Inkjet printing device

Abstract

To provide a compact inkjet printing device that can obtain a high image-quality printed matter and an inkjet printing method.SOLUTION: [1] An inkjet printing device comprises a printing medium supply part that supplies a printing medium and a printing unit that performs printing on the printing medium. The printing unit comprises a conveying body that conveys the printing medium, at least two non-white color inkjet heads, a white color inkjet head, and a drying mechanism that dries the printing medium. A distance between the white color inkjet head and the non-white color inkjet heads in a conveying direction is larger than a distance between the non-white color inkjet heads. [2] An inkjet printing method includes a conveying step of conveying the printing medium and a printing step of executing printing on the printing medium. A distance between the white color inkjet head and the non-white color inkjet heads in the conveying direction is larger than a distance between the non-white color inkjet heads.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to inkjet printing devices. [Background technology]

[0002] Inkjet printing is a method of directly ejecting ink from minute nozzles and depositing it on a printing medium to produce printed matter with characters and images. This method has many advantages, including being easy to produce full color, being inexpensive, and not contacting the printing medium, so in recent years it has been applied not only to consumer printing but also to commercial and industrial printing fields. In the fields of commercial printing and industrial printing, high-speed inkjet printing is being considered for the purpose of increasing productivity, in which a so-called single-pass method is used, in which a linear fixed print head is provided that can print across the entire width of the print medium, and which continuously prints on a roll-type print medium. Flexible packaging is also widely used for packaging food, etc. In flexible packaging, the name and other information of the packaged product is printed on a thin, flexible resin printing medium made of synthetic resin or the like. In recent years, in the field of printing, inkjet printing devices that use water-based inks containing pigments have been considered from the viewpoints of weather resistance, water resistance, and reducing the environmental impact of printed matter.

[0003] In high-speed printing, it is necessary to sufficiently dry the ink on the printing medium after printing in a short time. For example, Patent Document 1 describes an inkjet printing apparatus using an air-blowing drying method, which includes an ejection means for ejecting ink onto a sheet material and a transport device for blowing air onto the sheet material with the ink attached and transporting the sheet material, in which the transport device includes a transport means for carrying one side of the sheet material on a curved carrying surface of a sheet material carrying member and transporting the sheet material, and an air blowing means for blowing air from the other side of the sheet material, and the carrying surface of the sheet material carrying member is composed of a plurality of linear members arranged so that the blown air passes around the sheet material. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2018-16069 Summary of the Invention [Problem to be solved by the invention]

[0005] The printing device described in Patent Document 1 has the problem that after ink is ejected from one inkjet head onto a sheet material, ink is ejected from another inkjet head without the ink adhering to the sheet being allowed to dry, resulting in a deterioration in image quality due to ink mixing. In addition to the air drying method, other known methods for drying ink on printing media include the heat drying method, which dries the ink by irradiating it with infrared rays, etc. However, the heat drying method generally has the disadvantage of requiring a large installation space for the ink drying unit, making the device larger and requiring more complex wiring for power cables, etc. An object of the present invention is to provide a compact inkjet printing apparatus and inkjet printing method that can produce high-quality printouts. [Means for solving the problem]

[0006] The present inventors have found that it is possible to provide a compact inkjet printing device that can prevent ink mixture and produce high-quality printouts by providing inkjet heads for white ink and non-white ink on a transport drum and making the distance between the white inkjet head and the non-white inkjet head greater than the distance between the non-white inkjet heads themselves. That is, the present invention provides the following [1] and [2]. [1] An inkjet printing device comprising: a printing medium supply unit that supplies a printing medium made of a sheet-shaped resin; and a printing unit that prints on the printing medium, the printing unit includes a transport drum that transports the print medium, at least two non-white inkjet heads that eject black and chromatic inks toward the print medium transported by the transport drum, a white inkjet head that ejects white ink toward the print medium transported by the transport drum, and a drying mechanism that dries the print medium transported by the transport drum, and the distance between the white inkjet head and the non-white inkjet head is greater than the distance between the non-white inkjet heads themselves. [2] An inkjet printing method including: a transporting step in which a printing medium made of a sheet-like resin is transported; and a printing step in which printing is performed on the printing medium, wherein the printing step includes: a non-white inkjet discharging step in which ink is discharged toward the printing medium from at least two non-white inkjet heads that discharge black and chromatic color inks; and a white inkjet discharging step in which ink is discharged toward the printing medium from a white inkjet head that discharges white ink, wherein the distance between the white inkjet head and the non-white inkjet head in the transport direction is greater than the distance between the non-white inkjet heads themselves. [Effects of the Invention]

