Heat insulation and flame shielding sheet, assembled battery using the same, and battery module package

Abstract

To provide a lightweight, thin heat insulating and fireproof that is used by being interposed between cells of a battery pack in which battery cells are connected in series or parallel and stacked.SOLUTION: A heat insulating and fireproof sheet contains 25 to 70 weight% of silica-based inorganic fibers having hydroxyl groups, 2 to 25 weight% of glass fibers, 5 to 40 weight% of fibrous minerals, and 3 to 20 weight% of binder, and has a thickness of 3 mm or less, in which the weight ratio of the silica-based inorganic fibers to the glass fibers is 30 / 1 to 1.5 / 1, and may further contain inorganic particles that exhibit heat insulating properties.SELECTED DRAWING: Figure 7

Description

Technical Field

[0001] The present invention relates to a heat insulation and flame shielding sheet that can be interposed between battery cells constituting a battery pack or a battery module that serves as a power source for an electric motor driving an electric vehicle, a hybrid vehicle, etc., or can be used for heat insulation and flame shielding of a housing that packages an assembly of cells (battery module), and also relates to a battery pack and a battery module package using these.

Background Art

[0002] In an electric vehicle or a hybrid vehicle driven by an electric motor, etc., 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] When a certain battery cell rapidly heats up and causes thermal runaway due to an internal short circuit or overcharging of the battery, etc., it propagates 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, etc., which may cause a major accident such as ignition. For this reason, in a battery pack, as a technique for suppressing the heat propagated to adjacent cells and further suppressing the spread of fire 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 for the packaging of the battery module, for example, as shown in FIG. 2, 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 barrier sheet 10 to the back surface of this lid 12’a using an adhesive 10a, it is possible to prevent high-temperature lithium electrolyte ejected due to thermal runaway of one of the packaged battery cells and the flame generated thereby from affecting surrounding devices.

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

[0006] As a sheet that is lightweight and has heat insulation and flame resistance properties, it has been proposed to use a woven fabric, non-woven fabric, or paper made of inorganic fibers. Alumina fibers as inorganic fibers have very excellent properties such as high heat resistance (melting point of about 2000°C), combustion resistance, and high insulation, but they 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 has been proposed as a heat insulation and flame barrier sheet having desired heat insulation and flame barrier properties.

[0007] For example, in JP-T-2021-531631 (Patent Document 1), a sheet obtained by papermaking a material having flame resistance containing two types of glass fibers with different diameters, "a mixture of at least two fine particle fillers selected from glass bubbles, kaolin clay, talc, mica, calcium carbonate, and aluminum trihydrate", and an inorganic binder has been proposed.

[0008] In addition, in International Publication No. 2019 / 187313 (Patent Document 2), as a heat insulation sheet used by sandwiching a laminated battery pack in which a plurality of battery cells are fixed in a laminated state between the laminated surfaces of the battery cells, an inorganic fiber sheet in which inorganic particles (inorganic hollow particles or inorganic foamed particles) are filled in the gaps of inorganic fibers has been proposed. Here, examples of the inorganic fibers include "for example, magnesium silicate (sepiolite), rock wool, ceramic fiber, glass fiber, potassium titanate fiber, calcium silicate". Further, as Example 1, 80% by weight of magnesium silicate (sepiolite), 10% by weight of glass fiber, and 10% by weight of nylon fiber were suspended and dispersed to form a slurry for papermaking, which was wet-papered into a sheet shape, dried, and then hot-pressed to produce an inorganic fiber sheet with a thickness of 0.7 mm. It is described that a heat insulation sheet was prepared by adhering polyethylene films (thickness 50 μm) to both sides of the obtained sheet. Note that examples containing inorganic particles are not disclosed.

[0009] Japanese Unexamined Patent Application Publication No. 2021-34278 (Patent Document 3) discloses a heat insulation sheet obtained by papermaking a slurry in which two types of inorganic particles, namely, silica nanoparticles (first particles) and metal oxide particles such as titania and alumina (second particles), and linear or needle-like inorganic fibers (glass fibers in the examples) are included, and optionally a binder (organic binders such as polymer flocculants and acrylic emulsions, inorganic binders such as silica sol and alumina sol) are dispersed in water. Since the heat insulation property improves as the content of silica nanoparticles increases, it has been proposed that the first inorganic particles, the second inorganic particles, and the inorganic balloons that function as heat insulating materials be contained in an amount of 50 to 80% by mass based on the entire heat insulation sheet. Note that in the examples, it is described that a slurry containing 8% by weight of pulp fibers in addition to the above components was papermade to obtain a heat insulation sheet.

[0010] Patent No. 6997263 and Patent No. 7000626 (Patent Documents 4 and 5) propose a heat transfer suppression sheet containing inorganic particles (oxide particles such as alumina and titania, porous or hollow particles with high porosity) that exhibit a heat insulation effect and two types of inorganic fibers. As the two types of inorganic fibers, a combination of a thick and linear first fiber and a thin and dendritic second fiber is used. By using the combination of the two types of inorganic fibers, it is explained that inorganic particles of 30 to 90% by weight can be stably retained due to the entanglement of the fibers and the shape can be maintained even during high-temperature runaway. However, regarding the first inorganic fiber and the second inorganic fiber, the specific types of fibers used are not described, and there is no disclosure regarding the prevention of powder falling and the heat insulation effect for the produced heat transfer suppression sheet.

[0011] By the way, aerogel (porous silica particles) is known as porous particles with excellent heat insulation properties. Japanese Unexamined Patent Application Publication No. 2015-163815 (Patent Document 6) discloses an insulating material (insulating sheet) containing 35 to 210 parts by weight of aerogel particles (average particle size of 2 to 140 μm and specific surface area of 400 m 2 / g or more) having a high heat insulation effect based on 100 parts by weight of the main fiber, and further containing at least one water-soluble polymer selected from the group consisting of a cationic polymer and an amphoteric polymer, and / or a binder containing a low-melting synthetic fiber. 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 are 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 embodiment, organic fibers (such as pulp, polyester fibers, 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.

[0012] Further, Japanese Patent Application Laid-Open No. 2020-200901 (Patent Document 7) proposes a heat-insulating sheet using aerogel particles, glass beads, or ceramic beads having a large number of nanometer-sized pores as a heat-insulating component and using bio-dissolvable rock wool as a fiber. 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 100 parts by weight of the fiber (rock wool) serving as the base material (

[0026] ). In the examples of Patent Document 7, an aerogel dispersion obtained by adding and mixing aerogel to an aqueous binder solution and a dispersion of bio-dissolvable 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 (hot wire method) of the produced heat-insulating sheet are shown.

Prior Art Documents

Patent Documents

[0013]

Patent Document 1

Patent Document 2

[0014] Typical glass fibers as inorganic fibers are low in price, but the use temperature of general-purpose types (e.g., E-glass) is limited to about 700 °C. Therefore, during thermal runaway exceeding 700 °C, they will melt and cannot maintain the sheet shape. In Patent Document 1, it is reported that the glass fiber content was 7 to 25% by weight (Examples), and due to the coexistence of clay, mica, and glass bubbles, it was able to withstand the torch flame test. In addition, evaluation tests including the torch flame test are performed on a laminated sheet obtained by stacking multiple layers of inorganic paper made by the papermaking method using sodium silicate as an inorganic binder, followed by pressing and drying. When it is thin, it has been shown that holes are formed in the laminated sheet.

[0015] In Patent Document 2, the glass fiber content is 10% by weight or less, but there is no example of retaining particles. When containing inorganic particles such as aerogel, it has been proposed to sandwich both sides with plastic films. In the case of a heat insulation sheet interposed between batteries, since both sides of the heat insulation sheet are held by the batteries, even after the plastic film burns out during thermal runaway, it is possible to exist between the batteries and exhibit a heat transfer suppression effect. However, as shown in FIG. 2, when used by attaching to the cover of the housing, when the plastic film on the battery side burns out, the sheet shape cannot be maintained and the inorganic particles will fall off.

[0016] In Patent Documents 3 to 5, sheets with an inorganic particle content of 30% by weight or more, and further 50% by weight or more, have been proposed. In Patent Document 3, a sheet with a thickness of 1 mm was created by a papermaking method with a glass fiber content of 10% by weight and a pulp fiber content of 8% by weight, and the thermal conductivity up to 850 °C was measured while changing the content ratio of silica nanoparticles and titania particles. However, since the evaluation by a flame test has not been conducted, it is not clear whether the shape can be maintained when exposed to a flame near 1000 °C as a heat insulation sheet fixed to a cover of a housing or the like. Furthermore, in Patent Documents 4 and 5, neither the prevention of powder falling nor the heat insulation effect has been shown with specific examples.

[0017] Patent Document 6 specifically shows the heat insulation effect using an aerogel, but the heat source temperature is about 100 °C. There is no disclosure regarding the flame shielding property and the heat insulation property in a high temperature range of 500 °C or more, which are required as countermeasures for thermal runaway when a lithium-ion battery undergoes thermal runaway, and it is unclear.

