Sheet, refractory material using same, and secondary battery

Abstract

The present invention addresses the problem of providing: a sheet having excellent heat resistance at a high temperature while being flexible; and a refractory material and a secondary battery employing the sheet.　A sheet according to the present invention comprises: a resin A having a limiting oxygen index pursuant to JIS K7201-2 (2007) of 25 or less; a resin B having a limiting oxygen index pursuant to JIS K7201-2 (2007) of 25 or more; and insulating inorganic particles. At least one of the resin A and the resin B has a fiber shape, of which the fiber length is 38-120 mm, and the number of crimps is 4.5-120 peaks.

Description

Sheet, fireproof material using same, and secondary battery

[0001] The present invention relates to a sheet having excellent heat resistance, and a fire-resistant material and a secondary battery using the same.

[0002] In recent years, hybrid and electric vehicles have been attracting attention from the perspective of environmental protection. In order for electric vehicles to become more widely used in society, performance improvements such as further improvements in efficiency and extended battery life, as well as improved safety and fuel economy, are required.

[0003] Battery modules and battery packages containing battery cells for in-vehicle secondary batteries are required to have certain flame retardancy, heat resistance, heat insulation, and electrical insulation properties, so it has been common to combine a heat-resistant metal casing with a heat-resistant and insulating mica sheet or the like.

[0004] For example, known nonwoven fabrics include a wet-laid nonwoven fabric with excellent flame retardancy, which is made by cutting flame-retardant rayon and polyphenylene sulfide fibers into short pieces, dispersing them in water, and then weaving them (see, for example, Patent Document 1), and a nonwoven fabric containing non-melting fibers with a limiting oxygen index of 27 or more and thermoplastic fibers with a limiting oxygen index of 30 or more (see, for example, Patent Document 2).Also known are spun yarns and nonwoven fabrics that are composites of flame-retardant fibers containing amorphous silica (see, for example, Patent Document 3), and a nonwoven fabric made of flame-resistant yarn and polyphenylene sulfide (see, for example, Patent Document 4).

[0005] JP 2011-184839 A International Publication No. 2022 / 111424 JP 2008-522056 A International Publication No. 2019 / 188275

[0006] However, in recent years, from the perspective of improving fuel efficiency by reducing the weight of battery packages and saving space in the packages, it is considered necessary for battery packaging materials to have the formability to conform to the shape of the battery.

[0007] In this case, in the battery module or battery package having the battery cells of the above-mentioned in-vehicle secondary battery, although the shape of the metal casing can be designed by press molding or the like, the mica sheet combined with it has a high rigidity and may crack when bent, which poses a problem in terms of formability. In other words, a material that is flexible while maintaining flame retardancy and heat resistance against a high-temperature burner of, for example, about 1000°C is required.

[0008] As a flexible material, for example, the wet-laid nonwoven fabric disclosed in Patent Document 1 is thin and flexible, but lacks flame retardancy and heat resistance against a high-temperature burner, for example, at around 1000°C. Furthermore, the nonwoven fabric disclosed in Patent Document 2 does not develop holes when heated with a high-temperature burner for 10 minutes, but cracks occur in the heated area and carbonization progresses, so suppression of embrittlement is required. The nonwoven fabric disclosed in Patent Document 3 does not develop holes when heated with a high-temperature burner for 10 minutes, but residues of carbonized flame-retardant fibers remain on the silica fibers, which still retain their fibrous shape, widening gaps in the nonwoven fabric and allowing flames to escape through these gaps. The nonwoven fabric disclosed in Patent Document 4 does not develop holes when heated with a 1000°C burner for 10 minutes, but decomposition of the polyphenylene sulfide carbide progresses in the center of the flame, thinning the carbonized film, and progressing embrittlement, so improvement of flame retardancy and heat resistance is also required.

[0009] In view of the above-mentioned circumstances, an object of the present invention is to provide a sheet that is flexible yet has excellent heat resistance at high temperatures, and a fire-resistant material and a secondary battery that use the same.

[0010] To address the above-mentioned problems, the present invention employs the following means: (1) A sheet containing resin A, resin B, and inorganic particles, wherein resin A is non-meltable and has a limiting oxygen index of 25 or less in accordance with JIS K 7201-2 (2007), and resin B is thermoplastic and has a limiting oxygen index of 25 or more in accordance with JIS K 7201-2 (2007), at least one of resin A and resin B is in the form of fibers, the fibers having a fiber length of 38 to 120 mm and a number of crimps of 4.5 to 120, and the inorganic particles are insulating. (2) The sheet according to (1) above, wherein the inorganic particles are contained in resin A. (3) The sheet according to (1) or (2) above, wherein the resin A comprises at least one selected from the group consisting of cellulose-based materials, thermosetting resins, and flame-retardant materials obtained by subjecting raw materials selected from acrylonitrile-, pitch-, cellulose-, and phenol-based resins to a flame-retardant treatment. (4) The sheet according to any one of (1) to (3) above, wherein the inorganic particles comprise at least one selected from silica and titanium dioxide. (5) The sheet according to any one of (1) to (4) above, wherein the resin A comprises at least a cellulose-based material. (6) The sheet according to any one of (1) to (5) above, wherein the resin B comprises at least one selected from anisotropic melt polyester, poly(butylene terephthalate), poly(acrylonitrile butadiene styrene), polysulfone, poly(ether-ether-ketone), poly(ether-ketone-ketone), polyethersulfone, polyarylate, polyarylene sulfide, polyphenylsulfone, polyetherimide, polyamideimide, and copolymers thereof. (7) The sheet according to any one of (1) to (6) above, wherein the resin A is contained in an amount of 15 to 80% by mass of the mass of the sheet. (8) The sheet according to any one of (1) to (7) above, wherein the resin B is contained in an amount of 20 to 85% by mass of the mass of the sheet. (9) The sheet according to any one of (1) to (8) above, wherein the mass of the inorganic particles is 20 to 60% by mass of the mass of the resin A. (10) The density of the sheet is 50 to 800 kg / m ３(11) The sheet according to any one of (1) to (9), wherein the sheet is a dry nonwoven fabric. (12) The sheet according to JIS C 2139-3-2 (2018) has a surface resistance of 1.0 × 10 at a site after heating the sheet with a Bunsen burner at 1000°C for 180 seconds. ６ (13) A fire-resistant material using the sheet according to any one of (1) to (12). (14) A secondary battery using the sheet according to any one of (1) to (12) as a fire-resistant material.

[0011] The sheet of the present invention has the above-mentioned constitution and is therefore flexible and highly heat-resistant.

[0012] Fig. 1 is a schematic diagram of an apparatus for measuring heat resistance. Fig. 2 is a schematic diagram showing an example of a cross section of a sheet of the present disclosure. Fig. 3 is a schematic diagram showing an example of another aspect of a cross section of a sheet of the present disclosure. Fig. 4 is a schematic diagram showing a cross section of a fire-resistant material and a secondary battery using the sheet of the present disclosure.

[0013] The sheet of the present disclosure contains resin A having a limiting oxygen index of 25 or less in accordance with JIS K 7201-2 (2007), resin B having a limiting oxygen index of 25 or more in accordance with JIS K 7201-2 (2007), and insulating inorganic particles.

[0014] <<Limiting Oxygen Index>> The limiting oxygen index in this disclosure is determined in accordance with JIS K 7201-2 (2007). The limiting oxygen index is the volume percentage of the minimum amount of oxygen required to sustain the combustion of a substance in a nitrogen and oxygen mixed gas, and it can be said that the higher the limiting oxygen index, the more difficult it is to burn. A substance with a limiting oxygen index of 25 or more according to JIS K 7201-2 (2007) is difficult to burn, and even if it ignites, the fire will quickly extinguish once the source of fire is removed. In some cases, the fire will be extinguished by carbonization. Conversely, the lower the limiting oxygen index, the easier it is to burn and the less likely it is that a carbonized residue will remain after combustion.

[0015] The limiting oxygen index is measured using samples of each resin material, which are hot-press molded or dissolved in an appropriate solvent and cast, with a length of 80 to 150 mm, a width of 10±0.5 mm, and a thickness of 4±0.25 mm. If the measurement sample is too weak to stand on its own, it can be measured by fixing the measurement sample wound up on a stainless steel rod as described in JIS K7201-2 (2007). When measuring using a sheet sample, the evaluation is performed as follows: (1) Identification of each resin type: The constituent resin types are identified using a microscopic Fourier transform infrared spectrophotometer (FT-IR). (2) Separation and removal of each resin layer from the sheet: After identifying the resin type in (1) above, each resin layer is separated and removed using an acid, alkali, or an appropriate organic solvent depending on the resin type. The concentration of the acid, alkali, or organic solvent, as well as the treatment temperature and time for removal, can be adjusted as appropriate. When separating the thermoplastic resin from the non-melting resin, the thermoplastic resin may be heated to a temperature close to the melting point of the thermoplastic resin, and the non-melting resin may be separated by filtration.

[0016] (3) Measurement of limiting oxygen index: Samples are prepared from each of the separated resins as described above, and the limiting oxygen index is measured.

[0017] Melting point and glass transition temperature: The melting point is a value measured by a method conforming to JIS K7121 (2012), and refers to the melting peak temperature when heated at 10°C / min under a nitrogen flow using a differential scanning calorimeter. The glass transition temperature is a value measured by a method conforming to JIS K7121 (2012), and refers to the inflection point or peak temperature in the endothermic / exothermic curve when heated at 10°C / min under a nitrogen flow using a differential scanning calorimeter.

