JP2019104865A - Active ray curable inkjet ink and inkjet image formation method - Google Patents

Abstract

To provide an active ray curable inkjet ink excellent in solubility even when heating and cooling are repeated, and good in discharge stability of an inkjet head, image quality and image preservability, and an inkjet image formation method.SOLUTION: The active ray curable inkjet ink is an active ray curable inkjet ink containing a photopolymerizable compound and a gelatinizer, the photopolymerizable compound contains a monomer having molecular weight in a range of 100 to 270, glass transition point (Tg) of 10 (°C) or higher, and ClogP value in a range of 2.5 to 3.95 of 5 mass% or more, and one or a plurality of kinds of the gelatinizer, and the gelatinizer contains a compound having a linear part with 12 or more carbon atoms.SELECTED DRAWING: None

Description

  The present invention relates to an actinic radiation-curable inkjet ink and an inkjet image forming method, and in particular, the solubility is excellent even when heating and cooling are repeated, and the ejection stability of the inkjet head, the image quality and the image storage stability are good. The present invention relates to an actinic ray curable inkjet ink and an inkjet image forming method.

  One of the ink jet recording methods is an ultraviolet ray curable ink jet method in which droplets of ultraviolet ray curable ink jet ink are landed on a recording medium and then irradiated with ultraviolet rays to be cured to form an image. The ultraviolet curable ink jet recording method has recently been attracting attention because it can form an image having high abrasion resistance and adhesiveness even on a recording medium having no ink absorbability.

On the other hand, addition of a gelling agent has been studied as a method of enhancing the pinning property of an inkjet ink used in the inkjet recording system (see, for example, Patent Document 1). That is, it has been studied to suppress the coalescence of dots by discharging an ink droplet in a liquid state at high temperature and causing the ink droplet to land on a recording medium at the same time as the ink droplet is cooled and gelated.
However, in a UV curable inkjet ink containing such a gelling agent (hereinafter, also referred to as "gel UV ink"), the gelling agent (for example, wax) is segregated by repeated heating and cooling (phase Separation) There is a problem that it does not become uniform. This occurs in the situation where the power is turned on and off repeatedly when using the printer. When phase separation occurs, desired ink performance can not be obtained, ejection failure, and the like occur, and therefore it can not be used as an ink.

International Publication No. 2014/206940

  The present invention has been made in view of the above problems and circumstances, and the problem to be solved is that the solubility of the gelling agent is excellent even when heating and cooling are repeated, and the ejection stability of the ink jet head, the image It is an object of the present invention to provide an actinic radiation curable ink jet ink and an ink jet image forming method which are excellent in quality and image storability.

In order to solve the above problems, the present inventor uses a specific photopolymerizable compound in the process of examining the causes of the above problems, etc., to use a gelling agent (for example, wax) by repeated heating and cooling. It has been found that it is possible to provide an actinic radiation curable inkjet ink and an inkjet image forming method capable of suppressing segregation (phase separation) and having good ejection stability of an inkjet head, and good image quality and image storability. .
That is, the above-mentioned subject concerning the present invention is solved by the following means.
1. An actinic radiation curable inkjet ink comprising a photopolymerizable compound and a gelling agent, comprising:
The said photopolymerizable compound has a glass transition point (Tg) 10 (degree C) or more within the range of molecular weight 100-270, and 5 mass of monomers whose ClogP value is in the range of 2.5-3.95 Contains at least%
An actinic radiation-curable inkjet ink comprising one or more kinds of the gelling agent, and the gelling agent contains a compound having a linear portion having 12 or more carbon atoms.

〔式中、Ｒａは、少なくとも炭素又は酸素を含む直鎖又は分岐構造の連結基を表す。Ｒｂは、脂環式構造を含み、かつ、少なくとも炭素又は酸素を含む直鎖構造を含んでもよい置換基を表す。〕 2. 2. The actinic ray curable inkjet ink according to item 1, wherein the monomer has a structure represented by the following general formula (I) or (II).

[Wherein, Ra represents a linear or branched linking group containing at least carbon or oxygen. R b represents a substituent which contains an alicyclic structure and which may contain a linear structure containing at least carbon or oxygen. ]

3. The actinic ray curable inkjet ink according to claim 1 or 2, wherein the monomer is the following compound (1) or (2).

  4. 4. The actinic ray curable inkjet ink according to any one of items 1 to 3, wherein the content of the gelling agent is in the range of 0.5 to 5.0% by mass. .

5. The gelling agent according to any one of claims 1 to 4, characterized in that it contains at least one selected from the group consisting of compounds having the structures represented by the following general formulas (G1) and (G2). An actinic radiation curable inkjet ink according to any one of the preceding claims.
General Formula _{(G1): R 11 -CO-} R 12
Formula _{(G2): R 13 -COO-} R 14
[Wherein, R _{11 to} R ₁₄ each independently represent an alkyl group containing a linear portion having 12 to 28 carbon atoms and which may contain a branch. ]

  6. 6. The actinic ray curable inkjet ink according to any one of the items 1 to 5, wherein one of the gelling agents is stearone.

  7. 7. The actinic ray curable inkjet ink according to any one of the items 1 to 6, wherein one of the gelling agents is a compound having a structure derived from montanic acid and a polymerizable group. .

  8. The actinic ray curable inkjet ink according to any one of the items 1 to 7, which contains 15% by mass or more of the monomer.

9. 9. An ink jet image forming method using the actinic ray curable ink jet ink according to any one of items 1 to 8, wherein
Allowing droplets of the actinic radiation curable inkjet ink to land on a recording medium;
And D. irradiating the droplets landed on the recording medium with an actinic ray to form a cured film constituting an image.

By the above means of the present invention, an actinic ray curable ink jet ink and an ink jet image forming method having excellent solubility even when heating and cooling are repeated, and excellent ink jet head discharge stability, image quality and image storability Can be provided.
The mechanism for expressing the effect of the present invention or the mechanism of action is not clear but is presumed as follows.
A compound wherein the photopolymerizable compound has a molecular weight and a glass transition temperature within the above range and a monomer having a specific ClogP value within the above range, and the gelling agent further comprises a linear portion having 12 or more carbon atoms By containing the above, the photopolymerizable compound acts as a compatibilizer when the gelling agent dissolves in other monomers in the ink, thereby enhancing the compatibility of the gelling agent with the ink and preventing phase separation. It is guessed that it can be done.
As a result, even when heating and cooling are repeated, the solubility is excellent, and the ejection stability of the ink jet head, the image quality and the image storability also become good.

The actinic radiation curable inkjet ink of the present invention is an actinic radiation curable inkjet ink containing a photopolymerizable compound and a gelling agent, and the photopolymerizable compound has a glass transition within a molecular weight range of 100 to 270. Containing 5% by mass or more of a monomer having a point (Tg) of 10 (° C.) and a C log P value in the range of 2.5 to 3.95, and containing one or more kinds of the gelling agent, The gelling agent is characterized in that it contains a compound having a linear moiety of 12 or more carbon atoms.
This feature is a technical feature common to or corresponding to the following embodiments.

