Image forming method and image forming apparatus

Abstract

The present invention provides an image forming method and image forming apparatus that can achieve low migration and high quality of printed materials without compromising the durability of the inkjet head. [Solution] An image forming method comprising an ejection step of ejecting an active-ray curable ink from an inkjet head toward a recording material, and a curing step of curing ink droplets of the active-ray curable ink that have landed on the recording material by irradiating them with an active ray, wherein the active-ray curable ink contains an active-ray polymerizable component, a polymerization initiator, and a polymer sensitizer having a molecular weight of 500 or more, and the inkjet head comprises a nozzle, a pressure chamber, a diaphragm, and a piezoelectric member with a bi-pitch structure. The upper limit operating temperature of the inkjet head is higher than 60°C, the pitch between nozzles is less than 1 / 75 inch, and the ejection step includes a step of heating the active-ray curable ink at a temperature higher than 60°C and 90°C or lower.

Description

Technical Field

[0001] The present invention relates to an inkjet image forming method and an image forming apparatus.

Background Art

[0002] Conventionally, as an image forming apparatus for forming an image on a recording material such as paper, an inkjet image forming apparatus using an active energy ray curable ink is known. Generally, an active energy ray curable ink contains an active energy ray polymerizable component, a polymerization initiator, a sensitizer, and the like.

[0003] In particular, in the printing of food packaging, the use of an active energy ray curable ink corresponding to low-migration is recommended. For example, Patent Document 1 discloses an ink composition for an active energy ray curable inkjet that has been made low-migration by containing specific components such as a polymer sensitizer.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, the low-migration active energy ray curable ink disclosed in Patent Document 1 has a higher viscosity than a general active energy ray curable ink that is not low-migration. Therefore, it may be difficult to appropriately eject an appropriate amount of ink droplets from the nozzles of an inkjet head.

[0006] For example, setting the driving conditions of a pressure source such as a piezoelectric element to eject high-viscosity active-wire curing ink can cause adjacent crosstalk to occur. Adjacent crosstalk is a phenomenon in which pressure fluctuations caused by the pressure source propagate to adjacent pressure chambers, etc., changing the ink ejection characteristics. Adjacent crosstalk is particularly likely to occur when the pitch between nozzles is small. On the other hand, if high-viscosity active-wire curing ink is heated to reduce its viscosity, it may be possible to eject the ink under driving conditions equivalent to those used when using active-wire curing ink that does not support low migration, thereby suppressing the occurrence of adjacent crosstalk. However, this can be a factor that accelerates the deterioration of the inkjet head.

[0007] The object of the present invention is to provide an image forming method and an image forming apparatus that can achieve low migration and high quality of printed materials without impairing the durability of the inkjet head. [Means for solving the problem]

[0008] The image forming method according to the present invention is The ejection process involves ejecting activated-ray curing ink from the inkjet head toward the recording material, The process includes a curing step of curing ink droplets of the active-ray curable ink that have landed on the recording material by irradiating them with an active ray, The aforementioned activated ray curing ink is Actively polymerizable components, Polymerization initiator and It contains a polymer sensitizer with a molecular weight of 500 or more, The aforementioned inkjet head is Multiple nozzles, Multiple pressure chambers communicating with each of the multiple nozzles, A diaphragm that forms part of the wall surface of multiple pressure chambers, The device comprises a piezoelectric member that generates pressure fluctuations in the pressure chamber by applying a driving voltage, The piezoelectric member is A driving piezoelectric element column is joined to the vibration region of the diaphragm corresponding to the pressure chamber, It comprises a non-driven piezoelectric element column that is joined to the non-vibrating region of the diaphragm corresponding to the partition wall of the pressure chamber, The upper limit operating temperature of the aforementioned inkjet head is higher than 60°C. The pitch between the nozzles is less than 1 / 75 inch. The ejection step includes a step of heating the active-ray curable ink to a temperature higher than 60°C and 90°C or lower.

[0009] The image forming apparatus according to the present invention is An inkjet head that ejects activated-ray curing ink toward the recording material, An active ray irradiation unit that irradiates ink droplets of the active ray-curable ink that have landed on the recording material with active rays to cure them, The system comprises a heating unit for heating the activated-wire-curable ink, The aforementioned activated ray curing ink is Actively polymerizable components, Polymerization initiator and It contains a polymer sensitizer with a molecular weight of 500 or more, The aforementioned inkjet head is Multiple nozzles, Multiple pressure chambers communicating with each of the multiple nozzles, A diaphragm that forms part of the wall surface of multiple pressure chambers, The device comprises a piezoelectric member that generates pressure fluctuations in the pressure chamber by applying a driving voltage, The piezoelectric member is A driving piezoelectric element column is joined to the vibration region of the diaphragm corresponding to the pressure chamber, It comprises a non-driven piezoelectric element column that is joined to the non-vibrating region of the diaphragm corresponding to the partition wall of the pressure chamber, The upper limit operating temperature of the aforementioned inkjet head is higher than 60°C. The pitch between the nozzles is less than 1 / 75 inch. The heating unit is capable of heating the active-wire-curable ink to a temperature higher than 60°C but 90°C or lower. [Effects of the Invention]

[0010] According to the present invention, it is possible to achieve Roman migration and high quality of printed matter without impairing the durability of the inkjet head.

Brief Description of the Drawings

[0011] [Figure 1] FIG. 1A and FIG. 1B are diagrams showing a schematic configuration of an image forming apparatus according to an embodiment of the present invention. [Figure 2] FIG. 2 is a block diagram showing a main part of a control system of the image forming apparatus. [Figure 3] FIG. 3 is a perspective view showing an external appearance of the inkjet head. [Figure 4] FIG. 4 is a cross-sectional view schematically showing an internal structure of the inkjet head. [Figure 5] FIG. 5 is a cross-sectional view schematically showing a structure of a piezoelectric member.

Embodiments for Carrying Out the Invention

[0012] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

[0013] <Image Forming Apparatus> FIG. 1A and FIG. 1B are diagrams showing a schematic configuration of an image forming apparatus 1 according to an embodiment of the present invention. FIG. 2 is a block diagram showing a main part of a control system of the image forming apparatus 1.

[0014] The image forming apparatus 1 is an inkjet type image forming apparatus (so-called inkjet printer) using an active energy ray curable ink. The image forming apparatus 1 discharges ink droplets of the active energy ray curable ink onto a recording material M, and cures the ink droplets by irradiation with active energy rays (for example, ultraviolet rays) to form a cured film on the recording material M. Note that FIGS. 1A and 1B schematically show the configuration of the image forming apparatus 1, and known techniques can be applied to each element.

[0015] As shown in Figures 1A, 1B, and 2, the image forming apparatus 1 includes an inkjet head 10 (10A to 10E), an active beam irradiation unit 20, a transport unit 30, and a control unit 40, etc. The image forming apparatus 1 employs a one-pass method in which the inkjet heads 10 (10A to 10E) are arranged in the transport direction of the recording material M, and printing is performed on the transported recording material M in one pass.

[0016] The image forming apparatus 1 may also include a maintenance unit for performing maintenance such as cleaning the inkjet head 10.

[0017] Recording material M is a recording medium capable of fixing active-ray curing ink ejected from the inkjet head 10. Recording material M is a long roll-shaped recording medium, such as a food packaging film. In the field of food packaging, low-migration active-ray curing inks are used to suppress the influence of ink components on the safety, odor, appearance, or taste of food. In this embodiment, low migration is achieved by using a polymer sensitizer with a molecular weight of 500 or more as the sensitizer contained in the active-ray curing ink.

[0018] The recording material M may be a non-absorbent recording material or an absorbent recording material. Examples of recording material M include plastic, paper, capsules, gel, metal foil, glass, wood, and cloth. Examples of plastic include polyester, polyvinyl chloride, polyethylene, polyurethane, polypropylene, acrylic resin, polycarbonate, polystyrene, acrylonitrile-butadiene-styrene copolymer, polyethylene terephthalate, and polybutadiene terephthalate.

