Silica aerogel blanket manufacturing method

Abstract

The present invention relates to a method for producing silica aerogel that includes a steam drying step.

Description

[Technical Field]

[0001] This application claims the benefit of priority based on Korean Patent Application No. 10-2022-0107778, filed on August 26, 2022, and all contents disclosed in the documents of this Korean patent application are incorporated herein by reference.

[0002] The present invention relates to a method for producing a silica aerogel blanket that includes a steam drying step. [Background technology]

[0003] Aerogel is a highly porous material composed of nanoparticles that has high porosity, specific surface area, and low thermal conductivity, and is therefore attracting attention as a highly efficient thermal insulator, soundproofing material, etc. Because aerogel has very low mechanical strength due to its porous structure, aerogel composites have been developed in which aerogel is impregnated and bonded to a fibrous blanket, such as inorganic or organic fibers, which are conventional thermal insulating fibers.

[0004] For example, a silica aerogel-containing blanket using silica aerogel is manufactured through a silica sol manufacturing step, a gelling step, an aging step, a surface modification step, and a drying step. In this case, if the aging step and the surface modification step are included, a large amount of solvent is required, and there is a problem that a large amount of waste liquid generated after the manufacturing is required, which requires additional disposal costs.

[0005] In addition, the conventional manufacturing process for aerogel involves complicated process steps, takes a long time, and requires additional equipment and space for aging and surface modification, resulting in high manufacturing costs at the time of commercialization for mass production. Therefore, despite the superior thermal insulation performance compared to conventional thermal insulation materials, commercialization has been difficult.

[0006] In the field of aerogel blankets, atmospheric hot air drying (hot air drying) has typically been used. However, because hot air drying heats the drying sample from the outside to the inside, the highly volatile organic solvent evaporates before the less volatile water. As a result, as the drying process progresses, the water content in the gel pores increases, causing frequent capillary action and shrinkage, leading to problems such as destruction of the pore structure. Aerogel blankets with destroyed pore structures have relatively poor insulation performance. This problem can be exacerbated if the blanket is dried immediately without replacing the solvent with an organic solvent with a low surface tension.

[0007] In addition, the hot air drying method takes a relatively long time for the temperature of the sample to rise to the optimum drying temperature, and therefore drying is performed at a temperature lower than the optimum drying temperature. Therefore, when drying an aerogel blanket using only hot air drying, there is a problem that the drying efficiency is significantly reduced. Furthermore, there is also a risk of oil mist explosion.

[0008] Supercritical drying has been proposed as a drying method to address the low drying efficiency and poor insulation performance of hot air drying. Supercritical drying involves introducing a supercritical fluid, such as supercritical carbon dioxide, into a high-pressure reactor to displace ethanol in a wet gel blanket, and then extracting the displaced ethanol. However, supercritical drying requires a separate drying device for supercritical extraction, resulting in high initial investment costs. Furthermore, supercritical drying requires pressurization, extraction, and decompression steps, resulting in a long drying time. In particular, the extraction step of supercritical drying relies on the principle that, in the initial stage, when the solvent content is higher than that of the supercritical fluid, a liquid fluid that is not in a supercritical state dilutes and removes the solvent. Therefore, the higher the solvent content, the longer the extraction time. Furthermore, since drying is performed in a supercritical extractor, continuous drying is not possible, and only a batch process is possible. Therefore, if only the supercritical drying process is applied among the drying processes, problems may arise in that commercialization / mass production of aerogel blankets is difficult. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] Korean Patent Application Publication No. 2001-0033498 (Published on April 25, 2001) Summary of the Invention [Problem to be solved by the invention]

[0010] An object of the present invention is to provide a method for producing a silica aerogel blanket that is dried efficiently within a short period of time and has excellent heat insulation properties. [Means for solving the problem]

[0011] In order to solve the above problems, the present invention provides a method for producing a silica aerogel blanket, comprising the steps of: 1) preparing a silica sol containing a silica precursor composition; 2) impregnating a blanket substrate with the silica sol; 3) gelling the silica sol while the blanket substrate is impregnated with the silica sol to produce a silica wet gel blanket; 4) surface-modifying the silica wet gel blanket; and 5) placing the surface-modified silica wet gel blanket in a steam dryer and then drying it by supplying steam, wherein the internal temperature of the steam dryer exceeds 70°C.

[0012] (2) The present invention provides the method for producing a silica aerogel blanket according to (1) above, wherein in step 5), steam is supplied at a flow rate of 0.1 to 25 kg / h.

[0013] (3) The present invention provides the method for producing a silica aerogel blanket according to (1) or (2) above, wherein the internal temperature of the steam dryer is 80 to 250°C.

[0014] (4) The present invention provides the method for producing a silica aerogel blanket according to any one of (1) to (3) above, wherein in step 5), steam is supplied for 30 minutes to 2 hours.