[0007] According to the present invention, it is possible to provide a compact inkjet printing apparatus and inkjet printing method that can produce high-quality printouts. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a schematic diagram illustrating the configuration of an inkjet printing apparatus according to a first embodiment. [Figure 2] FIG. 10 is a schematic diagram illustrating the configuration of an inkjet printing apparatus according to a second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0009] Preferred embodiments for carrying out the present invention will be described below with reference to the drawings. Note that the following embodiments do not limit the inventions according to the claims, and not all of the combinations of features described in the embodiments are essential to the solution of the invention.

[0010] [Inkjet printing apparatus 100 according to the first embodiment] As shown in FIG. 1, the inkjet printing device 100 according to the first embodiment includes a printing medium supply unit 10 as a printing medium supply section that supplies a printing medium P made of a sheet-like resin, and a printing unit 30 that prints on the printing medium P.

[0011] Examples of the printing medium P made of a sheet-like resin include transparent synthetic resin film sheets, such as polyester film sheets, vinyl chloride film sheets, polypropylene film sheets, polyethylene film sheets, and nylon film sheets. These film sheets may be biaxially oriented film sheets, uniaxially oriented film sheets, or unoriented film sheets. Among these, polyester film sheets and oriented polypropylene film sheets are more preferred, and polyester film sheets such as polyethylene terephthalate film sheets that have been surface-treated by corona discharge treatment or the like, and biaxially oriented polypropylene film sheets are even more preferred.

[0012] There are no particular restrictions on the thickness of the printing medium P. From the viewpoints of suppressing poor appearance of the printing medium P and availability, the thickness of the printing medium P is preferably 5 μm or more, more preferably 7 μm or more, even more preferably 10 μm or more, and is preferably 50 μm or less, more preferably 40 μm or less, even more preferably 30 μm or less. Commercially available transparent synthetic resin film sheets include Lumirror T60 (Toray Industries, Inc., polyethylene terephthalate), Taiko FE2001 (Futamura Chemical Co., Ltd., corona-treated polyethylene terephthalate), E5100, E5102 (Toyobo Co., Ltd., corona-treated polyethylene terephthalate), PVC80B P (Lintec Corporation, polyvinyl chloride), KYNAS KEE70CA (Lintec Corporation, polyethylene), YUPO SG90 PAT1 (Lintec Corporation, polypropylene), FOR, FOR-AQ, FOS, FOS-AQ (Futamura Chemical Co., Ltd., corona-treated polypropylene), P2161, P2111, DP053 (Toyobo Co., Ltd., corona-treated polypropylene), U1 (Tocello Co., Ltd., corona-treated polypropylene), and Bonyl RX (Kojin Film & Chemicals Co., Ltd., nylon).

[0013] The printing medium supply unit 10 is not particularly limited as long as it can supply the printing medium P to the printing unit 30 . The printing medium supply unit 10 of this embodiment is equipped with a supply section 11 that supports a rolled printing medium P in a rotatable and rotationally controllable manner and supplies the printing medium P downstream, and supply rollers 13, 13 that supply the printing medium P supplied from the supply section 11 toward the printing unit 30 (conveying drum 31) located downstream.

[0014] The printing unit 30 includes a transport drum 31 that transports the printing medium P, at least two non-white inkjet heads 33, 33 that eject black and chromatic inks toward the printing medium P transported by the transport drum 31, a white inkjet head 35 that ejects white ink toward the printing medium P transported by the transport drum 31, and a drying mechanism 40 (41, 42) that dries the printing medium P transported to the transport drum 31.