[0018] Resin A Resin A has the above-mentioned limiting oxygen index of 25 or less. Preferably, the limiting oxygen index is 23 or less. By setting the limiting oxygen index within the range of the present disclosure, Resin A is efficiently oxidatively decomposed, and it becomes easy to form a charcoal that combines insulating inorganic particles described below with Resin B. When Resin B combines insulating inorganic particles described below with Resin B to form a film, the charcoal contributes to maintaining the strength of the portion exposed to flame, further improving heat resistance. Furthermore, efficient oxidative decomposition of Resin A suppresses excessive carbonization of the portion exposed to flame, while the insulating properties of the inorganic particles make it easy to maintain the insulating properties of the portion exposed to flame.

[0019] Resin A is non-meltable. In the present disclosure, non-meltable refers to a material that does not liquefy but maintains its shape when exposed to a flame at 700°C, or that burns or carbonizes. Even if a melting peak is observed in the above-mentioned differential scanning calorimetry analysis, if the material does not liquefy due to the progression of combustion or carbonization when exposed to a flame at 700°C, it is considered non-meltable in the present disclosure.

[0020] Resin A preferably contains at least one selected from, for example, cellulose-based materials, thermosetting resins, and flame-retardant materials. These materials are preferably contained in an amount of 80% by mass or more, more preferably 90% by mass or more, and even more preferably 95% by mass or more, based on the mass of Resin A itself. Flame-retardant materials are preferably flame-retardant materials obtained by flame-retardant treatment using raw materials selected from acrylonitrile-based, pitch-based, cellulose-based, and phenol-based resins. Flame-retardant treatment refers to a process in which a ladder-like or cyclic structure having carbon atoms is formed from raw materials selected from acrylonitrile-based, pitch-based, cellulose-based, and phenol-based resins, thereby imparting heat resistance. For example, in the case of acrylonitrile-based raw materials, flame-retardant treatment can be performed by heat treatment in air at a temperature of 200 to 300°C for 30 to 60 minutes. Examples of thermosetting resins include epoxy-based resins, unsaturated polyester-based resins, cross-linked acrylic resins, and vinyl ester-based resins. Thermosetting resins are cured by heat. These may be used alone or in combination of two or more.

[0021] Of the above, it is more preferable that resin A contains at least one of a cellulose-based material and a thermosetting resin. It is even more preferable that resin A contains at least a cellulose-based material that can be easily formed into a film or fiber using known methods. When using a cellulose-based material in the form of a film, for example, cellophane, which is obtained by dissolving wood pulp using known methods and regenerating it into a film, can be used. When using a fibrous material, fibrous materials such as wood pulp, cotton, and hemp can be used as is, or rayon, cupra, or lyocell that have been dissolved and regenerated using known methods, or acetate obtained by modifying raw cellulose, can also be used.

[0022] The form of resin A preferably used in the present disclosure may be the above-mentioned film form, fiber form, or a form impregnated into a fiber substrate. For example, resin A may be impregnated as shown in 202 of FIG. 2, or may be in the form of fiber as shown in 302 of FIG. 3. In the present disclosure, a fiber form is preferred because it is easy to combine with resin B, which will be described later.

[0023] When used in the form of fibers, the number of crimps of the fibers is preferably in the range of 4.5 to 120, and more preferably in the range of 5.0 to 100. When the number of crimps of the fibers is 4.5 or more, preferably 5.0 or more, the binding force between the fibers is strong when exposed to high temperatures, making them less likely to develop holes and improving heat resistance at high temperatures. Furthermore, the fibers are resistant to friction, resulting in strong mechanical properties for the sheet. Conversely, when the number of crimps of the fibers is 120 or less, preferably 100 or less, the fibers are less entangled, improving flexibility. Furthermore, by keeping the crimps contained in the fibers within the above range, appropriate frictional force is generated between the fibers, and the shrinkage of the heat-resistant sheet can be suppressed relative to the shrinkage of the fibers, resulting in a sheet that is less likely to develop holes or cracks when exposed to high temperatures and has excellent heat resistance. The number of crimps in the present disclosure is determined by the crimp number specified in JIS L 1015 (2010) 8.12. However, while the above measurement method determines the number of crimps per 25 mm of fiber length, in this disclosure, the number of crimps is defined as the number of crimps per fiber. Even if the fiber length is not 20 mm, the sample is attached to a piece of paper and measured according to JIS to determine the number of crimps per fiber.

[0024] Furthermore, the fiber length is preferably within the range of 38 to 120 mm, more preferably within the range of 40 to 115 mm, and even more preferably within the range of 42 to 110 mm. By maintaining the fiber length within the above range, it becomes easy to form a dry nonwoven fabric by entangling a web formed by a carding or air-laid method using a needle punching method or a hydroentangling method after the web has been formed. By maintaining the fiber length at 38 mm or more, preferably 40 mm or more, and more preferably 42 mm or more, the mechanical properties of the sheet are improved, making it less likely to develop holes due to abrasion. Furthermore, by making the sheet bulky and thick, it is possible to obtain a sheet with excellent heat resistance. The fiber length is determined using the JIS L 1015 (2010) 8.4A method. The thickness of the single fiber is not particularly limited, but from the perspective of passability through the carding process, a single fiber fineness within the range of 0.1 to 10 dtex is preferred.

[0025] Examples of the sheet form when a fiber form is used include woven fabrics, knitted fabrics (hereinafter sometimes referred to as "woven / knitted fabrics"), nonwoven fabrics, etc. In the case of woven / knitted fabrics, spun yarns obtained by spinning the above-mentioned staple fibers by a known method, and continuous filament yarns can also be used. In such cases, the composite with resin B can be exemplified by a method in which fibers made of resin A are mixed and spun, or alternately woven or knitted into a woven / knitted fabric. In the case of nonwoven fabrics, if resin B is in a fibrous form, examples of the composite can include a method in which the tows are aligned and then cut, or a method in which the respective resins are made into staple fibers and then mixed in an opening process, carding process, air mixing process, etc.

[0026] The proportion of resin A in the sheet of the present disclosure is preferably 15% by mass or more of the sheet mass, more preferably 20% by mass or more. By setting the content of resin A at or above the above range, heat resistance is improved due to the influence of inorganic particles in the sheet. The upper limit is preferably 80% by mass or less, more preferably 70% by mass or less. By setting the proportion of resin A at or below the above range, fire spread when exposed to flame is less likely, a decrease in heat resistance can be suppressed, and hardening of the entire sheet due to inorganic particles can be suppressed. Note that when resin A contains inorganic particles, the mass including the inorganic particles is measured as the mass of resin A.

[0027] Inorganic Particles The inorganic particles in the sheet of the present disclosure are insulating. In the present disclosure, one or more types of inorganic particles may be used. In the present disclosure, insulating refers to a particle having a volume resistivity of 1.0 × 10 or more, as measured according to JIS C 2139-3-1 (2018) (Measurement of resistance characteristics by application of DC voltage—volume resistance and volume resistivity). ６ The test method is as described in the JIS, under the conditions described in 5.5.5 Conditioning and pretreatment of test specimens, that is, under the conditions of standard atmosphere B (23±2°C x 50±5% RH) described in JIS C 2142 (2016) (Solid electrical insulating materials - Standard conditions before and during the test) 8. Standard atmosphere. Specifically, the measurement was performed using the method described in the examples below. The insulating inorganic particles are not particularly limited, but metal oxides can be exemplified. Specific examples of inorganic particles include silica (SiO ２): volume resistivity = 1.0 × 10 １４ Ω·m, alumina (Al ２ O ３ ): volume resistivity = 1.0 × 10 １６ Ω·m, silicon nitride (Si ３ N ４ ): volume resistivity = 1.0 × 10 １６ Ω m, magnesium oxide (MgO): volume resistivity = 1.0 × 10 １４ Ω m, calcium oxide (CaO): volume resistivity = 1.0 × 10 １４ Ω·m, titanium dioxide (TiO ２ ): volume resistivity = 1.0 × 10 １４ Ω m, zinc oxide (ZnO): volume resistivity = 1.0 × 10 １５ Among these, it is preferable to use at least one selected from silica and titanium dioxide, which are less reactive with moisture in the air and are industrially available in a stable manner.

[0028] In the present disclosure, inorganic particles are preferably contained in resin A. This allows for a synergistic effect between the non-melting resin A and the insulating inorganic particles to be more fully realized, further improving heat resistance. Furthermore, the inorganic particles can be more effectively prevented from falling off the sheet, and flexibility can also be improved. To illustrate this with reference to the drawings, if the sheet is impregnated with resin A, the inorganic particles may be contained in the resin A, as shown at 204 in FIG. 2 . Furthermore, if the resin A is in the form of fibers, the inorganic particles may be contained in the fibers, as shown at 304 in FIG. 3 . The method for extracting inorganic particles contained in resin A and measuring their volume resistivity is as follows: First, a sufficient amount of resin A is collected from the sheet, the resin component is burned off in a heating furnace at 900°C, and the resin is cooled. The mass of the residue after cooling is measured, and then reheated and cooled for another 30 minutes to confirm that the mass loss rate is within 1% by mass before and after reheating. If the mass loss rate is greater than 1% by mass, the resin is reheated until the mass loss rate is within 1% by mass. The obtained residue is subjected to a pressure of 500 kgf / cm ２ The volume resistivity is measured. If the amount of residue obtained is small, the thickness and area of ​​the molded product may be appropriately adjusted to obtain the measured value.

