JP2017105902A - Active ray curable ink jet ink and image formation method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an active ray curable ink jet ink that prevents components in a cured film from being deposited on the surface, and has excellent surface curability, and an image formation method using the same.SOLUTION: An active ray curable ink jet ink contains a photopolymerizable compound, a photoinitiator, and a gelator, wherein the photopolymerizable compound substantially consists of only a polyfunctional photopolymerizable compound, and the photoinitiator comprises a compound represented by a specific general formula.SELECTED DRAWING: None

Description

  The present invention relates to an actinic ray curable inkjet ink and an image forming method.

  Inkjet image formation is used in various printing fields because it can be used for small-lot, multi-product production. As one of the image forming methods by ink jet, there is a method in which droplets of ink jet ink landed on a recording medium are cured with actinic rays (hereinafter also referred to as “actinic ray curable ink jet recording method”). According to the actinic ray curable ink jet recording method, a highly adhesive coating film can be formed on a recording medium having no water absorption or oil absorption.

  Here, the actinic radiation curable inkjet ink usually contains a photopolymerizable compound, a photoinitiator, and the like. The cured film of the actinic radiation curable inkjet ink is likely to contain an unreacted photopolymerizable compound, an unreacted photoinitiator, a photoinitiator residue, and the like. Therefore, the actinic ray effect type ink jet recording method has a problem that these compounds are deposited on the surface of the cured film over time (hereinafter, this phenomenon is also referred to as “migration”).

  In response to such problems, actinic ray curable inkjet inks containing a relatively high molecular weight photoinitiator and a polyfunctional photopolymerizable compound have been proposed (Patent Documents 1 and 2). In the ink, migration is suppressed by increasing the reactivity of the photopolymerizable compound and making it difficult for the photoinitiator or the like to move in the cured film.

JP 2013-209518 A European Patent Application No. 2606663

  As described above, according to the actinic ray curable ink jet recording method, printing on various recording media is possible. Therefore, application of the actinic ray curable ink jet recording method to printing of food packages and the like has also been studied. However, food packages have strict regulations (for example, Swiss Ordinance) from the viewpoint of food safety and environmental protection, and there are also restrictions on the migration amount of the ink cured film. In the actinic ray curable inkjet inks of Patent Document 1 and Patent Document 2 described above, migration can be suppressed to some extent, but for application to various uses such as food packages, the amount of migration is further reduced. Is desired. In addition, the actinic ray curable inkjet inks of Patent Document 1 and Patent Document 2 may have insufficient surface curability and further increase the surface curability.

  The present invention has been made in view of the above problems, and an actinic ray curable ink-jet ink in which components in a cured film hardly precipitate on the surface and has good surface curability, and an image forming method using the same. It is to provide.

（一般式（１）中、ｎは１以上３０以下の整数を表す） The first of the present invention is the following actinic ray curable inkjet ink.
[1] An actinic ray curable inkjet ink containing a photopolymerizable compound, a photoinitiator, and a gelling agent, wherein the photopolymerizable compound consists essentially of a polyfunctional photopolymerizable compound, The actinic ray curable inkjet ink, wherein the photoinitiator contains a compound represented by the following general formula (1).

(In general formula (1), n represents an integer of 1-30)

（一般式（Ｇ１）及び（Ｇ２）中、Ｒ^１〜Ｒ^４は、それぞれ独立に、炭素数１２以上２６以下の直鎖部分を含むアルキル基を表す）
［５］前記光重合性化合物が、プロピレンオキサイド変性（メタ）アクリレート化合物、及びエチレンオキサイド変性（メタ）アクリレート化合物のうちいずれか一方を少なくとも含み、前記プロピレンオキサイド変性（メタ）アクリレート化合物及び前記エチレンオキサイド変性（メタ）アクリレート化合物の総量が、前記活性光線硬化型インクジェットインクの全質量に対して３０質量％以上９７質量％以下であることを特徴とする、［１］〜［４］のいずれかに記載の活性光線硬化型インクジェットインク。 [2] The actinic ray curable inkjet ink according to [1], wherein the photoinitiator further contains an acylphosphine compound.
[3] The actinic ray curable inkjet ink according to [1] or [2], wherein the photoinitiator further includes a thioxanthone compound having a molecular weight of 300 or more and 3000 or less.
[4] The gelling agent according to any one of [1] to [3], wherein the gelling agent includes at least one compound among the compounds represented by the following general formulas (G1) and (G2). The actinic ray curable inkjet ink described.

(In the general formulas (G1) and (G2), R ^{1 to} R ⁴ each independently represents an alkyl group containing a straight chain portion having 12 to 26 carbon atoms)
[5] The photopolymerizable compound includes at least one of a propylene oxide-modified (meth) acrylate compound and an ethylene oxide-modified (meth) acrylate compound, and the propylene oxide-modified (meth) acrylate compound and the ethylene oxide. Any one of [1] to [4], wherein the total amount of the modified (meth) acrylate compound is 30% by mass to 97% by mass with respect to the total mass of the actinic radiation curable inkjet ink. The actinic ray curable inkjet ink described.

The second of the present invention is the following image forming method.
[6] A step of ejecting the actinic ray curable inkjet ink according to any one of [1] to [5] from a nozzle of an inkjet recording apparatus and landing on the recording medium, and the activity landing on the recording medium And a step of irradiating the light curable inkjet ink with an actinic ray to cure the actinic ray curable inkjet ink.

  According to the actinic ray curable ink-jet ink of the present invention, a cured film having a high surface curability can be obtained in which components in the cured film are hardly deposited on the surface.

1. Actinic ray curable inkjet ink The actinic ray curable inkjet ink of the present invention includes a photopolymerizable compound, a photoinitiator, and a gelling agent. In the present specification, “actinic ray curable inkjet ink” (hereinafter also referred to as “ink”) means an ink composition that can be cured by actinic rays, and “active rays” It means a light beam that can activate the photoinitiator and cure the ink. Examples of actinic rays include α rays, γ rays, X rays, ultraviolet rays, electron beams and the like. The actinic rays for curing the ink of the present invention are preferably ultraviolet rays and electron beams, and more preferably ultraviolet rays, from the viewpoints of availability of a light irradiation device and ink curability.

  As described above, the conventional actinic radiation curable inkjet ink has a problem that unreacted photopolymerizable compounds, photoinitiators, photoinitiator residues, and the like remaining in the cured film migrate. Therefore, in the techniques of Patent Document 1 and Patent Document 2 described above, the migration amount is reduced by combining a polyfunctional photopolymerizable compound and a relatively high molecular weight photoinitiator. However, in this method, the effect of suppressing migration is insufficient, and it has been required to further reduce the migration amount. It has also been desired to further improve the surface curability of the cured film.

  In contrast, in the present invention, migration is suppressed by combining a gelling agent, a photoinitiator having a specific structure, and a polyfunctional photopolymerizable compound. Specifically, (i) the absolute amount of components easily migrated contained in the cured film is reduced, and (ii) the migration amount is reduced by suppressing the movement of each component in the cured film. At the same time, the surface curability and internal curability of the ink are also improved. Hereinafter, these will be described.

  (I) In a general radical-active light curable ink-jet ink, oxygen reacts with radical active species during irradiation with active light, and polymerization of the photopolymerizable compound may be inhibited. On the other hand, since the ink of the present invention contains a gelling agent, the ink after landing on the recording medium gels. When the ink gels, the viscosity of the ink increases, and oxygen hardly diffuses and penetrates into the coating film. As a result, oxygen inhibition (hardening failure) hardly occurs on the surface of the ink coating film, and unreacted photopolymerizable compound and unreacted photoinitiator hardly remain in the cured film.

