JP7163262B2 - Thermal runaway suppression refractory sheet - Google Patents

Description

TECHNICAL FIELD 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 catches fire in a battery pack having a plurality of unit cells.

2. Description of the Related Art In recent years, with the diversification of electronic devices, there is a demand for a battery pack having a high capacity, a high voltage, a high output, and a high level of safety, and a plurality of battery cells. There are cylindrical, square, and pouch types for these cells, and in order to provide highly safe cells and battery packs, PTC elements are added to the cells and battery packs to prevent temperature rise. Techniques are known in which various protection means are provided, such as equipment, thermal fuses, and protection circuits that detect the internal pressure of the unit cell and cut off the current. A technique is also known in which a battery pack is provided with a control circuit for controlling charging and discharging of a unit cell so that the unit cell does not enter an abnormal state (for example, a thermal runaway state).

However, even with the protection means and control circuit as described above, when the cell is placed under abnormal conditions, thermal runaway may occur in the cell due to various causes. When thermal runaway occurs, the temperature of the unit cell rises rapidly to 300° C. or higher, and in some cases 400° C. or higher, and high-temperature combustible gas may blow out from the inside. In the worst case, a fire may occur, and the housing of the battery pack housing the unit cells may be damaged or melted.

As a technique for preventing such thermal runaway, Patent Document 1 discloses a heat insulating sheet in which silica xerogel is supported in the space of the glass fiber sheet and the silica xerogel is fixed by covering the outer periphery of the fiber sheet with a dense resin layer. disclosed. Although this heat insulating sheet can be used for rectangular or pouch-shaped elementary cells, it has a problem that it cannot be used for cylindrical-shaped elementary cells because of its lack of flexibility. Moreover, although the heat insulating property is excellent, since the silica xerogel is fixed by the resin layer, there is a problem that the fire resistance is inferior when the temperature of the unit cell exceeds 300°C.

In addition, in Patent Document 2, at least one of mineral powder and flame retardant is contained, endothermic reaction is started at 100 to 1000 ° C., and selected from the group consisting of phase change, expansion, foaming and hardening accordingly. A thermal runaway prevention sheet is disclosed in which at least one type of structural change occurs. This thermal runaway prevention sheet uses an aluminum foil laminated glass cloth as a base material, and a resin composition containing mineral powder and a flame retardant is supplied to a single screw extruder and extruded to obtain a heat absorbing sheet. A thermal runaway prevention sheet can be obtained by obtaining a material sheet and a fireproof insulation sheet, and then combining the heat-absorbing material sheet and the fireproof insulation sheet obtained by press working, resulting in extremely low productivity and high cost. Although it can be used for rectangular or pouch-shaped cells, it cannot be used for cylindrical cells because of its lack of flexibility.

WO 2018/110055 pamphlet JP 2018-206605 A

An object of the present invention is to prevent the spread of fire to adjacent lithium-ion batteries in a battery pack comprising a plurality of lithium-ion batteries, when one battery undergoes thermal runaway and catches fire. To provide a thermal runaway suppressing fire resistant sheet which has fire resistance, heat shielding properties, and excellent handleability as a suppressing fire resistant sheet.

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

(1) Consists of a substrate and an inorganic particle layer,
The base material contains glass fibers, wet heat adhesive binder fibers, and fibrillated heat-resistant fibers,
The content of the glass fiber is 75% by mass or more and 95% by mass or less, and the content of the wet heat adhesive binder fiber is 3% by mass or more and 20% by mass or less, based on the total fiber components contained in the base material. , the content of the fibrillated heat-resistant fiber is 2.0% by mass or more and 10.0% by mass or less,
The inorganic particle layer accounts for 45 to 65% by mass of the total sheet,
A fireproof sheet for suppressing thermal runaway, wherein the surface porosity of the inorganic particle layer is 10% or less.

(2) The thermal runaway suppressing fireproof sheet according to (1) above, wherein the surface porosity of the inorganic particle layer is 3% or less.

The thermal runaway suppressing refractory sheet of the present invention contains a substrate containing glass fibers, wet heat adhesive binder fibers and fibrillated heat resistant fibers. Glass fibers and fibrillated heat-resistant fibers are entangled, and the intertwined intersections are fixed with wet heat adhesive binder fibers, so the substrate has excellent wet strength. In addition, the substrate is excellent in the permeability of the substrate for forming the inorganic particle layer and the retention of the inorganic particle layer on the substrate. By providing an inorganic particle layer having a surface porosity of 10% or less, which accounts for 45 to 65% by mass of the entire sheet, on the substrate, excellent fire resistance, heat shielding properties, and handleability can be obtained.

