[invention Title]

COMPOSITE COMPOSITION INCLUDING AEROGEL AND METHOD OF PREPARING THE SAME

[Technical Field]

[0001] The present invention relates to a composite composition including an aerogel and a method of preparing the same, and more particularly, to a composite, composition having excellent heat resistance, flame retardancy, fluidity, heat insulation properties, and/or adhesiveness, lightweightedness , and including a large amount of aerogel, and a method of preparing the composition.

[Background Art]

[0002] In line with the advancement of building materials and the demand on new, energy saving materials, the need for ultra-light and/or ultra-insulating materials has increased.

[0003] Polyurethane and Styrofoam have mainly been used as lightweight organic insulating materials to date. However, polyurethane and Styrofoam may have critical limitations at high temperatures and may generate relatively toxic gas in the case of fire. Therefore, these materials are not only unsuitable for being used in high-temperature environments, but are also regulated due to the possibility of the generation of toxic gas therefrom. Also, Styrofoam may be difficult to be used for various types of insulating materials.. Polyurethane may be used for various types of insulating materials in comparison to Styrofoam, but may be problematic for use in a relatively narrow or deep surface due to insufficient fluidity. Since polyurethane must be foamed in order to obtain heat insulation properties, and a polyurethane coating layer may become thick or non-uniform during foaming, polyurethane may be unsuitable for use as a coating . material .

[0004] In contrast, aerogels are transparent or semi- transparent ultra-low density advanced materials having a porosity of 90% or more and a specific surface area ranging from a few hundreds of m ² /g to 1000 m ² /g. The aerogels having a nanoporous structure may have high light transparency and ultra-low thermal conductivity, and thus, may be relatively efficient ultra-insulating materials.

[0005] One of major difficulties in the typical case of mixing an aerogel and an inorganic filler, such as silica and/or an inorganic material, with an adhesive, is that the inorganic filler determining insulation performance may not be added in an amount above a predetermined amount, due to a rapid increase in viscosity occurring during the mixing of the aerogel and the inorganic filler. Thermal conductivity of a product must be 40 mW/mk or less in order to be used as an ultra-insulating product.

[0006] Also, aerogels are materials having a relatively low specific gravity ranging from 0.03 g/cm ³ to 0.3 g/cm ³ , in which a ratio of volume to weight is relatively large. Therefore, in order to realize a composite including an aerogel having thermal conductivity of 40 m /mk or less, a content of the aerogel in the composite must be 40 wt% or more and this content may correspond to a relatively high volume constituting a relatively large portion of the volume of the composite. Thus, mixing of a large amount of aerogel with other components constituting the composite may be relatively difficult and a relatively large difference may be caused according to the selection of the adhesive and a. mixing method thereof. In particular, in the case of mixing a large amount of aerogel, a phase separation between the aerogel and other components (e.g., the adhesive), an increase in viscosity during the mixing, and cracking may occur during coating of a composite composition. For example, in the typical case that an aerogel is simply mixed with paint, fluidity may almost disappear, even in the case in which the aerogel is mixed in an amount ranging from about 10 wt% to about 20 wt%, based on total weight, and thus, the mixing may become impossible.

[0007] In contrast, in the case that an aerogel is mixed with an organic compound and/or organic solvents to prepare an insulating composite, the organic compound and/or organic solvents may be easily adhered to the inside of hydrophobic pores of the aerogel having surface hydrophobically treated. Therefore, heat insulation properties of the aerogel may not be manifested because micropores of the aerogel may be filled with the organic compound and/or organic solvents. That is., the heat insulation properties of the aerogel may be damaged due to the mixing of the hydrophobically treated aerogel and the organic compound and/or organic solvents. Also, the hydrophobic aerogel may be separated and unmixed due to having physical properties different from those of a hydrophilic compound.

[0008] Therefore, a composite composition having viscosity, fluidity, and/or adhesiveness suitable for mixing and an insulating material as well as excellent heat insulation properties obtained by mixing a sufficient amount of aerogel is required.

[Disclosure]

[Technical Problem]

[0009] An aspect of the present invention provides a composite composition including a hydrophobic aerogel having excellent heat insulation properties, electrical insulation properties, heat resistance, flame retardancy, and/or adhesiveness.

[0010] Another aspect of the present invention provides a composite composition including a hydrophobic aerogel having fluidity and/or viscosity suitable for an insulating material.

