Method for manufacturing a metal container and a metal container

Abstract

To efficiently form irregularities of a desired size on the outer surface of the can body. [Solution] The method for manufacturing a metal container comprises a printing layer forming step of forming a printing layer made of ink containing thermally expandable microcapsules on the outer surface of the can body, a finishing varnish layer forming step of forming a finishing varnish layer made of varnish in which a thermosetting resin is dissolved in a solvent on the printing layer, and a drying step of drying the can body on which the printing layer and the finishing varnish layer are formed by heating. In the drying step, the heating temperature and heating time for the finishing varnish layer are set considering the particle size change characteristics of the thermally expandable microcapsules. By heating at the set heating temperature and heating time, the thermally expandable microcapsules in the printing layer are expanded while the thermosetting resin in the finishing varnish layer is cured, and the thermally expandable microcapsules are expanded to a desired particle size state at a heating time when the thermosetting resin in the finishing varnish layer reaches a predetermined curing state in which the particle size change of the thermally expandable microcapsules stops.

Description

Technical Field

[0001] The present invention relates to a method for manufacturing a metal container and a metal container.

Background Art

[0002] In the foaming printing technology for a can body such as a two-piece can, a printing layer made of an ink containing thermally expandable microcapsules and a finish varnish layer (top coat layer) are formed in this order on the outer peripheral surface of the can body, and by heating to expand the thermally expandable microcapsules, there is a technique for forming irregularities on the outer peripheral surface of the can body (see, for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, in the conventional method as described in Patent Document 1, the relationship between the expansion of the thermally expandable microcapsules in the printing layer and the curing of the finish varnish layer has not been sufficiently considered. Therefore, in the conventional method, in many cases, it has been difficult to efficiently form irregularities of a desired size on the outer peripheral surface of the can body by using thermally expandable microcapsules.

[0005] For example, to form sufficiently large irregularities on the outer surface of a can, conventional methods have involved increasing the amount (concentration) of thermally expandable microcapsules in the ink constituting the printing layer, or using thermally expandable microcapsules with a large initial particle size. Alternatively, pre-expandable microcapsules with a large initial particle size or fillers with a large initial particle size have been used in the ink constituting the printing layer. However, in such cases, there is a risk that microcapsules (or fillers, etc.) in the ink may remain on the printing plate or blanket during printing, making them difficult to transfer.

[0006] The present invention aims to address these circumstances. Specifically, the objective of the present invention is to provide a method for manufacturing a metal container and a metal container that can efficiently form irregularities of a desired size on the outer surface of a can body. [Means for solving the problem]

[0007] The present invention relates to a manufacturing method for producing a metal container having foam printing applied to the outer surface of a can body, comprising: a printing layer forming step of forming a printing layer made of ink containing thermally expandable microcapsules on the outer surface of the can body; a finishing varnish layer forming step of forming a finishing varnish layer made of varnish obtained by dissolving a thermosetting resin in a solvent on the printing layer; and a drying step of drying the can body having the printing layer and the finishing varnish layer formed on it by heating, wherein in the drying step, the heating temperature and heating time for the finishing varnish layer are set considering the particle size change characteristics of the thermally expandable microcapsules, and the thermally expandable microcapsules in the printing layer are expanded while the thermosetting resin in the finishing varnish layer is cured by heating at the set heating temperature and heating time, and the thermally expandable microcapsules are expanded to a desired particle size state at a heating time when the thermosetting resin in the finishing varnish layer reaches a predetermined cured state in which the particle size change of the thermally expandable microcapsules stops.

[0008] The present invention relates to a metal container having foam printing applied to the outer surface of a can body, wherein the can body has a printed layer made of ink containing thermally expandable microcapsules and a finishing varnish layer made of a finishing varnish in which a thermosetting resin is dissolved in a solvent, formed in this order on the outer surface of the can body and dried by heating, wherein the thermosetting resin in the finishing varnish layer is hardened when the thermally expandable microcapsules have expanded to a desired particle size, and the finishing varnish layer on the printed layer has an arithmetic mean roughness Ra of 0.2 μm or more and a maximum height roughness Rmax of 2.5 μm or more. [Effects of the Invention]

[0009] According to the present invention, it is possible to provide a method for manufacturing a metal container and a metal container that can efficiently form irregularities of a desired size on the outer surface of a can body. [Brief explanation of the drawing]

[0010] [Figure 1] This is a perspective view of a can body used in the manufacturing method of a metal container according to this embodiment. [Figure 2] This is a partial cross-sectional view of the can body and the printed layer and finishing varnish layer on its outer surface. [Figure 3] This diagram schematically shows the basic configuration of the printing apparatus used in this embodiment. [Figure 4] Figure 3 is a magnified view of the area near where the printing plate and blanket come into contact. [Figure 5] This is a flowchart illustrating the printing process performed in the manufacturing method of the metal container according to this embodiment. [Figure 6] This is a flowchart illustrating the printing layer formation process in step S2. [Figure 7] This graph schematically shows an example of the relationship between the heating time [s] of the heating device in the drying process of step S5, the gel fraction [%] of the thermosetting resin in the finishing varnish layer, and the particle size [μm] of the thermally expandable microcapsules in the printed layer. [Figure 8]This graph schematically shows another example of the relationship between the heating time [s] of the heating device in the drying process of step S5, the gel fraction [%] of the thermosetting resin in the finishing varnish layer, and the particle size [μm] of the thermally expandable microcapsules in the printed layer. [Figure 9] This graph shows the relationship between the heating time [s] of the research oven in Heating Test 1, when the set temperature [°C] was set to 200°C, the gel fraction [%] of the thermosetting resin in the finishing varnish layer (2W143-06 (current varnish)), and the particle size [μm] of the thermally expandable microcapsules (FN-100SSD (medium temperature expansion type)) in the printed layer. [Figure 10] This figure shows the measurement results for arithmetic mean roughness Ra [μm] and maximum height roughness Rmax [μm] in heating test 1. [Figure 11] This figure shows the measurement results for the gross value [-] in heating test 1. [Figure 12] This figure shows the measurement results for arithmetic mean roughness Ra [μm] and maximum height roughness Rmax [μm] in heating test 2. [Figure 13] This figure shows the measurement results of the gross value [-] in heating test 2. [Modes for carrying out the invention]

[0011] Hereinafter, embodiments of the present invention (this embodiment) will be described with reference to the drawings. In the following description, the same reference numerals in different figures indicate parts with the same function, and redundant explanations in each figure will be omitted as appropriate. Also, in the following description, "approximately" means "substantially". For example, "approximately cylindrical shape" includes not only "cylindrical shape" but also shapes similar to a cylindrical shape.

[0012] [Metal container] The manufacturing method of the metal container 1 according to this embodiment involves, as an example, applying foam printing to the outer surface 11 of a can body 10, such as a two-piece can as shown in Figure 1, to produce the metal container 1. The can body 10 has a substantially cylindrical shape, with an opening 12 at the top and a bottom 13 at the bottom.

[0013] This metal container 1 will later be filled with a beverage as its contents through the opening 12 inside the can body 10, and the opening 12 will be sealed with a lid (not shown), thus becoming a canned beverage product. The beverage as the contents is not particularly limited and can be any beverage such as a soft drink, an alcoholic beverage, etc. Note that the contents are not limited to beverages and can also be other foods (such as snacks, dried food, etc.) or articles other than foods (such as stationery, toys, etc.).

[0014] The can body 10 is a metal can body (metal can), for example, made of various metal plates such as an aluminum plate, an aluminum alloy plate, a surface-treated steel plate such as tin-free steel, a tinplate, a chromium-plated steel plate, an aluminum-plated steel plate, a nickel-plated steel plate, a tin-nickel-plated steel plate, and various alloy-plated steel plates thereof, and formed by drawing, ironing, redrawing, etc., and can be, for example, a two-piece can, a three-piece can, or other various types of metal cans. Note that a resin film such as a polyester film, a nylon film, or a polypropylene film may be laminated on the surface of the can body 10.

[0015] As shown in FIG. 2 for example, on the outer peripheral surface 11 of the can body 10 of the metal container 1, as foaming printing, a printing layer 21 made of ink 21A containing thermally expandable microcapsules 21C and a finishing varnish layer 22 made of a varnish (finishing varnish 22A) obtained by dissolving a thermosetting resin in a solvent are formed and dried in this order. The ink 21A constituting the printing layer 21 is a foaming ink in which thermally expandable microcapsules 21C that expand by heating are dispersed in a normal printing ink material 21B.

[0016] [Finishing varnish layer] The finishing varnish layer 22, also called the topcoat layer, is formed to protect the printed layer 21 and to provide gloss or a matte finish. As described above, the finishing varnish layer 22 consists of a finishing varnish 22A obtained by dissolving a thermosetting resin in a solvent (such as an organic solvent). This finishing varnish 22A may be transparent, for example. The thermosetting resin is not particularly limited, but examples include thermosetting polyester resin, thermosetting acrylic resin, thermosetting epoxy resin, etc.

