JP2011162756A - Method for producing porous silica-fiber composite, porous silica-fiber composite, and vacuum heat insulation material using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing a porous silica-fiber composite that is inexpensive and has high insulating performance and excellent mass productivity, flexibility, and constructivity, a porous silica-fiber composite, and a vacuum heat insulation material using the same. <P>SOLUTION: In the method for producing a porous silica-fiber composite, one or more selected from the group consisting of an alkyltrialkoxysilane, an aryltrialkoxysilane, and a bis(trialkoxysilyl)alkane are added under ice-cold conditions to a mixed liquid including an acid aqueous solution having pH of 3-4.5, a nonionic surfactant, a water-soluble aprotic polar organic solvent, and urea to produce siloxane sol; a fibrous structure is impregnated with the siloxane sol; the porous silica-fiber composite is prepared by generating porous silicon oxide gel through the reaction of the siloxane sol inside the fibrous structure at a certain temperature; and replacement of water contained inside by an alcoholic solvent and heating and drying under normal pressure are subsequently performed. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

The present invention relates to a method for producing a porous silica-fiber composite, a porous silica-fiber composite, and improvement of a vacuum heat insulating material using the same.

From the viewpoint of reducing energy costs and protecting the environment, a heat insulating material using a porous material such as airgel has attracted attention. Aerogel is a low-density substance in which the moisture contained in gel such as silica gel is replaced with gas (air) by supercritical drying, and is insulated to block all convection, conduction and radiation, which are the main methods of heat transfer. It has the characteristic that it is very excellent in property.

An airgel having a metal oxide such as silica or alumina as a skeleton is synthesized by a liquid phase method such as a sol-gel method using a metal alkoxide or the like as a precursor. For this reason, drying of the solvent is indispensable, but at this time, there is a problem that the shrinkage and destruction of the fine structure, the generation of cracks, etc. easily occur due to the surface tension of the solvent. Therefore, a supercritical drying method is used for drying airgel currently on the market. However, since supercritical drying requires a large-scale apparatus, the manufacturing cost increases, and there is a problem in terms of mass productivity.

For example, in Patent Document 1, (a) a reaction of generating a sol by adding a silicon compound having a hydrolyzable functional group and a non-hydrolyzable functional group in a molecule to an acidic aqueous solution containing a surfactant; And (b) a step of drying the gel formed by the step (a), and the step (b) is used for drying the gel. An alkylsiloxane aerogel for drying the gel under a temperature and pressure below the critical point of the solvent and a method for producing the same are disclosed.
Further, in Patent Document 2, fine particles 1 to 1 μm or less in average particle diameter of 1 μm or less with respect to a space of 100 parts by weight of a fiber structure having a bulk density of 0.01 g / cm ³ or more formed by entanglement and / or adhesion of fibers. A fiber / fine particle composite heat insulating material in which 250 parts by weight is held by the fiber structure is disclosed.

International Publication No. 2007/010949 Pamphlet JP 2002-333092 A

However, since the alkylsiloxane airgel described in Patent Document 1 does not use supercritical drying, the cost required for the drying process is smaller than that of the conventional airgel. However, the airgel is brittle and easily breaks due to bending stress or impact. Is not solved. Today's high-temperature equipment for automobiles, aircraft, and industry has a complicated shape in a small space, and in order to insulate them, there is a demand for heat insulation that has high thermal resistance, flexibility, and excellent workability. The alkylsiloxane airgel described in Patent Document 1 is difficult to sufficiently meet the above needs in terms of flexibility and workability.
Moreover, although the fine particle is hold | maintained inside the fiber structure, the fiber and fine particle composite heat insulating material described in Patent Document 2 may cause problems such as generation of dust due to dropout of fine particles and deterioration of heat insulation performance.

The present invention has been made in view of such circumstances, and is a method for producing a porous silica-fiber composite that is inexpensive, has high heat insulation performance, and is excellent in mass productivity, flexibility, and workability, and porous silica-fiber. It aims at providing a composite and a vacuum heat insulating material using the same.

