Can body, product can, and method for manufacturing can body

Abstract

The present invention provides a can body capable of securing sufficient pressure resistance and sufficient drop strength while securing a desired filling amount of a content, a product can, and a method for manufacturing the can body. Provided is a bottomed cylindrical can body including: a can bottom; and a cylindrical can barrel centered on a can axis and extending from the outer circumference of the can bottom along the can axis. The can bottom has a dome section provided in a center part of the can bottom, and an annular protrusion continuous from the outer circumferential edge of the dome section and annularly protruding outward of the can body substantially along the can axis direction. The annular protrusion has a recessed section provided so as to be continuous with the dome section and having a curved surface protruding radially outward of the can body, a grounding section supporting the can body, and an inner circumferential wall section extending from the grounding section to the recessed section. In a vertical cross-sectional view including the can axis of the can body, an angle θ, with respect to a plane orthogonal to the can axis, of a tangent M to an outer surface of the dome section at a position where a virtual line L1 parallel to the can axis and in contact with the innermost section of the inner circumferential wall section intersects with the outer surface of the dome section is 45-65°.

Description

Technical Field

[0001] The present invention relates to a can body with a can bottom reformed, a product can having contents filled in the can body, and a method for manufacturing the can body.Background Art

[0002] In the related art, as a container to be filled with contents such as a beverage, a drawn and ironed can body made of aluminum alloy and a drawn and ironed can body (two-piece can) made of resin-coated aluminum alloy are known. The can body (can container) is obtained by punching a metal plate into a circular shape, forming the punched metal plate into a bottomed cylindrical cup having a shallow depth by drawing, and then integrally forming a can bottom and a can barrel by drawing and ironing the cup, and other treatments.

[0003] Such a can body is required to reduce the thickness of the can barrel from the viewpoint of resource saving, and the can body having a reduced thickness is also required to have sufficient pressure resistance. In particular, in a can body having a dome portion on the can bottom, when a carbonated beverage or the like is used as contents, a phenomenon (buckling) in which the dome portion of the can bottom is inverted may occur when internal pressure due to carbon dioxide rises. Therefore, in the can body having the dome portion provided on the can bottom, sufficient pressure resistance capable of withstanding the internal pressure is required, and a device for having the pressure resistance is applied to the can bottom of the can body.

[0004] Specifically, in a can body provided on a can bottom thereof with a dome portion whose central portion is recessed toward the inside of the can body and an annular protruding portion around the dome portion, bottom reforming is performed on the annular protruding portion to secure pressure resistance due to thinning (for example, Patent Documents 1 to 3).

[0005] When a can body having a reduced thickness is dropped during transportation, for example, since a water hammer phenomenon occurs due to contents, a problem such as inclination of a can barrel or inversion of a dome portion is likely to occur. Therefore, the can body is required to have sufficient drop strength capable of withstanding an impact when dropped (for example, Patent Document 4).Citation ListPatent Literature

[0006] Patent Document 1: JP 2000-190961 A Patent Document 2: JP 2023-9470 A Patent Document 3: JP 2020-121761 A Patent Document 4: U.S. Patent No. 7740148 Summary of InventionTechnical Problem

[0007] However, in the can body having the dome portion on the can bottom in the related art, a form capable of preventing the dome portion from being inverted due to the water hammer phenomenon when the can body is dropped has not been sufficiently studied. For example, Patent Document 2 discloses that the outer diameter of a cylindrical barrel part of a primary can body is 66.1 mm or more and 66.3 mm or less, the angle between a tangent line on the inner surface of an outer peripheral edge portion of a dome portion and a plane orthogonal to a can axis is 27° or more and 29°or less, the radial width of a portion of a pressing surface disposed inward of an inner wall portion in the radial direction of the primary can body is 2.0 mm or more and 3.0 mm or less, and the inclination angle between the pressing surface and the plane is 20° or more and the angle (= 29°) between the tangent line and the plane or less. However, it has been found that even with the numerical limitation in Patent Document 2, having sufficient drop strength in the can body to be formed is difficult.

