Aerogels

Abstract

Provided is an aerogel which has excellent breakage resistance when flexed regardless of the thickness dimension, and which has high light transmittance (in particular, high visible light transmittance). The aerogel (1) is formed from a fibrous skeleton (3) that is continuous in the form of a mesh and a plurality of pores (2) demarcated by the skeleton (3), and contains Si, the skeleton (3) has a substantially polygonal contour section (31) that forms the contour of each of the plurality of pores (2), the contour section (31) has a plurality of branch sections (32) that correspond to the edges of the substantially polygon, and a plurality of knot sections (33) that correspond to the edges of the substantially polygon. The plurality of segments (33) are portions corresponding to the apexes of a substantially polygonal shape, and among the segments (33) constituting the pores (2), the average pitch between adjacent segments (33) is 1.50 times or more the average diameter (R2) of an inscribed circle drawn at the portions corresponding to the segments. The aerogel (1) has a transmittance (tau 550) of 60% or more in terms of 10 mm thickness when irradiated with visible light having a wavelength of 550 nm.

Description

Technical Field

[0001] The present invention relates to an aerogel, and more particularly to an aerogel containing Si. Background Art

[0002] Aerogels have a uniform mesoscale porous structure with high porosity (typically more than 90%) and low bulk density (0.004 to 0.500 g / cm 3 ) and extremely low thermal conductivity (less than 20 mW / mK), typically produced by the sol-gel method. Silica aerogel, in particular, not only offers high thermal insulation due to its low thermal conductivity but also high visible light transmittance, promising applications as a transparent thermal insulation material suitable for residential windows (typically around 60% visible light transmittance in highly insulated multi-layer windows) and displays.

[0003] On the other hand, silica aerogel is known to be a very brittle material due to its high porosity and thin structure based on a fine structure composed of nanoscale domains (typically less than 100 nm). Therefore, when used in a shape (overall shape) of a certain size (volume), it is easily broken when flexed, which poses problems with its handleability. Furthermore, due to its easy breakage when flexed, silica aerogel is also a material that is extremely difficult to bend. In particular, large-sized silica aerogels have the problem of being unable to withstand the flexural deformation caused by their own weight and thus breakage.

[0004] To address this issue, for example, Non-Patent Document 1 reports on improving the bending deformability of silica aerogels by modifying and reinforcing the skeleton surface with an organic component. Furthermore, Patent Document 1 and Non-Patent Document 2 disclose that a low-density gel having a skeleton composed of polysiloxane chains and organic polymer chains can be made highly bendable by introducing organic polymer chains into the skeleton of a thinly formed aerogel.

[0005] Prior art literature

[0006] Non-patent literature

[0007] Non-patent document 1: N. Leventis, CS-Leventis, G. Zhang, A.-MM Rawashdeh, NanoLett. 2002, 2, 957-960;

[0008] Non-patent literature 2: G. Zu, K. Kanamori, T. Shimizu, Y. Zhu, A. Maeno, H. Kaji, K. Nakanishi, J. Shen, Chem. Mater. 2018, 30, 2759-2770.

[0009] Patent Literature

[0010] Patent Document 1: International Publication No. 2019 / 039541. Summary of the Invention

[0011] Problems to be solved by the invention

[0012] However, existing methods for addressing this issue improve the bending deformability of silica aerogels, but significantly reduce their visible light transmittance. Furthermore, the methods of Patent Document 1 and Non-Patent Document 2 fail to investigate whether the aerogels can be bent significantly when the thickness is increased and the aerogels are formed. Therefore, based on the descriptions of Patent Document 1 and Non-Patent Document 2, it is unclear whether the aerogels obtained using the methods of Patent Document 1 and Non-Patent Document 2 can be bent significantly when the thickness is increased to, for example, 5 mm or more.

[0013] In this regard, the present inventors produced aerogels with a thickness of 8 to 10 mm based on the aerogels of Patent Document 1 and Non-Patent Document 2. However, the obtained aerogels were easily broken when bent and had no bending deformability.

[0014] Furthermore, conventional methods for addressing this problem have been to increase the density of the silica aerogel skeleton rather than to improve the silica aerogel's resistance to breakage when bent, which often results in a loss of thermal insulation properties.

[0015] The present invention has been made in view of such actual circumstances, and an object of the present invention is to provide an aerogel that has excellent resistance to breakage when bent, regardless of thickness, and has high light transmittance (particularly high visible light transmittance).

[0016] Another object of the present invention is to provide an aerogel having high resistance to breakage when bent and high thermal insulation properties.

[0017] Solutions for solving problems

[0018] In order to achieve the above-mentioned object, the gist of the present invention is as follows.

[0019] (1) An aerogel containing Si, formed by a fibrous skeleton continuous in a mesh shape and a plurality of pores demarcated by the skeleton, the skeleton having a roughly polygonal contour portion forming the contours of each of the plurality of pores, the contour portion having a plurality of branches and a plurality of nodes, the plurality of branches being portions corresponding to the sides of the roughly polygonal portion, the plurality of nodes being portions corresponding to the vertices of the roughly polygonal portion, the average spacing between adjacent nodes constituting the pores being 1.50 times or more the average diameter of an inscribed circle drawn on the portion corresponding to the node, and the transmittance (τ550) of the aerogel when irradiated with visible light having a wavelength of 550 nm is 60% or more when converted to a thickness of 10 mm.

[0020] (2) An aerogel containing Si, wherein the transmittance (τ 550 ) is 60% or more when converted to 10 mm thick, the average thickness of the aerogel is 5 mm or more and the maximum bending strain (ε max,L ) is 10% or more, the above maximum bending strain (ε max,L ) is calculated based on the deflection amount, and the above-mentioned deflection amount is measured by a three-point bending test when the ratio of the distance between the support points to the above-mentioned average thickness is set to be greater than 6 and less than 7.

