Inkjet ink and image forming method

Abstract

To provide an inkjet ink which can enhance the solubility of a gelling agent into ink and sufficiently increase the gelling property of ink, and to provide an image forming method using the same.SOLUTION: There is provided an inkjet ink containing a polymerizable compound which polymerizes by an active ray and a gelling agent, and undergoing sol-gel phase transition by a gelling agent, wherein the polymerizable compound includes a first polymerizable compound containing a benzene ring and an ethylene oxide group or a propylene oxide group in the molecule in which the total number of the ethylene oxide group and the propylene oxide group is two or more, the content of the first polymerizable compound is 5 mass% or more based on the total mass of the ink, the gelling agent is a compound which reversibly causes the inkjet ink to undergo a sol-gel phase transition by a temperature change and contains a hydrocarbon group having 22 or less carbon atoms.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to ink-jet inks and imaging methods. [Background technology]

[0002] Inkjet recording methods are used in various printing fields because they can form images easily and inexpensively. Known inkjet inks for use in inkjet recording methods include actinic ray-curable inkjet inks (hereinafter referred to as actinic ray-curable inkjet inks), which contain a polymerizable compound that is polymerized by actinic ray (hereinafter referred to as actinic ray-polymerizable compound) as a liquid component. When actinic ray-curable inkjet inks are irradiated with actinic ray, the actinic ray-polymerizable compound is polymerized and the coloring material is firmly attached to the recording medium. The formation of this cured film allows a desired image to be formed.

[0003] It is known that actinic radiation-curable inkjet inks contain a gelling agent to suppress excessive wetting and spreading of ink droplets after landing and improve pinning properties. The gelling agent can cause the ink to undergo a reversible sol-gel phase transition in response to a temperature change.

[0004] For example, Patent Document 1 discloses an actinic radiation curable inkjet ink containing a gelling agent containing an alkyl chain having 12 or more carbon atoms, a photopolymerizable compound containing a specific (meth)acrylate compound, and a photopolymerization initiator, and an image forming method using the same. Patent Document 1 states that the ink can cause a sol-gel phase transition of the ink even when the content of the gelling agent is small, and furthermore, the ejection stability and curing property of the ink can be improved.

[0005] Patent Document 2 discloses an actinic radiation curable inkjet ink composition that contains a gelling agent such as an aliphatic ketone or aliphatic ester having a carbon chain with 12 or more carbon atoms, an amine-modified oligomer, a pigment, and a polymer dispersant having a tertiary amine group. According to Patent Document 2, the inkjet ink composition increases the crosslink density of the ink cured film and suppresses the migration of the gelling agent, thereby suppressing blooming. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2013-226745 A [Patent Document 2] International Publication No. 2017 / 073654 Summary of the Invention [Problem to be solved by the invention]

[0007] As disclosed in Patent Documents 1 and 2, actinic ray curable inkjet inks containing a gelling agent are known.

[0008] In actinic radiation curable inks containing a gelling agent, the gelling agent is dissolved by heating the ink when it is ejected, and then the gelling agent is crystallized by a drop in the liquid temperature when the ink lands, thereby gelling the ink. To improve ejection properties from an inkjet head, the gelling agent is required to have high solubility in the ink when it is heated.

[0009] Furthermore, according to the studies of the present inventors, it was not possible to sufficiently gel the ink with the actinic ray curable inkjet inks described in Patent Documents 1 and 2. In order to sufficiently improve the pinning ability of the ink, it is desirable for the ink to thicken more sufficiently by cooling after landing on a substrate (to sufficiently improve the gelling ability of the ink).

[0010] The present invention has been made in consideration of the above circumstances, and has an object to provide an ink-jet ink that can increase the solubility of a gelling agent in the ink and sufficiently increase the gelling properties of the ink, and an image forming method using the same. [Means for solving the problem]

[0011] In order to solve the above problems, one aspect of the present invention relates to an ink-jet ink as set forth in the following items [1] to

[10] . [1] An ink-jet ink that is cured by actinic radiation, comprising: a polymerizable compound that is polymerized by actinic radiation; and a gelling agent, the gelling agent causing a sol-gel phase transition, the polymerizable compound includes a first polymerizable compound containing a benzene ring and an ethylene oxide group or a propylene oxide group in a molecule, the total number of the ethylene oxide groups and the propylene oxide groups being 2 or more; the content of the first polymerizable compound is greater than 5% by mass based on the total mass of the ink-jet ink; The gelling agent contains a linear or branched hydrocarbon group having 22 or less carbon atoms. Inkjet ink. [2] The ink-jet ink according to [1], wherein the first polymerizable compound includes a monofunctional polymerizable compound. [3] The ink-jet ink according to [1] or [2], wherein the content of the first polymerizable compound is greater than 5 mass % and less than 40 mass % relative to the total mass of the ink-jet ink. [4] The ink-jet ink according to any one of [1] to [3], wherein the first polymerizable compound includes a polymerizable compound in which the total number of the ethylene oxide groups or the propylene oxide groups in the molecule is 4 or more. [5] The ink-jet ink according to any one of [1] to [4], wherein the first polymerizable compound includes a polymerizable compound containing a linear or branched hydrocarbon group in the molecule. [6] The ink-jet ink according to any one of [1] to [5], wherein the content of the gelling agent is 0.5% by mass or more and 10.0% by mass or less, based on the total mass of the ink-jet ink. [7] The ink-jet ink according to any one of [1] to [6], wherein the gelling agent is at least one compound selected from the group consisting of aliphatic ketones, aliphatic esters, glycerol-based compounds, and pentaerythritol-based compounds. [8] The ink-jet ink according to any one of [1] to [7], wherein the gelling agent is an aliphatic ketone or an aliphatic ester. [9] The ink-jet ink according to any one of [1] to [8], wherein the gelling agent is an aliphatic ester.

[10] The inkjet ink according to any one of [1] to [9], further comprising a pigment.

[0012] In order to solve the above problems, another aspect of the present invention relates to an image forming method according to the following item

[11] .

[11] A step of applying the ink-jet ink according to any one of [1] to

[10] from an ink-jet head onto a surface of a recording medium; irradiating the applied inkjet ink with actinic radiation to cure the inkjet ink; The image forming method according to claim 1, Effect of the Invention

[0013] According to the present invention, it is possible to provide an ink-jet ink that can increase the solubility of a gelling agent in the ink and sufficiently increase the gelling property of the ink, and an image forming method using the same. [Brief description of the drawings]

[0014] [Figure 1] FIG. 1 is a flowchart showing an image forming method according to the present embodiment. [Diagram 2] FIG. 2 is a schematic diagram showing the configuration of an image forming apparatus capable of carrying out the image forming method according to this embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] Hereinafter, an embodiment of the present invention will be described in detail. However, the present invention is not limited to the following embodiment.

[0016] 1. Inkjet ink The inkjet ink in this embodiment contains a polymerizable compound that is polymerized by actinic radiation, and a gelling agent that contains a linear or branched hydrocarbon group having 22 or less carbon atoms. The actinic radiation polymerizable compound contains a first polymerizable compound that contains a benzene ring and an ethylene oxide group (hereinafter referred to as an EO group) or a propylene oxide group (hereinafter referred to as a PO group) in the molecule, and the total number of EO groups and PO groups is 2 or more. The content of the first polymerizable compound is more than 5% by mass with respect to the total mass of the actinic radiation-curable inkjet ink. The inkjet ink of the present invention is an inkjet ink that is cured by actinic radiation.

