Method of making an aerogel blanket and aerogel blanket made thereby

Abstract

The present invention provides a method of preparing an aerogel mat, in which a surface modification process is performed under acidic conditions while using a non-toxic catalyst, whereby a solvent replacement process or a washing process can be omitted to simplify the preparation process, and collapse of a gel structure due to shrinkage can be prevented even when atmospheric pressure drying is performed, and the efficiency of surface modification is also high, whereby an aerogel having excellent thermal conductivity and a degree of hydrophobicity can be prepared. The present invention also provides an aerogel mat prepared by the method, thereby having low thermal conductivity and low moisture impregnation due to uniform formation of hydrophobic groups within the substrate.

Description

TECHNICAL FIELD

[0001] Cross-reference to Related Applications

[0002] This application claims the benefit of Korean Patent Application No. 2020-0133466, filed October 15, 2020, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference. TECHNICAL FIELD

[0004] The present application relates to a method of preparing an aerogel felt, and an aerogel felt prepared by the preparation method, the method including gelation using a non-toxic base catalyst and a surface modification process under acid conditions. BACKGROUND

[0005] An aerogel is a material having superporosity, a high specific surface area (≥ 500 m 2 / g), a porosity of about 90 to 99.9%, and a pore diameter of 1-100 nm, and is a material having excellent properties such as superlightness, superinsulation, and superlow dielectricity. Thus, research on the development of aerogel materials and the practical use thereof as a transparent insulation material, an environmentally friendly high-temperature insulation material, an ultralow dielectric thin film for high-integration devices, a catalyst and a catalyst carrier, an electrode for supercapacitors, and an electrode material for seawater desalination has been actively conducted.

[0006] The greatest advantage of an aerogel is that the aerogel has superinsulation, with a thermal conductivity of 0.300 W / m·K or less, which is lower than that of conventional organic insulation materials such as polystyrene foam plastic, and can solve the fatal weakness of organic insulation materials, i.e., fire vulnerability and the generation of harmful gases upon a fire.

[0007] In general, an aerogel is produced by preparing a hydrogel from a precursor material and removing a liquid component inside the hydrogel without destroying the microstructure. Aerogels can be generally classified into three types, i.e., powder, granule, and monolith, and a silica aerogel is generally produced in the form of powder.

[0008] The above-described powder-type silica aerogel can be made into a composite having a fiber, and is commercialized in the form of an aerogel felt or an aerogel sheet. Such an aerogel felt and an aerogel sheet can be bent, folded, or cut into any size or shape due to its flexibility. Thus, the powder-type silica aerogel can be applied not only to industrial applications such as an insulation board for an LNG carrier, an industrial insulation material, a space suit, transportation, a vehicle, and an insulation material for power production, but also to household items such as a jacket and sports shoes. In addition, when the aerogel is used in a fireproof door and a roof and a floor in a house such as an apartment, it can have a great fireproof effect.

[0009] Specifically, the aerogel mat in the present specification refers to the concept of a material in which an aerogel is impregnated on a mat base material such as a fiber, and the method of preparing the aerogel mat is divided into a gel-casting method and a method of preparing an aerogel powder or particles and then depositing it on a mat base material using a binder.

[0010] The product manufactured by the gel-casting method occupies most of the use so far due to its good physical properties, and currently, the gel-casting method using a roll-to-roll technique is known as a commercially available technique. At this time, ammonia is generally used as a catalyst used in gelation, and ammonia is widely used due to its excellent aerogel physical properties capable of effectively preventing the collapse of the gel structure.

[0011] However, since the ammonia catalyst is a weak base component, it should be used in a large amount to secure the gel time and to secure the physical properties in the process, the process stability is lowered due to the toxic gas component, and some toxic gas components are even left in the final product, which causes a problem. Therefore, in order to secure the process stability and product eco-friendliness, it is necessary to develop a method and a product that can secure physical properties comparable to or higher than those of the ammonia catalyst while removing toxic substances throughout the process.

[0012] [Prior Art Documents]

[0013] [Patent Documents]

[0014] (Patent Document 1) KR 10-2012-0070948 A SUMMARY

[0015] Technical Problem

[0016] One aspect of the present application is to provide a method of preparing an aerogel mat by a gel-casting method, in which gelation is performed by catalyzing a sol with a non-toxic sodium-based alkali catalyst during the gelation process, and a surface modification process is performed under an acid condition, so that the gel structure does not collapse due to shrinkage even when atmospheric pressure drying is performed, and thus, a cost-saving effect can be expected compared to supercritical drying. In addition, since the toxic catalyst is replaced with a non-toxic material, safety can be secured, and since the collapse of the gel structure is inhibited by surface modification under an acid condition, sufficient thermal conductivity and improved hydrophobicity degree can be secured.

[0017] Another aspect of the present application is to provide a high thermal insulation aerogel mat prepared by the method of preparing an aerogel mat.

[0018] Technical Solution

[0019] According to an aspect of the present application, there is provided a method of preparing an aerogel felt, wherein the method comprises: 1) mixing a silica sol and a sodium-based alkali catalyst to obtain a catalyzed silica sol; 2) impregnating and gelling the catalyzed silica sol in a base material for a felt to obtain a wet gel-fiber composite; 3) introducing an acidic surface modification solution containing a surface modifier and a chlorine-based acid-induced aqueous solution into the wet gel-fiber composite to hydrophobize the wet gel-fiber composite; and 4) drying the hydrophobized wet gel-fiber composite.

[0020] Advantages

[0021] The preparation method of the present application is advantageous in that the gelling is performed by using a non-toxic sodium-based alkali catalyst to catalyze the sol during the gelling process, and the surface modification process is performed under an acid condition, so that the gel structure does not collapse due to shrinkage even when atmospheric pressure drying is performed, and thus a cost-saving effect can be expected compared to supercritical drying. In addition, since a toxic catalyst is replaced with a non-toxic material, safety can be ensured, and since the collapse of the gel structure is inhibited by the surface modification under an acid condition, sufficient thermal conductivity and an improved degree of hydrophobicity can be ensured. DETAILED DESCRIPTION

[0022] Hereinafter, the present application will be described in greater detail in order to facilitate the understanding of the present application. In this case, it should be understood that the words or terms used in the specification and claims should not be interpreted as having meanings defined in commonly used dictionaries. It should be further understood that the meanings of the words or terms used can be defined appropriately based on the principle that the inventor can define the meanings of the words or terms to best explain the present application.

