JP6022277B2 - Ink composition photocuring method, ink set comprising ink composition, image forming method, and ink composition - Google Patents

Description

  The present invention relates to a photocuring method for an ink composition, an ink set comprising the ink composition, an image forming method, and an ink composition, which are suitable for recording an image by ejecting ink by an inkjet method.

As an image recording method for forming an image on a recording medium such as paper based on an image data signal, there are an electrophotographic method, a sublimation type and a melt type thermal transfer method, an ink jet method and the like.
The ink jet method is an inexpensive printing apparatus and does not require a plate at the time of printing, and the ink composition is ejected only on the required image portion to form an image directly on a recording medium. It can be used efficiently, and the running cost is low especially for small lot production. Furthermore, it has low noise and is excellent as an image recording method, and has attracted attention in recent years.
In particular, an ink composition for ink jet recording (a radiation curable ink composition for ink jet recording) that can be cured by irradiation with radiation such as ultraviolet rays is cured by irradiation with radiation such as ultraviolet rays, and most of the components of the ink composition are cured. It is an excellent method in that it can be printed on various recording media because it is excellent in drying property and difficult to bleed out as compared with the solvent-based ink composition.

  Further, in recent years, from the viewpoint of energy saving and space saving, it is desired to use a UV light source as an LED. However, the α-hydroxyacetophenone photopolymerization initiator has a short absorption wavelength (around 280 nm), and a UV-LED light source. At (around 365 nm), the polymerization could hardly be started. Moreover, although thiochromanone or thioxanthone photopolymerization initiators have been reported to improve sensitivity due to combinations with amine-based, thiol-based, disulfide-based polymerization accelerators or chain transfer agents (see Non-Patent Documents 1 and 2). In the case of curing by cationic polymerization with a photoacid generator (see Patent Document 1), the sensitivity was not sufficient.

JP 2010-70693 A

Macromol. Chem. , 1981, 182, 2821 Macromolecules, 2006, 39, 3777.

An object of the present invention is to provide a photocuring method for an ink composition exhibiting high photocurability under acidic conditions, an ink set comprising the ink composition, an image forming method, and an ink composition.
Light curing, especially a UV-LED light source (emission wavelength around 365 nm), high photosensitivity method with high sensitivity, high productivity, ink set comprising an ink composition, image forming method, particularly inkjet image forming method, It is another object of the present invention to provide an ink composition.

  As a result of intensive studies in view of the above problems, the present inventors have found that thiochromanone or a thioxanthone-based photopolymerization initiator, a specific polymerization accelerator or chain transfer agent, and a specific acid can be used for light in the ultraviolet region. It has been found that an ink composition containing excellent photosensitivity and a combination of these compounds exhibits good curability for an ultraviolet light source, particularly a UV-LED light source. The present invention has been completed based on these findings.

  That is, the said subject was solved by the following means.

<1> (A) a polymerizable compound having an ethylenically unsaturated group, (B) a photopolymerization initiator represented by the following general formula (1) or (2), and (C) a nitrogen atom directly bonded to an aromatic ring An ink composition having a structure and containing at least one hydrogen donor each having an electron-withdrawing substituent on the aromatic ring or an atom in which the nitrogen atom constitutes a heterocycle is produced under acidic conditions. A photocuring method to cure ,
The photocuring method in which the hydrogen donor of (C) is represented by the following general formula (4) .

(In General Formulas (1) and (2), R ^{1 to} R ¹⁶ each independently represents a hydrogen atom, a halogen atom, an alkyl group or an alkoxy group .)

(In General Formula (4), R ^{39 to} R ⁴² are each independently a hydrogen atom , an alkyl group, an alkoxy group, a halogen atom, a fluoroalkyl group, a cyano group, an acyl group, an alkoxycarbonyl group, an aryloxycarbonyl group, or a carbamoyl group. .X representing the group, alkyl or arylsulfonyl group or a sulfamoyl group, an oxygen atom or a sulfur atom.)
<2 > The photocuring method according to <1 > , wherein the photopolymerization initiator (B) is represented by the general formula (1).
< 3 > The photocuring according to <1> or < 2>, wherein the polymerizable compound having the ethylenically unsaturated group in (A) is a bifunctional or higher functional (meth) acrylate compound or (meth) acrylamide compound. Method.
< 4 > The photocuring method according to any one of <1> to < 3 >, wherein the ink composition contains at least one colorant.
< 5 > The photocuring method according to any one of <1> to < 4 >, wherein the ink composition is an inkjet ink composition.
< 6 > The photocuring method according to any one of <1> to < 5 >, wherein the ink composition is photocured after forming an image.
< 7 > (A) a polymerizable compound having an ethylenically unsaturated group, (B) a photopolymerization initiator represented by the following general formula (1) or (2), and (C) a nitrogen atom directly bonded to the aromatic ring An ink composition A having an electron-withdrawing substituent on the aromatic ring or containing at least one hydrogen donor in which the nitrogen atom is a hetero ring, and a molecular weight of 50 to 200 And an ink composition B comprising an ink composition B containing pKa (in H ₂ O) 1 or more and 5 or less acid,
The ink set in which the hydrogen donor (C) is represented by the following general formula (4).

(In General Formulas (1) and (2), R ^{1 to} R ¹⁶ each independently represents a hydrogen atom, a halogen atom, an alkyl group or an alkoxy group .)

(In General Formula (4), R ^{39 to} R ⁴² are each independently a hydrogen atom , an alkyl group, an alkoxy group, a halogen atom, a fluoroalkyl group, a cyano group, an acyl group, an alkoxycarbonyl group, an aryloxycarbonyl group, or a carbamoyl group. Represents a group, an alkyl or arylsulfonyl group, or a sulfamoyl group, and X represents an oxygen atom or a sulfur atom.)
< 8 > The ink set according to < 7 >, wherein the photopolymerization initiator (B) is represented by the general formula (1).
< 9 > The ink set according to < 7 > or < 8 >, wherein the polymerizable compound having an ethylenically unsaturated group in (A) is a bifunctional or higher functional (meth) acrylate compound or (meth) acrylamide compound. .
< 10 > The ink set according to any one of < 7 > to < 9 >, wherein the ink composition A contains at least one colorant.
< 11 > The ink set according to any one of < 7 > to < 10 >, wherein the ink set is an inkjet ink set.
< 12 > An image forming method including the photocuring method according to any one of <1> to < 6 >.
< 13 > An image forming method using the ink set according to any one of < 7 > to < 11 >.
< 14 > An acid treatment step for applying the ink composition B on a recording medium, an ink application step for forming an image by applying the ink composition A on the recording medium, and light irradiation. < 13 > The image forming method according to < 13 >, further comprising a photocuring step of curing the image ink.
< 15 > (A) a polymerizable compound having an ethylenically unsaturated group, (B) a photopolymerization initiator represented by the following general formula (1) or (2), and (C) represented by the following general formula (4) An ink composition containing at least one hydrogen donor.

(In General Formulas (1) and (2), R ^{1 to} R ¹⁶ each independently represents a hydrogen atom, a halogen atom, an alkyl group or an alkoxy group .)

(In General Formula (4), R ^{39 to} R ⁴² are each independently a hydrogen atom , an alkyl group, an alkoxy group, a halogen atom, a fluoroalkyl group, a cyano group, an acyl group, an alkoxycarbonyl group, an aryloxycarbonyl group, or a carbamoyl group. Represents a group, an alkyl or arylsulfonyl group, or a sulfamoyl group, and X represents an oxygen atom or a sulfur atom.)
< 16 > The ink composition according to < 15 >, wherein the photopolymerization initiator (B) is represented by the general formula (1).

  In the present invention, “(meth) acrylate” represents both and / or acrylate and methacrylate, and “(meth) acrylamide” represents both and / or acrylamide and methacrylamide.

According to the present invention, it is possible to provide an ink composition exhibiting high photocurability under acidic conditions. Furthermore, a photocuring method of the ink composition, an ink set comprising the ink composition, and an image forming method can be provided.
In particular, the ink composition of the present invention exhibits an excellent polymerization rate under acidic conditions and can be applied over a wide range of pH conditions.
The specificity of the combination with the photopolymerization initiator and the development of the above-described excellent effects based on this are not known in the past and have been achieved for the first time in the present invention.

<Acid condition>
The acidic condition represents an acidic reaction system in which at least one acid is mixed. The amount of the acid mixed is not particularly limited as long as it is an amount sufficient to aggregate the ink composition. However, from the viewpoint that the ink composition can be easily fixed, the acid mixing amount is set to 0. 0 with respect to the total amount of the solid components of the ink composition. 1-1000 mass% is preferable, 1-500 mass% is more preferable, and 10-300 mass% is further more preferable. In the case of an aqueous solution, the pH is preferably from 1 to less than 7, more preferably from 2 to less than 7, and even more preferably from 3 to less than 7 as acidic conditions.

<< Ink composition >>
The ink composition of the present invention comprises (A) a polymerizable compound having an ethylenically unsaturated group, (B) a photopolymerization initiator represented by the following general formula (1), and (C) a nitrogen atom in an aromatic ring. a direct structure, or nitrogen atom having an electron attractive substituent contains at least one Oh Ru hydrogen donor in atoms constituting the heterocycle, respectively aromatic ring.
The ink composition of the present invention is particularly suitable for an inkjet ink composition.
In the present invention, an ink composition having excellent curing sensitivity under acidic conditions is obtained by a combination of the above-described compounds. After forming an image on a recording medium using the ink composition, active energy such as light is used. By irradiating a line, an image excellent in blocking resistance can be formed.

<(A) Polymerizable compound having an ethylenically unsaturated group>
The polymerizable compound having an ethylenically unsaturated group is a compound having at least one ethylenically unsaturated bond capable of radical polymerization in the molecule, and is particularly limited as long as it is a compound capable of initiating a polymerization reaction by a photopolymerization initiator. Not available, etc. The polymerizable compound may be any of a monomer, an oligomer, a polymer and the like.
In the present invention, the molecular weight of the polymerizable compound is preferably from 50 to 2000, more preferably from 80 to 1500, and even more preferably from 100 to 800, from the viewpoint of compatibility between film quality improvement and solubility.

  The ethylenically unsaturated group is a group having a carbon-carbon double bond, and this carbon-carbon double bond may be conjugated with another saturated bond, but is stable like a benzene ring. It does not include double bonds in aromatic rings.

Examples of the ethylenically unsaturated group include a vinyl group (—CH═CH ₂ ), a (meth) acryloyl group [—C (═O) CH═CH ₂ , —C (═O) C (CH ₃ ) ═CH. ₂ ], vinylsulfonyl groups (—SO ₂ CH═CH ₂ ), and groups having a partial structure of —C (═O) CH═CHC (═O) — such as maleimide.
Here, a vinyl _{group, -O-CH = CH 2,} > N-CH = CH 2, -S-CH = CH 2, -O-CH 2 CH = CH 2, such as -CH = CH ₂ in styrene Examples of the (meth) acryloyl group include a (meth) acryloyl group, a (meth) acryloyloxy group, and a (meth) acryloylamide group.
The polymerizable compound having an ethylenically unsaturated group is preferably a compound having a carbon-carbon double bond at the terminal in the molecule or a compound having a maleimide ring group in the molecule.

