Heat insulating sheet between battery cells for electric vehicles and its manufacturing method

Abstract

The heat insulating sheet (1) is used to provide insulation between battery cells of an electric vehicle. The heat insulating sheet (1) includes silica aerogel (2), fibers (3), and infrared-shielding particles (4). A photograph of a cross section of the heat insulating sheet (1) shows first particles (41) made of infrared-shielding particles (4) having a major axis of 0.5 μm or more and 1 μm or less, and second particles (42) made of infrared-shielding particles (4) having a major axis of 5 μm or more and 10 μm or less. The heat insulating sheet (1) can be obtained, for example, by preparing a sheet precursor in which fibers (3) are impregnated with a wet gel containing silica microparticles and infrared-shielding particles (4) dispersed in the gel, and then drying the gel in the sheet precursor.

Description

[Technical Field]

[0001] The present invention relates to a heat insulating sheet used for insulating between battery cells of an electric vehicle, and a method for manufacturing the same. [Background technology]

[0002] Silica aerogel has a porous structure with pores smaller than the mean free path of air, and its skeleton is formed by multiple connected silica particles. This fine porous structure gives silica aerogel low thermal conductivity, making it useful as a component material for insulation in automotive parts, residential building materials, industrial equipment, etc.

[0003] On the other hand, insulating materials containing silica aerogel often have low surface mechanical strength. Therefore, when external force is applied to the insulating material, powder from the insulating material's constituent substances tends to fall off, a phenomenon known as powder shedding. For example, insulating materials used to insulate between battery cells in electric vehicles are repeatedly subjected to loads caused by heat and battery expansion during charging. Furthermore, automotive insulating materials are subject to vibrations that occur while the vehicle is in operation. Therefore, when a sheet containing silica aerogel is used as insulating material for an automotive battery, the aforementioned loads and vibrations can cause powder shedding from the sheet, potentially resulting in a deterioration of the insulating performance.

[0004] Furthermore, powder shedding tends to occur in areas of the sheet surface that are subject to stress due to battery expansion and in areas close to the source of vibration. Therefore, if powder shedding occurs, it can cause imbalances in the distribution of the composition within the insulation material, potentially resulting in the formation of areas with poor insulation performance within the insulation material.

[0005] As a technique for suppressing the occurrence of powder falling, for example, Patent Document 1 describes a technique of blending a hot melt powder into a sheet containing silica aerogel, a technique of sealing the surface of the sheet with a film, etc. Furthermore, Patent Document 2 describes a technique of providing a heat insulating elastic member including an elastic layer on one side of a silica aerogel sheet and providing a cover layer on the other side, or covering the sheet and the entire sheet with an exterior body. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 2023-132944 [Patent Document 2] Japanese Patent Application Publication No. 2023-35097 Summary of the Invention [Problem to be solved by the invention]

[0007] However, when a sheet containing silica aerogel is covered with a film or the like, repeated external forces applied to the insulating material over a long period of use can easily cause the film to peel off from the sheet, resulting in powder shedding. In particular, when the sheet contains a substance with a relatively high specific gravity, such as silicon carbide, the substance is likely to fall off the sheet, resulting in a decrease in insulating properties. Furthermore, according to the technology of Patent Document 2, the hardened layer formed by the hot-melt powder may reduce the insulating performance of the sheet.

[0008] The present invention has been made in consideration of the above background, and aims to provide an insulating sheet between battery cells for electric vehicles that can maintain good insulating performance for a long period of time, and a method for manufacturing the same. [Means for solving the problem]

[0009] One aspect of the present invention is a heat insulating sheet used for insulating between battery cells of an electric vehicle, Silica aerogel, Fiber and infrared shielding particles, In a photograph of a cross section of the heat insulating sheet, first particles made of infrared shielding particles having a major axis of 0.5 μm or more and 1 μm or less and second particles made of infrared shielding particles having a major axis of 5 μm or more and 10 μm or less are present. And, a ratio of the number of the first particles to the number of the second particles present in the photograph (first particles:second particles) is 1:4 to 3:1; In the photograph, the sum of the ratio of the number of the first particles and the ratio of the number of the second particles to the number of the infrared shielding particles each having a major axis of 0.5 μm or more and 10 μm or less is 20% or more and 30% or less. , an insulating sheet between battery cells for electric vehicles.

[0010] Another aspect of the present invention is a method for producing an inter-cell insulating sheet for an electric vehicle battery according to the above aspect, preparing a sheet precursor in which the fibers are impregnated with a wet gel containing silica fine particles and infrared shielding particles dispersed in the gel; The method for producing an insulating sheet between battery cells for an electric vehicle includes drying the gel in the sheet precursor to form the insulating sheet. [Effects of the Invention]

[0011] The insulating sheet between battery cells for electric vehicles (hereinafter referred to as "insulation sheet") contains silica aerogel, fibers, and infrared-shielding particles. The infrared-shielding particles contain first particles and second particles having the specific major axis. The infrared-shielding particles have the effect of blocking radiant heat, thereby improving thermal insulation. It is known that the effect of blocking radiant heat by the infrared-shielding particles increases as the particle diameter of the infrared-shielding particles increases. On the other hand, as the particle diameter of the infrared-shielding particles increases, the infrared-shielding particles tend to bond together within the insulation sheet. As a result, heat transfer paths including the infrared-shielding particles are more likely to be formed, resulting in a decrease in thermal insulation. Therefore, in this type of insulation sheet, in order to improve the radiant heat blocking effect while avoiding the bonding of the infrared-shielding particles, infrared-shielding particles having a particle diameter of a predetermined value or less and a small particle diameter variation have generally been used.

[0012] In contrast to this common technical knowledge, by deliberately using infrared-shielding particles containing first particles and second particles, it is possible to prevent the first particles and second particles from falling off from the heat insulating sheet even when the heat insulating sheet is subjected to external force or vibration. Furthermore, by retaining the first particles and second particles within the heat insulating sheet for a long period of time, it is possible to maintain the good heat insulating performance of the heat insulating sheet for a long period of time.

[0013] Therefore, according to the above-described embodiment, it is possible to provide a heat insulating sheet that can maintain good heat insulating performance for a long period of time, and a method for manufacturing the same. [Brief explanation of the drawings]

[0014] [Figure 1] FIG. 1 is a cross-sectional view that schematically shows a cross section parallel to the thickness direction of a heat insulating sheet. DETAILED DESCRIPTION OF THE INVENTION

[0015] (Thermal insulation sheet) The structure of the heat insulating sheet will be described below.

[0016] [Silica aerogel] Silica aerogel is a porous structure composed of silica fine particles and has pores. The pores in silica aerogel are usually mesopores with diameters of 50 nm or less. Because the diameter of mesopores is smaller than the mean free path of air, the use of silica aerogel can suppress air convection within the pores. As a result, heat transfer due to convection is suppressed, improving thermal insulation performance. While there is no particular lower limit for the pore diameter from the viewpoint of suppressing air convection within the pores, a pore diameter of, for example, 10 nm or more is preferred.

[0017] The skeleton of silica aerogel is mainly composed of secondary particles formed by aggregation of silica fine particles as primary particles. The average particle diameter of the silica fine particles (primary particles) is usually about 2 to 5 nm. The average particle diameter of the silica fine particles can be measured by observation with an electron microscope.

[0018] The average particle size of the particles (mainly secondary particles) that make up the skeleton of silica aerogel is preferably 1 μm or more, and more preferably 10 μm or more. While there is no particular upper limit to the average particle size of the particles that make up the skeleton from the viewpoint of improving thermal insulation performance, the average particle size of the particles that make up the skeleton is preferably, for example, 200 μm or less. The average particle size of the particles that make up the skeleton is the median size (i.e., D50) determined from the volume-based particle size distribution measured by laser diffraction / scattering.