[0021] (3) The aerogel according to (1) or (2) above, wherein the thermal conductivity of the aerogel at 25°C is 20 mW / mK or less.

[0022] (4) The aerogel according to any one of (1) to (3) above, wherein the volume density (ρ b ) is 0.3g / cm 3 the following.

[0023] (5) Aerogel particles obtained by crushing the aerogel according to any one of (1) to (4) above into particles.

[0024] Effects of the Invention

[0025] According to the present invention, it is possible to provide an aerogel which has excellent resistance to breakage when bent, regardless of thickness, and has high light transmittance (particularly high visible light transmittance).

[0026] Furthermore, according to the present invention, it is possible to provide an aerogel having high resistance to breakage when bent and high thermal insulation properties. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is a schematic diagram showing an example of the fine structure of the aerogel of the present invention.

[0028] Figure 2 The following are photos of the aerogels when urea was used as the base catalyst and when five different concentrations of tetramethylammonium hydroxide (TMAOH) were used as the base catalyst. Figure 2 (a) shows the case where urea is used as the base catalyst, Figure 2 (b) shows the case where the TMAOH concentration is 0.010M, Figure 2 (c) shows the case where the TMAOH concentration is 0.10 M, Figure 2 (d) shows the case where the TMAOH concentration is 0.50 M, Figure 2 (e) shows the case where the TMAOH concentration is 1.0 M, and Figure 2 (f) shows the case where the TMAOH concentration is 2.0M.

[0029] Figure 3 The following are FE-SEM images of aerogels using urea as the base catalyst and three different concentrations of tetramethylammonium hydroxide (TMAOH) as the base catalyst. Figure 3 (a) shows the case where urea is used as the base catalyst, Figure 3 (b) shows the case where the TMAOH concentration is 0.010M, Figure 3 (c) shows the case where the TMAOH concentration is 0.50 M, Figure 3 (d) shows the case where the TMAOH concentration is 2.0M.

[0030] Figure 4 This is a photograph showing a rope-shaped aerogel with high flexibility similar to nylon thread.

[0031] Figure 5 This is a photograph showing an example of a state in which the produced aerogel was subjected to a three-point bending test.

[0032] Figure 6 FE-SEM images of aerogels of the present invention and comparative examples are shown in FIG. Figure 6 (a) is the FE-SEM image of the aerogel of Example 1 of the present invention, Figure 6 (b) is the FE-SEM image of the aerogel of Example 2 of the present invention, Figure 6 (c) is the FE-SEM image of the aerogel of Example 3 of the present invention, Figure 6 (d) is the FE-SEM image of the aerogel of Example 4 of the present invention, Figure 6 (e) is a FE-SEM image of the aerogel of Comparative Example 1.

[0033] Figure 7 are STEM images of aerogels of the present invention and comparative examples. Figure 7 (a) is a STEM image of the aerogel of Example 1 of the present invention, Figure 7(b) is a STEM image of the aerogel of Example 2 of the present invention, Figure 7 (c) is a STEM image of the aerogel of Example 3 of the present invention, Figure 7 (d) is a STEM image of the aerogel of Example 4 of the present invention, Figure 7 (e) is a STEM image of the aerogel of Comparative Example 1.

[0034] Figure 8 These are transmittance spectra of the aerogels of Examples 1 to 4 of the present invention and Comparative Example 1 when a sample having a thickness of 5.0 mm was irradiated with light in the visible light region (wavelength: 380 nm to 780 nm).

[0035] Figure 9 3 are stress-strain curves of the aerogels of Examples 1 to 4 of the present invention and Comparative Example 1 obtained by a three-point bending test. DETAILED DESCRIPTION

[0036] The following is a reference to the attached Figure 1 The present invention will be described in detail with reference to specific embodiments. The present invention is not limited to the following embodiments, and various modifications are possible without departing from the spirit of the present invention.

[0037] The aerogel 1 of the present invention is as follows Figure 1 As shown, it is formed by a fibrous skeleton 3 continuous in a mesh shape and a plurality of pores 2 demarcated by the skeleton, and contains Si, the skeleton 3 has a roughly polygonal contour portion 31 forming the contours of each of the plurality of pores 2, the contour portion 31 has a plurality of branches 32 and a plurality of nodes 33, the plurality of branches 32 are portions corresponding to the sides of the roughly polygonal shape, the plurality of nodes 33 are portions corresponding to the vertices of the roughly polygonal shape, and in the nodes 33 constituting the pores 2, the average arrangement spacing between adjacent nodes 33 is 1.50 times or more relative to the average diameter of the inscribed circle R2 drawn on the portion corresponding to the node 33, and the transmittance (τ 550 ) is more than 60% when converted to 10mm thickness.

[0038] Furthermore, the aerogel 1 of the present invention contains Si, and the transmittance (τ 550 ) is 60% or more when converted to 10mm thickness, the average thickness is 5mm or more and the maximum bending strain (ε max,L ) is 10% or more, the above maximum bending strain (ε max,L ) is calculated based on the deflection amount, and the above-mentioned deflection amount is measured by a three-point bending test when the ratio of the distance between the support points to the average thickness is set to be greater than 6 and less than 7.

[0039] The present inventors focused on the flexibility of the microstructure 10 of the Si-containing aerogel 1 and discovered that, for the fibrous skeleton 3 constituting the aerogel 1, by increasing the average spacing between adjacent nodes 33 relative to the inscribed circle of the nodes 33, the bending deformability of the branches 32 can be improved. More specifically, by increasing the average spacing between adjacent nodes 33 relative to the inscribed circle of the nodes 33, the skeleton 3 becomes a microstructure close to that of a fiber. As a result, the bending deformability of the skeleton 3 is further improved when subjected to an external force, thereby increasing the maximum bending strain (ε) of the aerogel 1. max,L ), and as a result, even if the aerogel 1 is bent, it is not easily damaged regardless of the thickness. Furthermore, the present inventors have found that in the aerogel 1, it is possible to achieve both excellent damage resistance when bent and high transmittance when irradiated with visible light (τ 550 ). In particular, even if the transmittance (τ 550 ) By reducing the microdomain size of the microstructure 10 (i.e., the sum of the pore diameter R1 of the pore 2 and the thickness t of the branch portion 32 (R1+t)), the average spacing between adjacent nodes 33 can be increased relative to the inscribed circle of the node 33, thereby similarly improving the bending deformability of the skeleton 3 when subjected to external force. Therefore, it is possible to provide an aerogel 1 that exhibits excellent resistance to breakage when bent and high light transmittance (particularly high visible light transmittance) regardless of thickness, that is, even when having a large average thickness of 5 mm or more.

