Millable silicone rubber composition for heat insulating buffer sponge for battery cells, and silicone rubber sponge

Abstract

The present invention provides a silicone rubber composition which is capable of forming a silicone rubber sponge that has high hardness and small compression set, and exhibits excellent heat insulation (low thermal conductivity) even in an environment where a large compressive stress is applied thereto.　A millable silicone rubber composition for a heat insulating buffer sponge for battery cells according to the present invention includes: (A) 100 parts by mass of a diorganopolysiloxane component which is composed of one or more diorganopolysiloxanes that each have two or more alkenyl groups on average in each molecule, the diorganopolysiloxane component (A) as a whole containing 0.50-3.00 mol% of an alkenyl group-containing constituent unit; (B) (B-1) 5-30 parts by mass of a vinyl silicone resin component which contains 0.50-10.0 mass% of a vinyl group as a whole and / or (B-2) 30-80 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

Millable silicone rubber composition for heat insulating and cushioning sponge for battery cells and silicone rubber sponge

[0001] The present invention relates to a millable silicone rubber composition and silicone rubber sponge that are suitable for use as a heat-insulating and cushioning sponge for battery cells, which insulates against heat conduction between battery cells and cushions and supports the expansion / contraction deformation of each battery cell.

[0002] Silicone rubber sponges obtained by foaming and curing millable silicone rubber have heat resistance, electrical insulation, flame retardancy, etc. due to the presence of porous groups, and also have reduced compression set and are lightweight. For these reasons, silicone rubber sponges are used in office automation equipment, automobiles, building materials, etc.

[0003] Patent Document 1 describes a heat-curable millable silicone rubber composition that uses thermally expandable microcapsules that expand and contract at a specific temperature as a foaming agent, and uses a high-temperature decomposition type organic foaming agent as an open-cell agent after curing, thereby making it possible to set a wide range of densities from low to high expansion ratios and obtaining a silicone rubber sponge with small compression set. Suitable applications include cushioning materials for office automation equipment and transportation equipment, but no direct use in secondary rechargeable batteries is mentioned.

[0004] Patent Document 2 describes a porous fire prevention sponge sheet made primarily of silicone, which has low hardness and is easily deformable, and is attached to the side of the battery cells in the direction in which they are arranged, taking advantage of the heat resistance of silicone rubber sponge, to prevent the heat from abnormally overheating battery cells from being transferred to adjacent cells, characterized in that the holes in the sheet are elongated and slender, and the length direction of the holes is oriented along the surface of the fire prevention sheet.

[0005] International Publication No. 2018 / 003811 Japanese Patent Application Laid-Open No. 2023-34388

[0006] The silicone rubber sponge disclosed in Patent Document 1 is a flexible sponge with excellent compression set but low hardness and resilience. When considering its application as a buffer between battery cells, such as in a lithium-ion battery, which is permanently subjected to a large applied pressure (compressive stress), the compressive stress from the battery cells would significantly compress the silicone rubber sponge, crushing most of the internal cells (sponge cells). Therefore, even though the silicone rubber sponge is known for its low thermal conductivity, it would be unable to maintain good thermal insulation properties in such an environment. Therefore, examples of suitable applications include buffering for office automation equipment and transportation equipment, but not for rechargeable batteries.

[0007] The silicone rubber sponge disclosed in Patent Document 2 has sponge cells (pores) that are elongated along the surface direction of the sheet, thereby providing high thermal insulation. However, the document does not disclose adjusting the composition of the silicone rubber sponge to improve thermal insulation.

[0008] The thermal insulation cushioning material for battery cells is required to absorb expansion due to heat generation from the battery and to have thermal insulation properties to prevent the spread of fire between batteries in the event of a fire. Therefore, it is an object of the present invention to provide a silicone rubber composition capable of forming a silicone rubber sponge that has high hardness, small compression set, and excellent thermal insulation properties (low thermal conductivity) even under environments where large compressive stress is applied.