[0018] Patent Document 7 describes, as the uses of heat insulating materials, in addition to heat insulating containers for pharmaceuticals and foods ((0002)), heat insulation of electronic components ((0003)), but it is not described that it is used for a thermal runaway sheet of a lithium-ion battery. Although the measurement results of the thermal conductivity are shown, the specific effects regarding the heat insulation property and the flame shielding property against a high temperature of 600 °C or more, which are required as countermeasures for thermal runaway, have not been shown, and the effects are unclear.

[0019] Since the bio-soluble rock wool that serves as 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 insulation sheet at a certain ratio. As a result, there is a risk of affecting the heat insulation and flame shielding properties of the heat insulation sheet, and there is also a possibility that the non-fibrous particles may damage the outer wall of the cell in contact with the sheet.

[0020] 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 flame shielding and heat insulation effect that can maintain its shape for at least 10 minutes even when exposed to a flame near 1000°C.

Means for Solving the Problems

[0021] The inventors of the present invention have variously studied the fibers and the structure of the sheet that can exhibit heat insulation properties during normal use (when the temperature rises to the extent that thermal runaway does not occur) and flame shielding and heat insulation properties even against flame exposure (1000°C or higher) in a lightweight and thin sheet. Since the lithium-ion battery used as the power source of an EV vehicle is a laminate of a large number of cells, the heat insulation and flame shielding sheet used by interposing it between individual cells is required to be mainly composed of an inorganic material, thin, and lightweight in relation to heat resistance. As a manufacturing method of 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.

[0022] By the way, aerogel particles, which are known to have a high heat insulation effect, have a hydrophobic and low-density surface in relation to the fact that they exhibit an excellent heat insulation effect due to air being trapped in nano-sized pores. This also makes it difficult for them to entangle and aggregate with fibers in the wet papermaking method using water as the dispersion medium. In order to exhibit the excellent heat insulation effect of aerogel particles, it is necessary to uniformly mix the hydrophobic aerogel particles and fibers in the papermaking raw material liquid (fiber-containing suspension).

[0023] Also, it is known that the heat insulation effect of aerogel particles is reduced in a high-temperature range of 500°C or higher where the proportion of radiant heat is high. Therefore, for heat insulation in the high-temperature range when thermal runaway occurs, it is desirable to have a heat insulation mechanism different from that of silica aerogel particles.

[0024] On the other hand, mineral clay is excellent in flame shielding properties, but generally has a tendency to have a high thermal conductivity. Therefore, when the content increases, the heat insulation property tends to decrease. Furthermore, when trying to produce a sheet by the wet papermaking method, it is likely to clog in the filtration and dehydration process using a mesh, and it is substantially difficult to paper a sheet having a thickness of 1 mm or more. For this reason, it is necessary to use it as a sheet in which a plurality of sheets are laminated, such as the inorganic paper produced in Patent Document 1, for example.

[0025] The inventors have found that in silica-based inorganic fibers having hydroxyl groups at their ends, when exposed to high temperatures, the fibers themselves can absorb heat through a dehydration condensation reaction and suppress an initial rapid temperature rise. That is, in silica-based inorganic fibers having hydroxyl groups at their ends, a dehydration condensation reaction occurs in a temperature range of about 300 to 600°C, and the initial temperature rise can be delayed by suppressing the temperature rise due to the endothermic reaction and further consuming thermal energy by the latent heat of vaporization of the generated water.

[0026] The inventors of the present invention have found that by using such silica-based inorganic fibers as the base fibers constituting the heat insulation and flame shielding sheet, as the heat insulation-imparting inorganic particles, while taking advantage of the excellent heat insulation properties of aerogel particles, at high temperatures where the heat insulation effect of aerogel particles decreases, and in the case of a rapid temperature rise or ignition that causes thermal runaway, the heat insulation and flame shielding properties are exhibited, and the risk of thermal runaway expansion and spread of a lithium-ion battery can be reduced, thus completing the present invention.

[0027] That is, the heat insulation and flame shielding sheet of the present invention is a heat insulation and flame shielding sheet having the following aspects. 〔Aspect 1〕 A heat insulation and flame shielding sheet having a thickness of 3 mm or less, containing 25 to 70% by weight of silica-based inorganic fibers having hydroxyl groups, 2 to 25% by mass of glass fibers, 5 to 40% by weight of fibrous minerals, and 3 to 20% by weight of a binder, wherein the content weight ratio (silica-based inorganic fibers / glass fibers) of the silica-based inorganic fibers to the glass fibers is 30 / 1 to 1.5 / 1.

[0028] 〔Aspect 2〕 In the above Aspect 1, further containing more than 0% by weight to 45% by weight of heat insulation-imparting inorganic particles, wherein the heat insulation-imparting inorganic particles include hydrophilized aerogel particles obtained by hydrophilizing the surface of hydrophobic aerogel particles having a porosity of 80% or more, an average particle diameter of 5 to 200 μm, a surface area of 300 to 1000 m 2 / g and a wetting angle with respect to water of 100° or more.

[0029] 〔Aspect 3〕 In the above Aspect 2, the particle density of the hydrophobic aerogel particles is 100 to 200 g / cm 3 3. 〔Aspect 4〕 In the above Aspect 2, the hydrophilized aerogel particles are those 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. 〔Aspect 5〕 In any one of the above Aspects 2 to 4, the heat insulation-imparting inorganic particles further include surface-hydrophilic nanoparticles having an average primary particle diameter of 1 nm to 50 nm.

[0030] [Aspect 6] In any one of the aspects 1 to 5, the fibrous mineral is at least one selected from sepiolite, palygorskite, potassium titanate whisker, and wollastonite. [Aspect 7] In any one of the aspects 1 to 5, the fibrous mineral is a layered silicate mineral.

[0031] The present invention also includes a battery pack or a battery pack module in which battery cells are connected in series or in parallel and housed in a housing, and the sheet according to any one of the aspects 1 to 7 is interposed between the battery cells. Further, the present invention also includes a battery pack or a battery pack module in which battery cells are connected in series or in parallel and housed in a housing, and the sheet according to any one of the aspects 1 to 7 is adhered to the inner wall surface of the housing with which the battery cells are in contact. [Advantages of the Invention]

[0032] The heat insulation and flame shielding sheet of the present invention is lightweight, excellent in heat insulation during normal use, and can withstand a rapid temperature rise due to thermal runaway and even a 10-minute exposure to a flame near 1000 °C, and can suppress the thermal runaway of lithium-ion batteries. [Brief Description of the Drawings]

[0033]

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MODE FOR CARRYING OUT THE INVENTION

[0034] The heat insulation and flame shielding sheet of the present invention is a paper-like sheet of inorganic fibers containing silica-based inorganic fibers having hydroxyl groups, glass fibers, fibrous minerals, and a binder, and further containing heat insulation-providing inorganic particles at a predetermined ratio if desired. Specifically, it is a paper-like sheet with a thickness of less than 3 mm, preferably 2 mm or less, which can be produced by wet papermaking of a papermaking suspension containing silica-based inorganic fibers having hydroxyl groups, glass fibers, fibrous minerals, a binder, and heat insulation-providing inorganic particles at a predetermined ratio.

[0035] <Composition of the papermaking suspension> First, the papermaking suspension used as a papermaking raw material for the heat insulation and flame shielding sheet of the present invention will be described. The papermaking suspension contains silica-based inorganic fibers having hydroxyl groups, glass fibers, fibrous minerals, and a binder, and further contains heat insulation-providing inorganic particles at a predetermined ratio in water or, in some cases, an aqueous medium containing an organic solvent or a surfactant. Each component will be described in detail below.

[0036] (1) Silica-based inorganic fibers The silica-based inorganic fibers used in the present invention are amorphous fibers containing SiO 2 as a fiber constituent component and having hydroxyl groups at the ends. The hydroxyl groups contained in the silica-based inorganic fibers undergo a condensation reaction at about 300 to 600 °C as shown in the following formula (1) to form new siloxane bonds (Si-O-Si bonds) and release H 2 O. The water generated by dehydration condensation vaporizes in a high-temperature atmosphere. At this time, it is considered that the heat energy given to the silica-based inorganic fiber-made sheet is consumed as the heat of vaporization, so that the temperature rise of the sheet can be delayed.

Chemical formula

[0037] Examples of silica-based inorganic fibers 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 weight percent of alumina, less than 0.5 percent of sodium oxide, and less than 0.5 percent of other components (ZrO 2 , TiO 2 , Li 2 O, K 2 O, CaO, MgO, SrO, BaO, Y 2 O 3 , La 2 O 3 , Fe 2 O 3 , and mixtures thereof). Si(OH) is present in part of the SiO- network. The melting point of such silica-based inorganic fibers 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 property degradation and property variations.

[0038] The silica-based inorganic fiber used in the present invention is not particularly limited in its composition 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, uncalcined BELCOTEX (registered trademark) of BELCHEM GmbH can be used.