[0017] The present inventors have found that by using the above-mentioned gelling agent in an ink containing a first polymerizable compound in an amount of more than 5 mass % relative to the total mass of the actinic radiation-curable inkjet ink, the solubility of the gelling agent in the ink can be increased, and the gelling properties of the ink can be sufficiently increased.

[0018] A gelling agent containing a linear or branched hydrocarbon group having 22 or less carbon atoms does not have an excessively high melting point and is easily melted when the ink is heated.

[0019] It is believed that the first polymerizable compound has a benzene ring in its molecule, and thus CH / π interaction occurs between the CH portion of the hydrocarbon group of the gelling agent and the π electrons of the benzene ring of the first polymerizable compound. This is believed to increase the affinity between the gelling agent and the first polymerizable compound. As a result, the gelling agent and the first polymerizable compound become more compatible with each other.

[0020] For these reasons, it is believed that the solubility of the gelling agent can be increased.

[0021] However, when a gelling agent containing a hydrocarbon group with 22 or less carbon atoms was used, the gelling properties of the ink were not sufficiently improved. This is thought to be because, when the carbon number of the hydrocarbon group is 22 or less, it becomes difficult for the molecules of the actinic radiation-polymerizable compound to be incorporated into the crystals of the gelling agent when the gelling agent crystallizes.

[0022] In contrast, the first polymerizable compound contains an EO group or a PO group in the molecule, and the total number of these is 2 or more, so that the polarity is high and the polarity is close to that of the gelling agent. Due to the close polarity with the gelling agent and the above-mentioned CH / π interaction, the molecules of the first polymerizable compound and the molecules of the gelling agent are likely to approach each other. When the gelling agent crystallizes in this state, the actinic radiation polymerizable compound is easily taken in and encapsulated in the crystals of the gelling agent, and the mobility of the molecules of the actinic radiation polymerizable compound is impaired, making the ink more likely to thicken. As a result, it is considered that the gelling property of the ink can be sufficiently improved. And, as a result of the study by the present inventors, it was found that the above effect can be achieved when the content of the first polymerizable compound is more than 5 mass % with respect to the total mass of the actinic radiation curable inkjet ink.

[0023] The actinic ray curable inkjet ink of the present invention based on the above findings will be described in more detail below.

[0024] 1-1.Active radiation polymerizable compounds The actinic ray polymerizable compound is a compound that polymerizes and crosslinks when irradiated with actinic rays. Examples of the actinic ray polymerizable compound include radical polymerizable compounds and cationic polymerizable compounds. Among these, the actinic ray polymerizable compound is preferably a radical polymerizable compound.

[0025] Examples of actinic rays include electron beams, ultraviolet rays, α rays, γ rays, X-rays, etc. Among these, ultraviolet rays and electron beams are preferred, and ultraviolet rays are more preferred.

[0026] As described above, the actinic ray polymerizable compound includes a first polymerizable compound that contains a benzene ring and an EO group or a PO group in the molecule, and the total number of EO groups and PO groups is two or more.

[0027] 1-1-1. First polymerizable compound Examples of the first polymerizable compound include radical polymerizable compounds and cationic polymerizable compounds. Of these, radical polymerizable compounds are preferred. The radical polymerizable compound is a compound having an ethylenically unsaturated bond capable of radical polymerization. The ink may contain only one type of radical polymerizable compound, or may contain two or more types in combination.

[0028] Examples of the first polymerizable compound as the radical polymerizable compound include unsaturated carboxylic acid ester and (meth)acrylate. Among these, (meth)acrylate is preferred. In this specification, "(meth)acrylate" means acrylate or methacrylate, and "(meth)acrylic" means acrylic or methacrylic.

[0029] The number of benzene rings contained in the molecule of the first polymerizable compound is preferably from 1 to 5, and more preferably from 1 to 3. By having the number of benzene rings be 3 or less, an excessive increase in the viscosity of the ink due to an increase in molecular weight can be suppressed.

[0030] The total number of EO groups and PO groups contained in the molecule of the first polymerizable compound is 2 or more. The first polymerizable compound preferably contains a polymerizable compound having a total number of EO groups and PO groups contained in the molecule of 4 or more. The polymerizable compound having the total number of 4 or more has a polarity closer to that of the gelling agent, and therefore can more sufficiently enhance the gelling property of the ink. The upper limit of the total number is not particularly limited, but is, for example, 20. The content of the first polymerizable compound having the total number of EO groups and PO groups of 4 or more is preferably 4.5% by mass or more, more preferably 5.0% by mass or more, based on the total mass of the actinic radiation curable inkjet ink. This can further enhance the gelling property of the ink.

[0031] The first polymerizable compound preferably includes a polymerizable compound having two or more EO groups in the molecule, and more preferably includes a polymerizable compound having four or more EO groups. A polymerizable compound having two or more EO groups in the molecule has a polarity closer to that of the gelling agent, and therefore can easily make the gelling agent and the actinic radiation polymerizable compound compatible when the ink is heated. This can further increase the solubility of the gelling agent. The upper limit of the number of the EO groups is not particularly limited, but is, for example, 20.

[0032] The first polymerizable compound preferably contains a polymerizable compound containing a linear or branched hydrocarbon group in the molecule. This increases the affinity between the first polymerizable compound and the hydrocarbon group of the gelling agent, thereby increasing the solubility of the gelling agent. The hydrocarbon group may be linear or branched, but is preferably linear.

[0033] The hydrocarbon group of the first polymerizable compound preferably has 3 or more and 25 or less carbon atoms, and more preferably has 6 or more and 19 or less carbon atoms.

[0034] The hydrocarbon group of the first polymerizable compound may be contained at the end of the molecular chain or at another site (for example, between the EO group or PO group and the benzene ring), but is preferably contained at the end of the molecular chain, because it is believed that this increases the affinity with the gelling agent and enhances the gelling ability.

[0035] The content of the first polymerizable compound containing a hydrocarbon group is preferably 5% by mass or more and 40% by mass or less, and more preferably 10% by mass or more and 30% by mass or less, based on the total mass of the actinic radiation curable inkjet ink. When it is 5% by mass or more, the affinity between the first polymerizable compound and the hydrocarbon group of the gelling agent is more sufficiently increased, so that the solubility of the gelling agent is more sufficiently increased. When it is 40% by mass or less, the pinning property can be further improved while the solubility of the gelling agent is sufficiently increased.

[0036] The first polymerizable compound may be monofunctional or polyfunctional, but is preferably monofunctional. When the first polymerizable compound is a monofunctional polymerizable compound, the solubility of the gelling agent can be further increased and the gelling property can be further increased. It is considered that the polarity of the monofunctional first polymerizable compound is closer to that of the gelling agent. This can further increase the compatibility between the actinic radiation polymerizable compound and the gelling agent, and further increase the solubility of the gelling agent. In addition, when the gelling agent crystallizes, the molecules of the first polymerizable compound and the molecules of the gelling agent are more likely to approach each other, and therefore the gelling property can be further increased.

