Image forming apparatus and image forming method

Abstract

To provide an image forming apparatus capable of forming images that are resistant to cracking, have high abrasion resistance, and exhibit high internal hardening properties. [Solution] An image forming apparatus having an inkjet ink containing a polymerizable compound that polymerizes with an active ray, wherein the content of the polymerizable compound having a melting point of 25°C or higher relative to the total mass of the polymerizable compound is less than 3% by mass, and when the weighted average value (by mass) of the number of ethylene oxide groups per molecule in the polymerizable compound is X and the weighted average value (by mass) of the number of propylene oxide groups per molecule in the polymerizable compound is Y, X + Y is 3 or more and 9 or less, and the image forming apparatus having a pre-irradiation unit for pre-curing the inkjet ink and a main irradiation unit for main curing the pre-cured inkjet ink.

Description

[Technical Field]

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

[0002] Inkjet recording methods are used in various printing fields because they can form images simply and inexpensively. Among the inks used in inkjet recording methods, inkjet inks that cure with active rays (hereinafter referred to as active-ray curable inkjet inks) are known, and whose liquid component is a polymerizable compound that polymerizes with active rays (hereinafter referred to as active-ray polymerizable compound). When irradiated with active rays, active-ray curable inkjet ink hardens through polymerization of the active-ray polymerizable compound, firmly adhering the colorant to the recording medium. It is known that the formation of this cured film allows for the creation of desired images.

[0003] For example, Patent Document 1 discloses an active energy ray curable composition containing a monofunctional polymerizable compound and a polyfunctional polymerizable compound. According to Patent Document 1, a coating film (average thickness 10 μm) formed using the above composition can be cured by an integrated light intensity of 1500 mJ / cm². 2 A laminate (3 layers) of cured material obtained by irradiation with the active energy rays of the above-mentioned material was found to have excellent stretchability and strength. Furthermore, according to Patent Document 1, the above composition can also be used as an inkjet ink. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2016-172841 [Overview of the project] [Problems that the invention aims to solve]

[0005] As shown in Patent Document 1, active-ray curing inkjet inks are known.

[0006] Incidentally, recording media on which images have been formed using active-ray curing inkjet ink may be bent during transport or storage. In such cases, cracks may appear in the formed image. Therefore, it is desirable that active-ray curing inkjet ink can form images that are less prone to cracking (folding) when the recording media is bent.

[0007] Furthermore, in order to prevent the formed image from peeling off the recording medium, active-wire curing inkjet inks are required to form images with enhanced abrasion resistance (scratch resistance) and internal curing properties (adhesion to the substrate).

[0008] The present invention has been made in view of the above circumstances, and aims to provide an image forming apparatus capable of forming images that are resistant to cracking, have high abrasion resistance and internal hardening properties. It also aims to provide an image forming method using the said image forming apparatus. [Means for solving the problem]

[0009] One aspect of the present invention, for solving the above problems, relates to the following image forming apparatus [1] to

[11] . [1] An image forming apparatus having an inkjet ink containing a polymerizable compound that polymerizes by an active ray, wherein the content of the polymerizable compound having a melting point of 25°C or higher relative to the total mass of the polymerizable compound is less than 3% by mass. Let X be the weighted average value (by mass) of the number of ethylene oxide groups per molecule in the polymerizable compound, and Y be the weighted average value (by mass) of the number of propylene oxide groups per molecule in the polymerizable compound, such that X + Y is between 3 and 9. A pre-irradiation section for pre-curing the inkjet ink, The main irradiation unit for fully curing the pre-cured inkjet ink, An image forming apparatus having the following features. [2] The image forming apparatus according to [1], wherein the inkjet ink has a viscosity of 10 mPa·s or more and 25 mPa·s or less at 60°C. [3] The image forming apparatus according to [1] or [2], wherein the inkjet ink comprises a gelling agent. [4] The image forming apparatus according to any one of [1] to [3], wherein the weighted average value (by mass) of the polymerizable groups in the polymerizable compound is 130 g / eq or more and 300 g / eq or less. [5] The image forming apparatus according to any one of [1] to [4], wherein the total mass of the polymerizable compound containing a benzene ring and the polymerizable compound containing a glycerol skeleton is 15% by mass or more and 60% by mass or less, relative to the total mass of the polymerizable compound. [6] The above X+Y is 3.5 or more and 7 or less, The image forming apparatus according to any one of [1] to [5], wherein the mass of the polymerizable compound containing a benzene ring is 5% by mass or more and 40% by mass or less, relative to the total mass of the polymerizable compound. [7] The above X+Y is 3.5 or more and 5.5 or less, The weighted average value (by mass) of the polymerizable groups in the aforementioned polymerizable compound is 150 g / eq or more and 250 g / eq or less. The image forming apparatus according to any one of [1] to [6], wherein the mass of the polymerizable compound containing a benzene ring is 10% by mass or more and 30% by mass or less, relative to the total mass of the polymerizable compound. [8] The above X+Y is 3 or more and 6 or less, The weighted average value (by mass) of the polymerizable groups in the aforementioned polymerizable compound is 140 g / eq or more and 300 g / eq or less. The image forming apparatus according to any one of [1] to [7], wherein the mass of the polymerizable compound containing a glycerol skeleton is 20% by mass or more and 55% by mass or less, relative to the total mass of the polymerizable compound. [9] The above X+Y is 3 or more and 5 or less, The image forming apparatus according to any one of [1] to [8], wherein Y' is the weighted average value (by mass) of the number of propylene oxide groups per molecule of the polymerizable compound containing a glycerol skeleton, and Y' is 3 or more and 3.5 or less.

[10] When the integrated light quantity ratio in the preliminary irradiation unit is L1 and the integrated light quantity ratio in the main irradiation unit is L2, the image forming apparatus according to any one of [1] to [9], where L1:L2 is 20%:80% to 40%:60%.

[11] The total integrated light quantity by the preliminary irradiation unit and the main irradiation unit is 600 mJ / cm 2 The image forming apparatus according to any one of [1] to

[10] , which is as follows.

[0010] Another aspect of the present invention for solving the above problems relates to the image forming method of the following

[12] .

[12] An image forming method using the image forming apparatus according to any one of [1] to

[11] .

Effects of the Invention

[0011] According to the present invention, it is possible to provide an image forming apparatus that can form an image that is difficult to crack and has high abrasion resistance and internal hardness. Further, according to the present invention, it is possible to provide an image forming method using the image forming apparatus.

Brief Description of the Drawings

[0012] [Figure 1] FIG. 1 is a flowchart showing the image forming method according to the present embodiment. [Figure 2] FIG. 2 is a schematic diagram showing the configuration of an image forming apparatus capable of implementing the image forming method according to the present embodiment. [Figure 3] FIGS. 3A to C show examples of illuminance distributions.

Modes for Carrying Out the Invention

[0013] Hereinafter, embodiments of the present invention will be described in detail. Note that the present invention is not limited to the following embodiments.

[0014] <上記]] ​In this embodiment, the active-ray curing inkjet ink (hereinafter referred to as active-ray curing inkjet ink) contains a polymerizable compound that polymerizes with active rays (hereinafter referred to as active-ray polymerizable compound), where X is the weighted average value (by mass) of the number of ethylene oxide groups per molecule in the active-ray polymerizable compound, and Y is the weighted average value (by mass) of the number of propylene oxide groups per molecule in the polymerizable compound, such that X + Y is between 3 and 9. Furthermore, the content of polymerizable compounds with a melting point of 25°C or higher relative to the total mass of the active-ray polymerizable compound is less than 3% by mass.

[0015] The inventors have found that by ensuring that the activated linear polymerizable compound contained in the ink satisfies the above-mentioned X+Y values, it is possible to reduce the occurrence of image cracking (hereinafter referred to as "folding crack") when the recording medium is bent, and to form an image with high scratch resistance and internal hardening properties. In order to reduce the occurrence of image folding cracks, it is necessary to increase the flexibility of the image, and in order to increase scratch resistance and internal hardening properties, it is necessary to increase the hardness of the image. Therefore, it can be difficult to achieve both simultaneously.

[0016] However, the active-ray curable inkjet ink according to this embodiment makes it possible to achieve both. In other words, when X+Y is 3 or more, the polymerization chain of the active-ray polymerizable compound contains more ethylene oxide groups (hereinafter referred to as EO groups) and propylene oxide groups (hereinafter referred to as PO groups). Since EO groups and PO groups enhance molecular mobility, when X+Y is 3 or more, the flexibility of the cured film (image) is sufficiently increased, and the image can more easily follow the recording medium when it is bent. This makes it less likely for the image to crack.

[0017] On the other hand, if X+Y is increased too much, the flexibility of the image will be excessively increased, which will reduce the hardness of the cured film and decrease the scratch resistance of the image. Therefore, by keeping X+Y below 9, it is possible to avoid excessively increasing the flexibility of the cured film while also minimizing the decrease in its hardness. This improves the scratch resistance of the image.

[0018] Furthermore, by keeping X+Y ≤ 9, it is possible to suppress the excessive increase in ink viscosity caused by the excessive formation of hydrogen bonds between molecules of the active-linear polymerizable compound, which reduces molecular mobility. This improves injection stability.

[0019] Furthermore, injection stability can be enhanced by limiting the content of polymerizable compounds with a melting point of 25°C or higher to less than 3% by mass relative to the total mass of the active linear polymerizable compound. Polymerizable compounds with a melting point of 25°C or higher tend to increase the viscosity of the ink at room temperature or at the temperature at which the ink is heated during ink ejection. In contrast, limiting the content to less than 3% by mass can improve injection stability.

[0020] Furthermore, the image forming apparatus according to this embodiment has a pre-irradiation unit and a main irradiation unit for irradiating with active rays. As a result, the active ray-curable inkjet ink applied to the recording medium is pre-cured in the pre-irradiation unit and then fully cured in the main irradiation unit, which makes the image less prone to cracking and improves the scratch resistance and internal hardening properties of the image.

[0021] In this specification, the weighted average value X of the number of EO groups per molecule refers to the sum of values ​​calculated by multiplying the number of EO groups in one molecule of polymerizable compound contained in the active-ray polymerizable compound by the mass ratio of that polymerizable compound in the active-ray polymerizable compound. Similarly, the weighted average value Y of the number of PO groups per molecule refers to the sum of values ​​calculated by multiplying the number of PO groups in one molecule of polymerizable compound contained in the active-ray polymerizable compound by the mass ratio of that polymerizable compound in the active-ray polymerizable compound.

