WO2008051029A1

WO2008051029A1 - Aerogel sheet and method for preparing thereof

Info

Publication number: WO2008051029A1
Application number: PCT/KR2007/005279
Authority: WO
Inventors: Gyung-Soo Kim; Hyun-Aee Chun; Hyun-Chul Choi; Dae Young Lim; Sung Won Byun; Yeon Sang Kim
Original assignee: Korea Institute Of Industrial Technology
Priority date: 2006-10-25
Filing date: 2007-10-25
Publication date: 2008-05-02
Also published as: KR101105436B1; WO2008051029A9; KR20090078357A

Abstract

Disclosed herein are a flexible aerogel sheet and a preparation method therefore via a dry process. The aerogel sheet includes a needle-punched non-woven fabric, and aerogel particles charged in the fabric. The preparation method includes: scattering aerogel particles in a needle- punched non-woven fabric web; preliminary needle punching the non- woven fabric web; main needle punching the preliminary needle-punched non- woven fabric web; and laminating the main needle -punched non- woven fabric web by thermal treating surfaces thereof. With the use of needle punching, the aerogel particles can be charged in voids in the non- woven fabric, and upper and lower non- woven fabric webs can be firmly attached to each other by bridged fibers, without a binder. Also, the needle punching provides the aerogel sheet with pressure -resistance and load-resistance and prevents deformation of the aerogel sheet due to damage to the aerogel particles. The aerogel sheet having no binder has no risk of clogging in aerogel pores, resulting in superior thermal-insulation property.

Description

AEROGEL SHEET AND METHOD FOR PREPARING

THEREOF

Technical Field

[1] The present invention relates to an aerogel sheet and a method for preparing the same, and more specifically, to an aerogel sheet using a needle-punched non-woven fabric, and a method for preparing the aerogel sheet via a dry process.

[2]

Background Art

[3] With recent trends toward high-technology, aerogel has increasingly attracted considerable attention. Aerogel is a transparent or translucent ultra low-density advanced- material that has a porosity of 90% or more, a specific surface area of hundreds to 1500 m /g, and an ultra- low density. Nano-porous aerogel is widely applicable to fields including catalysts, catalyst carriers, soundproof materials, etc. In particular, since silica aerogel has a very low thermal conductivity, it is a super- insulating material capable of being very efficiently used in refrigerators, automobiles, aircrafts, clothes, cryogenic storage tanks, industrial pipe lines, thermos bottles, etc.

[4]

[5] However, aerogel has been conventionally prepared in the form of mono-lithic aerogel, and thus, has a high brittleness. Therefore, aerogel has a very low strength and tends to be easily broken even by a slight shock. Furthermore, aerogel is difficult to be processed to have various thicknesses and shapes. Therefore, in spite of its excellent thermal-insulation property, it is very difficult to use aerogel alone for preparation of thermal-insulating materials. Accordingly, to solve these problems, various attempts have been tried to prepare thermal-insulating materials by use of composites including aerogel and other materials.

[6]

[7] For example, FIG. 1 illustrates the most widely used method for improving the brittleness of aerogel. As shown in FIG. 1, in the known method by a wet process, after impregnating fibers or fiber web with an aerogel precursor solution, gelation and supercritical drying are conducted, to prepare a flexible aerogel sheet.

[8] Other various methods for preparing an aerogel sheet by a wet process also have been proposed. For example, U.S. Patent No. 5,789,075 (Hoechst AG.) discloses a mat- shaped composite in which aerogel fragments, enclosed by cracks having an average volume of 0.001mm to lcm , are supported together by fibers.

[9] [10] WO 02/052086 (Aspen Aerogels Inc.) discloses a composite prepared with a reaction of aerogel using polyester under acid conditions and 5O⁰C. U.S. Patent No. 6,068,882 (Aspen Aerogels Inc.) discloses a thermal-insulating material prepared by impregnating a fiber matrix with an aerogel forming precursor and supercritically drying the resulting material under pressure. WO 93/06044 (Battle Memorial Institute) and WO 97/17308 (Aspen Aerogels Inc.) also disclose the preparation of an aerogel composite via a wet process.

[H]

[12] Considering again the preparation of a conventional aerogel sheet by a wet process, as shown in FIG. 1, after wet gel is prepared by impregnating fibers or fiber web with a sol-state aerogel precursor solution and proceeding gelation within the fiber web, the wet gel is supercritically dried, so as to prepare an aerogel-fiber composite.

[13]

[14] Such a kind of flexible aerogel sheet prepared by a wet process was commercialized by Aspen Aerogels Inc. in United States of America. All currently commercialized flexible aerogel sheets have been prepared by a wet process.

[15] However, in the above described conventional aerogel sheet preparation method by an in-situ wet process using an aerogel precursor, due to the fact that processes required for the preparation of an aerogel sheet, such as gelation and supercritical drying, are performed in fibers or fiber web, there are problems, for example, many difficulties in process, and consequently, a considerable increase in production price. Specifically, to prepare a flexible aerogel sheet, an aerogel-fiber composite, which is bulky due to fibers added therein, has to be subjected to supercritical drying, and this inevitably results in an increase in the scale of processing equipment, more particularly, supercritical drying equipment, and consequently, an increase in the manufacturing costs of the aerogel sheet.

[16]

[17] As known, supercritical drying equipment requires a high pressure of approximately

100 atm. even when using carbon dioxide that is known as the most mild process solvent. Therefore, in addition to the basically high price thereof, the processing equipment may have a considerable increase in price if the volume of an object to be dried is increased due to the resulting aerogel-fiber composite, or if the amount and size of a sample to be dried are increased for an improvement in productivity. Further, to utilize the prepared aerogel sheet as a thermal-insulating material, generally, it is necessary to perform a hydrophobic treatment for hydrophilic aerogel. The hydrophobic treatment is performed via a reaction of wet gel and organic silane compound, prior to drying. However, when wet gel is impregnated in fibers or fiber web, the hydrophobic reaction efficiency of wet gel may be reduced considerably due to the existence of fibers or fiber web, thus inevitably causing an increase of process costs and a degradation in the performance of products due to a reduced hy- drophobicity. Furthermore, there is a problem in that a supercritical drying time required for the preparation of an aerogel sheet is disadvantageously increased. In the case of a flexible aerogel sheet, wet gel impregnated in fibers has to be dried, and this causes an increase in a drying time, as compared to the case of drying only the wet gel. Consequently, the aerogel sheet for use as a thermal-insulating material may suffer from an increase in price, and such an increased price becomes a factor of limiting the application range of aerogel sheet products.

[18]

[19] To overcome the above described problems, such as a difficulty in a wet process and high manufacturing costs, methods by a dry process have been developed. As one example, referring to FIG. 2 illustrating a conventional known method for preparing an aerogel sheet by a dry process, thermoplastic resin is mainly used as a binder to held aerogel particles, so as to prepare an aerogel composite in the form of a sheet or film. In this case, examples of the binder include a thermoplastic resin such as polyvinyl- butyral, aqueous acrylic polymer, low melting-point fiber, etc. In a representative conventional method for preparing an aerogel sheet by a dry process, aerogel particles or beads are first mixed with thermoplastic resin as a binder, and then, heat is applied to the resulting mixture so as to melt the thermoplastic resin, thereby preparing an aerogel-polymer composite.

