Inorganic powder sheet and manufacturing method thereof

Abstract

Provided are an inorganic powder sheet that has small compressive deformation while maintaining high heat insulation and heat resistance, and a method for producing the same. The inorganic powder sheet includes, as inorganic powder, 80% by weight or more of vermiculite subjected to expansion treatment and 20% by weight or less of organic fiber, and has a heat insulating property. With the above features, an inorganic powder sheet is realized that has small compressive deformation while maintaining high heat insulation and heat resistance.

Description

Inorganic powder sheet and manufacturing method thereof

[0001] The present invention relates to an inorganic powder sheet and a method for producing the same.

[0002] Heat insulating sheets for insulating heat-generating bodies are used in a variety of applications. For example, in automotive or stationary power supply devices that stack multiple secondary battery cells, a large number of high-capacity secondary battery cells are often used due to the demand for higher output and higher capacity. In such power supply devices, there is a concern that one secondary battery cell may become too hot for some reason, causing thermal runaway and adversely affecting other adjacent secondary battery cells. For this reason, thermal insulation between adjacent secondary battery cells is required in the event of thermal runaway. In addition, high heat resistance and flame resistance are required. In light of these circumstances, attempts have been made to insulate secondary battery cells by interposing inorganic powder sheets between them.

[0003] However, secondary battery cells such as lithium-ion secondary batteries are constructed with current collectors inserted into hard aluminum exterior cans, and it is known that the exterior cans expand during rapid charging and discharging. As a result, there has been a problem in that the thermal diffusion sheet interposed between the expanded exterior cans is pressed under high pressure and becomes thin, resulting in a decrease in insulation performance. For this reason, there has been a demand for a thermal diffusion sheet with minimal volume change.

[0004] Japanese Patent Application Laid-Open No. 2020-187870

[0005] An object of the present invention is to provide an inorganic powder sheet that maintains high thermal insulation and heat resistance while undergoing little compression deformation, and a method for producing the same. Means for solving the problem and effects of the invention

[0006] The inorganic powder sheet according to a first embodiment of the present invention is an inorganic powder sheet having heat insulating properties, and contains, as inorganic powders, 80% by weight or more of expanded vermiculite and 20% by weight or less of organic fibers. With this configuration, an inorganic powder sheet is realized that maintains high heat insulating properties and heat resistance while exhibiting little compressive deformation.

[0007] Furthermore, in the inorganic powder sheet according to a second aspect of the present invention, in any one of the above aspects, the median diameter of the vermiculite is 20 μm to 70 μm.

[0008] Furthermore, in an inorganic powder sheet according to a third aspect of the present invention, in any one of the above aspects, the organic fiber contains one or more of para-aramid fiber, para-aramid pulp, meta-aramid pulp, polyphenylene sulfide fiber, PET fiber, flame-retardant PET fiber, flame-retardant rayon fiber, and natural cellulose fiber.

[0009] Furthermore, in the inorganic powder sheet according to a fourth aspect of the present invention, in any one of the above aspects, the inorganic powder sheet has a film thickness of 0.1 mm to 1.0 mm.

[0010] Furthermore, in any one of the above-mentioned embodiments, the inorganic powder sheet according to a fifth aspect of the present invention has a bending resistance of 15 mN or more and 50 mN or less, and a density of 1.00 g / cm 3 Above, 1.90g / cm 3 The above-described configuration makes it possible to realize an inorganic powder sheet that is easy to process by reducing resistance to bending while maintaining rigidity.

[0011] Furthermore, the inorganic powder sheet according to the sixth aspect of the present invention, in any of the above aspects, has a thermal conductivity of 0.3 W / m·K or less before compression, and a compression rate of 10% or less when compressed at 4 MPa.

[0012] Furthermore, the inorganic powder sheet according to the seventh embodiment of the present invention is an inorganic powder sheet having heat insulating properties, in which the thermal conductivity before compression is 0.3 W / m·K or less, and the compression rate when compressed at 4 MPa is 10% or less.

