Inorganic fiber sheet

Abstract

The present invention provides a novel inorganic fiber sheet which is suitable for use in a high temperature environment.　One embodiment of the present invention is an inorganic fiber sheet which includes inorganic fibers and an inorganic coating layer that covers the inorganic fibers. The ratio (MS / MB) of the content MS of the inorganic fibers to the content MB of the inorganic coating layer is 0.25 to 9.00. The average fiber length of the inorganic fibers is 10 µm to 20 mm, and the average aspect ratio of the inorganic fibers is 20 to 20,000. An interlacing point of the inorganic fibers is formed at least in a partial region in which the inorganic coating layer is formed.

Description

Inorganic fiber sheet

[0001] The present invention relates to an inorganic fiber sheet.

[0002] Inorganic fiber sheets have a variety of uses. Various performance characteristics are required of inorganic fiber sheets depending on the use. For example, when inorganic fiber sheets are used as building materials, they are required to have soundproofing properties, the ability to quickly extinguish flames after ignition, and high flame retardancy.

[0003] As such an inorganic fiber sheet, for example, Patent Document 1 discloses a fibrous molded body containing inorganic fibers, a flame retardant, an organic binder, etc., and which is needle-punched.

[0004] JP 2014-152410 A

[0005] However, conventional inorganic fiber sheets have problems such as a decrease in strength when exposed to a high-temperature environment.

[0006] Therefore, an object of the present invention is to provide a novel inorganic fiber sheet suitable for use in high-temperature environments.

[0007] As a result of extensive research, the present inventors have found that the above-mentioned problems can be solved by using an inorganic fiber sheet containing a specific component.

[0008] One aspect of the present invention is an inorganic fiber sheet including inorganic fibers and an inorganic coating layer that coats the inorganic fibers. Ｂ The content M of the inorganic fibers relative to Ｓ The ratio (M Ｓ / M Ｂ ) is 0.25 to 9.00. The inorganic fibers have an average fiber length of 10 μm to 20 mm and an average aspect ratio of 20 to 20,000. Intertwining points between the inorganic fibers are formed in at least a portion of the region where the inorganic coating layer is formed.

[0009] The inorganic coating layer is preferably a layer formed by fusing inorganic particles having an average major axis of 500 nm or less. The inorganic fibers preferably contain clay mineral fibers. The inorganic fibers preferably further contain fibers other than the clay mineral fibers, and the content of the clay mineral fibers in the inorganic fibers is preferably 1 to 50 mass%. The inorganic coating layer preferably contains one or more types selected from the group consisting of silica and alumina. At least a portion of the alumina is preferably boehmite. At least a portion of the alumina is preferably α-alumina. The apparent density of the inorganic fiber sheet is 0.10 to 1.00 g / cm ３ It is preferable that the inorganic fiber sheet has a thickness of 1.0 mm or less.

[0010] According to the present invention, a novel inorganic fiber sheet suitable for use in high-temperature environments is provided.

[0011] FIG. 1 is an SEM photograph of an example of an inorganic fiber sheet according to the present disclosure.

[0012] Hereinafter, when an upper limit value and a lower limit value are separately described, it is considered that a numerical range combining any upper limit value and any lower limit value is substantially disclosed.

[0013] In the following, unless otherwise specified, various measurements are carried out at room temperature (23° C.).

[0014] The structure / components, physical properties / properties, production method, and uses of the inorganic fiber sheet according to the present disclosure will be described below.

[0015] <<<Structure / Components of Inorganic Fiber Sheet>>> An SEM photograph of an example of an inorganic fiber sheet according to the present disclosure is shown in Figure 1. As shown in Figure 1, the inorganic fiber sheet according to the present disclosure includes inorganic fibers and an inorganic coating layer that coats the inorganic fibers, and also has intertwining points between the inorganic fibers formed in at least a portion of the region where the inorganic coating layer is formed.

[0016] In other words, the inorganic fiber sheet according to the present disclosure has a skeleton of an inorganic fiber layer formed from inorganic fibers, the inorganic fibers are coated with an inorganic component such as an inorganic binder to form an inorganic coating layer, and in at least a portion of the region, a plurality of inorganic fibers are bound together via the inorganic component such as an inorganic binder to form entanglement points between the inorganic fibers, thereby forming a structure.

