JP2012006807A - Composite particle, heat insulating material, and method for producing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a composite particle and a heat insulating material exhibiting excellent heat insulating properties even in use in a high temperature, and to provide a method for producing the same.SOLUTION: The composite particle (1) is a heat insulating particle and includes a first particle (10) having an average particle diameter of 50 μm or more and having thermal conductivity of 0.025 W/(m*K) or less at 25°C; and a second particle (20) having the average particle diameter of 0.5-10 μm and covering the first particle (10).

Description

  The present invention relates to composite particles, heat insulating materials and methods for producing them, and more particularly to prevention of radiant heat transfer in use at high temperatures.

  Conventionally, for example, in Patent Document 1, a second material such as silicon carbide in which fine particles made of a first inorganic compound such as silica fine particles are coated with a porous body formed of secondary particles associated in a ring shape or a spiral shape. There are described porous coated particles having excellent heat insulating properties, including core particles made of the above inorganic compound.

JP 2005-81495 A

  Silica fine particles having an average particle diameter of about several nanometers to several tens of nanometers as described in Patent Document 1 are excellent in heat insulating properties. When compressing to raise, there is a problem that a large pressure is required and dust generation is likely to occur.

  Therefore, for example, it is conceivable to use silica granules having an average particle diameter of about several hundreds of μm and excellent heat insulating properties. Such silica granules are easier to handle than the above-mentioned silica fine particles, can increase the bulk density by simple compression, and do not easily generate dust.

  However, for example, when the silica granules are infrared transmissive, radiant heat transfer cannot be sufficiently prevented when used at a high temperature of several hundred degrees Celsius or higher.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide composite particles, a heat insulating material, and a production method thereof that exhibit excellent heat insulation even when used at high temperatures. .

  The composite particles according to an embodiment of the present invention for solving the above-mentioned problems are first particles having an average particle diameter of 50 μm or more and a thermal conductivity at 25 ° C. of 0.025 W / (m · K) or less. And an average particle diameter of 0.5 to 10 μm, and second particles covering the first particles. ADVANTAGE OF THE INVENTION According to this invention, the composite particle which shows the heat insulation excellent also in the use in high temperature can be provided.

  The first particles may be infrared transmissive. The first particles may have an infrared transmittance of 20% or more at a wavelength of 4 μm. The first particles may be one or more selected from the group consisting of airgel granules, pulverized granules, and hollow particles. The first particles may be silica particles.

  In order to solve the above problems, a heat insulating material according to an embodiment of the present invention includes any one of the above composite particles. ADVANTAGE OF THE INVENTION According to this invention, the heat insulating material which shows the heat insulation excellent also in the use in high temperature can be provided.

  Further, the heat insulating material may include 2 to 40 parts by weight of the second particles with respect to 100 parts by weight of the first particles. In addition, the heat insulating material may further include an outer skin material that accommodates the composite particles. Moreover, the said heat insulating material is good also as being used at the temperature of 150 degreeC or more.

  In the method for producing composite particles according to an embodiment of the present invention for solving the above problems, the average particle diameter is 50 μm or more, and the thermal conductivity at 25 ° C. is 0.025 W / (m · K) or less. The first particles have an average particle diameter of 0.5 to 10 μm and are dry-mixed with the second particles covering the first particles. ADVANTAGE OF THE INVENTION According to this invention, the manufacturing method of the composite particle which shows the heat insulation excellent also in use at high temperature can be provided.

  The manufacturing method of the heat insulating material which concerns on one Embodiment of this invention for solving the said subject accommodates the said composite particle in an outer_layer | skin material, It is characterized by the above-mentioned. ADVANTAGE OF THE INVENTION According to this invention, the manufacturing method of the heat insulating material which shows the heat insulation excellent also in use at high temperature can be provided.

  ADVANTAGE OF THE INVENTION According to this invention, the composite particle which shows the heat insulation outstanding also in the use in high temperature, a heat insulating material, and these manufacturing methods can be provided.