[0011] Another aspect of the _: present invention provides a composite composition including a large amount of hydrophobic aerogel.

[0012] Another aspect of the present invention provides a method of preparing a composite composition allowing a hydrophobic aerogel and a hydrophilic binder to be. effectively mixed therein.

[0013] Another aspect of the present invention provides a method of preparing a composite composition having excellent heat insulation properties, heat .resistance, fluidity, adhesiveness, and/or flame retardancy.

[0014] Another aspect of the present invention provides a method . of preparing a composite composition including a hydrophobic aerogel having fluidity and/or viscosity suitable for an insulating material.

[0015] Another aspect of the present invention provides a method of preparing a composite composition including a large amount of hydrophobic aerogel.

[Technical Solution]

[0016] According to an aspect of the present invention, there is provided a composite composition including polyvinyl alcohol, water, and a hydrophobic aerogel in a weight ratio ranging from 1:2:0.2 to 1:30:5, wherein a viscosity of the composite composition is within a range of 50 cP to 50,000 cP.

[0017] The composite composition may further include a surfactant in a weight ratio of the surfactant to the hydrophobic aerogel ranging from 1 to 10.

[0018] The composite composition may further include an inorganic filler in a weight ratio of the inorganic filler to the hydrophobic aerogel of 1 or less (excluding 0) .

[0019] The composite composition may further include a hardener in a weight ratio of the hardener to the polyvinyl alcohol ranging from 1 to 5.

[0020] An average particle diameter of the hydrophobic aerogel may be within a ^" range of Ιμπι to 5 mm.

[0021] Thermal conductivity of a heat insulation composite may be within a range of 30 m /mk to 39 m /mk.

[0022] According to another aspect of. the present invention, there is provided a method of preparing a composite composition including: mixing water at a temperature ranging from 50°C to 100°C and polyvinyl alcohol in a weight ratio ranging from 2:1 to 30:1 to prepare an aqueous polyvinyl alcohol solution having a viscosity ranging from 50 cP to 50,000 cP; and adding a hydrophobic aerogel to the aqueous polyvinyl alcohol solution in a weight ratio of the polyvinyl alcohol to the hydrophobic aerogel ranging from 1:0.2 to 1:5 and mixing at a speed ranging from 400 rpm to 10,000 rpm.

[0023] The method may further include adding a surfactant in a weight ratio of the surfactant to the hydrophobic aerogel ranging from 1 to 10, before the adding of the hydrophobic aerogel, together with the hydrophobic aerogel, or after the adding of the hydrophobic aerogel.

[0024] The method may further include adding an inorganic filler in a weight ratio of the inorganic filler to the hydrophobic aerogel of 1 or less (excluding 0) , before the adding of the hydrophobic aerogel, together with the hydrophobic aerogel, or after the adding of the hydrophobic aerogel .

[0025] The method may further include adding a hardener in a weight ratio of the hardener to the polyvinyl alcohol ranging from 1 to -5, after the adding of the hydrophobic aerogel.

[0026] An average particle diameter of the hydrophobic aerogel may be within a range of lpm to 5 mm.

[0027 ] Thermal conductivity of. a heat insulation composite may be. within a range of 20 mW/mk to 39 mW/mk.

[0028 ] A viscosity of the composite composition may be within a range of 50 cP to 50,000 cP.

[Advantageous Effects]

[0029] A composite composition containing a hydrophobic aerogel according to an embodiment of the present invention includes a large amount of aerogel, and exhibits low thermal conductivity, e.g., a thermal conductivity ranging from about 20mW/mk to about 39 mW/mk, and excellent heat insulation properties, heat resistance, flame retardancy, ^■ and/or adhesiveness. Also, since the composite composition may exhibit excellent viscosity and/or fluidity even in the case of including a large amount of aerogel, the application thereof may be facilitated and the composite composition may be suitable for any application without limitation. In particular, the composite composition may be suitable for a narrow or deep surface, or a curved surface. The composite composition may be used as a heat insulation composite in the shape of a panel, a board, or a thin coating layer, but the present invention is not limited thereto. The composite composition may also be used as an adhesive and/or a coating agent. For example, the composite composition may be used as a heat insulation composite, an adhesive, or a coating agent for freezers and/or refrigerators, or building materials.