  In addition, the ink of the present invention contains a compound represented by the following general formula (1) as a photoinitiator. The said compound has the outstanding decomposition | disassembly performance, and generates a radical efficiently by actinic light irradiation. Therefore, the photopolymerizable compound can be sufficiently reacted, and the unreacted photopolymerizable compound hardly remains in the cured film. In addition, the compound represented by the general formula (1) includes a structure (amine) that traps oxygen in the molecule and performs chain transfer. Therefore, since the said compound suppresses the above-mentioned oxygen inhibition, the amount of unreacted photopolymerizable compounds can be reduced.

  In addition, the ink of the present invention contains substantially only a polyfunctional photopolymerizable compound as the photopolymerizable compound. Since the polyfunctional photopolymerizable compound has two or more reactive functional groups, the reaction efficiency is high. Therefore, when the photopolymerizable compound is composed only of the polyfunctional photopolymerizable compound, the unreacted photopolymerizable compound hardly remains in the cured film.

  That is, in the ink of the present invention, a combination of a gelling agent, a photoinitiator having a specific structure, and a polyfunctional photopolymerizable compound allows an unreacted photopolymerizable compound and an unreacted compound contained in the cured film of the ink. The amount of photoinitiator (component that easily migrates) can be greatly reduced. At the same time, the cured film has excellent surface curability and internal curability.

  (Ii) On the other hand, the ink of the present invention gels after landing on the recording medium, but even after the ink is cured, the movement of each component is suppressed by the action of the gelling agent. In addition, the cured film of the ink of the present invention includes a two-dimensional or three-dimensional network generated by polymerization of a photopolymerizable compound. Therefore, even if the cured film contains an unreacted photopolymerizable compound, an unreacted photoinitiator, a photoinitiator residue, etc., these movements are suppressed, and the components in the cured film remain on the surface. It becomes difficult to precipitate.

  Furthermore, the photoinitiator represented by the above general formula (1) has a high affinity with the photopolymerizable compound and the gelling agent, and the photopolymerizable compound cured product or gelled in the cured film of the ink. Interacts with the agent. Therefore, the unreacted photoinitiator and its residue contained in the cured film are unlikely to move through the cured film and hardly deposit on the surface. Furthermore, since the photoinitiator has a relatively long molecular chain, it is easily captured by a network formed by a cured product of a photopolymerizable compound, and therefore, it is difficult to move in the cured film.

  That is, in the ink of the present invention, the combination of the gelling agent, the photoinitiator having a specific structure, and the polyfunctional photopolymerizable compound can sufficiently suppress the movement of various components contained in the cured film of the ink. it can.

  Based on the above, according to the ink of the present invention, the amount of the component deposited on the surface of the cured film can be extremely reduced, and the surface curability and internal curability of the cured film can be greatly enhanced. Hereinafter, each component included in the actinic ray curable inkjet ink of the present invention will be described, and then the physical properties of the ink will be described.

(1) Photopolymerizable compound The photopolymerizable compound is a compound that crosslinks or polymerizes upon irradiation with actinic rays. The photopolymerizable compound contained in the actinic ray curable inkjet ink of the present invention is substantially composed of a polyfunctional photopolymerizable compound. In the present specification, the “polyfunctional photopolymerizable compound” means a photopolymerizable compound having two or more photopolymerizable functional groups. “Substantially” means that the photopolymerizable compound having only one photopolymerizable functional group (also referred to as monofunctional photopolymerizable compound) is 10% by mass or less based on the total mass of the photopolymerizable compound. Means. As for content of a monofunctional photopolymerizable compound, it is more preferable that it is 5 mass% or less with respect to the photopolymerizable compound total mass, and it is especially preferable that it is not contained.

  When the photopolymerizable compound consists essentially of a polyfunctional photopolymerizable compound, as described above, when the ink coating is irradiated with an actinic ray, the reaction efficiency of the photopolymerizable compound is improved, and the cured film contains It becomes difficult for unreacted photopolymerizable compounds to remain.

  The polyfunctional photopolymerizable compound may be any compound that contains two or more polymerizable groups in the molecule (however, at least one radical polymerizable group), and has two or more radical polymerizable groups. A compound is preferred. Examples of polyfunctional photopolymerizable compounds having two or more radically polymerizable groups include compounds having two or more ethylenically unsaturated bonds in the molecule (monomers, oligomers, polymers, or mixtures thereof), etc. It is. Only one type of polyfunctional photopolymerizable compound may be contained in the ink of the present invention, or two or more types may be contained.

  More specifically, the polyfunctional polymerizable compound is preferably an unsaturated carboxylic acid ester compound having 2 or more unsaturated groups in the molecule, and 2 or more and 6 or less (meth) in the molecule. More preferably, it is a compound having an acrylate group (hereinafter also referred to as “(meth) acrylate compound”). The (meth) acrylate compound may be a monomer, but may be an oligomer in which these are polymerized or a mixture of a monomer and an oligomer. In the present specification, the “(meth) acrylate group” includes an acrylate group and a methacrylate group.

Examples of (meth) acrylate compounds include triethylene glycol di (meth) acrylate, tetraethylene 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, tricyclodecane dimethanol di (meth) acrylate, hydroxypivalate neopentyl glycol di (meth) acrylate, polytetramethylene glycol Bifunctional acrylate monomers such as di (meth) acrylate, 3-methylpentanediol diacrylate, 2- (2-vinylethoxy) ethyl acrylate;
Trimethylolpropane tri (meth) acrylate, pentaerythritol tri (meth) acrylate, pentaerythritol tetra (meth) acrylate, dipentaerythritol hexa (meth) acrylate, ditrimethylolpropane tetra (meth) acrylate, glycerin propoxytri (meth) acrylate , Trifunctional or higher acrylate monomers such as pentaerythritol ethoxytetra (meth) acrylate;
And oligomers thereof.

  Here, the polyfunctional photopolymerizable compound is a propylene oxide-modified (meth) acrylate compound or an ethylene oxide-modified (meth) acrylate compound in which the (meth) acrylate compound is modified with propylene oxide or ethylene oxide. Particularly preferred. “Modified with propylene oxide or ethylene oxide” means that one or more repeating units composed of propylene oxide or ethylene oxide are introduced into the molecular chain. The number of repeating units composed of propylene oxide or ethylene oxide contained in the propylene oxide-modified (meth) acrylate compound or ethylene oxide-modified (meth) acrylate compound is 1 or more and 14 or less for one (meth) acrylate group. Is preferably 3 or more and 14 or less. When the number of repeating units composed of propylene oxide or ethylene oxide groups is in the above range, the following effects are easily obtained.

  The photoinitiator represented by the general formula (1) described later has an ethylene oxide group. Therefore, when the polyfunctional photopolymerizable compound has an ethylene oxide group or a propylene oxide group, their affinity becomes very high, and unreacted photoinitiator or photoinitiator residue is left in the cured film of the ink. It becomes difficult to move. That is, these compounds are difficult to migrate.

  In addition, when an ethylene oxide-modified (meth) acrylate compound or a propylene oxide-modified (meth) acrylate compound is combined with a gelling agent that can form a card house structure, these can easily interact to form a card house structure. The pinning property of the ink becomes very high. Further, the ethylene oxide-modified (meth) acrylate compound and the propylene oxide-modified (meth) acrylate compound are easily dissolved in other components at a high temperature. Furthermore, since they are less likely to shrink during curing, the resulting printed matter is less likely to curl.

