Aqueous slurry comprising hydrophilized aerogel particles and suspension for papermaking using the same

Abstract

To provide a suspension for papermaking for providing a lightweight and thin heat-insulating flameproof sheet, and a hydrophilized aerogel slurry used therefor.SOLUTION: In an aqueous slurry comprising hydrophilized aerogel particles, at least a part of the surface of the hydrophobic aerogel particles is coated with a hydrophilic polymer having a plurality of hydroxyl groups. A suspension for papermaking comprising the aqueous slurry and inorganic fibers is provided. A sheet obtained by subjecting the suspension for papermaking to wet papermaking is lightweight and thin and has excellent heat insulating and flameproof properties.SELECTED DRAWING: Figure 7

Description

Technical Field

[0001] The present invention relates to an aqueous slurry containing hydrophilized aerogel particles and a suspension for papermaking using the same.

Background Art

[0002] In electric vehicles or hybrid vehicles driven by an electric motor, a battery pack in which a plurality of battery cells are connected in series or in parallel and modularized is mounted as a power source for the driving electric motor. As this battery cell, a lithium-ion secondary battery capable of high capacity and high output is mainly used.

[0003] If a certain battery cell rapidly heats up and causes thermal runaway due to an internal short circuit or overcharging of the battery, it may spread to other adjacent battery cells, causing thermal runaway of the adjacent battery cells in a chain reaction, or a high-temperature lithium electrolyte may spout from the battery cell that has caused thermal runaway, which may cause a major accident such as ignition. For this reason, in a battery pack, as a technique for suppressing the heat transmitted to adjacent cells and further suppressing the spread of fire by a flame when a certain battery cell undergoes thermal runaway, for example, as shown in FIG. 1, it has been proposed to interpose a heat insulation and flame shielding sheet 10 between battery cells 11, 11. A plurality of battery cells are usually housed together in a housing 12.

[0004] In addition, as packaging of a battery module, for example, as shown in FIG. 2, there is a type in which rectangular battery cells 11' are arranged in parallel, housed in a housing 12', and then sealed with a lid 12'a of the housing 12'. By attaching a heat insulation and flame shielding sheet 10 to the back surface of this lid 12'a using an adhesive 10a, it is possible to prevent the high-temperature lithium electrolyte ejected due to thermal runaway of one of the packaged battery cells and the flame generated thereby from affecting peripheral devices.

[0005] Conventionally, it has been proposed to use a mica sheet (a sheet containing at least 80% mica) having excellent insulation and flame barrier functions for such a heat insulation and flame shielding sheet. However, since the mica sheet has a high bulk density, in the battery applications of electric vehicles, there is a demand for a heat insulation and flame shielding sheet that is lighter in weight and has the same level of functions.

[0006] As a sheet that is lightweight and has heat insulation and flame resistance, it has been proposed to use a woven fabric, non-woven fabric, or paper of inorganic fibers. Alumina fibers as inorganic fibers have excellent properties such as high heat resistance (melting point of about 2000 °C), combustion resistance, and high insulation, but are more expensive than other inorganic fibers. Therefore, it is not suitable for use as the constituent fibers of the sheet. Under such circumstances, a heat insulation sheet combining inorganic fibers and inorganic particles having a heat insulation effect has been proposed as a heat insulation and flame shielding sheet having desired heat insulation and flame shielding properties.

[0007] As particles having excellent heat insulation properties, aerogels (porous silica particles) are known. Japanese Patent Application Laid-Open No. 2015-163815 (Patent Document 1) discloses that, based on 100 parts by weight of the main fiber, 35 to 210 parts by weight of aerogel particles having a high heat insulation effect (average particle size of 2 to 140 μm and specific surface area of 400 m 2 / g or more) are blended, and further contains a binder containing at least one water-soluble polymer selected from the group consisting of a cationic polymer and an amphoteric polymer, and / or a low melting point synthetic fiber (heat insulation sheet). Examples of the main fiber include synthetic fibers such as polyester fibers and aramid fibers, as well as inorganic fibers such as ceramic fibers, alumina fibers, and glass fibers (

[0018] ), but in the examples, only sheets using organic fibers such as pulp, polyester fibers, and vinylon binder fibers have been produced. Regarding the binder, since methyl silicate particles exhibit anionic or amphoteric properties, it is explained that by using a cationic polymer and / or an amphoteric polymer as the binder, the aggregation of pulp and porous silica particles can be promoted and the yield can be increased (

[0026] ). In a specific example, organic fibers (such as pulp, polyester fibers, and vinylon binder fibers), aerogel, and a water-soluble polymer are added to water and stirred to prepare a papermaking slurry, and a heat-insulating sheet is produced by a papermaking method. The obtained heat-insulating sheet is wound around a paper cup or a stainless steel rod, and the temperature of the surface of the heat-insulating sheet is measured (for 60 seconds) when hot water at 95 °C is put into the paper cup and when the stainless steel rod is heated to 100 °C. The results are shown.

[0008] In addition, Japanese Patent Application Laid-Open No. 2020-200901 (Patent Document 2) proposes a heat-insulating sheet that uses aerogel particles, glass beads, or ceramic beads having a large number of nanometer-sized pores as heat-insulating components and uses bio-soluble rock wool as fibers. It is disclosed that a felt-like or paper-like heat-insulating sheet with a thickness of 1.72 to 6.3 mm is formed using a papermaking slurry containing a slurry containing a fiber component, a heat-insulating component, and a binder (Table 1 of the examples). Here, examples of the binder include starch, polyvinyl alcohol, acrylic starch, and acrylic polyvinyl alcohol (

[0025] ), and it is described that 50 to 300 parts are blended with respect to 100 parts by weight of the fiber (rock wool) serving as the base material (

[0026] ). In the examples of Patent Document 2, an aerogel dispersion obtained by adding and mixing aerogel to an aqueous binder solution and a dispersion of bio-soluble rock wool are prepared separately, and the aerogel dispersion is added to the fiber dispersion to prepare a papermaking slurry. Using such a papermaking slurry, it is applied onto a laminate of filter paper and a net, and the heat-insulating sheet is produced by heating and pressing in a state where the net and the filter paper are laminated. In the examples, the measurement results of the thermal conductivity (heat ray method) of the produced heat-insulating sheet are shown.

Prior Art Documents

Patent Documents

[0009]

Patent Document 1

Patent Document 2

SUMMARY OF THE INVENTION

PROBLEMS TO BE SOLVED BY THE INVENTION

[0010] Patent Document 1 specifically shows the heat insulation effect using an aerogel, but the heat source temperature is about 100°C. There is no disclosure and it is unclear about the heat shielding property and the heat insulation property in a high temperature range of 500°C or higher, which are required as countermeasures against thermal runaway when a lithium-ion battery undergoes thermal runaway.

[0011] Patent Document 2 describes, as the use of a heat insulating material, in addition to a heat insulating container for pharmaceuticals and foods ((0002)), heat insulation of electronic components ((0003)), but does not describe using it for a thermal runaway sheet of a lithium-ion battery. Although the measurement results of the thermal conductivity are shown, no specific effects are shown regarding the heat insulation property and the heat shielding property against a high temperature of 600°C or higher, which are required as countermeasures against thermal runaway, and the effects are unclear.

[0012] Since the bio-soluble rock wool that is the base fiber of the sheet belongs to inorganic fibers, it is non-combustible (fire-resistant) and is said to have heat resistance up to about 700°C. On the other hand, rock wool is manufactured by melting raw materials such as slag and rock in an electric furnace at 1500 - 1600°C, and blowing the melt away by centrifugal force and solidifying it in the air. Based on such a manufacturing method, rock wool contains non-fibrous particles (shots) that could not become fibers. Since it is difficult to completely remove such non-fibrous particles even if they can be reduced during the papermaking process, it is difficult to avoid mixing them into the heat insulating sheet at a certain ratio. As a result, there is a risk of affecting the heat insulation property and the heat shielding property of the heat insulating sheet, and there is also a possibility that the non-fibrous particles will damage the outer wall of the cell in contact with the sheet.

[0013] The present invention has been made in view of the above circumstances, and its object is to provide a heat insulation and flame shielding sheet that is a lightweight and thin sheet with a thickness of more than 0.5 mm, 1 mm or more, and 3 mm or less, preferably 2 mm or less, and can exhibit a heat insulation and flame shielding effect of maintaining its shape for at least 10 minutes even when exposed to a flame near 1000°C. In addition, an aqueous slurry of aerogel particles that is lightweight and has excellent heat insulation properties and a raw material liquid for papermaking using the same are provided.

Means for Solving the Problems

[0014] The inventors of the present invention have variously studied the structure of fibers and sheets that can exhibit heat insulation properties during normal use (when the temperature rises to a level where thermal runaway does not occur) and flame shielding and heat insulation properties even when exposed to a flame (1000°C or higher) in a lightweight and thin sheet. Since a lithium-ion battery used as a power source for an EV vehicle is a laminate of a large number of cells, the heat insulation and flame shielding sheet interposed between individual cells is required to be mainly composed of an inorganic material, thin, and lightweight in relation to heat resistance. As a method for manufacturing a lightweight and thin sheet with a thickness of more than 0.5 mm, 1 mm or more, and less than 3 mm, preferably 2 mm or less, using a material mainly composed of an inorganic material, there is a wet papermaking method.

