JP2013154508A - Image forming apparatus and image forming method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus and image forming method in which a desirable image recording in which the occurrence of density unevenness originating from a swath width is controlled can be achieved.SOLUTION: An inkjet recording apparatus (10) performs the image forming of a multipath method in which the number of paths of a main scanning direction is m, and the number of paths of a sub-scanning direction is n (m and n are integers of two or more) by using an ink that is cured by the irradiation of ultraviolet rays. Temporary curing lights (32A, 32B) are made to scan to the main scanning direction with an inkjet head (24), and an ink hit to a recording medium (12) is made to be cured temporarily. The temporary curing light has the distribution of an irradiation energy in which the irradiation energy for each unit area of the recording medium conveyance direction downstream side exceeds the irradiation energy for each unit area of the same direction upstream side.

Description

  The present invention relates to an image forming apparatus and an image forming method, and more particularly to an ink jet image forming technique using an ink that is cured by irradiation with actinic rays such as ultraviolet rays.

  2. Description of the Related Art Conventionally, as a general-purpose image forming apparatus, an ink jet recording apparatus that forms a desired image on a recording medium by discharging color ink from an ink jet head is known.

  In an ink jet recording apparatus, ink droplets are ejected while scanning an ink jet head along a main scanning direction (a direction orthogonal to the recording medium conveyance direction), and predetermined in the sub-scanning direction (a direction parallel to the recording medium conveyance direction). When the image formation is performed for the area having the length and the image formation is completed for the area, the recording medium is moved by a predetermined amount in the sub-scanning direction to form the image of the next area, and this procedure is repeated to repeat the entire surface of the recording medium. There is a serial-type image formation in which image formation is performed, and in the serial-type image formation, there is a multi-pass method that realizes a predetermined recording resolution by a plurality of scans (passes) in the main scanning direction.

  In recent years, not only permeable media such as paper but also non-permeable media such as resin films (including media that slightly penetrates ink) have been used, and actinic rays have been applied to ink landed on the media. As an example, an ultraviolet curable structure in which ultraviolet rays are irradiated and cured has been proposed.

  In a configuration in which serial image formation is employed, a light source for ultraviolet irradiation is mounted on a carriage on which the inkjet head is mounted, and an ink droplet immediately after landing on the medium is scanned by scanning the ultraviolet light source following the inkjet head. UV rays are applied to the ink droplets to avoid misalignment of ink droplets and landing interference.

  In such a configuration, in the sub-scanning direction, density unevenness called “banding unevenness” or gloss unevenness may occur in a cycle corresponding to the swath width.

  The “swath width” is the length in the sub-scanning direction determined by the shuttle scan repetition cycle of the carriage, and the length in the sub-scanning direction of the nozzle row composed of a plurality of nozzles used is expressed as the total number of passes. It is obtained by dividing.

  As a method of eliminating the banding unevenness, the image unevenness is visually recognized in a spatial frequency by a method of forming an image so that an edge of a region (band) having a swath width is undulated (for example, Patent Document 1). There are known ways to make it difficult.

  Japanese Patent Application Laid-Open No. 2004-151867 is a printing apparatus configured such that when printing is performed using a plurality of printing passes, the printing pass is set so that the boundary of the printing pass extends in an oblique direction, and banding of the printing pass cycle becomes inconspicuous. Is disclosed. The printing apparatus disclosed in Patent Document 1 is configured such that the boundary of the print path is stepped by performing image formation while changing the allocation of the used nozzles and the dummy nozzles.

  In Patent Document 2, the effective nozzle rows arranged along the main scanning direction are arranged so as to be shifted in the sub-scanning direction, whereby the images printed by the effective nozzle rows are shifted in the sub-scanning direction. Discloses an ink jet printer configured to reduce the density difference between passes.

  In Patent Document 3, the nozzles of two nozzle arrays arranged in the main scanning direction (A) are arranged so as to partially overlap in the transport direction (B), and the joint of the print data is along the main scanning direction. Inkjet printers configured to suppress the occurrence of banding by changing in the transport direction and allocating to effective nozzles are disclosed.

  Patent Document 4 discloses an ink jet output device that prevents the generation of texture noise by selecting each nozzle in an order such that the time difference in drive timing between adjacent nozzles is random throughout the entire ink jet head. ing.

  Patent Document 5 discloses that in bidirectional printing, light dots and dark dots are alternately arranged in the same swath, and a plurality of bands having different color overlaps are formed in the main scanning direction and sub-scanning. Disclosed is an inkjet printer configured to be alternately arranged in a direction to average the overall color tone.

JP 2008-284863 A JP 2010-005811 A JP 2010-000713 A JP 9-216350 A JP 2001-232824 A

  However, there is no technique for reducing the unevenness by directly acting on the cause of the generation of periodic unevenness for each swath width, like the techniques disclosed in Patent Documents 1 to 5 above. In this case, a technique that makes the unevenness inconspicuous or difficult to visually recognize is used. In addition, when the techniques disclosed in Patent Documents 1 to 5 are applied, there is a concern about a decrease in productivity.

  The present invention has been made in view of such circumstances, and an object thereof is to provide an image forming apparatus and an image forming method capable of realizing preferable image recording in which occurrence of density unevenness due to swath width is suppressed. .

  In order to achieve the above object, an image forming apparatus according to the present invention includes an inkjet head in which a plurality of nozzles for ejecting a liquid that is cured by irradiation with actinic rays are arranged, and a liquid ejected from the inkjet head. A medium conveying means for conveying the medium to be attached; a scanning means for moving the inkjet head relative to the medium; and a droplet ejection position on a scanning line along the scanning direction of the scanning means m times (m is 2 or more). (Integer) scanning, and droplet ejection is performed n times (n is an integer of 2 or more) at the droplet ejection position on the scanning line along the transport direction of the transport means. The droplet ejection of the inkjet head by N times (N = m × n) scanning is controlled so as to form an image with a predetermined resolution with a droplet ejection interval smaller than the nozzle pitch in the transport direction. A droplet ejection control unit that controls the feed amount in the transport direction by the medium transport unit for each scan constituting the N scans, and the medium that moves together with the inkjet head by the scanning unit, Provisional curing means for irradiating actinic rays to such an extent that the liquid adhering thereto is incompletely cured, and the provisional curing means has an irradiation energy per unit area on the downstream side in the transport direction of the medium transport means. It has an irradiation energy distribution in the transport direction that exceeds the irradiation energy per unit area on the upstream side, and the liquid contains a radical polymerizable compound as component A, a radical polymerization initiator as component B, and a colorant as component C. Component A contains a monofunctional radically polymerizable compound as component A-1 and a polyfunctional radically polymerizable compound as component A-2 Component A-1 contains an N-vinyl compound as Component A-1-1 and a compound represented by the following formula (I) as Component A-1-2, The content is 50 weight percent or more and 90 weight percent or less based on the total weight of the component A, and the content of the component A-1-1 is 10 weight percent or more and 40 weight percent or more based on the total weight of the component A-1. The content of the component A-1-2 is 5 weight percent or more and 90 weight percent or less with respect to the total weight of the component A-1, and the component A-2 is represented by the following formula (II): And an amount of the component A-2 is 0.1 weight percent or more and 25 weight percent or less based on the total weight of the component A.

(In formula (I), R ¹ , R ² and R ³ each independently represents a hydrogen atom, a methyl group or an ethyl group, and X ¹ represents a single bond or a divalent linking group.)

(In the formula (II), R ¹¹ each independently represents a hydrogen atom or an optionally substituted alkyl group having 1 to 6 carbon atoms, and R ¹² represents a hydrogen atom or an optionally substituted carbon atom 1. represents an alkyl group of from, R ¹³ represents independently a hydrogen atom, or a methyl group, X ² is a single bond or a divalent linking group, 5 p, from 0 q and r are each independently Represents an integer.)

(In the formula (II), R ¹¹ each independently represents a hydrogen atom or an optionally substituted alkyl group having 1 to 6 carbon atoms, and R ¹² represents a hydrogen atom or an optionally substituted carbon atom 1. represents an alkyl group of from, R ¹³ represents independently a hydrogen atom, or a methyl group, X ² is a single bond or a divalent linking group, 5 p, from 0 q and r are each independently Represents an integer.)

  According to the present invention, in multi-pass pixel formation in which an image having a predetermined resolution is formed by N (= m × n) scans, the unit area on the downstream side in the transport direction of the medium transport unit of the temporary curing unit The irradiation energy per unit area exceeds the irradiation energy per unit area on the upstream side, and the distribution of the irradiation energy of the actinic ray in the same direction is provided, so that the upstream dot and the downstream side in the same direction within one swath width Density unevenness having periodicity corresponding to the swath width due to the difference in irradiation energy per unit area of the actinic ray with the dot is suppressed.

1 is an external perspective view of an ink jet recording apparatus according to an embodiment of the present invention. Explanatory drawing which shows typically the paper conveyance path of the inkjet recording device shown in FIG. Plane perspective view showing the arrangement configuration of the inkjet head and ultraviolet irradiation section shown in FIG. Block diagram showing schematic configuration of control system of inkjet recording apparatus Schematic diagram for explaining drawing operation by N-pass multi-pass printing Explanatory drawing of the droplet ejection position recorded by each scan of 8 times writing Explanatory drawing of the droplet ejection position recorded by each scan of 8 times writing Figure showing an example of how to fill a 2x4 grid Perspective view of temporary curing light source unit The perspective diagram which described the light ray inside the temporary curing light source unit shown in FIG. Explanatory drawing (a) of exposure conditions (condition 1) of the temporary hardening light source which concerns on a prior art: Irradiation energy per unit area of an upstream side in a temporary hardening light source unit (Hereinafter, it may only describe as irradiation energy.) (B): Illumination in the media transport direction (X direction) in FIG. 11 (a), which represents the irradiation distribution on the media surface when is 6 millijoules per square centimeter and the downstream irradiation energy is 6 millijoules per square centimeter Graph showing distribution cross section A graph showing read data of a K100% image formed when the exposure condition of the temporary curing light source is Condition 1 Explanatory drawing (a) of the exposure conditions (condition 2) of the temporary curing light source which concerns on a prior art: In a temporary curing light source unit, the upstream irradiation energy is 8 millijoules per square centimeter, and the downstream irradiation energy is 8 millijoules per square centimeter. (B): Illumination distribution cross section in the media transport direction (X direction) in FIG. 13 (a) A graph showing read data of a K100% image formed when the exposure condition of the temporary curing light source is Condition 2 Explanatory drawing (a) of the exposure conditions (condition 3) of the temporary curing light source which concerns on embodiment of this invention: In a temporary curing light source unit, the irradiation energy of upstream is 4 millijoules per square centimeter, and the irradiation energy of downstream is 8 mm. FIG. 15B is a graph showing the illumination distribution on the media transport direction (X direction) in FIG. A graph showing read data of a K100% image formed when the exposure condition of the temporary curing light source is Condition 3 The graph which shows the reading data of the C100% image formed when the exposure conditions of the temporary hardening light source are the conditions 1 The graph which shows the reading data of the C100% image formed when the exposure conditions of the temporary hardening light source are the conditions 2 A graph showing read data of a K100% image formed when the exposure condition of the temporary curing light source is Condition 3 Table showing banding evaluation results when the light intensity ratio is changed The schematic diagram which shows the arrangement configuration of the ultraviolet irradiation part using the temporary curing light source unit which concerns on a modification The perspective view which looked at the temporary hardening light source unit which concerns on a modification from the lower surface side The figure which shows the structure in the housing of the temporary curing light source unit which concerns on a modification The perspective view which showed the example of the division | segmentation components (mirror member) arrange | positioned inside a housing In the temporary curing light source unit according to the modified example, a perspective view showing light rays at the time of whole surface irradiation In the temporary curing light source unit according to the modified example, a perspective view showing a state at the time of irradiation only upstream. In the temporary curing light source unit according to the modified example, a perspective view showing a state during irradiation only downstream.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

[Overall configuration of inkjet recording apparatus]
FIG. 1 is an external perspective view of an ink jet recording apparatus according to an embodiment of the present invention. The ink jet recording apparatus 10 (image forming apparatus) is a wide format printer that forms a color image on a recording medium 12 (medium) using ultraviolet curable ink (liquid). A wide format printer is a device suitable for recording a wide drawing range such as a large poster or a commercial wall advertisement. Here, the one corresponding to A3 Nobi or higher is called “wide format”.

  The ink jet recording apparatus 10 includes an apparatus main body 20 and support legs 22 that support the apparatus main body 20. The apparatus main body 20 includes a drop-on-demand type ink jet head 24 that ejects ink toward a recording medium (medium) 12, a platen 26 that supports the recording medium 12, a guide mechanism 28 as a head moving unit, and a carriage 30. (Scanning means) is provided.

  The guide mechanism 28 is disposed above the platen 26 so as to extend along a scanning direction (Y direction) perpendicular to the conveyance direction (X direction) of the recording medium 12 and parallel to the medium support surface of the platen 26. ing. The carriage 30 is supported so as to reciprocate in the Y direction along the guide mechanism 28. An ink jet head 24 is mounted on the carriage 30, and temporary curing light sources (pinning light sources) 32 </ b> A and 32 </ b> B (temporary curing means) for irradiating the ink on the recording medium 12 with ultraviolet rays, and a main curing light source (curing light source). 34A, 34B (main curing means) are mounted.

  The temporary curing light sources 32A and 32B are light sources that irradiate ultraviolet rays for temporarily curing the ink so that the adjacent droplets do not coalesce after the ink droplets ejected from the inkjet head 24 have landed on the recording medium 12. is there. The main curing light sources 34 </ b> A and 34 </ b> B are light sources that irradiate ultraviolet rays for performing additional exposure after temporary curing and finally completely curing (main curing) the ink. Although details will be described later, one or both of the main curing light sources 34A and 34B are configured to be movable in the X direction so as to be aligned with the inkjet head 24 and the temporary curing light sources 32A and 32B in the Y direction.

  The ink jet head 24, the temporary curing light sources 32 </ b> A and 32 </ b> B, and the main curing light sources 34 </ b> A and 34 </ b> B arranged on the carriage 30 move integrally with the carriage 30 along the guide mechanism 28. The reciprocating direction (Y direction) of the carriage 30 may be referred to as a “main scanning direction”, and the conveyance direction (X direction) of the recording medium 12 may be referred to as a “sub scanning direction”. The Y direction corresponds to the “first direction”, and the X direction corresponds to the “second direction”.

  As the recording medium 12, various media such as paper, non-woven fabric, vinyl chloride, synthetic chemical fiber, polyethylene, polyester, and tarpaulin can be used regardless of the material, regardless of permeable medium or non-permeable medium. it can.

  The recording medium 12 is fed from the back side of the apparatus in a roll paper state (see FIG. 2), and after printing, is wound by a winding roller (not shown in FIG. 1, reference numeral 44 in FIG. 2) on the front side of the apparatus. .

  Ink droplets are ejected from the inkjet head 24 to the recording medium 12 conveyed on the platen 26, and the temporary curing light sources 32A and 32B and the main curing light sources 34A and 34B are applied to the ink droplets adhering to the recording medium 12. Ultraviolet rays are irradiated.

  The steps of partially curing the ink using the temporary curing light sources 32A and 32B so as to prevent the movement and deformation of the ink droplet immediately after the droplet ejection are “preliminary curing”, “partial curing”, and “semi-curing”. , “Pinning” or “set”. In this specification, the terms “temporary curing” and “pinning” are used. On the other hand, after the temporary curing, a process of further curing the ink by performing further UV irradiation using the main curing light sources 34A and 34B is called “main curing” or “curing”.

  In FIG. 1, an attachment portion 38 for an ink cartridge 36 is provided on the left front surface of the apparatus main body 20. The ink cartridge 36 is a replaceable ink supply source (ink tank) that stores ultraviolet curable ink. The ink cartridge 36 is provided corresponding to each color ink used in the inkjet recording apparatus 10 of this example. Each color-specific ink cartridge 36 is connected to the inkjet head 24 by an ink supply path (not shown) formed independently. When the remaining amount of ink for each color is low, the ink cartridge 36 is replaced.

  Although not shown, a maintenance unit for the inkjet head 24 is provided on the right side of the apparatus main body 20 toward the front. The maintenance unit is provided with a cap for keeping the ink-jet head 24 moisturized during non-printing and a wiping member (blade, web, etc.) for cleaning the nozzle surface (ink ejection surface) of the ink-jet head 24. The cap for capping the nozzle surface of the inkjet head 24 is provided with an ink receiver for receiving ink droplets ejected from the nozzle for maintenance.