[0019] The inkjet head 10 has a configuration that allows it to eject active-ray curable ink through a nozzle 101 (see Figure 3). The image forming apparatus 1 is equipped with five inkjet heads 10A to 10E, which eject active-ray curable inks of white (W), cyan (C), magenta (M), yellow (Y), and black (K) toward the recording material M. Note that inkjet heads 10A to 10E are just examples of inkjet heads provided in the image forming apparatus 1, and the number of inkjet heads 10 and the colors of the inks are not limited to these. The detailed configuration of the inkjet head 10 will be described later.

[0020] In this embodiment, the inkjet head 10 has a heating unit 122 capable of heating the active-ray curable ink to a predetermined temperature of over 60°C. The heating unit 122 is located, for example, near the ink tank and / or ink flow path in the ink circulation unit 121. As a heating method for the heating unit 122, for example, resistance heating, induction heating, microwave heating, or infrared heating can be applied.

[0021] Furthermore, the inkjet head 10 has an upper limit operating temperature higher than 60°C. For example, the upper limit operating temperature of the inkjet head 10 is 90°C. "An upper limit operating temperature higher than 60°C" means that even if the active-wire curable ink is heated to a temperature higher than 60°C during ejection, there is no deterioration of the components of the inkjet head 10 or the adhesive layers between the components, and ejection characteristics equivalent to those when the heating temperature is 60°C or lower can be ensured.

[0022] Conventional inkjet heads have a maximum operating temperature of 60°C or less for durability reasons, and heating the ink to a temperature higher than 60°C may cause the inkjet head to deteriorate. In contrast, in this embodiment, even if the ink is heated to a temperature higher than 60°C during ejection, the ejection characteristics of the inkjet head 10 are not impaired. Therefore, a high-viscosity active-ray curable ink can be heated to a temperature higher than 60°C to adjust to an appropriate viscosity before the ejection process can be performed.

[0023] Furthermore, the inkjet head 10 is, for example, an ink-circulating type inkjet head having an ink circulation unit 121 (see Figure 2). By circulating the ink, it is possible to prevent problems such as nozzle clogging caused by ink stagnation.

[0024] The active ray irradiation unit 20 irradiates ink droplets that have landed on the recording material M with an active ray (e.g., ultraviolet light). In the example shown in Figure 1A, the active ray irradiation unit 20 is located downstream of the inkjet head 10E, which is located at the downstream end in the transport direction. As shown in Figure 1B, the active ray irradiation unit 20 may include a first active ray irradiation unit 21 and a second active ray irradiation unit 22. The first active ray irradiation unit 21 is an irradiation unit for pinning, located downstream of each of the inkjet heads 10A to 10D in the transport direction. The second active ray irradiation unit 22 is an irradiation unit for final curing, located downstream of the inkjet head 10E in the transport direction. Furthermore, shields (not shown) to prevent leakage of ultraviolet light may be placed upstream and downstream of the active ray irradiation unit 20 in the transport direction.

[0025] The transport unit 30 includes a paper feed unit 31, a winding unit 32, and transport rollers 33, etc., and transports the recording material M. In accordance with instructions from the control unit 40, the recording material M is fed out from the paper feed unit 31 and transported by the transport rollers 33, etc., and the printed recording material M is wound onto the winding unit 32.

[0026] The transport unit 30 may include transport members such as a transport drum that wraps around and transports the recording material M. In this case, the inkjet heads 10A to 10B may be arranged so as to face the outer surface of the transport drum.

[0027] The control unit 40 includes a CPU (Central Processing Unit) 41 as an arithmetic / control device, and ROM (Read Only Memory) 42 and RAM (Random Access Memory) 43 as main memory. The ROM 42 stores basic programs and basic setting data. The CPU 41, for example, reads a program corresponding to the processing content from the ROM 42, loads it into the RAM 43, and executes the loaded program to centrally control the operation of the inkjet heads 10A to 10B, the active beam irradiation unit 20, and the transport unit 30.

[0028] The control unit 40 generates a drive signal based on image data received from an external device 43 (e.g., a personal computer) via the communication interface 44, and controls the head drive unit 112 of the inkjet heads 10A to 10E. Furthermore, the control unit 40 controls the operation of the ink circulation unit 121 and heating unit 122 of the inkjet heads 10A to 10E based on the output results from various sensors (not shown) provided on the inkjet heads 10A to 10E.

[0029] Furthermore, some or all of the processing performed by the control unit 40 may be carried out by electronic circuits such as a DSP (Digital Signal Processor), ASIC (Application Specific Integrated Circuit), or PLD (Programmable Logic Device) provided according to the processing. In addition, the image forming apparatus 1 may be equipped with auxiliary storage devices such as an HDD (Hard Disk Drive), SSD (Solid State Drive), or SD (Secure Digital) card.

[0030] In the image forming apparatus 1, the recording material M is transported by the transport unit 30 according to instructions from the control unit 40, and an image is formed on the recording material M by the inkjet heads 10A to 10E and the active ray irradiation unit 20.

[0031] <Inkjet head> The specific structures of the inkjet heads 10A to 10E will be described with reference to Figures 3 to 5. Figure 3 is a perspective view showing the external appearance of the inkjet heads 10A to 10E. Figure 4 is a schematic cross-sectional view showing the internal structure of the inkjet heads 10A to 10E. Figure 5 is a schematic cross-sectional view showing the structure of the piezoelectric member 111.

[0032] This disclosure uses a Cartesian coordinate system (X, Y, Z) for explanation. The negative direction of the Z axis is the ink ejection direction of the inkjet heads 10A to 10E, the direction along the Y axis is the alignment direction of the nozzles 101, and the direction along the X axis is the flow direction of the ink relative to the pressure chamber 102. Hereinafter, the directions along the X axis, Y axis, and Z axis will be referred to as the "X-axis direction," "Y-axis direction," and "Z-axis direction," respectively.

[0033] As shown in Figures 3 to 5, the inkjet heads 10A to 10E include a nozzle 101, a pressure chamber 102, an ink flow path 103, and a pressure generating unit 110, etc. The ink flow path 103 includes an ink supply path 104, an ink flow path 105, an individual circulation path 106, a common circulation path 107, an ink flow path 105, and an ink discharge path (not shown).

[0034] The inkjet heads 10A to 10E eject ink droplets from the nozzles 101 when the ink stored in the pressure chamber 102 is pressurized by the pressure generating unit 110. The nozzles 101 may be arranged in one row or multiple rows along the Y axis. In this embodiment, the nozzles 101 are arranged in four rows along the Y axis.

[0035] The nozzle 101 is a hole that penetrates the nozzle substrate 11 in the Z-axis direction. The diameter of the nozzle 101 is, for example, 15 to 50 μm. The nozzle pitch (the distance between adjacent nozzles 101 in the Y-axis direction) is, for example, less than 1 / 75 inch. When the nozzle pitch is less than 1 / 75 inch, high-resolution images can be formed, but adjacent crosstalk is more likely to occur.

[0036] A pressure chamber 102 is provided one-to-one for each of the multiple nozzles 101. The pressure chamber 102 is an ink storage space that stores the ink discharged from the nozzles 101. Adjacent pressure chambers 102 in the Y-axis direction are separated by a partition wall 102a (see Figure 5). The pressure chamber 102 communicates with the ink supply passage 104 and also with the nozzles 101 via the ink flow passage 105.

[0037] The individual circulation channels 106 are connected to the nozzle 101 and the common circulation channel 107. Multiple individual circulation channels 106 are connected to the common circulation channel 107, and ink flowing from multiple individual circulation channels 106 merges there.

[0038] When the nozzles 101 are arranged in multiple rows (four rows in this embodiment), the pressure chambers 102 and individual circulation channels 106 are formed in multiple rows corresponding to the nozzles 101. The common circulation channel 107 may be provided for each row of nozzles 101, or it may be shared by multiple rows of nozzles 101.

[0039] The pressure generating unit 110 generates pressure fluctuations by pressurizing the ink stored in the pressure chamber 102. The pressure generating unit 110 includes a piezoelectric member 111 (see Figure 5), a head drive unit 112 (see Figure 2), and a control board (not shown).

