Can lid and method for manufacturing the same

Abstract

To provide a can lid which suppresses deformation of a tab hole and prevents a tab from coming off a can lid main body, and to provide a manufacturing method of the same.SOLUTION: A can lid includes: a can lid main body which is attached to an opening part of a can body and is formed of an aluminum alloy having an opening piece partitioned by a score on an approximately disc-shaped panel part; and a tab for opening a can to open the opening piece. A rivet, which protrudes from the panel part and fixes the tab for opening a can between the panel part and a rivet head, is formed on an inner side of the panel part. A reinforced part, which is deformed by compressing or bending the tab for opening a can in an annular area surrounded by an outer peripheral edge of the rivet head and a circle with a diameter larger than an outer diameter of the rivet head by 1 mm, is formed at least in a range of 45° on both sides of a linear line extending toward a tab nose contacting with the opening piece of the tab for opening a can from a center of the rivet in a plane view of the can lid main body.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present invention relates to a can lid wound around an opening end of a can body and a method for manufacturing the same.

Background Art

[0002] For a can lid for beverages, an opening tab is attached to a rivet formed on the can lid body. By pulling up a pulling portion (tab tail portion) formed on the rear end side of the opening tab, the vicinity of the rivet serves as a fulcrum and the pressing portion (the tip of the tab) serves as a point of action, so that an opening piece surrounded by a score on the panel surface can be pressed and immersed to break the score and open the drinking mouth. At this time, the panel is broken along the score shape, but the opening piece is pushed into the can without leaving the panel.

[0003] In such a can lid, since the opening tab is supported by a rivet, there is a risk of rotating around the rivet due to vibration or the like and deviating from a preferable position at the time of opening the can. In order to prevent such rotation of the opening tab around the rivet, for example, a can lid described in Patent Document 1 and a method for manufacturing a can lid described in Patent Document 2 are known.

[0004] In the can lid described in this Patent Document 1, a protrusion that protrudes radially inward and bites into the side surface of the rivet is formed on the inner peripheral edge of a through hole that disposes the rivet in a penetrating state in the opening tab. The protrusion locks the relative rotation between the opening tab and the rivet, and fixes the tab at an optimal position for opening the can. Since such a protrusion is formed by pressing and crushing a mold against the periphery of the through hole of the opening tab, its tip is formed sharply. Then, the through hole is extrapolated to the rivet and the rivet is caulked. As a result, the rivet head is formed in a shape larger than the through hole of the opening tab, the opening tab is attached to the can lid body so as not to fall off, and the relative rotation between the opening tab and the can lid body is suppressed.

[0005] In addition, in the method for manufacturing a can lid described in Patent Document 2, a rivet protrusion is formed on the can lid body, and in a tab placement step of externally inserting a through hole formed in the tab into the rivet protrusion and placing the tab on the can lid body, and after the tab placement step, a diameter expansion portion forming step of crushing the head of the rivet protrusion to form a rivet having a diameter expansion portion with an outer diameter larger than the inner diameter of the through hole, and after the tab placement step, a recess forming step of crushing the vicinity of the inner edge of the through hole of the tab in the thickness direction to form a recess, thereby thickening the thickness of the inner edge of the through hole are provided. In this case, it is described that the diameter expansion portion forming step and the recess forming step may be performed simultaneously or either one may be performed first.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0007] By the way, when opening a beverage can lid made of an aluminum alloy, if the tab for opening the can is not sufficiently crimped, there has been a problem that the tab for opening the can detaches from the rivet portion of the can lid body and cannot be opened. In recent years, the thinning of the tab material has been progressing. For tabs with a plate thickness of about 0.31 mm or less for opening the can, as shown in Fig. 9(a), even if the tab 1J for opening the can is sufficiently crimped, when lifting the tab 1J for opening the can as shown by the arrow A in Fig. (a) during can opening, until the score breaks, a lifting force with the tab nose 16J as a fulcrum acts on the rivet 25J as shown by the arrow B by the inner peripheral edge of the tab hole 15J of the tab 1J for opening the can. At this time, as shown in Fig. 9(b), the tab 1J for opening the can bends between the rivet 25J and the tab nose 16J and the tab hole 15J is deformed, so that the tab J1 for opening the can detaches from the rivet 25J and there is a problem that it cannot be opened. In this regard, making the outer diameter of the rivet head 251J of the rivet larger than the inner diameter of the tab hole 15J is one of the countermeasures, but the processing of the rivet itself becomes severe and there is a possibility of generating a rivet crack. Also, attempts to reduce the opening force, such as forming the score deeper, are accompanied by difficulties such as a decrease in the blow-up performance when the internal pressure of the can rises.

