JP2005097557A - Pigment dispersion and active ray-hardenable inkjet ink composition - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a pigment dispersion having excellent pigment dispersibility and dispersion stability and an active ray-hardenable inkjet ink composition using the dispersion. <P>SOLUTION: In a pigment dispersion including photo-polymerizable compound and a pigment, the hydrophilicity δm on the pigment surface is adjusted to ≤ 22. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a novel pigment dispersion and an actinic ray curable inkjet ink composition, and more particularly to a pigment dispersion with improved pigment dispersibility and dispersion stability and an actinic ray curable inkjet ink using the same. .

  In recent years, inkjet recording methods can be used to create images easily and inexpensively, and thus have been applied to various printing fields such as photographs, various printing, marking, and special printing such as color filters. In particular, a recording device that emits and controls fine dots, ink that has improved color reproduction range, durability, emission suitability, etc., and ink absorbability, coloring material color development, surface gloss, etc. have been dramatically improved. It is also possible to obtain image quality comparable to silver halide photography using special paper. The image quality improvement of today's ink jet recording system is achieved only when all of the ink jet recording apparatus, ink, and special paper are available.

  However, in an inkjet system that requires dedicated paper, the recording medium is limited and the cost of the recording medium increases. Therefore, many attempts have been made to record on a transfer medium different from dedicated paper by an ink jet method. Specifically, there are a phase change inkjet method using a wax ink solid at room temperature, a solvent-based inkjet method using an ink mainly composed of a fast-drying organic solvent, an ultraviolet curable inkjet method in which crosslinking is performed by ultraviolet light after recording, and the like. Although it is mentioned, all of them have various problems at present.

  For example, in the phase change ink jet method, since wax is used as ink, sufficient image strength and fixability cannot be obtained. In addition, in the solvent-based ink jet method, ink easily volatilizes, odor (environment), head clogging due to ink drying, ink permeability varies depending on the recording medium used, so bleeding and drying are not stable, ink bleeding is likely to occur, etc. There's a problem.

  On the other hand, the ultraviolet curable ink jet method has been attracting attention in recent years because it has a relatively low odor compared to the solvent ink jet method and can be recorded on a recording medium having no quick drying and no ink absorption. For example, JP-B-5-54667, JP-A-6-200204, and JP-T 2000-504778 disclose ultraviolet curable ink-jet ink. In either method, an acrylic monomer is used as the polymerizable compound. However, the polymerizable monomers used in the ink are those that have skin irritation and sensitization from the viewpoints of lowering the viscosity for obtaining stable ink ejection properties, increasing the curing sensitivity, or adhesion of the recording medium. It was selected and was very dangerous for the user. Moreover, as disclosed in JP 2000-504778, there is a method of containing 80 to 95% by mass of relatively safe alkoxy acrylate or polyalkoxy acrylate, but 80% by mass of monofunctional or polyfunctional monomer. % Or more of the recording medium does not provide sufficient adhesion to the recording medium, and ink bleed or bleed on a wide range of recording media such as a highly permeable recording medium or a polyethylene terephthalate film that is very wettable and easy to bleed. There were problems such as the generation of odor due to unreacted monomers.

  Possible causes of insufficient curing sensitivity include bleeding of the printed image before the ink is cured and penetration into the porous recording medium. This penetration further exacerbates problems such as residual odor of unreacted monomers. I was letting. As one method for supplementing the curing sensitivity, means such as increasing the intensity of the light source and extending the irradiation time can be considered. However, these methods all increase the cost of the apparatus.

  In this way, radiation-curing inkjet systems such as ultraviolet rays are superior to other inkjet systems, but they are not as good as aqueous inkjet systems in terms of safety and equipment costs. The development of an immediate solution is eagerly desired.

As a means for solving such a problem, there is an ultraviolet curable ink jet method using a compound that is cured by cationic polymerization. For example, an active energy ray-curable ink composition using a compound having an oxetane ring (hereinafter referred to as an oxetane compound) is disclosed (for example, see Patent Document 1). Oxetane compounds have no skin irritation or sensitization problems. In addition, it has the feature that it can be cured with a light source with a relatively low output without being inhibited by oxygen like radical polymerization of acrylic monomers, but the problem is that the dispersibility and dispersion stability of the pigment are poor. There is.
JP-A-8-143806 (Claims)

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a pigment dispersion excellent in dispersibility and dispersion stability of the pigment and an actinic ray curable inkjet ink composition using the same. It is in.

The above object of the present invention is achieved by the following configurations.
(Claim 1)
A pigment dispersion containing a photopolymerizable compound and a pigment, wherein the pigment surface has a hydrophilicity δm of 22 or less.
(Claim 2)
A pigment dispersion containing a photopolymerizable compound having an oxetane ring and a pigment, wherein the pigment surface has a hydrophilicity δm of 22 or less.
(Claim 3)
The pigment dispersion according to claim 1 or 2, wherein the pigment surface has a hydrophilicity δm of 21.5 or less.
(Claim 4)
An actinic radiation curable inkjet ink composition comprising a photopolymerizable compound, a photopolymerization initiator, and a pigment, wherein the hydrophilicity δm of the pigment surface is 22 or less.
(Claim 5)
An actinic ray curable ink jet ink composition comprising a photopolymerizable compound having an oxetane ring, a photopolymerization initiator, and a pigment, wherein the pigment surface has a hydrophilicity δm of 22 or less. Ink composition.
(Claim 6)
The actinic ray curable inkjet ink composition according to claim 4 or 5, wherein the pigment surface has a hydrophilicity δm of 21.5 or less.

