Printing apparatus and printing method

Abstract

To reduce poor discharging caused by a fact that liquid containing a color material is cured in the vicinity of a nozzle by light leaking out from an irradiation part.SOLUTION: A printing device comprises: a discharging head which has a first nozzle row that discharges first liquid containing a photopolymerization initiator for starting a polymerization reaction of a polymerizable compound by light irradiation toward a recording medium and a second nozzle row that discharges second liquid not containing the photopolymerization initiator but containing the polymerizable compound and a color material toward the recording medium; a driving part that changes a relative position between the discharging head and the recording medium; an irradiating part that irradiates the recording medium which has the first liquid and the second liquid adhering thereto with the light. The discharging head discharges the first liquid and the second liquid so that the second liquid overlaps with the first liquid on a surface of the recording medium. A distance between the irradiating part and the first nozzle row is longer than a distance between the irradiating part and the second nozzle row.SELECTED DRAWING: Figure 4

Description

Technical Field

[0001] The present invention relates to a technique for printing on a recording medium using a photocurable liquid containing a coloring material.

Background Art

[0002] An inkjet printer that discharges an ultraviolet curable ink called UV ink from the nozzles of a discharge head toward a recording medium is known. This type of inkjet printer is provided with an irradiator for irradiating ultraviolet rays toward the recording medium to which the UV ink adheres beside the discharge head. However, when ultraviolet rays leaked from the irradiator enter the discharge surface having a large number of nozzles in the discharge head, the UV ink adhering to the discharge surface may cure, resulting in discharge defects such as nozzle clogging. Therefore, maintenance is performed to wipe off the cured UV ink from the discharge surface. However, when the UV ink adhering to the discharge surface is overly cured, a situation may occur where the cured UV ink cannot be easily removed from the discharge surface. The technique disclosed in Patent Document 1 facilitates maintenance by tilting the irradiator located between the print heads in the conveyance direction of the recording medium toward the print head that discharges ink that is relatively difficult to cure.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] If the curing of the UV ink can be further suppressed on the discharge surface, discharge defects such as nozzle clogging can be reduced. In addition, the above problems also exist in printing apparatuses other than inkjet printers that discharge UV ink, such as inkjet printers that discharge ink curable by visible light.

Means for Solving the Problem

[0005] The printing apparatus of the present invention includes a first nozzle row that discharges a first liquid containing a photopolymerization initiator that initiates a polymerization reaction of a polymerizable compound toward a recording medium by irradiation with light, and a second nozzle row that discharges a second liquid containing the polymerizable compound and a coloring material without containing the photopolymerization initiator toward the recording medium, a discharge head having the second nozzle row, a drive unit that changes a relative position between the discharge head and the recording medium, an irradiation unit that irradiates the recording medium to which the first liquid and the second liquid are attached with the light, and includes discharging the first liquid and the second liquid from the discharge head so that the second liquid overlaps the first liquid on the surface of the recording medium, a mode in which a distance between the irradiation unit and the first nozzle row is longer than a distance between the irradiation unit and the second nozzle row.

[0006] Further, the printing method of the present invention includes a discharge head that discharges a liquid that cures by irradiation with light toward a recording medium, a drive unit that changes a relative position between the discharge head and the recording medium, and an irradiation unit that irradiates the recording medium with the light, and is a printing method in a printing apparatus in which the discharge head has a first nozzle row and a second nozzle row, a distance between the irradiation unit and the first nozzle row is longer than a distance between the irradiation unit and the second nozzle row, discharging a first liquid containing a photopolymerization initiator that initiates a polymerization reaction of a polymerizable compound from the first nozzle row toward the recording medium, discharging a second liquid containing the polymerizable compound and a coloring material without containing the photopolymerization initiator from the second nozzle row toward the recording medium, and a discharging step of overlapping the second liquid with the first liquid on the surface of the recording medium, an irradiation step of irradiating the recording medium to which the first liquid and the second liquid are attached with the light, and includes a mode.

Brief Description of the Drawings

[0007]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Mode for Carrying Out the Invention

[0008] Hereinafter, embodiments of the present invention will be described. Of course, the following embodiments are merely illustrative of the present invention, and not all of the features shown in the embodiments are necessarily essential to the solution means of the invention.

[0009] (1) Outline of the technology included in the present invention: First, the outline of the technology included in the present invention will be described with reference to the examples shown in FIGS. 1 to 10. It should be noted that the drawings of the present application are schematic diagrams showing examples, and the magnification ratios in each direction shown in these drawings may be different, and the drawings may not be consistent. Of course, each element of the present technology is not limited to the specific examples indicated by the reference numerals. In the "outline of the technology included in the present invention", the content in parentheses means a supplementary explanation of the immediately preceding term. Also, in the present application, the numerical range "Min to Max" means not less than the minimum value Min and not more than the maximum value Max. The composition ratio represented by the chemical formula indicates the stoichiometric ratio, and the substances represented by the chemical formula include those deviating from the stoichiometric ratio.

[0010] [Aspect 1] The printing apparatus 1 according to one aspect of the present technology includes a discharge head 20, a drive unit 50, and an irradiation unit 60. The discharge head 20 includes a first nozzle row 41 that discharges a first liquid LQ1 containing a photopolymerization initiator that initiates a polymerization reaction of a polymerizable compound by irradiation with light toward a recording medium ME1, and a second nozzle row 42 that discharges a second liquid LQ2 that does not contain the photopolymerization initiator and contains the polymerizable compound and a coloring material toward the recording medium ME1. The drive unit 50 changes the relative position between the discharge head 20 and the recording medium ME1. The irradiation unit 60 irradiates the recording medium ME1 to which the first liquid LQ1 and the second liquid LQ2 are attached with the light. The present printing apparatus 1 discharges the first liquid LQ1 and the second liquid LQ2 from the discharge head 20 so that the second liquid LQ2 overlaps the first liquid LQ1 on the surface ME1a of the recording medium ME1. The distance L1 between the irradiation unit 60 and the first nozzle row 41 is longer than the distance L2 between the irradiation unit 60 and the second nozzle row 42.

[0011] The second liquid LQ2 discharged from the second nozzle row 42 relatively close to the irradiation unit 60 contains a polymerizable compound and a coloring material but does not contain a photoinitiator. Thus, even if the light leaking from the irradiation unit 60 enters the vicinity of the second nozzle row 42, curing of the second liquid LQ2 is suppressed in the vicinity of the second nozzle row 42. The first liquid LQ1 discharged from the first nozzle row 41 relatively far from the irradiation unit 60 contains a photoinitiator. When the second liquid LQ2 overlaps the first liquid LQ1 on the surface ME1a of the recording medium ME1, the photoinitiator initiates the polymerization reaction of the polymerizable compound by the light irradiated from the irradiation unit 60, and the second liquid LQ2 containing the polymerizable compound and the coloring material cures rapidly. Since the first nozzle row 41 that discharges the first liquid LQ1 containing the photoinitiator is relatively far from the irradiation unit 60, it is difficult for the light leaking from the irradiation unit 60 to enter the vicinity of the first nozzle row 41. Thereby, curing of the first liquid LQ1 is suppressed in the vicinity of the first nozzle row 41. Therefore, the above-described aspect 1 can provide a printing apparatus that reduces ejection failure caused by curing of the liquid containing the coloring material in the vicinity of the nozzle due to the light leaking from the irradiation unit.

[0012] Here, the ejection head may include two or more separate heads. The first nozzle row and the second nozzle row may be provided in separate heads. The driving unit may move the ejection head without moving the recording medium, may move the recording medium without moving the ejection head, may move both the ejection head and the recording medium, or may move the ejection head without moving the recording medium in a first direction and move the recording medium without moving the ejection head in a second direction intersecting the first direction. In any case, it includes changing the relative position between the ejection head and the recording medium. Light includes ultraviolet rays abbreviated as UV, visible light, and the like. The overlap of the second liquid and the first liquid on the surface of the recording medium includes both the case where the second liquid overlaps the first liquid adhered to the recording medium and the case where the first liquid overlaps the second liquid adhered to the recording medium. The first liquid adhered to the recording medium may have a portion that does not overlap the second liquid. The distance between the irradiation unit and the first nozzle row shall be the distance between the irradiation unit and the nozzle with the shortest distance from the irradiation unit among the plurality of nozzles included in the first nozzle row. The distance between the irradiation unit and the second nozzle row shall be the distance between the irradiation unit and the nozzle with the shortest distance from the irradiation unit among the plurality of nozzles included in the second nozzle row. In the present application, "first", "second",... are terms for identifying each component included in a plurality of similar components and do not mean order. Note that the above remarks also apply in the following aspects.