It is explanatory drawing about an example of the composite particle which concerns on one Embodiment of this invention. It is explanatory drawing about an example of the heat insulating material which concerns on one Embodiment of this invention. It is explanatory drawing which shows an example of the result of having measured the infrared transmittance of the composite particle by FT-IR in the Example which concerns on one Embodiment of this invention. It is explanatory drawing which shows an example of the result of having measured the relationship between the silicon carbide content of composite particle | grains, and infrared transmittance in the Example which concerns on one Embodiment of this invention. It is explanatory drawing which shows an example of the result of having measured the thermal conductivity of the composite particle in the Example which concerns on one Embodiment of this invention.

  Hereinafter, an embodiment of the present invention will be described. Note that the present invention is not limited to this embodiment.

  FIG. 1 is an explanatory diagram of an example of composite particles according to the present embodiment. As shown in FIG. 1, the composite particle 1 includes a first particle (hereinafter referred to as “core particle 10”) and a second particle (hereinafter referred to as “coated particle 20”) that covers the core particle 10. ,including.

  The core particle 10 is a particle having an average particle diameter of 50 μm or more. The average particle diameter of the core particle 10 can be, for example, 100 μm or more, and can be 400 μm or more. When the average particle diameter of the core particle 10 is in such a range, for example, the core particle 10 is easy to handle and can be compressed easily compared to ultrafine silica particles having an average particle diameter of several nanometers to several tens of nanometers. The bulk density can be increased and dust generation is less likely to occur. The average particle diameter of the core particle 10 can be measured by, for example, a laser diffraction / scattering particle diameter measuring apparatus.

  Moreover, the average particle diameter of the core particle 10 can be 10 times or more of the average particle diameter of the coating particle 20 mentioned later, for example, and it is preferable to set it as 100 times or more. When the average particle diameter of the core particle 10 is in such a range as that of the coated particle 20, for example, the core particle 10 can be easily and efficiently coated with the coated particle 20.

  Although the upper limit of the average particle diameter of the core particle 10 is not particularly limited, the average particle diameter can be set to 2000 μm or less, for example. That is, the average particle diameter of the core particle 10 can be, for example, 50 to 2000 μm, 100 to 2000 μm, or 400 to 2000 μm.

  The core particle 10 is a particle having a thermal conductivity at 25 ° C. of 0.025 W / (m · K) or less. The thermal conductivity of the core particle 10 at 25 ° C. can be, for example, 0.020 W / (m · K) or less, or 0.015 W / (m · K) or less.

Thus, the core particle 10 itself is a particle having excellent heat insulating properties. The thermal conductivity of the core particle 10 can be measured by, for example, a GHP (guarded hot plate) method using a powder of the core particle 10 having a bulk density adjusted to 100 to 150 kg / m ³ as a sample.

  The core particle 10 may be infrared transmissive. That is, in this case, the core particle 10 is a particle having transparency that transmits infrared rays. Therefore, the core particle 10 alone cannot sufficiently prevent radiant heat transfer at a high temperature. In such a case, the effect of preventing radiant heat transfer due to the use of coated particles 20 described later becomes particularly remarkable.

The core particle 10 may have an infrared transmittance of 20% or more at a wavelength of 4 μm. The infrared transmittance of the core particle 10 can be measured by, for example, a Fourier transform infrared spectrometer. Specifically, the core particle 10 has a density of 2 g / cm ³ and a thickness of 200 μm, for example, obtained by press-molding a dry mixed powder of 90 parts by weight of KBr powder and 10 parts by weight of the core particle 10. In the FT-IR (Fourier transform infrared spectroscopy) by the KBr (potassium bromide) method using a disk sample of the above, the infrared transmittance at a wavelength of 4 μm is 20% or more.

  The core particle 10 may have a thermal conductivity at 400 ° C. of 0.08 W / (m · K) or more. The thermal conductivity of the core particle 10 at 400 ° C. may be, for example, 0.1 W / (m · K) or more, or 0.15 W / (m · K) or more. The thermal conductivity of the core particle 10 at 400 ° C. can be set to 0.08 to 0.3 W / (m · K), for example, and is set to 0.10 to 0.25 W / (m · K). It can also be set to 0.15 to 0.25 W / (m · K).

  The core particle 10 is not particularly limited as long as it has the above-described characteristics, and can be any inorganic particle or organic particle. The core particle 10 can be an airgel granule, for example.

  The airgel granule is not particularly limited as long as it has the characteristics as the core particle 10 described above, and can be any inorganic airgel granule or organic airgel granule. However, it is preferable that the core particle 10 is an inorganic airgel granule from a viewpoint of stability in use at a high temperature.

