Aerogel and method for producing same

Abstract

In particular, by optimizing the parameters of total light transmittance during irradiation with visible light, the present invention provides: an aerogel that is in a sound state free of defects such as cracks and can be produced with a high yield even when having a relatively large area (specifically, a square surface region of 300 mm on each side); and a method for producing same.　The aerogel has a pore structure formed of a network-like continuous fibrous skeleton and a plurality of pores defined by the skeleton, and contains Si. The aerogel has at least a surface having a size including a square surface region of 300 mm on each side. The standard deviation of total light transmittance when irradiated with visible light having a wavelength of 550 nm is 0.60% or less in terms of a 10 mm thickness in the surface region.

Description

Aerogel and method for producing the same

[0001] The present invention relates to an aerogel and a method for producing the same.

[0002] Aerogel has a uniform mesoscale porous structure, a high porosity (typically 90% or more), and a low bulk density (0.004 to 0.500 g / cm ３ Silica aerogel is a material with extremely low thermal conductivity (20 mW / mK or less), and is typically produced by the sol-gel method. Among these, silica aerogel, which contains Si, combines high thermal insulation properties due to its low thermal conductivity with high visible light transmittance, making it promising for use as a transparent insulating material in residential windows (highly insulated double-glazed windows typically have a visible light transmittance of around 60%) and displays.

[0003] Silica aerogel is produced by hydrolyzing a monomer solution of a silane compound in a solvent such as water to produce a sol, crosslinking the sol (condensation reaction) to form a gel (condensation compound), and then drying the gel. However, silica aerogel is very fragile and difficult to handle during production due to its high porosity and thin structure consisting of nanometer-order domains (typically less than 100 nm). Furthermore, to produce large silica aerogels, the gel must be dried using a supercritical drying method using supercritical fluids at high temperatures and pressures, which requires expensive equipment.

[0004] Therefore, a method has been proposed in which flexibility is imparted to the skeleton that constitutes the pore structure, thereby avoiding fracture due to shrinkage deformation or recovery deformation during the drying process and enabling drying at normal pressure with low manufacturing costs. For example, Patent Document 1 describes a method of obtaining a transparent silica aerogel by drying at normal pressure, by performing a reaction to generate a sol and a reaction to gel the sol in a single step, thereby controlling the skeleton structure to be uniform and suppressing visible light scattering. Furthermore, Non-Patent Document 1 describes a method of obtaining a silica aerogel by drying at normal pressure, by converting the pore structure into an organic-inorganic hybrid.

[0005] Patent No. 5250900

[0006] K. Kanamori, M. Aizawa, K. Nakanishi, T. Hanada, Adv. Mater., 19, 1589-1593 (2007)

[0007] In the methods for producing silica aerogel described in Patent Document 1 and Non-Patent Document 1, when the gel is dried, the inherent solvent present inside the gel is expelled from the gel, and the volume of the gel shrinks to 20% or less due to capillary force. However, once a certain amount of the inherent solvent present inside the gel is expelled from the gel, gas enters the pores of the gel, and the volume of the gel is restored to approximately the same volume as before the shrinkage.

[0008] However, when the volume of the gel shrinks, if the shape of the gel is no longer similar to the shape before shrinkage, bending stress caused by deformation occurs in the gel, causing the gel to break, making it difficult to obtain an aerogel of the desired shape and size.

[0009] Furthermore, when drying the gel, if the solvent remaining on the surface and inside of the shrunken gel is not discharged uniformly from the gel, the solvent remaining in the gel will cause deformation and bending stress in the gel when the gel is restored to its original volume, causing the gel to break, making it difficult to obtain an aerogel of the desired shape and size.

[0010] In particular, when shrinking a large gel to obtain a large silica aerogel measuring 300 mm square or more, not only does the bending stress due to deformation increase with the increase in size, but also the temperature distribution at each location after the sol is poured into a mold and the material flow caused by the temperature distribution tend to cause differences in the polycondensation conditions at each location, which tends to result in non-uniform pore structure. As a result, the volume shrinkage during drying of the gel causes non-uniform capillary forces due to non-uniform pore sizes, which leads to gel rupture, making it virtually impossible to produce silica aerogel with a high yield using drying at atmospheric pressure.

[0011] The present invention has been made in view of the above circumstances, and has as its object to provide an aerogel that is in a sound state free from defects such as cracks and that can be produced with a high yield even in a relatively large area (specifically, a size including a square surface area of ​​300 mm on each side), by optimizing the parameter of total light transmittance when irradiated with visible light, and a method for producing the same.

[0012] In order to achieve the above object, the gist of the present invention is as follows.

[0013] (1) An aerogel containing Si, having a pore structure formed by a continuous fibrous skeleton in a network form and a plurality of pores defined by the skeleton, wherein the aerogel has at least a surface area that is 300 mm square, and the standard deviation of the total light transmittance when the surface area is irradiated with visible light having a wavelength of 550 nm is 0.60% or less, calculated as a thickness of 10 mm.

[0014] (2) The aerogel according to (1) above, wherein the total light transmittance when irradiated with visible light is 50% or more in terms of a thickness of 10 mm.

[0015] (3) The aerogel according to (1) or (2) above, which is produced by drying under normal pressure.

[0016] (4) A method for producing an aerogel, the method comprising: a sol production step of adding a silicon compound to an aqueous solution and hydrolyzing the compound to produce a sol; a gelation step of injecting the sol into a casting dish, crosslinking the sol in the casting dish to produce a gel, and curing the gel; a solvent washing and replacement step of supplying a first solvent having a low surface tension of 45 mN / m or less at 20°C into the casting dish, and washing and replacing the inherent solvent present on the surface and inside of the gel with the first solvent; and a drying step of supplying a second solvent having a higher specific gravity than the first solvent and undergoing two-phase separation from the first solvent into the casting dish and drying it to produce a Si-containing aerogel, wherein at least one of the gelation step, the solvent washing and replacement step, and the drying step is performed while the sol or gel produced in the casting dish is held in the casting dish and rocked in a horizontal direction parallel to the bottom surface of the casting dish.

[0017] (5) The method for producing an aerogel according to (4) above, wherein each step from the gelling step to the drying step is carried out in the same reaction chamber.

[0018] (6) The method for producing an aerogel according to (4) above, wherein at least the gelling step and the drying step among the steps from the gelling step to the drying step are carried out in separate reaction chambers.

[0019] (7) The method for producing an aerogel according to (5) or (6) above, wherein the gelation step is carried out by adjusting the concentration of water vapor contained in the atmosphere in the reaction chamber to a range of 60% or more and 100% or less of the saturated water vapor pressure.

[0020] (8) The method for producing an aerogel according to any one of (5) to (7), wherein the drying step is carried out by adjusting the vapor concentration of the solvent contained in the atmosphere in the reaction chamber to a range of 70% or more and less than 100%.

[0021] (9) The method for producing an aerogel according to any one of (5) to (8) above, wherein the drying step is carried out under atmospheric pressure in the reaction chamber.

[0022] (10) An apparatus for producing an aerogel, the apparatus comprising: a casting dish in which a silicon compound is added to an aqueous solution, the sol is hydrolyzed, and the resulting sol is subjected to a crosslinking reaction to produce a gel and is cured; a casting means for injecting the sol into the casting dish; a first solvent supplying means for supplying a first solvent having a low surface tension of 45 mN / m or less at 20°C into the casting dish, and washing and replacing the inherent solvent present on the surface and inside of the gel with the first solvent; a second solvent supplying means for supplying a second solvent having a higher specific gravity than the first solvent and undergoing two-phase separation from the first solvent into the casting dish; a drying means for drying the second solvent while it is supplied into the casting dish, thereby producing a Si-containing aerogel; and a rocking mechanism for rocking the sol or gel formed in the casting dish in a horizontal direction parallel to the bottom surface of the casting dish while it is held by the casting dish.

[0023] According to the present invention, by optimizing the parameter of total light transmittance when irradiated with visible light, in particular, it is possible to provide an aerogel that is in a sound state without defects such as cracks, with a high yield, even for a relatively large area (specifically, a size including a square surface area of ​​300 mm on each side), and a method for producing the same.

[0024] Figure 1 is a graph showing the relationship between the standard deviation of total light transmittance and the probability of aerogel breakage when irradiated with visible light having a wavelength of 550 nm, with the horizontal axis representing the standard deviation of total light transmittance and the vertical axis representing the probability of aerogel breakage. Figure 2 is a flowchart showing the order of steps in the method for producing an aerogel according to the present invention. Figure 3 is a conceptual diagram showing the state of the sol and gel in each step of the method for producing an 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 poured into the casting dish in the gelation step. Figure 3(b) is a conceptual diagram showing the state of the gel and the casting dish after the gelation step. Figure 3(c) is a conceptual diagram showing the state of multiple casting dishes in a reaction chamber immersed in a first liquid phase composed of a first solvent in the solvent washing and replacement step. Figure 3(d) is a conceptual diagram showing the state after the first solvent not retained in the casting dish in the reaction chamber has been discharged in the solvent washing and replacement step. Figure 4 is a conceptual diagram showing the state of the gel during the drying step of the aerogel manufacturing method according to the present invention. Figure 4(a) is a conceptual diagram showing the state in which the gel held in all casting dishes in the reaction chamber is immersed in the second liquid phase. Figure 4(b) is a conceptual diagram showing the state in which the first solvent and excess second solvent in the reaction chamber are discharged and the second solvent is supplied to multiple casting dishes during the drying step. Figure 4(c) is a conceptual diagram showing the state in which the aerogel that has finished drying during the drying step has floated to the interface of the second liquid phase. Figure 5 is a schematic diagram showing an example of a reaction apparatus used in the aerogel manufacturing method according to the present invention. Figure 6 is a graph showing the standard deviation of the total light transmittance when irradiated with visible light having a wavelength of 550 nm for each of the aerogels of the present invention and comparative examples.

[0025] Specific embodiments of the present invention will be described in detail below with reference to the drawings. Note that the present invention is not limited to the following embodiments, and various modifications are possible within the scope of the present invention.

