Bottle can cap and method for producing the same

Abstract

To provide a cap which can be produced without largely changing the conventional facility, and has an opening end part with a shape more suitable to conveyance.SOLUTION: In a bottle can cap, a disk-shaped top plate part and a peripheral wall part extending into a disk shape from the periphery of the top plate part are integrally formed, and it is preferable that the maximum height of a protruding part in a fracture face on an outer peripheral side from a trimming end face of an inner peripheral side formed at an opening end of the peripheral wall part be 20 μm or lower, and a distance of the opening end in a radial direction relative to a 1 mm height position on the peripheral wall part be 44 μm or less. The bottle can cap is formed by trimming using a trim cutter subjected to precise shot peening treatment.SELECTED DRAWING: Figure 8

Description

[Technical Field]

[0001] The present invention relates to a cap for sealing the mouth of a bottle-shaped body and a method for manufacturing the same. [Background technology]

[0002] As a container for various beverages, it is attached to the mouth of a bottle-shaped body (bottle-shaped body). Bottle cans that are sealed with a cap are becoming popular. This bottle can cap, as disclosed in Patent Document 1, for example, The top plate and the peripheral wall are integrally formed from aluminum or an aluminum alloy, and a disk-shaped resin liner is provided on the inner surface of the top plate. In addition, when the cap is punched out from the rolled material and drawn into a cylindrical cup shape with a bottom, It is described that the cup-shaped open end is trimmed by cutting it with a trim cutter.

[0003] These caps are packed in large numbers into bags and transported to the filling factory, so depending on the shape of the opening end after trimming, there is a risk that the caps may be scratched or tiny metal pieces may fall off due to contact with each other inside the bag. Although there are methods such as fine blanking and shaving to adjust the shape of the open end, these methods require significant modifications to the equipment, which is problematic. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2017-141056 Summary of the Invention [Problem to be solved by the invention]

[0005] The present invention has been made in consideration of the above circumstances, and aims to provide a cap that can be manufactured without making major changes to conventional equipment and has an opening end with a shape that is more suitable for transportation. [Means for solving the problem]

[0006] The cap of the present invention is formed integrally with a disk-shaped top plate portion and a peripheral wall portion extending cylindrically from the periphery of the top plate portion, and the maximum height of the protrusion from the inner trimming end face formed at the opening end of the peripheral wall portion to the outer fracture surface is 20 μm or less.

[0007] The trimmed end surface at the open end of the peripheral wall is formed by the trim cutter on the outer periphery of the punch (described later), and is therefore flat, whereas the fractured surface on the outside of it is rougher than the trimmed end surface. The maximum height of the protrusion from the trimmed end surface to the fractured surface is kept to 20 μm or less, which prevents scratches from occurring even when the product is transported in a bag.

[0008] In the cap of the present invention, the radial distance of the open end from a position 1 mm high on the peripheral wall portion is 44 μm or less.

[0009] A large radial distance from the open end at a height of 1 mm of the peripheral wall indicates a large warpage of the lower end of the peripheral wall. This large distance results in a large radial protrusion, making the cap susceptible to contact and damage by other caps during transport in a bagged state. The cap of the present invention minimizes this radial distance to 44 μm or less, thereby preventing scratches. Furthermore, minimizing this radial distance also reduces the maximum height of the protrusion on the fracture surface.

[0010] The method for manufacturing a cap of the present invention is a method for manufacturing a cap having a disk-shaped top plate portion and a peripheral wall portion cylindrically extending from the peripheral edge of the top plate portion, which is a method for manufacturing a cap through a cap shell forming step of punching a rolled plate made of an aluminum alloy into a disk-shaped blank and then trimming it by drawing with a drawing punch and a drawing die to form a cap shell having a disk-shaped top plate portion and a cylindrical portion extending from the peripheral edge of the top plate portion, and a peripheral wall portion forming step of processing the cylindrical portion of the cap shell to form the peripheral wall portion, a trim cutter is formed on the outer periphery of the punch along the circumferential direction, and a surface of the trim cutter facing forward in the direction of travel of the punch is precision shot peened to have an arithmetic mean roughness of 0.30 μm or less; In the cap shell forming process, while holding the flange portion at the peripheral edge of the blank, the central portion is drawn into a circular cup portion to form a cap shell body, and at the end of the drawing process, the surface of the trim cutter is pressed against the inside of the bend between the flange portion and the circular cup portion in the cap shell body to trim the base of the circular cup portion.