[0013] Furthermore, in any one of the above-mentioned inorganic powder sheets according to an eighth embodiment of the present invention, the bending resistance is 15 mN or more and 50 mN or less.

[0014] Furthermore, in the inorganic powder sheet according to a ninth aspect of the present invention, in any one of the above aspects, when the surface temperature of the inorganic powder sheet is set to 250° C. and compressed at 3 MPa, the back surface temperature of the inorganic powder sheet after 10 minutes is 240° C. or less. With the above configuration, it is possible to suppress a decrease in the heat insulating property of the inorganic powder sheet due to compression.

[0015] Furthermore, in the inorganic powder sheet according to a tenth aspect of the present invention, in any one of the above aspects, the median diameter in the cumulative distribution of particle size distribution measurement of the vermiculite is 20 μm to 70 μm.

[0016] Furthermore, an inorganic powder sheet laminate according to an eleventh embodiment of the present invention comprises at least one layer of the inorganic powder sheet according to any one of the above embodiments and a flame-retardant or flame-proof additional layer laminated thereon.

[0017] Furthermore, an inorganic powder sheet laminate according to a twelfth embodiment of the present invention comprises a sheet material serving as a base material, and an inorganic powder sheet according to any of the above embodiments laminated on at least one surface of the sheet material.

[0018] Furthermore, a method for producing an inorganic powder sheet according to a thirteenth embodiment of the present invention is a method for producing an inorganic powder sheet having heat insulating properties, and includes the steps of blending 80% by weight or more of expanded vermiculite and 20% by weight or less of organic fibers as inorganic powders, dispersing the mixture in water to form a slurry, and wet-laid papermaking the slurry, and thermally calendering the resulting sheet, thereby realizing an inorganic powder sheet that maintains high heat insulating properties and heat resistance while exhibiting little compressive deformation.

[0019] Furthermore, in the method for producing an inorganic powder sheet according to a fourteenth embodiment of the present invention, the median diameter in the cumulative distribution of particle size distribution measurement of the vermiculite is 20 μm to 70 μm.

[0020] Furthermore, in the method for producing an inorganic powder sheet according to a fifteenth embodiment of the present invention, in any one of the above, the organic fiber contains one or more of para-aramid fiber, para-aramid pulp, meta-aramid pulp, polyphenylene sulfide fiber, PET fiber, flame-retardant PET fiber, flame-retardant rayon fiber, and natural cellulose fiber.

[0021] Fig. 1 is an exploded perspective view showing a power supply device according to a first embodiment of the present invention; Fig. 2 is a schematic cross-sectional view showing a test for measuring the change in back surface temperature over time relative to a surface temperature of 250°C when compressed at 3 MPa; Fig. 3 is a schematic view showing a test before compression; Fig. 4 is a graph showing the change in back surface temperature over time relative to a surface temperature of 250°C when compressed at 3 MPa; Fig. 5 is a graph showing the change in back surface temperature over time without compression; Fig. 6 is a schematic cross-sectional view showing an example of an inorganic powder sheet laminate;

[0022] Embodiments of the present invention will be described below with reference to the drawings. However, the embodiments described below are merely examples for embodying the technical concept of the present invention, and the present invention is not limited thereto. Furthermore, this specification in no way specifies the components set forth in the claims as components of the embodiments. The dimensions, materials, shapes, and relative positions of components described in the embodiments are not intended to limit the scope of the present invention, and are merely illustrative unless otherwise specified. The size and relative positions of components shown in the drawings may be exaggerated for clarity. Furthermore, in the following description, the same names and symbols indicate identical or similar components, and detailed descriptions will be omitted as appropriate. Furthermore, the elements constituting the present invention may be configured with the same components, so that one component serves multiple functions, or conversely, the functions of one component may be shared by multiple components. [Embodiment 1]

