Method for producing hydrophobic silica aerogel blanket and silica aerogel blanket

Abstract

The present invention relates to a method for producing a silica aerogel blanket that has excellent surface modification efficiency, is free of residual chlorine, and has high hydrophobicity, and to the silica aerogel blanket free of residual chlorine produced thereby.

Description

[Technical Field]

[0001] The present invention claims the benefit of priority based on Korean Patent Application No. 10-2022-0091299, filed on July 22, 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 has excellent surface modification efficiency, is free of residual chlorine, and has high hydrophobicity, and to the silica aerogel blanket free of residual chlorine produced thereby. [Background technology]

[0003] Aerogel is a super-porous material with a high specific surface area (≥ 500 m) with a porosity of 90% to 99.9% and a pore size ranging from 1 nm to 100 nm. 2 / g) material, which has excellent properties such as ultra-lightweight, super heat insulation, and ultra-low dielectric constant. For this reason, in addition to research and development of aerogel materials, active research is also being conducted on their applications as transparent heat insulation materials, environmentally friendly high-temperature heat insulation materials, ultra-low dielectric thin films for highly integrated devices, catalysts and catalyst supports, electrodes for supercapacitors, and electrode materials for seawater desalination.

[0004] The greatest advantage of aerogel is that it has super-insulation properties, exhibiting thermal conductivity of 0.300 W / m·K or less, which is lower than that of conventional organic insulation materials such as Styrofoam, and that it can solve the fatal weaknesses of organic insulation materials, such as vulnerability to fire and the generation of toxic gases during a fire.

[0005] However, despite its excellent material properties, aerogel is used only in very limited applications due to its complex manufacturing process and high manufacturing cost. Furthermore, its high porosity means that its mechanical strength is very weak, making it susceptible to even small impacts. Therefore, in recent years, research has been conducted into aerogel blanket composite technology that can overcome these drawbacks of aerogel itself and enable it to be processed into various shapes.

[0006] Aerogel blankets are made by combining aerogel materials and forming them into mattresses or sheets. They are flexible and can be bent, folded, and cut. They can be used in a variety of industrial applications, including pipe insulation and clothing. Their flexibility is possible because aerogel blankets are composites made of fiber and aerogel. The fiber enhances the aerogel blanket's flexibility and mechanical strength, while the aerogel provides insulating properties through its porosity. The core composite technology of aerogel blankets is the combination of the characteristics of fiber and aerogel, leveraging each other's advantages and complementing their shortcomings.

[0007] Such aerogel blankets are new materials with superior heat resistance and insulation properties compared to conventional polymer insulation materials such as polytyrofoam and polyurethane foam, and are attracting attention as advanced materials that can solve energy conservation and environmental problems that will emerge in the future.

[0008] Silica aerogel blankets are manufactured by mixing fibers with silica sol derived from water glass or alkoxide precursors, gelling the mixture, and then aging, surface-modifying, and drying. The surface modification is performed by adding a hydrophobizing agent and an acid catalyst after the silica sol is impregnated into the fibers. Because the hydrophobizing agent is immiscible with water and unreactive with wet gels, especially hydrogels made from water glass, solvent substitution with an amphipathic organic solvent such as ethanol has been used. Alternatively, a hydrophobizing agent such as trimethylchlorosilane (TMCS) has been used, generating HCl as a catalyst. However, solvent substitution with an amphipathic organic solvent takes a long time and generates a large amount of diluted organic solvent. Using TMCS as a hydrophobizing agent results in the generation of HCl, which remains in the final silica aerogel blanket.

[0009] Residual chlorine in silica aerogel blankets can cause corrosion, so there is a need to develop a method for producing highly hydrophobic silica aerogel blankets that has excellent surface modification efficiency and does not generate residual chlorine. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] US5,789,075B Summary of the Invention [Problem to be solved by the invention]

[0011] The problem to be solved by the present invention is to provide a method for producing a silica aerogel blanket that has excellent surface modification efficiency, does not contain residual chlorine, and therefore eliminates corrosion problems that may occur when the silica aerogel blanket is used, and exhibits excellent stability. Another problem to be solved by the present invention is to provide a chlorine-free silica aerogel blanket. [Means for solving the problem]

[0012] In order to solve the above problems, the present invention provides a method for producing a silica aerogel blanket and a silica aerogel blanket. [1] The present invention provides a method for producing a silica aerogel blanket, comprising the steps of: 1) preparing a silica sol containing a water glass solution; 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 wet gel; 4) immersing the wet gel in an acid mixture aqueous solution containing an aqueous solution of acetic acid and nitric acid to surface-modify the wet gel with an alkyldisiloxane compound; and 5) drying the surface-modified wet gel, wherein the acetic acid concentration (w / w) after step 4) is 30% to 90% and the nitric acid concentration (w / w) is 5% to 10%.