[0011] In this trimming method, the trim cutter is pressed from the inside against the bent portion of the cap shell blank formed by drawing, so the inner periphery of the opening end of the peripheral wall of the cap shell is finished into a flat trimmed end surface due to contact with the trim cutter, but the outer periphery, which is not contacted by the trim cutter, becomes a fractured surface. If the material is not broken smoothly at this fractured surface, the maximum height of the protrusion is likely to be large.

[0012] In the present invention, precision shot peening is performed on the surface of the trim cutter, thereby increasing the surface hardness of the trim cutter and forming a finely uneven surface with the shot peened material. The arithmetic mean roughness of the surface is set to 0.30 μm or less. This makes it easier for cracks to propagate outward from the surface of the trim cutter when trimming the bent portion of the cap shell element, and allows for rapid fracture of the material at the fracture surface, resulting in the formation of a cap shell with a small protrusion. [Effects of the Invention]

[0013] According to the present invention, it is possible to provide a cap that can be manufactured without making major changes to conventional equipment and that has an opening end with a shape that is more suitable for transportation. [Brief explanation of the drawings]

[0014] [Figure 1] 1 is a front view showing a cap according to an embodiment of the present invention, with the right half cut away from the central axis. FIG. [Figure 2] 2 is a front view of a cap shell in the process of being formed into the cap shown in FIG. 1, with the right half sectioned from the center axis. [Figure 3] FIG. 2 is a front view of the bottle can shown in FIG. 1 before the cap is attached, with the right half of the bottle can cut away from the center axis. [Figure 4] 1 is a longitudinal cross-sectional view of a main part showing an example of a mold in a cap shell manufacturing apparatus. [Figure 5] 5 is a vertical cross-sectional view showing a state in the middle of molding the cap shell from the state shown in FIG. 4. FIG. [Figure 6] FIG. 10 is a vertical cross-sectional view showing a state in which the cap shell element body is being trimmed in a mold. [Figure 7] FIG. 7 is an enlarged view of the vicinity of the trimming cutter in FIG. 6. [Figure 8] 1A and 1B are micrographs of a longitudinal section of the open end of a cap shell, where (a) shows a conventional product and (b) shows the product of the embodiment. [Figure 9]These are micrographs of the open end of the cap shell taken from a position higher than that shown in FIG. 7, where (a) shows the conventional product and (b) shows the product according to the embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0015] Hereinafter, an embodiment of the present invention will be described. 1, the cap 10 of one embodiment has a cap body 20 made of an aluminum alloy and a resin liner 30 provided inside the cap body 20. The cap body 20 is integrally formed with a disk-shaped top plate portion 21 and a peripheral wall portion 22 that extends cylindrically from the periphery of the top plate portion 21 toward the lower end side (the lower side in FIG. 1) with the cap central axis C as its center.

[0016] The peripheral wall portion 22 of the cap body 20 is formed, at the upper end side near the top plate portion 21, with a knurl portion 23 that bulges radially outward relative to the cap center axis C toward the lower end, a groove 24 that is connected to the lower end of the knurl portion 23 and is recessed inward, a thread forming portion 25, a bead 26 that bulges outward, a breakable portion 28 that is smaller in diameter than the bead 26 and has multiple slits 27 spaced apart circumferentially, and a cylindrical skirt portion 29 that is larger in diameter than the breakable portion 28 and extends to the lower end of the cap body 20, all of which are formed to surround the peripheral wall portion 22 around the cap center axis C.