[0023] 1. A method of preparing an aerogel felt

[0024] The method of preparing an aerogel felt according to an embodiment of the present application comprises: 1) mixing a silica sol and a sodium-based alkali catalyst to obtain a catalyzed silica sol; 2) impregnating and gelling the catalyzed silica sol in a base material for a felt to obtain a wet gel-fiber composite; 3) introducing an acidic surface modification solution containing a surface modifier and a chlorine-based acid-induced aqueous solution into the wet gel-fiber composite to hydrophobize the wet gel-fiber composite; and 4) drying the hydrophobized wet gel-fiber composite.

[0025] The preparation method is to replace a toxic gelation catalyst used in a general gel-casting method, thereby solving problems caused by the use of the toxic gelation catalyst. Specifically, the method is characterized in that a non-toxic sodium-based alkali catalyst is replaced with a toxic ammonia-based catalyst, and a surface modification process is performed under an acid condition to obtain a thermal conductivity and a degree of hydrophobicity that can be achieved when the ammonia catalyst is used.

[0026] More specifically, the toxic ammonia-based catalyst is a weak base, and thus, it should be used in a large amount to secure a gelation time and physical properties, but there is no problem of collapse of a gel structure caused by shrinkage during drying even when a solvent is evaporated due to a relatively low pH in the process. In contrast, the non-toxic sodium-based alkali catalyst is a strong base, and thus, there is a problem of collapse of a gel structure during drying due to an increase in pH in the process. To solve this problem, the surface modification process is acidified to neutralize the sodium-based alkali catalyst as a strong base, so that the pH is lowered by the generation of a salt, thereby preventing collapse of the gel structure. Thus, even when a non-toxic catalyst is used, an aerogel mat having high thermal conductivity and a high degree of hydrophobicity can be prepared.

[0027] In addition, when the sodium-based alkali catalyst is used, a shrinkage phenomenon occurs seriously during drying, so that an atmospheric pressure drying process cannot be applied, and precise control is required to prevent shrinkage by supercritical drying. However, in the preparation method, shrinkage of a gel structure can be controlled by acidification of the surface modification process, so that an atmospheric pressure drying process can be applied.

[0028] Further, because the sodium-based alkali catalyst is a strong base, only a small amount of the catalyst is required to induce sufficient gelation, and because the surface modification process is acidified, a neutralization reaction is caused by the catalyst as a strong base, and a salt is generated in the surface modification process, so that an additional effect of improving surface modification efficiency can also be expected.

[0029] Hereinafter, each step of the method of preparing the aerogel mat of the present application will be described in detail.

[0030] Step 1: Catalytic Process

[0031] Step 1) of the embodiment of the present application is a step of mixing a silica sol and a sodium-based alkali catalyst to obtain a catalytic silica sol.

[0032] In the present application, the catalytic silica sol can be prepared by mixing the silica sol and the sodium-based alkali catalyst, and the alkali catalyst is used to promote gelation in step 2) by increasing the pH of the silica sol.

[0033] The silica sol of the embodiments of the present application contains a silica precursor and an organic solvent, and can be prepared by mixing the silica precursor and the organic solvent. In step 1), the catalytic silica sol can be prepared by mixing the silica sol and the base catalyst, wherein the silica sol can be prepared by mixing the silica precursor and the organic solvent, and it can further contain water, and the hydrated organic solvent can be used. In addition, the silica precursor can be hydrolyzed at a low pH to facilitate gelation, at which time the acid catalyst can be used to lower the pH.

[0034] The silica precursor that can be used to prepare the silica sol can be a silicon-containing alkoxide compound, particularly tetraalkyl orthosilicate, such as tetramethyl orthosilicate (TMOS), tetraethyl orthosilicate (TEOS), methyltriethyl orthosilicate, dimethyldiethyl orthosilicate, tetrapropyl orthosilicate, tetraisopropyl orthosilicate, tetrabutyl orthosilicate, tetra-sec-butyl orthosilicate, tetra-t-butyl orthosilicate, tetrahexyl orthosilicate, tetracyclohexyl orthosilicate, and tetradodecyl orthosilicate. More specifically, the silica precursor of the embodiments of the present application can be tetraethyl orthosilicate (TEOS).

[0035] In addition, as the acid catalyst that can be further contained in the silica sol of the embodiments of the present application, any acid catalyst that can bring the pH to 3 or less can be used without limitation. As examples, hydrochloric acid, nitric acid, or sulfuric acid can be used. At this time, the acid catalyst can be added in an amount that brings the pH of the sol to 3 or less, and can be added in the form of an aqueous solution dissolved in an aqueous solvent.

[0036] The silica precursor of the embodiments of the present application can be in a state in which the silica precursor is hydrolyzed by a preliminary reaction with the acid catalyst. For example, tetraalkyl orthosilicate, such as tetramethyl orthosilicate (TMOS), tetraethyl orthosilicate (TEOS), methyltriethyl orthosilicate, dimethyldiethyl orthosilicate, tetrapropyl orthosilicate, tetraisopropyl orthosilicate, tetrabutyl orthosilicate, tetra-sec-butyl orthosilicate, tetra-t-butyl orthosilicate, tetrahexyl orthosilicate, tetracyclohexyl orthosilicate, and tetradodecyl orthosilicate, which is in a pre-hydrolyzed state by a reaction with the acid catalyst, can be directly applied.

[0037] The amount of the silica precursor can be an amount that brings the content of the silica (SiO2) contained in the silica sol to 3 to 30% by weight. If the content of the silica is less than 3% by weight, the content of the silica aerogel in the mat finally produced is too low to achieve a desired level of thermal insulation effect. If the content of the silica is greater than 30% by weight, the mechanical properties of the mat, particularly its flexibility, can be deteriorated due to excessive formation of the silica aerogel.