[Description of recording medium transport path]
FIG. 2 is an explanatory diagram schematically showing a recording medium conveyance path in the inkjet recording apparatus 10. As shown in FIG. 2, the platen 26 is formed in an inverted bowl shape, and its upper surface serves as a support surface (medium support surface) of the recording medium 12. A pair of nip rollers 40 constituting medium conveying means for intermittently conveying the recording medium 12 are disposed on the upstream side in the recording medium conveying direction (X direction) in the vicinity of the platen 26. The nip roller 40 moves the recording medium 12 on the platen 26 in the recording medium conveyance direction.

  The recording medium 12 sent out from the supply-side roll (feed-out supply roll) 42 constituting the roll-to-roll type medium transport means is provided at the entrance of the printing unit (upstream side of the platen 26 in the recording medium transport direction). The pair of nip rollers 40 are intermittently conveyed in the recording medium conveyance direction. The recording medium 12 that has reached the printing unit immediately below the ink jet head 24 is printed by the ink jet head 24 and is taken up by the take-up roll 44 after printing. A guide 46 for the recording medium 12 is provided on the downstream side of the printing unit in the recording medium conveyance direction.

  A temperature adjusting unit 50 for adjusting the temperature of the recording medium 12 during printing is provided on the back surface (the surface opposite to the surface supporting the recording medium 12) of the platen 26 at a position facing the inkjet head 24 in the printing unit. Is provided. When the recording medium 12 at the time of printing is adjusted to a predetermined temperature, the physical properties such as the viscosity of the ink droplets that have landed on the recording medium 12 and the surface tension become the desired values, and the desired dot diameter is set. Can be obtained. In addition, as needed, the pre temperature control part 52 may be provided in the upstream of the temperature control part 50, and the after temperature control part 54 may be provided in the downstream of the temperature control part 50.

[Description of inkjet head]
FIG. 3 is a perspective plan view showing an example of an arrangement form of the inkjet head 24, the temporary curing light sources 32A and 32B, and the main curing light sources 34A and 34B arranged on the carriage 30. FIG.

  The inkjet head 24 includes yellow (Y), magenta (M), cyan (C), black (K), light cyan (LC), light magenta (LM), clear (transparent) ink (CL), and white (white). Nozzle rows 61Y, 61M, 61C, 61K, 61LC, 61LM, 61CL, and 61W for ejecting (dropping) the respective color inks are provided for each color of ink (W).

  In FIG. 3, the nozzle rows are illustrated by dotted lines, and individual illustrations of the nozzles are omitted. In the following description, the nozzle rows 61Y, 61M, 61C, 61K, 61LC, 61LM, 61CL, and 61W may be collectively referred to by the reference numeral 61 to represent the nozzle rows.

  The ink color type (number of colors) and the color combination are not limited to the present embodiment. For example, a mode in which the LC and LM nozzle rows are omitted, a mode in which one of the CL and W nozzle rows is omitted, a mode in which a metal ink nozzle row is added, a metal ink nozzle row in place of the W nozzle row It is possible to adopt a form in which a nozzle row for discharging special color ink is added. Further, the arrangement order of the nozzle rows for each color is not particularly limited. However, a configuration in which an ink having a low curing sensitivity to ultraviolet light among a plurality of ink types is disposed on the side close to the temporary curing light source 32A or 32B is preferable.

  By forming a head module for each color nozzle row 61 and arranging them, it is possible to form an inkjet head 24 capable of color drawing. For example, a head module 24Y having a nozzle row 61Y that discharges yellow ink, a head module 24M having a nozzle row 61M that discharges magenta ink, a head module 24C having a nozzle row 61C that discharges cyan ink, and black ink A head module 24K having a nozzle row 61K for discharging, and head modules 24LC, 24LM, 24CL, 24W having nozzle rows 61LC, 61LM, 61CL, 61W for discharging ink of each color of LC, LM, CL, W, respectively. A mode is also possible in which the carriages 30 are arranged at equal intervals so as to be aligned along the reciprocating direction of the carriage 30 (main scanning direction, Y direction).

  A module group (head group) of the head modules 24Y, 24M, 24C, 24K, 24LC, and 24LM for each color may be interpreted as an “inkjet head”, or each module may be interpreted as an “inkjet head”. It is. Alternatively, a configuration in which an ink flow path is separately formed for each color within one inkjet head 24 and a nozzle row that ejects a plurality of colors of ink with one head is also possible.

  In each nozzle row 61, a plurality of nozzles are arranged in a row (linearly) along the recording medium conveyance direction (sub-scanning direction, X direction) at regular intervals. In the inkjet head 24 of this example, the arrangement pitch (nozzle pitch) of the nozzles constituting each nozzle row 61 is 254 μm (100 dpi), the number of nozzles constituting one row of nozzle rows 61 is 256, and the total length Lw of the nozzle row 61 The total length of the nozzle row is about 65 mm (254 μm × 255 = 64.8 mm). Further, the discharge frequency is 15 kHz, and three types of discharge droplet amounts of 10 picoliter, 20 picoliter, and 30 picoliter can be distinguished by changing the drive waveform.

  As an ink ejection method of the inkjet head 24, a method (piezo jet method) in which ink droplets are ejected by deformation of a piezoelectric element (piezo actuator) is employed. In addition to a configuration that uses an electrostatic actuator as the energy generation element (electrostatic actuator method), a mode in which ink is heated using a heating element (heating element) such as a heater to generate bubbles, and ink droplets are ejected with that pressure. (Thermal jet method) can also be adopted.

  However, since the ultraviolet curable ink generally has a higher viscosity than the solvent ink, when using the ultraviolet curable ink, it is preferable to adopt a piezo jet method having a relatively large ejection force.

[About drawing mode]
In the inkjet recording apparatus 10 shown in this example, multi-pass drawing control is applied, and the print resolution can be changed by changing the number of print passes. For example, three types of drawing modes, a high production mode, a standard mode, and a high image quality mode, are prepared, and the printing resolution is different in each mode. The drawing mode can be selected according to the printing purpose and application.

  In the following description, the print resolution is expressed in the form of (print resolution in the main scanning direction) × (print resolution in the sub-scanning direction).

  In the high production mode, printing is executed with a resolution of 600 dpi (in dots per inch) × 400 dpi. In the high production mode, a resolution of 600 dpi is realized by two passes (two scans) in the main scanning direction.

  In the first scan (outward travel of the carriage 30), dots are formed with a resolution of 300 dpi. In the second scan (return pass), dots are formed such that the middle of the dots formed in the first scan (forward pass) is interpolated at 300 dpi, and a resolution of 600 dpi is obtained in the main scan direction.

  On the other hand, in the sub-scanning direction, the nozzle pitch is 100 dpi, and dots are formed at a resolution of 100 dpi in the sub-scanning direction by one main scanning (one pass). Therefore, a resolution of 400 dpi is realized by performing interpolation printing by four-pass printing (four scans). The main scanning speed of the carriage 30 in the high production mode is 1270 mm / sec.

  In the standard mode, printing is performed at a resolution of 600 dpi × 800 dpi, and a resolution of 600 dpi × 800 dpi is obtained by 2-pass printing in the main scanning direction and 8-pass printing in the sub-scanning direction.

  In the high image quality mode, printing is performed at a resolution of 600 dpi × 1200 dpi or 1200 dpi × 1200 dpi, and a resolution of 600 dpi × 1200 dpi or 1200 dpi × 1200 dpi is obtained with two or four passes in the main scanning direction and 12 passes in the sub-scanning direction. ing.

[About swath width by single ring scanning]
In the drawing mode of the wide format machine, drawing conditions for single ring (interlace) are determined for each resolution setting. Specifically, since the inkjet head discharge nozzle row width Lw (nozzle row length) is divided by the number of passes (number of scan repetitions) to produce a single ring, the nozzle row width of the ink jet head and the main scan The swath width differs depending on the number of passes in the direction and the sub-scanning direction (the number of divisions to be interlaced).

  The details of the single-pass drawing by the multipath method are described in, for example, Japanese Patent Application Laid-Open No. 2004-306617.

  As an example, the relationship between the number of passes and swath width by single ring drawing when using a QS-10 head (100 dpi, 256 nozzles) manufactured by FUJIFILM Dimatix is as shown in the following table (Table 1). The swath width assumed by the drawing is a value obtained by dividing the nozzle row width to be used by the product of the number of passes in the main scanning direction and the number of passes in the sub scanning direction.

[Arrangement of UV irradiation section]
As shown in FIG. 3, provisional curing light sources 32 </ b> A and 32 </ b> B are arranged on both the left and right sides of the carriage movement direction (Y direction) of the inkjet head 24. Further, main curing light sources 34 </ b> A and 34 </ b> B are disposed downstream of the inkjet head 24 in the recording medium conveyance direction (X direction). The main curing light sources 34A and 34B are arranged on the outer side (further farther) than the temporary curing light sources 32A and 32B in the Y direction from the inkjet head 24. The main curing light sources 34A and 34B are configured to be movable in the direction opposite to the recording medium conveyance direction (−X direction), and are aligned with the temporary curing light sources 32A and 32B and the inkjet head 24 along the carriage movement direction. The arrangement can be changed.

  The color ink droplets ejected from the color ink nozzles (nozzles included in the nozzle arrays 61Y, 61M, 61C, 61K, 61LC, and 61LM) and landed on the recording medium 12 immediately follow the color ink droplets. Ultraviolet light for temporary curing is irradiated by the passing temporary curing light sources 32A and 32B.

  Although details will be described later, the temporary curing light sources 32A and 32B can have a distribution of irradiation energy in the recording medium conveyance direction, and can reduce a difference in total irradiation energy irradiated to each dot. As an example of the distribution of the irradiation energy, the temporary curing light sources 32A and 32B are divided into two in the recording medium conveyance direction, and the irradiation energy on the downstream side in the same direction is doubled with respect to the irradiation energy on the upstream side in the same direction. It is done.

  Ink droplets on the recording medium 12 that have passed through the printing area of the inkjet head 24 as the recording medium 12 is intermittently conveyed are irradiated with ultraviolet rays for main curing by the main curing light sources 34A and 34B. In this way, by temporarily setting the ink droplets in a temporarily cured state, it is possible to take the dot development time (the time for the dots to spread to a predetermined size) while preventing landing interference, Uniformity can be achieved and the interaction between the droplet and the medium can be promoted to increase the adhesion.

[Description of control system of inkjet recording apparatus]
FIG. 4 is a block diagram showing the configuration of the inkjet recording apparatus 10. As shown in the figure, the ink jet recording apparatus 10 is provided with a control device 102 as control means. As the control device 102, for example, a computer having a central processing unit (CPU) can be used. The control device 102 functions as a control device that controls the entire inkjet recording apparatus 10 according to a predetermined program, and also functions as a calculation device that performs various calculations.

  The control device 102 includes a recording medium conveyance control unit 104 (conveyance control unit), a carriage drive control unit 106, a light source control unit 108, an image processing unit 110, and a droplet ejection control unit 112 (a droplet ejection control unit). Each of these units is realized by a hardware circuit or software, or a combination thereof.

  The recording medium conveyance control unit 104 controls the conveyance driving unit 114 for conveying the recording medium 12 (see FIG. 1). The conveyance drive unit 114 includes a drive motor that drives the nip roller 40 shown in FIG. 2 and a drive circuit thereof. The recording medium 12 conveyed on the platen 26 (see FIG. 1) is intermittently fed in the sub-scanning direction in units of swath widths in accordance with the reciprocating scanning (movement of the printing pass) in the main scanning direction by the inkjet head 24.

  The carriage drive control unit 106 shown in FIG. 4 controls the main scanning drive unit 116 for moving the carriage 30 (see FIG. 1) in the main scanning direction. The main scanning drive unit 116 includes a drive motor connected to a moving mechanism of the carriage 30 and a control circuit thereof.

  The light source control unit 108 is a control unit that controls the light emission of the temporary curing light sources 32A and 32B via the light source drive circuit 118 and the light emission of the main curing light sources 34A and 34B via the light source drive circuit 119. As the temporary curing light sources 32A and 32B and the main curing light sources 34A and 34B, UV lamps such as UV-LED elements (ultraviolet LED elements, denoted by reference numeral 314A in FIG. 9) and metal halide lamps are applied.

  The light source drive circuit 118 that controls the light emission of the temporary curing light sources 32A and 32B controls the light emission amount of the UV-LED elements so that the light emission amount is distributed in the recording medium conveyance direction. The amount of light emitted from the UV-LED element can be adjusted by adjusting the current supplied to the UV-LED element.

  For example, when the current supplied to the UV-LED element increases, the amount of light emitted from the UV-LED element increases. When the current supplied to the UV-LED element decreases, the amount of light emitted from the UV-LED element decreases.

  The control device 102 is connected to an input device 120 such as an operation panel and a display device 122. The input device 120 is means for inputting a manual external operation signal to the control device 102. For example, various forms such as a keyboard, a mouse, a touch panel, and operation buttons can be adopted.

  Various forms such as a liquid crystal display, an organic EL display, and a CRT can be adopted as the display device 122. By operating the input device 120, the operator can select a drawing mode, input printing conditions, and input / edit attached information. Various information such as input contents and search results are stored on the display device 122. It can be confirmed through the display.

  Further, the ink jet recording apparatus 10 is provided with an information storage unit 124 for storing various types of information and an image input interface 126 for taking in image data for printing. As the image input interface, a serial interface or a parallel interface may be applied. In this part, a buffer memory (not shown) for speeding up communication may be mounted.

  Image data input via the image input interface 126 is converted into print data (dot data) by the image processing unit 110. The dot data is generally generated by performing color conversion processing and halftone processing on multi-tone image data.

  The color conversion process is a process of converting image data expressed in sRGB or the like (for example, 8-bit image data for each RGB color) into color data for each ink color used in the inkjet recording apparatus 100.

  The halftone process is a process for converting the color data of each color generated by the color conversion process into dot data of each color by a process such as an error diffusion method or a threshold matrix. Various known means such as an error diffusion method, a dither method, a threshold matrix method, and a density pattern method can be applied as the halftone processing means. Halftone processing generally converts gradation image data having gradation values of 3 or more into gradation image data having gradation values less than the original gradation value.

  In the simplest example, it is converted into binary (dot on / off) dot image data, but in halftone processing, it corresponds to the dot size type (for example, three types such as large dot, medium dot, small dot). It is also possible to perform multi-level quantization.

  The binary or multi-valued image data (dot data) obtained in this way controls the drive (on) / non-drive (off) of each nozzle, and in the case of multiple values, controls the droplet amount (dot size). Used as ink ejection data (droplet ejection control data).

  The droplet ejection control unit 112 generates an ejection control signal for the head drive circuit 128 based on the dot data generated by the image processing unit 110. Further, the droplet ejection control unit 112 includes a drive waveform generation unit (not shown). The drive waveform generator is a means for generating a drive voltage signal for driving an energy generating element (in this example, a piezo element) corresponding to each nozzle of the inkjet head 24.

  The waveform data of the drive voltage signal is stored in advance in the information storage unit 124, and waveform data to be used is output as necessary. The signal (drive waveform) output from the drive waveform generation unit is supplied to the head drive circuit 128. Note that the signal output from the drive waveform generation unit may be digital waveform data or an analog voltage signal.

  A common driving voltage signal is applied to each energy generating element of the inkjet head 24 via the head driving circuit 128, and the switching element is connected to the individual electrode of each energy generating element in accordance with the droplet ejection timing of each nozzle. By switching on / off (not shown), ink is ejected from the corresponding nozzle.

  The information storage unit 124 stores programs executed by the CPU of the control device 102, various data necessary for control, and the like. The information storage unit 124 stores resolution setting information according to the drawing mode, the number of passes (the number of scan repetitions), control information for the temporary curing light sources 32A and 32B, and the main curing light sources 34A and 34B.

  The encoder 130 is attached to the drive motor of the main scanning drive unit 116 and the drive motor of the transport drive unit 114, and outputs a pulse signal corresponding to the rotation amount and rotation speed of the drive motor. Is sent to the controller 102. Based on the pulse signal output from the encoder 130, the position of the carriage 30 and the position of the recording medium 12 are grasped.

  The sensor 132 is attached to the carriage 30, and the width of the recording medium 12 is grasped based on the sensor signal obtained from the sensor 132.

[Description of drawing method of multi-pass printing method]
FIG. 5 is a schematic diagram of a drawing operation by the multipass printing method. Here, in order to simplify the description, a head 240 having one nozzle row will be described as an example. Further, the configuration in which the recording medium is intermittently fed in the sub-scanning direction will be described assuming that the recording medium is stopped and the head 240 is relatively intermittently moved in the sub-scanning direction for convenience of illustration.