[0039] Uncalcined BELCOTEX (registered trademark) has a hydroxyl group in which the metal or metal oxide ion (e.g., Al 3+ , TiO 2+ or Ti 4+ , and ZrO 2+ or Zr 4+ ) contained in the starting glass material has been proton-substituted remaining.

[0040] 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.

[0041] The silica-based inorganic fibers as described above have a solid content ratio in the suspension for papermaking of 25% by weight or more, 30% by weight or more, 40% by weight or more, and 70% by weight or less, 65% by weight or less, 50% by weight or less. Within these ranges, they are appropriately selected according to the contents of heat-insulating inorganic particles and fibrous minerals. Note that the content ratio of the silica-based inorganic fibers in the heat-insulating and flame-shielding sheet is approximately the same as the solid content ratio of the suspension for papermaking.

[0042] If the content ratio of the silica-based inorganic fibers is too small, the heat energy consumption effect by the silica-based inorganic fibers formed into a sheet cannot be obtained, and the effect of suppressing the temperature rise at the initial stage of thermal runaway becomes insufficient. On the other hand, if it is too much, in relation to the reduction of the proportion of other components relatively, the strength such as the tensile strength decreases, and even if the problem of thermal shrinkage can be solved by the glass fibers described later, it is not satisfactory in terms of handleability.

[0043] (2) Glass fibers Glass fibers can impart tensile strength to the sheet. In particular, in relation to the silica-based inorganic fibers, it can suppress thermal shrinkage at high temperatures. That is, glass fibers not only do not have heat insulation at high temperatures, especially at high temperatures exposed to flames, but also melt and shrink and cannot maintain the fiber shape. However, by suppressing the content ratio in the sheet, even if the glass fibers melt, it only needs 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 the lid body as shown in FIG. 2, the melted glass does not drip.

[0044] As the size of the glass fiber, the fiber diameter is 1 to 10 μm, preferably 3 to 9 μm, more preferably about 4 to 6 μm. The fiber length may be any length and strength that can be intertwined with the silica-based inorganic fiber and the organic fiber described later. On the other hand, since glass fiber melts in a high-temperature region where it is exposed to flames, if the glass mass generated by melting becomes too large, it will sag due to its own weight. Therefore, as the glass fiber, it is preferable to use staple fibers having a fiber length of 1 to 15 mm, preferably 2 to 10 mm.

[0045] The glass fiber used in the present invention is not particularly limited in terms of type. Since a high degree of heat resistance is not required from the role of the glass fiber in the present invention, E-glass fiber is preferably used from the viewpoints of availability and cost.

[0046] The content rate of the glass fiber in the suspension for papermaking is 2% by weight or more, 5% by weight or more, 25% by weight or less, 20% by weight or less, 15% by weight or less, 10% by weight or less, and less than 7% by weight from the above role. Note that the content rate of the glass fiber in the heat insulation and flame shielding sheet is about the same as the solid content rate of the suspension for papermaking.

[0047] From the above role of the glass fiber, the content rate of the glass fiber in the heat insulation and flame shielding sheet is preferably selected from the above range according to the content rate of the silica-based inorganic fiber. Further, as the weight ratio of the silica-based inorganic fiber: glass fiber, it 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. If the proportion of the glass fiber becomes too high, it tends to be difficult to maintain the sheet shape in a high-temperature region (above 700 °C) where the glass melts or when exposed to flames.

[0048] (3) Fibrous minerals The fibrous mineral used in the present invention is a mineral that can recognize particle shapes such as fibrous, dendritic, needle-like, columnar, and rod-like in microscopic observation, and may be classified into mineral clay or mineral fiber. 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.

[0049] The heat-insulating inorganic particles described below have a small heat-insulating effect and cannot be expected to have a shading property at high temperatures (for example, 500 °C or higher) where thermal runaway occurs. In this regard, clay minerals are excellent in heat resistance and flame resistance. On the other hand, since clay causes an increase in the viscosity of the suspension, 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 hardly occurs.

[0050] From such a viewpoint, the average primary particle diameter of the fibrous mineral 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 a fibrous mineral with a curved or curled shape, and it may be classified based on the minimum particle diameter using a sieve.

[0051] As the above fibrous mineral, at least one selected from sepiolite, palygorskite, potassium titanate whisker, and wollastonite is preferably used.

[0052] Sepiolite and palygorskite are layered silicates classified as clay minerals having a fibrous form. These 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 structure. Due to differences in its origin, it undergoes hydrothermal action under high temperature and pressure, resulting in a high crystallinity α-type with long fibers, and a β-type with low crystallinity, short fibers (blocky or clay-like form), which is formed by sedimentation on the shallow sea floor or lake bottom. Both types can be used. The α-type can usually be confirmed in a fibrous form under an electron microscope (1000 times magnification), while the β-type exhibits a granular shape under an electron microscope (1000 times magnification) and is usually difficult to recognize as a fibrous form.

[0053] The layered structure of sepiolite has a chain structure, is porous, has a large specific surface area, and excellent adsorbability. It has thixotropy and becomes fibrous when crushed in a slurry using water as the 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.

[0054] Wollastonite is an acicular crystal mineral (metasilicate), with a width corresponding to the fiber diameter of 1 μm or less and a length of about 50 μm.

[0055] 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 obtainable ones, it is 15 - 30 μm.

[0056] Such fibrous mineral particles can entangle with silica-based inorganic fibers and glass fibers in the papermaking suspension. Therefore, even in the sheet state created by papermaking, they can be stably retained, the problem of powder falling is less likely to occur, and it can effectively contribute to increasing the strength of the sheet. Also, fibrous mineral particles or those entangled with them are less likely to cause clogging in the dehydration filtration process, so they are also excellent in handling properties in the papermaking process. On the other hand, for other mineral particles, such as platy clay minerals like mica and talc, they hardly entangle with fibers in a slurry state. Therefore, their contribution to increasing the strength of the sheet is small, and the obtained sheet tends to lack stiffness and has poor handling properties.

[0057] Furthermore, since these fibrous minerals are excellent in heat resistance, they also contribute to improving the tensile strength of the sheet under high temperatures. In this regard, glass fibers cannot contribute to an increase in tensile strength under high temperatures, so these fibrous minerals play a more effective role. On the other hand, the heat insulation effect of these minerals tends to be inferior to that of the heat insulation-providing inorganic particles and inorganic fibers described later. Therefore, if the amount is too large, the content of other components with a heat insulation effect will relatively decrease, resulting in a reduction in the heat insulation property of the heat insulation and flame shielding sheet.

[0058] From the above viewpoints, in the suspension for papermaking, as the content rate of the fibrous minerals in the heat insulation and flame shielding sheet, it is selected as appropriate in relation to the content rate of other components within the range of 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.

[0059] (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 a role of binding fibers to each other and fibers to inorganic particles, flocculants conventionally 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 or the like.

[0060] (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. 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 insulation-providing inorganic particles in the papermaking process.

[0061] 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 applying heat and pressure 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.

[0062] 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, etc. Further, thermoplastic resin fibers having a core-sheath structure using fibers with a low softening temperature in the surface layer part may be used.

[0063] When using thermoplastic resin fibers as the organic binder, staple fibers with 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 insulation and flame shielding sheet, it is preferable to have a length similar to that of the inorganic fibers (glass fibers, silica-based inorganic fibers).

[0064] Examples of the organic binder having a form other than fibers include powdery or fluid polymers. For example, latexes such as acrylic latex, (meth)acrylic latex, etc.; powdery thickening substances such as polyvinyl alcohol powder, starch, etc.; copolymers of styrene and butadiene, vinyl pyridine, acrylonitrile, copolymers of acrylonitrile and styrene, etc.

[0065] These organic binders can impart strength to the wet sheet during papermaking. After papermaking and after removal of the dispersion medium, even if they solidify, they can be softened again by heating, which is advantageous when shaping into a desired shape, such as slitting or bending. Organic binders such as those described above not only soften during normal use but also during heating, particularly during the heating before glass melting, to hold the inorganic particles in a more stable state by softening in accordance with the retention state of the inorganic particles between the inorganic fibers.

[0066] 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 step 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 filtration-molded. In relation to such a role, the organic binder corresponding to the flocculant is preferably added after the preparation of a fiber-containing liquid in which fibers and particles are homogeneously mixed and further after mixing a slurry containing a heat insulation imparting agent with the fiber-containing liquid.

[0067] The above-described organic binders can be used alone or in combination of two or more. When used in combination of two or more, it may be a combination of organic binders with different forms (for example, a combination of organic fibers and latex), or a combination of binders with different roles, such as a combination of organic fibers and a polymer flocculant.

[0068] 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 papermaking suspension 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.

[0069] (4-2) Inorganic binder Examples of the inorganic binder include colloidal oxides such as colloidal silica, alumina sol, and titania sol; water glass, calcium silicate; and aluminum sulfate classified as a fixing agent or an inorganic flocculant.

