Flame-spread preventive sheet, method for producing same, and battery

Abstract

To provide a flame-spread preventive sheet which can accommodate variations in pressure across the thickness direction of the sheet using a single material, and can retain its thickness even after exposure to high pressure, a method for producing the flame-spread preventive sheet, and a battery.SOLUTION: The present invention relates to a flame-spread preventive sheet 1, a method for producing the same, and a battery, wherein the flame-spread preventive sheet 1 is disposed at least between a plurality of heat sources, and can prevent flame spread by suppressing heat transfer to other heat sources when one heat source is overheated. The flame-spread preventive sheet 1 comprises: a first rubber sheet 2 and a second rubber sheet 3 laminated together. The first rubber sheet 2 is a porous sheet, and the second rubber sheet 3 is a solid sheet.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a fire prevention sheet, a manufacturing method thereof, and a battery. [Background technology]

[0002] Currently, there is a growing movement around the world to gradually replace conventional gasoline or diesel vehicles with electric vehicles in order to reduce the burden on the global environment. Electric vehicles are becoming more and more popular, particularly in European countries such as France, the Netherlands, and Germany, as well as in China. The widespread use of electric vehicles requires high-performance batteries.

[0003] Some batteries may go into thermal runaway during discharge or charging, causing fires, smoke, etc. In recent years, automobile batteries in which multiple battery cells are arranged and mounted in a housing are known. In such a battery in which multiple battery cells are arranged and mounted, if one battery cell ignites or emits smoke, etc., there is a risk that the heat will be transferred to the surrounding battery cells, causing further malfunctions such as fires, smoke, and explosions. In order to minimize damage caused by such malfunctions, methods have been considered that make it difficult for the heat of an abnormally hot battery cell to be transferred to the surrounding battery cells. For example, a method is known in which a fire-prevention sheet such as a fire-resistant material or a heat insulating layer is provided between multiple battery cells (see Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2018-206604 A Summary of the Invention [Problem to be solved by the invention]

[0005] The container of the battery cell (also simply called "cell") that constitutes the battery expands when it is overheated during discharge and / or charging. For this reason, a ceramic sheet with high hardness, even if it has excellent fire resistance, is not suitable for preventing fire spread between cells. In general, when a resin cushion is compressed, the compression stress depends on the hardness of the cushion. The conventionally known fire spread prevention member disclosed in Patent Document 1 is a single-layer fireproof material formed from a urethane resin composition. For this reason, the compression stress depends on the hardness of the fireproof material. Therefore, the above fire spread prevention member can withstand use when the pressure between the cells is constant, but is not suitable for use when the pressure between the cells fluctuates. For example, when a sheet with low hardness and easy crushing is used, it is crushed too thin under high pressure, and sufficient thickness cannot be secured. On the other hand, when a sheet with high hardness and not easy crushing is used, it is hardly crushed under low pressure, and it is difficult to make the cells adhere to each other. A method of using a sheet in which different materials with different hardness are laminated can be considered, but there is a problem that the manufacturing process becomes complicated and the cost increases. Resolving these challenges will also contribute to achieving the Applicant's Sustainable Development Goal of "ensuring access to affordable, reliable, sustainable and modern energy for all".

[0006] The present invention has been made to solve such problems, and aims to provide a fire spread prevention sheet made of a single material that can also withstand fluctuations in pressure applied in the thickness direction of the sheet, a manufacturing method thereof, and a battery. [Means for solving the problem]

