Composite insulation

Abstract

To provide a composite heat insulating material having excellent thermal insulation properties at high temperature even if it is thin.SOLUTION: A composite heat insulating material includes: a first base fabric made of a silica fiber having a hydroxyl group; a second base fabric made of a silica fiber having a hydroxyl group; and a heat insulation layer held by the first base fabric and the second base fabric. The heat insulation layer includes particles of a heat insulating material and a silica short fiber whose length is 0.5-5 mm. The particles of the heat insulating material are at least one kind selected from silica aerogel particles and ceramic particles. The heat insulation layer may further include a film-forming inorganic binder.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a sandwich-type composite heat insulating material in which a heat insulating material such as silica aerogel particles or ceramic particles is sandwiched between a silica fiber base fabric. [Background technology]

[0002] In the exhaust systems of gasoline and diesel vehicles, a catalytic converter is installed downstream of the exhaust manifold to catalyze the oxidation-reduction decomposition reaction of exhaust gases in order to convert air pollutants in the exhaust gases (hydrocarbons, NOx, CO, N2O, etc.) into harmless N2 and oxygen and emit them.

[0003] As shown in Figure 1, a typical catalytic converter 1 contains a honeycomb ceramic catalyst carrier 3 housed inside a stainless steel casing 2, with heat insulating material 4 filling the gap between the casing 2 and the catalyst carrier 3. As exhaust gas passes through the pores of the honeycomb, it comes into contact with the supported catalyst and is purified.

[0004] The insulating material 4 has the functions of protecting the ceramic carrier from external vibrations and impacts, absorbing the difference in thermal expansion between the ceramic carrier and the stainless steel casing, positioning the catalyst carrier, and insulating the surrounding equipment from high-temperature exhaust gases, and is generally made of inorganic fiber masses such as glass wool or rock wool (for example, paragraph 0009 of JP 2018-168806 A).

[0005] In addition to glass wool and rock wool, Japanese Patent Application Laid-Open No. 2013-24214 proposes a catalytic converter retaining material that surrounds the catalyst carrier, which is a wet laminated composite of a retaining part made of a first fiber selected from alumina fiber, mullite fiber, aluminosilicate fiber, silica fiber, soluble fiber, and a mixed fiber group thereof, and a heat insulating part made of a second fiber selected from glass fiber, rock wool, aluminosilicate fiber, silica fiber, soluble fiber, and a mixed fiber group thereof. Furthermore, JP2013-514496A proposes a mat made from a plurality of sol-gel inorganic fibers that are wetly laid in a sheet and physically entangled by needling as a mat that can be attached between a casing and a ceramic catalyst carrier. This mat is formed by wet laminating a layer of stabilized sol-gel fibers, entangling the fibers by needling, and then firing the layer (wet lamination). [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 2018-168806 [Patent Document 2] Japanese Patent Application Laid-Open No. 2013-24214 [Patent Document 3] Special Publication No. 2013-514496 Summary of the Invention [Problem to be solved by the invention]

[0007] The purification catalyst supported on catalytic converters is generally a three-way catalyst that simultaneously performs oxidation, reduction, and decomposition. Since the temperature at which the three-way catalytic reaction can be effectively performed is approximately 400 to 700°C, it is necessary to maintain the catalyst support within this temperature range in order to achieve a high level of purification of exhaust gases.

[0008] In this regard, the exhaust gas temperature during driving is high, at over 500°C, and catalytic converters can function effectively. However, at the beginning of driving or during acceleration, the exhaust gas temperature is low, so it is necessary to effectively raise the temperature of the catalyst carrier. In particular, to meet recent strict exhaust gas regulations, it is necessary to prevent temperature drops due to heat radiation from the casing at an early stage of driving, or to ensure that the purification catalyst functions effectively immediately after starting driving after a temporary stop. To satisfy these requirements, it is necessary to have a heat insulation system that can maintain the high temperature of the catalyst carrier even when the catalyst carrier is stopped. In other words, it is necessary to minimize the temperature drop of the catalyst carrier and to have excellent heat insulation performance that can block the outside air temperature. Therefore, the heat insulation material provided around the catalyst carrier is required to have heat insulation performance that can satisfy these requirements.

[0009] Currently, the insulating material packed into catalytic converters, i.e., mats or blankets made of glass fiber, rock wool, silica fiber, or alumina fiber, needs to be at least 2 cm thick to achieve the desired insulating (heat-retaining) effect. However, due to the size restrictions imposed by the casing and catalyst carrier, it is practically difficult to increase the thickness.

[0010] The present invention has been made in consideration of the above circumstances, and its object is to provide a composite insulating material that can exhibit the desired insulating effect even at a thickness of approximately 3 to 18 mm, and a method for manufacturing the same. [Means for solving the problem]

[0011] The composite heat insulating material of the present invention has the following configuration. [Form 1] Silica fiber with hydroxyl groups and does not contain any fibers other than silica fibers. The first base fabric is composed of silica fibers having hydroxyl groups. Contains no fibers other than silica fibers A composite heat insulating material including: a second base fabric composed of a group of fibers; and a heat insulating layer sandwiched between the first base fabric and the second base fabric, the heat insulating layer including particles of a heat insulating material and short silica fibers having a fiber length of 0.5 to 5 mm, The insulating layer is a composite insulating material sandwiched with one side in contact with a first base fabric and the other side in contact with a second base fabric. [Form 1-2] The short silica fibers may have a fiber length of 0.5 to 3 mm.

[0012] [Form 2] 2. The composite heat insulating material according to claim 1, wherein the particles of the heat insulating material are at least one selected from silica aerogel particles and ceramic particles.

[0013] [Form 3] 3. The composite heat insulating material according to claim 1 or 2, wherein the particles of the heat insulating material have a particle diameter of 0.5 μm to 1 mm.

[0014] [Form 4] The heat insulating layer further comprises a film-forming inorganic binder. as layered silicates Including and a film composed of the layered silicate is present in the gaps between the silica short fibers and the particles of the heat insulating material. A composite insulation material in any one of forms 1 to 3. [Form 5] The heat insulating layer is any one of the forms 1 to 3, which is a mixture of particles of the heat insulating material and the short silica fibers. Composite insulation material.

[0015] [Form 6] A composite thermal insulating material according to any one of embodiments 1 to 5, wherein the silica fibers contained in the first base fabric and the silica fibers contained in the second base fabric have different fiber diameters and fiber lengths. [Form 7] A composite thermal insulating material having any one of forms 1 to 6, wherein the silica fibers contained in the first base fabric and the silica fibers contained in the second base fabric have fiber lengths of 30 to 150 mm.

