JP2008069214A - Ink composition, inkjet recording method, printed product and method for producing lithographic printing plate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an ink composition having excellent hardenability by the irradiation with active radiation, and providing an image obtained by hardening the ink composition, and having excellent flexibility, adhesion to a base material, and blocking characteristics; to provide an inkjet recording method using the ink composition; and to provide a printed product. <P>SOLUTION: The ink composition contains (A) N-vinyllactams and (B) a dendrimer having one or more polymerization-initiating species-forming structures at the terminals. The inkjet recording method uses the ink composition. The printed product is recorded by the inkjet recording method. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

The present invention relates to an ink composition suitably used for ink jet recording, an ink jet recording method, a printed matter obtained using the ink composition, and a method for producing a lithographic printing plate.
Specifically, the inkjet recording is possible for a long period of stable inkjet recording, is cured with high sensitivity to irradiation with actinic radiation, and the cured product has sufficient flexibility and adhesion to a recording medium even after ink curing. The present invention relates to an ink composition suitable for recording, an ink jet recording method, a printed matter using the ink composition, and a method for producing a lithographic printing plate obtained using the ink.

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 electrophotographic system requires a process of forming an electrostatic latent image on a photosensitive drum by charging and exposure, and there is a problem that the system becomes complicated and consequently the manufacturing cost becomes high. In addition, although the thermal transfer system is inexpensive, there are problems such as high running costs and waste materials due to the use of ink ribbons.
On the other hand, the ink jet method is an inexpensive device and ejects ink only to a required image portion to form an image directly on a recording medium. Therefore, the ink can be used efficiently and the running cost is low. Furthermore, there is little noise and it is excellent as an image recording method.

  Ink compositions that can be cured by irradiation with radiation such as ultraviolet rays, particularly inks for ink jet recording (radiation curable ink jet recording inks), require ink compositions that cure with high sensitivity and form high-quality images. ing. By achieving high sensitivity, high curability is imparted by irradiation with actinic radiation, so that sufficient curing is achieved in addition to reducing power consumption and extending life by reducing the load on the actinic radiation generator. As a result, there are various advantages such as suppression of volatilization of uncured low molecular weight substances and reduction in the strength of the formed image. In addition, there is a need for an ink composition in which the obtained image (printed material) is unlikely to crack or peel off, and has excellent impact resistance, flexibility, and substrate adhesion of a cured film. Since the cured film has high flexibility, impact resistance, and substrate adhesion, it can be displayed and stored for a long period of time in various environments while maintaining high image quality, and handling of the printed material becomes easy. There are benefits. The improvement in image strength by increasing the sensitivity results in high printing durability in the image area when this ink composition is used for forming the image area of a lithographic printing plate.

An ink composition containing N-vinyl lactams has been disclosed as an ink composition that is cured with high sensitivity and has excellent impact resistance, flexibility, and substrate adhesion of a cured film (Patent Document 1). However, the ink composition described in Patent Document 1 is a high-viscosity ink composition containing a polymer and an oligomer as main components of the ink, and is difficult to be ejected by inkjet.
Further, an ink composition having excellent adhesion is disclosed as an ink composition that can be cured by irradiation with radiation such as ultraviolet rays (Patent Document 2). However, it does not sufficiently satisfy all of curability, cured film flexibility, and substrate adhesion of the cured film.

Japanese Patent No. 2880845 JP-T-2004-514014

  An object of the present invention is an ink composition that is excellent in curability with respect to irradiation of actinic radiation, has excellent image flexibility, adhesion to a substrate, and blocking properties obtained by curing the ink composition, and Another object of the present invention is to provide an ink jet recording method and a printed matter using the ink composition.

The above object has been achieved by the means described in <1>, <10> and <12> below. It shows below with <2>-<9> and <11> which are preferable embodiments.
<1> an ink composition comprising (A) N-vinyl lactams and (B) a dendritic polymer having at least one polymerization initiation species generation structure at the terminal;
<2> The ink composition according to <1>, wherein the N-vinyllactam is N-vinylcaprolactam,
<3> The polymerization initiation species generation structure is a benzoin ether structure, a benzyl ketal structure, an α, α-dialkoxyacetophenone structure, an α-hydroxyalkylphenone structure, an α-aminoalkylphenone structure, an acylphosphine oxide structure, or an acylphosphine sulfide structure. The ink composition according to <1> or <2>, wherein the ink composition is a structure selected from the group consisting of an α-haloketone structure, an α-halosulfone structure, and an α-halophenylglyoxalate structure,
<4> The structure according to any one of the above items <1> to <3>, wherein the polymerization initiation species generation structure is a structure selected from the group consisting of a benzophenone structure, a thioxanthone structure, a 1,2-diketone structure, and an anthraquinone structure. Ink composition,
<5> The ink composition according to any one of the above <1> to <4>, wherein the dendritic polymer has five or more polymerization initiation species generation structures at its terminals.
<6> The ink composition according to any one of <1> to <5>, wherein the dendritic polymer has at least one compatible group and / or ionic group at the terminal.
<7> The ink composition according to any one of <1> to <6>, wherein the dendritic polymer has one or more compatible groups at its terminal.
<8> The ink composition according to any one of <1> to <7>, wherein the dendritic polymer is a hyperbranched polymer.
<9> The ink composition according to any one of the above items <1> to <8>, which is for inkjet recording.
<10> (A ′) a step of discharging the ink composition according to any one of the above <1> to <9> on a recording medium, and (B ′) the discharged ink composition Irradiating actinic radiation to cure the ink composition;
<11> The actinic radiation is irradiated by a light emitting diode that generates ultraviolet rays having an emission peak wavelength in a range of 350 to 420 nm and a maximum illuminance on a recording medium surface of 10 to 2,000 mW / cm ^2. The inkjet recording method according to <10>, wherein
<12> A printed matter recorded by the inkjet recording method according to <10> or <11>.

  According to the present invention, an ink composition that is excellent in curability with respect to irradiation with actinic radiation, has excellent image flexibility, adhesion to a substrate, and blocking properties obtained by curing the ink composition, and In addition, an ink jet recording method using the ink composition and a printed matter can be provided.

(1) Ink composition The ink composition of the present invention (hereinafter also simply referred to as “ink”) has (A) N-vinyl lactams and (B) one or more polymerization initiation species generating structures at the end. It contains the dendritic polymer which has.
Hereinafter, the present invention will be described in detail.

The term “radiation” as used in the present invention is not particularly limited as long as it is an actinic radiation that can impart energy capable of generating a starting species in the ink composition by the irradiation, and widely includes α rays, γ rays, X Among them, ultraviolet rays and electron beams are preferable, and ultraviolet rays and electron beams are particularly preferable from the viewpoints of curing sensitivity and device availability. Therefore, the ink composition of the present invention is preferably an ink composition that can be cured by irradiating ultraviolet rays as radiation.
In addition, when the ink composition of the present invention is used, the polymerization initiator and the reaction decomposition product are less likely to move in the printed image, soaking out of the image surface, dispersion outside the image, penetration into the recording medium, etc. Therefore, safety is improved, and the ink composition of the present invention can be suitably used particularly for food packaging.

(A) N-vinyl lactams The ink composition of the present invention contains N-vinyl lactams. Preferable examples of N-vinyl lactams include compounds represented by the following formula (I).

  In the formula (I), n represents an integer of 1 to 5, and n is 2 to 4 from the viewpoints of flexibility after the ink composition is cured, adhesion to a recording medium, and availability of raw materials. It is preferable that n is an integer of 2 or 4, and n is 4, that is, N-vinylcaprolactam is particularly preferable. N-vinylcaprolactam is preferable because it is excellent in safety, is generally available and can be obtained at a relatively low price, and provides particularly good ink curability and adhesion of a cured film to a recording medium.

  The N-vinyl lactams may have a substituent such as an alkyl group or an aryl group on the lactam ring, and may be linked with a saturated or unsaturated ring structure.

The preferred content of (A) N-vinyl lactam in the ink composition of the present invention is in the range of 10 wt% to 40 wt%. N-vinyl lactams are compounds having a relatively high melting point. A content of 40% by weight or less is preferable because it shows good solubility even at a low temperature of 0 ° C. or less, and the temperature range in which the ink composition can be handled becomes wide. Moreover, since it is excellent in sclerosis | hardenability, a cured film softness | flexibility, and the base-material adhesiveness of a cured film, it is preferable that it is a content rate of 10 weight% or more. More preferably, it is in the range of 12 wt% or more and 40 wt% or less, and particularly preferably in the range of 15 wt% or more and 35 wt% or less.
The N-vinyl lactams may be included in the ink composition alone or in a plurality of types.

(B) Dendritic polymer having at least one polymerization initiating species generating structure at the terminal The ink composition of the present invention has a dendritic polymer having at least one polymerization initiating species generating structure at the terminal (hereinafter referred to as “polymer polymerization”). Also referred to as “initiator”).
The dendritic polymer having one or more polymerization-initiating species-generating structures that can be used in the present invention has a structure capable of generating a polymerization-initiating species by actinic radiation or heat at the end of the branched chain. It is a multi-branched polymer having at least one branched end group. If the location where the polymerization initiating species generation structure is present in the dendritic polymer is in the center, the polymerization initiating species cannot sufficiently react in the ink composition due to factors such as steric hindrance.

The dendritic polymer in the polymer polymerization initiator indicates a polymer having many branch points and is also referred to as a multi-branched polymer.
The dendritic polymer includes a dendrimer, a hyperbranched polymer, a star polymer that is a polymer in which a polymer chain that becomes three or more arms is connected by a core that is the center of the arm, and one or more main chains and a structure. A graft polymer which is a polymer having side chains with different steric configurations and the like can be exemplified. Among these, a dendrimer or a hyperbranched polymer is preferable, and a hyperbranched polymer is more preferable.

The dendrimer in the present invention refers to a multi-branched compound having a regular branched structure and a uniform molecular weight. Even if it has a plurality of branched chain portions centering on the core portion, it has a low regularity. It does not include a branch polymer or a compound in which the branched chain portion is linear and does not have a branched structure.
For dendrimers, see Angew. Chem. , Int. Ed. , 38, P884 (1999).
As a method for synthesizing the dendrimer, a known method can be used. A divergent method in which the synthesis proceeds from the core toward the outside, a convergent method in which the synthesis proceeds from the terminal functional group toward the inside, or a combination of the two. There are many examples of reports.
Examples of the preparation of dendrimers include NEWCOME, G. et al. R. As disclosed in other “Dendricular Moleculars: Concepts, Synthesis, Perspectives”, VCH: WEINHEIM, 2001, there is a method of performing multi-step synthesis based on a scheme in which branching and deprotection are repeated. Suitable dendrimers are described in TOMALIA et al., “A new class of polymers: starburst-dendritic macromolecules”, Polym. J. et al. 1985, Vol. 17, p. 117, polyamidoamine (PAMAM) Starburst ^R dendrimer, and HAWKER et al. "Preparation of polymers with controllable molecular architecture, A new convergent." Am. Chem. Soc. 1990, 112, 7638, a polybenzyl ether dendrimer prepared convergently.

The hyperbranched polymer is a mixture of compounds having different molecular weights and different degrees of branching because the structure regulation and molecular weight distribution are not as precise as dendrimers.
The hyperbranched polymer that can be used in the present invention is a multi-branched polymer synthesized by self-condensation of so-called ABx-type molecules having a total of 3 or more of two kinds of substituents in one molecule, or in one molecule. It is a multi-branched polymer synthesized by self-condensation of a molecule having a polymerization initiating group and a polymerizable group, so-called inimer.
For example, the hyperbranched polymer described in the book of Koji Ishizu, “Nanotechnology of Branched Polymer” (2000, IPC Co., Ltd.) can be mentioned.

  Examples of methods for producing these hyperbranched polymers include M.I. As described in Suzuki et al; Macromolecules, 25, 7071 (1992), 31, 1716 (1998), by a ring-opening polymerization of a cyclic compound using a primary amine as a nucleophilic component and a palladium catalyst. Examples include synthesis methods.

In the present invention, not only a polymer obtained by complete hyperbranching polymerization but also a polymer obtained by subcritical polymerization of an A ₂ + B ₃ type monomer, for example, is also obtained. Considered to be a branched polymer (hyperbranched polymer).

A mandatory criterion for fully hyperbranched polymerization is BURCHARD, W. et al. "Solution properties of branched macromolecules", Advances in Polymer Science, 1999, 143, no. II, as disclosed in pp. 113-194, lies in the critical conversion rate when occur gelation of the system and is network structure is obtained (critical conversion) p _c not exist.

