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

Abstract

To provide a can body, a product can, and a manufacturing method of the can body capable of securing sufficient pressure resistance strength and sufficient drop strength while securing a desired filling volume of contents.SOLUTION: A can body has a can bottom and a cylindrical can drum centering on a can axis extending from an outer periphery of the can bottom along the can axis, wherein the can bottom has a dome part that is provided in a center part of the can bottom and an annular convex part that is continuous from an outer circumferential edge part of the dome part and protrudes annularly outward from the can body substantially along a can axial direction, and the annular convex part is a bottomed cylindrical can body having a recess part that is provided continuously with the dome part and has a curved surface convex to the radial outside of the can body, a ground part that supports the can body, and an inner circumferential wall part that extends from the ground part to the recess part. In a longitudinal sectional view including the can axis of the can body, an angle θ of a tangent line M to an outer surface of the dome part at a position where a virtual line L1, which is parallel to the can axis and is in contact with the innermost part of the inner circumferential wall part, intersects an outer surface of the dome part with respect to a plane orthogonal to the can axis is between 45° or more and 65°or less.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a can body having a bottom reformed at its bottom, a finished can in which the can body is filled with contents, and a method for manufacturing the can body. [Background technology]

[0002] Conventionally, drawn and ironed aluminum alloy can bodies and drawn and ironed resin-coated aluminum alloy can bodies (two-piece cans) have been known as containers for filling with beverages and other contents. These can bodies (can containers) are obtained by punching out a metal plate into a circle, drawing to form a shallow cylindrical cup with a bottom, and then drawing and ironing the cup to integrally form the can bottom and can body, as well as other processes.

[0003] In such can bodies, there is a demand for a thinner can body from the viewpoint of resource saving, but there is also a demand for sufficient pressure resistance even in the thinned can body. In particular, in a can body with a dome part at the bottom, when the contents are carbonated beverages or the like, a phenomenon in which the dome part at the can bottom inverts (buckling) may occur when the internal pressure due to carbon dioxide gas increases. Therefore, a can body with a dome part at the bottom is required to have sufficient pressure resistance to withstand the internal pressure, and the bottom of the can body is designed to have sufficient pressure resistance.

[0004] Specifically, in a can body having a dome portion at the bottom of the can body whose center is recessed toward the inside of the can body and an annular protrusion around the dome portion, bottom reforming is performed on the annular protrusion to ensure pressure resistance even when the wall is thinned (for example, Patent Documents 1 to 3).

[0005] However, if a thin-walled can body is dropped, for example, during transportation, the contents may cause a water hammer phenomenon, which may lead to problems such as tilting of the can body or inversion of the dome part. Therefore, there is a demand for a can body with sufficient drop strength to withstand the impact of being dropped (for example, Patent Document 4). [Prior art documents] [Patent documents]

[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. 7,740,148 Summary of the Invention [Problem to be solved by the invention]

[0007] However, in the conventional can body having a dome portion on the bottom, sufficient consideration has not been given to a configuration capable of preventing the dome portion from inverting due to the water hammer phenomenon when dropped. For example, Patent Document 2 describes that the outer diameter of the cylindrical body of the primary can body is 66.1 mm to 66.3 mm, the angle of the tangent of the inner surface of the outer peripheral edge of the dome portion with respect to a plane perpendicular to the can axis is 27° to 29°, the radial width of the portion located radially inward of the inner wall of the pressing surface is 2.0 mm to 3.0 mm, and the inclination angle of the pressing surface with respect to the plane is 20° or more and the angle (=29°) with respect to the tangent plane. However, it has been found that it is difficult to ensure sufficient drop strength in the formed can body even with the numerical limitations in Patent Document 2.

