JP4367612B2 - Porous body-coated particles, and a precursor for heat insulating material and the heat insulating material containing the porous body-coated particles - Google Patents

Description

  The present invention relates to a porous body-coated particle and a method for producing the same, and further relates to a heat insulating material precursor and the heat insulating material containing the porous body-coated particle.

More low thermal conductivity, as an excellent heat insulating material in the heat insulating performance, low thermal ultrafine particulate anhydrous silica, which is a conductive material (e.g., Nippon Aerosil Co., Ltd .: trade name Aerosil), ceramic fiber, and further oxidation of titanium oxide Known is a low thermal conductive heat insulating material (see Patent Documents 1 to 6) obtained by mixing a radiation absorption / scattering material composed of particles such as zirconium, press forming, and then machining.

JP-A-7-267756 Japanese National Patent Publication No. 10-509940 Japanese National Patent Publication No. 10-509941 Japanese National Patent Publication No. 11-513349 Japanese National Patent Publication No. 10-514959 Special Table 2000-506570

  The above ultrafine anhydrous silica and supercritical dry silica are fine particles having a diameter of several nanometers to several tens of nanometers, and have a thermal conductivity (hereinafter the same) of 0.01 W / (m · K) at room temperature (25 ° C.). It is a low thermal conductivity material. However, since ultrafine anhydrous silica and supercritical dry silica are fine particles having a diameter of several nanometers to several tens of nanometers, they associate with each other by intermolecular force to form secondary particles, as schematically shown in FIG. The secondary particles 10 are interspersed between the fibers of the inorganic fibers 20 such as ceramic fibers and glass fibers. Therefore, heat conduction occurs between the fibers where the inorganic fibers 20 are intertwined, and the low thermal conductivity of the ultrafine anhydrous silica or supercritical dry silica is greatly impaired. For example, the thermal conductivity of the glass fiber is about 0.1 W / (m · K), and the heat insulating performance of the entire heat insulating material greatly depends on the thermal conductivity of the glass fiber.

  Further, the radiation absorption / scattering material 1a is effective in reducing heat conduction in a high temperature range exceeding 200 ° C., but solid conduction occurs between adjacent radiation absorption / scattering materials, and in particular, heat conduction in a low temperature range of 200 ° C. or less. Becomes larger. Further, solid conduction occurs between the radiation absorbing / scattering material 1 a and the inorganic fiber 20.

  Furthermore, since the kneaded material of the inorganic fiber 20, the ultrafine anhydrous silica, the supercritical dry silica, and the radiation absorption scattering material 1a is press-molded without using a binder with an emphasis on heat insulation performance, the mechanical strength is increased. Is insufficient, the heat insulating material is cracked, the cut end face is likely to be chipped, etc., and there are also disadvantages in that it is inferior in handleability and workability. Furthermore, the secondary particles 10 of ultrafine anhydrous silica or supercritical dry silica only penetrate between the fibers, and the adhesion between the secondary particles 10 and the inorganic fibers 1 is small, and the secondary particles 10 are removed. Separate (powders) to contaminate the outside. Therefore, for example, there is also a problem that it is difficult to use in applications that require cleanliness such as semiconductor manufacturing equipment.

  Accordingly, an object of the present invention includes a heat insulating material that is excellent in heat insulating performance and also excellent in mechanical strength, handleability, and workability, and a porous coated particle suitable for obtaining the heat insulating material and the porous coated particle. It is in providing the precursor for heat insulating materials.