Surface observation image of thermal runaway suppression fireproof sheet with large surface porosity Surface observation image of thermal runaway suppression fireproof sheet with small surface porosity Configuration diagram of thermal runaway suppression refractory sheet thermal insulation evaluation equipment

In the present invention, the thermal runaway suppressing refractory sheet contains a base material and an inorganic particle layer, and on the base material containing glass fiber, wet heat adhesive binder fiber and fibrillated heat resistant fiber, 45 to 45 to 45% of the total sheet It is a thermal runaway suppression fireproof sheet provided with an inorganic particle layer having a surface porosity of 10% or less, which accounts for 65% by mass.

Glass fibers in the present invention include, for example, 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 μm or more and 18 μm or less, more preferably 3 μm or more and 15 μm or less, and even more preferably 5 μm or more and 12 μm or less. If the fiber diameter is less than 1 μm, the glass fibers are too thin and may fall off from the substrate during papermaking, resulting in insufficient strength and thickness. If the fiber diameter exceeds 18 μm, the glass fiber becomes too thick, the gap between the substrates becomes large, the processability is inferior, and furthermore, there is irritation to the skin, which hinders workability and makes it difficult to use. may become.

The fiber length of the glass fiber in the present invention is preferably 1 mm or more and 30 mm or less, more preferably 3 mm or more and 15 mm or less, and even more preferably 5 mm or more and 12 mm or less. 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.

In addition, the content of the glass fiber in the present invention is preferably 75% by mass or more and 95% by mass or less, and more preferably 80% by mass or more and 93% by mass or less, based on the total fiber components contained in the base material. More preferably, it is 85% by mass or more and 90% by mass or less. If the content is less than 75% by mass, the fire resistance may deteriorate. Glass fibers may come off during coating to provide a layer.

The binder fiber used in the present invention is a wet heat adhesive binder fiber. A wet heat adhesive binder fiber is a fiber that exhibits an adhesive function by flowing or easily deforming from a fibrous state at a certain temperature in a wet state. Specifically, it is a thermoplastic fiber that is softened by hot water (for example, about 80 to 120 ° C.) and can be self-adhered or adhered to other fibers. alcohol, polyvinyl acetal, etc.), cellulosic 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 salts thereof, 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, etc.) etc. As the wet heat adhesive binder fiber used in the present invention, polyvinyl fiber is preferable, and polyvinyl alcohol (PVA) fiber is more preferable. Easier to hold between fibers.

The fineness of the wet heat adhesive binder fiber is preferably 0.1 decitex or more and 5.6 decitex or less, more preferably 0.4 decitex or more and 2.2 decitex or less, and 0.6 decitex or more and 1.1 decitex. It is more preferably less than decitex. If the fineness is less than 0.1 decitex, the fiber itself becomes very expensive, and the substrate may become dense and thin. On the other hand, when it exceeds 5.6 decitex, the contact points with the glass fibers are reduced, and it may become difficult to maintain the strength in a wet state. In addition, a uniform formation may not be obtained. The fiber length of the wet heat adhesive binder fiber is preferably 1 mm or more and 15 mm or less, more preferably 2 mm or more and 10 mm or less, and even more preferably 3 mm or more and 5 mm or less. If the fiber length is less than 1 mm, it may fall off from the papermaking wire during papermaking, and sufficient strength may not be obtained. On the other hand, if the thickness exceeds 15 mm, tangling or the like may occur when dispersed in water, and a uniform texture may not be obtained.

The content rate of the wet 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 with respect to the total fiber components contained in the base material. more preferably 5% by mass or more and 10% by mass or less. If the content of the wet heat adhesive binder fiber is less than 3% by mass, the strength of the base material is lowered, and the paper may be broken when the inorganic particles are applied, or the glass fibers may fall off. On the other hand, if the content of the wet heat adhesive binder fiber exceeds 20% by mass, when the substrate is made into paper by a wet papermaking method, the releasability from the dryer may deteriorate, and the inorganic particles are not coated. In some cases, the permeability to the substrate may decrease, and the fire resistance of the thermal runaway suppressing fireproof sheet may deteriorate.

