JP6054022B2 - Actinic radiation curable ink jet ink and image recording method - Google Patents

Description

  The present invention relates to an actinic radiation curable inkjet ink and an image recording method.

  Conventionally, actinic ray curable compositions that are cured by irradiation with active energy rays such as ultraviolet rays and electron beams include coatings used for application to plastics, paper, and inorganic materials, adhesives, printing inks, printed circuit board materials, and It has been put to practical use in various applications such as electrically insulating substrate materials. Actinic ray curable compositions are also used in ink jet inks. In recent years, such inks have attracted attention because they can be recorded on a recording medium having a high curing rate and no ink absorbability.

  As an inkjet ink comprising an actinic ray curable composition, there is an ultraviolet curable ink that is cured by ultraviolet rays. Ink jets using ultraviolet curable inks have been studied to perform high-speed recording taking advantage of the high curing speed. However, when high-speed recording is performed, there is a problem in that since the interval between adjacent ink droplets (dots) is small, adjacent dots are likely to be united and image quality is likely to be degraded. In order to suppress the coalescence of adjacent dots, it has been studied to improve the pinning property of the ultraviolet curable ink. As a method for improving the pinning property of the ink, an ultraviolet curable ink containing a gelling agent has been proposed (see, for example, Patent Documents 1 to 3).

JP 2006-193745 A Special table 2009-510184 gazette US Publication No. 2009/0046134

  These inks have pinning properties because the ink gels at a certain temperature or lower. However, since the ink described in the above-mentioned patent document does not have sufficient gel forming ability, it cannot form a high-definition image when recording is performed continuously.

  As a result of investigations by the inventors, it has been clarified that the above-mentioned problems vary depending on the kind of pigment used in the ink, and are particularly deteriorated when a lake pigment is used. Lake pigments have a merit that the cost can be reduced by limiting the use for indoor use and the like because the lake pigments are inferior in light resistance but cheaper than ordinary pigments. However, the ultraviolet curable ink having a lake pigment has a problem that the pinning property of the ink is not improved even if a gelling agent is added to the ink in order to improve the pinning property. Therefore, there is a problem that a high-definition image cannot be formed and it is difficult to use as a pigment of an ultraviolet curable ink.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an actinic radiation curable ink jet ink that can suppress poor gelation and can form a high-definition image at high speed.

The first of the present invention relates to the following actinic ray curable ink jet ink.
[1] A polymerizable compound, a pigment, an acidic group-containing pigment dispersant, a gelling agent, and a photopolymerization initiator, and the polymerizable compound, pigment, acidic group-containing pigment dispersant, gelling agent, and photopolymerization start The content of metal ions other than the metal ions constituting one of the agents is less than 10 ppm by mass, and a cone plate rheometer with a diameter of 75 mm and a cone angle of 1.0 ° is used at 25 ° C. and a shear rate of 11.7. An actinic radiation curable inkjet ink having a viscosity measured at / s of 1000 mPa · s or more.
[2] The actinic radiation curable inkjet ink according to [1], wherein the acid value of the pigment dispersant having an acidic group is 5 mgKOH / g or more and less than 50 mgKOH / g.
[3] The actinic radiation-curable inkjet ink according to [1] or [2], wherein the total acid value and amine value of the gelling agent is 0.01 mgKOH / g or more and less than 10 mgKOH / g.
[4] The actinic radiation curable inkjet ink according to any one of [1] to [3], wherein the gelling agent is a dialkyl ketone or a fatty acid amide.
[5] The active ray curable inkjet ink according to any one of [1] to [4], wherein the pigment is a lake pigment.
[6] The ink undergoes a sol-gel phase transition reversibly depending on the temperature. A cone plate type rheometer having a diameter of 75 mm and a cone angle of 1.0 ° is used. The active ray according to any one of [1] to [5], wherein the gelation temperature at which the viscosity becomes 200 mPa · s when the temperature is lowered to 20 ° C. at a rate of 11.7 / s is 30 ° C. or more and less than 100 ° C. Curable ink-jet ink.
[7] The active ray curable inkjet ink according to any one of [1] to [6], wherein the content of the pigment is 0.1 to 15% by mass with respect to the ink.

The second of the present invention relates to the following image recording method.
[8] A step of ejecting droplets of the actinic radiation curable ink jet ink according to any one of [1] to [7] from a recording head and adhering to the recording medium, and adhering to the recording medium And a step of irradiating the ink droplet with actinic radiation to cure.

  The actinic radiation curable ink-jet ink of the present invention has a good pinning property because gelation failure due to excess metal ions is suppressed. Thereby, a high-definition image can be formed at high speed.

It is a figure which shows an example of a structure of the principal part of the inkjet recording apparatus of a line recording system. It is a figure which shows an example of a structure of the principal part of the inkjet recording device of a serial recording system.

1. Actinic radiation curable inkjet ink The actinic radiation curable inkjet ink of the present invention includes at least a polymerizable compound, a pigment, a pigment dispersant having an acidic group, a gelling agent, and a photopolymerization initiator. In the present invention, “excess metal ions contained in ink” means “other than metal ions constituting any of a polymerizable compound, a pigment, a pigment dispersant having an acidic group, a gelling agent, and a photopolymerization initiator”. A metal ion capable of forming a salt with a pigment dispersant having an acidic group. “A metal ion other than a metal ion constituting any one of a polymerizable compound, a pigment, a pigment dispersant having an acidic group, a gelling agent and a photopolymerization initiator” typically means “a metal constituting a pigment. “Metal ions other than ions”.

About the polymerizable compound The polymerizable compound is a polymerizable compound that is crosslinked or polymerized by irradiation with actinic rays. The actinic ray is, for example, an electron beam, an ultraviolet ray, an α ray, a γ ray, and an X-ray, and is preferably an ultraviolet ray or an electron beam. The polymerizable compound is a cationic polymerizable compound, a radical polymerizable compound, or a mixture thereof.

  Examples of the radical polymerizable compound include a (meth) acrylate compound. The (meth) acrylate compound may be a monofunctional monomer, a bifunctional monomer, or a trifunctional or higher polyfunctional monomer.

  Examples of monofunctional monomers include isoamyl (meth) acrylate, stearyl (meth) acrylate, lauryl (meth) acrylate, octyl (meth) acrylate, decyl (meth) acrylate, isomyristyl (meth) acrylate, isostearyl (meth) acrylate 2-ethylhexyl-diglycol (meth) acrylate, 2-hydroxybutyl (meth) acrylate, 2- (meth) acryloyloxyethyl hexahydrophthalic acid, butoxyethyl (meth) acrylate, ethoxydiethylene glycol (meth) acrylate, methoxy Diethylene glycol (meth) acrylate, methoxypolyethylene glycol (meth) acrylate, methoxypropylene glycol (meth) acrylate, phenoxyethyl (meth) acrylate , Tetrahydrofurfuryl (meth) acrylate, isobornyl (meth) acrylate, 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 2-hydroxy-3-phenoxypropyl (meth) acrylate, 2- ( Includes (meth) acryloyloxyethyl succinic acid, 2- (meth) acryloyloxyethyl phthalic acid, 2- (meth) acryloyloxyethyl-2-hydroxyethyl-phthalic acid, t-butylcyclohexyl (meth) acrylate, etc. It is.

  Examples of bifunctional monomers 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-tricyclo Examples include decane di (meth) acrylate, neopentyl glycol di (meth) acrylate hydroxypivalate, polytetramethylene glycol di (meth) acrylate, and the like.

  Examples of trifunctional or higher polyfunctional monomers include trimethylolpropane tri (meth) acrylate, pentaerythritol tri (meth) acrylate, pentaerythritol tetra (meth) acrylate, dipentaerythritol hexa (meth) acrylate, ditrimethylolpropane tetra (Meth) acrylate, glycerin propoxytri (meth) acrylate, pentaerythritol ethoxytetra (meth) acrylate and the like are included.

  Among these, stearyl acrylate, lauryl acrylate, isostearyl acrylate, ethoxydiethylene glycol acrylate, isobornyl acrylate, tripropylene glycol di (meth) acrylate, tetraethylene glycol diacrylate, glycerin propoxytril due to high photosensitivity. Acrylate is particularly preferred.

The (meth) acrylate compound may be a modified product. Examples of modified products of (meth) acrylate compounds include ethylene oxide modified (meth) acrylate compounds; propylene oxide modified (meth) acrylate compounds; caprolactone modified (meth) acrylate compounds; caprolactam modified (meth) acrylate compounds, and the like. An ethylene oxide-modified (meth) acrylate compound is preferable. The ethylene oxide-modified (meth) acrylate compound is a bifunctional to hexafunctional (meth) having a structure represented by (—CH ₂ —CH ₂ —O—) m (m is an integer of 4 to 14) in the molecule. An acrylate compound is preferred.

  Examples of such ethylene oxide modified (meth) acrylate compounds include 1,6-hexanediol di (meth) acrylate, trimethylolpropane tri (meth) acrylate, pentaerythritol tetra (meth) acrylate and dipentaerythritol hexa ( An ethylene oxide-modified (meth) acrylate compound obtained by adding 4 to 6 moles of ethylene oxide to 1 mole of a bifunctional to hexafunctional (meth) acrylate compound selected from the group consisting of (meth) acrylates is included. . The ethylene oxide-modified (meth) acrylate compound has high photosensitivity, exceeds the gelation temperature, and can dissolve well the gelling agent described later.

