Can body

Abstract

To suppress buckling of a lid body while securing a constant withstanding pressure load on a can main body.SOLUTION: A can body comprises a bottomed cylindrical can main body 1 having a can axis in its center, and also has: a dome part 4 formed at a center part of a bottom part 3 of the can main body 1, the dome part being in a concave curved-surface shape concave toward a can-axially upper end side; an annular convex part 5 formed on an outer peripheral side of the dome part 4 continuously in a circumferential direction around the can axis, the annular convex part extending toward the can-axially upper end side while extending toward a radially outer peripheral side relative to the can axis after protruding toward the can-axially lower end; and a concave part 5b formed at an inner wall part 5a of the annular convex part 5 protruding from the dome part 4 toward the can-axially lower end side, the concave part being made concave toward the radially outer peripheral side relative to the can axis through bottom reformation processing. A bottom growth amount as an amount of protrusion deformation of a projection end 5d, protruding most toward the can-axially lower end side, of the annular convex part 5 toward the can-axially lower end side when internal pressure of 706 kPa is made to act on the inside of the can main body 1 in a no-load state is 1.0-2.0 mm.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a can body such as an aluminum can, which has a bottomed cylindrical can body centered on a can axis, and which is filled with contents such as a beverage and has an upper opening sealed with a lid. [Background technology]

[0002] In such can bodies, a dome-shaped concave curved surface recessed toward the upper end of the can body is formed in the center of the bottom of the can body, and an annular protrusion is formed continuously in the circumferential direction around the can axis on the outer periphery of this dome, which protrudes toward the lower end of the can axis direction as it moves radially outward relative to the can axis and then moves toward the upper end.

[0003] Such cans are filled with contents such as shochu and carbonated water (known as shochu highball, or chuhai for short) or whiskey and carbonated water (known as highball), and then sealed by wrapping a lid with a pull tab around the top opening, and then distributed on the market as so-called two-piece cans.

[0004] In recent years, there has been a strong demand for thinner can bodies and lids in order to conserve resources used in the metal materials that form such can bodies and to conserve energy during material production. For example, in the case of aluminum alloy can bodies, there is a demand for can bodies to be manufactured by forming a cup-shaped blank by drawing an aluminum alloy plate having a thickness of approximately 0.230 mm to 0.300 mm.

[0005] However, with such thin-walled cans, the pressure resistance of the can body is significantly reduced, and if the contents filled inside are something like the carbonated beverage mentioned above, internal pressure acts on the filled can, which has been filled with the contents and sealed with the lid, causing a phenomenon known as bottom growth, in which the tip of the annular protrusion at the bottom of the can body protrudes and deforms toward the lower end in the axial direction of the can, which could cause a blockage in the chute used to transport the filled can, or a phenomenon known as buckling, in which the dome portion bulges and protrudes toward the lower end of the can body in the direction of the can's axis.

[0006] Therefore, in order to suppress bottom growth and buckling at the bottom of the can body, Patent Document 1 proposes a can body in which a dome portion and an annular convex portion are formed at the bottom of the can body, and in which, in a vertical cross section along the can axis, the inner wall of the annular convex portion that is connected to the dome portion is formed by bottom reforming processing with a first concave curved surface portion that is curved outward in the radial direction perpendicular to the can axis when viewed in vertical cross section along the can axis, and the dome portion is formed with a dome top located on the can axis, a second concave curved surface portion that is connected to the radially outer side of the dome top and has a concave curved shape with a smaller radius of curvature than the dome top, and a tapered portion that is located on the outer peripheral edge of the dome portion, connects the first concave curved surface portion and the second concave curved surface portion, and is linear and tangent to the first concave curved surface portion and the second concave curved surface portion. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2016-043991 Summary of the Invention [Problem to be solved by the invention]

[0008] In the can body described in Patent Document 1, the first and second concave curved surface portions connected to both ends of the tapered portion are formed to be curved. Specifically, when viewed in vertical cross section of the can body, the radius of curvature of the first and second concave curved surface portions connected to the linear tapered portion becomes small, resulting in a sharper curve.

[0009] This makes it easier for stress to concentrate on these first and second concavely curved surface portions, ensuring that stress is concentrated in multiple stable locations, thereby improving the strength of the bottom of the can body and suppressing deformation. Therefore, when the internal pressure of the can body increases, stress is dispersed to the first and second concavely curved surface portions, increasing the pressure resistance of the can body and suppressing bottom growth and buckling of the bottom of the can body.