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

[11] . [1] A millable-type silicone rubber composition for a heat-insulating, shock-absorbing sponge for battery cells, comprising: (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) containing 0.50 to 3.00 mol % of alkenyl group-containing structural units in total; and (B) (B-1) and / or (B-2) (B-1) 5 to 30 parts by mass of a vinyl silicone resin component (B-1) containing 0.50 to 10.0 mass % of vinyl groups in total; (B-2) 30 to 80 parts by mass of silica at least partially modified on the surface with a crosslinkable functional group for diorganopolysiloxane component (A); (C) a foaming agent; and (D) a curing agent. [2] The millable-type silicone rubber composition for a heat-insulating cushioning sponge for battery cells of [1], characterized by containing both the (B-1) component and the (B-2) component. [3] The millable-type silicone rubber composition for a heat-insulating cushioning sponge for battery cells of [1], further containing 1.0 to 50.0 parts by mass of (E) a hollow filler. [4] The millable-type silicone rubber composition for a heat-insulating cushioning sponge for battery cells of [1], further containing (F) an infrared shielding agent. [5] A heat-insulating cushioning silicone rubber sponge for battery cells, which is a foamed and cured product of the millable-type silicone rubber composition for a heat-insulating cushioning sponge for battery cells of [1] to [4]. [6] The heat-insulating cushioning silicone rubber sponge for battery cells of [5], having an expansion ratio of 1.5 to 10.0 times. [7] The heat-insulating cushioning silicone rubber sponge for battery cells of [5], having an Asker C hardness of 45 to 90 degrees. [8] The heat-insulating and shock-absorbing silicone rubber sponge for battery cells of [5], which has a compression set of 20% or less, measured at a temperature of 23°C for 24 hours and a compression ratio of 25%, according to JIS K6262, Method A. [9] The heat-insulating and shock-absorbing silicone rubber sponge for battery cells of [5], which has a dummy cell temperature of 150°C or less, measured by the following heat insulation evaluation method.(Method for evaluating thermal insulation properties) A ​​3.0 mm thick silicone rubber sponge sheet is sandwiched between two 0.5 mm thick insulating sheets with a thermal conductivity of 0.05 W / m K and placed on a dummy cell (a metal plate at 25°C). A heat-generating cell (a hot plate at 600°C) is pressed against the silicone rubber sponge sheet sandwiched between the insulating sheets from the opposite side of the dummy cell with a load of 1.0 MPa. The highest temperature reached on the surface of the dummy cell 60 minutes after the heat-generating cell is pressed against it is defined as the dummy cell temperature.

[10] The heat-insulating and cushioning silicone rubber sponge for battery cells of [5], having a group of elongated holes with a major axis aligned in the thickness direction of the silicone rubber sponge.

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

[0010] The silicone rubber composition of the present invention can form a silicone rubber sponge that has high hardness, small compression set, and excellent heat insulating properties (low thermal conductivity) even under conditions of high compressive stress.

[0011] FIG. 1 is a diagram showing a method for measuring thermal insulation under stress.

[0012] The present invention provides a millable-type silicone rubber composition for a heat-insulating, shock-absorbing sponge for battery cells, comprising: (A) 100 parts by mass of a diorganopolysiloxane component comprising one or more diorganopolysiloxanes having an average of two or more alkenyl groups per molecule, the diorganopolysiloxane component (A) containing 0.50 to 3.00 mol % of alkenyl group-containing structural units in total; (B) (B-1) and / or (B-2) (B-1) 5 to 30 parts by mass of a vinyl silicone resin component (B-1) containing 0.50 to 10.0 mass % of vinyl groups in total; (B-2) 30 to 80 parts by mass of silica at least partially modified on the surface with crosslinkable functional groups for diorganopolysiloxane component (A); (C) a foaming agent; and (D) a curing agent.

[0013] A preferred embodiment of the millable silicone rubber composition for heat-insulating buffer sponges for battery cells (hereinafter also referred to as "millable silicone rubber composition") of the present invention and the silicone rubber sponge, which is its foamed and cured product, will be described below. (A) Diorganopolysiloxane Component The millable silicone rubber composition contains a diorganopolysiloxane. Unlike vinyl silicone resins, diorganopolysiloxanes are chain polymers. Therefore, it is preferable that they do not contain M units or Q units other than at the molecular terminals. However, branching is permitted as long as it does not impair the rubber elasticity of the silicone rubber sponge. The diorganopolysiloxane may be used alone or in combination of two or more types.

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

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

[0016] Therefore, the diorganopolysiloxane contains alkenyl group-containing structural units, and from the viewpoint of exhibiting appropriate rubber elasticity through appropriate crosslinking by thermal curing, has an average of two or more alkenyl groups per molecule. In the molecule, the alkenyl group-containing structural units may be present at any position other than the terminals of the main chain, or at the terminals of the main chain or in side chains.

[0017] The diorganopolysiloxane component (A) contains 0.50 to 3.00 mol %, preferably 0.50 to 2.00 mol %, and more preferably 0.50 to 1.50 mol % of alkenyl group-containing structural units. Within this range, the resulting sponge exhibits high hardness and excellent compression set. If the content is lower than this range, the crosslink density will be too low, resulting in an insufficient hardness of the resulting sponge. The sponge's pores cannot be maintained under stress, resulting in insufficient heat insulation. On the other hand, if the content is higher than this range, the sponge is more likely to crack when stressed or strained.