[0017] In the present disclosure, the term "inorganic coating layer" may refer to an inorganic component such as an inorganic binder that constitutes the inorganic coating layer. Also, in the present disclosure, the term "inorganic fiber" may refer to an inorganic fiber layer (an aggregate constituted by a plurality of inorganic fibers) that is constituted by a plurality of inorganic fibers.

[0018] The inorganic fiber sheet according to the present disclosure may contain components (other components) other than the inorganic components that constitute the inorganic fibers and the inorganic coating layer.

[0019] The inorganic fibers, the inorganic coating layer, and other components will be described in detail below.

[0020] <<Inorganic Fibers>> The inorganic fibers form a layer that serves as the base material of the inorganic fiber sheet.

[0021] Examples of inorganic fibers include carbon fibers, glass fibers, rock wool fibers, asbestos, alumina fibers, silica fibers, titania fibers, ceramic fibers (fibers mainly composed of alumina and silica), metal fibers (stainless steel fibers, copper fibers, etc.), and clay mineral fibers.

[0022] The inorganic fibers preferably contain clay mineral fibers. By including clay mineral fibers in the inorganic fibers, it is easy to obtain an inorganic fiber sheet that can suppress a decrease in strength and maintain handleability when continuously used in a high-temperature environment.

[0023] Examples of the clay minerals (silicate minerals) that constitute the clay mineral fibers include sepiolite, bentonite, montmorillonite, kaolin, saponite, mica, palygorskite, wollastonite, etc. The clay minerals may be natural or synthetic.

[0024] When the inorganic fibers contain clay mineral fibers, it is preferable that the inorganic fibers further contain fibers other than clay mineral fibers. That is, it is preferable that the inorganic fibers contain clay mineral fibers and fibers other than clay mineral fibers. In this case, the content of clay mineral fibers in the inorganic fibers is preferably 1 to 50 mass% based on the total inorganic fibers, and more preferably 5 to 20 mass%. In this way, by using a combination of clay mineral fibers and other fibers as the inorganic fibers, it is easy to obtain an inorganic fiber sheet that can suppress a decrease in strength and maintain handleability when continuously used in a high-temperature environment.

[0025] The average fiber length of the inorganic fibers is preferably 10 μm to 20 mm, and more preferably 10 μm to 15 mm. The average aspect ratio of the inorganic fibers is preferably 20 to 20,000, and more preferably 50 to 10,000. By setting the average fiber length and average aspect ratio of the inorganic fibers within these ranges, it is easy to obtain an inorganic fiber sheet that can suppress strength loss and maintain handleability when continuously used in a high-temperature environment. The average fiber length and average aspect ratio of the inorganic fibers are measured using the following measurement method. (Measurement Method) The inorganic fibers in the inorganic fiber sheet are observed using an optical microscope, and the average fiber length and average fiber diameter of the inorganic fibers are calculated as the average values ​​of 50 fibers. The average aspect ratio of the inorganic fibers is calculated as [average fiber length of inorganic fibers] / [average fiber diameter of inorganic fibers].

[0026] <<Inorganic Coating Layer>> The inorganic coating layer is a layer that is composed of an inorganic component and that coats the inorganic fibers.

[0027] The inorganic coating layer is, for example, a layer formed by fusing together inorganic particles (preferably inorganic particles having an average major axis of 500 nm or less), as will be described later.

[0028] The inorganic component constituting the inorganic coating layer is not particularly limited, and examples of the inorganic component constituting the inorganic coating layer include inorganic oxides, inorganic carbides, inorganic nitrides, and inorganic borides, and inorganic oxides (e.g., silica, alumina, titania, zirconia, zinc oxide, etc.) are preferred.

[0029] The inorganic coating layer preferably contains one or more inorganic components selected from the group consisting of silica and alumina. In this case, the total content of silica and alumina in the inorganic coating layer is preferably 50 mass% or more, 70 mass% or more, or 90 mass% or more, based on the entire inorganic coating layer. By using silica, alumina, or the like as the inorganic coating layer, it is easy to obtain an inorganic fiber sheet that can suppress a decrease in strength and maintain handleability when continuously used in a high-temperature environment.