[0010] However, when bottom growth and buckling at the bottom of the can body are suppressed by increasing the pressure resistance of the can body in this way, if the lid body is also made thin-walled to save resources and energy, the pressure resistance of the lid body will decrease, and when the internal pressure of the can body increases in a filled can, there is a risk of buckling of the lid body, in which the lid body bulges out toward the upper end of the can body.

[0011] The present invention has been made against this background, and aims to provide a can body that can suppress buckling of the lid body when internal pressure acts on the can body, while ensuring a certain pressure-resistant load in the can body. [Means for solving the problem]

[0012] In order to achieve the object by solving the above-mentioned problems, the present invention provides a can body having a bottomed cylindrical can body centered on a can axis, wherein a dome portion having a concave curved surface recessed toward the upper end in the can axis direction is formed in the center of the bottom of the can body, and an annular convex portion is formed on the outer periphery of the dome portion, which protrudes toward the lower end in the can axis direction and then faces the outer periphery in the radial direction relative to the can axis, and the annular convex portion is formed continuously in the circumferential direction around the can axis, and the annular convex portion protruding toward the upper end in the can axis direction from the dome portion is formed on the inner wall of the annular convex portion by bottom reforming, the annular convex portion being recessed toward the outer periphery in the radial direction relative to the can axis, and a bottom growth amount, which is the amount of protrusion deformation of the tip of the annular convex portion toward the lower end in the can axis direction when an internal pressure of 706 kPa is applied to the inside of the can body from an unloaded state, is 1.0 mm the thickness of the dome portion of the bottom of the can body on the can axis is within the range of 0.270 mm to 0.290 mm; the tip of the annular convex portion is formed into a convex arc shape in a cross section along the can axis, with the periphery of the tip being convex toward the lower end of the can axis direction; the radius of this convex arc inside the can body is R (mm), the diameter of a circle formed by the tip around the can axis is D (mm), the diameter of a circle formed by the bottom of the recess that is most recessed toward the outer periphery in the radial direction relative to the can axis is d (mm), and the thickness of the bottom of the can body in the radial direction relative to the can axis at the position between this bottom portion and the tip of the annular convex portion where the tip protrudes most toward the can axis side is t (mm), the bottom reform depth, expressed as the absolute value of (D-2×(R+t)-d) / 2, is within the range of 0.680 mm to 1.085 mm. After filling the contents (gas volume 3.0) inside, a lid with a pressure resistance of 740 kPa is attached to the top opening and sealed. When a retention test is carried out at 60°C for 10 to 40 minutes, no buckling of the lid occurs. It is characterized by:

[0013] In a can body configured in this manner, when an internal pressure of 706 kPa is applied to the inside of the can body from an unloaded state, the bottom growth amount, which is the amount of protrusion deformation of the tip of the annular protrusion that protrudes most toward the bottom end in the can axial direction, is within the range of 1.0 mm to 2.0 mm.In other words, a certain amount of bottom growth is allowed in the annular protrusion as long as it does not cause clogging of the chute for transporting filled cans.

[0014] Therefore, even if internal pressure acts on the can body with the lid attached to the top opening and sealed, the internal pressure can be absorbed by bottom growth of the annular convex portion at the bottom of the can body. Therefore, with the can body configured as described above, the internal pressure acting on the lid can be reduced, making it possible to prevent buckling of the lid.

[0015] If the bottom growth of the annular convex portion when an internal pressure of 706 kPa is applied to the can body is less than 1.0 mm, buckling of the lid cannot be prevented. Conversely, if the bottom growth of the annular convex portion when an internal pressure of 706 kPa is applied to the can body is more than 2.0 mm, clogging may occur in the chute used to transport filled cans. The can body of the present invention is preferably applied to a can body having a thin-walled can body for resource and energy conservation, as described above. In the can body of such a can body, the thickness of the dome portion of the bottom of the can body above the can axis is approximately equal to the thickness of the sheet material before it is formed into the can body (original sheet thickness). Therefore, it is desirable that the thickness of the dome portion of the bottom of the can body on the can axis be within the range of 0.270 mm to 0.290 mm. If the thickness of the dome portion on the can axis is less than 0.270 mm, it may not be possible to ensure the pressure resistance strength required for the can body, and conversely, if it exceeds 0.290 mm, it may not be possible to achieve sufficient resource and energy conservation. Furthermore, when the tip of the annular protrusion is formed in a convex arc shape that is convex toward the lower end of the can axis direction in a cross section along the can axis, the radius of this convex arc inside the can body (punch R described later) is R (mm), the diameter of a circle formed around the can axis by the tip is D (mm), the diameter of a circle formed around the can axis by the bottom of the recess that is most recessed radially toward the outer periphery of the can axis (bottom reform inner diameter) is d (mm), and the thickness of the bottom of the can body in the radial direction relative to the can axis at the position where the tip protrudes most toward the can axis between this bottom and the tip of the annular protrusion is t (mm). It is desirable that the bottom reform depth, expressed as the absolute value of (D-2×(R+t)-d) / 2, be within the range of 0.680 mm to 1.085 mm. If the bottom reform depth exceeds 1.085 mm, the extensibility of the annular convex portion at the bottom of the can body may be impaired, making it impossible to set the bottom growth amount within the range of 1.0 mm to 2.0 mm, i.e., 1.0 mm or more. On the other hand, if the bottom reform depth is below 0.680 mm, the pressure resistance of the annular convex portion may be reduced.