[0016] [Form 8] The aforementioned The particles of the insulating material include silica aerogel particles. A composite insulation material in any one of forms 1 to 7. [Effects of the Invention]

[0017] The composite heat insulating material of the present invention has heat insulating materials such as silica aerogel particles and ceramic particles stably sandwiched between a first base fabric and a second base fabric made of silica fiber, and therefore has excellent heat resistance and heat insulating properties. Moreover, the short silica fibers contained in the insulation layer contribute to increasing the strength of the insulation layer. Therefore, it also has excellent durability such as shape stability. [Brief explanation of the drawings]

[0018] [Figure 1] 1 is a schematic cross-sectional view showing the structure of a catalytic converter used in an automobile. [Figure 2] 1 is a schematic diagram showing the structure of a composite heat insulating material according to a first embodiment of the present invention. [Figure 3] 2 is a schematic diagram showing the structure of a composite heat insulating material according to a second embodiment of the present invention. FIG. [Figure 4] 3 is a schematic diagram showing the structure of a composite heat insulating material according to a third embodiment of the present invention. FIG. [Figure 5] FIG. 10 is a schematic diagram showing the structure of a composite heat insulating material according to a fourth embodiment of the present invention. [Figure 6] FIG. 10 is a schematic diagram showing the structure of a composite heat insulating material according to a fifth embodiment of the present invention. [Figure 7] FIG. 10 is a schematic diagram showing the configuration of a heat insulating material of Reference Example 2. [Figure 8] 1 is a graph showing the results of a thermal conductivity test of composite heat insulating materials (Nos. 1 to 4, Reference Example 1). [Figure 9] 1 is a graph showing the results of a thermal conductivity test of composite heat insulating materials (Nos. 3 and 5, Reference Examples 1 and 2). [Figure 10] FIG. 2 is a schematic diagram for explaining a bending strength test method. [Figure 11] 1 is a graph showing the results of a bending strength test of a composite heat insulating material (No. 3, Reference Example 2). [Figure 12] 1 is a graph showing the results of bending strength tests of composite heat insulating materials (Nos. 1 and 5, Reference Example 4). [Figure 13] This is an electron microscope photograph of the cross section of No. 1 composite insulation material. [Figure 14] This is an electron microscope photograph of the cross section of No. 3 composite insulation material. [Figure 15] 1 is a chart showing the results of a peel strength test (No. 5, Reference Example 4). [Figure 16] This is an optical microscope photograph and a three-dimensional image of the bonded interface of No. 5. [Figure 17] 10 shows an optical microscope photograph and a three-dimensional image of the bonding interface of Reference Example 4. [Figure 18]1 is a chart showing the peel strength test results of No. 1. DETAILED DESCRIPTION OF THE INVENTION

[0019] [Method for manufacturing composite heat insulating material] The composite thermal insulating material of the present invention is produced by a method including a step of heating and pressurizing a sandwich body, which has a thermal insulating layer containing hydroxyl-containing short silica fibers and particles of a thermal insulating material sandwiched between a first base fabric and a second base fabric made of hydroxyl-containing silica fibers, at 300 to 700° C. The particles of the thermal insulating material are silica aerogel particles, ceramic particles, or a mixture thereof.

[0020] (1) Silica fiber base fabric The base fabrics used as the first and second base fabrics and made of silica fibers having hydroxyl groups (hereinafter sometimes simply referred to as "silica fiber base fabrics") are plate-like aggregates of silica fibers having hydroxyl groups, and specifically have the form of fabric such as woven fabric, knitted fabric or nonwoven fabric; felt; mat; blanket; etc.

[0021] The silica fiber with hydroxyl groups used as the base fabric fiber contains 81% or more by weight of SiO2, with Si(OH) present in part of the SiO- network. When fired, the fibers undergo dehydration condensation as shown in formula (1) below, forming siloxane bonds that bond the fibers together.

[0022] [ka]

[0023] The silica fiber constituting the base fabric is not particularly limited as long as it contains Si(OH) in its composition. For example, AlO 1.5 ·18〔(SiO2) 0.6 (SiO 1.5 OH) 0.4 Examples of the composition include:

[0024] The silica fiber preferably has the following typical composition: SiO2:81~97% by weight; Al2O3: 3 to 19 wt%; and 2% by weight or less of components selected from ZrO2, TiO2, Na2O, Li2O, K2O, CaO, MgO, SrO, BaO, Y2O3, La2O3, Fe2O3 and mixtures thereof (referred to as "other components").

[0025] Specifically, a starting glass material having the following composition is melted: 55-80% by weight of SiO2, 5-19 wt% Al2O3, 15-26 wt.% Na2O, 0-12 wt% ZrO2, 0-12 wt% TiO2, and Li2O, K2O, CaO, MgO, SrO, BaO, Y2O3, La2O3, Fe2O3 and mixtures thereof up to 1.5% by weight; forming filaments from the melt; The resulting filaments are acid extracted; The extracted filaments can be produced by removing any remaining acid and / or salt residues and then drying them.

[0026] In the acid treatment, alkali metal ions are replaced by protons, but the ions (Al 3+ , TiO 2+ or Ti 4+ , and ZrO 2+ or Zr 4+ ) remains. It is believed that the metal ions replaced by protons in the silicon dioxide skeleton leave a certain number of hydroxyl groups depending on the valence. These hydroxyl groups form new Si-O-Si bonds by dehydration condensation shown in the above formula (1) at around 300 to 700°C.

[0027] The silica fibers constituting the base fabric are filaments obtained by melt-spinning a material having the above composition, and have a diameter of 6 to 13 μm, preferably about 7 to 10 μm. The fiber length is not particularly limited, but is preferably 30 to 150 mm, more preferably 50 to 130 mm, from the viewpoint of fabric formation so that the fibers can be entangled in a flat aggregate.

[0028] As the silica fiber, commercially available products can be used, such as BELCOTEX (registered trademark) from BELCHEM GmbH. BELCOTEX® fiber is generally made from silicic acid modified with alumina, and in standard staple fiber pre-yarns, it has an average fineness of about 550 tex. BELCOTEX® fiber is amorphous and typically contains about 94.5 weight percent silica, about 4.5 weight percent alumina, less than 0.5 weight percent oxides, and less than 0.5 weight percent other components. It has a mean diameter of about 9 μm with little diameter variation, a melting point of 1500°C to 1550°C, and is heat resistant up to 1100°C.

[0029] It should be noted that silica fibers other than BELCOTEX can also be used as long as they have hydroxyl groups. The silica fiber constituting the base fabric is not limited to one type, and may be a combination of two or more types of silica fiber having different fiber diameters and fiber lengths.

[0030] In the base fabric, the silica fibers are preferably entangled with each other. A web formed by a wet method or a dry method can be entangled by a conventionally known method such as a hydroentanglement method or a needle punching method. Among these, a mat (needle mat) in which the fibers are entangled by needle punching to stabilize a plate-like body of a predetermined thickness is preferably used.

[0031] The thickness of the silica fiber base fabrics used as the first and second base fabrics is not particularly limited, but is preferably 3 to 25 mm, more preferably 5 to 20 mm. If the thickness is too thin, the short silica fibers sandwiched between the base fabrics tend to bond insufficiently during the heating and pressurizing process. The upper limit of the thickness is appropriately selected depending on the application, particularly the size of the catalytic converter to be used, and the gap between the catalyst carrier and the casing where the heat insulating material is installed.

