Insulation sheet and method for manufacturing same, insulation fibers and method for manufacturing same, and fiber-containing suspension used to manufacture insulating sheet

Abstract

The thermally insulating sheet according to the present invention is a thermally insulating sheet containing matrix fibers and thermally insulating particles, wherein the matrix fibers are bonded or woven to each other to form a sheet body, and the thermally insulating particles are present inside and / or outside of the matrix fibers. A thermally insulating sheet of an embodiment is a thermally insulating sheet containing matrix fibers, binder fibers, and a binding agent, wherein the matrix fibers are bonded to each other by a film made by the melted binder fibers, and the thermally insulating particles are carried by the binding agent in gaps between the bonded matrix fibers. The thermally insulating fibers according to the present invention are present with thermally insulating particles at least partially embedded in the matrix fibers. The thermally insulating particles are formed from an aerogel having a three-dimensional network structure, the framework of which is formed of clusters that are aggregates of primary particles, have a three-dimensional network structure, the framework of which is formed of the primary particles, and the particle diameters of 50% or more of the volume of the thermally insulating particles vary so that the mode is found between 0.1 µm and 1.0 µm, and the matrix fibers include thermoplastic resin.

Description

Technical Field

[0001] The present invention relates to a thermally insulating sheet and a method for producing the same, a thermally insulating fiber and a method for producing the same, and a fiber-containing suspension used for the production of a thermally insulating sheet.Background Art

[0002] Materials having thermally insulating properties and heat resistance are attracting attention as a measure against global warming. For example, a battery in which many battery cells are integrated employs a structure where thermally insulating sheets are placed between adjacent cells to reduce an effect of overheating of some cells on the adjacent cells. To prevent overheating of the cells causing thermal runaway, the thermally insulating sheets placed in-between are required to be heat-resistant, and also be flame-retardant and fire-resistant in case of firing. Also, to increase the amount of energy stored per battery volume, the thermally insulating sheet is required to be as thin as possible. Thus, thermally insulating sheets are required to achieve the required thermally insulating properties and flame retardancy and to be as thin as possible at the same time.

[0003] PTL 1 discloses resin-coated flame-retardant fiber yarn. Flame-retardant fiber yarn is coated with two resin-coated layers with the outer layer containing titanium dioxide particles, whereby translucency, thermal insulation, and flame retardance are to be achieved. The method for producing the same is described as follows. A resin solution containing a titanium dioxide-free adhesive resin is applied to a glass fiber bundle, which is flame-retardant fiber yarn, and then an excessive resin solution is squeezed, followed by heating to form an inner resin-coated layer. Next, a resin solution containing titanium dioxide is applied to the glass fiber bundle with the inside resin-coated layer formed thereon, and then an excessive resin solution is squeezed, followed by heating to form a resin layer containing titanium dioxide outside the inside resin-coated layer (for details, see paragraphs 0026 to 0045 of PTL 1). A woven fabric is to obtained by weaving the thus-obtained resin-coated flame-retardant fiber yarn used as the warp and the woof (for details, see paragraph 0046 of PTL 1).

[0004] PTL 2 discloses a lightweight, thermal- and sound-insulating material having thermally insulating properties and excellent sound insulation properties. The material has, as a basic structure, a cell in which an aggregate of silica aerogel particles is surrounded by a network of organic nanofibers with anionic functional groups, and a solid composite with a three-dimensional continuous structure of multiple closely packed cells is formed inside a non-woven fabric or continuous cell foam, which is said to be lightweight and have excellent sound insulation properties.

[0005] PTL 3 discloses aerogel ultrafine particles characterized in containing fine particles that are made from aerogel having three-dimensional network structure of which framework is formed of clusters, which are aggregates of primary particles. This PTL 3 is an invention by the inventors of this application and is commercially called as TIISA ®< (a registered trademark of Thermalytica Inc.). Aerogel ultrafine particles have thermal conductivity equivalent to that of high-performance aerogel and a bulk density of 0.01 g / cm 3< or less, which is about one-tenth or smaller than that of general aerogel. This means that the aerogel ultrafine particles are lightweight, high-performance insulating material. While a framework of a general aerogel is formed of secondary particles, the framework of aerogel ultrafine particles is formed mainly of primary particles that make up the secondary particles, whereby the aerogel ultrafine particles are extremely ultrafine particles and the particle diameters of 50% or more of the volume of the thermally insulating particles vary so that the mode is found between 0.1 µm and 1.0 µm.

[0006] PTL 4 discloses a fiber-reinforced thermoplastic resin sheet and silica nanoparticle-carrying glass fiber nonwoven fabric. The fiber-reinforced thermoplastic resin sheet comprises a thermoplastic matrix resin and silica nanoparticles with average primary particle size ranging from 1 nm to 100 nm contained in the glass fibers.

[0007] PTL 5 discloses an insulating material that is said to have high strength and excellent thermally insulating properties. The insulating material comprises aerogel particles, an adhesive to bond the same, and a composite adhesive coated in which a thermal bonding adhesive component is coated by a protective film.CITATION LISTPatent Document

[0008] PTL 1: International Publication WO2013 / 136552 PTL 2: Japanese Patent Application Laid-Open No. 2022-41332 PTL 3: International Publication WO2022 / 107365 PTL 4: Japanese Patent Application Laid-Open No. 2018-95673 PTL 5: Japanese Patent Application Laid-Open No. 2015-124779 SUMMARY OF THE INVENTIONProblems to be Solved by the Invention

[0009] A principal object of the present invention is to provide a thermally insulating sheet with high thermally insulating properties. Another object of the present invention is to add further flame retardancy to the thermally insulating sheet. A further object of the present invention is to provide a fiber-containing suspension and a thermally insulating fiber suitable for the production of such a thermally insulating sheet.

[0010] Means for solving these problems will be described below, but other issues and novel features will become apparent from the description herein and the accompanying drawings.Means for Solving Problems

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

[0012] That is, a thermally insulating sheet according to the present invention is a thermally insulating sheet containing matrix fibers and thermally insulating particles, wherein the matrix fibers are bonded or woven / knitted to each other to form a sheet body, and the thermally insulating particles are present inside and / or outside of the matrix fibers.

[0013] A method for producing a thermally insulating sheet according to the present invention comprises the steps of: preparing a thermally insulating particle-containing suspension by dispersing thermally insulating particles, preparing a binding agent solution by dissolving a binding agent, preparing a fiber-containing suspension by mixing the thermally insulating particle-containing suspension, the binding agent solution, the matrix fibers, and a binder fiber, and forming a sheet body by removing a liquid component from the fiber-containing suspension (i.e., papermaking).

[0014] Another method for producing a thermally insulating sheet according to the present invention comprises: obtaining a particle-containing resin by mixing thermoplastic resin and thermally insulating particles, obtaining short fibers by storing the particle-containing resin in a container having fine holes disposed in a chamber, and by rotating the container while heating it to eject the particle-containing resin from the fine holes, and forming the short fibers into a sheet,

[0015] Yet another method for producing a thermally insulating sheet according to the present invention comprises: preparing a particle-containing resin by melting thermoplastic resin and mixing the melted thermoplastic resin with thermally insulating particles, obtaining fibers by extruding the melted particle-containing resin from fine holes, obtaining yarn by spinning the fibers, and weaving / knitting the yarn.

[0016] The fiber-containing suspension for the production of a thermally insulating sheet according to the present invention is produced by mixing the thermally insulating particle-containing suspension in which thermally insulating particles are dispersed in a solvent, and a binding agent solution, matrix fibers, and binder fibers.

[0017] Yet another fiber-containing suspension for the production of a thermally insulating sheet according to the present invention, wherein: the thermally insulating particle-containing suspension in which thermally insulating particles are dispersed in a solvent, a binding agent solution, thermally insulating fibers, and binder fibers are mixed, the thermally insulating fibers have thermally insulating particles for fibers bonded to surfaces of matrix fibers by a binding agent for fibers, the thermally insulating particles for fibers are formed from an aerogel having a three-dimensional network structure, the framework of which is formed of clusters that are aggregates of primary particles, have a three-dimensional network structure, the framework of which is formed of the primary particles, and the particle diameters of 50% or more of the volume of the thermally insulating particles vary so that the mode is found between 0.1 µm and 1.0 µm, and the matrix fibers are silica fibers.

[0018] The thermally insulating fibers according to the present invention have thermally insulating particles bonded to surfaces of matrix fibers by a binding agent, the thermally insulating particles are formed from an aerogel having a three-dimensional network structure, the framework of which is formed of clusters that are aggregates of primary particles, have a three-dimensional network structure, the framework of which is formed of the primary particles, and the particle diameters of 50% or more of the volume of the thermally insulating particles vary so that the mode is found between 0.1 µm and 1.0 µm, and the matrix fibers are silica fibers.

[0019] Another thermally insulating fiber according to the present invention, wherein: thermally insulating particles are present at least partially embedded in the matrix fibers, the thermally insulating particles are formed from an aerogel having a three-dimensional network structure, the framework of which is formed of clusters that are aggregates of primary particles, have a three-dimensional network structure, the framework of which is formed of the primary particles, and the particle diameters of 50% or more of the volume of the thermally insulating particles vary so that the mode is found between 0.1 µm and 1.0 µm, and the matrix fibers include thermoplastic resin.