[0029] Regardless of whether or not the inorganic particles are contained in resin A, the mass of the inorganic particles is preferably 20% by mass or more of the mass of resin A, more preferably 25% by mass or more, and even more preferably 30% by mass or more. As described above, it is preferable that the inorganic particles are contained in resin A at the above-mentioned mass% or more. Here, for example, 20% by mass of resin A means that the mass of the inorganic particles is 20% by mass relative to the total mass of resin A itself and the inorganic particles. Therefore, when all the inorganic particles are contained in resin A, the volume resistivity is calculated by dividing the mass measured after collecting the inorganic particles using the above-mentioned method for measuring volume resistivity by the mass of resin A containing the inorganic particles. For inorganic particles not contained in resin A, the mass% is calculated by dividing the mass by the total mass of resin A and the inorganic particles. The amount of inorganic particles added in the manufacturing process may differ from the mass collected from the sheet as described above. In such cases, the mass collected from the sheet is used as the mass of the inorganic particles in the present disclosure. When the proportion of inorganic particles is above the above-mentioned range, when the sheet of the present disclosure is exposed to high temperatures, holes are less likely to form in the high-temperature areas, and heat resistance tends to be improved. On the other hand, the proportion of inorganic particles is preferably 60% by mass or less, more preferably 55% by mass or less, and even more preferably 50% by mass or less. When the proportion of inorganic particles is within the above range, for example, when inorganic particles are contained in resin A, the mechanical properties of resin A tend to be improved and it becomes easier to form a sheet.

[0030] The number average particle diameter of the inorganic particles is preferably 0.1 μm or more, more preferably 0.2 μm or more. Having an inorganic particle diameter above the above range provides excellent handleability and reduces secondary aggregation. Therefore, for example, when inorganic particles are contained in resin A, the inorganic particles can be uniformly dispersed, resulting in stable heat resistance. On the other hand, the average particle diameter of the inorganic particles is preferably 5.0 μm or less, more preferably 2.0 μm or less. When the average particle diameter of the inorganic particles is below the above range, the mechanical properties of resin A tend to improve and sheet formation tends to be easier. The number average particle diameter is determined by imaging the inorganic particles using an optical microscope or scanning electron microscope and reading the particle diameter from a scale. When the inorganic particles are not perfectly round or spherical, the shortest axial length is considered to be the particle diameter. Images are taken of multiple locations, and the average particle diameter of 50 particles is calculated.

[0031] Resin B: Resin B in the present disclosure exhibits thermoplastic properties. Its thermoplasticity allows it to flow to the surface and gaps of the non-melting resin A as the temperature increases, facilitating its formation into a film. In the present disclosure, compounding with inorganic particles contributes to maintaining the strength of areas exposed to flames and improving heat resistance. Here, "thermoplastic" refers to a material that softens, flows, or melts as the temperature increases, and generally refers to a material that exhibits a melting point or glass transition temperature as determined by differential scanning calorimetry (DSC). Resin B preferably contains at least one selected from the group consisting of anisotropic melting polyesters, poly(alkylene terephthalates), poly(acrylonitrile butadiene styrene), polysulfones, poly(ether-ether-ketones), poly(ether-ketone-ketones), polyethersulfones, polyarylates, polyarylene sulfides, polyphenylsulfones, polyetherimides, polyamideimides, and copolymers thereof. The poly(alkylene terephthalate) is preferably poly(butylene terephthalate). These may be used alone or in combination of two or more kinds, and may contain additives.

[0032] Resin B has a limiting oxygen index of 25 or more, preferably 27 or more. Having a limiting oxygen index within the above range suppresses combustion in air and prevents excessive fire spread of Resin A. Furthermore, when the carbonized Resin B and inorganic particles combine to form a film in the sheet, even better heat resistance is exhibited.

[0033] Of the above, the most preferred resin B is polyarylene sulfide and its copolymers, in terms of the high limiting oxygen index, the range of melting points, and ease of availability, and in particular polyphenylene sulfide (hereinafter sometimes referred to as "PPS") and its copolymers (PPS and its copolymers may be hereinafter sometimes referred to as "PPS polymer"). Representative examples of PPS polymers include polyphenylene sulfide, polyphenylene sulfide sulfone, polyphenylene sulfide ketone, random copolymers thereof, block copolymers thereof, and mixtures thereof. Particularly preferred PPS polymers are those having -(C ６ H ４ The polyphenylene sulfide preferably contains 90 mol % or more of p-phenylene sulfide units represented by the formula (III) (-S)-. From the viewpoint of mass, polyphenylene sulfide containing 80 mass % or more, and even 90 mass % or more of p-phenylene sulfide units is desirable. In particular, PPS polymer is most preferred because the inclusion of sulfur atoms in the polymer structure produces sulfuric acid during thermal decomposition of the polymer or flame retardant, thereby realizing a mechanism for dehydrating and carbonizing the polymer substrate.

[0034] Furthermore, even if the limiting oxygen index of a polymer is not originally within the range specified in the present disclosure, it can be preferably used if the limiting oxygen index falls within the range specified in the present disclosure by mixing with a flame retardant. Of course, a polymer having a limiting oxygen index within the range specified in the present disclosure may also contain a flame retardant. As the flame retardant, it is preferable that the flame retardant contains sulfur molecules for the same reasons as those for the PPS polymer. From this perspective, a sulfur-based flame retardant is preferred as the flame retardant.

[0035] The shape of resin B preferably used in the present disclosure may be a film shape, a fiber shape, or a shape impregnated into a fiber substrate, similar to resin A, but a fiber shape is preferred because it is easy to combine with resin A. The preferred number of crimps, fiber length, single fiber fineness, and sheet form of the fiber are the same as those of the preferred fibers for resin A described above. Illustrative examples using figures include 203 in FIG. 2 and 303 in FIG. 3.

[0036] As described above, the resin B in the present disclosure is preferably a PPS polymer, and is preferably in the form of a fiber. Here, the fiber made of a PPS polymer (hereinafter sometimes referred to as "PPS fiber") has a polymer structural unit of -(C ６ H ４ It is a synthetic fiber made of a polymer having (-S)- as a main structural unit. In the present disclosure, the undrawn PPS fiber and drawn yarn can be used in combination within the range of the present disclosure. Of course, it is also possible to use a combination of drawn yarn and undrawn yarn of a fiber that satisfies the range of the present disclosure instead of the PPS fiber.

[0037] The proportion of resin B in the sheet of the present disclosure is preferably 20% by mass or more of the sheet mass, more preferably 30% by mass or more. By setting the content of resin B at or above the above range, excessive fire spread of resin A, which has a low limiting oxygen index, is suppressed, improving the heat resistance of the sheet. Conversely, the upper limit is preferably 85% by mass or less, more preferably 80% by mass or less. By setting the content of resin B at or below the above range, the proportion of non-melting resin A becomes relatively high, suppressing excessive softening of the sheet due to a rise in the temperature of flame contact and making it less likely for holes to form in the flame contact area and its surrounding areas. Furthermore, a relatively large amount of inorganic particles makes the flame contact area less conductive.

[0038] In the present disclosure, at least one of the resin A and resin B described above is in the form of a fiber. By making them in the form of a fiber, the effects described above can be achieved. It is more preferable that both are in the form of a fiber. When they are in the form of a fiber, the fiber length and number of crimps of at least one of the resin A and resin B are in the above-mentioned ranges. It is preferable that both are in the above-mentioned ranges.

[0039] Resins Other Than Resin A and Resin B In addition to resin A and resin B, one or more other resins may be added to the sheet to further impart specific performance or effects. For example, to improve the mechanical properties of the sheet, for example, vinylon fiber, fibers other than resin B, such as polyester fiber or nylon fiber, may be used in fibrous form. Furthermore, adhesives for bonding resin A and resin B may also be added as resins other than resin A and resin B. The content of resins other than resin A and resin B is not particularly limited as long as it does not impair the effects of the present disclosure, but is preferably 20% by mass or less of the sheet mass, and more preferably 15% by mass or less. When using resins other than resin A and resin B, there is no particular limit as long as the desired performance is imparted, and it may even be 0% by mass.

[0040] <Sheet> The thickness of the sheet of the present disclosure is measured by a method conforming to JIS L-1913 (2010) Method A, and is preferably 0.10 mm or more. When the sheet thickness is equal to or greater than the above range, the heat resistance is more excellent. On the other hand, the sheet thickness is preferably 5.00 mm or less. When the sheet thickness is equal to or less than the above range, the flexibility is excellent, the entire package becomes thinner, and space-saving effects are obtained.

[0041] The basis weight of the sheet of the present disclosure is measured based on the mass per unit area specified in JIS L-1913 (2010) 6.2. ２ It is specified that test pieces of a size of 30 cm square (90,000 mm) or more must be taken. ２ ) and measure the mass of the sample as 1 m ２ Mass per unit (g / m ２ However, if the test piece is small, it may be cut into a rectangle of the largest possible size, measured with a steel ruler to determine the area, and the value obtained by dividing the sample mass by the area of ​​the sample may be used, as specified in JIS. The basis weight of the sheet is 50 g / m ２ It is preferable that the weight is 80 g / m or more. ２ More preferably, it is 100 g / m or more. ２When the basis weight is in the above range or more, the sheet has better abrasion resistance and heat resistance. On the other hand, the basis weight of the sheet is 500 g / m or more. ２ Preferably, the weight is 400 g / m or less. ２ More preferably, it is 300 g / m or less. ２ When the basis weight is within the above range, the sheet becomes more flexible and the package becomes lighter, resulting in the advantage of weight reduction.

