Radiation-curable inkjet ink and image formation method

Abstract

To provide a radiation-curable inkjet ink and an image formation method using the same, which are able to form images that hardly cause surface stickiness and cracking at folds and can sufficiently enhance pinning properties.SOLUTION: A radiation-curable inkjet ink comprises a radiation-polymerizable compound and a crystalline polyester resin. The radiation-polymerizable compound includes a multifunctional radiation-polymerizable compound, with a content from 60 mass% to 90 mass% inclusive based on the total mass of the radiation-polymerizable compound. The absolute value of the difference between the HSP value of the radiation-polymerizable compound and the HSP value of the crystalline polyester resin (ΔHSP value) is from 6 to 10 inclusive.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an actinic radiation curable ink-jet ink and 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 are actinic radiation-curable inkjet inks that contain an actinic radiation-polymerizable compound as a liquid component. When actinic radiation-curable inkjet inks are irradiated with actinic radiation, the actinic radiation-polymerizable compound is polymerized and the ink is cured, causing the coloring material to adhere firmly to the recording medium. The formation of this cured film allows the formation of a desired image.

[0003] As one type of actinic radiation curable inkjet ink, an ink containing a crystalline polyester resin is known.

[0004] For example, Patent Document 1 discloses an active energy ray curable ink composition containing a crystalline polyester composed of at least two or more polyvalent carboxylic acids and one or more polyhydric alcohols, and a polymerizable compound. Patent Document 1 states that the polyvalent carboxylic acid contains a trivalent or higher carboxylic acid in a ratio of 0.5 to 10 mol % relative to the total molar number of the polyvalent carboxylic acids, thereby improving the curability, stretchability, and adhesion to a recording medium of the ink. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2016-117807 A Summary of the Invention [Problem to be solved by the invention]

[0006] As disclosed in Patent Document 1, an actinic ray curable ink containing a crystalline polyester resin is known.

[0007] However, when an image is formed using the actinic ray curable ink described in Patent Document 1, the surface of the image becomes sticky.

[0008] Furthermore, actinic radiation curable inks are required to form images that are less susceptible to cracks when the recording medium is folded.

[0009] Furthermore, when an image is formed by an inkjet method using an actinic ray curable ink, it is desirable for the actinic ray curable ink to have high pinning properties. With high pinning properties, the ink is prevented from wetting and spreading, making it difficult for adjacent dots to become identical, and therefore it is possible to form an image with higher resolution. Therefore, there is a demand for an actinic ray curable inkjet ink with sufficiently improved pinning properties.

[0010] The present invention has been made in consideration of the above circumstances, and has an object to provide an actinic ray-curable ink-jet ink that can form an image that is less prone to surface stickiness and fold cracks and can sufficiently improve pinning properties, 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 actinic ray-curable ink-jet ink as set forth in the following items [1] to [3]. [1] An actinic ray-curable ink-jet ink comprising: an actinic ray-polymerizable compound; and a crystalline polyester resin, wherein the actinic ray-polymerizable compound comprises a polyfunctional actinic ray-polymerizable compound whose content relative to the total mass of the actinic ray-polymerizable compound is 60 mass% or more and 90 mass% or less, and wherein an absolute value of a difference (ΔHSP value) between an HSP value of the actinic ray-polymerizable compound and an HSP value of the crystalline polyester resin is 6 or more and 10 or less. [2] The actinic ray curable inkjet ink according to [1], wherein the difference (ΔHSP value) between the HSP value of the actinic ray polymerizable compound and the HSP value of the crystalline polyester resin is 6 or more and 8 or less. [3] The actinic ray curable inkjet ink according to [1] or [2], wherein the content of the polyfunctional actinic ray polymerizable compound is 70 mass % or more and 90 mass % or less based on the total mass of the actinic ray polymerizable compound.

[0012] In order to solve the above problems, one aspect of the present invention relates to an image forming method according to the following item [4]. [4] An image forming method comprising the steps of: applying the actinic ray-curable inkjet ink according to any one of [1] to [3] to a surface of a recording medium by an inkjet method; and irradiating the applied actinic ray-curable inkjet ink with actinic rays to cure it. Effect of the Invention

[0013] According to the present invention, it is possible to provide an actinic ray-curable ink-jet ink that can form an image that is less prone to surface stickiness and fold cracks and can sufficiently improve pinning properties, 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. Actinic radiation curable inkjet ink The actinic ray curable inkjet ink in this embodiment contains an actinic ray polymerizable compound and a crystalline polyester resin.