  The polymerizable compound having an ethylenically unsaturated group is preferably a water-soluble compound from the viewpoint of ejection stability of the ink composition. The solubility of the polymerizable compound having an ethylenically unsaturated group is not particularly limited, but the solubility in water at 25 ° C. is preferably 2% by mass or more, more preferably 5% by mass or more, and 10% by mass. %, More preferably 20% by mass or more, and most preferably one that is uniformly mixed with water at an arbitrary ratio.

Specific examples of such polymerizable compounds include (meth) acrylamide compounds, (meth) acrylate compounds, vinyl compounds, maleimide compounds, vinyl sulfone compounds, N-vinylamide compounds, and the like. These compounds are more preferably bifunctional or more. More preferred are (meth) acrylamide compounds, (meth) acrylate compounds and vinyl compounds, and particularly preferred are bifunctional or higher functional (meth) acrylamide compounds. In the ink composition of the present invention, these polymerizable compounds may be used alone or in combination of two or more. When two or more types are used in combination, two or more types selected from (meth) acrylamide compounds, (meth) acrylate compounds, vinyl compounds, maleimide compounds, vinylsulfone compounds, and N-vinylamide compounds may be used in combination. Preferably, at least one of them is a (meth) acrylamide compound.
The polymerizable compound has a poly (ethyleneoxy) chain, a poly (propyleneoxy) chain, an ionic group (for example, a carboxyl group, a sulfo group, etc.), a hydroxyl group, etc. in the molecule from the viewpoint of improving water solubility. It may be.

  As the (meth) acrylamide compound, any of a monofunctional (meth) acrylamide compound and a polyfunctional (meth) acrylamide compound can be used, and a polyfunctional (meth) acrylamide compound is preferable. Specific examples of the monofunctional (meth) acrylamide compound and the polyfunctional (meth) acrylamide compound are shown below, but the present invention is not limited thereto.

  Monomer 21, 27, 28, 42, 44, and 51 are preferable from the viewpoint of curability and solubility.

  These (meth) acrylamide compounds can be synthesized by a general method for synthesizing acrylamide compounds (for example, Journal of the American Chemical Society, 1979, 101, 5383).

  As the (meth) acrylate compound, any of a monofunctional (meth) acrylate compound (a compound having one (meth) acrylate group) and a polyfunctional (meth) acrylate compound can be used. ) Acrylate compound.

  Specifically, monofunctional (meth) acrylate compounds are isoamyl (meth) acrylate, stearyl (meth) acrylate, lauryl (meth) acrylate, octyl (meth) acrylate, isooctyl (meth) acrylate, decyl (meth) acrylate, Isoamylstil (meth) acrylate, isostearyl (meth) acrylate, 2-ethylhexyl diglycol (meth) acrylate, 2-hydroxybutyl (meth) acrylate, butoxyethyl (meth) acrylate, methoxydiethylene glycol (meth) acrylate, methoxypolyethylene glycol (Meth) acrylate, methoxypropylene glycol (meth) acrylate, tetrahydrofurfuryl (meth) acrylate, isobornyl (meth) acrylate 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 2- (meth) acryloxyethyl succinic acid, 2- (meth) acryloxyethyl-2-hydroxyethylphthalic acid, lactone-modifiable Examples thereof include flexible (meth) acrylate, t-butylcyclohexyl (meth) acrylate, 2- (2-ethoxyethoxy) ethyl acrylate, cyclopentenyl acrylate, cyclopentenyloxyethyl acrylate, and dicyclopentanyl acrylate.

  Polyfunctional (meth) acrylate compounds include bis (4-acryloxypolyethoxyphenyl) propane, neopentyl glycol di (meth) acrylate, ethoxylated (2) neopentyl glycol di (meth) acrylate (neopentyl glycol ethylene oxide 2) Compound obtained by diacrylated molar adduct), propoxylated (2) neopentyl glycol di (meth) acrylate (compound obtained by diacrylated neopentylglycol propylene oxide 2 mol adduct), 1,6-hexanediol di ( (Meth) acrylate, 1,9-nonanediol di (meth) acrylate, ethylene glycol di (meth) acrylate, diethylene glycol di (meth) acrylate, triethylene glycol di (meth) acrylate, tetrae Lenglycol di (meth) acrylate, polyethylene glycol di (meth) acrylate, dipropylene glycol di (meth) acrylate, tripropylene glycol di (meth) acrylate, tetrapropylene glycol di (meth) acrylate, polypropylene glycol di (meth) acrylate , Pentaerythritol tri (meth) acrylate, pentaerythritol tetra (meth) acrylate, dipentaerythritol tetra (meth) acrylate, trimethylolpropane tri (meth) acrylate, tetramethylol methane tetra (meth) acrylate, tetramethylol methane tri (meth) ) Acrylate, dimethylol tricyclodecane di (meth) acrylate, modified glycerin tri (meth) acrylate, modified vinyl Phenol A di (meth) acrylate, propylene oxide (PO) adduct di (meth) acrylate of bisphenol A, ethylene oxide (EO) adduct di (meth) acrylate of bisphenol A, dipentaerythritol hexa (meth) acrylate, caprolactone modified Examples include dipentaerythritol hexa (meth) acrylate.

  1-50 mass% is preferable with respect to the total amount of a solid component, as for content of the polymeric compound which has an ethylenically unsaturated group in an ink composition, 1-40 mass% is more preferable, and 1-30 mass%. Is more preferable.

<Photopolymerization initiator>
In this invention, the photoinitiator represented by the following general formula (1) or (2) of (B) is used as a photoinitiator.

In general formulas (1) and (2), R ^{1 to} R ¹⁶ each independently represents a hydrogen atom, a halogen atom, an alkyl group or an alkoxy group.

Examples of the halogen atom in R ^{1 to} R ¹⁶ include a fluorine atom, a chlorine atom, and a bromine atom.
R ¹ number of carbon atoms in the alkyl group in to R ¹⁶ is preferably 1 to 10, more preferably 1 to 5, 1 to 3 is more preferable. Examples of the alkyl group include methyl, ethyl, isopropyl, n-propyl, n-butyl, t-butyl, and t-octyl.
R ¹ number of carbon atoms of the alkoxy group in to R ¹⁶ is preferably 1 to 10, more preferably 1 to 5, 1 to 3 is more preferable. Examples of the alkoxy group include methoxy, ethoxy, isopropoxy, n-propyloxy, n-butyloxy, and n-octyloxy.

  These alkyl groups and alkoxy groups may have a substituent, such as a hydroxyl group, a carboxy group or a salt thereof, a sulfo group or a salt thereof, an alkyl group, an aryl group, a heterocyclic group (ring The number of members is preferably a 5- or 6-membered ring, which may be an aromatic ring or a saturated or unsaturated ring, and the hetero atom of the ring constituting atom is preferably an oxygen atom, a sulfur atom or a nitrogen atom), an alkoxy group, an alkylthio group, an amino group (Including amino group, alkylamino group, arylamino group), acyl group, alkoxycarbonyl group, aryloxycarbonyl group, acylamide group, sulfonamide group, carbamoyl group, sulfamoyl group, alkyl or arylsulfonyl group, cyano group, etc. Can be mentioned.

  Of these groups, a hydroxyl group, a carboxy group or a salt thereof, a sulfo group or a salt thereof, and an alkoxy group are preferable. Here, the alkoxy group includes those containing 2 to 10 oxyalkylene repeating units in which the alkyl moiety is divided by an oxygen atom.

At least one of R ^{1 to} R ⁴ is preferably a halogen atom, more preferably a chlorine atom, a bromine atom, or an iodine atom. At least one of R ^{9 to} R ¹⁶ is a halogen atom, an alkyl group (preferably having a carbon number of 1 to 10, more preferably 1 to 5, particularly preferably 1 to 3), and an alkoxy group (preferably having a carbon number of 1 to 10). More preferably, it is 1-5, particularly preferably 1-3) .

  In the present invention, the molecular weight of the photopolymerization initiator represented by the general formula (1) is preferably 100 to 2000, more preferably 200 to 1800, and still more preferably 300 to 1500, from the viewpoints of volatilization inhibition and solubility.

Specific examples of the compound represented by the general formula (1) or (2) are shown below, but the present invention is not limited thereto .

  The compound represented by the general formula (1) or (2) of the present invention is, for example, disclosed in JP-A-2004-189695, Tetrahedron, Vol. 49, p939 (1993), Journal of Organic Chemistry, p893 (1945). And can be easily synthesized by the method described in Journal of Organic Chemistry, p4939 (1965), or a method based thereon.

In the present invention, the photopolymerization initiator is used the photoinitiator you express by the general formula (1) or (2), be used which in one, the general formula (1) or ( You may use together 2 or more types of photoinitiators contained in 2). The content of the photopolymerization initiator in the ink composition is preferably 0.1 to 40% by mass, more preferably 1 to 30% by mass, and still more preferably 5 to 20% by mass with respect to the total amount of solid components.
In the present specification, “total amount of solid components” or “total solid content” refers to the total mass of components excluding the solvent component from the total composition of the composition.
Moreover, it is preferable to use 0.1-30 mass parts of photoinitiators with respect to 100 mass parts of polymeric compounds which have an ethylenically unsaturated group, It is more preferable to use 1-20 mass parts, 5-15 More preferably, parts by mass are used.

<Hydrogen donor>
In the present invention, (C) a hydrogen donor having a structure in which a nitrogen atom is directly connected to an aromatic ring and the aromatic ring has an electron-withdrawing substituent or the nitrogen atom is an atom constituting a hetero ring is used. To do.
In this hydrogen donor, the radical species generated by the photopolymerization initiator pulls out a hydrogen atom, becomes an active radical species, and acts as a polymerization accelerator or chain transfer agent for the polymerizable compound having an ethylenically unsaturated group. Works.

  The hydrogen donor of the present invention has a structure in which a nitrogen atom is directly connected to an aromatic ring. Here, the aromatic ring may be a carbocyclic aromatic ring or a heterocyclic aromatic ring, A carbocyclic aromatic ring is preferred. Examples of the carbocyclic aromatic ring include a benzene ring, a polybenzene condensed ring (for example, naphthalene ring, phenanthrene ring), and a carbocyclic ring that is not an aromatic ring, such as a 3- to 7-membered cycloalkane, 5 to 7 The member cycloalkene may be condensed. As the heterocyclic aromatic ring, those in which the ring-constituting hetero atom is at least a nitrogen atom, an oxygen atom, or a sulfur atom are preferable, and a 5- to 7-membered ring (preferably a 5- or 6-membered ring) is preferable. , Carbocyclic aromatic rings, carbocyclic rings other than aromatic rings (for example, cycloalkanes, cycloalkenes), and heterocyclic rings including heterocyclic aromatic rings (the number of ring members and ring-forming heteroatoms are the same as the above heterocyclic aromatic rings Are preferred) may be condensed.

