Aerogel and method for producing same

Abstract

Provided are an aerogel and a method for producing the same, in particular, an aerogel having a good state in which defects such as cracks do not exist at a high yield even if the aerogel has a relatively large area (specifically, including the size of a square surface region of 300 mm square) by implementing a parameter that optimizes the total light transmittance when irradiated with visible light, and a method for producing the aerogel. An aerogel which contains Si and has a pore structure formed from a fibrous skeleton that is continuous in a mesh shape and a plurality of pores demarcated by the skeleton, the aerogel having at least a surface having a size that includes a square surface region of 300 mm square, and that has a surface area having a surface area that is larger than the surface area when visible light having a wavelength of 550 nm is irradiated onto the surface region. The standard deviation of the total light transmittance of the aerogel is 0.60% or less in terms of 10 mm thickness.

Description

TECHNICAL FIELD

[0001] The present application relates to an aerogel and a method for manufacturing the same. BACKGROUND

[0002] An aerogel is a material having properties of high porosity (typically 90% or more), low bulk density (0.004 to 0.500 g / cm 3 ), and extremely low thermal conductivity (20 mW / mK or less), while having a uniform porous structure with mesoscopic scale, and is typically produced by a sol-gel method. Among them, a silica aerogel, which is a Si-containing aerogel, has high visible light transmittance in addition to high thermal insulation due to low thermal conductivity, and is expected to be applied as a transparent thermal insulation material that can be applied to residential windows (typically, visible light transmittance is about 60% in a multi-layer window with high thermal insulation), displays, and the like.

[0003] A silica aerogel is produced by hydrolyzing a monomer solution of a silane compound with water or the like as a solvent to produce a sol, forming a gel (condensed compound) by allowing the sol to undergo a cross-linking reaction (condensation reaction), and then drying the gel. However, a silica aerogel is a very fragile material that is difficult to handle during production due to its high porosity and the dilute structure resulting from the fine structure composed of nano-scale domains (typically 100 nm or less). In addition, in order to obtain a large-sized silica aerogel, it is necessary to dry the gel by a supercritical drying method using a supercritical fluid at high temperature and high pressure, and the production requires an expensive device.

[0004] Therefore, a method has been proposed in which by imparting flexibility to the skeleton that constitutes the pore structure, breakage due to shrinkage deformation, recovery deformation in the drying process is avoided, and thus drying can be performed at normal pressure at low production cost. For example, in Patent Literature 1, a method is described in which by performing the reaction for producing a sol and the reaction for gelation of the sol in one stage, the skeleton structure is controlled to be uniform to suppress visible light scattering, and thus a transparent silica aerogel is obtained by drying at normal pressure. In addition, in Non-Patent Literature 1, a method is described in which by hybridizing the pore structure with organic-inorganic, a silica aerogel is obtained by drying at normal pressure.

[0005] Prior Art Documents

[0006] Patent Literature

[0007] Patent Literature 1: Japanese Patent No. 5250900

[0008] Non-Patent Literature

[0009] Non-patent literature 1: K. Kanamori, M. Aizawa, K. Nakanishi, T. Hanada, Adv. Mater., 19, 1589-1593 (2007). SUMMARY

[0010] PROBLEMS TO BE SOLVED BY THE INVENTION

[0011] In the manufacturing method of the silica aerogel described in patent literature 1 and non-patent literature 1, when the gel is dried, the volume of the gel shrinks to 20% or less due to capillary force as the internal solvent present inside the gel is discharged to the outside of the gel. However, when the internal solvent present inside the gel is discharged to the outside of the gel to some extent, gas enters the pores of the gel, and thus the volume of the gel recovers to approximately the same volume as before the shrinkage.

[0012] Here, when the volume of the gel shrinks, when the shape of the gel is not a similar shape to the shape before the shrinkage, a bending stress caused by deformation is generated in the gel, and thus the gel breaks, and therefore it is difficult to obtain an aerogel of a desired shape and size.

[0013] Further, when the gel is dried, when the discharge of the solvent remaining on the surface and inside of the shrunk gel to the outside of the gel becomes uneven, the solvent remaining in the gel causes a bending stress caused by deformation to be generated in the gel when the volume of the gel recovers, and thus the gel breaks, and therefore it is difficult to obtain an aerogel of a desired shape and size.

[0014] In particular, in the case where a large gel is shrunk in order to obtain a large silica aerogel having a size of 300 mm square or more, not only does the bending stress caused by deformation become large as the size increases, but also the condensation conditions of each portion after the sol is injected into the portions of the mold easily become different due to the temperature distribution in each portion and further the material flow generated by the temperature distribution, and therefore the pore structure easily becomes uneven. As a result, due to the shrinkage of the volume when the gel is dried, an uneven capillary force caused by the uneven pore size is generated, and thus the gel breaks, and therefore it is practically impossible to manufacture a silica aerogel at a high yield using drying under ordinary pressure.

[0015] The present application was completed in view of such actual circumstances, and aims to provide an aerogel and a manufacturing method thereof, and in particular, by realizing parameters that optimize the total light transmittance when visible light is irradiated, even a relatively large area (specifically, a size including a square surface region of 300 mm square) can be provided with an aerogel in a perfect state in which there are no defects such as cracks at a high yield.

[0016] MEANS FOR SOLVING THE PROBLEMS

[0017] To achieve the above object, the gist of the present application is configured as follows.

[0018] (1) An aerogel containing Si, having a pore structure formed of a skeleton in the form of a fiber that is continuous in a network and a plurality of pores defined by the skeleton, the aerogel having at least a surface area including a square surface of 300 mm on a side, and when visible light having a wavelength of 550 nm is irradiated to the surface area, a standard deviation of total light transmittance of the aerogel is 0.60% or less in terms of 10 mm thickness.

[0019] (2) The aerogel according to the above (1), wherein the total light transmittance when the visible light is irradiated is 50% or more in terms of 10 mm thickness.

[0020] (3) The aerogel according to the above (1) or (2), wherein the aerogel is produced by atmospheric pressure drying.

[0021] (4) A method of producing an aerogel, the method comprising: a sol production step of producing a sol by hydrolysis of a silicon compound added to an aqueous solution; a gelation step of injecting the sol into a casting mold, and allowing the sol to undergo a cross-linking reaction in the casting mold, and curing while producing a gel; a solvent washing and replacing step of supplying a first solvent having a surface tension of 45 mN / m or less at 20°C to the casting mold, and washing and replacing an intrinsic solvent present on the surface and inside of the gel with the first solvent; and a drying step of producing an aerogel containing Si by drying in a state where a second solvent having a specific gravity greater than the first solvent and being two-phase separated from the first solvent is supplied to the casting mold, at least one of the gelation step, the solvent washing and replacing step, and the drying step being performed while shaking the sol or the gel produced in the casting mold in a horizontal shaking direction parallel to a bottom surface of the casting mold.

[0022] (5) The method of producing an aerogel according to the above (4), wherein each of the steps from the gelation step to the drying step is performed in the same reaction chamber.

[0023] (6) The method of producing an aerogel according to the above (4), wherein, of the steps from the gelation step to the drying step, at least the gelation step and the drying step are performed in different reaction chambers.

[0024] (7) The method for manufacturing aerogel according to (5) or (6) above, wherein the gelation process is performed by adjusting the concentration of water vapor contained in the environment of the reaction chamber to a range of 60% or more and 100% or less relative to the saturated water vapor pressure.

[0025] (8) The method for manufacturing aerogel according to any one of (5) to (7) above, wherein the drying process is performed by adjusting the vapor concentration of the solvent contained in the environment of the reaction chamber to a range of 70% or more and less than 100%.

[0026] (9) The method for manufacturing aerogel according to any one of (5) to (8) above, wherein the drying process is carried out by setting the environment inside the reaction chamber to normal pressure.

[0027] (10) An apparatus for manufacturing an aerogel, comprising: a casting dish for cross-linking a sol generated by hydrolyzing a silicon compound in an aqueous solution, thereby generating a gel while simultaneously curing it; a casting unit for injecting the sol into the casting dish; a first solvent supply unit for supplying a first solvent with a surface tension of less than 45 mN / m at 20°C into the casting dish, thereby cleaning and replacing the intrinsic solvent present on the surface and inside the gel with the first solvent; a second solvent supply unit for supplying a second solvent with a specific gravity greater than the first solvent and which is phase-separated from the first solvent into the casting dish; a drying unit for drying the aerogel containing Si while the second solvent has been supplied into the casting dish; and a shaking mechanism for shaking the sol or gel formed in the casting dish in a horizontal shaking direction parallel to the bottom surface of the casting dish while maintaining it in the casting dish.

[0028] Invention Effects

[0029] According to the present invention, an aerogel and a method for manufacturing the same are provided, particularly by optimizing the parameters of total light transmittance under visible light irradiation, so that even over a relatively large area (specifically, including the size of a square surface area of ​​300 mm square), an aerogel in a perfect state free from defects such as cracks can be provided with a high yield. Attached Figure Description

[0030] Figure 1 This is a graph showing the relationship between the standard deviation of total light transmittance and the breakage probability for the aerogel of the present invention, with the standard deviation of total light transmittance when irradiated with visible light having a wavelength of 550 nm as the horizontal axis and the breakage probability of the aerogel as the vertical axis.

[0031] Figure 2This is a flowchart showing the sequence of steps in the method for manufacturing aerogel according to the present invention.

[0032] Figure 3 This is a conceptual diagram illustrating the states of the sol and gel in each step of the method for manufacturing the aerogel according to the present invention, up to the solvent washing and replacement step. Figure 3 (a) is a conceptual diagram showing the state of the sol and the casting dish when the sol is injected into the casting dish during the gelation process. Figure 3 (b) is a conceptual diagram showing the state of the gel and the casting dish after the gelation process. Figure 3 (c) is a conceptual diagram showing the state in which multiple casting vessels in the reaction chamber are immersed in a first liquid phase composed of a first solvent during the solvent cleaning and replacement process. Figure 3 (d) is a conceptual diagram showing the state after the first solvent that was not held in the casting dish is removed from the reaction chamber during the solvent cleaning and replacement process.

[0033] Figure 4 This is a conceptual diagram illustrating the state of the gel during the drying process in each step of the method for manufacturing aerogel according to the present invention. Figure 4 (a) is a conceptual diagram showing the state of the gel in all the casting dishes held in the reaction chamber being immersed in the second liquid phase. Figure 4 (b) is a conceptual diagram showing the state in which the first solvent and the remaining second solvent are discharged from the reaction chamber and the second solvent is supplied to multiple pouring vessels during the drying process. Figure 4 (c) is a conceptual diagram showing the state of the aerogel after drying in the drying process floating to the interface of the second liquid phase.

