JP7043822B2 - Active ray curable inkjet ink - Google Patents

Description

The present invention relates to an active ray-curable inkjet ink, and more particularly to an active ray-curable inkjet ink that can suppress blooming peculiar to gel ink and has good image curability and image quality.

As one of the inkjet recording methods, there is an ultraviolet curable inkjet method in which a droplet of an ultraviolet curable inkjet ink is landed on a recording medium and then irradiated with ultraviolet rays to cure the image. The ultraviolet curable inkjet recording method has been attracting attention in recent years because it can form an image having high scratch resistance and adhesion even on a recording medium having no ink absorption.

It is known that a hindered phenol compound is used as a polymerization inhibitor in such an ultraviolet curable inkjet ink (see, for example, Patent Documents 1 and 2).

On the other hand, as a method for improving the pinning property of the inkjet ink used in the inkjet recording method, the addition of a gelling agent has been studied. That is, it has been studied to suppress the coalescence of dots by ejecting ink droplets in a liquid state at a high temperature and landing them on a recording medium and at the same time cooling the ink droplets to form a gel.
However, the inkjet ink containing such a gelling agent (hereinafter, also referred to as “gel ink”) has a problem peculiar to gel ink such as blooming due to precipitation of the gelling agent.

Japanese Unexamined Patent Publication No. 2005-179416 Japanese Unexamined Patent Publication No. 2009-220582

The present invention has been made in view of the above problems and situations, and the solution thereof is to provide an active ray-curable inkjet ink that can suppress blooming peculiar to gel ink and has good image curability and image quality. That is.

In order to solve the above problems, the present inventor uses a compound having four or more hindered phenol moieties instead of a polymerization inhibitor as in the past in the process of investigating the cause of the above problems. We have found that it is possible to suppress peculiar blooming, and have reached the present invention.

1. 1. An active photocurable inkjet ink containing a photopolymerizable compound, a photopolymerization initiator and a gelling agent.
The gelling agent is selected from at least one of fatty acid ketone, fatty acid ester, petroleum wax, fatty acid amide, and higher fatty acid.
Furthermore, it contains a compound having 4 or more hindered phenol sites ,
The activity characterized in that the content of the compound having four or more hindered phenol moieties is in the range of 0.1 to 1.0% by mass with respect to the total mass of the active photocurable inkjet ink. Light-curing inkjet ink.

2 . The active photocurable inkjet ink according to item 1, wherein the gelling agent is a compound having a structure represented by the following general formula (G1) or general formula (G2).
General formula (G1): R ₁₁ -CO-R ₁₂
General formula (G2): R ₁₃ -COO-R ₁₄
[In the formula, R ₁₁ to R ₁₄ each independently represent a linear hydrocarbon group having a carbon number in the range of 9 to 25. ]

3 . Item 1 or 2 , wherein the content of the gelling agent is in the range of 0.5 to 10.0% by mass with respect to the total mass of the active photocurable inkjet ink. The active light curable inkjet ink described.

By the above means of the present invention, it is possible to provide an active ray-curable inkjet ink that can suppress blooming peculiar to gel ink and has good image curability and image quality.
Although the mechanism of expression or mechanism of action of the effect of the present invention has not been clarified, it is inferred as follows.
First, by using a compound having a hindered phenol moiety having a substituent having a large steric hindrance as a hydrophobic component in combination, the aromatic ring interacts with the hydrophobic part of the gelling agent (see part A in FIG. 1). ..
Furthermore, since the number of the hindered phenol sites is four or more, the hydroxy groups of the hindered phenol sites form hydrogen bonds in the coating film, so that the gelling agent can be trapped in the crosslinked structure ( See part B in FIG. 1). As a result, precipitation of the gelling agent after curing by UV irradiation can be suppressed. Therefore, the more hindered phenol sites there are, the higher the blooming inhibitory effect.
On the other hand, in the case of phenol that is not hindered, hydrogen bonds in the coating film are too strong, so that radicals generated after UV irradiation are trapped, which is not preferable. By using the hindered phenol type, steric hindrance becomes large and the reaction rate with radicals decreases. Further, when there is only one hindered phenol moiety, an interaction with the gelling agent is formed, but it is difficult to trap the gelling agent in the long term.
From the above, it is presumed that blooming can be suppressed by containing a compound having four or more hindered phenol sites.

The figure for demonstrating the blooming suppression mechanism in the inkjet ink of this invention.

The active photocurable inkjet ink of the present invention is an active photocurable inkjet ink containing a photopolymerizable compound, a photopolymerization initiator and a gelling agent, and the gelling agent is a fatty acid ketone, a fatty acid ester, or petroleum. The active ray is selected from at least one of a system wax, a fatty acid amide, and a higher fatty acid, and further contains a compound having 4 or more hindered phenol moieties, and the content of the compound having 4 or more hindered phenol moieties is the active ray. It is characterized in that it is in the range of 0.1 to 1.0% by mass with respect to the total mass of the curable inkjet ink .
This feature is a technical feature common to or corresponding to each of the following embodiments.

Further, it is preferable that the gelling agent is a compound having a structure represented by the general formula (G1) or the general formula (G2) from the viewpoint of the pinning effect and the interaction with the hindered phenol moiety. ..

Further, the content of the gelling agent is in the range of 0.5 to 10.0% by mass with respect to the total mass of the active light-curing inkjet ink, which is the effect of pinning property and the effect of suppressing blooming. Preferred from the point of view.

Further, the content of the compound having the hindered phenol moiety is in the range of 0.1 to 1.0% by mass with respect to the total mass of the active photocurable inkjet ink, which is the effect of suppressing blooming. Preferred from the viewpoint.

Hereinafter, the present invention, its constituent elements, and modes and embodiments for carrying out the present invention will be described. In addition, in this application, "-" is used in the sense that the numerical values described before and after it are included as the lower limit value and the upper limit value.

1. 1. Active Ray Curable Inkjet Ink The active ray curable inkjet ink of the present invention (hereinafter, also referred to as “inkjet ink” or “ink”) is an active ray containing a photopolymerizable compound, a photopolymerization initiator and a gelling agent. It is a curable inkjet ink, and is further characterized by containing a compound having four or more hindered phenol moieties.

The active light curable inkjet ink of the present invention is an ink composition that can be cured by active light.
The “active ray” is a light ray capable of imparting energy to generate a starting species in the ink composition by its irradiation, and includes α-rays, γ-rays, X-rays, ultraviolet rays, electron beams and the like. Among them, ultraviolet rays and electron beams are preferable, and ultraviolet rays are more preferable, from the viewpoint of curing sensitivity and availability of an apparatus.

1-1. A compound having four or more hindered phenol moieties In the present invention, the hindered phenol moiety has a phenolic hydroxy group and a structure having at least one substituent having a highly sterically hindered substituent at at least one ortho position with respect to the hydroxy group. Refers to the part having.
The compound having four or more hindered phenol moieties according to the present invention refers to a hindered phenol (derivative) having four or more phenolic hydroxy groups, and further, in the present application, a tetrafunctional or higher functional hindered phenolic compound ( Also called derivative).

It is preferable that the compound having a hindered phenol moiety (hereinafter, also referred to as “hindered phenol compound”) has four hindered phenol moieties in that the effect of suppressing browning is high.

