Image formation method

Abstract

To provide an image formation method that enhances pinning properties, enables the formation of low-odor images, and significantly enhances image luster.SOLUTION: An image formation method includes the steps of: applying an inkjet ink to the surface of a recording medium by the inkjet technique, where the inkjet ink contains an active-ray polymerizable compound and a crystalline polyester resin, and the inkjet ink is polymerized with active rays; and irradiating the applied inkjet ink with active rays in an atmosphere with an oxygen concentration of at least 0.1 vol.% and at most 15.0 vol.% to cure the inkjet ink.SELECTED DRAWING: Figure 1

Description

[Technical field]

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

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

[0003] It is known that actinic ray curable inkjet ink contains a gelling agent in order to suppress excessive wetting and spreading of the ink after it lands and to improve pinning properties.

[0004] As an actinic radiation curable inkjet ink containing a gelling agent, for example, Patent Document 1 discloses a curable ink containing a wax and a cyclohexyl-based crystalline gelling agent (tan δ>0.08, melting point Tm>90° C.) Patent Document 1 states that the ink can improve pinning properties while flattening the surface of the formed image.

[0005] Furthermore, actinic ray-curable inkjet inks are required to suppress odors originating from unreacted actinic ray-polymerizable compounds remaining in the cured film.

[0006] As an image forming method using an actinic ray-curable inkjet ink that can suppress the above-mentioned odor, for example, Patent Document 2 discloses a method for producing a cured film in which an actinic ray-curable inkjet ink having a weight ratio of a polymerization initiator to a monomer within a specific range and a viscosity of 20 mPa s or less is irradiated with actinic rays in an environment where the oxygen concentration is lower than that of atmospheric air to cure the ink. Patent Document 2 claims that the above method reduces the amount of unreacted monomer in the cured film, thereby suppressing the odor. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] JP 2014-091830 A [Patent Document 2] JP 2015-080921 A Summary of the Invention [Problem to be solved by the invention]

[0008] An actinic ray curable inkjet ink capable of enhancing pinning properties is known, as in Patent Document 1. Also, an image forming method capable of suppressing odors from an image is known, as in Patent Document 2.

[0009] Incidentally, in order to form images with little unnatural gloss on a variety of substrates, it is desirable to increase the gloss of the images formed with ink.

[0010] However, the image forming method using an actinic ray-curable inkjet ink of Patent Document 1 and the image forming method of Patent Document 2 fail to sufficiently improve the glossiness of the formed image.

[0011] The present invention has been made in consideration of the above circumstances, and has an object to provide an image forming method that can improve pinning properties, form a low-odor image, and sufficiently improve the glossiness of the image. [Means for solving the problem]

[0012] In order to solve the above problems, one aspect of the present invention relates to an actinic ray-curable ink-jet ink as set forth in the following items [1] to [7]. [1] A step of applying an ink-jet ink that is cured by actinic radiation, the ink-jet ink including a polymerizable compound that is polymerized by actinic radiation and a crystalline polyester resin, to a surface of a recording medium by an ink-jet method; and irradiating the applied ink-jet ink with actinic rays in an atmosphere having an oxygen concentration of 0.1% by volume or more and 15.0% by volume or less to cure the ink-jet ink. Image forming method. [2] The image forming method according to [1], wherein the crystalline polyester resin contains a styrene-acrylic segment. [3] The image forming method according to [1] or [2], wherein the curing step is a step of curing the ink-jet ink by irradiating the ink with actinic radiation in an atmosphere having an oxygen concentration of 1.0 vol.% or more and 8.0 vol.% or less. [4] The image forming method according to any one of [1] to [3], wherein the ink-jet ink further contains a pigment. [5] The image forming method according to any one of [1] to [4], wherein the content of the gelling agent is less than 1.0% by mass based on the total mass of the ink-jet ink. [6] The image forming method according to any one of [1] to [5], wherein the polymerizable compound includes a hydrophilic polymerizable compound, the content of which is 5% by mass or more and 50% by mass or less relative to the total mass of the polymerizable compound. [7] The image forming method according to [6], wherein the polymerizable compound includes a hydrophilic polymerizable compound, the content of which is 20% by mass or more and 50% by mass or less relative to the total mass of the polymerizable compound. Effect of the Invention

[0013] According to the present invention, it is possible to provide an image forming method capable of improving pinning properties, forming an image with low odor, and sufficiently increasing the glossiness of the image. [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. Image forming method The image forming method according to this embodiment includes a step (step S10) of applying an inkjet ink that is cured by actinic radiation (hereinafter referred to as an actinic radiation curable inkjet ink) to the surface of a recording medium by an inkjet method, and a step (step S20) of curing the inkjet ink by irradiating the applied inkjet ink with actinic radiation in an atmosphere having an oxygen concentration of 0.1% by volume or more and 15.0% by volume or less. The actinic radiation curable inkjet ink contains a polymerizable compound that is polymerized by actinic radiation (hereinafter referred to as an actinic radiation polymerizable compound) and a crystalline polyester resin.

[0017] In the actinic radiation curable ink containing a gelling agent as in Patent Document 1, the pinning property is increased, but the gloss of the image is low. After the ink lands, the gelling agent crystallizes, and the crystallized gelling agent moves to the image surface, so that it is considered that unevenness due to the crystals of the gelling agent occurs on the image surface. As a result, it is considered that the gloss of the image is reduced. In addition, when ink droplets are overlapped, the gelling agent crystals move to the surface of the ink droplets that land on the recording medium, so that the wettability between the ink droplets is reduced. As a result, the overlapped droplets are less likely to wet and spread on the droplets on the recording medium, so that the image surface is less likely to become smooth, and the gloss of the image is considered to be reduced. For these reasons, there is a trade-off between the pinning property of the ink and the gloss of the image.

[0018] In response to this, the present inventors attempted to increase the pinning ability and the glossiness of the image by using a crystalline polyester resin in an actinic radiation curable ink. The reasons for this are as follows.

[0019] When the heated ink is ejected from an inkjet head, the crystalline polyester resin dissolves in the actinic radiation polymerizable compound. When the ink lands on a recording medium in this state, the temperature of the ink drops, causing the crystalline polyester resin to crystallize and precipitate. When the crystals of the crystalline polyester resin precipitate, it is believed that a three-dimensional structure is formed by entangling non-crystalline portions of the molecular chains of the crystalline polyester resin. It is believed that the pinning ability of the ink is enhanced by the inclusion of the actinic radiation polymerizable compound in this three-dimensional structure.

[0020] In addition, since the crystalline polyester resin has a high affinity with the actinic radiation polymerizable compound, it is considered that it is difficult for the resin to migrate to the image surface even when it crystallizes, compared to the gelling agent. Therefore, the inventors of the present invention considered that it is possible to reduce the area on the image surface where the crystals of the polyester resin precipitate and cause unevenness, thereby improving the glossiness of the image. Furthermore, since the crystals of the crystalline polyester resin are difficult to migrate to the image surface (ink droplet surface), it is considered that when the ink droplets are deposited in layers, the wettability between the droplets is increased, and the deposited droplets are likely to wet and spread. As a result, the image surface is easily made smooth, and the inventors of the present invention considered that it is possible to sufficiently improve the glossiness of the image even when the ink is deposited in layers.

[0021] However, even with actinic radiation curable ink containing a crystalline polyester resin, it has not been possible to sufficiently improve the glossiness of an image when the image is formed in an atmospheric environment.