[0018] The alkenyl group-containing structural unit content is the value for the diorganopolysiloxane component (A) as a whole, and when two or more diorganopolysiloxanes are contained, it is the average of the respective contents. For example, the amount of alkenyl groups may be adjusted by blending a diorganopolysiloxane having a low alkenyl group-containing structural unit content with a diorganopolysiloxane having a high alkenyl group-containing structural unit content.

[0019] Specifically, such diorganopolysiloxanes are those having a weight average molecular weight of 1.0×10 ５ ~1.0 x 10 ６ Examples of commercially available diorganopolysiloxanes include alkenyl-terminated polydimethylsiloxanes listed below. Examples of commercially available diorganopolysiloxanes include 110-0, 110-5, 110-6, 110-7, 112-5, 112-6, and 112-7 manufactured by DONGJUE SILICONE (NANJING) CO., LTD.

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

[0021] (B) (B-1) Vinyl silicone resin component and / or (B-2) Silica at least partially surface-modified with crosslinkable functional groups for component (A) The millable silicone rubber composition contains, as component (B), at least one of the following components (B-1) and (B-2). From the viewpoint of obtaining silicone rubber sponge hardness while suppressing an increase in viscosity, it is preferable to contain at least component (B-1), and it is even more preferable to contain both components (B-1) and (B-2).

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

[0023] The weight average molecular weight of the vinyl silicone resin component is preferably 100 to 10,000, and more preferably 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 mixed with component (A) and, if necessary, heated to dissolve in component (A), thereby reducing the viscosity of the composition. Furthermore, since the vinyl group in the structure can form a crosslinked structure with component (A), it has the effect of increasing the hardness and strength of the resulting sponge, without worsening the compression set. The vinyl silicone resin can be used alone or in combination of two or more types.

[0025] The vinyl silicone resin component (B-1) contains 0.50 to 10.0% by mass of vinyl groups, preferably 0.50 to 5.0% by mass, and more preferably 0.50 to 2.0% by mass, based on 100% by mass of vinyl silicone resin. If the vinyl content is less than 0.50% by mass, the hardness decreases, the sponge pores cannot be maintained under stress, and the heat insulation and compression set deteriorate. If the vinyl content exceeds 10.0% by mass, the crosslink density becomes too high, causing significant destruction of the crosslinked structure during compression and worsening the compression set. The vinyl group content is the value for the vinyl silicone resin component (B-1) as a whole. If 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 Co., Ltd.

[0027] In the millable silicone rubber composition, the vinyl silicone resin component (B-1) is present in an amount of 5 to 30 parts by mass, preferably 5 to 20 parts by mass, and more preferably 5 to 15 parts by mass, per 100 parts by mass of the diorganopolysiloxane component (A). If the content is less than 5 parts by mass, the hardness of the resulting silicone rubber sponge decreases, the compression set under stress increases, and the viscosity of the composition increases, resulting in problems such as a low expansion ratio and cracks in the foamed sponge. If the content exceeds 30 parts by mass, the composition becomes too tacky, making roll processing and molding difficult.

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

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

[0030] At least a portion of the surface of the silica is modified with a crosslinkable functional group for the diorganopolysiloxane component (A). Examples of the crosslinkable functional group include a vinyl group, a methacrylic group, and an acrylic group. The crosslinkable functional group may be a single type or a combination of two or more types. The method of modification with the crosslinkable functional group may involve chemically treating the surface of the silica before mixing with the component (A), or, when mixing unmodified or partially hydrophobized silica with the component (A), adding a surface treatment agent such as a silane coupling agent containing the crosslinkable functional group and kneading under heat, thereby modifying the silica during kneading.

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

[0032] In the millable silicone rubber composition, the amount of 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 per 100 parts by mass of the diorganopolysiloxane component (A). If the content is less than 30 parts by mass, the hardness of the resulting silicone rubber sponge will be low, and the sponge's pores will not be able to maintain their shape under stress, resulting in poor heat insulation. On the other hand, if the content exceeds 80 parts by mass, the resulting silicone rubber sponge will be too hard to exhibit appropriate rubber elasticity or cushioning function, or the viscosity of the composition will be too high, making roll processing difficult, reducing the expansion ratio, or causing the sponge to crack during expansion.

[0033] (C) Foaming Agent The millable silicone rubber composition contains a foaming agent. The foaming agent is a component that, when heated while dispersed in the millable silicone composition, forms pores within the millable silicone rubber composition by (i) physically expanding the size of the foaming agent within the composition, or (ii) undergoing a chemical decomposition reaction to generate gas, forming a porous structure when the composition hardens, making the composition sponge-like.