Examples of the compound having four or more hindered phenol sites and the compound given as a reference example include those shown below.
(1) Level 2 hindered system

The content of the compound having four or more hindered phenol moieties is preferably in the range of 0.1 to 1.0% by mass with respect to the total mass of the inkjet ink. When it is 0.1% by mass or more, the blooming suppressing effect is excellent, and when it is 1.0% by mass or less, radicals generated after UV irradiation can be trapped and prevented from inhibiting the polymerization reaction.

1-2. Photopolymerizable Compounds Examples of photopolymerizable compounds include radically polymerizable compounds and cationically polymerizable compounds.
The photopolymerizable compound has an action of cross-linking or polymerizing by being irradiated with the above-mentioned active light rays and curing the ink. The photopolymerizable compound may be any of a monomer, a polymerizable oligomer, a prepolymer or a mixture thereof. The ink of the present invention may contain only one type of photopolymerizable compound, or may contain two or more types of the photopolymerizable compound.

The content of the photopolymerizable compound is preferably in the range of 1 to 97% by mass with respect to the total mass of the ink of the present invention, for example, from the viewpoint of film physical properties such as curability and flexibility, and is 30 to 95. It is more preferably in the range of% by mass.
The radically polymerizable compound is preferably an unsaturated carboxylic acid ester, more preferably a (meth) acrylate.
In the present invention, "(meth) acrylate" means acrylate or methacrylic acid, "(meth) acryloyl group" means acryloyl group or metaacryloyl group, and "(meth) acrylic" means acrylic. Or it means methacrylic.

Examples of (meth) acrylates include isoamyl (meth) acrylate, stearyl (meth) acrylate, lauryl (meth) acrylate, octyl (meth) acrylate, decyl (meth) acrylate, isomilstill (meth) acrylate, and 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 (meth) acrylate, tetrahydrofurfuryl (meth) acrylate, isobornyl (meth) acrylate, 2-hydroxyethyl (meth) ) Acrylate, 2-hydroxypropyl (meth) acrylate, 2-hydroxy-3-phenoxypropyl (meth) acrylate, 2- (meth) acryloyloxyethyl succinic acid, 2- (meth) acryloyloxyethyl phthalic acid, 2 -Monofunctional acrylates containing (meth) acryloyloxyethyl-2-hydroxyethyl-phthalic acid and t-butylcyclohexyl (meth) acrylates, triethylene glycol di (meth) acrylates, tetraethylene glycol di (meth) acrylates, 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-Nonandiol di (meth) acrylate, neopentyl glycol di (meth) acrylate, dimethylol-tricyclodecandi (meth) acrylate, di (meth) acrylate with bisphenol A structure, neopentyl glycol di hydroxypivalate ( Bifunctional (meth) acrylates including meta) acrylates, polytetramethylene glycol di (meth) acrylates, polyethylene glycol diacrylates and tripropylene glycol diacrylates, as well as trimethylol propanetri (meth) acrylates, pentaerythritol tri (meth). ) Acrylate, Pe Trifunctional or higher (meth) acrylates including entaerythritol tetra (meth) acrylates, dipentaerythritol hexa (meth) acrylates, ditrimethylolpropane tetra (meth) acrylates, glycerin propoxytri (meth) acrylates and pentaerythritol ethoxytetra (meth) acrylates. ) Acrylate, an oligomer having a (meth) acryloyl group including a polyester acrylate oligomer, and modified products thereof.

Examples of the modified product include ethylene oxide-modified (EO-modified) acrylate in which an ethylene oxide group is inserted, and propylene oxide-modified (PO-modified) acrylate in which propylene oxide is inserted.
The photopolymerizable compound is a (meth) acrylate compound having a molecular weight in the range of 280 to 1500 and a ClogP value in the range of 4.0 to 7.0 (hereinafter, simply "(meth) acrylate compound A"). Also referred to as).
It is more preferable that the (meth) acrylate compound A has two or more (meth) acrylate groups.
The molecular weight of the (meth) acrylate compound A is in the range of 280 to 1500, more preferably in the range of 300 to 800, as described above.
In order to stably eject the ink from the inkjet recording head, the ink viscosity at 80 ° C. can be set to 3 to 20, preferably 7 to 14 mPa · s.
By including the (meth) acrylate compound having a molecular weight of 280 or more and the gelling agent in the ink composition, the viscosity of the ink after landing is increased and the penetration of the ink into the substrate can be suppressed, so that the ink has curability. Can be expected to have the effect of suppressing the decrease in ink. On the other hand, by containing a (meth) acrylate compound having a molecular weight of 1500 or less, it is possible to suppress an excessive increase in the sol viscosity of the ink, and it is expected that the gloss uniformity of the coating film will be improved.

Here, the molecular weight of the (meth) acrylate compound A can be measured using the following commercially available software package 1 or 2.
Software Package 1: MedChem Software (Released 3.54, August 1991, Medicinal Chemistry Project, Pomona College, Claremont, CA),
Software Package 2: Chem Draw Ultra ver. 8.0. (April 2003, CambridgeSoft Corporation, USA)

In the present invention, when the ink contains the (meth) acrylate compound A as at least a part of the photopolymerizable compound, the ink using the (meth) acrylate compound having a ClogP value of less than 4.0 as the photopolymerizable compound is used. The gloss value tends to be lower than that. Therefore, when used as an ink for forming an image on a substrate having a relatively low 60 ° gloss value before the corona discharge treatment, the gloss difference between the printed portion and the non-printed portion can be reduced, which is preferable. Since the (meth) acrylate compound A is more hydrophobic than the (meth) acrylate compound having a ClogP value of less than 4.0, more gelling agents repel and move to the surface of the cured film of the ink, increasing unevenness. As a result, it is considered that the gloss value of the printed portion is lowered. Further, the ClogP value of the (meth) acrylate compound A is more preferably in the range of 4.5 to 6.0.

Here, the "logP value" is a coefficient indicating the affinity of the organic compound for water and 1-octanol.
The 1-octanol / water partition coefficient P is the partition equilibrium when a trace amount of the compound is dissolved as a solute in the solvent of the two-component phase of 1-octanol and water, and is the ratio of the equilibrium concentration of the compound in each solvent. They are shown by their loglogP for the base 10. That is, the "logP value" is a logarithmic value of the partition coefficient of 1-octanol / water, and is known as an important parameter representing the prohydrophobicity of the molecule.

The "LogP value" is a logP value calculated by calculation. The ClogP value can be calculated by a fragment method, an atomic approach method, or the like. More specifically, in order to calculate the ClogP value, the literature (C. Hansch and A. Leo, "Substituts for Partitions for Correlation Analysis in Chemistry and Biology" (John Wiley & Sons, 19), N. The method or the following commercially available software package 1 or 2 may be used.
Software Package 1: MedChem Software (Released 3.54, August 1991, Medicinal Chemistry Project, Pomona College, Claremont, CA),
Software Package 2: Chem Draw Ultra ver. 8.0. (April 2003, CambridgeSoft Corporation, USA)
The numerical value of the ClogP value described in the present specification and the like is the “ClogP value” calculated by using the software package 2.