[0037] The first polymerizable compound is, for example, a compound represented by general formula (1).

[0038] [ka]

[0039] In the general formula (1), P represents a polymerizable group, X represents an ethylene oxide group, Y represents a propylene oxide group, and m and n are independently integers of 0 or more, and m+n≧2. The positions of X and Y may be interchanged. X and Y may be arranged in a block form, or may be arranged randomly in a mixed form. l represents an integer of 1 or more. Ar represents a structure containing a substituted or unsubstituted benzene ring (valence is l).

[0040] In the general formula (1), P is a polymerizable group. Examples of the polymerizable group include a (meth)acryloyl group, a vinyl group, etc. Among these, a (meth)acryloyl group is preferred.

[0041] In general formula (1), Ar represents a structure containing a substituted or unsubstituted benzene ring having a valence of l. When the benzene ring has a substituent, examples of the substituent include a linear or branched hydrocarbon group, a phenyl group, a hydroxyl group, and the like. Among these, a linear or branched hydrocarbon group is preferred from the viewpoint of further increasing the affinity between the first polymerizable compound and the gelling agent and further increasing the solubility of the gelling agent. The hydrocarbon group is preferably linear.

[0042] In general formula (1), m and n are integers of 0 or more, and m+n≧2. The combination of m and n is not particularly limited as long as m+n≧2 is satisfied, but when m is 2 or more, n is preferably 0. Also, when n is 2 or more, m is preferably 0. From the viewpoint of more sufficiently enhancing the gelling properties of the ink, m+n is preferably 4 or more.

[0043] l is an integer of 1 or more, and is preferably 1 or more and 2 or less.

[0044] In general formula (1), m is preferably 2 or more, and more preferably 4 or more, which can further increase the solubility of the gelling agent.

[0045] Specific examples of the monofunctional first polymerizable compound include EO or PO modified compounds such as benzyl acrylate, phenol acrylate, and nonylphenol acrylate.

[0046] Specific examples of the polyfunctional first polymerizable compound include EO or PO modified compounds such as bisphenol A diacrylate.

[0047] The content of the first polymerizable compound is more than 5% by mass relative to the total mass of the actinic radiation curable inkjet ink. The content is preferably more than 5% by mass and not more than 40% by mass, and more preferably 10% by mass or more and not more than 30% by mass. When the content is not more than 40% by mass, the solubility of the gelling agent can be sufficiently increased while the pinning property can be further improved.

[0048] The content of the first polymerizable compound relative to the total mass of the active ray polymerizable compounds is preferably from 5% by mass to 50% by mass, and more preferably from 10% by mass to 35% by mass.

[0049] 1-1-2. Second polymerizable compound In this embodiment, the actinic ray polymerizable compound may include a second polymerizable compound that is a polymerizable compound other than the first polymerizable compound.

[0050] Examples of the second polymerizable compound include radical polymerizable compounds and cationic polymerizable compounds. Among these, radical polymerizable compounds are preferred.

[0051] Examples of the radical polymerizable compound include unsaturated carboxylic acid esters and (meth)acrylates. Among these, (meth)acrylates are preferred. The (meth)acrylates may be monofunctional or polyfunctional.

[0052] Examples of monofunctional (meth)acrylates include isoamyl acrylate, stearyl acrylate, lauryl acrylate, octyl acrylate, decyl acrylate, isomyristyl acrylate, isostearyl acrylate, 2-ethylhexyl-diglycol acrylate, butoxyethyl acrylate, ethoxydiethylene glycol acrylate, methoxydiethylene glycol acrylate, methoxypolyethylene glycol acrylate, methoxypropylene glycol acrylate, phenoxyethyl acrylate, 2-hydroxy-3-phenoxypropyl acrylate, cumylphenoxylethyl acrylate, tetrahydrofurfuryl acrylate, isobornyl acrylate, 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, 2-hydroxybutyl acrylate, and t-butylcyclohexyl acrylate.

[0053] Examples of the difunctional (meth)acrylate include triethylene glycol di(meth)acrylate, tetraethylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, dipropylene glycol di(meth)acrylate, tripropylene glycol di(meth)acrylate, 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, hydroxypivalic acid neopentyl glycol di(meth)acrylate, polytetramethylene glycol di(meth)acrylate, and tricyclodecane dimethanol di(meth)acrylate.

[0054] Examples of the tri- or higher functional (meth)acrylate include trimethylolpropane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol hexa(meth)acrylate, ditrimethylolpropane tetra(meth)acrylate, glycerin propoxy tri(meth)acrylate, and pentaerythritol ethoxy tetra(meth)acrylate.

[0055] The second polymerizable compound as a (meth)acrylate may be, for example, one modified with an alkylene oxide such as ethylene oxide (EO) or propylene oxide (PO), or caprolactone (modified (meth)acrylate). In this case, when the (meth)acrylate contains a benzene ring, the total number of modifications with EO or PO is 1.

[0056] Examples of the cationically polymerizable compound include an epoxy compound, a vinyl ether compound, and an oxetane compound.

[0057] Examples of the epoxy compounds 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-methyloxiranyl)-7-oxabicyclo[4,1,0]heptane, 2-(3,4-epoxycyclohexyl-5,5-spiro-3, 4-epoxy)cyclohexanone-meta-dioxane and bis(2,3-epoxycyclopentyl) ether, diglycidyl ether of 1,4-butanediol, diglycidyl ether of 1,6-hexanediol, triglycidyl ether of glycerin, triglycidyl ether of trimethylolpropane, diglycidyl ether of polyethylene glycol, diglycidyl ether of propylene glycol, diglycidyl ether of ethylene glycol, propylene glycol, and glycerin.

[0058] Examples of the vinyl ether compound include monovinyl ether compounds including 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 including 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.

[0059] Examples of the oxetane compound include 3-hydroxymethyl-3-methyloxetane, 3-hydroxymethyl-3-ethyloxetane, 3-hydroxymethyl-3-propyloxetane, 3-hydroxymethyl-3-normal butyloxetane, 3-hydroxymethyl-3-benzyloxetane, 3-hydroxyethyl-3-methyloxetane, 3-hydroxyethyl-3-ethyloxetane, 3-hydroxyethyl-3-propyloxetane, 3-hydroxypropyl-3-methyloxetane, 3-hydroxypropyl-3-ethyloxetane, 3-hydroxypropyl-3-propyloxetane, 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.

[0060] The content of the second polymerizable compound is preferably from 45% by mass to 86% by mass, and more preferably from 55% by mass to 81% by mass, based on the total mass of the actinic ray-curable inkjet ink.

[0061] The content of the actinic ray-polymerizable compound can be from 1% by mass to 97% by mass, preferably from 30% by mass to 95% by mass, more preferably from 50% by mass to 95% by mass, and even more preferably from 70% by mass to 95% by mass, based on the total mass of the actinic ray-curable inkjet ink.

[0062] 1-2. Gelling agent In this embodiment, the actinic ray curable inkjet ink undergoes a sol-gel phase transition (before irradiation with actinic rays) due to a gelling agent. Specifically, the gelling agent is a compound that dissolves in an actinic ray polymerizable compound contained in the ink when the ink containing the gelling agent is heated (for example, at 90° C.), and crystallizes in the ink at around room temperature (for example, 35° C.), gelling the ink.