[0017] In this embodiment, the varnish 22A used in the finishing varnish layer 22 is referred to as the "current varnish" if it has been used by the inventors in the past, and as the finishing varnish 22A used in the present invention, a varnish that starts and progresses curing at a lower temperature than the current varnish is referred to as the "low-temperature curing varnish". An example of the "current varnish" is "2W143-06" described later. An example of the "low-temperature curing varnish" is "2WB301-2" described later. In this embodiment, examples of using the "current varnish" and "low-temperature curing varnish" are mainly described, but the invention is not limited to these, and a "high-temperature curing varnish", which starts and progresses curing at a higher temperature than the current varnish, may also be used.

[0018] [Thermally expandable microcapsules] The thermally expandable microcapsules 21C contained in the printed layer 21 consist of a shell enclosing an internally contained volatile component. The internally contained volatile component is, for example, a hydrocarbon. This hydrocarbon may be a mixture of, for example, hexane, heptane, etc., in which the timing of gasification (vaporization) is controlled. The shell is formed, for example, from a thermoplastic polymer. The timing of softening of this thermoplastic polymer (i.e., the timing at which it reaches its softening temperature (Tg)) may be controlled by changing the polymer polymerization ratio.

[0019] The particle size of the thermally expandable microcapsule 21C before expansion (original particle size) is preferably 20 μm or less, more preferably 15 μm or less, and even more preferably 10 μm or less.

[0020] The concentration (addition rate) of the thermally expandable microcapsules 21C in ink 21A is preferably 2.5 wt% or less, and more preferably 1.5 wt% or less.

[0021] The thickness (film thickness) of the shell of the thermally expandable microcapsule 21C before expansion is not particularly limited, but may be several micrometers. If this film thickness is too large, it becomes difficult for the volatile gas components contained within to permeate the shell and diffuse to the outside when the thermally expandable microcapsule 21C contracts after expansion.

[0022] When heated, the heat-expandable microcapsule 21C expands as its shell softens and its film thickness decreases, while the volatile components contained within gasify, increasing the internal pressure inside the capsule. When the heat reaches its maximum expansion state, where its particle size (outer diameter) is at its maximum (maximum expansion diameter), the internal pressure inside the capsule balances with the tension of the polymer (resin) constituting the shell and the sum of the external pressure, thus maintaining the maximum expansion state.

[0023] As heating continues, the thermally expandable microcapsules 21C shrink as the volatile gases contained within the capsules diffuse through the shell to the outside, and the internal pressure inside the shell becomes smaller than the sum of the tension of the polymer (resin) that makes up the shell and the external pressure, causing the particle size to decrease. During shrinkage, the thermally expandable microcapsules 21C shrink without creating negative pressure inside the capsule, because outside air enters the capsule through the shell instead of the volatile gases contained within the capsules diffusing through the shell to the outside.

[0024] When heated, the thermosetting resin constituting the finishing varnish layer 22 reaches a predetermined curing state that stops the particle size change of the thermally expandable microcapsules. At this point, the thermally expandable microcapsules 21C are fixed by the finishing varnish layer 22, and their particle size change stops. Based on this, by stopping the particle size change of the thermally expandable microcapsules 21C when their particle size reaches a desired size, it is possible to form irregularities of a desired size on the outer surface 11 of the can body 10, based on the particle size state of the thermally expandable microcapsules 21C. The size of the irregularities formed on the outer surface 11 of the can body 10 can be any desired size required by the manufacturer, etc., and is not particularly limited. That is, the surface roughness of the finishing varnish layer 22 on the printed layer 21 is not particularly limited. For example, the finishing varnish layer 22 on the printed layer 21 may have a surface roughness with an arithmetic mean roughness Ra of 0.2 μm or more and a maximum height roughness Rmax of 2.5 μm or more. For example, irregularities based on this surface roughness may be formed on the outer surface 11 as irregularities of a desired size.

[0025] Examples of the types of thermally expandable microcapsules 21C contained in the printed layer 21 include "low-temperature expansion type," "medium-temperature expansion type," and "ultra-high-temperature expansion type" microcapsules. Among the thermally expandable microcapsules 21C, the "low-temperature expansion type" microcapsules have relatively low expansion initiation temperatures (heating temperatures [°C] at which expansion begins) and maximum expansion temperatures (heating temperatures [°C] at which the maximum particle size [μm] is reached). Among the thermally expandable microcapsules 21C, the "medium-temperature expansion type" microcapsules have higher expansion initiation temperatures (heating temperatures [°C] at which expansion begins) and maximum expansion temperatures (heating temperatures [°C] at which the maximum particle size [μm] is reached) than the "low-temperature expansion type" microcapsules. Among the thermally expandable microcapsules 21C, the "ultra-high temperature expansion type" microcapsules have higher expansion initiation temperatures (heating temperatures [°C] at which expansion begins) and maximum expansion temperatures (heating temperatures [°C] at which the maximum particle size [μm] is reached) than the "medium temperature expansion type" microcapsules.

[0026] Examples of "low-temperature expanding" microcapsules include those with an average particle size (average original particle size) of 6-10 μm, an expansion start temperature of 100-110°C, and a maximum expansion temperature of 125-135°C (e.g., "FN-80GS", "FN-80GSD" described later), and those with an average particle size (average original particle size) of 10-20 μm, an expansion start temperature of 70-80°C, and a maximum expansion temperature of 100-110°C (e.g., "F-35", "F-35D").

[0027] Examples of "medium-temperature expanding" microcapsules include those with an average particle size (average original particle size) of 6-11 μm, an expansion start temperature of 120-130°C, and a maximum expansion temperature of 145-155°C (e.g., "FN-100SS" and "FN-100SSD" described later), and those with an average particle size (average original particle size) of 10-20 μm, an expansion start temperature of 125-135°C, and a maximum expansion temperature of 150-160°C (e.g., "FN-100S" and "FN-100SD"). Examples of "ultra-high temperature expanding" microcapsules include those with an average particle size (average original particle size) of 10-15 μm, an expansion start temperature of 155-165°C, and a maximum expansion temperature of 210-220°C (e.g., "FN-190SSD" described later).

[0028] [Printing device] The printing apparatus 100 used in the printing process performed by the manufacturing method of the metal container 1 according to this embodiment has, for example, the basic configuration shown in Figure 3. The printing apparatus 100 shown in Figure 3 is a plate-type offset printing apparatus that prints by transferring ink to the outer surface 11 (Figure 1) of a can body (object to be printed) 10 having a substantially cylindrical shape such as a two-piece can. Figure 4 shows an enlarged view of the area near where the printing plate 114 and blanket 125, which will be described later and shown in Figure 3, come into contact. This printing apparatus 100 includes an inking unit 110, a blanket wheel 120, a transport unit 130, a mandrel wheel 140, a burnish applicator 150, and a transfer unit 160.

[0029] The inking unit (inker unit) 110 that supplies ink to the printing plate 114 consists of multiple inking units 110, each different for each ink color, for example, the first inking unit 110a to the eighth inking unit 110h. These multiple inking units 110 are each arranged along the outer surface of the blanket wheel 120. The inking unit 110 includes an ink supply section 111 that contains a predetermined ink, and a plate cylinder 113 on which a printing plate 114 corresponding to the ink of each ink supply section 111 is mounted.

[0030] The multiple ink supply units 111 consist, for example, the first ink supply unit 111a to the eighth ink supply unit 111h. The multiple printing plates 114 consist of the first printing plates 114a to the eighth printing plates 114h, each capable of receiving ink from the first ink supply units 111a to the eighth ink supply units 111h. The plate cylinder 113 consists of the first plate cylinder 113a to the eighth plate cylinder 113h, each mounted with the first printing plates 114a to the eighth printing plates 114h.

[0031] In the example of the printing apparatus 100 shown in Figure 3, the first ink supply units 111a to the fifth ink supply units 111e contain, as an example, inks of the following colors (normal inks): yellow (Y), magenta (M), cyan (C), and black (K), which consist only of process color ink materials, and special color inks 21A (foaming inks) which contain thermally expandable microcapsules 21C before expansion in the aforementioned normal printing ink material 21B.

[0032] In this example, the first ink supply unit 111a contains standard yellow (Y) ink, the second ink supply unit 111b contains standard magenta (M) ink, and the third ink supply unit 111c contains standard cyan (C) ink. The fourth ink supply unit 111d contains, as an example of a special color, navy (N) foamed ink (ink 21A). The fifth ink supply unit 111e contains standard black (K) ink. On the other hand, the sixth ink supply units 111f to the eighth ink supply units 111h do not contain any ink. Therefore, ink is not supplied to the sixth printing plates 114f to the eighth printing plates 114h, which correspond to the sixth ink supply units 111f to the eighth ink supply units 111h. The colors of the inks contained in the first ink supply unit 111a to the fifth ink supply unit 111e are not limited to those described herein.

[0033] As shown in Figure 4, the ink supply unit 111 includes an ink roller group 112 composed of a fountain roller and a foam roller, etc. The ink supply unit 111 supplies ink stored in an ink storage unit (not shown) to the printing plate 114 mounted on the plate cylinder 113 by the rotation of each roller of the ink roller group 112. Temperature-controlled water is circulated inside some of the rollers of the ink roller group 112 to maintain the ink temperature appropriately.

[0034] The plate cylinder 113 has a roughly cylindrical shape that can rotate around a support shaft, and a printing plate 114 is detachably mounted on its outer surface. The plate cylinder 113 is positioned so that its distance from the blanket wheel 120 can be changed.