[0040] The piezoelectric element 111 is a pressure source that pressurizes the ink contained in the pressure chamber 102. For example, a push-mode type laminated piezo actuator is used for the piezoelectric element 111. The piezoelectric element 111 deforms, for example, by expanding and contracting in the Z-axis direction when a driving voltage is applied.

[0041] The driving frequency of the piezoelectric element 111 is preferably 30 kHz or higher. While a driving frequency of 30 kHz or higher allows for faster printing, it limits the conditions necessary to ensure stable ejection performance (for example, the viscosity of the active-wire curable ink) and also makes adjacent crosstalk more likely to occur.

[0042] The head drive unit 112 controls the ink ejection operation of each inkjet head 10A to 10E in accordance with the instructions of the control unit 40 so that printing processing corresponding to the image data is performed. Specifically, the head drive unit 112 individually controls the drive voltage to the plurality of drive piezoelectric element columns 111A of the piezoelectric member 111.

[0043] The control board is a flexible printed circuit board on which a control IC, for example, which functions as a head drive unit 112, is mounted. The control board has power supply lines (conductor patterns) that supply drive voltage to the drive piezoelectric element column 111A and the non-drive piezoelectric element column 111B of the piezoelectric member 111.

[0044] In this embodiment, the piezoelectric member 111 has a bi-pitch structure in which driving piezoelectric element columns 111A and non-driving piezoelectric element columns 111B are alternately arranged along the Y-axis. The driving piezoelectric element columns 111A and non-driving piezoelectric element columns 111B are formed in a comb-like shape at predetermined intervals by, for example, forming grooves in the base material of the piezoelectric member 111 by half-cut dicing.

[0045] The driving piezoelectric element column 111A is joined to a displaceable vibration region of the diaphragm layer 13b of the actuator substrate 13 that corresponds to the pressure chamber 102. The non-driving piezoelectric element column 111B is joined to a non-displaceable, non-vibrating region of the diaphragm layer 13b of the actuator substrate 13 that corresponds to the partition wall 102a of the pressure chamber 102.

[0046] The drive piezoelectric element column 111A is driven by the drive voltage from the head drive unit 112 and expands and contracts in the Z-axis direction. As the vibration region of the actuator substrate 13 joined to the drive piezoelectric element column 111A is displaced in the Z-axis direction, pressure fluctuations occur in the ink in the corresponding pressure chamber 102, causing ink to be ejected from the nozzle 101.

[0047] In the case of a typical piezoelectric element without a non-driven piezoelectric element column 111B, pressure fluctuations may occur in the pressure chamber 102 adjacent to the pressure chamber 102 that is subject to pressure fluctuations, potentially changing the ink ejection characteristics. In the bi-pitch piezoelectric member 111, the non-driven piezoelectric element column 111B is joined to the non-vibrating region of the actuator substrate 13 and supports the partition wall of the pressure chamber 102, thereby reducing mutual interference (so-called adjacent crosstalk) between individual pressure chambers 102.

[0048] The nozzle 101, pressure chamber 102, and ink flow path 103 are formed, for example, inside the nozzle substrate 11, common flow path substrate 12, actuator substrate 13, and protective substrate 14, or by being coupled to these.

[0049] The nozzle substrate 11 is, for example, a laminated substrate having a nozzle layer 11a and individual channel layers 11b. An ink-repellent film may be formed on the nozzle surface (the negative side in the Z-axis direction) of the nozzle substrate 11. The nozzle layer 11a is, for example, composed of a Si substrate with a thickness of 10 to 20 μm. The individual channel layer 11b is, for example, composed of a Si substrate with a thickness of 100 to 300 μm. An SiO2 oxide film layer (symbol omitted) with a thickness of, for example, 0.3 to 1.0 μm is interposed at the interface between the nozzle layer 11a and the individual channel layer 11b.

[0050] The nozzle layer 11a is provided with an opening that forms the nozzle 101, extending through in the Z-axis direction. The individual channel layer 11b is provided with an opening that forms the ink flow path 105 and the individual circulation channel 106, extending through in the Z-axis direction. The openings in the nozzle layer 11a and the individual channel layer 11b can be formed, for example, by dry etching, wet etching, or press working.

[0051] While it is preferable to provide the individual circulation channels 106 on the nozzle substrate 11 from the viewpoint of removing air bubbles and foreign matter near the nozzle 101, they may also be provided on the common channel substrate 12.

[0052] The common channel substrate 12 is a laminated substrate having, for example, a common channel layer 12a, a damper layer 12b, and an air chamber layer 12c. The common channel layer 12a is composed of, for example, a Si substrate with a thickness of 100 to 300 μm. The damper layer 12b is composed of, for example, a Si substrate with a thickness of 1 to 50 μm. The air chamber layer 12c is composed of, for example, a Si substrate with a thickness of 1 to 100 μm.

[0053] Each of the common flow channel layer 12a, damper layer 12b, and air chamber layer 12c is provided with an opening that penetrates in the Z-axis direction to form the ink flow path 105. The common flow channel layer 12a is also provided with an opening that penetrates in the Z-axis direction to form the common circulation channel 107. The air chamber layer 12c is also provided with an opening that penetrates in the Z-axis direction to form the air chamber 108. The openings in the common flow channel layer 12a, damper layer 12b, and air chamber layer 12c can be formed, for example, by dry etching, wet etching, or press working.

[0054] The damper layer 12b is sandwiched between the common flow channel layer 12a and the air chamber layer 12c. In the damper layer 12b, the portion sandwiched between the opening for the common circulation channel 107 provided in the common flow channel layer 12a and the opening for the air chamber 108 provided in the air chamber layer 12c functions as a damper 109. The damper 109 has a thin film shape that can elastically deform in response to pressure fluctuations in the common circulation channel 107, thereby suppressing pressure fluctuations in the common circulation channel 107.

[0055] The actuator substrate 13 is, for example, a laminated substrate having a pressure chamber layer 13a and a diaphragm layer 13b. The pressure chamber layer 13a is, for example, composed of a Si substrate of about 100 to 300 μm. The diaphragm layer 13b is, for example, composed of a thin, elastically deformable Si substrate of about 1 to 10 μm.

[0056] The pressure chamber layer 13a is provided with an opening that penetrates in the Z-axis direction to form the pressure chamber 102. The diaphragm layer 13b is provided with an opening that penetrates in the Z-axis direction to form the ink supply passage 104. The openings in the pressure chamber layer 13a and the diaphragm layer 13b can be formed, for example, by dry etching, wet etching, or press working.

[0057] The protective substrate 14 is, for example, a substrate made of 42 alloy. The protective substrate 14 is provided with, for example, an opening for forming an ink supply passage 104, which penetrates in the Z-axis direction. The protective substrate 14 also has a space for housing a pressure generating unit 110 and the like.

[0058] A common ink chamber member 16 is positioned on the upper surface (the positive side in the Z-axis direction) of the protective substrate 14. The upper surface of the protective substrate 14 and the common ink chamber member 16 form a common supply ink chamber 123 and a common discharge ink chamber (not shown).

[0059] The common supply ink chamber 123 is provided, for example, approximately in the center of the common ink chamber member 16 in the Y-axis direction, extending in the X-axis direction, and is in communication with a plurality of ink supply passages 104. Ink is supplied to and filled into the common supply ink chamber 123 from an ink supply port (not shown). Two common discharge ink chambers (not shown) are provided, for example, at both ends of the common ink chamber member 16 in the Y-axis direction, extending in the X-axis direction, and are in communication with a common circulation passage 107. The discharged ink fills the common discharge ink chamber, and the ink is discharged from an ink discharge port (not shown).

[0060] The nozzle substrate 11 and the common flow path substrate 12, the common flow path substrate 12 and the actuator substrate 13, the actuator substrate 13 and the protective substrate 14, and the protective substrate 14 and the common ink chamber member 16 are bonded and fixed together, for example, with an adhesive. For example, an epoxy adhesive with thermosetting properties is used as the adhesive. The adhesives used to bond each component may be the same adhesive or different adhesives. For example, a combination of a rubber-based adhesive and an epoxy-based adhesive may be used.