[0020] A method for producing thermally insulating fiber according to the present invention is the method for producing thermally insulating fiber according to the present invention, comprising the steps of: preparing a thermally insulating particle-containing suspension by dispersing the thermally insulating particles; preparing a binding agent solution by dissolving a binding agent; preparing a slurry by mixing the thermally insulating particle-containing suspension and the binding agent solution, depositing the slurry on the matrix fibers as an evaporation source.

[0021] Another method for producing thermally insulating fiber according to the present invention is the method for producing thermally insulating fiber according to the present invention, comprising the steps of: preparing a binding agent solution by dissolving a binding agent; depositing the binding agent solution on the matrix fibers as an evaporation source, mechanically applying thermally insulating particles to the matrix fibers with the binding agent solution adhered to the surface by vapor deposition.

[0022] The term "to disperse (the particles)" means to put the particles into a liquid and disperse them in the liquid, not to dissolve them. The term "a papermaking step (a step of forming a sheet body)" includes a step of spreading a suspension containing matrix fibers thinly, removing excess liquid, and drying to form a sheet body. In this specification, "polyvinyl alcohol" may be abbreviated as "PVA", "polyvinyl alcohol fiber" as "PVA fiber," and "polyvinyl alcohol powder" as "PVA powder.Effect of the Invention

[0023] The effect to be produced by the above-described embodiment will be briefly described below.

[0024] That is, it is possible to provide a thermally insulating sheet with high thermally insulating properties, a thermally insulating fiber suitable for adding flame retardancy to that thermally insulating sheet, and a fiber-containing suspension suitable for the production of that thermally insulating sheet.BRIEF DESCRIPTION OF THE DRAWINGS

[0025] FIG. 1 is an explanatory view of an example structure of a thermally insulating sheet according to an embodiment of the present invention. FIG. 2 is an explanatory view showing relationships in length between matrix fibers and a binder fiber. FIG. 3 is an explanatory view of an example structure of a flame-retardant fiber with thermally insulating particles bonded to a surface of a matrix fiber. FIG. 4 is a flowchart of an example method for producing a thermally insulating sheet according to an embodiment of the present invention. FIG. 5 is a flowchart of an example method for producing a flame-retardant fiber according to an embodiment of the present invention. FIG. 6 is a flowchart showing an example method for producing a thermally insulating sheet with flame retardancy added. FIG. 7 is an explanatory view showing a structure of aerogel ultrafine particles, an example of thermally insulating particles. FIG. 8 is an explanatory view showing particle size distribution of aerogel ultrafine particles, an example of thermally insulating particles. FIG. 9 is a photograph of an actual piece of glass wool coated with a flame-retardant layer containing aerogel ultrafine particles, showing the results of an experiment in which the glass wool was roasted with a flame. FIG. 10 is an optical micrograph showing the results of an experiment in which glass wool coated with a flame-retardant layer containing aerogel ultrafine particles was roasted with a flame. FIG. 11 is an explanatory view of an example matrix fiber composed of a mixture of thermoplastic resin and thermally insulating particles. FIG. 12 is a flowchart of an example method for producing a thermally insulating sheet according to Embodiment 8. FIG. 13 is an explanatory view of an example structure of an apparatus for producing matrix fibers of a thermally insulating sheet according to Embodiment 8. FIG. 14 is a flowchart showing an example method for producing a thermally insulating sheet according to Embodiment 9. FIG. 15 is a schematic view of a known spinning apparatus. FIG. 16 is a schematic view of an apparatus used in Examples. FIG. 17 is scanning electron microscope (SEM) photographs showing the experimental results. DETAILED DESCRIPTION OF THE INVENTION1. Outline of Embodiment

[0026] First, an outline of a typical embodiments disclosed in the present application will be given. Reference numerals in the drawings that are referred to in parentheses in the outline of the typical embodiments are merely illustrative of what is included in the concept of components to which they refer.[1] Thermally insulating sheet carrying thermally insulating particles (FIG. 1, FIG. 11)

[0027] A thermally insulating sheet (100) described in this embodiment is a thermally insulating sheet (100) containing matrix fibers (6, 300) and thermally insulating particles (1, 14), wherein the matrix fibers (6, 300) are bonded or woven / knitted to each other to form a sheet body, and the thermally insulating particles (1, 14) are present inside and / or outside of the matrix fibers (6, 300).

[0028] This can realize a thermally insulating sheet with excellent thermally insulating properties.[2] Carrying aerogel ultrafine particles (FIGS. 7, 8)

[0029] In the thermally insulating sheet of [1], the thermally insulating particles are formed from an aerogel having a three-dimensional network structure, the framework of which is formed of clusters that are aggregates of primary particles, have a three-dimensional network structure, the framework of which is formed of the primary particles, and the particle diameters of 50% or more of the volume of the thermally insulating particles vary so that the mode is found between 0.1 µm and 1.0 µm.

[0030] This can realize a thinner thermally insulating sheet utilizing the small particle size of the aerogel ultrafine particles.[3] Thermally insulating sheet in which thermally insulating particles are carried in gaps between matrix fibers bonded by a film made by melted binder fibers (FIG. 1).

[0031] In the thermally insulating sheet of [1] or [2], the matrix fibers are silica fibers, a thermally insulating sheet (100) containing matrix fibers (6), binder fibers (7), and a binding agent (2, but not shown in FIG. 1), wherein: the matrix fibers are bonded to each other by a film made by the melted binder fibers, and the thermally insulating particles (1) are carried by the binding agent in gaps between the bonded matrix fibers.

[0032] This can realize a thinner thermally insulating sheet.[4] Addition of flame retardancy (FIG. 3)

[0033] In the thermally insulating sheet of [3], the thermally insulating particles are bonded to surfaces of the matrix fibers by the binding agent.

[0034] Thus, with the presence of the thermally insulating particles on the surface of the matrix fiber, in addition to thermally insulating properties, flame retardancy can be added to make the entire thermally insulating sheet flame retardant. The term "flame retardancy added" as used herein refers to the fact that some kind of processing of a specific material makes the material more difficult to burn than it was before the processing.[5] Thermally insulating sheet formed by weaving / knitting matrix fibers carrying thermally insulating particles embedded in thermoplastic resin (FIG. 11)

[0035] In the thermally insulating sheet of [1] or [2], the matrix fibers (300) contain thermoplastic resin (8), the thermally insulating particles (14) are present at least partially embedded in the thermoplastic resin (8) in the matrix fibers (300), and the sheet body is woven / knitted from yarns spun from the matrix fibers (300).

[0036] The matrix fiber (300) is a thermally insulating sheet made by spinning yarn by a known spinning method, and weaving or knitting the spun yarn by a known method to form a sheet body.

[0037] This can realize a thermally insulating sheet with high thermally insulating properties without the use of a binding agent.[6] Thermally insulating sheet formed by matrix fibers in which thermally insulating particles are embedded in thermoplastic resin, bonded by a film made by melted thermoplastic resin (FIG. 11)

[0038] In the thermally insulating sheet of [1] or [2], the matrix fibers (300) contain thermoplastic resin (8), the thermally insulating particles (14) are present at least partially embedded in the thermoplastic resin (8) in the matrix fibers (300), and the sheet body is formed by the matrix fibers being bonded to each other by a film made by the melted thermoplastic resin.

[0039] This can realize a thermally insulating sheet with high thermally insulating properties without the use of a binding agent.[7] Method for producing thermally insulating sheet (FIG. 4)

[0040] A typical embodiment of the present invention is a method for producing a thermally insulating sheet, which comprises the following steps.

[0041] (S1): A step of preparing a thermally insulating particle-containing suspension by dispersing the thermally insulating particles. (S2): A step of preparing a binding agent solution by dissolving a binding agent. (S3): A step of preparing a fiber-containing suspension by mixing the thermally insulating particle-containing suspension, the binding agent solution, the matrix fibers, and binder fibers. (Papermaking step, S4): A step of forming a sheet body by removing a liquid component from the fiber-containing suspension.

[0042] This provides the method for producing a thermally insulating sheet described in [1] to [6].[8] Aerogel ultrafine particles are carried in gaps of silica fibers (FIG. 1, FIG. 4).

[0043] In the method for producing the thermally insulating sheet of [7],the matrix fibers are silica fibers, the thermally insulating particles are formed from an aerogel having a three-dimensional network structure, the framework of which is formed of clusters that are aggregates of primary particles, have a three-dimensional network structure, the framework of which is formed of the primary particles, and the particle diameters of 50% or more of the volume of the thermally insulating particles vary so that the mode is found between 0.1 µm and 1.0 µm.

[0044] This can provide a method for producing a thinner thermally insulating sheet by utilizing the small particle size of the aerogel ultrafine particles as in [2] above.[9] Production method when thermally insulating particles are hydrophobic

[0045] In the method for producing a thermally insulating sheet according to [7] or [8], the thermally insulating particles are hydrophobic and the thermally insulating particle-containing suspension contains alcohol.

[0046] This can provide a method for producing a thermally insulating sheet with high thermally insulating properties even if the thermally insulating particles are hydrophobic.

[10] Method for producing thermally insulating sheet

[0047] A method for producing a thermally insulating sheet as another embodiment of the present invention comprises the following steps.

[0048] A step of obtaining a particle-containing resin by mixing thermoplastic resin and thermally insulating particles.