[0015] (5) The present invention provides the method for producing a silica aerogel blanket according to any one of (1) to (4), wherein the blanket substrate is a film, a sheet, a net, a fiber, a porous material, a foam, a nonwoven fabric, or a laminate of two or more layers thereof.

[0016] (6) The present invention provides the method for producing a silica aerogel blanket according to any one of (1) to (5) above, wherein the silica precursor composition contains water glass.

[0017] (7) The present invention provides the method for producing a silica aerogel blanket according to (6) above, wherein the gelation is carried out using one or more acid catalysts selected from the group consisting of acetic acid, oxalic acid, nitric acid, sulfuric acid, and hydrofluoric acid.

[0018] (8) The present invention provides a method for producing a silica aerogel blanket according to (6) or (7), wherein the surface modification is performed by immersing the silica wet gel blanket in an aqueous acid mixture containing acetic acid and an acid catalyst, and then modifying the surface with an alkyldisiloxane compound.

[0019] (9) The present invention provides the method for producing a silica aerogel blanket according to any one of (1) to (8), wherein the silica precursor composition is a mixture of a silicone-containing alkoxide compound, an alcohol, and an acidic aqueous solution.

[0020] (10) In the present invention, the silicone-containing alkoxide compound is tetramethyl orthosilicate (TMOS), tetraethyl orthosilicate (TEOS), methyl triethyl orthosilicate, dimethyl diethyl orthosilicate, tetrapropyl orthosilicate, tetraisopropyl orthosilicate, tetrabutyl orthosilicate, tetra secondary butyl orthosilicate, tetra tertiary butyl orthosilicate, tetrahexyl orthosilicate, tetracyclohexyl orthosilicate, orthosilicate, and tetradodecyl orthosilicate. [Effects of the Invention]

[0021] According to the present invention, a silica aerogel blanket having high heat insulating properties can be produced while being dried efficiently within a short period of time. DETAILED DESCRIPTION OF THE INVENTION

[0022] The present invention will now be described in more detail so that the present invention may be more easily understood.

[0023] The terms and words used in the description of the present invention and the claims should not be interpreted in a limited way to their ordinary or dictionary meanings, but should be interpreted in a way that is consistent with the technical idea of ​​the present invention, based on the principle that the inventors can appropriately define the concepts of terms in order to best describe their invention.

[0024] The method for producing a silica aerogel blanket of the present invention includes the steps of: 1) preparing a silica sol containing a silica precursor composition; 2) impregnating a blanket substrate with the silica sol; 3) gelling the silica sol while the blanket substrate is impregnated with the silica sol to produce a silica wet gel blanket; 4) modifying the surface of the silica wet gel blanket; and 5) placing the surface-modified silica wet gel blanket in a steam dryer and drying it by supplying steam, wherein the internal temperature of the steam dryer is above 70°C.

[0025] Each step of the present invention will now be described in detail.

[0026] Step 1) The step 1) is a step of preparing a silica sol containing a silica precursor composition.

[0027] The silica precursor is a material that allows the aerogel to contain silica, and may be, for example, water glass or a silicone-containing alkoxide compound.

[0028] The water glass may be sodium silicate (Na2SiO3), which is an alkali silicate obtained by fusing silicon dioxide (SiO2) with an alkali. When the silica precursor is water glass, the silica precursor composition may be a water glass solution obtained by adding distilled water to water glass and mixing to dilute the water glass.

[0029] The water glass solution may contain 1 wt % to 13 wt % silicon dioxide (SiO2). If the silicon dioxide content in the water glass solution is lower than the above range, aerogel may not be sufficiently formed, and if the silicon dioxide content is higher than the above range, gelation may not proceed easily or the specific surface area may decrease.

[0030] It is not always necessary to use a water glass solution as the silica precursor, and a silicone-containing alkoxide compound can also be used. Specifically, tetramethyl orthosilicate (TMOS), tetraethyl orthosilicate (TEOS), methyl triethyl orthosilicate, dimethyl diethyl orthosilicate, tetrapropyl orthosilicate, tetraisopropyl orthosilicate, tetrabutyl orthosilicate, tetra secondary butyl orthosilicate, tetra tertiary butyl orthosilicate, tetrahexyl orthosilicate, tetracyclohexyl orthosilicate, orthosilicate), tetradodecyl orthosilicate, etc. More specifically, the silica precursor may be tetraethyl orthosilicate (TEOS).

[0031] When the silica precursor is a silicone-containing alkoxide-based compound, the silica precursor composition may be a mixture of a silicone-containing alkoxide-based compound, an alcohol, and an acidic aqueous solution.

[0032] The alcohol may be a monohydric alcohol such as methanol, ethanol, isopropanol, or butanol; or a polyhydric alcohol such as glycerol, ethylene glycol, propylene glycol, diethylene glycol, dipropylene glycol, or sorbitol, and a mixture of two or more of these may be used. Among them, in consideration of miscibility with water and aerogel, a monohydric alcohol having 1 to 6 carbon atoms such as methanol, ethanol, isopropanol, or butanol may be used.

