JP7377029B2 - Thermal runaway suppression fireproof sheet - Google Patents

Description

The present invention relates to a thermal runaway suppressing fireproof sheet that suppresses the thermal runaway of adjacent unit cells and prevents the spread of fire when one unit cell undergoes thermal runaway and ignites in a battery pack including a plurality of unit cells.

BACKGROUND ART In recent years, with the diversification of electronic devices, there has been a demand for battery packs that include high capacity, high voltage, high output, and highly safe unit cells or multiple unit cells. In particular, in order to provide highly safe unit cells and battery packs, unit batteries and battery packs are equipped with PTC elements and thermal fuses to prevent temperature increases, as well as sensors that sense the internal pressure of the unit cells. Techniques are known that include various protection means, such as a protection circuit that interrupts current. Furthermore, a technique is also known in which a battery pack is provided with a control circuit that controls charging and discharging of a unit cell so that the unit cell does not go into an abnormal state (for example, a thermal runaway state).

However, even if the battery is equipped with the above-mentioned protection means and control circuit, if the battery is placed under abnormal conditions, the battery may undergo thermal runaway for various reasons. When thermal runaway occurs, the temperature of the unit cell rapidly rises to 300° C. or higher, and in some cases to 400° C. or higher, and there is a possibility that high-temperature flammable gas may blow out from inside. In the worst case scenario, there is a risk that the battery pack will catch fire and the housing of the battery pack containing the cells will be damaged or melted.

As a technique for preventing such thermal runaway, Patent Document 1 discloses a heat insulating sheet that supports silica xerogel in the space of a glass fiber sheet and fixes the silica xerogel by covering the outer periphery of the fiber sheet with a dense resin layer. Disclosed. Although this heat insulating sheet has excellent heat insulating properties, since the silica xerogel is fixed with a resin layer, it has a problem of poor heat resistance and fire resistance when the temperature of the unit cell exceeds 300°C.

Further, Patent Document 2 discloses that the powder contains at least one of a mineral powder and a flame retardant, starts an endothermic reaction at 100 to 1000°C, and accordingly selects from the group consisting of phase change, expansion, foaming, and hardening. A thermal runaway prevention sheet is disclosed in which at least one structural change occurs. This thermal runaway prevention sheet uses aluminum foil laminated glass cloth as the base material, and a resin composition containing mineral powder and flame retardant is fed into a single screw extruder and extrusion molded to absorb heat. The thermal runaway prevention sheet is obtained by obtaining a heat-absorbing material sheet or a fire-resistant heat-insulating sheet, and then pressing the obtained heat-absorbing material sheet or fire-resistant heat-insulating sheet in combination, which is extremely low in productivity and costly. There was a problem with getting high. Moreover, since it is a resin composition, there is a problem of poor fire resistance when the unit cell catches fire.

Further, in Patent Document 3, an inorganic fiber sheet containing 30 to 95% by mass of one or more inorganic fibers selected from the group consisting of glass fibers and biosoluble inorganic fibers and 5 to 40% by mass of β-type sepiolite. A manufacturing method comprising: (i) manufacturing a nonwoven fabric by wet paper-making the slurry containing the inorganic fiber; and (ii) adhering a slurry containing β-type sepiolite to the nonwoven fabric. A method for manufacturing an inorganic fiber sheet is disclosed. However, this inorganic fiber sheet is suitable for use as a base material for filters that are fired after being made into a honeycomb molded body, and the wet strength of the nonwoven fabric itself is insufficient, and when used without firing. There was a problem that inorganic fiber sheets were inferior in fire resistance and nonflammability.

International Publication No. 2018/110055 pamphlet Japanese Patent Application Publication No. 2018-206605 JP 2017-025458 Publication

The problem of the present invention is that even with a low basis weight, the base material has strong wet strength, the inorganic particle layer has excellent coating properties, and in a battery pack equipped with multiple lithium-ion cells, one cell can run away from heat. An object of the present invention is to provide a thermal runaway suppressing fireproof sheet that is excellent in fire resistance and nonflammability, as a thermal runaway suppressing fireproof sheet that can prevent the spread of fire to adjacent lithium ion cells when a fire ignites.

As a result of intensive research to solve the above problems, the following invention was discovered.

(1) A thermal runaway suppressing fireproof sheet that prevents the spread of fire to adjacent cells when one cell ignites in a battery pack equipped with a plurality of cells,
The thermal runaway suppressing fireproof sheet contains a base material and an inorganic particle layer,
The base material contains glass fibers, wet heat adhesive binder fibers, and fibrillated heat-resistant fibers,
With respect to all the fiber components contained in the base material, the content of glass fiber is 75% by mass or more and 95% by mass or less, the content of the moist heat adhesive binder fiber is 3% by mass or more and 20% by mass or less, The content of fibrillated heat-resistant fibers is 2.0% by mass or more and 10.0% by mass or less,
A thermal runaway suppressing fireproof sheet, wherein the inorganic particle layer contains inorganic particles and an inorganic binder.

(2) The thermal runaway suppressed fireproof sheet according to (1) above, wherein the moist heat adhesive binder fiber is a silanol-modified polyvinyl alcohol fiber.

(3) The thermal runaway suppressing fireproof sheet according to (1) or (2) above, wherein the fibrillated heat-resistant fiber has a modified freeness of 40 ml or more.