[0061] In the inkjet head 10, ink supplied from the common ink supply chamber 123 is discharged to the common discharge ink chamber (not shown) via the ink supply path 104, pressure chamber 102, ink flow path 105, individual circulation path 106, common circulation path 107, and ink discharge path. The ink discharged to the common discharge ink chamber is circulated back to the common ink supply chamber 123 by an ink circulation unit 121, which includes, for example, an ink tank and a circulation pump.

[0062] <Activated Ray Curing Ink> The active-wire curing ink used in this embodiment is a low-migration compatible ink that meets certain safety standards regarding curability and odor, and is particularly suitable for printing on food packaging.

[0063] Active-ray curing inks contain active-ray polymerizable components that polymerize when irradiated with active rays. Examples of active rays include electron beams, ultraviolet rays, infrared rays, alpha rays, gamma rays, and X-rays. Of these, ultraviolet rays or electron beams are preferred, and ultraviolet rays are more preferred because they cause less damage to the recording material.

[0064] The above-mentioned activated ray polymerizable component may be a monomer, a polymerizable oligomer, a prepolymer, or a mixture thereof. Furthermore, the above-mentioned activated ray polymerizable component may be a radical activated ray polymerizable compound, a cationic activated ray polymerizable compound, or a mixture thereof.

[0065] Radical-active ray polymerizable compounds can be any compounds having an ethylenically unsaturated double bond group in their molecule. Examples of radical-active ray polymerizable compounds include (meth)acrylates. In this invention, "(meth)acrylate" means acrylate or methacrylate, and "(meth)acryloyl group" means acryloyl group or methacryloyl group. Radical-active ray polymerizable compounds may be monofunctional or polyfunctional compounds. Polyfunctional compounds can form crosslinked structures in the cured film (printed material) obtained by extruding and curing an active-ray curable ink, thereby increasing the hardness of the cured film. These radical-active ray polymerizable compounds may be used individually or in combination of two or more types.

[0066] Examples of monofunctional (meth)acrylates include isoamyl (meth)acrylate, stearyl (meth)acrylate, lauryl (meth)acrylate, benzyl (meth)acrylate, octyl (meth)acrylate, decyl (meth)acrylate, isomirsutyl (meth)acrylate, isostearyl (meth)acrylate, 2-ethylhexyl-diglycol (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 2-(meth)acryloyloxyethylhexahydrophthalic acid, butoxyethyl (meth)acrylate, ethoxydiethylene glycol (meth)acrylate, methoxydiethylene glycol (meth)acrylate, This includes methoxypolyethylene glycol (meth)acrylate, methoxypropylene glycol (meth)acrylate, phenoxyethyl (meth)acrylate, tetrahydrofurfuryl (meth)acrylate, isobornyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 2-hydroxy-3-phenoxypropyl (meth)acrylate, 2-(meth)acryloyloxyethyl succinic acid, 2-(meth)acryloyloxyethyl phthalic acid, 2-(meth)acryloyloxyethyl-2-hydroxyethyl phthalic acid, and t-butylcyclohexyl (meth)acrylate. The above monofunctional (meth)acrylates may be used individually or in combination of two or more types.

[0067] Examples of polyfunctional (meth)acrylates include triethylene glycol di(meth)acrylate, tetraethylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, tripropylene glycol di(meth)acrylate, polypropylene glycol di(meth)acrylate, 1,4-butanediol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, 1,9-nonanediol di(meth)acrylate, neopentyl glycol di(meth)acrylate, dimethylol-tricyclodecane di(meth)acrylate, bisphenol A PO adduct di(meth)acrylate, hydroxypivalate neopentyl glycol di(meth)acrylate, polytetramethylene glycol di(meth)acrylate, polyethylene glycol This includes bifunctional (meth)acrylates such as chol di(meth)acrylate, dipropylene glycol di(meth)acrylate, and tripropylene glycol di(meth)acrylate; trifunctional (meth)acrylates such as trimethylolpropane tri(meth)acrylate and pentaerythritol tri(meth)acrylate; trifunctional or more (meth)acrylates such as pentaerythritol tetra(meth)acrylate, dipentaerythritol hexa(meth)acrylate, ditrimethylolpropane tetra(meth)acrylate, glycerin propoxytri(meth)acrylate, and pentaerythritol ethoxytetra(meth)acrylate; oligomers having a (meth)acryloyl group, including polyester acrylate oligomers; and modified products thereof. Examples of the above modified products include ethylene oxide-modified (EO-modified) (meth)acrylates with an ethylene oxide group inserted, and propylene oxide-modified (PO-modified) (meth)acrylates with a propylene oxide group inserted. The above polyfunctional (meth)acrylates may be used individually or in combination of two or more types.

[0068] Cationically polymerizable compounds can be any compounds that have a cationically polymerizable group in their molecule. Examples of cationically polymerizable compounds include epoxy compounds, vinyl ether compounds, and oxetane compounds. These cationically polymerizable compounds may be used individually or in combination of two or more.

[0069] Examples of the epoxy compounds mentioned above include 3,4-epoxycyclohexylmethyl-3',4'-epoxycyclohexanecarboxylate, bis(3,4-epoxycyclohexylmethyl)adipate, vinylcyclohexene monoepoxide, ε-caprolactone-modified 3,4-epoxycyclohexylmethyl-3',4'-epoxycyclohexanecarboxylate, 1-methyl-4-(2-methyloxyranyl)-7-oxabicyclo[4,1,0]heptane, 2-(3,4-epoxycyclohexyl-5,5-spiro-3,4-epoxy)cyclohexanone-meth-dioxane and bis(2,3-epoxycyclopentyl) ethers, alicyclic epoxy resins, diglycidyl ether of 1,4-butanediol, diglycidyl ether of 1,6-hexanediol, and glycerin. This includes aliphatic epoxy compounds such as polyglycidyl ethers of polyether polyols obtained by adding one or more alkylene oxides (such as ethylene oxide and propylene oxide) to aliphatic polyhydric alcohols such as ligricidyl ether, triglycidyl ether of trimethylolpropane, diglycidyl ether of polyethylene glycol, diglycidyl ether of propylene glycol, ethylene glycol, propylene glycol, and glycerin; and aromatic epoxy compounds such as di or polyglycidyl ethers of bisphenol A or its alkylene oxide adducts, di or polyglycidyl ethers of hydrogenated bisphenol A or its alkylene oxide adducts; and novolac-type epoxy resins. The above epoxy compounds may be used individually or in combination of two or more.

[0070] Examples of the vinyl ether compounds mentioned above include monovinyl ether compounds such as ethyl vinyl ether, n-butyl vinyl ether, isobutyl vinyl ether, octadecyl vinyl ether, cyclohexyl vinyl ether, hydroxybutyl vinyl ether, 2-ethylhexyl vinyl ether, cyclohexanedimethanol monovinyl ether, n-propyl vinyl ether, isopropyl vinyl ether, isopropenyl ether-o-propylene carbonate, dodecyl vinyl ether, diethylene glycol monovinyl ether, and octadecyl vinyl ether, as well as di or trivinyl ether compounds such as ethylene glycol divinyl ether, diethylene glycol divinyl ether, triethylene glycol divinyl ether, propylene glycol divinyl ether, dipropylene glycol divinyl ether, butanediol divinyl ether, hexanediol divinyl ether, cyclohexanedimethanol divinyl ether, and trimethylolpropane trivinyl ether. The vinyl ether compounds may be used individually or in combination of two or more types.

