Method for manufacturing can body

Abstract

The present invention provides a method for manufacturing a can body capable of suppressing a manufacturing cost. This method for manufacturing a can body provided with a bottom part (12) and a body part (11) comprises: a preform can formation step (S1) for forming a preform can (10) having, on the bottom part (12), an annular leg part (13) that serves as a first grounding part (15); a bottom coating step (S2) for applying a coating agent to a first grounding part region (R1) including the first grounding part (15) of the preform can (10); and a seamless can formation step (S4) that deforms again the bottom part (12) of the preform can (10) to form an annular protruding part (21) serving as a second grounding part (15) and has a recessed part. In the bottom coating step (S2), coating is performed by applying the coating agent to a planned grounding part region as well that is planned to be a second grounding part region (R2) including the second grounding part (24).

Description

Can body manufacturing method

[0001] The present invention relates to a method for manufacturing a can body.

[0002] Seamless cans (DI cans) formed by drawing and ironing or other processes are widely used as can bodies for storing beverages, food, and the like. In response to recent demands for resource conservation, thinner materials are being used for such seamless cans. Even seamless cans made from thinner materials sometimes require special bottom modifications to ensure sufficient pressure resistance. In this process, a preform can is first formed, followed by a bottom reforming process to produce a seamless can. In this case, a clear coating (bottom coating) has traditionally been applied to the can body's contact surface to improve transportability to each process and reduce friction at the contact surface during transport.

[0003] For example, Patent Document 1 discloses a method for manufacturing seamless cans, which involves a first bottom coating process in which a bottom coating is applied to a portion of a preformed can that will become the ground contact portion when the can is in the preformed state, and a second bottom coating process in which a bottom coating is applied again to a portion of a seamless can that will become the ground contact portion when the can is in the seamless state. Since the portion that will become the ground contact portion when the can is in the preformed can is different from the portion that will become the ground contact portion when the can is in the seamless state, coating is applied to each of the cans in order to ensure transportability of the can body in each state.

[0004] JP 2024-072083 A

[0005] In Patent Document 1, the coating process is carried out twice because the grounding portions of the preform can and the seamless can are different, but this complicates the manufacturing process and increases manufacturing costs.

[0006] SUMMARY OF THE INVENTION An object of the present invention is to solve the problems of the prior art and to provide a method for manufacturing a can body that does not complicate the manufacturing process and that can reduce manufacturing costs.

[0007] The method for manufacturing a can body of the present invention is a method for manufacturing a can body having a bottom and a body, and comprises a preform can formation process for forming a preform can having an annular leg portion on the bottom that will become a first ground contact portion, a bottom coating process for applying a coating agent to a first ground contact portion area including the first ground contact portion of the preform can, and a seamless can formation process for deforming the bottom of the preform can again to form an annular protrusion that will become a second ground contact portion, thereby forming a seamless can having a recess, and is characterized in that in the bottom coating process, the coating agent is also applied to a planned ground contact portion area that will become a second ground contact portion area including the second ground contact.

[0008] In the can body manufacturing method of the present invention, by coating the ground contact area that is to become the second ground contact area and the first ground contact area in the bottom coating process, not only the first ground contact area of ​​the preform can but also the second ground contact area can be coated in one process, thereby preventing the manufacturing process from becoming complicated and reducing manufacturing costs.

[0009] In the bottom coating step, it is preferable to coat the intended ground contact area and the first ground contact area using a common coating device, which can further reduce manufacturing costs.

[0010] It is preferable that the height from the tip of the leg of the region consisting of the first ground contact region and the planned ground contact region is 3 mm or more. By having a height of 3 mm or more, both regions can be sufficiently covered with the coating layer.

[0011] The coating agent used in the bottom coating step is preferably an ultraviolet-curable paint, which eliminates the need to install a separate heating device such as an oven for curing the coating layer, thereby further reducing manufacturing costs.

[0012] The first ground contact region and the intended ground contact region are preferably continuous, which makes it easier to coat both regions at once in the bottom coating step.

[0013] According to the method for manufacturing a can body of the present invention, it is possible to manufacture a can body without complicating the manufacturing process and while suppressing manufacturing costs.

[0014] 1 is a flowchart illustrating each step in a manufacturing method of the present embodiment. FIG. 2 is a cross-sectional view of a preform can. FIG. 3 is a cross-sectional view of a seamless can. FIG. 4 is a schematic partial cross-sectional view of a leg for illustrating a first ground contact portion. FIG. 5 is a schematic partial cross-sectional view of a leg for illustrating a second ground contact portion. (A) to (C) are schematic partial cross-sectional views for illustrating bottom reforming processing.