[0008] An object of the present invention is to solve such problems. The inventor of the present invention has made intensive efforts and analyzed the above, and as a result, has found that the inversion of a dome portion due to a water hammer phenomenon occurring at the time of drop is caused by an outer peripheral side of the dome portion. In view of this, an object of the present invention is to provide a can body capable of having sufficient pressure resistance and sufficient drop strength while having a desired filling amount of contents, a product can, and a method for manufacturing the can body.Solution to Problem

[0009] In order to solve such a problem, a can body according to the present invention has a bottomed cylindrical shape and includes a can bottom and a cylindrical can barrel extending from an outer periphery of the can bottom along a can axis and centered on the can axis, wherein the can bottom includes as a dome portion provided at a central portion of the can bottom and an annular protruding portion continuously extending from an outer peripheral edge portion of the dome portion and annularly protruding outward from the can body substantially along a direction of the can axis, the annular protruding portion includes a recessed portion provided continuously with the dome portion and having a curved surface convex outward in a radial direction of the can body, a ground contact portion configured to support the can body, and an inner peripheral wall portion extending from the ground contact portion to the recessed portion, and in a longitudinal sectional view including the can axis, an angle θ between a tangent line M on an outer surface of the dome portion and a plane orthogonal to the can axis at a position where a virtual line L1 parallel to the can axis and in contact with an innermost portion of the inner peripheral wall portion intersects the outer surface of the dome portion is 45° or more and 65° or less.

[0010] A product can according to the present invention is formed by filling the can body according to the present invention with contents and seaming a flange portion formed in an opening of the can barrel and a lid portion.

[0011] A method for manufacturing a can body according to the present invention is a method for manufacturing a can body having a bottomed cylindrical shape including a can bottom and a cylindrical can barrel extending from an outer periphery of the can bottom along a can axis and centered on the can axis, and includes: a step of forming a dome portion provided at a central portion of the can bottom and forming, as an annular protruding portion continuously extending from an outer peripheral edge portion of the dome portion and annularly protruding outward from the can body substantially along a direction of the can axis, the annular protruding portion including a recessed portion provided continuously with the dome portion and having a curved surface convex outward in a radial direction of the can body, a ground contact portion configured to support the can body, and an inner peripheral wall portion extending from the ground contact portion to the recessed portion; and a step of performing, after the step of forming the dome portion and the annular protruding portion, performing bottom reforming of pressing, along a direction of the can axis, a forming tool having a forming surface along a curved surface of the dome portion against the dome portion from an inside of the can body so that in a longitudinal sectional view including the can axis, an angle θ between a tangent line M on an outer surface of the dome portion and a plane orthogonal to the can axis at a position where a virtual line L1 parallel to the can axis and in contact with an innermost portion of the inner peripheral wall portion intersects the outer surface of the dome portion is 45° or more and 65° or less.Advantageous Effects of Invention

[0012] A can body, a product can, and a method for manufacturing the can body of the present invention can have sufficient pressure resistance and sufficient drop strength while having a desired filling amount of contents.Brief Description of Drawings

[0013] FIG. 1 is a longitudinal sectional view of a main part of a can body in the present embodiment (longitudinal sectional view including a can axis O and along a direction of the can axis O). FIG. 2 is an enlarged view of the main part in FIG. 1. FIG. 3 is a flowchart for explaining an example of a method for manufacturing the can body in the present embodiment. FIG. 4 is an explanatory view for explaining a reforming step in the method for manufacturing the can body in the present embodiment (longitudinal sectional view including the can axis O and along the direction of the can axis O). FIG. 5 is a table showing test results of a single body drop test and a case drop test using a can body (drawn and ironed can body made of aluminum alloy). FIG. 6 is a table showing test results of a single body drop test and a case drop test using a can body (drawn and ironed PET-coated aluminum alloy can body). Description of Embodiments

[0014] An embodiment of the present invention (present embodiment) is described below with reference to the drawings. In the following description, the same reference signs in different drawings denote elements having the same function, and redundant descriptions with regard to each drawing are omitted as appropriate. The cross-sectional views of FIGS. 1 and 4 illustrate the cross-sectional shapes in line drawings in which the description of a plate thickness is omitted.

[0015] As illustrated in FIG. 1, a can body 1 according to the present embodiment is a bottomed cylindrical can body including a can bottom 2 and a cylindrical can barrel 3 extending from an outer periphery of the can bottom 2 along a can axis (a central axis of the can barrel) O and centered on the can axis O. The can barrel 3 and the can bottom 2 have the same shape over the entire circumference around the can axis O in a longitudinal sectional view including the can axis O and along the direction of the can axis O.