[0022] The active-ray curable inkjet ink of the present invention, based on the above findings, will be described in more detail below.

[0023] 1-1.Active radiation polymerizable compounds Active-ray polymerizable compounds are compounds that polymerize and crosslink upon irradiation with active rays. Examples of active rays include electron beams, ultraviolet rays, alpha rays, gamma rays, and X-rays. Of these, ultraviolet rays and electron beams are preferred, with ultraviolet rays being more preferred.

[0024] As described above, when X is the weighted average value (by mass) of the number of EO groups per molecule in the active ray polymerizable compound, and Y is the weighted average value (by mass) of the number of PO groups per molecule in the polymerizable compound, then X + Y is between 3 and 9.

[0025] X+Y is preferably 3.5 to 8, more preferably 3.5 to 7, more preferably 3.5 to 6, and more preferably 3.5 to 5.5. When X+Y is 3.5 or higher, the flexibility of the cured film is further increased, making it less likely for the image to crack. Also, when X+Y is 8 or lower, the hardness of the cured film is less likely to decrease, improving the scratch resistance of the image. Furthermore, when X+Y is 8 or lower, the ink viscosity is less likely to increase.

[0026] In the above X+Y, X is preferably between 1.5 and 7, and more preferably between 1.5 and 6. Since EO groups have higher molecular mobility than PO groups, a larger number of EO groups can further increase the flexibility of the cured film. Therefore, when X is 1.5 or higher, cracking of the image can be made less likely. Also, when X is 7 or lower, the hardness of the cured film is less likely to decrease, and the scratch resistance of the image can be further increased.

[0027] In the activated linear polymerizable compound, the weighted average value (by mass) of the number of repeating EO groups and PO groups per molecule is preferably 2 or more and 10 or less, and more preferably 2 or more and 8 or less.

[0028] In this specification, the number of repeating EO groups and PO groups per molecule refers to the number of consecutive EO groups or PO groups in the molecular chain. When a molecule contains multiple units consisting of consecutive EO groups or PO groups, the above number of repeating groups is the sum of the number of consecutive EO groups or PO groups divided by the number of such units. Furthermore, the weighted average value of the above number of repeating groups refers to the sum of the values ​​calculated by multiplying the above number of repeating groups per molecule of polymerizable compound contained in the active-ray polymerizable compound by the mass ratio of that polymerizable compound in the active-ray polymerizable compound, for each polymerizable compound.

[0029] When the weighted average of the number of repetitions is 2 or more, the EO group or PO group is continuous in the polymerization chain, which lengthens the region with high molecular mobility and further enhances the flexibility of the cured product. This further suppresses cracking in the image. In addition, when the weighted average of the number of repetitions is 10 or less, the hardness of the cured film is less likely to decrease, and the abrasion resistance of the image is further enhanced.

[0030] In this embodiment, the active-ray polymerizable compound includes an active-ray polymerizable compound having an EO group or an active-ray polymerizable compound having a PO group. Examples of active-ray polymerizable compounds having an EO group and active-ray polymerizable compounds having a PO group include radical polymerizable compounds and cationic polymerizable compounds. Of these, radical polymerizable compounds are preferred. A radical polymerizable compound is a compound having an ethylenically unsaturated bond that can be radically polymerized. The ink may contain only one radical polymerizable compound or a combination of two or more.

[0031] Examples of radical polymerizable compounds include unsaturated carboxylic acid esters and (meth)acrylates. Of these, (meth)acrylates are preferred. In this specification, "(meth)acrylate" means acrylate or methacrylate, and "(meth)acrylic" means acrylic or methacrylic.

[0032] Examples of (meth)acrylates containing an EO group include: polyethylene glycol diacrylate, EO-modified 1,6-hexanediol di(meth)acrylate, and EO-modified pentaerythritol tetraacrylate. Also included are EO-modified dipentaerythritol pentaacrylate and EO-modified dipentaerythritol hexaacrylate. Furthermore, EO-modified trimethylolpropane tri(meth)acrylate and EO-modified phenol acrylate are also included. Additionally, EO-modified nonylphenol (meth)acrylate, EO-modified cresol (meth)acrylate, and EO-modified bisphenol A diacrylate are also present.

[0033] Examples of (meth)acrylates containing a PO group include: tripropylene glycol diacrylate, PO-modified neopentyl glycol diacrylate, and PO-modified trimethylolpropane triacrylate. Also included are PO-modified glyceryl triacrylate, PO-modified bisphenol A diacrylate, and PO-modified nonylphenol acrylate.

[0034] The activated linear polymerizable compound may include a cationic polymerizable compound having an EO group and a cationic polymerizable compound having a PO group.

[0035] The content of the EO group-containing active-ray polymerizable compound and the PO group-containing active-ray polymerizable compound is preferably 65% ​​by mass or more, relative to the total mass of the active-ray polymerizable compound. The upper limit of the above content is not particularly limited, and is, for example, 100% by mass.

[0036] In this embodiment, the activated linear polymerizable compound may include polymerizable compounds that do not contain EO groups and PO groups, as long as the value of X+Y satisfies the above conditions.

[0037] Examples of polymerizable compounds that do not contain EO and PO groups include radical polymerizable compounds and cationic polymerizable compounds. Of these, radical polymerizable compounds are preferred.

[0038] Examples of the radical polymerizable compounds mentioned above include unsaturated carboxylic acid esters and (meth)acrylates. Of these, (meth)acrylates are preferred. The (meth)acrylates may be monofunctional or polyfunctional. In this specification, "(meth)acrylate" is a general term for "acrylate" and "methacrylate," and means one or both of them. "(meth)acryloyl group" is a general term for "acryloyl group" and "methacryloyl group," and means one or both of them.

[0039] Examples of monofunctional (meth)acrylates include: isoamyl acrylate, stearyl acrylate, lauryl acrylate, octyl acrylate, decyl acrylate, and isomiristyl acrylate. Also included are isostearyl acrylate, 2-ethylhexyl-diglycol acrylate, butoxyethyl acrylate, and phenoxyethyl acrylate. Furthermore, cumylphenoxyethyl acrylate, tetrahydrofurfuryl acrylate, isobornyl acrylate, and 2-hydroxyethyl acrylate are also included. Additionally, 2-hydroxypropyl acrylate, 2-hydroxybutyl acrylate, and t-butylcyclohexyl acrylate are also included.

[0040] Examples of bifunctional (meth)acrylates include: 1,4-butanediol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, and 1,9-nonanediol di(meth)acrylate. Also included are neopentyl glycol di(meth)acrylate, neopentyl glycol di(meth)acrylate hydroxypivalate, and polytetramethylene glycol di(meth)acrylate.

[0041] Examples of (meth)acrylates with three or more functionalities include: trimethylolpropane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol hexa(meth)acrylate, and others.

[0042] Examples of cationic polymerizable compounds include epoxy compounds and vinyl ether compounds.

[0043] Examples of the epoxy compounds mentioned above include: 3,4-epoxycyclohexylmethyl-3′,4′-epoxycyclohexanecarboxylate and bis(3,4-epoxycyclohexylmethyl)adipate. Also included are ε-caprolactone-modified 3,4-epoxycyclohexylmethyl-3′,4′-epoxycyclohexanecarboxylate and 1-methyl-4-(2-methyloxyranyl)-7-oxabicyclo[4,1,0]heptane. Furthermore, 2-(3,4-epoxycyclohexyl-5,5-spiro-3,4-epoxy)cyclohexanone-meth-dioxane and bis(2,3-epoxycyclopentyl)ether. Additionally, diglycidyl ether of 1,4-butanediol, diglycidyl ether of 1,6-hexanediol, triglycidyl ether of glycerin, and the like.

[0044] Examples of the vinyl ether compounds mentioned above include: ethyl vinyl ether, n-butyl vinyl ether, isobutyl vinyl ether, octadecyl vinyl ether, and cyclohexyl vinyl ether. Also included are hydroxybutyl vinyl ether, 2-ethylhexyl vinyl ether, cyclohexanedimethanol monovinyl ether, n-propyl vinyl ether, and isopropyl vinyl ether. Furthermore, monovinyl ether compounds including isopropenyl ether-o-propylene carbonate, dodecyl vinyl ether, diethylene glycol monovinyl ether, and octadecyl vinyl ether, as well as ethylene glycol divinyl ether, diethylene glycol divinyl ether, and triethylene glycol divinyl ether. Also included are propylene glycol divinyl ether, dipropylene glycol divinyl ether, and butanediol divinyl ether. Additionally, di or trivinyl ether compounds including hexanediol divinyl ether, cyclohexanedimethanol divinyl ether, and trimethylolpropane trivinyl ether, etc.

[0045] The weighted average value (mass basis) of the polymerizable groups in the active-ray polymerizable compound is preferably 130 g / eq to 300 g / eq, 150 g / eq to 250 g / eq, or 140 g / eq to 300 g / eq. The weighted average value (mass basis) of the polymerizable groups in the active-ray polymerizable compound is preferably 160 g / eq to 300 g / eq, more preferably 180 g / eq to 300 g / eq, and even more preferably 200 g / eq to 300 g / eq. A value of 130 g / eq or higher allows for a moderate reduction in the degree of crosslinking of the polymer in the active-ray polymerizable compound, thereby further increasing the flexibility of the cured film. This further suppresses cracking of the image. A value of 300 g / eq or lower allows for a further increase in the degree of curing of the cured film without excessively reducing the degree of crosslinking of the polymer, thereby further suppressing peeling of the image.

[0046] Furthermore, the weighted average value (by mass) of the polymerizable groups is preferably 160 g / eq to 200 g / eq when the active-ray curable inkjet ink contains a yellow pigment as a colorant. Also, the weighted average value (by mass) of the polymerizable groups is preferably 160 g / eq to 210 g / eq when the active-ray curable inkjet ink contains a black pigment as a colorant. Furthermore, the weighted average value (by mass) of the polymerizable groups is preferably 200 g / eq to 250 g / eq when the active-ray curable inkjet ink contains a red pigment as a colorant. Furthermore, the weighted average value (by mass) of the polymerizable groups is preferably 200 g / eq to 260 g / eq when the active-ray curable inkjet ink contains a blue pigment as a colorant. Yellow and black pigments readily absorb active rays. Therefore, when using yellow or black pigments, it is preferable to lower the weighted average value compared to when using other pigments (for example, red and blue pigments) in order to facilitate sufficient curing of the active-ray curable inkjet ink.

