JP7181179B2 - 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. In particular, in order to provide highly safe cells and battery packs, the cells and battery packs are equipped with PTC elements and thermal fuses to prevent temperature rise, and furthermore, the internal pressure of the cells is sensed. Techniques are known that provide various protection means such as a protection circuit that cuts off 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 has the effect of slowing down the temperature rise of adjacent unit cells, it has the problem of inferior heat resistance, fire resistance, and strength of the unit cells.

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, extruded, and heat absorbed. A thermal runaway prevention sheet can be obtained by obtaining a heat resistant material sheet and a fireproof heat insulating sheet, and then combining the obtained heat absorbing material sheet and fireproof heat insulating sheet to press work. I had a problem getting high. In addition, 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. comprising a step (i) of wet papermaking the slurry containing the inorganic fibers to produce a nonwoven fabric, and a step (ii) of attaching a slurry containing β-sepiolite to the nonwoven fabric. Disclosed is a method for producing an inorganic fiber sheet having However, this inorganic fiber sheet is preferably used as a base material of a filter that is fired after being made into a honeycomb molded body, and the wet strength of the nonwoven fabric itself is not sufficient, and it is difficult to use it without firing. There is a problem that inorganic fiber sheets are inferior in fire resistance and noncombustibility.

WO 2018/110055 pamphlet JP 2018-206605 A JP 2017-025458 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 fireproof sheet excellent in fire resistance and heat insulation as a suppressing fireproof sheet.

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

(1) containing a substrate and an inorganic particle layer,
The base material contains glass fibers, wet heat adhesive binder fibers and fibrillated heat resistant fibers, the inorganic particle layer contains inorganic particles and an inorganic binder, and the inorganic particle layer is contained in the base material. A thermal runaway suppressing refractory sheet characterized by having a coating layer that covers the surface of a fiber that covers the surface of the base material and a heat insulating layer that is present on at least one surface of the base material surface.

(2) The thermal runaway suppressing fireproof sheet according to (1) above, wherein the inorganic binder contained in the heat insulating layer contains bentonite.

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. Then, the inorganic particle layer contains inorganic particles and an inorganic binder, and the inorganic particle layer is a coating layer that covers the surface of the fiber contained in the base material, and at least one surface of the base material surface. It has excellent fire resistance and heat insulation because it has a heat insulation layer that exists in the

4 is a surface observation image of a coating layer that covers the surface of fibers contained in the thermal runaway suppression refractory sheet. 4 is a surface observation image of a heat insulating layer present on at least one side of the surface of the thermal runaway suppressing refractory sheet.

In the present invention, the thermal runaway suppressing refractory sheet contains a substrate and an inorganic particle layer, the substrate contains glass fibers, wet heat adhesive binder fibers and fibrillated heat resistant fibers, and the inorganic particle layer comprises an inorganic Containing particles and an inorganic binder, the inorganic particle layer having a coating layer covering the surface of the fibers contained in the substrate and a heat insulating layer present on at least one surface of the substrate surface It is a sheet characterized by

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 1-18 μm, more preferably 2-13 μm, even more preferably 3.1-10 μm. If the fiber diameter is less than 1 μm, the glass fibers may be too fine to 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 base materials becomes large, the coating property of the coating solution for forming the inorganic particle layer is inferior, and the skin is irritated. It may hinder workability and make it difficult to use.

Further, the fiber length of the glass fiber in the present invention is preferably 1 to 30 mm, more preferably 2 to 15 mm, 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.

In addition, the content of the glass fiber in the present invention is preferably 75 to 95% by mass, more preferably 80 to 93% by mass, more preferably 85 to 90% by mass, based on the total fiber components contained in the base material. % by mass is more preferred. 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.

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

Examples of crosslinkable functional groups include silanol groups, carboxyl groups, and methylol groups. A fiber can be obtained by dissolving polyvinyl alcohol modified with a monomer having such a crosslinkable functional group in water without cross-linking by adjusting the pH or the like, and cross-linking 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 acidified (pH 5 to 6) to crosslink while spinning. and heat treatment after drying.