[0030]. The composite composition containing an aerogel according to the embodiment of the present invention may be prepared by using a method according to an embodiment of the present invention. According to the method according to the embodiment of the present invention, a hydrophobic aerogel and a hydrophilic polyvinyl alcohol, in which preparation of a uniform mixture has been typically impossible, may be uniformly mixed according, to appropriate viscosity and/or fluidity. Therefore, a final product having the composite composition of the present invention dried and/or cured thereon (e.g., heat insulation composite, coating, coating layer, etc.) may exhibit excellent heat insulation properties. Further, more improved heat insulation properties may be obtained by synergistic action of air bubbles generated during the preparation of the aerogel composite composition and the aerogel .

[Description of Drawings] [0031] The above and other aspects, 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:

[0032] FIG. 1 a conceptual view illustrating a state in which polyvinyl alcohol and hydrophobic aerogel are physically mixed in a composite composition of the present invention;

[0033] FIG. 2 is a photograph showing insulation composites prepared in Inventive Examples 2 and 4;

[0034] FIG. 3 is a photograph showing that the insulation composites prepared in Inventive Examples 2 and 4 are hydrophobic;

[0035] FIG. 4 is a photograph showing a composite composition prepared in Inventive Example 3;

[0036] FIG. 5 is a photograph showing that an insulation composite coating layer prepared from the composite composition of Inventive Example 3 is hydrophobic;

[0037] FIG. 6 is a photograph showing that cracking may be generated in an insulation composite of Comparative Example 3; and

[0038] FIG. 7 a photograph showing that a composite composition of Comparative Example 7 is not mixed.

[Best Mode]

[0039] In a typical composite composition containing an aerogel and the preparation of the same, heat insulation properties of the aerogel may be damaged by micropores of the hydrophobic aerogel being filled with an organic adhesive in the case of mixing the hydrophobic aerogel and the organic adhesive. In contrast, in the case of mixing a hydrophobic aerogel and a hydrophilic adhesive, the hydrophobic aerogel and the hydrophilic adhesive are not mixed with each other due to their contrasting physical properties. Also, in the case of mixing a large amount of aerogel in consideration of heat insulation properties of a heat insulation composite, preparation of an applicable composite composition may not only be difficult due to an increase in viscosity and/or a decrease in fluidity, but there may also have limitations in the application of the composite composition.

[0040] The present invention is suggested to address the typical limitations described above, and a composite composition including an aerogel according to an embodiment of the present invention may include a large amount of hydrophobic aerogel. Therefore, . a heat insulation composite formed of the composite composition, for example, may include a maximum of about 80 wt% of the hydrophobic aerogel,, in which the heat insulation composite may exhibit excellent heat insulation properties, electrical insulation properties, and/or flame retardancy, and may be lightweight. Also, the composite composition of the present invention may not only have the hydrophobic aerogel uniformly mixed with the hydrophilic polyvinyl alcohol adhesive, but fluidity may also be good. Thus, various applications of the composite composition may be facilitated.

[0041] The composite composition containing an aerogel according to the embodiment of the present invention includes polyvinyl alcohol, water, and a hydrophobic aerogel in a weight ratio of polyvinyl alcohol : water : hydrophobic aerogel ranging from 1:2:0.2 to 1:30:5, that is 1 : 2~30 : 0.2~5 , and the weight ratio may be. within a range of 1:5:0.2 to 1:10:5, and for example, may be within a range of 1:6:0.2. to 1:8:5. The composite composition . has a viscosity ranging from 50 cP to 50,000 cP, for example, 500 cP to 42,000 cP.

[0042] A weight ratio of polyvinyl alcohol to water is within a range of 1:2 to 1:30, may be within a range of 1:5 to 1:10, and for example, may be within a range of 1:6 to 1:8. Polyvinyl alcohol and water may be included in the above weight ratio ranges in view of viscosity of the heat insulation composite composition, solubility of polyvinyl alcohol with respect to water, uniform mixing of water and polyvinyl alcohol, and prevention of separation.