Thus, a hyperbranched polymer can be obtained by polycondensation of AB ₂ or AB _m type monomers with complementary functionalities A and B, and only one coupled reaction ( A coupling reaction is a bond between A and B. Details of this type of polyfunctional polycondensation can be found in flory, p. J. et al. , “Molecular size distribution in three-dimensional polymers, VI, Branched polymer con- taining A-R-Bf-1-type units 27, Journal of the Amer.

  Synthetic methods suitable for producing hyperbranched polyphenylenes are described in US Pat. No. 4,857,630 (DU PONT) and KIM, Y. et al. H. “Hyperbranched polyphenylenes”, Polymer Preprints (American Chemical Society, Division of Polymer Chemistry), 1988, 29, no. 2, 310-311.

Further, a hyperbranched polymer production method based on polycondensation of AB ₂ monomer is disclosed in US Pat. No. 5,196,502 (KODAK), US Pat. No. 5,225,522 (KODAK) and US Pat. ing.

Another suitable means for producing hyperbranched polymers is the polymerization of linear AB * type inimers. An inimer is a compound having not only a common moiety capable of linear polymerization, such as a vinyl group or a strained cyclic component, but also a group having a polymerization initiating ability in the same molecule.
For example, VANDENBERG, E.I. J. et al. , "Polymerization of glycoside and its derivatives: a new rearrangement polymerization", Journal of Polymer Science, 1985, Vol. 23, no. 4, pages 915-949, FRECHET, J. et al. "Self-condensing vinyl polymerization: an approach to dendritic materials", Science (Washington, DC), 1995, 269, no. Cyclic inimers were used in the preparation of hyperbranched polymers in US Pat. No. 5,227, p.

There may be not only linear AB type compounds (usually referred to as “linear copolymerization monomers”) but also poly-B-functional compounds of B _f structure, which are generally referred to as “central molecules”. Is displayed. As well as an overview of structural functionality, a rigorous definition of the degree of branching (DB), a related parameter related to the functionality of the hyperbranched polymer, is also described in HOLTER, D. et al. Et al., “Degree of branching in hyperbranched polymers”, Acta Polymerica. 1997, Vol. 23, no. 48, pp. 30-35, HOLTER, E .; J. et al. “Degree of branching (DB) in hyperbranched polymers, Part 2, Enhancement of the DB, Scope and limitations”, Acta Polymerica. 1997, 48, no. 8, pages 298-309 and FREY, H. et al. Other, “Degree of branching in hyperbranched polymers, Part 3, Polymerization of AB monomers with AB and AB monomers, Journal of 99. 2-3, pages 67-76.

The latest technologies related to hyperbranched polymer research are reviewed below:
(A) JIKEI, M .; "Hyperbranched polymers: a promising new class of materials", Progress in Polymer Science, 2001, 26, no. 8, pp. 1233-1285,
(B) NEWCOME, G .; R. Others, “Dendricular Moleculars: Concepts, Synthesis, Perspectives”, VCH: WEINHEIM, 2001,
(C) KIM, Y. “Hyperbranched Polymers 10 years after”, Journal of Polymer Science, Part A: Polymer Chemistry, 1998, Vol. 36, no. 11, pages 1685 to 1698,
(D) VOIT, B.E. “New developments in hyperbranched polymers”, Journal of Polymer Science, Part A: Polymer Chemistry, 2000, 38, no. 14, pages 2505-2525,
(E) SUNDER, A.M. Et al., "Controlling the growth of polymer trees: concepts and perspectives for hyperbranched polymers", Chemistry--A European Journal. 2000, Vol. 6, no. 14, pp. 2499-2506.
From these comments, hyperbranched polymers are not only distinctly different from regularly branched dendrimers, but are also based on A ₂ + B ₃ polymerization of _two polyfunctional monomers, resulting in a subcritical level of polymerization. It is clear that it is also distinctly different from the branched structure when it is not stopped in (which inevitably results in gelation, ie the formation of a network).

Hyperbranched polymers generally exhibit a broad molecular weight distribution. The polydispersity Mw / Mn is generally 5 or more and more frequently exceeds 10. Recently, a new concept has been introduced based on the slow addition of AB ₂ or potential AB ₂ monomers that display adequate reactivity towards polyfunctional (B _f ) center molecules. Such a procedure is described in RADKE, W. et al. Et al., “Effect of Core-Forming Molecules on Molecular Weight Distribution and Degree of Branching in the Synthesis of Hyperbranched Polymers, 31”, 19 2, pp. 239-248 and HANSELMANN, R.M. , Et al., "Hyperbranched Polymers Prepared via the Core-Dilution / Slow Addition Technique: Computer Simulation of Molecular Weight and 19" 12, pages 3790-3801.

  The size of the hyperbranched polymer for the polymeric initiator suitable for the present invention depends on the application selected. For most inkjet applications, an inkjet ink with a low viscosity, usually less than 100 mPa · s, is required. Therefore, for inkjet applications, the Mw imparted to the hyperbranched polymer is preferably less than 100,000, more preferably less than 50,000, and most preferably less than 20,000.

  The hyperbranched polymer for a polymer initiator that can be used in the present invention is preferably obtained by a method of slowly adding a monomer. The resulting hyperbranched polymer exhibits a narrow polydispersity. In the present invention, a hyperbranched polymer having a polydispersity (Mw / Mn) of less than 3 is particularly suitable.

  Suitable hyperbranched polymers are GAO, C.I. “Hyperbranched polymers: from synthesis to applications”, Progress in Polymer Science, 2000, 29, no. 3, pages 183 to 275.

  Other suitable hyperbranched polymers are shown below in PC-1 to PC-8, but are not limited thereto.

Prior to subjecting the hyperbranched polymer to derivatization with a reactive initiator (derivative), it may be used for terminal grafting. This results in a hyperbranched multiple arm graft star copolymer, which may also be used as a dendritic polymer.
Suitable examples of this type of polymer are SUNDER, A. et al. “Hyperbranched Polymer-Polyols Based on Polyglycol: Polarity Design by Block Copolymerization with Propylene Oxide”, Macromolecules, 2000, 33. 2, pages 309-314 and MAIER, S.M. “Synthesis of poly (glycerol) -block-poly (methyl acrylate) multi-arm star polymers”, Macromolecular Rapid Communications, 2000, 21, no. 5, pages 226-230.

  As the dendritic polymer that can be used in the present invention, any hyperbranched polymer can be used, but hyperbranched polyglycidol or a hyperbranched copolymer of glycidol and another epoxide is particularly preferable. Their preparation can be easily performed in a single step procedure using commercially available monomers such that they exhibit a narrow molecular weight distribution over a wide range of molecular weights. A polymer polymerization initiator in which a polymerization initiating species generating structure is introduced into the terminal portion of such a hyperbranched polymer is particularly preferable.

The preparation of branched polyols based on glycerol units generally involves the reaction of glycidol with a hydrogen-containing compound (eg glycerol) as described in JP 61-43627 (DAICEL CHEM IND.). It is carried out by causing an acid to be present as a catalyst or causing an organic acid to be present as a catalyst as disclosed in JP-A-58-198429 (NIPPON YUSHI). In addition, TOKAR, R.I. Et al., “Cationic polymerization of glycidol: coexistence of the activated monomer and active chain end mechanism”, Macromolecules, 1994, 27, 320 and DWORAK, A. et al. Others, “Cationic polymerisation of glycoside. Polymer structure and polymerization mechanism”, Macromolecular Chemistry and Physics, 1995, 196, no. 6, it is also possible to achieve the polymerization of glycidol by cationic polymerization using a cationic initiator such as BF ₃ as disclosed on pages 1963 to 1970. However, the polydispersity exhibited by the hyperbranched polymer produced by the cationic polymerization method is a value exceeding 3, and it is impossible to control the molecular weight.

  A suitable procedure for producing hyperbranched polyglycerols with controlled molecular weight is disclosed in DE 199447631 (BAYER). It is reported by SUNDER, A.I. Et al., “Controlled Synthesis of Hyperbranched Polyglycers by Ring-Opening Multibranching Polymerization”, Macromolecules, 1999, Vol. 32, no. 13, 4240-4246, by dissolving an initiator, which is a suitable polyol, in diglyme or other hydrocarbon and adding glycidol diluted with hydrocarbon or ether to it. Achieved. Such a monomer is added as a solution having a tetrahydrofuran (THF) content of preferably 20 to 99.9% by weight, more preferably 60 to 90% by weight. Use of a multifunctional initiator facilitates complete incorporation of the initiator.

  The high-molecular polymerization initiator that can be used in the present invention has at least one polymerization-initiating species-generating structure at the terminal portion, preferably at least 5, and most preferably at least 7.

As the polymerization initiating species generating structure, any initiator known in the prior art and a structure for generating a polymerization initiating species in its derivatives can be used.
In general, photoinitiators fall into two general categories. The two main types of photoinitiators are the type of photoinitiator that generates active species during the splitting process and the type of photoinitiator that generates active species during the hydrogen abstraction process.

  Photoinitiators that cause Norrish type I reactions directly generate free radicals that can be photolyzed and initiate polymerization by the homogeneous cleavage mechanism of α-cleavage. The absorbed radiation causes bond cleavage between the carbonyl group and the adjacent carbon.

  A photoinitiator that causes a Norrish type II reaction is activated by radiation, free radicals by drawing hydrogen or drawing electrons from a co-initiator or synergist (which actually becomes a free radical to start). Is generated. The disadvantage of comparing hydrogen abstraction with homogeneous splitting is that a bimolecular reaction is required.

  A polymerization initiation species generating structure that generates radical polymerization initiation species by a Norrish type I reaction is a benzoin ether structure, a benzyl ketal structure, an α, α-dialkoxyacetophenone structure, an α-hydroxyalkylphenone structure, an α-aminoalkylphenone structure An acylphosphine oxide structure, an acylphosphine sulfide structure, an α-haloketone structure, an α-halosulfone structure or an α-halophenylglyoxalate structure can be preferably exemplified.

  The polymerization initiation species generating structure that generates radical polymerization initiation species by the Norrish type II reaction can preferably illustrate a benzophenone structure, a thioxanthone structure, a 1,2-diketone structure or an anthraquinone structure, and more preferably a benzophenone structure.

  In addition, as the polymerization initiating species generation structure, CRIVELLO, J. et al. V. In addition, a structure that can generate a polymerization initiator having the polymerization initiator described in “Photoinitiators for Free Radical Cationic and Anionic Photopolymerization”, Surface Coatings Technology, 1998, III, pages 208 to 224 is also preferable.

There is no restriction | limiting in particular as a manufacturing method of the said polymeric polymerization initiator, A well-known method can be used, for example, the compound and dendritic polymer which have at least 1 sort (s) of polymerization initiation seed production | generation structure are made to react. A polymer polymerization initiator can be obtained.
Various known synthetic reactions can be used as a method of reacting a compound having a polymerization initiating species generating structure with a dendritic polymer. In the case of hyperbranched polyglycidol, esterification and etherification are particularly preferred.

  Although the preferable example of the high molecular polymerization initiator which can be used for this invention is shown below, it is not limited to these. The structure shown is a structure corresponding to one molecular weight having one degree of derivatization in the distribution found in each prepared sample. The structure is an example of a more general structure as one specific example when the molecular weight and the degree of derivatization are various. It goes without saying that each sample is a mixture of individual compounds that are similar but differ in both molecular weight and degree of derivatization, and that their chemical properties can also vary over a wide range of molecular weights.

  Preferred examples of the polymer polymerization initiator that can be used in the present invention include the hyperbranched polyethers shown below.

  R, R1 and R2 of the hyperbranched polyether can be independently selected from R in PE-1 to PE-11 shown below, and R, R1 and R2 are different from each other even though R, R1 and R2 are different from each other. And all two or three of R2 may be the same.

  Moreover, as a polymeric polymerization initiator which can be used for this invention, the hyperbranched polyester shown below can also be illustrated preferably.

  R of the hyperbranched polyester can be arbitrarily selected from R in PES-1 to PES-4 shown below.

Moreover, it is preferable that the polymeric polymerization initiator which can be used for this invention has a compatible group and / or an ionic group further in the terminal part.
The compatible group is a group for improving the compatibility between a polymer polymerization initiator and a polymerizable compound containing N-vinyl lactam, and is a group having an alkyl chain, an aryl chain, an alkoxy chain, or a polyalkoxy chain. Can be preferably exemplified.
The ionic group is a group for improving the solubility in water so that it can be easily dissolved in water or an aqueous solution, and examples thereof include acidic groups and basic groups, salts thereof, carboxyl groups, Preferred examples include a carboxylate group or a salt thereof, a sulfo group, a sulfonate group or a salt thereof, an amino group, or an ammonium group or a salt thereof.
Preferred examples of the polymer polymerization initiator having a compatible group at the terminal that can be used in the present invention include the following hyperbranched polyethers.

