JP2017132861A - Active ray curing type inkjet ink and inkjet image formation method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an active ray curing type inkjet ink containing a gelling agent, in which the storage stability of the ink (suppression of phase separation between the gelling agent and a liquid component other than the gelling agent) is satisfactory, and also, an image quality is satisfactory, and an inkjet image formation method using the active ray curing type inkjet ink.SOLUTION: Provided is an active ray curing type inkjet ink containing a photopolymerizable compound and a gelling agent, in which the gelling agent includes a crystalline gelling agent and a non-crystalline gelling agent.SELECTED DRAWING: None

Description

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

  The inkjet image forming method is used in various printing fields because it can form an image easily and inexpensively. As one of the ink jet image forming methods, a liquid of an ink jet ink composition (hereinafter also simply referred to as “active light curable ink jet ink”, “ink jet ink”, or “ink”) having a property of being cured by irradiation with active light. There is a method of forming an image by landing droplets on a recording medium and then irradiating actinic rays to cure the ink-jet ink. When such an inkjet ink is used, an image having high scratch resistance and adhesion can be formed even on a non-absorbing recording medium having no ink absorbability.

  When the ink-jet ink contains a gelling agent, the ink gels due to crystallization of the gelling agent when it cools after landing on the recording medium. It is hard to occur (for example, refer to Patent Document 1).

JP 2007-63553 A

  When the gelling agent and the liquid component (components obtained by removing the gelling agent from the ink) are phase-separated by standing at room temperature, the storage stability of the ink may be deteriorated. In addition, when the phase-separated ink is redissolved, the gelling agent does not dissolve uniformly, pinning due to the desired phase change cannot be obtained, high-definition image quality cannot be obtained, and ink ejection stability There was a case where the problem that the property deteriorated occurred.

  In view of the above-described problems, the present invention provides good storage stability of the ink (inhibition of phase separation between the gelling agent and the component excluding the gelling agent) in the actinic ray curable inkjet ink containing the gelling agent. It is an object of the present invention to provide an actinic ray curable inkjet ink having good image quality and an inkjet image forming method using such an actinic ray curable inkjet ink.

  The above-mentioned problem according to the present invention is solved by the following means.

[1] An actinic ray curable inkjet ink containing a photopolymerizable compound and a gelling agent,
The actinic ray curable inkjet ink, wherein the gelling agent contains a crystalline gelling agent and an amorphous gelling agent.
[2] The actinic ray curable inkjet ink of [1], wherein the non-crystalline gelling agent contains a hydrogen bonding gelling agent.
[3] The actinic ray curable inkjet according to [1] or [2], wherein the content of the crystalline gelling agent is 1% by mass or more and 7% by mass or less based on the total mass of the ink. ink.
[4] The crystalline gelling agent contains a gelling agent containing an alkyl group having 12 to 26 carbon atoms in the straight chain portion, according to any one of [1] to [3] Actinic ray curable inkjet ink.
[5] The photopolymerizable compound contains a photopolymerizable compound A having a viscosity at 25 ° C. of 80 mPa · s to 300 mPa · s, and the photopolymerizable compound A is based on the total mass of the photopolymerizable compound. The actinic ray curable inkjet ink according to any one of [1] to [4], which is contained in an amount of 40% by mass or more.
[6] The actinic ray curable inkjet ink according to any one of [1] to [5], wherein the non-crystalline gelling agent contains a sorbitan structure.
[7] A step of landing a droplet of the actinic radiation curable inkjet ink according to any one of [1] to [6] on a recording medium, and irradiating the droplet landed on the recording medium with an actinic ray An inkjet image forming method comprising a step of forming a cured film constituting an image.

  According to the present invention, in an actinic ray curable inkjet ink containing a gelling agent, the storage stability of the ink (inhibition of phase separation between the gelling agent and the liquid component excluding the gelling agent) is good, and the image quality An actinic ray curable ink-jet ink having a good quality and an inkjet image forming method using such an actinic ray curable ink-jet ink are provided.

FIG. 1A is a side view showing an example of a configuration of a main part of a line recording type ink jet recording apparatus, which is one aspect of an ink jet recording apparatus using an actinic ray curable ink jet ink according to the present invention. FIG. 1B is a top view illustrating an example of a configuration of a main part of a line recording type inkjet recording apparatus, which is an aspect of an inkjet recording apparatus in which the actinic ray curable inkjet ink according to the present invention is used. FIG. 2 is a top view showing an example of a configuration of a main part of a serial recording type ink jet recording apparatus in which the actinic ray curable ink jet ink according to the present invention is used.

  As a result of intensive studies, the inventor of the present invention, by combining a crystalline gelling agent and an amorphous gelling agent, makes it difficult to separate the phases of the ink (the liquid component excluding the gelling agent and the gelling agent). It has been found that high-definition image quality can be obtained with excellent phase separation suppression.

  Although details are not clear, it is considered that the amorphous gelling agent is different from the crystalline gelling agent in the solidification mechanism due to gelation. The crystalline gelling agent has a solidification mechanism that holds the liquid component in the voids of the card house structure formed by physically combining plate-like crystals. Easy to hold. On the other hand, the non-crystalline gelling agent has a solidification mechanism in which the molecules in the liquid component are linked in a string form by an interaction such as hydrogen bonding, and form a network structure, so that the liquid component is retained. It is easy to hold the liquid component firmly by the action. By utilizing the difference in the solidification function due to gelation, ink storage stability (inhibition of phase separation between the gelling agent and the liquid component excluding the gelling agent) is excellent, and high-definition image quality is achieved. It is thought that it is obtained.

  The actinic ray curable inkjet ink of the present invention (in the present specification, also referred to as “inkjet ink” or simply “ink”) is an actinic ray curable inkjet ink containing a photopolymerizable compound and a gelling agent. The gelling agent contains a crystalline gelling agent and an amorphous gelling agent.

  Hereinafter, the present invention, its components, and modes and modes for carrying out the present invention will be described in detail. In the present invention, “to” is used to mean that the numerical values described before and after it are included as a lower limit value and an upper limit value. Further, in the present invention, “mass%” refers to the content of each constituent component expressed by mass% when the total mass of the actinic ray curable inkjet ink is 100 mass%, unless otherwise specified.

[Actinic ray curable inkjet ink]
The actinic ray curable inkjet ink of the present invention is an ink composition curable by actinic rays. “Actinic rays” are rays that can give energy to generate an initiation species in the ink composition by irradiation, and include α rays, γ rays, X rays, ultraviolet rays, electron rays, and the like. Of these, ultraviolet rays and electron beams are preferable from the viewpoint of curing sensitivity and device availability, and ultraviolet rays are more preferable.

  Hereinafter, various compounds constituting the actinic ray curable inkjet ink of the present invention will be described in detail.

[Photopolymerizable compound]
The actinic ray curable inkjet ink of the present invention contains a photopolymerizable compound. The photopolymerizable compound is a compound that polymerizes when irradiated with actinic rays. The photopolymerizable compound can be a radical polymerizable compound or a cationic polymerizable compound. A radical polymerizable compound is preferred.

  The radically polymerizable compound is a compound (monomer, oligomer, polymer or mixture thereof) having a radically polymerizable ethylenically unsaturated bond. Only one kind of radically polymerizable compound may be contained in the ink, or two or more kinds thereof may be contained.

