Heat insulating sheet and manufacturing method thereof, heat insulating fiber and manufacturing method thereof, and fiber-containing suspension used in manufacturing heat insulating sheet

Abstract

This insulation sheet includes matrix fibers and insulating microparticles, wherein: the matrix fibers are mutually bonded or interlaced to form a sheet body; and the insulating microparticles are present in the interior and / or on the outer side of the matrix fibers. In one embodiment, the insulation sheet includes matrix fibers, binder fibers, and a binding agent, wherein: the matrix fibers are mutually bonded by a film formed as the binder fibers melt; and insulating microparticles are supported by the binding agent in gaps between the bonded matrix fibers. These insulation fibers are present in in the interior of matrix fibers in a state in which at least a portion of the insulating microparticles are embedded. The insulating microparticles are formed with, as a raw material, an aerogel having a three-dimensional mesh structure, the framework of which is formed of clusters that are aggregates of primary particles, and have a three-dimensional mesh structure, the framework of which is formed of the primary particles. The particle diameters of at least 50% of the volume of said microparticles vary so that the mode is found between 0.1 μm and 1.0 μm. The matrix fibers include a thermoplastic resin.

Description

[Technical Field]

[0001] The present invention relates to a heat insulating sheet and a method for producing the same, a heat insulating fiber and a method for producing the same, and a fiber-containing suspension used in producing the heat insulating sheet. [Background technology]

[0002] Materials that offer insulating and heat-resistant properties are attracting attention as a measure against global warming. For example, in batteries that integrate many battery cells, a structure is adopted in which an insulating sheet is sandwiched between adjacent cells to reduce the impact of overheating of some cells on adjacent cells. In this case, the insulating sheet sandwiched between the cells must be heat-resistant to prevent the cells from overheating and causing thermal runaway, and must also be flame-retardant and fire-resistant in case of fire. On the other hand, to increase the amount of electricity stored per volume of a battery, the insulating sheet must be as thin as possible. Thus, insulating sheets are required to achieve the required insulating and flame-retardant properties while remaining as thin as possible.

[0003] Patent Document 1 discloses a resin-coated flame-retardant fiber yarn. The flame-retardant fiber yarn is coated with two resin coating layers, with the outer layer containing titanium dioxide particles, thereby achieving light transmission, heat insulation, and flame retardancy. The manufacturing method is described as follows: A resin solution containing a titanium dioxide-free adhesive resin is applied to a glass fiber bundle, which is the flame-retardant fiber yarn. After squeezing out the excess resin solution, the bundle is heated to form an inner resin coating layer. Next, a titanium dioxide-containing resin solution is applied to the glass fiber bundle with the inner resin coating layer formed thereon. After squeezing out the excess resin solution, the bundle is heated to form a titanium dioxide-containing resin layer on the outer side of the inner resin coating layer (see paragraphs 0026 to 0045 of the same document for details). The resin-coated flame-retardant fiber yarn can be woven as warp and weft yarns to produce a woven fabric (ibid., paragraph 0046).

[0004] Patent Document 2 discloses a lightweight thermal and sound-insulating material with excellent thermal insulation and sound-proofing properties. The basic structure is composed of cells in which aggregates of silica aerogel particles are surrounded by a network of organic nanofibers with anionic functional groups, and a solid composite with a three-dimensional continuous structure in which multiple cells are closely spaced is formed inside a nonwoven fabric or open-cell foam, which is said to be lightweight and have excellent sound-insulating properties.

[0005] Patent Document 3 discloses ultrafine aerogel particles characterized by using aerogel as a raw material, the raw material having a three-dimensional network structure in which the skeleton is formed by clusters that are aggregates of primary particles, and containing fine particles having a three-dimensional network structure in which the skeleton is formed by the primary particles. Patent Document 3 is an invention by the inventors of the present application, and is commercially known as TIISA (a registered trademark of Thermalytica Inc.). The ultrafine aerogel particles have a thermal conductivity equivalent to that of high-performance aerogel, and a bulk density of 0.01 g / cm. 3 Its particle size is less than one-tenth that of ordinary aerogel, making it a lightweight, high-performance heat-insulating material. While the skeleton of ordinary aerogel is formed from secondary particles, ultrafine aerogel particles have a skeleton formed mainly from the primary particles that make up the secondary particles, making them extremely small particles, with 50% or more of their volume dispersed with a mode of particle diameter between 0.1 μm and 1.0 μm.

[0006] Patent Document 4 discloses a fiber-reinforced thermoplastic resin sheet and a glass fiber nonwoven fabric carrying silica microparticles. The fiber-reinforced thermoplastic resin sheet is composed of a thermoplastic matrix resin and silica microparticles contained in the glass fibers and having an average primary particle diameter in the range of 1 to 100 nm.

[0007] Patent Document 5 discloses a heat insulating material that is said to have high strength and excellent heat insulating properties. The heat insulating material is composed of aerogel particles, an adhesive that bonds them, and a composite adhesive in which a heat-fusible adhesive component is coated with a protective film. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] International Publication WO2013 / 136552 [Patent Document 2] Japanese Patent Publication No. 2022-41332 [Patent Document 3] International Publication WO2022 / 107365 [Patent Document 4] Japanese Patent Application Laid-Open No. 2018-95673 [Patent Document 5] Japanese Patent Application Laid-Open No. 2015-124779 Summary of the Invention [Problem to be solved by the invention]

[0009] A primary object of the present invention is to provide a thermal insulation sheet having high thermal insulation performance. Another object of the present invention is to further impart flame retardancy to the thermal insulation sheet. A further object of the present invention is to provide a fiber-containing suspension and a thermal insulation fiber suitable for producing such a thermal insulation sheet.

[0010] The means for solving these problems will be described below, but other problems and novel features will become apparent from the description of this specification and the accompanying drawings. [Means for solving the problem]

[0011] According to the present invention, the following is true.

[0012] In other words, the insulating sheet of the present invention is an insulating sheet comprising base fibers and insulating microparticles, the base fibers being bonded to each other or woven or knitted to form a sheet body, and the insulating microparticles being present inside and / or outside the base fibers.

[0013] The method for manufacturing an insulating sheet according to the present invention includes the steps of dispersing insulating microparticles to prepare an insulating microparticle-containing suspension, dissolving a binder to prepare a binder solution, mixing the insulating microparticle-containing suspension, the binder solution, base fibers, and binder fibers to prepare a fiber-containing suspension, and removing liquid components from the fiber-containing suspension to form a sheet (papermaking process).

[0014] Another method for manufacturing an insulating sheet according to the present invention includes the steps of mixing a thermoplastic resin with insulating microparticles to obtain a microparticle-containing resin, placing the microparticle-containing resin in a container having fine holes placed in a chamber, rotating the container while heating it to eject the microparticle-containing resin from the fine holes to obtain short fibers, and forming the short fibers into a sheet.

[0015] Yet another method for manufacturing an insulating sheet according to the present invention includes the steps of melting a thermoplastic resin and mixing the melted thermoplastic resin with insulating microparticles to prepare a microparticle-containing resin, extruding the melted microparticle-containing resin through pores to obtain fibers, spinning the fibers to obtain yarns, and weaving and knitting the yarns.

[0016] The fiber-containing suspension for manufacturing the heat insulating sheet according to the present invention is prepared by mixing a heat insulating microparticle-containing suspension in which heat insulating microparticles are dispersed in a solvent, a binder solution, base fibers, and binder fibers.

[0017] Another fiber-containing suspension for producing an insulating sheet according to the present invention is a mixture of an insulating microparticle-containing suspension in which insulating microparticles are dispersed in a solvent, a binder solution, insulating fibers, and binder fibers, and the insulating fibers have insulating microparticles for the fibers adhered to the surface of the base fiber by a fiber binder, and the insulating microparticles for the fibers are made from aerogel having a three-dimensional mesh structure with a skeleton formed by clusters that are aggregates of primary particles, and are microparticles with a three-dimensional mesh structure with a skeleton formed by the primary particles, with more than 50% of their volume being dispersed with a particle diameter of 0.1 μm or more and 1.0 μm or less as the most common value, and the base fiber is silica fiber.

[0018] The insulating fiber of the present invention has insulating microparticles bonded to the surface of a base fiber with a binder, the insulating microparticles being made from aerogel having a three-dimensional mesh structure with a skeleton formed of clusters that are aggregates of primary particles, and the insulating microparticles have a three-dimensional mesh structure with a skeleton formed of the primary particles, and more than 50% of the volume of the microparticles are dispersed with a particle diameter of 0.1 μm or more and 1.0 μm or less with a mode, and the base fiber is silica fiber.

[0019] Another insulating fiber according to the present invention has insulating microparticles at least partially embedded inside a base fiber, the insulating microparticles being made from an aerogel having a three-dimensional mesh structure with a skeleton formed of clusters that are aggregates of primary particles, and the insulating microparticles are microparticles having a three-dimensional mesh structure with a skeleton formed of the primary particles, with 50% or more of their volume being dispersed with a particle diameter of 0.1 μm or more and 1.0 μm or less as a mode, and the base fiber containing a thermoplastic resin.