[0043] Polyvinyl alcohol and the hydrophobic aerogel are included in a weight ratio of polyvinyl alcohol to the hydrophobic aerogel ranging from 1:0.2 to 1:5. Polyvinyl alcohol and the hydrophobic aerogel may be included in the above weight ratio range in view of heat insulation properties, uniform mixing of polyvinyl alcohol and the hydrophobic aerogel, and prevention of separation. [0044 ] Any polyvinyl alcohol may be used as the foregoing polyvinyl alcohol. A number-average molecular weight of the polyvinyl alcohol used is 5,000 or more, may be within a range of 20,000 to 100, 000, and for example, may be within a range of 40,000 to 100,000, but the number-average molecular weight of the poly vinyl alcohol is not limited thereto. Further, the polyvinyl alcohol may have no functional group reacting with an inorganic material, for example, an acetic acid group. The reason for this is to prevent a . loss of porosity of the aerogel _. due to the functional group.

[ 0045] An aerogel having a porous surface modified to be hydrophobic may be used as the hydrophobic aerogel. The hydrophobic aerogel is not particularly limited and any hydrophobic aerogel well known in the art may be used.

[0046] For example, a method of preparing an aerogel is generally known and the aerogel may be prepared by using methods described in references, such as R.K. Colloid, Chemistry of Silica and Silicates, 1954, Chapter 6; and G. . Scherer, Sol-Gel Science, 1990, Chapters 2 and 3.

[ 0047 ] Water glass or metal alkoxide may be used as a precursor of the aerogel, but the precursor of the aerogel is not limited thereto. In the case that water glass is used as a precursor of the aerogel, it is general to require a pretreatment process for removing salt therefrom. Each alkyl group having 1 to 6 carbon atoms, for example, 1 to 4 carbon atoms may be used as metal alkoxide. Such compound is not particularly limited, but at least one selected from the group consisting of tetraethoxysilane (TEOS) , tetramethoxysilane (TMOS) , tetra-n-propoxysilane, aluminum isopropoxide , aluminum-sec-butoxide, cerium isopropoxide, hafnium tert- butoxide, magnesium aluminum isopropoxide, yttrium isopropoxide, titanium isopropoxide, and zirconium isopropoxide may be used alone or a combination of two or more thereof may be used together. In particular, tetraethoxysilane including silane, for example, may be used as metal alkoxide.

[0048] A hydrophobic aerogel is an aerogel surface treated to be hydrophobic in order to prevent the absorption of moisture from the air, _. in which the hydrophobic surface treatment may be performed by using any method well known in the art. For example, a silylated aerogel may be used, but the present invention is not limited thereto.

[0049] The hydrophobic treatment of the surface of the aerogel is a silylation treatment, in which a chemical formula R ¹ 4- _n - SiX _n or R ³ Si-0-SiR ³ may be used (herein, n is 1 to 3, R ¹ is a Ci to Cio, for example, Ci to C ₅ alkyl group, or a C ₆ or Cio aromatic group, a heteroaromatic group, or hydrogen, X is a halogen element selected from the group consisting of fluorine (F) , chlorine (CI) , brome (Br) , and iodine (I) , and may be CI, or a Ci to Cio, for example, Ci to C ₅ alkoxy group, an aromatic alkoxy group, or a heteroaromatic alkoxy group, and R ³ are the same or different, and are a C _x to Cio alkyl group, or a C6 or Cio aromatic group, a heteroaromatic group, or hydrogen) . [0050] Specific examples, of a silylating agent may be hexamethyldisilane, ethyltrimethoxysilane, ethyltriethoxysilane, triethylethoxysilane, trimethylethoxysilane, methyltrimethoxysilane, methoxytrimethylsilane, . trimethylchlorosilane, and triethylchlorosilane, but the silylating agent is not limited thereto.

[0051] An average particle diameter of the hydrophobic aerogel may be within a range of 1 μιχι to 5 mm. The hydrophobic aerogel having an average particle diameter ranging from 1 μπι to 5 mm may be used in view of viscosity control, a mixable amount of aerogel, and possibility of uniform mixing of aerogel.

[0052] A surfactant, an inorganic filler and/or a hardener may further be added to the composite composition, if necessary.

[0053] The surfactant may further be added as needed so as to allow the hydrophobic aerogel and the hydrophilic polyvinyl alcohol to be well mixed. Any surfactant well known in the art may be used as the surfactant, and, for example, alcohols (e.g., ethanol) and polyethylene glycol. (PEG) may be used alone or a combination of two or more thereof may be used together, but the surfactant is not limited thereto.