[0007] (1) In order to achieve the above object, a fire spread prevention sheet according to one embodiment is a fire spread prevention sheet that is disposed at least between a plurality of heat sources and is capable of preventing the spread of fire by suppressing heat transfer to the other heat sources when the heat source is in an overheated state, A first rubber sheet; A second rubber sheet; The above are laminated. The first rubber sheet is a porous sheet, The second rubber sheet is a solid sheet. (2) In the fire spread prevention sheet according to another embodiment, the first rubber sheet may preferably have a thickness equal to or greater than the thickness of the second rubber sheet. (3) In the fire spread prevention sheet according to another embodiment, preferably, the ratio of the thickness of the first rubber sheet to the thickness of the second rubber sheet may be 70:30 to 50:50. (4) In the fire spread prevention sheet according to another embodiment, the first rubber sheet and the second rubber sheet may preferably be silicone rubber sheets. (5) A method for producing a fire prevention sheet according to one embodiment for achieving the above object is a method for producing any one of the fire prevention sheets described above, a first vulcanization step of vulcanizing the first curable rubber sheet in an uncured state of the first rubber sheet; a second vulcanization step of vulcanizing the second curable rubber sheet in an uncured state of the second rubber sheet; a post-cure lamination step of laminating the first rubber sheet and the second rubber sheet; Includes. (6) A method for producing a fire prevention sheet according to one embodiment for achieving the above object is a method for producing any one of the fire prevention sheets described above, a pre-cure lamination step of laminating a first curable rubber sheet in a pre-cure state of the first rubber sheet and a second curable rubber sheet in a pre-cure state of the second rubber sheet; a third vulcanization step of vulcanizing the laminated sheet that has been subjected to the pre-curing lamination step; Includes. (7) In the method for producing a fire spread prevention sheet according to another embodiment, the pre-curing lamination step may be preferably performed by calendar molding. (8) In order to achieve the above object, a battery according to one embodiment includes a housing and a plurality of battery cells. Any of the fire spread prevention sheets described above is provided at least between the battery cells, among between the battery cells and between the battery cells and the housing. Effect of the Invention

[0008] According to the present invention, it is possible to provide a fire spread prevention sheet made of a single material that can also withstand fluctuations in pressure applied in the thickness direction of the sheet, a manufacturing method thereof, and a battery. [Brief description of the drawings]

[0009] [Figure 1] FIG. 1 shows a perspective view of a fire spread prevention sheet according to a first embodiment and an enlarged view of a part A of a side surface thereof. [Diagram 2] FIG. 2 shows a vertical cross-sectional view of the battery according to the first embodiment and an enlarged view of one fire spread prevention sheet sandwiched between battery cells in the vertical cross-sectional view. [Diagram 3] Figure 3 shows the change in thickness when stress is applied in the thickness direction to a solid sheet (thickness: 1.73 mm), a sponge sheet (thickness: 3.04 mm), and a fire prevention sheet (thickness: 4.77 mm) made by bonding a solid sheet and a sponge sheet. (3A) shows the curves when the thickness of each sheet is taken as the starting point. (3B) shows the curves when it is assumed that the thickness of each sheet is the same as the thickness of the fire prevention sheet. [Figure 4] Figure 4 shows a cross-sectional view (4A) of a fire spread prevention sheet common to the second and third embodiments, in which the thickness of the sponge sheet (A):the thickness of the solid sheet (B) = 6:4, a curve (4B) showing the stress-thickness relationship of the fire spread prevention sheet of the second embodiment in which the hardness of the solid sheet is relatively high, and a curve (4C) showing the stress-thickness relationship of the fire spread prevention sheet of the third embodiment in which the hardness of the solid sheet is relatively low compared to the second embodiment. [Diagram 5]FIG. 5 shows a cross-sectional view (5A) of a fire spread prevention sheet according to a fourth embodiment, in which a first rubber sheet and a second rubber sheet of the same quality as the fire spread prevention sheet according to the third embodiment are laminated using the same manufacturing method as the third embodiment, and the thickness ratio of the two sheets is changed from 6:4 to 5.6:4.4, making the thickness of the first rubber sheet slightly thinner than in the third embodiment, and a curve (5B) showing the relationship between stress and thickness of the fire spread prevention sheet. [Figure 6] FIG. 6 shows a cross-sectional view (6A) of a fire spread prevention sheet according to a fifth embodiment, in which a first rubber sheet and a second rubber sheet of the same quality as the fire spread prevention sheet according to the fourth embodiment are laminated using the same manufacturing method as the fourth embodiment, and the thickness ratio of the two sheets is changed from 5.6:4.4 to 6.3:3.7, thereby increasing the thickness of the first rubber sheet compared to the fourth embodiment, and a curve (6B) showing the relationship between stress and thickness of the fire spread prevention sheet. [Figure 7] FIG. 7 shows a cross-sectional view (7A) of the fire spread prevention sheet of the sixth embodiment, which is manufactured using a different manufacturing method from the fire spread prevention sheet of the fifth embodiment and has a thickness ratio of the first rubber sheet to the second rubber sheet of 6.4:3.6, a curve (7B) showing the relationship between stress and thickness of the fire spread prevention sheet, and a microscope photomicrograph (7C) of the cross-section of the fire spread prevention sheet. [Figure 8] FIG. 8 shows a cross-sectional view (8A) of a fire spread prevention sheet of the seventh embodiment, which is manufactured using a different manufacturing method than the fire spread prevention sheet of the sixth embodiment and has the same thickness ratio of the first rubber sheet to the second rubber sheet as the sixth embodiment, a curve (8B) showing the relationship between stress and thickness of the fire spread prevention sheet, and a microscope photomicrograph (8C) of a cross-section of the fire spread prevention sheet. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Next, each embodiment of the present invention will be described with reference to the drawings. Note that each embodiment described below does not limit the invention according to the claims, and all of the elements and combinations thereof described in each embodiment are not necessarily essential to the solution of the present invention.

