JP2007230858A - Heat insulating material and its production method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent detachment of inorganic particulate in an inorganic particulate-containing heat insulating material, further, to make each surface smooth and satisfactory while having no crack, and further to eliminate restriction on using temperature and shape. <P>SOLUTION: In the heat insulating material, a coating layer is formed on at least a part of the surface of a heat insulating formed body comprising silica particulate, alumina particulate, aluminum silicate particulate or their mixture having a BET (Brunauer-Emett-Teller) specific surface area of 15 to 500 m<SP>2</SP>/g and a primary particle diameter of 0.003 to 1 μm, and the coating layer comprises inorganic particles with the average particle diameter of 0.05 to 50 μm, and a binder. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a heat insulating molded body containing inorganic fine particles as a main raw material and a method for producing the same.

  In order to improve the heat insulation effect by suppressing the transmission of inorganic materials such as airgel, fume-like silica, alumina, etc., and heat insulating material by pressure, inorganic fine particles, reinforcing fibrous materials, and radiant light A heat insulating material obtained by blending a milk white material or the like and press-molding is widely used.

  However, in such a heat insulating material containing inorganic fine particles, since the bonding force between the fine particles is small, the surface thereof is very fragile and the inorganic fine particles are easily detached. For this reason, inorganic fine particles frequently adhere to the hands and clothes of workers who manufacture and construct such heat insulating materials, and when used indoors where a blower is installed, There is a problem that inorganic fine particles are scattered.

  In order to solve such a problem of detachment of inorganic fine particles, it is generally performed to cover a heat insulating material with a surface layer material such as a metal film, a plastic film, or a glass fiber woven fabric. However, there are problems such as the use temperature being limited by the type of surface layer material, and being applicable only to flat heat insulating materials.

  In addition, measures such as forming a dense film made of a glaze on the surface of the heat insulating material (see Patent Document 1) or increasing the density of the surface with a binder or the like (see Patent Document 2) are also taken. However, the former has a problem that the coating itself cracks or the coating peels off due to the sintering of the glaze, and the latter is a method of agglomerating inorganic fine particles on the surface of the heat insulating material, so that the surface of the heat insulating material has cracks. There is a problem that occurs. These problems cause defects such as poor appearance and detachment of inorganic fine particles from cracks.

JP 61-106476 A JP 2005-36975 A

  The present invention has been made in view of such circumstances, and prevents the removal of inorganic fine particles in a heat insulating material containing inorganic fine particles, has no cracks, has a smooth and good surface, and further uses temperature and shape. The purpose is to eliminate the restrictions.

In order to achieve the above object, the present invention provides the following heat insulating material and method for producing the same.
(1) At least the surface of a heat insulating molded article containing silica fine particles, alumina fine particles, aluminum silicate fine particles or a mixture thereof having a BET specific surface area of 15 to 500 m ² / g and a primary particle size of 0.003 to 1 μm. A heat insulating material characterized in that a coating layer is partially formed and the coating layer contains inorganic particles having an average particle diameter of 0.05 to 50 μm and a binder.
(2) The heat insulating material according to claim 1, wherein the binder comprises at least one of a hydrolyzate of an alkoxide compound and a metal oxide sol.
(3) At least a part of the hydrolyzate of the alkoxide compound has an alkyl group bonded directly to a metal atom, and the heat insulating material (4) heat insulating molded body according to the above (2) is a fibrous material The heat insulating material according to any one of (1) to (3) above, comprising at least one of a substance and a milk white material.
(5) The inorganic particles constituting the coating layer are silica, alumina, silicate, aluminosilicate or milk white particles, or a mixture thereof. Any one of the heat insulating materials.
(6) The heat insulating material according to any one of (1) to (5) above, wherein the coating layer contains at least one of a fibrous substance and an organic thickener.
(7) A molded body material containing silica fine particles, alumina fine particles, aluminum silicate fine particles or a mixture thereof having a BET specific surface area of 15 to 500 m ² / g and a primary particle size of 0.003 to 1 μm is formed into a predetermined shape. A heat insulating material obtained by applying a dispersion containing inorganic particles having an average particle diameter of 0.05 to 50 μm and a binder to the heat insulating molded body obtained by impregnation, or drying after impregnation. Production method.
(8) The method for producing a heat insulating material according to the above (7), wherein the binder comprises at least one of a hydrolyzate of an alkoxide compound and a sol of metal oxide.
(9) The method for producing a heat insulating material according to the above (8), wherein at least a part of the hydrolyzate of the alkoxide compound has an alkyl group directly bonded to a metal atom. The method for producing a heat insulating material according to any one of the above (7) to (9), which is alcohol or a mixed liquid of alcohol and water.
(11) The method for producing a heat insulating material according to any one of (7) to (10) above, wherein the dispersion contains at least one of a fibrous substance and an organic thickener.