[0013] [2] The present invention provides the method for producing a silica aerogel blanket according to [1] above, wherein the acetic acid concentration (w / w) is 35% to 80%.

[0014] [3] The present invention provides the method for producing a silica aerogel blanket according to [1] or [2] above, wherein the nitric acid concentration (w / w) is 5% to 10%.

[0015] [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 4), a process of immersing the wet gel in an acid mixture aqueous solution is carried out, and then a process of surface modification with the alkyldisiloxane compound is carried out sequentially.

[0016] [5] The present invention provides the method for producing a silica aerogel blanket according to any one of [1] to [4] above, wherein in step 4), the acid mixture aqueous solution and the alkyldisiloxane compound are sequentially added to the wet gel, or the acid mixture aqueous solution and the alkyldisiloxane compound are simultaneously added to the wet gel.

[0017] [6] The present invention provides the method for producing a silica aerogel blanket according to any one of [1] to [5] above, wherein in step 4), the alkyldisiloxane compound is added in a volume ratio of 1 to 3 times the volume of the wet gel.

[0018] [7] In the present invention, the alkyldisiloxane compound is hexa(C 1-8 The present invention provides a method for producing a silica aerogel blanket according to any one of the above items [1] to [6], wherein the silica aerogel blanket is a (alkyl)disiloxane.

[0019] [8] The present invention provides a method for producing a silica aerogel blanket according to any one of [1] to [7] above, wherein the method for producing a silica aerogel blanket is carried out under chlorine-free (Cl-free) conditions.

[0020] [9] The present invention provides a silica aerogel blanket having a thermal conductivity of 12 mW / mK to 19 mW / mK and a Cl content of 0 ppm to 500 ppm.

[0021]

[10] The present invention provides the silica aerogel blanket according to [9], wherein the silica aerogel blanket has a Cl content of 0 ppm to 200 ppm. [Effects of the Invention]

[0022] The method for producing hydrophobic silica aerogel according to the present invention can produce a silica aerogel blanket that is highly hydrophobic, has excellent surface modification efficiency, and is free of residual chlorine. Therefore, the method can be usefully applied to industries that require such a silica aerogel, particularly industries that require silica aerogel with high hydrophobicity, or industries that require silica aerogels with various ranges of hydrophobicity as described above. DETAILED DESCRIPTION OF THE INVENTION

[0023] The present invention will now be described in more detail so that the present invention may be more easily understood. The terms and words used in this specification and 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 explain their inventions.

[0024] Generally, silica wet gels prepared using water glass have pores filled with water, which is a solvent. When the solvent is simply removed by drying, the liquid solvent evaporates into a gas phase, and the high surface tension of water at the gas / liquid interface causes shrinkage and cracking of the pore structure, resulting in a decrease in surface area and a change in the pore structure. Therefore, in order to maintain the pore structure of the wet gel, it is necessary to replace the water, which has a high surface tension, with an organic solvent, which has a relatively low surface tension. In addition, a technology is needed to wash and dry the wet gel without shrinkage while maintaining the structure of the wet gel.

[0025] In addition, although dried silica aerogel maintains low thermal conductivity immediately after drying, it has the drawback of gradually increasing its thermal conductivity as it absorbs water from the air due to the hydrophilic nature of the silanol groups (Si-OH) on the silica surface.

[0026] Therefore, to prevent the shrinkage and cracking of the pore structure caused by the high surface tension of water at the gas / liquid interface during drying of silica wet gel, and to reduce the water absorption rate of the dried silica aerogel and maintain its low thermal conductivity, it is necessary to modify the silica aerogel surface to make it hydrophobic. Therefore, a method of modifying the silica aerogel surface to make it hydrophobic using a surface modifier is widely used.

[0027] To modify the wet gel to be hydrophobic, one or more surface modifiers selected from the group consisting of trimethylchlorosilane (TMCS), hexamethyldisilazane (HMDS), dimethyldiethoxysiloxane (DMDES), hexamethyldisiloxane (HMDSO), and trimethylethoxysilane (TMES) are typically used.

[0028] Among the surface modifiers, hexamethyldisilazane (HMDS), dimethyldiethoxysiloxane (DMDES), hexamethyldisiloxane (HMDSO), and trimethylethoxysilane (TMES) are used because they are immiscible with water and unreactive with wet gels, particularly hydrogels made by gelling water glass. Therefore, they are preferentially converted into an organogel by solvent substitution using an amphiphilic organic solvent such as ethanol, and then reacted with the surface modifier to modify the surface with hydrophobic groups. However, this method has drawbacks, such as the long time required for solvent substitution required to convert the hydrogel into an organogel and the production of a large amount of diluted organic solvent.