[0011] First Embodiment FIG. 1 shows a perspective view of a fire spread prevention sheet according to a first embodiment and an enlarged view of a part A of a side surface thereof.

[0012] The fire spread prevention sheet 1 according to this embodiment is a sheet that is disposed at least between multiple heat sources, and when some of the multiple heat sources are in an overheated state, can prevent the spread of fire by suppressing heat transfer from the some heat sources to the other heat sources. Here, the "heat source" is, for example, a battery cell disposed inside a battery for an automobile, a battery used for something other than an automobile, or a battery cell disposed inside the battery. However, the "heat source" also includes, in addition to a battery or battery cell, for example, a heater or a component thereof, and a component in an electric device or electronic device (such as a circuit board or a component on a circuit).

[0013] The fire spread prevention sheet 1 is formed by laminating a first rubber sheet 2 and a second rubber sheet 3. The first rubber sheet 2 is a porous sheet. The second rubber sheet 3 is a solid sheet. Here, "solid" refers to a form having fewer holes compared to "porous". A solid sheet is not limited to a sheet without holes at all, and is broadly interpreted to include a sheet having a small number of holes, but refers to a sheet having an extremely small number of holes compared to a porous (also called foamed) sheet. The first rubber sheet 2 may be called a sponge sheet. The second rubber sheet 3 may be called a solid sheet or a non-sponge sheet.

[0014] The ratio of the thickness of the first rubber sheet 2 to the thickness of the second rubber sheet 3 is preferably first rubber sheet 2:second rubber sheet 3=85:15 to 15:85, and more preferably first rubber sheet 2:second rubber sheet 3=75:25 to 25:75. The thickness of the first rubber sheet 2 is even more preferably the same as or greater than the thickness of the second rubber sheet. A more preferable ratio of the thickness of the first rubber sheet 2 to the thickness of the second rubber sheet 3 is, for example, in the range of 70:30 to 50:50.

[0015] The total thickness of the fire spread prevention sheet 1 is not particularly limited, but is preferably 1 to 20 mm, and more preferably 2 to 8 mm. The thicknesses of the first rubber sheet 2 and the second rubber sheet 3 can be set, for example, within the following ranges. The thickness of the first rubber sheet 2 can be set in the range of 0.5 to 15 mm, and the thickness of the second rubber sheet 3 can be set in the range of 15 to 0.5 mm. In addition, the thickness of the first rubber sheet 2 can be set in the range of 1 to 6 mm, and the thickness of the second rubber sheet 3 can be set in the range of 1 to 6 mm.