[0042] The density of the sheet of the present disclosure can be determined by dividing the basis weight obtained by the above method by the thickness. ３ It is preferable that the saturation is 60 kg / m or more. ３ More preferably, it is 70 kg / m or more. ３ When the density is in the above range or more, the sheet has excellent abrasion resistance, and the sheet is less likely to burn at high temperatures due to the small air layer, and the sheet also tends to have improved heat resistance. ３ Preferably, it is 700 kg / m or less. ３ More preferably, it is 600 kg / m or less. ３ When the density is within the above range or less, the flexibility of the sheet is superior.

[0043] The sheet of the present disclosure is preferably a dry nonwoven fabric for reasons such as the ease of adjusting the thickness and density, the ease of mixing resin A and resin B, and excellent performance. Examples of such a nonwoven fabric include 201 in Figure 2 and 301 in Figure 3.

[0044] The sheet of the present disclosure has a surface resistance of 1.0 × 10 in accordance with JIS C 2139-3-2 (2018) at a site after heating with a Bunsen burner at 1000 ° C for 180 seconds. ６It is preferable that the surface resistance is Ω or more. Since JIS recommends that measurements be made at three or more locations when the number of test specimens is not specified, it is preferable that measurements be made at three locations, and that all three locations be within the above range. By keeping the surface resistance within the above range, a sheet with excellent heat resistance can be obtained. The surface resistance tends to improve by increasing the mass of the resin A, resin B, and inorganic particles of the present disclosure, particularly the mass of the resin A and inorganic particles.

[0045] <<Sheet Manufacturing Method>> The manufacturing method of the sheet of the present disclosure is not particularly limited, and the sheet can be manufactured by, for example, the following method, but is not limited thereto. The sheet of the present disclosure can be manufactured by combining resin A containing inorganic particles with resin B. For example, when one resin is in a film form and the other resin is in a fibrous form, the fibrous resin can be manufactured by combining the film-form resin with a fiber sheet formed by a known technique. Furthermore, when both resins are in a fibrous form, examples of the manufacturing method include a dry nonwoven fabric method in which the respective fibers are blended and a web is formed by a carding method or an air-laid method, and then a nonwoven fabric is formed by needle punching or hydroentangling; a method in which individual sheets are produced and then blended to form a sheet; and a method in which blended spun yarns or twisted filaments are used to form a woven or knitted fabric.

[0046] As a fiber manufacturing method, for example, a method for manufacturing PPS fiber, which is preferably used as resin B in the present disclosure, is preferably a method in which a polymer having the above-mentioned phenylene sulfide structural unit is melted at or above its melting point and spun from a spinneret to form a fiber. The spun fiber is generally an undrawn PPS fiber as is. Undrawn PPS fiber is largely amorphous and has a high breaking elongation. On the other hand, such fibers have poor thermal dimensional stability, so drawn yarns are commercially available that are oriented by hot drawing after spinning to improve the fiber strength and thermal dimensional stability. Several PPS drawn yarns are available, including "TORCON" (registered trademark) (manufactured by Toray Industries, Inc.) and "PROCON" (registered trademark) (manufactured by Toyobo Co., Ltd.). Furthermore, a method for manufacturing flame-retardant rayon fiber containing inorganic particles, for example, as a cellulose-based fiber preferably used as resin A in the present disclosure, includes, but is not limited to, a method in which inorganic particles such as silica or titanium dioxide are added to a cellulose-containing viscose solution and the fiber is obtained by a two-bath tension spinning method. The method for imparting crimps is not particularly limited, and examples thereof include known methods such as mechanical pressing using a stuffing box or jet pressing using steam.

[0047] Examples of methods for producing sheets include dry nonwoven fabrics, in which short fibers are formed into a web by carding or air-laid methods and then needle-punched or hydroentangled to form a nonwoven fabric, and methods for producing woven or knitted fabrics using thread-like materials such as spun yarns or filaments. Sheet production using the dry nonwoven fabric method is preferred because it is easy to adjust the density of the sheet by combining the blend ratio of resin A and resin B and the finishing process described below. Furthermore, when a film-like resin is to be compounded with the resulting fiber sheet, methods such as coating and dipping are available.

[0048] The sheet thus obtained may be used as it is, or may be subjected to the following finishing process before use.

[0049] The obtained sheet may be used as is, or may be heat-set using a tenter or the like to suppress thermal shrinkage at high temperatures, or may be subjected to calendering to smooth and densify the surface. The setting temperature is preferably a temperature that is effective in suppressing high-temperature shrinkage, and is preferably 130 to 250°C, more preferably 150 to 230°C.

[0050] Calendering is primarily used to adjust the thickness of the sheet, i.e., its density. While the density is not particularly limited, if the density is too low, holes are likely to form when exposed to flame, reducing heat resistance at high temperatures. On the other hand, if the density is too high, the sheet becomes too hard, so it must be adjusted appropriately. The speed, pressure, and temperature of the calender are not limited as long as they do not impair the effects of the present disclosure.

[0051] <<Uses of the Sheet>> The sheet of the present disclosure thus obtained is flexible and has high heat resistance, and exhibits a fire spread prevention effect, particularly when combined with combustible materials, making it suitable for use as a fire-resistant material for clothing, wall materials, flooring materials, ceiling materials, covering materials, etc. that require flame retardancy. In particular, it can be suitably used as a fire-resistant protective clothing, a fire-spread prevention covering material for urethane sheet materials for automobiles and aircraft, etc., and as a fire spread prevention material for bed mattresses.

[0052] Furthermore, since the sheet can suppress electrical conduction when exposed to high temperatures, it can be suitably used for heat-resistant insulation in high-temperature environments and in secondary batteries for automobiles. For example, it can also be suitably used as a fire-resistant material for battery modules and battery packages having battery cells of secondary batteries.

[0053] Next, the present disclosure will be specifically described based on examples. However, the present disclosure is not limited to these examples. Various modifications and alterations are possible within the scope of the technical scope of the present disclosure. The methods for measuring various properties used in the examples are as follows.

[0054] (Weight) In accordance with JIS L-1913 (2010) 6.2 Mass per unit area, the weight of a 30 cm square sample was measured as a test piece, and the weight was measured at 1 m ２Weight per unit (g / m ２ ) is expressed as

[0055] (Thickness) Measured in accordance with JIS L-1913 (2010) 6.1A method.

[0056] (Density) The density was recorded as the value obtained by dividing the (basis weight) by the (thickness).

[0057] (Fineness) Measured in accordance with JIS L 1015 (2010) 8.4A method.

[0058] (Number of crimps) Measured in accordance with JIS L 1015 (2010) 8.12.1 Number of crimps. JIS specifies the number of crimps per 25 mm, but here, the number of crimps per fiber was used. Even when the fiber length was less than 20 mm, the sample was attached to a piece of paper and measured in accordance with JIS.

[0059] (Heat Resistance) Heat resistance was evaluated as follows using a Bunsen burner with an inner diameter of 11 mm. As shown in FIG. 1 , a Bunsen burner 1 with a flame length L of 38 mm was set vertically, and a test specimen 2 was placed at a 45-degree angle with respect to the horizontal plane. The heating time until the flame penetrated the test specimen 2 was measured in seconds. Note that methane gas with a purity of 97% or higher was supplied to the Bunsen burner, and the amount of air supplied was adjusted so that the temperature of the tip of the flame was 1000°C. If the flame penetrated the test specimen 2 within 180 seconds (3 minutes) of heating or if the fire spread to the entire test specimen, the test specimen was deemed "not heat resistant" and given a rating of F. If the flame did not penetrate test specimen 2 even after being exposed to flame for 180 seconds (3 minutes) or more and the fire did not spread to the test specimen, it was rated as "heat resistant." If the time it took for the flame to penetrate was 180 seconds (3 minutes) or more but less than 600 seconds (10 minutes), it was rated as B, and if the flame did not penetrate after 600 seconds (10 minutes) of exposure to flame, it was rated as A.

[0060] (Bending resistance) The bending resistance was evaluated by a method conforming to the 41.5 degree cantilever method (ISO method) of JIS L 1913 (general nonwoven fabric testing method, 2010). Samples were taken at three random locations in each of the warp and weft directions, and measurements were taken, and the average values ​​were recorded.

[0061] (Folding Endurance) Folding endurance was evaluated according to the MIT testing method for folding endurance in JIS P 8115 (General Nonwoven Fabric Testing Methods, 2001). Using a No. 702 MIT folding endurance tester (manufactured by Mize Testing Instruments Co., Ltd.), a sample measuring 15 mm in width and 110 mm in length was set in a bending clamp with an R of 0.38 mm. The bending clamp was adjusted (for thin fabrics or thick fabrics) depending on the thickness of the sample. A bending test was performed with a load of 1 kgf, a bending angle of 135°, and a test speed of 175 cpm, and the number of times the sample broke was recorded. If the sample did not break after 10,000 folds, it was recorded as "no break" and the condition of the sample was confirmed. Samples were randomly sampled in three locations in each of the warp and weft directions, and the average values ​​were recorded.