[0008] The present invention aims to address such circumstances. As a result of the inventor's diligent analysis, he has discovered that the inversion of the dome part due to the water hammer phenomenon that occurs when the can is dropped is caused by the outer periphery of the dome part. In light of this, the present invention aims to provide a can body, a finished can, and a method for manufacturing a can body that can ensure sufficient pressure resistance and sufficient drop strength while ensuring a desired filling amount of the contents. [Means for solving the problem]

[0009] In order to solve the above problems, the can body of the present invention is a cylindrical can body with a bottom, comprising a can bottom and a cylindrical can body centered on the can axis extending from the outer periphery of the can bottom along the can axis, the can bottom having a dome portion provided in the center of the can bottom and an annular convex portion continuing from the outer periphery of the dome portion and protruding in an annular shape to the outside of the can body approximately along the can axis direction, the annular convex portion having a recess portion provided continuous with the dome portion and having a curved surface that convex radially outwardly of the can body, a ground portion that supports the can body, and an inner wall portion extending from the ground portion to the recessed portion, wherein in a vertical cross section including the can axis, an angle θ of a tangent M to the outer surface of the dome portion relative to a plane perpendicular to the can axis at a position where a virtual line L1 that is parallel to the can axis and tangent to the innermost part of the inner wall portion intersects with the outer surface of the dome portion is between 45° and 65°.

[0010] The finished can according to the present invention is characterized in that it is produced by filling the can body according to the present invention with a content, and then rolling up the flange portion and the lid portion formed at the opening of the can body.

[0011] The manufacturing method of the can body according to the present invention is a manufacturing method of a bottomed cylindrical can body having a can bottom and a cylindrical can body centered on the can axis extending from the outer periphery of the can bottom along the can axis, the manufacturing method including forming a dome portion provided in the center of the can bottom, and forming the annular convex portion continuing from the outer periphery of the dome portion and protruding annularly to the outside of the can body approximately along the can axis direction, the annular convex portion having a curved surface that is convex radially outwardly of the can body and a ground portion that supports the can body, and an inner circumferential wall portion that extends from the ground portion to the recess portion. and after the process of forming the dome portion and the annular convex portion, a bottom reforming process in which a forming tool having a processed surface that conforms to the curved surface of the dome portion is pressed against the dome portion from inside the can body along the can axial direction so that, in a vertical cross section including the can axis, an angle θ of a tangent M to the outer surface of the dome portion with respect to a plane perpendicular to the can axis at a position where a virtual line L1 that is parallel to the can axis and tangent to the innermost part of the inner wall portion intersects with the outer surface of the dome portion is 45° or more and 65° or less. Effect of the Invention

[0012] According to the can body, the product can, and the method for manufacturing the can body of the present invention, it is possible to ensure a desired filling amount of the contents while also ensuring sufficient pressure resistance and sufficient drop strength. [Brief description of the drawings]

[0013] [Figure 1] FIG. 2 is a longitudinal cross-sectional view of a main portion of a can body in this embodiment (a longitudinal cross-sectional view including a can axis O and taken along the can axis O direction). [Diagram 2] FIG. 2 is an enlarged view of a main part in FIG. [Diagram 3] 4 is a flowchart for explaining an example of a method for manufacturing a can body in the present embodiment. [Figure 4] FIG. 2 is an explanatory diagram (a longitudinal cross-sectional view including the can axis O and along the can axis O direction) for explaining the reforming process in the can body manufacturing method in this embodiment. [Diagram 5]1 is a table showing the test results of a single drop test and a case drop test using a can body (aluminum alloy drawn and ironed can body). [Figure 6] 1 is a table showing the test results of a single drop test and a case drop test using a can body (a PET-coated aluminum alloy drawn and ironed can body). DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] Hereinafter, an embodiment of the present invention (the present embodiment) will be described with reference to the drawings. In the following description, the same reference numerals in different drawings indicate parts with the same functions, and duplicated explanations in each drawing will be omitted as appropriate. Also, the cross-sectional views in Figures 1 and 4 show the cross-sectional shapes in line drawings with the plate thickness omitted.

[0015] 1, the can body 1 according to this embodiment is a bottomed cylindrical can body including a can bottom 2 and a cylindrical can body 3 that extends from the outer periphery of the can bottom 2 along a can axis (the central axis of the can body) O and is centered on the can axis O. The can body 3 and the can bottom 2 have the same shape all around the can axis O in a vertical cross-sectional view including the can axis O and along the can axis O direction.