[0016] The volume of the holes (also called "voids") 2a in the first rubber sheet 2 relative to the volume of the first rubber sheet 2 is preferably 30 / 100 to 97 / 100, and more preferably 40 / 100 to 90 / 100. The holes 2a contribute to the function of increasing the heat insulating property of the first rubber sheet 2, and also contribute to the function of facilitating elastic deformation of the first rubber sheet 2 when compressed and released.

[0017] The rubber constituting the first rubber sheet 2 and the second rubber sheet 3 is preferably configured to include a thermosetting elastomer such as silicone rubber, urethane rubber, isoprene rubber, ethylene propylene rubber, natural rubber, ethylene propylene diene rubber, nitrile rubber (NBR) or styrene butadiene rubber (SBR); a thermoplastic elastomer such as a urethane-based, ester-based, styrene-based, olefin-based, butadiene-based or fluorine-based elastomer, or a composite thereof. Of the rubbers, silicone rubber, which has a relatively high heat resistance, can be more preferably used. Therefore, the first rubber sheet 2 and the second rubber sheet 3 are preferably silicone rubber sheets.

[0018] FIG. 2 shows a vertical cross-sectional view of the battery according to the first embodiment and an enlarged view of one fire spread prevention sheet sandwiched between battery cells in the vertical cross-sectional view.

[0019] The battery 10 according to this embodiment is, for example, a battery for an electric vehicle, and includes a plurality of battery cells (also simply referred to as "cells") 20 arranged in a line. The number of battery cells 20 is eight in this embodiment, but may be two to seven or nine or more. The battery 10 is a storage battery, and is preferably a lithium-ion battery. The battery 10 includes a bottomed housing 11 that opens on one side. The battery cells 20 are arranged inside 12 of the housing 11. The battery cells 20 are preferably in close contact with each other in the housing 11 by applying a force in a compressive direction from both sides of the housing 11 using a screw or the like (not shown). The bottom of the housing 11 is provided with a through hole 13 for flowing cooling water, which is an example of a coolant. The coolant may be referred to as a cooling medium or a coolant. The battery cells 20 are arranged in the housing 11 with a fire spread prevention sheet 1 sandwiched between adjacent battery cells 20.

[0020] As described above, the battery 10 according to the first embodiment includes a plurality of battery cells 20 in the housing 11, and includes the fire spread prevention sheet 1 at least between the battery cells 20, among between the battery cells 20 and between the battery cells 20 and the housing 11. The fire spread prevention sheet 1 does not have to be disposed between the battery cells 20 and the housing 11.

[0021] The fire spread prevention sheet 1 arranged between the battery cells 20 is a sheet having a form in which a first rubber sheet 2 and a second rubber sheet 3 are laminated in the thickness direction. The fire spread prevention sheet 1 is compressed between the battery cells 20 and compressed, and even if the situation in which the compression is released thereafter is repeated many times, it elastically deforms in the thickness direction and is likely to recover to its original thickness. In addition, the fire spread prevention sheet 1 is compressed in the thickness direction at the stage where it is stored in the housing 11 in a compressed state between the battery cells 20, and is further compressed at the stage where the battery cells 20 heat and expand during charging and / or discharging of the battery 10 thereafter. The fire spread prevention sheet 1 has a function of reducing heat transfer from the overheated battery cells 20 to the adjacent battery cells 20 when some of the battery cells 20 are overheated, thereby preventing the spread of fire, and preferably has a function of easily deforming against multiple stages of compression in the battery 10 and maintaining adhesion with the battery cells 20.

[0022] Figure 3 shows the change in thickness when stress is applied in the thickness direction to a solid sheet (thickness: 1.73 mm), a sponge sheet (thickness: 3.04 mm), and a fire prevention sheet (thickness: 4.77 mm) made by bonding a solid sheet and a sponge sheet. (3A) shows the curves when the thickness of each sheet is taken as the starting point. (3B) shows the curves when it is assumed that the thickness of each sheet is the same as the thickness of the fire prevention sheet.