[0040] [About the structure of aerogel]

[0041] like Figure 1 As shown, the aerogel 1 has a microstructure 10 containing Si and formed of a fibrous skeleton 3 continuous in a network and a plurality of pores 2 defined by the skeleton 3 .

[0042] (Microstructure of aerogel)

[0043] The microstructure 10 of the aerogel 1 is a microstructure containing silicon atoms in the molecule. As an example, a microstructure of a polysilsesquioxane system can be cited. Among them, the microstructure of the polysilsesquioxane system can be formed by the hydrolysis and polycondensation reaction of silicon alkoxide. In particular, polymethylsilsesquioxane (PMSQ, MeSiO 1.5 PMSQ aerogels can form transparent aerogels and can be formed by combining the hydrolysis and polycondensation reactions of methyltrialkoxysilane (MeSi(OR)3) with a surfactant as a phase separation inhibitor. Examples of the hydrolysis and polycondensation reactions used to form PMSQ aerogels include a hydrolysis reaction using an acid catalyst represented by the following formula (I) and a polycondensation reaction using a basic catalyst represented by the following formula (II).

[0044] MeSi(OR)3+3H2O→MeSi(OH)3+3ROH: formula (I)

[0045] MeSi(OH)3→MeSiO 1.5 +1.5H2O: Formula (II)

[0046] (Aerogel skeleton)

[0047] The aerogel 1 of the present invention has a fibrous skeleton 3 continuous in a network as a microstructure 10. This allows the skeleton 3 of the aerogel 1 to be easily deformed when subjected to external force, thereby improving the aerogel's resistance to breakage when bent.

[0048] Here, the skeleton 3 of the aerogel 1 is preferably configured to have a substantially polygonal outline 31 that defines the contours of each of the plurality of pores 2. This outline 31 includes a plurality of branches 32 and a plurality of nodes 33. The branches 32 correspond to the sides of the substantially polygonal shape, and the nodes 33 correspond to the vertices of the substantially polygonal shape. This allows the aerogel 1 to have a microstructure sufficient for exhibiting high thermal insulation and high visible light transmittance. Furthermore, when the aerogel 1 bends, the skeleton 3 having the branches 32 and nodes 33 disperses and absorbs the resulting force over a wider area of ​​the aerogel 1, thereby improving the aerogel 1's resistance to damage.

[0049] In particular, the average spacing P between adjacent nodes 33 of the skeleton 3 of the aerogel 1 (average spacing) is preferably 1.50 times or greater than the average diameter R2 of the inscribed circle (the inscribed circle of the node 33) drawn in the portion corresponding to the node 33. In the fine structure 10 of the aerogel 1, the branches 32 are relatively long and the nodes 33 are relatively small, which facilitates the formation of a fine structure closer to a fiber-like structure in the skeleton 3. This improves the bending deformability of the branches 32, thereby enhancing the flexibility of the aerogel 1 and, as a result, further improving the resistance of the aerogel 1 to breakage when bent.

[0050] Here, the diameter R2 of the inscribed circle drawn at the portion corresponding to the node 33 is the maximum diameter of the inscribed circle that can be drawn without being exposed from the skeleton 3, with the portion corresponding to the node 33 as the center. Figure 1 The described substantially quadrilateral may be, for example, a substantially pentagon or a substantially hexagon. In addition, the branch portion 32 corresponds to the side of the substantially polygon, but is not limited to a straight line and may be partially or entirely curved.

[0051] The flexibility of the fibrous skeleton 3, which is continuous in a network, of such an aerogel 1 can be adjusted by varying the conditions used to produce the aerogel 1. Specifically, by adjusting the conditions for hydrothermal treatment of the gel, which has been aged after gelation, a fibrous skeleton 3 can be formed in which the average spacing between adjacent nodes 33 is long relative to the average diameter of the inscribed circle of the nodes 33 and the aerogel is continuous in a network. This improves the aerogel's resistance to breakage when flexed. While the temperature for the hydrothermal treatment is not particularly limited, it is preferably between 60°C and 70°C to moderately promote the polycondensation reaction and further improve the aerogel's flexural deformability.

[0052] In addition, the skeleton 3 of the aerogel 1 can also be adjusted by changing the type of surfactant used in producing the aerogel 1 , the ratio of the surfactant to the silicon alkoxide concentration, or the added amounts of the surfactant and the silicon alkoxide.

[0053] Here, when a surfactant having a large molecular weight is used as a surfactant for producing the aerogel 1, a microstructure 10 having a structure closer to the fibrous skeleton 3 can be easily obtained. On the other hand, from the perspective of providing the microstructure 10 with a fibrous skeleton 3, it is also useful to adjust the composition of the sol so that the aqueous solvent content is increased when producing the aerogel 1.