  Examples of commercially available ethylene oxide-modified (meth) acrylate compounds include 4EO-modified hexanediol diacrylate CD561 (molecular weight 358), 3EO-modified trimethylolpropane triacrylate SR454 (molecular weight 429), 6EO-modified trimethylolpropane manufactured by Sartomer. Triacrylate SR499 (molecular weight 560), 4EO modified pentaerythritol tetraacrylate SR494 (molecular weight 528); polyethylene glycol diacrylate NK ester A-400 (molecular weight 508), polyethylene glycol diacrylate NK ester A-600 (manufactured by Shin-Nakamura Chemical Co., Ltd.) Molecular weight 742), polyethylene glycol dimethacrylate NK ester 9G (molecular weight 536), polyethylene glycol dimethacrylate NK Ester 14G (molecular weight 770); include Osaka Organic Chemical Industry Co., Ltd. of tetraethylene glycol diacrylate V # 335HP (molecular weight 302), and the like.

  The molecular weight of the ethylene oxide-modified (meth) acrylate compound is preferably 400-1500. If the molecular weight is less than 400, the ink may not be sufficiently gelled. On the other hand, when the molecular weight exceeds 1500, the viscosity of the ink becomes too high, and the ejection property may be lowered.

  The (meth) acrylate compound may be a polymerizable oligomer, and examples of such a polymerizable oligomer include an epoxy (meth) acrylate oligomer, an aliphatic urethane (meth) acrylate oligomer, and an aromatic urethane (meth) acrylate. Examples include oligomers, polyester (meth) acrylate oligomers, and linear (meth) acrylic oligomers.

  Among these (meth) acrylate compounds, ethylene oxide-modified (meth) acrylate compounds are preferable. The content of the ethylene oxide-modified (meth) acrylate compound is preferably 10 to 40% by mass with respect to the entire ink. When the content of the ethylene oxide-modified (meth) acrylate compound is less than 10% by mass, the flexibility of the ink cured film may not be sufficient, and when it exceeds 40% by mass, the high-speed curability may not be sufficient. .

  Examples of the cationically polymerizable compound include styrene derivatives, vinyl ether compounds, oxirane compounds, oxetane compounds and the like.

  The vinyl ether compound may be a monofunctional vinyl ether compound or a polyfunctional vinyl ether compound.

  Examples of monofunctional vinyl ether compounds include methyl vinyl ether, ethyl vinyl ether, propyl vinyl ether, n-butyl vinyl ether, t-butyl vinyl ether, 2-ethylhexyl vinyl ether, n-nonyl vinyl ether, lauryl vinyl ether, cyclohexyl vinyl ether, cyclohexyl methyl vinyl ether, 4- Methylcyclohexyl methyl vinyl ether, benzyl vinyl ether, dicyclopentenyl vinyl ether, 2-dicyclopentenoxyethyl vinyl ether, methoxyethyl vinyl ether, ethoxyethyl vinyl ether, butoxyethyl vinyl ether, methoxyethoxyethyl vinyl ether, ethoxyethoxyethyl vinyl ether, methoxypolyethylene glycol vinyl ether Tetrahydrofurfuryl vinyl ether, 2-hydroxyethyl vinyl ether, 2-hydroxypropyl vinyl ether, 4-hydroxybutyl vinyl ether, 4-hydroxymethylcyclohexyl methyl vinyl ether, diethylene glycol monovinyl ether, polyethylene glycol vinyl ether, chloroethyl vinyl ether, chlorobutyl vinyl ether, chloroethoxyethyl Vinyl ether, phenyl ethyl vinyl ether, phenoxy polyethylene glycol vinyl ether and the like are included.

Examples of polyfunctional vinyl ether compounds include ethylene glycol divinyl ether, diethylene glycol divinyl ether, polyethylene glycol divinyl ether, propylene glycol divinyl ether, butylene glycol divinyl ether, hexanediol divinyl ether, bisphenol A alkylene oxide divinyl ether, bisphenol F alkylene oxide di Divinyl ethers such as vinyl ether;
Trimethylolethane trivinyl ether, trimethylolpropane trivinyl ether, ditrimethylolpropane tetravinyl ether, glycerin trivinyl ether, pentaerythritol tetravinyl ether, dipentaerythritol pentavinyl ether, dipentaerythritol hexavinyl ether, ethylene oxide-added trimethylolpropane trivinyl ether, propylene oxide Addition trimethylolpropane trivinyl ether, ethylene oxide addition ditrimethylolpropane tetravinyl ether, propylene oxide addition ditrimethylolpropane tetravinyl ether, ethylene oxide addition pentaerythritol tetravinyl ether, propylene oxide addition pentaerythritol te La ether, ethylene oxide adduct of dipentaerythritol hexavinyl ether, include multifunctional vinyl ethers such as propylene oxide adduct of dipentaerythritol hexa vinyl ether.

  The vinyl ether compound may be a vinyl ether compound having a structure represented by (—C (═O) —O—) n (n is an integer of 2 to 5) in the molecule.

Examples of vinyl ether compounds having a structure represented by (—C (═O) —O—) n (n is an integer of 2 to 5) in the molecule include (—C (═O) —O in the molecule. -) A bifunctional vinyl ether compound having a structure represented by n (n is 2 or 3) is included. Examples of such commercially available vinyl ether compounds include VEctomer 4010, VEctomer 4020, VEctomer 4040, VEctomer 4060, and VEctomer 5015 (ALDRICH, VEctomer series). Among them, the following compounds A-1 to A-8 are more preferable. preferable.

  The molecular weight of the vinyl ether compound having a structure represented by (—C (═O) —O—) n (n is an integer of 2 to 5) in the molecule is preferably 300 to 1,000. If the molecular weight is less than 300, the gelation of the ink may not be sufficient. On the other hand, when the molecular weight is more than 1000, the viscosity of the ink becomes too high, and the ejection property may be lowered.

  The oxirane compound may be a known epoxy compound, and may be a monofunctional epoxy compound or a polyfunctional epoxy compound. Examples of monofunctional epoxy compounds include phenyl glycidyl ether, p-tert-butylphenyl glycidyl ether, butyl glycidyl ether, 2-ethylhexyl glycidyl ether, allyl glycidyl ether, 1,2-butylene oxide, 1,3-butadiene monooxide 1,2-epoxydodecane, epichlorohydrin, 1,2-epoxydecane, styrene oxide, cyclohexene oxide, 3-methacryloyloxymethylcyclohexene oxide, 3-acryloyloxymethylcyclohexene oxide, 3-vinylcyclohexene oxide, etc. It is.

Examples of polyfunctional epoxy compounds include bisphenol A diglycidyl ether, bisphenol F diglycidyl ether, bisphenol S diglycidyl ether, brominated bisphenol A diglycidyl ether, brominated bisphenol F diglycidyl ether, brominated bisphenol S diglycidyl ether Epoxy novolac resin, hydrogenated bisphenol A diglycidyl ether, hydrogenated bisphenol F diglycidyl ether, hydrogenated bisphenol S diglycidyl ether, 3,4-epoxycyclohexylmethyl-3 ', 4'-epoxycyclohexanecarboxylate, 2- (3,4-epoxycyclohexyl-5,5-spiro-3,4-epoxy) cyclohexane-meta-dioxane, bis (3,4-epoxycyclohexylmethyl) Dipetate, vinylcyclohexene oxide, 4-vinylepoxycyclohexane, bis (3,4-epoxy-6-methylcyclohexylmethyl) adipate, 3,4-epoxy-6-methylcyclohexyl-3 ', 4'-epoxy-6'- Methylcyclohexanecarboxylate, methylenebis (3,4-epoxycyclohexane), dicyclopentadiene diepoxide, di (3,4-epoxycyclohexylmethyl) ether of ethylene glycol, ethylenebis (3,4-epoxycyclohexanecarboxylate), epoxy Dioctyl hexahydrophthalate, di-2-ethylhexyl epoxyhexahydrophthalate, 1,4-butanediol diglycidyl ether, 1,6-hexanediol diglycidyl ether, glycerin Triglycidyl ether, trimethylolpropane triglycidyl ether, polyethylene glycol diglycidyl ether, polypropylene glycol diglycidyl ethers;
1,1,3-tetradecadiene dioxide, limonene dioxide, 1,2,7,8-diepoxyoctane, 1,2,5,6-diepoxycyclooctane and the like are included.

  Oxetane compounds (compounds having an oxetane ring) include oxetane compounds described in JP-A Nos. 2001-220526 and 2001-310937. Examples of monofunctional oxetane compounds include 3-ethyl-3-hydroxymethyloxetane, 3- (meth) allyloxymethyl-3-ethyloxetane, (3-ethyl-3-oxetanylmethoxy) methylbenzene, 4-fluoro- [1- (3-ethyl-3-oxetanylmethoxy) methyl] benzene, 4-methoxy- [1- (3-ethyl-3-oxetanylmethoxy) methyl] benzene, [1- (3-ethyl-3-oxetanylmethoxy) ) Ethyl] phenyl ether, isobutoxymethyl (3-ethyl-3-oxetanylmethyl) ether, isobornyloxyethyl (3-ethyl-3-oxetanylmethyl) ether, isobornyl (3-ethyl-3-oxetanylmethyl) ether 2-ethylhexyl (3-ethyl-3-oxetanylmethyl) Ether, ethyldiethylene glycol (3-ethyl-3-oxetanylmethyl) ether, dicyclopentadiene (3-ethyl-3-oxetanylmethyl) ether, dicyclopentenyloxyethyl (3-ethyl-3-oxetanylmethyl) ether, dicyclo Pentenyl (3-ethyl-3-oxetanylmethyl) ether, tetrahydrofurfuryl (3-ethyl-3-oxetanylmethyl) ether, tetrabromophenyl (3-ethyl-3-oxetanylmethyl) ether, 2-tetrabromophenoxyethyl ( 3-ethyl-3-oxetanylmethyl) ether, tribromophenyl (3-ethyl-3-oxetanylmethyl) ether, 2-tribromophenoxyethyl (3-ethyl-3-oxetanylmethyl) ether, Roxyethyl (3-ethyl-3-oxetanylmethyl) ether, 2-hydroxypropyl (3-ethyl-3-oxetanylmethyl) ether, butoxyethyl (3-ethyl-3-oxetanylmethyl) ether, pentachlorophenyl (3-ethyl- 3-oxetanylmethyl) ether, pentabromophenyl (3-ethyl-3-oxetanylmethyl) ether, bornyl (3-ethyl-3-oxetanylmethyl) ether, and the like are included.