On the other hand, fibers may be obtained by a method of spinning non-self-crosslinkable unmodified polyvinyl alcohol and then applying various organic or inorganic crosslinkers to crosslink it. Examples of inorganic cross-linking agents include phosphoric acid, ammonium phosphate, ammonium sulfate, and titanyl sulfate, and examples of organic cross-linking agents include methylol-based, epoxy-based, isocyanate-based, and aldehyde-based cross-linking agents. After adding these cross-linking agents to the undenatured polyvinyl alcohol spinning dope and spinning, or after spinning the undenatured polyvinyl alcohol alone and passing it through a cross-linking agent-containing bath, heat treatment can be performed to promote cross-linking. can. Moreover, it is also possible to use these methods together.

Although the wet heat adhesive binder fibers used in the present invention are not limited to the above, silanol-modified polyvinyl alcohol fibers are particularly preferred because of their good adhesion to glass fibers.

The fineness of the wet heat adhesive binder fiber is preferably 0.1 to 5.6 decitex, more preferably 0.4 to 2.2 decitex, and 0.6 to 1.1 decitex. More preferred. 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 to 15 mm, more preferably 2 to 10 mm, even more preferably 3 to 5 mm. 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 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, based on the total fiber components contained in the base material. is more preferable, and 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 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 preferably 40 ml or more, more preferably 50 ml or more and 700 ml or less, still more preferably 100 ml or more and 600 ml or less, and particularly preferably 300 ml or more and 450 ml or less. is. If the modified freeness exceeds 700 ml, the fibrillation is not so advanced and the entanglement with the glass fibers is reduced, which may reduce the effect of improving the wet strength. In addition, the effect of improving the permeability and liquid retention of the inorganic particle layer-forming coating liquid 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 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 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 a sieve plate, and the sample concentration is 0.1% by mass. It is a value measured in accordance with 2012.

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 base material in which a dense network structure is formed by the fibers between the fibrillated heat-resistant fiber and the glass fiber, and which has high wet strength and can improve the permeability and liquid retention of the coating liquid for forming the inorganic particle layer. becomes easier to obtain.

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, which may reduce the wet tensile strength. The fibrillated heat-resistant fibers come to fall off from the fiber, and the number of intersections increases too much.

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.

Fibrillated heat-resistant fibers are made from heat-resistant resins such as fibrous and pulp-like fibers through refiners, beaters, mills, grinders, rotary homogenizers that apply shear force with high-speed rotating blades, and high-speed rotating cylindrical inner blades. A double-cylinder high-speed homogenizer that generates a shearing force between the fixed outer blades, an ultrasonic crusher that makes finer particles by impact with ultrasonic waves, and a pressure difference of at least 20 MPa to the heat-resistant resin suspension. It can be obtained by passing through a small-diameter orifice at high speed, colliding and rapidly decelerating, and processing with a high-pressure homogenizer or the like that applies shearing force and cutting force to the heat-resistant resin.

In the present invention, the content of fibrillated heat-resistant fibers is preferably 2% by mass or more and 10% by mass or less, and 3% by mass or more and 8% by mass or less, based on the total fiber components contained in the base material. is more preferable, more preferably 3.5% by mass or more and 6% by mass or less, and particularly preferably 3.5% by mass or more and 5% by mass or less. If the content of the fibrillated heat-resistant fiber exceeds 10% by mass, the fire resistance may deteriorate. In addition, the thickness of the base material may become too thin, and the voids in the base material may be reduced, so the permeability and liquid retention of the coating liquid for forming the inorganic particle layer are reduced, and the content of inorganic particles is reduced. As a result, fire resistance and heat insulation may deteriorate. On the other hand, when the content of the fibrillated heat-resistant fibers is less than 2% 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, resulting in the effect of improving the wet strength. becomes less likely to occur.

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. Synthetic resin fibers such as base, benzoate, polyclar, phenolic resin, melamine resin, furan resin, urea resin, aniline resin, unsaturated polyester, fluorine resin, silicone resin, derivatives thereof; metal fiber, carbon fiber, alumina, silica , ceramics, rock fibers and other inorganic fibers 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 0.25 mm or more, more preferably 0.40 mm or more, and even more preferably 0.60 mm or more. Also, 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 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. When the thickness of the base material exceeds 2.00 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. When the thickness of the substrate is less than 0.25 mm, voids in the substrate become large, making it difficult to coat, and it may be necessary to coat a large amount of inorganic particles.

The density of the substrate in the invention is preferably 0.07 g/cm ³ or more, more preferably 0.10 g/cm ³ or more. Also, 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 substrate becomes too weak, and the substrate may be damaged during handling or coating. The rigidity of the base material becomes too high, which may make it difficult to wind up with a papermaking reeler or may reduce the coating amount of the inorganic particle layer.

