Method for manufacturing seamless can

Abstract

A method for manufacturing a seamless can according to the present invention comprises: a step for forming a preformed can in which a dome portion formed at the center of a bottom portion and protruding toward the inside of the can, and a leg portion including an annular ground portion formed so as to surround the dome portion are formed; a first bottom coating step for coating the outer surface of at least the ground portion of the preformed can; a bottom remolding step of inserting a pressing body into the interior of the preformed can coated in the first bottom coating step, and pressing the bottom of the preformed can by means of the pressing body and a molding die provided on the outer surface side of the preformed can, thereby forming an annular curved end having a ground contact portion; and a second bottom coating step for coating the outer surface of at least the ground portion of the bent end portion formed in the bottom remolding step, whereby it is possible to provide a seamless can in which a bottom coating film is reliably applied to the bottom ground portion.

Description

Technical Field

[0001] The present invention relates to a method for manufacturing a seamless can, and more particularly, to a method for manufacturing a seamless can capable of reliably applying bottom coating to a grounding portion of a seamless can that has undergone bottom re-forming, and a seamless can in which bottom coating has been reliably applied and bottom re-forming has been performed. Background Art

[0002] As a can body for storing beverages, foods, etc., seamless cans (DI cans) formed by drawing and ironing processes are widely used. In such seamless cans, in order to save resources and reduce weight, thinning of the can body portion is required. On the other hand, even for a thinned can body, sufficient pressure resistance is required. Therefore, in order to ensure pressure resistance, arch forming in which the can bottom is formed into a shape having a dome top portion recessed toward the inside of the can body and an annular leg portion surrounding the dome top portion is widely performed (for example, Patent Document 1 below).

[0003] In addition, in the forming process of seamless cans, in order to improve the transportability of the can body to each process and reduce the friction of the grounding portion of the can body during transport, a transparent coating (bottom coating) has been conventionally applied to the grounding portion of the can body (for example, Patent Document 2 below).

[0004] In such seamless cans, in order to have higher pressure resistance in a thinned can body, various proposals have been made regarding the shape of the bottom.

[0005] For example, in Patent Document 3 below, a method for manufacturing a can body is proposed, which is characterized by having: a preformed can forming process of forming a preformed can by forming a dome top portion and an annular leg portion on the bottom of a bottomed cylindrical body, the dome top portion being recessed toward the inside of the bottomed cylindrical body, the leg portion protruding toward the side opposite to the recessed side of the dome top portion, and in a longitudinal sectional view along the can axis direction, the inner peripheral portion of the leg portion being inclined in the can axis direction with the grounding point of the leg portion as a base point; a coating process of coating at least one of the inner surface and the outer surface of the preformed can; and a bottom re-forming process of forming a formed can having a bent end portion around the dome top portion by pressing the inner surface of the dome top portion of the preformed can coated in the coating process.

[0006] According to this manufacturing method, a preformed can in which a coating film is accurately applied to the inner and outer surfaces of the bent end portion at the bottom can be manufactured, and compared with the conventional bottom re-forming process using a roll, the inner peripheral portion of the bent end portion can be recessed deeper toward the main body portion, so that a can body with higher pressure resistance can be formed.

[0007] Prior Art Documents

[0008] Patent Documents

[0009] Patent Document 1: Japanese Patent No. 3603975 Gazette

[0010] Patent Document 2: Japanese Unexamined Patent Application Publication No. 4-267733

[0011] Patent Document 3: Japanese Unexamined Patent Application Publication No. 2022-46224 Summary of the Invention

[0012] Problems to be Solved by the Invention

[0013] In the manufacturing method described in the above Patent Document 3, at the stage before the bottom re-forming process, as described above, it is necessary to perform bottom coating on the grounding portion at the bottom of the pre-forming can.

[0014] However, in the above Patent Document 3, in the bottom re-forming process, the grounding portion of the pre-forming can is formed along the forming die by a pressing body inserted into the inside of the pre-forming can and abutting against the inner surface of the round top portion, and as a result, the portion that serves as the grounding portion in the pre-forming can becomes the outer peripheral wall of the bottom. As a result, in the can body after the bottom re-forming process, since a part of the portion that serves as the inner peripheral wall of the annular leg portion in the pre-forming can becomes the new grounding portion, it becomes a state where the bottom coating is not applied to the grounding portion, and it is difficult to ensure the transportability of the can body.