  ADVANTAGE OF THE INVENTION According to this invention, the pigment dispersion excellent in the dispersibility and dispersion stability of a pigment, and the actinic-light curable inkjet ink composition using the same can be provided.

  Hereinafter, the best mode for carrying out the present invention will be described in detail, but the present invention is not limited thereto.

  As a result of intensive studies in view of the above problems, the present inventor has used pigments having a surface hydrophilicity of δm of 22 or less in the pigment dispersion and the actinic ray curable inkjet ink composition. It has been found that the dispersibility and dispersion stability are remarkably improved, and the present invention has been achieved.

  Hereinafter, the present invention will be described in detail.

  In the present invention, a pigment dispersion containing a photopolymerizable compound and a pigment, or an actinic ray curable inkjet ink composition containing a photopolymerizable compound, a photopolymerization initiator and a pigment, the hydrophilicity of the pigment surface contained therein The characteristic δm is 22 or less.

  The pigment surface hydrophilicity δm referred to in the present invention is the surface hydrophilicity δm determined by the titration method described in Coloring Materials, 73 [3], 136 (2000). A pigment to be measured is suspended on the surface of a certain amount (Bml) of water, and acetone is dropped from a burette whose tip is submerged in water so as not to be in direct contact with the pigment while slowly stirring in this state. The dripping amount (Aml) of acetone required for the pigment floating on the water surface to settle is determined, and the degree of hydrophilicity δm is determined according to the following equation (1).

δm = (A · δ _acetone + B · δ _water ) / (A + B)
In the formula, δ _acetone represents the degree of hydrophilicity of acetone [9.75 (cal ^1/2 · cm ^−1/2 )], and δ _water represents the degree of hydrophilicity of water [23.43 (cal ^1/2).・ Cm ^−1/2 )].

  In the present invention, the hydrophilicity δm of the pigment surface is characterized by 22 or less, preferably 21.5 or less, more preferably 10.0 to 21.5. When δm exceeds 22, the dispersibility is significantly deteriorated.

  In the present invention, in order to set the hydrophilicity of the pigment surface to 22 or less as defined in the present invention, a known surface treatment method such as pigment derivative treatment, rosin treatment, polymer treatment, surface grafting treatment, plasma treatment or the like is used. This can be achieved by appropriate selection or combination.

  The pigments that can be used in the present invention are listed below.

  As red or magenta pigments, 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 Orange; 13, 16, 20, 36, blue or cyan pigments include pigment blue; 1, 15, 15: 1, 15: 2, 15: 3, 15: 4, 15: 6, 1 17-1, 22, 27, 28, 29, 36, 60, Pigment Green; 7, 26, 36, 50 as a green pigment; Pigment Yellow; 1, 3, 12, 13, 14 as a yellow pigment 17, 34, 35, 37, 55, 74, 81, 83, 93, 94, 95, 97, 108, 109, 110, 120, 128, 137, 138, 139, 151, 153, 154, 155, 157 166, 167, 168, 180, 185, 193, Pigment Black; 7, 26, 28 as the black pigment, and Pigment White; 6, 18, 21 as the white pigment can be used according to the purpose.

  For the dispersion of the pigment, for example, a ball mill, sand mill, attritor, roll mill, agitator, Henschel mixer, colloid mill, ultrasonic homogenizer, pearl mill, wet jet mill, paint shaker, or the like can be used. Further, it is preferable to add a dispersant when dispersing the pigment. As the dispersant, a polymer dispersant is preferably used. As the polymer dispersant, Avecia's Solsperse series, Ajinomoto Fine Techno's Adisper series, BYK Chemie's Disperbyk series, Enomoto Kasei's Disparon series And PLAAD series. Moreover, it is also possible to use a synergist according to various pigments as a dispersion aid. These dispersants and dispersion aids are preferably added in an amount of 1 to 60 parts by mass with respect to 100 parts by mass of the pigment. The dispersion medium is used using a solvent or a polymerizable compound, but the actinic ray curable ink used in the present invention is preferably solventless because it reacts and cures immediately after ink landing. If the solvent remains in the cured image, the durability of the image deteriorates and the VOC problem of the remaining solvent occurs. Therefore, it is preferable in view of dispersibility that the dispersion medium is not a solvent but a polymerizable compound, and among them, a monomer having the lowest viscosity is selected.

  In the pigment dispersion, the average particle size of the pigment particles is preferably 200 nm or less, and more preferably 150 nm or less. Moreover, selection of a pigment, a dispersing agent, a dispersion medium, dispersion conditions, and filtration conditions are appropriately set so that the maximum particle diameter is 0.3 to 10 μm, preferably 0.3 to 3 μm. In the ink composition according to the present invention, the color material concentration is preferably 1% by mass to 10% by mass of the entire ink.

  Next, the photopolymerizable compound according to the present invention will be described.

  One of the characteristics of the pigment dispersion or the actinic ray curable inkjet ink composition of the present invention is that it contains a polymerizable compound, particularly a photopolymerizable compound having an oxetane ring.

  The oxetane compound according to the present invention is a compound having an oxetane ring, and any known oxetane compound as introduced in JP-A Nos. 2001-220526 and 2001-310937 can be used.