[0015] The transport cylinder 31 is not particularly limited as long as it can transport the printing medium P, and the diameter and width of the transport cylinder 31 can be changed appropriately depending on the width of the printing medium P, etc. The diameter of the conveying drum 31 can be, for example, 0.5 to 2.5 m, preferably 0.7 to 2 m, and more preferably 1 to 1.5 m. From the viewpoint of productivity, the transport speed of the printing medium P is preferably 10 m / min or more, more preferably 20 m / min or more, and even more preferably 30 m / min or more.

[0016] The surface temperature of the conveying drum 31 is preferably 30°C or higher, more preferably 40°C or higher, and preferably 60°C or lower, more preferably 50°C or lower, in order to prevent the printing medium P made of sheet-like resin from shrinking due to heat.

[0017] The conveying drum 31 is preferably provided with a control unit that controls the surface temperature of the conveying drum 31 within the above range. The control unit is not particularly limited as long as it can control the surface temperature of the conveying drum 31 within the above range. In this embodiment, the conveying drum 31 has an internal cylindrical space 32. The control unit is configured to inject water into the space 32 and control the injected water to a specific temperature, thereby controlling the surface temperature of the conveying drum 31 within a specific range. The temperature of the water in the space 32 formed within the conveying drum 31 is preferably 30°C or higher, more preferably 40°C or higher, and preferably 60°C or lower, more preferably 50°C or lower, from the viewpoint of controlling the surface temperature of the conveying drum 31 within the above range.

[0018] The non-white inkjet head 33 ejects black and chromatic color inks toward the print medium P being transported by the transport drum 31. Chromatic color inks include cyan, magenta, and yellow, which are the three primary colors of subtractive color mixing. Furthermore, adding one or more chromatic colors selected from red, blue, orange, green, and violet is preferable because it widens the color reproduction range. In this embodiment, two non-white inkjet heads 33 are installed, but the number of ink heads may be at least two, and can be changed as appropriate depending on the colors of ink required for printing on the print medium P. Preferably, the combination of inks of three or more colors, four or more colors, or five or more colors can be used. Furthermore, the distance D1 between the non-white inkjet heads 33, 33 can also be changed as appropriate.

[0019] The white inkjet head 35 ejects white ink toward the print medium P being transported by the transport drum 31. The white inkjet head 35 is disposed opposite the transport drum 31 that transports the printing medium P so that the distance D2 between the white inkjet head 35 and the non-white inkjet heads 33 in the transport direction is greater than the distance D1 between the non-white inkjet heads 33. The distance D2 between the white inkjet head 35 and the non-white inkjet heads 33 is preferably at least ¼, more preferably at least ⅓, and even more preferably at least ½ of the circumference of the transport drum 31. With this configuration, the inkjet printing device 100 according to this embodiment is less likely to mix with the white ink, which is more susceptible to color mixing than other colors, and the black and chromatic color inks on the printing medium P onto which ink is ejected from the inkjet heads 33, 35 while being transported by the transport drum 31, thereby producing high-quality printed matter.

[0020] The non-white inkjet head 33 and the white inkjet head 35 may be installed at positions where the distances D1 and D2 satisfy the above-mentioned relationship. In the inkjet printing device 100 according to this embodiment, the white inkjet head 35 is disposed downstream of the non-white inkjet head 33. However, the non-white inkjet head 33 may be disposed downstream of the white inkjet head 35 as long as the distances D1 and D2 satisfy the relationship described above. Furthermore, in this embodiment, one white inkjet head 35 is installed, but a plurality of white inkjet heads 35 may be installed as long as the distances D1 and D2 satisfy the above-mentioned relationship. The inkjet heads 33 and 35 may use a piezo system, a thermal system, or the like, with the piezo system being more preferred.

