Mirable-type silicone rubber composition for heat-insulating buffer sponge for battery cells and silicone rubber sponge

Abstract

Provided is a silicone rubber composition capable of forming a silicone rubber sponge that has high hardness, low compression set, and can exhibit excellent heat insulation (low thermal conductivity) even in an environment where a large compressive stress is applied. The milable silicone rubber composition for a heat insulation buffer sponge for a battery cell of the present invention comprises: 100 parts by mass of a diorganopolysiloxane component composed of one or more diorganopolysiloxanes having an average of 2 or more alkenyl groups in one molecule, and the diorganopolysiloxane component (A) contains 0.50 to 3.00 mol% of alkenyl group-containing structural units as a whole; 5 to 30 parts by mass of a vinyl silicone resin component (B-1) containing 0.50 to 10.0% by mass of vinyl groups as a whole; 30 to 80 parts by mass of silica in which at least a part of the surface is modified with a crosslinkable functional group with respect to the diorganopolysiloxane component (A); (C) a foaming agent; and (D) a curing agent.

Description

Technical Field

[0001] The present invention relates to a millable silicone rubber composition and a silicone rubber sponge suitably used for a heat insulating and buffering sponge for battery cells, which insulates heat conduction between battery cells and buffers and supports the expansion / contraction deformation of each battery cell.

Background Art

[0002] A silicone rubber sponge obtained by foaming and curing a millable silicone rubber has heat resistance, electrical insulation, flame retardancy, etc. due to the presence of a porous group, and has a suppressed compression set and is lightweight. Therefore, silicone rubber sponges are used in OA equipment, automobiles, building materials, etc.

[0003] Patent Document 1 describes a thermosetting millable silicone rubber composition that can obtain a silicone rubber sponge with a wide range of densities from low foaming ratio to high foaming ratio while having a small compression permanent strain by using a thermally expandable microcapsule that expands and contracts at a specific temperature as a foaming agent and using a high-temperature decomposable organic foaming agent as a cell-forming agent after curing. Suitable applications include OA equipment and cushioning materials for transportation equipment as examples, and directly, secondary battery applications are not mentioned.

[0004] Patent Document 2 describes a porous flame-retardant sponge sheet mainly made of a low-hardness and easily deformable silicone for making it difficult to transfer the heat of an abnormally heated battery cell to adjacent cells by attaching it to the side surface located in the direction in which the battery cells are arranged, using the heat resistance of the silicone rubber sponge, wherein the holes in the sheet are in an elongated shape and the length direction of the holes is directed along the surface of the flame-retardant sheet.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0006] The silicone rubber sponge disclosed in Patent Document 1 is a flexible sponge that is excellent in compression set but has low hardness and resilience. When considering applying this to a cushioning material between battery cells such as a lithium-ion battery to which a large pressing force (compressive stress) is permanently applied, due to the compressive stress applied from the battery cell, the silicone rubber sponge is greatly compressed, and most of the internal cells (sponge cells) are crushed. Therefore, even a silicone rubber sponge known for its low thermal conductivity cannot maintain good heat insulation performance in such an environment. Therefore, suitable applications include OA equipment and cushioning materials for transportation equipment, and secondary battery applications are not mentioned.

[0007] The silicone rubber sponge disclosed in Patent Document 2 is a silicone rubber sponge having high heat insulation performance by making the shape of the sponge cells (holes) elongated along the plane direction of the sheet. However, improving the heat insulation performance by adjusting the composition of the silicone rubber sponge has not been disclosed.

[0008] The heat insulation cushioning material for battery cells is required to absorb the expansion due to the heat generation of the battery and to have heat insulation performance so as not to spread the fire between the batteries when a fire occurs. Therefore, it is an object to provide a silicone rubber composition capable of forming a silicone rubber sponge that is hard, has a small compression set, and can exhibit excellent heat insulation performance (low thermal conductivity) even in an environment where a large compressive stress is applied.

Means for Solving the Problems

[0009] The present invention is, for example, the following [1] to

[11] . [1] A diorganopolysiloxane component composed of one or more diorganopolysiloxanes having an average of 2 or more alkenyl groups in one molecule, and containing 0.50 to 3.00 mol% of alkenyl group-containing structural units as the whole diorganopolysiloxane component (A), 100 parts by mass of the diorganopolysiloxane component, and (B) (B-1) and / or (B-2) (B-1) A vinyl silicone resin component containing 0.50 to 10.0% by mass of vinyl groups as the whole vinyl silicone resin component (B-1), 5 to 30 parts by mass of the vinyl silicone resin component, (B-2) 30 to 80 parts by mass of silica in which at least a part of the surface is modified with a crosslinkable functional group with respect to the diorganopolysiloxane component (A), (C) A foaming agent, and (D) A curing agent, containing A milable silicone rubber composition for a heat insulating and buffering sponge for a battery cell. [2] The milable silicone rubber composition for a heat insulating and buffering sponge for a battery cell according to [1], characterized by containing both the component (B-1) and the component (B-2). [3] The milable silicone rubber composition for a heat insulating and buffering sponge for a battery cell according to [1], further containing 1.0 to 50.0 parts by mass of a hollow filler (E). [4] The milable silicone rubber composition for a heat insulating and buffering sponge for a battery cell according to [1], further containing an infrared ray shielding agent (F). [5] A heat insulating and buffering silicone rubber sponge for a battery cell, which is a foamed cured body of the milable silicone rubber composition for a heat insulating and buffering sponge for a battery cell according to [1] to [4]. [6] The heat insulating and buffering silicone rubber sponge for a battery cell according to [5], having a foaming ratio of 1.5 to 10.0 times. [7] The heat insulating and buffering silicone rubber sponge for a battery cell according to [5], having an Asker C hardness of 45 to 90 degrees. [8]The heat-insulating buffer silicone rubber sponge of [5], having a compression set of 20% or less as measured according to Method A of JIS K6262 under the conditions of temperature: 23°C, time: 24 hours, and compression ratio: 25%. [9]The heat-insulating buffer silicone rubber sponge of [5], having a dummy cell temperature measured by the following heat-insulating property evaluation method of 150°C or less. (Heat-insulating property evaluation method) A silicone rubber sponge sheet with a thickness of 3.0 mm is sandwiched between two heat-insulating sheets with a thickness of 0.5 mm and a thermal conductivity of 0.05 W / m·K, and is placed on a dummy cell, which is a metal plate at 25°C. A heating cell, which is a hot plate at 600°C, is pressed against the silicone rubber sponge sheet sandwiched between the heat-insulating sheets with a load of 1.0 MPa from the side opposite to the dummy cell. The maximum temperature reached on the surface of the dummy cell 60 minutes after pressing the heating cell is defined as the dummy cell temperature.