[0017] As described above, the image formed using the actinic radiation curable ink described in Patent Document 1 had a sticky surface. Since the polymerizable compound in the ink described in Patent Document 1 is composed of a monofunctional polymerizable compound, it is considered that the degree of crosslinking of the cured film formed by curing the ink is low. Therefore, it is considered that the crystalline polyester resin contained in the ink seeps out onto the surface of the cured film, causing the image surface to become sticky.

[0018] In contrast, the actinic ray curable inkjet ink of the present embodiment contains an actinic ray polymerizable compound in an amount of 60% by mass or more of a polyfunctional actinic ray polymerizable compound relative to the total mass of the actinic ray polymerizable compound, and therefore the degree of crosslinking of the cured film can be increased and the bleeding of the crystalline polyester resin in the ink can be suppressed, thereby making it possible to make the image surface less sticky.

[0019] In addition, by setting the content of the polyfunctional actinic radiation polymerizable compound to 90% by mass or less based on the total mass of the actinic radiation polymerizable compound, the degree of crosslinking of the cured film can be prevented from becoming too high, and the hardness of the cured film can be appropriately reduced, so that even if the recording medium is folded, the image is less likely to crack.

[0020] Furthermore, the present inventors have found that the pinning property of the actinic ray-curable inkjet ink can be sufficiently improved by adjusting the absolute value of the difference (ΔHSP value) between the HSP value of the actinic ray-polymerizable compound and the HSP value of the crystalline polyester resin to be 6 or more and 10 or less.

[0021] When the absolute value of the difference in HSP values ​​(ΔHSP value) is 10 or less, the crystalline polyester resin becomes more compatible with the actinic ray polymerizable compound when the heated ink is ejected from the inkjet head. When the ink lands on a recording medium in a state in which the crystalline polyester resin is compatible with the actinic ray polymerizable compound, the temperature of the ink drops and the crystalline polyester resin crystallizes and precipitates. At this time, when the absolute value of the difference in HSP values ​​(ΔHSP value) is 6 or more, the solubility of the crystalline polyester resin in the actinic ray polymerizable compound can be appropriately reduced, making it easier to precipitate crystals of the crystalline polyester resin when the ink lands.

[0022] It is believed that when crystals of the crystalline polyester resin are precipitated, the non-crystalline portions of the molecular chains of the crystalline polyester resin become entangled with each other to form a three-dimensional structure, which is believed to sufficiently enhance the pinning ability of the actinic ray-curable inkjet ink.

[0023] Furthermore, when the absolute value of the difference in HSP values ​​(ΔHSP value) is 6 or more, crystals of the crystalline polyester resin are easily precipitated, so that stickiness on the image surface due to bleeding of the crystalline polyester resin that does not crystallize can be suppressed.

[0024] In addition, the image may become sticky when the crystallized crystalline polyester resin precipitates excessively on the image surface. Here, when the ΔHSP value is 10 or less, the crystalline polyester resin becomes more compatible with the actinic radiation polymerizable compound, and the crystalline polyester resin is more likely to crystallize on the inner side of the image after the ink is deposited. Therefore, the stickiness of the image caused by the crystals of the crystalline polyester resin precipitate excessively on the image surface can also be suppressed.

[0025] 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.

[0026] 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.

[0027] 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.

[0028] 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.

[0029] 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.

[0030] 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.

[0031] 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, and hydroxypivalic acid neopentyl glycol di(meth)acrylate. , difunctional (meth)acrylates including polytetramethylene glycol di(meth)acrylate, polyethylene glycol diacrylate, and tripropylene glycol diacrylate, as well as trifunctional or higher (meth)acrylates including 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.

[0032] The radical polymerizable compound preferably contains a (meth)acrylate modified with ethylene oxide (EO) or propylene oxide (PO) (hereinafter, simply referred to as "modified (meth)acrylate"). The modified (meth)acrylate has higher photosensitivity. In addition, the modified (meth)acrylate is more compatible with other components even at high temperatures.