[0008] Therefore, in the can lids described in Patent Documents 1 and 2 above, although it is effective for preventing the rotation of the tab for opening the can, further improvement is desired for measures against tab detachment of the tab for opening the can during opening, and there is a limit to thinning.

[0009] The present invention has been made in view of such circumstances, and an object thereof is to provide a can lid capable of suppressing deformation of the tab hole and preventing tab detachment from the can lid body, and a manufacturing method thereof.

Means for Solving the Problems

[0010] The can lid of the present invention is attached to the opening of the can body and includes a can lid body made of an aluminum alloy having an opening piece partitioned by a score on a substantially disc-shaped panel portion, and an opening tab for opening the opening piece. Inside the panel portion, a rivet is formed that protrudes from the panel portion and fixes the opening tab between the panel portion and the rivet head. In a plan view of the can lid body, within a range of 45° on both sides of a straight line extending from at least the center of the rivet toward the tab nose that contacts the opening piece of the opening tab, a reinforcing portion is formed by deforming the opening tab by compression or bending within an annular region surrounded by the outer peripheral edge of the rivet head and a circle having a diameter 1 mm larger than the outer diameter of the rivet head.

[0011] In the present invention, since the reinforcing portion is formed within the annular region 1 mm around the outer periphery of the rivet head, it becomes difficult for the opening tab to deform at the portion between the rivet and the tab nose. When opening the can by breaking the score using the opening tab to open the opening piece, the deformation of the opening tab due to the opening force B shown in Fig. 9(a) is reduced, and it is possible to suppress the opening tab from coming off the can lid body. In particular, the range of 45° on both sides of the annular region is near the portion where the tab nose contacts during can opening, and since the force acting is larger than other portions, at least by forming the reinforcing portion in this range, the deformation of the tab hole can be suppressed. If the reinforcing portion is formed radially inward (rivet side) from the annular region, the thickness of the tab hole end face may decrease, resulting in a decrease in the strength of the tab hole, or cracks may occur in the rivet head due to variations in the thickness of the tab hole end face. On the other hand, if the reinforcing portion is formed radially outward (opposite side to the rivet) from the annular region, the distance between the rivet head and the reinforcing portion is too far, so the opening tab is likely to deform and come off.

[0012] The manufacturing method of the can lid of the present invention includes a can lid body made of an aluminum alloy that is attached to the opening of the can body and has an opening piece partitioned by a score on a substantially disc-shaped panel portion, and an opening tab for opening the opening piece. A manufacturing method of a can lid in which a rivet that protrudes from the panel portion and fixes the opening tab is formed inside the panel portion, the method comprising: a main body forming step of deforming the panel portion of the can lid body to form a protrusion; After inserting the tab hole formed in the opening tab into the protrusion and attaching the opening tab, the tip of the protrusion is crushed to form a rivet head on the opening tab, thereby forming the rivet and fixing the opening tab to the panel portion. A tab fixing step; and before the tab fixing step, in a plan view of the opening tab, at least within a range of 45° on both sides of a straight line extending from the center of the rivet toward a tab nose that contacts the opening piece of the opening tab, An intensifying portion forming step of deforming the opening tab by compression or bending within an annular region surrounded by the outer peripheral edge of the rivet head and a circle having a diameter 1 mm larger than the outer diameter of the rivet head to form an intensifying portion.

[0013] Here, if an intensifying portion is formed on the opening tab simultaneously with or after fixing the opening tab to the can lid body, it is necessary to pressurize the opening tab on the can lid body, and the intensifying portion may not be appropriately formed on the opening tab, or the can lid body may be dented by the above pressurization. On the other hand, in the present invention, since the reinforcing portion is formed in the annular region of the opening tab and then fixed to the can lid body, the reinforcing portion can be surely formed on the opening tab, and the can lid body can be prevented from being dented. And, the can lid manufactured by such a manufacturing method has a reinforcing portion formed in an annular region of 1 mm around the outer periphery of the rivet head. Therefore, when the score is broken using the opening tab to open the opening piece, it is possible to prevent the tab hole from being deformed and coming off from the can lid body.