[10] The heat-insulating buffer silicone rubber sponge of [5], having an elongated hole group with a major axis along the thickness direction of the silicone rubber sponge.

[11] A battery unit having a plurality of battery cells and the heat-insulating buffer silicone rubber sponge of [5] between each battery cell.

Advantages of the Invention

[0010] The silicone rubber composition of the present invention can form a silicone rubber sponge that has high hardness, a small compression set, and can exhibit excellent heat-insulating property (low thermal conductivity) even in an environment with a large compressive stress applied.

Brief Description of the Drawings

[0011]

Figure 1

Embodiments for Carrying Out the Invention

[0012] The present invention relates to a diorganopolysiloxane component composed of one or more kinds of diorganopolysiloxanes having an average of 2 or more alkenyl groups in one molecule, wherein the diorganopolysiloxane component (A) as a whole contains 0.50 to 3.00 mol% of alkenyl group-containing structural units, 100 parts by mass of the diorganopolysiloxane component, and (B) (B-1) and / or (B-2) (B-1) Vinyl silicone resin component A vinyl silicone resin component containing 0.50 to 10.0% by mass of vinyl groups as a whole, 5 to 30 parts by mass of the vinyl silicone resin component, (B-2) 30 to 80 parts by mass of silica in which at least a part of the surface is modified with a crosslinkable functional group with respect to the diorganopolysiloxane component (A), (C) A foaming agent, and (D) A curing agent, containing, A mailable silicone rubber composition for a heat insulating and buffering sponge for a battery cell.

[0013] Preferred embodiments of the mailable silicone rubber composition for a heat insulating and buffering sponge for a battery cell (hereinafter also referred to as "mailable silicone rubber composition") of the present invention and a silicone rubber sponge which is a foamed and cured product thereof will be described. (A) Diorganopolysiloxane component The mailable silicone rubber composition contains a diorganopolysiloxane. The diorganopolysiloxane is a chain polymer, unlike the vinyl silicone resin. Therefore, it is preferably free of M units and Q units other than the molecular terminals. However, it may be branched as long as the rubber elasticity of the silicone rubber sponge is not impaired. The diorganopolysiloxane may be used alone or in combination of two or more.

[0014] Examples of the organic groups (organic radicals) of the organopolysiloxane include monovalent hydrocarbon groups having 1 to 12 carbon atoms, preferably 1 to 5 carbon atoms. Examples of the hydrocarbon groups include alkyl groups such as methyl group, ethyl group, propyl group, butyl group, hexyl group, dodecyl group, cycloalkyl groups such as cyclohexyl group, alkenyl groups such as vinyl group, allyl group, butenyl group, hexenyl group, aryl groups such as phenyl group, tolyl group, etc. The organic groups may be a single type or two or more types, but two or more types are preferred and at least contain an alkenyl group. As the alkenyl group, at least one selected from the group consisting of vinyl group, allyl group, propenyl group, isopropenyl group, 2-methyl-1-propenyl group, 2-methylallyl group, 2-butenyl group is preferred. Also, the organic group preferably has a methyl group.

[0015] The weight-average molecular weight of the organopolysiloxane component is 1.0×10 5 ~1.0×10 6 is preferred. The weight-average molecular weight is the value measured by gel permeation chromatography (GPC).

[0016] Therefore, the organopolysiloxane contains alkenyl group-containing structural units and has an average of two or more alkenyl groups in one molecule from the viewpoint of exhibiting appropriate rubber elasticity by crosslinking with appropriate thermosetting. In the molecule, the alkenyl group-containing structural units may be present at either the end of the main chain or the side chain in addition to the end of the main chain.

[0017] The organopolysiloxane component (A) contains 0.50 to 3.00 mol% of alkenyl group-containing structural units, preferably 0.50 to 2.00 mol%, and more preferably 0.50 to 1.50 mol%. When within the above range, high hardness and excellent compression set can be exhibited when made into a sponge. If the content is less than the above range, the crosslinking density is too low and the resulting sponge does not have sufficient hardness, and the pores of the sponge cannot be maintained during stress loading, and the heat insulation property is not sufficiently good. On the other hand, if the content is higher than the above range, when stress or strain is applied to the sponge, the sponge is likely to crack.

[0018] The content of the alkenyl group-containing structural unit is a value based on the whole organopolysiloxane component (A). When two or more organopolysiloxanes are included, it is the average of the respective contents. For example, the amount of the alkenyl group may be adjusted by blending an organopolysiloxane with a low content of alkenyl group-containing structural units and an organopolysiloxane with a high content of alkenyl group-containing structural units.

[0019] Specific examples of such organopolysiloxanes include alkenyl-terminated polydimethylsiloxanes having a weight average molecular weight of 1.0×10 5 ~1.0×10 6 . Also, as commercially available products of such organopolysiloxanes, 110-0, 110-5, 110-6, 110-7, 112-5, 112-6, 112-7, etc. manufactured by DONGJUE SILICONE (NANJING) CO., LTD. can be mentioned.

[0020] As long as the conditions of the above alkenyl group are satisfied, the terminal of the molecular chain of the organopolysiloxane may be blocked with a trimethylsilyl group, a dimethylvinylsilyl group, a dimethylhydroxysilyl group, a trivinylsilyl group, or the like.

[0021] (B) (B-1) Vinyl silicone resin component and / or (B-2) Silica in which at least a part of the surface is modified with a crosslinkable functional group with respect to the component (A) The mirable silicone rubber composition contains, as component (B), at least one of the following components (B-1) and (B-2). From the viewpoint of obtaining the hardness of the silicone rubber sponge while suppressing the increase in viscosity, it is preferably to contain at least component (B-1), and more preferably to contain both component (B-1) and component (B-2).

[0022] (B-1) Vinyl silicone resin component The vinyl silicone resin is a silicone resin having a vinyl group. The silicone resin is a kind of organopolysiloxane, and preferably has a structure in which at least one selected from the group consisting of M, D, T, and Q units is three-dimensionally condensed and has T units and / or Q units. Examples of the organo group of the organopolysiloxane include those exemplified as the organo group of component (A).