  As an embodiment of the present invention, it is preferable that the monomer has a structure represented by the general formula (I) or (II), such as the size and configuration of the polarity of the hydrophilic group and the hydrophobic group in the molecule. The balance from the above is preferred in that it is suitable for dissolving the gelling agent in the solvent component (monomer).

  In addition, it is preferable that the monomer is the compound (1) or (2), that the balance from the viewpoint of the size and configuration of the polarity and the like of the hydrophilic group and the hydrophobic group in the molecule be the gelling agent Is preferable in that it is suitable for being dissolved in a monomer).

  Further, the content of the gelling agent is preferably in the range of 0.5 to 5.0% by mass from the viewpoint of the solubility of the gelling agent in the solvent component and the pinning effect.

  In addition, the gelling agent contains at least one selected from the group consisting of compounds having the structures represented by the general formulas (G1) and (G2), the solubility of the gelling agent in the solvent component, and It is preferable in terms of the pinning effect.

  Moreover, it is preferable from the point of image storage property that one type of the gelling agent is stearone.

  Moreover, it is preferable from the point of image storability that one of the gelling agents is a compound having a structure derived from montanic acid and a polymerizable group.

  Moreover, it is preferable to contain 15 mass% or more of the said monomers from the point of character quality and repeating solubility.

  The inkjet image forming method according to the present invention is an inkjet image forming method using the actinic radiation curable inkjet ink, wherein droplets of the actinic radiation curable inkjet ink are landed on a recording medium, and the recording medium And D. irradiating the droplets landed thereon with actinic rays to form a cured film that constitutes an image. Thereby, the discharge stability of the ink jet head is excellent, and the formed image quality and the image storability also become good.

  BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention, its components, and modes and modes for carrying out the present invention will be described. In the present application, “to” is used in the meaning including the numerical values described before and after that as the lower limit value and the upper limit value.

1. Actinic Light Curing Ink Jet Ink The actinic light curable ink jet ink (hereinafter, also referred to as “ink jet ink” or “ink”) of the present invention is an active light ray curable ink jet ink containing a photopolymerizable compound and a gelling agent. And the photopolymerizable compound has a molecular weight of 100 to 270 and a glass transition point (Tg) of 10 (.degree. C.) or more, and a ClogP value of 2.5 to 3.95. 5% by mass or more, and contains one or more kinds of the gelling agents, and the gelling agent contains a compound having a linear portion having 12 or more carbon atoms.

The actinic radiation curable inkjet ink of the present invention is an ink composition curable by actinic radiation.
The "actinic ray" is a ray capable of giving energy to generate a starting species in the ink composition by the irradiation, and includes alpha rays, gamma rays, X rays, ultraviolet rays, electron rays and the like. Among them, ultraviolet rays and electron beams are preferable, and ultraviolet rays are more preferable, in view of curing sensitivity and availability of the apparatus.

1-1. Photopolymerizable Compound Examples of the photopolymerizable compound according to the present invention include radically polymerizable compounds and cationically polymerizable compounds.
The photopolymerizable compound crosslinks or polymerizes by being irradiated with the above-mentioned actinic ray, and has the function of curing the ink. In the ink of the present invention, the photopolymerizable compound according to the present invention may contain only one type, or two or more types.
The photopolymerizable compound according to the present invention has a molecular weight of 100 to 270, a glass transition point (Tg) of 10 (° C.) or more, and a ClogP value of 2.5 to 3.95. In an amount of 5% by mass or more.
The molecular weight of the monomer is preferably in the range of 200-250.
Moreover, the glass transition point (Tg) of a monomer is preferably in the range of 30 to 60 (° C.). Glass transition point (Tg) (or also referred to as glass transition temperature (° C.)) is a value determined by a method according to JIS-K-7121 using DSC (Differential Scanning Calorimetry). It is. The unit is (° C.).

Furthermore, the ClogP value of the monomer is preferably in the range of 2.9 to 3.95, and the content of the monomer is 5% by mass or more, preferably 15% by mass or more.
Here, the “log P value” referred to in the present application is a coefficient indicating the affinity of the organic compound for water and 1-octanol.
The 1-octanol / water partition coefficient P is the ratio of equilibrium concentrations of compounds in respective solvents at the distribution equilibrium when a trace amount of the compound is dissolved as a solute in the solvent of the two liquid phases of 1-octanol and water, Indicate their logarithm logP to base 10. That is, the “log P value” is a logarithmic value of the 1-octanol / water partition coefficient, and is known as an important parameter representing the hydrophobicity of molecules.

The "ClogP value" is a calculated logP value. The ClogP value can be calculated by a fragment method, an atom approach method or the like. More specifically, to calculate the ClogP value, the fragment described in the literature (C. Hansch and A. Leo, "Substituent Constants for Correlation Analysis in Chemistry and Biology" (John Wiley & Sons, New York, 1969)). The method or the following commercially available software package 1 or 2 may be used.
Software Package 1: MedChem Software (Release 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 values of ClogP values described in the present specification and the like are “ClogP values” calculated using the software package 2.

The following compounds may be mentioned as monomers having a molecular weight of 100 to 270, a glass transition point (Tg) of 10 (° C.) or more, and a C log P value of 2.5 to 3.95.

〔式中、Ｒａは、少なくとも炭素又は酸素を含む直鎖又は分岐構造の連結基を表す。Ｒｂは、脂環式構造を含み、かつ、少なくとも炭素又は酸素を含む直鎖構造を含んでもよい置換基を表す。〕 The monomer preferably has a structure represented by the following general formula (I) or (II).

[Wherein, Ra represents a linear or branched linking group containing at least carbon or oxygen. R b represents a substituent which contains an alicyclic structure and which may contain a linear structure containing at least carbon or oxygen. ]

  In particular, the monomer according to the present invention is preferably the compound (1) or (2).

The photopolymerizable compound according to the present invention may further contain a photopolymerizable compound other than the monomer.
Other photopolymerizable compounds include, for example, (meth) acrylate monomers or oligomers having a ClogP value of less than 4.0, (meth) acrylate monomers or oligomers having a ClogP value of more than 7.0, or other polymerizable compounds There are oligomers and the like.
Examples of these (meth) acrylate monomers or oligomers include PO modified NPG diacrylate (SR 9003, manufactured by Sartomer, molecular weight 328), ditrimethylolpropane tetraacrylate (SR 355, manufactured by Sartomer, molecular weight 467), 4EO modified hexane Diol diacrylate (CD561, manufactured by Sartomer, molecular weight 358); 3EO modified trimethylolpropane triacrylate (SR454, manufactured by Sartomer, molecular weight 429); 4EO modified pentaerythritol tetraacrylate (SR494, manufactured by Sartomer, molecular weight 528); 6EO Modified trimethylolpropane triacrylate (SR 499, manufactured by Sartomer, molecular weight 560); caprolactone acrylate (SR 49) B, manufactured by Sartomer, molecular weight 344); polyethylene glycol diacrylate (NK ester A-400, manufactured by Shin-Nakamura Chemical Co., molecular weight 508), (NK ester A-600, manufactured by Shin-Nakamura Chemical Co., molecular weight 708); 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 # 335 HP, manufactured by Osaka Organic Chemical Company, molecular weight 302); Stearyl Acrylate (STA, manufactured by Osaka Organic Chemical Co., Ltd.); phenol 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.
As the cationically polymerizable compound, only one type may be contained in the actinic radiation curable inkjet ink, or two or more types may be contained.
The epoxy compounds are aromatic epoxides, alicyclic epoxides or aliphatic epoxides, and aromatic epoxides and alicyclic epoxides are preferred in order to enhance the curability.