The 1st aspect of this invention in alignment with the said objective solves the said subject by providing the manufacturing method of the porous silica-fiber composite as described in following (1)-(7).
(1) pH 3 to 4.5 acidic aqueous solution 100 parts by weight, nonionic surfactant 10 to 40 parts by weight, water-soluble aprotic polar organic solvent 30 to 50 parts by weight, urea 30 to 70 parts by weight 50 to 100 parts by weight of one or more alkoxysilane compounds selected from the group consisting of alkyltrialkoxysilanes, aryltrialkoxysilanes, and bis (trialkoxysilyl) alkanes are added to a mixed solution containing the components under ice-cooling. Then, the step A for producing a siloxane sol in the mixed solution, the step B for impregnating the fiber structure with the mixed solution containing the siloxane sol, and the reaction of the siloxane sol at a constant temperature inside the fiber structure. The porous silicon oxide gel is formed inside the fibrous structure by forming a porous silicon oxide gel. Step C for preparing a composite, Step D for immersing the porous silica-fiber composite in an alcohol solvent, and substituting the alcohol solvent for water contained therein, and subjecting the porous silica-fiber composite to normal pressure And a step E for drying the alcohol solvent contained therein, and a method for producing a porous silica-fiber composite.
(2) The porous silica-fiber composite according to (1), further comprising a step F of reacting a silanol group contained in the porous silica gel with an alkylating agent between the step D and the step E. Production method.
(3) The method for producing a porous silica-fiber composite according to any one of (1) and (2), wherein the fiber structure is a nonwoven fabric.
(4) The method for producing a porous silica-fiber composite according to any one of (1) to (3), wherein the fiber structure includes hollow fibers, and the porous silica gel is formed therein.
(5) The method for producing a porous silica-fiber composite according to any one of (1) to (4), wherein the water-soluble aprotic polar organic solvent is N, N-dimethylformamide.
(6) The alcohol solvent is one or more selected from the group consisting of methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, and 2-methyl-2-propanol (1) To 5. The method for producing a porous silica-fiber composite according to any one of (5).
(7) The alkylating agent is one or more selected from the group consisting of alkyltrihalosilanes, dialkyldihalosilanes, trialkylhalosilanes, alkyltrialkoxysilanes, dialkyldialkoxysilanes, and trialkylalkoxysilanes ( The method for producing a porous silica-fiber composite according to any one of 2) to (6).

The second aspect of the present invention is:
(8) By providing a porous silica-fiber composite manufactured by the manufacturing method according to the first aspect of the present invention (described in any one of (1) to (7) above), It is a solution.

The third aspect of the present invention is:
(9) By providing a vacuum heat insulating material in which the porous silica-fiber composite according to the second aspect of the present invention (described in (8) above) is sealed under reduced pressure inside the packaging material having gas barrier properties. It solves the problem.

According to the present invention, a method for producing a porous silica-fiber composite having low cost, high heat insulation performance, and excellent mass productivity, flexibility, and workability, a porous silica-fiber composite, and a vacuum using the same Insulation is provided.

2 is a scanning electron micrograph of the porous silica-fiber composite obtained in Example 1. FIG. It is a flowchart which shows the manufacturing process of the vacuum heat insulating material which concerns on the 2nd Embodiment of this invention.

Next, embodiments of the present invention will be described with reference to the accompanying drawings for understanding of the present invention.
The porous silica-fiber composite according to the first embodiment of the present invention (hereinafter sometimes abbreviated as “composite”) is a production method having the following steps (hereinafter abbreviated as “present production method”). May be used).
(1) pH 3 to 4.5 acidic aqueous solution 100 parts by weight, nonionic surfactant 10 to 40 parts by weight, water-soluble aprotic polar organic solvent 5 to 15 parts by weight, urea 30 to 70 parts by weight 50 to 100 parts by weight of one or more alkoxysilane compounds selected from the group consisting of alkyltrialkoxysilanes, aryltrialkoxysilanes, and bis (trialkoxysilyl) alkanes are added to a mixed solution containing the components under ice-cooling. Step A of generating a siloxane sol in the mixed solution
(2) Step B of impregnating the fiber structure with the mixed liquid containing the siloxane sol prepared in Step A
(3) By reacting the siloxane sol at a constant temperature inside the fiber structure to form a porous silicon oxide gel (hereinafter sometimes referred to as “porous gel”), the oxidation is performed. Step C of preparing a porous silica-fiber composite in which a silicon gel is formed inside the fiber structure
(4) Step D in which the porous silica-fiber composite prepared in Step C is immersed in an alcohol solvent, and the water contained therein is replaced with the alcohol solvent.
(5) Step E of heating the porous silica-fiber composite under normal pressure to dry the alcohol solvent contained therein