[0049] A step of obtaining short fibers by storing the particle-containing resin in a container having fine holes, and by rotating the container while heating it to eject the particle-containing resin from the fine holes.

[0050] A step of forming the short fibers into a sheet.

[0051] This can produce a thermally insulating sheet carrying thermally insulating particles without the use of a binding agent.

[11] Method for producing thermally insulating sheet woven / knitted from short fibers

[0052] The method for producing the thermally insulating sheet of

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

[0053] This can produce an insulating sheet carrying thermally insulating particles that consists of a woven / knitted, relatively strong sheet.Method for producing thermally insulating sheet from short fibers by forming

[0054]

[12] In the step of forming the short fibers into a sheet in the method for producing a thermally insulating sheet in

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

[0055] This allows for simple production of a thermally insulating sheet without weaving / knitting processes.

[13] Method for producing thermally insulating sheet woven / knitted from spun yarn

[0056] A method for producing a thermally insulating sheet as yet another embodiment of the present invention comprises the following steps.

[0057] A step of preparing a particle-containing resin by melting thermoplastic resin and mixing the melted thermoplastic resin with thermally insulating particles.

[0058] A step of obtaining fibers by extruding the melted particle-containing resin from fine holes into a solidifying liquid.

[0059] A step of obtaining yarn by spinning the fibers.

[0060] A step of weaving / knitting the yarn.

[0061] This can produce an insulating sheet carrying thermally insulating particles that consists of a woven / knitted, relatively strong sheet.

[14] Method for producing thermally insulating sheet with added flame-retardant properties (FIG. 6)

[0062] A typical embodiment of the present invention is a method for producing a thermally insulating sheet, which comprises the following steps.

[0063] A step of preparing a thermally insulating particle-containing suspension by dispersing the thermally insulating particles (1).

[0064] A step of preparing a binding agent solution by dissolving a binding agent.

[0065] A step of preparing a fiber-containing suspension by mixing thermally insulating fibers, binder fibers, the thermally insulating particle-containing suspension, and the binding agent solution.

[0066] A step of forming a sheet body by removing a liquid component from the fiber-containing suspension.

[0067] Also, the thermally insulating fibers have thermally insulating particles for fibers bonded to surfaces of matrix fibers by a binding agent for fibers, the thermally insulating particles for fibers are formed from an aerogel having a three-dimensional network structure, the framework of which is formed of clusters that are aggregates of primary particles, have a three-dimensional network structure, the framework of which is formed of the primary particles, and the particle diameters of 50% or more of the volume of the thermally insulating particles vary so that the mode is found between 0.1 µm and 1.0 µm, and the matrix fibers are silica fibers.

[0068] This can provide a method for producing a flame-retardant thermally insulating sheet with high flame retardancy due to silica fibers, which are the matrix fibers.

[15] Ultrasonic deposition or thermal deposition (FIG. 6)

[0069] In the method for producing the thermally insulating sheet described in

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

[0070] This allows more efficient adhesion of thermally insulating particles (aerogel ultrafine particles) to the surface of silica fiber, which is the matrix fiber.

[16] Production method when thermally insulating particles are hydrophobic

[0071] In the method for producing a thermally insulating sheet described in

[14] , the thermally insulating particles are hydrophobic, and the thermally insulating particle-containing suspension in Step 1 and a suspension containing the thermally insulating particles for fibers contain alcohol.

[0072] This can provide a method for producing flame-retardant fibers even if the thermally insulating particles are hydrophobic.

[17] Fiber-containing suspension

[0073] A typical embodiment of the present invention is a fiber-containing suspension for the production of thermally insulating sheet, wherein a thermally insulating particle-containing suspension in which thermally insulating particles are dispersed in a solvent, a binding agent solution, matrix fibers, and binder fibers are mixed in the fiber-containing suspension, used in the above method for producing a thermally insulating sheet.

[18] Fiber-containing suspension with added flame retardancy

[0074] A typical embodiment of the present invention is a fiber-containing suspension for the production of a thermally insulating sheet used in the method for producing a thermally insulating sheet, in which the thermally insulating particle-containing suspension in which thermally insulating particles are dispersed in a solvent, a binding agent solution, thermally insulating fibers, and binder fibers are mixed, the thermally insulating fibers have thermally insulating particles for fibers bonded to surfaces of matrix fibers by a binding agent for fibers, the thermally insulating particles for fibers are formed from an aerogel having a three-dimensional network structure, the framework of which is formed of clusters that are aggregates of primary particles, have a three-dimensional network structure, the framework of which is formed of the primary particles, and the particle diameters of 50% or more of the volume of the thermally insulating particles vary so that the mode is found between 0.1 µm and 1.0 µm, and the matrix fibers are silica fibers.

[0075] This fiber-containing suspension can be provided as a raw material for a papermaking step (S4) and other steps.

[19] Flame-retardant thermally insulating fiber with aerogel ultrafine particles bonded to surface thereof (FIG. 3)

[0076] A typical embodiment of the present invention is a thermally insulating fiber (flame-retardant fiber) (200), in which flame retardancy is added to the fiber, comprised as follows. A flame-retardant fiber herein refers to a thermally insulating fiber that has flame retardancy added along with thermally insulating properties.

[0077] The thermally insulating particles (1) are bonded to surfaces of matrix fibers (6) by a binding agent (2).

[0078] Here, the thermally insulating particles are formed from an aerogel having a three-dimensional network structure, the framework of which is formed of clusters that are aggregates of primary particles, have a three-dimensional network structure, the framework of which is formed of the primary particles, and the particle diameters of 50% or more of the volume of the thermally insulating particles vary so that the mode is found between 0.1 µm and 1.0 µm. Also, the matrix fibers are silica fibers.

[0079] This can provide silica fiber, the matrix fiber, with a flame-retardant fiber with higher flame retardancy.

[20] Thermally insulating fiber with aerogel ultrafine particles bonded to surface thereof (FIG. 11)

[0080] A typical embodiment of the present invention is a thermally insulating fiber (300), comprised as follows.

[0081] Thermally insulating particles (14) are present at least partially embedded in the matrix fibers (300), the thermally insulating particles (14) are formed from an aerogel having a three-dimensional network structure, the framework of which is formed of clusters that are aggregates of primary particles, have a three-dimensional network structure, the framework of which is formed of the primary particles, and the particle diameters of 50% or more of the volume of the thermally insulating particles vary so that the mode is found between 0.1 µm and 1.0 µm, and the matrix fibers (300) contain thermoplastic resin (8).

[0082] This can provide thermally insulating fibers with added thermally insulating properties to the matrix fibers without the use of a binding agent.

[21] Method for producing flame-retardant fiber with aerogel ultrafine particles bonded to surface thereof (FIG. 5(a))

[0083] A method for producing a thermally insulating fiber (200) as described in

[19] , comprising each of the following steps.

[0084] (S11): A step of preparing a thermally insulating particle-containing suspension by dissolving thermally insulating particles (aerogel ultrafine particles). (S12): A step of preparing a binding agent solution by dissolving a binding agent. (S13): A step of preparing a slurry by mixing the thermally insulating particle-containing suspension and the binding agent solution. (S14): A step of depositing the slurry on the matrix fibers as an evaporation source.

[0085] A production method is provided for adding higher flame retardancy to a matrix fiber by depositing thermally insulating particles (aerogel ultrafine particles) contained in a slurry onto the surface of the matrix fiber.

[22] Method for producing flame-retardant fiber with aerogel ultrafine particles bonded to surface thereof (FIG. 5(b))

[0086] A method for producing a thermally insulating fiber (200) as described in

[19] , comprising each of the following steps.

[0087] (S15): A step of preparing a binding agent solution by dissolving a binding agent. (S16): A step of depositing the binding agent solution on the matrix fibers as an evaporation source. (S17, Powdering step): A step of mechanically applying thermally insulating particles to the matrix fibers with the binding agent solution adhered to the surface by vapor deposition.

[0088] This provides another production method for adding flame retardancy to matrix fibers.

[23] Ultrasonic deposition or thermal deposition (FIG. 5)

[0089] In the method for producing thermally insulating fiber described in

[21] , the deposition in Step 4 (S14) is ultrasonic deposition or thermal deposition.

[0090] This allows more efficient adhesion of thermally insulating particles (aerogel ultrafine particles) to the surface of silica fiber, which is the matrix fiber.

[24] Production method when thermally insulating particles are hydrophobic

[0091] In the method for producing flame-retardant fibers described in

[19] to

[23] , the thermally insulating particles are hydrophobic and the thermally insulating particle-containing suspension contains alcohol.

[0092] This can provide a method for producing flame-retardant fibers even if the thermally insulating particles are hydrophobic.2. Details of the embodiments

[0093] Details of the embodiments will be described in further detail.[Embodiment 1]

[0094] FIG. 1 is an explanatory view of an example structure of a thermally insulating sheet of the present invention. A thermally insulating sheet 100 of the present invention contains matrix fibers 6, binder fibers 7, and a binding agent (2, but not shown in FIG. 1); the matrix fibers 6 are bonded to each other by a film (not shown in FIG. 1) made by the melted binder fibers 7, and thermally insulating particles 1 are carried in gaps between the bonded matrix fibers 6. The reference numeral 3 will be discussed below and in more detail in Embodiments 4 and 5.