[0022] When the actinic radiation curable ink is irradiated with actinic radiation in an atmospheric environment to cure the ink, the polymerization reaction of the actinic radiation polymerizable compound is difficult to proceed near the surface of the image due to oxygen inhibition. Therefore, the degree of cure of the image surface is likely to be low, and curing shrinkage is likely to occur. At this time, due to the crystalline polyester resin, the image surface has few areas where crystals are precipitated, and many areas where crystals are not precipitated are formed between the areas. In this state, if curing shrinkage occurs, it is thought that the stress associated with the curing shrinkage is concentrated in the areas where crystals are not precipitated that are formed between the areas where crystals are precipitated, and micropores are likely to be formed. It is thought that the gloss of the image was not sufficiently increased due to these micropores.

[0023] Therefore, the present inventors have found that the glossiness of an image can be sufficiently improved by curing the ink by irradiation with actinic rays in an atmosphere with a low oxygen concentration (specifically, in an atmosphere with an oxygen concentration of 0.1% by volume or more and 15.0% by volume or less). It is believed that by curing the ink under the above oxygen concentration, oxygen inhibition can be suppressed, the degree of curing of the image surface can be increased, and curing shrinkage can be suppressed. This is believed to be because, as a result, the formation of the above-mentioned micropores can be suppressed.

[0024] For these reasons, it is believed that by curing an actinic ray curable ink containing a crystalline polyester resin under a low oxygen concentration, it is possible to sufficiently increase the gloss of an image while improving the pinning ability.

[0025] Furthermore, by curing the ink in an atmosphere with an oxygen concentration within the above range, inhibition of the reaction of the actinic radiation polymerizable compound due to oxygen inhibition can be suppressed. Furthermore, the crystals of the crystalline polyester resin formed after the ink has landed have low gas permeability, so odors are unlikely to pass out of the cured film. For these reasons, odors originating from unreacted actinic radiation polymerizable compound in the cured film can be suppressed.

[0026] The actinic ray curable inkjet ink of the present invention based on the above findings will be described in more detail below.

[0027] 1-1. Step of applying ink to the surface of the recording medium (step S10) In this process, the actinic radiation curable inkjet ink is applied to the surface of the recording medium by an inkjet method.

[0028] 1-1-1. Actinic radiation curable inkjet ink The actinic ray curable inkjet ink used in this process contains an actinic ray polymerizable compound and a crystalline polyester resin.

[0029] <Active radiation polymerizable compound> 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.

[0030] Examples of the actinic radiation 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.

[0031] The radical polymerizable compound is a compound (monomer, oligomer, polymer, or a mixture thereof) having an ethylenically unsaturated bond capable of radical polymerization. The radical polymerizable compound may be used alone or in combination of two or more kinds.

[0032] Examples of compounds having a radically polymerizable ethylenically unsaturated bond include unsaturated carboxylic acids and their salts, unsaturated carboxylic acid ester compounds, unsaturated carboxylic acid urethane compounds, unsaturated carboxylic acid amide compounds and their anhydrides, acrylonitrile, styrene, unsaturated polyesters, unsaturated polyethers, unsaturated polyamides, unsaturated urethanes, etc. Examples of unsaturated carboxylic acids include (meth)acrylic acid, itaconic acid, crotonic acid, isocrotonic acid, maleic acid, etc.

[0033] The radical polymerizable compound is preferably an unsaturated carboxylic acid ester compound, more preferably a (meth)acrylate. In this specification, "(meth)acrylate" means acrylate or methacrylate, and "(meth)acrylic" means acrylic or methacrylic.

[0034] Examples of monofunctional (meth)acrylates include isoamyl (meth)acrylate, stearyl (meth)acrylate, lauryl (meth)acrylate, octyl (meth)acrylate, decyl (meth)acrylate, isomylstyryl (meth)acrylate, isostearyl (meth)acrylate, 2-ethylhexyl-diglycol (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 2-(meth)acryloyloxyethylhexahydrophthalic acid, butoxyethyl (meth)acrylate, ethoxydiethylene glycol (meth)acrylate, methoxydiethylene glycol (meth)acrylate, methoxypoly ... Examples of suitable acrylates include ethylene glycol (meth)acrylate, methoxypropylene glycol (meth)acrylate, phenoxyethyl (meth)acrylate, tetrahydrofurfuryl (meth)acrylate, isobornyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 2-hydroxy-3-phenoxypropyl (meth)acrylate, 2-(meth)acryloyloxyethyl succinate, 2-(meth)acryloyloxyethyl phthalate, 2-(meth)acryloyloxyethyl-2-hydroxyethyl-phthalate, and t-butylcyclohexyl (meth)acrylate.

[0035] Examples of polyfunctional (meth)acrylates include triethylene glycol di(meth)acrylate, tetraethylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, tripropylene glycol di(meth)acrylate, polypropylene glycol di(meth)acrylate, 1,4-butanediol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, 1,9-nonanediol di(meth)acrylate, neopentyl glycol di(meth)acrylate, dimethylol-tricyclodecane di(meth)acrylate, hydroxypivalic acid neopentyl glycol di(meth)acrylate, polytetrafluoroethylene ... Examples of the difunctional (meth)acrylates include lamethylene glycol di(meth)acrylate, polyethylene glycol diacrylate, and tripropylene glycol diacrylate, as well as 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, pentaerythritol ethoxy tetra(meth)acrylate, glycerin diacrylate, and glycerin triacrylate.

[0036] The content of the polyfunctional (meth)acrylate is preferably 75% by mass or more and 100% by mass or less, more preferably 90% by mass or more and 100% by mass or less, and even more preferably 95% by mass or more and 100% by mass or less, based on the total mass of the monofunctional (meth)acrylate and the polyfunctional (meth)acrylate. This can increase the polymerization degree of the active radiation polymerizable compound and increase the curing degree of the entire image. This can increase the curing degree of the image surface and suppress the formation of micropores due to curing shrinkage, thereby increasing the gloss of the image.

[0037] Examples of the cationically polymerizable compound include an epoxy compound, a vinyl ether compound, and an oxetane compound.

[0038] Examples of the epoxy compounds include cycloaliphatic epoxy resins such as 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, triglyceride of glycerin, and the like. Examples of the epoxy compounds include aliphatic epoxy compounds including polyglycidyl ethers of polyether polyols obtained by adding one or more alkylene oxides (such as ethylene oxide and propylene oxide) to aliphatic polyhydric alcohols such as ethylene glycol, propylene glycol, and glycerin, as well as di- or polyglycidyl ethers of bisphenol A or its alkylene oxide adducts, di- or polyglycidyl ethers of hydrogenated bisphenol A or its alkylene oxide adducts, and novolac-type epoxy resins.

[0039] 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.

[0040] Examples of the oxetane compound include 3-hydroxymethyl-3-methyloxetane, 3-hydroxymethyl-3-ethyloxetane, 3-hydroxymethyl-3-propyloxetane, 3-hydroxymethyl-3-n-butyloxetane, 3-hydroxymethyl-3-phenyloxetane, 3-hydroxymethyl-3-benzyloxetane, 3-hydroxyethyl-3-methyloxetane, 3-hydroxyethyl-3-ethyloxetane, 3-hydroxyethyl-3-propyloxetane, 3-hydroxyethyl -3-phenyloxetane, 3-hydroxypropyl-3-methyloxetane, 3-hydroxypropyl-3-ethyloxetane, 3-hydroxypropyl-3-propyloxetane, 3-hydroxypropyl-3-phenyloxetane, 3-hydroxybutyl-3-methyloxetane, 1,4 bis{[(3-ethyl-3-oxetanyl)methoxy]methyl}benzene, 3-ethyl-3-(2-ethylhexyloxymethyl)oxetane and di[1-ethyl(3-oxetanyl)]methyl ether.

[0041] The actinic ray polymerizable compound preferably contains a hydrophilic actinic ray polymerizable compound whose content relative to the total mass of the actinic ray polymerizable compound is 5.0 mass% or more and 50.0 mass% or less. In this specification, the term "hydrophilic actinic ray polymerizable compound" refers to a compound having an HSP value of 19 (MPa) or less. 1 / 2 The HSP value can be determined by inputting the chemical structural formula of the actinic radiation polymerizable compound into computer software Hansen Solubility Parameters in Practice 5th Edition 5.0.13 (HSPiP, manufactured by Tegara Corporation).