  In the oxetane compound according to the present invention, when a compound having 5 or more oxetane rings is used, the viscosity of the ink composition becomes high, so that handling becomes difficult, and the glass transition temperature of the ink composition becomes high. The resulting cured product will not be sufficiently sticky. The compound having an oxetane ring used in the present invention is preferably a compound having 1 to 4 oxetane rings.

  Hereinafter, although the specific example of the compound which has an oxetane ring based on this invention is demonstrated, this invention is not limited to these.

  An example of a compound having one oxetane ring is a compound represented by the following general formula (A).

In the general formula (A), R ¹ is a hydrogen atom, a methyl group, an ethyl group, a propyl group, a butyl group or other alkyl group having 1 to 6 carbon atoms, a fluoroalkyl group having 1 to 6 carbon atoms, an allyl group, an aryl group , Furyl group or thienyl group. R ² is an alkyl group having 1 to 6 carbon atoms such as methyl group, ethyl group, propyl group, butyl group, 1-propenyl group, 2-propenyl group, 2-methyl-1-propenyl group, 2-methyl- C2-C6 alkenyl group such as 2-propenyl group, 1-butenyl group, 2-butenyl group, 3-butenyl group, phenyl group, benzyl group, fluorobenzyl group, methoxybenzyl group, phenoxyethyl group, etc. A group having an aromatic ring, an alkylcarbonyl group having 2 to 6 carbon atoms such as an ethylcarbonyl group, a propylcarbonyl group, and a butylcarbonyl group, an alkylcarbonyl group having 2 to 6 carbon atoms such as an ethoxycarbonyl group, a propoxycarbonyl group, and a butoxycarbonyl group; Alkoxycarbonyl group, ethylcarbamoyl group, propylcarbamoyl group, butylcarbamoyl group, pentylcarbamoyl Is N- alkylcarbamoyl group having a carbon number of 2-6 and the like.

  An example of a compound having two oxetane rings includes a compound represented by the following general formula (B).

In the general formula (B), R ¹ is the same group as that in the general formula (A). R ³ is, for example, a linear or branched alkylene group such as an ethylene group, a propylene group or a butylene group, a linear or branched poly (alkyleneoxy) such as a poly (ethyleneoxy) group or a poly (propyleneoxy) group. ) Group, propenylene group, methylpropenylene group, butenylene group or other linear or branched unsaturated hydrocarbon group, alkylene group containing carbonyl group or carbonyl group, alkylene group containing carboxyl group, alkylene containing carbamoyl group Group.

Moreover, as R < ³ >, the polyvalent group selected from the group shown by the following general formula (C), (D) and (E) can also be mentioned.

In the general formula (C), R ⁴ represents a hydrogen atom, an alkyl group having 1 to 4 carbon atoms such as a methyl group, an ethyl group, a propyl group, or a butyl group, a methoxy group, an ethoxy group, a propoxy group, or a butoxy group. An alkoxy group having 1 to 4 carbon atoms, a halogen atom such as a chlorine atom or a bromine atom, a nitro group, a cyano group, a mercapto group, a lower alkyl carboxyl group, a carboxyl group, or a carbamoyl group.

In the general formula (D), R ⁵ represents an oxygen atom, a sulfur atom, a methylene group, NH, SO, SO ₂ , C (CF ₃ ) ₂ , or C (CH ₃ ) ₂ .

In general formula (E), R < ⁶ > is a C1-C4 alkyl group, such as a methyl group, an ethyl group, a propyl group, a butyl group, or an aryl group. n is an integer of 0-2000. R ⁷ is a methyl group, an ethyl group, a propyl group, a butyl group having 1 to 4 carbon atoms, or an aryl group. R ⁷ may further include a group selected from the group represented by the following general formula (F).

In the general formula (F), R ⁸ is an alkyl group having 1 to 4 carbon atoms such as a methyl group, an ethyl group, a propyl group, or a butyl group, or an aryl group. m is an integer of 0-100.

  Specific examples of the compound having two oxetane rings include the following compounds.

Exemplary compound 1 is a compound in which R ¹ is an ethyl group and R ³ is a carboxyl group in the general formula (B). Exemplary compound 2 is a compound in which, in the general formula (B), R ¹ is an ethyl group, R ³ is the general formula (E), R ⁶ and R ⁷ are methyl groups, and n is 1.

Among the compounds having two oxetane rings, preferred examples other than the above compounds include compounds represented by the following general formula (G). In the general formula (G), R ¹ has the same meaning as R ¹ in the general formula (A).

  An example of a compound having 3 to 4 oxetane rings includes a compound represented by the following general formula (H).

In formula (H), R ¹ has the same meaning as R ¹ in the general formula (A). As R ⁹ , for example, a branched alkylene group having 1 to 12 carbon atoms such as groups represented by the following A to C, a branched poly (alkyleneoxy) group such as a group represented by the following D, or the following E And branched polysiloxy groups such as those shown. j is 3 or 4.

In A above, R ¹⁰ is a lower alkyl group such as a methyl group, an ethyl group or a propyl group. Moreover, in said D, p is an integer of 1-10.

  Illustrative compound 3 is an example of a compound having 3 to 4 oxetane rings.

  Furthermore, examples of the compound having 1 to 4 oxetane rings other than those described above include compounds represented by the following general formula (I).

In general formula (I), R ⁸ has the same meaning as R ⁸ in the general formula (F). R ¹¹ is an alkyl group having 1 to 4 carbon atoms such as a methyl group, an ethyl group, a propyl group or a butyl group, or a trialkylsilyl group, and r is 1 to 4.