[0016] The can body 1 is a drawn and ironed can body made of metal manufactured by drawing, ironing, and the like, a metal plate as a material of the can body 1. In the present embodiment, the metal material (material of the metal plate) constituting the material of the can body 1 is an aluminum alloy (also referred to as "aluminum alloy"). That is, the can body 1 is a drawn and ironed can body made of aluminum alloy and composed of a single layer of an aluminum alloy layer (also referred to as an "aluminum alloy layer"), but is not limited thereto and may be composed of a layer of another metal material.

[0017] Alternatively, the can body 1 may be a drawn and ironed can body made of resin-coated metal in which one surface (can body inner surface side) of a metal plate (metal layer) as a material thereof is coated with a first resin layer and the other surface (can body outer surface side) of the metal layer is coated with a second resin layer. In this case, for example, the metal layer (metal plate) is used as an aluminum alloy layer, the first resin layer and the second resin layer are used as PET layers, and the can body 1 may be a drawn and ironed polyethylene terephthalate (PET)-coated aluminum alloy can body in which both surfaces of the aluminum alloy layer are coated with the PET layers (the first resin layer and the second resin layer). The can body 1 is not limited thereto, and may be a drawn and ironed can body made of resin-coated metal including a layer of another metal material and a layer of another resin material.

[0018] As illustrated in FIGS. 1 and 2, the can bottom 2 has a dome portion 4 provided at a central portion of the can bottom 2, an annular protruding portion 5 continuously extending from an outer peripheral edge portion (an outer peripheral edge portion of an outer peripheral dome portion 42) 43 of the dome portion 4 and annularly protruding outward from the can body 1 substantially along the direction of the can axis O, and an outer wall portion 6 that is provided on the outside of the annular protruding portion 5 and is connected to the can barrel 3.

[0019] The dome portion 4 is provided at the center of the can bottom 2, and has a curved surface having a shape recessed in a dome shape toward the inside of the can body 1 along the direction of the can axis O. The dome portion 4 has a central dome portion 41 having a radius of curvature R1 set in advance and positioned on the can axis O, and an outer peripheral dome portion 42 having a radius of curvature R2 and formed continuously on the outside of the central dome portion 41.

[0020] In the longitudinal sectional view including the can axis O illustrated in FIG. 2, an angle (hereinafter, also referred to as a "dome tangent angle") θ between a tangent line M on an outer surface of the dome portion 4 and a plane (that is, a ground contact surface G) orthogonal to the can axis O at a position m where a virtual line L1 parallel to the can axis O and in contact with an innermost portion 53A of an inner peripheral wall portion 53 intersects the outer surface of the dome portion 4 (outer peripheral dome portion 42) is preferably 45° or more and 65° or less. In the longitudinal sectional view including the can axis O illustrated in FIG. 2, the innermost portion 53A of the inner peripheral wall portion 53 is a portion of the annular protruding portion 5 closest to the can axis O of the outer surface of the can body 1.

[0021] The inversion of the dome portion 4 due to the water hammer phenomenon occurring when the can body 1 is dropped is often caused by the outer peripheral dome portion 42 on the outer peripheral side of the central dome portion 41. Therefore, setting the dome tangent angle θ to 45° or more and raising the curved surface of the outer peripheral dome portion 42 (that is, the tangent angle θ) in this way makes the dome portion less likely to be inverted by the pressure of the water hammer phenomenon and can have sufficient drop strength. When the dome tangent angle θ is less than 45°, securing sufficient drop strength is difficult. The dome tangent angle θ being larger than 65° makes it difficult to achieve both a desired filling amount (content volume) according to a can height and sufficient drop strength and cannot have sufficient pressure resistance since, although the cause is not clear, the pressure of the water hammer phenomenon greatly affects the central dome portion 41 side. In the present embodiment, the "can height" means a height from the ground contact portion 52 of the product can to an upper end of a lid portion (not illustrated) along the direction of the can axis O.

[0022] The can body 1, which is any of a drawn and ironed can body made of metal and a drawn and ironed can body made of resin-coated metal, can have, by setting the dome tangent angle θ in the can bottom 2 to a value in a range of 45° or more and 65° or less, sufficient pressure resistance and sufficient drop strength while filling the can body 1 with the desired amount of contents (such as beverage) according to the can height. As long as the dome tangent angle θ is in the range of 45° or more and 65° or less, the radius of curvature of the dome portion 4 may be a single radius of curvature, a plurality of curvature radii, or a gradually changing radius of curvature, and may include a conical surface, as long as a desired filling amount according to the can height can be secured. Moreover, the outer peripheral dome portion 42 may be linear in the longitudinal sectional view including the can axis O illustrated in FIG. 2.

