Can

Abstract

To improve the strength of a bottom without causing large-scaled alterations, etc. of an installation in weight reduction.SOLUTION: A can comprises, in a bottom provided at one end of a circular cylindrical can body having an outer diameter of 65 mm or greater and 67 mm or smaller, a tread portion that annularly protrudes outward with respect to a can-axis direction, a heel portion that is provided radially outside of the tread portion and connects between the can body and the tread portion, a counter portion that is provided radially inside of the tread portion and inclining toward the can-axis direction, and a dome portion that is provided radially inside of the counter portion and recessed inward with respect to the can-axis direction. The dome portion has a central depth of 9.5 mm or greater and 11.0 mm or smaller and a central wall thickness of 0.220 mm or greater and 0.240 mm or smaller. The tread portion has a tread point having a diameter of 46.5 mm or greater and 47.5 mm or smaller, to connect between an upper end of the counter portion and an outer peripheral edge of the dome portion by a concavely-arcuate surface and provide a depth in the can-axis direction from the tread portion to a center of curvature of the concavely-arcuate surface of 3.8 mm or greater and 4.6 mm or smaller.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a metal can filled with a beverage or other content. [Background technology]

[0002] Aluminum cans that can contain beverages, food, and other contents include two-piece cans in which the can lid is joined by double seaming, and bottle cans in which the cap is joined by seaming. The DI molding method is known as a manufacturing method for these cans. In this DI molding, a preformed, large-diameter, shallow cup is drawn and ironed to form a bottom integrally at one end of the cylindrical can body. The bottom has a contact portion that protrudes annularly outward in the axial direction of the can, a heel portion that connects to the can body on the outside of the contact portion, and a dome portion that is recessed inward in the axial direction of the can inside the contact portion. This bottom portion remains in almost the same shape as the final product.

[0003] For such cans, the thickness of the can material has been reduced (thinning) in order to reduce costs and weight, but simply reducing the thickness of the can material leads to a decrease in strength. For example, after filling the can with contents, problems such as an increase in bottom growth, in which the ground contact part extends in the can axial direction, and buckling, in which the dome part inverts, bulges, and deforms due to internal pressure, etc., are likely to occur.

[0004] For this reason, in Patent Document 1, a heel portion is formed on the outside of the ground contact portion, in a cross-sectional view of the bottom including the can axis, from a convex arc portion that describes an arc tangent to the can body portion, a concave arc portion that describes an arc tangent to the annular protrusion portion, and a straight line portion connecting these convex arc portion and concave arc portion, and the radius of curvature R2 of the concave arc portion is set within the range of 9.0 mm≦R2≦18.0 mm. It is described that since the original thickness of the aluminum plate is set to 0.25 mm to 0.27 mm and the heel portion is formed from the convex arc portion, the straight line portion, and the concave arc portion, it is possible to provide a can body with high pressure resistance and little deformation of the bottom due to internal pressure.

[0005] In response to this, Patent Document 2 discloses a can with an original sheet thickness (sheet thickness of the blank before processing) of 0.225 mm to 0.240 mm and a mass of the blank of 9.8 g to 11.4 g, which is further lightened, and in which an annular convex portion and a dome portion that serve as the ground contact portion are formed in the can bottom by drawing and ironing after cup forming, and then a bottom reforming process is performed on the inner peripheral wall of the annular convex portion to form a recess that is recessed radially outward in a direction perpendicular to the can axis. It is described that this reforming process significantly increases the pressure resistance strength (bulge strength) of the can, and effectively suppresses an increase in the amount of bottom growth and the occurrence of buckling. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2009-292480 A [Patent Document 2] JP 2017-136604 A Summary of the Invention [Problem to be solved by the invention]

[0007] Of these patent documents, the can described in Patent Document 2 is considerably lighter in weight than the can in Patent Document 1. However, if a reforming process is further carried out after the drawing and ironing process, a large-scale modification of the equipment is required, which leads to high costs.

