JP2018014221A - Power storage device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent liquid spill by ensuring sealability of a case, even if the corner of the case on the side provided with a current cutoff device is deformed.SOLUTION: A power storage device (secondary battery 10) includes a case 11 having a square box case body 12 provided with an opening 12a, and a lid 13 closing the opening 12a, an electrode assembly 14 housed in the case 11, and a current cutoff device 40. The current cutoff device 40 includes a deformation plate 42 and a fracturable conductive plate (negative electrode conductive member 28). A holder 30 for holding an electrode terminal (negative electrode lead-out terminal 27) on the side provided with the current cutoff device 40 and the conductive plate are fixed on the outside of the deformation plate 42, and impact absorption means 45 for absorbing the impact applied to the corner 11a of the lid 13 is provided between the lid 13 and holder 30.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a power storage device, and more particularly to a power storage device including a current interrupt device that interrupts a current in an energization path by deformation of a deformation plate when an internal pressure of a case reaches a set pressure.

  Conventionally, secondary batteries such as lithium ion secondary batteries have been installed in vehicles such as EVs (Electric Vehicles) and PHVs (Plug in Hybrid Vehicles) as power storage devices for storing electric power used in electrical components. Yes. The secondary battery includes a case, an electrode assembly housed in the case, and two electrode terminals that protrude outside the case and have different polarities.

  Some secondary batteries include a current interrupting device that interrupts current in response to an increase in internal pressure of the case. The current interrupting device is provided on an energization path that electrically connects the electrode terminal of one polarity and the electrode assembly (see, for example, Patent Document 1).

  As shown in FIG. 7, the power storage device 100 of Patent Document 1 includes a case body 61, an electrode assembly 63 including a negative electrode current collecting tab 63 a and a positive electrode current collecting tab 63 b, a negative electrode side crimping terminal 65, and a positive electrode side. A crimping terminal 67, a lid 69, a current interrupting device 80, and the like are provided. The caulking terminal 65 is attached to an opening 69 a formed in the lid 69 of the case body 61. External terminals 70 and bolts 74 for external connection are disposed outside the case body 61. The caulking terminal 65, the external terminal 70, and the bolt 74 are electrically connected to each other and constitute a negative terminal. A resin gasket 72 is disposed between the upper surface of the lid 69 and the external terminal 70 and between the upper surface of the lid 69 and the crimping terminal 65. In addition, the lid 69 is insulated from the external terminal 70 and the caulking terminal 65 by the gasket 72.

  A deformation plate 82 is laser welded to the end of the crimping terminal 65 in the z direction (vertical direction in FIG. 7). A breakable plate (breakable energizing plate) 84 is laser welded to the central portion of the deformable plate 82. The deformation plate 82 and the break plate 84 constitute a current interrupt device 80. The current interrupt device 80 is electrically connected to the negative electrode current collecting tab 63a of the electrode assembly 63 through the connection terminal 85 or the like. The current interrupt device 80 has an energization path that connects the connection terminal 85, the fracture plate 84, the deformation plate 82, and the crimping terminal 65 in series. For this reason, the electrode assembly 63 and the crimping terminal 65 are electrically connected via the energization path of the current interrupt device 80.

  The caulking terminal 65 has a cylindrical portion 65a, a base portion 65b, and a fixing portion 65c. The base portion 65b has an annular shape in plan view and is located on the z direction side of the cylindrical portion 65a. The outer diameter of the base portion 65b is larger than the diameter of the opening 69a. The caulking terminal 65 has an annular portion 86a formed on the inner peripheral side of a substantially cylindrical holder 86 fitted to the outer peripheral surface of the base portion 65b in a state where the cylindrical portion 65a passes through the opening 69a. 69 is provided between the lower surface of 69 and the upper surface of the base portion 65b.

  The caulking terminal 67 on the positive electrode side is electrically connected to the positive electrode current collecting tab 63 b of the electrode assembly 63 inside the case body 61 and is electrically insulated from the lid 69 and electrically connected to the external terminal 71 and the bolt 75. It is connected to the. The external terminal 71 and the bolt 75 are insulated from the lid 69. A current interrupt device is not prepared on the positive electrode side. The caulking terminals 65 and 67 are fixed to the lid 69 by caulking (by plastic deformation).