[0029] Furthermore, when trimethylchlorosilane (TMCS) is used among the surface modifiers, it is reactive with wet gels or hydrogels, eliminating the solvent substitution process, but it has the drawback that any remaining trimethylchlorosilane after surface modification is converted to hexamethyldisiloxane (HMDSO) and inactivated. Therefore, to solve the drawbacks of using trimethylchlorosilane (TMCS) alone, a method was developed in which a small proportion of trimethylchlorosilane (TMCS) is mixed with hexamethyldisiloxane (HMDSO) and the HCl generated from trimethylchlorosilane is used as a catalyst to convert the inactive species hexamethyldisiloxane into trimethylchlorosilane, thereby modifying the surface.

[0030] However, in both the method using trimethylchlorosilane and the method using a mixture of hexamethyldisiloxane (HMDSO) and trimethylchlorosilane, trimethylchlorosilane generates HCl after the surface modification reaction as shown in the following reaction formula 1. This means that some chlorine remains in the final silica aerogel blanket, which can lead to corrosion (corrosion under insulation, CUI).

[0031] Meanwhile, instead of mixing trimethylchlorosilane with hexamethyldisiloxane (HMDSO), another method is to add HCl as a catalyst to hexamethyldisiloxane. In this method, the hexamethyldisiloxane fills the pores and converts the hydrogel into an organic gel, while also modifying the surface. However, some of the added chlorine remains in the final silica aerogel blanket.

[0032] [ka]

[0033] In contrast, the method for producing a silica aerogel blanket of the present invention does not use a compound containing chlorine (Cl) during the production process, so the final hydrophobic silica aerogel blanket produced does not contain residual chlorine.

[0034] The method for producing a silica aerogel blanket of the present invention includes the steps of: 1) preparing a silica sol containing a water glass solution; 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 wet gel; 4) immersing the wet gel in an acid mixture aqueous solution containing an aqueous solution of acetic acid and nitric acid to surface-modify the wet gel with an alkyldisiloxane compound; and 5) drying the surface-modified wet gel, wherein the acetic acid concentration (w / w) after step 4) is 30% to 90% and the nitric acid concentration (w / w) is 5% to 10%.

[0035] The method for producing a silica aerogel blanket of the present invention uses acetic acid, an amphiphilic substance that can dissolve in both water and the alkyldisiloxane compound used as a surface modifier, and nitric acid, which can promote the protonation of the alkyldisiloxane compound. The amounts of acetic acid and nitric acid used are adjusted so that the concentration of acetic acid and nitric acid [weight (w) / weight (w)] after the surface modification in step 4) satisfies a certain value. This method achieves an excellent surface modification rate and prevents residual chlorine from being contained in the final silica aerogel blanket.

[0036] 1) Preparing a silica sol containing a water glass solution The silica sol in step 1) can be produced by mixing a water glass solution as a silica precursor with an acid catalyst.

[0037] The acid catalyst in the silica sol may be contained in a molar ratio of 1 to 3 relative to the water glass in the water glass solution. The water glass solution may be a diluted solution obtained by adding distilled water to water glass, and the water glass may be sodium silicate (Na2SiO3), which is an alkali silicate obtained by dissolving silicon dioxide (SiO2) and an alkali.

[0038] The water glass dispersion may contain 1% by weight to 13% by weight of silicon dioxide (SiO2). If the silicon dioxide content in the water glass dispersion is lower than the above range, aerogel is not sufficiently formed, and if the silicon dioxide content is higher than the above range, gelation may not occur easily or the specific surface area may decrease.

[0039] The acid catalyst may be one or more organic acids and inorganic acids that do not contain chlorine in the molecular structure of the compound, in order to eliminate chlorine from the silica aerogel blanket that is finally produced. For example, the acid catalyst may be one or more selected from the group consisting of acetic acid, oxalic acid, nitric acid, sulfuric acid, and hydrofluoric acid. Specifically, considering the acid mixture aqueous solution used in the surface modification of step 4), nitric acid, acetic acid, or a mixture thereof may be used.

[0040] The acid 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, the gelation in step 3) may not be easy or the gelation rate may be too fast or slow, which may result in a decrease in processability.

[0041] 2) Impregnating the blanket substrate with silica sol The step 2) is a step of impregnating the silica sol into a blanket substrate.

[0042] The blanket substrate according to an embodiment of the present invention may be a porous substrate to improve the thermal insulation of the silica aerogel blanket. When a porous blanket substrate is used, the silica sol can easily penetrate into the substrate, and aerogel can be uniformly formed within the blanket substrate, resulting in a silica aerogel blanket with excellent thermal insulation.

