Printing method for metal containers

Abstract

To provide a printing method of a metal container having a clear and highly durable identification display.SOLUTION: In a printing method of a metal container, a bandgap of at least one kind of pigment contained in a painting layer is smaller than light energy hν of a laser beam to be emitted. The metal container includes a body having a lid part attached so as to close a cylindrical part and both ends of the cylindrical part, which is composed of metal. The body in which a painting layer constituting an outer face of the body is formed includes a discoloration part provided by discoloring a part including a surface of the painting layer by a laser beam of a wavelength of visible light or UV, and the discoloration part is formed in the range of 0.3-10 μm from the surface of the painting layer. The laser beam includes a plurality of laser beams emitted from a plurality of heads arranged in a row, and the discoloration part is formed of the plurality of laser beams.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a method for printing on a metal container, and more particularly to a method for applying an identification mark to the surface by using a laser beam. [Background technology]

[0002] Conventionally, metal containers such as drums and pails have been painted in a variety of colors and further marked with surface identification marks to distinguish between different types. Although there are many combinations of paint colors and surface identification marks, drums are manufactured while controlling the type of drum according to manufacturing instructions, etc. Surface identification marks are, for example, sprayed with paint, silkscreen printed, printed with a stamp, or attached with a sticker. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2003-285811 Summary of the Invention [Problem to be solved by the invention]

[0004] In the manufacturing process of metal containers such as drums, a wide variety of different colored drums must be sent through a single production line, making it necessary to apply complex identification markings within a short takt time. When printing on the surface of metal containers by spraying paint, silkscreen printing, stamping, or other methods, there are issues such as the print becoming faint and unclear, and limitations in expressing complex characters or symbols. Furthermore, the print can peel off during use of the metal container, posing an issue regarding the durability of the identification markings.

[0005] The present invention aims to solve the above problems and provides a method for printing on metal containers a clear and durable identification mark. [Means for solving the problem]

[0006] The printing method for metal containers according to the present invention involves printing on a metal container, and the band gap of at least one type of pigment contained in a paint layer is smaller than the light energy hν of the irradiated laser light. The metal container comprises a body made of metal, having a cylindrical portion and lid portions attached to close both ends of the cylindrical portion, the body having the paint layer that forms the outer surface of the body formed thereon, and a discolored portion formed by discoloring a portion including the surface of the paint layer with the laser light of a visible or UV wavelength, the discolored portion being formed in a range of 0.3 μm to 10 μm from the surface of the paint layer, the laser light including multiple laser beams irradiated from multiple heads arranged side by side, and the discolored portion being formed by the multiple laser beams. [Effects of the Invention]

[0007] According to the present invention, a printing area is created by discoloring a portion of the coating layer, including the surface, using laser light of visible or UV wavelengths, thereby providing a printing method for metal containers with identification marks that are highly durable. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is an external perspective view showing an example of a metal container 100 according to a first embodiment. [Figure 2] 1 is an enlarged view of the cross-sectional structure of the print section 10 of the metal container 100 according to the first embodiment. [Figure 3] 1 is a schematic diagram of a laser beam 30 irradiated onto a metal container 100 according to the first embodiment. [Figure 4] 1 is a schematic diagram of a part of a manufacturing apparatus 90 for a metal container 100 according to a first embodiment. [Figure 5] 1 is a diagram showing an example of a functional configuration related to control of a laser marking step of an apparatus 90 for manufacturing a metal container 100 according to the first embodiment. [Figure 6] 1 is an example of a flowchart of control of a laser marking step of the manufacturing apparatus 90 for the metal container 100 according to the first embodiment. [Figure 7] 1 shows examples of the paint colors, paints, and components contained in the metal container 100 according to the first embodiment, and the color development of the printed portion 10 with each paint color. [Figure 8] 1 shows an example of the appearance of the printing section 10 of the metal container 100. [Figure 9] FIG. 10 is a diagram showing examples in which laser marking was performed on each paint color and the evaluation results thereof. [Figure 10] FIG. 1 is a diagram showing examples and comparative examples in which printing such as laser marking is applied to each paint color, and the evaluation results thereof. [Figure 11] 10 shows an example of the results of composition analysis by X-ray diffraction of a discolored portion of the printed portion 10 of the metallic container 100 according to the first embodiment. [Figure 12] 10 shows an example of the results of composition analysis by X-ray diffraction of a discolored portion of the printed portion 10 of the metallic container 100 according to the first embodiment. [Figure 13] 1 is a schematic diagram of a reduction reaction of Fe2O3 caused by laser light irradiation of the printed portion 10 of the metallic container 100 according to the first embodiment. [Figure 14] 2 shows an example of a laser beam irradiated onto the metal container 100 according to the first embodiment. [Figure 15] 1 shows the band gap of the material contained in the coating layer 21 of the metallic container 100 according to the first embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0009] The following describes embodiments based on the drawings. In each drawing, the same reference numerals are used to denote the same or equivalent parts, and this applies throughout the entire specification. Furthermore, the forms of the components shown in the entire specification are merely examples and are not intended to limit the scope of the present invention.

[0010] Embodiment 1 <Configuration of Metal Container 100> FIG. 1 is an external perspective view showing an example of a metal container 100 according to the first embodiment. The metal container 100 according to the first embodiment is, for example, a metal drum, and is exemplified by a drum having an internal capacity of approximately 200 L as specified in JIS Z 1601:2017. However, the metal container 100 is not limited to this, and the concept also includes metal containers of more than 200 L, such as drums, pails, 18L cans, or tanks. Furthermore, drums include not only closed types (tight head drums) in which a base plate and a top plate are joined by seaming to a body, but also open types in which the top plate is detachable from the body.

[0011] 1 is a drum can, and includes a cylindrical portion 101, which is a cylindrical portion called a body, and lid portions 102 at both ends in the central axis direction of the cylindrical portion 101. The lid portion 102 is composed of a lid portion 102A called a top plate provided at one end in the central axis direction of the cylindrical portion 101, and a lid portion 102B called a bottom plate provided at the other end. The cylindrical portion 101 and the lid portion 102 are sometimes collectively referred to as the main body.

[0012] The lids 102 are fixed to both ends of the cylindrical portion 101 by seaming. However, the method of fixing the lids 102 is not limited to seaming, and may be performed by means of welding, crimping, brazing, or the like. Furthermore, the metal container 100 may have not only a configuration in which the lids 102A and 102B are fixed to both ends of the cylindrical portion 101 in the central axis direction to close the cylindrical portion 101, but also a configuration in which only one of the lids is fixed.