The amount of the (meth) acrylate compound A contained in the ink is not particularly limited, but is preferably in the range of 1 to 40% by mass, preferably in the range of 5 to 30% by mass, based on the total mass of the ink. More preferred. By setting the amount of the (meth) acrylate compound A to 1% by mass or more, the ink does not become too hydrophilic and the gelling agent is sufficiently dissolved in the ink, so that the ink easily undergoes a sol-gel phase transition. On the other hand, by setting the amount of the (meth) acrylate compound A to 40% by mass or less, the photopolymerization initiator can be sufficiently dissolved in the ink.

More preferred examples of the (meth) acrylate compound A are (1) trifunctional or higher having 3 to 14 structures represented by (-C (CH ₃ ) H-CH ₂ -O-) in the molecule. It contains a methacrylate or acrylate compound, and (2) a bifunctional or higher functional methacrylate or acrylate compound having a cyclic structure in the molecule. These (meth) acrylate compounds have high photocurability and less shrinkage when cured. Furthermore, the reproducibility of the sol-gel phase transition is high.

A trifunctional or higher methacrylate or acrylate compound having 3 to 14 structures represented by (-C (CH ₃ ) H-CH ₂ -O-) in the molecule includes, for example, 3 or more hydroxy groups. The hydroxy group of the compound is propylene oxide-modified, and the obtained modified product is esterified with (meth) acrylic acid.
Specific examples of this compound include
3PO-modified trimethylolpropane triacrylate Photomer 4072 (molecular weight: 471, ClogP: 4.90, manufactured by Cognis),
3PO-modified trimethylolpropane triacrylate Miramer M360 (molecular weight: 471, ClogP: 4.90, manufactured by Miwon)
Etc. are included.

The bifunctional or higher methacrylate or acrylate compound having a cyclic structure in the molecule is, for example, an esterified hydroxy group of a compound having two or more hydroxy groups and a tricycloalkane with (meth) acrylic acid. ..
Specific examples of this compound include
Tricyclodecanedimethanol diacrylate NK ester A-DCP (molecular weight: 304, ClogP: 4.69),
Tricyclodecanedimethanol dimethacrylate NK ester DCP (molecular weight: 332, ClogP: 5.12)
Etc. are included.
As another specific example of the (meth) acrylate compound A, 1,10-decanediol dimethacrylate NK ester DOD-N (molecular weight: 310, LogP: 5.75, manufactured by Shin-Nakamura Chemical Co., Ltd.) and the like are also included.

The photopolymerizable compound may further contain a photopolymerizable compound other than the (meth) acrylate compound A.
Other photopolymerizable compounds include, for example, (meth) acrylate monomers or oligomers with a ClogP value of less than 4.0, (meth) acrylate monomers or oligomers with a ClogP value greater than 7.0, and other polymerizable properties. There are oligomers and the like.
Examples of these (meth) acrylate monomers or oligomers are 4EO-modified hexanediol diacrylates (CD561, manufactured by Sartomer, molecular weight 358); 3EO-modified trimethylol propantriacrylates (SR454, manufactured by Sartomer, molecular weight 429); 4EO-modified pentaerythritol tetraacrylate (SR494, manufactured by Sartomer, molecular weight 528); 6EO-modified trimethylol propantriacrylate (SR499, manufactured by Sartomer, molecular weight 560); caprolactone acrylate (SR495B, manufactured by Sartomer, molecular weight 344); polyethylene glycol. Diacrylate (NK ester A-400, manufactured by Shin-Nakamura Chemical Co., Ltd., molecular weight 508), (NK ester A-600, manufactured by Shin-Nakamura Chemical Co., Ltd., molecular weight 708); polyethylene glycol dimethacrylate (NK ester 9G, manufactured by Shin-Nakamura Chemical Co., Ltd.) , Molecular weight 536), (NK ester 14G, manufactured by Shin-Nakamura Chemical Co., Ltd.); Tetraethylene glycol diacrylate (V # 335HP, manufactured by Osaka Organic Chemical Co., Ltd., molecular weight 302); Stearyl acrylate (STA, manufactured by Osaka Organic Chemical Co., Ltd.); EO-modified acrylate (M144, manufactured by Miwon); nonylphenol EO-modified acrylate (M166, manufactured by Miwon) and the like are included.
Examples of other polymerizable oligomers include epoxy acrylates, aliphatic urethane acrylates, aromatic urethane acrylates, polyester acrylates, linear acrylic oligomers and the like.

The cationically polymerizable compound used as the photopolymerizable compound may be an epoxy compound, a vinyl ether compound, an oxetane compound or the like.
Only one type of the cationically polymerizable compound may be contained in the active light-curable inkjet ink, or two or more types may be contained.
The epoxy compound is an aromatic epoxide, an alicyclic epoxide, an aliphatic epoxide, or the like, and in order to enhance the curability, the aromatic epoxide and the alicyclic epoxide are preferable.

The aromatic epoxide can be a di or polyglycidyl ether obtained by reacting a polyhydric phenol or an alkylene oxide adduct thereof with epichlorohydrin.
Examples of the polyvalent phenol to be reacted or an alkylene oxide adduct thereof include bisphenol A or an alkylene oxide adduct thereof.
The alkylene oxide in the alkylene oxide adduct may be ethylene oxide, propylene oxide or 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 aliphatic polyhydric alcohols include ethylene glycol, propylene glycol, alkylene glycols such as 1,6-hexanediol and the like. The alkylene oxide in the alkylene oxide adduct may be ethylene oxide, propylene oxide or 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, and isopropenyl ether. Monovinyl ether compounds such as -o-propylene carbonate, dodecyl vinyl ether, diethylene glycol monovinyl ether, octadecyl vinyl ether; ethylene glycol divinyl ether, diethylene glycol divinyl ether, triethylene glycol divinyl ether, propylene glycol divinyl ether, dipropylene glycol divinyl ether, butanediol di. Di or trivinyl ether compounds such as vinyl ether, hexanediol divinyl ether, cyclohexanedimethanol divinyl ether, trimethylolpropane trivinyl ether and the like are included. Among these vinyl ether compounds, di or trivinyl ether compounds are preferable in consideration of curability and adhesion.

The oxetane compound is a compound having an oxetane ring, and examples thereof include the oxetane compounds described in JP-A-2001-220526, JP-A-2001-310937, and JP-A-2005-255821. Among them, the compound represented by the general formula (1) described in paragraph number 0089 of JP-A-2005-255821, the compound represented by the general formula (2) described in paragraph number 0092 of the same publication, and the paragraph number. Examples thereof include the compound represented by the general formula (7) of 0107, the compound represented by the general formula (8) of paragraph number 0109, the compound represented by the general formula (9) of paragraph number 0116, and the like. The general formulas (1), (2), (7), (8) and (9) described in JP-A-2005-255821 are shown below.

1-3. Photopolymerization Initiator The photopolymerization initiator contains a photoradical initiator when the photopolymerizable compound is a compound having a radically polymerizable functional group, and the photopolymerizable compound has a cationically polymerizable functional group. When it is a compound having, it contains a photoacid generator.
The ink of the present invention may contain only one type of photopolymerization initiator, or may contain two or more types of photopolymerization initiator. The photopolymerization initiator may be a combination of both a photoradical initiator and a photoacid generator.
Photoradical initiators include cleaved radical initiators and hydrogen abstraction initiators.