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

[0035] In the millable silicone rubber composition, the amount of 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, per 100 parts by mass of the diorganopolysiloxane component (A). When the content of the blowing agent (C) is within the above range, a good balance between hardness, compression set, and expansion ratio is achieved, which is preferable from the viewpoint of heat insulating properties under stress.

[0036] (D) Curing Agent The millable silicone rubber composition contains a curing agent. The curing agent is added to impart appropriate elasticity to the millable silicone composition when it is foamed. Examples of curing agents include organic peroxide curing agents such as alkyl peroxy esters, peroxy ketals, dialkyl peroxides, hydroperoxides, and ketone peroxides, and addition reaction curing agents consisting of organopolysiloxanes having two or more silicon-bonded hydrogen atoms (hydrosilyl groups) per molecule and a platinum compound that acts as a curing catalyst. The crosslinking initiation temperature of the curing agent is preferably 70 to 200°C. Commercially available products include organic peroxide curing agents such as Perhexa HC, Perhexa C, Perhexa V, Perhexa 25B, Perbutyl P, Perbutyl C, Percumyl D, Niper BM™, Perhexa 25Z, Perhexyl Z, Perbutyl ZT, and Perbutyl Z (all manufactured by NOF Corporation), and TC-1, TC-3, TC-4, TC-8, and TC-12 (all manufactured by Momentive Performance Materials, Inc.).

[0037] In the millable silicone rubber composition, the amount of curing agent (D) is preferably 0.01 to 10.0 parts by mass, and more preferably 0.1 to 5.0 parts by mass, per 100 parts by mass of the diorganopolysiloxane component (A). The content of curing agent (D) in this range is preferred from the viewpoint of suppressing compression set.

[0038] (E) Hollow Filler: The Millable silicone rubber composition preferably contains a hollow filler. A hollow filler is a filler containing an air layer inside a shell made of a material such as glass or ceramic. Adding a hollow filler to a Millable silicone rubber composition can further improve the thermal insulation properties under stress when the composition is foamed, cured, and then formed into a sponge. Silicone rubber sponges have elongated pores that provide air insulation, which reduces the volume ratio of solid silicone rubber that transmits heat and improves thermal insulation. However, adding a hollow filler creates an insulating layer derived from the hollow filler inside the solid silicone rubber, further improving thermal insulation. Furthermore, because the insulating layer derived from the hollow filler is covered on the outside with a rigid shell made of glass or ceramic, the insulating layer does not deform even when the sponge is compressed, and therefore the hardness of the silicone rubber sponge does not decrease, making it possible to further improve thermal insulation under stress.

[0039] Examples of hollow fillers include inorganic hollow fillers and organic hollow fillers. Examples of materials constituting the shell of inorganic hollow fillers include glass, ceramic, shirasu, silica, etc. Examples of materials constituting the shell of organic hollow fillers include phenolic 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, and iM30K (all manufactured by 3M Japan), and E-SPHERES SL75, SL125, SL150, SL300, and SLG (all manufactured by Taiheiyo Cement Corporation).

[0040] When a hollow filler is contained, the amount of hollow filler (E) in the millable silicone rubber composition 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 per 100 parts by mass of the diorganopolysiloxane component (A). A content of hollow filler (E) within the above range is preferable in terms of heat insulating properties under stress and suppression of compression set.

[0041] It is also preferable that the millable silicone rubber composition contains both a hollow filler and a vinyl silicone resin. When a vinyl silicone resin is blended into a millable silicone rubber composition, the hardness of the silicone rubber sponge can be improved while suppressing an increase in viscosity, but this can cause stickiness, which can make the millable silicone rubber composition more likely to stick to the rolls during kneading in the manufacturing process. When a hollow filler is further blended into a millable silicone rubber composition blended with a vinyl silicone resin, sticking to the rolls of the kneading machine is suppressed, and processability is improved.

[0042] (F) Infrared Shielding Agent The Millable silicone rubber composition preferably contains an infrared shielding agent. The infrared shielding agent reflects and scatters infrared rays emitted from a heat source and serves to enhance the insulating properties of the sponge. Examples of infrared shielding agents include titanium oxide, titanium oxide-coated surfaces of mica, ITO (tin-doped indium oxide), ATO (antimony-doped tin oxide), and infrared absorbing pigments, with titanium oxide being preferred. The infrared shielding agent is preferably particles with a particle diameter of approximately several μm. Furthermore, considering that electrical insulation is often required for battery buffer materials, it is more preferred that the infrared shielding agent be electrically insulating.