[0062] (Volume resistivity of inorganic particles) The volume resistivity was measured using a method conforming to JIS C 2139-3-1 (2018) (Measurement of resistance characteristics by applying DC voltage - volume resistivity and volume resistivity). Here, 5.5.3 Preparation of test specimens states that the method should not change the state of the material and do not damage the test specimen, and that the test specimen should have a simple shape such as a flat plate or tube. 5.5.1 General matters states that unless otherwise specified, a length of 100 mm or more, a width of 100 mm or more, and a thickness of 1±0.5 mm are recommended. Therefore, inorganic particles were measured at a pressure of 500 kgf / cm ２ The specimens were molded to a diameter of 100 mm and a thickness of 1 mm at a pressure of 100 V, which is the condition when not specified in the individual specifications described in 5.2 Power Source and Applied Voltage and 6.2 Measurement of Volume Resistivity. The measurement was taken after 1 minute of application of an applied voltage of 100 V, which is the condition when not specified in the individual specifications described in 5.2 Power Source and Applied Voltage and 6.2 Measurement of Volume Resistivity. Measurement was performed using a High Resistance Meter 4339B (manufactured by Agilent Technologies Inc.) and an accessory for measuring plate-shaped materials, 16008B (main electrode φ26 mm, guard electrode inner diameter φ38 mm, pressure during measurement 100 g). From the above measurement, the silica (SiO ２ ) is volume resistivity = 1.0 x 10 １４ Ω·m, titanium dioxide (TiO ２ ) is volume resistivity = 1.0 x 10 １４ Ω·m, and it was confirmed that both were insulating.

[0063] (Surface Resistivity of Sheet) Using a 12.7 mm outer diameter propane gas Bunsen burner (manufactured by Tokyo Glass Instruments Co., Ltd.), a flame with the tip temperature adjusted to 1000°C was applied to the sheet for 180 seconds to prepare a flame-exposed sample. Next, samples that were flamed using the method described in the heat resistance evaluation and samples that were not flamed were measured under the conditions described in JIS C 2139-3-2 (2018) (Measurement of resistance characteristics by application of DC voltage - surface resistance and surface resistivity) 5.7 Test Procedure. Specifically, the surface resistance of each sample was measured under the conditions of standard atmosphere B (23±2°C x 50±5% RH) described in JIS C 2142 (2016) (Solid electrical insulating materials - Standard conditions before and during test) 8. Standard atmosphere. The samples were then left in an environment of 25°C x 65% RH for 24 hours and used for measurement. Measurements were performed in accordance with JIS C 2139-3-2 (2018) (Measurement of resistance characteristics by application of DC voltage - surface resistance and surface resistivity), using electrode C1 (inner diameter 50 mm) described in 5.3.6 Electrode configuration C (concentric ring electrode) as the electrode, and the measurement voltage was 100 V, the recommended voltage when not specified in the individual standards described in 5.2 Voltage. Specifically, a surface resistance measurement electrode SME-8301 (manufactured by Hioki E.E. Corporation) was connected to a Super Megohmmeter SM-8213, and measurements were taken by pressing the measurement electrode against the sample. Surface resistance (Ω) was measured when the surface resistance was 1.0 x 10 ６ The above cases were considered to be no continuity, and measurements were carried out on samples taken at three random locations.

[0064] (Resin A and Resin B Contents in the Sheet) In this example, the contents were calculated based on the amounts of raw materials used. When measuring the contents using a sheet, the evaluation was performed as follows. (1) Identification of Each Resin Type: The constituent resin types were identified using a microscopic Fourier transform infrared spectrophotometer (FT-IR). (2) Separation and Removal of Each Resin Layer from the Sheet: After identifying the resin types in (1) above, each resin layer was separated and removed using an acid, alkali, or an appropriate organic solvent depending on the resin type. The concentration of the acid, alkali, or organic solvent, as well as the treatment temperature and time for removal, can be adjusted as appropriate. Resin B can be separated from Resin A by heating to near the melting point of Resin B and filtering and separating Resin A. (3) Measurement of the Content of Each Resin: After identifying the resin types in (1) above, the mass of each resin was measured by separating them by appearance or by a dissolution method using a solvent appropriate for each resin type. The content ratio was calculated by dividing the mass of each resin by the mass of the sheet before performing (2) above.

[0065] (Content and components of inorganic particles in resin A) The ash content of resin A was measured according to JIS L 1015 (Testing methods for synthetic fiber staples, 2010), and the measured value was taken as the content of inorganic particles. The obtained ash content was subjected to elemental analysis using an energy dispersive X-ray fluorescence analyzer EDAX EAGLE II (manufactured by AMETEK Corporation) under the conditions of a rhodium cathode, a tube voltage of 35 kV, Cps of 5000, and an analysis time of 100 seconds.

[0066] Next, the yarns used in the following examples and comparative examples will be described.

[0067] <PPS fiber drawn yarn 1> As the drawn PPS fiber drawn yarn 1, "TORCON" (registered trademark) manufactured by Toray Industries, Inc., product number S371, with a single fiber fineness of 2.2 dtex (diameter 14 μm) and a cut length of 51 mm was used. This PPS fiber has a limiting oxygen index of 34 and a melting point of 284°C, making it thermoplastic. The number of crimps was 12.0 crimps per 25 mm (12.0 / 25 × 51 = 24.5 crimps per short fiber).

[0068] <<PPS fiber drawn yarn 2>> A "TORCON" (registered trademark) manufactured by Toray Industries, Inc., product number S307, with a single fiber fineness of 1.0 dtex (diameter 9 μm) and a cut length of 6 mm was used as the drawn PPS fiber drawn yarn 2. This PPS fiber has a limiting oxygen index of 34 and a melting point of 284°C, making it thermoplastic. The number of crimps was 6.0 crimps per 25 mm (6.0 / 25 × 6 = 1.4 crimps per short fiber).

[0069] <<PPS fiber drawn yarn 3>> A "TORCON" (registered trademark) manufactured by Toray Industries, Inc., product number S371, with a single fiber fineness of 2.2 dtex (diameter 14 μm) and a cut length of 38 mm was used as the drawn PPS fiber drawn yarn 3. This PPS fiber has a limiting oxygen index of 34 and a melting point of 284°C, making it thermoplastic. The number of crimps was 12.0 crimps per 25 mm (12.0 / 25 × 38 = 18.2 crimps per short fiber).

[0070] <<PPS Fiber Drawn Yarn 4>> A tow of "TORCON" (registered trademark) product number S307 manufactured by Toray Industries, Inc., with a single fiber fineness of 1.0 dtex (diameter 9 μm) was used as the drawn PPS fiber drawn yarn 4, and short fibers with a cut length of 38 mm were obtained without passing through a crimper. This PPS fiber had a limiting oxygen index of 34 and a melting point of 284°C, making it thermoplastic. It was not passed through a crimper, and the number of crimps was 0 crimps / 25 mm (0 / 25 x 38 = 0 crimps per short fiber).

[0071] <<Undrawn PPS Fiber Yarn 1>> As the undrawn PPS fiber undrawn yarn 1, "TORCON" (registered trademark) manufactured by Toray Industries, Inc., product number S111, with a single fiber fineness of 2.2 dtex (diameter 14 μm) and a cut length of 51 mm was used. This PPS fiber has a limiting oxygen index of 34 and a melting point of 284°C, making it thermoplastic. The number of crimps was 6.0 crimps per 25 mm (6.0 / 25 × 51 = 12.2 crimps per short fiber).

[0072] <<Undrawn PPS Fiber Yarn 2>> As the undrawn PPS fiber undrawn yarn 2, "TORCON" (registered trademark) manufactured by Toray Industries, product number S111, with a single fiber fineness of 2.2 dtex (diameter 14 μm) and a cut length of 6 mm was used. This PPS fiber has a limiting oxygen index of 34 and a melting point of 284°C, making it thermoplastic. The number of crimps was 6.0 crimps per 25 mm (6.0 / 25 × 6 = 1.4 crimps per short fiber).

[0073] <<Undrawn PPS Fiber Yarn 3>> As the undrawn PPS fiber yarn 3, "TORCON" (registered trademark) manufactured by Toray Industries, Inc., product number S111, with a single fiber fineness of 2.2 dtex (diameter 14 μm) and a cut length of 38 mm was used. This PPS fiber has a limiting oxygen index of 34 and a melting point of 284°C, making it thermoplastic. The number of crimps was 6.0 crimps per 25 mm (6.0 / 25 × 38 = 9.1 crimps per short fiber).

[0074] <<Undrawn PPS Fiber Yarn 4>> Tow of Toray's "TORCON" (registered trademark), product number S111, having a single fiber fineness of 2.2 dtex (diameter 14 μm) was used as the undrawn PPS fiber undrawn yarn 4, and short fibers with a cut length of 38 mm were obtained without passing through a crimper. This PPS fiber had a limiting oxygen index of 34 and a melting point of 284°C, making it thermoplastic. It was not passed through a crimper, and the number of crimps was 0 crimps / 25 mm (0 / 25 x 38 = 0 crimps per short fiber).

[0075] <Flame-retardant rayon fiber 1> "FR CORONA" (registered trademark) manufactured by Daiwabo Rayon Co., Ltd., with a single fiber fineness of 3.3 dtex (diameter 18 μm) and a cut length of 51 mm, was used as the flame-retardant rayon fiber 1. The limiting oxygen index of this flame-retardant rayon fiber was 18, and the rayon component does not melt in air, making it non-meltable. The number of crimps was 6.8 crimps / 25 mm (6.8 / 25 x 51 = 13.9 crimps per short fiber). The proportion of inorganic particles contained in the flame-retardant rayon was 29.3 mass%. Elemental analysis revealed that the inorganic element was 100% Si (silicon), and other inorganic elements were not detected below the detection limit, so the inorganic particles were determined to be SiO ２ The average particle size of the inorganic particles contained in the fibers was 0.6 μm.