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 0.001 to 0.5% by mass. This papermaking slurry is further diluted to a predetermined concentration before papermaking. The wet paper web thus made is nipped by 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 and an inorganic binder. This inorganic particle layer has a coating layer that covers the entire surface of the fibers contained in the substrate, and a heat insulating layer that completely covers at least one surface of the substrate surface. That is, there are an inorganic particle layer that is a coating layer and an inorganic particle layer that is a shielding layer. This provides the effect of fire resistance and heat insulation of the sheet.

FIG. 1 is a surface observation image of a coating layer covering the surface of fibers contained in a thermal runaway suppression refractory sheet, and is an electron microscope (SEM) observation photograph. The entire surface of the wet heat adhesive binder fiber contains inorganic particles (kaolin) and an inorganic binder (sepiolite), although it cannot be confirmed in FIG. It is coated with a coating layer, which is an inorganic particle layer that is formed on the substrate. The fire resistance of the sheet is exhibited by covering the entire surface of the fiber with the coating layer.

FIG. 2 is a surface observation image and an SEM observation photograph of a heat insulating layer present on at least one side of the surface of the thermal runaway suppression refractory sheet. At least one surface of the substrate surface is completely covered with a heat insulating layer that is an inorganic particle layer. By providing the heat-insulating layer on the surface of the base material, heat flow is blocked when heat is applied from one side, preventing a rapid temperature rise of the sheet and improving heat-insulating properties.

In the present invention, when the inorganic particle layer has a heat insulating layer, the thermal runaway suppressing refractory sheet has a Frazier air permeability of 3 cm ³ /sec/cm ² or less, and the heat insulating property of blocking the heat flow applied from one side is improved. Cheap. The Frazier air permeability of the thermal runaway-suppressing fireproof sheet is more preferably 2 cm ³ /sec/cm ² or less, and even more preferably 1 cm ³ /sec/cm ² or less. If the thermal runaway suppression fireproof sheet has a Frazier air permeability of more than 3 cm ³ /sec/cm ² , the heat flow may be transmitted through the uncovered portion of the sheet, resulting in poor heat insulation.

Examples of inorganic particles include silicon oxides such as amorphous silica; aluminas such as α-alumina and γ-alumina; alumina hydrates such as boehmite; aluminum oxides such as diaspore and gibbsite and their hydrates; kaolin, calcined kaolin, talc, clay minerals such as natural mica, synthetic mica, barium titanate, magnesium hydroxide, calcium hydroxide, gypsum dihydrate, and calcium aluminate oxide, calcium carbonate, magnesium carbonate, barium carbonate, Inorganic particles such as titanium dioxide 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 are excellent in fire resistance and noncombustibility 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 10.00 μm or less, more preferably 0.30 μm or more and 7.0 μm or less, and 0.5 μm or more and 5 μm or less. More preferred. 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 the inorganic particles obtained from the SEM photograph of the inorganic particles.

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. In particular, the unit crystals of montmorillonite, which is the main component of bentonite, are very thin plate crystals with a thickness of about 1 nm and a width of 100 to 1000 nm. In this case, the montmorillonite is preferable as an inorganic binder for the heat insulating layer because the heat insulating layer is easily formed due to the water swelling property and thickening property of the montmorillonite. 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, relative to the total amount of the inorganic particles. is more preferable, and more preferably 10% by mass or more and 30% by mass or less. If the amount of the inorganic binder is less than 2% by mass, the inorganic particles may easily fall off from the substrate. Moreover, when the amount of the inorganic binder exceeds 100% by mass, the coatability of the inorganic particles may deteriorate.

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 inorganic 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.

The content of the inorganic particle layer is a value calculated by "coating amount of the inorganic particle layer (g/m ² )/substrate basis weight (g/m ² ) × 100", and is preferably 90% by mass or more. 100% by mass or more is more preferable, and 130% by mass or more is even more preferable. If the content of the inorganic particle layer is 90% by mass or more, even when the thermal runaway suppressing refractory sheet is exposed to flame, the sheet is hardly melted or damaged. The higher the content of the inorganic particle layer, the thicker the sheet and the higher the fire resistance.

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, impregnation such as 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 by coating equipment are used. can be, but is not limited to.

In the present invention, a size press is preferably used as the apparatus for forming the coating layer, and a rod coater or air knife coater is preferably used as the apparatus for forming the heat insulating layer.