[20]

[21] Other various aerogel sheet preparation methods by a dry process also have been proposed. For example, WO 97/10188 (Hoechst AG.) discloses a method in which aerogel granules, 8% by weight of poly vinyl-butyral (Mowital®), and 2% by weight of high-strength fibers are mixed between release papers by using the polyvinyl-butyral as a thermoplastic resin binder, and then, the resulting aerogel-fiber composite is molded at a temperature of 22O⁰C for 30 minutes, to prepare an aerogel sheet having a thickness of 18mm.

[22]

[23] WO 98/32602 and WO 98/32709 (Cabot Inc.) disclose the preparation of an aerogel composite in which thermoplastic resin such as polyvinyl-butyral is used as a binder. In these cases, aerogel is first mixed with polyvinyl-butyral and then, the resulting mixture is uniformly spread over compressed polyethylene-terepthalate (PET) (or polyvinyl-butyral). Thereafter, additional PET (or polyvinyl butyral) is scattered over the mixture, followed by compression, to mold an aerogel composite.

[24]

[25] U.S. 2003/0215640 discloses a composite preparation method in which an aqueous acrylic binder is added to aerogel, and U.S. 2005/0143515 discloses a composite preparation method in which a thermoplastic resin binder such as poly- tetra-fluoro-ethylene (PTFE) is added to aerogel.

[26]

[27] U.S. Patent No. 5,786,059 (Hoechst AG.) and WO 97/23675 (Cabot Inc.) disclose a composite material including at least one fiber web layer and aerogel particles. Here, the fiber web layer is made of bi-component fibers having a low melting point region and a high melting point region, the low melting point region serving as a binder. Accordingly, the fibers are able to be bound with one another, in addition to being bound with the aerogel particles, by virtue of their low melting point region, thereby preparing a composite material.

[28]

[29] U.S. Patent No. 6,887,563 (Cabot Inc.) discloses a composite preparation method in which aerogel particles, a binder, and a fiber material are mixed with one another, and the resulting mixture is molded and solidified, thereby preparing an aerogel-fiber composite.

[30]

[31] In the conventional method for preparing an aerogel composite by a dry process, aerogel particles or beads are previously prepared and then, subjected to a post- treatment for preparation of the aerogel composite. This has the effect of achieving more simplified preparation process and reduced production price as compared to the conventional method by a wet process. Furthermore, separating the preparation of aerogel particles from the preparation of aerogel composite has many advantages of, for example, enabling the use of low-price water glass. In conclusion, the preparation of an aerogel composite by a dry process is far more free than the aerogel composite preparation by a wet process, in selection of materials and processes, and enables the design of flexible sheet products having different thicknesses and shapes.

[32]

[33] However, due to the use of thermoplastic resin as a binder, most of conventional aerogel composite preparation methods by a dry process have a problem in that nano- pores of aerogel may be clogged by the thermoplastic resin during fusion of the aerogel particles, resulting in a degradation in the thermal-insulation property of the aerogel composite. Moreover, when using the aerogel-binder composite as shown in FIG. 2, the greater the amount of aerogel particles for the purpose of improving the thermal- insulation property of the composite, the smaller the amount of the binder. This results in a considerable degradation in the formability of the composite, thereby making the forming of a sheet impossible, or seriously deteriorating the mechanical strength of the formed sheet. Also, when using a liquid-phase binder as disclosed in U.S. 2003/0215640, aerogel particles, which have a large surface area, act to absorb a great amount of binder, and this makes it impossible to increase the charge rate of aerogel particles.

[34]

Disclosure of Invention Technical Problem

[35] In attempts to solve the problems of the prior art, it is one object of the present invention to provide an aerogel sheet which can maintain the nano-porosity of aerogel, and achieve superior thermal-insulation and load-resistance properties by virtue of a high charge rate of aerogel.

[36] It is another object of the present invention to provide an aerogel sheet in which upper and lower non- woven fabric layers are firmly attached to each other, the shape and thickness of the aerogel sheet being adjustable.

[37] It is a further object of the present invention to provide a non-woven fabric sheet which contains aerogel therein without using a binder.

[38] It is a still further object of the present invention to provide a method for preparing an aerogel sheet which can maintain the nano-porosity of aerogel, and achieve superior thermal-insulation and load-resistance properties by virtue of a high charge rate of aerogel.

[39] It is still another object of the present invention to provide a method for preparing an aerogel sheet in which upper and lower non- woven fabric layers are firmly attached to each other, the shape and thickness of the aerogel sheet being adjustable.

[40] It is yet another object of the present invention to provide a method for preparing a non- woven fabric sheet which contains aerogel therein without using a binder.

[41]

Technical Solution

[42] In accordance with one aspect of the present invention, there is provided an aerogel sheet comprising: needle-punched non- woven fabric; and aerogel particles charged in the needle-punched non-woven fabric.

[43] In accordance with another aspect of the present invention, there is provided a method for preparing an aerogel sheet comprising: scattering aerogel particles in a needle-punched non- woven fabric web; preliminary needle punching the non- woven fabric web in which the aerogel particles were scattered; main needle punching the preliminary needle-punched non- woven fabric web; and laminating the main needle- punched non- woven fabric web by thermal treating surfaces thereof.

[44]

[45] In accordance with yet another aspect of the present invention, there is provided a method for preparing an aerogel sheet comprising: scattering aerogel particles in a first needle-punched non-woven fabric web; stacking a second non- woven fabric web over the aerogel particles scattered in the first non- woven fabric web; preliminary needle punching the stacked non- woven fabric webs; main needle punching the preliminary needle-punched non- woven fabric webs; and laminating the main needle-punched non- woven fabric webs by thermal treating surfaces thereof. [46]

Advantageous Effects

[47] A flexible aerogel sheet according to the present invention has the following several effects.

[48] Firstly, as a result of preparing the aerogel sheet without using a separate binder, the aerogel sheet has no risk of a degradation in the nano porosity of aerogel, and consequently, can achieve superior thermal-insulation property.

[49] Secondly, since aerogel particles are previously prepared, and then, charged into a non- woven fabric at a normal temperature and normal pressure, the preparation of the aerogel sheet according to the present invention has no need for a long process time and expensive supercritical drying process that have been required in a conventional method for preparing aerogel in fibers or fiber web by a wet process, resulting in a simplified overall process and reduced production costs.

[50] Thirdly, since the aerogel particles are charged into voids by a needle punching process in the aerogel sheet, the aerogel sheet prepared according to the present invention can prevent leakage of the aerogel particles therefrom without using a separate binder.

[51] Fourthly, when upper and lower non- woven fabric layers are stacked in two layers, fibers of the two fabric layers can be bridged by the needle punching process, thereby allowing the upper and lower non- woven fabric layers to be firmly attached to each other without using a separate binder.