[0015] In addition, it may be considered to perform bottom coating in advance on the portion that becomes the grounding portion after the bottom re-forming process in the pre-forming can, but coating the inner peripheral wall of the annular leg portion requires spraying or the like, and adjustment of the angle and position is complicated, so it is difficult in terms of productivity.

[0016] Therefore, an object of the present invention is to provide a manufacturing method of a can body and a can body formed by the manufacturing method, in which in the manufacturing method of a seamless can that performs bottom re-forming process using a pressing body inserted into the inside of a pre-forming can and abutting against the inner surface of the round top portion and a forming die located on the outer surface side of the pre-forming can, a bottom coating film is reliably applied to the bottom grounding portion.

[0017] Means for Solving the Problems

[0018] According to the present invention, there is provided a method for manufacturing a seamless can, the seamless can having a bottom and a body portion, the method for manufacturing the seamless can being characterized by comprising: a step of forming a preform can, the preform can being formed with a rounded top portion and a foot portion, the rounded top portion protruding inwardly of the can at the center of the bottom, the foot portion including: an inner peripheral wall extending downward in the can axis direction from the outer peripheral edge of the rounded top portion, a conical outer peripheral wall extending downward in the can axis direction from the lower end of the body portion and having an outer diameter decreasing as it goes downward, and an annular grounding portion located at the lower ends of the inner peripheral wall and the outer peripheral wall and formed so as to surround the rounded top portion; a first bottom coating step of coating the outer surface of at least the grounding portion of the preform can; a bottom reshaping step of inserting a pressing body into the interior of the preform can coated in the first bottom coating step, and pressing the bottom of the preform can by the pressing body and a forming die provided on the outer surface side of the preform can, thereby bending the inner peripheral wall radially inward of the can to form an annular bent end portion having a grounding portion; and a second bottom coating step of coating the outer surface of at least the grounding portion of the bent end portion formed in the bottom reshaping step.

[0019] In the method for manufacturing a seamless can of the present invention, preferably,

[0020] (1) The coating in the second bottom coating step is a coating using an ultraviolet curable coating;

[0021] (2) A printing step and an inner surface coating step are provided between the first bottom coating step and the bottom reshaping step;

[0022] (3) A necking process and a flanging process are provided after the second bottom coating step;

[0023] (4) A necking process and a flanging process are provided before the second bottom coating step.

[0024] According to the present invention, there is also provided a seamless can having a bottom and a body portion, the seamless can being characterized in that a rounded top portion and an annular foot portion are formed on the bottom, the rounded top portion protruding inwardly of the can at the center of the bottom, the foot portion including: a conical inner peripheral wall extending downward in the can axis direction from the outer peripheral edge of the rounded top portion and having an inner diameter decreasing as it goes downward, a conical outer peripheral wall extending downward in the can axis direction from the lower end of the body portion and having an outer diameter decreasing as it goes downward, and an annular bent end portion formed by the inner peripheral wall and the lower portion of the outer peripheral wall and having a grounding portion, and a coating film formed of an ultraviolet curable coating is formed near the bent end portion of the outer peripheral wall and at the grounding portion of the bent end portion.

[0025] The seamless can of the present invention is preferably an aluminum seamless can.

[0026] In addition, according to the present invention, there is provided a content-filled can, characterized in that the content-filled can is formed by filling the content into the seamless can described above and sealing it with a cover by roll seaming.

[0027] Advantages of the Invention

[0028] In the method for manufacturing the seamless can of the present invention, since the bottom re-forming process using the pressing body inserted into the pre-formed can and the bottom of the forming die located on the outer surface side of the pre-formed can is carried out, even when the grounding portion is formed at the portion where the bottom coating is not applied, the grounding portion of the can bottom is always effectively protected by the bottom coating film through the second bottom coating process after the bottom re-forming process. When the can body is conveyed after the bottom re-forming process, the friction of the can body can be reduced, and the conveyability can be improved.

[0029] In addition, since it is a bottom coating, there is no need for position adjustment for spraying, etc., and the bottom coating film can be easily and reliably formed on the bottom grounding portion. Therefore, the productivity is also excellent.