[0033] The alcohol as described above can be used in an appropriate amount by those skilled in the art, taking into consideration the degree of hydrophobicity in the aerogel that is finally produced, and accelerating the surface modification reaction.

[0034] The acid catalyst contained in the acidic aqueous solution may specifically include one or more inorganic acids such as nitric acid, hydrochloric acid, acetic acid, sulfuric acid, and hydrofluoric acid, which may serve to hydrate the silicon-containing alkoxide-based compound.

[0035] Regardless of the type of the silica precursor, the silica precursor may be used in an amount that allows the silica content in the silica sol to be 1 to 13 wt %, but is not limited thereto. When the content of the silica precursor satisfies the above range, it is preferable in that the mechanical properties, particularly flexibility, of the silica aerogel blanket are ensured at an excellent level and the insulating effect is improved.

[0036] Step 2) The step 2) is a step of impregnating the silica sol into a blanket substrate.

[0037] The term "impregnation" as used in the present invention may mean that the flowable catalyzed sol is poured into the blanket substrate, and the catalyzed sol penetrates into the pores inside the blanket substrate.

[0038] The impregnation can be performed in a reaction vessel capable of accommodating the blanket substrate. The sol can be poured into the reaction vessel or placed in the reaction vessel containing the sol to wet the blanket substrate. At this time, to ensure good bonding between the blanket substrate and the sol, the blanket substrate can be lightly pressed to ensure sufficient impregnation. The blanket substrate can then be pressed to a certain thickness with a certain pressure to remove excess sol, thereby reducing the subsequent drying time.

[0039] According to one embodiment of the present invention, the blanket substrate may be a film, sheet, net, fiber, porous material, foam, nonwoven fabric, or a laminate of two or more layers thereof. Furthermore, depending on the intended use, the surface may be roughened or patterned. Specifically, the blanket substrate may be a fiber that can further improve insulation performance by including spaces or voids within the blanket substrate that facilitate aerogel formation, and a material with low thermal conductivity can be used.

[0040] Specifically, the blanket substrate may be, but is not limited to, polyamide, polybenzimidazole, polyaramid, acrylic resin, phenolic resin, polyester, polyether ether ketone (PEEK), polyolefin (such as polyethylene, polypropylene, or copolymers thereof), cellulose, carbon, cotton, wool, hemp, nonwoven fabric, glass fiber, or ceramic wool.

[0041] Step 3) The step 3) is a step of gelling the silica sol while the silica sol is impregnated into the blanket substrate, thereby producing a silica wet gel blanket.

[0042] In the present invention, gelation refers to the formation of a network structure from a precursor material, and the network structure may refer to a planar network structure in which certain specific polygons are connected, which have one or more types of atomic arrangement, or a structure in which the vertices, corners, faces, etc. of certain polyhedra are shared to form a three-dimensional framework.

[0043] When the silica precursor is water glass, gelation can be performed using an acid catalyst, which can be any one or more of organic acids and inorganic acids that do not contain chlorine in the molecular structure of the compound, such as one or more selected from the group consisting of acetic acid, oxalic acid, nitric acid, sulfuric acid, and hydrofluoric acid, and more specifically, acetic acid, nitric acid, sulfuric acid, or a mixture of two or more thereof.

[0044] The acid catalyst may be included in an amount that allows the pH of the silica sol to be 3 to 10. If the pH of the silica sol is outside the above range, gelation may not occur easily or the gelation rate may be too fast or slow, resulting in a decrease in processability.

[0045] When the silica precursor is a silicone-containing alkoxide-based compound, gelation can be performed using a base catalyst, which increases the pH of the silica sol to promote gelation.

[0046] The base catalyst includes, but is not limited to, inorganic bases such as sodium hydroxide, potassium hydroxide, and the like; or organic bases such as ammonium hydroxide.

[0047] Specific examples of the organic base include ammonium hydroxide (NH4OH), tetramethylammonium hydroxide (TMAH), tetraethylammonium hydroxide (TEAH), tetrapropylammonium hydroxide (TPAH), tetrabutylammonium hydroxide (TBAH), methylamine, ethylamine, isopropylamine, monoisopropylamine, 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, monopropanolamine, and dibutanolamine, and any one or a mixture of two or more of these may be used.

[0048] More specifically, in the present invention, the base may be ammonium hydroxide (NH4OH) or sodium hydroxide (NaOH).

[0049] The base catalyst may be contained in an amount that allows the pH of the silica sol to be 3 to 10. If the pH of the silica sol is outside the above range, gelation may not occur easily or the gelation rate may be excessively slow, resulting in a decrease in processability. In addition, since the base may precipitate when added in a solid state, it is preferably added in the form of a solution diluted with the alcohol (polar organic solvent).