Hereinafter, each process will be described in more detail.
(1) Process A
Formation of the siloxane sol in step A is performed in the presence of an acid catalyst. The production of siloxane oligomers by hydrolysis and condensation reactions of alkoxysilane compounds is catalyzed by both acids and bases. However, since the reaction rate is too high with a base catalyst, a silicon oxide gel having a high density is obtained. This is because it is preferable to use an acid catalyst having a lower reaction rate for forming the gel.

The acid used for the preparation of the acidic aqueous solution having a pH of 3 to 4.5 is not particularly limited as long as it is water-soluble. Any organic acid and inorganic acid can be used in consideration of price, availability, safety and the like. Can be used. Specific examples of organic acids include monocarboxylic acids such as acetic acid, formic acid and propionic acid, dicarboxylic acids such as oxalic acid, malonic acid, succinic acid and maleic acid, oxycarboxylic acids such as lactic acid and tartaric acid, citric acid and malic acid And polyvalent carboxylic acids. Specific examples of the inorganic acid include hydrochloric acid, nitric acid, sulfuric acid, phosphoric acid and the like.

In order to form a porous gel having a high porosity, a surfactant is added to the acidic aqueous solution. A method for synthesizing porous inorganic oxides by sol-gel method using nanoscale molecular aggregates (micelles, etc.) formed by amphiphilic surfactants in water as a template. Widely used. However, when a cationic surfactant is used in the preparation of a porous gel, a porous gel having a fine structure can be obtained. On the other hand, the mechanical strength of the porous gel is reduced, and the fine structure is destroyed by shrinkage during drying. Problems occur.

Therefore, in step A, a nonionic surfactant is used. Examples of the nonionic surfactant include polyethylene oxide, polypropylene oxide, polyethylene oxide-polypropylene oxide copolymer, and the like. When these nonionic surfactants are used, polyoxyethylene chains are adsorbed on silanol groups, and a hydrophobic environment is partially formed. Accordingly, the compatibility gradually decreases and phase separation occurs, so that a porous gel having a network structure can be formed with the progress of polymerization.

The addition amount of a nonionic surfactant is 10-40 weight part with respect to 100 weight part of acidic aqueous solution, Preferably it is 15-25 weight part. If the amount of the nonionic surfactant added is too large, gelation does not proceed in the subsequent step, and if it is too small, the porosity of the resulting porous gel is lowered.

A major problem in the production of porous gels is the destruction of the microstructure accompanying shrinkage during drying. In conventional airgel synthesis, drying is performed in a supercritical state in order to avoid this problem, which causes an increase in manufacturing cost, difficulty in mass production, and the like. Therefore, in this production method, a water-soluble aprotic polar organic solvent is used in order to suppress the occurrence of cracks associated with drying by reducing the volatility and surface tension of the reaction solution.

Specific examples of the water-soluble aprotic polar organic solvent include N, N-dimethylformamide (DMF), N, N-dimethylacetamide (DMA), dimethyl sulfoxide (DMSO), N-methylpyrrolidone (NMP), sulfolane. Most preferred is N, N-dimethylformamide.

The addition amount of the water-soluble aprotic polar organic solvent is 5 to 15 parts by weight, preferably 6 to 10 parts by weight with respect to 100 parts by weight of the acidic aqueous solution. If the addition amount is too small, sufficient shrinkage and crack suppressing effects cannot be obtained, and if it is too much, the production cost increases.
An appropriate amount of a water-soluble organic solvent such as methanol may be added as necessary.