[0030] Furthermore, when the inorganic coating layer contains alumina, it is preferable that at least a portion of the alumina is in the form of boehmite (alumina monohydrate). For example, it is preferable that 50 mass% or more, 70 mass% or more, or 90 mass% or more of the total amount of alumina is boehmite. In this way, when the alumina constituting the inorganic coating layer is boehmite, it is easy to obtain an inorganic fiber sheet that can suppress a decrease in strength and maintain handleability when continuously used in a high-temperature environment. In addition, from another perspective, when the inorganic coating layer contains alumina, it is preferable that at least a portion of the alumina is α-alumina. For example, it is preferable that 50 mass% or more, 70 mass% or more, or 90 mass% or more of the total amount of alumina is α-alumina. α-alumina is a trigonal alumina. In this way, when the alumina constituting the inorganic coating layer is α-alumina, it is easy to obtain an inorganic fiber sheet that has excellent insulation properties, etc.

[0031] <<Other Components>> Examples of other components include conventionally known additives that can be blended into inorganic fiber sheets. Specific examples of other components include surfactants, dispersants, thickeners, antifoaming agents, paper strength agents, etc.

[0032] When inorganic particles (such as colloidal silica or alumina sol) are used to form the inorganic coating layer of the inorganic fiber sheet according to the present disclosure, it is preferable to include an aggregation aid as a raw material component. Such aggregation aids will be described later.

[0033] <<Content of each component>> Content M of inorganic coating layer Ｂ The content M of the inorganic fibers relative to Ｓ The ratio (MＳ / M Ｂ ) is preferably 0.25 to 9.00, and more preferably 0.30 to 7.50. When the content of the inorganic coating layer and the content of the inorganic fibers are in such a ratio, the function of the inorganic fibers as a skeleton and the function of the inorganic coating layer in improving performance are well balanced, and it is easy to obtain an inorganic fiber sheet that can suppress a decrease in strength and maintain handleability when continuously used in a high-temperature environment.

[0034] The content of other components in the inorganic fiber sheet is, for example, 10 mass % or less, 5 mass % or less, 3 mass % or less, or 1 mass % or less, based on the total amount of the inorganic fiber sheet. The lower limit of the content of other components is, for example, 0.0 mass % or 0.1 mass %.

[0035] Here, the content of organic components in the inorganic fiber sheet is preferably 10% by mass or less, 5% by mass or less, 3% by mass or less, 1% by mass or less, or 0.5% by mass or less. By providing an inorganic fiber sheet with such a low content of organic components, it can be preferably used even in high-temperature environments.

[0036] <<<Physical Properties / Characteristics of Inorganic Fiber Sheet>>> <<Apparent Density>> The apparent density of the inorganic fiber sheet is 0.05 g to 2.00 g / cm ３ is preferably 0.10 g to 1.0 g / cm ３ By setting the apparent density of the inorganic fiber sheet within this range, strength, handleability, and the like can be improved.

[0037] <<Thickness>> The thickness of the inorganic fiber sheet is preferably 2.0 mm or less, more preferably 1.5 mm or less, and particularly preferably 1.0 mm or less. By setting the thickness of the inorganic fiber sheet in this range, it is possible to improve handleability, etc. The lower limit of the thickness of the inorganic fiber sheet is, for example, 0.01 mm or 0.1 mm.

[0038] <<Tensile Strength After High-Temperature Treatment>> The tensile strength of the inorganic fiber sheet measured by the following test method is preferably 0.1 N / 15 mm or more, and more preferably greater than 0.4 N / 15 mm. Having a tensile strength in this range after high-temperature treatment makes the inorganic fiber sheet particularly suitable for use in high-temperature environments. (Test Method) A sample measuring 15 mm wide x 10 cm long is prepared. The sample is heated to 650°C for 10 hours using an electric furnace. The tensile strength of the heated sample is measured according to JIS P8113:2006. The average value is calculated with n=10, and this is the tensile strength.

[0039] <<Bending Resistance After High-Temperature Treatment>> The bending resistance of the inorganic fiber sheet measured by the following test method is preferably 0.1 mN or more, and more preferably greater than 0.8 mN. Having a bending resistance after high-temperature treatment in this range makes the inorganic fiber sheet particularly suitable for use in high-temperature environments. (Test Method) A sample measuring 25.4 mm wide x 38.1 mm long is prepared. The sample is heated to 650°C for 10 hours using an electric furnace. After heating, the bending resistance (Gurley) of the sample is measured according to J. TAPPI Paper and Pulp Test Method No. 40-83. The average value is calculated using n=10 and used as the bending resistance.

[0040] <<<Method for Producing Inorganic Fiber Sheet>>> There are no particular limitations on the method for producing the inorganic fiber sheet according to the present disclosure. Hereinafter, a specific example of producing the inorganic fiber sheet according to the present disclosure by papermaking will be described in detail.