In order to achieve the above object, the present invention provides the following porous-coated particles, and a composite and a heat insulating material including the porous-coated particles.
(1) The core particles made of the second inorganic compound are covered with a porous body formed of secondary particles in which fine particles made of the first inorganic compound are associated in a ring shape or a spiral shape. Porous coated particles.
(2) The porous material-coated particle according to (1), wherein the core particle has an average particle diameter of 30 μm or less.
(3) The porous material-coated particles according to (1) or (2), wherein the fine particles have an average particle diameter of 5 to 50 nm.
(4) The porous body-coated particle according to any one of (1) to (3) above, wherein a ring inner diameter of the secondary particle is 0.1 μm or less.
(5) The porous material-coated particle according to any one of (1) to (4), wherein the core particle is 5 to 50% by mass and the fine particle is 50 to 95% by mass.
(6) At least one fiber material selected from inorganic fibers and porous coated fibers in which the inorganic fibers are covered with a porous body formed of the secondary particles, and any one of the above (1) to (5) A precursor for a heat insulating material, comprising the porous material-coated particles according to item 1.
(7) The precursor for a heat insulating material according to (6), wherein the porous body-coated particles are 55 to 95% by mass and the fiber material is 5 to 45% by mass.
(8) A heat insulating material obtained by pressure-molding the heat insulating material precursor according to (6) or (7).
(9) The heat insulating material according to (8), wherein the bulk density is 200 to 600 kg / m ³ and the bending strength is 0.3 MPa or more.
(10) The heat insulating material according to the above (9), wherein the heat conductivity at 1000 ° C. is 0.04 W / (m · K) or less.

  According to the present invention, a heat insulating material excellent in heat insulating performance and further excellent in mechanical strength, handleability and workability, a porous coated particle suitable for obtaining the heat insulating material, and a heat insulating material including the porous coated particle. A precursor for the material is provided.

  Hereinafter, the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a schematic view showing porous body-coated particles of the present invention, and FIG. 2 is a schematic view showing enlarged secondary particles of fine particles (hereinafter referred to as “inorganic fine particles”) made of an inorganic compound. As shown in the drawing, in the porous body-coated particle 100 of the present invention, the secondary particles 10 in which a plurality of inorganic fine particles 10a are associated in a ring shape or a spiral shape are attached to the core particle 1 made of an inorganic compound and further deposited. The core particle 1 is covered with a porous body made of inorganic fine particles 10a.

  The core particle 1 can be a particle made of a radiation absorption / scattering material such as silicon carbide, titanium oxide, or zirconium oxide. Here, the radiation absorption / scattering material may be inorganic particles having an absolute refractive index of 1.5 or more, and is not limited to the particles. The core particle 1 is preferably subjected to an oxidation heat treatment in order to improve the adhesion of the inorganic fine particles 10a. By this oxidation heat treatment, fine particles made of oxide are generated on the surface of the core particle 1 to form fine irregularities, and the adhesion of the inorganic fine particles 10a is increased. The treatment conditions may be heating at 800 to 1200 ° C. for 3 to 12 hours in air or in an oxygen atmosphere. The core particle 1 preferably has an average particle diameter of 30 μm or less in consideration of heat insulating performance and mechanical strength when used as a heat insulating material.

  As the inorganic fine particle 10a, for example, ultrafine anhydrous silica, supercritical dry silica, or the like can be used. As described above, these have a thermal conductivity of about 0.01 W / (m · K), which is also preferable in the present invention. In addition, fine particles such as alumina can also be used. The inorganic fine particles 10a preferably have an average particle diameter of 5 to 50 nm. As described above and as shown in FIG. 2, such fine particles associate with each other by intermolecular force, electrostatic force, or the like to form ring-shaped or spiral secondary particles 10. The inner diameter (R) is preferably 0.1 μm (100 nm) or less. This is because heat transfer through the secondary particles 10 can be substantially prevented if the mean free path of air serving as a heat transfer medium is about 100 nm at room temperature and the ring inner diameter (R) is about 0.1 μm or less. As will be described later, the secondary particles 10 are laminated in a deformed state to form a porous body. At that time, the ring inner diameter (R) is also reduced, and is below the mean free path of air. The inorganic fine particles 10a having an average particle diameter of 5 to 50 nm tend to form secondary particles 10 having such a ring inner diameter (R). A plurality of these inorganic fine particles 10a may be used in combination. Furthermore, other inorganic fine particles may be mixed as necessary.

