JP5825089B2 - UV curable non-aqueous inkjet ink - Google Patents

Description

  The present invention relates to an ultraviolet curable non-aqueous inkjet ink, particularly to an ultraviolet curable non-aqueous inkjet ink containing a donor monomer and an acceptor monomer.

  Non-aqueous inks have also been proposed as conventional ultraviolet curable ink-jet inks for industrial use (for example, Patent Document 1), and a photopolymerization initiator in the ink generates radicals or the like by active energy, thereby polymerizing monomers. And cured and fixed on the medium to form an image.

  Patent Document 1 describes that a polymer dispersant for stably dispersing an organic pigment is blended in a non-aqueous radical polymerization ink-jet ink. The polymer dispersant has a main chain skeleton composed of urethane, acrylic and amide skeletons, and has a block structure or a comb structure. These polymer dispersants are said to improve the storage stability of the ink.

  Further, an ultraviolet curable composition containing a charge transfer complex polymerization compound (referred to as a CT polymerization compound) as a polymerization monomer has been proposed (for example, see Non-Patent Document 1). Furthermore, it is also proposed to CT polymerize a monomer composition containing a combination of an electron-rich monomer (donor monomer) such as vinyl ether and an electron-deficient monomer (acceptor monomer) such as maleimide (Patent Documents 2 and 3). See).

  Furthermore, Patent Document 4 discloses that in an aqueous ultraviolet curable ink-jet ink, an image can be formed without causing separation of water and the organic solvent by setting the SP value representing the compatibility of the organic solvent with water within an appropriate range. Have been described. Here, the SP value is a characteristic value representing the compatibility (or affinity) of the organic solvent with respect to water.

JP 2009-73945 A Japanese Patent No. 3353020 Japanese Patent Laid-Open No. 11-124403 JP 2007-91910 A

Sonny Jonsson, et.al, Polymer Materials Sci. & Enginer. 1995, 72, 470-472

  It is conceivable to use an ultraviolet curable composition containing an acceptor monomer and a donor monomer as an inkjet ink. However, the inkjet ink needs a pigment dispersant for dispersing the pigment, and the dispersant for appropriately dispersing the pigment contained in the ultraviolet curable composition containing the acceptor monomer and the donor monomer is Not proposed.

  For example, Patent Document 1 discloses a polymer dispersant having a comb structure as a dispersant for radical polymerization type ink-jet ink. However, there is no suggestion on how to select a polymer dispersant for an inkjet ink that includes a monomer solvent containing a donor monomer and an acceptor monomer.

  Since the surface of the inorganic pigment is active, in an inkjet ink containing an inorganic pigment not containing an appropriate dispersant, the monomer in the ink may be polymerized and gelled. For this reason, coating the surface of the inorganic pigment may suppress gelation, but it leads to an increase in ink cost.

  This inventor examined the polymeric dispersing agent for disperse | distributing the pigment contained in the ultraviolet curable composition containing an acceptor monomer and a donor monomer appropriately. As a result, it was found that the storage stability of the ink and the ejection stability from the ink head vary greatly depending on the type of the polymer dispersant. It is considered that the polymer dispersant has an important relationship with the polarity of the monomer composition as a solvent. However, since the acceptor monomer and the donor monomer are polarized due to complex formation or the like, it has been found that the polarity relationship between the polarized monomer composition and the polymer dispersant must be considered.

  Accordingly, an object of the present invention is to provide a polymer dispersant suitable as a dispersant for dispersing a pigment in an ultraviolet curable composition containing an acceptor monomer and a donor monomer.

The present invention relates to the following non-aqueous inkjet ink.
[1] Polymerization is performed based on a charge density difference between the donor monomer and the acceptor monomer, including a monomer solvent containing a donor monomer and an acceptor monomer, a pigment, a polymer dispersant, and no water. UV curable non-aqueous inkjet ink,
The donor monomer is triethylene glycol vinyl ether;
The acceptor monomer is methylmaleimide;
The polymer dispersant has a comb structure having a main chain and a side chain bonded to the main chain,
And the non-aqueous inkjet ink whose difference of SP value of the said polymer dispersing agent and SP value of the said monomer solvent is 1.6 or less.
[2] The non-aqueous inkjet ink according to [1], wherein the main chain of the polymer dispersant is polyurethane, polyacrylate, polyester, polyamide, or polyurea.
[3] The non-aqueous inkjet ink according to [1], wherein a content ratio of the polymer dispersant to the pigment is 0.3 to 0.7 by weight.
[4] The non-aqueous inkjet ink according to [1], wherein the pigment has a refractive index of 1.5 or more.

  The ultraviolet curable ink-jet ink of the present invention contains an acceptor monomer and a donor monomer, and has a high curability because it undergoes a polymerization reaction utilizing the difference in charge density between the two. In addition, since the dispersibility of the pigment contained in the ink is high, the storage stability of the ink is high, and the ejection stability from the inkjet head is also high.

1 is a diagram illustrating a serial head type inkjet recording apparatus. FIG. It is a figure which shows the line-head-type inkjet recording device.

  The inkjet ink of the present invention contains a monomer solvent containing a donor monomer and an acceptor monomer, a pigment, and a polymer dispersant, and does not contain water.

<Acceptor monomer>
The acceptor monomer contained in the inkjet ink of the present invention is a monomer having an electron-deficient unsaturated bond. The value of the atomic charge of the carbon atom constituting the unsaturated bond in the acceptor monomer is preferably −0.3 or more, more preferably −0.28 or more.

The acceptor monomer contained in the inkjet ink of the present invention is preferably a compound having an unsaturated bond represented by the general formula (4) or the general formula (5).

In the general formula (4) or the general formula (5), EWG ₁ and EWG ₂ each represent a partial structure in which an electron-withdrawing group is directly connected to an unsaturated bond. A part of EWG ₁ or EWG ₂ may be bonded to have a cyclic structure. The electron-withdrawing group represents a cyano group, a halogen group, a pyridyl group, a pyrimidyl group, a nitro group, a group represented by the following general formula (a), or a group represented by the following general formula (b).

Further, EWG ₁ and EWG ₂ may be bonded to each other to form the following electron-withdrawing linking group to form a cyclic structure. Examples of the electron-withdrawing linking group include —CO—O—CO—, —CO—N (R _X ) —CO—, —S (O) _n —O—CO—, —S (O) _n —. N (R) —CO—, —S (O) _n —O—S (O) _n —, or —S (O) _n —N (R _X ) —S (O) _n — and the like are included.

EWG ₁ and EWG ₂ may form a cyclic structure via a linking group such as a linear alkylene group, a branched alkylene group, a cyclic alkylene group, an alkylene group having a hydroxyl group, an arylene group or an arylalkylene group, and a substituent. You may have. Further, a part of EWG ₁ or EWG ₂ may form a polyfunctional polymerizable monomer having two or more unsaturated bond portions via a linking group.

In the above general formulas (a) and (b), Q ₁ represents OH, OR ′, NR′R ″ or R ′. R ′ and R ″ each represent a hydrogen atom, a linear alkyl group, a branched alkyl group, a cyclic alkyl group, an alkyl group having a hydroxyl group, an aryl group or an arylalkyl group, and may further have a substituent.

  Specific examples of the unsaturated compound represented by the general formula (4) or the general formula (5) include a vinylene imide compound, a vinylene dicarboxylic acid, a vinylene dicarboxylic acid ester, a vinylene monocarboxylic acid amide monocarboxylic acid, and a vinylene monocarboxylic acid amide. Monocarboxylic acid esters, vinylene dicarboxylic acid amides, vinylene nitrile compounds substituted with nitrile groups at both ends of the vinylene skeleton, vinyl halide compounds substituted with halogen groups at both ends of the vinylene skeleton, vinylene ketone compounds substituted with carbonyl at both ends of the vinylene skeleton, vinyl Range thiocarboxylic acid anhydride, vinylene thioimide compound, vinylene thiocarboxylic acid, vinylene thiocarboxylic acid ester, vinylene monothiocarboxylic acid amide monothiocarboxylic acid, vinylene monothiocarboxylic acid amide monothiocarbo Ester, vinyl range thio carboxylic acid amide, compounds pyridyl group which is substituted vinylene backbone ends, but such compounds structure pyrimidyl group is substituted on vinylene skeleton ends include, but are not limited to.

  Preferred examples of the unsaturated compound as an acceptor monomer include vinylene imides such as maleic anhydride and maleimide, vinylenedicarboxylic acids such as maleic acid and fumaric acid, and vinylene dicarboxylic acid esters such as maleic acid ester and fumaric acid ester. It is. More preferably, maleic anhydride, maleic acid, fumaric acid, maleic acid esters, fumaric acid esters, and maleimide compounds are preferable from the viewpoint of increasing sensitivity.

Moreover, in this invention, the unsaturated compound represented by General formula (4) or General formula (5) is at least 1 sort (s) chosen from following General formula (A-1)-General formula (A-13). An unsaturated compound is preferred.

In General Formula (A-1) to General Formula (A-13), R ₁ , R ₂ , R ₃ , and R ₄ are each independently a hydrogen atom, a linear alkyl group, a branched alkyl group, or a cyclic alkyl group. Represents a hydroxyl group-containing alkyl group, an aryl group or an arylalkyl group, and may further have a substituent, and a linking group for forming a polyfunctional polymerizable monomer having two or more unsaturated bond moieties; can do. X ₁ represents a halogen atom.

  Among the unsaturated compounds represented by the general formulas (A-1) to (A-13), the acceptor monomer is represented by the general formula (A-1), the general formula (A-2), or the general formula (A). The unsaturated compound represented by −6) is more preferable.

  Although the unsaturated compound represented with general formula (A-1)-general formula (A-13) below is demonstrated below, it is not limited to these. The charge of the carbon atom of the unsaturated bond which the unsaturated compound demonstrated below shows all values of -0.3 or more.

  Examples of monofunctional unsaturated compounds represented by the general formulas (A-1) to (A-13) include maleic anhydride as an example of a compound having vinylene dicarboxylic anhydride, and an example of a compound having vinylene imide. Maleimide, N-methylmaleimide, N-ethylmaleimide, N-butylmaleimide, N-2-ethylhexylmaleimide, N-dodecylmaleimide, N-octadecylmaleimide, N-phenylmaleimide, N-cyclohexylmaleimide, N- (p-carbo Methoxyphenyl) maleimide, 4,4′-dimaleimidobisphenol F, N-butylmaleimide, N- (2-chlorophenyl) maleimide, N- (4-chlorophenyl) maleimide, 2,3-dimethyl-1-N- (2 -Methacryloxyethylmaleimide; maleic acid, fumaric acid; Examples of dicarboxylic acid esters include dimethyl maleate, diethyl maleate, diisopropyl maleate, di-n-butyl maleate, di-tert-butyl maleate, di (2-ethylhexyl) maleate, dimethyl fumarate, fumarate Examples include diethyl acid, diisopropyl fumarate, di-n-butyl fumarate, di-tert-butyl fumarate, and di (2-ethylhexyl) fumarate, but these are not limited to these specific examples.