[0070] 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.

[0071] 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.

[0072] The above inorganic binders can be used alone or in combination of two or more. The content rate of the inorganic binder in the papermaking suspension 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.

[0073] The organic binder and the inorganic binder can be used either singly or in combination. When used in combination, the content rate of the binder in the papermaking suspension is 3 to 20% by weight, preferably 5 to 15% by weight.

[0074] (5) Heat-insulating inorganic particles Examples of the heat insulating inorganic particles used in the present invention include porous or hollow inorganic particles such as silica aerogel, glass bubble, and glass balloon; a group of nanoparticles that can function like porous particles by forming aggregates (agglomerates) of nanoparticles; and ceramic particles such as titanium oxide, alumina, and silica having no binder function (crystalline silica powder, amorphous silica, fumed silica, etc.) that can scatter radiant heat. Preferably, they are hollow or porous silica particles or a group of nanoparticles that can obtain a heat insulating effect and weight reduction by air, and more preferably porous silica particles (silica aerogel).

[0075] The silica particles used as the heat insulating inorganic particles are network aggregates (aggregates) or agglomerates in which nanoparticles of nanosize (about 5 to 50 nm) are aggregated. As the aggregates or agglomerates, they have nanopores with 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.

[0076] Wet silica (precipitated silica) is generally silica synthesized in water using sodium silicate synthesized from silica sand and soda ash and a mineral acid as raw materials, and is obtained as amorphous aggregated particles (agglomerates as secondary particles) having a macropore structure and can act like porous particles. The silica particles produced by the sol-gel method are network aggregates in which nanoparticles of nanosize (about 5 to 50 nm) are aggregated, and the nanoparticles are silanol-bonded to each other. It corresponds to porous particles (primary particles) having nanopores with a porosity of 70% by volume or more, preferably 80% by volume or more, and more preferably 90% by volume or more. Preferably, it is a surface-hydrophobic aerogel having nanopores that form a tortuous long air path capable of inhibiting heat and electric conductivity.

[0077] Hereinafter, as representative heat insulating inorganic particles, hydrophilized aerogel particles and aggregates of nanoparticles with surface hydrophilicity will be described.

[0078] (5-1) Regarding hydrophilized silica aerogel In the sol-gel method, porous silica aerogel can be obtained. Specifically, in addition to bifunctional silane and trifunctional silane compounds, a sol containing at least a tetrafunctional silane compound is subjected to a crosslinking reaction to gelate, and the obtained wet gel is molded as necessary. Then, the water and / or organic solvent present on the surface and inside of the wet gel are dried, exchanged with an organic solvent (solvent exchange), and depending on the type of organic solvent, supercritical drying or atmospheric pressure drying is performed to obtain it. 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.

[0079] As described above, by end-capping the silanol groups present on the surface of the 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. The silica aerogel in which the surfaces of the individual silica particles that make up the aggregates (aggregates) are also hydrophobically capped has hydrophobic pores inside the particles, and even in a slurry using water as a dispersion medium, water intrusion into the pores can be prevented, so based on air, the thermal conductivity can be reduced.

[0080] Such aerogel particles with surface hydrophobicity usually have a wetting angle with respect to water of 100 degrees or more, 110 degrees or more, 130 degrees or more, 150 degrees or more.

[0081] As the heat insulating inorganic particles used in the present invention, aerogel particles with a hydrophobic surface are preferably used. Specifically, the surface area is about 300 m 2 / g to about 1,000 m 2 / g, preferably 500 m 2 / g to about 1,000 m 2 / g, and the BET surface area is 700 m 2 / g to 800 m 2Use a silica aerogel having a porous structure with a porosity of at least 80%, preferably 85% or more, more preferably 90% or more, at / g.

[0082] The surface-hydrophobic aerogel particles used as 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 100 to 200 g / cm 3 and is preferably such. By using aerogel particles of such a size, it is possible to provide a heat-insulating and flame-retarding sheet that is excellent in yield in the papermaking process, lightweight, and excellent in heat insulation. 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 may be obtained by pulverization.

[0083] In the case of aerogels in which the surfaces of these inorganic particle powders are hydrophobic and have a high surface tension, in the papermaking suspension, 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 above-described hydrophobic silica aerogel is used after being hydrophilized.

[0084] Examples of the method for hydrophilizing the surface-hydrophobic aerogel include a method of making the surface properties easy to wet 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.

[0085] 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, examples thereof include 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. Note that alkylene oxide type surfactants such as polyoxyethylene, polyoxypropylene, and polyoxyethylene·polyoxypropylene condensates can increase the hydrophilicity of the aerogel, but tend to separate from the fiber-containing liquid using water as the medium, making it difficult to mix with the fibers.

[0086] When the above organic solvents or surfactants are included, the content in the aerogel slurry described later is preferably 10% by weight or less. If the content of the surfactant or organic solvent becomes too high, the preparation process of the papermaking suspension, particularly the foaming during mixing and stirring, tends to increase.

[0087] Examples of the hydrophilic polymer used for the hydrophilization treatment include polysaccharides such as cellulose nanofibers, starch, amylose, cationized starch, and carboxymethyl cellulose; vinyl-based hydrophilic polymers such as polyvinyl alcohol, polyvinyl acetate, ethylene-vinyl alcohol-based 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. As polyvinyl alcohol, in addition to unmodified polyvinyl alcohol, 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 may be used as long as the water solubility and hydrophilicity are not impaired.

[0088] These hydrophilic polymers are used in an aqueous solution state. Since they also function as thickeners, an aqueous solution with 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.

[0089] These hydrophilic polymers tend to be larger in size than the pores of the aerogel, and from their molecular structure, it is considered that they exist so as to surround the surface of the aerogel particles such that the hydrophilic groups face the dispersion medium side. As a result, the surface state becomes compatible with the dispersion medium, and in the aerogel-containing slurry, it can be dispersed in the state of aerogel particles as aggregates. Therefore, the above-mentioned hydrophilic polymer may be used in an amount sufficient and necessary 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 hydrophilic polymer / hydrophobic aerogel particles (weight ratio). Within this range, it is appropriately selected according to the type of the hydrophilic polymer and the type of the hydrophobic aerogel particles.

[0090] Among the above-mentioned hydrophilization treatment methods, 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 substantially only water, and the wastewater treatment in the dehydration process is simplified.

[0091] Incidentally, the above-mentioned surfactant and hydrophilic polymer may be used as an organic binder or an emulsifier in the papermaking method, but in the preparation process of the suspension for papermaking, the handling of both is different. 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 (an aqueous solution of a surfactant or a 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 the aerogel and the 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.

[0092] (5-2) Hydrophilic silica nanoparticle groups The hydrophilic silica nanoparticle groups used in the present invention generally correspond 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, they exist as amorphous aggregated particles (aggregates). In the state of aggregates, they can act like porous particles having a macroporous structure. In the case of aggregates of hydrophilic silica nanoparticles, they can be used without any special surface treatment.

[0093] In the case of hydrophilic aerogel particle groups, the primary average particle diameter is about 1 to 50 nm, preferably about 5 to 30 nm, and the surface of the silica nanoparticles is hydrophilic. The silica nanoparticles exist in the state of so-called secondary particles, agglomerates (aggregates), in which individual nanoparticles are not bonded to each other, and the secondary particle diameter is about 100 nm to 100 μm. However, the hydrophilic silica nanoparticle groups are easily crushed and diffused as aggregates as secondary particles in water. As a result, in the preparation of the papermaking suspension, they are easily mixed with inorganic fibers such as silica-based inorganic fibers and glass fibers, and a mixed liquid in which the inorganic fibers and the hydrophilic silica nanoparticles are entangled is easily obtained. 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 with water depending on the mesh size used in the dehydration step in the papermaking method, and the yield tends to be poor.

[0094] (5-3) Content of heat-insulating inorganic particles In the heat insulation and flame shielding sheet of the present invention, the above-mentioned heat insulation-providing inorganic particles are not essential components, but it is preferable to contain them. In particular, hydrophilized silica aerogel can exhibit an excellent heat insulation effect during normal use (heating up to about 200°C at most). Therefore, in a laminated battery or a battery module in which a large number of cells are stacked, when a certain cell overheats, it can prevent heat from propagating to adjacent battery cells or battery modules. In addition, by containing silica aerogel, which is a porous particle, the weight of the heat insulation and flame shielding sheet can be reduced.

[0095] On the other hand, hydrophilized silica aerogel, which imparts a heat insulation effect based on the low thermal conductivity of air and heat insulation-providing inorganic particles, has a small heat insulation effect at high temperatures that cause thermal runaway. At high temperatures (about 1000°C) that cause thermal runaway, silica-based inorganic fibers and fibrous minerals having heat resistance of 1000°C or higher exhibit flame shielding and heat resistance. Therefore, from the viewpoint of the heat insulation and flame shielding functions in both normal use and high temperature ranges where thermal runaway occurs, the content of the heat insulation-providing inorganic particles is 0 wt% or more, 5 wt% or more, 10 wt% or more, 15 wt% or more, 20 wt% or more, 25 wt% or more, 30 wt% or more, 35 wt% or more, and 45 wt% or less, 40 wt% or less. If the content exceeds half, papermaking becomes difficult, and the heat resistance and flame shielding properties in high temperature ranges where thermal runaway occurs become insufficient.