[0034] Figure 5 This is a schematic diagram illustrating an example of a reaction apparatus used in a method for manufacturing an aerogel according to the present invention.

[0035] Figure 6 This is a graph showing the standard deviation of the total light transmittance when the aerogels of the present invention and the comparative examples are irradiated with visible light having a wavelength of 550 nm. Detailed Implementation

[0036] The following is a reference to the appendix. Figure 1 The specific embodiments of the present invention will be described in detail below. Furthermore, the present invention is not limited to the following embodiments, and various modifications can be made without changing the spirit of the invention.

[0037] [About the composition of aerogels]

[0038] The aerogel of the present invention contains Si and has a porous structure formed by a continuous fibrous framework and a plurality of pores defined by the framework. The aerogel has at least a surface of the following size: including a square surface area of ​​300 mm square, and when visible light with a wavelength of 550 nm is irradiated onto the surface area, the standard deviation of the total light transmittance of the aerogel is less than 0.60% when converted to a thickness of 10 mm.

[0039] The inventors focused on the standard deviation of light transmittance at three points: the center of the square surface region, the corner of the square surface region, and the center of the edge of the square surface region, when visible light is irradiated onto the square surface region containing Si aerogel. They discovered that in one or both of the gelation process, which involves cross-linking the sol to form a gel, and the drying process, which involves drying the gel, the sol or gel formed in the casting dish is kept in the casting dish while being shaken in a horizontal shaking direction parallel to the bottom surface of the casting dish. This reduces the deviation of the total light transmittance when visible light is irradiated onto the aerogel, even over a relatively large area. At this point, by optimizing the parameter of total light transmittance when irradiated with visible light, and more specifically, by making the standard deviation of total light transmittance when irradiating the aerogel with visible light of 550 nm wavelength (hereinafter, sometimes simply referred to as "standard deviation of total light transmittance") less than 0.60% when converted to a thickness of 10 mm, even for relatively large areas (specifically, including the size of a square surface area of ​​300 mm square), it is possible to manufacture aerogels in perfect condition without defects such as cracks with a high yield.

[0040] In this specification, "no defects such as cracks" in aerogel means that no defects such as cracks can be seen when the aerogel is observed with the naked eye. More specifically, it means that there are no defects such as cracks longer than 100 μm or pores longer than 100 μm.

[0041] Figure 1 This is a graph showing the relationship between the standard deviation of total light transmittance and the breakage probability for the aerogel of the present invention, with the standard deviation of total light transmittance when irradiated with visible light having a wavelength of 550 nm as the horizontal axis and the breakage probability of the aerogel as the vertical axis. Figure 1 In this study, when the standard deviation of total light transmittance was varied, instances of aerogel fracture were plotted with a "fracture probability = 1," and instances of unfractured aerogel were plotted with a "fracture probability = 0." Then, based on these plots, a logistic regression curve was calculated using the standard deviation of total light transmittance (%) as the explanatory variable and the presence or absence of fracture as the target variable, and plotted as a solid line. Figure 1In the chart, when the standard deviation of the total light transmittance of the aerogel, calculated over a 10mm thickness, is 0.65% or less, the breakage probability is less than 0.5; when the standard deviation of the total light transmittance of the aerogel, calculated over a 10mm thickness, is 0.60% or less, no instances of aerogel breakage have been observed. Furthermore, when the standard deviation of the total light transmittance of the aerogel, calculated over a 10mm thickness, is 0.50% or less, the breakage probability in the logistic regression curve is also approximately 0. Therefore, the standard deviation of the total light transmittance of the aerogel, calculated over a 10mm thickness, is preferably 0.60% or less, and more preferably 0.50% or less. This can also be seen from the threshold of the explanatory variable where the breakage probability reaches 50% when a logistic regression curve is performed with the standard deviation of the total light transmittance as the explanatory variable and the presence or absence of breakage as the target variable. Figure 2 The values ​​shown are greater than 0.60%, which clearly demonstrate this.

[0042] The specific structure of the aerogel of the present invention will be described below.

[0043] Here, the aerogel of the present invention has at least a surface area of ​​the following size: including a square surface area of ​​300 mm. In aerogels with such a large surface size, there is a tendency for increased bending stress during shrinkage and recovery, particularly on the outer side of the surface. Even in this case, the standard deviation of total light transmittance when exposed to visible light can be reduced, thereby enabling the production of aerogels in perfect condition without defects such as cracks with a high yield. Therefore, the aerogel can be preferably used in applications requiring large areas, such as thermal insulation materials for buildings.

[0044] Furthermore, when the aerogel of the present invention is irradiated with visible light having a wavelength of 550 nm on a 300 mm square surface region, the standard deviation of the total light transmittance is less than 0.60% when converted to a thickness of 10 mm. Here, the 300 mm square surface region can be selected, for example, by a 300 mm square that overlaps with the center (center of gravity) of the aerogel. In addition, the location for measuring the total light transmittance in the surface region is not particularly limited. From the viewpoint of evaluating, for example, the fragility of the aerogel during drying, multiple locations including the center and the outer perimeter can be set from the 300 mm square surface region (especially the center of the square, the corners of the square, and the center of the sides of the square (the center of the sides connecting adjacent corners of the square)).

[0045] Relatedly, in square aerogels, which are the most common shape for industrial products, the non-uniformity of the pore structure relative to other locations (typically the center of the square) is mostly found at the corners and the center of the sides of the square. Furthermore, at the corners and the center of the sides, the deviation in total light transmittance relative to the center of the square manifests in various forms due to manufacturing conditions (chamber shape, gel arrangement, heat transfer method, stirring method, etc.). Therefore, by obtaining the standard deviation of the total light transmittance at these three points—the center, corners, and center of the sides—and reducing these standard deviations, it is possible to minimize aerogel breakage during drying. Thus, by using aerogels with small standard deviations in these three points of total light transmittance, even with relatively large areas, it is possible to provide aerogels in perfect condition without defects such as cracks with a high yield.

[0046] In addition, the standard deviation of total light transmittance is the standard deviation of the total light transmittance obtained at all measurement locations when converted to a value with a thickness of 10 mm.

[0047] In this way, by ensuring that the standard deviation of the total transmittance when irradiated with visible light is less than 0.60% when converted to a thickness of 10 mm, the pore structure of the aerogel, comprising a continuous fibrous framework in a network, is arranged substantially uniformly along the surface direction. This results in both high uniformity of the aerogel and the high uniformity of its precursor gel. For example, when manufacturing the aerogel using atmospheric pressure drying, during the atmospheric pressure drying process, the gel shrinks in volume, and subsequently, the volume is restored to obtain the aerogel. This allows for shrinkage and restoration of the gel shape while maintaining a similar shape, thereby minimizing the generation of bending stress caused by deformation within the gel. Therefore, the aerogel of the present invention, even with a relatively large area, can achieve a high yield and be in perfect condition free of defects such as cracks.

[0048] Furthermore, the total light transmittance of the aerogel of the present invention, when irradiated with visible light having a wavelength of 550 nm in a 300 mm square surface area, is preferably 50% or more, more preferably 70% or more, based on a 10 mm thickness. As a result, the elements absorbing or reflecting visible light in the aerogel are reduced, thus making it easier for uneven portions that generate bending stress to become apparent, thereby further reducing the likelihood of bending stress caused by deformation.

[0049] The aerogel of the present invention is a square surface area comprising 300 mm on each side. Therefore, the aerogel of the present invention has a longitudinal and transverse dimension of 300 mm or more when viewed from above. On the other hand, there is no particular upper limit to the size of the aerogel of the present invention; when viewed from above, one or both of the longitudinal and transverse dimensions may be 5000 mm or 3000 mm.

[0050] The thickness of the aerogel of the present invention is not particularly limited, and the average thickness can be in the range of, for example, 1 mm or more and 30 mm or less. Here, from the viewpoint of facilitating the shrinkage and recovery of the gel in the casting dish, the aerogel is preferably plate-shaped, and particularly preferably has two sides composed of planes, in which case the thickness of the aerogel is preferably uniform.

[0051] The aerogel of the present invention has a fine Si-containing structure formed by a continuous fibrous framework and multiple pores defined by the framework.

[0052] Here, the fine structure of aerogels refers to a fine structure containing silicon atoms within the molecule. As an example, fine structures such as polysilsesquioxanes can be cited. The fine structures of polysilsesquioxanes can be formed through the hydrolysis and condensation polymerization of silanolates. In particular, polymethylsilsesquioxanes (PMSQ, MeSiO2) are examples. 1.5 Aerogels can form transparent aerogels by combining the hydrolysis and condensation reaction of methyltrialkoxysilane (MeSi(OR)3) with a surfactant as a phase separation inhibitor. Examples of the hydrolysis and condensation reactions that form PMSQ aerogels include, for example, the hydrolysis reaction using an acid catalyst shown in Formula (I) and the condensation reaction using an alkaline catalyst shown in Formula (II).

[0053]

[0054]

[0055] Furthermore, the microstructure of aerogels has a continuous fibrous framework. As a result, by forming multiple micropores from the fibrous framework, the density of the aerogel is reduced, thus decreasing its thermal conductivity and improving its insulation properties.

[0056] Here, the average pore size of the multiple pores in the microstructure of the aerogel is not particularly limited, and can be in the range of, for example, 5 nm or more and 100 nm or less. The average pore size can be the average inner diameter when the pore is approximated as a tube and the inner diameter of the tube is approximated as a circle. Furthermore, the lower limit of the average inner diameter of the pores can be 5 nm or more, 7 nm or more, 10 nm or more, 20 nm or more, 30 nm or more, or 50 nm or more. Furthermore, the upper limit of the average inner diameter of the pores can be 100 nm or less, 90 nm or less, 80 nm or less, or 70 nm or less. The aforementioned average pore size is below the mean free path (MFP) of the elements constituting air molecules at atmospheric pressure; therefore, the aerogel placed in air at atmospheric pressure will be in a state where air enters the interior of the pores.

[0057] Furthermore, the porosity of the aerogel, i.e., the proportion of the pore volume of the through-holes (pores) to the total volume of the aerogel, is not particularly limited, but is preferably 70% or more. In particular, the porosity can be 75% or more, 80% or more, 85% or more, or 90% or more. Even with such high porosity, the aerogel of the present invention can be obtained by drying under normal pressure.

[0058] Furthermore, the density of aerogels can be as low as, for example, 0.15 g / cm³. 3 The density of the aerogel can be determined, for example, by mercury porosimetry. The lower the density of the aerogel, the lower its thermal conductivity, and consequently, the better its insulation properties. Even with a density of 0.15 g / cm³, the aerogel of this invention... 3 It is also not easy to break at this point, and the thermal conductivity decreases to about 0.01 W / m·K to 0.02 W / m·K.