  The polyfunctional polymerizable monomer that is an acceptor monomer has a conventionally known linking group skeleton. For example, it may be a polyfunctional maleimide derivative as described in US Pat. No. 6,034,150, JP-A-11-124403, and the like.

  Below, the maleimide derivative preferable as an acceptor monomer is demonstrated. The maleimide derivative as the acceptor monomer is preferably a maleimide compound having a chiral structure in the molecule from the viewpoints of solubility, low viscosity, and injection stability required as an inkjet ink.

The maleimide compound having a chiral group is not particularly limited as long as it has at least one chiral carbon atom in the molecule. As this preferred maleimide compound, a compound represented by the following general formula (1) is preferable.

In the general formula (1), R ₁ and R ₂ each independently represent a hydrogen atom or an alkyl group having 1 to 6 carbon atoms, and R ₁ and R ₂ may be linked to form a ring. Y ₁ , Y ₃ and Z represent a divalent organic linking group in which groups selected from an alkylene group, an alkyleneoxy group, a phenylene group, an ester group, an ether group and a thioether group are combined. Y ₂ represents a divalent group having an asymmetric carbon. n represents an integer of 1 to 6, n1 represents 0 or 1, and n2 represents 0 or 1.

Examples of the alkyl group represented by R ₁ and R ₂ include a methyl group, an ethyl group, a propyl group, a butyl group, and a hexyl group. R ₁ and R ₂ may combine to form a cyclopropylene ring, a cyclobutylene ring, a cyclopentene ring, a cyclohexene ring, or the like.

The divalent organic linking group represented by Y ₁ and Y ₃ is an alkylene group (eg, methylene group, ethylene group, butylene group, hexylene group, etc.), an alkyleneoxy group (eg, ethyleneoxy group, polyethyleneoxy group, Butyleneoxy group, polybutyleneoxy group), alkyleneoxycarbonyl group (for example, ethyleneoxycarbonyl group, hexyleneoxycarbonyl group, etc.), alkylene ester group (for example, methylene ester group, hexylene ester group, phenylene group), phenyl Group (for example, methylphenylene group, oxycarbonylphenylenecarbonyloxy group, carbonyloxyphenyleneoxycarbonyl group, etc.).

Y ₂ represents a divalent group having an asymmetric carbon (chiral carbon). Specifically, it is represented by the following formula.

  In the above formula, X represents an alkyl group having 1 to 18 carbon atoms, an alkenyl group having 1 to 18 carbon atoms, an alkyloxy group having 1 to 18 carbon atoms, an alkylcarbonyloxy group having 1 to 18 carbon atoms, or a hydroxyl group. Preferably, a C1-C4 methyl group, an ethyl group, a propyl group, and an isobutyl group are mentioned.

In the general formula (1), Z represents an n-valent linking group. In the case of n = 1, Z is a hydrogen atom, an alkyl group (methyl group, ethyl group, hexyl group), a hydroxyl group, a carboxyl group, or an alkyl ester group. In the case of n = 2, Z has the same meaning as the divalent organic linking group represented by Y ₁ or Y ₃ . In the case of n = 3, Z is a glycerol group, a trimethylol alkyl group, a triazine group, or the like. When n = 4, Z is a pentaerythritol group or the like, and when n = 6, Z is a bistrimethylolalkyl group or the like.

  In order to eject the ink jet ink from the ink jet head, the molecular weight of the maleimide compound having a chiral group is preferably 200 to 1,000, more preferably 200 to 800. If it is smaller than 200, it is easy to crystallize and clogging is likely to occur during injection. On the other hand, if the molecular weight is larger than 1000, the viscosity becomes high and injection becomes difficult.

More preferred examples of the maleimide compound having a chiral group include a maleimide compound represented by the following structural formula.

n11 and n12 are integers of 0 to 6, and n13 is preferably an integer of 1 to 30. R _{1, R 2,} Z is synonymous with _{R 1, R} 2, Z in the general formula (1). X has the same meaning as X in the formula given as an example of the divalent group having an asymmetric carbon (chiral carbon) represented by Y ₂ . Particularly preferably, R ₁ and R ₂ are a hydrogen atom, X is an alkyl group having 1 to 4 carbon atoms, n12 is 0, and Z is an alkylene or polyoxyalkylene having 1 to 18 carbon atoms.

Although the specific example of the maleimide compound which has a chiral group represented by General formula (1) below is shown, it is not limited to this.

  Methods for synthesizing these maleimide compounds are known, and can be synthesized, for example, using the method described in JP-A-11-124403 or Macromolecular Chemical and physics, 2009, 210, 269-278.

In the inkjet ink of the present invention, as a more preferable maleimide derivative that can be applied as an acceptor monomer, a maleimide derivative represented by the following general formula (2) is exemplified from the viewpoint of low viscosity, solubility, and injection stability.

In the general formula (2), R ₁₁ and R ₁₂ each independently represent a hydrogen atom or an alkyl group having 1 to 6 carbon atoms, and R ₁₁ and R ₁₂ may be bonded to each other to form a ring. . A ₁₁ and A ₁₃ each independently represent an alkylene group, and A ₁₂ represents a trivalent hydrocarbon group having an asymmetric center. Y represents carbonyloxy (—C (═O) —O—) or oxycarbonyl (—O—C (═O) —). p represents 1 or 2. R ₁₃ represents an alkyl group or alkyleneoxy group having a molecular weight of 15 to 600 when p is 1, and an alkylene group or alkyleneoxy group having a molecular weight of 14 to 600 when p is 2. m represents 0 or 1, and n represents 0 or 1.

In the general formula (2), examples of the alkyl group represented by R ₁₁ and R ₁₂ include a methyl group, an ethyl group, a propyl group, a butyl group, and a hexyl group. R ₁₁ and R ₁₂ may be bonded to form a cyclopropene ring, a cyclobutylene ring, a cyclopentene ring, a cyclohexene ring, or the like.

Examples of the divalent organic linking group represented by A ₁₁ and A ₁₃ include a methylene group, an ethylene group, a butylene group, a hexylene group, an ethyleneoxy group, a polyethyleneoxy group, a butyleneoxy group, a polybutyleneoxy group, and an ethyleneoxycarbonyl group. Hexyleneoxycarbonyl group, methylene ester group, hexylene ester group, phenylene group, methylphenylene group, oxycarbonylphenylenecarbonyloxy group, and carbonyloxyphenyleneoxycarbonyl group.

A ₁₂ represents a trivalent group having an asymmetric carbon (chiral carbon).

In the general formula (2), A ₁₁ and A ₁₃ are preferably a methylene group, A ₁₂ is —CHR ₁₄ —, and R ₁₃ is an alkyl group having 2 to 12 carbon atoms or an alkylene group. At this time, R ₁₄ represents an alkyl group having 1 to 12 carbon atoms, an alkenyl group having 1 to 18 carbon atoms, an alkyloxy group having 1 to 18 carbon atoms, an alkylcarbonyloxy group having 1 to 18 carbon atoms, or a hydroxyl group. Preferably, R ₁₄ is an alkyl group having 1 to 4 carbon atoms (such as a methyl group, an ethyl group, a propyl group, or an isobutyl group).

When p is 1, the alkyl group having a molecular weight of 15 to 600 represented by R ₁₃ is a linear or branched alkyl group having 1 to 18 carbon atoms, specifically, methyl group, ethyl group, propyl group. Group, butyl group, hexyl, group, neopentyl group, dodecyl group, 2,2,4-octyl group, and the like.

When p is 2, the alkylene group having a molecular weight of 14 to 600 represented by R ₁₃ is a linear or branched alkylene group having 1 to 18 carbon atoms; specifically, a methylene group, an ethylene group, or a propylene group. Butylene group, hexylene group, nepopentylene group, dodecylene group, 2,2,4-octylene group and the like.

Examples of the alkyleneoxy group represented by R ₁₃ when p is 1 include a hydroxy or alkoxy polyethyleneoxy group, a hydroxy or alkoxypolyproleneoxy group, a hydroxy or alkoxypolybutyleneoxy group, and the like. It is not limited.

R ₁₃ is preferably a linear or branched alkylene group having 1 to 18 carbon atoms, or a linear or branched alkyl group having 1 to 18 carbon atoms, and more preferably a linear or branched alkyl group having 4 to 12 carbon atoms. An alkylene group is a linear or branched alkyl group having 4 to 12 carbon atoms.

Further preferred maleimide derivatives include maleimide derivatives represented by the following general formulas (II) to (IV).

In the general formulas (II) to (IV), R ₁₄ is an alkyl group having 1 to 12 carbon atoms, an alkenyl group having 1 to 18 carbon atoms, an alkyloxy group having 1 to 18 carbon atoms, or an alkyl group having 1 to 18 carbon atoms. Represents an alkylcarbonyloxy group or a hydroxyl group. Preferably, an alkyl group having 1 to 4 carbon atoms (methyl group, ethyl group, propyl group, isobutyl group, etc.) can be used. p represents 1 or 2. R ₁₅ represents a linear alkyl group having 4 to 12 carbon atoms or an alkylene group.

Specific examples of the maleimide derivative represented by the general formula (2) of the present invention are shown below.

<About donor monomer>
The donor monomer in the present invention is a monomer having an electron-rich unsaturated bond, and the value of an atomic charge of the unsaturated bond is preferably −0.45 or less, more preferably. Is -0.50 or less.

In two or more kinds of polymerizable monomers having an unsaturated bond, the donor monomer (polymerizable monomer having the minimum charge of carbon atoms constituting the unsaturated bond) is an unsaturated compound represented by the following general formula (6) It is preferable that

In the general formula (6), X represents —O—, —NR ₄ —, —S—, or —SO—. Y represents a hydrogen atom, a linear alkyl group, a branched alkyl group, a cycloalkyl group, an alkyl group having a hydroxyl group, an aryl group, or an arylalkyl group, and may further have a substituent. R ₁ , R ₂ , and R ₃ each independently represent a hydrogen atom, a linear alkyl group, a branched alkyl group, a cycloalkyl group, an alkyl group having a hydroxyl group, an aryl group, or an arylalkyl group; You may have. Further, a part of R ₂ or R ₃ and Y may be bonded to form a cyclic structure. Moreover, you may form the polyfunctional donor monomer which one part of Y has a 2 or more unsaturated bond through a coupling group.