[0015] (Embodiment 1) The manufacturing process of a seamless can according to this embodiment will be described with reference to the flowchart of Fig. 1. As shown in Fig. 1, the manufacturing process of a seamless can according to this embodiment includes a preform can forming step S1 (cupping step S11, preform can molding step S12, trimming step S13, cleaning step S14) for forming a preform can, a bottom coating step S2 for applying a bottom coat to the obtained preform can, a coating step S3 (printing step S31, inner surface coating step S32) for printing on the outer surface of the preform can and painting on the inner surface, and a seamless can forming step S4 (bottom reforming step S41, neck and flange processing step S42) for forming a seamless can from the bottom coated and painted preform can.

[0016] The preform can 10 will now be described with reference to Fig. 2. The up-down direction used in the following description is shown in Fig. 2.

[0017] The preform can 10 comprises a cylindrical body 11 and a bottom 12 that closes an opening on one side of the body 11. The bottom 12 has annular legs 13 formed along its outer periphery that protrude downward in the axial direction of the preform can 10, and also has a dome-shaped dome portion 14 that protrudes upward in the axial direction in the center surrounded by the outer periphery. The legs 13 have first ground contact portions 15 whose lower axial ends (tips) contact the conveying surface S.

[0018] Next, the seamless can 20 will be described with reference to FIG.

[0019] The bottom 12 of the seamless can 20 is formed by bottom reforming the preform can 10. In this embodiment, the preform can 10 is subjected to bottom reforming and neck / flange processing. The seamless can 20 also comprises a cylindrical body 11 and bottom 12. The outer peripheral edge of the bottom 12 of the seamless can 20 is provided with an annular protrusion 21 formed at the tip of the leg portion 13 that protrudes axially downward and toward the can radially inward at the outer periphery. In this case, the protrusion 21 has a bent shape at a recess 23 because the tip 22 of the protrusion 21 protrudes axially downward and toward the can radially inward. The recess 23 is the base end of the protrusion 21 and is recessed relative to the surrounding area. In other words, the protrusion 21 is formed by deforming the leg portion 13 of the preform can 10 through the bottom reforming process. The protrusion 21 also has a second grounding portion 24, the axially lower end (tip) of which contacts the conveying surface S. The seamless can 20 also has a dome-shaped dome portion 14 that protrudes axially upward in the central portion surrounded by the annular protrusion 21. A neck portion 26 having a smaller diameter than the body portion 11 and a flange portion 27 at the open end are formed on the axially upper side of the body portion 11 of the seamless can (opposite the bottom portion 12).

[0020] In the seamless can 20 of this embodiment, the recessed portion 23 of the protruding portion 21 is bent axially downward and radially inward. This allows the dome portion 14 to easily deform due to changes in internal pressure, resulting in high pressure resistance. After filling the seamless can 20 with contents, a can lid is seamed over the open end to seal it, and the can is provided to consumers as a filled can. The can lid used for such a filled can may have a conventionally known shape, such as an easy-open lid provided with a score for forming a contents dispensing opening and an opening tab, and may be either a full-open type or a partial-open type (stay-on-tab type). The contents to be filled include beverages such as soft drinks and carbonated drinks, as well as food. However, the bottom shape has excellent pressure resistance, making it particularly suitable for filling beverages with self-generating pressure, such as beer and carbonated drinks.

[0021] The first ground contact portion 15 and the second ground contact portion 24 will now be described with reference to FIGS. 4 and 5. FIG. 4 is a schematic enlarged cross-sectional view of the leg portion 13 near the first ground contact portion 15, and FIG. 5 is a schematic enlarged cross-sectional view of the leg portion 13 near the second ground contact portion 24. In the leg portion 13, the axially lower tip becomes the first ground contact portion 15, and this first ground contact portion 15 and its surroundings constitute the first ground contact portion region R1 where a coating layer (described later) is formed by coating. Similarly, in the protrusion 21, the axially lower tip becomes the second ground contact portion 24, and this second ground contact portion 24 and its surroundings constitute the second ground contact portion region R2 where a coating layer is formed by coating. As shown in FIG. 4, the second ground contact portion planned region R3 (planned ground contact region) that will become the second ground contact portion region R2 is located above the inner surface of the leg 13 relative to the first ground contact portion 15 that will contact the ground in the preform can state. Furthermore, the region that was the first ground contact portion region R1 is located above the outer surface of the protrusion 21 relative to the second ground contact portion region R2, as shown in FIG. 5. That is, when the bottom reforming process is performed on the bottom portion 12, the contact portion that contacts the conveying surface S moves.