[0021] The drying mechanism 40 is a mechanism for drying the printing medium P transported to the transport drum 31. Examples of the drying mechanism 40 include an air-blowing drying device and a heat-type drying device, but from the viewpoint of obtaining a compact inkjet printing device, an air-blowing drying device is preferable. The drying mechanism 40 may be installed downstream of the non-white inkjet head 33 and the white inkjet head 35 .

[0022] In this embodiment, the drying mechanism 40 is configured to include a first drying device 41 installed downstream of the non-white inkjet head 33 and a second drying device 42 installed downstream of the white inkjet head 35.

[0023] The outer surface temperature (printing surface temperature) of the first drying section P1 of the printing medium P dried by the first drying device 41 is preferably 35° C. or higher, more preferably 40° C. or higher, and preferably 75° C. or lower, more preferably 60° C. or lower. When the outer surface temperature of the first drying section P1 of the printing medium P is within the above range, the printing medium P, which is made of a sheet-like resin, can be properly dried while suppressing shrinkage due to heat. The temperature of the outer surface of the first drying portion P1 of the printing medium P can be changed as appropriate depending on the type of resin that constitutes the printing medium P, the type of ink, and the like.

[0024] When the first drying device 41 is an air-blowing type drying device, the temperature of the air (hot air) blown by the first drying device 41 is preferably 80°C or higher, more preferably 90°C or higher, and preferably 120°C or lower, more preferably 110°C or lower, at the air outlet of the first drying device 41. If the temperature of the hot air blown by the first drying device 41 at the air outlet of the first drying device 41 is within the above range, it is easy to adjust the outer surface temperature of the first drying section P1 of the printing medium P to the above range. The temperature of the hot air blown by the first drying device 41 at the air outlet of the first drying device 41 can be changed as appropriate depending on the type of resin constituting the printing medium P, the type of ink, and the like. The hot air flow rate is, for example, 0.5 to 15 L / min, preferably 1 to 10 L / min, and more preferably 2 to 5 L / min. The hot air speed is, for example, 0.2 to 3 m / s, preferably 0.3 to 2 m / s, and more preferably 0.5 to 1.5 m / s.

[0025] The air blower type drying device can be configured, for example, to blow warm air from an air nozzle toward the print medium P being transported by the transport drum 31. The air nozzle can spray air onto the print medium P substantially uniformly using a slit nozzle or a nozzle group in which a plurality of air nozzles are installed at regular intervals.

[0026] When a heat-type drying device is used, it is configured to dry the print medium P by irradiating heat rays from an infrared heater or the like toward the print medium P. The infrared heater is a heating element in which a composite oxide coating containing Si, Fe, Zr, Ti, Mn, etc. is provided on the surface of quartz glass, ceramic, etc. It is preferable to use infrared rays in the near-infrared to mid-infrared range, and examples of infrared heaters include short-wavelength infrared heaters, carbon heaters, and mid-wavelength infrared heaters. The irradiation conditions for the short-wavelength infrared heater can be a rated voltage of 220V, an output of 3000 to 5000W, a coil temperature of 1400 to 2500°C, and a maximum energy wavelength of approximately 0.9 to 1.7µm.

[0027] In this embodiment, two first drying devices 41 are installed downstream of the two non-white inkjet heads 33. That is, a plurality of first drying devices 41 are installed downstream of each of the non-white inkjet heads 33. By installing the first drying device 41 downstream of each non-white inkjet head 33, the ink ejected onto the printing medium P can be properly dried, and no deterioration in image quality due to ink mixing occurs, resulting in high-quality printed matter.

[0028] The outer surface temperature (printing surface temperature) of the second drying section P2 of the printing medium P dried by the second drying device 42 is preferably 70°C or higher, more preferably 80°C or higher, and preferably 110°C or lower, more preferably 100°C or lower. When the outer surface temperature of the second drying section P2 of the printing medium P is within the above range, the printing medium P, which is made of a sheet-like resin, can be properly dried while suppressing shrinkage due to heat. The temperature of the outer surface of the second drying section P2 of the printing medium P can be changed as appropriate depending on the type of resin that constitutes the printing medium, the type of ink, and the like.