[0050] Additional process: Aging process In the present invention, after the gelation in step 3), the prepared silica wet gel blanket may be further subjected to an aging step, which is a process for leaving the silica wet gel blanket at an appropriate temperature to complete chemical changes. The aging step can further strengthen the network structure formed above and enhance the mechanical stability of the silica aerogel blanket.

[0051] The aging step must be carried out within an appropriate temperature range to optimally strengthen the pore structure, and the aging step of the present invention may be carried out by leaving the mixture at a temperature of 30 to 70°C for 3 to 50 hours. When the aging temperature is within the above temperature range, productivity can be ensured by aging at an appropriate level and loss due to evaporation of the organic solvent can be prevented. Furthermore, the aging time within the above range is a range that satisfies the thermal conductivity and hydrophobicity, and may be preferably 6 to 48 hours, more preferably 18 to 48 hours.

[0052] According to one embodiment of the present invention, the aging step may be carried out in a separate reaction vessel after recovering the silica wet gel blanket after gelation has been completed, or may be carried out in the reaction vessel in which gelation has been carried out. From the viewpoint of process efficiency and equipment simplification, it is preferable to carry out the aging step in the reaction vessel in which gelation has been carried out.

[0053] Step 4) The step 4) is a step of surface modifying the silica wet gel blanket.

[0054] When hydrophilic functional groups on the aerogel surface are replaced with hydrophobic functional groups, the repulsive force between the hydrophobic functional groups can minimize pore shrinkage due to the surface tension of the solvent during drying. Dried aerogels maintain low thermal conductivity immediately after drying, but the hydroxyl functional groups on the aerogel surface—for example, hydrophilic silanol groups (Si-OH) on the silica surface in the case of silica aerogels—absorb water from the air, gradually increasing the thermal conductivity. Therefore, to maintain low thermal conductivity, the aerogel surface must be modified to be hydrophobic.

[0055] The surface modification of the present invention may be carried out without limitation using a compound that hydrophobizes the surface of the wet gel.

[0056] For example, the compound may be a silane-based compound, a siloxane-based compound, a silanol-based compound, a silazane-based compound, or a combination thereof.

[0057] Specifically, trimethylchlorosilane (TMCS), dimethyldimethoxysilane, dimethyldiethoxysilane, methyltrimethoxysilane, trimethylethoxysilane, vinyltrimethoxysilane, ethyltriethoxysilane, phenyltriethoxysilane, phenyltrimethoxysilane, tetraethoxysilane, dimethyldichlorosilane, 3-aminopropyl Silane compounds including methyltriethoxysilane, etc.; siloxane compounds including polydimethylsiloxane, polydiethylsiloxane, or octamethylcyclotetrasiloxane, etc.; silanol compounds including trimethylsilanol, triethylsilanol, triphenylsilanol, and t-butyldimethylsilanol, etc.; 1,2-diethyldisilazane, 1,1,2,2-tetramethyldisilazane, 1,1,3,3-tetramethyldisilazane, etc. disilazane, 1,1,1,2,2,2-hexamethyldisilazane (HMDS), 1,1,2,2-tetraethyldisilazane, or 1,2-diisopropyldisilazane; or a combination thereof, specifically, hexamethyldisilazane.

[0058] For example, when a silicone-containing alkoxide compound is used as the silica precursor, the surface modifier may be used in the form of a solution diluted with an organic solvent, and the organic solvent may be an alcohol (organic solvent). In this case, the surface modifier may be diluted to 1 to 15% by volume based on the volume of the total diluted solution.

[0059] The surface modifier may be added in an amount of 0.01 to 10% by volume based on the silica wet gel blanket. When the amount is within this range, the amount of the surface modifier is sufficient to provide excellent surface modification reactivity and facilitate surface modification, thereby suppressing condensation reactions of unmodified silanol groups during drying and ensuring superior porosity in the resulting silica aerogel blanket.

[0060] The step 4) may be carried out by adding the surface modifier at a temperature of 50 to 90°C, preferably 50 to 80°C, for 1 to 24 hours.

[0061] For example, when water glass is used as the silica precursor, toluene may be added to the wet gel before the surface modification in step 4. When toluene is added, the toluene may be added after the addition of the aqueous acid mixture to the wet gel and before the addition of the alkyldisiloxane compound, or the toluene may be added simultaneously with the aqueous acid mixture and the alkyldisiloxane compound.

[0062] When toluene is further added in step 4), the toluene can be included in the hydrophobic organic solution layer. When sulfuric acid is used as the acid catalyst, adding the toluene causes the reaction between sulfuric acid and toluene to form p-toluenesulfonic acid, which acts as a catalyst to activate the surface modification reaction by the alkyldisiloxane compound, thereby achieving a superior surface modification reaction rate.