  Examples of compounds having an ethylenically unsaturated bond capable of radical polymerization include unsaturated carboxylic acids and salts thereof, unsaturated carboxylic acid ester compounds, unsaturated carboxylic acid urethane compounds, unsaturated carboxylic acid amide compounds and anhydrides thereof, Examples include acrylonitrile, styrene, unsaturated polyester, unsaturated polyether, unsaturated polyamide, and unsaturated urethane. Examples of the unsaturated carboxylic acid include (meth) acrylic acid, itaconic acid, crotonic acid, isocrotonic acid, maleic acid and the like.

  Especially, it is preferable that a radically polymerizable compound is an unsaturated carboxylic ester compound, and it is more preferable that it is (meth) acrylate. The (meth) acrylate may be not only a monomer described later but also an oligomer, a mixture of a monomer and an oligomer, a modified product, an oligomer having a photopolymerizable functional group, and the like.

  In the present specification, “(meth) acrylate” includes acrylate monomer and / or acrylate oligomer, methacrylate monomer and / or methacrylate oligomer.

Examples of (meth) acrylates 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, Methoxydiethylene glycol (meth) acrylate, methoxypolyethylene glycol (meth) acrylate, methoxypropylene glycol (meth) acrylate, phenoxyethyl (meta Acrylate, tetrahydrofurfuryl (meth) acrylate, isobornyl (meth) acrylate, 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 2-hydroxy-3-phenoxypropyl (meth) acrylate, 2- ( (Meth) acryloyloxyethyl succinic acid, 2- (meth) acryloyloxyethyl phthalic acid, 2- (meth) acryloyloxyethyl-2-hydroxyethyl-phthalic acid, t-butylcyclohexyl (meth) acrylate, etc. Functional monomers;
Triethylene glycol di (meth) acrylate, tetraethylene glycol di (meth) acrylate, polyethylene glycol di (meth) acrylate, tripropylene glycol di (meth) acrylate, polypropylene glycol di (meth) acrylate, 1,4-butanediol di (Meth) acrylate, 1,6-hexanediol di (meth) acrylate, 1,9-nonanediol di (meth) acrylate, neopentyl glycol di (meth) acrylate, dimethylol-tricyclodecane di (meth) acrylate, bisphenol A PO adduct di (meth) acrylate, neopentyl glycol di (meth) acrylate hydroxypivalate, polytetramethylene glycol di (meth) acrylate, polyethylene glycol Diacrylate, tripropylene glycol diacrylate, difunctional monomers such as tricyclodecane dimethanol diacrylate;
Trimethylolpropane tri (meth) acrylate, pentaerythritol tri (meth) acrylate, pentaerythritol tetra (meth) acrylate, dipentaerythritol hexa (meth) acrylate, ditrimethylolpropane tetra (meth) acrylate, glycerin propoxytri (meth) acrylate And trifunctional or higher polyfunctional monomers such as pentaerythritol ethoxytetra (meth) acrylate.

  From the viewpoint of photosensitivity, (meth) acrylate is stearyl (meth) acrylate, lauryl (meth) acrylate, isostearyl (meth) acrylate, ethoxydiethylene glycol (meth) acrylate, isobornyl (meth) acrylate, tetraethylene glycol di ( (Meth) acrylate, glycerin propoxytri (meth) acrylate and the like are preferable.

  The (meth) acrylate may be a modified product. Examples of modified products include ethylene oxide-modified (meth) acrylates such as ethylene oxide-modified trimethylolpropane tri (meth) acrylate and ethylene oxide-modified pentaerythritol tetraacrylate; caprolactone modifications such as caprolactone-modified trimethylolpropane tri (meth) acrylate (Meth) acrylates; and caprolactam-modified (meth) acrylates such as caprolactam-modified dipentaerythritol hexa (meth) acrylate.

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

  The cationically polymerizable compound can be an epoxy compound, a vinyl ether compound, an oxetane compound, or the like. Only one kind of cationic polymerizable compound may be contained in the actinic ray curable inkjet ink, or two or more kinds thereof may be contained.

  The epoxy compound is an aromatic epoxide, an alicyclic epoxide, an aliphatic epoxide, or the like, and an aromatic epoxide or an alicyclic epoxide is preferable in order to increase curability.

  The aromatic epoxide may be a di- or polyglycidyl ether obtained by reacting a polyhydric phenol or an alkylene oxide adduct thereof with epichlorohydrin. Examples of the polyhydric phenol to be reacted or its alkylene oxide adduct include bisphenol A or its alkylene oxide adduct. The alkylene oxide in the alkylene oxide adduct can be ethylene oxide, propylene oxide, and the like.

  The alicyclic epoxide can be a cycloalkane oxide-containing compound obtained by epoxidizing a cycloalkane-containing compound with an oxidizing agent such as hydrogen peroxide or peracid. The cycloalkane in the cycloalkane oxide-containing compound can be cyclohexene or cyclopentene.

  The aliphatic epoxide can be a di- or polyglycidyl ether obtained by reacting an aliphatic polyhydric alcohol or an alkylene oxide adduct thereof with epichlorohydrin. Examples of the aliphatic polyhydric alcohol include alkylene glycols such as ethylene glycol, propylene glycol, and 1,6-hexanediol. The alkylene oxide in the alkylene oxide adduct can be ethylene oxide, propylene oxide, and the like.

Examples of vinyl ether compounds include ethyl vinyl ether, n-butyl vinyl ether, isobutyl vinyl ether, octadecyl vinyl ether, cyclohexyl vinyl ether, hydroxybutyl vinyl ether, 2-ethylhexyl vinyl ether, cyclohexanedimethanol monovinyl ether, n-propyl vinyl ether, isopropyl vinyl ether, isopropenyl ether. Monovinyl ether compounds such as o-propylene carbonate, dodecyl vinyl ether, diethylene glycol monovinyl ether, octadecyl vinyl ether;
Diethylene glycol divinyl ether, diethylene glycol divinyl ether, triethylene glycol divinyl ether, propylene glycol divinyl ether, dipropylene glycol divinyl ether, butanediol divinyl ether, hexanediol divinyl ether, cyclohexane dimethanol divinyl ether, trimethylolpropane trivinyl ether, etc. Or a trivinyl ether compound etc. are contained. Of these vinyl ether compounds, di- or trivinyl ether compounds are preferred in view of curability and adhesion.

  The oxetane compound is a compound having an oxetane ring, and examples thereof include oxetane compounds described in JP-A Nos. 2001-220526, 2001-310937, and JP-A-2005-255821. Among them, the compound represented by the general formula (1) described in paragraph No. 0089 of JP-A-2005-255821, the compound represented by the general formula (2) described in paragraph No. 0092 of the same publication, the paragraph Examples include a compound represented by general formula (7) of number 0107, a compound represented by general formula (8) of paragraph number 0109, a compound represented by general formula (9) of paragraph number 0116, and the like. General formulas (1), (2), (7), (8), and (9) described in JP-A-2005-255821 are shown below.

  The content of the photopolymerizable compound in the actinic ray curable inkjet ink 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.