[0020] The method for manufacturing insulating fiber according to the present invention is a method for manufacturing insulating fiber according to the present invention, and includes the steps of dispersing the insulating microparticles to prepare an insulating microparticle-containing suspension, dissolving a binder to prepare a binder solution, mixing the insulating microparticle-containing suspension with the binder solution to prepare a slurry, and depositing the slurry as an evaporation source onto the base fiber.

[0021] Another method for manufacturing insulating fiber according to the present invention is a method for manufacturing insulating fiber according to the present invention, which includes the steps of dissolving a binder to prepare a binder solution, vapor-depositing the binder solution onto a base fiber using the binder solution as an evaporation source, and mechanically applying insulating microparticles to the base fiber having the binder solution attached to its surface by the vapor deposition.

[0022] Note that "dispersing (the fine particles)" means adding the fine particles to a liquid and dispersing them in the liquid, not dissolving them. The "papermaking process (sheet formation process)" includes a process of thinly spreading a suspension containing base fibers, removing excess liquid, and then drying to form a sheet. In addition, in this specification, "polyvinyl alcohol" may be abbreviated as "PVA" (polyvinyl alcohol), "polyvinyl alcohol fiber" as "PVA fiber," and "polyvinyl alcohol powder" as "PVA powder." [Effects of the Invention]

[0023] The effects obtained by the embodiment are briefly described below.

[0024] That is, it is possible to provide a heat insulating sheet having high heat insulating properties, a heat insulating fiber suitable for further imparting flame retardancy to the heat insulating sheet, and a fiber-containing suspension suitable for producing the heat insulating sheet. [Brief explanation of the drawings]

[0025] [Figure 1] FIG. 1 is a schematic explanatory view showing an example of the configuration of a heat insulating sheet according to one embodiment of the present invention. [Figure 2] FIG. 2 is an explanatory diagram showing the relationship between the lengths of the base fibers and the binder fibers. [Figure 3] FIG. 3 is an explanatory diagram showing an example of the configuration of a flame-retardant fiber formed by adhering heat-insulating fine particles to the surface of a base fiber. [Figure 4] FIG. 4 is a flowchart showing an example of a method for producing a heat insulating sheet according to one embodiment of the present invention. [Figure 5] FIG. 5 is a flowchart showing an example of a method for producing a flame-retardant fiber according to one embodiment of the present invention. [Figure 6] FIG. 6 is a flowchart showing an example of a method for manufacturing a heat insulating sheet to which flame retardancy has been added. [Figure 7] FIG. 7 is an explanatory diagram showing the structure of ultrafine aerogel particles, which are an example of heat insulating particles. [Figure 8] FIG. 8 is an explanatory diagram illustrating the particle size distribution of ultrafine aerogel particles, which are an example of heat insulating particles. [Figure 9] Figure 9 is a photograph of an actual object showing the results of an experiment in which glass wool coated with a flame-retardant layer containing ultrafine aerogel particles was burned with a flame. [Figure 10] Figure 10 is an optical microscope photograph showing the results of an experiment in which glass wool coated with a flame-retardant layer containing ultrafine aerogel particles was burned with a flame. [Figure 11] FIG. 11 is an explanatory diagram showing an example of a base fiber formed by mixing a thermoplastic resin and heat insulating particles. [Figure 12] FIG. 12 is a flowchart showing an example of a method for producing a heat insulating sheet according to the eighth embodiment. [Figure 13] FIG. 13 is an explanatory diagram showing an example of the configuration of an apparatus for producing base fibers for the heat insulating sheet according to the eighth embodiment. [Figure 14] FIG. 14 is a flowchart showing an example of a method for producing a heat insulating sheet according to the ninth embodiment. [Figure 15] FIG. 15 is a schematic diagram showing an example of a known spinning apparatus. [Figure 16] FIG. 16 is a schematic diagram showing the apparatus used in the examples. [Figure 17] FIG. 17 is a scanning electron microscope (SEM) photograph showing the experimental results. DETAILED DESCRIPTION OF THE INVENTION

[0026] 1. Overview of the embodiment First, an outline of the exemplary embodiments disclosed in the present application will be described. In the outline of the exemplary embodiments, reference numerals in parentheses in the drawings merely illustrate components included in the concept of the components to which the reference numerals are attached.

[0027] [1] Heat-insulating sheet carrying heat-insulating particles (Fig. 1, Fig. 11) The insulating sheet shown in this embodiment is an insulating sheet (100) comprising base fibers (6,300) and insulating microparticles (1, 14), in which the base fibers (6,300) are bonded or woven to form a sheet body, and the insulating microparticles (1, 14) are present inside and / or outside the base fibers (6,300).

[0028] This makes it possible to realize a heat insulating sheet with excellent heat insulating properties.

[0029] [2] Supporting ultrafine aerogel particles (Figures 7 and 8) In the heat insulating sheet of [1], the heat insulating microparticles are made from aerogel having a three-dimensional network structure with a skeleton formed of clusters that are aggregates of primary particles, and are microparticles having a three-dimensional network structure with a skeleton formed of the primary particles, with 50% or more of the volume being dispersed with a particle diameter of 0.1 μm or more and 1.0 μm or less as the mode.

[0030] This makes it possible to realize a thin heat insulating sheet by taking advantage of the small particle diameter of the ultrafine aerogel particles.

[0031] [3] A thermal insulation sheet in which insulating particles are held in the gaps between the base fibers, which are bonded together by a film formed by dissolving binder fibers (Figure 1). In the heat insulating sheet of [1] or [2], the base fiber is a silica fiber, and the heat insulating sheet (100) includes a base fiber (6), a binder fiber (7), and a binder (2, not shown in Figure 1), and the base fibers are bonded to each other by a film formed by dissolving the binder fiber, and heat insulating microparticles (1) are supported in the gaps between the bonded base fibers by the binder.

[0032] This makes it possible to realize a thin heat insulating sheet.

[0033] [4] Adding flame retardancy (Figure 3) In the heat insulating sheet of [3], the heat insulating particles are adhered to the surface of the base fiber by the binder.

[0034] As a result, the presence of the heat-insulating fine particles on the surface of the matrix fibers imparts flame retardancy in addition to heat insulation, making it possible to impart flame retardancy to the entire heat-insulating sheet. Here, in this specification, "imparting flame retardancy" refers to the process of applying some kind of processing to a specific object, making the object less flammable than before the processing.

[0035] [5] A thermal insulation sheet formed by weaving and knitting a matrix fiber carrying thermal insulating particles embedded in a thermoplastic resin (Fig. 11). In the heat insulating sheet of [1] or [2], the base fiber (300) contains a thermoplastic resin (8), the heat insulating microparticles (14) are present in a state where at least a part of them is embedded in the thermoplastic resin (8) in the base fiber (300), and the sheet body is formed by weaving and knitting threads spun from the base fiber (300).

[0036] The base fiber (300) is spun by a known spinning method, and the spun yarn is woven or knitted by a known method to form a sheet body, which is a heat insulating sheet.

[0037] This makes it possible to realize a heat insulating sheet with high heat insulating performance without using a binder.

[0038] [6] A thermal insulation sheet formed by bonding a base fiber in which thermal insulating particles are embedded in a thermoplastic resin with a film formed by melting the thermoplastic resin (Figure 11). In the heat insulating sheet of [1] or [2], the base fiber (300) contains a thermoplastic resin (8), the heat insulating particles (14) are present in a state where they are at least partially embedded in the thermoplastic resin (8) in the base fiber (300), and the sheet body is formed by the base fibers being bonded to each other with a film formed by melting the thermoplastic resin.

[0039] This makes it possible to realize a heat insulating sheet with high heat insulating performance without using a binder.

[0040] [7] Manufacturing method of heat insulating sheet (Figure 4) A typical embodiment of the present invention is a method for manufacturing a heat insulating sheet, which includes the following steps.

[0041] (S1): A step of dispersing heat insulating fine particles to prepare a suspension containing heat insulating fine particles. (S2): A step of dissolving the binder to prepare a binder solution. (S3): A step of preparing a fiber-containing suspension by mixing the heat insulating microparticle-containing suspension, the binder solution, base fibers, and binder fibers. (Papermaking step, S4): A step of removing the liquid component from the fiber-containing suspension to form a sheet body.

[0042] This provides the methods for producing the heat insulating sheets described in [1] to [6].

[0043] [8] Aerogel ultrafine particles are supported in the gaps between silica fibers (Figures 1 and 4) In the method for manufacturing a heat insulating sheet of [7], the base fiber is a silica fiber, and the heat insulating microparticles are made from aerogel having a three-dimensional network structure with a skeleton formed by clusters that are aggregates of primary particles, and are microparticles having a three-dimensional network structure with a skeleton formed by the primary particles, with 50% or more of their volume being dispersed with a particle diameter of 0.1 μm or more and 1.0 μm or less as the mode.

[0044] This makes it possible to provide a method for producing a thin heat insulating sheet by taking advantage of the small particle size of the ultrafine aerogel particles, as in the above [2].

[0045] [9] Manufacturing method when heat insulating particles are hydrophobic In the method for producing a heat insulating sheet according to [7] or [8], the heat insulating fine particles are hydrophobic, and the suspension containing the heat insulating fine particles contains alcohol.