[0042] When the content of the hydrophilic actinic radiation polymerizable compound is 5.0% by mass or more, an interaction between the polar portion of the crystalline polyester and the hydrophilic actinic radiation polymerizable compound is easily formed, so that the crystals of the crystalline polyester resin are less likely to move to the image surface, and the glossiness of the image can be more sufficiently improved. In addition, the above interaction makes it easier for the actinic radiation polymerizable compound to be encapsulated in the crystals of the crystalline polyester resin. As a result, the pinning property of the ink can be further improved. When the content is 50.0% by mass or less, the compatibility between the crystalline polyester resin and the actinic radiation polymerizable compound can be appropriately reduced, making it easier to precipitate the crystals of the crystalline polyester resin when the ink is landed. From these viewpoints, the content of the hydrophilic actinic radiation polymerizable compound is more preferably 10.0% by mass or more and 50.0% by mass or less, and even more preferably 20.0% by mass or more and 50.0% by mass or less, based on the total mass of the actinic radiation polymerizable compound. In particular, when the content is 20.0% by mass or more and 50.0% by mass or less, the above-mentioned effect becomes remarkable.

[0043] The HSP value of the hydrophilic actinic polymerizable compound is 19 (MPa). 1 / 2 More than 22 (MPa) 1 / 2 It is preferable that the temperature is 19 (MPa) or less. 1 / 2 More than 20 (MPa) 1 / 2 It is more preferable that:

[0044] Examples of hydrophilic actinic radiation polymerizable compounds include polyethylene glycol diacrylate, hydroxyacrylate, EO-modified bisphenol A diacrylate, EO-modified trimethylolpropane tri(meth)acrylate, PO-modified bisphenol A diacrylate, etc. Among these, compounds having an ethylene oxide group in the molecule, such as polyethylene glycol diacrylate, are preferred.

[0045] The content of the actinic radiation polymerizable compound can be from 1% by mass to 97% by mass, preferably from 1% by mass to 90% by mass, and more preferably from 1% by mass to 85% by mass, based on the total mass of the actinic radiation curable inkjet ink.

[0046] <Crystalline polyester resin> In this specification, the term "crystalline" polyester resin means a polyester resin having a clear endothermic peak during heating in an endothermic curve obtained by differential scanning calorimetry (DSC). Specifically, the term "crystalline" polyester resin means a peak having a half-width of 15°C or less when measured by differential scanning calorimetry (DSC) at a heating rate of 10°C / min.

[0047] The melting point (Tm) of the crystalline polyester resin is preferably 50° C. or higher and 100° C. or lower, and more preferably 60° C. or higher and 80° C. or lower. If it is 50° C. or higher, the crystallization speed of the crystallized polyester resin when the ink lands can be increased, and the pinning property can be further improved. If it is 100° C. or lower, crystallization of the crystalline polyester resin during ink ejection can be suppressed, and ejection stability can be further improved.

[0048] The melting point (Tm) of the crystalline polyester resin can be determined, for example, using a differential scanning calorimeter "Diamond DSC" (manufactured by PerkinElmer). The measurement is performed under the following measurement conditions (heating and cooling conditions): a first heating process in which the temperature is raised from room temperature (25°C) to 150°C at a heating rate of 10°C / min and isothermally held at 150°C for 5 minutes, a cooling process in which the temperature is cooled from 150°C to 0°C at a cooling rate of 10°C / min and isothermally held at 0°C for 5 minutes, and a second heating process in which the temperature is raised from 0°C to 150°C at a heating rate of 10°C / min in this order. The above measurement is performed by sealing 3.0 mg of the crystalline polyester resin sample in an aluminum pan and setting it in the sample holder of the differential scanning calorimeter "Diamond DSC". An empty aluminum pan is used as a reference. In the above measurement, an analysis is performed on the endothermic curve obtained in the first heating process, and the top temperature of the endothermic peak (half width within 15°C) derived from the crystalline polyester resin is regarded as the melting point (Tm) of the crystalline polyester resin.

[0049] The recrystallization temperature (Rc) of the crystalline polyester resin is preferably 50° C. or higher and 90° C. or lower, and more preferably 50° C. or higher and 80° C. or lower. If the temperature is 50° C. or higher, the crystalline polyester resin is more likely to crystallize when the ink lands, and the pinning ability can be further improved. If the recrystallization temperature (Rc) is 90° C. or lower, the crystalline polyester resin is less likely to crystallize when the ink is ejected, and the ejection stability of the ink can be further improved.

[0050] The recrystallization temperature (Rc) of the crystalline polyester resin can be determined, for example, using a differential scanning calorimeter "Diamond DSC" (manufactured by PerkinElmer). The measurement is performed under the following measurement conditions: a heating process in which the temperature is raised from room temperature (25°C) to 100°C at a rate of 10°C / min, and the temperature is kept isothermal at 100°C for 1 minute, and a cooling process in which the temperature is cooled from 100°C to 0°C at a cooling rate of 0.1°C / min. The above measurement is performed by sealing 3.0 mg of a sample of the crystalline polyester resin in an aluminum pan and setting it in the sample holder of the differential scanning calorimeter "Diamond DSC". An empty aluminum pan is used as a reference. In the above measurement, an analysis is performed from the heat generation curve obtained by the cooling process, and the top temperature of the heat generation peak derived from the crystalline resin is taken as the recrystallization temperature (Rc) of the crystalline polyester resin.

[0051] The crystalline polyester resin can be obtained by a polycondensation reaction between a divalent or higher alcohol (a polyhydric alcohol component) and a divalent or higher carboxylic acid (a polycarboxylic acid component).

[0052] A polyhydric alcohol compound is a compound having two or more hydroxyl groups in one molecule. Examples of polyhydric alcohol components include dihydric alcohols such as ethylene glycol, propylene glycol, butanediol, diethylene glycol, hexanediol (1,2-hexanediol, 1,6-hexanediol), cyclohexanediol, octanediol, decanediol, dodecanediol, ethylene oxide adduct of bisphenol A, and propylene oxide adduct of bisphenol A, trihydric or higher polyols such as glycerin, pentaerythritol, hexamethylolmelamine, hexaethylolmelamine, tetramethylolbenzoguanamine, and tetraethylolbenzoguanamine, as well as ester compounds and hydroxycarboxylic acid derivatives thereof.

[0053] From the viewpoint of increasing the crystallinity of the crystalline polyester resin, the polyhydric alcohol compound is preferably a dihydric aliphatic alcohol, more preferably a dihydric linear aliphatic alcohol. The polyhydric alcohol compound may be used alone or in combination of two or more kinds.

[0054] The polycarboxylic acid compound is a compound having two or more carboxyl groups in one molecule, and alkyl esters, acid anhydrides, and acid chlorides of polycarboxylic acid compounds can be used. Examples of polycarboxylic acid components include oxalic acid, succinic acid, maleic acid, mesaconic acid, adipic acid, β-methyladipic acid, azelaic acid, sebacic acid, nonanedicarboxylic acid, decanedicarboxylic acid, undecanedicarboxylic acid, dodecanedicarboxylic acid, tetradecanedicarboxylic acid, fumaric acid, citraconic acid, diglycolic acid, cyclohexane-3,5-diene-1,2-dicarboxylic acid, malic acid, citric acid, hexahydroterephthalic acid, malonic acid, pimelic acid, tartaric acid, mucic acid, phthalic acid, isophthalic acid, terephthalic acid, tetrachlorophthalic acid, chlorophthalic acid, nitrophthalic acid, p-carboxyphenylacetic acid, p-phenylacetic acid, and the like. Examples of the polycarboxylic acid include dicarboxylic acids such as diphenyl diacetic acid, m-phenylenediglycolic acid, p-phenylenediglycolic acid, o-phenylenediglycolic acid, diphenylacetic acid, diphenyl-p,p'-dicarboxylic acid, naphthalene-1,4-dicarboxylic acid, naphthalene-1,5-dicarboxylic acid, naphthalene-2,6-dicarboxylic acid, anthracene dicarboxylic acid, and dodecenyl succinic acid, and tricarboxylic acids such as trimellitic acid, pyromellitic acid, naphthalene tricarboxylic acid, naphthalene tetracarboxylic acid, pyrene tricarboxylic acid, and pyrene tetracarboxylic acid, as well as their alkyl esters, acid anhydrides, and acid chlorides. The polycarboxylic acid compounds may be used alone or in combination of two or more kinds.

