Method for manufacturing can body

Abstract

To provide a method for manufacturing a can body capable of suppressing a manufacturing cost.SOLUTION: A method for manufacturing a can body including a bottom portion 12 and a body portion 11 includes a preform-can forming step S1 of forming a preform can 10 having an annular leg portion 13 serving as a first contact portion 15 on the bottom portion 12, a bottom coating step S2 of applying a coating agent to a first contact portion region R1 including the first contact portion 15 of the preform can 10, and a seamless-can forming step S4 of forming an annular protruding portion 21 serving as a second contact portion 15 by deforming the bottom portion 12 of the preform can 10 again to form a recess portion. In the bottom coating step S2, coating is performed by applying the coating agent also to a planned ground-contact region that is planned to be the second ground-contact region R2 including the second ground-contact portion 24.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] Seamless cans (DI cans), formed by drawing and ironing processes, are widely used as can bodies for storing beverages, food, and other items. In response to recent demands for resource conservation, thinner materials are being used for these 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 the 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 the 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. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2024-072083 Summary of the Invention [Problem to be solved by the invention]

[0005] In Patent Document 1, the coating process was carried out twice because the grounding portion differs between preform cans and seamless cans, 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. [Means for solving the problem]

[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. [Effects of the Invention]

[0013] According to the method for manufacturing a can body of the present invention, a can body can be manufactured without complicating the manufacturing process and while suppressing manufacturing costs. [Brief explanation of the drawings]

[0014] [Figure 1] 1 is a flowchart illustrating each step in a manufacturing method according to the present embodiment. [Figure 2] FIG. 2 is a cross-sectional view of a preform can. [Figure 3] FIG. 1 is a cross-sectional view of a seamless can. [Figure 4] FIG. 4 is a schematic partial cross-sectional view of a leg portion for explaining a first ground contact portion. [Figure 5] FIG. 10 is a schematic partial cross-sectional view of a leg portion for explaining a second ground contact portion. [Figure 6] 5A to 5C are schematic partial cross-sectional views for explaining bottom reforming processing. DETAILED DESCRIPTION OF THE INVENTION

[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, and 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 and 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 and neck and flange processing step S42) for forming a seamless can from the bottom-coated and painted preform can.

[0016] Here, the preform can 10 will be described with reference to Fig. 2. The up and down directions used in the following description are shown in Fig. 2.

[0017] The preform can 10 consists of 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 in the center surrounded by the outer periphery that protrudes upward in the axial direction. The legs 13 have first contact portions 15 at their lower axial ends (tips) that 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 has been subjected to bottom reforming and neck and flange processing. The seamless can 20 also comprises a cylindrical body 11 and bottom 12. The outer periphery 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 the 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 protruding portion 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 protruding portion 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 the can, 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 equipped 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 is particularly pressure-resistant, making it 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 lower axial end becomes the first ground contact portion 15, and this first ground contact portion 15 and its surroundings constitute a first ground contact portion region R1 where a coating layer (described later) is formed by coating. Similarly, in the protrusion 21, the lower axial end becomes the second ground contact portion 24, and this second ground contact portion 24 and its surroundings constitute a second ground contact portion region R2 where a coating layer is formed by coating. As shown in FIG. 4, a second ground contact portion planned region (planned ground contact region) R3 that will become the second ground contact portion region R2 is located higher on the inner surface of the leg 13 than 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 higher on the outer surface of the protrusion 21 than 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 planned 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 planned 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 planned 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, the preform can forming step S1 is performed. Specifically, in the cupping step S11, a metal plate such as an aluminum alloy plate is drawn to form a cup-shaped body. Next, in the 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-mentioned method, and conventionally known methods such as drawing, drawing and deep drawing, drawing and ironing, and drawing, bending and stretching and ironing can be used. The axially upper open end of the obtained preform can 10 is trimmed in the trimming step S13, and then the preform can is washed in the washing 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 planned 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 planned 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 planned 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-curable paints can be heated after UV irradiation. For example, UV-curable paints can be applied using a roller as a coating device (roll coating method), and then a coating layer can be formed by UV irradiation. In this case, using UV-curable paints 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] Furthermore, the region consisting of the first ground contact region R1 and the second ground contact planned region R3 preferably has a height H (see FIG. 4) from the tip of the leg portion 13 of 3 mm or more. By having the height H from the tip of the leg portion 13 of 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. Furthermore, the height H is preferably 5 mm or less to use the coating agent without waste. Furthermore, the height H2 of the first ground contact region R1 from the tip of the leg portion 13 is preferably 0.5 mm to 0.7 mm. This range ensures stable conveyance and enables the coating agent to be used without waste. Note that, although the position of the second ground contact planned region R3 is set higher than the first ground contact region R1 in FIG. 4, depending on the shapes of the leg portion 13 and the protrusion 21, the height of the second ground contact planned region R3 from the conveyance 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 applied to 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 carried out 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 coating or the like. Note that in this coating process S3, the bottom coating process S2 in which coating is carried out on the first ground contact area R1 and the second ground contact area R3 may be carried out simultaneously.