[0014] As one aspect of the manufacturing method of the can lid of the present invention, in the intensifying portion forming step, it is preferable to form a recess having a rectangular cross-section as the intensifying portion by performing coining on the annular region. In the above aspect, since the concave portion is compression-formed by coining, the portion where the concave portion is formed is work-hardened, and the tab for opening the can can be reinforced.

[0015] As another aspect of the method for manufacturing a can lid of the present invention, in the reinforcing portion forming step, a bending process may be performed on the annular region to form a curved portion protruding in a direction opposite to the can lid body direction as the reinforcing portion. In the above aspect, the tab for opening the can can be reinforced by strengthening the cross-sectional shape by the curved portion.

[0016] In this method for manufacturing a can lid, the curved portion may be formed in the circumferential direction of the annular region, and in the tab fixing step, the curved portion formed in the reinforcing portion forming step may be further crushed. In the above aspect, since the curved portion is formed in the circumferential direction of the annular region, when the curved portion is crushed, the curved portion extends radially toward the side surface of the rivet, and its tip approaches or contacts the side surface of the rivet. For this reason, when scoring is broken using the tab for opening the can to open the opening piece, it is possible to suppress deformation of the tab hole and detachment of the tab from the can lid body, and it is also possible to suppress rotation of the tab for opening the can.

Advantages of the Invention

[0017] According to the present invention, by providing a reinforcing portion on the tab for opening the can, deformation of the tab hole can be suppressed and detachment of the tab from the can lid body can be prevented.

Brief Description of the Drawings

[0018]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

[0019] Hereinafter, each embodiment of the can lid and the manufacturing method of the can lid according to the present invention will be described with reference to the drawings.

[0020] [First Embodiment] The can lid 100 of this embodiment is a so-called stay-on tab type can lid used for cans for beverages etc. As shown in FIG. 1, it is composed of a can lid body 2 and an opening tab 1 attached to this can lid body 2. Further, the can lid 100 configured in this way is manufactured into a can 101 that seals the inside of the can body 3 by being wound around the opening end portion of the can body 3 filled with the contents, as shown in FIG. 2. Although illustration is omitted, the can body 3 is formed in a bottomed cylindrical shape. These can body 3, can lid body 2, and opening tab 1 are each formed of an aluminum alloy (for example, Al-Mg alloy, Al-Mn alloy, Al-Mg-Mn alloy, etc.).

[0021] As shown in FIGS. 1 and 2, the can lid body 2 includes a substantially disc-shaped panel portion 21 and an annular countersink portion 22 provided so as to protrude downward along the outer peripheral portion of the panel portion 21. A panel boss 23 formed in a concave shape is provided in a part of the panel portion 21. On the bottom surface of the panel boss 23, a score 24 that defines an opening piece 27, a rivet 25 that protrudes from the panel portion 21 and is inserted into a tab hole 15 of the opening tab 1 for opening the can, and a finger hook recess 26 that is disposed on the opposite side of the opening piece 27 via the rivet 25 are provided.

[0022] The score 24 is configured to be broken by the pressing of the opening tab 1 and to push the opening piece 27 into the can to open the drinking port. An inner bead 28 protruding upward along the score 24 is formed on the opening piece 27, and the opening piece 27 is reinforced. The rivet 25 is formed by performing a deep drawing process on the central portion of the upper surface of the panel portion 21 and a coining process of pressing the periphery thereof in a ring shape to project the central portion of the panel portion 21 upward, and has a rivet head 251 having a shape that projects radially outward at its tip. Further, the finger hook recess 26 is formed along the rear end portion of the opening tab 1. Thereby, the opener can easily place a finger on the rear end portion and easily pull up the rear end portion. In addition, a convex portion 29 called a dimple is formed between the rivet 25 and the finger hook recess 26. The convex portion 29 protrudes from the upper surface of the panel boss 23 and two convex portions 29 are formed at intervals in the width direction of the opening tab 1. By the outer edge portion of the opening tab 1 being caught by the convex portion 29, it is possible to prevent the opening tab 1 from rotating around the rivet 25.