[0054] A weight ratio of the surfactant to the hydrophobic aerogel may be within a range of 1 to 10. That is, an amount of the surfactant may be used within a range of 1 g to 10 g based on 1 g of the hydrophobic aerogel. The amount of ^" the surfactant may be used within the above range in view of an improvement of miscibility between the hydrophobic aerogel and the hydrophilic polyvinyl alcohol due to the addition of the surfactant, and the miscibility may not be further improved even in the case that an amount greater than the upper limit amount is added. In particular, a weight ratio of ethanol (a purity 95 wt% or more) to the aerogel may be within a range of 1 to 10 and a weight ratio of PEG based on a 5 wt% solution to the aerogel may be within a range of 1 to 8.

[0055] However, since the surfactant may allow polyvinyl alcohol to penetrate into micropores of the hydrophobic aerogel, the surfactant, if possible, may not be used. In the case of adding the surfactant, a minimum amount of the surfactant may be used to manifest heat insulation properties.

[0056] A separate inorganic filler may be further added in view of economic factors and temperature tolerance. Any inorganic filler well known in the art may be used as the inorganic filler, and, for example, loess powder, mica, talc, silica, diatomite, perlite, vermiculite, activated carbon, or zeolite may be used, but the inorganic filler is not limited thereto. These inorganic . fillers may be used alone or a combination of two or more thereof may be used together.

[0057] In the case of using the foregoing inorganic filler, since the heat insulation properties of the heat insulation composite may be decreased in comparison to that in the case of only including the hydrophobic aerogel, a separate inorganic filler, for example, may not be added in view of the heat insulation properties. However, the inorganic filler may be used together in view of economic factors.

[0058] Meanwhile, in the case that the composite composition according to the embodiment of the present invention is used for a high temperature application, heat resistance may be improved through mixing with the inorganic filler. Since the inorganic filler is mixed, the composite composition or the heat insulation composite formed of the composite composition may have excellent heat resistance at a temperature ranging from about 80°C. to about 100°C.

[0059] The inorganic filler may be further added to the hydrophobic aerogel in a weight ratio of 1 or less (for example, lg or less of the inorganic ^' filler for 1 g of the hydrophobic aerogel) , for example, in a weight ratio ranging from 0.001 to 1. In the case that a large amount of the inorganic filler is added, the heat insulation properties may not only be decreased, but severe cracking may also occur in a coating layer during the coating of the composite composition. Therefore, the inorganic filler may be added in a weight ratio of 1 or less. with respect to the weight of the aerogel.

[0060] Since the composite composition according to the embodiment of the present invention may be cured by itself according to the time elapsed to form a heat insulation composite, the composite composition may be used as a final product without a separate hardener. However, a separate hardener may be further added as needed, in order to reduce curing time.

[0061] Any hardener well known in the art may be used as the hardener, and, for example, hardeners, such as borax, boric acid, and an ammonium zirconium carbonate solution, may be used alone or a combination of two or more thereof may be used together, but the hardener is not limited thereto. A concentration of a hardener solution may be within a range of 1 wt% to 25 wt%.

[0062] Since curing of the composite composition may be completed in a . short period of time when the hardener is added, the hardener may be further added to a mixture of water, polyvinyl alcohol, a hydrophobic aerogel, a random surfactant, and/or a random inorganic■ filler during construction.

[0063] The hardener may be further added in an amount by which polyvinyl alcohol may be forcibly cured in a short period of time. A weight ratio of the hardener solution to polyvinyl alcohol is 5 or less and may be within a range of 1 to 5.

[0064] A viscosity of the composite composition including the aerogel is within a range of 50 cP to 50, 000 cP, and may be within a range of 500 cP to 42,000 cP, in which the application of the composite composition to an insulating material may not only be facilitated, but a uniform mixing state may be maintained without separation even in the case that the composite composition is left standing for a few days or more. Also, the heat insulation composite formed of the composite composition has excellent thermal conductivity ranging from 30 mW/mk to 39 m /mk, and thus, exhibits excellent heat insulation properties.

[0065] Ultra fine hollow ceramic bodies or _. hollow glass bodies, a typical heat insulation paint filler, may not only be relatively expensive, but may also not function as a heat insulator because considerable- portions thereof may break during a mixing process. In contrast, no matter how small the portions of aerogel constituting the composite composition are after breaks, each particle of the aerosol itself may again function as a hollow body, and thus, the aerosol may be superior in view of functionality. In particular, as illustrated in FIG. 1, a hydrophobic aerogel uniformly mixed with a . hydrophilic polyvinyl alcohol solution is simply physically mixed with the polyvinyl alcohol and air space of inner micropores of the aerogel is maintained as it is, and thus, each aerosol particle may act as an ultra-insulating hollow ceramic microbody. Therefore, the heat insulation composite formed of the composite composition according to the embodiment of the present invention may exhibit excellent heat insulation properties.