[0035] Multiple printing plates 114 (first printing plate 114a to eighth printing plate 114h) are produced by a platemaking system (not shown) based on original image data, and may consist of, for example, a resin relief plate in which the image area on which ink is applied is formed of a photosensitive resin layer or the like.

[0036] In the example of the printing apparatus 100 shown in Figure 3, the first ink supply unit 111a supplies standard yellow (Y) ink to the first printing plate 114a, and the second ink supply unit 111b supplies standard magenta (M) ink to the second printing plate 114b. In addition, the third ink supply unit 111c supplies standard cyan (C) ink to the third printing plate 114c, and the fourth ink supply unit 111d supplies navy (N) foamed ink (ink 21A) to the fourth printing plate 114d. Furthermore, the fifth ink supply unit 111e supplies standard black (K) ink to the fifth printing plate 114e.

[0037] Then, in the printing apparatus 100, the corresponding inks are sequentially and continuously transferred from each of the first printing plates 114a to the fifth printing plates 114e onto the same blanket 125. In the printing apparatus 100, after all the inks have been transferred (layered) onto the same blanket 125, all the inks of all the colors on that blanket 125 are simultaneously transferred to the outer surface 11 of the can body 10, at which point the can body 10 is transferred from the mandrel 141 to a heating device (oven) 170, which is an example of a drying device. With such a printing apparatus 100, a large number of can bodies 10 can be printed at high speed. For example, an air outlet for blowing out cold air may be installed near the plate cylinder 113, in which case the temperature of the plate cylinder 113 and the printing plates 114 can be properly maintained.

[0038] The blanket wheel 120 is a device that rotates a blanket 125 that rotates in rotational contact with the printing plate 114 and the ink tank 10, respectively, to transfer the ink supplied to the printing plate 114 to the ink tank 10. As shown in Figure 3, the blanket wheel 120 has a substantially cylindrical shape that can rotate around a support shaft 122. As shown in Figure 4, a plurality of segments 121 are provided on the outer surface of the blanket wheel 120 at predetermined intervals along the circumferential direction of the blanket wheel 120. A blanket 125 is mounted on the outer surface of each of the plurality of segments 121.

[0039] The blanket 125 is an intermediate transfer body that mediates the transfer of ink from the printing plate 114 to the can 10. The blanket 125 includes a base layer made of woven fabric and foam, and a rubber layer made of acrylonitrile butadiene rubber or the like. The base layer is detachably attached to the outer surface of the segment 121 via an adhesive or the like. The rubber layer is the layer to which the ink on the printing plate 114 is transferred, and is positioned on the outer surface of the base layer to constitute the outer surface of the blanket 125.

[0040] In the printing apparatus 100, the blanket wheel 120 rotates in the direction of the arrow shown in Figure 3 (counterclockwise), so that the inks of the first printing plate 114a to the fifth printing plate 114e are sequentially transferred to the same (single) blanket 125.

[0041] The transport unit 130, which transports the unprinted cans 10 to the mandrel wheel 140, is located above the mandrel wheel 140 and upstream of the area where the cans 10 held by the mandrel 141 and the blanket 125 come into contact in the direction of rotation of the mandrel wheel 140. The transport unit 130 transports the cans 10 one by one from above the mandrel wheel 140 to the top of the mandrel wheel 140 by gravity.

[0042] The mandrel wheel 140, which rotates the mandrel 141 that holds the can body 10, is provided adjacent to the blanket wheel 120 in the radial direction. The mandrel wheel 140 has a substantially disc shape that can rotate around a support shaft. Multiple mandrels 141 are provided on the outer circumference of the mandrel wheel 140 at predetermined intervals along the circumferential direction of the mandrel wheel 140.

[0043] The mandrel 141 has a substantially cylindrical shape that can be inserted into the inside of the can body 10. Multiple mandrels 141 are provided so as to protrude in a direction intersecting the mandrel wheel 140, and are cantilevered to the outer circumference of the mandrel wheel 140. The number of mandrels 141 is preferably an integer multiple of the number of blankets 125.

[0044] The mandrel 141 holds the can body 10 by adhering its tip to the inner surface of the bottom of the can body 10 through air suction or the like. The mandrel 141 is provided so that its orientation can be changed, and the radial position of the mandrel wheel 140 can be changed. The mandrel 141 is provided so that it can rotate around its central axis while holding the can body 10.

[0045] The varnish applicator 150, which applies the above-mentioned finishing varnish 22A to the ink-transferred can body 10, is provided adjacent to the mandrel wheel 140 in the radial direction. The varnish applicator 150 is provided downstream in the rotational direction of the mandrel wheel 140 from the area where the can body 10 held by the mandrel 141 and the blanket 125 come into contact.

[0046] The transfer unit 160, which transfers the can body 10 that has passed through the varnish applicator 150 from the mandrel 141 and transports it to the heating device (oven) 170, is provided adjacent to the mandrel wheel 140 in the radial direction. The transfer unit 160 is provided downstream in the rotational direction of the mandrel wheel 140 from the area where the can body 10 held on the mandrel 141 and the varnish applicator 150 come into contact. The heating device (oven) 170 is an example of a drying device that fixes multiple inks, including the ink 21A (foaming ink) mentioned above, and the finishing varnish 22A to the outer surface 11 of the can body 10.

[0047] In the printing apparatus 100, instead of the example described here, the printing operation of the printing apparatus 100 may be performed by storing navy (N: dark blue) foamed ink (ink 21A) in two ink supply units, namely the fourth ink supply unit 111d and the fifth ink supply unit 111e. In this case, a sufficient amount of navy (N: dark blue) foamed ink can be secured, so even when printing the foamed ink over a relatively wide area of ​​the outer surface 11 of the can body 10, a thick layer of foamed ink can be formed. In this case, the sixth ink supply unit 111f will store black (K) normal ink.

[0048] [Foam Printing] In the manufacturing method of the metal container 1 according to this embodiment, a metal container 1 is manufactured by using such a printing apparatus 100 and going through steps S1 to S5, for example, as shown in the flowchart of Figure 5, to apply printing, including foam printing, to the outer surface 11 of the can body 10.

[0049] (Step S1: Can transport process) In the can transport process of step S1, the printing device 100 transports the can 10 to the top of the mandrel wheel 140 using the transport unit 130. The printing device 100 holds the can 10, which has been transported to the top of the mandrel wheel 140, with the mandrel 141. Before the can 10 comes into contact with the blanket 125, the printing device 100 rotates the mandrel 141 to press-pin the can 10 and rotates the mandrel wheel 140 to move the can 10 into the contact area with the blanket 125. That is, the can 10 rotates on its own axis due to the rotation of the mandrel 141 and revolves around the mandrel wheel 140 due to the rotation of the mandrel wheel 140.

[0050] (Step S2: Printed layer formation process) In the printing layer formation step S2, the printing apparatus 100 forms a printing layer 21 (Figure 2) consisting of ink 21A containing thermally expandable microcapsules 21C, and other colored printing layers (not shown) on the outer surface 11 of the can body 10. This printing layer formation step S2 comprises, in this order, the ink supply step S21 shown in Figure 6, the blanket transfer step S22, and the can body transfer step S23.

[0051] (Step S21: Ink supply process) In the ink supply process of step S21, the printing apparatus 100 rotates the ink roller group 112 in each of the multiple ink supply units 111 to supply the ink contained in the ink supply unit 111 to the printing plate 114 mounted on the plate cylinder 113.

[0052] In step S21, the printing apparatus 100, as an example, supplies yellow (Y) standard ink from the first ink supply unit 111a to the first printing plate 114a, magenta (M) standard ink from the second ink supply unit 111b to the second printing plate 114b, and cyan (C) standard ink from the third ink supply unit 111c to the third printing plate 114c. The printing apparatus 100 also supplies navy (N) foaming ink (ink 21A) from the fourth ink supply unit 111d to the fourth printing plate 114d, and black (K) standard ink from the fifth ink supply unit 111e to the fifth printing plate 114e. Each printing plate 114 to which ink has been supplied moves to the contact area between the printing plate 114 and the blanket 125 by the rotation of the plate cylinder 113.

[0053] (Step S22: Blanket transfer process) In the blanket transfer process of step S22, following step S21, the printing apparatus 100 rotates the blanket wheel 120 to bring the blanket 125 into contact with the printing plate 114 to which ink has been supplied, and transfers the ink supplied to the printing plate 114 to the blanket 125.

[0054] In step S22, the printing apparatus 100 transfers the following inks to the same blanket 125 in the following order, as an example: the yellow (Y) normal ink on the first printing plate 114a, the magenta (M) normal ink on the second printing plate 114b, the cyan (C) normal ink on the third printing plate 114c, the navy (N) foaming ink (ink 21A) on the fourth printing plate 114d, and the black (K) normal ink on the fifth printing plate 114e. As a result, an image corresponding to the pattern of the image formed on the printing plate 114 is transferred to the blanket 125.