[0055] From the viewpoint of enhancing the crystallinity of the crystalline polyester resin, the polyvalent carboxylic acid compound is preferably a divalent aliphatic carboxylic acid.

[0056] From the viewpoint of further improving the pinning property of the ink, the crystalline polyester resin is preferably a styrene-acrylic modified polyester resin. Since the aromatic ring of the styrene-based monomer constituting the styrene-acrylic modified polyester resin forms a three-dimensional structure, the actinic radiation polymerizable compound described above is more easily encapsulated within the crystals of the crystalline polyester resin. This is believed to further improve the pinning property of the ink.

[0057] In this specification, "styrene-acrylic modified polyester resin" refers to a resin in which a crystalline polyester segment composed of a polyester resin and a styrene-acrylic segment composed of a styrene-acrylic copolymer are bonded via a bireactive compound. The crystalline polyester segment refers to a collection of structural units derived from the crystalline polyester resin in the styrene-acrylic modified polyester resin. The styrene-acrylic segment refers to a collection of structural units derived from styrene-acrylic in the styrene-acrylic modified polyester resin.

[0058] The styrene-acrylic modified polyester resin can also be obtained by carrying out a polymerization reaction to produce a styrene-acrylic resin in the presence of a crystalline polyester resin prepared in advance, or by carrying out a polymerization reaction to produce a crystalline polyester resin in the presence of a styrene-acrylic resin prepared in advance.

[0059] The bireactive compound is a compound having a substituent capable of reacting with both the crystalline polyester segment and the styrene-acrylic segment, and a polymerizable unsaturated group. Examples of the bireactive compound include (meth)acrylic acid, fumaric acid, maleic acid, maleic anhydride, etc.

[0060] The styrene monomer, which is a component constituting the styrene-acrylic copolymer, is a monomer that contains a styrene structure and has an ethylenically unsaturated bond capable of radical polymerization. Examples of the styrene monomer include styrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, p-methoxystyrene, p-phenylstyrene, p-chlorostyrene, p-ethylstyrene, pn-butylstyrene, p-tert-butylstyrene, pn-hexylstyrene, pn-octylstyrene, pn-nonylstyrene, pn-decylstyrene, pn-dodecylstyrene, 2,4-dimethylstyrene, 3,4-dichlorostyrene, and derivatives thereof. These styrene monomers may be used alone or in combination of two or more. When using a (meth)acrylic acid monomer that can also act as a bireactive compound, such as acrylic acid or methacrylic acid, it is not necessary to use a bireactive compound in addition to the (meth)acrylic acid monomer during the synthesis of the styrene-acrylic modified polyester resin.

[0061] The (meth)acrylic acid monomer, which is a component constituting the styrene-acrylic copolymer, is a monomer having an ethylenically unsaturated bond that contains a (meth)acrylic group and can undergo radical polymerization. Examples of the acrylic acid monomer include acrylic acid, methacrylic acid, methyl acrylate, ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, cyclohexyl acrylate, phenyl acrylate, β-ethyl hydroxyacrylate, γ-propyl aminoacrylate, and diacrylates of dihydric alcohols such as ethylene glycol, propylene glycol, butylene glycol, and hexylene glycol, and dimethacrylates or trimethacrylates of trihydric or higher alcohols such as pentaerythritol and trimethylolpropane. Examples of methacrylic acid compounds include methyl methacrylate, ethyl methacrylate, butyl methacrylate, hexyl methacrylate, 2-ethylhexyl methacrylate, stearyl methacrylate, dimethylaminoethyl methacrylate, and diethylaminoethyl methacrylate. These (meth)acrylic acid monomers may be used alone or in combination of two or more.

[0062] Other polymerizable compounds can also be used in the synthesis of styrene-acrylic copolymers. Examples of other polymerizable compounds that can be used include monofunctional vinyl monomers and polyfunctional vinyl monomers. Examples of the monofunctional vinyl monomers include acid monomers such as maleic anhydride and vinyl acetic acid, acrylamide, methacrylamide, acrylonitrile, ethylene, propylene, butylene vinyl chloride, and N-vinylpyrrolidone.

[0063] Examples of the polyfunctional vinyl monomer include butadiene, divinylbenzene, and the like.

[0064] The styrene-acrylic copolymer can be obtained by adding any commonly used polymerization initiator such as a peroxide, a persulfide, or an azo compound to the polymerization of the monomer, and polymerizing the monomer by a known polymerization method such as bulk polymerization, solution polymerization, emulsion polymerization, mini-emulsion, suspension polymerization, or dispersion polymerization. During the polymerization, a commonly used chain transfer agent such as an alkyl mercaptan or a mercapto fatty acid ester can be used for the purpose of adjusting the molecular weight.

[0065] The styrene-acrylic modification rate, which indicates the proportion of styrene-acrylic polymerized segments in the crystalline polyester resin, is preferably 0.1% by mass or more and 40.0% by mass or less, more preferably 0.1% by mass or more and 35.0% by mass or less, and even more preferably 0.2% by mass or more and 30.0% by mass or less, based on the total mass of the crystalline polyester resin. If it is 0.1% by mass or more, the pinning property of the ink can be more sufficiently improved. If it is 40.0% by mass or less, the content of the crystalline polyester segment increases, and the crystalline polyester resin is more likely to crystallize. This makes it possible to further improve the pinning property and the gloss of the image.

[0066] Specifically, the styrene-acrylic modification rate can be determined from the ratio of the mass of the aromatic vinyl monomer and the (meth)acrylic acid ester monomer to the total mass of the resin material used to synthesize the styrene-acrylic modified polyester resin, i.e., the total mass of the monomer constituting the unmodified polyester resin that becomes the polyester segment, the aromatic vinyl monomer and the (meth)acrylic acid ester monomer that become the styrene-acrylic polymer segment, and the bireactive compound for bonding them.

[0067] The weight average molecular weight (Mw) of the crystalline polyester resin can usually be from 5,000 to 50,000, but is preferably from 7,000 to 30,000, and more preferably from 10,000 to 25,000. By having it be 5,000 or more, the viscosity of the precoat agent can be increased, making it easier for the precoat agent to remain on the surface of the recording medium without being absorbed by the recording medium, and by having it be 50,000 or less, the melting point of the crystalline resin can be lowered, making it easier to apply the precoat agent to the recording medium.

[0068] The weight average molecular weight (Mw) of the crystalline polyester resin is measured using a GPC apparatus (HLC-8120GPC, manufactured by Tosoh Corporation) and a column (TSKguardcolumn+TSKgelSuperHZ-M3 series, manufactured by Tosoh Corporation) by flowing tetrahydrofuran as a carrier solvent at a flow rate of 0.2 mL / min while maintaining the column temperature at 40° C. 10 μL of the prepared sample solution is injected into the GPC apparatus together with the carrier solvent, the sample is detected using a refractive index detector (RI detector), and the molecular weight distribution of the sample can be calculated using a calibration curve measured using monodisperse polystyrene standard particles.