[0054] The aerogel 1 of the present invention has high resistance to breakage when bent, regardless of its thickness. Here, the maximum bending strain (ε max,L ) is preferably 10% or more, more preferably 15% or more, and the maximum bending strain (ε max,L ) is calculated based on the deflection amount measured by a three-point bending test with a ratio of the distance between support points to the average thickness set to 6 or more and 7 or less. As a result, the amount of bending strain allowed when the aerogel 1 is bent increases, so that even if the aerogel 1 is bent, it is not easily damaged. In addition, the maximum bending strain (ε) obtained by the three-point bending test is max,L ) is preferably a value when the ratio of the distance between the fulcrums to the average thickness is in the range of 6 or more and 7 or less, and more preferably a value when the ratio of the distance between the fulcrums to the average thickness is 6 under a more stringent condition. The maximum bending strain (ε) obtained by the three-point bending test when the ratio of the distance between the fulcrums to the average thickness is 6 is set to max,L ) is 10% or more or 15% or more, thereby inevitably making it possible to make the maximum bending strain (ε) obtained by the three-point bending test when the ratio of the distance between the supporting points to the average thickness is in the range of 6 or more and 7 or less. max,L ) are respectively more than 10% or more than 15%.

[0055] The thickness of the aerogel 1 is not particularly limited, and the average thickness can be 5 mm or greater, particularly 7 mm or greater. Even with such a large thickness, the aerogel 1 of the present invention can improve its resistance to breakage when flexed. The upper limit of the average thickness of the aerogel 1 is not particularly limited, and can be, for example, 100 mm.

[0056] (Aerogel pores)

[0057] The aerogel 1 of the present invention has a plurality of fine pores 2 defined by a skeleton 3 as a fine structure 10. This makes it difficult for visible light passing through the aerogel 1 to be scattered, thereby increasing the light transmittance of the aerogel for visible light.

[0058] The fine structure 10 of the aerogel 1 can be adjusted by changing the conditions during the production of the aerogel 1. As a specific example, when producing the aerogel 1, the temperature of the solution when adding the alkali catalyst to the sol is set to a range of 0°C to 10°C, preferably 0°C to 5°C, and the sol after the addition of the alkali catalyst is stirred at an appropriate rotation speed for a time period of 1 minute to 60 minutes. This allows a more uniform fine structure 10 that is less susceptible to light scattering to be formed uniformly over a wide area, thereby forming an aerogel 1 having high light transmittance (particularly high visible light transmittance).

[0059] In addition, when producing the aerogel 1 , finer pores 2 can be formed by changing the type and concentration of the base catalyst used when converting the silicon alkoxide sol-gel. Figure 2 The following are photos of the appearance of aerogels when urea is used as a base catalyst for gelation, and when tetramethylammonium hydroxide (TMAOH) is used as a base catalyst as an organic base catalyst and its concentration is changed. Figure 2 (a) shows the case where urea is used as the base catalyst, Figure 2 (b) shows the case where the TMAOH concentration is 0.010M, Figure 2 (c) shows the case where the TMAOH concentration is 0.10 M, Figure 2 (d) shows the case where the TMAOH concentration is 0.50 M, Figure 2 (e) shows the case where the TMAOH concentration is 1.0 M, Figure 2 (f) shows the case where the TMAOH concentration is 2.0 M. Here, Figure 2 The aerogel shown was obtained by the same method as in Example 1 described later, except for the presence or absence of addition of the alkali catalyst and the amount of the alkali catalyst added.

[0060] Here, according to Figure 2When tetramethylammonium hydroxide (TMAOH) as an organic base catalyst is used as a base catalyst and its concentration is 0.50M or more, finer pores 2 can be formed, and as a result, the transmittance (τ 550 , Figure 2 T 550 On the other hand, when urea is used as a base catalyst for gelation, the transmittance (τ 550 ) is 34%. In addition, when the concentration of TMAOH is as low as 0.010M, the transmittance (τ 550 ) also becomes lower.

[0061] Furthermore, the pores 2 of aerogel 1 can be made finer by reducing the molecular weight of the surfactant used in producing aerogel 1. By thus making the pores 2 finer, an aerogel having a higher transmittance when irradiated with visible light can be obtained.

[0062] Furthermore, it is considered that even when the concentration of TMAOH is changed, the fact that the aerogel 1 forms the fibrous skeleton 3 itself does not change. Figure 3 The following are FE-SEM images of aerogels when urea was used as a base catalyst for gelation, and when tetramethylammonium hydroxide (TMAOH) was used as a base catalyst as an organic base catalyst and its concentration was changed. Figure 3 (a) shows the case where urea is used as the base catalyst, Figure 3 (b) shows the case where the TMAOH concentration is 0.010M, Figure 3 (c) shows the case where the TMAOH concentration is 0.50 M, Figure 3 (d) shows the case where the TMAOH concentration is 2.0 M. Figure 3 Regardless of whether tetramethylammonium hydroxide (TMAOH) is used as the base catalyst or urea is used as the base catalyst, there is no significant difference in that the obtained microstructure 10 has a fibrous skeleton 3 .

[0063] The average pore size of the plurality of pores 2 in the microstructure 10 of the aerogel 1 is not particularly limited and can be, for example, in the range of 5 nm to 100 nm. Figure 1 The pore diameter R1 of the pores 2 is the average of the diameters of the pores 2. Figure 1As shown, when an imaginary circle C is drawn in which the area of ​​the opening portion of the pore 2 outside the imaginary circle C is equal to the area of ​​the portion not opened by the pore 2 inside the imaginary circle C, the diameter of the imaginary circle C can be taken as the pore diameter R1 of the pore 2.

[0064] Furthermore, the average thickness t of the branch portions 32 of the fine structure 10 constituting the aerogel 1 is not particularly limited and can be, for example, in the range of 1 nm to 20 nm.

[0065] The aerogel 1 of the present invention has high light transmittance (especially high visible light transmittance). Here, the transmittance (τ 550 ) is preferably 60% or more, more preferably 80% or more, when converted to 10 mm thickness. In the aerogel 1 of the present invention, the transmittance (τ 550 ) is high, thereby improving the uniformity of the microstructure 10, thereby reducing the occurrence of stress concentration on the local area of ​​the skeleton 3, and reducing the microdomain size of the microstructure 10 of the aerogel 1 (i.e., the sum of the pore diameter R1 of the pore 2 and the thickness t of the branch portion 32 (R1 + t)). In this case, as described above, by forming the skeleton 3 into a microstructure close to a fiber, even if the microdomain size of the microstructure 10 is small, the bending deformability of the skeleton 3 when subjected to external force is high, thereby improving the damage resistance of the aerogel 1 when it is bent.