[52] Fifthly, the needle punching process also has the effect of providing the aerogel sheet with desired pressure-resistance and load-resistance, thereby preventing damage to the aerogel particles and consequently, deformation of the aerogel sheet.

[53]

Brief Description of the Drawings

[54] The above and other objects, features and other advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which:

[55] FIG. 1 is a view illustrating a conventional aerogel sheet preparation method by a wet process; [56] FIG. 2 is a view illustrating a conventional aerogel sheet preparation method by a dry process and the side cross section of an aerogel sheet prepared by the method;

[57] FIG. 3 is a side sectional view illustrating an aerogel sheet according to a first embodiment of the present invention, in which aerogel beads are charged into a needle- punched non- woven fabric;

[58] FIG. 4 is a side sectional view illustrating an aerogel sheet according to a second embodiment of the present invention, in which aerogel powder is charged into a needle-punched non- woven fabric;

[59] FIG. 5 is a side sectional view illustrating an aerogel sheet according to a third embodiment of the present invention, in which aerogel beads and aerogel powder are charged into a needle-punched non- woven fabric;

[60] FIG. 6 is a side sectional view illustrating an aerogel sheet according to a fourth embodiment of the present invention, in which an IR opacifier is charged, along with aerogel beads, into a needle-punched non-woven fabric;

[61] FIG. 7 is a side sectional view illustrating an aerogel sheet according to a fifth embodiment of the present invention, in which aerogel beads are charged into two layers of needle-punched non- woven fabric;

[62] FIG. 8 is a view illustrating an aerogel sheet preparation method according to an exemplary embodiment of the present invention, which is used in the examples;

[63] FIG. 9 is an electron microscope photograph illustrating the cross section of an aerogel sheet, which is prepared by Example 9 of the present invention;

[64] FIG. 1OA is a diagram illustrating the cross sectional structure of a sample cell, which is used in an apparatus for measuring the thermal-insulation property of an aerogel sheet prepared by Example 12 of the present invention; and

[65] FIG. 1OB is a graph illustrating the thermal-insulation property of the aerogel sheet measured in Example 12.

[66]

Best Mode for Carrying Out the Invention

[67] The present invention provides an aerogel sheet in which aerogel particles are separately prepared and then, added to a needle-punched non- woven fabric, in a dry process, without using a separate binder, thereby being capable of maintaining the nano-porosity of aerogel and achieving superior thermal-insulation and load-resistance properties by virtue of a high charge rate of aerogel particles.

[68] FIGS. 3 to 7 are side sectional views illustrating the aerogel sheet according to preferred embodiments of the present invention. As shown in FIGS. 3 to 5, the aerogel sheet 10 according to the present invention includes a needle-punched non- woven fabric 11, and aerogel particles, for example, aerogel beads 12 and/or aerogel powder 13, that are charged into the needle-punched non-woven fabric 11.

[69]

[70] The needle-punched non-woven fabric, in which the aerogel particles are charged, is not limited in the kind and properties thereof.

[71] The needle-punched non- woven fabric is made of short fibers. Preferably, the short fibers may be conjugate fibers including two or more kinds of polymers having different melting points from each other. When using the needle-punched non- woven fabric made of conjugate fibers, the non-woven fabric can be heated, in the following thermal lamination process, at a temperature equal to a lower melting point of the conjugate fibers. This is advantageous for efficient thermal lamination of the non- woven fabric.

[72] Here, the conjugate fibers are called "conjugate yarns", and are prepared by extruding bi-component polymers from a spinning hole. The conjugate fibers have a cross section in which the bi-component polymers are divided into two layers and bonded to each other.

[73]

[74] Representative examples of conjugate fibers include a side-by-side type, a sheath- core type, etc., but are not limited thereto. In the present invention, preferably, the conjugate fibers include two or more polymers selected from the group consisting of polyester, polyamide, and polyolefin.

[75] More preferably, the conjugate fibers include poly-ethylene-terepthalate (PET) and a polyolefin based polymer having a lower melting point than that of the PET. Most preferably, the polyolefin based polymer includes polyethylene or polypropylene. Meanwhile, it is preferable that the conjugate fibers include polyester-based fibers in fields of requiring the property of heat-resistance.

[76]

[77] In addition, the conjugate fibers for use in the present invention may have a modified cross section selected from a triangular shape, elliptical shape, star shape, etc. as well asa circular cross section.

[78] In the aerogel sheet according to the present invention, the greater the content of aerogel, the aerogel sheet exhibits superior thermal insulation property. In the present invention, the content of aerogel particles charged in the needle-punched non- woven fabric is preferably within a range of 10~90 wt%, and more preferably, within a range of 30~70 wt%, on the basis of the total weight of the aerogel sheet. If the content of aerogel particles is less than 10 wt%, it may cause a degradation in the thermal- insulation property of the aerogel sheet and thus, is undesirable. Also, if the content of aerogel particles is more than 90 wt%, it may cause a difficulty in processing and an insufficient strength of products. [79]

[80] In the present invention, the properties, shape, and preparation method of the aerogel particles to be charged into the needle-punched non-woven fabric are not specially limited to the above description, and any other generally known aerogel particles may be used. The aerogel particles may have an average diameter within a range from approximately sub-D (less than ID) to several millimeters, and more preferably, within a range from approximately sub-D to 5mm, but not limited thereto. The above mentioned size is the size of generally prepared aerogel.

[81] Also, the density of aerogel particles has an effect on the thermal conductivity and process-ability of aerogel. Preferably, the aerogel particles have a density of approximately 0.01~0.5 g/cm . If the aerogel particles have a density of less than approximately 0.01g/cm , it may cause a difficulty in processing when the aerogel particles are charged at a high rate. Also, if the density of aerogel particles is more than 0.5g/cm , the aerogel particles may have poor thermal insulation property.

[82]

[83] Preferably, hydrophobically surface modified aerogel particles are used as aerogel particles. In particular, in the present invention, the aerogel particles are made of a precursor such as water glass or alkoxy-silane, and may be hydrophobically surface modified with silyl-group.