[0063] In this embodiment, the gelling agent contains a linear or branched hydrocarbon group having 22 or less carbon atoms. The hydrocarbon group is preferably linear. This makes it difficult for steric hindrance to occur during crystallization of the gelling agent, and the gelling agent can be more easily approached by the molecules of the active radiation polymerizable compound. As a result, the crystals of the gelling agent are more likely to encapsulate the active radiation polymerizable compound, and the gelling property can be further improved. In addition, the number of carbon atoms is preferably 20 or less, and more preferably 18 or less. The lower limit of the number of carbon atoms is preferably 14, from the viewpoint of making it easier for the crystals of the gelling agent to encapsulate the active radiation polymerizable compound.

[0064] When the gelling agent contains multiple hydrocarbon groups in the molecule, the number of hydrocarbon groups is preferably 2 or more, more preferably 3 or more, and even more preferably all of the hydrocarbon groups in the molecule have 22 or less carbon atoms.

[0065] It is preferable that the gelling agent crystallizes in the ink, and forms a structure in which the actinic radiation-polymerizable compound is encapsulated in a three-dimensional space formed by the gelling agent crystallized into plate-like shapes (such a structure will be referred to hereinafter as a "house of cards structure"). When a house of cards structure is formed, the liquid actinic radiation-polymerizable compound is held within the space, further enhancing the gelling properties of the ink. This makes it more difficult for the ink to wet and spread when formed on the recording medium, improving the pinning properties of the ink.

[0066] Examples of gelling agents that can facilitate the formation of a house-of-cards structure through crystallization include aliphatic ketones, aliphatic esters, glycerol-based compounds, pentaerythritol-based compounds, petroleum-based waxes, vegetable-based waxes, animal-based waxes, mineral-based waxes, hydrogenated castor oil, modified waxes, higher fatty acids, higher alcohols, hydroxystearic acid, fatty acid amides including N-substituted fatty acid amides and special fatty acid amides, higher amines, esters of sucrose fatty acids, synthetic waxes, dibenzylidene sorbitol, dimer acids and dimer diols.

[0067] Among these, from the viewpoint of increasing the polarity and further increasing the solubility in the actinic radiation polymerizable compound, the gelling agent is preferably an aliphatic ketone, an aliphatic ester, a glycerol-based compound, a pentaerythritol-based compound, a higher fatty acid, or a higher alcohol. Moreover, an aliphatic ketone, an aliphatic ester, a glycerol-based compound, or a pentaerythritol-based compound is more preferable, and an aliphatic ketone, an aliphatic ester, or a pentaerythritol-based compound is even more preferable. Furthermore, from the viewpoint of further increasing the gelling property of the ink, among these, an aliphatic ketone or an aliphatic ester is even more preferable, and an aliphatic ester is particularly preferable. Note that only one type of gelling agent may be included, or two or more types may be included in combination.

[0068] Examples of the aliphatic ketones include dibehenyl ketone, distearyl ketone, dieicosyl ketone, dipalmityl ketone, dilauryl ketone, dimyristyl ketone, myristyl palmityl ketone, and palmityl stearyl ketone.

[0069] Examples of fatty esters include fatty acid esters of monoalcohols such as behenyl behenate, icosanoic acid ethyl ester, stearyl stearate, palmityl stearate, myristyl myristate, cetyl myristate, oleyl palmitate, etc. Also included are fatty acid esters of polyhydric alcohols such as sorbitan fatty acid esters, propylene glycol fatty acid esters, ethylene glycol fatty acid esters, and polyoxyethylene fatty acid esters.

[0070] Examples of glycerol-based compounds include glycerol monolaurate, diglycerol monopalmyrate, diglycerol monopalmitate, diglycerol monostearate, diglycerol monooleate, diglycerol monobehenate, etc. In this specification, the term "glycerol-based compound" refers to a compound having a structure derived from glycerol.

[0071] Examples of pentaerythritol-based compounds include pentaerythritol tetrastearate, pentaerythritol monooleate, pentaerythritol tetrapalmitate, pentaerythritol trimyristate, etc. In this specification, the term "pentaerythritol-based compound" refers to a compound having a structure derived from pentaerythritol.

[0072] Examples of higher fatty acids include behenic acid, arachidic acid, stearic acid, palmitic acid, myristic acid, lauric acid, oleic acid, and erucic acid.

[0073] Examples of higher alcohols include stearyl alcohol and behenyl alcohol.

[0074] Among the 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.

[0075] General formula (G1):R a -CO-R b General formula (G2):R c -COO-R d

[0076] In general formula (G1), R a and R b each independently represents a linear hydrocarbon group having 14 to 22 carbon atoms, and in general formula (G2), R c and R d each independently represents a linear hydrocarbon group having 14 to 22 carbon atoms.

[0077] In general formulae (G1) and (G2), R a ~R dWhen the number of carbon atoms is 14 or more, the crystallinity of the gelling agents represented by general formula (G1) and general formula (G2) is increased, and more sufficient spaces are generated in the house-of-cards structure. Therefore, the actinic radiation polymerizable compound (A) is easily and sufficiently encapsulated in the spaces, and the gelling property and pinning property of the ink are improved.

[0078] Also, R a ~R d When the number of carbon atoms is 22 or less, the melting point of the gelling agent represented by general formula (G1) and general formula (G2) does not become too high, and the solubility of the gelling agent is increased.

[0079] Examples of aliphatic ketones represented by general formula (G1) include dibehenyl ketone (carbon number: 21-22), distearyl ketone (carbon number: 17-18), dieicosyl ketone (carbon number: 19-20), dipalmityl ketone (carbon number: 15-16), dimyristyl ketone (carbon number: 13-14), dilauryl ketone (carbon number: 11-12), lauryl myristyl ketone (carbon number: 13-14), and ketones represented by general formula (G2). Prime numbers: 11-14), lauryl palmityl ketone (11-16), myristyl palmityl ketone (13-16), myristyl stearyl ketone (13-18), myristyl behenyl ketone (13-22), palmityl stearyl ketone (15-18), palmityl behenyl ketone (15-22) and stearyl behenyl ketone (17-22). The number of carbon atoms in the parentheses above indicates the number of carbon atoms in each of the two hydrocarbon groups separated by the carbonyl group.

[0080] Examples of the aliphatic ester represented by the general formula (G2) include behenyl behenate (carbon number: 21-22), icosanoic acid icosyl (carbon number: 19-20), stearyl stearate (carbon number: 17-18), palmityl stearate (carbon number: 17-16), lauryl stearate (carbon number: 17-12), cetyl palmitate (carbon number: 15-16), stearyl palmitate (carbon number: 15-18), myristyl Myristyl phosphate (carbon number: 13-14), cetyl myristate (carbon number: 13-16), octyldodecyl myristate (carbon number: 13-20), stearyl oleate (carbon number: 17-18), stearyl erucate (carbon number: 21-18), stearyl linoleate (carbon number: 17-18), behenyl oleate (carbon number: 18-22), and arachidyl linoleate (carbon number: 17-20). The number of carbons in the parentheses above indicates the number of carbons in each of the two hydrocarbon groups separated by the ester group.