[0059] In addition to the above-described composition, the aerogel of the present invention may also contain other components for purposes such as imparting functionality, improving appearance, and imparting decorative properties. These may include, for example, antistatic agents, lubricants, inorganic pigments, organic pigments, inorganic dyes, and organic dyes. Furthermore, the aerogel of the present invention may contain water, organic solvents, surfactants, catalysts, and their decomposition products as unavoidable components in the manufacturing process. Additionally, the aerogel of the present invention may also contain dust introduced into the manufacturing space or manufacturing apparatus as an unavoidable component in the manufacturing process.

[0060] [The composition of the manufacturing method for aerogels]

[0061] As an example of a method for manufacturing the aforementioned aerogel, the following method can be cited.

[0062] Figure 3This is a flowchart showing the sequence of steps in the method for manufacturing aerogel 1 according to the present invention. Figure 3 This is a conceptual diagram showing the state of sol 11 and gel 12 in each step of the method for manufacturing aerogel 1 according to the present invention up to the solvent cleaning and replacement step S3. Figure 3 (a) is a conceptual diagram showing the state of the sol 11 and the casting dish 3 when the sol 11 is injected into the casting dish 3 in the gelation process S2. Figure 3 (b) is a conceptual diagram showing the state of gel 12 and casting dish 3 after the gelation process S2. Figure 3 (c) is a conceptual diagram showing the state in which multiple casting dishes 3 in the reaction chamber 2 are immersed in the first liquid phase L1 composed of the first solvent during the solvent cleaning and replacement process S3. Figure 4 (d) is a conceptual diagram showing the state after the first solvent not retained in the casting dish 3 is discharged from the reaction chamber 2 in the solvent cleaning and replacement step S3. Furthermore, Figure 4 This is a conceptual diagram showing the state of sol 11 and gel 12 in each step after solvent cleaning and replacement step S3 in the manufacturing method of aerogel 1 according to the present invention. Figure 4 (a) is a conceptual diagram showing the state in which multiple casting dishes 3 in the reaction chamber 2 are immersed in the second liquid phase L2 composed of the second solvent during the solvent cleaning and replacement process S3. Figure 4 (b) is a conceptual diagram showing the state in which the first solvent and the remaining second solvent in the reaction chamber 2 are discharged and the second solvent is supplied to multiple pouring vessels 3 during the solvent cleaning and replacement process S3. Figures 2-4 (c) is a conceptual diagram showing the state of the aerogel 1 after drying in the drying process S4, floating to the interface of the second liquid phase L2.

[0063] like Figure 5As shown, the method for manufacturing the aerogel 1 of the present invention includes: a sol generation step S1, in which a sol 11 is generated by adding a silicon compound to an aqueous solution for hydrolysis; a gelation step S2, in which the sol 11 is injected into a casting dish 3, and the sol 11 undergoes a cross-linking reaction within the casting dish 3, while simultaneously curing a gel (wet gel) 12; a solvent cleaning and replacement step S3, in which a first solvent with a surface tension of less than 45 mN / m at 20°C is supplied into the casting dish 3 where the gel 12 has been formed, and the intrinsic solvent present on the surface and inside of the gel 12 is cleaned and replaced with the first solvent; and a drying step S4, in which the casting dish 3 is dried while a second solvent with a specific gravity greater than that of the first solvent and which is phase-separated from the first solvent is supplied, thereby forming a Si-containing aerogel 1. At least one of the gelation step S2, the solvent cleaning and replacement step S3, and the drying step S4 is performed while the sol 11 or gel 12 formed in the casting dish 3 is held in the casting dish 3 and shaken in a horizontal shaking direction parallel to the bottom surface 31 of the casting dish 3.

[0064] In the manufacturing method of the aerogel 1 of the present invention, in at least one of the gelation step S2, the solvent cleaning and replacement step S3, and the drying step S4, the sol 11 or gel 12 formed in the casting dish 3 is held in the casting dish 3 and shaken in a horizontal shaking direction parallel to the bottom surface 31 of the casting dish 3. This causes the environment in contact with the sol 11 or gel 12 to flow relative to the sol 11 or gel 12 as a whole due to the shaking, thereby improving the uniformity of the surrounding environment (temperature, component concentration, flow rate) of the sol 11 or gel 12. As a result, the uniformity of the sol 11 or gel 12 after the gelation step S2 or the drying step S4 can be improved, and thus the uniformity of the aerogel 1 can also be improved. Therefore, an aerogel 1 with a small standard deviation of total light transmittance when irradiated with visible light can be obtained.

[0065] Relatedly, a common method for homogenizing the environment surrounding the sol 11 or gel 12 is to apply a driving force to the fluid (gas, liquid) constituting the environment and stir it. However, when a driving force is applied to the fluid constituting the environment, the driving force is significantly attenuated due to the distance from the point of application and the spatial shape, making it impossible to uniformly transmit the driving force to the entire environment surrounding the sol 11 or gel 12. In this respect, in the method for manufacturing the aerogel 1 of the present invention, the sol 11 or gel 12 is agitated while being held in the pouring dish 3, rather than the fluid constituting the environment. This allows the entire sol 11 or gel 12 to be agitated in its original state, thus homogenizing the environment surrounding the sol 11 or gel 12.

[0066] At this point, the gel 12 is particularly brittle, so it is not desirable to shake violently in random directions including the thickness direction of the gel 12. Even in such a case, by taking advantage of the fact that the gel 12 is held in a two-dimensional shape (plate-like) by the pouring dish 3, the pouring dish 3 holding the gel 12 can be shaken along a surface parallel to the bottom surface 31 of the pouring dish 3, so that the gel 12 is not easily broken even by relatively violent shaking.

[0067] Here, the shaking of the pouring dish 3 containing the sol 11 or gel 12 is desired to be carried out within a limited space such as the reaction chamber 2, and is expected to be continuous; therefore, rotational motion is preferred. As an example, as described later... Figure 3 As shown, the casting dish 3 (or the casting dish support 30 holding the casting dish 3) is positioned horizontally in the reaction chamber 2 with the surface of the sol 11 or gel 12 (the bottom surface 31 of the casting dish 3) as the horizontal plane. At the same time, the reaction chamber 2 is rotated alternately to the right and left with the height direction Y of the reaction chamber 2 as the axis (central axis M). This allows the casting dish 3 holding the sol 11 or gel 12 to be shaken in a horizontal shaking direction parallel to the bottom surface 31 of the casting dish 3.

[0068] Furthermore, when the sol 11 or gel 12 is shaken by a rotational motion in a certain direction in the horizontal shaking direction, the fluid constituting the environment around the sol 11 or gel 12 will flow synchronously with the rotational motion due to the frictional resistance with the sol 11 or gel 12, and thus the relative speed of the shaking relative to the sol 11 or gel 12 may decrease. Therefore, from the viewpoint of suppressing this, it is preferable to change the shaking speed of the casting dish 3 in at least one direction. This can improve the uniformity of the environment in contact with the surface of the sol 11 or gel 12, and especially when shaking multiple casting dishes 3 in the same apparatus, it is also possible to improve the uniformity of the environment in contact with the sol 11 or gel 12 held in different casting dishes 3. At this time, when changing the shaking speed of the casting dish 3, the shaking direction can also be reversed in the opposite direction, especially when the shaking of the casting dish 3 is carried out by rotational motion, it is also possible to change only the speed without changing the shaking direction of the casting dish 3. Furthermore, the shaking speed of the pouring vessel 3 can be temporarily changed to zero, thereby making the shaking of the pouring vessel 3 intermittent. In addition, the change in shaking speed can be carried out periodically or irregularly.

[0069] When the pouring dish 3 is rotated in a horizontal shaking direction by rotating it with the center of the sol 11 or gel 12 as the rotation center, the relative velocity between the sol 11 or gel 12 and the fluid constituting its surrounding environment depends on the distance from the rotation center, so shaking near the rotation center may become insufficient. Therefore, from the viewpoint of further improving the uniformity of the environment surrounding the sol 11 or gel 12, it is preferable to complicate the motion when shaking the pouring dish 3. As an example, the pouring dish 3 can also be shaken by making the pouring dish support 30 holding the pouring dish 3 move in a planetary motion along the surface direction of the sol 11 or gel 12. In this way, by constantly changing the shaking direction and shaking speed of the pouring dish 3, the uniformity of the environment in contact with the sol 11 or gel 12 held in the pouring dish 3 can be further improved. From the viewpoint of further improving the uniformity of the environment in contact with the sol 11 or gel 12 held in the casting dish 3, it is preferable to repeatedly perform the operation of changing the direction of motion to the opposite direction when the casting dish support 30 is made to perform planetary motion.

[0070] Here, the pouring dish support 30 can be as follows: Figure 3 As shown, multiple casting dishes 3 are arranged in a manner that arranges multiple pieces along the thickness direction of the obtained aerogel 1. As a result, the area of ​​the casting dish support 30 along the surface direction of the aerogel 1 can be reduced, thus making it easy to shake the casting dish 3 holding the sol 11 or gel 12.

[0071] The manufacturing apparatus used in the method for manufacturing the aerogel 1 of the present invention is preferably a manufacturing apparatus in which each step from the gelation step S2 to the drying step S4 is performed within the same reaction chamber 2. Therefore, it is not necessary to open the reaction chamber 2 between each step of the sol-forming step S1, the gelation step S2, the solvent washing and displacement step S3, and the drying step S4. Thus, non-uniformity of the sol 11 or gel 12 caused by the time difference resulting from the rapid environmental change until the reaction chamber 2 is opened can be suppressed within the same sol 11 or gel 12. Furthermore, since it is not necessary to move the sol 11 or gel 12 between the apparatuses for each step of the sol-forming step S1, the gelation step S2, the solvent washing and displacement step S3, and the drying step S4, it is particularly effective in preventing breakage of the gel 12 when it is moved.

[0072] On the other hand, the manufacturing apparatus used in the method for manufacturing aerogel 1 of the present invention can be a manufacturing apparatus in which at least the gelation step S2 and the drying step S4 are performed in different reaction chambers in each step from gelation step S2 to drying step S4. Therefore, the time-consuming gelation step S2 and drying step S4 in the manufacturing process of aerogel 1 can be performed separately, thus enabling more efficient manufacturing of aerogel 1. Even in this case, from the viewpoint of preventing the gel from breaking due to rapid drying, it is preferable that the solvent washing and replacement step S3 and the drying step S4 are performed in the same reaction chamber.