[0013] [Aspect 2] The first liquid LQ1 may contain the polymerizable compound. The first nozzle row 41 may discharge the first liquid LQ1 containing the photopolymerization initiator and the polymerizable compound. In this case, when the photopolymerization initiator in the first liquid LQ1 starts the polymerization reaction of the polymerizable compound by the light irradiated from the irradiation unit 60, the polymerization reaction of the polymerizable compound in the first liquid LQ1 promotes the polymerization reaction of the polymerizable compound in the second liquid LQ2. Therefore, in this aspect, the liquid attached to the recording medium can be quickly cured. Note that although not included in the above Aspect 2, when the first liquid does not contain a polymerizable compound, the liquid on the surface of the recording medium is cured by the photopolymerization initiator of the first liquid starting the polymerization reaction of the polymerizable compound of the second liquid, so it is included in this technology.

[0014] [Aspect 3] The first liquid LQ1 may contain a second colorant. The first nozzle row 41 may discharge the first liquid LQ1 containing the photopolymerization initiator and the second colorant. For example, when the liquid contains a resin component, the cured resin may turn yellow due to aging. In this case, it is conceivable to add a blue colorant to the liquid in advance so that the yellowing is less noticeable. Thus, in this aspect, a base color can be added to the image formed on the recording medium ME1, so a preferable printing apparatus can be provided.

[0015] [Aspect 4] As illustrated in FIG. 2 and the like, the driving unit 50 may change the relative position of the discharge head 20 with respect to the recording medium ME1 in the main scanning direction D1, and when the first liquid LQ1 and the second liquid LQ2 are not discharged from the discharge head 20 toward the recording medium ME1, the relative position of the recording medium ME1 with respect to the discharge head 20 may be changed in the feed direction D2 intersecting the main scanning direction D1. Here, the feed direction D2 is set to be a direction from the upstream side S1 to the downstream side S2. The irradiation unit 60 may be disposed on the downstream side S2 with respect to the first nozzle row 41 and may be at a position where it can irradiate the second liquid LQ2 attached to the recording medium ME1. By disposing the irradiation unit 60 on the downstream side S2 in the feed direction D2 with respect to the first nozzle row 41, light can be easily irradiated onto the first liquid LQ1 attached to the recording medium ME1, and the distance L1 between the irradiation unit 60 and the first nozzle row 41 can be made longer more easily than the distance L2 between the irradiation unit 60 and the second nozzle row 42. Therefore, this aspect can provide a preferable serial type printing apparatus. Here, when the liquid is not discharged from the discharge head toward the recording medium, it is not limited to the case where no liquid is discharged from the discharge head at all, and also includes the case where the liquid is discharged from the discharge head without being directed toward the recording medium, such as during flushing. This proviso also applies to the following aspects.

[0016] [Aspect 5] ​As illustrated in FIGS. 2 and 3, the second nozzle row 42 may be disposed on the downstream side S2 with respect to the first nozzle row 41. In one main scan of the ejection head 20 that relatively moves in the main scanning direction D1, the area of the recording medium ME1 that can be irradiated by the irradiation unit 60 may include the area where the second liquid LQ2 can be ejected from the second nozzle row 42, and may not include the area where the first liquid LQ1 can be ejected from the first nozzle row 41. In one main scan, since the second liquid LQ2 is ejected and light is irradiated in the area that can be irradiated by the irradiation unit 60, the second liquid LQ2 containing the coloring material cures in a state where the shape of the dots of the second liquid LQ2 is sufficiently maintained. Therefore, this aspect can provide a serial type printing apparatus that improves the image quality of an image formed on a recording medium.

[0017] [Aspect 6] As illustrated in FIGS. 5, 7, etc., the drive unit 50 may change the relative position of the recording medium ME1 with respect to the ejection head 20 in the relative movement direction D4. Here, the relative movement direction D4 is set to be the direction from the upstream side S1 to the downstream side S2. The second nozzle row 42 may be arranged on the downstream side S2 with respect to the first nozzle row 41. The irradiation unit 60 may be arranged on the downstream side S2 with respect to the second nozzle row 42. For example, in the case of a line-type printing apparatus in which the recording medium ME1 moves in the feeding direction D2 without the ejection head 20 moving, the relative movement direction D4 is the feeding direction D2 of the recording medium ME1. By arranging the first nozzle row 41, the second nozzle row 42, and the irradiation unit 60 in this order in the feeding direction D2, light can be irradiated onto the recording medium ME1 to which the first liquid LQ1 and the second liquid LQ2 are attached, and the distance L1 between the irradiation unit 60 and the first nozzle row 41 can be more easily made longer than the distance L2 between the irradiation unit 60 and the second nozzle row 42. Also, even in the case of a serial-type printing apparatus that moves the ejection head 20 in the main scanning direction D1, the relative movement direction D4 can be applied to the main scanning direction D1. In this case, by arranging the first nozzle row 41, the second nozzle row 42, and the irradiation unit 60 in this order in the main scanning direction D1, light can be irradiated onto the recording medium ME1 to which the first liquid LQ1 and the second liquid LQ2 are attached, and the distance L1 between the irradiation unit 60 and the first nozzle row 41 can be more easily made longer than the distance L2 between the irradiation unit 60 and the second nozzle row 42. Therefore, this aspect can provide a preferable printing apparatus.

[0018] [Aspect 7] As illustrated in FIG. 7, the driving unit 50 may change the relative position of the ejection head 20 with respect to the recording medium ME1 in the main scanning direction D1, and may change the relative position of the recording medium ME1 with respect to the ejection head 20 in the feeding direction D2 intersecting the main scanning direction D1 when the first liquid LQ1 and the second liquid LQ2 are not ejected from the ejection head 20 toward the recording medium ME1. In the main scanning direction D1, the irradiation unit 60, the second nozzle row 42, the first nozzle row 41, the second nozzle row 42, and the irradiation unit 60 may be arranged in this order. In this aspect, since an image can be formed on the recording medium ME1 in both the forward main scan and the reverse main scan, a preferable serial type printing apparatus can be provided.

[0019] [Aspect 8] As illustrated in FIG. 10, the ejection head 20 may include a first head 21 having the first nozzle row 41 and a second head 22 having the second nozzle row 42. The driving unit 50 may include a first main scanning unit (for example, a first carriage driving unit 51a) that includes a first carriage 52a on which the first head 21 is mounted and changes the relative position of the first carriage 52a with respect to the recording medium ME1 in the main scanning direction D1, and a second carriage 52b on which the second head 22 is mounted and that is separate from the first carriage 52a, and a second main scanning unit (for example, a second carriage driving unit 51b) that changes the relative position of the second carriage 52b with respect to the recording medium ME1 in the main scanning direction D1. In this aspect, a preferable serial type printing apparatus can be provided.

[0020] [Aspect 9] Incidentally, a printing method according to one aspect of the present technology includes a discharge head 20 that discharges a liquid that cures upon irradiation with light toward a recording medium ME1, a drive unit 50 that changes the relative position between the discharge head 20 and the recording medium ME1, and an irradiation unit 60 that irradiates the recording medium ME1 with the light. This is a printing method in a printing apparatus 1 in which the discharge head 20 has a first nozzle row 41 and a second nozzle row 42. Here, the distance L1 between the irradiation unit 60 and the first nozzle row 41 is longer than the distance L2 between the irradiation unit 60 and the second nozzle row 42. This printing method includes the following steps (A) and (B). (A) A discharge step ST1 of discharging a first liquid LQ1 containing a photopolymerization initiator that initiates a polymerization reaction of a polymerizable compound by irradiation with the light from the first nozzle row 41 toward the recording medium ME1, and discharging a second liquid LQ2 that does not contain the photopolymerization initiator and contains the polymerizable compound and a colorant from the second nozzle row 42 toward the recording medium ME1, and overlaying the second liquid LQ2 on the first liquid LQ1 on the surface ME1a of the recording medium ME1. (B) An irradiation step ST2 of irradiating the recording medium ME1 to which the first liquid LQ1 and the second liquid LQ2 are attached with the light. This aspect can provide a printing method for reducing ejection failure caused by curing of a liquid containing a colorant in the vicinity of the nozzle due to light leaking from the irradiation unit.

[0021] Furthermore, the present technology is applicable to a printing system including the above-described printing apparatus, a printing method for the printing system, and the like. The printing apparatus may be composed of a plurality of dispersed parts.

[0022] (2) Specific example of a printing system including a printing apparatus: FIG. 1 schematically illustrates a printing system including a printing apparatus that uses a UV ink as a liquid that cures upon irradiation with light. Here, ultraviolet rays, abbreviated as UV, are an example of light. The ink is assumed to include a liquid that does not contain a coloring material. The printing system SY1 shown in FIG. 1 includes a host device HO1 and a printing apparatus 1. Note that the printing system SY1 may include additional elements not shown in FIG. 1, and the printing apparatus 1 may include additional elements not shown in FIG. 1. FIG. 1 shows a serial printer, which is a type of UV inkjet printer, as the printing apparatus 1. The printing apparatus 1 includes a controller 10, a nonvolatile memory 15, a RAM 16, a communication I / F 17, a discharge head 20, a drive unit 50, an irradiation unit 60, etc. Here, RAM is an abbreviation for Random Access Memory, and I / F is an abbreviation for interface. The controller 10, the nonvolatile memory 15, the RAM 16, and the communication I / F 17 are connected to a bus and can input and output information to and from each other.