  Specific examples of the unsaturated compound represented by the general formula (6) include alkenyl ethers such as vinyl ether and propenyl ether, alkenyl thioethers such as vinyl thioether and propenyl thioether, and alkenyl sulfoxides such as vinyl sulfoxide and propenyl sulfoxide. , Vinyl esters in which a vinyl group is bonded to the oxygen atom of a carboxylate ester, vinylamines in which a vinyl group is bonded to a nitrogen atom in an amino group, vinylamides in which a vinyl group is bonded to a nitrogen atom in an amide group, nitrogen atoms in an imidazole ring And vinyl imidazole having a vinyl group bonded thereto, vinyl carbazole having a vinyl group bonded to a nitrogen atom of a carbazole ring, a cyclic 5-membered ring containing a vinylene skeleton and an oxygen atom in the ring, and a cyclic 6-membered ring compound.

The compound represented by the general formula (6) is more preferably a compound represented by the following general formulas (D-1) to (D-9).

In General Formulas (D-1) to (D-9), R ₅ to R ₉ are each independently a hydrogen atom, a linear alkyl group, a branched alkyl group, a cyclic alkyl group, an alkyl group having a hydroxyl group, or aryl. Represents a group or an arylalkyl group, and may further have a substituent. R ₅ to R ₉ may be a linking group for forming a polyfunctional polymerizable monomer having two or more unsaturated bond portions. Z represents —O—, —N (R ₁₀ ) — or —S—. R ₁₀ represents a hydrogen atom, a linear alkyl group, a branched alkyl group, a cyclic alkyl group, an alkyl group having a hydroxyl group, an aryl group, or an arylalkyl group, and may further have a substituent.

Among the unsaturated compounds represented by the general formula (6), in the monofunctional unsaturated compound, Y is a hydrogen atom, a linear alkyl group, a branched alkyl group, a cycloalkyl group, an alkyl group having a hydroxyl group, an aryl group, or Represents an arylalkyl group. X represents —O—, —N (R ₁₁ ) CO—, —NR ₄ —, —S—, or —SO—, R ₁₁ represents a hydrogen atom, an alkyl group, a cycloalkyl group, or an aryl group; R ₁₁ may be linked to Y to form a ring.

  Specific examples of the monofunctional unsaturated compound represented by the general formula (6) include vinyl thioether; vinyl methyl sulfoxide as a polymerizable monomer containing vinyl sulfoxide; vinyl-tert-butyl sulfide, vinyl methyl sulfide, vinyl ethyl sulfide, and the like. Is included.

  The monofunctional unsaturated compound represented by the general formula (6) may be a polymerizable monomer having a vinylene skeleton and a 5-membered or 6-membered ring compound containing a nitrogen atom or an oxygen atom in the ring. Examples of the 5-membered or 6-membered ring compound include imidazole, pyrrole, furan, dihydrofuran, pyran, dihydropyran and the like.

  Specific examples of N-vinyl compounds having a structure in which a vinyl group is substituted on a nitrogen atom include N-vinylformamide, N-vinylcarbazole, N-vinylindole, N-vinylpyrrole, N-vinylacetamide, N-vinyl. Pyrrolidone, N-vinylcaprolactam, N-vinyl-N-ethylurea, N-vinyloxazolidone, N-vinylsuccinimide, N-vinylethylcarbamate and derivatives thereof are included. Among these compounds, N-vinylcaprolactam and N-vinylformamide are particularly preferable. N-vinylformamide can be obtained from, for example, Arakawa Chemical Industries, Ltd.

The compound represented by the general formula (6) may be a monofunctional vinyl ether compound represented by the general formula (3). A monofunctional vinyl ether compound is particularly preferable because it can enhance the storage stability of the inkjet ink.

In the formula _{(3), R 3, R} 4, R 5 represents a hydrogen atom, an alkyl group, a cycloalkyl group or an aryl group, _{R 6} represents an alkyl group, a cycloalkyl group or an aryl group.

  Examples of monofunctional vinyl ether compounds include n-propyl vinyl ether, isopropyl vinyl ether, n-butyl vinyl ether, isobutyl vinyl ether, 2-ethylhexyl vinyl ether, octadecyl vinyl ether, cyclohexyl vinyl ether, allyl vinyl ether, hydroxyethyl vinyl ether, hydroxybutyl vinyl ether, 9-hydroxy Nonyl vinyl ether, 4-hydroxycyclohexyl vinyl ether, cyclohexanedimethanol monovinyl ether, triethylene glycol monovinyl ether and the like are included.

  Furthermore, various known vinyl ether compounds may be used. For example, a compound containing a (meth) acryloyl group and a vinyl ether group in the molecule disclosed in Japanese Patent No. 3461501, a vinyl ether compound having an alicyclic skeleton containing at least an oxygen atom disclosed in Japanese Patent No. 4037856, A vinyl ether having an alicyclic skeleton disclosed in JP-A-2005-015396, a 1-indanyl vinyl ether disclosed in JP-A-2008-137974, and disclosed in JP-A-2008-150341 4-acetoxycyclohexyl vinyl ether and the like.

  The inkjet ink in the invention preferably contains a polyfunctional donor monomer together with a monofunctional donor monomer. Thereby, curing sensitivity, weather resistance and solvent resistance can be improved.

Examples of the polyfunctional unsaturated compound in the unsaturated compound represented by the general formula (6) are represented by the general formula (D-1) to the general formula (D-9), and R ^{5 to} R ⁹ are 2 It becomes a linking group for forming a polyfunctional polymerizable monomer having one or more unsaturated bond moieties. Especially, it is especially preferable that it is a compound represented by general formula (D-1).

  Although the example of the polyfunctional unsaturated compound which has an unsaturated bond represented by general formula (D-1)-general formula (D-9) is shown, it is not limited to this. All of the charges of carbon atoms constituting the unsaturated bond of the polymerizable monomer exemplified below are −0.45 or less.

  Examples of bifunctional vinyl ether compounds include 1,4-butanediol divinyl ether, 1,6-hexanediol divinyl ether, neopentyl glycol divinyl ether, nonanediol divinyl ether, cyclohexanediol divinyl ether, cyclohexanedimethanol divinyl ether, diethylene glycol Examples include divinyl ether, triethylene glycol divinyl ether (TEGDVE), trimethylolpropane divinyl ether, ethylene oxide-modified trimethylolpropane divinyl ether, pentaerythritol divinyl ether, and the like.

  Examples of the bifunctional vinyl ether compound include a vinyl ether compound having an alicyclic skeleton containing at least an oxygen atom disclosed in Japanese Patent No. 4037856, and an alicyclic skeleton disclosed in Japanese Patent Application Laid-Open No. 2005-015396. There are also vinyl ethers, 1-indanyl vinyl ether disclosed in JP 2008-137974 A, 4-acetoxycyclohexyl vinyl ether disclosed in JP 2008-150341 A, and the like.

  Introduce a substituent at the α-position or β-position of the vinyl ether group by substituting the vinyl ether group of the above-mentioned bifunctional vinyl ether compound with a propenyl ether group, an isopropenyl ether group, a butenyl ether group or an isobutenyl ether group. These compounds can also be used as polyfunctional unsaturated compounds.

  Among these bifunctional vinyl ether compounds, in consideration of curability, adhesion, and surface hardness, diethylene glycol divinyl ether, triethylene glycol divinyl ether, cyclohexanediol divinyl ether, cyclohexane dimethanol divinyl ether, and the like are curable. Are excellent in terms of compatibility, odor, and safety.

<Trifunctional or higher polyfunctional vinyl ether compound>
Specific examples of the trifunctional or higher polyfunctional vinyl ether compound include trimethylolpropane trivinyl ether, ethylene oxide modified trimethylolpropane trivinyl ether, pentaerythritol trivinyl ether, pentaerythritol tetravinyl ether, ethylene oxide modified pentaerythritol trivinyl ether, ethylene oxide modified Examples include pentaerythritol tetravinyl ether, dipentaerythritol hexavinyl ether, and ethylene oxide-modified dipentaerythritol hexavinyl ether.

The trifunctional vinyl ether compound can be represented by the following general formula (A). As represented by the general formula (A), a compound having an oxyalkylene group in the molecule is preferable for obtaining compatibility and solubility with other ink components and adhesion to a substrate. The total number of oxyalkylene groups in the compound represented by formula (A) is preferably 10 or less. If it exceeds 10, the water resistance of the cured film may be lowered. The compound represented by the general formula (A) has an oxyethylene group, but the oxyethylene group may be another oxyalkylene group having a different carbon number. 1-4 are preferable and, as for carbon number of an oxyalkylene group, it is more preferable that it is 1 or 2.

In the above general formula (A), R ₁₁ represents hydrogen or an organic group. Examples of the organic group represented by R ₁₁ include an alkyl group having 1 to 6 carbon atoms such as a methyl group, an ethyl group, a propyl group, or a butyl group, a fluoroalkyl group having 1 to 6 carbon atoms, an aryl group, and a furyl group. Or thienyl group, allyl group, 1-propenyl group, 2-propenyl group, 2-methyl-1-propenyl group, 2-methyl-2-propenyl group, 1-butenyl group, 2-butenyl group, 3-butenyl group, etc. An alkenyl group having 1 to 6 carbon atoms, phenyl group, benzyl group, fluorobenzyl group, aryl group such as methoxybenzyl group or phenoxyethyl group, alkoxy group such as methoxy group, ethoxy group and butoxy group, propylcarbonyl group, An alkylcarbonyl group having 1 to 6 carbon atoms such as a butylcarbonyl group or a pentylcarbonyl group, an ethoxycarbonyl group, a propoxycarbonyl group; Includes a group such as an alkoxycarbamoyl group having 1 to 6 carbon atoms such as a butoxycarbonyl group, an alkoxycarbamoyl group having 1 to 6 carbon atoms such as an ethoxycarbamoyl group, a propylcarbamoyl group or a butylpentylcarbamoyl group. It is not limited. Among these, as the organic group, a hydrocarbon group containing no hetero atom is preferable from the viewpoint of curability. Moreover, p, q, and r are 0 or an integer greater than or equal to 1, and p + q + r is an integer of 3-10.

Examples of the polyfunctional vinyl ether compound having four or more vinyl ether groups include compounds represented by the following general formulas (B) and (C).

In the general formula (B), R ₁₂ is a linking group containing any one of a methylene group, an alkylene group having 1 to 6 carbon atoms, an oxyalkylene group, and an ester group. p, q, l and m are each 0 or an integer of 1 or more, and the total number of p + q + l + m is an integer of 3 to 10.