Examples of cleaved radical initiators include acetophenone-based initiators, benzoin-based initiators, acylphosphine oxide-based initiators, benzyls and methylphenylglioxyesters.
Examples of acetophenone-based initiators include diethoxyacetophenone, 2-hydroxy-2-methyl-1-phenylpropan-1-one, benzyldimethylketal, 1- (4-isopropylphenyl) -2-hydroxy-2-. Methylpropane-1-one, 4- (2-hydroxyethoxy) phenyl- (2-hydroxy-2-propyl) ketone, 1-hydroxycyclohexyl-phenylketone, 2-methyl-2-morpholino (4-thiomethylphenyl) Includes propane-1-one and 2-benzyl-2-dimethylamino-1- (4-morpholinophenyl) -butanone.
Examples of benzoin-based initiators include benzoin, benzoin methyl ether and benzoin isopropyl ether.
Examples of acylphosphine oxide-based initiators include 2,4,6-trimethylbenzoindiphenylphosphine oxide.

Examples of hydrogen-withdrawn radical initiators include benzophenone-based initiators, thioxanthone-based initiators, aminobenzophenone-based initiators, 10-butyl-2-chloroacrydone, 2-ethylanthraquinone, 9,10-. Includes phenanthrenquinone and camphorquinone.
Examples of benzophenone-based initiators include benzophenone, methyl-4-phenylbenzophenone o-benzoyl benzoate, 4,4'-dichlorobenzophenone, hydroxybenzophenone, 4-benzoyl-4'-methyl-diphenylsulfide, and acrylicized benzophenone. , 3,3', 4,4'-tetra (t-butylperoxycarbonyl) benzophenone and 3,3'-dimethyl-4-methoxybenzophenone.
Examples of thioxanthone-based initiators include 2-isopropylthioxanthone, 2,4-dimethylthioxanthone, 2,4-dichlorothioxanthone and 2,4-dichlorothioxanthone.
Examples of aminobenzophenone-based initiators include Michlerketone and 4,4'-diethylaminobenzophenone.

Examples of photoacid generators include the compounds described in Organic Electronics Materials Study Group, "Organic Materials for Imaging", Bunshin Publishing (1993), pp. 187-192.
The content of the photopolymerization initiator may be in the range where the ink can be sufficiently cured, and can be, for example, in the range of 0.01 to 10% by mass with respect to the total mass of the ink of the present invention.

1-4. Gelling agent The gelling agent according to the present invention is limited to the case of wax gel.
In the wax gel, the gelling agent itself becomes a plate-like crystal, which takes a cardhouse structure and forms a gel structure.

The gelling agent according to the present invention can temporarily fix (pinning) droplets of ink that have landed on a recording medium in a gel state. When the ink is pinned in a gel state, the wet spread of the ink is suppressed and it becomes difficult for adjacent dots to coalesce, so that a higher-definition image can be formed. The inkjet ink of the present invention may contain only one type of gelling agent, or may contain two or more types of the gelling agent.

The content of the gelling agent is preferably in the range of 0.5 to 10.0% by mass with respect to the total mass of the ink from the viewpoint of the pinning effect and the blooming suppressing effect.
From the above viewpoint, the content of the gelling agent in the inkjet ink is more preferably in the range of 1.0 to 5.0% by mass.

Further, from the following viewpoints, it is preferable that the gelling agent crystallizes in the ink at a temperature equal to or lower than the gelation temperature of the ink. The gelling temperature is a temperature at which the gelling agent undergoes a phase transition from the sol to the gel when the solized or liquefied ink is cooled by heating, and the viscosity of the ink suddenly changes. Specifically, the solified 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 rises sharply is set to the temperature of the ink. It can be a gelling temperature.

When the gelling agent crystallizes in the ink, a structure may be formed in which an ink medium such as a solvent or a photopolymerizable compound is contained in the three-dimensional space formed by the gelling agent crystallized in a plate shape. (Such a structure is hereinafter referred to as "card house structure").
When the card house structure is formed, the liquid ink medium is held in the space, so that the ink droplets are less likely to get wet and spread, and the pinning property of the ink is further improved. When the pinning property of the ink is improved, it becomes difficult for the ink droplets that have landed on the recording medium to coalesce with each other, and a higher-definition image can be formed.
In order to form the card house structure, it is preferable that the solvent in the ink, the ink medium such as a photopolymerizable compound and the gelling agent are compatible with each other. On the other hand, if the ink medium such as a solvent or a photopolymerizable compound in the ink and the gelling agent are phase-separated, it may be difficult to form a cardhouse structure.

Examples of gelling agents suitable for forming a curdhouse structure by crystallization include fatty acid ketones (ketone waxes), fatty acid esters (ester waxes), petroleum waxes, fatty acid amides, higher fatty acids, and higher alcohols.

Examples of the above-mentioned ketone wax include dilignoceryl ketone, dibehenyl ketone, distearyl ketone, dieicosyl ketone, dipalmityl ketone, dilauryl ketone, dimyristyl ketone, myristyl palmityl ketone and palmityl stearyl ketone. Is done.

Examples of the above ester wax include behenyl behenylate, icosyl icosate, stearyl stearate, palmityl stearate, cetyl palmitate, myristyl myristate, cetyl myristate, myricyl serotate, stearyl stearate, oleyl palmitate, and glycerin fatty acid. Includes esters, sorbitan fatty acid esters, propylene glycol fatty acid esters, ethylene glycol fatty acid esters and polyoxyethylene fatty acid esters.
Examples of commercial products of the above ester wax include EMALEX series, manufactured by Nippon Emulsion (“EMALEX” is a registered trademark of the company), Rikemar series and Poem series, and RIKEN Vitamin (“Rikemar” and “Poem”). Is also a registered trademark of the company).

Examples of the petroleum-based wax include paraffin wax, microcrystalline wax and petroleum-based wax containing petroleum lactam.

Examples of the higher fatty acids include behenic acid, arachidic acid, stearic acid, palmitic acid, myristic acid, lauric acid, oleic acid and erucic acid.
Examples of the higher alcohols include stearyl alcohol and behenyl alcohol.
Examples of the hydroxystearic acid include 12-hydroxystearic acid.
Examples of the fatty acid amides include lauric acid amides, stearic acid amides, behenic acid amides, oleic acid amides, erucic acid amides, ricinoleic acid amides and 12-hydroxystearic acid amides.
Examples of commercially available fatty acid amides include Diamid Y, Nikka Amide Series, Nihon Kasei (“Diamid” and “Nikka Amide” are registered trademarks of the same company), ITOWAX Series, Itoh Oil Chemicals, and FATTYAMID. The series, made by Kao, is included.

Among these gelling agents, ketone wax, ester wax, higher fatty acid, higher alcohol and fatty acid amide are preferable from the viewpoint of pinning effect and interaction with hindered phenol moiety, and from the above viewpoint, the following general The ketone wax represented by the formula (G1) and the ester wax represented by the following general formula (G2) are more preferable.
The ketone wax represented by the following general formula (G1) and the ester wax represented by the following general formula (G2) may contain only one type in the ink, and two or more types are contained. May be good. Further, the ketone wax represented by the following general formula (G1) and the ester wax represented by the following general formula (G2) may contain only one of them or both of them in the ink. May be.