[0023] The inorganic powder sheet according to the embodiment of the present invention can be used appropriately in applications requiring thermal insulation and preventing fire spread. For example, it is suitable for applications such as lithium-ion secondary batteries, where prevention of fire spread is required from a safety perspective when high temperatures are reached, such as during thermal runaway. Here, an example is described in which the inorganic powder sheet is used as a spacer interposed between adjacent secondary battery cells in a power supply device in which multiple rectangular secondary battery cells are stacked and connected in series or parallel. Such power supply devices are used as power sources for electric vehicles such as electric cars, hybrid cars, electric buses, trains, and electric carts, as backup power sources for factories and base stations, and even as home storage batteries. The inorganic powder sheet can be suitably used as an inorganic powder sheet sandwiched between objects that repeatedly expand and contract.

[0024] FIG. 1 shows an exploded perspective view of a power supply device according to a first embodiment. The power supply device 100 shown in this figure includes multiple secondary battery cells 20 and an inorganic powder sheet 10 interposed between the secondary battery cells 20. The secondary battery cells 20 have rectangular exterior cans 21 with a bottom, and multiple cells are stacked with their main surfaces facing each other. The stacking is performed, for example, by covering both end faces of a battery stack 25 formed by stacking the secondary battery cells 20 with end plates 30 and fastening the end plates 30 together with fastening members. The battery stack 25 is also fixed to a base plate 40 as needed. The base plate 40 can function as a cooling plate, for example, by circulating a refrigerant therethrough.

[0025] Each secondary battery cell 20 houses an electrode assembly inside an outer can 21, and the open end is sealed with a sealing plate 22. In FIG. 1 , the sealing plate 22, which is located on the top surface of the outer can 21, is provided with a pair of electrodes 23 and an explosion-proof valve 24. The multiple secondary battery cells 20 are electrically connected to each other in series and / or parallel by connecting the electrodes 23 to each other with bus bars. The explosion-proof valve 24 is a component that opens when it detects an increase in the internal pressure of the outer can 21 and discharges high-pressure gas from inside the outer can 21. Each explosion-proof valve 24 is connected to a gas duct for guiding high-pressure gas to the outside as necessary.

[0026] An inorganic powder sheet 10 is interposed between adjacent secondary battery cells 20. The inorganic powder sheet 10 is also called a spacer or separator, and provides insulation to prevent short-circuiting of the outer casings 21 between adjacent secondary battery cells 20. (Inorganic Powder Sheet 10)

[0027] The inorganic powder sheet has heat insulating and insulating properties. This inorganic powder sheet contains inorganic powder and organic fibers. Preferably, it contains 80% by weight or more of inorganic powder and 20% by weight or less of organic fibers. Expanded vermiculite can be used as the inorganic powder. Here, 80% by weight to 82.5% by weight of expanded vermiculite and 20% by weight to 17.5% by weight of organic fibers are blended. This composition achieves an inorganic powder sheet with low compressive deformation while maintaining high heat insulating and heat resistance. The vermiculite preferably has a volume average particle size of 1 μm to 500 μm, more preferably 1 to 200 μm. Furthermore, the particle size distribution of the vermiculite preferably has a median diameter of 20 μm to 70 μm in the cumulative distribution. The volume average particle size and median diameter can be measured using known devices, such as a laser diffraction particle size distribution analyzer. By setting the organic fiber content at or below the upper limit of the above range, the voids in the inorganic powder sheet are reduced and the density is increased, which tends to reduce compression deformation, and by setting the organic fiber content at or above the lower limit of the above range, powder falling off of the inorganic powder sheet tends to be reduced.