[0008] The present invention has been made in view of the above circumstances, and has an object to improve the strength of the bottom portion in order to reduce the weight without requiring major changes to equipment, etc. [Means for solving the problem]

[0009] The can of the present invention is a can having a bottom provided at one end of a cylindrical can body having an outside diameter of 65 mm or more and 67 mm or less, the bottom comprising a grounding portion protruding annularly outward in a can axial direction, a heel portion provided radially outward of the grounding portion and connecting the can body and the grounding portion, a counter portion connected to an inner peripheral edge of the grounding portion and inclined toward the can axial direction, and a dome portion provided radially inside the counter portion and recessed inward in the can axial direction, The depth of the center of the dome portion is 9.5 mm or more and 11.0 mm or less, the plate thickness of the center of the dome portion is 0.220 mm or more and 0.240 mm or less, the diameter of the grounding point at the grounding portion is 46.5 mm or more and 47.5 mm or less, the upper end of the counter portion and the outer peripheral edge of the dome portion are connected by a concave arc surface, and the depth in the can axial direction from the grounding portion to the center of curvature of the concave arc surface is 3.8 mm or more and 4.6 mm or less.

[0010] This can has a relatively small diameter of the grounding point of the grounding part (hereinafter sometimes referred to as the grounding diameter) of 46.5 mm to 47.5 mm, which increases the pressure resistance, and a large depth of the counter part (depth to the center of curvature of the concave arc surface) of 3.8 mm to 4.6 mm, which suppresses the increase in the amount of growth. This allows the plate thickness of the center of the dome part to be thinned to 0.220 mm to 0.240 mm, which reduces the weight.

[0011] The smaller the diameter of the grounding part, the higher the pressure resistance, but if it is less than 46.5 mm, cracks are likely to occur during molding and the can may become unstable when grounded. If the diameter of the grounding part exceeds 47.5 mm, the pressure resistance may decrease. The increase in the growth amount can be suppressed by increasing the depth of the counter portion, but if it exceeds 4.6 mm, there is a risk of cracks occurring during molding, and if it is less than 3.8 mm, the effect of suppressing the increase in the growth amount cannot be expected.

[0012] Furthermore, the outer diameter of the can body is between 65 mm and 67 mm, and the depth of the center of the dome is between 9.5 mm and 11.0 mm. Other than limited areas such as the diameter of the contact part and the depth of the counter part, this does not differ significantly from conventional cans, so no major changes to equipment will be required.

[0013] In the can of the present invention, the dome portion has a shape in which a center-side curved surface is formed in a longitudinal section having an arcuate shape on the can axis, and at least one outer-periphery-side curved surface is arranged in an annular shape radially outward from the center-side curved surface and has a smaller radius of curvature than the center-side curved surface, and in a longitudinal section passing through the can axis, the center-side curved surface and the outer-periphery-side curved surface are connected with a common tangent to each other.

[0014] When buckling occurs in the dome portion, the deformation often starts near the connection between the central curved surface on the can shaft, which has a large radius of curvature, and the outer circumferential curved surface, which has a small radius of curvature on the radially outer side. For this reason, by making the connection between the respective curved surfaces continuous through a common tangent in a vertical cross section passing through the can shaft, an inflection point where the curvature changes suddenly is prevented from occurring.

[0015] In the can of the present invention, it is preferable that the outer peripheral edge of the outer curved surface is connected to the inner peripheral edge of the concave arc surface, the radius of curvature of the central curved surface is 55 mm or more and 65 mm or less, the central angle of the central curved surface about the can axis is 6° or more and 40° or less, and the radius of curvature of the outer curved surface is 37 mm or more and 39 mm or less.

[0016] In order to increase the depth of the counter portion without increasing the depth of the dome portion, it is effective to greatly expand the center-side curved surface in the radial direction, but if the central angle of the center-side curved surface exceeds 40°, the width between the outer periphery of the center-side curved surface and the counter portion becomes narrow, and the radius of curvature of the outer periphery curved surface becomes too small compared to the center-side curved surface, resulting in a sudden change in curvature, making buckling more likely to occur. If the central angle is less than 6°, it is difficult to make the counter portion deeper.

[0017] In the can of the present invention, the weight of the constituent metals is preferably 9.7 g or more and 10.7 g or less, so that the weight can be kept small and weight reduction can be promoted. Effect of the Invention

[0018] According to the present invention, the diameter of the grounding portion is made small while the counter portion is formed deep, thereby improving the pressure resistance and suppressing an increase in the amount of growth. Moreover, since the depth of the center of the dome portion is not significantly different from that of conventional cans, weight reduction can be achieved without requiring major equipment changes, etc. [Brief description of the drawings]