[0023] The annular protruding portion 5 includes a recessed portion 51 provided continuously with the outer peripheral edge portion 43 of the dome portion 4 and having a curved surface convex outward in the radial direction of the can body 1, a ground contact portion (support portion) 52 that is grounded to the ground contact surface G and supports the can body 1, and an inner peripheral wall portion 53 extending from the ground contact portion 52 to the recessed portion 51. The annular protruding portion 5 is formed to protrude toward the outside of the can body 1 substantially along the direction of the can axis O to form the ground contact portion 52 having an annular shape on the outer periphery of the dome portion 4.

[0024] In the longitudinal sectional view including the can axis O illustrated in FIG. 2, a recess depth d is defined as a distance (radial distance) between the virtual line L1 and a virtual line L2 parallel to the can axis O and tangent to the outermost portion 51A of the recessed portion 51 of the annular protruding portion 5. That is, the recess depth d is a radial distance between the outermost portion 51A of the recessed portion 51, which is a portion of the outer surface of the can body 1 farthest from the can axis O, and the innermost portion 53A of the annular protruding portion 5, which is a portion of the outer surface of the can body 1 closest to the can axis O. The recess depth d is preferably 0.50 mm or more and 0.85 mm or less in order to have sufficient filling amount (content volume) and pressure resistance.

[0025] The ground contact portion 52 is a portion that, when the can body 1 is placed on the ground contact surface (horizontal surface) G that is substantially horizontal, is grounded to the ground contact surface G, and supports the can body 1 by the ground contact portion 52 being grounded to the ground contact surface G. The annular protruding portion 5 has two convex curved surfaces with the ground contact portion 52 interposed therebetween. Specifically, as illustrated in FIG. 2, the annular protruding portion 5 has a first convex curved surface portion 55A on a side closer to the can axis O than the ground contact portion 52, and has a second curved surface portion 55B having a radius of curvature larger than that of the first convex curved surface portion 55A on a side farther from the can axis O than the ground contact portion 52. In the can body 1, a ground contact diameter φ, which is a diameter of the ground contact portion 52, is preferably 42.0 mm or more and 47.0 mm or less in order to have sufficient filling amount (content volume) and pressure resistance in the can body 1 in which an external diameter of the can barrel 3 is about 50 mm (commonly known as 200 diameter) or more and about 66 mm (commonly known as 211 diameter) or less, which is very commonly distributed as a product can application using a beverage or the like as contents, which is referred to as a so-called beverage can.

[0026] A radius of curvature R3 of the recessed portion 51 of the annular protruding portion 5 near the outermost portion 51A, which is a portion farthest from the can axis O of the outer surface of the can body 1, is preferably 0.3 mm or more and 2.0 mm or less in order to have sufficient filling amount (content volume) and pressure resistance, and particularly preferably 0.3 mm or more and 1.2 mm or less in order to have more sufficient filling amount (content volume) and pressure resistance.

[0027] A thickness T1 (= original plate thickness) of the aluminum alloy layer (single layer) at the portion (that is, on the can axis O of the central dome portion 41) of the dome portion 4 intersecting the can axis O (hereinafter, simply referred to as "thickness of aluminum alloy layer") is preferably 0.18 mm or more and 0.26 mm or less. When the thickness of the aluminum alloy layer is too small, the occurrence of barrel breakage or the like may increase in drawing and ironing after cup forming, resulting in a lower yield rate. On the other hand, when the thickness of the aluminum alloy layer is too large, the amount of material used increases, resulting in a difficulty in achieving resource saving. By setting the thickness T1 of the aluminum alloy layer within this range, the can body 1 can be made thinner to save resources, and barrel breakage or the like can be suppressed to improve the yield rate.

[0028] Alternatively, when the can body 1 is the drawn and ironed PET-coated aluminum alloy can body in which the surface of the aluminum alloy layer on the can body inner surface side is coated with the PET layer as the first resin layer and the surface of the aluminum alloy layer on the can body outer surface side is coated with the PET layer as the second resin layer, instead of the drawn and ironed can body made of aluminum alloy and composed of the aluminum alloy layer (single layer), it is preferable that on the can axis O of the central dome portion 41, a thickness T21 of the PET layer as the first resin layer on the can body inner surface side is 0.011 mm or more and 0.017 mm or less, a thickness T22 of the PET layer as the second resin layer on the can body outer surface side is 0.009 mm or more and 0.012 mm or less, and a thickness T23 (= T1) of the aluminum alloy layer between the first and second resin layers (PET layers) is 0.18 mm or more and 0.26 mm. By setting the thicknesses T21, T22, and T23 within the above ranges, the can body 1 can be made thinner to save resources, and barrel breakage or the like can be suppressed to improve the yield rate.

