CAN BODY, PRODUCT CAN AND CAN BODY MANUFACTURING METHOD

Abstract

The invention relates to a can body capable of withstanding pressure and drop strength while maintaining the desired amount of contents filled, a product can, and a method for producing the can body. The can body is cylindrical and has a base, comprising a base and a cylindrical barrel extending from the outer periphery of the base along the axis of the can and located centrally on the axis of the can. The base consists of a dome located at the center of the base and a continuous annular protrusion extending from the outer periphery of the dome and protruding annularly from the can body essentially along the direction of the axis of the can. The annular protrusion consists of a recess located continuously with the dome and having a convex surface convex outward in the radial direction of the can body, a ground contact area configured to support the can body, and an inner periphery extending from the ground contact area to the recess.In the longitudinal section projection including the can axis, the angle θ between the tangent line M on the outer surface of the arch and the plane orthogonal to the can axis at the position where the imaginary line L1 is parallel to the can axis and touches the innermost part of the outer wall intersecting with the outer surface of the arch is 45° or more and 65° or less.

Description

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

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

[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 beverages and other contents. These can bodies (can containers) are obtained by punching out a metal plate into a circular shape, drawing the metal plate to form a shallow, bottomed, cylindrical cup, and then drawing and ironing the cup to integrally form the can bottom and can body, as well as other processes.

[0003] For such can bodies, there is a demand for thinner can bodies from the viewpoint of resource conservation, but there is also a demand for sufficient pressure-resistant strength to be ensured even for thinner can bodies. In particular, for can bodies with a dome bottom, when carbonated beverages or the like are contained, an increase in internal pressure due to carbon dioxide gas can cause the dome bottom to invert (buckling). Therefore, can bodies with a dome bottom are required to have sufficient pressure-resistant strength to withstand the internal pressure, and measures have been taken to ensure pressure-resistant strength for the can body bottom.

[0004] Specifically, in a can body having a dome portion at the bottom of the can body, the central portion of which is recessed toward the inside of the can body, and an annular convex portion around the dome portion, bottom reforming is performed on the annular convex portion 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 portion. 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).

[0006] JP 2000-190961 A JP 2023-9470 A JP 2020-121761 A U.S. Patent No. 7,740,148 A

[0007] However, in conventional can bodies with a dome portion on the can 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 a primary can body is 66.1 mm to 66.3 mm, the angle of the tangent to the inner surface of the outer peripheral edge of the dome portion relative 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 relative to the plane of the primary can body is 2.0 mm to 3.0 mm, and the inclination angle of the pressing surface relative to the plane is 20° to 29°. However, it has been found that even with the numerical limitations in Patent Document 2, it is difficult to ensure sufficient drop strength in the formed can body.

[0008] The present invention addresses these issues. Through extensive analysis, the inventors have discovered that the inversion of the dome due to the water hammer phenomenon that occurs when a container is dropped is caused by the outer periphery of the dome. Based on this finding, 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 drop strength while ensuring a desired filling amount of contents.

[0009] In order to solve these problems, the can body of the present invention is a cylindrical can body with a bottom, which includes a can bottom and a cylindrical can body centered on the can axis and extending from the outer periphery of the can bottom along the can axis, wherein the can bottom has a dome portion provided in the center of the can bottom and an annular convex portion that continues from the outer periphery of the dome portion and protrudes annularly outward from the can body approximately along the can axis direction, the annular convex portion has a recess portion that is provided continuous with the dome portion and has a curved surface that convex radially outward of the can body, a ground portion that supports the can body, and an inner wall portion that extends from the ground portion to the recess, and is characterized in that, in a vertical cross section including the can axis, the 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 an imaginary 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 product can according to the present invention is characterized in that it is formed by filling the can body according to the present invention with a content, and then fastening the flange portion and the lid portion formed at the opening of the can body.

[0011] The can body manufacturing method according to the present invention is 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 from the outer periphery of the can bottom along the can axis, and includes forming a dome portion provided in the center of the can bottom, and forming an annular convex portion that is continuous with the outer periphery of the dome portion and protrudes annularly outward from the can body substantially along the can axis direction, the annular convex portion having a recess portion that is continuous with the dome portion and has a curved surface that convex outward in the radial direction 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. 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 processing 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 an imaginary 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.

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

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

[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 function, and duplicated explanations in each drawing will be omitted as appropriate. In addition, the cross-sectional views of Figures 1 and 4 show the cross-sectional shape in line drawings with plate thicknesses 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 section 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 referred to as an "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 referred to as an "aluminum alloy layer"), but is not limited to this and may be composed of a layer of another metal material.

