JP2015054434A - Image formation method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image formation method which uses a matrix head of single path method, for good granularity in an image, with occurrence of streaky irregularity being suppressed.SOLUTION: The image formation method includes, in a following sequence, a step in which an ultraviolet curing type ink composition having different hue is discharged from two or more ink jet heads 241, 242, 243, 244, 245, 246, 247 to an impermeable medium, a step in which the discharged ink composition is semi-cured by ultraviolet ray radiation each time of discharge completion of ink composition in respective colors, and a step in which the ink composition is entirely cured by radiating ultraviolet ray to an entire image in the atmosphere whose oxygen concentration is 1 vol.% or less.

Description

  The present invention relates to an image forming method.

As an image recording method for forming an image on a recording substrate such as paper based on an image data signal, there are an electrophotographic method, a sublimation type and a melt type thermal transfer method, an ink jet method and the like.
The ink jet method uses an ink composition because the printing apparatus is inexpensive and does not require a plate at the time of printing, and the ink composition is ejected only on the required image portion to form an image directly on the recording substrate. Goods can be used efficiently, especially in the case of small lot production. Furthermore, it has low noise and is excellent as an image recording method, and has attracted attention in recent years.

  Such an ink jet image forming apparatus (hereinafter also referred to as “inkjet apparatus”) supplies ink from an ink tank to a pressure chamber via an ink supply path, and an electric signal corresponding to image data is applied to a piezoelectric element. By applying and driving the piezoelectric element, the diaphragm constituting a part of the pressure chamber is deformed, the volume of the pressure chamber is reduced, and ink in the pressure chamber is ejected as droplets from the ejection port. ing.

  In the ink jet apparatus as described above, one image is formed on the recording substrate by combining dots formed by the ink ejected from the ejection ports. In recent years, it has been desired to form high-quality images that are comparable to photographic prints in inkjet printers. In contrast, the diameter of the discharge port is reduced to reduce the ink droplets discharged from the discharge port, and the discharge ports are arranged at high density to increase the number of pixels per image, thereby improving the image quality. It is considered to be realized. As a method for increasing the density of the arrangement of the discharge ports, it has been conventionally proposed to arrange the discharge ports in a two-dimensional matrix.

Inkjet heads (hereinafter also simply referred to as “heads”) include a shuttle system and a line system (single-pass system).
The shuttle system is a system that uses a short serial head and performs recording while scanning the head in the width direction of the substrate. According to this method, since the number of necessary ejection ports is small and the head can be made small, there is an advantage that the apparatus can be provided at a low price, but there is a disadvantage that the productivity of the apparatus is low.
The single pass method is a method that forms an image on the entire surface of the substrate by moving the full line head and the substrate only once relative to each other using a full line head that covers the entire area of the substrate. It is. According to this system, there is a disadvantage that the apparatus becomes expensive compared with the apparatus using the shuttle system, but there is an advantage that the productivity of the apparatus is high.

In Patent Document 1, a plurality of discharge ports are arranged in a lattice shape composed of a plurality of rows inclined at a certain angle with respect to the head main scanning direction and a plurality of columns orthogonal to the head main scanning direction. By making the planar shape of the diaphragm forming one surface of the pressure chamber provided corresponding to the outlet into a substantially square or rhombus, the discharge efficiency of the pressure chamber is improved and the discharge ports are arranged at high density An image forming apparatus is described.
Patent Document 2 describes an image forming apparatus that uses a head in which ejection openings are arranged in a two-dimensional matrix as a single-pass head, and a plurality of nozzles that eject droplets are two-dimensionally arranged. A liquid discharge head having a discharge surface, or a liquid discharge head in which a plurality of head modules having a plurality of nozzles for discharging droplets are arranged in a staggered manner, and liquid droplets discharged from the nozzles of the liquid discharge head Conveying means for conveying the recording medium to which the liquid is adhered, a main body frame for supporting the conveying means, a head moving means for movably supporting the liquid discharge head with respect to the main body frame, and the movable liquid discharge Head fixing means for fixing the head to the main body frame at a droplet discharge position to the recording medium, and the head fixing means is connected to the conveying means. A pressure fixing means for fixing the head for urging the liquid discharge head in the width direction of the recording medium perpendicular to the conveyance direction of the recording medium, and a spring for the pressure applying means for fixing the head Resonance frequency defined by a constant and the mass of the liquid ejection head is a nozzle that forms dots adjacent in the width direction on the recording medium, out of the distance between nozzles in the transport direction in the nozzle array of the liquid ejection head Spatial distances in the transport direction of the nozzle pairs corresponding to the connecting portions in the line, the relative vibration frequency in the width direction of the transport unit and the liquid discharge head when transporting the recording medium, and the recording medium by the transport unit The image forming apparatus is characterized in that it is configured so as to be different from the frequency component of the vibration pitch depending on the transport speed.

JP 2001-334661 A JP 2012-71473 A

According to the image forming apparatus described in Patent Document 1, an image with reduced graininess can be obtained on a non-penetrable medium by properly using several types of droplets having different volumes.
However, according to the image forming method described above, when small droplets are ejected, the size of the droplets varies between the ejection ports, so that periodic streaky irregularities (hereinafter simply referred to as “straight lines”) appear in the image. ")") Occurs.
Therefore, when the image is formed using only relatively large droplets in order to make the droplet sizes uniform, the occurrence of unevenness can be suppressed, but the granularity of the image becomes strong.
As described above, when an image is formed on a non-penetrable medium using a matrix head, it is difficult to achieve both reduction in graininess and reduction in stripes.

  The problem to be solved by the present invention is to form an image on a non-penetrable medium using a single-pass type matrix head with reduced graininess in the image and suppressing the occurrence of uneven stripes. It is to provide an image forming method capable of

The above-described problem of the present invention has been solved by the following solution <1>. They are listed together with <2> to <9> which are preferred embodiments.
<1> A discharge step of discharging an ultraviolet curable ink composition having a different hue from two or more inkjet heads onto a non-penetrable medium, and the discharge of the ink composition of each color from the discharged ink composition A step of semi-curing each by ultraviolet irradiation and a step of completely curing the ink composition by irradiating ultraviolet rays in an atmosphere having an oxygen concentration of 1% by volume or less. A nozzle plate having an outlet is provided, and the plurality of discharge ports are arranged in a two-dimensional matrix of 4 × 4 or more with respect to the traveling direction of the non-penetrable medium, and the density of the plurality of discharge ports arranged is 600 npi The inkjet head is a single-pass method, the amount of the ink composition to be ejected is 10 pl to 20 pl, In step, at least a magenta ink, light magenta ink, cyan ink, and an image forming method characterized by discharging the four color ink compositions of light cyan ink,
<2> The image forming method according to <1>, wherein the printing speed is 20 m / min or more,
<3> An undercoat step of applying an undercoat liquid onto the non-penetrable medium, an undercoat liquid semi-curing step of semi-curing the undercoat liquid by ultraviolet irradiation, and discharging the ink composition onto the semi-cured undercoat liquid An image forming method according to <1> or <2>, including the discharging step in this order,
<4> The non-penetrable medium has a total film thickness of 10 μm to 90 μm, and includes one or more resin films selected from the group consisting of a polyethylene terephthalate film, a polyethylene film, a polypropylene film, and a nylon film. The image forming method according to any one of <1> to <3>, which is a single-layer or laminated base material,
<5> The image forming method according to any one of <1> to <4>, which is for package printing;
<6> The image forming method according to any one of <1> to <5>, wherein the ultraviolet light source in the step of completely curing the ink composition is UV-LED and / or UV-LD,
<7> The inkjet head includes a plurality of pressure chambers that communicate with each of the plurality of ejection ports, a plurality of ink supply ports that supply an ink composition to each of the plurality of pressure chambers, and the plurality of ink supplies. The image forming method according to any one of <1> to <6>, comprising: a common liquid chamber that supplies an ink composition to a mouth; and a plurality of pressure generating units that deform each of the plurality of pressure chambers. ,
<8> The image forming method according to <7>, wherein the inkjet head further includes an electrical wiring that is disposed so as to penetrate the common liquid chamber and that supplies a drive signal to the pressure generating unit.
<9> The image forming method according to <7> or <8>, wherein the pressure chamber and the common liquid chamber provided in the inkjet head are disposed on the opposite side of the pressure generating unit.

  According to the present invention, on a non-penetrable medium, an image forming method capable of forming an image in which graininess in an image is reduced and generation of streak is suppressed by using a single-pass type matrix head. Can be provided.

It is a schematic sectional drawing which shows an example of the internal structure of an inkjet head. It is the schematic which shows an example of the discharge port arrangement | sequence of a nozzle plate. It is a plane perspective view which shows an example of a head structure. It is an enlarged view which expands and shows a part of FIG. FIG. 4 is a cross-sectional view taken along line AA in FIG. 3 and FIG. It is a perspective perspective view which expands and shows an example of a head structure partially. It is a plane perspective view which expands and shows an example of a head structure partially. FIG. 9 is a cross-sectional view taken along line 9-9 in FIG. 7. 1 is a schematic diagram illustrating an example of an image forming apparatus. It is the schematic which shows an example of a nitrogen purge exposure machine. It is a plane perspective view which shows the structure of a comparison head. It is the schematic which shows the image forming apparatus which uses a comparison head.

In the image forming method of the present invention, as an essential step, ultraviolet curable ink compositions having different hues are ejected from two or more inkjet heads onto a non-penetrable medium (hereinafter also simply referred to as “substrate”). A discharge step (hereinafter also referred to as “ink discharge step”), and a step of semi-curing the discharged ink composition by ultraviolet irradiation at the end of discharge of each color ink composition (hereinafter referred to as “pinning step”). And a step of completely curing the ink composition by irradiating ultraviolet rays in an atmosphere having an oxygen concentration of 1 vol% or less (hereinafter also referred to as “curing step”) in this order. In addition, other steps can be provided as necessary.
In the image forming method of the present invention, the inkjet head includes a nozzle plate having a plurality of discharge ports, and the plurality of discharge ports are two-dimensionally 4 × 4 or more with respect to the traveling direction of the non-penetrable medium. The density of the plurality of ejection openings arranged in a matrix is 600 npi or more, the inkjet head is a single pass system, and the amount of the ejected ink composition is 10 pl to 20 pl, In the ejection step, at least four ink compositions of magenta ink, light magenta ink, cyan ink, and light cyan ink are ejected (hereinafter, light magenta ink and light cyan ink are collectively referred to as “light Also called “ink”.)

  The “ink ejection process”, “pinning process”, and “curing process”, which are essential processes in the image forming method of the present invention, will be described below. In the present invention, the description of “lower limit to upper limit” representing a numerical range represents “lower limit or higher and lower limit or lower”, and the description of “upper limit to lower limit” represents “lower limit or higher and lower limit or higher”. That is, it represents a numerical range including an upper limit and a lower limit. In the present invention, “mass%” and “wt%” are synonymous, and “part by mass” and “part by weight” are synonymous.

(Ink ejection process)
In the ink ejection process, an ultraviolet curable ink composition (hereinafter also simply referred to as “ink” or “ink composition”) having different hues is ejected from two or more inkjet heads onto an impermeable medium. Form. In this step, the ink composition can be applied in an image form on the non-penetrable medium, and a desired visible image can be formed.

<Non-penetrating medium>
The non-penetrable medium in the present invention refers to a base material into which liquid droplets do not substantially penetrate. “Substantially no liquid permeates” means, for example, that the liquid permeation rate after 1 minute is 5% or less.

As the non-penetrable medium, known base materials can be used without limitation, and synthetic resins, rubbers, resin-coated papers, metals, and the like can be used. Among these, synthetic resins are preferably used. In addition, these base materials may have a single layer structure or a laminated structure of two or more layers.
As the synthetic resin, known synthetic resins can be used without limitation. For example, polyvinyl chloride; polystyrene; polyurethane; polyolefin such as polyethylene and polypropylene; polyester such as polyethylene terephthalate and polybutadiene terephthalate; Polyamides such as nylon; acrylic resin, polycarbonate, acrylonitrile-butadiene-styrene copolymer, diacetate, triacetate, polyimide, cellophane, celluloid, and the like.

These synthetic resins may be transparent or opaque. The synthetic resin is preferably used in the form of a film used for so-called soft packaging, and various non-absorbable plastics and films thereof can be used. Examples of various plastic films include polyethylene terephthalate film, polypropylene film, nylon film, polyvinyl chloride film, polyethylene film, and triacetyl cellulose film. Polyethylene terephthalate film, polyethylene film, polypropylene film, and nylon film A single layer or laminated base material including one or two or more resin films selected from the group consisting of is preferable. Moreover, the said film may be biaxially stretched as needed.
Polyethylene terephthalate film has high barrier properties against hydrocarbon-based organic compounds, and nylon film is excellent in strength, heat resistance, cold resistance, pinhole resistance, etc. Also, polyethylene film and biaxial Since the stretched polypropylene film has high heat sealability, each is suitable. Moreover, it is also possible to give these characteristics to a base material by laminating | stacking the said film on a base material.

The total film thickness of the non-penetrable medium is preferably 5 μm to 90 μm, and more preferably 10 μm to 80 μm. Note that the total film pressure refers to the film pressure of the base material in the case of a single-layer base material, and the total value of the film pressures of the stacked base materials in the case of a stacked base material.
As a method for laminating the resin film, a known method can be used without any particular limitation, and dry lamination, extrusion coating, and coextrusion coating can be exemplified.