  Examples of polyfunctional oxetane compounds include 3,7-bis (3-oxetanyl) -5-oxa-nonane, 3,3 '-(1,3- (2-methylenyl) propanediylbis (oxymethylene)) bis -(3-ethyloxetane), 1,4-bis [(3-ethyl-3-oxetanylmethoxy) methyl] benzene, 1,2-bis [(3-ethyl-3-oxetanylmethoxy) methyl] ethane, 1, 3-bis [(3-ethyl-3-oxetanylmethoxy) methyl] propane, ethylene glycol bis (3-ethyl-3-oxetanylmethyl) ether, dicyclopentenylbis (3-ethyl-3-oxetanylmethyl) ether, tri Ethylene glycol bis (3-ethyl-3-oxetanylmethyl) ether, tetraethylene glycol bis (3-ethyl-3 Oxetanylmethyl) ether, tricyclodecanediyldimethylene (3-ethyl-3-oxetanylmethyl) ether, trimethylolpropane tris (3-ethyl-3-oxetanylmethyl) ether, 1,4-bis (3-ethyl-3) -Oxetanylmethoxy) butane, 1,6-bis (3-ethyl-3-oxetanylmethoxy) hexane, pentaerythritol tris (3-ethyl-3-oxetanylmethyl) ether, pentaerythritol tetrakis (3-ethyl-3-oxetanylmethyl) ) Ether, polyethylene glycol bis (3-ethyl-3-oxetanylmethyl) ether, dipentaerythritol hexakis (3-ethyl-3-oxetanylmethyl) ether, dipentaerythritol pentakis (3-ethyl-3- Xetanylmethyl) ether, dipentaerythritol tetrakis (3-ethyl-3-oxetanylmethyl) ether, caprolactone-modified dipentaerythritol hexakis (3-ethyl-3-oxetanylmethyl) ether, caprolactone-modified dipentaerythritol pentakis (3-ethyl) -3-oxetanylmethyl) ether, ditrimethylolpropane tetrakis (3-ethyl-3-oxetanylmethyl) ether, EO-modified bisphenol A bis (3-ethyl-3-oxetanylmethyl) ether, PO-modified bisphenol A bis (3-ethyl) -3-Oxetanylmethyl) ether, EO-modified hydrogenated bisphenol A bis (3-ethyl-3-oxetanylmethyl) ether, PO-modified hydrogenated bisphenol A bis (3-ethyl-3) -Oxetanylmethyl) ether, EO-modified bisphenol F (3-ethyl-3-oxetanylmethyl) ether and the like.

  Among these cationically polymerizable compounds, a vinyl ether compound is preferable because of its high curability, and (—C (═O) —O—) n (n is an integer of 2 to 5) in the molecule described above. A vinyl ether compound having the structure represented is more preferred.

  The content of the vinyl ether compound having a structure represented by (—C (═O) —O—) n (n is an integer of 2 to 5) in the molecule is 20 to 60% by mass with respect to the whole ink. It is preferable. When the content of the vinyl ether compound having a structure represented by (—C (═O) —O—) n (n is an integer of 2 to 5) in the molecule is less than 20% by mass, the curability of the ink is increased. If it exceeds 60% by mass, the flexibility of the ink cured film may be lowered.

A cationically polymerizable compound and a radically polymerizable compound may be used in combination in order to be cured at high speed and to increase the flexibility of the cured film. In that case, the radical polymerizable compound is (A) “bifunctional to hexafunctional having a structure represented by (—CH ₂ —CH ₂ —O—) m (m is an integer of 4 to 14) in the molecule. (B) a vinyl ether having a structure represented by (—C (═O) —O—) n (n is an integer of 2 to 5) in the molecule. It is preferable to include a “compound”. The (A) (meth) acrylate compound has high adhesion to the recording medium and flexibility of the cured product, but the curing rate may be slightly low. On the other hand, the vinyl ether compound (B) has a high curing rate, but the adhesion to the recording medium and the flexibility of the cured product may not be sufficient. On the other hand, the mixture of the (A) (meth) acrylate compound and the (B) vinyl ether compound has a high curing rate and can also increase the flexibility of the resulting cured product.

  Furthermore, the ink of the present invention containing a mixture of (A) (meth) acrylate compound and (B) vinyl ether compound and a gelling agent described later can be gelled with good reproducibility. The reason is not necessarily clear, but (A) four or more ethylene oxide groups (polar groups) contained in the (meth) acrylate compound and (B) two or more ester groups (polar groups) contained in the vinyl ether compound Further, it is considered that the gelling agent is easily oriented and the gel state becomes uniform.

  The total content of the polymerizable compounds is preferably 1 to 97% by mass and more preferably 30 to 95% by mass with respect to the entire ink.

About photopolymerization initiators Photopolymerization initiators are known photopolymerization initiators described in “Application and Market of UV / EB Curing Technology” (CMC Publishing Co., Ltd., edited by Yoneho Tabata / edited by Radtech Research Association). It's okay. The photopolymerization initiator can be a photo radical generator or a photo acid generator.

The photo radical initiator includes an intramolecular bond cleavage type and an intramolecular hydrogen abstraction type. Examples of intramolecular bond cleavage type photopolymerization initiators include diethoxyacetophenone, 2-hydroxy-2-methyl-1-phenylpropan-1-one, benzyldimethyl ketal, 1- (4-isopropylphenyl) -2. -Hydroxy-2-methylpropan-1-one, 4- (2-hydroxyethoxy) phenyl- (2-hydroxy-2-propyl) ketone, 1-hydroxycyclohexyl-phenylketone, 2-methyl-2-morpholino (4 Acetophenone systems such as -thiomethylphenyl) propan-1-one, 2-benzyl-2-dimethylamino-1- (4-morpholinophenyl) -butanone;
Benzoins such as benzoin, benzoin methyl ether, benzoin isopropyl ether;
Acylphosphine oxide systems such as 2,4,6-trimethylbenzoindiphenylphosphine oxide;
Benzyl and methylphenylglyoxyesters are included.

Examples of intramolecular hydrogen abstraction type photopolymerization initiators include benzophenone, methyl 4-phenylbenzophenone o-benzoylbenzoate, 4,4'-dichlorobenzophenone, hydroxybenzophenone, 4-benzoyl-4'-methyl-diphenyl. Benzophenone series such as sulfide, acrylated benzophenone, 3,3 ′, 4,4′-tetra (t-butylperoxycarbonyl) benzophenone, 3,3′-dimethyl-4-methoxybenzophenone;
Thioxanthone systems such as 2-isopropylthioxanthone, 2,4-dimethylthioxanthone, 2,4-diethylthioxanthone, 2,4-dichlorothioxanthone;
Aminobenzophenone series such as Mihira-ketone and 4,4'-diethylaminobenzophenone;
Examples include 10-butyl-2-chloroacridone, 2-ethylanthraquinone, 9,10-phenanthrenequinone, camphorquinone, and the like.

  The photoacid generator may be a chemical amplification type photoresist or a compound used in photocationic polymerization (Organic Electronics Materials Research Group, “Organic Materials for Imaging”, Bunshin Publishing (1993), pages 187-192. reference). Examples of the photoacid generator include aromatic onium salts, photosulfonic acid generators, photohydrochloric acid generators, photoodoric acid generators, iron allene complexes, and the like.

  Examples of the aromatic onium constituting the aromatic onium salt include aromatic diazonium, aromatic ammonium, aromatic iodonium, aromatic sulfonium, aromatic phosphonium and the like.

Examples of aromatic diazonium include the following.

Examples of aromatic ammonium include:

Examples of aromatic iodonium include:

Examples of aromatic sulfoniums include:

Examples of aromatic phosphoniums include the following.

Examples of the counter anion constituting the aromatic onium salt include B (C ₆ F ₅ ) ⁴⁻ , PF ⁶⁻ , AsF ⁶⁻ , SbF ⁶⁻ , CF ₃ SO ^{3− and the} like.

Examples of the photosulfonic acid generator include the following.

Examples of the photohydrochloric acid generator and photoodoric acid generator include the following.

Examples of iron allene complexes include:

  In order to contain the photoacid generator in the ink of the present invention, it is preferable to dissolve the photoacid generator in a solvent. Examples of the solvent for easily dissolving the photoacid generator at room temperature (about 25 ° C.) include a cyclic ester compound and a carbonate ester compound. Examples of cyclic ester compounds include ethylene carbonate, propylene carbonate, β-propiolactone, β-butyrolactone, α-methyl-β-butyrolactone, γ-butyrolactone, γ-valerolactone, δ-valerolactone, ε-caprolactone, γ-caprolactone, γ-heptanolactone, and the like are included.

  The content of the photopolymerization initiator is preferably 1 to 10% by mass, more preferably 2 to 8% by mass with respect to the whole ink, although it depends on the actinic ray and the kind of the polymerizable compound. .