[0013] The lid 102A has two openings 103 and 104. The openings 103 and 104 are formed, for example, by attaching a cap to a nozzle, and are used as holes for injecting or discharging liquid from one end and for venting air from the other end. The nozzle and cap that form the openings 103 and 104 are formed so as not to protrude beyond a chime 107 that is formed at the end of the tubular portion 101 of the metal container 100 and protrudes in the direction of the central axis.

[0014] The tubular portion 101 has a generally cylindrical shape and includes a ring-shaped zone 105 (bead) protruding from the middle in the central axis direction. The ring-shaped zone 105 is formed around the entire circumference of the cylindrical tubular portion 101. The ring-shaped zone 105 is provided at multiple locations in the central axis direction. Note that the metal container 100 may not be provided with the ring-shaped zone 105.

[0015] Between the annular zone 105 and the chimes 107 is a cylindrical portion 106, which has a generally smooth cylindrical surface.

[0016] 2 is an enlarged view of the cross-sectional structure of the print section 10 of the metallic container 100 according to embodiment 1. The cylindrical section 101 of the metallic container 100 comprises a metallic base material 20 and a coating layer 21. The base material 20 is made of steel and may have a chemical conversion coating on its surface.

[0017] 7, the coating layer 21 is made of paint for producing the standard drum colors DM-1 to DM-14 or other colors specified by the user. The paint that makes up the coating layer 21 contains the necessary pigment for each color, and the pigments are compounds such as titanium dioxide, carbon black, yellow iron oxide, ferric oxide, chlorinated phthalocyanine green, copper phthalocyanine (pigment blue 15), iron oxyhydroxide, and polybrominated chlorinated copper phthalocyanine.

[0018] As shown in Fig. 1, printed portion 10 is provided on cylindrical portion 101 of metal container 100. In the first embodiment, printed portion 10 is formed by discoloring paint layer 21 using laser marking. In Fig. 1, printed portion 10 is provided on drum portion 106, in a portion above chime 107 on the base plate side.

[0019] As shown in Fig. 2, the printed section 10 has a discolored section 22 formed by laser marking, which is a portion of the coating layer 21 including the surface 23. The discolored section 22 is formed in a range of 0.3 µm to 10 µm from the surface 23, and is formed so as not to reach the base material 20. In Fig. 2, the surface 23 forms the outer surface of the metal container 100. The discolored section 22 is also called a discolored layer, and the non-discolored portion of the coating layer 21 facing the base material 20 of the discolored section 22 is sometimes called a non-discolored layer.

[0020] FIG. 3 is a schematic diagram of the laser beam 30 irradiated onto the metal container 100 according to the first embodiment. The laser beam 30 is composed of light rays in the visible or ultraviolet wavelength range. Lasers are classified into Class 1 to Class 4, and the laser beam 30 according to the first embodiment is a high-power laser of Class 4. The focal point of the laser beam 30 can be moved relative to the surface 23 of the coating layer 21, as shown in FIGS. 3(a) to 3(c). FIG. 3(a) shows a state in which the focal point is focused on the surface 23 of the coating layer 21, FIG. 3(b) shows a state in which the focal point is located further back than the surface 23 (i.e., on the base material 20 side), and FIG. 3(c) shows a state in which the focal point is located closer to the surface 23. When the focal point is located further back or closer to the surface 23 as in FIGS. 3(b) and 3(c), the area irradiated by the laser beam 30 is wider than when the focal point is focused on the surface 23 as in FIG. 3(a). 3 represents the amount of variation in the focal position of the laser light 30 when it is focused on the surface 23. In other words, as the dimension D increases, the area of ​​the surface 23 that is hit by the laser light 30 increases.

[0021] When the laser beam 30 is focused on the surface 23 as shown in Figure 3(a), the amount of energy imparted per unit area of ​​the surface 23 increases, but the irradiation area becomes smaller. This makes it easier to discolor a portion of the coating layer 21, but the area of ​​the discolored portion 22 may be small and visibility may be low. Therefore, in the metal container 100 according to the first embodiment, the focal position of the laser beam 30, the output power of the laser beam 30, and the scanning speed of the laser beam 30 are changed depending on the susceptibility of the paint constituting the coating layer 21 to discoloration, thereby adjusting the visibility of the printed portion 10 as a collection of discolored portions 22.

[0022] 4 is a schematic diagram of a portion of a manufacturing apparatus 90 for manufacturing a metal container 100 according to embodiment 1. The manufacturing apparatus 90 for a metal container 100 includes at least a conveying device 40 for moving the metal container 100, a head 31 for irradiating the metal container 100 with laser light 30, and a positioning jig 32 for determining the position of the metal container 100 when laser marking is performed.

[0023] The conveying device 40 is, for example, a belt conveyor, and is used to place multiple metal containers 100 on it and move them to predetermined positions where each process is performed. The conveying device 40 is sent to the laser marking process. The conveying device 40 moves the metal containers 100 in front of the head 31 that performs laser marking. The moved metal containers 100 abut against a positioning jig 32 and are positioned so that their distance from the head 31 is a predetermined value. The position of the metal container 100 in the feed direction x can be determined by controlling the conveying device 40 or by using a jig 33 that abuts against the metal container 100 from the feed direction x side. The positioning jigs 32 and 33 may be configured so that the distance in the y direction from the head 31 and the position in the x direction can be determined with high accuracy. For example, the metal container 100 can be pressed against the positioning jig 32 from the opposite side of the positioning jig 32 to abut against the positioning jig 32.

[0024] The head 31 irradiates the laser light 30 and is arranged on the side of the conveying device 40. At least one head 31 is arranged on the side of the conveying device 40, and the laser light 30 is irradiated from the head 31 to perform laser marking on the target metal container 100. The manufacturing apparatus 90 according to the first embodiment particularly illustrates a case where the laser marking step is performed using two heads 31, but the present invention is not limited to this.

[0025] In FIG. 4, two heads 31 are arranged side by side in the z direction, and each head irradiates a single metal container 100 placed on the conveying device 40 with a laser beam 30. The laser beam 30 emitted from one head can irradiate an irradiation area 35, for example, 25 cm square. The irradiation areas 35 of two adjacent heads partially overlap each other. This configuration shortens the time required to mark the printing area 10 of the metal container 100 with a predetermined identification mark. Furthermore, even if the printing area 10 has a large area, the irradiation areas 35 of the two heads 31 can cover the entire area of ​​the printing area 10, eliminating the need to divide the laser marking process into two. Furthermore, because multiple heads 31 are used to simultaneously print on the printing area 10, misalignment of the characters or symbols printed by the two heads 31 can be prevented. If two heads 31 were arranged separately for each of the two laser marking processes, the metal container 100 would need to be positioned accurately relative to the heads 31 for each of the two laser marking processes. As a result, there is a risk that the discolored portions 22 of the printed area 10 formed in each of the two laser marking processes will be misaligned. On the other hand, as described above, since printing is performed simultaneously with multiple laser beams 30 using multiple heads 31, the positional deviation of the marks printed with each laser beam 30 can be minimized.