[0029] Such a can body 1 can be manufactured by a manufacturing method having steps shown in a flowchart of FIG. 3, for example. The method for manufacturing the can body 1 is not limited to the example of FIG. 3. In the example of FIG. 3, a metal plate such as an aluminum alloy is first punched into a circular shape, and then the circular shape is subjected to drawing (cupping) by a cupping press to form a cup (cupping step S1). Subsequently, the formed cup is subjected to drawing and ironing to form a can preform (not illustrated) (can preform forming step S2). The can preform has the can barrel 3 and a can bottom. The can bottom has a dome portion recessed toward the inside of the can preform and an annular protruding portion protruding toward the side opposite to the recessed side of the dome portion.

[0030] In the can preform forming step S2, the dome portion 4 (before bottom reforming) provided at the center of the can bottom 2 of the can body 1 is formed as a dome portion of the can bottom of the can preform. At the same time, as the annular protruding portion of the can bottom of the can preform, the annular protruding portion 5 (before bottom reforming) is formed continuously extending from the outer peripheral edge portion 43 of the dome portion 4 (before bottom reforming) and annularly protruding outward from the can body 1 substantially along the direction of the can axis O. That is, the can preform forming step S2 forms, as the annular protruding portion of the can preform, the annular protruding portion 5 (before bottom reforming) including the recessed portion 51 provided continuously with the dome portion 4 (before bottom reforming) and having a curved surface convex outward in the radial direction of the can body 1, the ground contact portion 52 supporting the can body 1, and the inner peripheral wall portion 53 extending from the ground contact portion 52 to the recessed portion 51.

[0031] Subsequently, ears at an opening end of the can preform are trimmed using a trimmer (not illustrated) (trimming step S3). Subsequently, after performing a process such as coating or printing on at least the outer surface of the can barrel 3 (outer surface coating printing step S4) as necessary, a process of coating at least the inner surfaces of the can barrel 3 and the can bottom (inner surface coating step S5) is performed by spraying or the like as necessary, and then bottom reforming is performed on the can bottom by pressing the inner surface of the dome portion of the can preform to be pressed along the direction of the can axis O (bottom reforming step S6).

[0032] Subsequently, a necking forming tool (not illustrated) is used to perform die processing (necking) stepwise at a portion connected to an opening (not illustrated) in the can barrel 3 of the can body 1, thereby forming a neck portion (not illustrated) (necking step S7). Subsequently, the end portion (mouth) of the opening of the can barrel 3 is curled toward the outside of the can body 1 by a roller (not illustrated) to form a flange portion (not illustrated) (flanging step S8). For example, the can body 1 as a formed can is manufactured by such processing from S1 to S8. Subsequently, the can body 1 is filled with contents (such as beverage), and a seaming step S9 (not illustrated) of seaming and sealing the flange portion (not illustrated) and a lid portion (not illustrated) is performed, thereby manufacturing a can container (product can) filled with the contents.

[0033] In the bottom reforming step (S6) described above, the can bottom of the can preform having the dome portion and the annular protruding portion having the ground contact portion (support portion) is subjected to bottom reforming by using, for example, a forming tool F including an inner tool F1 and an outer tool F2 illustrated in FIG. 4. At this time, both the forming of the dome portion 4 having the central dome portion 41 and the outer peripheral dome portion 42 in the can body 1 and the forming of the annular protruding portion 5 in the can body 1 are performed by the forming tool F (the inner tool F1 and the outer tool F2).

[0034] The inner tool F1 is used to perform forming processing on the curved surface of the dome portion of the can preform from the inside of the can preform, and has a forming surface S for obtaining a desired dome portion 4. The inner tool F1 presses only the outer peripheral portion P of the forming surface S against the dome portion of the can preform to perform forming and may thus be hollow to exclude a central portion of the forming surface S which is not pressed against the dome portion. The outer tool F2 has a chuck C for forming the annular protruding portion 5 of the can body 1.