[0063] The concentration (w / w%) of the acid catalyst after step 4) refers to the concentration of the acid catalyst contained in the aqueous acid mixture layer after step 4), and can be expressed by the following mathematical formula 2. The concentration of the acid catalyst can be calculated by measuring the weight of the water in the aqueous acid mixture layer after step 4) and then measuring the weight of the acid catalyst in the aqueous acid mixture layer by gas chromatography (GC).

[0064] [Mathematical formula 2] Acid catalyst concentration (w / w%) = weight of acid catalyst / (weight of acid catalyst + total weight of water in the acid mixture aqueous solution layer) × 100

[0065] As described above, when the immersion process in the acid mixture aqueous solution is completed, the acid concentration inside the wet gel and the acid concentration outside the wet gel are in equilibrium. Therefore, by measuring the acid concentration in the acid mixture aqueous solution layer after the immersion, the acid concentration inside the wet gel can be determined, and thus the acid concentration involved in the surface modification can be determined.

[0066] The water contained in the acid mixture aqueous solution layer after step 4) may be any of the water contained in the acetic acid aqueous solution and the acid catalyst, the water contained in the wet gel, and the water resulting from the hydrophobization reaction of the hydrophilic wet gel that remains after step 4), and the total weight of these water is the total weight of water in the acid mixture aqueous solution layer.

[0067] Step 4) may be performed by sequentially immersing the wet gel in an aqueous solution of an acid mixture and then modifying the surface with the alkyldisiloxane compound.

[0068] In the method for manufacturing a silica aerogel blanket according to one embodiment of the present invention, when the wet gel is immersed in the acid mixture aqueous solution in step 4), an acid mixture aqueous solution containing acetic acid and an acid catalyst is used, and the acetic acid fills a certain volume relative to the wet gel. After step 4), it is confirmed whether the concentration of acetic acid satisfies the aforementioned value, thereby enabling the wet gel, particularly the hydrogel manufactured using a water glass solution, to be quickly and sufficiently surface-modified effectively.

[0069] The alkyldisiloxane compound may be added in a volume ratio of 1 to 3 times, specifically 1 to 2.5 times, more specifically 1 to 2 times, based on the volume of the wet gel.

[0070] The alkyldisiloxane compound should be added in a volume equal to or greater than the volume of the wet gel to modify the wet gel and perform solvent substitution for the wet gel. Increasing the amount of alkyldisiloxane compound added requires increasing the size of the equipment. Therefore, the alkyldisiloxane compound may be added in the above range based on the volume of the wet gel.

[0071] The alkyldisiloxane compound may be a hexaalkyldisiloxane compound, specifically, hexa(C 1-8 The alkyl disiloxane may be, more specifically, hexamethyl disiloxane.

[0072] The surface modification reaction may be carried out at a temperature of 25° C. to 95° C. In addition, a stirring step may be performed during the process of immersing the wet gel in the aqueous acid mixture solution and the process of surface modifying the wet gel with the alkoxydisiloxane compound.

[0073] At this time, the stirring speed is not particularly limited, but may be, for example, 50 rpm to 700 rpm.

[0074] Furthermore, step 4) according to one embodiment of the present invention may be carried out for 2 to 24 hours, and is preferably carried out for 4 to 22 hours or 8 to 20 hours in order to maintain a good level of surface modification effect and improve the economic efficiency of the process.

[0075] In the manufacturing method according to one embodiment of the present invention, when step 4) is performed by sequentially immersing the wet gel in an acid mixture aqueous solution and then surface-modifying the wet gel with the alkyldisiloxane compound, the immersion in the acid mixture aqueous solution may be performed for 30 minutes to 4 hours, specifically 30 minutes to 3 hours, and more specifically 1 hour to 3 hours, and the surface-modification with the alkyldisiloxane compound may be performed for 1 hour 30 minutes to 20 hours, specifically 3 hours to 19 hours, and more specifically 6 hours to 18 hours.

[0076] In the present invention, when the silica precursor is water glass, the surface modification can be performed using a surface modifier containing an organosilane compound, and when the silica precursor is a silicone-containing alkoxide-based compound, the surface modification can be performed using a polar solvent and a surface modifier containing an organosilane compound.

[0077] The polar solvent may be methanol, ethanol, or isopropyl alcohol, and the organosilane compound may be trimethylchlorosilane (TMCS), hexamethyldisilazane (HMDS), methyltrimethoxysilane (MTMS), trimethylethoxysilane (TMES), ethyltriethoxysilane (ETES), or phenyltriethoxysilane (PTES), preferably trimethylethoxysilane or hexamethyldisilazane.