  As an inorganic airgel granule, it selects from the group which consists of a silica airgel granule, an alumina airgel granule, and a zirconia airgel granule, for example, and can use 1 type (s) or 2 or more types. Among these, silica airgel granules can be particularly preferably used from the viewpoint of heat insulation, stability at high temperature, cost, and the like. The airgel granules can be produced by a known method such as supercritical drying of an airgel raw material (for example, silica gel).

  Moreover, as the core particles 10, for example, nanoparticles such as fumed silica are compressed and molded, and pulverized granules obtained by pulverizing the obtained molded body, or glass materials such as natural volcanic glass are rapidly used. Fine hollow particles (foamed hollow particles) obtained by heating and foaming can be used. That is, the core particle 10 can be, for example, one or more selected from the group consisting of airgel granules, pulverized granules, and hollow particles.

  In addition, as the core particle 10, it is preferable to use inorganic particles from the viewpoint of stability in use at a high temperature. As the inorganic particles, the above-described inorganic airgel granules can be preferably used, but the inorganic particles are not limited thereto, and any inorganic particles having the characteristics as the above-described core particles 10 can be used. That is, for example, the above-mentioned pulverized granules and hollow particles obtained from inorganic nanoparticles such as fumed silica and inorganic materials such as glass materials can be used. Therefore, the core particle 10 can be made into 1 type, or 2 or more types selected from the group which consists of an inorganic airgel granule, an inorganic ground granule, and an inorganic hollow particle, for example.

  Moreover, as an inorganic particle, the 1 type (s) or 2 or more types selected from the group which consists of a silica particle, an alumina particle, and a zirconia particle can be used preferably, for example. Among these, silica particles can be preferably used from the viewpoints of heat insulation, stability at high temperature, cost, and the like.

  As the silica particles, the above-described silica airgel granules can be particularly preferably used. However, the silica particles are not limited thereto, and any silica particles having the characteristics as the above-described core particles 10 can be used. That is, for example, the above-mentioned pulverized granules and hollow particles obtained from silica nanoparticles such as fumed silica and silica materials such as glass materials can be used. Therefore, the silica particles can be, for example, one or more selected from the group consisting of silica airgel granules, silica pulverized granules, and silica foamed hollow particles.

  The shape of the core particle 10 is not particularly limited as long as it does not impair the above characteristics. That is, the core particle 10 can be, for example, an irregular particle having a rough surface (for example, a porous particle such as an airgel granule) or a spherical particle having a smooth surface.

  The coated particles 20 are particles having an average particle diameter of 0.5 to 10 μm. For example, the average particle size of the coated particles 20 is preferably 1 to 5 μm, and more preferably 1 to 4 μm. When the average particle diameter of the coated particle 20 is within such a range, the coated particle 20 can effectively prevent radiant heat transfer at a relatively high temperature by so-called Mie scattering.

  That is, the coated particle 20 has an average particle diameter that is about the same as the wavelength of infrared rays that provides radiant heat transfer, and preferably has an average particle diameter that is about half the wavelength. Specifically, for example, according to the Wien equation: λmax = 2898 / (273 + t) (λmax is a peak wavelength (μm), t is a temperature (° C.)), the peak wavelength at a temperature of 100 to 1000 ° C. is approximately It is calculated as 2-8 μm. Therefore, for example, if the average particle diameter of the coated particles 20 is 1 to 4 μm corresponding to about half of the peak wavelength, the radiant heat transfer at 100 to 1000 ° C. is effectively performed by Mie scattering by the coated particles 20. Can be prevented.

  The coated particle 20 is not particularly limited as long as it is a particle having an average particle size suitable for Mie scattering as described above. That is, the coated particle 20 may be, for example, a particle that is inferior in heat insulation compared to the core particle 10.

  In this case, the coated particles 20 are particles having a thermal conductivity at 25 ° C. larger than that of the core particles 10, for example. Specifically, the thermal conductivity of the coated particles 20 at 25 ° C. can be set to, for example, 270 W / (m · K) or more.