[0069] The content of the crystalline polyester resin is preferably 5.0% by mass or less, and more preferably 2.0% by mass or less, based on the total mass of the actinic radiation curable inkjet ink. By making the content 5.0% by mass or less, ejection stability can be further improved. From the viewpoint of further improving the glossiness of the image, the content of the crystalline polyester resin is preferably 1.0% by mass or more, more preferably 3.0% by mass or more, and even more preferably 4.5% by mass or more, based on the total mass of the actinic radiation curable inkjet ink.

[0070] <Other ingredients> (Coloring agent) In this embodiment, the actinic ray curable inkjet ink may contain a colorant as necessary.

[0071] The colorant may be a dye or a pigment, with pigments being preferred because they have good dispersibility in the ink components and are weather resistant. The pigment may be selected from, for example, yellow pigments, red or magenta pigments, blue or cyan pigments, black pigments, and white pigments, depending on the color of the image to be formed.

[0072] In conventional actinic radiation curable inkjet inks, when the ink contains a pigment, the gloss of the image tends to vary from color to color. In particular, as in Patent Document 1, when the ink contains a gelling agent, the difference in gloss between colors is significant. When the gelling agent crystallizes when the ink lands, it is believed that the pigment present as a solid in the ink can become a crystal nucleus. At this time, the affinity between the pigment and the gelling agent differs for each type of pigment, so the ease with which the gelling agent crystals grow also differs, and the size of the unevenness on the image surface differs for each color.

[0073] In contrast, in this embodiment, the crystalline polyester resin contained in the ink makes it difficult for unevenness to occur on the image surface, so the magnitude of unevenness on the image surface for each color is also unlikely to occur. Also, since the affinity of the crystalline polyester resin with the pigment is extremely low, it is considered that the difference in affinity between the pigment and the crystalline polyester resin due to the type of pigment is unlikely to contribute to the growth of crystals in the crystalline polyester. For these reasons, it is considered that when the ink contains a pigment, this embodiment has the effect of reducing the difference in glossiness between colors.

[0074] Examples of yellow pigments include CI Pigment Yellow (hereinafter, also simply referred to as "PY") 1, PY3, PY12, PY13, PY14, PY17, PY34, PY35, PY37, PY55, PY74, PY81, PY83, PY93, PY94, PY95, PY97, PY108, PY109, PY110, PY137, PY138, PY139, PY153, PY154, PY155, PY157, PY166, PY167, PY168, PY180, PY185, and PY193.

[0075] Examples of red or magenta pigments include CI Pigment Red (hereinafter referred to simply as "PR") 3, PR5, PR19, PR22, PR31, PR38, PR43, PR48:1, PR48:2, PR48:3, PR48:4, PR48:5, PR49:1, PR53:1, PR57:1, PR57:2, PR58:4, PR63:1, PR81, PR81:1, PR81:2, PR81:3, PR81:4, PR88, PR104, PR108, PR112, PR122, PR123, PR144, PR146, PR149, PR166, PR168, PR169, PR170, PR177, PR178, PR179, PR184, PR185, PR208, PR216, PR226, and PR257, CI Pigment These include CI Pigment Orange (hereinafter referred to simply as "PO") 13, PO16, PO20, and PO36, as well as CI Pigment Violet (hereinafter referred to simply as "PV") 3, PV19, PV23, PV29, PV30, PV37, PV50, and PV88, as well as CI Pigment Orange (hereinafter referred to simply as "PO") 13, PO16, PO20, and PO36.

[0076] Examples of blue or cyan pigments include CI Pigment Blue (hereinafter also simply referred to as "PB") 1, PB15, PB15:1, PB15:2, PB15:3, PB15:4, PB15:6, PB16, PB17-1, PB22, PB27, PB28, PB29, PB36, and PB60.

[0077] Examples of green pigments include CI Pigment Green (hereinafter also simply referred to as "PG") 7, PG26, PG36, and PG50.

[0078] Examples of black pigments include CI Pigment Black (hereinafter also simply referred to as "PBk") 7, PBk26, and PBk28.

[0079] 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.

[0080] 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.

[0081] The content of the colorant is preferably 0.1% by mass to 10% by mass, and more preferably 1% by mass to 5% by mass, based on the total mass of the actinic radiation curable inkjet ink. The content of the white pigment is preferably 3% by mass to 8% by mass.

[0082] (Pigment dispersant) The actinic radiation curable inkjet 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.

[0083] The content of the pigment dispersant is preferably 10% by mass or more and 200% by mass or less, and 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, and 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 becomes stable.

[0084] (Gelling agent) In this embodiment, the actinic ray curable inkjet ink may contain a gelling agent.

[0085] The gelling agent causes the ink to become a sol when heated and to become a gel at about room temperature, whereby the ink that has been heated and turned into a sol is ejected from an inkjet head, and the ink that has been gelled by cooling after landing on a recording medium is provisionally solidified, thereby more sufficiently enhancing the pinning ability of the ink.

[0086] The gelling agent is preferably a compound that dissolves in the actinic radiation polymerizable compound contained in the ink at a temperature higher than the gelling temperature of the ink, and crystallizes in the ink at a temperature equal to or lower than the gelling temperature of the ink. Here, "gelling temperature" refers to the temperature at which the ink undergoes a phase transition from sol to gel and the viscosity of the ink suddenly changes when the ink that has been solated or liquefied by heating is cooled. Specifically, the solated or liquefied ink is cooled while the viscosity is measured with a rheometer (e.g., MCR300 manufactured by Anton Paar), and the temperature at which the viscosity suddenly increases can be determined as the gelling temperature of the ink.

[0087] Examples of gelling agents include gelling agents that crystallize in the ink at a temperature equal to or lower than the gelling temperature of the ink, and form a structure in which the radical polymerizable compound is encapsulated in a three-dimensional space formed by the gelling agent that has crystallized into a plate shape (such a structure will be referred to as a "house of cards structure" hereinafter). When a house of cards structure is formed, the liquid actinic radiation polymerizable compound is held within the space, so that dots formed by the ink adhering to the recording medium are less likely to wet and spread, and the pinning ability of the ink is more sufficiently improved.

[0088] Examples of gelling agents that are prone to forming a house-of-cards structure through crystallization include aliphatic ketones, aliphatic esters, petroleum-based waxes, vegetable waxes, animal waxes, mineral 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 acid and dimer diol.

[0089] Examples of aliphatic ketones include dilignoceryl ketone, dibehenyl ketone, distearyl ketone, dieicosyl ketone, dipalmityl ketone, dilauryl ketone, dimyristyl ketone, myristyl palmityl ketone, and palmityl stearyl ketone.

[0090] 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, and oleyl palmitate, and fatty acid esters of polyhydric alcohols such as glycerin fatty acid esters, sorbitan fatty acid esters, propylene glycol fatty acid esters, ethylene glycol fatty acid esters, and polyoxyethylene fatty acid esters.

[0091] Examples of higher fatty acids include behenic acid, arachidic acid, stearic acid, palmitic acid, myristic acid, lauric acid, oleic acid, and erucic acid.

[0092] Examples of higher alcohols include stearyl alcohol and behenyl alcohol.

[0093] Among these, from the viewpoint of further improving the pinning property, the gelling agent is preferably an aliphatic ketone, an aliphatic ester, a higher fatty acid, or a higher alcohol, and more preferably an aliphatic ketone represented by the following general formula (G1) or an aliphatic ester represented by the following general formula (G2). Only one type of gelling agent may be contained, or two or more types may be contained in combination.

[0094] General formula (G1):R a -CO-R b General formula (G2):R c -COO-R d

[0095] In general formula (G1), R a and R b each independently represents a linear hydrocarbon group having 12 to 26 carbon atoms, which may have a branched chain. In the general formula (G2), R c and R d each independently represents a linear hydrocarbon group having 12 to 26 carbon atoms, which may have a branched chain.