[0029] When the second drying device 42 is an air-blowing type drying device, the temperature of the air (hot air) blown by the second drying device 42 is preferably 100°C or higher, more preferably 110°C or higher, and preferably 140°C or lower, more preferably 130°C or lower, at the air outlet of the second drying device 42. If the temperature of the hot air blown by the second drying device 42 at the air outlet of the second drying device 42 is within the above range, it is easy to adjust the temperature of the second drying section P2 of the printing medium P to the above range. The temperature of the hot air blown by the second drying device 42 at the air outlet of the second drying device 42 can be changed as appropriate depending on the type of resin that constitutes the printing medium P, the type of ink, and the like. The volume of the hot air and the speed of the blown air are the same as above. The same applies when a heat-type drying device is used.

[0030] In this embodiment, the second drying device 42 is, but is not limited to, an open / close type drying oven, and is a blower type drying device that blows air toward the printing medium P. The second drying device 42 according to this embodiment is disposed between the transport drum 31 and the second drying device 42, with guide rollers 37, 37 separating them to guide the printing medium P to the second drying device 42. However, this is not limited thereto, and the second drying device 42 may be disposed opposite and near the transport drum 31, similar to the first drying device 41. In addition, the second drying device 42 in this embodiment is configured to dry the printing medium P by passing through it, but like the first drying device 41 in this embodiment, it may be installed in a position opposite the conveying drum 31 and near the printing medium P, or it may be installed near the printing medium P guided by the guide rollers 37, 37.

[0031] In this embodiment, the temperature of a first drying section P1 of the printing medium P, which is dried by a first drying device 41 installed near the transport drum 31, is set lower than the temperature of a second drying section P2 of the printing medium P, which is dried by a second drying device 42 installed away from the transport drum 31. This configuration makes it possible to prevent the temperature of the surface of the transport drum 31 from rising, and to further suppress shrinkage of the printing medium P due to heat. Furthermore, since the inkjet printing device 100 according to this embodiment is equipped with multiple drying mechanisms 40 (41, 42), the printing medium P onto which ink has been ejected is not dried at high temperatures all at once, thereby further preventing the printing medium P from shrinking due to heat.

[0032] In this embodiment, the printing medium P supplied from the supply unit 11 is supplied to the transport drum 31 by the supply rollers 13, 13. In this embodiment, the process of ejecting black or chromatic ink from the non-white inkjet head 33 onto the printing medium P transported by the transport drum 31, and then drying the printing medium P by the first drying device 41 is performed twice. Thereafter, white ink is ejected from the white inkjet head 35 onto the transported printing medium P, and the printing medium P is guided to the second drying device 42 by the guide rollers 37, 37, and dried by the second drying device 42.

[0033] The inkjet printing apparatus 100 according to this embodiment can appropriately dry the print medium P, which is made of a sheet of resin, while preventing it from shrinking due to heat, preventing deterioration in image quality due to ink mixing and producing high-quality prints. Furthermore, because an air-blowing type drying device is used as the drying mechanism 40, the inkjet printing apparatus 100 according to this embodiment is compact.

[0034] The inkjet printing apparatus 100 according to the first embodiment has been described above. Next, an inkjet printing apparatus 200 according to a second embodiment will be described with reference to Fig. 2. Components that are the same as or similar to those in the above-described embodiment will be assigned the same reference numerals, and descriptions thereof may be omitted.

[0035] [Inkjet printing apparatus 200 according to a second embodiment] As shown in Figure 2, the inkjet printing device 200 according to the second embodiment includes a printing medium supply unit 10 that supplies printing medium P made of sheet-like resin, a printing unit 30 that prints on the printing medium P, and a printing medium recovery unit 50 that recovers the printing medium P that has been printed on by the printing unit 30.

[0036] The inkjet printing device 200 may be equipped with a corona treatment device (not shown) that performs a corona discharge treatment on the printing medium P before it is supplied from the printing medium supply unit 10 to the printing unit 30. By performing a corona discharge treatment on the printing medium P, the surface of the printing medium P is modified, making it suitable for image printing using ink ejected from the inkjet heads 33 and 35.