[0026] Furthermore, when the metal container 100 is a drum, the printing unit 10 needs to display a large amount of information, such as marks, numbers, codes, etc., such as JIS and UN marks. Therefore, in the past, the drum was printed with a stamp or the like, and then a label incorporating the identification information was separately attached. On the other hand, the head 31 according to the first embodiment prints the identification marking using a laser beam 30, so that detailed characters or symbols can be printed with high precision. Furthermore, the manufacturing apparatus 90 shown in FIG. 4 performs the laser marking process automatically, thereby preventing problems such as attaching an incorrect label to the metal container 100.

[0027] The manufacturing apparatus 90 in the first embodiment may be equipped with a color identification sensor 36. In the manufacturing apparatus 90, the color identification sensor 36 is disposed, for example, at a position corresponding to the metal container 100 before it enters the laser marking process. That is, in FIG. 4, the color of the surface of the cylindrical portion 101 of the metal container 100 at position A is detected by the color identification sensor 36. The color identification sensor 36 may be disposed inside the head 31 shown in FIG. 4, and may be disposed at any position as long as the color identification sensor 36 can detect the surface of the metal container 100 that has the same paint as the portion irradiated with the laser light 30.

[0028] The color identification sensor 36, for example, irradiates the surface of the metal container 100 with laser light, detects the light reflected from the surface with a light-receiving element, and identifies the color of the surface. The type of paint layer 21 on the metal container 100 is identified by registering the color of the paint layer 21 of the metal container 100 as a sample in advance and detecting whether the color of the metal container 100 flowing through the manufacturing equipment 90 matches any of the registered colors. The control device 50 has a database that associates the registered colors with the irradiation conditions of the laser light 30, and instructs the head 31 on the irradiation conditions that correspond to the color of the paint layer 21.

[0029] The color of the coating layer 21 may be determined by an imaging device 34 provided in the head 31. Also, a color identification sensor 36 may be provided in the head 31.

[0030] The manufacturing apparatus 90 includes a control device 50 for controlling each part of the manufacturing apparatus 90. The control device 50 controls, for example, the irradiation conditions of the laser light 30 of the head 31, the operation of the conveying device 40, and the capture of images by the imaging device, as well as determining the type of the coating layer 21. The control device 50 is communicably connected to each part of the manufacturing apparatus 90 and acquires and transmits information from each part. The control unit 51 includes, for example, a central processing unit (CPU), a read-only memory (ROM), and a random access memory (RAM). The CPU is also referred to as a central processing unit, central arithmetic unit, processor, microprocessor, microcomputer, or digital signal processor (DSP). In the control unit 51, the CPU reads programs and data stored in the ROM and uses the RAM as a work area to perform overall control of the control device 50.

[0031] The storage unit 52 is, for example, a non-volatile semiconductor memory such as a flash memory, an EPROM (Erasable Programmable ROM), or an EEPROM (Electrically Erasable Programmable ROM), and serves as a so-called secondary storage device. In the first embodiment, the storage unit 52 stores information acquired by each unit of the manufacturing apparatus 90. Furthermore, the storage unit 52 stores programs, data, etc. for communication between the control device 50 and each unit constituting the manufacturing apparatus 90.

[0032] FIG. 5 is a diagram showing an example of a functional configuration related to control of the laser marking process of the manufacturing apparatus 90 for metal containers 100 according to the first embodiment. The laser marking process of the manufacturing apparatus 90 for metal containers 100 uses the hardware configuration shown in FIG. 4 to perform laser marking on the metal containers 100 that are transported through the manufacturing apparatus 90. The control device 50 communicates with the head 31, the color identification sensor 36, and the conveying device 40 wirelessly or via a wired connection to control the laser marking. The control device 50 may have functions other than those shown in FIG. 5, or may communicate with another control device provided in the manufacturing apparatus 90 and perform the laser marking process in conjunction with the functions realized by the other control device. Some of the functional blocks provided in the control unit 51 may be provided in a control device provided in another piece of hardware.

[0033] As shown in FIG. 5, the control unit 51 includes a color identification sensor control unit 51a, a color identification unit 51b, an irradiation condition setting unit 51c, a printing control unit 51d, and a transport device control unit 51e. The color identification sensor control unit 51a activates the color identification sensor 36 based on information obtained from the transport device control unit 51e regarding the position of the metal container 100 to be laser marked on the transport device 40. The color identification sensor 36 is, for example, a reflective photoelectric sensor that obtains color information on the surface of the metal container 100 using reflected light and transmits it to the color identification unit 51b. The color identification unit 51b reads information from the sample color information data 52a stored in the memory unit 52, compares it with the color information obtained by the color identification sensor 36, and sends it to the irradiation condition setting unit 51c. The irradiation condition setting unit 51c reads irradiation conditions from the irradiation condition data 52b in the memory unit 52 based on the color information comparison result and transmits it to the print control unit 51d. If there is a change in the print design, the print control unit 51d reads out the print design from the print design data 52c and transmits it to the head 31 together with the irradiation conditions.

[0034] The printing control unit 51d commands the head 31 to perform laser marking based on the position information of the metal container 100 to be laser marked, which is obtained from the conveying device control unit 51e. In FIG. 5, the conveying device control unit 51e receives information about the operation of the conveying device 40 from the conveying device 40, but it may also detect the position of the metal container 100 using a sensor, for example, and use that information as information about the operation of the conveying device 40. The conveying device control unit 51e sends information about at least the position of the metal container 100 to be laser marked to the printing control unit 51d. The conveying device control unit 51e also sends information about the position of the metal container 100 to be color-identified to the color identification sensor control unit 51a. The conveying device control unit 51e operates the conveying device 40 upon receiving from the printing control unit 51d that the head 31 has completed laser marking.

[0035] FIG. 6 is an example of a flowchart for controlling the laser marking process of the manufacturing apparatus 90 for metal containers 100 according to the first embodiment. When the metal container 100 to be laser marked on the conveying device 40 reaches a predetermined position, i.e., position A in FIG. 4, the color identification sensor 36 acquires surface color information (step S1). The color identification unit 51b compares the surface color information of the target metal container 100 with the color information data of the specimen and determines which of the color information data of the specimen the surface color of the target metal container 100 matches. Based on the determination result, the irradiation condition setting unit 51c reads the irradiation conditions from the irradiation condition data 52b (step S2). If the irradiation conditions match those of the metal container 100 laser-marked before the target metal container 100 (Yes in step S3), the irradiation condition setting unit 51c does not output the irradiation conditions to the print control unit 51d (step S4). In addition, if the irradiation conditions do not match the irradiation conditions of the metal container 100 that was laser marked immediately before the target metal container 100 (No in step S3), the irradiation condition setting unit 51c outputs new irradiation conditions to the printing control unit 51d (step S5).