[0041] <<Mixing Step>> A raw material slurry containing at least inorganic fibers, inorganic components (raw material components constituting the inorganic coating layer), and a liquid medium is mixed. In other words, the inorganic fibers and inorganic components are dispersed in the liquid medium, and other components are dispersed as needed, to mix the raw material slurry.

[0042] The inorganic fibers and other components are as described above.

[0043] The liquid medium is usually water. The liquid medium may be a liquid medium other than water that can be used for papermaking (for example, an aqueous medium such as alcohol), or a mixture of water and a liquid medium other than water. The solids concentration in the raw material slurry may be appropriately set taking into consideration the ease of production, production costs, etc., and is not particularly limited.

[0044] In this example, inorganic particles such as silica and alumina are used as the inorganic component. The inorganic particles aggregate near the intertwining points of the inorganic fibers during the papermaking process. The inorganic particles then fuse to coat the inorganic fibers and bond the inorganic fibers together. Thus, in the manufacturing method of this example, inorganic particles are used as a raw material, and an inorganic coating layer is formed by the fusion of the inorganic particles.

[0045] The shape of the inorganic particles is not particularly limited and may be spherical, scaly, hollow, porous, etc. The inorganic particles may also be in the form of an aggregate / fused body of primary particles, such as silica gel or fumed silica.

[0046] The inorganic particles may be added to the raw material slurry in the form of a water-dispersed sol such as silica sol or alumina sol.

[0047] The inorganic particles may be subjected to an appropriate surface treatment.

[0048] The inorganic particles preferably have an average maximum length (average length) of 500 nm or less. By using such inorganic particles as raw materials, the inorganic particles are easily fused to each other, and an appropriate inorganic coating layer is easily formed. The average maximum length of the inorganic particles is calculated by observing the inorganic particles with a scanning electron microscope and averaging the values ​​of 50 particles.

[0049] The ratio of inorganic fibers to inorganic coating layer in the inorganic fiber sheet can be adjusted by changing the ratio of inorganic fibers to inorganic components in the raw material slurry. Although it depends on the papermaking conditions, the ratio of each component in the inorganic fiber sheet tends to be proportional to the ratio of the corresponding component in the raw material slurry.

[0050] When inorganic particles are used as a raw material for forming an inorganic coating layer, the addition of an aggregating aid to the raw material slurry promotes the aggregation of the inorganic particles, making it easier to form the inorganic coating layer. In particular, the addition of the aggregating aid makes it easier to produce a thick inorganic fiber sheet (e.g., a thickness of 0.5 to 2 mm).

[0051] As described above, preferred inorganic coating layers include those containing α-alumina. The α-alumina contained in the inorganic coating layer may be produced by calcining alumina hydrate to increase its crystallinity. In light of this, a method for producing an inorganic fiber sheet having a coating layer containing α-alumina when the inorganic fiber sheet is formed from a highly heat-resistant material may involve first producing an inorganic fiber sheet having an inorganic coating layer containing an alumina hydrate such as boehmite according to the method described above, and then calcining the inorganic fiber sheet to convert the alumina hydrate contained in the inorganic fiber sheet to α-alumina. In this manner, the inorganic fiber sheet may be a calcined product that has been heat-treated. The calcination conditions are not particularly limited, and examples include a heating temperature of 1000 to 1400°C and a heating time of 0.5 to 2.0 hours. The heating atmosphere may be selected appropriately from air, an inert gas atmosphere, or the like, taking into account the material of the inorganic fiber sheet, etc. Note that if the inorganic fiber sheet contains a component with low heat resistance, it is preferable not to perform the heat treatment at such a high temperature.

[0052] Examples of the flocculation aid include known flocculation aids such as inorganic flocculation aids, organic flocculation aids, polymer flocculants, and pH adjusters.

[0053] The content of the aggregation aid may be, for example, 0.1 to 1.0 mass %, or 0.1 to 0.5 mass %, when the total amount of the inorganic components and the inorganic fibers is 100 mass parts.

[0054] <<Papermaking Process>> The raw material slurry is made into paper using a known papermaking machine to obtain a wet sheet.

[0055] Specifically, the papermaking process can be carried out using a cylinder paper machine, an inclined paper machine, a Fourdrinier paper machine, a short wire paper machine, or a combination of these paper machines.