[0096] In general formulae (G1) and (G2), R a ~R d When the number of carbon atoms is 12 or more, the crystallinity of the gelling agent represented by general formula (G1) and general formula (G2) is increased, and more sufficient space is generated in the house-of-card structure, so that the actinic radiation polymerizable compound (A) is easily and sufficiently enclosed in the space, improving the pinning property of the ink.

[0097] Also, R a ~R dBy making the number of carbon atoms in the group equal to or less than 26, it is possible to prevent the melting point of the gelling agent represented by general formula (G1) and general formula (G2) from rising excessively, which prevents the solation temperature of the ink containing the gelling agent from rising too high, allowing the ink to be discharged at a lower heating temperature.

[0098] Examples of aliphatic ketones represented by general formula (G1) include dilignoceryl ketone (carbon number: 23-24), 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 ketone (carbon number: 13-14), and glyceryl ketone (carbon number: 14-16). These include myristyl ketone (carbon number: 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.

[0099] 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.

[0100] The content of the gelling agent is preferably less than 1.0% by mass, more preferably less than 0.5% by mass, and even more preferably less than 0.1% by mass, based on the total mass of the actinic radiation curable inkjet ink. By having the content of the gelling agent be less than 1.0% by mass, it is possible to reduce unevenness on the image surface caused by the gelling agent crystallized after the ink has landed, and to further increase the glossiness of the image.

[0101] (Activin Radiation Polymerization Initiator) In this 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, and 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.

[0102] The radical polymerization initiator includes an intramolecular bond cleavage type radical polymerization initiator and an intramolecular hydrogen abstraction type radical polymerization initiator.

[0103] 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.

[0104] 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.

[0105] 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.

[0106] 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.

[0107] (Polymerization inhibitor) In this embodiment, the actinic ray curable inkjet ink may contain a polymerization inhibitor.

[0108] 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.

[0109] The content of the polymerization inhibitor is not particularly limited, but is preferably from 0.1% by mass to 10% by mass based on the total mass of the actinic ray-curable inkjet ink.

[0110] (Surfactant) In this embodiment, the actinic ray curable inkjet ink may contain a surfactant for adjusting the surface tension.

[0111] 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.

[0112] 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.

[0113] 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.

[0114] <Physical properties of actinic radiation curable inkjet ink> When the actinic ray curable inkjet ink does not contain a gelling agent, the viscosity of the actinic ray curable inkjet ink at 40°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. When the viscosity is in the above range, the ejection property of the ink from the inkjet head can be further improved. Furthermore, the viscosity at 25°C is preferably 1000 mPa·s or more.

[0115] 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 40°C from the obtained temperature change curve.

[0116] When the actinic ray curable inkjet ink contains a gelling agent, 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. This can improve the ejection properties when the ink is heated and ejected from the inkjet head. The viscosity can be determined by reading the viscosity at 80°C on the temperature change curve in the above-mentioned measurement method.

[0117] <Method of preparing actinic radiation curable inkjet ink> The actinic radiation curable inkjet ink can be prepared by mixing the actinic radiation polymerizable compound, the crystalline polyester resin, and any other components under heating. At this time, it is preferable to filter the obtained 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 actinic radiation polymerizable compound, and then mix the pigment dispersion with other components. The pigment dispersion may further contain a dispersant.

[0118] 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.

[0119] 1-2. Method of applying ink to the surface of a recording medium 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 either 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, or 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.

[0120] In this embodiment, the ink is heated to a temperature equal to or higher than the melting point of the crystalline polyester resin, and ink droplets are ejected from the inkjet head. From the viewpoint of improving the ejection properties of the ink from the inkjet head, it is preferable that the temperature of the ink when ejected from the inkjet head is set to the melting point of the crystalline polyester resin + 10°C or higher. On the other hand, from the viewpoint of suppressing deterioration of the inkjet head due to high temperatures, it is preferable that the temperature of the ink when ejected from the inkjet head is set to the melting point of the crystalline polyester resin + 20°C or lower.

[0121] The method for heating the actinic radiation-curable inkjet ink is not particularly limited. For example, at least one of 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 a filter, and the piezo head can be heated by a panel heater, a ribbon heater, or warm water.

[0122] 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.

[0123] 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), aluminum-deposited paper, 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.

[0124] Among these, aluminum-deposited paper is preferred. Since aluminum-deposited paper is a high-gloss recording medium, the glossiness of the printed portion is easily visually recognized in comparison with the non-printed portion. Therefore, the effect of increasing the glossiness of the image by the image forming method of this embodiment is easily noticeable.

[0125] The actinic ray 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.

[0126] In this step, new ink droplets may be applied in an overlapping manner on the droplets of the actinic ray curable ink applied onto the recording medium.

[0127] 2-2. Step of curing the actinic ray curable inkjet ink (step S20) In this process, the actinic ray curable inkjet ink applied to the recording medium in step S10 is irradiated with actinic rays in an atmosphere having an oxygen concentration of 0.1% by volume or more and 15.0% by volume or less to cure the ink, thereby forming an image consisting of a cured film of the actinic ray curable inkjet ink.

[0128] The oxygen concentration is preferably 1.0% by volume or more and 8.0% by volume or less, and more preferably 1.0% by volume or more and 5.0% by volume or less. When the oxygen concentration is 1.0% by volume or more, the gloss of the image is not excessively increased, and an appropriate appearance can be obtained. When the oxygen concentration is 1.0% by volume or more, the device design for adjusting the oxygen concentration can be facilitated. When the oxygen concentration is 8.0% by volume or less, oxygen inhibition of the polymerization reaction of the actinic radiation polymerizable compound can be suppressed, and odor due to unreacted actinic radiation polymerizable compound can be further suppressed. When the oxygen concentration is 8.0% by volume or less, unevenness due to micropores on the image surface can be more unlikely to occur, and the gloss of the image can be further increased.

[0129] In the above oxygen concentration range, the method of irradiating the ink with actinic rays includes, for example, a method of irradiating the ink applied to the recording medium with actinic rays while flowing an inert gas such as nitrogen around the ink, or a method of placing an actinic ray irradiation device and a recording medium to which the ink has been applied in a space from which oxygen gas can be exhausted, and irradiating the ink with actinic rays while supplying the inert gas into the space, etc. The oxygen concentration can be measured by a fluorescent oxygen concentration meter.

[0130] 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.

[0131] When irradiating ultraviolet light from an LED light source, the cumulative light intensity is 400 mJ / cm 2 More preferably, 600 mJ / cm 2It is more preferable that the integrated light amount is in the above range. By setting the integrated light amount in the above range, the polymerization reaction of the active radiation polymerizable compound can be further promoted, and the odor caused by the unreacted active radiation polymerizable compound can be further suppressed. The upper limit of the integrated light amount is not particularly limited, but is, for example, 2000 mJ / cm. 2 It is.

[0132] 3. Image forming equipment An image forming apparatus 100 capable of carrying out the above-mentioned image forming method will now be described.

[0133] Fig. 1 is a schematic diagram showing the configuration of an image forming apparatus 100 according to the present embodiment. As shown in Fig. 1, the image forming apparatus 100 has an inkjet head 110, a transport unit 120, an oxygen concentration adjusting unit 130, and an irradiation unit 140. In Fig. 1, the arrow indicates the transport direction of a recording medium.

[0134] 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.

[0135] 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.

[0136] 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).

[0137] 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.