[0043] Commercially available titanium oxide products include TITANIX JR-1000 (manufactured by Teika Corporation). Furthermore, commercially available products of mica or the like whose surfaces are coated with titanium oxide include IMPACT Velvet, Impact Sparkle, Optique Satin Violet, TC Gold, and Chromatique Silver Gray (all manufactured by Sandream Impact).

[0044] When an infrared shielding agent is included, the amount of the infrared shielding agent (F) in the millable silicone rubber composition 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, per 100 parts by mass of the diorganopolysiloxane component (A). A content of the infrared shielding agent (F) within the above range is preferable in terms of heat insulating properties and compression set under stress load.

[0045] (Other Optional Components) The heat-insulating shock absorber rubber of the present invention may contain any optional components within the range that does not impair the effects of the present invention. Examples of such optional components include hardness adjusters, crosslinking aids such as triallyl isocyanurate and trimethylolpropane trimethacrylate, colorants such as pigments and dyes, fillers such as reinforcing silica, diatomaceous earth, and crushed quartz that do not have a crosslinkable functional group on their surface, wetters, silane coupling agents that do not have a crosslinkable functional group, cure retarders, heat-resistant additives such as metal oxides, fire-resistant (ceramic) agents such as mica, platinum or platinum group compounds, and flame retardants such as metal oxides and carbon black, components that adjust the foaming temperature and foaming speed of the foaming agent, and dispersants.

[0046] <Method of Producing Millable-Type Silicone Rubber Composition and Silicone Rubber Sponge> The millable-type silicone rubber composition and silicone rubber sponge may be prepared by known methods, for example, by the following method. Components (A), (B), and optional components (E) and (F) are kneaded at room temperature in a kneading machine such as a mixer. The temperature is then raised to 120 to 170°C, and kneading is continued until the torque change stabilizes. The kneaded mixture is then removed from the kneading machine, and components (C) and (D) are added, followed by kneading at room temperature using a mill, kneader, roll, or the like to obtain a millable-type silicone rubber composition.

[0047] The obtained millable-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 metal plates: 13 mm) and allowed to foam and cure for 5-60 minutes, after which it is removed from the metal plates to obtain a silicone rubber sponge. The shape and dimensions of the silicone rubber sponge and the foaming and curing temperatures can be adjusted as desired depending on the application and the types of components (C) and (D). The methods for producing the millable-type silicone rubber composition and silicone rubber sponge are not limited to those described above, and can be adjusted and modified as appropriate depending on the application.

[0048] <Physical Properties of Silicone Rubber Sponge> The silicone rubber sponge, which is a foamed and cured product of the millable silicone rubber composition, preferably has the following physical properties.

[0049] (Hardness) The hardness of the silicone rubber sponge, measured as an Asker C hardness by the method described in the Examples, is preferably 45 to 90 degrees, more preferably 50 to 85 degrees, taking into consideration the buffering function of the buffer material between battery cells used in secondary batteries, such as lithium-ion batteries. Having a hardness equal to or greater than the lower limit provides good thermal insulation under stress, adequately maintains the position of the cells, and adequately applies pressure to expanded cells. On the other hand, having a hardness equal to or less than the upper limit provides sufficient cushioning against external impacts, preventing physical damage to the battery cells.

[0050] (Thermal insulation properties under stress load) Considering the problem of thermal runaway in secondary batteries such as lithium-ion batteries, the temperature of the dummy cell measured by the method described in the Examples is preferably 150° C. or less, and more preferably 140° C. or less. By keeping the temperature of the dummy cell at 150° C. or less, when one battery cell generates abnormal heat, heat transfer to adjacent cells can be sufficiently suppressed, and thermal runaway throughout the battery casing can be prevented.

[0051] (Compression set) Considering the buffering function of the inter-cell buffer material in secondary batteries, such as lithium-ion batteries, the compression set value measured by the method described in the Examples is preferably 20% or less, more preferably 15% or less. A compression set value of 20% or less allows appropriate pressure to be applied to the cells over the long term, preventing a decrease in charge capacity. Furthermore, the battery cells can be adequately protected from external vibrations, preventing abnormalities in the battery cells and maintaining their position within the casing.

[0052] (Expansion Ratio) Considering the relationship between heat insulating properties and compression set under stress load, the expansion ratio measured by 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 insulating properties can be obtained. On the other hand, if the expansion ratio is 10.0 times or less, sufficient hardness can be maintained and compression set is also unlikely to occur.