[0081] The content of the gelling agent is preferably 0.5% by mass or more and 10.0% by mass or less, and more preferably 2.0% by mass or more and 7.0% by mass or less, based on the total mass of the actinic radiation curable inkjet ink. When the content is 0.5% by mass or more, the gelling property of the ink can be further improved. Also, when the content is 10.0% by mass or less, the solubility of the gelling agent in the actinic radiation polymerizable compound can be further improved.

[0082] The HSP distance between the gelling agent and the actinic radiation polymerizable compound is 5.0 (MPa). 1 / 2 Above 7.0 (MPa) 1 / 2 It is preferable that the temperature is 5.5 (MPa) or less. 1 / 2 More than 6.0 (MPa) 1 / 2 More preferably, it is 5.0 (MPa) or less. 1 / 2 By setting the pressure to 7.0 (MPa) or more, the gelling agent is more likely to crystallize when the ink lands, and the gelling properties of the ink are further improved. 1 / 2When the HSP distance is less than 100%, the solubility of the gelling agent is further increased. Each component value of the HSP value of the gelling agent and each component value of the HSP value of the active ray polymerizable compound used in calculating the HSP distance is a weighted average value for each gelling agent and each active ray polymerizable compound. Each component value of the HSP value is calculated by computer software HSPiP (version 5.4.01, manufactured by Tegara Corporation).

[0083] In this embodiment, a small amount of a gelling agent that does not contain a linear hydrocarbon group having 22 or less carbon atoms may be contained within the range in which the effects of the present invention are achieved.

[0084] 1-3.Other The actinic ray curable inkjet ink composition according to this embodiment may further contain other components such as a colorant, a surfactant, a polymerization inhibitor, and a moisturizer, as long as the effects of the present invention are achieved.

[0085] (Coloring agent) The colorant may be a dye or a pigment, with pigments being preferred since they have good dispersibility in the ink components and are weather resistant. The pigment may be selected from, for example, yellow pigments, red pigments, blue pigments, black pigments, and white pigments depending on the color of the image to be formed.

[0086] 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, and 193. Of these, from the viewpoints of further reducing the amount of impurities in the ink composition and further increasing the electrical resistance value of the insulating film, PY185 and PY150 are preferred.

[0087] 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) 13, 16, 20, 36, etc. Among 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 value of the insulating film.

[0088] 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 viewpoints of further reducing the amount of impurities in the ink composition and further increasing the electrical resistance value of the insulating film.

[0089] Examples of black pigments include CI Pigment Black (hereinafter also simply referred to as "PBk") 7, PBk26, and PBk28.

[0090] The white pigment may be any pigment that imparts a white color to the cured film formed by curing the white ink. Examples of the white pigment include inorganic pigments such as titanium oxide, zinc oxide, calcium carbonate, barium sulfate, and aluminum hydroxide. Among these, titanium oxide is preferred.

[0091] The crystal form of the titanium oxide may be any of rutile, anatase, and brookite types. From the viewpoint of making it easier to reduce the particle size of the white pigment, the anatase type, which has a small specific gravity, is preferred, and from the viewpoint of further improving the hiding power of the image formed, the rutile type, which has a large refractive index in the visible light region, is preferred.

[0092] The content of the colorant is preferably from 0.1% to 10% by mass, and more preferably from 1% to 5% by mass, based on the total mass of the ink composition. The content of the white pigment is preferably from 3% to 8% by mass.

[0093] (Pigment dispersant) The actinic radiation curable ink may contain a pigment dispersant for dispersing the pigment. Examples of the pigment dispersant include hydroxyl group-containing carboxylate ester, salt of long chain polyaminoamide and high molecular weight acid ester, salt of high molecular weight polycarboxylate, salt of long chain polyaminoamide and polar acid ester, high molecular weight unsaturated acid ester, polymer copolymer, modified polyurethane, modified polyacrylate, polyether ester type anionic surfactant, naphthalene sulfonate formalin condensate salt, aromatic sulfonate formalin condensate salt, polyoxyethylene alkyl phosphate ester, polyoxyethylene nonylphenyl ether, and stearylamine acetate.

[0094] The content of the pigment dispersant is preferably 10% by mass or more and 200% by mass or less, more preferably 20% by mass or more and 100% by mass or less, based on the total mass of the pigment. When the content of the dispersant is 10% by mass or more, based on the total mass of the pigment, the dispersion stability of the pigment is improved. When the content of the dispersant is 200% by mass or less, based on the total mass of the pigment, the ejection of the ink from the inkjet head is more likely to be stable.

[0095] (Activin Radiation Polymerization Initiator) In the present embodiment, the actinic ray curable inkjet ink may contain an actinic ray polymerization initiator (hereinafter, simply referred to as a "polymerization initiator"). The polymerization initiator may be any one that can initiate polymerization of the actinic ray polymerizable compound by irradiation with actinic rays. For example, when the actinic ray curable inkjet ink contains a radical polymerizable compound, the polymerization initiator may be a radical polymerization initiator. When the actinic ray curable ink contains a cationic polymerizable compound, the polymerization initiator may be a cationic polymerization initiator (photoacid generator). Note that when the actinic ray curable inkjet ink can be sufficiently cured without a polymerization initiator, such as when the actinic ray curable inkjet ink is cured by irradiation with electron beams, the polymerization initiator is not necessary.

[0096] The radical polymerization initiator includes an intramolecular bond cleavage type radical polymerization initiator and an intramolecular hydrogen abstraction type radical polymerization initiator.

[0097] Examples of the intramolecular bond cleavage type radical polymerization initiator include acetophenone-based initiators including diethoxyacetophenone, 2-hydroxy-2-methyl-1-phenylpropan-1-one, benzyl dimethyl ketal, 1-(4-isopropylphenyl)-2-hydroxy-2-methylpropan-1-one, 4-(2-hydroxyethoxy)phenyl-(2-hydroxy-2-propyl)ketone, 1-hydroxycyclohexyl-phenyl ketone, 2-methyl-2-morpholino(4-methylthiophenyl)propan-1-one, and 2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)-butanone, benzoins including benzoin methyl ether, and benzoin isopropyl ether, acylphosphine oxide-based initiators including 2,4,6-trimethylbenzoin diphenylphosphine oxide, and benzyl and methylphenyl glyoxyesters.

[0098] Examples of the intramolecular hydrogen abstraction type radical polymerization initiator include benzophenone-based initiators including benzophenone, o-benzoylmethylbenzoate, 4-phenylbenzophenone, 4,4'-dichlorobenzophenone, hydroxybenzophenone, 4-benzoyl-4'-methyl-diphenyl sulfide, acrylated benzophenone, 3,3',4,4'-tetra(t-butylperoxycarbonyl)benzophenone, and 3,3'-dimethyl-4-methoxybenzophenone; thioxanthone-based initiators including 2-isopropylthioxanthone, 2,4-dimethylthioxanthone, 2,4-diethylthioxanthone, and 2,4-dichlorothioxanthone; aminobenzophenone-based initiators including Michler's ketone and 4,4'-diethylaminobenzophenone; 10-butyl-2-chloroacridone, 2-ethylanthraquinone, 9,10-phenanthrenequinone, and camphorquinone.