[0026] [Regarding the Structure of the Aerogel] The aerogel of the present invention is a Si-containing aerogel having a pore structure formed by a continuous fibrous skeleton in a network form and a plurality of pores defined by this skeleton, wherein the aerogel has at least a surface that includes a square surface area of ​​300 mm on each side, and the standard deviation of the total light transmittance when this surface area is irradiated with visible light having a wavelength of 550 nm is 0.60% or less, calculated as a 10 mm thickness.

[0027] The inventors focused on the standard deviation of light transmittance at three points - the center of the square surface area, the corner positions of the square surface area, and the center positions of the sides of the square surface area - when visible light was irradiated onto a square surface area of ​​a Si-containing aerogel, and found that by performing one or both of the gelation step in which the sol is crosslinked to form a gel and the drying step in which the gel is dried while the sol or gel formed in the casting dish is held in the casting dish and oscillated in a horizontal oscillation direction parallel to the bottom surface of the casting dish, it is possible to reduce the variation in total light transmittance when visible light is irradiated onto the aerogel, even for a relatively large area. In this case, by optimizing the parameters of the total light transmittance when irradiated with visible light, more specifically, by making the standard deviation of the total light transmittance when irradiated with visible light having a wavelength of 550 nm (hereinafter, sometimes simply referred to as the "standard deviation of the total light transmittance") 0.60% or less in terms of a 10 mm thickness, it is possible to produce aerogel that is in a sound state without defects such as cracks, with a high yield, even for a relatively large area (specifically, a size including a square surface area of ​​300 mm on each side).

[0028] In this specification, the aerogel being "free from defects such as cracks" means that no defects such as cracks are visible when the aerogel is visually inspected, and more specifically, it means that there are no defects such as cracks of 100 μm or more in length or pinholes of 100 μm or more.

[0029] FIG. 1 is a graph showing the relationship between the standard deviation of total light transmittance and the probability of aerogel fracture when irradiated with visible light having a wavelength of 550 nm, with the standard deviation of total light transmittance on the horizontal axis and the probability of aerogel fracture on the vertical axis. In FIG. 1, when the standard deviation of total light transmittance is changed, examples in which the aerogel fractured are plotted as "probability of fracture = 1," and examples in which the aerogel did not fracture are plotted as "probability of fracture = 0." Next, from 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 objective variable, and is depicted by the solid line in the graph of FIG. 1. In this case, when the standard deviation of the aerogel's total light transmittance was 0.65% or less in terms of 10 mm thickness, the probability of fracture was below 0.5, and when the standard deviation of the aerogel's total light transmittance was 0.60% or less in terms of 10 mm thickness, no examples of aerogel fracture were observed. Furthermore, when the standard deviation of the total light transmittance of the aerogel was 0.50% or less, converted to a 10 mm thickness, the probability of breakage was also approximately 0 in the logistic regression curve. Therefore, the standard deviation of the total light transmittance of the aerogel, converted to a 10 mm thickness, is preferably 0.60% or less, and more preferably 0.50% or less. This is also evident from the fact that when a logistic regression curve was performed using the standard deviation of the total light transmittance as the explanatory variable and the presence or absence of breakage as the response variable, the threshold value of the explanatory variable at which the probability of breakage was 50% was greater than 0.60%, as shown in Figure 1.

[0030] The specific configuration of the aerogel of the present invention will be described below.

[0031] The aerogel of the present invention has a surface area of ​​at least 300 mm square. Aerogels with such large surface dimensions tend to experience large bending stresses during contraction and restoration, particularly on the outer surface. Even in this case, the standard deviation of the total light transmittance when irradiated with visible light can be reduced, thereby enabling aerogels in a sound state free of defects such as cracks to be obtained with a high yield. Therefore, the aerogel can be preferably used in applications requiring large areas, such as construction insulation.

[0032] Furthermore, the aerogel of the present invention has a standard deviation of total light transmittance of 0.60% or less, calculated based on a 10 mm thickness, when a 300 mm square surface area of ​​the surface is irradiated with visible light having a wavelength of 550 nm. Here, the 300 mm square surface area can be extracted, for example, by a 300 mm square located at a position overlapping the center (center of gravity) of the aerogel. The measurement points for total light transmittance in the surface area are not particularly limited. However, from the perspective of evaluating the ease of fracture of the aerogel during drying, for example, multiple points, including the center and periphery, may be set within the 300 mm square surface area (particularly, the center position of the square, the corner positions of the square, and the center positions of the sides of the square (three points: the center positions of the sides connecting adjacent corners of the square)).

[0033] In this regard, in square aerogels, which are the most common shape for industrial products, the positions where the pore structure becomes non-uniform relative to other positions (typically the center of the square) are often the corners and the center of the square. Furthermore, the variation in total light transmittance relative to the center of the square often appears differently at the corners and the center of the square, depending on the manufacturing conditions (chamber shape, gel arrangement, temperature transfer to the gel, stirring method, etc.). Therefore, by taking the standard deviation of the total light transmittance at three points (the center of the square, the corners, and the center of the square) and reducing the standard deviations at these three points, it is possible to reduce the likelihood of the aerogel breaking during drying. Therefore, by using an aerogel with a small standard deviation of the total light transmittance at these three points, it is possible to provide aerogels that are in a sound state without defects such as cracks, even for relatively large areas, with a high yield.

[0034] The standard deviation of the total light transmittance is the standard deviation when the total light transmittance obtained at all measurement points is converted into a value for a thickness of 10 mm and used as the population.

[0035] By achieving a standard deviation of the total light transmittance when irradiated with visible light of 0.60% or less (equivalent to a 10 mm thickness), the pore structure of the aerogel, which contains a continuous, mesh-like fibrous skeleton, is arranged substantially uniformly along the surface, resulting in high homogeneity of the aerogel and its precursor gel. For example, when producing an aerogel using atmospheric drying, the shape of the gel can be shrunk and restored while maintaining a similar shape when the volume of the gel is shrunk during atmospheric drying and when the volume of the gel is subsequently restored to obtain the aerogel. This reduces the occurrence of bending stress due to deformation in the gel. Therefore, the aerogel of the present invention can be produced with a high yield and in a sound state without defects such as cracks, even when it has a relatively large area.

[0036] Furthermore, the aerogel of the present invention preferably has a total light transmittance of 50% or more, more preferably 70% or more, calculated as a 10 mm thickness, when a 300 mm square surface area of ​​the surface is irradiated with visible light having a wavelength of 550 nm. This reduces the amount of elements in the aerogel that absorb or reflect visible light, making it easier for inhomogeneous portions that cause bending stress to appear, making it even more difficult for bending stress to occur due to deformation.

[0037] The size of the aerogel of the present invention is a size that includes a square surface area of ​​300 mm square. Therefore, when the surface of the aerogel of the present invention is viewed in plan, both the vertical and horizontal dimensions are 300 mm or more. On the other hand, the upper limit of the size of the aerogel of the present invention is not particularly limited, but when the surface is viewed in plan, one or both of the vertical and horizontal dimensions may be 5000 mm or 3000 mm.

[0038] The thickness of the aerogel of the present invention is not particularly limited, but the average thickness can be, for example, in the range of 1 mm to 30 mm. Here, from the viewpoint of facilitating the contraction and restoration of the gel in the casting dish, the aerogel is preferably plate-shaped, and in particular, has flat surfaces on both sides, and in this case, the thickness of the aerogel is preferably uniform.

[0039] The aerogel of the present invention has a Si-containing microstructure formed of a continuous fibrous skeleton in the form of a network and a plurality of pores defined by the skeleton.

[0040] Here, the microstructure of aerogel is a microstructure containing silicon atoms in the molecule, and an example of such a microstructure is a polysilsesquioxane-based microstructure. Among these, the polysilsesquioxane-based microstructure can be formed by hydrolysis and polycondensation of silicon alkoxide. In particular, polymethylsilsesquioxane (PMSQ, MeSiO １．５ ) aerogels can form transparent aerogels, and methyltrialkoxysilane (MeSi(OR) ３ The PMSQ aerogel can be formed by a combination of the hydrolysis and polycondensation reactions of MeSi(OR) and a surfactant as a phase separation inhibitor. Examples of the hydrolysis and polycondensation reactions used to form the PMSQ aerogel include the acid-catalyzed hydrolysis reaction shown in formula (I) below and the base-catalyzed polycondensation reaction shown in formula (II). ３ +3H ２ O → MeSi(OH) ３ +3ROH: Formula (I) MeSi(OH) ３ → MeSiO １．５ +1.5H ２ O: Formula (II)

[0041] Furthermore, the microstructure of aerogel has a continuous fibrous skeleton in a mesh-like pattern, which forms a number of minute pores, thereby reducing the density of the aerogel and reducing the thermal conductivity of the aerogel, thereby improving its thermal insulation properties.

[0042] Here, the average pore diameter of the multiple pores in the microstructure of the aerogel is not particularly limited, but can be, for example, in the range of 5 nm to 100 nm. Here, the average pore diameter of the pores can be the average inner diameter when the pores are approximated by tubes and the inner diameter of the tubes is approximated by a circle. The lower limit of the average inner diameter of the pores may 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. The upper limit of the average inner diameter of the pores may be 100 nm or less, 90 nm or less, 80 nm or less, or 70 nm or less. Since the average pore diameter of the pores is a dimension less than the mean free path (MFP) of the elemental molecules constituting air at atmospheric pressure, the aerogel placed in air at atmospheric pressure will have air trapped inside the pores.

[0043] The porosity of the aerogel, i.e., the ratio of the volume of through holes (pores) to the total volume of the aerogel, is not particularly limited, but is preferably 70% or more. In particular, the porosity, i.e., the ratio of the volume of through holes (pores) to the total volume of the aerogel, may be 75% or more, 80% or more, 85% or more, or 90% or more. Even when the aerogel has such a high porosity, it can be obtained by drying at normal pressure.