[0019] The content of silica aerogel in the heat insulating sheet is preferably 10% by mass or more, more preferably 20% by mass or more, and even more preferably 30% by mass or more, which can more reliably achieve the improved heat insulating performance due to the silica aerogel.

[0020] On the other hand, the content of silica aerogel in the heat insulating sheet is preferably 60% by mass or less, more preferably 50% by mass or less, and even more preferably 40% by mass or less. In this case, a decrease in the mechanical strength of the heat insulating sheet can be more easily avoided. As a result, powder falling off from the heat insulating sheet can be made less likely.

[0021] The preferred range of the silica aerogel content can be determined by any combination of the upper and lower limits described above. For example, the preferred range of the silica aerogel content in the heat insulating sheet may be 10% by mass to 60% by mass, 20% by mass to 50% by mass, or 30% by mass to 40% by mass.

[0022] Silica aerogel can be obtained, for example, by gelling a sol containing silica particles and a liquid dispersion medium in which the silica particles are dispersed, followed by drying to remove the liquid dispersion medium from the gel. The method for drying the gel is not particularly limited, and drying can be performed, for example, in an atmosphere under normal pressure or in a supercritical fluid. Alternatively, the gel can be dried by freeze-drying or drying under ambient pressure.

[0023] A gel obtained by drying in an atmosphere under normal pressure is sometimes called a "xerogel," a gel obtained by drying in a supercritical fluid is sometimes called an "aerogel," a gel obtained by freeze-drying is sometimes called a "cryogel," and a gel obtained by drying under ambient pressure is sometimes called an "ambigel." However, the silica aerogel contained in the heat insulating sheet may be produced by any of these methods. In other words, the term "silica aerogel" in this specification encompasses "aerogel," "xerogel," "cryogel," and "ambigel" made of silica fine particles.

[0024] Silica aerogel may be subjected to hydrophobic treatment during its production process. If the hydrophobic treatment is performed before the drying process, drying in a supercritical fluid is not required, and the silica aerogel can be dried in an atmosphere under normal pressure. Therefore, in this case, the silica aerogel production process can be further simplified and the production cost can be further reduced.

[0025] [Infrared Shielding Particles] Infrared-shielding particles have the functions of absorbing heat from a heat source and re-emitting it from the surface on the heat source side, as well as scattering infrared rays. Therefore, by incorporating infrared-shielding particles into a heat insulating sheet, radiant heat from the heat source can be blocked, thereby improving heat insulating performance, particularly at high temperatures.

[0026] The infrared-shielding particles that appear in a photograph of the cross section of the heat insulating sheet include at least first particles having a major axis of 0.5 μm to 1 μm and second particles having a major axis of 5 μm to 10 μm. In addition to the first and second particles, the photograph may also include infrared-shielding particles having a major axis outside the aforementioned range. By using infrared-shielding particles such that both the first and second particles appear in a photograph of the cross section of the heat insulating sheet, the heat insulating sheet can maintain good heat insulating performance for a long period of time.

[0027] The reasons why the first particles and second particles achieve the above-mentioned effects are thought to be, for example, as follows: The first particles have a relatively small particle size, so the mass of each particle is small and the ratio of surface area to mass is large. Therefore, it is thought that they are less likely to fall downward from their initial position even when vibrations or repeated loads are applied to the insulation sheet. Furthermore, the second particles have a relatively large particle size, so it is thought that they are more likely to be captured by fibers, etc., when vibrations or repeated loads are applied to the insulation sheet and they fall downward from their initial position.

[0028] Therefore, by using infrared-shielding particles in which both the first particles and the second particles appear in a photograph of the cross section of the heat insulating sheet, it is thought that the first particles and the second particles are less likely to fall off even when the heat insulating sheet is subjected to vibration, repeated loads, etc. Furthermore, it is thought that the first particles and the second particles are retained in the heat insulating sheet for a long period of time, thereby making it possible to maintain the heat insulating performance.

[0029] From the viewpoint of more reliably obtaining the above-mentioned effect, the ratio of the number of the first particles to the number of the second particles present in the photograph is preferably first particles:second particles = 1:4 to 4:1, preferably 1:4 to 3:1, more preferably 1:4 to 2:1, and even more preferably 1:4 to 1:1. From the same viewpoint, in the photograph, the sum of the proportion of the number of the first particles and the proportion of the number of the second particles to the infrared shielding particles having a major axis of 0.5 μm or more is preferably 5% to 30%, more preferably 10% to 30%, even more preferably 15% to 30%, and particularly preferably 20% to 30%.

[0030] It is preferable that the infrared-shielding particles that appear in a photograph of the cross section of the heat insulating sheet further contain third particles having a major axis of more than 1 μm and less than 5 μm. The third particles have a moderately large particle diameter, which provides high performance in blocking radiant heat from a heat source. Furthermore, the third particles are less likely to connect within the heat insulating sheet, which makes it easy to avoid the formation of a heat transfer path including the third particles. Therefore, by using infrared-shielding particles that show third particles in a photograph of the cross section of the heat insulating sheet, the initial heat insulating performance of the heat insulating sheet can be further improved. From the viewpoint of more reliably achieving this effect, it is preferable that the proportion of the number of the third particles among the infrared-shielding particles present in the photograph is 70% or more and 95% or less, and more preferably 70% or more and 90% or less.

[0031] Examples of methods for adjusting the numbers of the first particles, the second particles, and the other particles present in the photograph include a method for adjusting the particle size distribution of infrared-shielding particles used in manufacturing the heat insulating sheet. More specifically, the numbers of the first particles, the second particles, and the other particles present in the photograph can be adjusted to within desired ranges by, for example, a method for classifying infrared-shielding particles, a method for mixing and using multiple types of infrared-shielding particles having different particle size distributions, a method for combining these methods, or the like.

[0032] The method for determining the presence or absence of first particles and second particles and the method for counting the number of these particles are as follows. First, the heat insulating sheet is cut to obtain a test piece of a predetermined size. After forming a platinum coating on the surface of this test piece, the test piece is processed using a sample cross-section processing device (for example, the "Cross Section Polisher (registered trademark) SM09010" manufactured by JEOL Ltd.) under conditions of an acceleration voltage of 4 kV and a processing time of 20 hours, thereby exposing a cross section approximately parallel to the thickness direction of the heat insulating sheet.

[0033] After forming an osmium coating on the processed cross section, a backscattered electron image of the cross section is observed using an electron microscope (e.g., Hitachi's "SEM S-3400N") at an accelerating voltage of 15 kV and a magnification of 200x. A photograph of the cross section of the test piece is then obtained based on this backscattered electron image. Figure 1 shows a schematic diagram of a cross-sectional photograph. The photograph of the cross section of the heat insulating sheet 1 shows silica aerogel 2, infrared shielding particles 4, and fibers 3. The infrared shielding particles 4 have, for example, a polygonal outline. The fibers 3 have, for example, a circular or elliptical outline. For each infrared shielding particle 4 present in the photograph, the rectangle with the smallest area among the rectangles circumscribing the particle is identified. The length of the long side of the identified rectangle is taken as the major axis of each infrared shielding particle 4.

[0034] Based on the major axis determined in this manner, it is possible to determine whether each infrared shielding particle 4 is a first particle 41, a second particle 42, or a particle other than these. The number of first particles 41 and second particles 42 can be obtained by identifying the first particles 41 and the second particles 42 by the method described above, and then counting the number of each particle present in the photograph. If particles other than the first particles and second particles, such as third particles, are present in the photograph, the major axis and number of these particles can be measured by the same method as described above.