  Of course, the coated particle 20 may be a particle having a heat insulating property equal to or higher than that of the core particle 10. However, by using particles that are inferior in heat insulation than the core particles 10 as the coated particles 20, it is possible to reduce the cost, and it is possible to realize the composite particles 1 and the heat insulating material suitable for industrial mass production.

  The coated particle 20 is not particularly limited as long as it has a mean particle size suitable for Mie scattering as described above, and can be any inorganic particle or organic particle. However, the coated particles 20 are preferably inorganic particles from the viewpoint of stability in use at a high temperature. As the inorganic particles, for example, one or more selected from the group consisting of silicon carbide particles, titanium oxide particles, zinc oxide particles, aluminum oxide particles, and zirconium oxide particles can be preferably used.

  The composite particle 1 is a heat insulating particle including any one of the core particles 10 described above and any one of the coated particles 20 described above. That is, in the example shown in FIG. 1, the composite particle 1 is a heat insulating particle composed of the core particle 10 covered with the covering particle 20. The surface of each core particle 10 is coated with a large number of coated particles 20.

  The coated particle 20 preferably covers the entire surface of the core particle 10. However, a part of the surface of the core particle 10 may be covered with the covering particle 20 as long as the effect of preventing radiation heat transfer by the covering particle 20 is obtained.

  The amount of the covering particle 20 with respect to the core particle 10 is not particularly limited as long as the composite particle 1 can have a desired heat insulating property. That is, the composite particle 1 includes, for example, the coated particle 20 in an amount necessary for coating all or a part of the surface of the individual core particle 10 with one layer of the coated particle 20 or more. it can. In particular, it is preferable that the composite particle 1 includes the coated particle 20 in an amount necessary for coating the entire surface of the individual core particle 10 with one layer of the coated particle 20 or more. Note that the amount necessary to coat the entire surface of each core particle 10 with one layer of the covering particles 20 is, for example, a geometric shape such as an average particle diameter of the core particles 10 and an average particle diameter of the covering particles 20. It can be calculated theoretically based on scientific conditions.

  Further, as shown in FIG. 1, the coated particle 20 covering the core particle 10 maintains its original shape (the shape before the core particle 10 is coated). Therefore, the coated particles 20 covering the core particles 10 can effectively prevent radiant heat transfer by Mie scattering based on the original average particle diameter and shape.

  Such a composite particle 1 has an average particle diameter of 50 μm or more, a core particle 10 having a thermal conductivity at 25 ° C. of 0.025 W / (m · K) or less, and an average particle diameter of 0.5 to 10 μm. And the coated particles 20 that coat the core particles 10 can be produced by a dry mixing method.

  That is, the composite particles 1 are manufactured by coating the core particles 10 with the coated particles 20 by dry-mixing any of the core particles 10 described above and any of the coated particles 20 described above. Can do.

  Since the average particle diameter of the core particle 10 and the average particle diameter of the coated particle 20 are in the above-described relationship, the coated particle 20 can be simply applied to the surface of the core particle 10 simply by dry mixing without using a binder. And can be attached efficiently. In particular, as described above, when the average particle diameter of the core particle 10 is 10 times or more of the average particle diameter of the coated particle 20, preferably 100 times or more, the core particle 10 by the coated particle 20 is used. Can be efficiently achieved.

  In the composite particle 1 obtained by such dry mixing, the coated particle 20 directly adheres to the surface of the core particle 10 without using a binder, thereby covering the core particle 10. In particular, when the core particle 10 having a porous surface such as an airgel granule is used, the covering particle 20 can be efficiently attached to the surface.

  Moreover, as shown in FIG. 1, the coated particles 20 can be attached to the core particles 10 by dry mixing while maintaining the original granular shape. The dry mixing method is not particularly limited as long as the core particle 10 and the coated particle 20 can be coated with the coated particle 20 by mixing the core particle 10 and the coated particle 20 in a dry state. A method in which the core particles 10 and the coated particles 20 are added to and agitated can be preferably used (see, for example, Patent Document 1 above).

  The heat insulating material according to the present embodiment includes the composite particles 1 described above. That is, the heat insulating material can be, for example, a heat insulating powder material including the composite particles 1.

  The ratio of the core particles 10 and the covering particles 20 included in the heat insulating material made of the heat insulating powder material is not particularly limited as long as the heat insulating material has a desired heat insulating property as a whole. That is, the heat insulating material includes, for example, the coated particles 20 in an amount necessary for coating all or a part of the surface of the individual core particles 10 with one layer of the coated particles 20 or more. it can.