[0033] Examples of the modified (meth)acrylate include EO modified bisphenol A diacrylate, EO modified trimethylolpropane tri(meth)acrylate, and PO modified bisphenol A diacrylate.

[0034] Examples of the cationically polymerizable compound include an epoxy compound, a vinyl ether compound, and an oxetane compound.

[0035] 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.

[0036] 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.

[0037] 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.

[0038] The HSP value of an actinic ray-polymerizable compound can be determined by inputting the chemical structural formula of the actinic ray-polymerizable compound into computer software Hansen Solubility Parameters in Practice 5th Edition 5.0.13 (HSPiP, manufactured by Tegara Corporation).

[0039] In this embodiment, the content of the polyfunctional actinic ray polymerizable compound contained in the actinic ray polymerizable compound is 60% by mass or more and 90% by mass or less, preferably 70% by mass or more and 90% by mass or less, and more preferably 80% by mass or more and 90% by mass or less, based on the total mass of the actinic ray polymerizable compound. When the content is 70% by mass or more, the crosslinking degree of the cured film can be increased, and the bleeding of the crystalline polyester resin can be further suppressed. This can further suppress the stickiness of the image surface.

[0040] The number of functional groups of the polyfunctional actinic radiation polymerizable compound is preferably from 2 to 5, more preferably from 2 to 4, and even more preferably from 2 to 3. When the number of functional groups is 5 or less, the degree of crosslinking of the cured film does not become too high, and image cracks are more unlikely to occur when folded.

[0041] 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 90% by mass, and even more preferably from 70% by mass to 90% by mass, relative to the total mass of the actinic ray-curable inkjet ink.

[0042] 1-2.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.

[0043] The melting point (Tm) of the crystalline polyester resin is preferably 50° C. or higher, more preferably 60° C. or higher, even more preferably 68° C. or higher, and particularly preferably 75° C. or higher. If it is 50° C. or higher, the crystalline polyester resin is more likely to crystallize when the ink lands on a recording medium, and the pinning property of the ink can be more sufficiently improved, and if it is 68° C. or higher, the pinning property can be further improved. The melting point (Tm) may be equal to or lower than the ink heating temperature at the time of ink ejection, and is preferably, for example, 80° C. or lower. This allows the crystalline polyester resin to be sufficiently dissolved in the ink at the time of ink ejection, thereby suppressing a decrease in the ejection stability of the ink.

[0044] 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.

[0045] 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.

[0046] 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).

[0047] 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.

[0048] 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.

[0049] 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.

[0050] The polyvalent carboxylic acid compound is preferably a divalent aliphatic carboxylic acid, and more preferably dodecanedicarboxylic acid or tetradecanedicarboxylic acid.

[0051] The weight average molecular weight (Mw) of the crystalline polyester resin can usually be 5,000 or more and 50,000 or less, but is preferably 7,000 or more and 30,000 or less, and more preferably 10,000 or more and 25,000 or less. When the molecular weight is 7,000 or more, the viscosity of the actinic ray-curable inkjet ink can be further increased, and the pinning property of the actinic ray-curable inkjet ink can be further improved. In addition, when the molecular weight is 30,000 or less, the viscosity of the actinic ray-curable inkjet ink does not increase too much, and a decrease in ejection stability can be suppressed.

[0052] 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.

[0053] The HSP value of the crystalline polyester resin can be determined using computer software Hansen Solubility Parameters in Practice 5th Edition 5.0.13 (HSPiP, manufactured by Tegara Corporation). Specifically, the HSP value can be calculated by inputting the types of polyhydric alcohol components and polyvalent carboxylic acid components constituting the crystalline polyester resin and the number of repeating units contained in the crystalline polyester resin into the software. The number of repeating units can be estimated from the molecular weight of the crystalline polyester resin.

[0054] The content of the crystalline polyester resin is preferably 1.0% by mass or more and 10.0% by mass or less, more preferably 1.0% by mass or more and 7.5% by mass or less, and even more preferably 1.0% by mass or more and 5.0% by mass or less, based on the total mass of the actinic ray curable inkjet ink. By having the content be 1.0% by mass or more, the pinning property of the actinic ray curable inkjet ink can be further improved. In addition, by having the content be 10.0% by mass or less, the viscosity of the actinic ray curable inkjet ink can be prevented from becoming too high, and a decrease in ejection stability can be prevented.