[0053] (Group of Slots) The silicone rubber sponge preferably has groups of slots with their major axes aligned with the thickness direction of the silicone rubber sponge when placed between battery cells. Having the major axes in this direction provides excellent heat insulation and suppression of compression set under stress. The direction of the major axes of the slots can be adjusted, for example, by the method described in WO 2023 / 032114.

[0054] <Applications> Because the silicone rubber sponge has the above physical properties, it is used for insulating and cushioning battery cells. When a battery cell is charged, it generates heat and expands. The silicone rubber sponge can absorb the deformation caused by the expansion of the battery cell. Furthermore, its insulating properties can prevent the spread of fire between battery cells in the event of a fire. A preferred use is a battery unit having multiple battery cells and the above-mentioned insulating and cushioning silicone rubber sponge for battery cells between each battery cell. The silicone rubber sponge is preferably fixed to a support member. The fixing may be either physical or chemical. The battery unit may consist of one or more. Examples of battery cells include storage batteries such as lithium-ion batteries.

[0055] The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to these examples.

[0056] <Methods for measuring and evaluating 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 tester, Type C (manufactured by Kobunshi Keiki Co., Ltd.).

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

[0058] (3) Compression Set The compression set of the silicone rubber sponge was measured in accordance with Method A of JIS K6262 under the conditions of a temperature of 23°C, a time of 24 hours, and a compression ratio of 25%. The calculation method is as follows: Compression set (%) = {(t0 - t2) / (t0 - t1)} x 100 t0: initial thickness of test piece (mm) t1: spacer thickness (mm) t2: thickness of test piece after removal from the compression device and leaving for 30 minutes (mm)

[0059] (4) Expansion Ratio A test piece approximately 10 mm square was cut from the obtained silicone rubber sponge to prepare it, and its specific gravity was measured to the nearest 0.001 using an automatic hydrometer (D-1, manufactured by Toyo Seiki Co., Ltd.). Furthermore, the specific gravity of a solid rubber sheet obtained by curing the silicone rubber sponge under appropriate curing conditions, but omitting the foaming agent (C), was also measured in the same manner. These values ​​were used to calculate the expansion ratio using the following formula: Expansion Ratio (times) = Specific Gravity of Solid Rubber Sheet / Specific Gravity of Silicone Rubber Sponge x 100 (%)

[0060] (5) Judgment Judging was made based on the results of (1) to (4) according to the following criteria. ◎ and ◯ were judged to be acceptable. ◎: Hardness was 50 to 85 degrees, and the heat insulating property under stress was 140°C or less, and the compression set was 15% or less. ○: Hardness was 45 degrees or more and less than 50 degrees or more than 85 degrees and 90 degrees or less, and the thermal conductivity under stress was 140°C or more and 150°C or less, and the compression set was 15% or more and 20% or less. ×: Other than ◎ and ◯

[0061] Example 1 100 parts by weight of diorganopolysiloxane (1), 20 parts by weight of vinyl silicone resin (1), 50 parts by weight of silica (1), 0.5 parts by weight of silane coupling agent, 25 parts by weight of hollow filler, and 3 parts by weight of infrared shielding agent were kneaded until uniform using a Laboplastomill 10C100-B600 mixer (manufactured by Toyo Seiki Co., Ltd.) at a rotation speed of 20 rpm. Next, the temperature was raised to 150 ° C., and the mixture was kneaded at a rotation speed of 40 rpm until the change in kneading torque stabilized. Thereafter, the kneaded mixture was removed from the mixer, and 5.0 parts by weight of thermally expandable microcapsules as a foaming agent, 0.05 parts by weight of curing agent (1), and 3.0 parts by weight of curing agent (2) were added and kneaded using a LABOLATORY MILL (manufactured by Kansai Roll Co., Ltd.) to obtain a millable silicone rubber composition. The millable silicone rubber composition was then formed into a sheet of appropriate thickness and dusted with mica powder (A-21S, manufactured by Yamaguchi Mica Co., Ltd.) to reduce surface tackiness. This sheet was inserted between two metal plates heated to 200°C (distance between metal plates: 13 mm) and allowed to foam and cure for 30 minutes, after which it was removed from the metal plates to obtain a silicone rubber sponge.

[0062] Examples 2 and 3 Millable-type silicone rubber compositions and silicone rubber sponges 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 millable 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 millable 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 millable 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 Millable-type silicone rubber compositions and silicone rubber sponges 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 Millable-type silicone rubber compositions and silicone rubber sponges 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 millable silicone rubber composition and a silicone rubber sponge were obtained in the same manner as in Example 1, except that the hollow filler and infrared shielding agent were not added.