[0037] The corona treatment device is not particularly limited as long as it can perform corona discharge treatment on the printing medium P. Examples of commercially available corona treatment devices include the Corona Surface Modification Evaluation Device TEC-4AX (manufactured by Kasuga Electric Co., Ltd.). The irradiation distance to the printing medium P is preferably 0.5 mm or more and 10 mm or less to ensure a stable distance that does not interfere with the printing medium P. The corona discharge amount is 1 W·min / m 2 More than 100W min / m 2 It is preferable that:

[0038] The printing medium P that has been subjected to corona discharge treatment by a corona treatment device (not shown) can be supplied to the printing unit 30 by a plurality of supply rollers 13.

[0039] The printing unit 30 of this embodiment includes a transport drum 31 that transports the printing medium P, a non-white inkjet head 33, a first drying device 41 installed downstream of the non-white inkjet head 33, a white inkjet head 35, and a second drying device 42 installed downstream of the white inkjet head 35.

[0040] The surface temperature of the conveying drum 31 is preferably 30°C or higher, more preferably 40°C or higher, and preferably 60°C or lower, more preferably 50°C or lower, in order to prevent the printing medium P made of sheet-like resin from shrinking due to heat.

[0041] The conveying drum 31 is preferably equipped with a control unit that controls the surface temperature of the conveying drum 31 within the above range. The control unit is not particularly limited as long as it can control the surface temperature of the conveying drum 31 within the above range. As described above, the control unit may be configured to inject water into a space (not shown) formed within the conveying drum 31 and control the injected water to a specific temperature, thereby controlling the surface temperature of the conveying drum 31 within a specific range.

[0042] In this embodiment, there are four non-white inkjet heads 33 and four first drying devices 41. As described above, by installing the first drying devices 41 downstream of each non-white inkjet head 33, the ink ejected onto the printing medium P can be properly dried, and no deterioration in image quality due to ink mixing occurs, resulting in high-quality printed matter.

[0043] In this embodiment, as in the above-described embodiment, one white inkjet head 35 and one second drying device 42 are installed. However, multiple second drying devices 42 may be installed. By installing multiple second drying devices 42, the ink ejected onto the printing medium P can be dried more appropriately at a lower temperature than when one second drying device 42 is installed, and high-quality printed matter can be obtained while preventing deterioration in image quality due to ink mixing and suppressing shrinkage of the printing medium P due to heat.

[0044] The numbers of the non-white inkjet heads 33, the first drying devices 41, the white inkjet heads 35, and the second drying devices 42 can be changed as appropriate. Furthermore, the relative positions of the non-white inkjet head 33, the first drying device 41, the white inkjet head 35, and the second drying device 42 can be moved as appropriate, as long as they are installed so that the distance D2 (see FIG. 1) between the white inkjet head 35 and the non-white inkjet head 33 in the transport direction is greater than the distance D1 (see FIG. 1) between the non-white inkjet heads 33, 33. When moving the relative positions, as described above, it is preferable that the distance D2 (see FIG. 1) between the white inkjet head 35 and the non-white inkjet heads 33 is set to be preferably ¼ or more, more preferably ⅓ or more, and even more preferably ½ or more of the circumference of the transport drum 31.

[0045] In this embodiment, the first drying device 41 and the second drying device 42 are, but are not limited to, air blowing type drying devices that blow air toward the print medium P from a slit nozzle (not shown). As described above, the temperature of the first drying section (see FIG. 1) of the printing medium P dried by the first drying device 41 is preferably 35° C. or higher, more preferably 40° C. or higher, and preferably 75° C. or lower, more preferably 60° C. or lower. When the temperature of the first drying section (see FIG. 1) of the printing medium P is within the above range, the printing medium P, which is made of a sheet-like resin, can be properly dried while suppressing shrinkage due to heat. Furthermore, the temperature of the air blown by the first drying device 41 at the air outlet of the first drying device 41 is preferably 80°C or higher, more preferably 90°C or higher, and preferably 120°C or lower, more preferably 110°C or lower. If the temperature of the air blown by the first drying device 41 at the air outlet of the first drying device 41 is within the above range, it is easy to adjust the temperature of the first drying section P1 (see FIG. 1) of the printing medium P to be within the above range.