General formula (G1): R ₁₁ -CO-R ₁₂
General formula (G2): R ₁₃ -COO-R ₁₄
[In the formula, R ₁₁ to R ₁₄ each independently represent a linear hydrocarbon group having a carbon number in the range of 9 to 25. ]

Since the ketone wax represented by the general formula (G1) or the ester wax represented by the general formula (G2) has 9 or more carbon atoms in the linear hydrocarbon group, the crystallinity of the gelling agent And more sufficient space is created in the above card house structure. Therefore, the ink medium such as the solvent and the photopolymerizable compound is easily encapsulated in the space, and the pinning property of the ink is further improved.
Further, since the linear hydrocarbon group has 25 or less carbon atoms, the melting point of the gelling agent does not rise excessively, so that it is not necessary to excessively heat the ink when ejecting the ink.
From the above viewpoint, it is particularly preferable that R ₁₁ and R ₁₂ or R ₁₃ and R ₁₄ are linear hydrocarbon groups having 13 or more and less than 23 carbon atoms.
Further, from the viewpoint of raising the gelation temperature of the ink and gelling the ink more rapidly after landing, carbon in which either R ₁₁ or R ₁₂ or R ₁₃ or R ₁₄ is saturated is saturated. It is preferably a hydrocarbon group having 11 or more atoms and less than 23 atoms.
From the above viewpoint, it is more preferable that both R ₁₁ and R ₁₂ or both R ₁₃ and R ₁₄ are saturated hydrocarbon groups having 11 or more and less than 23 carbon atoms.

Examples of the ketone wax represented by the above general formula (G1) include dilignoceryl ketone (carbon number: 23 to 24), dibehenyl ketone (carbon number: 21 to 22), and distearyl ketone (carbon number: 17). ~ 18), Dieicosyl Ketone (Carbons: 19-20), Dipalmityl Ketone (Carbons: 15-16), Dimyristyl Ketone (Carbons: 13-14), Dilauryl Ketone (Carbons: 11) ~ 12), Lauryl myristyl ketone (carbon number: 11-14), Lauryl palmityl ketone (carbon number: 11-16), Myristyl palmityl ketone (carbon number: 13-16), Myristyl stearyl ketone (carbon number: 13) ~ 18), myristylbehenyl ketone (carbon number: 13-22), palmitylstearyl ketone (carbon number: 15-18), balmitylbehenyl ketone (carbon number: 15-22) and stearylbehenyl ketone (carbon number: 17) ~ 22) is included. The number of carbon atoms in parentheses indicates the number of carbon atoms of each of the two hydrocarbon groups separated by the carbonyl group.

Examples of commercially available ketone waxes represented by the general formula (G1) include 18-Pentriacontanon, Alfa Aeser, Hentriacontane-16-on, Alfa Aeser and Kao wax T-1, Kao. Is done.

Examples of the fatty acid or ester wax represented by the general formula (G2) include behenyl behenylate (carbon number: 21 to 22), icosyl icosanate (carbon number: 19 to 20), and stearyl stearate (carbon number: 17). ~ 18), palmitic acid stearate (carbon number: 17-16), lauryl stearate (carbon number: 17-12), cetyl palmitate (carbon number: 15-16), stearyl palmitate (carbon number: 15-18) ), Myristyl myristate (carbon number: 13-14), cetyl myristate (carbon number: 13-16), octyldodecyl myristate (carbon number: 13-20), stearyl oleate (carbon number: 17-18) , Stearic acid stearyl (carbons: 21-18), stearyl linoleate (carbons: 17-18), behenyl oleate (carbons: 18-22) and arachidyl linoleate (carbons: 17-20) Is done. The number of carbon atoms in parentheses indicates the number of carbon atoms of each of the two hydrocarbon groups divided by the ester group.

Examples of commercially available ester waxes represented by the general formula (G2) include Unistar M-2222SL and Spalm Aceti, manufactured by NOF CORPORATION (“Unistar” is a registered trademark of the company), Exepearl SS and Exepearl MY-M, and Kao. Made by the company ("EXEPAR" is a registered trademark of the company), EMALEX CC-18 and EMALEX CC-10, manufactured by NOF CORPORATION ("EMALEX" is a registered trademark of the company), Amrepus PC, manufactured by Higher Alcohol Industry Co., Ltd. ("Amrepus") Is a registered trademark of the company).
Since these commercially available products are often a mixture of two or more types, they may be separated and purified and contained in the ink as necessary.

1-5. Coloring Material The inkjet ink of the present invention may further contain a coloring material, if necessary.
The coloring material may be a dye or a pigment, but a pigment is preferable because it has good dispersibility with respect to the constituents of the ink and is excellent in weather resistance. The pigment is not particularly limited, and examples thereof include organic pigments or inorganic pigments having the following numbers listed 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 Pigments selected from Orange 13, 16, 20, 36, or mixtures thereof, and the like are 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, pigments selected from 60, or mixtures 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, and the like are included.
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, 6878, 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, 4973, 5205, 5208, 5214, 5221, 5000P, Chromo Fine Green 2GN, 2GO, 2G-550D, 5310, 5370, 6830, Chromo Fine Black A-1103, Seika Fast Yellow 10GH, A-3, 2035, 2054, 2200, 2270 , 2300, 2400 (B), 2500, 2600, ZAY-260, 2700 (B), 2770, Seika 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, 1843LT, 3840, 3870, Seika Fast Bordeaux 10B-430, Seika Light Rose R40, Seika Light Violet B800, 7805, Seika Fast Maroon 460N, Seika Fast Orange 900, 2900, Seika Light Blue C718, A612, Cyanin Blue 4933M, 4933GN-EP, 4940, 4973 (manufactured by Dainichi Seika Kogyo Co., Ltd.); 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 (manufactured by DIC); Colortex Yellow 301, 314, 315, 316, P-624, 314, U10GN, U3GN, UNN, UA-414, U263, Finecol Yellow w T-13, T-05, Pigment Yellow1705, Colortex Orange 202, Colortex Red101, 103, 115, 116, D3B, P-625, 102, H-1024, 105C, UFN, UCN, UBN, U3BN, URN, UGN , UG276, U456, U457, 105C, USN, Colorex Maroon601, Colortex BrownB610N, PigmentX Violet600, PigmentRed 122, ColortexBlue516, 517,518,518, A818, P-908, (Manufactured by Sanyo Pigment Co., Ltd.); Lionol Yellow1405G, Lionol Blue FG7330, FG7350, FG7400G, FG7405G, ES, ESP-S (manufactured by Toyo Ink Co., Ltd.), Toner Magenta E02, Permanent RubinGenF6B, TonerH. BlueB2G (manufactured by Hext Industry); Novoperm P-HG, Hostaperm Pink E, Hostaperm Blue B2G (manufactured by Clariant); Carbon Black # 2600, # 2400, # 2350, # 2200, # 1000, # 990, # 980, # 9 , # 960, # 950, # 850, MCF88, # 750, # 650, MA600, MA7, MA8, MA11, MA100, MA100R, MA77, # 52, # 50, # 47, # 45, # 45L, # 40, Examples thereof include # 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, a paint shaker, or the like.
The dispersion of the pigment is such that the volume average particle size of the pigment particles is preferably in the range of 0.08 to 0.5 μm, the maximum particle size is preferably in the range of 0.3 to 10 μm, and more preferably 0.3 to 3 μm. It is preferable that the operation is performed so as to be within the range of.
The dispersion of the pigment is adjusted by the selection of the pigment, the dispersant, and the dispersion medium, the dispersion conditions, the filtration conditions, and the like.