[0076] Flame-Retardant Rayon Fiber 2 (1) Viscose Solution Production A viscose stock solution containing 8.5% by mass of cellulose, 5.7% by mass of sodium hydroxide, and 2.6% by mass of carbon disulfide was prepared. Next, titanium dioxide (TA-300 manufactured by Fuji Titanium Industrial Co., Ltd.), a mixed solution of sodium hydroxide and water, and the resulting viscose solution was adjusted to a composition of 7.2% by mass of cellulose and 7.4% by mass of sodium hydroxide to obtain a titanium dioxide-added viscose solution. The titanium dioxide content was 35% by mass relative to the cellulose mass. (2) Spinning The titanium dioxide-added viscose solution was spun using a two-bath tension spinning method at a spinning speed of 50 m / min and a draw ratio of 50% to obtain a fiber with a fineness of 3.3 dtex. The composition of the first bath (spinning bath) was 115 g / L of sulfuric acid and 350 g / L of sodium sulfate, and the temperature was 35°C. The temperature of the second bath (hot water bath) was 80°C. The titanium dioxide-added viscose liquid was extruded through a nozzle to produce a rayon long fiber bundle containing titanium dioxide. (3) Crimping and Cutting The long fiber bundle was passed through a crimper to crimp it to 7.1 crimps / 25 mm, and then cut to a fiber length of 51 mm using a cutter. The number of crimps in the fiber was 7.1 / 25 x 51 = 14.5 crimps. The inorganic particle content of the obtained short cuts was measured to find that it was 27.6% by mass in total, of which 14.5% was TiO. ２ 27.5% by mass, Na ２ The O content was 0.1% by mass. The limiting oxygen index was 20, and the rayon component did not melt in air, so it was non-meltable. The average particle size of the inorganic particles contained in the fiber was 0.5 μm.

[0077] Flame-retardant rayon fiber 3: Daiwabo Rayon's "FR CORONA" (registered trademark) was used as flame-retardant rayon fiber 3, with a single fiber fineness of 3.3 dtex (diameter 18 μm) and a cut length of 5 mm. This flame-retardant rayon fiber had a limiting oxygen index of 18, and the rayon component did not melt in air, making it non-meltable. The number of crimps was 6.8 crimps / 25 mm (6.8 / 25 × 6 = 1.4 crimps per short fiber). The proportion of inorganic components contained in the flame-retardant rayon was 29.3% by mass. Elemental analysis revealed that the inorganic component was 100% silicon (Si), with no other inorganic components detected below the detection limit. The average particle size of inorganic particles contained in the fiber was 0.6 μm.

[0078] <Flame-retardant rayon fiber 4> "FR CORONA" (registered trademark) manufactured by Daiwabo Rayon Co., Ltd., with a single fiber fineness of 3.3 dtex (diameter 18 μm) and a cut length of 38 mm was used as the flame-retardant rayon fiber 4. The limiting oxygen index of this flame-retardant rayon fiber was 18, and the rayon component does not melt in air, making it non-meltable. The number of crimps was 6.8 crimps / 25 mm (6.8 / 25 x 38 = 10.3 crimps per short fiber). The proportion of inorganic particles contained in the flame-retardant rayon was 29.3 mass%. Elemental analysis revealed that the inorganic element was 100% Si (silicon), and other inorganic elements were not detected below the detection limit, so the inorganic particles were determined to be SiO ２ The average particle size of the inorganic particles contained in the fibers was 0.6 μm.

[0079] Flame-Retardant Rayon Fiber 5 (1) Viscose Solution Production A viscose stock solution containing 8.5% by mass of cellulose, 5.7% by mass of sodium hydroxide, and 2.6% by mass of carbon disulfide was prepared. Next, titanium dioxide (TA-300 manufactured by Fuji Titanium Industrial Co., Ltd.), a mixed solution of sodium hydroxide and water, and the resulting viscose solution was adjusted to a composition of 7.2% by mass of cellulose and 7.4% by mass of sodium hydroxide, to obtain a titanium dioxide-added viscose solution. The titanium dioxide content was 20% by mass relative to the cellulose mass. (2) Spinning The titanium dioxide-added viscose solution was spun using a two-bath tension spinning method at a spinning speed of 50 m / min and a draw ratio of 50%, yielding a fiber with a fineness of 3.3 dtex. The composition of the first bath (spinning bath) was 115 g / L of sulfuric acid and 350 g / L of sodium sulfate, and the temperature was 35°C. The temperature of the second bath (hot water bath) was 80°C. The titanium dioxide-added viscose liquid was extruded through a nozzle to produce a rayon long fiber bundle containing titanium dioxide. (3) Cutting The long fiber bundle was cut to a fiber length of 38 mm using a cutter without passing it through a crimper. The number of crimps in the fiber was 0 / 25 x 38 = 0 crimps, since it had not been passed through a crimper. The content of inorganic particles in the obtained short cuts was measured to find that the total content was 18.9% by mass, of which 18.9% was TiO ２ 18.8% by mass, Na ２ The O content was 0.1% by mass. The limiting oxygen index was 20, and the rayon component did not melt in air, so it was non-meltable. The average particle size of the inorganic particles contained in the fiber was 0.5 μm.

[0080] [Example 1] (Production of nonwoven fabric) The PPS fiber drawn yarn 1, PPS fiber undrawn yarn 1, and flame-retardant rayon fiber 1 obtained above were mixed in a fiber opener, then further mixed in a punching machine, and then passed through a carding machine to form a web. The obtained web was laminated in a cross-lap machine and then felted in a needle punch machine to obtain a nonwoven fabric sheet consisting of the PPS fiber drawn yarn, undrawn yarn, and flame-retardant rayon fiber. The mass mixture ratio of the PPS fiber drawn yarn, undrawn yarn, and flame-retardant rayon fiber in the nonwoven fabric was 40:30:30, and the basis weight was 203 g / m ２, thickness 1.76 mm, density 115 kg / m ３ The structure of the obtained nonwoven fabric was roughly similar to that shown in Figure 3. (Heat resistance) For 600 seconds (10 minutes), flames did not penetrate the nonwoven fabric, and it had sufficient flame-proofing and heat-insulating properties, so the heat resistance was rated A. (Bending resistance) The bending resistance measured by the cantilever method was 65 mm in the vertical direction and 70 mm in the horizontal direction, indicating that the nonwoven fabric was flexible. (Folding endurance) Even after 10,000 MIT folding tests, some fuzzing was observed at the folded portions, but the sample did not break in either the vertical or horizontal direction, demonstrating good folding endurance. (Surface resistance of the sheet) The surface resistance of all three test specimens was 1.0 x 10 before and after exposure to flame (3 minutes). ６ Ω or more, and no continuity was observed.

[0081] [Example 2] In Example 1, the mass mixing ratio of the drawn yarn of PPS fiber, the undrawn yarn, and the flame-retardant rayon was changed to 60:30:10, and the basis weight was 201 g / m ２ , thickness 2.03 mm, density 99 kg / m ３ A nonwoven fabric sheet of 10000 mm was obtained. This sheet did not develop any holes for 236 seconds, so its heat resistance was rated B. The bending resistance measured by the cantilever method was 71 mm in the vertical direction and 73 mm in the horizontal direction, indicating that the nonwoven fabric was flexible. Furthermore, even after 10,000 MIT folding tests, slight fuzzing was observed at the folded portions, but the sample did not break in either the vertical or horizontal directions, demonstrating good folding resistance. The surface resistance of the sheet was 1.0 x 10 ６ No conduction was observed above Ω. The structure of the obtained nonwoven fabric was roughly similar to that shown in FIG.

[0082] [Example 3] In Example 1, the mass mixing ratio of the drawn yarn of the PPS fiber, the undrawn yarn, and the flame-retardant rayon was changed to 10:5:85, and the basis weight was 205 g / m ２ , thickness 2.21 mm, density 93 kg / m ３A nonwoven fabric sheet was obtained. This sheet had fire spread and residual flames on the flame-retardant rayon, and the area of ​​the flame spread was larger than the area in contact with the flame, but no holes were formed for 450 seconds, so the heat resistance was rated B. The bending resistance measured by the cantilever method was 56 mm in the vertical direction and 58 mm in the horizontal direction, indicating that the nonwoven fabric was flexible. Furthermore, even after 10,000 MIT folding tests, although some fuzzing was observed in the folded areas, the sample did not break in either the vertical or horizontal direction, demonstrating good folding resistance. The surface resistance of the sheet was 1.0 x 10 both before and after contact with the flame. ６ No conduction was observed above Ω. The structure of the obtained nonwoven fabric was roughly similar to that shown in FIG.

[0083] [Example 4] A nonwoven fabric was produced under the same conditions as in Example 1, except that the flame-retardant rayon fiber 1 was replaced with the flame-retardant rayon fiber 2. The fibers constituting the nonwoven fabric were PPS fiber drawn yarn 1, PPS fiber undrawn yarn 1, and flame-retardant rayon fiber 2, in a ratio of 40:30:30. The basis weight was 197 g / m ２ , thickness 1.78 mm, density 111 kg / m ３ The nonwoven fabric had sufficient heat resistance for 600 seconds (10 minutes) without the flame penetrating the nonwoven fabric, and therefore the heat resistance was rated A. The bending resistance measured by the cantilever method was 71 mm in the vertical direction and 69 mm in the horizontal direction, indicating that the nonwoven fabric was flexible. Furthermore, even after 10,000 MIT folding tests, some fuzzing was observed at the folded portion, but the sample did not break in either the vertical or horizontal direction, demonstrating good folding resistance. The surface resistance of the sheet was 1.0 × 10 for all three test specimens both before and after exposure to flame (3 minutes). ６ The electrical resistance was Ω or more, and no electrical continuity was observed. The structure of the obtained nonwoven fabric was roughly similar to that shown in FIG.