[0046] This makes it possible to provide a method for producing a heat insulating sheet with high heat insulating performance even if the heat insulating fine particles are hydrophobic.

[0047]

[10] Manufacturing method of heat insulating sheet A method for producing a heat insulating sheet according to another embodiment of the present invention includes the following steps.

[0048] A step of mixing a thermoplastic resin with heat insulating fine particles to obtain a fine particle-containing resin.

[0049] A step of placing the microparticle-containing resin in a container having fine holes, rotating the container while heating it, and ejecting the microparticle-containing resin from the fine holes to obtain short fibers.

[0050] forming the short fibers into a sheet.

[0051] This makes it possible to obtain a heat insulating sheet carrying heat insulating fine particles without using a binder.

[0052]

[11] A method for manufacturing a heat insulating sheet by weaving or knitting short fibers The method for producing a heat insulating sheet according to

[10] includes the steps of spinning the short fibers to obtain yarn, and weaving and knitting the yarn.

[0053] This makes it possible to obtain a heat insulating sheet made of a woven or knitted sheet having a relatively high strength and carrying heat insulating particles.

[12] A method for manufacturing a heat insulating sheet by molding the heat insulating sheet from short fibers In the step of forming the short fibers into a sheet in the method for producing a heat insulating sheet according to

[10] , the short fibers are spread into a thin film and heated to form the sheet.

[0054] This allows the heat insulating sheet to be easily manufactured without any weaving or knitting process.

[0055]

[13] A method for manufacturing a heat insulating sheet by weaving and knitting a heat insulating sheet from spun yarn. A method for producing a heat insulating sheet according to yet another embodiment of the present invention includes the following steps.

[0056] A step of melting a thermoplastic resin and mixing the melted thermoplastic resin with heat insulating fine particles to prepare a fine particle-containing resin. A step of extruding the molten resin containing the fine particles through the pores into a coagulating liquid to obtain fibers. spinning the fibers to obtain yarn. weaving and knitting the yarn.

[0057] This makes it possible to obtain a heat insulating sheet made of a woven or knitted sheet having a relatively high strength and carrying heat insulating particles.

[0058]

[14] Manufacturing method for flame-retardant heat insulation sheet (Figure 6) A typical embodiment of the present invention is a method for manufacturing a heat insulating sheet, which includes the following steps.

[0059] A step of dispersing the heat insulating fine particles (1) to prepare a suspension containing the heat insulating fine particles. A step of dissolving a binder to prepare a binder solution. A step of preparing a fiber-containing suspension by mixing insulating fibers, binder fibers, the insulating microparticle-containing suspension, and the binder solution. A step of removing the liquid component from the fiber-containing suspension to form a sheet body.

[0060] Furthermore, the heat insulating fiber has heat insulating particles for the fiber bonded to the surface of the base fiber by a fiber binder, The insulating microparticles for the fibers are made from aerogel having a three-dimensional mesh structure with a skeleton made up of clusters, which are aggregates of primary particles, and are microparticles with a three-dimensional mesh structure with a skeleton made up of the primary particles, with 50% or more of their volume dispersed with a particle diameter of 0.1 μm or more and 1.0 μm or less as the most common value, and the base fiber is silica fiber.

[0061] This allows the silica fiber, which is the base fiber, to have high flame retardancy, making it possible to provide a method for producing a flame-retardant heat insulating sheet.

[0062]

[15] Ultrasonic or thermal evaporation (Figure 6) In the method for producing a heat insulating sheet described in

[14] , the vapor deposition is ultrasonic vapor deposition or thermal vapor deposition.

[0063] This allows the heat insulating particles (ultrafine aerogel particles) to be more efficiently bonded to the surface of the silica fiber, which is the base fiber.

[0064]

[16] Manufacturing method when heat insulating particles are hydrophobic In the method for producing a heat insulating sheet described in

[14] , the heat insulating microparticles are hydrophobic, and the heat insulating microparticle-containing suspension in the first step and the heat insulating microparticle-containing suspension for the fibers contain alcohol.

[0065] This makes it possible to provide a method for producing a flame-retardant fiber even when the heat insulating fine particles are hydrophobic.

[0066]

[17] Fiber-containing suspension A typical embodiment of the present invention is a fiber-containing suspension for producing an insulating sheet, which is a mixture of an insulating microparticle-containing suspension in which insulating microparticles are dispersed in a solvent, a binder solution, base fibers, and binder fibers, used in the method for producing the insulating sheet.

[0067]

[18] Fiber-containing suspension with added flame retardancy A typical embodiment of the present invention is a fiber-containing suspension for use in the production of an insulating sheet, which is a mixture of an insulating microparticle-containing suspension in which insulating microparticles are dispersed in a solvent, a binder solution, insulating fibers, and binder fibers, and the insulating fibers are formed by bonding insulating microparticles for the fibers to the surface of base fibers using a fiber binder, and the insulating microparticles for the fibers are made from aerogel having a three-dimensional mesh structure with a skeleton formed by clusters that are aggregates of primary particles, and are microparticles with a three-dimensional mesh structure with a skeleton formed by the primary particles, with more than 50% of their volume being dispersed with a particle diameter of 0.1 μm or more and 1.0 μm or less as a mode, and the base fibers are silica fibers.

[0068] This fiber-containing suspension can be provided as a raw material for the papermaking process (S4) or the like.

[0069]

[19] Thermal insulation fiber with flame retardant properties, with ultrafine aerogel particles bonded to the surface (Figure 3) A typical embodiment of the present invention is a thermal insulating fiber (flame retardant fiber) (200) to which flame retardancy has been added, and is configured as follows: In this specification, flame retardant fiber refers to a thermal insulating fiber to which flame retardancy has been added as well as thermal insulating properties.

[0070] The heat insulating particles (1) are bonded to the surface of the base fiber (6) by a binder (2).

[0071] The heat insulating particles are made from aerogel having a three-dimensional network structure with a skeleton formed of clusters that are aggregates of primary particles, and are particles having a three-dimensional network structure with a skeleton formed of the primary particles, with 50% or more of the volume of the particles dispersed with a mode of particle diameter between 0.1 μm and 1.0 μm. The matrix fibers are silica fibers.

[0072] This makes it possible to provide a flame-retardant fiber having higher flame retardancy than the silica fiber, which is the base fiber.

[0073]

[20] Thermal insulation fiber with ultrafine aerogel particles bonded to the surface (Figure 11) A representative embodiment of the present invention is an insulating fiber (300) constructed as follows.

[0074] The heat insulating particles (14) are present in a state where they are at least partially embedded inside the matrix fibers (300), The heat insulating fine particles (14) are made from an aerogel having a three-dimensional network structure whose skeleton is made up of clusters that are aggregates of primary particles, and are fine particles having a three-dimensional network structure whose skeleton is made up of the primary particles, and 50% or more of the volume of the fine particles are dispersed with a particle diameter of 0.1 μm or more and 1.0 μm or less as a mode. The matrix fiber (300) includes a thermoplastic resin (8).

[0075] This makes it possible to provide a heat insulating fiber in which heat insulating properties are imparted to the base fiber without using a binder.

[0076]

[21] Manufacturing method for flame-retardant fiber with aerogel ultrafine particles bonded to the surface (Figure 5(a))

[19] A method for producing the heat insulating fiber (200) described in

[19] , comprising the following steps:

[0077] (S11): A step of dissolving insulating fine particles (ultrafine aerogel particles) to prepare a suspension containing insulating fine particles. (S12): A step of dissolving a binder to prepare a binder solution. (S13): A step of mixing the heat insulating fine particle-containing suspension with the binder solution to prepare a slurry. (S14): A step of depositing the slurry as an evaporation source onto the base fiber.

[0078] A manufacturing method is provided for imparting higher flame retardancy to the base fiber by depositing heat insulating fine particles (ultrafine aerogel particles) contained in the slurry onto the surface of the base fiber.

[0079]

[22] Manufacturing method for flame-retardant fiber with aerogel ultrafine particles bonded to the surface (Figure 5(b))

[19] A method for producing the heat insulating fiber (200) described in

[19] , comprising the following steps:

[0080] (S15): A step of dissolving a binder to prepare a binder solution. (S16): A step of depositing the binder solution onto the base fiber as an evaporation source. (S17, powdering step): A step of mechanically coating the base material fibers with the binder solution attached to their surfaces by the vapor deposition with heat insulating particles.

[0081] This provides another manufacturing method for imparting flame retardancy to the matrix fibers.

[0082]

[23] Ultrasonic or thermal evaporation (Figure 5) In the method for producing a heat insulating fiber described in

[21] , the vapor deposition in the fourth step (S14) is ultrasonic vapor deposition or thermal vapor deposition.

[0083] This allows the heat insulating fine particles (ultrafine aerogel particles) to be more efficiently bonded to the surface of the silica fiber, which is the base fiber.

[0084]

[24] Manufacturing method when heat insulating particles are hydrophobic In the method for producing a flame-retardant fiber according to any one of

[19] to

[23] , the heat insulating fine particles are hydrophobic, and the suspension containing the heat insulating fine particles contains alcohol.