In the general formula (C), R ₁₃ represents a linking group containing any of a methylene group, an alkylene group having 1 to 6 carbon atoms, an oxyalkylene group, and an ester group. p1, q1, r1, l1, m1, and s1 are each 0 or an integer of 1 or more, and the total number of p1 + q1 + r1 + l1 + m1 + s1 is an integer of 3 to 10.

  In the general formulas (B) and (C), an oxyethylene group is exemplified, but an oxyalkylene group having a different carbon number may be used. The number of carbon atoms in the oxyalkylene group is preferably 1 to 4, and more preferably 1 or 2.

<Other polymerizable monomers>
The inkjet ink of the present invention may contain other polymerizable monomer other than the acceptor monomer and the donor monomer as long as the effects of the present invention are not impaired. The charge of the carbon atom constituting the unsaturated bond of the other polymerizable monomer is more than −0.45 and preferably less than −0.30. By adding other polymerizable monomers, reduction in curing shrinkage, adjustment of viscosity, imparting adhesion to a substrate, imparting flexibility, and the like can be achieved.

  The other polymerizable monomer is preferably a compound having at least one ethylenically unsaturated bond capable of radical polymerization in the molecule, and may be any of a monomer, an oligomer and a polymer. Only one type of radically polymerizable monomer may be used, or two or more types may be used in combination at an arbitrary ratio in order to improve the desired properties. It is preferable to use two or more kinds in combination for controlling performance such as reactivity and physical properties. The cyclic allyl sulfide monomer can be copolymerized with other methacrylate monomers and acrylate monomers.

  Examples of polymerizable monomers having an ethylenically unsaturated bond capable of radical polymerization include unsaturated carboxylic acids such as acrylic acid and methacrylic acid and their salts; anhydrides having ethylenically unsaturated groups, acrylonitrile, styrene, Various unsaturated polyesters, unsaturated polyethers, unsaturated polyamides, unsaturated urethanes and the like are included.

  Specifically, 2-hydroxyethyl acrylate, butoxyethyl acrylate, carbitol acrylate, cyclohexyl acrylate, tetrahydrofurfuryl acrylate, benzyl acrylate, tridecyl acrylate, 2-phenoxyethyl acrylate, bis (4-acryloxypolyethoxyphenyl) Propane, polyethylene glycol diacrylate, polypropylene glycol diacrylate, dipentaerythritol tetraacrylate, trimethylolpropane triacrylate, oligoester acrylate, N-methylolacrylamide, diacetone acrylamide, epoxy acrylate, isobornyl acrylate, dicyclopentenyl acrylate, Dicyclopentenyloxyethyl acrylate, disic Acrylic acid derivatives such as lopentanyl acrylate; methyl methacrylate, n-butyl methacrylate, allyl methacrylate, glycidyl methacrylate, benzyl methacrylate, dimethylaminomethyl methacrylate, polyethylene glycol dimethacrylate, polypropylene glycol dimethacrylate, 2,2-bis (4- Methacryl derivatives such as methacryloxypolyethoxyphenyl) propane; and other derivatives of allyl compounds such as allyl glycidyl ether, diallyl phthalate and triallyl trimellitate.

  More specifically, Shinzo Yamashita, “Crosslinker Handbook”, (1981 Taiseisha); Kato Kiyosumi, “UV / EB Curing Handbook (Materials)” (1985, Polymer Publications); Radtech Study Group, “Application and Market of UV / EB Curing Technology”, p. 79, (1989, CMC); Eiichiro Takiyama, “Polyester Resin Handbook”, (1988, Nikkan Kogyo Shimbun) Commercially available products or radically polymerizable and crosslinkable monomers, oligomers and polymers known in the industry can be used.

  Among these acrylates and methacrylates, from the viewpoint of curability and film properties after curing, acrylates of alcohols having ether oxygen atoms such as tetrahydrofurfuryl acrylate and 2-phenoxyethyl acrylate are adhesive, flexible, It is preferable from the viewpoint of curability. For the same reason, an acrylate of an alcohol having an alicyclic structure is also preferable, and a bicyclo ring structure or a tricyclo ring structure such as isobornyl acrylate, dicyclopentenyl acrylate, dicyclopentenyloxyethyl acrylate, dicyclopentanyl acrylate, etc. An acrylate having is preferable. Of these, dicyclopentenyl acrylate and dicyclopentenyloxyethyl acrylate having a double bond in the alicyclic structure are particularly preferable.

  Examples of the radical polymerizable monomer include JP-A-7-159983, JP-B-7-31399, JP-A-8-224982, JP-A-10-863, JP-A-9-134011, JP-T-2004. There are photocurable polymerizable monomers used in the photopolymerizable composition described in each publication such as 5114014, and these can also be applied to the polymerizable monomer of the ink inkjet ink in the present invention.

  Further, other polymerizable monomers include (meth) acrylic monomers or prepolymers, (meth) acrylic acid esters such as epoxy monomers or prepolymers, urethane monomers or prepolymers (hereinafter referred to as acrylate compounds as appropriate). It may be. Specific examples thereof include 2-ethylhexyl-diglycol acrylate, 2-hydroxy-3-phenoxypropyl acrylate, 2-hydroxybutyl acrylate, hydroxypivalate neopentyl glycol diacrylate, 2-acryloyloxyethyl phthalate, methoxy -Polyethylene glycol acrylate, tetramethylol methane triacrylate, 2-acryloyloxyethyl-2-hydroxyethylphthalic acid, dimethylol tricyclodecane diacrylate, ethoxylated phenyl acrylate, 2-acryloyloxyethyl succinic acid, nonylphenol EO addition Acrylate, modified glycerin triacrylate, bisphenol A diglycidyl ether acrylic acid adduct, modified bisphenol A diacrylate, phenoxy-poly Ethylene glycol acrylate, 2-acryloyloxyethyl hexahydrophthalic acid, PO adduct diacrylate of bisphenol A, EO adduct diacrylate of bisphenol A, dipentaerythritol hexaacrylate, pentaerythritol triacrylate tolylene diisocyanate urethane prepolymer Lactone-modified flexible acrylate, butoxyethyl acrylate, propylene glycol diglycidyl ether acrylic acid adduct, pentaerythritol triacrylate hexamethylene diisocyanate urethane prepolymer, 2-hydroxyethyl acrylate, methoxydipropylene glycol acrylate, ditrimethylolpropane Tetraacrylate, pentaerythritol triacrylate hexamethyle Diisocyanate urethane prepolymer, stearyl acrylate, isoamyl acrylate, isomyristyl acrylate, isostearyl acrylate, and the like lactone-modified acrylate.

  These acrylate compounds are polymerizable monomers used in conventional UV curable inks, and have low skin irritation and sensitization (ease of rash). Further, since it has a relatively low viscosity, it can stabilize the ink ejection properties, and the polymerization sensitivity and the adhesion to the substrate are also good. Furthermore, (meth) acrylic monomers have lower skin irritation than acrylic monomers.

  Among them, monofunctional acrylates are often low-viscosity, and can be adjusted from the standpoint of improving injection properties. Also, the cured film can be made flexible even on flexible substrates, and shrinkage can be cured. Since generation | occurrence | production can be prevented, it is preferable.

  As the oligomer that can be used in combination with the monofunctional acrylate, an epoxy acrylate oligomer and a urethane acrylate oligomer are particularly preferable. The polyfunctional monomer has good sensitivity and cured film strength. In such a polyfunctional monomer, examples of the bifunctional monomer include bifunctional acrylate, polyethylene glycol diacrylate, and polypropylene glycol diacrylate. Mention may be made of polyfunctional acrylates, dipentaerythritol tetraacrylate, trimethylolpropane triacrylate, oligoester acrylate.

<Monomer solvent>
Thus, the inkjet ink of the present invention includes an acceptor monomer, a donor monomer, and any other polymerizable monomer. A mixture of these polymerizable monomers serves as a monomer solvent for the inkjet ink.

  It is considered that the acceptor monomer and the donor monomer contained in the monomer solvent form a complex (also referred to as a charge transfer complex or a CT complex) due to the difference in charge. Since polarization occurs when the complex is formed, it is difficult to predict the polarity of the monomer solvent from the polarity of the acceptor monomer itself and the polarity of the donor monomer itself.

  The difference in SP value of the monomer solvent from the SP value of the polymer dispersant described later is preferably 1.6 or less. The SP value of the monomer solvent can be determined by a cloud point titration method. The SP value may be measured by the cloud point titration method according to the method described in K.W.Suh, J.M.Corbett; J. Apply Polym. Sci., 12 (10), p2359-2370 (1968). By reducing the difference between the SP value of the monomer solvent and the SP value of the polymer dispersant, the dispersion stability of the pigment in the inkjet ink can be increased.

[Colorant]
When coloring the inkjet ink of this invention, it is preferable to contain a pigment as a coloring agent. The pigment may be a colorless inorganic pigment such as carbon black, titanium oxide, calcium carbonate, or a colored organic pigment.

  Examples of organic pigments include insoluble azo pigments such as toluidine red, toluidine maroon, Hansa yellow, benzidine yellow, pyrazolone red, soluble azo pigments such as ritol red, heliobordeaux, pigment scarlet, permanent red 2B; alizarin, indanthrone Derivatives from vat dyes such as thioindigo maroon; phthalocyanine organic pigments such as phthalocyanine blue and phthalocyanine green; quinacridone organic pigments such as quinacridone red and quinacridone magenta; perylene organic pigments such as perylene red and perylene scarlet; Isoindolinone organic pigments such as indolinone yellow and isoindolinone orange; pyranthrone organic pigments such as pyranthrone red and pyranthrone orange; thioindigo Machine pigments, condensed azo organic pigments, benzimidazolone organic pigments, quinophthalone organic pigments such as quinophthalone yellow; isoindoline organic pigments such as isoindoline yellow; other pigments such as flavanthron yellow, acylamide yellow, nickel Azo yellow, copper azomethine yellow, perinone orange, anthrone orange, dianthraquinonyl red, dioxazine violet and the like are included.

  Organic pigments are exemplified below by color index (CI) numbers.

C. I. Pigment Yellow 12, 13, 14, 17, 20, 24, 74, 83, 86, 93, 109, 110, 117, 120, 125, 128, 129, 137, 138, 139, 147, 148, 150, 151, 153, 154, 155, 166, 168, 180, 185;
C. I. Pigment orange 16, 36, 43, 51, 55, 59, 61;
C. I. Pigment Red 9, 48, 49, 52, 53, 57, 97, 122, 123, 149, 168, 177, 180, 192, 202, 206, 215, 216, 217, 220, 223, 224, 226, 227, 228, 238, 240;
C. I. Pigment violet 19, 23, 29, 30, 37, 40, 50;
C. I. Pigment blue 15, 15: 1, 15: 3, 15: 4, 15: 6, 22, 60, 64;
C. I. Pigment green 7, 36;
C. I. Pigment Brown 23, 25, 26.