Here, the nitrogen atom directly bonded to the aromatic ring may be bonded to the aromatic ring with a single bond or may be bonded with a double bond. In addition, the remaining bond of the nitrogen atom bonded to the aromatic ring may be linked to this aromatic ring via a linking group, and as a result, a structure in which a nitrogen-containing heterocycle is condensed to the aromatic ring may be taken.
1-3 are preferable, as for the number of the nitrogen atoms directly connected to the aromatic ring, 1 or 2 is preferable, and 1 is especially preferable.

The hydrogen donor used in the present invention preferably has a pKa in water at room temperature (25 ° C.) of −5.0 to 8.0.
Moreover, the aromatic ring to which the nitrogen atom is directly bonded may have a substituent.
In the present invention, among such substituents, those having at least one electron-withdrawing substituent are preferable. The electron-withdrawing substituent has a positive Hammett σ value (σp value in the case of o or p position relative to the nitrogen atom, and σm value in the case of m position). When the aromatic ring has a plurality of substituents, the sum of Hammett σ values (σp value and σm value of existing groups) of these substituents is preferably 0 or more.
The sum of the above-mentioned σ values of the Hammett of the substituent or the Hammetts of all the substituents is preferably 0.1 to 1.5, more preferably 0.2 to 1.0, and 0.3 to 0 .8 is particularly preferred.

  An electron-withdrawing substituent having a positive Hammett σp value or σm value is an aryl group, alkenyl group, alkynyl group, carboxyl group, sulfo group, alkyl or arylsulfinyl group, nitro group, halogen atom, fluoroalkyl group, cyano group , Acyl group, alkoxycarbonyl group, aryloxycarbonyl group, carbamoyl group, alkyl or arylsulfonyl group and sulfamoyl group, halogen atom, fluoroalkyl group, cyano group, acyl group, alkoxycarbonyl group, aryloxycarbonyl group, A group selected from a carbamoyl group, an alkyl or arylsulfonyl group and a sulfamoyl group is preferable, and among them, an alkoxycarbonyl group or an aryloxycarbonyl which is hydrolyzed to reduce the electron-withdrawing effect A group other than the group, that is, a group selected from a halogen atom, a fluoroalkyl group, a cyano group, an acyl group, a carbamoyl group, an alkyl or arylsulfonyl group, and a sulfamoyl group is more preferable.

Substituents that may be substituted by the aromatic ring include alkyl groups, alkoxy groups, aryloxy groups, alkylthio groups, arylthio groups, hydroxyl groups, amino groups (amino groups) as substituents other than the above electron-withdrawing substituents. , An alkylamino group, an arylamino group, and a heterocyclic amino group).
Among these, an alkyl group and an alkoxy group are preferable, and a preferable range is the same as the alkyl group and the alkoxy group in R ^{1 to} R ³⁰ . Moreover, these alkyl groups and alkoxy groups may further have a substituent.

The hydrogen donor having a structure in which a nitrogen atom is directly bonded to an aromatic ring is preferably a carbocyclic aromatic or heterocyclic aromatic amine compound having at least one electron-withdrawing substituent, or a nitrogen-containing heterocyclic compound, and the above carbocyclic ring More preferred are aromatic aromatic or heterocyclic aromatic amine compounds, and more preferred are the above carbocyclic aromatic amine compounds.
In the carbocyclic aromatic or heterocyclic aromatic amine compound, the hydrogen atom at the α-position of the substituent substituted on the nitrogen atom of the amine is on the other hand, and in the nitrogen-containing heterocyclic compound, A structure in which the hydrogen atom of the mercapto group to be substituted can donate hydrogen is preferable.

As the heterocyclic ring of the nitrogen-containing heterocyclic compound having a mercapto group, a 5- or 6-membered heterocyclic ring is preferable, an aromatic heterocyclic ring is more preferable, and a ring in which a benzene ring is condensed to the heterocyclic ring is more preferable. Here, examples of the aromatic nitrogen-containing heterocycle include a thiazole ring, an oxazole ring, an imidazole ring, a pyrazole ring, a pyridine ring, a pyrazine ring, a pyridazine ring, and a ring in which a benzene ring is condensed, and a mercapto group. Have a ring-constituting carbon atom bonded to a ring-constituting nitrogen atom.
In the present invention, the aromatic nitrogen-containing heterocycle is preferably a 5-membered ring, particularly preferably a thiazole ring, an oxazole ring or a ring condensed with a benzene ring.

  Among these, in the present invention, a compound represented by the following general formula (3) or (4) is preferable. Among these, a compound represented by the following general formula (2) is preferable.

In General formula (3), R < ³¹ > -R < ³⁵ > represents a hydrogen atom or a substituent each independently. However, at least one of R ^{31 to} R ³⁵ is an electron-withdrawing substituent. R ³⁶ represents a hydrogen atom, an alkyl group or an aryl group. R ³⁷ and R ³⁸ each independently represent a hydrogen atom or an alkyl group.

In the general formula ^{(4), R} 39 ~R ⁴² each independently represent a hydrogen atom or a substituent. X represents an oxygen atom or a sulfur atom.

As a substituent in R < ³¹ > -R < ³⁵ >, the substituent which the alkyl group in R < ¹ > -R < ¹⁶ > and an alkoxy group may have is mentioned.
Among these, an alkyl group, an alkoxy group, and an electron-withdrawing substituent are preferable, and an alkyl group and an alkoxy group have the same preferable ranges as the alkyl group and alkoxy group in R ^{1 to} R ¹⁶ . The electron-withdrawing substituent is preferably a substituent as described above.

The alkyl group in R ^{36 to} R ³⁸ has the same preferred range as the alkyl group in R ^{1 to} R ¹⁶ .
The aryl group for R ³⁶ preferably has 6 to 12 carbon atoms, and more preferably a phenyl group which may have a substituent. Examples of the substituent which may have an alkyl group at R ¹ to R ^16, alkoxy group substituent group which may have.

Of R ^{31 to} R ³⁵ , those in which 3 or 4 are hydrogen atoms are preferred, and those in which 4 are hydrogen atoms are more preferred.
R ³⁶ is preferably an alkyl group, and more preferably an alkyl group having a hydrogen bond at the α-position.
R ³⁷ and R ³⁸ are preferably a hydrogen atom or an alkyl group having 1 to 3 carbon atoms, and particularly preferably a hydrogen atom.

Among the compounds represented by the general formula (3), among them, R ³³ is a halogen atom (preferably a fluorine atom or a chlorine atom), a fluoroalkyl group (preferably trifluoromethyl), an alkoxycarbonyl group (preferably methoxycarbonyl, ethoxy). Carbonyl), a carbamoyl group (preferably carbamoyl, N-methylcarbamoyl, N, N-dimethylcarbamoyl), and a cyano group are particularly preferable. R ³⁶ is a hydrogen atom, an alkyl group (preferably methyl, ethyl, 2-hydroxyethyl) or an aryl group (preferably phenyl which may have a substituent).

  In the present invention, the molecular weight of the hydrogen donor represented by the general formula (3) is preferably 50 to 1500, more preferably 80 to 1000, and still more preferably 100 to 500, from the viewpoints of volatilization inhibition and solubility.

  Specific examples of the compound represented by the general formula (3) are shown below, but the present invention is not limited thereto.

In the general formula ^{(4), R} 39 ^{~R 42} is each independently represent a hydrogen atom or a substituent, Examples of the substituent ^include an alkyl group in R 1 ^{to R 16,} the substituent which may have an alkoxy group Groups.
R ^{39 to} R ⁴² are preferably a hydrogen atom or the aforementioned electron-withdrawing substituent. Further, among R ^{39 to} R ⁴² , one is an electron-withdrawing substituent and the rest are all preferably hydrogen atoms.
X represents an oxygen atom or a sulfur atom, preferably a sulfur atom.

  In the present invention, the molecular weight of the hydrogen donor represented by the general formula (4) is preferably from 50 to 1500, more preferably from 80 to 1000, and even more preferably from 100 to 500, from the viewpoints of volatilization inhibition and solubility.

  Specific examples of the compound represented by the general formula (4) are shown below, but the present invention is not limited thereto.

  The content of the hydrogen donor in the ink composition is preferably 0.1 to 40% by mass, more preferably 1 to 30% by mass, and still more preferably 1 to 20% by mass with respect to the total amount of solid components.

  The content of the hydrogen donor in the ink composition is preferably 5 to 1500% by mass, more preferably 10 to 1000% by mass, and still more preferably 20 to 500% by mass with respect to the amount of the photopolymerization initiator.

<Other compounds>
In addition to the polymerizable compound having an ethylenically unsaturated group, the photopolymerization initiator, and the hydrogen donor, the ink composition of the present invention contains other compounds such as a medium, a colorant, and a dispersant as necessary. May be.
In addition, the ink composition of the present invention can be a clear ink (colorless ink) composition that does not contain a colorant (coloring material) or an ink composition that contains a colorant. It is preferable to contain.

[Medium]
The ink composition of the present invention may contain a medium, and can contain both organic and aqueous media. The aqueous medium contains at least water, and preferably contains at least one water-soluble organic solvent as required.
The water used for the aqueous medium is preferably water that does not contain ionic impurities such as ion-exchanged water and distilled water.

  Examples of the water-soluble organic solvent include alcohol solvents, ketone solvents, ether solvents, amide solvents, nitrile solvents, and sulfone solvents. Among these, examples of alcohol solvents include ethanol, isopropanol, n-butanol, t-butanol, isobutanol, diacetone alcohol, and ethylene glycol. Examples of the ketone solvent include acetone, methyl ethyl ketone, diethyl ketone, and methyl isobutyl ketone. Examples of the ether solvent include dibutyl ether, tetrahydrofuran, dioxane and the like. Examples of amide solvents include dimethylformaldehyde and diethylformaldehyde. Examples of the nitrile solvent include acetonitryl. Examples thereof include dimethyl sulfoxide, dimethyl sulfone, and sulfolane.

  The content of the medium in the ink composition can be appropriately selected depending on the purpose, but is usually preferably 10 to 95% by mass, more preferably 30 to 90% by mass with respect to the total mass of the ink composition.

[Colorant]
The ink composition of the present invention preferably contains a colorant.
The ink composition of the present invention (hereinafter sometimes simply referred to as “ink”) can be used not only for the formation of a single color image but also for the formation of a multicolor image (for example, a full color image). Two or more colors can be selected to form an image. When forming a full-color image, the ink composition can be used as, for example, a magenta color ink, a cyan color ink, and a yellow color ink. Further, it may be used as black color ink.

In addition, the ink composition of the present invention contains red (R), green (G), blue (B), white (W) other than yellow (Y), magenta (M), cyan (C), and black (Black). ) Color tone ink composition, or a so-called special color ink composition in the printing field.
The ink composition of each color tone can be prepared by changing the hue of a colorant (for example, pigment) as desired.