[0023] The nonvolatile memory 15 is a rewritable large-capacity memory that stores information necessary for the operation of the printing apparatus 1, such as firmware. As the nonvolatile memory 15, a nonvolatile semiconductor memory such as a flash memory, a magnetic storage device such as a hard disk, etc. can be used. The RAM 16 is a large-capacity volatile semiconductor memory that stores input images and the like received from the host device HO1 or an external memory (not shown). The communication I / F 17 is connected to the host device HO1 by wire or wirelessly and inputs and outputs information to and from the host device HO1. The host device HO1 includes computers such as personal computers and tablet terminals, mobile phones such as smartphones, digital cameras, digital video cameras, etc.

[0024] The controller 10 includes a CPU 11, a memory 12 such as a ROM, etc., and a resolution conversion unit 13a, a color conversion unit 13b, a halftone processing unit 13c, a nozzle assignment unit 13d, a drive signal transmission unit 13e, etc. are realized. Here, CPU is an abbreviation for Central Processing Unit, and ROM is an abbreviation for Read Only Memory. The controller 10 controls the main scanning and sub-scanning by the drive unit 50, the ejection of the ink droplets 37 by the ejection head 20, and the irradiation of UV by the irradiation unit 60 based on the image data corresponding to the output image IM0 illustrated in FIG. 2. The main scanning means the relative movement between the ejection head 20 and the recording medium ME1 in the main scanning direction, and the sub-scanning means the relative movement between the ejection head 20 and the recording medium ME1 in the feed direction D2. The controller 10 can be configured by an SoC or the like. SoC is an abbreviation for System on a Chip. The CPU 11 is a device that mainly performs information processing and control in the printing apparatus 1.

[0025] The resolution conversion unit 13a converts the resolution of the input image from the host device HO1 or the like to the set resolution. The input image is represented by, for example, original RGB data having multi-level integer values of R, G, and B for each pixel. Here, R means red, G means green, and B means blue. The resolution conversion unit 13a converts the original RGB data into input color gradation data DA1 of the set resolution. The input color gradation data DA1 is represented by, for example, RGB data having multi-level integer values of R, G, and B for each pixel. The number of gradations of the RGB data and the original RGB data includes 2 8 、2 16 、etc.

[0026] The color conversion unit 13b refers to, for example, a color conversion look-up table in which the correspondence between the gradation values of R, G, and B and the gradation values of C, M, Y, and K is defined, and converts the input color gradation data DA1 into output color gradation data DA2 having multi-level integer values of C, M, Y, and K for each pixel. Here, C means cyan, M means magenta, Y means yellow, and K means black. The number of gradations of the output color gradation data DA2 includes 28 , 2 16 , etc. The output color gradation data DA2 represents the usage amount of the ink 36 for each pixel.

[0027] The halftone processing unit 13c performs predetermined halftone processing such as dithering method, error diffusion method, or density pattern method on the gradation values of each pixel constituting the output color gradation data DA2 to reduce the number of gradations of the gradation values and generate halftone data DA3. The halftone data DA3 represents the dot formation state. The halftone data DA3 may be binary data representing the presence or absence of dot formation, or may be multi-value data of three or more gradations capable of corresponding to dots of different sizes such as small, medium, and large dots. The binary data can be, for example, data corresponding 1 to dot formation and 0 to no dot. The four-value data can represent each of the small, medium, and large dots with 2 bits.

[0028] The nozzle assignment unit 13d generates nozzle data DA4 by performing nozzle assignment processing for rearranging the halftone data DA3 in the order in which dots are formed by the drive unit 50. The nozzle assignment processing in a serial printer is also called rasterization processing.

[0029] The drive signal transmission unit 13e generates a drive signal SG corresponding to the voltage signal applied to the drive element 32 of the ejection head 20 from the nozzle data DA4 and outputs it to the drive circuit 31. For example, if the nozzle data DA4 is "dot formation", the drive signal transmission unit 13e outputs a drive signal SG for ejecting ink droplets 37 for dot formation. Also, when the nozzle data DA4 is four-value data, a drive signal SG for ejecting ink droplets 37 corresponding to each of the small, medium, and large dots is output.

[0030] Each of the above units 13a to 13e may be configured by an ASIC, and may directly read data to be processed from the RAM 16 or directly write the processed data to the RAM 16. Here, ASIC is an abbreviation for Application Specific Integrated Circuit. Further, the printing apparatus 1 may receive any one of input gradation data DA1, output gradation data DA2, halftone data DA3, and nozzle data DA4 from the host device HO1 and generate a drive signal SG.

[0031] The drive unit 50 controlled by the controller 10 includes a carriage drive unit 51, a carriage 52, a roller drive unit 55, a pair of conveyance rollers 56, a pair of discharge rollers 57, a platen 58, and the like. A discharge head 20 and an irradiation unit 60 are mounted on the carriage 52. The drive unit 50 reciprocates the carriage 52 by driving the carriage drive unit 51, and sends the recording medium ME1 in the feed direction D2 along the conveyance path 59 by driving the roller drive unit 55. Here, the feed direction D2 is defined as the direction from the upstream side S1 to the downstream side S2. In FIG. 1, the feed direction D2 is the right direction, the upstream side S1 is the left side, and the downstream side S2 is the right side. The carriage drive unit 51 performs a main scan for moving the carriage 52 in the main scan direction D1 shown in FIG. 2 and the like according to the control of the controller 10. As shown in FIG. 2, the main scan direction D1 collectively refers to the forward direction D11 and the reverse direction D12 opposite to the forward direction D11. The roller drive unit 55 performs a sub-scan for sending the recording medium ME1 in the feed direction D2 by rotating the rollers 56a and 57a of the roller pairs 56 and 57 according to the control of the controller 10. The material of the recording medium ME1 is not particularly limited, and various materials such as resin, metal, paper, etc. can be considered. The shape of the recording medium ME1 is also not particularly limited, and various shapes such as rectangular, roll-shaped, etc. can be considered, and a three-dimensional shape may also be possible.

[0032] The carriage 52 on which the ejection head 20 and the irradiation unit 60 are mounted may be equipped with an ink cartridge 35 that supplies ink 36 to the ejection head 20 as ink droplets 37. Of course, the ink 36 may be supplied to the ejection head 20 from an ink cartridge 35 installed outside the carriage 52 via a tube. The carriage 52 is fixed to an endless belt (not shown) and is movable along the guide 53 in the main scanning direction D1 shown in FIG. 2 and the like. The guide 53 is a long member whose longitudinal direction is oriented in the main scanning direction D1. The carriage drive unit 51 is composed of a servo motor and moves the carriage 52 in the forward direction D11 and the reverse direction D12 according to a command from the controller 10.

[0033] The pair of conveyance rollers 56 upstream from the ejection head 20 includes a drive conveyance roller 56a that contacts one surface of the recording medium ME1 and a driven conveyance roller 56b that contacts the other surface of the recording medium ME1. During sub-scanning, the pair of conveyance rollers 56 feeds the recording medium ME1 held in a nip toward the ejection head 20 and the irradiation unit 60 by the rotation of the drive conveyance roller 56a. The pair of discharge rollers 57 downstream from the ejection head 20 includes a drive discharge roller 57a that contacts one surface of the recording medium ME1 and a driven discharge roller 57b that contacts the other surface of the recording medium ME1. During sub-scanning, the pair of discharge rollers 57 conveys the recording medium ME1 held in a nip toward a discharge tray (not shown) by the rotation of the drive discharge roller 57a.

[0034] The roller drive unit 55 is composed of a servo motor and rotates the rollers 56a and 57a according to a command from the controller 10. The rollers 56a and 57a feed the recording medium ME1 in the feed direction D2 by rotating.

[0035] The platen 58 supports the recording medium ME1 in the conveyance path 59. The ejection head 20 controlled by the controller 10 ejects ink droplets 37 toward the recording medium ME1 supported by the platen 58, thereby attaching ink 36 to the recording medium ME1. The irradiation unit 60 controlled by the controller 10 irradiates UV toward the ink 36 attached to the recording medium ME1, thereby curing the ink 36 attached to the recording medium ME1.

[0036] As illustrated in FIG. 2, the ejection head 20 includes a first head 21 having a first nozzle row 41 and a second head 22 having a second nozzle row 42. Details of the first head 21 and the second head 22 will be described later. The ejection head 20 has a nozzle row 33 including a plurality of nozzles 34 on the nozzle surface 20a, and includes a drive circuit 31, drive elements 32, and the like. The nozzle surface 20a is the ejection surface of the ink droplets 37 as liquid droplets. The drive circuit 31 applies a voltage signal to the drive element 32 in accordance with the drive signal SG input from the drive signal transmission unit 13e. As the drive element 32, a piezoelectric element that applies pressure to the ink 36 in the pressure chamber communicating with the nozzle 34, a drive element that generates bubbles in the pressure chamber by heat to eject the ink droplets 37 from the nozzle 34, or the like can be used. The nozzle is a small hole through which the ink droplets 37 are ejected. Ink 36 is supplied from the ink cartridge 35 to the pressure chamber of the ejection head 20. The combination of the ink cartridge 35 and the nozzle row 33 is provided for each of, for example, CL, C, M, Y, and K. Here, CL means clear, and the CL ink means clear ink as the first liquid LQ1. The ink 36 in the pressure chamber is ejected as ink droplets 37 from the nozzle 34 toward the recording medium ME1 by the drive element 32. Thereby, dots of the ink droplets 37 are formed on the recording medium ME1.