[0043] The blanket substrate usable in accordance with one embodiment of the present invention may be a film, sheet, net, fiber, foam, nonwoven fabric, or a laminate of two or more of these layers. Furthermore, depending on the intended use, the surface may be roughened or patterned. More specifically, the blanket substrate may be a fiber that includes spaces or voids within the blanket substrate that facilitate the insertion of silica aerogel, thereby further improving the insulation performance. Furthermore, the blanket substrate preferably has low thermal conductivity.

[0044] Specifically, the blanket substrate may be polyamide, polybenzimidazole, polyaramid, acrylic resin, phenolic resin, polyester, polyether ether ketone (PEEK), polyolefin (e.g., polyethylene, polypropylene, or copolymers thereof), cellulose, carbon, cotton, wool, hemp, nonwoven fabric, glass fiber, ceramic wool, or the like. More specifically, the blanket substrate in the present invention may be glass fiber.

[0045] According to one embodiment of the present invention, impregnation may be performed by pouring silica sol into a reaction vessel containing the blanket substrate or by wetting the blanket substrate with silica sol. In this case, the blanket substrate may be lightly pressed to enhance the bond between the blanket substrate and the silica sol, allowing for sufficient impregnation. The blanket substrate may then be pressed to a predetermined thickness with a certain pressure to remove excess silica sol, thereby shortening the drying time.

[0046] 3) A step of gelling the silica sol while the silica sol is impregnated into the blanket substrate to produce a wet gel Step 3) is a step for producing a hydrophobic silica wet gel blanket, and the wet gel blanket can be produced by leaving the silica sol impregnated in the blanket substrate to gel.

[0047] Here, the gelation may be a sol-gel reaction, and the "sol-gel reaction" may be a reaction that causes a network structure to be formed from silicon unit precursor materials.

[0048] Here, the network structure may refer to a planar network structure in which certain polygons having one or more types of atomic arrangements are connected, or a structure in which vertices, corners, faces, etc. of certain polyhedra are shared to form a three-dimensional skeletal structure.

[0049] In the method according to one embodiment of the present invention, after the gelation in step 3), a step of aging the produced silica wet gel blanket may be further carried out. The aging is not particularly limited, and may be carried out by leaving the mixture at a temperature of from room temperature (25° C.) to 90° C. for 1 hour to 24 hours, for example.

[0050] In the manufacturing method according to an embodiment of the present invention, the silica wet gel blanket is aged after being manufactured, thereby forming a more solid network structure of the wet gel in the silica wet gel blanket, thereby providing excellent pore characteristics.

[0051] 4) A step of immersing the wet gel in an aqueous solution of an acid mixture containing an aqueous solution of acetic acid and nitric acid, and surface-modifying the wet gel with an alkyldisiloxane compound. Step 4) is a process of immersing the wet gel in an aqueous acid mixture containing an aqueous solution of acetic acid and nitric acid, and modifying the surface with an alkyldisiloxane compound to form a hydrophobic silica wet gel blanket.

[0052] In one embodiment of the present invention, the acid mixture aqueous solution may be added to the wet gel, and after the wet gel is immersed in the acid mixture aqueous solution, the alkyldisiloxane compound may be added to the wet gel. In another embodiment of the present invention, the acid mixture aqueous solution and the alkyldisiloxane compound may be added to the wet gel simultaneously.

[0053] Regardless of the time of addition, the aqueous acid mixture and the alkyldisiloxane compound added to the wet gel will undergo layer separation into an upper alkyldisiloxane compound layer and a lower acid mixture layer, with the aqueous acid mixture containing water, which has a higher density than the alkyldisiloxane compound, located at the bottom. Even when the aqueous acid mixture and the alkyldisiloxane compound are both added to the wet gel, the hydrophobic alkyldisiloxane compound and the aqueous acid mixture containing water will separate into layers, and the wet gel containing water will be located in the aqueous acid mixture layer and will be immersed in the aqueous acid mixture.

[0054] During the immersion of the wet gel in the acid mixture aqueous solution, the acid mixture aqueous solution diffuses into the wet gel, and the moisture present in the wet gel moves out of the wet gel to the acid mixture aqueous solution layer. Thus, when the immersion in the acid mixture aqueous solution is completed, the acid concentration inside the wet gel and the acid concentration of the acid mixture aqueous solution outside the wet gel can be equilibrated.