  Among the above pigments, quinacridone-based, phthalocyanine-based, benzimidazolone-based, isoindolinone-based, condensed azo-based, quinophthalone-based, and isoindoline-based organic pigments are preferable because of excellent light resistance.

  The organic pigment is preferably fine particles having an average particle diameter in the ink of 10 to 150 nm as measured by laser scattering. When the average particle size of the pigment is less than 10 nm, the light resistance is lowered due to the small particle size, and when it exceeds 150 nm, it is difficult to stably maintain the dispersion, and the pigment is likely to precipitate. Stability is lowered, and a problem that minute mist called satellite occurs. However, in the case of titanium oxide, the average particle diameter is 150 to 300 nm, preferably 180 to 250 nm, in order to provide whiteness and concealment.

  In addition, it is preferable that coarse particles are removed by sufficient dispersion or filtration so that the maximum particle size of the pigment in the ink does not exceed 1.0 μm. When coarse particles are present, the injection stability tends to decrease.

  The organic pigment can be refined by the following method. That is, a mixture comprising at least three components of an organic pigment, a water-soluble inorganic salt of 3 mass times or more of the organic pigment, and a water-soluble solvent is made into a clay, kneaded with a kneader or the like, and then poured into water. Stir with a speed mixer to make a slurry. Next, filtration and washing of the slurry are repeated, and the water-soluble inorganic salt and the water-soluble solvent are removed by aqueous treatment. In the miniaturization step, a resin, a pigment dispersant and the like may be added.

  Examples of the water-soluble inorganic salt include sodium chloride and potassium chloride. These inorganic salts are used in the range of 3 to 20 times the mass of the organic pigment, but after the dispersion treatment, chlorine ions (halogen ions) are removed by washing with water. When the amount of the inorganic salt is less than 3 times by mass, a treated pigment having a desired size cannot be obtained. When the amount is more than 20 times by mass, the cleaning process in the subsequent step is enormous, and the substantial processing amount of the organic pigment is reduced.

  The water-soluble solvent is not particularly limited as long as it is a solvent that can be used for making an appropriate clay state of an organic pigment and a water-soluble inorganic salt used as a crushing aid and performing sufficient crushing efficiently, and is soluble in water. However, since the temperature rises during kneading and the solvent easily evaporates, a high boiling point solvent having a boiling point of 120 to 250 ° C. is preferable from the viewpoint of safety. As water-soluble solvent, 2- (methoxymethoxy) ethanol, 2-butoxyethanol, 2- (i-pentyloxy) ethanol, 2- (hexyloxy) ethanol, diethylene glycol, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether , Triethylene glycol, triethylene glycol monomethyl ether, liquid polyethylene glycol, 1-methoxy-2-propanol, 1-ethoxy-2-propanol, dipropylene glycol, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, low molecular weight Examples include polypropylene glycol.

  The pigment may be surface-treated by a known technique such as an acid treatment or a basic treatment, a synergist, or various coupling agents. This is because the adsorption with the pigment dispersant is promoted to ensure dispersion stability.

  Examples of inorganic pigments include white pigments, pearl pigments, metal pigments and the like. Examples of white pigments include titanium oxide powder. Examples of pearl pigments include pearl mica powder. Pearl mica is an artificial pigment that reproduces pearl luster and is a particle in which mica particles are covered with a titanium oxide film. As a result, an interface having a large difference in refractive index is created to facilitate reflection. Examples of the metal pigment include aluminum powder.

  These inorganic pigments have a high refractive index. Therefore, even if an active energy ray is irradiated to an application image of inkjet ink containing these inorganic pigments, the active energy ray may not reach the deep part of the image, and the ink in the deep part of the image may be insufficiently cured. In particular, if the inorganic pigment is unevenly distributed in the deep part of the image without uniformly dispersing the inorganic pigment in the ink, the effect tends to be further insufficient.

  On the other hand, since the ink-jet ink of the present invention contains an appropriate polymer dispersant, the inorganic pigment can be uniformly dispersed and the coated image can be sufficiently cured. Therefore, the ink-jet ink of the present invention has sufficient curing sensitivity even if it contains a pigment having a high refractive index of 1.5 or more. As a result, the scratch resistance of the image is improved.

  The pigment content in the ink-jet ink is preferably 1.5 to 8% by mass in order to obtain a sufficient concentration and sufficient light resistance, but in the case of a white ink containing titanium oxide as a pigment, it is 10 to 30% by mass. % Is preferably included.

(Pigment dispersant)
The pigment dispersant contained in the inkjet ink of the present invention is preferably a polymer dispersant. The weight average molecular weight of the polymer dispersant is preferably 1000 or more. Further, the polymer dispersant preferably has a comb structure having a main chain and side chains.

  The main chain of the polymer dispersant contained in the inkjet ink may be polyurethane, polyacrylate, polyester, polyamide, or the like. The main chain of the polymer dispersant preferably has a pigment adsorption functional group. Examples of the pigment adsorbing functional group include a tertiary amino-containing group, a carboxyl group, and a sulfonic acid group.

  The side chain of the polymer dispersant contained in the inkjet ink has a solvent affinity group. The polarity of the solvent affinity group is preferably set according to the polarity of the monomer solvent of the inkjet ink (mixed monomer including a donor monomer and an acceptor monomer). Specifically, the polarity of the solvent affinity group is preferably low or medium polarity. By setting the polarity of the solvent affinity group to medium or low polarity, the compatibility of the polymer dispersant with respect to the monomer solvent is increased. Examples of solvophilic groups include groups consisting of polyether, polyalkylene polyamine or polycarboxylic acid partial alkyl ester structures.

  Such a polymer dispersant is, for example, a copolymer of (meth) acrylic ester and styrene. What is necessary is just to introduce | transduce a solvent affinity group into the ester site | part of (meth) acrylic ester, and to introduce | transduce the tertiary amino group which is a pigment adsorption functional group into the phenyl group of styrene.

  The difference between the SP value of the polymer dispersant contained in the inkjet ink of the present invention and the SP value of the monomer solvent is preferably 1.6 or less. The SP value of the polymer dispersant can be determined by a cloud point titration method. The SP value may be measured by the cloud point titration method according to the method described in K.W.Suh, J.M.Corbett; J. Apply Polym. Sci., 12 (10), p2359-2370 (1968).

  Since the inkjet ink of the present invention contains such a polymer dispersant, the dispersibility of the pigment is high. The reason is not particularly limited, but it is considered that the side chain acting as the solvent affinity group of the polymer dispersant takes in the monomer solvent and the pigment adsorbing functional group of the main chain takes in the pigment. Since the side chain incorporating the polarized monomer solvent can sufficiently spread, the monomer solvent can be sufficiently incorporated.

As described above, the polymer dispersant contained in the inkjet ink of the present invention may be selected according to the SP value of the monomer solvent. For example, the polymer dispersant may be appropriately selected from the following commercially available polymer dispersants having a comb structure. Can do.
Efka 5063, Efka 5065 (Wilver Ellis Co., Ltd.), DisperBYK-2000, DisperBYK-2001, DisperBYK-2009, DisperBYK-2022, DisperBYK-2025, DisperBYK-2050, J-9133, J-9150 (BYK Japan Co., Ltd.) ), Solsperse 24000SC, Solsperse 24000GR, Solsperse 32000, Solsperse 39000, Solsperse 56000, Solsperse 71000 (Nippon Lubrizol Co., Ltd.), Ajisper PB-821, Ajisper PB-822, Ajisper PB-824, Ajimoto PB-881 (Ajinomoto Fine Techno) Co., Ltd.), Floren NC-500, Floren Dopa-33, Floren Dopa-17HF, Floren KDG-2400 (Kyoeisha Chemical Co., Ltd.)

  The content of the pigment dispersant in the inkjet ink is preferably 30 to 70 parts by mass with respect to 100 parts by mass of the pigment. If the amount is less than 30 parts by mass, dispersion stability may be difficult to obtain. If the amount is more than 70 parts by mass, the ink viscosity may increase and the ejection stability may deteriorate.

(Photopolymerization initiator)
The inkjet ink of the present invention preferably contains a radical photopolymerization initiator or a sensitizer as a photopolymerization initiator from the viewpoint of obtaining high sensitivity.

  The radical photopolymerization initiator contained in the inkjet ink of the present invention is preferably a molecular cleavage type or a hydrogen abstraction type. Specific examples of the radical photopolymerization initiator include benzoin isobutyl ether, 2,4-diethylthioxanthone, 2-isopropylthioxanthone, benzyl, 2,4,6-trimethylbenzoyldiphenylphosphine oxide, 2-benzyl-2-dimethylamino- 1- (4-morpholinophenyl) -butan-1-one, bis (2,6-dimethoxybenzoyl) -2,4,4-trimethylpentylphosphine oxide, bis (2,4,6-trimethylbenzoyl) -phenylphosphine An oxide or the like is preferably used.

  Further, as molecular cleavage type photopolymerization initiators, 1-hydroxycyclohexyl phenyl ketone, benzoin ethyl ether, benzyldimethyl ketal, 2-hydroxy-2-methyl-1-phenylpropan-1-one, 1- (4-isopropylphenyl) -2-Hydroxy-2-methylpropan-1-one and 2-methyl-1- (4-methylthiophenyl) -2-morpholinopropan-1-one, 1- [4- (2-hydroxyethoxy) -phenyl] -2-Hydroxy-2-methyl-1-propan-1-one may be used in combination.

  Further, examples of the hydrogen abstraction type photopolymerization initiator include benzophenone, 4-phenylbenzophenone, isophthalphenone, 4-benzoyl-4′-methyl-diphenyl sulfide, and bis (2,4- 1,2-octanedione, a polymerization initiator of cyclopentadiene-1-yl) -bis (2,6-difluoro-3- (1H-pyrrol-1-yl) -phenyl) titanium, an oxime ester type -(4- (phenylthio) -2- (O-benzoyloxime)), ethanone, 1- (9-ethyl-6- (2-methylbenzoyl) -9H-carbazol-3-yl)-, 1- (O -Acetyl oxime).