  In particular, it is preferable that the heat insulating material includes the coated particles 20 in an amount necessary for coating the entire surface of the individual core particles 10 with one layer of the coated particles 20 or more. However, for example, when the heat insulating property of the coated particle 20 is inferior to that of the core particle 10, the heat insulating material cannot be provided with sufficient heat insulating property as a whole due to the content of the coated particle 20 being excessive. There is.

  Therefore, it is preferable that the heat insulating material includes the coated particles 20 as long as the effect of preventing radiation heat transfer by the coated particles 20 is sufficiently obtained and the heat insulating material can have a desired heat insulating property as a whole.

  That is, the heat insulating material includes, for example, 2 to 40 parts by weight of the coated particles 20 with respect to 100 parts by weight of the core particles 10. The content of the coated particles 20 with respect to 100 parts by weight of the core particles 10 is, for example, preferably 2 to 35 parts by weight, and more preferably 15 to 35 parts by weight.

  When the heat insulating material includes the core particles 10 and the coated particles 20 in such a ratio, the heat insulating material has excellent heat insulating properties even when the heat insulating properties of the coated particles 20 are lower than the core particles 10. be able to. The heat insulating material can further include coated particles 20 that do not cover the core particles 10. In this case, the coated particles 20 are present between the composite particles 1, for example.

  Moreover, the heat insulating powder material which comprises the above-mentioned heat insulating material can also contain another material in the range which can provide desired heat insulation as a whole. That is, the heat insulating material can further include, for example, a fiber material. In this case, the heat insulating material includes a fiber material dispersed between the composite particles 1.

  As the fiber material, inorganic fibers or organic fibers can be used, and inorganic fibers are preferably used from the viewpoint of stability in use at high temperatures. As the inorganic fiber, for example, glass fiber, alumina fiber, silica alumina fiber, silica fiber, and zirconia fiber can be used.

However, in order to make use of the excellent heat insulating properties of the composite particles 1, the heat insulating material made of a heat insulating powder material preferably contains the composite particles 1 as a main component. That is, the amount of the composite particles 1 contained in the heat insulating powder material is, for example, preferably 40% by weight or more, and more preferably 60% by weight or more. Moreover, the bulk density of the heat insulating material made of the heat insulating powder material is preferably 100 kg / m ³ or more, and more preferably 120 kg / m ³ or more.

  As shown in FIG. 2, the heat insulating material 2 may further include composite particles 1 and a skin material 30 that accommodates the composite particles 1. That is, in this case, the heat insulating material 2 includes, for example, a heat insulating powder material including the composite particles 1 and a skin material 30 that accommodates the heat insulating powder material.

  The skin material 30 is not particularly limited as long as it is a material that can accommodate the composite particles 1. That is, the skin material 30 can be, for example, a sheet of an inorganic material and / or an organic material, and is preferably a sheet of an inorganic material from the viewpoint of stability in use at a high temperature.

  As the inorganic material sheet, for example, an inorganic fiber sheet can be preferably used. As the inorganic fiber sheet, for example, a woven fabric or a non-woven fabric (cross, felt, blanket, paper, etc.) of inorganic fibers such as glass fibers, alumina fibers, silica alumina fibers, silica fibers, zirconia fibers and the like can be used.

  As the organic material sheet, for example, a porous resin sheet can be used. As the porous resin sheet, for example, a resin sheet made porous by a stretching method can be preferably used. Specifically, for example, a porous sheet of a fluorine resin such as polytetrafluoroethylene (PTFE) or a polyolefin resin such as polyethylene or polypropylene can be preferably used, and a porous PTFE sheet having a relatively high heat resistance is particularly preferable. It can be preferably used.

  In the case where the outer skin material 30 is composed of a flexible sheet, the heat insulating material 2 is thin, and can have flexibility, for example, in addition to having excellent heat insulating properties based on the composite particles 1. Therefore, in this case, the heat insulating material 2 can be applied by being deformed along the curved surface of the structure, for example.