[0037] FIG. 2 is a plan view schematically illustrating the operation of the serial type printing apparatus 1. FIG. 3 is a bottom view schematically illustrating the configuration of the ejection head 20 and the irradiation unit 60. The carriage 52 shown in FIGS. 2 and 3 is equipped with a first head 21, a second head 22, and a plurality of irradiation units 60. The second head 22 and the plurality of irradiation units 60 are arranged on the downstream side S2 with respect to the first head 21. The plurality of irradiation units 60 include a first irradiation unit 60a located at a position facing the forward direction D11 from the second head 22, and a second irradiation unit 60b located at a position facing the reverse direction D12 from the second head 22.

[0038] The first head 21 has a first nozzle row 41 including a plurality of nozzles 34a arranged at intervals of a nozzle pitch Np in the nozzle alignment direction D3 on the nozzle surface 20a. The nozzles 34a discharge clear ink 36CL as the first liquid LQ1 as ink droplets 37. The clear ink 36CL contains a polymerizable compound and a photoinitiator that initiates the polymerization reaction of the polymerizable compound by UV irradiation as a UV ink component, but does not contain a coloring material. Thus, the clear ink 36CL is a generally colorless and transparent liquid.

[0039] The second head 22 has a plurality of second nozzle rows 42 each including a plurality of nozzles 34b arranged at intervals of a nozzle pitch Np in the nozzle alignment direction D3 on the nozzle surface 20a. The nozzles 34b discharge a second liquid LQ2 containing a pigment as a coloring material as ink droplets 37. The second liquid LQ2 contains a cyan ink 36c containing a cyan pigment, a magenta ink 36m containing a magenta pigment, a yellow ink 36y containing a yellow pigment, and a black ink 36k containing a black pigment. These inks may be referred to as color inks 36c, 36m, 36y, and 36k. The second liquid LQ2 contains a polymerizable compound as a UV ink component, but does not contain a photoinitiator. The second head 22 has a magenta nozzle row including a plurality of nozzles 34b that discharge magenta ink 36m, a cyan nozzle row including a plurality of nozzles 34b that discharge cyan ink 36c, a yellow nozzle row including a plurality of nozzles 34b that discharge yellow ink 36y, and a black nozzle row including a plurality of nozzles 34b that discharge black ink 36k as the second nozzle row 42. Further, the ejection head 20 collectively refers to the first head 21 and the second head 22, the nozzle array 33 collectively refers to the first nozzle array 41 and the second nozzle array 42, and the nozzle 34 collectively refers to the nozzles 34a and 34b.

[0040] As shown in FIG. 3, the nozzle arrangement direction D3 may be orthogonal to the main scanning direction D1, or may intersect obliquely without being orthogonal to the main scanning direction D1. In other words, as shown in FIG. 3, the nozzle arrangement direction D3 may coincide with the feeding direction D2, or may be offset within a range of less than 90° from the feeding direction D2. The plurality of nozzles 34 included in the nozzle array 33 may be arranged in a line as shown in FIG. 3, or may be arranged in a staggered pattern.

[0041] Each irradiation unit 60 includes a housing 61 having an opening facing the recording medium ME1, and a light source 62 disposed in the internal space of the housing 61 in a direction facing the recording medium ME1. The light source 62 emits UV having a peak wavelength in the range of 360 to 420 nm, for example, around 395 nm. The UV emitted from the light source 62 is irradiated from the opening of the housing 61 toward the recording medium ME1. Although an LED, that is, a light-emitting diode is preferable as the light source 62, a metal halide lamp or the like can also be used. Since the first irradiation unit 60a and the second irradiation unit 60b are respectively arranged at positions on the downstream side S2 of the first nozzle array 41 and facing the forward direction D11 and the backward direction D12 from the second nozzle array 42, the irradiation unit 60 is positioned so as to be able to irradiate the second liquid LQ2 adhering to the recording medium ME1.

[0042] As shown in FIGS. 2 and 3, the distance L1 between the irradiation unit 60 and the first nozzle row 41 is longer than the distance L2 between the irradiation unit 60 and the second nozzle row 42. Here, the distance L1 is the distance in a state where the irradiation unit 60 and the first nozzle row 41 are projected onto a plane along the main scanning direction D1 and the feeding direction D2, and is the distance between the irradiation unit 60 and the nozzle among the plurality of nozzles 34a included in the first nozzle row 41 that has the shortest distance from the irradiation unit 60. The distance L2 is the distance in a state where the irradiation unit 60 and the second nozzle row 42 are projected onto a plane along the main scanning direction D1 and the feeding direction D2, and is the distance between the irradiation unit 60 and the nozzle among the plurality of nozzles 34b included in the second nozzle row 42 that has the shortest distance from the irradiation unit 60.

[0043] The printing apparatus 1 shown in FIG. 2 performs bidirectional printing in which ink droplets 37 are ejected from the ejection head 20 when the carriage 52 is moved in the forward direction D11 and the backward direction D12. The carriage 52 and the recording medium ME1 operate as follows, for example.

[0044] In the first main scan, the carriage 52 is moved in the forward direction D11 by driving of the carriage drive unit 51. The ejection head 20 ejects the ink droplets 37 toward the recording medium ME1 while moving in the forward direction D11. In the example shown in FIG. 2, the first head 21 ejects the clear ink 36CL to the most downstream area A1 on the surface ME1a of the recording medium ME1 from the first nozzle row 41. Although the clear ink 36CL is ejected as the ink droplets 37 from each nozzle 34a, the clear ink 36CL is ejected so that no gap is formed in the area A1, and thus the clear ink 36CL is applied to the entire surface of the area A1. After the ejection of the ink droplets 37 is completed in the first main scan, in the sub-scan, the recording medium ME1 is moved by one band in the feeding direction D2 by driving of the roller drive unit 55.

[0045] In the second main scan, the carriage 52 moves in the return direction D12 by the drive of the carriage drive unit 51. The ejection head 20 ejects ink droplets 37 toward the recording medium ME1 while moving in the return direction D12. In the example shown in FIG. 2, the first head 21 ejects the clear ink 36CL from the first nozzle row 41 to the area A2 following the area A1 from the upstream side S1. Here too, the clear ink 36CL is applied to the entire surface of the area A2. After the ejection of the ink droplets 37 is completed in the second main scan, in the sub-scan, the recording medium ME1 moves by one band in the feed direction D2 by the drive of the roller drive unit 55.

[0046] In the third main scan, the carriage 52 moves in the forward direction D11 by the drive of the carriage drive unit 51. When the ejection head 20 is moving in the forward direction D11, it ejects ink droplets 37 toward the recording medium ME1. In the example shown in FIG. 2, the first head 21 ejects clear ink 36CL from the first nozzle row 41 into the area A3 following the area A2 toward the upstream side S1, and the second head 22 ejects the second liquid LQ2 from the second nozzle row 42 into the most downstream area A1. The ejection of the second liquid LQ2 is performed according to the nozzle data DA4 shown in FIG. 1. When cyan ink 36c is ejected from the nozzle 34b, a dot DT0 of C is formed in the area A1. When magenta ink 36m is ejected from the nozzle 34b, a dot DT0 of M is formed in the area A1. When yellow ink 36y is ejected from the nozzle 34b, a dot DT0 of Y is formed in the area A1. When black ink 36k is ejected from the nozzle 34b, a dot DT0 of K is formed in the area A1. Therefore, the first liquid LQ1 and the second liquid LQ2 are ejected from the ejection head 20 so that the second liquid LQ2 overlaps the first liquid LQ1 on the surface ME1a of the recording medium ME1. Also, in the third main scan, the controller 10 turns off the light source 62 of the first irradiation unit 60a and turns on the light source 62 of the second irradiation unit 60b to irradiate the area A1 with UV from the second irradiation unit 60b. The UV from the second irradiation unit 60b is not irradiated to the area A3. Therefore, in the third main scan, the area of the recording medium ME1 that can be irradiated by the irradiation unit 60 includes the area A1 where the second liquid LQ2 can be ejected from the second nozzle row 42 and does not include the area A3 where the first liquid LQ1 can be ejected from the first nozzle row 41. After the ejection of the ink droplets 37 is completed in the third main scan, in the sub-scan, the recording medium ME1 moves one band in the feed direction D2 by the drive of the roller drive unit 55.