[84] The aerogel particles are hydrophobically modified with silylation. Preferably, the aerogel particles are silylated to form surface-modified hydrophobic silica gels. At this time, a silane compound is used as a silylating agent, which is represented by Formulas 1 and/or 2 below:

[85] (R 1) 4-n SiX n (1)

[86] wherein n is 1 to 3; R is a C -C alkyl group, preferably, a C -C alkyl group, C aromatic group (wherein, the aromatic group can be unsubstituted or substituted with C -C alkyl group.), C heteroaromatic group (wherein, the heteroaromatic group can be unsubstituted or substituted with C -C alkyl group.), or hydrogen; X is a halogen atom selected from F, Cl, Br and I, preferably, Cl, C -C alkoxy group, preferably, a C -C alkoxy group, C aromatic group (wherein, the aromatic group can be unsubstituted or

6 substituted with C -C alkoxy group.), or C heteroaromatic group (wherein, the heteroaromatic group can be unsubstituted or substituted with C -C alkoxy group.); and

[87] R₃Si-O-SiR₃ (2)

[88] wherein each R is same or different; and R is a C -C alkyl group, preferably, a C

-C 5 alkyl group, C 6 aromatic group (wherein, the aromatic group can be unsubstituted or substituted with C -C alkyl group.), C heteroaromatic group (wherein, the heteroaromatic group can be unsubstituted or substituted with C -C alkyl group.), or hydrogen. [89]

[90] Examples of the silylating agent include at least one selected from the group consisting of hexamethyldisilane, ethyltrimethoxysilane, ethyltriethoxysilane, tri- ethylethoxysilane, trimethylethoxysilane, methyltrimethoxysilane, ethyltrimethoxysilane, methoxytrimethylsilane, trimethylchlorosilane, and tri- ethylchlorosilane, but are not limited thereto.

[91] The aerogel particles, used in the aerogel sheet of the present invention, may be hy- drophobically surface-modified aerogel particles or powder prepared by a method disclosed in Korean Patent Applications No. 2006-87884, 2006-98634, 2007-45207 and PCT/KR2007/4944 but are not limited thereto.

[92]

[93] For example, in the method for preparing hydrophobically surface-modified aerogel particles as disclosed in the above Korean Patent Application No. 2006-87884, first, water glass (sodium silicate) is added to HCl at a temperature of 30~90°C until an acidity reaches pH 3~5 to form silica gel under acid conditions of pH 3~5. Then, after washing the silica gel with distilled water, followed by filtering, the surface of the silica gel is silylated. The surface silylated silica gel is solvent replaced with n-butanol, to simultaneously remove both moisture and reaction residues in the silica gel. Finally, the silica gel is dried, to complete the hydrophobically surface-modified aerogel particles.

[94]

[95] In another method for preparing hydrophobically surface-modified aerogel powder as disclosed in the above Korean Patent Application No. 2006-98634 and PCT/ KR2007/4944. Firstly, water glass (sodium silicate) is added to HCl at a temperature of 30~90°C until an acidity reaches pH 3~5 to form silica gel under acid conditions of pH 3~5. Then, the silica gel is washed with distilled water using a mixer, followed by filtering. Meanwhile, a silylating solution of a silylating agent and n-butanol is prepared, and the washed and filtered silica gel is added to the silylating solution under acid conditions of pH 1~5 by use of an acid selected from hydrochloric acid, sulfuric acid, phosphoric acid, and nitric acid. By adding the silica gel to the silylating solution, silylation and solvent replacement are conducted simultaneously. Finally, the silica gel is dried, to prepare the hydrophobically surface-modified aerogel powder. Specifically, the silylating solution is prepared with l-10wt% of silylating agent and 90-99wt% of n-butanol.

[96]

[97] Further, hydrophobically surface-modified aerogel particle having lager particle size, which is prepared with using seed particle as disclosed in Korean Patent Application No. 2007-45207 and PCT/KR2007/4944 can be used as well in this invention. Fristly, water glass (sodium silicate) and seed particle are added HCl at 30 to 9O⁰C until an acidity reaches pH 3-5, to form silica hydrogel under acidic conditions of pH 3-5 and the formed silica silica hydrogel is washed with distilled water using a mixer, followed by filtering. Meanwhile, a silylating solution of a silylating agent and n-butanol is prepared, and the washed and filtered silica gel is added to the silylating solution under acid conditions of pH 1~5 by use of an acid selected from hydrochloric acid, sulfuric acid, phosphoric acid, and nitric acid. By adding the silica gel to the silylating solution, silylation and solvent replacement are conducted simultaneously. Finally, the silica gel is dried, to prepare the hydrophobically surface-modified aerogel powder. Specifically, the silylating solution is prepared with l-10wt% of silylating agent and 90-99wt% of n-butanol. The seed particles are at least one selected from the group consisting of fumed silica, TiO , Fe O and Al O and added in an amount of 0.5

2 2 3 2 3 to 20% by weight, based on the weight of the sodium silicate. Further, the seed particles have a size of 0.1 to 500 D.

[98]

[99] The flexible aerogel sheet according to the present invention is prepared by charging aerogel into a needle-punched non-woven fabric, and the aerogel may be aerogel beads and/or aerogel powder. FIG. 3 is a side sectional view illustrating the aerogel sheet 10 according to a first embodiment of the present invention, in which aerogel beads 12 are charged into a needle -punched non- woven fabric 11. FIG. 4 is a side sectional view illustrating the aerogel sheet 10 according to a second embodiment of the present invention, in which aerogel powder 13 is charged into the needle- punched non- woven fabric 11.

[100]

[101] In accordance with a third embodiment of the present invention, aerogel having a large particle diameter, for example, aerogel beads, and aerogel having a small particle diameter, for example, aerogel powder, are charged together into the needle-punched non-woven fabric. In this case, the small particle diameter aerogel is charged into pores of the large particle diameter aerogel, and this has the effect of achieving an increase in the charge rate of aerogel. FIG. 5 is a side sectional view illustrating the aerogel sheet 10 according to the third embodiment of the present invention, in which the aerogel beads 12 and the aerogel powder 13 are charged together into the needle-punched non- woven fabric 11.

[102]

[103] Additionally, an IR opacifier may be charged into the needle-punched non- woven fabric, in order to intercept heat transfer by radiation, and consequently, to achieve a further improvement in the thermal-insulation property of the aerogel sheet. FIG. 6 is a side sectional view illustrating the aerogel sheet 10 according to a fourth embodiment of the present invention, in which the IR opacifier 14 is charged into the needle- punched non-woven fabric 11. Examples of the IR opacifier may include carbon black, titanium dioxide, iron oxide, or zirconium dioxide, or a mixture thereof, but are not limited thereto.

[104]

[105] If necessary, the aerogel sheet of the present invention may be prepared by stacking two or more aerogel sheets one above another. The number of aerogel sheets to be stacked is not specially limited. For example, a plurality of aerogel sheets, each having a thickness within a range of approximately l~10mm, may be stacked one above another to have a desired thickness required in specific use places of the aerogel sheets.

[106] FIG. 7 illustrates the aerogel sheet 10 having two aerogel layers. To prepare the multi-layer aerogel sheet 10, first, a plurality of aerogel sheets, each having a single aerogel layer or a plurality of aerogel layers, are prepared, followed by stacking one above another. Alternatively, aerogel layers and needle-punched non-woven fabric layers may be stacked alternately one above another. In the resulting multi-layer aerogel sheet, some aerogel layers may contain aerogel beads, and the other aerogel layers may contain aerogel powder.

[107]

[108] In the present invention, additionally, the needle-punched non- woven fabric is subjected, at a surface thereof, to thermal laminating, to prevent leakage of aerogel particles charged therein.