[0085] This makes it possible to provide a method for producing a flame-retardant fiber even when the heat insulating fine particles are hydrophobic.

[0086] 2. Details of the embodiment The embodiment will be described in further detail.

[0087] [Embodiment 1] Figure 1 is a schematic explanatory diagram showing an example of the configuration of a heat insulating sheet of the present invention. The heat insulating sheet 100 of the present invention comprises base fibers 6, binder fibers 7, and a binder (2, not shown in Figure 1), the base fibers 6 are bonded to one another by a film (not shown in Figure 1) formed by dissolving the binder fibers 7, and heat insulating particles 1 are carried in the gaps between the bonded base fibers 6. The reference numeral 3 will be described later and in more detail in embodiments 4 and 5.

[0088] This makes it possible to provide a heat insulating sheet with high heat insulating performance. By using binder fibers 7 that are much shorter than the matrix fibers 6, many layers of matrix fibers 6 are formed within a certain thickness, creating gaps between the matrix fibers 6 that form the layers, and these gaps can hold many heat insulating particles 1, improving the heat insulating performance of the heat insulating sheet 1.

[0089] Examples of the binder fibers 7 that can be used include polyvinyl alcohol (PVA) fibers, polyester fibers, polyester composite fibers, acrylic fibers, acrylic fibers, nylon, polyurethane fibers, and polycarbonate fibers. Examples of the binder that can be used include polyvinyl alcohol (PVA) powder, methyl cellulose, starch glue, and gum arabic glue.

[0090] The length of the binder fibers 7 is preferably several tens of micrometers. The matrix fibers 6 are, for example, silica fibers, and are several tens of millimeters longer than the binder fibers 7. While the matrix fibers 6 extend planarly (horizontally in FIG. 1), the binder fibers 7 serve to connect the matrix fibers 6 vertically (thicknesswise of the thermal insulation sheet 100). The matrix fibers 6 and the binder fibers 7 are bonded together by a film (not shown in FIG. 1) formed by melting, and gaps are formed between the bonded matrix fibers 6, within which the thermal insulating particles 1 are supported. For example, PVA fibers, an example of the binder fibers 7, melt into a film when heated to 65°C to 85°C in a water-wet state. Here, "melt" refers to dissolution in water, not melting due to heat. Matrix fibers 6, such as silica fibers, have mechanical strength, but heat conducts along the fibers, so thermal insulation performance cannot be expected. In the heat insulating sheet 100 of the present invention, the matrix fibers 6 are long and extend in a direction parallel to the front and back surfaces of the sheet, providing mechanical strength in the plane direction to the heat insulating sheet 100. Meanwhile, in the thickness direction, the heat insulating particles 1 are carried in the gaps between the matrix fibers 6, as shown in Figure 1, thereby providing the heat insulating sheet 100 with heat insulating performance in the thickness direction.

[0091] The appropriate length of the binder fiber 7 will now be explained. Generally, insulation sheets require better insulation performance in the thickness direction than in the in-plane direction. Therefore, binder fibers that extend from one surface of the insulation sheet to the other are not desirable. Because the thermal conductivity of binder fibers is higher than that of silica fibers, which are often used as matrix fibers, if binder fibers extend from one surface of the insulation sheet to the other in the thickness direction, heat will be conducted through the binder fibers, which will reduce the insulation performance in the thickness direction. Even taking into account bending due to heat applied during manufacturing, the maximum length of the binder fibers is preferably several millimeters, which is approximately the same as the thickness of the insulation sheet.

[0092] On the other hand, the appropriate minimum length of the binder fibers 7 is 10 μm to several tens of μm. FIG. 2 is an explanatory diagram showing the relationship between the lengths of the base fibers 6 and the binder fibers 7. When the base fibers 6 are adjacent to each other so as to be in contact with each other (a), the length of the binder fibers 7 is required to be at least approximately equal to the diameter of the base fibers 6 in order to bond the adjacent base fibers 6. When the base fibers 6 are coated with some kind of material or when the base fibers 6 are separated from each other due to the presence of insulating particles or the like in the present invention (b), (c), or (d), the minimum length of the binder fibers 7 required is one to several times the distance between the base fibers 6 to be connected. That is, when two fibers are connected (b), the minimum length is approximately equal to the distance between the base fibers 6; when three fibers are connected in a straight line (c), the minimum length is approximately twice the distance between the base fibers 6; and when three fibers are connected in a stitching pattern (d), the minimum length is approximately three to four times the distance between the base fibers 6. The diameter of silica fibers, which are commonly used as matrix fibers, is 8 μm to 12 μm as measured by the inventors, and the minimum value is set to be within several times this range. Note that the minimum value here does not mean that binder fibers shorter than this length are not included, but simply means that binder fibers shorter than this length have a small contribution to the purpose of bonding the matrix fibers.

[0093] As described above, by appropriately designing the lengths of the matrix fibers 6 and the binder fibers 7, it is possible to adjust the strength and heat insulating performance.

[0094] As the heat insulating fine particles 1, it is preferable to use ultrafine aerogel particles as described in Patent Document 3.

[0095] Figure 7 is an explanatory diagram comparing the structures of ordinary aerogel fine powder and ultrafine aerogel particles, whose skeletons are formed by primary particles. The three-dimensional network structure of ordinary aerogel fine powder 13 is composed of units of secondary particles 12, which are clusters of primary particles 11 (Figure 7(a)), whereas the ultrafine aerogel particles 14 have a three-dimensional network structure formed with the primary particles 11 as the skeleton (Figure 7(b)).

[0096] Commonly available aerogels are granules with a three-dimensional network structure composed of secondary particles 12. Therefore, even if they are finely pulverized using a pulverizer, the skeletal structure remains unchanged. The experimental results are shown below. Figure 8 shows an example of the particle size frequency distribution for aerogel granules, aerogel powder, aerogel fine powder, and ultrafine aerogel particles, which are fine particles with a skeleton formed by primary particles, from bottom to top. The aerogel granules are the same as commonly available aerogel granules. The aerogel powder was produced by pulverizing aerogel granules at 5,000 to 7,000 rpm for 2 minutes using a Spinmix Homogenizer SX08 manufactured by Mitsui Electric Seiki Co., Ltd. The aerogel fine powder was produced by further reducing the particle size by pulverizing aerogel granules at 21,000 rpm for 20 seconds using a STEALTH885 manufactured by Blendtec. The horizontal axis of Figure 8 represents particle size, and the vertical axis represents the frequency distribution of relative particle mass. The right-hand vertical axis shows frequency, and the left-hand vertical axis shows cumulative values. Figure 8 shows the results of observations using a laser diffraction particle size distribution (PSD) analyzer. In this specification, particle size is explained based on PSD measurements. However, because PSD measurements observe not only the particle size itself but also particle agglomerations, the true particle size is likely to be smaller than the measured value. If there are differences in particle size depending on the measurement method, please convert them for better understanding. More specifically, Figure 8 shows the particle size distribution measured using a Shimadzu SALD-2300 laser diffraction particle size distribution analyzer. Particle size distribution is an index that indicates the size (particle diameter) of particles contained in the sample particle group being measured and their proportion (relative particle amount, with the total being 100%). The order of particle amount is based on volume.

[0097] Commonly available aerogel granules have a mean particle size of approximately 400 μm and only one peak in relative particle amount (bottom row of Figure 8). When these aerogel granules are crushed using the equipment described above, the aerogel powder has an average particle size of approximately 90 μm, and the aerogel fine powder has an average particle size of approximately 50 μm, but each has only one peak in relative particle amount (third and second rows). In contrast, ultrafine aerogel particles have a first peak at an average particle size of approximately 20 μm and a second peak at an average particle size of approximately 0.3 μm, with the first peak at an average particle size of approximately 20 μm accounting for 21.2% of the relative particle amount, and the second peak at an average particle size of approximately 0.3 μm accounting for 78.8% of the relative particle amount. This is because the first peak, with an average particle size of approximately 20 μm, is composed of fine particles with a three-dimensional mesh structure whose skeleton is made up of secondary particles 12, while the second peak, with an average particle size of approximately 0.3 μm, is composed of fine particles with a three-dimensional mesh structure whose skeleton is made up of primary particles.

[0098] Because the skeleton of the three-dimensional network structure of ordinary aerogel is made up of secondary particles, it is difficult to produce fine particles with a particle size of 10 μm or less, no matter how high the milling conditions are. To produce fine particles with a three-dimensional network structure whose skeleton is made up of primary particles, it is necessary to fundamentally change the manufacturing method, which differs from the usual aerogel manufacturing process, by significantly changing not only the milling conditions but also the aging conditions.

[0099] In the heat insulating sheet 100 of the present invention, the heat insulating particles 1 are preferably the ultrafine aerogel particles described above, i.e., heat insulating particles made from aerogel having a three-dimensional network structure with a skeleton formed by clusters that are aggregates of primary particles 11, with the three-dimensional network structure formed by the skeleton of the primary particles, and with at least 50% of the volume dispersed with a mode particle diameter of 0.1 μm to 1.0 μm. Furthermore, silica fiber is preferably used as the matrix fiber 6, PVA fiber is preferably used as the binder fiber, and PVA is preferably used as the binding agent. As mentioned above, silica fiber, a typical matrix fiber 6, has a diameter of approximately 10 μm, which is not a size relationship that allows aerogel granules of several hundred μm to be supported in the gaps between the matrix fibers. Therefore, ultrafine aerogel particles of 1 μm or less are preferred for achieving a structure that supports the gaps.