[0016] It is desirable that the rate of increase in the bottom growth amount relative to an increase in internal pressure be stable, since this prevents excessive stress from being applied to the annular convex portion. Therefore, it is desirable that the bottom growth amount of the tip of the annular convex portion when an internal pressure of 686 kPa is applied to the inside of the can body from an unloaded state be within a range of 0.89 mm to 1.71 mm, and that the bottom growth amount of the tip of the annular convex portion when an internal pressure of 618 kPa is applied to the inside of the can body from an unloaded state be within a range of 0.55 mm to 1.29 mm.

[0017] That is, if the amount of bottom growth when an internal pressure of 686 kPa or 618 kPa is applied is smaller than the above range, the tip of the annular convex portion will rapidly protrude and deform when the amount of bottom growth when an internal pressure of 706 kPa is applied falls within the range of 1.0 mm to 2.0 mm, resulting in stress concentration. Also, if the amount of bottom growth when an internal pressure of 686 kPa or 618 kPa is applied is larger than the above range, the tip of the annular convex portion will rapidly protrude and deform when the internal pressure changes from no load to these values, again resulting in stress concentration. [Effects of the Invention]

[0022] As described above, according to the present invention, even if internal pressure acts on the can body when the lid is attached to the upper opening of the can body and sealed, the internal pressure can be absorbed by a certain degree of bottom growth of the annular convex portion at the bottom of the can body, and even if the lid is made thin-walled to save resources and energy, buckling of the lid due to such internal pressure can be prevented. [Brief explanation of the drawings]

[0023] [Figure 1] 1 is a cross-sectional view of a can body taken along a can axis, showing one embodiment of the present invention. [Figure 2] FIG. 2 is an enlarged cross-sectional view of the bottom of the can body of the embodiment shown in FIG. [Figure 3] FIG. 2 is a cross-sectional view taken along the can axis when measuring the amount of bottom growth of the can body before necking is applied to the upper opening side in the embodiment shown in FIG. 1. [Figure 4] FIG. 2 is a diagram showing the relationship between the internal pressure of the can body and the amount of bottom growth in the embodiment shown in FIG. DETAILED DESCRIPTION OF THE INVENTION

[0024] Figures 1 and 2 show one embodiment of the present invention, and Figure 3 shows the state in this embodiment where the bottom growth amount of a can body is measured before necking is applied to the upper opening side. Also, Figure 4 is a diagram showing the relationship between the internal pressure of the can body and the bottom growth amount in the embodiment shown in Figure 1.

[0025] The can body of this embodiment includes a cylindrical can body 1 with a bottom, which is made of a metal material such as aluminum or an aluminum alloy and is centered on a can axis C as shown in Fig. 1. That is, the can body 1 is configured by integrally forming a substantially cylindrical body portion 2 centered on the can axis C and a substantially disk-shaped bottom portion 3 that closes an opening at the lower end side of the body portion 2 (the lower side in Figs. 1 and 2, and the upper side in Fig. 3).

[0026] The bottom 3 of this can body 1 is formed in the center of the bottom 3 with a dome section 4 having a concave curved surface that is recessed toward the upper end in the direction of the can axis C (lower side in Figures 1 and 2, upper side in Figure 3), and on the outer periphery of this dome section 4, an annular protrusion 5 is formed continuously in the circumferential direction around the can axis C, protruding toward the lower end in the direction of the can axis C and then moving toward the outer periphery in the radial direction relative to the can axis C toward the upper end in the direction of the can axis C. Here, in this embodiment, the thickness of the dome section 4 of the bottom 3 of this can body 1 above the can axis C is within a range of 0.270 mm to 0.290 mm.