[0095] This can provide a thermally insulating sheet with high thermally insulating properties. By employing the binder fibers 7 that are very shorter in length than the matrix fibers 6, many layers of matrix fibers 6 are formed within a certain thickness, gaps are created between the matrix fibers 6 that form the layers, and many thermally insulating particles 1 can be carried in those gaps. Therefore, the thermally insulating properties of the thermally insulating sheet 1 is improved.

[0096] As the binder fiber 7, for example, polyvinyl alcohol (PVA) fiber, polyester fiber, polyester-based composite fiber, acrylic fiber, acrylic-based fiber, nylon, polyurethane fiber, polycarbonate fiber, etc., can be employed. As the binding agent, polyvinyl alcohol (PVA) powder, methylcellulose, starch glue, gum arabic glue, etc., can be employed.

[0097] The binder fiber 7 is preferably several 10 µm long. The matrix fiber 6 is, for example, a silica fiber, which is significantly longer than the binder fiber 7 by several 10 mm. While the matrix fiber 6 extends in a planar direction (the left and right direction in FIG. 1), the binder fiber 7 serves to connect the matrix fiber 6 vertically (in the thickness direction of the thermally insulating sheet 100). The matrix fibers 6 and the binder fibers 7 are bonded to each other by a film (not shown in FIG. 1) made by them melted, and gaps are formed in the bonded matrix fibers 6 in which gaps thermally insulating particles 1 are carried. For example, PVA fiber, an example of binder fiber 7, melts and forms a film when heated to 65°C to 85°C when wet with water. Here, "dissolve" means dissolution in water, not melting by heat. The matrix fiber 6, such as silica fiber, has mechanical strength, but heat conducts along the fiber, so thermally insulating properties is not expected. In the thermally insulating sheet 100, the matrix fibers 6 are long and extend in a direction parallel to the front and back surfaces of the sheet, giving the thermally insulating sheet 100 mechanical strength in the face direction. In the thickness direction, the thermally insulating particles 1 are carried in the gaps between the matrix fibers 6, as shown in FIG. 1, giving the thermally insulating sheet 100 thermally insulating properties in the thickness direction.

[0098] The appropriate length of the binder fiber 7 will be explained. In general, thermally insulating properties in the thickness direction is required for thermally insulating sheets rather than in the in-plane direction. Therefore, binder fibers from one surface of the thermally insulating sheet to the other are undesirable. This is because the thermal conductivity of binder fibers is higher than that of silica fibers, which are often used as matrix fibers, and if binder fibers reach from one surface to the other in the thickness direction of the thermally insulating sheet, heat will be conducted through those binder fibers, which will act to impair the thermally insulating properties in the thickness direction. Considering bending due to heat applied during production, the maximum length of the binder fibers should be a few millimeters, which is equivalent to the thickness of the thermally insulating sheet.

[0099] The minimum appropriate length of the binder fiber 7 is from 10 µm to several tens of 10 µm. FIG. 2 is an explanatory view showing relationships in length between the matrix fibers 6 and the binder fiber 7. When the matrix fibers 6 are adjacent to each other so that they are in contact with each other (a), the binder fiber 7 must be at least as long as the diameter of the matrix fiber 6 in order to bond the adjacent matrix fibers 6. When the matrix fibers 6 are coated with some kind of coating, and when the matrix fibers 6 are separated from each other by thermally insulating particles or other material in the gaps between the matrix fibers 6 as in the present invention (b), (c) and (d), the minimum required length of the binder fiber 7 is one to several times the distance of the matrix fibers 6 to be connected. That is, when two fibers are to be connected (b), the minimum required length of the binder fiber 7 is about equal to the distance between the matrix fibers 6, when three fibers are to be connected in a straight line (c), the minimum required length of the binder fiber 7 is about twice the distance between the matrix fibers 6, and when three fibers are to be connected in a sawing manner (d), the minimum required length of the binder fiber 7 is about three to four times the distance between the matrix fibers 6. Since the diameter of silica fibers, which are generally used as matrix fibers, is between 8 µm and 12 µm as measured by the inventors, the minimum value should be within several times the diameter of this silica fibers. The minimum value here does not mean that binder fibers of lesser lengths are not included, but only that binder fibers of lesser lengths have a smaller contribution to the purpose of bonding the matrix fibers.

[0100] As described above, strength and thermally insulating properties can be adjusted by properly designing the length of the matrix fiber 6 and the binder fiber 7.

[0101] It is suitable to employ the aerogel ultrafine particles described in PTL 3 as thermally insulating particles 1.

[0102] FIG. 7 is an explanatory view of a comparison of the structure of general aerogel fine powder and aerogel ultrafine particles of which framework is formed of primary particles. The three-dimensional network structure of general aerogel fine powder 13 is based on secondary particles 12, which is a cluster of primary particles 11 as a unit (FIG. 7(a)), whereas this aerogel ultrafine particles 14 have a three-dimensional network structure of which framework is formed of primary particles 11 (FIG. 7(b)).

[0103] The aerogels that are commonly distributed are granules, since they have a three-dimensional network structure of which framework is formed of secondary particles 12 as a unit. Therefore, the structure of the framework does not change when this is pulverized into smaller pieces using a pulverizer. The following are the results of the experiments. FIG. 8 is an explanatory view showing, from the bottom to the top, an example of the frequency distribution of particle size for aerogel granules, aerogel powder, aerogel fine powder, and aerogel ultrafine particles, which is ultrafine particles of which framework is formed of primary particles. Aerogel granules are the commonly distributed aerogel granules themselves. Aerogel powder is that produced by pulverizing aerogel granules at 5,000 to 7,000 rpm for 2 minutes using a SX08 spin-mix homogenizer manufactured by Mitsui Electric Co., Ltd. The aerogel fine powder has been attempted to further reduce the particle size by grinding aerogel granules at 21,000 rpm for 20 seconds using a STEALTH 885 manufactured by Blendtec. In FIG. 8, the particle size is plotted along the horizontal axis and the frequency distribution of the particle size is plotted along the vertical axis. The frequency is shown along the vertical axis on the right and the integrated value long the vertical axis on the left. FIG. 8 shows observational results using a laser diffraction particle size distribution (PSD) measurement device. In this specification, the particle size is described as measured in PSD measurement. In the PSD measurement, however, not only the diameter of the particles themselves but also the agglomeration of particles is observed as a particle size, so the true particle size is likely to be smaller than the measured value. Any difference in particle size depending on the measurement method should be conversed and understood. More specifically, FIG. 8 shows the particle size distribution using a Laser Diffraction Particle Size Analyzer SALD-2300 manufactured by Shimadzu Corporation. Particle size distribution is an indicator of what size (particle size) of particles are contained at what proportion (relative particle quantity with the total as 100%) in a group of sample particles to be measured, and the dimension (order) of the particle quantity is volume-based.

[0104] Generally distributed aerogel granules have only one peak of relative particle volume with an average particle size of about 400 µm (FIG. 8, bottom row). When the aerogel granules are pulverized using equipment as described above, the aerogel powder and aerogel fine powder have an average particle size of about 90 µm and 50 µm, respectively, each with a single peak in relative particle volume (3rd and 2nd rows). In contrast, aerogel ultrafine particles have a first peak with an average particle size of about 20 µm and a second peak with an average particle size of about 0.3 µm, and the relative particle volume is 21.2% for the first peak with an average particle size of about 20 µm and 78.8% for the second peak with an average particle size of 0.3 µm. This is because the first peak with an average particle diameter of about 20 µm is formed by ultrafine particles with a three-dimensional network structure of which framework is formed of secondary particles 12 as a unit, while the second peak with an average particle diameter of about 0.3 µm is formed by ultrafine particles with a three-dimensional network structure of which framework is formed of primary particles.

[0105] Since the framework of the three-dimensional network structure of general aerogel is formed of secondary particles, it is difficult to produce particles with a diameter of 10 µm or less, no matter how high the milling conditions are raised. To produce particles which have a three-dimensional network structure of which framework is formed of the primary particles, unlike general aerogel production processes, a fundamental change in the production method is required, such as a drastic change in aging conditions as well as the milling conditions.

[0106] In the thermally insulating sheet 100 of the present invention, it is preferable that the thermally insulating particles 1 are formed from the aerogel ultrafine particles described above, that is, aerogel having a three-dimensional network structure, the framework of which is formed of clusters that are aggregates of primary particles 11,have a three-dimensional network structure, the framework of which is formed of the primary particles, and the particle diameters of 50% or more of the volume of the thermally insulating particles vary so that the mode is found between 0.1 µm and 1.0 µm. Silica fiber is suitable as the matrix fiber 6, PVA fiber is suitable as the binder fiber, and PVA is suitable as the binding agent. As described above, silica fiber, which is a typical matrix fiber 6, is about 10 µm thick, so it does not have the size relationship to support several hundred µm aerogel granules in the gaps between the matrix fibers, and aerogel ultrafine particles of 1 µm or less are suitable for the structure to be supported in the gaps.