[0047] In the fourth main scan, the carriage 52 moves in the return direction D12 by the drive of the carriage drive unit 51. When the discharge head 20 is moving in the return direction D12, it discharges the ink droplets 37 toward the recording medium ME1. In the example shown in FIG. 2, the first head 21 discharges the clear ink 36CL from the first nozzle row 41 to an area (not shown) following the area A3 to the upstream side S1, and the second head 22 discharges the second liquid LQ2 from the second nozzle row 42 to the area A2. Also, in the fourth main scan, the controller 10 turns off the light source 62 of the second irradiation unit 60b and turns on the light source 62 of the first irradiation unit 60a, thereby irradiating the area A2 with UV from the first irradiation unit 60a. Therefore, in the fourth main scan, the area of the recording medium ME1 that can be irradiated by the irradiation unit 60 includes the area A2 where the second liquid LQ2 can be discharged from the second nozzle row 42 and does not include the area where the first liquid LQ1 can be discharged from the first nozzle row 41. After the discharge of the ink droplets 37 is completed in the fourth main scan, in the sub-scan, the recording medium ME1 moves one band in the feed direction D2 by the drive of the roller drive unit 55. Thereafter, the main scan in which the carriage 52 moves in the forward direction D11, the sub-scan, the main scan in which the carriage 52 moves in the return direction D12, and the sub-scan are repeated.

[0048] As described above, the carriage drive unit 51 changes the relative position of the discharge head 20 with respect to the recording medium ME1 in the main scan direction D1, and when the first liquid LQ1 and the second liquid LQ2 are not discharged from the discharge head 20 toward the recording medium ME1, the roller drive unit 55 changes the relative position of the recording medium ME1 with respect to the discharge head 20 in the feed direction D2. The discharge head 20 discharges the first liquid LQ1 and the second liquid LQ2 during the main scan.

[0049] Next, examples of the compositions of the first liquid LQ1 and the second liquid LQ2 will be described. The first liquid LQ1 contains a photoinitiator. The first liquid LQ1 may or may not contain a polymerizable compound like the above-described clear ink 36CL. Also, the first liquid LQ1 may or may not contain a colorant like the clear ink 36CL. For example, when the first liquid LQ1 contains a resin component, the cured resin may turn yellow due to aging. In this case, by adding a blue colorant to the first liquid LQ1 in advance, the yellowing can be made less noticeable. In this example, the blue colorant is an example of the second colorant. On the other hand, the second liquid LQ2 does not contain a photoinitiator and contains a polymerizable compound and a colorant.

[0050] The polymerizable compound polymerizes by the action of the photoinitiator and cures the ink containing the first liquid LQ1 and the second liquid LQ2. For the polymerizable compound, various (meth)acrylate monomers, various (meth)acrylate oligomers, various vinyl monomers, various vinyl ether monomers, etc. can be used, and vinyl ether group-containing (meth)acrylic acid esters (referred to as monomer A) represented by the following general formula (1) can be used. CH2=CR 1 -COOR 2 -O-CH=CH-R 3 …(1) However, R 1 is a hydrogen atom or a methyl group, R 2 is a divalent organic residue having 2 to 20 carbon atoms, and R 3 is a hydrogen atom or a monovalent organic residue having 1 to 11 carbon atoms. For monomer A, various monomers disclosed in JP-A-2014-195889 can be used. The content of the polymerizable compound in the first liquid LQ1 and the second liquid LQ2 can be, for example, about 60 to 95% by mass.

[0051] The photoinitiator initiates the polymerization reaction of the polymerizable compound by UV irradiation. As the photoinitiator, an alkylphenone-based photoinitiator, an acylphosphine-based photoinitiator, a titanocene-based photoinitiator, a thioxanthone-based photoinitiator, etc. can be used. The content of the photoinitiator in the first liquid LQ1 can be, for example, about 9 to 14% by mass.

[0052] As the colorant, pigments such as inorganic pigments and organic pigments can be used. As the inorganic pigment, carbon black, metal oxides such as iron oxide and titanium oxide, etc. can be used. As the organic pigment, azo pigments such as monoazo-based azo pigments and disazo-based azo pigments, condensed polycyclic pigments such as phthalocyanine pigments, perylene pigments, perinone pigments, and anthraquinone pigments, lake pigments such as dyed lake pigments, fluorescent pigments, etc. can be used. The average particle diameter of the pigment by the dynamic light scattering method can be, for example, about 30 to 2000 nm. The colorant added to the first liquid LQ1 and the second liquid LQ2 may be one type or two or more types. The content of the colorant in the color inks 36c, 36m, 36y, 36k can be, for example, about 1.5 to 6% by mass.

[0053] Incidentally, the first liquid LQ1 and the second liquid LQ2 may contain additives such as a dispersant, a surfactant also called a leveling agent, a polymerization inhibitor, a polymerization accelerator, a penetration accelerator, a wetting agent, etc. as necessary.

[0054] By the way, if there is a UV irradiation part beside the discharge head that discharges the UV ink containing the photoinitiator and the polymerizable compound from the nozzle surface, the UV ink may cure on the nozzle surface due to the UV leaking from the irradiation part, and discharge defects such as nozzle clogging may occur. If the UV ink adhering to the nozzle surface cures too much, a situation may occur where the UV ink cannot be easily removed from the nozzle surface even if maintenance is performed to wipe the UV ink from the discharge surface.

[0055] In this specific example, a second nozzle row 42 for discharging a second liquid LQ2 containing a polymerizable compound and a colorant without containing a photoinitiator is provided in a discharge head 20, and a first nozzle row 41 for discharging a first liquid LQ1 containing a photoinitiator is farther from an irradiation unit 60 than the second nozzle row 42. As shown in FIGS. 2 and 3, a distance L1 between the irradiation unit 60 and the first nozzle row 41 is longer than a distance L2 between the irradiation unit 60 and the second nozzle row 42. Thereby, poor discharge due to curing of the liquid containing the colorant in the vicinity of the nozzle by the UV leaking from the irradiation unit 60 is reduced.

[0056] (3) Operations and effects of the serial type printing apparatus according to the specific example: FIG. 4 schematically illustrates the operation of the serial type printing apparatus 1 shown in FIGS. 1 and 2. A main scan SC1 shown at the upper part of FIG. 4 corresponds to the first main scan shown in FIG. 2. A main scan SC2 shown at the lower part of FIG. 4 corresponds to the third main scan shown in FIG. 2. FIG. 4 shows the state of an area A1 on the surface ME1a of a recording medium ME1.

[0057] In the first main scan SC1, a first head 21 mounted on a carriage 52 moves in a forward direction D11, and ink droplets 37 of a clear ink 36CL as a first liquid LQ1 are discharged from a nozzle 34a of the first nozzle row 41 toward the area A1 during the movement. The clear ink 36CL contains a photoinitiator and a polymerizable compound, and may contain a second colorant. In the first main scan SC1, the entire surface of the area A1 is coated with the clear ink 36CL. After the discharge of the clear ink 36CL is completed, a sub-scan, a main scan in a reverse direction D12, and a sub-scan are performed.

[0058] In the second main scan SC2, the second head 22 and the irradiation unit 60 mounted on the carriage 52 move in the forward direction D11, and during this movement, ink droplets 37 of the second liquid LQ2 are ejected from the nozzles 34b of the second nozzle row 42 toward the area A1. The second liquid LQ2 does not contain a photoinitiator and contains a polymerizable compound and a colorant, and in this specific example, it includes at least a part of the color inks 36c, 36m, 36y, 36k. The dots DT0 of the second liquid LQ2 are overlaid on the clear ink 36CL on the surface ME1a of the recording medium ME1. Therefore, on the surface ME1a of the recording medium ME1, the first liquid LQ1 and the second liquid LQ2 are ejected from the ejection head 20 so that the second liquid LQ2 overlaps the first liquid LQ1. In the area where the main scan in the reverse direction D12 is performed, such as the area A2, the second liquid LQ2 similarly overlaps the first liquid LQ1 on the surface ME1a of the recording medium ME1, only the moving directions of the first head 21 and the second head 22 are different. From the above, a discharge step ST1 is performed in which the first liquid LQ1 is discharged from the first nozzle row 41 toward the recording medium ME1, the second liquid LQ2 is discharged from the second nozzle row 42 toward the recording medium ME1, and the second liquid LQ2 is overlaid on the first liquid LQ1 on the surface ME1a of the recording medium ME1.

[0059] Here, in the second main scan SC2, the controller 10 shown in FIG. 1 turns off the first irradiation unit 60a located at the position facing the forward direction D11 from the second head 22, and turns on the second irradiation unit 60b located at the position facing the reverse direction D12 from the second head 22. As a result, UV is irradiated from the second irradiation unit 60b toward the area A1 where the clear ink 36CL and the color inks 36c, 36m, 36y, 36k are attached to the recording medium ME1, the clear ink 36CL and the color inks 36c, 36m, 36y, 36k are cured, and the output image IM0 is formed on the recording medium ME1. In the area where the main scan in the reverse direction D12 is performed, such as the area A2, the second irradiation unit 60b is turned off and the first irradiation unit 60a is turned on to irradiate UV. From the above, an irradiation step ST2 is performed in which UV is irradiated toward the recording medium ME1 to which the first liquid LQ1 and the second liquid LQ2 are attached. Since the time from the ejection of the color inks 36c, 36m, 36y, 36k to UV irradiation is shorter than the time from the ejection of the clear ink 36CL to UV irradiation, a high-quality output image IM0 is formed.