When the sol-gel reaction for forming a porous gel is performed only in the presence of an acid catalyst, the reactivity is too low to leave a large amount of unreacted sol (siloxane oligomer), and the porous gel has sufficient strength. Is difficult to get. Therefore, in the initial stage of the sol-gel reaction, the reaction is carried out in the presence of an acid catalyst to suppress the formation of a dense gel, and at the stage where the reaction has progressed to some extent, the unreacted siloxane sol is completely reacted. It is preferable to add a base catalyst. In this production method, urea is added to the reaction solution, and the reaction solution is made basic using ammonia generated by hydrolysis under acidic conditions. An advantage of adding urea is that the microstructure of the porous gel can be controlled by changing the addition amount.

The addition amount of urea is 30 to 70 parts by weight, preferably 35 to 50 parts by weight with respect to 100 parts by weight of the acidic aqueous solution. If the addition amount is too large, gelation does not proceed on the contrary, and if it is too small, a sufficient reaction rate cannot be obtained. In order to avoid rapid hydrolysis of urea, it is preferable to add urea to the reaction solution at a low temperature (for example, under ice cooling).

Examples of the alkoxysilane compound used as a raw material for forming a porous gel by sol-gel reaction include alkyltrialkoxysilane, aryltrialkoxysilane, and bis (trialkoxysilyl) alkane (hereinafter collectively referred to as “trialkoxysilane compound”). May be used). Since porous gels obtained using these alkoxysilane compounds are less susceptible to shrinkage and cracking during drying than porous gels obtained using tetraalkoxysilane, they are preferably used as raw materials for this production method. be able to.

Examples of the alkyl group include a linear or branched alkyl group having 5 or less carbon atoms or an arylalkyl group having 10 or less carbon atoms, and examples of the aryl group include a phenyl group and a naphthyl group. Specific examples of the alkyltrialkoxysilane include methyltrimethoxysilane (MTMS), methyltriethoxysilane, ethyltrimethoxysilane, ethyltriethoxysilane, propyltrimethoxysilane, and propyltriethoxysilane. Specific examples of the aryltrialkoxysilane include phenyltrimethoxysilane and phenyltriethoxysilane. Specific examples of the bis (trialkoxysilyl) alkane include 1,2-bis (trimethoxysilyl) ethane, bis (trimethoxysilylethyl) benzene and the like. As the trialkoxysilane compound, only one of these may be used alone, or any two or more of them may be mixed and used at an arbitrary ratio.

The addition amount of the trialkoxysilane compound is 50 to 100 parts by weight, preferably 70 to 100 parts by weight with respect to 100 parts by weight of the acidic aqueous solution. In order to avoid rapid progress of the reaction, the trialkoxysilane compound is added to the reaction solution in several portions under ice cooling. By the action of the acid catalyst, generation of silanol groups by hydrolysis of alkoxysilyl groups and condensation of silanol groups proceed, and a sol solution containing a siloxane monomer and an oligomer is obtained.

(2) Process B
The fiber structure is impregnated with the mixed solution (sol solution) containing the siloxane sol obtained as described above. In the present invention, the “fiber structure” refers to a material composed of long fibers, short fibers, or a mixture thereof and having a predetermined shape and structure such as a sheet shape, and preferably a non-woven fabric. Hereinafter, the case where a nonwoven fabric is used as an example of a preferable fiber structure will be described. There is no restriction | limiting in particular about the material and manufacturing method of a nonwoven fabric, The arbitrary things which have a desired property can be used. Examples of non-woven fabric materials include polyethylene phthalate (PET), synthetic fibers such as aramid fibers, natural fibers such as cotton and wool, inorganic fibers such as silica fibers and carbon fibers, and combinations of any two or more of these. Things. Nonwoven specific gravity (basis weight), for example 180~250g / ^{m 2,} preferably about 200 g / ^{m 2.}

The impregnation of the sol solution into the non-woven fabric can be performed using any method such as immersion, spraying or coating of the non-woven fabric in the sol solution. The impregnation amount of the sol solution is, for example, 20 to 40 kg per 1 kg of the nonwoven fabric.

Note that a nonwoven fabric or woven fabric made of hollow fibers may be used as the fiber structure, and in this case, the inside of the hollow fibers may be impregnated with a sol solution.