  The total amount of the propylene oxide-modified (meth) acrylate compound and the ethylene oxide-modified (meth) acrylate compound contained in the ink is preferably 30% by mass to 97% by mass with respect to the total mass of the ink, and 35% by mass. It is more preferably 90% by mass or less, and further preferably 40% by mass or more and 85% by mass or less. When the content of the propylene oxide-modified (meth) acrylate compound and the ethylene oxide-modified (meth) acrylate compound is 30% by mass or more, the above-described migration suppressing effect and the like are easily obtained. On the other hand, when the content of the propylene oxide-modified (meth) acrylate compound and the ethylene oxide-modified (meth) acrylate compound is 97% by mass or less, the amount of the photoinitiator or gelling agent is relatively sufficient, Curability and pinning properties are likely to increase.

  Examples of ethylene oxide modified (meth) acrylate compounds include polyethylene glycol di (meth) acrylate, ethylene oxide modified trimethylolpropane tri (meth) acrylate, ethylene oxide modified pentaerythritol tetra (meth) acrylate, ethylene oxide modified hexanediol di Acrylate and the like are included.

  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 529); polyethylene glycol # 400 diacrylate (NK ester A-400 (molecular weight 508)) manufactured by Shin-Nakamura Chemical Co., polyethylene glycol # 600 diacrylate (NK ester A-600 (molecular weight 742)), polyethylene glycol dimethacrylate (NK ester 9G (molecular weight 536)), polyethylene glycol Call dimethacrylate (NK ester 14G (molecular weight 770); Osaka Organic Chemical Industry Co., Ltd. of tetraethylene glycol diacrylate (V # 335HP (molecular weight 302)); and the like.

  On the other hand, examples of the propylene oxide-modified (meth) acrylate compound include polypropylene glycol di (meth) acrylate, propylene oxide-modified neopentyl glycol di (meth) acrylate, propylene oxide adduct di (meth) acrylate of bisphenol A, and glycerin propoxy. Tri (meth) acrylate and the like are included.

  Examples of commercially available propylene oxide-modified (meth) acrylate compounds include 3PO-modified trimethylolpropane triacrylate (Photomer 4072 (molecular weight 471)) manufactured by Cognis, dipropylene glycol diacrylate (NK ester) manufactured by Shin-Nakamura Chemical Co., Ltd. APG-100 (molecular weight 242)), tripropylene glycol diacrylate (NK ester APG-200 (molecular weight 300)), polypropylene glycol # 400 diacrylate (NK ester APG-400 (molecular weight 533)), polypropylene glycol # 700 diacrylate (NK ester APG-700 (molecular weight 823)), 6PO-modified trimethylolpropane triacrylate CD501 (molecular weight 645) manufactured by Sartomer, and the like are included.

  In addition, the polyfunctional photopolymerizable compound may be an oligomer obtained by polymerizing the above-described (meth) acrylate compound and a compound having another functional group. Examples of such oligomers include epoxy (meth) acrylate oligomers, aliphatic urethane (meth) acrylate oligomers, aromatic urethane (meth) acrylate oligomers, polyester (meth) acrylate oligomers, and the like.

  The total amount of the above-described photopolymerizable compound is preferably 1% by mass or more and 97% by mass or less, and more preferably 30% by mass or more and 95% by mass or less with respect to the total mass of the ink. When the total amount of the photopolymerizable compound is 1% by mass or more, a cured film having high strength can be obtained. On the other hand, when the total amount of the photopolymerizable compound is 97% by mass or less, the amount of the photoinitiator and the gelling agent is relatively sufficient, the curability is good, and a cured film with a small migration amount is obtained. It becomes easy.

上記一般式中、ｎは１以上３０以下の整数を表す。なお、本発明のインクには、光開始剤として、ｎの値が異なる複数種類の一般式（１）で表される化合物が含まれていてもよい。上記一般式（１）で表される化合物の市販品の例には、Ｏｍｉｎｏｐｏｌ ９１０（ＩＧＭ社製）が含まれる。 (2) Photoinitiator The ink of the present invention includes a radical initiator that is activated by irradiation with actinic rays to generate radicals as a photoinitiator. The photoinitiator includes at least a compound represented by the following general formula (1).

In the above general formula, n represents an integer of 1 to 30. In addition, the ink of this invention may contain the compound represented by multiple types of general formula (1) from which the value of n differs as a photoinitiator. Examples of commercial products of the compound represented by the general formula (1) include Ominopol 910 (manufactured by IGM).

  The compound represented by the general formula (1) is preferably contained in an amount of 0.1% by mass to 12% by mass and more preferably 1% by mass to 10% by mass with respect to the total mass of the ink. Preferably, it is more preferably 2% by mass or more and 8% by mass or less. When the amount of the compound represented by the general formula (1) is 0.1% by mass or more, the surface curability of the ink is likely to be sufficiently increased, and oxygen inhibition is easily suppressed. When the amount of the compound is 12% by mass or less, the amount of unreacted photoinitiator and the amount of photoinitiator residue can be reduced, and migration is easily suppressed.

  The ink of the present invention preferably further contains an acylphosphine compound and a thioxanthone compound as a photoinitiator. When these compounds are contained, the curability of the ink is further increased, and the amount of the unreacted photopolymerizable compound remaining in the cured product can be reduced.

  Examples of the acylphosphine compounds include benzoins such as benzoin, benzoin methyl ether, and benzoin isopropyl ether; bis (2,4,6-trimethylbenzoyl) -phenylphosphine oxide and the like. Examples of commercially available acylphosphine compounds include IRGACURE819 (manufactured by BASF) and DAROCURE TPO (manufactured by BASF). The ink of the present invention may contain only one kind of acylphosphine compound or two or more kinds. Among the above compounds, IRGACURE819 is particularly preferable from the viewpoint of migration suppression and surface curability.

  The acylphosphine compound preferably has a molecular weight (however, in the case of an oligomer, a weight average molecular weight) of 210 or more and 3000 or less. When the molecular weight of the acylphosphine compound is 310 or more, the acylphosphine compound and the residue thereof are difficult to migrate in the cured film of the ink. On the other hand, when the molecular weight is 3000 or less, the compatibility between the acylphosphine compound and other components in the ink is improved. As described above, when the acylphosphine compound is an oligomer, its molecular weight is determined by a weight average molecular weight, and the weight average molecular weight is a polystyrene equivalent molecular weight measured by gel permeation chromatography (GPC).

  The acylphosphine compound is preferably contained in an amount of 0.01% by mass or more and 12% by mass or less, more preferably 1% by mass or more and 10% by mass or less, and more preferably 2% by mass or more and 8% by mass with respect to the total mass of the ink. % Or less is more preferable. When the amount of the acylphosphine compound is 0.01% by mass or more, the internal curability of the ink is likely to be sufficiently increased, and migration is easily suppressed in the cured film. Further, when the amount of the acylphosphine compound is 12% by mass or less, it is difficult for the surplus photoinitiator to remain in the cured product, and the migration amount is easily reduced.

  On the other hand, examples of the thioxanthone compound include 2-isopropylthioxanthone, 2,4-dimethylthioxanthone, 2,4-diethylthioxanthone, 2,4-dichlorothioxanthone and the like. Examples of commercially available thioxanthone compounds include SPEEDCURE 7010 (manufactured by Lambson), SPEEDCURE CPTX (manufactured by Lambson), SPEEDCURE ITX (manufactured by Lambson), and the like. The ink of the present invention may contain only one type of thioxanthone compound or two or more types.

  The molecular weight of the thioxanthone compound (however, in the case of an oligomer, the weight average molecular weight) is preferably 300 or more and 3000 or less from the viewpoint of suppression of migration amount and ejection stability. As described above, when the thioxanthone compound is an oligomer, its molecular weight is determined by a weight average molecular weight, and the weight average molecular weight is a polystyrene-equivalent molecular weight measured by gel permeation chromatography (GPC).