[0100] This allows for the provision of a thin insulating sheet that takes advantage of the extremely small particle diameter of the ultrafine aerogel particles. Even when the insulating sheet 100 of this embodiment is thinned to 3 mm or less, the use of ultrafine aerogel particles as the insulating particles 1 can improve the thermal conductivity from approximately 40 mW / mK to less than 30 mW / mK. When insulating particles with large particle diameters are thinned, the number of particles aligned in the thickness direction is small, and the contribution of the particle shells to thermal conduction is significant. In contrast, when the ultrafine aerogel particles are thinned, the gaps (voids) between the particles are larger than the particles themselves, resulting in low thermal conduction through the particle shells. Furthermore, the voids hinder air convection, improving the insulating performance.

[0101] [Addition of flame retardancy] In the heat insulating sheet 100, it is preferable to adhere heat insulating particles 1 to the surface of the matrix fibers 6 using a binder 2. This gives the matrix fibers 6 flame retardancy as well as heat insulating properties, making it possible to impart flame retardancy to the entire heat insulating sheet 100.

[0102] FIG. 3 is an explanatory diagram showing an example of the configuration of a flame-retardant fiber 200 (a thermal insulating fiber to which flame retardancy has been added) formed by adhering thermal insulating particles 1 to the surface of a matrix fiber 6. While it is more reliable to form a flame-retardant layer 3 containing the thermal insulating particles 1 so as to completely cover the surface of the matrix fiber 6, it has been confirmed that the effect of enhancing flame retardancy can also be achieved by forming the flame-retardant layer 3 in an island pattern as shown in FIG. 3. For example, when ultrafine aerogel particles are used as the thermal insulating particles 1, it is possible to impart flame retardancy to the extent that the surface of the thermal insulating sheet 100 will not burn even when heated with a high-temperature flame exceeding 1000°C. Details will be explained in embodiments 3 to 5 and examples.

[0103] [Embodiment 2] A method for producing the heat insulating sheet 100 of the first embodiment will now be described.

[0104] 4 is a flow chart showing an example of a method for manufacturing a heat insulating sheet according to one embodiment of the present invention. The method for manufacturing the heat insulating sheet 100 comprises the following steps.

[0105] First step (S1): Disperse the insulating microparticles 1 to prepare a suspension containing the insulating microparticles. Here, "dispersing (the microparticles)" means adding the microparticles to a liquid (medium) and stirring to disperse them; it does not mean dissolving them. If the insulating microparticles 1 are hydrophobic, they are dispersed in alcohol; if they are hydrophilic, they are dispersed in water. If the insulating microparticles 1 are ultrafine aerogel particles whose surfaces are modified with trimethylsiloxy groups or other hydrophobic groups, they exhibit strong hydrophobicity and have a high affinity with alcohol (e.g., ethanol). Therefore, alcohol is preferably used as the medium in the first step (S1). On the other hand, if hydrophobic ultrafine aerogel particles are treated at a high temperature of around 450°C, the trimethylsiloxy groups on the surface disappear, exposing the silica and making them hydrophilic. Therefore, the suspension containing the insulating microparticles can be prepared using water as the medium, eliminating the need for alcohol (e.g., ethanol). The hydrophobic functional groups of silica aerogel are generally known to begin thermal decomposition at 390°C, but because of its insulating properties, a higher temperature of around 450°C is preferable in order to sufficiently heat the center of the sample. Step 2 (S2): Prepare a binder solution by dissolving a binder, such as PVA powder, in water at room temperature, heating to about 80°C, stirring to dissolve, and then returning to room temperature. Third step (S3): The insulating microparticle-containing suspension prepared in the first step (S1), the binder solution prepared in the second step (S2), the base fiber 6, and the binder fiber 7 are mixed to prepare a fiber-containing suspension. Fourth step (S4): This is a papermaking step in which the fiber-containing suspension prepared in the third step (S3) is made into paper.

[0106] The fourth step (S4) of "making" is a similar process to papermaking (a process in the manufacturing of Japanese paper), in which the liquid components are removed from the suspension, leaving the solid components in the suspension as a thin film to form a sheet. More specifically, by passing the fiber-containing suspension from the third step (S3) through a liquid-permeable mesh, the liquid (medium) passes through, leaving the matrix fibers 6 and binder fibers 7 on the mesh. The remaining matrix fibers 6 and binder fibers 7 are entangled with each other and wet with a liquid containing insulating particles 1 and a binder. Because the matrix fibers 6 are longer than the binder fibers 7, they spread along the mesh, while the binder fibers 7 are shorter and are sandwiched between the matrix fibers 6. The matrix fibers 6 and binder fibers 7 spread entangled on the mesh, and the insulating particles 1 and binder solution are held in the gaps between them. When peeled off the mesh, they become a sheet. The sheet is pressed vertically as is or several sheets are stacked together to squeeze out excess liquid, and then dried to produce a nonwoven fabric, i.e., the heat insulating sheet 100 of Embodiment 1. When heated for drying, the surfaces of the binder fibers 7 melt partially or entirely to form a film that bonds to the adjacent base fibers 6. When the binder fibers 7 are PVA fibers, drying is preferably carried out at 65°C to 85°C.

[0107] Since the fiber-containing suspension prepared in the fourth step (S4) contains the binder solution from the second step (S2), the binder continues to function even after drying, holding the insulating microparticles 1 in place so that they do not spill out through the gaps between the base fibers 6.

[0108] This provides a method for producing the heat insulating sheet 100 of the first embodiment.

[0109] The concentration of the insulating microparticles 1 in the first step (S1) is, for example, 0.1 to 0.5 wt%, the concentration of the polyvinyl alcohol in the second step (S2) is, for example, 0.075 g / dl, and the contents of the base fibers 6 and binder fibers 7 in the fiber-containing suspension are, for example, 0.5 wt% and 0.025 wt%, respectively.

[0110] The content of insulating particles 1 in the suspension containing insulating particles should be as high as possible within the range in which they are uniformly dispersed in the liquid. The content of insulating particles 1 should be limited to the amount that does not cause aggregation, and an appropriate amount of medium is added. If the amount of medium added is too small, the insulating particles 1 in the suspension will aggregate and form clusters, preventing uniform dispersion. On the other hand, if the amount of medium is too large, the content of insulating particles 1 per unit volume will decrease, so there is a trade-off. Optimization design is carried out through experiments, etc.

[0111] For the fiber-containing suspension, the strength of the sheet, for example the tensile strength, can be increased by increasing the content of matrix fibers 6. Also, the sheet can be further strengthened by increasing the content of binder fibers 7, but at the expense of thermal insulation performance.

[0112] [Embodiment 3] A flame-retardant fiber according to one embodiment of the present invention will now be described. As explained in embodiment 1 with reference to FIG. 3, this flame-retardant fiber can be produced by bonding heat-insulating fine particles 1 to the surface of a matrix fiber 6 using a binder. If this flame-retardant fiber is used as the matrix fiber in embodiments 1 and 2, flame retardancy can be imparted to the heat-insulating sheet 100. In this case, ultrafine aerogel particles are particularly suitable as the heat-insulating fine particles 1.

[0113] When silica aerogel, a material containing highly pure silicon dioxide, is used as the raw material for ultrafine aerogel particles, they become insulating particles that retain the flame-retardant properties of silica. Taking typical silica fibers as the base fiber 6 as an example, their diameter is approximately 8 μm to 12 μm. However, as explained with reference to FIG. 8, conventional aerogel fine powder has a particle diameter of several tens to several hundreds of μm, making it impossible to adhere to the surface of silica fibers. On the other hand, the average particle diameter of ultrafine aerogel particles is mostly in the range of 0.3 μm to 0.7 μm, allowing them to adhere to the surface of silica fibers. As explained in the "Adding Flame Retardancy" section of the first embodiment, it is more reliable to form the flame-retardant layer 3 containing insulating particles 1 so as to completely cover the surface of the base fiber 6. However, flame retardancy can also be enhanced by forming the flame-retardant layer 3 in an island pattern, as shown in FIG. 3. As mentioned above, ultrafine aerogel particles are suitable for the insulating particles 1. However, this is not limiting. Any fine particles having flame retardancy and a particle diameter sufficiently smaller than the diameter of the matrix fiber may be used.

[0114] [Embodiment 4] A method for producing a flame-retardant fiber according to embodiment 3 will now be described. Fig. 5 is a flow chart showing an example of a method for producing a flame-retardant fiber according to one embodiment of the present invention. A production method (a) in which heat insulating particles 1 are vapor-deposited onto the surface of a base fiber 6, and a production method (b) in which heat insulating particles 1 are powdered onto the surface of a base fiber 6 are shown.

[0115] (a) A method for producing a flame-retardant fiber by vapor-depositing heat insulating particles 1 onto the surface of a base fiber 6 includes the following steps.