  The head 240 has a nozzle row in which a plurality of nozzles 242 are arranged at a constant nozzle pitch in the sub-scanning direction. This nozzle row corresponds to the nozzle rows 61Y, 61M, 61C, 61K of the respective colors described with reference to FIG.

  When the head 240 is moving in the main scanning direction (left-right direction in FIG. 5), droplet ejection is performed from the nozzle 242. Two-dimensional drawing is performed on the recording medium by a combination of the reciprocating movement of the head 240 along the main scanning direction and the intermittent feeding of the recording medium in the sub-scanning direction (vertical direction in FIG. 5).

  When an image having a desired recording resolution is completed by N scans (scans), the relative position of the paper and the head in the sub scan direction at the N + 1 scan by intermittent movement (relative movement) in N sub scans is The relationship is as shown in the figure.

  That is, in order to perform N-time writing, intermittent feeding is performed for the first time, the second time, the third time, and so on, and the N + 1th time is just connected to the position corresponding to the length of the head (nozzle row). In order for the N-time writing operation to be seamlessly connected, the N + 1-th scan is performed by moving in the sub-scan direction by “nozzle row length + 1 nozzle pitch” from the sub-scan position of the first scan.

  As an example, using a head 100 having a nozzle array with a nozzle array density of 100 npi (nozzle per inch) and 256 nozzles 102 arranged in two main scanning directions and four sub-scanning directions (main 2 × sub 4). Consider a case in which a recording resolution of 600 dpi main scanning × 400 dpi sub-scanning is realized with 8 passes (8 times writing).

  The interval between the droplet ejection points (pixels) determined from the recording resolution is called the “droplet ejection point interval”, “pixel interval”, or “dot interval”. This is called a “droplet grid” or “pixel grid”.

  In the case of the recording resolution of main scanning 600 dpi × sub scanning 400 dpi, the droplet ejection point interval in the main scanning direction is 25.4 mm (millimeters) / 600 dpi≈42.3 μm (micrometer), and the droplet ejection point interval in the sub scanning direction is 25.4 mm / 400 dpi = 63.5 μm. This represents the size “42.3 μm × 63.5 μm” of one cell (corresponding to one pixel) of the droplet ejection dot lattice.

  Regarding the feed control of the recording medium and the control of the droplet ejection position (droplet ejection timing) from the head 240, the feed amount and position are controlled in units of droplet ejection point intervals determined from this recording resolution. The droplet ejection point interval determined from the recording resolution may be referred to as “resolution pitch” or “pixel pitch”.

  When N = 8 (main 2 × sub 4), the droplet ejection point line (scanning line) in the main scanning direction is filled with two scans, and the droplet ejection point line (scanning line) in the sub scanning direction is scanned four times. As shown in FIG. 4, 2 × 4 droplet ejection point grids are recorded in 8 scans (passes).

  FIG. 6 schematically shows the relationship between the numbers (1 to 8) of the respective scans by the eight-time drawing operation and the droplet ejection positions recorded by the scans. In FIG. 6, each cell numbered 1 to 8 represents a droplet ejection position (pixel position) recorded by the nozzle 242, and the numbers 1 to 8 were recorded when the pixel position was scanned a number of times. This represents the number of scans to be performed. The cells (pixels) to which the number “1” is attached represent the droplet ejection position recorded in the first scan.

  As is clear from FIG. 7, in the arrangement distribution of the numbers 1 to 8 representing the scanning order for recording each droplet ejection position, the main 2 × second 4 “2 × 4” lattice is the basic unit of repetition. Yes. This 2 × 4 lattice is referred to as “basic unit lattice” or “2 × 4 lattice”.

  The 2 × 4 lattice filling method (droplet ejection order) is not limited to the examples shown in FIGS. FIGS. 8A to 8G show examples of how to fill a 2 × 4 lattice. Of course, there are other ways of filling than those exemplified here.

[Detailed description of temporary curing light source]
Next, the temporary curing light source unit applied to the temporary curing light sources 32A and 32B will be described in detail. The same configuration can be applied to the temporary curing light sources 32A and 32B.

  FIG. 9 is a perspective view of the provisional curing light source unit 300, and the internal structure is shown by broken lines. FIG. 10 is a perspective side view showing light rays inside the temporary curing light source unit shown in FIG.

  As shown in FIG. 9, the temporary curing light source unit 300 has a light source box structure having a substantially rectangular parallelepiped shape including a bottom plate 302, LED mounting plates 304 </ b> A and 304 </ b> B, and a housing 322.

  The LED mounting plates 304A and 304B are provided on both end faces in the longitudinal direction (medium transport direction) of the temporary curing light source unit 300, and each has four UV-LED elements 314 (in FIG. 9, the UV of the LED mounting plate 304A). -A UV-LED element group including LED element 314A only) is provided.

  Reflecting plates 306 that are inclined obliquely downward from both end faces in the longitudinal direction toward the center are provided in the upper part of the housing 322. In addition, a partition member 308 is provided at a substantially central portion in the same direction so that ultraviolet rays from the UV-LED element group provided on the upstream side in the same direction do not reach the downstream region 302B in the same direction on the bottom plate 302. In addition, the ultraviolet rays from the UV-LED element group provided on the downstream side in the same direction are configured not to reach the upstream region 302A in the same direction of the bottom plate 302.

  The inner surface of the housing 322, the surface facing the bottom plate 302 of the reflecting plate 306, and the surface facing the UV-LED element group of the partition member 308 are reflecting surfaces (reflectors) by aluminum vapor deposition.

  FIG. 10 is a perspective view showing light rays in the temporary curing light source unit 300 shown in FIG. The solid line from the UV-LED elements 314A and 314B shown in the figure to the bottom plate 302 through the reflector 306 or the partition member 308 represents the ultraviolet rays from the UV-LED elements 314A and 314B.

  The ultraviolet light emitted from the UV-LED element 314A on the upstream side in the medium transport direction is reflected so that the ultraviolet light is guided to the upstream region 302A of the bottom plate 302, and from the UV-LED element 314B on the downstream side in the medium transport direction. The emitted ultraviolet light is reflected, and the ultraviolet light is guided to the downstream region 302B of the bottom plate 302.

  In the provisional curing light source unit 300 having such a configuration, the ultraviolet light emission part is divided into two, an upstream half in the medium conveyance direction and a downstream half in the same direction, and the irradiation energy can be adjusted independently. Distribution of ultraviolet irradiation energy in the medium transport direction by appropriately adjusting the lighting, extinction, and light emission amount of the UV-LED element 314A corresponding to the upstream area 302A and the UV-LED element 314314B corresponding to the downstream area 302B. Can be generated.

  Turning on / off the UV-LED elements 314A and 314B and adjusting the amount of emitted light are supplied to the UV-LED elements 314A and 314B by the light source driving circuit 118 in response to a command from the control device 102 in the control system shown in FIG. The current value can be adjusted.

  The UV-LED elements 314A and 314B include, for example, an ultraviolet light emitting LED, NC4U134A (product), having an emission wavelength (peak value) of 385 nanometers (380 to 390 nanometers) manufactured by Nichia Corporation. Name) can be applied.

It is preferable that the irradiation width in the main scanning direction of the temporary curing light sources 32A and 32B is 20 mm in full width at half maximum. Irradiation width in the sub-scanning direction is slightly longer than the total length L _w of the full width at half maximum nozzle row (for example, 5% of the total length L _w of the nozzle row 10% longer) mode in which the preferred.

[Explanation of irradiation energy of temporary curing light source]
Next, the relationship between the irradiation energy of the upstream region 302A and the irradiation energy of the downstream region 302B in the medium conveyance direction of the temporary curing light sources 32A and 32B will be described in detail.

(Exposure conditions of a temporary curing light source according to the prior art)
Conventionally, the irradiation energy of UV light sources (temporary curing light sources 32A and 32B) provided in parallel with the nozzle array 61 (see FIG. 3) is substantially uniform (substantially uniform) in the recording medium conveyance direction.

  FIG. 11 is an explanatory diagram of exposure conditions (condition 1) according to the prior art, and FIG. 11 (a) shows the pre-curing light sources 32A and 32B (see FIG. 3) with an upstream irradiation energy of every 6 millijoules. It is a figure showing irradiation distribution in a media surface when a square centimeter and downstream irradiation energy are 6 millijoules per square centimeter. FIG. 11B is a graph showing an illuminance distribution cross section in the media transport direction (X direction) in FIG.

  In FIG. 11A, the horizontal axis is a position in the Y direction (scanning direction of the carriage 30), and is represented by a distance (millimeter) from the center of the UV-LED. The vertical axis is the position in the X direction (recording medium conveyance direction), and is expressed by the distance (millimeter) from the center of the exposure area in the same direction.

  In FIG. 11B, the horizontal axis represents the irradiation energy (watts per square millimeter), the vertical axis represents the position in the X direction, and is represented by the distance (millimeter) from the center of the exposure region in the same direction. .

  Under the above exposure conditions (condition 1), the scanning speed of the carriage (see FIG. 1) is 1270 millimeters per second, the recording resolution is 600 dpi × 400 dpi (pass number 8), and the black density is 100% (hereinafter referred to as K100%). A solid image was formed.

  FIG. 12 shows read data obtained by reading a K100% solid image formed by using the scanner with the exposure condition as condition 1, the horizontal axis is the position in the X direction, and the vertical axis is the read data value. . The read data value is 8-bit data decomposed into RGB and represents the density.

  The amplitude of the read data value represents a density difference, that is, density unevenness. Since the read data value has a periodicity corresponding to the swath width, the solid image of K100% has a density of the swath width period. It is understood that unevenness (banding) has occurred.

  That is, when the irradiation energy of the temporary curing light sources 32A and 32B is substantially uniform in the X direction, density unevenness having periodicity corresponding to the swath width period may occur as shown in FIG. sell.

  FIG. 13 is an explanatory diagram of exposure conditions (condition 2) according to the prior art. FIG. 13 (a) shows the above-described condition 1 in which both the upstream irradiation energy and the downstream irradiation energy are every 8 millijoules. It is a figure showing the irradiation distribution in a media surface when it is set as a square centimeter. FIG. 13B is a graph showing an illuminance distribution cross section in the medium transport direction (X direction) in FIG.

  Further, FIG. 14 shows that the exposure condition is condition 2, the carriage 30 transport speed and the image recording resolution (number of passes) are the same as described above, 1270 millimeters per second, 600 dpi × 400 dpi solid K100%. It represents data read by an image scanner.

  As shown in FIG. 14, when the total irradiation energy of ultraviolet rays is made larger than Condition 1, density unevenness (banding) is improved, but density unevenness having a periodicity slightly corresponding to the swath width period is still generated. It is grasped that it is doing.

  When multi-pass printing (singling droplet ejection) is performed, ink ejected from the nozzles on the downstream side in the same direction (lower side in FIG. 3) of the nozzle row is upstream in the same direction (upper side in FIG. 3). The total exposure amount (total irradiation energy of ultraviolet rays) is smaller than the ink ejected from the nozzles.

  For example, when multi-pass printing is performed by dividing the nozzle row into 8 and the number of passes is “8”, the ink ejected from the nozzle on the most upstream side of the nozzle row is caused by the UV light source located beside the nozzle. In addition to exposure, there is also exposure from a UV light source located beside the nozzle following the nozzle, and the total number of exposures (the number of times the UV light source passes over the ink) is eight, the same as the number of passes. .

  On the other hand, since the ink ejected from the nozzle on the most downstream side of the nozzle row passes only by the UV light source located on the side of the nozzle, the number of exposures is one.

  That is, the difference in the total irradiation energy (total exposure amount) between the ink ejected from the nozzle on the upstream side in the recording medium conveyance direction of the nozzle array and the ink ejected from the nozzle on the downstream side in the same direction is the swath width period. It is thought that this is the cause of density unevenness having periodicity corresponding to.

(Exposure conditions for pre-curing treatment according to an embodiment of the present invention)
FIG. 15 is an explanatory diagram of exposure conditions (condition 3) of the temporary curing light sources 32A and 32B (see FIG. 3) in the temporary curing process according to the embodiment of the present invention. FIG. 15A is a diagram showing an irradiation distribution on the media surface in the temporary curing light source unit 300 when the irradiation energy on the upstream side is 4 millijoules per square centimeter and the irradiation energy on the downstream side is 8 millijoules per square centimeter. It is. FIG. 15B is a graph showing an illuminance distribution cross section in the medium transport direction (X direction) in FIG.

  FIG. 16 shows a K100% solid image formed with an exposure condition of condition 3 and a carriage 30 transport speed and image recording resolution (number of passes) of 1,270 millimeters per second and 600 dpi × 400 dpi, as described above. Data read by the scanner is shown.

  In the read data value shown in the figure, the amplitude having a period corresponding to the swath width period is not visually recognized, and it can be understood that the density unevenness having the periodicity corresponding to the swath width period is improved.

  In addition, it is estimated that the improvement in the visibility of density unevenness having periodicity corresponding to the swath width period can obtain the same effect from the result of the 100% density solid image even for density other than 100%. The

  That is, it can be said that improvement in the visibility of density unevenness having a periodicity corresponding to the swath width period is expected at substantially all densities.

(About colors other than black (K))
Next, it will be described whether the same conditions as black can be applied to colors other than black. 17 to 19 show read data obtained by reading a solid image of cyan (C) having a density of 100% (hereinafter referred to as a C100% image) with a scanner. The read data shown in FIG. The read data shown in FIG. 18 is for a C100% image whose exposure condition is condition 2. Further, the read data shown in FIG. 19 is for a C100% image whose exposure condition is condition 3.

  As shown in FIGS. 17 and 18, the C100% image formed under the exposure conditions 1 and 2 has an amplitude having periodicity corresponding to the swath width period. On the other hand, as shown in FIG. 19, it can be said that the C100% image formed under the exposure condition 3 has a reduced amplitude component having a periodicity as compared with the read data shown in FIGS. 17 and 18. .

  In summary, it has been confirmed that for non-black colors, density unevenness having a periodicity corresponding to the swath width period is improved in cyan as well as black. Based on the cyan result, the same effect can be obtained for other colors such as magenta and yellow.

(About irradiation energy ratio)
Next, whether or not density unevenness having periodicity is generated when the ratio of the irradiation energy on the upstream side in the recording medium conveyance direction to the irradiation energy on the downstream side in the same direction (irradiation energy ratio) is changed will be described.

  FIG. 20 is a table showing evaluation results of density unevenness (banding) when the ratio of irradiation energy on the downstream side in the same direction to irradiation energy on the upstream side in the recording medium conveyance direction is changed.

  The irradiation energy on the upstream side and the irradiation energy on the downstream side can be varied in four steps of 2.4 millijoules per square centimeter, 4.0 millijoules per square centimeter, 6.0 millijoules per square centimeter, and 8.0 millijoules per square centimeter, respectively. A solid image was formed, and the formed solid image was visually observed to determine whether or not density unevenness having periodicity occurred.

  The evaluation “A” in the figure means that the periodic density unevenness is hardly visually recognized and is a good image, and the evaluation “B” indicates that the periodic density unevenness is slightly visible but the permissible level. It means that it is an image.

  On the other hand, the evaluation “C” means that the image has a periodic density unevenness and does not reach the allowable level. Further, the numerical value in parentheses in the figure indicates the irradiation energy ratio (= downstream irradiation energy / upstream irradiation energy).

  As shown in the figure, when the irradiation energy ratio exceeds 1.0, all evaluations are “A”, and a good image in which periodic density unevenness is not visually recognized can be formed. On the other hand, when the irradiation energy ratio is 1.0, the evaluation may be any of “A”, “B”, and “C” depending on the irradiation energy, which is not stable.

  Further, when the irradiation energy ratio is less than 1.0, the evaluation is all “C”, and there is a high possibility that an image in which periodic density unevenness is visually recognized is formed.

  As described above, the irradiation energy ratio is summarized. By setting the exposure condition of the temporary curing light source to Condition 3 (downstream irradiation energy / upstream irradiation energy = 2.0), swaths are obtained in a K100% solid image and a C100% solid image. It is possible to greatly improve the visibility of density unevenness in the width period.

  In addition, based on the evaluation result shown in FIG. 20, it is possible to extend the range where the same effect can be extended to downstream irradiation energy> upstream irradiation energy (downstream irradiation energy / upstream irradiation energy> 1). I can say that.