[0023] The weight average molecular weight of the vinyl silicone resin component is preferably from 100 to 10,000, more preferably from 500 to 5,000. The weight average molecular weight is a value measured by gel permeation chromatography (GPC).

[0024] The vinyl silicone resin component can be dissolved in the component (A) by mixing with the component (A) and heating if necessary, thereby reducing the viscosity of the composition. Furthermore, since there are vinyl groups capable of forming a crosslinked structure with the component (A) in the structure, it has the effect of increasing the hardness and strength of the resulting sponge and does not deteriorate the compression set. The vinyl silicone resin may be used alone or in combination of two or more.

[0025] The vinyl silicone resin component (B-1) contains 0.50 to 10.0% by mass of vinyl groups in 100% by mass of the vinyl silicone resin, preferably 0.50 to 5.0% by mass, and more preferably 0.50 to 2.0% by mass. When the vinyl content is less than 0.50% by mass, the hardness decreases, the pores of the sponge cannot be maintained under stress loading, the heat insulation property deteriorates, and the compression set deteriorates. Also, when the vinyl group content exceeds 10.0% by mass, the crosslinking density becomes too high, causing significant destruction of the crosslinked structure during compression and deterioration of the compression set. The vinyl group content is a value for the entire vinyl silicone resin component (B-1), and when two or more vinyl silicone resins are included, it is the average of the respective contents.

[0026] Commercially available vinyl silicone resins include MQ200-1 manufactured by HUBEI JIAYUN CHEMICAL.

[0027] In the mirable type silicone rubber composition, the vinyl silicone resin component (B-1) is 5 to 30 parts by mass, preferably 5 to 20 parts by mass, and more preferably 5 to 15 parts by mass with respect to 100 parts by mass of the diorganopolysiloxane component (A). When the content is less than 5 parts by mass, the hardness of the resulting silicone rubber sponge decreases, the compression set under stress loading increases, the viscosity of the composition becomes high, the foaming ratio becomes low, and cracks occur in the sponge after foaming. Also, when the content exceeds 30 parts by mass, the adhesiveness of the composition becomes strong, making roll processing and molding difficult.

[0028] (B-2) Silica in which at least a part of the surface is modified with a crosslinkable functional group with respect to the diorganopolysiloxane component (A) (hereinafter also referred to as "modified silica") The modified silica plays a role of imparting sufficient hardness to the sponge after foaming and curing and maintaining good compression set.

[0029] The specific surface area of silica measured by the BET method is preferably 50 to 500 m 2 / g. Examples of silica include those so-called reinforcing silicas, such as fumed silica, precipitated silica, and calcined silica. Silica may be used alone or in combination of two or more. Examples of silica with an unmodified or partially hydrophobized surface include AEROSIL 90, 200, 300, R972, R974, R976 (manufactured by Evonik Industries AG).

[0030] At least a part of the surface of the silica is modified with a crosslinkable functional group for the organopolysiloxane component (A). Examples of the crosslinkable functional group include vinyl group, methacryl group, acrylic group, etc. The crosslinkable functional group may be used alone or in combination of two or more. As a method for modifying with the crosslinkable functional group, before mixing with the component (A) etc., the surface of the silica may be chemically treated to modify the silica. When mixing the silica with an unmodified or partially hydrophobized surface with the component (A) etc., a surface treatment agent such as a silane coupling agent containing the above crosslinkable functional group is added and heat-kneaded, so that the silica may be modified during kneading.

[0031] Examples of the surface treatment agent containing the above crosslinkable functional group include silane coupling agents such as KBE-1003, KBM-503 (manufactured by Shin-Etsu Chemical Co., Ltd.), divinyltetramethyldisilazane, and low molecular weight dimethylsilicodiol having a vinyl group. The surface treatment agent may be used alone or in combination of two or more.

[0032] In a mirable silicone rubber composition, with respect to 100 parts by mass of the organopolysiloxane component (A), the modified silica (B-2) is 30 to 80 parts by mass, preferably 30 to 60 parts by mass, and more preferably 40 to 60 parts by mass. When the content is less than 30 parts by mass, the hardness of the resulting silicone rubber sponge becomes low, the pores of the sponge cannot be maintained under stress loading, and the heat insulation property of the silicone rubber sponge does not increase. On the other hand, when the content exceeds 80 parts by mass, the hardness of the resulting silicone rubber sponge is too high and an appropriate rubber elasticity and buffering function are not exhibited, or the viscosity of the composition is too high, making roll processing difficult, or the foaming ratio becomes low, and cracks occur in the sponge during foaming, etc. Unfavorable situations occur.

[0033] (C) Blowing agent The mirable silicone rubber composition contains a blowing agent. The blowing agent, by applying heat in a state of being dispersed in the mirable silicone composition, forms a pore group in the mirable silicone rubber composition by (i) physically expanding the size of the blowing agent inside the composition or (ii) causing a chemical decomposition reaction to generate gas, and forms a porous structure when the composition hardens, and is a component that makes the composition spongy.

[0034] Examples of the blowing agent of type (i) include thermally expandable microcapsules in which a thermally expandable substance such as a hydrocarbon solvent is encapsulated in a shell material formed of a thermoplastic resin. Examples of the thermoplastic resin include acrylic resin and vinylidene chloride resin. Examples of the hydrocarbon solvent include toluene, cyclohexane, xylene, and hexane. Commercially available products of the blowing agent of type (i) include Matsumoto Microsphere F-35D, F-36, F-50, F-65, FN-78D, and F-100M (manufactured by Matsumoto Yushi Yakuhin Co., Ltd.). On the other hand, examples of the blowing agent of type (ii) include sodium bicarbonate, dinitrosopentamethylenetetramine, azodicarbonamide, azodicarbonamide, and azobisisobutyronitrile.

[0035] In the mirable silicone rubber composition, with respect to 100 parts by mass of the organopolysiloxane component (A), the blowing agent (C) is preferably 0.1 to 20.0 parts by mass, more preferably 0.5 to 10.0 parts by mass, and even more preferably 1.0 to 7.0 parts by mass. When the content of the blowing agent (C) is within the above range, the balance between hardness, compression set, and expansion ratio is good, which is preferable from the viewpoint of heat insulation during stress loading.