[0016] The can body 1 is a drawn and ironed metal can body produced by drawing, ironing, etc., a metal plate as its raw material. In this embodiment, the metal material (metal plate material) constituting the raw material of the can body 1 is an aluminum alloy (also called "aluminum alloy"). That is, the can body 1 is an aluminum alloy drawn and ironed can body consisting of a single layer of an aluminum alloy layer (also called "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 resin-coated drawn and ironed metal can body in which one surface (the inner surface side of the can body) of a metal plate (metal layer) is coated with a first resin layer and the other surface (the outer surface side of the can body) of the metal layer is coated with a second resin layer. In this case, for example, the metal layer (metal plate) may be an aluminum alloy layer (aluminum alloy layer), the first resin layer and the second resin layer are both polyethylene terephthalate (PET) layers, and both surfaces of the aluminum alloy layer (aluminum alloy layer) are coated with PET layers (first resin layer, second resin layer) to form the can body 1. However, the can body 1 is not limited to this, and may be a resin-coated drawn and ironed metal can body composed of a layer of another metal material and a layer of another resin material.

[0018] As shown in Figures 1 and 2, the can bottom 2 has a dome portion 4 provided in the center of the can bottom 2, an annular protrusion 5 that continues from the outer peripheral edge portion 43 of the dome portion 4 (the outer peripheral edge portion of the outer dome portion 42) and protrudes in a ring shape to the outside of the can body 1 approximately along the direction of the can axis O, and an outer wall portion 6 that is provided outside the annular protrusion 5 and connects to the can body 3.

[0019] Dome portion 4 is provided in the center of can bottom 2, and has a curved surface that is concave like a dome toward the inside of can body 1 along the direction of can axis O. This dome portion 4 has, for example, central dome portion 41 located on can axis O and having a preset radius of curvature R1, and peripheral dome portion 42 formed contiguous to the outside of central dome portion 41 and having a radius of curvature R2.

[0020] In the vertical cross section including the can axis O shown in Figure 2, the angle θ of a tangent M to the outer surface of the domed portion 4 at a position m where an imaginary line L1 that is parallel to the can axis O and tangent to the innermost portion 53A of the inner wall portion 53 intersects with the outer surface of the domed portion 4 (outer domed portion 42) relative to a plane perpendicular to the can axis O (i.e., the contact surface G) (hereinafter also referred to as the "dome tangent angle") is preferably 45° or more and 65° or less. Here, in the vertical cross section including the can axis O shown in Figure 2, the innermost portion 53A of the inner wall portion 53 is the point on the outer surface of the can body 1 in the annular convex portion 5 that is closest to the can axis O.

[0021] Inversion of the dome portion 4 due to the water hammer phenomenon that occurs when the can body 1 is dropped is often caused by the outer dome portion 42, which is more outer than the central dome portion 41. Therefore, by setting the dome tangent angle θ to 45° or more and raising the curved surface of the outer dome portion 42 (i.e., this tangent angle θ), the dome portion is less likely to invert under the pressure of the water hammer phenomenon, and sufficient drop strength can be ensured. If the dome tangent angle θ is less than 45°, it is difficult to ensure sufficient drop strength. If the dome tangent angle θ is greater than 65°, it is difficult to ensure both the desired filling amount (content amount) according to the can height and sufficient drop strength, and, although the cause is unclear, the pressure of the water hammer phenomenon largely affects the central dome portion 41, making it difficult to ensure sufficient pressure resistance. In this embodiment, the "can height" means the height along the can axis O direction from the ground portion 52 of the product can to the top end of the lid portion (not shown).