(Effect 1: Improved swathing banding)
As described above, the difference in the total irradiation energy (total exposure amount) between the ink ejected from the nozzle on the upstream side in the recording medium conveyance direction of the nozzle array and the ink ejected from the nozzle on the downstream side in the same direction. However, this is considered to cause the density unevenness of the swath width period.

  Then, the density unevenness of the swath width period is improved by reducing the difference in the total irradiation energy between the ink ejected from the nozzle on the upstream side in the same direction and the ink ejected from the nozzle on the downstream side in the same direction. It is considered possible.

  In the region of 1 swath width, the unevenness of the ink ejected from the nozzle on the upstream side in the recording medium conveyance direction (the ink ejected first) is lower, and the more wetting and spreading is from the nozzle on the downstream side in the same direction. The portion where the ejected ink (ink ejected later) comes into direct contact with the recording medium is reduced, and the ink ejected afterwards tends to wet and spread.

  As a result, there is less ink (dots) to be cured while the wetting spread is small and the contact angle is large, so that the existence probability of convex dots (droplet ejection points) that regularly reflect light when an image is viewed decreases.

  In other words, the height difference between the dots existing in the 1 swath width region becomes smaller, and therefore, the reflection of the dot that was previously ejected in the 1 swath width region and the dot that was subsequently ejected is reflected. By reducing the difference, it is estimated that the difference in glossiness in the region of 1 swath width is reduced, and the banding in the region of 1 swath width is improved.

(Effect 2: Improvement of density unevenness with a swath width period)
In addition, the semi-curing level (the degree of curing) of ink ejected from the nozzle on the upstream side in the recording medium conveyance direction and the semi-curing level of ink ejected from the nozzle on the downstream side in the same direction are the upstream side in the same direction. By adjusting the amount of light between the irradiation energy and the irradiation energy on the downstream side in the same direction, in the adjacent swath-width region, the dot at the upper end in the region on the downstream side in the same direction, which was previously ejected, When the dot at the lower end in the upstream region in the same direction where the droplet is dropped impacts and the movement of the dot occurs, it is adjusted to which side and to what extent it can be moved.

  That is, when considering an adjacent swath width region, the irradiation energy on the upstream side in the same direction of the temporary curing light sources 32A and 32B is applied to the upstream dot in the same direction in the downstream region in the recording medium conveyance direction. Therefore, it is cured using relatively weak ultraviolet rays. On the other hand, the dots on the downstream side in the same direction in the upstream region in the same direction are cured by relatively weak ultraviolet rays because the irradiation energy on the downstream side in the same direction of the temporary curing light sources 32A and 32B is applied.

  Landing interference occurs between these dots, and one dot moves toward the other dot, or both dots move closer to each other. Since the movement of dots when landing interference occurs depends on the semi-curing level of each dot, adjusting the irradiation energy on the upstream side in the same direction and the irradiation energy on the downstream side in the same direction allows the movement of dots to move. It is thought that the direction and the amount of movement can be adjusted.

  Therefore, it is possible to reduce the visibility of density unevenness having a periodicity corresponding to one swath period (low density streaks at the boundary between adjacent one swath width areas) due to the movement of dots due to landing interference. It is.

(Effect 3: Ensuring adhesion of dots to the recording medium)
On the other hand, by lowering the irradiation energy upstream of the temporary curing light sources 32A and 32B in the recording medium conveyance direction from the downstream side in the same direction, there is a concern that the adhesion of dots to the recording medium is reduced. In the apparatus configuration shown in FIG. 1, since the main curing process is performed by the main curing light sources 34A and 34B following the ink jet head 24, a decrease in the adhesion of dots to the recording medium is prevented.

  In the apparatus configuration shown in FIG. 1, the length of the inkjet head 24 in the recording medium conveyance direction and the length of the irradiation area of the temporary curing light sources 32A and 32B in the same direction are substantially the same. By further extending the length of the irradiation area of the curing light sources 32A and 32B to the downstream side in the same direction, it is possible to prevent a decrease in the adhesion of dots to the recording medium.

  In particular, the main curing light sources 34A and 34B are provided on the downstream side of the temporary curing light sources 32A and 32B in the recording medium conveying direction, and the main curing processing by the main curing light sources 34A and 34B is performed after the temporary curing processing by the temporary curing light sources 32A and 32B. The aspect has a remarkable effect of improving the adhesion of dots to the recording medium.

  In addition, when UV-LED elements are provided at both ends in the recording medium conveyance direction, the number of UV-LED elements on the upstream side in the same direction that reduces the irradiation energy relatively is more than the number of UV-LED elements on the downstream side in the same direction. It can also be reduced.

  Further, by reducing the current supplied to the UV-LED element on the upstream side in the same direction that relatively reduces the irradiation energy, it is possible to save power in the temporary curing light sources 32A and 32B.

[Modification]
Next, a modification of the above-described embodiment will be described. The temporary curing light source unit according to this modification is provided with a plurality of UV-LEDs 314 only at one end in the recording medium conveyance direction (X direction), and some of the plurality of UV-LEDs 314 are upstream. The region is irradiated with ultraviolet rays, and the remaining UV-LEDs are configured to irradiate the downstream region with ultraviolet rays.

  FIG. 21 is a schematic diagram illustrating an arrangement configuration of an ultraviolet irradiation unit to which the temporary curing light source unit according to the present modification is applied. In FIG. 21, the description of the inkjet head is omitted, and only the arrangement form of the temporary curing light source units 332A and 332B and the main curing light sources 334A and 334B is shown.

  Moreover, in FIG. 21, in order to show the arrangement | positioning form of each UV-LED element 315 which comprises this hardening light source 334A, 334B, the LED back side was displayed.

  The main curing light sources 334A and 334B in FIG. 21 each include 12 UV-LED elements 315, and an LED element array in which six LEDs are arranged at regular intervals in the Y direction is arranged in two lines in the X direction. It has become. This LED element group arranged in 6 × 2 rows has a staggered arrangement in which the upstream LED element row in the X direction and the downstream LED element row are displaced in the Y direction. Note that the number and arrangement of the LEDs constituting the main curing light sources 334A and 334B are not limited to this example.

  In the temporary curing light source units 332A and 332B shown in FIG. 21, a plurality of UV-LED elements 314 are arranged on the end face on the downstream side in the X direction, and the irradiation region can be selected by the UV-LED elements to be lit. It has a simple light source box structure.

  Here, each of the temporary curing light source units 332A and 332B shows an example in which four UV-LED elements 314 are arranged in a 2 × 2 array form of two rows on the upper and lower sides and two rows on the left and right sides. The number and arrangement form are not limited to this example.

  FIG. 22 is a perspective view of the temporary curing light source unit 332A (or 332B) viewed from the lower surface side. A pattern 348 for adjusting the light amount distribution is formed in a region near the UV-LED element 314 in the light emitting surface 347 of the light diffusion plate 346 disposed on the bottom surface of the housing 322.

  FIG. 23 shows the internal structure of the housing 322. In FIG. 23, the light diffusing plate 346 is not shown. As shown in FIG. 23, in the housing 322, a mirror member 352 is disposed as a divided component that separates the light transmission space of the UV-LED elements 314 arranged vertically.

  FIG. 24 is a perspective view showing an example of a divided component (mirror member 352) disposed inside the housing 322. FIG. As shown in FIGS. 23 and 24, the inside of the temporary curing light source unit (light source box) 332A (332B) has a double ceiling structure partitioned by a mirror member 352.

  Both the upper surface 352A and the lower surface 352B of the mirror member 352 function as reflecting surfaces. The ceiling surface of the frame member 354 constituting the housing 322 (the surface inside the housing 322) also functions as a reflection surface.

  FIG. 25 is a perspective view showing light rays when the entire surface is irradiated in the temporary curing light source unit 332. FIG. 26 is a perspective view showing a state when only the upstream is irradiated, and FIG. 27 is a perspective view showing a state when only the downstream is irradiated.

  The light emitted from the two UV-LED elements 314A arranged in the upper stage among the four UV-LED elements 314 arranged on one end face in the X direction of the housing 322 is a mirror member as shown in FIG. The light is reflected by the upper surface side (352 A) of 352 and the top surface 322 A of the housing 322, and is guided onto the recording medium 12. The irradiation region 261 by the upper UV-LED element 314A is an upstream region in the X direction in the entire irradiation range of the temporary curing light source unit 332A (332B).

  On the other hand, the light emitted from the two UV-LED elements 314B arranged in the lower stage among the four UV-LED elements 314 is reflected on the lower surface side (352B) of the mirror member 352 as shown in FIG. Then, the recording medium 12 is irradiated. The irradiation region 362 by the lower UV-LED element 314B is a downstream region in the X direction in the entire irradiation range of the temporary curing light source unit 332A (332B).

Thus, the arrangement of the mirror member 352 divides the ultraviolet irradiation region into two regions, the upstream side and the downstream side, and each irradiation region corresponds to the upstream region and the downstream region of the nozzle row.

  In such a configuration, the irradiation energy of the lower UV-LED element 314B for irradiating ultraviolet rays to the downstream area in the recording medium conveyance direction is equal to the irradiation energy of the upper UV-LED 314A for irradiating ultraviolet rays to the upstream area in the same direction. By adjusting the current supplied to the upper UV-LED element 314A and the lower UV-LED element 314B, the irradiation energy of the upstream region in the same direction is greater than the irradiation energy of the downstream region in the same direction. The irradiation energy control of the temporary curing light source units 332A and 332 is realized.

  According to such a modification, the number of UV-LED elements can be reduced, and power saving of the temporary curing light sources 32A and 32B can be achieved.

  In the embodiment and the modification described above, the irradiation region of the temporary curing light source is divided into two in the recording medium conveyance direction. However, the irradiation energy of the temporary curing light source is divided into three or more and irradiation energy in the same direction. May have a distribution.

  For example, in an aspect in which the irradiation region of the temporary curing light source is divided into three, the irradiation energy may be large, the irradiation energy may be small, and the irradiation energy may be small from the upstream side in the same direction. Moreover, in the aspect in which the irradiation area of the temporary curing light source is divided into four, the irradiation energy may be large, irradiation energy, irradiation energy, irradiation energy small from the upstream side in the same direction, or irradiation energy large, irradiation energy, irradiation Small energy, small irradiation energy, large irradiation energy, large irradiation energy, medium irradiation energy, or small irradiation energy may be used.

  Further, the aspect of dividing the irradiation area of the temporary curing light source in the recording medium conveyance direction is not limited to the aspect having the central portion in the same direction as a boundary, and the irradiation area is divided into 2: 1 or 3: 1 boundaries. Can be provided as appropriate. The number of divisions and the boundaries between the divided regions may be determined according to the number of passes.

  Furthermore, a form in which a light emitting light source such as a UV-LED element is arranged on the surface of the temporary curing light sources 32A and 32B facing the recording medium is also possible.

[Actinic rays]
An actinic ray is a radiation ray (radiation) that can give energy for generating a starting species in the ink composition by irradiation, and includes α rays, γ rays, X rays, ultraviolet rays, visible rays, electron rays, and the like. . Of these, ultraviolet rays and electron beams are preferable from the viewpoint of curing sensitivity and device availability, and ultraviolet rays are more preferable.

  In this example, ultraviolet rays are exemplified as an example of actinic rays for curing the ink. However, the polymerization initiator contained in the ink is decomposed to generate a polymerization initiating species such as a radical, and the function of the initiating species of the polymerizable compound is If the polymerization reaction occurs and is accelerated, it is possible to apply the other actinic rays described above.

  Although the peak wavelength of actinic rays is based also on the absorption characteristic of a sensitizer, it is preferable that it is 200-600 nanometer, for example, it is more preferable that it is 300-450 nanometer, and it is 320-420 nanometer. More preferably. In particular, the active light is particularly preferably ultraviolet light having a peak wavelength in the range of 340 to 410 nanometers.

  In the ink jet recording apparatus shown in this example, the peak wavelength is most preferably 380 to 390 nanometers (in the range of plus or minus 5 nanometers centered on 385 nanometers).

  NC4U134A manufactured by Nichia Corporation can be applied to the UV-LED element applied to the light source of the main curing light sources 34A and 34B, similarly to the temporary curing light sources 32A and 32B.

  The light source of the main curing light sources 34A and 34B is not limited to the UV-LED element 35, and a UV lamp or the like can be used. For example, mercury lamps and gas / solid lasers are mainly used as light sources for actinic rays, and mercury lamps and metal halide lamps are widely known as light sources used for curing ultraviolet light curable inks. Yes.

  On the other hand, mercury-free is strongly desired from the viewpoint of environmental protection, and replacement with a GaN-based semiconductor ultraviolet light-emitting device is very useful industrially and environmentally. Furthermore, LED (UV-LED) and LD (UV-LD) are small, have a long lifetime, high efficiency, and low cost, and are preferable as a light source for photo-curing inkjet.

〔recoding media〕
As the recording medium, various media such as paper, non-woven fabric, vinyl chloride, synthetic chemical fiber, polyethylene, polyester, and tarpaulin can be used regardless of the material, regardless of the permeable medium or the non-permeable medium.

  That is, as a recording medium applicable to the ink jet recording apparatus (image forming method) according to the present invention, a recording medium known as a support or a recording material can be used. For example, paper, paper laminated with plastic (eg, polyethylene, polypropylene, polystyrene, etc.), metal plate (eg, aluminum, zinc, copper, etc.), plastic film (eg, cellulose diacetate, cellulose triacetate, propionic acid) Cellulose, cellulose butyrate, cellulose acetate butyrate, cellulose nitrate, polyethylene terephthalate, polyethylene, polystyrene, polypropylene, polycarbonate, polyvinyl acetal, polyvinyl chloride (PVC), acrylic resin, etc.) A plastic film (composite aluminum plate etc.) etc. are mentioned. Moreover, a non-absorbable recording medium can be used suitably as a recording medium applied to the ink jet recording apparatus according to the present invention.

[Ink composition]
Next, the ink composition (ink) will be described in detail. In the following description, “A (numerical value) to B (numerical value)” means “A or more and B or less”.

  Further, “(meth) acryl” is a term including either “acryl” or “methacryl” or both of them. “(Meth) acrylate” is a term that includes either “acrylate” or “methacrylate”, or both.

(Outline of ink composition)
The ink composition is an oil-based ink composition that can be cured by actinic rays (actinic radiation, actinic energy rays) such as ultraviolet rays.

  The ink composition contains a radical polymerizable compound as component A, a radical polymerization initiator as component B, and a colorant as component C.

(Explanation of radical polymerizable compound (component A))
The radical polymerizable compound (component A) contains a monofunctional radical polymerizable compound (component A-1) and a polyfunctional radical polymerizable compound (component A-2). The content of Component A-1 is 50 to 90% by weight, preferably 50 to 80% by weight, more preferably 60 to 80% by weight, based on the total weight of Component A. Component A-1 is preferably a radically polymerizable compound having one ethylenically unsaturated group.

  Component A-1 contains an N-vinyl compound (component A-1-1) and a compound represented by the following formula (I) (component A-1-2).

(In the above formula (I), R ¹ , R ² and R ³ each independently represents a hydrogen atom, a methyl group or an ethyl group, and X ¹ represents a single bond or a divalent linking group. )
In the compound represented by the above formula (I), R ¹ is preferably a hydrogen atom or a methyl group, and more preferably a hydrogen atom. R ² and R ³ are each independently preferably a hydrogen atom or a methyl group, and more preferably R ² and R ³ are both hydrogen atoms.

The divalent linking group for X ¹ is not particularly limited as long as it does not significantly impair the effects of the present invention, but it is a divalent hydrocarbon group or a divalent group in which a hydrocarbon group and an ether bond are combined. It is preferably a divalent hydrocarbon group, a poly (alkyleneoxy) group, or a poly (alkyleneoxy) alkylene group. Moreover, it is preferable that carbon number of the said bivalent coupling group is 1-60, and it is more preferable that it is 1-20.

X ¹ is preferably a single bond, a divalent hydrocarbon group, or a divalent group in which a hydrocarbon group and an ether bond are combined, and is preferably a C 1-20 divalent hydrocarbon group. More preferably, it is a C1-C8 bivalent hydrocarbon group, and a methylene group is particularly preferable.

  Component A-1-1 can preferably contain N-vinyl lactams or N-vinylformamide, and the N-vinyl lactams are preferably compounds represented by the following formula (a).

  In the above formula (a), n represents an integer of 2 to 6, and n is 3 to 5 from the viewpoint of flexibility after the ink composition is cured, adhesion to a recording medium, and availability of raw materials. It is preferable that n is 3 or 5, and n is particularly preferably 5 (N-vinylcaprolactam). The compounds represented by the above formula (a) may be used alone or in combination of two or more.