  Preferable specific examples of the oxetane compound used in the present invention include the following compounds.

  The method for producing each compound having an oxetane ring described above is not particularly limited, and may be a conventionally known method, for example, Pattisson (DB Pattison, J. Am. Chem. Soc., 3455, 79). (1957)) discloses a method for synthesizing an oxetane ring from a diol. In addition to these, compounds having 1 to 4 oxetane rings having a high molecular weight of about 1000 to 5000 are also included. Examples of these specific compounds include the following compounds.

  In the pigment dispersion and the actinic ray curable inkjet ink composition of the present invention, a 2-substituted oxetane compound can also be used.

  Examples of the 2-substituted oxetane compound that can be used in the present invention include a compound having one or more oxetane rings in a molecule represented by the following general formula (1).

(Wherein R _{1 to} R ₆ each represent a hydrogen atom, a monovalent or divalent organic group, and at least one of R _{3 to} R ₆ is not a hydrogen atom.)
Examples of the compound having one oxetane ring in the molecule include compounds represented by the following general formulas (2) to (5).

  In general formulas (2) to (5), each Z is independently an oxygen or sulfur atom, or a divalent hydrocarbon group that may contain an oxygen or sulfur atom in the main chain.

R _{1 to} R ₆ are each independently a hydrogen atom, a fluorine atom, a methyl group, an ethyl group, a propyl group or a butyl group, such as an alkyl group having 1 to 6 carbon atoms, a fluoroalkyl group having 1 to 6 carbon atoms, An allyl group, an aryl group, a furyl group, or a thienyl group.

R ₇ and R ₈ are each independently an alkyl group having 1 to 6 carbon atoms such as methyl group, ethyl group, propyl group or butyl group, 1-propenyl group, 2-propenyl group, 2-methyl-1-propenyl. Group, 2-methyl-2-propenyl group, 1-butenyl group, 2-butenyl group or 3-butenyl group such as alkenyl group having 1 to 6 carbon atoms, phenyl group, benzyl group, fluorobenzyl group, methoxybenzyl group Or an aryl group such as a phenoxyethyl group, an alkylcarbonyl group having 1 to 6 carbon atoms such as a propylcarbonyl group, a butylcarbonyl group or a pentylcarbonyl group, an carbon number of 1 to 1 such as an ethoxycarbonyl group, a propoxycarbonyl group or a butoxycarbonyl group 6 alkoxycarbonyl groups, ethoxycarbamoyl group, propylcarbamoyl group or butylpentylca An alkoxycarbamoyl group having 1 to 6 carbon atoms such as a ruberamoyl group is represented.

In the general formulas (2) to (4), at least one of R _{3 to} R ₆ is not a hydrogen atom.

As the oxetane ring-containing compound used in the present invention, in the above general formulas (2) to (5), R ₁ is a lower alkyl group, particularly ethyl group, R ₇ and R ₈ are propyl group, butyl group, phenyl group or A benzyl group and Z are preferably hydrocarbon groups containing no oxygen or sulfur atom.

  In addition, as a compound which has a 2 or more oxetane ring in a molecule | numerator, the compound represented by the following general formula (6) or (7) can be mentioned.

  In the general formulas (6) and (7), m is 2, 3 or 4, and Z is each independently an oxygen or sulfur atom, or a divalent hydrocarbon group which may contain an oxygen or sulfur atom.

R _{1 to} R ₆ are each independently a hydrogen atom, a fluorine atom, a methyl group, an ethyl group, a propyl group or a butyl group, such as an alkyl group having 1 to 6 carbon atoms, a phenyl group, or a fluoro having 1 to 6 carbon atoms. An alkyl group, an allyl group, an aryl group or a furyl group;

In the general formula (6), at least one of R _{3 to} R ₆ is not a hydrogen atom.

R ₉ is, for example, a linear or branched alkylene group having 1 to 12 carbon atoms represented by the following general formula (8), or a linear or branched poly (alkyleneoxy) group.

In the general formula (8), R ₁₀ represents a lower alkyl group such as a methyl group, an ethyl group, or a propyl group.

Alternatively, R ₉ is a polyvalent group selected from the group of the following general formulas (9), (11) and (12).

In general formula (9), n is 0 or an integer of 1 to 2000, R ₁₁ is an alkyl group having 1 to 10 carbon atoms such as a methyl group, an ethyl group, a propyl group or a butyl group, and the following general formula (10) Represents a group selected from the group consisting of R ₁₂ represents an alkyl group having 1 to 10 carbon atoms such as a methyl group, an ethyl group, a propyl group, or a butyl group.

In General Formula (10), j represents 0 or an integer of 1 to 100, and R ₁₃ represents an alkyl group having 1 to 10 carbon atoms such as a methyl group, an ethyl group, a propyl group, or a butyl group.

In the general formula (11), R ₁₄ is a hydrogen atom, an alkyl group having 1 to 10 carbon atoms such as a methyl group, an ethyl group, a propyl group or a butyl group, an alkoxy group having 1 to 10 carbon atoms, a halogen atom, A nitro group, a cyano group, a mercapto group, a lower alkyl carboxylate group or a carboxyl group is represented.

In the general formula (12), R ₁₅ represents an oxygen atom, a sulfur atom, NH, SO, SO ₂ , CH ₂ , C (CH ₃ ) ₂ or C (CF ₃ ) ₂ .