R of the hyperbranched polyether can be arbitrarily selected from R in C-1 to C-8 shown below.
Moreover, as a compatible group, the R-COO group in the following C-1 to C-8 is mentioned preferably.

  (B) A suitable amount of the dendritic polymer having one or more polymerization-initiating species-generating structures at the terminals is 1 to 50% by weight of the total weight of the ink, more preferably 1 to 25% by weight of the total weight of the ink. More preferably, it is 2 to 20% by weight.

(C) Colorant When the ink composition of the present invention is used as a clear ink or the like, it is not particularly necessary to form a colored image. However, in order to improve the visibility of the formed image portion, or the ink composition is used. When a colored image is to be formed, a colorant can be contained.

  The colorant that can be used in the present invention is not particularly limited, but pigments and oil-soluble dyes that are excellent in weather resistance and excellent in color reproducibility are preferable, and are arbitrarily selected from known colorants such as soluble dyes. Can be used. The colorant that can be suitably used in the ink composition of the present invention or the ink composition for inkjet recording functions as a polymerization inhibitor in a polymerization reaction that is a curing reaction from the viewpoint of not reducing the sensitivity of the curing reaction by actinic radiation. It is preferred to select compounds that do not.

<Pigment>
Although it does not necessarily limit as a pigment which can be used for this invention, For example, the organic or inorganic pigment of the following number described in a color index can be used.
Examples of red or magenta pigments include Pigment Red 3, 5, 19, 22, 31, 38, 42, 43, 48: 1, 48: 2, 48: 3, 48: 4, 48: 5, 49: 1, 53. : 1, 57: 1, 57: 2, 58: 4, 63: 1, 81, 81: 1, 81: 2, 81: 3, 81: 4, 88, 104, 108, 112, 122, 123, 144 , 146, 149, 166, 168, 169, 170, 177, 178, 179, 184, 185, 208, 216, 226, 257, Pigment Violet 3, 19, 23, 29, 30, 37, 50, 88, Pigment Orange 13, 16, 20, 36,
Pigment Blue 1,15,15: 1,15: 2,15: 3,15: 4,15: 6,16,17-1,22,27,28,29,36,60 as a blue or cyan pigment ,
As a green pigment, Pigment Green 7, 26, 36, 50,
Examples of yellow pigments include Pigment Yellow 1, 3, 12, 13, 14, 17, 34, 35, 37, 55, 74, 81, 83, 93, 94, 95, 97, 108, 109, 110, 120, and 137. , 138, 139, 153, 154, 155, 157, 166, 167, 168, 180, 185, 193,
As the black pigment, Pigment Black 7, 28, 26,
As a white pigment, Pigment White 6, 18, 21
Etc. can be used according to the purpose.

<Oil-soluble dye>
Below, the oil-soluble dye which can be used by this invention is demonstrated.
The oil-soluble dye that can be used in the present invention means a dye that is substantially insoluble in water. Specifically, the solubility in water at 25 ° C. (the weight of the dye that can be dissolved in 100 g of water) is 1 g or less, preferably 0.5 g or less, more preferably 0.1 g or less. Accordingly, the oil-soluble dye means a so-called water-insoluble pigment or oil-soluble dye, and among these, an oil-soluble dye is preferable.

  Among the oil-soluble dyes that can be used in the present invention, any yellow dye can be used. For example, phenols, naphthols, anilines, pyrazolones, pyridones, aryl or heteryl azo dyes having open-chain active methylene compounds as coupling components; for example, azomethine dyes having open-chain active methylene compounds as coupling components; Examples include methine dyes such as benzylidene dyes and monomethine oxonol dyes; quinone dyes such as naphthoquinone dyes and anthraquinone dyes; and other dye species such as quinophthalone dyes, nitro / nitroso dyes, acridine And dyes and acridinone dyes.

  Of the oil-soluble dyes usable in the present invention, any magenta dye can be used. For example, aryl or heteryl azo dyes having phenols, naphthols, anilines as coupling components; for example, azomethine dyes having pyrazolones, pyrazolotriazoles as coupling components; for example arylidene dyes, styryl dyes, merocyanine dyes, oxonol dyes Methine dyes; carbonium dyes such as diphenylmethane dyes, triphenylmethane dyes, xanthene dyes; quinone dyes such as naphthoquinone, anthraquinone, anthrapyridone; condensed polycyclic dyes such as dioxazine dyes, etc. Can be mentioned.

  Among the oil-soluble dyes applicable to the present invention, any cyan dye can be used. For example, indoaniline dyes, indophenol dyes or azomethine dyes having pyrrolotriazoles as coupling components; polymethine dyes such as cyanine dyes, oxonol dyes, merocyanine dyes; carbonium dyes such as diphenylmethane dyes, triphenylmethane dyes, xanthene dyes Phthalocyanine dyes; anthraquinone dyes; for example, aryl or heteryl azo dyes having phenols, naphthols and anilines as coupling components; indigo / thioindigo dyes;

  Each of the above dyes may exhibit yellow, magenta, and cyan colors only after a part of chromophore (chromogenic atomic group) is dissociated. In this case, the counter cation may be an alkali metal or ammonium. Such inorganic cations may be used, and organic cations such as pyridinium and quaternary ammonium salts may be used, and furthermore, polymer cations having such a partial structure may be used.

Although not limited to the following, preferred specific examples include C.I. I. Solvent Black 3, 7, 27, 29 and 34; C.I. I. Solvent Yellow 14, 16, 19, 29, 30, 56, 82, 93 and 162; C.I. I. Solvent Red 1, 3, 8, 18, 24, 27, 43, 49, 51, 72, 73, 109, 122, 132 and 218; I. Solvent Violet 3; C.I. I. Solvent Blue 2,11,25,35,38,67 and 70; I. Solvent Green 3 and 7; I. Solvent orange 2; and the like.
Particularly preferred among these are: Nubian Black PC-0850, Oil Black HBB, Oil Yellow 129, Oil Yellow 105, Oil Pink 312, Oil Red 5B, Oil Scallet 308, Vali Fast Blue chemistry 2606e B2 (Manufactured by Co., Ltd.), Aizen Spiron Blue GNH (manufactured by Hodogaya Chemical Co., Ltd.), Neopen Yellow 075, Neopen Magenta SE1378, Neopen Blue 808, Neopen Blue FF4012, and Neo42 Cy FF4012.
In the present invention, the oil-soluble dye may be used alone or in combination of several kinds.

Moreover, when using an oil-soluble dye as a colorant, other water-soluble dyes, disperse dyes, pigments, and other colorants can be used in combination as long as the effects of the present invention are not impaired.
In the present invention, a disperse dye can be used as long as it is soluble in a water-immiscible organic solvent. The disperse dye generally includes a water-soluble dye, but in the present invention, the disperse dye is preferably used as long as it is soluble in a water-immiscible organic solvent. Preferable specific examples of the disperse dye include C.I. I. Disperse Yellow 5,42,54,64,79,82,83,93,99,100,119,122,124,126,160,184: 1,186,198,199,201,204,224 and 237 C. I. Disperse Orange 13, 29, 31: 1, 33, 49, 54, 55, 66, 73, 118, 119 and 163; I. Disperse Red 54, 60, 72, 73, 86, 88, 91, 92, 93, 111, 126, 127, 134, 135, 143, 145, 152, 153, 154, 159, 164, 167: 1,177 , 181, 204, 206, 207, 221, 239, 240, 258, 277, 278, 283, 311, 323, 343, 348, 356 and 362; I. Disperse Violet 33; C.I. I. Disperse Blue 56, 60, 73, 87, 113, 128, 143, 148, 154, 158, 165, 165: 1, 165: 2, 176, 183, 185, 197, 198, 201, 214, 224, 225 , 257, 266, 267, 287, 354, 358, 365 and 368; I. Disperse Green 6: 1 and 9;

  It is preferable that the colorant that can be used in the present invention is appropriately dispersed in the ink after being added to the ink composition of the present invention or the ink composition for inkjet recording. For dispersing the colorant, for example, a dispersion device such as a ball mill, a sand mill, an attritor, a roll mill, an agitator, a Henschel mixer, a colloid mill, an ultrasonic homogenizer, a pearl mill, a wet jet mill, or a paint shaker can be used.

In preparing the ink composition of the present invention, the colorant may be added by directly adding it together with the respective components. It can also be added after being uniformly dispersed or dissolved.
In the present invention, in order to avoid the problem of deterioration of solvent resistance when the solvent remains in the cured image and the problem of VOC (Volatile Organic Compound) of the remaining solvent, the colorant is a radical polymerizable compound. It is preferable to add and mix in advance in such a dispersion medium. In consideration of only dispersibility, it is preferable to select a monomer having the lowest viscosity as the polymerizable compound used for the addition of the colorant.

  These colorants may be used by appropriately selecting one type or two or more types according to the purpose of use of the ink composition.

When using a colorant such as a pigment that remains solid in the ink composition of the present invention, the average particle diameter of the colorant particles is preferably 0.005 to 0.5 μm, more preferably 0. It is preferable to set the colorant, the dispersant, the dispersion medium, the dispersion conditions, and the filtration conditions so that the thickness is 0.01 to 0.45 μm, more preferably 0.015 to 0.4 μm. This particle size control is preferable because clogging of the head nozzle can be suppressed and ink storage stability, ink transparency, and curing sensitivity can be maintained.
The content of the colorant in the ink composition of the present invention is appropriately selected depending on the color and the purpose of use. Is preferred.

(D) Other polymerizable compound In the ink composition of the present invention, a radical polymerizable compound or a cationic polymerizable compound other than (A) N-vinyllactams is used in combination as the other polymerizable compound as necessary. You can also When a cationic polymerizable compound is used in combination, a cationic polymerization initiator is also preferably used as a polymerization initiator.
The cationically polymerizable compound that can be used in the present invention is not particularly limited as long as it is a compound that initiates a polymerization reaction with an acid generated from a photoacid generator and cures. Cationic polymerizable monomers can be used. Examples of the cationic polymerizable monomer include JP-A-6-9714, JP-A-2001-31892, JP-A-2001-40068, JP-A-2001-55507, JP-A-2001-310938, JP-A-2001-310937, and 2001-2001. Examples thereof include epoxy compounds, vinyl ether compounds, oxetane compounds and the like described in each publication such as No. 220526.

  In addition, as the cationic polymerizable compound, for example, a polymerizable compound applied to a cationic polymerization type photocurable resin is known, and recently, a photo cationic polymerization type sensitized in a visible light wavelength region of 400 nm or more. Examples of the polymerizable compound applied to the photocurable resin are disclosed in JP-A-6-43633 and JP-A-8-324137. These can also be applied to the ink composition of the present invention.

In addition to (A) N-vinyl lactams, the ink composition of the present invention is preferably used in combination with other radical polymerizable compounds. When a radically polymerizable compound is used in combination, an ink composition having further excellent curability can be provided.
In the present invention, it is needless to say that the “radical polymerizable compound” means a radical polymerizable compound excluding N-vinyl lactams.
Examples of the radical polymerizable compound are described in JP-A-7-159983, JP-B-7-31399, JP-A-8-224982, JP-A-10-863, JP-A-9-80675, and the like. A photocurable material using a photopolymerizable composition is known.

  The radical polymerizable compound is a compound having an ethylenically unsaturated bond capable of radical polymerization, and may be any compound as long as it has at least one ethylenically unsaturated bond capable of radical polymerization in the molecule. , Oligomers, polymers and the like having a chemical form. One kind of radically polymerizable compound may be contained in any ratio in order to improve the desired properties, and two or more kinds thereof may be contained.