The thermal runaway suppressing fireproof sheet of the present invention contains a base material containing glass fibers, moist heat adhesive binder fibers, and fibrillated heat-resistant fibers. Glass fibers and fibrillated heat-resistant fibers are intertwined, and the intertwined intersections are fixed with moist heat adhesive binder fibers, so the wet strength of the base material is excellent even with a low basis weight. Excellent operational stability when coating. Further, when silanol-modified polyvinyl alcohol fibers are contained as the wet heat adhesive binder fibers of the base material, the adhesiveness with glass fibers is further increased, so that the wet strength of the base material can be further increased. In addition, by including an inorganic particle layer containing inorganic particles and an inorganic binder, it is possible to achieve the effect of excellent fire resistance and nonflammability when the unit cell ignites due to thermal runaway. In addition, since the base material contains fibrillated heat-resistant fibers, it has excellent permeability and liquid retention for the coating liquid for forming an inorganic particle layer, so the content of inorganic particles can be increased, resulting in fire resistance and noncombustibility. can be increased.

In the present invention, the thermal runaway suppressing fireproof sheet contains a base material and an inorganic particle layer, the base material contains glass fiber, a wet heat adhesive binder fiber, and a fibrillated heat-resistant fiber, and the inorganic particle layer contains an inorganic particle layer. This sheet is characterized by containing particles and an inorganic binder.

Examples of the glass fiber in the present invention include chopped strands, glass wool, and glass flakes. Any glass fiber may be used as long as it is hard to break and has the ability to form a base material. The fiber diameter of the glass fiber is preferably 1 to 18 μm, more preferably 2 to 13 μm, and even more preferably 3.1 to 10 μm. If the fiber diameter is less than 1 μm, the glass fiber may fall off from the base material during papermaking because it is too fine, resulting in insufficient strength and thickness. If the fiber diameter exceeds 18 μm, the glass fiber becomes too thick, resulting in large gaps between the base materials, poor workability, and irritation to the skin, which impairs workability and makes it difficult to use. It may happen.

Further, the fiber length of the glass fiber in the present invention is preferably 1 to 30 mm, more preferably 2 to 15 mm, and even more preferably 3 to 12 mm. If the fiber length is less than 1 mm, the strength may be insufficient, and if the fiber length exceeds 30 mm, the texture of the base material may deteriorate and the quality may vary.

Further, the content of glass fiber in the present invention is preferably 75 to 95% by mass, more preferably 80 to 93% by mass, and more preferably 85 to 90% by mass, based on the total fiber components contained in the base material. More preferably, it is expressed in mass %. If the content is less than 75% by mass, the fire resistance or nonflammability may deteriorate, and if the content exceeds 95% by mass, the bond between the glass fibers is weak, so the strength of the base material is weakened, Furthermore, during coating to provide an inorganic particle layer, glass fibers may fall off.

The binder fiber used in the present invention is a wet heat adhesive binder fiber. The wet heat adhesive binder fiber refers to a fiber that flows or easily deforms from a fibrous state at a certain temperature in a wet state to exhibit an adhesive function. Specifically, it is a thermoplastic fiber that can be softened in hot water (e.g., about 80 to 120°C) and self-adhesive or can adhere to other fibers, such as polyvinyl fibers (polyvinyl pyrrolidone, polyvinyl ether, polyvinyl (alcohol, polyvinyl acetal, etc.), cellulose fibers (C1-3 alkyl cellulose such as methyl cellulose, hydroxy C1-3 alkyl cellulose such as hydroxymethyl cellulose, carboxy C1-3 alkyl cellulose such as carboxymethyl cellulose, or its salts, etc.), modified vinyl Fibers made of copolymers (copolymers of vinyl monomers such as isobutylene, styrene, ethylene, vinyl ether, and unsaturated carboxylic acids such as maleic anhydride, or their anhydrides, or salts thereof) Examples include. As the wet heat adhesive binder fiber used in the present invention, polyvinyl fiber is preferable, and polyvinyl alcohol (PVA) fiber is more preferable, since the base material strength is higher, it is easy to form a film between the fibers, and inorganic particles are It becomes easier to hold between the fibers.

The wet heat adhesive binder fiber used in the present invention is a polyvinyl alcohol fiber modified with a monomer having a crosslinkable functional group, or a polyvinyl alcohol fiber that is crosslinked using a crosslinking agent during or after spinning under mild conditions. Polyvinyl alcohol fibers are more preferred because they can impart hot water resistance to the low-drawn yarn.

Examples of the crosslinkable functional group include a silanol group, a carboxyl group, and a methylol group. Fibers can be obtained by dissolving polyvinyl alcohol modified with a monomer having a crosslinkable functional group in water without crosslinking by adjusting the pH, etc., and crosslinking the polyvinyl alcohol after or during spinning. . The degree of modification is preferably 0.01 to 10 mol%, more preferably 0.1 to 5 mol%. As a preferred example, silanol-modified polyvinyl alcohol (denaturation degree 0.1 to 2 mol%) is dissolved in an alkaline solution (pH 9 to 13), and the solution is made acidic (pH 5 to 6) to crosslink and spin. , a method of performing heat treatment after drying.

On the other hand, fibers may also be obtained by spinning unmodified polyvinyl alcohol that does not have self-crosslinking properties and then applying various organic or inorganic crosslinking agents to crosslink it. Examples of inorganic crosslinking agents include phosphoric acid, ammonium phosphate, ammonium sulfate, titanyl sulfate, etc., and examples of organic crosslinking agents include methylol type, epoxy type, oisocyanate type, aldehyde type, etc. After these crosslinking agents are added to an unmodified polyvinyl alcohol spinning stock solution and spun, or after unmodified polyvinyl alcohol is spun alone and passed through a crosslinking agent-containing bath, crosslinking can be progressed by heat treatment. can. It is also possible to use these methods in combination.

The moisture-heat adhesive binder fiber used in the present invention is not limited to the above, but silanol-modified polyvinyl alcohol fiber is particularly preferred because it has good adhesiveness with glass fiber.