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.

Example 1
<Preparation of base material>
90 parts of glass fiber (trade name: ECS06I-33G, manufactured by Nippon Electric Glass Co., Ltd., fiber diameter 10 μm x fiber length 6 mm), silanol-modified PVA fiber (wet heat adhesive binder fiber, trade name: SPG056-11, Kuraray Co., Ltd.) 0.6 decitex x 3 mm), 5 parts of fibrillated heat-resistant fiber obtained by fibrillating a wholly aromatic polyamide fiber pulp to a modified freeness of 350 ml using a high-pressure homogenizer, to prepare a uniform papermaking slurry with a concentration of 0.5%, obtain a wet paper web using a cylinder paper machine, dry it with a cylinder dryer at a surface temperature of 140 ° C., and have a basis weight of 50 g / A substrate of m ² was made.

<Preparation of coating solution for forming inorganic particle layer (coating 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) were mixed in water and thoroughly stirred. , a sepiolite dispersion was prepared. Next, the total amount of the kaolin dispersion liquid and the total amount of the sepiolite dispersion liquid were mixed and stirred, and the concentration was adjusted with water to prepare a coating liquid having a solid concentration of 40%.

<Preparation of Inorganic Particle Layer (Heat Insulating Layer) Forming Coating Liquid 1>
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) were mixed in water and thoroughly stirred. , a sepiolite dispersion was prepared. Next, the total amount of the kaolin dispersion and the total amount of the sepiolite dispersion are mixed, 0.08 part of a water retention agent (trade name: SN Thickener 926, manufactured by San Nopco) is added, stirred, and the concentration is adjusted with water to obtain a solid content concentration of A 40% coating solution was prepared.

<Preparation of thermal runaway suppression fireproof sheet>
The above substrate is impregnated once with the coating liquid for forming the coating layer by a size press, dried, and after forming a coating layer with an absolute dry coating amount of 50 g / m ² , the coating for forming the heat insulating layer The working solution 1 was applied to the front and back surfaces once each with a rod coater and dried to form a heat insulating layer with an absolute dry coating amount of 92 g/m ² (46 g/m ² +46 g/m ² ). A refractory sheet for suppressing thermal runaway of 192 g/m ² was produced.

Example 2
<Preparation of Coating Solution 2 for Forming Inorganic Particle Layer (Heat Insulation 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 bentonite (trade name: Kunipia (registered trademark)-G, manufactured by Kunimine Industries Co., Ltd.) and 1.0 part of a water-soluble acrylic dispersant (Aron T-50) are mixed in water and sufficiently stirred. A bentonite dispersion was prepared. Next, the total amount of the kaolin dispersion and the total amount of the bentonite dispersion were mixed, stirred, and the concentration was adjusted with water to prepare a coating liquid having a solid concentration of 24%.

<Preparation of thermal runaway suppression fireproof sheet>
The base material prepared in Example 1 was impregnated once with the coating liquid for forming the coating layer by a size press, dried, and after forming a coating layer with an absolute dry coating amount of 50 g / m ² , heat insulation. The layer-forming coating solution 2 was applied once on each of the front and back surfaces with a rod coater, dried, and heat-insulated with an absolutely dry coating amount of 95 g/m ² (47.5 g/m ² +47.5 g/m ² ). Layers were formed to produce a thermal runaway suppressing fireproof sheet having a total basis weight of 195 g/m ² .

Example 3
A substrate having a basis weight of 100 g/m ² was produced in the same manner as in <Preparation of base material> in Example 1, except that the basis weight was changed. The substrate is impregnated with the coating liquid for forming the coating layer once by a size press, dried to form a coating layer with an absolute dry coating amount of 100 g/m ² , and then coated for forming the heat insulating layer. Liquid 2 was coated once on each of the front and back surfaces with a rod coater and dried to form a heat insulating layer with an absolutely dry coating amount of 70 g/m ² (35 g/m ² +35 g/m ² ), with a total basis weight of 270 g. /m ² of thermal runaway suppression fireproof sheet was produced.

Example 4
The substrate prepared in Example 3 was impregnated once with the coating liquid for forming the coating layer by a size press, dried, and after forming a coating layer with an absolute dry coating amount of 100 g / m ² , heat insulation. Layer-forming coating liquid 2 is applied once on the surface with a rod coater and dried to form a heat insulating layer with an absolute dry coating amount of 35 g/m ² and a total basis weight of 235 g/m ² for suppressing thermal runaway. A fireproof sheet was produced.