[0036] Next, if there is no instruction to change the print design (Yes in step S6), print control unit 51d does not acquire a print design and maintains the print design that has already been set (step S7). Alternatively, if there is an instruction to change the print design (No in step S6), print control unit 51d acquires a new print design from print design data 52c (step S8).

[0037] Next, the printing control unit 51d receives from the conveyance device control unit 51e information that the metal container 100 to be laser marked has reached the appropriate position, and instructs the head 31 to perform printing. At this time, the printing control unit 51d appropriately rewrites the instruction content in accordance with the irradiation conditions and print design set in the processes from step S3 to step S8, and instructs the head 31 (step S9). Note that the print design may be changed manually, for example, via an input device (not shown), or may be programmed in advance in the control device 50 in accordance with the production plan.

[0038] In the first embodiment, as shown in FIG. 4, the color identification sensor 36 detects the color of the surface of the cylindrical portion 101 of a metal container 100 located at a position (position A in FIG. 4) before the position where laser marking is performed (position B in FIG. 4). In other words, steps S1 to S8 shown in FIG. 6 are completed before the metal container 100 to be laser marked is placed at position B in FIG. 4. With this configuration, the manufacturing apparatus 90 performs color identification of the metal container 100 to be laser marked in advance, and completes setting of the irradiation conditions when the metal container 100 reaches the position where the laser light 30 is irradiated, thereby shortening the takt time of the entire laser marking process. Consequently, it becomes possible to mark the metal container 100 by laser marking without increasing the overall takt time.

[0039] The color identification sensor 36 is not limited to being used for the metal container 100 at position A in Fig. 4, but may be used at position B where laser marking is performed, for example. However, if color identification is performed at position B, the time that the metal container 100 remains at position B increases by the time required to perform the steps S3 to S8 shown in Fig. 6.

[0040] 7 shows examples of the paint colors, paints, and ingredients of the metal container 100 according to the first embodiment, and the coloring of the printed portion 10 with each paint color. The paint colors shown are DM-1 to DM-14, which are standard paint colors for drums, and two other colors designated by the user. The color of the discolored portion 22 caused by irradiation with the laser light 30 varies depending on the paint color.

[0041] The color development in the discolored area 22 is mainly due to (1) foaming, (2) condensation, (3) carbonization, and (4) chemical changes. (1) Foaming occurs when the laser beam 30 is irradiated onto the coating layer 21, resulting in the generation of gas bubbles within the substrate due to the thermal effect, resulting in whitish protrusions. In particular, dark-colored paints change color to a lighter shade of the coating color, providing good visibility. (2) Condensation occurs when the laser beam 30 is irradiated onto the coating layer 21, resulting in the coating layer 21 condensing and turning darker due to the thermal effect of the laser beam 30. (3) Carbonization occurs when the irradiated portion of the coating layer 21 is carbonized and turns black when the laser beam 30 is irradiated onto the coating layer 21. (4) Chemical changes occur due to the following phenomena. Because the coating layer 21 contains pigment substances containing metal ions, irradiation with the laser beam 30 causes changes in the valence of these metal ions, changes in the crystalline structure, or changes in the amount of hydration within the crystals. As a result, the state of the components contained in the coating layer 21 changes, resulting in color development. The chemical changes also include photochemical changes of metal compounds contained in the coating layer 21 caused by the light energy of the laser light 30, the mechanism of which will be described later.

[0042] The "Print Discoloration" column in Figure 7 indicates whether each paint color changes to black (a darker version of each paint color) or white (a lighter version of each paint color). Whether a dark or light color is easily visible varies depending on the paint color. For example, DM-1 is a white paint, and the paint layer 21 changes to a dark color (black) when exposed to laser light 30, making the discolored portion 22 easily visible. On the other hand, DM-2 is a black paint, and the paint layer 21 changes to a light color (white) when exposed to laser light 30.

[0043] The right column of the table in FIG. 7 lists the main compounds contained in the coating layer 21 and their amounts, along with the range of the content ratio.

[0044] Of the standard drum paint colors DM-1 to DM-14, all paint colors other than DM-2 and DM-12, as well as the user-specified paint color B, contain titanium dioxide as a component. Titanium dioxide is chemically converted to titanium pentoxide when irradiated with laser light 30. Titanium dioxide is primarily white, and by chemically converting to titanium pentoxide, it changes to a dark color such as black-gray or reddish-brown. Therefore, paint colors that contain titanium dioxide as a component tend to have discolored portions 22 that turn relatively black or dark.

[0045] The paint colors DM-2, DM-3, and DM-9 contain carbon black as an ingredient, which makes it easier for the paint layer 21 to turn white by foaming.

[0046] Of the paint colors, DM-8, DM-9, DM-12, DM-13, and User Designated B contain yellow iron oxide as a component. DM-5, DM-13, and User Designated A contain ferric oxide as a component. The yellow iron oxide and ferric oxide change to ferrous oxide or triiron tetroxide when irradiated with laser light 30. Ferrous oxide and triiron tetroxide are black and tend to change the discolored portion 22 of the paint layer 21 to black or a darker color.

[0047] The discolored areas 22 of each paint color shown in FIG. 7 are formed primarily by changes in the above-mentioned components. The discolored areas 22 are formed in the areas irradiated with the laser light 30, and the degree of color development varies depending on the intensity of the laser light 30, the focal position of the laser light 30, and the scanning speed of the laser light 30. For example, the discoloration is more pronounced when the amount of energy of the laser light 30 irradiated per unit area is high. Even if the intensity of the laser light 30 is the same, if the focal position of the laser light 30 is not focused, the amount of energy irradiated per unit area decreases, thereby suppressing discoloration. Furthermore, increasing the scanning speed reduces the amount of energy irradiated per unit area, thereby suppressing discoloration. In the metal container 100 according to embodiment 1, the visibility of the printed area 10 in each paint color is ensured while the time required for the laser marking process is adjusted so as not to increase.

[0048] FIG. 8 shows an example of the appearance of the printed portion 10 of a metal container 100. FIG. 8(a) shows an example of a discolored portion 22 when laser marking is performed on the paint color DM-1 shown in FIG. 7, and FIG. 8(b) shows an example of a discolored portion when laser marking is performed on the paint color DM-2 shown in FIG. 7. FIG. 8(c) shows an example of a discolored portion when laser marking is performed on the paint color DM-5 shown in FIG. 7. The tables of discolored samples in FIGS. 8(a), (b), and (c) were created by varying the output power, scanning speed, and focal position of the laser beam 30. The sample with the paint color DM-1 is white, a relatively light color, and changes color to a darker color when irradiated with the laser beam 30, forming the discolored portion 22. The sample with the paint color DM-2 is black, and changes color to a lighter color when irradiated with the laser beam 30, forming the discolored portion 22.