[0019] [Figure 1] 1 is a front view, partially in section, showing a can according to an embodiment of the present invention; [Diagram 2] 2 is an enlarged cross-sectional view showing half the diameter from the can axis of the bottom of the can shown in FIG. 1. FIG. [Diagram 3] 1A and 1B are cross-sectional views showing a cup and a cylindrical body formed during the manufacture of a can, in that order. [Figure 4] FIG. 4 is a cross-sectional view showing a part of a mold when forming a cylinder from a cup. [Diagram 5] FIG. 4 is a cross-sectional view showing a part of a mold for forming a bottom portion. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. The can of this embodiment is a cylindrical can 1 with a bottom made of, for example, aluminum or an aluminum alloy, as shown in Fig. 1. This can 1 is used as a so-called two-piece can (stay-on-tab can) that is sealed by sealing the open end of the can by wrapping a can lid (not shown) around it after filling the can with contents such as a beverage.

[0021] 1, the can 1 is made of a thin metal plate of aluminum or an aluminum alloy, and has a cylindrical can body 20 and a bottom 30 provided at one end of the can body 20. The can body 20 is formed with a shoulder 21 that gradually reduces in diameter upward, and a small-diameter neck 22 is formed at the upper end of the shoulder 21, and a flange 23 that extends radially outward is formed at the upper end of the neck 22. The diameter (outer diameter) D1 of the can body 20 is set within the range of 65 mm to 67 mm (for example, 66 mm), and the height H0 of the entire can is set within the range of 122 mm to 124 mm.

[0022] The bottom 30 is provided with a grounding portion 31 that protrudes outward in the direction of the can axis S1 (downward in Figures 1 and 2) in an annular shape centered on the can axis S1, a heel portion 32 that is provided radially outside the grounding portion 31 and connects the can body 20 and the grounding portion 31, a counter portion 33 that is connected to the inner peripheral edge of the grounding portion 31 radially inside the grounding portion 31 and has a tapered surface that extends at a slight angle with respect to the can axis S1, and a dome portion 34 that is provided radially inside the counter portion 33 and is recessed inward in the direction of the can axis S1 (upward in Figures 1 and 2).

[0023] 2, the ground contact portion 31 has an outer bent portion 37 formed in a convex shape radially outward from its apex, and an inner bent portion 38 formed in a convex shape radially inward. The outer bent portion 37 and the inner bent portion 38 may have different radii of curvature R1, R2 in the range of 0.8 mm to 2.0 mm, or may be the same. For example, the radius of curvature R1 of the outer surface of the outer bent portion 37 is set to 1.5 mm, and the radius of curvature R2 of the outer surface of the inner bent portion 38 is set to 1.0 mm.

[0024] The diameter (ground diameter) D2 of the ground point P of the ground portion 31 that protrudes most outward in the direction of the can axis S1 is set to 46.5 mm or more and 47.5 mm or less, and more preferably, 46.8 mm or more and 47.2 mm or less. For example, the ground diameter D2 is set to 47 mm.

[0025] The heel portion 32 has a convex curved portion 41 continuing from the lower end of the body portion 3, a tapered surface portion 42 continuing from the inner peripheral edge of the lower end of the convex curved portion 41, and a concave curved portion 43 continuing from the inner peripheral edge of the tapered surface portion 42, and the tapered surface portion 42 and the concave curved portion 43 are inclined so that the diameter gradually decreases downward. The inner peripheral edge of the lower end of the concave curved portion 43 is connected to the outer peripheral edge of the outer bent portion 37 of the ground contact portion 31. The inner peripheral edge of the convex curved portion 41 and the outer peripheral edge of the concave curved portion 43 are formed so that their tangent directions are in the same direction, and the tapered surface portion 42 between them is formed along the tangent direction in a vertical cross section passing through the can axis S1. The inclination angle θ1 of the tapered surface portion 42 with respect to a plane perpendicular to the can axis S1 is set to, for example, 33°. The radius of curvature R3 of the outer surface of the convex curved portion 41 is, for example, 2.7 mm, and the radius of curvature R4 of the outer surface of the concave curved portion 43 is, for example, 12 mm.

[0026] The counter portion 33 is formed with a tapered surface that extends at a slight incline in a direction that gradually reduces the diameter toward the top of the can axis S1, and in a vertical section passing through the can axis S1, the angle between the counter portion 33 and a vertical line (a line parallel to the can axis S1), i.e., the inclination angle θ2 of the counter portion 33, is formed to be 2.5° or more and 4.5° or less. This enables the pressure acting on the dome portion 34 to be smoothly transmitted to the grounding portion 31.