[0022] Whether the can body 1 is a drawn and ironed metal can body or a resin-coated drawn and ironed metal can body, by setting the dome tangent angle θ at the can bottom 2 to a value within the range of 45° to 65°, sufficient pressure resistance and sufficient drop strength can be ensured while filling the can with the desired amount of contents (beverage, etc.) depending on the can height. As long as the dome tangent angle θ is within the range of 45° to 65°, the radius of curvature of the dome portion 4 may be single or multiple, and may gradually change within a range that ensures the desired amount of filling depending on the can height, and may include a conical surface. Furthermore, in a vertical cross section including the can axis O shown in FIG. 2, the outer peripheral dome portion 42 may be straight.

[0023] The annular protrusion 5 has a recessed portion 51 that is continuous with the outer peripheral edge portion 43 of the dome portion 4 and has a curved surface that protrudes radially outward from the can body 1, a grounding portion (support portion) 52 that is grounded on the ground surface G and supports the can body 1, and an inner peripheral wall portion 53 that extends from the grounding portion 52 to the recessed portion 51. The annular protrusion 5 is formed to protrude toward the outside of the can body 1 approximately along the direction of the can axis O so as to form an annular grounding portion 52 around the outer periphery of the dome portion 4.

[0024] In a vertical cross-sectional view including the can axis O shown in Fig. 2, the distance (radial distance) between imaginary line L1 and imaginary line L2 that is parallel to the can axis O and tangent to the outermost portion 51A of the recessed portion 51 of the annular protrusion 5 is defined as the recess depth d. In other words, the recess depth d is the radial distance between the outermost portion 51A, which is the farthest portion from the can axis O on the outer surface of the can body 1 in the recessed portion 51, and the innermost portion 53A, which is the closest portion to the can axis O on the outer surface of the can body 1 in the annular protrusion 5. In order to ensure a sufficient filling amount (content) and pressure resistance, the recess depth d is preferably 0.50 mm or more and 0.85 mm or less.

[0025] The contact portion 52 is a portion that comes into contact with the contact surface G when the can body 1 is placed on a substantially horizontal contact surface (horizontal plane) G, and supports the can body 1 by contacting the contact surface G with the contact portion 52. The annular convex portion 5 has two convex curved surfaces on either side of the contact portion 52. Specifically, as shown in Fig. 2, the annular convex portion 5 has a first convex curved surface portion 55A on a side closer to the can axis O than the contact portion 52, and a second curved surface portion 55B having a larger radius of curvature than the first convex curved surface portion 55A on a side farther from the can axis O than the contact portion 52. In the can body 1, the ground diameter φ of the ground portion 52 is preferably 42.0 mm or more and 47.0 mm or less in order to ensure sufficient filling amount (contents) and pressure resistance for can bodies 1 having an outer diameter of the can body 3 of about 50 mm (commonly known as 200 diameter) or more and about 66 mm (commonly known as 211 diameter) or less, which are commonly used as product cans containing beverages and the like, known as beverage cans.

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

[0027] The thickness T1 (=original plate thickness) of the aluminum alloy layer (single layer) at the intersection of the dome portion 4 with the can axis O (i.e., on the can axis O of the central dome portion 41) (hereinafter simply referred to as the "thickness of the aluminum alloy layer") is preferably 0.18 mm or more and 0.26 mm or less. If the thickness of the aluminum alloy layer is too small, the occurrence of breakage and the like increases during the drawing and ironing process after cup forming, and there is a risk of a decrease in the yield rate. On the other hand, if the thickness of the aluminum alloy layer is too large, the amount of material used increases, making it difficult to conserve resources. By setting the thickness T1 of the aluminum alloy layer within this range, the can body 1 can be made thinner to conserve resources, and breakage and the like can be suppressed to improve the yield rate.

[0028] Alternatively, when the can body 1 is a PET-coated aluminum alloy drawn and ironed can body in which the surface of the aluminum alloy layer facing the inner surface of the can body is coated with a PET layer as a first resin layer and the surface of the aluminum alloy layer facing the outer surface of the can body is coated with a PET layer as a second resin layer, it is preferable that, on the can axis O of the central dome portion 41, the thickness T21 of the PET layer as the first resin layer facing the inner surface of the can body is 0.011 mm or more and 0.017 mm or less, the thickness T22 of the PET layer as the second resin layer facing the outer surface of the can body is 0.009 mm or more and 0.012 mm or less, and the 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 or less. By setting the thicknesses T21, T22, and T23 within these ranges, the can body 1 can be made thinner, saving resources, and the occurrence of breakage or the like can be suppressed, improving the yield rate.