  The compounding ratio between the core particles 1 and the inorganic fine particles 10a is preferably 5 to 50% by mass of the core particles 1 and 50 to 95% by mass of the inorganic fine particles 10a. If the blending ratio of the inorganic fine particles 10a is less than 50% by mass, the core particles 1 may not be sufficiently thickly covered with the secondary particles 10.

  In order to obtain the porous body-coated particles 100 of the present invention, a mixture obtained by dry-mixing the core particles 1 and the inorganic fine particles 10a with the above composition may be repeatedly passed through the minute gaps. Specifically, a rotary mixing device 30 as shown in FIG. 3 is used. The rotary mixing device 30 is configured by arranging a pressing member 32 inside a cylindrical chamber 31. The chamber 31 rotates in the direction of the arrow in the figure, and the pressing member 32 is fixed so that one end thereof forms a predetermined minute gap with the inner wall of the chamber 31.

  And the core particle 1 and the inorganic fine particle 10a are thrown into the rotation mixing apparatus 30 by the said compounding ratio (code | symbol 35 in the figure), and the chamber 31 is rotated. Along with this rotation, the secondary particles 10 composed of the inorganic fine particles 10a adhere to the surface of the core particle 1, and another secondary particle 10 is sequentially laminated thereon to form a laminated body. At that time, the secondary particles 10 adhere so as to be pushed into the surface of the core particle 1 by passing through a minute gap between the chamber 31 and the pressing member 32, and the secondary particles 10 are strongly pressed against each other even when they are stacked. The ring-shaped or spiral shape of the secondary particles 10 is deformed or decomposed into chain-like or individual inorganic fine particles 10a and complicatedly entangled with each other, so that the inorganic fine particles 10a or the secondary particles 10 are detached from the core particles 1. Never leave. Moreover, since many fine voids are formed between the particles of the inorganic fine particles 10a, the obtained laminate is a porous body.

4, using an oxidizing heat-treated carbon of silicon as the core particles 1, but as the inorganic fine particles 1a is an electron microscopic photograph of the porous coating particles 100 produced using the ultrafine particles of anhydrous silica, ultrafine particles on the surface porous secondary particles composed of Jo anhydrous silica are laminated is formed, it can be seen that the carbonization silicon is not exposed.

  The present invention also provides a heat insulating material containing the porous body-coated particles 100 described above. However, it is difficult to mold the porous body-coated particles 100 alone, and the obtained heat insulating material is also inferior in shape retention and mechanical strength. It will be low. Although it is conceivable to use a binder, since the heat insulation performance is lowered, a fiber material is mixed in the present invention to form a heat insulating material.

  As the fiber material, inorganic fibers themselves or those coated with a porous body made of the secondary particles 10 of the inorganic fine particles 1a as described above can be used. By using the inorganic fiber covered with the porous body, the inorganic fibers are not in direct contact with each other in the heat insulating material, and solid conduction does not occur, so that the heat insulating performance is excellent.

  As the inorganic fibers, alumina fibers, silica / alumina fibers, silica fibers, mullite fibers and other ceramic fibers, glass fibers, rock ole and the like can be used. Among these, inorganic fibers having low thermal conductivity, preferably thermal conductivity of 0.1 W / (m · K) or less, particularly 0.04 W / (m · K) or less are preferable, and silica such as silica / alumina fiber or silica fiber is preferable. A system fiber can be used conveniently. The inorganic fiber preferably has an average fiber diameter of 15 μm or less. When the average fiber diameter exceeds 15 μm, the surface area becomes large, so that it takes a long time to cover with the secondary particles 10 to be described later, which is not preferable in production. Furthermore, the average fiber length of the inorganic fibers is preferably 50 μm or more. When the average fiber length is less than 50 μm, the orientation of the porous body-coated fiber 100 when molded is small, and the mechanical strength is insufficient. These inorganic fibers may be used in combination.