[0056] <<Drying Step>> The wet sheet after papermaking is dehydrated and dried at a temperature of about 100 to 200°C (or 120 to 150°C). The drying time can be adjusted depending on the thickness of the wet sheet, etc., as long as the wet sheet is sufficiently dried. As described above, when the inorganic coating layer is formed by fusion of inorganic particles, the fusion of the inorganic particles can be controlled by adjusting the conditions (temperature and time) in the drying step. Furthermore, pressurized drying may be performed in the drying step.

[0057] Specifically, the drying step can be carried out using a known dryer such as a Yankee dryer, a cylinder dryer, an air dryer, or an infrared dryer.

[0058] <<<<Uses of Inorganic Fiber Sheet>>> The inorganic fiber sheet according to the present disclosure is mainly composed of inorganic fibers and an inorganic coating layer (inorganic component), and exhibits excellent performance even when exposed to high-temperature environments, making it applicable to a variety of uses.

[0059] Specific applications of the inorganic fiber sheet according to the present disclosure include, for example, heat insulating materials, building materials, packing materials, substrates, and the like.

[0060] The inorganic fiber sheet according to the present disclosure may be used by laminating other layers (adhesive layers) or the like.

[0061] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following in any way.

[0062] <<<Raw Materials>>> <<Inorganic Fibers>> <Inorganic Fiber 1> Clay mineral fiber (sepiolite-based) Average fiber length: 83 μm Aspect ratio: 415-830 <Inorganic Fiber 2> Clay mineral fiber (sepiolite-based) Average fiber length: 59 μm Aspect ratio: 295-590 <Inorganic Fiber 3> Alumina fiber Average fiber length: 1-4 mm or less Aspect ratio: 250-1333 <Inorganic Fiber 4> Asbestos Average fiber length: 8 μm Aspect ratio: 400 <Inorganic Fiber 5> Glass fiber Average fiber length: 13 mm Aspect ratio: 1300 <Inorganic Fiber 6> Glass fiber Average fiber length: 25 mm Aspect ratio: 1923 <Inorganic Fiber 7> Glass fiber (glass-milled fiber) Average fiber length: 100 μm Aspect ratio: 14 <Inorganic Fiber 8> Glass fiber (glass-milled fiber) Average fiber length: 100 μm Aspect ratio: 67 <Inorganic fiber 9> Glass wool Average fiber length: 10 mm Aspect ratio: 6667 <Inorganic fiber 10> Glass wool Average fiber length: 5 mm Aspect ratio: 25000

[0063] <<Inorganic Coating Layer>> <Inorganic Component 1> Colloidal silica Average length: 12 nm <Inorganic Component 2> Alumina sol (boehmite) Average length: 20 nm or less <Inorganic Component 3> Alumina sol (non-boehmite) Average length: 200 nm <Inorganic Component 4> Alumina sol (boehmite) Average length: 1400 nm <Inorganic Component 5> Titanium oxide sol Average length: 20 nm

[0064] <<Flocculation Aids>> <Flocculation Aid 1> Modified cationic polyacrylamide <Flocculation Aid 2> Anionic polyacrylamide

[0065] <<<Production of Inorganic Fiber Sheets>>> <<Examples 1 to 22, Comparative Examples 1 to 6>> Raw material slurries were prepared by dispersing inorganic fibers, inorganic components, and aggregating aids in water so that the solid content (parts by mass) of each in the inorganic fiber sheet would be the values ​​shown in Tables 1 and 2. Paper was made using the raw material slurries, and dried at 140°C for about 5 minutes to produce inorganic fiber sheets according to Examples 1 to 22 and Comparative Examples 1 to 6.

[0066] The thickness and density of the obtained inorganic fiber sheet are shown in Tables 1 and 2. The thickness and density of the inorganic fiber sheet were adjusted by adjusting the time and pressure during papermaking.

[0067] <<Example 23>> The inorganic fiber sheet of Example 1 (an inorganic fiber sheet containing boehmite) was fired at 1,300°C for 1.0 hour in an air atmosphere to obtain an inorganic fiber sheet of Example 23. It was confirmed that the boehmite constituting the inorganic fiber layer in the inorganic fiber sheet of Example 23 was modified to α-alumina. The inorganic fiber sheet of Example 23 was an inorganic fiber sheet having the same component ratios, density, and thickness as those of Example 1, except that it did not contain an agglomeration aid and contained α-alumina instead of boehmite.