  Further, as described above, the effect of the present invention is to reduce graininess in the image and to reduce unevenness. Due to the above effects, it is not necessary to correct graininess and unevenness during printing, and as a result, the printing time can be shortened. Therefore, the image forming method of the present invention is suitable for package printing requiring high productivity, and particularly suitable for package printing for food packaging.

<Inkjet head>
The ink jet head used in the present invention may be an on-demand system or a continuous system. In addition, as a discharge method, an electro-mechanical conversion method (for example, a single cavity type, a double cavity type, a bender type, a piston type, a shear mode type, a shared wall type, etc.), an electro-thermal conversion method (for example, a thermal type) Ink jet type, bubble jet (registered trademark) type), electrostatic attraction method (for example, electric field control type, slit jet type, etc.) and discharge method (for example, spark jet type) can be exemplified. It may be used. In addition, there is no restriction | limiting in particular about the discharge outlet etc. which are used when recording by the said inkjet method, According to the objective, it can select suitably.
In the image forming method of the present invention, two or more inkjet heads are used.

[Nozzle plate]
An ink jet head used in the image forming method of the present invention includes a nozzle plate having a plurality of ejection openings. FIG. 1 is a schematic cross-sectional view showing an example of the internal structure of an inkjet head.

  In the example illustrated in FIG. 1, the inkjet head 200 includes a nozzle plate 11 having discharge ports (nozzles) and an ink supply unit 20 provided on the side opposite to the discharge direction of the nozzle plate. The nozzle plate 11 is provided with a plurality of ejection ports 12 for ejecting ink.

In the nozzle plate provided in the inkjet head used in the present invention, a plurality of ejection openings are arranged in a two-dimensional matrix of 4 × 4 or more in the traveling direction of the medium, and preferably 8 × 8 or more. More preferably, it is 32 × 32 or more.
Further, the density of the plurality of discharge ports arranged is 600 npi or more, preferably 1,200 npi or more. In the present invention, npi represents the number of nozzles per 2.54 cm.

  FIG. 2 is a schematic diagram illustrating an example of the arrangement of nozzle plates arranged in a two-dimensional matrix. For example, as shown in FIG. 2, the nozzle plate may employ a configuration in which 32 × 64 discharge ports are arranged in a two-dimensional matrix. Further, part or all of the nozzle plate is formed of silicon. Silicon may be exposed in the nozzle opening and the surface in the ink ejection direction, and at least one selected from the group consisting of oxides and nitrides of metals (including silicon) and metals (excluding silicon) It is preferable that it is covered with a film containing.

  In addition, a configuration example of an inkjet head including a nozzle plate in which ejection openings are arranged in a two-dimensional matrix will be described with reference to FIGS.

FIG. 3 is a plan perspective view showing an example of the head structure, and FIG. 4 is an enlarged view showing a part thereof.
As shown in FIG. 3, the inkjet head 550 includes a plurality of ink chamber units 554 each having a nozzle 551 that is an ink discharge port, a pressure chamber 552 corresponding to each nozzle, and an ink supply port 553 in a two-dimensional matrix. It has an arranged structure. Moreover, 424 in the figure is a base material.
As shown in FIG. 4, by arranging the ink chamber units along an oblique column direction having a constant angle θ that is not orthogonal to the main scanning direction M, the projections are arranged in a line along the main scanning direction ( The substantial nozzle interval P that is orthogonally projected can be expressed by P = Ls / tan θ, where Ls is the adjacent nozzle interval in the sub-scanning direction. That is, by disposing the ink chamber units in a two-dimensional matrix, the substantial density of the ejection ports can be increased. The discharge port density in the present invention refers to the substantial discharge port density.

[Single pass method]
The ink jet head used in the present invention is a single pass system. As an inkjet head, a short serial head is used, and a shuttle system that performs recording while scanning the head in the width direction of the substrate, and a line head in which recording elements are arranged corresponding to the entire area of one side of the substrate In the present invention, a single-pass ink jet head is used. The single pass method is a mode in which an image is formed on the entire surface of the base material by an operation of moving the full line head and the base material only once relative to each other using a full line head that covers the entire area of the base material. It is. Examples of such a single path method are described in JP-A-2005-96443 and JP-A-2005-280346. In other words, in the single-pass method, an image can be recorded on the entire surface of the substrate by scanning the substrate in a direction orthogonal to the element arrangement direction of the full line head, and a carriage system such as a carriage that scans the short head is used. It becomes unnecessary. In addition, complicated scanning control between the carriage and the base material is not necessary, and only the base material moves, so that the recording speed can be increased as compared with the shuttle system. The image forming method of the present invention can be applied to any of these.

[Pressure chamber, ink supply port, common liquid chamber, pressure generator]
The inkjet head according to the present invention includes a plurality of pressure chambers communicating with each of the plurality of ejection ports, a plurality of ink supply ports for supplying an ink composition to each of the plurality of pressure chambers, and the plurality of ink supply ports. It is preferable to include a common liquid chamber for supplying the ink composition and a plurality of pressure generating means for deforming each of the plurality of pressure chambers.

  In FIG. 1, the ink supply unit 20 supplies ink to each of a plurality of pressure chambers 21 communicating with each of a plurality of ejection ports 12 of the nozzle plate 11 via a nozzle communication path 22 and each of the plurality of pressure chambers 21. A plurality of ink supply channels 23, a common liquid chamber 25 that supplies ink to the plurality of ink supply channels 23, and a pressure generating unit 30 that deforms each of the plurality of pressure chambers 21 are provided.

The ink supply channel 23 is formed between the ink supply unit 20 and the nozzle plate 11 so that the ink supplied to the common liquid chamber 25 is fed. One end of a supply adjustment path 24 connected to the pressure chamber 21 is connected to the ink supply flow path 23, and the amount of ink supplied from the ink supply flow path 23 is reduced to a required amount to the pressure chamber 21. The liquid can be sent. A plurality of supply adjustment paths 24 are provided in the ink supply flow path 23, and ink is supplied to the pressure chamber 21 provided adjacent to the pressure generating means 30 via the ink supply flow path 23.
In this way, it is possible to supply a large amount of ink to a plurality of ejection openings.

  The pressure generating means 30 is an actuator (piezoelectric element) configured by sequentially stacking a diaphragm 31, an adhesive layer 32, a lower electrode 33, a piezoelectric layer 34, and an upper electrode 35 from the pressure chamber 21 side. The electric wiring for supplying is connected and driven. A piezoelectric layer 34 is bonded together with an electrode to a vibration plate (pressurizing plate) 31 constituting the top surface of the pressure chamber 21. When voltage is applied to the electrode, the actuator is deformed according to an image signal, and ink is transferred. It is discharged from the nozzle through the nozzle communication path. When ink is ejected, new ink is supplied from the common liquid chamber 25 to the pressure chamber 21 through the ink supply channel 23.

  Further, a circulation restrictor 41 is provided in the vicinity of the discharge port 12 so that ink is always collected into the circulation path 42. Thereby, it is possible to prevent thickening of the ink in the vicinity of the ejection port during non-ejection.

FIG. 5 is a cross-sectional view taken along line AA of FIGS. 3 and 4 and is a schematic cross-sectional view showing an example of the arrangement of the pressure chamber, the ink supply port, the supply flow path, and the pressure generating means.
As shown in FIG. 5, the inkjet head 550 has a structure in which a nozzle plate 551A in which nozzles 551 are formed and a flow path plate 552P in which flow paths such as a pressure chamber 552 and a common liquid chamber 555 are formed are laminated and joined. . The nozzle plate 551A constitutes a nozzle surface (ink ejection surface) 550A of the inkjet head 550, and a plurality of nozzles 551 respectively communicating with the pressure chambers 552 are two-dimensionally formed.

  The flow path plate 552P constitutes a side wall portion of the pressure chamber 552 and a flow that forms an ink supply port 553 as a throttle portion (the most narrowed portion) of an individual supply path that guides ink from the common liquid chamber 555 to the pressure chamber 552. It is a path forming member. For convenience of explanation, although shown in FIG. 5 in a simplified manner, the flow path plate 552P has a structure in which one or a plurality of substrates are stacked.

  The nozzle plate 551A and the flow path plate 552P can be processed into a required shape by a semiconductor manufacturing process using silicon as a material.

  The common liquid chamber 555 communicates with an ink tank (not shown) that is an ink supply source, and ink supplied from the ink tank is supplied to each pressure chamber 552 via the common liquid chamber 555.

  A piezoelectric actuator 558 having an individual electrode 557 is joined to a diaphragm 556 that constitutes a part of the pressure chamber 552 (the top surface in FIG. 5). The diaphragm 556 of this example is made of silicon (Si) with a nickel (Ni) conductive layer functioning as an electrode pad 559 corresponding to the lower electrode of the piezoelectric element 558, and is arranged corresponding to each pressure chamber 552. Also serves as a common electrode for the actuator 558. It is also possible to form the diaphragm with a non-conductive material such as resin. In this case, a common electrode layer made of a conductive material such as metal is formed on the surface of the diaphragm member. Moreover, you may comprise the diaphragm which serves as a common electrode with metals (conductive material), such as stainless steel (SUS).

  By applying a drive voltage to the individual electrode 557, the piezo actuator 558 is deformed to change the volume of the pressure chamber 552, and ink is ejected from the nozzle 551 due to the pressure change accompanying this. When the piezo actuator 558 returns to its original state after ink ejection, new ink is refilled into the pressure chamber 552 from the common liquid chamber 555 through the ink supply port 553.

  The means for generating the discharge pressure (discharge energy) for discharging the droplets from each nozzle in the inkjet head is not limited to the piezo actuator (piezoelectric element), but the thermal method (the pressure of film boiling due to the heating of the heater) Various pressure generating elements (energy generating elements) such as heaters (heating elements) and other actuators based on other systems can be applied. Corresponding energy generating elements are provided in the flow path structure according to the ejection method of the head.

[High density nozzles]
The ink jet head according to the present invention preferably further includes an electrical wiring that is disposed so as to penetrate the common liquid chamber and that supplies a drive signal to the pressure generating means.
In order to increase the density of the discharge ports, electrical wiring for supplying drive signals to the electrodes (individual electrodes) of the pressure generating means that deforms the pressure chambers is vertically raised from the individual electrodes and penetrates the common liquid chamber. In this way, it can be connected to wiring such as an upper flexible cable.

  FIG. 6 shows a simplified perspective view of an example of an ink jet head having such a high discharge port density.

  In the inkjet head 550 shown in FIG. 6, a vibration plate 556 that forms the upper surface of the pressure chamber 552 is disposed on the upper side of the pressure chamber 552 having the nozzle 551 and the ink supply port 553. Piezoelectric elements 558 (piezoelectric actuators) as pressure generating means constituted by piezoelectric bodies such as piezos sandwiched between electrodes at the upper and lower sides are arranged in the corresponding portions, and the piezoelectric elements 558 have individual electrodes 557 on the upper surfaces thereof. .

An electrode pad 559 serving as an electrode connecting portion is drawn out from the end face of the individual electrode 557 to the outside, and an electric wiring 190 penetrating the common liquid chamber 555 is formed on the electrode pad 559 as a piezoelectric element 558 (pressure generating means). It is formed to rise substantially perpendicular to the surface including In the manufacturing process, the electrical wiring 190 is preferably formed in a tapered shape as shown in FIG.
A multilayer flexible cable 192 is disposed on the electric wiring 190, and a drive signal can be supplied to the individual electrode 557 of the piezoelectric element 558 through these wirings.

  Although not shown in FIG. 6, since the common liquid chamber 555 is filled with ink, the surfaces of the diaphragm 556 as the common electrode, the individual electrode 557, the electrical wiring 190, and the multilayer flexible cable 192 that come into contact with the ink are respectively shown. It is preferable to cover with an insulating protective film.

  FIG. 7 shows a part of the pressure chamber 552 shown in FIG. 6 in an enlarged plan perspective view. Each pressure chamber 552 has a substantially square shape. A nozzle 551 and an ink supply port 553 are formed at both corners of the diagonal line, an electrode pad 559 is drawn out to the nozzle 551 side, and an electric wiring 190 is formed thereon. .

Moreover, it is preferable that the said pressure chamber and the said common liquid chamber with which the inkjet head in this invention is provided are arrange | positioned on the opposite side of the said pressure generation means.
An example of the above configuration is shown in FIG. 8 as a cross-sectional view taken along the alternate long and short dash line 9-9 in FIG.

  As shown in FIG. 8, the inkjet head 550 is preferably formed by laminating a plurality of thin films and the like. For example, a flow path plate 196 in which a pressure chamber 552, an ink supply port 553, a nozzle flow path 551a connecting the pressure chamber 552 and the nozzle 551, and the like are formed on the nozzle plate 194 in which the nozzle 551 is formed. In the figure, the flow path plate 196 is represented as a single plate, but actually, the flow path plate 196 may be formed by stacking a plurality of plates.

  A diaphragm 556 that forms the top surface of the pressure chamber 552 is stacked on the flow path plate 196. It is preferable that the diaphragm 556 also serves as a common electrode for driving a piezoelectric element 558 described later together with the individual electrode 557. Further, the diaphragm 556 is provided with an opening corresponding to the ink supply port 553 of the pressure chamber 552, whereby the pressure chamber 552 and the common liquid chamber 555 formed on the upper side of the diaphragm 556 are directly communicated with each other.

  A piezoelectric body 558a is formed on a portion corresponding to substantially the entire upper surface of the pressure chamber 552 on the vibration plate 556, and an individual electrode 557 is formed on the upper surface of the piezoelectric body 558a. The piezoelectric body 558a sandwiched between the common electrode (vibrating plate 556) and the individual electrode 557 in this manner is deformed when a voltage is applied between the common electrode (vibrating plate 556) and the individual electrode 557, and the pressure chamber A piezoelectric element 558 is configured to reduce the volume of 552 and eject ink from the nozzle 551.