[0017] Alternatively, 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, can body 1 may be a PET-coated aluminum alloy drawn and ironed can body in which the metal layer (metal plate) is an 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 are coated with PET layers (first resin layer, second resin layer). However, can body 1 is not limited to this, and may also be a resin-coated metal drawn and ironed 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 an annular shape outside the can body 1 approximately along the can axis O direction, and an outer wall portion 6 that is provided outside the annular protrusion 5 and connects to the can body 3.

[0019] The dome portion 4 is provided in the center of the can bottom 2 and has a curved surface that is concave in a dome shape toward the inside of the can body 1 along the can axis O. The dome portion 4 has, for example, a central dome portion 41 that is located on the can axis O and has a preset radius of curvature R1, and an outer dome portion 42 that is formed contiguously with the outside of the central dome portion 41 and has a radius of curvature R2.

[0020] In the vertical cross section including the can axis O shown in Figure 2, a virtual line L1 that is parallel to the can axis O and tangent to the innermost part 53A of the inner peripheral wall 53 intersects with the outer surface of the dome 4 (outer dome 42) at a position m. The angle θ of the tangent line M to the outer surface of the dome 4 (outer dome 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 part 53A of the inner peripheral wall 53 is the part of the annular protrusion 5 that is closest to the can axis O on the outer surface of the can body 1.

[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 located further outward 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, ensuring sufficient drop strength. If the dome tangent angle θ is less than 45°, it becomes difficult to ensure sufficient drop strength. Furthermore, if the dome tangent angle θ is greater than 65°, it becomes difficult to achieve both the desired filling volume (content volume) corresponding to the can height and sufficient drop strength. Furthermore, although the cause is unclear, the water hammer pressure significantly affects the central dome portion 41, making it difficult to ensure sufficient pressure resistance. In this embodiment, "can height" refers to the height along the can axis O from the ground contact portion 52 of the product can to the top end of the lid (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 drop strength can be ensured while filling the can with the desired amount of contents (e.g., beverage) depending on the can height. Note that 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, gradually varying, or may include a conical surface, as long as the desired filling amount depending on the can height can be ensured. Furthermore, the outer dome portion 42 may be linear in a vertical cross section including the can axis O shown in FIG. 2 .

[0023] The annular protrusion 5 has a recessed portion 51 that is continuous with the outer peripheral edge 43 of the dome portion 4 and has a curved surface that protrudes radially outward from the can body 1, a grounding portion (supporting 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 outward from the can body 1 substantially along the can axis O direction so as to form the annular grounding portion 52 around the outer periphery of the dome portion 4.

[0024] 2 , the recess depth d is 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. That is, 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 annular protrusion 5. To ensure a sufficient filling amount (content volume) 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 protrusion 5 has two convex curved surfaces on either side of the contact portion 52. Specifically, as shown in Fig. 2 , the annular protrusion 5 has a first convex curved surface portion 55A on the side closer to the can axis O than the contact portion 52, and a second curved surface portion 55B, which has a larger radius of curvature than the first convex curved surface portion 55A, on the side farther from the can axis O than the contact portion 52. In the can body 1, the ground diameter φ, which is the diameter of such ground portion 52, is preferably 42.0 mm or more and 47.0 mm or less in order to ensure sufficient filling capacity (contents) and pressure resistance for can bodies 1 having an outer diameter of the can body 3 of approximately 50 mm (commonly known as 200 diameter) or more and approximately 66 mm (commonly known as 211 diameter) or less, which are commonly used as product cans containing beverages, etc., known as so-called 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 a sufficient filling amount (internal volume) 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 (internal volume) and pressure resistance.

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

[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 inside surface of the can body is coated with a PET layer as a first resin layer and the surface of this aluminum alloy layer facing the outside 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 inside 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 outside 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, which contributes to resource conservation, and also makes it possible to prevent breakage of the can body and improve the yield rate.

[0029] Such a can body 1 can be manufactured by a manufacturing method including the steps shown in the flowchart of FIG. 3 . The manufacturing method of the can body 1 is not limited to the example shown in FIG. 3 . In the example shown in FIG. 3 , a metal plate such as an aluminum alloy is first punched into a circular shape, 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. The can bottom has a dome portion recessed inward into the can preform and an annular protrusion protruding from the side opposite the recessed dome portion.

[0030] In this can preform molding step (S2), a dome portion 4 (before bottom reforming) is formed in the center of the can bottom 2 of the can body 1 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 formed as the annular convex portion of the can bottom of the can preform, which is continuous with the outer peripheral edge portion 43 of the dome portion 4 (before bottom reforming) and protrudes annularly outward from 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 formed as the annular convex portion of the can preform, which is continuous with the dome portion 4 (before bottom reforming) and has a recess portion 51 with a curved surface that convex radially outward from 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 opening 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 (exterior painting and printing step (S4)). Then, if necessary, at least the inner surface of the can body 3 and the can bottom is painted using a spray or the like (inner surface painting step (S5)). After that, the inner surface of the dome portion of the can preform is pressed along the can axis O, thereby performing bottom reforming on the can bottom (bottom reforming step (S6)).