[0035] By pressing the inner tool F1 downward, the dome portion 4 of the can body 1 is formed as described above, and the annular protruding portion of the can preform enters the chuck C of the outer tool F2, so that the annular protruding portion 5 corresponding to the mold shape of the chuck C is formed. In the pressing by the inner tool F1, the inner tool F1 is pressed against the dome portion of the can preform from the inside of the can preform along the direction of the can axis O so that the dome portion 4 having a dome tangent angle θ of 45° or more and 65° or less is formed in the longitudinal sectional view including the can axis O illustrated in FIG. 2.

[0036] As illustrated in FIG. 2, the inner peripheral wall portion 53 of the annular protruding portion 5 in the can body 1 subjected to the forming process reaches the outer peripheral edge portion (the outer peripheral edge portion of the outer peripheral dome portion 42) 43 of the dome portion 4 via the recessed portion 51. The outermost portion 51A of the recessed portion 51 is a bent portion plastically processed by compression by the forming tool F. The outermost portion 51A formed in this manner can be recessed deeper in a direction away from the can axis O with respect to the innermost portion 53A of the inner peripheral wall portion 53. Since the outermost portion 51A of the recessed portion 51 is a bent portion plastically processed by compression, known roll forming is not required. Therefore, the inner peripheral wall portion 53 of the annular protruding portion 5 has no roll forming mark that is formed when a curved surface is formed by roll forming. Since no aluminum oxide coating is damaged, no blackening occurs during heat sterilization after filling contents, and deterioration of the aesthetic appearance can be avoided.Example

[0037] Two types of drop tests, namely, (1) a single body drop test and (2) a case drop test, were performed using the can body 1 described above. The test results are illustrated in FIGS. 5 and 6.(1) Single Drop Test

[0038] As an example of the single body drop test, a test was performed in which carbonated water as contents was filled in a desired filling amount according to a can height, the body 1 was sealed with a can lid (lid portion) (not illustrated), and the can body 1 sufficiently shaken was dropped as a single body. In the can body 1 before the single body drop test, the liquid temperature of the contents (filling material) was 35°C, and the internal pressure in a state of being left to stand before shaking was 400 kPa or 500 kPa. In this single body drop test, a surface of a gray cast iron block, which was processed so that the top surface thereof is a flat surface having an inclination angle of 10°, on which one sheet of a material of a corrugated cardboard carton for packaging used for transporting product cans was placed was set as a drop surface. The can body 1 was freely dropped onto the drop surface from a height at which the shortest distance from the ground contact portion 52 to the drop surface is 20 cm, with the ground contact portion 52 facing downward and the can axis O extending in the vertical direction (not illustrated).(2) Case Drop Test

[0039] As an example of the case drop test, a test was performed in which 24 can bodies 1, each of which was filled with carbonated water as contents in a desired filling amount according to a can height and sealed with a can lid (lid portion) (not illustrated), were sufficiently shaken and dropped in a state of being accommodated in a rectangular parallelepiped corrugated cardboard carton for packaging used for transporting product cans. In the can body 1 before the case drop test, the liquid temperature of the contents (filling material) was 35°C, and the internal pressure in a state of being left to stand before shaking was 400 kPa or 500 kPa. In this case drop test, a dull finish steel plate made of SPCC and having a thick 20 mm placed on a horizontal concrete ground was used as a drop surface. The corrugated cardboard carton for packaging containing 24 can bodies 1 was freely dropped onto the drop surface from a height at which the shortest distances between the corrugated cardboard carton for packaging and the steel plate are 15 cm, with the ground contact portions 52 of the can bodies 1 contained therein facing downward and the longitudinal direction of the corrugated cardboard carton for packaging inclined by 20° from the horizontal state (not illustrated).

[0040] FIG. 5 illustrates, as "evaluation (single body)" and "evaluation (case)", the results of the single body drop test and the case drop test when the can body 1 is a drawn and ironed can body made of aluminum alloy and composed of a single layer of an aluminum alloy layer. FIG. 6 illustrates, as "evaluation (single body)" and "evaluation (case)", the results of the single body drop test and the case drop test when the can body 1 is a drawn and ironed PET-coated aluminum alloy can body in which both surfaces of the aluminum alloy layer on the can body inner surface side and the can body outer surface side are coated with a PET layer.