The fineness of the wet heat adhesive binder fiber is preferably 0.1 to 5.6 dtex, more preferably 0.4 to 2.2 dtex, and preferably 0.6 to 1.1 dtex. More preferred. When the fineness is less than 0.1 decitex, the fiber itself becomes very expensive, and the base material may become dense and thin. On the other hand, if it exceeds 5.6 decitex, the number of points of contact with the glass fibers will decrease, making it difficult to maintain strength in a wet state. Also, it may not be possible to obtain a uniform texture. The fiber length of the wet heat adhesive binder fiber is preferably 1 to 15 mm, more preferably 2 to 10 mm, and even more preferably 3 to 5 mm. If the fiber length is less than 1 mm, the fibers may fall off from the papermaking wire during papermaking, and sufficient strength may not be obtained. On the other hand, if it exceeds 15 mm, tangles may occur when dispersed in water, and a uniform formation may not be obtained.

The content of the moist heat adhesive binder fiber used in the present invention is preferably 3% by mass or more and 20% by mass or less, and 4% by mass or more and 15% by mass or less, based on the total fiber components contained in the base material. It is more preferable that the amount is at least 5% by mass and not more than 10% by mass. If the content of the wet heat adhesive binder fiber is less than 3% by mass, the strength of the base material decreases, and paper breakage may occur or glass fibers may fall off when applying inorganic particles. On the other hand, if the content of the wet heat adhesive binder fiber exceeds 20% by mass, the peelability from the dryer may deteriorate when the base material is made into paper using a wet papermaking method, and the inorganic particles may not be coated. In this case, the permeability into the base material may decrease, and the fire resistance of the thermal runaway suppressed fire-resistant sheet may deteriorate.

The fibrillated heat-resistant fibers used in the present invention include fully aromatic polyamide, fully aromatic polyester, polyimide, polyamideimide, polyetheretherketone, polyphenylene sulfide, polybenzimidazole, poly-p-phenylenebenzobisthiazole, poly- Fibrillated fibers made of heat-resistant resins such as p-phenylenebenzobisoxazole and polytetrafluoroethylene are used. Among these, wholly aromatic polyamides, which have high hydrophilicity and are easily fibrillated, are preferred.

The modified freeness of the fibrillated heat-resistant fiber in the present invention is 40 ml or more, preferably 50 ml or more and 700 ml or less, more preferably 100 ml or more and 600 ml or less, and still more preferably 300 ml or more and 450 ml or less. When the modified freeness exceeds 700 ml, fibrillation has not progressed so much that entanglement with glass fibers is reduced, and the effect of improving wet strength may be reduced. Furthermore, the effect of improving the permeability and liquid retention of the coating liquid for forming an inorganic particle layer may be reduced. On the other hand, if the modified freeness is less than 40 ml, the fine content of the fibrillated heat-resistant fibers may increase and the rate of shedding from the base material may increase, and the base material tends to become thinner and denser. As a result, the voids in the base material may decrease, and the permeability and liquid retention of the coating liquid for forming an inorganic particle layer may decrease.

In the present invention, modified freeness refers to JIS P8121-2:2012 except that an 80-mesh wire mesh with a wire diameter of 0.14 mm and an opening of 0.18 mm was used as the sieve plate, and the sample concentration was 0.1%. This is the value measured in accordance with the .

In the fibrillated heat-resistant fiber of the present invention, the mass weighted average fiber length is preferably 0.02 mm or more and 1.50 mm or less. Further, the length weighted average fiber length is preferably 0.02 mm or more and 1.00 mm or less. If the average fiber length is shorter than the preferred range, the fibrillated heat-resistant fibers may fall off from the base material. If the average fiber length is longer than the preferred range, fiber disintegration will be poor and poor dispersion will likely occur.

If the fibrillated heat-resistant fibers have the above mass-weighted average fiber length and length-weighted average fiber length, even if the content of the fibrillated heat-resistant fibers in the base material is small, the fibrillated heat-resistant fibers will A dense network structure of fibers is formed between the fibrillated heat-resistant fibers and the glass fibers, resulting in a base material with high wet strength that can improve the permeability and liquid retention of inorganic particle coating liquids. It becomes easier.

The average fiber width of the fibrillated heat-resistant fibers is preferably 0.5 μm or more and 40.0 μm or less, more preferably 3.0 μm or more and 35.0 μm or less, and even more preferably 5.0 μm or more and 30.0 μm or less. If the average fiber width exceeds 40.0 μm, the entanglement of the fibrillated heat-resistant fibers and glass fibers may decrease, resulting in a decrease in wet tensile strength. If the average fiber width is less than 0.5 μm, the base material The fibrillated heat-resistant fibers begin to fall off, and the number of intersections increases too much, so unless the wet heat adhesive binder fibers are increased, the wet tensile strength may decrease.

In the present invention, the mass-weighted average fiber length, length-weighted average fiber length, and average fiber width of the fibrillated heat-resistant fibers are determined in projected fiber length (Proj) mode using Kajaani FiberLab V3.5 (manufactured by Metso Automation). These are the measured mass-weighted average fiber length (L(w)), length-weighted average fiber length (L(l)), and fiber width.

Fibrillated heat-resistant fibers can be produced using heat-resistant fibers in refiners, beaters, mills, trituration devices, rotary homogenizers that apply shearing force using high-speed rotating blades, and high-speed rotating cylindrical inner blades and fixed outer blades. A double cylindrical high-speed homogenizer that generates shear force between the fibers, an ultrasonic crusher that atomizes the fibers by impacting them with ultrasonic waves, and a pressure difference of at least 20 MPa to the fiber suspension to make it pass through a small diameter orifice to achieve high speed. It can be obtained by processing using a high-pressure homogenizer or the like that applies shearing force and cutting force to the fibers by colliding them and rapidly decelerating them.