[0027] On the dome section 4 side of the inner wall section 5a of this annular protrusion 5 facing the can axis C, bottom reforming is performed on the bottom 3, thereby forming a recess 5b that is recessed in a concave curve shape on the radially outer periphery of the can axis C, as shown in Figure 2 in a cross section along the can axis C. Furthermore, as shown in Figure 2 in a cross section along the can axis C, the protrusion (lower end) 5c of the annular protrusion 5 is formed in a convex arc shape that is convex toward the lower end in the can axis C direction around a protrusion 5d that protrudes furthest toward the lower end in the can axis C direction.

[0028] Here, the inner wall 5a of the annular protrusion 5 facing the can axis C has been subjected to bottom reforming, so that the inner wall 5a is recessed from the dome portion 4 toward the radially outer periphery relative to the can axis C at the recess 5b, and then protrudes toward the radially inner periphery relative to the can axis C at the protruding end 5c in a convex curved cross section, leading to the protruding end 5d of the protruding end 5c having a convex arc cross section. The annular protrusion 5 also extends from the protruding end 5d toward the radially outer periphery relative to the can axis C, sloping upward in the direction of the can axis C, and continues to the lower end of the body 2.

[0029] Furthermore, the depth of recession from the position where the inner wall portion 5a of the annular protrusion 5 protrudes most radially inward relative to the can axis C to the bottom 5e of the recess 5b formed by the bottom reforming process, which is the most recessed radially outward relative to the can axis C, i.e., the bottom reform depth e, is expressed as the absolute value of (D-2×(R+t)-d) / 2, where R (mm) is the radius of the convex arc formed inside the can body 1 around the tip 5d of the annular protrusion 5 in a cross section along the can axis C, D (mm) is the diameter (ground diameter) of the circle formed by the tip 5d around the can axis C, d (mm) is the diameter (bottom reform inner diameter) of the circle formed by the bottom 5e of the recess 5b around the can axis C, and t (mm) is the thickness of the bottom 3 of the can body 1 in the radial direction relative to the can axis C at the position where the tip 5c protrudes most toward the can axis C from the bottom 5e to the tip 5d of the annular protrusion 5. In this embodiment, the bottom reform depth e is set within a range of 0.680 mm to 1.085 mm.

[0030] The bottom 3 of this can body 1 is formed so that when internal pressure is applied to the inside of the can body 1, the annular protrusion 5 deforms and protrudes toward the lower end in the direction of the can axis C, thereby causing bottom growth.When an internal pressure of 706 kPa is applied to the inside of the can body 1 from an unloaded state, the amount of bottom growth, which is the amount of protruding deformation of the tip 5d of the annular protrusion 5 toward the lower end in the direction of the can axis C, is within a range of 1.0 mm to 2.0 mm.

[0031] In this embodiment, the amount of bottom growth of the tip 5d of the annular protrusion 5 when an internal pressure of 686 kPa is applied to the inside of the can body 1 from an unloaded state is set to be within a range of 0.89 mm to 1.71 mm. Furthermore, in this embodiment, the amount of bottom growth of the tip 5d of the annular protrusion 5 when an internal pressure of 618 kPa is applied to the inside of the can body 1 from an unloaded state is set to be within a range of 0.55 mm to 1.29 mm.

[0032] In this embodiment, the barrel 2 of the can body 1 has a thin wall 2a at its lower end, which is continuous with the outer periphery of the bottom 3, and a flange 2b at its upper end, which is thicker than the wall 2a. The thick flange 2b has a shoulder 2c at its upper end, which tapers in diameter gradually toward the upper end, as shown in Fig. 1. At the top of the shoulder 2c, a lid attachment portion 2d, to which a lid with a pull tab (not shown) is attached by being fastened, is formed so as to extend radially outward from the can axis C.

[0033] The can body 1 of such a can body is manufactured by first punching a metal plate into a disk shape in a cupping press process using a cupping press and then drawing to form a shallow cup-shaped blank. In this embodiment, the metal plate formed into the cup-shaped blank in this cupping press process is an aluminum plate or an aluminum alloy plate conforming to A3004 or A3104 in JIS H 19, whose original thickness is within the range of 0.270 mm to 0.290 mm, which is approximately equal to the thickness of the dome portion 4 of the bottom portion 3 of the can body 1 on the can axis C, and which has a 0.2% proof stress of 255 N / mm after baking at 205°C for 20 minutes. 2 ~295N / mm 2 More preferably, the range is 265N / mm 2 ~284N / mm 2 The range is used.