[0068] <<<Evaluation>>> <<Tensile Strength After High-Temperature Treatment>> The tensile strength of the inorganic fiber sheets according to each Example and Comparative Example after high-temperature treatment was measured according to the method described above, and evaluated according to the following evaluation criteria. The evaluation results are shown in Tables 1 and 2.

[0069] (Evaluation criteria) A: More than 0.4 N / 15 mm B: 0.1 to 0.4 N / 15 mm C: Less than 0.1 N / 15 mm

[0070] <<Bending Resistance After High-Temperature Treatment>> The bending resistance of the inorganic fiber sheets according to each Example and Comparative Example after high-temperature treatment was measured according to the method described above, and evaluated according to the following evaluation criteria. The evaluation results are shown in Tables 1 and 2.

[0071] (Evaluation criteria) A: More than 0.8 mN B: 0.1 to 0.8 mN C: Less than 0.1 mN

[0072] <<Overall Evaluation>> For the tensile strength after high-temperature treatment and the bending resistance after high-temperature treatment, if both were A, the overall evaluation was "A," if at least one was B and neither was C, the overall evaluation was "B," and if at least one was C, the overall evaluation was "C." The evaluation results are shown in Tables 1 and 2.

[0073]

[0074]

[0075] For Examples 1 and 23, the dielectric loss tangent (tan δ) was measured at a frequency of 50 GHz using a measuring device with a product name of N5225A PNA microwave network analyzer (manufactured by Keysight Technologies, Inc.). The dielectric loss tangent (tan δ) of Example 1 was 1.4 × 10 －２ The dielectric loss tangent (tanδ) of Example 23 was 5.9 × 10 －４ It should be noted that, with regard to the maintenance of strength and handleability after continuous use at high temperatures, both Example 1 and Example 23 were rated A, but Example 1 was superior. From these evaluation results, it can be seen that by using highly crystallized α-alumina as the inorganic coating layer, it is possible to form an inorganic fiber sheet that has excellent strength, handleability, etc., while also having a reduced dielectric tangent. Furthermore, with such an inorganic fiber sheet, the amount of heat dissipation is reduced, and insulation properties are less likely to deteriorate.

[0076] The inorganic fiber sheet according to the present invention is mainly composed of inorganic fibers and an inorganic coating layer (inorganic component), and exhibits excellent performance even when exposed to high-temperature environments, and is therefore suitable for use as a heat insulating material, building material, packing material, substrate, etc. CROSS-REFERENCE TO RELATED APPLICATIONS

[0077] This application claims priority based on Japanese Patent Application No. 2023-143372, filed with the Japan Patent Office on September 5, 2023, the entire disclosure of which is incorporated herein by reference in its entirety.

Claims

1. A fiber sintered body comprising an inorganic fiber and an inorganic coating layer that coats the inorganic fiber, and a content M of the inorganic coating layer Ｂ The content M of the inorganic fibers Ｓ The ratio (M Ｓ / M Ｂ ) is 0.25 to 9.00, the inorganic fibers have an average fiber length of 10 μm to 20 mm, and an average aspect ratio of the inorganic fibers is 20 to 20,000, and in at least a portion of an area where the inorganic coating layer is formed, intertwining points between the inorganic fibers are formed.

2. The inorganic fiber sheet according to claim 1, wherein the inorganic coating layer is a layer formed by fusing together inorganic particles having an average major axis of 500 nm or less.

3. The inorganic fiber sheet according to claim 1, wherein said inorganic fibers include clay mineral fibers.

4. The inorganic fiber sheet according to claim 3, wherein the inorganic fibers further contain fibers other than the clay mineral fibers, and the content of the clay mineral fibers in the inorganic fibers is 1 to 50 mass %.

5. The inorganic fiber sheet according to any one of claims 1 to 3, wherein the inorganic coating layer contains at least one type selected from the group consisting of silica and alumina.

6. The inorganic fiber sheet according to claim 5, wherein at least a portion of said alumina is boehmite.

7. The inorganic fiber sheet according to claim 5, wherein at least a portion of said alumina is α-alumina.

8. The apparent density of the inorganic fiber sheet is 0.10 to 1.00 g / cm ３ The inorganic fiber sheet according to any one of claims 1 to 3.

9. The inorganic fiber sheet according to any one of claims 1 to 3, wherein the inorganic fiber sheet has a thickness of 1.0 mm or less.

Images