In the present invention, the content of fibrillated heat-resistant fibers is preferably 2.0% by mass or more and 10.0% by mass or less, and 3.0% by mass or more and 8% by mass or less, based on the total fiber components contained in the base material. It is more preferably .0 mass% or less, even more preferably 3.5 mass% or more and 6.0 mass% or less, and particularly preferably 3.5 mass% or more and 5.0 mass% or less. When the content of the fibrillated heat-resistant fiber exceeds 10.0% by mass, it is necessary to increase the amount of the wet heat adhesive binder fiber, and fire resistance and nonflammability may decrease. In addition, the thickness of the base material tends to become thinner, and the voids in the base material decrease, which reduces the permeability and liquid retention of the coating liquid for forming an inorganic particle layer, and reduces the content of inorganic particles, which increases fire resistance. The property and flammability may deteriorate. On the other hand, when the content of fibrillated heat-resistant fibers is less than 2.0% by mass, it is difficult to form a dense network structure between the fibrillated heat-resistant fibers or between the fibrillated heat-resistant fibers and the glass fibers, and the wet strength decreases. It becomes difficult to realize the improvement effect.

In the present invention, in addition to glass fibers, wet heat adhesive binder fibers, and fibrillated heat-resistant fibers, various fibers may be blended as needed within a range that does not impede performance. As a result, the number of voids can be further increased, and the retention of inorganic particles and the strength of the thermal runaway suppressed fireproof sheet can be improved. Such fibers include recycled fibers such as rayon, cupro, and lyocell fibers, semi-synthetic fibers such as acetate, triacetate, and promix, polyolefins, polyamides, polyacrylics, vinylon, vinylidene, polyvinyl chloride, and polyester. Synthetic resin fibers such as benzoate, polychlor, phenol, melamine, furan, urea, aniline, unsaturated polyester, fluorine, silicone, and derivatives thereof, inorganic fibers such as metal fibers, carbon fibers, alumina, silica, ceramics, rock fibers, etc. Fiber can be added.

The synthetic resin fiber may be a fiber (single fiber) made of a single resin, or a composite fiber made of two or more resins. Moreover, the number of synthetic resin fibers contained in the thermal runaway suppressing fireproof sheet of the present invention may be one type, or two or more types may be used in combination. Examples of composite fibers include core-sheath type, eccentric type, side-by-side type, sea-island type, orange type, and multi-bimetal type.

In the present invention, the thickness of the base material is preferably 0.25 mm or more, more preferably 0.40 mm or more, and even more preferably 0.60 mm or more. Moreover, it is preferably 2.00 mm or less, more preferably 1.50 mm or less, and even more preferably 1.20 mm or less. When the thickness of the base material is within the above range, the base material of the present invention can easily maintain the necessary tensile strength in the paper making process and the coating process, so it is easy to maintain the tensile strength required in the paper making process and the coating process. No loss of workability. When the thickness of the base material exceeds 2.00 mm, the rigidity of the base material becomes too strong, which may make it difficult to wind it up with a reeler in the papermaking process. If the thickness of the base material is less than 0.25 mm, the voids in the base material will become large, making it difficult to coat, and may require coating with a large amount of inorganic particles.

The density of the base material in the present invention is preferably 0.07 g/cm ³ or more, more preferably 0.10 g/cm ³ or more. Further, it is preferably 0.30 g/cm ³ or less, more preferably 0.20 g/cm ³ or less. If the density is less than 0.07 g/cm ³ , the tensile strength of the base material becomes too weak and there is a risk of damage during handling or coating, and if the density exceeds 0.30 g/cm ³ , If the rigidity of the base material becomes too high, it may become difficult to wind it up with a paper reeler, or the amount of coating of the inorganic particle layer may decrease.

The base material in the present invention is preferably a wet nonwoven fabric manufactured by a wet papermaking method. In the wet papermaking method, fibers are dispersed in water to form a uniform papermaking slurry, and this papermaking slurry is processed using a paper machine to produce a wet nonwoven fabric. Examples of the paper machine include a cylinder paper machine, a fourdrinier paper machine, an inclined paper machine, an inclined short-mesh paper machine, and a combination machine thereof. It can also be manufactured using a paper machine that has a plurality of head boxes and stacks wet paper webs on a wire. In addition to the fiber raw material, a dispersant, a paper strength enhancer, a thickener, an inorganic filler, an organic filler, an antifoaming agent, and the like can be appropriately added to the papermaking slurry, if necessary. The solid content concentration of the papermaking slurry is preferably about 0.5 to 0.001% by mass. This papermaking slurry is further diluted to a predetermined concentration before papermaking. The paper-formed wet paper web is then nipped with press rolls or the like, and then a Yankee dryer is used to melt the wet heat adhesive binder fibers to develop strength. By drying with a Yankee dryer, the dried surface becomes smooth and a surface with few surface irregularities can be formed. In addition, there is no problem even if a heating device such as a hot air dryer, heating roll, or infrared heater is used in combination as auxiliary drying. The drying temperature at this time is preferably a temperature at which moisture from the wet paper web can be sufficiently removed and strength can be developed by the wet heat adhesive binder fibers.

In the present invention, the inorganic particle layer is a layer containing inorganic particles and an inorganic binder. By filling the voids of the base material with this inorganic particle layer, the fire resistance and noncombustibility of the sheet can be achieved. Inorganic particles include aluminum hydroxide, aluminum hydroxide oxide, magnesium hydroxide, calcium hydroxide, dihydrated gypsum, and calcium aluminium oxide, clay, kaolin, calcined kaolin, calcium carbonate, magnesium carbonate, barium carbonate, talc, Inorganic particles with good water dispersibility such as titanium dioxide can be used.