[0138] The oxygen concentration adjusting unit 130 adjusts the oxygen concentration of the atmosphere around the ink that has landed on the recording medium when the irradiation unit 140 irradiates the ink with active rays. In this embodiment, the oxygen concentration adjusting unit 130 has an exhaust pipe 131 connected to an external exhaust device or the like, a supply pipe 132 connected to a device that generates an inert gas, such as a nitrogen gas generator, for supplying the inert gas near the surface of the recording medium, and a partition wall 133 that surrounds the irradiation unit 140 and the transport unit 120.

[0139] By adjusting the amount of exhaust from exhaust pipe 131 and the amount of gas supplied from supply pipe 132, the oxygen concentration in the space partitioned by partition wall 133 and transfer section 120 can be set to 0.1 volume % or more and 15.0 volume % or less.

[0140] The irradiation unit 140 irradiates the upper surface of the transport unit 120 with active rays. This allows droplets of the active ray-curable inkjet ink that have landed on the transported recording medium 200 to be irradiated with active rays, thereby curing the droplets. The irradiation unit 140 can be disposed immediately above the transport unit 120, downstream of the inkjet head 110.

[0141] 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 140.

[0142] 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 140 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

[0143] The present invention will now be described with reference to examples, which should not be construed as limiting the scope of the present invention.

[0144] 1. Preparation / synthesis of materials The materials used in the preparation of the actinic radiation curable inkjet ink are shown below.

[0145] 1-1. Pigment dispersion 9 parts by mass of a pigment dispersant (EFKA 7701, manufactured by BASF) and 71 parts by mass of dipropylene glycol diacrylate were placed in a stainless steel beaker, and heated to 65°C using a hot plate while stirring for 1 hour. After leaving the mixture to cool to room temperature (25°C), 20 parts by mass of a cyan pigment (Pigment Blue 15:4, Chromofine Blue 6332JC, manufactured by Dainichi Seika Chemicals Co., Ltd.) were added, and the resulting mixture was placed in a glass bottle together with 200 g of zirconia beads having a diameter of 0.5 mm and sealed. After dispersing for 4 hours using a paint shaker, the zirconia beads were removed to obtain pigment dispersion C.

[0146] Pigment dispersion liquid M was obtained in the same manner as pigment dispersion liquid C, except that the pigment added was changed to a magenta pigment (Pigment Violet 19, CINQUASIA MAGENTA RT-355D, manufactured by BASF) and the dispersion time using a paint shaker was changed to 6 hours.

[0147] Pigment dispersion Y was obtained in the same manner as pigment dispersion C, except that the pigment to be added was changed to a yellow pigment (Pigment Yellow 185, D1155, manufactured by BASF) and the dispersion time using a paint shaker was changed to 6 hours.

[0148] Pigment dispersion liquid K was obtained in the same manner as pigment dispersion liquid C, except that the pigment added was changed to a black pigment (Pigment Black 7, manufactured by Mitsubishi Chemical Corporation).

[0149] 1-2.Active radiation polymerizable compound Dipropylene glycol diacrylate (DPGDA) (HSP value: 17.5 (MPa) 1 / 2 ) Glycerin triacrylate (GlA) (HSP value: 18.3 (MPa) 1 / 2 ) Polyethylene glycol #600 diacrylate (PEGDA) (HSP value: 19.5 (MPa) 1 / 2 ) 3PO modified trimethylolpropane triacrylate (TMPTA) (HSP value: 17.4MPa) 1 / 2 )

[0150] The HSP value was determined by inputting the chemical structural formula of the actinic radiation-polymerizable compound into computer software Hansen Solubility Parameters in Practice 5th Edition 5.0.13 (HSPiP, manufactured by Tegara Corporation).

[0151] 1-3. Polymerization initiator Initiator 1 (Omnirad 819, IGM Resins BV) Initiator 2 (SpeedCure 2-ITX, Arkema Co., Ltd.) Initiator 3 (Irgastab UV-10, manufactured by BASF)

[0152] 1-4.Surfactants ·KF352 (Shin-Etsu Chemical Co., Ltd.)

[0153] 1-5.Crystalline polyester resin (Synthesis of crystalline polyester resin 1) The following raw material monomers were placed in a four-neck flask equipped with a nitrogen inlet tube, a dehydration tube, a stirrer and a thermocouple, and then heated to 170°C for dissolution to obtain crystalline polyester resin 1. The obtained crystalline polyester resin 1 had a weight average molecular weight (Mw) of 22,000, a melting point (Tm) of 76.8°C and a recrystallization temperature (Rc) of 70.0°C. Dodecanedicarboxylic acid 103.0 parts by mass Ethylene glycol 24.7 parts by weight

[0154] In the present examples, each weight average molecular weight (Mw) is a value determined using a GPC apparatus having an "HLC-8120" (manufactured by Tosoh Corporation) and a "TSKguard column + TSKgel Super HZM-M triple column" (manufactured by Tosoh Corporation) as a column, and a calibration curve determined from a standard polystyrene sample.

[0155] In the present examples, each melting point (Tm) was measured using a differential scanning calorimeter "Diamond DSC" (manufactured by PerkinElmer) under heating and cooling conditions of a temperature increase / decrease rate of 10°C / min, a temperature increase range of 25°C to 150°C, and a temperature decrease range of 150°C to 0°C.

[0156] In the present examples, the recrystallization temperature (Rc) and each melting point (Tm) were measured using a differential scanning calorimeter "Diamond DSC" (manufactured by PerkinElmer) under heating and cooling conditions of a temperature increase / decrease rate of 10°C / min, a temperature increase range from 25°C to 100°C, and a temperature decrease range from 100°C to 0°C.

[0157] (Synthesis of crystalline polyester resin 2) The following raw material compounds for the styrene-acrylic segment, including a bireactive compound, and a radical polymerization initiator were placed in a dropping funnel. Styrene 1.7 parts by mass 2-Ethylhexyl acrylate 0.5 parts by mass Acrylic acid 6.3 parts by mass Polymerization initiator (di-t-butyl peroxide) 7.0 parts by mass

[0158] Next, the raw material monomers for the crystalline polyester segment described below were placed in a four-neck flask equipped with a nitrogen inlet tube, a dehydration tube, a stirrer and a thermocouple, and were heated to 170° C. to dissolve. Succinic acid 50.0 parts by mass 1,12-dodecanediol 112.0 parts by mass

[0159] Then, under stirring, the raw material compound of the styrene-acrylic segment was dropped into the solution in which the raw material monomer of the crystalline polyester segment was dissolved over a period of 90 minutes, and the mixture was stirred for 60 minutes. Furthermore, the unreacted addition polymerization compound was removed under reduced pressure (8 kPa). Note that the amount of the compound removed at this time was very small compared to the ratio of the raw material compound of the resin. Then, 0.8 parts by mass of Ti(OBu) 4 The mixture was heated to 235°C, and reacted for 5 hours under normal pressure (101.3kPa) and for 1 hour under reduced pressure (8kPa). The mixture was then cooled to 200°C and reacted for 1 hour under reduced pressure (20kPa) to obtain crystalline polyester resin 2. The obtained crystalline polyester resin 2 had a weight average molecular weight (Mw) of 18000, a melting point (Tm) of 74.6°C, a recrystallization temperature (Rc) of 68.1°C, and a styrene-acrylic modification rate of 5.0%.

[0160] (Synthesis of crystalline polyester resin 3) Crystalline polyester resin 3 was obtained in the same manner as for crystalline polyester resin 2, except that the blending ratio of the raw material compounds for the styrene-acrylic segment and the radical polymerization initiator was changed as follows. Styrene 22.5 parts by weight 2-Ethylhexyl acrylate 7.0 parts by mass Acrylic acid 70.0 parts by mass Polymerization initiator (di-t-butyl peroxide) 7.0 parts by mass

[0161] The resulting crystalline polyester resin 3 had a weight average molecular weight (Mw) of 15,000, a melting point (Tm) of 71.0° C., a recrystallization temperature (Rc) of 65.8° C., and a styrene-acrylic modification rate of 38.0%.