The fibrillated heat-resistant fiber used in the present invention includes wholly aromatic polyamide, wholly 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 are highly hydrophilic and tend to fibrillate, 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, still more preferably 300 ml or more and 450 ml or less. If the modified freeness exceeds 700 ml, the fibrillation does not progress so much that it may be difficult to improve the binding properties between the glass fibers and the binding properties between the glass fibers and the wet heat adhesive binder fiber. In some cases, the effect of improving the permeability and liquid retention of the coating liquid for forming the inorganic particle layer is reduced. On the other hand, if the modified freeness is less than 40 ml, the fine content of the fibrillated heat-resistant fibers increases, which may increase the rate of falling off from the base material. As a result, the voids in the substrate are reduced, and the permeability and liquid retention of the coating liquid for forming the inorganic particle layer may be lowered.

In the present invention, the modified freeness is 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 is used as the sieve plate, and the sample concentration is set to 0.1%. It is a value measured according to

The fibrillated heat-resistant fiber of the present invention preferably has a mass-weighted average fiber length of 0.02 mm or more and 1.50 mm or less. Also, 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 substrate. If the average fiber length is longer than the preferred range, the fibers are not easily disaggregated, and poor dispersion tends to occur.

When the fibrillated heat-resistant fibers have the above weight-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, A dense network structure is formed by the fibers between the fibrillated heat-resistant fibers and the glass fibers, and a base material capable of enhancing the permeability and liquid retention of the inorganic particle layer-forming coating liquid can be obtained. .

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. When the average fiber width exceeds 40.0 μm, the entanglement between the fibrillated heat-resistant fiber and the glass fiber is reduced, so that the binding property between the glass fibers and the binding property between the glass fiber and the wet heat adhesive binder fiber are improved. It can get difficult. If the average fiber width is less than 0.5 μm, the fibrillated heat-resistant fibers will come off from the base material, and the number of crossing points will increase. It may become difficult to improve the binding property between the fiber and the wet heat adhesive binder fiber.

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

The fibrillated heat-resistant fiber is processed by a refiner, a beater, a mill, a grinder, a rotary homogenizer that applies a shearing force with a high-speed rotating blade, and a cylinder with a high-speed rotating inner blade and a fixed outer blade. A double-cylinder high-speed homogenizer that generates a shear force between them, an ultrasonic crusher that makes it finer by impact with ultrasonic waves, and a pressure difference of at least 20 MPa to the fiber suspension to pass it through a small diameter orifice to make it high speed. , can be obtained by colliding and rapidly decelerating the fibers, and treating the fibers with a high-pressure homogenizer or the like that applies a shearing force and a cutting force.

In the present invention, the content of the fibrillated heat-resistant fiber is preferably 2.0% by mass or more and 10.0% by mass or less, and preferably 3.0% by mass or more and 8 0% by mass or less, more preferably 3.5% by mass or more and 6.0% by mass or less, and particularly preferably 3.5% by mass or more and 5.0% by mass or less. If the content of the fibrillated heat-resistant fiber exceeds 10.0% by mass, it is necessary to increase the blending amount of the wet heat adhesive binder fiber, and the fire resistance may decrease. In addition, the thickness of the base material tends to be thin, and the voids in the base material are reduced. sexuality may worsen. On the other hand, when the content of the fibrillated heat-resistant fiber is less than 2.0% by mass, the adhesion between the fibrillated heat-resistant fibers, between the fibrillated heat-resistant fiber and the glass fiber, and between the glass fiber and the wet heat adhesive binder fiber It may become difficult to improve the binding property of.

In the present invention, in addition to the glass fiber, the wet heat adhesive binder fiber, and the fibrillated heat-resistant fiber, various fibers can be blended as necessary within a range that does not impair the performance. As a result, the voids can be further increased, and the retention of the inorganic particles and the strength of the thermal runaway suppressing refractory sheet can be improved. Such fibers include regenerated fibers such as rayon, cupra and lyocell fibers, semi-synthetic fibers such as acetate, triacetate and Promix, polyolefin, polyamide, polyacrylic, vinylon, vinylidene, polyvinyl chloride and polyester. benzoate, polyclar, phenol, melamine, furan, urea, aniline, unsaturated polyester, fluorine, silicone, synthetic resin fibers such as their derivatives, 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. Further, the synthetic resin fibers contained in the thermal runaway suppressing refractory sheet of the present invention may be of one type or may be used in combination of two or more types. 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 substrate is preferably 0.10 mm or more and 0.80 mm or less, more preferably 0.20 mm or more and 0.60 mm or less, and 0.30 mm or more and 0.50 mm or less. is more preferred. When the thickness of the substrate is within the above range, the substrate in the present invention can easily maintain the necessary tensile strength in the papermaking process and the coating process. Workability is not impaired. If the thickness of the base material exceeds 0.80 mm, the rigidity of the base material becomes too high, which may make it difficult to wind up with a reeler in the papermaking process. If the thickness of the substrate is less than 0.10 mm, the voids in the substrate become large, making it difficult to coat, and in addition, it may be necessary to coat a large amount of inorganic particles.