[0023] As shown in FIGS. 1 to 4, the tab 1 for opening a can has a curled edge formed by bending the peripheral edge of the tab body 11 forming the outer shape downward, thereby enhancing the overall rigidity. Near the center of the tab body 11, a fixing portion 12 for fixing to the rivet 25 of the can lid body 2 is provided. The fixing portion 12 is partitioned and formed by a U-shaped slot 13. The tab 1 for opening a can is attached to the can lid body 2 by inserting the rivet 25 of the can lid body 2 into the tab hole 15 formed in the fixing portion 12 and caulking the rivet 25 with the lower surface of the fixing portion 12 in contact with the bottom surface of the panel boss 23.

[0024] In addition, the tab 1 for opening a can includes a pressing portion 16 (corresponding to the tab nose of the present invention) provided at the tip of the tab body 11 for pressing down and opening the opening piece 27 of the can lid body 2, and a pulling portion 17 provided at the rear end portion disposed on the opposite side of the fixing portion 12 of the tab body 11 with respect to the pressing portion 16 and pulled up from the can lid body 2 to press down the pressing portion 16, and a tab panel 14 provided between the pulling portion 17 and the fixing portion 12 of the tab body 11 and having a concave upper surface formed to be convex toward the lower surface side. Note that the form of the tab panel 14 is not limited to the above form, and a so-called finger hole may be formed by blanking the tab panel portion in an oval shape and bending the cross section downward.

[0025] (Configuration of the reinforcing portion) As shown in FIGS. 3 and 4, in the fixing portion 12 of the tab for opening a can, a reinforcing portion 41 is formed in an annular region Ar1 that is surrounded by the outer peripheral edge of the rivet head 251 and a circle having a diameter 1 mm larger than the outer diameter of the rivet head 251 and is located outside the rivet head 251. This reinforcing portion 41 is formed by bending and consists of a curved portion that protrudes in a direction opposite to the can lid body 2. In the present embodiment, the reinforcing portion 41 is formed in substantially the entire area within the annular region Ar1 (the range of 180° on both sides of the above straight line, that is, the range of θ = 180°) and is formed so as to surround the outer peripheral edge of the rivet head 251. In other words, the reinforcing portion 41 is formed in the circumferential direction within the annular region Ar1 and is formed in an annular shape in plan view. Since this reinforcing portion 41 mainly reinforces the space between the rivet head 251 and the pressing portion 16 (tab nose), it is sufficient that it is formed at least in a range of 45° on both sides (the range of θ° on both sides shown in FIG. 3) of a straight line extending from the center of at least the rivet head 251 within the annular region Ar1 toward the pressing portion 16 (tab nose) of the tab 1 for opening a can.

[0026] By forming the reinforcing portion 41 formed of such a curved portion so as to surround the outer peripheral edge of the rivet head 251, the cross-sectional shape of the fixing portion 12 is strengthened, and the tab 1 for opening a can is reinforced. The outer diameter d1 of the rivet head 251 is set to 3.6 mm to 4.6 mm, the outer diameter d2 of the tab hole 15 is set to 3.2 mm to 4.2 mm, and the outer diameter d3 of the annular region Ar1 is set to 3.6 mm to 5.6 mm.

[0027] If the reinforcing portion 41 is formed radially inside (on the side of the rivet 25) of the annular region Ar1, the thickness of the tab hole end face may decrease, the strength of the tab hole may decrease, or cracks may occur in the rivet head due to variations in the thickness of the tab hole end face. On the other hand, if the reinforcing portion 41 is formed radially outside (on the side opposite to the rivet 25) of the annular region Ar1, the distance between the rivet head 251 and the reinforcing portion 41 is too far, so the tab 1 for opening a can is likely to be deformed and detached. Also, the range of 45° on both sides of the annular region Ar1 is near the portion where the pressing portion 16 contacts during can opening, and since the force acting is greater than that of other portions, it is necessary to form the reinforcing portion 41 at least in this range.