[0071] Examples of the above oxetane compounds include 3-hydroxymethyl-3-methyloxetane, 3-hydroxymethyl-3-ethyloxetane, 3-hydroxymethyl-3-propyloxetane, 3-hydroxymethyl-3-n-butyloxetane, 3-hydroxymethyl-3-phenyloxetane, 3-hydroxymethyl-3-benzyloxetane, 3-hydroxyethyl-3-methyloxetane, 3-hydroxyethyl-3-ethyloxetane, 3-hydroxyethyl-3-propyloxetane, and 3-hydroxyethyl oxetane. This includes 3-phenyloxetane, 3-hydroxypropyl-3-methyloxetane, 3-hydroxypropyl-3-ethyloxetane, 3-hydroxypropyl-3-propyloxetane, 3-hydroxypropyl-3-phenyloxetane, 3-hydroxybutyl-3-methyloxetane, 1,4-bis{[(3-ethyl-3-oxetanyl)methoxy]methyl}benzene, 3-ethyl-3-(2-ethylhexyloxymethyl)oxetane, and di[1-ethyl(3-oxetanyl)]methyl ether. The above oxetane compounds may be used individually or in combination of two or more.

[0072] The proportion of the active ray polymerizable component is preferably 70% to 100% by mass, more preferably 80% to 100% by mass, and even more preferably 90% to 100% by mass, based on the total mass of the active ray polymerizable component contained in the active ray curable ink.

[0073] The content of the active-ray polymerizable component can be 1% by mass or more and 97% by mass or less based on the total mass of the active-ray curable ink. Preferably, the content of the active-ray polymerizable component is 30% by mass or more and 95% by mass or less, more preferably 50% by mass or more and 90% by mass or less, and even more preferably 70% by mass or more and 90% by mass or less.

[0074] Furthermore, the content of the active-ray polymerizable component is preferably 30% by mass or more and 100% by mass or less, relative to the total mass of the liquid components contained in the active-ray curable ink. More preferably, the content of the active-ray polymerizable component is 50% by mass or more and 100% by mass or less, even more preferably 70% by mass or more and 100% by mass or less, even more preferably 90% by mass or more and 100% by mass or less, and particularly preferably 95% by mass or more and 100% by mass or less.

[0075] Active-ray curable inks contain a polymerization initiator that initiates the polymerization reaction of active-ray polymerizable components when irradiated with active rays. The polymerization initiator is a so-called photopolymerization initiator that initiates the polymerization reaction upon irradiation with active rays.

[0076] The polymerization initiator is preferably a radical polymerization initiator when the active-ray curable ink contains a radical-active-ray polymerizable compound, and preferably a cationic polymerization initiator (photoacid generator) when the active-ray curable ink contains a cationic-active-ray polymerizable compound. The radical polymerization initiator may be an intramolecular bond cleavage type radical polymerization initiator or an intramolecular hydrogen abstraction type radical polymerization initiator.

[0077] Examples of intramolecular bond cleavage type radical polymerization initiators include acetophenone-based initiators such as diethoxyacetophenone, 2-hydroxy-2-methyl-1-phenylpropan-1-one, benzyldimethylketal, 1-(4-isopropylphenyl)-2-hydroxy-2-methylpropan-1-one, 4-(2-hydroxyethoxy)phenyl-(2-hydroxy-2-propyl)ketone, 1-hydroxycyclohexylphenyl ketone, 2-methyl-2-morpholino(4-methylthiophenyl)propan-1-one, and 2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)-butanone; benzoins such as benzoin, benzoin methyl ether, and benzoin isopropyl ether; acylphosphine oxide-based initiators such as 2,4,6-trimethylbenzoindiphenylphosphine oxide; and benzyl and methylphenylglyoxyesters. The above intramolecular bond cleavage type radical polymerization initiators may be used individually or in combination of two or more types.

[0078] Examples of intramolecular hydrogen abstraction radical polymerization initiators include benzophenone-based initiators such as benzophenone, o-benzoylmethyl benzoate, 4-phenylbenzophenone, 4,4'-dichlorobenzophenone, hydroxybenzophenone, 4-benzoyl-4'-methyl-diphenyl sulfide, acrylic benzophenone, 3,3',4,4'-tetra(t-butylperoxycarbonyl)benzophenone, and 3,3'-dimethyl-4-methoxybenzophenone; thioxanthone-based initiators such as 2-isopropylthioxanthone, 2,4-dimethylthioxanthone, 2,4-diethylthioxanthone, and 2,4-dichlorothioxanthone; aminobenzophenone-based initiators such as Michler's ketone and 4,4'-diethylaminobenzophenone; 10-butyl-2-chloroacridone, 2-ethylanthraquinone, 9,10-phenanthrenequinone, and camphorquinone. The above intramolecular hydrogen abstraction type radical polymerization initiators may be used individually or in combination of two or more types.

[0079] Examples of cationic polymerization initiators include photoacid generators. Examples of photoacid generators include sulfonates that generate sulfonic acid, such as B(C6F5)4-, PF6-, AsF6-, SbF6-, and CF3SO3- salts of aromatic onium compounds including diazonium, ammonium, iodonium, sulfonium, and phosphonium; halides that photogenerate hydrogen halides; and iron allene complexes. The above photoacid generators may be used individually or in combination of two or more types.

[0080] The polymerization initiator content should be within a range that allows the active-ray curable ink to cure sufficiently. For example, it can be 0.01% to 10% by mass relative to the total mass of the active-ray curable ink.

[0081] The active-ray curable ink contains a sensitizer to promote the polymerization reaction of the active-ray polymerizable component when irradiated with an active ray. In this embodiment, a polymer sensitizer with a molecular weight of 500 or more is used as the sensitizer.

[0082] Examples of thioxanthone-based and acylphosphine-based polymer sensitizers include Omnipol-TX ((2-carboxymethoxythioxanthone)-(polytetramethylene glycol 250) diester) (number average molecular weight: 660) (manufactured by IGM Resins BV), SpeedCure 7010 (molecular weight 1839) (manufactured by Lambson), Genopol TX-1 (number average molecular weight: 820) (manufactured by RaHN), as well as oligo(2-hydroxy-2-methyl-1-(4-(1-methylvinyl)phenyl)propane) (manufactured by Lamberti, "ESACURE KIP 150", "ESACURE1"), polyethylene glycol 200-di(β-4(4-(2-dimethylamino-2-benzyl)butanonylphenyl)piperazine) (manufactured by IGM, "Omnipol This includes (910), (2-carboxymethoxythioxanthone)-(polytetramethylene glycol 250) diester (manufactured by IGM, "Omnipol TX"), (carboxymethoxymethoxybenzophenone)-(polyethylene glycol 250) diester (manufactured by IGM, "Omnipol BP"), etc. The above polymer sensitizers may be used individually or in combination of two or more types.

[0083] Polymer sensitizers with a molecular weight of 500 or more are less prone to migration, thus reducing the amount of volatile and migratory components remaining in the cured film (printed material) after extruding and curing active-ray curable ink. Furthermore, the curability of active-ray curable ink is improved, and oxygen inhibition during curing is reduced, eliminating the need for nitrogen purging, and allowing ink droplets to be cured solely by active-ray irradiation.

[0084] The polymer sensitizer content is preferably 0.5% to 10% by mass relative to the total mass of the active-ray curable ink. More preferably 1.0% or more by mass, even more preferably 1.5% or more by mass, and most preferably 2.0% or more by mass. Furthermore, it is more preferably 6.0% or less by mass, even more preferably 4.0% or less by mass, and most preferably 3.5% or less by mass.

[0085] Furthermore, the active-ray curing ink may contain other sensitizers to improve curability. These other sensitizers may be used individually or in combination of two or more.

[0086] Other sensitizers are not particularly limited, but examples of sensitizers include thioxanthones, benzophenones such as 4,4'-bis(diethylamino)benzophenone, anthraquinones, and coumarins. Specifically, examples include thioxanthone compounds such as 2,4-diethylthioxanthone, 2,4-dimethylthioxanthone, 2,4-diethylthioxanthe-9-one, 2,4-dichlorothioxanthone, 1-chloro-4-propoxythioxanthone, 2-chlorothioxanthone, 2-isopropylthioxanthone, and 4-isopropylthioxanthone; anthracene compounds such as 9,10-dibutoxyanthracene, 9,10-diethoxyanthracene, 9,10-dipropoxyanthracene, and 9,10-bis(2-ethylhexyloxy)anthracene; Michler ketone; and 4,4'-dialkylaminobenzophenones such as 4,4'-bis-(diethylamino)benzophenone.