[0032] The density of the base fabric is 80 kg / m 3 ~180kg / m 3 , more preferably 90 kg / m 3 ~160kg / m 3 If the density is too high, the heating and pressing required to integrate the sandwiched body tends to be insufficient. On the other hand, if the density is too low, the gaps between the fibers in the base fabric, which correspond to the pores in the base fabric, become large, and insulating materials such as silica aerogel and infrared absorbing materials, or short silica fibers, may become embedded, making it difficult to fabricate the sandwiched body.

[0033] (2) Short silica fibers The short silica fibers serve to hold the heat insulating material between the first and second backing fabrics. The short silica fibers can be the same as those used as constituent fibers of the first and second backing fabrics. Specifically, silica fibers containing 0.1 to 20% Al2O3 and 80 to 99.9% SiO2 are preferably used as silica fibers having hydroxyl groups. The size of the short silica fibers is a fiber diameter of 6 to 13 μm, preferably about 7 to 10 μm. The fiber length is 0.5 mm to 5 mm, preferably 1 to 3 mm. As such short silica fibers, for example, short fibers (staple fibers) of BELCOTEX (registered trademark) fibers can be used.

[0034] As the fiber length increases, the majority of the short fibers tend to lie face down along the surface of the mat, resulting in insufficient retention of the insulating material. Furthermore, the short fibers tend to become entangled, making defibration difficult. On the other hand, if the fiber length is less than 0.5 mm, the ability to retain the silica aerogel and infrared absorbing material decreases due to their size.

[0035] (3) Heat insulating materials (3-1) Silica aerogel The silica aerogel used in the present invention is silica particles having nano-sized pores (approximately 10 to 50 nm) and containing air in the pores. The porosity is 60% by volume or more, preferably 80% by volume or more, and more preferably 90% by volume or more, and the density is 0.1 to 0.4 g / cm. 3 Due to this porosity, it can provide excellent thermal insulation.

[0036] Silica aerogel has a secondary particle diameter of 10 to 500 μm. However, silica aerogel particles tend to aggregate and may exist as aggregates with a particle diameter of 1 to 5 mm. In such cases, it is preferable to use the silica aerogel after crushing and dispersion treatment. By crushing and dispersion, 90% or more of the silica aerogel can be made to have a particle diameter within the range of 5 μm to 1 mm, more preferably within the range of 10 μm to 500 μm. As the silica aerogel, a commercially available product having a particle size within the above range may be used, or a product obtained by subjecting it to an appropriate crushing and dispersion treatment may be used.

[0037] The silica aerogel used in the present invention is preferably a hydrophobic aerogel having hydrophobic groups on the surface. Specifically, the particle surface is made hydrophobic by bonding a tri-substituted silyl group represented by the following formula: 1 ,R 2 ,R 3 may be the same or different and are selected from alkyl groups having 1 to 18 carbon atoms or aryl groups having 6 to 18 carbon atoms, and are preferably methyl, ethyl, cyclohexyl, or phenyl.

[0038] [ka]

[0039] Silica aerogel is typically used in a ratio of silica aerogel to short fiber (weight ratio) of 2:8 to 8:2. While a higher silica aerogel content provides a higher thermal insulation effect, a higher content also reduces the relative fiber content, potentially reducing the stability of the material between the base fabrics. The amount of short fiber necessary and sufficient to stably hold the silica aerogel is appropriately selected based on the state of the short fibers, the type of short fibers (e.g., diameter and length of the short fibers), the presence or absence of a film-forming inorganic binder (described below), and the method of laying the silica short fibers and insulating material on the base fabric.

[0040] When silica short fibers and a heat insulating material are mixed dry (without a solvent) and laid down without using a film-forming binder, the weight ratio of aerogel to short fibers is 2:8 to 8:2, preferably 2:8 to 5:5, and more preferably 3:7 to 4:6, from the viewpoint of stable retention and heat insulating properties. On the other hand, by defibrating the short fibers to the extent that they exist as individual fibers, increasing the mixing homogeneity with the silica aerogel, and further using a film-forming inorganic binder, it is possible to reduce the amount of short fibers to about 1 / 35 of the aerogel. By first sufficiently defibrating the silica short fibers in a dispersion medium, preferably dispersing them to individual fibers, and then mixing them with the insulating material, and further adding a film-forming inorganic binder as necessary, it is possible to use silica aerogel / short fibers (weight ratio) at a ratio of 1 or more, 2 or more, 4 or more, 10 or more, up to a maximum of 35 or less, 30 or less, 20 or less, or 10 or less.

[0041] Silica aerogel is used for 1 m of base fabric, depending on the composition of the insulation layer. 2 It is possible to lay up to about 1.8 kg per m of base fabric. From the viewpoints of stability and ease of preparation of the mixture of the insulating material to be laid, it is preferable to lay up to about 1.8 kg per m of base fabric. 2 The amount is about 300 g to 1.5 kg, and more preferably about 500 g to 1 kg.

[0042] (3-2) Infrared absorbing material The infrared absorbing material can act as a thermal insulator from the outside in that it retains the thermal energy of the heat source in the thermal insulator.

[0043] As the infrared absorbing material having such a function, ceramic particles having a thermal emissivity of 0.6 to 0.9, preferably 0.65 to 0.85, can be used. The ceramic particles used have an average particle diameter of 0.5 to 4 μm, preferably 1 to 3 μm, and more preferably 1 to 2.5 μm, as measured by a light scattering method. Furthermore, the particle diameter distribution is preferably a cumulative 90% diameter (D 90 ) is 10 μm or less, preferably 8 μm or less, and more preferably 7 μm or less. Ceramic particles of this size absorb and then radiate infrared rays, particularly near-infrared rays. Therefore, infrared absorbing materials can be used as effective heat-retaining materials when maintaining high temperatures in the range of 400 to 900°C, preferably 500 to 900°C, where the proportion of radiant heat is high. In particular, in high-temperature ranges where radiant heat is dominant, the heat-retaining effect of silica aerogel, which exhibits heat insulation properties due to its pores, becomes smaller, so the heat-retaining effect of infrared absorbing materials is advantageous.

[0044] In consideration of the case where the ceramic particles are fixed and held near a heat source, it is preferable that the ceramic particles used as the infrared absorbing material are ceramic particles that are resistant to oxidation or melting even when used for a long period of time in a high temperature range, and ceramic particles such as carbides, nitrides, and borides that have a high melting point of 1500°C or higher are preferably used.

[0045] Ceramics that can be used as infrared absorbing materials include carbides such as WC, TiC, SiC, and ZrC; nitrides such as TiN, ZrN, and TaN; borides such as CrB, VB2, W2B5, WB, TaB, and MoB; and silicide particles such as TiSi, ZrSi, and WSi. Generally, these ceramic particles have a melting point of 1500°C or higher, while carbides, nitrides, and borides have a melting point of 2000°C or higher. Therefore, they are preferred because they can be used in high-temperature ranges based on the heat resistance of the base fabric. Among these, silicon carbides are preferred, and SiC is more preferred, in terms of their affinity with short silica fibers.