Comparative example 1
The substrate prepared in Example 1 was impregnated once with the coating liquid for forming the coating layer by a size press, dried, and a coating layer having an absolute dry coating amount of 51 g / m ² was formed. A thermal runaway suppressing refractory sheet with an amount of 101 g/m ² was produced.

Comparative example 2
The base material prepared in Example 1 was impregnated twice with the coating liquid for forming the coating layer using a size press to form a coating layer with an absolute dry coating amount of 140 g/m ² and a total basis weight of 190 g. /m ² of thermal runaway suppression fireproof sheet was produced.

Comparative example 3
The base material prepared in Example 3 was coated with the heat-insulating layer-forming coating liquid 2 once on each of the front and back sides using a rod coater, and the absolute dry coating amount was 74 g/m ² (37 g/m ² +37 g/m 2 ). ² ) was formed to prepare a thermal runaway suppressing refractory sheet having a total basis weight of 174 g/m ² .

The following physical properties were measured and evaluated for the thermal runaway-suppressing refractory sheet substrates and the thermal runaway-suppressing refractory sheets of Examples and Comparative Examples, and the results are shown in Table 1.

<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 amount of the coating layer was calculated by subtracting the basis weight of the substrate from the basis weight after forming the coating layer. Moreover, the coating weight of the heat-insulating layer was calculated by subtracting the basis weight after forming the coating layer or the basis weight of the substrate from the total basis weight.

<Fire resistance>
To evaluate the fire resistance of the refractory sheet for suppressing thermal runaway, 3 test pieces of 100 mm in the width direction × 100 mm in the flow direction were cut out from each sheet, and a burner (trade name: Lab Burner APTL, Co., Ltd.) was placed in the center of each test piece. (manufactured by Phoenix Dent) 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: Slight cracks and dents are observed on the surface of the refractory sheet exposed to flame.
x: There are holes and cracks in the fireproof sheet.

<Heat insulation>
To evaluate the heat insulating property of the thermal runaway suppressing refractory sheet, the surface temperature of the opposite side of each test piece was measured using a K thermocouple 5 minutes after the start of flame exposure during the refractory test.

As shown in Table 1, the thermal runaway suppression refractory sheets produced in Examples 1 to 4 contain a substrate and an inorganic particle layer, and the substrate comprises glass fibers, wet heat adhesive binder fibers, and fibrillated heat resistant A coating layer containing fibers, the inorganic particle layer containing inorganic particles and an inorganic binder, and the inorganic particle layer covering the surface of the fibers contained in the substrate, and at least one of the surfaces of the substrate and a heat insulating layer present on the surface of the Therefore, the thermal runaway suppressing fireproof sheets produced in Examples 1 to 4 were excellent in fire resistance and heat insulation.

Comparing Example 1 and Example 2, the thermal runaway suppressing refractory sheet of Example 2, in which the inorganic binder of the heat insulating layer is sepiolite, has better heat insulation than the thermal runaway suppressing refractory sheet in Example 1, in which bentonite is used. was excellent.

Comparing Example 3 and Example 4, the thermal runaway suppressing fireproof sheet of Example 3 having a heat insulating layer on both the front and back sides of the sheet is superior to the thermal runaway suppressing fireproof sheet of Example 4 having a heat insulating layer on only one side of the sheet. had better thermal insulation.

The thermal runaway suppressing refractory sheets of Comparative Examples 1 and 2 have only the coating layer as the inorganic particle layer and do not have the heat insulating layer. was insufficient.

The thermal runaway suppressing fireproof sheet of Comparative Example 3 had only the heat insulating layer as the inorganic particle layer and did not have the coating layer, but the fire resistance was insufficient.

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)

containing a substrate and an inorganic particle layer,
The base material contains glass fibers, wet heat adhesive binder fibers and fibrillated heat resistant fibers, the inorganic particle layer contains inorganic particles and an inorganic binder, and the inorganic particle layer is contained in the base material. A thermal runaway suppressing refractory sheet characterized by having a coating layer that covers the surface of a fiber that covers the surface of the base material and a heat insulating layer that is present on at least one surface of the base material surface. 2. The thermal runaway suppressing fireproof sheet according to claim 1, wherein the inorganic binder contained in the heat insulating layer contains bentonite.

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