Manufacturing method of laminate material for double cup type case

Abstract

To produce a laminate material for a double cup type case, which has a recess with a high side wall.SOLUTION: A method for producing a laminate material for double cup type case molding includes: a notch line forming step of forming a notch line 33 on a laminate sheet 20 that includes a heat-resistant resin layer laminated on one face of a metal foil and a heat-sealing resin layer laminated on the other face; and a recess forming step of forming two recesses 31A, 31B with the same opening shape at positions away from the notch line 33 on both sides of the notch line 33 with respect to the laminate sheet 20, a surface on a side of the heat-sealing resin layer being recessed while a surface on a side of the heat-resistant resin layer projecting.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present invention relates to a method for manufacturing a laminate material for a double-cup type case used as a packaging material for power storage devices such as lithium-ion batteries and electric double-layer capacitors.

Background Art

[0002] As a battery case formed by molding a laminate sheet, a single-cup type case in which a flat lid is placed on a concave portion (cup portion) and sealed, and a double-cup type case in which two concave portions (cup portions) are arranged facing each other and the periphery is sealed are often used. The concave portion is formed by performing deep drawing or the like on a flat laminate sheet, but since there is a limit to the forming depth, the double-cup type battery is more suitable than the single-cup type battery for manufacturing a high-capacity battery by increasing the case internal volume (see Patent Document 1).

[0003] In the double-cup type case, it is necessary to arrange the openings of the two concave portions to coincide, and it is difficult to align the concave portions. In the double-cup type case described in Patent Document 1, two concave portions are formed in a single laminate material, and the two concave portions are combined by folding this in half.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] As shown in FIG. 6, in the laminate material 100 for the double cup type case described above, the flat portion 102 between the two recesses 101A and 101B is the portion that becomes the flange of the case after being folded in half. If the width of this flat portion 102 is set too large, the flange becomes larger than necessary and the material is wasted. However, if the width of the flat portion 102 is adjusted to the finished dimension of the flange, the formability of the recesses 101A and 101B deteriorates. That is, when processing the laminate sheet using a punch that conforms to the top surface shape of the recesses 101A and 101B and a die having holes into which this punch is inserted, the material deforms so as to be drawn toward the recesses 101A and 101B on three sides of the laminate sheet that face the periphery of the laminate sheet among the four sides of the recesses 101A and 101B. However, the one side facing the flat portion 102 is difficult to deform because it is pulled from both of the recesses 101A and 101B, and strain occurs in the corner portions and angle portions of the recesses 101A and 101B, making them prone to cracking. As a result, the forming height of the recesses 101A and 101B is restricted, and the internal volume of the case is also restricted.

Means for Solving the Problems

[0006] In view of the above-described technical background, an object of the present invention is to provide a method for manufacturing a laminate material for a double cup type case that has good formability and can form recesses with high side walls.

[0007] That is, the present invention has the configurations described in the following [1] to [5].

[0008] [1] A cut line forming step of forming a cut line in a laminate sheet in which a heat-resistant resin layer is laminated on one surface of a metal foil and a heat-sealable resin layer is laminated on the other surface, A recess forming step of forming two recesses having the same opening shape in the laminate sheet at positions away from the cut line on both sides of the cut line, where the surface on the heat-sealable resin layer side is recessed and the surface on the heat-resistant resin layer side protrudes, A method for manufacturing a laminate material for forming a double cup type case, characterized by performing the above steps.

[0009] [2] The manufacturing method of the laminate material for double cup type case forming according to item 1 above, wherein the two recesses are formed at positions symmetric with respect to the cut line as the axis of symmetry.

[0010] [3] The manufacturing method of the laminate material for double cup type case forming according to item 1 or 2 above, wherein the openings of the two recesses are quadrilateral, and the side closest to the cut line of the opening is parallel to the cut line.

[0011] [4] The manufacturing method of the laminate material for double cup type case forming according to item 3 above, wherein the length L of the cut line and the length W of the adjacent side, which is the side closest to the cut line of the opening, satisfy the relationship of 1.4 ≧ L / W ≧ 0.25, and the distance F from the cut line to the adjacent side is 5 mm or more.

[0012] [5] The manufacturing method of the laminate material for double cup type case forming according to any one of items 1 to 4 above, wherein the cutting step and the recess forming step are performed simultaneously.