[0027] The upper end of counter portion 33 and the outer periphery of dome portion 34 are connected by concave arc surface 45. The depth H1 of counter portion 33 along the can axis S1 direction from the tip of ground portion 31 to the center C1 of the radius of curvature of concave arc surface 45 is 3.8 mm or more and 4.6 mm or less. The radius of curvature R5 of the outer surface of concave arc surface 45 is 1.7 mm or more and 2.7 mm or less.

[0028] More preferably, the inclination angle θ2 of the counter portion 33 is 3° to 4°, the depth H1 is 3.8 mm to 4.2 mm, and the curvature radius R5 of the concave arc surface 45 is 2.0 mm to 2.4 mm. For example, the inclination angle θ2 of the counter portion 33 is 3°40′, the depth H1 is 4.17 mm, and the curvature radius R5 of the concave arc surface 45 is 2.2 mm.

[0029] The dome portion 34 has a shape in which two curved surfaces with different radii of curvature are arranged side by side and connected to each other: a center-side curved surface 46 that has a vertical cross-sectional arcuate shape and is disposed on the can axis S1, and an outer peripheral curved surface 47 that is annularly disposed outside the center-side curved surface 46. The radius of curvature R6 of the outer surface of the center-side curved surface 46 is 55 mm or more and 65 mm or less, and the radius of curvature R7 of the outer surface of the outer peripheral curved surface 47 is 37 mm or more and 39 mm or less. In a vertical cross section passing through the can axis S1, the central angle θ3 of the center-side curved surface 46 (the spread angle of the sector formed by the arc of the center-side curved surface 46 and the center of curvature, centered on the can axis S1) is set to 6° or more and 40° or less, and the outer peripheral edge of the center-side curved surface 46 and the inner peripheral edge of the outer peripheral curved surface 47 are connected with a common tangent to each other.

[0030] The depth H2 of the deepest part of the dome portion 34, i.e., the center-side curved surface 46, on the can shaft S1 is set to 9.5 mm to 11.0 mm, and preferably 10.2 mm to 10.8 mm. The thickness t of the dome portion 34 on the can shaft S1 is close to the thickness of the flat plate before forming (original thickness), but since slight elongation occurs, the thickness is formed to 0.220 mm to 0.240 mm, whereas the original thickness is 0.235 mm to 0.245 mm.

[0031] With regard to the dimensions of the dome portion 34, it is more preferable that the radius of curvature R6 of the center side curved surface 46 be 55.8 mm or more and 60.2 mm or less, the radius of curvature R7 of the outer peripheral side curved surface 47 be 37.0 mm or more and 38.5 mm or less, the central angle θ3 of the center side curved surface 46 be 10° or more and 20° or less, and the thickness t of the dome portion 34 on the can axis S1 be 0.230 mm or more and 0.240 mm or less. For example, the radius of curvature R6 of the central curved surface 46 is 60 mm, the radius of curvature R7 of the outer peripheral curved surface 47 is 38 mm, the central angle θ3 of the central curved surface 46 is 20°, the depth H2 of the center of the dome portion 34 is 10.5 mm, and the plate thickness t of the dome portion is 0.235 mm. The weight of the constituent metal of can 1 (the weight of the metal alone without printing or painting) is within a range of 9.7 g to 10.7 g, and more preferably 10.1 g to 10.5 g.

[0032] Next, a method for manufacturing a can having such a structure will be described. A flat metal plate made of an aluminum alloy is pressed to form a relatively shallow, large-diameter cup 51 as shown in FIG. 3(A) (cup forming process), and then the cup 51 is further drawn and ironed to form a bottomed, cylindrical body 52 as shown in FIG. 3(B) (cylinder forming process). After printing and painting, the upper end of the cylinder 52 is processed to form the can 1 shown in FIG. 1.

[0033] In this series of manufacturing steps, the bottom portion 30 is formed in a cylinder forming step. In this cylinder forming process, redrawing of the cup 51, ironing of the cylindrical portion after redrawing, and forming of the bottom 30 are performed. As shown in Fig. 4, the cylinder forming device for performing the redrawing, ironing, and bottom forming processes has a redrawing die 60, an ironing die 70, and a bottom forming die 80 arranged side by side on the same axis S2, and the same punch sleeve 90 is used to perform these processes continuously.