[0055] The absolute value of the difference (ΔHSP value) between the HSP value of the actinic radiation-polymerizable compound and the HSP value of the crystalline polyester resin is 6 or more and 10 or less, preferably 6 or more and 8 or less, and more preferably 6 or more and 7.8 or less. When the difference in HSP value is 8 or less, the compatibility between the actinic radiation-polymerizable compound and the crystalline polyester can be further improved. When the compatibility is further improved, the amount of the crystalline polyester resin that precipitates as crystals when the ink lands is likely to increase. Therefore, the pinning ability of the actinic radiation-curable inkjet ink can be further improved.

[0056] The difference in HSP values ​​refers to the difference between the weighted average (mass basis) of the HSP values ​​of each actinic ray-polymerizable compound contained in the actinic ray-curable inkjet ink and the weighted average (mass basis) of the HSP values ​​of each crystalline polyester resin contained in the actinic ray-curable inkjet ink.

[0057] 1-3.Other ingredients 1-3-1. Coloring agents The actinic ray curable ink-jet ink of the present invention may contain a colorant, if necessary.

[0058] 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.

[0059] 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.

[0060] 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.

[0061] 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.

[0062] Examples of green pigments include CI Pigment Green (hereinafter also simply referred to as "PG") 7, PG26, PG36, and PG50.

[0063] An example of a black pigment is CI Pigment Black (hereinafter, simply referred to as "PBk"). )7, PBk26, and PBk28.

[0064] 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.

[0065] 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.

[0066] 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.

[0067] 1-3-2. Pigment dispersants 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.

[0068] 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.

[0069] 1-3-3. Actinic 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, 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.

[0070] The radical polymerization initiator includes an intramolecular bond cleavage type radical polymerization initiator and an intramolecular hydrogen abstraction type radical polymerization initiator.

[0071] 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.

[0072] 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.

[0073] Examples of cationic polymerization initiators include photoacid generators. Examples of photoacid generators include aromatic onium compounds such as diazonium, ammonium, iodonium, sulfonium, and phosphonium, such as B(C6F5)4. - , PF6 - , AsF6 - , SbF6 - , CF3SO3 - These include salts, sulfonates which generate sulfonic acids, halides which photogenerate hydrogen halides, and iron-allene complexes.

[0074] 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.

[0075] 1-3-4. Polymerization inhibitors In this embodiment, the actinic ray curable inkjet ink may contain a polymerization inhibitor.

[0076] 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.

[0077] 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.

[0078] 1-3-5.Surfactants In this embodiment, the actinic ray curable inkjet ink may contain a surfactant for adjusting the surface tension.

[0079] 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.

[0080] 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.

[0081] In this embodiment, in addition to the above-mentioned components, the actinic ray curable inkjet ink may contain, as necessary, a gelling agent, a fixing resin, a viscosity adjuster, a resistivity adjuster, a film-forming agent, an ultraviolet absorbing agent, an antioxidant, a color-fading inhibitor, an anti-fungal agent, an anti-rust agent, and the like.

[0082] 1-4. 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.

[0083] 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.

[0084] 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.

[0085] 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 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.

[0086] 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.

[0087] 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 applying droplets of the actinic ray curable inkjet ink to the surface of a recording medium by an inkjet method, and a step (step S20) of irradiating the applied droplets of the actinic ray curable inkjet ink with actinic rays to cure them.

[0088] 2-1. Step of applying actinic radiation curable inkjet ink to a recording medium (step S10) In this step, the actinic ray curable inkjet ink described above is applied to the surface of the recording medium (at a position corresponding to the image to be formed) by an inkjet method.

[0089] 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.

[0090] The droplets of the actinic radiation curable ink are heated to melt the crystalline polyester resin and then 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 + 3.0°C or more. On the other hand, from the viewpoint of suppressing volatilization of the actinic radiation polymerizable compound when the ink is ejected, it is preferable that the temperature of the ink when ejected from the inkjet head is set to 90°C or less, and more preferably 80°C or less.