The density of the substrate in the present invention is preferably 0.07 g/cm ³ or more and 0.20 g/cm ³ or less, more preferably 0.10 g/cm ³ or more and 0.18 g/cm ³ or less. If the density is less than 0.07 g/cm ^{3 ,} the tensile strength of the substrate becomes too weak, and the substrate may be damaged during handling or coating. In some cases, the stiffness of the base material becomes too high, making it difficult to take up the base material with a reeler of a paper machine, or in some cases, the coating amount of the inorganic particle layer decreases.

The substrate in the present invention is preferably a wet-laid nonwoven fabric produced by a wet-laid papermaking method. In the wet papermaking method, fibers are dispersed in water to form a uniform papermaking slurry, and the papermaking slurry is made by a paper machine to produce a wet nonwoven fabric. The paper machine includes a cylinder paper machine, a fourdrinier paper machine, an inclined paper machine, an inclined wire mesh paper machine, and a combination of these machines. It can also be manufactured on a paper machine that has multiple headboxes and stacks wet paper on a wire. In addition to the fiber raw material, the papermaking slurry may optionally contain a dispersant, a paper strength agent, a thickener, an inorganic filler, an organic filler, an antifoaming agent, and the like. 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 and then made into paper. Next, the paper wet paper web is nipped with a press roll 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 less unevenness can be formed. In addition, there is no problem even if a heating device such as a hot air dryer, a heating roll, or an infrared heater is used for auxiliary drying. The drying temperature at this time is preferably a temperature at which the moisture in the wet paper web can be sufficiently removed and the strength can be exhibited by the wet heat adhesive binder fibers.

In the present invention, the inorganic particle layer is a layer containing inorganic particles. By covering the surface of the base material with this inorganic particle layer, the effect of fire resistance and heat shielding properties of the sheet can be obtained. The coating amount of the inorganic particle layer applied to the substrate is adjusted based on the ratio of the inorganic particle layer to the entire sheet (inorganic particle layer ratio), and the inorganic particle layer accounts for 45 to 65 masses of the entire sheet. %, more preferably 50 to 65% by mass. If the proportion of the inorganic particle layer is less than 45% by mass, the coverage of the inside and surface of the substrate with the inorganic particle layer is poor, and the fire resistance and heat shielding properties of the sheet are poor. When the proportion of the inorganic particle layer exceeds 65% by mass, the specific gravity of the thermal runaway suppressing refractory sheet increases, and the heat shielding effect of the sheet decreases. In addition, the coating layer strength of the inorganic particle layer is weakened, and when the sheet is handled, powder may fall off, or the inorganic particle layer may be peeled off from the substrate surface, resulting in poor handleability.

In the present invention, the surface porosity of the inorganic particle layer is 10% or less, more preferably 3% or less. The surface porosity of the inorganic particle layer is defined as the ratio of the total area of the portion where the inorganic particle layer does not completely cover the surface of the substrate to the entire surface of the inorganic particle layer when the surface of the sheet is observed. be done.

The surface porosity of the inorganic particle layer can be measured, for example, by the following procedure.
<1> The surface of the inorganic coating layer of the refractory sheet for suppressing thermal runaway is observed with an electron microscope at a magnification of 50 (for example, surface images shown in FIGS. 1 and 2).
<2> With respect to the obtained surface image of the inorganic coating layer, the portion not covered with the inorganic particle layer is extracted from the observation area of 1 mm×1 mm, and the area is measured.
<3> 10 images are measured in the same manner, and "surface porosity (%) = total area of the portion not covered with the inorganic particle layer (unit: mm ² )/10 mm ² ×100" is calculated.