[0046] Such infrared absorbing materials are usually in particulate or powder form and tend to aggregate easily. Particularly when pressurized, they tend to solidify in an aggregated state and form aggregates with particle diameters of about 100 to 500 μm. When used in combination with short silica fibers, the infrared absorbing material can be held in the gaps between the short silica fibers, similar to silica aerogel. Although agglomerates of the infrared absorbing material generally tend to have poor adhesion to a silica fiber base fabric, they can be held on the base fabric by using a binder or short silica fibers in combination.

[0047] Although the content of the infrared absorbing material is not particularly limited, when the insulating layer is formed by coexistence with silica aerogel, the weight ratio of silica short fiber to infrared absorbing material is preferably 9:1 to 5:5, more preferably 9:1 to 6:4, or even 9:1 to 7:3. To stably hold both the silica aerogel and the infrared absorbing material with the silica short fiber, the weight ratio of silica short fiber to (total amount of silica aerogel and infrared absorbing material) is about 9:1 to 1:9, preferably 9:1 to 2:8, more preferably 9:1 to 4:6, even 8:2 to 5:5, or even more preferably 7:3 to 5:5.

[0048] (4) Film-forming inorganic binder In the composite thermal insulation material of the present invention, the thermal insulation material is held together by short silica fibers, but the thermal insulation layer may also contain a film-forming inorganic binder.

[0049] The film-forming inorganic binder is a dispersion (slurry) containing layered silicate as its main component, in which SiO2 tetrahedrons are connected to three oxygen atoms in common, forming a two-dimensional flat layer structure. The metals that make up the salt include aluminum, potassium, sodium, calcium, and magnesium.

[0050] As the layered silicate, sodium silicate of xNa2·ySiO2 (y / x=2 to 3) is preferred, and smectite (saponite, hectorite, stevensite, montmorillonite), vermiculite group minerals, etc. can be used, with the smectite group being preferred. The film-forming inorganic binder may be a synthetic layered silicate, a mineral such as a smectite or vermiculite mineral, or bentonite containing such a mineral as a main component. Such layered silicates swell when they absorb water and can form a film when dried.

[0051] The film-forming inorganic binder is usually used as a slurry in which water, a lower alcohol, or a mixture thereof is used as a dispersion medium. When used as a slurry, the solid content is usually 1 to 10 wt %, preferably 3 to 5 wt %, from the viewpoints of viscosity and ease of handling.

[0052] As the film-forming inorganic binder, commercially available products may be used, such as Kunimine Industries Co., Ltd.'s Kunipia series (main component mineral is montmorillonite), Sumecton series (main component minerals are saponite, stevensite, and hectorite), and Moistonite series (main component mineral is bentonite).

[0053] By using a film-forming inorganic binder in combination with short fibers, it is possible to reduce the amount of short fibers without compromising the thermal insulation material's stability. Even with a reduced amount of short fibers, the strength of the composite thermal insulation material can be maintained. The ability to reduce the amount of short fibers without impairing the retention stability of the insulating material or the strength of the composite insulating material is preferable for applications requiring thermal insulation in high temperature ranges where the rate of thermal conduction is high. On the other hand, if the amount of film-forming inorganic binder is too high, the viscosity becomes too high, which reduces handleability, reduces the mixing and dispersibility of the insulating material, and limits the application methods to silica fiber base fabrics.

[0054] When a film-forming binder is used in combination, its content is preferably at most about half the amount of the silica aerogel, specifically, 1 / 2 or less, preferably 1 / 3 to 1 / 10, and more preferably 1 / 3 to 1 / 8 of the weight of the silica aerogel.

[0055] (5) Formation of the clamping body and fabrication of the clamping body A mixture of silica short fibers and a heat insulating material is sandwiched between the first and second base fabrics. As the heat insulating material, the silica aerogel or the infrared absorbing material may be used alone, or a mixture of silica aerogel and an infrared absorbing material may be used. A mixture of silica aerogel and short silica fibers and a mixture of silica short fibers and an infrared absorbing material may be formed as separate layers and then laminated together to form a laminate. Silica aerogel exhibits excellent heat insulating properties mainly in the temperature range of 100 to 500°C because it can exhibit heat insulating effects by blocking heat conduction through pores. In addition, infrared absorbing materials absorb infrared rays and dissipate heat, so they have excellent heat retention properties in high temperature ranges of 400°C or higher, further 450°C or higher, and particularly 500°C or higher. Therefore, the usage mode can be appropriately selected depending on the application.

[0056] Therefore, the following modes can be mentioned as modes in which the material is sandwiched between the first and second base fabrics. a) Short silica fiber and silica aerogel mixture; b) a mixture of short silica fibers, silica aerogel and infrared absorber; c) A laminate of a mixture layer of short silica fibers and silica aerogel and a mixture layer of short silica fibers, silica aerogel, and an infrared absorbing material d) A laminate of a mixture layer of silica short fibers and silica aerogel and a mixture layer of silica short fibers and infrared absorbing material

[0057] When the film-forming binder is used in combination with the short fibers, the film-forming inorganic binder is present in the gaps between the silica short fibers, silica aerogel, and infrared absorbing material in the mixture (layer).

[0058] The method for mixing the short fibers with the silica aerogel and / or infrared absorber is not particularly limited. The silica short fibers and the insulating material (silica aerogel, infrared absorber) may be mixed in a predetermined ratio in a container and mixed in a dry state by stirring, shaking, or the like (a solvent-free mixture is obtained). Alternatively, the insulating material may be mixed and dispersed using an organic solvent, such as water, lower alcohols (e.g., methanol, ethanol, propanol), esters such as acetate esters, or ketones such as acetone, or a mixture of water and an organic solvent, as a dispersion medium (a dispersion is obtained). A surfactant may be added, if necessary, to prepare the dispersion. The dispersion-based mixing method has the advantage of allowing the addition of a film-forming inorganic binder.

[0059] The short fibers are preferably defibrated before addition and mixing. In this regard, when preparing a dispersion, the short fibers can be first defibrated by adding them to a dispersion medium and stirring, and then the insulating material can be added. Defibration in a dispersion medium allows for sufficient interfiber spacing compared to air defibration, and the insulating material can be added and mixed while maintaining the defibrated state. Therefore, homogeneity of the mixture of the short fibers, silica aerogel, and infrared absorbing material is easier to achieve than with a solvent-free mixture, and a highly homogeneous mixture is likely to be obtained. This means that the silica aerogel and infrared absorbing material can be stably maintained even when the amount of short fibers is reduced; in other words, the amount of silica aerogel and infrared absorbing material that can be maintained can be increased. On the other hand, in the method using a dispersion, it is necessary to dry the dispersion medium after laying it on the surface of the base fabric, as described below. In this respect, when a solvent-free mixture is used, the drying step is not required, and therefore productivity of the sandwich body is excellent.