Advantages of the Invention

[0013] According to the manufacturing method of the laminate material for double cup type case described in [1] above, the portion facing the other recess due to the cut line also faces the outer peripheral edge, and the material is fed into the die hole, improving the formability. As a result, a recess with a high side wall can be formed.

[0014] According to the manufacturing method of the laminate material for double cup type case described in [2] above, the cut line can be used as a marker for bending, and the alignment of the two recesses can be easily performed.

[0015] According to the manufacturing method of the laminate material for double cup type case described in [3] above, since the quadrilateral recesses are arranged parallel to the cut line, the positioning of the cut line and the positioning of the bending of the manufactured laminate material for double cup type case are easy.

[0016] According to the method for manufacturing the laminate material for a double cup type case described in [4] above, the width of the heat seal portion is ensured even after the formation of the concave portion, and a heat seal portion with high adhesion can be formed.

[0017] According to the method for manufacturing the laminate material for a double cup type case described in [5] above, the laminate material for forming a double cup type case can be efficiently produced.

Brief Description of the Drawings

[0018]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Embodiments for Carrying Out the Invention

[0019] The method for manufacturing the laminate material for a double cup type case of the present invention will be described in detail.

[0020] FIG. 1 shows a laminate material 1 for a double cup type case produced by the method of the present invention. The laminate material 1 for a double cup type case has two concave portions 11A and 11B that are recessed in the same direction, and by folding it in half with the concave portions 11A and 11B facing each other, one storage space is formed, and it is used as a case for a power storage device. The material of the laminate material 1 for a double cup type case is a laminate sheet in which resin films are bonded to both sides of a metal foil layer, and it is produced by processing a blank sheet cut to the required dimensions. [Constituent Materials of the Laminate Sheet] Fig. 2 shows the laminated structure of the laminate sheet 20. The laminate sheet 20 has a heat-resistant resin layer 23 bonded to one surface of a metal foil layer 21 via a first adhesive layer 22, and a heat-sealable resin layer 25 bonded to the other surface via a second adhesive layer 24. The materials of each layer constituting the laminate sheet 20 are not limited, but the preferred materials as the case of the power storage device are as follows.

[0021] (Metal Foil Layer) The metal foil layer 21 plays a role of imparting gas barrier properties to prevent the intrusion of oxygen and moisture. The metal foil layer 21 is not particularly limited, and examples include aluminum foil, copper foil, nickel foil, stainless steel foil, or clad foils thereof, annealed foils or non-annealed foils thereof. For aluminum foil, in order to form recesses by bulging forming or drawing forming, it is preferable to use aluminum alloy foil of A8079 or A8021 defined by JIS H4160(206) with good formability. It is also preferable to use a metal foil plated with a conductive metal such as nickel, tin, copper, or chromium, for example, plated aluminum foil. It is also preferable to perform chemical conversion treatment such as chromate treatment on the metal foil layer 21 as a base treatment to form a chemical conversion film.

[0022] The preferred thickness of the metal foil layer is 15 μm to 120 μm. By being 15 μm or more, the occurrence of pinholes and breaks during rolling or heat sealing when manufacturing the metal foil can be prevented, and by being 120 μm or less, the stress during bulging forming or drawing forming can be reduced and the formability can be improved. Also, by setting the thickness of the metal foil layer 21 to 120 μm or less, the weight increase and material cost can be suppressed.

[0023] In addition, it is preferable to provide a chemical conversion treatment layer such as a phosphoric acid chromate treatment or a zirconium-based chemical conversion treatment on at least the heat-sealable resin layer 25 side of the metal foil layer 21. By providing the chemical conversion treatment layer, not only can the corrosion resistance of the metal foil layer 21 be improved, but also the bond with the opposing second adhesive layer 24 can be strengthened, and thus the adhesive strength with the heat-sealable resin layer 25 can be enhanced.