  In N-vinyllactams, the hydrogen atom on the lactam ring may be substituted with a substituent such as an alkyl group or an aryl group, and the lactam ring may be linked to a saturated or unsaturated ring structure.

  One example of N-vinyl lactams applicable to component A-1-1 is N-vinyl caprolactam. N-vinylcaprolactam is preferable because it is excellent in safety, is general-purpose and can be obtained at a relatively low price, and provides particularly good ink curability and good adhesion of a cured film to a recording medium.

  Preferable examples of N-vinylformamide applicable to Component A-1-1 include compounds having the following structure.

  The content of Component A-1-1 is 10 to 40% by weight, preferably 15 to 30% by weight, based on the total weight of Component A-1.

  As the component A-1-2, cyclic trimethylolpropane formal acrylate can be applied. Specific examples of component A-1-2 are shown below, but are not limited to these compounds. In the following specific examples, R represents a hydrogen atom or a methyl group.

  Among these, cyclic trimethylolpropane formal (meth) acrylate is preferable, and cyclic trimethylolpropane formal acrylate (CTFA) is particularly preferable.

  The content of component A-1-2 is 5 to 90% by weight, preferably 30 to 90% by weight, based on the total weight of component A-1.

  Component A-2 contains at least two trifunctional ethylenically unsaturated compounds represented by the formula (II), and the content of Component A-2 is 0.1 to 25% by weight based on the total weight of Component A % Is preferable, 0.5 to 10% by weight is more preferable, and further preferably 2 to 9% by weight.

(In the formula (II), each R ¹¹ independently represents a hydrogen atom or an optionally substituted alkyl group having 1 to 6 carbon atoms, and R ¹² represents a hydrogen atom or an optionally substituted carbon number. 1 to 6 alkyl groups, R ¹³ independently represents a hydrogen atom or a methyl group, X ² represents a single bond or a divalent linking group, and p, q and r each independently represents 0 to Represents an integer of 5.)
In the compound represented by the above formula (II), R ¹² represents a hydrogen atom or an optionally substituted alkyl group having 1 to 6 carbon atoms, and the alkyl group may be linear or branched. Examples of the substituent include a halogen atom, a hydroxyl group, and an amino group. R ¹² is preferably a hydrogen atom, a methyl group, an ethyl group, a propyl group, a methylol group, or an ethylol group, and particularly preferably a hydrogen atom, a methyl group, an ethyl group, or a methylol group.

R ¹³ each independently represents a hydrogen atom or a methyl group, preferably a hydrogen atom.

In the formula (II), X ² represents a single bond or a divalent linking group, and the divalent linking group is not particularly limited as long as it does not significantly impair the effect of the ink composition. And a divalent linking group in which a hydrocarbon group and an ether bond are combined.

X ² is preferably a single bond, a divalent hydrocarbon group having 1 to 6 carbon atoms, or an oxyalkylene group having 1 to 6 carbon atoms, and particularly preferably a single bond or a methylene group.

  In said formula (II), p, q, and r represent the integer of 0-5 each independently. p, q, and r are each independently preferably 0 to 3, particularly preferably 0 to 2. Examples of preferable combinations of p, q, and r include p = q = r = 0, p = q = r = 1, or p = q = r = 2.

  Hereinafter, specific examples of the compound when p, q, and r have preferable values will be described, but the present invention is not limited thereto.

As a preferred embodiment of the compound of the above formula (II) when p = q = r = 0 is satisfied, trimethylolpropane triacrylate (when R ¹² is an ethyl group, R ¹³ is a hydrogen atom, and X ² is a methylene group) , Trimethylolpropane trimethacrylate (R ¹² is ethyl group, R ¹³ is methyl group, X ² is methylene group), trimethylol ethane triacrylate (R ¹² is methyl group, R ¹³ is hydrogen atom, X ² is If methylene), trimethylol ethane trimethacrylate ^{(R 12} is a methyl ^{group, R 13} is a methyl group, ^{X 2} in the case of methylene), tetramethylolmethane triacrylate ^{(R 12} is a methylol ^{group, R 13} is a hydrogen atom, X ² is a methylene group), tetramethylol methane trimethacrylate (R ¹² is a methylol group, R ¹³ is a methyl group, X ² is a methylene group), glycerin triacrylate (R ¹² is a hydrogen atom, R ¹³ is a hydrogen atom, X ² is a methylene group), glycerin trimethacrylate (R ¹² is a hydrogen atom, R ¹³ is a methyl group, and X ² is a methylene group).

  Preferable embodiments of the compound of the above formula (II) when p = q = r = 1 include compounds having the following structural formula.

  Preferable embodiments of the compound of the above formula (II) when p, q and r take other values include compounds of the following structural formula.

  The compound represented by the above formula (II) is preferably used in combination of two or more. In this case, a preferable embodiment includes a mixed use of the above formula (II-a) and the above formula (II-d), or a mixed use of trimethylolpropane triacrylate and the above formula (II-d). The use of a mixture of methylolpropane triacrylate and the above formula (II-d) is particularly preferred. At least one is preferably trimethylolpropane triacrylate, and its content is preferably 0.5 to 8% by weight based on the total weight of component A.

  In the ink composition, at least one trifunctional ethylenically unsaturated compound represented by the following formula (II ′) is used as component A-2 instead of the trifunctional ethylenically unsaturated compound represented by the above formula (II). It may contain seeds.

  In addition, even when the compound represented by the following formula (II ′) is applied as Component A-2, the content thereof is 0.1 to 25% by weight with respect to the total weight of Component A, and preferably 0 5 to 10% by weight, more preferably 2 to 9% by weight.

(In the formula (II ′), R ¹¹ represents a hydrogen atom or an optionally substituted alkyl group having 1 to 6 carbon atoms, and R ¹² represents a hydrogen atom or optionally substituted 1 to 1 carbon atoms. 6 represents an alkyl group, R ¹³ independently represents a hydrogen atom or a methyl group, X ² represents a single bond or a divalent linking group, and p, q and r each independently represents 0 to 5; Represents an integer and satisfies the relationship of p + q + r ≧ 1.)
In the compound represented by the formula ^{(II '), R 11,} R 12, R 13, and ^{X 2, R} 11 in the formula ^{(II), R 12, R} 13, and ^{X 2} in the above formula The preferred embodiment is also the same. p, q, and r each independently represent an integer of 0 to 5, and satisfy the relationship of p + q + r ≧ 1. p, q and r are each independently preferably 1 to 3, particularly preferably 1 or 2.

  Specific examples of the compound when p, q and r have preferred values are the compounds represented by the above formula (II-a) and the above formula (II) among the compounds exemplified in the preferred embodiment of the compound represented by the above formula (II). -B), the above formula (II-c) and the like, but are not limited thereto.

(Aspect containing Component A-1-3)
A-1 of the ink composition described above can further preferably contain a (meth) acrylate compound having an aromatic hydrocarbon ring as component A-1-3. Preferred examples of Component A-1-3 include aromatic monofunctional radical polymerizable monomers described in paragraphs [0048] to [0063] of JP-A-2009-96985. In the present invention, the monofunctional (meth) acrylate compound having an aromatic hydrocarbon ring is preferably a compound represented by the following formula (a-2).

(In formula (a-2), R ¹ represents a hydrogen atom or a methyl group, X ¹ represents a divalent linking group, and Ar represents a monovalent aromatic hydrocarbon group.)
In the above formula (a-2), R ¹ is preferably a hydrogen atom.

X ¹ represents a divalent linking group, and is an ether bond (—O—), an ester bond (—C (O) O— or —OC (O) —), an amide bond (—C (O) NR′— or -NR'C (O)-), a carbonyl group (-C (O)-), an imino group (-NR'-), an optionally substituted alkylene group having 1 to 15 carbon atoms, or A divalent group in which two or more of these are combined is preferable. R ′ represents a hydrogen atom, a linear, branched or cyclic alkyl group having 1 to 20 carbon atoms, or an aryl group having 6 to 20 carbon atoms. Examples of the substituent include a hydroxy group and a halogen atom.

The moiety comprising R ¹ and X ¹ (H ₂ C═C (R ¹ ) —C (O) O—X ¹ —) can be attached at any position on the aromatic hydrocarbon ring. Further, from the viewpoint of improving the affinity with the colorant, the end bonded to the aromatic hydrocarbon ring of X ¹ is preferably an oxygen atom, and more preferably an etheric oxygen atom. X ¹ in Formula (a-2) is preferably *-(LO) q-. Here, * shows a coupling | bonding position with the carboxylic ester bond of Formula (a-2), q is an integer of 0-10, L represents a C2-C4 alkylene group. q is preferably an integer of 0 to 4, more preferably an integer of 0 to 2, and even more preferably 1 or 2. (LO) q is preferably an ethylene oxide chain or a propylene oxide chain.

  Ar represents a monovalent aromatic hydrocarbon group.

  The monovalent aromatic hydrocarbon group includes a monovalent monocyclic or polycyclic aromatic hydrocarbon group having 1 to 4 rings, and specifically includes benzene, naphthalene, anthracene, 1H-indene, One from 9H-fluorene, 1H-phenalene, phenanthrene, triphenylene, pyrene, naphthacene, tetraphenylene, biphenylene, as-indacene, s-indacene, acenaphthylene, fluoranthene, acephenanthrylene, asanthrylene, chrysene, prianden, etc. Examples include a group excluding a hydrogen atom.

  Among them, in the present invention, a phenyl group and a naphthyl group are preferable, and a monocyclic aromatic hydrocarbon group, that is, a phenyl group is more preferable.

  The monovalent aromatic hydrocarbon group may have a substituent on the aromatic ring.

  Examples of the substituent include a halogen atom, an alkyl group, an alkenyl group, a carboxy group, an acyl group having 1 to 10 carbon atoms, a hydroxy group, a substituted or unsubstituted amino group, a thiol group, a siloxane group, or a substituent. It is preferably a hydrocarbon group or heterocyclic group having a total carbon number of 30 or less that may have.

  The substituent may further have a substituent, and examples thereof include a hydroxy group, an alkyl group having 1 to 10 carbon atoms, and an aryl group having 6 to 12 carbon atoms.

When the monovalent aromatic hydrocarbon group has a plurality of substituents, the substituents may be the same or different. The substituents may be bonded to form a 5-membered or 6-membered ring. The monovalent aromatic hydrocarbon group preferably has no substituent on the aromatic ring.

  In this example, the compound represented by the formula (a-2) is preferably a compound having a phenyl group, more preferably 2-phenoxyethyl (meth) acrylate or benzyl (meth) acrylate, and 2-phenoxyethyl. (Meth) acrylate is more preferred, and 2-phenoxyethyl acrylate (PEA) is particularly preferred.

  In the ink composition applied to this example, the content of Component A-1-3 is 5 to 40% by weight, more preferably 8 to 30% by weight, based on the total weight of Component A-1.

(Aspect including other polymerizable compound)
The ink composition may contain other polymerizable compounds other than the above-described compounds. The other polymerizable compound is not particularly limited, but an ethylenically unsaturated compound is preferable.

  As other polymerizable compounds, known polymerizable compounds can be used, and (meth) acrylate compounds, vinyl ether compounds, allyl compounds, unsaturated carboxylic acids and the like other than the above-described compounds can be exemplified.

  Examples thereof include a radical polymerizable monomer described in JP2009-221414A, a polymerizable compound described in JP2009-209289A, and an ethylenically unsaturated compound described in JP2009-191183A.

  The ink composition can preferably use a bifunctional (meth) acrylate compound other than the above-described compounds. As the bifunctional (meth) acrylate compound, a bifunctional (meth) acrylate compound having a hydrocarbon chain which may have a branch having 5 or more carbon atoms is preferable.

  Preferable examples of the bifunctional (meth) acrylate compound are bifunctional (meth) acrylate compounds having a hydrocarbon chain having 5 or more carbon atoms in the molecule, specifically, neopentyl glycol di (meth) acrylate, Propylene oxide (PO) modified neopentyl glycol di (meth) acrylate, hexanediol di (meth) acrylate, PO modified hexanediol di (meth) acrylate, nonanediol di (meth) acrylate, decanediol di (meth) acrylate, dodecane Diol di (meth) acrylate, tridecanediol di (meth) acrylate, octadecanediol di (meth) acrylate, 3-methyl-1,5-pentanediol di (meth) acrylate, 2-n-butyl-2-ethyl- 1,3-propanedi Ruji (meth) acrylate, cyclohexanedimethanol di (meth) acrylate, and, cyclohexanedimethanol (meth) acrylate. Among these, PO-modified neopentyl glycol di (meth) acrylate is particularly preferable.

  As the other polymerizable compound, a tri- or higher functional (meth) acrylate compound can also be used. Preferable examples of the tetrafunctional (meth) acrylate compound include pentaerythritol tetra (meth) acrylate, dipentaerythritol tetra (meth) acrylate, dipentaerythritol hexa (meth) acrylate and the like.

  Other polyfunctional (meth) acrylates include bis (4- (meth) acryloxypolyethoxyphenyl) propane, ethylene glycol di (meth) acrylate, diethylene glycol di (meth) acrylate, triethylene glycol di (meth) acrylate, Examples include tetraethylene glycol di (meth) acrylate, polyethylene glycol di (meth) acrylate, polypropylene glycol diacrylate, 2,2-bis (4- (meth) acryloxypolyethoxyphenyl) propane, and the like.

  Examples of other polymerizable compounds include unsaturated carboxylic acids such as acrylic acid, methacrylic acid, itaconic acid, crotonic acid, isocrotonic acid, maleic acid and their salts, anhydrides having an ethylenically unsaturated group, Examples include acrylonitrile, styrene, and various radically polymerizable compounds such as various unsaturated polyesters, unsaturated polyethers, unsaturated polyamides, and unsaturated urethanes.

  Specific examples of other polymerizable compounds include 2-ethylhexyl (meth) acrylate, 2-hydroxyethyl (meth) acrylate, butoxyethyl (meth) acrylate, carbitol (meth) acrylate, cyclohexyl (meth) acrylate, benzyl ( (Meth) acrylate, methyl (meth) acrylate, n-butyl (meth) acrylate, allyl (meth) acrylate, glycidyl (meth) acrylate, dimethylaminomethyl (meth) acrylate, oligoester (meth) acrylate, N-methylol (meta ) (Meth) acrylic acid derivatives such as acrylamide, diacetone (meth) acrylamide, and epoxy (meth) acrylate, and other ants such as allyl glycidyl ether, diallyl phthalate, and triallyl trimellitate Derivative compounds.

  More specifically, Shinzo Yamashita “Cross-linking agent handbook” (1981, Taiseisha); Kato Kiyosumi “UV / EB curing handbook (raw material)” (1985, Polymer publication society); Ed. “Application and Market of UV / EB Curing Technology” on page 79 (1989, CMC Publishing Co., Ltd.); “Polyester Resin Handbook” by Eiichiro Takiyama (1988, Nikkan Kogyo Shimbun) Radical polymerizable or crosslinkable monomers, oligomers and polymers known in the industry can be used.

  The molecular weight of the other polymerizable compound is preferably 80 to 2,000, more preferably 80 to 1,000, and still more preferably 80 to 800.

  It is also preferable to use a monofunctional vinyl ether compound as the other polymerizable compound. Examples of the monofunctional vinyl ether compound suitably used include ethylene glycol monovinyl ether, triethylene glycol monovinyl ether, hydroxyethyl monovinyl ether, ethyl vinyl ether, n-butyl vinyl ether, isobutyl vinyl ether, octadecyl vinyl ether, cyclohexyl vinyl ether, hydroxybutyl vinyl ether, Examples include 2-ethylhexyl vinyl ether, hydroxynonyl monovinyl ether, cyclohexanedimethanol monovinyl ether, n-propyl vinyl ether, isopropyl vinyl ether, dodecyl vinyl ether, diethylene glycol monovinyl ether, and the like.

  Moreover, a polyfunctional vinyl ether compound can also be used. Suitable polyfunctional vinyl ether compounds include, for example, ethylene glycol divinyl ether, diethylene glycol divinyl ether, triethylene glycol divinyl ether, propylene glycol divinyl ether, dipropylene glycol divinyl ether, butanediol divinyl ether, hexanediol divinyl ether, cyclohexane. Examples thereof include di- or trivinyl ether compounds such as dimethanol divinyl ether and trimethylolpropane trivinyl ether.

  When other polymerizable compound is contained, the content of the other polymerizable compound is preferably 1 to 50% by weight, more preferably 2 to 40% by weight, and more preferably 2 to 30% by weight based on the total weight of the polymerizable compound. % Is particularly preferred.