[0034] Next, this cup-shaped material is redrawn and ironed with a punch in a DI press process using a DI press machine, and is stretched in the direction of the can axis C, thereby forming a cylindrical body 11 with a bottom as shown in Figure 3, in which a cylindrical portion 12 centered on the can axis C is formed on the outer periphery and a dome portion 4 and an annular protrusion 5 similar to those of the can body 1 are formed on the bottom 3.

[0035] The thickness of this bottomed cylinder 11 and the dome portion 4 of the bottom 3 of the can body 1 above the can axis C is approximately equal to the original thickness of the metal plate that is formed into a cup-shaped material in the cupping press process, and the radius R (mm) inside the can body 1 of the convex arc formed by the periphery of the tip 5d of the annular convex portion 5 in a cross section along the can axis C is approximately equal to the radius (punch R) of the convex arc formed by the tip of the punch in a cross section along the can axis C.

[0036] The cylindrical portion 12 of the bottomed cylinder 11 has a constant outer diameter (diameter) that is approximately equal to the outer diameter of the barrel portion 2 of the can body 1. Furthermore, the portion of the cylindrical portion 12 on the bottom 3 side is the wall portion 13, which is a thin-walled portion with a reduced thickness as described above, and the portion on the upper end side (lower side in FIG. 3 ) opposite the bottom 3 is the flange portion 14, which is thicker than the wall portion 13 as described above.

[0037] To form the wall portion 13 and flange portion 14 having different thicknesses in the cylindrical portion 12, recesses of a depth taking into consideration the difference in wall thickness may be formed in positions corresponding to the flange portion 14 on the outer surface of the punch that performs the ironing process between the ironing dies in the DI press, as described above. Also, the inner wall portion 5a of the bottom 3 of the can body 1 is subjected to bottom reforming processing to form the recesses 5b as described above.

[0038] The bottomed cylinder 11 thus formed is trimmed using a trimmer in a trimming process where the upper edge of the cylindrical portion 12 is cut off by a predetermined trim amount to make the height uniform, then washed and dried in a first washing process, and then painted on the inner and outer surfaces in a painting process and baked. Furthermore, in a bottle neck forming process using a bottle necker, the painted bottomed cylinder 11 is reduced in diameter in the area of ​​the flange portion 14 of the cylindrical portion 12 to form the shoulder portion 2c, and in an expanding process the lid attachment portion 2d is formed, and after the bottle is filled with contents such as a carbonated beverage, the lid is tightened and attached.

[0039] In the can body formed and manufactured in the above-described manner, when an internal pressure of 706 kPa is applied to the inside of the can body 1 from an unloaded state, the bottom growth amount, which is the amount of protrusion deformation toward the lower end in the direction of the can axis C of the protruding end 5d of the annular protrusion 5 that protrudes furthest toward the lower end in the direction of the can axis C, is set within a range of 1.0 mm to 2.0 mm, as shown in Fig. 4. In other words, a certain degree of bottom growth is allowed in the annular protrusion 5 as long as it does not cause clogging in the chute for transporting filled cans.

[0040] Therefore, even if internal pressure acts on the can body 1 sealed with a lid attached to the lid attachment portion 2d at the top opening of the can body 1, the annular protrusion 5 on the bottom 3 of the can body 1 will bottom grow and absorb this internal pressure, thereby reducing the internal pressure acting on the lid. Therefore, with a can body configured as described above, it is possible to prevent buckling of the lid caused by such internal pressure.

[0041] To measure the amount of bottom growth of the annular protrusion 5 on the bottom 3 of such a can body 1, the bottom 3 is turned upward as shown in Fig. 3, the top opening of the bottomed cylinder 11 is airtightly sealed, and compressed air or the like is supplied to the inside to increase the internal pressure to 706 kPa, while measuring the amount of bottom growth (amount of protruding deformation) of the protrusion 5d of the annular protrusion 5 on the bottom 3 with a displacement meter 21. Note that measurements may also be made with the bottom of the bottomed cylinder 11 turned downward or sideways, and the amount of bottom growth of the protrusion 5d may also be measured on a can body 1 on which the shoulder 2c and the lid attachment portion 2d have been formed.