[0055] The amphiphilic substance acetic acid contained in the aqueous acid mixture allows a small amount of the alkyldisiloxane compound to dissolve in the aqueous acid mixture at the interface between the alkyldisiloxane compound layer and the aqueous acid mixture layer, allowing the alkyldisiloxane compound to modify the surface of the wet gel. During the surface modification of the wet gel, the aqueous solution that filled the wet gel is replaced with the alkyldisiloxane compound, filling the wet gel with the alkyldisiloxane compound, and the aqueous solution moves out of the wet gel and into the aqueous acid mixture layer. Upon completion of the immersion and surface modification processes, the acid concentration inside the wet gel and the acid concentration outside the wet gel reach equilibrium.

[0056] Since the wet gel contains water, it is initially located in the acid mixture aqueous solution layer. As the surface is modified, the wet gel becomes filled with the alkyldisiloxane compound, and the wet gel gradually rises and moves to the alkyldisiloxane compound layer.

[0057] In one embodiment of the present invention, when hexamethyldisiloxane is used as the alkyldisiloxane compound in step 4), a reaction as shown in Reaction Scheme 2 below can be carried out.

[0058] [ka]

[0059] The acetic acid concentration (w / w) after step 4) refers to the concentration of acetic acid contained in the aqueous acid mixture layer after step 4), and can be expressed by the following formula 1. The acetic acid concentration can be calculated by measuring the weight of water in the aqueous acid mixture layer after step 4) and measuring the weight of the acetic acid in the aqueous acid mixture layer by gas chromatography (GC). The weight of water in the aqueous acid mixture layer can be measured using a Karl Fischer moisture meter (Si Analytics Titro Line 7000).

[0060] [Formula 1] Acetic acid concentration (w / w) = weight of acetic acid in the aqueous acid mixture layer / (weight of acetic acid in the aqueous acid mixture layer + total weight of water in the aqueous acid mixture layer) × 100

[0061] Furthermore, the concentration of nitric acid (w / w) after step 4) refers to the concentration of nitric acid contained in the aqueous acid mixture layer after step 4), and can be expressed by the following formula 2. The concentration of nitric acid can be calculated by measuring the weight of water in the aqueous acid mixture layer after step 4) and using the weight of nitric acid in the aqueous acid mixture layer, where the amount of nitric acid after step 4) is the same as the amount of nitric acid added during the preparation of the aqueous acid mixture.

[0062] [Formula 2] Nitric acid concentration (w / w) = weight of nitric acid added / (weight of nitric acid added + total weight of water in the acid mixture aqueous solution layer) × 100

[0063] 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, when the acid concentration of the acid mixture aqueous solution layer after the immersion is measured, the acid concentration inside the wet gel can be determined, and thus the acid concentration involved in the surface modification can be determined.

[0064] After step 4), the water contained in the acid mixture aqueous solution layer may be any of the water contained in the acetic acid aqueous solution and the nitric acid aqueous solution, 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 may be the total weight of water in the acid mixture aqueous solution layer.

[0065] Step 4) may be performed by sequentially immersing the wet gel in an aqueous acid mixture solution and then modifying the surface with the alkyldisiloxane compound.

[0066] After step 4), the acetic acid concentration (w / w) may be 30% to 90%, specifically 35% to 80%, 36% to 80%, or more specifically 36% to 78%. When acetic acid is used in an amount that results in a 30% to 90% acetic acid concentration after step 4), the acetic acid can effectively contact the hydrophilic wet gel and the hydrophobic alkyldisiloxane compound, resulting in a smooth surface modification reaction. If the acetic acid concentration (w / w) is too low, the hydrophilic wet gel and the hydrophobic alkyldisiloxane compound do not react, resulting in a smooth surface modification reaction. Furthermore, if the acetic acid concentration is too high, more acetic acid than necessary must be added, which can reduce economic efficiency.

[0067] Furthermore, after step 4), the nitric acid concentration (w / w) may be 5% to 10%, specifically 5% to 9%, 5% to 8%, 5.5% to 8%, 5.5% to 7.5%, or more specifically 5.5% to 7.3%. When the nitric acid concentration is within the above range, protonation of the alkyldisiloxane compound is effectively promoted, resulting in an excellent surface modification reaction rate. If the nitric acid concentration is too low, the surface modification reaction rate decreases, the surface modification reaction by the alkyldisiloxane compound is insufficient, and the hydrophobicity of the wet gel decreases, which may result in an increase in the thermal conductivity of the final silica aerogel blanket. Furthermore, if the nitric acid concentration is too high, the oxidizing power of nitric acid increases, which may form dangerous by-products by reaction with acetic acid, thereby reducing stability.

[0068] In the method for manufacturing a silica aerogel blanket according to one embodiment of the present invention, in step 4), when the wet gel is immersed in the acid mixture aqueous solution, the weight ratio of acetic acid and nitric acid in the acid mixture aqueous solution is set to the above-mentioned range, and after step 4), it is confirmed whether the concentrations of acetic acid and nitric acid satisfy the above-mentioned values. This allows the wet gel, particularly the hydrogel manufactured using the water glass solution, to be quickly, sufficiently, and effectively surface-modified.