[0055] (Step S23: Can body transfer process) In the can transfer process of step S23, following step S22, the printing apparatus 100 moves the blanket 125, on which each ink, including ink 21A (foaming ink) (Figure 2), has been transferred, to the contact area between the can 10 and the blanket 125 by the rotation of the blanket wheel 120. Then, while pressing the can 10 held by the mandrel 141, the printing apparatus 100 brings the can 10 into contact with the blanket 125 that has moved to this contact area, thereby transferring the ink transferred to the blanket 125 to the can 10. As a result, an image corresponding to the pattern of the image formed on the printing plate 114 is transferred to the outer surface 11 of the can 10 via the blanket 125.

[0056] (Step S3: Finishing varnish layer formation process) In the finishing varnish layer formation process of step S3, following step S23, the printing apparatus 100 moves the cans on which each ink has been transferred, i.e., the cans 10 on which the printing layers of each ink, including the printing layer 21 (Figure 2) made of ink 21A, have been formed, to the varnish applicator 150 by the rotation of the mandrel wheel 140, and then to the transfer unit 160. The printing apparatus 100 then operates the varnish applicator 150 and applies the finishing varnish 22A to the cans 10 on which each ink has been transferred, thereby forming a finishing varnish layer 22 on the printing layers of each ink, including the printing layer 21.

[0057] (Step S4: Transfer process) In the transfer process of step S4 following step S3, the printing apparatus 100 operates the transfer unit 160 to transfer the can body 10, on which the finishing varnish layer 22 has been formed by passing through the varnish applicator 150, from the mandrel 141 to the heating device (oven) 170.

[0058] The printing device 100 rotates the plate cylinder 113, blanket wheel 120, mandrel 141, and mandrel wheel 140 in synchronous motion. The printing device 100 also operates the burnish applicator 150 and transfer unit 160 in synchronous motion with these components. Through this operation, the printing device 100 prints on the can body 10.

[0059] (Step S5: Drying process) In the drying process of step S5 following step S4, when the can body 10, which has the printing layers of each ink including the printing layer 21 and the finishing varnish layer 22 formed on it, is transferred to a heating device (oven) 170, which is an example of a drying device, the printing device 100 dries the can body 10 by heating in the heating device (oven) 170.

[0060] In the drying process of step S5, the printing apparatus 100 sets the heating temperature and heating time for the finishing varnish layer 22 in the heating device (oven) 170, taking into consideration the particle size change characteristics of the thermally expandable microcapsules 21C (Figure 2). The printing apparatus 100 then heats the printed layer 21 at the set heating temperature and heating time in the heating device (oven) 170, causing the thermally expandable microcapsules 21C in the printed layer 21 to expand while the thermosetting resin in the finishing varnish layer 22 hardens. As the thermally expandable microcapsules 21C in the printed layer 21 expand, they penetrate into the finishing varnish layer 22 formed on the printed layer 21, pushing up the finishing varnish layer 22. As a result, the surface of the finishing varnish layer 22 is made uneven based on the areas where thermally expandable microcapsules 21C are not present and areas where they are present. In this way, a metal container 1 is manufactured on the outer surface 11 of the can body 10, with printing including foam printing using thermally expandable microcapsules 21C.

[0061] [Formation of uneven surfaces using thermally expandable microcapsules] In the drying process of step S5, the printing apparatus 100 needs the finishing varnish 22A to be solidified (cured) when the thermally expandable microcapsules 21C are at a desired particle size state, in order to form irregularities of a desired size on the outer surface 11 of the can body 10 during heating in the heating device (oven) 170. Therefore, during this heating, it is necessary to expand the thermally expandable microcapsules 21C to a desired particle size state (i.e., a desired expansion rate [%]) for a heating time [s] that results in a predetermined curing state where the state of the thermosetting resin in the finishing varnish layer 22 stops the particle size change of the thermally expandable microcapsules 21C.

[0062] The thermosetting resin in the finishing varnish layer 22 begins to harden when its gel fraction [%] increases rapidly. In this embodiment, the "predetermined hardened state," which is the state of the thermosetting resin in the finishing varnish layer 22 (the state in which the particle size change of the thermally expandable microcapsules 21C is stopped), may be the state in which the gel fraction [%] of the thermosetting resin in the finishing varnish layer 22 has rapidly increased due to heating and has begun to harden. This predetermined hardened state varies depending on the type of thermosetting resin in the finishing varnish layer 22, but may be a state in which the gel fraction [%] of the thermosetting resin is a predetermined value [%] between 70% and 85%, for example, and may be a state in which the gel fraction [%] of the thermosetting resin is 80%.

[0063] When heated in the heating device (oven) 170, the thermally expandable microcapsules 21C begin to expand, and their particle size (outer diameter, expanded diameter) [μm] gradually increases. Immediately after reaching the maximum expanded diameter (maximum particle size) [μm], they begin to contract, and their particle size gradually decreases. The expansion rate [%] when the particle size of the thermally expandable microcapsules 21C is at the maximum expanded diameter (maximum particle size) [μm] is defined as 100%. In this case, for example, in the heating time [s] at which the thermosetting resin in the finishing varnish layer 22 reaches a predetermined curing state, the thermally expandable microcapsules 21C in the printing layer 21 are expanded to a desired particle size state (desired expansion rate [%]), for example, at an expansion rate of 80%. In this case, these greatly expanded thermally expandable microcapsules 21C form sufficiently large irregularities on the outer surface 11 of the can body 10 (the surface of the finishing varnish layer 22). Furthermore, for example, during the heating time [s] at which the thermosetting resin in the finishing varnish layer 22 reaches a predetermined curing state, the thermally expandable microcapsules 21C in the printing layer 21 expand to a desired particle size state (desired expansion rate [%]), for example, at an expansion rate of 20%. In this case, the slightly expanded thermally expandable microcapsules 21C form relatively small irregularities on the outer surface 11 of the can body 10 (the surface of the finishing varnish layer 22).

[0064] Here, we will explain in more detail the relationship between the curing state of the thermosetting resin in the finishing varnish layer 22 and the expansion state of the thermally expandable microcapsules 21C in the printing layer 21 during the drying process in step S5. Figure 7 is a schematic graph showing examples of the relationship between the heating time [s] of the heating device (oven) 170, the gel fraction [%] of the thermosetting resin in the finishing varnish layer 22, and the particle size [μm] of the thermally expandable microcapsules 21C in the printing layer 21 during the drying process in step S5. In Figure 7, graph a1 (dotted line) schematically shows the relationship between the heating time [s] of the heating device (oven) 170 and the gel fraction [%] of the thermosetting resin in the finishing varnish layer 22 made of the current varnish N1. Graph a2 (solid line) schematically shows the relationship between the heating time [s] of the heating device (oven) 170 and the gel fraction [%] of the thermosetting resin in the finishing varnish layer 22 made of the low-temperature curing varnish N2.

[0065] Graph b1 (dotted line) schematically shows the relationship between the heating time [s] of the heating device (oven) 170 and the particle size [μm] of microcapsule M1, an example of a thermally expandable microcapsule 21C, when using the finishing varnish layer 22 made of the current varnish N1 shown in Graph a1. Graph b2 (solid line) schematically shows the relationship between the heating time [s] of the heating device (oven) 170 and the particle size [μm] of microcapsule M1 (thermally expandable microcapsule 21C), when using the finishing varnish layer 22 made of the low-temperature curing varnish N2 shown in Graph a2.

[0066] In this schematic example in Figure 7, the finishing varnish layer 22 made of the current varnish N1 is heated at a heating temperature of 200°C in the heating device (oven) 170, and the finishing varnish layer 22 made of the low-temperature curing varnish N2 is heated at a heating temperature of 180°C. The predetermined value G1 of the gel fraction [%] shown in Figure 7 is the gel fraction [%] of the thermosetting resin in the finishing varnish layer 22 that results in a predetermined curing state where the particle size change of the microcapsules M1 (thermally expandable microcapsules 21C) is stopped.

[0067] For example, suppose a finishing varnish layer 22 made of the current varnish N1 is used, and heating is performed with the heating temperature of the heating device (oven) 170 set to, for example, 200°C. In this case, as shown in Figure 7, suppose the gel fraction [%] of the thermosetting resin in the current varnish N1 that constitutes the finishing varnish layer 22 changes as shown in graph a1. At this time, suppose the particle size [μm] of the microcapsules M1 (thermally expandable microcapsules 21C) in the printed layer 21 changes due to expansion and contraction caused by heating, for example as shown in graph b1 in Figure 7.

[0068] In this schematic example, the gel fraction [%] of the thermosetting resin in the current varnish N1 shown in graph a1 reaches a predetermined value G1 at a heating time Tb [s] (area enclosed in a circle in graph a1). At this heating time Tb [s], the particle size [μm] of the microcapsule M1 (thermally expandable microcapsule 21C) shown in graph b1 has decreased significantly due to shrinkage to a particle size [μm] corresponding to an expansion rate of approximately 20% (area enclosed in a circle in graph b1).

[0069] In contrast, if we replace the current varnish N1 with a finishing varnish layer 22 made of low-temperature curing varnish N2 and heat the heating device (oven) 170 at a temperature lower than 200°C, for example 180°C, then, as shown in Figure 7, the gel fraction [%] of the thermosetting resin in the low-temperature curing varnish N2 constituting the finishing varnish layer 22 will shift to the left of graph a1 at the time it reaches the predetermined value G1, changing as shown in graph a2, for example. Furthermore, because the heating temperature [°C] has been reduced from 200°C to 180°C, the changes in expansion and contraction of the microcapsules M1 become more gradual. As a result, the particle size [μm] of the microcapsules M1 (thermally expandable microcapsules 21C) in the printed layer 21 changes as shown in graph b2, which has a gentler slope than graph b1.