  The thioxanthone compound is preferably contained in an amount of 0.01% by mass or more and 12% by mass or less, more preferably 1% by mass or more and 10% by mass or less, and more preferably 2% by mass or more and 8% by mass with respect to the total mass of the ink. More preferably, it is contained below. When the amount of the thioxanthone compound is 0.01% by mass or more, the surface curability of the ink is likely to increase. Further, when the amount of the thioxanthone compound is 12% by mass or less, it is difficult for an excess photoinitiator to remain in the cured product, and migration is easily suppressed.

  The total amount of the photoinitiator is preferably 0.1% by mass or more and 12% by mass or less, more preferably 1% by mass or more and 10% by mass or less, and further preferably 2% by mass with respect to the total mass of the ink. % To 8% by mass.

(3) Gelling agent The actinic ray curable inkjet ink of the present invention contains a gelling agent. In the present specification, the “gelling agent” means an organic substance that becomes a solid at room temperature and becomes a liquid when heated, and has a function of reversibly changing the sol-gel phase of the ink depending on the temperature.

  Here, the gelling agent is preferably a compound that crystallizes below the gelation temperature of the ink. The ink gelation temperature refers to a temperature at which the viscosity of the ink changes suddenly when the ink that has been sol- lated or liquefied by heating is cooled and the gelling agent undergoes a phase transition from sol to gel. Specifically, the sol or liquefied ink is cooled while measuring the viscosity with a viscoelasticity measuring device (for example, MCR300, manufactured by Physica), and the temperature at which the viscosity rapidly increases is determined by the ink gel. Temperature.

  When the gelling agent is crystallized in the ink, a structure in which the photopolymerizable compound is included in the three-dimensional space formed by the gelling agent that has been crystallized in a plate shape may be formed (such a structure). Hereinafter also referred to as “card house structure”). When the card house structure is formed, the photopolymerizable compound is held in the space, so that the ink droplets are less likely to spread and the pinning property of the ink is improved. When the pinning property of the ink is increased, the ink droplets that have landed on the recording medium are less likely to coalesce, and a higher definition image can be formed.

  In order to retain the photopolymerizable compound in the card house structure, it is preferable that the photopolymerizable compound and the gelling agent are compatible in the ink. If the photopolymerizable compound and the gelling agent are phase-separated in the ink, the photopolymerizable compound may be difficult to be retained in the card house structure. Moreover, it is preferable that the compatibility between the photopolymerizable compound and the gelling agent is good from the viewpoint of stably discharging ink droplets from the ink jet recording apparatus.

  In addition, when the gelling agent forms a card house structure, in the cured film of the ink, the card house structure composed of the gelling agent also includes an unreacted photopolymerizable compound, an unreacted photoinitiator, a photoinitiator residue, etc. It functions as a filter that suppresses movement. In other words, in addition to the network made of the cured product of the photopolymerizable compound described above, a filter made of a gelling agent is formed in the cured film of the ink, so that the movement of components in the cured film is further suppressed. It becomes easy.

  Examples of gelling agents include aliphatic ketone compounds; aliphatic ester compounds; petroleum waxes such as paraffin wax, microcrystalline wax, and petrolactam; candelilla wax, carnauba wax, rice wax, wood wax, Plant waxes such as jojoba oil, jojoba solid wax, and jojoba esters; animal waxes such as beeswax, lanolin and whale wax; mineral waxes such as montan wax and hydrogenated wax; hardened castor oil or hardened castor oil derivatives; Modified waxes such as montan wax derivatives, paraffin wax derivatives, microcrystalline wax derivatives or polyethylene wax derivatives; higher fats such as behenic acid, arachidic acid, stearic acid, palmitic acid, myristic acid, lauric acid, oleic acid, and erucic acid Acid; higher alcohols such as stearyl alcohol and behenyl alcohol; hydroxystearic acid such as 12-hydroxystearic acid; 12-hydroxystearic acid derivatives; lauric acid amide, stearic acid amide, behenic acid amide, oleic acid amide, erucic acid amide, ricinol Fatty acid amides such as acid amides and 12-hydroxystearic acid amides (for example, Nikka Amide series manufactured by Nippon Kasei Co., Ltd. ITOWAX series manufactured by Ito Oil Co., Ltd., FATTYAMID series manufactured by Kao Corporation); N-stearyl stearic acid amide, N-oleyl palmitic acid N-substituted fatty acid amides such as amides; N, N′-ethylenebisstearylamide, N, N′-ethylenebis-12-hydroxystearylamide, and N, N′-xylylenebisstearylamide Special fatty acid amides such as dodecylamine, higher amines such as dodecylamine, tetradecylamine or octadecylamine; stearyl stearic acid, oleyl palmitic acid, glycerin fatty acid ester, sorbitan fatty acid ester, propylene glycol fatty acid ester, ethylene glycol fatty acid ester, polyoxyethylene Fatty acid ester compounds such as fatty acid esters (for example, EMALLEX series manufactured by Nippon Emulsion Co., Ltd., Richemar series manufactured by Riken Vitamin Co., Poem series manufactured by Riken Vitamin Co., Ltd.); Esters of sucrose fatty acids such as sucrose stearic acid and sucrose palmitic acid ( For example, Ryoto Sugar Ester Series manufactured by Mitsubishi Chemical Foods); synthetic waxes such as polyethylene wax and α-olefin maleic anhydride copolymer wax (Ba dimer acid; dimer diol (such as PRIDA series manufactured by CRODA); fatty acid inulin such as stearic acid inulin; fatty acid dextrins such as dextrin palmitate and dextrin myristate (leopard series manufactured by Chiba Flour Mills) Glyceryl behenate; glyceryl behenate; polyglyceryl behenate (NOMCOAT series manufactured by Nisshin Oilio Co., Ltd.); N-lauroyl-L-glutamic acid dibutylamide, N- (2-ethylhexanoyl) -L-glutamic acid Amide compounds such as dibutylamide (available from Ajinomoto Fine Techno); Dibenzylidenes such as 1,3: 2,4-bis-O-benzylidene-D-glucitol (available from Gelol D Shin Nippon Rika) Rubitoru acids; include like; JP 2005-126507, JP-low molecular oil-gelling agents described in JP 2010-111790 and JP 2005-255821 JP.

  The gelling agent preferably contains a linear alkyl group having 12 to 26 carbon atoms in the molecular structure, and the aforementioned “card house structure” is easily formed. The molecular structure of the gelling agent may have a branched chain.

  Specific examples of the gelling agent containing a linear alkyl group having 12 to 26 carbon atoms include aliphatic ketone compounds, aliphatic ester compounds, and higher fatty acids having a linear alkyl group having 12 to 26 carbon atoms. Higher alcohols, fatty acid amides and the like.

The gelling agent is more preferably an aliphatic ketone compound or an aliphatic ester compound, and is preferably a compound represented by the following general formula (G1) or (G2).

In general formulas (G1) and (G2), R ^{1 to} R ⁴ each independently represents an alkyl group containing a straight chain portion having 12 to 26 carbon atoms. R ^{1 to} R ⁴ may include a branched portion.

In the general formula (G1), the alkyl group represented by R ¹ and R ² is not particularly limited, but is preferably an alkyl group including a straight chain portion having 12 to 26 carbon atoms.