[0060] The color inks 36c, 36m, 36y, 36k ejected from the second nozzle row 42 relatively close to the irradiation unit 60 contain a polymerizable compound and a coloring material, but do not contain a photoinitiator. Thereby, even if the UV leaked from the irradiation unit 60 enters the vicinity of the second nozzle row 42, curing of the color inks 36c, 36m, 36y, 36k is suppressed in the vicinity of the second nozzle row 42. The clear ink 36CL ejected from the first nozzle row 41 relatively far from the irradiation unit 60 contains a photoinitiator. When the color inks 36c, 36m, 36y, 36k overlap the clear ink 36CL on the surface ME1a of the recording medium ME1, the photoinitiator in the clear ink 36CL starts the polymerization reaction of the polymerizable compound by the UV irradiated from the irradiation unit 60, and the polymerization reaction of the polymerizable compound in the clear ink 36CL promotes the polymerization reaction of the polymerizable compound in the color inks 36c, 36m, 36y, 36k. As a result, the clear ink 36CL and the color inks 36c, 36m, 36y, 36k are quickly cured. Since the first nozzle row 41 that ejects the clear ink 36CL is relatively far from the irradiation unit 60, it is difficult for the UV leaked from the irradiation unit 60 to enter the vicinity of the first nozzle row 41. Thereby, curing of the clear ink 36CL is suppressed in the vicinity of the first nozzle row 41. Therefore, this specific example can reduce ejection failure due to curing of the UV ink in the vicinity of the nozzle by the UV leaked from the irradiation unit 60. As a result, this specific example can reduce the cost of maintenance for wiping the cured UV ink from the nozzle surface. Further, in this specific example, since the amount of light of the UV irradiated to the recording medium ME1 can be increased, the printing efficiency can be improved and the running cost of printing can be reduced.

[0061] (4) Application example to a line-type printing apparatus: FIG. 5 is a plan view schematically illustrating the operation of the line-type printing apparatus 1A. The printing apparatus 1A is included in the concept of the printing apparatus 1. Referring to FIGS. 1 and 5, a printing apparatus 1A such as a line printer does not include a carriage 52, and while moving the recording medium ME1 in the feeding direction D2 without moving the ejection head 20, ejects ink droplets 37 from the nozzle row 33 toward the recording medium ME1. For convenience, the main scanning direction D1 is shown in FIG. 5, but this main scanning direction D1 corresponds to the width direction orthogonal to the feeding direction D2 in the recording medium ME1. The ejection head 20 has a nozzle row 33 in which nozzles 34 are arranged over substantially the entire width of the recording medium ME1 in the aforementioned width direction. The roller driving unit 55 as the driving unit 50 moves the recording medium ME1 in the feeding direction D2. In this case, the feeding direction D2 is an example of the relative movement direction D4, and the roller driving unit 55 changes the relative position of the recording medium ME1 with respect to the ejection head 20 in the relative movement direction D4.

[0062] Here, let the feeding direction D2 be the direction from the upstream side S1 to the downstream side S2. The printing apparatus 1A shown in FIG. 5 has, in the order of the feeding direction D2, a first head 21 having a first nozzle row 41 that ejects clear ink 36CL, a second head 22 having a second nozzle row 42 that ejects color inks 36c, 36m, 36y, 36k, and an irradiation unit 60 is disposed. In other words, the second nozzle row 42 is disposed on the downstream side S2 with respect to the first nozzle row 41, and the irradiation unit 60 is disposed on the downstream side S2 with respect to the second nozzle row 42. Therefore, the distance L1 between the irradiation unit 60 and the first nozzle row 41 is longer than the distance L2 between the irradiation unit 60 and the second nozzle row 42.

[0063] FIG. 6 schematically illustrates the operation of the line-type printing apparatus 1 shown in FIG. 5. The recording medium ME1 moves in the feeding direction D2, and during this movement, ink droplets 37 of the clear ink 36CL are ejected from the nozzles 34a of the first nozzle row 41 toward the recording medium ME1, whereby the clear ink 36CL is applied to substantially the entire surface ME1a. The clear ink 36CL contains a photopolymerization initiator and a polymerizable compound. Also, during the movement of the recording medium ME1, ink droplets 37 of the color inks 36c, 36m, 36y, 36k are ejected from the nozzles 34b of the second nozzle row 42 toward the recording medium ME1, whereby the dots DT0 of the color inks 36c, 36m, 36y, 36k are overlaid on the clear ink 36CL on the surface ME1a. The color inks 36c, 36m, 36y, 36k contain a polymerizable compound and a coloring material without containing a photopolymerization initiator. From the above, the ejection step ST1 is carried out.

[0064] Furthermore, during the movement of the recording medium ME1, UV is irradiated from the irradiation unit 60 toward the surface ME1a of the recording medium ME1 to which the clear ink 36CL and the color inks 36c, 36m, 36y, 36k are attached. Thereby, the clear ink 36CL and the color inks 36c, 36m, 36y, 36k are cured, and the output image IM0 is formed on the recording medium ME1. From the above, the irradiation step ST2 is carried out. In addition, since the color inks 36c, 36m, 36y, 36k are ejected after the clear ink 36CL is ejected, a high-quality output image IM0 is formed.

[0065] Since the color inks 36c, 36m, 36y, 36k ejected from the second nozzle row 42 relatively close to the irradiation unit 60 do not contain a photopolymerization initiator, curing of the color inks 36c, 36m, 36y, 36k is suppressed in the vicinity of the second nozzle row 42. Further, when the color inks 36c, 36m, 36y, 36k overlap with the clear ink 36CL containing a photopolymerization initiator and a polymerizable compound, the photopolymerization initiator starts the polymerization reaction of the polymerizable compound, curing the clear ink 36CL and the color inks 36c, 36m, 36y, 36k. Therefore, the line-type printing apparatus 1A can also reduce ejection failure caused by curing of the UV ink in the vicinity of the nozzles due to the UV leaking from the irradiation unit 60.

[0066] (5) Application example to another serial-type printing apparatus: FIG. 7 is a plan view schematically illustrating the operation of another serial-type printing apparatus 1B. The printing apparatus 1B is also included in the concept of the printing apparatus 1. On the carriage 52 shown in FIG. 7, a first irradiation unit 60a, a second nozzle row 42, a first nozzle row 41, a second nozzle row 42, and a second irradiation unit 60b are arranged in this order in the main scanning direction D1.

[0067] In the main scan in which the carriage drive unit 51 moves the carriage 52 in the forward direction D11, the controller 10 does not use the second head 22 located in the position facing the forward direction D11 from the first head 21, turns off the first irradiation unit 60a, and turns on the second irradiation unit 60b. In the main scan in the forward direction D11, the first head 21 discharges the clear ink 36CL from the first nozzle row 41 to a certain area of the recording medium ME1, and the second head 22 discharges the color inks 36c, 36m, 36y, 36k from the second nozzle row 42 to the same area. In the example shown in FIG. 7, the clear ink 36CL and the color inks 36c, 36m, 36y, 36k are discharged to the area A1 in the first main scan and are discharged to the area A3 in the third main scan. During the main scan in the forward direction D11, the reverse direction D12 becomes the relative movement direction D4 in which the relative position of the recording medium ME1 with respect to the discharge head 20 changes. In the carriage 52, in the order of the relative movement direction D4, the first nozzle row 41 that discharges the first liquid LQ1, the second nozzle row 42 that discharges the second liquid LQ2, and the second irradiation unit 60b are arranged.

[0068] In the main scan in which the carriage drive unit 51 moves the carriage 52 in the reverse direction D12, the controller 10 does not use the second head 22 located in the position facing the reverse direction D12 from the first head 21, turns off the second irradiation unit 60b, and turns on the first irradiation unit 60a. In the main scan in the reverse direction D12, the first head 21 discharges the clear ink 36CL from the first nozzle row 41 to a certain area of the recording medium ME1, and the second head 22 discharges the color inks 36c, 36m, 36y, 36k from the second nozzle row 42 to the same area. In the example shown in FIG. 7, the clear ink 36CL and the color inks 36c, 36m, 36y, 36k are discharged to the area A2 in the second main scan. During the main scan in the reverse direction D12, the forward direction D11 becomes the relative movement direction D4 in which the relative position of the recording medium ME1 with respect to the discharge head 20 changes. In the carriage 52, in the order of the relative movement direction D4, the first nozzle row 41 that discharges the first liquid LQ1, the second nozzle row 42 that discharges the second liquid LQ2, and the first irradiation unit 60a are arranged.