[0070] In the schematic example shown in Figure 7, the gel fraction [%] of the thermosetting resin in the low-temperature curing varnish N2 shown in graph a2 reaches a predetermined value G1 at a heating time Ta [s] that is earlier than the heating time Tb [s] (area enclosed in a circle in graph a2). At this heating time Ta [s], the particle size [μm] of the microcapsule M1 (thermally expandable microcapsule 21C) shown in graph b2 is the size of a particle size [μm] that corresponds to an expansion rate of approximately 80%, just after maximum expansion and slight contraction (area enclosed in a circle in graph b2). Thus, by lowering the heating temperature [°C] of the heating device (oven) 170, the particle size change characteristics of the microcapsule M1 (thermally expandable microcapsule 21C) change from graph b1 to graph b2.

[0071] Based on this, in the schematic example using the microcapsule M1 shown in Figure 7, when relatively small irregularities of a desired size are formed on the outer surface 11 of the can body 10, for example, the current varnish N1 may be used as the finishing varnish layer 22, and the heating temperature [°C] of the heating device (oven) 170 may be set to 200°C. In this case, the foam printing applied to the outer surface 11 of the can body 10 will have a high gloss and a slight foamy feel due to the relatively small irregularities.

[0072] On the other hand, in the schematic example using the microcapsules M1 shown in Figure 7, when relatively large irregularities of a desired size are formed on the outer surface 11 of the can body 10, for example, a low-temperature curing varnish N2 may be used as the finishing varnish layer 22, and the heating temperature [°C] of the heating device (oven) 170 may be set to 180°C. In this case, relatively large irregularities can be formed without increasing the content concentration (addition rate) [wt%] of microcapsules M1 (thermal-expandable microcapsules 21C) in the ink 21A, and without increasing the original particle size of the microcapsules M1 (thermal-expandable microcapsules 21C). In this case, the foam printing applied to the outer surface 11 of the can body 10 will have a high foamy feel and a matte feel (suppressed gloss) due to the relatively large irregularities.

[0073] Figure 8 is a schematic graph illustrating another example of the relationship between the heating time [s] of the heating device (oven) 170 in the drying process of step S5, the gel fraction [%] of the thermosetting resin in the finishing varnish layer 22, and the particle size [μm] of the thermally expandable microcapsules 21C in the printing layer 21. In Figure 8, graphs a11 to a13 (solid lines) all schematically show the relationship between the heating time [s] of the heating device (oven) 170 and the gel fraction [%] of the thermosetting resin in the finishing varnish layer 22 made of low-temperature curing varnish N11. Here, graph a11 is the graph obtained by heating with the heating temperature of the heating device (oven) 170 set to 180°C. Graph a12 is the graph obtained by heating with the heating temperature of the heating device (oven) 170 set to 190°C, and graph a13 is the graph obtained by heating with the heating temperature of the heating device (oven) 170 set to 200°C.

[0074] In Figure 8, graphs b11 to b13 (solid lines) schematically show the relationship between the heating time [s] of the heating device (oven) 170 and the particle size [μm] of the "medium-temperature expanding" microcapsule M2 (thermal-expandable microcapsule 21C). Here, graph b11 is obtained by heating with the heating temperature of the heating device (oven) 170 set to 180°C. Graph b12 is obtained by heating with the heating temperature of the heating device (oven) 170 set to 190°C, and graph b13 is obtained by heating with the heating temperature of the heating device (oven) 170 set to 200°C.

[0075] As shown in Figure 8, when the heating temperature of the heating device (oven) 170 is set to 180°C, the gel fraction [%] of the thermosetting resin in the low-temperature curing varnish N11 shown in graph a11 reaches a predetermined value G2 at a heating time Te [s] (area enclosed in a circle in graph a11). The predetermined value G2 shown in Figure 8 is the gel fraction [%] of the thermosetting resin in the low-temperature curing varnish N11 constituting the finishing varnish layer 22 that reaches a predetermined curing state where the particle size change of the microcapsules M2 (thermally expandable microcapsules 21C) is stopped. At this heating time Te [s], the particle size [μm] of the "medium-temperature expanding" microcapsules M2 (thermally expandable microcapsules 21C) shown in graph b11 is a particle size [μm] that corresponds to an expansion rate of approximately 95%, having contracted very slightly immediately after maximum expansion (area enclosed in a circle in graph b11).

[0076] Furthermore, as shown in Figure 8, when the heating temperature of the heating device (oven) 170 is set to 190°C, the gel fraction [%] of the thermosetting resin in the low-temperature curing varnish N11 shown in graph a12 reaches a predetermined value G2 at a heating time Td [s] (area enclosed in a circle in graph a12). At this heating time Td [s], the particle size [μm] of the microcapsule M2 (thermally expandable microcapsule 21C) shown in graph b12 is approximately the same as the maximum expansion diameter, corresponding to a particle size [μm] with an expansion rate of approximately 99% (area enclosed in a circle in graph b12).

[0077] Furthermore, as shown in Figure 8, when the heating temperature of the heating device (oven) 170 is set to 200°C, the gel fraction [%] of the thermosetting resin in the low-temperature curing varnish N11 shown in graph a13 reaches a predetermined value G2 at a heating time Tc [s] (area enclosed in a circle in graph a13). At this heating time Tc [s], the particle size [μm] of the microcapsule M2 (thermally expandable microcapsule 21C) shown in graph b13 has not reached its maximum expansion but has expanded relatively significantly, corresponding to a particle size [μm] with an expansion rate of approximately 75% (area enclosed in a circle in graph b13).

[0078] In this example shown in Figure 8, regardless of whether the heating temperature of the heating device (oven) 170 is set to 180°C, 190°C, or 200°C, relatively large irregularities are formed on the outer surface 11 of the can body 10 based on the relatively large-expanded microcapsules M1. Furthermore, when the heating temperature of the heating device 170 is set to 190°C, the particle size change of the "medium-temperature expanding" microcapsules M2 can be stopped at approximately the same size as the maximum expansion diameter. As a result, extremely large irregularities are formed on the outer surface 11 of the can body 10.

[0079] Based on the points explained in the examples in Figures 7 and 8, in the manufacturing method of the metal container 1 according to this embodiment, in the drying step S5, the heating temperature [°C] and heating time [s] for the finishing varnish layer 22 are set in the heating device (oven) 170, taking into consideration the particle size change characteristics of the thermally expandable microcapsules 21C. In other words, the heating temperature [°C] and heating time [s] in the heating device 170 are set so that the thermally expandable microcapsules 21C reach a desired particle size state at the heating time [s] in which the thermosetting resin in the finishing varnish layer 22 reaches a predetermined curing state. At this time, the heating time [s] in the heating device 170 is set so that the heating time [s] in which the thermosetting resin in the finishing varnish layer 22 reaches a predetermined curing state is included. For example, if the heating time [s] in which the thermosetting resin in the finishing varnish layer 22 reaches a predetermined curing state is 15s, the heating time [s] in the heating device 170 may be set to 20s.

[0080] Here, an example of the heat treatment process in the heating device (oven) 170 will be described. The heating device (oven) 170 includes, for example, a control unit (not shown) consisting of a CPU, and an arbitrary memory (not shown). This memory stores graph data showing the relationship between the heating time [s] of the heating device 170 and the gel fraction [%] of the thermosetting resin in the finishing varnish layer 22 at each of several heating temperatures [°C]. This memory also stores graph data showing the relationship between the heating time [s] of the heating device 170 and the particle size [μm] of the thermally expandable microcapsules 21C in the printing layer 21 at each of several heating temperatures [°C].

[0081] Furthermore, the heating device (oven) 170 includes, for example, an information input unit (not shown) for inputting information on the finishing varnish layer 22 to be used and the thermally expandable microcapsules 21C to be used. The heating device 170 also includes, for example, an operation reception unit (not shown) for receiving operations to specify the heating temperature [°C] and heating time [s]. The heating device 170 also includes, for example, a display unit (not shown) that displays a graph showing the relationship between the heating time [s] of the heating device 170, the gel fraction [%] of the thermosetting resin in the finishing varnish layer 22 to be used, and the particle size [μm] of the thermally expandable microcapsules 21C to be used, based on data stored in memory.

[0082] In the heating device 170, suppose that information about the finishing varnish layer 22 and the thermally expandable microcapsules 21C to be used is input into the information input unit, for example, by an operator's input operation. Then, based on this information, the control unit reads data from the memory to a graph showing the relationship between the gel fraction [%] of the thermosetting resin in the finishing varnish layer 22 to be used and the particle size [μm] of the thermally expandable microcapsules 21C to be used, and controls the display unit to display this graph.

[0083] For example, suppose an operator, referring to the graph displayed on the display unit, specifies the heating temperature [°C] for the finishing varnish layer 22 and the heating time [s] for the heating device 170, and this operation is received by the operation reception unit. Then, the control unit of the heating device 170 sets the heating temperature [°C] and heating time [s] in the heating device 170 based on the specified operation received by the operation reception unit. Then, the heating device (oven) 170 performs heating at the set heating temperature [°C] and heating time [s].