When the surface porosity of the inorganic particle layer is 10% or less, the thermal runaway suppressing refractory sheet has an improved heat shielding property to block a heat flow applied from one surface. When the surface porosity is 3% or less, the effect of blocking the heat flow is further improved. If the surface porosity exceeds 10%, heat flow is transmitted through the portion not covered with the inorganic particle layer, resulting in poor heat shielding properties. The surface porosity of the inorganic particle layer can be adjusted by adjusting the density of the substrate, the coating amount of the inorganic particle layer, the coating method of the inorganic particle layer, the particle size of the inorganic particles, and the like.

Examples of inorganic particles include silicon oxides such as amorphous silica, alumina hydrates such as α-alumina, γ-alumina and boehmite, aluminum oxides such as diaspore and gibbsite and their hydrates, alumina-silica composite oxides, and kaolin. , calcined kaolin, talc, sepiolite, clay minerals such as natural mica, synthetic mica, barium titanate, magnesium hydroxide, magnesium oxide, calcium hydroxide, gypsum dihydrate, and calcium aluminate oxide, calcium carbonate, magnesium carbonate, carbonate Barium, titanium dioxide, etc. can be used.

Among the inorganic particles, boehmite, kaolin, calcined kaolin, synthetic mica, and carbonate-based inorganic particles are preferable because the inorganic particles are solidified when exposed to flame, and can prevent the inorganic particles from falling off from the sheet. Furthermore, boehmite, kaolin, calcined kaolin, and synthetic mica are more preferable because they have excellent fire resistance and can maintain sheet strength even when held at high temperatures.

In the present invention, the particle diameter of the inorganic particles is preferably 0.08 μm or more and 10.00 μm or less, more preferably 0.30 μm or more and 5.0 μm or less. If the particle size exceeds 10.00 μm, the fire resistance of the thermal runaway-suppressing fireproof sheet may be deteriorated, and the heat insulating properties of the thermal runaway-suppressing fireproof sheet may be deteriorated when exposed to high temperatures. On the other hand, if the particle diameter is less than 0.08 μm, the inorganic particles tend to thicken when dispersed, making it difficult to disperse, and when applied to a substrate, the inorganic particles tend to fall off from the substrate, It is necessary to increase the amount of binder to prevent shedding. The particle size referred to in the present invention is a value obtained by converting the diameter of a perfect circle from the area of an inorganic particle obtained from an electron micrograph of the inorganic particle.

In the present invention, the inorganic particle layer may contain a binder. Various organic polymers can be used as the binder. Examples thereof include vinyl chloride copolymers, vinyl acetate copolymers, styrene-butadiene copolymer elastomers (styrene-butadiene rubber), acrylonitrile-butadiene copolymer elastomers, (meth)acrylate polymer elastomers, styrene- Various organic polymers such as (meth)acrylic acid ester polymer elastomer, polyvinylidene fluoride polymer, and silicone elastomer can be used.

In the present invention, the inorganic particle layer may contain an inorganic binder. Examples of inorganic binders 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 binder contained in the inorganic particle layer is preferably 2% by mass or more and 100% by mass or less, and more preferably 5% by mass or more and 50% by mass or less, relative to the total amount of the inorganic particles. More preferably, it is 10% by mass or more and 30% by mass or less. If the amount of the binder is less than 2% by mass, the inorganic particles may easily fall off from the substrate. On the other hand, when the amount of the binder exceeds 100% by mass, the fire resistance may be lowered and the coatability of the inorganic particles may be deteriorated.

The medium for preparing the coating liquid for forming the inorganic particle layer is not particularly limited as long as it can uniformly dissolve or disperse the binder and the 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, dimethylsulfoxide, Water or the like can be used as necessary. Moreover, the medium to be used is preferably a medium that does not expand the substrate or a medium that does not dissolve the substrate.

Various coating apparatuses can be used as an apparatus for coating the substrate with the inorganic particles to form the inorganic particle layer. For example, 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, etc. Impregnation or various coaters using coating equipment can be used, but is not limited to this.