  In the heat insulating material of the present invention, a coating layer in which inorganic particles and fibrous substances are bonded with a binder made of a hydrolyzate of an alkoxide compound, a sol of a metal oxide, or the like is formed on the surface of a heat insulating molded body containing inorganic fine particles. Is. Therefore, there is no detachment of inorganic fine particles, there is no crack, the surface is smooth, and the coating layer is inorganic, so there is no restriction on the use temperature. In addition, since the coating layer is formed by simply applying or impregnating a dispersion containing the constituent components of the coating layer and drying, the process is simple and the shape of the heat insulating molded body is not limited.

  Hereinafter, the present invention will be described in detail.

In the present invention, the heat insulating molded body is mainly composed of silica fine particles, alumina fine particles, aluminum silicate fine particles or a mixture thereof having a BET specific surface area of 15 to 500 m ² / g and a primary particle diameter of 0.003 to 1 μm. Contains as an ingredient. If the primary particle diameter of these inorganic fine particles exceeds 1 μm, the heat insulating molded product cannot obtain a sufficient heat insulating effect, and if it is smaller than 0.003 μm, it is very bulky and difficult to handle. In addition, when the BET specific surface area of the inorganic fine particles is less than 15 m ² / g or more than 500 m ² / g, the heat insulating molded body cannot obtain a sufficient heat insulating effect.

  Examples of the silica fine particles satisfying such BET specific surface area and primary particle diameter include silica obtained by combustion of halides, silica obtained by the reaction of sodium silicate and sulfuric acid, and silica obtained by condensation of alkoxide. It is done. Moreover, about the alumina fine particles and the aluminum silicate fine particles, those produced by the same method can be used.

  The heat insulating molded body can be formed only from the inorganic fine particles, but may contain a fibrous substance for reinforcement. Examples of fibrous materials include glass fibers, alumina fibers, mullite fibers, silica fibers, aluminum silicate fibers, silicate fibers, aluminosilicate fibers, carbon fibers, silicon carbide fibers and other inorganic fibers, polyethylene fibers, polypropylene fibers, polyamides Examples thereof include organic fibers such as fibers, or mixtures thereof, and the like, which are appropriately selected in consideration of the atmosphere, temperature, and the like in which the heat insulating material is used. In addition, although there is no restriction | limiting in a fiber diameter and fiber length and it is based also on the kind of fiber, a fiber diameter is 0.8-50 micrometers and 1-15 mm is suitable for fiber length.

  Furthermore, the heat insulating molded body may contain an opacifying material. The milk white material has a function of suppressing transmission of radiant light, and has an effect of improving heat insulation performance. Examples of the milk white material include titanium oxide, zirconium oxide, zirconium silicate, silicon carbide, zinc oxide, iron oxide, ilmenite, particles of boron nitride, or a mixture thereof. It is appropriately selected in consideration of the milky white effect and the like.

  In the case of containing a fibrous substance or milky white material, it is appropriate that the content of the fibrous material is 30% by mass or less of the total amount of the heat insulating molded body, and the content of the milky white material is 50% by mass or less of the total amount of the heat insulating molded body. It is. When the content of the fibrous substance exceeds 30% by mass, the influence on the heat insulating property of the heat insulating molded body is increased, and a sufficient heat insulating effect cannot be obtained. On the other hand, when the content of the milk white material exceeds 50% by mass, the heat conduction effect of the milk white material itself becomes larger than the radiation light suppressing effect, and a sufficient heat insulating effect cannot be obtained.

  The heat-insulating molded product can be obtained by filling a predetermined mold with inorganic fine particles and, if necessary, adding and mixing a fibrous substance or a milky white material, followed by pressurization. The molding conditions are appropriately set according to the type of inorganic fine particles, the type of fibrous material or milk white material and the blending ratio thereof, the shape of the resulting molded body, and the like.

The density of the heat insulating molded body is not particularly limited, but is preferably 150 to 600 kg / m ^{3 and} more preferably 200 to 400 kg / m ³ from the viewpoint of exerting heat insulating performance. Moreover, although there is no restriction | limiting in particular also about heat conductivity, 0.020-0.05W / m * K [100 degreeC] is preferable from a viewpoint of exhibiting heat insulation performance, and 0.025-0.035W / m * K. [100 ° C.] is more preferable.