[0107] This can realize a thin thermally insulating sheet that takes advantage of the extremely small particle size of aerogel ultrafine particles. In the thermally insulating sheet 100 of this embodiment, even when its thickness is reduced to 3 mm or less, thermal conductivity can be improved from about 40 mW / mK to less than 30 mW / mK by employing aerogel ultrafine particles as the thermally insulating particles 1. In thermally insulating particles with a large particle size, the number of particles lined up in the thickness direction is small and the contribution of heat conduction by the shell of the particles is large when the sheet is thinned. In contract, the aerogel ultrafine particles have an extremely small particle size and their gaps (voids) in the thickness direction are larger than the particles when the sheet is thinned, resulting in smaller heat conduction by the particle shell, and also the voids prevent air convection, thereby improving thermally insulating properties.[Addition of flame retardancy]

[0108] In the thermally insulating sheet 100, the thermally insulating particles 1 should be bonded to the surface of the matrix fiber 6 by the binding agent 2. This can add flame retardancy to the matrix fiber 6 along with thermally insulating properties, making the entire thermally insulating sheet 100 flame retardant.

[0109] FIG. 3 is an explanatory view of an example structure of a flame-retardant fiber 200 (thermally insulating fiber with added flame retardancy) with thermally insulating particles bonded to a surface of a matrix fiber 6. Although it is more reliable to form the flame-retardant layer 3 containing thermally insulating particles 1 to cover the entire surface of the matrix fiber 6, the flame-retardant layer 3 in the form of islands, as shown in FIG. 3, was found to be effective in increasing flame retardancy. For example, when aerogel ultrafine particles were employed as the thermally insulating particles 1, it was possible to add flame retardancy to the extent that the surface of the thermally insulating sheet 100 could be roasted with a flame at temperatures exceeding 1000°C without burning. Details will be explained in Embodiments 3 to 5 and Examples.[Embodiment 2]

[0110] A method for producing the thermally insulating sheet 100 of Embodiment 1 will be described.

[0111] FIG. 4 is a flowchart of an example method for producing a thermally insulating sheet according to an embodiment of the present invention. The method for producing a thermally insulating sheet 100 comprises the following steps.

[0112] Step 1 (S1): preparing a thermally insulating particle-containing suspension by dispersing the thermally insulating particles 1. Here, the term "dispersing (particles)" here means to put the particles into a liquid (medium) and stir to disperse them, not to dissolve them. When the thermally insulating particles 1 are hydrophobic, they are dispersed in alcohol; when hydrophilic, they are dispersed in water. When the thermally insulating particles 1 are aerogel ultrafine particles whose surfaces are modified with trimethylsiloxy groups or other hydrophobic groups, they are strongly hydrophobic and have a high affinity for alcohol (e.g., ethanol), so alcohol should be the medium in Step 1 (S1). On the other hand, when hydrophobic aerogel ultrafine particles are treated at a high temperature of about 450°C, the trimethylsiloxy groups on the surface disappear, exposing silica, which becomes hydrophilic, so the thermally insulating particle-containing suspension need only be a water-based liquid, and alcohol (e.g., ethanol) is not required. Although 390°C is generally known as the starting temperature for thermal decomposition of the hydrophobic functional groups of silica aerogels, a temperature as high as 450°C is preferable, with a margin to sufficiently heat the center of the sample as well due to its thermally insulating properties.

[0113] Step 2 (S2): preparing a binding agent solution by dissolving a binding agent. PVA powder, for example, is suitable as a binding agent. After PVA powder is put into water at room temperature, it is heated to about 80°C and stirred to dissolve, then returned to room temperature.

[0114] Step 3 (S3): preparing a fiber-containing suspension by mixing the thermally insulating particle-containing suspension prepared in Step 1 (S1), the binding agent solution prepared in Step 2 (S2), the matrix fiber 6 and the binder fiber 7.

[0115] Step 4 (S4): a papermaking step in which the fiber-containing suspension prepared in Step 3 (S3) is used for papermaking.

[0116] The term "papermaking" in Step 4 (S4) is a step similar to paper making (a step in the Japanese paper production method), in which the liquid component is removed from the suspension, leaving the solid component in the suspension as a thin film to form a sheet body. More specifically, by passing the fiber-containing suspension in Step 3 (S3) through a net that is stretched to allow the liquid to pass through, the liquid (medium) passes through and the matrix fibers 6 and binder fibers 7 remain on the net. The remaining matrix fibers 6 and the binder fibers 7 are entangled with each other and are wetted by the liquid containing the thermally insulating particles 1 and the binding agent. The matrix fibers 6 are longer than the binder fibers 7, so 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 the binder fibers 7 are spread over the net in an entangled state, and the gaps between them hold the thermally insulating particles 1 and the binding agent solution. When these are peeled off from the net, they become a sheet shape. The excess liquid is squeezed out by crushing a single sheet or vertically overlapped several sheets, and dried to form a nonwoven fabric, i.e., the thermally insulating sheet 100 of Embodiment 1. When heated for drying, the surface of the binder fiber 7 partially or completely melts to form a film, which is bonded to the matrix fiber 6 in contact. When the binder fiber 7 is PVA fiber, it should be dried at 65°C to 85°C.

[0117] Since the fiber-containing suspension prepared in Step 4 (S4) contains the binding agent solution from Step 2 (S2), the binding agent continues to function even after drying and the thermally insulating particles 1 are carried so that they do not spill out of the gaps between the matrix fibers 6.

[0118] This provides the method for producing the thermally insulating sheet 100 of Embodiment 1.

[0119] The concentration of the thermally insulating particles 1 in Step 1 (S1) is, for example, 0.1 to 0.5 wt%, the concentration of polyvinyl alcohol in Step 2 (S2) is, for example, 0.075 g / dl, and the content of the matrix fibers 6 and the binder fibers 7 in the fiber-containing suspension is, for example, 0.5 wt% and 0.025 wt% respectively.

[0120] The content of the thermally insulating particles 1 in the thermally insulating particle-containing suspension should be as high as possible to the extent that they are uniformly dispersed in the liquid. The maximum content of thermally insulating particles 1 is limited to the extent that they do not agglomerate, and a suitable amount of medium is added for this purpose. If the amount of medium added is too small, the thermally insulating particles 1 in the suspension will agglomerate and cluster, and will not be uniformly dispersed. On the other hand, too much medium lowers the content of thermally insulating particles 1 per unit volume, so there is a tradeoff. The design should be optimized through experiments, etc.

[0121] For fiber-containing suspension, the strength of the sheet, e.g., tensile strength, can be increased by increasing the content of the matrix fiber 6. While increasing the content of binder fiber 7 can further strengthen the sheet, thermally insulating properties is sacrificed.[Embodiment 3]

[0122] A flame-retardant fiber according to an embodiment of the present invention will be described. The flame-retardant fiber can be produced by bonding the thermally insulating particles 1 to the surface of the matrix fiber 6 by means of a binding agent, as described in Embodiment 1, citing FIG. 3. If this flame-retardant fiber is used as the matrix fiber in Embodiments 1 and 2, flame retardancy can be added to the thermally insulating sheet 100. Aerogel ultrafine particles are particularly suitable as thermally insulating particles 1 in this case.

[0123] When silica aerogel with high silicon dioxide purity is used as the raw material, aerogel ultrafine particles become thermally insulating particles with the flame retardancy of silica intact. Taking a common silica fiber as the matrix fiber 6 as an example, its diameter is about 8 µm to 12 µm, while the particle diameter of conventional aerogel fine powder is several 10 µm to several 100 µm, as explained citing FIG. 8, so it cannot be bonded in such a manner that it adheres to the surface of the silica fiber. However, the majority of the aerogel ultrafine particles have a direct particle size distribution of 0.3 µm to 0.7 µm, which allows them to adhere to the surface of the silica fiber. As explained in "Addition of Flame Retardancy" in Embodiment 1, although it is more reliable to form the flame-retardant layer 3 containing thermally insulating particles 1 to cover the entire surface of the matrix fiber 6, the flame-retardant layer 3 in the form of islands, as shown in FIG. 3 can increase flame retardancy. Aerogel ultrafine particles are suitable as thermally insulating particles 1, as described above. However, this is not limiting. Any particles having sufficiently smaller diameter than the diameter of the matrix fiber with flame retardancy may be used.[Embodiment 4]

[0124] A method for producing the flame-retardant fiber of Embodiment 3 will be described. FIG. 5 is a flowchart of an example method for producing a flame-retardant fiber according to an embodiment of the present invention. The production method (a) of depositing the thermally insulating particles 1 on the surface of the matrix fiber 6 and (b) of powdering the thermally insulating particles 1 on the surface of the matrix fiber 6 will be described.

[0125] (a) The method for producing the flame-retardant fiber by depositing the thermally insulating particles 1 on the surface of the matrix fiber 6 comprises the following steps.

[0126] Step 1 (S11): preparing a thermally insulating particle-containing suspension by dispersing the thermally insulating particles 1. As in S1, the thermally insulating particles 1 are dispersed with water as the medium if they are hydrophilic or with alcohol if they are hydrophobic. Step 2 (S12): preparing a binding agent solution by dissolving a binding agent. As in S2, PVA powder, for example, is suitable as a binding agent. After PVA powder is put into water at room temperature, it is heated to about 80°C and stirred to dissolve, then returned to room temperature. Step 3 (S13): preparing a slurry by mixing the thermally insulating particle-containing suspension prepared in Step 1 (S11) and the binding agent solution prepared in Step 2 (S12). Step 4 (S14): depositing the slurry prepared in Step 3 (S13) on the matrix fiber 6 as an evaporation source. The matrix fiber 6 can be in any form, such as sheet, blanket, pad or cotton, or it can be unraveled.