In the present invention, the inorganic particle layer contains various dispersants such as polyacrylic acid and sodium carboxymethylcellulose, in addition to the inorganic particles and the inorganic binder, and hydroxyethylcellulose and sodium carboxymethylcellulose to increase the liquid stability of the coating liquid. , various thickeners such as polyethylene oxide, various water retention agents, various wetting agents, preservatives, antifoaming agents, and other additives may be added as necessary. In general, a non-aqueous coating liquid using an organic solvent as a medium has a low surface tension, and an aqueous coating liquid using water as a medium has a high surface tension. Since the base material of the present invention has high receptivity for coating liquids, both non-aqueous coating liquids and water-based coating liquids can be coated without problems. It is preferable to use the water-based coating liquid used.

EXAMPLES The present invention will be described below with reference to Examples, but the present invention is not limited to these Examples. All percentages (%) and parts in the examples are based on mass unless otherwise specified. Moreover, the coating amount is the dry coating amount.

<Preparation of base material>
95 parts of glass fiber (trade name: ECS06I-33G, manufactured by Nippon Electric Glass Co., Ltd., fiber diameter 10 μm x fiber length 6 mm), PVA binder fiber (trade name: VPB107-1, manufactured by Kuraray Co., Ltd., 1.1 decitex x 3 mm, wet heat adhesive binder fiber), 3 parts of wholly 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. 2 parts of the fibrillated heat-resistant fibers were dispersed in water with 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, and the surface temperature was 140. C. to prepare a substrate having a basis weight of 100 g/ ^m.sup.2 and a thickness of 0.66 mm.

<Preparation of coating solution for forming inorganic particle layer>
Kaolin (trade name: ASP (registered trademark) NC X-1, manufactured by BASF CORPORATION) 100 parts, water-soluble acrylic dispersant (trade name: Aron (registered trademark) T-50, manufactured by Toagosei Co., Ltd.) 0 A kaolin dispersion was prepared by mixing .4 parts in water and stirring thoroughly. Next, 20 parts of sepiolite (trade name: Milcon (registered trademark) SP-2, manufactured by Showa KDE Co., Ltd.) and 1.0 part of a water-soluble acrylic dispersant (Aron T-50), a water retention agent (trade name: SN Thickener 926, manufactured by San Nopco) (0.08 part) was mixed in water and sufficiently stirred to prepare a sepiolite dispersion. Next, the total amount of the kaolin dispersion and the total amount of the sepiolite dispersion were mixed and stirred, and the concentration was adjusted with water to prepare a coating liquid.

The inorganic particle layer-forming coating solution was applied to the base material described above under the conditions described in Table 1 to prepare thermal runaway suppressing refractory sheets of Examples 1-7 and Comparative Examples 1-3.

The following physical properties were measured and evaluated for the thermal runaway suppressing refractory sheets of Examples and Comparative Examples, and the results are shown in Table 2.

<Base Weight of Base Material and Coating Amount of Inorganic Particle Layer>
Based on JIS P8124:2011, the basis weight of the substrate and the coating amount of the inorganic particle layer were measured. The coating weight of the inorganic particle layer was calculated by subtracting the basis weight of the substrate from the total basis weight of the thermal runaway suppressing fireproof sheet.

<Calculation of inorganic particle layer ratio>
The coating amount of the inorganic particle layer obtained by the above method was calculated according to the following formula.
Inorganic particle layer ratio = (coating amount of inorganic particle layer/total basis weight of thermal runaway suppressing refractory sheet) x 100

<Measurement of surface porosity>
The surface porosity of the thermal runaway suppression refractory sheets of Examples and Comparative Examples was calculated by the following method.
<1> The surface of the inorganic coating layer of the refractory sheet for suppressing thermal runaway is observed with an electron microscope at a magnification of 50 (for example, surface images shown in FIGS. 1 and 2).
<2> Regarding the obtained surface image of the inorganic coating layer, a portion not coated with the inorganic particle layer was extracted from the observed area of 1 mm×1 mm, and the area was determined.
<3> 10 images are measured in the same manner, and "surface porosity (%) = total area of the portion not covered with the inorganic particle layer (unit: mm ² )/10 mm ² ×100" is calculated.

<Fire resistance>
To evaluate the fire resistance of the thermal runaway-suppressing refractory sheet, three test pieces with a size of 100 mm in the width direction × 100 mm in the flow direction were cut out from each thermal runaway-suppressing refractory sheet, and a burner (trade name: Lab Burner) was placed in the center of each test piece. APTL (manufactured by Phoenix Dent Co., Ltd.) was applied for 5 minutes. After that, the surface of the fireproof sheet on the side exposed to the flame was visually observed and evaluated according to the following evaluation criteria. The burner flame temperature was 1170°C.