[0069] FIG. 8 schematically illustrates the operation of the serial type printing apparatus 1B shown in FIG. 7. Although the main scanning in the forward direction D11 is shown in FIG. 8, as described above, the relative movement direction D4 becomes the reverse direction D12 during the main scanning in the forward direction D11, and becomes the forward direction D11 during the main scanning in the reverse direction D12. Here, the relative movement direction D4 is defined as the direction from the upstream side S1 to the downstream side S2.

[0070] During the main scanning, while the carriage 52 is moving, ink droplets 37 of the clear ink 36CL are ejected from the nozzles 34a of the first nozzle row 41 toward the recording medium ME1, so that the clear ink 36CL is applied to substantially the entire surface ME1a. Also, while the carriage 52 is moving, ink droplets 37 of the color inks 36c, 36m, 36y, 36k are ejected from the nozzles 34b of the second nozzle row 42 toward the recording medium ME1, so that the dots DT0 of the color inks 36c, 36m, 36y, 36k are overlaid on the clear ink 36CL on the surface ME1a. From the above, the ejection step ST1 is carried out.

[0071] Furthermore, while the carriage 52 is moving, UV is irradiated from the irradiation unit 60 toward the surface ME1a of the recording medium ME1 to which the clear ink 36CL and the color inks 36c, 36m, 36y, 36k are attached. Thereby, the clear ink 36CL and the color inks 36c, 36m, 36y, 36k are cured, and the output image IM0 is formed on the recording medium ME1. From the above, the irradiation step ST2 is carried out.

[0072] Similar to the line type printing apparatus 1A, the serial type printing apparatus 1B can also reduce ejection defects caused by the hardening of the UV ink in the vicinity of the nozzles due to the UV leaking from the irradiation unit 60. In addition, when the printing apparatus 1B performs one-way printing in which printing is performed only during the main scanning in the forward direction D11, the second head 22 and the first irradiation unit 60a located in the forward direction D11 from the first head 21 may not be provided on the carriage 52.

[0073] Further, as illustrated in FIG. 9, one ejection head 20 may have both a first nozzle row 41 and a second nozzle row 42. FIG. 9 is a plan view schematically illustrating components mounted on a carriage 52 in another serial type printing apparatus 1C. The printing apparatus 1C is also included in the concept of the printing apparatus 1. In the ejection head 20 shown in FIG. 9, the second nozzle row 42 is disposed on the downstream side S2 in the feeding direction D2 from the first nozzle row 41. The plurality of irradiation units 60 are disposed on the downstream side S2 from the first nozzle row 41, and include a first irradiation unit 60a located at a position facing the forward direction D11 from the second nozzle row 42, and a second irradiation unit 60b located at a position facing the return direction D12 from the second nozzle row 42.

[0074] The operations of the carriage 52 and the recording medium ME1 are the same as those shown in FIG. 2. For example, in the third main scan, the carriage 52 moves in the forward direction D11, and during the movement, the ejection head 20 ejects the clear ink 36CL from the first nozzle row 41 to the area A3, and ejects the color inks 36c, 36m, 36y, 36k from the second nozzle row 42 to the area A1. The controller 10 irradiates the area A1 with UV from the second irradiation unit 60b. In the fourth main scan, the carriage 52 moves in the return direction D12, and during the movement, the ejection head 20 ejects the clear ink 36CL from the first nozzle row 41 to an area (not shown), and ejects the color inks 36c, 36m, 36y, 36k from the second nozzle row 42 to the area A2. The controller 10 irradiates the area A2 with UV from the first irradiation unit 60a.

[0075] Similar to the printing apparatus 1 shown in FIG. 2, the serial type printing apparatus 1C can also reduce ejection defects caused by hardening of the UV ink near the nozzles due to UV leakage from the irradiation unit 60.

[0076] On the other hand, as illustrated in FIG. 10, the first head 21 and the second head 22 may be mounted on separate carriages. FIG. 10 is a plan view schematically illustrating another serial type printing apparatus 1D. The printing apparatus 1D is also included in the concept of the printing apparatus 1. A drive unit 50 that changes the relative position between the ejection head 20 and the recording medium ME1 includes a first carriage drive unit 51a that includes a first carriage 52a, a second carriage drive unit 51b that includes a second carriage 52b, and a roller drive unit 55. The second carriage 52b is separate from the first carriage 52a and is disposed on the downstream side S2 with respect to the first carriage 52a. The first carriage 52a and the second carriage 52b are each independently movable in the main scanning direction D1. The first carriage drive unit 51a is an example of a first main scanning unit, and the second carriage drive unit 51b is an example of a second main scanning unit.

[0077] A first head 21 having a first nozzle row 41 that ejects clear ink 36CL is mounted on the first carriage 52a. The first carriage drive unit 51a moves the first carriage 52a in the main scanning direction D1. A second head 22 having a second nozzle row 42 that ejects color inks 36c, 36m, 36y, 36k, a first irradiation unit 60a, and a second irradiation unit 60b are mounted on the second carriage 52b. The second carriage drive unit 51b moves the second carriage 52b in the main scanning direction D1. Even when the first nozzle row 41 of the first head 21 mounted on the first carriage 52a is closest to the irradiation unit 60, the distance L1 between the irradiation unit 60 and the first nozzle row 41 is longer than the distance L2 between the irradiation unit 60 and the second nozzle row 42.

[0078] As described above, the first carriage drive unit 51a moves the first carriage 52a in the main scanning direction D1 on the upstream side S1 of the second carriage 52b, and the first head 21 discharges the clear ink 36CL to the areas A1, A2, A3,.... The second carriage drive unit 51b moves the second carriage 52b in the main scanning direction D1 on the downstream side S2 of the first carriage 52a, and the second head 22 discharges the color inks 36c, 36m, 36y, 36k to the areas A1, A2, A3,.... Here, when the second carriage 52b is moving in the forward direction D11, the controller 10 turns off the first irradiation unit 60a and irradiates UV from the second irradiation unit 60b toward the area where the color inks 36c, 36m, 36y, 36k are discharged. When the second carriage 52b is moving in the reverse direction D12, the controller 10 turns off the second irradiation unit 60b and irradiates UV from the first irradiation unit 60a toward the area where the color inks 36c, 36m, 36y, 36k are discharged.

[0079] The serial type printing apparatus 1D can also reduce ejection failure caused by the hardening of the UV ink near the nozzles due to the UV leaking from the irradiation unit 60, by the same operation as the printing apparatus 1 shown in FIG. 2.

[0080] (6) Modification example: Various modification examples are conceivable for the present invention. For example, the color of the colorant of the second liquid that does not contain a photoinitiator is not limited to C, M, Y, and K, and may include white, orange, green, light cyan with a lower concentration than C, light magenta with a lower concentration than M, dark yellow with a higher concentration than Y, light black with a lower concentration than K, and the like. Further, the present technology can also be applied when a part of C, M, Y, and K is not included in the color of the colorant of the second liquid. Furthermore, the color of the second colorant of the first liquid that contains a photoinitiator is not limited to blue, and various base colors such as white, C, M, Y, etc. can be applied. In addition to band printing, the serial type printing apparatus may perform overlap printing in which areas partially overlap each other, pseudo band printing in which main scanning of each area is performed two or more times, interlace printing in which the intervals between rasters are left empty and the intervals between rasters are filled in subsequent main scanning, and the like. Further, during sub-scanning, the serial type printing apparatus may move the carriage 52 in a direction opposite to the feed direction D2 in addition to moving the recording medium ME1 in the feed direction D2.

[0081] The printing apparatus may first attach a second liquid that does not contain a photopolymerization initiator to the recording medium and then attach the first liquid to the recording medium. For example, in the carriage 52, the first heads 21 are respectively arranged at positions facing the forward direction D11 and the return direction D12 from the second head 22 having the second nozzle row 42, and the irradiation unit 60 may be arranged on the downstream side S2 of the second head 22 so as to satisfy L1 > L2. For example, in the main scanning in the forward direction D11, the second liquid LQ2 is discharged from the second nozzle row 42 of the second head 22, and the first liquid LQ1 is discharged from the first nozzle row 41 of the first head 21 at a position facing the return direction D12 from the second head 22 so as to be applied to the recording medium ME1, whereby the first liquid LQ1 overlaps the second liquid LQ2. Even in this case, the photopolymerization initiator of the first liquid LQ1 starts the polymerization reaction of the polymerizable compound, and the first liquid LQ1 and the second liquid LQ2 are cured.

[0082] Even when the first liquid LQ1 does not contain a polymerizable compound, the photopolymerization initiator of the first liquid LQ1 starts the polymerization reaction of the polymerizable compound of the second liquid LQ2, so that the first liquid LQ1 and the second liquid LQ2 are cured in an integrated state on the surface ME1a of the recording medium ME1.