  An end portion of the individual electrode 557 on the nozzle 551 side is pulled out to form an electrode pad 559 as an electrode connection portion. Then, a columnar electric wiring 190 is formed on the electrode pad 559 so as to penetrate the common liquid chamber 555.

  A multilayer flexible cable 192 is formed above the electrical wiring 190. Each wiring (not shown) formed on the multilayer flexible cable 192 is connected to each electrical wiring 190 by an electrode pad 190a, and drives each piezoelectric element 558. For this purpose, a driving signal is supplied through each electric wiring 190.

  The space where the columnar electric wiring 190 (electric column) between the diaphragm 556 and the multilayer flexible cable 192 stands is a common liquid chamber 555 for pooling ink to be supplied to the pressure chamber 552. Since the ink is filled with ink, an insulating / protective film 198 is formed on the surface portion of the diaphragm 556, the individual electrode 557, the piezoelectric body 558 a and the electrical wiring 190, and the surface of the multilayer flexible cable 192 that contacts the ink.

  In this way, by bringing the common liquid chamber that was on the same side as the pressure chamber with respect to the pressure generating means to the upper side of the diaphragm and arranging the pressure chamber on the opposite side across the pressure generating means This eliminates the need for piping or the like for guiding ink from the common liquid chamber to the pressure chamber, which has been necessary in the past, and achieves higher nozzle density. In addition, since the size of the common liquid chamber can be increased, the supply of ink is stable, and high-frequency driving is possible even when the density is increased.

<Ultraviolet curable ink composition>
It does not specifically limit as an ultraviolet curable ink composition used by this invention, A well-known ultraviolet curable ink composition can be used.
The ultraviolet curable ink composition used in the present invention preferably contains a polymerizable compound, a polymerization initiator, a surfactant, a polymerization inhibitor, a colorant, and a dispersant.

[Polymerizable compound]
The ink composition of the present invention preferably contains a polymerizable compound.
The polymerizable compound that can be used in the present invention is preferably an addition polymerizable compound, and more preferably a radical polymerizable compound or a cationic polymerizable compound.
Moreover, the polymeric compound which can be used for this invention may be used individually by 1 type, or may use 2 or more types, for example, may use together a radically polymerizable compound and a cationically polymerizable compound. Good. Among these, it is preferable to use a radically polymerizable compound.

There is no restriction | limiting in particular as long as it does not deviate from the meaning of this invention as a radically polymerizable compound which can be used for this invention, A well-known radically polymerizable compound can be used.
Examples of the radical polymerizable compound are described in JP-A-7-159983, JP-B-7-31399, JP-A-8-224982, JP-A-10-863, JP-A-9-80675, and the like. A photocurable material using a photopolymerizable composition is known.

The radical polymerizable compound is a compound having an ethylenically unsaturated bond capable of radical polymerization, and may be any compound as long as it has at least one ethylenically unsaturated bond capable of radical polymerization in the molecule. , Oligomers, polymers and the like having a chemical form. The radically polymerizable compound may contain one kind at an arbitrary ratio in order to improve the desired properties, and may contain two or more kinds.
The radical polymerizable compound that can be used in the present invention includes an ethylenically unsaturated double bond group selected from the group consisting of a vinyl group, a (meth) acrylate group, a (meth) acrylamide group, and an N-vinyl group. The radically polymerizable monomer which has can be illustrated preferably.

  In the present invention, a (meth) acrylate compound is preferably exemplified as the radical polymerizable compound. Details will be described below.

≪ (Meth) acrylate compound≫
The ink composition of the present invention preferably contains a (meth) acrylate compound from the viewpoint of curability.
The (meth) acrylate compound preferably has a molecular weight of 1,000 or less, and preferably has a molecular weight of 200 to 750.
The (meth) acrylate compound means a methacrylate compound and / or an acrylate compound, and is more preferably an acrylate compound.
The (meth) acrylate compound may be either a polyfunctional (meth) acrylate compound or a monofunctional (meth) acrylate compound, and is not particularly limited, but preferably contains a polyfunctional (meth) acrylate compound.

≪Polyfunctional (meth) acrylate compound≫
The ink composition used in the present invention preferably contains a polyfunctional (meth) acrylate compound as the polymerizable compound.
The polyfunctional (meth) acrylate compound that can be used in the present invention is a polyfunctional monomer having two or more groups selected from the group consisting of an acryloxy group and a methacryloxy group. By containing a polyfunctional (meth) acrylate compound, an ink composition having excellent curability and high cured film strength can be obtained.
In the present invention, the ink composition preferably contains a polyfunctional (meth) acrylate compound.

  Polyfunctional (meth) acrylate compounds include bis (4- (meth) acryloxypolyethoxyphenyl) propane, neopentyl glycol di (meth) acrylate, ethoxylated (2) neopentyl glycol di (meth) acrylate (neopentyl) A compound obtained by di (meth) acrylate conversion of a glycol ethylene oxide 2 mol adduct, hereinafter, “ethylene oxide” is also referred to as “EO”), propoxylation (2) neopentyl glycol di (meth) acrylate (neopentyl glycol propylene) Compound obtained by di (meth) acrylate conversion of oxide 2 mol adduct), 1,6-hexanediol di (meth) acrylate, 1,9-nonanediol di (meth) acrylate, ethylene glycol di (meth) acrylate, diethyleneglycol Di (meth) acrylate, triethylene glycol di (meth) acrylate, tetraethylene glycol di (meth) acrylate, polyethylene glycol di (meth) acrylate, dipropylene glycol di (meth) acrylate, tripropylene glycol di (meth) acrylate, Tetrapropylene glycol di (meth) acrylate, polypropylene glycol di (meth) acrylate, pentaerythritol tri (meth) acrylate, pentaerythritol tetra (meth) acrylate, dipentaerythritol tetra (meth) acrylate, trimethylolpropane tri (meth) acrylate , Tetramethylol methane tetra (meth) acrylate, tetramethylol methane tri (meth) acrylate, dimethylol tris Rhodecane di (meth) acrylate, modified glycerin tri (meth) acrylate, modified bisphenol A di (meth) acrylate, propylene oxide (PO) adduct di (meth) acrylate of bisphenol A, ethylene oxide (EO) adduct di ( Examples include (meth) acrylate, dipentaerythritol hexa (meth) acrylate, caprolactone-modified dipentaerythritol hexa (meth) acrylate, 3-methylpentanediol di (meth) acrylate and the like, and 1,6-hexanediol di (meth) acrylate , Dipropylene glycol di (meth) acrylate, trimethylolpropane tri (meth) acrylate, 3-methylpentanediol di (meth) acrylate, propoxylated (2) neopentyl Recall diacrylate and polyethylene glycol di (meth) acrylate are preferred, and propoxylated (2) neopentyl glycol diacrylate, trimethylolpropane triacrylate, 3-methylpentanediol diacrylate, and polyethylene glycol di (meth) acrylate are more preferred.

  The content of the polyfunctional (meth) acrylate compound with respect to the total amount of the ink composition is preferably 50% by mass or more, and more preferably 80% by mass or more. More preferably, the ink composition is substantially composed of only a polyfunctional acrylate compound. “Substantially only the polyfunctional acrylate compound” means that the content of the polyfunctional acrylate compound with respect to the total amount of the ink composition is 95% by mass or more. When the content of the polyfunctional (meth) acrylate compound is in the above range, it is preferable because the residual monomer can be extremely reduced and the odor can be extremely reduced when cured at a low oxygen concentration.

≪Monofunctional (meth) acrylate compound≫
The ink composition of the present invention may use a monofunctional (meth) acrylate compound. Examples of the monofunctional (meth) acrylate compound include a radically polymerizable monomer described in JP2009-22214A, a polymerizable compound described in JP2009-209289A, and an ethylene described in JP2009-191183A. An unsaturated compound can be exemplified.

Monofunctional (meth) acrylate compounds include phenoxyethyl (meth) acrylate, tetrahydrofurfuryl (meth) acrylate, norbornyl (meth) acrylate, isobornyl (meth) acrylate, cyclohexyl (meth) acrylate, cyclopentyl (meth) acrylate, cycloheptyl (Meth) acrylate, cyclooctyl (meth) acrylate, cyclodecyl (meth) acrylate, dicyclodecyl (meth) acrylate, 3,3,5-trimethylcyclohexyl (meth) acrylate, 4-t-butylcyclohexyl (meth) acrylate, acryloyl morpho Phosphorus, N-phthalimidoethyl (meth) acrylate, pentamethylpiperidyl (meth) acrylate, tetramethylpiperidyl (meth) acrylate , 5- (meth) acryloyloxymethyl-5-ethyl-1,3-dioxacyclohexane, 2-ethylhexyl (meth) acrylate, 2-hydroxyethyl (meth) acrylate, 2-butoxyethyl (meth) acrylate, carbitol (Meth) acrylate, methyl (meth) acrylate, n-butyl (meth) acrylate, 2- (2-ethoxyethoxy) ethyl (meth) acrylate, 2- (2-butoxyethoxy) ethyl (meth) acrylate, dimethylaminomethyl (Meth) acrylate, lauryl (meth) acrylate, hydroxyethyl (meth) acrylate, 1-naphthyl (meth) acrylate, 2-naphthyl (meth) acrylate, 2-α-naphthyloxyethyl (meth) acrylate, 2-β- Naphthyloxyethyl (Meth) acrylate, 2-anthryl (meth) acrylate, 9-anthryl (meth) acrylate, 1-phenanthryl (meth) acrylate, 2-phenanthryl (meth) acrylate, EO-modified cresol (meth) acrylate, p-nonylphenoxyethyl (Meth) acrylate, p-nonylphenoxypolyethylene glycol (meth) acrylate, p-cumylphenoxyethylene glycol (meth) acrylate, 2-furyl (meth) acrylate, 2-furfuryl (meth) acrylate, 2-thienyl (meth) Examples include acrylate, 2-tenyl (meth) acrylate, 1-pyrrolyl (meth) acrylate, 2-pyridyl (meth) acrylate, and 2-quinolyl (meth) acrylate.
Among them, phenoxyethyl (meth) acrylate, isobornyl (meth) acrylate, benzyl (meth) acrylate, lauryl (meth) acrylate, and hydroxyethyl (meth) acrylate are preferable, and isoboronyl acrylate, lauryl acrylate, and hydroxyethyl acrylate are particularly preferable. .

≪Other polymerizable compounds≫
The ink composition of the present invention may contain other polymerizable compound in addition to the above component (meth) acrylate monomer. Examples of the other polymerizable compound include (meth) acrylamides and N-vinyl lactams. And radical polymerizable oligomers.

-(Meth) acrylamides-
The ink composition of the present invention may contain (meth) acrylamides as the polymerizable compound.
(Meth) acrylamides include (meth) acrylamide, N-methyl (meth) acrylamide, N-ethyl (meth) acrylamide, N-propyl (meth) acrylamide, N-isopropyl (meth) acrylamide, and Nn-butyl. Acrylic (meth) amide, Nt-butyl (meth) acrylamide, N-cyclohexyl (meth) acrylamide, N- (2-methoxyethyl) (meth) acrylamide, N, N-dimethyl (meth) acrylamide, N, N -Diethyl (meth) acrylamide, N-phenyl (meth) acrylamide, N-nitrophenyl acrylamide, N-ethyl-N-phenyl acrylamide, N-benzyl (meth) acrylamide, (meth) acryloylmorpholine, diacetone acrylamide, N- Methylo Examples include acrylamide, N-hydroxyethyl acrylamide, vinyl (meth) acrylamide, N, N-diallyl (meth) acrylamide, N-allyl (meth) acrylamide, and methylene bisacrylamide, and N, N-dimethyl (meth) acrylamide, N-hydroxyethyl (meth) acrylamide, N- (1,1-dimethyl-2-phenyl) ethyl (meth) acrylamide, N-diphenylmethyl (meth) acrylamide, N-phthalimidomethyl (meth) acrylamide, N- (1 , 1′-dimethyl-3- (1,2,4-triazol-1-yl)) propyl (meth) acrylamide or the like is preferable, and N, N-dimethylacrylamide or N-hydroxyethylacrylamide is more preferable. .

(Polymerization initiator)
The ink composition used in the present invention preferably contains a polymerization initiator.
Examples of the polymerization initiator include a radical polymerization initiator and a cationic polymerization initiator, but it is more preferable to contain a radical polymerization initiator.
As the polymerization initiator, a known polymerization initiator can be used. The polymerization initiator that can be used in the present invention may be used alone or in combination of two or more. Moreover, you may use together a radical polymerization initiator and a cationic polymerization initiator.
The polymerization initiator that can be used in the present invention is preferably a compound that absorbs ultraviolet rays and generates a polymerization initiating species.

Polymerization initiators that can be used in the present invention include (a) aromatic ketones, (b) acylphosphine compounds, (c) aromatic onium salt compounds, (d) organic peroxides, (e) thio compounds, (F) hexaarylbiimidazole compound, (g) ketoxime ester compound, (h) borate compound, (i) azinium compound, (j) metallocene compound, (k) active ester compound, (l) having a carbon halogen bond Compounds, and (m) alkylamine compounds. These polymerization initiators may use the above compounds (a) to (m) alone or in combination. Details of the polymerization initiator are known to those skilled in the art, and are described, for example, in JP-A-2009-185186.
The polymerization initiator in the present invention is suitably used alone or in combination of two or more, but it is preferable to use two or more in combination.