As the oxetane ring-containing compound used in the present invention, in the above general formulas (6) and (7), R ₁ is a lower alkyl group, particularly an ethyl group, R ₉ is R ₁₄ is a hydrogen atom in the general formula (11). In the general formula (8), R ₁₀ is an ethyl group, in the general formula (9), R ₁₂ is a methyl group, and in the general formula (10), R ₁₃ is a methyl group, and Z is oxygen or sulfur. Those which are hydrocarbon groups containing no atoms are preferred.

  Furthermore, examples of the compound having a plurality of oxetane rings in the molecule include compounds represented by the following general formula (13).

In the general formula (13), r is an integer of 25 to 200, R ₁₆ is an alkyl group or a trialkylsilyl group having 1 to 4 carbon atoms. R _{1 to} R ₆ are the same as those shown in the general formula (1), R ₁₃ is the same as that shown in the general formula (10), and at least one of R _{3 to} R ₆ is not a hydrogen atom.

  The compound having an oxetane ring substituted at least at the 2-position according to the present invention can be synthesized with reference to the following literature.

(1) Hu Xianming, Richard M. et al. Kellogg, Synthesis, 533-538, May (1995)
(2) A. O. Fitton, J .; Hill, D.C. Ejan, R.A. Miller, Synth. , 12, 1140 (1987)
(3) Toshiro Imai and Shinya Nishida, Can. J. et al. Chem. Vol. 59, 2503-2509 (1981)
(4) Nobujiro Shimizu, Shintaro Yamaoka, and Yuho Tsuno, Bull. Chem. Soc. Jpn. 56, 3853-3854 (1983)
(5) Walter Fisher and Cyril A.M. Grob, Helv. Chim. Acta. , 61, 2336 (1978)
(6) Chem. Ber. 101, 1850 (1968)
(7) “Heterocyclic Compounds with Three- and Four-membered Rings”, Part Two, Chapter IX, Interscience Publishers, John Wiley & Sons, New York, 1964.
(8) Bull. Chem. Soc. Jpn. 61, 1653 (1988)
(9) Pure Appl. Chem. , A29 (10), 915 (1992)
(10) Pure Appl. Chem. , A30 (2 &amp; 3), 189 (1993)
(11) Japanese Patent Laid-Open No. 6-16804 (12) DE1021858
Hereinafter, specific examples of the compound having an oxetane ring substituted at the 2-position according to the present invention are shown as exemplary compounds 1 to 15, but the compound according to the present invention is not limited thereto.

Exemplary Compound 1: trans-3-tert-Butyl-2-phenyloxetane Exemplary Compound 2: 3,3,4,4-Tetramethyl-2,2-diphenyloxetane Exemplary Compound 3: Di [3-ethyl (2-methoxy -3-oxetanyl)] methyl ether Exemplified compound 4: 1,4-bis (2,3,4,4-tetramethyl-3-ethyl-oxetanyl) butane Exemplified compound 5: 1,4-bis (3-methyl-) 3-ethyloxetanyl) butane Exemplified Compound 6: Di (3,4,4-trimethyl-3-ethyloxetanyl) methyl ether Exemplified Compound 7: 3- (2-ethyl-hexyloxymethyl) -2,2,3,4 -Tetramethyloxetane Exemplary Compound 8: 2- (2-Ethyl-hexyloxy) -2,3,3,4,4-pentamethyl-oxetane Exemplary Compound 9 4,4'-bis [(2,4-dimethyl-3-ethyl-3-oxetanyl) methoxy] biphenyl Exemplary compound 10: 1,7-bis (2,3,3,4,4-pentamethyl-oxetanyl) heptane Illustrative compound 11: Oxetanyl silsesquioxane Illustrative compound 12: 2-methoxy-3,3-dimethyloxetane Illustrative compound 13: 2,2,3,3-tetramethyloxetane Illustrative compound 14: 2- (4-methoxyphenyl) -3,3-dimethyloxetane Exemplified Compound 15: Di (2- (4-methoxyphenyl) -3-methyloxetane-3-yl) ether In the present invention, any known oxirane group is used as the photopolymerizable compound. A compound (hereinafter referred to as an epoxy compound) or a vinyl ether compound can be used.

  Examples of the epoxy compound include the following aromatic epoxides, alicyclic epoxides, and aliphatic epoxides.

  A preferable aromatic epoxide is a di- or polyglycidyl ether produced by the reaction of a polyhydric phenol having at least one aromatic nucleus or an alkylene oxide adduct thereof and epichlorohydrin, such as bisphenol A or an alkylene oxide thereof. Examples thereof include di- or polyglycidyl ethers of adducts, di- or polyglycidyl ethers of hydrogenated bisphenol A or its alkylene oxide adducts, and novolak-type epoxy resins. Here, examples of the alkylene oxide include ethylene oxide and propylene oxide.

  As the alicyclic epoxide, cyclohexene oxide obtained by epoxidizing a compound having at least one cycloalkane ring such as cyclohexene or cyclopentene ring with a suitable oxidizing agent such as hydrogen peroxide or peracid. Or a cyclopentene oxide containing compound is preferable.