[0096] (6) Precursor of thermosetting resin The heat insulation and flame shielding sheet of the present invention may further contain a precursor of a thermosetting resin. The precursor of a thermosetting resin 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 a cross-linking reaction upon heating or in the presence of a curing agent.

[0097] In addition to inorganic fibers (silica fibers, glass fibers), organic and / or inorganic binders, and inorganic particles (fibrous minerals, 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 is possible to undergo a crosslinking reaction with a part of the thermosetting resin layer to be laminated during thermosetting, so that an increase in interlayer adhesion can be achieved, which is preferable.

[0098] When the precursor of the thermosetting resin is contained, it is less than 5% by weight, preferably 1 to 3% by weight. 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-shielding sheet mainly composed of inorganic fibers tends to be impaired.

[0099] (7) 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.

[0100] As other fillers, clay minerals (layered silicates) other than the above fibrous minerals may be contained. Specifically, hydrous ferrosilicate 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.

[0101] Bentonite is a natural clay mineral mainly composed of montmorillonite. Smectite is a general term for a group of 2:1 type minerals, including montmorillonite, stevensite, hectorite, etc. The unit crystal of montmorillonite is a flat plate-like unit composed of a tetrahedral sheet, an octahedral sheet, and a tetrahedral sheet. A plurality of such unit crystals are stacked to form a layered structure. Since the unit crystal of montmorillonite is a very thin plate-like crystal with a thickness of about 1 nm and a width of 100 to 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 exhibits a high liquid limit and has a high water content. Smectite has a swelling property in which water or organic substances enter the interlayer and expand, and can contain a large amount of water in the interlayer (for example, more than 10 times the water content of kaolin). In addition, montmorillonite is easily affected by electrolytes and can be peptized. Therefore, by using it in combination with sepiolite, which has a high coating film forming ability, it is easy to form a coating film in the gaps between fibers in a state where inorganic particles are entrapped.

[0102] The layered silicate as described above exists as a powder with an equivalent circle diameter and an average particle diameter of 300 μm or less, preferably 200 μm or less, more preferably 10 to 100 μm, before the preparation of the papermaking suspension. However, when mixed with water, it exhibits viscosity, adhesiveness, and plasticity and has the ability to form a self-coating film. Therefore, after the papermaking suspension is formed 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 serve as a binder for stably holding inorganic fibers together.

[0103] Examples of other solid content fillers include neutralizing agents, lubricants, anti-blocking agents, fluidity improvers, mold release agents, flame retardants, colorants, wetting agents, adhesives, yield improvers, paper strength improvers, drainage aids, pH adjusters, and the like.

[0104] (8) Dispersion medium As the dispersion medium for the preparation of the papermaking suspension, 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 aerogel particles hydrophilized with an organic solvent or a surfactant are used as the heat insulating inorganic particles, the sizing solution can be kept within the above range.

[0105] <Preparation of Suspension for Papermaking> Each of the components listed above, namely, silica-based inorganic fibers, glass fibers, fibrous minerals, and binders, and further heat insulating inorganic particles, thermosetting resins, and other fillers blended as necessary, are added in predetermined amounts into a dispersion medium and stirred to prepare a suspension for papermaking. When preparing the suspension for papermaking, it may be further diluted with water as necessary.

[0106] The solid content concentration of the suspension for papermaking may be any concentration at which the above components can be uniformly stirred and mixed. Specifically, in terms of the solid content ratio, it is 0.01 to 10% by weight, preferably 0.05 to 3% by weight.

[0107] The order of blending the above components is not particularly limited, but a method of adding the fibers and inorganic particles while stirring in a dispersion medium is preferred. However, when hydrophobic heat insulating inorganic particles are contained, a dispersion liquid (slurry) of hydrophilized silica aerogel is separately prepared. Then, it is preferably prepared by mixing this aerogel slurry and the fiber-containing liquid and adding a binder to the mixed liquid. This makes it possible to obtain a sheet in which the heat-insulating inorganic particles, which are likely to aggregate in water and are likely to separate from the fibers like hydrophobic aerogels, are entangled with the fibers and dispersed in the fibers.

[0108] <Wet papermaking> Wet papermaking is a method in which the suspension for papermaking prepared above is lifted by a paper machine, pressed to remove moisture, and then dried to obtain a sheet-like material. As the paper machine, a cylinder mold paper machine, a fourdrinier paper machine, an inclined paper machine, an inclined short fourdrinier paper machine, or a combination of these can be used.

[0109] 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 when 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 those 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.

[0110] After papermaking, before drying, during drying, or after drying, the heat-insulating and flame-blocking sheet may be formed into a desired shape. Drying may usually be performed only by heating, or may be performed 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 pressed in a state of having a shape with slits or the like and then dried. In any case, since it has plasticity in the state before drying, it can be solidified in a state of having a predetermined shape such as slits or bending.

[0111] After drying, the obtained molded body (paper-like sheet) may be further subjected to secondary processing such as cutting, punching, and bending.

[0112] In addition, there is a method (external addition) in which a slurry containing heat insulation-providing inorganic particles, fibrous minerals, and a binder is impregnated into a fiber sheet obtained by papermaking the fiber-containing liquid by means such as spray coating, curtain coating, impregnation coating, bar coating, roll coating, blade coating, etc. The impregnation of fibrous minerals and inorganic particles by such external addition tends to stay in the surface layer portion, powderize after drying, and the powder is likely to scatter. In this regard, in the heat insulation and flame shielding sheet of the present invention, the heat insulation-providing inorganic particles are papermade together with the main inorganic fibers and fibrous minerals, so that due to the holding effect by entanglement with the fibers or fibrous minerals, the adhesion force of the inorganic particles and fibrous minerals in the sheet is increased, and even if they powderize after drying, they are not likely to scatter. That is, the inorganic particles are stably held in the sheet.

[0113] <Configuration of Heat Insulation and Flame Shielding Sheet> The heat insulation and flame shielding sheet according to the present invention is obtained by wet papermaking using a suspension for papermaking having the above composition and removing the dispersion medium by drying.

[0114] After papermaking, at the time of drying, by filling the forming mold, for example, as shown in FIG. 4, it may be a sheet 9 having a plurality of slits formed. Since the heat insulation and flame shielding sheet of the present invention has strength and flexibility, it can withstand processing and forming as shown in FIG. 4.

[0115] The thickness of the sheet is more than 0.5 mm, 0.8 mm or more, 1 mm or more, 1.3 mm or more, 1.5 mm or more, and less than 3 mm, 2.5 mm or less, 2.0 mm or less, 1.8 mm or less. If it is too thin, the strength is insufficient, and also the content of fibers and insulation-providing inorganic particles decreases too much, and it is difficult to obtain sufficient heat insulation performance. On the other hand, although it is less than 3 mm thick, the strength is improved by the fibrous minerals, and due to heating, it becomes a plastic and softened state by the thermoplastic resin fibers, so even if it is subjected to a pressing process, it does not need to be broken. In addition, since the heat insulation-providing inorganic particles can exist in a state of being held by the entanglement of a plurality of types of fibers, even if cutting or punching is performed, the scattering of the powder of the inorganic particles is suppressed.

[0116] The heat insulation and flame shielding sheet according to the present invention may be a single sheet manufactured by papermaking as described above, or may be a laminate in which an adhesive is applied and coated on one side and a release paper is further laminated. When sticking to the lid 12'a of the housing 12' of the battery module as shown in FIG. 2, an adhesive may be applied to one side of the heat insulation 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 sticking the adhesive layer 10a to the back surface of the lid 12'a, the heat insulation and flame shielding sheet can be stuck, so that the sheet construction work is simple.

[0117] The heat insulation and flame shielding sheet of the present invention 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. Further, by containing heat insulation-imparting 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 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, it is much lighter than a mica sheet (generally about 2000 kg / m 3 ). This is very useful for being lightweight as a heat insulation and flame shielding sheet interposed between each battery cell in a laminate (for example, FIG. 2) in which a large number of battery cells are laminated, such as a battery pack and a battery module used as power for an EV vehicle.

[0118] Also, for some reason, when 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 fibers consume thermal energy through a dehydration condensation reaction, and due to the low thermal conductivity of the silica-based inorganic fibers, the initial temperature rise can be suppressed. This means a delay in the rapid temperature rise due to thermal runaway and is significant. In addition, in the high temperature range of 600 to 800 °C where the strength of the glass fiber decreases and it becomes difficult to maintain the shape, it is considered that silica-based inorganic fibers with high heat resistance and superior heat resistance to glass fiber can contribute to maintaining the shape of the sheet. Furthermore, fibrous minerals can exhibit a flame shielding effect against flame exposure. Thus, the heat insulation and flame shielding sheet of the present invention can maintain the sheet shape, exhibit a heat insulation effect, and delay the heating of adjacent cells and flame exposure in a wide temperature range, such as during normal use (up to about 200 °C), when the temperature rises rapidly when one of the cells undergoes thermal runaway, further in the thermal runaway state at a high temperature of about 600 to 800 °C, and the exposure state to a flame near 1000 °C.