[0066] (Preferred properties of aerogel)

[0067] The preferred density of the aerogel 1 of the present invention is (ρ b ) is 0.3g / cm 3 As a result, the density of the skeleton 3 of the aerogel 1 decreases, creating more voids within the aerogel 1. This reduces the thermal conductivity of the aerogel 1 and improves its thermal insulation. To be suitable for use as a thermal insulation material, the thermal conductivity of the aerogel 1 of the present invention at 25°C is preferably 20 mW / mK or less, and more preferably 15 mW / mK or less. Even with such a low density and high thermal insulation, the aerogel 1 of the present invention can improve its resistance to breakage when flexed, making it suitable for use as a flexible thermal insulation material, such as windows.

[0068] (Shape of aerogel)

[0069] The overall shape of the aerogel 1 is formed based on the shape of the reaction container when the silicon alkoxide is polycondensed and gelled, and can be formed into a plate shape or a plurality of shapes. Figure 4 In particular, when formed into a rope shape, the aerogel 1 can have very high flexibility like nylon yarn. On the other hand, the aerogel 1 can also be in the form of aerogel particles formed by fragmentation into particles.

[0070] [About the manufacturing method]

[0071] Next, an example of the method for producing the aerogel of the present invention will be described.

[0072] The method for producing the aerogel of the present invention is not particularly limited. As one example, a method comprising the following steps can be used: a hydrolysis step of hydrolyzing an organosilicon alkoxide [step 1]; a solution preparation step of adding a surfactant and water to the resulting hydrolyzate to obtain a uniform solution [step 2]; a gelation step of adding an alkaline catalyst to the solution to polymerize the hydrolyzate to form a wet gel [step 3]; a washing step of washing the resulting gel [step 4]; and a supercritical drying step of supercritically drying the washed gel [step 5].

[0073] Here, the hydrolysis step [step 1] is a step of mixing an aqueous solution of an acid such as acetic acid with a silicon alkoxide such as methyltrimethoxysilane (MTMS), thereby hydrolyzing the alkoxy groups of the silicon alkoxide to produce a hydrolyzate having a silanol group.

[0074] The solution preparation step [step 2] is a step of adding a surfactant and water to the hydrolyzate in the hydrolysis step [step 1] to obtain a uniform solution.

[0075] The hydrolysis step [step 1] and the solution preparation step [step 2] may be performed simultaneously. For example, the surfactant added in the solution preparation step [step 2] may be added simultaneously to the hydrolysis step [step 1].

[0076] The gelation process [process 3] is a process of adding an alkali catalyst to the solution obtained in the solution preparation process [process 2]. By adding an alkali catalyst to the solution, the hydrolyzate of the silicon alkoxide can be polymerized to form a wet gel. Here, as the alkali catalyst, ammonium salts can be preferably used, for example, tetramethylammonium hydroxide (TMAOH) can be used. In addition, the hydrogen ion concentration (pH) of the sol after adding the alkali catalyst is preferably in the range of 9.0 to 14.0, more preferably in the range of 12.5 to 13.5. In this way, if the pH of the sol is increased, the decomposition and reformation of unstable siloxane bonds (similar to the so-called Ostwald ripening effect) are likely to occur. As described below, by lowering the temperature of the solution when the alkali catalyst is added, the uniformity of the obtained gel can be improved. As a result, the light transmittance of the aerogel can be improved.

[0077] From the perspective of improving the uniformity of the resulting gel and the visible light transmittance of the aerogel, the temperature of the solution when adding the alkali catalyst is preferably set to a range of 0°C to 10°C, preferably 0°C to 5°C. To lower the temperature of the solution when adding the alkali catalyst, the solution may be placed in an ice bath. Regarding this, if the temperature of the alkali catalyst when adding the sol is 10°C or higher, polycondensation proceeds too rapidly, resulting in reduced uniformity of the resulting gel, resulting in uneven appearance and a major factor in reduced light transmittance of the aerogel 1.

[0078] Furthermore, from the perspective of improving the visible light transmittance of the aerogel, the solution after adding the alkali catalyst is preferably stirred at an appropriate rotational speed for a period of time ranging from 1 minute to 60 minutes. During this period, the viscosity of the sol becomes high, so in order to obtain an aerogel 1 with high visible light transmittance, it is preferable to stir the sol so that it becomes uniform within a short period of time.

[0079] From the perspective of improving the mechanical strength of the aerogel, the obtained gel is preferably aged at room temperature or a temperature higher than room temperature and below the boiling point of the solvent, for example, for more than 24 hours. Furthermore, by adjusting the conditions for the hydrothermal treatment, the aged gel can form a fibrous skeleton 3 that is continuous in a mesh shape, and the average spacing between adjacent nodes 33 relative to the average diameter of the inscribed circle of the nodes 33 in the skeleton 3 becomes larger, thereby improving the aerogel's resistance to breakage when bent. In this regard, the temperature of the hydrothermal treatment of the aged gel is not particularly limited. From the perspective of allowing the polycondensation reaction to proceed moderately and further improving the bending deformability and flexibility of the skeleton, it is preferably in the range of 60°C to 70°C.

[0080] The washing step [step 4] is a step for washing the obtained gel. Water, alcohol, or a mixture thereof can be used as a washing liquid for washing the gel. Among these, alcohols that are liquid at room temperature (e.g., 20°C) can be used, such as methanol, ethanol, 1-propanol, and 2-propanol.