[0162] (Synthesis of crystalline polyester resin 4) Crystalline polyester resin 4 was obtained in the same manner as for crystalline polyester resin 2, except that the blending ratio of the raw material compounds for the styrene-acrylic segment and the radical polymerization initiator was changed as follows. Styrene 23.0 parts by mass 2-Ethylhexyl acrylate 10.5 parts by mass Acrylic acid 84.0 parts by mass Polymerization initiator (di-t-butyl peroxide) 7.0 parts by mass

[0163] The resulting crystalline polyester resin 4 had a weight average molecular weight (Mw) of 13,000, a melting point (Tm) of 68.5° C., a recrystallization temperature (Rc) of 63.3° C., and a styrene-acrylic modification rate of 42.0%.

[0164] 1-6. Gelling agents Gelling agent 1 (WE11, behenyl stearate, NOF Corporation) Gelling agent 2 (Lunac BA, behenic acid, manufactured by Kao Corporation)

[0165] 2. Preparation of actinic radiation curable inkjet ink For each of the prepared materials, the component amounts shown in Table 1 were placed in a stainless steel beaker and stirred at 105° C. for 45 minutes. The mixture was then filtered through a 3 μm Teflon (registered trademark) membrane filter manufactured by ADVANTEC Corp. to obtain cyan inks of actinic ray curable inkjet inks 1 to 12. In addition, for the actinic ray curable inkjet inks 1 to 12, the type of pigment dispersion was changed to pigment dispersion M, pigment dispersion Y, and pigment dispersion K, respectively, to prepare magenta inks, yellow inks, and black inks of inks 1 to 12.

[0166] 2. Image Formation The cyan ink, magenta ink, yellow ink, and black ink of any of the actinic radiation curable inkjet inks 1 to 12 were loaded into an inkjet head, and a monochromatic image was formed using a line-type inkjet recording device. The temperature of the inkjet head of the inkjet recording device was set to 80°C. Recording medium A (aluminum vapor deposition paper, Albright, US basis weight 105 g / m 2 , manufactured by Kayo Paper Co., Ltd.) or recording medium B (lightly coated paper, Aurora Coat, basis weight 127.9 g / m 2 An image was printed on a 300-millimeter-sized inkjet printer (manufactured by Nippon Paper Industries Co., Ltd.). After the image was formed, the image was irradiated with ultraviolet light while adjusting the oxygen concentration to harden the ink. A piezo head with a nozzle diameter of 20 μm and 512 nozzles (256 nozzles x 2 rows, staggered arrangement, nozzle pitch per row of 360 dpi) was used as the ejection recording head. The ejection conditions were that the amount of liquid per drop was 9.0 pl, the liquid was ejected at a liquid velocity of about 6 m / s, and recording was performed under conditions that the resolution in the nozzle arrangement direction was 1200 di. The recording speed was 500 mm / s. The image was formed in an environment of 23°C and 55% RH. dpi refers to the number of dots per inch (2.54 cm).

[0167] The oxygen concentration was adjusted and ultraviolet light was irradiated using an LED light source unit (peak wavelength 385 nm, peak illuminance 8 W / cm 2 The inert gas source was a N 2 A gas generator (N2 INMACT, manufactured by Kofloc Corporation) was connected to the blanket, and the pressure was 0.5 MPa·s and the flow rate was 8.8 m 3 Nitrogen gas was flowed into the blanket at 1000 x 1000 / h. The image was irradiated with ultraviolet light while adjusting the oxygen concentration. The oxygen concentration was measured using a fluorescent oxygen concentration meter (Microx TX3, manufactured by PreSens).

[0168] 3. Evaluation (Gloss uniformity) Using the cyan, magenta, yellow and black inks of actinic radiation curable inkjet inks 1 to 12, a natural image (high definition color digital standard image data "Cafeteria" issued by the Japan Standards Association) was printed on recording medium A. The printed image was visually observed and evaluated for gloss uniformity based on the following criteria. A: The image is highly glossy and homogeneous with no noticeable color difference or difference in gloss between the printed and non-printed areas. B: The gloss is somewhat low, but the image is homogeneous with no color difference. C: The gloss is somewhat low, there is a color difference, and the gloss feels unnatural. D: The gloss is low, there is a color difference, and the gloss feels unnatural. E: The gloss is extremely low, there is a color difference, and the gloss feels strange.

[0169] (High definition (pinning)) Using cyan ink, magenta ink, yellow ink, and black ink, the characters "book" were printed in 3-point, 5-point, and 7-point MS Mincho font on recording medium B. The characters obtained were visually observed and evaluated according to the following criteria. A: Even 3-point characters can be reproduced without losing detail. B: The details are lost in 3-point letters, but are reproduced without loss in 5-point letters. C: Details are lost in 5-point text, but are reproduced without loss in 7-point text. D: Even with 7-point text, details are lost.

[0170] (Odor) 10g / m on recording medium B 2 Ten 16cm x 4cm 3C images in cyan, magenta, and yellow were created with the amount of ink applied. The prints were stored in a glass bottle, and after one day, a panel of 20 subjects was asked to smell the odor remaining inside the bottle for a sensory evaluation. A: 0 people noticed an unpleasant odor B: 1 to 5 people noticed an unpleasant odor C: 6 to 10 people felt an unpleasant odor D: 11 or more people felt an unpleasant odor

[0171] Table 2 shows the results of evaluations of images formed by varying the actinic ray curable ink and the oxygen concentration during ultraviolet irradiation.

[0172] [Table 1]

[0173] [Table 2]

[0174] From the results of Experiments 1 to 19, it was found that by using an actinic ray-curable inkjet ink containing a crystalline polyester resin and forming an image by irradiating the ink with actinic rays in an atmosphere with an oxygen concentration of 0.1% by volume or more and 15.0% by volume or less, it is possible to improve the pinning ability, suppress odor, and increase the gloss of the image.

[0175] Moreover, from Experiment 9, it was found that the lower the content of the gelling agent, the higher the glossiness of the image. [Industrial Applicability]

[0176] The image forming method according to the present invention can enhance the glossiness of an image while improving pinning properties and suppressing odor, and therefore the present invention is useful in the field of image forming. [Explanation of symbols]

[0177] 100 Image forming device 110 Inkjet head 120 Conveyor 130 Oxygen concentration adjustment unit 140 Irradiation unit

Claims

1. applying an ink-jet ink, which contains a polymerizable compound that is polymerized by actinic radiation and a crystalline polyester resin and is cured by actinic radiation, to a surface of a recording medium by an ink-jet method; and irradiating the applied ink-jet ink with actinic rays in an atmosphere having an oxygen concentration of 0.1 vol.% or more and 15.0 vol.% or less to cure the ink-jet ink. Image forming method.

2. 2. The image forming method according to claim 1, wherein the crystalline polyester resin is a styrene-acrylic modified polyester resin.

3. the curing step is a step of curing the ink-jet ink by irradiating the ink with active rays in an atmosphere having an oxygen concentration of 1.0 vol % or more and 8.0 vol % or less; The image forming method according to claim 1 or 2.

4. The image forming method according to claim 1 , wherein the ink-jet ink further comprises a pigment.

5. The image forming method according to claim 1 , wherein the content of the gelling agent is less than 1.0% by mass based on the total mass of the ink-jet ink.

6. The image forming method according to claim 1 , wherein the polymerizable compound includes a hydrophilic polymerizable compound, the content of which is from 5.0% by mass to 50.0% by mass relative to the total mass of the polymerizable compound.

7. The image forming method according to claim 6 , wherein the polymerizable compound includes a hydrophilic polymerizable compound, the content of which is from 20% by mass to 50% by mass with respect to the total mass of the polymerizable compound.

Images