[0119] Furthermore, the heat insulation and flame shielding sheet using porous particles as the inorganic particles for imparting heat insulation is excellent in compressibility. Lithium-ion batteries have volume fluctuations such as the cells expanding during the warming-up state and contracting upon cooling even during normal use. Therefore, in a battery module of a cell stack type battery pack as shown in Fig. 2, particularly in a battery module where cells 11' are laminated closely within a 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 material for the volume fluctuations of the cells.

[0120] <Use> The heat insulation and flame shielding sheet of the present invention is used as a heat insulation and flame shielding sheet interposed between battery cells which are the minimum unit of a lithium-ion battery (for example, Fig. 1); a heat insulation and flame shielding sheet used for heat insulation of the lid of the housing when packaging a battery group formed by modularizing a plurality of lithium-ion battery cells electrically connected in series or parallel and disposed in a housing through a predetermined space in an outer housing (Fig. 2); and a heat insulation and flame shielding sheet used for the partition walls and isolation sheets of cylindrical cells as shown in Fig. 3 (Fig. 3).

[0121] When an individual cell or module enters a "thermal runaway" state, the electrolyte contained within the battery may catch fire, leading to explosions and fires. To prevent such a chain reaction of thermal runaway, within the battery pack and within the battery module, by interposing the heat insulation and flame shielding sheet of the present invention between the individual battery cells that make up 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 propagating to adjacent cells and further to other batteries within the battery module.

Embodiment

[0122] 〔Measurement and Evaluation Method〕 (1) Flame Exposure Test As shown in Fig. 5, the sheet (150 mm × 150 mm) 15 to be evaluated was fixed to the cationic electrodeposition paint steel plate 17 regarded as a battery cell box using an adhesive tape 16, and the sheet 15 was heated by a horizontally fixed burner flame 14 (adjust the flame 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 part of the steel plate 17 was measured with 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.

[0123] (2) Measurement of Thermal Conductivity (Heat Flux Method) As shown in Fig. 6, three sheets 31a, 31b, 31c produced in the embodiment 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. By measuring the temperature difference between the lower surface of the lowermost sheet 31a and the upper surface of the uppermost sheet 31c with two thermocouples 32a, 32b, and measuring the heat flux with the heat flux sensor 33, the thermal conductivity (λ) was calculated. When calculating the thermal conductivity (λ), the measured value after maintaining the temperature of the heater 30 at 200 °C for 6 hours was used so that the entire sheet was uniformly heated.

[0124] 〔Raw materials for heat insulation and flame shielding sheet〕 <Raw materials> (1) Silica-based inorganic fiber Chopped strands (fiber diameter 9 μm, fiber length 3 - 5 mm) of BELCOTEX (registered trademark) 110 of BELCHEM GmbH (composition: AlO 1.5 ·18〔(SiO 2 ) 0.6 (SiO 1.5 OH) 0.4 〕) were used either after heat treatment (fired silica-based inorganic fiber) at 300 °C for 1 hour or without heat treatment (unfired silica-based inorganic fiber).

[0125] (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 - 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 - 0.27 g / ml was used. · Potassium titanate (whisker) (Tismo manufactured by Otsuka Chemical Co., Ltd.) Fiber diameter 0.3 - 0.6 μm and fiber length 10 - 20 μm

[0126] (3) Glass fiber Glass fiber (E-glass) with a fiber diameter of 5 - 9 μm and a length of 3 - 9 mm was used.

[0127] (4) Organic binder · Pulp fiber (fiber diameter 20 - 30 μm) · Polyester fiber (fiber diameter 5 - 10 μm, fiber length 3 - 9 mm) · Polyvinyl alcohol fiber (fiber diameter 5 - 12 μm, fiber length 3 - 6 mm) · Acrylic latex

[0128] (5) Inorganic binder · 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.

[0129] (6) Inorganic particles for imparting heat insulation The following two types of inorganic particles for imparting heat insulation were used. (6-1) Hydrophobic aerogel Amorphous silica (surface area 700 to 800 m 2 / g, porosity 120 to 150 kg / m 3 , average pore diameter 20 nm, particle diameter 30 to 120 μm, DBP oil absorption 540 to 650 g / 100 g), and the hydrophilized aerogel (inorganic particles for imparting heat insulation I, II, III) obtained by performing the following hydrophilization treatment I, II, or III was used.

[0130] · Inorganic particles for imparting heat insulation I To 200 g of water, 20 g of the above hydrophobic aerogel and 20 g of an organic solvent (ethylene glycol monobutyl ether) were added and shaken to prepare an aerogel slurry. It is an aerogel slurry hydrophilized at an aerogel:organic solvent ratio of 1:1 (aerogel solid content ratio: 8.3%)

[0131] · Inorganic particles for imparting heat insulation 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 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%).

[0132] · Inorganic particles for imparting heat insulation III 300 g of water was added with 30 g of the above hydrophobic aerogel and 5 g of polyvinyl alcohol, and shaken to prepare an aerogel slurry. The aerogel slurry was hydrophilized with an aerogel: polyvinyl alcohol ratio of 6:1 (aerogel solid content ratio: 8.9%).

[0133] (6-2) Hydrophilic silica particles (wet silica) As the heat-insulating inorganic particles IV, amorphous precipitated silica was used, and hydrophilic silica nanoparticles having a large number of silanol groups on the surface were used. This was an aggregate of nanoparticles with an average primary particle size of several nm (an amorphous aggregate (secondary particle) of 1 to 10 μm. The specific surface area as the secondary particle was 200 to 250 m 2 / g, and the DOA oil absorption amount: 230 to 280 ml / 100 g.

[0134] (7) Others · Mica (Yamaguchi Mica AB-25S) Wet milled product Average particle size 24 μm, bulk specific gravity 0.17 g / ml · Kaolinite (Kaolin of Rinnsho Yakuhin Kogyo Co., Ltd. (for research experiments)

[0135] <Preparation of a suspension for papermaking and production of sheets No. 1 to 7 by a papermaking method (without heat-insulating inorganic particles)> In a container containing 2000 cc of water, the above raw material components were blended at the ratios (weight% of solid content) shown in Table 1, and further, 2 cc of polyacrylamide as a flocculant was added and blended. After stirring and mixing using a mixer, papermaking was carried out using a hand sheet former. After papermaking, it was placed in a drying oven and dried at 100 °C for 10 minutes. Thus, a measurement sheet of 150 mm × 150 mm × thickness of about 1.5 mm was obtained. For the obtained sheet, the above flame exposure test (exposure time: 10 minutes) was carried out, the heat insulation property (back surface temperature when converted to a thickness of 1.6 mm) was measured, and the appearance of the sheet after the test was visually observed. The results are shown in 1.

[0136] As Reference Example R1, the results of evaluating a mica sheet (commercially available product) by the same method are also shown in Table 1.

[0137]

Table 1

[0138] For No.3, 4, and 7, unfired silica-based inorganic fibers are used, and dehydration condensation reaction can occur at high temperature, expecting a heat energy consumption effect. The back surface temperature is low, having a heat insulation effect. However, in No.3, since it does not contain glass fibers or fibrous minerals, as a result of heat shrinkage at high temperature, cracks occurred in the sheet after the test.

[0139] No.5 is a sheet mainly composed of fibrous minerals without using silica-based inorganic fibers. There is no problem of heat shrinkage, and there are no cracks after the flame exposure test. On the other hand, regarding the bulk density, although weight reduction can be achieved compared to the mica sheet, it tends to be heavier than the sheet mainly composed of silica-based inorganic fibers (compared with No.4). Also, the heat insulation property also tends to be inferior to the case of using silica-based inorganic fibers.

[0140] No.6 is a sheet mainly composed of glass fibers. Since it melts at 1000°C when exposed to flames, sufficient heat insulation property could not be obtained. It was confirmed that the melting of the glass fibers was due to the fact that no fiber shape was observed at the contact part of the flame and its surroundings from the surface properties after the test.

[0141] On the other hand, for No.1 and 2, fired silica-based inorganic fibers are used, and it is considered that there is no heat shrinkage due to flame exposure of the silica-based inorganic fibers due to the prior heat treatment. Cracks did not occur in No.1, while cracks were observed in No.2. It is considered that this is because sepiolite having a fiber form can follow the volume expansion of the steel plate due to flame exposure by entangling with other fibers more than mica.

[0142] In No.1 and 2 using fired silica-based inorganic fibers, perhaps because the heat energy consumption effect due to dehydration condensation of the silica-based inorganic fibers could not be obtained, the heat insulation effect was inferior to that of No.3 and 4.