[0073] The following describes each step of the method for manufacturing the aerogel 1 of the present invention.

[0074] [Sol-gel generation process S1]

[0075] The sol-gel generation step S1 is a step in which a silicon compound is added to an aqueous solution for at least hydrolysis to generate a sol 11. The sol 11 used to manufacture the aerogel 1 of the present invention contains siloxane bonds and can be generated by adding various raw materials containing a silicon compound (the main raw material) to a prescribed aqueous solution and stirring to mix them, thereby utilizing the hydrolysis of the silicon compound.

[0076] Silicon compounds used as raw materials include silane compounds, and more specifically, at least one of difunctional, trifunctional, and tetrafunctional silane compounds.

[0077] Here, a difunctional silane compound refers to a silane compound with two siloxane bonds, a trifunctional silane compound refers to a silane compound with three siloxane bonds, and a tetrafunctional silane compound refers to a silane compound with four siloxane bonds.

[0078] Examples of bifunctional silane compounds include dialkoxysilanes and diacetoxysilanes. Preferred embodiments of dialkoxysilanes include those with 1 to 9 carbon atoms in the alkoxy group. Specifically, examples include dimethyldimethoxysilane, diethyldimethoxysilane, and diisobutyldimethoxysilane. These compounds can be used alone or in combination. In this invention, dimethyldimethoxysilane (DMDMS) is particularly preferred as a bifunctional silane compound.

[0079] Examples of trifunctional silane compounds include, for example, trialkoxysilanes and triacetoxysilanes. Preferred embodiments of trialkoxysilanes include those with 1 to 9 carbon atoms in the alkoxy group. Examples include methyltrimethoxysilane, ethyltrimethoxysilane, propyltrimethoxysilane, hexyltrimethoxysilane, octyltrimethoxysilane, methyltriethoxysilane, ethyltriethoxysilane, propyltriethoxysilane, pentyltriethoxysilane, hexyltriethoxysilane, and octyltriethoxysilane. These compounds can be used alone or in combination. In this invention, methyltrimethoxysilane (MTMS) is particularly preferred as a trifunctional silane compound.

[0080] Examples of tetrafunctional silane compounds include tetraalkoxysilanes and tetraacetoxysilanes. Preferred embodiments of tetraalkoxysilanes include tetraalkoxysilanes with 1 to 9 carbon atoms in the alkoxy group. Examples include tetramethoxysilanes, tetraethoxysilanes, tetrapropoxysilanes, and tetraisopropoxysilanes. These silane compounds can be used alone or in combination. In this invention, tetramethoxysilane (TMOS) is particularly preferred as a tetrafunctional silane compound.

[0081] In the sol-gel generation process S1, in addition to silicon compounds (the main raw material), surfactants, acids, and organic solvents can also be used as by-products.

[0082] In this process, the surfactant contributes to the formation of the pore structure of the aerogel 1 described later. Nonionic surfactants, ionic surfactants, etc., can be used as surfactants suitable for manufacturing the aerogel 1. Examples of ionic surfactants include cationic surfactants, anionic surfactants, and amphoteric surfactants. Among these, nonionic surfactants are preferred.

[0083] The amount of surfactant added varies depending on the type of silicon compound, the mixing ratio of the silicon compounds, and the type of surfactant. However, relative to 100 parts by mass of the total amount of silicon compound as the main raw material, it can be in the range of, for example, 0.001 parts by mass to 100 parts by mass, particularly preferably in the range of 0.01 parts by mass to 90 parts by mass, and even more preferably in the range of 0.1 parts by mass to 80 parts by mass.

[0084] Furthermore, acids can act as catalysts during hydrolysis, accelerating the reaction rate. Specific examples of acids include inorganic acids, organic acids, and organic acid salts. These acids can be used alone or in combination.

[0085] Examples of inorganic acids include hydrochloric acid, sulfuric acid, sulfurous acid, nitric acid, hydrofluoric acid, phosphoric acid, phosphorous acid, hypophosphoric acid, bromic acid, chloric acid, chlorogenic acid, and hypochlorous acid. Examples of organic acids include carboxylic acids such as acetic acid, formic acid, propionic acid, oxalic acid, malonic acid, succinic acid, citric acid, malic acid, adipic acid, and azelaic acid. Furthermore, acidic aluminum phosphate, acidic magnesium phosphate, and acidic zinc phosphate can be used as acid salts. In this invention, acetic acid, as an organic acid, is preferably used.

[0086] Furthermore, the concentration of acid added relative to the sol 11 obtained in the sol generation step S1 is preferably in the range of, for example, 0.0001 mol / L to 0.1 mol / L, particularly preferably in the range of 0.0005 mol / L to 0.05 mol / L, and even more preferably in the range of 0.001 mol / L to 0.01 mol / L.

[0087] Methanol, ethanol, 1-propanol, 2-propanol (isopropanol), 1-butanol, 2-butanol, tert-butanol, and other alcohols are preferred as organic solvents. These can be used alone or in combination of two or more. Furthermore, from the viewpoint of compatibility, the amount of organic solvent added to the prepared solution can be, for example, in the range of 4 mol to 10 mol relative to 1 mol of the total amount of silicon compound as the main raw material, particularly preferably in the range of 4.5 mol to 9 mol, and even more preferably in the range of 5 mol to 8 mol.

[0088] The solution temperature and stirring time in the sol-gel generation step S1 depend on the type and amount of silicon compounds, surfactants, water, acids, organic solvents, etc., contained in the mixed solution. For example, it is acceptable to process the solution at a temperature of 0°C to 70°C for 0.05 hours to 48 hours, preferably at a temperature of 20°C to 50°C for 0.1 hours to 24 hours. As a result, the silicon compounds are hydrolyzed to form colloids, thus generating sol 11.

[0089] In addition, the excipients and / or decomposition products of the excipients used in the sol generation process S1 can inevitably be mixed into the manufactured aerogel 1.

[0090] [Gelization process S2]

[0091] The gelation process S2 involves injecting the sol 11 generated in the sol generation process S1 into the casting dish 3, allowing the sol to undergo a cross-linking reaction within the casting dish 3, and simultaneously curing the gel 12. Through this process, such as... Figure 3 As shown in (a), after the sol 11 is injected into the casting dish 3, as... Figure 3As shown in (b), gel 12 is formed in the casting dish 3. Here, the gelation process S2 can be roughly divided into: a catalyst addition process S21 in which an alkaline catalyst is added to the sol 11; a casting process S22 in which the sol 11 with the added alkaline catalyst is injected into the casting dish 3; and a curing process S23 in which gel 12 is generated by curing the solution in the casting dish 3.

[0092] Among them, the alkaline catalyst added to the sol 11 in the catalyst addition step S21 can include: ammonium compounds such as ammonium hydroxide, ammonium fluoride, ammonium chloride, and ammonium bromide; alkali metal hydroxides such as lithium hydroxide, sodium hydroxide, potassium hydroxide, and cesium hydroxide; alkaline sodium phosphate salts such as sodium metaphosphate, sodium pyrophosphate, and sodium polyphosphate; and allylamine, diallylamine, triallylamine, isopropylamine, diisopropylamine, ethylamine, diethylamine, triethylamine, 2-ethylhexylamine, 3-ethoxypropylamine, and diisobutylamine. Aliphatic amines such as amines, 3-(diethylamino)propylamine, di-2-ethylhexylamine, 3-(dibutylamino)propylamine, tetramethylethylenediamine, tert-butylamine, sec-butylamine, propylamine, 3-(methylamino)propylamine, 3-(dimethylamino)propylamine, 3-methoxyamine, dimethylethanolamine, methyldiethanolamine, diethanolamine, and triethanolamine; and nitrogen-containing heterocyclic compounds such as morpholine, N-methylmorpholine, 2-methylmorpholine, piperazine and its derivatives, piperidine and its derivatives, and imidazole and its derivatives. The basic catalyst can be used alone or in combination of two or more.

[0093] The alkaline catalyst can also be a nitride that generates an alkaline catalyst through heating. The nitride is added as a compound to generate the alkaline catalyst during heating in the casting step S22 and the curing step S23. Specifically, examples include amide compounds such as urea, formamide, N-methylformamide, N,N-dimethylformamide, acetamide, N-methylacetamide, and N,N-dimethylacetamide, as well as heterocyclic compounds such as hexamethylenetetramine. Among these, urea is preferred from the perspective of accelerating the gel formation rate in the curing step S23. Since these nitrides that generate an alkaline catalyst through heating can generate an alkaline catalyst in the curing step S23, these nitrides can be added in the sol formation step S1 without performing the catalyst addition step S21.

[0094] Among them, ammonium hydroxide aqueous solution is preferred in terms of its high reaction-promoting effect as a catalyst, its ability to advance the cross-linking reaction from sol 11 to gel 12 in a short time, and its ability to form fewer defects. In addition, ammonium hydroxide aqueous solution is also excellent in terms of its high volatility, which means it will evaporate in the solvent washing and replacement step S3 and the drying step S4 described later and will not easily remain in the obtained aerogel 1.

[0095] The amount of alkaline catalyst added to the sol 11 is preferably in the range of 0.5 parts by mass to 5 parts by mass relative to the total amount of 100 parts by mass of the sol 11, and more preferably in the range of 1 part by mass to 4 parts by mass. Here, when the amount of alkaline catalyst added is less than 0.5 parts by mass, the cross-linking reaction cannot occur when the gel 12 is formed from the sol 11. In addition, when the amount of alkaline catalyst added is greater than 5 parts by mass, the cross-linking reaction is too fast, and the resulting gel 12 may become uneven.

[0096] The casting process S22 is the process of injecting the sol 11 with an added alkaline catalyst into the casting dish 3, which is used to obtain the desired shape of the aerogel product. Here, the casting dish 3 can be made of either metal or synthetic resin. From the viewpoint of considering both non-flammability for industrial use and the planarity and release properties of the shape, a dish coated with a release coating layer on a metal substrate is preferred. Examples of metals include stainless steel and ferroalloys such as steel. Furthermore, examples of the release coating layer include a coating layer formed from a fluoropolymer resin such as Teflon (registered trademark).

[0097] Furthermore, the casting dish 3 has a shape corresponding to the desired aerogel product. For example, in the case of obtaining a plate-shaped aerogel 1, a concave disc with one end open can be used as a mold. Here, from the viewpoint of facilitating the shrinkage and recovery of the gel in the casting dish 3, the surface of the casting dish 3 is preferably made of a plane.

[0098] The curing process S23 is a process in which the sol 11 filled in the casting dish 3 is cured in the casting dish to generate gel 12, and at the same time, the shape is formed along the inner wall of the casting dish 3.