[0017] Although the dimensions of the cap body 20 are not necessarily limited, the nominal diameter is 38 mm (the outer diameter of the knurl portion 23 and skirt portion 29 is 38.6 mm), the overall height is 17.4 mm to 17.8 mm, and the side wall thickness around the skirt portion 29 is 0.26 mm to 0.27 mm.

[0018] In a longitudinal cross section passing through the central axis C of the cap body 20, the opening end 20a of the peripheral wall 22 has a flat surface (trimmed end surface) S, as will be described later, but is not necessarily formed flat throughout the thickness direction, and a protrusion P (see FIG. 8) protruding in the axial direction may be formed on the outer periphery. The maximum height H3 of this protrusion P from the flat surface S is 20 μm or less. Similarly, in a longitudinal cross section passing through the central axis C of the cap body 20, the peripheral wall 22 may be deformed in a direction that slightly widens the opening end 20a, and the radial distance L (see FIG. 9) of the opening end 20a from a position 1 mm high from the opening end 20a on the outer periphery 22a of the peripheral wall 22 is 44 μm or less. These shapes will be described in detail later.

[0019] The liner 30 inserted into the cap 10 has a multilayer structure including a sliding layer 31 made of a hard resin, such as polyethylene or polypropylene, and disposed in a non-adhesive state on the top plate side, and a sealing layer 32 made of a resin, such as an elastomer resin, that is softer than the sliding layer 31 and disposed on the opposite side of the sliding layer 31 from the top plate 21, either directly or via an intermediate layer such as a barrier layer. In this case, the sliding layer 31 is formed to have a slightly larger diameter than the sealing layer 32.

[0020] 3, the bottle can 50 to which the cap 10 is attached is made of a thin metal plate of aluminum or aluminum alloy, and is formed by a cylindrical body 51 with a bottom, a tapered shoulder 52 that is bent radially inward at the upper end of the body 51 and gradually reduces in diameter upward in the axial direction of the can, and a mouth 53 that is continuous with the upper end of the shoulder 52. The mouth 53 also has a bulge 54 formed at the upper end of the shoulder 52, an external thread 55 that is continuous with the upper end of the bulge 54, and a curled portion 56 that is formed by folding the open end of the external thread 55 radially outward at the upper end.

[0021] Then, at a filling factory, the cap 10 is placed over the mouth 53 of a bottle can 50 filled with a beverage, and then the outer peripheral portion of the top plate 21 is pressed in the axial direction of the can to be drawn, and the peripheral wall 22 is pressed from the radially outward direction by a roll (not shown) to be threaded to match the male thread portion 55 of the bottle can 50, and the skirt portion 29 is folded around the bulge portion 54 to be attached to the mouth 53.

[0022] In the cap 10 described above, the cap manufacturing apparatus performs the following steps to manufacture the cap body 20: a cap shell forming process in which a rolled aluminum alloy plate 35 is press-molded to form a cap shell 43 in which a disk-shaped top plate portion 41 and a cylindrical portion 42 extending from the periphery of the top plate portion 41 are integrally formed, as shown in FIG. 2; a peripheral wall portion forming process in which the cylindrical portion 42 of the cap shell 43 is processed to form a peripheral wall portion 22; and a liner attachment process. The thickness of the rolled plate 35 is, for example, 0.220 mm or more and 0.240 mm or less for the metal portion alone, excluding the printed coating.

[0023] The rolled plate 35 may be painted on both sides. The purpose of the painting is to prevent corrosion, provide slipperiness, improve formability, etc., and the paint to be applied is, for example, a polyester-based resin paint or an epoxy-based resin paint. In addition, a printed layer on which letters or designs are printed may be included between the metal surface of the rolled plate 35 and the paint. The method for manufacturing the cap will be briefly described below in the order of steps.