[0044] The density of the aerogel is, for example, 0.15 g / cm ３ The density of the aerogel can be reduced to 0.15 g / cm or less. Here, the density of the aerogel can be determined by, for example, mercury intrusion porosimetry. The lower the density of the aerogel, the smaller the thermal conductivity, and accordingly the better the heat insulating properties. The aerogel of the present invention has a density of 0.15 g / cm or less. ３ Even if the thickness is less than this, the material is less likely to break, and the thermal conductivity at this time is small, at about 0.01 W / m·K to 0.02 W / m·K.

[0045] In addition to the above-described components, the aerogel of the present invention may contain other components intended to impart functionality, improve appearance, or impart decorative properties. For example, it may contain antistatic agents, lubricants, inorganic pigments, organic pigments, inorganic dyes, organic dyes, etc. The aerogel of the present invention may also contain water, organic solvents, surfactants, catalysts, and decomposition products thereof as components unavoidable during production. The aerogel of the present invention may also contain dust that is mixed in from the production space or production equipment as components unavoidable during production.

[0046] [Configuration of the Aerogel Manufacturing Method] The following method can be mentioned as an example of a manufacturing method that can obtain the above-described aerogel.

[0047] Fig. 2 is a flow chart showing the order of steps in the method for producing aerogel 1 according to the present invention. Fig. 3 is a conceptual diagram showing the state of sol 11 and gel 12 in the steps up to solvent washing and replacement step S3 of the method for producing aerogel 1 according to the present invention. Fig. 3(a) is a conceptual diagram showing the state of sol 11 and casting dish 3 when sol 11 is poured into casting dish 3 in gelation step S2. Fig. 3(b) is a conceptual diagram showing the state of gel 12 and casting dish 3 after gelation step S2. Fig. 3(c) is a conceptual diagram showing the state of multiple casting dishes 3 in reaction chamber 2 immersed in a first liquid phase L1 composed of the first solvent in solvent washing and replacement step S3. Fig. 3(d) is a conceptual diagram showing the state after the first solvent not retained in casting dish 3 in reaction chamber 2 has been discharged in solvent washing and replacement step S3. 4A and 4B are conceptual diagrams showing the state of the sol 11 and gel 12 in the solvent washing and replacement step S3 and subsequent steps of the method for producing an aerogel 1 according to the present invention. FIG. 4A is a conceptual diagram showing the state in which a plurality of casting dishes 3 in the reaction chamber 2 are immersed in a second liquid phase L2 composed of the second solvent in the solvent washing and replacement step S3. FIG. 4B is a conceptual diagram showing the state in which the first solvent and excess second solvent in the reaction chamber 2 are discharged and the second solvent is supplied into a plurality of casting dishes 3 in the solvent washing and replacement step S3. FIG. 4C is a conceptual diagram showing the state in which the aerogel 1 that has finished drying in the drying step S4 floats on the interface of the second liquid phase L2.

[0048] As shown in FIGS. 2 to 4, the method for producing the aerogel 1 of the present invention includes a sol production step S1 in which a silicon compound is added to an aqueous solution and hydrolyzed to produce a sol 11; a gelation step S2 in which the sol 11 is poured into a casting dish 3, and the sol 11 is subjected to a crosslinking reaction in the casting dish 3 to form a gel (wet gel) 12 and is cured; and a gelation step S3 in which a first solvent having a low surface tension of 45 mN / m or less at 20° C. is supplied into the casting dish 3 in which the gel 12 has been formed, and the internal solvent present on the surface and inside of the gel 12 is cured by the first solvent. The method includes a solvent washing and substitution step S3 in which the first solvent is washed and substituted with a solvent, and a drying step S4 in which a second solvent, which has a higher specific gravity than the first solvent and undergoes two-phase separation from the first solvent, is supplied into a casting dish 3 and dried to form a Si-containing aerogel 1. At least one of the gelling step S2, the solvent washing and substitution step S3, and the drying step S4 is performed while the sol 11 or gel 12 formed in the casting dish 3 is oscillated in a horizontal direction parallel to the bottom surface 31 of the casting dish 3 while being held in the casting dish 3.

[0049] In the method for producing aerogel 1 of the present invention, in at least one of the gelation step S2, the solvent washing and replacement step S3, and the drying step S4, the sol 11 or gel 12 formed in the casting dish 3 is oscillated in a horizontal direction parallel to the bottom surface 31 of the casting dish 3 while held in the casting dish 3. This causes the atmosphere 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 oscillating motion, thereby improving the uniformity of the environment around the sol 11 or gel 12 (ambient temperature, component concentration, flow rate). As a result, the homogeneity of the sol 11 or gel 12 after the gelation step S2 or the drying step S4 can be improved, and ultimately the homogeneity of the aerogel 1 can also be improved. Therefore, an aerogel 1 with a small standard deviation of the total light transmittance when irradiated with visible light can be obtained.

[0050] In this regard, a common method for homogenizing the environment around the sol 11 or gel 12 is to apply a driving force to the fluid (gas or liquid) that constitutes the environment and stir it. However, when applying a driving force to the fluid that constitutes the environment, the driving force is significantly attenuated depending on the distance from the application point of the driving force and the shape of the space, and therefore the driving force cannot be uniformly propagated throughout the entire environment around the sol 11 or gel 12. In this regard, in the method for producing the aerogel 1 of the present invention, the sol 11 or gel 12, rather than the fluid that constitutes the environment, is shaken while held in the casting dish 3, so that the entire sol 11 or gel 12 can be shaken in its original state, thereby homogenizing the environment around the sol 11 or gel 12.

[0051] At this time, since gel 12 is particularly brittle, it is not desirable to vigorously shake gel 12 in random directions, including the thickness direction. Even in this case, by taking advantage of the fact that gel 12 has a two-dimensional shape (plate shape) held by casting dish 3, casting dish 3 holding gel 12 can be swung along a plane parallel to bottom surface 31 of casting dish 3, making it possible to make gel 12 less likely to break even when shook relatively vigorously.

[0052] Here, the rocking of the casting dish 3 holding the sol 11 or gel 12 is preferably a rotational motion, since it is desirable that the rocking be completed within a limited space such as the reaction chamber 2 and that the rocking be continuous. As an example, as shown in Fig. 5 described later, the casting dish 3 (or the casting dish holder 30 holding the casting dish 3) is placed in the reaction chamber 2 so that the surface of the sol 11 or gel 12 (the bottom surface 31 of the casting dish 3) is horizontal, and the reaction chamber 2 is rotated alternately clockwise and counterclockwise around the axis (central axis M) which is the height direction Y of the reaction chamber 2, thereby rocking the casting dish 3 holding the sol 11 or gel 12 in a horizontal rocking direction parallel to the bottom surface 31 of the casting dish 3.

[0053] Furthermore, when the sol 11 or gel 12 is oscillated in a horizontal direction while rotating in a fixed direction, the fluid constituting the environment surrounding the sol 11 or gel 12 flows in synchronization with the rotational motion due to frictional resistance with the sol 11 or gel 12, which may attenuate the relative speed of the oscillation with respect to the sol 11 or gel 12. Therefore, to prevent this, it is preferable to change the oscillation speed of the casting dish 3 in at least one direction. This increases the uniformity of the environment in contact with the surface of the sol 11 or gel 12, and also increases the uniformity of the environment in contact with the sol 11 or gel 12 held in different casting dishes 3, particularly when multiple casting dishes 3 are oscillated in the same device. When changing the oscillation speed of the casting dish 3, the direction of oscillation may be reversed. However, particularly when the oscillation of the casting dish 3 is performed by rotational motion, it is also possible to change only the speed without changing the direction of oscillation of the casting dish 3. The oscillation speed of the casting dish 3 may also be temporarily changed to zero, thereby making the oscillation of the casting dish 3 intermittent. The oscillation speed may be changed periodically or irregularly.

[0054] When the casting dish 3 is oscillated in a horizontal direction by a rotational motion around the center of the casting dish 3 holding the sol 11 or gel 12, the relative velocity between the sol 11 or gel 12 and the fluid constituting the surrounding environment depends on the distance from the center of rotation, and therefore the oscillation may be insufficient near the center of rotation. Therefore, from the viewpoint of further enhancing the uniformity of the environment around the sol 11 or gel 12, it is preferable to complicate the motion when oscillating the casting dish 3. As an example, the casting dish 3 may be oscillated by planetary motion of the casting dish holder 30 holding the casting dish 3 along the surface direction of the sol 11 or gel 12. In this way, by constantly changing the oscillating direction and speed of the casting dish 3, the uniformity of the environment in contact with the sol 11 or gel 12 held in the casting dish 3 can be further enhanced. Among these, from the viewpoint of further increasing 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 change the direction of movement in the opposite direction when performing planetary motion of the casting dish holder 30.

[0055] 3, the casting pan holder 30 may be configured so that a plurality of casting pans 3 are arranged in the thickness direction of the resulting aerogel 1. This reduces the area of ​​the casting pan holder 30 along the surface direction of the aerogel 1, making it easier to rock the casting pan 3 holding the sol 11 or gel 12.

[0056] The manufacturing apparatus used in the method for manufacturing the aerogel 1 of the present invention preferably performs each step from the gelation step S2 to the drying step S4 within the same reaction chamber 2. This eliminates the need to open the reaction chamber 2 between the sol generation step S1, the gelation step S2, the solvent washing and replacement step S3, and the drying step S4. This eliminates the need to open the reaction chamber 2 between the sol 11 or gel 12 and the time lag required to respond to sudden environmental changes when the reaction chamber 2 is opened. Furthermore, since it is not necessary to transfer the sol 11 or gel 12 between the apparatuses for the sol generation step S1, the gelation step S2, the solvent washing and replacement step S3, and the drying step S4, this prevents the gel 12 from breaking during transfer.

[0057] On the other hand, in the manufacturing apparatus used in the manufacturing method of the aerogel 1 of the present invention, at least the gelling step S2 and the drying step S4 among the steps from the gelling step S2 to the drying step S4 may be performed in separate reaction chambers. This allows the time-consuming gelling step S2 and the drying step S4 to be performed separately in the manufacturing process of the aerogel 1, thereby enabling more efficient manufacturing of the aerogel 1. Even in this case, it is preferable to perform the solvent washing and substitution step S3 and the drying step S4 in the same reaction chamber from the viewpoint of preventing damage to the gel due to rapid drying.