  In the ink composition of the present invention, known dyes, pigments and the like can be used without particular limitation as the colorant. From the viewpoint of ink colorability, a colorant that is almost insoluble or hardly soluble in water is preferable. Specifically, various pigments, disperse dyes, oil-soluble dyes, dyes forming J aggregates, and the like can be mentioned. In consideration of light resistance, pigments are more preferable.

There is no restriction | limiting in particular in the kind of pigment used for the ink composition of this invention, A normal organic or inorganic pigment can be used.
Examples of organic pigments include azo pigments, polycyclic pigments, dye chelates, nitro pigments, nitroso pigments, and aniline black. Among these, azo pigments and polycyclic pigments are more preferable. Examples of the azo pigments include azo lakes, insoluble azo pigments, condensed azo pigments, and chelate azo pigments. Examples of the polycyclic pigment include phthalocyanine pigments, perylene pigments, perinone pigments, anthraquinone pigments, quinacridone pigments, dioxazine pigments, indigo pigments, thioindigo pigments, isoindolinone pigments, and quinophthalone pigments. Examples of dye chelates include basic dye chelates and acidic dye chelates.

  Examples of inorganic pigments include titanium oxide, iron oxide, calcium carbonate, barium sulfate, aluminum hydroxide, barium yellow, cadmium red, chrome yellow, and carbon black. Among these, carbon black is particularly preferable. In addition, as carbon black, what was manufactured by well-known methods, such as a contact method, a furnace method, a thermal method, is mentioned, for example.

  Specific examples of the pigment that can be used in the present invention include pigments described in paragraph numbers 0142 to 0145 of JP-A-2007-100071.

Moreover, when using a dye as a coloring component in this invention, what hold | maintained the dye to the water-insoluble support | carrier can be used as a coloring agent. As the dye, known dyes can be used without particular limitation. For example, the dyes described in JP-A-2001-115066, JP-A-2001-335714, JP-A-2002-249677 and the like can be used in the present invention. It can be used suitably. The carrier is not particularly limited as long as it is insoluble in water or hardly soluble in water, and inorganic materials, organic materials, and composite materials thereof can be used. Specifically, the carriers described in JP-A-2001-181549, JP-A-2007-169418, etc. can be suitably used in the present invention.
The carrier holding the dye (colorant) can be used as it is or in combination with a dispersant as required. As the dispersant, a dispersant described later can be suitably used.

The above colorants may be used alone or in combination of a plurality of types.
The content of the colorant (particularly the pigment) in the ink composition is preferably 1 to 25% by mass with respect to the total mass of the ink composition from the viewpoint of color density, granularity, ink stability, and ejection reliability. 5 to 20% by mass is more preferable.

[Dispersant]
When the ink composition of the present invention is water-based and the colorant is a pigment, it is preferable to constitute colored particles (hereinafter simply referred to as “colored particles”) dispersed in an aqueous solvent by a dispersant.
The dispersant may be a polymer dispersant or a low molecular surfactant type dispersant. The polymer dispersant may be either a water-soluble polymer dispersant or a water-insoluble polymer dispersant. In the present invention, a water-insoluble polymer dispersant is preferable from the viewpoint of dispersion stability and dischargeability when applied to an ink jet system.

-Water-insoluble polymer dispersant-
The water-insoluble polymer dispersant (hereinafter sometimes simply referred to as “dispersant”) is a water-insoluble polymer, and is not particularly limited as long as the pigment can be dispersed. A conventionally known water-insoluble polymer dispersant is used. be able to. The water-insoluble polymer dispersant can be constituted by including, for example, both a hydrophobic structural unit and a hydrophilic structural unit.

Here, as a monomer which comprises a hydrophobic structural unit, a styrene-type monomer, an alkyl (meth) acrylate, an aromatic group containing (meth) acrylate, etc. can be mentioned.
Moreover, as a monomer which comprises a hydrophilic structural unit, if it is a monomer containing a hydrophilic group, there will be no restriction | limiting in particular. Examples of the hydrophilic group include a nonionic group, a carboxyl group, a sulfonic acid group, and a phosphoric acid group. Examples of the nonionic group include a hydroxyl group, an amide group (where the nitrogen atom is unsubstituted), a group derived from an alkylene oxide polymer (for example, polyethylene oxide, polypropylene oxide, etc.), a group derived from a sugar alcohol, and the like.
From the viewpoint of dispersion stability, the hydrophilic structural unit in the present invention preferably contains at least a carboxyl group, and preferably includes a nonionic group and a carboxyl group.

Specific examples of the water-insoluble polymer dispersant include styrene- (meth) acrylic acid copolymer, styrene- (meth) acrylic acid- (meth) acrylic acid ester copolymer, (meth) acrylic acid ester- (meta ) Acrylic acid copolymer, polyethylene glycol (meth) acrylate- (meth) acrylic acid copolymer, styrene-maleic acid copolymer and the like.
Here, “(meth) acrylic acid” means acrylic acid or methacrylic acid.

  From the viewpoint of dispersion stability of the pigment, the water-insoluble polymer dispersant is preferably a vinyl polymer containing a carboxyl group, and has at least a structural unit derived from an aromatic group-containing monomer as a hydrophobic structural unit, and is hydrophilic. More preferred is a vinyl polymer having a structural unit containing a carboxyl group as the structural unit of the nature.

  In addition, the weight average molecular weight of the water-insoluble polymer dispersant is preferably 3,000 to 200,000, more preferably 5,000 to 100,000, and still more preferably 5,000 to 5,000, from the viewpoint of pigment dispersion stability. 80,000, particularly preferably 10,000 to 60,000.

The content of the dispersant in the colored particles in the present invention is preferably 10 to 90% by mass of the dispersant with respect to the pigment, from the viewpoint of the dispersibility of the pigment, the ink colorability, and the dispersion stability. % By mass is more preferable, and 30 to 50% by mass is particularly preferable.
When the content of the dispersant in the colored particles is within the above range, the pigment is preferably coated with an appropriate amount of the dispersant, and it tends to be easy to obtain colored particles having a small particle size and excellent stability over time.

  Here, the colored particles may contain other dispersant in addition to the water-insoluble polymer dispersant. For example, a conventionally known water-soluble low-molecular dispersant, water-soluble polymer, or the like can be used. The content of the dispersant other than the water-insoluble polymer dispersant can be used within the range of the content of the dispersant.

  The colored particles are preferably configured to contain the pigment and the water-insoluble polymer dispersant from the viewpoint of dispersion stability and dischargeability, and at least a part of the surface of the pigment is coated with the water-insoluble polymer dispersant. It is preferable to be configured. Such colored particles can be obtained as a colored particle dispersion by, for example, dispersing a mixture containing a pigment, a dispersant, and, if necessary, a solvent (preferably an organic solvent) with a disperser.

  The colored particle dispersion includes, for example, a step of adding an aqueous solution containing a basic substance (mixing / hydration step) to a mixture of the pigment, the water-insoluble polymer dispersant, and an organic solvent in which the dispersant is dissolved or dispersed. Then, the process (solvent removal process) except an organic solvent can be provided, and it can manufacture as a dispersion. Thereby, the colorant is finely dispersed, and a dispersion of colored particles having excellent storage stability can be produced.

  The organic solvent needs to be able to dissolve or disperse the dispersant, but in addition to this, it is preferable that the organic solvent has a certain degree of affinity for water. Specifically, those having a solubility in water at 20 ° C. of 10 to 50% by mass or less are preferable.

More specifically, the colored particle dispersion can be produced by a production method including the following step (1) and step (2), but is not limited thereto.
Step (1): A step of dispersing a mixture containing a basic substance and a solution containing water as a main component together with a pigment, a dispersant, and an organic solvent in which the dispersant is dissolved or dispersed Step (2): A step of removing at least a part of the organic solvent from the mixture after the dispersion treatment

  In step (1), first, a dispersant is dissolved or dispersed in an organic solvent to obtain a mixture (mixing step). Next, a solution containing a colorant and a basic substance and containing water as a main component, water, and, if necessary, a surfactant and the like are added to this mixture and mixed and dispersed to obtain an oil-in-water dispersion. Get.

  The basic substance is used for neutralization of an anionic group (preferably a carboxyl group) that the polymer may have. There is no particular limitation on the degree of neutralization of the anionic group. Usually, the liquid property of the finally obtained dispersion of colorant particles is preferably, for example, a pH of 4.5 to 10. The pH can also be determined by the desired degree of neutralization of the polymer.

Preferable examples of the organic solvent include alcohol solvents, ketone solvents, ether solvents, amide solvents, nitrile solvents, and sulfone solvents. Is mentioned. Among these, examples of the alcohol solvent include ethanol, isopropanol, n-butanol, t-butanol, isobutanol, diacetone alcohol, and the like. Examples of the ketone solvent include acetone, methyl ethyl ketone, diethyl ketone, and methyl isobutyl ketone. Examples of the ether solvent include dibutyl ether, tetrahydrofuran, dioxane and the like. Examples of amide solvents include dimethylformaldehyde and diethylformaldehyde. Examples of the nitrile solvent include acetonitryl. Examples thereof include dimethyl sulfoxide, dimethyl sulfone, and sulfolane.
Among these solvents, isopropanol, acetone and methyl ethyl ketone are preferable, and methyl ethyl ketone is particularly preferable. The organic solvent may be used alone or in combination.

In the production of the dispersion of the colored particles, a strong shearing force is applied using a two-roll, three-roll, ball mill, tron mill, disper, kneader, kneader, homogenizer, blender, single screw or twin screw extruder. The kneading and dispersing process can be performed while feeding. For details on kneading and dispersing, see T.W. C. "Paint Flow and Pigment Dispersion" by Patton, published by John Wiley and Sons (1964), and the like.
If necessary, use a vertical or horizontal sand grinder, pin mill, slit mill, ultrasonic disperser, etc., and fine dispersion using beads made of glass having a particle diameter of 0.01 to 1 mm, zirconia, etc. It can be obtained by performing processing.

  The method for removing the organic solvent in the production process of the colored particle dispersion is not particularly limited, and can be removed by a known method such as vacuum distillation.

The colored particles in the colored particle dispersion thus obtained maintain a good dispersion state, and the obtained colored particle dispersion has excellent temporal stability.
In the ink composition of the present invention, the colored particles may be used singly or in combination of two or more.

In the present invention, the volume average particle diameter of the colorant (or colored particles) is preferably 10 to 200 nm, more preferably 10 to 150 nm, and further preferably 10 to 100 nm. When the volume average particle size is 200 nm or less, the color reproducibility is good, and in the case of the ink jet method, the droplet ejection characteristics are good. Moreover, light resistance becomes favorable because a volume average particle diameter is 10 nm or more.
Further, the particle size distribution of the colorant (or colored particles) is not particularly limited, and may be either a wide particle size distribution or a monodisperse particle size distribution. Further, two or more colorants having a monodispersed particle size distribution may be mixed and used.
The volume average particle size and particle size distribution of the colorant (or colored particles) can be measured using, for example, a light scattering method.