[0127] This can provide a production method for adding higher flame retardancy to the matrix fiber. The deposition in Step 4 (S14) is suitable if it is ultrasonic deposition or thermal deposition. This allows more efficient adhesion of the thermally insulating particles 1 to the surface of the matrix fiber 6. Here, "more efficiently" means that more thermally insulating particles 1 can be adhered with less consumption. Instead of vapor deposition in Step 4 (S14), the slurry prepared in Step 3 (S13) can be sprayed or soaked with a sheet or blanket of matrix fiber 6 and then pulled up to dry.

[0128] The thermally insulating particles (aerogel ultrafine particles) are strongly hydrophobic when their surfaces are modified with trimethylsiloxy groups or other hydrophobic groups, while they have a high affinity for alcohol (e.g., ethanol), so ethanol was used as the medium in Step 1 (S1). As the ultrafine particles, any material that expresses heat resistance and hydrophobicity other than aerogel ultrafine particles may be used. Since hydrophobic ultrafine particles generally have a high affinity for alcohol and can be dispersed uniformly, they can replace other heat-resistant hydrophobic ultrafine particles and suitable media. On the other hand, if the thermally insulating particles (aerogel ultrafine particles) are hydrophilic, there is no need to use alcohol (ethanol), and water should be used as the medium in Step 1 (S1).

[0129] In the slurry to be prepared, the ratio of water, alcohol (e.g., ethanol), fine particles, and binding agent (e.g., PVA) is optimized by experimentation or other means according to the desired specifications. For example, a larger amount of PVA as a binding agent tends to increase the retention of ultrafine particles while decreasing flame retardancy.

[0130] (b) The method for producing the flame-retardant fiber by powdering the thermally insulating particles 1 on the surface of the matrix fiber 6 comprises the following steps.

[0131] Step 5 (S15): preparing a binding agent solution by dissolving a binding agent. As in S2 and S12, PVA powder, for example, is suitable as a binding agent. After PVA powder is put into water at room temperature, it is heated to about 80°C and stirred to dissolve, then returned to room temperature.

[0132] Step 6 (S16): depositing binding agent solution prepared in Step 5 (S15) on the matrix fiber 6 as an evaporation source.

[0133] Step 7 (S17, powdering step): mechanically applying thermally insulating particles 1 to the matrix fiber 6 with the binding agent solution has adhered to the surface in Step 6 (S16). Mechanically applying means to make the thermally insulating particles 1 adhere to the surface of the matrix fiber 6 wetted with the binding agent solution by mixing and stirring with thermally insulating particles 1, while the surface of the matrix fiber 6 is wet, i.e., the deposited binding agent solution has not yet dried.

[0134] Another production method is provided for adding flame retardancy to matrix fibers.

[0135] The flame-retardant fiber can be produced by either the production method (a) of depositing the thermally insulating particles 1 on the surface of the matrix fiber 6 and (b) of powdering the thermally insulating particles 1 on the surface of the matrix fiber 6. Aerogel ultrafine particles are particularly suitable as insulating particles 1 in this case for the reasons as explained in Embodiment 4.[Embodiment 5]

[0136] A thermally insulating sheet 100 with flame retardancy added in accordance with one embodiment of the present invention will be described. In the thermally insulating sheet 100 shown in FIG. 1, flame-retardant layers 3 containing thermally insulating particles 1 are formed on the surfaces of the matrix fibers 6. Although the flame-retardant layers 3 containing thermally insulating particles 1 may be formed to cover the entire surfaces of the matrix fibers 6, the flame-retardant layers 3 in the form of islands, as shown in FIG. 3, have an effect in increasing flame retardancy.

[0137] A method for the producing thermally insulating sheet 100 with added flame-retardant properties will be described.

[0138] FIG. 6 is a flowchart showing an example method for producing a thermally insulating sheet with flame retardancy added.

[0139] To construct a thermally insulating sheet 100 similar to that described in Embodiments 1 and 2, using as matrix fiber 6 the flame-retardant fiber 200 produced by the production method (a) of depositing the thermally insulating particles 1 on the surface of the matrix fiber 6 described in Embodiment 4 or by the production method (b) of powdering the thermally insulating particles 1 on the surface of the matrix fiber 6, each of the following steps is carried out sequentially.

[0140] Step 8 (S21): preparing a thermally insulating particle-containing suspension by dispersing the thermally insulating particles 1. The thermally insulating particle-containing suspension may be the same as that prepared in Step 1 (S11), or the content of the thermally insulating particles 1 may be optimized considering the papermaking step (Step 11, S24).

[0141] Step 9 (S22): preparing a second binding agent solution for fibers by dissolving polyvinyl alcohol powder in water. The binding agent solution prepared in Step 2 (S12) may be used, or the concentration of the binding agent may be optimized considering the papermaking step (Step 11, S24).

[0142] Step 10 (S23): preparing the fiber-containing suspension by mixing the above flame-retardant fiber 200, the binder fibers 7, the second thermally insulating particle-containing suspension for fibers prepared in Step 8 (S21), and the second binding agent solution for fibers prepared in Step 9 (S22).

[0143] Step 11 (S24): a papermaking step in which the fiber-containing suspension of Step 10 (S23) is used for papermaking.

[0144] This can provide a method for producing a thermally insulating sheet with added flame retardancy.

[0145] For this embodiment, as in embodiments 1 through 4, the thermally insulating particles 1 can be aerogel ultrafine particles, the matrix fiber 6 can be silica fiber, and the binding agent can be polyvinyl alcohol.

[0146] By using silica fibers as the matrix fiber 6, the thermally insulating sheet 100 can be constructed as in Embodiments 1 and 2. By bonding the flame-retardant layer 3 to the matrix fiber 6 as described in Embodiment 3, a flame-retardant fiber 200 can be obtained. Furthermore, by using this flame-retardant fiber as the matrix fiber 6, flame retardancy can be added to the thermally insulating sheet 100. This can realize a thermally insulating sheet that is not only thermally insulating but is also heat-resistant and flame-retardant, capable of withstanding flames at temperatures of 1,000°C or higher. Such thermally insulating sheets can be used to shield the space between adjacent battery cells or battery modules in batteries consisting of a large number of integrated battery cells to prevent thermal runaway.[Embodiment 6]

[0147] In the present embodiment, another embodiment of thermally insulating sheet according to the present invention will be described. The difference from the thermally insulating sheet 100 shown in FIG. 1 is that at least a portion of the thermally insulating particles 14 is embedded in the matrix fiber 300 that constitutes the thermally insulating sheet, as shown in FIG. 11. In other words, while the matrix fiber 300 is a fiber made of thermoplastic resin 8, the thermally insulating particles 14 are mixed and present in this thermoplastic resin 8. When the particle size of the thermally insulating particles 14 is relatively large and / or when the amount of the thermally insulating particles 14 is relatively large relative to the amount of the thermoplastic resin 8, the thermally insulating particles 14 may be present on the surface of the matrix fiber 300 with a portion of the thermally insulating particles 14 exposed from the thermoplastic resin 8. Alternatively, when the particle size of the thermally insulating particles 14 is sufficiently smaller than the diameter of the matrix fiber 300, or when the amount of the thermally insulating particles 14 is relatively small relative to the amount of thermoplastic resin 8, the thermally insulating particles 14 may be completely embedded in the thermoplastic resin 8 with no thermally insulating particles 14 on the surface of the matrix fiber 300.

[0148] The thermoplastic resins may include, for example, polyesters like aromatic polyesters such as polyethylene terephthalate (PET), polybutylene terephthalate (PBT), and polyalkylene terephthalate, aliphatic polyesters such as polylactic acid, as well as polyamide, polyurethane, polyurethane, polyolefin, and other known thermoplastic resins that can be used as materials for synthetic fibers. These thermoplastic resins can be used alone or in mixtures of two or more types.

[0149] For example, recycled resin made from thermoplastic resin molded products such as PET bottles that have been remelted and molded into pellets or powder may be used as thermoplastic resin.

[0150] The thermally insulating sheet of this embodiment is woven / knitted from yarn spun from the aforementioned 300 matrix fibers. The matrix fiber 300 can be spun by any known spinning method described below.

[0151] The yarn may also be woven / knitted in any known manner. In this embodiment, "weaving / knitting" means weaving or knitting yarn to form a textile or spinning yarn to form a woven / knitted fabric. Woven fabrics include any known woven structure, such as plain, twill, satin, amundsen, double, etc. Knitting fabrics include any known knitted structure, such as jersey, smooth, half, double raschel, etc.

[0152] The thermally insulating sheet of this embodiment is woven / knitted from yarn in which the thermally insulating particles 14 are mixed in the matrix fiber 300, a thermally insulating sheet with high thermally insulating properties can be obtained without using a binding agent to support the thermally insulating particles 14.[Embodiment 7]

[0153] In the present embodiment, another embodiment of thermally insulating sheet according to the present invention will be described. The thermally insulating sheet of this embodiment uses the same matrix fiber as the matrix fiber 300 described in Embodiment 6 above. That is, the matrix fibers include thermoplastic resin, the thermally insulating particles are present at least partially embedded in the thermoplastic resin in the matrix fibers, the sheet body is a thermally insulating sheet formed by the matrix fibers being bonded to each other by a film made by the melted thermoplastic resin.