[0032] Thereafter, a necking tool (not shown) is used to perform stepwise die processing (necking) at a portion of the can body 3 of the can body 1 that connects to an opening (not shown) to form a neck (not shown) (necking step (S7)). Subsequently, a roller (not shown) is used to curl the edge (mouth) of the opening of the can body 3 toward the outside of the can body 1 to form a flange (not shown) (flanging step (S8)). For example, by performing the steps S1 to S8, the can body 1 is manufactured as a formed can. Thereafter, a can container (product can) filled with the contents (such as a beverage) is produced by filling the can body 1 with contents, and then performing a seaming step (S9 (not shown)) in which the flange (not shown) and the lid (not shown) are seamed together to seal the contents.

[0033] In the bottom reforming step (S6) described above, the bottom reforming is performed on the can bottom of the can preform, which has a dome portion and an annular convex portion with a ground portion (support portion), using a forming tool F equipped with an inner tool F1 and an outer tool F2, for example, as shown in Fig. 4. In this process, the formation of the dome portion 4, which has a central dome portion 41 and an outer peripheral dome portion 42 in the can body 1, and the formation of the annular convex portion 5 in the can body 1 are both performed by the forming tools F (the inner tool F1 and the outer tool F2).

[0034] The inner tool F1 is used to form 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 fits into the chuck C of the outer tool F2, forming an annular protrusion 5 corresponding 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 is formed with a dome tangent angle θ of 45° to 65° in a vertical cross section including the can axis O shown in Figure 2.

[0036] As shown in FIG. 2 , the inner peripheral wall 53 of the annular protrusion 5 in the formed can body 1 extends through a recess 51 to the outer peripheral edge 43 of the dome section 4 (the outer peripheral edge of the outer dome section 42). The outermost portion 51A of this recess 51 is a bent portion formed by plastic deformation through compression with a forming tool F. The outermost portion 51A thus formed can be recessed deeper in a direction away from the can axis O than the innermost portion 53A of the inner peripheral wall 53. Because the outermost portion 51A of the recess 51 is a bent portion formed by plastic deformation through compression, conventional roll forming is not required. Therefore, the inner peripheral wall 53 of the annular protrusion 5 does not have any roll forming marks that would be produced when forming a curved surface by roll forming. Furthermore, because the aluminum oxide coating is not damaged, blackening does not occur during heat sterilization after filling the can, and deterioration of the can's appearance can be avoided.

[0037] [Examples] Two types of drop tests, (1) a single drop test and (2) a case drop test, were carried out using the above-described can body 1. The test results are shown in the tables of Figs.

[0038] (1) Single-unit Drop Test As an example of a single-unit drop test, a can body 1 was filled with carbonated water to a desired filling amount corresponding to the can height, sealed with a can lid (lid portion) (not shown), and thoroughly shaken. The liquid temperature of the contents (filled material) in the can body 1 before the single-unit drop test 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, a gray cast iron block with a flat top surface at an inclination angle of 10° was placed on a single-unit drop surface, on which a single piece of cardboard carton material used for packaging cans for shipping was placed. The can body 1 was dropped from a height (not shown) onto this drop surface, with the bottom surface 52 facing downward and the can axis O aligned vertically, such that the shortest distance from the bottom surface 52 to the drop surface was 20 cm.

[0039] (2) Case Drop Test As an example of the case drop test, 24 can bodies 1 filled with carbonated water as the contents to a desired filling amount corresponding to the can height and sealed with can lids (lid portions) (not shown) were placed in a rectangular cardboard packaging carton used for shipping product cans, and the carton was shaken thoroughly and then dropped. Before the case drop test, the liquid temperature of the contents (filled material) in the can body 1 was 35°C, and the internal pressure in the stationary state before shaking was 400 kPa or 500 kPa. In this case drop test, the drop surface was a 20 mm thick dull-finished steel plate made of SPCC placed on a horizontal concrete floor. A cardboard packaging carton containing 24 can bodies 1 was placed with the ground contact portions 52 of the can bodies 1 contained inside facing downward, the longitudinal direction of the cardboard packaging carton was tilted by 20° from the horizontal, and the carton was allowed to freely drop from a height such that the shortest distance between the cardboard packaging carton and the iron 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 a drawn and ironed aluminum alloy can body consisting of a single aluminum alloy layer, as indicated by "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 drawn and ironed aluminum alloy can body in which both the inner surface and the outer surface of the aluminum alloy layer are coated with PET layers, as indicated by "Evaluation (single)" and "Evaluation (case)."