[109] In the present invention, the term "laminating" means a technique for preparing a three-dimensional net structure by melting only fibers existing at the surface of the non- woven fabric for allowing the fibers to be secured to each other. The laminating may be conducted, for example, by use of a flat-bed laminating machine, but is not limited thereto.

[110] In the present invention, additionally, a single or two or more surface protective sheets may be stacked on one surface or both surfaces of the flexible aerogel sheet, to prevent the surface of the aerogel sheet from being damaged by an external force. The surface protective sheet may be a non-woven fabric, film, foam, or the like. The surface protective sheet may be made of generally known materials, and is not limited in the kind and properties thereof.

[I l l] If necessary, one surface or both surfaces of the flexible aerogel sheet may be subjected to a water-repellant process, coating process and/or sealing process.

[112]

[113] In another embodiment of the present invention, there is provided a method for preparing a flexible aerogel sheet comprising: scattering aerogel particles on a non- woven fabric web; conducting preliminary needle-punching and main needle-punching in sequence on the non-woven fabric web on which the aerogel particles were scattered; and laminating the main needle-punched non- woven fabric web by thermal treating surfaces thereof.

[114] In still another embodiment of the present invention, there is provided a method for preparing a flexible aerogel sheet comprising: scattering aerogel particles on a first non- woven fabric web, to produce an aerogel particle layer; stacking a second non- woven fabric web on the aerogeal particle layer; conducting preliminary needle- punching and main needle-punching in sequence on the stacked first and second non- woven fabric webs; and laminating the main needle-punched non- woven fabric webs by thermal treating surfaces thereof.

[115]

[116] By additionally stacking the second non- woven fabric web over the aerogel particle layer, the charge rate of aerogel particles and the mechanical strength of the aerogel sheet can be further increased. Accordingly, the resulting aerogel sheet products can reduce the loss of aerogel particles in use and consequently, achieve an increase in durability.

[117] The above described aerogel sheet preparation method of the present invention is called "Direct Loaded Carded Web Process" and shown in FIG. 8.

[118] It is noted that the needle-punched non- woven fabric web has a difficulty to obtain a desired level of basic weight at a time. Therefore, it is preferable that the needle- punched non- woven fabric web be prepared by stacking fibers several times while changing their orientations, on the basis of a cross-lapping method. The needle- punched non- woven fabric web may be made of single-component fibers, or bi- component conjugate fibers as described above.

[119]

[120] The needle-punched non- woven fabric is subjected to carding, to facilitate the charge of aerogel particles thereinto, and thus, has many empty spaces between fibers. Alternatively, a needle-punched non- woven fabric having fiber posts may be used.

[121] The amount of aerogel particles to be scattered on the needle-punched non- woven fabric web is preferably within a range of 10~90 wt%, and more preferably, within a range of 30~70 wt%, on the basis of the total weight of the aerogel sheet. If the amount of aerogel particles is less than 10 wt%, it may cause a degradation in the thermal- insulation property of the aerogel sheet and thus, is undesirable. Also, if the amount of aerogel particles is more than 90 wt%, it is undesirable in view of a difficulty in processing and the low strength of products. The aerogel particles, which are described in connection with the flexible aerogel sheet are used.

[122]

[123] The preliminary needle punching is to bridge the non- woven fabric web in a thickness direction for facilitating the transfer of the web on which the aerogel particles were scattered. After stacking additional non- woven fabric web on the basic non- woven fabric web on which the aerogel particles were scattered, or scattering aerogel particles on the basic non- woven fabric web, all the non-woven fabric webs are subjected to the preliminary needle punching. Preferably, the preliminary needle punching is conducted by a rate of 50~300 stroke/min, to provide the web with a sufficient tensile force required for the transfer of the webs.

[124] The main needle punching, which is performed on the preliminary needle -punched web, is to simultaneously achieve sufficient mixing and fixation between fibers and aerogel particles contained in the non-woven fabric web, or between fibers of the upper and lower non- woven fabric webs and the aerogeal particles therebetween. For this, the main needle punching is preferably conducted by a rate of 100~500 stroke/min. considering the mixing and fixation.

[125]

[126] Additionally, in the present invention, the surface of the needle-punched non- woven fabric web is thermally laminated, to prevent leakage of the aerogel particles from the surface of the non- woven fabric web. The laminating is preferably conducted at a temperature of 120 to 25O⁰C at the same speed as a transfer speed of the non- woven fabric web. If the temperature of the laminating is less than 12O⁰C, it may cause insufficient lamination and thus, have a problem of leakage of aerogel particles from the surface of the non-woven fabric web. Also, if the temperature of the laminating is more than 25O⁰C, it may cause excessive fusion at the surface of the non-woven fabric web, and thus, have a problem of damage to the surface of the web. More preferably, the laminating is conducted by use of a belt type laminating apparatus, for preserving the shape of the non- woven fabric.

[127]

[128] With the laminating, regardless of the use of additional needle-punched non- woven fabric on the aerogel particle layer, the aerogel particles are able to be fused between the fibers of the single needle-punched non- woven fabric or two needle-punched non- woven fabric layers, so as to prepare the aerogel sheet 10 shown in FIGS. 3 to 5. As described above, if necessary, different kinds of aerogel particles having different particle diameters, for example, aerogel beads and/or aerogel powder may be scattered, along with an IR opacifier, on the needle-punched non- woven fabric, so as to prepare the aerogel sheet 10 shown in FIG. 6.

[129]

[130] Furthermore, as described above, the aerogel sheet of the present invention may take the form of a stack in which two or more aerogel particle layers and non- woven fabric layers are stacked alternately one above another. For this, a plurality of aerogel sheets, each having a single aerogel particle layer or two or more aerogel particle layers, may be prepared, followed by stacking one above another. Alternatively, the plurality of aerogel particle layers may be stacked alternately with needle-punched non- woven fabrics in sequence. In the case of the multi-layer aerogel sheet, the size of aerogel particles in the aerogel particle layer and the content of the IR opacifier may be changed. Also, when a plurality of needle -punched non- woven fabric layers are used, fibers of the respective non- woven fabric layers may be equal to or different from one another.

[131]

[132] The aerogel sheet, prepared as described above, may be bent for the use thereof, or may be combined with other kinds of non- woven fabric layers, as occasion demands.

[133] Moreover, by providing a single surface protective sheet or multiple surface protective sheets on one surface or both surfaces of the flexible aerogel sheet according to the present invention, it is possible to prevent damage to the surface of the aerogel sheet by an external force.

[134] The surface protective sheet may be a non- woven fabric, film, foam, or the like.

The surface protective sheet may be made of generally known materials, and is not limited in the kinds and properties thereof. If necessary, one surface or both surfaces of the flexible aerogel sheet may be subjected to a water-repellant process, coating process and/or sealing process.