[0028] The organic fibers can be one or more of organic synthetic fibers such as para-aramid fiber, para-aramid pulp, meta-aramid pulp, polyphenylene sulfide fiber, PET fiber, flame-retardant PET fiber, and flame-retardant rayon fiber, or natural cellulose fibers such as wood (softwood or hardwood) pulp, cotton, and hemp. The form of the fibers is not limited, and they may be fibrillated. The Canadian Standard Freeness Method, JIS P 8121 (2012), can be suitably used to determine the degree of fiber fibrillation. The organic fiber content is preferably 0 to 20% by weight, more preferably 5 to 20% by weight. A content of the organic fiber below the upper limit of the above range tends to suppress deformation during compression and also suppress a decrease in heat resistance.

[0029] The inorganic powder sheet preferably has a thickness of 0.1 mm to 2.0 mm, more preferably 0.2 mm to 1.5 mm, and even more preferably 0.3 mm to 1.0 mm. By forming the inorganic powder sheet into a thin film, it can be used in a space-saving manner, and when used as a heat insulating sheet for a power supply device, for example, it is possible to avoid an increase in the size of the device when the inorganic powder sheet is interposed between multiple secondary battery cells and stacked.

[0030] Furthermore, the bending resistance of the inorganic powder sheet is preferably 50 mN or less, and more preferably 27 mN to 49 mN. If it is within the above range, the inorganic powder sheet tends to maintain its compression resistance and flexibility, resulting in excellent handleability.

[0031] Furthermore, the density of the inorganic powder sheet is 1.00 g / cm 3 It is preferable that the density is 1.30 g / cm or more. 3 By setting the density to the above-mentioned lower limit or more, characteristics of small compressive deformation can be obtained. There is no particular upper limit, but it is usually 1.90 g / cm 3 The following are the characteristics of the inorganic powder sheet. To achieve these properties, in the inorganic powder sheet manufacturing process, after the inorganic powder and organic fibers are made into a paper, heat and pressure processing may be performed using a hot calendar roll or the like. This allows the internal density to be adjusted to improve compression resistance. As a result, it is possible to realize an inorganic powder sheet that is easy to process by reducing resistance to bending while maintaining compression resistance. Furthermore, compared to thermal insulation sheets such as mica sheets, the flexibility of the inorganic powder sheet is high, allowing it to be wound into a roll, which makes it easy to manage, such as storage and transportation, as a roll, improving productivity and workability. Furthermore, its low specific gravity allows it to be lighter than thermal insulation sheets of the same area and thickness. For example, in automotive power supplies, weight reduction is strongly desired to improve fuel efficiency, and the inorganic powder sheet can be suitably applied to such applications.

[0032] Furthermore, the thermal conductivity of the inorganic powder sheet before compression is preferably 0.300 W / m K or less, more preferably 0.200 W / m K or less, and more preferably 0.145 W / m K to 0.149 W / m K. For example, the improved unsteady plane heat source method can be suitably used to measure thin film, low thermal conductivity materials as in the present invention.

[0033] On the other hand, the compression ratio when the inorganic powder sheet is compressed at 4 MPa is preferably 10% or less, more preferably 9% or less. There is no particular lower limit, but it is usually 0.1% or more. Preferably, it is 2.8 to 8.7%. As described above, the inorganic powder sheet according to this embodiment has a small displacement during compression, thereby realizing the advantage of being able to maintain its thermal insulation properties even in a compressed state. The compression conditions here are as follows: a universal material testing machine (manufactured by Instron) was used, and the sheet was pressed with a flat circular compression tool with a diameter of 50 mm at a rate of 0.1 mm / min until it reached 4 MPa.

[0034] In addition, when the inorganic powder sheet is compressed at 3 MPa by a heat press and one press plate is held at 250°C as the high-temperature side and the other press plate is held at 40°C as the low-temperature side, the surface temperature of the low-temperature side of the inorganic powder sheet after 10 minutes is preferably 240°C or less. Preferably, the temperature after 5 minutes is 192.4°C to 196.8°C, and the temperature after 10 minutes is 233.8°C to 235.7°C.

[0035] This makes it possible to suppress the deterioration of the heat insulating properties of the inorganic powder sheet due to compression. In particular, the powder sheet according to this embodiment has the excellent feature of being able to suppress the heat transmission during compression, despite having a higher thermal conductivity than a mica sheet.

[0036] Furthermore, the inorganic powder sheet may be formed as a single layer or may have a laminated structure of multiple layers. This allows for adding different properties. For example, an additional layer with flame retardancy or flame resistance may be added. Adding a material with excellent flame retardancy in this way can suppress the spread of fire at high temperatures. For example, the additional layer may be composed of inorganic fillers such as silicate minerals, metal oxides, and graphite, inorganic fibers such as glass fibers, organic fibers with excellent flame retardancy such as aramid, and organic fibers containing flame retardants. In this example, an additional sheet containing a blend of mica and organic fibers is used as the additional layer.

[0037] Furthermore, the inorganic powder sheet laminate may be constructed by laminating an inorganic powder sheet on at least one surface of a sheet material. Such an example is shown in the schematic cross-sectional view of Figure 6. The inorganic powder sheet laminate shown in this figure has a two-layer structure in which an inorganic powder sheet 10 is laminated on the upper surface of a sheet material 1. The inorganic powder sheet 10 is not limited to one layer, and two or more layers may be laminated. It may also be laminated on both surfaces of the sheet material 1.

[0038] The sheet material 1 serving as the substrate can be made of a flexible material or a highly rigid material. Flexible materials include elastic materials such as rubber, and sheet materials made of urethane sponge, etc. Highly rigid materials include hard resin plates, etc. Using such a substrate as the sheet material 1 can improve the heat insulating properties and heat resistance of the substrate. [Method for manufacturing an inorganic powder sheet]

[0039] Wet papermaking can be used to produce such inorganic powder sheets. For example, 80% by weight or more of expanded vermiculite and 20% by weight or less of organic fibers as inorganic powders are dispersed in water to form a papermaking slurry, which is then dehydrated and dried on a wire mesh to obtain a wet papermaking sheet. Known papermaking machines can be used, including Fourdrinier papermaking machines, cylinder papermaking machines, tilted short wire papermaking machines, and twin-wire papermaking machines. Furthermore, the density of the sheet can be adjusted, as needed, using equipment such as a wet press or touch press.

[0040] To increase the density of the wet-laid paper sheet, a further calendering process may be performed. In this case, the calendering process may be continuous with or independent from the wet-laid papermaking process. Known calendering devices can be used, such as metal rolls, resin rolls, rubber rolls, and double-belt presses. The calendering device may be heated to increase density and processing efficiency. Preferably, the calendering process is performed at a temperature below the melting point of the organic fiber to be blended. This achieves an inorganic powder sheet with minimal compression deformation while maintaining high thermal insulation and heat resistance. [Examples] (Example 1) 80% by weight of expanded vermiculite with a median diameter of 25 μm, 10% by weight of para-aramid pulp, and 10% by weight of softwood pulp were dispersed in water to form a papermaking slurry. The resulting papermaking slurry was wet-laid on a Fourdrinier papermaking machine to produce a paper with a basis weight of 170 g / m. 2 The obtained inorganic powder precursor sheets were stacked in three layers and subjected to thermal calendering by passing them between a pair of metal rolls at a roll temperature of 190°C and a nip pressure of 200 KPa / cm, thereby obtaining the inorganic powder sheet according to Example 1. (Example 2)

[0041] 82.5% by weight of expanded vermiculite with a median diameter of 58 μm, 8.75% by weight of para-aramid pulp, and 8.75% by weight of softwood pulp were dispersed in water to prepare a papermaking slurry. The obtained papermaking slurry was wet-formed on a Fourdrinier paper machine to produce a paper with a basis weight of 520 g / m. 2 The inorganic powder precursor sheet obtained was subjected to thermal calendering in the same manner as in Example 1, except that it was formed into a single layer, to obtain an inorganic powder sheet according to Example 2. (Example 3)

[0042] 90% by weight of natural mica with a median diameter of 27 μm and 10% by weight of para-aramid pulp were dispersed in water to prepare a papermaking slurry. The obtained papermaking slurry was wet-formed using a Fourdrinier paper machine to produce a paper with a basis weight of 210 g / m. 2 The obtained additional layer precursor sheet was laminated on both sides of the inorganic powder precursor sheet of Example 1 to form a three-layer structure, but the same thermal calendering process was carried out as in Example 1 to obtain an inorganic powder sheet according to Example 3. (Comparative Example 1)

[0043] As a comparative example, a commercially available mica sheet (WW-FMS-L) obtained from Wide Work Co., Ltd. was used. This mica sheet is said to contain mica and a few percent of silicone adhesive. The composition of the samples of each example and comparative example is as shown in Table 1. Measurements were also made on each of the obtained examples and comparative examples. (Basis weight)

[0044] The basis weights of the inorganic powder sheets according to Examples 1 to 3 and Comparative Example 1 were measured in accordance with JIS P 8124 (2011). (Thickness, Density)

[0045] The thickness and density of the inorganic powder sheets according to Examples 1 to 3 and Comparative Example 1 were measured in accordance with JIS P 8118 (2014). (Bending resistance)

[0046] The bending resistance of the inorganic powder sheets according to Examples 1 to 3 and Comparative Example 1 was measured in accordance with JIS L 1085 (1998) bending resistance test (Gurley method). The measurement was carried out using a Gurley type flexibility tester manufactured by Toyo Tester Kogyo Co., Ltd., with a support distance of 50 mm and a sample piece of 89 mm length and 25 mm width. (Thermal Conductivity)

[0047] The thermal conductivity of the inorganic powder sheets according to Examples 1 to 3 and Comparative Example 1 was measured using the improved unsteady plane heat source method in accordance with ASTM D7984-16. A thermal conductivity measuring device, TCi (Max-k) manufactured by C-Therm, was used. A 30 mm diameter circle was cut out of the inorganic powder sheet to serve as a sample. The sample sheet was placed on a sensor unit equipped with a built-in heater, and a 500 g weight was placed on the sample. Heating was initiated at a steady output in this state, and the change in sensor temperature over time was measured. The thermal effusivity and thermal conductivity were then measured using the following equation (1).

[0048]

[0049] The results are shown in Table 1.

[0050]

[0051] As shown in the table, it was confirmed that Examples 1 to 3 had lower bending resistance than Comparative Example 1. By increasing the flexibility in this way, an inorganic powder sheet can be obtained that is easy to form into a roll and has excellent portability and handling properties (4 MPa compression test).

[0052] Next, the volume change of the inorganic powder sheets according to each Example and Comparative Example when they were compressed under high pressure was measured. Specifically, the inorganic powder sheets were cut into 100 mm x 100 mm pieces to prepare sample sheets, and a universal testing machine (manufactured by Instron) was used to measure the compression length when the sheets were compressed at a rate of 0.1 mm / min with a flat circular compression tool having a diameter of 50 mm until a pressure of 4 MPa was reached. The compression length was calculated as a percentage of the sheet thickness before the test, and the 4 MPa compression rate was calculated (250°C heat compression test).

[0053] In addition, the time change in the back surface temperature relative to the surface temperature of 250°C was measured when the inorganic powder sheet according to each example and comparative example was compressed using a press. Here, the inorganic powder sheet was cut to 180 mm x 120 mm to form a sample sheet SS. As shown in the schematic cross-sectional view of FIG. 2, two stainless steel plates 12, each 10 mm thick and 180 mm x 120 mm in size, were placed between a first heat press plate 11 and a second heat press plate 16, each 300 mm x 300 mm in size. The sample sheet SS was sandwiched between them. Ten sheets of kraft paper 13 were laminated on the underside of the stainless steel plate 12 for the purposes of heat insulation and pressure homogenization. A thermocouple 15 was attached with aluminum tape to the surface of the stainless steel plate 12 where it contacted the kraft paper 13. Additionally, the temperature of the first heat press plate 11 was set to 250°C, and the temperature of the second heat press plate 16 was set to 40°C, and the entire apparatus was covered with glass fiber insulation. The pressure applied to the sample sheet was divided into two cases: 760 Pa and 3 MPa, and measurements were carried out using new sample sheets in each case.

[0054] The heat insulating performance was evaluated based on the temperature measured 5 and 10 minutes after the start of compression heating in the heat press. Blank measurements were also performed under each pressure condition without sandwiching the sample sheet between the stainless steel plates (350°C compression test).

[0055] Furthermore, the time change in the back surface temperature of the inorganic powder sheets according to Example 2 and Comparative Example 1 relative to a surface temperature of 350°C was measured. This was done using the test apparatus shown in Figure 3. To heat the sample on a hot plate, a laminate consisting of a 145 mm x 90 mm sample sheet SS sandwiched between 10 mm thick, 180 mm x 120 mm aluminum plates 17 was placed on top of a 250 mm x 150 mm hot plate 18. The hot plate 18 was heated to 350°C. A thermocouple 15 was placed on the top surface of the laminate, a glass needle mat 19 was placed on top of it for thermal insulation, and a 1.3 kg weight WT was placed on top. The pressure on the sample sheet was calculated to be 1.5 KPa.

[0056] The heat insulating performance was evaluated by placing the laminate on a hot plate stabilized at 350°C and measuring the temperature 5 and 10 minutes after heating. A blank measurement was also performed using a laminate without the sample sheet sandwiched between the aluminum plates. The results are shown in Table 2.

[0057]

[0058] As described above, it was confirmed that the inorganic powder sheets according to Examples 1 to 3 all had a lower 4 MPa compressibility than Comparative Example 1, despite having a lower bending resistance. As described above, the present invention has the advantage that it can be easily rolled or attached to a curved surface, and has small compressive deformation, compared to the Comparative Example.

[0059] In Table 2, when the insulation performance is ranked in descending order, the temperatures after 5 and 10 minutes for Comparative Example 1 are the lowest when the load is 760 Pa, but when the load is 3.0 MPa, the temperatures for Examples 1 to 3 are lower than those for Comparative Example 1. Thus, it was confirmed that the present invention is lighter than the comparative examples and can prevent a decrease in insulation performance due to compression.

[0060] Furthermore, Table 2 confirms that the inorganic powder sheet of Example 2 has higher heat insulating performance than Comparative Example 1, since the temperature after 5 minutes and 10 minutes of heating was lower in the 350°C heat insulating test.

[0061] 4 shows the change in the back surface temperature over time relative to the surface temperature of 250°C when compressed at 3 MPa. Comparing Examples 1 and 3, the initial rise in the back surface temperature of vermiculite was faster than that of mica, but the temperature reversed after about four minutes, confirming that vermiculite had higher heat insulating performance.

[0062] Furthermore, the results of measuring the back surface temperature in a 350°C insulation test are shown in Figure 5. Comparing Example 2 with Comparative Example 1, it was confirmed that Example 2 had better insulation performance than Comparative Example 1, since the temperature was lower than Comparative Example 1 after 2 minutes.

[0063] The inorganic powder sheet of the present invention can be used as a heat insulating sheet sandwiched between objects that repeatedly expand and contract. For example, it can be used as a heat insulating spacer interposed between secondary battery cells or secondary battery cell modules, a buffer sheet interposed between explosion-proof valves and gas ducts, or a heat insulating material for protecting drive circuits such as ECUs. It can also be used in construction applications as a heat insulating material to prevent fires from spreading, a heat-resistant material, and other building materials.

[0064] REFERENCE SIGNS LIST 1...Sheet material 10...Inorganic powder sheet 11...First heat-pressed plate 12...Stainless steel plate 13...Kraft paper 15...Thermocouple 16...Second heat-pressed plate 17...Aluminum plate 18...Hot plate 19...Glass needle mat 20...Secondary battery cell 21...Outer can 22...Sealing plate 23...Electrode 24...Explosion-proof valve 25...Battery stack 30...End plate 40...Base plate 100...Power supply device SS...Sample sheet WT...Weight

Claims

1. An inorganic powder sheet having heat insulating properties, As an inorganic powder, expanded vermiculite is 80% by weight or more, Organic fibers are 20% or less by weight. Including, The inorganic powder sheet has a thickness of 0.3 mm to 0.4 mm; The thermal conductivity before compression is 0.15 W / m K or less, The compression rate when compressed at 4 MPa is 10% or less, The inorganic powder sheet has a surface temperature of 250° C. and a back surface temperature of 240° C. or lower after 10 minutes when the inorganic powder sheet is compressed at 3 MPa.

2. The inorganic powder sheet according to claim 1, The inorganic powder sheet, wherein the median diameter of the vermiculite is 20 μm to 70 μm.

3. The inorganic powder sheet according to claim 1 or 2, The inorganic powder sheet, wherein the organic fibers include at least one of para-aramid fibers, para-aramid pulp, meta-aramid pulp, polyphenylene sulfide fibers, PET fibers, flame-retardant PET fibers, flame-retardant rayon fibers, and natural cellulose fibers.

4. The inorganic powder sheet according to any one of claims 1 to 3, The bending resistance is 15 mN or more and 50 mN or less, Density: 1.00 g / cm 3 Above, 1.90g / cm 3 The inorganic powder sheet is shown below.

5. The inorganic powder sheet according to claim 4, An inorganic powder sheet having a bending resistance of 15 mN or more and 50 mN or less.

6. The inorganic powder sheet according to any one of claims 1 to 5, The inorganic powder sheet has a median diameter of 20 μm to 70 μm in cumulative distribution of particle size distribution measurement of the vermiculite.

7. At least one layer of the inorganic powder sheet according to any one of claims 1 to 6, An inorganic powder sheet laminate comprising a flame-retardant or flame-resistant additional layer.

8. A sheet material serving as a base material; An inorganic powder sheet laminate comprising the inorganic powder sheet according to any one of claims 1 to 6 laminated on at least one surface of the sheet material.

9. A method for producing an inorganic powder sheet having heat insulating properties, comprising: A process of blending 80% by weight or more of expanded vermiculite and 20% by weight or less of organic fiber as inorganic powders, dispersing the mixture in water to form a slurry, and wet-laid papermaking the slurry; The paper is made into sheets and then heat-calendered. The inorganic powder sheet has a thickness of 0.3 mm to 0.4 mm; The thermal conductivity before compression is 0.15 W / m K or less, The compression rate when compressed at 4 MPa is 10% or less, obtaining an inorganic powder sheet having a back surface temperature of 240° C. or less after 10 minutes when the inorganic powder sheet is compressed at 3 MPa with a surface temperature of 250° C.; A method for producing an inorganic powder sheet comprising the steps of:

10. A method for producing an inorganic powder sheet according to claim 9, The method for producing an inorganic powder sheet, wherein the vermiculite has a median diameter of 20 μm to 70 μm in cumulative distribution of particle size distribution measurement.

11. A method for producing an inorganic powder sheet according to claim 9 or 10, The method for producing an inorganic powder sheet, wherein the organic fibers include at least one of para-aramid fibers, para-aramid pulp, meta-aramid pulp, polyphenylene sulfide fibers, PET fibers, flame-retardant PET fibers, flame-retardant rayon fibers, and natural cellulose fibers.