[0047] The equivalent weight of the polymerizable group mentioned above refers to the acrylic equivalent weight when the activated ray polymerizable compound is, for example, acrylate. The weighted average value of the equivalent weights of the polymerizable groups mentioned above refers to the sum of the values ​​obtained by multiplying the equivalent weight of the polymerizable group of each polymerizable compound by the mass ratio of each polymerizable compound in the activated ray polymerizable compound.

[0048] The active-ray polymerizable compound preferably contains a monofunctional polymerizable compound, and the content of the monofunctional polymerizable compound is more than 5% by mass and 40% by mass or less relative to the total mass of the active-ray curable inkjet ink. By including more than 5% by mass of the monofunctional polymerizable compound, the degree of crosslinking of the polymer of the active-ray polymerizable compound can be moderately reduced, thereby further increasing the flexibility of the cured film. This further suppresses cracking of the image. Furthermore, by keeping the above content of the monofunctional polymerizable compound at 40% by mass or less, the degree of crosslinking does not decrease too much, and the decrease in the scratch resistance of the image can be suppressed.

[0049] In this case, the activated ray polymerizable compound preferably further contains a polyfunctional polymerizable compound. This further suppresses the decrease in the image's scratch resistance. The mass ratio of monofunctional polymerizable compound to polyfunctional polymerizable compound (weight ratio of monofunctional / polyfunctional) is preferably 0 to 0.6, and more preferably 0.1 to 0.4.

[0050] (Polymerizable compounds with a glycerol skeleton) Polymerizable compounds preferably include compounds having a glycerol skeleton within their molecule. Having a glycerol skeleton within the molecule results in a branched structure. The branched structure has functional groups (e.g., acryloyl groups) at its ends that polymerize via active rays. Therefore, the compound can have three or more functional groups (three or more acryloyl groups). When such compounds polymerize, the polymer has both appropriate hardness and flexibility. Therefore, the resulting image is less likely to break when bent.

[0051] When the polymerizable compound contains a compound with a glycerol skeleton in its molecule, X+Y is preferably 3 to 6, and more preferably 3 to 5. Furthermore, when Y' is the weighted average value (by mass) of the number of propylene oxide groups per molecule in the polymerizable compound containing the glycerol skeleton, Y' is preferably 3 to 3.5.

[0052] The structural formula of glycerol, which forms the basis of the glycerol skeleton, is shown below.

[0053] [ka]

[0054] In this embodiment, "glycerol skeleton" refers to the portion of glycerol shown in structural formula (1) excluding the hydrogen atoms of the three hydroxyl groups. For example, "polyfunctional (meth)acrylate having a glycerol skeleton" refers to a compound in which the hydrogen atoms of the hydroxyl groups are replaced by other groups and which has two or more (meth)acryloyl groups at its termini.

[0055] A polyfunctional acrylate having a glycerol skeleton may be modified by introducing a polyoxyalkylene group (e.g., EO group, PO group) between the glycerol skeleton and the (meth)acryloyl group. In particular, a polyfunctional acrylate having a glycerol skeleton is preferably a PO-modified product in which a PO group has been introduced. The number of PO modifications is preferably in the range of 3 to 9, and more preferably in the range of 3 to 4.

[0056] By controlling the structure of the polyoxyalkylene group, the stereostructure and molecular weight of the polyfunctional acrylate having a glycerol backbone can be controlled, thereby controlling the hardness of the polymer and the viscosity of the ink. As a result, cracking and peeling during processing of the resulting recording can be further reduced. Furthermore, when used as an inkjet ink, the viscosity can be adjusted to exhibit good ejection properties.

[0057] A polyfunctional (meth)acrylate having a glycerol skeleton is not particularly limited as long as it satisfies the above definition. Examples of polyfunctional (meth)acrylates having a glycerol skeleton include: glycerin diacrylate, glycerin dimethacrylate, ethylene oxide-modified glycerin diacrylate, and ethylene oxide-modified glycerin dimethacrylate. Also, propylene oxide-modified glycerin diacrylate, propylene oxide-modified glycerin dimethacrylate, glycerin triacrylate, and glycerin trimethacrylate are also included. Furthermore, ethylene oxide-modified glycerin triacrylate, ethylene oxide-modified glycerin trimethacrylate, propylene oxide-modified glycerin triacrylate, and the like are also included.

[0058] A polyfunctional (meth)acrylate having a glycerol skeleton may be a compound in which three or more (meth)acryloyl groups are added to a polyglycerol skeleton. Examples of such compounds include ethylene oxide-modified diglycerin tetraacrylate and ethylene oxide-modified diglycerin tetramethacrylate. Other examples include propylene oxide-modified diglycerin tetraacrylate, propylene oxide-modified diglycerin tetramethacrylate, and ethylene oxide-modified tetraglycerin hexaacrylate. Other examples include ethylene oxide-modified tetraglycerin hexamethacrylate, propylene oxide-modified tetraglycerin hexaacrylate, and propylene oxide-modified tetraglycerin hexamethacrylate.

[0059] Examples of polyfunctional acrylates having a glycerol skeleton are shown in the following structural formulas (2) to (5). Structural formulas (2) and (3) represent a difunctional acrylate, structural formula (4) represents a trifunctional acrylate, and structural formula (5) represents a tetrafunctional acrylate. Structural formula (5) is a compound in which four acryloyl groups are added to a diglycerol skeleton. In this embodiment, the acryloyl groups in structural formulas (2) to (5) may be methacryloyl groups.

[0060] [ka]

[0061] In structural formulas (2) to (5), R1, R2, R3, and R4 each independently represent an alkylene group, a polyoxyalkylene group, or a hydrogen atom.

[0062] The alkylene group is not particularly limited and examples include methylene group, ethylene group, n-propylene group, isopropylene group, n-butylene group, isobutylene group, etc.

[0063] The polyoxyalkylene group is not particularly limited; for example, -(CH2CH2O) n -A structure represented by -(CH2CH2CH2O) n Examples of structures represented by - are shown. Note that n is an integer greater than or equal to 1.

[0064] Commercially available polyfunctional (meth)acrylates with a glycerol skeleton are preferably certified by the Japan Organic Resources Association as having a biomass content of 35% or more. "Biomass content" refers to the percentage (dry weight ratio) of biomass raw materials contained in the product. Examples of commercially available products that have obtained this certification include glycerin diacrylate "Aronix® M-920" (plant raw material ratio 45%, manufactured by Toagosei Co., Ltd.) and glycerin triacrylate "Aronix® M-930" (plant raw material ratio 37%, manufactured by Toagosei Co., Ltd.).

[0065] Based on the information in the Toagosei Group Research Annual Report 26TREND2020, No. 23, the ratio of plant-based raw materials can be expressed by the following formula (1). Formula (1) Ratio of plant-based raw materials [%] = (Molecular weight of plant-derived raw material skeleton ÷ Total molecular weight) × 100

[0066] Other commercially available products include, for example, propoxylated (3) glyceryl triacrylate "SR9020NS" (manufactured by Sartomer Co., Ltd.), diglycerin EO modified acrylate "Aronix® M-460" (30% plant-derived raw materials, manufactured by Toagosei Co., Ltd.), propoxylated (3.5) glyceryl triacrylate "EM2387" (manufactured by Choko Materials Industry Co., Ltd.), and ethoxylated (3) glyceryl triacrylate "EM2388" (manufactured by Choko Materials Industry Co., Ltd.).

[0067] (Meth)acrylates having a glycerol skeleton are preferably trifunctional rather than bifunctional. This further reduces folding, cracking, and peeling during processing of the resulting recordings. In addition, (meth)acrylates having a glycerol skeleton may be used in combination with different numbers of functional groups.

[0068] In the ink of this embodiment, the content of polyfunctional (meth)acrylate having a glycerol skeleton relative to the total mass of the polymerizable compound is 20% by mass or more. In addition, it is preferable that the content of trifunctional (meth)acrylate having a glycerol skeleton relative to the total mass of the polymerizable compound is 20% by mass or more. This reduces cracking during processing of the resulting recording.

[0069] It is preferable that the content of polyfunctional (meth)acrylate having a glycerol skeleton relative to the total mass of the polymerizable compound is within the range of 30% by mass or more and 60% by mass or less. This further reduces folding, cracking, and peeling during processing of the resulting recording. Furthermore, when used as an inkjet ink, the viscosity can be adjusted to exhibit good ejection properties.

[0070] In the ink of this embodiment, the ratio (Am / Wm) of the mass Am of the polyfunctional (meth)acrylate having a glycerol skeleton to the mass Wm of the gelling agent is preferably within the range of 3.5 to 16. This reduces cracking during processing of the resulting recorded material. Furthermore, when used as an inkjet ink, the viscosity can be adjusted to exhibit good ejection properties.

[0071] Furthermore, the inclusion of a polyfunctional (meth)acrylate having a glycerol skeleton tends to lower the overall solubility parameter (HSP value) of the polymerizable compound. This increases the compatibility between the polymerizable compound and the gelling agent. In other words, the solubility of the gelling agent increases, making it easier to include a larger amount of gelling agent in the ink. As a result, the pinning properties of the ink can be improved. From the viewpoint of the pinning properties of the ink, it is preferable that the mass ratio of the polyfunctional (meth)acrylate having a glycerol skeleton to the gelling agent is within the above range.

[0072] (Polymerizable compounds containing a benzene ring) It is preferable that the monofunctional polymerizable compound contains a compound having a benzene ring in its molecule. The presence of a benzene ring in the molecule is thought to increase the hardness of the cured film because the interaction between the benzene rings (π-π interaction) forms a stacked structure of benzene rings. Therefore, by having a benzene ring in the molecule of the monofunctional polymerizable compound, cracking of the image can be further suppressed while the scratch resistance of the image can be further improved.

[0073] The mass of the polymerizable compound containing a benzene ring relative to the total mass of the polymerizable compound is preferably 5% by mass or more and 40% by mass or less, and preferably 10% by mass or more and 30% by mass or less. The total mass of the polymerizable compound containing a benzene ring and the polymerizable compound containing a glycerol skeleton relative to the total mass of the polymerizable compound is preferably 15% by mass or more and 60% by mass or less.