  Inorganic particles having an average particle diameter of 0.05 to 50 μm are bonded to the entire surface of the heat insulating molded body or an arbitrary portion of the surface by at least one of an alkoxide compound hydrolyzate and a metal oxide sol. A coating layer is formed. This coating layer is obtained by applying a dispersion liquid containing inorganic particles having an average particle diameter of 0.05 to 50 μm and at least one sol of an alkoxide compound and a metal oxide to the whole surface or a part of the heat insulating molded body. Alternatively, it is formed by immersing all or part of the heat insulating molded body in the dispersion and then drying. In addition, when apply | coating a dispersion liquid, there is no restriction | limiting in the application method, Well-known application means, such as a brush, a roll, and a spray, can be used.

  When fine particles having an average particle size of less than 0.05 μm are used as the inorganic particles, the aggregation of the inorganic particles becomes remarkable, and the coating layer is cracked. Moreover, the smoothness of the surface is reduced with large-diameter particles exceeding 50 μm. In addition, although there is no restriction | limiting in the kind of inorganic particle, Considering heat resistance, the silica, alumina, and aluminum silicate which are used for the heat insulation molded object are preferable.

  The thickness of the coating layer is not particularly limited, but usually becomes a film thickness of 10% or less of the whole heat insulating material through application or impregnation of the dispersion and drying. However, from the viewpoint of heat insulation performance and production, 30 to 2000 μm is preferable, 40 to 500 μm is more preferable, and 45 to 250 μm is still more preferable. Moreover, if a coating layer is 10% or less of the thickness of the whole heat insulating material, a milk white material can also be used as an inorganic particle. As described above, when milk milk is used in a large amount, the effect of its own heat conduction appears. However, if milk milk is 10% or less of the total thickness of the heat insulating material, there is no problem even if milk milk is used. The milk white material can be exemplified by a milk white material used for the heat insulating molded body, but the milk white material used for the coating layer and the milk white material used for the heat insulating molded body may be the same or different.

  Furthermore, the above-mentioned inorganic particles can be mixed and used, and the combination and blending ratio thereof are appropriately set depending on the intended heat insulating performance.

  Since the dispersion permeates between the inorganic fine particles forming the heat insulating molded body by dipping or coating, when a highly polar dispersion medium is used, the inorganic fine particles are aggregated by the permeated dispersion medium, and the heat insulating molded body Cracks will occur. Such a problem is more conspicuous in a liquid having a large polarity such as water. Therefore, in the present invention, a mixed liquid of alcohol having a polarity smaller than water and water is used as a dispersion medium of the dispersion liquid. As the alcohol, methanol, ethanol, isopropyl alcohol and the like are preferable because they are excellent in safety and handleability. The water: alcohol mixing weight ratio is preferably 0: 100 to 70:30. Although it depends on the components contained in the dispersion, it is highly likely that the problems caused by the contact between the dispersion and the heat insulating molded body can be sufficiently reduced within this range.

  However, although alkoxide compounds such as tetramethoxysilane and tetraethoxysilane are represented by the general formula “M- (OR) n (M: metal atom, R: alkyl group)”, they react with water to produce a hydrolyzate “ M- (OH) n ", and the hydrolyzates of the alkoxide compounds are dehydrated and condensed to form" M-OM "to have a binder function. Therefore, when an alkoxide compound is used, it is necessary to use a mixture of water and alcohol in a sufficient amount for hydrolysis as a dispersion medium. In some cases, an acid such as hydrochloric acid or sulfuric acid for promoting hydrolysis, or It is necessary to add alkali such as ammonia or sodium hydroxide. The alkoxide compound is preferably a silicon alkoxide or an aluminum alkoxide as described above. There are many alkoxide compounds other than silicon and aluminum alkoxides, but they are extremely expensive and cannot be practically used.

  Moreover, at least a part of the hydrolyzate of the alkoxide compound may have an alkyl group directly bonded to a metal atom. In this case, there is an advantage that the obtained heat insulating material exhibits water repellency. However, when all of the hydrolyzate of the alkoxide compound has an alkyl group, the binding action is reduced and the dust generation suppressing effect is reduced. Therefore, (i) (a) having an alkyl group directly bonded to a metal atom. (Ii) (c) metal oxide sol and (b) metal atom in combination with (b) hydrolyzate of alkoxide compound having an alkyl group directly bonded to the metal atom (Iii) (a) hydrolyzate of an alkoxide compound not having an alkyl group directly bonded to a metal atom and (c) sol of a metal oxide And (b) a combined use of a hydrolyzate of an alkoxide compound having an alkyl group directly bonded to a metal atom.