[135]

[136] In the flexible aerogel sheet preparation method and the flexible aerogel sheet prepared by the method according to the present invention, the aerogel particles are charged into voids of the non- woven fabric defined by needling punching. This has the effect of eliminating the use of a separate binder, which has been essentially used for preparation of an aerogel sheet. Also, since no adhesive is used, the present invention has no risk of a degradation in the nano-porosity of aerogel during the preparing of the aerogel sheet or composite. Furthermore, since the aerogel particles are previously and separately prepared and then, charged into the needle -punched non- woven fabric, the present invention has no need for gelation and supercritical drying of aerogel with fiber that have been employed in conventional wet methods, and thus, can achieve a simplified process and low production costs.

[137]

[138] Furthermore, in the aerogel sheet according to the present invention, the aerogel p articles can be firmly secured within the non- woven fabric without using a separate binder because the fibers of the non- woven fabric are bridged by needle punching. In the case where upper and lower needle-punched non- woven fabric layers are used, the upper and lower non- woven fabric layers can be firmly attached to each other by needle punching. The needle punching also has the function of endowing the aerogel sheet with pressure-resistance and load-resistance properties, thereby preventing damage to aerogel particles in use and consequently, deformation of the aerogel sheet.

[139]

[140] The aerogel sheet according to the present invention has superior thermal-insulation property and consequently, low thermal conductivity of less than 4OmWVmK. Accordingly, the aerogel sheet of the present invention can be efficiently used in electronic appliances such as refrigerators and computers, automobiles, aircrafts, clothes, shoes, cryogenic storage tanks, cryogenic transfer lines, cryogenic transportation vehicles, LNG industries such as LNG ships, LNG storage tanks, and LNG transfer lines, industrial pipe lines, thermos bottles, thermos tanks, constructional insulating materials, etc.

[141]

Mode for the Invention

[142] Hereinafter, the present invention will be better understood from the following examples. These examples are not to be construed as limiting the scope of the invention.

[143]

[144] Example 1 : Preparation of hydrophobically surface-modified aerogel particles using sodium silicate

[145] A water glass solution (a solution of a 35% sodium silicate solution and water (1 :

3, v/v)) was slowly added to IL of IN hydrochloric acid solution with stirring, to adjust pH to 4. At this time, a temperature of a reactor was 6O⁰C. The solution was further stirred for about 2 hours, while the pH of 4 was maintained, thereby preparing wet silica gel. The wet silica gel was washed with a sufficient amount of distilled water several times, to remove Na⁺ ions contained therein, followed by removal of water contained therein. Then, 40Og of the wet silica gel (hydrogel) was immersed in 500ml of a diluted silane solution of 90% by weight of methanol and 10% by weight of hexamethyl-di-silane (HMDS), followed by refluxing at 120 to 15O⁰C for 4 hours, such that the surface of aerogel was hydrophobically modified. Thereafter, 40Og of the hydrophobically surface-modified silica gel was immersed in 500ml of n-butanol, followed by refluxing at 120 to 15O⁰C for 4 hours, to remove water contained in the gel via solvent replacement. The resulting silica gel was dried at 12O⁰C for 2 hours. The thermal conductivity of the prepared hydrophobically surface-modified aerogel particles was 9 mW/m-K(Modified hot-wire method, TQ-2A), the particle size thereof was approximately 0.3D to 500mm, and the density thereof was approximately 0.03~0.04g/cm³. [146]

[147] Example 2 : Preparation of hydrophobically surface-modified aerogel particles using sodium silicate

[148] Hydrophobically surface-modified aerogel particles were prepared in the same manner as in Example 1, except that ethyl-triethoxy-silane (ETES) was used as a surface modifier. The thermal conductivity of the prepared hydrophobically surface modified aerogel particles was 11 mW/m-K(Modified hot-wire method, TQ-2A), the particle size thereof was approximately 0.3D to 500mm, and the density thereof was approximately 0.03~0.04g/cm .

[149]

[150] Example 3 : Preparation of hydrophobically surface-modified aerogel particles using sodium silicate

[151] Hydrophobically surface-modified aerogel particles were prepared in the same manner as in Example 1, except that ethyl-tri-methoxy-silane (ETMS) was used as a surface modifier. The thermal conductivity of the prepared hydrophobically surface modified aerogel particles was 11 mW/mK (Modified hot-wire method, TQ-2A), the particle size thereof was approximately 0.3D to 500mm, and the density thereof was approximately 0.03~0.04g/cm .

[152]

[153] Example 4 : Preparation of hydrophobically surface-modified aerogel particles using Seed Particle

[154] 3% by weight of fumed silica (diameter: about 0.5 D), based on the weight of water glass, and a water glass solution (a 3-fold dilution of a 35% sodium silicate solution in water) were slowly added to IL of a IN hydrochloric acid solution with stirring, to adjust pH of the water glass solution to 3.5. At this time, a reaction temperature was 6O⁰C. The solution was further stirred for about 2 hours, while the pH of 3.5 was maintained, thereby preparing silica hydrogel. The hydrogel was put in a mixer, and was then washed with distilled water several times for 4 hours, to remove Na⁺ ions contained therein. The resulting silica hydrogel was simultaneously subjected to permanently hydrophobic surface-treatment and removal of water contained therein using a silylating solution. The simultaneous process is carried out by immersing the hydrogel in a silylating solution of 5 wt% ethyl trimethoxy silane (ETMS) in n-butanol under acidic conditions of pH 3.5 adjusted by hydrochloric acid, followed by refluxing at 120 to 15O⁰C for 4 hours. The resulting silica hydrogel was dried at 12O⁰C for 2 hours to remove the n-butanol from the surface thereof. The thermal conductivity and density of aerogel powder prepared thus was 12 mW/m-K and 0.12 g/ cm , respectively.

[155] [156] Example 5 : Preparation of hydrophobically surface-modified aerogel particles using sodium silicate

[157]

[158] A water glass solution (a solution of a 35% sodium silicate solution and water (1 :

3, v/v)) was slowly added to IL of IN hydrochloric acid solution with stirring, to adjust pH to 4. At this time, a temperature of a reactor was 8O⁰C. The solution was further stirred for about 2 hours under acid conditions of pH 3.5, thereby preparing wet silica hydrogel. The silica hydrogel was put in a mixer, and was then washed with distilled water several times for 4 hours, to remove Na⁺ ions contained therein. The amount of removed Na⁺ ions was 2,000 ppm. The resulting silica hydrogel was simultaneously subjected to permanently hydrophobic treatment of the surface and removal of water contained therein thereof with a silane compound and n-butanol. For this, the wet silica gel was immersed in a silylating solution of 5 wt% ethyl-tri-methoxy- silane (ETMS) in n-butanol under acid conditions of pH 3.5, followed by refluxing at 120 to 15O⁰C for 4 hours. The resulting silica hydrogel was dried at 15O⁰C for 2 hours to remove the n-butanol from the surface thereof. The thermal conductivity of prepared aerosol was 9 mW/mK(Modified hot-wire method, TCi- 2A), the particle size thereof was approximately 0.3D to 500mm, and the density thereof was approximately 0.03~0.04g/cm³.