[0084] [Example 5] The PPS fiber drawn yarn 1 and the PPS fiber undrawn yarn 1 obtained above were mixed in a 50:50 ratio using a fiber opener, then further mixed using a blow mill, and then passed through a carding machine to form a web. The obtained web was laminated using a cross-lap machine and then felted using a needle punch machine to produce a nonwoven fabric. The basis weight of the nonwoven fabric was 156 g / m ２ , thickness 1.55 mm, density 101 kg / m ３The obtained nonwoven fabric was dipped in a viscose liquid containing titanium dioxide particles prepared by the procedure of "(1) Production of viscose liquid" for flame-retardant rayon fiber 2, and the cellulose portion was regenerated in a bath of 115 g / L of sulfuric acid and 350 g / L of sodium sulfate to form a cellulose resin layer containing titanium dioxide particles, which was then dried. The cellulose resin containing titanium dioxide particles was formed into a sheet with a thickness of 4 mm, and a sample of 120 mm in length and 10 mm in width was used to measure the limiting oxygen index, which was found to be 20. The nonwoven fabric sheet after drying had a basis weight of 216 g / m ２ , thickness 1.50 mm, density 144 kg / m ３ The nonwoven fabric sheet had a composition of 1 part oriented PPS fiber yarn, 1 part unoriented PPS fiber yarn, and 36 parts 36 parts 28 parts cellulose containing inorganic particles. The total content of inorganic particles in the cellulose was 29.8% by mass. The inorganic particle component was TiO ２ 29.5% by mass, Na ２ The content of O was 0.3 mass%. The average particle size of the inorganic particles was 0.6 μm. The structure of the obtained nonwoven fabric was roughly similar to that shown in Figure 2. This nonwoven fabric sheet had sufficient heat resistance without flame penetrating the nonwoven fabric for 600 seconds (10 minutes), and therefore its heat resistance was rated A. The bending resistance measured by the cantilever method was flexible enough to bend the nonwoven fabric at 113 mm in the vertical direction and 110 mm in the horizontal direction. Furthermore, even after 10,000 MIT folding tests, the sample did not break in either the vertical or horizontal direction, demonstrating good folding endurance. The surface resistance of the sheet was 1.0 x 10 for all three test specimens before and after exposure to flame (3 minutes). ６ Ω or more, and no continuity was observed.

[0085] [Example 6] The nonwoven fabric obtained in Example 1 was treated using a double-sided heated metal roll thermal calender at a processing speed of 3 m / min, a heating temperature of 180°C, and a linear pressure of 150 kgf / cm, to adjust the thickness. The obtained sheet had a basis weight of 216 g / m ２ , thickness 0.45 mm, density 480 kg / m ３The nonwoven fabric sheet had sufficient heat resistance for 600 seconds (10 minutes) without the flame penetrating the nonwoven fabric, and therefore the heat resistance was rated A. The bending resistance measured by the cantilever method was flexible enough to bend the sheet at 105 mm in the vertical direction and 101 mm in the horizontal direction. Furthermore, even after 10,000 MIT folding tests, the sample did not break in either the vertical or horizontal direction, demonstrating good folding resistance. The surface resistance of the sheet was 1.0 x 10 for all three test specimens both before and after exposure to flame (3 minutes). ６ The electrical resistance was Ω or more, and no electrical continuity was observed. The structure of the obtained nonwoven fabric was roughly similar to that shown in FIG.

[0086] [Example 7] A nonwoven fabric was produced under the same conditions as in Example 1, except that the flame-retardant rayon fiber 1 was replaced with flame-retardant rayon fiber 4, the PPS fiber drawn yarn 1 was replaced with PPS fiber drawn yarn 3, and the PPS fiber undrawn yarn 1 was replaced with PPS fiber undrawn yarn 3. The fibers constituting the nonwoven fabric were the PPS fiber drawn yarn 3, the PPS fiber undrawn yarn 3, and the flame-retardant rayon fiber 4, in a ratio of 40:30:30. The basis weight was 208 g / m ２ , thickness 1.43 mm, density 145 kg / m ３ The nonwoven fabric had sufficient heat resistance for 600 seconds (10 minutes) without the flame penetrating the nonwoven fabric, and therefore the heat resistance was rated A. The bending resistance measured by the cantilever method was 58 mm in the vertical direction and 56 mm in the horizontal direction, indicating that the nonwoven fabric was flexible. Furthermore, even after 10,000 MIT folding tests, some fuzzing was observed at the folded portion, but the sample did not break in either the vertical or horizontal direction, demonstrating good folding resistance. The surface resistance of the sheet was 1.0 × 10 for all three test specimens both before and after exposure to flame (3 minutes). ６ The electrical resistance was Ω or more, and no electrical continuity was observed. The structure of the obtained nonwoven fabric was roughly similar to that shown in FIG.

[0087]

[0088] [Comparative Example 1] Referring to Patent Document 2 (WO 2022 / 111424), flame-retardant rayon fiber "DFG" (registered trademark) manufactured by Daiwabo Rayon Co., Ltd., with a fiber fineness of 3.3 dtex (diameter 18 μm) and a cut length of 51 mm, incorporating a phosphorus-based flame retardant, was used in place of the flame-retardant rayon fiber 1 in Example 1. This flame-retardant rayon fiber had a limiting oxygen index of 28, and the rayon component carbonized in air, making it non-meltable. The number of crimps was 5.9 crimps / 25 mm (5.9 / 25 x 51 = 12.0 crimps per short fiber). This rayon incorporated a phosphorus-based flame retardant and did not contain inorganic particles. A nonwoven fabric was obtained in the same manner as in Example 1, using a blend ratio of the above-obtained PPS fiber drawn yarn 1 / PPS fiber undrawn yarn 1 / flame-retardant rayon at a ratio of 40:30:30. The basis weight was 200 g / m. ２ , thickness 2.01 mm, density 100 kg / m ３ The nonwoven fabric cracked 125 seconds after contact with the flame, and the flame penetrated through the cracks, giving it a heat resistance rating of F. The thickness of the nonwoven fabric in the flame-contact area was not extremely thin, but carbonization had progressed excessively, and the carbonized area was prone to cracking. The bending resistance measured by the cantilever method was 60 mm in the vertical direction and 61 mm in the horizontal direction, indicating that the nonwoven fabric was flexible. Furthermore, even after 10,000 MIT folding tests, the sample did not break in either the vertical or horizontal direction, demonstrating good folding endurance. The surface resistivity of the sheet was 1.0 x 10 before contact with the flame. ６ Although no conduction was observed, after exposure to flame (3 minutes), carbonization progressed and cracks were observed, so the surface resistance was 1.0 × 10 １ Conduction was achieved at Ω.

[0089] [Comparative Example 2] With reference to Patent Document 3 (JP 2008-522056 A), a needle-punched nonwoven fabric was obtained using the flame-retardant rayon fiber used in Comparative Example 1, silica chop fiber KSF-75 (manufactured by Kowa Co., Ltd.) with a diameter of 7.5 μm and a cut length of 50 mm, PPS fiber drawn yarn 1, and PPS fiber undrawn yarn 1 in a blend ratio of 25:15:40:20, respectively. The obtained nonwoven fabric had a basis weight of 197 g / m ２ , thickness 1.96 mm, density 101 kg / m ３The nonwoven fabric cracked 170 seconds after exposure to flame, and the flame penetrated, so its heat resistance was rated F. At the flame-exposed area, PPS residues that had melted and carbonized into balls were present at the intersections of the silica fibers, and the fibers that make up the nonwoven fabric were coarse, causing cracks to appear in the coarse areas, allowing the flame to penetrate. The carbonized areas were in a state where they could easily crack. The bending resistance measured by the cantilever method showed flexibility, allowing bending at 135 mm in the vertical direction and 134 mm in the horizontal direction. After 10,000 MIT folding tests, the sample did not break in either the vertical or horizontal direction, but some areas where the silica fibers had broken due to repeated bending were observed. The surface resistance of the sheet was 1.0 x 10 before exposure to flame. ６ Although no electrical continuity was observed, after exposure to flame (3 minutes), carbonization of the flame-retardant rayon and PPS progressed, and the surface resistance of one specimen was 1.0 × 10 ６ Although the resistance was above Ω, the remaining two specimens were 1.0 × 10 ２ Variation was observed in Ω.

[0090] [Comparative Example 3] With reference to Patent Document 1 (JP 2011-184839 A), a wet papermaking sample was prepared using the following fibers. The PPS fiber oriented yarn 2, PPS fiber unoriented yarn 2, and flame-retardant rayon fiber 3 obtained above were added to water in a ratio of 40:30:30. The mixture was stirred and dispersed for 1 minute using a household mixer adjusted to 3000 rpm. Next, the dispersion was added to a hand-made papermaking machine (manufactured by Kumagai Riki Kogyo Co., Ltd.) measuring 25 cm x 25 cm and 40 cm in height, with a 140-mesh hand-made papermaking screen installed at the bottom, and further water was added to adjust the fiber concentration to 0.1% by mass. Next, a wet paper web was obtained by dewatering. The total amount of fiber in the papermaking machine was adjusted to 6.25 g, and a fiber density of 100 g / m was obtained. ２ Two wet webs can be stacked to obtain a wet web of 200 g / m. ２ The obtained wet web was placed on a filter paper and dried in an oven at 130°C for 3 minutes, and then treated with a double-sided heated metal roll thermal calender at a processing speed of 3 m / min, a heating temperature of 180°C, and a linear pressure of 150 kgf / cm to adjust the thickness. The obtained sheet had a basis weight of 225 g / m ２, thickness 0.35 mm, density 643 kg / m ３ The sheet cracked after 138 seconds and the flame penetrated, so the heat resistance was rated F. The bending resistance measured by the cantilever method was flexible enough to bend 145 mm in the vertical direction and 140 mm in the horizontal direction. The MIT folding endurance test showed that the sheet broke after 1,200 bendings in both the vertical and horizontal directions. The surface resistance of the sheet was 1.0 x 10 before contact with the flame. ６ Although no electrical continuity was observed, cracks were observed in the sheet after exposure to flame (3 minutes), and the ２ Conduction was measured at Ω. After drying, the flame-retardant rayon fibers were separated from the sheet, and the content of inorganic particles in the flame-retardant rayon was measured. The content was found to be 19.2% by mass, confirming that the inorganic particles had fallen off into the water during dispersion, stirring, and papermaking.