Among the inorganic particles, aluminum hydroxide oxide, clay, kaolin, calcined kaolin, and carbonate-based inorganic particles are preferred because they solidify when exposed to flame and can prevent the inorganic particles from falling off the sheet. Furthermore, aluminum hydroxide oxide, clay, kaolin, and calcined kaolin are more preferable because they have excellent fire resistance and nonflammability and can maintain sheet strength even when kept at high temperatures.

In the present invention, the particle diameter of the inorganic particles is preferably 0.08 μm or more and 2.00 μm or less, more preferably 0.30 μm or more and 1.50 μm or less. When the particle size exceeds 2.00 μm, the fire resistance of the thermal runaway suppressing fireproof sheet may deteriorate, and the heat insulation properties of the thermal runaway suppressing fireproof sheet when exposed to high temperatures may deteriorate. On the other hand, if the particle size is less than 0.08 μm, the inorganic particles tend to increase in viscosity and become difficult to disperse, and when coated on a substrate, the inorganic particles may easily fall off from the substrate. It is necessary to increase the amount of binder to prevent it from falling off. In addition, the particle diameter as used in the present invention is a value obtained by converting the diameter of a perfect circle from the area of the inorganic particles obtained from a SEM photograph of the inorganic particles.

In the present invention, the inorganic particle layer can contain an inorganic binder. Examples of the inorganic binder include sepiolite, colloidal silica, water glass, alumina sol, and bentonite. The above inorganic binders may be used alone or in combination of two or more.

In the present invention, the content of the inorganic binder contained in the inorganic particle layer is preferably 2% by mass or more and 100% by mass or less, and 5% by mass or more and 50% by mass or less, based on the total amount of inorganic particles. is more preferable, and even more preferably 10% by mass or more and 30% by mass or less. When the amount of the inorganic binder is less than 2% by mass, the inorganic particles may easily fall off from the base material. Furthermore, if the amount of the inorganic binder exceeds 100% by mass, the coating properties of the inorganic particles may deteriorate.

The medium for preparing the coating liquid for forming an inorganic particle layer is not particularly limited as long as it can uniformly dissolve or disperse the inorganic binder and inorganic particles. 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 etc. can be used as necessary. Further, the medium used is preferably a medium that does not expand the base material or a medium that does not dissolve the base material.

The content of the inorganic particle layer is a value calculated by "coating amount of inorganic particle layer (g/m ² )/base weight (g/m ² ) x 100", and is preferably 90% by mass or more, The content is more preferably 100% by mass or more, and even more preferably 130% by mass or more. If the content of the inorganic particle layer is 90% by mass or more, even when the thermal runaway suppressing fireproof sheet is exposed to flame, the sheet will hardly melt or be damaged. The higher the content of the inorganic particle layer, the thicker the sheet, and the higher the fire resistance and heat insulation properties.

Various coating devices can be used to coat inorganic particles onto a base material to form an inorganic particle layer. For example, impregnation such as 2-roll size press, gate roll coater, gravure coater, die coater, lip coater, blade coater, curtain coater, air knife coater, rod coater, kiss touch coater, dip coater, or various coaters using coating equipment. can be used, but is not limited to this.

In the present invention, the inorganic particle layer includes, in addition to the inorganic particles and inorganic binder, various dispersants such as polyacrylic acid and sodium carboxymethylcellulose, and hydroxyethylcellulose and sodium carboxymethylcellulose to increase the stability of the coating solution. , various thickeners such as polyethylene oxide, various water retention agents, various wetting agents, preservatives, antifoaming agents, and other various additives may be added as necessary. Generally, non-aqueous coating liquids using an organic solvent as a medium have a low surface tension, while aqueous coating liquids using water as a medium have a high surface tension. Since the substrate of the present invention has high receptivity to coating liquids, it can be coated with both non-aqueous coating liquids and aqueous coating liquids without any problem. However, in the present invention, only water is used as the medium. It is preferable to use the same aqueous coating liquid as previously used.

The present invention will be explained below with reference to Examples, but the present invention is not limited to these Examples in any way. In addition, in the examples, all percentages (%) and parts are based on mass unless otherwise specified. Moreover, the coating amount is a dry coating amount.

Example 1
<Preparation of base material>
90 parts of glass fiber (product name: ECS06I-33G, made by Nippon Electric Glass Co., Ltd., fiber diameter 10 μm x fiber length 6 mm), silanol-modified PVA fiber (moist heat adhesive binder fiber, product name: SPG056-11, Kuraray Co., Ltd.) 5 parts of fully aromatic polyamide fiber pulp (average fiber length 1.7 mm, average fiber diameter 10 μm) was fibrillated to a modified freeness of 350 ml using a high-pressure homogenizer. Five parts of the fibrillated heat-resistant fibers were dispersed in water using a pulper to prepare a uniform papermaking slurry with a concentration of 0.5%, and a wet paper web was obtained using a cylinder paper machine. It was dried using a cylinder dryer at 140° C. to produce a base material having a basis weight of 50.1 g/m ² and a thickness of 0.286 mm.

<Preparation of coating liquid for forming inorganic particle layer>
100 parts of kaolin (product name: ASP (registered trademark) NC .4 parts were mixed in water and thoroughly stirred to prepare a kaolin dispersion. Next, 20 parts of sepiolite (trade name: Mircon (registered trademark) SP-2, manufactured by Showa KDE Co., Ltd.) and 1.0 part of a water-soluble acrylic acid dispersant (Aron T-50) were mixed in water and thoroughly stirred. , a sepiolite dispersion was prepared. Next, the entire amount of the kaolin dispersion and the entire amount of the sepiolite dispersion were mixed and stirred, and the concentration was adjusted with water to prepare a coating solution with a solid content concentration of 40%.