[0099] Examples of cationic polymerization initiators include photoacid generators. Examples of photoacid generators include aromatic onium compounds, including diazonium, ammonium, iodonium, sulfonium, and phosphonium, B(C 6 F 5 ) 4 - , P.F. 6 - , AsF 6 - , SbF 6 - , C.F. 3 SO 3 - These include salts, sulfonates which generate sulfonic acids, halides which photogenerate hydrogen halides, and iron-allene complexes.

[0100] The content of the polymerization initiator is not particularly limited as long as the actinic ray curable inkjet ink is sufficiently cured by irradiation with actinic rays (e.g., ultraviolet rays) and does not deteriorate the coatability on the surface of a recording medium. For example, the content of the polymerization initiator is preferably 0.1% by mass or more and 20% by mass or less, and more preferably 1% by mass or more and 10% by mass or less, based on the total mass of the actinic ray curable inkjet ink.

[0101] (Polymerization inhibitor) In this embodiment, the actinic ray curable inkjet ink may contain a polymerization inhibitor.

[0102] Examples of polymerization inhibitors include (alkyl)phenols, 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, cupferron, aluminum N-nitrosophenylhydroxylamine, tri-p-nitrophenylmethyl, N-(3-oxyanilino-1,3-dimethylbutylidene)aniline oxide, dibutylcresol, cyclohexanone oxime cresol, guaiacol, o-isopropylphenol, butylaldoxime, methyl ethyl ketoxime, cyclohexanone oxime, and the like.

[0103] The content of the polymerization inhibitor is not particularly limited, but is preferably from 0.05% by mass to 10.00% by mass with respect to the total mass of the actinic ray-curable inkjet ink.

[0104] (Surfactant) In this embodiment, the actinic ray curable inkjet ink may contain a surfactant for adjusting the surface tension.

[0105] Examples of surfactants include anionic surfactants including dialkyl sulfosuccinates, alkyl naphthalene sulfonates, and fatty acid salts; nonionic surfactants including polyoxyethylene alkyl ethers, polyoxyethylene alkyl allyl ethers, acetylene glycols, and polyoxyethylene-polyoxypropylene block copolymers; cationic surfactants including alkylamine salts and quaternary ammonium salts, silicone surfactants, and fluorine-based surfactants.

[0106] The content of the surfactant is not particularly limited, but is preferably from 0.001% to 10% by mass, and more preferably from 0.001% to 1.0% by mass, based on the total mass of the actinic ray-curable inkjet ink.

[0107] In this embodiment, in addition to the above-mentioned components, the actinic ray curable inkjet ink may contain, as necessary, a fixing resin, a viscosity adjuster, a resistivity adjuster, a film forming agent, an ultraviolet absorbing agent, an antioxidant, a color fading inhibitor, an antifungal agent, an antirust agent, and the like.

[0108] 1-4. Physical properties of actinic radiation curable inkjet ink The viscosity of the actinic ray curable ink at 80° C. is preferably 3 mPa·s or more and 20 mPa·s or less, and more preferably 5 mPa·s or more and 15 mPa·s or less, which can improve the ejection properties when the ink is heated and ejected from an inkjet head.

[0109] The viscosity can be measured by a rheometer. For example, the precoat agent is heated to 100°C, and while measuring the viscosity by a stress-controlled rheometer (Physica MCR301 (diameter of cone plate: 75 mm, cone angle: 1.0°) manufactured by Anton Paar), the ink is cooled to 20°C under conditions of a shear rate of 11.7 (1 / s) and a temperature drop rate of 0.1°C / s to obtain a temperature change curve of the viscosity. The viscosity can be obtained by reading the viscosity at 80°C from the obtained temperature change curve.

[0110] 1-5. Method for preparing actinic radiation curable inkjet ink The actinic radiation curable inkjet ink can be prepared by mixing the actinic radiation polymerizable compound, the gelling agent, and any other components under heating. At this time, it is preferable to filter the obtained mixture through a filter. When preparing an ink containing a pigment, it is preferable to prepare a pigment dispersion containing the pigment and the actinic radiation polymerizable compound, and then mix the pigment dispersion with other components. The pigment dispersion may further contain a dispersant.

[0111] The pigment dispersion can be prepared by dispersing a pigment in an actinic radiation polymerizable compound. The pigment can be dispersed using, for example, a ball mill, a sand mill, an attritor, a roll mill, an agitator, a Henschel mixer, a colloid mill, an ultrasonic homogenizer, a pearl mill, a wet jet mill, a paint shaker, etc. At this time, a dispersant may be added.

[0112] In addition, when a plurality of types of actinic radiation-polymerizable compounds are used, the actinic radiation-polymerizable compounds may be mixed first to prepare an actinic radiation-polymerizable composition, and then the actinic radiation-polymerizable composition, the gelling agent, and any other components may be mixed under heating.

[0113] 2. Image forming method 1 is a flow chart showing an image forming method according to this embodiment. The image forming method according to this embodiment includes a step (step S10) of ejecting droplets of the actinic ray curable inkjet ink from an inkjet head and applying them to the surface of a recording medium. The image forming method further includes a step (step S20) of irradiating the applied droplets of the actinic ray curable inkjet ink with actinic rays to cure them.

[0114] 2-1. Step of applying actinic radiation curable inkjet ink to a recording medium (step S10) In this process, the actinic radiation curable inkjet ink described above is ejected from an inkjet head and applied to the surface of a recording medium (at a position corresponding to the image to be formed).

[0115] The ejection method from the inkjet head may be either an on-demand method or a continuous method. The on-demand inkjet head may be an electro-mechanical conversion type such as a single cavity type, a double cavity type, a bender type, a piston type, a share mode type, or a shared wall type. The inkjet head may also be an electro-thermal conversion type such as a thermal inkjet type or a bubble jet type ("Bubble Jet" is a registered trademark of Canon Inc.). The inkjet head may be either a scan type or a line type.

[0116] The droplets of the actinic radiation curable ink are heated and solubilized before being ejected from the inkjet head. Therefore, the temperature of the ink when filled into the inkjet head is preferably set to the gelling temperature of the ink +10°C or higher and the gelling temperature +30°C or lower. When the temperature of the ink inside the inkjet head is the gelling temperature +10°C or higher, the ink is less likely to gel inside the inkjet head or on the nozzle surface, resulting in a decrease in ejection performance. On the other hand, when the temperature of the ink inside the inkjet head is the gelling temperature +30°C or lower, the components are less likely to deteriorate due to high temperatures.

[0117] The method of heating the actinic radiation curable inkjet ink is not particularly limited. It is sufficient to heat the ink supply system such as the ink tank constituting the head carriage, the supply pipe and the anterior ink tank immediately before the head, the piping with the filter, the piezo head, etc. Heating can be performed by a panel heater, a ribbon heater, warm water, etc.

[0118] The amount of droplets of the actinic ray curable inkjet ink ejected is preferably 2 pL or more and 20 pL or less, from the viewpoint of further increasing the recording speed and image quality.

[0119] The recording medium is not particularly limited, and in addition to ordinary uncoated paper and coated paper, synthetic paper Yupo ("Yupo" is a registered trademark of Yupo Corporation), various plastics used in soft packaging, and their films can be used. 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.