Examples of the polymerizable compound having an ethylenically unsaturated bond capable of radical polymerization include unsaturated carboxylic acids such as acrylic acid, methacrylic acid, itaconic acid, crotonic acid, isocrotonic acid and maleic acid, esters thereof and salts thereof , Radically polymerizable compounds such as anhydrides having an ethylenically unsaturated group, acrylonitrile, styrene, and various unsaturated polyesters, unsaturated polyethers, unsaturated polyamides, and unsaturated urethanes.
Specifically, 2-ethylhexyl acrylate, 2-hydroxyethyl acrylate, butoxyethyl acrylate, carbitol acrylate, cyclohexyl acrylate, tetrahydrofurfuryl acrylate, benzyl acrylate, bis (4-acryloxypolyethoxyphenyl) propane, neopentyl glycol Diacrylate, 1,6-hexanediol diacrylate, ethylene glycol diacrylate, diethylene glycol diacrylate, triethylene glycol diacrylate, tetraethylene glycol diacrylate, polyethylene glycol diacrylate, polypropylene glycol diacrylate, pentaerythritol triacrylate, pentaerythritol Tetraacrylate, dipentaery Acrylic acid derivatives such as lithol tetraacrylate, trimethylolpropane triacrylate, tetramethylol methane tetraacrylate, oligoester acrylate, N-methylol acrylamide, diacetone acrylamide, epoxy acrylate, methyl methacrylate, n-butyl methacrylate, 2-ethylhexyl methacrylate , Lauryl methacrylate, allyl methacrylate, glycidyl methacrylate, benzyl methacrylate, dimethylaminomethyl methacrylate, 1,6-hexanediol dimethacrylate, ethylene glycol dimethacrylate, triethylene glycol dimethacrylate, polyethylene glycol dimethacrylate, polypropylene glycol dimethacrylate, trimethylol Methacryl derivatives such as tan trimethacrylate, trimethylolpropane trimethacrylate, 2,2-bis (4-methacryloxypolyethoxyphenyl) propane, and other derivatives of allyl compounds such as allyl glycidyl ether, diallyl phthalate, triallyl trimellitate More specifically, Shinzo Yamashita “Cross-linking agent handbook” (1981, Taiseisha); Kato Kiyosumi “UV / EB curing handbook (raw material)” (1985, Polymer publication society) Radtech Research Group, “Application and Market of UV / EB Curing Technology”, page 79 (1989, CMC); Eiichiro Takiyama “Polyester Resin Handbook” (1988, Nikkan Kogyo Shimbun) Radically polymerizable or crosslinkable monomers, oligomers and Polymers can be used.

<Preferred radical polymerizable compound>
As the radical polymerizable compound that can be used in the present invention, (meth) acrylic acid esters such as (meth) acrylic monomers or prepolymers, epoxy monomers or prepolymers, urethane monomers or prepolymers are preferably used. More preferably, they are the following compounds.

  That is, 2-ethylhexyl-diglycol acrylate, 2-hydroxy-3-phenoxypropyl acrylate, 2-hydroxybutyl acrylate, hydroxypivalate neopentyl glycol diacrylate, 2-acryloyloxyethyl phthalate, methoxy-polyethylene glycol acrylate, Tetramethylol methane triacrylate, 2-acryloyloxyethyl-2-hydroxyethylphthalic acid, dimethylol tricyclodecane diacrylate, ethoxylated phenyl acrylate, 2-acryloyloxyethyl succinic acid, nonylphenol EO adduct acrylate, modified glycerin Triacrylate, bisphenol A diglycidyl ether acrylic acid adduct, modified bisphenol A diacrylate, phenoxy Reethylene glycol acrylate, 2-acryloyloxyethyl hexahydrophthalic acid, bisphenol A PO adduct diacrylate, bisphenol A EO adduct diacrylate, dipentaerythritol hexaacrylate, pentaerythritol triacrylate tolylene diisocyanate urethane prepolymer, Lactone modified flexible acrylate, butoxyethyl acrylate, propylene glycol diglycidyl ether acrylic acid adduct, pentaerythritol triacrylate hexamethylene diisocyanate urethane prepolymer, 2-hydroxyethyl acrylate, methoxydipropylene glycol acrylate, ditrimethylolpropane tetraacrylate, Pentaerythritol triacrylate hexa Chi diisocyanate urethane prepolymer, stearyl acrylate, isoamyl acrylate, isomyristyl acrylate, isostearyl acrylate, and the like.

  These acrylate compounds can lower the viscosity relatively than the polymerizable compounds conventionally used in UV curable inks, provide stable ink ejection properties, and good polymerization sensitivity and adhesion to the recording medium. Therefore, it is preferable.

  In the present invention, the monomers listed as the polymerizable compound described above are preferable because they have high reactivity, low viscosity, and excellent adhesion to a recording medium.

  When the radically polymerizable compound is used in combination, the weight content ratio of the (A) N-vinyl lactam and the radically polymerizable compound in the ink composition is preferably 1: 9 to 1: 1. The ratio is preferably 1: 7 to 1: 1, and particularly preferably 1: 5 to 1: 1. By combining within the above ranges, better curability, flexibility of the cured film, and substrate adhesion of the cured film can be obtained.

  In the present invention, oligomers and polymers can be used together. Here, an oligomer means a compound having a molecular weight (weight average molecular weight for those having a molecular weight distribution) of 2,000 or more, and a polymer has a molecular weight (weight average molecular weight for those having a molecular weight distribution) of 10. Means more than 1,000 compounds. The oligomer or polymer may or may not have a radical polymerizable group. When the radically polymerizable group in one molecule of the oligomer or polymer is 4 or less (in terms of a compound having a molecular weight distribution, the average of the total number of molecules contained is 4 or less), an ink composition having excellent flexibility can be obtained. preferable. It can also be preferably used in the sense that the viscosity of the ink is adjusted to an optimum viscosity for jetting.

(E) Dispersant It is preferable to add a dispersant when dispersing the colorant. The type of the dispersant is not particularly limited, but a polymer dispersant is preferably used.
Dispersor BYK-101, DisperBYK-102, DisperBYK-103, DisperBYK-106, DisperBYK-111, DisperBYK-161, DisperBYK-162, DisperBYK-164D, DisperBYK-164D, , DisperBYK-168, DisperBYK-170, DisperBYK-171, DisperBYK-174, DisperBYK-182 (manufactured by BYK Chemie), EFKA4010, EFKA4046, EFKA5080, EFKA5504, EFKA5504, EFKA5504, 62, polymer dispersing agents such as EFKA7500, EFKA7570, EFKA7575, EFKA7580 (manufactured by Fuka Additive), Disperse Aid 6, Disperse Aid 8, Disperse Aid 15, Disperse Aid 9100 (San Nopco); Solsperse) 3000, 5000, 9000, 12000, 13240, 13940, 17000, 24000, 26000, 28000, 32000, 36000, 39000, 41000, 71000, etc. (Abyssia); Adeka Pluronic L31, F38, L42, L44, L61, L64, F68, L72, P95, F77, P84, F87, P94, L101, P103, F108, L121, P-123 ( Manufactured by Denka Co., Ltd.) and Isonet S-20 (manufactured by Sanyo Chemical Co., Ltd.), “Disparon KS-860, 873SN, 874 (polymer dispersant), # 2150 (aliphatic polycarboxylic acid), # 7004 (polyether ester type) ”.
In addition, pigment derivatives such as a phthalocyanine derivative (trade name: EFKA-745 (manufactured by Efka)), Solsperse 5000, 12000, Solsperse 22000 (manufactured by Avicia) can also be used.
The content of the dispersant in the ink composition of the present invention is appropriately selected depending on the purpose of use, but generally it is preferably 0.01 to 5% by weight with respect to the total weight of the ink composition.

(F) Surfactant It is preferable to add a surfactant to the ink composition of the present invention in order to impart stable discharge properties for a long time.
Examples of the surfactant include those described in JP-A Nos. 62-173463 and 62-183457. For example, anionic surfactants such as dialkylsulfosuccinates, alkylnaphthalenesulfonates, fatty acid salts, polyoxyethylene alkyl ethers, polyoxyethylene alkyl allyl ethers, acetylene glycols, polyoxyethylene / polyoxypropylene blocks Nonionic surfactants such as copolymers, and cationic surfactants such as alkylamine salts and quaternary ammonium salts. An organic fluoro compound may be used in place of the surfactant. The organic fluoro compound is preferably hydrophobic. Examples of the organic fluoro compounds include fluorine surfactants, oily fluorine compounds (eg, fluorine oil) and solid fluorine compound resins (eg, tetrafluoroethylene resin). No. (columns 8 to 17) and those described in JP-A Nos. 62-135826.
The content of the surfactant in the ink composition of the present invention is appropriately selected depending on the purpose of use, but generally it is preferably 0.0001 to 1% by weight with respect to the total weight of the ink composition. .

  If necessary, other components can be added to the ink composition of the present invention. Examples of other components include sensitizers, co-sensitizers, other polymerization initiators, ultraviolet absorbers, antioxidants, anti-fading agents, conductive salts, solvents, polymer compounds, basic compounds, and the like. Can be mentioned.

<Sensitizer>
A sensitizer may be added to the ink composition of the present invention to absorb specific actinic radiation and promote decomposition of the polymer polymerization initiator, particularly when used for inkjet recording. The sensitizer absorbs specific actinic radiation and enters an electronically excited state. The sensitizer in an electronically excited state comes into contact with the polymerization initiator, and effects such as electron transfer, energy transfer, and heat generation occur. As a result, the polymerization initiator undergoes a chemical change and decomposes to generate radicals, acids or bases.
The sensitizer that can be used in the present invention is preferably a sensitizing dye.
Examples of preferred sensitizing dyes include those belonging to the following compounds and having an absorption wavelength in the 350 nm to 450 nm region.
Polynuclear aromatics (eg, pyrene, perylene, triphenylene), xanthenes (eg, fluorescein, eosin, erythrosine, rhodamine B, rose bengal), cyanines (eg, thiacarbocyanine, oxacarbocyanine), merocyanines ( For example, merocyanine, carbomerocyanine), thiazines (for example, thionine, methylene blue, toluidine blue), acridines (for example, acridine orange, chloroflavin, acriflavine), anthraquinones (for example, anthraquinone), squalium (for example, squalium) ), Coumarins (eg 7-diethylamino-4-methylcoumarin).

  More preferable examples of the sensitizing dye include compounds represented by the following formulas (IX) to (XIII).

In the formula (IX), A ¹ represents a sulfur atom or NR ⁵⁰ , R ⁵⁰ represents an alkyl group or an aryl group, and L ² forms a basic nucleus of the dye together with the adjacent A ¹ and the adjacent carbon atom. R ⁵¹ and R ⁵² each independently represent a hydrogen atom or a monovalent nonmetallic atomic group, and R ⁵¹ and R ⁵² may be bonded to each other to form an acidic nucleus of the dye. Good. W represents an oxygen atom or a sulfur atom.

In formula (X), Ar ¹ and Ar ² each independently represent an aryl group and are linked via a bond with —L ³ —. Here, L ³ represents —O— or —S—. W is synonymous with that shown in Formula (IX).

In the formula (XI), A ₂ represents a sulfur atom or NR ⁵⁹ , L ⁴ represents a nonmetallic atomic group that forms a basic nucleus of the dye together with adjacent A ₂ and a carbon atom, R ⁵³ , R ⁵⁴ , R ⁵⁵ , R ⁵⁶ , R ⁵⁷ and R ⁵⁸ each independently represents a monovalent nonmetallic atomic group, and R ⁵⁹ represents an alkyl group or an aryl group.

In formula (XII), A ³ and A ⁴ each independently represent —S—, —NR ⁶² — or —NR ⁶³ —, wherein R ⁶² and R ⁶³ each independently represent a substituted or unsubstituted alkyl group, substituted or Represents an unsubstituted aryl group, and L ⁵ and L ⁶ each independently represent a nonmetallic atomic group that forms a basic nucleus of a dye in combination with adjacent A ³ , A ^4, and adjacent carbon atoms, and R ⁶⁰ , R ⁶¹ each independently represents a hydrogen atom or a monovalent non-metallic atomic group, or may be bonded to each other to form an aliphatic or aromatic ring.

In the formula (XIII), R ⁶⁶ represents an aromatic ring or a hetero ring which may have a substituent, and A ⁵ represents an oxygen atom, a sulfur atom or ═NR ⁶⁷ . R ⁶⁴ , R ⁶⁵ and R ⁶⁷ each independently represent a hydrogen atom or a monovalent non-metallic atomic group; R ⁶⁷ and R ⁶⁴ , and R ⁶⁵ and R ⁶⁷ each represent an aliphatic or aromatic ring. Can be combined to form.

  Preferable specific examples of the compounds represented by formulas (IX) to (XIII) include (E-1) to (E-20) shown below.

  The content of the sensitizer in the ink composition of the present invention is appropriately selected depending on the purpose of use, but generally it is preferably 0.05 to 4% by weight based on the weight of the whole ink composition. .