[0049] In the example of the first embodiment, samples were created using an MD-U1020C manufactured by Keyence Corporation. The laser used was a YVO4 laser with a wavelength of 355 nm and an output of 2.5 W (at 40 kHz). The printable area was 330 mm x 330 mm in the vertical and horizontal directions and 42 mm in the depth direction. That is, the surface of the cylindrical portion 101 of the metal container 100 is a cylindrical surface with a depth in the direction of irradiation of the laser beam 30, but it is possible to print with the laser beam 30 within a range of 42 mm in the depth direction. The samples were formed by forming the paint layer 21 of each paint color shown in Figure 7 on a steel plate placed within the printable area. Furthermore, samples No. 27 to No. 30 in Figure 10, which were created using an IR laser, were created using an MD-X1020 manufactured by Keyence Corporation. The laser used was a YVO4 laser with a wavelength of 1064 nm and an output of 13 W. The printable area is 330mm x 330mm in the vertical and horizontal directions, and 42mm in the depth direction.

[0050] In the table printed on the discolored sample in Figure 8, the discolored areas 22 shown in each of the columns labeled "A" to "O" in the left-right direction were irradiated with the laser beam 30 while varying the spot diameter from -21 mm to +21 mm. The central column labeled "H" was irradiated with the minimum spot diameter, i.e., with the spot focused on the surface 23.

[0051] In the table printed on the discoloration samples in the upper rows (a-1) and (b-1) of Figures 8(a) and (b), the symbols shown in rows "1" to "5" indicate that the scanning speed of the laser light 30 was changed from 2000 mm / min to 6000 mm / min, and the sample in row "5" has a faster scanning speed.

[0052] In the table printed on the discoloration samples in the lower rows (a-2) and (b-2) of Figures 8(a) and (b), the symbols shown in rows "1" to "5" indicate that the output of the laser light 30 was changed from 60% to 100%, and the sample in row "5" has a higher output.

[0053] First, in all discoloration samples, the discoloration portion 22 of the sample in the horizontally aligned "H" column shows less discoloration. This is because the spot diameter of the laser light 30 is smaller, resulting in a smaller discolored area and a smaller overall discolored area. The head 31 irradiates the laser light 30 as pulses. When the laser light 30 is focused on the surface 23, the area of ​​the surface 23 irradiated with the laser light 30 per pulse is small, making the discoloration portion 22 difficult to see. On the other hand, the spot diameter increases toward the "A" or "O" columns of the discoloration samples. Therefore, the area of ​​the surface 23 irradiated with the laser light 30 per pulse is larger, making the discoloration portion 22 more visible. However, due to the relationship between the output power and spot diameter of the laser light 30, if the energy received per unit area of ​​the surface 23 decreases, the discoloration becomes lighter and less visible. For example, in the tables of discolored samples in the lower rows (a-2) and (b-2), the discolored portions 22 are difficult to see in "1A," "1O," and their vicinity.

[0054] As can be seen from the upper rows (a-1) and (b-1) of Figures 8(a) and (b), as the scanning speed increases, the energy received per unit area of ​​the surface 23 decreases and the color becomes lighter.

[0055] As can be seen from the lower rows (a-2) and (b-2) of Figures 8(a) and (b), as the output of the laser light 30 decreases, the energy received per unit area of ​​the surface 23 decreases, and the color becomes lighter.

[0056] Furthermore, as shown in Figure 8(c), in an example of a discolored area 22 when laser marking is performed on a paint color DM-5, the discolored area 22 shown in each of the columns labeled "A" through "O" in a horizontal direction shows the same tendency as in the DM-1 and DM-2 examples, with the "H" column showing the lightest color and the color becoming darker toward the "A" and "O" columns. However, in the case of DM-5, color development due to foaming and color development due to chemical reactions occur simultaneously, so whether the color development due to foaming (white) or chemical reactions (black) predominates depends on the scanning speed and intensity of the laser beam 30. As for color development trends, as the amount of energy of the laser beam 30 received per unit area of ​​the surface 23 increases, white becomes dominant, and when the amount of energy is relatively low, black becomes dominant. When the output of the laser beam 30 is 100%, white predominates across almost the entire area from the "A" column to the "O" column, where the spot diameter is varied. In addition, DM-15 also produces color due to foaming (white) and color due to chemical changes (black), but in this case black is predominant throughout the entire area.

[0057] Fig. 9 shows examples in which laser marking was performed on each paint color, and the evaluation results. Fig. 10 shows examples and comparative examples in which printing such as laser marking was performed on each paint color, and the evaluation results. Using the manufacturing method for metal containers 100 including the laser marking step described above, laser light 30 was irradiated onto the paint layer 21 for each paint color, and the depth of the discolored portion 22 and the thickness of the non-discolored portion of the paint layer 21 (the distance from the discolored portion 22 to the base material 20) were measured, and the visibility, rust resistance, and rubbing resistance were evaluated. The visibility, rust resistance, and rubbing resistance were ranked from "1" to "5," with a rank of "3" or higher being the pass standard.

[0058] The visibility evaluation criteria were evaluated by visually assessing ease of visibility from a distance of 1 m. When visually inspected from a distance of 1 m, rank "1" was indistinguishable, rank "2" was difficult to distinguish 10 mm characters, rank "3" was distinguishable 10 mm square characters, rank "4" was clearly distinguishable 10 mm square characters, and rank "5" was clearly distinguishable 5 mm square characters.

[0059] The evaluation criteria for rust resistance were as follows: a sample was subjected to a salt spray test for the specified time listed below, and then tape-peeling was performed to observe the difference in peeling between the printed and non-printed areas. Rank "1" means that the printed area was noticeably peeled off after 120 hours of salt spray testing, rank "2" means that the printed area was noticeably peeled off after 168 hours of salt spray testing, rank "3" means that there was no difference between the printed and non-printed areas after 168 hours of salt spray testing, rank "4" means that there was no difference between the printed and non-printed areas after 240 hours of salt spray testing, and rank "5" means that there was no difference between the printed and non-printed areas after 336 hours of salt spray testing.

[0060] Rubbing resistance was evaluated by rubbing a printed surface with a 1kg load in a rubbing test, and the condition of the print was evaluated after a specified number of rubs. The rubber has a felt surface. Rank "1" means that more than half of the print is lost within 10 strokes, rank "2" means that more than half of the print is lost within 50 strokes, rank "3" means that some of the print is lost after 50 strokes but the print is still recognizable, rank "4" means that some of the print is lost after 100 strokes but the print is still recognizable, and rank "5" means that no part of the print is lost after 100 strokes.