[0022] In this embodiment, in the bottom coating step S2, not only the first ground contact region R1 but also the second planned ground contact region R3 is coated at the same time, so that the first ground contact region R1 and the second planned ground contact region R3 (second ground contact region R2) can be coated in one step without dividing the bottom coating step S2 into two steps. Details of the bottom coating step S2 will be described later.

[0023] In this case, in this embodiment, the first ground contact region R1 and the second ground contact region R3 are contiguous, which makes it easier to form a coating layer simultaneously using the same (common) coating device in the bottom coating step S2, simplifying the manufacturing process and further reducing manufacturing costs. If these regions were not contiguous, coating using the same coating device would result in the coating agent being applied to areas where a coating layer is not actually required, which could require masking or result in unnecessary use of a large amount of coating agent. In contrast, in this embodiment, the first ground contact region R1 and the second ground contact region R3 are contiguous, which makes it easier to form a coating layer when the first ground contact region R1 and the second ground contact region R3 are simultaneously coated in the bottom coating step S2 as described above, and further reduces manufacturing costs.

[0024] The manufacturing process will be described in detail below.

[0025] First, a preform can forming step S1 is performed. Specifically, in a cupping step S11, a metal plate such as an aluminum alloy plate is drawn to form a cup-shaped body. Next, in a preform can forming step S12, the cup-shaped body is formed into a preform can 10. Specifically, a bottomed cylindrical body is formed by drawing and ironing, and the formed bottom 12 is then pressed to form the preform can 10. Note that the method for forming the preform can 10 is not limited to the above-described method, and conventionally known methods such as drawing, drawing / deep drawing, drawing / ironing, and drawing / bending / ironing can be used. The axially upper open end of the obtained preform can 10 is trimmed in a trimming step S13, and then the preform can is cleaned in a cleaning step S14.

[0026] Next, in the bottom coating process S2, a coating layer is formed on the first ground contact region R1 and the second ground contact region R3 of the bottom 12 of the preform can 10 using a transparent paint that can reduce friction and improve transportability. In this case, in this embodiment, the coating agent is applied to the first ground contact region R1 and the second ground contact region R3 simultaneously to form the coating layer, so that the coating can be completed in a single process and manufacturing costs can be reduced. Furthermore, by using the same (common) coating device to simultaneously coat the first ground contact region R1 and the second ground contact region R3, there is no need to use separate devices, which does not complicate the manufacturing process, shortens the time required for the coating process, and further reduces manufacturing costs, which is advantageous.

[0027] In the bottom coating step S2, any known coating agent, coating method, baking method, coating conditions, etc. can be used. Known coating agents, such as UV-curable paints and thermosetting paints, can be used. Coating methods include roll coating, stamping, spraying, and misting. The baking method can also be selected depending on the paint and the desired coating state. UV irradiation may be applied to UV-curable paint, followed by heating. For example, UV-curable paint may be applied using a roller as a coating device (roll coating method), and then a coating layer may be formed by UV irradiation. In this case, using UV-curable paint eliminates the need for a separate oven for baking the coating layer after the bottom coating step S2, thereby reducing the complexity of the manufacturing process.

[0028] In addition, it is preferable that the height H (see FIG. 4) of the region consisting of the first ground contact region R1 and the second ground contact planned region R3 from the tip of the leg 13 is 3 mm or more. By having the height H from the tip of the leg 13 be 3 mm or more, a coating layer is sufficiently formed in the first ground contact region R1 and the second ground contact planned region R3. In addition, it is preferable that the height H be 5 mm or less in order to use the coating agent without waste. Furthermore, the height H of the first ground contact region R1 from the tip of the leg 13 is 3 mm or more. ２ A preferable range is 0.5 mm to 0.7 mm. This range ensures stable transportability and enables the coating agent to be used without waste. In FIG. 4, the position of the second ground contact region R3 is set higher than the first ground contact region R1, but depending on the shape of the leg portion 13 and the protrusion 21, the height of the second ground contact region R3 from the transport surface S may be lower than the first ground contact region R1.

[0029] Next, the coating process S3 (printing process S31, inner surface coating process S32) is carried out. In the printing process S31, printing is performed on the outer surface of the body 11 of the preform can 10, and if necessary, a finishing varnish layer is formed on this printed layer. Note that coating may be performed before printing to form an outer surface coating film, or a resin-coated metal plate or the like may be used instead of forming an outer surface coating film. Next, in the inner surface coating process S32, an inner surface coating film is formed on the inner surface of the preform can 10 by spray painting or the like. Note that in this coating process S3, the bottom coating process S2, in which coating is performed on the first ground contact area R1 and the second ground contact area R3, may be carried out simultaneously.

[0030] Finally, the seamless can forming step S4 (bottom reforming step S41, neck and flange processing step S42) is performed to form the seamless can 20. The bottom reforming process will be described with reference to FIG.