[0091] 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.

[0092] 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.

[0093] 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.

[0094] 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.

[0095] 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.

[0096] 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.

[0097] 3. Image forming equipment An image forming apparatus 100 capable of carrying out the above-mentioned image forming method will now be described.

[0098] Fig. 2 is a schematic diagram showing the configuration of an image forming apparatus 100 according to this embodiment. As shown in Fig. 1, the image forming apparatus 100 has an inkjet head 110, a transport section 120, and an irradiation section 130. In Fig. 1, the arrow indicates the transport direction of a recording medium.

[0099] 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.

[0100] 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.

[0101] 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).

[0102] 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.

[0103] 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.

[0104] 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.

[0105] 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

[0106] The present invention will now be described with reference to examples, which should not be construed as limiting the scope of the present invention.

[0107] 1. Preparation / synthesis of materials The materials used in the preparation of the actinic radiation curable inkjet ink are shown below.

[0108] 1-1. Pigment dispersion 21 parts by mass of a pigment (Pigment Red 122, Chromofine Red 6112JC, manufactured by Dainichiseika Color & Chemicals Mfg. Co., Ltd.), 9 parts by mass of a dispersant (Ajisper PB824, manufactured by Ajinomoto Fine-Techno Co., Ltd. ("Ajisper" is a registered trademark)), 70 parts by mass of an actinic radiation-polymerizable compound (the type was changed appropriately so as to obtain the compositions of Inks 1 to 8 described below), 0.02 parts by mass of a polymerization inhibitor, and zirconia beads "YTZ balls" (0.3 mm, manufactured by Nikkato Corporation) were placed in a 100 mL plastic container and dispersed for 3 hours using a paint shaker, after which the zirconia beads were removed to obtain a pigment dispersion.

[0109] 1-2. Active radiation polymerizable compounds (Monofunctional actinic radiation polymerizable compound) Active radiation polymerizable compound (m-1): 2-Hydroxy-3-phenoxypropyl acrylate (HSP value: 21.5 (MPa) 1 / 2 ) Actinic radiation polymerizable compound (m-2): Stearyl acrylate (HSP value: 16.3 (MPa) 1 / 2 )

[0110] (Polyfunctional actinic radiation polymerizable compound) Active radiation polymerizable compound (M-1): EO modified bisphenol A diacrylate (2 functional, HSP value: 20.0 (MPa) 1 / 2 ) Active radiation polymerizable compound (M-2): EO modified trimethylolpropane triacrylate (TMP(9EO)TA) (3 functional, HSP value: 19.0 (MPa) 1 / 2 )

[0111] The HSP value of each actinic radiation-polymerizable compound 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).

[0112] 1-3. Actinic polymerization initiator Doublecure 1819 (Double Bond Chemical)

[0113] 1-4.Additives Polymerization inhibitor (Irgastab UV10, manufactured by BASF) 0.8 parts by mass Surfactant (TSF-4452, Momentive Performance Materials) 0.2 parts by mass

[0114] 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 to dissolve, thereby obtaining 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, a recrystallization temperature (Rc) of 70.0°C, and an HSP value of 26.2 (MPa). 1 / 2 It was. Dodecanedicarboxylic acid 103.0 parts by mass Ethylene glycol 24.7 parts by weight

[0115] 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.

[0116] 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.

[0117] 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.

[0118] In addition, the HSP value of the crystalline polyester resin in this embodiment is a value measured using the same software as the HSP value of the actinic radiation polymerizable compound.Specifically, the type of polyhydric alcohol component and polyvalent carboxylic acid component that constitute the crystalline polyester resin, and the repeat number of the repeat unit that is contained in the crystalline polyester resin are inputted into the above software, and the above HSP value is calculated.