[0058] Each step of the method for producing the aerogel 1 of the present invention will be described below.

[0059] [Sol Generation Step S1] Among these steps, the sol generation step S1 is a step of adding at least a silicon compound to an aqueous solution and hydrolyzing the solution to generate the sol 11. The sol 11 for producing the aerogel 1 of the present invention contains siloxane bonds and can be generated by hydrolyzing the silicon compound by adding various raw materials including the silicon compound (main raw material) to a predetermined aqueous solution and mixing them by stirring.

[0060] Examples of the silicon compound raw material include silane compounds, and more specifically, at least one of bifunctional silane compounds, trifunctional silane compounds, and tetrafunctional silane compounds.

[0061] Here, a bifunctional silane compound refers to a silane compound having two siloxane bonds, a trifunctional silane compound refers to a silane compound having three siloxane bonds, and a tetrafunctional silane compound refers to a silane compound having four siloxane bonds.

[0062] Examples of bifunctional silane compounds include dialkoxysilane and diacetoxysilane. Desirable embodiments of dialkoxysilane include those in which the alkoxy group has 1 to 9 carbon atoms. Specific examples include dimethyldimethoxysilane, diethyldimethoxysilane, and diisobutyldimethoxysilane. These compounds may be used alone or in combination. In the present invention, it is particularly preferable to use dimethyldimethoxysilane (DMDMS) as the bifunctional silane compound.

[0063] Examples of trifunctional silane compounds include trialkoxysilane and triacetoxysilane. Desirable embodiments of trialkoxysilane include those in which the alkoxy group has 1 to 9 carbon atoms. Examples include methyltrimethoxysilane, ethyltrimethoxysilane, propyltrimethoxysilane, hexyltrimethoxysilane, octyltrimethoxysilane, methyltriethoxysilane, ethyltriethoxysilane, propyltriethoxysilane, pentyltriethoxysilane, hexyltriethoxysilane, and octyltriethoxysilane. These compounds may be used alone or in combination. In the present invention, it is particularly preferable to use methyltrimethoxysilane (MTMS) as the trifunctional silane compound.

[0064] Examples of tetrafunctional silane compounds include tetraalkoxysilane and tetraacetoxysilane. Desirable embodiments of the tetraalkoxysilane include those in which the alkoxy group has 1 to 9 carbon atoms. Examples include tetramethoxysilane, tetraethoxysilane, tetrapropoxysilane, and tetraisopropoxysilane. These silane compounds may be used alone or in combination. In the present invention, it is particularly preferable to use tetramethoxysilane (TMOS) as the tetrafunctional silane compound.

[0065] In the sol generating step S1, in addition to the silicon compound (main raw material), a surfactant, an acid, and an organic solvent can be used as auxiliary raw materials.

[0066] Among these, the surfactant contributes to the formation of the pore structure of the aerogel 1, which will be described later, during the gel formation process, which will be described later. Examples of surfactants that can be used in the production of the aerogel 1 include nonionic surfactants and ionic surfactants. Examples of ionic surfactants include cationic surfactants, anionic surfactants, and amphoteric surfactants. Of these, nonionic surfactants are preferably used.

[0067] The amount of surfactant added will vary depending on the type and mixing ratio of the silicon compound and the type of surfactant, but can be, for example, in the range of 0.001 to 100 parts by mass relative to 100 parts by mass of the total amount of the silicon compound as the main raw material. In particular, a range of 0.01 to 90 parts by mass is preferred, and a range of 0.1 to 80 parts by mass is even more preferred.

[0068] In addition, the acid acts as a catalyst during hydrolysis, accelerating the reaction rate of the hydrolysis. Specific examples of the acid include inorganic acids, organic acids, and organic acid salts. These acids may be used alone or in combination of two or more.

[0069] Among these, inorganic acids include hydrochloric acid, sulfuric acid, sulfurous acid, nitric acid, hydrofluoric acid, phosphoric acid, phosphorous acid, hypophosphorous acid, bromic acid, chloric acid, chlorous acid, and hypochlorous acid. Furthermore, 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, organic acid salts that can be used include aluminum acid phosphate, magnesium acid phosphate, and zinc acid phosphate. In the present invention, it is preferable to use acetic acid, which is an organic acid, as the acid.

[0070] The concentration of the acid added to the sol 11 obtained in the sol generation step S1 can be, for example, in the range of 0.0001 mol / L to 0.1 mol / L, and is 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.

[0071] As the organic solvent, alcohols such as methanol, ethanol, 1-propanol, 2-propanol (isopropanol), 1-butanol, 2-butanol, and t-butanol can be preferably used. These may be used alone or in combination of two or more. From the viewpoint of compatibility, the amount of organic solvent added to the solution to be prepared can be, for example, in the range of 4 mol to 10 mol per 1 mol of the total amount of the silicon compound as the main raw material, with a range of 4.5 mol to 9 mol being particularly preferred, and a range of 5 mol to 8 mol being even more preferred.

[0072] The temperature of the solution and the stirring time in the sol generation step S1 depend on the types and amounts of the silicon compound, surfactant, water, acid, organic solvent, etc. contained in the mixed solution, but may be, for example, in the range of 0.05 to 48 hours in a temperature environment of 0 to 70° C., and preferably 0.1 to 24 hours in a temperature environment of 20 to 50° C. This hydrolyzes the silicon compound and forms a colloid, thereby producing the sol 11.

[0073] The secondary materials and / or decomposition products of the secondary materials used in the sol generating step S1 may be mixed into the produced aerogel 1 as unavoidable components.

[0074] [Gelling Step S2] The gelling step S2 is a step of pouring the sol 11 produced in the sol production step S1 into a casting dish 3, causing a crosslinking reaction of the sol in the casting dish 3 to form a gel 12, and curing the gel 12. In this step, the sol 11 is poured into the casting dish 3 as shown in Fig. 3(a), and then the gel 12 is formed in the casting dish 3 as shown in Fig. 3(b). Here, the gelling step S2 can be broadly divided into a catalyst addition step S21 of adding a basic catalyst to the sol 11, a casting step S22 of pouring the sol 11 with the basic catalyst added into the casting dish 3, and a curing step S23 of curing the solution in the casting dish 3 to produce the gel 12.

[0075] Among these, the basic catalyst to be added to the sol 11 in the catalyst addition step S21 includes 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; basic sodium phosphate salts such as sodium metaphosphate, sodium pyrophosphate, and sodium polyphosphate; allylamine, diallylamine, triallylamine, isopropylamine, diisopropylamine, ethylamine, diethylamine, triethylamine, 2-ethylhexylamine, 3-ethoxypropylamine, diisobutylamine, 3-(diethyl) ... Examples of the basic catalyst include aliphatic amines such as 3-(methylamino)propylamine, di-2-ethylhexylamine, 3-(dibutylamino)propylamine, tetramethylethylenediamine, t-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 derivatives thereof, piperidine and derivatives thereof, and imidazole and derivatives thereof. Here, the basic catalyst may be used alone or in combination of two or more.

[0076] The basic catalyst may be a nitrogen compound that generates a basic catalyst upon heating. The nitrogen compound is added as a compound that generates a basic catalyst during heating in the casting step S22 or the curing step S23. Specific examples include amide compounds such as urea, formamide, N-methylformamide, N,N-dimethylformamide, acetamide, N-methylacetamide, and N,N-dimethylacetamide, and heterocyclic compounds such as hexamethylenetetramine. Of these, urea is preferably used because it can accelerate the gel formation rate in the curing step S23. Since these nitrogen compounds that generate a basic catalyst upon heating can generate a basic catalyst by heating in the curing step S23, they may be added in the sol formation step S1 without performing the catalyst addition step S21.

[0077] Among these, an aqueous solution of ammonium hydroxide is preferred because it has a high reaction-accelerating effect as a catalyst, can rapidly advance the crosslinking reaction from the sol 11 to the gel 12, and can form the aerogel 12 with fewer defects. Furthermore, an aqueous solution of ammonium hydroxide is highly volatile, so it volatilizes in the solvent washing and substitution step S3 and the drying step S4 described below, and is therefore less likely to remain in the resulting aerogel 1.

[0078] The amount of basic catalyst added to sol 11 is preferably in the range of 0.5 parts by mass to 5 parts by mass, and more preferably in the range of 1 part by mass to 4 parts by mass, relative to 100 parts by mass of the total amount of sol 11. If the amount of basic catalyst added is less than 0.5 parts by mass, the crosslinking reaction cannot proceed when forming gel 12 from sol 11. If the amount of basic catalyst added is more than 5 parts by mass, the crosslinking reaction may proceed too quickly, resulting in a non-uniform gel 12.

[0079] The casting step S22 is a step of pouring the sol 11 containing the basic catalyst into a casting dish 3 to obtain the desired shape of the aerogel product. The casting dish 3 can be made of either metal or synthetic resin. However, from the viewpoints of non-flammability in consideration of plant operation, flatness of the shape, and releasability, a dish having a metal substrate coated with a release coating layer is preferably used. Examples of metals include iron alloys such as stainless steel and steel. Examples of release coating layers include a coating layer made of a fluorine-based resin such as Teflon (registered trademark).

[0080] The casting dish 3 has a shape corresponding to the desired aerogel product. For example, a concave tray with an open end can be used as a mold to obtain a plate-shaped aerogel 1. The surface of the casting dish 3 is preferably flat, from the viewpoint of facilitating contraction and restoration of the gel in the casting dish 3.

[0081] The curing step S23 is a step of curing the sol 11 filled in the casting dish 3 in the casting dish to produce a gel 12 and molding it to fit the shape of the inner wall of the casting dish 3.

[0082] The curing step S23 involves applying a predetermined amount of energy for a predetermined period of time to promote the crosslinking reaction from the sol 11 to the gel 12. An example of the energy is thermal energy, and more specifically, heating to a temperature range of 30°C to 90°C, preferably 40°C to 80°C. The heating may be performed using a heater, or may be performed using steam heating with water vapor or organic solvent vapor. These energy methods may be used alone or in combination.