[0030] In addition, in the seamless can of the present invention, since the bottom re-forming process is carried out by means of the device having the specific pressing body and the forming die described above, the inner peripheral portion of the bent end of the seamless can bottom is deeply recessed toward the main body portion, and the pressure resistance can be significantly improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 is a longitudinal sectional view showing an example of the pre-formed can in the manufacturing method of the present invention.

[0032] Figure 2 is a view for explaining the bottom re-forming process of the manufacturing method of the present invention.

[0033] Figure 3 is a partially enlarged sectional view for explaining the seamless can of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0034] (Manufacturing Process)

[0035] The manufacturing process of the seamless can generally consists of a cup drawing process, a pre-formed can forming process, a trimming process, a cleaning process, a first bottom coating process, an outer surface coating and printing process, a printing process, an inner surface coating process, a bottom re-forming process, necking, and a flange processing process. In addition, there is also a second bottom coating process. In the present invention, a particularly important feature is that a second bottom coating process is added after the bottom re-forming process.

[0036] After deep-drawing a metal plate such as an aluminum alloy plate through a cup drawing process to form a cup-shaped body, in the preform can forming process, the cup-shaped body is subjected to deep-drawing and thinning processing to form a bottomed cylindrical body, and the bottom is subjected to stamping processing, thereby forming a preform can. As Figure 1 shown, the preform can is composed of a main body portion 1a and a bottom portion 1b. A dome portion 2 protruding inwardly of the can is formed at the center of the bottom portion 1b, and an annular leg portion 3 is formed so as to surround the dome portion 2. Figure 1 The leg portion 3 shown includes: an inner peripheral wall 3a in which the outer peripheral edge 2a of the dome portion 2 extends downward in the can axis direction, a tapered outer peripheral wall 3b that extends downward in the can axis direction from the lower end of the main body portion 1a and whose outer diameter decreases as it approaches the lower side, and a grounding portion 3c located at the lower ends of the inner peripheral wall 3a and the outer peripheral wall 3b.

[0037] After trimming (trimming process) and cleaning process of the open end portion 4 of the obtained preform can 1, in the first bottom coating process, a bottom coating film 11 formed of a transparent coating material capable of reducing friction and improving transportability is formed near the grounding portion of the bottom of the preform can, and then an outer surface coating and printing process is performed.

[0038] In the outer surface coating and printing process, an outer surface coating film is formed by coating the outer surfaces of the main body portion and the bottom portion of the preform can. In the printing process, printing is performed on the main body portion whose outer surface has been coated, and a clear coat layer is formed on the printing layer as needed. It should be noted that, as described later, in the case where it is not necessary to form an outer surface coating film by using a resin-coated metal plate or the like, the outer surface coating process can also be omitted. In addition, as long as a transparent coating suitable for bottom coating can be applied near the bottom grounding portion, the first bottom coating process can also be performed in the same process in the outer surface coating process. Then, in the inner surface coating process, an inner surface coating film is formed on the inner surface of the preform can by spraying or the like.

[0039] Next, by performing a bottom re-forming process, the preform can 1 that has undergone the inner surface coating process is formed into a seamless can 10 having the bottom shape of the final formed product after bottom re-forming.

[0040] Figure 2 is a view for explaining the bottom re-forming process. The preform can 1 having a bottom coating film 11 formed near the grounding portion of the bottom is placed on a forming die 21 that abuts against the outer peripheral wall 3b of the bottom below the main body portion 1a on the outer surface side of the preform can 1. Then, the pressing body 20 is inserted into the inside of the preform can 1 ( Figure 2 of (A)).

[0041] If the inner surface of the preform can 1 is pressed by the pressing body 20, the inner peripheral wall 3a of the preform can 1 is pressed in the can axis direction and bent inward in the can radial direction, becomingFigure 2 In the shape of 3a' of (B), on the other hand, the grounding portion 3c is formed as an outer peripheral wall 3b' along the molding surface of the molding die 21 ( Figure 2 of (B)).