  Examples of the aliphatic ketone compound represented by the general formula (G1) include 18-pentatriacontanone (C17-C17), dilignoceryl ketone (C24-C24), dibehenyl ketone (C22-C22), Distearyl ketone (C18-C18), dieicosyl ketone (C20-C20), dipalmityl ketone (C16-C16), dimyristyl ketone (C14-C14), dilauryl ketone (C12-C12), lauryl myristyl ketone (C12-C14), lauryl palmityl ketone (C12-C16), myristyl palmityl ketone (C14-C16), myristyl stearyl ketone (C14-C18), myristyl behenyl ketone (C14-C22), palmityl stearyl ketone (C16) -C18), Valmityl behenyl ketone (C 6-C22), include stearyl and behenyl ketone (C18-C22) and the like.

  Examples of commercially available compounds represented by the general formula (G1) include 18-Pentriacontanon (manufactured by Alfa Aeser), Hentriacontan-16-on (manufactured by Alfa Aeser), Kao wax T1 (manufactured by Kao Corporation), and the like. included. The ink may contain only one kind of aliphatic ketone compound or two or more kinds.

On the other hand, in the general formula (G2), the alkyl group represented by R ³ and R ⁴ is not particularly limited, but is preferably an alkyl group including a linear portion having 12 to 26 carbon atoms.

  Examples of the aliphatic ester compound represented by the general formula (G2) include behenyl behenate (C21-C22), icosyl icosylate (C19-C20), stearyl stearate (C17-C18), and palmityl stearate (C17). -C16), lauryl stearate (C17-C12), cetyl palmitate (C15-C16), stearyl palmitate (C15-C18), myristyl myristate (C13-C14), cetyl myristate (C13-C16), myristic Octyldodecyl acid (C13-C20), stearyl oleate (C17-C18), stearyl erucate (C21-C18), stearyl linoleate (C17-C18), behenyl oleate (C18-C22), myricyl serotate (C25) -C16), montanic acid Teariru (C27-C18), behenyl montanate (C27-C22), arachidyl linoleic acid (C17-C20), include triacontanoic palmityl (C29-C16) and the like.

  Examples of commercially available products of the aliphatic ester compound represented by the general formula (G2) include Unistar M-2222SL (manufactured by NOF Corporation), EXCEPARL SS (manufactured by Kao Corporation), EMALEXCC-18 (Japan Emulsion Co., Ltd.) Product), Amreps PC (manufactured by Higher Alcohol Industry Co., Ltd.), Exepearl MY-M (manufactured by Kao Corporation), Spalm Aceti (manufactured by NOF Corporation), EMALEX CC-10 (manufactured by Nippon Emulsion Co., Ltd.) and the like. Since these commercial products are often a mixture of two or more types, they may be separated and purified as necessary. Further, the ink may contain only one kind of aliphatic ester compound or two or more kinds.

  The ink of the present invention preferably contains two or more types of gelling agents, and particularly preferably contains two or more types of gelling agents selected from the compounds shown in Table 1 below.

  The gelling agent is preferably contained in an amount of 0.5% by mass to 10% by mass and more preferably 1% by mass to 5% by mass with respect to the total mass of the ink.

  When two or more kinds of gelling agents are used in combination, the ratio of each gelling agent is 5% by mass or more and less than 95% by mass, more preferably 20% by mass or more and 80% by mass with respect to the total mass of the gelling agent. It is preferable to adjust so that it may become a ratio of less than mass%.

(4) Other components The ink of the present invention may contain components other than the photopolymerizable compound, the photoinitiator, and the gelling agent, if necessary. Examples of other components include coloring materials, pigment dispersants, polymerization inhibitors, ultraviolet absorbers, antioxidants, and the like.

  The coloring material can be a dye or a pigment, but is preferably a pigment because it has good dispersibility with respect to the components of the ink and is excellent in weather resistance. The pigment is not particularly limited, and may be, for example, an organic pigment or an inorganic pigment having the following numbers described in the color index.

  Examples of red or magenta pigments include Pigment Red 3, 5, 19, 22, 31, 38, 43, 48: 1, 48: 2, 48: 3, 48: 4, 48: 5, 49: 1, 53. : 1, 57: 1, 57: 2, 58: 4, 63: 1, 81, 81: 1, 81: 2, 81: 3, 81: 4, 88, 104, 108, 112, 122, 123, 144 146, 149, 166, 168, 169, 170, 177, 178, 179, 184, 185, 208, 216, 226, 257, Pigment Violet 3, 19, 23, 29, 30, 37, 50, 88, Pigment A pigment selected from Orange 13, 16, 20, 36, or a mixture thereof is included.

  Examples of blue or cyan pigments include Pigment Blue 1, 15, 15: 1, 15: 2, 15: 3, 15: 4, 15: 6, 16, 17-1, 22, 27, 28, 29, 36. , 60 or a mixture thereof.

  Examples of green pigments include pigments selected from Pigment Green 7, 26, 36, 50 or mixtures thereof. Examples of yellow pigments include Pigment Yellow 1, 3, 12, 13, 14, 17, 34, 35, 37, 55, 74, 81, 83, 93, 94, 95, 97, 108, 109, 110, 137. 138, 139, 153, 154, 155, 157, 166, 167, 168, 180, 185, 193, or a mixture thereof.

  Examples of black pigments include pigments selected from Pigment Black 7, 28, 26, or mixtures thereof.

  Examples of commercially available pigments include chromofine yellow 2080, 5900, 5930, AF-1300, 2700L, chromofine orange 3700L, 6730, chromofine scarlet 6750, chromofine magenta 6880, 6886, 6891N, 6790, 6887, chromo Fine Violet RE, Chromo Fine Red 6820, 6830, Chromo Fine Blue HS-3, 5187, 5108, 5197, 5085N, SR-5020, 5026, 5050, 4920, 4927, 4937, 4824, 4933GN-EP, 4940, 4972, 5205, 5208, 5214, 5221, 5000P, chromofine green 2GN, 2GO, 2G-550D, 5310, 5370, 6830, chromophy Black A-1103, Seika Fast Yellow 10GH, A-3, 2035, 2054, 2200, 2270, 2300, 2400 (B), 2500, 2600, ZAY-260, 2700 (B), 2770, Seica Fast Red 8040, C405 (F), CA120, LR-116, 1531B, 8060R, 1547, ZAW-262, 1537B, GY, 4R-4016, 3820, 3891, ZA-215, Seika Fast Carmine 6B1476T-7, 1483LT, 3840, 3870, Seika Fast Bordeaux 10B-430, Seikalite Rose R40, Seikalite Violet B800, 7805, Seika Fast Maroon 460N, Seika Fast Orange 900, 2900, Seika Light Blue C718, A6 12, cyanine blue 4933M, 4933GN-EP, 4940, 4973 (manufactured by Dainichi Seika Kogyo); KET Yellow 401, 402, 403, 404, 405, 406, 416, 424, KET Orange 501, KET Red 301, 302, 303 304, 305, 306, 307, 308, 309, 310, 336, 337, 338, 346, KET Blue 101, 102, 103, 104, 105, 106, 111, 118, 124, KET Green 201 (Dai Nippon Ink Chemical-made); Colortex Yellow 301, 314, 315, 316, P-624, 314, U10GN, U3GN, UNN, UA-414, U263, Finecol Yellow T-13, T-05, Pigmen Yellow 1705, Colortex Orange 202, Colortex Red 101, 103, 115, 116, D3B, P-625, 102, H-1024, 105C, UFN, UCN, UBN, U3BN, URN, UGN, UG276, U456, U457, 105C, USN , Colortex Maron601, Colortex BrownB610N, Colortex violet600, Pigment Red 122, ColortexBlue 516, 517, 518, 519, A818, P-908, 510, Colortex Green402, 403, Color5 Blue G7330, FG7350, FG7400G, FG7405G, ES, ESP-S (manufactured by Toyo Ink), Toner Magenta E02, Permanent RubinF6B, Toner Yellow HG, Permanent Yellow GG-02, Hostape G2 Hostaper Pink E, Hostaperm Blue B2G (manufactured by Clariant); carbon black # 2600, # 2400, # 2350, # 2200, # 1000, # 990, # 980, # 970, # 960, # 950, # 850, MCF88, # 750, # 650, MA600, MA7, MA8, MA11, MA100, MA100R, MA77, # 52, 50, # 47, # 45, # 45L, # 40, # 33, # 32, # 30, # 25, # 20, # 10, # 5, # 44, CF9 (manufactured by Mitsubishi Chemical) and the like.