[0035] The above steps can also be performed using image processing software. For example, the method for measuring the long diameter of particles using ImageJ is as follows. First, a cross-sectional photograph measuring 960 pixels vertically and 1280 pixels horizontally is created from the backscattered electron image. Next, binarization is performed based on the pixel values of each pixel to identify the infrared-shielding particle regions and the glass fiber regions. After that, region segmentation is performed to create an image for measurement in which only the infrared-shielding particle regions have been extracted. At this time, regions with an area of 1 pixel are considered noise and are excluded from the measurement of the long diameter of the infrared-shielding particles.

[0036] Then, after detecting the outline of each infrared-shielding particle area in the measurement image, the rectangle with the smallest area among the rectangles circumscribing each area is identified by rectangle fitting. The length of the long side of this rectangle (unit: pixels) is measured, and the unit is converted to obtain the long diameter (unit: μm) of the infrared-shielding particle.

[0037] The infrared-shielding particles in the photograph are preferably unevenly distributed near the fibers. More specifically, the number of infrared-shielding particles present within a range of 13 μm from the surface of the fibers is preferably greater than the number of infrared-shielding particles present outside the range. In this case, since a relatively large number of infrared-shielding particles are present around the fibers, radiant heat from the heat source is more likely to be blocked by the infrared-shielding particles before it reaches the fibers. As a result, the fibers are protected from radiant heat and heat resistance can be improved. Furthermore, second particles having a relatively large particle size are easily captured by the fibers. Therefore, since a relatively large number of infrared-shielding particles are present near the fibers, powder falling is less likely to occur even when the insulation sheet is subjected to vibration or repeated loads, and it is expected that the insulation performance will be maintained for a longer period of time.

[0038] In order to more reliably obtain the above-mentioned effects, it is preferable that 70% or more of the infrared-shielding particles in the photograph are present within a range of 13 μm from the surface of the fiber.

[0039] From the viewpoint of obtaining the effect of protecting the fibers from radiant heat, the first particles, second particles, and third particles may all be unevenly distributed near the fibers in the photograph, or one or two types of particles among the first particles, second particles, and third particles may be unevenly distributed near the fibers. On the other hand, from the viewpoint of suppressing powder shedding, it is preferable that at least the second particles are unevenly distributed near the fibers. In other words, it is preferable that the number of the second particles present within a range of 13 μm from the surface of the fiber is greater than the number of the second particles present outside the range.

[0040] Examples of materials that can be used to form the infrared-shielding particles include silicon carbide, kaolinite, montmorillonite, titanium oxide, silicon nitride, mica, alumina, aluminum nitride, boron carbide, iron oxide, magnesium oxide, tin oxide, zinc oxide, tantalum oxide, manganese ferrite, manganese oxide, nickel oxide, nickel, silver oxide, silver, bismuth oxide, carbon black, graphite, titanium, titanium iron oxide, zirconium, zirconia, zirconium silicate, barium titanate, manganese dioxide, chromium oxide, titanium carbide, tungsten carbide, tungsten oxide, niobium oxide, indium tin oxide, cerium oxide, and mixtures thereof. The heat insulating sheet may contain infrared-shielding particles made of one type of these materials, or may contain two or more types of infrared-shielding particles made of different materials.

[0041] From the viewpoint of further enhancing the radiant heat blocking effect, it is desirable that the infrared-shielding particles be composed of a material having an emissivity of 0.6 or higher in the infrared wavelength range. Examples of such materials include silicon carbide, kaolinite, silicon nitride, mica, alumina, zirconia, aluminum nitride, zirconium silicate, cerium oxide, boron carbide, manganese oxide, tin oxide, and iron oxide. Furthermore, from the viewpoint of scattering incident infrared light to enhance the radiant heat blocking effect, it is also effective to use infrared-shielding particles composed of a material having a high refractive index in the infrared wavelength range. Examples of such materials include silicon carbide, titanium oxide, zirconia, silicon nitride, aluminum nitride, zinc oxide, tantalum oxide, tungsten oxide, niobium oxide, cerium oxide, manganese oxide, tin oxide, bismuth oxide, iron oxide, and barium titanate, which have a refractive index of 2.0 or higher in the visible light wavelength range.

[0042] Furthermore, by forming the infrared-shielding particles from a substance having a relatively large specific heat, the heat capacity of the infrared-shielding particles can be increased, thereby suppressing the temperature rise of the particles themselves. Furthermore, such substances also have excellent heat resistance. Therefore, by using infrared-shielding particles formed from such substances, the heat insulating performance and heat resistance of the heat insulating sheet can be further improved. Examples of substances having a relatively large specific heat include silicon carbide, titanium oxide, silicon nitride, mica, alumina, aluminum nitride, boron carbide, iron oxide, and magnesium oxide. Silicon carbide is particularly suitable because its thermal conductivity increases little even in high-temperature atmospheres of around 800°C.

[0043] The content of infrared-shielding particles in the heat insulating sheet is preferably 5% by mass or more, and more preferably 10% by mass or more. In this case, the effect of suppressing heat transfer due to radiation can be more reliably obtained. On the other hand, from the viewpoint of reducing contact between the infrared-shielding particles and with other components and making it difficult to form a heat transfer path, the content of infrared-shielding particles in the heat insulating sheet is preferably 30% by mass or less, and more preferably 20% by mass or less.

[0044] When determining a preferred range for the content of the infrared-shielding particles, the above-mentioned upper and lower limits for the content of the infrared-shielding particles can be combined in any manner. For example, a preferred range for the content of the infrared-shielding particles in the heat insulating sheet may be 5% by mass or more and 30% by mass or less, or 10% by mass or more and 20% by mass or less.

[0045] 〔fiber〕 The fibers in the heat insulating sheet ensure the mechanical strength of the heat insulating sheet and also have the effect of suppressing the powder shedding of silica aerogel and infrared shielding particles. The fibers may be inorganic or organic. Examples of inorganic fibers that can be used include glass fibers, ceramic fibers, quartz fibers, alumina fibers, silica fibers, silicon carbide fibers, boron fibers, and metal fibers (e.g., aluminum and iron).

[0046] Examples of organic fibers that can be used include chemical fibers such as polyamide fibers, polyimide fibers, aromatic polyamide fibers (aramid fibers), polyolefin fibers (e.g., polyethylene fibers, polypropylene fibers), fluorine fibers (e.g., polytetrafluoroethylene fibers), acrylic fibers, polyparaphenylenebenzbisoxazole (PBO) fibers, polyarylate fibers, nylon fibers, polyurethane fibers, polyamide fibers, polyetheretherketone (PEEK) fibers, polyethersulfone (PES) fibers, polyetherimide (PEI) fibers, polyetherketone (PEK) fibers, and polyphenylene sulfide (PPS) fibers, as well as natural fibers such as wood fibers, silk, hemp, and wool fibers. The heat insulating sheet may contain one type of fiber or two or more types of fibers.

[0047] The fibers contained in the heat insulating sheet are preferably those having strength and / or heat resistance. From this viewpoint, the fibers contained in the heat insulating sheet are more preferably inorganic fibers, and even more preferably glass fibers.