[0036] (D) Curing agent The mirable silicone rubber composition contains a curing agent. The curing agent is added to impart appropriate elasticity when the mirable silicone rubber composition is foamed. Examples of the curing agent include organic peroxide-based curing agents such as alkyl peroxy esters, peroxy ketals, dialkyl peroxides, hydroperoxides, and ketone peroxides, and addition reaction curing agents composed of an organopolysiloxane having two or more silicon atom-bonded hydrogen atoms (hydrosilyl groups) in one molecule and a platinum compound serving as a curing catalyst. The crosslinking start temperature of the curing agent is preferably 70 to 200°C. Commercially available products include organic peroxide-based curing agents such as Perhexa HC, Perhexa C, Perhexa V, Perhexa 25B, Perbutyl P, Perbutyl C, Parkmyl D, Naiper BMTM, Perhexa 25Z, Perhexyl Z, Perbutyl ZT, Perbutyl Z (manufactured by NOF Corporation), TC-1, TC-3, TC-4, TC-8, TC-12 (manufactured by Momentive Performance Materials).

[0037] In the mirable silicone rubber composition, with respect to 100 parts by mass of the organopolysiloxane component (A), the curing agent (D) is preferably 0.01 to 10.0 parts by mass, more preferably 0.1 to 5.0 parts by mass. When the content of the curing agent (D) is within the above range, it is preferable from the viewpoint of suppressing compression set.

[0038] (E) Regarding hollow fillers The mirable silicone rubber composition preferably contains a hollow filler. The hollow filler is a filler containing an air layer inside a shell made of a material such as glass or ceramic. When the hollow filler is added to a millable silicone rubber composition, the heat insulation property under stress load can be further enhanced when foaming and curing result in spongification. The silicone rubber sponge has elongated pores with an air heat insulation effect, so that the volume ratio of the solid silicone rubber that conducts heat decreases and the heat insulation property improves. However, when a hollow filler is added, a heat insulation layer derived from the hollow filler exists inside the solid silicone rubber, further improving the heat insulation property. Furthermore, since the heat insulation layer derived from the hollow filler is covered on the outside by a rigid shell such as glass or ceramic, the heat insulation layer does not deform even when the sponge is compressed. Therefore, the hardness of the silicone rubber sponge does not decrease, and it is possible to further improve the heat insulation property under stress load.

[0039] Examples of the hollow filler include inorganic hollow fillers and organic hollow fillers. Examples of the material constituting the shell of the inorganic hollow filler include glass, ceramic, shirasu, silica, etc. Examples of the material constituting the shell of the organic hollow filler include phenol resin, urea resin, polystyrene, etc. Inorganic hollow fillers are preferred, and it is more preferred that the material constituting the shell is glass. Commercially available products include, for example, Glass Bubbles K25, K37, S38, S42XHS, K46, iM16K, S60J, S60HS, iM30K (manufactured by 3M Japan Co., Ltd.), E-SPHERES SL75 SL125, SL150, SL300, SLG (manufactured by Taiheiyo Cement Corporation), etc.

[0040] When a hollow filler is included, in the millable silicone rubber composition, with respect to 100 parts by mass of the diorganopolysiloxane component (A), the hollow filler (E) is preferably 1.0 to 50.0 parts by mass, more preferably 10.0 to 40.0 parts by mass, and even more preferably 10.0 to 30.0 parts by mass. When the content of the hollow filler (E) is within the above range, it is preferable in terms of heat insulation property under stress load and compression set suppression.

[0041] The mirable silicone rubber composition preferably contains a hollow filler and a vinyl silicone resin. When a vinyl silicone resin is compounded into the mirable silicone rubber composition, the hardness of the silicone rubber sponge can be improved while suppressing an increase in viscosity. However, adhesiveness is generated, and it may easily adhere to the roll during kneading in the manufacturing process of the mirable silicone rubber composition. When a hollow filler is further compounded into the mirable silicone rubber composition containing a vinyl silicone resin, the adhesion to the roll of the kneader is suppressed and the processability is improved.

[0042] (F) Regarding infrared shielding agents The mirable silicone rubber composition preferably contains an infrared shielding agent. The infrared shielding agent reflects and scatters infrared rays radiated from a heat source and plays a role in enhancing the heat insulation property of the sponge. Examples of the infrared shielding agent include those obtained by coating the surface of titanium oxide, mica, etc. with titanium oxide, ITO (tin-doped indium oxide), ATO (antimony-doped tin oxide), infrared absorbing dyes, etc. Among these, titanium oxide is preferably mentioned. The infrared shielding agent preferably has particles with a particle diameter of about several μm. Also, considering that electrical insulation is often required for the buffer material for batteries, the infrared shielding agent is more preferably electrically insulating.

[0043] Examples of commercially available products of titanium oxide include TITANIX JR-1000 (manufactured by Teika Co., Ltd.). Furthermore, examples of commercially available products of those obtained by coating the surface of mica, etc. with titanium oxide include IMPACT Velvet, Impact Sparkle, Optique Satin Violet, TC Gold, Chromatique SilverGray (all manufactured by Sandream Impact Co., Ltd.).

[0044] When an infrared shielding agent is included, in the mirabelle type silicone rubber composition, with respect to 100 parts by mass of the diorganopolysiloxane component (A), the infrared shielding agent (F) is preferably 0.1 to 50.0 parts by mass, more preferably 0.1 to 30.0 parts by mass, and even more preferably 0.5 to 20.0 parts by mass. When the content of the infrared shielding agent (F) is within the above range, it is preferable in terms of heat insulation properties and compression set under stress loading.

[0045] (Other optional components) In the heat-insulating and cushioning rubber of the present invention, optional components can be blended within a range that does not inhibit the effects of the present invention. For example, crosslinking aids such as triallyl isocyanurate and trimethylolpropane trimethacrylate as hardness adjusters, colorants such as pigments and dyes, reinforcing silica, diatomaceous earth, and fillers such as pulverized quartz that do not have crosslinkable functional groups on the surface, wetting agents, silane coupling agents that do not have crosslinkable functional groups, curing retardants, heat-resistant additives typified by metal oxides, fire-resistant (ceramicizing) agents typified by mica, platinum or platinum group compounds, and further flame retardants typified by metal oxides and carbon black, components for adjusting the foaming temperature and foaming rate of foaming agents, dispersants, and the like can be mentioned.