[0078] In the surface modification, the polar solvent is preferably mixed at a volume ratio of 0.5 to 10.0 relative to the wet gel, and the organosilane compound is preferably mixed at a volume ratio of 0.1 to 10.0 relative to the wet gel, and the surface modifier containing the organosilane compound and polar solvent may be mixed at a volume ratio of 0.5 to 10.0 relative to the wet gel. If the volume ratio of the organosilane compound to the wet gel is less than 0.1, the reaction time may be too long, reducing the efficiency of surface modification. If the volume ratio of the organosilane compound to the wet gel is more than 10.0, there is a problem of rising costs and the unreacted surface modifier may cause shrinkage during drying.

[0079] The organic silane compound and the polar solvent may be mixed in this volume ratio, and the mixed surface modifier may contain the organic silane compound in an amount of 10 to 60 volume % relative to the total volume of the surface modifier. The content of the organic silane compound in the surface modifier can affect the degree of hydrophobicity and thermal conductivity, and a higher content can improve these properties, but if the content exceeds 60 volume %, there is no further increase in the surface modification efficiency and only an increase in the amount of waste organic silane compound, so the amount must be appropriately adjusted within the above range.

[0080] In a manufacturing method according to one embodiment of the present invention, the surface modification step may be carried out for 10 to 50 hours, preferably 15 to 50 hours, more preferably 18 to 48 hours, and even more preferably 24 to 48 hours. The duration of the surface modification step is for obtaining an appropriate degree of hydrophobicity, and it is preferable to carry out the step within the above range in order to achieve a certain level of thermal conductivity and hydrophobicity of the final aerogel blanket.

[0081] The surface modification step may be carried out in a separate reaction vessel after recovering the silica wet gel-fiber composite after gelation or aging has been completed, or may be carried out in the reaction vessel in which gelation or aging was carried out. From the viewpoint of process efficiency and equipment simplification, it is preferable to carry out the aging and surface modification steps in the reaction vessel in which gelation or aging was carried out.

[0082] After the surface modification step, a hydrophobic wet gel-fiber composite can be obtained.

[0083] Step 5) Step 5) is a step of placing the surface-modified silica wet gel blanket in a steam dryer and then drying it by supplying steam, and at this time, the internal temperature of the steam dryer exceeds 70°C.

[0084] The atmospheric drying process has the advantage of being simple and economical since it does not require high-pressure reaction conditions or special high-pressure equipment for supercritical drying, but it may cause problems such as a rapid decline in thermal insulation performance due to the collapse of the internal pore structure of the gel caused by evaporation of water or organic solvent at high temperatures, as compared to supercritical drying, and there is also a safety issue of the risk of oil mist explosion.

[0085] On the other hand, supercritical drying has the disadvantage of being performed under high pressure conditions, which requires high costs, and vacuum drying may cause a problem of deterioration in the physical properties of the aerogel blanket due to a drop in internal temperature during drying.

[0086] In the present invention, by introducing the steam drying method as a method for drying the silica wet gel blanket, shrinkage of the aerogel that occurs during drying is suppressed, heat insulation is improved, the drying time is shortened, and the necessary equipment and conditions are simplified, thereby improving the economic efficiency of drying. Furthermore, as mentioned above, the problems that occur when using other drying methods do not occur.

[0087] In the present invention, the steam dryer can be used regardless of its shape or name, but in order to fully achieve the object of the present invention of drying the silica wet gel blanket, it is necessary for the steam dryer to function to heat and maintain the temperature so that the steam does not condense within the steam dryer, and to be able to withstand the steam pressure and weak negative pressure.

[0088] In the present invention, the steam may be supplied at a flow rate of 0.1 to 25 kg / h, and specifically, the flow rate may be 5 to 25 kg / h, or 15 to 25 kg / h.

[0089] When the steam supply flow rate is within the above range, the heat transfer effect of the steam is excellent, resulting in excellent drying efficiency, improving the physical properties of the aerogel blanket, preventing a decrease in economic efficiency due to the use of more steam than necessary, and suppressing a decrease in the physical properties of the aerogel due to the induction of a condensation reaction by residues.

[0090] In the present invention, the internal temperature of the steam dryer exceeds 70°C. More specifically, it may be 80 to 250°C, 80 to 200°C, or 80 to 120°C.

[0091] When the internal temperature of the steam dryer is within the above range, it is possible to prevent steam condensation due to an excessively low temperature, which would hinder heat transfer, and to prevent the problem of difficulty in reducing energy costs due to the difference in physical properties between the inside and outside of the aerogel blanket caused by high temperatures due to ambient heat.

[0092] In the present invention, the specific method of applying steam is not limited as long as it is capable of transferring heat to the silica wet gel blanket, and for example, the direction, speed, and total amount of steam sprayed inside the steam dryer are not limited.

[0093] In the present invention, the drying time for adding steam may vary depending on the size of the silica wet gel blanket, but may be, for example, 30 minutes to 2 hours.

[0094] In particular, the effect of the drying method of the present invention can be further maximized when a water glass solution is used as a silica precursor in preparing the silica sol.

[0095] When water glass is used as the silica precursor, the surface modifier remains as a solvent in the silica wet gel after surface modification. However, since the surface modifier is hydrophobic and immiscible with water, the recovered surface modifier (solvent) and the condensed steam can be easily separated even after drying. As a result, the costly surface modifier can be easily recovered and reused, which can improve economic efficiency. This has the advantage of facilitating the recovery of the final product, the silica aerogel blanket.

[0096] Meanwhile, in the method for manufacturing an aerogel blanket according to an embodiment of the present invention, a washing step may be further performed before the drying step. The washing is for removing impurities and residual ammonia generated during the reaction to obtain a highly pure hydrophobic aerogel, and may be performed by a dilution process or an exchange process using an organic solvent.

[0097] Furthermore, according to one embodiment of the present invention, the method for manufacturing an aerogel blanket may specifically be a method for manufacturing a silica aerogel blanket, and the aerogel blanket manufactured by the method may be a silica aerogel blanket.

[0098] [Example] The present invention will be described in more detail below with reference to examples. However, the following examples are for illustrative purposes only and are not intended to limit the scope of the present invention.

[0099] Example 1 33.8 g of water glass was diluted with 108.1 g of water to prepare a water glass solution, to which 7.8 g of acetic acid (97%) was added to prepare a silica sol. The silica sol was impregnated into glass fibers, and the mixture was left for 10 minutes to obtain a glass fiber composite impregnated with the wet gel.

[0100] An acid mixture solution prepared by mixing 140 g of acetic acid (≥ 97%) and 15 g of 70% (w / w%) nitric acid aqueous solution was poured onto the glass fiber impregnated with the wet gel and immersed in an oven at 60°C for 2 hours, followed by adding 160 g of hexamethyldisiloxane (HMDSO) and maintaining the temperature in an oven at 75°C for 16 hours to carry out a surface modification reaction. In this case, the acetic acid was used in an amount of 1 L based on 1 L of the volume of the wet gel, and the hexamethyldisiloxane was used in an amount of 1.5 L based on 1 L of the volume of the wet gel.

[0101] Then, the surface-modified silica wet gel blanket was placed in a steam dryer, and steam was continuously injected to dry it (internal temperature of the steam dryer: 90°C, steam flow rate: 20 kg / h, time: 30 minutes).

[0102] Example 2 Tetraethyl orthosilicate (TEOS) and aqueous ethanol were mixed in a weight ratio of 3:1 to prepare a mixed solution. To the mixed solution, a hydrochloric acid solution diluted with water (concentration = 0.15 wt%) was added so that the pH of the mixed solution became 1, and then aqueous ethanol was further added to prepare a silica sol (silica content 4 wt%).

[0103] Next, a base catalyst was added to the silica sol at 0.5% by volume to initiate the gelation reaction, and glass fibers were deposited to produce a silica wet gel composite. A surface modifier solution prepared by mixing hexamethyldisilazane and ethanol in a volume ratio of 1:19 was added to the wet gel at 90% by volume, and the surface was modified at 70°C for 4 hours to produce a hydrophobic silica wet gel blanket.

[0104] Then, the surface-modified silica wet gel blanket was placed in a steam dryer, and steam was continuously injected to dry it (internal temperature of the steam dryer: 90°C, steam flow rate: 20 kg / h, time: 30 minutes).

[0105] Example 3 A silica aerogel blanket was produced in the same manner as in Example 1, except that the drying conditions were controlled to an internal temperature of the steam dryer of 150°C, a steam flow rate of 20 kg / h, and a drying time of 30 minutes.

[0106] Example 4 A silica aerogel blanket was produced in the same manner as in Example 1, except that the drying conditions were controlled to an internal temperature of the steam dryer of 90°C, a steam flow rate of 25 kg / h, and a drying time of 30 minutes.

[0107] Example 5 A silica aerogel blanket was produced in the same manner as in Example 1, except that the drying conditions were controlled to an internal temperature of the steam dryer of 90°C, a steam flow rate of 20 kg / h, and a drying time of 60 minutes.

[0108] Example 6 A silica aerogel blanket was produced in the same manner as in Example 1, except that the drying conditions were controlled to an internal temperature of the steam dryer of 200°C, a steam flow rate of 20 kg / h, and a drying time of 30 minutes.

[0109] Example 7 A silica aerogel blanket was produced in the same manner as in Example 1, except that the drying conditions were controlled to an internal temperature of the steam dryer of 90°C, a steam flow rate of 10 kg / h, and a drying time of 30 minutes.

[0110] Comparative Example 1 The silica wet gel blanket produced in the same manner as in Example 1 was placed in a convection oven and dried at 150°C for 90 minutes under normal pressure to completely remove the solvent and water, thereby producing a silica aerogel blanket.