Coloring materials Examples of pigments contained in the ink of the present invention include the following.

  C. I. Pigment Yellow 1, 2, 3, 4, 5, 6, 7, 9, 10, 12, 13, 14, 15, 16, 17, 24, 55, 60, 61, 62, 63, 65, 73, 74, 75, 77, 81, 83, 87, 93, 94, 95, 97, 98, 99, 100, 101, 104, 105, 106, 108, 109, 110, 111, 113, 114, 116, 117, 120, 123,124,126,127,128,129,130,133,138,139,150,151,153,154,155,165,167,168,169,170,172,173,174,175,176 179,180,181,182,183,185,191,193,194,199,205,206,209,212,213,214,21 5,219

  C. I. Pigment Red 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 14, 15, 16, 17, 18, 21, 22, 23, 31, 32, 38, 41, 48: 1, 48: 2, 48: 4, 49: 1, 52: 1, 52: 2, 53: 1, 54, 57: 1, 58: 1, 58: 2, 58: 3, 58: 4 60: 1, 63: 1, 64: 1, 68, 81: 1, 83, 88, 89, 95, 101, 112, 114, 119, 122, 123, 136, 144, 146, 147, 149, 150, 164, 166, 168, 169, 170, 171, 172, 175, 176, 177, 178, 179, 181, 182, 183, 184, 185, 187, 188, 190, 193, 194, 200, 202, 206, 207, 208, 209, 2 10, 211, 213, 214, 216, 220, 221, 224, 226, 237, 238, 239, 242, 245, 247, 248, 251, 253, 254, 255, 256, 257, 258, 260, 262 263, 264, 266, 268, 269, 270, 271, 272, 279, 282

  C. I. Pigment Violet 1, 2, 3, 5: 1, 13, 17, 19, 23, 25, 27, 29, 31, 32, 36, 37, 38, 42, 50

  C. I. Pigment Blue 1, 2, 3: 1, 3: 3, 5: 1, 13, 15: 1, 15: 2, 15: 3, 15: 4, 15: 5, 15: 6, 16, 17: 1, 18, 22, 24: 1, 25, 26, 27, 29, 56, 60, 61, 62, 63, 75, 79, 80

  C. I. Pigment Green 1, 4, 7, 8, 10, 36

  C. I. Pigment White 1, 2, 4, 5, 6, 7, 11, 12, 18, 19, 21, 22, 23, 26, 27, 28

  C. I. Pigment Black 1, 7, 10, 20, 31, 32

Among these pigments, the following lake pigments are preferably used when high weather resistance is not required for the ink.
C. I. Pigment Yellow 61, 62, 100, 104, 133, 150, 153, 168, 169, 179, 183, 191, 206, 209, 212;
C. I. Pigmet Red 48: 1, 48: 2, 48: 4, 49: 1, 52: 1, 52: 2, 53: 1, 57: 1, 58: 1, 58: 2, 58: 3, 58: 4 60: 1, 63: 1, 64: 1, 68, 81: 1, 193, 200, 237, 247, 257;
C. I. Pigment Blue 1, 2, 3: 1, 3: 3, 5: 1, 15: 1, 15: 2, 15: 3, 15: 4, 15: 5, 15: 6, 17: 1, 24: 1, 56, 61, 62, 63, 75, 79;
C. I. Pigment Green 1, 4, 7, 8, 10, 36;
C. I. Pigment Black 1, etc.

  Since these lake pigments are metal salts of dyes, they contain a relatively large amount of metal ions other than the metal ions constituting the pigment; specifically, Ca ions, Mg ions, Sr ions and the like. . Further, not only lake pigments, but also pigments obtained through a pulverization step by a salt milling method may contain metal ions such as Na ions. Metal ions other than the metal ions constituting the pigment (excess metal ions) form a salt with an acidic group contained in the pigment dispersant described later to form a dispersant salt. It is considered that the dispersant salt inhibits crystallization of the gelling agent and makes it difficult for the ink to gel.

  That is, the present inventors have found that one of the factors that make the ink difficult to gel is the interaction between excess metal ions contained in the ink and acidic groups in the pigment dispersant. It is presumed that the mechanism by which the ink hardly gels due to the interaction is as follows. In general, in an ultraviolet curable ink, a pigment is dispersed by a pigment dispersant having an acidic group. When excess metal ions are present in the ink, the excess metal ions form a salt with the acidic group of the pigment dispersant contained in the ink. When the acidic group of the pigment dispersant forms a salt with an excess metal ion to form a dispersant salt, an interaction between the dispersant salt and the polar group of the gelling agent occurs, resulting in uneven distribution of the gelling agent in the ink. Occurs. Further, when the nonpolar sites of the gelling agent gather to form a crystal structure, the nonpolar sites of the dispersant salt also gather. The polar part of the dispersant salt inhibits the assembly of non-polar parts of the gelling agent, so that the gelling agent can form only a stitch structure smaller than the original stitch structure. As a result, even when the ink is below the gelling temperature, the gelation of the ink is inhibited by the above-described dispersant salt, so that the gel strength of the ink is lowered and the ink cannot be pinned.

  As described above, since the lake pigment is insolubilized by metal chloride of the dye, it is considered that the lake pigment contains more excess metal ions than other pigments. Such extra metal ions are not limited to lake pigments, but may also be included in pigments obtained through a pulverization process such as a salt milling method, and these extra metal ions may cause gelling agents in the ink. The inventors have found that the function is inhibited.

  Therefore, in the present invention, the gelation of the ink is not inhibited by setting the content of excess metal ions in the ink to a certain value or less. Specifically, the amount of excess metal ions other than the metal ions constituting the pigment contained in the ink is preferably 10 mass ppm or less with respect to the entire pigment. For that purpose, it is preferable that the amount of excess metal ions contained in the pigment other than the metal ions constituting the pigment is 60 mass ppm or less with respect to the entire pigment.

The amount of excess metal ions contained in the pigment can be measured by the following procedure.
1) Add water to the pigment and dilute to make a liquid sample. This liquid sample is centrifuged by a centrifugal separator to separate it into a solid component and a liquid component.
2) The amount of metal ions contained in the solution component obtained in 1) is measured by ICP-AES. The obtained metal ion amount is defined as “excess metal ion amount contained in the pigment”.

  Adjustment of the amount of excess metal ions contained in the pigment can be performed by a method such as washing the pigment before containing in the ink with ion-exchanged water.

  The pigment content is preferably 0.1 to 15% by mass and more preferably 3 to 5% by mass with respect to the entire ink. This is because if the pigment content is too low, the resulting image will not be sufficiently colored, and if it is too high, the viscosity of the ink will increase and the ejection properties will decrease.

About Pigment Dispersant The pigment dispersant contained in the ink of the present invention preferably has an acidic group from the viewpoint of enhancing the dispersibility of the pigment. Examples of pigment dispersants having acidic groups include polyallylamine derivatives, hydroxyl group-containing carboxylic acid esters, salts of long chain polyaminoamides and high molecular weight acid esters, salts of high molecular weight polycarboxylic acids, long chain polyaminoamides and polar acid esters. And the like, preferably a polyallylamine derivative.

The polyallylamine derivative is preferably a compound represented by the following formula (I). X and Y in the following formula (I) each independently represent a hydrogen atom, a group derived from a polymerization initiator, or a group derived from a chain transfer catalyst. R ¹ represents a free amino group or a group represented by the following formula (II) or (III); at least one of R ¹ represents a group represented by the following formula (III). n represents an integer of 2 to 1000. R ² of the following formula (II) or (III) is obtained by removing a carboxyl group from any of a polyester having a free carboxylic acid, a polyamide having a free carboxylic acid, or a polyester amide having a free carboxylic acid. Indicates a group.

  The polyallylamine derivative represented by the formula (I) is obtained, for example, by reacting polyallylamine with a polyester having a free carboxyl group, a polyamide having a free carboxyl group, or a polyesteramide having a free carboxyl group. .

  The polyallylamine is obtained by polymerizing allylamine in the presence of a polymerization initiator and optionally in the presence of a chain transfer catalyst. Examples of polymerization initiators include ketone peroxides such as methyl ethyl ketone; diacyl peroxides such as benzoyl peroxide; peroxydicarbonates such as diisopropyl peroxydicarbonate; 1,1-bis (t-butylperoxy ) Peroxyketals such as cyclohexane; hydroperoxides such as t-butyl hydroperoxide; peroxyesters such as t-butyl peroxypivalate and the like.

  Examples of chain transfer catalysts include alkyl mercaptans such as lauryl mercaptan; thiocarboxylic acids such as mercaptoacetic acid, 2-mercaptopropionic acid and 3-mercaptopropionic acid; thiocarboxylic acids such as butyl thioglycolate and 2-ethylhexyl thioglycolate Acid esters and the like are included.

The polyester having a free carboxyl group to be reacted with polyallylamine is preferably a polyester compound represented by formula (IV) or formula (V). R ^{3 in the following} formula (IV) represents a linear or branched alkylene group having 2 to 20 carbon atoms; a represents an integer of 2 to 100. R ^{4 in the following} formula (V) represents a straight chain or branched alkylene group having 2 to 20 carbon atoms, a phenylene group, or —CH═CH—; R ⁵ is a straight chain having 2 to 20 carbon atoms or A branched alkylene group or a group obtained by removing two hydroxyl groups from polyalkylene glycol; b represents an integer of 2 to 100.

  Specific examples of the polyester compound represented by the formula (IV) include polycaprolactone.