[0046] <Method for producing mirabelle type silicone rubber composition and silicone rubber sponge> The mirabelle type silicone rubber composition and the silicone rubber sponge may be prepared by a known method, and can be prepared, for example, by the following method. The components (A), (B), and optional components (E) and (F) are kneaded at room temperature using a kneader such as a mixer. Next, the temperature is raised to 120 to 170 °C and kneaded until the change in torque stabilizes. Then, the kneaded mixture is taken out of the kneader, the components (C) and (D) are added, and kneaded at room temperature using a mill, kneader, roll, etc. to obtain a mirabelle type silicone rubber composition.

[0047] The obtained mirasol - type silicone rubber composition is formed into a sheet of appropriate thickness, and the sheet is inserted between two metal plates heated to 150 - 200°C (distance between the metal plates: 13 mm) and foamed and cured for 5 - 60 minutes, and then taken out from the metal plates to obtain a silicone rubber sponge. The shape, dimensions, and foaming and curing temperature of the silicone rubber sponge can be arbitrarily adjusted according to the use and the types of components (C) and (D). The production method of the mirasol - type silicone rubber composition and the silicone rubber sponge is not limited to the above - mentioned production method, and can be appropriately adjusted and changed according to the use.

[0048] <Physical properties of silicone rubber sponge> The silicone rubber sponge, which is a foamed and cured product of the mirasol - type silicone rubber composition, preferably has the following physical properties.

[0049] (Hardness) When the hardness of the silicone rubber sponge is measured by the measurement method described in the examples as Asker C hardness, considering the buffering function of the battery cell buffer material used in secondary batteries typified by lithium - ion batteries, it is preferably 45 - 90 degrees, more preferably 50 - 85 degrees. When the hardness is above the above - mentioned lower limit, the heat insulation property during stress loading is good, and it can sufficiently hold the position of the cells and sufficiently apply an appropriate pressing force to the expanded cells. On the other hand, when the hardness is below the above - mentioned upper limit, the impact applied from the outside can be sufficiently alleviated, and physical damage to the battery cells can be prevented.

[0050] (Heat insulation property during stress loading) Considering the problem of thermal runaway in secondary batteries typified by lithium - ion batteries, the temperature of the dummy cell measured by the measurement method described in the examples is preferably 150°C or lower, more preferably 140°C or lower. When the temperature of the dummy cell is 150°C or lower, when one battery cell generates abnormal heat, the heat transfer to the adjacent cells can be sufficiently suppressed, and the overall thermal runaway inside the battery casing can be prevented.

[0051] (Compressive permanent set) Considering the buffering function of the inter-cell buffer material of secondary batteries typified by lithium-ion batteries, the value of the compressive permanent set measured by the measurement method of the method described in the examples is preferably 20% or less, more preferably 15% or less. When the value of the compressive permanent set is 20% or less, an appropriate pressing force can be continuously applied to the cell for a long time, and a decrease in the charge capacity can be avoided. Furthermore, the battery cell can be sufficiently protected from vibrations applied from the outside, abnormalities in the battery cell can be prevented, and the position of the battery cell in the casing can be maintained.

[0052] (Expansion ratio) Considering the relationship between the heat insulation property and the compressive permanent set during stress loading, the expansion ratio measured by the measurement method of the method described in the examples is preferably 1.5 to 10.0 times, more preferably 1.5 to 7.0 times, and even more preferably 2.0 to 5.0 times. If the expansion ratio is 1.5 times or more, the proportion of pores (air layers) in the sponge is sufficient, and heat insulation can be obtained. On the other hand, if the expansion ratio is 10.0 times or less, sufficient hardness can be maintained, and furthermore, compressive permanent set is less likely to occur.

[0053] (Elongated pore group) The silicone rubber sponge preferably has an elongated pore group having a major axis along the thickness direction of the silicone rubber sponge when disposed between battery cells. By having the major axis in this direction, it is excellent in heat insulation during stress loading and in suppressing compressive permanent set. The direction of the major axis of the elongated pore group can be adjusted, for example, by the method described in International Publication No. 2023 / 032114.

[0054] <Use> Since the silicone rubber sponge has the above physical properties, it is used for heat insulation buffering applications of battery cells. When the battery cell is charged, it generates heat and expands. The silicone rubber sponge can absorb deformation due to the expansion of this battery cell. Also, due to its heat insulation property, it can prevent the spread of fire between battery cells when a battery cell catches fire. As a usage mode, it is preferable to use a battery unit having a plurality of battery cells and the above-mentioned heat-insulating and buffering silicone rubber sponges between the battery cells. The silicone rubber sponge is preferably fixed to a support member. As a fixing mode, either physical fixing or chemical fixing may be used. The battery unit may be single or plural. Examples of the battery cell include storage batteries such as lithium-ion batteries.

Examples

[0055] Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited by these Examples.

[0056] <Measurement and evaluation methods for each physical property> The physical properties of the Examples and Comparative Examples were measured and evaluated by the following methods. (1) Hardness The hardness of the silicone rubber sponge was measured in accordance with JIS K7312 using an Asker rubber hardness gauge type C (manufactured by Kobunshi Keiki Co., Ltd.).

[0057] (2) Heat insulation property under stress load The heat insulation property of the silicone rubber sponge under stress loading was evaluated using an apparatus as shown in Figure 1. First, an iron block with dimensions of 149×91×20 mm (hereinafter referred to as the heating cell 1) installed above was heated to 600°C. An aluminum block with dimensions of 149×91×50 mm (hereinafter referred to as the dummy cell 4) was installed below it and kept at a temperature of 25°C. The silicone rubber sponges obtained in the examples and comparative examples, cut and sliced to 140×90×3 mm, were placed between two heat insulation sheets with dimensions of 140×90×0.5 mm (thermal conductivity 0.05 W / m·K) M-themo I-50LD (manufactured by Awa Paper Co., Ltd.). Then, the upper heating cell was lowered and pressed against the two heat insulation sheets 2 and the silicone rubber sponge 3 sandwiched between them with a load of 1.0 MPa. The temperature was measured using a thermocouple installed between the dummy cell and the heat insulation material, and the heat insulation property was evaluated based on the maximum temperature reached on the surface of the dummy cell within 60 minutes after pressing the heating cell.