[0028] [Method for manufacturing a can lid] Next, the method for manufacturing a can lid according to the present embodiment will be described. As shown in FIG. 5, the method for manufacturing a can lid according to the present embodiment includes a main body forming step (S11) of deforming the panel portion 21 of the can lid main body 2 to form a protrusion, a tab forming step (S12) of forming an opening tab 1 to be fixed to the can lid main body 2, and in a plan view of the opening tab 1, at least within a range of 45° on both sides of a straight line extending from the center of at least the rivet 25 toward the pressing portion 16 (tab nose) that contacts the opening piece 27 of the opening tab 1, an annular region Ar1 surrounded by the outer peripheral edge of the rivet head 251 and a circle having a diameter 1 mm larger than the outer diameter d1 of the rivet head 251, a reinforcing portion forming step (S13) of deforming the opening tab 1 by bending to form a reinforcing portion 41, and after inserting the tab hole 15 formed in the opening tab 1 through the protrusion of the can lid main body 2 and attaching the opening tab 1, crushing the tip of the protrusion and forming the rivet head 251 on the opening tab 1 to form a rivet 25 and fix the opening tab 1 to the panel portion, a tab fixing step (S14). In the present embodiment, the can lid main body and the opening tab are formed separately, and the opening tab 1 is fixed to the can lid main body 2 by the tab fixing step (S14). Hereinafter, each step will be described.

[0029] (Main body forming step) In the main body forming step, an opening piece 27 partitioned by a score 24 is formed in a substantially disk-shaped panel portion 21 made of an aluminum alloy, and a protrusion protruding from the panel portion 21 is formed inside the panel portion 21. This protrusion is formed by performing a deep drawing process on the central portion of the upper surface of the panel portion 21 and a coining process of pressing the periphery thereof in a ring shape to project the central portion of the panel portion 21 upward. Since the tip of the protrusion is crushed by the tab fixing step described later to become the rivet 25, its outer diameter is set to a size slightly smaller than the outer diameter of the tab hole 15.

[0030] (Opening tab forming step) In the tab forming process for opening the can, a tab 1 for opening the can is formed and fixed to the can lid body 2. Specifically, the tab 1 for opening the can is formed by processing a metal plate with a thickness of 0.24 m or more and 0.31 mm or less. After forming the hole shape such as the tab hole 15 in the metal plate for the tab 1 for opening the can, the blank is punched out, shaped such as an uneven shape, and the peripheral edge of the tab body 11 is curled. Then, the peripheral edge of the rear end portion is crushed to form the pulling-up portion 17.

[0031] (Reinforcement portion forming process) Then, in a plan view of the tab 1 for opening the can, the tab 1 for opening the can is deformed by bending within an annular region Ar1 surrounded by the outer peripheral edge of the rivet head 251 and a circle with a diameter d3 that is 1 mm larger than the outer diameter d1 of the rivet head 251 to form a curved portion and form a reinforcement portion 41. Specifically, as shown in FIG. 10, a pressing block (tab hole reforming punch 61) having an annular recess 611 is brought into contact with the surface of the tab 1 for opening the can on the side opposite to the can lid body 2, and a pressing block (tab hole reforming die 62) having an annular convex portion 611 corresponding to the recess 621 is brought into contact with the surface on the can lid body 2 side, and pressing is performed in this state to perform a bending process on the annular region Ar1. As a result, as shown in FIG. 6, a curved portion protruding in a direction opposite to the can lid body 2 is formed as the reinforcement portion 41. Note that it is preferable that the width of the curved portion formed as the reinforcement portion 41 is 0.3 mm to 0.8 mm and the height is 0.05 mm to 0.17 mm. By setting the dimensions of this curved portion within the above range, the cross-sectional shape is strengthened, and as a result, the tab 1 for opening the can is reinforced.

[0032] (Tab fixing process) After inserting the tab hole 15 formed in the tab 1 for opening the can through the protrusion of the can lid body 2 and attaching the tab 1 for opening the can, the tip of the protrusion is crushed and the rivet head 251 is formed on the tab 1 for opening the can to form the rivet 25 and fix the tab 1 for opening the can to the panel portion 21. Thereby, the can lid 100 is formed.