(Photopolymerizable compound A)
The actinic ray curable inkjet ink has a viscosity of 80 mPa · s at 25 ° C. as a photopolymerizable compound from the viewpoint of storage stability of the ink (inhibition of phase separation between the gelling agent and the liquid component excluding the gelling agent). It is preferable to contain a photopolymerizable compound (hereinafter also referred to as photopolymerizable compound A) having a viscosity of 300 mPa · s or less.

  When the photopolymerizable compound A is contained in the actinic ray curable inkjet ink, the viscosity of the ink is increased, so that it is considered that the ink is difficult to move from the card house structure at the time of gelation (phase separation is difficult).

Examples of the photopolymerizable compound A include the following, but are not limited thereto.
Alkoxylated neopentyl glycol diacrylate (viscosity 131 mPa · s), polyethylene glycol # 600 diacrylate (viscosity 97.1 mPa · s), dioxane glycol diacrylate (viscosity 260 mPa · s), 9EO-modified trimethylolpropane triacrylate (viscosity 108 mPa) S) 4EO-modified pentaerythritol tetraacrylate (viscosity 131 mPa · s), 5EO-modified pentaerythritol tetraacrylate (viscosity 176 mPa · s), glycerin propoxyacrylate (viscosity 94.4 mPa · s), caprolactone-modified dipentaerythritol hexaacrylate ( Viscosity 80 mPa · s), caprolactone acrylate (viscosity 80 mPa · s), tricyclodecane dimethanol diacrylate (viscosity) 131 mPa · s), 6EO modified trimethylolpropane triacrylate (viscosity 92 mPa · s), 3PO modified trimethylolpropane triacrylate (viscosity 83 mPa · s), nonylphenol 8EO modified acrylate (viscosity 180 mPa · s), tricyclodecane dimethanol dimethanol Methacrylate (viscosity 100 mPa · s) and the like are included.

  The viscosity of the photopolymerizable compound is measured in the rotation mode using, for example, an apparatus MCR-300 (manufactured by Physica) (the cone plate uses 75Φ). Ten points are measured every 10 seconds at 25 ° C. and a shear rate of 1000 1 / s, and the viscosity obtained by averaging seven points from the last measurement point is taken as the viscosity of the photopolymerizable compound.

  The photopolymerizable compound A is preferably contained in an amount of 40% by mass to 100% by mass with respect to the total mass of the photopolymerizable compound from the viewpoint of the storage stability of the ink.

[Gelling agent]
The actinic ray curable inkjet ink of the present invention contains a gelling agent. In the present invention, the gelling agent is defined as "a compound that is an organic substance that is solid at normal temperature and becomes liquid when heated and has a function of reversibly sol-gel phase transition of ink according to temperature".

  The gelling agent may be a crystalline gelling agent that crystallizes in the ink at a temperature below the gelation temperature, or may be an amorphous gelling agent that does not crystallize in the ink even at a temperature below the gelation temperature. The gelation temperature refers to a temperature at which the viscosity of the ink changes suddenly when the ink sol- lated or liquefied by heating is cooled and the gelling agent undergoes 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 measured. The gelation temperature can be set.

(Crystalline gelling agent)
The actinic ray curable inkjet ink of the present invention contains a crystalline gelling agent as a gelling agent. The crystalline gelling agent has a solidification mechanism that holds a liquid component in a void of a card house structure formed by physically combining plate-like crystals.

  When a crystalline gelling agent is used as the gelling agent, the pinning property of the ink droplet after landing can be easily improved, and the image blurring due to the spreading of the ink droplet can be suppressed.

Examples of crystalline gelling agents include
An aliphatic ketone compound;
Aliphatic ester compounds;
Petroleum waxes such as paraffin wax, microcrystalline wax, petrolactam;
Plant waxes such as candelilla wax, carnauba wax, rice wax, wood wax, jojoba oil, jojoba solid wax, and jojoba ester;
Animal waxes such as beeswax, lanolin and whale wax;
Mineral waxes such as montan wax and hydrogenated wax;
Hydrogenated waxes of hardened castor oil and hardened castor oil derivatives;
Modified waxes such as montan wax derivatives, paraffin wax derivatives, microcrystalline wax derivatives or polyethylene wax derivatives;
Higher fatty acids such as behenic acid, arachidic acid, stearic acid, palmitic acid, myristic acid, lauric acid, oleic acid, and erucic acid;
Synthetic waxes such as polyethylene wax and α-olefin maleic anhydride copolymer wax (such as UNILIN series manufactured by Baker-Petrolite);
Etc. are included.

  In order to stably discharge ink droplets from the ink jet recording apparatus, it is preferable that the compatibility of the photopolymerizable compound and the crystalline gelling agent is good in the sol-like ink (at a high temperature). Furthermore, in order to stably suppress the coalescence of droplets even during high-speed printing, after the ink droplets have landed on the recording medium, the crystalline gelling agent quickly crystallizes to form a strong card house structure. It is preferable.

  The actinic ray curable inkjet ink may contain only one type of crystalline gelling agent, or may contain two or more types of crystalline gelling agent in combination.

  The crystalline gelling agent preferably contains a gelling agent containing an alkyl group having 12 to 26 carbon atoms in the straight chain portion. The alkyl group may be any one of a linear alkyl group, a branched alkyl group, and a cyclic alkyl group, and is preferably a linear alkyl group or a branched alkyl group. From the viewpoint of formation, it is more preferably a linear alkyl group.

  Examples of the gelling agent containing an alkyl group having 12 to 26 carbon atoms in the straight chain portion include aliphatic ketone compounds and aliphatic ester compounds having an alkyl group having 12 to 26 carbon atoms in the straight chain portion. Higher fatty acids, higher alcohols, fatty acid amides and the like.

Among these, an aliphatic ketone compound or an aliphatic ester compound is preferable. Furthermore, the gelling agent is more preferably a compound represented by the following general formula (G1) or (G2).
General formula (G1): R1-CO-R2
General formula (G2): R3-COO-R4

  In general formula (G1), the alkyl group represented by R1 and R2 is not particularly limited. However, from the viewpoint of crystallinity, each independently represents an alkyl group having a straight chain portion having 12 to 26 carbon atoms. Preferably there is.

  Examples of the aliphatic ketone compound represented by the general formula (G1) include dilignoceryl ketone (C24-C24), dibehenyl ketone (C22-C22), distearyl ketone (C18-C18), and 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 (C16-C22) ), Stearyl 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 aliphatic ketone compound contained in the actinic ray curable inkjet ink may be only one kind, or may be a mixture of two or more kinds.

  In general formula (G2), the alkyl groups represented by R3 and R4 are not particularly limited. However, from the viewpoint of crystallinity, they are each independently an alkyl group having a straight chain portion having 12 to 26 carbon atoms. Preferably there is.

  Examples of the aliphatic ester compound represented by the formula (G2) include behenyl behenate (C21-C22), icosyl icosylate (C19-C20), stearyl stearate (C17-C18), 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 acid Octyldodecyl (C13-C20), stearyl oleate (C17-C18), stearyl erucate (C21-C18), stearyl linoleate (C17-C18), behenyl oleate (C18-C22), myricyl serotate (C25- C16), montanate Lil (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 formula (G2) include Unistar M-2222SL (manufactured by NOF Corporation), EXCEPARL SS (manufactured by Kao Corporation), EMALEXCC-18 (manufactured by Nippon Emulsion Co., Ltd.). ), 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.