[0119] (Synthesis of crystalline polyester resin 2) 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 to dissolve, thereby obtaining crystalline polyester resin 2. The obtained crystalline polyester resin 2 had a weight average molecular weight (Mw) of 18,000, a melting point (Tm) of 74.6°C, a recrystallization temperature (Rc) of 68.1°C, and an HSP value of 28.3 (MPa). 1 / 2 It was. Tetradecanedicarboxylic acid 107.0 parts by mass Ethylene glycol 27.5 parts by weight

[0120] (Synthesis of crystalline polyester resin 3) 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 to dissolve, thereby obtaining crystalline polyester resin 3. The obtained 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 an HSP value of 23.6 (MPa). 1 / 2 It was. 1,6-Hexanediol 698.0 parts by mass Sebacic acid 1409.0 parts by mass Trimellitic anhydride 2.0 parts by mass

[0121] (Synthesis of crystalline polyester resin 4) 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 to dissolve, thereby obtaining crystalline polyester resin 4. The obtained 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 an HSP value of 29.1 (MPa). 1 / 2 It was. Trimellitic anhydride 100.0 parts by mass 1,4-butanediol 100.0 parts by mass Fumaric acid 100.0 parts by mass

[0122] (Synthesis of crystalline polyester resin 5) 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 to dissolve, thereby obtaining crystalline polyester resin 4. The obtained crystalline polyester resin 5 had a weight average molecular weight (Mw) of 12,500, a melting point (Tm) of 69.3°C, a recrystallization temperature (Rc) of 64.4°C, and an HSP value of 26.6 (MPa). 1 / 2 It was. 1,6-Hexanediol 425.0 parts by mass Trimellitic anhydride 58.0 parts by mass 1,5-Pentanediol 375.0 parts by mass Terephthalic acid 946.0 parts by mass

[0123] 2. Preparation of actinic radiation curable inkjet ink The pigment dispersion, actinic radiation polymerizable compound (m-1), actinic radiation polymerizable compound (M-1), polymerization initiator, and additives were added in amounts adjusted to obtain the composition shown in Table 1, and placed in a stainless steel beaker, which was stirred at 105° C. for 45 minutes. The mixture was then filtered through a 3 μm Teflon (registered trademark) membrane filter manufactured by ADVANTEC Corporation to obtain actinic radiation curable inkjet ink 1. Actinic radiation curable inkjet inks 2 to 10 were obtained in the same manner, except that the types and amounts of each component were adjusted so that the ink compositions obtained were those shown in Tables 1 and 2.

[0124] 2. Image Formation A monochromatic image was formed using any one of the actinic radiation curable inkjet inks 1 to 10 using a line-type inkjet recording device. The temperature of the inkjet head of the inkjet recording device was set to 80° C. The recording medium (coated paper, OK top coat, rice basis weight 12 g / m 2 A solid image of 5 cm x 5 cm was printed on a 1000-millimeter-long inkjet printer (Oji Paper Co., Ltd.). After the image was formed, the image was irradiated with ultraviolet light from an LED lamp (Phoseon Technology Co., Ltd., 395 nm, water-cooled LED) placed downstream of the recording device 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 of 360 dpi per row) was used as the ejection recording head. The ejection conditions were that the amount of liquid per drop was 2.5 pl, and the liquid was ejected at a droplet speed of about 6 m / s, and the image was recorded at a resolution of 1440 dpi x 1440 dpi. 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).

[0125] 3. Evaluation (Solubility of crystalline polyester resin) A clear ink was prepared that had the same components as actinic ray curable inks 1 to 10, except that no pigment was added. This clear ink was placed in a heat-resistant tube and stored in a high-temperature environment for 1 hour. The environmental temperature during storage was 50 to 90°C. After storage, the state of the ink in the heat-resistant tube was visually observed, and the solubility of the crystalline polyester resin was evaluated according to the following criteria. ◎: No insoluble matter was found in the ink, and no oil droplets or phase separation was found. ◯: A small amount of insoluble matter was observed in the ink, but no oil droplets were generated or phase separation was observed. △: Insoluble matter was found in the ink, but no oil droplets were formed or phase separation was observed, and there was no problem with the quality. ×: Insoluble matter was found in the ink, and the formation of oil droplets and phase separation were confirmed.