<Co-sensitizer>
The ink composition of the present invention preferably contains a co-sensitizer. In the present invention, the co-sensitizer has functions such as further improving the sensitivity of the sensitizer to actinic radiation or suppressing polymerization inhibition of the polymerizable compound by oxygen.
Examples of such co-sensitizers include amines such as MR Sander et al., "Journal of Polymer Society", Vol. 10, p. Publication, JP 52-134692, JP 59-138205, JP 60-84305, JP 62-18537, JP 64-33104, Research Disclosure 33825 Specific examples thereof include triethanolamine, p-dimethylaminobenzoic acid ethyl ester, p-formyldimethylaniline, p-methylthiodimethylaniline and the like.

  Other examples of co-sensitizers include thiols and sulfides such as thiol compounds described in JP-A-53-702, JP-B-55-500806, JP-A-5-142772, No. 56-75643, such as 2-mercaptobenzothiazole, 2-mercaptobenzoxazole, 2-mercaptobenzimidazole, 2-mercapto-4 (3H) -quinazoline, β-mercapto. And naphthalene.

Other examples include amino acid compounds (eg, N-phenylglycine), organometallic compounds described in Japanese Patent Publication No. 48-42965 (eg, tributyltin acetate), and hydrogen described in Japanese Patent Publication No. 55-34414. Donors, sulfur compounds described in JP-A-6-308727 (eg, trithiane), phosphorus compounds described in JP-A-6-250387 (diethyl phosphite, etc.), Si-- described in JP-A-8-54735 H, Ge-H compound, etc. are mentioned.
The content of the co-sensitizer in the ink composition of the present invention is appropriately selected depending on the purpose of use, but is generally 0.05 to 4% by weight with respect to the weight of the entire ink composition. preferable.

<Other polymerization initiators>
The ink composition of the present invention may contain another polymerization initiator in addition to (B) a dendritic polymer having one or more polymerization initiation species generating structures at its terminals. As other polymerization initiators that can be used in the present invention, known polymerization initiators can be used. The polymerization initiator that can be used in the present invention may be used alone or in combination of two or more. Moreover, when using together a cationically polymerizable compound, it is preferable to use together the dendritic polymer which has (B) 1 or more polymerization initiation seed production | generation structures in the terminal, and a cationic polymerization initiator.
Another polymerization initiator that can be used in the ink composition of the present invention is a compound that generates a polymerization initiating species by absorbing external energy. External energy used for initiating polymerization is roughly divided into heat and actinic radiation, and a thermal polymerization initiator and a photopolymerization initiator are used, respectively. Examples of the active radiation include γ rays, β rays, electron beams, ultraviolet rays, visible rays, and infrared rays.

[Radical polymerization initiator]
The radical polymerization initiator that can be used in the present invention includes (a) aromatic ketones, (b) acylphosphine compounds, (c) aromatic onium salt compounds, (d) organic peroxides, and (e) thio compounds. (F) hexaarylbiimidazole compound, (g) ketoxime ester compound, (h) borate compound, (i) azinium compound, (j) metallocene compound, (k) active ester compound, (l) carbon halogen bond And (m) an alkylamine compound. These radical polymerization initiators may use the above compounds (a) to (m) alone or in combination. The radical polymerization initiator in the present invention is preferably used alone or in combination of two or more.

  Preferred examples of (a) aromatic ketones, (b) acylphosphine compounds, and (e) thio compounds include “RADIATION CURING IN POLYMER SCIENCE AND TECHNOLOGY” P. FOUASSIER J.M. F. RABEK (1993), pp. Examples include compounds having a benzophenone skeleton or a thioxanthone skeleton described in 77-117. More preferable examples include α-thiobenzophenone compounds described in JP-B-47-6416, benzoin ether compounds described in JP-B-47-3981, α-substituted benzoin compounds described in JP-B-47-22326, Benzoin derivatives described in JP-B-47-23664, aroylphosphonic acid esters described in JP-A-57-30704, dialkoxybenzophenones described in JP-B-60-26483, JP-B-60-26403, JP-A Benzoin ethers described in JP-A-62-81345, JP-B-1-34242, US Pat. No. 4,318,791, α-aminobenzophenones described in European Patent 0284561A1, JP-A-2-21152 P-Di (dimethylaminobenzoyl) benze Thio-substituted aromatic ketones described in JP-A-61-194062, acylphosphine sulfides described in JP-B-2-9597, acylphosphines described in JP-B-2-9596, and JP-B-63-61950 Thioxanthones, and coumarins described in JP-B-59-42864.

  (C) As aromatic onium salt compounds, elements of Groups 15, 16 and 17 of the periodic table, specifically N, P, As, Sb, Bi, O, S, Se, Te, or I fragrances Group onium salts are included. For example, iodonium salts described in European Patent No. 104143, US Pat. No. 4,837,124, Japanese Patent Laid-Open No. 2-150848, Japanese Patent Laid-Open No. 2-96514, European Patent Nos. 370693, 233567, and 297443 are disclosed. The diazonium salts described in the specifications of U.S. Pat. Nos. 2,974,279, 279210, and 422570, U.S. Pat. Nos. 3,902,144, 4,933,377, 4,760013, 4,734,344, and 2,833,827 Benzenediazonium which may have a substituent), diazonium salt resins (formaldehyde resin of diazodiphenylamine, etc.), N-alkoxypyridinium salts, etc. (for example, US Pat. No. 4,743,528, JP-A-63) -138345, JP-A-63 142345, JP-A-63-142346, and JP-B-46-42363, specifically 1-methoxy-4-phenylpyridinium tetrafluoroborate, etc. The compounds described in JP-A 52-147277, 52-14278, and 52-14279 are preferably used. Generates radicals and acids as active species.

  (D) The organic peroxide includes almost all organic compounds having one or more oxygen-oxygen bonds in the molecule. Examples thereof include 3,3 ′, 4,4′-tetra (t -Butylperoxycarbonyl) benzophenone, 3,3 ', 4,4'-tetra (t-amylperoxycarbonyl) benzophenone, 3,3', 4,4'-tetra (t-hexylperoxycarbonyl) benzophenone, 3,3 ′, 4,4′-tetra (t-octylperoxycarbonyl) benzophenone, 3,3 ′, 4,4′-tetra (cumylperoxycarbonyl) benzophenone, 3,3 ′, 4,4′- Peroxyester compounds such as tetra (p-isopropylcumylperoxycarbonyl) benzophenone and di-t-butyldiperoxyisophthalate are preferred. .

  (F) Examples of hexaarylbiimidazole compounds include lophine dimers described in JP-B Nos. 45-37377 and 44-86516, such as 2,2′-bis (o-chlorophenyl) -4,4 ′, 5,5′-tetraphenylbiimidazole, 2,2′-bis (o-bromophenyl) -4,4 ′, 5,5′tetraphenylbiimidazole, 2,2′-bis (o, p-dichlorophenyl) -4,4 ', 5,5'-tetraphenylbiimidazole, 2,2'-bis (o-chlorophenyl) -4,4', 5,5'-tetra (m-methoxyphenyl) biimidazole, 2, 2′-bis (o, o′-dichlorophenyl) -4,4 ′, 5,5′-tetraphenylbiimidazole, 2,2′-bis (o-nitrophenyl) -4,4 ′, 5,5 ′ − Traphenylbiimidazole, 2,2′-bis (o-methylphenyl) -4,4 ′, 5,5′-tetraphenylbiimidazole, 2,2′-bis (o-trifluorophenyl) -4,4 Examples include ', 5,5'-tetraphenylbiimidazole.

  (G) Examples of the ketoxime ester compound include 3-benzoyloxyiminobutane-2-one, 3-acetoxyiminobutane-2-one, 3-propionyloxyiminobutane-2-one, and 2-acetoxyiminopentane-3. -One, 2-acetoxyimino-1-phenylpropan-1-one, 2-benzoyloxyimino-1-phenylpropan-1-one, 3-p-toluenesulfonyloxyiminotan-2-one, 2-ethoxy And carbonyloxyimino-1-phenylpropan-1-one.

  (H) Examples of the borate compound include compounds described in US Pat. Nos. 3,567,453, 4,343,891, European Patents 109,772, and 109,773. Can be mentioned.

  (I) Examples of azinium salt compounds include JP-A-63-138345, JP-A-63-142345, JP-A-63-142346, JP-A-63-143537, and JP-B-46-42363. The compound group which has NO bond of each gazette description can be mentioned.

  (J) Examples of metallocene compounds include titanocenes described in JP-A-59-152396, JP-A-61-151197, JP-A-63-41484, JP-A-2-249, and JP-A-2-4705. Examples thereof include iron-arene complexes described in JP-A-1-304453 and JP-A-1-152109.

  Specific examples of the titanocene compound include di-cyclopentadienyl-Ti-di-chloride, di-cyclopentadienyl-Ti-bis-phenyl, and di-cyclopentadienyl-Ti-bis-2,3. 4,5,6-pentafluorophen-1-yl, di-cyclopentadienyl-Ti-bis-2,3,5,6-tetrafluorophen-1-yl, di-cyclopentadienyl-Ti- Bis-2,4,6-trifluorophen-1-yl, di-cyclopentadienyl-Ti-2,6-difluorophen-1-yl, di-cyclopentadienyl-Ti-bis-2,4 -Difluorophen-1-yl, di-methylcyclopentadienyl-Ti-bis-2,3,4,5,6-pentafluorophen-1-yl, di-methylcyclopentadienyl-Ti- -2,3,5,6-tetrafluorophen-1-yl, di-methylcyclopentadienyl-Ti-bis-2,4-difluorophen-1-yl, bis (cyclopentadienyl) -bis (2,6-difluoro-3- (pyridin-1-yl) phenyl) titanium, bis (cyclopentadienyl) bis [2,6-difluoro-3- (methylsulfonamido) phenyl] titanium, bis (cyclopenta And dienyl) bis [2,6-difluoro-3- (N-butylbialoyl-amino) phenyl] titanium.

  (K) Examples of the active ester compound include the specifications of European Patent Nos. 0290750, 046083, 156153, 271851, and 0388343, U.S. Pat. Nos. 3,901,710, and 4,181,531. Nitrobenzol ester compounds described in JP-A-60-198538 and JP-A-53-133022, European Patents 0199672, 84515, 199672, 0441115, and 0101122. No. 4,618,564, U.S. Pat. No. 4,371,605, and U.S. Pat. No. 4,431,774, JP-A 64-18143, JP-A 2-245756, and JP-A-4-365048. Iminosulfonate compound, Japanese Examined Patent Publication No. 62-6223, Japanese Examined Publication No. 63 No. 14340, and compounds, and the like described in the JP-A No. 59-174831.

  (L) Preferable examples of the compound having a carbon halogen bond include, for example, compounds described in Wakabayashi et al., Bull. Chem. Soc. Japan, 42, 2924 (1969), compounds described in British Patent No. 1388492, Examples thereof include compounds described in Japanese Utility Model Publication No. 53-133428, compounds described in German Patent No. 3337024, and the like.

  Further, compounds described in J. Org. Chem., 29, 1527 (1964) by FC Schaefer et al., Compounds described in JP-A-62-258241, compounds described in JP-A-5-281728, and the like can be mentioned. it can. A compound as described in German Patent No. 2641100, a compound described in German Patent No. 3333450, a compound group described in German Patent No. 3021590, or a compound group described in German Patent No. 3021599, etc. Can be mentioned.

(Cationic polymerization initiator)
In the ink composition of the present invention, as described later, when a cationic polymerizable compound is used in combination, it is preferable to use a cationic polymerization initiator in combination.

First, B (C ₆ F ₅ ) ₄ ⁻ , PF ₆ ⁻ , AsF ₆ ⁻ , SbF ₆ ⁻ , CF ₃ SO ₃ ⁻ salt of aromatic onium compounds such as diazonium, ammonium, iodonium, sulfonium, phosphonium, etc. be able to. Secondly, sulfonated products that generate sulfonic acid can be mentioned. Thirdly, a halide that generates hydrogen halide can also be used. Fourthly, an iron allene complex can be mentioned.

  Examples of cationic polymerization initiators [(b-1) to (b-96)] suitably used in the present invention are listed below, but the present invention is not limited thereto.

In the ink composition of the present invention, the total amount of (B) the dendritic polymer having one or more polymerization initiation species generating structures at the terminal and the other polymerization initiator is the amount of the polymerizable compound containing N-vinyllactams. Preferably it is 0.01 to 35 weight% with respect to the total usage, More preferably, it is 0.5 to 20 weight%, More preferably, it is the range of 1.0 to 15 weight%. The ink composition can be cured at 0.01% by weight or more, and a cured film having a uniform degree of curing can be obtained at 35% by weight or less.
When the sensitizer described later is used in the ink composition of the present invention, the total amount of (B) the dendritic polymer having one or more polymerization initiation species generating structures at the terminal and other polymerization initiators is increased. The weight ratio of polymerization initiator to sensitizer with respect to the sensitizer is preferably 200: 1 to 1: 200, more preferably 50: 1 to 1:50, and even more preferably 20: 1 to 1: 5. It is a range.