[0024] (Heat-resistant resin layer) The heat-resistant resin layer 23 is the outer layer (base material layer) of the case, and as the heat-resistant resin constituting the heat-resistant resin layer 23, a heat-resistant resin that does not melt at the heat-sealing temperature during heat-sealing is used. As the heat-resistant resin, it is preferable to use a heat-resistant resin having a melting point 10°C or higher than the melting point of the heat-sealable resin constituting the heat-sealable resin layer 25, and it is particularly preferable to use a heat-resistant resin having a melting point 20°C or higher than the melting point of the heat-sealable resin. Examples of the heat-resistant resin layer 23 include a polyamide film, a polyester film, etc., and these stretched films are preferably used. Among them, in terms of moldability and strength, a biaxially stretched polyamide film or a biaxially stretched polyester film, or a multilayer film containing these is particularly preferable, and it is more preferable to use a multilayer film in which a biaxially stretched polyamide film and a biaxially stretched polyester film are laminated. The biaxially stretched polyamide film is not particularly limited, and examples include a biaxially stretched 6-nylon film, a biaxially stretched 6,6-nylon film, an MXD6 nylon film, etc. Also, examples of the biaxially stretched polyester film include a biaxially stretched polybutylene terephthalate (PBT) film, a biaxially stretched polyethylene terephthalate (PET) film, etc.

[0025] The thickness of the heat-resistant resin layer 23 is preferably 5 μm to 50 μm. By setting it above the preferable lower limit value, sufficient strength as a case material can be ensured, and by setting it below the preferable upper limit value, the stress during molding can be reduced and the moldability can be improved.

[0026] (Heat-sealable resin layer) The heat-sealing resin layer 25 is the inner layer (sealing layer) of the case, and has excellent chemical resistance against highly corrosive electrolytes used in lithium-ion secondary batteries and the like, and also plays a role of imparting heat-sealing properties to the case material.

[0027] The heat-sealing resin layer 25 is preferably an unstretched film of a thermoplastic resin. The unstretched film of the thermoplastic resin is not particularly limited, but in terms of chemical resistance and heat-sealing properties, it is preferably composed of polyethylene, polypropylene, an olefin copolymer, acid-modified products thereof, and ionomers. Further, as the olefin copolymer, EVA (ethylene-vinyl acetate copolymer), EAA (ethylene-acrylic acid copolymer), EMMA (ethylene-methacrylic acid copolymer) can be exemplified. Also, a polyamide film (for example, nylon 12) or a polyimide film can be used.

[0028] The thickness of the heat-sealing resin layer 25 is preferably 15 μm to 100 μm. By setting it above the preferred lower limit value, the sealing performance and strength of the heat-sealed portion can be ensured.

[0029] (First adhesive layer and second adhesive layer) As the first adhesive layer 22 and the second adhesive layer 24, for example, if an adhesive is applied in a dry lamination process, acrylic adhesives such as thermosetting type and two-component curing type, acid-modified polypropylene adhesives, polyurethane-based adhesives, epoxy-based adhesives, etc. can be recommended. Also, as an adhesive method other than the above, it may be adhered by a heat fusion (heat lamination) process using acid-modified polypropylene as the adhesive layer.

[0030] The laminate sheet used in the present invention only needs to have a structure in which a heat-resistant resin layer and a heat-sealing resin layer are laminated on a metal foil layer, and is not limited to the five-layer structure shown in the figure. For example, a protective layer may be laminated outside the heat-resistant resin layer. [Method for producing a laminate material for a double-cup type case] In the method for manufacturing a laminate material for a double - cup type case of the present invention, two steps are performed: a cut - line forming step and a recess forming step. (1) Cut - line forming step As shown in FIG. 3, in a rectangular blank (laminate sheet) 20, on both sides of a folding - planned line 30 that bisects the long side, rectangular - shaped recess - planned portions 31A, 31B that are the same shape as the folding - planned line 30 are set with the folding - planned line 30 as the target axis. The adjacent side 32, which is the side closest to the folding - planned line 30 of each of the recess - planned portions 31A, 31B, is parallel to the folding - planned line 30.

[0031] A cut - line 33 that penetrates in the thickness direction of the sheet is formed on the folding - planned line 30 of the blank 20. Since the cut - line 32 is on the folding - planned line 30, the cut - line 32 and the adjacent sides 32 of the recess - planned portions 31A, 31B are also parallel. (2) Recess forming step Recesses 11A, 11B are formed in the recess - planned portions 31A, 31B of the blank 20 in which the cut - line 33 has been formed.