  The volume average particle diameter of the pigment particles contained in the ink is preferably 0.08 to 0.5 μm, the maximum particle diameter is preferably 0.3 to 10 μm, and more preferably 0.3 to 3 μm. preferable.

  The total amount of the color material is preferably included in the range of 0.1% by mass to 20% by mass and more preferably 0.4% by mass to 10% by mass with respect to the total mass of the ink.

  Further, when the pigment contains the pigment, the ink may contain a pigment dispersant for dispersing the pigment. When the pigment dispersant is contained in the ink, the dispersibility of the pigment increases. The type of the pigment dispersant is not particularly limited, but is preferably a comb block copolymer having a tertiary amine structure in the main chain from the viewpoint of pigment dispersibility. In this specification, “comb block copolymer” refers to a copolymer in which a plurality of types of monomers and polymers are each graft-polymerized in a repeating unit constituting the main chain.

  When a tertiary amine structure is contained in the main chain of the comb block copolymer, the amine is strongly adsorbed on the acidic group on the pigment surface, and the comb type is used even at the ink discharge temperature (for example, about 85 ° C.) from the ink jet recording apparatus. The block copolymer is less likely to dissociate from the pigment. On the other hand, when plural types of monomers and polymers are bonded to the main chain of the comb block copolymer, the compatibility between the comb block copolymer and the photopolymerizable compound is improved. Therefore, when the ink contains a pigment dispersant made of a comb-type block copolymer, the dispersibility of the pigment becomes very good. In addition, although the group couple | bonded with nitrogen of the tertiary amine of a comb-type block copolymer is not specifically limited, It is preferable that it is a C1-C2 alkyl group.

  Specific examples of the comb block copolymer include BYK-2164, BYK-168, BYK N-22024, manufactured by BYK Chemie, BYK JET-9150, BYK JET-9151, manufactured by Altana, EFKA 4310, EFKA 4320, manufactured by BASF. , EFKA 4401, SOLSPERSE 39000 manufactured by Avecia, and Ajisper PB-821 manufactured by Ajinomoto Fine-Techno Co., Ltd. are included.

  Alternatively, the comb block copolymer having a secondary or primary amine may be tertiaryized to obtain a comb block copolymer having a tertiary amine. The method of tertiaryizing a secondary or primary amine can be a known method. For example, a secondary amine or a primary amine can be converted to a tertiary amine by reacting with an alcohol such as decyl alcohol in the presence of a reduction catalyst.

  The pigment dispersant may be a compound other than the comb block copolymer. Examples of other pigment dispersants include hydroxyl group-containing carboxylic acid esters, salts of long chain polyaminoamides and high molecular weight acid esters, salts of high molecular weight polycarboxylic acids, salts of long chain polyaminoamides and polar acid esters, Saturated acid ester, polymer copolymer, modified polyurethane, modified polyacrylate, polyether ester type anionic activator, naphthalene sulfonic acid formalin condensate salt, aromatic sulfonic acid formalin condensate salt, polyoxyethylene alkyl phosphate ester, Polyoxyethylene nonylphenyl ether, stearylamine acetate and the like are included. Examples of commercially available pigment dispersants include the Solsperse series from Avecia, the PB series from Ajinomoto Fine Techno, and the like.

  The ink of the present invention may further contain a dispersion aid as necessary. As the dispersion aid, a known compound is appropriately selected according to the pigment. The total amount of the pigment dispersant and the dispersion aid is preferably 1 to 50% by mass with respect to the total mass of the pigment.

  Further, the ink may further contain a photoinitiator auxiliary agent, a polymerization inhibitor, and the like as necessary. The photoinitiator aid can be a tertiary amine compound, and an aromatic tertiary amine compound is particularly preferable. Examples of aromatic tertiary amine compounds include N, N-dimethylaniline, N, N-diethylaniline, N, N-dimethyl-p-toluidine, N, N-dimethylamino-p-benzoic acid ethyl ester, N, N-dimethylamino-p-benzoic acid isoamyl ethyl ester, N, N-dihydroxyethylaniline, triethylamine, N, N-dimethylhexylamine and the like are included. Of these, N, N-dimethylamino-p-benzoic acid ethyl ester and N, N-dimethylamino-p-benzoic acid isoamyl ethyl ester are preferred. The ink of the present invention may contain only one kind of photoinitiation aid, or two or more kinds thereof. Examples of commercially available photoinitiator aids include SPEDDCURE 7040 from Lambson.

  The content of the photoinitiating aid is preferably 0.1% by mass or more and 5% by mass or less with respect to the total mass of the ink. When the amount of the photoinitiating aid is within the above range, the curability of the ink becomes good.

  Examples of polymerization inhibitors include (alkyl) phenol, hydroquinone, catechol, resorcin, 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, cupron, aluminum N-nitrosophenylhydroxylamine, tri-p-nitrophenylmethyl, N- (3-oxyanilino- 1,3-dimethylbutylidene) aniline oxide, dibutylcresol, cyclohexanone oxime cresol, guaiacol, o-isopropylphenol, butyraloxime, methyl ethyl ketoxime, cyclohexanone oxime, etc. It is included. Examples of commercially available polymerization inhibitors include Irgastab UV10 from BASF.

  The content of the polymerization inhibitor is preferably 0.001% by mass or more and 0.2% by mass or less with respect to the total mass of the ink. When the amount of the polymerization inhibitor is within the above range, the storage stability of the ink is improved.

  Further, the ink of the present invention may contain an ultraviolet absorber, an antioxidant and the like from the viewpoint of enhancing the weather resistance of the cured film. Although a well-known compound can be used for an ultraviolet absorber, it is preferable from the viewpoint of light resistance or ozone tolerance that the end of the absorption wavelength on the long wavelength side is 410 nm or less. The absorption wavelength of the ultraviolet absorber can be determined by measuring an ultraviolet-visible absorption spectrum. From the viewpoint of curability, the content of the ultraviolet absorber is preferably 2% by mass or less, more preferably 1% by mass or less, and 0.5% by mass or less with respect to the total mass of the ink. Is more preferable. On the other hand, from the viewpoint of absorbing the irradiated ultraviolet rays and increasing the light resistance of the cured film, the content of the ultraviolet absorber is preferably 0.1% by mass or more based on the total mass of the ink.

  A known compound can also be used as the antioxidant, but its content is preferably 0.8% by mass or less, and 0.5% by mass or less, based on the total mass of the ink, from the viewpoint of curability. It is more preferable that On the other hand, from the viewpoint of capturing radicals generated in the cured film of the ink and sufficiently suppressing oxidation of the cured film, the content of the antioxidant may be 0.05% by mass or more based on the total mass of the ink. preferable.

  In addition, the total amount of the ultraviolet absorber and the antioxidant is preferably 2.0% by mass or less, and 1.0% by mass or less with respect to the total mass of the ink, from the viewpoint of ink ejection stability and curability. More preferably.

  The ink of the present invention may further contain various additives, resins, and the like other than those described above as necessary. Examples of the various additives include surfactants, leveling additives, matting agents, infrared absorbers, antibacterial agents, basic compounds for enhancing the storage stability of the ink, and the like. Examples of the basic compound include basic alkali metal compounds, basic alkaline earth metal compounds, basic organic compounds such as amines, and the like.