  Preferred aliphatic epoxides include di- or polyglycidyl ethers of aliphatic polyhydric alcohols or alkylene oxide adducts thereof, and typical examples thereof include diglycidyl ether of ethylene glycol, diglycidyl ether of propylene glycol or Diglycidyl ether of alkylene glycol such as diglycidyl ether of 1,6-hexanediol, polyglycidyl ether of polyhydric alcohol such as di- or triglycidyl ether of glycerin or its alkylene oxide adduct, polyethylene glycol or its alkylene oxide adduct Diglycidyl ethers of polyalkylene glycols such as diglycidyl ethers, polypropylene glycols or diglycidyl ethers of adducts thereof Tel and the like. Here, examples of the alkylene oxide include ethylene oxide and propylene oxide.

  Among these epoxides, in view of fast curability, aromatic epoxides and alicyclic epoxides are preferable, and alicyclic epoxides are particularly preferable. In the present invention, one of the epoxides may be used alone, or two or more may be used in appropriate combination.

  Examples of the vinyl ether compound include ethylene glycol divinyl ether, diethylene glycol divinyl ether, triethylene glycol divinyl ether, propylene glycol divinyl ether, dipropylene glycol divinyl ether, butanediol divinyl ether, hexanediol divinyl ether, cyclohexanedimethanol divinyl ether, Di- or trivinyl ether compounds such as trimethylolpropane trivinyl ether, 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 -o- propylene carbonate, dodecyl vinyl ether, diethylene glycol monovinyl ether, and octadecyl vinyl ether.

  Among these vinyl ether compounds, in consideration of curability, adhesion, and surface hardness, di- or trivinyl ether compounds are preferable, and divinyl ether compounds are particularly preferable. In the present invention, one of the above vinyl ether compounds may be used alone, or two or more thereof may be used in appropriate combination.

  The actinic ray curable inkjet ink composition of the present invention contains a photopolymerization initiator. Examples of the photopolymerization initiator include aromatic onium salts. Examples of the aromatic onium salt include salts of group Va elements in the periodic table such as phosphonium salts (for example, triphenylphenacylphosphonium hexafluorophosphate), salts of group VIa elements such as sulfonium salts (for example, tetrafluoroborates). Triphenylsulfonium acid, triphenylsulfonium hexafluorophosphate, tris (4-thiomethoxyphenyl) hexafluorophosphate, sulfonium and triphenylsulfonium hexafluoroantimonate), and salts of Group VIIa elements, such as iodonium A salt (for example, diphenyliodonium chloride etc.) can be mentioned. The use of such an aromatic onium salt as a cationic polymerization initiator in the polymerization of an epoxy compound is disclosed in U.S. Pat. Nos. 4,058,401, 4,069,055, and 4,101,513. And No. 4,161,478.

  Preferred photopolymerization initiators include sulfonium salts of Group VIa elements. Among these, from the viewpoint of storage stability of ultraviolet curable and ultraviolet curable compositions, triarylsulfonium hexafluoroantimonate is preferable. In addition, the photopolymerization initiators described in pages 39 to 56 of the photopolymer handbook (published by Photographic Society Committee, 1989), JP-A 64-13142, JP-A-2-4804 Any compound can be used.

  Moreover, it is preferable to use the sulfonium salt which does not generate | occur | produce benzene by actinic ray irradiation as a photoinitiator.

In the present invention, “does not generate benzene by irradiation with actinic rays” means that benzene is not substantially generated. Specifically, 5 mass of an onium salt (photoacid generator) is contained in the ink composition. Occurs when an image containing approximately 100 m ² is printed with a thickness of 15 μm using an ink containing 100%, and the photoacid generator is sufficiently decomposed with an actinic ray that is sufficiently decomposed with the ink film surface kept at 30 ° C. It means that the amount of benzene to be produced is extremely small or less than 5 μg. The onium salt is preferably a sulfonium salt or an iodonium salt, and satisfies the above condition as long as it has a substituent on the benzene ring bonded to S ⁺ or I ⁺ .

The sulfonium salt is preferably a sulfonium salt compound represented by the following general formulas [1] to [4], and satisfies the above conditions as long as it has a substituent on the benzene ring bonded to S ⁺ .

In the above general formulas [1] to [4], R _{1 to} R ₁₇ each represent a hydrogen atom or a substituent, R _{1 to} R ₃ do not simultaneously represent a hydrogen atom, and R _{4 to} R ₇ represent simultaneously. It does not represent a hydrogen atom, R _{8 to} R ₁₁ do not represent a hydrogen atom at the same time, and R _{12 to} R ₁₇ do not represent a hydrogen atom at the same time.

The substituent represented by R _{1 to} R ₁₇ is preferably an alkyl group such as a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, an isobutyl group, a t-butyl group, a pentyl group, or a hexyl group, Alkoxy groups such as methoxy group, ethoxy group, propyl group, butoxy group, hexyloxy group, decyloxy group, dodecyloxy group, acetoxy group, propionyloxy group, decylcarbonyloxy group, dodecylcarbonyloxy group, methoxycarbonyl group, ethoxycarbonyl Group, carbonyl group such as benzoyloxy group, phenylthio group, halogen atom such as fluorine, chlorine, bromine and iodine, cyano group, nitro group and hydroxy group.

X represents a non-nucleophilic anion residue, for example, a halogen atom such as F, Cl, Br, or I, B (C ₆ F ₅ ) ₄ , R ₁₈ COO, R ₁₉ SO ₃ , SbF ₆ , AsF ₆ , PF ₆ , BF _{4 and the} like. However, R ₁₈ and R ₁₉ are each an alkyl group such as a methyl group, an ethyl group, a propyl group or a butyl group, a halogen atom such as fluorine, chlorine, bromine or iodine, a nitro group, a cyano group, a methoxy group or an ethoxy group. Represents an alkyl group or a phenyl group which may be substituted with an alkoxy group or the like. Among these, B (C ₆ F ₅ ) ₄ and PF ₆ are preferable from the viewpoint of safety.