The aromatic epoxide may be a di- or polyglycidyl ether obtained by reacting a polyhydric phenol or its alkylene oxide adduct with epichlorohydrin.
Examples of polyhydric phenols or alkylene oxide adducts thereof to be reacted include bisphenol A or alkylene oxide adducts thereof.
The alkylene oxide in the alkylene oxide adduct may be ethylene oxide, propylene oxide and the like.
The alicyclic epoxide may 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 may be cyclohexene or cyclopentene.
The aliphatic epoxide may be a di- or polyglycidyl ether obtained by reacting an aliphatic polyhydric alcohol or its alkylene oxide adduct 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 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, cyclohexane dimethanol 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 and octadecyl vinyl ether; ethylene glycol divinyl ether, diethylene glycol divinyl ether, triethylene glycol divinyl ether, propylene glycol divinyl ether, dipropylene Recall divinyl ether, butanediol divinyl ether, hexanediol divinyl ether, cyclohexanedimethanol divinyl ether, include di- or trivinyl ether compounds such as trimethylolpropane trivinyl ether and the like. Among these vinyl ether compounds, di- or trivinyl ether compounds are preferred in consideration of the 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 0089 of JP 2005-255821 A, the compound represented by the general formula (2) described in paragraph 0092 of the same publication, a paragraph number Examples thereof include a compound represented by General Formula (7), a compound represented by General Formula (8) of Paragraph No. 0109, a compound represented by General Formula (9) of Paragraph No. 0116, and the like. General formulas (1), (2), (7), (8) and (9) described in JP 2005-255821 A will be shown below.

1-2. Gelling Agent The gelling agent according to the present invention can temporarily fix (pin) ink droplets that have landed on a recording medium in a gel state. When the ink is pinned in a gel state, the wetting and spreading of the ink is suppressed and adjacent dots are less likely to be integrated, so that a higher definition image can be formed. In the inkjet ink of the present invention, only one type of gelling agent may be contained, or two or more types may be contained.

  The content of the gelling agent is preferably in the range of 0.5 to 5.0% by mass with respect to the total mass of the ink. By making content of a gelatinizer into the said range, the solubility with respect to the solvent component of a gelatinizer and a pinning property effect become favorable. From the above viewpoint, the content of the gelling agent in the inkjet ink is more preferably in the range of 0.5 to 2.5% by mass.

  In addition, from the following viewpoints, the gelling agent is preferably crystallized in the ink at a temperature equal to or lower than the gelling temperature of the ink. The gelation temperature is a temperature at which the gelling agent undergoes a phase transition from sol to gel when the solified or liquefied ink is cooled, and the viscosity of the ink suddenly changes. Specifically, a solified or liquefied ink is cooled while measuring its viscosity with a visco-elasticity measuring device (for example, MCR 300, manufactured by Physica), and the temperature at which the viscosity sharply rises is It can be at 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 included in a three-dimensional space formed by the plate-shaped crystallized gelling agent. (Such a structure is called "card house structure" below).
When the card house structure is formed, since the liquid ink medium is held in the space, the ink droplets are less likely to spread and spread, and the ink pinning performance is further enhanced. When the pinning property of the ink is enhanced, it is difficult for the ink droplets landed on the recording medium to be united with each other, and an image with higher definition can be formed.
In order to form a card house structure, it is preferable that a solvent in the ink, an ink medium such as a photopolymerizable compound, and a gelling agent be compatible. On the other hand, if the solvent in the ink, the ink medium such as the photopolymerizable compound, and the gelling agent are phase-separated, it may be difficult to form a cardhouse structure.

  Examples of gelling agents suitable for forming a cardhouse structure by crystallization include ketone waxes, ester waxes, petroleum waxes, vegetable waxes, animal waxes, mineral waxes, hydrogenated castor oil, modified waxes, higher fatty acids Also included are fatty acids amides including higher alcohols, hydroxystearic acid, N-substituted fatty acid amides and special fatty acid amides, higher amines, esters of sucrose fatty acids, synthetic waxes, dibenzylidene sorbitol, dimer acids and dimer diols.

  Examples of the ketone wax include dilignoceryl ketone, dibehenyl ketone, distearyl ketone, dieicosyl ketone, dipalmityl ketone, dilauryl ketone, dimyristyl ketone, myristyl palmityl ketone and palmityl stearyl ketone Be

Examples of the above ester waxes include behenyl behenyl becohenate, icosyl icosylate, stearyl stearate, palmityl stearate, cetyl palmitate, myristyl myristate, cetyl myristate, mytilyl cellitate, stearyl stearate, oleyl palmitate, glycerin fatty acid Included are esters, sorbitan fatty acid esters, propylene glycol fatty acid esters, ethylene glycol fatty acid esters and polyoxyethylene fatty acid esters.
Examples of the commercially available ester wax include the EMALEX series, manufactured by Nippon Emulsion Co., Ltd. (“EMALEX” is a registered trademark of the company), the Rikemar series and Poem series, and the Riken vitamin company (“Rikemar” and “Poem” Also includes the company's registered trademark).

Examples of the petroleum-based waxes include petroleum-based waxes including paraffin wax, microcrystalline wax and petrolactam.
Examples of the above-mentioned vegetable waxes include candelilla wax, carnauba wax, rice wax, wood wax, jojoba oil, jojoba solid wax and jojoba ester.
Examples of the animal waxes include beeswax, lanolin and spermaceti.
Examples of the mineral waxes include montan wax and hydrogenated waxes.
Examples of the modified wax include montan wax derivatives, paraffin wax derivatives, microcrystalline wax derivatives, 12-hydroxystearic acid derivatives and polyethylene wax derivatives.

Examples of the above-mentioned 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. Commercially available examples of behenyl alcohol include 1-docosanol, manufactured by Higher Alcohol Industry Co., Ltd.
Examples of the hydroxystearic acid include 12-hydroxystearic acid.
Examples of the above fatty acid amides include lauric acid amide, stearic acid amide, behen acid amide, oleic acid amide, erucic acid amide, ricinoleic acid amide and 12-hydroxystearic acid amide.
Examples of commercial products of the above fatty acid amide include Diamid Y, Nikka Amide series, manufactured by Nippon Kasei Co., Ltd. ("Diamid", "Nikka Amide" is a registered trademark of the company), ITOWAX series, Ito Oil Co., Ltd., and FATTYAMID The series includes Kao Corporation.