(3) Process C
Next, the nonwoven fabric impregnated with the sol solution is reacted at a constant temperature, and a porous gel is generated in a state of being attached to the nonwoven fabric. The reaction is performed, for example, by placing a nonwoven fabric impregnated with a sol solution in a sealed container and leaving it for a predetermined time under heating. The hydrolysis of urea is advanced by heating, and the sol solution is changed to basic (pH 9 to 11) using the ammonia produced thereby. By doing in this way, the speed | rate of silanol condensation reaction increases, the unreacted silanol group reacts, and the composite_body | complex in which the porous gel which has a highly strong network structure was formed in the inside of a nonwoven fabric is obtained.
The reaction temperature is 40 to 65 ° C., preferably 45 to 60 ° C., and the time required for the reaction is, for example, about 3 to 7 days when heated to 60 ° C.

(4) Process D
Since the composite obtained in this manner contains water having a high surface tension, if it is dried as it is, there is a risk of destruction of the fine structure accompanying shrinkage. Therefore, the composite is immersed in an alcohol solvent, and the water contained therein is replaced with the alcohol solvent.
As the alcohol solvent, any alcohol soluble in water can be used. Specific examples thereof include methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, and 2-methyl-2. -Propanol. Of these, only one type may be used alone, or any two or more types may be mixed and used at an arbitrary ratio.

The substitution of the solvent is performed by immersing the complex in an alcohol solvent in a suitable tank for a predetermined time (for example, 5 days). If necessary, the immersion may be performed while exchanging the alcohol solvent in the tank. In place of the alcohol solvent, an aprotic water-soluble polar organic solvent such as DMF may be used.

(5) Process E
Finally, the complex is obtained by heating the complex under normal pressure to dry the alcohol solvent. Drying may be performed under normal pressure or reduced pressure. When methanol is used in Step D, for example, hot air drying is performed at 100 ° C. for 48 hours under normal pressure.

As needed, you may have further the process F which makes the unreacted silanol group and alkylating agent which are contained in a porous gel react between the process D and the process E. By alkylating the unreacted silanol group in step F, the hydrophobicity inside the porous gel can be improved, and the destruction of the fine structure due to shrinkage during drying can be suppressed.
As the alkylating agent, any alkylating agent having reactivity with a silanol group can be used. As the alkylating agent, alkyl halides such as methyl iodide for converting silanol groups (Si—OH) into alkoxysilyl groups (Si—OR), and sulfonic acid alkyl esters such as methyl tosylate may be used. Selected from the group consisting of alkyltrihalosilanes, dialkyldihalosilanes, trialkylhalosilanes, alkyltrialkoxysilanes, dialkyldialkoxysilanes and trialkylalkoxysilanes that convert silanol groups to alkylsilyl ether groups (Si-O-SiR) One or more of the above are preferably used. Most preferred alkylating agents include trialkylsilane compounds such as trimethylsilane and trimethylmethoxysilane. Alternatively, hexamethyldisilazane (HMDS) may be used instead of the trialkylsilane compound.

The porosity of the porous gel contained in the composite is 50 to 85%, preferably 80 to 85%. Further, the porous gel has substantially spherical pores, and the pore volume determined by pore distribution measurement is 2 to ⁴ g · cm ³ per 1 g of the porous gel, and the peak of the pore volume distribution is About 15-25 nm. The pore distribution measurement can be performed using any known method such as a gas adsorption method or a mercury intrusion method.
The thermal conductivity is measured using an arbitrary method used for a porous heat insulating material (for example, a flat plate direct method according to JIS A1413, a flat plate comparison method according to JIS A1412, or the like) or a similar method thereto. be able to. Since the composite exhibits a thermal conductivity lower than that of air, it is difficult to accurately obtain the value in the atmosphere. For example, when measured using a method similar to the direct plate method of JIS A1413, Thermal conductivity values of 0.006 to 0.02 W · m ⁻¹ · K ⁻¹ are obtained. The reason why the composite exhibits such a low thermal conductivity is not necessarily clear, but is thought to be due to the substantially spherical pore shape and the low contribution of convection of the atmosphere contained in the pore.