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

[0031] First, as shown in FIG. 6(A), 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 transported smoothly from the bottom coating step S2 onward. 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] 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 forming die 31. At the same time, the radially outer peripheral surfaces of the leg portions 13 curve radially inward from the end of the forming die 31, starting from the recessed portions 23, to form the protruding portions 21. The axially lower end (tip) of this protruding portion 21 becomes the second ground contact portion 24. In this case as well, 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 a neck-flange forming process S42, where necking and flanging are performed to obtain a seamless can 20, which is a final molded product, having a reduced-diameter neck 26 and flange 27, as shown in Fig. 3. In this case, the coating layer 30 is formed on the second contact portion region R2, including the second contact portion 24 that contacts the conveying surface S of the seamless can 20, thereby ensuring smooth conveyance. (Variation)

[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. Any shape, such as a bottle-shaped can with a significantly reduced diameter at the axially upper end to form a neck and a screw, may be used. 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 a resin-coated metal plate, the aforementioned painting step S3 may be omitted, if necessary. In Figure 6, the coating layer 30 is formed so as to exactly cover the first ground contact area R1 and the second ground contact area R3, but it is sufficient that the coating layer 30 covers at least the first ground contact area R1 and the second ground contact area R3, and it may also be provided in an area wider than these, for example. [Explanation of symbols]

[0034] 10 Preform cans 11 Torso 12 Bottom 13 Legs 14 Dome section 15 First grounding part 20 Seamless cans 21 Protrusion 22 Tip 23 Recess 24 Second grounding part 26 Neck 27 Flange 30 coat layers 31 Molding mold 32 Pressurizing body R1 First ground contact area R2 Second ground area R3 Second contact area (planned contact area) S1 Preform can forming process S2 Bottom coat process S3 Painting process S4 Seamless can forming process S11 Cupping process S12 Preform can molding process S13 Trimming process S14 Cleaning process S31 Printing process S32 Interior painting process S41 Bottom Reform 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 that becomes a first ground contact portion at the bottom; a bottom coating step of applying a coating agent to a first ground contact portion region including the first ground contact portion of the preform can; a seamless can forming step of deforming the bottom of the preform can again to form an annular protrusion that becomes a second ground contact portion, thereby forming a seamless can having a recessed portion; A method for manufacturing a can body, characterized in that in the bottom coating process, the coating agent is also applied to a planned ground contact area that is intended to become a second ground contact area including the second ground contact.

2. 2. The 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. 2. The method for manufacturing a can body according to claim 1, wherein the height of the region consisting of the first ground contact region and the planned ground contact region from the tip of the leg is 3 mm or more.

4. 2. 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. The method for manufacturing a can body according to any one of claims 1 to 4, wherein the first ground contact area and the intended ground contact area are continuous.

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