Japanese Patent Laid-Open No. 2006-68103

  In a power storage device, an electrode assembly and an electrolytic solution are generally housed in a rectangular box-like case. Further, in order to increase the capacity per volume of the power storage device, it is necessary to reduce the space. In the case of a power storage device including a current interrupt device, the space in the case is small, particularly on the negative electrode side where the current interrupt device is provided. Therefore, for example, as illustrated in FIG. 8, when the power storage device 100 falls from a corner portion side of the case to a hard surface 90 such as the ground and the corner portion is deformed, the corner portion is closer to the current interrupting device. In this case, since the clearance between the case body 61 and the holder 86 is small, the holder 86 receives a force and the crimp terminal 65 is deformed, and the sealing performance of the terminal seal portion is impaired, and liquid leakage may occur.

  The present invention has been made in view of the above-described problems, and its object is to ensure the sealing property of the case and prevent liquid leakage even when the corner portion of the case on the side where the current interrupting device is provided is deformed. It is an object of the present invention to provide a power storage device that can prevent the above.

  A power storage device that solves the above problems includes a case having a rectangular box-like case body having an opening, a lid that closes the opening, an electrode assembly housed in the case, and a current interrupting device. It is an electrical storage apparatus which has. The current interrupt device includes a deformable plate and a breakable conductive plate, and the holder that supports the electrode terminal on the side where the current interrupt device is provided and the conductive plate are fixed outside the deformable plate. An impact absorbing means for absorbing an impact applied to a corner of the lid is provided between the lid and the holder.

  According to this configuration, even if an impact is applied to the corner portion of the case lid where the current interrupt device is provided, the impact applied to the corner portion of the lid body is absorbed by the impact absorbing means. . As a result, even if the case on the side where the current interrupting device is provided is deformed, the deformation prevents the sealing performance of the seal portion of the electrode terminal from being damaged to the extent that liquid leakage occurs. Therefore, even if the corner portion of the case on the side where the current interrupting device is provided is deformed, the sealing property of the case can be ensured to prevent liquid leakage.

  The impact absorbing means may be a gap. When the shock absorbing means is a gap, even if the corner portion of the case on the side where the current interrupting device is provided is deformed, the deformed portion is positioned in the gap portion, so that the sealing performance of the case is secured.

The gap may be provided between the holder and the inner surface of the case body on the lid side. According to this structure, the structure which provides a space | gap becomes simple.
The impact absorbing means may be configured by thickening a portion of the lid that contacts the inner surface of the case main body. According to this configuration, since the strength of the corner portion of the lid body is high, even if an impact is applied to the corner portion of the case, the deformation of the lid body is suppressed, and the necessary sealing performance of the case is ensured.

  The shock absorbing means may have a cushioning material in the gap portion. According to this configuration, since the shock applied to the corner portion of the lid is weakened by the cushioning material, it is possible to reduce the volume occupied by the shock absorbing means as compared with the case where the shock absorbing means is configured by only the gap. .

The holder and the conductive plate may be fixed by caulking. According to this configuration, it is not necessary to provide a separate member for fixing the holder and the conductive plate.
The caulking may be heat caulking. According to this configuration, it is possible to easily perform caulking.

  According to the present invention, even if the corner portion of the case on the side where the current interrupting device is provided is deformed, the sealing performance of the case can be ensured and liquid leakage can be prevented.

The schematic perspective view which shows the secondary battery of 1st Embodiment. The partially broken front view which similarly shows a secondary battery. The longitudinal cross-sectional view of the part of the electric current interruption apparatus of a secondary battery. The fragmentary sectional view which shows the secondary battery of another embodiment. (A) is a fragmentary sectional view which shows the secondary battery of another embodiment, (b) is a partial back view of a cover body. (A) is a fragmentary sectional view which shows the secondary battery of another embodiment, (b) is a schematic plan view of a holder. Sectional drawing which shows the secondary battery of a prior art. The schematic perspective view which shows the state of a drop test.

Hereinafter, an embodiment in which the power storage device is embodied as a secondary battery will be described with reference to FIGS.
As shown in FIG. 1, a secondary battery 10 as a power storage device includes a case 11, and the case 11 closes a square box-shaped case body 12 and an opening 12 a (shown in FIG. 3) of the case body 12. And a rectangular flat lid 13. An electrode assembly 14 is accommodated in the case 11. In addition, the secondary battery 10 of this embodiment is a lithium ion battery.