[0058] (3) Compression set The compression set of the silicone rubber sponge was measured according to Method A of JIS K6262 under the conditions of temperature: 23°C, time: 24 hours, and compression ratio: 25%. The calculation method is as follows. Compression set ratio (%) = {(t0 - t2) / (t0 - t1)} × 100 t0: Initial thickness of the test piece (mm) t1: Thickness of the spacer (mm) t2: Thickness of the test piece after being removed from the compression device and left for 30 minutes (mm)

[0059] (4) Foaming ratio A test piece cut from the obtained silicone rubber sponge to a size of about 10 mm square was prepared, and its specific gravity was measured to 0.001 units using an automatic specific gravity meter (D-1, manufactured by Toyo Seiki Co., Ltd.). Furthermore, the specific gravity of a solid rubber sheet cured under appropriate curing conditions by removing the (C) foaming agent from the composition of the same silicone rubber sponge was also measured in the same manner. Using these values, the foaming ratio was calculated from the following formula. Expansion ratio (times) = Specific gravity of solid rubber sheet / Specific gravity of silicone rubber sponge × 100 (%)

[0060] (5) Judgment (1) - (4) From the results, the judgment was made according to the following criteria. ◎ and 〇 were regarded as qualified. ◎: Hardness is 50 - 85 degrees, and the heat insulation property under stress load is 140°C or less, and the compression set is 15% or less. 〇: Hardness is more than 45 degrees and less than 50 degrees or more than 85 degrees and less than or equal to 90 degrees, and the thermal conductivity under stress load is more than 140°C and less than or equal to 150°C, and the compression set is more than 15% and less than or equal to 20%. ×: Other than ◎ and 〇

[0061] [Example 1] 100 parts by mass of diorganopolysiloxane (1), 20 parts by mass of vinyl silicone resin (1), 50 parts by mass of silica (1), 0.5 parts by mass of silane coupling agent, 25 parts by mass of hollow filler, and 3 parts by mass of infrared shielding agent were kneaded uniformly using a Laboplastmill 10C100 - B600 mixer (manufactured by Toyo Seiki Co., Ltd.) at a rotational speed of 20 rpm until uniform. Then, the temperature was raised to 150°C, and kneaded at a rotational speed of 40 rpm until the change in kneading torque became stable. Thereafter, the kneaded mixture was taken out from the mixer, and while using a LABOLATORY MILL (manufactured by Kansai Roll Co., Ltd.), 5.0 parts by mass of thermally expandable microcapsules as a blowing agent, 0.05 parts by mass of curing agent (1), and 3.0 parts by mass of curing agent (2) were added and kneaded to obtain a millable silicone rubber composition. Thereafter, the above - mentioned millable silicone rubber composition was formed into a sheet of appropriate thickness, and mica powder (manufactured by Yamaguchi Mica Co., Ltd., A - 21S) was dusted to reduce the adhesiveness of the surface. This sheet was inserted between two metal plates heated to 200°C (distance between metal plates: 13 mm) and foamed and cured for 30 minutes, and then taken out from the metal plates to obtain a silicone rubber sponge.

[0062] [Examples 2 and 3] A mirable-type silicone rubber composition and a silicone rubber sponge were obtained in the same manner as in Example 1, except that the amount of vinyl silicone resin (1) was changed to the amount shown in Table 1.

[0063] [Example 4] A mirable-type silicone rubber composition and a silicone rubber sponge were obtained in the same manner as in Example 1, except that vinyl silicone resin (2) was used instead of vinyl silicone resin (1).

[0064] [Example 5] A mirable-type silicone rubber composition and a silicone rubber sponge were obtained in the same manner as in Example 1, except that diorganopolysiloxane (2) was used instead of diorganopolysiloxane (1).

[0065] [Example 6] A mirable-type silicone rubber composition and a silicone rubber sponge were obtained in the same manner as in Example 1, except that diorganopolysiloxane (3) was used instead of diorganopolysiloxane (1).

[0066] [Examples 7 and 8] A mirable-type silicone rubber composition and a silicone rubber sponge were obtained in the same manner as in Example 1, except that the amount of silane coupling agent-coated silica was changed to the amount shown in Table 1.

[0067] [Examples 9 to 15] A mirable-type silicone rubber composition and a silicone rubber sponge were obtained in the same manner as in Example 1, except that the amount of thermally expandable microcapsules was changed to the amount shown in Table 1.

[0068] [Example 16] A mirable-type silicone rubber composition and a silicone rubber sponge were obtained in the same manner as in Example 1, except that a hollow filler and an infrared shielding agent were not compounded.

[0069] [Examples 17 and 18] A mirabile-type silicone rubber composition and a silicone rubber sponge were obtained in the same manner as in Example 1, except that the amount of the hollow filler was changed to the amount shown in Table 1.

[0070] [Example 19] A mirabile-type silicone rubber composition and a silicone rubber sponge were obtained in the same manner as in Example 1, except that the silane coupling agent-coated silica was not compounded, and instead, reinforcing silica (2) was compounded in the amount shown in Table 1.

[0071] [Examples 20 and 21] A mirabile-type silicone rubber composition and a silicone rubber sponge were obtained in the same manner as in Example 1, except that the silane coupling agent-coated silica was not compounded, and instead, reinforcing silica (2) was compounded in the amount shown in Table 1, and the amount of vinyl silicone resin (1) was changed to the amount shown in Table 1.

[0072] [Example 22] A mirabile-type silicone rubber composition and a silicone rubber sponge were obtained in the same manner as in Example 1, except that vinyl silicone resin (1) was not compounded.

[0073] [Examples 23 and 24] A mirabile-type silicone rubber composition and a silicone rubber sponge were obtained in the same manner as in Example 1, except that vinyl silicone resin (1) was not compounded, and the amount of the silane coupling agent-coated silica was changed to the amount shown in Table 1.

[0074] [Example 25] A mirabile-type silicone rubber composition and a silicone rubber sponge were obtained in the same manner as in Example 1, except that the infrared shielding agent was not compounded, and the amount of the hollow filler was changed to the amount shown in Table 1.

[0075] [Example 26] A mirabile-type silicone rubber composition and a silicone rubber sponge were obtained in the same manner as in Example 1, except that the hollow filler was not compounded.

[0076] [Example 27] A mirable silicone rubber composition and a silicone rubber sponge were obtained in the same manner as in Example 1, except that organopolysiloxane (4) and organopolysiloxane (5) were used instead of organopolysiloxane (1). The alkenyl group-containing structural unit is contained in the entire organopolysiloxane component (A) at 0.60 mol%.

[0077] [Example 28] A mirable silicone rubber composition and a silicone rubber sponge were obtained in the same manner as in Example 1, except that 4.0 parts of a linear silicone oil having 30 mol% of methylvinylsiloxy units and 6 siloxane units having hydroxyl groups at both ends was used instead of 0.5 part of the silane coupling agent.