[0143] <Preparation of Suspension for Papermaking, Fabrication and Evaluation of Sheets No. 21 to 27 Containing Inorganic Particles for Heat Insulation> In a container containing 2000 cc of water, the above raw material components were added and mixed to prepare a suspension for papermaking having the composition (weight % of solid content) shown in Table 2. The components were added and blended in the order of unburned silica-based inorganic fibers, glass fibers, fibrous minerals, organic fibers (PET fibers), inorganic particles for heat insulation, inorganic binders, and flocculants (polyacrylamide). Polyacrylamide was added in the range of 3 cc to 18 cc while checking the floc state of the suspension for papermaking.

[0144] When using hydrophobic inorganic particles I, II, and III for heat insulation, they were added as a slurry of hydrophilized inorganic particles for heat insulation prepared separately. Table 2 shows the amounts (weight %) converted to the solid content in the suspension for papermaking. When adding hydrophilic inorganic particles for heat insulation (hydrophilic silica particles), the powder was added directly to the fiber-containing liquid.

[0145] The suspension for papermaking prepared above was poured into a wet forming machine (filter mesh screen #80 (mesh opening 180 - 200 μm)) and suction dehydrated. After dehydration, it was heated and dried under pressure for 10 minutes using a hot press (100 °C). As a result, a sheet of 150 mm × 150 mm × thickness of about 1.2 - 2.1 mm was obtained. For each suspension for papermaking, three sample sheets were fabricated. The average yield calculated from the solid content of the suspension for papermaking was 80% - 90%.

[0146] For the fabricated sheets, the above flame exposure test and measurement of thermal conductivity (heat flux method) were performed. Table 2 shows the temperature (average value of the three fabricated sheets) converted to a thickness of 1.6 mm for the back surface temperature after 5 minutes of flame exposure. Also, the properties of the sheet (such as the presence or absence of cracks) after the flame exposure test were visually observed. The results are shown in Table 2. Also, the thermal conductivity of the sheet at a heat source temperature of 200 °C is shown in Table 2 together.

[0147] Reference Example R2: When hydrophobic aerogel particles (powder) were directly added to the fiber-containing liquid without hydrophilization treatment, even when shaken or stirred, the hydrophobic aerogel particle powder floated on the surface of the water layer to form a powder layer, and a papermaking suspension in which fibers and aerogel particles were mixed could not be prepared.

[0148] Reference Example R3: As a 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) were added, and an inorganic particle-containing slurry with heat insulation was obtained by shaking vigorously. When this aerogel-containing slurry was added to a separately prepared fiber-containing liquid, it separated from the fiber-containing liquid, and a uniform mixed liquid (papermaking suspension) could not be obtained even with stirring.

[0149]

Table 2

[0150] 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 hydrophilic nanoparticle groups as heat-insulating inorganic particles. It is considered that the hydrophobic aerogel particles with a high porosity were dispersed throughout the sheet, and excellent heat insulation performance was exhibited based on the low-thermal-conductivity air. 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 may be because the thermal conductivity of silica-based inorganic fibers is lower than that of glass fibers.

[0151] 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 surface of the sheet in the flame exposure test than No. 25. Such heat insulation effect is obtained by using hydrophilized silica aerogel particles as the heat-insulating inorganic particles. In addition to the heat insulation effect during normal use (below 200 °C), during a rapid temperature rise such as thermal runaway, it is considered that the temperature rise delay effect by silica fibers having hydroxyl groups and the fact that the rapid temperature rise of the entire sheet can be suppressed due to the inclusion of aerogel particles.

[0152] For all of Sheet Nos. 21 - 27, since unburned silica fibers and glass fibers are used and the glass fiber / silica fiber is 1 / 10 or more and glass fibers are contained, no cracks were observed after the flame exposure test. On the other hand, when the content ratio of glass fiber / silica fiber is 8 / 1 or more and the content of glass fiber is excessive compared to the content of silica fiber, the glass fiber was melted by the flame exposure (No. 27).

[0153] Also, even when the content ratio of glass fiber / silica fiber exceeds 1 / 7 and glass fibers are contained, Sheet No. 23 which does not contain clay minerals became cottony after the flame test and could not maintain the sheet shape.

[0154] 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 heat insulation effect was recognized both during normal use and during flame exposure. Since sepiolite has adsorbed water, during normal use, the heat energy consumption effect in the dehydration of adsorbed water is obtained. In the high temperature range such as during flame exposure, it may be because the fibrous minerals have a higher porosity of the entire sheet than the platy minerals and the pore opening effect at high temperatures is easily obtained. 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.

[0155] 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.

[0156] Furthermore, micrographs (magnification: 1000 times) of the heated surfaces of the sheets after the flame exposure tests for No. 21 and 23 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.

[0157] <Comparison of heat insulation effects between silica-based inorganic fibers and glass fibers> Regarding the heat-insulating and flame-blocking sheets No. 23 and 27 prepared above, a heat insulation test was conducted at 700°C 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 having a diameter of 40 mm was placed on a hot plate (100 mm × 100 mm) 22 heated to 700°C, and an evaluation sheet (150 mm × 150 mm) 21 was placed so that the circular opening 23a was at the center and held for 6 minutes.

[0158] Photographs of the heated portions of sheets No. 23 and 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 elasticity floated up, and there was a tendency for it to be difficult to maintain the sheet shape in the heated portion.

[0159] Micrographs (100 times) of the heated surfaces of the heated portions of sheets No. 23 and 27 are shown in FIGS. 14 and 15, respectively. Also, micrographs (100 times) of the unheated sides (backs) of sheets No. 23 and 27 are shown in FIGS. 16 and 17, respectively.

[0160] Regarding Sheet No. 27, when comparing Fig. 15 (heating surface) and Fig. 17 (back surface), it was found that on the heating surface, there were many places where the fibers were melted and fused, and the area of the molten and fused part was large. On the other hand, in No. 23, even on the heating 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, a part of the glass fibers begins to melt. Even for glass fibers having a fiber shape, their elasticity and strength decrease, and the entanglement force between the fibers decreases, and it seems that they have lifted from the sheet surface.

[0161] (2) Heat Insulation Test II As shown in Fig. 18, an insulation and flame shielding sheet (150 mm × 150 mm) 21' to be evaluated was placed on a SUS plate (100 mm × 100 mm) 22' equipped with a heater, and a thermocouple 24' was set at the heater corresponding part on the sheet, and the plate temperature and the sheet temperature were measured. The measurement was carried out as follows: after the plate temperature reached 200 °C, it was held for 10 minutes, then the heat temperature was raised by 100 °C and held for 10 minutes, and then the temperature was raised by 100 °C and held for 10 minutes. Such a temperature increase cycle was carried out up to 500 °C. The results of the temperature change in such a temperature increase cycle test are shown in Fig. 19. The dashed-dotted line indicates the heater temperature, the solid line indicates the temperature change of Sheet No. 23, and the dotted line indicates the temperature change of No. 27.

[0162] When the heater temperature was 300 °C to 500 °C, it was found that No. 23 tended to be about 3 to 6 °C lower than No. 27. This is considered to be due to the dehydration condensation of the silica-based inorganic fiber and the resulting delay in temperature increase.

[0163] <Supplementary Note> Based on the above preferred embodiments and examples, the present invention also encompasses various modified embodiments that can be conceived by those skilled in the art. As embodiments of the present invention, for example, the following forms can be mentioned.