  As shown in FIG. 2, the electrode assembly 14 includes a plurality of sheet-like positive electrodes 15 and a plurality of sheet-like negative electrodes 16, and the positive electrode 15 is a positive metal foil (in this embodiment, an aluminum foil). And a positive electrode active material layer present on both surfaces of the positive electrode metal foil. The negative electrode 16 has a negative electrode metal foil (a copper foil in this embodiment) and a negative electrode active material layer present on both surfaces of the negative electrode metal foil. The electrode assembly 14 is a layered type in which a separator 17 is interposed between a plurality of positive electrodes 15 and a plurality of negative electrodes 16 to insulate them. In FIG. 2, the negative electrode 16 is positioned on the front side of the figure, and a predetermined number of positive electrodes are arranged in the order of the separator 17, the positive electrode 15, the separator 17, the negative electrode 16, the separator 17, and the positive electrode 15 toward the back side. An electrode assembly 14 is configured by arranging the electrode 15, the negative electrode 16, and the separator 17.

  The positive electrode 15 has a tab 15 a having a shape protruding from a part of one side of the positive electrode 15. The negative electrode 16 has a tab 16 a having a shape protruding from a part of one side of the negative electrode 16. The plurality of positive electrode tabs 15a and the plurality of negative electrode tabs 16a are provided at positions where the positive electrode tab 15a and the negative electrode tab 16a do not overlap with each other in a state where the positive electrode 15 and the negative electrode 16 are stacked. . The positive electrodes 15 constituting the electrode assembly 14 are stacked such that the tabs 15a are arranged in a row along the stacking direction. Similarly, the negative electrodes 16 constituting the electrode assembly 14 are stacked such that the tabs 16a are arranged in a row along the stacking direction.

  The secondary battery 10 includes a positive electrode tab group 18 configured by collecting and stacking all the positive electrode tabs 15a toward one end side in the stacking direction of the electrode assembly 14. Further, the secondary battery 10 includes a negative electrode tab group 19 configured by gathering all negative electrode tabs 16a toward one end side in the stacking direction of the electrode assembly 14 and stacking them.

  As shown in FIGS. 1 and 2, the outer insulating member 21 constituting the positive terminal structure 20 and the outer insulating member 21 constituting the negative terminal structure 22 are disposed on the outer surface of the lid 13. Since the positive electrode terminal structure 20 and the negative electrode terminal structure 22 have basically the same configuration except for a current interrupt device described later, common members will be described using the same member numbers.

The positive terminal structure 20 and the negative terminal structure 22 include a rectangular outer insulating member 21 disposed on the outer surface of the lid 13. The outer insulating member 21 is made of synthetic resin.
The positive electrode terminal structure 20 includes an external connection terminal 24 and a positive electrode extraction terminal 25 that are electrically connected by a terminal connection member 23, and the outer insulating member 21 includes a positive electrode external connection terminal 24, a positive electrode extraction terminal 25, and a lid. 13 is insulated. The negative electrode terminal structure 22 includes a negative external connection terminal 26 and a negative electrode extraction terminal 27, and the outer insulating member 21 insulates the negative electrode external connection terminal 26 and the negative electrode extraction terminal 27 from the lid 13. The positive electrode extraction terminal 25 is electrically connected to the positive electrode tab group 18 via the positive electrode conductive member 25a, and the negative electrode extraction terminal 27 is electrically connected to the negative electrode tab group 19 via the negative electrode conductive member 28. Yes.

  As shown in FIGS. 2 and 3, the secondary battery 10 includes a current interrupting device 40 integrated with the negative electrode lead terminal 27 which is one of the electrode terminals. The current interrupting device 40 is disposed inside the case 11, and when the internal pressure of the case 11 reaches a predetermined set pressure, the energization that electrically connects the electrode assembly 14 and the negative electrode lead terminal 27. Cut off the current in the path.

  As shown in FIG. 3, the negative electrode conductive member 28 has an electrode connection portion 28 a electrically connected to the negative electrode tab group 19 and a terminal connection portion 28 b electrically connected to the negative electrode lead terminal 27. The electrode connection portion 28a is bent so as to be closer to the lid body 13 than the terminal connection portion 28b.