[0033] Here, if the reinforcing portion 41 is formed on the opening tab 1 simultaneously with or after the fixing of the opening tab 1 to the can lid body 2, it is necessary to press the opening tab 1 on the can lid body 2, and there is a risk that the reinforcing portion 41 cannot be appropriately formed on the opening tab 1, or the can lid body 2 may be dented by the above pressing. Therefore, in this embodiment, since the reinforcing portion 41 is formed in the annular region Ar1 of the opening tab 1 and then fixed to the can lid body 2, the reinforcing portion 41 can be surely formed on the opening tab 1, and the can lid body 2 can be prevented from being dented.

[0034] And, in the can lid 100 manufactured by such a manufacturing method, since the reinforcing portion 41 is formed in the annular region Ar1 with a radius of 1 mm around the outer periphery of the rivet head 251, the opening tab 1 is less likely to be deformed at the portion between the rivet 25 and the pressing portion 16. When opening the can by breaking the score 24 using the opening tab 1 to open the opening piece 27, the deformation of the opening tab 1 due to the pulling force B shown in Fig. 9(a) is reduced, and the can lid body 2 can be prevented from coming off. In particular, the range of 45° on both sides of the annular region Ar1 is near the portion where the pressing portion 16 contacts during can opening, and the force acting is larger than other portions. Therefore, by forming the reinforcing portion 41 at least in this range, the deformation of the tab hole 15 can be suppressed. Also, in the reinforcing portion forming step, by performing a bending process on the annular region Ar1 to form a curved portion protruding in the direction opposite to the can lid body 2 as the reinforcing portion 41, the cross-sectional shape is strengthened, so that the opening tab 1 can be reinforced.

[0035] [Second Embodiment] Next, the can lid and its manufacturing method according to the second embodiment of the present invention will be described with reference to the drawings. Fig. 7 is a cross-sectional view showing the step of forming a reinforcing portion on the opening tab of the can lid of this embodiment. In the following description, the description of the same and substantially the same configurations as the can lid 100 of the first embodiment will be omitted or simplified. In the lid of the can of the present embodiment, the shape of the reinforcing portion formed on the opening tab 1A is different from that of the reinforcing portion 41 of the first embodiment. Specifically, similar to the case of the first embodiment, a curved portion is formed in the reinforcing portion 41A of the present embodiment before fixing it to the can lid body 2. However, instead of fixing it to the can lid body 2 while maintaining its original state as in the first embodiment, as shown in FIG. 7, in the tab fixing step, the curved portion formed in the circumferential direction of the annular region Ar1 is sandwiched and further crushed by the pressing block 51 and the pressing block 52. More specifically, the pressing block 51 has an annular convex portion 512 that protrudes toward the can lid body 2 in the circumferential direction of the concave portion 511 for crushing the tip of the protrusion that becomes the rivet 25. The pressing block 52 has a convex portion 521 that supports the tip of the protrusion that becomes the rivet 25. By sandwiching and pressing the can lid body 2 and the opening tab 1A with these pressing block 51 and pressing block 52, the curved portion is pressed by the annular convex portion 512 to become the reinforcing portion 41A. Note that it is not necessary to crush the reinforcing portion 41A until it becomes flat, and this pressing is adjusted within a range that does not cause excessive deformation to the can lid body 2, that is, within a range that does not affect the pressure resistance strength, opening performance, etc. of the can lid.

[0036] In the present embodiment, since the curved portion is formed in the circumferential direction of the annular region Ar1, when the curved portion is crushed, the curved portion extends radially toward the side surface of the rivet 25, and thus the tip thereof approaches or contacts the side surface of the rivet 25. Therefore, when the score 24 is broken using the opening tab 1A to open the opening piece 27, it is possible to suppress the deformation of the tab hole 15 and its detachment from the can lid body 2, and also to suppress the rotation of the opening tab 1A.

[0037] [Third Embodiment] Next, the lid of the can and its manufacturing method according to the third embodiment of the present invention will be described with reference to the drawings. FIG. 8 is a cross-sectional view showing the process of forming a reinforcing portion on the opening tab of the lid of the present embodiment. In the following description, for the same and substantially the same configurations as the can lid 100 of the first embodiment, the description will be omitted or simplified. In the can lid of this embodiment, the opening tab 1B has a reinforcing portion with a shape different from that of the reinforcing portions 41 and 41A in the first and second embodiments. Specifically, as shown in FIG. 8, the reinforcing portion 41B of this embodiment is formed by coining in the circumferential direction of the annular region Ar1 in the reinforcing portion forming step, so that a concave portion having a rectangular cross-section with the surface opposite to the can lid body 2 being recessed is formed as the reinforcing portion 41B. The width of this concave portion is 0.3 mm to 0.9 mm, and the depth is 0.03 mm to 0.13 mm. In this embodiment, since the concave portion is compression-formed as the reinforcing portion 41B by coining, the portion where the concave portion is formed is work-hardened, and the opening tab 1 can be reinforced.