[0029] Such a can body 1 can be manufactured by a manufacturing method having the steps shown in the flow chart of FIG. 3, for example. The manufacturing method of 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 circle, and then a cup is formed by drawing (cupping) using a cupping press (cupping step (S1)). Next, the formed cup is drawn and ironed to form a can preform (not shown) (can preform forming step (S2)). The can preform has a can body 3 and a can bottom. This can bottom has a dome portion that is recessed toward the inside of the can preform, and an annular protrusion that protrudes to the side opposite the recessed side of the dome portion.

[0030] In this can preform molding step (S2), a dome portion 4 (before bottom reforming) provided at the center of the can bottom 2 of the can body 1 is molded as the dome portion of the can bottom of the can preform. At the same time, an annular convex portion 5 (before bottom reforming) is molded as the annular convex portion of the can bottom of the can preform, which is continuous from the outer peripheral edge portion 43 of the dome portion 4 (before bottom reforming) and protrudes annularly to the outside of the can body 1 approximately along the can axis O direction. That is, in this can preform molding step (S2), an annular convex portion 5 (before bottom reforming) is molded as the annular convex portion of the can preform, which is continuous from the dome portion 4 (before bottom reforming) and has a recess portion 51 having a curved surface that is convex radially outward of the can body 1, a ground portion 52 that supports the can body 1, and an inner peripheral wall portion 53 that extends from the ground portion 52 to the recess portion 51.

[0031] Next, a trimmer (not shown) is used to trim the edge of the open end of the can preform (trimming step (S3)). Then, if necessary, at least the outer surface of the can body 3 is painted, printed, or otherwise treated (outer surface painting and printing step (S4)), and then, if necessary, at least the inner surface of the can body 3 and the can bottom is painted by spraying or the like (inner surface painting step (S5)). After that, the inner surface of the dome part of the can preform is pressed along the can axis O to perform bottom reforming of the can bottom (bottom reforming step (S6)).

[0032] Thereafter, a necking tool (not shown) is used to perform die processing (necking) in stages at a portion of the can body 3 of the can body 1 that is connected to an opening (not shown) to form a neck (not shown) (necking process (S7)). Next, a roller (not shown) is used to curl the end (mouth) of the opening of the can body 3 toward the outside of the can body 1 to form a flange (not shown) (flanging process (S8)). For example, the can body 1 is manufactured as a formed can by the processes of S1 to S8. Thereafter, a can container (product can) filled with the contents (such as a beverage) is manufactured by filling the inside of the can body 1 with the contents (such as a beverage) and rolling up and sealing the flange (not shown) and the lid (not shown) in a rolling process (S9 (not shown)).

[0033] In the above-mentioned bottom reforming step (S6), bottom reforming is performed on the can bottom of a can preform having a dome portion and an annular protrusion having a ground portion (support portion) using a forming tool F equipped with an inner tool F1 and an outer tool F2 as shown in Fig. 4. At this time, the formation of the dome portion 4 having a central dome portion 41 and an outer peripheral dome portion 42 in the can body 1, and the formation of the annular protrusion 5 in the can body 1 are both 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 inside the can preform, and has a processing surface S for obtaining the desired dome portion 4. This inner tool F1 may be hollow so that only the outer peripheral portion P of the processing surface S is pressed against the dome portion of the can preform to form it, excluding the central portion of the processing surface S that is not pressed against the dome portion. The outer tool F2 has a chuck C for forming the annular protrusion 5 of the can body 1.