The active ray-curable inkjet ink according to the present invention may further contain a dispersant in order to enhance the dispersibility of the pigment.
Examples of dispersants include hydroxy group-containing carboxylic acid esters, long-chain polyaminoamide and high-molecular-weight acid ester salts, high-molecular-weight polycarboxylic acid salts, long-chain polyaminoamide and polar acid ester salts, and high-molecular-weight unsaturated acids. Esters, polymer copolymers, modified polyurethanes, modified polyacrylates, polyether ester type anionic activators, naphthalene sulfonic acid formalin condensate salt, aromatic sulfonic acid formalin condensate salt, polyoxyethylene alkyl phosphate ester, poly Oxyethylene nonylphenyl ether, stearylamine acetate and the like are included. Examples of commercially available dispersants include Avecia's Solsperse series, Ajinomoto Fine-Techno's PB series, and the like.

The active ray-curable inkjet ink according to the present invention may further contain a dispersion aid, if necessary. The dispersion aid may be selected according to the pigment.

The total amount of the dispersant and the dispersion aid is preferably in the range of 1 to 50% by mass with respect to the pigment.

The active ray-curable inkjet ink according to the present invention may further contain a dispersion medium for dispersing the pigment, if necessary. A solvent may be contained in the ink as a dispersion medium, but in order to suppress the residue of the solvent in the formed image, the above-mentioned photopolymerizable compound (particularly a monomer having a low viscosity) is used as the dispersion medium. Is preferable.

Examples of the dye include oil-soluble dyes and the like.
Examples of the oil-soluble dye include the following various dyes. Examples of magenta dyes include MS Magenta VP, MS Magenta HM-450, MS Magenta HSo-147 (all manufactured by Mitsui Toatsu Co., Ltd.), AIZENSOT Red-1, AIZEN SOT Red-2, AIZEN SOTRed-3, 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, KAYASET 802 (above, manufactured by Nippon Kayaku Co., Ltd.), PHLOXIN, ROSE BENGAL, ACID Red (above, manufactured by Daiwa Kasei Corp.), HSR-31, DIARESIN Red K (above, manufactured by Mitsubishi Kasei Corp.), Oil Red (manufactured by BASF Japan). ) Is included.

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

Examples of yellow dyes include MS Yellow HSm-41, Yellow KX-7, Yellow EX-27 (manufactured by Mitsui Toatsu Co., Ltd.), AIZEN SOT Yellow-1, AIZEN SOT YellowW-3, AIZEN SOT Yellow-6 (above, Hodogaya Chemical Co., Ltd.), MACROLLEX Yellow 6G, MACROLLEX FLUOR. Yellow 10GN (above, manufactured by Bayer Japan), KAYASET Yellow SF-G, KAYASET Yellow2G, KAYASET Yellow AG, KAYASET Yellow EG (above, manufactured by Nippon Kayaku Co., Ltd.), DAIWA Yellow 330H , HSY-68 (manufactured by Mitsubishi Kasei Corp.), SUDAN Yellow 146, NEOPEN Yellow 075 (manufactured by BASF Japan, Inc.) and the like are included.

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

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

1-6. Other Components The ink of the present invention may further contain other components including a polymerization inhibitor and a surfactant to the extent that the effects of the present invention can be obtained. Only one kind of these components may be contained in the ink of the present invention, or two or more kinds thereof may be contained.

1-6-1. Polymerization Inhibitors Examples of polymerization inhibitors include (alkyl) phenol, hydroquinone, catechol, resorcin, p-methoxyphenol, t-butylcatechol, t-butylhydroquinone, pyrogallol, 1,1-picrylhydrazyl, phenothiline, p-benzoquinone, nitrosobenzene, 2,5-di-t-butyl-p-benzoquinone, dithiobenzoyldisulfide, picric acid, cuperon, aluminum N-nitrosophenylhydroxyamine, tri-p-nitrophenylmethyl, N- (3) -Oxyanilino-1,3-dimethylbutylidene) aniline oxide, dibutyl cresol, cycloquinone oxime cresol, guayacol, o-isopropylphenol, butyraldoxime, methylethylketoxim and cyclohexanone oxime.

The amount of the polymerization inhibitor can be arbitrarily set as long as the effect of the present invention can be obtained.
The amount of the polymerization inhibitor can be, for example, 0.001% by mass or more and less than 1.0% by mass with respect to the total mass of the ink.

1-6-2. Surfactants Examples of surfactants include anionic surfactants such as dialkyl sulfosuccinates, alkylnaphthalene sulfonates and fatty acid salts, polyoxyethylene alkyl ethers, polyoxyethylene alkyl allyl ethers and acetylene glycols. And nonionic surfactants such as polyoxyethylene / polyoxypropylene block copolymers, cationic surfactants such as alkylamine salts and quaternary ammonium salts, and silicone-based and fluorine-based surfactants. ..

Examples of silicone-based surfactants include polyether-modified polysiloxane compounds, specifically KF-351A, KF-352A, KF-642 and X-22-4272, manufactured by Shin-Etsu Chemical Co., Ltd., BYK307, BYK345. , BYK347 and BYK348, manufactured by Big Chemie (“BYK” is a registered trademark of the company), and TSF4452, manufactured by Momentive Performance Materials.

The fluorine-based surfactant means a substance in which a part or the whole thereof is replaced with fluorine instead of hydrogen bonded to carbon of the hydrophobic group of a normal surfactant.
Examples of fluorine-based surfactants include Megafac F, DIC (“Megafac” is a registered trademark of the company), Surflon, AGC Seichemical (“Surflon” is a registered trademark of the company), Fluorad FC, 3M. ("Fluorad" is a registered trademark of the company), Monflor, Imperial Chemical Industry, Zonyls, E.I. , Made by Neos (“FTERRGENT” is a registered trademark of the company).

The amount of the surfactant can be arbitrarily set as long as the effect of the present invention can be obtained. The amount of the surfactant can be, for example, 0.001% by mass or more and less than 1.0% by mass with respect to the total mass of the ink.

1-7. Physical Properties From the viewpoint of further improving the ejection property from the inkjet head, the viscosity of the ink of the present invention at 80 ° C. is preferably in the range of 3 to 20 mPa · s, and preferably in the range of 7 to 12 mPa · s. Is more preferable. Further, from the viewpoint of sufficiently gelling the ink when it lands and the temperature drops to room temperature, the viscosity of the ink of the present invention at 25 ° C. is preferably 1000 mPa · s or more.

The gelation temperature of the ink of the present invention is preferably in the range of 30 to 70 ° C. When the gelation temperature of the ink is 40 ° C. or higher, the ink gels quickly after landing on the recording medium, so that the pinning property becomes higher. When the gelation temperature of the ink is 70 ° C. or lower, the ink is less likely to gel when the ink is ejected from the inkjet head whose ink temperature is usually about 80 ° C., so that the ink can be ejected more stably.
From the viewpoint of enabling ink to be ejected at a lower temperature and reducing the load on the image forming apparatus, the gelation temperature of the ink of the present invention is more preferably in the range of 40 to 60 ° C.