[0042] When the movement of the pressing body 20 ends, the shape of the annular foot portion is formed into an annular bent end portion 5 in which the inner peripheral wall 3a is bent inward in the can radial direction. The lowermost end of the bent end portion 5 becomes the grounding portion 3c", which becomes the bottom shape of the final molded product after the bottom re-molding.

[0043] by Figure 2 As can be seen, the bottom coating film 11 formed on the grounding portion 3c of the preformed can 1 becomes the outer peripheral wall 3b" of the can body 10 after the bottom re-molding in the bottom re-molding process. Therefore, no bottom coating film is formed on the grounding portion 3c" of the can body 10 after the bottom re-molding.

[0044] In the manufacturing method of the present invention, from such a viewpoint, a second bottom coating process is provided after the bottom re-molding process, and a transparent coating for reducing friction caused by transportation and improving transportability is applied in the vicinity of the grounding portion of the can body after the bottom re-molding in the same manner as in the first bottom coating process.

[0045] It should be noted that in the first bottom coating process and the second bottom coating process, the coatings, coating methods, baking methods, etc. used in the conventional bottom coating can all be adopted. However, in the manufacturing method of the present invention, especially in the second bottom coating process, it is preferable to use a roller coating method, an ultraviolet curable coating, and form a bottom coating film by ultraviolet irradiation. By using an ultraviolet curable coating, an oven for baking is not required after the bottom coating process, so that the simplification of the production line can be achieved. As the coating method, it is not limited to the roller coating method, and known methods can be applied.

[0046] The seamless can 10 having the bottom coating film 12 formed on the grounding portion 3c" by the second bottom coating process then undergoes a necking and flanging process. By performing the necking process and the flanging process, as Figure 3 shown, a seamless can 10 as the final molded product having a neck portion 6 and a flange portion 7 after necking can be obtained.

[0047] In the manufacturing method of the present invention, the second bottom coating process only needs to be located after the bottom reshaping process. As described above, it is not limited to the case of being located between the bottom reshaping process and the necking and flanging processes. That is, there is also a case where the necking and flanging processes are carried out before the bottom reshaping process. In this case, for the second bottom coating process, the second bottom coating process is carried out after the necking and flanging processes and the bottom reshaping process. Moreover, in a case where there is a necking and flanging process immediately after the bottom reshaping process, the second bottom coating process is also located after the necking and flanging processes.

[0048] In the manufacturing method of the present invention, the forming of the preformed can is not limited to the aforementioned method, and conventionally known methods such as deep drawing, deep drawing / deep drawing, deep drawing / thinning, deep drawing / bending stretch drawing / thinning can be adopted.

[0049] In addition, as long as the bottom shape is the above shape, the shape of the seamless can is not limited to Figure 3 the seamless can of the shown shape, and various shaped seamless cans such as so-called bottle cans with a significantly necked-down neck and a threaded portion can be manufactured.

[0050] Moreover, as the metal plate constituting the seamless can, all metal plates used in conventional seamless cans such as surface-treated steel plates and aluminum alloy plates can be used, but an aluminum alloy plate is particularly preferred. These metal plates can also be resin-coated metal plates with resin coating using thermoplastic resins such as polyester resin. In the case of using such resin-coated metal plates, if necessary, the aforementioned outer surface coating process and inner surface coating process can also be omitted.

[0051] (Seamless can)

[0052] According to the characteristics of the above manufacturing method, as Figure 3 shown, in the seamless can manufactured by the manufacturing method of the present invention, a round top 2' and an annular foot portion 3" are formed at the bottom 10b. The round top 2' protrudes inward from the center of the bottom of the can. The foot portion 3" includes: a conical inner peripheral wall 3a" whose outer peripheral edge 2a' of the round top 2' extends downward in the can axis direction and whose inner diameter decreases as it goes downward, a conical outer peripheral wall 3b" extending downward in the can axis direction from the lower end of the main body portion 10a and whose outer diameter decreases as it goes downward, and an annular bent end 5 formed by the lower portions of the inner peripheral wall 3a" and the outer peripheral wall 3b" and having a grounding portion 3c". In addition, a coating film 12 formed by the second bottom coating process is formed on the grounding portion 3c" and its vicinity. More preferably, the bottom coating film 12 is a coating film formed by an ultraviolet curable coating.

