JP5159232B2 - Ink composition and ink jet recording method using the same - Google Patents

Description

  The present invention relates to an ink composition and an ink jet recording method using the same. More specifically, the present invention relates to an ink composition suitable for inkjet recording and an inkjet recording method, which is cured with high sensitivity to irradiation with actinic radiation, and the cured product has sufficient flexibility even after ink curing. .

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 actinic radiation such as ultraviolet rays (radiation curable ink compositions), such as ink compositions for ink jet recording, can be cured with high sensitivity and form high-quality images. It has been demanded. 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.

The curable inkjet method using ultraviolet light has been attracting attention in recent years because it has a relatively low odor and can record on a recording medium having no quick drying and no ink absorption.
As the photopolymerization initiator used in such a photopolymerization-curable ink composition, benzyl, benzoin, benzoin ethyl ether, Michler's ketone, anthraquinone, acridine, phenazine, benzophenone, 2-ethylanthraquinone and the like are common ( Non-patent document 1, Patent document 1). However, when these general photopolymerization initiators are used, the curing sensitivity of the photopolymerizable composition is not sufficient, and it takes a long time for image exposure in image formation and attempts to form a fine image. In such a case, there is a problem that an image with good image quality cannot be formed if there is slight vibration during the image forming process. Furthermore, since the total amount of energy radiation of the light source for exposure increases, it is necessary to consider the radiation of a large amount of heat accompanying it.

Conventionally, as a method for increasing the sensitivity to radiation in a radiation curable polymerizable compound, it has been proposed to use a sensitizing dye together with a photopolymerization initiator, and the use of various polymerization initiation systems has been disclosed. For example, it has been proposed to use a thioxanthone compound as a sensitizing dye (for example, Patent Document 1 and Patent Document 2). However, sensitizing dyes such as thioxanthone compounds remain as monomers without being bonded to other compounds in the cured film even after curing of the polymerizable composition. Because it is a low molecular weight component that moves to the substance, it exhibits the same behavior as a plasticizer in the cured film, reducing the film strength, or causing the stickiness of the cured film surface and reducing the surface curing sensitivity. It tends to occur.
In this technical field using an ink composition, blocking between an image formed on an ink receiving layer and another substance in contact with the image, that is, transferring from an image of an ink to another substance, One of the important issues is to suppress the occurrence of undesired adhesion with other substances due to the ink. For this reason, although it has been proposed to apply a polyfunctional thioxanthone compound having excellent blocking resistance to the ink composition (for example, Patent Document 3), the obtained ink composition has a high viscosity and is suitable for an inkjet ink. Is unsuitable.
JP-A-6-308727 JP-A-56-143202 Special table 2005-512973

  An object of the present invention is an ink composition having a high blocking resistance in which high-quality images can be formed with high sensitivity even when irradiated with low-output radiation, and stickiness of the formed image surface is suppressed. And an ink jet recording method using the ink composition.

As a result of intensive studies to solve the above problems, the present inventors have found that an ink composition containing a sensitizing dye having a polymerizable group as a substituent is cured with high sensitivity and suppresses surface stickiness of the cured film. The present invention was completed by discovering excellent blocking resistance.
That is, the ink composition of the present invention contains (i) a sensitizing dye having a polymerizable group as a substituent, (ii) a polymerization initiator, and (iii) a polymerizable compound having an ethylenically unsaturated bond. It is characterized by that.
Examples of the sensitizing dye having used in the ink composition of the present invention: (i) a polymerizable group as a substituent, Ru der least one selected from compounds represented by the SL one general formula (II) . Hereinafter, such a sensitizing dye is appropriately referred to as “specific sensitizing dye”.

In one general formula (II), X is O, S, or represents NR ^b. n ₂ represents 0 or 1.
R ^b , R ¹¹ , R ¹² , R ¹³ , R ¹⁴ , R ¹⁵ , R ¹⁶ , R ¹⁷ , and R ¹⁸ each independently represent a hydrogen atom or a monovalent substituent, and at least one of them Is a polymerizable group which reacts with a radical.
Two of R ¹¹ , R ¹² , R ¹³ , and R ¹⁴ may be linked to each other to form a ring.

  When forming a colored image with the ink composition of the present invention, the ink composition preferably further contains (iv) a colorant. In addition, the ink composition of the present invention can be cured with high sensitivity by radiation irradiation, and therefore is suitable for inkjet recording.

  The ink jet 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) irradiating the ejected ink composition with actinic radiation to form an ink composition. And a step of curing the object.

Although the operation of the present invention is not clear, it is estimated as follows.
The sensitizing dye used in the present invention is characterized by having a polymerizable group. Since the sensitizing dye itself functions as a polymerizable compound, the number of polymerizable groups in the ink composition increases, resulting in a cured film. The cross-linking density in the resin is improved, and it is difficult to remain as a low molecular weight compound in a free state in the cured film. Therefore, the sensitizing dye moves to another substance that is in contact with it, or is oriented on the surface of the cured film. It is thought that the situation that causes stickiness can be suppressed. For this reason, the ink composition of the present invention containing such a sensitizing dye is considered to be cured with high sensitivity even when irradiated with low-power radiation, to suppress surface stickiness, and to have high blocking resistance. .

According to the present invention, an ink composition having high blocking resistance in which high-quality images can be formed with high sensitivity even when irradiated with low-output radiation, and stickiness of the formed image surface is suppressed. Things can be provided.
Furthermore, by using the ink composition of the present invention, it is possible to provide an ink jet recording method capable of forming an image having high image quality and excellent blocking resistance.

[Ink composition]
First, the ink composition of the present invention will be described in detail.
The ink composition of the present invention contains (i) a sensitizing dye having a specific structure having a polymerizable group as a substituent , (ii) a polymerization initiator, and (iii) a polymerizable compound having an ethylenically unsaturated bond. .
The ink composition of the present invention can be suitably used for inkjet recording.
Hereinafter, components essential to the ink composition of the present invention will be sequentially described.

<(I) Sensitizing dye having a polymerizable group as a substituent>
The ink composition of the present invention contains a sensitizing dye in order to promote decomposition of the polymerization initiator by irradiation with actinic rays, and a sensitizing dye having a polymerizable group that reacts with a radical is used as the sensitizing dye. It is characterized by.
In general, a sensitizing dye absorbs specific actinic radiation and enters an electronically excited state. The sensitizing dye in an electronically excited state is brought into contact with the polymerization initiator to cause actions such as electron transfer, energy transfer, and heat generation, thereby causing a chemical change of the polymerization initiator, that is, decomposition, radical, acid or base. The generation of active species such as these causes the active species generated here to cause and accelerate the polymerization and curing reaction of the polymerizable compound described later.

As the sensitizing dye, a compound corresponding to the wavelength of actinic radiation that generates an initiating species in the polymerization initiator used in the ink composition may be used, but it should be used for a curing reaction of a general ink composition. In view of the above, examples of preferable sensitizing dyes include those having an absorption wavelength in the 350 nm to 450 nm region and a high triplet energy.
Since the sensitizing dye used in the present invention itself has a polymerizable group, it is useful for improving the curing sensitivity and fixing the sensitizing dye in the cured film.
Examples of the polymerizable group contained in the sensitizing dye include a substituent having an ethylenically unsaturated bond. Preferred examples of the polymerizable group that reacts with a radical include an acryloyl group, a methacryloyl group, a styryl group, a vinyl group, and an allyl group, and more preferred are an acryloyl group and a methacryloyl group.
The sensitizing dye molecule may have at least one such polymerizable group, and may contain a plurality of polymerizable groups. Since the ink viscosity increases as the number of polymerizable groups increases, it is preferable that the number of polymerizable groups is small from the viewpoint of viscosity. The number of polymerizable groups is preferably one or two, and most preferably a compound having only one polymerizable group.
As such sensitizing dyes, sensitizing dyes represented by the SL one general formula (II) are exemplified up.

In the general formula (II), X O, S, or represents NR ^b. n ₂ represents an integer of 0 or 1.
R ^b , R ¹¹ , R ¹² , R ¹³ , R ¹⁴ , R ¹⁵ , R ¹⁶ , R ¹⁷ , and R ¹⁸ each independently represent a hydrogen atom or a monovalent substituent, and at least one of these represents It is a polymerizable group that reacts with radicals.
One polymerizable group is preferably contained, and R ¹² , R ¹⁷ and R ¹⁸ are preferable as the substitution position of the polymerizable group.

When R ^b , R ¹¹ , R ¹² , R ¹³ , R ¹⁴ , R ¹⁵ , R ¹⁶ , R ¹⁷ , and R ¹⁸ represent a monovalent substituent, the monovalent substituent includes a halogen atom, an aliphatic Group, aromatic group, heterocyclic group, cyano group, hydroxy group, nitro group, amino group, alkylamino group, alkoxy group, aryloxy group, amide group, arylamino group, ureido group, sulfamoylamino group, Alkylthio group, arylthio group, alkoxycarbonylamino group, sulfonamido group, carbamoyl group, sulfamoyl group, substituted sulfonyl group, alkoxycarbonyl group, heterocyclic oxy group, azo group, acyloxy group, carbamoyloxy group, silyloxy group, aryloxycarbonyl Group, aryloxycarbonylamino group, imide group, heterocyclic thio group, substituted group Finiru group, a substituted phosphoryl group, an acyl group, a carboxy group or a sulfo group. Of these, an alkyl group, a halogen atom, an alkoxy group, an alkylthio group, and a carboxy group are more preferable. Particularly preferred are an alkyl group and a halogen atom.
Preferred examples of the polymerizable group that reacts with a radical include acryloyl group, methacryloyl group, styryl group, vinyl group, and allyl group. More preferred is an acryloyl group, a methacryloyl group, and still more preferred is an acryloyl group.

In the general formula (II), as R ^b , R ¹¹ , R ¹² , R ¹³ , R ¹⁴ , R ¹⁵ , R ¹⁶ , R ¹⁷ , and R ¹⁸ represent a monovalent substituent, Preferred examples include those having 1 to 4 carbon atoms such as methyl group, ethyl group, propyl group, isopropyl group, n-butyl group, sec-butyl group, t-butyl group, and methyl group, ethyl group, propyl group. An isopropyl group is more preferable, and a methyl group and an ethyl group are particularly preferable.
Similarly, the alkoxy group has 1 to 4 carbon atoms such as methoxy group, ethoxy group, hydroxyethoxy group, isopropoxy group, propoxy group, n-butoxy group, isobutoxy group, sec-butoxy group, and t-butoxy group. Preferably, a methoxy group, an ethoxy group, an isopropoxy group, and a propoxy group are more preferable, and a methoxy group and an ethoxy group are particularly preferable.
Similarly, examples of the halogen atom include a fluorine atom, a chlorine atom, a bromine atom and an iodine atom, a chlorine atom, a bromine atom and an iodine atom are more preferred, and a chlorine atom and a bromine atom are particularly preferred.

Two of R ¹¹ , R ¹² , R ¹³ , and R ¹⁴ may be linked to each other, for example, condensed to form a ring.
Examples of the ring structure in the case where these form a ring include a 5- to 6-membered aliphatic ring and an aromatic ring, and may be a heterocyclic ring containing an element other than a carbon atom, or may be formed. The rings may be further combined to form a binuclear ring, for example, a condensed ring. Further, these ring structures may further have a substituent exemplified in the case where R ^{1 to} R ⁸ represent a monovalent substituent in the general formula (I). N, O, and S can be mentioned as an example of a hetero atom in case the formed ring structure is a heterocyclic ring.

Among these lower SL one general formula, (II-A) a sensitizing dye which is a cyclic compound containing a sulfur atom represented by the high curing sensitivity, and more preferable.

In the general formula (II-A), R ^b , R ¹¹ , R ¹² , R ¹³ , R ¹⁴ , R ¹⁵ , R ¹⁶ , R ¹⁷ , and R ¹⁸ are each independently a hydrogen atom, a halogen atom, a hydroxy group, It represents a cyano group, a nitro group, an amino group, an alkylthio group, an alkylamino group, an alkoxy group, an alkoxycarbonyl group, an acyloxy group, an acyl group, a carboxy group, or a sulfo group.
Preferred examples of the polymerizable group that reacts with a radical include acryloyl group, methacryloyl group, styryl group, vinyl group, vinyl ester group, and allyl group. More preferred is an acryloyl group, a methacryloyl group, a vinyl ester group, and even more preferred is an acryloyl group.

Two of R ¹¹ , R ¹² , R ¹³ , and R ¹⁴ may be linked to each other, for example, condensed to form a ring.
Examples of the ring structure in the case where these form a ring include a 5- to 6-membered aliphatic ring and an aromatic ring, and may be a heterocyclic ring containing an element other than a carbon atom, or may be formed. The rings may be further combined to form a binuclear ring, for example, a condensed ring. Further, these ring structures may further have the substituents exemplified when R ^{11 to} R ¹⁸ represent a monovalent substituent in the general formula (II) . N, O, and S can be mentioned as an example of a hetero atom in case the formed ring structure is a heterocyclic ring.

The sensitizing dyes which can be used further suitably include a sensitizing dye represented by the following Symbol one general formula (II-B).

In the general formula (II-B), R ^b , R ¹¹ , R ¹² , R ¹³ , R ¹⁴ , R ¹⁵ , R ¹⁶ , R ¹⁷ , and R ¹⁸ are each independently a hydrogen atom, a halogen atom, a hydroxy group, It represents a cyano group, a nitro group, an amino group, an alkylthio group, an alkylamino group, an alkoxy group, an alkoxycarbonyl group, an acyloxy group, an acyl group, a carboxy group, or a sulfo group.
Preferred examples of the polymerizable group that reacts with a radical include acryloyl group, methacryloyl group, styryl group, vinyl group, vinyl ester group, and allyl group. More preferred is an acryloyl group, a methacryloyl group, a vinyl ester group, and even more preferred is an acryloyl group.

Two of R ¹¹ , R ¹² , R ¹³ , and R ¹⁴ may be linked to each other, for example, condensed to form a ring.
Examples of the ring structure in the case where these form a ring include a 5- to 6-membered aliphatic ring and an aromatic ring, and may be a heterocyclic ring containing an element other than a carbon atom, or may be formed. The rings may be further combined to form a binuclear ring, for example, a condensed ring. Further, these ring structures may further have the substituents exemplified when R ^{11 to} R ¹⁸ represent a monovalent substituent in the general formula (II) . N, O, and S can be mentioned as an example of a hetero atom in case the formed ring structure is a heterocyclic ring.

Before SL one general formula (II-B), since the solubility is good, it preferred in ejection stability. Among the compounds represented by the general formula (II-B), the sensitizing dye represented by the following general formula, the following general formula (IV), the general formula (V), or the general formula (VI) is used as a raw material. From the viewpoints of availability and ease of synthesis. The compound is a novel compound and is particularly useful for the ink composition of the present invention.

In general formula (IV), R ¹ , R ² , R ³ , and R ⁴ each independently represent a hydrogen atom, an alkyl group, or a halogen atom. ^However, any one of ^{R 1, R 2, R 3} , R 4 is -X ^3.
R ⁵ and R ⁶ each independently represents a hydrogen atom or a methyl group.
Here, X ³ represents a monovalent substituent selected from the following group.

n represents 0 or 1.
L represents a divalent linking group formed by bonding one or more selected from the group consisting of an alkylene group, an alkyleneoxy group, and an ester group.
In each of the above formulas, “*” represents a linking site with a heterocyclic ring.

In the general formula (V), R ¹ , R ² , R ³ and R ⁴ each independently represents a hydrogen atom, an alkyl group, an alkoxy group or a halogen atom. X ¹ represents a monovalent substituent selected from the group shown below. n represents 0 or 1.

  L represents a divalent linking group formed by bonding one or more selected from the group consisting of an alkylene group, an alkyleneoxy group, and an ester group.

In the general formula (VI), R ¹ , R ² , R ³ , and R ⁴ each independently represent a hydrogen atom, an alkyl group, an alkoxy group, or a halogen atom. X ² represents a monovalent substituent selected from the group shown below. n represents 0 or 1.

  L represents a divalent linking group formed by bonding one or more selected from the group consisting of an alkylene group, an alkyleneoxy group, and an ester group.

Specific examples of the specific sensitizing dye that can be suitably used in the present invention [ compound represented by the general formula (II): exemplary compounds (II-1) to (II-75) are shown below. Is not limited to these.

Typical specific examples of the method for synthesizing the specific sensitizing dye represented by the general formula (II) are shown below.
[Synthesis of Exemplary Compound (II-35)]
Compound A (2.42 g) represented by the following formula and DMAP (dimethylaminopyridine) (0.10 g) were dissolved in THF (20 ml), and Compound B (2.32 g) was added. Further, the temperature was lowered to 0 ° C. using a cooling bath, and DCC (dicyclohexylcarbodiimide) was slowly added. Then, it heated up to room temperature and stirred for 3 hours. After completion of the reaction, water was added to the reaction solution and extracted with ethyl acetate. The extract was washed with dilute hydrochloric acid and saturated brine, dried over magnesium sulfate, filtered, and the filtrate was concentrated with an evaporator. The concentrated filtrate was purified using a silica gel column (developing solution: Hexane / ethylate = 3/2). Then, the target compound II-35 was obtained in a yield of 2.8 g.
Compound A can be synthesized by the method described in JP-A-2-255777.
The synthesis scheme is as shown below.

(Synthesis of II-47)
Compound A (2.42 g) and K ₂ CO _{3 (} 2.0 g) represented by the following formula were dissolved in 100 ml of DMF, and the temperature was lowered to 0 ° C. using a cooling bath. 2.0 g of allyl bromide was slowly added dropwise, and then the temperature was raised to room temperature and stirred for 3 hours. After completion of the reaction, the reaction solution was poured into water and the produced solid was filtered. This solid was recrystallized from ethyl acetate and hexane to obtain the target compound II-47 in a yield of 2.2 g.
The synthesis scheme is as shown below.

  Except for the compounds described above, the compounds can be synthesized by combining known reactions in the same manner as in the case production method.

The content of (i) the specific sensitizing dye in the ink composition of the present invention is about 0.05 to 30% by mass, preferably 0.5 to 25% by mass, more preferably solid content with respect to the ink composition. Is 1.0 to 20% by mass.
The content is described in relation to (ii) the polymerization initiator described later. (Ii) The mass ratio of the polymerization initiator: (i) the specific sensitizing dye is 200: 1 to 1: 200, preferably 50: It is suitable to be included in an amount of 1 to 1:50, more preferably 5: 1 to 1: 5.

[Other sensitizing dyes]
In the present invention, in addition to the specific sensitizing dye described above, a known sensitizing dye having no polymerizable group can be used in combination as long as the effects of the present invention are not impaired. The other sensitizing dye is 1: 5 to 100: 1, preferably 1: 1 to 100: 1, more preferably, in a mass ratio of the specific sensitizing dye to the other sensitizing dye with respect to the specific sensitizing dye. Can be added in an amount of 2: 1 to 100: 1.
Examples of known sensitizing dyes that can be used in combination include benzophenone, thioxanthone, especially also isopropylthioxanthone, thiochromanone, dibenzothiepinone, anthraquinone and 3-acylcoumarin derivatives, terphenyl, styryl ketone and 3- (aroylmethylene) thiazoline. , Camphorquinone, eosin, rhodamine and erythrosine.

The further example of the photosensitizer which can be used together is as follows.
(1) Thioxanthone Thioxanthone, 2-isopropylthioxanthone, 2-chlorothioxanthone, 2-dodecylthioxanthone, 2,4-di-ethylthioxanthone, 2,4-dimethylthioxanthone, 1-methoxycarbonylthioxanthone, 2-ethoxycarbonylthioxanthone, 3 -(2-methoxyethoxycarbonyl) thioxanthone, 4-butoxycarbonylthioxanthone, 3-butoxycarbonyl-7-methylthioxanthone, 1-cyano-3-chlorothioxanthone, 1-ethoxycarbonyl-3-chlorothioxanthone, 1-ethoxycarbonyl- 3-ethoxythioxanthone, 1-ethoxycarbonyl-3-aminothioxanthone, 1-ethoxycarbonyl-3-phenylsulfurylthioxanthone, 3,4- Di- [2- (2-methoxyethoxy) ethoxycarbonyl] thioxanthone, 1-ethoxycarbonyl-3- (1-methyl-1-morpholinoethyl) thioxanthone, 2-methyl-6-dimethoxymethylthioxanthone, 2-methyl-6 -(1,1-dimethoxybenzyl) thioxanthone, 2-morpholinomethylthioxanthone, 2-methyl-6-morpholinomethylthioxanthone, n-allylthioxanthone-3,4-dicarboximide, n-octylthioxanthone-3,4-di Carboximide, N- (1,1,3,3-tetramethylbutyl) thioxanthone-3,4-dicarboximide, 1-phenoxythioxanthone, 6-ethoxycarbonyl-2-methoxythioxanthone, 6-ethoxycarbonyl-2- Methylthioxanthate , Thioxanthone-2-polyethylene glycol ester, 2-hydroxy-3- (3,4-dimethyl-9-oxo -9H- thioxanthone-2-yloxy) -N, N, N-trimethyl-1-propanaminium chloride;

(2) Thiochromanone The compounds described in Japanese Patent Application No. 2007-006019 previously proposed by the present inventors, specifically the compounds shown below;

(3) Dibenzothiepinone Compounds described in Japanese Patent Application No. 2007-039491 previously proposed by the present invention, specifically the compounds shown below;

(4) Benzophenone Benzophenone, 4-phenylbenzophenone, 4-methoxybenzophenone, 4,4′-dimethoxybenzophenone, 4,4′-dimethylbenzophenone, 4,4′-dichlorobenzophenone, 4,4′-dimethylaminobenzophenone, 4 , 4'-diethylaminobenzophenone, 4-methylbenzophenone, 2,4,6-trimethylbenzophenone, 4- (4-methylthiophenyl) benzophenone, 3,3'-dimethyl-4-methoxybenzophenone, methyl-2-benzoylbenzoate 4- (2-hydroxyethylthio) benzophenone, 4- (4-tolylthio) benzophenone, 4-benzoyl-N, N, N-trimethylbenzenemethanaminium chloride, 2-hydroxy-3- (4-benzoylphenoxy) ) -N, N, N-trimethyl-1-propanaminium chloride monohydrate, 4- (13-acryloyl-1,4,7,10,13-pentaoxatridecyl) benzophenone, 4-benzoyl-N , N-dimethyl-N- [2- (1-oxo-2-propenyl) oxy] ethylbenzenemethanaminium chloride;

(5) 3-acylcoumarin 3-benzoylcoumarin, 3-benzoyl-7-methoxycoumarin, 3-benzoyl-5,7-di (propoxy) coumarin, 3-benzoyl-6,8-dichlorocoumarin, 3-benzoyl- 6-chlorocoumarin, 3,3′-carbonylbis [5,7-di (propoxy) coumarin], 3,3′-carbonylbis (7-methoxycoumarin), 3,3′-carbonylbis (7-diethylaminocoumarin) ), 3-isobutyroylcoumarin, 3-benzoyl-5,7-dimethoxycoumarin, 3-benzoyl-5,7-diethoxycoumarin, 3-benzoyl-5,7-dibutoxycoumarin, 3-benzoyl-5 7-di (methoxyethoxy) coumarin, 3-benzoyl-5,7-di (allyloxy) coumarin, 3-benzoyl-7- Dimethylaminocoumarin, 3-benzoyl-7-diethylaminocoumarin, 3-isobutyroyl-7-dimethylaminocoumarin, 5,7-dimethoxy-3- (1-naphthoyl) coumarin, 5,7-dimethoxy-3- (1-naphthoyl) ) Coumarin, 3-benzoylbenzo [f] coumarin, 7-diethylamino-3-thienoylcoumarin, 3- (4-cyanobenzoyl) -5,7-dimethoxycoumarin;

(7) 3- (Aroylmethylene) thiazoline 3-methyl-2-benzoylmethylene-β-naphthothiazoline, 3-methyl-2-benzoylmethylenebenzothiazoline, 3-ethyl-2-propionylmethylene-β-naphthothiazoline;

(8) Anthracene 9,10-dimethoxy-anthracene, 9,10-diethoxy-anthracene, 9,10-dimethoxy-2-ethyl-anthracene;

(9) Other carbonyl compounds Acetophenone, 3-methoxyacetophenone, 4-phenylacetophenone, benzyl, 2-acetylnaphthalene, 2-naphthaldehyde, 9,10-naphtholaquinone, 9-fluorenone, dibenzosuberone, xanthone, 2,5 -Bis (4-diethylaminobenzylidene) cyclopentanone, α- (para-dimethylaminobenzylidene) ketone, such as 2- (4-dimethylaminobenzylidene) indan-1-one or 3- (4-dimethylaminophenyl)- 1-Indan-5-ylpropenone, 3-phenylthiophthalimide, N-methyl-3,5-di (ethylthio) phthalimide.

<(Ii) Polymerization initiator>
The ink composition of the present invention contains a polymerization initiator.
In the present invention, a known polymerization initiator can be used. As the polymerization initiator in the present invention, a radical polymerization initiator is preferably used.

-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, (e) Thio compound, (f) hexaarylbiimidazole compound, (g) ketoxime ester compound, (h) borate compound, (i) azinium compound, (j) metallocene compound, (k) active ester compound, (l) carbon halogen Examples include a compound having a bond, and (m) an alkylamine compound.
As an example of the radical polymerization initiator mentioned above, the radical polymerization initiator described in paragraph number [0135]-[0208] of the specification of Unexamined-Japanese-Patent No. 2006-085049 can be mentioned, for example.
As described above, the radical polymerization initiators may be used alone or in combination of two or more.

  Examples of the radical polymerization initiator that can be most suitably used in relation to the specific sensitizing dye used in the present invention include those selected from the group consisting of α-aminoketones and acylphosphine oxides.

  Examples of compounds encompassed by α-aminoketones include 2-methyl-1-phenyl-2-morpholinopropan-1-one, 2-methyl-1- [4- (hexyl) phenyl] -2-morpho And linopropan-1-one, 2-ethyl-2-dimethylamino-1- (4-morpholinophenyl) -butanone-1, and the like. Further, it is also available as a commercial product such as Irgacure series manufactured by Ciba Geigy, for example, Irgacure 907, Irgacure 369, Irgacure 379, and the like, and these are compounds included in α-amino ketones, which are suitable for the present invention. Can be used.

  Examples of the acylphosphine oxide compounds include compounds described in JP-B 63-40799, JP-B 5-29234, JP-A-10-95788, JP-A-10-29997, and the like. Can do.

  The content of (ii) the polymerization initiator in the ink composition of the present invention is preferably in the range of 0.1 to 30% by mass, and in the range of 1.0 to 20% by mass in terms of solid content. Is more preferably 5.0 to 15.0% by mass.

  The content of the (ii) polymerization initiator in the ink composition of the present invention is preferably 0.01 to 35 parts by mass with respect to 100 parts by mass of the polymerizable compound (iii) having an ethylenically unsaturated bond described later. The content is preferably 0.1 to 30 parts by mass, and more preferably 0.5 to 30 parts by mass. In addition, content of a polymerization initiator here means the total content of the polymerization initiator containing the radical polymerization initiator mentioned above and the other polymerization initiator which can be used together.

<(Iii) Polymerizable compound having an ethylenically unsaturated bond>
The ink composition of the present invention contains a polymerizable compound. The polymerizable compound that can be suitably used in the present invention is a compound having an ethylenically unsaturated bond capable of radical polymerization, and any compound having at least one ethylenically unsaturated bond capable of radical polymerization in the molecule. Any type may be used, including those having chemical forms such as monomers, oligomers, and polymers.
Only one kind of radically polymerizable compound may be used, or two or more kinds thereof may be used in combination at an arbitrary ratio in order to improve desired properties. It is preferable to use two or more kinds in combination for controlling performance such as reactivity and physical properties.

Examples of the polymerizable compound having an ethylenically unsaturated bond include unsaturated carboxylic acids such as acrylic acid, methacrylic acid, itaconic acid, crotonic acid, isocrotonic acid, maleic acid and their salts, and ethylenically unsaturated groups. Examples thereof include radically polymerizable compounds such as anhydrides, acrylonitrile, styrene, 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, tetramethylolmethane 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 Kiyomi, “UV / EB curing handbook (raw material)” (1985, Polymer publication) ); Rad-Tech Study Group, “Application and Market of UV / EB Curing Technology”, p. 79, (1989, CMC); Eiichiro Takiyama, “Polyester Resin Handbook”, (1988, Nikkan Kogyo Shimbun) Commercially available products described in the above, or radically polymerizable or crosslinkable monomers known in the industry, Ligomers and polymers can be used.

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-9-134011 and the like. And a photocurable polymerizable compound used in the photopolymerizable composition.
In order to further improve sensitivity, bleeding, and adhesion to the recording medium, it is preferable to use monoacrylate in combination with a polyfunctional acrylate monomer or polyfunctional acrylate oligomer having a molecular weight of 400 or more, preferably 500 or more. In particular, in an ink composition used for recording on a flexible recording medium such as a PET film or a PP film, a combination of a monoacrylate selected from the above compound group and a polyfunctional acrylate monomer or polyfunctional acrylate oligomer is used. It is preferable because the film strength can be increased while the film is flexible to improve adhesion.
Furthermore, an aspect in which at least three kinds of polymerizable compounds of monofunctional, bifunctional, and trifunctional or higher polyfunctional monomers are used in combination further maintains sensitivity, bleeding, and adhesion to a recording medium. This is preferable from the viewpoint of further improvement.

As monoacrylates, stearyl acrylate, isoamyl acrylate, isomystil acrylate, and isostearyl acrylate have high sensitivity and low shrinkage to prevent curling. preferable.
As the oligomer that can be used in combination with the monoacrylate, an epoxy acrylate oligomer and a urethane acrylate oligomer are particularly preferable.
In addition, methacrylate has better skin irritation than acrylate.
Among the above compounds, when alkoxy acrylate is used in an amount of less than 70% by mass and the balance is acrylate, it is preferable because it has good sensitivity, bleeding characteristics, and odor characteristics.

  The content of all polymerizable compounds in the ink composition of the present invention is preferably 5 to 97% by mass, and more preferably 30 to 95% by mass.

The ink composition of the present invention contains the components (i) to (iii) as essential components, but other known components can be used in combination as additives of the ink composition depending on the purpose. Hereinafter, these optional components will be described.
<(Iv) Colorant>
When the ink composition of the present invention is applied to uses such as the formation of an image portion of a lithographic printing plate, it is not essential to form a colored image. Is not necessary, but in order to improve the visibility of the image portion formed by the ink composition, or when forming a colored image using the ink composition, it may contain (iv) a colorant. it can.

  The colorant that can be used in the present invention is not particularly limited, but (1) pigments and (2) oil-soluble dyes that are excellent in weather resistance and rich in color reproducibility are preferable. The known colorant can be selected and 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.

(1) Pigment The pigment that can be used in the present invention is not particularly limited. For example, organic or inorganic pigments having the following numbers described in the color index can be used.
Examples of the red or magenta pigment include Pigment Red 3, 5, 19, 22, 31, 38, 43, 48: 1, 48: 2, 48: 3, 48: 4, 48: 5, 49: 1, and 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, and the like.

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

(2) Oil-soluble dye The oil-soluble dye that can be used in the present invention is described below. 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 mass 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 dye, acridinone dye; and the like.

  Among the oil-soluble dyes that can be used in the present invention, any magenta dye can be used. For example, aryl or heteroaryl 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 and xanthene dyes; quinone dyes such as naphthoquinone, anthraquinone and anthrapyridone; condensed polycyclic dyes such as dioxazine dyes, etc. Can be mentioned.

  Of 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 is 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 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.
Among these, particularly preferred are the Black 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 Bile 2OSe 2B eO (Manufactured by Co., Ltd.), Aizen Spillon 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.
Further, when an oil-soluble dye is used 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. .

(3) Disperse dye In the present invention, a disperse dye may 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.

  It is also possible to add a dispersant when dispersing the colorant. The type of the dispersant is not particularly limited, but a polymer dispersant is preferably used, and examples of the polymer dispersant include Solsperse series manufactured by Zeneca. Moreover, it is also possible to use a synergist according to various pigments as a dispersion aid. In the present invention, these dispersant and dispersion aid are preferably added in an amount of 1 to 50 parts by mass with respect to 100 parts by mass of the colorant.

  In preparing the ink composition of the present invention, the colorant may be added by adding directly with each component. However, in order to improve dispersibility, a solvent or a specific monofunctional (meth) acrylic acid derivative according to the present invention is used in advance. Alternatively, it may be added to a dispersion medium such as other polymerizable compound used in combination as desired, and uniformly dispersed or dissolved, and then blended.

  In the present invention, in order to avoid the problem of deterioration of the solvent resistance of the image portion over time and the problem of VOC (Volatile Organic Compound) of the remaining solvent, which is a concern when the solvent remains in the cured image. The colorant is preferably added in advance to any one of a polymerizable compound containing a specific monofunctional (meth) acrylic acid derivative or a mixture thereof and blended. 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.

One or more colorants may be appropriately selected according to the intended use of the ink composition.
In the ink composition of the present invention, when using a colorant such as a pigment that remains in a solid state, the average particle diameter of the colorant particles is preferably 0.005 to 0.5 μm, more preferably. 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, and 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 purpose of use. However, in consideration of the ink physical properties and colorability, generally, the content of the colorant is 1 with respect to the total mass of the ink composition. It is preferable that it is -10 mass%, and it is more preferable to contain 2-8 mass%.

<Other ingredients>
If necessary, other components can be added to the ink composition of the present invention. Examples of other components include a polymerization inhibitor and a solvent.
A polymerization inhibitor may be added from the viewpoint of enhancing the storage stability. Further, when the ink composition of the present invention is used as an ink composition for ink jet recording, it is preferably discharged at a temperature in the range of 40 to 80 ° C. with a reduced viscosity, and also for preventing head clogging due to thermal polymerization. It is preferable to add a polymerization inhibitor. The polymerization inhibitor is preferably added in an amount of 200 to 20,000 ppm based on the total amount of the ink composition of the present invention. Examples of the polymerization inhibitor include hydroquinone, benzoquinone, p-methoxyphenol, TEMPO, TEMPOL, and cuperon Al.

In view of the fact that the ink composition of the present invention and the ink composition for ink jet recording are radiation curable ink compositions, it is preferable that no solvent is contained so that the ink composition can react quickly and be cured immediately after landing of the ink composition. However, a predetermined solvent can be included as long as the curing rate of the ink composition is not affected. In the present invention, an organic solvent or water can be used as the solvent. In particular, the organic solvent can be added in order to improve the adhesion to the recording medium (support such as paper). The addition of an organic solvent is effective because the VOC problem can be avoided.
The amount of the organic solvent is, for example, 0.1 to 5% by mass, preferably 0.1 to 3% by mass with respect to the mass of the entire ink composition of the present invention.

  In addition to this, a known compound can be added to the ink composition of the present invention as necessary. For example, surfactants, leveling additives, matting agents, polyester resins for adjusting film properties, polyurethane resins, vinyl resins, acrylic resins, rubber resins, washes, etc. are appropriately selected and added. be able to. In order to improve the adhesion to a recording medium such as polyolefin or PET, it is also preferable to contain a tackifier that does not inhibit the polymerization. Specifically, a high molecular weight adhesive polymer described in JP-A-2001-49200, pages 5 to 6 (for example, (meth) acrylic acid and an alcohol having an alkyl group having 1 to 20 carbon atoms). An ester, a copolymer of (meth) acrylic acid and an alicyclic alcohol having 3 to 14 carbon atoms, a copolymer of an ester of (meth) acrylic acid and an aromatic alcohol having 6 to 14 carbon atoms), and polymerizability. Examples thereof include a low molecular weight tackifying resin having an unsaturated bond.

-Properties of ink composition-
As described above, the ink composition of the present invention is required to contain (i) a specific sensitizing dye, (ii) a polymerization initiator, and (iii) a polymerizable compound. It contains a sensitizing dye and (iv) a coloring agent.
When these components are colored inks, (iv) the colorant content is preferably 1 to 10% by mass, more preferably 2 to 8% by mass, based on the total mass of the ink composition. The total (iii) polymerizable compound is preferably 5 to 97% by mass, more preferably 30 to 95% by mass in terms of solid content of the composition.
(Ii) The polymerization initiator is preferably from 0.01 to 35% by mass, more preferably from 0.1 to 30% by mass, and even more preferably from 0.5 to 30%, based on the total (iii) polymerizable compound. It is suitable to contain so that it may become 30 mass%.

The ink composition of the present invention can be suitably used as an ink for inkjet recording. The preferred physical properties in the usage mode as the ink for inkjet recording will be described.
When the ink composition is used as an ink for ink jet recording, the viscosity is preferably 7 to 30 mPa at the temperature at the time of ejection (for example, 40 to 80 ° C., preferably 25 to 50 ° C.) in consideration of the ejectability. · S, more preferably 7 to 25 mPa · s. For example, the viscosity of the ink composition of the present invention at room temperature (25 to 30 ° C.) is preferably 35 to 500 mPa · s, more preferably 35 to 200 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 monomers and odors can be reduced. Furthermore, 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 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 the wettability is preferably 30 mN / m or less.

[Inkjet recording method]
Next, an ink jet recording method of the present invention and an ink jet recording apparatus applicable to the method will be described.
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 the ink composition ejected onto the recording medium is active. In this method, an image is formed by irradiating radiation and curing the ink.

That is, 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) irradiating the ejected ink composition with actinic radiation, And a step of curing the composition.
By including the steps (a) and (b), the ink jet recording method of the present invention forms an image with 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 apparatus>
There is no restriction | limiting in particular as an inkjet recording device used for the 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, for example, 320 × 320 to 4000 × 4000 dpi, preferably 400 × 400 to 1600 × 1600 dpi, and more preferably 720 × 720 dpi. It can drive so that it can discharge with the resolution of. 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 has a constant temperature for the ejected ink, heat insulation and heating can be performed from the ink supply tank to the inkjet head portion. The temperature control method is not particularly limited, but for example, it is preferable to provide a plurality of temperature sensors at each piping site and perform heating control according to the ink flow rate and the environmental temperature. The temperature sensor can be provided near 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 thermal energy, it is preferable to insulate from other parts and reduce the heat capacity of the entire heating unit.

Next, (b) the step of irradiating the discharged 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 causes a specific monofunctionality ( This is because the polymerization reaction of the (meth) acrylic acid derivative and other polymerizable compound used in combination as required occurs and is accelerated, and the ink composition is cured. At this time, if a sensitizing dye is present together with the polymerization initiator in the ink composition, the sensitizing dye 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 achieve a more sensitive curing reaction.

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 sensitizing dye, 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 the present invention, the polymerization initiating system has sufficient sensitivity even with low-power actinic radiation. Thus, the output of the active radiation is preferably 2,000 mJ / cm ² or less, more preferably from 10 to 2,000 mJ / cm ^2, more preferably, be 20 to 1,000 mJ / cm ² Particularly preferably, it is 50 to 800 mJ / cm ² .
The active radiation, the illumination intensity on the exposed surface is, for example, 10 to 2,000 mW / cm ^2, preferably, it is suitable to be irradiated at 20 to 1,000 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. When 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.
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 suitably irradiated with such actinic radiation for, for example, 0.01 to 120 seconds, preferably 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 time (for example, 0.01 to 0.5 seconds, preferably 0.01 to 0.3 seconds, 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 the porous recording medium before the ink penetrates to a deep part where the light source does not reach, the residual unreacted monomer can be suppressed, and as a result, the odor can be reduced. .
Further, the 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 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 way, the ink composition of the present invention is cured with high sensitivity by irradiation with actinic radiation, and forms a hydrophobic image on the surface of the recording medium.

Here, the actinic radiation source used for curing the ink or preferred irradiation conditions thereof are also the same as those described in the ink jet recording method.
The ink composition of the present invention is cured with high sensitivity by actinic radiation, and can form a hydrophobic region excellent in adhesion to the support and film quality. For this reason, in addition to the formation of colored images, marking, etc., it can also be used, for example, for the formation of the image portion of a lithographic printing plate. By applying to this application, a lithographic plate having high image quality and excellent printing durability. It is also possible to obtain a printed version.
The ink composition of the present invention is excellent for ink jet recording for the reasons described above, but it is needless to say that it is also useful as a commonly used ink composition.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further more concretely, this invention is not limited to the form in these Examples.

[ Reference Example 1]
The following components were stirred with a high-speed water-cooled stirrer to obtain a white UV inkjet ink composition.
(White ink composition-1)
Light acrylate LA 15.4 parts [Lauryl acrylate: (iii) monofunctional acrylate]
Actylane 421 (Akcros acrylate monomer) 22.0 parts [propoxylated neopentyl glycol diacrylate: (iii) bifunctional acrylate]
・ Photomer 2017 (UV diluent manufactured by EChem) 15.0 parts ・ Solsperse 36000 (dispersant made by Noveon) 2.0 parts ・ 15.0 parts of MICROLITH WHITE R-A (pigment manufactured by Ciba Specialty Chemicals: (iv) component)
・ Genorad 16 (Rahn Stabilizer) 0.05 part ・ Rapi-Cure DVE-3 8.0 parts (ISP Europe (iii) vinyl ether)
Sensitizing dye [Compound I-1 (the following structure)] 10.0 parts · Darocur TPO 8.5 parts (Table 1, as "TPO" in Table 2)
(Ciba Specialty Chemicals (ii) Photoinitiator)
Irgacure 907 (described as “907” in Tables 1 and 2 below) 4.0 parts (Ciba Specialty Chemicals (ii) photopolymerization initiator)
・ Byk 307 (defoamer manufactured by BYK Chemie) 0.05 parts

<Evaluation of ink>
The obtained ink composition is ejected onto a polyvinyl chloride sheet and irradiated by passing it under the light of an ultraviolet light-emitting diode (UV-LED) at a specific speed to cure the ink, and the printed matter. Got.
In this example, the ink was ejected by a commercially available ink jet recording apparatus having a piezo ink jet nozzle, and NCCU033 manufactured by Nichia Chemical was used as a light emitting diode (UV-LED) for curing. The LED outputs ultraviolet light having a wavelength of 365 nm from one chip. When a current of about 500 mA is applied, light of about 100 mW is emitted from the chip. A plurality of these are arranged at intervals of 7 mm, and a power of 0.3 W / cm ² is obtained on the surface of the recording medium (hereinafter also referred to as a medium). The exposure time after the droplet ejection and the exposure time can be changed according to the transport speed of the medium and the distance between the head and the LED in the transport direction. In this embodiment, the exposure is performed about 0.5 seconds after landing.
The exposure energy on the medium can be adjusted between 0.01 and 15 J / cm ² depending on the setting of the distance to the medium and the conveyance speed.
At this time, the following evaluation was performed.

Evaluation item-Curing sensitivity-
Curing sensitivity was defined by the exposure energy at which the surface was not sticky after printing.
The presence or absence of stickiness on the surface after printing was determined by pressing plain paper (Fuji Xerox Co., Ltd., copy paper C2) immediately after printing, with stickiness when color shift occurred, and without stickiness when color shift did not occur. The lower the value, the higher the sensitivity, and the following criteria were evaluated.
○ Surface stickiness disappeared at an exposure energy of 300 mJ / cm ² .
Δ: Surface stickiness disappeared at an exposure energy of 600 mJ / cm ² .
X Exposure energy of> 900 mJ / cm ² was required to eliminate surface stickiness.

Blocking resistance The same paper as the printing paper was overlaid on the cured image, a mass of about 50 g / cm ² was applied, the plate was left at 50 ° C. for 24 hours, and the degree of transfer of the image portion onto the overlaid paper was visually evaluated.
○: No transfer product △: Slight transfer product ×: Transfer product-ejection stability-
After storing the obtained ink composition at room temperature for 2 weeks, using a commercially available inkjet recording apparatus having a piezo-type inkjet nozzle, recording on a recording medium was performed, and dots were missing when continuously printed at room temperature for 48 hours. In addition, the presence or absence of ink scattering was visually observed and evaluated according to the following criteria. The results are shown in Table 1 below.
◎: Dot drop or ink splatter does not occur ○: Dot drop or ink splatter occurs 1 to 3 times △: Dot drop or ink splatter occurs 4 to 10 times ×: Dot drop or ink splatter occurs 11 or more occurrences Note that the image formed at this time had a good white color.

  The ink supply system of the ink jet recording apparatus used for the evaluation consists of the original tank, supply pipe, ink supply tank immediately before the ink jet head, filter, and piezo ink jet head. The ink supply tank to the ink jet head part are insulated and heated. Went. 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 70 ° 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. In the present invention, dpi represents the number of dots per 2.54 cm.

[Example 2]
The following components were stirred with a high-speed water-cooled stirrer to obtain a white UV inkjet ink.
(White ink composition-2)
Light acrylate LA 15.4 parts [Lauryl acrylate: (iii) monofunctional acrylate]
Actylane 421 (Akcros acrylate monomer) 22.0 parts [propoxylated neopentyl glycol diacrylate: (iii) bifunctional acrylate]
-Photomer 2017 (UV diluent manufactured by EChem) 15.0 parts-Solsperse 36000 (dispersant made by Noveon) 2.0 parts-15.0 parts-MICROLITE WHITE R-A (pigment (iv) manufactured by Ciba Specialty Chemicals) )
・ Genorad 16 (Rahn Stabilizer) 0.05 part ・ Rapi-Cure DVE-3 8.0 parts (ISP Europe (iii) vinyl ether)
-(I) Specific sensitizing dye [Compound II-35 (the following structure)] 10.0 parts-Darocur TPO 8.5 parts (Ciba Specialty Chemicals (ii) Photopolymerization initiator)
Irgacure 907 4.0 parts (Ciba Specialty Chemicals (ii) photopolymerization initiator)
・ Byk 307 (defoamer manufactured by BYK Chemie) 0.05 parts

<Evaluation of ink>
The produced white ink composition is ejected onto a polyvinyl chloride sheet, passed under the light of an ultraviolet light emitting diode (UV-LED) at the predetermined speed, and irradiated by adjusting to a prescribed exposure amount. went. The printed matter with this ink was evaluated in the same manner as in Example 1. The results are shown in Table 1 below.

Example 3
The following components were stirred with a high-speed water-cooled stirrer to obtain a white UV inkjet ink.
(White ink composition-3)
Light acrylate LA 15.4 parts [Lauryl acrylate: (iii) monofunctional acrylate]
Actylane 421 (Akcros acrylate monomer) 22.0 parts [propoxylated neopentyl glycol diacrylate: (iii) bifunctional acrylate]
・ Photomer 2017 (UV diluent manufactured by EChem) 15.0 parts ・ Solsperse 36000 (dispersing agent manufactured by Noveon) 2.0 parts ・ 15.0 parts of MICROLITH WHITE RA-A (manufactured by Ciba Specialty Chemicals (iv) pigment)
・ Genorad 16 (Rahn Stabilizer) 0.05 part ・ Rapi-Cure DVE-3 8.0 parts (ISP Europe (iii) vinyl ether)
-(I) Specific sensitizing dye [Compound II-3 (following structure)] 10.0 parts-Darocur TPO 8.5 parts (Ciba Specialty Chemicals (ii) photoinitiator)
Irgacure 907 4.0 parts (Ciba Specialty Chemicals (ii) photopolymerization initiator)
・ Byk 307 (defoamer manufactured by BYK Chemie) 0.05 parts

<Evaluation of ink>
The produced white ink composition is printed on a sheet made of polyvinyl chloride, and passed through the light of an ultraviolet light emitting diode (UV-LED) at the predetermined speed, and irradiation is performed by adjusting to a prescribed exposure amount. went. The printed matter with this ink was evaluated in the same manner as in Example 1. The results are shown in Table 1 below.

Example 4
The following components were stirred with a high-speed water-cooled stirrer to obtain a white UV inkjet ink.
(White ink composition-3)
Light acrylate LA 15.4 parts [Lauryl acrylate: (iii) monofunctional acrylate]
Actylane 421 (Akcros acrylate monomer) 22.0 parts [propoxylated neopentyl glycol diacrylate: (iii) bifunctional acrylate]
・ Photomer 2017 (UV diluent manufactured by EChem) 15.0 parts ・ Solsperse 36000 (dispersing agent manufactured by Noveon) 2.0 parts ・ 15.0 parts of MICROLITH WHITE RA-A (manufactured by Ciba Specialty Chemicals (iv) pigment)
・ Genorad 16 (Rahn Stabilizer) 0.05 part ・ Rapi-Cure DVE-3 8.0 parts (ISP Europe (iii) vinyl ether)
-(I) Specific sensitizing dye [Compound II-7 (following structure)] 10.0 parts-Darocur TPO 8.5 parts (Ciba Specialty Chemicals (ii) Photopolymerization initiator)
Irgacure 907 4.0 parts (Ciba Specialty Chemicals (ii) photopolymerization initiator)
・ Byk 307 (defoamer manufactured by BYK Chemie) 0.05 parts

<Evaluation of ink>
The produced white ink composition is printed on a sheet made of polyvinyl chloride, and passed through the light of an ultraviolet light emitting diode (UV-LED) at the predetermined speed, and irradiation is performed by adjusting to a prescribed exposure amount. went. The printed matter with this ink was evaluated in the same manner as in Example 1. The results are shown in Table 1 below.

Example 5
The following components were stirred with a high-speed water-cooled stirrer to obtain a white UV inkjet ink.
(White ink composition-4)
Light acrylate LA 15.4 parts [Lauryl acrylate: (iii) monofunctional acrylate]
Actylane 421 (Akcros acrylate monomer) 22.0 parts [propoxylated neopentyl glycol diacrylate: (iii) bifunctional acrylate]
・ Photomer 2017 (UV diluent manufactured by EChem) 15.0 parts ・ Solsperse 36000 (dispersing agent manufactured by Noveon) 2.0 parts ・ 15.0 parts of MICROLITH WHITE RA-A (manufactured by Ciba Specialty Chemicals (iv) pigment)
-Genorad 16 (stabilizer manufactured by Rahn) 0.05 part-Rapi-Cure DVE-3 8.0 parts (vinyl ether manufactured by ISP Europe)
・ (I) Specific sensitizing dye [Compound II-43 (the following structure)] 10.0 parts ・ Darocur TPO 8.5 parts (Ciba Specialty Chemicals (ii) photopolymerization initiator)
Irgacure 907 4.0 parts (Ciba Specialty Chemicals (ii) photopolymerization initiator)
・ Byk 307 (defoamer manufactured by BYK Chemie) 0.05 parts

<Evaluation of ink>
The produced white ink composition is printed on a sheet made of polyvinyl chloride, and passed through the light of an ultraviolet light emitting diode (UV-LED) at the predetermined speed, and irradiation is performed by adjusting to a prescribed exposure amount. went. The printed matter with this ink was evaluated in the same manner as in Example 1. The results are shown in Table 1 below.

Example 6
The following components were stirred with a high-speed water-cooled stirrer to obtain a white UV inkjet ink.
(White ink composition-4)
Light acrylate LA 15.4 parts [Lauryl acrylate: (iii) monofunctional acrylate]
Actylane 421 (Akcros acrylate monomer) 22.0 parts [propoxylated neopentyl glycol diacrylate: (iii) bifunctional acrylate]
・ Photomer 2017 (UV diluent manufactured by EChem) 15.0 parts ・ Solsperse 36000 (dispersing agent manufactured by Noveon) 2.0 parts ・ 15.0 parts of MICROLITH WHITE RA-A (manufactured by Ciba Specialty Chemicals (iv) pigment)
-Genorad 16 (stabilizer manufactured by Rahn) 0.05 part-Rapi-Cure DVE-3 8.0 parts (vinyl ether manufactured by ISP Europe)
・ (I) Specific sensitizing dye [Compound II-51 (the following structure)] 10.0 parts ・ Darocur TPO 8.5 parts (Ciba Specialty Chemicals (ii) photopolymerization initiator)
Irgacure 907 4.0 parts (Ciba Specialty Chemicals (ii) photopolymerization initiator)
・ Byk 307 (defoamer manufactured by BYK Chemie) 0.05 parts

<Evaluation of ink>
The produced white ink composition is printed on a sheet made of polyvinyl chloride, and passed through the light of an ultraviolet light emitting diode (UV-LED) at the predetermined speed, and irradiation is performed by adjusting to a prescribed exposure amount. went. The printed matter with this ink was evaluated in the same manner as in Example 1. The results are shown in Table 1 below.

Example 7
The following components were stirred with a high-speed water-cooled stirrer to obtain a white UV inkjet ink.
(White ink composition-5)
Light acrylate LA 15.4 parts [Lauryl acrylate: (iii) monofunctional acrylate]
Actylane 421 (Akcros acrylate monomer) 22.0 parts [propoxylated neopentyl glycol diacrylate: (iii) bifunctional acrylate]
・ Photomer 2017 (UV diluent manufactured by EChem) 15.0 parts ・ Solsperse 36000 (dispersing agent manufactured by Noveon) 2.0 parts ・ 15.0 parts of MICROLITH WHITE RA-A (manufactured by Ciba Specialty Chemicals (iv) pigment)
・ Genorad 16 (Rahn Stabilizer) 0.05 part ・ Rapi-Cure DVE-3 8.0 parts (ISP Europe (iii) vinyl ether)
-(I) Specific sensitizing dye [Compound II-47 (the following structure)] 10.0 parts-Darocur TPO 8.5 parts (Ciba Specialty Chemicals (ii) Photopolymerization initiator)
Irgacure 907 4.0 parts (Ciba Specialty Chemicals (ii) photopolymerization initiator)
・ Byk 307 (defoamer manufactured by BYK Chemie) 0.05 parts

<Evaluation of ink>
The produced white ink composition was printed on a polyvinyl chloride sheet and irradiated by passing it at a specific speed under the light of an ultraviolet light emitting diode (UV-LED). The printed matter with this ink was evaluated in the same manner as in Example 1. The results are shown in Table 1 below.

Example 8
The following components were stirred with a high-speed water-cooled stirrer to obtain a white UV inkjet ink.
(White ink composition-5)
Light acrylate LA 15.4 parts [Lauryl acrylate: (iii) monofunctional acrylate]
Actylane 421 (Akcros acrylate monomer) 22.0 parts [propoxylated neopentyl glycol diacrylate: (iii) bifunctional acrylate]
・ Photomer 2017 (UV diluent manufactured by EChem) 15.0 parts ・ Solsperse 36000 (dispersing agent manufactured by Noveon) 2.0 parts ・ 15.0 parts of MICROLITH WHITE RA-A (manufactured by Ciba Specialty Chemicals (iv) pigment)
・ Genorad 16 (Rahn Stabilizer) 0.05 part ・ Rapi-Cure DVE-3 8.0 parts (ISP Europe (iii) vinyl ether)
・ (I) Specific sensitizing dye [Compound II-59 (the following structure)] 10.0 parts ・ Darocur TPO 8.5 parts (Ciba Specialty Chemicals (ii) photopolymerization initiator)
Irgacure 907 4.0 parts (Ciba Specialty Chemicals (ii) photopolymerization initiator)
・ Byk 307 (defoamer manufactured by BYK Chemie) 0.05 parts

<Evaluation of ink>
The produced white ink composition was printed on a polyvinyl chloride sheet and irradiated by passing it at a specific speed under the light of an ultraviolet light emitting diode (UV-LED). The printed matter with this ink was evaluated in the same manner as in Example 1. The results are shown in Table 1 below.

[ Reference Example 9]
The following components were stirred with a high-speed water-cooled stirrer to obtain a white UV inkjet ink.
(White ink composition-6)
Light acrylate LA 15.4 parts [Lauryl acrylate: (iii) monofunctional acrylate]
Actylane 421 (Akcros acrylate monomer) 22.0 parts [propoxylated neopentyl glycol diacrylate: (iii) bifunctional acrylate]
・ Photomer 2017 (UV diluent manufactured by EChem) 15.0 parts ・ Solsperse 36000 (dispersing agent manufactured by Noveon) 2.0 parts ・ 15.0 parts of MICROLITH WHITE RA-A (manufactured by Ciba Specialty Chemicals (iv) pigment)
・ Genorad 16 (Rahn Stabilizer) 0.05 part ・ Rapi-Cure DVE-3 8.0 parts (ISP Europe (iii) vinyl ether)
Sensitizing dye [Compound I-18 (structure shown below)] 10.0 parts · Darocur TPO 8.5 parts (Ciba Specialty Chemicals Co., Ltd. (ii) a photopolymerization initiator)
Irgacure 907 4.0 parts (Ciba Specialty Chemicals (ii) photopolymerization initiator)
・ Byk 307 (defoamer manufactured by BYK Chemie) 0.05 parts

<Evaluation of ink>
The produced white ink composition is printed on a sheet made of polyvinyl chloride, and passed through the light of an ultraviolet light emitting diode (UV-LED) at the predetermined speed, and irradiation is performed by adjusting to a prescribed exposure amount. went. The printed matter with this ink was evaluated in the same manner as in Example 1. The results are shown in Table 1 below.

Example 10
The following components were stirred with a high-speed water-cooled stirrer to obtain a white UV inkjet ink.
(White ink composition-7)
Light acrylate LA 15.4 parts [Lauryl acrylate: (iii) monofunctional acrylate]
Actylane 421 (Akcros acrylate monomer) 22.0 parts [propoxylated neopentyl glycol diacrylate: (iii) bifunctional acrylate]
・ Photomer 2017 (UV diluent manufactured by EChem) 15.0 parts ・ Solsperse 36000 (dispersing agent manufactured by Noveon) 2.0 parts ・ 15.0 parts of MICROLITH WHITE RA-A (manufactured by Ciba Specialty Chemicals (iv) pigment)
・ Genorad 16 (Rahn Stabilizer) 0.05 part ・ Rapi-Cure DVE-3 8.0 parts (ISP Europe (iii) vinyl ether)
・ (I) Specific sensitizing dye [Compound II-68 (the following structure)] 10.0 parts ・ Darocur TPO 8.5 parts (Ciba Specialty Chemicals (ii) photopolymerization initiator)
Irgacure 907 4.0 parts (Ciba Specialty Chemicals (ii) photopolymerization initiator)
・ Byk 307 (defoamer manufactured by BYK Chemie) 0.05 parts

<Evaluation of ink>
The produced white ink composition is printed on a sheet made of polyvinyl chloride, and passed through the light of an ultraviolet light emitting diode (UV-LED) at the predetermined speed, and irradiation is performed by adjusting to a prescribed exposure amount. went. The printed matter with this ink was evaluated in the same manner as in Example 1. The results are shown in Table 1 below.

Example 11
The following components were stirred with a high-speed water-cooled stirrer to obtain a white UV inkjet ink.
(White ink composition-3)
Light acrylate LA 15.4 parts [Lauryl acrylate: (iii) monofunctional acrylate]
Actylane 421 (Akcros acrylate monomer) 22.0 parts [propoxylated neopentyl glycol diacrylate: (iii) bifunctional acrylate]
・ Photomer 2017 (UV diluent manufactured by EChem) 15.0 parts ・ Solsperse 36000 (dispersing agent manufactured by Noveon) 2.0 parts ・ 15.0 parts of MICROLITH WHITE RA-A (manufactured by Ciba Specialty Chemicals (iv) pigment)
・ Genorad 16 (Rahn Stabilizer) 0.05 part ・ Rapi-Cure DVE-3 8.0 parts (ISP Europe (iii) vinyl ether)
-(I) Specific sensitizing dye [Compound II-3 (the following structure)] 6.0 parts-(i) Specific sensitizing dye (Compound I-14: the following structure) 4.0 parts-Darocur TPO 8.5 parts (Ciba Specialty Chemicals (ii) Photoinitiator)
Irgacure 907 4.0 parts (Ciba Specialty Chemicals (ii) photopolymerization initiator)
・ Byk 307 (defoamer manufactured by BYK Chemie) 0.05 parts

<Evaluation of ink>
The produced white ink composition is printed on a sheet made of polyvinyl chloride, and passed through the light of an ultraviolet light emitting diode (UV-LED) at the predetermined speed, and irradiation is performed by adjusting to a prescribed exposure amount. went. The printed matter with this ink was evaluated in the same manner as in Example 1. The results are shown in Table 1 below.

Example 12
(White ink composition-8)
-Phenoxyethyl acrylate (iii) component 21.0 parts-N-vinylcaprolactam (iii) component 14.0 parts-FA-512A [following structure] (iii) component 17.4 parts-Solperse 36000 (Distributor made by Noveon) ) 2.0 parts · 15.0 parts of MICROLITH WHITE R-A (Ciba Specialty Chemicals (iv) pigment)
・ Genorad 16 (Rahn Stabilizer) 0.05 part ・ Rapi-Cure DVE-3 8.0 parts (ISP Europe (iii) vinyl ether)
-(I) Specific sensitizing dye [Compound II-3 (the above structure)] 10.0 parts-Darocur TPO 8.5 parts (Ciba Specialty Chemicals (ii) Photopolymerization initiator)
Irgacure 907 4.0 parts (Ciba Specialty Chemicals (ii) photopolymerization initiator)
・ Byk 307 (defoamer manufactured by BYK Chemie) 0.05 parts

<Evaluation of ink>
The produced white ink composition is printed on a sheet made of polyvinyl chloride, and passed through the light of an ultraviolet light emitting diode (UV-LED) at the predetermined speed, and irradiation is performed by adjusting to a prescribed exposure amount. went. The printed matter with this ink was evaluated in the same manner as in Example 1. The results are shown in Table 1 below.
Example 13
The following components were stirred with a high-speed water-cooled stirrer to obtain a white UV inkjet ink.
(White ink composition-9)
Light acrylate LA 15.4 parts [Lauryl acrylate: (iii) monofunctional acrylate]
Actylane 421 (Akcros acrylate monomer) 22.0 parts [propoxylated neopentyl glycol diacrylate: (iii) bifunctional acrylate]
・ Photomer 2017 (UV diluent manufactured by EChem) 15.0 parts ・ Solsperse 36000 (dispersing agent manufactured by Noveon) 2.0 parts ・ 15.0 parts of MICROLITH WHITE RA-A (manufactured by Ciba Specialty Chemicals (iv) pigment)
・ Genorad 16 (Rahn Stabilizer) 0.05 part ・ Rapi-Cure DVE-3 8.0 parts (ISP Europe (iii) vinyl ether)
-(I) Specific sensitizing dye [Compound II-3 (the above structure)] 10.0 parts-Darocur TPO 8.5 parts (Ciba Specialty Chemicals (ii) Photopolymerization initiator)
Irgacure 184. 2.0 parts (Ciba Specialty Chemicals (ii) photoinitiator)
-2.0 parts of benzophenone ((ii) photopolymerization initiator: described as “benzophenone” in Tables 1 and 2 below)
・ Byk 307 (defoamer manufactured by BYK Chemie) 0.05 parts

<Evaluation of ink>
The produced white ink composition is printed on a sheet made of polyvinyl chloride, and passed through the light of an ultraviolet light emitting diode (UV-LED) at the predetermined speed, and irradiation is performed by adjusting to a prescribed exposure amount. went. The printed matter with this ink was evaluated in the same manner as in Example 1. The results are shown in Table 1 below.
Example 14
The following components were stirred with a high-speed water-cooled stirrer to obtain a white UV inkjet ink.
(White ink composition-10)
Light acrylate LA 15.4 parts [Lauryl acrylate: (iii) monofunctional acrylate]
Actylane 421 (Akcros acrylate monomer) 22.0 parts [propoxylated neopentyl glycol diacrylate: (iii) bifunctional acrylate]
・ Photomer 2017 (UV diluent manufactured by EChem) 15.0 parts ・ Solsperse 36000 (dispersing agent manufactured by Noveon) 2.0 parts ・ 15.0 parts of MICROLITH WHITE RA-A (manufactured by Ciba Specialty Chemicals (iv) pigment)
・ Genorad 16 (Rahn Stabilizer) 0.05 part ・ Rapi-Cure DVE-3 8.0 parts (ISP Europe (iii) vinyl ether)
(I) Specific sensitizing dye [Compound II-3 (the above structure)] 10.0 parts Irgacure 2959 8.5 parts (Ciba Specialty Chemicals (ii) photopolymerization initiator)
(Described as “2959” in Tables 1 and 2 below)
Irgacure 819 4.0 parts (Ciba Specialty Chemicals (ii) photoinitiator)
(Described as “819” in Tables 1 and 2 below)
・ Byk 307 (defoamer manufactured by BYK Chemie) 0.05 parts

<Evaluation of ink>
The produced white ink composition is printed on a sheet made of polyvinyl chloride, and passed through the light of an ultraviolet light emitting diode (UV-LED) at the predetermined speed, and irradiation is performed by adjusting to a prescribed exposure amount. went. The printed matter with this ink was evaluated in the same manner as in Example 1. The results are shown in Table 1 below.

Example 15
The following components were stirred with a high-speed water-cooled stirrer to obtain a white UV inkjet ink.
(White ink composition-10)
Light acrylate LA 15.4 parts [Lauryl acrylate: (iii) monofunctional acrylate]
Actylane 421 (Akcros acrylate monomer) 22.0 parts [propoxylated neopentyl glycol diacrylate: (iii) bifunctional acrylate]
・ Photomer 2017 (UV diluent manufactured by EChem) 15.0 parts ・ Solsperse 36000 (dispersing agent manufactured by Noveon) 2.0 parts ・ 15.0 parts of MICROLITH WHITE RA-A (manufactured by Ciba Specialty Chemicals (iv) pigment)
・ Genorad 16 (Rahn Stabilizer) 0.05 part ・ Rapi-Cure DVE-3 8.0 parts (ISP Europe (iii) vinyl ether)
(I) Specific sensitizing dye [Compound II-3 (the above structure)] 10.0 parts Irgacure 2959 8.5 parts (Ciba Specialty Chemicals (ii) photopolymerization initiator)
Irgacure 250 4.0 parts (Ciba Specialty Chemicals (ii) photoinitiator)
(Described as “Irg.250” in Tables 1 and 2 below)
・ Byk 307 (defoamer manufactured by BYK Chemie) 0.05 parts

<Evaluation of ink>
The produced white ink composition is printed on a sheet made of polyvinyl chloride, and passed through the light of an ultraviolet light emitting diode (UV-LED) at the predetermined speed, and irradiation is performed by adjusting to a prescribed exposure amount. went. The printed matter with this ink was evaluated in the same manner as in Example 1. The results are shown in Table 1 below.

Example 16
The following components were stirred with a high-speed water-cooled stirrer to obtain a white UV inkjet ink.
(White ink composition-11)
Light acrylate LA 15.4 parts [Lauryl acrylate: (iii) monofunctional acrylate]
Actylane 421 (Akcros acrylate monomer) 22.0 parts [propoxylated neopentyl glycol diacrylate: (iii) bifunctional acrylate]
・ Photomer 2017 (UV diluent manufactured by EChem) 15.0 parts ・ Solsperse 36000 (dispersing agent manufactured by Noveon) 2.0 parts ・ 15.0 parts of MICROLITH WHITE RA-A (manufactured by Ciba Specialty Chemicals (iv) pigment)
・ Genorad 16 (Rahn Stabilizer) 0.05 part ・ Rapi-Cure DVE-3 8.0 parts (ISP Europe (iii) vinyl ether)
-(I) Specific sensitizing dye [Compound II-3 (the above structure)] 10.0 parts-Irgacure OXE 01 8.5 parts ((ii) Photopolymerization initiator manufactured by Ciba Specialty Chemicals)
Irgacure 184 4.0 parts (Ciba Specialty Chemicals (ii) photoinitiator)
・ Byk 307 (defoamer manufactured by BYK Chemie) 0.05 parts

<Evaluation of ink>
The produced white ink composition is printed on a sheet made of polyvinyl chloride, and passed through the light of an ultraviolet light emitting diode (UV-LED) at the predetermined speed, and irradiation is performed by adjusting to a prescribed exposure amount. went. The printed matter with this ink was evaluated in the same manner as in Example 1. The results are shown in Table 2 below.
Example 17
The following components were stirred with a high-speed water-cooled stirrer to obtain a white UV inkjet ink.
(White ink composition-12)
Light acrylate LA 15.4 parts [Lauryl acrylate: (iii) monofunctional acrylate]
Actylane 421 (Akcros acrylate monomer) 22.0 parts [propoxylated neopentyl glycol diacrylate: (iii) bifunctional acrylate]
・ Photomer 2017 (UV diluent manufactured by EChem) 15.0 parts ・ Solsperse 36000 (dispersing agent manufactured by Noveon) 2.0 parts ・ 15.0 parts of MICROLITH WHITE RA-A (manufactured by Ciba Specialty Chemicals (iv) pigment)
・ Genorad 16 (Rahn Stabilizer) 0.05 part ・ Rapi-Cure DVE-3 8.0 parts (ISP Europe (iii) vinyl ether)
・ (I) Specific sensitizing dye [Compound II-3 (the above structure)] 10.0 parts Irgacure 907 8.5 parts (Cii Specialty Chemicals (ii) Photopolymerization initiator)
Irgacure 819 4.0 parts (Ciba Specialty Chemicals (ii) photoinitiator)
・ Byk 307 (defoamer manufactured by BYK Chemie) 0.05 parts