[0034] The redrawing mold 60 comprises an annular redraw die 61, a cylindrical cup holder 62 arranged opposite the redraw die 61, and the aforementioned punch sleeve 90, and the cup 51 held by the redraw die 61 and the cup holder 62 is redrawn by the punch sleeve 90 and the redraw die 61.

[0035] The ironing die 70 has multiple ironing dies 71, and forms the body wall of the cylindrical body formed by the redrawing process to a predetermined height by stretching it while ironing it between the punch sleeve 90 and the ironing dies 71. Although only one ironing die 71 is shown in Fig. 4, multiple ironing dies with successively smaller inner diameters are arranged coaxially according to the desired degree of ironing. The redrawing die 60 and the ironing die 70 are usually arranged with their axes S2 oriented horizontally, and the punch sleeve 90 advances from left to right along the axis S2 in FIG. 4 to perform processing.

[0036] A bottom forming die 70 is positioned ahead of the punch sleeve 90 in the direction of travel, for forming the bottom 30, including the dome portion 34 of the cylindrical body 52, between the tip of the punch sleeve 90 that has passed through the ironing die 71 at the most forward position.

[0037] At the tip of the punch sleeve 90, a recess 91 forms a tip arcuate surface 92 with a convex arcuate cross section that protrudes annularly in the axial tip direction, and a concave arcuate surface 93 and a convex arcuate surface 94 are formed in sequence from the outer circumferential edge of the tip arcuate surface 92, with the convex arcuate surface 94 being connected to the outer circumferential surface of the punch sleeve 90. The range from the tip arcuate surface 92 to the concave arcuate surface 93 and convex arcuate surface 94 forms the outer portion of the ground contact portion 31 of the bottom 30 of the cylindrical body 52 in the bottom forming die 80. The outer periphery of the recess 91 of the punch sleeve 90 extends straight in the axial direction from the inner periphery of the tip arcuate surface 92, and is recessed as a whole in a dome shape centered on the axis S2.

[0038] The bottom forming die 80 is provided in front of the row of the ironing dies 71, and includes an annular hold-down ring 81 that forms the outer bent portion 37 of the heel portion 32 and the concave curved portion 43 between the tip arcuate surface 92 and the concave arcuate surface 93 of the punch sleeve 90, and a dome forming die 82 that enters the concave portion 91 of the punch sleeve 90 and forms the inner bent portion 38, the counter portion 33, the concave arcuate surface 45, and the dome portion 34 while bending the bottom plate portion 53 of the cup 51 with the tip arcuate surface 92 of the punch sleeve 90. The hold-down ring 81 and the dome forming die 82 are concentrically arranged, and an annular gap is formed between them. The hold-down ring 81 is supported so as to be movable in the axis S2 direction relative to the dome forming die 82.

[0039] Then, with the cup 51 held between the cup holder 62 and the redraw die 61, the punch sleeve 90 advances to redraw and iron the cup 51 to form a cylindrical body 55 with a small diameter, and finally, the bottom 30 is formed between the cup 51 and the bottom forming die 80. Specifically, first, as shown in FIG. 5(A), the outer periphery of the bottom of the tubular body 55 is clamped between the outer periphery side portion from the tip of the punch sleeve 90 and the hold down ring 81, thereby starting the forming of the heel portion 32. Then, as shown in FIG. 5(B), the punch sleeve 90 advances in this state, so that the tip arc-shaped surface 92 of the punch sleeve 90 enters the gap between the hold down ring 81 and the dome-forming die 72, and the dome-forming die 82 enters the recess 91 of the punch sleeve 90, forming the grounding portion 31. Additionally, the counter portion 33, dome portion 34, etc. are formed between the inner portion from the tip of the tip arc-shaped surface 92 of the punch sleeve 90 and the dome-forming die 82, thereby forming the tubular body 52 having the bottom portion 30 shown in FIG. 1, etc.

[0040] 3(B), the body of the cylindrical body 52 formed in this manner is thinnest near the bottom 30 (wall portion 52A) and thick near the open end (flange portion 52B). For example, the wall portion 52A is formed to a thickness of 0.089 mm or more and 0.097 mm or less, and the flange portion 52B is formed to a thickness of 0.152 mm or more and 0.160 mm or less. The shape of the bottom portion 30 is formed to approximately the final shape of the can 1, including the thickness t of the dome portion 34 on the can axis S1. Then, printing, processing of the open end, etc. are performed, and the can 1 shown in FIG. 1 is completed.