<Ultraviolet absorber>
In the present invention, an ultraviolet absorber can be used from the viewpoint of improving the weather resistance of the obtained image and preventing discoloration.
Examples of the ultraviolet absorber are described in JP-A-58-185679, JP-A-61-190537, JP-A-2-782, JP-A-5-97075, JP-A-9-34057, and the like. Benzotriazole compounds, benzophenone compounds described in JP-A No. 46-2784, JP-A No. 5-194843, US Pat. No. 3,214,463, etc., JP-B Nos. 48-30492 and 56-21141 Cinnamic acid compounds described in JP-A-10-88106, JP-A-4-298503, JP-A-8-53427, JP-A-8-239368, JP-A-10-182621, JP The triazine compounds described in JP-A-8-501291, Research Disclosure No. Examples thereof include compounds described in US Pat. No. 24239, stilbene-based and benzoxazole-based compounds that absorb ultraviolet rays and emit fluorescence, so-called fluorescent brighteners.
Although the addition amount is appropriately selected according to the purpose, it is preferably 0.5 to 15% by weight in terms of solid content.

<Antioxidant>
An antioxidant can be added to improve the stability of the ink composition. Examples of the antioxidant include European published patents, 223739, 309401, 309402, 310551, 310552, 359416, and 3435443. JP, 54-85535, 62-262417, 63-113536, 63-163351, JP-A-2-262654, JP-A-2-71262, Examples thereof include those described in Kaihei 3-121449, JP-A-5-61166, JP-A-5-119449, US Pat. No. 4,814,262, US Pat. No. 4,980,275, and the like.
Although the addition amount is appropriately selected according to the purpose, it is preferably 0.1 to 8% by weight in terms of solid content.

<Anti-fading agent>
In the ink composition of the present invention, various organic and metal complex anti-fading agents can be used. Examples of the organic anti-fading agent include hydroquinones, alkoxyphenols, dialkoxyphenols, phenols, anilines, amines, indanes, chromans, alkoxyanilines, and heterocycles. Examples of the metal complex anti-fading agent include nickel complexes and zinc complexes. No. 17643, VII, I to J, No. 15162, ibid. No. 18716, page 650, left column, ibid. No. 36544 at page 527, ibid. 307105, page 872, ibid. The compounds described in the patent cited in No. 15162 and the compounds included in the general formulas and compound examples of representative compounds described in JP-A-62-215272, pages 127 to 137 can be used. .
Although the addition amount is appropriately selected according to the purpose, it is preferably 0.1 to 8% by weight in terms of solid content.

<Conductive salts>
Conductive salts such as potassium thiocyanate, lithium nitrate, ammonium thiocyanate, and dimethylamine hydrochloride can be added to the ink composition of the present invention for the purpose of controlling ejection properties.

<Solvent>
In order to improve the adhesion to the recording medium, it is also effective to add a very small amount of an organic solvent to the ink composition of the present invention.
As the solvent that can be used in the ink composition of the present invention, when a resin is used for the internal structure of the polymerizable particles, the solubility parameter value (SP value) of the resin and the solubility parameter value of the solvent to be used are The difference is preferably 2 or more, and more preferably 3 or more.
Examples of the solvent include ketone solvents such as acetone, methyl ethyl ketone, and diethyl ketone, alcohol solvents such as methanol, ethanol, 2-propanol, 1-propanol, 1-butanol, and tert-butanol, and chlorine such as chloroform and methylene chloride. Solvents, aromatic solvents such as benzene and toluene, ester solvents such as ethyl acetate, butyl acetate and isopropyl acetate, ether solvents such as diethyl ether, tetrahydrofuran and dioxane, glycols such as ethylene glycol monomethyl ether and ethylene glycol dimethyl ether Examples include ether solvents.
In this case, it is effective to add the solvent within a range that does not cause the problem of solvent resistance and VOC, and the amount is preferably 0.1 to 5% by weight, more preferably 0.1 to 3% by weight with respect to the whole ink composition. % Range.

<Polymer compound>
Various polymer compounds can be added to the ink composition of the present invention in order to adjust film physical properties. High molecular compounds include acrylic polymers, polyvinyl butyral resins, polyurethane resins, polyamide resins, polyester resins, epoxy resins, phenol resins, polycarbonate resins, polyvinyl butyral resins, polyvinyl formal resins, shellacs, vinyl resins, acrylic resins. Rubber resins, waxes and other natural resins can be used. Two or more of these may be used in combination. Of these, vinyl copolymer obtained by copolymerization of acrylic monomers is preferred. Furthermore, as a copolymer composition of the polymer compound, a copolymer containing “carboxyl group-containing monomer”, “alkyl methacrylate ester”, or “alkyl acrylate ester” as a structural unit is also preferably used.

<Basic compound>
The basic compound is preferably added from the viewpoint of improving the storage stability of the ink composition. As the basic compound that can be used in the present invention, known basic compounds can be used. For example, basic inorganic compounds such as inorganic salts, and basic organic compounds such as amines can be preferably used. .

In addition to this, if necessary, for example, leveling additives, matting agents, waxes for adjusting film physical properties, polymerization to inhibit the adhesion to recording media such as polyolefin and PET, and the like, The tackifier which does not do can be contained.
As a tackifier, specifically, a high molecular weight adhesive polymer (for example, (meth) acrylic acid and an alkyl group having 1 to 20 carbon atoms) described in JP-A-2001-49200, 5-6p. An ester with an alcohol having, an ester of (meth) acrylic acid and an alicyclic alcohol having 3 to 14 carbon atoms, a copolymer comprising an ester of (meth) acrylic acid and an aromatic alcohol having 6 to 14 carbon atoms) And a low molecular weight tackifier resin having a polymerizable unsaturated bond.

[Ink properties]
In the present invention, it is preferable to use an ink composition having a viscosity at 25 ° C. of 40 mPa · s or less, more preferably 5 mPa · s to 40 mPa · s, more preferably 7 mPa · s to More preferably, it is 30 mPa · s. Moreover, it is preferable that the viscosity in discharge temperature (Preferably 25-80 degreeC, More preferably, 25-50 degreeC) is 3-15 mPa * s, and it is more preferable that it is 3-13 mPa * s. It is preferable that the composition ratio of the ink composition of the present invention is appropriately adjusted so that the viscosity is in the above range. By setting the viscosity at room temperature high, even when a porous recording medium is used, ink penetration into the recording medium can be avoided and uncured monomer can be reduced. Furthermore, it is preferable that ink bleeding at the time of ink droplet landing can be suppressed, and as a result, the image quality is improved.

  The surface tension of the ink composition of the present invention at 25 ° C. is preferably 20 to 35 mN / m. More preferably, it is 23-33 mN / m. When recording on various recording media such as polyolefin, PET, coated paper, and uncoated paper, 20 mN / m or more is preferable from the viewpoint of bleeding and penetration, and 35 mN / m or less is preferable in terms of wettability.

(2) Inkjet recording method and inkjet recording apparatus The ink composition of the present invention is used for inkjet recording.
In the inkjet recording method of the present invention, the ink composition of the present invention is ejected onto a recording medium (support, recording material, etc.) for inkjet recording, and actinic radiation is applied to the ink composition ejected onto the recording medium. It is a method of forming an image by irradiating and curing the ink.

More specifically, the inkjet recording method of the present invention comprises (A ′) a step of ejecting the ink composition of the present invention onto a recording medium, and (B ′) active radiation on the ejected ink composition. And a step of curing the ink composition.
The ink jet recording method of the present invention includes the step (A ′) and the step (B ′), whereby an image is formed by the ink composition cured on the recording medium.

  In the step (A ′) in the ink jet recording method of the present invention, an ink jet recording apparatus described in detail below can be used.

[Inkjet recording device]
There is no restriction | limiting in particular as an inkjet recording device used for the inkjet recording method of this invention, The well-known inkjet recording device which can achieve the target resolution can be selected arbitrarily and can be used. That is, any known inkjet recording apparatus including a commercially available product can eject ink onto a recording medium in step (A ′) of the inkjet recording method of the present invention.
Examples of the ink jet recording apparatus that can be used in the present invention include an apparatus including an ink supply system, a temperature sensor, and an actinic radiation source.
The ink supply system includes, for example, an original tank containing the ink composition of the present invention, a supply pipe, an ink supply tank immediately before the inkjet head, a filter, and a piezo-type inkjet head. The piezo-type inkjet head has a multi-size dot of 1 to 100 pl, preferably 8 to 30 pl, preferably 320 × 320 to 4,000 × 4,000 dpi, more preferably 400 × 400 to 1,600 × 1, It can be driven so that it can discharge at a resolution of 600 dpi, more preferably 720 × 720 dpi. In the present invention, dpi represents the number of dots per 2.54 cm.

  As described above, since it is desirable that the radiation-curable ink, like the ink composition of the present invention, has a constant temperature for the ink to be ejected, heat insulation and heating are performed from the ink supply tank to the inkjet head portion. It can be carried out. The temperature control method is not particularly limited, but for example, it is preferable to provide a plurality of temperature sensors in each piping portion and perform heating control according to the ink flow rate and the environmental temperature. The temperature sensor can be provided in the vicinity of the ink supply tank and the nozzle of the inkjet head. Moreover, it is preferable that the head unit to be heated is thermally shielded or insulated so that the apparatus main body is not affected by the temperature from the outside air. In order to shorten the printer start-up time required for heating or to reduce the loss of heat energy, it is preferable to insulate from other parts and reduce the heat capacity of the entire heating unit.

Using the above inkjet recording apparatus, the ink composition of the present invention is ejected by heating the ink composition to preferably 25 to 80 ° C., more preferably 25 to 50 ° C. Preferably it is performed after lowering to 3 to 15 mPa · s, more preferably 3 to 13 mPa · s. In particular, it is preferable to use an ink composition having an ink viscosity at 25 ° C. of 50 mPa · s or less as the ink composition of the present invention since it can be discharged satisfactorily. By using this method, high ejection stability can be realized.
A radiation curable ink composition such as the ink composition of the present invention generally has a higher viscosity than a water-based ink usually used in ink jet recording inks, and therefore has a large viscosity fluctuation due to temperature fluctuations during ejection. The ink viscosity fluctuation has a great influence on the change of the droplet size and the change of the droplet discharge speed, and causes the image quality deterioration. Therefore, it is necessary to keep the temperature of the ink at the time of ejection as constant as possible. Therefore, in the present invention, the control range of the ink temperature is preferably set to ± 5 ° C. of the set temperature, more preferably ± 2 ° C. of the set temperature, and further preferably set to ± 1 ° C.

Next, (B ′) a step of irradiating the ejected ink composition with actinic radiation to cure the ink composition will be described.
The ink composition ejected on the recording medium is cured by irradiation with actinic radiation. This is because the polymerization initiator contained in the ink composition of the present invention is decomposed by irradiation with actinic radiation to generate radicals, acids, bases, and other starting species, and the function of the starting species is polymerization of a radical polymerizable compound. This is because the reaction occurs and is promoted. At this time, if a sensitizer is present together with the polymerization initiator in the ink composition, the sensitizer in the system absorbs actinic radiation to be in an excited state, and promotes decomposition of the polymerization initiator by contacting with the polymerization initiator. And a more sensitive curing reaction can be achieved.

  Here, α rays, γ rays, electron beams, X rays, ultraviolet rays, visible light, infrared rays, or the like can be used as the active radiation used. Although the peak wavelength of actinic radiation is based also on the absorption characteristic of a sensitizer, it is preferable that it is 200-600 nm, for example, it is more preferable that it is 300-450 nm, and it is further more preferable that it is 350-420 nm.

In addition, the polymerization initiation system of the ink composition of the present invention has sufficient sensitivity even with a low output actinic radiation. Therefore, it is appropriate to cure the exposed surface with an illuminance of 10 to 4,000 mW / cm ² , more preferably 20 to 2,500 mW / cm ² .