[0154] Since the matrix fibers in this embodiment contain thermoplastic resin, they can be easily melted by heat, etc. Therefore, without using binder fibers, the matrix fibers can be bonded to each other with a film made by the melted thermoplastic resin to form a sheet shape. As in Embodiment 6, the thermally insulating particles are mixed in the matrix fiber, so that a highly thermally insulating sheet can be obtained without supporting the thermally insulating particles using a binding agent.

[0155] The matrix fiber of this embodiment may be used as a substitute for the matrix fiber in Embodiment 1 to produce the thermally insulating sheet by the production method of Embodiment 2. That is, a thermally insulating sheet is produced using fibers in which at least a portion of the thermally insulating particles are embedded in the thermoplastic resin as the matrix fibers, and in a papermaking step using PVA fibers, a binding agent, and a suspension containing thermally insulating particles. Higher thermally insulating properties can be obtained because the matrix fibers contain thermally insulating particles.[Embodiment 8]

[0156] In this embodiment, another embodiment of the method for producing a thermally insulating sheet according to the present invention will be described.

[0157] The production method of this embodiment is also an example method for producing a thermally insulating sheet described in Embodiments 6 and 7 above. The method for producing a thermally insulating sheet of this embodiment comprises the following steps, as shown in FIG. 12.

[0158] Step 12 (S25): A step of obtaining a particle-containing resin by mixing thermoplastic resin and thermally insulating particles.

[0159] Step 13 (S26): A step of obtaining short fibers by storing the particle-containing resin in a container having fine holes, and by rotating the container while heating it to eject the particle-containing resin from the fine holes.

[0160] Step 14 (S27): A step of forming the short fibers into a sheet.

[0161] In Step 12, the particle-containing resin may be prepared in advance by heating and melting thermoplastic resin, adding thermally insulating particles to it, and stirring and mixing while heating, and then particle-containing resin may be crushed and put into the container to melt again. This results in a relatively uniform dispersion of thermally insulating particles in the thermoplastic resin.

[0162] Alternatively, the particle-containing resin may be obtained by placing the melted thermoplastic resin and the thermally insulating particles together in a container or other container. In this case, the particle-containing resin is composed of thermoplastic resin and thermally insulating particles that are not completely mixed.

[0163] In Step 13, as shown in FIG. 13, the particle-containing resin 9 obtained in Step 12 is contained in a container 400 having fine holes arranged in a chamber C. The container 400 is heated while the motor M is driven to rotate the container 400, then the particle-containing resin 9 is ejected through the fine holes of the container 400 by centrifugal force. Short fibers are obtained which are sprayed onto the inner wall of the chamber C. The particle-containing resin may be obtained by placing both the melted thermoplastic resin and the thermally insulating particles directly into the container with fine holes used in Step 13. In this case, Steps 12 and 13 are performed simultaneously.

[0164] The container is connected to the motor M by a rotary shaft 401 and can rotate around the rotary shaft 401 driven by the motor M. The side walls of the container 400 are provided with a number of fine holes that connect the inside of the container to the outside. The container 400 is heated by a heater H installed below to melt the particle-containing resin 9 inside, and the motor M is driven to rotate the container in this state. Centrifugal force due to rotation acts on the particle-containing resin 9 inside the container 400, and the particle-containing resin 9 is cooled quickly and becomes fibrous by being ejected through the fine holes of the container 400, and is sprayed onto the inner wall of the chamber C in the form of short fibers. The short fibers sprayed on the inner wall of the chamber C are fibers (cotton-like fibers) 500 with short fibers intertwined with each other.

[0165] In Step 14, the resulting short fibers 500 are formed into a sheet. Short fibers can be easily deformed by heating because they contain thermoplastic resin. Thus, for example, cotton fibers can be easily formed into a sheet by forming them into a sheet while heating. Alternatively, such short fibers can be spun by a known spinning method as in Embodiment 6, and woven / knitted as yarn to form a sheet.[Embodiment 9]

[0166] In this embodiment, another embodiment of the method for producing a thermally insulating sheet according to the present invention will be described.

[0167] The production method of this embodiment is also an example method for producing a thermally insulating sheet described in Embodiment 6 above. A method for producing a thermally insulating sheet as yet another embodiment of the present invention comprises the following steps, as shown in FIG. 14.

[0168] Step 15 (S28): A step of preparing a particle-containing resin by melting thermoplastic resin and mixing the melted thermoplastic resin with thermally insulating particles.

[0169] Step 16 (S29): A step of obtaining fibers by extruding the melted particle-containing resin from fine holes,

[0170] Step 17 (S30): A step of obtaining yarn by spinning the fibers.

[0171] Step 18 (S31): A step of weaving / knitting the yarn.

[0172] Step 15 can be performed in the same manner as Step 12 (S25 in FIG. 12) of Embodiment 8 above.

[0173] In Step 16, the melted the particle-containing resin is extruded through the fine holes to obtain fibers. The methods of obtaining fibers by extruding include any known chemical fiber spinning methods such as, for example, a method of extruding particle-containing resin 601 in a molten state into a cooled atmosphere (blowing cold air) using a spinning apparatus 600 as shown in Fig. 15 to make multiple fibers, and twisting such fibers to spin them (a melt spinning method),a method of extruding particle-containing resin in a solidifying liquid rather than in a cooled atmosphere (a wet spinning method) and a method of extruding particle-containing resin in a heated atmosphere instead of a cooled atmosphere (dry spinning method).

[0174] Steps 17 and 18 can be performed in the same manner as in Embodiment 6.[Examples][Example 1]

[0175] Aerogel ultrafine particles were bonded to glass wool, a silica fiber to form a flame-retardant layer as described in Embodiments 4 and 5, and the obtained glass wool was compared to one without a flame-retardant layer formed thereon.

[0176] Samples of the same thickness were cut out from a single glass wool blanket: a glass wool blanket sample without a flame-retardant layer and a glass wool blanket sample with a flame-retardant layer. These samples were roasted from one side with a flame at 1300°C for 60 seconds using a 170-9105 Mini Torch manufactured by Coleman Company, Inc. The roasted surface and the opposite surface were observed with naked eyes and using an optical microscope.

[0177] FIG. 9 is a photograph of an actual product. In the glass wool blanket sample without a flame-retardant layer (left side), it is observed that the flame-roasted side (hot side) has been melted, and the opposite side (cold side) has been thinned in the center where roasted. On the other hand, in the glass wool blanket sample with a flame-retardant layer (right side), dimples are observed on the flame-roasted side (hot side), but there is no change on the opposite side (cold side).

[0178] FIG. 10 is an optical microscope. In the glass wool blanket sample without a flame-retardant layer (left side), it is observed that the fibers have melted in the flame-roasted area on the hot side, while the glass wool blanket sample with flame-retardant layer (right side) shows almost no change before it was roasted with a flame.

[0179] As described above, flame retardancy is added to the matrix fibers by bonding aerogel ultrafine particles to form a flame-retardant layer.[Example 2]

[0180] The short fibers used in the method for producing the thermally insulating sheet described in Embodiment 8 were produced in the following manner.(Materials)

[0181] Cut pieces of PET bottles Aerogel ultrafine particles (product name: TIISAR, manufactured by Thermalytica Inc.) (Method for producing particle-containing resin) Cut pieces of PET bottles and aerogel ultrafine particles were placed in a stainless steel cup, heated with an alcohol lamp and stirred until the PET bottle pieces were completely melted, then stopped heating and cooled to room temperature to obtain particle-containing resin.

[0182] The content of aerogel ultrafine particles in the particle-containing resin was adjusted to 1 mass%, 3 mass%, 4 mass%, and no aerogel ultrafine particles (0 mass%) as a control. The cooled particle-containing resin was beaten with a hammer to break up the mass.(Method for producing short fibers)

[0183] Fine holes were drilled in the side of a 350 ml beverage aluminum bottle and set in the apparatus shown in FIG. 16. The size of the fine hole was 2 mm.

[0184] Each particle-containing resin was placed in the bottle and heated with a Bunsen burner while a motor was driven to rotate the bottle. The rotational speed was 1493 rpm (motor voltage 0.7 V). The particle-containing resin inside the bottle was ejected out through the fine holes while the bottle was rotating to collect cotton-like short fibers adhering to the inner wall of the box.(Observation of short fibers)

[0185] The collected short fibers were observed as follows.

[0186] Several fibers were taken from the short fibers and fixed to stand upright in a cylindrical plastic container approximately 20 mm in diameter and 20 mm high. A homogeneous mixture of epoxy and a hardener was poured into the container to cure the mixture and completely fix the fiber sample. Once the epoxy had cured, the entire container of fiber samples was cut thinly from the sides and the cut surfaces were polished. The surface to be observed was coated with platinum to give it conductivity, and a sample was obtained for SEM observation. Such samples were observed with a Schottky field emission scanning electron microscope (JSM-7900F, manufactured by JEOL Ltd.).