[0032] FIG. 4 shows an example of a forming method using two punches 40, a die 42, and a wrinkle suppressor 45. The punches 40 correspond to the inner surface shapes of the recesses 11A, 11B, and the top - surface shapes thereof correspond to the planar shapes of the recesses 11A, 11B. The two punches 40 have the same shape, and the openings of the two recesses 11A, 11B to be formed have the same shape. The die 42 has two die holes 43 into which the punches 40 are inserted. The wrinkle suppressor 45 corresponds to the peripheral shape of the two die holes 43. Then, the blank 20 is sandwiched and constrained between the die 42 and the wrinkle suppressor 45, and the punches 40 are inserted into the die holes 43 to form the side walls of the recesses 11A, 11B.

[0033] In this forming process, the material around the planned recessed portions 31A and 31B of the blank 20 is drawn into the die hole 43 by the tensile force of the punch 40, and the side walls of the recessed portions 11A and 11B rise up. Then, at the straight sides of the planned recessed portions 31A and 31B, the amount of material drawn in is larger than that at the corner portions, so the outer peripheral edge of the blank 20 curves toward the centers of the recessed portions 11A and 11B (see Fig. 1). Although the adjacent sides 32 of the planned recessed portions 31A and 31B do not face the outer peripheral edge of the blank 20, since the reverse tensile forces by the other punch 40 are eliminated by the cut lines 33, the material is drawn into the die hole 43 in the same manner as the outer peripheral edge, and the cut edges by the cut lines 33 curve toward the centers of the recessed portions 11A and 11B (see Fig. 1). By forming the cut lines 33 between the two recessed portions 11A and 11B, the portion facing the other recessed portion also comes to face the outer peripheral edge. As a result, the material is fed into the die hole 43 at the adjacent sides 32 in the same manner as the other sides, improving the formability and enabling the formation of the recessed portions 11A and 11B with high side walls.

[0034] In addition, if a difference is provided in the moving amounts of the two punches 40, a difference can be provided in the heights of the side walls of the two recessed portions 11A and 11B. Although the shapes of the openings of the two recesses of the aluminum material for the double - cup - type case need to be the same, it is not necessary for the heights (forming heights) of the side walls to be the same.

[0035] Also, when the two recessed portions are formed at positions with the cut line as the axis of symmetry, since the cut line and the planned bending line coincide, the cut line can be used as a marker for bending, and the alignment of the two recessed portions can be easily performed. Note that cases where the cut line and the planned bending line do not coincide are also included in the present invention. Furthermore, the planar shape of the recessed portion is not limited to a quadrangle, and the adjacent side is not limited to being parallel to the cut line either. However, when the quadrangular recessed portions are arranged parallel to the cut line, the positioning of the cut line and the bending positioning of the manufactured laminate material for the double - cup - type case are easy.

[0036] In the manufacturing method of the laminate material for the double - cup - type case of the present invention, the recess - forming step can be performed after the cut - line forming step, or the cut - line forming step and the recess - forming step can be performed simultaneously.

[0037] FIG. 5 shows an example of a processing tool that simultaneously performs a cut line forming step and a recess forming step. The wrinkle suppressor 50 includes a cutting blade 52 that can penetrate the blank 20 at an intermediate portion 51 corresponding to the intermediate portion between the two recess planned portions 31A and 31B. The die 53 has a blade receiving portion 54 formed at a corresponding position of the intermediate portion 51 of the wrinkle suppressor 50. When the blank 20 is sandwiched between the die 53 and the wrinkle suppressor 50 and the punch 40 is moved, the cutting blade 52 moves together with the punch 40 to form a cut line 33, and then recesses 11A and 11B are formed by the punch 40. When the cutting blade 52 moves by the thickness of the blank 20, the cut line 33 is instantaneously formed. On the other hand, the moving amount of the punch 40 is the height of the side walls of the recesses 11A and 11B, which is larger than the moving amount of the cutting blade 52 and takes more time. Also, since the blank 20 is gradually drawn into the die hole 43 while the punch 40 moves, increasing the amount of deformation, even if the cut line forming step and the recess forming step are started simultaneously, the cut line 33 is formed at the initial stage of the blank 20, so the recesses 11A and 11B can be formed without problems. Thus, by simultaneously performing the cut line forming step and the recess forming step, a laminate material for a double cup type case can be efficiently produced.