  The aliphatic ester compound contained in the ink may be only one type or a mixture of two or more types.

  The content of the crystalline gelling agent in the ink is preferably 1.0% by mass or more and 7.0% by mass or less with respect to the total mass of the actinic ray curable inkjet ink, from the viewpoints of pinning property and ejection stability. More preferably, it is 0 mass% or more and 3.0 mass% or less.

(Non-crystalline gelling agent)
The actinic ray curable inkjet ink of the present invention contains an amorphous gelling agent as a gelling agent. A non-crystalline gelling agent is formed by stringing the non-crystalline gelling agent molecules in the liquid component through interactions such as hydrogen bonding, coordination bonding, and π-π stacking, and the like. It has a solidification mechanism that holds the liquid component by forming a structure. Fibrous aggregates and network higher order structures can be easily confirmed by morphological observation with a transmission electron microscope.

  Among them, a compound having at least two long-chain alkyl groups or a hydrophobic part such as phenyl with a polar group in the molecule and capable of forming two or more hydrophobic bonds between the molecules is preferable. Alternatively, a compound having a structure capable of forming a hydrogen bond such as at least two hydroxyl groups, amide groups, carboxylic acid groups, ether groups, amino groups with a hydrophobic portion such as a long-chain alkyl group or phenyl interposed therebetween is preferable.

    Specific examples of the non-crystalline gelling agent include the following compounds.

  Actinic ray curable ink-jet ink contains at least one non-crystalline gelling agent and a crystalline gelling agent. By utilizing the difference in the solidification function of each gelling agent, the ink can be stored stably. It is considered that the property (inhibition of phase separation between the gelling agent and the liquid component excluding the gelling agent) is good and a high-definition image quality can be obtained.

  The amorphous gelling agent preferably contains a hydrogen bonding gelling agent from the viewpoint of the storage stability of the ink (inhibition of phase separation between the gelling agent and the liquid component excluding the gelling agent). The hydrogen bonding gelling agent refers to a compound having at least one hydrogen bonding group in the molecule among non-crystalline gelling agents. The hydrogen bonding group may be any functional group capable of hydrogen bonding, and examples thereof include a hydroxy group, a carboxy group, an amino group, an amide group, and a urea group.

  Examples of hydrogen bonding gelling agents include metal soaps, amino acids, alkyl phosphates, 12-hydroxystearic acid, sucrose fatty acid esters, dibenzylidene sorbitol, dehydroabietic acid calcium salt, dextrin fatty acid esters, inulin Fatty acid esters and the like are included.

  The hydrogen bonding gelling agent may be, for example, a gelling agent that can be gelled by particle dispersion, or may be fine particle silica or an organically modified viscosity mineral.

  The hydrogen bonding gelling agent may be a low molecular weight hydrogen bonding gelling agent or an oligomer type or polymer type hydrogen bonding gelling agent.

  Specific examples of the hydrogen bonding gelling agent include N-lauroyl-L-glutamic acid dibutylamide (GP1, manufactured by Ajinomoto Co., Inc.), N-2 ethylhexanoyl-L-glutamic acid dibutylamide (EB21, manufactured by Ajinomoto Co., Inc.), stearin. Acid inulin (Leopard ISK2, manufactured by Chiba Flour Mills), stearic acid inulin (Leopard ISL2, manufactured by Chiba Flour Mills), eicosaic behenate diglyceryl (Nomcoat HK-G, manufactured by Nisshin Oilio Co., Ltd.), eicosane behenate Polyglyceryl acid (NOMCOAT HK-P, manufactured by Nisshin Oillio Co., Ltd.), behenic acid (isostearic acid) glyceryl eicosane diacid (NOMUCOAT SG, manufactured by Nisshin Oilio Co., Ltd.), dibenzylidene sorbitol (Gerol D, manufactured by Nippon Nippon Chemical Co., Ltd.) , 12 hydroxystearic acid (12 hydroxystearic acid, Tokyo Kasei) Manufactured), octyldodecanol, dibutyllauroylglutamide, dibutylethylhexanoylglutamide (AJK-OD2046, manufactured by Higher Alcohol), glycerin tri-12-HSA (Riquemar TG-12, manufactured by Riken Vitamin Co.), sorbitan behenate (Riquemar B300, manufactured by Riken Vitamin Co., Ltd.), sorbitan monobehenate (nonion (registered trademark) BP-70R, manufactured by NOF Corporation), sorbitan tristearate (SS-30V, manufactured by Nikko Chemicals), sorbitan monooleate (Leodol) AO-10V (manufactured by Kao Corporation), sorbitan monolaurate (Rheidol Super SP-L10, manufactured by Kao Corporation) and the like.

  The hydrogen bonding gelling agent preferably contains a compound having a sorbitan structure from the viewpoints of storage stability (inhibition of phase separation between the gelling agent and the liquid component excluding the gelling agent) and ejection stability.

  The content of the non-crystalline gelling agent is based on the total mass of the actinic radiation curable inkjet ink from the viewpoint of storage stability (inhibition of phase separation between the gelling agent and the liquid component excluding the gelling agent) and ejection stability. On the other hand, 1.0 mass% or more and 7.0 mass% or less are preferable, and 1.0 mass% or more and 3.0 mass% or less are more preferable.

  The total content of the crystalline gelling agent and the amorphous gelling agent is preferably 2.0% by mass or more and 15% by mass or less, based on the total mass of the actinic ray curable inkjet ink, and is 2.0% by mass. % To 5% by mass is more preferable.

[Photoinitiator]
The actinic ray curable inkjet ink of the present invention may further contain a photoinitiator as necessary. The photoinitiator is a radical photoinitiator when the actinic ray curable inkjet ink of the present invention contains a radical polymerizable compound as a photopolymerizable compound, and the actinic ray curable inkjet ink of the present invention is cationically polymerizable as a photopolymerizable compound. When a compound is contained, it can be a photoacid generator.

  The radical photoinitiator includes an intramolecular bond cleavage type initiator and an intramolecular hydrogen abstraction type initiator.

  Examples of intramolecular bond cleavage type photoinitiators 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- Acetophenones such as thiomethylphenyl) propan-1-one, 2-benzyl-2-dimethylamino-1- (4-morpholinophenyl) -butanone; benzoins such as benzoin, benzoin methyl ether, benzoin isopropyl ether; 4,6-trimethylbenzoindiphenylphosphineoxy Acylphosphine oxide and the like; include a benzyl and methyl phenylglyoxylate ester.

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

  Of these, acylphosphine oxide and acylphosphonate can be preferably used from the viewpoint of sensitivity.

  Specifically, bis (2,4,6-trimethylbenzoyl) -phenylphosphine oxide, bis (2,6-dimethoxybenzoyl) -2,4,4-trimethyl-pentylphosphine oxide and the like are preferable.

  The content of the photoinitiator in the actinic radiation curable inkjet ink of the present invention is 0.01% by mass with respect to the total mass of the actinic radiation curable inkjet ink, although it depends on the type of actinic rays and photopolymerizable compounds. The content is preferably 12% by mass or less and more preferably 2% by mass or more and 8% by mass or less.