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

[0070] [Example 19] A millable 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 blended and instead reinforcing silica (2) was blended in the amount shown in Table 1.

[0071] [Examples 20 and 21] Millable-type silicone rubber compositions and silicone rubber sponges were obtained in the same manner as in Example 1, except that the silane coupling agent-coated silica was not blended, and instead reinforcing silica (2) was blended 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 millable silicone rubber composition and a silicone rubber sponge were obtained in the same manner as in Example 1, except that the vinyl silicone resin (1) was not blended.

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

[0074] Example 25 A millable-type silicone rubber composition and a silicone rubber sponge were obtained in the same manner as in Example 1, except that no infrared shielding agent was added and the amount of hollow filler was changed to the amount shown in Table 1.

[0075] Example 26 A millable silicone rubber composition and a silicone rubber sponge were obtained in the same manner as in Example 1, except that no hollow filler was added.

[0076] Example 27 A millable silicone rubber composition and a silicone rubber sponge were obtained in the same manner as in Example 1, except that diorganopolysiloxane (4) and diorganopolysiloxane (5) were used instead of diorganopolysiloxane (1). The diorganopolysiloxane component (A) as a whole contained 0.60 mol % of alkenyl group-containing constituent units.

[0077] Example 28 A millable 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 containing 30 mol% methylvinylsiloxy units and 6 siloxane units having hydroxyl groups at both ends was used instead of 0.5 parts by mass of the silane coupling agent.

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

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

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

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

[0082] Comparative Examples 4 and 5 Millable silicone rubber compositions and silicone rubber sponges 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 and no silane coupling agent-coated silica was added.

[0083] Comparative Examples 6 and 7 Millable silicone rubber compositions and silicone rubber sponges 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 and the vinyl silicone resin (1), hollow filler, and infrared shielding agent were not blended.

[0084] Comparative Example 8 A millable silicone rubber composition and a silicone rubber sponge were obtained in the same manner as in Example 1, except that diorganopolysiloxane (8) was used instead of diorganopolysiloxane (1) and the hollow filler and infrared shielding agent were not blended.

[0085] The results of measuring the various physical properties of the Examples and Comparative Examples are shown in Tables 1 and 2. In Tables 1 and 2, "alkenyl content" refers to the content of alkenyl group-containing structural units in the entire diorganopolysiloxane component (A), and "vinyl content" refers to 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) (manufacturer: DONGJUE SILICONE (NANJING) CO., LTD.) Diorganopolysiloxane (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.) Diorganopolysiloxane (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.) Diorganopolysiloxane (4): Vinyl group-containing dimethylpolysiloxane containing 10.00 mol% of alkenyl group-containing structural units. Diorganopolysiloxane (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.). Diorganopolysiloxane (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.). Diorganopolysiloxane (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.) Diorganopolysiloxane (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): (Me ２ R １ SiO １／２ ) ３ (SiO ４／２ ) ４ , R １ Vinyl silicone resin (2): (Me is a vinyl group or a methyl group) containing 2.00% by mass of vinyl groups (product number MQ200-1) (manufacturer: HUBEI JIAYUN CHEMICAL) ２ R １ SiO １／２ ) ３ (SiO ４／２ ) ４ , R １ is a vinyl group or a methyl group) Vinyl silicone resin (3): (Me ２ R １ SiO １／２ ) ３ (SiO ４／２ ) ４ , R １ (is vinyl group or methyl group) Contains 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 dimethylsilicone diol having a vinyl group: linear silicone oil having 30 mol% methylvinylsiloxy units and 6 siloxane units having hydroxyl groups at both ends (chemical formula: HO(SiRCH ３ ) ６(OH, R are methyl or vinyl groups) Thermally expandable microcapsules: Product name "FN-78D" (Manufacturer: Matsumoto Yushi Pharmaceutical Co., Ltd.) Azobisisobutyronitrile: Product name "ME800" (Manufacturer: Momentive Performance Materials Co., Ltd.) Organic peroxide curing agent (1): Main component compound name: p-methylbenzoyl peroxide, Product name "TC-12" (Manufacturer: Momentive Performance Materials Co., Ltd.) Organic peroxide curing agent (2): Main component compound name: 2,5-dimethyl-2,5-ditertiarybutylperoxyhexane, Product name "TC-8" (Manufacturer: Momentive Performance Materials Co., Ltd.) Hollow filler: Product name "Glass Bubbles K46" (Manufacturer: 3M Co., Ltd.) Infrared 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]

[0089]