[0038] (Preferred conditions for the cut line) As described above, the cut line 33 of the blank 20 contributes to improving the formability when forming two recesses 11A and 11B in a single sheet. Hereinafter, the preferred conditions for the cut line 33 will be described in detail with reference to FIG. 3.

[0039] The cut line 33 is formed to facilitate the drawing of the material on the adjacent side 32 into the die hole 43. Therefore, in order to improve the formability, it is preferable that the length L of the cut line 33 is set to a length corresponding to the length W of the adjacent side. Specifically, it is preferable to satisfy the condition of 1.4 ≧ L / W ≧ 0.25. When L / W < 0.25, it is difficult for the material to be drawn into the die hole 43, and when L / W > 1.4, the size of the blank size becomes large, so the material cost increases. A particularly preferable range of L / W is 1.3 ≧ L / W ≧ 0.5.

[0040] Further, the distance F from the cut line 33 to the adjacent side 32 is preferably 5 mm or more. Since the flat portion between the concave portions 11A and 11B of the laminate material 1 for the double cup type case is a portion to be double-folded and heat-sealed, it is necessary to secure the width of the heat-sealing portion and form a highly adhesive heat-sealing portion even after the material is drawn into the die hole 43 by the concave portion forming and the flat portion becomes narrow. From such a viewpoint, the distance F is preferably 5 mm or more, and particularly preferably 8 mm or more.

[0041] The method of the present invention is applicable not only to the laminate material for forming a double cup type case for producing one case from one blank, but also to the production of a multi-piece laminate material for producing a plurality of cases. The multi-piece laminate material forms recesses twice the number of cases on one blank, and is cut into laminate materials for one piece after the recesses are formed. When producing the multi-piece laminate material, by forming a cut line on the cutting planned line of the blank prior to forming the recesses, the same effect as the cut line on the folding planned line can be obtained, and good formability can be obtained for all the recesses.

Examples

[0042] Hereinafter, the present invention will be specifically described based on examples. Note that the present invention is not limited only to these examples.

[0043] A laminate sheet 20 having the structure shown in FIG. 2 was produced, and this was cut to produce laminate materials for forming double cup type cases of Examples 1 to 4 and Comparative Example 1 as blanks. [Production method] The laminate sheet 20 is common in all examples, and the materials and production methods of each layer are as follows.

[0044] As the metal foil layer 21, an aluminum foil of A8021 with a thickness of 40 μm defined by JIS H4160 was used. The aluminum foil was coated with a chemical conversion treatment liquid composed of phosphoric acid, polyacrylic acid (acrylic resin), chromium (III) salt compound, water, and alcohol on both sides, and then dried at 180°C to form a chemical conversion film with a chromium adhesion amount of 10 mg / m 2 per side. A two-component curable urethane-based adhesive was applied to one surface of the metal foil layer 21 having the chemical conversion film formed thereon to form a first adhesive layer 22 with a thickness of 2 μm, and a biaxially stretched nylon film with a thickness of 25 μm was laminated as the heat-resistant resin layer 23. Next, a two-component curable olefin-based adhesive was applied to the other surface of the metal foil layer 21 to form a second adhesive layer 24 with a thickness of 2 μm, and an unstretched polypropylene film with a thickness of 40 μm was laminated as the heat-sealable resin layer 25. Thereafter, a heat aging treatment was performed at 40°C for 10 days. (Examples 1 to 4) The laminate sheet 20 was cut into a rectangle having the dimensions shown in Table 1 and used as the blank 20. As shown in FIG. 3, the center of the long side of the blank 20 was defined as the planned folding line 30, and rectangular regions of 40 (W) mm × 60 mm (S) with the planned folding line 30 as the axis of symmetry were defined as the planned recessed portions 31A and 31B. The two sides with W = 40 mm are parallel to the planned folding line 30, and the side closer to the planned folding line 30 among the two sides is the adjacent side 32. Table 1 shows the distance F from the planned folding line 30 to the adjacent side 32 in each example. Also, the distances from the upper and lower edges of the blank 20 to the side with S = 60 mm are each 10 mm.

[0045] First, a cut line 33 with a length L was formed on the planned folding line 30. The midpoint of the cut line 33 and the midpoints of the adjacent sides 32 of the planned recessed portions 31A and 31B are on the same straight line.