[0041] In the can 1 of this embodiment, the ground diameter D2 of the bottom 30 is small and the depth H1 of the counter portion 33 is large, thereby improving the strength against internal pressure and effectively preventing the occurrence of buckling and an increase in the amount of bottom growth.

[0042] In this case, by setting the radius of curvature R6 of the outer surface of the center side curved surface 46 that forms the dome portion 34 to be 55 mm or more and 65 mm or less, and the radius of curvature R7 of the outer peripheral side curved surface 47 to be 37 mm or more and 39 mm or less, and connecting both curved surfaces 46, 47 with a common tangent to each other in a vertical cross section passing through the can axis S1, it is possible to form a smoothly curved surface without any sudden change in curvature in the dome portion 34, and to avoid local stress concentration in the dome portion 34. Also, in this case, by setting the central angle θ3 of the center side curved surface 46 to be 6° or more and 40° or less, it is possible to increase the depth H1 of the counter portion 33 without significantly changing the depth H2 of the dome portion 34 from that of a conventional can.

[0043] In order to increase the depth H1 of the counter portion 33 without increasing the depth H2 of the dome portion 34, it is preferable to greatly expand the center-side curved surface 46 in the radial direction, but if the central angle θ3 of the center-side curved surface 46 exceeds 40°, the width between the outer circumferential edge of the center-side curved surface 46 and the counter portion 33 becomes narrow, and the radius of curvature R7 of the outer circumferential curved surface 47 becomes too small compared to the center-side curved surface 46, making buckling more likely to occur. If the central angle θ3 is less than 6°, it is difficult to make the counter portion 33 deeper.

[0044] In addition, this can 1 has an increased pressure resistance and the amount of growth can be kept below a certain level, which ultimately makes it possible to reduce the thickness of the bottom 30 (reduce the original plate thickness). This can 1 is particularly suitable for contents such as beer and non-alcoholic beer that do not require heat sterilization after filling. In the embodiment, an example of applying the present invention to the bottom part of a so-called two-piece can has been described. However, since the process for forming the cylindrical body is similar to that for a so-called bottle-shaped can up to the case of a two-piece can, the present invention can also be applied to the bottom part of this bottle-shaped can. EXAMPLES

[0045] Next, the results of tests carried out to confirm the effects of the present invention will be described. Cans of each sample of the examples and comparative examples were formed using aluminum alloy plates according to the dimensions shown in Tables 1 to 3 below.

[0046] Table 1 shows the samples with different ground diameters D2 of the bottom, Table 2 shows the samples with different depths H1 of the counter part, and Table 3 shows the samples with different depths H2 of the dome part. The original thickness of the aluminum alloy plate from which each sample was formed was 0.240 mm. The reference characters in Tables 1 to 3 correspond to the reference characters in Figures 1 to 3. All samples were in the form of a two-piece can with a capacity of 350 ml, and the diameter D1 of the can body was 66 mm. The shapes of all samples were the same except for the bottom.

[0047] Each sample was evaluated for formability, as well as for "compression strength," "growth amount," and "drop strength." The moldability was rated as "good" when it was possible to mold without cracks or wrinkles on the bottom or the like, and "poor" when cracks or the like were generated.

[0048] For "compression strength", each sample can was attached to a hydraulic buckling tester (manufactured by Technonet Co., Ltd.) with the body of the can fixed at a position 95 mm from the ground, while the bottom was left unfixed and grounded, and the internal pressure of the can was increased by water pressure at a speed of 33 kPa / s, and the maximum pressure reached before the dome part inverted (buckled) was measured. Cans with a maximum pressure of 539 kPa or more were rated as "good", and all others were rated as "poor".

[0049] The amount of growth was measured by comparing the shape of the bottom before and after the final pressure of 539 kPa during the measurement of compressive strength. Those with a growth amount of less than 2 mm were rated as "good", and those with any other amount were rated as "poor".

[0050] For "drop strength," a can filled with liquid with the same volume, internal pressure, and gas volume as a typical 350ml can of beer was dropped vertically from the bottom onto a horizontal iron plate from a height of 20cm, and the presence or absence of buckling was observed. Cans that did not buckle were rated as "good," and those that did buckle were rated as "poor."

[0051] The evaluation results are shown in Tables 1 to 3.