[0084] Furthermore, the control unit, memory, information input unit, operation reception unit, and display unit described herein may each be integrated with or separate from the heating device (oven) 170, either in whole or in part.

[0085] In the heating device (oven) 170, heating is performed at the set heating temperature [°C] and heating time [s], thereby expanding the thermally expandable microcapsules 21C in the printed layer 21 while curing the thermosetting resin in the finishing varnish layer 22. This expands the thermally expandable microcapsules 21C to a desired particle size for a predetermined curing time [s] at which the thermosetting resin in the finishing varnish layer 22 stops changing the particle size of the thermally expandable microcapsules 21C. In this way, the manufacturing method of the metal container 1 according to this embodiment makes it possible to efficiently form irregularities of a desired size on the outer surface 11 of the can body 10.

[0086] [Examples] Next, we will describe the tests (examples) that were actually conducted based on this embodiment.

[0087] (Heating Test 1) As thermally expandable microcapsules, we prepared FN-80GSD (low temperature expansion type), FN-100SSD (medium temperature expansion type), and FN-190SSD (ultra-high temperature expansion type), all manufactured by Matsumoto Oil & Fat Pharmaceutical Co., Ltd. Then, we prepared 20g of microcapsule-containing ink by adding FN-80GSD (low temperature expansion type) at concentrations (addition rates) of 0.5wt%, 1.5wt%, and 2.5wt% to black ink (CPDI, 97 black) manufactured by Matsui Kagaku Co., Ltd. We also prepared 20g of microcapsule-containing ink by adding FN-100SSD (medium temperature expansion type) at concentrations (addition rates) of 0.5wt%, 1.5wt%, and 2.5wt% to black ink (CPDI, 97 black) manufactured by Matsui Kagaku Co., Ltd. In addition, 20g of microcapsule-containing ink was prepared by adding FN-190SSD (ultra-high temperature expansion type) to black ink (CPDI, 97 black) manufactured by Matsui Kagaku Co., Ltd. at concentrations (addition rate) of 0.5 wt%, 1.5 wt%, and 2.5 wt%.

[0088] Then, using an RI tester, the prepared microcapsule-containing ink was spread onto the outer surface of an ADI can (350 ml) used as a substrate, forming a printed layer of microcapsule-containing ink. When spreading the ink, the amount of ink supplied to the roller was 0.3 cc for the first can, and 0.05 cc was added for subsequent cans. In this case, the amount of microcapsule-containing ink per can was 55 ± 10 mg.

[0089] Subsequently, using a test coater, a finishing varnish layer was formed on the printed layer of the microcapsule-containing ink by applying DIC Graphics Co., Ltd.'s 2W143-06 (current varnish) as a finishing varnish. At this time, the amount of finishing varnish applied was 100 ± 15 mg per can. Then, the ADI cans with the printed layer and finishing varnish layer formed were heated and dried in a research oven (heating device). This formed irregularities on the outer surface of the ADI can based on the thermally expandable microcapsules.

[0090] Figure 9 is an example graph showing the relationship between the heating time [s] of the research oven (heating device) when the set temperature [°C] is set to 200°C, the gel fraction [%] of the thermosetting resin in the finishing varnish layer (2W143-06 (current varnish)), and the particle size [μm] of the thermally expandable microcapsules (FN-100SSD (medium temperature expansion type)) in the printed layer.

[0091] In the example shown in Figure 9, the gel fraction [%] of the thermosetting resin in 2W143-06 (current varnish) shown in graph a21 reaches a predetermined value G3 at a heating time Ti [s] (area enclosed in a circle in graph a21). This predetermined value G3 is the gel fraction [%] of the thermosetting resin in the finishing varnish layer (2W143-06) that reaches a predetermined cured state where the particle size change of the thermally expandable microcapsules (FN-100SSD) is stopped. At this heating time Ti [s], the particle size [μm] of the thermally expandable microcapsules (FN-100SSD (medium temperature expansion type)) shown in graph b21 becomes a particle size [μm] that corresponds to an expansion rate of approximately 80%, close to the maximum expansion (area enclosed in a circle in graph b21).

[0092] In the example shown in Figure 9, at a heating time Ti (= approximately 13 s) at which the gel fraction [%] of the thermosetting resin in 2W143-06 (current varnish) constituting the finishing varnish layer reaches a predetermined value G3 (= approximately 78%), the thermally expandable microcapsules (FN-100SSD (medium temperature expansion type)) reach a particle size [μm] corresponding to an expansion rate of approximately 80%. In heating test 1, considering the example in Figure 9, when using the thermally expandable microcapsules (FN-100SSD (medium temperature expansion type)), the heating temperature [°C] in the research oven (heating device) was set to 200°C, and the heating time [s] in the research oven (heating device) was set to a time including the heating time Ti (= approximately 13 s) shown in Figure 9 (20 s as an example).

[0093] In this heating test 1, even when using other thermally expandable microcapsules (FN-80GSD (low-temperature expansion type), FN-190SSD (ultra-high-temperature expansion type)), the heating temperature [°C] in the research oven (heating device) was set to 200°C, and the heating time [s] in the research oven (heating device) was set appropriately. At this time, the heating time [s] in the research oven was set so that it included a heating time [s] in which the thermosetting resin in the finishing varnish layer (2W143-06 (current varnish)) reaches a predetermined curing state where the particle size change of the thermally expandable microcapsules is stopped.

[0094] For each type of thermally expandable microcapsule (FN-80GSD (low temperature expansion type), FN-100SSD (medium temperature expansion type), FN-190SSD (ultra-high temperature expansion type)), heating was performed in a research oven (heating device) at a set heating temperature of 200°C and a set heating time [s]. This expanded the thermally expandable microcapsules in the printed layer while curing the thermosetting resin in the finishing varnish layer (2W143-06). By appropriately expanding each thermally expandable microcapsule, irregularities corresponding to the particle size state (expansion state) of the thermally expandable microcapsules were formed on the outer surface of the ADI can.

[0095] (Heating Test 2) When using FN-80GSD (low-temperature expansion type), FN-100SSD (medium-temperature expansion type), and FN-190SSD (ultra-high temperature expansion type) as thermally expandable microcapsules, the concentration (addition rate) of thermally expandable microcapsules in the microcapsule-containing ink was uniformly set to 1.5 wt%. In addition, 2WB301-2 (low-temperature curing varnish) manufactured by DIC Graphics Co., Ltd. was used as the finishing varnish applied to the printed layer of the microcapsule-containing ink. Furthermore, the heating temperature [°C] in the research oven (heating device) was set to 170°C, 180°C, 190°C, and 200°C. Otherwise, the test to form irregularities was conducted in the same manner as in Heating Test 1.

[0096] (Evaluation item 1: Surface roughness) The surface roughness of the finishing varnish layer, which serves as an indicator of foaming properties, was measured using a surface roughness meter (SURFCOM2000SD3, manufactured by Tokyo Seimitsu Co., Ltd.) for the irregularities formed on the outer surface of the ADI can during heating tests 1 and 2. Here, the measured values ​​used for surface roughness measurement were the arithmetic mean roughness Ra [μm] and the maximum height roughness Rmax [μm] of the finishing varnish layer. The measurement results for the arithmetic mean roughness Ra [μm] and maximum height roughness Rmax [μm] in heating test 1 are shown in Figure 10. The measurement results for the arithmetic mean roughness Ra [μm] and maximum height roughness Rmax [μm] in heating test 2 are shown in Figure 12.

[0097] (Evaluation Item 2: Gross Value) In heating tests 1 and 2, the gloss value (glossiness), which is an indicator of glossiness, was measured for the irregularities formed on the outer surface of the ADI can using a measuring device (handheld gloss meter Gloss Checker IG410 (manufactured by Horiba, Ltd.)). In this measurement, the gloss value [-] (unitless) at a 60° reflection angle was measured. On the outer surface of the ADI can, a lower gloss value [-] indicates a more matte (non-glossy) appearance, while a higher gloss value indicates a more glossy (glossy) appearance. The measurement results of the gloss value [-] in heating test 1 are shown in Figure 11. The measurement results of the gloss value [-] in heating test 2 are shown in Figure 13.

[0098] (Evaluation of Heat Test 1) In Figure 10, which shows the measurement results of the arithmetic mean roughness Ra [μm] and maximum height roughness Rmax [μm] when irregularities were formed in heating test 1, plot P11 shows Ra (=0.22 [μm]) and Rmax (=2.67 [μm]) when using microcapsule-containing ink made by adding 0.5 wt% FN-80GSD (low-temperature expanding type) to black ink (CPDI, 97 black). Plot P12 shows Ra (=0.43 [μm]) and Rmax (=3.17 [μm]) when using microcapsule-containing ink made by adding 1.5 wt% FN-80GSD (low-temperature expanding type) to black ink (CPDI, 97 black). Plot P13 shows the Ra (=0.65 [μm]) and Rmax (=4.11 [μm]) when using a microcapsule-containing ink prepared by adding 2.5 wt% of FN-80GSD (low-temperature expansion type) to black ink (CPDI, 97 black).