  A sensitizer can be used in combination with the radical photopolymerization initiator. Examples of sensitizers include trimethylamine, methyldimethanolamine, triethanolamine, p-diethylaminoacetophenone, ethyl p-dimethylaminobenzoate, isoamyl p-dimethylaminobenzoate, N, N-dimethylbenzylamine and 4, Amines that do not cause an addition reaction with a radically polymerizable monomer such as 4′-bis (diethylamino) benzophenone are included. Of course, it is preferable to select and use a radical photopolymerization initiator and a sensitizer that are excellent in solubility in the polymerizable monomer.

  The content of the photo radical polymerization initiator and the sensitizer in the inkjet ink is preferably 0.1 to 20% by mass, more preferably 1 to 12% by mass with respect to the total mass of the inkjet ink.

  Other examples of the radical photopolymerization initiator include a type in which an amine-based initiator aid is bonded as an initiator structure to a dendrimer core described in European Patent 1,674,499A, European Patent 2,161. , 264A, European Patent 2,189,477A, an initiator having a polymerizable group, an amine-based initiator, a plurality of those described in European Patent 1,927,632B1 A type having an amine-based initiator in one molecule, a type containing a plurality of thioxanthones in the molecule described in WO 2009/060235, represented by ESACURE ONE and ESACUR KIP150 commercially available from Lamberti Also included is an oligomer type polymerization initiator in which α-hydroxypropiophenone is bonded to the side chain.

  Moreover, the maleimide compound which is a polymerizable monomer itself can act as a photopolymerization initiator.

[Other additives]
The ink-jet ink may further contain various additives as necessary. Examples of various additives include surfactants, lubricants, fillers, antifoaming agents, gelling agents, thickeners, specific resistance adjusting agents, film forming agents, ultraviolet absorbers, antioxidants, anti-fading agents, Anti-corrosive agent, rust preventive agent, etc. are included. These are added depending on the purpose of improving the injection stability, compatibility with the print head and ink packaging container, storage stability, image storage stability, and other various performances. Furthermore, it can contain a small amount of solvent such as ester solvent, ether solvent, ether ester solvent, ketone solvent, aromatic hydrocarbon solvent, nitrogen-containing organic solvent.

  The solvent may be a solvent other than water. Specific examples of the solvent include dimethyl sulfoxide, diethyl sulfoxide, methyl ethyl sulfoxide, diphenyl sulfoxide, tetraethylene sulfoxide, dimethyl sulfone, methyl ethyl sulfone, methyl-isopropyl sulfone, methyl-hydroxyethyl sulfone, sulfolane, or N-methyl- 2-pyrrolidone, 2-pyrrolidone, β-lactam, N, N-dimethylformamide, N, N-diethylformamide, N, N-dimethylacetamide, 1,3-dimethyl-2-imidazolidinone, 3-methyl-2 -Oxazolidinone, γ-butyrolactone, γ-valerolactone, isophorone, cyclohexanone, propylene carbonate, anisole, methyl ethyl ketone, acetone, ethyl lactate, butyl lactate, dioxane, ethyl acetate, butyl acetate, diethylene glycol Methyl ether, dibasic ester, methoxybutyl acetate, and the like. When a solvent is added to the ink in an amount of 1.5 to 30%, preferably 1.5 to 15%, adhesion to a resin recording medium such as polyvinyl chloride is improved.

  Other specific examples of the solvent include alkylene glycol monoalkyl ethers such as diethylene glycol monoethyl ether, triethylene glycol monomethyl ether, dipropylene glycol monomethyl ether, tripropylene glycol monomethyl ether, ethylene glycol dibutyl ether, tetraethylene glycol dimethyl ether, etc. Alkylene glycol dialkyl ethers, alkylene glycol monoalkyl ether acetates such as ethylene glycol monobutyl ether acetate, diethylene glycol diethyl ether, dipropylene glycol dimethyl ether, dipropylene glycol diethyl ether, ethylene glycol diacetate, propylene glycol diacetate .

  Examples of the surfactant contained in the inkjet ink of the present invention include anionic surfactants such as dialkylsulfosuccinates, alkylnaphthalenesulfonates, fatty acid salts, polyoxyethylene alkyl ethers, polyoxyethylene alkyl allyl ethers , Nonionic surfactants such as acetylene glycols, polyoxyethylene / polyoxypropylene block copolymers, cationic surfactants such as alkylamine salts and quaternary ammonium salts, silicone-based and fluorine-based surfactants Etc. are included. In particular, a silicone-based or fluorine-based surfactant is preferable.

  By adding a silicone-based or fluorine-based surfactant, it is possible to further suppress ink mixing on recording media made of various hydrophobic resins such as vinyl chloride sheets and recording media that absorb slowly such as printing paper. And high-quality printed images can be obtained. These surfactants are particularly preferably used in combination with a water-soluble organic solvent having a low surface tension.

  Preferred examples of the silicone-based surfactant include polyether-modified polysiloxane compounds such as KF-351A, KF-642, X-22-4272 manufactured by Shin-Etsu Chemical Co., Ltd., BYK307, BYK345, BYK347 manufactured by Big Chemie. BYK348, TSF4452 manufactured by Toshiba Silicone Co., and the like.

  The fluorosurfactant means one obtained by substituting a part or all of hydrogen bonded to carbon of the hydrophobic group of a normal surfactant with fluorine. The fluorine-based surfactant preferably has a perfluoroalkyl group in the molecule.

  Fluorosurfactants are available from DIC under the name Megafac F; from Asahi Glass under the name Surflon; from Minnesota Mining & Manufacturing Company Fluorad Under the trade name FC; under the trade name Monflor from Imperial Chemical Industry; under the trade name Zonyls from EI DuPont Nemeras &Company; Ricobet from Farbeberke Hoechst (Licowet) under the trade name VPF; also commercially available from Neos under the trade name Fantage.

  The addition amount of the surfactant in the inkjet ink is preferably 0.1% by mass or more and less than 2.0% by mass with respect to the total mass of the ink.

  If the surface tension of the ink-jet ink is 15 mN / m or more (25 ° C.), the area around the nozzles of the ink-jet head is wet and the ejection ability is unlikely to decrease. Further, it is preferable that the surface tension of the ink-jet ink is less than 35 mN / m (25 ° C.) because it is well wetted with a coated paper or a resin-made recording medium whose surface energy is lower than that of normal paper, and whitening hardly occurs.

<Ink preparation method>
Ink jet ink is produced by dispersing a polymerizable monomer, a photopolymerization initiator, a colorant, and, when the colorant is a pigment, a pigment dispersant using a normal disperser such as a sand mill. .

  Preferably, a pigment concentrate is prepared in advance, and the pigment concentrate is diluted with a polymerizable monomer to prepare an inkjet ink. According to this method, sufficient dispersion can be performed with a normal disperser, and excessive dispersion energy and a great amount of dispersion time are not required. As a result, it is possible to prepare an ink that is less likely to be deteriorated during the dispersion step and has excellent stability.

  The prepared ink is preferably filtered through a filter having a pore diameter of 3 μm or less (preferably 1 μm or less).

<Recording medium>
In the image forming method of the present invention, an active energy ray-curable inkjet ink is ejected as a droplet onto a recording medium by an inkjet method. The ejected liquid droplets land on the recording medium, and the landed liquid droplets are irradiated with actinic rays.

  The recording medium in the image forming method of the present invention may be any of a wide range of synthetic resins conventionally used for various purposes. Specific examples of the recording medium include polyester, polyvinyl chloride, polyethylene, polyurethane, polypropylene, acrylic resin, polycarbonate, polystyrene, acrylonitrile-butadiene-styrene copolymer, polyethylene terephthalate, polybutadiene terephthalate, and the like. The thickness and shape of these synthetic resin base materials are not limited at all. In addition, metals, glass, printing paper, etc. can be used.

  Specific examples of polyvinyl chloride which is one of the recording media in the image forming method of the present invention include KSM-VS, KSM-VST, KSM-VT (above, manufactured by Kimoto Co., Ltd.), P-223RW, and P-224RW. P-249ZW, P-284ZC (manufactured by Lintec Corporation), MPI3023 (manufactured by Toyo Corporation), NIJ-CAPVC, NIJ-SPVCGT (manufactured by Nichie Corporation), JT5129PM, JT5728P, JT5822P, JT5829P , JT5829R, JT5829PM, JT5829RM, JT5929PM (manufactured by Mactac), VGL-137, SVGS-137, MD3-200, MD3-301M, MD5-100, MD5-101M, MD5-105 (and above, Metamark) 640M, 641G, 641M, 3105M, 3105SG, 3162G, 3164G, 3164M, 3164XG, 3164XM, 3165G, 3165SG, 3165M, 3169M, 3451SG, 3551G, 3551M, 3631, 3641M, 3651G, 3651M, 3651M, 3651G, 3641M (Above, manufactured by Orafol), IJ180CV2 (manufactured by 3M) and the like.

  The recording medium may be a resin substrate containing no plasticizer or a non-absorbing inorganic substrate. There are no particular restrictions on various properties such as the thickness, shape, color, softening temperature, and hardness of the substrate.

  Examples of resin substrates that do not contain a plasticizer include ABS resin, polycarbonate (PC) resin, polyacetal (POM) resin, polyamide (PA) resin, polyethylene terephthalate (PET) resin, polyimide (PI) resin, acrylic resin, Examples include polyethylene (PE) resin, polypropylene (PP) resin, and hard polyvinyl chloride (PVC) resin that does not contain a plasticizer.

  Examples of non-absorbing inorganic base materials include glass plates, metal plates such as iron and aluminum, ceramic plates, and the like. These inorganic substrates are characterized by not having an ink-absorbing layer on the surface.

  These substrates can be used alone or in combination of a plurality of types of substrates.

<Injection of inkjet ink>
Ink jet ink is ejected as droplets from a nozzle (eject port) of an ink jet head onto a recording medium. The ink jet head system may be an on-demand system or a continuous system. In addition, the injection method is an electro-mechanical conversion method (for example, single cavity type, double cavity type, bender type, piston type, shear mode type, shared wall type, etc.), electro-thermal conversion method (for example, thermal ink jet) Any of a type | mold, a bubble jet (trademark) type | mold, etc. may be sufficient.

  The droplet size ejected from the nozzles of the inkjet head can be adjusted by the nozzle diameter of the head, the magnitude of the voltage applied to the inkjet head, and the pattern. For example, by using a “pulling” method in which the pressure chamber communicating with the nozzle opening is expanded and then contracted, the mass of the ink droplet can be reduced, so that the droplet size can be reduced.