[0066] According to another embodiment of the present invention, a method of preparing a composite composition is provided. Water at a temperature ranging from 50°C to 100°C and polyvinyl alcohol are mixed, to prepare an aqueous polyvinyl alcohol solution having a viscosity ranging from 50 cP to 50,000 cP, for example, 500 cP to 42,000 cP, in which a weight ratio of polyvinyl alcohol to water is within a range of 1:2 to 1:30, may be within a range of 1:5 to 1:10, and for example, may be within a. range of 1:6 to 1:8. Then, a hydrophobic aerogel is added and mixed with the aqueous polyvinyl alcohol solution to prepare a composite composition, in which a weight ratio of polyvinyl alcohol to the hydrophobic aerogel is within a range of 1:0.2 to 1:5.

[0067] During the preparation of the aqueous polyvinyl alcohol solution, water at a temperature ranging from 50°C to 100°C is used in order to allow the polyvinyl, alcohol to be well dissolved in water. The hydrophobic aerogel and the hydrophilic water-soluble polyvinyl alcohol may not be well mixed by themselves. Therefore, in order to physically uniformly mix the hydrophobic aerogel and the hydrophilic water-soluble polyvinyl alcohol having contrasting physical properties without separation, a viscosity of the aqueous polyvinyl alcohol solution mixed with the hydrophobic aerogel must be maintained in an appropriate range of 50 cP to 50,000 cP, for example, 500 cP to 42,000 cP.

[0068] In order to maintain the appropriate viscosity range, the weight ratio of polyvinyl alcohol to water is within a range of 1:2 to 1:30, may be within a range of 1:5 to 1:10, and for example, may be within a range of 1:6 to 1:8. Any type of polyvinyl alcohol may be used as the foregoing polyvinyl alcohol. A number-average molecular weight of the polyvinyl alcohol used is 5,000 or more, may be within a range of 20,000 to 100, 000, and for example, may be within a range of 40, 000 to 100,000. Further, the polyvinyl alcohol may have no functional group reacting with an inorganic material, for example, an acetic acid group. The reason for this is to prevent a loss of porosity of the aerogel due to the functional group.

[0069] Since water and polyvinyl alcohol are mixed in the foregoing weight ratio range, the viscosity of the aqueous polyvinyl alcohol solution may be within a range of 50 cP to 50, 000 cP, for example, 500 cP to 42, 000 cP, in which the aqueous polyvinyl alcohol solution may be uniformly mixed with the hydrophobic aerogel without separation in a subsequent operation. Also, no separation of the aqueous polyvinyl alcohol solution must occur within 48 hours or more.

[0070] The hydrophobic aerogel is added to the aqueous polyvinyl alcohol solution in view of heat insulation properties, uniform mixing of water and polyvinyl alcohol, and prevention of the separation,, in which the weight ratio of polyvinyl alcohol to the hydrophobic aerogel is within a range of 1:0.2 to 1:5. Thereafter, a composite composition is prepared by . stirring a mixture of the aqueous polyvinyl alcohol solution and the hydrophobic aerogel at a speed of 400 rpna or more. - As described above, the aerogel having hyrophobicity may not be mixed with the hydrophilic polyvinyl alcohol. Therefore, in order to uniformly mix the hydrophobic aerogel and the hydrophilic polyvinyl alcohol, the stirring speed must be 400 rpm or more so that the aerogel may be mixed by flowing into the aqueous polyvinyl alcohol solution. The faster the stirring speed is, the better the hydrophobic aerogel and the hydrophilic polyvinyl alcohol are mixed. Therefore, although an upper limit of the stirring speed is not -particularly limited, the stirring may be performed at a speed ranging from about 400 rpm to about 10,000 rpm in consideration of energy consumption and facility overload in the preparation process.