[0087] Active-ray curing inks may contain colorants. By applying multiple types of active-ray curing inks with different types or amounts of colorants to a recording material and curing them, multi-color images can be formed. The colorants may be dyes, pigments, or a combination of both.

[0088] From the viewpoint of maintaining the image's color over a long period, the colorant is preferably a pigment. The pigment can be selected from, for example, yellow pigment, red or magenta pigment, blue or cyan pigment, and black pigment, depending on the color tone and color of the image to be formed. The pigment may also be a mixture of these.

[0089] Examples of yellow pigments include CIPigment Yellow (hereinafter also simply referred to as "PY") 1, PY3, PY12, PY13, PY14, PY17, PY34, PY35, PY37, PY55, PY74, PY81, PY83, PY93, PY94, PY95, PY97, PY108, PY109, PY110, PY137, PY138, PY139, PY153, PY154, PY155, PY157, PY166, PY167, PY168, PY180, PY185, and PY193.

[0090] An example of a red or magenta pigment is CIPigment Red (hereinafter also simply referred to as "PR"). 3, PR5, PR19, PR22, PR31, PR38, PR43, PR48:1, PR48:2, PR48:3, PR48:4, PR48:5, PR49:1, PR53:1, PR57:1, PR57:2, PR58:4, PR63:1, PR81, PR81:1, PR81:2, PR81:3, PR81:4, PR88, PR104, PR108, PR112, PR122, PR123, PR144, PR146, PR149, PR166, PR168, PR169, PR170, PR177, PR178, PR179, PR184, PR185, PR208, PR216, PR226, and PR257, CIPigment This includes Violet (hereinafter also simply referred to as "PV") 3, PV19, PV23, PV29, PV30, PV37, PV50, and PV88, as well as CIPigment Orange (hereinafter also simply referred to as "PO") 13, PO16, PO20, and PO36, among others.

[0091] Examples of blue or cyan pigments include CIPigment Blue (hereinafter also simply referred to as "PB") 1, PB15, PB15:1, PB15:2, PB15:3, PB15:4, PB15:6, PB16, PB17-1, PB22, PB27, PB28, PB29, PB36, and PB60.

[0092] Examples of green pigments include CIPigment Green (hereinafter also simply referred to as "PG") 7, PG26, PG36, and PG50.

[0093] Examples of black pigments include CIPigment Black (hereinafter also simply referred to as "PBk") 7, PBk26, and PBk28.

[0094] The above pigments may be used individually or in combination of two or more types.

[0095] The colorant content is preferably 0.1% by mass or more and 20.0% by mass or less relative to the total mass of the active-ray curable ink, and more preferably 0.4% by mass or more and 10.0% by mass or less. If the colorant content is 0.1% by mass or more relative to the total mass of the active-ray curable ink, the resulting cured film will have sufficient color development. If the colorant content is 20.0% by mass or less relative to the total mass of the active-ray curable ink, the viscosity of the ink will not become too high. The active-ray curable ink may also be a clear ink that does not contain any colorant, or contains only enough colorant so that the color of the cured film cannot be confirmed (or the cured film has light transmittance).

[0096] The pigment may be dispersed in a dispersant. The dispersant should be sufficient to adequately disperse the pigment. Examples of dispersants include hydroxyl group-containing carboxylic acid esters, salts of long-chain polyaminoamides and high molecular weight acid esters, salts of high molecular weight polycarboxylic acids, salts of long-chain polyaminoamides and polar acid esters, high molecular weight unsaturated acid esters, polymer copolymers, modified polyurethanes, modified polyacrylates, polyether ester-type anionic surfactants, naphthalene sulfonic acid formalin condensate salts, aromatic sulfonic acid formalin condensate salts, polyoxyethylene alkyl phosphate esters, polyoxyethylene nonylphenyl ether, and stearylamine acetate. The dispersants may be used individually or in combination of two or more types.

[0097] The dispersant content can be, for example, 20% to 70% by mass relative to the total mass of the pigment.

[0098] Active-ray curing inks may contain a gelling agent. The gelling agent is a compound that is solid at room temperature but becomes liquid when heated to approximately 70°C to 130°C, thereby causing the active-ray curing ink to undergo a sol-gel phase change due to temperature changes, for example, between room temperature and 70°C to 130°C. The gelling agent allows the active-ray curing ink to change into a sol phase upon heating, enabling its application to the recording material, while simultaneously causing the active-ray curing ink applied to the recording material to change into a gel phase, suppressing excessive wetting and spreading of the active-ray curing ink on the recording material (improving pinning properties).

[0099] Furthermore, the gelling agent captures residual unreacted active-ray polymerizable components (and polymerization initiators) in the crystal, suppressing their volatilization from the cured film. In addition, when polymerizable curable ink is applied to the recording material, the gelling agent seeps onto the surface of the ink and coats it. By forming a cured film in this state, the gelling agent coating the surface of the cured film can also suppress the volatilization of residual unreacted active-ray polymerizable components (and polymerization initiators) from the cured film.

[0100] Preferably, the gelling agent crystallizes in the ink at a temperature below the gelation temperature of the active-ray curable ink, forming a structure in which the photoactive-ray polymerizable component is enclosed in a three-dimensional space formed by the plate-like crystallized gelling agent. (Such a structure is hereinafter referred to as the "card house structure.") When the card house structure is formed, the liquid photoactive-ray polymerizable component is held within the above space, thereby further enhancing the pinning properties of the active-ray curable ink. From the viewpoint of making it easier to form the card house structure, it is preferable that the active-ray polymerizable component dissolved in the active-ray curable ink and the gelling agent are compatible.

[0101] The gelation temperature is the temperature at which, when an active-ray curable ink that has been sol-cured or liquefied by heating is cooled, the ink undergoes a phase transition from sol to gel, and the viscosity of the ink changes abruptly. Specifically, an active-ray curable ink that has been sol-cured or liquefied can be cooled while its viscosity is measured using, for example, a rheometer "MCR300" (manufactured by Anton Paar), and the temperature at which the viscosity rapidly increases can be defined as the gelation temperature of that ink. Conversely, a gelled active-ray curable ink can be heated while its viscosity is similarly measured, and the temperature at which the viscosity rapidly decreases can be defined as the sol-curing temperature of that ink.

[0102] Examples of gelling agents suitable for forming cardhouse structures by crystallization include ketone waxes, ester waxes, higher fatty acids, higher alcohols, and fatty acid amides, including N-substituted fatty acid amides and special fatty acid amides. These gelling agents may be used individually or in combination of two or more. For example, using ketone wax and ester wax in combination can further enhance the pinning properties of active-ray curable inks.

[0103] Examples of the above ketone waxes include dilignoseryl ketone, dibehenyl ketone, distearyl ketone, dieicosyl ketone, dipalmystyl ketone, dimyristyl ketone, myristyl palmityl ketone, and palmityl stearyl ketone. The above ketone waxes may be used individually or in combination of two or more types.

[0104] Examples of the ester waxes mentioned above include behenyl behenate, eicosyl eicosanoate, stearyl stearate, palmityl stearate, cetyl palmitate, myristyl myristate, cetyl myristate, stearyl stearate, oleyl palmitate, and glycerin fatty acid esters. These ester waxes may be used individually or in combination of two or more types.

[0105] Examples of the above-mentioned higher fatty acids include behenic acid, arachidic acid, stearic acid, palmitic acid, myristic acid, oleic acid, and erucic acid. These higher fatty acids may be used individually or in combination of two or more types.

[0106] Examples of the above-mentioned higher alcohols include stearyl alcohol and behenyl alcohol. These higher alcohols may be used individually or in combination of two or more types.

[0107] Examples of the above fatty acid amides include stearic acid amide, behenic acid amide, oleic acid amide, erucic acid amide, lauryl acid amide, ricinoleic acid amide, and 12-hydroxystearic acid amide. These fatty acid amides may be used individually or in combination of two or more types.