  In order to form a high-definition and high-quality image with little unevenness, the droplet size is preferably 0.1 to 12 pl. If the droplet size is smaller than 0.1 pl, the number of droplets for image formation becomes excessive, the time required for image formation becomes long, and nozzle clogging is likely to occur. In addition, when the droplet size is smaller than 0.1 pl, the surface area per unit volume when the ink jet ink is ejected from the nozzle or when it is landed on the base material is increased, so that it is easily affected by outside air. The droplet size may be larger than 12 pl, but the resolution of the formed image may be lowered because the dot diameter per dot is increased. For this reason, there are problems in the roughness of image quality and the reproducibility of fine characters when viewed from close.

  In the image forming method of the present invention, the inkjet ink may be ejected in a heated state. Since the viscosity of the inkjet ink is reduced by heating, the injection stability is increased. The heating temperature of the inkjet ink is preferably 35 to 100 ° C, more preferably 35 to 80 ° C. A method for heating and keeping the ink-jet ink at a predetermined temperature is not particularly limited. For example, insulate the ink supply system such as the ink tank, supply pipe, front chamber ink tank just before the head, pipe with filter, piezo head, etc. that make up the inkjet head carriage, and use panel heater, ribbon heater, warm water, etc. There is a method of heating to a predetermined temperature.

  The inkjet ink is preferably heated and kept at a control width of a set temperature ± 5 ° C., more preferably a control width of a set temperature ± 2 ° C., and particularly preferably a control width of a set temperature ± 1 ° C. .

<Irradiation of active energy rays to ink landed on recording medium>
The inkjet ink droplets ejected onto the recording medium are irradiated with active energy rays such as ultraviolet rays, and the components contained in the ink are cured.

  Examples of the active energy rays to be irradiated include ultraviolet rays, near ultraviolet rays, natural light (including filter cut products), and the like, and ultraviolet rays are preferable. Examples of the ultraviolet light irradiation light source include a light emitting diode (LED), a metal halide lamp, a xenon lamp, a carbon arc lamp, a chemical lamp, a low pressure mercury lamp, a high pressure mercury lamp, and the like. For example, H lamps, D lamps, V lamps, etc. manufactured by Fusion System are commercially available.

  The LED can be turned on instantaneously, has a long life, has little radiant heat, is easy to control the amount of light, has a very narrow emission wavelength width (half-value width), and has low power consumption. LED light sources are also commercially available. The wavelength of the irradiation light source is preferably 350 nm to 450 nm, and more preferably 365 nm to 400 nm. This is because it is safe because it is on the long wavelength side in the light ultraviolet region.

In the image forming method according to the present invention, it is preferable that the integrated light amount irradiated to the droplets of the inkjet ink that has landed on the recording medium is 200 mJ / cm ² or less per droplet. The ink-jet ink in the present invention can sufficiently undergo a curing reaction even if the integrated light quantity is 200 mJ / cm ² or less. Therefore, it is advantageous from the viewpoint of energy saving / space saving and cost.

In the image forming method of the present invention, the illuminance of the active energy ray irradiation light source is preferably 5 W / cm ² or less. A light source with an illuminance higher than 5 W / cm ² has a large amount of heat generation, which may cause problems such as deformation of a recording medium with low heat resistance, or increased leakage of light and ink curing on the head nozzle surface. . In addition, a light source with high illuminance has high energy consumption, a large light source space, and cost increases.

  In the image forming method of the present invention, the active energy ray is preferably irradiated for 0.001 second to 1.0 second after the ink droplet has landed on the recording medium, and more preferably 0.001 second. Irradiation for ~ 0.5 seconds. In order to form a high-definition image, it is preferable that the interval from landing to irradiation is as short as possible.

  The irradiation method of an active energy ray is not specifically limited, For example, it can carry out with the following method. A light source is provided on both sides of the head unit, the head and the light source are scanned by a shuttle method, and irradiation is performed after a certain time from ink landing. Further, the curing is completed by irradiating light from another light source that is not driven (see Japanese Patent Application Laid-Open No. 60-132767). Alternatively, light may be irradiated using an optical fiber, or ultraviolet light from a collimated light source may be reflected by a mirror surface provided on the side of the head unit and irradiated to the recording unit (US Pat. No. 6, 145,979).

  Moreover, you may divide active energy ray irradiation into two steps. For example, a method of first irradiating active energy rays by the above-described method between 0.001 and 2.0 seconds after ink landing, and further irradiating active energy rays after the completion of all printing is one of preferred embodiments. is there. By dividing the irradiation of the active energy ray into two stages, it is possible to further suppress the shrinkage of the recording material that occurs during ink curing.

<Total ink film thickness after ink landing>
In the ink jet recording method of the present invention, the total ink film thickness after the ink has landed on the recording medium and cured by irradiation with active energy rays is preferably 2 to 20 μm. This is for suppressing curling and wrinkling of the recording medium and changes in the texture of the recording medium. “Total ink film thickness” means the maximum value of the film thickness of ink drawn on a recording medium. Whether it is a single color or a two-color overlap (secondary color), a three-color overlap, or a four-color overlap (white ink base), the total ink film thickness is preferably 2 to 20 μm.

  In the image forming method of the present invention, 1) a monomer having a low electron density and a monomer having a high electron density are combined as the polymerizable monomer, and 2) the droplet size to be ejected is 0.1 to 12 pl. Regardless of the printing environment, a high-definition and high-quality image with reduced unevenness can be formed, and the amount of irradiation light can be reduced.

  First, 1) Since a monomer having a low electron density and a monomer having a high electron density are combined as the polymerizable monomer, the photosensitivity is high. It is considered that the reason why the photosensitivity is high is that charge transfer complex polymerization occurs. In addition, the light sensitivity does not deteriorate depending on the printing environment. Therefore, 2) Even if the droplet size to be ejected is reduced to 0.1 pl to 12 pl, it is easily photocured.

<Inkjet recording apparatus>
The inkjet recording method of the present invention can be performed using an inkjet recording apparatus (inkjet printer). Examples of the ink jet recording apparatus include, but are not limited to, a serial head type recording apparatus and a line head type recording apparatus. Hereinafter, each recording apparatus will be described with reference to the drawings, but the ink jet recording apparatus is not limited thereto.

  FIG. 1 is a front view of a serial head type ink jet recording apparatus and shows a configuration of a main part of the apparatus. The recording apparatus 1 includes a head carriage 2, a recording head 3, an irradiation unit 4, a platen unit 5, and the like. In the recording apparatus 1, the platen unit 5 is installed under the recording medium P. The platen unit 5 has a function of absorbing ultraviolet rays, and absorbs the ultraviolet rays that have passed through the recording medium P. As a result, a high-definition image can be stably reproduced.

  The recording medium P is guided by the guide member 6 and moves from the front side to the back side in FIG. 1 by the operation of the conveying means (not shown). A head scanning means (not shown) scans the recording head 3 held by the head carriage 2 by reciprocating the head carriage 2 in the Y direction.

  The head carriage 2 is installed facing the upper side of the recording medium P, and includes a plurality of recording heads 3 according to the number of colors of images to be printed on the recording medium P. The recording head 3 is arranged with the ejection port 31 facing the recording medium P. The head carriage 2 of the recording apparatus 1 in FIG. 1 stores four types of recording heads 3 of yellow (Y), magenta (M), cyan (C), and black (K). The number of colors of the recording head 3 is set as appropriate.

  Inside the recording head 3, a plurality of ink chambers are arranged, and each ink chamber is provided with ejection means (not shown). The injection means is, for example, a piezo element. The ink chamber disposed inside the recording head 3 is supplied with active energy ray-curable ink by an ink supply means (not shown). The active energy ray-curable ink supplied to the ink chamber is ejected from the ejection port 31 toward the recording medium P by the operation of the ejection unit.

  The inkjet ink ejected from the ejection port 31 of the recording head 3 is the above-described active energy ray-curable inkjet ink, and when irradiated with the active energy ray, the polymerizable monomer is crosslinked or polymerized by the action of the polymerization initiator. It has the property of causing a reaction to cure.

  The recording head 3 can scan from one end to the other end of the recording medium P along the Y direction by driving the head scanning means. The recording head 3 ejects ink-jet ink droplets to land on a certain area (landing possible area) of the recording medium P while scanning.

  After the recording head 3 is scanned as many times as necessary and ink is ejected to one landable area, the recording medium P is appropriately moved from the front side to the back side in FIG. Again, while the recording head 3 is scanned, the recording head 3 ejects ink-jet ink droplets to landable areas adjacent to the one landable area and landed.

  By repeating the above-described operation, an image composed of an aggregate of inkjet ink droplets is formed on the recording medium P.

  The irradiation unit 4 is installed on both sides of the head carriage 2 so as to be fixed substantially parallel to the recording medium P. The irradiation means 4 includes an irradiation light source 8 that emits ultraviolet light in the specific wavelength region described above, and a filter (not shown) that transmits ultraviolet light of a specific wavelength.

  The irradiation area of the irradiation unit 4 may be the same as or larger than the landing possible area by the recording head 3.

  In order to prevent the ink ejection unit 31 from being exposed to light, the entire recording head 3 is shielded from light, and the ink ejection unit 31 and the recording material of the recording head 3 are further separated from the distance h1 between the irradiation unit 4 and the recording medium P. It is preferable to increase the distance h2 from P (h1 <h2) or to increase the distance between the recording head 3 and the irradiation means 4. Further, it is preferable that a bellows structure 7 is provided between the recording head 3 and the irradiation means 4.

  FIG. 2 is a top view of the line head type ink jet recording apparatus, and shows the main configuration of the apparatus. The recording apparatus 1 includes a head carriage 2 in which a plurality of recording heads 3 are fixedly disposed, and an irradiation unit 4.

  The plurality of recording heads 3 provided in the head carriage 2 are arranged so as to cover the entire width of the recording medium P.

  The irradiation unit 4 is disposed downstream of the head carriage 2 in the conveyance direction of the recording medium P. The irradiation means 4 has a plurality of LED light sources, and the plurality of LED light sources are arranged so as to cover the entire width of the recording medium P. That is, the irradiation means 4 is arranged so as to cover the entire area of the ink print surface. Each LED light source has a maximum illuminance, for example, at 395 nm.

  In the line head type ink jet recording apparatus 1, the head carriage 2 and the irradiation means 4 are fixed, and only the recording medium P is conveyed. Ink droplets ejected from the fixedly arranged recording head 3 land on the transported recording medium P, and light from the irradiation unit 4 is irradiated to the landed ink, so that the ink is cured. Thereby, an image is formed.

  Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited thereto.

A monomer solvent was prepared by mixing “triethylene glycol” as a donor monomer and “methylmaleimide” as an acceptor monomer in a molar ratio of 3: 7. The SP value of the prepared monomer solvent was measured by a cloud point titration method. Specifically, the above-mentioned document (KWSuh, JMCorbett; J. Apply Polym. Sci., 12 (10), p2359-2370 (1968)) was referred to.