[0061] 9 and 10 show the laser light output [W], scanning speed [mm / sec], distance variation amount [mm], and number of overlapping prints [times] for the irradiation conditions of the laser light 30. Each of the evaluation results No. 1 to No. 31 shown in Fig. 9 and 10 is a collection of the results of evaluating multiple samples, and the irradiation conditions and evaluation results are shown with a range.

[0062] In the example shown in Figure 9, when color development occurs due to foaming or a photochemical reaction in the coating layer 21, even a surface discoloration of the discolored portion 22 of 0.3 µm to 2.5 µm is visible. Furthermore, when color development occurs due to foaming or a photochemical reaction, visibility tends to be higher when the discolored portion 22 is 2.5 µm to 10 µm. However, as can be seen from Samples Nos. 3, 4, 12, and 13, when color development occurs due to foaming, a certain degree of depth of the discolored portion 22 is required, and when the discolored portion 22 is shallow, visibility tends to be worse than when color development occurs due to a chemical reaction.

[0063] In the examples shown in Figure 9, rust resistance met the standard when the thickness of the non-discolored portion was 2.5 to 5 μm, and even higher when it was 5 μm or more. However, in the case of discoloration due to a photochemical reaction, rust resistance tended to be high even at thicknesses of 2.5 to 5 μm (comparison of samples Nos. 1 to 9 and Nos. 10 to 18). This is because the examples received additional points for less damage to the coating layer 21.

[0064] 9, when discoloration was caused by a photochemical reaction, the rubbing resistance tended to be highly rated regardless of the depth of the discoloration. However, when discoloration was caused by carbonization, the discolored area 22 bleeds due to friction, so although the pass criteria were met, the rubbing resistance was not highly rated.

[0065] In the samples Nos. 19 to 22 shown in FIG. 10, although laser light 30 in the UV wavelength range was used, the thickness of the portion of the coating layer 21 other than the discolored portion 22 (the non-discolored layer) was thin, and some of them did not meet the pass criteria for rust resistance (see samples Nos. 19 to 22). Although samples Nos. 19 to 22 are inferior to the example shown in FIG. 9 in terms of visibility, rust resistance, and rubbing resistance, they are advantageous in terms of rubbing resistance compared to the stamp printing shown in No. 31. Furthermore, since samples Nos. 19 to 22 are laser marked and do not use ink, they are superior to sample No. 31 in that they produce clearer prints without the need for ink, as compared to stamp printing or other printing that uses ink.

[0066] Furthermore, in Samples No. 23 to No. 26 shown in FIG. 10, although laser light 30 in the UV wavelength range was used, the discolored portion 22 was thin (0.1 μm to 0.3 μm), and generally tended to have lower visibility and rubbing resistance than the Example shown in FIG. 9. Furthermore, as shown in Samples No. 23 to No. 26, samples with coloring due to foaming had lower rubbing resistance than samples with coloring due to chemical changes. While Samples No. 23 to No. 26 are also inferior to the Example shown in FIG. 9 in terms of visibility, rust resistance, and rubbing resistance, they are superior to Sample No. 31, which shows discoloration due to chemical changes, in terms of rubbing resistance. Furthermore, Samples No. 23 to No. 26, like Samples No. 19 to No. 22, are laser-marked, and have clear printing without smearing during the printing process, making them superior to Sample No. 31.

[0067] The samples Nos. 27 to 30 in Figure 10 were printed using an IR (infrared) laser, and the heat generated carbonizes or foams the paint resin, resulting in printing. As a result, it was difficult to control the depth of the discolored area 22 within 5 μm from the surface 23 in these samples, and the depth of the discolored area 22 exceeded 5 μm, which tended to thin the paint layer 21 outside the discolored area 22, resulting in poor rust resistance and rubbing resistance.

[0068] The sample No. 31 in Figure 10 is a stamp print. This sample satisfies the standards for visibility and rust resistance because it is formed by placing ink on the surface of the coating layer 21. However, it did not meet the standards for rubbing resistance because it depends on the strength of the ink.

[0069] The printed portion 10 of the metal container 100 according to embodiment 1 can ensure visibility, rust resistance, and rubbing resistance by laser marking the discolored portion 22 to a depth of 0.3 μm to 10 μm from the surface. Furthermore, the laser marking may be performed so that the discolored portion 22 has a depth of 0.3 μm to 2.5 μm from the surface, thereby ensuring visibility, rust resistance, and rubbing resistance.

[0070] Furthermore, it is desirable that the printed portion 10 of the metal container 100 according to embodiment 1 has a thickness of at least 2.5 μm in the portion of the coating layer 21 other than the discolored portion 22 (non-discolored layer), which allows the printed portion 10 to maintain good rust resistance and rubbing properties.

[0071] The printed portion 10 of the metallic container 100 according to the first embodiment is formed by discoloration due to chemical reaction or foaming using laser light 30 in the visible or UV wavelength range, so it is possible to control the depth of the discolored portion 22 from the surface, ensuring visibility while ensuring an appropriate depth of the discolored portion 22. Furthermore, the printed portion 10 of the metallic container 100 according to the first embodiment is more susceptible to discoloration due to chemical reaction than discoloration due to carbonization, and is also highly rubbing-resistant.

[0072] The printed area 10 of the metal container 100 according to the first embodiment is formed by discoloration primarily due to chemical reactions or foaming using laser light 30 in the visible or UV wavelength range. This prevents the discolored area 22 from becoming too deep, and the thickness of the non-discolored layer is sufficient to ensure rust resistance and rubbing resistance. Therefore, the metal container 100 does not need a thick coating layer 21 to ensure the durability of the printed area 10. Laser marking using an IR laser requires the printing to be formed by foaming or carbonization to ensure the required visibility, making it difficult to control the depth of the discolored area 22 within the range of 0.3 μm to 10 μm. As can be seen from comparative samples Nos. 27 to 30, the discolored area 22 becomes deeper and the non-discolored layer becomes thinner. Therefore, compared to the printed area 10 of the metal container 100 according to the first embodiment, the non-discolored layer tends to become thinner in the printed area 10, resulting in inferior rust resistance and rubbing resistance.