[0116] First step (S11): A suspension containing heat insulating particles is prepared by dispersing the heat insulating particles 1. As in S1, if the heat insulating particles 1 are hydrophilic, they are dispersed in water, and if they are hydrophobic, they are dispersed in alcohol. Step 2 (S12): Prepare a binder solution by dissolving a binder. As in step S2, a suitable binder is PVA powder. The PVA powder is added to room temperature water, heated to about 80°C, stirred, and dissolved, and then returned to room temperature. Third step (S13): The suspension containing the heat insulating particles prepared in the first step (S11) is mixed with the binder solution prepared in the second step (S12) to prepare a slurry. Fourth step (S14): The slurry prepared in the third step (S13) is evaporated as an evaporation source onto the base fiber 6. The base fiber 6 may be in any form such as a sheet, blanket, pad, or cotton, or may be in a defibrated state.

[0117] This provides a manufacturing method for imparting higher flame retardancy to the base fiber. The vapor deposition in the fourth step (S14) is preferably ultrasonic vapor deposition or thermal vapor deposition. This allows the heat insulating particles 1 to be adhered to the surface of the base fiber 6 more efficiently. Here, "more efficiently" means that a larger amount of heat insulating particles 1 can be adhered with a smaller amount of consumption. Instead of vapor deposition in the fourth step (S14), a step of spraying the slurry prepared in the third step (S13) or immersing the base fiber 6 in a sheet or blanket form and then lifting it up and drying it can also be used.

[0118] When the surface of insulating fine particles (ultrafine aerogel particles) is modified with trimethylsiloxy groups or other hydrophobic groups, they exhibit strong hydrophobicity, but have a high affinity for alcohol (e.g., ethanol). Therefore, ethanol was used as the medium in the first step (S1). The fine particles can be any material other than ultrafine aerogel particles that exhibits heat resistance and hydrophobicity. Generally, hydrophobic fine particles have a high affinity for alcohol and can be dispersed uniformly, so other heat-resistant hydrophobic fine particles and a suitable medium can be used instead. On the other hand, if the insulating fine particles (ultrafine aerogel particles) are hydrophilic, there is no need to use alcohol (ethanol); water can be used as the medium in the first step (S1).

[0119] In the prepared slurry, the blending ratio of water, alcohol (e.g., ethanol), fine particles, and binder (e.g., PVA) is optimized through experiments, etc., depending on the target specifications. For example, increasing the amount of PVA binder increases the adhesion of the fine particles, but tends to decrease flame retardancy.

[0120] (b) A method for producing a flame-retardant fiber in which the heat insulating particles 1 are powdered onto the surface of the base fiber 6 includes the following steps.

[0121] Fifth step (S15): A binder solution is prepared by dissolving the binder. As in steps S2 and S12, a suitable binder is PVA powder, for example. The PVA powder is added to room-temperature water, heated to approximately 80°C, and stirred until dissolved. The mixture is then returned to room temperature. Sixth step (S16): The binder solution prepared in the fifth step (S15) is vapor-deposited onto the base fiber 6 as an evaporation source. Seventh step (S17, powdering step): The insulating microparticles 1 are mechanically applied to the base material fibers 6 on whose surfaces the binder solution has been attached in the sixth step (S16). Mechanical application means that the insulating microparticles 1 are mixed and stirred with the base material fibers 6 while the surfaces of the base material fibers 6 are wet, i.e., while the deposited binder solution is not yet dry, thereby adhering the insulating microparticles 1 to the surfaces of the base material fibers 6 that are wet with the binder solution.

[0122] Another manufacturing method is provided for imparting flame retardancy to the matrix fibers.

[0123] The flame-retardant fiber can be produced by either production method (a) in which the heat insulating particles 1 are vapor-deposited onto the surface of the base fiber 6, or production method (b) in which the heat insulating particles 1 are powdered onto the surface of the base fiber 6. For the reasons explained in the fourth embodiment, ultrafine aerogel particles are particularly suitable as the heat insulating particles 1 in this case.

[0124] [Embodiment 5] A flame-retardant heat insulating sheet 100 according to one embodiment of the present invention will now be described. In the heat insulating sheet 100 shown in Fig. 1, a flame-retardant layer 3 containing heat insulating particles 1 is formed on the surface of a matrix fiber 6. The flame-retardant layer 3 containing heat insulating particles 1 may be formed so as to cover the entire surface of the matrix fiber 6, but forming the flame-retardant layer 3 in an island pattern as shown in Fig. 3 also has the effect of enhancing flame retardancy.

[0125] A method for producing the flame-retardant heat insulating sheet 100 will now be described.

[0126] FIG. 6 is a flowchart showing an example of a method for manufacturing a heat insulating sheet to which flame retardancy has been added.

[0127] In order to construct an insulating sheet 100 similar to that described in embodiments 1 and 2 using flame-retardant fiber 200 as base fiber 6 manufactured by manufacturing method (a) of vapor-depositing insulating microparticles 1 on the surface of base fiber 6 shown in embodiment 4 or manufacturing method (b) of powdering insulating microparticles 1 on the surface of base fiber 6, the following steps are carried out sequentially.

[0128] Eighth step (S21): A suspension containing heat insulating particles is prepared by dispersing heat insulating particles 1. The suspension may be the same as the suspension containing heat insulating particles prepared in the first step (S11), or the content of the heat insulating particles 1 may be optimized in consideration of the papermaking process (eleventh step, S24). Ninth step (S22): Prepare a second binder solution for the fibers by dissolving polyvinyl alcohol powder in water. This can be the binder solution prepared in the second step (S12), or the binder concentration can be optimized taking into account the papermaking process (eleventh step, S24). Tenth step (S23): The flame-retardant fiber 200 and binder fiber 7 are mixed with the second insulating microparticle-containing suspension for the fiber prepared in the eighth step (S21), and the second binder solution for the fiber prepared in the ninth step (S22) to prepare a fiber-containing suspension. Eleventh step (S24): This is a papermaking step in which the fiber-containing suspension of the tenth step (S23) is made into paper.

[0129] This makes it possible to provide a method for producing a heat insulating sheet with added flame retardancy.

[0130] In this embodiment, similarly to the first to fourth embodiments, the heat insulating particles 1 can be ultrafine aerogel particles, the matrix fibers 6 can be silica fibers, and the binder can be polyvinyl alcohol.

[0131] By using silica fiber as the matrix fiber 6, it is possible to construct a heat insulating sheet 100 as in the first and second embodiments. As shown in the third embodiment, a flame-retardant layer 3 is bonded to the matrix fiber 6 to obtain a flame-retardant fiber 200. Furthermore, by using this flame-retardant fiber as the matrix fiber 6, it is possible to impart flame retardancy to the heat insulating sheet 100. This makes it possible to realize a heat insulating sheet that is not only insulating but also heat-resistant and flame-retardant, and can withstand high-temperature flames of 1000°C or more. Such a heat insulating sheet can be used to shield adjacent battery cells or battery modules in a battery constructed by integrating a large number of battery cells, thereby preventing thermal runaway.

[0132] [Embodiment 6] In this embodiment, another embodiment of the heat insulating sheet according to the present invention will be described. The difference from the heat insulating sheet 100 shown in FIG. 1 is that, as shown in FIG. 11, at least some of the heat insulating particles 14 are embedded in the matrix fibers 300 that constitute the heat insulating sheet. That is, the matrix fibers 300 are fibers made of thermoplastic resin 8, and the heat insulating particles 14 are mixed and present in this thermoplastic resin 8. If the particle diameter of the heat insulating particles 14 is relatively large and / or the amount of the heat insulating particles 14 is relatively large relative to the amount of thermoplastic resin 8, the heat insulating particles 14 may be present on the surface of the matrix fibers 300 with some of the heat insulating particles 14 exposed from the thermoplastic resin 8. Alternatively, if the particle diameter of the heat insulating particles 14 is sufficiently smaller than the diameter of the matrix fibers 300 or the amount of the heat insulating particles 14 is relatively small relative to the amount of thermoplastic resin 8, the heat insulating particles 14 may be completely embedded in the thermoplastic resin 8, and no heat insulating particles 14 may be present on the surface of the matrix fibers 300.

[0133] Examples of thermoplastic resins include known thermoplastic resins that can be used as materials for chemical fibers, such as polyethylene terephthalate (PET), polybutylene terephthalate (PBT), aromatic polyesters mainly composed of polyalkylene terephthalate, aliphatic polyesters such as polylactic acid, polyesters such as polylactic acid, as well as polyamides, polyurethanes, polyolefins, etc. These thermoplastic resins can be used alone or in combination of two or more.

[0134] Furthermore, as the thermoplastic resin, for example, recycled resin obtained by remelting a thermoplastic resin molded product such as a PET bottle and molding it into pellets or powder may be used.

[0135] The heat insulating sheet of this embodiment is formed by weaving and knitting threads made of the base fiber 300. The base fiber 300 can be spun by any known spinning method described below.

[0136] Furthermore, the yarns can be woven or knitted by any known method. In this embodiment, "woven or knitted" means weaving yarns to form a woven fabric or knitting yarns to form a knitted fabric. Examples of woven fabrics include any known weaves such as plain, twill, satin, amundsen, and double weave. Examples of knitted fabrics include any known knitted fabrics such as jersey, smooth, half, and double raschel.