[0048] The average diameter of the fibers in a photograph of the cross section of the thermal insulation sheet is preferably 0.6 to 2 times the average major axis of the second particles, more preferably 0.7 to 1.7 times, and even more preferably 0.8 to 1.5 times. In this case, since the diameter of the fibers is appropriately large compared to the major axis of the second particles, it is thought that the second particles are more likely to be captured by the fibers even when the thermal insulation sheet is subjected to vibration or repeated loads and falls downward from its initial position. As a result, it is thought that the second particles are less likely to fall off, and the thermal insulation performance can be maintained for a longer period of time.

[0049] The method for calculating the average diameter of fibers in a photograph of the cross section of an insulation sheet is as follows. First, a photograph of a cross section roughly parallel to the thickness direction of the insulation sheet is obtained using the same method as described above. If the cross section of fiber 3 is circular and extends in a direction roughly perpendicular to the cross section, the cross section of fiber 3a that appears in the photograph will be circular, as shown in Figure 1. Therefore, in this case, the diameter of the circle is the diameter of fiber 3a. On the other hand, if fiber 3 extends in a direction tilted relative to the cross section, the cross section of fiber 3b that appears in the photograph will be elliptical. Therefore, in this case, the minor axis of the ellipse is the diameter of fiber 3b.

[0050] Therefore, the average diameter of the fibers can be calculated by determining the diameters of the individual fibers present on the photograph by the above-mentioned method and then arithmetically averaging these values. Also, the average major axis of the secondary particles can be obtained by measuring the major axes of all the secondary particles on the photograph by the above-mentioned method and then arithmetically averaging these values.

[0051] The fibers in the thermal insulation sheet may be present in various forms. For example, the fibers in the thermal insulation sheet may be present in a separated state, or multiple fibers may form bundles. The fibers in the thermal insulation sheet may also form a fabric such as a woven fabric or a nonwoven fabric. Furthermore, the fibers in the thermal insulation sheet may be present in two or more of these forms.

[0052] The fibers in the heat insulating sheet preferably form a cloth, more preferably a nonwoven fabric. In this case, the mechanical strength of the heat insulating sheet can be further improved. In addition, by using a cloth (preferably a nonwoven fabric, more preferably a glass fiber nonwoven fabric) that has been perforated or fluffed during the manufacturing process of the heat insulating sheet, the void ratio and surface roughness of the heat insulating sheet surface can be easily adjusted.

[0053] The fiber content in the heat insulating sheet is preferably 20% by mass or more, and more preferably 30% by mass or more. In this case, the mechanical strength of the heat insulating sheet can be further increased. On the other hand, from the viewpoint of obtaining mechanical strength commensurate with the fiber content, the fiber content in the heat insulating sheet is preferably 70% by mass or less, and more preferably 60% by mass or less.

[0054] When determining a preferred range of the fiber content, the above-mentioned upper and lower limits of the fiber content can be combined arbitrarily. For example, a preferred range of the fiber content in the heat insulating sheet may be 20% by mass to 70% by mass, or 30% by mass to 60% by mass.

[0055] [Other ingredients] The heat insulating sheet may be composed of silica aerogel, infrared shielding particles, and fibers, and may also contain other components. Optional components that may be blended into the heat insulating sheet include, for example, binders, thickeners, flame retardants, preservatives, colorants, and radiation absorbing / reflecting materials.

[0056] ·binder The binder can reduce deterioration in a high-temperature atmosphere and suppress the occurrence of cracks. The binder may be made of an inorganic material or an organic material.

[0057] Examples of inorganic binders include talc, carbon black, kaolinite, montmorillonite, mica, silica (e.g., precipitated silica, gel silica, fused silica), wollastonite, magnesium silicate, titania, metal carbides (e.g., titanium carbide or tungsten carbide), metal oxides (e.g., manganese oxide, nickel oxide, tin oxide, silver oxide, bismuth trioxide, chromium oxide, iron oxide, alumina, zirconia, manganese dioxide), metal nitrides (e.g., silicon nitride, aluminum nitride), ilmenite, zirconium silicate, potassium titanate, glass flakes, water glass (sodium silicate), calcium carbonate, barium sulfate, hydraulic materials (e.g., cement, gypsum, magnesium silicate), quicklime, slaked lime, etc. The heat insulating sheet may contain one type of inorganic binder or two or more types of inorganic binders.

[0058] The type of inorganic binder added to the heat insulating sheet is not particularly limited, and an appropriate inorganic binder may be blended depending on the properties of the inorganic binder. For example, silica is preferred because it is highly compatible with silica aerogel and is inexpensive and readily available. Hydraulic materials are also preferred because they react with water, a solvent commonly used in the production of silica aerogel, to fill the gaps between the silica particles and bond the constituent materials together, thereby forming a high-strength heat insulating sheet, and are inexpensive and readily available. Alternatively, inorganic binders with large specific surface areas and hardness may be selected.

[0059] As the organic binder, it is preferable to use an aqueous binder that can be dissolved or dispersed in water (capable of forming an emulsion). Alternatively, as the organic binder, a substance that imparts hydrophilic groups to the silica aerogel or a so-called surfactant can also be used.

[0060] The glass transition temperature (Tg) of the organic binder is preferably −5° C. or lower, more preferably −20° C. or lower. Such an organic binder has excellent adhesion to silica aerogel. Furthermore, by using an organic binder whose glass transition temperature is within the above-mentioned specific range, the flexibility of the heat insulating sheet can be improved and the occurrence of cracks can be suppressed.

[0061] Examples of organic binders include resins such as acrylic resin, urethane resin, and a mixture of acrylic resin and urethane resin; and rubbers such as styrene butadiene rubber (SBR), nitrile rubber, silicone rubber, urethane rubber, and acrylic rubber. Among these, the organic binder is preferably a urethane resin and / or SBR. In this case, the flexibility of the heat insulating sheet can be further improved, resulting in a flexible sheet. When an organic binder is used, a crosslinking agent may also be used in combination. In this case, the organic binder can be crosslinked to further improve the strength of the sheet.

[0062] Thickener The thickener can improve the dispersibility of silica aerogel in a solvent (usually water) and improve processability. The thickener can also improve the flexibility of the insulation sheet and suppress the occurrence of cracks. Examples of thickeners that can be used include polysaccharides such as carboxymethyl cellulose (CMC), polyethylene oxide (PEO), carboxyethyl cellulose, carboxypropyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, xanthan gum, agarose, carrageenan, and glucomannan; and polyvinyl alcohol.

[0063] Flame retardants The flame retardant can enhance the flame retardancy of the heat insulating sheet. Examples of the flame retardant that can be used include halogen-based flame retardants, phosphorus-based flame retardants, and metal hydroxide-based flame retardants. As the flame retardant, it is preferable to use a phosphorus-based flame retardant (e.g., ammonium polyphosphate, red phosphorus, phosphate ester), more preferably to use a water-insoluble phosphorus-based flame retardant, and even more preferably to use ammonium polyphosphate.

[0064] [Structure of the heat insulating sheet] The thickness of the heat insulating sheet is not particularly limited, and may be, for example, 10 mm or less, 8 mm or less, 3 mm or less, 2.5 mm or less, or 2 mm or less. This allows the strength of the sheet to be maintained within a moderate thickness range. The lower limit of the thickness of the heat insulating sheet may be, for example, 0.1 mm. The lower limit of the thickness of the heat insulating sheet is preferably 0.5 mm, and more preferably 1 mm. It is preferable that the thickness of the heat insulating sheet is generally uniform throughout. For example, the variation in thickness of the heat insulating sheet may be 5% or less, 4% or less, or 3% or less.