[0038] In addition, as the organic solvent which can be used to prepare the silica sol of the present application, any material having excellent compatibility with the silica precursor and water can be used without limitation. Specifically, a polar organic solvent can be used, and more specifically, an alcohol can be used. Here, the alcohol can be specifically a monohydric alcohol such as methanol, ethanol, isopropanol, and butanol, or a polyhydric alcohol such as glycerol, ethylene glycol, propylene glycol, diethylene glycol, dipropylene glycol, and sorbitol, and any one thereof or a mixture of two or more thereof can be used. Among them, when considering its miscibility with water and the aerogel to be prepared, the alcohol can be a monohydric alcohol having 1 to 6 carbon atoms such as methanol, ethanol, isopropanol, and butanol.

[0039] The above organic solvent can be used in an appropriate amount in consideration of the content of the aerogel finally prepared.

[0040] The silica sol of the embodiment of the present application can include a silica precursor and water in a molar ratio of 1:4 to 1:1. In addition, the silica precursor and the organic solvent can be included in a weight ratio of 1:2 to 1:9, and preferably can be included in a weight ratio of 1:4 to 1:6. When the silica precursor satisfies the above molar ratio or weight ratio with water and the organic solvent, the productivity of the aerogel can be further increased, thereby having the effect of improving the thermal insulation performance. Specifically, the ratio can be adjusted within the above range so that the density of the silica precursor in the silica sol is 50 kg / m 3 to 100 kg / m 3 , preferably 50 kg / m 3 to 80 kg / m 3 , more preferably 60 kg / m 3 to 80 kg / m 3 .

[0041] According to the embodiment of the present application, the sodium-based alkali catalyst can be an inorganic base. Specifically, the sodium-based alkali catalyst can be sodium hydroxide (NaOH) or sodium silicate, and can be a sodium-containing inorganic base, which is generally referred to as a strong base.

[0042] Generally used amine or ammonia containing materials such as ammonia (NH3), ammonium hydroxide (NH4OH; aqueous ammonia), tetramethylammonium hydroxide (TMAH), tetraethylammonium hydroxide (TEAH), tetrapropylammonium hydroxide (TPAH), tetrabutylammonium hydroxide (TBAH), methylamine, ethylamine, isopropylamine, mono-isopropylamine, diethylamine, diisopropylamine, dibutylamine, trimethylamine, triethylamine, triisopropylamine, tributylamine, choline, monoethanolamine, diethanolamine, 2-aminoethanol, 2-(ethylamino)ethanol, 2-(methylamino)ethanol, N-methyldiethanolamine, dimethylaminoethanol, diethylaminoethanol, nitrilotriethanol, 2-(2-aminoethoxy)ethanol, 1-amino-2-propanol, triethanolamine, mono-isopropanolamine, dibutanolamine, or pyridine have a problem of generating ammonia in the process, thus discharging a toxic gas, and can cause serious safety problems. Since its effect on operators when contained in products and its effect on users of products become increasingly problematic, there is a need to replace such amine or ammonia catalysts.

[0043] In the present invention, since a non-toxic strong base is used as a sodium-based base catalyst as described above, compared to the use of a general catalyst, gelation can be achieved with only a small amount of catalyst, and thus the gelation efficiency can be improved. It is also advantageous in that toxic substances are removed in the process, and the gelation time can be reduced to improve productivity.

[0044] The content of the sodium-based base catalyst can be an amount to make the pH of the sol 9.0 to 11.0. When the pH of the catalytic silica sol is within the above range, productivity can be improved due to the increased gelation efficiency and reduced gelation time in Step 2 described later, and has the advantage of the disappearance of toxic substances in the process. In addition, since the sodium-based base catalyst can precipitate when introduced in a solid phase, it can be preferable that the sodium-based base catalyst be added in the form of a solution diluted with an aqueous solvent or the above-mentioned organic solvent.

[0045] At this time, the dilution ratio of the sodium-based base catalyst and the organic solvent (particularly alcohol) can be 1:4 to 1:100 based on volume. In addition, based on the volume of the catalytic silica sol, the sodium-based base catalyst can have a sodium ion concentration of 1 mmol / L to 100 mmol / L, preferably 5 mmol / L to 50 mmol / L, and the degree of dilution can be applied at a desired appropriate level in consideration of the reactivity of the strong base. The sodium ion concentration is preferably applied within the above range to the extent that it can promote the reaction as a catalyst.

[0046] Meanwhile, the sodium-based base catalyst can be an aqueous solution having a concentration of 10% to 50%, preferably 20% to 40%.

[0047] According to the embodiment of the present application, the catalytic silica sol can be further added with additives, if necessary. At this time, as the additives, all known additives which can be added at the time of preparing the aerogel can be applied, and for example, additives such as a light shielding agent and a flame retardant agent can be used.

[0048] Step 2: Impregnation and Gelation Process

[0049] Step 2) of the embodiment of the present application is a step for preparing a wet gel-fiber composite (wet gel mat), and is a step of impregnating the catalytic silica sol in the mat substrate and then gelating the catalytic silica sol impregnated in the mat substrate.

[0050] Step 2) is a step for impregnating the catalytic silica sol in the mat substrate, wherein an impregnation tank for impregnating the catalytic sol in the mat substrate is used by introducing the catalytic silica sol prepared in the above-described step 1) and the mat substrate into a reaction vessel, or a roll-to-roll technique of moving the mat substrate on a conveyer belt and spraying the catalytic silica sol on the moving mat substrate is utilized, or various methods such as a combination of the two methods can be applied.

[0051] As used in the present application, the term "impregnation" means that it is achieved by introducing the catalytic sol having fluidity into the mat substrate, and can mean that the catalytic sol penetrates into the pores within the mat substrate.