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

[0070] The alkyldisiloxane compound should be added at a volume ratio of at least 1:1 based on the volume of the wet gel to modify the wet gel and perform solvent substitution of the wet gel. Increasing the amount of alkyldisiloxane compound added requires an increase in the size of the equipment. Therefore, the alkyldisiloxane compound can 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 It may be a (alkyl)disiloxane, and more specifically, it may be hexamethyldisiloxane.

[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 step of immersing the wet gel in the aqueous acid mixture solution and the step of surface modifying the wet gel with the alkoxydisiloxane compound. At this time, the stirring speed is not particularly limited, but may be, for example, 50 rpm to 700 rpm.

[0073] Furthermore, step 4) according to one embodiment of the present invention may be carried out for 2 to 24 hours, and preferably for 4 to 22 hours or 8 to 20 hours in terms of maintaining an excellent level of surface modification effect and improving the economic efficiency of the process.

[0074] 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.

[0075] 5) Drying the surface-modified wet gel Step 5) is a step of drying the hydrophobic silica wet gel blanket to produce a hydrophobic silica aerogel blanket.

[0076] In this case, a washing step may be further performed before the drying step to remove impurities (sodium ions, unreacted materials, by-products, etc.) generated during the reaction to obtain a high-purity hydrophobic silica aerogel blanket. The washing step may be performed by adding a non-polar organic solvent to the hydrophobic silica wet gel and stirring for 20 minutes to 1 hour, but is not limited thereto.

[0077] The drying may be performed by methods such as atmospheric drying and supercritical drying, but is not limited to these. For example, atmospheric drying is a method of drying at atmospheric pressure for 1 to 12 hours at a temperature of 100 to 190°C, and supercritical drying is a method using CO2 in a supercritical state. Atmospheric drying has the advantage of being relatively simple and economical, while supercritical drying has the advantage of being able to effectively remove fluid from inside the gel.

[0078] The method for manufacturing a hydrophobic silica aerogel blanket according to one embodiment of the present invention can significantly improve the efficiency of surface modification, thereby providing excellent physical properties such as excellent porosity and high hydrophobicity, thereby ensuring excellent thermal insulation performance. In particular, the method for manufacturing a silica aerogel blanket according to one embodiment of the present invention performs hydrophobization of the aerogel under chlorine-free (Cl-free) conditions, so that the final silica aerogel blanket does not contain chlorine or contains minimal chlorine, thereby eliminating the possibility of chlorine causing corrosion of the silica aerogel blanket application site.

[0079] The silica aerogel blanket according to one embodiment of the present invention has a thermal conductivity of 12 mW / mK to 19 mW / mK and a Cl content of 0 ppm to 500 ppm.

[0080] Specifically, the thermal conductivity of the silica aerogel blanket according to one embodiment of the present invention may be 12 mW / mK or more, 13 mW / mK or more, 14 mW / mK or more, 15 mW / mK or more, 16 mW / mK to 19 mW / mK or less, 18.5 mW / mK or less, or 18.3 mW / mK or less.

[0081] The silica aerogel blanket according to one embodiment of the present invention does not contain Cl derived from the aerogel, but may contain a small amount of Cl derived from the silica aerogel blanket base material. Specifically, the Cl content of the silica aerogel blanket according to one embodiment of the present invention may be 0 ppm to 500 ppm, ppm to 400 ppm, 0 ppm to 300 ppm, or 0 ppm to 200 ppm.

[0082] The silica aerogel blanket produced by the method according to one embodiment of the present invention can be used in a variety of applications, including thermal insulation, including applications requiring thermal insulation at temperatures below 650°C. For example, it can be used as insulation for pipes such as double-casing pipes, insulation for aircraft and their components, insulation for buildings, insulation for spacecraft, insulation for automobiles, insulation for clothing, insulation for footwear, etc. The aerogel blanket can be used in the same manner as when an aerogel mat or multiple aerogels are used.

[0083] The present invention will be described in more detail below with reference to examples and experimental examples. However, the following examples and experimental examples are intended to illustrate the present invention and are not intended to limit the scope of the present invention.

[0084] [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 then left for 10 minutes to obtain a glass fiber composite impregnated with the wet gel.

[0085] An acid mixture aqueous 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 while maintaining the temperature. Then, hexamethyldisiloxane (HMDSO, 160 g) was added, and a surface modification reaction was carried out in an oven at 75°C for 16 hours while maintaining the temperature.