[0108] Examples of the above N-substituted fatty acid amides include N-stearyl stearate and N-oleyl palmitate. The above N-substituted fatty acid amides may be used individually or in combination of two or more types.

[0109] Examples of the special fatty acid amides mentioned above include N,N'-ethylenebisstearylamide, N,N'-ethylenebis-12-hydroxystearylamide, and N,N'-xylylenebisstearylamide. These special fatty acid amides may be used individually or in combination of two or more types.

[0110] The content of the gelling agent is preferably 0.5% by mass or more and less than 10.0% by mass, more preferably 1.0% by mass or more and less than 10.0% by mass, and even more preferably 2.0% by mass or more and 7.0% by mass or less, based on the total mass of the active-ray curable ink.

[0111] The active-ray curing ink may contain polymerization inhibitors, surfactants, polysaccharides, viscosity modifiers, resistivity modifiers, film-forming agents, UV absorbers, antioxidants, fade inhibitors, mold inhibitors, rust inhibitors, and the like. The above other components may be present in the composition as one type or as two or more types.

[0112] Examples of polymerization inhibitors include (alkyl)phenol, hydroquinone, catechol, resorcinol, p-methoxyphenol, t-butylcatechol, t-butylhydroquinone, pyrogallol, 1,1-picrylhydrazyl, phenothiazine, p-benzoquinone, nitrosobenzene, 2,5-di-t-butyl-p-benzoquinone, dithiobenzoyl disulfide, picric acid, cuperone, aluminum N-nitrosophenylhydroxylamine, tri-p-nitrophenylmethyl, N-(3-oxyanilino-1,3-dimethylbutylidene)aniline oxide, dibutylcresol, cyclohexanone oxime cresol, guaiacol, o-isopropylphenol, butyraldoxime, methyl ethyl ketoxime, and cyclohexanone oxime. These polymerization inhibitors may be used individually or in combination of two or more.

[0113] The content of the polymerization inhibitor can be 0.05% by mass or more and 0.2% by mass or less based on the total mass of the active-ray curable ink.

[0114] Examples of surfactants include silicone-based surfactants, acetylene glycol-based surfactants, and fluorine-based surfactants having a perfluoroalkenyl group. These surfactants may be used individually or in combination of two or more types.

[0115] The surfactant content is preferably 0.001% by mass or more and 10% by mass or less, relative to the total mass of the active-ray curable ink, and more preferably 0.001% by mass or more and 1.0% by mass or less.

[0116] Active-ray curing inks have high viscosity because they contain polymer sensitizers. Depending on the ink temperature at the time of ejection, the viscosity of active-ray curing ink can exceed 100 mPa·s, in which case ejection from the inkjet head 10 becomes difficult. The viscosity of active-ray curing ink can be determined, for example, by heating the active-ray curing ink to 100°C using a rheometer, measuring the viscosity with a stress-controlled rheometer "PhysicaMCR301" (manufactured by Anton Paar), and then cooling the ink to 20°C under conditions of a shear rate of 11.7 (1 / s) and a cooling rate of 0.1°C / s, and then obtaining a viscosity temperature dependence curve.

[0117] On the other hand, the viscosity of active-ray curable ink can be reduced by heating. For example, the viscosity of active-ray curable ink in the temperature range of 60°C to 90°C is 1 mPa·s to 50 mPa·s, preferably 3 mPa·s to 30 mPa·s. In other words, by heating the active-ray curable ink at a temperature of 60°C to 90°C during ejection, the viscosity of the active-ray curable ink can be reduced to a level that allows it to be ejected from the inkjet head 10. However, even after heating, the viscosity of active-ray curable ink is higher than that of active-ray curable ink that is not compatible with low migration, and adjacent crosstalk is more likely to occur.

[0118] When forming an image on a recording material M using the image forming apparatus 1 and active-ray curable ink described above, the active-ray curable ink is ejected from the inkjet head 10 toward the recording material M (ejection step). Then, the ink droplets of the active-ray curable ink that have landed on the recording material M are irradiated with an active ray to cure them (curing step).

[0119] In this embodiment, in the ejection process, the active-ray curable ink is heated to a temperature higher than 60°C but lower than or equal to 90°C before being ejected from the nozzle 101. This allows the viscosity of the active-ray curable ink containing the polymer sensitizer to be adjusted to a viscosity that can be ejected by the inkjet head 10, and an appropriate amount of ink can be properly ejected from the nozzle 101. If the heating temperature in the ejection process is 60°C or lower, the viscosity of the active-ray curable ink may not be sufficiently reduced, potentially leading to ejection failure. Furthermore, if the heating temperature is higher than 90°C, there is a concern that the deterioration of the inkjet head 10 will be accelerated. Therefore, it is preferable that the heating temperature in the ejection process be higher than 60°C but lower than or equal to 90°C.

[0120] The heating treatment of the active-wire curable ink in the ejection process is performed by the control unit 40 controlling the operation of the heating unit 122. The heating temperature of the heating unit 122 can be manually set by the user, for example, depending on the active-wire curable ink being used. Alternatively, the heating temperature of the heating unit 122 may be automatically set by the control unit 40 by referring to a table that associates the type of active-wire curable ink with the heating temperature, depending on the type of active-wire curable ink being used. The table to be referenced is stored, for example, in the ROM 42.

[0121] Thus, the image forming method and image forming apparatus 1 according to the embodiment are equipped with the following features individually or in appropriate combinations.

[0122] In other words, the image forming method according to the embodiment includes a discharge step of ejecting an active-ray curable ink from an inkjet head 10 toward a recording material M, and a curing step of curing ink droplets of the active-ray curable ink that have landed on the recording material M by irradiating them with an active ray. The active-ray curable ink contains an active-ray polymerizable component, a polymerization initiator, and a polymer sensitizer having a molecular weight of 500 or more. The inkjet head 10 includes a plurality of nozzles 101, a plurality of pressure chambers 102, a diaphragm layer 13b (diaphragm) that forms part of the wall surface of the plurality of pressure chambers 102, and a piezoelectric member 111 that generates pressure fluctuations in the pressure chambers 102 by applying a driving voltage. The piezoelectric member 111 has a driving piezoelectric element column 111A that is joined to the vibration region of the diaphragm layer 13b corresponding to the pressure chamber 102, and a non-driving piezoelectric element column 111B that is joined to the non-vibration region of the diaphragm layer 13b corresponding to the partition wall 102a of the pressure chamber 102. The maximum operating temperature of the inkjet head 10 is higher than 60°C, the pitch between the nozzles 101 is less than 1 / 75 inch, and the ejection process includes heating the active-ray curable ink to a temperature higher than 60°C and lower than or equal to 90°C.

[0123] The image forming apparatus 1 also includes an inkjet head 10 for ejecting active-ray curable ink, an active-ray irradiation unit 20 for curing ink droplets of active-ray curable ink that have landed on the recording material M by irradiating them with active rays, and a heating unit 122 for heating the active-ray curable ink. The active-ray curable ink contains an active-ray polymerizable component, a polymerization initiator, and a polymer sensitizer having a molecular weight of 500 or more. The inkjet head includes a plurality of nozzles 101, a plurality of pressure chambers 102, a diaphragm layer 13b (diaphragm) that forms part of the wall surface of the plurality of pressure chambers 102, and a piezoelectric member 111 that generates pressure fluctuations in the pressure chambers 102 by applying a driving voltage. The piezoelectric member 111 includes a driving piezoelectric element column 111A that is joined to the vibrating region of the diaphragm layer 13b corresponding to the pressure chamber 102, and a non-driving piezoelectric element column 111B that is joined to the non-vibrating region of the diaphragm layer 13b corresponding to the partition wall 102a of the pressure chamber 102. The upper limit operating temperature of the inkjet head 10 is higher than 60°C, and the pitch between the nozzles 101 is less than 1 / 75 inch. The heating unit 122 is capable of heating the active-wire curable ink to a temperature higher than 60°C and 90°C or lower.