[0099] Curing step S23 is a process that involves applying a specified amount of energy over a predetermined period of time to advance the cross-linking reaction from sol 11 to gel 12. Here, as an example of energy, thermal energy can be cited; more specifically, heating to a temperature range of 30–90°C, preferably to a temperature range of 40–80°C, can be cited. Heating can be performed using a heater or by using steam from water vapor or organic solvents. These energy sources can be used individually or in combination.

[0100] The curing time required in curing step S23 depends on the structure of the silicon compound, the type and amount of surfactant, water, acid, organic solvent, alkaline catalyst, etc., as well as the type and density of energy used in curing step S23, and can range from, for example, 0.01 hours to 7 days. Furthermore, by optimizing the type of alkaline catalyst and energy, gelation can be completed in the range of 0.01 hours to 24 hours. In addition, curing can also involve multi-stage variations in heat (temperature) and time.

[0101] In the curing process S23, warm water can be supplied to the reaction chamber 2 and immediately drained, thereby forming a water layer on the surface of the gel 12 to prevent cracking caused by drying. In addition to the warm water supplied to the reaction chamber 2 in the curing process S23, from the viewpoint of preventing damage to the gel 12, the liquid supplied to the reaction chamber 2 in the method for manufacturing the aerogel 1 of the present invention is preferably a liquid with a temperature difference of less than 10°C relative to the ambient temperature of the reaction chamber 2. That is, at least one of the warm water used in the curing process S23, the cleaning agent used in the cleaning process S24 (described later), the first solvent used in the solvent cleaning and replacement process S3, and the second solvent used in the drying process S4 is preferably supplied to the reaction chamber 2 with a temperature difference of less than 10°C relative to the ambient temperature of the reaction chamber 2.

[0102] Here, in the curing step S23, the concentration of water vapor contained in the environment within the reaction chamber 2 is preferably adjusted to a range of 60% or more and 100% or less relative to the saturated water vapor pressure, and more preferably to a range of 80% or more and 100% or less. Therefore, by appropriately controlling the evaporation of moisture from the gel 12 in the gelation step S2, the non-uniformity of the gel 12 caused by the evaporation of moisture contained in the gel 12 can be suppressed.

[0103] Furthermore, in the curing step S23, the gel 12 held in the pouring dish 3 is preferably agitated in a horizontal agitation direction parallel to the bottom surface 31 of the pouring dish 3. This improves the temperature uniformity of the gel 12, thereby further improving the uniformity of the pore structure of the gel 12. As a result, when the internal solvent is discharged from the gel in the drying step S4 described later, the uniformity of the pore structure (pore size) is improved, thereby generating capillary force in a nearly uniform state, and thus drying shrinkage can be performed in a shape that is nearly similar to the original shape. In particular, from the viewpoint of also improving the uniformity of the concentration of water vapor contained in the environment near the gel 12 and further improving the uniformity of the pore structure of the gel 12, it is preferable to agitate the gel 12 held in the pouring dish 3 in a horizontal agitation direction parallel to the bottom surface 31 of the pouring dish 3 while adjusting the concentration of water vapor contained in the environment within the reaction chamber 2 to the above-mentioned range.

[0104] Furthermore, the materials used in the gelation process S2 and their decomposition products can inevitably be mixed into the manufactured aerogel 1 as components.

[0105] After the gelation step S2, a further cleaning process S24 can be performed to clean the acid used to generate sol 11, the catalyst used to generate gel 12, reaction byproducts, etc.

[0106] As the cleaning agent used in cleaning process S24, a wide range of organic solvents can be used, and it is particularly preferred to use a solvent different from the first solvent described later. Here, as the cleaning agent, various organic solvents can be used, such as methanol, ethanol, n-propanol, isopropanol, 1-butanol, 2-butanol, tert-butanol, acetone, methyl ethyl ketone, methyl isobutyl ketone, xylene, 1,2-dimethoxyethane, acetonitrile, hexane, toluene, diethyl ether, chloroform, ethyl acetate, tetrahydrofuran, dichloromethane, N,N-dimethylformamide, dimethyl sulfoxide, acetic acid, formic acid, etc. The above-mentioned organic solvents can be used alone or in mixtures of two or more.

[0107] Among them, methanol, ethanol, isopropanol, acetone, methyl ethyl ketone, etc., which are soluble in both the organic solvent and water that constitute the first solvent described later, are preferably used as cleaning agents, either alone or in combination of two or more.

[0108] The cleaning process in S24 is carried out by filling the reaction chamber 2 with a cleaning agent, immersing the multiple casting dishes 3 on which the gel 12 is formed in the cleaning agent, and at least removing any methanol that is not retained in the casting dishes 3. This cleans the gel 12 of acids, reaction byproducts, etc., and removes them to the outside of the gel 12. At this time, since the cleaning agent is soluble in the first solvent described later, it may also remain in the casting dishes 3.

[0109] Here, the cleaning process S24 is preferably performed by adjusting the concentration of the cleaning agent contained in the environment within the reaction chamber 2 to a range of 80% or more and 100% or less relative to the saturated vapor pressure, and more preferably to a range of 90% or more and 100% or less. As a result, since the evaporation of the cleaning agent from the gel 12 is suppressed in the cleaning process S24, the non-uniformity of the gel 12 caused by the evaporation of the cleaning agent contained in the gel 12 can be suppressed.

[0110] Furthermore, in the cleaning process S24, it is preferable to agitate the gel 12 held in the pouring dish 3 along a horizontal agitation direction parallel to the bottom surface 31 of the pouring dish 3. This improves both the temperature uniformity of the gel 12 and the flow rate uniformity of the cleaning agent in contact with the gel 12, thereby further improving the uniformity of the pore structure of the gel 12. In particular, from the viewpoint of also improving the uniformity of the concentration of the cleaning agent contained in the environment surrounding the gel 12 and further improving the uniformity of the pore structure of the gel 12, it is preferable to agitate the gel 12 held in the pouring dish 3 along a horizontal agitation direction parallel to the bottom surface 31 of the pouring dish 3 while adjusting the concentration of the cleaning agent contained in the environment within the reaction chamber 2 to the aforementioned range.

[0111] The amount of cleaning agent used in cleaning process S24 also depends on the solvent replacement temperature and the apparatus (reaction chamber 2, pouring dish 3). Preferably, the amount of cleaning agent used is sufficient to immerse the entire gel 12 in the cleaning agent supplied to the pouring dish 3. Therefore, the amount of cleaning agent is preferably in the range of 2 to 100 times the total volume of the gel 12. Furthermore, cleaning process S24 is not limited to one time and can be performed multiple times.

[0112] [Solvent cleaning and replacement process S3]

[0113] The solvent cleaning and replacement step S3 involves supplying a first solvent with a surface tension as low as 45 mN / m at 20°C into the casting dish 3 where the gel 12 has formed. This first solvent is used to clean and replace the intrinsic solvents and surfactants present on and inside the gel 12. This allows the water and / or organic solvents present on and inside the gel 12, which are intrinsic solvents, to be replaced with organic solvents suitable for short-time drying.

[0114] In the solvent cleaning and replacement step S3, in order to clean the gel 12 with a first solvent having a surface tension of 45 mN / m or less at 20°C while suppressing shrinkage damage to the gel 12 in the drying step S4 described later, the water (or organic solvent) on the surface and inside of the gel 12 is replaced with the first solvent. As the first solvent, a liquid with a surface tension of 45 mN / m or less at 20°C can be used. As an example, dimethyl sulfoxide (43.5 mN / m), cyclohexane (25.2 mN / m), isopropanol (21 mN / m), heptane (20.2 mN / m), pentane (15.5 mN / m), etc., can be used.

[0115] The first solvent used in the solvent cleaning and replacement step S3 has a surface tension of 45 mN / m or less, 40 mN / m or less, 35 mN / m or less, 30 mN / m or less, 25 mN / m or less, 20 mN / m or less, or 15 mN / m or less at 20°C, and can be 5 mN / m or more, 10 mN / m or more, 15 mN / m or more, or 20 mN / m or more. Among these, an organic solvent containing aliphatic hydrocarbons with a surface tension in the range of 20 mN / m to 40 mN / m at 20°C is particularly preferred as the first solvent. Such an organic solvent can be used alone or in combination of two or more.

[0116] Furthermore, the first solvent used in the solvent cleaning and replacement step S3 preferably has the characteristic that, after the solvent cleaning and replacement step S3, the gel 12 settles in the first liquid phase L1 composed of the first solvent and is impregnated. Therefore, the first solvent preferably has an affinity for the gel 12 while having a smaller specific gravity than the gel 12. Here, the affinity between the first solvent and the gel 12 means that the solvent can penetrate into the pores of the gel 12, resulting in the solvent impregnating the gel 12. As an example of such a solvent, a solvent with a solubility parameter in the range of 7.0 to 9.5 can be cited.

[0117] Furthermore, as the first solvent used in the solvent cleaning and replacement step S3, it is preferable to use a solvent with a smaller specific gravity than the second solvent (described later) and a lower boiling point than the second solvent. From this perspective, as the first solvent, it is preferable to use an organic solvent with a boiling point of 50°C to 100°C. Examples of such solvents include hydrocarbon solvents such as hexane (specific gravity 0.65, boiling point 69°C) and heptane (specific gravity 0.68, boiling point 98°C); and ester solvents such as methyl acetate (specific gravity 0.93, boiling point 57°C) and ethyl acetate (specific gravity 0.90, boiling point 77°C).

[0118] Solvent cleaning and replacement process S3, as shown Figure 3 As shown in (c), after filling the reaction chamber 2 with the first solvent, multiple casting dishes 3, on which gel 12 has been formed, are immersed in the first liquid phase L1 composed of the first solvent, as follows: Figure 4 As shown in (d), the first solvent that is not retained in the casting dish 3 is discharged. This process cleans the gel 12 or the cleaning agent of impurities such as acids and reaction byproducts, and discharges them to the outside of the reaction chamber 2. Furthermore, the gel 12 after the solvent cleaning and replacement step S3 is placed in a liquid phase system composed of the first liquid phase L1 in the casting dish 3.

[0119] Here, in the solvent cleaning and replacement step S3, the concentration of the first solvent contained in the environment within the reaction chamber 2 is preferably adjusted to a range of 80% or more and 100% or less relative to the saturated vapor pressure, and more preferably to a range of 90% or more and 100% or less. Therefore, by suppressing the evaporation of the first solvent from the gel 12 in the solvent cleaning and replacement step S3, the non-uniformity of the gel 12 caused by the evaporation of the first solvent contained in the gel 12 can be suppressed.