Mercury lamps and gas / solid lasers are mainly used as actinic radiation 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. Furthermore, LED (UV-LED) and LD (UV-LD) are small, have a long lifetime, high efficiency, and low cost, and are expected as light sources for photo-curable ink jets.
Further, a light emitting diode (LED) and a laser diode (LD) can be used as the active radiation source. In particular, when an ultraviolet light source is required, an ultraviolet LED and an ultraviolet LD can be used. For example, Nichia Corporation has introduced a purple LED whose main emission spectrum has a wavelength between 365 nm and 420 nm. If even shorter wavelengths are required, US Pat. No. 6,084,250 discloses an LED that can emit actinic radiation centered between 300 nm and 370 nm. Other ultraviolet LEDs are also available and can emit radiation in different ultraviolet bands. The actinic radiation source particularly preferred in the present invention is a UV-LED, particularly preferably a UV-LED having a peak wavelength at 350 to 420 nm.
Incidentally, it is preferable that maximum illumination intensity of the LED on a recording medium is 10 to 2,000 mW / cm ^2, more preferably 20 to 1,000 mW / cm ^2, particularly preferably 50 to 800 mW / cm ² .

The ink composition of the present invention is appropriately irradiated with such actinic radiation, preferably for 0.01 to 120 seconds, more preferably for 0.1 to 90 seconds.
Actinic radiation irradiation conditions and a basic irradiation method are disclosed in JP-A-60-132767. Specifically, the light source is provided on both sides of the head unit including the ink ejection device, and the head unit and the light source are scanned by a so-called shuttle method. Irradiation with actinic radiation takes a certain period of time (preferably 0.01 to 0.5 seconds, more preferably 0.01 to 0.3 seconds, still more preferably 0.01 to 0.15 seconds) after ink landing. Will be done. In this way, by controlling the time from ink landing to irradiation to an extremely short time, it is possible to prevent the ink that has landed on the recording medium from spreading before curing. Further, since the ink can be exposed to a porous recording medium before the ink penetrates to a deep part where the light source does not reach, residual unreacted monomer can be suppressed, and as a result, odor can be reduced. Therefore, it is preferable.
Further, curing may be completed by another light source that is not driven. WO99 / 54415 pamphlet discloses a method using an optical fiber and a method of applying a collimated light source to a mirror surface provided on the side surface of the head unit and irradiating the recording unit with UV light as an irradiation method. The curing method can also be applied to the ink jet recording method of the present invention.

By adopting the ink jet recording method as described above, the dot diameter of the landed ink can be kept constant even on various recording media having different surface wettability, and the image quality is improved. In addition, in order to obtain a color image, it is preferable to superimpose in order from the color with the lowest brightness. By superimposing the inks in the order of low lightness, the irradiation line can easily reach the lower ink, and good curing sensitivity, reduction of residual monomers, reduction of odor, and improvement of adhesion can be expected. In addition, irradiation can be performed by discharging all colors and collectively exposing, but exposure for each color is preferable from the viewpoint of promoting curing.
In this manner, the ink composition of the present invention can form an image on the surface of a recording medium by being cured with high sensitivity by irradiation with actinic radiation.

(Printed matter)
The printed matter of the present invention is recorded by the ink jet recording method of the present invention using the ink composition of the present invention.
The recording medium that can be used in the present invention is not particularly limited. For example, paper, paper laminated with plastic (eg, polyethylene, polypropylene, polystyrene, etc.), metal plate (eg, aluminum, zinc, copper, etc.) ), Plastic or plastic film (eg, cellulose diacetate, cellulose triacetate, cellulose propionate, cellulose butyrate, cellulose acetate butyrate, cellulose nitrate, polyethylene terephthalate, polyethylene, polystyrene, polypropylene, polycarbonate, polyvinyl acetal, etc.), metal laminated For example, a paper or a plastic film or the like deposited or vapor-deposited.

Hereinafter, the present invention will be described in more detail with reference to examples and comparative examples. However, the present invention is not limited to these examples.
In the following description, “parts” means “parts by weight” unless otherwise specified.

The materials used in the present invention are as shown below.
・ IRGALITE BLUE GLVO (Cyan pigment, Ciba Specialty Chemicals)
・ CINQUASIA MAGENTA RT-335 D (Magenta pigment, manufactured by Ciba Specialty Chemicals)
・ NOVOPERM YELLOW H2G (yellow pigment, manufactured by Clariant)
・ SPECIAL BLACK 250 (Black pigment, manufactured by Ciba Specialty Chemicals)
・ KRONOS2300 (white pigment, manufactured by KRONOS)
・ N-vinylcaprolactam (manufactured by Aldrich)
Actilane 421 (propoxylated neopentyl glycol diacrylate, manufactured by Akcros)
-Actilane 422 (dipropylene glycol diacrylate, manufactured by Akcros)
・ Rapi-Cure DVE-3 (triethylene glycol divinyl ether, manufactured by ISP Europe)
・ Ebecryl 657 (acrylate oligomer, manufactured by Daicel Cytec)
-Firstcure ST-1 (polymerization inhibitor, manufactured by Chem First)
・ Lucirin TPO (Photoinitiator manufactured by BASF)
・ Benzophenone (Photoinitiator, Wako Pure Chemical Industries, Ltd.)
・ Irgacure 184 (Photoinitiator, manufactured by Ciba Specialty Chemicals)
・ Byk 307 (surfactant, manufactured by BYK Chemie)
・ Light acrylate IMA (Isomyristyl acrylate, manufactured by Kyoeisha)
-Firstcure ITX (sensitizer, manufactured by Chem First)
・ Solsperse 32000 (dispersant, manufactured by Avicia)

(Preparation of cyan mill base A)
300 parts by weight of IRGALITE BLUE GLVO, 500 parts by weight of Actylene 421 (Akcros acrylate monomer) and 200 parts by weight of Solsperse 32000 were mixed with stirring to obtain a pigment ink. The pigment mill base was prepared in a disperser motor mill M50 (manufactured by Eiger) and dispersed for 4 hours at a peripheral speed of 9 m / s using zirconia beads having a diameter of 0.65 mm.

(Preparation of magenta mill base B)
300 parts by weight of CINQUASIA MAGENTA RT-335 D, 300 parts by weight of Actilane 421 (Akcros acrylate monomer) and 400 parts by weight of Solsperse 32000 were mixed with stirring to obtain a pigment ink. The pigment mill base was prepared in a disperser motor mill M50 (manufactured by Eiger) and dispersed for 10 hours at a peripheral speed of 9 m / s using zirconia beads having a diameter of 0.65 mm.

(Preparation of yellow mill base C)
300 parts by weight of NOVOPERM YELLOW H2G, 300 parts by weight of Actilane 421 (Akcros acrylate monomer), and 400 parts by weight of Solsperse 32000 were mixed with stirring to obtain a pigment ink. The pigment mill base was prepared in a disperser motor mill M50 (manufactured by Eiger) and dispersed for 10 hours at a peripheral speed of 9 m / s using zirconia beads having a diameter of 0.65 mm.

(Preparation of black mill base D)
300 parts by weight of SPECIAL BLACK 250, 300 parts by weight of Actilane 421 (Akcros acrylate monomer) and 400 parts by weight of Solsperse 32000 were mixed by stirring to obtain a pigment ink. The pigment mill base was prepared in a disperser motor mill M50 (manufactured by Eiger) and dispersed for 7 hours at a peripheral speed of 9 m / s using zirconia beads having a diameter of 0.65 mm.

(Preparation of white mill base E)
500 parts by weight of KRONOS 2300, 400 parts by weight of Actilane 421 (Akcros acrylate monomer) and 100 parts by weight of Solsperse 32000 were mixed with stirring to obtain a pigment ink. The pigment mill base was prepared in a disperser motor mill M50 (manufactured by Eiger) and dispersed for 4 hours at a peripheral speed of 9 m / s using zirconia beads having a diameter of 0.65 mm.

<Inkjet image recording method>
Next, recording on a recording medium was performed using an inkjet recording experimental apparatus having a piezoelectric inkjet nozzle. The ink supply system was composed of an original tank, supply piping, an ink supply tank immediately before the inkjet head, a filter, and a piezo-type inkjet head, and heat insulation and heating were performed from the ink supply tank to the inkjet head portion. Temperature sensors were provided near the ink supply tank and the nozzles of the ink jet head, respectively, and temperature control was performed so that the nozzle portions were always 45 ° C. ± 2 ° C. The piezo-type inkjet head was driven so that 8 to 30 pl multi-size dots could be ejected at a resolution of 720 × 720 dpi. After landing, UV light was condensed to an exposure surface illuminance of 1,630 mW / cm ² , and the exposure system, main scanning speed, and ejection frequency were adjusted so that irradiation started 0.1 seconds after ink landed on the recording medium. . Further, the integrated light amount irradiated to the image was set to 4,500 mJ / cm ² . A HAN250NL high-cure mercury lamp (manufactured by GS Yuasa Corporation) was used as the ultraviolet lamp. In the present invention, dpi represents the number of dots per 2.54 cm. As a recording medium, an ester film E5000 (film thickness 125 μm, manufactured by Toyobo Co., Ltd.) was used.

(Measurement method of curing sensitivity)
In accordance with the inkjet recording method, a solid image having an average film thickness of 12 μm was drawn, and the degree of stickiness of the image was evaluated by palpation on the image surface after ultraviolet irradiation.
The curing sensitivity was evaluated according to the following criteria.
3: No stickiness in the image.
2: The image is slightly sticky.
1: Uncured ink is not hard enough to transfer to hand.

(Flexibility evaluation method: Bending test)
In this example, a bending test was performed as a method for evaluating the flexibility of the cured film.
According to the inkjet inkjet image recording method, two solid images having an average film thickness of 12 μm and 24 μm were drawn using an ester film E5000 (film thickness 125 μm, manufactured by Toyobo Co., Ltd.) as a recording medium. In the bending test, the recording material on which an image was formed was bent once at 25 ° C. and evaluated by the presence or absence of cracks in the image area. In general, when the average film thickness is increased, distortion applied to the image portion when the image portion is bent increases, and cracks are likely to occur. That is, by testing whether the image portion is cracked with a thicker film thickness, a measure of flexibility can be obtained.
The evaluation criteria are as follows.
3: Cracks do not occur in samples having an average film thickness of 12 μm and 24 μm.
2: Cracks do not occur in the sample having an average film thickness of 12 μm, but cracks occur in the bent portion of the image portion in the sample having an average film thickness of 24 μm.
1: In samples having an average film thickness of 12 μm and 24 μm, cracks occur in the bent portion of the image portion.

(Substrate adhesion evaluation method: cross hatch test (EN ISO 2409))
PET (Ester film E5000, film thickness 125 μm, manufactured by Toyobo Co., Ltd.) was used as a recording medium, and a solid image having an average film thickness of 12 μm was drawn on the substrate according to the inkjet ink jet image recording method. Thereafter, a cross hatch test (EN ISO 2409) was performed on the printed matter.

(Viscosity measurement method)
In this example, the viscosity was measured using a B-type viscometer: Brookfield LVDV-I (manufactured by Brookfield) at 25 ° C. and a rotor rotation speed of 20 rpm.

(Chemical resistance evaluation method)
PET (Ester film E5000, film thickness 125 μm, manufactured by Toyobo Co., Ltd.) was used as a recording medium, and a solid image having an average film thickness of 12 μm was drawn on the substrate according to the inkjet ink jet image recording method. Thereafter, the printed material was rubbed 10 times with a cotton swab impregnated with methyl ethyl ketone (MEK), the surface of the printed material was visually evaluated for damage, and evaluated according to the following criteria.
3: No change 2: The surface is scratched 1: The image is peeled off and the substrate surface is exposed

(Water resistance evaluation method)
PET (Ester film E5000, film thickness 125 μm, manufactured by Toyobo Co., Ltd.) was used as a recording medium, and a solid image having an average film thickness of 12 μm was drawn on the substrate according to the inkjet ink jet image recording method. Thereafter, the printed matter was rubbed 10 times with a cotton swab impregnated with water, the damage on the printed matter surface was visually evaluated, and evaluated according to the following criteria.
3: No change 2: The surface is scratched 1: The image is peeled off and the substrate surface is exposed

(Blocking evaluation method)
PET (Ester film E5000, film thickness 125 μm, manufactured by Toyobo Co., Ltd.) was used as a recording medium, and a solid image having an average film thickness of 12 μm was drawn on the substrate according to the inkjet ink jet image recording method. Thereafter, the PET film was overlaid on the printed matter, a weight of 10 kg was added so as to cover the entire surface, and the printed matter was allowed to stand at 30 ° C. for 24 hours. Thereafter, the superimposed PET was peeled off, and the presence or absence of transfer of the drawn image was evaluated.
3: No change 2: The image is thinly attached to the surface 1: The image is peeled off, transferred to the superimposed PET, and the substrate surface is exposed.