[0060] The mixture of short fibers and heat insulating material prepared above (solvent-free mixture, dispersion) is laid on the surface of a first base fabric, and then a second base fabric is placed on top of it to obtain a sandwiched body.

[0061] When a solvent-free mixture is used, the application method may be spraying, sprinkling, etc. After application, the mixture may be spread with a spatula, blade, roller, etc. to make the surface uniform. When a dispersion is used, methods such as spraying, blades, and squeezing can be used, depending on the viscosity and solids concentration of the dispersion. When a dispersion is used, the coating is dried after laying. The drying temperature and drying time are appropriately selected depending on the type of dispersion medium, the viscosity of the dispersion, and the solids concentration. In addition, to shorten the drying time, a clamping body may be placed in a leaking container and a load may be applied to squeeze out the dispersion medium.

[0062] The sandwiching body may include a layer of insulating material alone, which does not contain short fibers. Even if the sandwiching body includes a layer of insulating material alone, bonding strength can be ensured by bonding a layer of a mixture of silica short fibers and insulating material together by heating and pressurizing.

[0063] (5) Heat and pressure process The sandwiched body thus obtained is set in a heating and pressing device and heated and pressed. The pressure is usually about 1 to 15 kN, preferably 3 to 13 kN, and more preferably about 5 to 10 kN. If the pressure is too high, the silica fibers constituting the base fabric may be damaged. On the other hand, if the pressure is too low, the adhesion between the heat insulating layer and the base fabric may be insufficient. Furthermore, the entanglement and bonding of the short silica fibers per unit volume may decrease, making it impossible to ensure sufficient bonding strength, and the retention of the silica aerogel and infrared absorbing particles tends to become unstable. Furthermore, the strength of the composite heat insulating material tends to decrease.

[0064] The heating temperature is a temperature at which the hydroxyl group-containing silica fibers and short silica fibers can undergo dehydration condensation, specifically 300 to 700°C, preferably 350 to 600°C, and more preferably 400 to 500°C. The heating and pressing process is a process for bonding and integrating the first and second base fabrics with the layer containing the insulating material (the insulating layer). This bonding and integration is thought to be achieved by partial fusion between the short silica fibers and between the short silica fibers and the surface of the base fabrics. This fusion is thought to be achieved by dehydration condensation of the hydroxyl groups of the silica fibers when heated, forming siloxane bonds.

[0065] If a flat press is used as the press for the pressure application process, a flat composite insulation material will be obtained, but by devising the shape of the press mold, it is also possible to obtain composite insulation materials in semi-cylindrical or box shapes, etc.

[0066] The pressurizing time varies depending on the heating temperature, but at about 300 to 400°C, it is usually 1 to 3 hours, preferably 1.5 to 2.5 hours. At 400 to 600°C, it is 5 to 40 minutes, preferably 10 to 30 minutes. By increasing the heating temperature, the pressurizing time can be shortened, so it can be selected appropriately depending on the desired productivity.

[0067] <Composite insulation material> The composite insulating material of the present invention is manufactured by the above-mentioned manufacturing method, and depending on the type of insulating layer sandwiched between the first base fabric and the second base fabric, there are the following types of composite insulating material.

[0068] (1) First embodiment The composite thermal insulation shown in Figure 2 is a case in which the thermal insulation material contained in the thermal insulation layer 11 sandwiched between the first base fabric 5a and the second base fabric 5b is silica aerogel 7 alone. The silica aerogel particles 7 are held by entangled short silica fibers 6.

[0069] The first and second base fabrics are compressed products of the first and second base fabrics used in the above manufacturing method, and therefore the constituent fibers of the base fabrics are silica fibers. The type of backing depends on the type of backing used in the manufacturing process, such as woven or nonwoven fabric, mat, felt, blanket, etc. The thickness of each of the first and second base fabrics is usually 1 to 8 mm, preferably 3 to 5 mm, depending on the pressure applied. The bulk density of the base fabric is 100 to 300 kg / m 3 is preferably 130 to 270 kg / m 3 is.

[0070] The silica aerogel particles contained in the heat insulating layer 11 are the silica aerogel used in the manufacturing method described above. The silica aerogel particles are not crushed by the pressure applied during the heating and pressurizing step in the manufacturing process of the composite heat insulating material, so the porous state of the silica aerogel is maintained. Therefore, the inherent heat insulating performance of the silica aerogel can be exhibited in the composite heat insulating material.

[0071] The short silica fibers holding the silica aerogel have a fiber diameter of 6 to 13 μm, preferably 7 to 10 μm, and a fiber length of 0.5 to 5 mm, preferably 1 to 3 mm. Some or all of the hydroxyl groups contained in the short silica fibers used during production undergo dehydration condensation at the contact points with the silica short fibers and further with the base fabric, forming siloxane bonds and bonding them together. The silica aerogel is supported and held in the gaps between the entangled and partially bonded silica short fibers, and is thereby stably held between the first and second base fabrics.

[0072] The content ratio of the silica aerogel 7 to the silica short fibers 6 is substantially the same as the content ratio employed in the above-mentioned manufacturing method.

[0073] In the composite thermal insulation material of the first embodiment, a thermal insulation layer 11 containing silica aerogel is sandwiched between silica fiber base fabrics in a laminated and integrated state with the base fabrics 5a and 5b. Even in the thermal insulation layer 11, the silica aerogel maintains its pores intact, allowing the inherent thermal insulation performance of silica aerogel to be exhibited. Furthermore, the thermal insulation layer 11 can exhibit its thermal insulation function by utilizing pores not only in the micropores of the silica aerogel itself, such as the gaps between the short fibers and between the silica aerogel particles, but also in the gaps between the components of the thermal insulation layer (between the short fibers, between the short fibers and the thermal insulation material, and between the thermal insulation material). Therefore, the composite thermal insulator of the first embodiment can exhibit excellent thermal insulation performance that could not be achieved by using a silica fiber base fabric alone.

[0074] (2) Second embodiment 3, the insulating material contained in the insulating layer 12 sandwiched between the first base fabric 5a and the second base fabric 5b is a mixture of silica aerogel particles 7 and infrared absorbing material 8. The silica aerogel particles 7 and the infrared absorbing material (ceramic particles) 8 are each held by short silica fibers 6.

[0075] The composite insulating material of the second embodiment can be manufactured by using a mixture of silica aerogel, infrared absorbing material, and short silica fibers as an insulating layer sandwiched between a first base fabric and a second base fabric.

[0076] The infrared absorbing material is the same as the infrared absorbing material used in the production method, and is ceramic particles having a thermal emissivity of 0.6 to 0.9, preferably 0.65 to 0.85. The infrared absorbing material is agglomerated in the heating and pressurizing step from powder form, and the agglomerates are present in the heat insulating layer as agglomerates having a particle size of 100 to 500 μm, preferably an average particle size of 150 to 300 μm, as measured by electron microscope observation.

[0077] The configurations of the first and second base fabrics and the silica aerogel are the same as those in the first embodiment, and therefore description thereof will be omitted.