[0120] Furthermore, in the solvent cleaning and replacement step S3, it is preferable to agitate the gel 12 held in the casting dish 3 along a horizontal agitation direction parallel to the bottom surface 31 of the casting dish 3. This improves both the temperature uniformity of the gel 12 and the flow rate uniformity of the solvent in the first liquid phase L1 in contact with the gel 12. Therefore, while cleaning the pore structure of the gel 12 (removing surfactants, etc.) in a more uniform state, the uniformity of the pore structure of the gel 12 can be further improved. As a result, when the internal solvent is discharged from the gel in the drying step S4 described later, the uniformity of the pore structure (pore size) is improved, thereby generating capillary force in a nearly uniform state, allowing for drying shrinkage in a nearly similar shape. In particular, from the viewpoint of also improving the uniformity of the concentration of the first solvent contained in the environment near the gel 12 and further improving the uniformity of the pore structure of the gel 12, it is preferable to adjust the concentration of the first solvent contained in the environment within the reaction chamber 2 to the above-mentioned range while shaking the gel 12 held in the pouring dish 3 along a horizontal shaking direction parallel to the bottom surface 31 of the pouring dish 3.

[0121] The amount of the first solvent used in the solvent cleaning and replacement step S3 also depends on the solvent replacement temperature and the apparatus (reaction chamber 2, pouring dish 3). Preferably, it is an amount that allows the entire gel 12 to be immersed in the first liquid phase L1 within the pouring dish 3. Therefore, the amount of the first solvent is preferably in the range of 2 to 100 times the total volume of the gel 12. Furthermore, the solvent replacement in the solvent cleaning and replacement step S3 is not limited to one operation and can be performed multiple times. Moreover, the specific method of solvent replacement in the solvent cleaning and replacement step S3 can be any of the following: full replacement, partial replacement, and cyclic replacement.

[0122] In particular, when multiple solvent exchanges are performed, the type of organic solvent, temperature, and processing time can be set individually for each solvent exchange. Here, the solvent used in the final solvent exchange in the solvent cleaning and replacement process S3 is the first solvent that constitutes the first liquid phase L1 described later.

[0123] In addition, the materials used in the solvent cleaning and replacement process S3, and / or the decomposition products of the materials, can inevitably be mixed into the manufactured aerogel 1 as components.

[0124] [Drying process S4]

[0125] The drying step S4 is a process of drying to form a Si-containing aerogel 1 by supplying a second solvent, which has a specific gravity greater than that of the first solvent and is separated from the first solvent into the casting dish 3. Here, as the drying step S4, for the gel placed in the casting dish 3 having a first liquid phase L1 composed of the first solvent and after the solvent washing and replacement step S3, at least the following steps S41, S42 and S43 can be performed.

[0126] 1) In the first step S41, a second solvent with a specific gravity greater than that of the first solvent and which is separate from the first solvent is supplied into the reaction chamber 2 equipped with the casting dish 3;

[0127] 2) Second step S42, removing the first solvent constituting the first liquid phase L1 from the reaction chamber 2;

[0128] 3) In the third step S43, the gel 12 is dried at low temperature until it floats to the interface of the second liquid phase L2.

[0129] Here, in the drying step S4, the vapor concentration of the solvent contained in the environment within the reaction chamber 2 is preferably adjusted to a range of 70% or more and less than 100% relative to the saturated vapor pressure, and more preferably to a range of 90% or more and less than 100%. More specifically, in the third step S43 and the fourth step S44 of the drying step S4, it is preferable that at least the third step S43 adjusts the combined vapor concentration of the first solvent and the second solvent contained in the environment within the reaction chamber 2 to the aforementioned range. As a result, by appropriately controlling the evaporation rates of the first liquid phase L1, the second liquid phase L2, the first solvent, and the second solvent from the gel 12, the breakage of the gel 12 caused by the rapid evaporation of the solvent contained in the gel 12 can be suppressed.

[0130] Furthermore, in the drying step S4, the gel 12 held in the casting dish 3 is preferably agitated in a horizontal agitation direction parallel to the bottom surface 31 of the casting dish 3. More specifically, in the third step S43 and the fourth step S44 of the drying step S4, it is preferable that at least the third step S43 agitates the gel 12 held in the casting dish 3 in a horizontal agitation direction parallel to the bottom surface 31 of the casting dish 3. This improves the uniformity of the temperature of the gel 12, as well as the uniformity of the temperature distribution, vapor concentration distribution, and flow rate distribution in the environment within the reaction chamber 2. Therefore, the uniformity of the evaporation rates of the first liquid phase L1, the second liquid phase L2, the first solvent, and the second solvent from the gel 12 can be improved. As a result, when the solvent contained in the gel 12 is discharged from the gel, the uniformity of the pore structure (pore size) is improved, thereby generating capillary force in a near-uniform state, thus enabling drying shrinkage in a shape that is nearly similar to the original shape. Furthermore, when the pore structure swells due to rebound, the uniformity of the solvent vapor movement velocity in the pores is increased, thereby improving the uniformity of the pore structure (pore size), and thus improving the uniformity of the obtained aerogel 1. Here, from the viewpoint of also improving the uniformity of the solvent vapor concentration contained in the environment near the gel 12, and further improving the uniformity of the obtained aerogel 1, it is preferable to adjust the solvent vapor concentration contained in the environment within the reaction chamber 2 to the above-mentioned range while shaking the gel 12 held in the casting dish 3 along a horizontal shaking direction parallel to the bottom surface 31 of the casting dish 3.

[0131] Furthermore, the drying process S4 is preferably carried out at atmospheric pressure within the reaction chamber 2. This allows for the drying of the gel 12 without pressurization, enabling the production of aerogel 1 with a simplified apparatus compared to the conventional drying process using supercritical fluids, thus reducing the manufacturing cost of aerogel 1.

[0132] (First process S41)

[0133] The first step S41 is to supply a second solvent, which has a higher specific gravity than the first solvent and is separated from the first solvent into the casting dish 3. Thus, the gel 12 is located within a liquid system having a first liquid phase L1 and a second liquid phase L2.

[0134] Here, the first solvent constituting the first liquid phase L1 and the second solvent constituting the second liquid phase L2 are selected to be completely immiscible and separate phases. Furthermore, the second solvent is selected to have a higher specific gravity than the first solvent, thereby forming a liquid phase system in which the first liquid phase L1 is located on top and the second liquid phase L2 is located below.

[0135] Furthermore, as the second solvent, it is preferable to use a solvent with a boiling point higher than that of the first solvent, as long as it is possible to form a state in which the first liquid phase L1 evaporates first and the gel 12 is immersed in the second liquid phase L2 at the first temperature described later.

[0136] As the second solvent used in the first step S41, it is preferable to use a second solvent that is completely immiscible with the first solvent, capable of forming a state of phase separation into a first liquid phase L1 and a second liquid phase L2, and with a boiling point higher than that of the first solvent. Examples of second solvents include water (specific gravity 1.0, boiling point 100°C), silicone oil (specific gravity 0.94 to 0.98, boiling point 150°C or higher), fluorinated solvents (specific gravity 1.3 to 1.5, boiling point 98 to 150°C), mercury (specific gravity 13, boiling point 356°C), etc.

[0137] The amount of the second solvent used in the first step S41 is preferably an amount sufficient to impregnate the gel 12 held in all the casting dishes 3 with the second liquid phase L2. Thus, as... Figure 4 As shown in (a), the interface between the first liquid phase L1 and the second liquid phase L2 is located on the upper side of the gel 12 held in the casting dish 3, so the first solvent constituting the first liquid phase L1 can be easily removed.

[0138] (Second process S42)

[0139] The second step S42 is the step of removing the first solvent constituting the first liquid phase L1 from the reaction chamber 2. As a result, the first liquid phase L1 disappears, and the state is such that the second solvent is supplied to the multiple casting dishes 3.

[0140] Here, the first solvent is preferably discharged to the outside of the reaction chamber 2 in a liquid state. This allows the first solvent to be quickly discharged to the outside of the reaction chamber 2.

[0141] On the other hand, the first solvent can also be evaporated at a temperature higher than room temperature and discharged as a gas to the outside of the reaction chamber 2. This temperature is preferably in the range of 30°C to 50°C. However, setting this temperature above the boiling point of the first solvent would cause the gel 12 to break due to boiling, which is therefore not preferred.

[0142] In the second step S42, it is preferable to remove the first solvent constituting the first liquid phase L1 from the reaction chamber 2 at the same time as removing the remaining second solvent. In particular, from the viewpoint of rapidly discharging both the first and second solvents to the outside of the reaction chamber 2, it is preferable to simultaneously discharge the first solvent and the remaining second solvent to the outside of the reaction chamber 2 in a liquid state. At this time, the less dense first solvent remains inside the pores of the gel 12, such as... Figure 4As shown in (b), while the second solvent is supplied to multiple casting dishes 3, the gel 12 in the casting dishes 3 is partially immersed in the second liquid phase L2 and floats to the top of the second liquid phase L2. Furthermore, it can be observed that the gel 12 is in a state of shrinkage in the second liquid phase L2 at this time. By making the gel 12 float to the top of the second liquid phase L2 in this way, the friction between the gel and the substrate can be made almost zero during the shrinkage of the gel in the second step S42 and the volume recovery in the third step S43 and the fourth step S44 described later.

[0143] (Third process S43)

[0144] The third step, S43, involves drying the gel 12 at low temperature until it floats to the interface of the second liquid phase L2. Before the third step, S43, the gel 12 is located within the second liquid phase L2. In the second step, S42, the shrinking gel 1 swells due to its rebound, causing its pore structure to swell and its volume to recover. Therefore, an aerogel 1 with the desired high uniformity can be obtained.

[0145] The ambient temperature in the third step S43 is preferably within the range of 30°C to 60°C. By maintaining this temperature range, the second solvent remaining inside the gel 12 evaporates, thereby drying the gel 12. This reduces the specific gravity of the gel 12, causing it to move from the surface of the second liquid phase L2 to the top, ultimately... Figure 5 As shown in (c), a dried aerogel 1 can be obtained in a state where it floats from the second liquid phase L2. However, setting the temperature at this time above the boiling point of the second solvent will cause the gel 12 to break due to the boiling of the second solvent, which is not preferable.

[0146] The third step S43 preferably continues until the volume of the gel 12 caused by the rebound returns to a stable state.

[0147] (Fourth process S44)

[0148] After the third step S43, the aerogel 1 is preferably removed from the liquid phase system and further dried in a fourth step S44. By further performing the fourth step S44, the transparency of the aerogel 1 can be further improved.

[0149] Here, the drying conditions for aerogel 1 are not particularly limited, and it can be dried naturally in the atmosphere, for example. However, from the viewpoint of further improving the transparency of aerogel 1, it is preferable to perform high-temperature drying at a second temperature higher than the first temperature.