[0091] [Comparative Example 4] With reference to Patent Document 4 (WO 2019 / 188275), a flame-retardant fiber (oxidized polyacrylonitrile fiber) manufactured by Zoltek Corporation with a fiber fineness of 2.2 dtex (diameter 13 μm) and a cut length of 51 mm was used as a non-melting fiber containing no inorganic particles, and was used in place of the flame-retardant rayon fiber 1 in Example 1. The limiting oxygen index of this flame-retardant fiber was 41. The number of crimps was 11.9 crimps / 25 mm (11.9 / 25 x 51 = 24.3 crimps per short fiber). This flame-retardant fiber did not contain inorganic particles. A nonwoven fabric was obtained in the same manner as in Example 1, with a blend ratio of 1 PPS fiber drawn yarn 1 / 1 PPS fiber undrawn yarn 1 / flame-retardant fiber being 40:30:30. The basis weight was 197 g / m ２ , thickness 2.21 mm, density 89 kg / m ３ The nonwoven fabric showed no holes even after 10 minutes of flame contact, but cracks appeared after 175 seconds, and the flame penetrated through the cracks, so the heat resistance was rated F. Excessive carbonization had progressed in the flame contact area, and the carbonized area was in a state where cracks easily occurred. The bending resistance measured by the cantilever method was 52 mm in the vertical direction and 50 mm in the horizontal direction, indicating that the nonwoven fabric was flexible. Furthermore, even after 10,000 MIT folding tests, the sample did not break in either the vertical or horizontal direction, demonstrating good folding endurance. The surface resistance of the sheet was 1.0 x 10 before flame contact. ６Ω or more, and no continuity was observed. However, after contact with flame (3 minutes), carbonization progressed and cracks occurred, so the resistance was 1.0 × 10 １ Conduction was achieved at Ω.

[0092] Comparative Example 5 A nonwoven fabric was produced under the same conditions as in Comparative Example 3, except that the flame-retardant rayon fiber 3 used in Comparative Example 3 was replaced with flame-retardant rayon fiber 5, the PPS fiber drawn yarn 2 with PPS fiber drawn yarn 4, and the PPS fiber undrawn yarn 2 with PPS undrawn yarn 4. The fibers constituting the nonwoven fabric were PPS fiber drawn yarn 4, PPS fiber undrawn yarn 4, and flame-retardant rayon fiber 5, in a ratio of 40:30:30. When the fibers were added to water and stirred and dispersed for 1 minute in a household mixer adjusted to 3000 rpm, the fibers became tangled and clumped, making it difficult to obtain a uniform dispersion. Next, the dispersion was added to a 25 cm x 25 cm, 40 cm high hand-sheet papermaking machine (manufactured by Kumagai Riki Kogyo Co., Ltd.) equipped with a 140-mesh hand-sheet screen at the bottom, and further water was added to adjust the fiber concentration to 0.1% by mass. Next, the wet paper web was obtained by dewatering. The obtained wet paper web had a mixture of clumped fiber aggregates and holes visible to the naked eye, and was highly uneven. By adjusting the total amount of fiber in the paper machine to 6.25 g, a wet paper web of 100 g / m ２ Two wet webs can be stacked to obtain a wet web of 200 g / m. ２ The obtained wet web was placed on a filter paper and dried in an oven at 130°C for 3 minutes, and then treated with a double-sided heated metal roll thermal calender at a processing speed of 3 m / min, a heating temperature of 180°C, and a linear pressure of 150 kgf / cm to adjust the thickness. The obtained sheet had a basis weight of 204 g / m ２ , thickness 0.48 mm, density 425 kg / m ３ This sheet had a lot of unevenness, and cracks appeared in the thinner parts after 24 seconds, allowing the flame to penetrate, so the heat resistance was rated F. The bending resistance measured by the cantilever method was flexible enough to bend 153 mm in the vertical direction and 158 mm in the horizontal direction. The MIT folding endurance test showed that the sheet broke after 300 times from the thin parts in both the vertical and horizontal directions. The surface resistance of the sheet was 1.0 x 10 before contact with the flame.６ Although no electrical continuity was observed, cracks were observed in the sheet after exposure to flame (3 minutes), and the １ The flame-retardant rayon fibers were separated from the dried sheet, and the content of inorganic particles in the flame-retardant rayon was measured, which revealed that the content of titanium dioxide was 18.2% by mass and the content of sodium was 0.1% by mass.

[0093] [Reference Example 1] The following evaluation was carried out using a 0.5 mm thick hard laminated mica plate D581 manufactured by Okabe Mica Co., Ltd. The basis weight was 1020 g / m ２ , density is 2040 kg / m ３ (Heat resistance) After 600 seconds (10 minutes), the flame did not penetrate the nonwoven fabric, and the fabric had sufficient flame-proofing and heat-insulating properties, so the heat resistance was rated A. (Bending resistance) Since the fabric could not be bent, the bending resistance could not be measured by the cantilever method. (Folding endurance) It was difficult to bend the fabric at an angle of 135 degrees, so it was impossible to measure. When the fabric was bent by hand, cracks occurred in the mica plate. (Surface resistance of the sheet) The surface resistance of all three test specimens was 1.0 x 10 before and after exposure to flame (3 minutes). ６ Ω or more, and no continuity was observed.

[0094]

[0095] The present disclosure is flexible and has high heat resistance, and therefore exhibits a fire spread prevention effect, particularly when combined with combustible materials, making it suitable for use in clothing materials, wall materials, floor materials, ceiling materials, covering materials, etc. that require flame retardancy, and is particularly suitable for use in fire-resistant protective clothing, fire spread prevention covering materials for urethane sheet materials for automobiles and aircraft, etc., and fire spread prevention for bed mattresses.

[0096] Furthermore, since the sheet contains insulating inorganic particles, it can suppress electrical conductivity when exposed to high temperatures, making it suitable for use as heat-resistant insulation in high-temperature environments and as a fire-resistant material for battery modules and battery packages that have battery cells for in-vehicle secondary batteries.

[0097] REFERENCE SIGNS LIST 101 Bunsen burner 102 Test specimen L Flame length 201 Sheet 202 Resin A 203 Resin B 204 Inorganic particles 301 Sheet 302 Resin A 303 Resin B 304 Inorganic particles 401 Battery cell 402 Case material of battery package 403 Fireproof material

Claims

1. A sheet comprising resin A, resin B, and inorganic particles, wherein the resin A is non-meltable and has a limiting oxygen index of 25 or less in accordance with JIS K 7201-2 (2007), the resin B is thermoplastic and has a limiting oxygen index of 25 or more in accordance with JIS K 7201-2 (2007), at least one of the resins A and B is in the form of fibers, the fibers having a fiber length of 38 to 120 mm and a crimp number of 4.5 to 120, and the inorganic particles are insulating.

2. The sheet according to claim 1, wherein said inorganic particles are contained in said resin A.

3. The sheet according to claim 1 or 2, wherein the resin A comprises at least one selected from the group consisting of cellulose-based materials, thermosetting resins, and flame-retardant materials obtained by subjecting raw materials selected from acrylonitrile-, pitch-, cellulose-, and phenol-based resins to a flame-retardant treatment.

4. The sheet according to claim 1 or 2, wherein the inorganic particles include at least one selected from silica and titanium dioxide.

5. The sheet according to claim 1 or 2, wherein said resin A contains at least a cellulose-based material.

6. The sheet according to claim 1 or 2, wherein said resin B comprises at least one selected from the group consisting of anisotropic melt polyester, poly(butylene terephthalate), poly(acrylonitrile butadiene styrene), polysulfone, poly(ether-ether-ketone), poly(ether-ketone-ketone), polyethersulfone, polyarylate, polyarylene sulfide, polyphenylsulfone, polyetherimide, polyamideimide, and copolymers thereof.

7. The sheet according to claim 1 or 2, wherein the resin A is contained in an amount of 15 to 80% by mass of the mass of the sheet.

8. The sheet according to claim 1 or 2, wherein said resin B is contained in an amount of 20 to 85% by mass of the mass of said sheet.

9. The sheet according to claim 1 or 2, wherein the mass of the inorganic particles is 20 to 60% by mass of the mass of the resin A.

10. The density of the sheet is 50 to 800 kg / m ３ 3. The sheet according to claim 1 or 2, wherein 11. The sheet according to claim 1 or 2, wherein the sheet is a dry-laid nonwoven fabric.

12. The surface resistance of the sheet, measured in accordance with JIS C 2139-3-2 (2018), after heating it for 180 seconds with a Bunsen burner at 1000°C is 1.0 x 10 ６ The sheet according to claim 1 or 2, having a modulus of elasticity of Ω or more.

13. A fire-resistant material using the sheet according to claim 1 or 2.

14. A secondary battery using the sheet according to claim 1 or 2 as a fire-resistant material.

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