(Description of radical polymerization initiator (component B))
As the radical polymerization initiator (component B), a monoacylphosphine oxide compound and / or a bisacylphosphine oxide compound and a thioxanthone compound can be applied.

  The ink composition ejected onto the recording medium is cured by irradiation with actinic rays. This is because the radical polymerization initiator contained in the ink composition is decomposed by irradiation with actinic rays to generate polymerization initiation species such as radicals, and the polymerization reaction of the polymerizable compound occurs and accelerates in the function of the initiation species. It is to be done.

  The radical polymerization initiator is not only a compound that absorbs external energy such as actinic rays to generate a polymerization initiating species, but also a compound that absorbs specific active energy rays and promotes decomposition of the polymerization initiator (so-called, Sensitizers) are also included.

  When a sensitizer is present together with a radical polymerization initiator, the sensitizer in the system absorbs actinic radiation to be in an excited state, and when contacted with the radical polymerization initiator, promotes decomposition of the radical polymerization initiator, resulting in a higher level. A sensitive curing reaction can be achieved. Examples of the sensitizer include those described in JP-A-2008-208190.

  Further, as Component B, it is preferable to contain a monoacylphosphine oxide compound (Component B-1) and / or a bisacylphosphine oxide compound (Component B-2) and a thioxanthone compound (Component B-3).

  Combining component B with components A-1, A-2 and colorant (component C) described above provides excellent curability and ejection stability, and the substrate adhesion and glossiness of the resulting cured film An ink composition excellent in the above can be obtained.

  Hereinafter, the monoacylphosphine compound (component B-1), the bisacylphosphine oxide compound (component B-2), and the thioxanthone compound (component B-3) will be described in detail.

  There is no restriction | limiting in particular as a monoacyl phosphine compound (component B-1), Although a well-known thing can be used, It is preferable that it is a monoacyl phosphine oxide compound represented by following formula (b-1). .

(In the formula (b-1), R ^1D , R ^2D and R ^3D each independently represents an aromatic hydrocarbon group which may have a methyl group or an ethyl group as a substituent.)
As the monoacylphosphine oxide compound represented by the above formula (b-1), R ^{1D to} R ^3D are preferably each independently a phenyl group optionally having a methyl group as a substituent. R ^2D and R ^3D are each a phenyl group, and R ^1D is more preferably a phenyl group having 1 to 3 methyl groups.

  Among these, 2,4,6-trimethylbenzoyldiphenylphosphine oxide (Darocur TPO: manufactured by Ciba Japan, Lucirin TPO: manufactured by BASF) is preferable.

  The content of Component B-1 is preferably 0.1 to 3% by weight, more preferably 0.5 to 3% by weight, based on the entire ink composition.

  There is no restriction | limiting in particular as a bisacyl phosphine oxide compound (component B-2), Although a well-known thing can be used, It is preferable that it is a compound represented by following formula (b-2).

(In the formula (b-2), R ^1E , R ^2E and R ^3E each independently represents an aromatic hydrocarbon group optionally having a methyl group or an ethyl group as a substituent.)
A known compound can be used as the bisacylphosphine oxide compound. Examples thereof include bisacylphosphine oxide compounds described in JP-A-3-101686, JP-A-5-345790, and JP-A-6-298818.

  Specific examples include bis (2,6-dichlorobenzoyl) phenylphosphine oxide, bis (2,6-dichlorobenzoyl) -2,5-dimethylphenylphosphine oxide, bis (2,6-dichlorobenzoyl) -4- Ethoxyphenylphosphine oxide, bis (2,6-dichlorobenzoyl) -4-propylphenylphosphine oxide, bis (2,6-dichlorobenzoyl) -2-naphthylphosphine oxide, bis (2,6-dichlorobenzoyl) -1- Naphthylphosphine oxide, bis (2,6-dichlorobenzoyl) -4-chlorophenylphosphine oxide, bis (2,6-dichlorobenzoyl) -2,4-dimethoxyphenylphosphine oxide, bis (2,6-dichlorobenzoyl) decylphosphine Oxide, bis (2,6-dichlorobenzoyl) -4-octylphenylphosphine oxide, bis (2,4,6-trimethylbenzoyl) phenylphosphine oxide, bis (2,4,6-trimethylbenzoyl) -2 5-dimethylphenylphosphine oxide, bis (2,6-dichloro3,4,5-trimethoxybenzoyl) -2,5-dimethylphenylphosphine oxide, bis (2,6-dichloro-3,4,5-trimethoxy Benzoyl) -4-ethoxyphenylphosphine oxide, bis (2-methyl-1-naphthoyl) -2,5-dimethylphenylphosphine oxide, bis (2-methyl-1-naphthoyl) -4-ethoxyphenylphosphine oxide, bis ( 2-Methyl-1-naphthoyl) -2-na Tylphosphine oxide, bis (2-methyl-1-naphthoyl) -4-propylphenylphosphine oxide, bis (2-methyl-1-naphthoyl) -2,5-dimethylphenylphosphine oxide, bis (2-methoxy-1- Naphthoyl) -4-ethoxyphenylphosphine oxide, bis (2-chloro-1-naphthoyl) -2,5-dimethylphenylphosphine oxide, bis (2,6-dimethoxybenzoyl) -2,4,4-trimethylpentylphosphine oxide Etc.

  Among these, as bisacylphosphine oxide compounds, bis (2,4,6-trimethylbenzoyl) phenylphosphine oxide (IRGACURE 819: manufactured by BASF Japan Ltd.), bis (2,6-dimethoxybenzoyl) -2 4,4-trimethylpentylphosphine oxide and the like are preferable.

  The content of Component B-2 is preferably 0.5 to 10% by weight, more preferably 1 to 5% by weight, based on the entire ink composition.

  There is no restriction | limiting in particular as a thioxanthone compound (component B-3), Although a well-known thing can be used, It is preferable that it is a compound represented by following formula (b-3).

In the above formula (b-3), R ^1F , R ^2F , R ^3F , R ^4F , R ^5F , R ^6F , R ^7F and R ^8F are each independently a hydrogen atom, alkyl group, halogen atom, hydroxy group, cyano Group, nitro group, amino group, alkylthio group, alkylamino group (including the case of mono- and di-substitution. The same applies to the following), alkoxy group, alkoxycarbonyl group, acyloxy group, acyl group, carboxy group Represents a group or a sulfo group. The number of carbon atoms in the alkyl group, the alkylthio group, the alkylamino group, the alkoxy group, the alkoxycarbonyl group, the acyloxy group, and the alkyl moiety in the acyl group is preferably 1-20, and more preferably 1-8. Preferably, it is 1-4.

Two of R ^1F , R ^2F , R ^3F , R ^4F , R ^5F , R ^6F , R ^7F and R ^8F may be linked to each other to form a ring. Examples of the ring structure in the case where these form a ring include a 5- or 6-membered aliphatic ring, an aromatic ring, etc., and may be a heterocyclic ring containing an element other than a carbon atom. The rings may be further combined to form a binuclear ring, for example, a condensed ring. These ring structures may further have a substituent. Examples of the substituent include a halogen atom, a hydroxy group, a cyano group, a nitro group, an amino group, an alkylthio group, an alkylamino group, an alkoxy group, an alkoxycarbonyl group, an acyloxy group, an acyl group, a carboxy group, and a sulfo group. N, O, and S can be mentioned as an example of a hetero atom in case the formed ring structure is a heterocyclic ring.

  Examples of thioxanthone compounds include thioxanthone, 2-isopropylthioxanthone, 4-isopropylthioxanthone, 2-chlorothioxanthone, 2-dodecylthioxanthone, 2,4-dichlorothioxanthone, 2,3-diethylthioxanthone, 1-chloro-4-propoxythioxanthone, 2-cyclohexylthioxanthone, 4-cyclohexylthioxanthone, 2,4-diethylthioxanthone, 2,4-dimethylthioxanthone, 1-methoxycarbonylthioxanthone, 2-ethoxycarbonylthioxanthone, 3- (2-methoxyethoxycarbonyl) thioxanthone, 4-butoxy Carbonylthioxanthone, 3-butoxycarbonyl-7-methylthioxanthone, 1-cyano-3-chlorothioxanthone, 1-eth Sicarbonyl-3-chlorothioxanthone, 1-ethoxycarbonyl-3-ethoxythioxanthone, 1-ethoxycarbonyl-3-aminothioxanthone, 1-ethoxycarbonyl-3-phenylsulfylthioxanthone, 3,4-di [2- (2- Methoxyethoxy) ethoxycarbonyl] thioxanthone, 1-ethoxycarbonyl-3- (1-methyl-1-morpholinoethyl) thioxanthone, 2-methyl-6-dimethoxymethylthioxanthone, 2-methyl-6- (1,1-dimethoxybenzyl) ) Thioxanthone, 2-morpholinomethylthioxanthone, 2-methyl-6-morpholinomethylthioxanthone, n-allylthioxanthone-3,4-dicarboximide, n-octylthioxanthone-3,4-dicarboximide, -(1,1,3,3-tetramethylbutyl) thioxanthone-3,4-dicarboximide, 1-phenoxythioxanthone, 6-ethoxycarbonyl-2-methoxythioxanthone, 6-ethoxycarbonyl-2-methylthioxanthone, thioxanthone -2-polyethylene glycol ester, 2-hydroxy-3- (3,4-dimethyl-9-oxo-9H-thioxanthone-2-yloxy) -N, N, N-trimethyl-1-propaneaminium chloride . Among these, thioxanthone, 2,3-diethylthioxanthone, 2,4-diethylthioxanthone, 2,4-dichlorothioxanthone, 1-chloro-4-propoxythioxanthone, 2-cyclohexylthioxanthone from the viewpoint of availability and curability 4-cyclohexylthioxanthone, 2-isopropylthioxanthone, and 4-isopropylthioxanthone are preferable, and 2-isopropylthioxanthone and 4-isopropylthioxanthone are more preferable.

  The content of Component B-3 is preferably 0.5 to 10% by weight, more preferably 1 to 5% by weight, based on the entire ink composition.

  In addition, it is preferable that the component B further contains an α-aminoalkylphenone compound (component B-4). By containing Component B-4, an ink composition having further excellent curability can be obtained. Component B-4 is preferably a compound represented by the following formula (b-4).

In the above formula (b-4), R ¹ , R ² , and R ³ are each independently a hydroxy group, an alkyl group that may have a substituent, an alkoxy group that may have a substituent, Or, it represents an amino group which may have a substituent, and X represents a hydrogen atom, an amino group which may have a substituent, an alkylthio group which may have a substituent, or a substituent. It represents an alkyl group that may have. At least one of R ¹ , R ² or R ³ represents an optionally substituted amino group. In addition, the substituents in the case where R ¹ , R ² , R ³ , and X are amino groups may be bonded to each other to form a heterocyclic group. Examples of the substituent include an alkyl group having 1 to 10 carbon atoms.

  Component B-4 is preferably a compound represented by any one of the following formula (b-4-1) and the following formula (b-4-2).

In the above formula (b-4-1), R ⁴ , R ⁵ , R ⁶ , and R ⁷ each represents an alkyl group that may have a substituent, and R ⁴ , R ⁵ , and R ⁶ At least one of R ⁷ may be bonded to each other to form a heterocyclic group. R ^{1, R 2,} and the substituents, ^R 1, ^{R 2} as in the above formula (b-4), and are respectively a substituent synonymous.

In the above formula (b-4-2), R ⁸ represents an alkyl group which may have a substituent.

R ^{1, R 2,} and the substituents, ^R 1, ^{R 2} in the above formula (b-4), and has the same meaning as the substituent, ^{R 4} and ^{R 5,} the formulas (b-4-1 Are the same as R ⁴ and R ⁵ .

  There is no restriction | limiting in particular as said heterocyclic group, Although it can select suitably, For example, a morpholino group is preferable.

  Preferred examples of the α-aminoalkylphenone compound include IRGACURE369 (manufactured by BASF Japan Ltd.), IRGACURE907 (manufactured by BASF Japan Ltd.) and the like as commercially available products.

  The content of Component B-4 is preferably 0.5 to 10% by weight, more preferably 1 to 5% by weight, based on the entire ink composition.

  A preferred embodiment of Component B is to contain Component B-1 and / or B-2 and B-3, more preferably at least Component B-1 and the content thereof is an ink composition It is 3% by weight or less of the total weight. More preferably, the components B-1, B-3 and B-4 are contained in combination, and particularly preferably, the components B-1 to B-3 are contained in combination.

  The total content of component B is preferably 1 to 20% by weight of the total ink composition, more preferably 5 to 15% by weight, and still more preferably 8 to 10% by weight.

  In addition, as a component B, you may contain other polymerization initiators other than an above-described polymerization initiator. Other polymerization initiators include monoacylphosphine compounds, α-hydroxyketone compounds, aromatic ketones, aromatic onium salt compounds, organic peroxides, thio compounds, hexaarylbiimidazole compounds, ketoxime ester compounds, borates. Examples thereof include compounds, azinium compounds, metallocene compounds, active ester compounds, and compounds having a carbon halogen bond.

  Details of the polymerization initiator are known to those skilled in the art, and are described, for example, in paragraphs 0090 to 0116 of JP-A-2009-185186.

(Description of colorant (component C))
The colorant (component C) contributes to improving the visibility of the formed image portion. Although there is no restriction | limiting in particular as Component C, The pigment and oil-soluble dye which were excellent in weather resistance and were rich in color reproducibility are preferable, and can be arbitrarily selected from well-known colorants, such as a soluble dye, and can be used. Component C is preferably selected from a compound that does not function as a polymerization inhibitor from the viewpoint of not reducing the sensitivity of the curing reaction by actinic radiation.

  Below, the pigment and dye used as component C are demonstrated.

  Although it does not necessarily limit as a pigment, For example, the organic or inorganic pigment of the following number described in a color index can be used.

  Examples of red or magenta pigments include C.I. I. Pigment Red 3 (also referred to as “Pigment Red 3”), 5, 19, 22, 31, 38, 42, 43, 48: 1, 48: 2, 48: 3, 48: 4, 48: 5, 49: 1, 53: 1, 57: 1, 57: 2, 58: 4, 63: 1, 81, 81: 1, 81: 2, 81: 3, 81: 4, 88, 104, 108, 112, 122, 123, 144, 146, 149, 166, 168, 169, 170, 177, 178, 179, 184, 185, 202, 208, 216, 226, 257, C.I. I. Pigment violet 3 (also referred to as “Pigment Violet 3”), 19, 23, 29, 30, 37, 50, 88, C.I. I. Pigment Orange 13 (also referred to as “Pigment Orange 13”), 16, 20, 36, blue or cyan pigments include C.I. I. Pigment Blue 1 (also referred to as “Pigment Blue 1”), 15, 15: 1, 15: 2, 15: 3, 15: 4, 15: 6, 16, 17-1, 22, 27, 28, 29, 36, 60, green pigments include C.I. I. Pigment Green 7 (also referred to as “Pigment Green 7”), 26, 36, 50, yellow pigments include C.I. I. Pigment Yellow 1 (also referred to as “Pigment Yellow 1”), 3, 12, 13, 14, 17, 34, 35, 37, 55, 74, 81, 83, 93, 94, 95, 97, 108, 109, 110, 120, 137, 138, 139, 150, 153, 154, 155, 157, 166, 167, 168, 180, 185, 193, black pigments include C.I. I. Pigment Black 7 (also referred to as “Pigment Black 7”), 28, 26, and white pigments include C.I. I. Pigment White 6 (also referred to as “Pigment White 6”), 18, 21 or the like can be used depending on the purpose.

  Disperse dyes can be used as long as they are soluble in a water-immiscible organic solvent. Disperse dyes generally include water-soluble dyes, but are preferably used as long as they are soluble in a water-immiscible organic solvent.

  Preferable specific examples of the disperse dye include C.I. I. Disperse Yellow 5, 42, 54, 64, 79, 82, 83, 93, 99, 100, 119, 122, 124, 126, 160, 184: 1, 186, 198, 199, 201, 204, 224 and 237 C. I. Disperse Orange 13, 29, 31: 1, 33, 49, 54, 55, 66, 73, 118, 119 and 163; C.I. I. Disperse Red 54, 60, 72, 73, 86, 88, 91, 92, 93, 111, 126, 127, 134, 135, 143, 145, 152, 153, 154, 159, 164, 167: 1, 177 , 181, 204, 206, 207, 221, 239, 240, 258, 277, 278, 283, 311, 323, 343, 348, 356 and 362; I. Disperse Violet 33; C.I. I. Disperse Blue 56, 60, 73, 87, 113, 128, 143, 148, 154, 158, 165, 165: 1, 165: 2, 176, 183, 185, 197, 198, 201, 214, 224, 225 257, 266, 267, 287, 354, 358, 365 and 368; I. Disperse Green 6: 1 and 9 etc. are mentioned.