[0137] The insulating sheet of this embodiment is woven and knitted from yarn in which insulating microparticles 14 are mixed into the base fiber 300, so that an insulating sheet with high insulating properties can be obtained without supporting the insulating microparticles 14 with a binder.

[0138] [Embodiment 7] In this embodiment, another embodiment of the heat insulating sheet according to the present invention will be described. The heat insulating sheet of this embodiment uses matrix fibers similar to the matrix fibers 300 shown in the sixth embodiment. That is, the matrix fibers contain a thermoplastic resin, the heat insulating particles are present in a state where they are at least partially embedded in the thermoplastic resin of the matrix fibers, and the sheet body is a heat insulating sheet formed by the matrix fibers being bonded to each other with a film formed by melting the thermoplastic resin.

[0139] The matrix fibers of this embodiment contain a thermoplastic resin, which allows them to be easily melted by heat, etc., and therefore the matrix fibers can be bonded together with a film formed by melting the thermoplastic resin without using binder fibers, and formed into a sheet. Also, as in the sixth embodiment, since the matrix fibers contain heat-insulating particles, a heat-insulating sheet with high heat insulation properties can be obtained without using a binder to support the heat-insulating particles.

[0140] Alternatively, the matrix fibers of this embodiment may be used in place of the matrix fibers of embodiment 1 to produce a heat insulating sheet by the manufacturing method of embodiment 2. That is, fibers in which heat insulating microparticles are at least partially embedded in a thermoplastic resin are used as the matrix fibers, and the heat insulating sheet is produced by a papermaking process using PVA fibers, a binder, and a suspension containing the heat insulating microparticles. Because the matrix fibers contain the heat insulating microparticles, higher heat insulating performance can be obtained.

[0141] [Embodiment 8] In this embodiment, another embodiment of a method for producing a heat insulating sheet according to the present invention will be described.

[0142] The manufacturing method of this embodiment can also be cited as an example of a method for manufacturing the heat insulating sheets shown in the above-mentioned embodiments 6 and 7. As illustrated in Fig. 12, the manufacturing method of the heat insulating sheet of this embodiment includes the following steps.

[0143] Twelfth step (S25): A step of mixing a thermoplastic resin with heat insulating fine particles to obtain a fine particle-containing resin. Thirteenth step (S26): A step of placing the microparticle-containing resin in a container having fine holes, rotating the container while heating it, and ejecting the microparticle-containing resin from the fine holes to obtain short fibers. Fourteenth step (S27): A step of forming the short fibers into a sheet.

[0144] In the twelfth step, a resin containing microparticles may be prepared in advance by heating and melting the thermoplastic resin, adding the insulating microparticles thereto, and mixing the mixture by stirring while heating, and then crushing the resin and adding it to the container and melting it again. This allows the insulating microparticles to be dispersed relatively uniformly in the thermoplastic resin.

[0145] Alternatively, the microparticle-containing resin may be obtained by placing the molten thermoplastic resin and the heat insulating microparticles together in a container, etc. In this case, the thermoplastic resin and the heat insulating microparticles are not completely mixed together to form the microparticle-containing resin.

[0146] 13, the microparticle-containing resin 9 obtained in Step 12 is placed in a container 400 with fine holes disposed in a chamber C, and the container 400 is heated while being rotated by a motor M, causing the microparticle-containing resin 9 to be ejected by centrifugal force from the fine holes in the container 400 and sprayed onto the inner wall of the chamber C to obtain short fibers. The microparticle-containing resin may also be obtained by directly putting the molten thermoplastic resin and the insulating microparticles into the container with fine holes used in Step 13. In this case, Steps 12 and 13 are performed simultaneously.

[0147] The container is connected to a motor M by a rotating shaft 401, and is rotatable around the rotating shaft 401 by driving the motor M. The side wall of the container 400 is provided with a plurality of pores that connect the inside and outside of the container. The container 400 is heated by a heater H installed below to melt the microparticle-containing resin 9 inside, and in this state the motor M is driven to rotate the container. Centrifugal force due to the rotation acts on the microparticle-containing resin 9 inside the container 400, and the microparticle-containing resin 9 is rapidly cooled and turned into fibers as it is ejected from the pores of the container 400, and is then sprayed in the form of short fibers onto the inner wall of the chamber C. The short fibers sprayed onto the inner wall of the chamber C become fibers (cotton-like fibers) 500 in which the short fibers are entangled with each other.

[0148] In the fourteenth step, the obtained staple fibers 500 are formed into a sheet. Since the staple fibers contain a thermoplastic resin, they can be easily deformed by heating. Therefore, for example, they can be easily formed into a sheet by forming the cotton-like fibers into a sheet while heating them. Alternatively, the staple fibers can be spun by a known spinning method as in the sixth embodiment, and the resulting yarn can be woven or knitted into a sheet.

[0149] [Embodiment 9] In this embodiment, another embodiment of a method for producing a heat insulating sheet according to the present invention will be described.

[0150] The manufacturing method of this embodiment can also be cited as an example of a method for manufacturing the heat insulating sheet shown in the above-mentioned embodiment 6. A manufacturing method of a heat insulating sheet according to yet another embodiment of the present invention comprises the following steps, as exemplified in Figure 14.

[0151] Fifteenth step (S28): A step of melting a thermoplastic resin and mixing the melted thermoplastic resin with heat insulating fine particles to prepare a fine particle-containing resin. Sixteenth step (S29): A step of extruding the molten fine particle-containing resin through pores to obtain fibers. Seventeenth step (S30): A step of spinning the fibers to obtain yarn. Eighteenth step (S31): A step of weaving and knitting the yarn.

[0152] The fifteenth step can be carried out in the same manner as the twelfth step (S25 in FIG. 12) in the eighth embodiment.

[0153] In the 16th step, the molten microparticle-containing resin is extruded through the pores to obtain fibers. The extrusion method for obtaining fibers can be, for example, a method in which a molten microparticle-containing resin 601 is extruded into a cooled atmosphere (by blowing cold air) using a spinning apparatus 600 as shown in Fig. 15 to form a plurality of fibers, and then the fibers are twisted and spun (melt spinning method), a method in which a microparticle-containing resin is extruded into a solidifying liquid rather than a cooled atmosphere (wet spinning method), or a method in which a microparticle-containing resin is extruded into a heated atmosphere rather than a cooled atmosphere (dry spinning method), or other known chemical fiber spinning methods.

[0154] The seventeenth and eighteenth steps can be carried out in the same manner as in the sixth embodiment. [Example]

[0155] Example 1 As explained in the fourth and fifth embodiments, ultrafine aerogel particles were adhered to glass wool, which is a silica fiber, to form a flame-retardant layer, and the flame-retardant layer was compared with glass wool without the flame-retardant layer.

[0156] Samples of the same thickness were cut out from a single glass wool blanket to create a glass wool blanket sample without a flame-retardant layer and a glass wool blanket sample with a flame-retardant layer. One side was heated with a Coleman mini torch 170-9105 at 1300°C for 60 seconds, and the heated side and the opposite side were observed with the naked eye and an optical microscope.

[0157] Figure 9 is a photograph of the actual product. The glass wool blanket sample without a flame-retardant layer (left side) has melted on the side that was heated by the flame (hot side), and the opposite side (cold side) has also been observed to have thinned in the center where it was heated. On the other hand, the glass wool blanket sample with a flame-retardant layer (right side) has a dent on the side that was heated by the flame (hot side), but there is no change on the opposite side (cold side).

[0158] Figure 10 shows an optical microscope photograph. It can be seen that the fibers have melted in the area of ​​the glass wool blanket sample (left side) without a flame-retardant layer that was burned by the flame on the hot side, but the glass wool blanket sample (right side) with a flame-retardant layer shows almost no change from before it was burned by the flame.

[0159] As described above, by forming a flame-retardant layer by adhering ultrafine aerogel particles, flame retardancy is imparted to the base fiber. Example 2 The short fibers used in the method for producing a heat insulating sheet shown in embodiment 8 were produced by the following method. (Amount of material) Cut pieces of plastic bottle Aerogel ultrafine particles (product name: TIISA, manufactured by Thermalytica Inc.) (Method for producing fine particle-containing resin) The cut pieces of the PET bottle and ultrafine aerogel particles were placed in a stainless steel cup and stirred while being heated with an alcohol lamp until the pieces of the PET bottle were completely melted. Heating was stopped and the mixture was cooled to room temperature to obtain a resin containing the particles.

[0160] The content of ultrafine aerogel particles in the microparticle-containing resin was adjusted to 1 mass%, 3 mass%, 4 mass%, and as a control, no ultrafine aerogel particles (0 mass%). The cooled microparticle-containing resin was hit with a hammer to break up any lumps. (Method of producing short fibers) A small hole was drilled in the side of a 350 ml aluminum beverage bottle and set in the device shown in Figure 16. The size of the hole was 2 mm.