[0074] The monofunctional polymerizable compound having a benzene ring in its molecule preferably contains one to two benzene rings. Such polymerizable compounds can increase the strength of the cured film by stacking the benzene rings.

[0075] The monofunctional polymerizable compound having a benzene ring in the molecule may or may not contain an EO group or a PO group, but it is preferable that it contains an EO group or a PO group, and more preferably that it contains an EO group. When the polymerizable compound has a polymerizable compound containing a benzene ring, X+Y is preferably 3.5 to 7, and more preferably 3.5 to 5.5.

[0076] When the monofunctional polymerizable compound having the benzene ring contains an EO group, the weighted average value (by mass) of the number of EO groups per molecule in the monofunctional polymerizable compound having the benzene ring is preferably 2 or more, and more preferably 4 or more. The EO group and PO group can increase the flexibility of the cured film. When a monofunctional polymerizable compound combines a benzene ring with an EO group and a PO group, it is possible to achieve both improved strength of the cured film due to the stacking of the benzene ring and improved flexibility of the cured film due to the EO group or PO group. Furthermore, the stacking of the benzene ring temporarily separates when the cured film, whose flexibility has been increased by the EO group or PO group, is stretched, making it easier to stretch the cured film and making the folded cured film less likely to break (further increasing crack resistance). On the other hand, since the temporarily separated benzene rings stack again when the stretching is released, it is thought that a decrease in the strength of the cured film due to stretching is less likely to occur. In this way, the polymerizable compound is thought to further increase the flexibility of the cured film without reducing the strength of the cured film, while further suppressing cracking as shown in the image. The upper limit of the weighted average of the number of EO groups is preferably 8. The weighted average of the number of EO groups per molecule is the sum of the values ​​obtained by multiplying the number of EO groups contained in one molecule of the monofunctional polymerizable compound having a benzene ring by the mass ratio of the monofunctional polymerizable compound in the active ray polymerizable compound, for each monofunctional polymerizable compound (containing a benzene ring).

[0077] In this case, the weighted average value (by mass) of the number of repeating EO groups per molecule in the monofunctional polymerizable compound having the benzene ring is preferably 2 or more, and more preferably 4 or more. From the viewpoint of facilitating stacking of benzene rings, the upper limit of the weighted average value (by mass) of the number of repeating groups is preferably 8.

[0078] Examples of monofunctional polymerizable compounds having a benzene ring in the molecule include radical polymerizable compounds and cationic polymerizable compounds. Of these, radical polymerizable compounds are preferred. The radical polymerizable compounds are preferably (meth)acrylates.

[0079] Examples of monofunctional (meth)acrylates containing a benzene ring in the molecule include: phenoxyethyl acrylate, 2-hydroxy-3-phenoxypropyl acrylate, and cumylphenoxyethyl acrylate. Also included are phenol acrylates, nonylphenol (meth)acrylate, cresol (meth)acrylate, and their EO or PO modified forms.

[0080] The content of monofunctional polymerizable compounds having a benzene ring in the molecule is preferably 0% to 40% by mass, and more preferably 5% to 25% by mass, relative to the total mass of the active linear polymerizable compounds. A content of 5% by mass further enhances the degree of curing of the cured film, thereby further suppressing image peeling. A content of 25% by mass or less further suppresses the decrease in flexibility of the cured film, thereby further suppressing image cracking.

[0081] (Polymerizable compounds with a melting point of 25°C or higher) As described above, in this embodiment, the polymerizable compound with a melting point of 25°C or higher is contained in less than 3% by mass relative to the total mass of the polymerizable compound with a melting point of 25°C or higher. From the viewpoint of further improving injection stability, the above content of the polymerizable compound with a melting point of 25°C or higher is preferably less than 1% by mass, more preferably less than 0.1% by mass, and even more preferably 0% by mass.

[0082] Examples of polymerizable compounds with a melting point of 25°C or higher include octadecyl acrylate, tris(2-acryloyloxyethyl) isocyanurate, and behenyl acrylate.

[0083] Whether the melting point is 25°C or higher can be determined by whether the polymerizable compound is liquid (fluid) or solid (non-fluid) at 25°C. Alternatively, it may be measured by thermal analysis methods (DSC, DTA, etc.).

[0084] The weight-average molecular weight (Mw) of the active linear polymerizable compound is preferably between 160 and 300, and more preferably between 200 and 300. The above weight-average molecular weight can be measured using gel permeation chromatography (GPC).

[0085] The content of the active-ray polymerizable compound can be 1% by mass or more and 97% by mass or less, preferably 30% by mass or more and 95% by mass or less, more preferably 50% by mass or more and 95% by mass or less, and even more preferably 70% by mass or more and 95% by mass or less, based on the total mass of the active-ray curable inkjet ink.

[0086] 1-2. Others The active-ray curable inkjet ink composition according to this embodiment may further contain other components such as gelling agents, colorants, surfactants, polymerization inhibitors, and humectants, to the extent that it achieves the effects of the present invention.

[0087] (Gelling agent) In this embodiment, the active-ray curable inkjet ink may contain a gelling agent. The inclusion of a gelling agent in the active-ray curable inkjet ink causes the ink to undergo a sol-gel phase transition (before irradiation with active rays). Specifically, the gelling agent is a compound that dissolves in the active-ray polymerizable compound contained in the ink when the ink containing the gelling agent is heated (for example, to 80°C), and crystallizes in the ink at around room temperature (for example, to 35°C), causing the ink to gel.

[0088] Preferably, the gelling agent crystallizes in the ink, forming a structure in which the active-ray polymerizable compound is encapsulated in a three-dimensional space formed by the plate-like crystallized gelling agent (hereinafter referred to as the "card house structure"). When the card house structure is formed, the liquid active-ray polymerizable compound is retained within the space, thereby increasing the gelling properties of the ink. As a result, dots formed by the ink adhering to the recording medium become less likely to wet and spread, and the pinning properties of the ink are improved.

[0089] Examples of gelling agents that can facilitate the formation of cardhouse structures through crystallization include: aliphatic ketones, aliphatic esters, glycerol compounds, pentaerythritol compounds, petroleum waxes, plant waxes, animal waxes, and mineral waxes. Also included are hydrogenated castor oil, modified waxes, higher fatty acids, higher alcohols, hydroxystearic acid, and fatty acid amides including N-substituted fatty acid amides and specialty fatty acid amides. Furthermore, higher amines, sucrose fatty acid esters, synthetic waxes, dibenzylidene sorbitol, dimer acids, and dimer ols are also included.

[0090] Of these, from the viewpoint of increasing polarity and further enhancing solubility in the active ray polymerizable compound, the gelling agent is preferably an aliphatic ketone, aliphatic ester, higher fatty acid, or higher alcohol, with aliphatic ketones and aliphatic esters being more preferred. Note that the gelling agent may be present as a single agent or as a combination of two or more agents.

[0091] Examples of aliphatic ketones include dibehenyl ketone, distearyl ketone, dieicosyl ketone, dipalmityl ketone, dilauryl ketone, dimyristyl ketone, myristylpalmityl ketone, and palmitylstearyl ketone.

[0092] Examples of aliphatic esters include: behenyl behenate, eicosyl eicosanoate, stearyl stearate, palmityl stearate, myristyl myristate, and cetyl myristate. Also included are fatty acid esters of monoalcohols such as oleyl palmitate, glycerol fatty acid esters, and sorbitan fatty acid esters. Furthermore, fatty acid esters of polyhydric alcohols such as propylene glycol fatty acid esters, ethylene glycol fatty acid esters, and polyoxyethylene fatty acid esters are also included.

[0093] Examples of higher fatty acids include behenic acid, arachidic acid, stearic acid, palmitic acid, myristic acid, lauric acid, oleic acid, and erucic acid.

[0094] Examples of higher alcohols include stearyl alcohol and behenyl alcohol.

[0095] Among aliphatic ketones and aliphatic esters, from the viewpoint of further enhancing the gelling property, an aliphatic ketone represented by the following general formula (G1) or an aliphatic ester represented by the following general formula (G2) is more preferable.

[0096] General formula (G1): R a -CO-R b General formula (G2): R c -COO-R d

[0097] In general formula (G1), R a and R b each independently represent a linear hydrocarbon group having 12 or more and 22 or less carbon atoms. In general formula (G2), R c and R d each independently represent a linear hydrocarbon group having 12 or more and 22 or less carbon atoms.

[0098] In general formulas (G1) and (G2), when the carbon number of R a to R d is 12 or more, the crystallinity of the gelling agents represented by general formulas (G1) and (G2) is further enhanced, and more sufficient space is generated in the above card house structure. Therefore, the active energy ray-polymerizable compound (A) is more easily sufficiently encapsulated in the above space, and the gelling property and pinning property of the ink are further improved.

[0099] Also, when the carbon number of R a to R d is 22 or less, the melting point of the gelling agents represented by general formulas (G1) and (G2) does not increase too much, and the solubility of the gelling agents increases.

[0100] Examples of aliphatic ketones represented by general formula (G1) include: dibehenyl ketones (21-22 carbon atoms), distearyl ketones (17-18 carbon atoms), and dieicosyl ketones (19-20 carbon atoms). Also included are dipalmitol ketones (15-16 carbon atoms), dimyristyl ketones (13-14 carbon atoms), and dilauryl ketones (11-12 carbon atoms). Furthermore, lauryl myristyl ketones (11-14 carbon atoms), lauryl palmityl ketones (11-16 carbon atoms), myristyl palmityl ketones (13-16 carbon atoms), and myristyl stearyl ketones (13-18 carbon atoms). Additionally, myristyl behenyl ketones (13-22 carbon atoms) and palmityl stearyl ketones (15-18 carbon atoms) are included. Furthermore, it includes palmitylbehenyl ketone (15-22) and stearylbehenyl ketone (17-22), among others. The carbon numbers in parentheses above represent the number of carbon atoms in each of the two hydrocarbon groups separated by the carbonyl group.