[159]

[160] Example 6 : Preparation of hydrophobically surface-modified aerogel particles using sodium silicate

[161] Hydrophobically surface-modified aerogel particles were prepared in the same manner as in Example 5, except that methoxy-tri-methyl-silane (MTMS) was used as a surface modifier. The thermal conductivity of the prepared hydrophobically surface modified aerogel particles was 11 mW/mK (Modified hot-wire method, TQ-2A), the particle size thereof was approximately 0.3D to 500mm, and the density thereof was approximately 0.03~0.04g/cm .

[162]

[163] Example 7 : Preparation of hydrophobically surface modified aerogel particles using TEOS

[164] Tetra-ethyl-ortho-silicate (TEOS) and H O were mixed in a mole ratio of 1 : 3, and then, HCl as an acid catalyst was added to the mixture, to adjust a pH to 2. When mixing under the condition of pH 2, TEOS and H O were hydrolyzed and mixed, to produce a single solution. As NH OH as a basic catalyst was added to the resulting hydrolyzed solution to adjust pH to 8, wet gel (hydrogel) was obtained via gelation of the hydrolyzed solution. The resulting wet gel was subjected to aging at 5O⁰C for 24 hours. The aged wet gel was crushed by a crusher, to produce wet gel particles. After adding the wet gel particles into a silylating solution of 5 wt% ethyl-tri-methoxy-silane (ETMS) in n-butanol, followed by refluxing at 15O⁰C, the wet gel particles were subjected to a hydrophobic surface treatment. The resulting wet gel was washed with MeOH, and then, dried in supercritical drying equipment.

[165]

[166] Supercritical drying conditions used in Example 7 were as follows. First, an autoclave, in which the wet gel was put, was purged with carbon dioxide, and then, heated at 35~40°C. The internal pressure of the autoclave was increased up to approximately 1,500 psig during the heating. After maintaining the above temperature and pressure of the autoclave for 1~2 hours, the autoclave was vented by use of a pressure-relief valve, to reduce the pressure of the autoclave at a speed of 15~25 psi/ min for 2~3 hours. At this time, the temperature of the autoclave was maintained at a supercritical temperature of carbon dioxide (31⁰C) or higher. At a time point when the pressure of the autoclave was reduced less than 100 psig, a heater of the autoclave was turned off, and the residual n-butanol was discharged by use of nitrogen during cooling.

[167]

[168] The prepared wet gel was dried by use of the above supercritical drying equipment, thereby preparing aerogel powder. The thermal conductivity of the prepared aerogel particles was 14—15 mW/mK (Modified hot-wire method, TQ-2A), the particle size thereof was approximately 0.3D~500mm, and the density thereof was approximately 0.03-0.04 g/cm³.

[169]

[170] Example 8 : Preparation of sheet using aerogel particles

[171] FIG. 8 illustrates a method for preparing an aerogel sheet according to the present invention.

[172] In accordance with the method shown in FIG. 8, sheath-core type polyethylene- polyethylene-terepthalate composite short fibers were subjected to opening and carding processes. In this case, the fibers have a fineness of 4d (here, d is a denier of fiber, i.e. a diameter of fiber weighing one gram per 9,000 meters) and an average fiber length of 40mm. Subsequently, the resulting fibers were subjected to a cross-lapping process, to prepare a 100 GSM (Gram per Square Meter) non-woven fabric web.

[173]

[174] Thereafter, the aerogel particles prepared by Example 1 was scattered on the non- woven fabric web in an amount of 40wt% on the basis of the total weight of the aerogel sheet. Then, the non-woven fabric web was subjected to preliminary needle punching by a rate of 200 stroke/min and main needle punching by a rate of 300 stroke/min in sequence. The surface of the resulting needle-punched non- woven fabric web was subjected to thermal laminating at 18O⁰C for 2 minutes, to prepare an aerogel sheet. In this example, the preparation process speed of the aerogel sheet was 3.5 m/ min. The thermal conductivity of the prepared aerogel sheet was 21.5 mW/mK (Heat Flow Meter, HFM 436/3/E).

[175]

[176] Example 9 : Preparation of sheet using aerogel particles

[177] An aeorgel sheet was prepared in the same manner as in Example 8, except that the charge amount of the aerogel particles prepared by Example 5 was 50 wt%, and after scattering the aerogel particles to form an aerogel particle layer, the needle-punched non-woven fabric web, which was used as a lower layer in Example 8, was stacked over the aerogel particle layer, prior to performing the preliminary needle punching. A microscope photograph of the prepared aerogel sheet was illustrated in FIG. 9 (in 150 magnifications).

[178] As shown in FIG. 9, in the aerogel sheet prepared by the method according to the present invention, the aerogel particles were densely secured between bridged fiber posts. The thermal conductivity of the prepared aerogel sheet was 19.8 mW/mK (Heat Flow Meter, HFM 436/3/E).

[179]

[180] Example 10 : Preparation of Two-Layered Aerogel Sheet

[181] An aerogel sheet 1 was prepared in the same manner as in Example 8, except that the aerogel particles prepared in Example 2 were used. Meanwhile, another aerogel sheet 2 was prepared in the same manner as in Example 8, except that the aerogel particles prepared in Example 7 were used.

[182] Then, after stacking the aerogel sheet 1 and the aerogel sheet 2 one above another, both the aerogel sheets 1 and 2 were subjected to laminating at 100⁰C for 5 minutes, to prepare an aerogel sheet having two aerogel layers. The thermal conductivity of the prepared aerogel sheet was 20.0 mW/mK (Heat Flow Meter, HFM 436/3/E).

[183]

[184] Example 11 : Preparation of Aerogel Sheet

[185] An aerogel sheet was prepared in the same manner as in Example 8, except that the aerogel particles prepared in Example 2 and the aerogel particles prepared in Example 3 were mixed with a weight ratio of 1 : 1 for use thereof, and 10 parts by weight of carbon black having a particle diameter of ID or less than was scattered together with the aerogel particles, on the basis of 100 parts by weight of aerogel particles. (214) The thermal conductivity of the prepared aerogel sheet was 18.0 mW/mK (Heat Flow Meter, HFM 436/3/E).

[186]

[187] Example 12 : Measurement of the thermal-insulation property of aerogel sheet [188] The thermal-insulation property of the aerogel sheet prepared in Example 8 was measured. The aerogel sheet, which was prepared in Example 8 and has a thickness of 3mm, was interposed between a lower plate having heating wires and an upper plate having a temperature sensor. Then, the upper plate was lowered such that the aerogel sheet comes into close contact with the two plates, to prepare a sample cell shown in FIG. 1OA. After heating the lower plate to a temperature of 200⁰C, the temperature of the upper plate was measured, to evaluate the thermal-insulation property of the aerogel sheet according to the present invention. Meanwhile, for the purpose of comparison, the needle punched non-woven fabric, which was used in the preparation of the aerogel sheet in Example 8, was interposed between the upper and lower plates in the same manner as the aerogel sheet, to measure the thermal-insulation property of the needle-punched non- woven fabric. Similarly, the temperature of the upper plate was measured, and the result was illustrated in FIG. 1OB.