[0161] Each resin containing microparticles was placed in a bottle, and while heated with a Bunsen burner, a motor was driven to rotate the bottle. The rotation speed was 1493 rpm (motor voltage 0.7 V). While the bottle was rotating, the resin containing microparticles in the bottle was sprayed out from the holes, and the cotton-like short fibers adhering to the inner wall of the box were collected. (Observation of short fibers) The collected short fibers were observed as follows.

[0162] Several fibers were taken from the short fibers and fixed upright in a cylindrical plastic container approximately 20 mm in diameter and 20 mm in height. A homogeneous mixture of epoxy and hardener was poured into the container, and the mixture was allowed to harden, completely fixing the fiber sample. Once the epoxy had hardened, the fiber sample was thinly cut from the side of the container and the cut surface was polished. The surface to be observed was coated with platinum to make it conductive, and a sample for SEM observation was obtained. The sample was observed using a Schottky field emission scanning electron microscope (JSM-7900F, manufactured by JEOL Ltd.).

[0163] The observation results are shown in Figure 17. In Figure 17, the areas surrounded by white circles in each of the 200x magnification photographs are the cross-sections of the short fibers. In each of the 1000x magnification photographs, the areas surrounded by black circles are the ultrafine aerogel particles in the short fibers. In the 1000x magnification photographs, white lumps are visible in the 1% and 4% by mass fibers, which are not visible in the control fibers that do not contain ultrafine aerogel particles. These lumps represent ultrafine aerogel particles, and therefore indicate that fibers containing ultrafine aerogel particles were obtained.

[0164] The invention made by the inventor has been specifically described above based on an embodiment, but it goes without saying that the invention is not limited thereto and can be modified in various ways without departing from the spirit of the invention. [Industrial Applicability]

[0165] The present invention can be suitably used for a heat insulating sheet and a method for manufacturing the same, a heat insulating fiber and a method for manufacturing the same, and a fiber-containing suspension used in manufacturing a heat insulating sheet. [Explanation of symbols]

[0166] 1. Heat insulating particles (e.g., ultrafine aerogel particles) 2. Binder (e.g., PVA) 3. Flame-retardant layer 4. Binder layer 6 Base fiber (e.g., silica fiber) 7. Binder fiber (e.g., PVA fiber) 8 Thermoplastic resin 9 Resin containing fine particles 11 Primary particles 12 Secondary particles (aggregates of primary particles, clusters) 13 Aerogel fine powder (powder with a skeleton formed by secondary particles) 14 Fine particles whose skeleton is formed by primary particles (e.g., aerogel ultrafine particles) 100 Heat Insulation Sheet 200 Flame-retardant fiber 300 Base Fiber

Claims

1. A heat insulating sheet comprising matrix fibers and heat insulating particles, the matrix fibers are bonded or woven together to form a sheet; The heat insulating particles are present inside and / or outside the base material fibers, The heat insulating fine particles are made from an aerogel having a three-dimensional network structure whose skeleton is made up of clusters that are aggregates of primary particles, and are fine particles having a three-dimensional network structure whose skeleton is made up of the primary particles, with 50% or more of the volume of the fine particles being dispersed with a mode of particle diameter of 0.1 μm or more and 1.0 μm or less, The matrix fibers are silica fibers, the sheet body includes the base fiber, binder fiber, and a binder; the matrix fibers are bonded to one another by a film formed by dissolving the binder fibers, and the heat insulating particles are carried in the gaps between the bonded matrix fibers by the binder. Insulating sheet.

2. In claim 1, The heat insulating particles are bonded to the surface of the base fiber by the binder. Insulating sheet.

3. In claim 1, the matrix fibers include a thermoplastic resin; the heat insulating particles are present in a state where at least a part of them is embedded in the thermoplastic resin in the matrix fiber, The sheet body is formed by weaving or knitting yarns spun from the base fiber. Insulating sheet.

4. In claim 1, the matrix fibers include a thermoplastic resin; the heat insulating particles are present in a state where they are at least partially embedded in the thermoplastic resin of the matrix fiber; The sheet body is formed by bonding the base fibers to each other with a film formed by melting the thermoplastic resin. Insulating sheet.

5. A method for manufacturing a heat insulating sheet, a step of dispersing heat insulating fine particles to prepare a heat insulating fine particle-containing suspension; Dissolving a binder to prepare a binder solution; a step of preparing a fiber-containing suspension by mixing the heat insulating microparticle-containing suspension, the binder solution, base fibers, and binder fibers; and removing the liquid component from the fiber-containing suspension to form a sheet body, the binder fibers are binder fibers that bind the base fibers to each other with a film formed by dissolving the binder fibers; the binder is a binder that supports the heat insulating fine particles in gaps between the base material fibers, the matrix fibers are silica fibers; The heat insulating fine particles are made from an aerogel having a three-dimensional network structure whose skeleton is made up of clusters that are aggregates of primary particles, and are fine particles having a three-dimensional network structure whose skeleton is made up of the primary particles, with 50% or more of the volume of the fine particles being dispersed with a particle diameter of 0.1 μm or more and 1.0 μm or less as a mode. A manufacturing method for heat insulating sheets.

6. In claim 5, the heat insulating fine particles are hydrophobic, and the heat insulating fine particle-containing suspension contains alcohol; A manufacturing method for heat insulating sheets.

7. A method for manufacturing a heat insulating sheet, a step of dispersing heat insulating fine particles to prepare a suspension containing heat insulating fine particles; Dissolving a binder to prepare a binder solution; A step of preparing a fiber-containing suspension by mixing heat insulating fibers, binder fibers, the heat insulating microparticle-containing suspension, and the binder solution; and removing the liquid component from the fiber-containing suspension to form a sheet body, The insulating fiber is The insulating particles for the fibers are bonded to the surface of the base fiber by a binder for the fibers, The heat insulating fine particles for fibers are made from aerogel having a three-dimensional network structure with a skeleton formed of clusters that are aggregates of primary particles, and are fine particles having a three-dimensional network structure with a skeleton formed of the primary particles, with 50% or more of the volume of the fine particles dispersed with a mode of particle diameter of 0.1 μm or more and 1.0 μm or less, the matrix fibers are silica fibers; The binder fibers are binder fibers that bind the heat insulating fibers to each other with a film formed by dissolving the binder fibers. A manufacturing method for heat insulating sheets.

8. In claim 7, The insulating particles for the fibers and the binder for the fibers are deposited on the surface of the base fiber by ultrasonic deposition or thermal deposition; A manufacturing method for heat insulating sheets.

9. In claim 7, the heat insulating fine particles are hydrophobic, and the heat insulating fine particle-containing suspension contains alcohol; A manufacturing method for heat insulating sheets.

10. A suspension containing heat insulating particles, in which heat insulating particles are dispersed in a solvent, a binder solution, heat insulating fibers, and binder fibers for binding the heat insulating fibers to each other are mixed together, The insulating fiber is The insulating particles for the fibers are bonded to the surface of the base fiber by a binder for the fibers, The heat insulating fine particles for fibers are made from aerogel having a three-dimensional network structure with a skeleton formed of clusters that are aggregates of primary particles, and are fine particles having a three-dimensional network structure with a skeleton formed of the primary particles, with 50% or more of the volume of the fine particles dispersed with a mode of particle diameter of 0.1 μm or more and 1.0 μm or less, The matrix fibers are silica fibers. Fiber-containing suspension for the production of insulating sheets.

11. A method for producing a thermal insulating fiber in which thermal insulating particles are bonded to the surface of a base fiber by a binder, The heat insulating fine particles are made from an aerogel having a three-dimensional network structure whose skeleton is made up of clusters that are aggregates of primary particles, and are fine particles having a three-dimensional network structure whose skeleton is made up of the primary particles, with 50% or more of the volume of the fine particles being dispersed with a mode of particle diameter of 0.1 μm or more and 1.0 μm or less, the matrix fibers are silica fibers; a step of dispersing the heat insulating fine particles to prepare a heat insulating fine particle-containing suspension; Dissolving a binder to prepare a binder solution; a step of mixing the heat insulating fine particle-containing suspension with the binder solution to prepare a slurry; and depositing the slurry as an evaporation source onto the base fiber. Method for manufacturing insulating fibers.

12. A method for producing a thermal insulating fiber in which thermal insulating particles are bonded to the surface of a base fiber by a binder, The heat insulating fine particles are made from an aerogel having a three-dimensional network structure whose skeleton is made up of clusters that are aggregates of primary particles, and are fine particles having a three-dimensional network structure whose skeleton is made up of the primary particles, with 50% or more of the volume of the fine particles being dispersed with a mode of particle diameter of 0.1 μm or more and 1.0 μm or less, the matrix fibers are silica fibers; Dissolving a binder to prepare a binder solution; depositing the binder solution onto the base fiber as an evaporation source; and mechanically applying heat insulating particles to the base material fibers having the binder solution attached to their surfaces by the vapor deposition. Method for manufacturing insulating fibers.

13. In claim 11, The deposition performed in the deposition step is ultrasonic deposition or thermal deposition. Method for manufacturing insulating fibers.

14. In claim 11, the heat insulating fine particles are hydrophobic, and the heat insulating fine particle-containing suspension contains alcohol; Method for manufacturing insulating fibers.

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