◯: There are no holes, cracks, or melting in the fireproof sheet.
Δ: Melting and dents are slightly observed on the surface of the refractory sheet exposed to flame.
x: There are holes and cracks in the fireproof sheet.

<Heat insulation>
As an evaluation of the heat shielding property of the thermal runaway suppressing refractory sheet, a hot plate (model PA8015-CC-PCC200V, manufactured by MSA Factory Co., Ltd.) at 700 ° C. was applied from one side of each thermal runaway suppressing refractory sheet (sample) using the apparatus shown in FIG. ), and the surface temperature of the opposite surface after 5 minutes was measured using a K thermocouple. A K thermocouple was placed between the sample and the insulation.

A: The surface temperature of the surface opposite to the heating surface is 600°C or less.
○: The surface temperature of the surface opposite to the heating surface was in the range of more than 600°C and 625°C or less.
Δ: The surface temperature of the surface opposite to the heating surface was in the range of more than 625° C. and 650° C. or less.
x: The surface temperature of the surface opposite to the heating surface exceeds 650°C.

<Coating layer strength>
The strength of the coating layer of the thermal runaway-suppressing refractory sheet was obtained by stacking two thermal runaway-suppressing refractory sheets of each of the examples and comparative examples, and rubbing the two sheets against each other 30 times on a black cloth. The state was visually observed and evaluated according to the following evaluation criteria.

◯: No powder falling off or scratching of the coating layer was observed.
Δ: Powder drop is observed to some extent. Slight scratches on the coating layer are observed. It was determined that there was no problem in practical use.
x: Powder omission is observed. Detachment of the coating layer is observed in part.

By comparing Examples 1 to 4 with Comparative Example 1, it was found that the substrate was composed of a substrate and an inorganic particle layer, the substrate contained glass fibers, wet heat adhesive binder fibers, and fibrillated heat-resistant fibers, and the inorganic particle layer accounts for 45 to 65% by mass of the total sheet, and the thermal runaway suppressing refractory sheet in which the inorganic particle layer has a surface porosity of 10% or less has excellent fire resistance and heat shielding properties.

By comparing Examples 1 and 2 with Examples 3 and 4, the surface porosity of the inorganic particle layer provided on the base material is 3% or less, so that the thermal runaway suppression fire resistance with more excellent heat shielding properties It turns out that the sheet can be provided.

By comparing Examples 1 to 4 and Comparative Example 2, when the coating amount of the inorganic particle layer is too large and the inorganic particle layer ratio exceeds 65% by mass of the total sheet, the coating layer strength of the inorganic particle layer is reduced. It turns out that it falls and handleability worsens.

By comparing Examples 2 and 5 with Comparative Example 3, even if the coating method for providing the inorganic particle layer on the substrate is different, the inorganic particle layer accounts for 45 to 65% by mass of the total sheet, and the surface voids It can be seen that by coating the base material with the inorganic particle layer so that the ratio is 10% or less, it is possible to provide a thermal runaway suppressing fire resistant sheet with excellent fire resistance and heat shielding properties.

By comparing Examples 2 and 3 with Examples 6 and 7, when providing the inorganic particle layer on the substrate, the inorganic particle layer was formed on one side of the substrate by coating at least twice. It can be seen that the presence of the refractory sheet reduces the surface porosity and provides a thermal runaway suppressing refractory sheet with more excellent heat shielding properties.

The thermal runaway suppressing fireproof sheet of the present invention can be suitably used for a battery pack or the like in which a plurality of lithium ion cells are mounted.

Claims (2)

Consists of a base material and an inorganic particle layer,
The base material contains glass fibers, wet heat adhesive binder fibers, and fibrillated heat-resistant fibers,
The content of the glass fiber is 75% by mass or more and 95% by mass or less, and the content of the wet heat adhesive binder fiber is 3% by mass or more and 20% by mass or less, based on the total fiber components contained in the base material. , the content of the fibrillated heat-resistant fiber is 2.0% by mass or more and 10.0% by mass or less,
The inorganic particle layer accounts for 45 to 65% by mass of the total sheet,
A fireproof sheet for suppressing thermal runaway, wherein the surface porosity of the inorganic particle layer is 10% or less. 2. The thermal runaway suppressing fireproof sheet according to claim 1, wherein the surface porosity of the inorganic particle layer is 3% or less.

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