[0038] Note that the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the spirit of the present invention. For example, in the first and second embodiments described above, the reinforcing portions 41 and 41A are formed in the circumferential direction of the annular region Ar1. However, the present invention is not limited to this, and as long as they are formed within a range of 45° on both sides of a straight line extending from at least the center of the rivet 25 in the annular region Ar1 toward the pressing portion 16 (tab nose) that contacts the opening piece 27 of the opening tab 1, they do not have to be formed in an annular shape in the circumferential direction of the annular region Ar1. Also, in all of the embodiments, the reinforcing portions 41 and 41A are formed along the circumferential direction of the annular region Ar1. However, a plurality of them may be formed radially around the rivet 25.

[0039] In each of the above embodiments, the reinforcing portions 41 and 41A are formed by deforming the fixing portion 12 by bending, and the reinforcing portion 41B is formed by coining. However, the present invention is not limited to this. That is, the formation of the reinforcing portion is not limited to the above-described processing, and can be appropriately set as long as it is processing that can reinforce the cross-sectional shape of the fixing portion 12.

[0040] In the first embodiment described above, the reinforcing portion 41 is formed as a curved portion protruding in the direction opposite to the can lid body 2. However, the present invention is not limited to this, and a curved portion protruding toward the can lid body 2 may be formed. Also, a double curved portion may be formed within the annular region Ar1. In the third embodiment described above, as the reinforcing portion 41B, a concave portion having a rectangular cross section with the surface opposite to the can lid body 2 being concave is formed. However, the present invention is not limited to this, and a concave portion having a rectangular cross section with the surface on the can lid body 2 side being concave may be formed. Further, the shape of the concave portion is not limited to a rectangular cross section in a sectional view, and may be appropriately set, such as a semicircular cross section in a sectional view.

Example

[0041] As samples of the examples, 50 can lids each formed with a can-opening tab having the same shape as the can-opening tab 1A of the second embodiment were formed. Further, as materials for the comparative examples, 50 can lids each formed with a can-opening tab having the same shape as the can-opening tab 1J shown in FIG. 9 were formed. At this time, as the can-opening tab 1 for the sample of the example, a reinforcing portion was formed on the can-opening tab using the prototype die shown in FIG. 10. Specifically, the tab hole reforming punch 61 having an annular concave portion 611 is brought into contact with the surface of the can-opening tab 1 opposite to the can lid body 2, and the tab hole reforming die 62 having an annular convex portion 621 corresponding to the concave portion 611 is brought into contact with the surface on the can lid body 2 side, and pressure is applied in this state to perform bending processing on the annular region. This prototype die was set with the tool height of the stake punch in the lid riveting process being low in order to intentionally create a situation where tab detachment is occasionally seen during tab strength measurement, and the die was adjusted so that the tab hole diameter became 3.50 m with respect to the lower limit of the process standard of 3.68 mm. While maintaining this tab hole diameter, the above-described prototype die was attached to the tab forming process for processing, and further, forming was added so as to lightly crush the uppermost portion of the bending process by the annular convex portion 512 in the tab fixing process. The dimensions of each part were such that the width w2 of the concave portion 611 was 0.46 mm, the height h1 of the convex portion 621 was 0.12 mm, the diameter φ1 of the convex portion 621 was 4.3 mm, the radius of curvature R1 of the radially inner opening end of the concave portion 611 was 0.05 mm, and the radius of curvature of the convex portion 621 was 0.1 mm. On the other hand, as the normal die for manufacturing the sample of the comparative example, a general die not provided with the concave portion 611 and the convex portion 621 was used. That is, as a sample of the example, a can lid with an opening tab having a reinforcing portion formed in an annular region was prepared, and as a sample of the comparative example, a can lid with a conventional opening tab without a reinforcing portion formed was prepared. Each of these opening tabs was formed of an aluminum alloy (5182H48), and the plate thickness was set to 0.28 mm, the tab hole diameter was set to 3.3 mm, and the opening force of the score was set to 23 N.