[0073] FIG. 11 shows an example of the results of composition analysis by X-ray diffraction of a discolored portion of the printed portion 10 of the metal container 100 according to the first embodiment. FIG. 11(a) shows the results of X-ray diffraction analysis in which X-rays were incident on the coating layer 21 before discoloration, and FIG. 11(b) shows the results of X-ray diffraction analysis in which X-rays were incident on the discolored portion 22 of the coating layer 21 after discoloration. As an example, FIG. 11 shows the results of composition analysis of the discolored portion 22 of the coating color DM-5 before and after irradiation with laser light 30. DM-5 contains 10 to 15% ferric oxide as a component of the coating layer 21, as shown in FIG. 7. The coating layer 21 of DM-5 primarily turns black when irradiated with laser light 30; however, when the intensity of the laser light 30 is high, foaming of the coating layer 21 becomes dominant, resulting in a white discoloration. The diagrams shown at the top of Figures 11(a) and (b) are the X-ray diffraction patterns obtained from the samples, and the columns at the bottom of Figures 11(a) and (b) show the crystalline phases identified from the measurement results. Column P shows the position and intensity of the diffraction line of ferric oxide (Fe2O3), and column Q shows the position and intensity of the diffraction line of ferrous oxide (FeO). The horizontal axes of Figures 11(a) and (b) show the diffraction angle 2θ (°), ranging from 5° to 70°. The vertical axes of Figures 11(a) and (b) show the intensity of the diffracted X-rays (CPS), ranging from 0 to 2000 CPS.

[0074] Comparing Figure 11(a) and (b), ferrous oxide (FeO), which was not present before irradiation with the laser beam 30, appears after irradiation (see column Q indicated by the arrow in Figure 11(b)). Furthermore, the peak of ferric oxide (Fe2O3) attenuates after irradiation (see columns P in Figures 11(a) and 11(b)). In other words, the following reduction reaction occurs in the coating layer 21 of DM-5 due to irradiation with the laser beam 30: Fe2O3+ e- → 2FeO + 1 / 2O 2- ... (Formula 1) The ferric oxide is reduced to ferrous oxide by irradiation with the laser light 30. As a result, the discolored portion 22 appears black.

[0075] FIG. 12 shows an example of the results of composition analysis by X-ray diffraction of a discolored portion of the printed portion 10 of the metal container 100 according to the first embodiment. FIG. 12(a) shows the results of X-ray diffraction analysis in which X-rays were incident on the coating layer 21 before discoloration, and FIG. 12(b) shows the results of X-ray diffraction analysis in which X-rays were incident on the discolored portion 22 of the coating layer 21 after discoloration. FIG. 12 shows the results of composition analysis of the discolored portion 22 of the coating color DM-12 before and after irradiation with laser light 30. DM-12 contains 5 to 10% yellow iron oxide as a component of the coating layer 21, as shown in FIG. 7. The coating layer 21 of DM-12 primarily turns black when irradiated with laser light 30; however, if the intensity of the laser light 30 is too high, foaming of the coating layer 21 becomes dominant, and the color may turn white. The diagrams shown at the top of Figures 12(a) and (b) are the X-ray diffraction patterns obtained from the samples, and the columns at the bottom of Figures 12(a) and (b) show the crystalline phases identified from the measurements. Column P shows the position and intensity of the diffraction lines of ferric oxide (Fe2O3), column Q shows the position and intensity of the diffraction lines of ferrous oxide (FeO), and column R shows the position and intensity of the diffraction lines of yellow iron oxide (Fe2O3·H2O). The horizontal axes of Figures 12(a) and (b) represent the diffraction angle 2θ (°), ranging from 5° to 70°. The vertical axes of Figures 12(a) and (b) represent the intensity of the diffracted X-rays (CPS), ranging from 0 to 2000 CPS.

[0076] Comparing (a) and (b) of Figure 12, ferrous oxide (FeO) that was not present before the irradiation of the laser beam 30 appears after the irradiation (see column Q of Figure 12(b)). 3+ The O(OH) peak is attenuated (see column R in Figures 12(a) and 12(b)). In other words, the following reduction reaction occurs in the coating layer 21 of DM-12 due to irradiation with the laser beam 30. Fe2O3·H2O+e - → 2FeO+1 / 2O 2- +H2O ... (Formula 2) Yellow iron oxide (Fe2O3·H2O) is reduced to ferrous oxide by irradiation with laser light 30. As a result, discolored portion 22 appears black.

[0077] Fig. 13 is a schematic diagram illustrating the reduction reaction of Fe2O3 due to laser irradiation of the printed portion 10 of the metallic container 100 according to the first embodiment. The analysis results shown in Figs. 11 and 12 show that the ferric oxide and yellow iron oxide contained in the coating layer 21 are each reduced by irradiation with the laser beam 30. This is because the light energy hν of the laser beam 30 is greater than the band gap Eg of the substance (here, ferric oxide and yellow iron oxide), so electrons in the valence band are excited to the conduction band and become free electrons, resulting in a reduction reaction. Here, h is Planck's constant, and ν is the frequency of the laser beam 30.

[0078] Fig. 14 shows an example of laser light irradiated onto the metal container 100 according to embodiment 1. The laser light 30 irradiated in the example shown in Fig. 9 is a YVO4 laser in the UV wavelength region (355 nm), and the light energy hν is 3.49 eV.

[0079] FIG. 15 shows the band gap of the material contained in the coating layer 21 of the metal container 100 according to the first embodiment. In semiconductors and insulators, the energy level from the outermost shell of the valence band to the bottom of the conduction band is generally large. For electrons to transition from the valence band to the conduction band requires the absorption of energy (light or heat) greater than the band gap Eg. For example, in the case of the coating layer 21 with the coating color DM-5, the analysis results of which are shown in FIG. 11, the band gap of the ferric oxide contained therein is 2.0 to 2.2 eV. Therefore, with the laser beam 30 of the manufacturing apparatus 90 according to the first embodiment, the light energy hν exceeds the band gap of the ferric oxide, and a reduction reaction can be induced in the coating layer 21. The laser beam 30 of the manufacturing apparatus 90 according to the first embodiment can induce a reduction reaction in the coating layer 21 even when the output is reduced, and can be adjusted to favor blackening due to a photochemical reaction over whitening due to foaming.

[0080] 14, a YAG laser or YVO4 laser with a wavelength of 532 nm, and an argon laser with wavelengths of 488 nm, 514.4 nm, or 315 nm can also induce a reduction reaction in ferric oxide in a similar manner. In other words, laser light 30 with a wavelength in the visible light range can also be used as long as the light energy hν of laser light 30 exceeds the band gap of the discoloring substance contained in paint layer 21. In other words, in the embodiment shown in FIG. 9, color development through a photochemical reaction can be achieved even if laser light 30 with a wavelength in the visible light range is used instead of laser light 30 with a wavelength in the UV range.

[0081] On the other hand, in the case of laser light 30 with wavelengths of 1064 nm and 10600 nm shown in Fig. 14, the light energy hν is insufficient to exceed the band gap of the material shown in Fig. 15, so discoloration due to the reduction reactions shown in (Equation 1) and (Equation 2) above does not occur. In this case, the thermal energy of the laser light 30 carbonizes or foams the resin that makes up the coating layer 21, causing discoloration.