[0052] [Table 1]

[0053] [Table 2]

[0054] [Table 3]

[0055] As can be seen from the results in Table 1, Examples 1 to 4, in which the dimensions of the counter part and the dome part are as shown in Table 1 and the ground diameter D2 is 46.5 mm or more and 47.5 mm or less, were excellent in terms of pressure resistance, drop strength, and moldability. In Comparative Example 1, the ground diameter was too small, so there was a problem in that the dome part was pulled out due to cracks during molding. In Comparative Example 2, the ground diameter was too large, so the pressure resistance was poor, and therefore the growth amount could not be measured.

[0056] As can be seen from the results in Table 2, Examples 5 to 8, in which the diameter of the grounding portion, the dimensions of the dome portion, and the inclination angle θ2 of the counter portion were the values ​​shown in Table 1, and the depth H1 of the counter portion was 3.8 mm or more and 4.6 mm or less, were good in terms of pressure resistance, drop strength, and moldability. In Comparative Example 3, the depth of the counter portion was too small, so the amount of growth was large. In Comparative Example 4, the depth of the counter portion was too large, so normal molding was not possible.

[0057] As can be seen from the results in Table 3, in Examples 9 to 12 in which the diameter of the grounding portion, the dimensions of the counter portion, and the dimensions other than the depth H2 of the dome portion were the values ​​shown in Table 1, and the depth H2 of the dome portion was 9.5 mm to 11.0 mm, the compressive strength, drop strength, and moldability were all good. In Comparative Example 5, the depth of the dome portion was too small, so the compressive strength was poor, and therefore the growth amount could not be measured. In Comparative Example 6, the depth of the dome portion was too large, so it could not be molded normally.

[0058] In all of the examples, the plate thickness at the center of the dome portion was within the range of 0.220 mm to 0.240 mm. These results show that cans with a dome center depth H2 of 9.5 mm or more and 11.0 mm or less, a ground diameter D2 of 46.5 mm or more and 47.5 mm or less, and a counter depth H1 of 3.8 mm or more and 4.6 mm or less have excellent pressure resistance, drop strength, and formability, and can also suppress an increase in the amount of growth. [Explanation of symbols]

[0059] 1 can 20 Can body 30 bottom 31 Grounding part 32 Heel 33 Counter section 34 Dome section 37 Outer bend 38 Inner bend 45 Concave arc surface 46 Center side curved surface 47 Outer curved surface 51 Cups 52 Cylinder 53 Bottom plate part 55 Cylindrical body 60 Redrawing mold 70 Ironing mold 80 Bottom forming mold 90 Punch Sleeve 92 Tip arc surface 93 Concave arc surface 94 Convex arc surface 81 Hold Down Ring 82 Dome forming die

Claims

1. A can having a bottom provided at one end of a cylindrical can body having an outer diameter of 65 mm or more and 67 mm or less, the can body having a grounding portion protruding annularly outward in a can axial direction, a heel portion provided radially outward of the grounding portion and connecting the can body and the grounding portion, a counter portion connected to an inner peripheral edge of the grounding portion and inclined toward the can axial direction, and a dome portion provided radially inside the counter portion and recessed inward in the can axial direction, a can having a depth at a center of the dome portion of 9.5 mm or more and 11.0 mm or less, a plate thickness at the center of the dome portion of 0.220 mm or more and 0.240 mm or less, a diameter of a grounding point at the grounding portion of 46.5 mm or more and 47.5 mm or less, an upper end of the counter portion and an outer peripheral edge of the dome portion are connected by a concave arc surface, and a depth in the can axial direction from the grounding portion to a center of curvature of the concave arc surface of 3.8 mm or more and 4.6 mm or less.

2. 2. The can according to claim 1, wherein the dome portion has a shape in which a center-side curved surface that is formed on the can axis to have an arcuate longitudinal section and at least one outer-periphery-side curved surface that is arranged in an annular shape radially outward of the center-side curved surface and has a smaller radius of curvature than the center-side curved surface, and the center-side curved surface and the outer-periphery-side curved surface are connected to each other with a common tangent in a longitudinal section passing through the can axis.

3. 3. The can according to claim 2, characterized in that an outer peripheral edge of the outer curved surface is connected to an inner peripheral edge of the concave arc surface, the radius of curvature of the center curved surface is 55 mm or more and 65 mm or less, a central angle of the center curved surface about the can axis is 6° or more and 40° or less, and the radius of curvature of the outer curved surface is 37 mm or more and 39 mm or less.

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