[0041] In the tables of FIGS. 5 and 6, "θ", "d", "φ", and "R3" correspond to the "dome tangent angle θ", the "recess depth d", the "ground contact diameter φ", and the "radius of curvature R3" in the form illustrated in FIG. 2 described above. In the table of FIG. 5, "T1" corresponds to "thickness T1 of aluminum alloy layer" on the can axis O of the central dome portion 41 in the case of the above-described aluminum alloy layer in the can body 1 (drawn and ironed can body made of aluminum alloy). In the table of FIG. 6, "T21" (in the can body 1 (drawn and ironed PET-coated aluminum alloy can body)) corresponds to "thickness T21 of PET layer as a first resin layer" on the can body inner surface side on the can axis O of the central dome portion 41 described above, "T22" corresponds to "thickness T22 of PET layer as a second resin layer" on the can body outer surface side on the can axis O of the central dome portion 41 described above, and "T23" corresponds to "thickness T23 (= T1) of aluminum alloy layer" between the first and second resin layers (PET layers) on the can axis O of the central dome portion 41 described above.

[0042] In the columns of "evaluation (single body)" and "evaluation (case)" in the tables illustrated in FIGS. 5 and 6, in a state where the can body 1 after the drop test was placed on the ground contact surface (horizontal surface) G as a single body and stood by itself, when the inclination angle of the can barrel 3 was less than 2° and the inversion of the dome portion 4 was not observed, the can body 1 was evaluated as "pass" and indicated by "○". In a state where the can body 1 was caused to stand by itself in the same manner, a case where the inclination angle of the can barrel 3 was 2° or more or inversion was observed even in a part of the dome portion 4 was evaluated as "fail" and indicated by "x". Since the can body 1 that was not fillable with a desired filling amount (content volume) was not subjectable to the drop test, the can body 1 was determined to be unevaluable and indicated by "-" (also in this case, the can body 1 was evaluated as "fail").

[0043] In the can body 1, when the dome tangent angle θ was 65° or less, the contents could be filled in a desired filling amount according to the can height. Specifically, in Examples 1-1 to 1-3 and Comparative Examples 1-1 to 1-3 (all of which use a commonly known 202 diameter), the contents were filled with 190 ml that is a desired filling amount, and in Examples 1-4 to 1-6 (all of which use a commonly known 211 diameter), the contents were filled with 350 ml that is a desired filling amount.

[0044] In Example 2-1, Example 2-2, Comparative Example 2-1, and Comparative Example 2-2 (all of which use a commonly known 202 diameter), the contents were filled with 190 ml that is a desired filling amount. In Example 2-3, Example 2-4, and Comparative Example 2-3 (all of which use a commonly known 204 diameter), the contents were filled with 355 ml that is a desired filling amount. In Example 2-5 and Example 2-6 (all of which use a commonly known 211 diameter), the contents were filled with 350 ml that is a desired filling amount.

[0045] As illustrated in FIGS. 5 and 6, in both of the case where the can body 1 is the drawn and ironed can body made of aluminum alloy and the case where the can body 1 is the drawn and ironed PET-coated aluminum alloy can body, in Examples 1-1 to 1-6 and Examples 2-1 to 2-6 in which the dome tangent angle θ is 45° or more and 65° or less, the evaluation results of both of the "evaluation (single body)" and the "evaluation (case)" were "pass" (○).

[0046] On the other hand, in both of the case where the can body 1 is the drawn and ironed can body made of aluminum alloy and the case where the can body 1 is the drawn and ironed PET-coated aluminum alloy can body, in Comparative Example 1-1 to Comparative Example 1-3 and Comparative Example 2-1 to Comparative Example 2-3 in which the dome tangent angle θ is less than 45°, the evaluation results of both of the "evaluation (single body)" and the "evaluation (case)" were "fail" (x). In Comparative Examples 1-4 to 1-6 and Comparative Examples 2-4 to 2-6 in which the dome tangent angle θ is larger than 65°, since the can body 1 was not fillable with desired filling amounts (350 ml in Comparative Examples 1-4 to 1-6 (all of which use a commonly known 211 diameter), 355ml in Comparative Example 2-4 (uses a commonly known 204 diameter), and 350 ml in Comparative Examples 2-5 and 2-6 (all of which use a commonly known 211 diameter)), the drop test could not be performed, and the can body 1 was determined to be "unevaluable" (-) (also in this case, the can body 1 was evaluated as "fail").

[0047] From the above results, it is found that the can body 1, which is any of the drawn and ironed can body made of aluminum alloy and the drawn and ironed PET-coated aluminum alloy can body, can have, by setting the dome tangent angle θ to a value in a range of 45° or more and 65° or less, sufficient pressure resistance and sufficient drop strength while the contents are filled in a desired filling amount.