The polyamide having a free carboxyl group to be reacted with polyallylamine is preferably a polyamide compound represented by formula (VI) or formula (VII). R ^{6 in the} formula (VI) represents a linear or branched alkylene group having 2 to 20 carbon atoms; c represents an integer of 2 to 100. ^{R 4} of formula (VII) is the same as ^{R 4} of formula (V); ^{R 7} is a straight or branched alkylene group having 2 to 20 carbon atoms; d is an integer of 2 to 100 .

  Examples of commercially available polyallylamine derivatives include PB series (for example, Ajisper PB824) manufactured by Ajinomoto Fine Techno Co., Ltd.

  The acid value of the pigment dispersant is preferably 5 mgKOH / g or more and less than 50 mgKOH / g from the viewpoint of facilitating dispersion of the pigment. The acid value of the pigment dispersant is defined as the number of milligrams of potassium hydroxide required to neutralize the acid contained in 1 g of the pigment dispersant. The acid value of the pigment dispersant is measured according to JIS K 0070.

  The molecular weight of the pigment dispersant is preferably 2000 to 100,000 from the viewpoint of being easily dissolved in the ink component and functioning as a pigment dispersant.

  The total amount of the pigment dispersant is preferably 1 to 50% by mass and more preferably 15 to 40% by mass with respect to the pigment. If it is less than 1% by mass, the pigment cannot be sufficiently dispersed, and if it exceeds 50% by mass, the viscosity of the ink may increase.

  The actinic radiation curable inkjet ink of the present invention may further contain a dispersion aid as necessary. The dispersion aid may be selected according to the pigment.

  The actinic radiation curable inkjet ink may further include a dispersion medium for dispersing the pigment as necessary. A solvent may be included in the ink as a dispersion medium. However, in order to suppress the residual solvent in the formed image, a polymerizable compound (particularly a monomer having a low viscosity) as described above may be used as the dispersion medium. preferable.

  The pigment is dispersed so that the average particle diameter of the pigment particles is preferably 0.08 to 0.2 μm, and the maximum particle diameter is preferably 0.3 to 10 μm, more preferably 0.3 to 3 μm. Is preferred. The dispersion of the pigment is adjusted by the selection of the pigment, the dispersant, and the dispersion medium, the dispersion conditions, the filtration conditions, and the like.

  The pigment can be dispersed by, 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, and a paint shaker.

About gelling agent A gelling agent imparts a function of reversibly sol-gel phase transition of ink depending on temperature. That is, the ink of the present invention containing a gelling agent becomes a fluid solution (sol) at a high temperature, becomes a semisolid state (gel) having no fluidity at a low temperature, and is thermally reversible between the gel and the sol. It can transition to.

  The gel formed by the ink of the present invention has a structure in which a polymerizable compound or the like is included in a lamellar structure or a polymer network structure and loses independent mobility and aggregates. The polymer network structure constituting the gel may be a structure obtained by covalent bonding or hydrogen bonding of the gelling agent, or may be a structure formed by physical aggregation of the gelling agent. The gel having such a structure has high viscosity and elasticity and is solidified or semi-solidified.

  In particular, the gel formed by the ink of the present invention has a structure (card house structure) in which a polymerizable compound is enclosed in a space three-dimensionally surrounded by a plate crystal that is a crystallized product of a gelling agent. preferable. When the card house structure is formed, a liquid polymerizable compound can be held and ink droplets can be pinned. Thereby, coalescence of droplets can be suppressed.

  Any gelling agent may be used as long as it dissolves in the polymerizable compound at a temperature higher than the gelation temperature and crystallizes at the gelation temperature or lower, and includes a high molecular compound and a low molecular compound. .

  Examples of gelling agents for polymer compounds include fatty acid inulins such as inulin stearate; fatty acid dextrins such as dextrin palmitate and dextrin myristate (such as the Leopard series manufactured by Chiba Flour Mills); glyceryl behenate, glyceryl behenate, behenic acid Eicosan polyglyceryl and the like (Nomshin Eulio Co., Ltd. Nomucoat series etc.); L-glutamic acid derivatives (Ajinomoto Fine Techno Co., Ltd.) and the like are included.

  Examples of gelling agents for low molecular weight compounds include: dialkyl ketones such as 18-pentatriacontanone (stearone), 16-hentriacontanone, 12-tricosanone; fatty acid alcohols such as UNILIN 425; stearyl stearate, palmityl stearate , Fatty acid esters such as myristyl myristate; erucic acid amide (Faty AMID E, manufactured by Kao Corporation), oleic acid amide (Faty AMID T, manufactured by Kao Co., Ltd.), cured beef fatty acid amide (Faty AMID O-N, manufactured by Kao Corporation) , Fatty acid amides such as stearic acid amide (Nippon Kasei Co., Ltd., Nikka Amide AP1), N-lauroyl-L-glutamic acid dibutylamide (Ajinomoto Fitechno, GP-1); behenic acid, arachidic acid, stearic acid, palmitic Acid, myris Higher fatty acids such as acid, lauric acid, oleic acid, and erucic acid; oil wax such as jojoba ester (Floraester 70, manufactured by Ikeda Bussan Co., Ltd.); described in JP-A-2005-126507 and JP-A-2005-255821 Oil gelling agents are included. These gelling agents may be used alone or in combination of two or more.

  Among these, from the viewpoint of improving ink ejection properties, a low molecular compound; in particular, a low molecular compound having a molecular weight of less than 1000 is preferable. Of the low molecular weight compounds, dialkyl ketones or fatty acid esters are preferred from the viewpoints of easily forming a good gel state with the polymerizable compound and being difficult to inhibit gelation by excess metal ions. The number of carbon atoms of the two alkyl groups constituting the dialkyl ketone is preferably 10 to 20 independently. On the other hand, gelling agents having high polarity such as higher fatty acids and fatty acid amides are easily inhibited from gelation (crystallization) by excess metal ions.

  The total of the acid value and amine value of the gelling agent is preferably 0.01 mgKOH / g or more and less than 10 mgKOH / g, more preferably 0.01 to 3 mgKOH / g. If the total of the acid value and amine value of the gelling agent is 10 mg KOH / g or more, excess metal ions and salts are likely to be formed, and the formation of the original gel structure is likely to be hindered. Further, if the amine value of the gelling agent is too high, the gelling agent tends to interact with ink components (such as monomers and polymerization initiators) and impurities. On the other hand, since the impurities also interact with the pigment dispersant adsorbed on the pigment particles, the dispersibility of the pigment particles is lowered and the particles are easily aggregated.

  The acid value of the gelling agent is defined as the number of milligrams of potassium hydroxide required to neutralize the acid (carboxyl group present in the sample) contained in 1 g of the gelling agent. The acid value of the gelling agent can be measured according to JIS K 0070.

  The amine value of the gelling agent is defined as the number of mg of potassium hydroxide equivalent to perchloric acid required to neutralize all basic nitrogen contained in 1 g of the gelling agent. The amine value of the gelling agent can be measured by a potentiometric titration method described in JIS K 7237 (1995).

  The content of the gelling agent is preferably 2 to 10% by mass and more preferably 3 to 7% by mass with respect to the entire ink. If the content of the gelling agent is less than 2% by mass, the ink cannot be gelled (sol-gel phase transition due to temperature), and if it exceeds 10% by mass, the ink cannot be sufficiently dissolved in the ink. Injectability may be reduced.

Other components The actinic ray curable inkjet ink may further contain other components as necessary. Other components may be various additives, other resins, and the like. Examples of the additive include a surfactant, a leveling additive, a matting agent, an ultraviolet absorber, an infrared absorber, an antibacterial agent, and a basic compound for enhancing the storage stability of the ink. Examples of basic compounds include basic alkali metal compounds, basic alkaline earth metal compounds, basic organic compounds such as amines, and the like. Examples of other resins include resins for adjusting the physical properties of the cured film, such as polyester resins, polyurethane resins, vinyl resins, acrylic resins, rubber resins, and waxes. It is.

  Since the actinic radiation curable ink-jet ink contains the above-mentioned gelling agent, it undergoes a sol-gel phase transition reversibly with temperature. Actinic ray curable ink that undergoes a sol-gel phase transition is liquid at a high temperature (for example, about 80 ° C.), and thus can be ejected from an inkjet recording head. When the actinic ray curable inkjet ink is ejected at a high temperature, the ink droplets (dots) land on the recording medium, and then naturally cool to gel. Thereby, coalescence of adjacent dots can be suppressed and image quality can be improved.

  In order to improve the ink ejection properties, it is preferable that the viscosity of the ink at a high temperature is not more than a certain level. Specifically, the viscosity at 100 ° C. of the actinic radiation curable inkjet ink is preferably 3 to 20 mPa · s. On the other hand, in order to suppress coalescence of adjacent dots, it is preferable that the viscosity of the ink at normal temperature after landing is a certain level or more. Specifically, the viscosity at 25 ° C. of the actinic radiation curable inkjet ink is preferably 1000 mPa · s or more.

  The gelation temperature of the ink is preferably 30 ° C. or higher and lower than 100 ° C., more preferably 40 ° C. or higher and 70 ° C. or lower, and further preferably 50 ° C. or higher and 65 ° C. or lower. When the injection temperature is in the vicinity of 100 ° C., if the gelation temperature of the ink is 100 ° C. or more, gelation is likely to occur at the time of injection, resulting in low ejection properties, and recording is performed when the gelation temperature is less than 30 ° C. This is because it does not gel immediately after landing on the medium. The gelation temperature is a temperature at which the fluidity decreases due to gelation in the process of cooling the ink in the sol state.