[0086] The produced hydrophobic silica wet gel blanket was collected and then completely dried in a forced circulation oven at 150°C for 4 hours to produce a hydrophobic silica aerogel blanket.

[0087] [Example 2] A hydrophobic silica aerogel blanket was prepared in the same manner as in Example 1, except that the content of acetic acid (≧97%) was changed to 185 g when preparing the acid mixture aqueous solution, and a dilute nitric acid aqueous solution prepared by mixing 20 g of 70% (w / w) nitric acid aqueous solution with 95 g of water was used instead of the 70% (w / w) nitric acid aqueous solution.

[0088] [Example 3] A hydrophobic silica aerogel blanket was prepared in the same manner as in Example 1, except that the content of acetic acid (≧97%) was changed to 280 g when preparing the acid mixture aqueous solution, and a dilute nitric acid aqueous solution prepared by mixing 30 g of 70% (w / w) nitric acid aqueous solution with 142 g of water was used instead of the 70% (w / w) nitric acid aqueous solution.

[0089] [Example 4] A hydrophobic silica aerogel blanket was prepared in the same manner as in Example 1, except that the content of acetic acid (≧97%) in the acid mixture aqueous solution was changed to 80 g.

[0090] [Example 5] A hydrophobic silica aerogel blanket was prepared in the same manner as in Example 1, except that the content of acetic acid (≧97%) in the acid mixture aqueous solution was changed to 500 g.

[0091] [Comparative Example 1] A hydrophobic silica aerogel blanket was manufactured in the same manner as in Example 1, except that 140 g of 35 wt % hydrochloric acid was used instead of the aqueous acid mixture of acetic acid and nitric acid.

[0092] Comparative Example 2 A hydrophobic silica aerogel blanket was prepared in the same manner as in Example 1, except that 140 g of acetic acid (≧97%) was used instead of the aqueous acid mixture of acetic acid and nitric acid.

[0093] Comparative Example 3 A hydrophobic silica aerogel blanket was prepared in the same manner as in Example 1, except that 140 g of a 70% (w / w) aqueous solution of nitric acid was used instead of the aqueous acid mixture of acetic acid and nitric acid.

[0094] Comparative Example 4 A hydrophobic silica aerogel blanket was prepared in the same manner as in Example 1, except that a dilute aqueous nitric acid solution prepared by mixing 15 g of a 70% (w / w) aqueous nitric acid solution with 71.3 g of water was used together with 140 g of acetic acid (≧97%) in place of the 70% (w / w) aqueous nitric acid solution in Example 1.

[0095] Comparative Example 5 A hydrophobic silica aerogel blanket was prepared in the same manner as in Example 1, except that a dilute aqueous nitric acid solution prepared by mixing 20 g of a 70% (w / w) aqueous nitric acid solution with 100 g of water was used together with 70 g of acetic acid (≧97%) instead of the 70% (w / w) aqueous nitric acid solution in Example 1.

[0096] Comparative Example 6 A hydrophobic silica aerogel blanket was prepared in the same manner as in Example 1, except that the amount of 70% (w / w) nitric acid aqueous solution used in preparing the acid mixture aqueous solution was changed to 30 g. The amounts of components added during the surface modification reaction in Examples 1 to 5 and Comparative Examples 1 to 6 are shown in Table 1 below.

[0097] [Table 1]

[0098] [Experimental Example] 1) Acetic acid concentration after immersion For each of Examples 1 to 5 and Comparative Examples 1 to 6, the weight of water in the aqueous acid mixture solution after acid immersion was measured using a Karl Fischer moisture meter (Si Analytics Titro Line 7000). The amount of acetic acid in the aqueous acid mixture after acid immersion was obtained using gas chromatography (GC) analysis.

[0099] -Column: AT-1000 -Gas flow rate: Column (He) 4mL / min -Oven temperature: Initial Value & Time 40℃, 5 minutes -Injector temperature: 250℃ -Detector temperature: 270℃ Acetic acid concentration after acid immersion = weight of acetic acid / (weight of acetic acid + weight of water) x 100

[0100] 2) Nitric acid concentration after acid immersion For each of Examples 1 to 5 and Comparative Examples 1 to 6, the weight of water in the aqueous acid mixture solution after acid immersion was measured using a Karl Fischer moisture meter (Si Analytics Titro Line 7000).

[0101] Since the amount of nitric acid in the acid mixture aqueous solution after acid immersion was the same as the amount of nitric acid initially added, the nitric acid concentration was calculated using the weight of nitric acid initially added as the weight of nitric acid in the acid mixture aqueous solution. Nitric acid concentration after acid immersion = weight of nitric acid added / (weight of nitric acid added + weight of water)

[0102] 3) Measurement of thermal conductivity (mW / mK) The thermal conductivity of each of the silica aerogel blankets produced in Examples 1 to 5 and Comparative Examples 1 to 6 was measured at room temperature (about 23° C.) using an HFM 436 device manufactured by NETZSCH.