[0024] [Cap shell forming process] A rolled aluminum alloy plate 35 is punched out into a disk-shaped blank 36, and the peripheral edge of the blank 36 is pressed and trimmed to form a cap shell 43 as shown in Figure 2. In this cap shell 43, the cylindrical portion 42 is a substantially straight cylinder.

[0025] 4 is used to form the cap shell 43. The cap shell molding die 60 comprises an upper die 61 and a lower die 62. The upper die 61 has a cylindrical drawing punch 63 disposed in the center for drawing the blank 36, and an annular drawing die 64 surrounding the drawing punch 63, and is provided with an annular sheet holder 65 surrounding the drawing die 64. The lower die 62 also has an annular drawing die 66 facing the drawing die 64, and an annular cut edge die 67 surrounding the drawing die 66 and punching the blank 36 out of the rolled sheet 35 between the drawing die 66 and the drawing die 64.

[0026] The drawing punch 63 is formed with a cylindrical outer peripheral surface 69 having a smaller diameter than the forming hole 68 of the drawing die 66, and its tip is formed with a vertical cross-sectional arc surface (hereinafter referred to as the outer peripheral arc surface) 70, while the forming hole 68 has a cylindrical inner peripheral surface 71 formed with a circular cross section that has approximately the same shape as the top plate portion 41 of the formed cap shell 43, and a vertical cross-sectional arc surface (hereinafter referred to as the inner peripheral arc surface) 72 formed at the upper end of the inner peripheral surface 71. In this case, a clearance slightly larger than the plate thickness of the blank 36 is provided between the outer peripheral surface 69 of the drawing punch 63 and the inner peripheral surface 71 of the drawing die 66.

[0027] In this mold 60, the drawing punch 63 in the center of the upper mold 61 descends and enters into the forming hole 68 inside the drawing die 66 of the lower mold 62, thereby forming the cap shell 43 in a state where the top plate portion 41 faces downward and the open end faces upward.

[0028] The drawing punch 63 is provided with a trim cutter 80 at a midpoint in its height direction. The trim cutter 80 is made of, for example, die steel or cemented carbide, and is preferably made of SKD11. The trim cutter 80 is an annular flat plate having a leading end surface 81, a trailing end surface 82, and a cylindrical outer peripheral surface 83 that are parallel to each other (see FIG. 7 ), and is held in the drawing punch 63 with its outer peripheral portion slightly protruding radially from the outer peripheral surface 69 of the drawing punch 63. The corner on the leading end side of the portion protruding from the outer peripheral surface 69 of the drawing punch 63 (the corner formed by the leading end surface 81 and the outer peripheral surface 83) forms a trim edge 84.

[0029] The trim cutter 80 is provided at a position where a height H1 from the tip of the drawing punch 63 corresponds to a height H2 dimension of the inside of the intended cap shell 43. Specifically, the trim cutter 80 is provided at a position where it will be located near the boundary between the inner circumferential surface 71 and the inner circumferential arc surface 72 of the drawing die 66 when the drawing punch 63 and the drawing die 66 draw the blank 36 to the height of the cap shell 43, and the clearance between its outer diameter and the inner diameter of the forming hole 68 of the drawing die 66 is formed as small as possible (for example, 17% to 27% of the plate thickness of the blank 36 on one side). Furthermore, in this trim cutter 80, the front and rear tip surfaces 81 and rear end surface 82 are subjected to precision shot peening (for example, WPC treatment (registered trademark)), and although not visible to the naked eye, the shot peening material forms a finely uneven surface, with a Rockwell hardness of the surface of 58 HRC or more and 60 HRC or less and an arithmetic mean roughness Ra of 0.15 μm or more and 0.30 μm or less.

[0030] Although the entire surface of the trim cutter 80 may be precision shot peened, it is sufficient to treat at least the front end surface 81. The reason why the rear end surface 82 is also treated is that if wear or the like occurs on the trim edge 84 on the front end surface 81 side, the trim cutter 80 can be turned over, the rear end surface 82 can be directed toward the front end, and its outer circumferential corner (the corner on the opposite side of the front end surface 81 from the trim edge 84) can be used as the trim edge.