[0124] According to the image forming method and image forming apparatus 1 of the embodiment, the active-ray curable ink contains a polymer sensitizer with a molecular weight of 500 or more, which enables low migration of printed materials. Furthermore, nitrogen purging during curing is unnecessary, allowing for miniaturization and cost reduction of the apparatus. While polymerizing the sensitizer increases the viscosity of the active-ray curable ink, the active-ray curable ink is heated to a temperature higher than 60°C but lower than 90°C before dispensing to reduce its viscosity, allowing for the appropriate amount of ink to be appropriately dispensed from the nozzle 101.

[0125] Even when the viscosity of active-wire curing ink is reduced by heating, it remains higher than active-wire curing ink that does not support low migration, making it prone to adjacent crosstalk. However, by using a bi-pitch piezoelectric element 111, the occurrence of adjacent crosstalk can be suppressed. Therefore, even if the pitch between nozzles 101 is less than 1 / 75 inch, adjacent crosstalk does not occur, and high-definition printing can be achieved. Furthermore, since the upper limit operating temperature of the inkjet head 10 is higher than 60°C, even if the active-wire curing ink is heated to a temperature higher than 60°C but below 90°C, the inkjet head 10 does not deteriorate, and ejection performance is ensured.

[0126] Therefore, according to the image forming method and image forming apparatus 1 of the embodiment, it is possible to achieve low migration and high quality of printed materials without impairing the durability of the inkjet head 10.

[0127] Preferably, the polymer sensitizer is a thioxanthone compound. This enhances the curability when curing an active-ray curable ink by ultraviolet irradiation.

[0128] Preferably, the above-mentioned active ray polymerizable component is a radical-active ray polymerizable compound. This further reduces oxygen inhibition during curing and improves the quality of printed materials.

[0129] Preferably, the recording material M is a long roll of recording material. This makes it possible to reduce migration and improve the quality of roll-shaped printed materials, which are prone to migration.

[0130] Preferably, the recording material M is a food packaging film. This makes it possible to reduce migration and improve the quality of food packaging for which safety standards such as migration are established.

[0131] Preferably, the recording material M is made of polyester, polyvinyl chloride, polyethylene, polyurethane, polypropylene, acrylic resin, polycarbonate, polystyrene, acrylonitrile-butadiene-styrene copolymer, polyethylene terephthalate, or polybutadiene terephthalate. This makes it possible to reduce migration and improve the quality of printed materials printed on the recording material M, which is prone to migration.

[0132] Preferably, the inkjet head 10 has multiple nozzles 101 arranged in the width direction of the recording material M, and is a one-pass system that prints on the transported recording material M at once. This makes it possible to reduce migration and improve the quality of printed materials, as well as speed up the printing process.

[0133] Preferably, the inkjet head 10 is of the circulating type. This prevents ink from accumulating and causing problems such as nozzle clogging, making it suitable when using high-viscosity active-wire curing inks.

[0134] Preferably, the driving frequency of the piezoelectric element 111 is 30 kHz or higher. When the driving frequency is 30 kHz or higher, adjacent crosstalk is more likely to occur compared to when the driving frequency is less than 30 kHz. However, by using a bi-pitch piezoelectric element 111, the occurrence of adjacent crosstalk can be prevented. Therefore, it is possible to achieve lower migration and higher quality of printed materials, as well as faster printing processing.

[0135] Although the present invention has been specifically described above based on embodiments, the present invention is not limited to the above embodiments and can be modified without departing from its spirit.

[0136] For example, the image forming apparatus 1 may employ a multi-pass method in which the inkjet head 10 scans the recording material M multiple times in the width direction to perform printing. Furthermore, the recording material M is not limited to a roll, but may also be in sheet form. Moreover, the present invention is suitable not only for the manufacture of food packaging, but also for the manufacture of printed materials requiring low migration properties.

[0137] The embodiments disclosed herein should be considered in all respects to be illustrative and not restrictive. The scope of the present invention is indicated by the claims rather than by the foregoing description, and all modifications within the meaning and scope equivalent to the claims are intended to be included.

[0138] All disclosures in the specification, drawings, and abstract contained in the Japanese application 2024-039371, filed on March 13, 2024, are incorporated herein by reference. [Explanation of symbols]

[0139] 1. Image forming apparatus 10, 10A~10E inkjet heads 20 Active ray irradiation section 30 Conveying section 40 Control Unit 101 Nozzles 102 Pressure Chamber 103 Ink channel 111 Piezoelectric component 111A Drive Piezoelectric Element Pole 111B Non-driven piezoelectric element pole 112 Head drive unit 121 Ink circulation unit 122 Heating section M Recording material

Claims

1. The ejection process involves ejecting activated-ray curing ink from the inkjet head toward the recording material, The process includes a curing step of curing ink droplets of the active-ray curable ink that have landed on the recording material by irradiating them with an active ray, The aforementioned activated ray curing ink is Actively polymerizable components, Polymerization initiator and It contains a polymer sensitizer having a molecular weight of 500 or more, The aforementioned inkjet head is Multiple nozzles, Multiple pressure chambers communicating with each of the multiple nozzles, A diaphragm that forms part of the wall surface of multiple pressure chambers, The device comprises a piezoelectric member that generates pressure fluctuations in the pressure chamber by applying a driving voltage, The piezoelectric member is A driving piezoelectric element column is joined to the vibration region of the diaphragm corresponding to the pressure chamber, It comprises a non-driven piezoelectric element column that is joined to the non-vibrating region of the diaphragm corresponding to the partition wall of the pressure chamber, The upper limit operating temperature for the inkjet head is higher than 60°C. The pitch between the nozzles is less than 1 / 75 inch. The discharge step includes a step of heating the active-ray curable ink to a temperature higher than 60°C and 90°C or lower. Image forming method.

2. The aforementioned polymer sensitizer is a thioxanthone compound. The image forming method according to claim 1.

3. The aforementioned activated ray polymerizable component is a radical activated ray polymerizable compound. The image forming method according to claim 1 or 2.

4. The recording material is a long, roll-shaped recording material. The image forming method according to claim 1 or 2.

5. The aforementioned recording material is a food packaging film. The image forming method according to claim 1 or 2.

6. The recording material is formed from polyester, polyvinyl chloride, polyethylene, polyurethane, polypropylene, acrylic resin, polycarbonate, polystyrene, acrylonitrile-butadiene-styrene copolymer, polyethylene terephthalate, or polybutadiene terephthalate. The image forming method according to claim 1 or 2.

7. The inkjet head has multiple nozzles arranged in the width direction of the recording material and uses a one-pass method to print on the transported recording material at once. The image forming method according to claim 1 or 2.

8. The aforementioned inkjet head is of the circulating type. The image forming method according to claim 1 or 2.

9. The driving frequency of the piezoelectric element is 30 kHz or higher. The image forming method according to claim 1 or 2.

10. An inkjet head that ejects activated-ray curing ink toward the recording material, An active ray irradiation unit that irradiates ink droplets of the active ray-curable ink that have landed on the recording material with active rays to cure them, The system comprises a heating unit for heating the activated-wire-curable ink, The aforementioned activated ray curing ink is Actively polymerizable components, Polymerization initiator and It contains a polymer sensitizer having a molecular weight of 500 or more, The aforementioned inkjet head is Multiple nozzles, Multiple pressure chambers communicating with each of the multiple nozzles, A diaphragm that forms part of the wall surface of multiple pressure chambers, The device comprises a piezoelectric member that generates pressure fluctuations in the pressure chamber by applying a driving voltage, The piezoelectric member is A driving piezoelectric element column is joined to the vibration region of the diaphragm corresponding to the pressure chamber, It comprises a non-driven piezoelectric element column that is joined to the non-vibrating region of the diaphragm corresponding to the partition wall of the pressure chamber, The upper limit operating temperature for the inkjet head is higher than 60°C. The pitch between the nozzles is less than 1 / 75 inch. The heating unit is capable of heating the activated-ray curable ink to a temperature higher than 60°C and 90°C or lower. Image forming apparatus.

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