[189]

[190] As could be confirmed from FIG. 1OB, when using the flexible aerogel sheet of

Example 8 that is prepared in the method according to the present invention, the upper plate showed a very low temperature as compared to the case of using the non- woven fabric sheet. Accordingly, it could be appreciated that the flexible aerogel sheet according to the present invention has superior thermal insulation property.

[191]

Industrial Applicability

[192] As apparent from the above description, a flexible aerogel sheet according to the present invention has the following several effects.

[193] Firstly, as a result of preparing the aerogel sheet without using a separate binder, the aerogel sheet has no risk of a degradation in the nano porosity of aerogel, and consequently, can achieve superior thermal-insulation property. Secondly, since aerogel particles are previously prepared, and then, charged into a non- woven fabric at a normal temperature and normal pressure, the preparation of the aerogel sheet according to the present invention has no need for a long process time and expensive supercritical drying process that have been required in a conventional method for preparing aerogel in fibers or fiber web by a wet process, resulting in a simplified overall process and reduced production costs.

[194]

[195] Thirdly, since the aerogel particles are charged into voids that are defined in the aerogel sheet by a needle punching process, the aerogel sheet prepared according to the present invention can prevent leakage of the aerogel particles therefrom without using a separate binder. Fourthly, when upper and lower non- woven fabric layers are stacked in two layers, fibers of the two fabric layers can be bridged by the needle punching process, thereby allowing the upper and lower non- woven fabric layers to be firmly attached to each other without using a separate binder. Fifthly, the needle punching process also has the effect of providing the aerogel sheet with desired pressure- resistance and load-resistance, thereby preventing damage to the aerogel particles and consequently, deformation of the aerogel sheet.

[196]

[197] Although the exemplary embodiments of the invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and sprit of the invention as disclosed in the accompanying drawings.

Claims

[1] An aerogel sheet comprising: at least one needle-punched non-woven fabric; and aerogel particles charged in the needle-punched non-woven fabric. [2] The aerogel sheet according to claim 1, wherein the needle-punched non- woven fabric is thermally laminated. [3] The aerogel sheet according to claim 1, wherein the needle-punched non- woven fabric is made of conjugate fibers including two or more polymers having different melting points from each other. [4] The aerogel sheet according to claim 3, wherein the conjugate fibers include two or more polymers selected from the group consisting of polyester, polyamide, and polyolefin. [5] The aerogel sheet according to claim 4, wherein the conjugate fibers include a polyethyleneterepthalate (PET) and a polyolefin-based polymer having a lower melting point than a melting point of PET. [6] The aerogel sheet according to claim 1, wherein the aerogel particles are charged an amount of 10~90 wt% within the needle-punched non- woven fabric on the basis of total weight of the aerogel sheet. [7] The aerogel sheet according to claim 1, wherein the aerogel particles are hy- drophobically surface modified aerogel. [8] The aerogel sheet according to claim 7, wherein silylation of the hydrophobically surface-modified aerogel particles is conducted using at least one silylating agent selected from the group consisting of Formulas 1 and 2 below:

(R 1 ) 4-n SiX n (1) wherein n is 1 to 3; R is a C -C alkyl group, preferably, a C -C alkyl group, C aromatic group (wherein, the aromatic group can be unsubstituted or substituted with C -C alkyl group.), or C heteroaromatic group (wherein, the het- eroaromatic group can be unsubstituted or substituted with C -C alkyl group.) or hydrogen and X is a halogen atom selected from F, Cl, Br and I, preferably, Cl, C -C alkoxy group, preferably, a C -C alkoxy group, C aromatic group (wherein, the aromatic group can be unsubstituted or substituted with C -C alkoxy group.), or C heteroaromatic group (wherein, the heteroaromatic group can be unsubstituted or substituted with C -C alkoxy group.); and R Si-O-SiR (2) wherein each R is same or different; and R is a C -C alkyl group, preferably, a C -C alkyl group, C aromatic group (wherein, the aromatic group can be un-

1 5 6 substituted or substituted with C -C alkyl group.), C heteroaromatic group (wherein, the heteroaromatic group can be unsubstituted or substituted with C -C alkyl group.), or hydrogen.

[9] The aerogel sheet according to claim 8, wherein the silylating agent is at least one selected from the group consisting of hexamethyldisilane, ethyltrimethoxysilane, ethyltriethoxysilane, triethylethoxysilane, trimethylethoxysilane, methyltrimethoxysilane, ethyltrimethoxysilane, methoxytrimethylsilane, trimethylchlorosilane, and triethylchlorosilane.

[10] The aerogel sheet according to claim 1, wherein the density of the aerogel particles is within a range of 0.01~0.5 g/cm .

[11] The aerogel sheet according to claim 1, wherein an IR opacifier is additionally charged into the needle-punched non- woven fabric.

[12] The aerogel sheet according to claim 11, wherein the IR opacifier includes at least one selected from the group consisting of carbon black, titanium dioxide, iron oxide, and zirconium dioxide.

[13] The aerogel sheet according to claim 1, wherein the aerogel sheet comprises at least two layers of aerogel sheets.

[14] The aerogel sheet according to claim 1, wherein the thermal conductivity of the aerogel sheet is 40 mW/mK or less.

[15] The aerogel sheet according to claim 1, further comprising: at least one surface protective sheet added to one surface or both surfaces of the aerogel sheet.

[16] The aerogel sheet according to claim 1, wherein the aerogel sheet is subjected, at one surface or both surfaces thereof, to a water repellent process, a coating process and/or a sealing process.

[17] The aerogel sheet according to claim 1, wherein the aerogel sheet is used as electronic appliances such as refrigerators and computers, automobiles, aircrafts, clothes, shoes, cryogenic storage tanks, cryogenic transfer lines, cryogenic transportation vehicles, LNG industries such as LNG ships, LNG storage tanks and LNG transfer lines, industrial pipe lines, thermos bottles, thermos tanks, or constructional insulating materials.

[18] A method for preparing an aerogel sheet comprising: scattering aerogel particles in a needle-punched non- woven fabric web; preliminary needle punching the non- woven fabric web in which the aerogel particles were scattered; main needle punching the preliminary needle-punched non- woven fabric web; and laminating the main needle-punched non- woven fabric web by thermal treating surfaces thereof.

[19] A method for preparing an aerogel sheet comprising: scattering aerogel particles in a first needle-punched non-woven fabric web; stacking a second needle -punched non- woven fabric web over the aerogel particles scattered in the first non- woven fabric web; preliminary needle punching the stacked needle-punched non- woven fabric webs; main needle punching the preliminary needle-punched non- woven fabric webs; and laminating the main needle-punched non- woven fabric webs by thermal treating surfaces thereof. [20] The method according to claim 18 or 19, wherein the preliminary needle punching is conducted by a rate of 100~300 stroke/min. [21] The method according to claim 18 or 19, wherein the main needle punching is conducted by a rate of 200~500 stroke/min. [22] The method according to claim 18 or 19, wherein the laminating is conducted at a temperature of 150~250°C for l~10 minutes.