[0023] According to FIG. 3, in the low load region, the relatively soft sponge layer is compressed, so that the behavior of the sponge layer (= the layer of the first rubber sheet 2) is dominant in the fire spread prevention sheet 1 as a whole. In the high load region, when the sponge layer is completely compressed, the load curve rises sharply thereafter. In the high load region, the solid layer (= the layer of the second rubber sheet 3) is also compressed, so the load increases suddenly. Therefore, when compared at the same load, the fire spread prevention sheet 1 can ensure a thickness greater than that of a sponge alone. Since the fire spread prevention sheet 1 has a two-layer structure of a sponge layer and a solid layer, it can achieve effects that could not be achieved by a sponge alone or a solid alone, specifically, the following effects. One effect is that the adjacent battery cells do not come into contact even under high pressure, and a distance that can further suppress thermal chain reaction can be secured, while the load can be reduced by following the expansion and contraction movement of the adjacent heat source (battery cell, etc.) and a sudden rise in stress can be suppressed. The other effect is that by changing the ratio of hardness and thickness of the first rubber sheet 2 and the second rubber sheet 3, it is possible to control the thickness at a specified load and the stress at a specified thickness.

[0024] The fire spread prevention sheet 1 according to this embodiment can be obtained, for example, by the following manufacturing method. The manufacturing method includes a first vulcanization step of vulcanizing the first curable rubber sheet in an uncured state of the first rubber sheet 2, a second vulcanization step of vulcanizing the second curable rubber sheet in an uncured state of the second rubber sheet 3, and a post-cure lamination step of laminating the first rubber sheet 2 and the second rubber sheet 3 together.

[0025] The fire spread prevention sheet 1 according to this embodiment can also be obtained by, for example, the following manufacturing method. The manufacturing method includes a pre-cure lamination process of laminating a first curable rubber sheet in an uncured state of the first rubber sheet 2 and a second curable rubber sheet in an uncured state of the second rubber sheet 3, and a third vulcanization process of vulcanizing the laminated sheets that have been through the pre-cure lamination process.

[0026] Second and third embodiments Next, a second and third embodiment of the present invention will be described. In the second and subsequent embodiments, an example will be described in which the first rubber sheet 2 and the second rubber sheet 3 are both made of silicone rubber.

[0027] The structure of the battery is the same as that of the battery 10 in Fig. 2. Second and third embodiments of the fire spread prevention sheet 1 present between the battery cells 20 and, optionally, between the battery cells 20 and the inner wall of the housing 11 will be described below.

[0028] 4 shows a cross-sectional view (4A) of a fire spread prevention sheet common to the second and third embodiments, in which the thickness of the sponge sheet (A): the thickness of the solid sheet (B) = 6:4, a curve (4B) showing the stress-thickness relationship of the fire spread prevention sheet according to the second embodiment in which the hardness of the solid sheet is relatively high, and a curve (4C) showing the stress-thickness relationship of the fire spread prevention sheet according to the third embodiment in which the hardness of the solid sheet is relatively low compared to the second embodiment. (4B) and (4C) show curves measured with N=3.

[0029] In the fire spread prevention sheet 1 according to the second embodiment, the hardness of the second rubber sheet (=solid sheet) 3 is three times that of the first rubber sheet (=sponge sheet) 2. In the fire spread prevention sheet 1 according to the third embodiment, the hardness of the second rubber sheet (=solid sheet) 3 is minus 15.5% of the hardness of the solid sheet of the fire spread prevention sheet 1 according to the second embodiment. In both types of fire spread prevention sheets 1, the solid sheet and the sponge sheet are vulcanized individually and then laminated. That is, the manufacturing method of the fire spread prevention sheet according to the second embodiment and the third embodiment includes a first vulcanization step of vulcanizing the first curable rubber sheet in the pre-cured state of the first rubber sheet 2, a second vulcanization step of vulcanizing the second curable rubber sheet in the pre-cured state of the second rubber sheet 3, and a post-curing lamination step of laminating the first rubber sheet 2 and the second rubber sheet 3. A mixing roll was used to mold the solid sheet and the sponge sheet in the second embodiment and the third embodiment. In the present application, the hardness of each of the first rubber sheet 2 and the second rubber sheet 3 means the hardness based on JIS K 6253 and JIS K 7312.