  As the polymerization initiator, use at least one compound selected from the group consisting of a bisacylphosphine compound, a monoacylphosphine compound, an α-hydroxyketone compound, an α-aminoketone compound, a thioxanthone compound, and a thiochromanone compound. It is preferable to use at least two compounds selected from the group consisting of bisacylphosphine compounds, monoacylphosphine compounds, α-hydroxyketone compounds, α-aminoketone compounds, thioxanthone compounds, and thiochromanone compounds. .

Preferred examples of the bisacylphosphine compound and the monoacylphosphine compound include bisacylphosphine oxide compounds and monoacylphosphine compounds described in paragraphs 0080 to 0098 of JP-A-2009-096985.
Among these, as the bisacylphosphine oxide compound, bis (2,4,6-trimethylbenzoyl) phenylphosphine oxide is preferable.
As the monoacylphosphine oxide compound, 2,4,6-trimethylbenzoyldiphenylphosphine oxide is preferable.

Examples of α-hydroxyketone compounds include 1- [4- (2-hydroxyethoxy) -phenyl] -2-hydroxy-2-methyl-1-propan-1-one and 2-hydroxy-2-methyl-1-phenyl. Propan-1-one, 1-hydroxycyclohexyl phenyl ketone and the like can be mentioned.
Examples of the α-aminoketone compound include 2-methyl-1-phenyl-2-morpholinopropan-1-one, 2-methyl-1- [4- (hexyl) phenyl] -2-morpholinopropan-1-one, 2-ethyl-2-dimethylamino-1- (4-morpholinophenyl) -butan-1-one and the like can be mentioned.

Preferred examples of the thioxanthone compound include 2,4-diethylthioxanthone, 2-isopropylthioxanthone, and 4-isopropylthioxanthone.
Preferred examples of the thiochromanone compound include the following (I-1) to (I-31), more preferably (I-14), (I-17), and (I-19), and (I- 14) is particularly preferable.

≪Sensitizer≫
The polymerization initiator in the present invention may contain a compound functioning as a sensitizer (hereinafter also simply referred to as “sensitizer”) in order to absorb specific ultraviolet rays and promote decomposition of the polymerization initiator. .
Examples of the sensitizer include polynuclear aromatics (eg, pyrene, perylene, triphenylene, 2-ethyl-9,10-dimethoxyanthracene), xanthenes (eg, fluorescein, eosin, erythrosine, rhodamine B, Rose Bengal etc.), cyanines (eg thiacarbocyanine, oxacarbocyanine etc.), merocyanines (eg merocyanine, carbomerocyanine etc.), thiazines (eg thionine, methylene blue, toluidine blue etc.), acridines (eg , Acridine orange, chloroflavin, acriflavine, etc.), anthraquinones (eg, anthraquinone, etc.), squariums (eg, squalium), coumarins (eg, 7-diethylamino-4-methylcoumarin), benzopheno Class (e.g., benzophenone), thioxanthones (e.g., isopropylthioxanthone, etc.), a thiochromanone compound (e.g., a thiochromanone etc.) and the like.
Especially, as a sensitizer, thioxanthone is preferable and isopropyl thioxanthone is more preferable.
Moreover, a sensitizer may be used individually by 1 type and may use 2 or more types together.

The ink composition that can be used in the present invention preferably contains at least a compound represented by the following formula (1) or (2) as a sensitizer. By using the compound represented by the formula (1) or the formula (2), the amount of migration of components in the film to the outside (migration) is small, the odor of the printed matter is further suppressed, and the curability and blocking resistance are excellent. An ink jet ink composition is obtained.
Moreover, the undercoat liquid which can be used for this invention may contain the compound represented by following formula (1) or Formula (2).

（式（１）及び式（２）中、Ｒ¹、Ｒ²、Ｒ³及びＲ⁴はそれぞれ独立に、炭素数１〜５のアルキル基、又は、ハロゲン原子を表し、ｘ及びｙはそれぞれ独立に、２〜４の整数を表し、ｊ及びｍはそれぞれ独立に、０〜４の整数を表し、ｋ及びｎはそれぞれ独立に、０〜３の整数を表し、ｊ、ｋ、ｍ及びｎが２以上の整数のとき、複数存在するＲ¹、Ｒ²、Ｒ³及びＲ⁴はそれぞれ同一でも異なっていてもよく、Ｘ¹は炭化水素鎖、エーテル結合、エステル結合のいずれかを少なくとも含むｘ価の連結基を表し、Ｘ²は炭化水素鎖、エーテル結合、エステル結合のいずれかを少なくとも含むｙ価の連結基を表す。）

(In Formula (1) and Formula (2), R ¹ , R ² , R ³ and R ⁴ each independently represents an alkyl group having 1 to 5 carbon atoms or a halogen atom, and x and y are each independently Each represents an integer of 2 to 4, j and m each independently represents an integer of 0 to 4, k and n each independently represents an integer of 0 to 3, and j, k, m and n are When it is an integer of 2 or more, a plurality of R ¹ , R ² , R ³ and R ⁴ may be the same or different, and X ¹ includes at least ^one of a hydrocarbon chain, an ether bond and an ester bond x And X ² represents a y-valent linking group containing at least one of a hydrocarbon chain, an ether bond, and an ester bond.)

-Compound represented by Formula (1)-
The ink composition preferably contains a compound represented by the formula (1) as a sensitizer.
In formula (1), R ¹ and R ² each independently represents an alkyl group having 1 to 5 carbon atoms or a halogen atom, and the alkyl group having 1 to 5 carbon atoms is linear, branched or cyclic However, it is preferably linear or branched, preferably an alkyl group having 1 to 4 carbon atoms, more preferably an alkyl group having 2 or 3 carbon atoms, and ethyl. More preferably, it is a group or an isopropyl group.
Examples of the halogen atom include a fluorine atom, a chlorine atom, a bromine atom and an iodine atom, and a chlorine atom is preferable.
Among these, R ¹ and R ² are particularly preferably each independently an ethyl group, an isopropyl group, or a chlorine atom.
In formula (1), j represents an integer of 0 to 4, preferably 0 to 2, and more preferably 0 or 1. When j is an integer of 2 or more, a plurality of R ¹ may be the same or different.
In formula (1), k represents an integer of 0 to 3, preferably 0 to 2, more preferably 0 or 1, and still more preferably 0. When k is an integer of 2 or more, a plurality of R ² may be the same or different.
In formula (1), x represents an integer of 2 to 4, preferably 3 or 4, and more preferably 4.

In formula (1), X ¹ is an x-valent hydrocarbon chain having 2 to 300 carbon atoms which may contain an ether bond (—O—) and / or an ester bond (— (C═O) —O—). An x-valent linking group consisting of
In formula (1), the thioxanthone structure (the structure represented in [] in formula (1)) excluding X ¹ as a linking group has a plurality (x), but they are the same or different from each other. There is no particular limitation. From the viewpoint of synthesis, they are preferably the same.

  In the compound represented by the above formula (1), the position of substitution to thioxanthone is represented as follows.

When the substitution position of X ¹ is 1 to 4 positions, the substitution position of X ¹ is preferably the 2nd, 3rd or 4th position, more preferably the 2nd or 4th position. More preferably, it is a position.
The substitution position of R ¹ is not particularly limited, but is preferably 6-position or 7-position, and more preferably 6-position.
Further, the substitution position of R ² is not particularly limited, but is preferably 1-position, 2-position or 3-position, and more preferably 1-position.

  The compound represented by the formula (1) is preferably a compound represented by the following formula (1 ′).

R ^1, R ^2, j and k in the formula (1 ') are each and R ^1, R ^2, j and k synonymous in the formula (1), and preferred ranges are also the same.
In formula (1 ′), R ¹¹ each independently represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, preferably a hydrogen atom, a methyl group or an ethyl group, and more preferably a hydrogen atom.
In formula (1 ′), r each independently represents an integer of 1 to 6, preferably an integer of 1 to 3, more preferably 1 or 2, and still more preferably 1. When r is 2 or more, a plurality of R ¹¹ may be the same or different.
x ′ represents an integer of 2 to 4, preferably 2 or 3, and more preferably 2.
Y ¹ represents a residue obtained by removing a hydrogen atom of x ′ hydroxy groups from a polyhydroxy compound having at least x ′ hydroxy groups, and all (x ′ pieces) are obtained from polyhydroxy compounds having x ′ hydroxy groups. It is preferably a residue obtained by removing a hydrogen atom from a hydroxy group. Specifically, a residue obtained by removing hydrogen atoms of x ′ hydroxy groups from a polyhydroxy compound selected from the group consisting of ethylene glycol, propylene glycol, butylene glycol, glycerin, trimethylolpropane, ditrimethylolpropane, and pentaerythritol. It is preferably a group, and is preferably a residue obtained by removing all hydrogen atoms from a hydroxy group.
In formula (1 ′), A ¹ represents a group selected from the group consisting of the following (i) to (iii).

（式（i）〜式（iii）中、Ｒ¹²及びＲ¹³のいずれか一方は水素原子を表し、他方は水素原子、メチル基又はエチル基を表し、ａは１又は２の整数を表し、ｂは４又は５の整数を表し、ｚは１〜２０の整数を表し、＊はカルボニル炭素との結合位置を表し、＊＊はＹ¹との結合位置を表す。）

(In Formula (i) to Formula (iii), any one of R ¹² and R ¹³ represents a hydrogen atom, the other represents a hydrogen atom, a methyl group, or an ethyl group, a represents an integer of 1 or 2, b represents an integer of 4 or 5, z represents an integer of 1 to 20, * represents a bonding position with the carbonyl carbon, and ** represents a bonding position with Y ^1. )

A ¹ is preferably a group represented by the formula (i), and * — (OCH ₂ CH ₂ ) _z — **, * — (OCH ₂ CH ₂ CH ₂ CH ₂ ) _z — **, or , * —O (CH (CH ₃ ) CH ₂ ) _z — ** is more preferable. In this case, z is more preferably an integer of 3 to 10.

The molecular weight of the compound represented by the formula (1) is preferably 500 to 3,000, more preferably 800 to 2,500, and still more preferably 1,000 to 2,000.
When the molecular weight is 500 or more, elution of the compound from the cured film is suppressed, and an ink composition in which migration, odor, and blocking are suppressed is obtained. On the other hand, when it is 3,000 or less, the steric hindrance of the molecule is small, the degree of freedom of the molecule in the liquid / film is maintained, and high sensitivity is obtained.
In addition, when the compound represented by Formula (1) is a mixture of a plurality of compounds having different carbon numbers and the like, the weight average molecular weight is preferably in the above range.

  Specific examples of the compound represented by the formula (1) are shown below, but the present invention is not limited to the following compounds.

  Among these, the compound (IA) or (IE) is preferable, and the compound (IE) is more preferable.

  As the compound represented by the formula (1), a commercially available compound can also be used. Specifically, SPEEDCURE 7010 (1,3-di ({α- [1-chloro-9-oxo-9H-thioxanthen-4-yl] oxy} acetylpoly [oxy (1-methylethylene)]) oxy) -2 , 2-bis ({α- [1-chloro-9-oxo-9H-thioxanthen-4-yl] oxy} acetylpoly [oxy (1-methylethylene)]) oxymethyl) propane, CAS No. 1003567-83-6) OMNIPOL TX (Polybutyleneglycol bis (9-oxo-9H-thioxanthenyloxy) acetate, CAS No. 813452-37-8).

  The compound represented by the formula (1) can be produced by a known reaction and is not particularly limited. For example, the compound represented by the formula (1 ′) is represented by the following formula (1-1). It can prepare by making the compound and the compound represented by following formula (1-2) react.

Equation (1-1) and formula R ^1, R ^2, R ¹¹ in ^{(1-2), A 1, Y} 1, j, k, r and x 'has the formula (1' R ¹ in), R ² , R ¹¹ , A ¹ , Y ¹ , j, k, r and x ′, and the preferred range is also the same.
The above reaction is preferably performed in the presence of a solvent, and examples of suitable solvents include aromatic hydrocarbons such as benzene, toluene, and xylene.
The catalyst is preferably used in the presence of a catalyst. Examples of the catalyst include sulfonic acid (for example, p-toluenesulfonic acid, methanesulfonic acid), inorganic acid (for example, sulfuric acid, hydrochloric acid, phosphoric acid), Lewis acid (aluminum chloride, three Examples thereof include boron fluoride and organotitanate.
The reaction temperature and reaction time are not particularly limited.
After completion of the reaction, the product can be separated by isolation from the reaction mixture by known means, washing as necessary and drying.

-Compound represented by Formula (2)-
The ink composition preferably contains a compound represented by the formula (2) as a sensitizer.

（式（２）中、Ｒ³及びＲ⁴はそれぞれ独立に炭素数１〜５のアルキル基、又は、ハロゲン原子を表し、ｍは０〜４の整数を表し、ｎは０〜３の整数を表し、ｙは２〜４の整数を表し、ｍ及びｎが２以上の整数のとき、複数存在するＲ³及びＲ⁴はそれぞれ同一でも異なっていてもよく、Ｘ²は炭化水素鎖、エーテル結合、エステル結合のいずれかを少なくとも含むｙ価の連結基を表す。）

(In the formula (2), R ³ and R ⁴ each independently represents an alkyl group having 1 to 5 carbon atoms or a halogen atom, m represents an integer of 0 to 4, and n represents an integer of 0 to 3. Y represents an integer of 2 to 4, and when m and n are integers of 2 or more, a plurality of R ³ and R ⁴ may be the same or different, and X ² represents a hydrocarbon chain or an ether bond. And represents a y-valent linking group containing at least one of ester bonds.)