[0150] When drying aerogel 1 at a second temperature, the second temperature is preferably in the range of 50°C to 250°C. As conditions for high-temperature drying, the second temperature can be set to a range of 50°C to 100°C, and the drying time can be set to a range of 5 hours to 10 hours. Alternatively, the second temperature can be set to a range of 150°C to 250°C, and the drying time can be set to a range of 10 minutes to 90 minutes.

[0151] [Other processes]

[0152] The manufacturing method described above is for aerogel in the form of a plate (or cuboid), but the present invention is not limited thereto, and can also include any step of processing the plate-shaped aerogel into a desired shape. For example, in addition to plates of different shapes, the plate-shaped aerogel can be processed into various shapes such as films, cubes, spheres, cylinders, pyramids, and cones. As a processing method for the aerogel, known machining methods such as wire cutting and laser cutting can be used.

[0153] Furthermore, the method for manufacturing the aerogel 1 of the present invention can include, as an arbitrary step, a process of processing a plate-shaped or block-shaped aerogel into granular aerogel. As a method for processing the aerogel into granular form, a known crusher (crusher) such as a jaw crusher, roller crusher, or ball mill can be used.

[0154] [Regarding the composition of the aerogel manufacturing apparatus]

[0155] The manufacturing apparatus 10 for the aerogel 1 of the present invention is preferably the manufacturing apparatus used in the above-described manufacturing method, such as... Figure 5As schematically shown, it comprises: a casting dish 3, which performs a cross-linking reaction on a sol 11 generated by hydrolyzing a silicon compound in an aqueous solution, and simultaneously curing it to form a gel 12; a casting unit 4, which injects the sol 11 into the casting dish 3; a first solvent supply unit 5, which supplies a first solvent L10 with a surface tension of less than 45 mN / m at 20°C into the casting dish 3 where the gel 12 has been formed, and uses the first solvent L10 to clean and replace the intrinsic solvent present on the surface and inside of the gel 12; a second solvent supply unit 6, which supplies a second solvent L20 with a specific gravity greater than the first solvent L10 and which is phase-separated from the first solvent L10 into the casting dish 3; a drying unit 7, which dries the casting dish 3 while the second solvent L20 has been supplied to form a Si-containing aerogel; and a shaking mechanism 8, which shakes the sol 11 or gel 12 formed in the casting dish 3 in a horizontal shaking direction parallel to the bottom surface of the casting dish 3 while maintaining it in the casting dish 3. Therefore, aerogel with a standard deviation of less than 0.60% of total light transmittance when irradiated with visible light of wavelength 550nm was obtained as aerogel 1. Thus, even with a relatively large area (specifically, including the size of a square surface area of ​​300mm), aerogels in perfect condition without defects such as cracks can be manufactured with a high yield.

[0156] Here, as the casting unit 4, the first solvent supply unit 5, and the second solvent supply unit 6, pipelines with valves (not shown) can be used.

[0157] Furthermore, as the drying unit 7, at least the following can be included: a draining unit 71, which is used to perform the second step S42 in the drying process S4 described above, to remove the first solvent constituting the first liquid phase L1 from the reaction chamber 2 as draining liquid L3; and a temperature regulating unit 72, which is used to perform the third step S43 in the drying process S4, to regulate the ambient temperature in the reaction chamber 2 until the gel 12 floats to the interface of the second liquid phase L2.

[0158] Furthermore, as the shaking mechanism 8, a mechanism that shakes the reaction chamber 2 in a horizontal shaking direction parallel to the bottom surface of the pouring dish 3 can be used, especially in situations such as... Figure 5 In the method shown, the reaction chamber 2 can be rotated along the rotation axis M, and a known drive unit such as a motor can be used.

[0159] [Applications of aerogel]

[0160] Based on these advantages, the aerogel 1 of this embodiment is preferably used as a thermal insulation material in cryogenic containers, aerospace applications, construction, automotive, home appliances, semiconductors, and industrial equipment. Furthermore, in addition to its use as a thermal insulation material, the aerogel 1 of this embodiment can also be used for waterproofing, sound absorption, shock absorption, and as a catalyst carrier.

[0161] Example

[0162] Next, in order to further clarify the effects of the present invention, examples and comparative examples of the present invention will be described, but the present invention is not limited to these embodiments.

[0163] <Example of the Invention>

[0164] [Sol-gel generation process S1]

[0165] 3.28 g of a nonionic surfactant (BASF: Pluronic PE10500) was dissolved in 28.96 g of a 0.005 mol / L aqueous solution of acetic acid. Then, 4.00 g of urea (Nacalai Tesque), a compound that serves as a basic catalyst, was added and dissolved. 10.00 g of a silicon compound, the main raw material, was added to the aqueous solution, and the mixture was stirred at room temperature for 60 minutes to allow the silicon compound to undergo a hydrolysis reaction, generating sol 11.

[0166] Here, tetramethoxysilane (methyl orthosilicate manufactured by Tama Chemical Industries, Ltd., hereinafter sometimes referred to as "TMOS"), methyltrimethoxysilane (DOWSIL Z-6366 Silane manufactured by Toray Dow Corning Co., Ltd., hereinafter sometimes referred to as "MTMS"), and dimethyldimethoxysilane (manufactured by Tokyo Chemical Industry Co., Ltd., product number: D1052, hereinafter sometimes referred to as "DMDMS"), as the silicon compounds, are used, and are added in a ratio of 25% by mass of the tetrafunctional silane compound, 65% by mass of the trifunctional silane compound, and 10% by mass of the difunctional silane compound. In addition, both TMOS and MTMS were purified by vacuum distillation before use.

[0167] [Gelization process S2]

[0168] Then, as a pouring process S22, 1225 ml of the generated sol 11 is poured into a pouring dish 3 with a planar shape of 320 mm square and a height of 17.5 mm to a depth of 10 mm, and the pouring dish 3 with the sol 11 is placed on the pouring dish support 30.

[0169] Each step from gelation step S2 to drying step S4 is performed within the same reaction chamber 2. Here, as... Figure 3 As shown, the casting dish 3 (or the casting dish support 30 holding the casting dish 3) is positioned horizontally within the reaction chamber 2 with the surface of the sol 11 or gel 12 (the bottom surface of the casting dish 3) as the horizontal plane. Simultaneously, the reaction chamber 2 is rotated about its height direction Y (central axis M), thereby enabling the casting dish 3 holding the sol 11 or gel 12 to be rocked horizontally along its bottom surface 31. Furthermore, water is injected below the casting dish 3 within the reaction chamber 2, ensuring that the concentration of water vapor in the environment within the reaction chamber 2 equals the saturated water vapor pressure.

[0170] The sol 11 injected into the casting dish 3 is used as a curing step S23. It is left to stand at 60°C for 10 hours, and then gelled by heating to generate an alkaline catalyst. Afterwards, warm water at 60°C is supplied to the reaction chamber 2 and immediately drained, forming a 7.5mm thick water layer on top of the gel 12. Next, the reaction chamber 2 is heated to 80°C and left to stand for 72 hours, thereby maturing the gel. At this time, the shaking mechanism 8 is activated, and the operation of rotating the reaction chamber 2 90° to the right for 20 seconds and then 90° to the left for 20 seconds is repeated alternately around the central axis M. This causes the casting dish 3, containing either the sol 11 before gelation or the gel 12 after gelation, to be shaken in a horizontal shaking direction.

[0171] After the curing step S23, the rotation of the reaction chamber 2 is stopped, the shaking of the casting dish 3 is stopped, and the temperature inside the reaction chamber 2 is lowered to 60°C. Next, the cleaning process S24 is repeated five times: the reaction chamber 2 is filled with methanol (MeOH) at 60°C in an amount equivalent to five times the volume of the gel (approximately 6.2L), so that the casting dish 3 containing the gel is immersed in methanol. After maintaining this state for 8 hours, the methanol not retained in the casting dish 3 is drained, thereby cleaning the surfactants, acids, reaction byproducts, etc., contained in the gel. At this time, the shaking mechanism 8 is activated, and the operation of rotating the reaction chamber 2 90° to the right for 20 seconds and rotating it 90° to the left for 20 seconds is repeated alternately around the central axis M, thereby shaking the casting dish 3 containing the gel 12 in a horizontal shaking direction. Furthermore, the methanol used in the cleaning process S24 is methanol produced by Nacalai Tesque.

[0172] [Solvent cleaning and replacement process S3]

[0173] Next, as a solvent cleaning and replacement step S3, isopropanol and heptane are used sequentially as the first solvent. More specifically, the following process is repeated twice: isopropanol is supplied as the first solvent to the casting dish 3 where gel 12 is formed, and the intrinsic solvent present on the surface and inside of gel 12 is cleaned and replaced with isopropanol; then heptane is supplied as the first solvent to the casting dish 3, and the solvents such as isopropanol present on the surface and inside of gel 12 are cleaned and replaced with heptane. Here, the first solvent is supplied to the casting dish 3 at 60°C by supplying an amount equivalent to 5 times the volume of the gel (approximately 6.2 L) of the first solvent at 60°C to the reaction chamber 2 containing gel 12 and casting dish 3. Figure 3 As shown in (c), this places multiple casting dishes 3 within the reaction chamber 2 in a state of immersion in the first liquid phase L1 composed of the first solvent, and maintains this state for 8 hours. At this time, the shaking mechanism 8 is activated, and the operation of rotating the reaction chamber 2 90° to the right for 20 seconds and rotating it 90° to the left for 20 seconds is repeated alternately around the central axis M, thereby shaking the casting dishes 3 holding the gel 12 in a horizontal shaking direction. Then, as... Figure 4 As shown in (d), the first liquid phase L1 that was not retained in the casting dish 3 is discharged from the reaction chamber 2. The gel 12 in the casting dish 3 after the solvent cleaning and replacement process S3 is immersed in the first liquid phase L1 composed of heptane and is in a state of being submerged in the first liquid phase L1.

[0174] [Drying process S4]

[0175] After the solvent cleaning and replacement step S3, the reaction chamber 2 is cooled to 40°C. Next, as the first step S41 of the drying step S4, water is supplied to the casting dish 3 using water as a second solvent. Here, the water is supplied to the casting dish 3 by supplying a volume of 40°C water equivalent to 5 times the volume of the gel into the reaction chamber 2 containing the gel 12 and the casting dish 3. Figure 4 As shown in (a), this causes multiple casting dishes 3 in the reaction chamber 2 to be immersed in a second liquid phase L2 composed of water, thereby forming a liquid phase system in which heptane (forming the first liquid phase L1 on the upper side) and water (forming the second liquid phase L2 on the lower side) are separated into two liquid phases at the interface located above the gel 12.