Examples of the above N-substituted fatty acid amides include N-stearyl stearic acid amide and N-oleyl palmitic acid amide.
Examples of the above-mentioned special fatty acid amides include N, N'-ethylenebisstearylamide, N, N'-ethylenebis-12-hydroxystearylamide and N, N'-xylylene bisstearylamide.
Examples of the above-mentioned higher amines include dodecylamine, tetradecylamine and octadecylamine.

Examples of the esters of sucrose fatty acid include sucrose stearic acid and sucrose palmitic acid.
Examples of commercially available esters of sucrose fatty acid esters include Ryoto Sugar Ester Series, manufactured by Mitsubishi Chemical Foods ("Ryoto" is a registered trademark of the company).
Examples of the synthetic waxes include polyethylene waxes and alpha-olefin maleic anhydride copolymer waxes.
Examples of commercial products of the synthetic wax include UNILIN series, manufactured by Baker-Petrolite ("UNILIN" is a registered trademark of the company).

Examples of the above dibenzylidene sorbitol include 1,3: 2,4-bis-O-benzylidene-D-glucitol.
Examples of commercial products of dibenzylidene sorbitol include Gelol D, manufactured by Shin Nippon Rika Co., Ltd. ("Gelol" is a registered trademark of the company).
Examples of commercial products of the above dimer diol include PRIPROR series manufactured by CRODA ("PRIPR" is a registered trademark of the company).

Among these gelling agents, ketone waxes, ester waxes, higher fatty acids, higher alcohols and fatty acid amides are preferable from the viewpoint of enhancing the pinning property, and from the above viewpoints, ketones represented by the following general formula (G1) A wax and an ester wax represented by the following general formula (G2) are more preferable, and a ketone wax is preferable from the viewpoint of using it with the above-mentioned high polar photopolymerizable compound.
In the ink, 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, and two or more types are included. It is also good. Further, either one or both of the ketone wax represented by the following general formula (G1) and the ester wax represented by the following general formula (G2) may be contained in the ink. It may be

General Formula _{(G1): R 11 -CO-} R 12
In General Formula (G1), R ₁₁ and R _{12 each} represent a linear or branched hydrocarbon group having 12 or more carbon atoms. The carbon number is preferably in the range of 12 to 26.
Formula _{(G2): R 13 -COO-} R 14
In General Formula (G2), R ₁₃ and R _{14 each} represent a linear or branched hydrocarbon group having 12 or more carbon atoms. The carbon number is preferably in the range of 12 to 26.

The ketone wax represented by the general formula (G1) or the ester wax represented by the general formula (G2) is gelated because the number of carbon atoms of the linear or branched hydrocarbon group is 12 or more. The crystallinity of the agent is increased, and a sufficient space is created in the above card house structure. Therefore, the ink medium such as the solvent and the photopolymerizable compound is easily contained in the space, and the pinning property of the ink is further enhanced.
In addition, since the linear or branched hydrocarbon group has a carbon number of 26 or less, the melting point of the gelling agent does not increase excessively, and it is not necessary to heat the ink excessively when the ink is ejected. .
From the above viewpoint, it is particularly preferable that R ₁₁ and R ₁₂ or R ₁₃ and R _{14 be} a linear hydrocarbon group having 13 to 23 carbon atoms.
Also, from the viewpoint of increasing the gelation temperature of the ink and causing the ink to gel more rapidly after impact, carbon in which either R ₁₁ or R ₁₂ or R ₁₃ or R ₁₄ is saturated It is preferable that it is a hydrocarbon group having 11 to less than 23 atoms.
From the above viewpoint, it is more preferable that both of R ₁₁ and R ₁₂ or both of R ₁₃ and R ₁₄ be a saturated hydrocarbon group having 11 or more and less than 23 carbon atoms.

  Examples of ketone waxes represented by the above general formula (G1) include dilignoceryl ketone (number of carbons: 23 to 24), dibehenyl ketone (number of carbons: 21 to 22), and distearyl ketone (number of carbons: 17) 18), dieicosyl ketone (carbon number: 19 to 20), dipalmityl ketone (carbon number: 15 to 16), dimyristyl ketone (carbon number: 13 to 14), dilauryl ketone (carbon number: 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), myristyl behenyl ketone (carbon number: 13 to 22), palmityl stearyl ketone (carbon number: 15 to 18), valmityl behenyl ketone (carbon) Number: 15-22) and stearyl behenyl ketone (carbon number: 17-22) are included. In addition, carbon number in the said parenthesis represents carbon number of each of two hydrocarbon groups divided | segmented by the carbonyl group.

  Examples of commercially available ketone waxes represented by the general formula (G1) include Stearonne (manufactured by Alfa Aeser; Stearone), 18-Pentatriacontanon (manufactured by Alfa Aeser), Hentriacontan-16-on (manufactured by Alfa Aeser) And Kaowax T-1 (manufactured by Kao Corporation).

  Examples of the fatty acid or ester wax represented by the general formula (G2) include behenyl behenate (number of carbons: 21 to 22), icososyl eicosanate (number of carbon: 19 to 20), stearyl stearate (number of carbons: 17) -18), palmityl 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) , Stearyl erucate (carbon number: 21-18), stearyl linoleate (carbon number: 17-18), behenyl oleate (carbon number: 8-22) and linoleic acid arachidyl (carbon number: 17 to 20) are included. In addition, carbon number in the said parenthesis represents carbon number of each of two hydrocarbon groups divided | segmented by ester group.

Examples of commercial products of ester wax represented by the general formula (G2) include Unistar M-2222SL and Sparm Acetic, manufactured by NOF Corporation ("Unister" is a registered trademark of the company), EXEPEARL SS and EXEPEARL MY-M, Kao Products ("EXCEPEARL" is a registered trademark of the company, EMALEX CC-18 and EMALEX CC-10, made by Nippon Emulsion Co., Ltd. ("EMALEX" is a registered trademark of the company) and AMREPS PC, manufactured by Higher Alcohol Industry Co., Ltd. ("AMREPS" Includes the company's registered trademark).
Since these commercial products are often a mixture of two or more types, they may be separated and purified as necessary to be contained in the ink. Among these gelling agents, ketone waxes, ester waxes, higher fatty acids, higher alcohols and fatty acid amides are preferable from the viewpoint of further improving the pinning property.

In particular, one of the gelling agents according to the present invention is preferably a stearone in view of image storability.
Moreover, it is preferable from the point of image storability that one of the gelling agents is a compound having a structure derived from montanic acid and a polymerizable group. Examples of the compound having a structure derived from montanic acid and a polymerizable group include TP Licomont ER 165 (manufactured by CLAEIANT).

1-3. Photopolymerization initiator When the photopolymerizable compound is a compound having a radically polymerizable functional group, the photopolymerization initiator includes a photoradical initiator, and the photopolymerizable compound has a cationically polymerizable functional group. When it is a compound which it has, a photo-acid generator is included.
In the ink of the present invention, only one type of photopolymerization initiator may be contained, or two or more types may be contained. The photopolymerization initiator may be a combination of both a photo radical initiator and a photo acid generator.
The photo radical initiator includes a cleavage type radical initiator and a hydrogen abstraction type radical initiator.