  The shape of the skin material 30 is not particularly limited as long as it can accommodate the composite particles 1. That is, the outer skin material 30 is formed in a bag shape, for example, as shown in FIG. The bag-shaped outer covering material 30 can be sealed while holding the composite particles 1 inside.

  Further, it is preferable that the skin material 30 can effectively suppress the generation of dust due to leakage of the composite particles 1 or the like. That is, the skin material 30 can be, for example, an inorganic fiber sheet whose fiber density is adjusted or a porous resin sheet whose pore diameter is adjusted so as to prevent leakage of the composite particles 1.

  The heat insulating material 2 may include a plurality of outer skin materials 30. That is, in this case, the heat insulating material 2 can include, for example, a first outer skin material 30 that accommodates the composite particles 1 and a second outer skin material 30 that further accommodates the first outer skin material 30. . The plurality of skin materials 30 may be the same type or different types.

  The heat insulating material 2 including such a skin material 30 can be manufactured by housing the composite particles 1 in the skin material 30. That is, for example, first, the outer skin material 30 formed in a bag shape and the heat insulating powder material containing the composite particles 1 are prepared, and then the heat insulating powder material is put into the outer skin material 30. In addition, the skin material 30 is sealed.

  When the composite particles 1 are accommodated in the skin material 30, it is preferable to increase the bulk density of the composite particles 1. That is, for example, by packing the skin material 30 containing the heat insulating powder material containing the composite particles 1 under reduced pressure, the bulk density of the composite particles 1 can be easily and efficiently increased.

  The method for sealing the skin material 30 is not particularly limited. For example, when the skin material 30 is an inorganic fiber sheet, sewing is performed. When the skin material 30 is an organic material sheet, heat is applied. The opening portion of the outer skin material 30 can be closed by fusing.

  Such composite particles 1 and heat insulating material 2 exhibit excellent heat insulating properties (particularly solids) even at high temperatures, in addition to exhibiting excellent heat insulating properties mainly based on the properties of the core particles 10 at low temperatures. The heat insulation and gas heat transfer prevention) and the radiation heat transfer prevention effect by the coated particles 20 show excellent heat insulation.

  Therefore, the composite particle 1 and the heat insulating material 2 can be preferably used at a temperature of 150 ° C. or higher, for example. This operating temperature can be, for example, 200 ° C. or higher, or 350 ° C. or higher. More specifically, use temperature can be 150-700 degreeC, for example, can also be 200-700 degreeC, and can also be 350-700 degreeC. The composite particles 1 and the heat insulating material 2 can be preferably used even at lower temperatures. That is, the composite particle 1 and the heat insulating material 2 can be used at a temperature of 50 ° C. or higher (more specifically, for example, 50 to 700 ° C.).

  Examples of the place where the composite particles 1 and the heat insulating material 2 are constructed include structures such as devices, piping structures, and buildings. Specifically, for example, a semiconductor manufacturing apparatus exposed to a high temperature, a piping structure through which a high-temperature fluid flows, and a nuclear facility are exemplified.

  When the heat insulating material 2 is a heat insulating powder material containing the composite particle 1 described above, the heat insulating material 2 is filled in a gap having a predetermined shape formed in the structure, for example, so that the heat insulating material in the structure is insulated. Used for.

  Moreover, when the heat insulating material 2 has the above-mentioned outer skin material 30, the said heat insulating material 2 is affixed or wound around the surface of a structure, for example, and is used for the heat insulation in the said structure. In particular, when the outer skin material 30 is a flexible sheet, the heat insulating material 2 corresponds to the surface in a structure (for example, a semiconductor manufacturing apparatus) that is disposed in a narrow space and has a curved surface, for example. Construction can be performed while flexibly deforming the shape.

  Next, specific examples according to the present embodiment will be described.

[Manufacture of insulation materials]
Silica airgel granules (TLD301, manufactured by cabot) were used as the core particles 10. This silica airgel granule (simply referred to as “airgel granule” in the following examples) has an average particle size of 1000 μm (particle size range of 700 μm to 1200 μm), and a thermal conductivity at 25 ° C. of 0.013 W / (m・ K). The airgel granules were highly transparent and infrared transmissive particles. As the coated particles 20, silicon carbide particles (Shinano Random, manufactured by Shinano Denki Smelting Co., Ltd.) were used. The average particle diameter of the silicon carbide particles was 2.3 μm.