[0090] In the Examples, silicone rubber sponges were obtained that were rated as either excellent or excellent. Examples 1, 5, and 6 and Comparative Examples 1, 2, and 8 were rubber compositions with different amounts of alkenyl groups in the diorganopolysiloxane. In Examples 1, 5, and 6, as the amount of alkenyl groups increased, the hardness of the silicone rubber sponge increased and its heat insulating properties under stress improved. (In Comparative Examples 1 and 8, in which the amount of alkenyl groups in the diorganopolysiloxane was lower than in the present invention, heat insulating properties under stress were poor. In particular, although the amount of alkenyl groups in Comparative Example 8 was quite common for industrial use, its hardness was significantly lower than in Examples 1, 5, and 6, resulting in poor heat insulating properties under stress. On the other hand, in Comparative Example 2, in which the amount of alkenyl groups was higher than in the present invention, the sponge broke when compressed during compression set measurement.

[0091] The content of silane coupling agent-coated silica can be considered as follows. In Examples 22 to 24, which do not contain a vinyl silicone resin, the hardness of the silicone rubber sponge increases as the content of silane coupling agent-coated silica increases, and the heat insulating properties under stress also improve. A similar trend is observed in Examples 1, 7, and 8, which contain a vinyl silicone resin, but these have better heat insulating properties under stress than those without a vinyl silicone resin. On the other hand, Comparative Example 6, in which the content is less than 30 parts by mass, exhibits worse heat insulating properties under stress than the above examples. Furthermore, Comparative Example 7, in which the content is more than 80 parts by mass, exhibits a significantly higher viscosity of the composition, making it difficult to roll.

[0092] Examples 1 and 9 to 15 are silicone rubber sponges with different expansion ratios due to differences in the foaming agent content. All of the silicone rubber sponges have good hardness, heat insulating properties under stress, and compression set. Among these, Examples 1, 9, 10, and 12, which have expansion ratios of 2.0 to 6.2, have particularly excellent heat insulating properties under stress.

[0093] Regarding the hollow filler and infrared shielding agent, the effects of the present invention were obtained even in Example 16, which did not contain either, but Examples 25 and 26, which contained one of them, exhibited better heat insulating properties under stress than Example 16, and Example 1, which contained both, exhibited even better heat insulating properties under stress. Furthermore, in the Examples in which a hollow filler was added, sticking of the composition to the roll during kneading with a mill was suppressed more than in Examples 16 and 26.

[0094] Example 27 is a composition that combines two types of diorganopolysiloxane with different amounts of alkenyl groups, Example 28 is a composition that uses silica and a low-molecular-weight dimethylsilicone diol containing vinyl groups as component (B-2), and Example 29 is an example that uses azoisobutyronitrile as the blowing agent. All of the silicone rubber sponges exhibited good values ​​for hardness, heat insulating properties under stress, and compression set.

[0095] The silicone rubber sponge obtained from the millable silicone rubber composition is suitable for use as a heat-insulating, shock-absorbing sponge for battery cells.

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

Claims

1. A millable-type silicone rubber composition for a heat insulating cushioning sponge for battery cells, comprising: (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) containing 0.50 to 3.00 mol % of alkenyl group-containing structural units in total; and (B) (B-1) and / or (B-2) (B-1) 5 to 30 parts by mass of a vinyl silicone resin component (B-1) containing 0.50 to 10.0 mass % of vinyl groups in total; (B-2) 30 to 80 parts by mass of silica at least a portion of the surface of which is modified with a crosslinkable functional group for the diorganopolysiloxane component (A); (C) a foaming agent; and (D) a curing agent.

2. A millable type silicone rubber composition for a heat insulating and cushioning sponge for battery cells 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 and cushioning sponge for battery cells according to claim 1, further comprising 1.0 to 50.0 parts by mass of (E) a hollow filler.

4. A millable type silicone rubber composition for a heat insulating cushioning sponge for battery cells 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 claims 1 to 4.

6. The heat insulating and shock absorbing 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 shock absorbing silicone rubber sponge for battery cells according to claim 5, which has an Asker C hardness of 45 to 90 degrees.

8. 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 and a compression ratio of 25%.

9. The heat-insulating and cushioning silicone rubber sponge for battery cells according to claim 5, wherein the dummy cell temperature measured by the following heat-insulating property evaluation method is 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 placed on a dummy cell which is a metal plate at 25° C. A heat-generating cell which is a hot plate at 600° C. is pressed against the silicone rubber sponge sheet sandwiched between the heat-insulating sheets from the opposite side of the dummy cell with a load of 1.0 MPa, and the maximum temperature reached on the surface of the dummy cell within 60 minutes after the heat-generating cell is pressed against it is defined as the dummy cell temperature.

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

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

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