[0035] The downward pressing of the inner tool F1 forms the dome portion 4 of the can body 1 as described above, and the annular protrusion of the can preform enters the chuck C of the outer tool F2 to form an annular protrusion 5 according to the shape of the chuck C. In this pressing by the inner tool F1, the inner tool F1 is pressed against the dome portion of the can preform from inside the can preform along the can axis O direction so that the dome portion 4 with a dome tangent angle θ of 45° to 65° is formed in a vertical cross section including the can axis O shown in Fig. 2.

[0036] As shown in FIG. 2, the inner peripheral wall 53 of the annular projection 5 in the formed can body 1 reaches the outer peripheral edge 43 of the dome section 4 (the outer peripheral edge of the outer peripheral dome section 42) via the recess 51. The outermost portion 51A of the recess 51 is a bent portion plastically processed by compression with a forming tool F. The outermost portion 51A formed in this manner can be recessed deeper in a direction away from the can axis O than the innermost portion 53A of the inner peripheral wall 53. Since the outermost portion 51A of the recess 51 is a bent portion plastically processed by compression, known roll forming is not required. Therefore, the inner peripheral wall 53 of the annular projection 5 does not have roll forming marks that are generated when a curved surface is formed by roll forming. In addition, the aluminum oxide coating is not damaged, so that blackening does not occur during heat sterilization after filling the contents, and deterioration of the aesthetic appearance can be avoided.

[0037] [Example] Two types of drop tests, namely (1) a single drop test and (2) a case drop test, were conducted using the above-mentioned can body 1. The test results are shown in the tables of Figs. 5 and 6.

[0038] (1) Single unit drop test As an example of the single unit drop test, a can body 1 was dropped by itself after being filled with carbonated water as the content in a desired amount according to the can height, sealed with a can lid (lid part) (not shown), and sufficiently shaken. In the can body 1 before the single unit drop test, the liquid temperature of the content (filling) was 35°C, and the internal pressure in the stationary state before shaking was 400 kPa or 500 kPa. In this single unit drop test, the drop surface was a gray cast iron block processed so that the top surface was a flat surface with an inclination angle of 10°, on which a sheet of material for a packaging cardboard carton used for transporting product cans was laid. The can body 1 was dropped freely from a height where the shortest distance from the grounding part 52 to the drop surface was 20 cm with the can axis O aligned vertically with the grounding part 52 facing downward (not shown).

[0039] (2) Case drop test As an example of the case drop test, a test was conducted in which 24 can bodies 1, each of which was filled with carbonated water as the content in a desired amount according to the can height and sealed with a can lid (lid portion) (not shown), were placed in a rectangular parallelepiped packaging cardboard carton used for transporting product cans, and the can bodies were sufficiently shaken and then dropped. In the can body 1 before the case drop test, the liquid temperature of the content (filling) was 35°C, and the internal pressure in the stationary state before shaking was 400 kPa or 500 kPa. In this case drop test, a 20 mm thick dull-finished steel plate made of SPCC placed on a horizontal concrete ground was used as the drop surface. The packaging cardboard carton containing 24 can bodies 1 was placed with the grounding portion 52 of the can bodies 1 placed inside facing down, the longitudinal direction of the packaging cardboard carton was tilted by 20° from the horizontal state, and the carton was allowed to freely drop from a height at which the shortest distance between the packaging cardboard carton and the steel plate was 15 cm (not shown).

[0040] Fig. 5 shows the results of a single drop test and a case drop test when the can body 1 is an aluminum alloy drawn and ironed can body consisting of a single aluminum alloy layer, labeled as "Evaluation (single)" and "Evaluation (case)." Fig. 6 shows the results of a single drop test and a case drop test when the can body 1 is a PET-coated aluminum alloy drawn and ironed can body in which both the inner surface side and the outer surface side of the aluminum alloy layer are coated with a PET layer, labeled as "Evaluation (single)" and "Evaluation (case)."