[0103] 4) Measurement of residual Cl The amount of residual Cl in each of the silica aerogel blankets prepared in Examples 1 to 5 and Comparative Examples 1 to 6 was measured using a combustion ion chromatography (combustion IC) system (AQF-2100H, ICS-3000, Thermo Fisher Scientific).

[0104] [Table 2]

[0105] In Examples 1 to 5, silica aerogel blankets were produced using an acid mixture aqueous solution containing an aqueous solution of acetic acid and nitric acid, and the acid mixture aqueous solution layer after acid immersion had an acetic acid concentration (w / w) of 30% to 90% and a nitric acid concentration (w / w) of 5 to 10%, and it was confirmed that silica aerogel blankets with low thermal conductivity were produced.

[0106] In Comparative Example 1, hydrochloric acid (HCl) was used as the acid, and 5,000 ppm or more of Cl was detected in the produced silica aerogel blanket, and the thermal conductivity also showed a relatively slightly higher value than in Examples 1 to 3.

[0107] Comparative Example 2 was an example in which only acetic acid was used without nitric acid, and it was confirmed that the surface modification rate was slow, resulting in an increase in thermal conductivity and a decrease in physical properties. Comparative Example 3 was an example in which only nitric acid was used without acetic acid, and because acetic acid, an amphipathic solvent, was not used, the reaction between hexamethyldisiloxane and the wet gel did not occur, and no surface modification occurred at all, resulting in high thermal conductivity.

[0108] In addition, Comparative Example 4 is an example in which the nitric acid concentration in the acid mixture aqueous solution layer after acid immersion is less than 5%, and Comparative Example 5 is an example in which the acetic acid concentration in the acid mixture aqueous solution layer after acid immersion is less than 30%. In each case, the amounts of nitric acid and acetic acid used in the acid mixture aqueous solution were insufficient compared to the appropriate amounts, and the produced silica aerogel blankets exhibited high thermal conductivity, confirming that their physical properties were degraded.

[0109] On the other hand, in Comparative Example 6, both acetic acid and nitric acid were used, but the nitric acid concentration in the acid mixture aqueous solution layer after acid immersion was 10% or more. The amount of nitric acid used exceeded the appropriate amount, causing a side reaction between acetic acid and nitric acid, and preventing the reaction for surface modification of the wet gel.

Claims

1. 1) preparing a silica sol containing a water glass solution; 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 wet gel; 4) immersing the wet gel in an aqueous acid mixture containing an aqueous solution of acetic acid and nitric acid, and surface-modifying the wet gel with an alkyldisiloxane compound; 5) drying the surface-modified wet gel; Including, After step 4), the concentration (w / w) of acetic acid is 30% or more and 90% or less, and the concentration (w / w) of nitric acid is 5% or more and 10% or less.

2. 2. The method for producing a silica aerogel blanket according to claim 1, wherein the acetic acid concentration (w / w) is 35% or more and 80% or less.

3. 2. The method for producing a silica aerogel blanket according to claim 1, wherein the nitric acid concentration (w / w) is 5.5% or more and 8% or less.

4. 2. The method for manufacturing a silica aerogel blanket according to claim 1, wherein in step 4), the wet gel is immersed in an acid mixture aqueous solution and then surface-modified with the alkyldisiloxane compound.

5. 2. The method for producing a silica aerogel blanket according to claim 1, wherein in step 4), the acid mixture aqueous solution and the alkyldisiloxane compound are sequentially added to the wet gel, or the acid mixture aqueous solution and the alkyldisiloxane compound are simultaneously added to the wet gel.

6. 2. The method for producing a silica aerogel blanket according to claim 1, wherein in step 4), the alkyldisiloxane compound is added in a volume ratio of 1 to 3 times the volume of the wet gel.

7. The alkyldisiloxane compound is hexa(C １－８ 2. The method for producing a silica aerogel blanket according to claim 1, wherein the silica aerogel is a (alkyl)disiloxane.

8. The method for producing a silica aerogel blanket according to any one of claims 1 to 7, wherein the method is carried out under chlorine-free (Cl-free) conditions.

9. The thermal conductivity is 12 mW / mK or more and 19 mW / mK or less, A silica aerogel blanket having a chlorine (Cl) content of 0 ppm to 500 ppm.

10. 10. The silica aerogel blanket of claim 9, wherein the silica aerogel blanket has a chlorine (Cl) content of 0 ppm to 200 ppm.

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