[0081] The supercritical drying step [Step 5] is a step in which the washed gel is dried using a supercritical fluid. A supercritical fluid is a fluid at a higher temperature and pressure than its critical point. An example of a supercritical fluid is carbon dioxide, which has a higher temperature and pressure than its critical point of 31°C and 7.4 MPa.

[0082] By subjecting the obtained gel to a washing step [step 4] and a supercritical drying step [step 5], the surfactant, alkali catalyst, and other raw materials and their decomposition products that serve as impurities in the aerogel 1 are substantially removed. At this time, the surfactant, alkali catalyst, and other raw materials and their decomposition products may be incorporated into the obtained aerogel 1 as unavoidable components.

[0083] Furthermore, aerogel 1 is not limited to homogeneous aerogels and may also be included in the form of a composite material. An example of a composite material includes at least a base material and a reinforcing material layered on the base material. One or both of these base material and reinforcing material may be composed of the aforementioned aerogel 1. Furthermore, a composite material includes aerogel 1 in which other substances, such as fibers, are dispersed.

[0084] As a method for producing a composite (composite material) having aerogel 1, a method can be exemplified by performing a gelation step (step 3) in which a fibrous material is added to a solution prior to the gelation step (step 3) to disperse or precipitate (or float), and then an alkali catalyst is added to polymerize the hydrolyzate to form a wet gel. Alternatively, as another method for producing a composite (composite material), a method can be exemplified in which a fibrous material is first formed, the solution prior to the gelation step (step 3) is impregnated into the fibrous material, and then the gelation step (step 3) is performed.

[0085] In particular, when producing a composite (composite material) comprising aerogel 1, it is preferred to use a thin fibrous material, more specifically a fibrous material having a fiber diameter of 1 nm or greater, from the perspective of improving the affinity between the solution and the fibrous material prior to the gelation step (step 3) and obtaining a composite with high light transmittance. Furthermore, it is preferred to perform the gelation step (step 3) while the solution and the fibrous material are homogeneously mixed prior to the gelation step (step 3), also from the perspective of obtaining a composite with high light transmittance.

[0086] While the embodiments of the present invention have been described above, the present invention is not limited to the above embodiments but encompasses all aspects encompassed by the concept of the present invention and the claims, and various modifications can be made within the scope of the present invention.

[0087] Example

[0088] Next, in order to further clarify the effects of the present invention, examples of the present invention and comparative examples will be described, but the present invention is not limited to these examples.

[0089] (Examples 1 to 4 of the present invention)

[0090] The starting compositions of Examples 1 to 4 of the present invention are shown in Table 1. Methyltrimethoxysilane (hereinafter sometimes referred to as "MTMS", manufactured by Shin-Etsu Chemical Co., Ltd.) and a 5 mM aqueous solution of acetic acid (hereinafter sometimes referred to as "HOAc", purity ≥ 99.7%, manufactured by Kishida Chemical Co., Ltd.) in the amounts listed in Table 1 were mixed in a reaction vessel and stirred continuously at room temperature for 15 minutes to hydrolyze the MTMS and produce a uniform sol. Subsequently, the surfactants of the types and amounts listed in Table 1 and the distilled water (hereinafter sometimes referred to as "H2O") in the amounts listed in Table 1 were added to the resulting uniform sol, and stirring was continued for approximately 1 hour to homogenize the sol at room temperature.

[0091] Here, among the surfactants listed in Table 1, “F127” is a nonionic surfactant Pluronic F127 (EO 106 PO 70 EO 106 , maximum molecular weight M w : 12600, HLB value 18-23, manufactured by Sigma-Aldrich.) "F68" is a nonionic surfactant Pluronic F68 (EO 76 PO 29 EO 76 , maximum molecular weight M w : 8400, HLB value> 24, manufactured by Sigma-Aldrich.) In addition, "P105" is a nonionic surfactant Synperonic P105 (EO 37 PO 56 EO 37 , maximum molecular weight M w : 6500, HLB value 12-18, manufactured by Croda Japan Co., Ltd.) In addition, "P94" is a nonionic surfactant Pluronic P94 (EO 26 PO 48 EO 26 , maximum molecular weight M w : 5000, HLB value: 13.5, manufactured by BASF).

[0092] Next, the obtained sol was placed in an ice bath together with the reaction container and cooled to 4°C over 30 minutes. While stirring in the ice bath until no bubbles were generated, a 0.50M aqueous solution of tetramethylammonium hydroxide (hereinafter sometimes referred to as "TMAOH", 25% aqueous solution, manufactured by Tokyo Chemical Industry Co., Ltd.) as an alkaline catalyst was carefully added in the amount described in Table 1 and stirred for 3 minutes. Here, the pH (hydrogen ion concentration) of the sol was measured, and the result was the value described in Table 1. Thereafter, the sol was transferred to a sealed container and allowed to stand at room temperature for 1 hour to gel. At this time, the gelation of the sol occurred within 15 minutes. Furthermore, the obtained gel was allowed to stand at 60°C for 3 days to mature, and then subjected to hydrothermal treatment at 60°C for 24 hours.

[0093] To prevent gel breakage due to osmotic pressure, the gel after hydrothermal treatment was washed with a mixed solvent of H2O and methanol (hereinafter sometimes referred to as "MeOH," purity ≥99.5%, manufactured by Kishida Chemical Industry Co., Ltd.) (H2O:MeOH = 100:0, 90:10, 70:30, 50:50, 30:70, 10:90, or 0:100 (vol%)) from the first to fifth washes, and with 2-propanol (hereinafter sometimes referred to as "IPA," purity ≥99.0%, manufactured by Kishida Chemical Industry Co., Ltd.) from the sixth to eighth washes, each immersed at 60°C for at least 8 hours. The resulting alcogel was supercritically dried for 10 hours using carbon dioxide at a pressure of 14 MPa and a temperature of 80°C as a supercritical fluid to obtain an aerogel (PMSQ aerogel).