  As the metal oxide sol, an alumina, zirconia, titania, and silica sol can be suitably used because of its excellent binder effect, easy availability, and excellent handleability. Further, the particle size of the metal oxide sol is preferably 5 to 200 nm, and if it is less than 5 nm, the binder effect is too strong, so that the coating layer is cracked, and if it exceeds 200 nm, a sufficient binder effect cannot be obtained. The dispersion medium of the metal oxide sol is not particularly limited as long as it can be dissolved in the dispersion medium of the dispersion liquid. However, when the aqueous metal oxide sol is used, the polarity of the dispersion medium is increased. Care must be taken with the amount added. On the other hand, a metal oxide sol using alcohols as a dispersion medium is preferable because such attention is unnecessary. The metal oxide sol enters the gaps between the inorganic particles in the applied or impregnated dispersion, and the particles are precipitated by drying. The inorganic particles are bonded to each other by the cohesive force of the particles derived from the metal oxide sol.

  The content of each of the inorganic particles, the alkoxide compound, and the metal oxide sol in the dispersion is not limited as long as the inorganic particles can be held on the surface of the heat insulating molded body in a state where the inorganic particles are bonded to each other. It depends on the type of sol. For example, when tetraethoxysilane is used, the amount is preferably 5 to 200 parts by weight with respect to 100 parts by weight of the inorganic particles, and when a metal oxide sol is used, the solid content is 5 to 100 with respect to 100 parts by weight of the inorganic particles. It is preferable to use parts by weight.

  Moreover, the coating layer may contain a fibrous substance for reinforcement. The fibrous material can prevent cracks (small cracks) from entering the coating layer. Examples of the fibrous substance include those blended in the heat insulating molded body, and are appropriately selected in consideration of the atmosphere, temperature, and the like in which the heat insulating material is used. However, in consideration of the smoothness of the resulting coating layer, the fiber diameter is preferably 50 μm or less, similar to the inorganic particles. The fiber length is appropriately set depending on the type of fibrous substance, but is preferably 10 mm or less. If the content of the fibrous substance in the coating layer is too large, voids are generated in the coating layer due to fiber entanglement and the like, resulting in a decrease in the effect of preventing the removal of inorganic fine particles from the heat insulating molded body. May cause peeling of the coating layer and deterioration of the smoothness of the surface. Therefore, in this invention, it is preferable that content of a fibrous substance shall be 40 mass% or less of the coating layer whole quantity.

  In order to contain the fibrous substance in the coating layer, these may be added to the dispersion medium together with the inorganic particles, the alkoxide compound, and the sol of the metal oxide, and the addition amount is adjusted so as to be the content in the coating layer described above. .

  An organic thickener may be added to the dispersion. Since the dispersion applied or impregnated on the heat insulating molded body penetrates into the inside of the heat insulating molded body, an organic thickener is added to reduce the fluidity of the dispersion to suppress penetration. A coating layer is easily formed. As the organic thickener, polyvinyl alcohol, celluloses such as methylcellulose and ethylcellulose are suitable because they are excellent in the thickening effect and have the effect of increasing the film strength of the coating layer. However, since there is a risk of producing a strange odor or smoke when using the heat insulating material, the amount of the organic thickener added is preferably 5% by mass or less of the total amount of the dispersion medium.

  The amount of application and impregnation amount of the dispersion to the heat insulating molded body is appropriately set according to the composition and concentration of the dispersion, the size and shape of the heat insulating molded body, the area and shape of the part where the coating layer is formed, Preferably, the thickness of the coating layer is adjusted. Then, by drying the applied or impregnated dispersion, a coating layer in which inorganic particles are bonded with a hydrolyzate of an alkoxide compound or a sol of a metal oxide is formed. Since the coating layer to be formed also has voids between the inorganic particles, shrinkage due to drying is suppressed, and generation of cracks is suppressed.

  Moreover, application | coating or immersion of a dispersion liquid and subsequent drying can also be performed repeatedly. Even if a crack occurs in the coating layer, a coating layer having a smooth surface without cracks can be obtained by forming a new coating layer thereon. By repeatedly applying or immersing the dispersion and drying, it is possible to form the thick coating layer of about 2000 μm.