  And the heat insulating powder material which consists of the said airgel granule (composite particle 1) coat | covered with the said silicon carbide particle was obtained by dry-mixing an airgel granule and silicon carbide particle by a predetermined ratio. The addition ratio of the silicon carbide particles to 100 parts by weight of the airgel granules was five types of 2.5 parts by weight, 5.0 parts by weight, 10 parts by weight, 20 parts by weight or 40 parts by weight.

  For comparison, a heat insulating powder material made of airgel granules without adding silicon carbide powder was also prepared. In addition, the airgel granule (namely, composite particle 1) coat | covered with the silicon carbide particle | grains obtained by dry mixing was an opaque particle | grain.

[Measurement of infrared transmittance]
The infrared transmittance of the heat insulating powder material containing the composite particles 1 obtained as described above was measured. As a measuring method, FT-IR (Fourier transform infrared spectroscopy) by KBr (potassium bromide) method was used. That is, first, KBr powder and composite particles 1 are added so that 10 parts by weight of airgel granules (in the case of composite particles 1, the airgel granules contained in composite particles 1) are added to 90 parts by weight of KBr powder. Or airgel granule was dry-mixed and the mixed powder was obtained. Next, this mixed powder was pulverized until the particle diameter became 50 μm or less. And the disk sample of density 2g / cm < ³ > and thickness 200micrometer was produced by press-molding the mixed powder after a grinding | pulverization. This disk sample was used for the measurement by FT-IR.

In FIG. 3, the measurement result by FT-IR is shown. In FIG. 3, the horizontal axis indicates the wave number (cm ⁻¹ ), and the vertical axis indicates the transmittance (%). And in FIG. 3, when only an airgel granule is used (AG), and 2.5 parts by weight, 5.0 parts by weight, 10 parts by weight, 20 parts by weight or 40 parts by weight of silicon carbide particles are added to the airgel granules. Results obtained for each of the additions (AG / SiC (2.5), AG / SiC (5.0), AG / SiC (10), AG / SiC (20), AG / SiC (40))) Indicates.

FIG. 4 shows the relationship between the addition rate (parts by weight) of silicon carbide particles and the infrared transmittance (%) at a wavelength of 4 μm based on the measurement results shown in FIG. In FIG. 4, the horizontal axis represents the addition rate (SiC addition rate) (parts by weight) of silicon carbide powder to 100 parts by weight of the airgel granules, and the vertical axis represents the transmittance at a wave number of 2500 cm ⁻¹ (wavelength λ = 4 μm). (%). In addition, according to the above-mentioned Wien equation, wave number 2500 cm ⁻¹ (wavelength λ = 4 μm) is a peak wavelength in radiation at 450 ° C.

  As shown in FIG. 3 and FIG. 4, it was confirmed that the infrared transmittance of the heat insulating powder material was remarkably lowered as the addition rate of silicon carbide particles to the airgel granules increased. In particular, when the addition rate of the silicon carbide particles exceeds 20 parts by weight, the infrared transmittance of the heat insulating powder material is reduced to 10% or less when the silicon carbide particles are not added (in the case of only airgel granules). It was. The infrared transmittance of the airgel granule alone was 33%.

[Manufacture of insulation materials]
As the core particles 10 and the coated particles 20, the same airgel granules and silicon carbide particles as those used in Example 1 were used. The airgel granules coated with the silicon carbide particles are dry-mixed so that the airgel granules and the silicon carbide particles are in a predetermined ratio and the density of the airgel granules is 0.1 g / cm ^3. A heat insulating powder material comprising (composite particles 1) was obtained. The addition ratio of the silicon carbide particles to 100 parts by weight of the airgel granules was five types of 2.5 parts by weight, 5.0 parts by weight, 16.7 parts by weight, 25.9 parts by weight, or 33.3 parts by weight.

  For comparison, a heat insulating powder material made of airgel granules without adding silicon carbide powder was also prepared. In addition, the airgel granule (namely, composite particle 1) coat | covered with the silicon carbide particle | grains obtained by dry mixing was an opaque particle like the above-mentioned Example 1.