Examples of cleavable radical initiators include acetophenone based initiators, benzoin based initiators, acyl phosphine oxide based initiators, benzyl and methylphenylglyoxy esters.
Examples of acetophenone-based initiators include diethoxyacetophenone, 2-hydroxy-2-methyl-1-phenylpropan-1-one, benzyl dimethyl ketal, 1- (4-isopropylphenyl) -2-hydroxy-2- Methylpropan-1-one, 4- (2-hydroxyethoxy) phenyl- (2-hydroxy-2-propyl) ketone, 1-hydroxycyclohexyl-phenyl ketone, 2-methyl-2-morpholino (4-thiomethylphenyl) Propan-1-one and 2-benzyl-2-dimethylamino-1- (4-morpholinophenyl) -butanone are included.
Examples of benzoin-based initiators include benzoin, benzoin methyl ether and benzoin isopropyl ether.
Examples of acyl phosphine oxide based initiators include 2,4,6-trimethylbenzoin diphenyl phosphine oxide.

Examples of hydrogen abstraction type radical initiators include benzophenone-based initiators, thioxanthone-based initiators, aminobenzophenone-based initiators, 10-butyl-2-chloroacridone, 2-ethyl anthraquinone, 9,10- Included are phenanthrene quinone and camphor quinone.
Examples of benzophenone-based initiators include benzophenone, methyl 4-phenylbenzophenone o-benzoylbenzoate, 4,4'-dichlorobenzophenone, hydroxybenzophenone, 4-benzoyl-4'-methyl-diphenyl sulfide, acrylated benzophenone And 3,3 ', 4,4'-tetra (t-butylperoxycarbonyl) benzophenone and 3,3'-dimethyl-4-methoxybenzophenone.
Examples of thioxanthone-based initiators include 2-isopropyl thioxanthone, 2,4-dimethyl thioxanthone, 2,4-diethyl thioxanthone and 2,4-dichloro thioxanthone.
Examples of aminobenzophenone based initiators include Michler's ketone and 4,4'-diethylaminobenzophenone.

Examples of photoacid generators include the compounds described in "Organic Materials for Imaging", edited by Research Group of Organic Electronics Materials, Bunshin Publishing (1993), pp. 187-192.
The content of the photopolymerization initiator may be in the range in which 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.
Examples of commercial products of the photopolymerization initiator include Irgacure 379 (manufactured by BASF), Genocure ITX (manufactured by Rahn A.G.), Genocure EPD (manufactured by Rahn A.G.), and the like.

The actinic radiation curable inkjet ink of the present invention may further contain a photopolymerization initiator auxiliary agent, a polymerization inhibitor and the like, as required.
The photoinitiator auxiliary 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-dihydroxyethyl aniline, triethylamine, N, N-dimethylhexyl amine and the like are included. Among these, N, N-dimethylamino-p-benzoic acid ethyl ester and N, N-dimethylamino-p-benzoic acid isoamyl ethyl ester are preferable. These compounds may be used alone or in combination of two or more.

1-4. Colorant The inkjet ink of the present invention may further contain a colorant, if necessary.
The colorant may 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 examples thereof include organic pigments or inorganic pigments of the following numbers described in Color Index.

  Examples of red or magenta pigments include Pigment Red 3, 5, 19, 22, 31, 38, 43, 48: 1, 48: 2, 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 The pigment selected from Orange 13, 16, 20, 36 or a mixture thereof is included.

  Examples of blue or cyan pigments are 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, and the like.

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 or the like.
Examples of black pigments include pigments selected from Pigment Black 7, 28, 26 or a mixture thereof.

  Examples of commercially available pigments include Black Pigment (manufactured by Mikuni), Chromo Fine Yellow 2080, 5900, 5930, AF-1300, 2700 L, Chromo Fine Orange 3700 L, 6730, Chromo Fine Scarlet 6750, Chromo Fine Magenta 6880, 6886 , 6891 N, 6790, 6887, chromofine violet RE, chromofine red 6820, 6830, chromofine blue HS-3, 5187, 5108, 5197, 5085 N, SR-5020, 5026, 5050, 4920, 4927, 4937, 4824, 4933 GN-EP, 4940, 4973, 5205, 5208, 5214, 5221, 5000 P, Chromo fine green 2 GN, 2 GO, 2 G-550 D, 5310, 5370, 6830, Chromo fine black A-1103, SEKA fast yellow 10 GH, A-3, 2035, 2054, 2200, 2270, 2300, 2400 (B), 2500, 2600, ZAY-260, 2700 (B ), 2770, Seika Fast Red 8040, C405 (F), CA 120, LR-116, 1531 B, 8060 R, 1547, ZAW-262, 1537 B, GY, 4R-4016, 3820, 3891, ZA-215, Seika Fast Carmine 6B1476T -7, 1483LT, 3840, 3870, Seika Fast Bordeaux 10B-430, Seika Light Rose R40, Seika Light Violet B800, 7805, Seika Fast Maroon 460 N, Seika Fast Orange 00, 2900, Seika Light Blue C718, A612, Cyanine Blue 4933 M, 4933 GN-EP, 4940, 4973 (manufactured by Dainichiseika 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, 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 Y llow T-13, T-05, Pigment 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 Maroon 601, Colortex BrownB610N, Colortex Violet 600, Pigment Red 122, Colortex Blue 516, 517, 518, 519, A818, P-908, 510, Colortex Green 402, 403, Colortex Black 702, U905 (Manufactured by Sanyo Dye Co., Ltd.); Lionol Y llow 1405 G, Lionol Blue FG 7330, FG 7350, FG 7400 G, FG 7405 G, ES, ESP-S (manufactured by Toyo Ink Co., Ltd.), Toner Magenta E02, Permanent Rubin F 6 B, Toner Yellow HG, Permanent Yellow GG-02, Hostapeam Blue B 2 G (manufactured by Hoechst Industries); Novoperm P-HG, Hostaperm Pink E, Hostaperm Blue B2G (manufactured by Clariant); carbon black # 2600, # 2400, # 2350, # 2200, # 1000, # 990, # 980, # 970, # 960, # 960, # 950, # 850, MCF88, # 750, # 650, MA600, MA7, MA8, M 11, MA100, MA100R, MA77, # 52, # 50, # 47, # 45, # 45, # 40, # 33, # 32, # 30, # 25, # 20, # 10, # 5, # 44, CF9 (made by Mitsubishi Chemical) etc. are mentioned.