[0030] The curve (4B) has a clear turning point where the stress changes suddenly. In the so-called low compression region before the turning point, it was found that the compression characteristics of the fire spread prevention sheet 1 according to the second embodiment depend on the compression characteristics of the sponge sheet. The position of the turning point is approximately equal to the thickness of the sponge sheet at which the sponge sheet is continuously crushed until there are almost no voids. For this reason, it is considered that the position of the turning point can be freely changed by controlling the thickness of the sponge sheet.

[0031] The curve (4C) is a curve in which the thickness gradually decreases as the stress increases, and the point at which the stress change becomes extreme is unclear. It was found that the high compression region after the point of change depends on the compression characteristics of the solid sheet, which has a higher hardness than the sponge sheet. As a result of using a relatively soft silicone rubber for the solid sheet, the fire spread prevention sheet 1 of the third embodiment has characteristics close to those of the sponge sheet alone. The stress-thickness curve is gradual, with an unclear point of change. It is believed that the behavior of the stress-thickness curve can be changed by changing the hardness of the solid sheet.

[0032] <Fourth embodiment> Next, a fourth embodiment of the present invention will be described.

[0033] The structure of the battery is the same as that of the battery 10 in Fig. 2. A fourth embodiment of the fire prevention sheet present between the battery cells 20 and, optionally, between the battery cells 20 and the inner wall of the housing 11 will be described below.

[0034] 5 shows a cross-sectional view (5A) of a fire spread prevention sheet according to a fourth embodiment, in which a first rubber sheet and a second rubber sheet of the same quality as the fire spread prevention sheet according to the third embodiment are laminated by the same manufacturing method as the third embodiment (using a mixing roll), and the thickness ratio of the two sheets is changed from 6:4 to 5.6:4.4, making the thickness of the first rubber sheet slightly thinner than that of the third embodiment, and shows a curve (5B) showing the relationship between the stress and thickness of the fire spread prevention sheet. (5B) shows a curve measured with N=3.

[0035] In the third embodiment, the change point was reached when the fire spread prevention sheet 1 was compressed by about 26% of its total thickness. In contrast, in the fourth embodiment, the change point was reached when the fire spread prevention sheet 1 was compressed by about 23% of its total thickness. This result shows that it is possible to advance the location of the change point by reducing the thickness ratio of the first rubber sheet 2.

[0036] <Fifth embodiment> Next, a fifth embodiment of the present invention will be described.

[0037] The structure of the battery is the same as that of the battery 10 in Fig. 2. A fifth embodiment of the fire prevention sheet present between the battery cells 20 and, optionally, between the battery cells 20 and the inner wall of the housing 11 will be described below.

[0038] 6 shows a cross-sectional view (6A) of a fire spread prevention sheet according to a fifth embodiment, in which a first rubber sheet and a second rubber sheet of the same quality as the fire spread prevention sheet according to the fourth embodiment are laminated by the same manufacturing method as the fourth embodiment (using a mixing roll), and the thickness ratio of the two sheets is changed from 5.6:4.4 to 6.3:3.7 to increase the thickness of the first rubber sheet compared to the fourth embodiment, and shows a curve (6B) showing the relationship between the stress and thickness of the fire spread prevention sheet. (6B) shows a curve measured with N=3.

[0039] In comparison with the fourth embodiment, the ratio of the sponge sheet was increased and the ratio of the solid sheet was decreased. As a result, in the fourth embodiment, the change point was reached when the total thickness was compressed by about 23%, whereas in the fifth embodiment, the change point was reached when the total thickness was compressed by about 28%. From this result, it was found that it is possible to delay the position of the change point by increasing the thickness ratio of the first rubber sheet 2.