[0111] Comparative Example 2 A silica wet gel blanket produced in the same manner as in Example 1 was vacuum-dried in a vacuum oven at 150° C. for 90 minutes to produce a silica aerogel blanket.

[0112] Comparative Example 3 The silica wet gel blanket produced in the same manner as in Example 1 was placed in a supercritical extractor, carbon dioxide was injected, the temperature inside the extractor was raised to 50°C over 1 hour, and supercritical drying was performed at 50°C and 100 bar to produce a silica aerogel blanket.

[0113] Comparative Example 4 A silica aerogel blanket was produced in the same manner as in Example 1, except that the drying conditions were controlled to an internal temperature of the steam dryer of 70°C, a steam flow rate of 20 kg / h, and a drying time of 30 minutes.

[0114] Experimental Example 1 Five samples measuring 15 cm x 15 cm were prepared from each of the silica aerogel blankets manufactured in each example and comparative example, and the thermal conductivity of the samples was measured at room temperature (23±5°C) using a NETZSCH HFM 436 Lambda instrument.

[0115] The thermal conductivity is measured by a heat flux transducer placed between a hot plate and a cold plate, which measures the heat flow of the sample. This allows a calibration factor (N) to be obtained from a reference material with known thermal conductivity. The calculated thermal conductivity can then be calculated from this N value and the measured heat flow of the sample. During this process, the thickness of the sample is also measured.

[0116] [Table 1]

[0117] As shown in Table 1, Examples 1 to 7, which were dried according to the present invention, were confirmed to have undergone drying without shrinkage and exhibited excellent heat insulating properties. Furthermore, the drying time required to achieve these properties was short. On the other hand, Comparative Examples 1 and 2 required a much longer time to complete drying at the level of the Examples, indicating that the drying time was longer than that of steam drying. Comparative Example 3, which was subjected to supercritical drying, was confirmed to have required a drying time eight times longer to achieve properties similar to those of the Examples.

[0118] In addition, in Comparative Example 4, shrinkage occurred during drying due to the thinner thickness, and the insulation performance was also found to be lower than in Examples. This was found to be because the steam drying temperature was low, causing steam to condense on the inner wall surface of the steam dryer and the surface of the blanket, preventing the steam from fully functioning as a heat transfer medium, resulting in the formation of water droplets on the surface of the blanket, slowing down the drying process or causing shrinkage.

Claims

1. 1) providing a silica sol comprising a silica precursor composition; 2) impregnating a blanket substrate with the silica sol; 3) gelling the silica sol while the silica sol is impregnated into a blanket substrate to produce a silica wet gel blanket; 4) surface modifying the silica wet gel blanket; 5) placing the surface-modified silica wet gel blanket in a steam dryer and then supplying steam to dry it; The method for producing a silica aerogel blanket, wherein the internal temperature of the steam dryer is greater than 70°C.

2. 2. The method for producing a silica aerogel blanket according to claim 1, wherein in step 5), the steam is supplied at a flow rate of 0.1 kg / h or more and 25 kg / h or less.

3. 2. The method for producing a silica aerogel blanket according to claim 1, wherein the internal temperature of the steam dryer is 80°C or higher and 250°C or lower.

4. 2. The method for producing a silica aerogel blanket according to claim 1, wherein in step 5), steam is supplied for 30 minutes or more and 2 hours or less.

5. 2. The method for producing a silica aerogel blanket according to claim 1, wherein the blanket substrate is a film, a sheet, a net, a fiber, a porous body, a foam, a nonwoven fabric, or a laminate of two or more layers thereof.

6. 10. The method for producing a silica aerogel blanket according to claim 1, wherein the silica precursor composition comprises water glass.

7. 7. The method for producing a silica aerogel blanket according to claim 6, wherein the gelation is carried out using one or more acid catalysts selected from the group consisting of acetic acid, oxalic acid, nitric acid, sulfuric acid, and hydrofluoric acid.

8. 7. The method for producing a silica aerogel blanket according to claim 6, wherein the surface modification is performed by immersing the silica wet gel blanket in an acid mixture aqueous solution containing acetic acid and an acid catalyst, and then modifying the surface with an alkyldisiloxane compound.

9. The method for producing a silica aerogel blanket according to any one of claims 1 to 8, wherein the silica precursor composition is a mixture of a silicone-containing alkoxide compound, an alcohol, and an acidic aqueous solution.

10. The silicone-containing alkoxide-based compound includes tetramethyl orthosilicate (TMOS), tetraethyl orthosilicate (TEOS), methyl triethyl orthosilicate, dimethyl diethyl orthosilicate, tetrapropyl orthosilicate, tetraisopropyl orthosilicate, and tetrabutyl orthosilicate. orthosilicate), tetra secondary butyl orthosilicate, tetra tertiary butyl orthosilicate, tetrahexyl orthosilicate, tetracyclohexyl orthosilicate, and tetradodecyl orthosilicate.

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