[0120] The actinic radiation curable inkjet ink may be applied to a recording medium by directly impacting the ejected ink on the recording medium, or by impacting the ejected ink on an intermediate transfer body to form an intermediate image, and then transferring the intermediate image from the intermediate transfer body to the recording medium.

[0121] 2-2. Step of curing the actinic ray curable inkjet ink (step S20) In this process, the droplets of the actinic ray-curable inkjet ink applied to the recording medium in step S10 are irradiated with actinic rays to cure the droplets, thereby forming an image made of a cured film of the actinic ray-curable inkjet ink.

[0122] The actinic radiation can be selected from, for example, electron beams, ultraviolet rays, α rays, γ rays, and X-rays, but is preferably ultraviolet rays or electron beams. The ultraviolet rays are preferably light having a peak wavelength of 360 nm or more and 410 nm or less. The ultraviolet rays are preferably irradiated from an LED light source. LEDs emit less radiant heat than conventional light sources (e.g., metal halide lamps, etc.). Therefore, when exposed to actinic radiation, LEDs are less likely to melt the ink and less likely to cause uneven gloss.

[0123] 3. Image forming equipment An image forming apparatus 100 capable of carrying out the above-mentioned image forming method will now be described.

[0124] Fig. 2 is a schematic diagram showing the configuration of an image forming apparatus 100 according to this embodiment. As shown in Fig. 2, the image forming apparatus 100 has an inkjet head 110, a conveying section 120, and an irradiating section 130. In Fig. 2, the arrow indicates the conveying direction of the recording medium.

[0125] The inkjet head 110 has a nozzle surface 113 on which the nozzles 111 are provided, on a surface facing the transport unit 120 when forming an image, and ejects actinic ray curable inkjet ink onto the recording medium 200 transported by the transport unit 120. From the viewpoint of improving the ejection properties of the actinic ray curable inkjet ink, the inkjet head 110 may have a temperature adjustment means for adjusting the temperature of the ink to adjust the ink to a low viscosity. Examples of the temperature adjustment means include a panel heater, a ribbon heater, and a heating means that uses warm water.

[0126] The inkjet head 110 may be a scanning type inkjet head whose width in a direction perpendicular to the transport direction of the recording medium is smaller than that of the recording medium 200, or may be a line type inkjet head whose width in a direction perpendicular to the transport direction of the recording medium is larger than that of the recording medium 200.

[0127] The nozzles 111 have ejection openings on a nozzle surface 113. The number of nozzles 111 may be equal to or greater than the number of inks used in image formation (for example, four).

[0128] When forming an image, the conveying unit 120 conveys the recording medium 200 so that the recording medium 200 facing the inkjet head 110 moves directly below the inkjet head 110 in the vertical direction. For example, the conveying unit 120 has a driving roller 121, a driven roller 122, and a conveying belt 123.

[0129] The irradiation unit 130 irradiates the upper surface of the transport unit 120 with active rays. This allows the droplets of the active ray-curable inkjet ink that has landed on the transported recording medium 200 to be irradiated with active rays, thereby curing the droplets. The irradiation unit 130 can be disposed immediately above the transport unit 120, downstream of the inkjet head 110.

[0130] In addition to the above configuration, the image forming apparatus 100 may have an ink tank (not shown) for storing actinic ray curable ink before ejection, an ink flow path (not shown) that connects the ink tank and the inkjet head 110 so that the ink can flow therethrough, and a control unit (not shown) that controls the operation of the inkjet head 110, the transport unit 120, and the irradiation unit 130.

[0131] The image forming apparatus 100 may also have an intermediate transfer body and a transfer unit (both not shown). At this time, the inkjet head 110 ejects actinic ray curable inkjet ink onto the intermediate transfer body, causing it to land on the surface of the intermediate transfer body, and forms an intermediate image on the surface of the intermediate transfer body, which is made up of droplets of the actinic ray curable inkjet ink. Thereafter, 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 actinic rays, thereby curing the droplets of the actinic ray curable inkjet ink. EXAMPLES

[0132] The present invention will now be described with reference to examples, which should not be construed as limiting the scope of the present invention.

[0133] 1. Preparation / synthesis of materials The materials used in the preparation of the actinic radiation curable inkjet ink are shown below.

[0134] 1-1. Pigment dispersion 9 parts by mass of a 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 and stirred for 1 hour while being heated to 65°C on a hot plate. Then, the mixture was cooled to room temperature, and 20 parts by mass of a cyan pigment (Pigment Blue 15:4, Chromofine Blue 6332JC, manufactured by Dainichi Seika Chemicals Co., Ltd.) was added to the stainless steel beaker after stirring, and then the mixture was placed in a glass bottle together with 200g of zirconia beads (diameter 0.3mm, manufactured by Nikkato Co., Ltd.) and sealed. This pigment-containing liquid was dispersed using a paint shaker, and the zirconia beads were removed to obtain a pigment dispersion. The dispersion treatment time was 4 hours when a cyan pigment and a black pigment were used, and 6 hours when a magenta pigment and a yellow pigment were used.

[0135] 1-2.Active radiation polymerizable compound (Monofunctional actinic radiation polymerizable compound) m1: 2EO modified phenol acrylate (with benzene ring, number of EO groups: 2) m2: 4EO modified phenol acrylate (with benzene ring, number of EO groups: 4) m3: 4EO modified nonylphenol acrylate (with benzene ring, number of EO groups: 4) m4: 8EO modified nonylphenol acrylate (with benzene ring, number of EO groups: 8) m5: 2PO modified nonylphenol acrylate (with benzene ring, number of PO groups: 2) m6: 2-phenoxyethyl acrylate (with benzene ring, number of EO groups: 1) m7: Lauryl acrylate m8: Caprolactone acrylate

[0136] (Polyfunctional actinic radiation polymerizable compound) M1: 10EO modified bisphenol A diacrylate (containing benzene ring, number of EO groups: 10) M2: Tripropylene glycol diacrylate (number of PO groups: 3) M3: Polyethylene glycol diacrylate #400 (number of EO groups: 9) M4: 3EO modified trimethylolpropane triacrylate (number of EO groups: 3) M5: 6EO modified trimethylolpropane triacrylate (number of EO groups: 6) M6: Dioxane glycol diacrylate M7: 2EO modified 1,6-hexanediol diacrylate (number of EO groups: 2) M8: 3EO modified trimethylolpropane triacrylate (number of EO groups: 3) M9: 2PO-modified neopentyl glycol diacrylate (number of EO groups: 2) M10: (2,4,6-trioxo-1,3,5-triazinane-1,3,5-triyl)tris(ethane-2,1-diyl)triacrylate M11: 8-functional polybranched acrylate (Eternal Materials, ETERCURE 6361-100, number of EO groups: 9) M12: Bifunctional polyester acrylate oligomer (Arkema, CN2270NS, number of PO groups: 5) M13: 9EO modified trimethylolpropane triacrylate (number of EO groups: 9) M14: Polyethylene glycol diacrylate #600 (number of EO groups: 14) M15: 3EO modified trimethylolpropane triacrylate (number of EO groups: 3) M16: 3PO modified glyceryl triacrylate

[0137] 1-3. Gelling agents G1: Stearyl stearate (ester type, maximum number of carbon atoms in the hydrocarbon group: 18) G2: Behenyl behenate (ester type, maximum number of carbon atoms in the hydrocarbon group: 22) G3: Stearone (ketone type, maximum number of carbon atoms in the hydrocarbon group: 17) G4: Pentaerythritol tetrastearate (pentaerythritol type, maximum number of carbon atoms in the hydrocarbon group: 17) G5: Glycerol monolaurate (glycerol type, maximum carbon number of the hydrocarbon group is 11)

[0138] 1-4. Polymerization initiator Initiator 1 (Omnirad 819, IGM Resins BV) Initiator 2 (Speedcure 2-ITX, Arkema)

[0139] 1-5. Polymerization inhibitors Irgasutab UV-10 (BASF)

[0140] 1-6.Surfactants KF-352A (Shin-Etsu Chemical Co., Ltd.)