[Preparation of Benzophenone-Linked Polymer Initiator PI-1 (PG ₈ BP _5.8 Ac _2.2 )]
2 parts of polyglycidol PG ₈ (manufactured by HYPERPOLYMERS GmbH) and 0.4 parts of p-benzophenoxyacetic acid (based on the OH amount of PG ₈ ) were placed in a flask containing a magnetic stir bar and a Dean-Stark attached. equiv) and p- to the amount of OH of toluenesulfonic acid (PG ₈ was added 0.1 eq). 34.6 parts by weight of toluene was added. The mixture was heated at 136 ° C. for 1 hour. After removing volatile components under reduced pressure, the residue was dissolved in chloroform. It was then added acetic anhydride (2 eq relative to the amount of OH of PG ₈₎ and triethylamine (2 eq relative to the amount of OH of PG _8). The mixture was refluxed for 6 hours. After cooling, the mixture after addition of water was stirred at room temperature for 1 hour. The mixture was then washed twice with 2N HCl, twice with deionized water, twice with 10% aqueous NaOH, and then three times with deionized water. The organic phase was dried over anhydrous Na ₂ SO ₄ . After removing the solvent under reduced pressure, the residue was dried overnight at 40 ° C. under reduced pressure to obtain a benzophenone-linked polymer initiator.

  In the obtained benzophenone-linked polymer initiator PI-1, an average of 5.8 of the average 8 hydroxyl end groups of the hyperbranched polyglycidol is acylated with p-benzophenoxyacetic acid, and the average 2.2 were acylated with acetyl chloride. The number average molecular weight of the polymer initiator PI-1 was 2,000.

[Preparation of Polymer Initiator PI-2 (PG ₁₅ BP _4.8 Ac _10.2 )]
A benzophenone-linked polymer initiator in the same manner as PI-1, except that polyglycidol PG ₁₅ (manufactured by HYPERPOLYMERS GmbH), which is a hyperbranched polyglycidol having an average of 15 hydroxyl groups, is used instead of polyglycidol PG _8. PI-2 was prepared.

  In the obtained benzophenone-linked polymer initiator PI-2, an average of 4.8 of the average 15 hydroxyl end groups of the hyperbranched polyglycidol is acylated with p-benzophenoxyacetic acid, and the average And 10.2 were acylated with acetyl chloride. The number average molecular weight of the polymer initiator PI-2 was 2,600.

[Example 1]
The following components were stirred with a high-speed water-cooled stirrer to obtain a cyan UV inkjet ink. The viscosity was 22 mPa · s (= 22 cP).
(Cyan ink composition A)
-(C) (D) (E) Cyan Mill Base A 6.0 parts-(A) N-Vinylcaprolactam 30.0 parts-(D) Actilane 422 35.9 parts-(D) Rapi-Cure DVE-3 9・ 5 parts ・ (D) First cure ST-1 0.05 part ・ Lucirin TPO (photoinitiator manufactured by BASF) 8.5 parts ・ (B) Benzophenone-linked polymer initiator (PI-1) 10.0 parts Irgacure 184 (CSC photoinitiator) 2.0 parts (F) Byk 307 (BYK Chemie surfactant) 0.05 parts ((A) :( D) Weight content ratio is 1: 2. 3)

[Example 2]
The following components were stirred with a high-speed water-cooled stirrer to obtain a cyan UV inkjet ink. The viscosity was 21 mPa · s.
(Cyan ink composition B)
(C) (D) (E) Cyan Mill Base A 6.0 parts (A) N-vinylcaprolactam 30.0 parts (D) Actilane 422 35.9 parts (D) Rapi-Cure DVE-3 9・ 5 parts ・ (D) First cure ST-1 0.05 part ・ Lucirin TPO (photoinitiator manufactured by BASF) 8.5 parts ・ (B) Benzophenone-linked polymer initiator (PI-2) 10.0 parts Irgacure 184 (CSC photoinitiator) 2.0 parts (F) Byk 307 (BYK Chemie surfactant) 0.05 parts ((A) :( D) Weight content ratio is 1: 2. 3)

(Evaluation of ink)
Ink jet recording was performed using the obtained ink composition. An image having a film thickness of 12 μm could be drawn. Table 1 shows the evaluation results of curability, cured film flexibility, adhesion, chemical resistance, water resistance, and blocking properties.

[Comparative Example 1]
A cyan ink composition was prepared using 10.0 parts of benzophenone (manufactured by Wako Pure Chemical Industries, Ltd.) instead of the benzophenone-linked polymer initiator (PI-1) used in Example 1, and the same as in Example 1. evaluated.

As shown in Examples 1 and 2, the use of the polymer polymerization initiator improves chemical resistance, water resistance, and blocking properties compared to Comparative Example 1 in which these polymer polymerization initiators are not used. it is obvious.
This result shows that a cured film having a high molecular weight is formed even in the surface layer in which the polymer polymerization initiator has an efficient initiation ability and is susceptible to polymerization inhibition by oxygen. Therefore, the solubility of the remaining molecules can be kept low, and it is considered that the polar organic solvent (MEK) and water are less likely to penetrate. Similarly, the peelability from PET is improved and the blocking property is improved.

[Examples 3 to 9]
The polymerization initiator containing the polymer polymerization initiator used in Example 1 was replaced with the polymerization initiator shown in the following table to prepare a cyan ink composition, which was evaluated in the same manner as in Example 1.
As a result, in all Examples, it was confirmed that the curability, the flexibility of the cured film, the adhesion, the chemical resistance, the water resistance, and the blocking property were good as in Example 1.

Example 10
The following components were stirred with a high-speed water-cooled stirrer to obtain a magenta UV inkjet ink. The viscosity was 22 mPa · s.
(Magenta ink composition)
(C) (D) (E) Magenta mill base B 12.0 parts (A) N-vinylcaprolactam 30.0 parts (D) Actilane 422 30.9 parts (D) Rapi-Cure DVE-3 8・ 5 parts ・ (D) First cure ST-1 0.05 part ・ Lucirin TPO (photoinitiator manufactured by BASF) 8.5 parts ・ (B) Benzophenone-linked polymer initiator (PI-1) 10.0 parts Irgacure 184 (CSC photoinitiator) 3.0 parts (F) Byk 307 (BYK Chemie surfactant) 0.05 parts ((A) :( D) Weight content ratio is 1: 2. 1)

Example 11
The following components were stirred with a high-speed water-cooled stirrer to obtain a yellow UV inkjet ink. The viscosity was 23 mPa · s.
(Yellow color ink composition)
(C) (D) (E) Yellow mill base C 12.0 parts (A) N-vinylcaprolactam 30.0 parts (D) Actilane 422 30.9 parts (D) Rapi-Cure DVE-3 8・ 5 parts ・ (D) First cure ST-1 0.05 part ・ Lucirin TPO (photoinitiator manufactured by BASF) 8.5 parts ・ (B) Benzophenone-linked polymer initiator (PI-1) 10.0 parts Irgacure 184 (CSC photoinitiator) 3.0 parts (F) Byk 307 (BYK Chemie surfactant) 0.05 parts ((A) :( D) Weight content ratio is 1: 2. 1)

Example 12
The following components were stirred with a high-speed water-cooled stirrer to obtain a black UV inkjet ink. The viscosity was 20 mPa · s.
(Black ink composition)
(C) (D) (E) Black mill base D 6.0 parts (A) N-vinylcaprolactam 30.0 parts (D) Actilane 422 36.9 parts (D) Rapi-Cure DVE-3 9・ 5 parts ・ (D) First cure ST-1 0.05 part ・ Lucirin TPO (photoinitiator manufactured by BASF) 8.5 parts ・ (B) Benzophenone-linked polymer initiator (PI-1) 10.0 parts Irgacure 184 (CSC photoinitiator) 2.0 parts (F) Byk 307 (BYK Chemie surfactant) 0.05 parts ((A) :( D) Weight content ratio is 1: 2. 3)

Example 13
The following components were stirred with a high-speed water-cooled stirrer to obtain a white UV inkjet ink. The viscosity was 24 mPa · s.
(White ink composition)
(C) (D) (E) White mill base E 31.0 parts (A) N-vinylcaprolactam 29.0 parts (D) Actilane 422 12.9 parts (D) Rapi-Cure DVE-3 9・ 5 parts ・ (D) First cure ST-1 0.05 part ・ Lucirin TPO (photoinitiator manufactured by BASF) 8.5 parts ・ (B) Benzophenone-linked polymer initiator (PI-1) 10.0 parts Irgacure 184 (CSC photoinitiator) 2.0 parts (F) Byk 307 (BYK Chemie surfactant) 0.05 parts ((A) :( D) Weight content ratio is 1: 1. 8)

Example 14
The following components were stirred with a high-speed water-cooled stirrer to obtain a clear UV inkjet ink. The viscosity was 16 mPa · s.
(Clear color ink composition)
(A) N-vinylcaprolactam 35.0 parts (D) Actilane 422 37.9 parts (D) Rapi-Cure DVE-3 9.5 parts (D) First cure ST-1 0.05 parts Lucirin TPO (photoinitiator manufactured by BASF) 8.5 parts (B) Benzophenone-linked polymer initiator (PI-1) 10.0 parts Irgacure 184 (photoinitiator manufactured by CSC) 2.0 parts ( F) Byk 307 (surfactant manufactured by BYK Chemie) 0.05 part ((A) :( D) weight content ratio is 1: 1.9)

(Evaluation of ink)
Ink jet recording was performed using the obtained ink composition. An image having a film thickness of 12 μm could be drawn. Evaluation of curability, flexibility of cured film, adhesion, chemical resistance, water resistance, and blocking property was performed in the same manner as in Example 1.

  As a result, each of the produced color inks and clear inks has good curability, flexibility of cured film, adhesion, chemical resistance, water resistance, and blocking properties as in Example 1, as in Example 1. It could be confirmed.

Example 15
The UV light after landing is condensed to an exposure surface illuminance of 400 mW / cm ² , and the cumulative amount of light applied to the image is set to 3,000 mJ / cm ^{2. The} lamp includes a UV-LED lamp: NCCU033 (Nichia Corporation) Inkjet recording was carried out using the respective color inks and clear inks produced in Examples 1 to 14 in the same manner as in the inkjet recording except that the above-described inkjet recording was used. There was no missing dot in the obtained image, and a bright image with a thickness of 12 μm could be drawn. Evaluation of curability, flexibility of cured film, adhesion, chemical resistance, water resistance, and blocking property was performed in the same manner as in Example 1.
As a result, even under the above exposure conditions, each color ink and clear ink produced in Examples 1 to 14 are examples of curability, flexibility of a cured film, adhesion, chemical resistance, water resistance, and blocking property. It was confirmed to be as good as 1.

Claims (12)

(A) N-vinyl lactams and
(B) An ink composition comprising a dendritic polymer having at least one polymerization-initiating species-generating structure at its terminal.   2. The ink composition according to claim 1, wherein the N-vinyl lactam is N-vinyl caprolactam.   The polymerization initiation species generation structure is benzoin ether structure, benzyl ketal structure, α, α-dialkoxyacetophenone structure, α-hydroxyalkylphenone structure, α-aminoalkylphenone structure, acylphosphine oxide structure, acylphosphine sulfide structure, α- The ink composition according to claim 1 or 2, wherein the ink composition has a structure selected from the group consisting of a haloketone structure, an α-halosulfone structure and an α-halophenylglyoxalate structure.   The ink composition according to claim 1 or 2, wherein the polymerization initiating species generating structure is a structure selected from the group consisting of a benzophenone structure, a thioxanthone structure, a 1,2-diketone structure, and an anthraquinone structure.   The ink composition according to any one of claims 1 to 4, wherein the dendritic polymer has five or more polymerization initiation species-generating structures at its terminals.   The ink composition according to any one of claims 1 to 5, wherein the dendritic polymer has at least one compatible group and / or ionic group at its terminal.   The ink composition according to any one of claims 1 to 6, wherein the dendritic polymer has one or more compatible groups at its terminal.   The ink composition according to claim 1, wherein the dendritic polymer is a hyperbranched polymer.   The ink composition according to any one of claims 1 to 8, which is for inkjet recording. (A ′) a step of discharging the ink composition according to any one of claims 1 to 9 onto a recording medium; and
(B ′) an inkjet recording method comprising a step of irradiating the ejected ink composition with actinic radiation to cure the ink composition. The actinic radiation is ultraviolet light emitted by a light emitting diode that generates ultraviolet light having an emission peak wavelength in the range of 350 to 420 nm and a maximum illuminance on the surface of the recording medium of 10 to 2,000 mW / cm ^2. The inkjet recording method according to claim 10.   A printed matter recorded by the ink jet recording method according to claim 10.