[0176] After the first step S41, the heptane and remaining water in reaction chamber 2 are immediately discharged for the second step S42. At this time, as... Figure 6 As shown in (b), the gel 12 in the casting dish 3 contains heptane inside the pores and is in a state of being partially immersed in the second liquid phase L2 composed of water and floating to the top of the second liquid phase L2.

[0177] Following the second step S42, the ambient temperature inside reaction chamber 2 is maintained at 40°C, and gel 12 is dried at low temperature as the third step S43. More specifically, the gas inside reaction chamber 2 is continuously discharged at a rate of 500 ml / min using an exhaust device. After the heptane vapor contained in the discharged gas is recovered by a cooler, the dried gas heated to 40°C is returned to reaction chamber 2, thereby drying gel 12. At this time, cellulose filter paper (Grade 1 filter paper manufactured by Whatman, with a particle retention capacity of 11 μm) is placed over the top surface of the open container as a ventilation membrane, and the concentration of the vapors of the first and second solvents in the space divided by the heptane liquid surface and the ventilation membrane is adjusted to approximately 50%. In the third step S43 of the drying process S4, the shaking mechanism 8 is activated, and the operation of rotating the reaction chamber 2 to the right by 90° for 20 seconds and rotating the reaction chamber 2 to the left by 90° for 20 seconds is repeated alternately with the central axis M as the center, thereby causing the pouring dish 3 holding the gel 12 to shake in the horizontal shaking direction.

[0178] In the third step S43, the gel 12 is dried at low temperature until the dried gel 12 floats to the surface of the second liquid phase L2, and the drying time is approximately 45 hours. This yields a translucent aerogel.

[0179] The aerogel after the third step S43 is further processed as the fourth step S44, using an additional thermostat (Yamato Scientific Corporation IS601) to perform additional drying at a drying temperature of 80°C until the size of the aerogel recovers to 95% of the size of the casting dish 3 (304 mm square), thus obtaining the aerogel 1 of the present invention.

[0180] Furthermore, by repeating these operations 26 times, a total of 27 aerogel sheets 1 were obtained. These 27 aerogel sheets 1 also included aerogels with the following conditions modified: the type and amount of surfactant added in the sol generation step S1; the ratio of TMOS, MTMS, and DMDMS in the silicon compound; the curing time in the gelation step S2; the temperature, time, number of cycles, and shaking speed in the solvent washing and displacement step S3; and the temperature, exhaust speed, and shaking speed in the drying step S4.

[0181] <Comparative Example>

[0182] Sol 11 was injected into casting dish 3 and placed on casting dish support 30. In this example, the shaking of casting dish 3, which holds sol 11 and gel 12, caused by the rotation of reaction chamber 2 during gelation step S2, solvent washing and replacement step S3, and drying step S4 was not performed. Other conditions were the same as in the example of the present invention, and a comparative aerogel (comparative example) was obtained. Furthermore, by repeating this operation seven times, a total of eight aerogel sheets 1 were obtained.

[0183] <Evaluation>

[0184] (Observation of crack formation in aerogel)

[0185] The aerogels obtained in the examples of the present invention and the comparative examples were visually observed. The results showed that the aerogel obtained in the examples of the present invention could produce an area without cracks across all 27 aerogel sheets. On the other hand, the aerogel obtained in the comparative examples showed fractures in all 8 aerogel sheets, failing to produce an aerogel with a square surface area of ​​300 mm square. Therefore, the aerogel obtained in the examples of the present invention can achieve a higher yield than the aerogel of the comparative examples, resulting in an aerogel with a perfect state free of defects such as cracks.

[0186] (Determination of the transmittance of aerogels)

[0187] Furthermore, the transmittance of the obtained aerogel was determined based on spectral data obtained using a V-670 UV-Vis-NIR spectrophotometer (manufactured by JASCO Corporation, Japan) equipped with an integrating sphere. Here, the total transmittance values ​​at the three points irradiated with visible light at a wavelength of 550 nm were converted to the total transmittance (T) of a 10 mm thick sample using the Lambert-Beer formula. 550The above three points are determined by using a vernier caliper to measure the total transmittance at each measurement location. These three points are the center of a 300mm square surface area overlapping the center (center of gravity) of the aerogel, the position of a corner of the square, and the center of a side of the square (the center of the side connecting adjacent corners of the square). Here, the center of the square is defined as the location within a 50mm square area having the same center as the square in the surface area. Similarly, the corner of the square is defined as the location within a 50mm square area overlapping the square in the surface area, having the same corner as the square in the surface area. Furthermore, the center of a side of the square is defined as the location within a 50mm square area overlapping the square in the surface area, where the center of the side connecting adjacent corners of the square is located at the same position as the square in the surface area. The sample thickness is measured using a vernier caliper at each measurement location after determining the total transmittance. Based on the total transmittance values ​​obtained for each part of the aerogel, the standard deviation of the total transmittance at these three points for each aerogel is calculated, and the average of the obtained standard deviations is taken as the standard deviation result.

[0188] The result is, as ​ As shown, the standard deviation of the total light transmittance of the aerogel of the present invention when irradiated with visible light having a wavelength of 550 nm (the standard deviation of the three points mentioned above) is about 0.30%, while the standard deviation of the total light transmittance of the aerogel of the comparative example when irradiated with visible light having a wavelength of 550 nm is about 1.00%.

[0189] Therefore, it is demonstrated that the aerogel of this invention yields a large-size aerogel without crack formation. It is thus evident that by utilizing an aerogel with a small standard deviation in total light transmittance when irradiated with visible light at a wavelength of 550 nm, crack formation can be suppressed.

[0190] <Overall Evaluation>

[0191] It is known that the aerogel of the present invention has a small standard deviation of total light transmittance when irradiated with visible light of a wavelength of 550 nm. Therefore, aerogels in a perfect state free of defects such as cracks can be obtained with a high yield. Furthermore, it is known that the aerogel of the present invention with a small standard deviation of total light transmittance when irradiated with visible light of a wavelength of 550 nm is obtained by using the manufacturing method of the present invention, which involves shaking the casting dish 3 holding the sol 11 or gel 12, in one or both of the gelation step S2 and the drying step S4.

[0192] Explanation of reference numerals in the attached figures

[0193] 1: Aerogel;

[0194] 10: Apparatus for manufacturing aerogels;

[0195] 11: Sol;

[0196] 12: Gel (moistened gel);

[0197] 2: Reaction chamber;

[0198] 3: Pouring dish;

[0199] 30: Pouring dish support;

[0200] 31: The bottom surface of the pouring dish;

[0201] 4: Casting unit;

[0202] 5: First solvent supply unit;

[0203] 6: Second solvent supply unit;

[0204] 71: Drainage unit;

[0205] 72: Temperature control unit;

[0206] 8: Shaking mechanism;

[0207] S1: Sol-gel generation process;

[0208] S2: Gelation process;

[0209] S21: Catalyst addition process;

[0210] S22: Pouring process;

[0211] S23: Maintenance procedure;

[0212] S3: Solvent cleaning and replacement process;

[0213] S4: Drying process;

[0214] S41: First process;

[0215] S42: Second process;

[0216] S43: Third process;

[0217] L1: First liquid phase;

[0218] L10: First solvent;

[0219] L2: Second liquid phase;

[0220] L20: Second solvent.

Claims

1. An aerogel containing Si, having a porous structure formed by a continuous fibrous framework and a plurality of pores defined by said framework. The aerogel has at least the following surface size: including a square surface area of ​​300 mm x 100 mm, and When the surface area is irradiated with visible light with a wavelength of 550 nm, the standard deviation of the total light transmittance of the aerogel is less than 0.60% when converted to a thickness of 10 mm.

2. The aerogel according to claim 1, wherein, The total transmittance of visible light when irradiated is more than 50% when the thickness is 10 mm.

3. The aerogel according to claim 1 or 2, wherein, The aerogel is generated by drying under normal pressure.

4. A method for manufacturing an aerogel, the method comprising: The sol-gluoride generation process involves adding a silicon compound to an aqueous solution for hydrolysis to generate a sol. In the gelation process, the sol is injected into a casting dish, and the sol undergoes a cross-linking reaction in the casting dish to form a gel while simultaneously curing it. The solvent cleaning and replacement process involves supplying a first solvent with a surface tension as low as 45 mN / m at 20°C into the casting dish, and using this first solvent to clean and replace the intrinsic solvent present on the surface and inside the gel; and The drying process involves supplying a second solvent, which has a specific gravity greater than that of the first solvent and is phase-separated from the first solvent, into the casting dish to generate an aerogel containing Si. At least one of the gelation process, the solvent washing and replacement process, and the drying process is performed by shaking the sol or gel generated in the casting dish while keeping it in the casting dish in a horizontal shaking direction parallel to the bottom surface of the casting dish.

5. The method for manufacturing aerogel according to claim 4, wherein, Each step from the gelation process to the drying process is performed within the same reaction chamber.

6. The method for manufacturing aerogel according to claim 4, wherein, In each step from the gelation step to the drying step, at least the gelation step and the drying step are carried out in different reaction chambers.

7. The method for manufacturing aerogel according to claim 5 or 6, wherein, The gelation process is performed by adjusting the concentration of water vapor in the environment of the reaction chamber to a range of 60% to 100% relative to the saturated water vapor pressure.

8. The method for manufacturing aerogel according to claim 5 or 6, wherein, The drying process is carried out by adjusting the vapor concentration of the solvent in the environment of the reaction chamber to a range of 70% or more and less than 100%.

9. The method for manufacturing aerogel according to claim 5 or 6, wherein, The drying process is carried out by setting the environment inside the reaction chamber to normal pressure.

10. An apparatus for manufacturing aerogel, comprising: A casting dish that allows a sol generated by adding a silicon compound to an aqueous solution for hydrolysis to undergo a cross-linking reaction, thereby curing the gel while simultaneously generating it. A pouring unit that injects the sol into the pouring dish; The first solvent supply unit supplies a first solvent with a surface tension of less than 45 mN / m at 20°C into the casting dish, and uses the first solvent to clean and replace the intrinsic solvent present on the surface and inside the gel. The second solvent supply unit supplies a second solvent with a specific gravity greater than that of the first solvent and which is phase-separated from the first solvent into the pouring vessel. A drying unit, which dries the vessel while the second solvent is supplied to the casting dish to generate an aerogel containing Si. A shaking mechanism that shakes the sol or gel formed in the pouring dish in a horizontal shaking direction parallel to the bottom surface of the pouring dish to keep it in the pouring dish.

Images