[0187] The results of the observations are shown in FIG. 17. In FIG. 17, the area circled in white in each 200x photograph is the cross section of the short fiber. The areas circled in black in each 1000x photograph are the aerogel ultrafine particles in the short fiber. In the 1 mass% and 4 mass% fibers in the 1000x photographs, white clumps that do not appear in the control fiber without aerogel ultrafine particles are visible, indicating aerogel ultrafine particles, and thus fibers with aerogel ultrafine particles inside were obtained.

[0188] While the present invention made by the present inventors has been described in detail with respect to the embodiments thereof, the present invention is not limited to these embodiments. Various changes may be made without departing from the spirit and scope of the present invention.Industrial Applicability

[0189] The present invention can be suitably used for a thermally insulating sheet, a thermally insulating fiber and a method for producing the same, as well as a fiber-containing suspension used for the production of a thermally insulating sheet.EXPLANATION OF SIGN

[0190] 1 Thermally insulating particles (e.g., aerogel ultrafine particles) 2 Binding agent (e.g., PVA) 3 Flame-retardant layer 4 Binding agent layer 6 Matrix fiber (e.g., silica fiber) 7 Binder fiber (e.g., PVA fiber) 8 Thermoplastic resin 9 Particle-containing resin 11 Primary particles 12 Secondary particles (aggregate / cluster of primary particles) 13 Aerogel fine powder (powder of which framework is formed of secondary particles) 14 particles of which framework is formed of primary particles (e.g., aerogel ultrafine particles) 100 Thermally insulating sheet 200 Flame-retardant fiber 300 Matrix fiber

Claims

1. A thermally insulating sheet containing matrix fibers and thermally insulating particles, wherein the matrix fibers are bonded or woven / knitted to each other to form a sheet body, and the thermally insulating particles are present inside and / or outside of the matrix fibers.

2. The thermally insulating sheet according to claim 1, wherein the thermally insulating particles are formed from an aerogel having a three-dimensional network structure, the framework of which is formed of clusters that are aggregates of primary particles, have a three-dimensional network structure, the framework of which is formed of the primary particles, and the particle diameters of 50% or more of the volume of the thermally insulating particles vary so that the mode is found between 0.1 µm and 1.0 µm.

3. The thermally insulating sheet according to claim 1 or 2, wherein the matrix fibers are silica fibers, the sheet body contains the matrix fibers, binder fibers, and a binding agent, and the matrix fibers are bonded to each other by a film made by the melted binder fibers, and the thermally insulating particles are carried by the binding agent in gaps between the bonded matrix fibers.

4. The thermally insulating sheet according to claim 3, wherein the thermally insulating particles are bonded to surfaces of the matrix fibers by the binding agent.

5. The thermally insulating sheet according to claim 1 or 2, wherein the matrix fibers include thermoplastic resin, the thermally insulating particles are present at least partially embedded in the thermoplastic resin in the matrix fibers, and the sheet body is woven / knitted from yarns spun from the matrix fibers.

6. The thermally insulating sheet according to claim 1 or 2, wherein the matrix fibers include thermoplastic resin, the thermally insulating particles are present at least partially embedded in the thermoplastic resin in the matrix fibers, and the sheet body is formed by the matrix fibers being bonded to each other by a film made by the melted thermoplastic resin.

7. A method for producing a thermally insulating sheet, comprising the steps of: preparing a thermally insulating particle-containing suspension by dispersing thermally insulating particles, preparing a binding agent solution by dissolving a binding agent, preparing a fiber-containing suspension by mixing the thermally insulating particle-containing suspension, the binding agent solution, the matrix fibers, and binder fibers; and forming a sheet body by removing a liquid component from the fiber-containing suspension.

8. The method for producing a thermally insulating sheet according to claim 7, wherein the matrix fibers are silica fibers, and the thermally insulating particles are formed from an aerogel having a three-dimensional network structure, the framework of which is formed of clusters that are aggregates of primary particles, have a three-dimensional network structure, the framework of which is formed of the primary particles, and the particle diameters of 50% or more of the volume of the thermally insulating particles vary so that the mode is found between 0.1 µm and 1.0 µm.

9. The method for producing a thermally insulating sheet according to claim 7 or 8, wherein the thermally insulating particles are hydrophobic and the thermally insulating particle-containing suspension contains alcohol.

10. A method for producing a thermally insulating sheet, comprising the steps of: obtaining a particle-containing resin by mixing thermoplastic resin and thermally insulating particles, obtaining short fibers by storing the particle-containing resin in a container having fine holes, and by rotating the container while heating it to eject the particle-containing resin from the fine holes, and forming the short fibers into a sheet.

11. The method for producing a thermally insulating sheet according to claim 10, comprising the steps of: spinning the short fibers to obtain yarn, and weaving / knitting the yarn.

12. The method for producing a thermally insulating sheet according to claim 10, wherein in the step of forming the short fibers into a sheet, the short fibers are spread into a thin film and heated to form them into a sheet.

13. A method for producing a thermally insulating sheet, comprising the steps of: preparing a particle-containing resin by melting thermoplastic resin and mixing the melted thermoplastic resin with thermally insulating particles, obtaining fibers by extruding the melted particle-containing resin from fine holes, obtaining yarn by spinning the fibers, and weaving / knitting the yarn.

14. A method for producing a thermally insulating sheet, comprising the steps of: preparing a thermally insulating particle-containing suspension by dispersing thermally insulating particles, preparing a binding agent solution by dissolving a binding agent, preparing a fiber-containing suspension by mixing thermally insulating fibers, binder fibers, the thermally insulating particle-containing suspension, and the binding agent solution, and forming a sheet body by removing a liquid component from the fiber-containing suspension, wherein the thermally insulating fibers have thermally insulating particles for fibers bonded to surfaces of matrix fibers by a binding agent for fibers, wherein the thermally insulating particles for fibers are formed from an aerogel having a three-dimensional network structure, the framework of which is formed of clusters that are aggregates of primary particles, have a three-dimensional network structure, the framework of which is formed of the primary particles, and the particle diameters of 50% or more of the volume of the thermally insulating particles vary so that the mode is found between 0.1 µm and 1.0 µm, and wherein the matrix fibers are silica fibers.

15. The method for producing a thermally insulating sheet according to claim 14, wherein the thermally insulating particles for fibers and the binding agent for fibers are deposited on the surface of the matrix fibers by ultrasonic deposition or thermal deposition.

16. The method for producing a thermally insulating sheet according to claim 14, wherein the thermally insulating particles are hydrophobic and the thermally insulating particle-containing suspension contains alcohol.

17. A fiber-containing suspension for the production of thermally insulating sheet, wherein a thermally insulating particle-containing suspension in which thermally insulating particles are dispersed in a solvent, a binding agent solution, matrix fibers, and binder fibers are mixed in the fiber-containing suspension.

18. A fiber-containing suspension for the production of a thermally insulating sheet, wherein the thermally insulating particle-containing suspension in which thermally insulating particles are dispersed in a solvent, a binding agent solution, thermally insulating fibers, and binder fibers are mixed, the thermally insulating fibers have thermally insulating particles for fibers bonded to surfaces of matrix fibers by a binding agent for fibers, the thermally insulating particles for fibers are formed from an aerogel having a three-dimensional network structure, the framework of which is formed of clusters that are aggregates of primary particles, have a three-dimensional network structure, the framework of which is formed of the primary particles, and the particle diameters of 50% or more of the volume of the thermally insulating particles vary so that the mode is found between 0.1 µm and 1.0 µm, and the matrix fibers are silica fibers.

19. A thermally insulating fiber, wherein thermally insulating particles are bonded to surfaces of matrix fibers by a binding agent, the thermally insulating particles are formed from an aerogel having a three-dimensional network structure, the framework of which is formed of clusters that are aggregates of primary particles, have a three-dimensional network structure, the framework of which is formed of the primary particles, and the particle diameters of 50% or more of the volume of the thermally insulating particles vary so that the mode is found between 0.1 µm and 1.0 µm, and the matrix fibers are silica fibers.

20. A thermally insulating fiber, wherein thermally insulating particles are present at least partially embedded in the matrix fibers. the thermally insulating particles are formed from an aerogel having a three-dimensional network structure, the framework of which is formed of clusters that are aggregates of primary particles, have a three-dimensional network structure, the framework of which is formed of the primary particles, and the particle diameters of 50% or more of the volume of the thermally insulating particles vary so that the mode is found between 0.1 µm and 1.0 µm, and the matrix fibers include thermoplastic resin.

21. A method for producing the thermally insulating fiber according to claim 19, comprising the steps of: preparing a thermally insulating particle-containing suspension by dispersing the thermally insulating particles, preparing a binding agent solution by dissolving a binding agent, preparing a slurry by mixing the thermally insulating particle-containing suspension and the binding agent solution, and depositing the slurry on the matrix fibers as an evaporation source.

22. A method for producing the thermally insulating fiber according to claim 19, comprising the steps of: preparing a binding agent solution by dissolving a binding agent, depositing the binding agent solution on the matrix fibers as an evaporation source, and mechanically applying thermally insulating particles to the matrix fibers with the binding agent solution adhered to the surface by vapor deposition.

23. The method for producing thermally insulating fiber according to claim 21, wherein the deposition performed in the depositing step is ultrasonic deposition or thermal deposition.

24. The method for producing thermally insulating fiber according to claim 21, wherein the thermally insulating particles are hydrophobic and the thermally insulating particle-containing suspension contains alcohol.

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