[0099] Plot P21 shows the Ra (=0.46 [μm]) and Rmax (=5.29 [μm]) when using a microcapsule-containing ink prepared by adding 0.5 wt% FN-100SSD (medium-temperature expanding type) to black ink (CPDI, 97 black). Plot P22 shows the Ra (=0.77 [μm]) and Rmax (=5.63 [μm]) when using a microcapsule-containing ink prepared by adding 1.5 wt% FN-100SSD (medium-temperature expanding type) to black ink (CPDI, 97 black). Plot P23 shows the Ra (=1.03 [μm]) and Rmax (=6.12 [μm]) when using a microcapsule-containing ink prepared by adding 2.5 wt% FN-100SSD (medium-temperature expanding type) to black ink (CPDI, 97 black).

[0100] Plot P31 shows the Ra (=0.07 [μm]) and Rmax (=1.33 [μm]) when using a microcapsule-containing ink made by adding 0.5 wt% FN-190SSD (ultra-high temperature expansion type) to black ink (CPDI, 97 black). Plot P32 shows the Ra (=0.09 [μm]) and Rmax (=2.3 [μm]) when using a microcapsule-containing ink made by adding 1.5 wt% FN-190SSD (ultra-high temperature expansion type) to black ink (CPDI, 97 black). Plot P33 shows the Ra (=0.12 [μm]) and Rmax (=2.58 [μm]) when using a microcapsule-containing ink made by adding 2.5 wt% FN-190SSD (ultra-high temperature expansion type) to black ink (CPDI, 97 black).

[0101] In Figure 11, which shows the measurement results of the gross value [-] when unevenness is formed in heating test 1, graph C11 shows a gross value of 24.67 [-] when using microcapsule-containing ink made by adding 0.5 wt% FN-80GSD (low-temperature expansion type) to black ink (CPDI, 97 black). Graph C12 shows a gross value of 23.5 [-] when using microcapsule-containing ink made by adding 1.5 wt% FN-80GSD (low-temperature expansion type) to black ink (CPDI, 97 black). Graph C13 shows a gross value of 21.67 [-] when using microcapsule-containing ink made by adding 2.5 wt% FN-80GSD (low-temperature expansion type) to black ink (CPDI, 97 black).

[0102] Furthermore, Graph C21 shows a gross value of 21.67[-] when using microcapsule-containing ink prepared by adding 0.5 wt% FN-100SSD (medium temperature expansion type) to black ink (CPDI, 97 black). Graph C22 shows a gross value of 19.83[-] when using microcapsule-containing ink prepared by adding 1.5 wt% FN-100SSD (medium temperature expansion type) to black ink (CPDI, 97 black). Graph C23 shows a gross value of 18.17[-] when using microcapsule-containing ink prepared by adding 2.5 wt% FN-100SSD (medium temperature expansion type) to black ink (CPDI, 97 black).

[0103] Furthermore, Graph C31 shows a gross value of 26.17[-] when using microcapsule-containing ink prepared by adding 0.5 wt% FN-190SSD (ultra-high temperature expansion type) to black ink (CPDI, 97 black). Graph C32 shows a gross value of 25.67[-] when using microcapsule-containing ink prepared by adding 1.5 wt% FN-190SSD (ultra-high temperature expansion type) to black ink (CPDI, 97 black). Graph C33 shows a gross value of 25.17[-] when using microcapsule-containing ink prepared by adding 2.5 wt% FN-190SSD (ultra-high temperature expansion type) to black ink (CPDI, 97 black).

[0104] As shown in plots P21-P23 of Figure 10, in heating test 1 using 2W143-06 (current varnish) as the finishing varnish, the maximum height roughness Rmax [μm] was larger when FN-100SSD (medium temperature expansion type) was used as the thermally expandable microcapsule compared to when FN-80GSD (low temperature expansion type) and FN-190SSD (very high temperature expansion type) were used. Furthermore, the largest values ​​were obtained for both the arithmetic mean roughness Ra [μm] and the maximum height roughness Rmax [μm] when the content concentration (addition rate) of FN-100SSD (medium temperature expansion type) in the microcapsule-containing ink was 2.5 wt%.

[0105] As shown in Figure 10, regardless of which of the thermally expandable microcapsules used—FN-80GSD (low temperature expansion type), FN-100SSD (medium temperature expansion type), or FN-190SSD (ultra-high temperature expansion type)—the higher the content concentration (addition rate) [wt%], the higher the surface roughness value (arithmetic mean roughness Ra [μm] and maximum height roughness Rmax [μm]).

[0106] Furthermore, as can be seen from Figures 10 and 11, the larger the surface roughness values ​​(arithmetic mean roughness Ra [μm], maximum height roughness Rmax [μm]), the smaller the resulting gloss value [-]. For example, when using the FN-100SSD (medium temperature expansion type) and obtaining the largest values ​​for arithmetic mean roughness Ra [μm] and maximum height roughness Rmax [μm] as shown in plot P23, the resulting gloss value [-] was the smallest, as shown in graph C23 of Figure 11. In other words, in this case, the foam printing applied to the outer surface of the ADI can had a matte finish (suppressed gloss) along with a high degree of foaminess due to relatively large irregularities.

[0107] Under the conditions of heating test 1 when the measurement results shown in Figures 10 and 11 were obtained, for example, FN-80GSD (low-temperature expansion type) or FN-100SSD (medium-temperature expansion type) can be used as the thermally expandable microcapsules. In this case, the finishing varnish layer on the printed layer can form irregularities with an arithmetic mean roughness Ra of 0.2 μm or more and a maximum height roughness Rmax of 2.5 μm or more.

[0108] (Evaluation of Heat Test 2) In Figure 12, which shows the measurement results of the arithmetic mean roughness Ra [μm] and maximum height roughness Rmax [μm] when irregularities were formed in heating test 2, plot P41 shows Ra (=0.63 [μm]) and Rmax (=5.62 [μm]) when a microcapsule-containing ink containing FN-80GSD (low-temperature expansion type) in black ink (CPDI, 97 black) was heated at a heating temperature of 170°C. Plot P42 shows Ra (=0.58 [μm]) and Rmax (=5.22 [μm]) when a microcapsule-containing ink containing FN-80GSD (low-temperature expansion type) in black ink (CPDI, 97 black) was heated at a heating temperature of 180°C. Plot P43 shows the Ra (=0.56 [μm]) and Rmax (=4.45 [μm]) when a microcapsule-containing ink containing FN-80GSD (low-temperature expansion type) in black ink (CPDI, 97 black) is heated at a heating temperature of 190°C. Plot P44 shows the Ra (=0.5 [μm]) and Rmax (=3.97 [μm]) when a microcapsule-containing ink containing FN-80GSD (low-temperature expansion type) in black ink (CPDI, 97 black) is heated at a heating temperature of 200°C.

[0109] Plot P51 shows the Ra (=1.37 [μm]) and Rmax (=8.01 [μm]) when a microcapsule-containing ink containing FN-100SSD (medium-temperature expanding type) in black ink (CPDI, 97 black) is heated at a heating temperature of 170°C. Plot P52 shows the Ra (=1.24 [μm]) and Rmax (=7.18 [μm]) when a microcapsule-containing ink containing FN-100SSD (medium-temperature expanding type) in black ink (CPDI, 97 black) is heated at a heating temperature of 180°C. Plot P53 shows the Ra (=1.15 [μm]) and Rmax (=6.29 [μm]) when a microcapsule-containing ink containing FN-100SSD (medium-temperature expanding type) in black ink (CPDI, 97 black) is heated at a heating temperature of 190°C. Plot P54 shows the Ra (=1 [μm]) and Rmax (=5.9 [μm]) when a microcapsule-containing ink containing FN-100SSD (medium temperature expansion type) in black ink (CPDI, 97 black) is heated at a heating temperature of 200°C.

[0110] Plot P61 shows the Ra (=0.08 [μm]) and Rmax (=0.76 [μm]) when a microcapsule-containing ink containing FN-190SSD (ultra-high temperature expansion type) in black ink (CPDI, 97 black) is heated at a heating temperature of 170°C. Plot P62 shows the Ra (=0.09 [μm]) and Rmax (=0.97 [μm]) when a microcapsule-containing ink containing FN-190SSD (ultra-high temperature expansion type) in black ink (CPDI, 97 black) is heated at a heating temperature of 180°C. Plot P63 shows the Ra (=0.11 [μm]) and Rmax (=1.35 [μm]) when a microcapsule-containing ink containing FN-190SSD (ultra-high temperature expansion type) in black ink (CPDI, 97 black) is heated at a heating temperature of 190°C. Plot P64 shows the Ra (=0.13 [μm]) and Rmax (=1.96 [μm]) when a microcapsule-containing ink containing FN-190SSD (ultra-high temperature expansion type) in black ink (CPDI, 97 black) is heated at a heating temperature of 200°C.