  The viscosity at 100 ° C., the viscosity at 25 ° C. and the gelation temperature of the ink can be determined by measuring the temperature change of the dynamic viscoelasticity of the ink with a rheometer. Specifically, a temperature change curve of viscosity is obtained when the ink is heated to 100 ° C. and cooled to 20 ° C. under conditions of a shear rate of 11.7 (/ s) and a temperature decrease rate of 0.1 ° C./s. And the viscosity in 100 degreeC and the viscosity in 25 degreeC can be calculated | required by reading the viscosity in 100 degreeC and 25 degreeC in the temperature change curve of a viscosity, respectively. The gelation temperature can be determined as the temperature at which the viscosity becomes 200 mPa · s in the temperature change curve of the viscosity.

  As the rheometer, a stress control type rheometer Physica MCR series manufactured by Anton Paar can be used. The cone plate can have a diameter of 75 mm and a cone angle of 1.0 °.

  In the actinic radiation curable ink-jet ink of the present invention, the content of excess metal ions (impurity metal ions) other than metal ions constituting the pigment is less than 10 mass ppm;

The content of excess metal ions (other than the metal ions constituting the pigment) in the ink can be measured by the following procedure.
1) A polymerizable compound is added to the ink and diluted to obtain a liquid sample. And a liquid sample is centrifuged with a centrifuge, and it isolate | separates into a solid component and a liquid component.
2) The dried solid component is made into a solution with concentrated hydrochloric acid in a sealed microwave decomposition apparatus. The amount of metal ions in the concentrated hydrochloric acid solution obtained is measured by ICP-AES, and the amount of metal ions contained in the solid component is determined.
3) Similarly, the amount of metal ions contained in the solution component is measured by ICP-AES to obtain the amount of metal ions contained in the solution component.
4) The total amount of metal ions of the solid component obtained in 2) above and the amount of metal ions of the solution component obtained in 3) above are added to obtain the “total amount of metal ions contained in the ink”.
5-1) When the pigment is not a lake pigment, “the total amount of metal ions contained in the ink” becomes “the amount of excess metal ions contained in the ink”.
5-2) On the other hand, when the pigment is a rake pigment, the “total amount of metal ions contained in the ink” minus the “amount of metal ions constituting the pigment” is the “excess metal contained in the ink”. The amount of ions ”. “Amount of metal ions constituting the pigment” is determined after measuring the amount of chelate (dye) contained in the solution obtained in 2) above with an ultraviolet visible photometer; and the amount of chelate (dye) obtained From the stoichiometric ratio, the “amount of metal ions forming a salt with a chelate” is calculated.

Further, the content of excess metal ions (other than the metal ions constituting the pigment) in the ink can also be measured by the following procedure.
1) A polymerizable compound is added to the ink and diluted to obtain a liquid sample. Then, the liquid sample is centrifuged while being heated to a temperature higher than the gelation temperature (about 80 ° C.). Thereby, the salt of the excess metal ion and the dispersant (dispersant salt) is separated as a solution component; the pigment is separated as a solid content.
2) The amount of metal ions contained in the obtained solution component is measured by ICP-AES or the like.

  As described above, the amount of excess metal ions derived from the pigment is reduced below a certain level in the active ray curable inkjet ink of the present invention. Therefore, it is possible to suppress excessive metal ions derived from the pigment from forming a salt with the acidic group of the pigment dispersant; inhibiting the crystallization of the gelling agent. Therefore, the ink of the present invention has high pinning properties, can suppress the coalescence of adjacent dots, and can improve the image quality.

2. Method for producing actinic radiation curable inkjet ink The actinic radiation curable inkjet ink of the present invention includes: 1) a step of preparing a pigment having an impurity metal ion content of 60 mass ppm or less in the pigment; and 2) preparation. And a step of mixing the pigmented compound, the polymerizable compound, the pigment dispersant having an acidic group, and the gelling agent under heating.

  The pigment having an impurity metal ion content of 60 mass ppm or less in the pigment may be a commercially available product or may be a product obtained by purifying a commercially available pigment. As described above, the content of the pigment in the obtained ink is preferably 1 to 10% by mass.

3. Inkjet recording apparatus and image recording method using the same An actinic radiation curable inkjet recording apparatus used in the present invention will be described. Actinic ray curable ink jet recording apparatuses include a line recording method (single pass recording method) and a serial recording method. The line recording method (single-pass recording method) is preferable from the viewpoint of high-speed recording, although it may be selected according to the required image resolution and recording speed.

  FIG. 1 is a diagram illustrating an example of a configuration of a main part of a line recording type ink jet recording apparatus. Among these, Fig.1 (a) is a side view, FIG.1 (b) is a top view. As shown in FIG. 1, an inkjet recording apparatus 10 includes a head carriage 16 that houses a plurality of ejection recording heads 14, and an actinic ray irradiation unit that is disposed downstream of the head carriage 16 (in the conveyance direction of the recording medium). 18 and a temperature control unit 19 disposed on the lower surface of the recording medium 12.

  The head carriage 16 is fixedly arranged so as to cover the entire width of the recording medium 12 and accommodates a plurality of ejection recording heads 14 provided for each color. Ink is supplied to the ejection recording head 14. For example, the ink may be supplied directly or by an ink supply unit (not shown) from an ink cartridge (not shown) that is detachably attached to the inkjet recording apparatus 10.

  A plurality of ejection recording heads 14 are arranged in the transport direction of the recording medium 12 for each color. The number of ejection recording heads 14 arranged in the conveyance direction of the recording medium 12 is set according to the nozzle density of the ejection recording head 14 and the resolution of the print image. For example, when an image having a resolution of 1440 dpi is formed using the ejection recording head 14 having a droplet amount of 2 pl and a nozzle density of 360 dpi, the four ejection recording heads 14 are shifted with respect to the conveyance direction of the recording medium 12. What is necessary is just to arrange. Further, when an image having a resolution of 720 × 720 dpi is formed using the ejection recording head 14 having a droplet amount of 6 pl and a nozzle density of 360 dpi, the two ejection recording heads 14 may be arranged in a shifted manner. dpi represents the number of ink droplets (dots) per 2.54 cm.

  The actinic radiation irradiating unit 18 covers the entire width of the recording medium 12 and is arranged on the downstream side of the head carriage 16 in the recording medium conveyance direction. The actinic radiation irradiation unit 18 irradiates the droplets ejected by the ejection recording head 14 and landed on the recording medium with the actinic radiation to cure the droplets.

In the case where the active ray is ultraviolet rays, the active ray irradiation unit 18 (ultraviolet irradiation means) is preferably a high-pressure mercury lamp, metal halide lamp, LED, or the like because it can irradiate ultraviolet rays having an illuminance of 100 mW / cm ² or more. An LED is more preferable because of its low electric power. Specifically, a 395 nm, water-cooled LED manufactured by Phoseon Technology can be used.

  When the actinic ray is an electron beam, examples of the actinic ray irradiation unit 18 (electron beam irradiation means) include electron beam irradiation means such as a scanning method, a curtain beam method, and a broad beam method. Therefore, a curtain beam type electron beam irradiation means is preferable. Examples of the electron beam irradiation means include “Curetron EBC-200-20-30” manufactured by Nissin High Voltage Co., Ltd., “Min-EB” manufactured by AIT Co., Ltd., and the like.

  The temperature control unit 19 is disposed on the lower surface of the recording medium 12 and maintains the recording medium 12 at a predetermined temperature. The temperature control unit 19 can be, for example, various heaters.

  Hereinafter, an image recording method using the line recording type inkjet recording apparatus 10 will be described. The recording medium 12 is conveyed between the head carriage 16 and the temperature control unit 19 of the inkjet recording apparatus 10. On the other hand, the recording medium 12 is adjusted to a predetermined temperature by the temperature control unit 19. Next, high-temperature ink is ejected from the ink ejection recording head 14 of the head carriage 16 and adhered (landed) on the recording medium 12. Then, the actinic radiation irradiating unit 18 irradiates the ink droplets attached on the recording medium 12 with the actinic radiation and cures the ink droplets.

  The temperature of the ink in the ejection recording head 14 when ejecting ink from the ink ejection recording head 14 is preferably 80 to 140 ° C. in order to improve the ink ejection properties. If the ink temperature in the ejection recording head 14 is less than 80 ° C., the ink gels in the ejection recording head 14 or on the nozzle surface, and the ink ejection property tends to be lowered. On the other hand, when the temperature of the ink in the ejection recording head 14 exceeds 140 ° C., the ink becomes too high, and the ink component may deteriorate.

  The amount of droplets ejected from each nozzle of the ink ejection recording head 14 is 0.5 pl to 2.5 pl in order to form a high resolution image, although it depends on the resolution of the image. It is preferable.

  Irradiation with actinic radiation is performed within 0.001 to 1 second, preferably 0.001 to 0.5 after the ink droplets are deposited on the recording medium, in order to prevent the adjacent ink droplets from coalescing. Preferably it is performed within seconds. The irradiation of the active ray is preferably performed after ink is ejected from all the ink ejection recording heads 14 accommodated in the head carriage 16.

  When the active ray is an electron beam, the acceleration voltage of electron beam irradiation is preferably 30 to 250 kV and more preferably 30 to 100 kV in order to perform sufficient curing. When the acceleration voltage is 100 to 250 kV, the electron beam irradiation amount is preferably 30 to 100 kGy, and more preferably 30 to 60 kGy.

  The ink film thickness after curing is preferably 2 to 25 μm.