[0052] As long as step 2) of the embodiment of the present application is a step of introducing the mat substrate and the catalytic silica sol into a reaction vessel, the order of introduction is not particularly limited. Specifically, in step 2), the introduction can be performed by any one of the following methods: a method of introducing the mat substrate into a reaction vessel and then introducing the catalytic silica sol into the reaction vessel; a method of introducing the catalytic silica sol into a reaction vessel and then introducing the mat substrate into the reaction vessel; and a method of introducing the mat substrate while introducing the catalytic silica sol into the reaction vessel.

[0053] As another example, in step 2), in order to impregnate and gelate the catalytic silica sol in the mat substrate, the following methods can be applied: a method of impregnating the silica sol in the mat substrate by spraying the silica sol on the mat substrate while the mat substrate is moving on a conveyer belt, or a method of combining an impregnation tank with a roll-to-roll method.

[0054] In addition, in terms of improving the thermal insulation of the aerogel mat, the mat substrate of the embodiment of the present application can specifically be a porous substrate. When a porous mat substrate is used, the silica sol is easily penetrated into the substrate, thereby uniformly forming the aerogel inside the mat substrate, so that the prepared silica aerogel mat can have excellent thermal insulation.

[0055] The mat-use substrate that can be used according to the embodiments of the present application can be a film, a sheet, a web, a fiber, a foam, a nonwoven fabric body, or a laminate of two or more layers thereof. In addition, depending on the use of the mat-use substrate, surface roughness can be formed or patterned on the surface thereof. More specifically, the mat-use substrate can be a fiber capable of further improving thermal insulation performance by including spaces or voids through which aerogels can be easily inserted into the mat-use substrate. Further, the mat-use substrate can preferably have low thermal conductivity.

[0056] Specifically, the mat-use substrate can be polyamide, polybenzimidazole, aramid, acrylic resin, phenol resin, polyester, polyether ether ketone (PEEK), polyolefin (e.g., polyethylene, polypropylene, or a copolymer thereof, etc.), cellulose, carbon, cotton, wool, hemp, nonwoven fabric, glass fiber, or ceramic cotton, etc. More specifically, the mat-use substrate in the present application can be glass fiber.

[0057] When the catalytic silica sol introduced in step 1 is introduced, in order to improve the bonding between the mat-use substrate and the catalytic silica sol, the mat-use substrate can be lightly pressed to achieve sufficient impregnation. Thereafter, the mat-use substrate can be pressed to a predetermined thickness at a constant pressure to remove excess sol, thereby shortening the drying time.

[0058] According to the embodiments of the present application, the catalytic silica sol can be introduced in an amount of 80% to 120% by volume, preferably 90% to 110% by volume, based on the volume of the mat-use substrate. In addition, preferably, the introduction amounts of the mat-use substrate and the catalytic silica sol can satisfy the above-described introduction ratio thereof under the condition that the introduction amount with respect to the reaction vessel is satisfied. When the volume of the catalytic silica sol with respect to the silica of the mat-use substrate satisfies the introduction ratio (introduction amount), the catalytic silica sol is more uniformly impregnated in the mat-use substrate, so that the prepared aerogel mat can have more uniform physical properties, and since the catalytic silica sol can be entirely impregnated in the mat-use substrate, loss of raw materials can be prevented, and the problem of the catalytic silica sol being gelled alone can be prevented.

[0059] According to the embodiments of the present application, the catalytic silica sol is impregnated in the mat-use substrate, thereby being gelled, and thus a wet gel-fiber composite is obtained. The gelation can be a network structure formed from the catalytic silica sol, wherein the network structure can mean a planar net structure having specific polygons arranged with one or more kinds of atoms connected to each other, or a structure in which specific polyhedrons share their vertices, edges, faces, etc. with each other to form a three-dimensional skeletal structure.

[0060] According to the embodiment of the present application, the gelation can be induced by impregnating the felt base material with the catalytic silica sol, and then leaving the impregnated felt base material for 0.5 hours to 2.0 hours, and the gelation can be performed at a temperature range of 20°C to 50°C, preferably at room temperature.

[0061] According to the embodiment of the present application, after completion of step 1), step 2) can be started to sequentially perform step 1) and step 2).

[0062] According to another embodiment of the present application, step 2) can be started before completion of step 1), and when step 2) is performed as described above before completion of step 1), the catalytic sol can be introduced into the reaction vessel in its entirety until completion of the gelation, particularly before completion of the gelation.

[0063] Additional Process: Maturation Process

[0064] The preparation method of the embodiment of the present application can additionally perform a maturation step as a process for completely achieving a chemical change by leaving the wet gel-fiber composite at a suitable temperature. The maturation step can make the network structure formed more stably, and thus can enhance the mechanical stability of the aerogel felt of the present application.

[0065] The maturation step should be performed at a suitable temperature range to enhance the optimal pore structure. The maturation step of the present application can be performed by leaving the wet gel-fiber composite at a temperature of 30°C to 70°C for 3 hours to 50 hours. When the maturation temperature is within the above range, the productivity can be ensured due to an appropriate maturation level, and the loss of the solvent due to evaporation of the organic solvent can be prevented. In addition, the maturation time within the above range is a range that can satisfy the thermal conductivity and the degree of hydrophobicity, and can be preferably 6 hours to 48 hours, more preferably 18 hours to 48 hours.

[0066] In the above maturation step, no additional catalyst can be introduced. When an additional basic catalyst is introduced in the maturation step, the pH of the wet gel-fiber composite can become too high, and thus, there can be a problem that the collapse of the gel structure due to shrinkage becomes serious in the drying process, and there can be a possibility that the fiber itself can be damaged. In addition, when an acid catalyst is additionally introduced, a neutralization reaction can occur in the wet gel-fiber composite during the maturation process, and thus, the silanol group that should be substituted with a hydrophobic group is lost, so that the surface modification efficiency can be deteriorated. Therefore, it can be preferable that no additional catalyst is introduced in the maturation step.

[0067] Further, according to embodiments of the present application, the ripening step can be performed in a separate reaction vessel after recovering the gelled silica wet-gel-fiber composite, or can be performed within the reaction vessel in which the gelation has been performed. The ripening step can preferably be performed in the reaction vessel in which the gelation has been performed in terms of efficiency of the process and simplification of the equipment.