[0041] 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 Fig. 2. Furthermore, "T1" in the table of Fig. 5 corresponds to the "thickness T1 of the aluminum alloy layer" on the can axis O of the central dome portion 41 in the case of the aluminum alloy layer described above in the can body 1 (a drawn and ironed aluminum alloy can body). In the table of FIG. 6 , “T21” (for can body 1 (PET-coated aluminum alloy drawn and ironed can body)) corresponds to the “thickness T21 of the PET layer, which is the first resin layer” on the inner surface of the can body of the central dome portion 41 on the can axis O, “T22” corresponds to the “thickness T22 of the PET layer, which is the second resin layer” on the outer surface of the can body of the central dome portion 41 on the can axis O, and “T23” corresponds to the “thickness T23 (=T1) of the aluminum alloy layer” between the first and second resin layers (PET layers) of the central dome portion 41 on the can axis O.

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

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

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

[0045] As shown in FIGS. 5 and 6 , in both cases where the can body 1 was a drawn and ironed aluminum alloy can body and a drawn and ironed PET-coated aluminum alloy can body, in Examples 1-1 to 1-6 and 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 body)” and “Evaluation (case)” were “Pass” (◯).

[0046] In contrast, in both the cases where the can body 1 was an aluminum alloy drawn and ironed can body and a PET-coated aluminum alloy drawn and ironed can body, the evaluation results for Comparative Examples 1-1 to 1-3 and 2-1 to 2-3, in which the dome tangent angle θ was less than 45°, were "failed" (×) in both "evaluation (single container)" and "evaluation (case)." Furthermore, in Comparative Examples 1-4 to 1-6 and 2-4 to 2-6, in which 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 of which used the so-called 211 diameter), 355 ml for Comparative Example 2-4 (which used the so-called 204 diameter), and 350 ml for Comparative Examples 2-5 and 2-6 (which both used the so-called 211 diameter)). Therefore, the drop test could not be performed, and the result was "impossible to evaluate" (-) (also a "fail" result).

[0047] From the above results, it can be seen that, for the can body 1, whether it is a drawn and ironed aluminum alloy can body or a drawn and ironed PET-coated aluminum alloy 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 filling amount.

[0048] Although the embodiments of the present invention have been described in detail above with reference to the drawings, the specific configuration is not limited to the above-described embodiments. Furthermore, the above-described examples are merely examples, and it goes without saying that sufficient pressure resistance and drop strength can be ensured for any can body 1, regardless of can height and filling volume, from the commonly known 200 diameter to the commonly known 211 diameter. Furthermore, the present invention also includes design changes within the scope of the present invention. Furthermore, the above-described examples can be combined by utilizing each other's technology as long as there are no particular contradictions or problems in their purpose, configuration, etc.

[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 surface portion, 55B: second curved surface portion

Claims

1. A can body having a bottom, and a cylindrical can body centered on the can axis extending from the outer periphery of the can bottom along the can axis, wherein the can bottom has a dome section provided in the center of the can bottom, and an annular convex section continuing from the outer periphery of the dome section and protruding in an annular shape to the outside of the can body generally along the can axis direction, wherein the annular convex section has a recess section provided continuous with the dome section and having a curved surface that convex radially outwardly of the can body, a ground section supporting the can body, and an inner wall section extending from the ground section to the recessed section, wherein in a vertical cross section including the can axis, an angle θ of a tangent M to the outer surface of the dome section relative to a plane perpendicular to the can axis at a position where an imaginary line L1 that is parallel to the can axis and tangent to the innermost part of the inner wall section intersects with the outer surface of the dome section is between 45° and 65°.

2. The can body according to claim 1, characterized in that, in a longitudinal cross-sectional view including the can axis, a recess depth d, which is the radial distance between the imaginary line L1 and an imaginary line L2 that is parallel to the can axis and touches the outermost part of the recessed portion, is 0.50 mm or more and 0.85 mm or less, a ground diameter φ, which is the diameter of the grounding portion, is 42.0 mm or more and 47.0 mm or less, a radius of curvature R3 near the outermost part of the recessed portion is 0.3 mm or more and 2.0 mm or less, 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 the point where the dome portion intersects with the can axis is 0.18 mm or more and 0.26 mm or less.

3. The can body according to claim 2, characterized in that 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 finished can, characterized in that the can body according to claim 1 is filled with contents and the flange portion and the lid portion formed at the opening of the can body are rolled up and fastened.

5. A method for manufacturing 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, comprising the steps of forming a dome portion provided at the center of the can bottom, and forming an annular convex portion that is continuous with the outer periphery of the dome portion and protrudes annularly to the outside of the can body approximately along the can axis direction, the annular convex portion having a recess portion that is continuous with the dome portion and has a curved surface that convex 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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