[0040] Sixth embodiment Next, a sixth embodiment of the present invention will be described.

[0041] The structure of the battery is the same as that of the battery 10 in Fig. 2. A sixth embodiment of the fire prevention sheet present between the battery cells 20 and, optionally, between the battery cells 20 and the inner wall of the housing 11 will be described below.

[0042] 7 shows a cross-sectional view (7A) of a fire-spread prevention sheet according to the sixth embodiment, which is manufactured by a different manufacturing method from that of the fifth embodiment, and in which the ratio of the thickness of the first rubber sheet to the second rubber sheet is 6.4:3.6, a curve (7B) showing the relationship between the stress and thickness of the fire-spread prevention sheet, and a microscope photo (7C) of the cross-section of the fire-spread prevention sheet. (7B) shows the curve measured with N=2.

[0043] In this embodiment, unlike the fifth embodiment, a manufacturing method was performed in which the first rubber sheet 2 in a pre-vulcanized state and the second rubber sheet 3 in a pre-vulcanized state were laminated together and then vulcanized (using a mixing roll). That is, the manufacturing method of the fire spread prevention sheet according to the sixth embodiment includes a pre-cure lamination process in which the first curable rubber sheet in a pre-cure state of the first rubber sheet 2 and the second curable rubber sheet in a pre-cure state of the second rubber sheet 3 are laminated together, and a third vulcanization process in which the laminated sheet that has undergone the pre-cure lamination process is vulcanized. Due to this difference in manufacturing method, the fire spread prevention sheet 1 according to this embodiment does not have a skin layer (a thin rubber layer without voids) at the boundary between the first rubber sheet 2 and the second rubber sheet 3, which was seen in the fire spread prevention sheets 1 according to the first to fifth embodiments (see 7C). In addition, a more clear change point appeared in the stress-thickness curve (see 7B) of the fire spread prevention sheet 1 according to this embodiment compared to (6B). It is presumed that the structure with an unclear skin layer is related to the appearance of the change point. When the skin layer exists, the compression of the skin layer starts after the first rubber sheet 2 is compressed. Since the skin layer is very thin compared to the second rubber sheet 3, there is no sudden increase in pressure as when the second rubber sheet 3 is compressed. Then, when the compression of the second rubber sheet 3 starts, the pressure increases suddenly. The skin layer is positioned as a so-called buffer region that generates a change that is intermediate between the pressure change of the first rubber sheet 2 and the pressure change of the second rubber sheet 3. If such a situation is depicted as a curve of stress and thickness, the stress-thickness curve of the entire fire spread prevention sheet 1 will be a curve with an unclear change point. On the other hand, when the skin layer does not exist, the compression of the second rubber sheet 3 starts immediately after the compression of the first rubber sheet 2. For this reason, the difference in the crushability of both sheets 2 and 3 appears as a change point.

[0044] Even though the manufacturing method was changed as in this embodiment, the adhesion between the first rubber sheet 2 and the second rubber sheet 3 was sufficient. It was confirmed that both sheets 2 and 3 were completely integrated as the fire spread prevention sheet 1.

[0045] Seventh embodiment Next, a seventh embodiment of the present invention will be described.

[0046] The structure of the battery is the same as that of the battery 10 in Fig. 2. A seventh embodiment of a fire prevention sheet present between the battery cells 20 and, optionally, between the battery cells 20 and the inner wall of the housing 11 will be described below.

[0047] 8 shows a cross-sectional view (8A) of a fire spread prevention sheet according to a seventh embodiment, which is manufactured by a different manufacturing method from that of the fire spread prevention sheet according to the sixth embodiment, and in which the ratio of the thickness of the first rubber sheet to the second rubber sheet is the same as that of the sixth embodiment, a curve (8B) showing the relationship between the stress and thickness of the fire spread prevention sheet, and a microscope photo (8C) of the cross section of the fire spread prevention sheet. (8B) shows the curve measured with N=3.