  EXAMPLES Hereinafter, although an Example and a comparative example are given and this invention is further demonstrated, this invention is not restrict | limited at all by this.

Example 1
Uniformly 70 parts by weight of silica fine particles having a primary particle diameter of 0.012 μm and a BET specific surface area of 200 m ² / g, 10 parts by weight of E-glass fibers having an average diameter of 10 μm and an average fiber length of 3 mm, and 20 parts by weight of silicon carbide The mixture was pressure-molded to obtain a heat-insulating molded body having a density of 300 kg / m ³ and a thermal conductivity of 0.04 W / m · K [100 ° C.].

  Subsequently, 100 parts by weight of silica particles having an average particle diameter of 0.7 μm, 3 parts by weight of E-glass fibers having an average diameter of 10 μm and an average fiber length of 3 mm, 67 parts by weight of ethanol, 30 parts by weight of water, 150 parts by weight of tetraethoxysilane and methylcellulose A dispersion composed of double parts was applied to the entire surface of the heat insulating molded body, put in a heating furnace at 100 ° C. and dried to obtain a test body.

(Example 2)
100 parts by weight of silica particles having an average particle diameter of 0.7 μm, 3 parts by weight of E-glass fibers having an average diameter of 10 μm and an average fiber length of 3 mm, 50 parts by weight of ethanol and 100 parts by weight of silica sol (solid content: 20%, medium: ethanol) A test body was obtained in the same manner as in Example 1 except that the dispersion liquid consisting of

(Example 3)
100 parts by weight of silica particles having an average particle diameter of 0.7 μm, 3 parts by weight of E-glass fibers having an average diameter of 10 μm and an average fiber length of 3 mm, 90 parts by weight of ethanol, 25 parts by weight of silica sol (solid content: 20%, medium: ethanol) A test specimen was obtained in the same manner as in Example 1 except that a dispersion composed of 75 parts by weight of tetraethoxysilane was used.

Example 4
100 parts by weight of silica particles having an average particle diameter of 0.7 μm, 3 parts by weight of E-glass fibers having an average diameter of 10 μm and an average fiber length of 3 mm, 67 parts by weight of ethanol, 30 parts by weight of water, 125 parts by weight of tetraethoxysilane, dimethyldiethoxy A test body was obtained in the same manner as in Example 1 except that a dispersion composed of 50 parts by weight of silane and 2 parts by weight of methylcellulose was used.

(Example 5)
100 parts by weight of silica particles having an average particle diameter of 0.7 μm, 3 parts by weight of E-glass fibers having an average diameter of 10 μm and an average fiber length of 3 mm, 40 parts by weight of ethanol, 10 parts by weight of water, silica sol (solid content: 20%, medium ethanol) ) A test specimen was obtained in the same manner as in Example 1 except that a dispersion comprising 75 parts by weight and 50 parts by weight of dimethyldiethoxysilane was used.

(Example 6)
100 parts by weight of silica particles having an average particle diameter of 0.7 μm, 3 parts by weight of E-glass fibers having an average diameter of 10 μm and an average fiber length of 3 mm, 90 parts by weight of ethanol, 15 parts by weight of water, silica sol (solid content: 20%, medium ethanol) ) A test specimen was obtained in the same manner as in Example 1 except that a dispersion comprising 25 parts by weight, 50 parts by weight of tetraethoxysilane and 50 parts by weight of dimethyldiethoxysilane was used.

(Example 7)
100 parts by weight of silica particles having an average particle diameter of 0.7 μm, 3 parts by weight of E-glass fibers having an average diameter of 10 μm and an average fiber length of 3 mm, 67 parts by weight of ethanol, 30 parts by weight of water, 200 parts by weight of dimethyldiethoxysilane, and methylcellulose 2 A test body was obtained in the same manner as in Example 1 except that the dispersion liquid consisting of parts by weight was used.

(Comparative Example 1)
The heat insulating molded body produced in Example 1 was used as a test body.

(Comparative Example 2)
An attempt was made to form a coating layer using a dispersion composed of 100 parts by weight of silica particles having an average particle size of 0.7 μm and 200 parts by weight of ethanol, but the silica particles were not bonded to each other, so that the coating layer could not be formed.

(Comparative Example 3)
Although an attempt was made to form a coating layer using a dispersion composed of 100 parts by weight of silica particles having an average particle size of 0.7 μm and 200 parts by weight of water, the silica particles were not bonded to each other, so that the coating layer could not be formed. The molded product was also greatly deformed.