  Further, in order to coat the inorganic fiber with the porous body composed of the secondary particles 10 of the inorganic fine particles 10a, similarly to the porous body-coated particles 100, the inorganic fibers and the inorganic fine particles 10a can be obtained using the rotary mixing device 30 shown in FIG. Obtained by rotary mixing.

  In order to obtain a heat insulating material, a precursor for heat insulating material obtained by mixing these fiber materials and the above-mentioned porous body-coated particles 100 is prepared, and this heat insulating material precursor is filled in a predetermined mold and press-molded. That's fine. FIG. 5 schematically shows the heat insulating material of the present invention, in which the porous material-coated particles 100 are between the fiber materials 200 (here, the inorganic fibers 20 covered with the porous material composed of the secondary particles 10 of the inorganic fine particles 10a). At that time, since the porous body-coated particles 100 are coated with a porous body composed of the secondary particles 10 of the inorganic fine particles 10a, solid conduction does not occur between the core particles, and the heat insulating performance is excellent. It will be a thing. In addition, when the fiber material 200 is the inorganic fiber 20 covered with the porous body made of the secondary particles 10 of the inorganic fine particles 10a, solid conduction between the fiber materials is eliminated, and the heat insulation performance is further improved.

  In addition, the mixture ratio of the porous body covering particle 100 and the fiber material 200 in the precursor for heat insulating material is 55 to 95 mass of the whole of the porous body covering particle 100 in consideration of the heat insulating performance and mechanical characteristics of the heat insulating material to be obtained. %, And the fiber material 200 is preferably 5 to 45% by mass.

Moreover, a heat insulating material excellent in heat insulating performance and mechanical strength can be obtained by setting the bulk density to 200 to 600 kg / m ³ , preferably 300 to 500 kg / m ³ . Specifically, the bending strength is 0.3 MPa or more and it is difficult to break, and the thermal conductivity at 1000 ° C. is 0.04 W / (m · K) or less, which shows excellent heat insulation performance. Furthermore, even when cut, there is no chipping of the cut end face, and the workability is excellent. In addition, the inorganic fine particles 10a are not detached and the outside is not contaminated.

  Examples The present invention will be further described below with reference to examples and comparative examples, but the present invention is not limited thereby.

(Example 1)
Silicon carbide having an average particle diameter of 3 μm was subjected to an oxidation heat treatment in air at 1000 ° C. for 8 hours to obtain core particles. 25 mass% of the core particles and 75 mass% of silica fine particles having an average particle diameter of 7 nm and a thermal conductivity (25 ° C.) of 0.01 W / (m · K) are put into the rotary mixing device 30 shown in FIG. The minute gap between the chamber 31 and the pressing member 32 was set to 2000 μm, and it was continuously rotated for 30 minutes at a rotational speed of 1000 min ⁻¹ . When the contents were taken out and observed with an electron microscope, as shown in FIG. 4 , the surface was completely covered with a porous body made of silica fine particles.

  The produced porous body-coated particles 80% by mass and 20% by mass of silica-based ceramic fiber having an average fiber diameter of 10 μm and an average fiber length of 5000 μm are dry-mixed to form a heat-insulating material precursor. A molded product having a side of 150 mm and a thickness of 10 mm was produced by press molding. The press pressure was 6 MPa. Table 1 shows the bulk density, bending strength, and thermal conductivity of the obtained molded product.

(Example 2)
3% by mass of the silica-based ceramic fiber and 97% by mass of silica fine particles used in Example 1 were put into the rotary mixing device 30 shown in FIG. 3, and the minute gap between the chamber 31 and the pressing member 32 was set to 2000 μm, and the rotation was performed. A silica-based ceramic fiber coated with silica fine particles was produced by continuously rotating at a speed of 1000 min ^{−1 for} 30 minutes.

  20% by mass of the silica-based ceramic fiber coated with the prepared silica fine particles and 80% by mass of the porous material-coated particles of Example 1 were dry-mixed to obtain a heat-insulating material precursor, and this heat-insulating material precursor was used. A molded product having a side of 150 mm and a thickness of 10 mm was produced by press molding. The press pressure was 6 MPa. Table 1 shows the bulk density, bending strength, and thermal conductivity of the obtained molded product.