[0068] Step 3: Surface Modification Process

[0069] According to embodiments of the present application, the step 3) is a step of introducing an acid surface modification solution containing a surface modifier and an aqueous solution of a chlorine-based acid to the wet-gel-fiber composite prepared in the step 2) to hydrophobize the wet-gel-fiber composite.

[0070] When the hydrophilic functional groups present on the surface of the aerogel are replaced with hydrophobic functional groups, the pore shrinkage due to the solvent surface tension during drying of the aerogel can be minimized by the repulsive force between the hydrophobic functional groups. The dried aerogel maintains low thermal conductivity immediately after drying. However, due to the presence of hydroxyl functional groups on the surface of the aerogel, for example, when the aerogel is a silica aerogel, the hydrophilic silanol groups (Si-OH) present on the surface of the silica absorb water in the air, thus there is a disadvantage that the thermal conductivity gradually increases. Therefore, in order to maintain low thermal conductivity, it is necessary to modify the surface of the aerogel to be hydrophobic.

[0071] Accordingly, the surface modification of the embodiments of the present application can be performed by a surface modifier containing a polar solvent and an organic silane compound.

[0072] As the polar solvent, methanol, ethanol, or isopropanol, or the like can be used, and as the organic silane compound, trimethylchlorosilane (TMCS), hexamethyldisilazane (HMDS), methyltrimethoxysilane (MTMS), trimethylethoxysilane (TMES), ethyltriethoxysilane (ETES), or phenyltriethoxysilane (PTES), or the like can be used. Preferably, trimethylethoxysilane or hexamethyldisilazane can be used.

[0073] The surface modification is preferably performed by mixing the polar solvent at a volume ratio of 0.5 to 10.0 with respect to the wet-gel, and mixing the organic silane compound at a volume ratio of 0.1 to 10.0 with respect to the wet-gel. The surface modifier containing the organic silane compound and the polar solvent can be mixed at a volume ratio of 0.5 to 10.0 with respect to the wet-gel. When the volume ratio of the organic silane compound with respect to the wet-gel is less than 0.1, the reaction time becomes too long, which can result in a decrease in surface modification efficiency. When the volume ratio of the organic silane compound is greater than 10.0, there is a problem of an increase in cost, and unreacted surface modifier can cause shrinkage during drying.

[0074] The organosilane compound and the polar solvent can be mixed in the above volume ratio, and the surface modifier in the mixed state can contain 10 to 60% by volume of the organosilane compound based on the total volume of the surface modifier. The content of the organosilane compound in the surface modifier can affect the degree of hydrophobicity and the thermal conductivity, and as the content increases, the hydrophobicity and the thermal conductivity can be improved. When the content is greater than 60% by volume, there is no additional increase in the surface modification efficiency in addition to the increase in the amount of wasted organosilane compound, making it necessary to appropriately adjust the amount within the above range. In addition, in order to achieve the above effects while minimizing the deviation in the surface modification efficiency (i.e., the degree of hydrophobicity) of the final aerogel mat, the content can be preferably 15 to 50% by volume, more preferably 25 to 50% by volume, and even more preferably 25 to 50% by volume, depending on the amount of the acid aqueous solution introduced.

[0075] Further, according to the embodiment of the present application, the acidic surface modification solution can further include a chlorine-based acid-induced aqueous solution in addition to the surface modifier. The chlorine-based acid-induced aqueous solution can be an acid diluted in an aqueous solution state, can be diluted to a concentration of 10 to 50% by weight, and can be preferably 20 to 40% by weight. The acidic surface modification solution is a mixture of the surface modifier, which is an organosilane compound diluted with a polar solvent, and the chlorine-based acid in an aqueous solution state, and the number of moles of the acid in the acidic surface modification solution can be determined based on the sodium-based alkali catalyst of step 1).

[0076] Specifically, the number of moles of the acid in the acidic surface modification solution can be 0.5 to 15 equivalents, and preferably 1 to 10 equivalents, with respect to the number of moles of sodium ions in the sodium-based alkali catalyst, in terms of equivalent ratio. When the number of moles of the acid satisfies the above range, the pH can be set to a polar acid level, so that the conditions of the surface modification reaction can become an acid condition, and thus, the collapse of the gel structure occurring in a neutral to alkaline condition can be prevented, and the acidic surface modification solution can be used as a medium for facilitating the surface modification reaction.

[0077] More specifically, taking the case where trimethylethoxysilane (TMES) is used as the surface modifier as an example, when the acid aqueous solution is included in the surface modification solution, the TMES reacts with (Si 3+ )(3OH -) to proceed the surface modification. Competitively, TMES reacts with water and forms hexamethyldisiloxane (HMDSO) and ethanol, and hexamethyldisiloxane has a very stable structure, thus cannot induce the surface modification reaction with the surface of the silica gel, thereby reducing the surface modification efficiency, which can result in collapse of the gel structure due to shrinkage during the drying process. However, when the chlorine-based acid-induced aqueous solution is introduced, for example, when the aqueous hydrochloric acid solution is introduced, the reaction between TMES and the hydrochloric acid can proceed in a competitive advantage compared to the reaction between TMES and water, and through the reaction between TMES and the hydrochloric acid, trimethylchlorosilane (TMCS) can be formed. Since TMCS is an organosilane compound that can be used as a surface modifier to proceed the surface modification reaction in the same manner as TMES, the surface modification efficiency can be maximized. That is, since the formation of HMDSO and ethanol, which deteriorate the surface modification efficiency, is inhibited, and at the same time, the reaction of generating the surface modifier is performed, the surface modification efficiency can be maximized compared to when the chlorine-based acid-induced aqueous solution is not added. In this mechanism, as described above, the degree of activation can vary depending on the equivalent ratio of the acid to the base catalyst, and when the acid is introduced into the acidic surface modification solution to satisfy the above range, the effect can be maximized.