[0042] If the bottom growth of the annular projection 5 falls below 1.0 mm when an internal pressure of 706 kPa is applied to the inside of the can body 1, the can body 1 will not be able to absorb the internal pressure sufficiently, making it impossible to prevent buckling of the lid. Conversely, if the bottom growth of the annular projection 5 exceeds 2.0 mm when an internal pressure of 706 kPa is applied to the inside of the can body 1, there is a risk of clogging in the chute used to transport filled cans in which the contents have been filled into the can body 1 and the lid has been attached. Note that 706 kPa is the guaranteed pressure resistance value for a 206-caliber can body as shown in Figure 1.

[0043] In addition, in this embodiment, the amount of bottom growth of the annular protrusion 5 when an internal pressure of 686 kPa is applied to the inside of the can body 1 from an unloaded state is within the range of 0.89 mm to 1.71 mm, and the amount of bottom growth of the annular protrusion 5 when an internal pressure of 618 kPa is applied to the inside of the can body 1 from an unloaded state is within the range of 0.55 mm to 1.29 mm.Since the rate of increase in the amount of bottom growth relative to an increase in internal pressure is stable, it is possible to avoid undue stress being applied to the annular protrusion 5.

[0044] That is, if the amount of bottom growth when an internal pressure of 686 kPa or 618 kPa is applied is smaller than the above range, the tip 5d of the annular protrusion 5 will rapidly protrude and deform, causing stress concentration, until the amount of bottom growth when an internal pressure of 706 kPa is applied falls within the range of 1.0 mm to 2.0 mm. Also, if the amount of bottom growth when an internal pressure of 686 kPa or 618 kPa is applied is larger than the above range, the tip 5d of the annular protrusion 5 will rapidly protrude and deform before reaching these internal pressures from an unloaded state, also causing stress concentration.

[0045] In the can body of the above embodiment, the thickness of the domed portion 4 of the bottom 3 of the can body 1 above the can axis C is within a range of 0.270 mm to 0.290 mm. In the can body 1 of such a can body, the thickness of the domed portion 4 of the bottom 3 of the can body 1 above the can axis C is approximately equal to the thickness of the sheet material before it is formed into the can body 1. In the can body 1 formed from such a thin sheet material, controlling the amount of bottom growth of the annular protrusion 5 as described above suppresses buckling of the lid, which is effective in saving resources and energy used for the metal material formed into the can body 1.

[0046] Furthermore, in this embodiment, the tip 5c of the annular protrusion 5 is formed in a convex arc shape in a cross section along the can axis C, with the periphery of the tip 5d being convex toward the lower end side in the can axis C direction, and the radius (punch R) of this convex arc inside the can body 1 is R (mm), the diameter (ground diameter) of the circle formed by the tip 5d around the can axis C is D (mm), and the diameter of the recess 5b formed in the inner wall 5a of the annular protrusion 5 by the bottom reforming process on the outer circumferential side in the radial direction relative to the can axis C is When the diameter of the circle (bottom reform inner diameter) formed by the most recessed bottom 5e around the can axis C is d (mm), and the thickness of the bottom 3 of the can body 1 in the radial direction relative to the can axis C at the position where the tip 5c protrudes furthest toward the can axis C between this bottom 5e and the tip 5d of the annular protrusion 5 is t (mm), the bottom reform depth e, expressed as the absolute value of (D-2×(R+t)-d) / 2, is within the range of 0.680 mm to 1.085 mm.

[0047] Therefore, buckling of the lid can be suppressed by reliably setting the bottom growth amount within the range of 1.0 mm or more, 1.0 mm to 2.0 mm, without impairing the buckling strength or pressure resistance strength of the annular protrusion 5. That is, if the bottom reform depth e exceeds 1.085 mm, the extensibility of the annular protrusion 5 at the bottom 3 of the can body 1 may be impaired, making it impossible to set the bottom growth amount within the range of 1.0 mm or more, 1.0 mm to 2.0 mm. On the other hand, if the bottom reform depth e is less than 0.680 mm, the pressure resistance strength of the annular protrusion 5 may be impaired. [Example]

[0048] Next, the effects of the present invention will be described with reference to an example of the present invention. In this example, a can body was formed from an aluminum alloy material with an original thickness of 0.285 mm, and the can height H1 from the tip 5d of the annular protrusion 5 on the bottom 3 of the can body 1 to the upper opening of the lid body attachment part 2d was 122.2 mm, the height H2 from the tip 5d to the lower end of the shoulder 2c was 102.2 mm, and the height H3 to the upper end of the shoulder 2c was 118 mm. The inside diameter A of the body 2 was 66.3 mm, the inside diameter B of the lid body attachment part 2d was 57.3 mm, the radial outward projection E of the lid body attachment part 2d relative to the can axis C was 2.25 mm, the radius r of the projecting part of the lid body attachment part 2d in a cross section taken along the can axis C was 1.8 mm, and the diameter (ground diameter) D of the circle formed by the tip 5d around the can axis C was 48 mm.