[0048] The manufacturing method of this embodiment is a manufacturing method in which a sheet of the first rubber sheet 2 in a pre-vulcanization state and a sheet of the second rubber sheet 3 in a pre-vulcanization state are laminated together and then vulcanized, as in the sixth embodiment. However, unlike the molding method of the sixth embodiment in which a mixing roll is used, in this embodiment, a calendar molding method is adopted. That is, the manufacturing method of the fire spread prevention sheet according to the seventh embodiment includes a pre-cure lamination process in which a first curable rubber sheet in a pre-cure state of the first rubber sheet 2 and a second curable rubber sheet in a pre-cure state of the second rubber sheet 3 are laminated together, and a third vulcanization process in which the laminated sheet that has undergone the pre-cure lamination process is vulcanized, and the pre-cure lamination process is performed by calendar molding.

[0049] In the case of calendar molding, the process of separating and laminating becomes relatively high pressure compared to the manufacturing method of the sixth embodiment. As a result, air bubbles inside the first rubber sheet 2 escape to the outside and approach the second rubber sheet 3 (see 8C). Therefore, the low compression region where the behavior of a sponge sheet appears behaves similarly to that of a solid sheet. In other words, the pressure-thickness curve of the fire spread prevention sheet 1 is similar to that of a solid sheet alone (see 8B). When molding with a calendar roll, it is necessary to determine the composition of the materials of both sheets 2 and 3, taking into account that the voids in the sponge sheet are small or few. [Industrial Applicability]

[0050] INDUSTRIAL APPLICABILITY The present invention can be used in the field of preventing the spread of fire caused by an overheated state of a heat source. [Explanation of symbols]

[0051] 1 Fire prevention sheet, 2 First rubber sheet (porous sheet), 3 Second rubber sheet (solid sheet), 10 Battery, 11 Housing, 20 Battery cell (an example of a heat source).

Claims

1. A fire prevention sheet that is disposed at least between a plurality of heat sources and can prevent the spread of fire by suppressing heat transfer to other heat sources when the heat sources are in an overheated state, A first rubber sheet; A second rubber sheet; The above are laminated. The first rubber sheet is a porous sheet, A fire spread prevention sheet, characterized in that the second rubber sheet is a solid sheet.

2. 2. The fire spread prevention sheet according to claim 1, wherein the thickness of the first rubber sheet is equal to or greater than the thickness of the second rubber sheet.

3. 3. The fire spread prevention sheet according to claim 2, wherein a ratio of a thickness of the first rubber sheet to a thickness of the second rubber sheet is 70:30 to 50:

50.

4. 2. The fire spread prevention sheet according to claim 1, wherein the first rubber sheet and the second rubber sheet are silicone rubber sheets.

5. A method for producing the fire spread prevention sheet according to any one of claims 1 to 4, a first vulcanization step of vulcanizing the first curable rubber sheet in an uncured state of the first rubber sheet; a second vulcanization step of vulcanizing the second curable rubber sheet in an uncured state of the second rubber sheet; a post-cure lamination step of laminating the first rubber sheet and the second rubber sheet; A method for producing a fire spread prevention sheet, comprising:

6. A method for producing the fire spread prevention sheet according to any one of claims 1 to 4, a pre-cure lamination step of laminating a first curable rubber sheet, which is the first rubber sheet before curing, and a second curable rubber sheet, which is the second rubber sheet before curing; a third vulcanization step of vulcanizing the laminated sheet that has been subjected to the pre-curing lamination step; A method for producing a fire spread prevention sheet, comprising:

7. The method for producing a fire spread prevention sheet according to claim 6, characterized in that the pre-curing lamination step is carried out by calendar molding.

8. A battery having a plurality of battery cells in a housing, A battery comprising the fire spread prevention sheet according to claim 1 , at least between the battery cells, among between the battery cells and between the battery cells and the housing.

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