<Production of thermal runaway suppression fireproof sheet>
The base material is impregnated with a coating liquid using a size press, dried, and has an absolutely dry coating weight of 55.1 g/m ² , a total basis weight of 105.2 g/m ² , and a thickness of 0.306 mm. A sheet was produced.

Example 2
90 parts of the glass fiber used in Example 1, 5 parts of the silanol-modified PVA fiber used in Example 1, and a pulp of wholly aromatic polyamide fiber (average fiber length 1.7 mm, average fiber diameter 10 μm) , 5 parts of fibrillated heat-resistant fibers that had been fibrillated to a modified freeness of 45 ml using a high-pressure homogenizer were processed using the same paper-making method as in Example 1 to have a basis weight of 49.9 g/m ² and a thickness of 0.270 mm. A base material was prepared.

This base material was impregnated with the coating liquid used in Example 1 using a size press and dried to give an absolute dry coating weight of 53.5 g/m ² , a total basis weight of 103.4 g/m ² , and a thickness of 0.304 mm. A fireproof sheet with thermal runaway suppression was produced.

Example 3
90 parts of the glass fiber used in Example 1 and 5 parts of PVA fiber (wet heat adhesive binder fiber, trade name: VPB107-1, manufactured by Kuraray Co., Ltd., 1.1 decitex x 3 mm) were used in Example 1. A base material having a basis weight of 50.2 g/m ² and a thickness of 0.295 mm was prepared from 5 parts of fibrillated heat-resistant fibers using the same paper-making method as in Example 1.

This base material was impregnated with the coating liquid used in Example 1 using a size press, and dried to give an absolute dry coating weight of 59.1 g/m ² , a total basis weight of 109.3 g/m ² , and a thickness of 0.318 mm. A fireproof sheet with thermal runaway suppression was produced.

Example 4
90 parts of the glass fiber used in Example 1, 5 parts of the silanol-modified PVA fiber used in Example 1, a pulp of wholly aromatic polyamide fiber (average fiber length 1.7 mm, average fiber diameter 10 μm), 5 parts of fibrillated heat-resistant fibers fibrillated to a modified freeness of 650 ml using a high-pressure homogenizer were processed using the same papermaking method as in Example 1 to form a base material with a basis weight of 50.5 g/m ² and a thickness of 0.293 mm. was created.

This base material was impregnated with the coating solution used in Example 1 using a size press and dried to give an absolutely dry coating weight of 56.8 g/m ² , a total basis weight of 107.3 g/m ² , and a thickness of 0.313 mm. A fireproof sheet with thermal runaway suppression was produced.

Example 5
90 parts of the glass fiber used in Example 1, 5 parts of the silanol-modified PVA fiber used in Example 1, a pulp of wholly aromatic polyamide fiber (average fiber length 1.7 mm, average fiber diameter 10 μm), 5 parts of fibrillated heat-resistant fibers fibrillated to a modified freeness of 35 ml using a high-pressure homogenizer were made into a base material with a basis weight of 48.5 g/m ² and a thickness of 0.263 mm using the same papermaking method as in Example 1. was created.

This base material was impregnated with the coating liquid used in Example 1 using a size press, and dried to give an absolute dry coating weight of 52.0 g/m ² , a total basis weight of 100.5 g/m ² , and a thickness of 0.296 mm. A fireproof sheet with thermal runaway suppression was produced.

Example 6
93 parts of the glass fiber used in Example 1, 5 parts of the silanol-modified PVA fiber used in Example 1, and 2 parts of the fibrillated heat-resistant fiber used in Example 1 were processed using the same papermaking method as in Example 1. A base material having a basis weight of 50.1 g/m ² and a thickness of 0.313 mm was produced.

This base material was impregnated with the coating solution used in Example 1 using a size press and dried to give an absolute dry coating weight of 58.0 g/m ² , a total basis weight of 108.1 g/m ² , and a thickness of 0.317 mm. A fireproof sheet with thermal runaway suppression was produced.

Example 7
85 parts of the glass fiber used in Example 1, 5 parts of the silanol-modified PVA fiber used in Example 1, and 10 parts of the fibrillated heat-resistant fiber used in Example 1 were processed using the same papermaking method as in Example 1. A base material having a basis weight of 49.8 g/m ² and a thickness of 0.266 mm was produced.

This base material was impregnated with the coating solution used in Example 1 using a size press, and dried to give an absolute dry coating weight of 47.3 g/m ² , a total basis weight of 97.1 g/m ² , and a thickness of 0.281 mm. A fireproof sheet with thermal runaway suppression was produced.

Example 8
As a coating solution for forming an inorganic particle layer, 100 parts of kaolin used in Example 1 and 0.4 parts of a water-soluble acrylic acid dispersant (Aron T-50) were mixed in water and thoroughly stirred to form a kaolin dispersion. was prepared. Next, 15 parts of bentonite (trade name: Kunipia (registered trademark) G, manufactured by Kunimine Kogyo Co., Ltd.) and 1.0 part of a water-soluble acrylic acid dispersant (Aron T-50) were mixed in water and thoroughly stirred. A bentonite dispersion was prepared. Next, the entire amount of the kaolin dispersion and the entire amount of the bentonite dispersion were mixed and stirred, and the concentration was adjusted with water to prepare a coating solution with a solid content concentration of 20%.

This coating solution was applied to both the front and back surfaces of the base material prepared in Example 1 using a rod coater, and dried to give an absolutely dry coating weight of 50.5 g/m ² , total basis weight of 100.6 g/m ² , and thickness. A 0.292 mm thermal runaway suppressed fireproof sheet was produced.