[0101] Examples of aliphatic esters represented by general formula (G2) include: behenyl behenate (21-22 carbon atoms), eicosyl eicosanoate (19-20 carbon atoms), and stearyl stearate (17-18 carbon atoms). Also included are palmityl stearate (17-16 carbon atoms), lauryl stearate (17-12 carbon atoms), and cetyl palmitate (15-16 carbon atoms). Furthermore, stearyl palmitate (15-18 carbon atoms), myristyl myristate (13-14 carbon atoms), and cetyl myristate (13-16 carbon atoms). Additionally, octyldodecyl myristate (13-20 carbon atoms), stearyl oleate (17-18 carbon atoms), and stearyl erucate (21-18 carbon atoms). Furthermore, it includes stearyl linoleate (17-18 carbon atoms), behenyl oleate (18-22 carbon atoms), and arachidyl linoleate (17-20 carbon atoms). The carbon numbers in parentheses above represent the number of carbon atoms in each of the two hydrocarbon groups separated by the ester group.

[0102] The gelling agent content is preferably 0.5% to 10% by mass, and more preferably 1.5% to 8% by mass, relative to the total mass of the active-ray curable inkjet ink. When the content is 1.5% by mass or more, the gelling and pinning properties of the ink can be further enhanced. Furthermore, when the content is 8% by mass or less, the solubility of the gelling agent in the active-ray polymerizable compound can be further enhanced.

[0103] (Coloring agent) The coloring agent can be a dye or a pigment, but pigments are preferred because they have good dispersibility with the ink components and excellent weather resistance. Depending on the colors of the image to be formed, the pigment can be selected from, for example, yellow pigment, red pigment, blue pigment, black pigment, and white pigment.

[0104] Examples of yellow pigments include: Pigment Yellow (PY) 1, 3, 12, 13, 14, 17, 34, 35, 37, 55, 74, 81, 83, 93, 94, 95, 97, 108, 109, 110, 137, 138, 139, 153, 154, 155, 157, 166, 167, 168, 180, 185, 193, etc. Of these, PY185 and PY150 are preferred from the viewpoint of further reducing the amount of impurities in the ink composition and further increasing the electrical resistance of the insulating film.

[0105] Examples of red pigments include: Pigment Red (PR) 3, 5, 19, 22, 31, 38, 43, 48:1, 48:2, 48:3, 48:4, 48:5, 49:1, 53:1, 57:1, 57:2, 58:4, 63:1, 81, 81:1, 81:2, 81:3, 81:4, 88, 104, 108, 112, 122, 123, 144, 146, 149, 166, 168, 169, 170, 177, 178, 179, 184, 185, 202, 208, 216, 226, 257; Pigment Violet (PV) 3, 19, 23, 29, 30, 37, 50, 88; Pigment Orange (PO) This includes 13, 16, 20, 36, etc. Of these, PR122 and PV19 are preferred from the viewpoint of further reducing the amount of impurities in the ink composition and further increasing the electrical resistance of the insulating film.

[0106] Examples of blue pigments include Pigment Blue (PB) 1, 15, 15:1, 15:2, 15:3, 15:4, 15:6, 16, 17:1, 22, 27, 28, 29, 36, and 60. Of these, PB15:3 and PB15:4 are preferred from the viewpoint of further reducing the amount of impurities in the ink composition and further increasing the electrical resistance of the insulating film.

[0107] Examples of black pigments include CIPigment Black (hereinafter also simply referred to as "PBk") 7, PBk26, and PBk28.

[0108] The white pigment can be any pigment that causes the cured film formed by the hardening of the white ink to exhibit a white color. Examples of white pigments include inorganic pigments such as titanium dioxide, zinc oxide, calcium carbonate, barium sulfate, and aluminum hydroxide. Of these, titanium dioxide is preferred.

[0109] The crystalline form of the titanium dioxide described above may be rutile, anatase, or blue kite. However, from the viewpoint of making it easier to reduce the particle size of the white pigment, the anatase type, which has a lower specific gravity, is preferred. Furthermore, from the viewpoint of improving the opacity of the formed image, the rutile type, which has a higher refractive index in the visible light region, is preferred.

[0110] The colorant content is preferably 0.1% to 10% by mass, and more preferably 1% to 5% by mass, relative to the total mass of the ink composition. The white pigment content is preferably 3% to 8% by mass.

[0111] (Pigment dispersant) The above-mentioned active-ray curable ink may contain a pigment dispersant for dispersing the pigment. Examples of pigment 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, and salts of long-chain polyaminoamides and polar acid esters. Also included are high molecular weight unsaturated acid esters, polymer copolymers, modified polyurethanes, modified polyacrylates, and polyether ester-type anionic surfactants. Furthermore, naphthalene sulfonic acid formalin condensate salts, aromatic sulfonic acid formalin condensate salts, polyoxyethylene alkyl phosphate esters, polyoxyethylene nonylphenyl ether, and stearylamine acetate are also included.

[0112] The pigment dispersant content is preferably 10% by mass or more and 200% by mass or less relative to the total mass of the pigment, and more preferably 20% by mass or more and 100% by mass or less. When the dispersant content is 10% by mass or more relative to the total mass of the pigment, the dispersion stability of the pigment is enhanced, and when the dispersant content is 200% by mass or less relative to the total mass of the pigment, the ink ejection performance from the inkjet head becomes more stable.

[0113] (Activated ray polymerization initiator) In this embodiment, the active-ray curable inkjet ink may contain an active-ray polymerization initiator (hereinafter simply referred to as "polymerization initiator"). The polymerization initiator only needs to be capable of initiating the polymerization of the active-ray polymerizable compound by irradiation with an active ray. For example, when the active-ray curable inkjet ink contains a radical polymerizable compound, the polymerization initiator can be a radical polymerization initiator, and when the active-ray curable ink contains a cationic polymerizable compound, the polymerization initiator can be a cationic polymerization initiator (photoacid generator). However, when the active-ray curable inkjet ink can be sufficiently cured without a polymerization initiator, such as when curing the active-ray curable inkjet ink by electron beam irradiation, the polymerization initiator is not necessary.

[0114] Radical polymerization initiators include intramolecular bond cleavage type radical polymerization initiators and intramolecular hydrogen abstraction type radical polymerization initiators.

[0115] Examples of intramolecular bond cleavage radical polymerization initiators include: diethoxyacetophenone, 2-hydroxy-2-methyl-1-phenylpropan-1-one, and benzyldimethyl ketal. Also included are 1-(4-isopropylphenyl)-2-hydroxy-2-methylpropan-1-one and 4-(2-hydroxyethoxy)phenyl-(2-hydroxy-2-propyl)ketone. Furthermore, acetophenone-based initiators including 1-hydroxycyclohexylphenyl ketone, 2-methyl-2-morpholino(4-methylthiophenyl)propan-1-one, and 2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)-butanone are also included. Benzoins, including benzoin, benzoin methyl ether, and benzoin isopropyl ether, are also included. Additionally, acylphosphine oxide-based initiators, including 2,4,6-trimethylbenzoin diphenylphosphine oxide, and benzyl and methylphenylglyoxyesters are also included.

[0116] Examples of intramolecular hydrogen abstraction radical polymerization initiators include: benzophenone, o-benzoylmethyl benzoate, 4-phenylbenzophenone, 4,4'-dichlorobenzophenone, hydroxybenzophenone, and 4-benzoyl-4'-methyl-diphenyl sulfide. Also included are benzophenone-based initiators, such as acrylic benzophenone, 3,3',4,4'-tetra(t-butylperoxycarbonyl)benzophenone, and 3,3'-dimethyl-4-methoxybenzophenone. Furthermore, thioxanthone-based initiators, such as 2-isopropylthioxanthone, 2,4-dimethylthioxanthone, 2,4-diethylthioxanthone, and 2,4-dichlorothioxanthone, are included. Finally, aminobenzophenone-based initiators, such as Michler's ketone and 4,4'-diethylaminobenzophenone, are included. It also contains 10-butyl-2-chloroacridone, 2-ethylanthraquinone, 9,10-phenancelenequinone, and camphorquinone, among others.

[0117] Examples of cationic polymerization initiators include photoacid generators. Examples of photoacid generators include: B(C6F5)4 aromatic onium compounds, including diazonium, ammonium, iodonium, sulfonium, and phosphonium. - PF6 - AsF6 - SbF6 - CF3SO3 - This includes sulfonates that generate sulfonic acid, such as salts, and halides that photocatalyze hydrogen halides. It also contains iron allene complexes, among others.

[0118] The content of the polymerization initiator is not particularly limited, as long as it does not reduce the applicability to the surface of the recording medium, and the active-ray curable inkjet ink is sufficiently cured by irradiation with active rays (e.g., ultraviolet light). For example, the content of the polymerization initiator is preferably 0.1% to 20% by mass, and more preferably 1% to 10% by mass, based on the total mass of the active-ray curable inkjet ink.

[0119] (Polymerization inhibitor) In this embodiment, the active-ray curable inkjet ink may contain a polymerization inhibitor.

[0120] Examples of polymerization inhibitors include: (alkyl)phenol, hydroquinone, catechol, resorcinol, p-methoxyphenol, t-butylcatechol, t-butylhydroquinone, and pyrogallol. Also included are 1,1-picrylhydrazyl, phenothiazine, p-benzoquinone, nitrosobenzene, 2,5-di-t-butyl-p-benzoquinone, and dithiobenzoyl disulfide. Furthermore, picric acid, cuperone, aluminum N-nitrosophenylhydroxylamine, tri-p-nitrophenylmethyl, and N-(3-oxyanilino-1,3-dimethylbutylidene)aniline oxide. Additionally, dibutylcresol, cyclohexanone oxime cresol, guaiacol, o-isopropylphenol, butyraldoxime, methyl ethyl ketoxime, and cyclohexanone oxime are also included.

[0121] The content of the polymerization inhibitor is not particularly limited, but it is preferably 0.05% by mass or more and 10.00% by mass or less based on the total mass of the active-ray curable inkjet ink.

[0122] (Surfactants) In this embodiment, the active-ray curable inkjet ink may contain a surfactant for adjusting the surface tension.

[0123] Examples of surfactants include anionic surfactants, such as dialkyl sulfosuccinates, alkylnaphthalene sulfonates, and fatty acid salts; nonionic surfactants, such as polyoxyethylene alkyl ethers, polyoxyethylene alkyl allyl ethers, acetylene glycols, and polyoxyethylene-polyoxypropylene block copolymers; cationic surfactants, such as alkylamine salts and quaternary ammonium salts; silicone-based surfactants; and fluorine-based surfactants.