[0031] Then, the disk-shaped blank 36 punched between the outer peripheral edge 73 at the tip (lower end) of the draw die 64 and the inner peripheral edge 74 at the tip (upper end) of the cut edge die 67 is clamped between the tip surface 75 of the draw die 64 and the tip surface 76 of the draw die 66, and is drawn into a cap shell shape between the draw die 66 and the draw punch 63.

[0032] 5, during this drawing process, the peripheral edge of the blank 36 is clamped between the tip surface 75 of the draw die 64 and the tip surface 76 of the drawing die 66 and formed into a flat surface, but the inside of this clamped portion (the central part of the blank 36) is formed into a circular cup shape by the drawing punch 63 and the drawing die 66. If this state during forming is called a cap shell body 37, the cap shell body 37 has a form in which an annular flange portion 40 is formed integrally with a central circular cup portion 38 via a bent portion 39.

[0033] Then, at the end of this drawing, as shown in Figures 6 and 7, with the circular cup portion 38 of the cap shell body 37 stretched from the bent portion 39 between the inner circular arc surface 72 of the drawing die 66 and the outer circular arc surface 70 of the drawing punch 63, the trim edge 84 of the trim cutter 80 is brought into axial contact with the bent portion 39, and the ends of the tip surface 81 and outer peripheral surface 83 that make up the trim edge 84 are pressed axially while biting into the bent portion 39 of the cap shell body 37, thereby cutting and separating the cap shell body 37 at the base portion on the bent portion 39 side of the circular cup portion 38, thereby forming the cap shell 43.

[0034] The bent portion 39 of the cap shell element 37 is supported by the inner circumferential arc surface 72 of the drawing die 66, and this inner circumferential arc surface 72 is formed so as to gradually widen radially outward as it extends from the inner circumferential surface 71 upward in the axial direction of the can. Therefore, the outer diameter of the trim edge 84 can be set as close as possible to the minimum inner diameter of the inner circumferential arc surface 72 of the drawing die 66, and the base of the circular cup portion 38 can be trimmed with high precision.

[0035] Even so, it is necessary to leave a small gap between the trim edge 84 and the inner circular arc surface 72 of the drawing die 66 so that they do not come into contact with each other. Therefore, the opening end 20a of the cap shell 43 (which is given the same symbol as the opening end 20a of the cap body 20 because the area near the opening end is hardly processed in the subsequent peripheral wall forming process) is formed on the inner side as a flat surface S (see Figure 8(a)) formed by pressing the tip surface 81 of the trim edge 84, but on the outer side as a fracture surface P (see Figure 8(a)) formed by breaking at the location between the trim edge 84 and the inner circular arc surface 72 of the drawing die 66.

[0036] Because of this cutting method, the open end 20a of the formed cap shell 43 has different shapes on the inside and outside in the thickness direction, with the inner peripheral portion being pressed axially by the tip surface 81 of the trim cutter 80 to form a flat surface S, and a small portion of the outer peripheral portion being formed as a fractured surface P. In this case, the fractured surface P is formed as if torn off from the outer peripheral end of the trim cutter 80 because the inner peripheral portion is pressed toward the axial tip of the can by the trim cutter 80, and therefore is formed as a protruding portion that protrudes in the axial direction from the flat surface S. Therefore, in this specification, the same reference numerals as those for the fractured surfaces may be used when describing the protruding portions.

[0037] In this embodiment, the tip surface 81 of the trim cutter 80 (the surface facing forward in the direction of travel) is subjected to precision shot peening, which increases the surface hardness of the trim cutter 80 and forms a finely uneven surface using the shot peening material.The arithmetic mean roughness Ra of the surface is set to 0.15 μm or more and 0.30 μm or less.As a result, when trimming the base portion of the circular cup portion 38 of the cap shell body 37 (the boundary portion with the bent portion 39), cracks tend to propagate outward from the surface of the trim cutter 80, and the material at the fracture surface P is quickly broken, resulting in the formation of a cap shell 43 with a small protrusion.