Dispersion of the pigment can be carried out by, for example, a ball mill, sand mill, attritor, roll mill, agitator, Henschel mixer, colloid mill, ultrasonic homogenizer, pearl mill, wet jet mill, paint shaker and the like.
In the dispersion of the pigment, the volume average particle diameter of the pigment particles is preferably in the range of 0.08 to 0.5 μm, and the maximum particle diameter is preferably in the range of 0.3 to 10 μm, more preferably 0.3 to 3 μm It is preferable to be performed 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 actinic radiation curable inkjet ink according to the present invention may further comprise a dispersant to enhance the dispersibility of the pigment.
Examples of dispersants include hydroxy group-containing carboxylic acid esters, salts of long chain polyaminoamide and high molecular weight acid ester, salts of high molecular weight polycarboxylic acid, salts of long chain polyaminoamide and polar acid ester, high molecular weight unsaturated acid Ester, polymer copolymer, modified polyurethane, modified polyacrylate, polyether ester type anionic surfactant, naphthalene 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 the Solsperse series from Avecia, the PB series from Ajinomoto Fine Techno, and the like.

  The actinic radiation curable ink jet 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 actinic radiation curable ink jet ink according to the present invention may further contain a dispersing medium for dispersing the pigment, if necessary. Although a solvent may be contained in the ink as a dispersion medium, in order to suppress the solvent remaining in the formed image, it is preferable to use a photopolymerizable compound as described above (in particular, a monomer having a low viscosity) as a dispersion medium Is preferred.

Examples of the dye include oil-soluble dyes and the like.
The oil-soluble dyes include the following various dyes. Examples of magenta dyes include MS Magenta VP, MS Magenta HM-1450, 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, Hodogaya Chemical Co., Ltd.), RESOLIN Red FB 200%, MACROLEX Red Violet R, MACROLEX ROT5B (above, Bayer Japan Co., Ltd.), KAYASET Red B, KAYASET Red 130, KAYASET Red 802 (all manufactured by Nippon Kayaku Co., Ltd.), PHLOXIN, ROSE BENGAL, ACID Red (all manufactured by Daiwa Kasei Co., Ltd.), HSR-31, DIAR SIN Red K (manufactured by Mitsubishi Kasei Co., Ltd.), is included Oil Red (manufactured by BASF Japan Co., Ltd.).

  Examples of cyan dyes include MS Cyan HM-1238, MS Cyan HSo-16, Cyan HSo-144, MS Cyan VPG (all manufactured by Mitsui Toatsu Co., Ltd.), 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 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, Nippon Kayaku Co., Ltd.), DAIWA Blue 7000, Oleosol Fast Blue GL (above, Daiwa Chemical Co., Ltd.), DIARESIN Blue P (Mitsubishi Kasei Co., Ltd.), SUDAN Blue 670 NEOPEN Blue 808, ZAPON Blue 806 (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 Co., Ltd.), AIZEN SOT Yellow-1, AIZEN SOT YelloW-3, AIZEN SOT Yellow-6 (above, Hodogaya Chemical Co., Ltd.), MACROLEX Yellow 6G, MACROLEX FLUOR. Yellow 10GN (above, Bayer Japan Co., Ltd.), KAYASET Yellow SF-G, KAYASET Yellow 2 G, KAYASET Yellow AG, KAYASET Yellow EG (above, Nippon Kayaku Co., Ltd. made), DAIWA Yellow 330 HB (Daiwa Kasei Co., Ltd.) HSY-68 (manufactured by Mitsubishi Kasei Corp.), SUDAN Yellow 146, NEOPEN Yellow 075 (manufactured by BASF Japan Ltd.), and the like.

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

  The content of the colorant 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, based on the total amount of the ink.

1-5. Other Components The ink of the present invention may further contain other components including a polymerization inhibitor and a surfactant as long as the effects of the present invention can be obtained. One of these components may be contained in the ink of the present invention, or two or more thereof may be contained.

1-5-1. Polymerization Inhibitor Examples of the polymerization inhibitor include (alkyl) phenol, hydroquinone, catechol, resorcinol, p-methoxyphenol, t-butyl catechol, t-butyl hydroquinone, pyrogallol, 1,1-picrylhydrazyl, phenothiazine, p-benzoquinone, nitrosobenzene, 2,5-di-t-butyl-p-benzoquinone, dithiobenzoyl disulfide, picric acid, cuperone, aluminum N-nitrosophenylhydroxyamine, tri-p-nitrophenylmethyl, N- (3 -Oxyanilino-1,3-dimethylbutylidene) aniline oxide, dibutylcresol, cyclohexanone oxime cresol, guaiacol, o-isopropylphenol, butyraldoxime, methyl ethyl ketoxime and cyclohexanone It contains oxime.
Commercially available examples of the polymerization inhibitor include Genorad 18 (manufactured by Rahn AG) and the like.

The amount of the polymerization inhibitor can be arbitrarily set as long as the effects 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.

1-5-2. Surfactants Examples of surfactants include anionic surfactants such as dialkyl sulfosuccinates, alkyl naphthalene sulfonates and fatty acid salts, polyoxyethylene alkyl ethers, polyoxyethylene alkyl allyl ethers, acetylene glycols And nonionic surfactants such as polyoxyethylene / polyoxypropylene block copolymers; cationic surfactants such as alkylamine salts and quaternary ammonium salts; and surfactants of silicone type and fluorine type. .

  Examples of silicone surfactants include polyether-modified polysiloxane compounds, specifically, Tego rad 2250, manufactured by Evonik, KF-351A, KF-352A, KF-642 and X-22-4272, Shin-Etsu Co., Ltd. Chemical Industries, BYK 307, BYK 345, BYK 347 and BYK 348, made by Big Chemie ("BYK" is a registered trademark of the company), and TSF 4452, made by Momentive Performance Materials, Inc. are included.

The fluorine-based surfactant means a part or all of which is substituted with fluorine, instead of hydrogen bonded to carbon of the hydrophobic group of a normal surfactant.
Examples of fluorine-based surfactants include Megafac F, manufactured by DIC ("Megafac" is a registered trademark of the company), Surflon, manufactured by AGC Sei Chemical ("Surflon" is a registered trademark of the company), Fluorad FC, 3M Made in Japan (“Fluorad” is a registered trademark of the company), Monflor, Imperial Chemical Industries, Inc., Zonyls, E. I. Dupont Nemeras & Co., Licowet VPF, Rubebelke / Hoechst, and FTERGENT And Neos (FTERGENT is a registered trademark of the company).

  The amount of surfactant can be set arbitrarily as long as the effects of the present invention can be obtained. The amount of 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.

1-6. Physical Properties From the viewpoint of enhancing the dischargeability from the inkjet head, the viscosity at 80 ° C. of the ink of the present invention is preferably in the range of 3 to 20 mPa · s, and is in the range of 7 to 9 mPa · s. Is more preferred. Further, from the viewpoint of causing the ink to be sufficiently gelled when the ink lands and is cooled to normal temperature, the viscosity at 25 ° C. of the ink of the present invention is preferably 1000 mPa · s or more.