[0049] In this example, bottom reforming was performed on the inner wall 5a of the annular protrusion 5 in the bottom 3 of such a can body 1 so as to form recesses 5b of different sizes, and 100 cans of each type were manufactured, each with a different diameter d (bottom reform inner diameter) of a circle formed around the can axis C by the bottom 5e that is the most recessed part of the recess 5b on the outer periphery in the radial direction relative to the can axis C, and a different bottom reform depth e, and the amount of bottom growth was measured using the measurement method shown in Figure 3. These are referred to as Examples 1 to 6.

[0050] In Examples 1 to 6, the thickness (wall thickness) of the wall portion 2a of the body portion 2 was 0.101 mm, the thickness (flange thickness) of the flange portion 2b was 0.161 mm, the mass of the can body 1 was 11.7 g, and the radius of the convex arc formed around the tip 5d of the tip portion 5c in a cross section along the can axis C inside the can body 1 was 1.2 mm, which was equal to the tip radius of the punch (punch R).

[0051] In Examples 1 to 6, the contents were filled into the can body, and then lids were attached to produce filled cans. A retention test was conducted at 60°C for 10 to 40 minutes to check for buckling of the lids and for clogging of the chute used to transport the filled cans. The contents were whiskey and carbonated water (highball) with a gas volume (GV) of 3.0, and the pressure strength of the lids was 740 kPa. The specifications of Examples 1 to 3 are shown in Table 1, along with the pressure strength, buckling strength, bottom growth amount, and pressure strength of the can body 1.

[0052] Additionally, as a comparative example for Examples 1 to 6, 100 can bodies having external dimensions substantially equal to those of Examples 1 to 6 were formed from an aluminum alloy having an original plate thickness of 0.285 mm, the same as those of Examples 1 to 6, and the amount of bottom growth was measured. This is Comparative Example 1. However, the bottom reform inner diameter d and the bottom reform depth e of Comparative Example 1 were larger than those of Examples 1 to 6.

[0053] Furthermore, 100 can bodies having approximately the same outer dimensions as those of Examples 1 to 6 and Comparative Example 1 were formed from an aluminum alloy having an original plate thickness of 0.335 mm, which was thicker than those of Examples 1 to 6 and Comparative Example 1, and the amount of bottom growth was measured. This is Comparative Example 2. However, this Comparative Example 2 was not subjected to bottom reforming processing.

[0054] Furthermore, 100 can bodies having approximately the same size as Examples 1 to 6 were formed from an aluminum alloy having an original plate thickness of 0.285 mm, the same as in Examples 1 to 6 and Comparative Example 1, and the amount of bottom growth was measured. This is Comparative Example 3. However, in Comparative Example 3, bottom reforming processing was not performed either.

[0055] In Comparative Examples 1 to 3, filled cans were also produced by filling them with the same contents as in Examples 1 to 6 and attaching lids, and the presence or absence of buckling in the lids and clogging in the chute that transports the filled cans were checked under the same conditions. The specifications for Comparative Examples 1 to 3 are also shown in Table 1, along with the pressure-resistant strength, buckling strength, bottom growth amount, and pressure-resistant strength of the can body. The specifications shown in Table 1 are the average values ​​for 100 can bodies and filled cans for each of Examples 1 to 6 and Comparative Examples 1 to 3.

[0056] [Table 1]

[0057] In Table 1, in the can bodies of Examples 1 to 6, in which the bottom growth amount when an internal pressure of 706 kPa was applied to the can body 1 was within the range of 1.0 mm to 2.0 mm, the bottom growth amount when an internal pressure of 686 kPa was applied was within the range of 0.89 mm to 1.71 mm, and the bottom growth amount when an internal pressure of 618 kPa was applied was within the range of 0.55 mm to 1.29 mm, even though the original plate thickness was thinned to 0.285 mm, none of the filled cans manufactured from 100 can bodies experienced buckling of the lid, and there was no clogging in the chute that transports the filled cans.