[0078] The chlorine-based acid-induced aqueous solution can specifically include a chlorine-based acid, or can generate a chlorine-based acid in the aqueous solution. For example, the chlorine-based acid-induced aqueous solution can be an aqueous solution containing hydrochloric acid, trimethylchlorosilane, dimethyldichlorosilane, methyltrichlorosilane, or the like. When a nitrogen-based acid or a sulfur-based acid that is not a chlorine-based acid is used, TMCS cannot be formed through the above-described mechanism, thus the surface modification efficiency can be reduced, and thus the degree of hydrophobicity can be reduced.

[0079] In the preparation method of the embodiment of the present application, the surface modification process of step 3) can be performed for 10 hours to 50 hours, preferably 15 hours to 50 hours, more preferably 18 hours to 48 hours, and even more preferably 24 hours to 48 hours. The performance time of the surface modification process is for obtaining an appropriate degree of hydrophobicity, and in order to achieve a thermal conductivity and a degree of hydrophobicity of the final aerogel mat higher than a predetermined level, it is preferable to perform the surface modification process within the above range.

[0080] The surface modification step can be performed in a separate reaction vessel after recovering the gelled or aged silica wet gel-fiber composite, or can be performed in the reaction vessel in which the gelation or aging has been performed. The aging and surface modification steps can preferably be performed in the reaction vessel in which the gelation or aging has been performed in terms of efficiency of the process and simplification of the equipment.

[0081] After performing the above-described surface modification step, a hydrophobic wet gel-fiber composite can be obtained.

[0082] Additional Process: Washing Process

[0083] The preparation method of the embodiment of the present application can further perform a washing step after performing the surface modification step and before performing the drying step. The washing can be used to remove impurities (sodium ions, unreacted substances, by-products, salts, etc.) generated during the reaction to obtain a hydrophobic silica aerogel of high purity.

[0084] The washing can be washing using ethanol and an aqueous acid solution or ethanol. In the surface modification process, a salt can be generated by a neutralization reaction between a sodium-based alkali catalyst for gelation and an acidic surface modification solution, and sodium ions can be easily removed by the generation of the salt. When washing by the neutralization reaction is performed with an aqueous acid solution, the effect of removing impurities can be further maximized by inducing the generation of a salt by the neutralization reaction performed in the surface modification step, in which case the degree of hydrophobicity can be further improved.

[0085] The aqueous acid solution can be the same as the aqueous acid solution contained in the acidic surface modification solution in the surface modification process, and the washing can be repeated several times. However, it is necessary to appropriately control the washing in consideration of the possibility that the hydrophobic group can be separated when the washing is repeated too many times.

[0086] Step 4: Drying Process

[0087] The hydrophobic wet gel-fiber composite, which has performed the step 3) of hydrophobization according to the embodiment of the present application, is subjected to a drying step to prepare a hydrophobic aerogel mat.

[0088] The drying step of the embodiment of the present application can be performed by a process of removing a solvent while maintaining the pore structure of the ripened gel, and the drying step can be performed by a supercritical drying process or an atmospheric pressure drying process.

[0089] The supercritical drying process can be performed using supercritical carbon dioxide. Carbon dioxide (CO2) is in a gaseous state at room temperature and atmospheric pressure. However, when the temperature and pressure exceed predetermined temperature and pressure limits called supercritical points, no evaporation process occurs, such that the carbon dioxide becomes in a critical state that cannot distinguish between a gas and a liquid. The carbon dioxide in the critical state is called supercritical carbon dioxide.

[0090] Supercritical carbon dioxide has a molecular density close to that of a liquid, but has a low viscosity, thereby having properties close to those of a gas. Accordingly, supercritical carbon dioxide has a high diffusion rate and a high thermal conductivity, such that it has a high drying efficiency, and the drying process time can be shortened.

[0091] Specifically, the supercritical drying process performs a solvent replacement process in which the ripened wet gel mat is placed in a supercritical drying reactor, then filled with liquid CO2 therein, and then the alcohol solvent within the wet gel is replaced with CO2. Thereafter, the temperature is raised to 40 to 70°C at a predetermined temperature raising rate (specifically, 0.1 to 1.0°C / min), and a pressure greater than the pressure at which carbon dioxide becomes a supercritical state (specifically, a pressure of 100 to 150 bars) is maintained for a predetermined time (specifically, 20 minutes to 1 hour). Generally, carbon dioxide becomes in a supercritical state at a temperature of 31°C and a pressure of 73.8 bars. After maintaining the carbon dioxide at the predetermined temperature and the predetermined pressure to maintain for 2 to 12 hours, more specifically, 2 to 6 hours in a supercritical state, the pressure is generally decreased, thereby completing the supercritical drying process to produce an aerogel mat.

[0092] Further, the atmospheric pressure drying process can be performed at a temperature of 70 to 200°C and atmospheric pressure (1 ± 0.3 atm) according to a general method, such as hot air drying, IR drying, and oven drying.

[0093] According to the embodiments of the present application, in the production method, the atmospheric pressure drying is preferably performed. Although the supercritical drying can be performed, in the case of the supercritical drying, a high pressure apparatus is required, and it is difficult to control various process conditions, which greatly affects an increase in product price. However, the application of the supercritical drying lies in that it is an effective method of removing a solvent without collapse of a gel structure. However, when the production method of the present application is applied, since the collapse of the gel structure can be prevented even when the atmospheric pressure drying is applied without applying the supercritical drying, an advantage lies in that the supercritical drying process requiring a high pressure apparatus is not necessary, and an effect equivalent to that of the supercritical drying can be obtained only using the atmospheric pressure drying.

[0094] As a result of the above drying process, a mat containing a porous aerogel having a nano-sized pore can be produced. In particular, the silica aerogel of the embodiments of the present application has excellent physical properties, a low tap density, and a high porosity, and particularly, a high degree of hydrophobicity, and a silica-containing aerogel mat containing the same has excellent mechanical flexibility as well as a low thermal conductivity.

[0095] Further, before or after the drying process, a compression process for controlling the thickness and making the internal structure and surface shape of the mat uniform, a molding process for having a suitable shape or form according to the use, or a lamination process for laminating separate functional layers can be further performed.