[Other polymerization initiators]
The ink composition of the present invention contains an optional amount of a polymerization initiator other than the compound represented by the general formula (1) of the present invention (hereinafter referred to as “other polymerization initiator”) as necessary. Also good.
As another polymerization initiator, a radical polymerization initiator is preferable. Specific examples of the radical polymerization initiator include (a) aromatic ketones, (b) acylphosphine compounds, (c) aromatic onium salt compounds, (d) organic oxides, (e) thio compounds, ( f) hexaarylbiimidazole compound, (g) ketoxime ester compound, (h) borate compound, (i) azinium compound, (j) metallocene compound, (k) active ester compound, (l) compound having carbon halogen bond And (m) alkylamine compounds and the like. More specifically, polymerization initiators described in Kiyomi Kato's “UV Curing System”, pages 65 to 148, published by General Technology Center Co., Ltd. (1989), and the like can be mentioned. Another polymerization initiator may be used individually by 1 type, and may use 2 or more types together.
However, when used only for polymerization under acidic conditions, only the compound represented by the general formula (1) of the present invention functions sufficiently.

[Physical properties of ink composition]
The surface tension (25 ° C.) of the ink composition of the present invention is preferably 20 mN / m or more and 60 mN / m or less. More preferably, it is 20 mN or more and 45 mN / m or less, More preferably, it is 25 mN / m or more and 40 mN / m or less.
The surface tension is measured under conditions of 25 ° C. using an Automatic Surface Tensiometer CBVP-Z (manufactured by Kyowa Interface Science Co., Ltd.).

The viscosity at 25 ° C. of the ink composition of the present invention is preferably 1.2 mPa · s or more and 15.0 mPa · s or less, more preferably 2 mPa · s or more and less than 13 mPa · s, and still more preferably. Is 2.5 mPa · s or more and less than 10 mPa · s.
The viscosity is measured using a VISCOMETER TV-22 (manufactured by TOKI SANGYO CO. LTD) under conditions of 25 ° C.

  The pH of the ink composition is preferably pH 6 to 11 from the viewpoint of the stability of the ink composition. When the ink set described later is used, it is preferable that the ink composition aggregates at a high speed by contact with the treatment liquid, and thus pH 7 to 10 is more preferable, and pH 7 to 9 is further preferable.

<< Ink set >>
The ink set of the present invention contains at least a part of the above-described ink composition of the present invention (hereinafter referred to as ink composition A) and an aggregating agent capable of forming an aggregate upon contact with the ink composition A. It consists of parts of ink composition B which is a treatment liquid.
By forming an image using the ink composition A and a treatment liquid containing an aggregating agent, an image having good image quality, high curing sensitivity, and excellent blocking resistance can be formed.
Hereinafter, the treatment liquid of the ink set will be described.

<Treatment liquid (ink composition B)>
Ink composition B (hereinafter, simply referred to as “treatment liquid”) that is a treatment liquid of the ink set includes at least an acid that aggregates the components in the ink composition, and includes other components as necessary.

[acid]
The acid used in the treatment liquid is capable of aggregating (fixing) the ink composition by contacting the ink composition on the recording medium, and functions as a fixing agent. For example, when the treatment liquid is applied to a recording medium (preferably coated paper), the ink composition further drops and comes into contact with the aggregating agent in the state where the aggregating agent is present on the recording medium. In addition, the components in the ink composition can be aggregated to fix the ink composition on the recording medium.

Acids include, for example, sulfuric acid, hydrochloric acid, nitric acid, phosphoric acid, polyacrylic acid, acetic acid, glycolic acid, malonic acid, malic acid, maleic acid, ascorbic acid, succinic acid, glutaric acid, fumaric acid, citric acid, tartaric acid, lactic acid Sulfonic acid, orthophosphoric acid, metaphosphoric acid, pyrrolidone carboxylic acid, pyrone carboxylic acid, pyrrole carboxylic acid, furan carboxylic acid, pyridine carboxylic acid, coumaric acid, thiophene carboxylic acid, nicotinic acid, oxalic acid, acetic acid, benzoic acid are preferred Can be mentioned. In the present invention, an acid having a molecular weight of 35 or more and 1000 or less is preferable, an acid having a molecular weight of 50 or more and 500 or less is more preferable, and an acid having a molecular weight of 50 or more and 200 or less is particularly preferable, from the viewpoint of both suppression of volatilization and solubility in a solvent. In the ink set of the present invention, those having a molecular weight of 50 to 200 are used. The pKa (in H ₂ O, 25 ° C.) is preferably from −10 to 7 acids, more preferably from 1 to 7 acids, more preferably from 1 to 7 from the viewpoint of achieving both ink bleeding prevention and photocurability. An acid of 5 or less is particularly preferred, and an acid of 1 or more and 5 or less is used in the ink set of the present invention.

Among these, acids with high water solubility are preferable. In addition, from the viewpoint of fixing the whole ink by reacting with the ink composition, a trivalent or lower acid is preferable, and a divalent or higher and trivalent acid is particularly preferable.
In this invention, an acid may be used individually by 1 type and may use 2 or more types together.

  When the treatment liquid contains an acid, the pH (25 ° C.) of the treatment liquid is preferably 0.1 to 6.8, more preferably 0.5 to 6.0, and 0.8 to 5 More preferably, it is 0.0.

  The content of the acid is preferably 40% by mass or less, more preferably 15 to 40% by mass, further preferably 15% to 35% by mass, and 20% to 30% by mass with respect to the total mass of the treatment liquid. Particularly preferred. By setting the acid content to 15 to 40% by mass, the components in the ink composition can be more efficiently fixed.

The amount of acid applied to the recording medium is not particularly limited as long as it is an amount sufficient to aggregate the ink composition, but from the viewpoint that the ink composition is easily fixed, 0.5 g / m ² to 4. it is preferably 0 g / ^{m 2,} more preferably ^{0.9g / m 2 ~3.75g / m 2} .

[Cationic polymer]
The cationic polymer is preferably at least one cationic polymer selected from poly (vinyl pyridine) salts, polyalkylaminoethyl acrylate, polyalkylaminoethyl methacrylate, poly (vinyl imidazole), polyethyleneimine, polybiguanide and polyguanide.
Among the cationic polymers, polyguanides (preferably poly (hexamethylene guanidine) acetate, polymonoguanide, polymeric biguanide), polyethyleneimine, and poly (vinyl pyridine), which are advantageous from the viewpoint of aggregation rate, are preferable.
A cationic polymer may be used individually by 1 type, and may use 2 or more types together.

  The mass average molecular weight of the cationic polymer is preferably smaller in terms of the viscosity of the treatment liquid. When the treatment liquid is applied to the recording medium by an inkjet method, a range of 500 to 500,000 is preferable, a range of 700 to 200,000 is more preferable, and a range of 1,000 to 100,000 is more preferable. . When the mass average molecular weight is 500 or more, it is advantageous from the viewpoint of the aggregation rate, and when it is 500,000 or less, it is advantageous from the viewpoint of ejection reliability. However, this is not the case when the treatment liquid is applied to the recording medium by a method other than inkjet.

  The treatment liquid contains a cationic polymer, but the pH (25 ° C.) of the treatment liquid is preferably 1.0 to 10.0, more preferably 2.0 to 9.0. More preferably, it is 0-7.0.

1-35 mass% is preferable with respect to the total mass of the said processing liquid, and, as for content of a cationic polymer, 5-25 mass% is more preferable.
The amount of the cationic polymer applied to the coated paper is not particularly limited as long as it is an amount sufficient to stabilize the ink composition, but 0.5 g / m from the viewpoint that the ink composition is easily fixed. ^{2 to} 4.0 g / m ² is preferable, and 0.9 g / m ^{2 to} 3.75 g / m ² is more preferable.

<< Photocuring method >>
The photocuring method of the present invention includes a polymerizable compound having an ethylenically unsaturated group as the component (A), a photopolymerization initiator represented by the general formula (1) or (2) as a component (B), and (C) A structure in which a nitrogen atom is directly connected to an aromatic ring, and the aromatic ring has an electron-withdrawing substituent or at least one hydrogen donor in which the nitrogen atom is an atom constituting a hetero ring. The ink composition to be cured is photocured under acidic conditions.

The acidic condition means that the ink composition or the environment for curing the ink composition is an acidic condition when the ink composition is cured. You may combine with the composition B.
Further, the ink receiving surface of the recording medium may be acidified with the ink composition B, or a recording medium having an ink receiving surface in an acidic state may be used in advance.
Moreover, the active energy ray irradiation process mentioned later is applied preferably at the time of photocuring.

<< Image Forming Method >>
The image forming method of the present invention uses the ink composition (ink composition A) or the above-described photocuring method in the image forming stage, and incorporates a colorant into the ink composition to form a color image forming ink composition. You may use as a thing.
In the image forming method of the present invention, preferably, an acid treatment step (treatment liquid application step) of applying the treatment liquid ink composition B, which is a part of the ink set, onto the recording medium, and the ink on the recording medium. It includes at least an ink application step for applying the composition A to form an image and a photocuring step (active energy ray irradiation step) for curing the ink of the formed image by light irradiation. Moreover, it is comprised further including another process as needed.

[recoding media]
The recording medium used in the image forming method of the present invention is not particularly limited, but general printing paper mainly composed of cellulose, such as so-called high-quality paper, coated paper, and art paper, used for general offset printing or the like is used. Can do. General printing paper mainly composed of cellulose is relatively slow in ink absorption and drying in image recording by a general ink jet method using water-based ink, and color material movement is likely to occur after droplet ejection, and image quality is likely to deteriorate. However, according to the ink jet recording method of the present invention, it is possible to record a high-quality image excellent in color density and hue by suppressing the movement of the color material.

  As the recording medium, commercially available media can be used. For example, “OK Prince fine quality” manufactured by Oji Paper Co., Ltd., “Shiorai” manufactured by Nippon Paper Industries Co., Ltd., and Nippon Paper Industries ( High-quality paper (A) such as “New NPI fine quality” manufactured by Nippon Paper Industries Co., Ltd., high-quality coated paper such as “Silver Diamond” manufactured by Nippon Paper Industries Co., Ltd., “OK Everlight Coat” manufactured by Oji Paper Co., Ltd. and Nippon Paper Industries Light coated paper (A3), such as “Aurora S” manufactured by Co., Ltd., “OK Coat L” manufactured by Oji Paper Co., Ltd., and “Aurora L” manufactured by Nippon Paper Industries Co., Ltd., Oji Coated paper (A2, B2) such as “OK Top Coat +” manufactured by Paper Industries Co., Ltd. and “Aurora Coat” manufactured by Nippon Paper Industries Co., Ltd. “OK Kanto +” manufactured by Oji Paper Co., Ltd. and Mitsubishi Paper Industries ( Art paper (A1) such as “Tokuhishi Art” manufactured by Co., Ltd. and the like. It is also possible to use various photographic papers for ink jet recording.