  The current interrupting device 40 is located between the base portion 27a of the negative electrode lead terminal 27 and the terminal connection portion 28b of the negative electrode conductive member 28 as a conductive plate. More specifically, the negative electrode tab group 19 is joined with a negative electrode conductive member 28 for electrically connecting the electrode assembly 14 and the negative electrode terminal structure 22. In this embodiment, the base 27 a of the negative electrode lead terminal 27 is electrically connected to the negative electrode conductive member 28 via the current interrupt device 40, and the negative electrode conductive member 28 is electrically connected to the negative electrode tab group 19. Thus, an energization path between the electrode assembly 14 and the negative electrode lead terminal 27 is configured. In other words, the current interrupt device 40 constitutes a part of the energization path when not operating, and interrupts the energization path when activated by receiving the pressure of the gas generated inside the case 11.

  As shown in FIG. 3, the negative electrode lead terminal 27 that is the electrode terminal on the side where the current interrupt device 40 is provided is supported by the holder 30. The holder 30 is made of an insulating material (made of resin in this embodiment), and is provided so as to cover the outside of the base portion 27 a of the negative electrode lead terminal 27. More specifically, the holder 30 has a substantially cylindrical shape and has a recess 30a that can accommodate the base portion 27a of the negative electrode lead terminal 27. The cylindrical portion 27b of the negative electrode lead terminal 27 is loosely inserted between the holder 30 and the cylindrical portion 27b. A sealing member 31 is provided on the surface. A seal ring 32 is provided between the holder 30 and the negative electrode conductive member 28.

  The current interrupt device 40 includes a contact plate 41 joined to the negative electrode conductive member 28 and the base portion 27 a of the negative electrode lead terminal 27. The contact plate 41 is made of a conductive material, and has a bowl shape that protrudes toward the electrode assembly 14. And the contact plate 41 has covered the recessed part of the base 27a from the electrode assembly 14 side. The outer peripheral portion of the contact plate 41 protruding from the recess of the base portion 27a and the end surface of the base portion 27a are fixed by welding.

  The negative electrode conductive member 28 has a recess 28 c formed on the surface opposite to the surface in contact with the seal ring 32. The negative electrode conductive member 28 is formed with a thin thickness at a portion in contact with the contact plate 41 by forming the recess 28c. Further, a groove 28 d is formed in the negative electrode conductive member 28 at a portion in contact with the contact plate 41.

  The current interrupt device 40 includes a deformable plate 42 that receives the internal pressure of the case 11 and deforms. The deformation plate 42 is a diaphragm made of an elastic material, for example, a metal plate, and is disposed at a position closer to the electrode assembly 14 than the terminal connection portion 28b. The deformation plate 42 has a disk shape and covers the recess 28c from the electrode assembly 14 side. The outer peripheral portion of the deformable plate 42 and the terminal connection portion 28b are fixed by welding over the entire periphery of the outer peripheral portion of the deformable plate 42. The deformation plate 42 hermetically separates the inside of the case 11 from the outside of the case 11.

  The deformation plate 42 is convex from the lid 13 side to the electrode assembly 14 side (downward) in the normal state, and a portion facing the negative electrode welded portion P in the convex portion is directed to the lid 13. And a protruding protrusion 42a. The protrusion 42a faces the negative electrode welded portion P surrounded by the groove 28d.

  An insulating portion 43 that covers the terminal connection portion 28 b and the deformation plate 42 is provided closer to the electrode assembly 14 than the terminal connection portion 28 b and the deformation plate 42 of the negative electrode conductive member 28. The insulating portion 43 is arranged so that the side opposite to the negative electrode tab group 19 is located near the inner surface of the case body 12.

  The holder 30 and the negative electrode conductive member 28 are fixed outside the deformation plate 42. The holder 30 is fixed to the negative electrode conductive member 28 by caulking. For example, a plurality of holes are formed in the negative electrode conductive member 28, a protrusion that can be fitted into the hole is formed in the holder 30, and the hole and the protrusion are fitted and fixed. Caulking is performed by heat caulking. The negative electrode conductive member 28 is formed such that the end opposite to the electrode connection portion 28 a is the same as the distance between the holder 30 and the inner surface of the case body 12.