[0053] In the seamless can of the present invention, as described above, the inner peripheral portion 3a" of the bent end portion 5 at the bottom of the seamless can is deeply recessed toward the outer side in the can radial direction. Therefore, the round top portion is liable to be deformed due to the change in internal pressure and has high pressure resistance strength.

[0054] In the seamless can of the present invention, a seamless can having an opening portion with a shape as Figure 3 shown is provided to consumers as a content filling can. This content filling can is formed by crimp-sealing a can lid at the opening end after filling the content. As the can lid for such a content filling can, a conventionally well-known shape such as an easy-open lid provided with a score for forming an opening for pouring out the content and a pull tab for opening can be adopted, and it can be either a full-open type or a stay-on-tab type.

[0055] In addition, the content to be filled can be a conventionally well-known content such as food in addition to beverages such as soft drinks and carbonated drinks. In particular, due to the bottom shape having excellent pressure resistance, beverages having self-generated pressure such as beer and carbonated drinks can be preferably filled.

[0056] Explanation of reference numerals

[0057] 1: Preformed can; 1a: Body portion; 1b: Bottom; 2: Round top portion; 3: Leg portion; 3a: Inner peripheral wall; 3b: Outer peripheral wall; 3c: Grounding portion; 4: Opening end; 5: Bent end; 6: Neck portion; 7: Flange portion; 10: Seamless can; 10a: Body portion; 10b: Bottom; 11: Coating film formed by the first bottom coating process; 12: Coating film formed by the second bottom coating process; 20: Pressing body; 21: Forming die.

Claims

1. A method for manufacturing a seamless can, the seamless can having a bottom and a body portion, characterized in that the method for manufacturing the seamless can includes: A step of forming a preform can, the preform can having a rounded top and a foot portion, the rounded top protruding inwardly of the can at the center of the bottom, and the foot portion including: An inner peripheral wall extending downward in the direction of the can axis from the outer peripheral edge of the top of the circle, a conical outer peripheral wall extending downward in the direction of the can axis from the lower end of the main body portion and having an outer diameter decreasing as it goes downward, and an annular grounding portion located at the lower ends of the inner peripheral wall and the outer peripheral wall and formed so as to surround the top of the circle; A first bottom coating step of coating the outer surface of at least the grounding portion of the preformed can; A bottom reshaping step of inserting a pressing body into the interior of the preformed can coated in the first bottom coating step, and pressing the bottom of the preformed can by the pressing body and a forming die provided on the outer surface side of the preformed can, thereby bending the inner peripheral wall inward in the can radial direction to form an annular bent end portion having a grounding portion; and A second bottom coating step of coating the outer surface of at least the grounding portion of the bent end portion formed in the bottom reshaping step.

2. The method for manufacturing a seamless can according to claim 1, wherein, The coating in the second bottom coating step is a coating using an ultraviolet curable coating.

3. The method for manufacturing a seamless can according to claim 1 or 2, wherein, A printing step and an inner surface coating step are provided between the first bottom coating step and the bottom reshaping step.

4. The method for manufacturing a seamless can according to claim 1 or 2, wherein, A necking process and a flanging process are provided after the second bottom coating step.

5. The method for manufacturing a seamless can according to claim 1 or 2, wherein, A necking process and a flanging process are provided before the second bottom coating step.

6. A seamless can having a bottom and a body portion, characterized in that, A rounded top and an annular foot portion are formed on the bottom, the rounded top protruding inwardly of the can at the center of the bottom, and the foot portion including: A conical inner peripheral wall extending downward in the direction of the can axis from the outer peripheral edge of the top of the circle and having an inner diameter decreasing as it goes downward, a conical outer peripheral wall extending downward in the direction of the can axis from the lower end of the main body portion and having an outer diameter decreasing as it goes downward, and an annular bent end portion formed by the lower portions of the inner peripheral wall and the outer peripheral wall and having a grounding portion A coating film formed of an ultraviolet curable coating is formed near the bent end portion of the outer peripheral wall and at the grounding portion of the bent end portion.

7. The seamless can according to claim 6, wherein, The seamless can is an aluminum seamless can.

8. A can for filling a content, characterized in that, The content filling can is formed by roll-sealing the seamless can filled with content according to claim 6 or 7 with a lid.

Images