The composite can be used as it is as a heat insulating material, a sound absorbing material or the like. Since a porous gel is formed inside a fibrous structure such as a nonwoven fabric, it is less likely to break than a porous gel alone, and can be used in a state where deformation such as bending is added as necessary. In addition, when using it, for example on the high temperature conditions more than the heat-resistant temperature of a nonwoven fabric, it can also be used, after heat-processing at high temperature and thermally decomposing a nonwoven fabric.

In the vacuum heat insulating material according to the second embodiment of the present invention, the porous silica-fiber composite according to the first embodiment of the present invention is sealed under reduced pressure inside the packaging material having gas barrier properties. . A vacuum heat insulating material is manufactured by a process as shown in FIG. 2, for example. In the flowchart shown in FIG. 2, the steps from solution preparation to drying are the same as the manufacturing steps of the complex according to the first embodiment. The composite obtained in this way is molded into a predetermined shape and size and then sealed under reduced pressure inside a packaging material having gas barrier properties, whereby a vacuum heat insulating material is obtained. In this way, by sealing the composite under reduced pressure inside the packaging material having gas barrier properties, the contribution of atmospheric convection in the pores to the heat conduction is almost eliminated, so the heat insulation performance is higher than that of the composite in the atmosphere. can get. Moreover, hydrolysis of the hydrophobic group covering the surface of the porous gel contained in the composite is suppressed, and the pore structure can be maintained for a long period of time. Therefore, the vacuum heat insulating material can maintain high heat insulating performance over a long period of time.

As the packaging material, a gas barrier film made of PET or the like on which aluminum is deposited is preferably used.
The vacuum sealing can be performed using any known method and apparatus such as a vacuum packaging machine.

Next, examples carried out for confirming the effects of the present invention will be described.
Example 1 Production of Porous Silica Gel-Nonwoven Fabric Composite (1) Preparation of Reaction Solution (Sol Solution) Acetic acid (manufactured by Daicel Chemical) 0.21% by weight was added to 30% by weight of pure water, and after stirring, pH 3-4. Make an acidic aqueous solution of 5. Subsequently, 6 wt% of PE-108 (polyoxyethylene-polyoxypropylene copolymer: manufactured by Sanyo Chemical Co., Ltd.) was added and stirred until dissolved. To the obtained solution, 12% by weight of urea (manufactured by Mitsui Chemicals) was added and stirred until dissolved, and then 2% by weight of DMF was added and stirred. The obtained aqueous solution was cooled to 0 ° C. or lower, and 28.5% by weight of KBM-13 (methyltrimethoxysilane: manufactured by Shin-Etsu Chemical Co., Ltd.) was added and stirred.

(2) Impregnated spunbond (Toyobo) A non-woven fabric was impregnated with a sol solution and placed in a sealed container (made of Kawanabe Stainless Steel) and completely sealed. The container was kept at 60 ° C. in a thermostatic chamber and aged for 5 days to complete the sol-gel reaction.

(3) Substitution with methanol The composite obtained as described above was washed with methanol and then immersed in methanol at room temperature for 5 days in order to replace the water contained therein with methanol.

(4) Drying After that, it was dried in a drying cabinet at 100 ° C. for 48 hours. When the porous silica gel-nonwoven fabric composite thus obtained was confirmed with a scanning electron microscope (SEM), a porous structure having spherical pores with a diameter of 20 to 50 nm was confirmed as shown in FIG. It was. As a result of measuring the pore distribution using a mercury porosimeter, it was confirmed that there were 3.5 cm ³ pores per gram and the peak pore diameter was about 20 nm.
A simple thermal conductivity measuring device using a method similar to JIS A1413 (Method for measuring thermal conductivity of heat insulating agent (flat plate direct method)) was made, and the thermal conductivity of the obtained porous silica gel-nonwoven fabric composite was measured. As a result, a numerical value of about 0.0068 W · m ⁻¹ · K ⁻¹ was obtained.