Among the above, the water absorption coefficient Ka of the recording medium is 0.05 to 0.5 from the viewpoint of obtaining a high-quality image having a large color density and hue better than before, with a large effect of suppressing color material movement. mL ^/ m 2 ^{· ms 1/2} is preferable, more preferably 0.1~0.4mL ^/ m 2 ^{· ms 1/2,} more preferably 0.2~0.3mL ^/ m 2 ^{· ms 1/2.}

  The water absorption coefficient Ka is synonymous with that described in JAPAN TAPPI paper pulp test method No. 51: 2000 (issued by Japan Paper Pulp Technology Association). Specifically, the absorption coefficient Ka is an automatic scanning absorption meter. It is calculated from the difference in the amount of water transferred between the contact time of 100 ms and the contact time of 900 ms using KM500Win (manufactured by Kumagai Riki Co.).

  Among the recording media, so-called coated paper used for general offset printing is preferable. The coated paper is obtained by applying a coating material to the surface of high-quality paper, neutral paper, or the like that is mainly surface-treated with cellulose as a main component and is not surface-treated. The coated paper tends to cause quality problems such as image gloss and scratch resistance in image formation by ordinary aqueous inkjet, but in the inkjet recording method of the present invention, gloss unevenness is suppressed and gloss and resistance are reduced. An image having good rubbing properties can be obtained. In particular, it is preferable to use a coated paper having a base paper and a coat layer containing kaolin and / or calcium bicarbonate. More specifically, art paper, coated paper, lightweight coated paper or finely coated paper is more preferable.

[Acid treatment step (treatment liquid application step)]
In the treatment liquid application step, a treatment liquid containing a flocculant contained in the ink set is applied on the recording medium. For applying the treatment liquid to the recording medium, a known liquid application method can be used without particular limitation, and any method such as spray application, application using an application roller, application by an inkjet method, immersion, etc. can be selected. .

  Specifically, for example, a size press method represented by a horizontal size press method, a roll coater method, a calendar size press method, etc .; a size press method represented by an air knife coater method, etc .; Knife coater method; transfer roll coater method such as gate roll coater method, direct roll coater method, reverse roll coater method, roll coater method represented by squeeze roll coater method; bill blade coater method, short duel coater method; Blade coater method typified by stream coater method, etc .; Bar coater method typified by rod bar coater method, etc .; Bar coater method typified by rod bar coater method, etc .; Cast coater method; Gravure coater method; Coater method; die coater method; brush coater method; and the like transfer method.

  Moreover, the method of apply | coating by controlling a coating amount by using the coating device provided with the liquid quantity limiting member like the coating device of Unexamined-Japanese-Patent No. 10-230201 may be used.

  The region to which the treatment liquid is applied may be the entire surface application to be applied to the entire recording medium or may be the partial application to be partially applied to the region to which ink is applied in the ink application process. In the present invention, the application amount of the treatment liquid is uniformly adjusted, and fine lines and fine image portions are uniformly recorded, and from the viewpoint of suppressing density unevenness such as image unevenness, coating is performed by application using an application roller or the like. It is preferable to apply the entire surface of the paper.

  Examples of the method of applying the treatment liquid by controlling the application amount of the treatment liquid within the above range include a method using an anilox roller. An anilox roller is a roller with a ceramic-sprayed roller surface processed with a laser to give it a pyramid shape, a diagonal line, a turtle shell shape, or the like. The treatment liquid enters the dent portion formed on the roller surface, is transferred when it comes into contact with the paper surface, and is applied in an application amount controlled by the dent of the anilox roller.

[Ink application process]
In the ink application process, the ink composition contained in the ink set is applied onto the recording medium. The ink composition application method is not particularly limited as long as the ink composition can be applied in a desired image-like manner, and a known ink application method can be used. For example, a method of applying an ink composition onto a recording medium by means of an ink jet method, a copying method, a printing method, or the like can be given. Among these, the step of applying the ink composition by an ink jet method is preferable from the viewpoint of compactness of the recording apparatus and high-speed recording properties.

[Inkjet method]
In image formation by an ink jet method, by supplying energy, an ink composition is discharged onto a recording medium to form a colored image. As a preferable ink jet recording method for the present invention, the method described in paragraph Nos. 0093 to 0105 of JP-A No. 2003-306623 can be applied.

The inkjet method is not particularly limited, and is a known method, for example, a charge control method that discharges ink using electrostatic attraction, a drop-on-demand method (pressure pulse method) that uses vibration pressure of a piezoelectric element, Any of an acoustic ink jet method in which an electric signal is converted into an acoustic beam, irradiated onto ink, and ink is ejected using radiation pressure may be used.
The ink jet head used in the ink jet method may be an on-demand method or a continuous method. Furthermore, there are no particular limitations on the ink nozzles used when recording by the ink jet method, and they can be appropriately selected according to the purpose.
Inkjet methods include a method of ejecting many low-density inks called photo inks in a small volume, a method of improving the image quality using a plurality of inks having substantially the same hue and different concentrations, and colorless and transparent inks. The method used is included.

  Also, as an ink jet system, a short serial head is used, a shuttle system that performs recording while scanning the head in the width direction of the recording medium, and a line head in which recording elements are arranged corresponding to the entire area of one side of the recording medium There is a line system using. In the line method, an image can be recorded on the entire surface of the recording medium by scanning the recording medium in a direction orthogonal to the arrangement direction of the recording elements, and a carriage system such as a carriage for scanning a short head is not necessary. Further, since complicated scanning control of the carriage movement and the recording medium is not required, and only the recording medium is moved, the recording speed can be increased as compared with the shuttle system.

  In the present invention, the order in which the treatment liquid application step and the ink application step are performed is not particularly limited, but from the viewpoint of image quality, it is preferable that the ink application step is performed after the treatment liquid application step. That is, the ink application step is preferably a step of applying the ink composition onto the recording medium to which the treatment liquid has been applied.

[Active energy ray irradiation process]
The image forming method of the present invention preferably includes a step of irradiating the ink composition applied on the recording medium with active energy rays. By irradiating active energy rays, the polymerizable compound contained in the ink composition is polymerized to form a cured film containing a colorant. Thereby, the abrasion resistance and blocking resistance of the image are more effectively improved.

The ink composition applied on the recording medium is cured by irradiation with active energy rays. This is because the polymerization initiator of the present invention contained in the ink composition is decomposed by irradiation with active energy rays to generate radicals, whereby the polymerization reaction of the polymerizable compound is initiated and accelerated, and the ink composition is cured. It is to do.
When an acid is contained in the treatment liquid, the ink composition is further aggregated (fixed) by the acid supplied from the compound upon irradiation with the active energy ray, and the image area quality (rubbing resistance / blocking resistance) Etc.).

In the present invention, α-rays, γ-rays, electron beams, X-rays, ultraviolet rays, visible light, infrared light, and the like can be used as active energy rays. As described above, the photopolymerization initiator of the present invention has high absorption particularly for light in the ultraviolet region. From this viewpoint, the wavelength of the active energy ray is preferably 200 to 600 nm, and preferably 300 to 450 nm. More preferred is 350 to 420 nm.
The output of the active energy ray is preferably 5000 mJ / cm ² or less, more preferably 10~4000mJ / cm ^2, more preferably 20~3000mJ / cm ^2.

Mercury lamps and gas / solid lasers are mainly used as active energy ray sources, and mercury lamps and metal halide lamps are widely known as light sources used for curing UV photocurable ink jet recording inks. Yes. However, from the viewpoint of environmental protection, mercury-free is strongly desired, and replacement with a GaN-based semiconductor ultraviolet light-emitting device is very useful industrially and environmentally. In addition, LEDs and LDs are small, have a long life, have high efficiency, and are low in cost, and are expected as light sources for photocurable ink jets.
In the present invention, a light emitting diode (LED) and a laser diode (LD) can be used as an active energy ray source. In particular, an ultraviolet LED (UV-LED) and an ultraviolet LD (UV-LD) can be used as an ultraviolet ray source. For example, Nichia Corporation has introduced a purple LED whose main emission spectrum has a wavelength between 365 nm and 420 nm.
A particularly preferable active energy ray source in the present invention is a UV-LED, and a UV-LED having a peak wavelength in the range of 350 to 420 nm is particularly preferable.

[Ink drying process]
The image forming method of the present invention may include an ink drying step for drying and removing a solvent (for example, water, the above-described aqueous medium) in the ink composition applied onto the recording medium, if necessary. Good. The ink drying step is not particularly limited as long as at least a part of the ink solvent can be removed, and a commonly used method can be applied.

  EXAMPLES Hereinafter, although this invention is demonstrated in detail based on an Example, this invention is not limited to these Examples.

[Preparation of polymerizable compound]

[Synthesis of Polymerizable Compound M-1]
To a 1 L three-necked flask equipped with a stirrer was added 40.0 g (182 mmol) of 4,7,10-trioxa-1,13-tridecanediamine, 37.8 g (450 mmol) of sodium bicarbonate, 100 g of water, and 200 g of tetrahydrofuran. In an ice bath, 35.2 g (389 mmol) of acrylic acid chloride was added dropwise over 20 minutes. After dropping, the mixture was stirred at room temperature for 5 hours, and then tetrahydrofuran was distilled off from the obtained reaction mixture under reduced pressure. Next, the aqueous layer was extracted four times with 200 ml of ethyl acetate, and the obtained organic layer was dried over magnesium sulfate, filtered, and the solvent was distilled off under reduced pressure to obtain 35 of the target polymerizable compound M-1 solid. 0.0 g (107 mmol, 59% yield) was obtained.

[Synthesis of Polymerizable Compound M-2]
A polymerizable compound M-2 was synthesized according to the following scheme.

(1) Synthesis of intermediate M-2 (B) In a 1 L three-necked flask equipped with a stirrer bar, 121 g (1 equivalent) of tris (hydroxymethyl) aminomethane M-2 (A) (manufactured by Tokyo Chemical Industry Co., Ltd.) Then, 84 ml of 50% aqueous potassium hydroxide solution and 423 ml of toluene were added and stirred, and the reaction system was maintained at 20 to 25 ° C. in a water bath, and 397.5 g (7.5 equivalents) of acrylonitrile was added dropwise over 2 hours. After dripping, after stirring for 1.5 hours, 540 ml of toluene was added to the reaction system, the reaction mixture was transferred to a separatory funnel, and the aqueous layer was removed. The remaining organic layer was dried over magnesium sulfate, filtered through Celite, and the solvent was distilled off under reduced pressure to obtain an intermediate M-2 (B): acrylonitrile adduct. Since the analysis result by ¹ H-NMR and MS of the obtained substance was in good agreement with the known substance, it was used for the next reduction reaction without further purification.