[0015] By the way, aerogel particles, which are known to have a high heat insulation effect, have a hydrophobic surface and a low density because air is trapped in nano-sized pores, which results in an excellent heat insulation effect. This also makes it difficult for them to entangle and aggregate with fibers in the wet papermaking method using water as a dispersion medium. In order to exhibit the excellent heat insulation effect of aerogel particles, it is necessary to uniformly mix hydrophobic aerogel particles and fibers in the raw material liquid for papermaking (fiber-containing suspension).

[0016] The inventors of the present invention have found that in order to make use of the excellent heat insulation properties of aerogel particles as heat insulation-imparting inorganic particles contained in the raw material liquid for papermaking, which is the raw material for a heat insulation and flame shielding sheet using inorganic fibers as base fibers, it is necessary for the aerogel particles to be dispersible in an aqueous medium, and thus completed the present invention.

[0017] That is, the aqueous slurry of the present invention has the following aspects. (1) An aqueous slurry containing hydrophilized aerogel particles in which at least a part of the surface of the hydrophobic aerogel particles is coated with a hydrophilic polymer having a plurality of hydroxyl groups. (2) The aqueous slurry according to aspect (1), wherein the hydrophobic aerogel particles are silica aerogels having an average particle size of 5 to 200 μm and a wetting angle with respect to water of 100° or more. (3) The aqueous slurry according to aspect (1) or (2), wherein the hydrophilic polymer is a water-soluble polymer. (4) The particle density of the hydrophobic aerogel particles is 100 to 200 g / cm 3 The aqueous slurry according to any one of aspects (1) to (3). (5) The aqueous slurry according to any one of aspects (1) to (4), wherein the content ratio of the hydrophilic polymer to the hydrophobic aerogel is 1 / 2 to 1 / 100 in terms of hydrophilic polymer / hydrophobic aerogel particles (weight ratio). (6) The aqueous slurry according to any one of aspects (1) to (5), wherein the content rate of the organic solvent and / or surfactant contained in the aqueous slurry is less than 10% by weight.

[0018] The present invention also includes a method for producing the aqueous slurry of the present invention. That is, the method for producing the aqueous slurry of the present invention is a method for producing the aqueous slurry according to any one of aspects (1) to (6), and includes a step of adding and mixing silica aerogel particles having a hydrophobic surface and an average particle size of 5 to 200 μm to an aqueous solution of a hydrophilic polymer.

[0019] The present invention also includes a suspension for papermaking using the aqueous slurry of the present invention. The suspension for papermaking of the present invention is a suspension for papermaking containing the aqueous slurry according to any one of aspects (1) to (6) and inorganic fibers.

Advantages of the Invention

[0020] The slurry containing the hydrophilized aerogel particles of the present invention can be dispersed in an aqueous medium, and by using this, a papermaking suspension in which inorganic fibers and aerogel particles are homogeneously mixed can be prepared. The heat insulation and flame shielding sheet obtained from the papermaking suspension is lightweight and excellent in heat insulation and flame shielding properties.

Brief Description of Drawings

[0021]

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Mode for Carrying Out the Invention

[0022] <Inorganic Particles for Providing Heat Insulation, Slurry Using the Same, and Method for Producing the Same> Examples of the inorganic particles for providing heat insulation used in the present invention include porous or hollow inorganic particles such as silica aerogel, glass bubble, and glass balloon. Preferably, they are hollow or porous silica particles capable of obtaining a heat-insulating effect by air and weight reduction, and more preferably porous silica particles (silica aerogel).

[0023] The silica particles used as the inorganic particles for providing heat insulation are network-like aggregates or agglomerates in which nano-sized particles (about 5 to 50 nm) are aggregated. As the aggregates or agglomerates, they have nano-sized pores and a porosity of 50% by volume or more. Such silica particles are produced by a sol-gel method, a dry method (fumed silica), a wet method (precipitated silica), etc., and the particle diameter and aggregation state obtained vary depending on the production method and production conditions.

[0024] Wet silica (precipitated silica) is generally silica synthesized in water from sodium silicate and mineral acid synthesized from silica sand and soda ash, and is obtained as amorphous aggregated particles (aggregates as secondary particles) having a macroporous structure, and can act like porous particles. Silica particles produced by the sol-gel method are network aggregates in which nano-sized particles (about 5 to 50 nm) are aggregated, and the nanoparticles are silanol-bonded to each other. It corresponds to porous particles (primary particles) having nano-sized pores with a porosity of 70% by volume or more, preferably 80% by volume or more, more preferably 90% by volume or more. Preferably, it is a surface-hydrophobic aerogel having nano-sized pores that form a tortuous long air path capable of inhibiting heat and electrical conductivity.

[0025] Hereinafter, hydrophilized aerogel particles will be described as typical heat-insulating inorganic particles.

[0026] [Hydrophilized silica aerogel] In the sol-gel method, porous silica aerogel is obtained. Specifically, in addition to bifunctional silane and trifunctional silane compounds, a sol containing at least a tetrafunctional silane compound is crosslinked and gelled, and the obtained wet gel is molded as necessary, and then the water and / or organic solvent present on the surface and inside of the wet gel are dried and exchanged with an organic solvent (solvent exchange), and depending on the type of organic solvent, it is obtained by supercritical drying or atmospheric pressure drying. The aerogel obtained as the dried gel body has a pore size of about 1 to 20 nm, which is below the mean free path of gas molecules.

[0027] As described above, by end-capping the silanol groups present on the surface of silica aerogel produced by the sol-gel method with a hydrophobic group such as a silylating agent, aerogel particles with a hydrophobic surface can be obtained. In the silica aerogel in which the surfaces of the individual silica particles that make up the aggregates are also hydrophobically capped, the pores inside the particles also become hydrophobic, and even in a slurry using water as a dispersion medium, water can be prevented from entering the pores. Therefore, based on air, the thermal conductivity can be reduced.

[0028] Such aerogel particles with a hydrophobic surface usually have a wetting angle with respect to water of 100 degrees or more, 110 degrees or more, 130 degrees or more, or 150 degrees or more.

[0029] As the heat-insulating inorganic particles used in the present invention, aerogel particles with a hydrophobic surface are preferably used. Specifically, silica aerogel having a surface area of about 300 m 2 / g to about 1,000 m 2 / g, preferably 500 m 2 / g to about 1,000 m 2 / g, a BET surface area of 700 m 2 / g to 800 m 2 / g, and a porous structure with a porosity of at least 80%, preferably 85% or more, more preferably 90% or more is used.

[0030] The aerogel particles with a hydrophobic surface used as the heat-insulating inorganic particles usually have an average particle diameter of 5 to 200 μm, preferably 5 μm to 150 μm, more preferably 10 to 100 μm. The particle density is preferably 100 to 200 g / cm 3 . By using aerogel particles of such a size, a heat-insulating and flame-retardant sheet excellent in yield in the papermaking process, lightweight, and excellent in heat insulation can be provided. Note that depending on the manufacturing method, it may be in the form of aggregates of 200 μm or more to about several mm. In this case, aerogel particles within the above range can be obtained by pulverization.

[0031] In the case of an aerogel in which the surfaces of these inorganic particle powders are hydrophobic and have a high surface tension, in the suspension for papermaking, it becomes difficult for the aerogel particles to aggregate with each other and to be sufficiently mixed with other components (inorganic fibers, thermoplastic resin fibers). In the present invention, the hydrophobic silica aerogel as described above is used after being subjected to a hydrophilization treatment.

[0032] As a method for hydrophilizing the surface hydrophobic aerogel, there are a method of making the surface properties easily wettable with water by mixing with an organic solvent or a surfactant; a method of coating at least a part of the surface of the aerogel particles with a hydrophilic polymer that cannot penetrate into the pores inside, and the like.

[0033] The organic solvent or surfactant used for the hydrophilization treatment is a solvent or surfactant that can exist at the interface between water and silica aerogel to such an extent that it does not affect the aggregated structure of the silica aerogel particles, and is further a solvent that can be mixed with fibers in water. Specifically, there are mentioned polyhydric alcohol alkyl ether-based organic solvents having about 3 to 7 carbon atoms such as ethylene glycol monoethyl ether, ethylene glycol dimethyl ether, propylene glycol monomethyl ether, and diethylene glycol monomethyl ether. Incidentally, alkylene oxide type surfactants such as polyoxyethylene, polyoxypropylene, and polyoxyethylene·polyoxypropylene condensates can enhance the hydrophilicity of the aerogel, but tend to separate from the fiber-containing liquid using water as a medium, and it is difficult to mix with fibers.

[0034] When the above-mentioned organic solvent or surfactant is contained, the content in the aerogel slurry is preferably 10% by weight or less. When the content of the surfactant or organic solvent becomes too high, the tendency is that there is a lot of foaming during the preparation process of the suspension for papermaking, particularly during mixing and stirring.

[0035] Examples of the hydrophilic polymer used for the hydrophilization treatment include polysaccharides such as cellulose nanofibers, starch, amylose, cationized starch, and carboxymethyl cellulose; and vinyl-based hydrophilic polymers such as polyvinyl alcohol, polyvinyl acetate, ethylene-vinyl alcohol resins, and polyacrylic acid. Among these, it is preferably a water-soluble polymer, and more preferably a water-soluble polymer having a plurality of primary or secondary hydroxyl groups. In the case of saponified products such as polyvinyl alcohol, the saponification degree is preferably 77 to 99 mol% from the viewpoint of water solubility. Examples of polyvinyl alcohol include not only unmodified polyvinyl alcohol but also modified polyvinyl alcohol having a plurality of alcoholic hydroxyl groups in the side chain and modified polyvinyl alcohol having an oxyalkylene group, a sulfonic acid group, etc. introduced into the side chain, as long as the water solubility and hydrophilicity are not impaired.

[0036] These hydrophilic polymers are used in the form of an aqueous solution. Since they also function as thickeners, an aqueous solution with a high viscosity can be obtained. By adding an aerogel to the thickened aqueous solution and homogenizing it by stirring and shaking, the surface of the aerogel particles can be hydrophilized.

[0037] These hydrophilic polymers tend to be larger in size than the pores of the aerogel, and from their molecular structure, they are considered to exist so as to surround the surface of the aerogel particles so that the hydrophilic groups face the dispersion medium side. As a result, the surface state becomes compatible with the dispersion medium, and the aerogel particles can be dispersed in the form of aggregates in the aerogel-containing slurry. Therefore, the above-mentioned hydrophilic polymer may be used in an amount sufficient to make the surface of the hydrophobic aerogel particles hydrophilic, and is usually used in the range of 1 / 2 to 1 / 100 in terms of the weight ratio of the hydrophilic polymer / hydrophobic aerogel particles. Within this range, it is appropriately selected according to the type of the hydrophilic polymer and the type of the hydrophobic aerogel particles.

[0038] Among the hydrophilization treatment methods as described above, from the viewpoints of environmental friendliness, manufacturing environment, and handleability, it is preferable to use a water-soluble polymer. Thereby, the dispersion medium of the fiber-containing liquid and the suspension for papermaking can be made substantially only water, and the wastewater treatment in the dehydration step is simplified.

[0039] The aerogel hydrophilized as described above (hydrophilized aerogel) is obtained by dispersing hydrophobic aerogel particles used as heat-insulating inorganic particles in an aqueous solution of a hydrophilic polymer, and is prepared separately from the fiber-containing liquid containing inorganic fibers and other constituent components, which will be described later, in the preparation of the raw material liquid for papermaking (suspension for papermaking).

[0040] In addition, the surfactant and hydrophilic polymer contained in the hydrophilized aerogel slurry may be used as an organic binder or an emulsifier in the papermaking method, but their handling is different in the preparation process of the suspension for papermaking. That is, when a water-soluble resin or a surfactant is used as a binder or an emulsifier, usually, a binder and an aerogel are added to the fiber-containing liquid. However, generally, the specific gravity difference between the hydrophobic aerogel and the aqueous layer (aqueous solution of surfactant and hydrophilic polymer) is large, and emulsification tends to be difficult. On the other hand, when used as a hydrophilization treatment agent for aerogel, a mixed solution of aerogel and a hydrophilic polymer solution is prepared separately from the fiber-containing liquid, and these are mixed. In this case, since the hydrophobic aerogel has become hydrophilic, even if there is a specific gravity difference, it can be mixed with the fiber-containing liquid. That is, it becomes possible to disperse the hydrophilized aerogel particles in the fiber-containing liquid.

[0041] <Raw material liquid for papermaking (suspension for papermaking)> The suspension for papermaking of the present invention contains inorganic fibers and the hydrophilized aerogel slurry of the present invention. By wet papermaking such a suspension for papermaking, a heat-insulating and flame-shielding sheet with a thickness of less than 3 mm, preferably 2 mm or less, can be obtained.

[0042] Hereinafter, components other than the hydrophilized aerogel slurry contained in the raw material liquid for papermaking will be described in detail.

[0043] [Inorganic fiber] (1) Silica-based inorganic fiber The silica-based inorganic fiber used in the present invention is an amorphous fiber containing SiO2 as a fiber constituent component and having a hydroxyl group at the end. The hydroxyl group contained in the silica-based inorganic fiber can undergo a condensation reaction as shown in the following formula (1) at about 300 to 600 °C to form a new siloxane bond (Si-O-Si bond) and release H2O. The water generated by dehydration condensation vaporizes in a high-temperature atmosphere. At this time, since the heat energy given to the silica-based inorganic fiber sheet is consumed as the heat of vaporization, it is considered that the temperature rise of the sheet can be delayed. [Chemical formula]

[0044] Examples of the silica-based inorganic fiber having a hydroxyl group include silica-based amorphous fibers made from silicic acid modified with alumina, generally containing 90 to 97% by weight of silica, about 3 to 9% by weight of alumina, less than 0.5% of sodium oxide, and less than 0.5% of other components (ZrO2, TiO2, Li2O, K2O, CaO, MgO, SrO, BaO, Y2O3, La2O3, Fe2O3, and mixtures thereof). Si(OH) is present in a part of the SiO- network. The melting point of such silica-based inorganic fiber is in the range of 1500 °C to 1550 °C and has heat resistance of 1000 °C or higher. In addition, such silica-based amorphous fibers are excellent in that they substantially do not contain non-fibrous particles (shots) that cause deterioration of properties and variations in properties.

[0045] The composition of the silica-based inorganic fiber used in the present invention is not particularly limited as long as it is a silica-based inorganic fiber capable of undergoing the dehydration condensation reaction as described above. As a commercially available silica-based inorganic fiber, unburned BELCOTEX (registered trademark) of BELCHEM GmbH can be used.

[0046] Unfired BELCOTEX® has, in the process of manufacturing filaments or staple fibers from starting glass materials, metal or metal oxide ions (e.g., Al 3+ , TiO 2+ or Ti 4+ , and ZrO 2+ or Zr 4+ ) contained in the starting glass materials, with hydroxyl groups substituted by protons remaining.

[0047] The silica-based inorganic fibers used in the present invention are staple fibers having a diameter of 6 to 13 μm, preferably about 7 to 10 μm, and a length of 3 to 30 mm, or staple fibers having a diameter of 6 to 13 μm, preferably about 7 to 10 μm, and generally a length of 1 to 50 mm, preferably 3 to 30 mm, more preferably 3 to 20 mm, can be used.

[0048] The silica-based inorganic fibers as described above have a solid content in the suspension for papermaking of 25 wt% or more, 30 wt% or more, 40 wt% or more, and 70 wt% or less, 65 wt% or less, 50 wt% or less. Within these ranges, they are appropriately selected according to the content of heat-insulating inorganic particles and fibrous minerals. Note that the content rate of the silica-based inorganic fibers in the heat-insulating and flame-shielding sheet is about the same as the solid content rate of the suspension for papermaking.

[0049] If the content rate of the silica-based inorganic fibers is too low, the heat energy consumption effect by the silica-based inorganic fibers formed into a sheet cannot be obtained, and the suppressing effect on the temperature rise at the initial stage of thermal runaway becomes insufficient. On the other hand, if it is too high, in relation to the reduction of the proportion of other components relatively, the strength including the tensile strength decreases, and even if the problem of thermal shrinkage can be solved by the glass fibers described later, it cannot satisfy in terms of handleability.

[0050] (2) Glass fibers Glass fibers can impart tensile strength to a sheet. In particular, in relation to silica-based inorganic fibers, heat shrinkage at high temperatures can be suppressed. That is, glass fibers not only do not have heat insulation properties at high temperatures, especially at high temperatures exposed to flames, but also melt and shrink and cannot maintain their fiber shape. However, by suppressing the content rate in the sheet, even if the glass fibers melt, it is only necessary to spread in a film shape in the gaps between the fibers. This is because the glass fibers begin to melt in the temperature range where the silica fibers undergo dehydration condensation and shrink, so that the melted glass is confined between the silica fibers, which can suppress dripping and offset the shrinkage of the silica-based inorganic fibers. Therefore, for example, even in the specification of being attached to a lid body and used as shown in FIG. 2, the melted glass does not drip.

[0051] As the size of the glass fibers, the fiber diameter is about 1 to 10 μm, preferably 3 to 9 μm, more preferably about 4 to 6 μm. The fiber length only needs to be a length and strength that can be intertwined with the silica-based inorganic fibers and the organic fibers described later. On the other hand, since glass fibers melt in a high temperature range where they are exposed to flames, if the glass lumps generated by melting become too large, they will drip due to their own weight. Therefore, as the glass fibers, it is preferable to use staple fibers with a fiber length of 1 to 15 mm, preferably 2 to 10 mm.

[0052] The glass fibers used in the present invention are not particularly limited in terms of type. Since a high degree of heat resistance is not required from the role of the glass fibers in the present invention, E glass fibers are preferably used from the viewpoints of easy availability and cost.

[0053] The content rate of the glass fibers in the suspension for papermaking is 2% by weight or more, 5% by weight or more, and 25% by weight or less, 20% by weight or less, 15% by weight or less, 10% by weight or less, less than 7% by weight from the above-mentioned role. Note that the content rate of the glass fibers in the heat insulation and flame shielding sheet is about the same as the solid content rate of the suspension for papermaking.

[0054] The content ratio of glass fiber in the heat insulation and flame shielding sheet is preferably selected from the above range according to the content ratio of silica-based inorganic fiber due to the above role of glass fiber. Further, the weight ratio of silica-based inorganic fiber to glass fiber is preferably about 30:1 to 1.5:1, more preferably 20:1 to 2:1, and still more preferably 10:1 to 3:1. When the ratio of glass fiber becomes too high, it tends to be difficult to maintain the sheet shape in a high temperature range (above 700 °C) where glass melts or when exposed to flames.

[0055] (3) Fibrous minerals The fibrous minerals used in the present invention are minerals that can recognize particle shapes such as fibrous, dendritic, acicular, columnar, and rod-shaped in microscopic observation, and may be classified into mineral clays or mineral fibers. The aspect ratio, which is the ratio of the width corresponding to the fiber diameter to the total length corresponding to the fiber length (total length / width), is 10 or more, preferably 15 or more, and 200 or less, preferably 150 or less.

[0056] Clay minerals are excellent in heat resistance and flame resistance. On the other hand, clay causes an increase in the viscosity of the suspension, so it is likely to cause clogging in the papermaking process (especially the filtration and dehydration process using a mesh). In this regard, fibrous minerals have the advantage that the problem of clogging is less likely to occur.

[0057] From such a viewpoint, the average primary particle diameter of the fibrous minerals to be used is 5 μm or more, 10 μm or more, 20 μm or more, and 200 μm or less, 100 μm or less, 80 μm or less, 70 μm or less. The average particle here refers to the particle diameter converted into a spherical shape based on the end length projected in two dimensions in the case of fibrous minerals with curves or curls, and it may be classified using a sieve based on the minimum particle diameter.

[0058] As the above fibrous minerals, at least one selected from sepiolite, palygorskite, potassium titanate whisker, and wollastonite is preferably used.

[0059] Sepiolite and palygorskite are layered silicates classified as clay minerals with a fibrous form. They have a width corresponding to the fiber diameter of less than 0.1 μm, and the length (fiber length) measurable by microscopic observation is at most about 150 μm. Sepiolite is a magnesium hydrosilicate with a 2:1 ribbon-type structure. Due to differences in origin, it undergoes hydrothermal action under high temperature and high pressure, resulting in a high crystallinity α-type with long fibers, and a β-type with low crystallinity and short fibers (blocky or clay-like form) formed by sedimentation on the shallow seabed or lake bottom. Both types can be used. The α-type can usually be confirmed in a fibrous form by an electron microscope (1000 times magnification), while the β-type exhibits a granular form under an electron microscope (1000 times magnification) and is usually difficult to be recognized as a fibrous form.

[0060] The layered structure of sepiolite has a chain structure, is porous, has a large specific surface area, and is excellent in adsorptivity. It has thixotropy and becomes fibrous when crushed in a slurry using water as a dispersion medium. Also, due to its excellent plasticity and flexibility, it can enter the gaps between fibers and then dry and solidify to function as a binder between fibers.

[0061] Wollastonite is an acicular crystal mineral (metasilicate). The width corresponding to the fiber diameter is 1 μm or less, and the length is about 50 μm.

[0062] Potassium titanate is used as an acicular single crystal (whisker). Usually, the fiber diameter is 0.1 - 0.5 μm, and the length is 10 - 50 μm. For easily available ones, it is 15 - 30 μm.

[0063] Such fibrous minerals can entangle with silica-based inorganic fibers and glass fibers in the suspension for papermaking. Therefore, even in the sheet state formed by papermaking, they can be stably retained, the problem of powder falling is less likely to occur, and they can effectively contribute to increasing the strength of the sheet. Also, fibrous minerals or those formed by their entanglement are less likely to cause clogging in the dehydration and filtration process, so they are also excellent in handling properties in the papermaking process. On the other hand, in the case of other mineral particles, such as platy clay minerals like mica and talc, they hardly entangle with fibers in a slurry state, so their contribution to increasing the strength of the sheet is small, and the resulting sheet tends to be lacking in stiffness and poor in handleability.

[0064] Furthermore, since these fibrous minerals are excellent in heat resistance, they also help to improve the tensile strength of the sheet under high temperatures. In this regard, since glass fibers cannot contribute to the increase in tensile strength under high temperatures, they play a more effective role. On the other hand, since the heat insulation effect of these minerals tends to be inferior to that of aerogels and inorganic fibers used as inorganic particles for imparting heat insulation, if the amount is too large, the content of other components with heat insulation effects will relatively decrease, resulting in a possible reduction in the heat insulation performance of the heat insulation and flame shielding sheet.

[0065] From the above viewpoints, in the suspension for papermaking, the content of fibrous minerals in the heat insulation and flame shielding sheet is 5% by weight or more, 8% by weight or more, 10% by weight or more, 15% by weight or more, and 40% by weight or less, 35% by weight or less, 30% by weight or less, 20% by weight or less, and is appropriately selected in relation to the content of other components.

[0066] 〔Other components〕 (4) Binder As the binder, an organic binder and / or an inorganic binder can be used. The binder referred to in the present invention is a concept that includes, in addition to compounds having the role of binding fibers to each other and fibers to inorganic particles, flocculants commonly used in the papermaking method (wet dehydration forming). A flocculant is a substance that can promote the aggregation of fibers and particles contained in the suspension for papermaking and improve the yield by forming cross-linked products and the like.

[0067] (4-1) Organic binder The organic binder that can be used in the present invention can be used in various forms such as powder, granular, colloidal solution, high-viscosity fluid, and fibrous. Examples of the fibrous binder include thermoplastic resin fibers. In the papermaking process, the thermoplastic resin fibers can act as these binders by intertwining with glass fibers and silica-based inorganic fibers having a high elastic modulus and further intertwining with heat-insulating inorganic particles.

[0068] In addition, the thermoplastic resin fibers can be softened and melted by heat in the drying process after papermaking to bind the fibers together. Therefore, by heating and pressing during drying, the springback of glass fibers and silica-based inorganic fibers can be suppressed, and the thickness of the obtained sheet can be easily controlled.

[0069] Examples of the thermoplastic resin fibers that can be used include pulp fibers, polyester fibers (softening temperature: about 240°C, melting temperature: about 255 - 260°C), polypropylene fibers (softening temperature: about 140 - 160°C, melting temperature: about 165 - 173°C), polyethylene fibers (softening temperature: about 100 - 115°C, melting temperature: about 125 - 135°C), acrylic fibers (softening temperature: about 190 - 240°C), polyvinyl chloride fibers (softening temperature: about 60 - 100°C, melting temperature: about 200 - 210°C), vinylidene fibers (softening temperature: 145 - 165°C, melting temperature: about 165 - 185°C), nylon fibers (softening temperature: about 180°C, melting temperature: about 215 - 220°C), vinylon fibers (softening point: 220 - 230°C), polyvinyl alcohol-based fibers, and the like. Further, thermoplastic resin fibers having a core-sheath structure using fibers with a low softening temperature in the surface layer portion may be used.

[0070] When using thermoplastic resin fibers as the organic binder, staple fibers having a fiber diameter of 3 μm to 50 μm, preferably 5 μm to 30 μm, and a fiber length of 1 to 20 mm, preferably 3 to 10 mm, are preferably used. Since the thermoplastic resin fibers need to be homogeneously intertwined with the inorganic fibers that are the main body of the heat-insulating and flame-blocking sheet, it is preferable that they have a length similar to that of the inorganic fibers (glass fibers, silica-based inorganic fibers).

[0071] Examples of organic binders having a form other than fibers include powdery or fluid polymers. For example, latexes such as acrylic latex and (meth)acrylic latex; powdery thickening substances such as polyvinyl alcohol powder and starch; copolymers of styrene and butadiene, vinyl pyridine, acrylonitrile, copolymers of acrylonitrile and styrene, and the like.

[0072] These organic binders can impart strength to the wet sheet during papermaking. After papermaking and after removal of the dispersion medium, they can be solidified and can be softened again by heating, which is advantageous when forming into a desired shape, such as slitting or bending. The above organic binders can not only be used during normal use, but also soften in accordance with the retention state of inorganic particles between inorganic fibers during heating, particularly during heating before glass melting, thereby enabling the inorganic particles to be retained in a more stable state.

[0073] Furthermore, polymer flocculants such as polyacrylamide, acrylamide-sodium acrylate copolymer, and sodium polyacrylate may also be contained as one type of organic binder. In the dehydration process using a mesh in the wet papermaking method, particles smaller than the mesh opening pass through the mesh and cannot be filtered. In this case, a polymer flocculant is added to the fiber-containing liquid (papermaking suspension) to form aggregated flocs of a size that can be filter-formed. In relation to such a role, the organic binder corresponding to the flocculant is preferably added after preparing a fiber-containing liquid in which fibers and particles are homogeneously mixed, and further after mixing a separately prepared silica aerogel slurry with the fiber-containing liquid.

[0074] The above organic binders can be used alone or in combination of two or more. When used in combination of two or more, a combination of organic binders having different forms (for example, a combination of organic fibers and latex) may be used, or a combination of binders having different roles, such as a combination of organic fibers and a polymer flocculant, may also be used.

[0075] The organic binder may be contained in an amount sufficient to relieve the post-processing of the sheet obtained by the papermaking method, flexibility during heat processing, or expansion and contraction of the sheet during temperature rise during normal use. If the content is too high, it will cause a decrease in heat resistance. Also, at high temperatures exceeding the normal use temperature (up to about 200 °C), the organic components may generate heat due to oxidation or generate decomposition gases. In that case, there is also a possibility of rupture, ignition, and smoke generation. Therefore, the solid content concentration in the suspension for papermaking is 1% by weight or more, 3% by weight or more, 5% by weight or more, 10% by weight or less, and 8% by weight or less.

[0076] (4-2) Inorganic binder Examples of the inorganic binder include colloidal oxides such as colloidal silica, alumina sol, and titania sol; water glass and calcium silicate; and aluminum sulfate classified as a fixing agent or an inorganic flocculant.

[0077] Among these, colloidal silica can enter the fiber gaps and act as a binder for glass fibers and silica-based inorganic fibers by the coagulation of silica colloidal particles due to drying.

[0078] Aluminum sulfate improves the drainage and yield of the fiber group and is usually added as a fixing agent or a yield improver in the papermaking method.

[0079] The above inorganic binders can be used alone or in combination of two or more. The content rate of the inorganic binder in the suspension for papermaking is used at about 1% by weight or more, 3% by weight or more, 10% by weight or less, 7% by weight or less, and 5% by weight or less.

[0080] The organic binder and the inorganic binder can be used either alone or in combination. When used in combination, the content rate of the binder in the suspension for papermaking is 3 to 20% by weight, preferably 5 to 15% by weight.

[0081] (5) Precursor of thermosetting resin The suspension for papermaking of the present invention may further contain a precursor of a thermosetting resin. The thermosetting resin precursor is a monomer or oligomer of a thermosetting resin (such as a phenol resin (e.g., a resol resin), a polyimide resin, a melamine resin, a diallyl phthalate resin, etc.), and is in a liquid or powder form. The precursor of the thermosetting resin cures by undergoing a crosslinking reaction upon heating or in the presence of a curing agent.

[0082] In addition to inorganic fibers (such as silica fibers and glass fibers), organic and / or inorganic binders, and inorganic particles (fibrous minerals and heat-insulating inorganic particles), when it is desired to impart a specific shape to a sheet obtained by papermaking a suspension for papermaking containing a precursor of a thermosetting resin and further laminate a thermosetting resin layer to increase the strength of the sheet. By containing the precursor of the thermosetting resin, it can react with a part of the thermosetting resin layer to be laminated during thermosetting, so that the interlayer adhesion can be increased, which is preferable.

[0083] When the precursor of the thermosetting resin is contained, it is less than 5% by weight, preferably 1 - 3% by weight. This is because when the content increases, the adhesion strength with the thermosetting resin layer formed later increases, but the flexibility based on the inorganic fibers of the heat-insulating and flame-blocking sheet mainly composed of inorganic fibers tends to be impaired.

[0084] (6) Other fillers As the solid content of the suspension for papermaking, in addition to the above components, fillers as follows may be contained in less than 10% by weight, preferably less than 5% by weight, more preferably 3% by weight or less based on the total solid content.

[0085] As other fillers, clay minerals (layered silicates) other than the above fibrous minerals may be contained. Specifically, hydrous ferro-silicate minerals such as mica, kaolinite, smectite, montmorillonite, sericite, illite, glauconite, chlorite, talc, etc., or mixtures thereof can be used. Among these, smectite, montmorillonite, bentonite, and mixtures thereof are preferably used.

[0086] Bentonite is a natural clay mineral with montmorillonite as the main component. Smectite is a general term for a group of 2:1 type minerals, including montmorillonite, stevensite, hectorite, etc. The unit crystal of montmorillonite consists of a flat unit composed of a tetrahedral sheet, an octahedral sheet, and a tetrahedral sheet. Multiple such unit crystals are stacked to form a layered structure. Since the unit crystal of montmorillonite forms very thin plate-like crystals with a thickness of about 1 nm and a width of 100 - 1000 nm, smectite, like sepiolite, can enter the gaps between fibers in the papermaking suspension and form a coating film by drying and solidifying, and can function as these binders. Montmorillonite shows a high liquid limit and has a high water content. Smectite has the property of swelling with water or organic substances entering between the layers and can contain a large amount of water between the layers (for example, more than 10 times the water content of kaolin). In addition, montmorillonite is easily affected by electrolytes and can be peptized, so when used in combination with sepiolite with high coating film forming ability, it is easy to form a coating film in the gaps between fibers in a state of entrapping inorganic particles.

[0087] The above-mentioned layered silicates exist as powders with an average particle diameter of 300 μm or less, preferably 200 μm or less, more preferably 10 - 100 μm in terms of the equivalent circle diameter in the state before preparing the papermaking suspension. However, when mixed with water, they show viscosity, adhesiveness, and plasticity and have the ability to form self-coating films. Therefore, after the papermaking suspension is made into paper and dried, the clay can solidify and coagulate in the gaps between fibers in a state including inorganic particles (inorganic binders, inorganic particles for imparting heat insulation). Thereby, it can enhance the cohesive force of inorganic fibers and inorganic particles and play the role of a binder for stably holding inorganic fibers together.

[0088] Examples of other solid content fillers include neutralizing agents, lubricants, antiblocking agents, fluidity improvers, mold release agents, flame retardants, colorants, wetting agents, adhesives, yield improvers, paper strength improvers, drainage agents, pH adjusters, etc.

[0089] (7) Hydrophilic silica nanoparticle group The hydrophilic silica nanoparticle group used in the present invention generally corresponds to wet silica (precipitated silica) synthesized in water using sodium silicate synthesized from silica sand and soda ash and a mineral acid as raw materials. Before dispersion, it exists as amorphous aggregated particles (aggregates). In the state of aggregates, it can act like porous particles having a macroporous structure, and as a kind of heat-insulating inorganic particles distinguishable from hydrophilized aerogel, it may be contained in the suspension for papermaking. In the case of aggregates of hydrophilic silica nanoparticles, it is distinguishable from hydrophobic aerogel particles in that it can be added and mixed into the fiber-containing liquid without any special surface treatment.

[0090] In the case of the hydrophilic silica nanoparticle group, the primary average particle size is about 1 to 50 nm, about 5 to 30 nm of silica nanoparticles, and the surface is hydrophilic. The silica nanoparticles exist in the state of agglomerates (aggregates), which are so-called secondary particles in which individual nanoparticles do not form bonds with each other, and the secondary particle size is about 100 nm to 100 μm. However, the hydrophilic silica nanoparticle group is easily crushed and diffused as aggregates as secondary particles in water. As a result, in the preparation of the suspension for papermaking, it is easy to mix with inorganic fibers such as silica-based inorganic fibers and glass fibers, and it is easy to obtain a mixed liquid in which the inorganic fibers and the hydrophilic silica nanoparticles are entangled. On the other hand, in the aggregates, since the individual silica particles are not bonded, they may be crushed into nanoparticles by a mixing operation such as stirring. When the generated nanoparticles have insufficient entanglement with inorganic fibers, binders, and fibrous minerals, they tend to flow out together with water depending on the mesh size used in the dehydration process in the papermaking method, and the yield tends to be poor.

[0091] (8) Dispersion medium As the dispersion medium for the preparation of the suspension for papermaking, any medium that can uniformly dissolve or disperse the above-mentioned silica-based inorganic fibers, glass fibers, fibrous minerals, inorganic particles, and organic fibers may be used. For example, aromatic hydrocarbons such as toluene, ethers such as tetrahydrofuran, ketones such as methyl ethyl ketone, alcohols such as isopropyl alcohol, N-methyl-2-pyrrolidone (NMP), dimethylacetamide, dimethylformamide, dimethyl sulfoxide, water, and mixtures of one or more of these can be used. Organic solvents other than water are blended as necessary in relation to particle dispersibility, but water is preferred from the viewpoints of the environment and wastewater treatment. The content rates of the surfactant and the organic solvent are 0.1% by weight or less, preferably 0.01% or less, and more preferably 0.001% by weight or less. Even when using aerogel particles hydrophilized with an organic solvent or a surfactant as the heat insulation-providing inorganic particles, the suspension for papermaking can be kept within the above range.

[0092] <Preparation of Suspension for Papermaking and Sheet> (1) Preparation of Suspension for Papermaking Each of the components listed above, namely inorganic fibers (silica-based inorganic fibers, glass fibers, fibrous minerals), binders, and thermosetting resins and other fillers blended as necessary, are added in predetermined amounts into a dispersion medium, and further, a separately prepared hydrophilized aerogel slurry is added and stirred to prepare a suspension for papermaking. When preparing the suspension for papermaking, it may be further diluted with water as necessary.

[0093] The order of blending the above components is not particularly limited, but a method of adding the fibers and inorganic particles while stirring in the dispersion medium is preferred. Separately, it is preferable to prepare by mixing a dispersion (slurry) of hydrophilized silica aerogel prepared and a fiber-containing liquid, and adding a binder to the mixture. Thereby, even in the case of adding heat insulation-providing inorganic particles that are likely to aggregate in water and easily separate from fibers like hydrophobic aerogels, it becomes possible to obtain a sheet in a state where it is entangled with the fibers and dispersed within the fibers.

[0094] The solid content concentration of the suspension for papermaking may be any concentration as long as the above components can be uniformly stirred and mixed. Specifically, the solid content ratio is 0.01 to 10% by weight, preferably 0.05 to 3% by weight.

[0095] The content rate of the heat-insulating inorganic particles in the suspension for papermaking is 0% by weight or more, 5% by weight or more, 10% by weight or more, 15% by weight or more, 20% by weight or more, 25% by weight or more, 30% by weight or more, 35% by weight or more, and 45% by weight or less, 40% by weight or less. If the content exceeds half, papermaking becomes difficult, and the heat resistance and flame shielding property in a high-temperature range where thermal runaway occurs become insufficient. The hydrophilized silica aerogel can exhibit an excellent heat-insulating effect during normal use (heating up to about 200°C at most). Therefore, in a laminated battery or battery module with a large number of cells stacked, when a certain cell overheats, it can prevent the heat from spreading to adjacent battery cells or battery modules. Also, by containing silica aerogel, which is a porous particle, the weight of the heat-insulating and flame-shielding sheet can be reduced.

[0096] <Wet papermaking> Wet papermaking is a method in which the suspension for papermaking prepared above is lifted by a papermaking machine, pressed to remove moisture, and then dried to obtain a sheet-like material. As the papermaking machine, a cylinder mold papermaking machine, a fourdrinier papermaking machine, an inclined papermaking machine, an inclined short fourdrinier papermaking machine, or a combination of these can be used.

[0097] After papermaking, the obtained wet sheet is heated and dried to remove the dispersion medium. The drying temperature is equal to or higher than the temperature at which the dispersion medium (water or the organic solvent if it contains an organic solvent) can be evaporated, preferably 80°C or higher. The upper limit of the drying temperature is preferably lower than the temperature at which thermosetting starts when a precursor of a thermosetting resin is contained, and lower than the melting point of the thermoplastic fibers when thermoplastic fibers are included. Therefore, depending on the type of thermoplastic resin fibers used, the presence or absence of a precursor of a thermosetting resin, etc., it is usually 60 to 200°C, preferably 80 to 150°C.

[0098] After papermaking, before drying, during drying, or after drying, it may be shaped to obtain a heat-insulating and flame-shielding sheet in a desired shape. Drying may be usually carried out only by heating, or may be carried out by heating under pressure. When used for the partition sheet of a battery module as shown in Fig. 3, as shown in Fig. 4, it may be dried after pressing in a state where a shape having slits or the like is imparted. In any case, since it has plasticity in the state before drying, it can be solidified in a state where a predetermined shape such as a slit or a bend is imparted.

[0099] After drying, the obtained molded body (paper-like sheet) may be further subjected to secondary processing such as cutting, punching, and bending.

[0100] In addition, there is a method (external addition) in which a slurry containing heat-insulating inorganic particles, fibrous minerals, and a binder is impregnated into a fiber sheet obtained by papermaking a fiber-containing liquid by a method such as spray coating, curtain coating, impregnation coating, bar coating, roll coating, or blade coating. In such impregnation of fibrous minerals and inorganic particles by external addition, it tends to remain in the surface layer portion, powderize after drying, and the powder is likely to scatter. In this regard, in the heat-insulating and flame-shielding sheet of the present invention, since the heat-insulating inorganic particles are papermade together with the main inorganic fibers and fibrous minerals, the adhesion force of the inorganic particles and fibrous minerals in the sheet is enhanced by the holding effect due to entanglement with the fibers or fibrous minerals, and even if it powderizes after drying, it is difficult to scatter. That is, the inorganic particles are stably held in the sheet.

[0101] <Configuration of heat-insulating and flame-shielding sheet> By wet papermaking a suspension for papermaking having the above composition and removing the dispersion medium by drying, a heat-insulating and flame-shielding sheet can be obtained.

[0102] After papermaking, during drying, by filling a molding die, for example, as shown in Fig. 4, it may be a sheet 9 having a plurality of slits formed. Since the heat-insulating and flame-shielding sheet of the present invention has strength and flexibility, it can withstand processing and shaping as shown in Fig. 4.

[0103] The thickness of the sheet is greater than 0.5 mm, greater than or equal to 0.8 mm, greater than or equal to 1 mm, greater than or equal to 1.3 mm, greater than or equal to 1.5 mm, and less than 3 mm, less than or equal to 2.5 mm, less than or equal to 2.0 mm, less than or equal to 1.8 mm. If it is too thin, the strength is insufficient, and the content of fibers and heat-insulating inorganic particles decreases too much, making it difficult to obtain sufficient heat-insulating performance. On the other hand, although it is thinner than 3 mm, the strength is improved by fibrous minerals, and it becomes plastic and softened by thermoplastic resin fibers when heated. Therefore, even when it is subjected to a pressing process, it does not need to be broken. In addition, since the heat-insulating inorganic particles can exist in a state held by the entanglement of multiple types of fibers, the scattering of the powder of the inorganic particles is suppressed even when cutting or punching is performed.

[0104] The heat-insulating and flame-shielding sheet may be the sheet manufactured by papermaking alone as described above, or it may be a laminate in which an adhesive is applied and coated on one side and a release paper is further laminated. When it is adhered to the lid 12'a of the housing 12' of the battery module as shown in Figure 2, an adhesive may be applied to one side of the heat-insulating and flame-shielding sheet 10 to form an adhesive layer 10a, and a release paper may be laminated thereon. By peeling off the release paper and adhering the adhesive layer 10a to the back surface of the lid 12'a, the heat-insulating and flame-shielding sheet can be adhered, so the sheet construction work is simple.

[0105] The heat-insulating and flame-shielding sheet having the above configuration is superior in heat insulation in the high-temperature range compared to a sheet obtained by papermaking by simply adding a binder to silica-based inorganic fibers. In addition, by containing heat-insulating inorganic particles, it is also excellent in heat insulation during normal use (less than 300 °C where thermal runaway does not occur). Furthermore, although it also depends on the basis weight of the sheet, the bulk density can be 400 kg / m 3 or less, 300 kg / m 3 or less, 250 kg / m 3 or less, 100 kg / m 3 or more, 150 kg / m 3 or more. Therefore, mica sheet (generally 2000 kg / m 3It is much lighter compared to (a certain degree). This is very useful in terms of being lightweight for a laminate (for example, Fig. 2) formed by stacking a large number of battery cells, such as a battery pack or a battery module used as the power source of an EV vehicle, as a heat insulation and flame shielding sheet interposed between each battery cell.

[0106] Also, for some reason, if one of the cells undergoes thermal runaway, it will enter a high-temperature region where it is difficult to obtain the heat insulation effect of the aerogel. However, the silica-based inorganic fiber consumes thermal energy through a dehydration condensation reaction, and due to the low thermal conductivity of the silica-based inorganic fiber, the initial temperature rise can be suppressed. This means a delay in the rapid temperature rise due to thermal runaway, which is significant. Also, in the high-temperature range of 600 to 800 °C where the strength of the glass fiber decreases and it becomes difficult to maintain its shape, it is considered that the silica-based inorganic fiber, which has high heat resistance and is superior in heat resistance to glass fiber, can contribute to maintaining the shape of the sheet. Furthermore, for exposure to flames, the fibrous mineral can exhibit a flame shielding effect. Thus, the heat insulation and flame shielding sheet produced from the stock solution for papermaking of the present invention can maintain the sheet shape and exhibit a heat insulation effect in a wide temperature range, such as during normal use (up to about 200 °C), during a rapid temperature rise when one of the cells undergoes thermal runaway, further in a thermal runaway state at a high temperature of about 600 to 800 °C, and an exposure state to a flame near 1000 °C, and can delay the heating of adjacent cells and the exposure to flames.

[0107] Furthermore, the heat insulation and flame shielding sheet using porous particles as the inorganic particles for imparting heat insulation is excellent in compressibility. Even during normal use, a lithium-ion battery has volume fluctuations such that the cells expand in a heated state and contract upon cooling. Therefore, in a battery module of the cell laminate type battery pack as shown in Fig. 2, especially where the cells 11' are closely stacked within the housing 12', the heat insulation and flame shielding sheet using porous particles as the inorganic particles for imparting heat insulation can be expected to serve as a buffer for the volume fluctuations of the cells.

[0108] <Use of the heat insulation and flame shielding sheet> The heat insulation and flame shielding sheet produced from the papermaking raw material liquid of the present invention is used as a heat insulation and flame shielding sheet interposed between battery cells which are the minimum units of a lithium ion battery (for example, FIG. 1); when packaging a battery group in which a plurality of lithium ion battery cells electrically connected in series or in parallel are arranged in a housing through a predetermined space in an outer housing, a heat insulation and flame shielding sheet used for heat insulation of the lid of the housing (FIG. 2); and a heat insulation and flame shielding sheet used for the partition wall and isolation sheet of a cylindrical cell as shown in FIG. 3 (FIG. 3).

[0109] When an individual cell or module is in a "thermal runaway" state, the electrolyte contained in the battery may catch fire and cause an explosion and a fire. In order to prevent such a chain of thermal runaway, in the battery pack and in the battery module, by interposing the heat insulation and flame shielding sheet of the present invention between the individual battery cells constituting these or between the battery module and the housing, the heat insulation and flame shielding sheet can prevent a thermal runaway event occurring in an individual battery cell from spreading to adjacent ionization cells and further to other batteries in the battery module.

Example

[0110] 〔Measurement and evaluation method〕 (1) Flame exposure test As shown in FIG. 5, a sheet (150 mm × 150 mm) 15 to be evaluated is fixed to a cationic electrodeposition paint steel plate 17 regarded as a battery cell box using an adhesive tape 16, and the sheet 15 is heated by a horizontally fixed burner flame 14 (the flame is adjusted so that the temperature at 5 mm from the heating side surface of the sheet becomes 1000 ° C.), and the temperature (back surface temperature) of the flame corresponding portion of the steel plate 17 is measured by a temperature sensor 13. After heating with the above burner flame for 10 minutes or 5 minutes, the state of the sheet (presence or absence of cracks, sheet appearance, etc.) was observed.

[0111] (2) Measurement of thermal conductivity (heat flux method) As shown in Fig. 6, three sheets 31a, 31b, and 31c fabricated in the examples were stacked and placed on the heater 30. Thermocouples 32a were set between the heater 30 and the lowermost sheet 31a, and a thermocouple 32b was set on the uppermost sheet 31c. A heat flux sensor (Kyoto Electronics Industry Co., Ltd. K500B-20) 33 was set on the thermocouple 32b. The thermal conductivity (λ) was calculated by measuring the temperature difference between the lower surface of the lowermost sheet 31a and the upper surface of the uppermost sheet 31c with the two thermocouples 32a and 32b, and measuring the heat flux with the heat flux sensor 33. When calculating the thermal conductivity (λ), the measured value after holding for 6 hours after the temperature of the heater 30 reached 200°C was used so that the entire sheet was uniformly heated.

[0112] [Inorganic particle slurry with heat insulation imparted] (1) Inorganic particles with heat insulation imparted The following two types of inorganic particles with heat insulation imparted were used. (1-1) Hydrophobic aerogel Amorphous silica (surface area 700 - 800 m 2 / g, porosity 120 - 150 kg / m 3 , average pore diameter 20 nm, particle diameter 30 - 120 μm, DBP oil absorption 540 - 650 g / 100 g) with surface hydrophobicity (wetting angle 120 - 150 degrees) produced by the sol-gel method, and the hydrophilized aerogel (inorganic particles with heat insulation imparted I, II, III) obtained by performing the following hydrophilization treatments I, II, or III was used.

[0113] · Inorganic particles with heat insulation imparted I 20 g of the above hydrophobic aerogel and 20 g of an organic solvent (ethylene glycol monobutyl ether) were added to 200 g of water, and shaken to prepare an aerogel slurry. It is an aerogel slurry hydrophilized with an aerogel:organic solvent ratio of 1:1 (aerogel solid content ratio: 8.3%)

[0114] · Inorganic particles with heat insulation imparted II To 200 g of water, 20 g of the above hydrophobic aerogel, 20 g of an aqueous solution of 2.3% cellulose nanofiber, and 20 g of an organic solvent (ethylene glycol monobutyl ether) were added, and the mixture was shaken to prepare an aerogel slurry. It is an aerogel slurry hydrophilized at an aerogel:cellulose nanofiber ratio of 43:1 (aerogel solid content ratio: 8.6%).

[0115] · Heat-insulating inorganic particles III To 300 g of water, 30 g of the above hydrophobic aerogel and 5 g of polyvinyl alcohol were added, and the mixture was shaken to prepare an aerogel slurry. It is an aerogel slurry hydrophilized at an aerogel:polyvinyl alcohol ratio of 6:1 (aerogel solid content ratio: 8.9%).

[0116] (1-2) Hydrophilic silica particles (wet silica) As heat-insulating inorganic particles IV, amorphous precipitated silica was used, which is hydrophilic silica nanoparticles having a large number of silanol groups on the surface. These were aggregates of nanoparticles with an average primary particle diameter of several nm (irregular aggregates (secondary particles) of 1 to 10 μm. The specific surface area as secondary particles was 200 to 250 m 2 / g, and the DOA oil absorption amount: 230 to 280 ml / 100 g.

[0117] When using hydrophobic heat-insulating inorganic particles I, II, and III, they were added as a separately prepared slurry of hydrophilized heat-insulating inorganic particles. Table 2 shows the amounts (weight %) converted to the solid content in the suspension for papermaking. When adding hydrophilic heat-insulating inorganic particles (hydrophilic silica particles), the powder was added directly to the fiber-containing liquid.

[0118] 〔Raw materials of the fiber-containing liquid〕 (1) Silica-based inorganic fibers BELCOTEX (registered trademark) 110 of BELCHEM GmbH (composition is AlO 1.5 · 18〔(SiO2) 0.6 (SiO 1.5 OH) 0.4〕) The chopped strands (fiber diameter: 9 μm, fiber length: 3 to 5 mm) were used either with heat treatment (fired silica-based inorganic fibers) at 300 °C for 1 hour or without heat treatment (unfired silica-based inorganic fibers).

[0119] (2) Fibrous minerals · Sepiolite Two types of sepiolite, α-type or β-type, were used. As the α-type sepiolite, a classified product containing 40% of particles with a particle diameter of 150 μm or less and having a bulk density of 0.13 to 0.15 g / ml was used. As the β-type sepiolite, a product containing 80% of particles with a particle diameter of 45 μm or less and having a bulk density of 0.20 to 0.27 g / ml was used. · Potassium titanate (whisker) (Tismo manufactured by Otsuka Chemical Co., Ltd.) Fiber diameter: 0.3 to 0.6 μm, fiber length: 10 to 20 μm

[0120] (3) Glass fibers Glass fibers (E-glass) with a fiber diameter of 5 to 9 μm and a length of 3 to 9 mm were used.

[0121] (4) Organic binders · Pulp fibers (fiber diameter: 20 to 30 μm) · Polyester fibers (fiber diameter: 5 to 10 μm, fiber length: 3 to 9 mm) · Polyvinyl alcohol fibers (fiber diameter: 5 to 12 μm, fiber length: 3 to 6 mm) · Acrylic latex

[0122] (5) Inorganic binders · Aluminum sulfate · Colloidal silica Snowtex 30 (registered trademark) was used. Snowtex 30 is a colloidal solution in which silica nanoparticles (amorphous) with an average primary particle diameter of 10 to 20 nm are monodispersed, and the specific surface area of the silica particles is 130 to 280 m 2 / g.

[0123] (6) Others · Kaolinite (kaolin for research and experiment by Hayashi Junyaku Kogyo Co., Ltd.)

[0124] <Preparation of Suspension for Papermaking, Production and Evaluation of Sheets No. 21 to 27 Containing Inorganic Particles for Heat Insulation> Into a container containing 2000 cc of water, the slurry of inorganic particles for heat insulation prepared above and the fiber-containing liquid were added and mixed to prepare a suspension for papermaking having the composition (weight % of solid content) shown in Table 1. The components were added and blended in the order of unburned silica-based inorganic fiber, glass fiber, fibrous mineral, organic fiber (PET fiber), inorganic particles for heat insulation (slurry), inorganic binder, and flocculant (polyacrylamide). Polyacrylamide was added in the range of 3 cc to 18 cc while checking the state of the flocs in the suspension for papermaking.

[0125] The suspension for papermaking prepared above was injected into a wet forming machine (filter mesh screen #80 (mesh opening 180 to 200 μm)) and suction dehydrated. After dehydration, using a hot press machine (100 °C), it was heated and dried under pressure for 10 minutes. Thereby, a sheet of 150 mm × 150 mm × thickness of about 1.2 to 2.1 mm was obtained. For each suspension for papermaking, 3 sample sheets were produced. The average yield calculated from the solid content of the suspension for papermaking was 80% to 90%.

[0126] For the produced sheets, the above flame exposure test and measurement of thermal conductivity (heat flux method) were performed. Regarding the back surface temperature after 5 minutes of flame exposure, the temperature (average value of the 3 produced sheets) when converted to a thickness of 1.6 mm is shown in Table 1. Also, the properties (such as the presence or absence of cracks) of the sheet after the flame exposure test were visually observed. The results are shown in Table 1. Also, the thermal conductivity of the sheet when the heat source is 200 °C is shown in Table 1 together.

[0127] Reference Example R2: When hydrophobic aerogel particles (powder) were directly added to the fiber-containing liquid without hydrophilization treatment, even when shaken and stirred, the hydrophobic aerogel particle powder floated on the water layer surface to form a powder layer, and a suspension for papermaking in which fibers and aerogel particles were mixed could not be prepared.

[0128] Reference Example R3: As the hydrophilization treatment agent, a polyoxyethylene-polyoxypropylene condensate, which is a nonionic surfactant, was used. After adding 10 g of the hydrophilization treatment agent to 100 g of water, 10 g of hydrophobic aerogel particles (powder) was added, and the mixture was shaken vigorously to obtain a heat-insulating inorganic particle-containing slurry. When this aerogel-containing slurry was added to a separately prepared fiber-containing liquid, it separated from the fiber-containing liquid, and a uniform mixture (paper-making suspension) could not be obtained even by stirring.

[0129]

Table 1

[0130] Regarding the thermal conductivity at a heat source temperature of 200 °C, Sheets No. 21 to 24, 26, and 27 containing hydrophilized aerogel particles as heat-insulating inorganic particles were superior to Sheet No. 25 containing a hydrophilic nanoparticle group as heat-insulating inorganic particles. It is considered that the excellent heat insulation performance was achieved based on air with low thermal conductivity due to the dispersion of hydrophobic aerogel particles with a high porosity throughout the sheet. Also, from the comparison between No. 27 and No. 23, the sheet mainly composed of silica-based inorganic fibers had a lower thermal conductivity than the sheet mainly composed of glass fibers. It is considered that this is because the thermal conductivity of silica-based inorganic fibers is lower than that of glass fibers.

[0131] Regarding the flame exposure test, the sheets using hydrophilized aerogel particles as heat-insulating inorganic particles (see No. 21, 22, 23, 24, 26, and 27) had a lower temperature on the back side of the sheet in the flame exposure test than No. 25. Such a heat insulation effect is considered to be due to, in addition to the heat insulation effect during normal use (less than 200 °C) obtained by using hydrophilized silica aerogel particles as heat-insulating inorganic particles, the temperature rise delay effect by silica fibers having hydroxyl groups and the suppression of a rapid temperature rise of the entire sheet due to the inclusion of aerogel particles when the temperature rises rapidly like in thermal runaway.

[0132] Sheet Nos. 21 - 27 all contained unfired silica fibers and glass fibers, with the glass fiber / silica fiber ratio being 1 / 10 or more and the glass fibers being contained. As a result, no cracks were observed after the flame exposure test. On the other hand, when the content ratio of glass fiber / silica fiber was 8 / 1 or more and the content of glass fibers was excessive compared to the content of silica fibers, the glass fibers had melted due to flame exposure (No. 27).

[0133] Also, even when the content ratio of glass fiber / silica fiber exceeded 1 / 7 and the glass fibers were contained, Sheet No. 23 which did not contain clay minerals became cottony after the flame test and could not maintain its sheet shape.

[0134] From the comparison with No. 22 and 26, it is considered that using fibrous minerals as clay minerals has a higher heat insulation effect. Such a heat insulation effect was observed both during normal use and during flame exposure. Since sepiolite has adsorbed water, during normal use, a heat energy consumption effect due to dehydration of the adsorbed water can be obtained. In a high - temperature range such as during flame exposure, perhaps because the fibrous minerals have a higher porosity as a whole sheet compared to platy minerals, it is easier to obtain an opening effect at high temperatures. Note that No. 26 had a low hardness of the produced sheet and was inferior in handleability due to insufficient strength compared to other sheets.

[0135] Microscopic photographs (magnification 1000 times) of the cross - sections in the thickness direction of the sheets of No. 21 and 23 are shown in Figs. 7 and 8. From these photographs, it can be seen that the heat - insulating inorganic particles exist throughout the sheet, entwined with the fibers or embedded in the fiber gaps.

[0136] Furthermore, microscopic photographs (magnification 1000 times) of the heating surfaces of the sheets of No. 21 and 23 after the flame exposure test are shown in Figs. 9 and 10. From these photographs, it can be confirmed that the silica - based inorganic fibers, heat - insulating inorganic particles, and fibrous mineral clay (in the case of No. 21) remain.

[0137] <Comparison of Heat Insulation Effects between Silica-based Inorganic Fibers and Glass Fibers> Regarding the heat insulation and flame shielding sheets No. 23 and No. 27 prepared above, a heat insulation test at 700 °C was conducted as follows. (1) Heat Insulation Test I As shown in Fig. 11, a ceramic heat insulation board (300 mm × 300 mm × thickness 15 mm) 23 with a circular opening 23a of 40 mm in diameter was placed on a hot plate (100 mm × 100 mm) 22 heated to 700 °C, and a sheet (150 mm × 150 mm) 21 to be evaluated was placed so that the circular opening 23a was at the center and held for 6 minutes.

[0138] Photographs of the heated parts of sheets No. 23 and No. 27 after the test are shown in Figs. 12 and 13, respectively. Comparing the two, in No. 23, the sheet papermaking state was maintained, but in No. 27, the glass fibers that had lost their elasticity floated up, and there was a tendency for it to be difficult to maintain the sheet shape in the heated part.

[0139] Microscopic photographs (100 times) of the heated surfaces of the heated parts of sheets No. 23 and No. 27 are shown in Figs. 14 and 15, respectively. Also, microscopic photographs (100 times) of the unheated sides (backs) of sheets No. 23 and No. 27 are shown in Figs. 16 and 17, respectively.

[0140] Regarding sheet No. 27, comparing Fig. 15 (heated surface) and Fig. 17 (back surface), it was found that there were many places where the fibers were melted and fused on the heated surface, and the area of the molten and fused part was large. On the other hand, in No. 23, even on the heated surface, most of the fibers maintained their fiber state (Figs. 14 and 16). Since No. 27 is mainly composed of glass fibers, at 700 °C, some of the glass fibers began to melt, and even the glass fibers with a fiber shape had reduced elasticity and strength, and the entanglement force between the fibers decreased, so it seems that they floated up from the sheet surface.

Industrial Applicability

[0141] By using the stock solution for papermaking of the present invention, a lightweight and thin heat insulation and flame shielding sheet can be provided. Such a heat insulation and flame shielding sheet is used between individual cells in a battery module in which a plurality of lithium ion batteries, particularly a battery module in which a plurality of cells are stacked and packaged in a housing, so as to insulate the temperature rise during normal use of each cell from propagating to adjacent cells. Further, when a certain cell undergoes thermal runaway for some reason, it can be used to insulate heat and shield flames so as not to cause thermal runaway of other cells in the battery module.

Explanation of reference numerals

[0142] 9, 10 Heat insulation and flame shielding sheet 8, 11, 11' Battery cell 12 Housing

Claims

1. An aqueous slurry containing hydrophilically treated aerogel particles, at least a portion of the surface of which is coated with a hydrophilic polymer having a plurality of hydroxyl groups.

2. 2. The aqueous slurry according to claim 1, wherein the hydrophobic aerogel particles are silica aerogel particles having an average particle size of 5 to 200 μm and a wetting angle with respect to water of 100° or more.

3. The aqueous slurry according to claim 1 , wherein the hydrophilic polymer is a water-soluble polymer.

4. The particle density of the hydrophobic aerogel particles is 100 to 200 g / cm ３ 2. The aqueous slurry according to claim 1 ,

5. 2. The aqueous slurry according to claim 1, wherein the content ratio of the hydrophilic polymer to the hydrophobic aerogel is 1 / 2 to 1 / 100 in terms of hydrophilic polymer / hydrophobic aerogel particles (weight ratio).

6. 2. The aqueous slurry according to claim 1, wherein the content of the organic solvent and / or surfactant contained in the aqueous slurry is less than 10% by weight.

7. 7. The method for producing an aqueous slurry according to claim 1, further comprising the step of adding and mixing silica aerogel particles having a hydrophobic surface and an average particle size of 5 to 200 μm to an aqueous solution of a hydrophilic polymer.

8. A papermaking suspension comprising the aqueous slurry according to any one of claims 1 to 6 and inorganic fibers.

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