(Comparative Example 4)
Silica sol (solid content: 20%, medium: ethanol) was applied instead of the dispersion, but the heat-insulating molded product was destroyed due to shrinkage of the coating layer.

[Evaluation of dust generation]
About each test body of Examples 1-7 and Comparative Example 1, dusting property evaluation was performed according to the following procedure. The results are shown in Table 1.
(1) A pressure-sensitive adhesive tape (cello tape (registered trademark) “CT-24” manufactured by Nichiban Co., Ltd., width: 24 mm) was applied to the surface of the test body with a pressure of 3 × 104 N / m ² .
(2) After standing for 5 seconds, the adhesive tape was peeled off from the specimen.
(3) The peeled adhesive tape was affixed on black paper, the brightness index was measured, and the dust generation index was determined according to the following formula. Lightness index is L value of L ^* a ^* b display system, color difference meter ("CR-300" manufactured by Minolta Co., Ltd., measuring head 91mm width x 201mm height x 60mm depth x 670g weight x measuring diameter 8mm) It measured using. The brightness index was measured five times for the same specimen, and the average value was measured.
Dust generation index = Lightness index of the adhesive tape peeled from the specimen-Lightness index of the adhesive tape itself

[Evaluation of water repellency]
Pure water 1g was dripped on the surface of the test body of Example 1 and 4-7, and water repellency was evaluated from the water absorption condition.

  In the pressure-sensitive adhesive tape to which no deposit is adhered, the light from the light source is almost transmitted through the pressure-sensitive adhesive tape, and the L value is low because the light is hardly reflected from the black paper. On the other hand, in the pressure-sensitive adhesive tape to which the adhering matter has adhered, the L value becomes high because the light from the light source is reflected by the adhering matter. Therefore, the larger the amount of deposits on the adhesive tape, the larger the dusting index. As shown in Table 1, in the test sample of the example in which the coating layer according to the present invention was formed, the dust generation index was small, and the silica particles and the glass fibers were firmly bonded in the coating layer. Recognize.

  Also, with respect to water repellency, in Example 1, pure water was absorbed by the test specimen within 1 second, and the surface of the test specimen was depressed, but in Examples 4 to 7, pure water was used. Was not absorbed by the specimen and remained on the surface after 24 hours.

Claims (11)

At least part of the surface of the heat insulating molded body containing silica fine particles, alumina fine particles, aluminum silicate fine particles or a mixture thereof having a BET specific surface area of 15 to 500 m ² / g and a primary particle diameter of 0.003 to 1 μm. A heat insulating material, wherein a coating layer is formed, and the coating layer contains inorganic particles having an average particle diameter of 0.05 to 50 µm and a binder.   The heat insulating material according to claim 1, wherein the binder comprises at least one of a hydrolyzate of an alkoxide compound and a sol of a metal oxide.   The heat insulating material according to claim 2, wherein at least a part of the hydrolyzate of the alkoxide compound has an alkyl group directly bonded to a metal atom.   The heat insulating material according to any one of claims 1 to 3, wherein the heat insulating molded body contains at least one of a fibrous substance and a milk white material.   The inorganic particles constituting the coating layer are silica, alumina, silicate, aluminosilicate, opalescent particles, or a mixture thereof, according to any one of claims 1 to 4. Insulation material.   The insulating layer according to any one of claims 1 to 5, wherein the coating layer contains at least one of a fibrous substance and an organic thickener. Obtained by molding a molding material containing silica fine particles, alumina fine particles, aluminum silicate fine particles or a mixture thereof having a BET specific surface area of 15 to 500 m ² / g and a primary particle size of 0.003 to 1 μm into a predetermined shape. A method for producing a heat insulating material, comprising: applying a dispersion containing inorganic particles having an average particle size of 0.05 to 50 μm and a binder to or impregnating the heat insulating molded body, followed by drying.   The method for producing a heat insulating material according to claim 7, wherein the binder comprises at least one of a hydrolyzate of an alkoxide compound and a sol of a metal oxide.   The method for producing a heat insulating material according to claim 8, wherein at least a part of the hydrolyzate of the alkoxide compound has an alkyl group directly bonded to a metal atom.   The method for producing a heat insulating material according to any one of claims 7 to 9, wherein the dispersion medium of the dispersion liquid is alcohol or a mixed liquid of alcohol and water.   The method for producing a heat insulating material according to any one of claims 7 to 10, wherein the dispersion contains at least one of a fibrous substance and an organic thickener.