[0124] The surfactant content is not particularly limited, but is preferably 0.001% by mass or more and 10% by mass or less, relative to the total mass of the active-ray curable inkjet ink, and more preferably 0.001% by mass or more and 1.0% by mass or less.

[0125] In this embodiment, the active-ray curable inkjet ink may, in addition to the above components, optionally contain a fixing resin, viscosity modifier, resistivity modifier, film-forming agent, ultraviolet absorber, antioxidant, fade inhibitor, mold inhibitor, rust inhibitor, and the like.

[0126] 1-3. Physical properties of activated-ray curing inkjet inks The viscosity of the active-ray curing ink at 60°C is preferably 10 mPa·s to 25 mPa·s, and more preferably 10 mPa·s to 15 mPa·s. This improves the ejection performance when the ink is heated and ejected in the inkjet head. In this embodiment, the viscosity can be adjusted to the above range by ensuring that X+Y satisfies the above value. Furthermore, if the ink contains a gelling agent, the viscosity can also be adjusted to the above range by adjusting the amount of gelling agent.

[0127] When the active-ray curing ink contains a gelling agent, the viscosity of the active-ray curing ink at 80°C is preferably 6 mPa·s to 25 mPa·s, and more preferably 7 mPa·s to 15 mPa·s. This improves the ejection performance when the ink is heated and ejected in the inkjet head.

[0128] The viscosity can be measured using a rheometer. For example, the pre-coat agent is heated to 100°C, and while measuring the viscosity with a stress-controlled rheometer (Anton Paar Physica MCR301 (cone plate diameter: 75 mm, cone angle: 1.0°)), the ink is cooled to 20°C under conditions of a shear rate of 11.7 (1 / s) and a cooling rate of 0.1°C / s to obtain a viscosity temperature dependence curve. The viscosity can then be determined by reading the viscosity at 60°C from the obtained temperature dependence curve.

[0129] 1-4. Method for preparing active-ray curable inkjet ink Active-ray curable inkjet inks can be prepared by mixing the above-mentioned active-ray polymerizable compound, a gelling agent, and any other components under heating. It is preferable to filter the resulting mixture through a predetermined filter. When preparing an ink containing a pigment, it is preferable to prepare a pigment dispersion containing the pigment and the active-ray polymerizable compound, and then mix the pigment dispersion with the other components. The pigment dispersion may further contain a dispersant.

[0130] The above-mentioned pigment dispersion can be prepared by dispersing the pigment in an activated ray polymerizable compound. The pigment dispersion can be performed using, for example, a ball mill, sand mill, attritor, roll mill, agitator, Henschel mixer, colloid mill, ultrasonic homogenizer, pearl mill, wet jet mill, or paint shaker. A dispersant may also be added at this time.

[0131] Furthermore, when using multiple types of active-ray polymerizable compounds, the active-ray polymerizable compounds may be mixed first to prepare an active-ray polymerizable composition, and then the active-ray polymerizable composition, the gelling agent, and any other components may be mixed under heating.

[0132] 2. Image forming method Figure 1 is a flowchart illustrating the image forming method according to this embodiment. The image forming method according to this embodiment includes a step (S10) of ejecting droplets of the above-mentioned active-ray curable inkjet ink from an inkjet head and applying them to the surface of a recording medium. The image forming method also includes a step (S20) of pre-irradiating the applied droplets of active-ray curable inkjet ink with an active ray to pre-cure them. Furthermore, the method includes a step (S30) of fully curing the pre-cured material.

[0133] 2-1. Step of applying active-ray curable inkjet ink to a recording medium (Step S10) In this process, the above-mentioned active-ray curable inkjet ink is ejected from the inkjet head and applied to the surface of the recording medium (at a position corresponding to the image to be formed).

[0134] The ink ejection method from the inkjet head may be either on-demand or continuous. On-demand inkjet heads may use electromechanical conversion methods such as single-cavity, double-cavity, bender, piston, shear-mode, and shared-wall types. They may also use electro-thermal conversion methods such as thermal inkjet and bubble jet ("bubble jet" is a registered trademark of Canon). Furthermore, the inkjet head may be either a scanning or line-type inkjet head.

[0135] When the droplets of the above-mentioned active-ray curable ink contain a gelling agent, they are ejected from the inkjet head in a heated, sol-like state, and therefore preferably as follows: Specifically, it is preferable to set the temperature of the ink when it is filled into the inkjet head to be between the gelling temperature of the ink and 30°C. If the temperature of the above-mentioned active-ray curable ink inside the inkjet head is 10°C or higher than the gelling temperature, a decrease in ejection performance due to the ink gelling inside the inkjet head or on the nozzle surface is less likely to occur. On the other hand, if the temperature of the ink inside the inkjet head is 30°C or lower than the gelling temperature, deterioration of the components due to high temperature is less likely to occur.

[0136] The method for heating active-ray curing inkjet ink is not particularly limited. For example, at least one of the ink supply system, such as the ink tanks, supply pipes, and pre-chamber ink tanks immediately before the head, which constitute the head carriage, as well as filtered piping and piezo heads, can be heated by a panel heater, ribbon heater, and warm water.

[0137] From the viewpoint of further improving recording speed and image quality, the amount of ejected droplets of active-ray curable inkjet ink is preferably 2 pL to 20 pL.

[0138] The recording medium is not particularly limited and can be ordinary uncoated paper, coated paper, synthetic paper YUPO ("YUPO" is a registered trademark of YUPO Corporation), various plastics and their films used for flexible packaging. Examples of various plastic films include PP film, PET film, OPS film, OPP film, ONy film, PVC film, PE film, and TAC film. Other plastics that can be used include polycarbonate, (meth)acrylic resin, ABS, polyacetal, PVA, and rubbers.

[0139] The active-ray curing inkjet ink can be applied to a recording medium by either directly depositing the ejected ink onto the recording medium, or by depositing the ejected ink onto an intermediate transfer medium to form an intermediate image, and then transferring the intermediate image from the intermediate transfer medium to the recording medium.

[0140] 2-2. Process for pre-curing and fully curing the active-ray curing inkjet ink (Processes S20, S30) In this process, droplets of active-ray curable inkjet ink applied to the recording medium in step S10 are irradiated with active rays to pre-cur and fully cure the droplets. This forms an image consisting of a cured film of the active-ray curable inkjet ink. Furthermore, the formed image is less prone to cracking and has high abrasion resistance and internal hardening properties.

[0141] The active ray can be selected from, for example, electron beams, ultraviolet rays, alpha rays, gamma rays, and X-rays, but ultraviolet rays or electron beams are preferred. The ultraviolet ray is preferably light having a peak wavelength of 360 nm to 410 nm. Furthermore, the ultraviolet ray is preferably irradiated from an LED light source. LEDs emit less radiant heat compared to conventional light sources (e.g., metal halide lamps). Therefore, when irradiated with an active ray, LEDs make it less likely for the ink to melt and less likely to cause uneven gloss.

[0142] When the total integrated light amount is set to 100%, and the integrated light amount ratio due to preliminary irradiation is L1, and the integrated light amount ratio due to main irradiation is L2, the ratio L1:L2 is preferably 20%:80% to 40%:60%, and preferably 20%:80% to 30%:70%.

[0143] The total integrated light intensity of the pre-irradiation and main irradiation can be set appropriately according to the amount of ink applied, etc., and is not particularly limited. For example, the total integrated light intensity could be 400 mJ / cm². 2 More than 500mJ / cm 2 More than 600mJ / cm 2 It may be greater than or equal to the above. The upper limit of the total integrated light intensity is, for example, 800 mJ / cm². 2The following is possible. Also, from the perspective of reducing energy consumption, the total integrated light intensity should be 600 mJ / cm². 2 The following is preferable:

[0144] Figures 3A-C show schematic illuminance distributions to illustrate an example of integrated light intensity. In Figures 3A-C, the horizontal axis represents the transport distance of the recording medium from the upstream end of the active light irradiation area, and the vertical axis represents illuminance. The dashed lines in Figures 3A-C indicate the center position when the active light irradiation area is divided in half in the direction of recording medium transport. The left half of Figures 3A-C represents the upstream side (preliminary irradiation), and the right half represents the downstream side (main irradiation).

[0145] As shown in Figure 3A, the illuminance distribution may be a smooth bimodal distribution with one peak in the upstream section and one peak in the downstream section. Alternatively, as shown in Figure 3B, the illuminance distribution may have a peak only in the downstream section. Furthermore, as shown in Figure 3C, the distribution may have a stepwise change in illuminance. In the illuminance distribution of Figure 3B, during pre-irradiation, the illuminance gradually increases as the transport distance increases, reaching a peak during main irradiation. Here, the integrated light quantity can be calculated by multiplying the illuminance by the irradiation time of the active rays. In this embodiment, since the transport speed of the recording medium is constant, the value obtained by multiplying the illuminance by the transport distance can be treated as a value equivalent to the integrated light quantity. That is, in Figures 3A-C, the integrated light quantity on the upstream side and the integrated light quantity on the downstream side can be compared by comparing the area of ​​the shaded area on the left half with the area of ​​the shaded area on the right half. In this embodiment, the area of ​​the shaded area on the right half (downstream side) is larger than the area of ​​the shaded area on the left half (downstream side).

[0146] 3. Image forming apparatus The following describes an image forming apparatus 100 capable of performing the image forming method described above.

[0147] Figure 2 is a schematic diagram showing the configuration of the image forming apparatus 100 according to this embodiment. As shown in Figure 2, the image forming apparatus 100 has an inkjet head 110, a transport unit 120, and an irradiation unit 130. The irradiation unit 130 has a pre-irradiation unit 131 and a main irradiation unit 132. In Figure 2, the arrows indicate the transport direction of the recording medium.

[0148] The inkjet head 110 has a nozzle surface 113 on which the nozzle 111 ejection ports are located, which faces the transport unit 120 when forming an image, and ejects active-ray curable inkjet ink onto the recording medium 200 transported by the transport unit 120. From the viewpoint of improving the ejection performance of the active-ray curable inkjet ink, the inkjet head 110 may have a temperature adjustment means for adjusting the ink temperature to lower the viscosity of the ink. Examples of temperature adjustment means include a panel heater, a ribbon heater, and a heating means using warm water.

[0149] The inkjet head 110 may be a scanning-type inkjet head whose width in the direction perpendicular to the transport direction of the recording medium is smaller than that of the recording medium 200. Alternatively, it may be a line-type inkjet head whose width in the direction perpendicular to the transport direction of the recording medium is larger than that of the recording medium 200.