[0078] [Example 29] A mirable silicone rubber composition and a silicone rubber sponge were obtained in the same manner as in Example 1, except that azobisisobutyronitrile was used instead of the thermally expandable microcapsules as the foaming agent.

[0079] [Comparative Example 1] A mirable silicone rubber composition and a silicone rubber sponge were obtained in the same manner as in Example 1, except that organopolysiloxane (6) was used instead of organopolysiloxane (1), and the hollow filler and the infrared shielding agent were not compounded.

[0080] [Comparative Example 2] A mirable silicone rubber composition and a silicone rubber sponge were obtained in the same manner as in Example 1, except that organopolysiloxane (7) was used instead of organopolysiloxane (1), and the hollow filler and the infrared shielding agent were not compounded.

[0081] [Comparative Example 3] Instead of using vinyl silicone resin (1), vinyl silicone resin (3) was used, and a mirable type silicone rubber composition and a silicone rubber sponge were obtained in the same manner as in Example 1, except that silane coupling agent-coated silica, a hollow filler, and an infrared shielding agent were not compounded.

[0082] [Comparative Examples 4 and 5] The amount of vinyl silicone resin (1) was changed to the amount shown in Table 1, and a mirable type silicone rubber composition and a silicone rubber sponge were obtained in the same manner as in Example 1, except that silane coupling agent-coated silica was not compounded.

[0083] [Comparative Examples 6 and 7] The amount of silane coupling agent-coated silica was changed to the amount shown in Table 1, and a mirable type silicone rubber composition and a silicone rubber sponge were obtained in the same manner as in Example 1, except that vinyl silicone resin (1), a hollow filler, and an infrared shielding agent were not compounded.

[0084] [Comparative Example 8] Instead of using diorganopolysiloxane (1), diorganopolysiloxane (8) was used, and a mirable type silicone rubber composition and a silicone rubber sponge were obtained in the same manner as in Example 1, except that a hollow filler and an infrared shielding agent were not compounded.

[0085] The results of measuring the physical properties of the examples and comparative examples are shown in Tables 1 and 2. In Tables 1 and 2, the "alkenyl amount" is the content of alkenyl group-containing structural units in the entire diorganopolysiloxane component (A), and the "vinyl amount" indicates the vinyl group content in the entire vinyl silicone resin component (B-1). The materials used in the examples and comparative examples shown in Tables 1 and 2 are as follows. Diorganopolysiloxane (1): Vinyl group-containing dimethylpolysiloxane, containing 1.00 mol% of alkenyl group-containing structural units (product number: 110-6) (manufacturing company: DONGJUE SILICONE (NANJING) CO., LTD.) Organopolysiloxane (2): Vinyl group-containing dimethylpolysiloxane, containing 0.50 mol% of alkenyl group-containing structural units (Product number: 110-5) (Manufacturer: DONGJUE SILICONE (NANJING) CO., LTD.) Organopolysiloxane (3): Vinyl group-containing dimethylpolysiloxane, containing 3.00 mol% of alkenyl group-containing structural units (Product number: 110-7) (Manufacturer: DONGJUE SILICONE (NANJING) CO., LTD.) Organopolysiloxane (4): Vinyl group-containing dimethylpolysiloxane, containing 10.00 mol% of alkenyl group-containing structural units Organopolysiloxane (5): Vinyl group-containing dimethylpolysiloxane, containing 0.10 mol% of alkenyl group-containing structural units (Product number: 110-1) (Manufacturer: DONGJUE SILICONE (NANJING) CO., LTD.) Organopolysiloxane (6): Vinyl group-containing dimethylpolysiloxane, containing 0.30 mol% of alkenyl group-containing structural units (Product number: 110-4) (Manufacturer: DONGJUE SILICONE (NANJING) CO., LTD.) Organopolysiloxane (7): Vinyl group-containing dimethylpolysiloxane, containing 5.00 mol% of alkenyl group-containing structural units (Product number: 112-7) (Manufacturer: DONGJUE SILICONE (NANJING) CO., LTD.) Organopolysiloxane (8): Vinyl group-containing dimethylpolysiloxane, containing 0.13 mol% of alkenyl group-containing structural units (Product number: 110-2) (Manufacturer: DONGJUE SILICONE (NANJING) CO., LTD.)

[0086] Vinyl silicone resin (1): (Me2R1SiO 1 / 2 )3(SiO 4 / 2 )4, R1 is a vinyl group or a methyl group) containing 2.00% by mass of vinyl groups (Product number MQ200-1) (Manufacturer: HUBEI JIAYUN CHEMICAL) Vinyl silicone resin (2): (Me2R1SiO 1 / 2)3(SiO 4 / 2 )4, R1 is a vinyl group or a methyl group) containing 0.50% by mass of vinyl group Vinyl silicone resin (3): (Me2R1SiO 1 / 2 )3(SiO 4 / 2 )4, R1 is a vinyl group or a methyl group) containing 0.30% by mass of vinyl group

[0087] Silane coupling agent-coated silica: Silica (1) Product name "AEROSIL R972" (Manufacturer: Evonik), Silane coupling agent Product name "KBM-503" (Manufacturer: Shin-Etsu Chemical Co., Ltd.) Low molecular weight dimethyl silicone diol having a vinyl group: A linear silicone oil having 30 mol% of methylvinylsiloxy units and 6 siloxane units having hydroxyl groups at both ends (Chemical formula: HO(SiRCH3)6OH, R is a methyl group or a vinyl group) Thermally expandable microcapsules: Product name "FN-78D" (Manufacturer: Matsumoto Yushi Seiyaku Co., Ltd.) Azobisisobutyronitrile: Product name "ME800" (Manufacturer: Momentive Performance Materials Inc.) Organic peroxide curing agent (1): Main component compound name: p-methylbenzoyl peroxide, Product name "TC-12" (Manufacturer: Momentive Performance Materials Inc.) Organic peroxide curing agent (2): Main component compound name: 2,5-dimethyl-2,5-di-tert-butylperoxyhexane, Product name "TC-8" (Manufacturer: Momentive Performance Materials Inc.) Hollow filler: Product name "Glass Bubbles K46" (Manufacturer: 3M) Infrared ray shielding agent: (Compound name: Titanium oxide) Product name "TITANIX JR-1000" (Manufacturer: Teika Co., Ltd.) Reinforcing silica (2): Product name "AEROSIL R974" (Manufacturer: Evonik)