[0058] In contrast, in Comparative Example 1, in which the amount of bottom growth was 0.92 mm, which is less than 1.0 mm, buckling of the lid was observed in 10 of 100 can bodies. Furthermore, in Comparative Example 2, in which the original plate thickness was as thick as 0.335 mm, no buckling of the lid was observed, but the mass of the can body was 13.3 g, which was more than 1 g heavier than in Example 1, and therefore resource and energy savings in the metal material (aluminum alloy material) formed into the can body could not be achieved. Furthermore, in Comparative Examples 1 and 2, no clogging occurred in the chute.

[0059] On the other hand, in Comparative Example 3, although no buckling of the lid was observed, the amount of bottom growth was large at 3 mm or more, and therefore clogging frequently occurred in the chute that transports filled cans after the contents have been filled into the can body and the lid has been attached. [Explanation of symbols]

[0060] 1 can body 2. Torso 2a, 13 Wall section 2b, 14 flange 2c Shoulder 2d Lid mounting part 3 bottom 4 Dome section 5 Annular convex part 5a Inner wall 5b Recess 5c Tip 5d tip 5e: The bottom of the recess 5b that is most recessed on the outer circumferential side in the radial direction relative to the can axis C 11 Bottomed cylinder 12 Cylindrical part 21 Displacement meter C Can shaft D: Diameter of the circle formed by the tip 5d of the tip 5c around the can axis C (ground diameter) R is the radius (punch R) of the convex arc formed by the periphery of the tip 5d of the tip 5c in the cross section along the can axis C inside the can body 1 d: Diameter of the circle formed by the bottom 5e of the recess 5b around the can axis C (bottom reform inner diameter) t is the thickness of the bottom 3 of the can body 1 in the radial direction relative to the can axis C at the position where the tip 5c protrudes most toward the can axis C between the bottom 5e of the recess 5b and the tip 5d of the annular protrusion 5. e Bottom reform depth

Claims

1. A can body having a bottomed cylindrical can body centered on a can axis, A dome portion having a concave curved surface recessed toward the upper end in the can axis direction is formed in the center of the bottom of the can body, and an annular convex portion is formed on the outer periphery of this dome portion, protruding toward the lower end in the can axis direction and then extending radially outward relative to the can axis toward the upper end in the can axis direction, and the annular convex portion is formed continuously in the circumferential direction around the can axis, a recessed portion recessed radially outwardly relative to the can shaft is formed by bottom reforming on an inner wall portion of the annular protrusion protruding from the dome portion toward the lower end in the can shaft direction, a bottom growth amount, which is the amount of protruding deformation of the tip of the annular convex portion toward the lower end in the can axial direction when an internal pressure of 706 kPa is applied to the inside of the can body from an unloaded state, is set within a range of 1.0 mm to 2.0 mm, the thickness of the dome portion of the bottom of the can body on the can axis is within a range of 0.270 mm to 0.290 mm; a protruding end of the annular protrusion is formed in a convex arc shape that is convex toward the lower end in the can axis direction in a cross section taken along the can axis, When the radius of this convex arc inside the can body is R (mm), the diameter of the circle formed by the tip around the can shaft is D (mm), the diameter of the circle formed by the bottom of the recess that is most recessed on the outer circumferential side in the radial direction relative to the can shaft is d (mm), and the thickness of the bottom of the can body in the radial direction relative to the can shaft at the position where the tip protrudes most toward the can shaft side between this bottom portion and the tip of the annular protrusion is t (mm), the bottom reform depth expressed by the absolute value of (D-2×(R+t)-d) / 2 is within the range of 0.680 mm to 1.085 mm, A can body characterized in that, after filling the interior with contents (gas volume 3.0), a lid having a pressure resistance of 740 kPa is attached to the upper opening and sealed, and when a retention test is conducted at 60°C for 10 to 40 minutes, no buckling of the lid occurs.

2. The can body according to claim 1, characterized in that the bottom growth amount of the tip of the annular convex portion when an internal pressure of 686 kPa is applied to the inside of the can body from an unloaded state is within the range of 0.89 mm to 1.71 mm.

3. The can body according to claim 1 or claim 2, characterized in that the bottom growth amount of the tip of the annular convex portion when an internal pressure of 618 kPa is applied to the inside of the can body from an unloaded state is within the range of 0.55 mm to 1.29 mm.

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