[0078] The content ratio of the silica aerogel, the infrared absorbing material, and the short silica fibers in the mixture is substantially the same as the content ratio employed in the manufacturing method.

[0079] In the composite thermal insulation material of the second embodiment, the thermal insulating material contained in the thermal insulation layer 12 is silica aerogel and an infrared absorbing material. The infrared absorbing material exhibits excellent heat retention performance at high temperatures of 500°C or higher, i.e., in high-temperature ranges where radiant heat accounts for a high proportion of heat transfer. Since the heat retention and insulating effect of transparent silica aerogel is not significant in the high-temperature range of 500°C or higher where the proportion of radiant heat is high, it is preferable to use it in combination with an infrared absorbing material that exhibits excellent heat retention in such high-temperature ranges, as this will enable the heat retention and insulating effect to be exerted over a wide temperature range.

[0080] (3) Third embodiment The composite insulation material shown in Figure 4 is a laminate in which the insulation layer 13 sandwiched between the first base fabric 5a and the second base fabric 5b is a layer (first insulation layer) 13a of a mixture (first mixture) of short silica fibers 6 and silica aerogel particles 7 and a layer (second insulation layer) 13b of a mixture (second mixture) of short silica fibers 6, silica aerogel particles 7, and infrared absorbing material (ceramic particles) 8.

[0081] The composite heat insulating material of the third embodiment can be manufactured by the following steps in preparing the sandwich body: first laying a first mixture of short silica fibers and silica aerogel on a first base fabric, then laying a second mixture of short silica fibers, silica aerogel, and infrared absorbing material, and then overlaying a second base fabric; or alternatively, laying the second mixture on a second base fabric, then laying the first mixture, and then overlaying the first base fabric.

[0082] The composite insulation material of the third embodiment has an infrared absorbing material that absorbs infrared rays and plays a role in heat retention, so by installing the second insulation layer 13b containing the infrared absorbing material on the high heat side (heat source side), or on the catalyst carrier side when insulating the catalytic reaction section, it can exhibit excellent heat retention functions.

[0083] (4) Fourth embodiment The composite insulation material shown in Figure 5 is a laminate in which the insulation layer 14 sandwiched between the first base fabric 5a and the second base fabric 5b is a combination of a layer (first insulation layer) 13a of a mixture (first mixture) of short silica fibers 6 and silica aerogel particles 7 and a layer (third insulation layer) 13c of a mixture (third mixture) of short silica fibers 6 and infrared absorbing material (ceramic particles) 8.

[0084] The composite insulating material of the fourth embodiment can be manufactured by the following steps in preparing the sandwich body: first laying a first mixture on a first base fabric, then laying a third mixture, and then overlapping a second base fabric; or alternatively, laying the third mixture on a second base fabric, then laying the first mixture, and then overlapping the first base fabric.

[0085] In the composite insulation material of the fourth embodiment, the infrared absorbing material absorbs infrared rays and plays a role in heat retention, so by installing the third insulation layer 13c containing the infrared absorbing material on the high heat side, i.e., the catalyst carrier side, it can exhibit excellent heat retention function.

[0086] In the composite heat insulating material of the above embodiment, the content ratio of the silica short fiber, silica aerogel, and infrared absorbing material contained in each heat insulating layer corresponds to the content ratio adopted in the manufacturing method of the composite heat insulating material.

[0087] In the above first to fourth embodiments, the insulating layer sandwiched between the first base fabric and the second base fabric contained short silica fibers, but a thin layer that does not contain short silica fibers may be interposed as long as it is within the range that ensures integration as a composite insulating material (fifth embodiment).

[0088] When the heat insulating layer is produced using a dispersion liquid, and the dispersion liquid contains a film-forming inorganic binder, the film-forming binder will be appropriately present in the voids (excluding the pores in the silica aerogel) of the heat insulating layer in the above embodiment. Film-forming inorganic binders can contribute to the stable retention of insulating materials, especially silica aerogel. Although film-forming inorganic binders are thought to reduce the insulating properties due to thermal conduction, the use of film-forming inorganic binders in combination can reduce the amount of short silica fibers that cause thermal conduction in the thickness direction of the insulating material, thereby improving the overall insulating properties.

[0089] The composite heat insulating material of the present invention having the above-described configuration can adjust its heat insulating performance, hardness, and strength by adjusting the thickness and configuration of the heat insulating layer. When the type of heat insulating material and the configuration of the heat insulating layer are the same, the heat insulating performance usually depends on the thickness. Therefore, the thickness and configuration of the heat insulating layer can be selected appropriately depending on the application.

[0090] [Applications of composite insulation materials] The composite heat insulating material of the present invention has excellent heat insulating properties and heat resistance. Therefore, it can be preferably used in applications requiring high-temperature insulation in a thin layer. For example, it can be preferably used as a heat insulating material to be filled in an automobile catalytic converter. Furthermore, it is not limited to automobiles, and can be preferably used as a heat insulating material when a high-temperature structure needs to be isolated from peripheral equipment when there is a large temperature difference between the high-temperature structure and the outside air, or as a heat-retaining heat insulating material when it is necessary to protect the high-temperature structure from the outside air and maintain a high temperature state. [Example]

[0091] [Manufacturing of laminated insulation materials] (1) Materials used (1-1) 1st base fabric, 2nd base fabric As the first and second base fabrics, technical needle mats (isoTHERM (registered trademark) BCT) manufactured by Frenzelit were used. The needle mat is made of BELCOTEX (registered trademark) 110 (composition: AlO 1.5 ·18〔(SiO2) 0.6 (SiO 1.5 OH) 0.4 ], fiber diameter 9 μm) is formed into a mat using the needle punch method, and the mat has a nominal thickness of 6 mm.

[0092] (1-2) Short Fiber BELCOTEX (registered trademark) 110 from BELCHEM (composition: AlO 1.5 ·18〔(SiO2) 0.6 (SiO 1.5 OH) 0.4 ) staple fibers (fiber diameter 9 μm, average fiber length 3 mm) were used.

[0093] (1-3) Silica aerogel The silica aerogel used was prepared by crushing silica aerogel aggregates with diameters of 1.2 to 4.0 mm in a mixer manufactured by CABOT. The particle size of the crushed silica aerogel was measured using a laser diffraction / scattering particle size distribution analyzer LA-920 (manufactured by Horiba, Ltd., dispersion liquid: ethanol) and found to be between 10 and 400 μm.

[0094] (1-4) Infrared absorbing material SiC powder from Nippon Keical Co., Ltd. (particle size distribution measured by light scattering method: D 50 is 1.8 μm, D 90 The emissivity of this SiC powder is approximately 0.82.

[0095] (1-5) Film-forming inorganic binder We used "Kunipia F" (aqueous dispersion with 4% solids), a refined bentonite manufactured by Kunimine Industries Co., Ltd. This is an aqueous dispersion of montmorillonite powder, and the viscosity of a 4% dispersion is 30 mPa·s.