The viscosity of the ink of the present invention at 80 ° C., the viscosity at 25 ° C. and the gelation temperature can be determined by measuring the temperature change of the dynamic viscoelasticity of the ink with a rheometer.
In the present invention, these viscosities and gelation temperatures are values obtained by the following methods.
The ink of the present invention is heated to 100 ° C., and the shear rate is 11.7 while measuring the viscosity with a stress-controlled rheometer Physica MCR301 (cone plate diameter: 75 mm, cone angle: 1.0 °) manufactured by Antonio Par. (1 / s), the ink is cooled to 20 ° C. under the condition of a temperature lowering rate of 0.1 ° C./s, and a temperature change curve of viscosity is obtained.
The viscosity at 80 ° C. and the viscosity at 25 ° C. can be obtained by reading the viscosities at 80 ° C. and 25 ° C. on the temperature change curve of the viscosity, respectively. The gelation temperature can be obtained as a temperature at which the viscosity becomes 200 mPa · s in the temperature change curve of the viscosity.

From the viewpoint of further improving the ejection property from the inkjet head, the average dispersed particle size of the pigment particles according to the present invention is preferably in the range of 50 to 150 nm, and the maximum particle size is preferably in the range of 300 to 1000 nm. .. A more preferable average dispersed particle size is in the range of 80 to 130 nm.
The average dispersed particle size of the pigment particles in the present invention means a value obtained by a dynamic light scattering method using a data sizer nano ZSP manufactured by Malvern. Since the ink containing the coloring material has a high density and does not transmit light with this measuring device, the ink is diluted 200 times before measurement. The measurement temperature is normal temperature (25 ° C).

2. 2. Image forming method The image forming method of the present invention includes 1) a step of ejecting the inkjet ink of the present invention from a nozzle of an inkjet head and landing it on a recording medium, and in the case of an active light curable ink, 2) on a recording medium. It includes a step of irradiating the landed ink with active light to cure the ink.

Step 2-1.1) In the step 1), the ink droplets are ejected from the inkjet head and landed on the recording medium at a position corresponding to the image to be formed.
The ejection method from the inkjet head may be either an on-demand method or a continuous method.
On-demand inkjet heads include electric-mechanical conversion methods such as single cavity type, double cavity type, bender type, piston type, shared mode type and shared wall type, as well as thermal inkjet type and bubble jet (registered trademark). (Bubble jet is a registered trademark of Canon Inc.) Any of the electric-heat conversion methods such as the type may be used.

By ejecting ink droplets from the inkjet head in a heated state, ejection stability can be improved. The temperature of the ink at the time of ejection is preferably in the range of 40 to 100 ° C., and more preferably in the range of 40 to 90 ° C. in order to further improve the ejection stability. In particular, it is preferable to perform ejection at an ink temperature such that the viscosity of the ink is in the range of 7 to 15 mPa · s, more preferably in the range of 8 to 13 mPa · s.

In the sol-gel phase transition type ink, in order to improve the ejection property of the ink from the inkjet head, the temperature of the ink when filled in the inkjet head is from (gelling temperature +10) ° C. to (gelling). The temperature is preferably set to +30) ° C. When the temperature of the ink in the inkjet head is less than (gelling temperature +10) ° C., the ink gels in the inkjet head or on the nozzle surface, and the ink ejection property tends to deteriorate. On the other hand, if the temperature of the ink in the inkjet head exceeds (gelation temperature +30) ° C., the ink becomes too hot, and the ink components may deteriorate.

The method of heating the ink is not particularly limited. For example, at least one of the ink tank, the supply pipe, the ink supply system such as the front chamber ink tank immediately before the head, the pipe with a filter, the piezo head, etc. constituting the head carriage is heated by a panel heater, a ribbon heater, heat insulating water, or the like. be able to.
The amount of ink droplets to be ejected is preferably in the range of 2 to 20 pL in terms of recording speed and image quality.

The recording medium is not particularly limited, and is composed of plastics such as polyester, polyvinyl chloride, polyethylene, polyurethane, polypropylene, acrylic resin, polycarbonate, polystyrene, acrylonitrile-butadiene-styrene copolymer, polyethylene terephthalate, and polybutadiene terephthalate. Non-absorbent recording media (plastic base material), non-absorbable inorganic recording media such as metals and glass, and absorbent papers (for example, office copy paper, high-quality printing paper, and coated paper for printing). can do.

In the step 2-2-2), the ink landed on the recording medium in the step 1) is irradiated with an active ray to form an image in which the ink is cured.
The active ray can be selected from, for example, electron beam, ultraviolet ray, α ray, γ ray, X-ray and the like, but ultraviolet ray is preferable.
Irradiation of ultraviolet rays can be carried out under the condition of a wavelength of 395 nm by using, for example, a water-cooled LED manufactured by Phoseon Technology. By using an LED as a light source, it is possible to suppress poor curing of the ink due to melting of the ink by the radiant heat of the light source.

In the irradiation of ultraviolet rays, the peak illuminance on the image surface of ultraviolet rays having a wavelength in the range of 370 to 410 nm is preferably in the range of 0.5 to 10 W / cm ² , more preferably in the range of 1 to 5 W / cm ² . Do so as to be. From the viewpoint of suppressing the irradiation of the ink with radiant heat, the amount of light applied to the image is preferably less than 350 mJ / cm ² .
Irradiation with active light is preferably performed within 0.001 to 1.0 seconds after the ink has landed, and is performed within 0.001 to 0.5 seconds in order to form a high-definition image. More preferred.

Irradiation with active light may be performed in two stages.
First, the ink may be temporarily cured by irradiating the ink with an active ray within 0.001 to 2.0 seconds after the ink has landed, and after all printing is completed, the ink may be further irradiated with an active ray to cure the ink. .. By dividing the irradiation of the active light into two stages, the shrinkage of the recording material that occurs during ink curing is less likely to occur.

Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited thereto.
1. 1. Inkjet ink materials The following inkjet ink materials were used.
1-1. Photopolymerizable compound SR306 NS: Tripropylene glycol diacrylate (manufactured by Sartmer)
-SR351 NS: Trimethylolpropane triacrylate (manufactured by Sartmer)
-SR247: Neopentyl glycol diacrylate (manufactured by Sartmer)
SR9003: 2PO-modified neopentyl glycol diacrylate (manufactured by Sartmer)

1-2. Photopolymerization initiator, IRGACURE TPO (manufactured by BASF Japan, Inc.) (Indicated as "IRC TPO" in the table)
・ IRGACURE 819 (manufactured by BASF Japan Ltd.) (Indicated as "IRC 819" in the table)

1-3. Phenolic compounds (bifunctional hindered phenolic compounds)
・ IRGANOX 245 (manufactured by BASF Japan Ltd.) (Indicated as "IRN245" in the table)
・ IRGANOX 259 (manufactured by BASF Japan Ltd.) (Indicated as "IRN 259" in the table)
・ IRGANOX 1035 (manufactured by BASF Japan Ltd.) (Indicated as "IRN 1035" in the table)
(Trifunctional hindered phenolic compound)
・ IRGANOX 1330 (manufactured by BASF Japan Ltd.) (Indicated as "IRN 1330" in the table)
(4-functional hindered phenolic compound)
・ IRGANOX 1010 (manufactured by BASF Japan Ltd.) (Indicated as "IRN 1010" in the table)
(One-sided hindered phenolic compound)
・ IRGANOX 1135L (manufactured by BASF Japan Ltd.) (Indicated as "IRN 1135L" in the table)
・ IRGANOX 1076 (manufactured by BASF Japan Ltd.) (Indicated as "IRN 1076" in the table)
(Bifunctional phenolic compound)
・ Nocrack NS-6 (manufactured by Ouchi Shinko Kagaku Co., Ltd.)
・ ADEKA STAB AO-40 (manufactured by ADEKA)

The IRGANOX 1135 (manufactured by BASF Japan), IRGANOX 1076 (manufactured by BASF Japan), Nocrack NS-6 (manufactured by Ouchi Shinko Kagaku Co., Ltd.), and ADEKA STAB AO-40 (manufactured by ADEKA) have the structures shown below. be.