[Preparation of pigment dispersion]
A pigment dispersion was prepared using the prepared monomer solvent. One of the following pigments was blended in the pigment dispersion.
Yellow pigment: PY150
Magenta pigment: PR122 or PR202 / V19
Cyan pigment: PB15: 4
Black pigment: PB7
Inorganic pigment: Titanium oxide, pearl mica or aluminum paste

The kind of the polymer dispersing agent mix | blended for every Example and comparative example. The polymer dispersant blended in each example and comparative example is shown below.

  Furthermore, Irgastab UV-10 (Ciba Specialty Chemicals) was blended with the pigment dispersion as a photopolymerization inhibitor.

A pigment dispersion having the following mass composition with the dispersant / pigment mass ratio adjusted to a range of 0.2 to 0.8 was prepared.

  The prepared pigment dispersion and monomer solvent were mixed at a mass ratio of 3: 7 (pigment dispersion: monomer solvent) to obtain an inkjet ink.

Image formation The obtained ink-jet ink prints four color inks (Yellow, Magenta, Cyan, Black) at a resolution of 720 dpi x 720 dpi on a vinyl chloride film sheet, which is a recording medium, and optionally an inorganic pigment ink. And cured by irradiation with light. The amount of each ink applied was the same. The irradiation light was ultraviolet light (385 nm) from an LED light source, and the integrated light amount was 100 mJ / cm ² .

[Measure the number of missed shots]
The 512 nozzles of the inkjet head (Konica Minolta Head, product name KM512) were observed with a microscope (× 50 times), and it was confirmed that there was no nozzle clogging before image formation, and then image formation was performed. After the image formation, the state of the 512 nozzles of the inkjet head was again observed with a microscope (× 50 times), and the number of nozzles clogged was counted as the number of missed shots. A single shot miss was judged as bad.

[Measurement of refractive index of pigment]
The refractive index of a mixed pigment of four color pigments or the total refractive index of a mixed pigment of four color pigments and an inorganic pigment was measured. The mixed pigment of four color pigments has a refractive index of 2 mm in thickness, 30 mm in width, and 20 mm in length in a transparent cell filled with the same amount of the four color pigments. A refractometer KPR-2000 (manufactured by Shimadzu Corporation) The refractive index was measured. On the other hand, the total refractive index of the mixed pigment of four color pigments and the inorganic pigment is as follows. Color pigments were filled in the same mass, and inorganic pigments were filled in the same cells; these cells were placed side by side, and the refractive index was measured with a refractometer KPR-2000 (manufactured by Shimadzu Corporation). Thus, the refractive index when passing through the pigment layer can be measured when entering the pigment from the air. The higher the refractive index, the more easily the light is diffusely reflected, making it difficult for the light to reach the deep layer of the pigment.

[Evaluation by manual peeling]
Each ink was printed with a solid color (720 × 720 dpi, width 50 mm × length 50 mm), and cured by ultraviolet irradiation. Vertical and horizontal cracks were made in the printed image every 5 mm with a cutter. The adhesive surface of Cellotape (registered trademark) was pressed against the printed image with cracks at a strength of 1 kg / cm ² . Thereafter, the end of the cello tape (registered trademark) was pulled up in the vertical direction to peel off the cello tape (registered trademark). The number of printing angles (5 mm × 5 mm) that came with the cello tape (registered trademark) was counted.
(Evaluation criteria)
Count is 0-2: ○
Count is 3-10: ○ △
Count is 11-30: △
Count is 31-50: ×
Count is 50 or more: XX

[Example 1-1]
In Example 1-1, the polymer dispersant is BYK Jet-9150, and Yellow pigment ink, Magenta pigment ink, Cyan pigment ink, Black pigment ink, and three types of inorganic pigment inks are prepared. The dispersant / pigment mass ratio was adjusted to a range of 0.2 to 0.8.

[Example 1-2]
In Example 1-2, the polymeric dispersant is BYK Jet-9150, Yellow pigment ink, Magenta pigment ink (different from the Magenta pigment ink of Example 1-1), Cyan pigment ink, and Black pigment ink. Three types of inorganic pigment inks were prepared, and the dispersant / pigment mass ratio was adjusted to a range of 0.2 to 0.8.

[Example 2-1]
In Example 2-1, the polymeric dispersant as Solsperse 24000GR, and Yellow pigment ink, and Magenta pigment ink, and Cyan pigment ink, and Black pigment ink, 3 kinds of inorganic pigment inks were prepared, respectively dispersing agent / Mass ratio of pigment was adjusted to a range of 0.2 to 0.8.

[Example 2-2]
In Example 2-2, the polymer dispersant is Solsperse 24000GR, Yellow pigment ink, Magenta pigment ink (different from the Magenta pigment ink of Example 2-1), Cyan pigment ink, Black pigment ink, 3 Different types of inorganic pigment inks were prepared, and the mass ratio of the dispersant / pigment was adjusted in the range of 0.2 to 0.8.

[Comparative Example 1-1]
In Comparative Example 1-1, as EFKA 7701 high molecular weight dispersant, and Yellow pigment ink, Magenta
Pigment ink, Cyan pigment ink, Black pigment ink, and three kinds of inorganic pigment inks were prepared, and the mass ratio of the dispersant / pigment was adjusted in the range of 0.2 to 0.8.

[Comparative Example 1-2]
In Comparative Example 1-2, as EFKA 7701 high molecular weight dispersant, and Yellow pigment ink, Magenta
Pigment ink (different from Magenta pigment ink of Comparative Example 1-1), Cyan pigment ink, and Black
A pigment ink and three types of inorganic pigment inks were prepared, and the dispersant / pigment mass ratio was adjusted to a range of 0.2 to 0.8.

[Comparative Example 2-1]
In Comparative Example 2-1, as BYK 2090 the polymeric dispersant, and Yellow pigment ink, and Magenta pigment ink, and Cyan pigment ink, and Black pigment ink, 3 kinds of inorganic pigment inks were prepared, respectively dispersing agent / Mass ratio of pigment was adjusted to a range of 0.2 to 0.8.

[Comparative Example 2-2]
In Comparative Example 2-2, the polymeric dispersant is BYK 2090, Yellow pigment ink, Magenta pigment ink (different from Magenta pigment ink in Comparative Example 2-1), Cyan pigment ink, Black pigment ink, 3 Different types of inorganic pigment inks were prepared, and the mass ratio of the dispersant / pigment was adjusted in the range of 0.2 to 0.8.

[Comparative Example 3-1]
In Comparative Example 3-1, as EFKA 5045 the polymeric dispersant, and Yellow pigment ink, and Magenta pigment ink, and Cyan pigment ink, and Black pigment ink, 3 kinds of inorganic pigment inks were prepared, respectively dispersing agent / Mass ratio of pigment was adjusted to a range of 0.2 to 0.8.

[Comparative Example 3-2]
In Comparative Example 3-2, the polymer dispersant is efka 5045, Yellow pigment ink, Magenta pigment ink (different from the Magenta pigment ink of Comparative Example 3-1,) Cyan pigment ink, Black pigment ink, 3 Different types of inorganic pigment inks were prepared, and the mass ratio of the dispersant / pigment was adjusted in the range of 0.2 to 0.8.

[Comparative Example 4-1]
In Comparative Example 4-1, as Johncril 62 a polymeric dispersant, and Yellow pigment ink, and Magenta pigment ink, and Cyan pigment ink, and Black pigment ink, 3 kinds of inorganic pigment inks were prepared, respectively dispersing agent / Mass ratio of pigment was adjusted to a range of 0.2 to 0.8.

[Comparative Example 4-2]
In Comparative Example 4-2, the polymer dispersant is Johncril 62, Yellow pigment ink, Magenta pigment ink (different from Magenta pigment ink of Comparative Example 4-1), Cyan pigment ink, Black pigment ink, 3 Different types of inorganic pigment inks were prepared, and the mass ratio of the dispersant / pigment was adjusted in the range of 0.2 to 0.8.

  From the results of Examples 1 and 2 (Tables 4 to 7), the difference from the SP value (10.1) of the monomer solvent is small (1.6 or less) and has a high comb-shaped structure. When a molecular dispersant was blended, any organic pigment or inorganic pigment was blended, and the storage stability (number of injection defects) was good, and the formed scratch resistance was also good.

  On the other hand, when a polymer dispersant having an SP value having a large difference from the SP value of the monomer solvent (over 1.6) is blended, even if it has a comb structure (Comparative Example 1), it has a comb structure. Even if it was not (Comparative Example 4), there were cases where the hand-rubbing peel resistance of the image was lowered or ink could not be ejected. Further, even if the polymer dispersant has an SP value with a small difference from the SP value of the monomer solvent (1.6 or less), a polymer dispersant having no comb structure is blended (Comparative Examples 2 and 3). ), The abrasion resistance of the image may be reduced and ink ejection may not be possible.

  The reason why the hand-rubbing resistance of the image is lowered or the ink cannot be ejected is considered to be that the dispersion stability of the pigment is lowered and the ink cannot be dispersed in the ink.

  Since the inkjet ink of the present invention contains an acceptor monomer and a donor monomer, the curing sensitivity is high. Therefore, fine image formation is possible. Moreover, since the dispersion stability of the pigment is high, the storage stability is also good. Therefore, it can be applied to inkjet inks for various purposes.

DESCRIPTION OF SYMBOLS 1 Recording device 2 Head carriage 3 Recording head 31 Injection port 4 Irradiation means 5 Platen part 6 Guide member 7 Bellows structure 8 Irradiation light source P Recording medium

Claims (4)

An ultraviolet curable type that contains a monomer solvent containing a donor monomer and an acceptor monomer, a pigment, a polymer dispersant, and does not contain water, and performs polymerization by a charge density difference between the donor monomer and the acceptor monomer. Non-aqueous inkjet ink,
The donor monomer is triethylene glycol vinyl ether
The acceptor monomer is methylmaleimide;
The polymer dispersant has a comb structure having a main chain and a side chain bonded to the main chain,
And the non-aqueous inkjet ink whose difference of SP value of the said polymer dispersing agent and SP value of the said monomer solvent is 1.6 or less.   The non-aqueous inkjet ink according to claim 1, wherein a main chain of the polymer dispersant is polyurethane, polyacrylate, polyester, polyamide, or polyurea.   The non-aqueous inkjet ink according to claim 1, wherein a content ratio of the polymer dispersant to the pigment is 0.3 to 0.7 by weight.   The non-aqueous inkjet ink according to claim 1, wherein the pigment has a refractive index of 1.5 or more.

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