[0096] (2) Manufacture of insulation materials Composite insulation No.1: The short fibers were placed in a container and air was blown onto them to loosen the tangled fibers. Silica aerogel was then added (short fibers:silica aerogel = 4:3 (weight ratio)) and mixed in a mill to prepare a material for a heat insulating layer (first mixture). The first mixture prepared above was spread on a needle mat (length x width x thickness: 150 mm x 150 mm x 6 mm) at a concentration of 0.16 g / cm by a spraying method.2 After laying the material in an amount of 1000, a needle mat was placed on top to prepare a sandwich. The sandwiched body thus produced was set in a press, and while the sandwiched body was compressed (10 kN) by the press in the vertical direction of the base fabric, it was heated at 350°C for 2 hours to obtain composite thermal insulation material No. 1 of the first embodiment. The thickness of the obtained composite thermal insulation material was 8 mm.

[0097] Composite insulation No. 2: A 15:4 (weight ratio) mixture of silica aerogel and infrared absorbing material was used as the insulating material. The mixture of short silica fiber and insulating material was mixed in a ratio of 20:19 (weight ratio) (second mixture), and the mixture was applied to the surface of the glass at a concentration of 0.17 g / cm by the spraying method. 2 After laying the material in an amount of 1000, a needle mat was placed on top to prepare a sandwich. Using the prepared sandwiched body, a composite heat insulating material No. 2 of the second embodiment was obtained in the same manner as in No. 1. The thickness of the obtained composite heat insulating material was 8 mm.

[0098] Composite insulation No. 3: The second mixture prepared with composite insulation material No. 2 was applied to the needle mat by the spraying method at a concentration of 0.17 g / cm. 2 Then, on this second mixture layer, the first mixture prepared with the composite heat insulating material No. 1 was applied at a rate of 0.16 g / cm. 2 A needle mat was placed on this first mixture to prepare a sandwich. The prepared sandwiched body was compressed in the same manner as in No. 1, and then heated and pressurized to obtain a third embodiment of composite heat insulating material No. 3. The thickness of the obtained composite heat insulating material was 10 mm.

[0099] Composite insulation No. 4: An infrared absorbing material was spread on the needle mat to form an infrared absorbing layer. On this infrared absorbing layer, the first mixture prepared in the composite heat insulating material No. 1 was applied at a rate of 0.16 g / cm. 2 A needle mat was placed on this first mixture to prepare a sandwich. The prepared sandwiched body was compressed in the same manner as No. 1, and then heated and pressurized to obtain composite insulation No. 4 of the fifth embodiment having the configuration shown in Figure 6. The thickness of the obtained composite insulation was 8 mm. The SiC formed agglomerates to form an infrared absorbing material layer, but the adhesion to the needle mat was insufficient, so it could not be used as a bonded and integrated composite insulation.

[0100] Composite insulation No. 5: 55 g of a nonionic surfactant (4% aqueous solution) was added to a container containing 960 g of water, followed by 6 g of silica fiber and stirring to defibrate the short fibers so that they could be dispersed as individual fibers. 67 g of SiC powder was then added and stirred, followed by 11 g of anionic surfactant (4% aqueous solution). 183 g of silica aerogel and 54 g of a film-forming inorganic binder were then added and stirred to prepare a slurry for the insulation layer. The weight ratio of short silica fiber to silica aerogel in the slurry for the insulation layer was 1:30. The silica aerogel content in the solids was approximately 60 wt%. The slurry for the heat insulating layer prepared above was applied to a needle mat (length x width x thickness: 150 mm x 150 mm x 6 mm) as the first base fabric using a squeezer to a thickness of 10 mm. The coating amount was approximately 0.16 g / cm. 2 It was. After coating, the second base fabric was placed on top of the second base fabric, and then the mixture was left to dry at 74°C for 24 hours, at 90°C for 1 hour, and at 130°C for 1 hour to prepare a sandwiched body. The prepared sandwiched body was set in a press and heated and pressurized in the same manner as in No. 1 to obtain composite heat insulating material No. 5 having the same configuration as in the first embodiment. The thickness of the obtained composite heat insulating material was 8 mm.

[0101] Reference example 1: Six layers of needle mats were stacked as the first and second base fabrics, and pressed at 350°C for two hours (pressure: 10 kN) to produce a silica fiber-only insulation material. The thickness of the resulting composite insulation material was 8 mm.

[0102] Reference example 2: The needle mats used as the first and second base fabrics were previously baked at 800°C to shrink (mainly in the planar direction). Calcium silicate was added instead of short fibers to the insulation slurry used in No. 5, and the mixture was mixed and stirred to prepare an insulation slurry. The resulting slurry was applied to the mat surface using a squeezer. After coating, the laminate was folded as shown in Figure 7 to produce a laminate (10.5 mm thick) in which the insulating material was sandwiched between base fabrics. After squeezing out the water from the laminate using pressure (10 kN), it was dried in a drying oven at 74°C for 24 hours, 90°C for 1 hour, and 130°C for 1 hour to produce a composite insulating material. In Figure 7, 20 is the base fabric, and 21 is the insulating layer made of silica aerogel and infrared absorbing material.

[0103] Reference example 3: An attempt was made to prepare a composite thermal insulation material in the same manner as No. 1, except that only silica aerogel was used as the thermal insulation layer material (no short fibers were included). When an attempt was made to remove the composite heat insulating material obtained by heating and pressing, the silica aerogel spilled out, and the composite heat insulating material could not be substantially produced.

[0104] Reference example 4: A composite heat insulating material was prepared in the same manner as in No. 5, except that a slurry for a heat insulating layer to which short fibers had not been added was used as the slurry for a heat insulating layer.

[0105] [Evaluation method and results] <Thermal insulation> The thermal conductivity of the composite thermal insulators Nos. 1 to 4 and Reference Example 1 prepared above was measured by the steady-state heat flow method using Fourier's law. The measurement was performed by heating the thermal insulators from 200 to 700°C at a temperature increase rate of 0.17°C / min and measuring the thermal conductivity (λ) of the thermal insulator in the thickness direction at each temperature range. The smaller the thermal conductivity (λ), the better the thermal insulation properties. Note that Nos. 3 and 4 were set in the measuring device so that the layer containing the infrared absorbing material (SiC) was on the higher temperature side. The measurement results are shown in Figure 8.

[0106] Further, the thermal conductivity of the composite heat insulating materials Nos. 3 and 5, Reference Example 1, and Reference Example 2 prepared above was measured in the same manner, and the results are shown in FIG.

[0107] In Figure 8, composite insulation materials Nos. 1 to 4 had superior insulation properties below 300°C compared to the needle mat used alone as the base fabric (Reference Example 1: black circles). This is thought to be due to the insulating effect of the aerogel. On the other hand, No. 1 (black triangles) had a higher insulation coefficient than Reference Example 1 above 350°C. It is thought that the thermal conduction of the short fibers impaired the insulation properties at high temperatures. In this regard, by using an infrared absorbing material in combination, as in Nos. 2 to 4, excellent insulation properties could be maintained even at high temperatures above 350°C.