It is preferable that the gelation temperature of the ink of this invention exists in the range of 30-70 degreeC. When the gelation temperature of the ink is 40 ° C. or more, the ink gels rapidly after landing on the recording medium, and thus the pinning property becomes higher. When the gelation temperature of the ink is 70 ° C. or less, the ink is less likely to gel at the time of ejection of the ink from the ink jet head having an ink temperature of usually about 80 ° C., so that the ink can be ejected more stably.
The gelation temperature of the ink of the present invention is more preferably in the range of 40 to 60 ° C. from the viewpoint of enabling discharge of the ink at a lower temperature and reducing the load on the image forming apparatus.

The viscosity at 80 ° C., the viscosity at 25 ° C., and the gelling temperature of the ink of the present invention can be determined by measuring the temperature change of the dynamic viscoelasticity of the ink with a rheometer.
In the present invention, these viscosity and gelation temperature are values obtained by the following method.
The ink of the present invention is heated to 100 ° C., and the shear rate is 11.7 while the viscosity is measured by a stress-controlled rheometer Physica MCR 301 (diameter of cone plate: 75 mm, cone angle: 1.0 °) manufactured by Anton Paar. The ink is cooled to 20 ° C. under the conditions of (1 / s), temperature decrease rate of 0.1 ° C./s to obtain a temperature change curve of viscosity.
The viscosity at 80 ° C. and the viscosity at 25 ° C. can be determined by reading the viscosity at 80 ° C. and 25 ° C., respectively, in the temperature change curve of viscosity. The gelation temperature can be determined as a temperature at which the viscosity is 200 mPa · s in the temperature change curve of viscosity.

From the viewpoint of enhancing the dischargeability from the ink jet head, the average dispersed particle diameter of the pigment particles according to the present invention is preferably in the range of 50 to 150 nm, and the maximum particle diameter is preferably in the range of 300 to 1000 nm. . A further 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 determined by a dynamic light scattering method using Datasizer Nano ZSP, manufactured by Malvern. In addition, since the ink containing the coloring material has a high density and light is not transmitted by this measuring device, the ink is diluted by 200 times and then measured. The measurement temperature is normal temperature (25 ° C.).

2. Image Forming Method The image forming method of the present invention comprises 1) the step of discharging the ink jet ink of the present invention from the nozzle of the ink jet head to land the ink on a recording medium, and 2) in the case of actinic radiation curable ink. Irradiating the landed ink with an actinic ray to cure the ink.

2-1. Step 1) In the step 1), ink droplets are ejected from an ink jet head to land on the position of the recording medium according to the image to be formed.
The discharge method from the inkjet head may be either an on-demand method or a continuous method.
On-demand ink jet heads include single-cavity, double-cavity, bender, piston, shear mode and shared wall electro-mechanical conversion systems, as well as thermal ink jet and bubble jet (registered trademark) (Bubble jet may be any of electro-thermal conversion system such as Canon-registered trademark type).

  Ejection stability can be enhanced by ejecting ink droplets from the ink jet head in a heated state. The temperature of the ink at the time of ejection is preferably in the range of 40 to 100 ° C., and in order to further enhance the ejection stability, it is more preferably in the range of 40 to 90 ° C. In particular, ejection is preferably performed 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, the temperature of the ink when filled in the ink jet head is (gelling temperature + 10) ° C ~ (gelling) of the ink in order to enhance the dischargeability of the ink from the ink jet head. Preferably, the temperature is set to +30) ° C. When the temperature of the ink in the ink jet head is less than (gelling temperature +10) ° C., the ink is gelled in the ink jet head or on the nozzle surface, and the ink dischargeability tends to be reduced. On the other hand, if the temperature of the ink in the ink jet head exceeds (gelling temperature + 30) ° C, the ink becomes too hot, and the ink component may be degraded.

The method of heating the ink is not particularly limited. For example, at least one of an ink tank constituting a head carriage, an ink supply system such as a supply pipe and an ink chamber in the front chamber immediately before the head, a pipe with a filter, a piezo head, etc. be able to.
The amount of ink droplets when 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 made of, for example, plastics such as polyester, polyvinyl chloride, polyethylene, polyurethane, polypropylene, acrylic resin, polycarbonate, polystyrene, acrylonitrile-butadiene-styrene copolymer, polyethylene terephthalate and polybutadiene terephthalate. Non-absorbing recording media (plastic base materials), non-absorbing inorganic recording media such as metals and glasses, and absorbing papers (for example, office copy paper, high quality paper for printing and coated paper for printing) can do.

2-2. Step 2) In the step 2), the ink landed on the recording medium in the step 1) is irradiated with an actinic ray to form an image formed by curing the ink.
The actinic ray may be selected from, for example, electron beam, ultraviolet ray, α ray, γ ray, and X ray, and preferably ultraviolet ray.
The irradiation of ultraviolet light can be performed under the conditions of a wavelength of 395 nm using, for example, a water-cooled LED manufactured by Phoseon Technology. By using the LED as a light source, curing failure of the ink due to melting of the ink by radiant heat of the light source can be suppressed.

The ultraviolet irradiation preferably has a peak illuminance on the image surface of ultraviolet light having a wavelength in the range of 370 to 410 nm, 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 as you become. It is preferable that the light quantity irradiated to an image is less than 350 mJ / cm < ² > from a viewpoint of suppressing that radiation heat is irradiated to ink.
The irradiation of the actinic ray is preferably performed between 0.001 and 1.0 seconds after ink deposition, and may be performed between 0.001 and 0.5 seconds to form a high-definition image. More preferable.

The irradiation of actinic radiation may be performed in two steps.
First, an actinic ray may be irradiated during 0.001 to 2.0 seconds after the ink lands to temporarily cure the ink, and after all printing is completed, an actinic ray may be further irradiated to substantially cure the ink. . By dividing the irradiation of the actinic radiation into two steps, shrinkage of the recording material, which occurs upon curing of the ink, is less likely to occur.

EXAMPLES Hereinafter, the present invention will be specifically described by way of examples, but the present invention is not limited thereto.
1. Ink Jet Ink Material The following were used as ink jet ink materials.
1-1. Photopolymerizable Compound As the photopolymerizable compound, those shown in the following Table I were used.

1-2. Binder exapmple compound described in paragraph [0027] of European Patent No. 1367103

1-3. Gelling agent, BALC ... Behenyl alcohol (manufactured by Higher Alcohol Industry Co., Ltd .; 1-docosanol)
··································· Epepear SS (made by Kao; stearyl stearate): compound represented by the general formula (G2) ··········· Stearonne (manufactured by Alfa Aesar; Stearone): denoted by General formula (G1) Compounds · ER 165 ... TP Licomont ER 165 (CLARIANT): compounds having a polymerizable group derived from montanic acid

1-4. Photopolymerization initiator · IRC 379 ... Irgacure 379 (manufactured by BASF)
-GNC ITX ... Genocure ITX (made by Rahn A. G.)
GNC EPD: Genocure EPD (manufactured by Rahn A. G.)

1-5. Polymerization inhibitor, GNR 18 ... Genorad 18 (manufactured by Rahn A.G.)