[0083] The time required for curing in the curing step S23 depends on the composition of the silicon compound, the types and amounts of surfactant, water, acid, organic solvent, basic catalyst, etc., as well as the type and density of energy used in the curing step S23, but can be set in the range of 0.01 hour to 7 days, for example. Here, if the type of basic catalyst and the type of energy are optimized, gelation may be completed in the range of 0.01 hour to 24 hours. Curing may also be performed in which heat (temperature) and time are changed in multiple stages.

[0084] In the curing step S23, warm water may be supplied into the reaction chamber 2 and then immediately discharged to form a water layer on the surface of the gel 12 to prevent cracks from occurring due to drying. In addition to the warm water supplied into the reaction chamber 2 in the curing step S23, the liquid supplied into the reaction chamber 2 in the method for producing the aerogel 1 of the present invention is preferably a liquid having a temperature difference of 10° C. or less from the ambient temperature of the reaction chamber 2, from the viewpoint of preventing damage to the gel 12. That is, at least one of the warm water used in the curing step S23, the cleaning agent used in the cleaning treatment S24 described below, the first solvent used in the solvent cleaning and replacement step S3, and the second solvent used in the drying step S4 is preferably supplied into the reaction chamber 2 at a temperature difference of 10° C. or less from the ambient temperature of the reaction chamber 2.

[0085] Here, the curing step S23 is preferably carried out by adjusting the concentration of water vapor contained in the atmosphere in the reaction chamber 2 to a range of 60% to 100% of the saturated water vapor pressure, and more preferably to a range of 80% to 100%. This appropriately controls the evaporation of water from the gel 12 in the gelling step S2, thereby preventing the gel 12 from becoming non-homogenous due to the evaporation of water contained in the gel 12.

[0086] Furthermore, in the curing step S23, it is preferable to oscillate the gel 12 held in the casting dish 3 in a lateral oscillation direction parallel to the bottom surface 31 of the casting dish 3. This increases the uniformity of the temperature of the gel 12, thereby further improving the homogeneity 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 below, the uniformity of the pore structure (pore size) is increased, and capillary forces are generated in a nearly uniform state, allowing the gel 12 to dry and shrink to a shape that is nearly similar. In particular, from the perspective of also increasing the uniformity of the concentration of water vapor contained in the atmosphere near the gel 12 and further improving the homogeneity of the pore structure of the gel 12, it is preferable to oscillate the gel 12 held in the casting dish 3 in a lateral oscillation direction parallel to the bottom surface 31 of the casting dish 3 while adjusting the concentration of water vapor contained in the atmosphere in the reaction chamber 2 to be within the above range.

[0087] The materials used in the gelling step S2 and decomposition products of the materials may be mixed into the produced aerogel 1 as unavoidable components.

[0088] After the gelling step S2, a cleaning treatment S24 may be further carried out to wash away the acid used to generate the sol 11, the catalyst used to generate the gel 12, reaction by-products, and the like.

[0089] A wide variety of organic solvents can be used as the cleaning agent in the cleaning process S24, and it is particularly preferable to use a solvent different from the first solvent described below. Examples of the cleaning agent that can be used include various organic solvents such as methanol, ethanol, n-propanol, isopropanol, 1-butanol, 2-butanol, t-butanol, acetone, methyl ethyl ketone, methyl isobutyl ketone, xylene, 1,2-dimethoxyethane, acetonitrile, hexane, toluene, diethyl ether, chloroform, ethyl acetate, tetrahydrofuran, methylene chloride, N,N-dimethylformamide, dimethyl sulfoxide, acetic acid, and formic acid. The above organic solvents may be used alone or in combination of two or more.

[0090] Among these, it is preferable to use, as the cleaning agent, methanol, ethanol, isopropanol, acetone, methyl ethyl ketone, and the like, which are soluble in both the organic solvent constituting the first solvent described below and water, either alone or in combination of two or more kinds.

[0091] The cleaning in the cleaning process S24 can be performed by filling the reaction chamber 2 with a cleaning agent, immersing the plurality of casting dishes 3 on which the gels 12 have been formed in the cleaning agent, and then draining at least the methanol that is not retained in the casting dishes 3. This allows the acid, reaction by-products, and the like contained in the gels 12 to be washed away and discharged to the outside of the gels 12. At this time, the cleaning agent may remain in the casting dishes 3 because it is soluble in the first solvent described below.

[0092] Here, the cleaning process S24 is preferably performed by adjusting the concentration of the cleaning agent contained in the atmosphere in the reaction chamber 2 to a range of 80% to 100% of the saturated vapor pressure, and more preferably to a range of 90% to 100%. This suppresses evaporation of the cleaning agent from the gel 12 in the cleaning process S24, thereby suppressing heterogeneity of the gel 12 due to evaporation of the cleaning agent contained in the gel 12.

[0093] Furthermore, in the cleaning process S24, it is preferable to oscillate the gel 12 held in the casting dish 3 in a lateral oscillation direction parallel to the bottom surface 31 of the casting dish 3. This increases the temperature uniformity of the gel 12 and the uniformity of the flow rate of the cleaning agent in contact with the gel 12, thereby further improving the homogeneity of the pore structure of the gel 12. In particular, from the viewpoint of increasing the uniformity of the concentration of the cleaning agent contained in the atmosphere near the gel 12 and further improving the homogeneity of the pore structure of the gel 12, it is preferable to oscillate the gel 12 held in the casting dish 3 in a lateral oscillation direction parallel to the bottom surface 31 of the casting dish 3 while adjusting the concentration of the cleaning agent contained in the atmosphere in the reaction chamber 2 to fall within the above-described range.

[0094] The amount of cleaning agent used in the cleaning process S24 depends on the temperature at which the solvent is substituted and the apparatus (reaction chamber 2 and casting dish 3), but it is preferable to use an amount that allows all of the gels 12 to be entirely immersed in the cleaning agent supplied to the casting dish 3. Therefore, it is preferable to use an amount of cleaning agent that is in the range of 2 to 100 times the total volume of the gels 12. Furthermore, the cleaning process S24 is not limited to being performed once, and may be performed multiple times.

[0095] [Solvent Washing and Replacement Step S3] The solvent washing and replacement step S3 is a step of supplying a first solvent having a low surface tension of 45 mN / m or less at 20°C into the casting dish 3 containing the gel 12, and using the first solvent to wash away and replace the inherent solvent and surfactant present on the surface and inside of the gel 12. This allows the water and / or organic solvent, which is the inherent solvent present on the surface and inside of the gel 12, to be replaced with an organic solvent suitable for drying in a short time.

[0096] In the solvent washing and replacement step S3, the gel 12 is washed with a first solvent having a surface tension of 45 mN / m or less at 20°C, and the water (or organic solvent) on the surface and inside of the gel 12 is replaced with the first solvent to prevent shrinkage damage to the gel 12 in the drying step S4 described below. As the first solvent, a liquid having a surface tension of 45 mN / m or less at 20°C can be used, and examples of such a liquid include dimethyl sulfoxide (43.5 mN / m), cyclohexane (25.2 mN / m), isopropanol (21 mN / m), heptane (20.2 mN / m), and pentane (15.5 mN / m).

[0097] The first solvent used in the solvent washing and replacement step S3 may have a surface tension at 20°C 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, and may have a surface tension at 20°C of 5 mN / m or more, 10 mN / m or more, 15 mN / m or more, or 20 mN / m or more. Among these, it is particularly preferable to use an organic solvent containing an aliphatic hydrocarbon having a surface tension at 20°C in the range of 20 mN / m to 40 mN / m as the first solvent. Such organic solvents may be used alone or in combination of two or more.

[0098] Furthermore, the first solvent used in the solvent washing and replacement step S3 preferably has the property of allowing the gel 12 to settle and be immersed in the first liquid phase L1 constituted by the first solvent after the solvent washing and replacement step S3 is performed. Therefore, the first solvent preferably has affinity with the gel 12 and a specific gravity lower than that of the gel 12. Here, the fact that the first solvent has affinity with the gel 12 means that the solvent can penetrate into the pores of the gel 12, thereby allowing the solvent to be impregnated into the gel 12. An example of such a solvent is a solvent having a solubility parameter in the range of 7.0 to 9.5.

[0099] Furthermore, as the first solvent used in the solvent washing and replacement step S3, it is preferable to use a solvent that has a lower specific gravity and a lower boiling point than the second solvent described below. From this viewpoint, it is preferable to use an organic solvent with a boiling point of 50° C. to 100° C. as the first solvent, and examples thereof 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.).

[0100] The solvent washing and replacement step S3 can be performed by filling the reaction chamber 2 with the first solvent, immersing multiple casting dishes 3 on which gels 12 have been formed in a first liquid phase L1 composed of the first solvent, and then discharging any first solvent that is not retained in the casting dishes 3, as shown in Fig. 3(d). This allows impurities such as acid and reaction by-products contained in the gels 12 and cleaning agent to be washed out of the reaction chamber 2. Furthermore, the gels 12 after the solvent washing and replacement step S3 are placed in a liquid phase system composed of the first liquid phase L1 in the casting dishes 3.

[0101] Here, the solvent washing and replacement step S3 is preferably performed by adjusting the concentration of the first solvent contained in the atmosphere in the reaction chamber 2 to a range of 80% to 100% of the saturated vapor pressure, and more preferably to a range of 90% to 100%. This suppresses evaporation of the first solvent from the gel 12 in the solvent washing and replacement step S3, and therefore makes it possible to suppress heterogeneity of the gel 12 due to evaporation of the first solvent contained in the gel 12.