[0041] "θ," "d," "φ," and "R3" in the tables of Figures 5 and 6 correspond to the "dome tangent angle θ," "recess depth d," "ground diameter φ," and "radius of curvature R3" in the configuration shown in Figure 2. Also, "T1" in the table of Figure 5 corresponds to the "thickness T1 of the aluminum alloy layer" on the can axis O of central dome portion 41 in the case of the aluminum alloy layer described above in can body 1 (aluminum alloy drawn and ironed can body). In addition, "T21" in the table of Figure 6 (for can body 1 (PET-coated aluminum alloy drawn and ironed can body)) corresponds to "thickness T21 of the PET layer, which is the first resin layer" on the inner surface of the can body on the can axis O of the above-mentioned central dome portion 41, "T22" corresponds to "thickness T22 of the PET layer, which is the second resin layer" on the outer surface of the can body on the can axis O of the above-mentioned central dome portion 41, and "T23" corresponds to "thickness T23 (=T1) of the aluminum alloy layer" between the first and second resin layers (PET layers) on the can axis O of the above-mentioned central dome portion 41.

[0042] In the columns of "Evaluation (single unit)" and "Evaluation (case)" in the tables shown in Figs. 5 and 6, when the can body 1 after the drop test was placed on the ground surface (horizontal surface) G by itself and allowed to stand on its own, the can body 3 was rated as "passed" and indicated with "◯" if the inclination angle of the can body 3 was less than 2° and no inversion of the dome portion 4 was observed. Similarly, when the can body 1 was allowed to stand on its own, the can body 3 was rated as "failed" and indicated with "x" if the inclination angle of the can body 3 was 2° or more or even a part of the dome portion 4 was inverted. Note that for can bodies 1 that could not be filled with the desired filling amount (content), a drop test could not be performed and therefore evaluation was not possible and indicated with "-" (also in this case it was marked as "failed").

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

[0044] In addition, in Example 2-1, Example 2-2, Comparative Example 2-1, and Comparative Example 2-2 (all using the commonly known 202 diameter), the contents were filled at the desired filling amount of 190 ml. In addition, in Example 2-3, Example 2-4, and Comparative Example 2-3 (all using the commonly known 204 diameter), the contents were filled at the desired filling amount of 355 ml. In addition, in Example 2-5 and Example 2-6 (all using the commonly known 211 diameter), the contents were filled at the desired filling amount of 350 ml.

[0045] As shown in Figures 5 and 6, in both cases where the can body 1 was an aluminum alloy drawn and ironed can body or a PET-coated aluminum alloy drawn and ironed can body, in Examples 1-1 to 1-6 and Examples 2-1 to 2-6 in which the dome tangent angle θ was 45° or more and 65° or less, the evaluation results for both "Evaluation (single unit)" and "Evaluation (case)" were "Pass" (◯).

[0046] In contrast, in both cases where the can body 1 was an aluminum alloy drawn and ironed can body or a PET-coated aluminum alloy drawn and ironed can body, in Comparative Examples 1-1 to 1-3 and 2-1 to 2-3 where the dome tangent angle θ was less than 45°, the evaluation results for both "evaluation (single)" and "evaluation (case)" were "failed" (x). In Comparative Examples 1-4 to 1-6 and 2-4 to 2-6 where the dome tangent angle θ was greater than 65°, the can body 1 could not be filled with the desired amount (350 ml for Comparative Examples 1-4 to 1-6 (all using the commonly known 211 diameter), 355 ml for Comparative Example 2-4 (using the commonly known 204 diameter), and 350 ml for Comparative Examples 2-5 and 2-6 (all using the commonly known 211 diameter)), so the drop test could not be performed and the result was "impossible to evaluate" (-) (also "failed" in this case).

[0047] From the above results, it can be seen that for the can body 1, whether it is an aluminum alloy drawn and ironed can body or a PET-coated aluminum alloy drawn and ironed can body, by setting the dome tangent angle θ to a value within the range of 45° or more and 65° or less, it is possible to ensure sufficient pressure resistance and sufficient drop strength while filling the contents with the desired amount.