[0126] (Pinning property) Using the line-type inkjet recording device and each of the inks 1 to 10, dots were printed on the recording medium. When the 400 dots formed were observed using an optical microscope, it was confirmed that the active radiation polymerizable compound was seeping out from the periphery of the dot. Here, the longest distance from the center of the dot to the periphery of the part where the active radiation polymerizable compound was seeping out was defined as the "outer diameter" of the dot, and the distance from the center of the dot to the periphery of the dot body (the part where the active radiation polymerizable compound starts to seep out) was defined as the "inner diameter" of the dot. Then, the percentage of dots whose difference between the outer diameter and the inner diameter was 10% or more of the inner diameter was calculated, and the pinning property was evaluated according to the following evaluation criteria. ◎: The above number percentage was 0-5% ◯: The above number percentage was 6-10% △: The above number percentage was 11-20%. ×: The number percentage was 21% or more, and it was confirmed that adjacent droplets were united.

[0127] (Sticky image) The formed monochrome image was touched with a finger and the stickiness of the image was evaluated according to the following criteria. 〇: The image was not sticky. △: The image was slightly sticky, but not at a level that caused any quality problems. ×: The image was sticky.

[0128] (Folding suitability) The image surface formed above was cut out and folded 180° so that the image surface was on the outside, and then a 500g aluminum block was placed on top and left to stand for 30 seconds. After that, the folded part was opened, and the state of the fold was observed with the optical microscope (50x) and evaluated according to the following criteria. ○: No cracks were found in the image at the fold ×: Cracks in the image were observed at the fold.

[0129] The evaluation results for actinic ray-curable inkjet inks 1 to 10 are summarized in Tables 1 and 2. In Tables 1 and 2, the absolute value of the difference in HSP value between the actinic ray-polymerizable compound and the crystalline polyester resin (ΔHSP value) represents the difference between the weighted average value of the HSP value of the actinic ray-polymerizable compound contained in the ink and the HSP value of the crystalline polyester resin. The numerical value of each component in Tables 1 and 2 represents mass %.

[0130] [Table 1]

[0131] [Table 2]

[0132] In the actinic ray curable inkjet inks 1 to 4, the difference between the SP value of the actinic ray polymerizable compound and the SP value of the crystalline polyester resin was 6 or more and 10 or less, and therefore the pinning property was good.

[0133] It was also found that bleeding out was suppressed when the difference in SP value was 6 or more and 10 or less, and the content of the polyfunctional actinic ray polymerizable compound relative to the total mass of the actinic ray polymerizable compounds was 60 mass% or more. This is believed to be because the crosslink density of the cured film increased due to the increase in the content of the polyfunctional polymerizable compound, making it difficult for the crystalline polyester resin to bleed out of the cured film.

[0134] In addition, from the results of actinic radiation curable inkjet ink 8, it was found that the folding cracks of the image were suppressed by setting the ratio of the multifunctional actinic radiation polymerizable compound to 90 mass % or less. This is considered to be because the crosslink density of the cured film was appropriately lowered, which prevented the hardness of the cured film from becoming too high. [Industrial Applicability]

[0135] The image forming method according to the present invention can enhance pinning properties and suppress image stickiness and image cracking due to folding, and is therefore useful in the field of image forming. [Explanation of symbols]

[0136] 100 Image forming device 110 Inkjet head 120 Conveyor 130 Irradiation unit

Claims

1. an actinic radiation polymerizable compound; A crystalline polyester resin, the actinic ray polymerizable compound includes a polyfunctional actinic ray polymerizable compound, the content of which is 60 mass% or more and 90 mass% or less with respect to the total mass of the actinic ray polymerizable compound, the absolute value of the difference (ΔHSP value) between the HSP value of the actinic radiation polymerizable compound and the HSP value of the crystalline polyester resin is 6 or more and 10 or less; Actinic radiation curable inkjet ink.

2. 2. The actinic ray curable ink-jet ink according to claim 1, wherein an absolute value of a difference (ΔHSP value) between an HSP value of the actinic ray polymerizable compound and an HSP value of the crystalline polyester resin is 6 or more and 8 or less.

3. 2 . The actinic ray curable inkjet ink according to claim 1 , wherein a content of the polyfunctional actinic ray polymerizable compound is 70% by mass or more and 90% by mass or less with respect to a total mass of the actinic ray polymerizable compound.

4. applying the actinic ray curable inkjet ink according to any one of claims 1 to 3 to a surface of a recording medium by an inkjet method; a step of irradiating the applied actinic ray curable inkjet ink with actinic ray to cure it; The image forming method according to claim 1,

Images