[0108] Comparing No. 3 (open triangles) and No. 5 (open circles) in Figure 9, No. 5 had better heat insulation than No. 3, possibly because No. 5 contained less short fibers or because the use of the dispersion method improved the uniformity of the dispersion of the silica aerogel and infrared absorbing material. In Figure 9, the composite insulation material containing no short silica fibers (Reference Example 2: black squares) had the best insulation properties. This is thought to be because it did not contain short fibers. However, No. 5, which used the dispersion method to reduce the amount of short silica fibers in the insulation layer, was able to maintain insulation properties at the same level as Reference Example 2, which did not contain short silica fibers, even at high temperatures of 350°C or higher.

[0109] <Bending strength> Using a bending tester (EZtest manufactured by Shimadzu Corporation), a load was applied as shown in Figure 10(A) and the load was measured against the displacement d (mm) shown in Figure 10(B) to measure and evaluate the bending strength of the composite thermal insulation material. Figure 11 shows the measurement results for composite thermal insulation material No. 3 and Reference Example 2 (dotted line), while Figure 12 shows the measurement results for composite thermal insulation materials No. 1 and No. 5 (solid line) and Reference Example 4 (dashed line).

[0110] As can be seen from Figure 11, even though the two materials were compressed to the same degree, the bending strength of the composite insulation No. 3 of the present invention, which contains short fibers in the insulating layer, was much greater. It is believed that the stiffness and strength of the composite insulation were improved by undergoing the heating and pressurizing process. Furthermore, when comparing the measurement data of Reference Example 4 and No. 5 in Figure 12, although the composition of the insulating layer and the method of forming the insulating layer (both using dispersion liquid) were the same except for the presence or absence of short fibers, No. 5 had a bending strength that was more than 2.5 times greater than that of Reference Example 4. From these results, it was confirmed that the rigidity and strength of the composite insulation can be increased by adding short fibers to the insulating layer.

[0111] Furthermore, Figure 12 confirms that the bending strength of No. 5 is higher than that of No. 1. It was surprising that No. 5, whose insulation layer was formed using the dispersion method, had higher rigidity, even though the amount of short fibers contained in the insulation layer of No. 1 was more than 30 times that of No. 1. This is thought to be because the dispersion method allowed for sufficient defibration of the short fibers, improving the uniformity of the mixture with the silica aerogel and SiC, and because the use of a film-forming binder ensured the stable retention of the silica aerogel and SiC even with a small amount of short fibers. The strength of Reference Example 2 (see Figure 11) was significantly lower than that of Reference Example 4. Both contained a film-forming inorganic binder, but Reference Example 2 did not undergo the heating and pressurizing process for laminating and integrating the base fabric and the heat insulating layer, i.e., the room temperature pressurization to squeeze out the water did not cause the silica fibers to fuse together through siloxane bonds, which is thought to be why no increase in rigidity was achieved.

[0112] Composite insulation materials No. 1 and No. 3 were cut in the thickness direction of the insulation material, and the cut cross sections were observed under a microscope. The electron microscope photographs taken are shown in Figure 13 (No. 1) and Figure 14 (No. 3). As can be seen from the microscope photographs, spherical silica aerogel particles and infrared absorbers are held by short silica fibers. Furthermore, Figure 14 shows that the infrared absorbers were held in the form of agglomerates by the short silica fibers. The area surrounded by a solid line in Figure 14 is recognized as SiC agglomerates.

[0113] <Adhesion between base fabric and thermal insulation layer> For composite heat insulating material No. 5 and Reference Example 4, strip-shaped test pieces 30 mm wide and 150 mm long were prepared. The first and second base fabrics of the prepared test piece were clamped with a chuck, and a peel test was carried out using a peel tester in which the first and second base fabrics were pulled at a speed of 5 mm / min. The relationship between the tensile load and the displacement of each test piece is shown in Figure 15. No. 5 (solid line), which contained short fibers, had a peel load that was about 20% higher than that of Reference Example 4 (dashed line).

[0114] The interface between the base fabric and the insulating layer of composite thermal insulation material No. 5 and Reference Example 4 was observed using a Keyence microscope (VHX-7000). Optical microscope photographs and 3D shape images of the interface of No. 5 and Reference Example 4 are shown in Figure 16 (No. 5) and Figure 17 (Reference Example 4), respectively. While some lifting was observed at the interface in Reference Example 4, no noticeable lifting was observed in No. 5, confirming the high integrity of the bonded interface. This indicates that the short fibers not only help to retain the silica aerogel but also contribute to bonding and integrating it with the base fabric.

[0115] Furthermore, the results of a similar peel test on No. 1 are shown in Figure 18. No. 1 did not contain SiC and had a higher amount of short fibers than No. 5 (approximately 20 times), so it had a peel strength 30 times or more that of No. 5. [Industrial Applicability]

[0116] The composite heat insulating material of the present invention has superior heat insulating properties compared to conventional mats made of heat-resistant inorganic fibers. Therefore, it is useful as a heat insulating material for parts requiring high heat insulation, such as catalytic converters in automobiles, with a thickness of about 3 to 18 mm. Furthermore, by using it as a heat insulating material for parts where high temperatures need to be maintained, it is possible to reduce heating energy consumption. [Explanation of symbols]

[0117] 1 catalytic converter 2 Casing 3 Honeycomb catalyst carrier 4. Insulation 5a, 5b base fabric 6. Short silica fibers 7. Silica aerogel particles 8. Infrared absorbing material (ceramic particles) 11, 12, 13, 14, 15 Heat insulating layer

Claims

1. a first base fabric composed of a group of fibers including silica fibers having hydroxyl groups and including no fibers other than silica fibers; A second base fabric composed of a group of fibers including silica fibers having hydroxyl groups and not including fibers other than silica fibers; and A heat insulating layer sandwiched between the first base fabric and the second base fabric, the heat insulating layer containing particles of a heat insulating material and short silica fibers having a fiber length of 0.5 to 5 mm. A composite heat insulating material comprising: The insulating layer is a composite insulating material sandwiched in a state where one side is in contact with a first base fabric and the other side is in contact with a second base fabric.

2. 2. The composite heat insulating material according to claim 1, wherein the particles of the heat insulating material are at least one kind selected from silica aerogel particles and ceramic particles.

3. 2. The composite heat insulating material according to claim 1, wherein the particles of the heat insulating material have a particle diameter of 0.5 μm to 1 mm.

4. A composite insulation material as described in claim 1, wherein the insulating layer further contains layered silicate, and a film composed of the layered silicate exists in the gaps between the silica short fibers and the particles of the insulating material.

5. A composite insulation material as described in claim 1, wherein the insulating layer is a mixture of particles of the insulating material and short silica fibers.

6. 2. The composite heat insulating material according to claim 1, wherein the fiber length of the short silica fibers is 0.5 to 3 mm.

7. 10. The composite insulation of claim 1, wherein the particles of insulating material comprise silica aerogel particles.

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