[0096] When the aerogel mat is prepared according to the above preparation method, processes such as a solvent replacement process for removing impurities and a process of exchanging with a solvent that is easily volatile can not be performed, so that the process can be easily simplified, and since the aerogel mat having sufficiently excellent physical properties can be provided without performing a washing process, which is also an additional process, the degree of freedom of the process design for process simplification can be sufficiently secured.

[0097] 3. Aerogel mat

[0098] The present application provides an aerogel mat having uniform thermal conductivity and a degree of hydrophobicity, particularly having an excellent degree of hydrophobicity. Specifically, the aerogel mat can have a short-term degree of hydrophobicity of 4.0% or less and a long-term degree of hydrophobicity of 26.0% or less, preferably a short-term degree of hydrophobicity of 3.5% or less and a long-term degree of hydrophobicity of 25.4%, more preferably a short-term degree of hydrophobicity of 2.5% and a long-term degree of hydrophobicity of 22.0% or less, even more preferably a short-term degree of hydrophobicity of 2.0% or less and a long-term degree of hydrophobicity of 20.0% or less. In addition, the ratio of the short-term degree of hydrophobicity to the long-term degree of hydrophobicity (short-term degree of hydrophobicity / long-term degree of hydrophobicity) can be 15.0% or less, preferably 13.0% or less, more preferably 12.0% or less, even more preferably 10.0% or less. Here, the short-term degree of hydrophobicity and the long-term degree of hydrophobicity are obtained by the following measurement method.

[0099] According to ASTM C1511, a sample having a size of 25.4 cm x 25.4 cm is floated on distilled water at 21±2℃, and a 6.4 mm mesh screen is placed on the sample to sink the sample to 127 mm below the water surface. After 15 minutes (short term) and 96 hours (long term), the screen is removed, and when the sample rises to the surface, the sample is picked up with a clamp. After that, the aerogel sample is taken out, and the surface water is absorbed onto a wiper with 2 seconds according to ASTM D1763. In this process, the weight of the sample before immersion and the weight of the sample after removing the surface water after immersion are measured to calculate the weight increase rate, and the average value of three samples is defined as the short-term degree of hydrophobicity and the long-term degree of hydrophobicity.

[0100] The aerogel mat of the embodiment of the present application is prepared according to the above preparation method, and thus has an excellent degree of hydrophobicity level, that is, a very low moisture impregnation rate, and since the moisture impregnation rate does not increase even when the aerogel mat is exposed to moisture for a long time, the aerogel mat can have an excellent degree of hydrophobicity, and can also have an excellent thermal conductivity.

[0101] The aerogel mat of the present application can be effectively used as a heat insulating material, a thermal insulating material, or a non-combustible material for an airplane, a ship, an automobile, a building structure, etc., and for a heat insulating and cooling plant facility, such as a pipe and an industrial furnace of various industrial facilities.

[0102] Examples

[0103] Hereinafter, the examples of the present application will be described in detail so that those skilled in the art can easily practice the present application. However, the present application can be presented in many different forms and should not be limited to the embodiments set forth herein.

[0104] Example 1

[0105] Pre-hydrolyzed TEOS (silica content = 20.1 wt%, HTEOS) and ethanol (moisture content of 8 wt%) were mixed in a reactor so that the target density was 70 kg / m3 3 To this, sodium hydroxide (NaOH) having a concentration of 33% was introduced as a sodium-based alkali catalyst so that the molar concentration of sodium ions with respect to the volume of the silica sol was 10 mmol / L to prepare a catalytic silica sol. Glass fibers (glass fiber fiber mat, 10 mm) were placed in the reactor containing the catalytic silica sol as a mat-use substrate to impregnate the silica sol on the mat-use substrate, and the reactor was left to stand for 1 hour in a sealed state to gel the impregnated silica sol to obtain a wet gel-fiber composite. Thereafter, the temperature was raised to 60°C, and then the reactor was left to stand for 24 hours to perform maturation.

[0106] Thereafter, trimethylethoxysilane was prepared into a 40 vol% solution in ethanol (moisture content of 8 wt%) to have the same volume ratio as the wet gel-fiber composite, and a 50 mmol / L aqueous hydrochloric acid solution was introduced into the solution to prepare an acidic surface modification solution so that the molar concentration of hydrochloric acid in the acidic surface modification solution was 5 equivalents based on the sodium ions of the sodium-based alkali catalyst. The acidic surface modification solution was introduced into the reactor to perform hydrophobization at 60°C for 24 hours.

[0107] Finally, oven drying was performed at 150°C and atmospheric pressure for 1 hour to prepare a silica aerogel mat.

[0108] Examples 2 to 14 and Comparative Examples 1 to 9

[0109] A silica aerogel mat was prepared in the same manner as in Example 1, except that the conditions of Example 1 were changed to the conditions listed in Table 1 below.

[0110] [Table 1]

[0111]

[0112] 1) SS: (sodium silicate), 2) Ammonia input amount: 35 mmol / L

[0113] Experimental Example

[0114] 1) Thermal conductivity at room temperature (mW / mK) and thickness (mm)

[0115] In the aerogel felts prepared in each of the examples and comparative examples, five samples each having a size of 30 cm x 30 cm were prepared for each felt. The thermal conductivity at room temperature (23 ± 5°C) was measured for each sample using an HFM 436 Lambda device of NETZSCH Co., Ltd. At this time, the aerogel felt roll manufactured in each of the examples and comparative examples was cut at a predetermined interval of 50 cm from the innermost side to the outermost side to obtain five samples. The thermal conductivity of each of the five samples was measured.

[0116] For the thermal conductivity, the heat flow of the sample placed between a hot plate and a cold plate was measured by a heat flux transducer in the device, whereby a calibration coefficient (N) can be obtained from a reference material whose thermal conductivity value is known, and the calculated value of the thermal conductivity can be obtained from the N value and the measured value of the heat flow of the sample. In this process, the thickness of the sample is also derived as a measured value.

[0117] 2) Short-term moisture impregnation rate (wt%)

[0118] The moisture impregnation rate of the silica aerogel felt prepared in each of the examples and comparative examples was measured.