  The above compounds can be obtained from THE CHEMICAL SOCIETY OF JAPAN Voi. 71 no. 11, 1998, as well as the photoacid generator described in “Organic Materials for Imaging”, edited by Organic Electronics Materials Research Group, Bunshin Publishing (1993), can be easily synthesized by a known method.

  In the present invention, it is particularly preferable that the sulfonium salt represented by the general formulas [1] to [4] is at least one sulfonium salt selected from the following general formulas [5] to [13]. X represents a non-nucleophilic anion residue and is the same as described above.

  In the actinic ray curable ink composition of the present invention, various additives other than those described above can be used. For example, surfactants, leveling additives, matting agents, polyester resins for adjusting film properties, polyurethane resins, vinyl resins, acrylic resins, rubber resins, and waxes can be added. In addition, for the purpose of improving storage stability, any known basic compound can be used, but representative examples include basic organic compounds such as basic alkali metal compounds, basic alkaline earth metal compounds, and amines. Compounds and the like. It is also possible to combine a radically polymerizable monomer and an initiator into a radical / cation hybrid type curable ink.

  In the actinic ray curable ink composition of the present invention, when the viscosity at 25 ° C. is 7 to 50 mPa · s, ejection is stable regardless of the curing environment (temperature and humidity), and good curability is obtained. Is preferred.

  Examples of the present invention will be specifically described below, but the embodiments of the present invention are not limited to these examples.

Example 1
<< Preparation of pigment dispersion >>
[Preparation of hydrophilicity δm of pigment]
(Preparation of treated pigment 1)
To the purified water, phthalocyanine sulfonic acid was added and stirred to prepare a phthalocyanine sulfonic acid mixed solution. Subsequently, C.I. as a pigment was added to this phthalocyanine sulfonic acid mixed solution. I. Pigment Blue 15: 4 was added, and the mixture was stirred and mixed for 30 minutes, and then filtered through Nutsche. This filtered solid was dried at 120 ° C. for 2 hours to prepare treated pigment 1 having a hydrophilicity δm of 21.3.

(Preparation of treated pigments 2-7)
In the preparation of the treated pigment 1, treated pigments 2 to 7 were prepared in the same manner except that the concentration of phthalocyanine sulfonic acid in the phthalocyanine sulfonic acid mixed solution was appropriately adjusted.

[Preparation of Pigment Dispersion 1]
Pigment: treated pigment 1 (hydrophilicity δm: 21.3) 10.0 parts by mass Dispersant: Azisper PB822 (polymer dispersant manufactured by Ajinomoto Fine Techno Co., Ltd.)
1.5 parts by mass Photopolymerizable compound: Aron Oxetane OXT-221 (Oxetane compound manufactured by Toagosei Co., Ltd.) 88.5 parts by mass After the above additives were mixed, zirconia beads having a diameter of 0.5 mm were used in a bead mill. The pigment dispersion 1 was prepared by dispersing for 2 hours.

[Preparation of pigment dispersions 2 and 3]
In the preparation of the pigment dispersion 1, pigment dispersions 2 and 3 were prepared in the same manner except that the treated pigments 2 and 3 were used in place of the treated pigment 1.

[Preparation of Pigment Dispersion 4]
Pigment: treated pigment 1 (hydrophilicity δm: 21.3) 7.0 parts by weight Dispersant: PLAAD ED-251 (pigment dispersant manufactured by Kashiwagi Kasei Co., Ltd.) 2.8 parts by weight Photopolymerizable compound: VIKOFLEX9010 (ATOFINA) Epoxy compound manufactured by Chemicals Inc) 90.2 parts by mass The above additives were mixed, and then dispersed in a bead mill for 2 hours using zirconia beads having a diameter of 0.5 mm to prepare pigment dispersion 4.

[Preparation of pigment dispersions 5 and 6]
In the preparation of the pigment dispersion 4, pigment dispersions 5 and 6 were prepared in the same manner except that the treated pigments 2 and 3 were used in place of the treated pigment 1.

[Preparation of pigment dispersions 7 to 10]
In the preparation of the pigment dispersion 1, pigment dispersions 7 to 10 were prepared in the same manner except that the treated pigments 4 to 7 were used instead of the treated pigment 1.

<< Evaluation of pigment dispersion >>
The pigment dispersions 1 to 10 prepared as described above were subjected to the following measurements and evaluations.

[Measurement of hydrophilicity δm of pigment surface]
The hydrophilicity degree δm of the pigment particle surface used in the preparation of each pigment dispersion was determined according to the following method.

  A pigment to be measured is suspended on the surface of a certain amount (Bml) of water, and acetone is dropped from a burette whose tip is submerged in water so as not to be in direct contact with the pigment while slowly stirring in this state. The dripping amount (Aml) of acetone required for the pigment floating on the water surface to settle was determined, and the degree of hydrophilicity δm was determined according to the following equation (1).

δm = (A · δ _acetone + B · δ _water ) / (A + B)
In the formula, δ _acetone represents the degree of hydrophilicity of acetone [9.75 (cal ^1/2 · cm ^−1/2 )], and δ _water represents the degree of hydrophilicity of water [23.43 (cal ^1/2).・ Cm ^−1/2 )].