(2) Synthesis of intermediate M-2 (C) 24 g of intermediate M-2 (B) obtained previously in a 1 L autoclave, 48 g of Ni catalyst (Raney nickel 2400, manufactured by WR Grace & Co.), 600 ml of a 25% aqueous ammonia: methanol = 1: 1 solution was added and suspended, and the reaction vessel was sealed. 10 Mpa of hydrogen was introduced into the reaction vessel and reacted at a reaction temperature of 25 ° C. for 16 hours.
The disappearance of the raw materials was confirmed by ¹ H-NMR, the reaction mixture was filtered through Celite, and the Celite was washed several times with methanol. The filtrate was evaporated under reduced pressure to obtain intermediate M-2 (C): amine. The obtained material was used for the next reduction reaction without further purification.

(3) Synthesis of polymerizable compound M-2 30 g of intermediate M-2 (C) obtained previously in a 2 L three-necked flask equipped with a stirrer, 120 g (14 equivalents) of NaHCO ₃ , 1 L of dichloromethane, and 50 ml of water In addition, 92.8 g (10 equivalents) of acrylic acid chloride was added dropwise over 3 hours in an ice bath, and then stirred at room temperature for 3 hours. After confirming disappearance of the raw material by ¹ H-NMR, the solvent was distilled off from the reaction mixture under reduced pressure, the reaction mixture was dried over magnesium sulfate, filtered through celite, and the solvent was distilled off under reduced pressure. Finally, it was purified by column chromatography (ethyl acetate / methanol = 4: 1) to obtain a yellow liquid (yield 40%) at room temperature.

[Polymerizable compound M-3]
As the polymerizable compound M-3, a product manufactured by Tokyo Chemical Industry Co., Ltd. was used.

[Preparation of photopolymerization initiator]
Photopolymerization initiators I-1 and I-6 were manufactured by Wako Pure Chemical Industries, Ltd.
Photoinitiator I-2 is a product of Bioorg. Med. Chem. 7, 1321 (1999), photopolymerization initiator I-3 is Tetrahedron, 49, 939 (1993), photopolymerization initiator I-4 is JP-A-2009-084220, photopolymerization initiator I-5. Can be obtained by the method described in Synlett, 16, 2453 (2005) or a method based thereon.

[Hydrogen donor]
Hydrogen donors A-1 to A-4, A-6, and B-1 to B-3 were all manufactured by Tokyo Chemical Industry Co., Ltd. A-5 was synthesized according to a known method (J. Org. Chem., 2006, 71, 5117).

Example 1
Each monomer solution was prepared as follows.

[Preparation of monomer solution]
(Monomer solution 1)
Polymeric compound M-1 (500 mg), photopolymerization initiator I-1 (25 mg), hydrogen donor A-1 (25 mg), malonic acid (50 mg) were dissolved in methanol (2 ml) to prepare monomer solution 1. did.

(Monomer solution 2-9)
Monomer solutions 2 to 9 were prepared in the same manner as the monomer solution 1 except that the hydrogen donor A-1 in the monomer solution 1 was changed to A-2 to A-6 and B-1 to B-3 by the same mass. It was adjusted.

(Monomer solution 10-14)
Monomer solutions 10 to 14 were prepared in the same manner as in the monomer solution 1 except that the malonic acid in the monomer solution 2 was changed to benzoic acid, malic acid, maleic acid, oxalic acid, and acetic acid in an equal mass.

(Monomer solution 15-20)
Monomer solutions 15 to 20 were prepared in the same manner as in the monomer solution 4 except that the malonic acid in the monomer solution 4 was changed to benzoic acid, malic acid, phosphoric acid, maleic acid, oxalic acid, and acetic acid in an equal mass.

(Monomer solutions 21, 22)
Monomer solutions 21 and 22 were prepared in the same manner as the monomer solution 5 except that the same amount of malonic acid in the monomer solution 5 was changed to malic acid and phosphoric acid, respectively.

(Monomer solution 23-27)
Monomer solutions 23 to 27 were prepared in the same manner as the monomer solution 2 except that the photopolymerization initiator I-1 in the monomer solution 2 was changed to the photopolymerization initiators I-2 to I-6 by an equal mass.

(Monomer solution 28, 29)
Except for changing the photopolymerization initiator I-1 in the monomer solution 4 to the photopolymerization initiator I-2, and the polymerizable compound M-1 to the polymerizable compounds M-2 and M-3, respectively, in the same mass. Prepared monomer solutions 28 and 29 in the same manner as monomer solution 4.

[Comparative hydrogen donor]
The following hydrogen donors R-1 to R-5 for comparison were those manufactured by Wako Pure Chemical Industries, Ltd.

(Monomer solutions c1 to c5)
The monomer solutions c1 to c5 were prepared in the same manner as the monomer solution 1 except that the hydrogen donor A-1 in the monomer solution 1 was changed to the above-described comparative hydrogen donors R-1 to R-5 by the same mass. did.

(Monomer solution c6)
A monomer solution c6 was prepared in the same manner as the monomer solution 1 except that the hydrogen donor A-1 in the monomer solution 1 was not added.

(Monomer solution c7, c8)
Monomer solutions c7 and c8 were prepared in the same manner as the monomer solution 4 except that the photopolymerization initiator I-1 in the monomer solution 4 was changed to an equal mass to J-1 and J-2, respectively.

(Monomer solution c9 to c11)
Monomer solutions c9 to c11 were prepared in the same manner as the monomer solution 2, except that the photopolymerization initiator I-1 in the monomer solution 2 was changed to an equal mass to J-3 to J-5, respectively.

Here, pKa in H ₂ O (25 ° C.) of these acids is as follows.
Malonic acid is 2.8 (pKa1), malic acid is 3.4 (pKa1), acetic acid is 4.8, benzoic acid is 4.2, oxalic acid is 1.2, maleic acid is 1.9 (pKa1), The phosphoric acid is 2.12 (pKa1).

[Photocuring experiment]
(Experiment 1)
Monomer solution 1 (10 μL) was dropped onto the copper thin film with a microsyringe and exposed for 5 seconds using an ultraviolet light emitting diode irradiation device (365 nm, 110 mW / cm ² ) manufactured by Nichia Corporation. Before and after the exposure, how much the peak derived from the unsaturated bond decreases was observed using FT-IR (Varian 3100 FT-IR, manufactured by VARIAN) to determine the polymerization rate. In addition, each corresponding monomer solution to which no acid was added was prepared, and the polymerization rate was measured in the same manner as the monomer solution to which acid was added, and [(polymerization rate in the monomer solution to which no acid was added)-( Polymerization rate in acid-added monomer solution)] / (polymerization rate in monomer solution to which no acid was added) × 100 = Δ The polymerization reduction rate was determined, and the degree of decrease in the polymerization rate in the presence of acid was examined.

(Experiments 2 to 29, c1 to c11)
Experiments 2 to 29 and c1 to c11 were performed in the same manner as Experiment 1 except that the monomer solution 1 was changed to the monomer solutions 2 to 29 and c1 to c11.

  The obtained results are shown in Table 1 below.

As is clear from the results in Table 1, the combination of the thiochromanone or thioxanthone photopolymerization initiator and the hydrogen donor of the present invention was compared with the combination of the comparative hydrogen donor, and the UV-LED light after the addition of acid. It can be seen that the polymerization rate at (365 nm) is remarkably excellent.
Moreover, compared with the conditions in which no acid is present, the decrease in the polymerization rate is relatively small in the presence of an acid (a value where the Δ polymerization rate is negative improves the polymerization rate), and there is also an improvement in the reverse.
On the other hand, when a comparative hydrogen donor or a comparative photopolymerization initiator is used, the polymerization rate in the presence of an acid is low, and in the presence of the acid, the polymerization rate is not obtained in the monomer solutions c1 to c6, c10, and c11. Is greatly reduced. In the monomer solutions c7 to c9, the Δ polymerization decrease rate is relatively small, but the polymerization rate itself in the presence of an acid is 12 to 38%, which is significantly lower than that of the monomer solution of the present invention.
The combination of the photopolymerization initiator of the present invention and the hydrogen donor is considered to be excellent in the polymerization rate. The radical species derived from the hydrogen donor is protonated by an acid, and the reactivity in the polymerization initiation process is considered to decrease. Thus, it is considered that the introduction of an electron withdrawing substituent or heterocyclization as in the present invention reduced the basicity of the hydrogen donor on nitrogen, suppressed protonation, and maintained the reactivity.

Example 2
An ink set was prepared as follows, an image was formed by an ink jet method, and a curability test was performed.

[Synthesis of Polymer Dispersant P-1]
To a 1000 ml three-necked flask equipped with a stirrer and a condenser tube, 88 g of methyl ethyl ketone was added and heated to 72 ° C. under a nitrogen atmosphere. Here, 50 g of methyl ethyl ketone was mixed with 0.85 g of dimethyl 2,2′-azobisisobutyrate and benzyl methacrylate. A solution in which 60 g, 10 g of methacrylic acid and 30 g of methyl methacrylate were dissolved was dropped over 3 hours. After completion of the dropwise addition, the reaction was further continued for 1 hour, and then a solution of 0.42 g of dimethyl 2,2′-azobisisobutyrate in 2 g of methyl ethyl ketone was added, heated to 78 ° C. and heated for 4 hours. The obtained reaction solution was reprecipitated twice in a large excess amount of hexane, and the precipitated resin was dried to obtain 96 g of a polymer dispersant P-1.
The composition of the obtained resin was confirmed by ¹ H-NMR, and the mass average molecular weight (Mw) determined by gel permeation chromatography (GPC) was 44,600. Furthermore, when the acid value was calculated | required by the method as described in JIS specification (JISK0070: 1992), it was 65.2 mgKOH / g.

[Preparation of dispersion of resin-coated pigment]
-Resin-coated magenta pigment dispersion-
Chromophthal Jet Magenta DMQ (Pigment Red 122, manufactured by BASF Japan Ltd.) 10 parts by mass, 5 parts by mass of the above polymer dispersant P-1, 42 parts by mass of methyl ethyl ketone, 5.5 parts by mass of 1 mol / L NaOH aqueous solution, and ion exchange 87.2 parts by mass of water was mixed and dispersed with a bead mill using 0.1 mmφ zirconia beads for 2 to 6 hours.
Methyl ethyl ketone was removed from the obtained dispersion under reduced pressure at 55 ° C., and a part of water was further removed to obtain a dispersion (colored particles) of a resin-coated magenta pigment having a pigment concentration of 10.2% by mass. It was.

[Preparation of ink sets 1 to 7]
In the following manner, magenta inks 1 to 7 and treatment liquid 1 were prepared according to the following ink formulations 1 to 7, and ink sets 1 to 7 including combinations of these magenta inks and treatment liquid 1 were obtained.

(Preparation of magenta inks 1 to 7)
Using the above resin-coated magenta pigment dispersion, the resin-coated magenta pigment dispersion, ion-exchanged water, a polymerization initiator, a polymerizable compound and a surfactant are mixed so that the following ink formulations 1 to 7 are obtained. Magenta inks 1 to 7 were prepared by filtration through a 5 μm membrane filter.