1-6. Surfactant Tego rad 2250 (manufactured by Evonik)

1-7. Preparation of pigment dispersion The following two compounds were placed in a stainless beaker. The mixture was heated and stirred for 1 hour while heating on a 65 ° C. hot plate.
BYK-9151 (manufactured by BASF) 10 parts by mass PO-modified NPG diacrylate (SR 9003, manufactured by Sartomer, molecular weight 328) 70 parts by mass After cooling to room temperature, 20 parts by mass of the following pigment is added thereto. The mixture was sealed in a glass bottle with 200 g of 5 mm zirconia beads and sealed. This was subjected to dispersion processing for the following time with a paint shaker, and then the zirconia beads were removed.
Black Pigment (made by Mikuni)

2. Preparation of Inks The ink components (photopolymerizable compounds, photopolymerization initiators, binders, gelling agents, pigment dispersions, polymerization inhibitors, surfactants) described in the following Tables II to IV are mixed to 80 ° C. The mixture was heated and stirred. Thereafter, while heating the mixture, the mixture was filtered through a Teflon (registered trademark) 3 μm membrane filter manufactured by ADVANTEC to obtain inks 1 to 33.

3. Evaluation The repeated solubility of the obtained ink, and the obtained ink were used to form an image as follows, and the head ejection stability, the character quality and the image storage stability were evaluated.

(Repeated solubility)
Each ink obtained above was repeatedly heated and cooled from room temperature to 90 ° C. 20 times. Thereafter, the viscosity of the upper and lower portions of the ink was measured to evaluate the hardness of the ink at room temperature.
Evaluation criteria ◎: The viscosity difference between the upper and lower portions of the ink is 0%.
○: The viscosity difference between the upper and lower portions of the ink is more than 0% and 15% or less.
Δ: The difference in viscosity between the upper and lower portions of the ink is more than 15% and not more than 30%.
X: The viscosity difference between the upper and lower portions of the ink is greater than 30%.

(Image formation method)
Each ink obtained above was loaded into a Bk head of a single pass type inkjet recording apparatus having a piezoelectric type inkjet recording head. From this device, recording was carried out on a printing coat (OK top coat, 127.9 g / m ² basis weight, manufactured by Oji Paper Co., Ltd.).
The ink jet recording apparatus used had an ink supply system having an ink tank, an ink flow path, a sub ink tank immediately in front of the ink jet recording head, a pipe with a filter, and a piezo head. During image formation, the ink from the ink tank to the head portion was heated to 90 ° C. A voltage was applied so that 2 pL droplets were discharged from the ink jet recording apparatus. Further, in the inkjet recording head, two piezo heads having a nozzle resolution of 600 dpi are arranged to obtain a nozzle resolution of 1200 dpi (dpi represents the number of dots per 2.54 cm). Using this inkjet recording apparatus, a monochrome solid image of 1,200 x 1,200 dpi, 3 pt morning black letters, 3 pt morning white letters (white letters in the solid image) were formed.
After printing, light (395 nm, 8 W / cm ² , water cooled unit) was irradiated from a Phoseon Technology LED lamp to cure the ink. The amount of light was measured with a Hamamatsu Photonics Co., Ltd. ultraviolet integrated actinometer C9536, H9958. The distance from the LED lamp to the recording medium surface was 20 mm.
The conveyance speed of the recording medium was 800 mm / sec. The temperature of the paper transport table was adjusted, and the recording medium was heated to 45 ° C.

(Head discharge stability)
Each ink obtained above was ejected using a printer, and the presence or absence of a missing nozzle and ejection bending was observed with a strobe camera, and the ejection stability was evaluated according to the following criteria.
Evaluation criteria ◎: No occurrence of nozzle missing was observed.
:: In all the nozzles 512, bending in the discharge direction was observed with 1 to 5 nozzles.
B: Out of all the nozzles 512, ejection failure was observed in 1 to 5 nozzles.
×: Out of all the nozzles 512, a discharge failure was observed at six or more nozzles.

(Character quality)
For the images formed by the above image forming method, the quality of 3 pt Mincho letters was evaluated based on the following criteria.
Evaluation criteria ◎: Both black and white letters are reproduced.
○: Some characters are broken in one of the black and white characters.
Fair: Some characters are broken in both black and white characters.
X: The characters are both black and white.

(Image preservation)
The solid image formed by the above-described image forming method was stored at 40 ° C. for one month, and evaluated based on the following criteria.
Evaluation criteria ◎: The surface gloss and the like are the same as the image before storage.
○: The surface gloss is almost the same as the image before storage Δ: A slight haze was observed on the surface, but it was practically acceptable
X: Deterioration such as surface whitening or powder blowing.

  From the above results, it is understood that the inkjet ink of the present invention is superior in solubility to the inkjet ink of the comparative example even when heating and cooling are repeated. In addition, when an image is formed using the inkjet ink of the present invention, it can be seen that the ejection stability of the inkjet head is good, and the quality and image storability of the formed image are also good.

Claims (9)

An actinic radiation curable inkjet ink comprising a photopolymerizable compound and a gelling agent, comprising:
The photopolymerizable compound has a glass transition point (Tg) of 10 (° C.) or more within a molecular weight range of 100 to 270, and a C log P value of 5% by mass of a monomer within a range of 2.5 to 3.95. Contain more than
An actinic radiation-curable inkjet ink comprising one or more kinds of the gelling agent, and the gelling agent contains a compound having a linear portion having 12 or more carbon atoms. The actinic ray curable inkjet ink according to claim 1, wherein the monomer has a structure represented by the following general formula (I) or (II).

[Wherein, Ra represents a linear or branched linking group containing at least carbon or oxygen. R b represents a substituent which contains an alicyclic structure and which may contain a linear structure containing at least carbon or oxygen. ] The actinic ray curable inkjet ink according to claim 1 or 2, wherein the monomer is the following compound (1) or (2).

  The actinic ray curable inkjet ink according to any one of claims 1 to 3, wherein the content of the gelling agent is in the range of 0.5 to 5.0% by mass. . The gelling agent according to any one of claims 1 to 4, characterized in that it contains at least one selected from the group consisting of compounds having the structures represented by the following general formulas (G1) and (G2). An actinic radiation curable inkjet ink according to any one of the preceding claims.
General Formula _{(G1): R 11 -CO-} R 12
Formula _{(G2): R 13 -COO-} R 14
[Wherein, R _{11 to} R ₁₄ each independently represent an alkyl group containing a linear portion having 12 to 28 carbon atoms and which may contain a branch. ]   The actinic ray curable inkjet ink according to any one of claims 1 to 5, wherein one of the gelling agents is stearone.   The actinic radiation curable inkjet ink according to any one of claims 1 to 6, wherein one of the gelling agents is a compound having a structure derived from montanic acid and a polymerizable group. .   The actinic ray curable inkjet ink according to any one of claims 1 to 7, containing 15% by mass or more of the monomer. A method of forming an inkjet image using the actinic ray curable inkjet ink according to any one of claims 1 to 8,
Allowing droplets of the actinic radiation curable inkjet ink to land on a recording medium;
And D. irradiating the droplets landed on the recording medium with an actinic ray to form a cured film constituting an image.