[0150] The nozzle 111 has an outlet on the nozzle surface 113. The number of nozzles 111 can be equal to or greater than the number of inks used for image formation (e.g., 4).

[0151] The transport unit 120 transports the recording medium 200 so that, when forming an image, the recording medium 200 facing the inkjet head 110 moves directly below the inkjet head 110 in the vertical direction. For example, the transport unit 120 has a drive roller 121, a driven roller 122, and a transport belt 123.

[0152] The irradiation unit 130 consists of a pre-irradiation unit 131 and a main irradiation unit 132. The pre-irradiation unit 131 pre-cures the active-ray curable inkjet ink, and the main irradiation unit 132 fully cures the pre-cured ink. The integrated light intensity of the pre-irradiation unit is less than that of the main irradiation unit. Performing pre-irradiation and main irradiation in this manner enhances the internal curing properties of the image. The "pre-irradiation unit and main irradiation unit" are not particularly limited as long as they can perform pre-irradiation and main irradiation. The "pre-irradiation unit and main irradiation unit" may be separate, independent irradiation units as shown in Figure 2, or they may be the upstream and downstream sides of a single irradiation unit. In this case, the pre-irradiation unit is located upstream in the transport direction, and the main irradiation unit is located downstream of the pre-irradiation unit. Each irradiation unit irradiates the ink on the transported recording medium with an active ray.

[0153] The upstream pre-irradiation section 131 and the downstream main irradiation section 132 can be configured, for example, by varying the arrangement density of the active ray irradiation sources (e.g., ultraviolet irradiation LEDs) that irradiate with active rays. For example, the pre-irradiation section 131 can have a lower arrangement density of active ray irradiation sources, while the main irradiation section 132 can have a higher arrangement density of active ray irradiation sources. Furthermore, the pre-irradiation section 131 and the main irradiation section 132 can be configured by varying the distance from the recording medium to which the ink has been applied. For example, the pre-irradiation section 131 can have a greater distance between the active ray irradiation source and the recording medium, while the main irradiation section can have a closer distance between the active ray irradiation section and the recording medium.

[0154] In addition to the above configuration, the image forming apparatus 100 may also have an ink tank (not shown) for storing active-ray curable ink before ejection. It may also have an ink channel (not shown) that allows ink to flow between the ink tank and the inkjet head 110. Furthermore, it may have a control unit (not shown) that controls the operation of the inkjet head 110, the transport unit 120, and the irradiation unit 130.

[0155] The image forming apparatus 100 may also have an intermediate transfer body and a transfer unit (neither of which are shown). In this case, the inkjet head 110 ejects active-ray curable inkjet ink onto the intermediate transfer body, causing it to land on the surface of the intermediate transfer body, and forming an intermediate image on the surface of the intermediate transfer body by the aggregation of droplets of active-ray curable inkjet ink. Subsequently, the transfer unit transfers the intermediate image from the surface of the intermediate transfer body to the surface of the recording medium. Then, the irradiation unit 130 irradiates the intermediate image transferred to the surface of the recording medium with active rays to cure the droplets of active-ray curable inkjet ink. [Examples]

[0156] The present invention will be described below with reference to examples. The scope of the present invention is not to be limited by the examples.

[0157] 1. Preparation / Synthesis of Materials The materials used in the preparation of the active-ray curing inkjet ink are listed below.

[0158] 1-1. Pigment dispersion 9 parts by mass of pigment dispersant (EFKA-7701, manufactured by BASF) and 71 parts by mass of tripropylene glycol diacrylate were placed in a stainless steel beaker and heated on a hot plate at 65°C for 1 hour while stirring. After cooling to room temperature, 20 parts by mass of one of the following pigments were added to the stainless steel beaker, and then the mixture was placed in a glass bottle with 200 g of zirconia beads (0.5 mm in diameter, manufactured by Nikkatoh Co., Ltd.) and sealed tightly. This pigment-containing solution was dispersed using a paint shaker, and then the zirconia beads were removed to obtain a pigment dispersion. The dispersion time was 4 hours when using cyan or black pigment, and 6 hours when using magenta or yellow pigment. • Cyan pigment (C pigment): Pigment Blue 15:4 (Chromofine Blue 6332JC, manufactured by Dainichi Seika Kogyo Co., Ltd.) • Magenta pigment (M pigment): Mixed crystal of Pigment Violet 19 and Red 202 (CINQUASIA MAGENTA RT-355D, manufactured by BASF) • Yellow pigment (Y pigment): Pigment Yellow 185 (D1155, manufactured by BASF) • Black pigment (K pigment): Pigment Black 7 (#52, manufactured by Mitsubishi Chemical Corporation)

[0159] 1-2.Active radiation polymerizable compound m1: Polyester acrylate (ETERCURE 6361-100: Manufactured by Choko Materials Industry Co., Ltd.) (8-functional, number of EO groups: 8, average number of EO group repeats: 1, molecular weight: 561, acrylic equivalent: 70 g / eq, melting point: less than 25°C) m2: Tripropylene glycol diacrylate (EM223: manufactured by Choko Materials Industry Co., Ltd.) (Bifunctional, Number of PO groups: 3, Average number of PO group repeats: 3, Molecular weight: 300, Acrylic equivalent: 150 g / eq, Melting point: Below 25°C) m3: Polyester acrylate oligomer (CN2270NS: manufactured by Arkema) (Bifunctional, Number of PO groups: 5, Average number of PO group repeats: 2.5, Molecular weight: 692, Acrylic equivalent: 251 g / eq, Melting point: Below 25°C) m4:3EO-modified trimethylolpropane triacrylate (EM2382: manufactured by Choko Materials Industry Co., Ltd.) (Trifunctional, Number of EO groups: 9, Average number of EO group repeats: 3, Molecular weight: 692, Acrylic equivalent: 231 g / eq, Melting point: Below 25°C) m5:14EO-modified polyethylene glycol diacrylate #600 (M286: manufactured by Miwon) (Bifunctional, Number of EO groups: 14, Average number of EO group repetitions: 14, Molecular weight: 708, Acrylic equivalent: 354 g / eq, Melting point: Below 25°C) m6:3PO-modified trimethylolpropane triacrylate (M360: manufactured by Miwon) (Trifunctional, Number of PO groups: 3, Average number of PO group repeats: 1, Molecular weight: 470, Acrylic equivalent: 157 g / eq, Melting point: Below 25°C) m7:4EO-modified nonylphenol acrylate (M164: manufactured by Miwon) (Number of EO groups: 4, Average number of EO group repeats: 4, Molecular weight: 450, Acrylic equivalent: 450 g / eq, Melting point: Below 25°C) m8: Lauryl acrylate (D4129(LA): Manufactured by Tokyo Chemical Industry Co., Ltd.) (Monofunctional: Number of EO or PO groups: 0, Molecular weight: 240, Acrylic equivalent: 240 g / eq, Melting point: Below 25°C) m9:4EO-modified phenol acrylate (M144: manufactured by Miwon) (Monofunctional, Number of EO groups: 4, Average number of EO group repeats: 4, Molecular weight: 324, Acrylic equivalent: 324 g / eq, Melting point: Below 25°C) m10:3PO-modified glyceryl triacrylate (SR9020NS: manufactured by Arkema) (Trifunctional, Number of PO groups: 3, Average number of PO group repeats: 1, Molecular weight: 429, Acrylic equivalent: 143 g / eq, Melting point: Below 25°C) m11: Octadecyl acrylate (SR9020NS: Manufactured by Osaka Organic Chemical Industry Co., Ltd.) (Monofunctional: Number of EO or PO groups: 0, Molecular weight: 324, Acrylic equivalent: 324 g / eq, Melting point: 30°C) m12:8EO-modified nonylphenol acrylate (M166: manufactured by Miwon) (Monofunctional, Number of EO groups: 8, Average number of EO group repeats: 8, Molecular weight: 626, Acrylic equivalent: 624 g / eq, Melting point: Below 25°C) m13: Decanediol diacrylate (DOD-N: Manufactured by Shin-Nakamura Chemical Industry Co., Ltd.) (Bifunctional, Number of EO or PO groups: 0, Molecular weight: 282, Acrylic equivalent: 141 g / eq, Melting point: Below 25°C) m14: Tricyclodecane dimethanol diacrylate (A-DCP: manufactured by Shin-Nakamura Chemical Industry Co., Ltd.) (Bifunctional, Number of EO or PO groups: 0, Molecular weight: 304, Acrylic equivalent: 152 g / eq, Melting point: Below 25°C) m15:9EO-modified trimethylolpropane triacrylate (M3190: manufactured by Miwon) (Trifunctional, Number of EO groups: 9, Average number of EO group repeats: 3, Molecular weight: 693, Acrylic equivalent: 231 g / eq, Melting point: Below 25°C) m16: Ditrimethylolpropanetetraacrylate (SR355: manufactured by Arkema) (Tetrafunctional, Number of EO or PO groups: 0, Molecular weight: 466, Acrylic equivalent: 117 g / eq, Melting point: Below 25°C) m17: 2.5PO-modified nonylphenol acrylate (EM2181: manufactured by Choko Materials Industry Co., Ltd.) (Monofunctional, Number of PO groups: 2.5, Average number of PO group repeats: 2.5, Molecular weight: 419, Acrylic equivalent: 419 g / eq, Melting point: Below 25°C) m18: (5-ethyl-1,3-dioxan-5-yl)methyl acrylate (E1334: manufactured by Tokyo Chemical Industry Co., Ltd.) (Monofunctional, Number of EO or PO groups: 0, Molecular weight: 200, Acrylic equivalent: 200 g / eq, Melting point: Below 25°C) m19: Isobornyl acrylate (IBXA: manufactured by Osaka Organic Chemical Industry Co., Ltd.) (Monofunctional, Number of EO or PO groups: 0, Molecular weight: 208, Acrylic equivalent: 208 g / eq, Melting point: Below 25°C) m20: Tris(2-acryloyloxyethyl) isocyanurate (T2325: Manufactured by Tokyo Chemical Industry Co., Ltd.) (Trifunctional, Number of EO or PO groups: 0, Molecular weight: 423, Acrylic equivalent: 141 g / eq, Melting point: 53°C) m21: 3.5PO-modified glyceryl triacrylate (EM2387: manufactured by Choko Kogyo Co., Ltd.) (Trifunctional, number of EO or PO groups: 3.5, molecular weight: 458, acrylic equivalent: 153 g / eq, melting point: less than 25°C) m22:3EO-modified glyceryl triacrylate (EM2388: manufactured by Choko Kogyo Co., Ltd.) (Trifunctional, number of EO or PO groups: 3, molecular weight: 386, acrylic equivalent: 129 g / eq, melting point: less than 25°C) m23: 6PO-modified glyceryl triacrylate (MX-1: synthetic product synthesized by known methods) (Trifunctional, number of EO or PO groups: 6, molecular weight: 603, acrylic equivalent: 201 g / eq, melting point: less than 25°C) m24:2EO-modified phenol acrylate (Monofunctional, Number of EO groups: 2, Average number of EO group repeats: 2, Molecular weight: 236, Acrylic equivalent: 236 g / eq, Melting point: Below 25°C) m25:2EO-modified phenol acrylate (Monofunctional, Number of EO groups: 2, Average number of EO group repeats: 2, Molecular weight: 236, Acrylic equivalent: 236 g / eq, Melting point: Below 25°C)

[0160] Of the above-mentioned activated ray polymerizable compounds, the melting points of m11 and m20 were taken from catalog values, while the melting points of the other activated ray polymerizable compounds were determined to be below 25°C by confirming that they are liquid at room temperature (25°C).