[0071] Since the stirring is performed at a speed of 400 rpm or more, for example, 400 rpm to 10, 000 rpm, the hydrophobic aerogel and the hydrophilic polyvinyl alcohol are physically uniformly mixed as the aerogel flows into the aqueous polyvinyl alcohol solution by a mixer blade. Mixing times may vary according to volumes of reactants and a uniformly mixed composite composition may be obtained by mixing the solution for about 15 minutes to about 40 minutes based on about 3 liters .

[0072] Meanwhile, a surfactant, an inorganic filler and/or a hardener may be further added during the preparation of the composite composition, if necessary. The surfactant and/or the inorganic filler may be added and mixed before the adding of the hydrophobic aerogel, together with the hydrophobic aerogel, or after the adding of the hydrophobic aerogel.

[0073] The surfactant may be further added as needed so as to allow the hydrophobic aerogel and the hydrophilic polyvinyl alcohol to be well mixed. Any surfactant well known in the art may be used as the surfactant, and, for example, alcohols (e.g., ethanol) and polyethylene glycol (PEG) may be used alone or a combination of two or more thereof may be used together, but the surfactant is not limited thereto.

[0074] A weight ratio of the surfactant to the hydrophobic aerogel may be within a range of 1 to 10. The amount of the surfactant may be used within the above range in view of an improvement of miscibility between the hydrophobic aerogel and the hydrophilic polyvinyl alcohol due to the addition of the surfactant, and the miscibility may not be further improved even in the case that an amount more than the upper limit amount is added. In particular, a weight ratio of ethanol (purity 95 wt% or more) to the hydrophobic aerogel may be within a range of 1 to 10 and a weight ratio of PEG based on a 5 wt% solution to the hydrophobic aerogel may be _. within a range of 1 to 8.

[0075] However, since the surfactant may allow polyvinyl alcohol to penetrate into micropores of the hydrophobic aerogel, the surfactant, if possible, may not be used. In the case of adding the surfactant, a minimum amount of the surfactant may be used to manifest heat insulation properties.

[0076] The inorganic filler may be further added in view of economic factors and temperature tolerance. Any inorganic filler well known in the art may be used as the inorganic filler, and, for example, loess powder, mica, talc, silica, diatomite, perlite, vermiculite, activated carbon, or zeolite may be used, but the inorganic filler is not limited thereto. These inorganic fillers may be used alone or a combination of two or more thereof may be used together.

[0077] In the case of using the foregoing inorganic filler, since the heat insulation properties of the heat insulation composite may be decreased in comparison to that in the case of only including the aerogel, a separate inorganic filler, for example, may not be added in view of the heat insulation properties. However, the inorganic filler may be used together in view of economic factors.

[0078] In the case that the heat insulation composite is used for high temperature application, heat resistance may be improved by adding the inorganic filler. Since the inorganic filler is mixed, the heat insulation composite may have excellent heat resistance at a temperature ranging from about 80°C to about 100°C.

[0079] The inorganic filler may be further added to the hydrophobic aerogel in a weight ratio of 1 or less, for example, in a weight ratio ranging from 0.001 to 1. In the case that a large amount of the inorganic filler is added, the heat insulation properties may not only be decreased,, but severe cracking may also occur in an insulation composite coating layer. Therefore, the inorganic filler may be added in a weight ratio of 1 or less with respect to the weight of the aerogel . [0080] Since the composite . composition may be cured by itself according to the time elapsed, the composite composition may be used as a final product without a separate hardener. However, a separate hardener may be further added as needed, in order to reduce curing time.

[0081] Any hardener well known in the art may be used as the hardener, and, for example, hardeners, such as borax, boric acid, and an ammonium zirconium carbonate solution, may be used alone or a combination of two or more thereof may be used together, but the hardener is not limited thereto. A concentration of a hardener solution may be within a range of 1 wt% to 25 wt%.

[0082] The hardener may be further added in an amount by which polyvinyl alcohol may be forcibly cured in a short period of time. A weight ratio of the hardener solution to polyvinyl alcohol is 5 or less and may be within a range of 1 to 5.

[0083] Since curing of the composite composition may be completed in a short period of time when the hardener is added, the hardener may be added to a mixture of water, polyvinyl alcohol, a hydrophobic aerogel, a random surfactant, and/or a random inorganic filler during construction. The hardener may be mixed during the preparation process of the heat insulation composite or may be further added after the preparation of the composite composition.