[0102] Furthermore, in the solvent washing and replacement step S3, it is preferable to oscillate the gel 12 held in the casting dish 3 in a horizontal oscillation direction parallel to the bottom surface 31 of the casting dish 3. This increases the temperature uniformity of the gel 12 and the uniformity of the flow rate of the solvent in the first liquid phase L1 in contact with the gel 12. This allows the pore structure of the gel 12 to be washed (removed from surfactants, etc.) in a more uniform state, and further increases the homogeneity of the pore structure of the gel 12. As a result, when the inherent solvent is discharged from the gel in the drying step S4 described below, the uniformity of the pore structure (pore size) is increased, and capillary forces are generated in a more uniform state, allowing the gel to dry and shrink to a shape that is close to a similar shape. In particular, from the viewpoint of increasing the uniformity of the concentration of the first solvent contained in the atmosphere near the gel 12 and further increasing the homogeneity of the pore structure of the gel 12, it is preferable to oscillate the gel 12 held in the casting dish 3 in a horizontal oscillation direction parallel to the bottom surface 31 of the casting dish 3 while adjusting the concentration of the first solvent contained in the atmosphere in the reaction chamber 2 to be within the above range.

[0103] The amount of the first solvent used in the solvent washing and replacement step S3 depends on the temperature and the apparatus (reaction chamber 2 and casting dish 3) at which the solvent is replaced, but it is preferable to use an amount that allows all of the gels 12 to be entirely immersed in the first liquid phase L1 in the casting dish 3. Therefore, it is preferable to use an amount of the first solvent that is in the range of 2 to 100 times the total volume of the gels 12. Furthermore, the solvent replacement in the solvent washing and replacement step S3 is not limited to one time, and may be performed multiple times. Furthermore, the specific method of solvent replacement in the solvent washing and replacement step S3 may be any of total replacement, partial replacement, and circulatory replacement.

[0104] In particular, when the solvent exchange is performed multiple times, the type of organic solvent, the temperature, and the treatment time may be set independently for each time. Here, in the solvent washing and exchange step S3, the solvent used in the final solvent exchange becomes the first solvent constituting the first liquid phase L1 described below.

[0105] The materials used in the solvent washing and substitution step S3 and / or decomposition products of the materials may be mixed into the produced aerogel 1 as unavoidable components.

[0106] [Drying Step S4] The drying step S4 is a step of drying a second solvent, which has a higher specific gravity than the first solvent and undergoes two-phase separation with the first solvent, supplied into the casting dish 3 and then dried to form a Si-containing aerogel 1. The drying step S4 can include at least the following steps: a first step S41, a second step S42, and a third step S43, for the gel placed in the casting dish 3 and having a first liquid phase L1 composed of the first solvent, after the solvent washing and replacement step S3. 1) a first step S41 of supplying a second solvent, which has a higher specific gravity than the first solvent and undergoes two-phase separation with the first solvent, into the reaction chamber 2 in which the casting dish 3 is placed; 2) a second step S42 of removing the first solvent constituting the first liquid phase L1 from the reaction chamber 2; and 3) a third step S43 of drying the gel 12 at low temperature until the gel 12 floats to the interface of the second liquid phase L2.

[0107] Here, the drying step S4 is preferably performed by adjusting the vapor concentration of the solvent contained in the atmosphere in the reaction chamber 2 to a range of 70% or more and less than 100% of the saturated vapor pressure, and more preferably to a range of 90% or more and less than 100%. More specifically, of the third step S43 and the fourth step S44 of the drying step S4, at least the third step S43 is preferably performed by adjusting the total vapor concentration of the first solvent and the second solvent contained in the atmosphere in the reaction chamber 2 to the above range. This appropriately controls the evaporation rates of the first solvent and the second solvent from the first liquid phase L1, the second liquid phase L2, and the gel 12, thereby preventing the gel 12 from breaking due to rapid evaporation of the solvent contained in the gel 12.

[0108] Furthermore, in the drying step S4, it is preferable to oscillate the gel 12 held in the casting dish 3 in a lateral oscillation direction parallel to the bottom surface 31 of the casting dish 3. More specifically, of the third step S43 and the fourth step S44 of the drying step S4, it is preferable to oscillate the gel 12 held in the casting dish 3 in a lateral oscillation direction parallel to the bottom surface 31 of the casting dish 3 in at least the third step S43. This improves the temperature uniformity of the gel 12 and the uniformity of the temperature distribution, vapor concentration distribution, and flow rate distribution in the atmosphere within the reaction chamber 2. This improves the uniformity of the evaporation rates of the first and second solvents from the first liquid phase L1, the second liquid phase L2, and the gel 12. As a result, when the solvent contained in the gel 12 is expelled from the gel, the uniformity of the pore structure (pore size) is improved, which generates capillary forces in a nearly uniform manner, allowing the gel 12 to dry and shrink to a shape that is nearly similar to the original shape. Furthermore, when the pore structure is swelled by springback, the uniformity of the migration speed of the solvent vapor in the pores is increased, thereby increasing the uniformity of the pore structure (pore size), thereby improving the homogeneity of the resulting aerogel 1. Here, from the viewpoint of also increasing the uniformity of the solvent vapor concentration contained in the atmosphere near gel 12 and further improving the homogeneity of the resulting aerogel 1, it is preferable to oscillate gel 12 held in casting dish 3 in a horizontal oscillation direction parallel to bottom surface 31 of casting dish 3 while adjusting the solvent vapor concentration contained in the atmosphere in reaction chamber 2 to fall within the above range.

[0109] Furthermore, the drying step S4 is preferably performed under normal pressure in the atmosphere inside the reaction chamber 2. This allows the drying of the gel 12 without pressurization, and therefore the aerogel 1 can be produced with a simpler device than in a conventional drying step using a supercritical fluid, thereby reducing the production cost of the aerogel 1.

[0110] (First Step S41) The first step S41 is a step of supplying a second solvent, which has a higher specific gravity than the first solvent and undergoes two-phase separation from the first solvent, into the casting dish 3. As a result, the gel 12 is positioned in a liquid phase system having a first liquid phase L1 and a second liquid phase L2.

[0111] Here, the first solvent constituting the first liquid phase L1 and the second solvent constituting the second liquid phase L2 are selected to be solvents that do not mix completely with each other and are separated into two phases. In addition, a solvent having a higher specific gravity than the first solvent is selected as the second 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 on the bottom.

[0112] Furthermore, it is preferable to use a solvent having a boiling point higher than that of the first solvent as the second solvent, but this is not limited to this as long as the first liquid phase L1 evaporates first at the first temperature described below and a state in which the gel 12 is immersed in the second liquid phase L2 can be created.

[0113] The second solvent used in the first step S41 is preferably one that can form a phase-separated state into a first liquid phase L1 and a second liquid phase L2 without completely mixing with the first solvent, and that has a boiling point higher than that of the first solvent. Examples of such a second solvent 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), fluorine-based solvents (specific gravity 1.3 to 1.5, boiling point 98 to 150°C), and mercury (specific gravity 13, boiling point 356°C).

[0114] The amount of the second solvent used in the first step S41 is preferably an amount that allows all of the gels 12 held in the casting dish 3 to be immersed in the second liquid phase L2. As a result, as shown in Fig. 4(a), the interface between the first liquid phase L1 and the second liquid phase L2 is positioned above the gels 12 held in the casting dish 3, and the first solvent that constituted the first liquid phase L1 can be easily removed.

[0115] (Second Step S42) The second step S42 is a 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 second solvent is supplied into the multiple casting dishes 3.

[0116] Here, it is preferable that the first solvent is discharged in a liquid state to the outside of the reaction chamber 2. This allows the first solvent to be quickly discharged to the outside of the reaction chamber 2.

[0117] On the other hand, the first solvent may be evaporated at a temperature higher than room temperature and discharged in a gaseous state to the outside of the reaction chamber 2. The temperature at this time is preferably in the range of 30° C. to 50° C. However, it is not preferable to set the temperature at this time to a temperature equal to or higher than the boiling point of the first solvent, because the gel 12 will break due to boiling of the first solvent.

[0118] In the second step S42, it is preferable to remove the first solvent constituting the first liquid phase L1 from the reaction chamber 2 and also remove the excess second solvent. In particular, from the viewpoint of quickly discharging the first and second solvents from the reaction chamber 2, it is preferable to discharge the first solvent in a liquid state together with the excess second solvent from the reaction chamber 2. At this time, the first solvent, which has a low specific gravity, remains inside the pores of the gel 12. As shown in FIG. 4( b), the second solvent is supplied into the multiple casting dishes 3, and the gel 12 in the casting dishes 3 is partially immersed in the second liquid phase L2 and floats on top of the second liquid phase L2. It is also observed that the gel 12 at this time is in a contracted state within the second liquid phase L2. By floating the gel 12 on top of the second liquid phase L2 in this manner, friction between the gel and the substrate can be reduced to almost zero when the gel contracts in the second step S42 or when its volume is restored in the third step S43 and fourth step S44 described below.

[0119] (Third Step S43) In the third step S43, the gel 12 is dried at a low temperature until it floats to the interface of the second liquid phase L2. Before the third step S43, the gel 12 is located in the second liquid phase L2. However, the gel 12 that was shrunk in the second step S42 recovers its volume by swelling its pore structure due to springback. Therefore, an aerogel 1 having the desired high homogeneity can be obtained.

[0120] The ambient temperature in the third step S43 is preferably in the range of 30°C to 60°C. By maintaining the temperature in this range, the second solvent remaining inside the gel 12 evaporates, and the drying of the gel 12 progresses, decreasing the specific gravity of the gel 12. As a result, the gel 12 moves upward from the liquid surface of the second liquid phase L2. Finally, as shown in Figure 4(c), a dried aerogel 1 floating above the second liquid phase L2 can be obtained. Note that it is not preferable to set the temperature at this time to a temperature above the boiling point of the second solvent, because the boiling of the second solvent will cause the gel 12 to break.

[0121] The third step S43 is preferably continued until the recovery of the volume of the gel 12 due to springback reaches a steady state.

[0122] (Fourth Step S44) After the third step S43, the aerogel 1 is preferably taken out of 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 increased.

[0123] Here, the drying conditions for the aerogel 1 are not particularly limited, and for example, the aerogel 1 may be naturally dried in the atmosphere. Among these, from the viewpoint of further increasing the transparency of the aerogel 1, it is preferable to dry the aerogel 1 at a high temperature at a second temperature higher than the first temperature.

