles of the present embodiment can be produced by a production method mainly comprising: a sol generation step; a wet gel generation step of gelating the sol obtained in the sol generation step and then aging to obtain a wet gel; a cleaning and solvent replacement step of cleaning and (as necessary) replacing the solvent of the wet gel obtained in the wet gel generation step; a drying step of drying the wet gel after the cleaning and solvent replacement; and a pulverization step of pulverizing the aerogel obtained by the drying.

[0102] Also, the aerogel particles can be produced by a production method mainly comprising a sol generation step, a wet gel generation step, a wet gel pulverization step of pulverizing the wet gel obtained in the wet gel generation step, a cleaning and solvent replacement step, and a drying step.

[0103] The obtained aerogel particles can be further adjusted in size by sieving, fractionation, or the like. By adjusting the size of the particles, dispersibility can be improved. In addition, "sol" refers to a state before a gelation reaction occurs, and in the present embodiment, refers to a state in which the above-described silicon compound and, as the case can be, the silica particles are dissolved or dispersed in a solvent. Also, the wet gel refers to a gel solid in a wet state that does not have fluidity despite containing a liquid medium.

[0104] (Sol generation step)

[0105] The sol generation step is a step of generating a sol after mixing a silicon compound and silica particles (a solvent containing silica particles can also be used) as necessary and performing a hydrolysis reaction. In this step, an acid catalyst can also be added to the solvent in order to promote the hydrolysis reaction. Also, as shown in Japanese Patent No. 5250900, a surfactant, a thermohydrolyzable compound, or the like can be added to the solvent. In addition, in order to suppress heat radiation and the like, a component such as carbon graphite, an aluminum compound, a magnesium compound, a silver compound, a titanium compound, or the like can be added to the solvent.

[0106] As the solvent, for example, water or a mixture of water and an alcohol can be used. As the alcohol, methanol, ethanol, n-propanol, 2-propanol, n-butanol, 2-butanol, t-butanol, or the like can be given. Among these, from the viewpoint of reducing the interfacial tension with the gel wall, as an alcohol having a low surface tension and a low boiling point, methanol, ethanol, 2-propanol, or the like can be given. These can be used alone or two or more kinds can be used in combination.

[0107] For example, when an alcohol is used as the solvent, the amount of the alcohol can be set to 4 to 8 moles, but can also be 4 to 6.5 moles, or can also be 4.5 to 6 moles, with respect to 1 mole of the total amount of the silicon compound group and the polysiloxane compound group. By setting the amount of the alcohol to 4 moles or more, further good compatibility is easily obtained, and by setting it to 8 moles or less, further shrinkage of the gel is easily suppressed.

[0108] As the acid catalyst, an inorganic acid such as fluoric acid, hydrochloric acid, nitric acid, sulfuric acid, sulfurous acid, phosphoric acid, phosphorous acid, hypophosphorous acid, bromic acid, chloric acid, chlorous acid, hypochlorous acid, or the like; an acid phosphate salt such as acid aluminum phosphate, acid magnesium phosphate, acid zinc phosphate, or the like; an organic carboxylic acid such as acetic acid, formic acid, propionic acid, oxalic acid, malonic acid, succinic acid, citric acid, malic acid, adipic acid, azelaic acid, or the like can be given. Among these, as an acid catalyst that further improves the water resistance of the obtained aerogel, an organic carboxylic acid can be given. As this organic carboxylic acid, acetic acid can be given, but formic acid, propionic acid, oxalic acid, malonic acid, or the like can also be given. These can be used alone or two or more kinds can be used in combination.

[0109] By using an acid catalyst, the hydrolysis reaction of the silicon compound can be promoted, and a sol can be obtained in a shorter time.

[0110] The amount of the acid catalyst to be added can be set to 0.001 to 0.1 parts by mass with respect to 100 parts by mass of the total amount of the polysiloxane compound group and the silicon compound group.

[0111] As the surfactant, a nonionic surfactant, an ionic surfactant, or the like can be used. These can be used alone or two or more kinds can be used in combination.

[0112] As the nonionic surfactant, for example, a compound including a hydrophilic portion of polyoxyethylene or the like and a hydrophobic portion mainly formed of an alkyl group, a compound including a hydrophilic portion of polyoxypropylene or the like, and the like can be used. As the compound including a hydrophilic portion of polyoxyethylene or the like and a hydrophobic portion mainly formed of an alkyl group, polyoxyethylene nonylphenyl ether, polyoxyethylene octylphenyl ether, polyoxyethylene alkyl ether, and the like can be given. As the compound including a hydrophilic portion of polyoxypropylene or the like, polyoxypropylene alkyl ether, a block copolymer of polyoxyethylene and polyoxypropylene, and the like can be given.

[0113] As the ionic surfactant, a cationic surfactant, an anionic surfactant, a zwitterionic surfactant, and the like can be given. As the cationic surfactant, cetyltrimethylammonium bromide, cetyltrimethylammonium chloride, and the like can be given, and as the anionic surfactant, sodium dodecylsulfate, and the like can be given. Further, as the zwitterionic surfactant, an amino acid-based surfactant, a betaine-based surfactant, an amine oxide-based surfactant, and the like can be given. As the amino acid-based surfactant, for example, acyl glutamic acid and the like can be given. As the betaine-based surfactant, for example, lauryldimethylaminoethanobetaine, stearyldimethylaminoethanobetaine, and the like can be given. As the amine oxide-based surfactant, for example, lauryldimethylamine oxide can be given.

[0114] It is considered that these surfactants play a role of reducing the difference in chemical affinity between the solvent and the gradually growing siloxane polymer in the reaction system and inhibiting phase separation in the wet gel generation process described later.

[0115] The addition amount of the surfactant also depends on the kind of the surfactant or the kind and amount of the silicon compound, and for example, it can be set to 1 to 100 parts by mass with respect to 100 parts by mass of the total amount of the polysiloxane compound group and the silicon compound group. In addition, the addition amount can also be 5 to 60 parts by mass.

[0116] It is considered that the thermohydrolyzable compound generates an alkali catalyst by thermal hydrolysis, makes the reaction solution alkaline, and promotes the sol-gel reaction in the wet gel generation process described later. Therefore, as the thermohydrolyzable compound, as long as it is a compound that can make the reaction solution alkaline after hydrolysis, it is not particularly limited, and urea; acid amides such as formamide, N-methylformamide, N,N-dimethylformamide, acetamide, N-methylacetamide, N,N-dimethylacetamide; cyclic nitrogen compounds such as hexamethylenetetramine, and the like can be given. Among these, urea is particularly easy to obtain the above-mentioned promoting effect.

[0117] The amount of the thermohydrolytic compound to be added is not particularly limited as long as it is an amount sufficient to promote the sol-gel reaction in the wet gel production process described later. For example, when urea is used as the thermohydrolytic compound, the amount thereof to be added can be set to 1 to 200 parts by mass relative to 100 parts by mass of the total amount of the polysiloxane compound group and the silicon compound group. Alternatively, the amount can be 2 to 150 parts by mass. By setting the amount to be added to 1 part by mass or more, further good reactivity is easily obtained, and by setting the amount to be added to 200 parts by mass or less, further suppression of the precipitation of crystals and the decrease in the gel density is easily achieved.

[0118] The hydrolysis in the sol production process also depends on the types and amounts of the silicon compound, the silica particles, the acid catalyst, the surfactant, and the like in the mixed solution, and can be performed, for example, at a temperature environment of 20 to 60°C for 10 minutes to 24 hours, or at a temperature environment of 50 to 60°C for 5 minutes to 8 hours. Thus, the hydrolytic functional group in the silicon compound is sufficiently hydrolyzed, and the hydrolysis product of the silicon compound is more reliably obtained.

[0119] However, when the thermohydrolytic compound is added to the solvent, the temperature environment in the sol production process can be adjusted to a temperature at which the hydrolysis of the thermohydrolytic compound is suppressed to suppress the gelation of the sol. The temperature at this time can be any temperature as long as it is a temperature at which the hydrolysis of the thermohydrolytic compound is suppressed. For example, when urea is used as the thermohydrolytic compound, the temperature environment in the sol production process can be set to 0 to 40°C, but can also be 10 to 30°C.

[0120] (Wet gel production process)

[0121] The wet gel production process is a process in which the sol obtained in the sol production process is gelled and then aged to obtain a wet gel. In this process, an alkali catalyst can be used in order to promote the gelation.

[0122] As the base catalyst, carbonates such as calcium carbonate, potassium carbonate, sodium carbonate, barium carbonate, magnesium carbonate, lithium carbonate, ammonium carbonate, copper (II) carbonate, iron (II) carbonate, silver (I) carbonate; bicarbonates such as calcium bicarbonate, potassium bicarbonate, sodium bicarbonate, ammonium bicarbonate; alkali metal hydroxides such as lithium hydroxide, sodium hydroxide, potassium hydroxide, cesium hydroxide; ammonium compounds such as ammonium hydroxide, ammonium fluoride, ammonium chloride, ammonium bromide; alkali phosphoric acid sodium salts such as sodium metaphosphate, sodium pyrophosphate, sodium polyphosphate; aliphatic amines such as allylamine, diallylamine, triallylamine, isopropylamine, diisopropylamine, ethylamine, diethylamine, triethylamine, 2-ethylhexylamine, 3-ethoxypropylamine, diisobutylamine, 3-(diethylamino)propylamine, di-2-ethylhexylamine, 3-(dibutylamino)propylamine, tetramethylethylenediamine, t-butylamine, sec-butylamine, propylamine, 3-(methylamino)propylamine, 3-(dimethylamino)propylamine, 3-methoxypropylamine, dimethylethanolamine, methyldiethanolamine, diethanolamine, triethanolamine; nitrogen-containing heterocyclic compounds such as morpholine, N-methylmorpholine, 2-methylmorpholine, piperazine and derivatives thereof, piperidine and derivatives thereof, imidazole and derivatives thereof; and the like can be given. Among these, ammonium hydroxide (ammonia) is excellent in terms of volatility, in that it is difficult to remain in the aerogel particles after drying, and in terms of economics, in that it does not impair water resistance. The above-mentioned base catalyst can be used alone or in combination with two or more.

[0123] By using a base catalyst, the dehydration condensation reaction or dealcoholization condensation reaction of the silicon compound and the silica particles in the sol can be promoted, and the gelation of the sol can be performed in a shorter time. Furthermore, a wet gel having higher strength (rigidity) can be obtained. In particular, since ammonia has high volatility and is difficult to remain in the aerogel particles, by using ammonia as a base catalyst, an aerogel particle having more excellent water resistance can be obtained.

[0124] The amount of the base catalyst to be added can be 0.5 to 5 parts by mass, but can also be 1 to 4 parts by mass, relative to 100 parts by mass of the total amount of the polysiloxane compound group and the silicon compound group. By being 0.5 parts by mass or more, the gelation can be performed in a shorter time, and by being 5 parts by mass or less, the decrease in water resistance can be more suppressed.

[0125] The gelation of the sol in the wet gel production step can be performed in a closed container so as not to volatilize the solvent and the base catalyst. The gelation temperature can be 30 to 90°C, but can also be 40 to 80°C. By being 30°C or more, the gelation can be performed in a shorter time, and a wet gel having higher strength (rigidity) can be obtained. Furthermore, by being 90°C or less, the volatilization of the solvent (particularly alcohol) is easily suppressed, and thus the gelation can be performed while suppressing the volume shrinkage.

[0126] The ripening in the wet gel production step can be performed in a closed container to prevent volatilization of the solvent and the base catalyst. By ripening, the combination of the components constituting the wet gel is enhanced, and as a result, a wet gel having a high strength (stiffness) sufficient to suppress shrinkage upon drying can be obtained. The ripening temperature can be set to 30 to 90°C, but can also be 40 to 80°C. By setting the ripening temperature to 30°C or higher, a wet gel having a higher strength (stiffness) can be obtained, and by setting the ripening temperature to 90°C or lower, volatilization of the solvent (particularly alcohol) is easily suppressed, and thus gelation can be performed while suppressing volume shrinkage.

[0127] In addition, since the point in time at which gelation of the sol ends is difficult to determine in many cases, the gelation of the sol and the ripening thereafter can be continuously performed by a series of operations.

[0128] The gelation time and the ripening time can be appropriately set according to the gelation temperature and the ripening temperature. When silica particles are contained in the sol, the gelation time can be particularly shortened compared to the case where no silica particles are contained. The reason is presumed to be that the silanol group or the reactive group possessed by the silicon compound in the sol forms a hydrogen bond or a chemical bond with the silanol group of the silica particles. In addition, the gelation time can be set to 10 to 120 minutes, but can also be 20 to 90 minutes. By setting the gelation time to 10 minutes or more, a homogeneous wet gel is easily obtained, and by setting it to 120 minutes or less, the cleaning and solvent replacement process to the drying process described later can be simplified. In addition, as a whole of the gelation and ripening processes, the total time of the gelation time and the ripening time can be set to 4 to 480 hours, but can also be 6 to 120 hours. By setting the total of the gelation time and the ripening time to 4 hours or more, a wet gel having a higher strength (stiffness) can be obtained, and by setting it to 480 hours or less, the ripening effect is more easily maintained.

[0129] In order to reduce the density or increase the average pore diameter of the obtained aerogel particles, the gelation temperature and the ripening temperature can be increased within the above range, or the total of the gelation time and the ripening time can be extended within the above range. Also, in order to increase the density or reduce the average pore diameter of the obtained aerogel particles, the gelation temperature and the ripening temperature can be decreased within the above range, or the total of the gelation time and the ripening time can be shortened within the above range.

[0130] (Wet gel pulverization step)

[0131] When the wet gel pulverization process is performed, the wet gel obtained in the wet gel production process is pulverized. The pulverization can be performed, for example, by placing the wet gel in a Henschel-type stirrer, or performing the wet gel production process in the stirrer, and operating the stirrer under appropriate conditions (rotation speed and time). Also, more simply, the pulverization can be performed by placing the wet gel in a container that can be closed, or performing the wet gel production process in the container that can be closed, and oscillating using an oscillation device such as a vibrator for an appropriate time. In addition, as needed, a jet-type pulverizer, a roll mill, a bead mill, or the like can be used to adjust the particle diameter of the wet gel.

[0132] (Washing and solvent replacement process)

[0133] The washing and solvent replacement process is a process having a process of washing the wet gel obtained by the wet gel production process or the wet gel pulverization process (washing process), and a process of replacing the washing liquid in the wet gel with a solvent suitable for the drying conditions (drying process described later) (solvent replacement process). The washing and solvent replacement process can also be performed in a manner in which the process of washing the wet gel is not performed and only the solvent replacement process is performed, but from the viewpoint of reducing impurities such as unreacted materials, by-products, and the like in the wet gel, and enabling the production of aerogel particles of higher purity, it is also possible to wash the wet gel.

[0134] In the washing process, the wet gel obtained by the wet gel production process or the wet gel pulverization process is washed. This washing can be performed repeatedly using water or an organic solvent, for example. At this time, the washing efficiency can be improved by heating.

[0135] As the organic solvent, various organic solvents such as methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, acetone, methyl ethyl ketone, 1,2-dimethoxyethane, acetonitrile, hexane, toluene, diethyl ether, chloroform, ethyl acetate, tetrahydrofuran, dichloromethane, N,N-dimethylformamide, dimethyl sulfoxide, acetic acid, formic acid, and the like can be used. The above-mentioned organic solvents can be used alone or in combination with two or more.

[0136] In the solvent replacement process described later, in order to suppress shrinkage of the gel caused by drying, a solvent having a low surface tension can be used. However, a solvent having a low surface tension generally has a very low mutual solubility with water. Therefore, when a solvent having a low surface tension is used in the solvent replacement process, as the organic solvent used in the cleaning process, a hydrophilic organic solvent having a high mutual solubility with both water and the solvent having a low surface tension can be mentioned. In addition, the hydrophilic organic solvent used in the cleaning process can function as a pre-replacement for the solvent replacement process. Among the above organic solvents, as the hydrophilic organic solvent, methanol, ethanol, 2-propanol, acetone, methyl ethyl ketone, and the like can be mentioned. In addition, methanol, ethanol, methyl ethyl ketone, and the like are excellent in terms of economy.

[0137] As the amount of water or the organic solvent used in the cleaning process, an amount sufficient to replace and clean the solvent in the wet gel can be set. The amount can be set to an amount of 3 to 10 times with respect to the capacity of the wet gel. The cleaning can be repeated until the water content in the wet gel after cleaning becomes 10% by mass or less with respect to the mass of the silica.

[0138] The temperature environment in the cleaning process can be set to a temperature below the boiling point of the solvent used in the cleaning, and for example, when methanol is used, it can be set to heating at around 30 to 60°C.

[0139] In the solvent replacement process, in order to suppress shrinkage of the aerogel in the drying process, the solvent of the cleaned wet gel is replaced with a specified replacement solvent. At this time, the replacement efficiency can be improved by heating. As the replacement solvent, specifically, in the drying process, when drying is performed at a temperature lower than the critical point of the solvent used in drying and at atmospheric pressure, a solvent having a low surface tension described later can be mentioned. On the other hand, when supercritical drying is performed, as the replacement solvent, for example, ethanol, methanol, 2-propanol, dichlorodifluoromethane, carbon dioxide, or a solvent obtained by mixing two or more of them can be mentioned.

[0140] As the solvent having a low surface tension, a solvent having a surface tension of 30 mN / m or less at 20°C can be given. Further, the surface tension can be 25 mN / m or less, or can be 20 mN / m or less. As the solvent having a low surface tension, for example, aliphatic hydrocarbons such as pentane (15.5), hexane (18.4), heptane (20.2), octane (21.7), 2-methylpentane (17.4), 3-methylpentane (18.1), 2-methylhexane (19.3), cyclopentane (22.6), cyclohexane (25.2), 1-pentene (16.0), and the like; aromatic hydrocarbons such as benzene (28.9), toluene (28.5), m-xylene (28.7), p-xylene (28.3), and the like; halogenated hydrocarbons such as dichloromethane (27.9), chloroform (27.2), carbon tetrachloride (26.9), 1-chloropropane (21.8), 2-chloropropane (18.1), and the like; ethers such as diethyl ether (17.1), propyl ether (20.5), isopropyl ether (17.7), butyl ethyl ether (20.8), 1,2-dimethoxyethane (24.6), and the like; ketones such as acetone (23.3), methyl ethyl ketone (24.6), methyl propyl ketone (25.1), diethyl ketone (25.3), and the like; esters such as methyl acetate (24.8), ethyl acetate (23.8), propyl acetate (24.3), isopropyl acetate (21.2), isobutyl acetate (23.7), ethyl butyrate (24.6), and the like, and the like (the values in parentheses represent the surface tension at 20°C, in [mN / m]). Among these, the aliphatic hydrocarbons (hexane, heptane, and the like) are excellent in the surface tension and the working environment. Further, among these, by using a hydrophilic organic solvent such as acetone, methyl ethyl ketone, 1,2-dimethoxyethane, and the like, it is possible to serve as the organic solvent in the above-described cleaning step as well. Further, among these, from the viewpoint of further facilitating drying in the drying step described later, a solvent having a boiling point of 100°C or less at normal pressure can be used. The above-described solvent can be used alone or two or more kinds can be used in combination.

[0141] The amount of the solvent used in the solvent replacement step can be set to an amount sufficient to replace the solvent in the wet gels after cleaning. The amount can be set to an amount of 3 to 10 times the volume of the wet gels.

[0142] The temperature environment in the solvent replacement step can be set to a temperature of 100°C or less at normal pressure, for example, 30 to 60°C or so when heptane is used.

[0143] In addition, when silica particles are included in the gel, the solvent replacement step is not necessary. As a presumed mechanism, the following is described. That is, the shrinkage of the gel in the drying step is suppressed by the silica particles functioning as a support for a three-dimensional network skeleton, and the skeleton is supported. Therefore, it is considered that the gel can be directly supplied to the drying step without replacing the solvent used in the washing. Thus, by using silica particles, the washing and solvent replacement steps to the drying step can be simplified.

[0144] (Drying step)

[0145] In the drying step, the wet gel after the washing and (as necessary) solvent replacement described above is dried. Thereby, an aerogel (aerogel block or aerogel particles) can be obtained. That is, an aerogel obtained by drying the wet gel produced from the sol described above can be obtained.

[0146] The drying method is not particularly limited, and a publicly known normal pressure drying, supercritical drying, or freeze drying can be used. Among these, from the viewpoint of easily producing an aerogel having a low density, normal pressure drying or supercritical drying can be used. Furthermore, from the viewpoint of being able to produce at low cost, normal pressure drying can be used. In addition, in the present embodiment, normal pressure means 0.1 MPa (atmospheric pressure).

[0147] The aerogel can be obtained by drying the wet gel after the washing and (as necessary) solvent replacement at a temperature lower than the critical point of the solvent used in the drying and at atmospheric pressure. The drying temperature differs depending on the kind of the solvent (when the solvent replacement is not performed, the solvent used in the washing) to be replaced, and can be set to 20 to 150°C, particularly in view of the point that drying at a high temperature accelerates the evaporation speed of the solvent and sometimes large cracks are generated in the gel. In addition, the drying temperature can also be 60 to 120°C. Furthermore, the drying time differs depending on the capacity of the wet gel and the drying temperature, and can be set to 4 to 120 hours. In addition, applying a pressure lower than the critical point to accelerate the drying is also included in the normal pressure drying, within a range not hindering the productivity.

[0148] The aerogel can also be obtained by supercritical drying the wet gel after the washing and (as necessary) solvent replacement. The supercritical drying can be performed by a publicly known method.

[0149] As a method of performing supercritical drying, for example, a method in which a solvent contained in the wet gel is removed at a temperature and a pressure above the critical point of the solvent can be given. Alternatively, as a method of performing supercritical drying, a method in which all or a part of the solvent contained in the wet gel is replaced with carbon dioxide having a lower critical point than the solvent by impregnating the wet gel in liquefied carbon dioxide under conditions of, for example, 20 to 25°C and 5 to 20 MPa or so, and then removing the carbon dioxide alone or a mixture of the carbon dioxide and the solvent can be given.

[0150] The aerogel obtained by this atmospheric pressure drying or supercritical drying can be further dried at an atmospheric pressure and at 105 to 200°C for 0.5 to 2 hours or so. Thereby, an aerogel having a low density and small pores is further easily obtained. The additional drying can also be performed at an atmospheric pressure and at 150 to 200°C.

[0151] (Pulverization Step)

[0152] When the wet gel pulverization step is not performed, the aerogel (aerogel block) obtained by drying is pulverized to obtain the aerogel particles. For example, this can be performed by placing the aerogel in a jet mill, a roll mill, a bead mill, a hammer mill, or the like, and operating at an appropriate rotation speed and time.

[0153] <Emulsion>

[0154] In the present embodiment, the emulsion can be an emulsion in which the binder resin is emulsified using a high-molecular emulsifier in a liquid medium.

[0155] As the liquid medium, a water-based solvent containing water is preferable. In the water-based solvent, an organic solvent can be contained in addition to water. The organic solvent can be, for example, an alcohol such as methanol, ethanol, isopropanol, butanol, ethylene glycol, propylene glycol, or the like; an ether such as diethyl ether, tetrahydrofuran, 1,4-dioxane, or the like; a ketone such as acetone, methyl ethyl ketone, or the like; a carboxylic acid such as acetic acid, propionic acid, or the like; a nitrogen-containing compound such as acetonitrile, dimethylformamide, triethylamine, or the like, as long as it has a solubility with water.

[0156] The content of the liquid medium in the emulsion is not particularly limited, and can be, for example, 20 to 900 parts by mass, or 50 to 250 parts by mass, with respect to 100 parts by mass of the solid content.

[0157] The content of the liquid medium in the coating liquid is not particularly limited, and can be appropriately changed depending on the viscosity or the like of the desired coating liquid. For example, the content of the liquid medium in the coating liquid can be an amount in which the solid content concentration of the coating liquid is within the preferable range described later. In addition, the liquid medium in the coating liquid can be only the liquid medium in the emulsion, or can contain a liquid medium added when the emulsion and the aerogel particles are mixed or after the mixing.

[0158] The solid content concentration of the coating liquid may be, for example, 10% by mass or more, preferably 15% by mass or more, and more preferably 20% by mass or more. Also, the solid content concentration of the coating liquid may be, for example, 70% by mass or less, preferably 60% by mass or less, and more preferably 50% by mass or less.

[0159] The binder resin may be any resin that is emulsified in a liquid medium by a high-molecular emulsifier. Examples of the binder resin include urethane resins, alkyd resins, silicone resins, acrylic resins, olefin resins, fluorine resins, vinyl acetate resins, chlorovinyl resins, polyesters, polyamides, polyimides, and copolymers of two or more monomers that form these resins. Among these, from the viewpoint of more excellent softness of the formed thermal insulation material, ethylene-vinyl acetate copolymers, ethylene-chlorovinyl copolymers, acrylic resins, and silicone resins can be preferably used, and from the viewpoint of excellent film-forming properties at low temperatures, vinyl acetate resins can be preferably used.

[0160] The content of the binder resin in the emulsion is not particularly limited and may be, for example, 20% by mass or more or 30% by mass or more. Also, the content of the binder resin in the emulsion may be, for example, 80% by mass or less or 60% by mass or less.

[0161] The content of the binder resin in the coating liquid may be, for example, 30% by volume or less, preferably 25% by volume or less, and more preferably 20% by volume or less, based on the total volume of the solid content. Also, the content of the binder resin in the coating liquid may be, for example, 1% by volume or more, 5% by volume or more, or 10% by volume or more, based on the total volume of the solid content.

[0162] The high-molecular emulsifier may be any emulsifier that can emulsify the binder resin in a liquid medium. In the present specification, the "high-molecular emulsifier" refers to an emulsifier that is formed by polymerization of monomers (and modification of the polymer as needed). The high-molecular emulsifier can have a molecular weight distribution.

[0163] The number average molecular weight (Mn) of the high-molecular emulsifier may be, for example, 1000 or more, 5000 or more, 8000 or more, 10000 or more, or 20000 or more. Also, the number average molecular weight of the high-molecular emulsifier may be, for example, 1000000 or less, 50000 or less, 200000 or less, 100000 or less, or 50000 or less. Note that the number average molecular weight of the high-molecular emulsifier is a value measured by GPC.

[0164] Examples of the high-molecular emulsifier include polyvinyl alcohol (PVA) and hydroxyethyl cellulose.

[0165] The content of the high-molecular emulsifier in the emulsion may be, for example, 0.001 parts by mass or more, 0.01 parts by mass or more, 0.05 parts by mass or more, or 0.1 parts by mass or more, relative to 100 parts by mass of the binder resin, from the viewpoint of stabilization of the emulsion. Also, the content of the high-molecular emulsifier in the emulsion may be, for example, 80 parts by mass or less, 20 parts by mass or less, 10 parts by mass or less, or 5 parts by mass or less, relative to 100 parts by mass of the binder resin, from the viewpoint of viscosity.

[0166] The content of the high-molecular emulsifier in the coating liquid may be, for example, 0.0001 parts by mass or more, 0.001 parts by mass or more, 0.005 parts by mass or more, or 0.01 parts by mass or more, relative to 100 parts by mass of the binder resin, from the viewpoint of stabilization of the emulsion. Also, the content of the high-molecular emulsifier in the coating liquid may be, for example, 80 parts by mass or less, 20 parts by mass or less, 10 parts by mass or less, or 5 parts by mass or less, relative to 100 parts by mass of the binder resin, from the viewpoint of ease of handling at the time of blending.

[0167] The method for producing the emulsion is not particularly limited, and for example, a method in which the binder resin is synthesized in the presence of a high-molecular emulsifier in a liquid medium

[0168] The emulsion can further contain other components other than those described above. As the other components, for example, fillers, solvents, pigments, dyes, preservatives, antifoaming agents, and the like can be mentioned.

[0169] <Water-soluble high-molecular>

[0170] The coating liquid of the present embodiment can further contain a water-soluble high-molecular having a hydrophobic group. The water-soluble high-molecular can be added at the time of mixing the emulsion and the aerogel particles or after the mixing.

[0171] As the hydrophobic group, for example, an alkyl group (preferably a long-chain alkyl group having 6 to 26 carbon atoms), an ester group, an alkoxy group, a halogen, and the like can be mentioned. Among these, as the hydrophobic group, an alkyl group is preferable, a long-chain alkyl group having 8 to 26 carbon atoms is more preferable, a long-chain alkyl group having 10 to 26 carbon atoms is further preferable, a long-chain alkyl group having 12 to 26 carbon atoms is further preferable, and a long-chain alkyl group having 15 to 26 carbon atoms can also be used.

[0172] As the water-soluble high-molecular, for example, a modified carboxyvinyl polymer, a modified polyether urethane, a cellulose-based resin, a polyethylene oxide, a polyvinyl alcohol, a polyacrylate, a polyvinylpyrrolidone, a dextrin-based resin, a chitin-based resin, a chitosan-based resin, and the like can be mentioned.

[0173] As the water-soluble polymer, a cellulose-based resin can be preferably used. As the cellulose-based resin, for example, methylcellulose, carboxymethylcellulose, hydroxyethylcellulose, hydroxypropylmethylcellulose, and a modified body thereof which is further modified (for example, hydrophobized) can be mentioned.

[0174] As the cellulose-based resin, a cellulose-based resin having an alkyl group is preferable, and a cellulose-based resin having a long-chain alkyl group having 6 to 26 carbon atoms is more preferable. According to this cellulose-based resin, the effect of the present application can be more remarkably exerted. The number of carbon atoms of the long-chain alkyl group is preferably 8 to 26, more preferably 10 to 26, further preferably 12 to 26, and more further preferably 15 to 26.

[0175] As the cellulose-based resin, for example, a cellulose-based resin having a structural unit represented by the following formula (A-1) is preferable.

[0176]

[0177] In formula (A-1), R A represents a hydrogen atom, an alkyl group, a hydroxyalkyl group, -R A1 -O-R A2 represents a group represented by -R A1 represents an alkanediyl group or a hydroxyalkanediyl group, R A2 represents an alkyl group.) The three R A may be the same or different from each other. Among them, at least one of the three R A is an alkyl group or a group represented by -R A1 -O-R A2 .

[0178] In formula (A-1), as the alkyl group in R A , an alkyl group having 1 to 26 carbon atoms is preferable. Further, the alkyl group in R A is more preferably a short-chain alkyl group having 1 to 3 carbon atoms or a long-chain alkyl group having 6 to 26 carbon atoms. The number of carbon atoms of the long-chain alkyl group is preferably 8 to 26, more preferably 10 to 26, further preferably 12 to 26, and more further preferably 15 to 26.

[0179] In formula (A-1), as the hydroxyalkyl group in R A , a hydroxyalkyl group having 1 to 26 carbon atoms is preferable, a hydroxyalkyl group having 1 to 10 carbon atoms is more preferable, and a hydroxyalkyl group having 1 to 5 carbon atoms is further preferable.

[0180] In formula (A-1), the alkanediyl group in R A1 is preferably an alkanediyl group having 1 to 26 carbon atoms, more preferably an alkanediyl group having 1 to 10 carbon atoms, and further preferably an alkanediyl group having 1 to 5 carbon atoms. Further, the alkanediyl group in R A1The hydroxyalkanediyl group in is preferably a hydroxyalkanediyl group having 1 to 26 carbon atoms, more preferably a hydroxyalkanediyl group having 1 to 10 carbon atoms, and still more preferably a hydroxyalkanediyl group having 1 to 5 carbon atoms.

[0181] In formula (A-1), R A2 , preferably an alkyl group having 1 to 26 carbon atoms. A2 The alkyl group in is more preferably a short-chain alkyl group having 1 to 3 carbon atoms or a long-chain alkyl group having 6 to 26 carbon atoms, and more preferably a long-chain alkyl group. The long-chain alkyl group preferably has 8 to 26 carbon atoms, more preferably 10 to 26, further preferably 12 to 26, and even more preferably 15 to 26 carbon atoms.

[0182] In formula (A-1), preferably 3 R A At least one of them is a long chain alkyl group or 3 R A At least one of them is -R A1 -OR A2 The group represented by R A2 A long-chain alkyl group.

[0183] The content of the long-chain alkyl group having 6 to 26 carbon atoms in the cellulose resin is preferably 0.01 to 5% by mass, more preferably 0.01 to 3% by mass, based on the total amount of the cellulose resin.

[0184] In this embodiment, the content of the water-soluble polymer in the coating liquid may be, for example, 0.01% by volume or more, preferably 0.1% by volume or more, and more preferably 0.3% by volume or more, based on the total volume of the solid components in the coating liquid. Furthermore, the content of the water-soluble polymer may be, for example, 10% by volume or less, preferably 5% by volume or less, and more preferably 3% by volume or less, based on the total volume of the solid components in the coating liquid.

[0185] <Other ingredients>

[0186] The coating liquid of this embodiment may further contain a thickener, a fibrous substance, a pigment, a leveling agent, and the like as components other than those described above.

[0187] Examples of the thickener include fine particles such as fumed silica and clay minerals.

[0188] The fibrous substance can exhibit an anchoring function between the aerogel particles and can further increase the strength of the coating film formed from the composite material. The fibrous substance is not particularly limited and organic fibers and inorganic fibers can be given as examples. As the organic fibers, for example, polyamide-based fibers, polyimide-based fibers, polyvinyl alcohol-based fibers, polyvinylidene chloride-based fibers, polyvinyl chloride-based fibers, polyester-based fibers, polyacrylonitrile-based fibers, polyethylene-based fibers, polypropylene-based fibers, polyurethane-based fibers, phenol-based fibers, polyether ester-based fibers, polylactic acid-based fibers, polycarbonate-based fibers, and the like can be given. As the inorganic fibers, for example, glass fibers, carbon fibers, ceramic fibers, metal fibers, and the like can be given.

[0189] <Method for producing the coating liquid>

[0190] In the present embodiment, the coating liquid is produced by a production method including a preparation step of preparing an emulsion containing a high molecular emulsifier, a binder resin, and a liquid medium, and aerogel particles, and a mixing step of mixing the emulsion and the aerogel particles prepared in the preparation step to cause at least a part of the aerogel particles to coagulate, thereby obtaining a coating liquid containing coagula of the aerogel particles, the high molecular emulsifier, the binder resin, and the liquid medium.

[0191] In the preparation step, components other than the emulsion and the aerogel particles (for example, the above-described <water-soluble polymer>, <other components>, and the like) can also be prepared.

[0192] In the mixing step, the components prepared in the preparation step are mixed to cause the aerogel particles to coagulate. The mixing method is not particularly limited as long as the aerogel particles can form coagula, and for example, a method of stirring the components prepared in the preparation step can be given.

[0193] The stirring speed affects the size of the coagula. The greater the stirring speed, the greater the shear stress applied to the coating liquid, and thus the size of the coagula tends to decrease. Therefore, from the viewpoint of obtaining coagula of an appropriate size as described later, it is preferable to produce the coating liquid at a small stirring speed.

[0194] Further, the viscosity at the time of mixing also affects the size of the coagula. Even if the stirring speed is the same, the shear stress applied to the coating liquid changes depending on the viscosity. If the viscosity is high, greater shear stress is applied to the coating liquid, and the coagula are small-sized. On the other hand, if the viscosity of the coating liquid is low, even if the stirring speed is the same, the shear stress applied to the coating liquid becomes small, and the coagula become large. Therefore, by adjusting the stirring speed depending on the viscosity of the coating liquid, a coating liquid of a desired coagula size can be produced.

[0195] Further, the size of the coagula can also be changed using an additive. As the additive that strongly affects the size of the coagula, a surface modifier, a surfactant, a dispersant, and the like can be given.

[0196] The surface modifier and the surfactant reduce the surface energy of the aerogel particles and the solution. The lower the surface energy, the weaker the force to be reduced at the interface, and the size of the agglomerate tends to be smaller. Therefore, the addition of the surface modifier and the surfactant reduces the surface energy, and the agglomerate is small-sized.

[0197] The dispersant suppresses the approach of the particles to each other by electrostatic repulsive force or steric repulsive force by attaching to the surface of the particles. The dispersant attaches to the surface of the aerogel particles to suppress the approach of the aerogel particles to each other, and thus the agglomerate is small-sized by the addition of the dispersant.

[0198] Also, the amount of the liquid medium at the time of mixing also affects the size of the agglomerate. Even if the composition of the coating liquid finally manufactured is the same, the size of the agglomerate is different between (i) a method in which all the amount of the liquid medium is put in from the initial stage of mixing and (ii) a method in which a small amount of the liquid medium is mixed at the initial stage, and then the liquid medium is added. In the method of (ii) described above, the viscosity of the coating liquid at the initial stage is higher, and in the case where the additive is added, the concentration thereof is also higher, as compared with the method of (i) described above. Therefore, in the method of (ii) described above, the agglomerate tends to be small-sized, as compared with the method of (i) described above. By using these methods in accordance with the conditions such as the composition of the coating liquid, the mixing device (stirring device), and the like, it is possible to form the agglomerate of the desired size.

[0199] The larger the size of the agglomerate, the smaller the contact interface of the aerogel and the resin component becomes, and the penetration of the resin component into the pores of the aerogel is more easily suppressed. From this viewpoint, in the present embodiment, it is preferable to form the agglomerate having a diameter of 20 μm or more, more preferably to form the agglomerate having a diameter of 40 μm or more, and further preferably to form the agglomerate having a diameter of 50 μm or more. On the other hand, from the viewpoint of avoiding a decrease in the film strength due to the continuity of the relatively weak aerogel, the diameter of the agglomerate is preferably 400 μm or less, and more preferably 300 μm or less.

[0200] In the present embodiment, the average diameter of the agglomerate is preferably 2 times or more, more preferably 4 times or more, and further preferably 8 times or more, the average diameter of the aerogel particles prepared in the preparation step. Thereby, the contact interface of the aerogel and the resin component becomes smaller, and the penetration of the resin component into the pores of the aerogel is more easily suppressed. Also, the average diameter of the agglomerate is preferably 40 times or less, more preferably 30 times or less, and further preferably 20 times or less, the average diameter of the aerogel particles prepared in the preparation step. Thereby, a decrease in the film strength due to the continuity of the relatively weak aerogel is suppressed, and a higher film strength can be easily obtained.

[0201] In addition, in the present specification, the average diameter of the agglomerate indicates a value measured by the following method.

[0202] [Method for measuring average diameter of agglomerates in coating liquid]

[0203] In a 100 mL plastic cup, about 20 g of the coating liquid was taken, and water was added in an amount of 2 g at a time while stirring using a spatula, whereby the dilution was performed while gradually making it compatible. The diluted sample was taken on a glass plate, and a microscope photograph of the sample was obtained using an optical microscope (manufactured by OLYMPUS, model: BX51). The obtained microscope photograph was analyzed using image editing software ImageJ, and the diameters of a plurality of agglomerates in the microscope photograph were calculated. The average of the obtained values was taken as the average diameter of the agglomerates.

[0204] Also, in the present specification, the meaning of the average diameter of the aerogel particles is the same as the average particle diameter D50 of the aerogel particles described above.

[0205] In the present embodiment, when the dilution liquid obtained by diluting the coating liquid is observed using an optical microscope, the area occupied by the agglomerates having a diameter of 20 μm or more (more preferably, agglomerates having a diameter of 50 μm or more) in the area occupied by the aerogel particles and the agglomerates in the observation field is preferably 50% or more, more preferably 60% or more, and further preferably 70% or more, and can be 100%.

[0206] In addition, in the present specification, the dilution liquid obtained by diluting the coating liquid and the observation method of the dilution liquid can be the same as the sample prepared in the above-mentioned [Method for measuring average diameter of agglomerates in coating liquid] and the observation method of the sample. Also, the "area in the observation field" is calculated using image editing software ImageJ to analyze the microscope photograph.

[0207] <Method for manufacturing thermal insulation material>

[0208] In the present embodiment, the thermal insulation material is manufactured by a manufacturing method including a coating step of coating the above-mentioned coating liquid on a support to obtain a coating film, and a removing step of removing at least a part of the liquid medium from the coating film to obtain the thermal insulation material. According to this manufacturing method, the agglomerates of the aerogel particles are formed in the coating liquid, and the penetration of the resin into the aerogel pores is sufficiently suppressed, and thus a thermal insulation material having high thermal insulation and high film-forming properties can be obtained.

[0209] The support on which the coating liquid is coated is not particularly limited. The support can be peeled off from the thermal insulation material after the thermal insulation material is manufactured, or can be used in a state where it is not peeled off from the thermal insulation material. The support can be, for example, a suitable object of the thermal insulation material. The material constituting the support is not particularly limited, and can be, for example, a metal, a ceramic, a glass, a resin, a composite material thereof, or the like. Also, the form of the support can be appropriately selected according to the purpose of use, the material, or the like, and can be, for example, a block shape, a sheet shape, a powder shape, a fiber shape, or the like.

[0210] The coating method of the coating liquid is not particularly limited, and examples thereof include dip coating, spray coating, spin coating, roll coating, and the like.

[0211] As the coating method of the coating liquid, a coating method in which the pressure applied to the coating liquid is 1.5 MPa or less can be used. According to such a coating method, the breakage of the agglomerates of the coating liquid due to the load at the time of coating can be suppressed. For example, the coating methods such as roll coating, trowel coating, and air spray are likely to reduce the pressure applied to the coating liquid, and thus are preferred.

[0212] Further, in the present embodiment, the binder resin in the emulsion is covered with the polymeric emulsifier by using the polymeric emulsifier, and thus the agglomerates of the fine particles of the binder resin and the aerogel particles are less likely to come into contact, the binder resin is less likely to enter the gaps in the agglomerates of the aerogel particles, and the agglomerates of the aerogel particles are less likely to collapse. Therefore, in the present embodiment, the agglomerates of the aerogel particles are likely to be maintained without collapsing even when a certain degree of pressure is applied at the time of coating the coating liquid. Therefore, in the present embodiment, as the coating method of the coating liquid, a coating method in which the pressure applied to the coating liquid exceeds 1.5 MPa can be appropriately used. As such a coating method, for example, coating using airless spray, die coater, lip coater, or the like can be mentioned.

[0213] In the removing step, by removing at least a part of the liquid medium from the coating film, a thermal insulation material formed of a composite material containing the agglomerates of the aerogel particles, the binder resin, and the polymeric emulsifier can be formed.

[0214] The method of removing the liquid medium from the coating film is not particularly limited, and examples thereof include a method of performing a heating (for example, 40 to 150°C) treatment, a reduced pressure (for example, 10,000 Pa or less) treatment, or both of these treatments.

[0215] The thickness of the thermal insulation material is not particularly limited, and can be, for example, 0.01 to 30 mm, or 0.1 to 20 mm.

[0216] The thermal insulation material has fine pores generated from the aerogel particles. From the viewpoint of obtaining higher thermal insulation, the fine pore volume of the thermal insulation material is preferably 0.15 cm 3 / g or more, more preferably 0.20 cm 3 / g or more, further preferably 0.60 cm 3 / g or more. The upper limit of the fine pore volume of the thermal insulation material is not particularly limited. The fine pore volume of the thermal insulation material can be, for example, 5.0 cm 3 / g or less.

[0217] The thermal conductivity of the thermal insulation material is, for example, 0.05 W / (m-K) or less, preferably 0.04 W / (m-K) or less, and more preferably 0.035 W / (m-K) or less. The lower limit of the thermal conductivity of the thermal insulation material is not particularly limited. The thermal conductivity of the thermal insulation material can be, for example, 0.01 W / (m-K) or more.

[0218] The thermal insulation material manufactured by the manufacturing method of the present embodiment has excellent thermal insulation, heat resistance, flame retardancy, and the like derived from the aerogel. Therefore, the thermal insulation material can be used for applications such as a thermal insulation material in ultra-low temperature containers, aerospace fields, building fields, automobile fields, home appliance fields, semiconductor fields, industrial equipment, and the like. In addition, the thermal insulation material can be used as a hydrophobic material, an acoustic material, a vibration damping material, a catalyst support material, and the like, in addition to the use as a thermal insulation material.

[0219] The above describes the preferred embodiments of the present application, but the present application is not limited to the above-described embodiments.

[0220] Examples

[0221] The present application is further described in detail below using examples, but the present application is not limited to these examples.

[0222] (Example 1)

[0223] In a 500 mL separable flask, 6 parts by mass of Sangelose 90L (manufactured by DAIDO CHEMICAL CORPORATION) as a water-soluble polymer, 46 parts by mass of isopropyl alcohol (manufactured by FUJIFILM Wako Pure Chemical Corporation, reagent), and 840 parts by mass of hot water were taken, and a dispersion liquid was obtained by stirring at 200 rpm for 1 minute using a mechanical stirrer. Next, the flask was cooled in an ice water bath and stirring was performed at 200 rpm using a mechanical stirrer to dissolve the Sangelose 90L, and a pre-gel as an aqueous solution of Sangelose 90L was obtained. In a planetary mixer (manufactured by PRIMIX Corporation, model 2P-1), 892 parts by mass of the pre-gel and 1000 parts by mass of a vinyl acetate emulsion were taken and stirring was performed at 100 rpm. Next, 100 parts by mass of aerogel particles (manufactured by CABOT, product name: ENOVA MT1100, particle diameter 2-24 μm, average particle diameter (D50) 10 μm) were added, and stirring was then performed at 50 rpm to obtain a coating liquid. In addition, a vinyl acetate emulsion was manufactured using polyvinyl alcohol (polymerization degree 1700) as a polymeric emulsifier, similarly to Example 1 of Japanese Patent Publication No. 6-18966. In the coating liquid, the content of the aerogel particles was 74.7 vol% based on the total volume of the solid components, the content of the water-soluble polymer was 0.4 vol%, and the content of the vinyl acetate resin was 24.9 vol%.

[0224] (Example 2)

[0225] A coating liquid was obtained similarly to Example 1, except that the vinyl acetate emulsion was changed to an ethylene-vinyl acetate copolymer emulsion (manufactured by Sumika Chemtex Co., Ltd., product name: Sumikaflex 400HQ) manufactured using a vinyl alcohol-based emulsifier. In addition, in the coating liquid, the content of the aerogel particles was 72.9 vol% based on the total volume of the solid components, the content of the water-soluble polymer was 0.4 vol%, and the content of the ethylene-vinyl acetate copolymer resin was 26.7 vol%.

[0226] (Example 3)

[0227] A coating liquid was obtained in the same manner as in Example 1, except that the vinyl acetate emulsion was changed to an ethylene-vinyl acetate-cyclohexane emulsion (manufactured by Sumika Chemtex, product name: Sumika Flex 801 HQ) manufactured using a polyvinyl alcohol-based emulsifier. In addition, in the coating liquid, the content of the aerogel particles was 74.7 vol%, the content of the water-soluble polymer was 0.4 vol%, and the content of the ethylene-vinyl acetate-cyclohexane copolymer resin was 24.9 vol%, based on the total volume of the solid components.

[0228] (Comparative Example 1)

[0229] A coating liquid was obtained in the same manner as in Example 1, except that the vinyl acetate emulsion was changed to a silicone-acryl emulsion manufactured in the same manner as in Example 1 of Japanese Patent Application Publication No. 11-80486 using a radical polymerizable emulsifier (manufactured by Adeka, product name: Adeka Rea Soap SE-10N). In addition, in the coating liquid, the content of the aerogel particles was 76.6 vol%, the content of the water-soluble polymer was 0.4 vol%, and the content of the silicone-acryl resin was 23.0 vol%, based on the total volume of the solid components.

[0230] <Cracking Evaluation of Thermal Insulation Material>

[0231] The coating liquid obtained in the example was applied to a 70 mm x 150 mm carbon steel plate coated with a commercially available rust-preventive coating material using airless spraying (manufactured by Graco, super ropeless airless hand device, chip nozzle FFLP514, pressure 10 MPa) so that the film thickness after drying was 1 mm. The thermal insulation material was obtained by leaving it at room temperature of 23°C for 12 hours and removing the liquid medium from the coating liquid. The cracking condition was evaluated as A for the case where the entire thermal insulation material was free from cracking, B for the case where a part of the thermal insulation material was cracked, and C for the case where the entire thermal insulation material was cracked.

[0232] <Evaluation of Pore Volume of Thermal Insulation Material>

[0233] The thermal insulation material was produced in the same manner as in the above-described <Cracking Evaluation of Thermal Insulation Material>. 100 mg of the produced thermal insulation material was taken, and the pore volume was calculated using a high-sensitivity gas adsorption analyzer (manufactured by Quantachrome, AutoSorb iQ).

[0234] <Evaluation of Thermal Conductivity of Thermal Insulation Material>

[0235] On an aluminum foil (manufactured by UACJ Corporation, product name: My Foil thick type 50, thickness: 50 μm), a frame of 200 mm in length and 3 mm in thickness made of a fluororesin was prepared, and a coating liquid was applied in the frame using a doctor blade. The obtained heat insulating material was left to stand at room temperature of 23°C for 12 hours and liquid medium was removed from the coating liquid, thereby obtaining a heat insulating material. The thermal conductivity of the obtained heat insulating material was measured by a steady state method using a thermal conductivity measuring device "HFM-446" (manufactured by NETZSCH Corporation, product name).

[0236] The results of the above evaluation are shown in Table 1.

[0237] [Table 1]

[0238] Example 1 Example 2 Example 3 Comparative Example 1 Average diameter of the agglomerates (pm) 70 95 52 60 Coating pressure (MPa) 10 10 10 10 Evaluation of the crazing A A B C Pore volume (cm 3 / g) 0.45 1.55 0.98 0.08 Thermal conductivity (W / (m-K)) 0.036 0.037 0.036 0.070

Claims

1. A method for producing a coating liquid, comprising: A preparation step of preparing an emulsion containing a polymer emulsifier, a binder resin and a liquid medium, aerogel particles, and a water-soluble polymer having a hydrophobic group; and a mixing step of mixing the emulsion prepared in the preparation step, the aerogel particles, and the water-soluble polymer to agglomerate at least a portion of the aerogel particles, thereby obtaining a coating liquid containing agglomerates of the aerogel particles, the polymer emulsifier, the binder resin, the water-soluble polymer, and the liquid medium; The polymer emulsifier is selected from the group consisting of polyvinyl alcohol and hydroxyethyl cellulose, The water-soluble polymer is a cellulose resin having an alkyl group with 6 to 26 carbon atoms.

2. The manufacturing method according to claim 1, wherein The average diameter of the aggregates is 2 to 40 times the average diameter of the aerogel particles prepared in the preparation step.

3. The manufacturing method according to claim 1 or 2, wherein: When the diluted solution obtained by diluting the coating solution is observed under an optical microscope, the aggregates having a diameter of 20 μm or more account for 50% or more of the area occupied by the aerogel particles and the aggregates within the observation field.

4. The manufacturing method according to any one of claims 1 to 3, wherein The total content of the aerogel particles and the aggregates in the coating liquid is 70% by volume or more based on the total volume of the solid content.

5. A method for manufacturing a thermal insulation material, comprising: a coating step of coating the coating liquid produced by the production method according to any one of claims 1 to 4 on a support to obtain a coating film; and The removing step is to remove at least a portion of the liquid medium from the coating film to obtain a thermal insulation material.

6. The manufacturing method according to claim 5, wherein: The pore volume of the thermal insulation material is 0.15 cm 3 / g or above.

7. The manufacturing method according to claim 5 or 6, wherein: The coating step is a step of applying the coating liquid by a coating method in which a pressure exceeding 1.5 MPa is applied to the coating liquid.

8. A coating liquid comprising agglomerates of aerogel particles, a polymer emulsifier, a binder resin, a water-soluble polymer, and a liquid medium. When the diluted solution of the coating solution is observed using an optical microscope, the area occupied by the aerogel particles and the aggregates within the observation field is not less than 50% by the aggregates having a diameter of 20 μm or more. The polymer emulsifier is selected from the group consisting of polyvinyl alcohol and hydroxyethyl cellulose, The water-soluble polymer is a cellulose resin having an alkyl group with 6 to 26 carbon atoms.

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