  Examples of photoacid generators include chemically amplified photoresists and compounds used for photocationic polymerization (Organic Electronics Materials Study Group, “Organic Materials for Imaging”, Bunshin Publishing (1993), 187. To page 192).

[Color material]
The actinic ray curable inkjet ink of the present invention may further contain a coloring material as necessary. 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 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. The pigment dispersion is such that the volume average particle diameter of the pigment particles is preferably 0.08 μm to 0.5 μm, and the maximum particle diameter is preferably 0.3 μm to 10 μm, more preferably 0.3 μm to 3 μm. It is preferable to be performed. 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.

[Pigment dispersant]
The actinic ray curable inkjet ink of the present invention may contain a pigment dispersant. By including a pigment dispersant in the ink, the dispersibility of the pigment can be enhanced. More preferably, the pigment dispersant contains a comb block copolymer having a tertiary amine (hereinafter also simply referred to as a copolymer). In the present invention, the comb block copolymer is a copolymer in which another type of polymer is graft-polymerized as a side chain for each unit of monomers constituting the main chain with respect to a linear polymer forming the main chain. Say.

  The content of the pigment dispersant is not limited, but is preferably 2.0% by mass or more and 8.0% by mass or less with respect to the total mass of the actinic ray curable inkjet ink. The content of the pigment dispersant is more preferably 2.0% by mass or more and 5.0% by mass or less.

  In addition to the copolymer, the pigment dispersant includes, for example, a hydroxyl group-containing carboxylic acid ester, a salt of a long chain polyaminoamide and a high molecular weight acid ester, a salt of a high molecular weight polycarboxylic acid, a salt of a long chain polyaminoamide and a polar acid ester, Molecular weight unsaturated 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 phosphoric acid You may contain pigment dispersants, such as ester, polyoxyethylene nonyl phenyl ether, and stearylamine acetate. Examples of commercially available pigment dispersants include the Solsperse series from Avecia, the PB series from Ajinomoto Fine Techno, and the like.

  Since the copolymer has a tertiary amine, the electron density of the amine, which is a functional group having adsorptivity to the pigment, is increased and strong basicity is exerted, so the copolymer strongly adsorbs to the acidic group on the pigment surface. Can do. Therefore, the copolymer according to the present invention hardly dissociates from the pigment even at around 85 ° C. where the inkjet ink is discharged. Further, when a copolymer having a tertiary amine in the main chain is used as the copolymer according to the present invention, the side chain is compatible with the photopolymerizable compound, and the pigment dispersant itself is easily dispersed, so that the pigment dispersant is adsorbed. The dispersibility of the pigment can also be improved.

  The substituent of the amine is not particularly limited, but an alkyl group having 1 or 2 carbon atoms is preferable.

  The type of the copolymer is not particularly limited as long as it is a pigment dispersant that satisfies the above conditions. Preferred examples of such a pigment dispersant include BYK-2164, BYK-168, BYK N-22024, manufactured by BYK Chemie, BYK JET-9150, BYK JET-9151, manufactured by Altana, EFKA 4310 manufactured by BASF, EFKA 4320, EFKA 4401, Avecia's SOLSPERSE 39000, Ajinomoto Fine Techno Co., Ltd. Ajisper PB-824, and the like are included.

  The amine of the comb-type block copolymer having a secondary or primary amine may be replaced with other substituents by a known method to tertiaryize the amine. For example, a secondary amine or a primary amine of a comb block copolymer can be reacted with an alcohol such as decyl alcohol in the presence of a reduction catalyst to form a tertiary amine substituted with an alkyl group.

  The actinic ray 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 total amount of the pigment dispersant and the dispersion aid is preferably 1% by mass or more and 50% by mass or less based on the pigment.

  The actinic ray curable inkjet ink of the present invention may further include a dispersion medium for dispersing the pigment as necessary. Although a solvent may be included in the ink as a dispersion medium, in order to suppress the residual solvent in the formed image, a photopolymerizable compound as described above (particularly a monomer having a low viscosity) is used as the dispersion medium. Is preferred.

  The dye can be an oil-soluble dye or the like. Examples of oil-soluble dyes include the following various dyes. Examples of magenta dyes include MS Magenta VP, MS Magenta HM-1450, MS Magenta HSo-147 (manufactured by Mitsui Toatsu), AIZENSOT Red-1, AIZEN SOT Red-2, AIZEN SOTRed-3, and AIZEN SOT. Pink-1, SPIRON Red GEH SPECIAL (above, manufactured by Hodogaya Chemical Co., Ltd.), RESOLIN Red FB 200%, MACROLEX Red Violet R, MACROLEX ROT5B (above, manufactured by Bayer Japan), KAYASET Red B, KAYASE RED130, 802 (above, Nippon Kayaku Co., Ltd.), PHLOXIN, ROSE Bengal, ACID Red (above, Daiwa Kasei Co., Ltd.), H R-31, DIARESIN Red K (manufactured by Mitsubishi Kasei Corp.), include Oil Red (manufactured by BASF Japan Ltd.).

  Examples of cyan dyes include MS Cyan HM-1238, MS Cyan HSo-16, Cyan HSo-144, MS Cyan VPG (manufactured by Mitsui Toatsu), AIZEN SOT Blue-4 (manufactured by Hodogaya Chemical Co., Ltd.), RESOLIN BR. Blue BGLN 200%, MACROLEX Blue RR, CERES Blue GN, SIRIUS SUPRATURQ. Blue Z-BGL, SIRIUS SUTRA TURQ. Blue FB-LL 330% (above, Bayer Japan), KAYASET Blue FR, KAYASET Blue N, KAYASET Blue 814, Turq. Blue GL-5 200, Light Blue BGL-5200 (manufactured by Nippon Kayaku Co., Ltd.), DAIWA Blue 7000, Oleosol Fast Blue GL (manufactured by Daiwa Kasei Co., Ltd.), DIARESIN Blue P (manufactured by Mitsubishi Kasei Co., Ltd.), SUDAN 70 Blu , NEOPEN Blue 808, ZAPON Blue 806 (above, manufactured by BASF Japan Ltd.) and the like.

  Examples of yellow dyes include MS Yellow HSm-41, Yellow KX-7, Yellow EX-27 (manufactured by Mitsui Toatsu), AIZEN SOT Yellow-1, AIZEN SOT YellowW-3, AIZEN SOT Yellow-6 (above, Manufactured by Hodogaya Chemical Co., Ltd.), MACROLEX Yellow 6G, MACROLEX FLUOR. Yellow 10GN (above, manufactured by Bayer Japan), KAYASET Yellow SF-G, KAYASET Yellow 2G, KAYASET Yellow AG, KAYASET Yellow EG (above, manufactured by Nippon Kayaku), DAIWA YELLOW 330H HSY-68 (manufactured by Mitsubishi Kasei Co., Ltd.), SUDAN Yellow 146, NEOPEN Yellow 075 (above, manufactured by BASF Japan Ltd.) and the like.

  Examples of black dyes include MS Black VPC (Mitsui Toatsu Co., Ltd.), AIZEN SOT Black-1, AIZEN SOT Black-5 (above, manufactured by Hodogaya Chemical Co., Ltd.), RESORIN Black GSN 200%, RESOLIN BlackBS (above, Bayer Japan), KAYASET Black A-N (Nippon Kayaku), DAIWA Black MSC (Daiwa Kasei), HSB-202 (Mitsubishi Kasei), NEPTUNE Black X60, NEOPEN Black X58 (above, BASF Japan product).