[0124] When the aerogel 1 is dried at a high temperature at the 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 may be set in the range of 50°C to 100°C, and the drying time may be set in the range of 5 hours to 10 hours. Alternatively, the second temperature may be set in the range of 150°C to 250°C, and the drying time may be set in the range of 10 minutes to 90 minutes.

[0125] [Other Steps] The above-described manufacturing method has been described as a method for manufacturing a plate-shaped (or rectangular parallelepiped) aerogel, but the present invention is not limited to this, and may also include processing the plate-shaped aerogel into a desired shape as an optional step. For example, a plate-shaped aerogel can be processed into various shapes such as a film, cube, sphere, cylinder, pyramid, cone, etc., in addition to different plate shapes. Known mechanical processing methods such as wire cutting and laser cutting can be used to process the aerogel.

[0126] The aerogel 1 of the present invention may also include an optional process of processing a bulk aerogel, such as a plate-like aerogel, into granular aerogel. As a means for processing into granular aerogel, a known crusher (crusher) such as a jaw crusher, a roll crusher, or a ball mill can be used.

[0127] [Configuration of the Aerogel Manufacturing Apparatus] The aerogel manufacturing apparatus 10 of the present invention is preferably used in the above-described manufacturing method, and as shown in FIG. 5 , includes a casting dish 3 for adding a silicon compound to an aqueous solution, hydrolyzing the resulting sol 11, causing a crosslinking reaction to form a gel 12, and curing the gel 12; a casting means 4 for injecting the sol 11 into the casting dish 3; and a first solvent L10 having a low surface tension of 45 mN / m or less at 20° C. that is supplied into the casting dish 3 in which the gel 12 has been formed, and an internal solvent L10 present on the surface and inside of the gel 12. The apparatus includes a first solvent supplying means 5 for washing and replacing the solvent with a first solvent L10, a second solvent supplying means 6 for supplying a second solvent L20, which has a specific gravity greater than that of the first solvent L10 and undergoes two-phase separation from the first solvent L10, into the casting dish 3, a drying means 7 for drying the second solvent L20 while it is supplied into the casting dish 3 to form a Si-containing aerogel, and a swinging mechanism 8 for swinging the sol 11 or gel 12 formed in the casting dish 3 in a horizontal swinging direction parallel to the bottom surface of the casting dish 3 while it is held in the casting dish 3. This makes it possible to obtain an aerogel 1 having a standard deviation of total light transmittance of 0.60% or less when irradiated with visible light having a wavelength of 550 nm, converted into a 10 mm thickness. Therefore, even if the aerogel has a relatively large area (specifically, a size including a surface area of ​​a 300 mm square), it is possible to produce a sound aerogel free from defects such as cracks with a high yield.

[0128] Here, the casting means 4, the first solvent supply means 5 and the second solvent supply means 6 can be pipes equipped with valves (not shown).

[0129] The drying means 7 can include at least a drainage means 71 used to perform the second step S42 of the drying process S4 described above, which removes the first solvent constituting the first liquid phase L1 from the reaction chamber 2 as waste liquid L3, and a temperature adjustment means 72 used to perform the third step S43 of the drying process S4, which adjusts the ambient temperature in the reaction chamber 2 until the gel 12 floats to the interface of the second liquid phase L2.

[0130] Furthermore, the rocking mechanism 8 can be a mechanism that rocks the reaction chamber 2 in a horizontal direction parallel to the bottom surface of the casting dish 3. In particular, in the case where the reaction chamber 2 is rotated along the rotation axis M as shown in FIG. 5, a known driving means such as a motor can be used.

[0131] [Applications of Aerogel] Because of these advantages, the aerogel 1 of the present embodiment can be preferably used as a thermal insulating material in cryogenic containers, the space field, the construction field, the automotive field, the home appliance field, the semiconductor field, industrial equipment, etc. In addition to its application as a thermal insulating material, the aerogel 1 of the present embodiment can also be used for water repellency, sound absorption, vibration silencing, catalyst support, etc.

[0132] Next, in order to further clarify the effects of the present invention, examples of the present invention and comparative examples will be described, but the present invention is not limited to these examples.

[0133] <Example of the Invention> [Sol Generation Step S1] 3.28 g of a nonionic surfactant (BASF: Pluronic PE10500) was dissolved in 28.96 g of a 0.005 mol / L aqueous acetic acid solution, and then 4.00 g of urea (Nacalai Tesque) was added as a compound that generates a basic catalyst and dissolved. 10.00 g of a silicon compound (main raw material) was added to this aqueous solution, and the mixture was stirred and mixed at room temperature for 60 minutes to cause a hydrolysis reaction of the silicon compound, thereby generating Sol 11.

[0134] Here, the silicon compounds used were tetramethoxysilane (methyl orthosilicate manufactured by Tama Chemicals Co., Ltd., hereinafter sometimes abbreviated as "TMOS"), which is a tetrafunctional silane compound; methyltrimethoxysilane (DOWSIL Z-6366 Silane manufactured by Dow Corning Toray Co., Ltd., hereinafter sometimes abbreviated as "MTMS"), which is a trifunctional silane compound; and dimethyldimethoxysilane (Tokyo Chemical Industry Co., Ltd., product code: D1052, hereinafter sometimes abbreviated as "DMDMS"), which is a bifunctional silane compound. The silicon compounds were added in ratios of 25% by mass of the tetrafunctional silane compound, 65% by mass of the trifunctional silane compound, and 10% by mass of the bifunctional silane compound. Both TMOS and MTMS were purified by distillation under reduced pressure before use.

[0135] [Gelling step S2] Thereafter, in the casting step S22, 1225 ml of the generated sol 11 was poured into a casting dish 3 having a square planar shape of 320 mm on each side and a height of 17.5 mm to a depth of 10 mm, and the casting dish 3 poured with the sol 11 was placed in a casting dish holder 30.

[0136] The subsequent steps from gelation step S2 to drying step S4 were carried out in the same reaction chamber 2. Here, as shown in Fig. 5, casting dish 3 (or casting dish holder 30 holding casting dish 3) was placed in reaction chamber 2 so that the surface of sol 11 or gel 12 (the bottom surface of casting dish 3) was horizontal, and reaction chamber 2 was rotated around the axis (central axis M) which was the height direction Y of reaction chamber 2, so that casting dish 3 holding sol 11 or gel 12 swung in a horizontal direction along bottom surface 31 of casting dish 3. In addition, water was poured below casting dish 3 in reaction chamber 2 so that the concentration of water vapor contained in the atmosphere in reaction chamber 2 became equal to the saturated water vapor pressure.

[0137] In a curing step S23, the sol 11 poured into the casting dish 3 was left standing at 60° C. for 10 hours to generate a basic catalyst by heating and cause gelation, and then hot water at 60° C. was supplied into the reaction chamber 2 and immediately discharged to form a water layer with a thickness of 7.5 mm on the upper surface of the gel 12. The temperature inside the reaction chamber 2 was then raised to 80° C. and the gel was allowed to mature by being left standing for 72 hours. During this process, the rocking mechanism 8 was operated to alternately rotate the reaction chamber 2 clockwise around the central axis M to a rotation angle of 90° in 20 seconds and counterclockwise to a rotation angle of 90° in 20 seconds, thereby rocking the casting dish 3 holding the sol 11 before gelation or the gel 12 after gelation in a horizontal rocking direction.

[0138] After the curing step S23, the rotation of the reaction chamber 2 was stopped, the rocking of the casting dish 3 was stopped, and the temperature inside the reaction chamber 2 was lowered to 60°C. Next, the reaction chamber 2 was filled with methanol (MeOH) at 60°C in an amount (approximately 6.2 L) equivalent to five times the volume of the gel, so that the casting dish 3 containing the formed gel was immersed in methanol. This state was maintained for eight hours, and then the methanol not retained in the casting dish 3 was discharged to wash away surfactants, acids, reaction by-products, etc. This cleaning step S24 was repeated five times. During this process, the rocking mechanism 8 was operated to alternately rotate the reaction chamber 2 clockwise around the central axis M to a rotation angle of 90° over 20 seconds and then counterclockwise over 20 seconds to a rotation angle of 90° over 20 seconds, thereby rocking the casting dish 3 containing the gel 12 in a horizontal rocking direction. The methanol used in the cleaning treatment S24 was manufactured by Nacalai Tesque, Inc.

[0139] [Solvent Washing and Replacement Step S3] Next, in the solvent washing and replacement step S3, isopropanol and heptane were used in this order as the first solvent. More specifically, isopropanol was supplied as the first solvent into the casting dish 3 in which the gel 12 had been formed. The inherent solvent present on the surface and inside of the gel 12 was washed and replaced with isopropanol. Then, heptane was supplied as the first solvent into the casting dish 3. The solvent present on the surface and inside of the gel 12, such as isopropanol, was washed and replaced with heptane. This process was repeated twice. Here, the first solvent was supplied into the casting dish 3 under the condition of 60°C. The first solvent was supplied into the reaction chamber 2 in which the gel 12 and the casting dish 3 were placed in an amount (approximately 6.2 L) equivalent to five times the gel volume. As shown in FIG. 3(c), the multiple casting dishes 3 in the reaction chamber 2 were immersed in a first liquid phase L1 composed of the first solvent, and this state was maintained for 8 hours. During this process, the rocking mechanism 8 was operated to alternately rotate the reaction chamber 2 clockwise around the central axis M by 90° over 20 seconds and then counterclockwise over 20 seconds to rotate the reaction chamber 2 by 90°, thereby rocking the casting dish 3 holding the gel 12 in a horizontal direction. Then, as shown in FIG. 3( d ), the first liquid phase L1 not held in the casting dish 3 in the reaction chamber 2 was discharged. After the solvent washing and replacement step S3, the gel 12 in the casting dish 3 was immersed in the first liquid phase L1 composed of heptane and was submerged in the first liquid phase L1.