  It is preferable that the colorant is appropriately dispersed in the ink composition after being added to the ink composition. For dispersing the colorant, for example, a dispersion device such as a ball mill, a sand mill, an attritor, a roll mill, an agitator, a Henschel mixer, a colloid mill, an ultrasonic homogenizer, a pearl mill, a wet jet mill, or a paint shaker can be used.

  The colorant may be directly added together with each component when preparing the ink composition. In order to improve dispersibility, it may be added to a dispersion medium such as a solvent or a polymerizable compound used in the present invention in advance and uniformly dispersed or dissolved, and then blended.

  In order to avoid the deterioration of the solvent resistance when the solvent remains in the cured image and the problem of the VOC (Volatile Organic Compound) of the remaining solvent, the colorant is not a polymerizable compound. It is preferable to add and mix in advance in the dispersion medium.

  That is, it is preferable not to contain a solvent. In consideration of only dispersibility, it is preferable to select a monomer having the lowest viscosity as the polymerizable compound used for the addition of the colorant. One or more colorants may be appropriately selected and used according to the purpose of use of the ink composition.

  When using a colorant such as a pigment that remains in the ink composition as a solid, the average particle diameter of the colorant particles is preferably 0.005 to 0.5 micrometers, more preferably 0.00. It is preferable to set the colorant, the dispersant, the dispersion medium, the dispersion conditions, and the filtration conditions so as to be 01 to 0.45 micrometers, more preferably 0.015 to 0.4 micrometers. This particle size control is preferable because clogging of the head nozzle can be suppressed and the storage stability, transparency, and curing sensitivity of the ink composition can be maintained.

  The content of Component C in the ink composition is appropriately selected depending on the color and intended use. Component C is preferably 0.1 to 20% by weight, more preferably 0.5 to 10% by weight, and further preferably 1 to 5% by weight, based on the weight of the entire ink composition. preferable.

(Dispersant)
The ink composition preferably contains a dispersant. In particular, when a pigment is used, a dispersant is preferably contained in order to stably disperse the pigment in the ink composition. As the dispersant, a polymer dispersant is preferable. The “polymer dispersing agent” in the present invention means a dispersing agent having a weight average molecular weight of 1,000 or more.

  As the polymer dispersant, DISPERBYK-101, DISPERBYK-102, DISPERBYK-103, DISPERBYK-106, DISPERBYK-111, DISPERBYK-161, DISPERBYK-162, DISPERBYK-163, DISPERBYK-164, DISPERBY-16-ER, , DISPERBYK-168, DISPERBYK-170, DISPERBYK-171, DISPERBYK-174, DISPERBYK-182 (manufactured by BYK Chemie); EFKA7462, EFKA7500, EFKA7570, EFKA7575, EFKA7580 (manufactured by Efka Additive); Disperse Aid 6, Disperse Aid 8, Disperse Aid 15, Disperse Aid 9100 (manufactured by Sannopco); Solsperse (SOLSPERSE) 3000 Various Solsperse dispersants (manufactured by Noveon) such as 5000, 9000, 12000, 13240, 13940, 17000, 22000, 24000, 26000, 28000, 32000, 36000, 39000, 41000, 71000; Adeka Pluronic L31, F38, L42, L44 , L61, L64, F68, L72, P95, F77, P84, F87, P94, L101, P103, F108, L121, -123 (manufactured by ADEKA); Ionnet S-20 (manufactured by Sanyo Chemical Industries); Dispalon KS-860, 873SN, 874 (polymer dispersing agent), # 2150 (aliphatic polycarboxylic acid), # 7004 (polyether ester type) (manufactured by Enomoto Kasei Co., Ltd.).

  The content of the dispersant in the ink composition is appropriately selected depending on the purpose of use, but is preferably 0.05 to 15% by weight with respect to the total weight of the ink composition.

(Surfactant)
The ink composition does not contain a silicone surfactant and a fluorosurfactant, or the total content of the silicone surfactant and the fluorosurfactant is 0 with respect to the total weight of the ink composition. It is preferably less than 0.01% by weight, does not contain a silicone-based surfactant and a fluorosurfactant, or is more preferably 0.005% by weight or less, and a silicone-based surfactant and a fluorosurfactant It is particularly preferred not to contain a surfactant.

  Examples of surfactants other than silicone surfactants and fluorine surfactants include those described in JP-A Nos. 62-173463 and 62-183457. For example, anionic surfactants such as dialkylsulfosuccinates, alkylnaphthalenesulfonates, fatty acid salts, polyoxyethylene alkyl ethers, polyoxyethylene alkyl allyl ethers, acetylene glycols, polyoxyethylene / polyoxypropylene blocks Nonionic surfactants such as copolymers, and cationic surfactants such as alkylamine salts and quaternary ammonium salts.

  Further, surfactants other than silicone surfactants and fluorine surfactants are not contained, or the content thereof is less than 0.01% by weight with respect to the total weight of the ink composition. Preferably, it is not contained, or its content is more preferably 0.005% by weight or less, and particularly preferably not contained.

  Examples of the silicone surfactant available as a commercial product include BYK-307 (manufactured by BYK Chemie).

(Oligomer)
The ink composition preferably contains an oligomer. The oligomer is generally a polymer in which a finite number of monomers (generally 5 to 100) are bonded, and a known compound called an oligomer can be arbitrarily selected, but the weight average molecular weight is 400 to 10 It is preferable to select a polymer of 1,000 (more preferably 500 to 5,000).

  This oligomer may have a radical polymerizable group. As the radical polymerizable group, an ethylenically unsaturated group is preferable, and a (meth) acryloxy group is more preferable.

  The oligomer may be any oligomer, for example, olefin (ethylene oligomer, propylene oligomer, butene oligomer, etc.), vinyl (styrene oligomer, vinyl alcohol oligomer, vinyl pyrrolidone oligomer, acrylate oligomer, methacrylate oligomer, etc.), diene (Butadiene oligomer, chloroprene rubber, pentadiene oligomer, etc.), ring-opening polymerization system (di-, tri-, tetraethylene glycol, polyethylene glycol, polyethylimine, etc.), polyaddition system (oligoester acrylate, polyamide oligomer, polyisocyanate oligomer) ), Addition condensation oligomers (phenol resin, amino resin, xylene resin, ketone resin, etc.). In this, oligoester (meth) acrylate is preferable, in which urethane (meth) acrylate, polyester (meth) acrylate, and epoxy (meth) acrylate are more preferable, and urethane (meth) acrylate is still more preferable.

  Preferred examples of the urethane (meth) acrylate include aliphatic urethane (meth) acrylates and aromatic urethane (meth) acrylates, and more preferred are aliphatic urethane (meth) acrylates.

  The urethane (meth) acrylate is preferably a tetrafunctional or lower urethane (meth) acrylate, and more preferably a bifunctional or lower urethane (meth) acrylate.

  By containing urethane (meth) acrylate, an ink composition having excellent adhesion to the substrate and excellent curability can be obtained.

  Regarding the oligomer, the oligomer handbook (supervised by Junji Furukawa, Chemical Industry Daily Co., Ltd.) can also be referred to.

  Moreover, what is shown below can be illustrated as a commercial item of an oligomer.

  Examples of the urethane (meth) acrylate include R1204, R1211, R1213, R1217, R1218, R1301, R1302, R1303, R1304, R1306, R1308, R1901, and R1150 manufactured by Daiichi Kogyo Seiyaku Co., Ltd. EBECRYL series (for example, EBECRYL230, 270, 4858, 8402, 8804, 8807, 8803, 9260, 1290, 1290K, 5129, 4842, 8210, 210, 4827, 6700, 4450, 220) manufactured by Co., Ltd. NK Oligos U-4HA, U-6HA, U-15HA, U-108A, U200AX, etc. manufactured by Kogyo Co., Ltd., Aronix M-1100, M-1200, M-1210, M-1310 manufactured by Toagosei Co., Ltd. M-1600, M-1960, Sartomer Co. CN964A85, CN962, CN983, and the like.

  Examples of the polyester (meth) acrylate include EBECRYL series (for example, EBECRYL770, IRR467, 81, 84, 83, 80, 675, 800, 810, 812, 1657, 1810, IRR302, 450, manufactured by Daicel Cytec Co., Ltd. 670, 830, 870, 1830, 1870, 2870, IRR267, 813, IRR483, 811, etc.), Aronix M-6100, M-6200, M-6250, M-6500, M-7100, manufactured by Toagosei Co., Ltd. , M-8030, M-8060, M-8100, M-8530, M-8560, M-9050 and the like.

  Moreover, as an epoxy (meth) acrylate, for example, EBECRYL series (for example, EBECRYL600, 860, 2958, 3411, 3600, 3605, 3700, 3701, 3703, 3702, 3708, RDX63182, 6040, manufactured by Daicel Cytec Co., Ltd. Etc.).

  An oligomer may be used individually by 1 type, or may use 2 or more types together.

  The oligomer content is preferably 0.1 to 50% by weight, more preferably 0.5 to 20% by weight, and more preferably 1 to 10% by weight with respect to the total weight of the ink composition. More preferably it is.

(Other ingredients)
The ink composition may contain a co-sensitizer, an ultraviolet absorber, an antioxidant, an anti-fading agent, a conductive salt, a solvent, a basic compound, and the like, as necessary, in addition to the above-described components. As these other components, known components can be used. Examples thereof include those described in JP2009-221416A.

  From the viewpoint of enhancing the storage stability, it is preferable to contain a polymerization inhibitor. When used as an ink composition for image formation by an inkjet method, it is preferable to discharge in the range of 25 to 80 ° C. by heating and lowering the viscosity, and a polymerization inhibitor is added to prevent head clogging due to thermal polymerization. It is preferable.

  Examples of the polymerization inhibitor include nitroso polymerization inhibitors, hydroquinone, benzoquinone, p-methoxyphenol, TEMPO, TEMPOL, cuperon Al, hindered amines, etc. Among them, nitroso polymerization inhibitors and hindered amine polymerization inhibitors are preferable. Specific examples of the nitroso polymerization inhibitor are shown below, but are not limited thereto.

  Examples of commercially available nitroso polymerization inhibitors include FIRSTCURE ST-1 (manufactured by Chem First). Examples of commercially available hindered amine polymerization inhibitors include TINUVIN292, TINUVIN770DF, TINUVIN765, and TINUVIN123.

  The content of the polymerization inhibitor is preferably 0.01 to 2% by weight, more preferably 0.1 to 1.5% by weight, and still more preferably 0.2 to 1.2% by weight. Within the above numerical range, polymerization at the time of preparation and storage of the ink composition can be suppressed, and clogging of the ink jet nozzle can be prevented.

For example, the UV-LED element 35 has an emission wavelength (peak value) of 385 nanometers (380 nanometers to 390 nanometers), an ultraviolet light emitting LED manufactured by Nichia Corporation, NC4U134A (trade name) Can be applied.
SR9035: Ethylene oxide 15 mol addition trimethylolpropane triacrylate, manufactured by Sartomer)

  Examples of the ink composition described above are shown below. The ink composition is not limited by the examples. In the following description, “parts” means “parts by weight” and “%” means “% by weight” unless otherwise specified.

(Material)
・ IRGALITE BLUE GLVO (cyan pigment, manufactured by BASF Japan Ltd.)
・ CINQUASIA MAGENTA RT-355-D (magenta pigment, manufactured by BASF Japan Ltd.)
・ NOVOPERM YELLOW H2G (yellow pigment, manufactured by Clariant)
SPECIAL BLACK 250 (Black pigment, manufactured by BASF Japan Ltd.)
・ SOLSPERSE32000 (dispersant, manufactured by Noveon)
・ NVC (V-CAP, N-Vinylcaprolactam, manufactured by IS Japan Co., Ltd.)
・ NVF: N-vinylformamide (Beamset 770, manufactured by Arakawa Chemical Industries, Ltd.)
CTFA (SR531, cyclic trimethylolpropane formal acrylate, containing 5% by weight of trimethylolpropane triacrylate, manufactured by Sartomer)
-PEA (SR339, phenoxyethyl acrylate, manufactured by Sartomer)
IBOA (SR506, isobornyl acrylate, manufactured by Sartomer)
SR351S (trimethylolpropane triacrylate, manufactured by Sartomer)
SR454 (compound of formula (II-a), manufactured by Sartomer)
SR9020 (compound of formula (II-b), manufactured by Sartomer)
SR9021 (compound of formula (II-c), manufactured by Sartomer)
・ DPGDA (SR508, dipropylene glycol diacrylate, manufactured by Sartomer)

CN964A85 (oligomer, bifunctional aliphatic urethane acrylate, containing 15 wt% tripropylene glycol diacrylate, manufactured by Sartomer)
CN962 (oligomer, bifunctional aliphatic urethane acrylate, manufactured by Sartomer)
IRGACURE 369 (α-aminoalkylketone photopolymerization initiator, 2-benzyl-2-dimethylamino-1- (4-morpholinophenyl) -butan-1-one, manufactured by BASF Japan Ltd.)
IRGACURE 819 (photopolymerization initiator, bis (2,4,6-trimethylbenzoyl) phenylphosphine oxide, manufactured by BASF Japan Ltd.)
・ TPO (DAROCURE TPO, photopolymerization initiator, 2,4,6-trimethylbenzoyldiphenylphosphine oxide, manufactured by BASF Japan Ltd.)
・ ITX (sensitizer, isopropylthioxanthone, manufactured by Shell Chemicals Japan)
ST-1 (FIRSTCURE ST-1, a polymerization inhibitor, a mixture of tris (N-nitroso-N-phenylhydroxyamine) aluminum salt (8% by weight) and phenoxyethyl acrylate (92% by weight), manufactured by Chem First )
BYK-307 (silicone surfactant, manufactured by BYK Chemie)
(Preparation of magenta mill base)
・ Magenta pigment: CINQUASIA MAGENTA RT-355D (manufactured by Ciba Specialty Chemicals) 30 parts by weight ・ SR9003 (propoxylated (2) neopentyl glycol propylene oxide 2 mol adduct compound 49 parts by weight / SOLSPERSE 32000 (dispersing agent, manufactured by Noveon) 20 parts by weight / FIRSTCURE ST-1 (polymerization inhibitor, manufactured by Chem First) 1 part by weight The above ingredients are mixed with stirring to obtain a magenta mill base. The pigment mill base was prepared in a disperser Motor Mill M50 (manufactured by Eiger) and dispersed for 8 hours at a peripheral speed of 9 meters per second using 0.65 mm diameter zirconia beads.
(Preparation of cyan mill base)
Cyan pigment: IRGALITE BLUE GLVO (Ciba Specialty Chemicals) 30 parts by weight SR9003 49 parts by weight SOLPERSE32000 20 parts by weight FIRSTCURE ST-1 1 part by weight The mixture was stirred and mixed under conditions to obtain a cyan mill base.

(Preparation of yellow mill base)
Yellow pigment: NOVOPERM YELLOW H2G (manufactured by Clariant)
30 parts by weight, SR9003 29 parts by weight, BYK168 (dispersant, manufactured by BYK Chemie) 40 parts by weight, FIRSTCURE ST-1 (polymerization inhibitor, manufactured by Chem First) 1 part by weight The above components are the same as the preparation of magenta mill base The mixture was stirred and mixed under the following dispersion conditions to obtain a yellow mill base.

(Preparation of black mill base)
Black pigment: SPECIAL BLACK 250 (manufactured by Ciba Specialty Chemicals) 30 parts by weight SR9003 49 parts by weight SOLSPERSE32000 20 parts by weight FIRSTCURE ST-1 1 part by weight The above components are dispersed in the same manner as in the preparation of the magenta mill base. The mixture was stirred and mixed under the conditions to obtain a black mill base.

  As described above, the image forming apparatus and the image forming method according to the embodiment of the present invention have been described in detail. However, the image forming apparatus and the image forming method can be appropriately changed without departing from the gist of the present invention.

[Invention disclosed in this specification]
As can be understood from the description of the embodiment described in detail above, the present specification includes disclosure of various technical ideas including the invention described below.