  The content of the color material is preferably 0.1% by mass or more and 20% by mass or less, and more preferably 0.4% by mass or more and 10% by mass or less with respect to the total amount of the ink.

[Other ingredients]
The actinic ray curable inkjet ink of the present invention may further contain a dispersion aid as required. The dispersion aid may be selected according to the pigment. The actinic ray curable inkjet ink of the present invention may further include a dispersion medium for dispersing the pigment as necessary. Although a solvent may be included in the ink as the dispersion medium, it is preferable that the photopolymerizable compound is a dispersion medium in order to suppress the residual solvent in the formed image.

  The actinic ray curable inkjet ink of the present invention may further contain a photoinitiator auxiliary agent, a polymerization inhibitor, and the like as necessary. The photoinitiator assistant may be a tertiary amine compound, preferably an aromatic tertiary amine compound. 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. Only one kind of these compounds may be contained in the actinic ray curable inkjet ink, or two or more kinds thereof may be contained.

  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.

  The actinic ray curable inkjet ink of the present invention may further contain at least one of an ultraviolet absorber and an antioxidant from the viewpoint of enhancing the weather resistance of the cured film.

  The ultraviolet absorber preferably has a long-wave absorption wavelength of 410 nm or less from the viewpoint of light resistance and ozone resistance. 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 further preferably 0.5% by mass or less. On the other hand, from the viewpoint of absorbing the irradiated ultraviolet rays and sufficiently reducing the photocatalytic action of the inorganic white pigment, the content of the ultraviolet absorber is preferably 0.1% by mass or more.

  From the viewpoint of curability, the content of the antioxidant is preferably 0.8% by mass or less, and more preferably 0.5% by mass or less. On the other hand, the content of the antioxidant is preferably 0.05% by mass or more from the viewpoint of capturing radicals generated in the cured film of the ink and sufficiently suppressing the oxidation of the resin or the like.

  From the viewpoints of ejection stability and curability, the total amount of the ultraviolet absorber and the antioxidant is preferably 2.0% by mass or less and preferably 1.0% by mass or less with respect to the total mass of the ink. More preferred.

  In addition to the above, the actinic ray curable inkjet ink of the present invention may further contain other components as necessary. Other components may be various additives, other resins, and the like. Examples of additives include surfactants, leveling additives, matting agents, infrared absorbers, antibacterial agents 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, and rubber resins.

[Preparation of actinic ray curable inkjet ink]
The actinic ray curable ink-jet ink of the present invention can be obtained by mixing a photopolymerizable compound, a crystalline gelling agent, an amorphous gelling agent and arbitrary components under heating. 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.

[Physical properties of actinic radiation curable inkjet ink]
Since the actinic ray curable inkjet ink of the present invention contains a gelling agent, it can reversibly undergo a sol-gel phase transition depending on the temperature. The sol-gel phase transition type actinic ray curable ink is a sol at a high temperature (for example, about 80 ° C.) and can be ejected from an ink ejection recording head. However, after landing on a recording medium, the gel is naturally cooled. Turn into. Thereby, coalescence of adjacent ink droplets can be suppressed and image quality can be improved.

  In order to improve the discharge property of the actinic radiation curable inkjet 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. Specifically, the viscosity of the ink at 80 ° C. is preferably 3 mPa · s or more and 20 mPa · s or less, more preferably 6.0 mPa · s or more and 15.0 mPa · s or less, and 7.0 or more and 12 or less. More preferably, it is 0.0 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 viscosity in 80 degreeC and the viscosity in 25 degreeC can be calculated | required by reading the viscosity in 80 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 °.

[Inkjet image forming method]
In the inkjet image forming method of the present invention, a step of causing inkjet ink droplets to land on a recording medium by an inkjet method, and a cured film constituting an image is formed by irradiating the inkjet ink landed on the recording medium with actinic rays. Process.

(Step of landing inkjet ink droplets on the recording medium)
In this step, inkjet ink droplets are ejected from an inkjet head and landed on a recording medium. The ink jet ink droplets are preferably landed on a position corresponding to the image to be formed on the recording medium.

  The on-demand method or the continuous method may be used as the discharge method from the inkjet head. Examples of on-demand inkjet heads include electro-mechanical conversion systems including single cavity, double cavity, vendor, piston, shear mode and shared wall, thermal inkjet and bubble jet (bubble) The jet includes an electric-thermal conversion system including a Canon (registered trademark) type.

  The ejection stability of the inkjet ink droplets can be improved by ejecting the droplets from the inkjet head in a heated state. The temperature of the inkjet ink at the time of ejection is preferably 35 ° C. or more and 100 ° C. or less, and more preferably 35 ° C. or more and 80 ° C. or less from the viewpoint of further improving ejection stability. From the viewpoint of further improving the ejection stability, it is preferable to emit at an ink temperature such that the viscosity of the inkjet ink is 7 mPa · s to 15 mPa · s, more preferably 8 mPa · s to 13 mPa · s.

  Examples of a method for heating inkjet ink to a predetermined temperature include at least one of an ink tank constituting a head carriage, an ink supply system such as a supply pipe and an anterior chamber ink tank immediately before the head, a pipe with a filter, and a piezo head. Is heated to a predetermined temperature by any one of a panel heater, a ribbon heater, warm water and the like.

  From the viewpoint of increasing the recording speed and improving the image quality, it is preferable that the droplet amount of the ink-jet ink when ejected is 2 pL or more and 20 pL or less.

(Process of forming a cured film constituting an image by irradiating an ink jet ink landed on a recording medium with an actinic ray)
In this step, the ink jet ink landed in the previous step is irradiated with actinic rays to form a cured film constituting an image. By irradiating the inkjet ink with actinic rays, the inkjet ink is cured and a cured film is formed.

  From the viewpoint of enhancing the curability of the inkjet ink, the actinic ray is preferably applied for 0.001 second or more and 1.0 second or less after ink landing. It is more preferable to irradiate between 001 seconds and 0.5 seconds.

  Examples of actinic rays that can be applied to the inkjet ink include electron beams, ultraviolet rays, α rays, γ rays, and X-rays. Among these, it is preferable to irradiate ultraviolet rays from the viewpoint of easy handling and little influence on the human body. The light source is preferably a light emitting diode (LED) from the viewpoint of suppressing the occurrence of ink curing failure due to melting of the inkjet ink by the radiant heat of the light source. Examples of LED light sources capable of irradiating with ultraviolet rays for forming a cured film include 395 nm, water-cooled LED, manufactured by Phoseon Technology.

From a more suppressing the radiation of radiant heat into the inkjet ink, LED light source is installed 410nm UV light below above 370nm as peak irradiance in the image surface is 0.5 W / cm ² or more 10 W / cm ² or less, it is more preferable to be installed so that 1W / cm ² or more 5W / cm ² or less, or amount of light applied to an image is preferred to be installed to be less than 350 mJ / cm ^2.

  From the viewpoint of more efficiently suppressing the shrinkage of the recording material that occurs during ink curing, it is preferable to divide the irradiation of actinic rays into two stages. For example, first, after the ink jet ink has landed, actinic light is irradiated by the above-described method for 0.001 second or more and 2.0 seconds or less to temporarily cure the ink jet ink. The ink-jet ink can be fully cured.