[0048] Although the embodiments of the present invention have been described in detail with reference to the drawings, specific forms are not limited to these embodiments. The above embodiment is merely an example, and it is needless to say that any can body 1 having different can heights and different filling amounts from a commonly known 200 diameter to a commonly known 211 diameter can have sufficient pressure resistance and sufficient drop strength. Even though there is a change in design or the like within a range not departing from the gist of the present invention, the change is included in the present invention. The above-described embodiments can be combined with each other by applying techniques to each other as long as there is no particular contradiction or problem in the purpose, form, and the like.Reference Signs List

[0049] 1: Can body, 2: Can bottom, 3: Can barrel, 4: Dome portion, 5: Annular protruding portion, 6: Outer wall portion, 41: Central dome portion, 42: Outer peripheral dome portion, 43: Outer peripheral edge portion, 51: Recessed portion, 51A: Outermost portion, 52: Ground contact portion (support portion), 53: Inner peripheral wall portion, 53A: Innermost portion 55A: first convex curved surface portion, 55B: Second curved surface portion

Claims

1. A can body, comprising: a can bottom; and a can barrel extending from an outer periphery of the can bottom along a can axis, centered on the can axis, and having a cylindrical shape, wherein the can bottom comprises a dome portion provided at a central portion of the can bottom and an annular protruding portion continuously extending from an outer peripheral edge portion of the dome portion and annularly protruding outward from the can body substantially along a direction of the can axis, the annular protruding portion comprises a recessed portion provided continuously with the dome portion and having a curved surface convex outward in a radial direction of the can body, a ground contact portion configured to support the can body, and an inner peripheral wall portion extending from the ground contact portion to the recessed portion, and in a longitudinal sectional view including the can axis, an angle θ between a tangent line M on an outer surface of the dome portion and a plane orthogonal to the can axis at a position where a virtual line L1 parallel to the can axis and in contact with an innermost portion of the inner peripheral wall portion intersects the outer surface of the dome portion is 45° or more and 65° or less.

2. The can body according to claim 1, wherein in the longitudinal sectional view including the can axis, a recess depth d, which is a radial distance between the virtual line L1 and a virtual line L2 parallel to the can axis and tangent to an outermost portion of the recessed portion, is 0.50 mm or more and 0.85 mm or less, and a ground contact diameter φ, which is a diameter of the ground contact portion, is 42.0 mm or more and 47.0 mm or less, a radius of curvature R3 near the outermost portion of the recessed portion is 0.3 mm or more and 2.0 mm or less, the can body is a drawn and ironed can body made of aluminum alloy and composed of a single layer of an aluminum alloy layer or a drawn and ironed polyethylene terephthalate (PET)-coated aluminum alloy can body in which both surfaces of an aluminum alloy layer are coated with a PET layer, and a thickness of the aluminum alloy layer at a portion intersecting the can axis of the dome portion is 0.18 mm or more and 0.26 mm or less.

3. The can body according to claim 2, wherein the radius of curvature R3 near the outermost portion of the recessed portion is 0.3 mm or more and 1.2 mm or less.

4. A product can in which the can body according to claim 1 is filled with contents and a flange portion formed in an opening of the can barrel and a lid portion are seamed.

5. A method for manufacturing a can body having a bottomed cylindrical shape including a can bottom and a cylindrical can barrel extending from an outer periphery of the can bottom along a can axis and centered on the can axis, the method comprising: a step of forming a dome portion provided at a central portion of the can bottom and forming, as an annular protruding portion continuously extending from an outer peripheral edge portion of the dome portion and annularly protruding outward from the can body substantially along a direction of the can axis, the annular protruding portion including a recessed portion provided continuously with the dome portion and having a curved surface convex outward in a radial direction of the can body, a ground contact portion configured to support the can body, and an inner peripheral wall portion extending from the ground contact portion to the recessed portion; and a step of performing, after the step of forming the dome portion and the annular protruding portion, bottom reforming of pressing, along a direction of the can axis, a forming tool having a forming surface along a curved surface of the dome portion against the dome portion from an inside of the can body so that in a longitudinal sectional view including the can axis, an angle θ between a tangent line M on an outer surface of the dome portion and a plane orthogonal to the can axis at a position where a virtual line L1 parallel to the can axis and in contact with an innermost portion of the inner peripheral wall portion intersects the outer surface of the dome portion is 45° or more and 65° or less.

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