[Measurement of thermal conductivity]
The thermal conductivity of the heat insulating powder material containing the composite particles 1 obtained as described above was measured. As a measuring method, GHP method was used. That is, first, a heat insulating powder material was packed in a bag made of glass fiber cloth. And the glass fiber bag which accommodated the heat insulating powder material was inserted | pinched with the flat plate, and the heat conductivity was measured by GHP method. The density of the heat insulating powder material at the time of measurement was about 100 kg / m ³ . The heat conductivity of the heat insulating powder material was calculated by subtracting the previously measured heat conductivity of the glass fiber bag from the heat conductivity of the glass fiber bag containing the heat insulating powder material.

  In FIG. 5, the measurement result of thermal conductivity is shown. 5, the horizontal axis indicates the temperature at the time of measurement (° C.), and the vertical axis indicates the thermal conductivity (W / (m · K), and FIG. 5 shows the case where only the airgel granules are used (AG ), And 2.5 parts by weight, 5.0 parts by weight, 16.7 parts by weight, 25.9 parts by weight or 33.3 parts by weight of silicon carbide (AG / SiC (2.5 ), AG / SiC (5.0), AG / SiC (16.7), AG / SiC (25.9), and AG / SiC (33.3)).

  As shown in FIG. 5, the thermal conductivity of the heat insulating powder material to which silicon carbide particles were not added (the heat insulating powder material consisting only of airgel granules) rapidly increased as the temperature increased. On the other hand, by adding silicon carbide particles, the thermal conductivity of the heat insulating powder material was reduced as compared with the case where the silicon carbide particles were not added. The effect of reducing the thermal conductivity by the addition of the silicon carbide particles was confirmed even at 100 ° C., and was remarkable at 200 ° C. or higher, more remarkable at 300 ° C., and particularly remarkable at 400 ° C.

  Here, the amount of the silicon carbide particles required to coat the entire surface of each particle of the airgel granules used in this example with one layer of silicon carbide particles is theoretically 5.7 parts by weight. Calculated. In this regard, as shown in FIG. 5, when the addition amount of silicon carbide particles exceeds the theoretical amount (when the addition amount is 16.7 parts by weight or more), a particularly remarkable effect of reducing thermal conductivity is obtained. was gotten. In particular, when the amount of silicon carbide particles added exceeds 20 parts by weight (when the amounts added are 25.9 parts by weight and 33.3 parts by weight), an extremely remarkable effect of reducing the thermal conductivity was obtained.

  Further, the effect of reducing the thermal conductivity due to the addition of the silicon carbide particles does not increase monotonously as the addition amount of the silicon carbide particles increases, but the addition amount of the silicon carbide particles falls within a predetermined range (for example, 100 The tendency to obtain the highest thermal conductivity reduction effect was confirmed by setting the amount to 15 to 35 parts by weight based on parts by weight of the airgel granules.

  1 composite particle, 2 heat insulating material, 10 core particle, 20 coated particle, 30 skin material.

Claims (11)

A first particle having an average particle diameter of 50 μm or more and a thermal conductivity at 25 ° C. of 0.025 W / (m · K) or less;
Second particles having an average particle diameter of 0.5 to 10 μm and covering the first particles;
A composite particle comprising: The composite particle according to claim 1, wherein the first particle is infrared transmissive. The composite particle according to claim 1, wherein the first particle has an infrared transmittance of 20% or more at a wavelength of 4 μm. The composite particles according to any one of claims 1 to 3, wherein the first particles are one or more selected from the group consisting of airgel granules, pulverized granules, and hollow particles. The composite particles according to any one of claims 1 to 4, wherein the first particles are silica particles. The heat insulating material characterized by including the composite particle as described in any one of Claims 1 thru | or 5. The heat insulating material according to claim 6, comprising 2 to 40 parts by weight of the second particles with respect to 100 parts by weight of the first particles. The heat insulating material according to claim 6 or 7, further comprising an outer skin material that accommodates the composite particles. The heat insulating material according to any one of claims 6 to 8, wherein the heat insulating material is used at a temperature of 150 ° C or higher. A first particle having an average particle diameter of 50 μm or more and a thermal conductivity at 25 ° C. of 0.025 W / (m · K) or less; an average particle diameter of 0.5 to 10 μm; A method of producing composite particles, comprising dry-mixing second particles to be coated. The composite particle according to any one of claims 1 to 5 is accommodated in an outer skin material.

Images