[0084] A viscosity of the composite composition prepared according to the foregoing method is within a range of 50 cP to 50,000 cP, and may be within a range of 500 cP to 42,000 cP, in which the hydrophobic aerogel and the hydrophilic polyvinyl alcohol, may be uniformly mixed and thus, a uniform mixing state, may be maintained without separation for a few days or more. In addition, the composite composition may exhibit excellent heat resistance, heat insulation properties, flame retardancy, and/or fluidity.

[0085] Hereinafter, the present invention will be described in more detail, according to the following examples. However, the following examples are merely presented to exemplify the present invention, and the scope of the present invention is not limited thereto.

[0086] Examples

[0087] Composite compositions of Inventive Examples and Comparative Examples were prepared by using the following method under the conditions presented in the following Table 1. The preparation conditions for each Inventive Example and Comparative Example are the same as those presented in Table 1. Polyvinyl alcohol was dissolved in water at 70°C to prepare an aqueous polyvinyl alcohol solution. Thereafter, hydrophobic silica aerogel powder (EM-POWER, CO., LTD.- product EMP-SAP) having an average particle diameter of 10 μιτι was added to the aqueous polyvinyl alcohol solution and a composite solution was then prepared by stirring and mixing in a mixer for 20 minutes. In the case that other additives were further added, other additives of Table 1 together with the aerogel powder were added to the aqueous polyvinyl alcohol solution and stirring and mixing were then performed. Viscosities of the aqueous polyvinyl alcohol solutions and the prepared composite compositions are presented in the following Table 1.

[0088] [Table 1]

Note 1) Hydrophobic perlite powder used as a filler was ONYXELL by Kyungdong Ceratech Co., Ltd.

2) The hardener in Inventive Example 3 was added and stirred after the preparation of a composite composition by adding the aerogel.

3) Aluminum silicate used as a filler was INSULADD by

SIENG.

4) Perlite powder used as a filler was NEWPERSHINE by GFC product

5) Zeolite used as a filler was Aplite by AK ChemTech Co.,

Ltd.

[0089] As illustrated in Table 1, in the case that a compositional ratio of polyvinyl alcohol, water, and aerogel, a stirring speed, and a content of inorganic filler were not satisfied within ranges of the present invention, viscosities of composite compositions were high and a suitable composite composition was not prepared.

[0090] The composite composition of Inventive Example 2 was introduced into a mold having a size of 250 mm * 250 mm ^χ 10 mm and cured at a temperature of 70 °C to prepare a heat insulation composite having the shape of a board as illustrated in FIG. 2. Thermal conductivity of the heat insulation composite was 36 mW/mk and surface hydrophobicity was exhibited as illustrated in FIG. 3.

[0091] The composite composition of Inventive Example 3 was prepared as a thick liquid-phase slurry, as illustrated in FIG. 4. No separation. occurred in the composite composition when it was left standing for 48 hours or more. A half side of a hot plate at 160°C was coated to a thickness ranging from 1 mm to 2 mm with the composite composition of Inventive Example 3. Thereafter, ^" the surface temperature of the surface of the hot plate coated with the composite composition of Inventive Example 3 was decreased to 60°C. Also, as illustrated in FIG. 4, a surface of the heat insulated composite coating exhibited hydrophobicity. Thermal conductivity was 35 m /mk.

[0092] The composite composition of Inventive Example 4 was introduced into a mold having a size of 250 mm ^χ 250 mm ^χ 10 mm and cured at a temperature of 70 °C to prepare a heat insulation composite having the shape of a board as illustrated in FIG. 2. Thermal conductivity of the heat insulation composite was 32 mW/mk and also exhibited surface hydrophobicity as illustrated in FIG. 3.

[0093] A half side of a hot plate at 160°C was coated to a thickness ranging from 1 mm to 2 mm with the composite composition of Comparative Example 3. As illustrated in FIG. 6, severe cracking occurred in a coating layer of the composite composition and a surface temperature was 110°C. Thermal conductivity of a heat insulation composite formed of the composite composition of Comparative Example 3 was relatively high at 89 mW/mk.

[0094] With respect to the composite composition of Comparative Example. 7, ^■" . an / aqueous polyvinyl alcohol solution and aerogel powder were not mixed as illustrated in FIG. 7.

[0095] While the present invention has been illustrated and described in connection with the . exemplary embodiments, it will be apparent to those skilled in .the - art that modifications and variations can be made without departing from the spirit and scope of the invention as defined by the appended claims .