[0119] Specifically, according to ASTM C1511, a sample having a size of 25.4 cm x 25.4 cm was floated on distilled water at 21 ± 2°C, and a 6.4 mm mesh screen was placed on the sample to sink the sample to 127 mm below the water surface. After 15 minutes, the screen was removed, and when the sample rose to the surface, the sample was picked up with a clamp and hung vertically for 60 ± 5 seconds. Thereafter, the weight before impregnation and the weight after impregnation were measured, respectively, and the above process was repeated for three samples of each sample to confirm the average value of the weight increase rate, which is expressed as the moisture impregnation rate when the surface water is not removed.

[0120] In addition, according to ASTM D1763, an aerogel sample was taken, and the weight was measured after the surface water was absorbed onto a paper towel with 2 seconds. The average value of the weight increase rate with respect to the weight of three samples before impregnation and after removal of the surface water after impregnation is expressed as the moisture impregnation rate when the surface water is removed. The lower the moisture impregnation rate, the higher the degree of hydrophobicity of the aerogel felt.

[0121] 3) Long-term moisture impregnation rate (wt%)

[0122] The moisture impregnation rates of the silica aerogel felts prepared in each of the examples and comparative examples were measured.

[0123] Specifically, according to ASTM C1511, a sample having a size of 25.4 cm x 25.4 cm was floated on distilled water at 21 ± 2°C, and a 6.4 mm mesh screen was placed on the sample to sink the sample to 127 mm below the water surface. After 96 hours, the screen was removed, and when the sample rose to the surface, the sample was picked up with a clamp and hung vertically for 60 ± 5 seconds. Thereafter, the weight before impregnation and the weight after impregnation were measured, respectively, and the above process was repeated for three samples for each sample to confirm the average of the weight increase rate, which was expressed as the moisture impregnation rate when the surface water was not removed.

[0124] Further, according to ASTM D1763, the aerogel sample was taken out, and the weight was measured after the surface water was absorbed onto a paper towel with 2 seconds. The weights of three samples before impregnation and after impregnation with the surface water removed were measured, and the average of the weight increase rate was expressed as the moisture impregnation rate when the surface water was removed. The lower the moisture impregnation rate, the higher the degree of hydrophobicity of the aerogel felt.

[0125] [Table 2]

[0126]

[0127] Referring to Table 2, Examples 1 to 14 had low thermal conductivity and low short-term and long-term moisture impregnation rates, and thus were confirmed to have achieved excellent effects as a thermal insulation material. On the other hand, Comparative Examples 1 to 4, which did not use hydrochloric acid, had high thermal conductivity even when the concentration of the surface modifier was changed, and thus were confirmed to be unsuitable for thermal insulation performance, and the level of short-term and long-term hydrophobicity degree was poor. In particular, since moisture penetrated into the inside of the aerogel felt, there was no significant difference even when the surface water was removed, thereby confirming that the impregnated moisture was not easily removed. In addition, Comparative Examples 5 and 6, which used an ammonia catalyst as in the prior art, had thermal conductivity and short-term hydrophobicity degree similar to those of the examples, but the long-term hydrophobicity degree was poor. Further, it was confirmed that a large amount of moisture was impregnated in the inside of the aerogel felt rather than on the surface of the aerogel felt, and thus it was confirmed that it was difficult to remove the moisture.

[0128] Further, Comparative Examples 7 and 8 were cases in which nitric acid was used instead of hydrochloric acid in the acidic surface modification solution, and it was confirmed that when nitric acid was used, the physical properties were not affected by whether an alkali catalyst of ammonia or an alkali catalyst of sodium hydroxide was used, and thus it was confirmed that there was a synergistic effect of sodium hydroxide and hydrochloric acid of the acidic surface modification solution.

Claims

1. A method for preparing an aerogel mat, the method comprising: 1) mixing a silica sol and a sodium-based alkali catalyst to obtain a catalyzed silica sol, wherein the sodium-based alkali catalyst is contained in an amount such that the pH of the silica sol is 9.0 to 11.0; 2) impregnating and gelating the catalyzed silica sol in a mat base material to obtain a wet gel-fiber composite; 3) introducing an acid surface modification solution containing a surface modifier and a chlorine-based acid-induced aqueous solution into the wet gel-fiber composite to hydrophobize the wet gel-fiber composite; and 4) drying the hydrophobized wet gel-fiber composite, wherein the chlorine-based acid-induced aqueous solution is introduced such that the number of moles of the acid in the aqueous solution is 0.5 equivalents to 15 equivalents relative to the number of moles of sodium ions in the sodium-based alkali catalyst, wherein the surface modifier is an organosilane compound diluted to 10% by volume to 50% by volume in an organic solvent, wherein the organosilane compound is one or more selected from the group consisting of hexamethyldisilazane (HMDS), methyltrimethoxysilane (MTMS), trimethylethoxysilane (TMES), ethyltriethoxysilane (ETES), and phenyltriethoxysilane (PTES), wherein the silica sol contains a silica precursor and an organic solvent, and wherein the silica precursor is a tetraalkyl orthosilicate.

2. The method of claim 1, wherein, The sodium-based alkali catalyst is an aqueous solution containing any one of sodium hydroxide and sodium silicate.

3. The method of claim 1, wherein, The catalyzed silica sol is introduced in an amount of 80% by volume to 120% by volume based on the volume of the mat base material.

4. The method of claim 1, wherein, The chlorine-based acid-induced aqueous solution is an aqueous solution containing one or more selected from the group consisting of hydrochloric acid, trimethylchlorosilane, dimethyldichlorosilane, and methyltrichlorosilane.

5. The method according to claim 1, further comprising a maturation step after step 2).

6. The method of claim 5, wherein, The maturation is performed at a temperature of 40°C to 80°C for 6 hours or more.

7. The method according to claim 1, further comprising a washing step using water or an aqueous acid solution after step 3).

8. The method of claim 1, wherein, The drying of step 4) is performed by an atmospheric pressure drying process at a pressure of 1 ± 0.3 atm and a temperature of 70°C to 200°C.

9. The method of claim 1, wherein, The mat base material is a porous base material.

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