[0031] First, as shown in FIG. 6A , the preform can 10 on which the coating layer 30 was formed in the bottom coating step S2 is placed on a molding die 31 formed to fit the shape of the bottom surface of the seamless can 20. Here, the coating layer 30 covers the first ground contact region R1 and the second ground contact planned region R3. Because the coating layer 30 is formed in the first ground contact region R1, the preform can 10 can be smoothly transported after the bottom coating step S2. When the preform can 10 is placed on the molding die 31, the first ground contact regions 15, which are the tips of the legs 13, are raised. Next, a pressing body 32 is inserted into the preform can 10 from above to below in the axial direction to press the bottom 12 of the preform can 10.

[0032] As shown in Figures 6(B) and 6(C), when the pressing body 32 presses the inner surface of the preform can 10, the radially outer peripheral surfaces of the leg portions 13 of the preform can 10 are pressed axially along the mold 31. At the same time, the radially outer peripheral surfaces of the leg portions 13 curve radially inward from the end of the mold 31 along the mold 31, starting from the recessed portion 23, to form the protrusions 21. The axially lower end (tip) of the protrusions 21 becomes the second ground contact portion 24. Even in this case, the coating layer 30 formed in the bottom coating step S2 covers the second ground contact portion 24 and the second ground contact portion region R2. The resulting seamless can 20 is then subjected to necking and flange forming in a necking and flange forming step S42, where necking and flange forming are performed to obtain the seamless can 20, which is a final molded product, having a reduced-diameter neck portion 26 and flange portion 27, as shown in Figure 3. In this case, the coating layer 30 is formed in the second ground contact region R2 including the second ground contact portion 24 that contacts the conveying surface S of the seamless can 20, thereby ensuring smooth conveyance. (Modification)

[0033] The present invention is not limited to the above-described embodiment. The shape of the seamless can 20 is not particularly limited as long as the recess 23 is bent to form the protruding portion 21 as described above. It may have any shape, such as a bottle-shaped can with a significantly reduced diameter at the axially upper end to form a neck portion and a threaded neck. Furthermore, the metal plate constituting the seamless can 20 can be any metal plate conventionally used for seamless cans, such as a surface-treated steel plate or an aluminum alloy plate, but aluminum alloy plate is particularly preferred. These metal plates may also be resin-coated metal plates coated with a thermoplastic resin such as polyester resin. When using such resin-coated metal plates, the painting step S3 described above may be omitted, if necessary. In FIG. 6 , the coating layer 30 is formed so as to exactly cover the first ground contact region R1 and the second planned ground contact region R3. However, the coating layer 30 may be formed over a wider area as long as it covers at least the first ground contact region R1 and the second planned ground contact region R3.

[0034] REFERENCE SIGNS LIST 10 Preform can 11 Body 12 Bottom 13 Leg 14 Dome 15 First ground contact portion 20 Seamless can 21 Protrusion 22 Tip 23 Recess 24 Second ground contact portion 26 Neck 27 Flange 30 Coating layer 31 Mold 32 Pressing body R1 First ground contact portion region R2 Second ground contact portion region R3 Second ground contact portion planned region (planned ground contact portion region) S1 Preform can forming process S2 Bottom coating process S3 Painting process S4 Seamless can forming process S11 Cupping process S12 Preform can forming process S13 Trimming process S14 Cleaning process S31 Printing process S32 Inner surface painting process S41 Bottom reforming process S42 Neck and flange processing process S Conveying surface

Claims

1. A method for manufacturing a can body having a bottom and a body, comprising: a preform can forming step of forming a preform can having an annular leg portion on the bottom that will become a first ground contact portion; a bottom coating step of applying a coating agent to a first ground contact portion area including the first ground contact portion of the preform can; and a seamless can forming step of deforming the bottom of the preform can again to form an annular protrusion that will become a second ground contact portion, thereby forming a seamless can having a recess, wherein in the bottom coating step, the coating agent is also applied to a planned ground contact portion area that will become a second ground contact portion area including the second ground contact, thereby coating the can body.

2. A method for manufacturing a can body according to claim 1, wherein in the bottom coating step, the intended ground contact area and the first ground contact area are coated using a common coating device.

3. A method for manufacturing a can body according to claim 1, wherein the height of the area consisting of the first ground contact area and the planned ground contact area from the tip of the leg is 3 mm or more.

4. The method for manufacturing a can body according to claim 1, wherein the coating agent used in the bottom coating step is an ultraviolet curable paint.

5. A method for manufacturing a can body according to any one of claims 1 to 4, characterized in that the first ground contact area and the intended ground contact area are continuous.

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