[0161] 1-3. Gelling agent G1: Behenyl behenate (WEP-3, manufactured by NOF Corporation) G2: Stearyl stearate (Exceparl SS, manufactured by Kao Corporation)

[0162] 1-4. Active ray polymerization initiators • Initiator 1 (Omnirad 819, manufactured by IGM Resins BV) • Initiator 2 (Speedcure 2-ITX, manufactured by Arkema)

[0163] 1-5. Polymerization inhibitors Irgasutab UV-10 (manufactured by BASF)

[0164] 1-6. Surfactants KF-352A (manufactured by Shin-Etsu Chemical Co., Ltd.)

[0165] 2. Preparation of active-ray curable inkjet ink Pigment dispersions, active-ray polymerizable compounds, gelling agents, polymerization initiators, polymerization inhibitors, and surfactants were placed in stainless steel beakers to achieve the compositions shown in Tables 1-5, and the mixture was stirred at 105°C for 45 minutes. Subsequently, the mixture was filtered through an ADVANTEC Teflon® 3μm membrane filter to obtain active-ray curable inkjet inks (Comparative Examples Inks 1-4, Example Inks 1-19).

[0166] [Table 1]

[0167] [Table 2]

[0168] [Table 3]

[0169] [Table 4]

[0170] [Table 5]

[0171] 3. Image Formation Monochromatic images were formed using a line-type inkjet recorder with any of the active-ray curing inkjet inks from Comparative Examples 1-4 and Examples 1-18. The inkjet head temperature of the inkjet recorder was set to 80°C. A 5cm x 5cm solid image was printed on a recording medium (OK Topcoat+ 127g, manufactured by Oji Paper Co., Ltd.). A piezo head was used as the ejection head. The ejection conditions were such that the volume of one drop was 9.0 pl, and the droplet velocity was approximately 6 m / s, recording at a resolution of 1200 dpi x 1200 dpi. The recording speed was 500 mm / s. Image formation was performed in an environment of 23°C and 55% RH. dpi represents the number of dots per inch (2.54 cm). After image formation, ultraviolet light was irradiated using a pre-irradiation unit and a main irradiation unit equipped with LED lamps (Phoseon Technology, 395 nm, water-cooled LEDs) located downstream of the recorder. The irradiation conditions were set to seven different types, A, B, and C-1 to C-5, as shown in Table 6 below. A and B are the irradiation conditions for the comparative example, and C1-1 to C-5 are the irradiation conditions for the example. The illuminance distribution for C-1 to C-5, as shown in Figure 3B, shows a gradual increase in illuminance during the preliminary irradiation and a peak during the main irradiation.

[0172] [Table 6]

[0173] 4. Evaluation (cracked) A paper folding machine (AFV-564FKT, manufactured by Horizon Co., Ltd.) was used to perform mountain folds on the image formed on the recording medium. The state of the image was then observed, and the percentage of the area where the recording medium was not exposed due to cracking (non-exposed area) was determined by image analysis. The crackability was evaluated according to the following criteria. A crackability of 3 or higher is preferable. 5: No image cracks were found. 4: Cracks were visible in the image, and only a small amount of white background was exposed. 3: Cracks were observed in the image, and white areas were exposed in less than half of the area. 2: Cracks were observed in the image, and white areas were exposed in more than half of the area. 1: Cracks were observed in the image, and white areas were exposed throughout the entire image.

[0174] (Scratch resistance) A polycarbonate lens-shaped molded body was rubbed back and forth 15 times against an image formed on a recording medium, applying the loads shown below. The load at which the image peeled off was recorded. The loads were 200g, 250g, 300g, 350g, and 400g. A scratch resistance of 250g or higher is preferable.

[0175] (Tape release properties (internal curing)) An image formed on a recording medium was covered with Nichiban tape, and after being passed back and forth 10 times with a roller bearing a load of 500g, the tape was peeled off, and the area of ​​the peeled-off image was checked. The following criteria were used for evaluation. A tape peelability of 3 or higher is preferable. 4: No peeling 3: It is peeling off very slightly. 2: Half of it is peeling off 1: The entire surface is peeling off.

[0176] (Injection properties) For each sample's image output, we visually checked for any white streaks (white streaks due to poor printing) in the 100% printed area during the 10th and 100th prints. 3: There were no white spots, or there were one or two white spots, but they were at a level that did not cause any practical problems. 2: The number of areas with white spots was five or less, which was at a level that was practically acceptable. 1: Numerous white areas occurred, causing practical problems.

[0177] (viscosity) The viscosity at 60°C was determined for Comparative Examples Inks 1-4 and Example Inks 1-19. Viscosity was determined from the complex viscosity at 60°C in the viscosity change curve measured using a modular compact rheometer (MCR302e, Anton Paar) while varying the temperature from 90°C to 30°C in vibration mode. Based on the measured viscosity, evaluation was performed according to the following criteria. 2: The viscosity was 10-25 mPa·s. 1: The viscosity was outside the range of 10-25 mPa·s.

[0178] The evaluation results are summarized in Tables 7-13. The parameters of each ink used are also shown.

[0179] [Table 7]

[0180] [Table 8]

[0181] [Table 9]

[0182] [Table 10]

[0183] [Table 11]

[0184] [Table 12]

[0185] [Table 13]

[0186] As can be seen from Tables 7-13, by pre-curing and fully curing the inkjet ink using the example inks, it was found that images with high resistance to cracking, abrasion resistance, and tape peelability (internal curing) could be formed. In addition, example inks 1-18 also showed high injection stability. [Industrial applicability]

[0187] The inkjet ink of the present invention can form an image that is less prone to cracking when the recording medium is bent, while also being less likely to peel off the recording medium. Therefore, the present invention is useful in the field of image formation. [Explanation of Symbols]

[0188] 100 Image forming apparatus 110 Inkjet Heads 120 Conveying section 130 Irradiation area 131 Preliminary irradiation section 132 Main irradiation area

Claims

1. An image forming apparatus having an inkjet ink containing a polymerizable compound that polymerizes by an active ray, The content of polymerizable compounds with a melting point of 25°C or higher relative to the total mass of the polymerizable compounds is less than 3% by mass. Let X be the weighted average value (by mass) of the number of ethylene oxide groups per molecule in the polymerizable compound, and Y be the weighted average value (by mass) of the number of propylene oxide groups per molecule in the polymerizable compound, such that X + Y is 3 or more and 9 or less. A pre-irradiation section for pre-curing the inkjet ink, The main irradiation unit for fully curing the pre-cured inkjet ink, An image forming apparatus having the following features.

2. The image forming apparatus according to claim 1, wherein the inkjet ink has a viscosity of 10 mPa·s or more and 25 mPa·s or less at 60°C.

3. The image forming apparatus according to claim 1, wherein the inkjet ink contains a gelling agent.

4. The image forming apparatus according to claim 1, wherein the weighted average value (by mass) of the polymerizable groups in the polymerizable compound is 130 g / eq or more and 300 g / eq or less.

5. The image forming apparatus according to claim 1, wherein the total mass of the polymerizable compound containing a benzene ring and the polymerizable compound containing a glycerol skeleton, relative to the total mass of the polymerizable compound, is 15% by mass or more and 60% by mass or less.

6. The above X + Y is 3.5 or more and 7 or less, The image forming apparatus according to claim 1, wherein the mass of the polymerizable compound containing a benzene ring is 5% by mass or more and 40% by mass or less, relative to the total mass of the polymerizable compound.

7. The above X + Y is 3.5 or more and 5.5 or less, The weighted average value (by mass) of the polymerizable groups in the polymerizable compound is 150 g / eq or more and 250 g / eq or less. The image forming apparatus according to claim 1, wherein the mass of the polymerizable compound containing a benzene ring is 10% by mass or more and 30% by mass or less, relative to the total mass of the polymerizable compound.

8. The above X + Y is 3 or more and 6 or less, The weighted average value (by mass) of the polymerizable groups in the polymerizable compound is 140 g / eq or more and 300 g / eq or less. The image forming apparatus according to claim 1, wherein the mass of the polymerizable compound containing a glycerol skeleton is 20% by mass or more and 55% by mass or less, relative to the total mass of the polymerizable compound.

9. The above X + Y is 3 or more and 5 or less, The image forming apparatus according to claim 1, wherein Y' is the weighted average value (by mass) of the number of propylene oxide groups per molecule in the polymerizable compound containing a glycerol skeleton, and Y' is 3 or more and 3.5 or less.

10. The image forming apparatus according to claim 1, wherein when the integrated light intensity ratio in the pre-irradiation section is L1 and the integrated light intensity ratio in the main irradiation section is L2, L1:L2 is 20%:80% to 40%:60%.

11. The total integrated light intensity from the pre-irradiation unit and the main irradiation unit is 600 mJ / cm². ２ The image forming apparatus according to claim 1, which is as follows:

12. An image forming method using an image forming apparatus according to any one of claims 1 to 11.

Images