In formula (2), R ³ and R ⁴ each independently represents an alkyl group having 1 to 5 carbon atoms or a halogen atom, and the alkyl group having 1 to 5 carbon atoms is linear, branched or cyclic However, it is preferably linear or branched, preferably an alkyl group having 1 to 4 carbon atoms, more preferably an alkyl group having 2 or 3 carbon atoms, and ethyl. More preferably, it is a group or an isopropyl group. Examples of the halogen atom include a fluorine atom, a chlorine atom, a bromine atom and an iodine atom, and a chlorine atom is preferable. R ³ and R ⁴ are particularly preferably an ethyl group, an isopropyl group, or a chlorine atom.
In formula (2), m represents an integer of 0 to 4, preferably 0 to 2, and more preferably 0 or 1. When m is an integer of 2 or more, a plurality of R ³ may be the same or different from each other.
In formula (2), n represents an integer of 0 to 3, preferably 0 to 2, more preferably 0 or 1, and still more preferably 0. When n is an integer of 2 or more, a plurality of R ⁴ may be the same or different.
In formula (2), y represents an integer of 2 to 4, preferably 2 or 3, and more preferably 2.

In formula (2), X ² is a y-valent linkage containing at least one selected from the group consisting of a hydrocarbon chain, an ether bond (—O—) and an ester bond (— (C═O) —O—). Represents a group.
In the formula (2), there are a plurality (y) of benzophenone structures (the structures represented in [] in the formula (2)) excluding the linking group X ² , but they are the same or different from each other. There is no particular limitation. From the viewpoint of synthesis, they are preferably the same.

  In the compound represented by the above formula (2), the position of substitution with benzophenone is represented as follows.

Assuming that the substitution position of X ² is 1 to 5, the substitution position of X ² is preferably the 2nd or 3rd position, and more preferably the 3rd position.
The substitution position of R ³ is not particularly limited, but is preferably 2′-position or 3′-position, and more preferably 3′-position.
Further, the substitution position of R ⁴ is not particularly limited, but is preferably 2-position, 3-position or 4-position.

  The compound represented by the formula (2) is preferably a compound represented by the following formula (2 ′).

R ^3, R ⁴ in the formula (2 '), m and n are each and R ^3, R ^4, m and n in Formula (2) synonymous, and preferred ranges are also the same.
In formula (2 ′), R ²¹ each independently represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, preferably a hydrogen atom, a methyl group or an ethyl group, and more preferably a hydrogen atom.
In formula (2 ′), each t independently represents an integer of 1 to 6, preferably an integer of 1 to 3, more preferably 1 or 2, and still more preferably 1. When t is 2 or more, a plurality of R ²¹ may be the same or different.
y ′ represents an integer of 2 to 4, preferably 2 or 3, and more preferably 2.
Y ² represents a residue obtained by removing a hydrogen atom of y ′ hydroxy groups from a polyhydroxy compound having at least y ′ hydroxy groups, and all (y ′ groups) are obtained from polyhydroxy compounds having y ′ hydroxy groups. It is preferably a residue obtained by removing a hydrogen atom from a hydroxy group. Specifically, a residue obtained by removing hydrogen atoms of y ′ hydroxy groups from a polyhydroxy compound selected from the group consisting of ethylene glycol, propylene glycol, butylene glycol, glycerin, trimethylolpropane, ditrimethylolpropane and pentaerythritol. It is preferably a group, and is preferably a residue obtained by removing all hydrogen atoms from a hydroxy group.
In formula (2 ′), A ² represents a group selected from the group consisting of the following formulas (i) to (iii).

（式（i）〜式（iii）中、Ｒ¹²及びＲ¹³のいずれか一方は水素原子を表し、他方は水素原子、メチル基又はエチル基を表し、ａは１又は２の整数を表し、ｂは４又は５の整数を表し、ｚは１〜２０の整数を表す。なお、＊はカルボニル炭素との結合位置を示し、＊＊はＹ²との結合位置を示す。）

(In Formula (i) to Formula (iii), any one of R ¹² and R ¹³ represents a hydrogen atom, the other represents a hydrogen atom, a methyl group, or an ethyl group, a represents an integer of 1 or 2, b represents an integer of 4 or 5, and z represents an integer of 1 to 20. In addition, * represents a bonding position with the carbonyl carbon, and ** represents a bonding position with Y ^2. )

A ² is preferably a group represented by the formula (i), and * — (OCH ₂ CH ₂ ) _z — **, * — (OCH ₂ CH ₂ CH ₂ CH ₂ ) _z — **, or , * —O (CH (CH ₃ ) CH ₂ ) _z — ** is more preferable. In this case, z is more preferably an integer of 3 to 10.

The molecular weight of the compound represented by the formula (2) is preferably 500 to 3,000, more preferably 800 to 2,500, and still more preferably 1,000 to 2,000.
When the molecular weight is 500 or more, elution of the compound from the cured film is suppressed, and an ink composition in which migration, odor, and blocking are suppressed is obtained. On the other hand, when it is 3,000 or less, the steric hindrance of the molecule is small, the degree of freedom of the molecule in the liquid / film is maintained, and high sensitivity is obtained.
In addition, when the compound represented by Formula (2) is a mixture of a plurality of compounds having different carbon numbers and the like, the weight average molecular weight is preferably in the above range.

  Specific examples of the compound represented by formula (2) are shown below, but the present invention is not limited to the following compounds.

  As the compound represented by the formula (2), a commercially available compound can also be used. Specifically, OMNIPOL BP (Polybutyleneglycol bis (4-benzoylphenoxy) acetate, CAS No. 515136-48-8) is exemplified.

  The compound represented by the formula (2) can be produced by a known reaction and is not particularly limited. For example, the compound represented by the above formula (2 ′) is represented by the following formula (2-1): It can prepare by making the compound represented and the compound represented by following formula (2-2) react.

（式（２−１）及び式（２−２）におけるＲ³、Ｒ⁴、Ｒ²¹、Ａ²、Ｙ²、ｍ、ｎ、ｔ及びｙ’は式（２’）におけるＲ³、Ｒ⁴、Ｒ²¹、Ａ²、Ｙ²、ｍ、ｎ、ｔ及びｙ’とそれぞれ同義であり、好ましい範囲も同様である。）

(R ³ in the formula (2-1) and formula ^{(2-2), R 4, R} 21, A 2, Y 2, m, n, t and y 'formula (2' R ³ in), R ⁴ , R ²¹ , A ² , Y ² , m, n, t and y ′, respectively, and the preferred range is also the same.)

The above reaction is preferably performed in the presence of a solvent, and examples of suitable solvents include aromatic hydrocarbons such as benzene, toluene, and xylene.
The catalyst is preferably used in the presence of a catalyst. Examples of the catalyst include sulfonic acid (for example, p-toluenesulfonic acid, methanesulfonic acid), inorganic acid (for example, sulfuric acid, hydrochloric acid, phosphoric acid), Lewis acid (aluminum chloride, three Examples thereof include boron fluoride and organotitanate.
The reaction temperature and reaction time are not particularly limited.

  After completion of the reaction, the product can be separated by isolation from the reaction mixture by known means, washing as necessary and drying.

The content of the compound represented by the formula (2) is preferably 1 to 5% by mass of the entire ink composition from the viewpoint of increasing sensitivity and suppressing migration, odor and blocking, and 2 to 4%. More preferably, it is mass%.
Moreover, as a compound represented by Formula (2), the compound represented by Formula (2-1) is more preferable.

  The content of the compound represented by the formula (1) or the formula (2) is preferably 0.01 to 10% by mass, and preferably 0.05 to 8.0% by mass with respect to the entire ink composition. More preferably, it is more preferably 0.1 to 5.0% by mass, and particularly preferably 0.1 to 2.4% by mass. Within the above range, the curability is excellent.

The total content of the polymerization initiator is preferably 1.0 to 15.0% by mass of the total ink composition, more preferably 1.5 to 10.0% by mass, and 3.0 to 8%. More preferably, it is 0.0 mass%. It is excellent in curability as it is the said range.
The content ratio (mass ratio) between the polymerization initiator and the polymerizable compound used in combination with the polymerization initiator is preferably polymerization initiator: polymerizable compound = 0.5: 100 to 30: 100, respectively. 1: 100 to 15: 100 is more preferable, and 2: 100 to 15: 100 is even more preferable.

  The ink composition in the present invention does not contain a polymerization initiator having a molecular weight of less than 340, or its content exceeds 0% by mass of the entire ink composition from the viewpoint of suppressing migration, odor and blocking. It is preferably 0% by mass or less, not contained, or more preferably greater than 0% by mass and 0.5% by mass or less, not contained, or greater than 0% by mass and 0.3% by mass More preferably, it is particularly preferably not contained.

[Surfactant]
The ink composition used in the present invention preferably contains a surfactant.
As the surfactant, a silicon-based surfactant or an acetylene glycol-based surfactant is preferable, and either a silicon-based surfactant or an acetylene glycol-based surfactant is included, but both are included. May be.
Further, the ink composition of the present invention may contain one kind of surface tension adjusting agent alone or two or more kinds.

Examples of silicone surfactants include polyether-modified silicone surfactants, methylstyrene-modified silicone surfactants, olefin-modified silicone surfactants, alcohol-modified silicone surfactants, alkyl-modified silicone surfactants, And polydialkylsiloxanes.
Moreover, as a silicon-type surfactant, a commercial item can be widely used, for example, BYK307, 322, 323, 331, 333, 347, 348, 349, 377, 378, UV3510, 3570 (made by BYK Chemie), KF351, 352, 353, 354, 355, 412, 413, 414, 618, 945, 8012, 865, 6001, 6002 (manufactured by Shin-Etsu Silicon Co., Ltd.), TSF4440, 4460, 4700, 4701, 4421 (GE Toshiba Silicon Co., Ltd.) Manufactured), and the like.

  Examples of the acetylene glycol surfactants include 2,4,7,9-tetramethyl-5-decyne-4,7-diol and 2,4,7,9-tetramethyl-5-decyne-4, An alkylene oxide adduct of 7-diol can be used, and at least one selected from these is preferable. Examples of commercially available products of these compounds include E series such as Olphine E1010 manufactured by Nissin Chemical Industry Co., Ltd.

  When a surfactant (surface tension adjusting agent) is contained in the ink composition, the surfactant has a surface tension of 20 to 60 mN / m from the viewpoint of satisfactorily discharging the ink composition by an ink jet method. It is preferable to contain the quantity of the range which can be adjusted, More preferably, it is 20-45 mN / m from the point of surface tension, More preferably, it is 25-40 mN / m.

  The specific amount of the surfactant in the ink composition is not particularly limited, except that the range of the surface tension is preferable, and is preferably 0.1% by mass or more, more preferably 0.1 to 10% by mass. %, And more preferably 0.1 to 3% by mass.

(Polymerization inhibitor)
Moreover, it is preferable that the radically polymerizable composition of this invention contains a polymerization inhibitor from a viewpoint of storage stability and suppression of head clogging.
The content of the polymerization inhibitor is preferably 0.01 to 5% by mass and more preferably 0.1 to 2% by mass with respect to the total mass of the ink composition.
Further, the ink composition of the present invention may contain one kind of polymerization inhibitor or two or more kinds.
Examples of the polymerization inhibitor include nitroso polymerization inhibitors, hindered amine polymerization inhibitors, hydroquinone, benzoquinone, p-methoxyphenol, TEMPO, TEMPOL, and cuperon Al. Among these, a nitroso polymerization inhibitor is preferable, and examples include 1-nitroso-2-naphthol, 2-nitroso-1-naphthol, nitrosobenzene, tris (N-nitroso-N-phenylhydroxyamine) ammonium salt, and the like. Tris (N-nitroso-N-phenylhydroxyamine) ammonium salt is particularly preferred.

[Colorant]
Moreover, when using the ink composition of this invention as a coloring ink composition, it is preferable to contain the following coloring agents.
The colorant that can be used in the present invention is not particularly limited, but pigments and oil-soluble dyes that are excellent in weather resistance and excellent in color reproducibility are preferable, and are arbitrarily selected from known colorants such as soluble dyes. Can be used. From the viewpoint of not reducing the sensitivity of the curing reaction by actinic radiation, it is preferable to select a compound that does not function as a polymerization inhibitor in the polymerization reaction, which is a curing reaction, as the colorant that can be suitably used in the present invention.

≪Pigment≫
Although it does not necessarily limit as a pigment which can be used for this invention, 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 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, 208, 216, 226, 257, Pigment Violet 3, 19, 23, 29, 30, 37, 50, 88, Pigment Orange 13, 16, 20, 36,
Pigment Blue 1,15,15: 1,15: 2,15: 3,15: 4,15: 6,16,17-1,22,27,28,29,36,60 as a blue or cyan pigment ,
As a green pigment, Pigment Green 7, 26, 36, 50,
As yellow pigments, 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, 153, 154, 155, 157, 166, 167, 168, 180, 185, 193,
As the black pigment, Pigment Black 7, 28, 26,
As a white pigment, Pigment White 6, 18, 21
Etc. can be used according to the purpose.

≪Oil-soluble dye≫
Below, the oil-soluble dye which can be used by this invention is demonstrated.
The oil-soluble dye that can be used in the present invention means a dye that is substantially insoluble in water. Specifically, the solubility in water at 25 ° C. (the mass of the dye that can be dissolved in 100 g of water) is 1 g or less, preferably 0.5 g or less, more preferably 0.1 g or less. Therefore, the oil-soluble dye means a so-called water-insoluble pigment or oil-soluble dye, and among these, an oil-soluble dye is preferable.