[0046] Next, a double-cup forming die consisting of a punch 40 with a top surface dimension of short side 40 mm × long side 60 mm (corner R = 2 mm, shoulder R = 1 mm) as shown in FIG. 4, a die 42 having a die hole 43 with a short side of 40.5 mm × long side of 60.5 mm (corner R = 2.25 mm, shoulder R 1 mm), and a wrinkle suppressor 45 was attached to a 25 t press, and recesses 11A and 11B were formed in the planned recessed portions 31A and 31B of the blank 20 by deep drawing. In this forming, the surface on the side of the heat-sealable resin layer 25 of the blank 20 was pressed with a pressure of 0.3 MP by the wrinkle suppressor 45, the two punches 40 were moved at a forming speed of 20 spm (stroke / min), and the forming height was changed in 0.5 mm units to produce the laminate material 1 for the double-cup type case having the shape shown in FIG. 1. The two recesses 11A and 11B were set to the same height. (Comparative Example 1) Recesses were formed in the same manner as in Examples 1 to 4 except that no cut line was formed in the blank 20. [Evaluation] The forming height, appearance, and sealing property of the laminate material for the double-cup type case formed in each example were evaluated by the following methods. The evaluation results are shown in Table 1. (Forming Height) The forming height of the corner portions of the recesses 11A and 11B of the laminate material 1 for the double-cup type case was measured with a caliper, and a pinhole inspection was performed in a dark room. The formed products without pinholes were regarded as qualified products. Five laminate materials for the double-cup type case were produced for each example, and the forming height at which all five passed was taken as the forming height H of that example. (Appearance) In a dark room, illumination was applied from the side of the heat-sealable resin layer 25 of the laminate material 1 for the double-cup type case, and the presence or absence of wrinkles and delamination in the vicinity of the adjacent side 32 was visually observed and judged. Those without wrinkles and delamination were evaluated as having good appearance. (Sealing Property) The laminate material 1 for the double - cup type case was folded in half along the planned folding line 30, and the four sides around the facing concave portions were heat - sealed at 200 °C × 0.2 MPa × 3 seconds using a heat - sealing machine. An infiltration inspection liquid was poured from the top surface of the concave portion of the sealed product, and it was left for 12 hours with the folded and sealed portion on the lower side to check for leakage from the folded and sealed portion. Those without leakage were evaluated as having good sealing properties.

[0047]

Table 1

[0048] From Table 1, it was confirmed that by forming a cut - line between the concave portions, the formability was improved due to the formation of the side walls.

Industrial Applicability

[0049] The present invention can be suitably used for manufacturing a double - cup type case with a large capacity.

Explanation of Signs

[0050] 1... Laminate material for double - cup type case 11A, 11B... Concave portions 20... Laminate sheet (blank) 21... Metal foil layer 23... Heat - resistant resin layer 25... Heat - fusible resin layer 30... Planned folding line 31A, 31B... Planned concave portions 32... Adjacent side 33... Cut - line 40... Punch 42... Die 52... Cutting edge 53 Die

Claims

1. A cut line forming step of forming a cut line in a laminate sheet in which a heat-resistant resin layer is laminated on one surface of a metal foil and a heat-sealable resin layer is laminated on the other surface; With respect to the laminate sheet, at positions away from the cut line on both sides of the cut line and with the cut line as the axis of symmetry, the surface on the heat-sealable resin layer side is recessed and the surface on the heat-resistant resin layer side protrudes, and two recesses having the same opening shape are formed. A recess forming step; A method for manufacturing a laminate material for forming a double cup type case, characterized in that the cut line forming step and the recess forming step are performed simultaneously.

2. The method for manufacturing a laminate material for forming a double cup type case according to claim 1, wherein the two recesses are formed at positions with the cut line as the axis of symmetry.

3. The method for manufacturing a laminate material for forming a double cup type case according to claim 1 or 2, wherein the openings of the two recesses are quadrilateral, and the side closest to the cut line of the opening is parallel to the cut line.

4. The method for manufacturing a laminate material for forming a double cup type case according to claim 3, wherein the length L of the cut line and the length W of the proximity side, which is the side closest to the cut line of the opening, satisfy the relationship of 1.4 ≥ L / W ≥ 0.25, and the distance F from the cut line to the proximity side is 5 mm or more.

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