[0088]

Table 1

[0089]

Table 2

[0090] In the examples, silicone rubber sponges with a judgment of ◎ or 〇 are obtained. Examples 1, 5, 6 and Comparative Examples 1, 2, 8 are rubber compositions with different amounts of alkenyl groups in the organopolysiloxane. In Examples 1, 5, 6, as the amount of alkenyl groups increases, the hardness of the silicone rubber sponge increases, and the heat insulation property during stress loading is improved. (In Comparative Examples 1 and 8 where the amount of alkenyl groups in the organopolysiloxane is less than that of the present invention, the heat insulation property during stress loading is poor. In particular, the amount of alkenyl groups in Comparative Example 8 is a very common amount for industrial applications, but compared with Examples 1, 5, 6, the hardness is significantly lower, and therefore the heat insulation property during stress loading deteriorates. On the other hand, in Comparative Example 2 where the amount of alkenyl groups is more than that of the present invention, the sponge was destroyed when compressed during the measurement of compression set.

[0091] Regarding the content of the silane coupling agent-coated silica, the following considerations are made. In Examples 22 to 24 by mass without vinyl silicone resin, as the content of the silane coupling agent-coated silica increases, the hardness of the silicone rubber sponge increases, and the heat insulation property during stress loading also increases. Also, in Examples 1, 7, 8 by mass containing vinyl silicone resin, the same tendency is observed, but the heat insulation property during stress loading is more excellent than that without vinyl silicone resin. On the other hand, Comparative Example 6 where the content is less than 30 parts by mass has a worse heat insulation property during stress loading than the above examples. Also, Comparative Example 7 where the content is more than 80 parts by mass has a significantly higher viscosity of the composition, making roll processing difficult.

[0092] Examples 1, 9 to 15 are silicone rubber sponges with different expansion ratios due to different contents of the foaming agent. All of these silicone rubber sponges have good hardness, heat insulation properties under stress loading, and compression set. Among them, Examples 1, 9, 10, and 12 with an expansion ratio of 2.0 to 6.2 times have particularly excellent heat insulation properties under stress loading.

[0093] Regarding the hollow filler and the infrared shielding agent, although the effects of the present invention are obtained even in Example 16 where neither of them is added, Examples 25 and 26 where one of them is added exhibit better heat insulation properties under stress loading than Example 16, and Example 1 where both are added shows even better heat insulation properties under stress loading. Also, during kneading by a mill, the adhesion of the composition to the roll was suppressed more in the examples where the hollow filler was added than in Examples 16 and 26.

[0094] Example 27 is a composition using two types of diorganopolysiloxanes with different amounts of alkenyl groups in combination, Example 28 is a composition using silica and a low molecular weight dimethyl silicone diol having a vinyl group as the (B-2) component, and Example 29 is an example using azoisobutyronitrile as the foaming agent. All of these silicone rubber sponges have good values for hardness, heat insulation properties under stress loading, and compression set.

Industrial Applicability

[0095] The silicone rubber sponge obtained from the mirable-type silicone rubber composition is suitably used as a heat insulation and cushioning sponge for battery cells.

Explanation of Symbols

[0096] 1 Heat-generating cell 2 Heat insulation sheet 3 Silicone rubber sponge 4 Dummy cell

Claims

1. (A) 100 parts by mass of a diorganopolysiloxane component consisting of one or more diorganopolysiloxanes having an average of two or more alkenyl groups per molecule, the diorganopolysiloxane component (A) as a whole containing 0.50 to 3.00 mol % of alkenyl group-containing structural units, and (B) (B-1) and / or (B-2) (B-1) Vinyl silicone resin component (B-1) 5 to 30 parts by mass of a vinyl silicone resin component containing 0.50 to 10.0% by mass of vinyl groups as a whole, (B-2) 30 to 80 parts by mass of silica at least part of the surface of which has been modified with a crosslinkable functional group for the diorganopolysiloxane component (A), (C) a blowing agent, and (D) a curing agent, Including, Millable type silicone rubber composition for heat insulating cushioning sponge for battery cells.

2. 2. The millable silicone rubber composition for a heat insulating and shock absorbing sponge for a battery cell according to claim 1, characterized in that it contains both the component (B-1) and the component (B-2).

3. The millable silicone rubber composition for a heat insulating cushioning sponge for a battery cell according to claim 1, further comprising (E) 1.0 to 50.0 parts by mass of a hollow filler.

4. The millable silicone rubber composition for a heat insulating cushioning sponge for a battery cell according to claim 1, further comprising (F) an infrared shielding agent.

5. A heat insulating and shock absorbing silicone rubber sponge for battery cells, which is a foamed and cured product of the millable type silicone rubber composition for heat insulating and shock absorbing sponge for battery cells according to any one of claims 1 to 4.

6. 6. The heat insulating and cushioning silicone rubber sponge for battery cells according to claim 5, wherein the foaming ratio is 1.5 to 10.0 times.

7. The heat insulating and cushioning silicone rubber sponge for battery cells according to claim 5, having an Asker C hardness of 45 to 90 degrees.

8. 6. The heat insulating and shock absorbing silicone rubber sponge for battery cells according to claim 5, which has a compression set of 20% or less when measured according to JIS K6262, Method A, at a temperature of 23°C for 24 hours at a compression rate of 25%.

9. 6. The heat insulating and cushioning silicone rubber sponge for battery cells according to claim 5, wherein a dummy cell temperature measured by the following heat insulating property evaluation method is 150° C. or lower. (Insulation evaluation method) A 3.0 mm thick silicone rubber sponge sheet was sandwiched between two 0.5 mm thick insulation sheets with a thermal conductivity of 0.05 W / m K and placed on a dummy cell (a metal plate at 25°C). A heating cell (a hot plate at 600°C) was pressed against the silicone rubber sponge sheet sandwiched between the insulation sheets with a load of 1.0 MPa from the opposite side of the dummy cell, and the maximum temperature reached on the surface of the dummy cell within 60 minutes after the heating cell was pressed against it was recorded as the dummy cell temperature.

10. 6. The heat insulating and cushioning silicone rubber sponge for battery cells according to claim 5, having a group of elongated pores having major axes aligned in a thickness direction of the silicone rubber sponge.

11. A battery unit comprising a plurality of battery cells and the heat insulating and shock absorbing silicone rubber sponge for battery cells according to claim 5 between each of the battery cells.

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