[0065] At least one surface in the thickness direction of the heat insulating sheet may be provided with an uneven shape or a plurality of voids. The position and shape of the voids provided in the heat insulating sheet are not particularly limited and may take various forms. For example, the voids may be arranged at regular intervals on the surface of the heat insulating sheet, or may be arranged randomly. Examples of the shape of the voids include circular, polygonal, and irregular shapes. The uneven shape provided in the heat insulating sheet may be arranged over the entire surface of the heat insulating sheet, or may be arranged only in part of the surface. The concave and convex portions in the uneven shape may be arranged uniformly over the entire surface, or may be arranged biasedly in part of the surface.

[0066] When unevenness and / or voids are provided on both the first surface and the second surface in the thickness direction of the heat insulating sheet, the properties of the first surface and the second surface may be the same or different. From the viewpoint of more effectively suppressing powder falling from the heat insulating sheet, it is preferable that the properties of the first surface and the second surface of the heat insulating sheet are different from each other. That is, for example, when voids are provided on both the first surface and the second surface, it is preferable that the number of voids provided on the first surface is greater than the number of voids provided on the second surface. Furthermore, for example, when unevenness is provided on both the first surface and the second surface, it is preferable that the surface roughness of the first surface is greater than the surface roughness of the second surface.

[0067] When the heat insulating sheet is placed between battery cells, the magnitude of external force or vibration applied to one surface in the thickness direction of the heat insulating sheet may be greater than the magnitude of external force or vibration applied to the other surface. In this case, by placing the heat insulating sheet so that the magnitude of external force or vibration applied to the first surface is greater than the magnitude of external force or vibration applied to the second surface, powder of the constituent material of the heat insulating sheet that is generated from the first surface due to external force or vibration can be easily captured by the pores and recesses on the surface. Furthermore, because the first surface has a predetermined shape and / or is formed of fiber, adhesion to films, etc. can be improved. Therefore, even when external force, vibration, etc. is applied to the heat insulating sheet, peeling between the film, etc. and silica aerogel, etc. can be suppressed.

[0068] On the other hand, by arranging the heat insulating sheet as described above, the magnitude of external forces and vibrations applied to the second surface can be reduced, and the amount of powder of the constituent materials of the heat insulating sheet that is generated from the second surface due to external forces, vibrations, etc. can be reduced. Therefore, even if the number of voids on the second surface is smaller than that on the first surface, or the surface roughness of the second surface is smaller than that of the first surface, the powder of the constituent materials of the heat insulating sheet that is generated from the second surface can be easily captured. Furthermore, since the voids and uneven shapes provided on the surface themselves cause powder shedding, reducing the number of voids on the second surface or reducing the surface roughness of the second surface can suppress powder shedding caused by the voids and uneven shapes.

[0069] Therefore, by arranging an insulation sheet whose first surface and second surface have different properties in an orientation that corresponds to the magnitude of the external force or vibration, it is possible to suppress powder falling off the insulation sheet.

[0070] [Application] The heat insulating sheet has an excellent balance between the effect of suppressing powder falling and heat insulating properties, and therefore can be suitably used as a heat insulating sheet between battery cells for automobiles. More specifically, by placing the heat insulating sheet between the cells of an automobile battery, heat transfer between the cells can be reduced.

[0071] When the properties of the first surface and the second surface of the heat insulating sheet are different, as described above, it is preferable to position the heat insulating sheet in an orientation such that the stress generated on the first surface, i.e., the surface with a large number of pores and / or high surface roughness, is greater than the stress generated on the second surface. More specifically, it is preferable to position the first surface closer to the battery cell, closer to the vibration source, or closer to the motor than the second surface. By positioning the heat insulating sheet in this manner, it is possible to suppress powder falling off from the heat insulating sheet and further improve heat insulating performance.

[0072] (Insulation material) A heat insulating material can be obtained by laminating the heat insulating sheet with other members. The heat insulating material may include, for example, a film, an elastic layer, a base layer, an adhesive layer, etc. in addition to the heat insulating sheet.

[0073] 〔film〕 The heat insulating material may further have a film covering at least one surface in the thickness direction of the heat insulating material sheet. By covering the surface of the heat insulating material sheet with a film, powder falling from the surface can be further suppressed. The film may cover only one surface in the thickness direction of the heat insulating material sheet. Alternatively, the entire heat insulating material sheet may be covered and sealed with the film.

[0074] When the properties of the first surface and the second surface of the heat insulating sheet are different, it is preferable that the film covers at least the first surface, i.e., the surface with a large number of pores and / or high surface roughness, and it is more preferable that the film covers both the first surface and the second surface. In this way, by covering at least the first surface of the heat insulating sheet with a film, powder falling can be more effectively suppressed. From the viewpoint of further enhancing this effect, it is preferable to position the heat insulating sheet in an orientation such that the external force or vibration applied to the first surface is greater than the external force or vibration applied to the second surface.

[0075] The material constituting the film is not particularly limited. For example, the film may be made of polyimide, polycarbonate, PET, p-phenylene sulfide, polyetherimide, cross-linked polyethylene, flame-retardant chloroprene rubber, polyvinyl fluoride, rigid polyvinyl chloride, polybutylene terephthalate, PTFE, PFA, FEP, ETFE, rigid PVC, flame-retardant PET, polystyrene, polyethersulfone, polyamideimide, polyacrylonitrile, polyethylene, polypropylene, polyamide, etc.

[0076] [Elastic layer] The heat insulating material may have an elastic layer for alleviating stress generated in the heat insulating material sheet and for applying a compressive load to the battery cell. The elastic layer may be provided on one surface in the thickness direction of the heat insulating material sheet, or on both surfaces. When the properties of the first surface and the second surface of the heat insulating material sheet are different, it is preferable that the elastic layer is provided on at least the first surface. In this case, the above-mentioned stress alleviation effect can be more effectively utilized. From the viewpoint of further enhancing this effect, it is preferable to orient the heat insulating material sheet in a direction such that the external force or vibration applied to the first surface is greater than the external force or vibration applied to the second surface.

[0077] The elastic layer may be made of a material having rubber elasticity. For example, the elastic layer may be made of natural rubber or synthetic rubber. The main component of the elastic layer is preferably polyisoprene, hydrogenated polyisoprene, polybutadiene, styrene-butadiene copolymer, isobutylene-isoprene copolymer, ethylene-propylene copolymer, ethylene-propylene-diene terpolymer (EPDM), or silicone.

[0078] The shape of the elastic layer can take various forms. The elastic layer preferably has a ridge on the back side of the surface that contacts the heat insulating sheet (for example, the surface that contacts the cells). In this case, the stress generated in the heat insulating sheet can be further alleviated. As a result, powder falling can be more effectively suppressed.

[0079] [Lamination method] The method of laminating the heat insulating sheet and other layers can take various forms. For example, the heat insulating sheet and other layers can be laminated by applying a slurry containing the constituent materials of the heat insulating sheet to at least one surface of the layer to be laminated with the heat insulating sheet and then drying the slurry. To apply the slurry, known coating devices such as a blade coater, bar coater, die coater, Comma Coater (registered trademark), roll coater, or brush can be used as needed. The temperature for drying the slurry can be appropriately set within a range of, for example, 80 to 180°C. The time for drying the slurry can be appropriately set within a range of, for example, several minutes to several tens of minutes.

[0080] Alternatively, the heat insulating sheet and the other layer may be prepared separately and then laminated together by adhering these layers via an adhesive layer. Examples of materials that can be used to form the adhesive layer include epoxy resin, phenolic resin, acrylic resin, melamine resin, vinyl acetate resin, silicone resin, urethane resin, polyethylene, and polypropylene.