(Comparative Example 1)
80 mass% of silicon carbide having an average particle diameter of 3 μm and 20 mass% of silica-based ceramic fiber having an average fiber diameter of 10 μm and an average fiber length of 5000 μm are dry-mixed to obtain a precursor for heat insulating material. A molded product having a side of 150 mm and a thickness of 10 mm was produced by press molding. The press pressure was 6 MPa. Table 1 shows the bulk density, bending strength, and thermal conductivity of the obtained molded product.

(Comparative Example 2)
80% by mass of silicon carbide having an average particle diameter of 3 μm and 20% by mass of silica-based ceramic fiber coated with silica fine particles prepared in Example 2 were dry-mixed to obtain a precursor for a heat insulating material. A molded product having a side of 150 mm and a thickness of 10 mm was produced by press molding. The press pressure was 6 MPa. Table 1 shows the bulk density, bending strength, and thermal conductivity of the obtained molded product.

  From Table 1, it can be seen that the molded articles of Example 1 and Example 2 according to the present invention have high mechanical strength, low thermal conductivity, and excellent heat insulation performance. Moreover, it turns out that mechanical strength and heat insulation performance increase more by using the fiber material coat | covered with the inorganic fine particle from the comparison with Example 1 and Example 2. FIG.

  On the other hand, the molded article of Comparative Example 1 in which both the core particles and the inorganic fibers are not coated with the inorganic fine particles has low mechanical strength and is greatly inferior in heat insulation performance. The molded product of Comparative Example 2 using the fiber material coated with inorganic fine particles is inferior to the molded product of the Examples, although both mechanical properties and heat insulation performance are improved.

It is a schematic diagram which shows the porous body covering particle | grains of this invention. It is a schematic diagram which shows the secondary particle which consists of inorganic fine particles. It is a schematic block diagram which shows the rotary mixing apparatus for manufacturing the porous body covering fine particle of this invention. It is the electron micrograph which image | photographed the porous body covering particle | grains of this invention. It is a schematic diagram which shows the heat insulating material containing the porous body covering particle | grains of this invention. It is a schematic diagram which shows the conventional heat insulating material.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Core particle 10 Secondary particle 10a Inorganic fine particle 20 Inorganic fiber 30 Rotary mixing apparatus 31 Chamber 32 Pressing member 35 Input 100 Porous body covering particle 200 Fiber material

Claims (10)

A porous body coating characterized in that core particles composed of a second inorganic compound are coated with a porous body formed of secondary particles in which fine particles composed of a first inorganic compound are associated in a ring shape or a spiral shape. particle. 2. The porous body-coated particle according to claim 1, wherein the core particle has an average particle diameter of 30 μm or less. 3. The porous body-coated particle according to claim 1, wherein the fine particle has an average particle diameter of 5 to 50 nm. 4. The porous body-coated particle according to claim 1, wherein a ring inner diameter of the secondary particle is 0.1 μm or less. The said core particle is 5-50 mass%, and the said microparticles | fine-particles are 50-95 mass%, The porous body covering particle as described in any one of Claims 1-4 characterized by the above-mentioned. The porous material according to any one of claims 1 to 5, and at least one fiber material selected from an inorganic fiber and a porous material-coated fiber in which the inorganic fiber is coated with a porous material formed of the secondary particles. The precursor for heat insulating materials characterized by containing body covering particle | grains. The precursor for a heat insulating material according to claim 6, wherein the porous body-coated particles are 55 to 95% by mass and the fiber material is 5 to 45% by mass. A heat insulating material obtained by pressure-molding the heat insulating material precursor according to claim 6 or 7. The heat insulating material according to claim 8, wherein the bulk density is 200 to 600 kg / m ³ and the bending strength is 0.3 MPa or more. The heat insulating material according to claim 9, wherein the heat conductivity at 1000 ° C. is 0.04 W / (m · K) or less.