[0038] [Peripheral wall forming process] In the peripheral wall forming process, the cap shell 43 formed as described above is sandwiched between an inner molding tool (not shown) placed inside the cap shell 43 and a relatively large, arc-shaped outer molding tool (not shown) placed outside the cap shell 43, and the cap shell 43 is rolled along the arc of the outer molding tool while the inner molding tool is rotated, thereby forming a knurl portion 23, a groove 24, a bead 26, a breakable portion 28 having multiple slits 27, and a skirt portion 29 in the cylindrical portion 42 of the cap shell 43, thereby forming the cap body 20.

[0039] Then, the cap 10 is manufactured by attaching a separately prepared liner 30 to the cap body 20 thus manufactured.

[0040] A predetermined amount of this cap 10 is contained in a bag (not shown) made of resin such as polyethylene and transported to a filling factory. At the filling factory, the cap 10 is removed from the bag, placed over the mouth 53 of a bottle can 50 filled with a beverage, and then tightened by a capping machine (not shown). When the caps 10 are transported in this bag, they move within the bag, and therefore, if the protrusion P at the opening end 20a of the cap body 20 is large, there is a risk that other caps 10 may be damaged.

[0041] The opening end 20a of the cap 10 in this embodiment is cut by the tip surface 81 of the trim edge 84, which has been subjected to precision shot peening in the trim cutter 80. This means that the flat surface S on the inner periphery is highly flat, and the portion of the fracture surface P on the outer periphery that continues to the flat surface S is formed into a sharp surface due to cracks caused by the trim edge 84, and a protrusion P that protrudes slightly in the axial direction is formed in a small area on the outer periphery. Since the range (range in the thickness direction) in which this protrusion P is formed is small, the height H3 of the protrusion P from the flat surface S is also small. Therefore, even when the caps 10 are transported in a bag, scratches due to contact with each other are suppressed, and the caps can be used as good quality caps. [Example]

[0042] Cap shells were molded using a conventional cap shell molding die and the cap shell molding die of this embodiment, and the shape of the open end of the resulting cap shell was confirmed. The cap shell molding die of this embodiment used a trim cutter whose surface had been precision shot peened, while the conventional cap shell molding die used a trim cutter that had not been precision shot peened. In both cases, the trim cutter material was SKD11, and precision shot peening was performed only on the tip surface 81. The precision shot peened trim cutter had an arithmetic mean roughness of the treated surface of 0.2 μm.

[0043] A JIS 3000 series aluminum alloy plate was used as the rolled plate, and a cap shell was formed. The peripheral wall was then processed to form a cap with a nominal diameter of 38 mm (the outer diameter of the knurl and skirt portions was 38.6 mm). The alloy plate had a thickness of 0.230 mm, and both sides were coated with polyester paint. Furthermore, the printing was plain. The cap produced from the cap shell molded using the cap shell molding die of this embodiment was used as an example, and the cap produced from the cap shell molded using a conventional cap shell molding die was used as a comparative example. The clearance between the trim cutter and the drawing die was set to 0.05 mm.

[0044] The axial height of the protruding portion from the flat surface and the radial warpage of the open ends of the caps of these examples and comparative examples were measured, and the roughness of the cap ends was also evaluated as an alternative to evaluating transportability.

[0045] The height of the protrusion was determined by cutting the cap along a longitudinal section passing through the central axis C, taking an image of the longitudinal section of the opening end magnified 300 times using an optical microscope, drawing a line on the image passing through the tip of the protrusion P at the opening end and parallel to the flat surface S, as shown in Figure 8(a), and determining the distance H3 of that line from the flat surface S to determine the height of the protrusion P.