1-4. Gelling agent / paraffin (HNP-1: manufactured by Nippon Seiro Co., Ltd.)
・ Lauric acid amide (Diamid Y: manufactured by Nihon Kasei Co., Ltd.)
Stearyl stearate (Exepearl SS: manufactured by Kao Corporation) (Compound of general formula (G2))
-Stearon (Kaowax T-1: manufactured by Kao Corporation) (compound of general formula (G1))
・ Nomcoat HK-G (glyceryl diacrylate, icosane behenate)

1-5. Polymerization inhibitor-Irgastab UV10 (manufactured by BASF Japan) (indicated as "IRS UV10" in the table)

1-6. Surfactant KF-352 (manufactured by Shin-Etsu Chemical Co., Ltd.)

1-7. Pigment dispersion (preparation of cyan pigment dispersion)
9% by mass of Efka4310BASF, a pigment dispersant, 71% by mass of trimethylolpropane triacrylate ((EM232, Eternal Chemical)), a photopolymerizable compound, in a stainless steel beaker, which is hot at 65 ° C. The mixture was heated and stirred for 1 hour while heating on the plate.
The mixture was cooled to room temperature, and the pigment NX-053 Blue C.I. I. Name PB-15: 4 (manufactured by Dainichiseika Co., Ltd.) was added in an amount of 20% by mass. 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 with a paint shaker for 5 hours. Then, the zirconia beads were removed to obtain a cyan pigment dispersion.

2. 2. Preparation of Ink Mix according to the ink components (photopolymerizable compound, photopolymerization initiator, phenol compound, gelling agent, pigment dispersion, polymerization inhibitor and surfactant) shown in Tables I and II below, and mix them according to 80. The mixture was heated to ° C and stirred. Then, while heating the mixed solution, filtration was performed with a membrane filter of Teflon (registered trademark) 3 μm manufactured by ADVANTEC to obtain inks 1 to 30.

3. 3. Evaluation Using the obtained ink, an image was formed as follows, and the blooming, image quality and curability at that time were evaluated.
(Image formation method)
Each image was formed on a printing coated paper (OK top coat, rice basis weight 128 g / m ² , manufactured by Oji Paper Co., Ltd.) by the following procedure.
As the ejection recording head of the line type inkjet recording apparatus, a piezo head having a nozzle diameter of 20 μm and 512 nozzles (256 nozzles × 2 rows, staggered arrangement, 1 row nozzle pitch 360 dpi) was used.
The temperature of the inkjet head was set to 80 ° C., and the ejection conditions were such that the amount of one drop was 2.5 pl. .. The recording speed was 500 mm / s. Image formation was performed in an environment of 23 ° C. and 55% RH. In addition, dpi represents the number of dots per 2.54 cm.
After forming the image, the ink was cured by irradiating the image with ultraviolet rays by an LED lamp (395 nm, water-cooled LED manufactured by Phoseon Technology) arranged in the downstream part of the recording device.

(Blooming)
A 5 cm × 5 cm solid image formed on a printing coated paper (OK top coat rice basis weight 128 g / m ² manufactured by Oji Paper Co., Ltd.), which is a recording medium, was stored for one month in an environment of 40 ° C. by the above method. .. The image after storage was visually observed and blooming was evaluated according to the following criteria.
7: No deposits are observed on the image surface.
6: There is a thin precipitate on the surface of the image (less than 10% of the printed surface), which can be visually confirmed.
5: A thin precipitate is present on the surface of the image (10% or more and less than 25% of the printed surface), which can be visually confirmed.
4: A thin precipitate is present on the surface of the image (25% or more and less than 40% of the printed surface), which can be visually confirmed.
3: There is a thin precipitate on the surface of the image (40% or more and less than 55% of the printed surface), which can be visually confirmed.
2: There is a thin precipitate on the surface of the image (55% or more and less than 70% of the printed surface), which can be visually confirmed.
1: The surface of the image is covered with a substance on the powder, which can be clearly confirmed visually.

(Image quality (pinning))
By the above-mentioned image forming method, the characters without the Chinese characters "mouth, four, day, time, cause, trouble, solid, country, eye, figure, country" were printed on the recording medium. The omitted characters were MS Mincho with a resolution of 1400 dpi x 1440 dpi, 3 points and 5 points. The printed character image was visually observed. Character quality was evaluated based on the following criteria.
All 3: 3 point omissions are clearly recorded in detail.
Only a part of the 2: 3 point omitted characters can be read, but all the 5 point omitted characters are readable.
Some of the 1: 5 point omitted characters are unreadable.

(Curability)
By the above method, a solid image of 5 cm × 5 cm was formed on a printing coated paper (OK top coat rice basis weight 128 g / m ² manufactured by Oji Paper Co., Ltd.) which is a recording medium. According to the method described in "JIS standard K5701-1 6.2.3 friction resistance test", a printing coated paper cut to a size of 4 cm ² is placed on the image and rubbed with a load of 500 g. I matched it. Then, the degree of decrease in image density was visually observed and evaluated according to the following criteria.
3: No change in the image is observed even after rubbing 50 times or more.
A decrease in image density is observed at the stage of rubbing 2:50 times, but it is within a practically acceptable range.
With less than 1:50 rubbing, a clear decrease in image density was observed, and the quality was not practical.

From the above results, the image formed by using the inkjet ink of the present invention containing a compound having four or more hindered phenol sites has blooming and image quality (pinning property) as compared with the image formed by using the ink of the comparative example. ) And curability, it can be seen that it is good.

Claims (3)

An active photocurable inkjet ink containing a photopolymerizable compound, a photopolymerization initiator and a gelling agent.
The gelling agent is selected from at least one of fatty acid ketone, fatty acid ester, petroleum wax, fatty acid amide, and higher fatty acid.
Furthermore, it contains a compound having 4 or more hindered phenol sites ,
The activity characterized in that the content of the compound having four or more hindered phenol moieties is in the range of 0.1 to 1.0% by mass with respect to the total mass of the active photocurable inkjet ink. Light-curing inkjet ink. The active photocurable inkjet ink according to claim 1, wherein the gelling agent is a compound having a structure represented by the following general formula (G1) or general formula (G2).
General formula (G1): R ₁₁ -CO-R ₁₂
General formula (G2): R ₁₃ -COO-R ₁₄
[In the formula, R ₁₁ to R ₁₄ each independently represent a linear hydrocarbon group having a carbon number in the range of 9 to 25. ] According to claim 1 or 2 , the content of the gelling agent is in the range of 0.5 to 10.0% by mass with respect to the total mass of the active photocurable inkjet ink. The active light curable inkjet ink described.

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