  Between the lid 13 and the holder 30, an impact absorbing means 45 that absorbs an impact applied to the corner 11 a of the lid 13 is provided. The corner portion 11a means an end portion of the lid 13 that extends in the short direction. In this embodiment, a gap S is provided as the shock absorbing means 45. Even if the case 11 is deformed due to an impact applied to the corner portion 11a of the lid 13, the gap S causes the sealing performance of the sealing member 31 as a sealing portion of the electrode terminal (negative electrode lead terminal 27) due to the deformation. It is formed in such a size that it is prevented from being damaged so as to occur. In this embodiment, since the distance between the negative electrode conductive member 28 and the inner surface of the case body 12 is the same as the distance between the holder 30 and the inner surface of the case body 12, the holder 30 and the inner surface of the case body 12 A gap S is formed not only between the negative electrode conductive member 28 and the inner surface of the case body 12.

Next, the operation of the secondary battery 10 configured as described above will be described.
Since the secondary battery 10 has the current interrupt device 40, when the electrode reaction proceeds abnormally and the pressure in the case 11 becomes equal to or higher than a preset pressure, the deformation plate 42 is deformed toward the lid body 13, The protrusion 42 a breaks the negative electrode welded portion P between the terminal connection portion 28 b and the contact plate 41. As a result, the electrical connection between the negative electrode lead terminal 27 and the negative electrode conductive member 28 is interrupted, and the current in the energization path is interrupted.

  Between the lid 13 and the holder 30, there is provided an impact absorbing means 45 that absorbs an impact applied to the corner 11 a of the lid 13. For example, the corner of the lid 13 is dropped by the fall of the secondary battery 10. Even if the case 11 is deformed by an impact applied to the portion 11a, the deformation prevents the sealing performance of the seal member 31 of the negative electrode lead terminal 27 from being damaged to the extent that liquid leakage occurs. Further, since the holder 30 and the conductive plate (the negative electrode conductive member 28) are fixed outside the deformation plate 42, the holder 30 does not adversely affect the operation of the current interrupting device 40.

According to this embodiment, the following effects can be obtained.
(1) A power storage device (secondary battery 10) includes a rectangular box-like case body 12 having an opening 12a, a case 11 having a lid 13 that closes the opening 12a, and an electrode accommodated in the case 11 An assembly 14 and a current interrupt device 40 are included. The current interrupt device 40 includes a deformable plate 42 and a breakable conductive plate (negative electrode conductive member 28), and a holder 30 that supports the electrode terminal (negative electrode lead terminal 27) on the side where the current interrupt device 40 is provided. The conductive plate is fixed outside the deformable plate 42, and an impact absorbing means 45 that absorbs an impact applied to the corner 11 a of the lid 13 is provided between the lid 13 and the holder 30. .

  According to this configuration, even if an impact is applied to the corner 11 a on the side where the current interrupt device 40 is provided with respect to the lid 13 of the case 11, the impact applied to the corner 11 a of the lid 13 is impacted. Absorbed by the absorbing means 45. As a result, even if the case 11 on the side where the current interrupting device 40 is provided is deformed, it is prevented that the sealing performance of the seal portion of the electrode terminal is impaired due to the deformation such that liquid leakage occurs. Therefore, even if the corner portion 11a of the case 11 on the side where the current interrupting device 40 is provided is deformed, the sealing performance of the case 11 can be secured and liquid leakage can be prevented.

  (2) The shock absorbing means 45 is the gap S. When the shock absorbing means 45 is the gap S, even if the corner portion 11a of the case 11 on the side where the current interrupting device 40 is provided is deformed, the deformed portion is positioned in the gap S. Sealability is ensured. Further, when the shock absorbing means 45 is the gap S, it can be formed without providing the shock absorbing means 45 parts.

(3) The gap S is provided between the holder 30 and the inner surface of the case body 12 on the lid body 13 side. According to this configuration, the structure for providing the gap S is simplified.
(4) Since the gap S is formed not only between the holder 30 and the inner surface of the case body 12 but also between the negative electrode conductive member 28 and the inner surface of the case body 12, the gap S becomes wider. The shock absorbing function is increased.

(5) The holder 30 and the conductive plate (negative electrode conductive member 28) are fixed by caulking. According to this configuration, it is not necessary to provide a separate member for fixing the holder 30 and the conductive plate.
(6) Caulking between the holder 30 and the conductive plate (the negative electrode conductive member 28) is performed by heat caulking. Therefore, the caulking work becomes easier than other caulking.