  Among the oil-soluble dyes usable in the present invention, any yellow dye can be used. For example, phenols, naphthols, anilines, pyrazolones, pyridones, aryl or heteryl azo dyes having open-chain active methylene compounds as coupling components; for example, azomethine dyes having open-chain active methylene compounds as coupling components; Examples include methine dyes such as benzylidene dyes and monomethine oxonol dyes; quinone dyes such as naphthoquinone dyes and anthraquinone dyes; and other dye species such as quinophthalone dyes, nitro / nitroso dyes, and acridines. And dyes and acridinone dyes.

  Among the oil-soluble dyes usable in the present invention, any magenta dye can be used. For example, aryl or hetaryl azo dyes having phenols, naphthols, anilines as coupling components; for example, azomethine dyes having pyrazolones, pyrazolotriazoles as coupling components; for example arylidene dyes, styryl dyes, merocyanine dyes, oxonol dyes Methine dyes; carbonium dyes such as diphenylmethane dyes, triphenylmethane dyes and xanthene dyes; quinone dyes such as naphthoquinone, anthraquinone and anthrapyridone; condensed polycyclic dyes such as dioxazine dyes, etc. Can be mentioned.

  Among the oil-soluble dyes applicable to the present invention, any cyan dye can be used. For example, indoaniline dyes, indophenol dyes or azomethine dyes having pyrrolotriazoles as coupling components; polymethine dyes such as cyanine dyes, oxonol dyes, merocyanine dyes; carbonium dyes such as diphenylmethane dyes, triphenylmethane dyes, xanthene dyes Phthalocyanine dyes; anthraquinone dyes; for example, aryl or heteryl azo dyes having phenols, naphthols and anilines as coupling components; indigo / thioindigo dyes;

  Each of the above dyes may exhibit yellow, magenta, and cyan colors only after a part of chromophore (color-forming atomic group) is dissociated. In this case, the counter cation may be an alkali metal or ammonium. Such inorganic cations may be used, and organic cations such as pyridinium and quaternary ammonium salts may be used, and furthermore, polymer cations having such a partial structure may be used.

Although not limited to the following, preferred specific examples include C.I. I. Solvent Black 3, 7, 27, 29 and 34; C.I. I. Solvent Yellow 14, 16, 19, 29, 30, 56, 82, 93 and 162; C.I. I. Solvent Red 1, 3, 8, 18, 24, 27, 43, 49, 51, 72, 73, 109, 122, 132 and 218; I. Solvent Violet 3; C.I. I. Solvent Blue 2,11,25,35,38,67 and 70; I. Solvent Green 3 and 7; I. Solvent orange 2; and the like.
Among these, particularly preferred are the Black Black PC-0850, Oil Black HBB, Oil Yellow 129, Oil Yellow 105, Oil Pink 312, Oil Red 5B, Oil Scallet 308, Vali Fast Blue chemistry 2606e Bile 2OSe 2B eO (Manufactured by Co., Ltd.), Aizen Spillon Blue GNH (manufactured by Hodogaya Chemical Co., Ltd.), Neopen Yellow 075, Neopen Magenta SE1378, Neopen Blue 808, Neopen Blue FF4012, and Neo42 Cy FF4012.
In the present invention, the oil-soluble dye may be used singly or in combination of several kinds.

Moreover, when using an oil-soluble dye as a colorant, other water-soluble dyes, disperse dyes, pigments, and other colorants can be used in combination as long as the effects of the present invention are not impaired.
In the present invention, a disperse dye can be used as long as it is soluble in a water-immiscible organic solvent. The disperse dye generally includes a water-soluble dye, but in the present invention, the disperse dye is preferably used as long as it is 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; 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;

  It is preferable that the colorant that can be used in the present invention 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 added by directly adding it together with each component in the preparation of the ink composition. However, in order to improve dispersibility, the colorant is added in advance to a dispersion substrate such as a solvent or a radical polymerizable compound used in the present invention. It can also be blended after being uniformly dispersed or dissolved.
In the present invention, in order to avoid the problem of deterioration of solvent resistance when the solvent remains in the cured image and the problem of VOC (Volatile Organic Compound) of the remaining solvent, the colorant is a radical polymerizable compound. It is preferable to add and mix in advance in such a dispersion substrate. In consideration of only dispersibility, it is preferable to select a monomer having a low viscosity as the polymerizable compound used for adding the colorant.

  These colorants may be used by appropriately selecting one type or two or more types according to the purpose of use of the ink composition.

When using a colorant such as a pigment that remains solid in the ink composition, the average particle diameter of the colorant particles is preferably 0.005 to 0.5 μm, more preferably 0.01 to It is preferable to set the colorant, the dispersant, the dispersion base material, the dispersion conditions, and the filtration conditions so as to be 0.45 μm, more preferably 0.015 to 0.4 μm. This particle size control is preferable because clogging of the head nozzle can be suppressed and ink storage stability, ink transparency, and curing sensitivity can be maintained.
In the present invention, the content of the colorant in the ink composition is appropriately selected depending on the color and purpose of use, but is preferably 0.01 to 30% by mass with respect to the mass of the entire ink composition.

[Dispersant]
The ink composition of the present invention preferably contains a dispersant for the purpose of improving the dispersibility of the colorant.
As the dispersant, a polymer dispersant is preferable. The “polymer dispersant” in the present invention means a dispersant having a mass average molecular weight of 1,000 or more.

Examples of the polymer dispersant include DISPERBYK-101, DISPERBYK-102, DISPERBYK-103, DISPERBYK-106, DISPERBYK-111, DISPERBYK-161, DISPERBYK-162, DISPERBYK-163, DISPERBYK-164, DISPERBYK-166, DISPERBYK-166, and DISPERBYK-166. , 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 Corporation), Ionette S-20 (manufactured by Sanyo Chemical Industries, Ltd.); Disparon 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 mass with respect to the mass of the entire ink composition.

[Other ingredients]
In addition to the above components, the ink composition of the present invention includes an organic solvent, a co-sensitizer, an ultraviolet absorber, an antioxidant, an anti-fading agent, a conductive salt, a polymer compound, a basic compound, if necessary. Compounds, leveling additives, matting agents, polyester resins for adjusting film properties, polyurethane resins, vinyl resins, acrylic resins, rubber resins, waxes and the like may be included. As these other components, known components can be used, for example, those described in JP-A-2009-212416.

≪Organic solvent≫
In order to improve the adhesion to the substrate, an extremely small amount of an organic solvent may be added to the ink composition of the present invention.
Examples of the solvent that can be used in the ink composition of the present invention include ketone solvents such as acetone, methyl ethyl ketone, and diethyl ketone, methanol, ethanol, 2-propanol, 1-propanol, 1-butanol, tert-butanol, and the like. Alcohol solvents, chlorine solvents such as chloroform and methylene chloride, aromatic solvents such as benzene and toluene, ester solvents such as ethyl acetate, butyl acetate and isopropyl acetate, diethyl ether, tetrahydrofuran, dioxane, and diethylene glycol diethyl ether Examples include ether solvents, glycol ether solvents such as ethylene glycol monomethyl ether and ethylene glycol dimethyl ether, and lactone solvents such as γ-butyrolactone.
Moreover, when the ink composition in this invention contains the organic solvent, it is preferable to provide a drying process between an ink discharge process and a hardening process.
In the case of containing an organic solvent, it is effective to add the solvent within a range that does not cause the problem of solvent resistance and VOC. It is in the range of 1-3% by weight.

<Ink ejection process>
In the ink ejection step in the image forming method of the present invention, ultraviolet curable ink compositions having different hues are ejected from two or more inkjet heads.
Specifically, the above-mentioned ultraviolet curable ink composition is applied onto a substrate by an ink jet method from an ejection port arranged in a nozzle plate provided in the above-described ink jet head. In this step, the ink composition can be applied in an image form on the substrate, and a desired visible image can be formed.
The appropriate amount of liquid discharged from the discharge ports arranged on the nozzle plate is 10 pl to 20 pl, and preferably 10 pl to 15 pl.
In the ejection step of ejecting the ink composition, at least four ink compositions of magenta ink, light magenta ink, cyan ink, and light cyan ink are ejected.

As described above, in the ink ejection step, at least four colors of magenta ink, light magenta ink, cyan ink, and light cyan ink are used, but ink compositions of other colors may be further used.
Specifically, it is also preferable to further contain black, yellow, and white ink compositions. In this case, the ink composition includes black ink, yellow ink, white ink, magenta ink, cyan ink, light cyan ink, And a total of seven colors of light magenta ink.
The “light cyan ink” in the present invention refers to an ink composition in which the colorant content is 1/3 to 1/10 of the “cyan ink”, and the content is 1/5 to 1/10. Preferably there is.
The “light magenta ink” in the present invention refers to an ink composition in which the colorant content is 1/3 to 1/10 of the “magenta ink”, and the content is 1/3 to 1/5. It is preferable that

  The order of each colored ink composition to be ejected is not particularly limited, but it is preferably ejected from a colored ink composition having low lightness. As the ink composition, black ink, yellow ink, white ink, magenta ink are used. , Cyan ink, light cyan ink, and light magenta ink are used on the support in the order of black, cyan, magenta, yellow, light cyan, light magenta, and white. It is preferable. This is because, when the ink compositions are stacked in order from the lightness of the lightness, the irradiation line easily reaches the lower ink composition, and good curing sensitivity, reduction of residual monomers, and improvement of adhesion can be expected.

(Pinning process)
The image forming method of the present invention includes a step of semi-curing the ejected ink composition by ultraviolet irradiation at the end of ejection of the ink composition of each color.

<Semi-cured>
In the present invention, “semi-cured” means partially cured (partial cured), which means a state where the ink composition is partially cured but not completely cured. Specifically, a state in which a penetrating medium such as plain paper is pressed against the cured ink composition and 10% by mass to 90% by mass of the ink composition is transferred is referred to as semi-cured. It is preferable that a mass% to 80 mass% is transferred. Moreover, the state which does not transfer at all is called complete curing.
When the ink composition applied on the substrate is semi-cured, the degree of curing in the depth direction of the ink composition may be uneven, and the ink composition is cured in the depth direction. It is preferable that it is advanced.

  For example, when a radically polymerizable ink composition is cured in air or air partially substituted with an inert gas, radical polymerization is performed on the surface of the ink composition in order to suppress the radical polymerization of oxygen. Tends to be disturbed. As a result, the degree of curing in the depth direction becomes non-uniform, curing proceeds more inside the ink composition, and surface curing tends to be delayed.

  As described above, as an example of an embodiment of the present invention, a radical photopolymerizable ink composition is used in the presence of radical polymerization-inhibiting oxygen and partially photocured, whereby the ink composition The degree of cure of can be higher on the inside than on the outside.

  Here, the peak wavelength of the ultraviolet light used depends on the absorption characteristics of the polymerization initiator and the sensitizer, but is preferably 200 to 400 nm, more preferably 300 to 400 nm, for example, 350 More preferably, it is -400 nm.

<Ultraviolet light source>
Mercury lamps, gas / solid lasers, etc. are mainly used as ultraviolet light sources in the pinning process, and mercury lamps and metal halide lamps are widely known as light sources used for curing UV photocurable ink jet recording ink. It has been. However, from the viewpoint of environmental protection, mercury-free is strongly desired, and replacement with a GaN-based semiconductor ultraviolet light-emitting device is very useful industrially and environmentally.
Moreover, it is preferable to use an ultraviolet light emitting diode (UV-LED) and / or an ultraviolet laser diode (LD) as an ultraviolet light source. UV-LEDs and UV-LDs are small, have a long lifetime, high efficiency, and low cost, and are expected as light sources for photo-curable ink jets. For example, Nichia Corporation has introduced a purple LED whose main emission spectrum has a wavelength between 365 nm and 420 nm. If even shorter wavelengths are required, the LED may be an LED capable of emitting ultraviolet light centered between 300 nm and 370 nm as disclosed in US Pat. No. 6,084,250. It can be illustrated. Other ultraviolet LEDs are also available and can be irradiated with ultraviolet light of different wavelengths. A particularly preferable ultraviolet light source in the present invention is a UV-LED, and a UV-LED having a peak wavelength of 350 to 420 nm is particularly preferable.
Note that maximum illumination intensity on the LED of the substrate is preferably from 10 to 2,000 mW / cm ^2, more preferably 20 to 1,000 mW / cm ^2, is 50 to 800 mW / cm ² Is particularly preferred.

<Ultraviolet irradiation method>
In the pinning step, the ink composition is appropriately irradiated with such ultraviolet light for 0.01 to 15 seconds, more preferably 0.05 to 10 seconds.
The irradiation condition of ultraviolet light and the basic irradiation method are disclosed in JP-A-60-132767. Specifically, the ultraviolet light irradiation is performed for a certain period of time after the ink composition has landed (preferably 0.01 to 0.5 seconds, more preferably 0.01 to 0.3 seconds, still more preferably 0.01). ˜0.15 seconds). In this way, by controlling the time from landing to irradiation of the ink composition to an extremely short time, it is possible to prevent the ink composition that has landed on the support from bleeding before curing.

In addition, the polymerization initiation system in the ink composition described above has sufficient sensitivity even with a low output actinic radiation. Therefore, it is appropriate to cure the exposed surface with an illuminance of 10 to 4,000 mW / cm ² , more preferably 20 to 2,500 mW / cm ² .

<Example of recording device>
FIG. 9 is a schematic view showing an example of an ink jet recording apparatus that can be suitably used in the image forming method of the present invention. Hereinafter, the execution method of the pinning process will be described in detail with reference to FIG.