  The total amount of various additives such as a surfactant is preferably 1% by mass or less, and more preferably 0.5% by mass or less, with respect to the total mass of the ink, from the viewpoint of suppressing migration.

  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, and rubber resins.

(5) Preparation method of actinic ray curable ink-jet ink The ink of the present invention can be obtained by mixing a photopolymerizable compound, a photoinitiator, a gelling agent, and arbitrary components under heating. it can. It is preferable to filter the obtained liquid mixture with a predetermined filter. At this time, a dispersion containing a pigment and a dispersant may be prepared in advance, and the remaining components may be added thereto and mixed while heating.

  The pigment can be dispersed using, for example, a ball mill, sand mill, attritor, roll mill, agitator, Henschel mixer, colloid mill, ultrasonic homogenizer, pearl mill, wet jet mill, paint shaker, or the like.

(6) Physical properties of actinic ray curable inkjet ink The ink of the present invention reversibly undergoes sol-gel phase transition depending on temperature. The ink of the present invention is a sol when ejected from an ink jet recording apparatus (usually about 80 ° C.), and is naturally cooled and gelled after landing on the recording medium.

  In the ink of the present invention, it is preferable that the viscosity of the ink at a high temperature is not more than a certain value in order to improve the dischargeability from the ink jet recording apparatus. Specifically, the viscosity of the ink at 80 ° C. is preferably 3 mPa · s or more and 20 mPa · s, more preferably 6.0 mPa · s or more and 15.0 mPa · s or less, and 7.0 mPa · s or more. More preferably, it is 12.0 mPa · s or less. On the other hand, in order to suppress coalescence of adjacent ink droplets, 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 ray curable inkjet ink is preferably 1000 mPa · s or more.

  The viscosity at 80 ° C., the viscosity at 25 ° C., and the gelation temperature of the actinic radiation curable inkjet ink of the present invention 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 25 ° C. under conditions of a shear rate of 11.7 (1 / s) and a temperature decrease rate of 0.1 ° C./s. . And the said viscosity can be calculated | required by reading the viscosity in 80 degreeC, and the viscosity in 25 degreeC, respectively. The gelation temperature can be determined as the temperature at which the viscosity becomes 200 mPas 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 °.

2. Image Forming Method The image forming method of the present invention includes 1) a step of ejecting the actinic ray curable ink jet ink from the nozzles of an ink jet recording apparatus and landing on the recording medium; Irradiating the curable ink-jet ink with actinic rays to cure the actinic-light curable ink-jet ink.

(First step)
In the first step, ink-jet ink droplets are ejected from an ink-jet head and landed on a recording medium at a position corresponding to an image to be formed.

  The ejection method from the ink jet head may be either an on-demand method or a continuous method. On-demand inkjet heads include electro-mechanical conversion systems such as single cavity type, double cavity type, bender type, piston type, shear mode type and shared wall type, as well as thermal inkjet type and bubble jet. Any of electric-thermal conversion methods such as Canon Inc. (registered trademark) type may be used.

  By discharging ink droplets from the inkjet head in a heated state, the discharge stability can be improved. The temperature of the ink when ejected is preferably 35 ° C. or more and 100 ° C. or less, and more preferably 35 ° C. or more and 80 ° C. or less in order to further improve the ejection stability. In particular, the emission is preferably performed at an ink temperature such that the viscosity of the ink is 7 mPa · s or more and 15 mPa · s or less, more preferably 8 mPa · s or more and 13 mPa · s or less.

  In order to improve the ejection property of the ink from the ink jet head, it is preferable to set the temperature of the ink when the ink jet head is filled to the gel temperature of the ink + 10 ° C. or higher and the gel temperature + 30 ° C. or lower. When the temperature of the ink in the ink jet head is less than the gelation temperature + 10 ° C., the ink gels in the ink jet head 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 ink jet head exceeds the gelation temperature + 30 ° C., the ink becomes too high, and the ink component may deteriorate.

  The method for heating the ink is not particularly limited. For example, at least one of an ink tank constituting the head carriage, an ink supply system such as a supply pipe and an anterior chamber ink tank just before the head, a pipe with a filter, and a piezo head is heated by a panel heater, a ribbon heater, or warm water. be able to.

  The amount of ink droplets to be ejected is preferably 2 pL or more and 20 pL or less from the viewpoint of recording speed and image quality.

  The recording medium is not particularly limited, and other than ordinary uncoated paper, coated paper, etc., synthetic paper YUPO, various plastics used for soft packaging, and films thereof can be used. Examples of the various plastic films include PP film, PET film, OPS film, OPP film, ONy film, PVC film, PE film, and TAC film. As other plastics, polycarbonate, acrylic resin, ABS, polyacetal, PVA, rubbers and the like can be used. Moreover, it is applicable also to metals and glass.

  The recording medium for food packaging is appropriately selected according to the application, and may be, for example, polypropylene.

  In addition, it is preferable from the viewpoint of gelation of the ink that the temperature of the recording medium when the ink droplets land is controlled to 20 ° C. or more and 40 ° C. or less.

(Second step)
In the second step, the ink landed on the recording medium in the first step is irradiated with actinic rays to form an image made of a cured film of ink.

  The actinic ray can be selected from, for example, electron beam, ultraviolet ray, α ray, γ ray, X ray, etc., but is preferably ultraviolet ray, and light having a peak wavelength from 365 nm to 405 nm is irradiated from the LED light source. Is preferred. An example of the LED light source is a water-cooled LED (peak wavelength: 395 nm) manufactured by Phoseon Technology. LEDs have less radiant heat than conventional light sources (for example, metal halide lamps). Therefore, when irradiated with actinic rays, the ink is difficult to melt and gloss unevenness and the like are difficult to occur.

Here, the case of irradiating light having a peak wavelength 365nm or 405nm or less, a peak illuminance in the recording medium surface or the ink droplet surface, it is preferable that a 0.5 W / cm ² or more 10.0 W / cm ² or less it is preferable to 1.0 W / cm ² or more 5.0 W / cm ² or less.

  Irradiation with actinic rays is preferably performed from 0.001 second to 1.0 second after the ink has landed on the recording medium. In order to form a high-definition image, 0.001 second to 0 More preferably, it is performed within 5 seconds.

  On the other hand, irradiation with actinic rays may be performed in two stages. In this case, the ink is preliminarily cured by irradiation with an actinic ray between 0.001 seconds and 2.0 seconds after the ink lands on the recording medium, and after the completion of all the printing, the actinic light is further irradiated. Can be fully cured. By dividing the irradiation of actinic rays into two stages, it becomes difficult for the ink to cure and shrink.

  Hereinafter, the present invention will be described in more detail with reference to examples. However, the scope of the present invention is not construed as being limited by these descriptions.

[Preparation of cyan pigment dispersion]
A cyan pigment dispersion was prepared by the following procedure.
9% by mass of EFKA4130 (manufactured by BASF) as a pigment dispersant, 71% by mass of tricyclodecane dimethanol diacrylate (A-DCP: manufactured by Shin-Nakamura Chemical Co., Ltd.) as a polyfunctional photopolymerizable compound in a stainless beaker The mixture was heated and stirred for 1 hour while heating on a hot plate at 65 ° C.
The mixed solution was cooled to room temperature, and further, 20% by mass of Pigment Blue 15: 4 (manufactured by Dainichi Seika Co., Ltd.) as a pigment was added. This solution was placed in a glass bottle together with 200 g of zirconia beads having a diameter of 0.5 mm, sealed, and dispersed in a paint shaker for 5 hours. Thereafter, the zirconia beads were removed to obtain a cyan pigment dispersion.