Example 9
As a coating liquid for forming an inorganic particle layer, 100 parts of non-swellable mica (product name: Micromica MK-100, manufactured by Katakura Co-op Agri Co., Ltd.) and a water-soluble acrylic acid dispersant (product name: Aron T-50, (manufactured by Toagosei Co., Ltd.) was mixed in water and sufficiently stirred to prepare a mica dispersion. Next, 20 parts of sepiolite used in Example 1 and 1.0 part of a water-soluble acrylic acid dispersant (Aron T-50) were mixed in water and thoroughly stirred to prepare a sepiolite dispersion. Next, the entire amount of the mica dispersion and the entire amount of the sepiolite dispersion were mixed and stirred, and the concentration was adjusted with water to prepare a coating solution with a solid content concentration of 40%.

This coating liquid was impregnated into the base material prepared in Example 1 using a size press, and dried to give an absolutely dry coating weight of 54.0 g/m ² , a total basis weight of 104.1 g/m ² , and a thickness of 0.299 mm. A fireproof sheet that suppresses thermal runaway was produced.

Comparative example 1
The same paper making method as in Example 1 was used except that 90 parts of the glass fiber used in Example 1, 5 parts of the wet heat adhesive PVA fiber used in Example 3, and 5 parts of unbeaten NBKP were used to produce a paper with a basis weight of 50.2 g/ A base material having ^a size of 0.295 mm and a thickness of 0.295 mm was prepared.

This base material was impregnated with the coating solution used in Example 1 using a size press and dried to give an absolute dry coating weight of 56.5 g/m ² , a total basis weight of 106.7 g/m ² , and a thickness of 0.296 mm. A fireproof sheet with thermal runaway suppression was produced.

Comparative example 2
A base material having a basis weight of 50.2 g/m ² and a thickness of 0.295 mm prepared in Comparative Example 1 was impregnated with a sepiolite dispersion liquid as a coating liquid for forming an inorganic particle layer using a size press, dried, and completely dry coated. A thermal runaway suppressed fireproof sheet with a work load of 16.7 g/m ² , a total basis weight of 66.9 g/m ² , and a thickness of 0.295 mm was produced.

Comparative example 3
95 parts of the glass fibers used in Example 1 and 5 parts of the silanol-modified PVA fibers used in Example 1 were made into paper with a basis weight of 50.0 g/m ² and a thickness of 0.294 mm using the same paper making method as in Example 1. A base material was prepared.

This base material was impregnated with the coating solution used in Example 1 using a size press and dried to give an absolute dry coating weight of 55.8 g/m ² , a total basis weight of 105.8 g/m ² , and a thickness of 0.307 mm. A fireproof sheet with thermal runaway suppression was produced.

Comparative example 4
As a coating liquid for forming an inorganic particle layer, 100 parts of kaolin used in Example 1, 0.4 parts of a water-soluble acrylic acid dispersant, and a vinyl chloride emulsion (trade name: Vinibran (registered trademark) 278, solid content concentration) were used. 43% (manufactured by Nissin Chemical Industry Co., Ltd.) in water and thoroughly stirred to prepare a coating liquid with a solid content concentration of 40%.

This coating liquid was impregnated into the base material prepared in Example 1 with a basis weight of 50.1 g/m ² and a thickness of 0.286 mm using a size press, and dried, with an absolute dry coating weight of 55.5 g/m ² A thermal runaway suppressed fireproof sheet having a total basis weight of 105.6 g/m ² and a thickness of 0.318 mm was produced.

Comparative example 5
A base material having a basis weight of 99.0 g/m ² and a thickness of 0.582 mm was prepared using the same formulation as in Comparative Example 1.
This base material was impregnated with the coating solution used in Example 1 using a size press, and dried to give an absolute dry coating weight of 99.0 g/m ² , a total basis weight of 198.0 g/m ² , and a thickness of 0.582 mm. A fireproof sheet with thermal runaway suppression was produced.

The following physical properties were measured and evaluated for the base materials for thermal runaway suppressed fireproof sheets and thermal runaway suppressed fireproof sheets of Examples and Comparative Examples, and the results are shown in Table 1.

<Basic weight of base material and coating amount of inorganic particle layer>
The basis weight of the base material and the coating amount of the inorganic particle layer were measured in accordance with JIS P8124:2011. The coating amount of the inorganic particle layer was calculated by subtracting the basis weight of the base material from the total basis weight of the thermal runaway suppressing fireproof sheet.

<Thickness of base material and thermal runaway suppression fireproof sheet>
The thickness at a load of 5N was measured using an outside micrometer specified in JIS B7502:2016.

<Tensile strength of base material>
For each base material, cut out five sample pieces measuring 250 mm in the flow direction x 50 mm in the width direction so that the long side is in the flow direction, and use a tabletop universal testing machine (manufactured by A&D Co., Ltd., product name STB-1225S). ), a tensile test was conducted at a tensile speed of 100 mm/min according to JIS P8113:1998. The maximum value of the tensile stress was defined as the "tensile strength", and the average value of the five sheets was taken.

<Wet tensile strength of base material>
For each base material, cut out five sample pieces measuring 250 mm in the flow direction x 50 mm in the width direction so that the long side is in the flow direction, immerse them in 23°C ion exchange water for 3 minutes, take out the sample pieces, and then Lightly wipe off the ion-exchanged water with Kim Towel (registered trademark), and test at a tensile speed of 100 mm using a tabletop universal testing machine (manufactured by A&D Co., Ltd., product name STB-1225S) in accordance with JIS P8113:1998. A tensile test was conducted at /min. The maximum value of the tensile stress was defined as the "wet tensile strength", and the average value of the five sheets was taken as the "wet tensile strength".