[0081] Furthermore, for example, the heat insulating sheet can be housed in a film formed into a bag shape, and then the opening of the film can be closed to seal the heat insulating sheet.

[0082] (Method of manufacturing heat insulating sheets) The method for producing the heat insulating sheet can take various forms. For example, the heat insulating sheet can be produced by compression molding a mixture containing silica aerogel particles, infrared shielding particles, fibers, and a suitable dispersion medium, and then drying the dispersion medium. The heat insulating sheet obtained by such a method has a structure in which the infrared shielding particles and fibers are held in the gaps between the silica aerogel particles.

[0083] Alternatively, the heat insulating sheet may be produced by a method in which a sheet precursor is produced in which the fibers are impregnated with a wet gel containing silica fine particles and infrared shielding particles dispersed in the gel, and the gel in the sheet precursor is dried to form the heat insulating sheet. In this case, a heat insulating sheet having the desired properties can be more easily obtained.

[0084] The sheet precursor can be produced in various ways. For example, a sheet precursor can be obtained by impregnating fibers with a dispersion containing a hydrolyzable silane compound and infrared-shielding particles, hydrolyzing the silane compound in the dispersion to form a sol of silica microparticles, and then gelling the sol. Alternatively, a sheet precursor can be obtained by dispersing infrared-shielding particles in a sol of silica microparticles, impregnating fibers with the dispersion, and gelling the sol. Furthermore, a sheet precursor can be obtained by mixing a wet gel with infrared-shielding particles to produce a dispersion, and then impregnating fibers with the dispersion. By drying the sheet precursor obtained by these methods, a heat insulating sheet can be obtained in which silica aerogel fills the gaps between the fibers and the infrared-shielding particles are dispersed in the silica aerogel. From the perspective of more easily obtaining a heat insulating sheet with desired properties, it is more preferable to produce the sheet precursor by gelling a sol of silica microparticles impregnated into fibers.

[0085] The sol containing silica fine particles can be obtained, for example, by preparing a silane solution containing a hydrolyzable silane compound and infrared shielding particles, and hydrolyzing the silane compound in the silane solution. When carrying out the hydrolysis, the silane solution may be ice-cooled or stirred as necessary. The hydrolysis of the silane compound can also be carried out in a state where the fiber is impregnated with the silane solution.

[0086] Examples of hydrolyzable silane compounds include methyltrimethoxysilane (MTMS), trimethylmethoxysilane (TMS), dimethyldimethoxysilane (DMS), trimethylethoxysilane, dimethyldiethoxysilane (DMDS), methyltriethoxysilane (MTES), ethyltriethoxysilane (ETES), diethyldiethoxysilane, ethyltriethoxysilane, propyltrimethoxysilane, propyltriethoxysilane, phenyltrimethoxysilane, phenyltriethoxysilane (PhTES), hexamethyldisilazane, and hexaethyldisilazane.

[0087] Examples of solvents for the silane solution include water, methanol, ethanol, isopropanol, ethyl acetate, ethyl acetoacetate, acetone, dichloromethane, and tetrahydrofuran. The solvent for the silane solution is preferably an acidic aqueous solution, more preferably an aqueous acetic acid solution. The silane solution may also contain a hydrolyzable compound such as urea. Furthermore, the silane solution may also contain a surfactant such as aliphatic ammonium or alkylbenzylammonium, as needed.

[0088] The method for gelling a sol containing silica fine particles is not particularly limited, and examples thereof include a method of leaving the sol standing in a sealed container, a method of adding an appropriate catalyst to the sol, and a method of irradiating the sol with energy rays such as ultraviolet rays. Among these, it is preferable to gel the sol by leaving it standing in a sealed container. When leaving the sol standing in a sealed container, the sol can be heated, for example, to a temperature of 50°C or higher or 60°C or higher, as necessary.

[0089] A wet gel is formed by gelling the sol. Silica aerogel can be obtained by drying the wet gel and removing the liquid dispersion medium and unreacted products from the gel. Various methods can be used to dry the wet gel, including supercritical drying, atmospheric pressure drying, freeze drying, and drying under ambient pressure. Supercritical drying involves contacting the wet gel with a supercritical fluid, such as supercritical carbon dioxide, to exchange the supercritical fluid for the liquid dispersion medium. The sheet precursor may be compressed during drying, if necessary. This reduces uneven thickness of the heat insulating sheet.

[0090] In the manufacturing process of the heat insulating sheet, pores may be formed by perforation or other methods as needed, which allows the properties of the sheet surface to be adjusted. There are no particular restrictions on the timing of forming pores, and pores can be formed at any stage in the manufacturing process of the heat insulating sheet.

[0091] Furthermore, in the manufacturing process of the heat insulating sheet, a hydrophobic treatment of the gel may be carried out as necessary. In the hydrophobic treatment, a trimethylsilylating agent is reacted with the wet gel or silica aerogel. This allows hydrophilic functional groups (e.g., hydroxyl groups) on the silica surface to be converted into hydrophobic functional groups (e.g., trimethylsilyl groups). The timing for carrying out the hydrophobic treatment may be any timing, as long as it is after the formation of the silica microparticles. From the viewpoint of further simplifying the manufacturing process of the heat insulating sheet, it is preferable to carry out the hydrophobic treatment on the wet gel.

[0092] When hydrophobizing treatment is performed, the content of hydrophobized silica relative to the mass of the heat insulating sheet is preferably 5% by mass or more, and more preferably 7% by mass or more. Meanwhile, the content of hydrophobized silica relative to the mass of the heat insulating sheet is preferably 30% by mass or less, and more preferably 25% by mass or less. Furthermore, the mass ratio of hydrophobized silica to non-hydrophobized silica (hydrophobized / non-hydrophobized) is preferably 0.1 or more, and more preferably 0.2 or more. Meanwhile, the mass ratio of hydrophobized silica to non-hydrophobized silica is preferably 1.5 or less, more preferably 1.2 or less, and even more preferably 1.0 or less. [Example]

[0093] Experimental examples of the heat insulating sheet and its manufacturing method will be described below.

[0094] (Experimental Example 1) The heat insulating sheet of this example is produced by preparing a sheet precursor in which the fibers are impregnated with a wet gel containing silica fine particles and infrared shielding particles dispersed in the gel, and then drying the gel in the sheet precursor. The method for producing the heat insulating sheet of this example is described in detail below.

[0095] First, 1.00 g of cetyltrimethylammonium bromide (also known as hexadecyltrimethylammonium bromide, manufactured by Nacalai Tesque, Inc., hereinafter abbreviated as "CTAB") as a cationic surfactant was dissolved in 10.00 g of an aqueous solution of acetic acid with a concentration of 0.01 mol / L. 0.50 g of urea (manufactured by Nacalai Tesque, Inc.) as a hydrolyzable compound was added to this acidic aqueous solution and dissolved.

[0096] Next, 5.0 mL of methyltrimethoxysilane ("LS-530" manufactured by Shin-Etsu Chemical Co., Ltd., specific gravity: 0.95, hereafter abbreviated as "MTMS") as a hydrolyzable silane compound was added to the acidic aqueous solution. After the addition of MTMS, the acidic aqueous solution was stirred and mixed under ice cooling for 30 minutes, thereby hydrolyzing the MTMS and forming silica microparticles in the aqueous solution. This produced a sol of silica microparticles. 0.7 g of silicon carbide particles whose particle size had been adjusted was added to this sol, producing a dispersion in which the silicon carbide particles were dispersed in the sol. The dispersion was then left to stand in an atmosphere at 60°C for 3 hours, causing a portion of the sol in the dispersion to gel.

[0097] The silicon carbide particles used in this example were obtained by classifying a mixed powder of silicon carbide powder with a particle size of #400 and silicon carbide powder with a particle size of #6000. The mixed powder can be classified using a known classifier, such as a centrifugal classifier (Turboplex (registered trademark) manufactured by Hosokawa Micron Corporation) or an airflow classifier (Elbow Jet (registered trademark) manufactured by Nittetsu Mining Co., Ltd.).

[0098] Next, a glass fiber nonwoven fabric (Nitigura Mat MNA-300-1000-30m, 3 mm thick, manufactured by Nippon Glass Fiber Industrial Co., Ltd.) placed on a 50 μm thick polypropylene film was impregnated with the dispersion and then sealed in an airtight container together with the polypropylene film. The resulting product was then left to stand in the airtight container for a further 96 hours, allowing the sol in the nonwoven fabric to completely gel and the gel to mature. This resulted in a sheet precursor containing a wet gel.

[0099] The sheet precursor thus obtained was removed from the sealed container, and the water in the sheet precursor was then replaced with 2-propanol. More specifically, the sheet precursor was immersed in 2-propanol at 60°C for 24 hours, and the heat insulating sheet was then removed from the 2-propanol. After replacing the 2-propanol, the sheet was immersed in 2-propanol at 60°C for 48 hours to perform solvent replacement.

[0100] Next, supercritical drying was performed using the following method to dry the gel in the sheet precursor and produce silica aerogel. First, the solvent-substituted sheet precursor was placed in a 400 mL autoclave filled with 2-propanol. After closing the autoclave lid, the pressure inside the autoclave was increased to 882 N / cm using liquefied carbon dioxide. 2 (approx. 90kgf / cm 2 The autoclave was pressurized until the pressure reached 0.01%. This pressure was maintained for 1.5 hours to carry out the first liquid phase substitution. After the first liquid phase substitution was completed, the supply of liquefied carbon dioxide gas was stopped. The autoclave was then left to stand for 17.5 hours while remaining sealed, allowing the liquefied carbon dioxide gas to diffuse into the gel.

[0101] Next, the pressure inside the autoclave was increased to 882 N / cm using liquefied carbon dioxide. 2 (approx. 90kgf / cm 2 The autoclave was pressurized again until the pressure reached 0.05%. This pressure was maintained for 1 hour to carry out a second liquid phase substitution. After the second liquid phase substitution was completed, the supply of liquefied carbon dioxide gas was stopped. The autoclave was then left to stand for 5 hours while remaining sealed, allowing the liquefied carbon dioxide gas to diffuse into the gel.

[0102] Next, the pressure inside the autoclave was increased to 882 N / cm using liquefied carbon dioxide. 2 (approx. 90kgf / cm 2 The autoclave was pressurized again until the pressure reached 80°C. This pressure was maintained for 0.75 hours to carry out the third liquid phase substitution. After the third liquid phase substitution was completed, the supply of liquefied carbon dioxide was stopped. Then, while keeping the autoclave sealed, the temperature inside the autoclave was raised from room temperature to 80°C over 1.5 hours.

[0103] After the temperature inside the autoclave reached 80°C, the resistance was 4.9N / (cm 2 ·min)(0.5kgf / (cm 2 The pressure inside the autoclave was reduced to atmospheric pressure at a rate of 0.5 sq. min. After the pressure inside the autoclave reached atmospheric pressure, the autoclave was cooled to room temperature over 2 hours.

[0104] The heat insulating sheet of Experimental Example 1 was obtained by the above method. The thickness of the heat insulating sheet of Experimental Example 1 was 3 mm. Of the surfaces in the thickness direction of the heat insulating sheet of Experimental Example 1, the surface roughness of the surface not in contact with the film was greater than the surface roughness of the surface in contact with the film. Therefore, in the heat insulating sheet of this example, the surface not in contact with the film becomes the first surface, and the surface in contact with the film becomes the second surface.

[0105] (Experimental Examples 2 to 8) The methods for producing the heat insulating sheets of these experimental examples were generally the same as the method for producing the heat insulating sheet of experimental example 1, except that the particle size distribution of the silicon carbide particles was changed.

[0106] (Ratio of first particle to third particle) Tables 1 and 2 show the ratios of the numbers of first particles, second particles, and third particles present in the photographs of the cross sections of the heat insulating sheets of Experimental Examples 1 to 8. Note that the "third particles" in Tables 1 and 2 are particles having a major axis of more than 1 μm and less than 5 μm in the photographs. The method for measuring the major axis of each particle and the method for calculating the ratio of the number of each particle are as described above.

[0107] (Evaluation of powder shedding prevention effect) The insulation sheet was cut into small square pieces with sides of 5 cm. Both sides of this small piece were covered with 50 μm-thick PET film, and then one of the PET films was bonded to a rubber sheet to create a sample. The rubber sheet had a structure consisting of multiple connected protrusion units (in cross section, each unit consisted of a protrusion with a base width of 10.86 mm, a height of approximately 7 mm, and a 60° taper extending widthwise, surrounded by a recess; the total width including the recess and protrusion was approximately 20.5 mm), and the recess of the protrusion unit was positioned so that it faced the film.

[0108] Next, the sample was attached to a jig of a vibrator. The jig had a pair of metal plates and a powder receiver. The sample was placed upright between the metal plates so that the surface of the heat insulating sheet in the thickness direction was approximately vertical, and then the sample was fixed in place while applying pressure so that it was compressed by 50%.

[0109] After attaching the sample to the jig in this way, a vibration test was conducted in which the sample was subjected to 800,000 vibrations at an acceleration of 3G and a frequency of 5Hz. After the vibration test was completed, the rubber sheet was removed from the sample. The film was then peeled off from the surface of the insulation sheet, and the powder that had fallen from the insulation sheet was collected.

[0110] Next, the mass ratio of silicon carbide particles contained in the powder that fell from the heat insulating sheet was calculated using the following method. First, predetermined masses of silica aerogel, silicon carbide particles, and a mixture of silica aerogel and silicon carbide particles in a mass ratio of 1:1 were prepared, and their volumes were measured. Next, the volumes of the silica aerogel, silicon carbide particles, and the mixture thereof were plotted on a graph with the mass ratio of silicon carbide particles on the vertical axis and volume on the horizontal axis. A calibration curve was then created by approximating these three plotted points with a straight line.

[0111] Next, a sample with the same mass as the silica aerogel used to prepare the calibration curve was taken from the powder that had fallen from the heat insulating sheet, and the volume of the sample was measured.Then, based on the calibration curve, the sample volume was converted into the mass ratio of silicon carbide particles in the sample.

[0112] The powder shedding suppression effect was evaluated based on the mass ratio of silicon carbide particles in the sample obtained as described above. In the "Powder shedding suppression effect" column of Tables 1 and 2, the mass ratio of silicon carbide particles in Experimental Example 6 was used as the reference, and the symbol "A" was entered when the mass ratio of silicon carbide particles was 1 / 5 or less, the symbol "B" was entered when it was more than 1 / 5 and 1 / 4 or less, the symbol "C" was entered when it was more than 1 / 4 and 1 / 3 or less, the symbol "D" was entered when it was more than 1 / 3 and 1 / 2 or less, and the symbol "E" was entered when it was more than 1 / 2. Note that the symbol "-" was entered in the "Powder shedding suppression effect" column of Experimental Example 6, which was the reference.