(Measurement of viscosity)
Using a viscoelasticity measuring apparatus MCR300 (Nihon Shibel Hegner), the viscosity at 25 ° C. was measured under a condition of Share Rate of 12 (1 / s).

[Evaluation of dispersibility: Observation of coarse pigment particles]
Each pigment dispersion was coated on a polyethylene terephthalate film using a wire bar so that the wet film thickness was 20 μm, and observed using a magnifying glass (100 times) to confirm the presence or absence of coarse pigment particles.

[Evaluation of dispersion stability]
A predetermined amount of each pigment dispersion is sampled in a centrifuge tube, and after centrifuging for 1 hour under the conditions of 1600G using a centrifuge, the pigment dispersion is visually observed and dispersed according to the following criteria. The stability was evaluated.

◯: No supernatant is observed Δ: Some supernatant is observed, but there is no practical problem x: Clearly the supernatant is observed Table 1 shows the results obtained as described above.

  As is apparent from the results in Table 1, the pigment dispersion of the present invention containing a photopolymerizable compound and a pigment and having a pigment surface hydrophilicity δm of 22 or less has a dispersibility and dispersion stability compared to the comparative example. It turns out that it is excellent in property.

Example 2
<Preparation of ink composition>
[Preparation of Ink Composition 1]
Pigment Dispersion 1 40.0 parts by mass Photopolymerizable compound: Aron oxetane OXT-221 (Oxetane compound manufactured by Toagosei Co., Ltd.) 27.9 parts by mass Photopolymerizable compound: Celoxide 2021P (produced by Daicel Chemical Industries, Ltd.)
27.1 parts by mass Photopolymerization initiator: Adekaoptomer SP-152 (manufactured by Asahi Denka Kogyo Co., Ltd.) 5.0 parts by mass The above additives were mixed and stirred, and then filtered through a membrane filter to obtain ink composition 1. Prepared.

[Preparation of ink composition 2]
Ink composition 2 was prepared in the same manner as in the preparation of ink composition 1 except that pigment dispersion 2 was used instead of pigment dispersion 1.

[Preparation of ink composition 3]
Ink composition 3 was prepared in the same manner as in the preparation of ink composition 1, except that pigment dispersion 3 was used instead of pigment dispersion 1.

[Preparation of Ink Composition 4]
Pigment Dispersion 4 57.1 parts by weight Photopolymerizable compound: VIKOFLEX9010 (epoxy compound manufactured by ATOFINA Chemicals Inc) 37.9 parts by weight Photopolymerization initiator: Adekaoptomer SP-152 (manufactured by Asahi Denka Kogyo Co., Ltd.) 5.0 mass Part After mixing and stirring the above additives, ink composition 1 was prepared by filtration through a membrane filter.

[Preparation of Ink Composition 5]
Ink composition 5 was prepared in the same manner as in the preparation of ink composition 4 except that pigment dispersion 5 was used instead of pigment dispersion 4.

[Preparation of Ink Composition 6]
Ink composition 6 was prepared in the same manner except that pigment dispersion 6 was used in place of pigment dispersion 4 in the preparation of ink composition 4.

[Preparation of Ink Composition 7]
Ink composition 7 was prepared in the same manner except that pigment dispersion 7 was used instead of pigment dispersion 1 in the preparation of ink composition 1.

[Preparation of ink composition 8]
Ink composition 8 was prepared in the same manner as in the preparation of ink composition 1 except that pigment dispersion 8 was used instead of pigment dispersion 1.

[Preparation of ink composition 9]
Ink composition 9 was prepared in the same manner as in the preparation of ink composition 1, except that pigment dispersion 9 was used instead of pigment dispersion 1.

[Preparation of Ink Composition 10]
Ink composition 10 was prepared in the same manner as in the preparation of ink composition 1 except that pigment dispersion 10 was used instead of pigment dispersion 1.

<Evaluation of ink composition>
For the ink compositions 1 to 10 prepared as described above, in the same manner as in Example 1, measurement of the hydrophilicity δm of the pigment surface, measurement of the viscosity of the ink composition, evaluation of dispersibility ( Observation of coarse pigment particles) and dispersion stability were evaluated, and the obtained results are shown in Table 2.

  As apparent from the results in Table 2, the ink composition of the present invention containing a photopolymerizable compound, a photopolymerization initiator, and a pigment and having a pigment surface hydrophilicity δm of 22 or less is compared with the comparative example. It can be seen that the ink composition has excellent properties in terms of dispersibility and dispersion stability.

Claims (6)

A pigment dispersion containing a photopolymerizable compound and a pigment, wherein the pigment surface has a hydrophilicity δm of 22 or less. A pigment dispersion containing a photopolymerizable compound having an oxetane ring and a pigment, wherein the pigment surface has a hydrophilicity δm of 22 or less. The pigment dispersion according to claim 1 or 2, wherein the pigment surface has a hydrophilicity δm of 21.5 or less. An actinic radiation curable inkjet ink composition comprising a photopolymerizable compound, a photopolymerization initiator, and a pigment, wherein the hydrophilicity δm of the pigment surface is 22 or less. An actinic ray curable ink jet ink composition comprising a photopolymerizable compound having an oxetane ring, a photopolymerization initiator, and a pigment, wherein the pigment surface has a hydrophilicity δm of 22 or less. Ink composition. The actinic ray curable inkjet ink composition according to claim 4 or 5, wherein the pigment surface has a hydrophilicity δm of 21.5 or less.