[0046] In this embodiment, the second drying device 42 is installed downstream of the white inkjet head 35 and opposite the transport drum 31 . As described above, the temperature of the second drying section (see FIG. 1) of the printing medium P dried by the second drying device 42 is preferably 70° C. or higher, more preferably 80° C. or higher, and preferably 110° C. or lower, more preferably 100° C. or lower. When the temperature of the second drying section (see FIG. 1) of the printing medium P is within the above range, the printing medium P, which is made of a sheet-like resin, can be properly dried while suppressing shrinkage due to heat. Furthermore, the temperature of the air blown by the second drying device 42 at the air outlet of the second drying device 42 is preferably 100°C or higher, more preferably 110°C or higher, and preferably 140°C or lower, more preferably 130°C or lower. If the temperature of the air blown by the second drying device 42 at the air outlet of the second drying device 42 is within the above range, it is easy to adjust the temperature of the second drying section of the printing medium P (see FIG. 1) to be within the above range.

[0047] The printing medium recovery unit 50 according to this embodiment is not particularly limited as long as it can recover the printing medium P that has been printed by the printing unit 30 . The print medium collection unit 50 according to this embodiment is configured to include a guide roller 53 that guides the print medium P to the collection section 51.

[0048] In this embodiment, the printing medium P supplied from the supply unit 11 is subjected to corona discharge treatment by a corona treatment device (not shown) as necessary, and is then supplied to the transport drum 31 by multiple supply rollers 13. In this embodiment, a process in which black or chromatic ink is ejected from the non-white inkjet head 33 toward the printing medium P transported by the transport drum 31, and the printing medium P is then dried by the first drying device 41, is performed four times. Thereafter, white ink is ejected from the white inkjet head 35 toward the transported printing medium P, and the printing medium P is then dried by the second drying device 42. The printing medium P dried by the second drying device 42 is guided by multiple guide rollers 53 and collected in the collection unit 51.

[0049] The inkjet printing apparatus 200 according to this embodiment can appropriately dry the print medium P, which is made of a sheet of resin, while preventing it from shrinking due to heat, preventing deterioration in image quality due to ink mixing and producing high-quality prints. In addition, because an air-blowing type drying device is used as the drying mechanism 40, the inkjet printing apparatus 200 according to this embodiment is also compact.

[0050] While the preferred embodiments of the present invention have been described above, the technical scope of the present invention is not limited to the scope described in the above embodiments. Various modifications and improvements can be made to the above embodiments. For example, in the above-described embodiment, a sheet made of resin is used as the printing medium P, but it is also possible to use paper, a laminate of paper and resin, or the like as the printing medium P. Furthermore, for example, the number and installation positions of the supply roller 13, guide roller 37, guide roller 53, etc. can be changed as appropriate depending on the size of the transport drum 31 and the inkjet printing device. Furthermore, for example, a cooling roller for cooling the print medium P dried by the second drying device 42 may be provided downstream of the second drying device 42. Furthermore, for example, in the above-described embodiment, the conveying drum 31 rotates clockwise, but it may also rotate counterclockwise. Furthermore, not only the inkjet printing apparatus 200 according to the second embodiment but also the inkjet printing apparatus 100 according to the first embodiment may be provided with a corona treatment device. The corona treatment device may be arranged, for example, between the printing medium P being supplied from the printing medium supply unit 10 to the printing unit 30.

[0051] Next, the inkjet printing method of the present invention will be described. Components that are the same as or similar to those in the above-described embodiment will be given the same reference numerals, and descriptions thereof may be omitted.