[0083] (7) Conclusion: As described above, according to the present invention, it is possible to provide a technique for reducing ejection failure caused by curing of a liquid containing a coloring material near the nozzle due to light leaking from the irradiation unit in various modes. Of course, the basic operations and effects described above can also be obtained by a technique consisting only of the constituent elements according to the independent claims. In addition, configurations in which the respective configurations disclosed in the above-described examples are mutually replaced or the combinations are changed, known techniques, and configurations in which the respective configurations disclosed in the above-described examples are mutually replaced or the combinations are changed, etc. are also feasible. The present invention includes these configurations and the like.

Explanation of Reference Numerals

[0084] 1... Printing device, 10... Controller, 20... Discharge head, 20a... Nozzle surface, 21... First head, 22... Second head, 33... Nozzle row, 34, 34a, 34b... Nozzles, 36... Ink, 36CL... Clear ink, 36c... Cyan ink, 36m... Magenta ink, 36y... Yellow ink, 36k... Black ink, 37... Ink droplet, 41... First nozzle row, 42... Second nozzle row, 50... Driving unit, 51... Carriage driving unit, 51a... First carriage driving unit, 51b... Second carriage driving unit, 52... Carriage, 52a... First carriage, 52b... Second carriage, 55... Roller driving unit, 60... Irradiation unit, 60a... First irradiation unit, 60b... Second irradiation unit, A1 to A3... Areas, D1... Main scanning direction, D2... Feeding direction, D3... Nozzle arrangement direction, D4... Relative movement direction, D11... Forward direction, D12... Return direction, DT0... Dot, L1, L2... Distances, IM0... Output image, LQ1... First liquid, LQ2... Second liquid, ME1... Recording medium, ME1a... Surface, S1... Upstream side, S2... Downstream side, ST1... Discharge process, ST2... Irradiation process, SY1... Printing system.

Claims

1. A first liquid containing a photopolymerization initiator that initiates a polymerization reaction of a polymerizable compound upon irradiation with light, a first nozzle array that discharges the first liquid toward a recording medium, a second liquid that does not contain the photopolymerization initiator and contains the polymerizable compound and a coloring material, and a second nozzle array that discharges the second liquid toward the recording medium, a discharge head having the same, a drive unit that changes the relative position between the discharge head and the recording medium, and an irradiation unit that irradiates the recording medium to which the first liquid and the second liquid are attached with the light, comprising: discharging the first liquid and the second liquid from the discharge head so that the second liquid overlaps the first liquid on the surface of the recording medium, the distance between the irradiation unit and the first nozzle array being longer than the distance between the irradiation unit and the second nozzle array, wherein the drive unit, changes the relative position of the discharge head with respect to the recording medium in the main scanning direction, and when the first liquid and the second liquid are not discharged from the discharge head toward the recording medium, changes the relative position of the recording medium with respect to the discharge head in the feed direction intersecting the main scanning direction, wherein the feed direction is a direction from the upstream side to the downstream side, the irradiation unit is disposed on the downstream side of the first nozzle array and is at a position where it can irradiate the second liquid adhering to the recording medium, the second nozzle array is disposed on the downstream side of the first nozzle array, in one main scan of the discharge head that relatively moves in the main scanning direction, the area of the recording medium that can be irradiated by the irradiation unit includes the area where the second liquid can be discharged from the second nozzle array and does not include the area where the first liquid can be discharged from the first nozzle array, a printing apparatus.

2. A first liquid containing a photopolymerization initiator that initiates a polymerization reaction of a polymerizable compound upon irradiation with light, a first nozzle array that discharges the first liquid toward a recording medium, a second liquid that does not contain the photopolymerization initiator and contains the polymerizable compound and a coloring material, and a second nozzle array that discharges the second liquid toward the recording medium, a discharge head having the same, a drive unit that changes the relative position between the discharge head and the recording medium, and an irradiation unit that irradiates the recording medium to which the first liquid and the second liquid are attached with the light, comprising: discharging the first liquid and the second liquid from the discharge head so that the second liquid overlaps the first liquid on the surface of the recording medium, the distance between the irradiation unit and the first nozzle array being the same as the distance between the irradiation unit and the second nozzle array, ​ ​ ​ ​ ​ ​ ​ ​ ​ longer than the distance, the ejection head includes a first head having the first nozzle row and a second head having the second nozzle row, and the drive unit includes a first main scanning unit that includes a first carriage on which the first head is mounted and changes a relative position of the first carriage with respect to the recording medium in a main scanning direction, and a second main scanning unit that includes a second carriage on which the second head is mounted and is separate from the first carriage and changes a relative position of the second carriage with respect to the recording medium in the main scanning direction, a printing apparatus.

3. The first liquid contains the polymerizable compound, and the first nozzle row ejects the first liquid containing the photopolymerization initiator and the polymerizable compound, The printing apparatus according to claim 1 or 2.

4. The first liquid contains a second colorant, and the first nozzle row ejects the first liquid containing the photopolymerization initiator and the second colorant, The printing apparatus according to any one of claims 1 to 3.

5. The drive unit changes a relative position of the recording medium with respect to the ejection head in a relative movement direction, wherein the relative movement direction is a direction from an upstream side to a downstream side, the second nozzle row is disposed on the downstream side of the first nozzle row, and the irradiation unit is disposed on the downstream side of the second nozzle row, The printing apparatus according to claim 2.

6. The drive unit changes a relative position of the ejection head with respect to the recording medium in a main scanning direction, and changes a relative position of the recording medium with respect to the ejection head in a feed direction intersecting the main scanning direction when the first liquid and the second liquid are not ejected from the ejection head toward the recording medium, in the main scanning direction, the irradiation unit, the second nozzle row, the first nozzle row, the second nozzle row, and the irradiation unit are arranged in this order, The printing apparatus according to claim 2.

7. An ejection head that ejects a liquid that cures by irradiation with light toward a recording medium, a drive unit that changes a relative position between the ejection head and the recording medium, and an irradiation unit that irradiates the recording medium with the light, wherein the ejection head has a first nozzle row and a second nozzle row, and the drive unit changes a relative position of the ejection head with respect to the recording medium in a main scanning direction, and when the first liquid and the second liquid are not ejected from the ejection head toward the recording medium, ​ ​ ​ ​ ​ ​ ​ ​ Changing the relative position of the recording medium with respect to the head in a feeding direction intersecting the main scanning direction A printing method in a printing apparatus, comprising: The distance between the irradiation unit and the first nozzle row is longer than the distance between the irradiation unit and the second nozzle row, and with the feeding direction being from the upstream side to the downstream side, the irradiation unit is disposed on the downstream side of the first nozzle row and is at a position where it can irradiate the second liquid adhering to the recording medium, and the second nozzle row is disposed on the downstream side of the first nozzle row, In one main scan of the discharge head that relatively moves in the main scanning direction, an area of the recording medium that can be irradiated by the irradiation unit includes an area where the second liquid can be discharged from the second nozzle row and does not include an area where the first liquid can be discharged from the first nozzle row, discharging a first liquid containing a photopolymerization initiator that initiates a polymerization reaction of a polymerizable compound by irradiation of light from the first nozzle row toward the recording medium, and discharging a second liquid that does not contain the photopolymerization initiator and contains the polymerizable compound and a colorant from the second nozzle row toward the recording medium, and a discharging step of overlaying the second liquid on the first liquid on the surface of the recording medium, and an irradiation step of irradiating the light toward the recording medium to which the first liquid and the second liquid have adhered. A printing method comprising:

8. A printing method in a printing apparatus including a discharge head that discharges a liquid that cures by irradiation of light toward a recording medium, a drive unit that changes a relative position between the discharge head and the recording medium, and an irradiation unit that irradiates the recording medium with the light, wherein the discharge head has a first nozzle row and a second nozzle row, the distance between the irradiation unit and the first nozzle row is longer than the distance between the irradiation unit and the second nozzle row, and the discharge head includes a first head having the first nozzle row and a second head having the second nozzle row, the drive unit includes a first main scanning unit that includes a first carriage on which the first head is mounted and changes a relative position of the first carriage with respect to the recording medium in the main scanning direction, and a second main scanning unit that includes a second carriage on which the second head is mounted and is separate from the first carriage and changes a relative position of the second carriage with respect to the recording medium in the main scanning direction. ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ A first liquid containing a photopolymerization initiator that initiates a polymerization reaction of a polymerizable compound by irradiation with light is discharged from the first nozzle array toward the recording medium, and a second liquid that does not contain the photopolymerization initiator and contains the polymerizable compound and a coloring material is discharged from the second nozzle array toward the recording medium, and a discharging step of overlapping the second liquid with the first liquid on the surface of the recording medium and an irradiation step of irradiating the recording medium to which the first liquid and the second liquid are attached with the light, wherein the printing method includes and a discharging step of discharging the first liquid containing a photopolymerization initiator that initiates a polymerization reaction of a polymerizable compound by irradiation with light from the first nozzle array toward the recording medium, and discharging a second liquid that does not contain the photopolymerization initiator and contains the polymerizable compound and a coloring material from the second nozzle array toward the recording medium, and overlapping the second liquid with the first liquid on the surface of the recording medium and an irradiation step of irradiating the recording medium to which the first liquid and the second liquid are attached with the light

Images