[0113] [Table 1]

[0114] [Table 2]

[0115] As shown in Table 1, the cross-sectional photographs of the heat insulating sheets of Experimental Examples 1 to 5 show both first particles made of infrared-shielding particles with a major axis of 0.5 μm or more and 1 μm or less, and second particles made of infrared-shielding particles with a major axis of 5 μm or more and 10 μm or less. Therefore, these heat insulating sheets were able to suppress powder shedding more than the heat insulating sheet of Experimental Example 6 (see Table 2), which did not contain second particles. Furthermore, the heat insulating sheets of Experimental Examples 1 to 5 are less prone to powder shedding than the heat insulating sheet of Experimental Example 6, and therefore can maintain the state in which the infrared-shielding particles are retained within the heat insulating sheet for a long period of time. Therefore, the heat insulating sheets of Experimental Examples 1 to 5 can maintain good heat insulating performance for a long period of time.

[0116] On the other hand, as shown in Table 2, the heat insulating sheet of Experimental Example 7 does not contain secondary particles, just like Experimental Example 6. Therefore, the heat insulating sheet of Experimental Example 7 was prone to powder falling, just like the heat insulating sheet of Experimental Example 6.

[0117] The heat insulating sheet of Experimental Example 8 did not contain primary particles. Therefore, the heat insulating sheet of Experimental Example 8 was more susceptible to powder shedding than the heat insulating sheets of Experimental Examples 1 to 5. On the other hand, a comparison of Experimental Examples 6 to 7 with Experimental Example 8 shows that the heat insulating sheet of Experimental Example 8 was able to suppress powder shedding more than Experimental Examples 6 to 7. This may be because, for example, the second particles, which have a relatively large particle size, are easily captured by the fibers even when they fall off the silica aerogel, and are easily retained inside the heat insulating sheet.

[0118] The above describes aspects of the insulation sheet and its manufacturing method based on experimental examples, but the specific aspects of the insulation sheet and its manufacturing method according to the present invention are not limited to the aspects of the experimental examples, and the configuration can be changed as appropriate within the scope that does not detract from the spirit of the present invention.

[0119] For example, the heat insulating sheet can take the following aspects (1-1) to (1-8).

[0120] [1-1] A heat insulating sheet used for insulating between battery cells of an electric vehicle, Silica aerogel, Fiber and Infrared shielding particles, A thermal insulation sheet, in which a photograph of a cross section of the thermal insulation sheet shows first particles made of infrared-shielding particles having a major axis of 0.5 μm or more and 1 μm or less, and second particles made of infrared-shielding particles having a major axis of 5 μm or more and 10 μm or less.

[0121] [1-2] The heat insulating sheet according to [1-1], wherein the ratio of the number of the first particles to the number of the second particles present in the photograph is first particles:second particles = 1:4 to 4:1. [1-3] The heat insulating sheet according to [1-1] or [1-2], wherein in the photograph, the sum of the ratio of the number of the first particles to the number of the second particles among the infrared shielding particles having a major axis of 0.5 μm or more is 5% or more and 30% or less.

[0122] [1-4] The insulating sheet between battery cells for an electric vehicle according to any one of [1-1] to [1-3], wherein in the photograph, the number of the infrared-shielding particles present within a range of 13 μm from the surface of the fiber is greater than the number of the infrared-shielding particles present outside the range. [1-5] A heat insulating sheet according to any one of [1-1] to [1-4], in which 70% or more of the first particles and the second particles in the photograph are present within a range of 13 μm from the surface of the fiber.

[0123] [1-6] A heat insulating sheet according to any one of [1-1] to [1-5], wherein the average diameter of the fibers in the photograph is 0.6 to 2 times the average major axis of the secondary particles. [1-7] The heat insulating sheet according to any one of [1-1] to [1-6], wherein the silica aerogel fills the gaps between the fibers, and the infrared shielding particles are dispersed in the silica aerogel. [1-8] The heat insulating sheet according to any one of [1-1] to [1-7], wherein the infrared shielding particles include silicon carbide particles.

[0124] The method for manufacturing the heat insulating sheet may also take the following aspects [1-9]. [1-9] A method for producing a heat insulating sheet according to any one of [1-1] to [1-8], preparing a fabric made from the fibers; a silica sol containing silica fine particles, the infrared shielding particles, and a liquid dispersion medium for dispersing the particles is impregnated into the cloth to prepare a sheet precursor; The method for producing a heat insulating sheet includes removing the liquid dispersion medium from the sheet precursor to form the heat insulating sheet.

[0125] The heat insulating sheet may take the following aspects (2-1) to (2-7).

[0126] [2-1] A heat insulating sheet used for insulating between battery cells of an electric vehicle, Silica aerogel, Fiber and infrared shielding particles, A thermal insulation sheet, in which a photograph of a cross section of the thermal insulation sheet shows third particles made of infrared-shielding particles having a major axis greater than 1 μm and less than 5 μm, and second particles made of infrared-shielding particles having a major axis greater than 5 μm and less than 10 μm.

[0127] [2-2] An insulating sheet according to [2-1], wherein in the photograph, the proportion of the number of the secondary particles among the infrared-shielding particles having a major axis of 0.5 μm or more is 5% or more and 30% or less. [2-3] An insulating sheet between battery cells for an electric vehicle according to [2-1] or [2-2], wherein in the photograph, the number of the infrared-shielding particles present within a range of 13 μm from the surface of the fiber is greater than the number of the infrared-shielding particles present outside the range. [2-4] An insulating sheet according to any one of [2-1] to [2-3], in which 70% or more of the second particles and the third particles in the photograph are present within a range of 13 μm from the surface of the fiber.

[0128] [2-5] A heat insulating sheet according to any one of [2-1] to [2-4], wherein the average diameter of the fibers in the photograph is 0.6 to 2 times the average major axis of the secondary particles. [2-6] The heat insulating sheet according to any one of [2-1] to [2-5], wherein the silica aerogel fills the gaps between the fibers, and the infrared shielding particles are dispersed in the silica aerogel. [2-7] The heat insulating sheet according to any one of [2-1] to [2-6], wherein the infrared shielding particles include silicon carbide particles.

Claims

1. A heat insulating sheet used for insulating between battery cells of an electric vehicle, Silica aerogel, Fiber and infrared shielding particles, a photograph of a cross section of the heat insulating sheet shows first particles made of infrared shielding particles having a major axis of 0.5 μm or more and 1 μm or less, and second particles made of infrared shielding particles having a major axis of 5 μm or more and 10 μm or less; a ratio of the number of the first particles to the number of the second particles present in the photograph (first particles:second particles) is 1:4 to 3:1; In the photograph, the sum of the ratio of the number of the first particles and the ratio of the number of the second particles to the number of the infrared shielding particles having a major axis of 0.5 μm or more and 10 μm or less is 20% or more and 30% or less.

2. 2. The insulating sheet for insulating between battery cells for an electric vehicle according to claim 1, wherein the average diameter of the fibers in the photograph is 0.6 to 2 times the average major axis of the secondary particles.

3. 2. The insulating sheet for insulating between battery cells for an electric vehicle according to claim 1, wherein the silica aerogel fills gaps between the fibers, and the infrared shielding particles are dispersed in the silica aerogel.

4. The electric vehicle battery inter-cell insulation sheet according to claim 1 , wherein the infrared shielding particles include silicon carbide particles.

5. A method for manufacturing an inter-cell insulating sheet for an electric vehicle battery according to any one of claims 1 to 4, comprising: preparing a sheet precursor in which the fibers are impregnated with a wet gel containing silica fine particles and infrared shielding particles dispersed in the gel; The method for producing an insulating sheet between battery cells for an electric vehicle includes drying the gel in the sheet precursor to form the insulating sheet.

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