[Ink prescription]
-Ink formula 1
・ Resin-coated magenta pigment dispersion: 6% by mass
-Photopolymerization initiator I-2: 1.5% by mass
・ Hydrogen donor A-3: 1.5% by mass
Polymerizable compound M-1 15% by mass
・ Olfin E1010 ... 1% by mass
(Nissin Chemical Co., Ltd .; surfactant)
・ Acetonitrile ... 60% by mass
・ Ion-exchanged water: added to 100% by mass as a whole.

-Ink formula 2-
・ Resin-coated magenta pigment dispersion: 6% by mass
-Photopolymerization initiator I-2: 1.5% by mass
・ Hydrogen donor A-4: 1.5% by mass
Polymerizable compound M-1 15% by mass
・ Olfin E1010 ... 1% by mass
(Nissin Chemical Co., Ltd .; surfactant)
・ Acetonitrile ... 60% by mass
・ Ion-exchanged water: added to 100% by mass as a whole.

-Ink formula 3-
・ Resin-coated magenta pigment dispersion: 6% by mass
-Photopolymerization initiator I-3: 1.5% by mass
・ Hydrogen donor A-4: 1.5% by mass
Polymerizable compound M-1 15% by mass
・ Olfin E1010 ... 1% by mass
(Nissin Chemical Co., Ltd .; surfactant)
・ Acetonitrile ... 60% by mass
・ Ion-exchanged water: added to 100% by mass as a whole.
-Ink formula 4-
・ Resin-coated magenta pigment dispersion: 6% by mass
-Photopolymerization initiator I-2: 1.5% by mass
・ Hydrogen donor A-4: 1.5% by mass
・ Polymerizable compound M-2 15% by mass
・ Olfin E1010 ... 1% by mass
(Nissin Chemical Co., Ltd .; surfactant)
・ Acetonitrile ... 60% by mass
・ Ion-exchanged water: added to 100% by mass as a whole.

-Ink formula 5-
・ Resin-coated magenta pigment dispersion: 6% by mass
-Photopolymerization initiator I-2: 1.5% by mass
・ Hydrogen donor B-1: 1.5% by mass
Polymerizable compound M-1 15% by mass
・ Olfin E1010 ... 1% by mass
(Nissin Chemical Co., Ltd .; surfactant)
・ Acetonitrile ... 60% by mass
・ Ion-exchanged water: added to 100% by mass as a whole.

-Ink formula 6 (comparative ink formula)-
・ Resin-coated magenta pigment dispersion: 6% by mass
-Photopolymerization initiator I-2 ... 3% by mass
Polymerizable compound M-1 15% by mass
・ Olfin E1010 ... 1% by mass
(Nissin Chemical Co., Ltd .; surfactant)
・ Acetonitrile ... 60% by mass
・ Ion-exchanged water: added to 100% by mass as a whole.

-Ink formula 7 (comparative ink formula)-
・ Resin-coated magenta pigment dispersion: 6% by mass
-Photopolymerization initiator I-2: 1.5% by mass
・ Hydrogen donor R-1: 1.5% by mass
Polymerizable compound M-1 15% by mass
・ Olfin E1010 ... 1% by mass
(Nissin Chemical Co., Ltd .; surfactant)
・ Acetonitrile ... 60% by mass
・ Ion-exchanged water: added to 100% by mass as a whole.

  When pH (25 degreeC) of the magenta ink 1-7 was measured using pH meter WM-50EG (made by Toa DKK Co., Ltd.), all were 8.8.

[Inkjet recording]
As a recording medium (coated paper), Tokishi Art Double Sided N (Mitsubishi Paper) (basis weight: 104.7 g / m ² ) was prepared, and an image was formed as shown below. The following evaluation was performed.

Using ink sets 1 to 7 prepared above, line images and solid images were formed by four-color single-pass recording.
At this time, a line image was formed by ejecting a 1200-dot line of 1 dot width, a 2-dot width line, and a 4-dot width line in a single pass in the main scanning direction.
The solid image was formed by discharging the ink composition over the entire surface of a sample obtained by cutting the recording medium into A5 size. The conditions for recording are as follows.

(1) Treatment liquid application process The entire surface of the recording medium is processed with a roll coater whose application amount is controlled by an anilox roller (number of lines: 100 to 300 / inch) so that the application amount is 1.4 g / m ^2. The liquid (treatment liquid 1) was applied.

(2) Processing Step Next, a drying treatment and a permeation treatment were performed on the recording medium coated with the treatment liquid under the following conditions.
・ Wind speed: 10m / s
-Temperature: Heated by a contact type flat heater from the opposite side (back side) of the recording surface of the recording medium so that the surface temperature of the recording surface of the recording medium was 60 ° C.

(3) Ink application process On the coated surface of the recording medium coated with the treatment liquid, ink was ejected by the inkjet method under the following conditions to form a line image and a solid image, respectively.
・ Head: 1,200 dpi / 20 inch wide piezo full line head for 4 colors ・ Discharge droplet volume: 2.0 pL
・ Drive frequency: 30kHz

(4) Ink drying step The recording medium provided with ink was dried under the following conditions.
・ Drying method: blow drying ・ Wind speed: 15m / s
-Temperature: Heated by a contact type flat heater from the opposite side (back side) of the recording surface of the recording medium so that the surface temperature of the recording surface of the recording medium was 60 ° C.

(5) Immobilization step Next, using a metal halide lamp, the recorded image was irradiated with ultraviolet rays as an active energy ray under an energy condition of 2000 mJ / cm ² to obtain an image recorded matter.

[Evaluation]
Each of the obtained image samples was subjected to an ink curability test as follows.

[Curing sensitivity]
Of unprinted Tokubishi Art double-side N (manufactured by Mitsubishi Paper Mills) paperweight (weight 470 g, size 15 mm × 30 mm × 120 mm) around the attached (area Tokubishi Art and an evaluation sample contacts the unprinted is 150 mm ^2), the printing The sample was rubbed three times (corresponding to a load of 260 kg / m ² ). The marking screen after rubbing was visually observed and evaluated according to the following evaluation criteria.

(Evaluation criteria)
A: No peeling of the image (coloring material) was visible on the printing surface.
B: Slight peeling of the image (coloring material) was observed on the printing surface.
C: The peeling of the image (coloring material) can be visually recognized on the printing surface, which is a level causing a practical problem.

  The obtained results are shown in Table 2 below.

  As can be seen from Table 2, it can be seen that the ink sets of the present invention are all excellent in curing sensitivity and suitable for ink jet image formation.

Claims (16)

(A) a polymerizable compound having an ethylenically unsaturated group, (B) a photopolymerization initiator represented by the following general formula (1) or (2), and (C) a structure in which a nitrogen atom is directly connected to an aromatic ring. A photo-curing ink composition containing at least one hydrogen donor each having an electron-withdrawing substituent on the aromatic ring or an atom in which the nitrogen atom constitutes a heterocycle under acidic conditions. A curing method,
The photocuring method in which the hydrogen donor of (C) is represented by the following general formula (4).

(In General Formulas (1) and (2), R ^{1 to} R ¹⁶ each independently represents a hydrogen atom, a halogen atom, an alkyl group or an alkoxy group.)

(In General Formula (4), R ^{39 to} R ⁴² are each independently a hydrogen atom , an alkyl group, an alkoxy group, a halogen atom, a fluoroalkyl group, a cyano group, an acyl group, an alkoxycarbonyl group, an aryloxycarbonyl group, or a carbamoyl group. Represents a group, an alkyl or arylsulfonyl group, or a sulfamoyl group, and X represents an oxygen atom or a sulfur atom.) Photopolymerization initiator of said (B) is a light curing method according to claim 1 represented by the general formula (1). The photocuring method according to claim 1 or 2 , wherein the polymerizable compound having the ethylenically unsaturated group (A) is a bifunctional or higher functional (meth) acrylate compound or (meth) acrylamide compound. It said ink composition, photocuring process according to any one of claims 1 to 3 containing at least one colorant. It said ink composition, photocuring process according to any one of claims 1-4 is an inkjet ink composition. The photocuring method according to any one of claims 1 to 5 , wherein the ink composition is photocured after forming an image. (A) a polymerizable compound having an ethylenically unsaturated group, (B) a photopolymerization initiator represented by the following general formula (1) or (2), and (C) a structure in which a nitrogen atom is directly connected to an aromatic ring. And an ink composition A containing at least one hydrogen donor each having an electron-withdrawing substituent on the aromatic ring or an atom in which the nitrogen atom constitutes a heterocycle, and a molecular weight of 50 to 200, And an ink set comprising an ink composition B containing pKa (in H ₂ O) 1 or more and 5 or less acid,
The ink set in which the hydrogen donor (C) is represented by the following general formula (4).

(In General Formulas (1) and (2), R ^{1 to} R ¹⁶ each independently represents a hydrogen atom, a halogen atom, an alkyl group or an alkoxy group.)

(In General Formula (4), R ^{39 to} R ⁴² are each independently a hydrogen atom , an alkyl group, an alkoxy group, a halogen atom, a fluoroalkyl group, a cyano group, an acyl group, an alkoxycarbonyl group, an aryloxycarbonyl group, or a carbamoyl group. Represents a group, an alkyl or arylsulfonyl group, or a sulfamoyl group, and X represents an oxygen atom or a sulfur atom.) The ink set according to claim 7 , wherein the photopolymerization initiator (B) is represented by the general formula (1). The ink set according to claim 7 or 8 , wherein the polymerizable compound having an ethylenically unsaturated group (A) is a bifunctional or higher functional (meth) acrylate compound or (meth) acrylamide compound. The ink set according to any one of claims 7 to 9 , wherein the ink composition A contains at least one colorant. The ink set according to any one of claims 7 to 10 , wherein the ink set is an inkjet ink set. The image forming method comprising the photocurable method according to any one of claims 1-6. An image forming method using the ink set according to any one of claims 7 to 11 . An acid treatment step of applying the ink composition B on a recording medium, an ink application step of forming the image by applying the ink composition A on the recording medium, and an ink of an image formed by light irradiation The image forming method according to claim 13 , further comprising a photocuring step of curing the material. (A) a polymerizable compound having an ethylenically unsaturated group, (B) a photopolymerization initiator represented by the following general formula (1) or (2), and (C) hydrogen represented by the following general formula (4) An ink composition containing at least one donor.

(In General Formulas (1) and (2), R ^{1 to} R ¹⁶ each independently represents a hydrogen atom, a halogen atom, an alkyl group or an alkoxy group.)

(In General Formula (4), R ^{39 to} R ⁴² are each independently a hydrogen atom , an alkyl group, an alkoxy group, a halogen atom, a fluoroalkyl group, a cyano group, an acyl group, an alkoxycarbonyl group, an aryloxycarbonyl group, or a carbamoyl group. Represents a group, an alkyl or arylsulfonyl group, or a sulfamoyl group, and X represents an oxygen atom or a sulfur atom.) The ink composition according to claim 15 , wherein the photopolymerization initiator (B) is represented by the general formula (1).