[Preparation of ink]
In accordance with the ink components described in Tables 2 to 4 below, the following components and the pigment dispersion were mixed, heated to 80 ° C. and stirred. Thereafter, the mixture was heated with a Teflon (registered trademark) 3 μm membrane filter manufactured by ADVANTEC, and ink samples 1 to 32 were obtained. In addition, the component amount of a table | surface is the mass%.

[Gelling agent]
Stearyl stearate (Exepar SS: manufactured by Kao Corporation, C17-C18)
Distearyl ketone (Kao wax T1: Kao Corporation, C18-C18)
Lauric acid amide (Diamid Y: Nippon Kasei Co., Ltd., C12)
Ethylene glycol distearate (EMALEX EG-di-S: manufactured by Nippon Emulsion Co., Ltd., C17-C17)

[Photopolymerizable compound]
(Polyfunctional photopolymerizable compound)
Tricyclodecane dimethanol diacrylate (A-DCP: Shin-Nakamura Chemical Co., Ltd.)
6EO-modified trimethylolpropane triacrylate (SR499: manufactured by SARTOMER)
4EO-modified pentaerythritol tetraacrylate (SR494: manufactured by SARTOMER)
PO-modified neopentyl glycol diacrylate 3PO-modified trimethylolpropane triacrylate (Photomer 4072: manufactured by Cognis)
3-methylpentanediol diacrylate 2- (2-vinyloxyethoxy) ethyl acrylate (VEEA: manufactured by Nippon Shokubai Co., Ltd.)
(Monofunctional photopolymerizable compound)
Tetrahydrofurfuryl acrylate (V # 150: Osaka Organic Chemical Co., Ltd.)

[Photoinitiator]
(Compound represented by the general formula (1))
Ominopol 910 (made by IGM)
(Acylphosphine compounds)
DAROCURE TPO (BASF, molecular weight 348)
IRGACURE 819 (BASF, molecular weight 418)
(Thioxanthone compounds)
SPEEDCURE CPTX (manufactured by Lambson, molecular weight 304)
SPEEDCURE 7010 (manufactured by Lambson, molecular weight 1899)
SPEEDCURE ITX (manufactured by Lambson, molecular weight 254)

[Photoinitiator]
SPEEDCURE 7040 (Lambson)

[Polymerization inhibitor]
Irgastab UV10 (manufactured by BASF)

[Surfactant]
KF-352 (manufactured by Shin-Etsu Chemical Co., Ltd.)

[Image forming method]
Using each ink sample shown in Tables 2 to 4, two piezo heads with a resolution of 600 dpi are arranged in the transport direction, and the recording resolution is 1200 × 1200 dpi, and the droplet volume is 4 pl. % Solid image was drawn.

(Exposure method)
Film-OTP3162 (A4 size, polypropylene sheet, 40 μm) is scanned at a speed of 30 m / min, metal halide lamp lamp (Metahara, manufactured by GS Yuasa) 120 W / cm, maximum illumination on the image surface 280 mW / cm ² , 400 mJ / cm ² (measured with a 365 nm sensor, Iwasaki Electric UVPF-A1) or deep ultraviolet LED lamp wavelength 254 nm (low wavelength LED, manufactured by Nikkiso Co., Ltd.), maximum illuminance on the image surface 1 W / cm ² , 400 mJ / cm ² (254 nm (Measured with a sensor, Iwasaki Electric UVPF-A1).

[Evaluation method]
(Ink surface curability)
The solid image portion (100% printed portion) was left for 24 hours in an environment of 25 ° C. and 60% RH. Thereafter, the pencil hardness of the surface was measured according to JIS-K-5400. Evaluation was performed according to the following criteria.
◎: Pencil hardness 2H or more ○: Pencil hardness B
Δ: Pencil hardness F, H
X: Pencil hardness 2B or less

(Migration amount evaluation)
Put the water: ethanol = 5: 95 mixture 100ml in contact with the back (film surface) of the circular solid print with a diameter of 10cm, and keep the mixture in a metal sealed container so that the mixture does not volatilize. And left at 60 ° C. for 10 days. Thereafter, the total migration amount of each photopolymerizable compound, initiator, photoinitiator residue after reaction, and the like contained in the water and ethanol mixed solution was calculated and evaluated in four stages.
A: Migration amount is less than 10 ppb O: Migration amount is 10 ppb or more and less than 50 ppb Δ: Migration amount is 50 ppb or more and less than 100 ppb ×: Migration amount is 100 ppb or more

  The evaluation results are shown in Tables 2 to 4 below.

  As shown in Tables 2 to 4, when the actinic ray curable inkjet ink does not contain a gelling agent (samples 26, 27, 31, and 32), migration is likely to occur and the surface curability is low. It was easy. On the other hand, when the actinic ray curable inkjet ink contains a gelling agent, migration was suppressed and surface curability was also improved (Samples 1 to 22). However, even if the actinic ray curable ink-jet ink contained a gelling agent, when it did not contain a photoinitiator, the surface curability was poor and migration was likely to occur (Samples 28 and 29). Further, when the photoinitiator includes a photoinitiator other than the compound represented by the general formula (1) (sample 30), the surface curability was good, but migration was likely to occur. Furthermore, migration was also likely to occur when a monofunctional photopolymerizable compound was included as the photopolymerizable compound (Samples 23 to 25).

  On the other hand, in an actinic ray curable inkjet ink containing a photopolymerizable compound consisting essentially of a polyfunctional photopolymerizable compound, a photoinitiator represented by the general formula (1), and a gelling agent. Migration was easily suppressed, and surface curability was likely to increase (Samples 1 to 22).

According to the actinic ray curable ink-jet ink according to the present invention, a cured film having a good surface curability can be obtained in which components are hardly deposited on the surface. Therefore, the present invention can be applied to an image method for various recording media. For example, an image can be formed on a recording medium for food packaging.

Claims (6)

An actinic ray curable inkjet ink comprising a photopolymerizable compound, a photoinitiator, and a gelling agent,
The photopolymerizable compound consists essentially of a polyfunctional photopolymerizable compound,
The photoinitiator contains a compound represented by the following general formula (1),
Actinic ray curable inkjet ink.

(In general formula (1), n represents an integer of 1-30) The photoinitiator further comprises an acylphosphine compound,
The actinic ray curable inkjet ink according to claim 1. The photoinitiator further includes a thioxanthone compound having a molecular weight of 300 or more and 3000 or less,
The actinic ray curable inkjet ink according to claim 1. The gelling agent contains at least one compound among the compounds represented by the following general formulas (G1) and (G2),
The actinic-light curable inkjet ink as described in any one of Claims 1-3.

(In the general formulas (G1) and (G2), R ^{1 to} R ⁴ each independently represents an alkyl group containing a straight chain portion having 12 to 26 carbon atoms) The photopolymerizable compound includes at least one of a propylene oxide modified (meth) acrylate compound and an ethylene oxide modified (meth) acrylate compound,
The total amount of the propylene oxide-modified (meth) acrylate compound and the ethylene oxide-modified (meth) acrylate compound is 30% by mass to 97% by mass with respect to the total mass of the actinic radiation curable inkjet ink, To
The actinic-light curable inkjet ink as described in any one of Claims 1-4. Discharging the actinic ray curable inkjet ink according to any one of claims 1 to 5 from a nozzle of an inkjet recording apparatus and landing on a recording medium;
Irradiating the actinic ray curable inkjet ink landed on the recording medium with an actinic ray to cure the actinic ray curable inkjet ink;
An image forming method comprising: