JP2007270089A - Inkjet white ink composition - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inkjet white ink composition excellent in discharge property, wherein dispersion stability of a white pigment is excellent in the ink composition, and development of nozzle clogging resulting from settlement of the pigment is suppressed even when the ink composition is applied to an inkjet recording system. <P>SOLUTION: A UV-curing inkjet white ink composition comprises a pigment dispersed with a polymer dispersant, a curable compound, and a polymerization initiator, wherein the polymer dispersant is a vinyl polymer having a substituent composed of an acid or its salt at a terminal. The polymer dispersant is preferably a compound having at least one of a sulfonyl group and a phosphonyl group in the molecule. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an ink-jet ink composition, and more specifically, UV curing-type ink-jet white ink in which sedimentation of a pigment is suppressed and clogging of an ink-jet nozzle is eliminated by using a specific polymer dispersant. It relates to a composition.

  High concealability and coloring power are essential for ink compositions, particularly white ink compositions. This is because, when printing on a colored medium, if the concealability is low, the color of the print medium is transparent, resulting in poor color reproducibility. When printing on a colored medium, white ink is first applied, and ink of other colors is applied thereon. Therefore, the amount of white ink used is large compared to other colors, and the demand is surely increasing. As a method for applying the white ink, screen printing is often used, but there are problems such as being limited to plane printing and difficult to draw finely.

On the other hand, ink-jet ink is simpler and more compact than conventional printing methods, and is non-contact printing, so printing on a three-dimensional medium is possible, and its use is further expanded.
Application of the white ink by the ink jet method has solved the problems caused by the conventional screen printing, and printing on a three-dimensional medium and fine depiction are possible.
However, in ink jet printing, it is necessary for the ink viscosity to be low in order to ensure ink dischargeability. If the dispersion stability of the white pigment with excellent concealment is not sufficient, pigment settling will occur, and the ink jet nozzle will When clogging occurs and a printed image is defective or is remarkable, ink cannot be ejected and printing is not possible.
For this reason, a novel dispersant has been proposed for the purpose of improving the dispersion stability of a titanium oxide white pigment that is useful as a white pigment but has a large specific gravity and thus easily settles (see, for example, Patent Document 1). However, the dispersibility is not sufficient for application to a low-viscosity ink composition. Therefore, a white ink composition for inkjet which is a low-viscosity composition and has excellent dispersion stability of a white pigment is obtained. The current situation is what is expected.
JP 2002-347336 A

  The object of the present invention made in consideration of the above problems is excellent in the dispersion stability of the white pigment in the ink composition, and even when applied to an ink jet recording system, the occurrence of nozzle clogging due to the precipitation of the pigment is suppressed. An object of the present invention is to provide a white ink composition for ink jet which is excellent in dischargeability.

  As a result of intensive studies, the present inventors have improved the dispersion stability of the pigment in the ink composition and suppressed the precipitation of the pigment, thereby eliminating the nozzle clogging. It is necessary to increase the efficiency, whereby it is possible to stably disperse the pigment in the curable compound serving as the dispersion medium, and furthermore, an acidic group is introduced at the terminal of the dispersant to The inventors have found that the dispersion stability of the ink can be improved by increasing the adsorption efficiency of the dispersant, and the present invention has been completed.

That is, the present invention is as follows.
<1> An ultraviolet curable inkjet white ink composition comprising a pigment dispersed with a polymer dispersant, wherein the polymer dispersant is a vinyl polymer having a substituent consisting of an acid or a salt thereof at a terminal.
<2> The white ink composition for inkjet according to <1>, wherein the polymer dispersant has at least one of a sulfonyl group and a phosphonyl group in the molecule.
<3> The white ink composition for inkjet according to <1>, comprising a curable compound capable of dissolving the polymer dispersant.
<4> One or more selected from the group consisting of a cation polymerizable compound having at least one of an oxirane group or an oxetane group and a radical polymerizable compound having at least one (meth) acryl group. <3> The white ink composition for inkjet according to.

According to the present invention, the dispersion stability of the white pigment in the ink composition is excellent, and even when applied to an inkjet recording system, the occurrence of nozzle clogging due to the precipitation of the pigment is suppressed, and the inkjet performance is excellent. A white ink composition can be provided.
In addition, since the ink composition of the present invention has good dispersion stability of the pigment, it has excellent adhesion to the recording medium and can record good characters or images on a recording medium such as printing paper. It also has the advantage of.

Details of the present invention will be described below.
The white ink composition of the present invention includes a white pigment dispersed with a polymer dispersant, and the polymer dispersant is a vinyl polymer having a substituent composed of an acid or a salt thereof at a terminal. It can be suitably used for ultraviolet curable ink jet recording. The ink composition of the present invention further contains a curable compound and a photopolymerization initiator in order to develop an ultraviolet curable product. Hereinafter, each component used in the ink composition of the present invention will be described.
[White pigment]
The white pigment preferably used in the present invention will be described.
The white pigment is not particularly limited, and all inorganic white pigments, organic white pigments, or hollow particles that are generally commercially available can be used. Furthermore, a pigment dispersed in an insoluble resin or the like as a dispersion medium, or a pigment grafted with a resin can be used.

Specific examples of the inorganic white pigment include basic lead carbonate (2PbCO ₃ Pb (OH) ₂ , so-called silver white), zinc oxide (ZnO, so-called zinc white), titanium oxide (TiO ₂ , so-called titanium white). Strontium titanate (SrTiO ₃ , so-called titanium strontium white), etc. can be used.
Of these, titanium oxide has a lower specific gravity than other inorganic white pigments, a large refractive index, and is chemically and physically stable. Excellent durability against alkalis and other environments. Therefore, titanium oxide is preferred as the white pigment.

Titanium oxide is generally rarely used untreated and is treated with silica, alumina, zinc, zirconia, and organic matter, and the weather resistance and lipophilicity differ depending on the treatment method. Just choose.
When used in an ink composition as in the present invention, titanium oxide treated with alumina, zinc, zirconia, or a basic organic material is preferred. With respect to titanium oxide treated with these materials, the amount treated with alumina, zinc, zirconia, basic organic matter, that is, the amount of these compounds attached to the titanium oxide surface is 50% of the total weight of the surface deposit. It is preferable that it is mass% or more.
As the surface treatment method, a known method can be appropriately selected and applied, and a commercially available surface-treated titanium oxide pigment obtained by performing a surface treatment according to the purpose in advance can also be used. Since the acidic and basic properties of the pigment surface change depending on the type of surface deposit, it is effective to use a compound having an acidic group for a basic surface pigment and a basic compound for an acidic surface pigment, for example. Is.
The inorganic white pigment is not limited to titanium oxide, and other white pigments, that is, the white pigments listed above or other known inorganic white pigments may be appropriately used depending on the purpose.

Since the organic white pigment has a specific gravity smaller than that of the inorganic white pigment, it can stably exist in a dispersion having a low viscosity. Examples of the organic white pigment include resin particles made of highly cross-linked resin materials such as melamine and acrylic, and low molecular resin particles having a molecular weight of about 500 described in US Pat. No. 5,514,213. It is done.
The organic white pigment is also available as a commercial product. For example, the Shigenox series manufactured by Hakko Chemical Co., Ltd. can be used.

The hollow particles exhibit high concealability due to light scattering in the voids in the particles and have a specific gravity smaller than that of the inorganic white pigment and can exist stably in a dispersion having a low viscosity. Inorganic, organic and inorganic / organic mixed hollow particles can be used.
As specific examples of the hollow particles, an opt bead series manufactured by Nissan Chemical Industries, an SX series manufactured by JSR, a microsphere MFL series manufactured by Matsumoto Yushi Seiyaku, etc. can be used.

  For example, ball mill, sand mill, attritor, roll mill, jet mill, homogenizer, paint shaker, kneader, agitator, Henschel mixer, colloid mill, ultra-fine pigment dispersion when adjusting the ink composition using these white pigments. Any known dispersing device such as a sonic homogenizer, a pearl mill, or a wet jet mill can be used.

As a dispersion medium containing various components such as pigments in the ink composition, it is possible to prepare the cationic polymerizable compound, which is a low molecular weight component described in detail below, as a dispersion medium without adding a special solvent. However, a more appropriate solvent may be added depending on the purpose.
The ink composition of the present invention is a radiation curable ink, and after applying the ink onto a recording medium, the ink composition is cured by irradiating with ultraviolet rays to form an image. Therefore, a solvent is used from the viewpoint of curability. It is preferable not to add. Specifically, in the case of using a solvent for ink preparation, there is a concern that if the solvent remains in the cured ink image, the solvent resistance of the formed image may be deteriorated. This is because the problem of (Volatile Organic Compound) occurs.
As the dispersion medium in the ink composition of the present invention, it is preferable to use only a curable compound, and in particular, to select a curable compound having a low viscosity from the viewpoints of dispersion suitability and improved handling of the ink composition.

The average particle diameter of the pigment particles is preferably 0.05 to 1.0 μm, and the selection of the pigment, the dispersant, the dispersion medium, the dispersion conditions, and the filtration so that the maximum particle diameter is 5 μm or less, preferably 1 μm or less. Set conditions. By controlling the particle size, clogging of the head nozzle can be suppressed, and ink storage stability, ink transparency, and curing sensitivity can be maintained.
In addition, the value measured based on the image image | photographed with the transmission electron microscope (TEM) is employ | adopted here for the average particle diameter and maximum particle diameter of a white pigment.

(Polymer dispersant)
Next, the polymer dispersant that improves the dispersion stability of the white pigment will be described.
As in the ink composition of the present invention, in a non-aqueous dispersion using a curable compound as a main dispersion medium, dispersion stabilization by steric repulsion is effective, and high dispersion stability is achieved by using a polymer compound as a dispersant. Is obtained.
In general, when a polymer dispersant is used, there is a concern that the viscosity of the ink composition is increased. Therefore, a dispersant that can adsorb efficiently to the pigment, has a strong adsorbing power, and can be adsorbed stably to the pigment is preferable. Polymer dispersants that are poorly adsorbed to pigments have poor adsorption efficiency and weak adsorptive power, which increases the amount of dispersant required to ensure stable adsorption of pigments and adverse effects such as increasing the viscosity of the system. This is not preferable.

In the present invention, a vinyl polymer having a substituent consisting of an acid or a salt thereof at the terminal is used as a polymer dispersant. Here, the vinyl polymer used has an acid group or a salt of an organic acid at the terminal, and is adsorbed to the pigment by this acidic group with high efficiency, and also has excellent adsorption power. Stability is also improved.
Acid groups include inorganic acids such as sulfonic acid, phosphonic acid and phosphoric acid, and inorganic and organic salts thereof.
The salt structure of the organic acid is preferably an organic acid such as an organic carboxylic acid, which has a salt structure such as an alkali metal salt such as a sodium salt or an ammonium salt.
In order to achieve the dispersion stability of the pigment, the degree of dissociation on the pigment surface and the salt exchange properties greatly affect its performance, so it is necessary to select appropriately depending on the pigment and the dispersion medium. As an acidic group to be introduced, an acid group having a high acidity such as sulfonic acid or phosphonic acid exhibits an excellent effect.
In addition, the vinyl polymer in the present invention is not particularly limited as long as it has a vinyl bond in the structural unit constituting the polymer, a copolymer having a vinyl bond and different structural units, or vinyl. In addition to a structure having a bond, it also includes a copolymer containing other structural units not having a vinyl bond as long as the effects of the present invention are not impaired.

  The weight average molecular weight of the specific vinyl polymer used as the polymer dispersant in the present invention is 200,000 or less, and preferably 100,000 or less. When the weight average molecular weight is 200,000 or more, the solubility in a solvent is lowered and the dispersibility tends to be lowered. Further, the weight average molecular weight is preferably 300 or more, and more preferably 500 or more. If the molecular weight is too low, there is a concern that the stability over time will decrease.

There are various methods for introducing an acidic group into the terminal of the vinyl polymer, and these can be used as appropriate in the present invention. Specifically, for example, a method using an acid group-containing chain transfer agent, a reactive group (vinyl group, (meth) acrylate group, hydroxyl group, amine, epoxy, etc.) is incorporated at the end of the vinyl polymer, Examples include a method of reacting a compound having an acidic group that can react with a reactive group.
There is no restriction | limiting in particular in the method of introduce | transducing an acidic group into the terminal of a vinyl polymer, The effect of this invention can be acquired because these groups exist in a terminal.

When an acidic group is introduced into the end of the vinyl polymer using a chain transfer agent, the polymer may be synthesized in the presence of a chain transfer agent together with the raw material monomer and the polymerization initiator constituting the vinyl polymer. Regarding the use of a chain transfer agent, there are a usage method of introducing an adsorbing group using the chain transfer agent and a usage method of causing a general chain transfer to stop the reaction using the chain transfer agent.
When the former method, i.e., the method of introducing an acidic group into the vinyl polymer terminal using a chain transfer agent, the polymer is prepared by coexisting the chain transfer agent together with the raw material monomer and the polymerization initiator constituting the vinyl polymer. What is necessary is to synthesize. Here, the chain transfer agent is charged by post-addition.
Examples of chain transfer agents that can be used in this method include olefins such as 2,4-diphenyl-4-methyl-1-pentene, mercaptoethanol, mercaptopropanol, methyl mercaptopropionate, ethyl mercaptopropionate, and mercaptopropion. Examples include sulfur-containing compounds such as acid, thioglycolic acid, thiosalicylic acid, thiophenol, and thiocresol, but are not limited to these, and if a reactive group capable of introducing an acidic group at the terminal can be introduced, Any one can be used.

  In addition, a reactive group (for example, a hydroxyl group, an epoxy group, an amino group, a substituent having an unsaturated double bond) is incorporated at the terminal of a vinyl polymer (indicated by R in the following structure), and the reactive group In the case of taking a method of reacting a compound having an acidic group capable of reacting with the compound, the compound having a reactive group at the terminal and the vinyl polymer are first reacted, and then described in the compound having a hydroxyl group at the terminal. An acidic group may be introduced as in the scheme shown.

The chain transfer agent used in the latter means for controlling the molecular weight can be used without particular limitation as long as it is a substance that moves the active site of the reaction by a chain transfer reaction in the polymerization reaction. The ease of the transfer reaction of the chain transfer agent is represented by the chain transfer constant Cs, but the chain transfer constant Cs × 10 ⁴ (60 ° C.) of the chain transfer agent used in the present invention is 0.01 or more. Is more preferably 0.1 or more, and particularly preferably 1 or more.
As specific examples of the chain transfer agent that can be used in the present invention, the following thiol compounds are preferable.

Similarly, chain transfer agents that can be used include, for example, halogen compounds such as carbon tetrachloride and carbon tetrabromide, alcohols such as isopropyl alcohol and isobutyl alcohol, 2-methyl-1-butene, and 2, 4- Olefins such as diphenyl-4-methyl-1-pentene, ethanethiol, butanethiol, dodecanethiol, mercaptoethanol, mercaptopropanol, methyl mercaptopropionate, ethyl mercaptopropionate, mercaptopropionic acid, thioglycolic acid, ethyl disulfide, Examples thereof include, but are not limited to, sulfur-containing compounds such as sec-butyl disulfide, 2-hydroxyethyl disulfide, thiosalicylic acid, thiophenol, thiocresol, benzyl mercaptan, and phenethyl mercaptan. Not to.
More preferably, ethanethiol, butanethiol, dodecanethiol, mercaptoethanol, mercaptopropanol, methyl mercaptopropionate, ethyl mercaptopropionate, mercaptopropionic acid, thioglycolic acid, ethyl disulfide, sec-butyl disulfide, 2-hydroxyethyl disulfide Thiosalicylic acid, thiophenol, thiocresol, benzyl mercaptan, phenethyl mercaptan, and particularly preferred chain transfer agents include ethanethiol, butanethiol, mercaptoethanol, mercaptopropanol, methyl mercaptopropionate, ethyl mercaptopropionate, mercaptopropionic acid Thioglycolic acid, ethyl disulfide, 2-hydroxyethyl disulfide, etc. It is.

  Such a chain transfer agent may use only 1 type, and may use 2 or more types together, unless the effect is impaired. Further, those having the former and latter functions may be used in combination. The addition amount of the chain transfer agent at the time of synthesis is preferably 0.002 to 0.2 mol / g or more based on the total amount of charged monomers. A particularly preferred addition amount is in the range of 0.004 to 0.15 mol / g.

  Polymerization solvents used in the synthesis of the polymer dispersant include acetone, methyl ethyl ketone, methanol, ethanol, propanol, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, diethylene glycol dimethyl ether, 1-methoxy-2-propanol, and 2-methoxyethyl. Acetate, 1-methoxy-2-propyl acetate, dimethoxyethane, methyl lactate, ethyl lactate, ethyl acetate, N, N-dimethylacetamide, N, N-dimethylformamide, dimethyl sulfoxide, tetrahydrofuran, toluene, water, etc. Yes, but not limited to this.

Examples of a method for introducing an acidic group at the terminal include a method using a polar group-containing ethylenically unsaturated monomer. When a monomer having an acidic group as a polar group is used, the acidic group can be directly introduced into the terminal.
When this method is adopted, in the polymerization reaction under N ₂ atmosphere, at the timing of adding the chain transfer agent added later, instead of the chain transfer agent, the polar group-containing ethylenically unsaturated monomer is added and reacted. Good.

  Examples of the acidic group-containing ethylenically unsaturated monomer include commercially available vinyl sulfonate, allyl sulfonate, p-styrene sulfonate, 4-sulfobutyl methacrylate, methacryloxybenzene sulfonate, and allyloxybenzene sulfonate. Etc. are available. Furthermore, it is generally used as a reactive emulsifier, Japan Emulsifier Co., Ltd. Antox MS-60, Antox MS-2N (trade name), Kao Co., Ltd., Ramtel S-180, Ramtel S An acidic group can also be introduced using -180A (trade name).

  Monomers that can be copolymerized with monomers containing sulfonate groups to form vinyl polymers include ethylenically unsaturated carboxylic acid ester monomers, aromatic vinyl monomers, ethylenically unsaturated nitrile monomers, Examples include ethylenically unsaturated acid monomers, alkyl vinyl ether monomers, vinyl ester monomers, and ethylenically unsaturated polyvalent carboxylic acid anhydrides.

  Examples of the ethylenically unsaturated carboxylic acid ester monomer include alkyl (meth) acrylate monomers and alkoxyalkyl (meth) acrylate monomers.

  Alkyl (meth) acrylate monomers include methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, butyl (meth) acrylate, isobutyl (meth) acrylate, pentyl (meth) acrylate, hexyl (meth) acrylate Octyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, lauryl (meth) acrylate, stearyl (meth) acrylate, cyclohexyl (meth) acrylate, and the like. Among these, methyl (meth) acrylate is preferable.

  The alkyl group of the alkyl (meth) acrylate monomer may be an alkyl group having a substituent, and is preferably an aralkyl group. Specific examples of such compounds include benzyl (meth) acrylate, phenoxyethyl (meth) acrylate, phenoxypolyethylene glycol (meth) acrylate, and nonylphenol ethylene oxide adduct (meth) acrylate. Among these, benzyl (meth) acrylate and phenoxyethyl (meth) acrylate are preferable.

  Examples of the alkoxyalkyl (meth) acrylate monomer include methoxyethyl (meth) acrylate and butoxyethyl (meth) acrylate. Examples of unsaturated carboxylic acid ester monomers include glycidyl (meth) acrylate.

  Examples of the aromatic vinyl monomer include styrene, α-methylstyrene, vinyltoluene, monochlorostyrene, p-methylstyrene, and hydroxymethylstyrene.

  Examples of the ethylenically unsaturated nitrile monomer include acrylonitrile, methacrylonitrile, 2-ethylpropenenitrile, 2-propylpropenenitrile, 2-chloropropenenitrile, 2-butenenitrile and the like.

  Examples of the alkyl vinyl ether monomers include allyl glycidyl ether, methyl vinyl ether, ethyl vinyl ether, isobutyl vinyl ether, n-butyl vinyl ether, 2-ethylhexyl vinyl ether, n-octyl vinyl ether, lauryl vinyl ether, cetyl vinyl ether, stearyl vinyl ether and the like.

  Vinyl ester monomers include vinyl formate, vinyl acetate, vinyl propionate, isopropenyl acetate, vinyl valerate, vinyl caprate, vinyl laurate, vinyl stearate, vinyl benzoate, vinyl versatate, vinyl pivalate, etc. Can be mentioned.

  Examples of the ethylenically unsaturated polyvalent carboxylic acid anhydride include maleic anhydride and itaconic anhydride.

These monomers that can be copolymerized with a monomer containing a sulfonate group can be used alone or in combination of two or more.
Among these, an ethylenically unsaturated carboxylic acid monomer is preferable, and an alkyl (meth) acrylate monomer is more preferable.

The copolymer used in the present invention may have —COOM (M represents an alkali metal or ammonium salt) or a hydroxyl group as a polycondensable group.
In the case of introducing -COOM, for example, synthesis is performed by adding -COOM by reaction to an acrylic copolymer obtained by copolymerizing a monomer containing a sulfonate group and a monomer copolymerizable therewith. Can do.
Moreover, what copolymerized the polar group containing compound which can be copolymerized with the monomer containing a sulfonate group, and the monomer copolymerizable with these may be used. As the copolymerizable compound containing —COOM, specifically, (meth) acrylic acid and maleic acid salts can be used.

  Examples of copolymerizable hydroxyl group-containing monomers include hydroxyethyl (meth) acrylate, hydroxypropyl (meth) acrylate, polyethylene glycol mono (meth) acrylate, polypropylene glycol mono (meth) acrylate, polyethylene glycol polypropylene glycol mono (meth) Hydroxyalkyl (meth) acrylates such as acrylate, glycerol mono (meth) acrylate, 3-chloro-2-hydroxypropyl (meth) acrylate, vinyl ethers such as hydroxyethyl vinyl ether, hydroxypropyl vinyl ether, hydroxybutyl vinyl ether, hydroxyethyl mono (Meth) allyl ether, hydroxypropyl mono (meth) allyl ether, hydroxybutyl mono (meth) (Meth) allyl ethers such as ril ether, diethylene glycol mono (meth) allyl ether, dipropylene glycol mono (meth) allyl ether, glycerin mono (meth) allyl ether, 3-chloro-2-hydroxypropyl (meth) allyl ether, (Meth) allyl alcohol etc. are mentioned. The vinyl alcohol monomer can be introduced by copolymerizing vinyl acetate and saponifying with a caustic alkali in a solvent.

Furthermore, as another method for introducing an acidic group, a hydroxyl group-containing polymer such as polyvinyl alcohol is added to Cl— (CH ₂ ) _n —SO ₃ M, Cl— (CH ₂ ) _n —OSO ₃ M, Cl— (CH ₂ ) -P (OM) _{2 and the} like.
Specific examples of the reaction include a method in which methyl methacrylate is first polymerized in a methyl ethyl ketone under a nitrogen atmosphere, and after adding mercaptopropanol, the above compound is added and reacted.

Specific examples of the polymer dispersant thus obtained include sodium terminal sulfonate of polyacrylic acid derivatives and terminal ammonium phosphate salts of polymethacrylic acid derivatives. Two or more polymer dispersants may be used in combination depending on the purpose.
It is preferable to select a polymer dispersant that can be dissolved or uniformly dispersed in the curable compound as a dispersion medium. If the polymer dispersant used is poor in solubility or dispersibility in the curable compound, the adsorption to the pigment may be insufficient, and the desired dispersion stability may not be obtained. Since the polymer dispersant used here contains a hydrophilic group and a hydrophobic group, it is difficult to completely dissolve, and the solution (dispersion) often becomes turbid, but when measured by the 90-degree scattering photometry method, It can be judged that the transmitted light T% when the polymer dispersant is dissolved in the monomer by 2% is in the range of 100 to 50%.

  The amount of the specific polymer dispersant used in the present invention is preferably in the range of 1 to 10% by mass, particularly preferably in the range of 1 to 4% by mass, based on the total amount of the white pigment. In the range of this addition amount, sufficient adsorptivity to the pigment is achieved, and the surface tension of the ink composition decreases due to the surfactant action resulting from the increase in viscosity of the ink composition and the polymer dispersant, There is no concern of lowering the ejectability by inkjet.

[Curable compound]
The ink composition of the present invention contains a curable compound. The curable compound is cured by an initiating species generated from a coexisting radical polymerization initiator or cationic polymerization initiator to form an ink image.
The curable compound used in the present invention is not particularly limited, and any compound having a generally known photocurable group can be used regardless of the type of monomer, oligomer, or polymer. As described above, in consideration of the relationship with the polymer dispersant used in combination and the viscosity of the ink composition, a monomer or an oligomer having a relatively low molecular weight is preferable.
One or more curable compounds may be used in combination for the purpose of adjusting the reaction rate, ink physical properties, cured film physical properties, and the like.
As the curable compound, a radical polymerizable compound or a cationic polymerizable compound can be used. Hereinafter, each compound will be described.

(Radically polymerizable compound)
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. Only one kind of such radically polymerizable compounds may be used, or two or more kinds thereof may be used in combination at an arbitrary ratio in order to improve desired properties. A polyfunctional compound having two or more functional groups is more preferable than a monofunctional compound. More preferably, two or more polyfunctional compounds are used in combination for controlling performance such as reactivity and physical properties.

In the ink composition of the present invention, (meth) acrylate can be suitably used as the radical polymerizable compound. Examples of the (meth) acrylate include the following compounds.
In addition, (meth) acrylate represents that it can take the structure of both an acrylate and a methacrylate. The same applies hereinafter.

Specific examples of monofunctional (meth) acrylates include hexyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, tert-octyl (meth) acrylate, isoamyl (meth) acrylate, decyl (meth) acrylate, and isodecyl (meth). Acrylate, stearyl (meth) acrylate, isostearyl (meth) acrylate, cyclohexyl (meth) acrylate, 4-n-butylcyclohexyl (meth) acrylate, bornyl (meth) acrylate, isobornyl (meth) acrylate, benzyl (meth) acrylate, 2-ethylhexyl diglycol (meth) acrylate, butoxyethyl (meth) acrylate, 2-chloroethyl (meth) acrylate, 4-bromobutyl (meth) acrylate, cyanoeth (Meth) acrylate, benzyl (meth) acrylate, butoxymethyl (meth) acrylate, 3-methoxybutyl (meth) acrylate, alkoxymethyl (meth) acrylate, alkoxyethyl (meth) acrylate, 2- (2-methoxyethoxy) ethyl ( (Meth) acrylate, 2- (2-butoxyethoxy) ethyl (meth) acrylate, 2,2,2-tetrafluoroethyl (meth) acrylate, 1H, 1H, 2H, 2H perfluorodecyl (meth) acrylate, 4-butyl Phenyl (meth) acrylate, phenyl (meth) acrylate, 2,4,5-tetramethylphenyl (meth) acrylate, 4-chlorophenyl (meth) acrylate, phenoxymethyl (meth) acrylate, phenoxyethyl (meth) acrylate Over DOO, glycidyl (meth) acrylate, glycidyl Giro carboxybutyl (meth) acrylate, glycidyl Giro carboxyethyl (meth) acrylate, glycidyl Giro hydroxypropyl (meth) acrylate,

  Tetrahydrofurfuryl (meth) acrylate, hydroxyalkyl (meth) acrylate, 2-hydroxyethyl (meth) acrylate, 3-hydroxypropyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 2-hydroxybutyl (meth) acrylate 4-hydroxybutyl (meth) acrylate, 3-hydroxypropyl (meth) acrylate, dimethylaminoethyl (meth) acrylate, diethylaminoethyl (meth) acrylate, dimethylaminopropyl (meth) acrylate, diethylaminopropyl (meth) acrylate, tri Methoxysilylpropyl (meth) acrylate, trimethylsilylpropyl (meth) acrylate, polyethylene oxide monomethyl ether (meth) acrylate Oligoethylene oxide monomethyl ether (meth) acrylate, polyethylene oxide (meth) acrylate, oligoethylene oxide (meth) acrylate, oligoethylene oxide monoalkyl ether (meth) acrylate polyethylene oxide monoalkyl ether (meth) acrylate, dipropylene glycol (meth) acrylate, Polypropylene oxide monoalkyl ether (meth) acrylate, oligopropylene oxide monoalkyl ether (meth) acrylate, 2-methacryloyloxytyl succinic acid, 2-methacryloyloxyhexahydrophthalic acid, 2-methacryloyloxyethyl-2-hydroxy Propyl phthalate, butoxydiethylene glycol (meth) acrylate, trifluoroethyl (meth) Chlorate, perfluorooctylethyl (meth) acrylate, 2-hydroxy-3-phenoxypropyl (meth) acrylate, ethylene oxide modified phenol (meth) acrylate, ethylene oxide modified cresol (meth) acrylate, ethylene oxide modified nonylphenol (meth) acrylate , Polyethylene oxide modified nonylphenol (meth) acrylate, ethylene oxide modified-2-ethylhexyl (meth) acrylate, carbitol (meth) acrylate, oligoester (meth) acrylate, epoxy (meth) acrylate, urethane (meth) acrylate, methyl ( (Meth) acrylate, n-butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, lauryl (meth) acryl Rate, allyl (meth) acrylate, glycidyl (meth) acrylate, benzyl (meth) acrylate, dimethylaminomethyl (meth) acrylate, and the like.

  Specific examples of the bifunctional (meth) acrylate include 1,6-hexanediol di (meth) acrylate, 1,10-decanediol di (meth) acrylate, neopentyl glycol di (meth) acrylate, and 2,4-dimethyl. -1,5-pentanediol di (meth) acrylate, butylethylpropanediol (meth) acrylate, ethoxylated cyclohexanemethanol di (meth) acrylate, polyethylene glycol di (meth) acrylate, oligoethylene glycol di (meth) acrylate, Ethylene glycol di (meth) acrylate, 2-ethyl-2-butyl-butanediol di (meth) acrylate, hydroxypivalic acid neopentyl glycol di (meth) acrylate, ethylene oxide modified bisphenol A di ( ) Acrylate, bisphenol F polyethoxydi (meth) acrylate, polypropylene glycol di (meth) acrylate, oligopropylene glycol di (meth) acrylate, 1,4-butanediol di (meth) acrylate, 2-ethyl-2-butylpropanediol Di (meth) acrylate, 1,9-nonanedi (meth) acrylate, propoxylated ethoxylated bisphenol A di (meth) acrylate, tricyclodecane di (meth) acrylate, diethylene glycol di (meth) acrylate, triethylene glycol di (meth) ) Acrylate, tetraethylene glycol di (meth) acrylate, polyethylene glycol di (meth) acrylate, 1,6-hexanediol di (meth) acrylate, ethylene glycol Di (meth) acrylate, triethylene glycol di (meth) acrylate, polyethylene glycol di (meth) acrylate, polypropylene glycol di (meth) acrylate.

  Specific examples of trifunctional (meth) acrylates include trimethylolpropane tri (meth) acrylate, trimethylolethane tri (meth) acrylate, trimethylolpropane alkylene oxide-modified tri (meth) acrylate, pentaerythritol tri (meth) acrylate , Dipentaerythritol tri (meth) acrylate, trimethylolpropane tri ((meth) acryloyloxypropyl) ether, isocyanuric acid alkylene oxide modified tri (meth) acrylate, propionate dipentaerythritol tri (meth) acrylate, tri ((meta ) Acryloyloxyethyl) isocyanurate, hydroxypivalaldehyde modified dimethylolpropane tri (meth) acrylate, sorbitol tri (meth) acrylate Rate, propoxylated trimethylolpropane tri (meth) acrylate, ethoxylated glycerin triacrylate, trimethylolethane tri (meth) acrylate, trimethylolpropane tri (meth) acrylate.

  Specific examples of tetrafunctional (meth) acrylates include pentaerythritol tetra (meth) acrylate, sorbitol tetra (meth) acrylate, ditrimethylolpropane tetra (meth) acrylate, dipentaerythritol tetra (meth) acrylate propionate, ethoxylated penta Examples include erythritol tetra (meth) acrylate, dipentaerythritol tetra (meth) acrylate, and tetramethylolmethane tetra (meth) acrylate.

  Specific examples of pentafunctional (meth) acrylates include sorbitol penta (meth) acrylate, dipentaerythritol penta (meth) acrylate, and the like.

  Specific examples of hexafunctional (meth) acrylate include dipentaerythritol hexa (meth) acrylate, sorbitol hexa (meth) acrylate, phosphazene alkylene oxide modified hexa (meth) acrylate, captolactone modified dipentaerythritol hexa (meth) acrylate , Etc.

  In the present invention, the polymerizable compound is at least selected from (a) at least one trifunctional or higher (meth) acrylate, and (b) a monofunctional (meth) acrylate and a bifunctional (meth) acrylate. It is preferable to include one type from the viewpoints of viscosity adjustment, crosslinking density adjustment, and physical property control after curing (strength, adhesiveness, etc.). In this case, the mixing ratio (molar ratio) of (a) :( b) is preferably 15:85 to 40:60, and more preferably 20:80 to 50:50.

Examples of radically polymerizable compounds other than the listed compounds include unsaturated carboxylic acids such as acrylic acid, methacrylic acid, itaconic acid, crotonic acid, isocrotonic acid, maleic acid and their salts, esters, urethanes, amides, and the like. Examples thereof include anhydrides, acrylonitrile, styrene, various unsaturated polyesters, unsaturated polyethers, unsaturated polyamides, and unsaturated urethanes. Specific examples include acrylic acid derivatives such as bis (4-acryloxypolyethoxyphenyl) propane and diacetone acrylamide, methacrylic derivatives such as 2,2-bis (4-methacryloxypolyethoxyphenyl) propane, and allyl glycidyl. Derivatives of allyl compounds such as ether, diallyl phthalate, triallyl trimellitate, etc. are mentioned, and more specifically, “Crosslinking agent handbook” (Yamashita Shinzo, 1981 Taiseisha), “UV / EB curing handbook (raw material) Ed.) "(Kyoto Kato ed., Kobunshi Publishing Co., Ltd. (1985))," Application and Market of UV / EB Curing Technology "(Radtech Research Group, 79 pages (1989), CMC)," Polyester Resin Commercial products or industries described in "Handbook" (by Eiichiro Takiyama, Nikkan Kogyo Shimbun (1988)) Known radical polymerizable or crosslinkable monomers may be used oligomers and polymers.
When the radically polymerizable compound is used as the curable compound, the content in the ink composition is preferably 5 to 95% by mass, more preferably 10 to 90% by mass, and more preferably 50 to 90% by mass with respect to the total amount of the ink composition. % Is particularly preferred.

(Cationically polymerizable compound)
The cationically polymerizable compound can be arbitrarily selected for the purpose of adjusting the degree of polymerization and the physical properties of the ink composition. Among these, oxirane compounds, oxetane compounds, vinyl ethers, styrenes, and the like are preferable from the viewpoint of polymerization rate and versatility. These may be used alone or in combination of two or more. Examples are shown below.

[Oxirane compounds]
Examples of the oxirane compound include aromatic epoxides and alicyclic epoxides. Aromatic epoxides include di- or polyglycidyl ethers produced by the reaction of polyphenols having at least one aromatic nucleus or their alkylene oxide adducts and epichlorohydrin, such as bisphenol A or its alkylene oxides. Examples thereof include di- or polyglycidyl ethers of adducts, di- or polyglycidyl ethers of hydrogenated bisphenol A or alkylene oxide adducts thereof, and novolak type epoxy resins. Here, examples of the alkylene oxide include ethylene oxide and propylene oxide.

Examples of the alicyclic epoxide include cyclohexene oxide obtained by epoxidizing a compound having at least one cycloalkane ring such as cyclohexene or cyclopentene ring with an appropriate oxidizing agent such as hydrogen peroxide or peracid. Preferred examples include cyclopentene oxide-containing compounds. Examples of the aliphatic epoxide include dihydric polyhydridyl ethers of aliphatic polyhydric alcohols or alkylene oxide adducts thereof, and typical examples thereof include diglycidyl ether of ethylene glycol, diglycidyl ether of propylene glycol or 1,6. -Diglycidyl ether of alkylene glycol such as diglycidyl ether of hexanediol, polyglycidyl ether of polyhydric alcohol such as di- or triglycidyl ether of glycerin or its alkylene oxide adduct, diglycidyl of polyethylene glycol or its adduct of alkylene oxide Polyalkylene glycol diglycol represented by diglycidyl ether of ether, polypropylene glycol or its alkylene oxide adduct Jill ether, and the like. Here, examples of the alkylene oxide include ethylene oxide and propylene oxide.
Among these oxirane compounds, aromatic epoxides and alicyclic epoxides are preferable from the viewpoint of excellent curing speed, and alicyclic epoxides are particularly preferable.
Further, among the oxirane compounds, those having a small number of functional groups are preferable because they can simultaneously have solubility and viscosity adjusting effects as described above.

  Examples of monofunctional epoxides used in the present invention include, for example, phenyl glycidyl ether, p-tert-butylphenyl glycidyl ether, butyl glycidyl ether, 2-ethylhexyl glycidyl ether, allyl glycidyl ether, 1,2-butylene oxide, 1 , 3-butadiene monooxide, 1,2-epoxydodecane, epichlorohydrin, 1,2-epoxydecane, styrene oxide, cyclohexene oxide, 3-methacryloyloxymethylcyclohexene oxide, 3-acryloyloxymethylcyclohexene oxide, 3- Examples include vinylcyclohexene oxide.

  Examples of polyfunctional epoxides include, for example, bisphenol A diglycidyl ether, bisphenol F diglycidyl ether, bisphenol S diglycidyl ether, brominated bisphenol A diglycidyl ether, brominated bisphenol F diglycidyl ether, brominated bisphenol S diglycidyl. Ether, epoxy novolac resin, hydrogenated bisphenol A diglycidyl ether, hydrogenated bisphenol F diglycidyl ether, hydrogenated bisphenol S diglycidyl ether, 3,4-epoxycyclohexylmethyl-3 ′, 4′-epoxycyclohexanecarboxylate, 2 -(3,4-epoxycyclohexyl-5,5-spiro-3,4-epoxy) cyclohexane-meta-dioxane, bis (3,4-epoxycyclohexyl) Til) adipate, vinylcyclohexene oxide, 4-vinylepoxycyclohexane, bis (3,4-epoxy-6-methylcyclohexylmethyl) adipate, 3,4-epoxy-6-methylcyclohexyl-3 ′, 4′-epoxy-6 '-Methylcyclohexanecarboxylate, methylenebis (3,4-epoxycyclohexane), dicyclopentadiene diepoxide, ethylene glycol di (3,4-epoxycyclohexylmethyl) ether, ethylenebis (3,4-epoxycyclohexanecarboxylate) , Epoxyhexahydrophthalate dioctyl, epoxyhexahydrophthalate di-2-ethylhexyl, 1,4-butanediol diglycidyl ether, 1,6-hexanediol diglycidyl ether, Resin triglycidyl ether, trimethylolpropane triglycidyl ether, polyethylene glycol diglycidyl ether, polypropylene glycol diglycidyl ethers, 1,1,3-tetradecadiene dioxide, limonene dioxide, 1,2,7,8-di Examples thereof include epoxy octane, 1,2,5,6-diepoxycyclooctane and the like.

[Oxetane compounds]
The oxetane compound in the present invention refers to a compound having an oxetane ring, and arbitrarily selected from known oxetane compounds as described in JP-A Nos. 2001-220526, 2001-310937, and 2003-341217. Can be used.
As the compound having an oxetane ring that can be used in the ink composition of the present invention, a compound having 1 to 4 oxetane rings in its structure is preferable, and as described above, the viscosity and tackiness of the ink composition are particularly preferable. From the viewpoint, it is preferable to use a compound having one oxetane ring. By using such a compound, it becomes easy to maintain the viscosity of the ink composition in a good handling property range, and it is possible to obtain high adhesion of the cured ink to the recording medium. .

  Examples of monofunctional oxetanes include oxetane compounds used in the present invention, such as 3-ethyl-3-hydroxymethyloxetane, 3- (meth) allyloxymethyl-3-ethyloxetane, and (3-ethyl-3 -Oxetanylmethoxy) methylbenzene, 4-fluoro- [1- (3-ethyl-3-oxetanylmethoxy) methyl] benzene, 4-methoxy- [1- (3-ethyl-3-oxetanylmethoxy) methyl] benzene, [ 1- (3-ethyl-3-oxetanylmethoxy) ethyl] phenyl ether, isobutoxymethyl (3-ethyl-3-oxetanylmethyl) ether, isobornyloxyethyl (3-ethyl-3-oxetanylmethyl) ether, isobornyl (3-Ethyl-3-oxetanylmethyl) ether, 2-ethyl Hexyl (3-ethyl-3-oxetanylmethyl) ether, ethyldiethylene glycol (3-ethyl-3-oxetanylmethyl) ether, dicyclopentadiene (3-ethyl-3-oxetanylmethyl) ether, dicyclopentenyloxyethyl (3- Ethyl-3-oxetanylmethyl) ether, dicyclopentenyl (3-ethyl-3-oxetanylmethyl) ether, tetrahydrofurfuryl (3-ethyl-3-oxetanylmethyl) ether, tetrabromophenyl (3-ethyl-3-oxetanyl) Methyl) ether, 2-tetrabromophenoxyethyl (3-ethyl-3-oxetanylmethyl) ether, tribromophenyl (3-ethyl-3-oxetanylmethyl) ether, 2-tribromophenoxyethyl (3-ethyl) Ru-3-oxetanylmethyl) ether, 2-hydroxyethyl (3-ethyl-3-oxetanylmethyl) ether, 2-hydroxypropyl (3-ethyl-3-oxetanylmethyl) ether, butoxyethyl (3-ethyl-3- Oxetanylmethyl) ether, pentachlorophenyl (3-ethyl-3-oxetanylmethyl) ether, pentabromophenyl (3-ethyl-3-oxetanylmethyl) ether, bornyl (3-ethyl-3-oxetanylmethyl) ether, and the like. .

  Examples of the polyfunctional oxetane include 3,7-bis (3-oxetanyl) -5-oxa-nonane, 3,3 ′-(1,3- (2-methylenyl) propanediylbis (oxymethylene)) bis. -(3-ethyloxetane), 1,4-bis [(3-ethyl-3-oxetanylmethoxy) methyl] benzene, 1,2-bis [(3-ethyl-3-oxetanylmethoxy) methyl] ethane, 1, 3-bis [(3-ethyl-3-oxetanylmethoxy) methyl] propane, ethylene glycol bis (3-ethyl-3-oxetanylmethyl) ether, dicyclopentenylbis (3-ethyl-3-oxetanylmethyl) ether, tri Ethylene glycol bis (3-ethyl-3-oxetanylmethyl) ether, tetraethylene glycol bis (3-ethyl) -3-oxetanylmethyl) ether, tricyclodecanediyldimethylene (3-ethyl-3-oxetanylmethyl) ether, trimethylolpropane tris (3-ethyl-3-oxetanylmethyl) ether, 1,4-bis (3- Ethyl-3-oxetanylmethoxy) butane, 1,6-bis (3-ethyl-3-oxetanylmethoxy) hexane, pentaerythritol tris (3-ethyl-3-oxetanylmethyl) ether, pentaerythritol tetrakis (3-ethyl-3 -Oxetanylmethyl) ether, polyethylene glycol bis (3-ethyl-3-oxetanylmethyl) ether, dipentaerythritol hexakis (3-ethyl-3-oxetanylmethyl) ether, dipentaerythritol pentakis (3-ethyl) 3-oxetanylmethyl) ether, dipentaerythritol tetrakis (3-ethyl-3-oxetanylmethyl) ether, caprolactone-modified dipentaerythritol hexakis (3-ethyl-3-oxetanylmethyl) ether, caprolactone-modified dipentaerythritol pentakis ( 3-ethyl-3-oxetanylmethyl) ether, ditrimethylolpropanetetrakis (3-ethyl-3-oxetanylmethyl) ether, EO-modified bisphenol A bis (3-ethyl-3-oxetanylmethyl) ether, PO-modified bisphenol A bis ( 3-ethyl-3-oxetanylmethyl) ether, EO-modified hydrogenated bisphenol A bis (3-ethyl-3-oxetanylmethyl) ether, PO-modified hydrogenated bisphenol A bis (3-ethyl) And polyfunctional oxetanes such as ru-3-oxetanylmethyl) ether and EO-modified bisphenol F (3-ethyl-3-oxetanylmethyl) ether.

[Vinyl ethers]
Examples of monofunctional vinyl ethers include, for example, methyl vinyl ether, ethyl vinyl ether, propyl vinyl ether, n-butyl vinyl ether, t-butyl vinyl ether, 2-ethylhexyl vinyl ether, n-nonyl vinyl ether, lauryl vinyl ether, cyclohexyl vinyl ether, cyclohexyl methyl vinyl ether, 4 -Methylcyclohexyl methyl vinyl ether, benzyl vinyl ether, dicyclopentenyl vinyl ether, 2-dicyclopentenoxyethyl vinyl ether, methoxyethyl vinyl ether, ethoxyethyl vinyl ether, butoxyethyl vinyl ether, methoxyethoxyethyl vinyl ether, ethoxyethoxyethyl vinyl ether, methoxypolyethylene glycol vinyl D Ter, tetrahydrofurfuryl vinyl ether, 2-hydroxyethyl vinyl ether, 2-hydroxypropyl vinyl ether, 4-hydroxybutyl vinyl ether, 4-hydroxymethylcyclohexyl methyl vinyl ether, diethylene glycol monovinyl ether, polyethylene glycol vinyl ether, chloroethyl vinyl ether, chlorobutyl vinyl ether, chloro Examples thereof include ethoxyethyl vinyl ether, phenylethyl vinyl ether, phenoxy polyethylene glycol vinyl ether and the like.

  Examples of polyfunctional vinyl ethers include, for example, ethylene glycol divinyl ether, diethylene glycol divinyl ether, polyethylene glycol divinyl ether, propylene glycol divinyl ether, butylene glycol divinyl ether, hexanediol divinyl ether, bisphenol A alkylene oxide divinyl ether, bisphenol F alkylene oxide. Divinyl ethers such as divinyl ether; trimethylolethane trivinyl ether, trimethylolpropane trivinyl ether, ditrimethylolpropane tetravinyl ether, glycerin trivinyl ether, pentaerythritol tetravinyl ether, dipentaerythritol pentavinyl ether, dipentaerythritol hex Vinyl ether, ethylene oxide-added trimethylolpropane trivinyl ether, propylene oxide-added trimethylolpropane trivinyl ether, ethylene oxide-added ditrimethylolpropane tetravinyl ether, propylene oxide-added ditrimethylolpropane tetravinyl ether, ethylene oxide-added pentaerythritol tetravinyl ether, propylene oxide-added penta And polyfunctional vinyl ethers such as erythritol tetravinyl ether, ethylene oxide-added dipentaerythritol hexavinyl ether, and propylene oxide-added dipentaerythritol hexavinyl ether.

[Styrenes]
Specific examples include styrene, methyl styrene, dimethyl styrene, trimethyl styrene, ethyl styrene, isopropyl styrene, chloromethyl styrene, methoxy styrene, acetoxy styrene, chloro styrene, dichloro styrene, bromo styrene, vinyl benzoic acid methyl ester, 3 -Methylstyrene, 4-methylstyrene, 3-ethylstyrene, 4-ethylstyrene, 3-propylstyrene, 4-propylstyrene, 3-butylstyrene, 4-butylstyrene, 3-hexylstyrene, 4-hexylstyrene, 3 -Octylstyrene, 4-octylstyrene, 3- (2-ethylhexyl) styrene, 4- (2-ethylhexyl) styrene, allylstyrene, isopropenylstyrene, butenylstyrene, octenylstyrene, 4- - butoxycarbonyl styrene, 4-methoxystyrene, and a 4-t-butoxystyrene.

In the present invention, it is preferable from the viewpoint of curing speed that the curable compound includes at least one selected from an oxirane compound and an oxetane compound which are cationic polymerizable compounds. In this case, the mixing ratio (molar ratio) of oxirane compound: oxetane compound is preferably 90:10 to 10:90, and more preferably 70:30 to 30:70. Also. It is also preferable to use an oxetane compound and styrene at a mixing ratio of 90:10 to 50:50.
When the cationic polymerizable compound is used as the curable compound, the content in the ink composition is preferably 5 to 95% by mass, more preferably 10 to 90% by mass, and more preferably 50 to 90% by mass with respect to the total amount of the ink composition. Is particularly preferred.

(Polymerization initiator)
The ink composition of the present invention contains a known polymerization initiator capable of generating an initiation species by ultraviolet exposure and curing the curable compound. As the polymerization initiator, a radical polymerization initiator or a cationic polymerization initiator can be used, and a curable compound to be used, that is, a compound suitable for the radical polymerizable compound or the cationic polymerizable compound is selected and used in combination.

(Radical polymerization initiator)
Preferred radical polymerization initiators that can be used in the present invention include (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.
The radical polymerization initiator in the present invention may be used alone or in combination.
The radical polymerization initiator in the present invention is preferably 0.01 to 35% by mass, more preferably 0.1 to 30% by mass, and still more preferably 0.5 to 30% by mass, based on the total amount of the radical polymerizable compound. It is suitable to contain in the range of%.

(Cationic polymerization initiator)
When a cationically polymerizable compound is used as the curable compound, the ink composition of the present invention preferably contains a photoacid generator. This photoacid generator (hereinafter also referred to as “cationic polymerization initiator”) refers to a compound that generates an acid upon irradiation with actinic rays or actinic radiation to initiate cationic polymerization, and includes known compounds and mixtures thereof. It can be appropriately selected and used.

  Examples of the cationic polymerization initiator in the present invention include diazonium salts, phosphonium salts, sulfonium salts, iodonium salts, imide sulfonates, oxime sulfonates, diazodisulfones, disulfones, and o-nitrobenzyl sulfonates.

Further, these cationic polymerization initiators, or compounds obtained by introducing a group or compound having an equivalent function into the main chain or side chain of the polymer, such as US Pat. No. 3,849,137 and German Patent No. 3914407. JP, 63-26653, JP, 55-164824, JP, 62-69263, JP, 63-146038, JP, 63-163452, JP, 62-153853, The compounds described in JP-A 63-146029 can be used.
Further, compounds capable of generating an acid by light described in US Pat. No. 3,779,778, European Patent 126,712 and the like can also be used.

  As the cationic polymerization initiator, those listed above may be used alone or in combination of two or more. The content of the cationic polymerization initiator in the ink composition is preferably 0.1 to 20% by mass, and more preferably 0.5 to 10% by mass. When the content of the cationic polymerization initiator is within the above range, excellent curability is obtained, and problems such as embrittlement of the obtained cured ink image and generation of acid due to the remaining initiator do not occur.

[Other ingredients]
In the ink composition of the present invention, various additives can be used in combination with the above-described essential components as necessary, as long as the effects of the present invention are not impaired. These additives will be described.

[Polymerization inhibitor]
In the present invention, it is preferable to use a polymerization inhibitor that inhibits the progress of polymerization other than the cationic polymerization in order to effectively proceed the polymerization by the cationic polymerization initiator.
Suitable polymerization inhibitors include phenolic hydroxyl group-containing compounds and quinones, N-oxide compounds, piperidine 1-oxyl free radical compounds, pyrrolidine 1-oxyl free radical compounds, N-nitrosophenylhydroxylamines, and cations. It is a compound selected from the group consisting of dyes. Preferred polymerization inhibitors include haloid quinone, p-methoxyphenol, di-t-butyl-p-cresol, pyrogallol, resorcinol, catechol, t-butylcatechol, hydroquinone, benzoquinone, 4,4-thiobis (3-methyl-6- t-butylphenol), 2,2'-methylenebis (4-methyl-6-t-butylphenol), 2,2,6,6-tetramethylpiperidine and its derivatives, di-t-butylnitroxide, 2,2,6 , 6-tetramethylpiperidine-N-oxide and its derivatives, such as piperidine 1-oxyl free radical, 2,2,6,6-tetramethylpiperidine 1-oxyl free radical, 4-oxo-2,2,6,6 -Tetramethylpiperidine 1-oxyl free radical, 4-hydroxy Ci-2,2,6,6-tetramethylpiperidine 1-oxyl free radical, 4-acetamido-2,2,6,6-tetramethylpiperidine 1-oxyl free radical, 4-maleimide-2,2,6 6-tetramethylpiperidine 1-oxyl free radical, 4-phosphonoxy-2,2,6,6-tetramethylpiperidine 1-oxyl free radical, 3-carboxy-2,2,5,5-tetramethylpyrrolidine 1-oxyl Examples include free radicals, N-nitrosophenylhydroxylamine cerium salt, N-nitrosophenylhydroxylamine aluminum salt, crystal violet, methyl violet, ethyl violet, and Victoria Pure Blue BOH. The addition amount of the polymerization inhibitor is preferably about 0.01% by mass to about 5% by mass with respect to the mass of the ink composition.

[Ultraviolet absorber]
From the viewpoint of improving the weather resistance of the resulting image and preventing discoloration, an ultraviolet absorber can be used.
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 No. 24239, compounds that emit ultraviolet light by absorbing ultraviolet rays typified by stilbene and benzoxazole compounds, so-called fluorescent brighteners, and the like.
The amount added is appropriately selected according to the purpose, but is generally about 0.01 to 10% by mass of the ink composition.

〔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.
The addition amount is appropriately selected according to the purpose, but is generally about 0.001 to 1% by mass of the ink composition.

〔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.
Examples of the solvent include ketone solvents such as acetone, methyl ethyl ketone, diethyl ketone, and cyclohexanone, alcohol solvents such as methanol, ethanol, 2-propanol, 1-propanol, 1-butanol, and tert-butanol, chloroform, and methylene chloride. Chlorine 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, ethylene glycol monomethyl ether, ethylene glycol dimethyl ether, etc. And glycol 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 mass, more preferably 0.1 to 3% by mass with respect to the whole ink composition. % Range.

[Polymer compound]
Various polymer compounds can be added to the ink composition in order to adjust film properties. Examples of the polymer compound include styrene polymers, acrylic polymers, cyclic ether polymers, polyvinyl butyral resins, polyurethane resins, polyamide resins, polyester resins, epoxy resins, phenol resins, polycarbonate resins, polyvinyl butyral resins, and polyvinyl formal resins. Shellac, vinyl resin, acrylic resin, rubber resin, wax, and other natural resins can be used. Two or more of these may be used in combination. Of these, copolymerization of styrene monomers, acrylic monomers, and cyclic ethers is preferred. Furthermore, as a copolymer composition of the polymer binder, a copolymer containing “cyclic ether group-containing monomer” and “vinyl ether group-containing monomer” as a structural unit is also preferably used.
The addition amount is appropriately selected according to the purpose, but is generally about 0.01 to 10.0% by mass of the ink composition.

[Surfactant]
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 addition amount is appropriately selected according to the purpose, but is generally about 0.001 to 5.0% by mass of the ink composition.

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 the tackifier, specifically, a high molecular weight adhesive polymer described in JP-A-2001-49200, 5-6p (for example, (meth) acrylic acid and an alkyl group having 1 to 20 carbon atoms). An ester with an alcohol having, an ester of (meth) acrylic acid with an alicyclic alcohol having 3 to 14 carbon atoms, a copolymer comprising an ester of (meth) acrylic acid with an aromatic alcohol having 6 to 14 carbon atoms) And a low molecular weight tackifying resin having a polymerizable unsaturated bond.

[Preferred physical properties of ink composition]
The ink composition of the present invention preferably has an ink viscosity of 50 mPa · s or less, more preferably 30 mPa · s or less at the temperature at the time of ejection in consideration of ejection properties. It is preferable to adjust and determine the composition ratio. The ink viscosity at 25 ° C. is 10 to 300 mPa · s, preferably 10 to 100 mPa · s. By setting the viscosity at room temperature high, even when a porous recording medium is used, ink penetration into the recording medium can be prevented, uncured monomer can be reduced, and odor can be reduced. Dot bleeding at the time of landing can be suppressed, and as a result, the image quality is improved. If the ink viscosity at 25 ° C. is less than 10 mPa · s, the effect of preventing bleeding is small. Conversely, if the ink viscosity is more than 500 mPa · s, problems may occur in the delivery of the ink liquid.

  The surface tension of the ink composition of the present invention is preferably 20 to 30 mN / m, more preferably 23 to 28 mN / m. When recording on various recording media such as polyolefin, PET, coated paper, and non-coated paper, 20 mN / m or more is preferable from the viewpoint of bleeding and penetration, and 30 mN / m or less is preferable in terms of wettability.

[Inkjet recording method]
The ink composition of the present invention can be suitably used as an ink for inkjet recording. There are no particular restrictions on the ink jet recording method, for example, a charge control method that ejects ink using electrostatic attraction, a drop-on-demand method (pressure pulse method) that uses the vibration pressure of a piezo element, and an electrical signal that is acoustic Either an acoustic ink jet system that irradiates ink by irradiating it with ink instead of using a beam, or a thermal ink jet system that uses ink to form bubbles by heating the ink and use the generated pressure. Also good. The inkjet recording method includes a method of ejecting a large number of low-density inks called photo inks in a small volume, a method of improving image quality using a plurality of inks having substantially the same hue and different concentrations, and colorless and transparent. A method using ink.
Among these, the ink is suitable as a drop-on-demand type (pressure pulse type) ink jet recording ink using a piezo element.

EXAMPLES Hereinafter, although this invention is demonstrated concretely based on an Example, this invention is not limited to these Examples.
Example 1
[Synthesis Example 1: Synthesis of Polymer Dispersant 1]
In a nitrogen atmosphere, the mixture was heated to 80 ° C. using methyl ethyl ketone as a solvent, and 2,2′-azobisisobutyronitrile (abbreviation A.I.B) of 1 mol% of the total amount of monomers as an initiator with respect to the following monomers. N.) was added, and the following compound I, which is a chain transfer agent, was post-added and polymerized for 4 hours to obtain a polymer dispersant 1. The charged amount is as shown below.
Compound I (the following structure) 7.5 wt%
Methyl methacrylate 25.0wt%
Ethyl acrylate 17.5wt%
Methyl ethyl ketone 50.0wt%

[Ink adjustment]
The pigment, polymerization initiator, sensitizing dye, 3 types of curable compounds and the polymer compound 1 obtained in Synthesis Example 1 were dispersed with a disperser at the following blending ratio to prepare an ink composition.
Pigment: Alumina-treated titanium oxide (particle surface alumina treatment rate 60%) 15 wt%
Polymerization initiator: Triphenylsulfonium salt (UVI-6992, manufactured by Dow Chemical Company)
15 wt%
Sensitizing dye: 9,10-dibutoxyanthracene 1 wt%
Polymerizable compound: 3,4-epoxycyclohexylmethyl-3 ′, 4′-epoxycyclohexanecarboxylate (Celoxide 2021A: manufactured by Daicel UC Corporation)
45wt%
Polymerizable compound: 3,7-bis (3-oxetanyl) -5-oxanonane (OXT-22)
1: Toagosei Co., Ltd.) 20wt%
Triethylene glycol divinyl ether 2wt%
Polymer dispersant: Methyl ethyl ketone solution of polymer dispersant 1 obtained in Synthesis Example 1
2wt%

(Example 2)
[Synthesis Example 2: Synthesis of Polymer Dispersant 2]
In a nitrogen atmosphere, the mixture was heated to 80 ° C. using methyl ethyl ketone as a solvent, and 2,2′-azobisisobutyronitrile (abbreviation A.I.B) of 1 mol% of the total amount of monomers as an initiator with respect to the following monomers. N.) was added, and the following compound II, which is a chain transfer agent, was post-added and polymerized for 4 hours to obtain a polymer dispersant 2. The charged amount is as shown below.
Compound II (the following structure) 7.5 wt%
Methyl methacrylate 25.0wt%
Ethyl acrylate 17.5wt%
Methyl ethyl ketone 50.0wt%

[Ink adjustment]
An ink composition of Example 2 was prepared in the same manner as in the ink formulation example of Example 1, except that the polymer dispersant 2 was used instead of the polymer dispersant 1.

(Comparative Example 1)
An ink composition of Comparative Example 1 was produced in the same manner as in Example 1 except that the polymer dispersant used in the ink composition of Example 1 was not added.
(Comparative Example 2)
Instead of the polymer dispersant 1 used in the ink composition of Example 1, polymethyl methacrylate (weight average molecular weight: 15,000), which is a comparative polymer dispersant having no acid group at the terminal, was used. Otherwise, the ink composition of Comparative Example 2 was prepared in the same manner as in Example 1.

  Evaluation of the viscosity, dispersibility, sedimentation, redispersibility, concealability, ejection stability, curability, adhesion, and weather resistance of the ink compositions of Examples 1 and 2 and Comparative Examples 1 and 2 by the following methods. did.

[Evaluation of ink composition]
(1. Viscosity)
The viscosity of each inkjet ink at 40 ° C. was measured using an E-type viscometer (manufactured by Toki Sangyo).
A: Less than 30 mPas B: 30 mPas or more, less than 100 mPas C: 100 mPas or more (a level causing a problem in ejection)

(2. Dispersibility)
(2-1. Presence / absence of aggregated particles)
Dispersibility was evaluated using an optical microscope.
A: No particles of 1 μm or more (good dispersibility and no large aggregated particles are seen).
B: There are particles of 1 μm or more (aggregation of pigment particles occurs).

(2-2. Precipitation)
The state of pigment precipitation after standing for 1 month at room temperature in a 50 ml glass container was visually evaluated. Three-stage evaluation of 3, 2, 1 was performed in order of the amount of sedimentation.

(2-3. Redispersibility)
After forced sedimentation in a centrifuge (rotation speed 5000 rpm, 30 minutes), constant stirring was performed to evaluate redispersibility. Three-stage evaluation of 3, 2, 1 was performed in order of good redispersibility.

(2-4. Discharge stability)
After the ink composition was continuously printed by an ink jet printer for 60 minutes, A was evaluated to be ejected without any problem, B was evaluated for some satellites, and C was evaluated for missing nozzles.

The obtained ink composition was printed on art paper with an inkjet printer (printing density 300 dpi, droplet ejection frequency 4 kHz, nozzle number 64), and then an energy of 15 mJ / cm ^{2 with} a Deep UV lamp (US-7, SP-7). The sample was exposed under the following conditions to obtain a print sample.
Samples 10 minutes after printing were evaluated for the following evaluation items 3 to 5.

(3. Curability)
The printed surface was evaluated by a tack-free test. The cured film was touched with a finger to check for stickiness and evaluated according to the following criteria.
A: When there is no stickiness B: When there is slight stickiness C: When stickiness is extremely sticky In addition, the exposure energy by the Deep UV lamp used for curing the ink is 7.5 mJ / cm ² with respect to the sample obtained with A evaluation. A print sample was prepared in the same manner except that, and even when it was evaluated in the same manner, the case where there was no stickiness was evaluated as S.

(4. Adhesiveness)
After cutting the cut surface in a grid pattern with a cutter, attach an adhesive tape to the surface, and then visually observe the remaining state of the cured film on the substrate when the adhesive tape is peeled off according to the following criteria: did.
A: No peeling was observed B: Partial peeling was observed C: Remarkable peeling was observed D: Insufficient curing and could not be evaluated

(2. Concealment)
It was applied to black paper with a bar coater, and the concealability of the coating after curing was visually evaluated. Three-stage evaluation of 3, 2, 1 was performed in order of good concealability.

(5. Light resistance)
The photographic paper on which the image is formed is irradiated with xenon light (100,000 lx) for 3 days using a weather meter (Atlas C.165), and the image density before and after the xenon irradiation is measured using a reflection densitometer (X-Rite 310TR). It was measured and evaluated as the dye residual ratio according to the following criteria. The reflection density was fixed at 1.0 and measured.
A: Dye remaining ratio is 80% or more B: Dye remaining ratio is 70% or more and less than 80% C: Dye remaining ratio is less than 70%

As shown in Table 1, the ink composition of the present invention using the polymer dispersant having an acidic group at the terminal has a low viscosity, the precipitation of the pigment is suppressed, and the dispersibility and redispersibility are good. It can be seen that the ink ejection stability is excellent. Furthermore, the image formed by the ink composition of the present invention had good adhesion and concealment with the recording medium while maintaining the curability and weather resistance of the coating film.
With such an ink composition, there is little clogging and ink supply to the apparatus is stable. In contrast, the ink composition of Comparative Example 1 that does not contain the polymer dispersant according to the present invention is inferior in ink stability, in particular, dispersibility, sedimentation, and redispersibility, and can be ejected normally. could not. Further, in Comparative Example 2 containing a polymer dispersant outside the scope of the present invention, the dispersibility, sedimentation, and redispersibility are inferior, the discharge stability is not satisfied, and the formed image is concealed. The level was low and problematic in practical use.

Claims (4)

  An ultraviolet curable inkjet white ink composition comprising a white pigment dispersed with a polymer dispersant, wherein the polymer dispersant is a vinyl polymer having a substituent consisting of an acid or a salt thereof at a terminal.   The white ink composition for inkjet according to claim 1, wherein the polymer dispersant has at least one of a sulfonyl group and a phosphonyl group in the molecule.   The white ink composition for inkjet according to claim 1, comprising a curable compound capable of dissolving the polymer dispersant.   The curable compound is at least one selected from the group consisting of a cationic polymerizable compound having at least one of an oxirane group or an oxetane group and a radical polymerizable compound having at least one (meth) acryl group. Item 4. The white ink composition for inkjet according to item 3.