The base material is conveyed by the feed roller 201 and the take-up roller 202, and in FIG. 9, it is conveyed from left to right. An application roller 211 and a UV-LED light source 221 are arranged in the first part in the transport direction. These are used in a step of applying an undercoat liquid on the substrate and a step of semi-curing the undercoat liquid by ultraviolet irradiation, which will be described later.
The seven inkjet heads 241 to 247 respectively correspond to seven colors of black, cyan, magenta, yellow, light cyan, light magenta, and white in the order of the substrate conveyance direction.
Between the inkjet heads 241 to 247, UV-LED light sources 222 to 227 are arranged, respectively, and each time the ejection of each color is completed, ultraviolet rays are irradiated to semi-cure the ejected ink composition.
A nitrogen purge exposure machine 231 for performing a curing process, which will be described later, is disposed further on the side of the substrate transport direction of the inkjet head 247 corresponding to white.

  As in this arrangement example, an ultraviolet light source is arranged between each inkjet head, and the ink composition droplets discharged onto the substrate by each recording head, that is, the image is semi-cured, so that they are close to each other. It is possible to prevent the landing of the ink composition droplets of different colors that have landed and the movement of the landed ink composition droplets.

  In the present image forming method, the substrate transport speed, that is, the printing speed is preferably 20 m / min to 300 m / min, more preferably 25 m / min to 200 m / min, and 30 m / min. More preferably, it is -100 m / min.

(Curing process)
The image forming method of the present invention includes a step of completely curing the ink composition by irradiating ultraviolet rays in an atmosphere having an oxygen concentration of 1% by volume or less.

<Ultraviolet light source>
The ultraviolet light source that can be used in the curing step is the same as the ultraviolet light source that can be used in the pinning step.

<Ultraviolet irradiation method>
In the present invention, the ink composition is completely cured by irradiation with ultraviolet rays in an atmosphere having an oxygen concentration of 1% by volume or less. By suppressing the oxygen concentration in the curing atmosphere, the energy of active rays necessary for curing can be reduced, and it is also effective in improving migration, odor, and shrink, which are important as package print characteristics.
In general, radically-polymerized ink compositions are particularly prone to oxygen polymerization inhibition on the surface in contact with air, and surface curing failure is particularly likely to occur. Due to this curable deterioration of the surface, the monomer remains in the film, or the formation of a cross-linked structure of the film with the polyfunctional monomer makes the performance of keeping low molecular components in the film insufficient, and migration and odor are remarkably deteriorated. However, it is presumed that exposure in an environment having a low oxygen concentration reduces the degree of inhibition of oxygen polymerization and improves migration and odor.
Also, only the surface of the cured film is selectively subjected to oxygen polymerization inhibition, resulting in a difference in curability from the inside of the film where good curability can be obtained, resulting in distribution of volume shrinkage, resulting in packaging A thin support body tends to cause shrinkage. Also in this regard, it is presumed that the shrinkage can be improved by making the volume shrinkage rate uniform between the film surface and the inside by exposing in an environment having a low oxygen concentration.

Normally, the oxygen concentration is 21% by volume in the atmosphere (1 atm). Therefore, in order to reduce the oxygen concentration to 1% by volume or less, (a) the atmosphere at the time of exposure is reduced to 0.047 atm or less. Alternatively, (b) it can be achieved by mixing a gas other than air and oxygen (for example, an inert gas such as nitrogen or argon) in an amount of 95.3% by volume or more with respect to the air.
The poor oxygen atmosphere in the present invention is not particularly limited, and any of the above methods can be used.

The oxygen concentration is preferably 0.8% by volume or less, more preferably 0.5% by volume or less, and particularly preferably 0.1% by volume or less.
There is no particular limitation on the lower limit of the oxygen partial pressure. By substituting the vacuum or atmosphere with a gas other than air (eg, nitrogen), the oxygen partial pressure can be reduced to virtually zero, which is also a preferred method.

FIG. 10 shows an example of the nitrogen purge exposure machine 231 shown in FIG.
As shown in FIG. 10, the LED light source unit 1 is surrounded by an inert gas blanket 2 and connected to an inert gas generator 4 through an inert gas pipe 3. An inert gas generator 4 which is a means for making the atmosphere in the inert gas blanket 2 an oxygen-poor atmosphere supplies an inert gas into the inert gas blanket 2 through an inert gas generation pipe 3. In the initial state, the atmosphere in the inert gas blanket 2 is air, but when the inert gas generator 4 is operated, the air in the inert gas blanket 2 is replaced with the inert gas. In addition, 5 in a figure represents the base material. As described above, N ₂ or the like can be used as the inert gas.

  In the curing step, the ink composition is appropriately irradiated with such ultraviolet light for 0.01 to 15 seconds, more preferably 0.05 to 10 seconds.

In addition, the polymerization initiation system in the ink composition described above has sufficient sensitivity even with a low output actinic radiation. Accordingly, it is appropriate that the exposure surface illuminance is preferably 100 to 4,000 mW / cm ² , more preferably 200 to 5,000 mW / cm ² .

(Other processes)
In addition to the essential steps described above, the image forming method in the present invention includes, as an optional step, an undercoat step for applying an undercoat solution onto a non-penetrable medium, and an undercoat solution semi-curing step for semi-curing the undercoat solution by ultraviolet irradiation. And a discharge step of discharging the ink composition onto the semi-cured undercoat liquid.
As other steps, the image forming method of the present invention preferably includes a drying step and a laminating step as optional steps.

<Undercoating step for applying an undercoating liquid on a non-penetrating medium>
[Undercoat liquid]
The undercoat liquid in the present invention contains at least a polymerizable compound and a photopolymerization initiator. Further, as the undercoat liquid, it is preferable to use the ultraviolet curable ink composition which does not contain a colorant or contains a white colorant.

The undercoat liquid preferably has a viscosity of 10 mPa · s to 2,000 mPa · s, and more preferably 50 mPa · s to 1,200 mPa · s.
By setting the viscosity of the undercoat liquid to 10 mPa · s or more, more preferably 50 mPa · s or more, it is possible to apply the undercoat liquid even to a substrate to which liquid does not easily adhere.
Moreover, the surface roughness of the undercoat layer formed on the substrate can be reliably reduced by setting the viscosity of the undercoat liquid to 2,000 mPa · s or less, more preferably 1200 mPa · s or less. it can.

The surface tension of the undercoat liquid at 25 ° C. is preferably 20 mN / m or more and 40 mN / m or less, more preferably 20.5 mN / m or more and 35.0 mN / m or less, and 21 mN / m or more and 30.0 mN. / M or less is more preferable, and 21.5 mN / m or more and 28.0 mN / m or less is particularly preferable. When the content is in the above range, a printed matter having excellent blocking resistance can be obtained.
In addition, as a measuring method of the surface tension of the undercoat liquid at 25 ° C., a known method can be used. For example, a method of measuring using an automatic surface tension meter CBVP-Z manufactured by Kyowa Interface Science Co., Ltd. or a method of measuring using SIGMA 702 manufactured by KSV INSTRUMENTS LTD is preferred.

The surface tension of the undercoat liquid is preferably not more than the surface tension of the ink composition, and more preferably satisfies all of the following conditions (A), (B) and (C).
(A) The surface tension of the undercoat liquid is smaller than the surface tension of any ink composition.
(B) At least one of the surfactants contained in the undercoat liquid is
γs (0) −γs (saturation)> 0 (mN / m)
Satisfy the relationship.
(C) The surface tension of the undercoat liquid is
γs <(γs (0) + γs (saturation) ^maximum ) / 2
Satisfy the relationship.

Here, γs is the value of the surface tension of the undercoat liquid. γs (0) is the value of the surface tension of the liquid excluding all surfactants in the composition of the undercoat liquid. γs (saturation) is obtained when one of the surfactants contained in the undercoat liquid is added to the above “liquid excluding all surfactants” to increase the concentration of the surfactant. The surface tension value of the liquid with the surface tension saturated. The γs (saturation) ^maximum is the maximum value of γs (saturation) obtained for all the surfactants that satisfy the above condition (B) among the surfactants contained in the undercoat liquid.
The condition (A) is preferably satisfied for all ink compositions.

In the present invention, as described above, in order to form an ink dot of a desired size on a recording medium, it is preferable that the surface tension γs of the undercoat liquid is smaller than the surface tension γk of any ink.
Further, from the viewpoint of more effectively preventing the expansion of ink dots from landing to exposure, it is more preferable that γs <γk-3 (mN / m), and γs <γk-5 (mN / m). It is particularly preferred that

[Applying undercoat liquid]
In the undercoating step of applying the undercoating liquid on the non-penetrable medium, the undercoating liquid is preferably applied to the same area as the image formed by discharging the colored liquid droplets on the substrate or an area wider than the above image.
The amount of the undercoat liquid applied (weight ratio per unit area) is within a range of 0.05 to 5 when the maximum discharge amount (per color) of the ink composition is 1. Preferably, the range of 0.07 to 4 is more preferable, and the range of 0.1 to 3 is particularly preferable.

As a method for applying the undercoat liquid on the substrate, a known liquid applying method can be used without particular limitation, and any method such as spray application, application using an application roller, application by an ink jet method, and immersion is selected. be able to.
Specifically, for example, a size press method represented by a horizontal size press method, a roll coater method, a calendar size press method, etc .; a knife coater method represented by an air knife coater method; a transfer roll such as a gate roll coater method Roll coater method represented by coater method, direct roll coater method, reverse roll coater method, squeeze roll coater method, etc .; bill blade coater method, short duel coater method; blade coater method represented by two stream coater method; rod Examples include a bar coater method typified by a bar coater method, a cast coater method, a gravure coater method, a curtain coater method, a die coater method, a brush coater method, and a transfer method.
Moreover, the method of apply | coating by controlling a coating amount by using the coating device provided with the liquid quantity limiting member like the coating device of Unexamined-Japanese-Patent No. 10-230201 may be used.

The region to which the undercoat liquid is applied may be the entire surface application to be applied to the entire base material, or may be the partial application to be partially applied to the region where image formation such as ink jet recording is performed in the ink ejection process. In the present invention, the application amount of the undercoat liquid is uniformly adjusted, and fine lines and fine image portions are uniformly recorded, and from the viewpoint of suppressing density unevenness such as image unevenness, coating is performed by application using an application roller or the like. It is preferable to apply the entire surface to the entire paper.
Examples of the method of applying the undercoat liquid by controlling the application amount of the undercoat liquid within the above range include a method using an anilox roller. An anilox roller is a roller with a ceramic-sprayed roller surface processed with a laser to give it a pyramid shape, a diagonal line, a turtle shell shape, or the like. The undercoat liquid enters the dent portion formed on the roller surface, is transferred when it comes into contact with the paper surface, and is applied at a coating amount controlled by the dent of the anilox roller.

The thickness of the undercoat liquid layer formed by applying the undercoat liquid on the substrate and the undercoat layer obtained by curing the undercoat liquid layer is preferably 0.1 μm or more and 20 μm or less, and more preferably 0.2 μm or more and 10 μm or less. Preferably, it is 0.5 μm or more and 8 μm or less.
It is preferable that the thickness of the undercoat liquid layer and the undercoat layer is in the above range since the flexibility and adhesion of the cured image can be maintained well.

<Undercoat liquid semi-curing step for semi-curing undercoat liquid by UV irradiation>
The image forming method in the present invention preferably includes an undercoat liquid semi-curing step in which the undercoat liquid is semi-cured by ultraviolet irradiation.
In the present invention, “semi-curing of the undercoat liquid” means partially cured (partially cured) as in the case of the ink composition, and the undercoat liquid is partially cured. The state which has not hardened. Specifically, a state in which a penetrating medium such as plain paper is pressed against the undercoat liquid after curing and 10% by mass to 90% by mass of the undercoat liquid is transferred is called semi-cured, and 30% by mass of the ejected undercoat liquid. % To 80% by mass is preferably transferred. Moreover, the state which does not transfer at all is called complete curing. When the undercoat liquid is semi-cured, the degree of curing may be non-uniform, and the undercoat liquid is preferably cured in the depth direction.
Moreover, the preferable aspect about the semi-curing of undercoat liquid and the ultraviolet light source used for semi-curing is the same as the preferable aspect about the semi-curing of the said ink composition and the ultraviolet light source used for semi-curing.

<Discharge process for discharging the ink composition onto the semi-cured undercoat liquid>
The image forming method in the invention preferably includes a discharge step of discharging the ink composition onto the semi-cured undercoat liquid.
The ejection process is the same as the ink ejection process. That is, “the step of discharging the ink composition onto the semi-cured undercoat liquid” means that the ink discharge process is performed on the semi-cured undercoat liquid layer.

  FIG. 9 shows a configuration example of the ink jet apparatus. The step of applying the undercoat liquid onto the non-penetrable medium by the application roller 211 in FIG. 9 is semi-cured by UV irradiation with the UV-LED light source 221. Each step can be performed.

<Drying process>
The image forming method of the present invention may include a drying step of evaporating water and a water-soluble organic solvent used together as necessary from the ink composition applied or discharged onto the substrate by a heating means.
The drying step is preferably performed between the ink discharge step and the curing step in the image forming method of the present invention.
Moreover, when the ink composition in this invention contains the organic solvent, it is preferable to provide a drying process between an ink discharge process and a hardening process.
Hereinafter, a process of fixing by applying heat to the ink composition applied by the image forming method of the present invention will be described.
The drying means is not limited as long as it can dry water and a water-soluble organic solvent used in combination as necessary, but is not limited to heat drying treatment such as heat drum, hot air, infrared lamp, heat oven, heat plate heating, etc. Can be used.
The heating temperature is not particularly limited as long as water present in the ink composition and the water-soluble organic solvent used in combination as needed can be evaporated to form a film, but if it is 40 ° C. or higher, the heating temperature is not limited. Since an effect is acquired, it is preferable, 40 to 150 degreeC is more preferable, and 40 to 80 degreeC is still more preferable.
The drying / heating time is not particularly limited as long as water present in the ink composition and the water-soluble organic solvent used in combination as needed can be evaporated and a film of the resin agent can be formed. It can be appropriately set in consideration of the composition and printing speed of the composition.