[Conveying process]
The conveyance speed of the recording medium is preferably 30 m / min or more and 120 m / min or less from the viewpoint of high-speed recording.

[recoding media]
The recording medium used in the inkjet image forming method of the present invention is only required to form an image with the ink of the present invention. For example, polyester, polyvinyl chloride, polyethylene, polyurethane, polypropylene, acrylic resin, polycarbonate, polystyrene, acrylonitrile- Non-absorbing recording media composed of plastics containing butadiene-styrene copolymer, polyethylene terephthalate and polybutadiene terephthalate, non-absorbing inorganic recording media such as metals and glass, and papers (for example, coated paper for printing) And coated paper B for printing). Among them, it can be preferably used for an OK topcoat, a maricoat, and the like of papers that are required to be coated with an overcoat solution.

  By ejecting ink droplets from the inkjet recording head, the ink droplets adhere to the recording medium. In order to form high image quality with high reproducibility, the temperature of the recording medium when the ink droplets land is preferably set to 20 ° C. or higher and 50 ° C. or lower.

[Inkjet recording apparatus]
An actinic ray curable ink jet recording apparatus using the actinic ray curable ink jet of 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.

  1A and 1B are diagrams illustrating an example of a configuration of a main part of a line recording type inkjet recording apparatus. Among these, FIG. 1A is a side view, and FIG. 1B is a top view. As shown in FIGS. 1A and 1B, the ink jet recording apparatus 10 covers a head carriage 16 that accommodates a plurality of ink ejection recording heads 14 and the entire width of the recording medium 12, and the head carriage 16 (recording medium The actinic ray irradiation unit 18 disposed on the downstream side in the transport direction) and the temperature control unit 19 disposed on the lower surface of the recording medium 12 are provided.

  The head carriage 16 is fixedly arranged so as to cover the entire width of the recording medium 12 and accommodates a plurality of ink 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. dpi represents the number of ink droplets (dots) per 2.54 cm.

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

When the actinic ray is ultraviolet ray, examples of the actinic ray irradiating unit 18 (ultraviolet ray irradiating means) include a fluorescent tube (low pressure mercury lamp, germicidal lamp), a cold cathode tube, an ultraviolet laser, and an operating pressure of several hundred Pa to 1 MPa. Low pressure, medium pressure, high pressure mercury lamp, metal halide lamp and LED. From the viewpoint of curability, ultraviolet irradiation means for irradiating ultraviolet rays having an illuminance of 100 mW / cm ² or more; specifically, high-pressure mercury lamps, metal halide lamps, and LEDs are preferable, and LEDs are more preferable from the viewpoint of low power consumption and radiant heat. preferable.

  When the actinic ray is an electron beam, examples of the actinic ray irradiating unit 18 (electron beam irradiating unit) include electron beam irradiating 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 inkjet image forming 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 ray irradiating unit 18 irradiates the ink droplets attached on the recording medium 12 with an actinic ray to cure.

  When the ink is ejected from the ink ejection recording head 14, the temperature of the ink in the ink ejection recording head 14 is 10 ° C. or more and 30 ° C. or less than the gelation temperature of the ink in order to improve the ink ejection performance. It is preferable that the temperature is set to a high temperature.

  The amount of droplets ejected from each nozzle of the ink ejection recording head 14 is preferably 0.5 pl or more and 10 pl or less, depending on the viscosity of the ink, but is ejected only in a desired region. Therefore, it is more preferably 0.5 pl or more and 4.0 pl or less, and further preferably 1.5 pl or more and 4.0 pl or less. Even when such an amount of ink is applied, since the sol-gel phase transition is performed in the ink according to the present invention, the ink does not excessively wet and spread, and can be discharged only to a desired location.

  The ink droplets adhering to the recording medium are cooled and rapidly gelled by the sol-gel phase transition. Thereby, the ink droplets can be pinned without excessively spreading. Furthermore, since the droplets rapidly gel and increase in viscosity, oxygen hardly enters the ink surface adhering to the recording medium, and curing of the ink surface is not easily inhibited by oxygen.

  Here, by ejecting ink droplets from the ink ejection recording head 14, the ink droplets adhere to the recording medium. The temperature of the recording medium when ink droplets adhere is preferably set to a temperature that is 10 ° C. or higher and 20 ° C. or lower than the gelation temperature of the ink.

  Irradiation with actinic rays is performed within 10 seconds after the ink droplets are deposited on the recording medium, preferably within 0.001 seconds or more and within 5 seconds, more preferably, in order to prevent the adjacent ink droplets from joining together. It is preferable to carry out within 0.01 second or more and 2 seconds or less. Irradiation with actinic rays is preferably performed after ink is ejected from all the ink ejection recording heads 14 accommodated in the head carriage 16.

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

  The total ink film thickness after curing is preferably 2 μm or more and 25 μm or less. The “total ink film thickness” is the maximum value of the ink film thickness drawn on the recording medium.

  FIG. 2 is a top view 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. 1A and 1B can be configured except that 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 are provided.

  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.

  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 pigment dispersion]
The pigment dispersion was adjusted by the following procedure.

  9 parts of Ajisper PB824 (manufactured by Ajinomoto Fine Techno Co., Ltd.) which is a pigment dispersant, 71 parts of tripropylene glycol diacrylate (M-220: Toa Gosei Co., Ltd., viscosity 12 mPa · s) which is a photopolymerizable compound, stainless beaker The mixture was heated and stirred for 1 hour while heating on a hot plate at 65 ° C.

  The mixed liquid was cooled to room temperature, and 20 parts of Pigment Blue 15: 4 (chromofine blue 6332JC, manufactured by Dainichi Seika Kogyo Co., Ltd.) as a pigment was further 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 8 hours. Thereafter, the zirconia beads were removed to obtain a pigment dispersion.

[Preparation of ink]
In accordance with the actinic radiation curable inkjet ink components described in the following table, the following components and the pigment dispersion were mixed, heated to 80 ° C. and stirred. Under heating, the solution obtained with a Teflon (registered trademark) 3 μm membrane filter manufactured by ADVANTEC was filtered. 1-15 were obtained. In addition, the unit of the component of a table | surface is the mass%.

[Photopolymerizable compound]
Polyethylene glycol diacrylate (NK ester A-400: manufactured by Shin-Nakamura Chemical Co., Ltd., viscosity at 25 ° C. 57 mPa · s)
4EO-modified pentaerythritol tetraacrylate (SR494: SARTOMER, viscosity 131 mPa · s at 25 ° C.)
3PO-modified trimethylolpropane triacrylate (EM2381 manufactured by Changko Chemical Co., Ltd., viscosity 83 mPa · s at 25 ° C.)