[0164] 1. 25 to 70% by weight of silica-based inorganic fiber having a hydroxyl group; 2 to 25% by mass of glass fiber; 5 to 40% by weight of fibrous mineral; Binder: 3 to 20% by weight; A heat insulation and flame shielding sheet with a thickness of 3 mm or less, comprising: 2. Silica-based inorganic fibers having hydroxyl groups: 25 to 70% by weight; Glass fibers: 2 to 25% by mass; Fibrous minerals: 5 to 40% by weight; Binder: 3 to 20% by weight; and Inorganic particles for imparting heat insulation: more than 0% to 45% by weight A heat insulation and flame shielding sheet with a thickness of 3 mm or less, comprising: The inorganic particles for imparting heat insulation include hydrophilized aerogel particles obtained by hydrophilizing the surface of hydrophobic aerogel particles having a porosity of 80% or more and an average particle diameter of 5 to 200 μm. 3. The heat insulation and flame shielding sheet according to Appendix 1 or 2, wherein the weight ratio of the silica-based inorganic fibers to the glass fibers (silica-based inorganic fibers / glass fibers) is 30 / 1 to 1.5 / 1. 4. The heat insulation and flame shielding sheet according to any one of Appendices 1 to 3, wherein the thickness of the heat insulation and flame shielding sheet is more than 0.5 mm. 5. The heat insulation and flame shielding sheet according to any one of Appendices 2 to 4, wherein the contact angle of the surface of the hydrophobic aerogel used for the hydrophobic aerogel particles with respect to water is 100° or more. 6. The heat insulation and flame shielding sheet according to Appendix 5, wherein the hydrophilized aerogel particles are those obtained by contacting the surface of the hydrophobic aerogel particles with an organic solvent, a surfactant, or a hydrophilic polymer. 7. The heat insulation and flame shielding sheet according to Appendix 6, wherein the hydrophilized aerogel particles have a porosity of 90% or more and an average particle diameter of 5 to 200 μm, and at least a part of the surface of the silica aerogel particles having a hydrophobic surface is coated with a hydrophilic polymer. 8. The surface area of the hydrophobic aerogel particles is 300 to 1000 m 2 / g. The heat insulation and flame shielding sheet according to any one of Appendices 5 to 7. 9. The particle density of the hydrophobic aerogel particles is 100 to 200 g / cm 3 The heat insulation and flame shielding sheet according to any one of Appendices 5 to 8. 10. The heat insulation and flame shielding sheet according to any one of Appendices 6 to 9, wherein the hydrophilic polymer is a polymer having a plurality of hydroxyl groups. 11. The heat insulation and flame shielding sheet according to Appendix 10, wherein the hydrophilic polymer is a water-soluble polymer. 12. The heat insulation and flame shielding sheet according to Appendix 10 or 11, wherein the amount of the hydrophilic polymer with respect to the hydrophobic aerogel particles in the hydrophilized aerogel particles is 1 / 2 to 1 / 100 in terms of hydrophilic polymer / hydrophobic aerogel particles (weight ratio). 13. The heat insulation and flame shielding sheet according to any one of Appendices 2 to 12, wherein the heat insulation-providing inorganic particles contain surface-hydrophilic nanoparticles having an average primary particle diameter of 1 nm to 50 nm. 14. The heat insulation and flame shielding sheet according to any one of Appendices 1 to 13, wherein the fibrous mineral is at least one selected from sepiolite, palygorskite, potassium titanate whisker, and wollastonite. 15. The heat insulation and flame shielding sheet according to any one of Appendices 1 to 13, wherein the fibrous mineral is potassium titanate whisker or wollastonite. 16. The heat insulation and flame shielding sheet according to any one of Appendices 1 to 13, wherein the fibrous mineral is a layered silicate mineral. 17. The heat insulation and flame shielding sheet according to Appendix 16, wherein the silicate mineral is α-type sepiolite or β-type sepiolite. 18. The heat insulation and flame shielding sheet according to any one of Appendices 1 to 17, wherein the binder contains thermoplastic resin fibers. 19. The heat insulation and flame shielding sheet according to any one of Appendices 1 to 18, wherein the binder contains an organic flocculant. 20. The heat insulation and flame shielding sheet according to any one of Appendices 1 to 19, wherein the binder contains an inorganic binder. 21. The heat insulation and flame shielding sheet according to Appendix 20, wherein the inorganic binder contains colloidal silica. 22. The heat insulation and flame shielding sheet according to Appendix 20 or 21, wherein the inorganic binder contains an inorganic metal salt. 23. The bulk density is 100 to 400 kg / m 3 The heat insulation and flame shielding sheet according to any one of Appendices 1 to 22.

[0165] 24. A step of preparing a hydrophilized aerogel slurry in which silica aerogel particles having a hydrophobic surface, a porosity of 80% or more, and an average particle size of 5 to 200 μm are dispersed in an aqueous solution containing a hydrophilizing treatment agent; A step of adding and mixing the hydrophilized aerogel slurry to an aqueous dispersion containing silica-based inorganic fibers having hydroxyl groups, glass fibers, fibrous minerals, and a binder, and preparing a suspension containing 25 to 70% by weight of the silica-based inorganic fibers, 2 to 25% by mass of the glass fibers, 5 to 40% by weight of the fibrous minerals, 3 to 20% by weight of the binder, and more than 0 to 45% by weight of the hydrophilized aerogel; and A step of wet papermaking the suspension to obtain a sheet having a thickness of less than 3 mm A method for manufacturing a heat-insulating and flame-shielding sheet including the above steps. 25. A method for manufacturing a heat-insulating and flame-shielding sheet according to any one of Appendices 2 to 23, A step of preparing a hydrophilized aerogel slurry in which silica aerogel particles having a hydrophobic surface, a porosity of 80% or more, and an average particle size of 5 to 200 μm are dispersed in an aqueous solution of a water-soluble polymer; A step of adding and mixing the hydrophilized aerogel slurry to an aqueous dispersion containing silica-based inorganic fibers having hydroxyl groups, glass fibers, fibrous minerals, and a binder containing thermoplastic resin fibers; A step of wet papermaking the obtained mixed solution and then heating and pressurizing it to obtain a sheet having a thickness of less than 3 mm A method for manufacturing a heat-insulating and flame-shielding sheet including the above steps. 26. The method for manufacturing a heat-insulating and flame-shielding sheet according to Appendix 24 or 25, further including a step of adding an inorganic binder and / or an organic flocculant to the obtained mixed solution or suspension. 27. The method for manufacturing a heat-insulating and flame-shielding sheet according to any one of Appendices 24 to 26, wherein the content of the surfactant in the hydrophilized aerogel slurry is 10% by weight or less. 28. The method for manufacturing a heat-insulating and flame-shielding sheet according to any one of Appendices 24 to 27, wherein the content of the organic solvent in the hydrophilized aerogel slurry is 10% by weight or less. 29. The method for manufacturing a heat insulation and flame shielding sheet according to any one of Appendices 1 to 28, wherein the dispersion medium of the aqueous dispersion is water. 30. In a battery pack or battery pack module in which battery cells are connected in series or in parallel and housed in a housing, a battery pack or battery pack module in which the sheet according to any one of Appendices 1 to 23 is interposed between the battery cells. 31. In a battery pack or battery pack module in which battery cells are connected in series or in parallel and housed in a housing, a battery pack or battery pack module in which the sheet according to any one of Appendices 1 to 23 is adhered to the inner wall surface of the housing with which the battery cells are in contact.

Industrial Applicability

[0166] Since the heat insulation and flame shielding sheet of the present invention is a lightweight and thin paper-like sheet, in a battery module in which a battery pack using a plurality of lithium-ion batteries, particularly a battery pack in which a plurality of cells are stacked, is packaged in a housing, heat insulation is provided so that the temperature rise during normal use of individual cells does not propagate to adjacent cells. Further, when a certain cell undergoes thermal runaway for some reason, it can be interposed between individual cells to insulate heat and shield flames so as not to cause thermal runaway of other cells in the battery module.

Explanation of Signs

[0167] 9, 10 Heat insulation and flame shielding sheet 8, 11, 11' Battery cell 12 Housing

Claims

1. 25 to 70% by weight of silica-based inorganic fibers having hydroxyl groups; 2 to 25% by mass of glass fibers; 5-40% by weight of fibrous minerals; 3-20% by weight of binder; A heat insulating and fireproofing sheet having a thickness of 3 mm or less, The weight ratio of the silica-based inorganic fibers to the glass fibers (silica-based inorganic fibers / glass fibers) is 30 / 1 to 1.5 / 1.

2. Further, the composition contains more than 0% by weight to 45% by weight of heat insulating inorganic particles, The heat insulating inorganic particles have a porosity of 80% or more, an average particle size of 5 to 200 μm, and a surface area of ​​300 to 1000 m. ２ 2. The heat insulating and flame-shielding sheet according to claim 1, comprising hydrophilic-treated aerogel particles obtained by subjecting hydrophobic aerogel particles having a surface with a viscosity of 100° or more and a wetting angle with respect to water of 100° or more to a hydrophilic treatment.

3. The particle density of the hydrophobic aerogel particles is 100 to 200 g / cm ３ The heat insulating and flameproofing sheet according to claim 2 .

4. The heat insulating and flame-shielding sheet according to claim 2 , wherein the hydrophilic treated aerogel particles are formed by coating at least a portion of the surface of the hydrophobic aerogel particles with a hydrophilic polymer having a plurality of hydroxyl groups.

5. The heat insulating and flame-shielding sheet according to claim 2, wherein the heat insulating inorganic particles further contain nanoparticles having a hydrophilic surface and an average primary particle diameter of 1 nm to 50 nm.

6. The heat insulating and flame-shielding sheet according to claim 1 , wherein the fibrous mineral is at least one selected from the group consisting of sepiolite, palygorskite, potassium titanate whiskers, and wollastonite.

7. The heat insulating and flame absorbing sheet according to claim 1 , wherein the fibrous mineral is a layered silicate mineral.

8. 8. An assembled battery or assembled battery module in which battery cells are connected in series or parallel and housed in a housing, the assembled battery or assembled battery module having the sheet according to claim 1 interposed between the battery cells.

9. 8. An assembled battery or assembled battery module in which battery cells are connected in series or parallel and housed within a housing, the assembled battery or assembled battery module having the sheet according to any one of claims 1 to 7 attached to an inner wall surface of the housing with which the battery cells are in contact.

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