[0046] To measure radial warpage, the cap was similarly cut and an image of the vertical cross section of the opening end was taken using an optical microscope at a magnification of 300 times. As shown in Figure 9(a), on the image, a straight line was drawn along the outer surface of the peripheral wall of the cap toward the opening end at position A, which was 1 mm away from the tip of the protrusion toward the top plate in the can axial direction, and the radial distance L from the line to the outer surface farthest from the line at the opening end was measured, and this was taken as the radial warpage.

[0047] The height H3 of the protrusion P and the radial warp L were measured over the entire circumference for 20 pieces, and the average value of the 20 pieces was calculated for each of the four items: average value, maximum value, minimum value, and difference between the maximum and minimum values.

[0048] To evaluate the roughness of the cap edge, a gloved human hand was used to palpate the open end of the cap, and a sensory test was conducted to check the roughness of the open end. 20 pieces each from the Examples and Comparative Examples were tested, and the evaluation was given as "Good" if all of the caps were smooth enough to move the finger around once around the cap, and as "Poor" if the finger was smooth enough to move around the cap but felt rough, or if any of the caps got caught in the process. These results are shown in Table 1.

[0049] [Table 1]

[0050] As can be seen from these results, the caps of the examples had smaller protrusion heights and warpage than the comparative examples, were not rough, and were less likely to be damaged during transportation. In particular, the protrusion height was approximately 30 μm smaller than the comparative examples, with a maximum of 14.0 μm, indicating that the protrusions were extremely small. Furthermore, the maximum warpage L of the caps of the examples was 44.0 μm or less. 8 and 9 are photographs of the longitudinal cross section of the open end of the cap, with (a) being the comparative example and (b) being the example. These photographs also show that the example has an extremely small protrusion and small warpage compared to the comparative example. [Explanation of symbols]

[0051] 10 Caps 20 Cap body 20a open end 21 Top plate 22 Peripheral wall section 35 Rolled Plate 36 Blank 37 Cap shell body 38 Circular cup part 39 Bend 40 flange 41 Top plate 42 Cylindrical section 43 Cap Shell 50 bottle cans 60 Cap shell molding die 61 Upper mold 62 Lower mold 63 Aperture Punch 64 Draw Die 66 Drawing die 68 Molding hole 67 Cut Edge Die 80 Trim Cutter 81 Tip surface 83 Outer surface 84 Trim Edge S Flat surface (trimmed end surface) P Fracture surface (protrusion)

Claims

1. A cap characterized in that a disk-shaped top plate portion and a peripheral wall portion extending cylindrically from the periphery of the top plate portion are formed integrally, and the maximum height of a protrusion from an inner trimming end face formed at the opening end of the peripheral wall portion to a fracture surface on the outer peripheral side is 20 μm or less.

2. 2. The cap according to claim 1, wherein the radial distance of the open end from a position 1 mm high on the peripheral wall is 44 μm or less.

3. A method for manufacturing a cap having a disk-shaped top plate portion and a peripheral wall portion extending cylindrically from a peripheral edge of the top plate portion, which are integrally formed, comprising: a cap shell forming step in which a disk-shaped blank is punched out from a rolled aluminum alloy plate and then drawn and trimmed using a drawing punch and a drawing die to form a cap shell having a disk-shaped top plate portion and a cylindrical portion extending from the periphery of the top plate portion formed integrally therewith; a peripheral wall portion forming step of processing the cylindrical portion of the cap shell to form the peripheral wall portion, The punch has a trim cutter formed on its outer periphery along a circumferential direction, The trim cutter has a surface facing forward in the direction of travel of the punch that has been subjected to precision shot peening to have an arithmetic mean roughness of 0.30 μm or less, In the cap shell forming step, a central portion of the blank is drawn into a circular cup portion while a flange portion of the peripheral edge of the blank is held, thereby forming a cap shell element; A method for manufacturing a cap, characterized in that at the end of the drawing process, the surface of the trim cutter is pressed against the inside of the bend between the flange portion and the circular cup portion in the cap shell body to trim the base portion of the circular cup portion.

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