[0052] [Inkjet printing method] The inkjet printing method of the present invention includes a transport step in which a printing medium P made of a sheet-like resin is transported, and a printing step in which printing is performed on the printing medium P. The printing step includes a non-white inkjet ejection step in which ink is ejected toward the printing medium P from at least two non-white inkjet heads 33 that eject black and chromatic color inks, and a white inkjet ejection step in which ink is ejected toward the printing medium P from a white inkjet head 35 that ejects white ink, and a distance D2 (see Figure 1) between the white inkjet head 35 and the non-white inkjet head 33 in the transport direction is greater than the distance D1 (see Figure 1) between the non-white inkjet heads 33, 33.

[0053] The inkjet printing apparatuses 100 and 200 described above can be used in the inkjet printing method of the present invention. The conveying step can be a step of conveying the printing medium P made of a sheet-like resin to the printing unit 30. The printing process includes a non-white inkjet ejection process in which ink is ejected from at least two non-white inkjet heads 33 that eject black and chromatic inks toward the printing medium P transported by the transport process, and a white inkjet ejection process in which ink is ejected from a white inkjet head 35 that ejects white ink toward the printing medium P.

[0054] In the inkjet printing method of the present invention, the distance D2 (see FIG. 1) between the white inkjet head 35 and the non-white inkjet heads 33 in the transport direction is greater than the distance D1 (see FIG. 1) between the non-white inkjet heads 33. The distance D2 (see FIG. 1) between the white inkjet head 35 and the non-white inkjet heads 33 is preferably at least ¼, more preferably at least ⅓, and even more preferably at least ½ of the circumference of the transport drum 31. With this configuration, the inkjet printing method of this embodiment reduces the likelihood of color mixing between the white ink, which is more susceptible to color mixing than other colors, and the black and chromatic color inks on the printing medium P onto which ink is ejected from the inkjet heads 33, 35 while being transported by the transport drum 31, thereby producing high-quality printed matter. [Explanation of symbols]

[0055] 100, 200: Inkjet printing device, 10: printing medium supply unit; 11: supply section; 13: supply roller; 30: printing unit, 31: conveying cylinder, 32: space, 33: non-white inkjet head, 35: white inkjet head, 37: guide roller, 40: Drying mechanism, 41: First drying device, 42: Second drying device, 50: Printing medium recovery unit, 51: Recovery section, 53: Guide roller

Claims

1. a printing medium supply unit that supplies a printing medium made of a sheet-shaped resin; a printing unit that prints on the print medium, The printing unit includes a transport cylinder that transports the printing medium; at least two non-white inkjet heads that eject black and chromatic inks toward the print medium transported by the transport cylinder; a white inkjet head disposed downstream of the non-white inkjet head and configured to eject white ink toward the print medium being transported by the transport drum; a drying mechanism that dries the print medium transported to the transport drum, the drying mechanism includes at least two first drying devices respectively installed downstream of the at least two non-white inkjet heads, and a second drying device installed downstream of the white inkjet head; The first drying device and the second drying device are both blower type drying devices, a distance between the white inkjet head and the non-white inkjet head in the transport direction is greater than a distance between the non-white inkjet heads themselves; a distance in the transport direction between a first drying device installed downstream of a non-white inkjet head installed on the most downstream side and the white inkjet head is greater than a distance between a first drying device installed downstream of the non-white inkjet head installed on the most downstream side and the non-white inkjet head closest to the first drying device; Inkjet printing device.

2. 2. The inkjet printing apparatus according to claim 1, wherein the distance between the white inkjet head and the non-white inkjet head is equal to or greater than 1 / 4 of the circumference of the transport drum.

3. 3. The inkjet printing apparatus according to claim 1, wherein the temperature of the outer surface of the printing medium in the first drying section of the printing medium dried by the first drying device is 35°C or higher and 75°C or lower, and the temperature of the outer surface of the printing medium in the second drying section of the printing medium dried by the second drying device is 70°C or higher and 110°C or lower.

4. 4. The inkjet printing apparatus according to claim 1, further comprising a control unit for controlling a temperature of the surface of the transport drum.

5. 5. The inkjet printing apparatus according to claim 1, wherein the temperature of the surface of the transport drum is 30° C. or higher and 60° C. or lower.

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