[0082] Furthermore, a 355 nm YAG laser or YVO4 laser with high light energy hν can also promote the chemical reaction of titanium dioxide (TiO2), which is contained in the paint colors DM-1 to DM-14 shown in Figure 7 except for DM-2 and DM-12, as well as the paint color specified by user B.

[0083] As described above, the metal container 100, manufacturing apparatus 90 for the metal container 100, and printing method for the metal container 100 according to the first embodiment can provide a discolored portion 22 in the coating layer 21 by laser marking, thereby preventing the printing from fading during transportation and use of, for example, a drum can. For example, when the printed portion 10 is formed by stamping, silk screen printing, or other means, ink for identification is applied to the surface of the coating layer 21, and the ink is easily removed by rubbing, etc., resulting in low durability of the printed portion 10. On the other hand, the printed portion 10 formed by laser marking according to the first embodiment has excellent visibility, rust resistance, and rubbing resistance, as shown in FIG.

[0084] Furthermore, according to the metal container 100, manufacturing apparatus 90 for the metal container 100, and printing method for the metal container 100 of embodiment 1, the discolored portion 22 is provided in an area 5 μm or less from the surface 23 of the paint layer 21, so there is no damage to the metal that is the base material 20 of the metal container 100. Furthermore, the laser marking process does not expose the base material 20, and a sufficient thickness of the untarnished paint layer 21 from the discolored portion 22 to the surface of the base material 20 can be ensured. This makes it possible to suppress damage such as rust and corrosion from the printed portion 10 even when the metal container 100 is used for a long period of time.

[0085] Furthermore, the metal container 100, manufacturing apparatus 90 for the metal container 100, and printing method for the metal container 100 according to embodiment 1 use laser light 30 in the visible or UV wavelength range, which causes at least one substance contained in the coating layer 21 to undergo a chemical reaction and discoloration due to the light energy hν, thereby minimizing damage to not only the base material 20 but also the coating layer 21 itself. The coating layer 21 contains a resin that constitutes the paint, and the coating layer 21 of each coating color shown in FIG. 7 may contain an amino alkyd resin, for example. The coating layer 21 is preferably 30 μm or less in thickness, and more preferably 20 μm or less in consideration of the surface strength, weight, and cost of the coating layer 21.

[0086] Furthermore, the laser marking process directly discolors the paint in the coating layer 21, eliminating the need for consumables such as ink or cleaning fluid, thus reducing the cost of consumables and their management. Furthermore, by arranging multiple laser marking heads 31 to process the printed area 10 in a single process, even when the printed area 10 has a large area and a large amount of information to be printed, a highly accurate printed area 10 can be obtained without affecting the takt time of the metal container 100. Furthermore, the laser marking process uses a YAG laser, YVO4 laser, or argon laser that includes the wavelength range shown in Figure 14 , and the metal container 100 is provided with a discoloration area 22 caused by a photochemical reaction using the light energy hν of the laser light 30. Therefore, the printed area 10 discolors only a portion of the coating layer 21 to provide an identification mark or other marking, without impairing the performance of the metal container 100. The discoloration area 22 on the metal container 100 is not limited to discoloration caused by a photochemical reaction alone and may also include discoloration caused by other chemical reactions.

[0087] In the metal container 100 according to the first embodiment, the printed portion 10 is provided on the side surface of the cylindrical portion 101, but the printed portion 10 may be provided on the lid portion 102.

[0088] Although the present invention has been described above based on the embodiments, the present invention is not limited to the configurations of the above-described embodiments. In particular, the combination of components is not limited to the combinations in the embodiments, and the components described in each embodiment can be modified as appropriate. For example, we would like to emphasize that the gist (technical scope) of the present invention also includes various modifications, applications, and uses that a person skilled in the art may make as needed. [Explanation of symbols]

[0089] 10 Printing section, 20 Base material, 21 Paint layer, 22 Discolored section, 23 Surface, 30 Laser light, 31 Head, 32 Positioning jig, 33 Jig, 34 Imaging device, 35 Irradiation range, 36 Color identification sensor, 40 Conveying device, 50 Control device, 51 Control section, 51a Color identification sensor control section, 51b Color identification section, 51c Irradiation condition setting section, 51d Printing control section, 51e Conveying device control section, 52 Memory section, 52a Sample color information data, 52b Irradiation condition data, 52c Printing design data, 90 Manufacturing device, 100 Metal container, 101 Tube section, 102 Lid section, 102A Lid section, 102B Lid section, 103 Opening, 104 Opening, 105 Ring, 106 Section, 107 Chime.

Claims

1. A method for printing on a metal container, the metal container having a body having a cylindrical portion made of metal and lid portions attached so as to close both ends of the cylindrical portion, and a coating layer forming an outer surface of the body, comprising: A discolored portion is formed by irradiating the coating layer with a laser beam having a wavelength of visible light or UV to discolor a part of the coating layer, including the surface thereof, The band gap of at least one pigment contained in the coating layer is is smaller than the light energy hν of the irradiated laser light, determining the type of the coating layer from the color of the surface of the main body; The laser light is irradiated at a focal position according to the type of the coating layer, The depth dimension of the discolored portion formed from the surface of the coating layer is: A method for printing on a metal container, wherein the thickness is 0.3 μm or more and 10 μm or less.

2. A method for printing on a metal container, the metal container having a body having a cylindrical portion made of metal and lid portions attached so as to close both ends of the cylindrical portion, and a coating layer forming an outer surface of the body, comprising: A discolored portion is formed by irradiating the coating layer with a laser beam having a wavelength of visible light or UV to discolor a part of the coating layer, including the surface thereof, The band gap of at least one pigment contained in the coating layer is is smaller than the light energy hν of the irradiated laser light, determining the type of the coating layer from the color of the surface of the main body; Irradiating the laser light with an output according to the type of the coating layer, The depth dimension of the discolored portion formed from the surface of the coating layer is: A method for printing on a metal container, wherein the thickness is 0.3 μm or more and 10 μm or less.

3. A method for printing on a metal container, the metal container having a body having a cylindrical portion made of metal and lid portions attached so as to close both ends of the cylindrical portion, and a coating layer forming an outer surface of the body, comprising: A discolored portion is formed by irradiating the coating layer with a laser beam having a wavelength of visible light or UV to discolor a part of the coating layer, including the surface thereof, The band gap of at least one pigment contained in the coating layer is is smaller than the light energy hν of the irradiated laser light, determining the type of the coating layer from the color of the surface of the main body; irradiating the laser light at a scanning speed according to the type of the coating layer; The depth dimension of the discolored portion formed from the surface of the coating layer is: A method for printing on a metal container, wherein the thickness is 0.3 μm or more and 10 μm or less.

Images