[0111] In Figure 13, which shows the measurement results of the gross value [-] when unevenness is formed in heating test 2, graph C41 shows a gross value of 21.17 [-] when a microcapsule-containing ink containing FN-80GSD (low-temperature expansion type) in black ink (CPDI, 97 black) is heated at a heating temperature of 170°C. Graph C42 shows a gross value of 21.67 [-] when a microcapsule-containing ink containing FN-80GSD (low-temperature expansion type) in black ink (CPDI, 97 black) is heated at a heating temperature of 180°C. Graph C43 shows a gross value of 22.17 [-] when a microcapsule-containing ink containing FN-80GSD (low-temperature expansion type) in black ink (CPDI, 97 black) is heated at a heating temperature of 190°C. Graph C44 shows a gross value of 22.33[-] when a microcapsule-containing ink containing FN-80GSD (low-temperature expansion type) in black ink (CPDI, 97 black) is heated at a heating temperature of 200°C.

[0112] Furthermore, Graph C51 shows a gross value of 15.5[-] when a microcapsule-containing ink containing FN-100SSD (medium-temperature expanding type) in black ink (CPDI, 97 black) is heated at a heating temperature of 170°C. Graph C52 shows a gross value of 17.83[-] when a microcapsule-containing ink containing FN-100SSD (medium-temperature expanding type) in black ink (CPDI, 97 black) is heated at a heating temperature of 180°C. Graph C53 shows a gross value of 18.83[-] when a microcapsule-containing ink containing FN-100SSD (medium-temperature expanding type) in black ink (CPDI, 97 black) is heated at a heating temperature of 190°C. Graph C54 shows a gross value of 19.67[-] when a microcapsule-containing ink containing FN-100SSD (medium temperature expansion type) in black ink (CPDI, 97 black) is heated at a heating temperature of 200°C.

[0113] Furthermore, Graph C61 shows a gross value of 27.17[-] when a microcapsule-containing ink containing FN-190SSD (ultra-high temperature expansion type) in black ink (CPDI, 97 black) is heated at a heating temperature of 170°C. Graph C62 shows a gross value of 26.83[-] when a microcapsule-containing ink containing FN-190SSD (ultra-high temperature expansion type) in black ink (CPDI, 97 black) is heated at a heating temperature of 180°C. Graph C63 shows a gross value of 24.83[-] when a microcapsule-containing ink containing FN-190SSD (ultra-high temperature expansion type) in black ink (CPDI, 97 black) is heated at a heating temperature of 190°C. Graph C64 shows a gross value of 24.5[-] when a microcapsule-containing ink containing FN-190SSD (ultra-high temperature expansion type) in black ink (CPDI, 97 black) is heated at a heating temperature of 200°C.

[0114] As shown in plots P51-P54 of Figure 12, in heating test 2, in which unevenness was formed using 2WB301-2 (low-temperature curing varnish) as the finishing varnish, the arithmetic mean roughness Ra [μm] and maximum height roughness Rmax [μm] were larger when FN-100SSD (medium-temperature expanding type) was used as the thermally expandable microcapsule compared to when FN-80GSD (low-temperature expanding type) and FN-190SSD (ultra-high temperature expanding type) were used. Furthermore, when using FN-100SSD (medium-temperature expanding type) in the microcapsule-containing ink, the largest values ​​for both arithmetic mean roughness Ra [μm] and maximum height roughness Rmax [μm] were obtained at the lowest heating temperature of 170°C.

[0115] As shown in Figure 12, even when the type of finishing varnish layer, the type of thermally expandable microcapsules, and the content concentration (addition rate) [wt%] of thermally expandable microcapsules were the same, changing the heating temperature [°C] in the research oven (heating device) resulted in different values ​​for the obtained arithmetic mean roughness Ra [μm] and maximum height roughness Rmax [μm]. In other words, even under the same conditions for the type of finishing varnish layer, the type of thermally expandable microcapsules, and the content concentration (addition rate) [wt%] of thermally expandable microcapsules, changing the heating temperature [°C] in the research oven (heating device) changes the curing state of the finishing varnish layer and the particle size change characteristics of the thermally expandable microcapsules. As a result, the particle size state of the thermally expandable microcapsules differs at the heating time [s] in which the thermosetting resin constituting the finishing varnish layer reaches a predetermined curing state where the particle size change of the thermally expandable microcapsules stops. Consequently, it is thought that the state of unevenness corresponding to that particle size state differs.

[0116] Furthermore, as can be seen from Figures 12 and 13, the larger the surface roughness values ​​(arithmetic mean roughness Ra [μm], maximum height roughness Rmax [μm]), the smaller the resulting gloss value [-]. For example, when using the FN-100SSD (medium temperature expansion type) and obtaining the largest values ​​for arithmetic mean roughness Ra [μm] and maximum height roughness Rmax [μm] as shown in plot P51, the resulting gloss value [-] was the smallest, as shown in graph C51 of Figure 13. In other words, in this case, the foam printing applied to the outer surface of the ADI can had a matte finish (suppressed gloss) along with a high degree of foaminess due to relatively large irregularities.

[0117] Under the conditions of heating test 2 when the measurement results shown in Figures 12 and 13 were obtained, for example, FN-80GSD (low-temperature expansion type) or FN-100SSD (medium-temperature expansion type) can be used as the thermally expandable microcapsules. In this case, the finishing varnish layer on the printed layer can form irregularities with an arithmetic mean roughness Ra of 0.2 μm or more and a maximum height roughness Rmax of 2.5 μm or more.

[0118] [summary] As described above, in the manufacturing method of the metal container 1 according to this embodiment, in order to form irregularities of a desired size on the outer surface 11 of the can body 10, the heating temperature [°C] and heating time [s] for the finishing varnish layer 22 are set in the heating device, taking into consideration the particle size change characteristics of the thermally expandable microcapsules 21C used. This allows the thermally expandable microcapsules 21C to expand to the desired particle size state in a heating time [s] at which the thermosetting resin in the finishing varnish layer 22 reaches a predetermined curing state where the particle size change of the thermally expandable microcapsules 21C stops. In this way, the manufacturing method of the metal container 1 according to this embodiment can efficiently form irregularities of a desired size on the outer surface 11 of the can body 10.

[0119] Although this embodiment has been described in detail above with reference to the drawings, the specific configuration is not limited to the embodiment described above. Furthermore, any design changes, etc., that do not depart from the gist of the present invention are also included in this invention. In addition, the examples of each configuration described above can be combined by utilizing each other's technologies, as long as there are no particular contradictions or problems in their purpose and configuration. [Explanation of Symbols]

[0120] 1: Metal container, 10: Can body, 11: Outer surface, 12: Opening, 13: Bottom, 21: Printing layer, 21A: Ink, 21B: Printing ink material, 21C: Thermally expandable microcapsules, 22: Finishing varnish layer, 22A: Finishing varnish, 100: Printing device, 110: Inking unit, 110a~110h: First inking unit~Eighth inking unit, 111: Ink supply unit, 111a~111h: First ink supply unit~Eighth ink supply unit, 112: Ink roller group, 113: Plate cylinder, 113a~113h: 1st plate cylinder to 8th plate cylinder, 114: Printing plate, 114a~114h: 1st printing plate to 8th printing plate, 120: Blanket wheel, 121: Segment, 122: Support shaft, 125: Blanket, 130: Conveyor unit, 140: Mandrel wheel, 141: Mandrel, 150: Burnish applicator, 160: Transfer unit, 170: Heating device (oven)

Claims

1. A manufacturing method for producing a metal container having foam printing applied to the outer surface of the can body, A printing layer formation step in which a printing layer made of ink containing thermally expandable microcapsules is formed on the outer surface of the can body, A finishing varnish layer formation step is performed to form a finishing varnish layer on the printed layer, which consists of a varnish made by dissolving a thermosetting resin in a solvent. The process includes a drying step of drying the can body on which the printed layer and the finishing varnish layer are formed by heating, In the drying process, Considering the particle size change characteristics of the thermally expandable microcapsules, the heating temperature and heating time for the finishing varnish layer are set, and by heating at the set heating temperature and heating time, the thermally expandable microcapsules in the printed layer are expanded while the thermosetting resin in the finishing varnish layer is cured, and the thermally expandable microcapsules are expanded to a desired particle size state at a heating time when the thermosetting resin in the finishing varnish layer reaches a predetermined curing state where the particle size change of the thermally expandable microcapsules stops. A method for manufacturing a metal container, characterized by the following:

2. The original particle size of the aforementioned thermally expandable microcapsule is 20 μm or less. A method for manufacturing a metal container according to feature 1.

3. The concentration of the thermally expandable microcapsules in the ink is 2.5 wt% or less. A method for manufacturing a metal container according to feature 1.

4. A metal container having foam printing applied to the outer surface of the can body, The aforementioned can body has a printed layer made of ink containing thermally expandable microcapsules and a finishing varnish layer made of a finishing varnish in which a thermosetting resin is dissolved in a solvent, formed on its outer surface in this order and dried by heating. The thermosetting resin in the finishing varnish layer is cured while the thermally expandable microcapsules are expanded to a desired particle size. The finishing varnish layer on the printed layer has an arithmetic mean roughness Ra of 0.2 μm or more and a maximum height roughness Rmax of 2.5 μm or more. A metal container characterized by the following features.

5. The original particle size of the aforementioned thermally expandable microcapsule is 20 μm or less. The metal container according to feature 4.

6. The concentration of the thermally expandable microcapsules in the ink is 2.5 wt% or less. The metal container according to feature 4.

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