[0042] For each of these samples (50 each) of the example and the comparative example, the strength of the opening tab was measured. The strength of the opening tab was measured by rotating the opening tab 90° in the circumferential direction of the can lid body to move the tab nose away from the score, and then measuring the maximum load until any of the defects described below occurred when the opening tab was pulled up. The defects of the opening tab after measurement included the number of any of the defects of "tab detachment" where the opening tab came off from the rivet, "tab crack" where a crack occurred in the opening tab, and "tab bending" where the opening tab bent near the rivet head. These results are shown in Table 1.

[0043]

Table 1

[0044] As can be seen from the results in Table 1, the tab strength of the example using the prototype die was higher than that of the comparative example using the conventional normal die in terms of the maximum value, minimum value, and average value. Also, for the defects of the opening tab after measurement, 9 cases of "tab detachment" occurred in the opening tab of the comparative example, while the defect of "tab detachment" was 0 in the example. From these facts, it was found that even for a can lid with a tab hole diameter smaller than normal and prone to tab detachment, by forming a reinforcing portion in the above annular region, the opening tab is reinforced and tab detachment during can opening can be prevented.

Explanation of Reference Signs

[0045] 1, 1A, 1B Opening tab 2 Can lid body 3 Can body 11 Tab body 12 Fixing part 13 Slot 14 Tab panel 15 Tab hole 16 Pushing part (tab nose) 17 Pulling part 21 Panel part 22 Countersink part 23 Panel boss 24 Score 25 Rivet 26 Finger-hooking recess 27 Opening piece 28 Inner bead 29 Protrusion 41, 41A, 41B Reinforcing part 51, 52 Pressing block 61 Tab hole reforming punch 611 Recess 62 Tab hole reforming die 621 Protrusion 100 Can lid 101 Can Ar1 Annular region

Claims

1. A can lid body made of an aluminum alloy, which is attached to the opening of the can body, has an opening piece partitioned by a score on a substantially disc-shaped panel portion, and an opening tab for opening the opening piece, inside the panel portion, a rivet is formed which protrudes from the panel portion and fixes the opening tab between the panel portion and the rivet head, in a plan view of the can lid body, within a range of 45° on both sides of a straight line extending at least from the center of the rivet toward the tab nose that contacts the opening piece of the opening tab, an annular region surrounded by the outer peripheral edge of the rivet head and a circle with a diameter 1 mm larger than the outer diameter of the rivet head, a reinforcing portion is formed along the circumferential direction by deforming the opening tab by compression or bending, A can lid, characterized in that the inner peripheral edge of the reinforcing portion is separated radially outward from the outer peripheral edge of the rivet head.

2. A method for manufacturing the can lid according to Claim 1, a main body forming step of deforming the panel portion of the can lid body to form a protrusion, inserting a tab hole formed in the opening tab through the protrusion to attach the opening tab, and then crushing the tip of the protrusion to form a rivet head on the opening tab, thereby forming the rivet and fixing the opening tab to the panel portion; a tab fixing step; before the tab fixing step, in a plan view of the opening tab, within a range of 45° on both sides of a straight line extending at least from the center of the rivet toward the tab nose that contacts the opening piece of the opening tab, an annular region surrounded by the outer peripheral edge of the rivet head and a circle with a diameter 1 mm larger than the outer diameter of the rivet head, a reinforcing portion forming step of deforming the opening tab by compression or bending to form a reinforcing portion. A method for manufacturing a can lid, characterized by comprising the steps.

3. The method for manufacturing a can lid according to Claim 2, characterized in that in the reinforcing portion forming step, coining is performed on the annular region to form a concave portion having a rectangular cross-section as the reinforcing portion.

4. The method for manufacturing a can lid according to Claim 2, characterized in that in the reinforcing portion forming step, bending is performed on the annular region to form a curved portion protruding in a direction opposite to the can lid body direction as the reinforcing portion.

5. The manufacturing method of the can lid according to claim 4, wherein the bending part is formed in the circumferential direction of the annular region, and in the tab fixing step, the bending part formed in the reinforcing part forming step is further crushed.

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