[0140] [Drying Step S4] After the solvent washing and replacement step S3, the temperature inside the reaction chamber 2 was lowered to 40°C. Next, in the first step S41 of the drying step S4, water was used as the second solvent and water was supplied into the casting dish 3. Here, water was supplied into the casting dish 3 in an amount of 40°C equivalent to five times the volume of the gel into the reaction chamber 2 in which the gel 12 and the casting dish 3 were placed. As shown in FIG. 4(a), this immersed the multiple casting dishes 3 in the reaction chamber 2 in the second liquid phase L2 composed of water, and formed a liquid phase system in which heptane (forming the first liquid phase L1 located on the upper side) and water (forming the second liquid phase L2 located on the lower side) separated into two liquid phases at the interface above the gel 12.

[0141] Immediately after the first step S41, in the second step S42, the heptane and excess water were discharged from the reaction chamber 2. At this time, as shown in FIG. 4(b), the gel 12 in the casting dish 3 contained heptane in its pores and was partially immersed in the second liquid phase L2 composed of water, floating on top of the second liquid phase L2.

[0142] After the second step S42, in the third step S43, the ambient temperature in the reaction chamber 2 was maintained at 40°C, and the gel 12 was dried at a low temperature. More specifically, the gas in the reaction chamber 2 was continuously exhausted at an exhaust rate of 500 ml / min using an exhaust device, heptane vapor contained in the exhaust gas was collected using a cooler, and then the dried gas heated to 40°C was returned to the reaction chamber 2, thereby drying the gel 12. At this time, the open upper surface of the container was covered with cellulose filter paper (Whatman filter paper, Grade 1, particle retention capacity 11 μm) as an air-permeable membrane, and the total vapor concentration of the first solvent and the second solvent in the space partitioned by the heptane liquid surface and the air-permeable membrane was adjusted to about 50%. In the third step S43 of this drying step S4, the rocking mechanism 8 was operated to alternately rotate the reaction chamber 2 clockwise around the central axis M to a rotation angle of 90° in 20 seconds and then rotate the reaction chamber 2 counterclockwise to a rotation angle of 90° in 20 seconds, thereby rocking the casting dish 3 holding the gel 12 in a horizontal direction.

[0143] The low-temperature drying of the gel 12 in the third step S43 was carried out until the dried gel 12 floated to the surface of the second liquid phase L2, and the drying time was about 45 hours. As a result, a translucent aerogel was obtained.

[0144] After the third step S43, the aerogel was further dried in a fourth step S44 in an additional incubator (IS601 manufactured by Yamato Scientific Co., Ltd.) at a drying temperature of 80°C until the size of the aerogel recovered to 95% of the size of the casting dish 3 (a size of 304 mm square), thereby obtaining an aerogel 1 of the present invention.

[0145] Furthermore, these operations were repeated 26 times to obtain a total of 27 sheets of aerogel 1. These 27 sheets of aerogel 1 included those in which 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 aging time in the gelation step S2, the temperature, time, number of cycles, and rocking speed in the solvent washing and replacement step S3, and the temperature, exhaust speed, and rocking speed in the drying step S4 were changed.

[0146] Comparative Example: The sol 11 was poured into a casting dish 3 and placed in a casting dish holder 30. In this example, the casting dish 3 holding the sol 11 and gel 12 was not rocked by rotating the reaction chamber 2 in the gelation step S2, the solvent washing and replacement step S3, and the drying step S4, but the other conditions were the same as those of the inventive example, and a comparative aerogel (comparative example) was obtained. Furthermore, by repeating this operation seven times, a total of eight sheets of aerogel 1 were obtained.

[0147] <Evaluation> (Observation of cracks in aerogels) The aerogels obtained in the examples of the present invention and the comparative examples were visually observed. As a result, the aerogels obtained in the examples of the present invention were able to be obtained with crack-free areas on the entire surface in all 27 aerogels. On the other hand, in the comparative example, breakage occurred in all eight aerogels, and it was not possible to obtain aerogels capable of obtaining a square surface area of ​​300 mm on each side. Therefore, the aerogels obtained in the examples of the present invention were able to be obtained with a higher yield and in a sound state without defects such as cracks than the aerogels in the comparative examples.

[0148] (Measurement of transmittance of aerogel) The transmittance of the obtained aerogel was determined from spectral data obtained using a V-670 ultraviolet-visible-near-infrared spectrophotometer (manufactured by Japan Jusco Co., Ltd.) equipped with an integrating sphere. Here, visible light having a wavelength of 550 nm was irradiated onto three points on the surface area of ​​a 300 mm square at a position overlapping the center (center of gravity) of the aerogel: the center position of the square, the position of a corner of the square, and the center position of a side of the square (the center position of the side connecting adjacent corners of the square). The total transmittance values ​​were calculated using the Lambert-Beer equation to calculate the total transmittance (T ５５０ ) was calculated. Here, the center position of the square was defined as a position within a 50 mm square area having the same center as the square of the surface region. The positions of the corners of the square were defined as positions within a 50 mm square area having the same corners as the square of the surface region and overlapping with the square of the surface region. The center position of the side of the square was defined as a position within a 50 mm square area where the center position of the side connecting adjacent corners of the square was in the same position as the square of the surface region and overlapping with the square of the surface region. The thickness of the sample was measured using a vernier caliper at each measurement position after measuring the total transmittance. The standard deviation of these three points of the total light transmittance for each aerogel was calculated from the total transmittance values ​​calculated for each location within the aerogel, and the average of the obtained standard deviations was used as the standard deviation result.

[0149] As a result, as shown in FIG. 6, the aerogel of the present invention had a standard deviation of the total light transmittance (the standard deviation of the above-mentioned three points) of about 0.30% when irradiated with visible light having a wavelength of 550 nm, whereas the aerogel of the comparative example had a standard deviation of about 1.00% when irradiated with visible light having a wavelength of 550 nm.

[0150] Therefore, it was shown that the aerogels of the present invention were large and free of cracks. This also revealed that the occurrence of cracks can be suppressed by using an aerogel with a small standard deviation of the total light transmittance when irradiated with visible light having a wavelength of 550 nm.

[0151] <Overall Evaluation> The aerogels of the examples of the present invention have a small standard deviation of total light transmittance when irradiated with visible light having a wavelength of 550 nm, and it was revealed that aerogels in a sound state free of defects such as cracks can be obtained with a high yield. Furthermore, it was found that the aerogels of the examples of the present invention having a small standard deviation of total light transmittance when irradiated with visible light having a wavelength of 550 nm can be obtained by applying the manufacturing method of the present invention, in which the casting dish 3 holding the sol 11 or gel 12 is rocked in one or both of the gelling step S2 and the drying step S4.

[0152] REFERENCE SIGNS LIST 1 aerogel 10 aerogel manufacturing apparatus 11 sol 12 gel (wet gel) 2 reaction chamber 3 casting dish 30 casting dish holder 31 bottom surface of casting dish 4 casting means 5 first solvent supply means 6 second solvent supply means 71 drainage means 72 temperature adjustment means 8 rocking mechanism S1 sol generation step S2 gelation step S21 catalyst addition step S22 casting step S23 curing step S3 solvent washing replacement step S4 drying step S41 first step S42 second step S43 third step L1 first liquid phase L10 first solvent L2 second liquid phase L20 second solvent

Claims

1. A Si-containing aerogel having a pore structure formed of a continuous fibrous skeleton in a mesh-like shape and a plurality of pores defined by said skeleton, said aerogel having at least a surface area of ​​a square of 300 mm on each side, and a standard deviation of total light transmittance when said surface area is irradiated with visible light having a wavelength of 550 nm, calculated as a thickness of 10 mm, of 0.60% or less.

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

3. The aerogel according to claim 1 or 2, which is produced by drying at atmospheric pressure.

4. A method for producing an aerogel comprising: a sol production step of adding a silicon compound to an aqueous solution and producing a sol by hydrolysis; a gelling step of injecting the sol into a casting dish and crosslinking the sol in the casting dish to produce a gel and curing the gel; a solvent washing and replacement step of supplying a first solvent having a low surface tension of 45 mN / m or less at 20°C into the casting dish and washing and replacing the inherent solvent present on the surface and inside of the gel with the first solvent; and a drying step of supplying a second solvent having a higher specific gravity than the first solvent and undergoing two-phase separation from the first solvent in the state where it is supplied into the casting dish and drying it to produce a Si-containing aerogel, wherein at least one of the gelling step, the solvent washing and replacement step, and the drying step are performed while the sol or gel produced in the casting dish is oscillated in a lateral direction parallel to the bottom surface of the casting dish while being held in the casting dish.

5. The method for producing an aerogel according to claim 4, wherein each step from the gelling step to the drying step is carried out in the same reaction chamber.

6. The method for producing an aerogel according to claim 4, wherein at least the gelling step and the drying step among the steps from the gelling step to the drying step are carried out in separate reaction chambers.

7. The method for producing an aerogel described in claim 5 or 6, wherein the gelation process is carried out by adjusting the concentration of water vapor contained in the atmosphere in the reaction chamber to a range of 60% or more and 100% or less of the saturated water vapor pressure.

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

9. The method for producing an aerogel according to claim 5 or 6, wherein the drying step is carried out under normal pressure in the reaction chamber.

10. An apparatus for producing an aerogel comprising: a casting dish in which a silicon compound is added to an aqueous solution, and the sol produced by hydrolyzing the solution is subjected to a cross-linking reaction to produce a gel and the gel is cured; a casting means for injecting the sol into the casting dish; a first solvent supplying means for supplying a first solvent having a low surface tension of 45 mN / m or less at 20°C into the casting dish, and washing and replacing the inherent solvent present on the surface and inside of the gel with the first solvent; a second solvent supplying means for supplying a second solvent having a higher specific gravity than the first solvent and which undergoes two-phase separation from the first solvent into the casting dish; a drying means for drying the second solvent while it is supplied into the casting dish, to produce an aerogel containing Si; and a rocking mechanism for rocking the sol or gel formed in the casting dish in a horizontal rocking direction parallel to the bottom surface of the casting dish while the second solvent is held by the casting dish.

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