<Lamination process>
In the printing method of the present invention, it is preferable to laminate a completely cured ink composition using a laminate film after the curing step.
This is because laminating can suppress elution, blocking, and odor of ink components from the printed material, and can be preferably used particularly for food packaging.
As the laminate film, a resin film is used, and examples thereof include a polyethylene terephthalate film, a polypropylene film, a nylon film, a polyvinyl chloride film, a polyethylene film, and a triacetyl cellulose film. Moreover, those films may be biaxially stretched.
As a method for laminating, a known method can be used without any particular limitation, and dry lamination can be exemplified.
When a resin film is used as the base material, it is preferable to use a resin film having high adhesiveness with the resin film used on the surface on which the base material is laminated, although it depends on the laminating method selected. .
Moreover, since a polypropylene film has high heat-sealability, it can be suitably used in this step.

Hereinafter, the present invention will be described in more detail with reference to examples and comparative examples. However, the present invention is not limited to these examples.
In the following description, “parts” means “parts by mass” unless otherwise specified.

(Material used)
The materials used in the present invention are as shown below.
<Colorant>
・ IRGALITE BLUE GLVO (Cyan pigment, manufactured by BASF Japan)
・ CINQUASIA MAGENTA RT-355-D (magenta pigment, manufactured by BASF Japan)
・ NOVOPERM YELLOW H2G (yellow pigment, manufactured by Clariant)
SPECIAL BLACK 250 (black pigment, manufactured by BASF Japan)
・ Taipeku CR60-2 (white pigment, manufactured by Ishihara Sangyo Co., Ltd.)

<Dispersant>
・ SOLSPERSE32000 (Noveon dispersant)

<(Component A) polymerizable compound>
SR9003 (propoxylated (2) neopentyl glycol diacrylate, manufactured by Sartomer)
・ 3-methyl-1,5-pentanediol diacrylate (SR341, manufactured by Sartomer)
・ Polyethylene glycol diacrylate (PEGDA, SR344, manufactured by Sartomer)

<(Component B) Polymerization initiator>
IRGACURE 819 (bis (2,4,6-trimethylbenzoyl) phenylphosphine oxide, manufactured by BASF, molecular weight 419)
Speedcure 7010 (Compound IB described above, manufactured by Lambson, molecular weight 1,899)

<Polymerization inhibitor>
UV-12 (FLORSTAB UV12, nitroso polymerization inhibitor, tris (N-nitroso-N-phenylhydroxylamine) aluminum salt, manufactured by Kromachem)

<Surfactant>
BYK307 (silicone surfactant, manufactured by BYK Chemie)

(Preparation of each mill base)
<Preparation of cyan mill base A>
300 parts by mass of IRGALITE BLUE GLVO, 620 parts by mass of SR9003, and 80 parts by mass of SOLPERSE32000 were mixed with stirring to obtain cyan mill base A. Cyan mill base A was prepared in a disperser motor mill M50 (manufactured by Eiger) and dispersed for 4 hours at a peripheral speed of 9 m / s using zirconia beads having a diameter of 0.65 mm.

<Preparation of magenta mill base B, yellow mill base C, black mill base D and white mill base E>
Magenta mill base B, yellow mill base C, black mill base D and white mill base E were prepared in the same manner as cyan mill base A with the composition and dispersion conditions shown in Table 1. In addition, the number in a table | surface represents the mass part which each raw material used.

(Preparation of ink composition)
Each material was stirred and mixed at a rate of 5,000 rpm at room temperature for 20 minutes using a mixer (Silverson L4R) at the ratio shown in Table 2, and cyan ink C-1, magenta ink M-1, and yellow ink were mixed. Y-1, black ink K-1, light cyan ink Lc-1, light magenta ink Lm-1, white ink W-1, and undercoat liquid U-1 were prepared. In addition, the number in a table | surface represents the mass part which each raw material used.

Example 1
<Device configuration>
In the inkjet apparatus shown in FIG. 9, a samba 1200 head manufactured by FUJIFILM DIMATIX is used as each of the inkjet heads 241 to 247 in the order of black ink, cyan ink, magenta ink, yellow ink, light cyan ink, light magenta ink, and white ink. Arranged. Moreover, between the inkjet heads of each color, LED light source units (LEDZero Solidcure, manufactured by Integration Technology) having a peak wavelength of 385 nm were disposed as the ultraviolet light sources 221 to 227. The light quantity of the LED light source unit was adjusted so that each ink could be kept in a semi-cured state.
The droplet ejection size was set to 13 pl. The drawing speed was set to 30 m / min, and the ejection frequency was set to form a 1,200 dpi image at the above speed. The discharge port density of the Samba 1200 head is 1,200 npi.
In Example 1, the application of the undercoat liquid U-1 by the application roller 211 and the semi-curing of the undercoat liquid by the LED light source 221 were not performed.
As an ultraviolet light source, an LED light source unit having a peak wavelength of 385 nm (LEDZero Solidcure, manufactured by Integration Technology) is placed in an inert gas blanket, and an N ₂ gas generator with compressor, Maxi-Flow30 (Inhouse Gas, Inc.) is used as the inert gas source. Manufactured at a pressure of 0.2 MPa · s, and N ₂ was allowed to flow at a flow rate of 10 L / min so that the oxygen concentration in the blanket was 1%.
As the base material, a resin film having a three-layer structure in which an oriented polypropylene (OPP) film (25 μm), a polyethylene terephthalate film (12 μm), and a nylon film (15 μm) are laminated from above is used on the OPP film. An image was formed. In addition, the number in () represents the thickness of each resin film.

<Image forming method>
Using the printing apparatus having the above-described configuration, on the base material, the mesh percentage was changed from 0% (mesh%) to 300% (mesh%) in 30% increments, and white ink was superimposed on the substrate at 100% (mesh%). A 3.5 × 10 cm color patch was prepared, and various performance tests shown below were performed. Note that 300% (halftone) means a state in which cyan ink, magenta ink, yellow ink, light cyan ink, and light magenta ink are superimposed on black ink 100% (halftone%) so that the total amount becomes 200%. Say.

(Example 2)
In the inkjet apparatus shown in FIG. 9, image formation was performed in the same manner as in Example 1 except that the undercoat liquid U-1 was applied by the application roller 211 and the undercoat liquid was semi-cured by the UV-LED light source 221. The following performance tests were conducted. The thickness of the undercoat layer was 1 μm.

(Comparative Examples 1-7)
An image was formed in the same manner as in Example 1 except that the droplet size, the head used, and whether or not the light ink was used were changed according to the description in Table 3, and various performance tests shown below were performed. In Comparative Examples 3, 4, 6, and 7 in which two or more types of droplet sizes are set, small droplets are used from the highlight portion to the intermediate concentration portion (25% in mesh%). To gradually increase the number of droplets over the shadow area, and use only large droplets in the solid area. At this time, the tone jump was set in consideration of the connection of gradations.
Details of the comparison head are shown in FIGS.
As shown in FIG. 11, an ink jet head 601 similar to the above-mentioned Samba 1200 head is produced except that the ink chamber units 602 having nozzles are arranged one-dimensionally (one row) and the substantial discharge port density is 150 npi. did. FIG. 12 shows a part of the ink jet apparatus when the comparison head is used. In order to form an image of 1,200 dpi, as shown in FIG. 12, eight produced inkjet heads 601 are arranged by shifting by 20 μm in a direction perpendicular to the substrate transport direction S, and the effective discharge port density is set to 1. The comparison head 604 with 200 npi was created. As the ink jet device when the comparison head is used, the ink jet heads 241 to 247 in FIG. 9 are replaced with the comparison head 604, respectively. Reference numeral 606 denotes an ultraviolet light source for a semi-curing process.
As a comparative example, the application of the undercoat liquid U-1 by the application roller 605 and the semi-curing of the undercoat liquid by the ultraviolet light source 603 were not performed.

<Evaluation of graininess>
The color patch prepared under the above conditions is observed from a distance of 50 cm, and the granularity of the image of the highlight part (30% (mesh%)) and the medium density part (90% (mesh%)) is as follows. Evaluation was made in 5 stages. The number of evaluation persons was 10, and the average value of the evaluation points of the 10 persons was rounded off to obtain the evaluation value, which is shown in Table 3.
5: Roughness cannot be recognized.
4: Although I can recognize a slight roughness, I don't care.
3: Roughness is recognized but acceptable.
2: I'm worried about roughness.
1: I am very worried about the roughness.
An evaluation score of 3 or more is an allowable range.

<Evaluation of Sujimura>
The color patch prepared under the above conditions was observed from a distance of 50 cm, and the presence or absence of periodic streaky unevenness was evaluated in five stages as follows. The number of evaluation persons was 10, and the average value of the evaluation points of the 10 persons was rounded off to obtain the evaluation value, which is shown in Table 3.
5: No stripe-like unevenness is observed.
4: A streak-like unevenness is slightly observed, but is not a concern.
3: Streaky unevenness is observed but acceptable.
2: Worried about stripe-like unevenness.
1: Striped unevenness is very worrisome.
An evaluation score of 3 or more is an allowable range.

DESCRIPTION OF SYMBOLS 1 LED light source unit 2 Inert gas blanket 3 Inert gas piping 4 Inert gas generator 5 Base material 11 Nozzle plate 12 Discharge port 20 Ink supply unit 21 Pressure chamber 22 Nozzle communication path 23 Ink supply path 24 Supply adjustment path 25 Common liquid chamber 30 Pressure generating means 31 Diaphragm 32 Adhesive layer 33 Lower electrode 34 Piezoelectric layer 35 Upper electrode 41 Circulating restrictor 42 Circulating path 190 Electrical wiring 190a Electrode pad 192 Multilayer flexible cable 194 Nozzle plate 196 Channel plate 198 Insulation / protection Film 200 Inkjet head 201 Delivery roller 202 Take-up roller 211 Application roller 221 to 227 UV-LED light source 231 Nitrogen purge exposure machine 241 to 247 Inkjet head 424 Base material 550 Inkjet head 550A Ink Ejection surface 551 Nozzle 551A Nozzle plate 551a Nozzle channel 552 Pressure chamber 552P Channel plate 553 Ink supply port 554 Ink chamber unit 555 Common liquid chamber 556 Vibration plate 557 Individual electrode 558 Piezoelectric element (Piazo actuator, piezoelectric actuator)
558a Piezoelectric body 559 Electrode pad 601 Inkjet head 602 Ink chamber unit 603, 606 Ultraviolet light source 604 Comparison head 605 Coating roller 607 Delivery roller M Main scanning direction S Substrate transport direction θ Ink chamber unit arrangement angle P with respect to main scanning direction P Substantially Nozzle spacing Ls Adjacent nozzle spacing in the sub-scanning direction

Claims (9)

A discharge step of discharging ultraviolet curable ink compositions having different hues from two or more inkjet heads on a non-penetrable medium;
A step of semi-curing the ejected ink composition by ultraviolet irradiation at the end of ejection of the ink composition of each color;
Irradiating ultraviolet rays in an atmosphere having an oxygen concentration of 1 vol% or less to completely cure the ink composition in this order,
The inkjet head includes a nozzle plate having a plurality of ejection openings,
The plurality of discharge ports are arranged in a two-dimensional matrix of 4 × 4 or more with respect to the traveling direction of the non-penetrable medium,
The density of the plurality of discharge ports arranged is 600 npi or more,
The inkjet head is a single pass system,
The amount of the ink composition discharged is 10 pl to 20 pl,
An image forming method comprising: ejecting at least four ink compositions of magenta ink, light magenta ink, cyan ink, and light cyan ink in the ejection step.   The image forming method according to claim 1, wherein the printing speed is 20 m / min or more. An undercoating step of applying an undercoating liquid on the non-penetrable medium;
An undercoat liquid semi-curing step for semi-curing the undercoat liquid by ultraviolet irradiation;
The image forming method according to claim 1, further comprising a discharge step of discharging the ink composition onto the semi-cured undercoat liquid in this order.   The non-penetrable medium has a total film thickness of 10 μm to 90 μm and includes one or two or more resin films selected from the group consisting of a polyethylene terephthalate film, a polyethylene film, a polypropylene film, and a nylon film, or The image forming method according to claim 1, wherein the image forming method is a laminated base material.   The image forming method according to claim 1, which is for package printing.   The image forming method according to claim 1, wherein the ultraviolet light source in the step of completely curing the ink composition is UV-LED and / or UV-LD. A plurality of pressure chambers communicating with each of the plurality of ejection ports;
A plurality of ink supply ports for supplying an ink composition to each of the plurality of pressure chambers;
A common liquid chamber for supplying an ink composition to the plurality of ink supply ports;
The image forming method according to claim 1, further comprising: a plurality of pressure generating units that deform each of the plurality of pressure chambers.   The image forming method according to claim 7, wherein the inkjet head further includes an electrical wiring that is disposed so as to penetrate the common liquid chamber and that supplies a driving signal to the pressure generating unit.   9. The image forming method according to claim 7, wherein the pressure chamber and the common liquid chamber provided in the inkjet head are arranged on the opposite side of the pressure generating unit.

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