  (First aspect): an inkjet head in which a plurality of nozzles for ejecting liquid that is cured by irradiation with actinic rays are arranged; medium transport means for transporting a medium to which the liquid ejected from the inkjet head is attached; Scanning means for moving the inkjet head relative to the medium; and performing droplet ejection by m times (m is an integer of 2 or more) of the droplet ejection position on the scanning line along the scanning direction of the scanning means; The droplet ejection interval is smaller than the nozzle pitch in the transport direction in the nozzle array by performing droplet ejection by moving the droplet ejection position on the scanning line along the transport direction of the transport means n times (n is an integer of 2 or more). The droplet ejection control means for controlling the droplet ejection of the inkjet head by N times (N = m × n) scanning and the N times scanning so as to form an image having a predetermined resolution. A transport control unit that controls a feed amount in the transport direction by the medium transport unit for each scan to be performed, and an activity that moves together with the inkjet head by the scanning unit and incompletely cures the liquid adhering to the medium Provisional curing means for irradiating the light beam, and the provisional curing means includes a conveyance direction in which the irradiation energy per unit area on the downstream side in the conveyance direction of the medium conveyance means exceeds the irradiation energy per unit area on the upstream side. The liquid contains a radical polymerizable compound as component A, a radical polymerization initiator as component B, and a colorant as component C. The component A is a simple component A-1. A functional radical polymerizable compound, and a polyfunctional radical polymerizable compound as component A-2, wherein the component A-1 is a component A-1-1; N-vinyl compound as a component, and a compound represented by the following formula (I) as a component A-1-2, the content of the component A-1 is 50 weight percent or more based on the total weight of the component A 90 weight percent or less, and the content of the component A-1-1 is 10 weight percent or more and 40 weight percent or less based on the total weight of the component A-1, and the content of the component A-1-2 Is 5 weight percent or more and 90 weight percent or less with respect to the total weight of the component A-1, and the component A-2 contains at least two compounds represented by the following formula (II), The image forming apparatus, wherein the content of A-2 is 0.1 weight percent or more and 25 weight percent or less with respect to the total weight of the component A.

  According to this aspect, in multi-pass pixel formation in which an image having a predetermined resolution is formed by N (= m × n) scans, the unit area on the downstream side in the transport direction of the medium transport unit of the temporary curing unit The irradiation energy per unit area exceeds the irradiation energy per unit area on the upstream side, and the distribution of the irradiation energy of the actinic ray in the same direction is provided, so that the upstream dot and the downstream side in the same direction within one swath width Density unevenness having periodicity corresponding to the swath width due to the difference in irradiation energy per unit area of the actinic ray with the dot is suppressed.

  (Second aspect): In the temporary curing means, the ratio of the minimum value of irradiation energy per unit area to the maximum value of irradiation energy per unit area in the distribution of irradiation energy is 1.3 or more and 3.3 or less. An image forming apparatus.

  In such an aspect, an aspect in which the ratio of the minimum value of irradiation energy per unit area to the maximum value of irradiation energy per unit area in the distribution of irradiation energy is preferably 2.0 or more.

  (Third Aspect): The temporary curing means has an actinic ray emitting part divided into two in the carrying direction, and the irradiation energy per unit area of the emitting part downstream in the carrying direction is the carrying direction. An image forming apparatus that exceeds the irradiation energy per unit area of the upstream emitting portion.

  In such an aspect, it is preferable that the boundary between the upstream side in the medium conveyance direction of the emitting unit and the downstream side in the same direction be the central position in the same direction of the emitting unit before division.

  (Fourth aspect): The temporary curing means has a box shape, and has an emission portion of an actinic ray on a bottom plate facing the recording medium, and emits an actinic ray toward the inside of the box shape. An image forming apparatus having an internal structure in which an element is disposed on at least one of both end faces in the transport direction and guides actinic rays to the emitting portion.

  In this aspect, the light emitting elements may be provided on both end faces in the box-shaped transport direction, or may be provided on one end face in the box-shaped transport direction.

  (Fifth aspect): An image forming apparatus provided with a main curing unit that moves together with the ink jet head and the temporary curing unit by the scanning unit and irradiates active light to a degree that completely cures the liquid adhering to the medium. .

  According to this aspect, the adhesion between the medium and the liquid is ensured by completely curing the liquid attached to the medium.

  In this aspect, it is preferable that the main curing unit is disposed upstream of the temporary curing unit in the medium conveyance direction.

  (Sixth aspect): The image forming apparatus, wherein the component A-1-1 is N-vinylcaprolactam.

  (Seventh aspect): Component A-1 of the liquid contains a (meth) acrylate compound having an aromatic hydrocarbon ring as Component A-1-3, and Component A-1-3 includes Component A- An image forming apparatus having 5 weight percent or more and 40 weight percent or less with respect to the total weight of 1.

  (Eighth embodiment): The liquid component B contains a monoacylphosphine oxide compound as component B-1, and / or a bisacylphosphine oxide compound as component B-2, and a thioxanthone compound as component B-3 Forming equipment.

  (Ninth aspect): In the liquid, at least one of the compounds represented by the formula (II) is trimethylolpropane triacrylate, and the content thereof is 0.5% by weight or more based on the total weight of the component A An image forming apparatus of 8 weight percent or less.

  (Tenth embodiment): The image forming apparatus, wherein the component B of the liquid contains the component B-1, and the content thereof is 3% by weight or less based on the total weight of the ink composition.

  (Eleventh aspect): The image forming apparatus wherein the component A-2 of the liquid contains at least one compound represented by the following formula (II ').

(In the formula (II ′), R ¹¹ represents a hydrogen atom or an optionally substituted alkyl group having 1 to 6 carbon atoms, and R ¹² represents a hydrogen atom or an optionally substituted carbon atom having 1 to 6 carbon atoms. R ¹³ represents each independently a hydrogen atom or a methyl group, X ² represents a single bond or a divalent linking group, and p, q and r are each independently an integer of 0 to 5. And satisfies the relationship of p + q + r ≧ 1.)
(Twelfth aspect): Scanning in the scanning direction is performed by scanning an inkjet head in which a plurality of nozzles that eject liquid that is cured by irradiation with actinic rays are arranged m times (m is an integer of 2 or more) in the scanning direction. The nozzle is formed by ejecting droplets at a droplet ejection position on the line and performing droplet ejection by moving the droplet ejection position on the scanning line in the transport direction of the medium to which the liquid is attached n times (n is an integer of 2 or more). Injecting liquid from the ink jet head by N times (N = m × n) scanning so as to form an image with a predetermined resolution with a droplet ejection interval smaller than the nozzle pitch in the medium conveyance direction in the array A droplet curing step, and a temporary curing step of irradiating an actinic ray to such an extent that the ejected liquid is incompletely cured from a temporary curing means that moves together with the inkjet head, and the droplet ejection step includes the step of The amount of feed of the medium in the transport direction is controlled for each scan constituting the scan, and the actinic ray irradiated in the temporary curing step has an irradiation energy per unit area on the downstream side in the transport direction. The liquid has a distribution of irradiation energy in the transport direction exceeding the irradiation energy per unit area, and the liquid contains a radical polymerizable compound as component A, a radical polymerization initiator as component B, and a colorant as component C. The component A contains a monofunctional radical polymerizable compound as the component A-1 and a polyfunctional radical polymerizable compound as the component A-2, and the component A-1 contains N- A vinyl compound and a compound represented by the following formula (I) as component A-1-2 are contained, and the content of component A-1 is 50 parts by weight with respect to the total weight of component A. And the content of the component A-1-1 is not less than 10 weight percent and not more than 40 weight percent with respect to the total weight of the component A-1, and the content of the component A-1-2 The content is 5 weight percent or more and 90 weight percent or less with respect to the total weight of the component A-1, and the component A-2 contains at least two compounds represented by the following formula (II): The image forming method, wherein the content of the component A-2 is 0.1 weight percent or more and 25 weight percent or less with respect to the total weight of the component A.

(In formula (I), R ¹ , R ² and R ³ each independently represents a hydrogen atom, a methyl group or an ethyl group, and X ¹ represents a single bond or a divalent linking group.)

(In the formula (II), R ¹¹ each independently represents a hydrogen atom or an optionally substituted alkyl group having 1 to 6 carbon atoms, and R ¹² represents a hydrogen atom or an optionally substituted carbon atom 1. represents an alkyl group of from, R ¹³ represents independently a hydrogen atom, or a methyl group, X ² is a single bond or a divalent linking group, 5 p, from 0 q and r are each independently Represents an integer.)

  DESCRIPTION OF SYMBOLS 10 ... Inkjet recording device, 12 ... Recording medium, 24, 240 ... Inkjet head, 32A, 32B, 332A, 332B ... Temporary curing light source, 34A, 34B, 334A, 334B ... Main curing light source, 61 ... Nozzle array, 108 ... Light source Control part 118 ... Light source drive circuit, 242 ... Nozzle, 300 ... Temporary curing light source unit, 302 ... Bottom plate, 306 ... Reflector plate, 308 ... Partition member, 314, 314A, 314B ... UV-LED element, 322 ... Housing, 352 ... Mirror members

Claims (12)

An inkjet head in which a plurality of nozzles for ejecting liquid that is cured by irradiation with actinic rays are arranged;
Medium conveying means for conveying a medium to which the liquid ejected from the inkjet head is attached;
Scanning means for moving the inkjet head relative to the medium;
The droplet ejection position on the scanning line along the scanning direction of the scanning unit is ejected m times (m is an integer of 2 or more), and the droplet ejection position on the scanning line along the transport direction of the transport unit is n times. By performing droplet ejection by moving (n is an integer equal to or greater than 2), N times (in order to form an image with a predetermined resolution with a droplet ejection interval smaller than the nozzle pitch in the transport direction in the nozzle array ( N = m × n) droplet ejection control means for controlling droplet ejection of the inkjet head;
A transport control means for controlling a feed amount in the transport direction by the medium transport means for each scan constituting the N scans;
Temporary curing means for irradiating with the actinic ray to such an extent that the scanning means moves together with the ink jet head and incompletely cures the liquid adhering to the medium;
With
The temporary curing means has a distribution of irradiation energy in the transport direction in which the irradiation energy per unit area on the downstream side in the transport direction of the medium transport means exceeds the irradiation energy per unit area on the upstream side,
The liquid contains a radical polymerizable compound as component A, a radical polymerization initiator as component B, and a colorant as component C,
Component A contains a monofunctional radically polymerizable compound as Component A-1 and a polyfunctional radically polymerizable compound as Component A-2,
Component A-1 contains an N-vinyl compound as Component A-1-1 and a compound represented by the following formula (I) as Component A-1-2:
The content of the component A-1 is 50 weight percent or more and 90 weight percent or less with respect to the total weight of the component A,
The content of the component A-1-1 is not less than 10 weight percent and not more than 40 weight percent based on the total weight of the component A-1.
The content of the component A-1-2 is 5 weight percent or more and 90 weight percent or less with respect to the total weight of the component A-1.
The component A-2 contains at least two compounds represented by the following formula (II), and the content of the component A-2 is 0.1 weight percent or more based on the total weight of the component A An image forming apparatus of 25 weight percent or less.
(In formula (I), R ¹ , R ² and R ³ each independently represents a hydrogen atom, a methyl group or an ethyl group, and X ¹ represents a single bond or a divalent linking group.)
(In the formula (II), R ¹¹ each independently represents a hydrogen atom or an optionally substituted alkyl group having 1 to 6 carbon atoms, and R ¹² represents a hydrogen atom or an optionally substituted carbon atom 1. represents an alkyl group of from, R ¹³ represents independently a hydrogen atom, or a methyl group, X ² is a single bond or a divalent linking group, 5 p, from 0 q and r are each independently Represents an integer.)   2. The ratio of the minimum value of irradiation energy per unit area to the maximum value of irradiation energy per unit area in the distribution of irradiation energy of the temporary curing means is 1.3 or more and 3.3 or less. Image forming apparatus.   The temporary curing means has an actinic ray emitting part divided into two in the conveying direction, and the irradiation energy per unit area of the emitting part on the downstream side in the conveying direction is equal to that of the emitting part on the upstream side in the conveying direction. The image forming apparatus according to claim 1, wherein the image forming apparatus exceeds the irradiation energy per unit area. The temporary curing means has a box shape and has an actinic ray emitting part on a bottom plate facing the recording medium,
The light emitting element which generates an actinic ray toward the inside of the box shape is disposed on at least one of both end faces in the transport direction, and has an internal structure for guiding the actinic ray to the emitting part. The image forming apparatus according to any one of the above.   5. The apparatus according to claim 1, further comprising a main curing unit that moves together with the inkjet head and the temporary curing unit by the scanning unit and irradiates the active light beam to a degree that completely cures the liquid adhering to the medium. The image forming apparatus described in the item.   6. The image forming apparatus according to claim 1, wherein the component A-1-1 is N-vinylcaprolactam. Component A-1 of the liquid contains a (meth) acrylate compound having an aromatic hydrocarbon ring as Component A-1-3,
The image forming apparatus according to claim 1, wherein the component A-1-3 is 5 weight percent or more and 40 weight percent or less based on the total weight of the component A-1.   The component B of the liquid contains a monoacylphosphine oxide compound as the component B-1, and / or a bisacylphosphine oxide compound as the component B-2, and a thioxanthone compound as the component B-3. The image forming apparatus according to claim 1.   In the liquid, at least one of the compounds represented by the formula (II) is trimethylolpropane triacrylate, and the content thereof is 0.5 weight percent or more and 8 weight percent or less based on the total weight of the component A. The image forming apparatus according to claim 1.   The image forming apparatus according to claim 1, wherein the component B of the liquid contains the component B-1, and the content thereof is 3% by weight or less based on the total weight of the ink composition. 11. The image forming apparatus according to claim 1, wherein the liquid component A-2 contains at least one compound represented by the following formula (II ′).
(In the formula (II ′), R ¹¹ represents a hydrogen atom or an optionally substituted alkyl group having 1 to 6 carbon atoms, and R ¹² represents a hydrogen atom or an optionally substituted carbon atom having 1 to 6 carbon atoms. R ¹³ represents each independently a hydrogen atom or a methyl group, X ² represents a single bond or a divalent linking group, and p, q and r are each independently an integer of 0 to 5. And satisfies the relationship of p + q + r ≧ 1.) An inkjet head on which a plurality of nozzles for ejecting liquid that is cured by irradiation with actinic rays is arranged is scanned m times (m is an integer of 2 or more) in the scanning direction to the droplet ejection position on the scanning line in the scanning direction. By performing droplet ejection and performing droplet ejection by moving the droplet ejection position n times (n is an integer of 2 or more) on the scanning line in the conveyance direction of the medium to which the liquid is attached, the medium conveyance direction in the nozzle array A droplet ejection step of ejecting liquid from the inkjet head by N times (N = m × n) scanning so as to form an image having a predetermined resolution with a droplet ejection interval smaller than the nozzle pitch of
A temporary curing step of irradiating with an actinic ray to such an extent that the ejected liquid is incompletely cured from a temporary curing means that moves together with the inkjet head;
Including
In the droplet ejection step, the feed amount of the medium in the transport direction is controlled for each scan constituting the N scans,
The actinic ray irradiated in the temporary curing step has a distribution of irradiation energy in the transport direction in which the irradiation energy per unit area on the downstream side in the transport direction exceeds the irradiation energy per unit area on the upstream side,
The liquid contains a radical polymerizable compound as component A, a radical polymerization initiator as component B, and a colorant as component C,
Component A contains a monofunctional radically polymerizable compound as Component A-1 and a polyfunctional radically polymerizable compound as Component A-2,
Component A-1 contains an N-vinyl compound as Component A-1-1 and a compound represented by the following formula (I) as Component A-1-2:
The content of the component A-1 is 50 weight percent or more and 90 weight percent or less with respect to the total weight of the component A,
The content of the component A-1-1 is not less than 10 weight percent and not more than 40 weight percent based on the total weight of the component A-1.
The content of the component A-1-2 is 5 weight percent or more and 90 weight percent or less with respect to the total weight of the component A-1.
The component A-2 contains at least two compounds represented by the following formula (II), and the content of the component A-2 is 0.1 weight percent or more based on the total weight of the component A An image forming method of 25 weight percent or less.
(In formula (I), R ¹ , R ² and R ³ each independently represents a hydrogen atom, a methyl group or an ethyl group, and X ¹ represents a single bond or a divalent linking group.)
(In the formula (II), R ¹¹ each independently represents a hydrogen atom or an optionally substituted alkyl group having 1 to 6 carbon atoms, and R ¹² represents a hydrogen atom or an optionally substituted carbon atom 1. represents an alkyl group of from, R ¹³ represents independently a hydrogen atom, or a methyl group, X ² is a single bond or a divalent linking group, 5 p, from 0 q and r are each independently Represents an integer.)