[0048] Although the embodiments of the present invention have been described above in detail with reference to the drawings, the specific configuration is not limited to the above-mentioned embodiment. Moreover, the above-mentioned embodiment is merely an example, and it goes without saying that sufficient pressure resistance and sufficient drop strength can be ensured for any can body 1 with a different can height and filling amount from the commonly known 200 diameter to the commonly known 211 diameter. Moreover, the present invention includes design changes and the like within the scope of the present invention. Moreover, the above-mentioned examples can be combined by utilizing each other's technologies as long as there is no particular contradiction or problem in the purpose, configuration, and the like. [Explanation of symbols]

[0049] 1: can body, 2: can bottom, 3: can body, 4: dome portion, 5: annular convex portion, 6: outer wall portion, 41: central dome portion, 42: outer peripheral dome portion, 43: outer peripheral edge portion, 51: recess portion, 51A: outermost portion, 52: ground contact portion (support portion), 53: inner peripheral wall portion, 53A: innermost portion, 55A: first convex curved portion, 55B: second curved portion

Claims

1. A can has a can bottom and a cylindrical can body that extends from an outer periphery of the can bottom along the can axis and is centered on the can axis, the can bottom has a dome portion provided in a central portion of the can bottom, and an annular convex portion that is continuous with an outer peripheral edge portion of the dome portion and protrudes annularly to the outside of the can body substantially along the can axial direction, the annular protrusion is a bottomed cylindrical can body having a recess portion provided continuously with the dome portion and having a curved surface that protrudes radially outwardly of the can body, a ground portion that supports the can body, and an inner circumferential wall portion that extends from the ground portion to the recess portion, The can body is characterized in that, in a vertical cross section including the can axis, an angle θ of a tangent M to the outer surface of the dome portion at a position where a virtual line L1 that is parallel to the can axis and tangent to the innermost part of the inner wall portion intersects with the outer surface of the dome portion, relative to a plane perpendicular to the can axis, is 45° or more and 65° or less.

2. a recess depth d, which is a radial distance between the imaginary line L1 and an imaginary line L2 that is parallel to the can axis and touches the outermost portion of the recessed portion, is 0.50 mm or more and 0.85 mm or less in a vertical cross-sectional view including the can axis, The diameter of the ground contact portion is 42.0 mm or more and 47.0 mm or less. The 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 according to claim 1, characterized in that the can body is an aluminum alloy drawn and ironed can body consisting of a single aluminum alloy layer, or a PET-coated aluminum alloy drawn and ironed can body in which both sides of the aluminum alloy layer are coated with polyethylene terephthalate (PET) layers, and a thickness of the aluminum alloy layer at a point where the dome portion intersects with the can axis is 0.18 mm or more and 0.26 mm or less.

3. 3. The can body according to claim 2, wherein a 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. 2. A finished can, comprising the can body according to claim 1 filled with a content, and a flange portion formed at an opening of the can body and a lid portion rolled up together.

5. A method for manufacturing a bottomed cylindrical can body having a can bottom and a cylindrical can body centered on the can axis and extending along the can axis from an outer periphery of the can bottom, comprising the steps of: a step of forming a dome portion provided at the center of the can bottom, and forming an annular convex portion that is continuous with an outer peripheral edge of the dome portion and protrudes annularly outward from the can body generally along the can axial direction, the annular convex portion having a recess portion that is continuous with the dome portion and has a curved surface that convexly faces radially outwardly of the can body, a ground portion that supports the can body, and an inner peripheral wall portion that extends from the ground portion to the recess portion; and performing a bottom reforming process after the process of forming the dome portion and the annular convex portion, in which a forming tool having a processed surface that conforms to the curved surface of the dome portion is pressed against the dome portion from inside the can body along the can axial direction so that, in a vertical cross section including the can axis, an angle θ of a tangent M to the outer surface of the dome portion relative to a plane perpendicular to the can axis at a position where a virtual line L1 that is parallel to the can axis and tangent to the innermost part of the inner wall portion intersects with the outer surface of the dome portion is 45° or greater and 65° or less.

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