[Gelling agent]
(Crystalline gelling agent)
Capric acid (Poem M200: Riken Vitamin Co., C10)
Caprylic caprate (C10-C10)
Distearyl ketone (Kao wax T1: Kao Corporation, C18-C18)
Dipalmityl ketone (Hentriacontan-16-on: Arfa Aeser, C16-C16)
Behenyl behenate (Unistar M-2222SL: NOF Corporation, C21-C22)
Behenyl stearate (WE11: NOF Corporation, C17-C21)
Stearyl stearate ((Exepar SS: manufactured by Kao Corporation, C17-C18))
(Non-crystalline gelling agent)
Aluminum isostearate (metal soap: manufactured by Wako, hydrogen bonding gelling agent))
N-2 ethylhexanoyl-L-glutamic acid dibutylamide (EB21: Ajinomoto Co., Inc., hydrogen bonding gelling agent)
N-lauroyl-L-glutamic acid dibutyramide (GP1: Ajinomoto Co., Inc., hydrogen bonding gelling agent)
12 hydroxystearic acid (12 hydroxystearic acid: manufactured by Tokyo Chemical Industry Co., Ltd., hydrogen bonding gelling agent)
Behenic acid (isostearic acid) glyceryl eicosane diacid (Nomucoat SG: Nisshin Oilio Co., Ltd., hydrogen bonding gelling agent)
Inulin stearate (Leopard ISK2: manufactured by Chiba Flour Mills, hydrogen bonding gelling agent)
Sorbitan monolaurate (Leodol Super SP-L10: manufactured by Kao Corporation, hydrogen bonding gelling agent, containing sorbitan structure)
Sorbitan behenate (Riquemar B-300; manufactured by Riken Vitamin Co., Ltd., hydrogen bonding gelling agent, containing sorbitan structure)
Sorbitan monobehenate (Nonion (registered trademark) BP-70R: NOF Corporation, hydrogen bonding gelling agent, sorbitan structure-containing)
Sorbitan tristearate (SS-30V: manufactured by Nikko Chemicals, hydrogen-bonding gelling agent, containing sorbitan structure)

[Photoinitiator]
DAROCURE TPO (Ciba Specialty Chemicals)

[Polymerization inhibitor]
Irgastab UV10 (manufactured by BASF)

[Inkjet image forming method]
The actinic ray curable inkjet ink obtained in each of the examples and comparative examples was loaded into a line type inkjet recording apparatus having an inkjet recording head equipped with a piezo inkjet nozzle. The ink supply system was composed of an ink tank, an ink flow path, a sub ink tank immediately before the ink jet recording head, a pipe with a filter, and a piezo head. The temperature of the ink jet head was set to 80 ° C. Further, the recording medium conveyance table was set to 40 ° C. A solid image of 5 cm × 5 cm or a density gradation patch is printed on a recording medium, and after an image is formed, an LED lamp (Phoseon Technology 395 nm, water-cooled LED) disposed downstream of the recording apparatus is used. The ink was cured by irradiating the image with ultraviolet rays.

  As the ink jet recording head, a piezo head having a nozzle diameter of 20 μm and a nozzle number of 512 nozzles (256 nozzles × 2 rows, staggered arrangement, 1 row nozzle pitch 360 dpi) was used. The ejection conditions were such that the amount of one droplet was 2.5 pl, and ejection was performed at a droplet velocity of about 6 m / s, and recording was performed at a resolution of 1440 dpi × 1440 dpi. The recording speed was 500 mm / s. Image formation was performed in an environment of 23 ° C. and 55% RH. dpi represents the number of dots per 2.54 cm.

After printing, the image surface was completely cured by applying an energy amount of 600 mJ / cm ² with an LED lamp (4 W / cm ² , water cooled unit, manufactured by Phoseon Technology). Irradiation was performed at a distance of 5 mm from the tube surface (irradiation width 20 mm in the conveying direction). The integrated light amount was measured using an ultraviolet integrated light meter (C9536-2 and H9958-2, manufactured by Hamamatsu Photonics), and the recording medium conveyance speed was adjusted.

[Evaluation method]
(Evaluation of phase separation of gelling agent by storage at room temperature)
Each adjusted ink was put into a 200 ml beaker, redissolved at 90 ° C. and then cooled at room temperature. After standing at room temperature for 1 week, the upper and lower inks were taken out, and viscosity measurement (MCR300, Physica) Made).
◎: No difference between upper and lower parts ○: Lower viscosity drop within 5% △: Lower viscosity drop within 10% ×: No lower ink gelation

(Evaluation of ejection stability)
Ink jet recording apparatus equipped with each prepared ink was used to eject ink from the ink jet head, and visually observed for the absence of nozzles and ejection bending, and the ejection stability was evaluated according to the following criteria.
◎: No nozzle missing was observed. ○: Nozzle missing was observed in 1 to 4 nozzles in all nozzles 512. △: Nozzle missing was observed in 5 or more nozzles in all nozzles 512. The

(Evaluation of image quality / leveling properties)
By the above method, a solid image of 5 cm × 5 cm was printed on a recording medium for printing coated paper A (manufactured by OK TOPCOAT rice basis weight 128 g / m ² Oji Paper Co., Ltd.) was visually evaluated, density unevenness in accordance with the following evaluation criteria Was evaluated.
A: Observed from a position 5 cm away, no density unevenness is observed in the image. O: Observed from a position 15 cm away, no density unevenness is observed in the image. Δ: Observed from a position 15 cm away. Density unevenness is observed in a part, but no density unevenness is observed from a position separated by 30 cm. X: Density unevenness is observed in an image observed from a position separated by 30 cm.

  The evaluation results are shown in Tables 1 to 3. In addition, the unit% of the component of a table | surface is the mass%.

  The actinic radiation curable inkjet ink according to the present invention is an actinic radiation curable inkjet ink containing a gelling agent, and the storage stability of the ink (inhibition of phase separation between the gelling agent and the liquid component excluding the gelling agent) Is suitable for such an inkjet image forming method.

DESCRIPTION OF SYMBOLS 10, 20 Inkjet recording device 12 Recording medium 14, 24 Ink discharge recording head 16, 26 Head carriage 18, 28 Actinic ray irradiation unit 19 Temperature control unit 27 Guide unit

Claims (7)

An actinic ray curable inkjet ink containing a photopolymerizable compound and a gelling agent,
The actinic ray curable inkjet ink, wherein the gelling agent contains a crystalline gelling agent and an amorphous gelling agent.   The actinic ray curable inkjet ink according to claim 1, wherein the non-crystalline gelling agent contains a hydrogen bonding gelling agent.   The actinic ray curable inkjet ink according to claim 1, wherein the content of the crystalline gelling agent is 1% by mass or more and 7% by mass or less based on the total mass of the ink.   The actinic ray according to any one of claims 1 to 3, wherein the crystalline gelling agent contains a gelling agent containing an alkyl group having 12 to 26 carbon atoms in the straight chain portion. A curable inkjet ink.   The photopolymerizable compound contains a photopolymerizable compound A having a viscosity at 25 ° C. of not less than 80 mPa · s and not more than 300 mPa · s, and the photopolymerizable compound A is 40% relative to the total mass of the photopolymerizable compound. The actinic ray curable inkjet ink according to claim 1, wherein the actinic ray curable inkjet ink is contained by mass% or more.   The actinic ray curable inkjet ink according to any one of claims 1 to 5, wherein the non-crystalline gelling agent contains a sorbitan structure.   A step of landing droplets of the actinic ray curable inkjet ink according to any one of claims 1 to 6 on a recording medium, and irradiating the droplets that have landed on the recording medium with an actinic ray to form an image An inkjet image forming method comprising a step of forming a cured film to be formed.

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