[0094] (Comparative Example 1)

[0095] The starting composition of Comparative Example 1 is shown in Table 1. In a reaction vessel, 12.0 mL of a 5 mM aqueous solution of acetic acid, 3.0 g of urea, and 0.40 g of a surfactant were mixed and stirred continuously at room temperature for 30 minutes to obtain a homogeneous mixture. Here, a cationic surfactant, n-hexadecyltrimethylammonium chloride (CTAC, maximum molecular weight M w : 320, HLB value: 15.8, manufactured by Tokyo Chemical Industry Co., Ltd.) was used as a surfactant.

[0096] Next, 5.0 mL of MTMS was added to the reaction container, and the mixture was stirred at room temperature for 30 minutes to hydrolyze the MTMS and obtain a uniform sol.

[0097] The resulting sol was transferred to a sealed container and allowed to stand at 60°C for 4 days to gel and mature. The pH of the solution contained in the matured gel was measured, and the results were the values ​​listed in Table 1. Furthermore, the matured gel was hydrothermally treated at 60°C for 24 hours.

[0098] To prevent gel breakage due to osmotic pressure, the gel was washed with MeOH for the first to third washes and with 2-propanol for the fourth to sixth washes, each immersed at 60°C for at least 8 hours. The resulting alcogel was supercritically dried for 10 hours using carbon dioxide at a pressure of 14 MPa and a temperature of 80°C as a supercritical fluid to obtain an aerogel (PMSQ aerogel).

[0099] [Various measurement and evaluation methods]

[0100] The aerogels of the above-mentioned inventive examples and comparative examples were evaluated for the following properties. The evaluation conditions for each property are as follows.

[0101] [1] Calculation of the volume density of aerogel

[0102] The diameter, height, and weight of the cylindrical aerogel were measured, and the volume density (ρ b The results are shown in Table 2.

[0103] [2] Determination of aerogel transmittance

[0104] The transmittance of the obtained aerogel was determined based on spectral data obtained using a V-670 UV-visible-near-infrared spectrophotometer with an integrating sphere (manufactured by JASCO Co., Ltd.). Here, the total transmittance value when a sample with a thickness of 5.0 mm was irradiated with visible light of a wavelength of 550 nm was converted to the total transmittance (T) of a sample with a thickness of 10 mm using the Lambert-Beer equation. 550 The results are shown in Table 2.

[0105] [3] Evaluation of the bending properties of aerogels

[0106] The bending properties of the obtained aerogel were measured by a three-point bending test using a material testing machine (AUTOGRAPH AG-X plus, manufactured by Shimadzu Corporation). In the three-point bending test, a cylindrical sample with a length of 80 mm in the longitudinal direction (the height direction of the cylinder) was used, and the sample was arranged so that the radial direction of the bottom surface of the cylinder became the thickness direction of the sample. At this time, the average thickness of the sample is as described in Table 2. In addition, as Figure 5As shown, two fulcrums were set under the specimen, and the distance between the fulcrums (span length) along the length of the specimen was set to the value listed in Table 2. Therefore, the ratio of the distance between the fulcrums to the average thickness of the aerogel was as listed in Table 2. The testing machine head was placed at positions equidistant along the length of the specimen between the two fulcrums set under the specimen. A load was applied to the specimen from above using the tensile testing machine head to deform the specimen, and the downward deflection of the loaded portion when the specimen fractured was measured. The load applied to the specimen by the tensile testing machine head was set so that the crosshead speed was 0.5 mm / min.

[0107] The maximum bending stress (σ) of the sample when the distance between the supporting points is L (mm) is calculated using the following equations (a) and (b) based on the load F (N) applied to the sample when the sample breaks and the amount of downward deflection Δl (mm) at the site where the load is applied. max,L ) and maximum bending strain (ε max,L ). In the following formula, D is the diameter of the cylindrical sample. The results are shown in Table 2.

[0108] σ max,L =8L·F / πD 3 :Formula (a)

[0109] ε max,L =6D·△Ⅰ╱L 2 :Formula (b)

[0110] The minimum diameter R of the aerogel that could be bent was calculated using the following formula (c). Here, the minimum diameter R of the aerogel that could be bent was calculated based on the curvature of the arc when the inner contour between two supporting points of the sample immediately before fracture is approximated. The results are shown in Table 2.

[0111] R=a / 6×L×ε max,L +(3 / a) 2 ×1 / ε max，L -2D: Formula (c)

[0112] a=L / D: Formula (d)

[0113] [4] Observation of the pore and skeleton structure of aerogel

[0114] The pore and skeleton structures of the resulting aerogel were observed using a field emission scanning electron microscope (FE-SEM: Regulus 8220, manufactured by Hitachi High-Technologies Corporation) and a scanning transmission electron microscope (STEM: JEM-1400 Plus, manufactured by JEOL Ltd.). Prior to observation, the aerogel was crushed with fine sandpaper of #2000 or greater grit. Aerogel fragments adhering to the sandpaper, which were visually detectable, were removed by blowing them off with a blower. For the remaining aerogel fragments, which were difficult to remove with the blower and were too small to be visually detected, the areas adhering to the sandpaper were transferred to carbon tape, which was then mounted on a sample stage for observation. FE-SEM observations were performed at a magnification of 200,000 times, with a 640 nm x 500 nm square field of view defined as one field of view. Furthermore, STEM observations were performed at a magnification of 100,000 times, with a 560 nm x 480 nm square field of view. Furthermore, these structural observations were performed without metal sputtering the aerogel to prevent structural changes due to accumulation of sputtered metal.

[0115] exist Figure 6 (a) to (g) show FE-SEM images of aerogels according to the present invention and comparative examples. From the resulting FE-SEM images, 50 locations were randomly selected with as little bias as possible, where the roughly polygonal outlines of the pores in the fibrous skeleton were clearly visible, and where branches corresponding to the sides of the roughly polygonal shape and nodes corresponding to the vertices of the roughly polygonal shape were clearly visible. The distance from the center of each node to the center of the adjacent node was measured, and the average spacing between adjacent nodes was calculated by averaging the measured values.

[0116] In addition, from the obtained FE-SEM image, 50 locations that clearly show the roughly polygonal contours of the pores and clearly show the nodes equivalent to the vertices of the roughly polygons are randomly selected as unbiased as possible. For each node, the diameter of the inscribed circle drawn in the portion equivalent to the node is measured, and the average diameter of the inscribed circle drawn in the portion equivalent to the node is calculated by calculating the average of the measured values.

[0117] Then, using these calculated values, the ratio of the average arrangement pitch between adjacent nodes to the average diameter of the inscribed circle drawn in the portion corresponding to the node was determined.

[0118] Furthermore, 50 pores were randomly selected from the obtained FE-SEM images with as little deviation as possible, the pore diameters of each pore were measured, and the average of the measured values ​​was calculated to calculate the average pore diameter. The results are shown in Table 2.

[0119] In addition, Figure 7 (a) to (g) show STEM images of aerogels from the inventive examples and comparative examples. From the resulting aerogel STEM images, 30 locations where branches were clearly visible were randomly selected with as little bias as possible. The widths of each selected branch were measured, and the average of the measured values ​​was calculated to determine the average thickness of the branches that constitute the aerogel skeleton. The results are shown in Table 2.

[0120] [5] Evaluation of thermal conductivity of aerogel

[0121] The thermal conductivity of the obtained aerogel was measured using a heat flow meter (HFM 436 Lambda, manufactured by NETZSCH) under a normal pressure environment at an air temperature of 25° C. The results are shown in Table 2.

[0122] [Table 1]

[0123]

[0124] [Table 2]

[0125]

[0126] According to the results in Table 1 and Table 2, the aerogels of Examples 1 to 4 of the present invention are all composed of a fibrous skeleton continuous in a network form and a plurality of pores defined by the skeleton.

[0127] In addition, according to the results in Table 1 and Table 2, the transmittance (τ 550 ) is 60% or more when converted to 10mm thickness. In particular, the transmittance (τ 550 )like Figure 8 shown.

[0128] In addition, according to the results in Table 1 and Table 2, the maximum bending strain (ε max,L ) is 10% or more, the above maximum bending strain (ε max,L ) is calculated based on the deflection measured by a three-point bending test with a support distance of 60 mm. In particular, the stress-strain curve obtained by the three-point bending test with a support distance of 60 mm is as follows: Figure 9 shown.

[0129] On the other hand, the aerogel of Comparative Example 1 has a spherical skeleton like a particle aggregate, rather than a fibrous skeleton continuous in a mesh. In addition, the maximum bending strain (ε) calculated from the deflection measured by a three-point bending test with a support distance of 60 mm for the aerogel of Comparative Example 1 ismax,60 ) is less than 10%.

[0130] These results confirm that the aerogel of the present invention has a microstructure composed of a fibrous skeleton continuous in a mesh-like manner and a plurality of pores defined by these skeletons, and contains Si. It is an aerogel that has excellent resistance to breakage when bent and has high light transmittance (especially high visible light transmittance).

[0131] In addition, the aerogels of the examples of the present invention have extremely low thermal conductivity. For example, the thermal conductivity of the aerogel of Example 4 of the present invention is 14.5 mW / mK at 25°C.

[0132] Furthermore, the aerogels of the present invention have high bendability. The minimum bendable diameter R of the aerogels of Examples 1 to 4 is 132.16 mm or less. Therefore, any tube with an A-nominal 125A (outer diameter: 139.8 mm) or a diameter greater than that can be attached to a surface by bending without breaking. By using the aerogels of the present invention, the thickness of the insulation material can be made thinner than before when insulating or cooling water or steam passing through the piping. Furthermore, by increasing the light transmittance of the insulation material compared to the past, the piping can be directly observed without removing the insulation material, allowing for immediate identification of abnormalities such as deterioration of the piping.

[0133] Description of Reference Numerals

[0134] 1: Aerogel;

[0135] 10: Microstructure;

[0136] 2: fine pores;

[0137] 3: skeleton;

[0138] 31: contour;

[0139] 32: Branch;

[0140] 33: Section;

[0141] C: imaginary circle;

[0142] P: The spacing between adjacent nodes;

[0143] R1: pore diameter;

[0144] R2: The diameter of the inscribed circle drawn at the part equivalent to the node;

[0145] t: The thickness of the branch.

Claims

1. An aerogel comprising Si and comprising a fibrous skeleton continuous in a mesh-like manner and a plurality of pores defined by the skeleton. The skeleton has a substantially polygonal outline portion forming the outline of each of the plurality of pores. The contour portion includes a plurality of branch portions and a plurality of node portions, wherein the plurality of branch portions are portions corresponding to sides of the substantially polygonal shape, and the plurality of node portions are portions corresponding to vertices of the substantially polygonal shape. The average spacing between adjacent nodes constituting the pores is 1.50 times or more the average diameter of an inscribed circle drawn at a portion corresponding to the node. The transmittance (τ 550 ) is more than 60% when converted to 10mm thickness.

2. An aerogel comprising Si, The transmittance (τ 550 ) is more than 60% when converted to 10mm thickness, The average thickness of the aerogel is greater than 5 mm and the maximum bending strain (ε max,L ) is 10% or more, The maximum bending strain is calculated from the deflection amount measured by a three-point bending test when the ratio of the distance between supporting points to the average thickness is set to 6 or more and 7 or less.

3. The aerogel according to claim 1 or 2, wherein The thermal conductivity of the aerogel at 25° C. is less than 20 mW / mK.

4. The aerogel according to claim 1 or 2, wherein The volume density of the aerogel (ρ b ) is 0.3g / cm 3 the following.

5. Aerogel particles, which are formed by crushing the aerogel according to claim 1 or 2 into particles.

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