The embodiment is not limited to the above embodiment, and may be embodied as follows, for example.
As shown in FIG. 4, the end of the negative electrode conductive member 28 may be provided so as to extend to the vicinity of the inner surface of the case main body 12. In this case, since the deformation of the case body 12 is hindered by the negative electrode conductive member 28, the holder 30 is less likely to receive a force from the case body 12 when an impact is applied to the corner portion 11 a of the case 11.

  ○ As shown in FIGS. 5A and 5B, the shock absorbing means 45 is not constituted by the gap S, but the thick portion 46 in which the portion of the lid 13 that contacts the inner surface of the case body 12 is thickened. It may be constituted by doing. The thick portion 46 is formed in a columnar shape such as a cylinder, for example. According to this configuration, since the strength of the corner portion 11a of the lid body 13 is high, even if an impact is applied to the corner portion 11a of the case 11, deformation of the lid body 13 is suppressed, and a necessary seal of the case 11 is obtained. Sex is secured.

  The structure of the thick part 46 which thickened the part which contact | abuts the inner surface of the case main body 12 of the cover body 13 is not restricted to what was formed in columnar shapes, such as a cylinder, The rib extended along the width direction of the cover body 13 It may be constituted by. The ribs are not limited to extending over the entire width direction of the lid body 13 and may be two divided ribs.

  The shock absorbing means 45 may have a buffer material in the space S portion. For example, as shown in FIGS. 6A and 6B, the cushioning material 47 may be configured with ribs extending along the inner surface of the case body 12 in the gap S in the holder 30. According to this configuration, the shock applied to the corner portion 11a of the lid body 13 is weakened by the shock absorbing material 47, so that the volume occupied by the shock absorbing means 45 is reduced as compared with the case where the shock absorbing means 45 is configured by only the gap. It becomes possible.

  As shown in FIG. 6A, when the cushioning material 47 is configured integrally with the holder 30, the caulking position where the holder 30 is fixed to the negative electrode conductive member 28 by caulking is a portion extending from the holder 30. May be.

  The shock absorbing material 47 constituting the shock absorbing means 45 does not need to be configured integrally with the holder 30. For example, another cushioning material 47 may be accommodated in the gap S illustrated in FIG. 3 or FIG. Examples of the buffer material 47 include rubber, foamed resin, and cloth.

○ When the holder 30 and the conductive plate (the negative electrode conductive member 28) are fixed by caulking, the caulking need not be heat caulking.
The fixing of the holder 30 and the conductive plate (negative electrode conductive member 28) is not limited to caulking. For example, it may be fixed with an adhesive.

  DESCRIPTION OF SYMBOLS S ... Air gap, 11 ... Case, 12 ... Case main body, 12a ... Opening part, 13 ... Cover, 14 ... Electrode assembly, 27 ... Negative electrode lead-out terminal as an electrode terminal, 28 ... Negative electrode conductive member as a conductive plate, 30 DESCRIPTION OF SYMBOLS ... Holder, 40 ... Current interruption device, 42 ... Deformation plate, 45 ... Shock absorption means, 47 ... Buffer material.

Claims (7)

A power storage device having a square box-like case body having an opening, a case having a lid for closing the opening, an electrode assembly housed in the case, and a current interrupting device,
The current interrupt device includes a deformable plate and a breakable conductive plate, and the holder supporting the electrode terminal on the side where the current interrupt device is provided and the conductive plate are fixed outside the deformable plate. And an impact absorbing means for absorbing an impact applied to a corner portion of the lid body is provided between the lid body and the holder.   The power storage device according to claim 1, wherein the shock absorbing means is a gap.   The power storage device according to claim 2, wherein the gap is provided between the holder and an inner surface of the case body on the lid side.   2. The power storage device according to claim 1, wherein the impact absorbing means is configured by thickening a portion of the lid that contacts the inner surface of the case main body.   The power storage device according to claim 2, wherein the shock absorbing means has a buffer material in the space.   The power storage device according to any one of claims 1 to 5, wherein the holder and the conductive plate are fixed by caulking.   The power storage device according to claim 6, wherein the caulking is heat caulking.

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