  As described above, the actinic radiation curable ink-jet ink of the present invention has reduced excessive metal ions derived from the pigment. Therefore, the actinic radiation curable ink-jet ink of the present invention is ejected from the ejection recording head 14 and landed on the recording medium 12, and immediately becomes a gel when the temperature becomes below the gelation temperature. Therefore, good pinning properties are obtained, and dot coalescence is suppressed. The ink droplets of the present invention that have become a gel on the recording medium 12 are cured by irradiation with actinic rays and fixed on the recording medium. Thereby, even when an image is formed at a high speed, a high-quality image can be formed.

  FIG. 2 is a diagram illustrating an example of a configuration of a main part of the serial recording type inkjet recording apparatus 20. As shown in FIG. 2, the inkjet recording apparatus 20 has a width narrower than the entire width of the recording medium, instead of the head carriage 16 fixedly arranged so as to cover the entire width of the recording medium, and a plurality of ink ejection devices. Except for having a head carriage 26 that accommodates the recording head 24 and a guide portion 27 for moving the head carriage 26 in the width direction of the recording medium 12, the configuration can be the same as in FIG.

  In the serial recording type inkjet recording apparatus 20, the head carriage 26 ejects ink from the ejection recording head 24 accommodated in the head carriage 26 while moving in the width direction of the recording medium 12 along the guide portion 27. After the head carriage 26 has completely moved in the width direction of the recording medium 12 (for each pass), the recording medium 12 is fed in the transport direction. Except for these operations, an image is recorded in substantially the same manner as the line recording type inkjet recording apparatus 10 described above.

  In the following, the invention will be described in more detail with reference to examples. These examples do not limit the scope of the present invention.

1. Preparation of Pigment Dispersion 1) Preparation of Pigment Dispersion 1 The following pigment dispersant and polymerizable compound were placed in a stainless beaker and dissolved by heating and stirring for 1 hour while heating on a 65 ° C. hot plate. The resulting solution was cooled to room temperature, the following pigment was added, and the mixture was sealed in a glass bottle with 200 g of zirconia beads having a diameter of 0.5 mm, and dispersed with a paint shaker for 8 hours. Thereafter, the zirconia beads were removed to prepare a pigment dispersion 1 having the following composition.

[Composition of Pigment Dispersion Liquid 1]
Pigment dispersant: Ajisper PB824 (manufactured by Ajinomoto Fine Techno Co., polyallylamine derivative, acid value 40 mgKOH / g)
9 parts by mass Polymerizable compound: NK ester 4G (manufactured by Shin-Nakamura Chemical Co., Ltd., polyethylene glycol # 200 dimethacrylate) 71 parts by mass Pigment: Pigment Red 57: 1 (manufactured by Dainichi Seika, Red No. 8, metal ions constituting the pigment) Content: 10.3 mass%, content of metal ions other than metal ions constituting the pigment (excess metal ions): 806 mass ppm before cleaning (Fe43, Ca491, Mg204, Sr2, Ba1, Al15, Mo50 ppm) 46 mass ppm after washing)
20 parts by mass

2) Preparation of Pigment Dispersion 2 Pigment Dispersion 2 having the following composition was prepared in the same manner as in the preparation of Pigment Dispersion 1, except that the type of pigment was changed as follows.
[Composition of Pigment Dispersion Liquid 2]
Pigment dispersant: Ajisper PB824 (manufactured by Ajinomoto Fine Techno Co., Ltd.)
9 parts by mass Polymerizable compound: NK ester 4G (polyethylene glycol # 200 dimethacrylate manufactured by Shin-Nakamura Chemical Co., Ltd.) 71 parts by mass Pigment: Pigment Red 57: 1 (manufactured by Clariant, PermanentRubine L5B 01, content of metal ions constituting the pigment 10.3 mass%, content of metal ions other than metal ions constituting the pigment (excess metal ions): 750 mass ppm before cleaning (Fe41, Cu4, Ni3, Ca482, Mg195, Al25 ppm), 58 mass after cleaning ppm)
20 parts by mass

3) Preparation of Pigment Dispersion 3 Pigment Dispersion 3 having the following composition was prepared in the same manner as in Preparation of Pigment Dispersion 1, except that the type of pigment was changed as follows.
[Composition of Pigment Dispersion Liquid 3]
Pigment dispersant: Ajisper PB824 (manufactured by Ajinomoto Fine Techno Co., Ltd.)
9 parts by mass Polymerizable compound: NK ester 4G (polyethylene glycol # 200 dimethacrylate manufactured by Shin-Nakamura Chemical Co., Ltd.) 71 parts by mass Pigment: Pigment Red 48: 2 (manufactured by Fuji Dye, FujiRed 5R 758, containing metal ions constituting the pigment Amount: 8.7% by mass, content of metal ions other than metal ions constituting the pigment (excess metal ions): 843 mass ppm (Fe39, Cu3, Ni2.5, Ca543, Mg217, Al38 ppm) before washing, washing After 57 mass ppm)
20 parts by mass

4) Preparation of Pigment Dispersion Liquid 4 In the preparation of Pigment Dispersion Liquid 1, the following composition was similarly obtained except that the kind of pigment was changed as follows and the dispersion treatment time in the paint shaker was changed to 5 hours: A pigment dispersion 4 was prepared.
[Composition of Pigment Dispersion Liquid 4]
Pigment dispersant: Ajisper PB824 (manufactured by Ajinomoto Fine Techno Co., Ltd.)
9 parts by mass Polymerizable compound: NK ester 4G (polyethylene glycol # 200 dimethacrylate manufactured by Shin-Nakamura Chemical Co., Ltd.) 71 parts by mass Pigment: Pigment 150 (manufactured by Lanxess, Lavascreen GelbG01, content of metal ions constituting the pigment: 18.7 % By mass, content of metal ions other than metal ions constituting the pigment (excess metal ions): 274 mass ppm before washing (Fe64, Ca44, Mg142, Al20 ppm), 24 mass ppm after washing)
20 parts by mass

5) Preparation of Pigment Dispersion Liquid 5 In the preparation of Pigment Dispersion Liquid 1, the following composition was similarly obtained except that the type of pigment was changed as follows and the dispersion treatment time in the paint shaker was changed to 5 hours: A pigment dispersion 5 was prepared.
[Composition of Pigment Dispersion Liquid 5]
Pigment dispersant: Ajisper PB824 (manufactured by Ajinomoto Fine Techno Co., Ltd.)
9 parts by mass Polymerizable compound: NK ester 4G (polyethylene glycol # 200 dimethacrylate manufactured by Shin-Nakamura Chemical Co., Ltd.) 71 parts by mass Pigment: Pigment Blue 15: 4 (manufactured by Dainichi Seika, Chromofine Blue 6332JC, metal ions constituting the pigment) Content: 12.4 mass%, content of metal ions other than metal ions constituting the pigment (excess metal ions): 1345 mass ppm before washing (Fe164, Ni7, Mg398, Ca 776 ppm), 32 mass ppm after washing )
20 parts by mass

6) Preparation of Pigment Dispersant 6 In the preparation of Pigment Dispersion Liquid 1, the pigment dispersion was similarly changed except that the type of the pigment dispersant was changed to Disperbyk-111 (manufactured by Big Chemie Japan, acid value: 100 mgKOH / g). Liquid 6 was prepared.

7) Preparation of Pigment Dispersion Liquid 7 In Pigment Dispersion Liquid 1, magnesium carbonate is added as a metal salt, and the content of metal ions (excess metal ions) other than metal ions constituting the pigment is 2000 mass ppm. Dispersion 7 was obtained.

2. Ink Preparation (Example 1)
The following components were mixed and stirred at 50 ° C. The obtained solution was filtered through a Teflon (registered trademark) 3 μm membrane filter manufactured by ADVATEC to prepare an ink.

[Ink composition]
Polymerizable compound: APG-200 (Tripropylene glycol diacrylate manufactured by Shin-Nakamura Chemical Co., Ltd.) 25 parts by mass
A-400 (manufactured by Shin-Nakamura Chemical Co., Ltd., polyethylene glycol # 400 diacrylate, 40 parts by mass Gelling agent: 18-pentatriacontanone (acid value: 3 mgKOH / g, amine value: 0 mgKOH / g) 3 parts by weight Photopolymerization initiator : DAROCURE TPO (manufactured by Chiba) 5 parts by mass
ITX (manufactured by DKSH) 2 parts by mass Pigment dispersion: 25 parts by mass of pigment dispersion 1

(Examples 2 to 5)
An ink was prepared in the same manner as in Example 1 except that the type of the pigment dispersion was changed as shown in Table 1.

(Examples 6 to 7)
An ink was prepared in the same manner as in Example 1 except that the type of gelling agent was changed as shown in Table 1.

(Example 8)
An ink was prepared in the same manner as in Example 1 except that the type of the pigment dispersant was changed as shown in Table 1.

(Comparative Examples 1-2)
An ink was prepared in the same manner as in Example 1, except that the type of the pigment dispersion or the presence or absence of the gelling agent was changed as shown in Table 1.

  The viscosity, gelation temperature, ink storage stability, and pigment particle size variation rate of the inks obtained in each Example and Comparative Example were measured by the following methods.

Measurement of Viscosity and Gelation Temperature of Ink The obtained ink was set in a stress control type rheometer (Physica MCR300, manufactured by Anton Paar) capable of controlling temperature. Next, after the ink was heated to 100 ° C., it was cooled to 20 ° C. under conditions of a temperature drop rate of 0.1 ° C./s and a shear rate of 11.7 (/ s), and the dynamic viscoelasticity at the time of temperature drop was measured. The dynamic viscoelasticity was measured using a cone plate (CP75-1, manufactured by Anton Paar) having a diameter of 75.033 mm and a cone angle of 1.017 °. Moreover, temperature control was performed by the Peltier device type | mold temperature control apparatus (TEK150P / MC1) attached to PhysicaMCR300.