<Coatability of inorganic particle layer>
The ease of coating when forming an inorganic particle layer on a base material was evaluated using the following evaluation criteria.

○: When applying the coating liquid, there are no paper breaks, cracks, or cracks on the base material. ×: When applying the coating liquid, there are no paper breaks, cracks, or cracks on the base material. If there is

<Fire resistance>
To evaluate the fire resistance of thermal runaway suppressing fireproof sheets, three test pieces with a size of 100 mm in the width direction x 100 mm in the machine direction were cut out from each sheet, and a burner (product name: Labo Burner APTL, Inc.) was placed in the center of each test piece. A flame (manufactured by Phoenix Dent) was applied for 5 minutes. Thereafter, the surface of the fireproof sheet on the side to which the flame was applied was visually observed and evaluated using the following evaluation criteria. The flame temperature of the burner was 1170°C.

○: There are no holes, cracks, or melting in the fireproof sheet.
△: Slight melting and dents are observed on the surface of the fireproof sheet exposed to flame.
×: There are holes and cracks in the fireproof sheet.

<Nonflammability>
To evaluate the noncombustibility of thermal runaway suppressing fireproof sheets, cut out two test pieces with a size of 100 mm in the width direction x 100 mm in the flow direction from each sheet, and place each test piece in a heating electric furnace that can maintain the temperature at 750°C ± 5°C. It was inserted and evaluated using the following evaluation criteria.

○: No fire after insertion.
×: After insertion, the sheet surface ignites.

As shown in Table 1, the thermal runaway suppressing fireproof sheets produced in Examples 1 to 9 contained a base material and an inorganic particle layer, and the base material contained glass fibers, moist heat adhesive binder fibers, and fibrillated heat resistant sheets. It contains fibers, and the inorganic particle layer contains inorganic particles and an inorganic binder. Glass fibers and fibrillated heat-resistant fibers are closely intertwined, and the wet heat adhesive binder fibers fix the intertwined intersections, resulting in strong wet tensile strength, lowering the basis weight to 50 g/m ² , and forming an inorganic particle layer. There was no paper breakage even when the coating solution was applied. Further, the thermal runaway suppressed fireproof sheets produced in Examples 1 to 9 were excellent in fire resistance and nonflammability.

Comparing Example 1 and Example 3, it was found that the wet tensile strength was further improved by using silanol-modified polyvinyl alcohol fiber as the wet heat adhesive binder fiber.

Comparing Example 1 and Example 4, it was found that when the modified freeness of the fibrillated heat-resistant fibers was increased, the entanglement between the glass fibers and the fibrillated heat-resistant fibers was reduced, resulting in a decrease in wet tensile strength. Ta.

On the other hand, when comparing Example 2 and Example 5. Modified method of fibrillated heat-resistant fibers When the freeness becomes too low, the fine content increases, resulting in a decrease in basis weight and increased entanglement, but the intersections cannot be fixed unless the moist heat adhesive binder fibers are increased. Therefore, it was found that the wet tensile strength decreased.

The thermal runaway suppressing fireproof sheets of Comparative Examples 1 to 3 and Comparative Example 5 do not contain fibrillated heat-resistant fibers, but Comparative Examples 1 to 3 with a basis weight of 50 g/m ² have a weak wet tensile strength. Paper breakage occurred when applying the coating solution for forming an inorganic particle layer. In Comparative Example 5, which had a basis weight of 99.0 g/m ² , there was no paper breakage when applying the coating liquid for forming an inorganic particle layer.

In the thermal runaway suppression sheets of Comparative Examples 1 and 2 and Comparative Example 5 containing cellulose components, when inserted into an electric furnace at 750° C., the surface ignited and the nonflammability was insufficient. Further, the thermal runaway suppressed fireproof sheet of Comparative Example 2 was impregnated with only the inorganic binder sepiolite as the inorganic particle layer, but the fire resistance was also insufficient.

The thermal runaway suppressing fireproof sheet of Comparative Example 4 used an organic binder in the inorganic particle layer, but when inserted into an electric furnace at 750°C, the surface caught fire and its nonflammability was insufficient.

The thermal runaway suppressing fireproof sheet of the present invention can be suitably used for battery packs equipped with a plurality of lithium ion cells.

Claims (3)

A thermal runaway suppressing fireproof sheet that prevents the spread of fire to adjacent cells when one cell ignites in a battery pack equipped with multiple cells,
The thermal runaway suppressing fireproof sheet contains a base material and an inorganic particle layer,
The base material contains glass fibers, wet heat adhesive binder fibers, and fibrillated heat-resistant fibers, and the content of glass fibers is 75% by mass or more and 95% by mass or less with respect to the total fiber components contained in the base material. The content of the moist heat adhesive binder fiber is 3% by mass or more and 20% by mass or less, the content of the fibrillated heat-resistant fiber is 2.0% by mass or more and 10.0% by mass or less,
A thermal runaway suppressing fireproof sheet, wherein the inorganic particle layer contains inorganic particles and an inorganic binder. The thermal runaway suppressing fireproof sheet according to claim 1, wherein the moist heat adhesive binder fiber is a silanol-modified polyvinyl alcohol fiber. The thermal runaway suppressing fireproof sheet according to claim 1 or 2, wherein the fibrillated heat-resistant fiber has a modified freeness of 40 ml or more.
Modified freeness: Measured in accordance with JIS P8121-2:2012, except that an 80-mesh wire mesh with a wire diameter of 0.14 mm and an opening of 0.18 mm was used as a sieve plate, and the sample concentration was 0.1%. value.