Example 2: Production of vacuum heat insulating material After packing the porous silica gel-nonwoven fabric composite (thickness 6 mm) produced in Example 1 with an aluminum vapor-deposited gas barrier film (PET), a high vacuum packaging machine (manufactured by V-tec) is used. The inside of the package was depressurized to 0.5 Torr, and the film was sealed to complete the vacuum heat insulating material.

Using the vacuum heat insulating material obtained as described above, a cold storage container with a lid having an inner size of 455 × 260 × 83 (mm) was produced. Moreover, the cold storage container (internal dimension 455x260x83 (mm)) with the lid | cover made from the polystyrene foam (expansion magnification 70-80 times) which can accommodate this cold storage container inside was prepared.
A plate ice (300 × 180 × 80 () is provided for each of (A) a vacuum heat insulating material insulated container, (B) a foamed polystyrene cold insulated container, and (C) a foamed polystyrene cold insulated container containing a vacuum heat insulating material insulated container inside. mm) and a weight of about 1.7 kg), and after sealing the lid with a PET film tape, the time until the ice completely melted at room temperature was measured.

The measurement results for the cold storage containers (A), (B), and (C) were 17 hours, 15 hours, and 22 hours, respectively. From these measurement results and the thermal conductivity of expanded polystyrene (0.035 W · m ⁻¹ · K ⁻¹ ), the thermal conductivity of the vacuum heat insulating material was estimated to be 0.0076 W · m ⁻¹ · K ⁻¹ . .

INDUSTRIAL APPLICABILITY The present invention can be used for applications such as buildings (roofs, walls, floors, etc.), industrial plants (reactors, distillation towers, pipelines, etc.), freezers, heat insulating materials such as cold cars, and sound absorbing materials for houses.

Claims (9)

100 parts by weight of an acidic aqueous solution having a pH of 3 to 4.5, 10 to 40 parts by weight of a nonionic surfactant, 5 to 15 parts by weight of a water-soluble aprotic polar organic solvent, and 30 to 70 parts by weight of urea. 50 to 100 parts by weight of one or more alkoxysilane compounds selected from the group consisting of alkyltrialkoxysilanes, aryltrialkoxysilanes, and bis (trialkoxysilyl) alkanes are added to the mixed liquid under ice cooling, Producing a siloxane sol in the mixed solution; and
Step B of impregnating the fiber structure with a mixed liquid containing the siloxane sol;
Porous silica fiber in which the silicon oxide gel is formed inside the fiber structure by reacting the siloxane sol at a constant temperature inside the fiber structure to generate a porous silicon oxide gel. Preparing a complex, step C;
Step D of immersing the porous silica-fiber composite in an alcohol solvent, and substituting water contained therein with the alcohol solvent;
A process for producing a porous silica-fiber composite comprising the step E of heating the porous silica-fiber composite under normal pressure to dry the alcohol solvent contained therein. The method for producing a porous silica-fiber composite according to claim 1, further comprising a step F of reacting a silanol group contained in the porous silica gel with an alkylating agent between the step D and the step E. The method for producing a porous silica-fiber composite according to any one of claims 1 and 2, wherein the fiber structure is a nonwoven fabric. The method for producing a porous silica-fiber composite according to any one of claims 1 to 3, wherein the fiber structure includes hollow fibers, and the porous silica gel is formed therein. The method for producing a porous silica-fiber composite according to any one of claims 1 to 4, wherein the water-soluble aprotic polar organic solvent is N, N-dimethylformamide. The alcohol solvent is one or more selected from the group consisting of methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, and 2-methyl-2-propanol. Item 6. A method for producing a porous silica-fiber composite according to any one of Items 1 to 5. 3. The alkylating agent is one or more selected from the group consisting of alkyltrihalosilanes, dialkyldihalosilanes, trialkylhalosilanes, alkyltrialkoxysilanes, dialkyldialkoxysilanes, and trialkylalkoxysilanes. 6. The method for producing a porous silica-fiber composite according to any one of 6 above. A porous silica-fiber composite produced by the production method according to claim 1. A vacuum heat insulating material obtained by sealing the porous silica-fiber composite according to claim 8 under reduced pressure inside a packaging material having gas barrier properties.