In the obtained temperature change curve of dynamic viscoelasticity, the viscosity at 25 ° C. was read and taken as “viscosity at 25 ° C.”. The viscosity of the obtained ink was evaluated based on the following criteria.
A: Viscosity at 25 ° C. of 50,000 mPa · s or more ○: Viscosity at 25 ° C. of 10,000 mPa · s or more and less than 50,000 mPa · s Δ: Viscosity at 25 ° C. of 5000 mPa · s or more and less than 10,000 mPa · s ×: At 25 ° C. Viscosity less than 5000 mPa · s

  Furthermore, from the obtained temperature change curve of the dynamic viscoelasticity, a temperature at which the viscosity becomes 200 mPa · s or more is read and set as a gelation temperature (° C.).

Measurement of storage stability of ink First, the ink was put in a container, and the viscosity (initial viscosity) of the ink at 80 ° C. was measured in the same manner as described above. Next, the container containing the ink was stored in a thermostatic bath at 100 ° C. for 14 days, and the viscosity of the ink at 80 ° C. was measured every day. Then, the number of days required for the viscosity after storage at 80 ° C. to increase by 1 mPa · s with respect to the initial viscosity before storage was evaluated. Then, the storage stability of the ink was evaluated based on the following criteria.
◎: The number of days required for the viscosity to increase by 1 mPa · s is 14 days or more. ○: The number of days required for the viscosity to increase by 1 mPa · s is 7 days or more and less than 14 days. △: The number of days required for the viscosity to increase by 1 mPa · s. 3 days or more and less than 7 days X: The number of days required for the viscosity to increase by 1 mPa · s is less than 3 days

Measurement of variation rate of particle diameter of pigment The average particle diameter r _{0 of the} pigment contained in the ink immediately after preparation and the average particle diameter r _{1 of the} pigment contained in the ink after storage at 100 ° C. for 3 days were determined as Zeta Sizer Nano S90. (Malvern). The average particle diameter r _{0 of} the pigment contained in the obtained ink immediately after preparation and the average particle diameter r ₁ of the pigment contained in the ink after storage were respectively applied to the following formulas to determine the particle size variation rate.
Particle size variation rate (%) = (r ₁ −r ₀ ) / r ₀ × 100

And the particle size variation rate of the pigment particles was evaluated based on the following criteria.
◎: Particle size variation rate is less than 10% ○: Particle size variation rate is 10% or more and less than 20% Δ: Particle size variation rate is 20% or more and less than 30% ×: Particle size variation rate is 30% or more

  Further, an image was formed by the following method using a line-type ink jet recording apparatus, using the ink obtained in each example and comparative example.

Image Forming Method A monochromatic image was formed using the line recording type inkjet recording apparatus shown in FIG. The ink supply system of the ink jet recording apparatus includes an ink tank, a supply pipe, a sub ink tank immediately before the head, a pipe with a filter, and a piezo head (discharge recording head) in this order. Then, the obtained ink was supplied to the ink supply system of the ink jet recording apparatus, and the entire ink supply system from the ink tank to the head portion was heated to 100 ° C.

On the other hand, coated paper A for printing was prepared as a recording medium, and the temperature was adjusted to 25 ° C. by a temperature control unit. Then, ink droplets were ejected onto the coated paper A for printing, and a blank character and a solid image of 5 cm × 5 cm were formed. Thereafter, the ink was cured by irradiating ultraviolet rays with an LED lamp (manufactured by Phoseon Technology, 8 W / cm ² , 395 nm, water cooled unit) disposed in the downstream part of the ink jet recording apparatus to form an image. The ultraviolet irradiation was performed from a position 5 mm away from the coated paper surface.

  A piezo head having a resolution of 360 dpi was used, the applied voltage was adjusted so that the amount of one droplet was 2.0 pl, and an image having a resolution of 1440 dpi × 1440 dpi was recorded. dpi represents the number of dots per 2.54 cm. The image was formed in an environment of 23 ° C. and 55% RH.

  Then, 1) ink ejection stability, 2) character image quality, and 3) solid image uniformity were evaluated by the following methods.

1) Ink ejection stability When the obtained ink was ejected from the piezo head of the ink jet recording apparatus, the missing nozzle was visually observed. The emission stability was evaluated based on the following criteria.
○: No nozzle missing was found Δ: Nozzle missing was found in 1 to 4 nozzles out of 512 nozzles ×: 5 or more nozzles out of 512 nozzles No nozzle missing

2) Character image quality On the coated paper A for printing, the character characters “mouth, fourth, day, times, cause, trouble, gut, country, eyes, figure, country” were printed on the printing paper A. The extracted characters were MS Mincho with a resolution of 1400 dpi × 1440 dpi, 3 points, 4 points, and 5 points. The printed character image was visually observed. The character quality was evaluated based on the following criteria.
◎: All 3 point extracted characters are clearly recorded in detail ○: 3 point extracted characters can be read only partially, but all 4 point extracted characters are readable △: 4 point extracted Only a part of the characters can be read, but all the 5 points can be read. ×: Some 5 points cannot be read.

3) Uniformity of solid image A monochromatic solid image of 1440 × 1440 dpi was formed on the coated paper A for printing by the above-described image forming method. About each obtained image, it was visually observed whether the solid image obtained after 1 m printing and the solid image obtained after 500 m printing were free of white spots (unprinted portions due to dot coalescence). The quality of solid images was evaluated according to the following criteria. Δ or more is a practically favorable range.
○: No white spots △: White spots are observed in one or two places, but there is no practical problem ×: Many white spots occur

Table 1 shows the evaluation results of Examples 1-8 and Comparative Examples 1-2. The “excess metal ion content” in Table 1 is a value calculated from the charged amount of pigment.

  As shown in Table 1, the inks of Examples 1 to 8 in which the content of extra metal ions derived from the pigment is less than 10 ppm by mass have high gelation temperatures and relatively low viscosities at 25 ° C. I understand that it is expensive. Accordingly, it can be seen that the pinning property of the ink is good and the image quality of the obtained image is high.

  On the other hand, the ink of Comparative Example 1 in which the content of extra metal ions derived from the pigment is 10 mass ppm or more has a low gelation temperature, and the ink of Comparative Example 2 that does not contain a gelling agent does not gel in the first place. It can also be seen that the viscosity at 25 ° C. is low. Thereby, it can be seen that the pinning property of the ink is lowered and the image quality of the obtained image is also low.

  Among the inks of Examples 1 to 8, it can be seen that the inks of Examples 6 to 8 have a low gelling temperature and a slightly lower viscosity at 25 ° C. The inks of Examples 6 and 7 are considered to have a low melting point of the gelling agent alone. In the ink of Example 8, since the total of the acid value and the amine value of the pigment dispersant is too high, the pigment dispersant forms a salt with excess metal ions and lowers the melting point of the gelling agent. Conceivable.

  The actinic radiation curable ink-jet ink of the present invention has a good pinning property because gelation failure due to excess metal ions is suppressed. Thereby, a high-definition image can be formed at high speed.

DESCRIPTION OF SYMBOLS 10, 20 Inkjet recording device 12 Recording medium 14, 24 Ink discharge recording head 16, 26 Head carriage 18 Active ray irradiation unit 19 Temperature control unit 27 Guide unit

Claims (8)

A radical polymerizable compound, a lake pigment, a pigment dispersant having an acidic group, a gelling agent and a photo radical polymerization initiator;
The gelling agent is a dialkyl ketone, a fatty acid ester or a higher fatty acid;
The content of metal ions other than the metal ions constituting any one of the radical polymerizable compound, the lake pigment, the pigment dispersant, the gelling agent, and the photo radical polymerization initiator is less than 10 ppm by mass, An actinic radiation curable inkjet ink having a viscosity of 1000 mPa · s or more measured at 25 ° C. and a shear rate of 11.7 / s with a cone plate rheometer having a diameter of 75 mm and a cone angle of 1.0 °. The actinic radiation curable inkjet ink according to claim 1 , wherein an acid value of the pigment dispersant is 5 mgKOH / g or more and less than 50 mgKOH / g. The actinic radiation curable inkjet ink according to claim 1 or 2 , wherein the total acid value and amine value of the gelling agent is 0.01 mgKOH / g or more and less than 10 mgKOH / g. The actinic radiation curable inkjet ink according to any one of claims 1 to 3 , wherein the gelling agent is a dialkyl ketone or a fatty acid ester. The ink is a reversible sol-gel phase transition with temperature,
When a cone plate type rheometer with a diameter of 75 mm and a cone angle of 1.0 ° is used to lower the temperature from 100 ° C. to 20 ° C. at a temperature drop rate of 0.1 ° C./s and a shear rate of 11.7 / s, the viscosity is 200 mPa · s. The actinic radiation curable inkjet ink according to any one of claims 1 to 4 , wherein the gelation temperature is 30 ° C or higher and lower than 100 ° C. The content of the lake pigment is 0.1 to 15 mass% relative to the ink, active ray-curable inkjet ink according to any one of claims 1-5. The radical polymerizable compound is a is ethylene oxide-modified (meth) acrylate compounds, active ray curable ink-jet ink according to any one of claims 1-6. A step of causing the droplets of the actinic radiation curable inkjet ink according to any one of claims 1 to 7 to be ejected from a recording head and adhered onto a recording medium;
And a step of irradiating the ink droplets adhering to the recording medium with an actinic radiation to cure the ink droplets.

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