[0141] 2. Preparation of actinic radiation curable inkjet ink 12.0 parts by mass of cyan pigment dispersion, 25.0 parts by mass of actinic radiation polymerizable compound m1, 10.0 parts by mass of actinic radiation polymerizable compound M2, 8.5 parts by mass of actinic radiation polymerizable compound M3, 13.0 parts by mass of actinic radiation polymerizable compound M4, 17.3 parts by mass of actinic radiation polymerizable compound M5, 5.5 parts by mass of actinic radiation polymerizable compound M7, 5.0 parts by mass of gelling agent 1, 3.0 parts by mass of initiator 1, 0.5 parts by mass of initiator 2, 0.1 parts by mass of polymerization inhibitor, and 0.1 parts by mass of surfactant were placed in a stainless steel beaker and stirred at 105° C. for 45 minutes. Then, the mixture was filtered through a 3 μm Teflon (registered trademark) membrane filter manufactured by ADVANTEC to obtain actinic radiation curable inkjet ink 1. Actinic radiation-curable inkjet inks 2 to 47 were obtained in the same manner, except that the type and amount of actinic radiation-polymerizable compound and the type and amount of gelling agent were changed as shown in Tables 1 to 5 (the numbers in the tables are parts by mass).

[0142] 3. Evaluation (Solubility of gelling agent) A container containing 10 mL of each actinic radiation curable inkjet ink was placed in an oven heated to 80°C, and the container was removed from the oven after 10 minutes and 30 minutes, and the ink in the container was observed. The solubility of the gelling agent was then evaluated according to the following evaluation criteria. (Evaluation Criteria) ◎: No insoluble matter or oil droplet separation was observed 10 minutes after the container was placed in the oven. ○: A small amount of undissolved gelling agent or oil droplet separation was observed 10 minutes after the container was placed in the oven, but no insoluble matter or oil droplet separation was observed 30 minutes after the container was placed in the oven. △: 30 minutes after the container was placed in the oven, some residual gelling agent or oil droplets were observed. ×: 30 minutes after the container was placed in the oven, the gelling agent remained undissolved or oil droplets were separated.

[0143] (Gelling property (thickening property)) A heat-resistant tube containing 10 mL of each actinic radiation-curable inkjet ink was heated to 35° C., and the gelling state of each ink in the container was confirmed. The gelling property was then evaluated according to the following evaluation criteria. ◎: The gel did not crumble after shaking the heat-resistant tube 10 times. ○: The gel did not crumble after shaking the heat-resistant tube 5 times, but the gel crumbled after shaking it 6 to 10 times. △: The gel did not crumble after shaking the heat-resistant tube four times, but the gel crumbled after shaking it five times. ×: The gel crumbled when the heat-resistant tube was shaken 1 to 3 times.

[0144] The evaluation results are summarized in Tables 6 to 7.

[0145] [Table 1]

[0146] [Table 2]

[0147] [Table 3]

[0148] [Table 4]

[0149] [Table 5]

[0150] [Table 6]

[0151] [Table 7]

[0152] The results of Inks 1 to 41 and Inks 42 to 47 show that by containing a gelling agent containing a linear hydrocarbon group having 22 or less carbon atoms, and a first polymerizable compound containing a benzene ring and an EO group or a PO group, and the total number of EO groups and PO groups being 2 or more, the solubility of the gelling agent was increased, and the gelling properties of the ink were sufficiently improved.

[0153] Furthermore, from the results for Ink 2, it was found that the gelling property was further improved when the ink contained a first polymerizable compound in which the total number of EO groups and PO groups was 4 or more. Furthermore, it was found that the solubility of the gelling agent was further improved when the ink contained a first polymerizable compound containing a hydrocarbon group in the molecule. [Industrial Applicability]

[0154] The ink-jet ink of the present invention can sufficiently increase the solubility of the gelling agent in the ink and the gelling property of the ink, and therefore the present invention is useful in the field of image formation. [Explanation of symbols]

[0155] 100 Image forming device 110 Inkjet head 120 Conveyor 130 Irradiation unit

Claims

1. 1. An ink-jet ink that is cured by actinic radiation, comprising: a polymerizable compound that is polymerized by actinic radiation; and a gelling agent, the gelling agent causing a sol-gel phase transition, the ink-jet ink being cured by actinic radiation, the polymerizable compound includes a first polymerizable compound containing a benzene ring and an ethylene oxide group or a propylene oxide group in a molecule, the total number of the ethylene oxide groups and the propylene oxide groups being 2 or more; the content of the first polymerizable compound is greater than 5% by mass with respect to the total mass of the ink-jet ink; The gelling agent contains a linear or branched hydrocarbon group having 22 or less carbon atoms. Inkjet ink.

2. The ink-jet ink of claim 1 , wherein the first polymerizable compound comprises a monofunctional polymerizable compound.

3. The ink-jet ink according to claim 1 , wherein a content of the first polymerizable compound is more than 5% by mass and not more than 40% by mass with respect to a total mass of the ink-jet ink.

4. The ink-jet ink according to claim 1 , wherein the first polymerizable compound includes a polymerizable compound having a total number of the ethylene oxide groups or the propylene oxide groups in the molecule of the polymerizable compound being 4 or more.

5. The ink-jet ink according to claim 1 , wherein the first polymerizable compound includes a polymerizable compound containing a linear or branched hydrocarbon group in the molecule.

6. The ink-jet ink according to claim 1 , wherein the content of the gelling agent is from 0.5% by mass to 10.0% by mass, both inclusive, based on the total mass of the ink-jet ink.

7. The ink-jet ink according to claim 1 , wherein the gelling agent is at least one compound selected from the group consisting of an aliphatic ketone, an aliphatic ester, a glycerol-based compound, and a pentaerythritol-based compound.

8. The ink-jet ink of claim 1 , wherein the gelling agent is an aliphatic ketone or an aliphatic ester.

9. The ink-jet ink of claim 1 , wherein the gelling agent is an aliphatic ester.

10. The ink-jet ink of claim 1 further comprising a pigment.

11. A step of applying the ink-jet ink according to any one of claims 1 to 10 from an ink-jet head onto a surface of a recording medium; irradiating the applied inkjet ink with actinic radiation to cure the inkjet ink; The image forming method according to claim 1,

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