<Evaluation of ink>
The produced white ink composition is printed on a sheet made of polyvinyl chloride, and passed through the light of an ultraviolet light emitting diode (UV-LED) at the predetermined speed, and irradiation is performed by adjusting to a prescribed exposure amount. went. The printed matter with this ink was evaluated in the same manner as in Example 1. The results are shown in Table 2 below.
Example 18
The following components were stirred with a high-speed water-cooled stirrer to obtain a cyan UV inkjet ink.
(Cyan ink composition-1)
Light acrylate L-A (iii) component 19.4 parts Actylene 421 (Akcros acrylate monomer) 28.0 parts [propoxylated neopentyl glycol diacrylate: (iii) bifunctional acrylate]
Photomer 2017 (UV diluent manufactured by EChem) 18.0 parts Solsperse 32000 (Noveon dispersant) 0.4 parts Irgalite Blue GLVO 3.6 parts (Ciba Specialty Chemicals (iv) pigment)
・ Genorad 16 (Rahn Stabilizer) 0.05 part ・ Rapi-Cure DVE-3
(ISP Europe (iii) vinyl ether) 8.0 parts (i) Specific sensitizing dye [Compound II-3 (structure)] 10.0 parts Darocur TPO 8.5 parts (Ciba Specialty Chemicals ( ii) Photopolymerization initiator)
Irgacure 907 [specific polymerization initiator] 4.0 parts (Ciba Specialty Chemicals (ii) photoinitiator)
-Byk 307 (defoamer manufactured by BYK Chemie) 0.05 parts <Evaluation of ink>
The produced cyan ink composition is printed on a sheet made of polyvinyl chloride, and passed through the light of an ultraviolet light emitting diode (UV-LED) at the predetermined speed, and irradiation is performed by adjusting to a prescribed exposure amount. Went. The printed matter with this ink was evaluated in the same manner as in Example 1. The results are shown in Table 2 below.

[Example 18]
The following components were stirred with a high-speed water-cooled stirrer to obtain a magenta UV inkjet ink.
(Magenta ink composition-1)
Light acrylate L-A (iii) component 13.4 parts Actylene 421 (Akcros acrylate monomer) 34.0 parts [propoxylated neopentyl glycol diacrylate: (iii) bifunctional acrylate]
-Photomer 2017 (UV diluent manufactured by EChem) 18.0 parts-Solsperse 32000 (dispersant manufactured by Noveon) 0.4 parts-Cinquasia Magenta RT-355 D 3.6 parts (Ciba Specialty Chemicals pigments (Ivive) )
・ Genorad 16 (Rahn Stabilizer) 0.05 part ・ Rapi-Cure DVE-3 8.0 parts (ISP Europe (iii) vinyl ether)
-(I) Specific sensitizing dye [Compound II-3 (the above structure)] 10.0 parts-Darocur TPO 8.5 parts (Ciba Specialty Chemicals (ii) Photopolymerization initiator)
Irgacure 907 [(ii) Polymerization initiator] 4.0 parts (Ciba Specialty Chemicals photoinitiator)
-Byk 307 (defoamer manufactured by BYK Chemie) 0.05 parts <Evaluation of ink>
The produced magenta color ink composition is printed on a sheet made of polyvinyl chloride, and passed through the light of an ultraviolet light emitting diode (UV-LED) at the predetermined speed, and then irradiated by adjusting to a prescribed exposure amount. Went. The printed matter with this ink was evaluated in the same manner as in Example 1. The results are shown in Table 2 below.

[Example 19]
The following components were stirred with a high-speed water-cooled stirrer to obtain a yellow UV inkjet ink.
(Yellow color ink composition-1)
Light acrylate LA (iii) component 10 parts Actylene 421 (Akcros acrylate monomer) 42.4 parts Photomer 2017 (EChem UV diluent) 17.0 parts Solsperse 32000 (Noveon dispersant) ) 0.4 part · Chromophthal Yellow LA 3.6 parts (Ciba Specialty Chemicals (iv) pigment)
・ Genorad 16 (Rahn Stabilizer) 0.05 part ・ Rapi-Cure DVE-3 4.0 part (ISP Europe (iii) vinyl ether)
-(I) Specific sensitizing dye [Compound II-3 (the above structure)] 10.0 parts-Darocur TPO 8.5 parts (Ciba Specialty Chemicals (ii) Photopolymerization initiator)
Irgacure 907 [specific polymerization initiator] 4.0 parts (Ciba Specialty Chemicals (ii) photoinitiator)
-Byk 307 (defoamer manufactured by BYK Chemie) 0.05 parts <Evaluation of ink>
The produced yellow ink composition is printed on a sheet made of polyvinyl chloride, and passed through the light of an ultraviolet light emitting diode (UV-LED) at the predetermined speed to irradiate by adjusting to a prescribed exposure amount. Went. The printed matter with this ink was evaluated in the same manner as in Example 1. The results are shown in Table 2 below.

[Example 20]
The following components were stirred with a high-speed water-cooled stirrer to obtain a black UV inkjet ink.
(Black ink composition-1)
-Light acrylate LA (iii) component 22.4 parts-Actilane 421 (Akcros acrylate monomer) 29.0 parts-Photomer 2017 (EChem UV diluent) 18.0 parts-Solsperse 32000 (Noveon) (Dispersant) 0.4 parts, 2.6 parts Microlith Black C-K (Civa Specialty Chemicals (iv) pigment)
・ Genorad 16 (Stabilizer manufactured by Rahn) 0.05 part ・ Rapi-Cure DVE-3 5.0 parts (ISP Europe (iii) vinyl ether)
-(I) Specific sensitizing dye [Compound II-3 (the above structure)] 10.0 parts-Darocur TPO 8.5 parts (Ciba Specialty Chemicals (ii) Photopolymerization initiator)
Irgacure 907 [specific polymerization initiator] 4.0 parts (Ciba Specialty Chemicals (ii) photoinitiator)
・ Byk 307 (defoamer manufactured by BYK Chemie) 0.05 parts

<Evaluation of ink>
The produced black ink composition is printed on a sheet made of polyvinyl chloride and passed through the light of an ultraviolet light emitting diode (UV-LED) at the predetermined speed, and irradiation is performed by adjusting to a prescribed exposure amount. went. The printed matter with this ink was evaluated in the same manner as in Example 1. The results are shown in Table 2 below.
(Comparative Example 1)
The following components were stirred with a high-speed water-cooled stirrer to obtain a white UV inkjet ink.
(White ink composition-C1)
-Light acrylate LA 18.4 parts [acrylic acid lauryl ester: (iii) monofunctional acrylate]
Actylene 421 (acrylate monomer manufactured by Akcros) 26.0 parts [propoxylated neopentyl glycol diacrylate: (iii) bifunctional acrylate]
・ Photomer 2017 (UV diluent made by EChem) 18.0 parts ・ Solsperse 36000 (dispersant made by Noveon) 2.0 parts ・ 15.0 parts ・ MICROLIGHT WHITE R-A (made by Ciba Specialty Chemicals (iv) pigment)
・ Genorad 16 (Rahn Stabilizer) 0.05 part ・ Rapi-Cure DVE-3 8.0 parts (ISP Europe (iii) vinyl ether)
Darocur TPO 8.5 parts (Ciba Specialty Chemicals (ii) photoinitiator)
Irgacure 907 4.0 parts (Ciba Specialty Chemicals (ii) photopolymerization initiator)
・ Byk 307 (defoamer manufactured by BYK Chemie) 0.05 parts

<Evaluation of ink>
The produced white ink composition is printed on a sheet made of polyvinyl chloride, and passed through the light of an ultraviolet light emitting diode (UV-LED) at the predetermined speed, and irradiation is performed by adjusting to a prescribed exposure amount. went. The printed matter with this ink was evaluated in the same manner as in Example 1. The results are shown in Table 2 below.

(Comparative Example 2)
The following components were stirred with a high-speed water-cooled stirrer to obtain a white UV inkjet ink.
(White ink composition-C2)
Light acrylate LA 16.4 parts [acrylic acid lauryl ester: (iii) monofunctional acrylate]
Actilane 421 (Akcros acrylate monomer) 23.0 parts [propoxylated neopentyl glycol diacrylate: (iii) bifunctional acrylate]
・ Photomer 2017 (UV diluent manufactured by EChem) 15.0 parts ・ Solsperse 36000 (dispersing agent manufactured by Noveon) 2.0 parts ・ 15.0 parts of MICROLITH WHITE RA-A (manufactured by Ciba Specialty Chemicals (iv) pigment)
・ Genorad 16 (Rahn Stabilizer) 0.05 part ・ Rapi-Cure DVE-3 8.0 parts (ISP Europe (iii) vinyl ether)
2-chlorothioxanthone (comparative sensitizing dye: the following structure) 8.0 parts (described as “CLTX” in Tables 1 and 2 below)
Darocur TPO 8.5 parts (Ciba Specialty Chemicals (ii) photoinitiator)
Irgacure 907 4.0 parts (Ciba Specialty Chemicals (ii) photopolymerization initiator)
・ Byk 307 (defoamer manufactured by BYK Chemie) 0.05 parts

<Evaluation of ink>
The produced white ink composition is printed on a sheet made of polyvinyl chloride, and passed through the light of an ultraviolet light emitting diode (UV-LED) at the predetermined speed, and irradiation is performed by adjusting to a prescribed exposure amount. went. The printed matter with this ink was evaluated in the same manner as in Example 1. The results are shown in Table 2 below.

(Comparative Example 3)
The following components were stirred with a high-speed water-cooled stirrer to obtain a white UV inkjet ink.
(White ink composition-C2)
Light acrylate LA 16.4 parts [acrylic acid lauryl ester: (iii) monofunctional acrylate]
Actilane 421 (Akcros acrylate monomer) 23.0 parts [propoxylated neopentyl glycol diacrylate: (iii) bifunctional acrylate]
・ Photomer 2017 (UV diluent manufactured by EChem) 15.0 parts ・ Solsperse 36000 (dispersing agent manufactured by Noveon) 2.0 parts ・ 15.0 parts of MICROLITH WHITE RA-A (manufactured by Ciba Specialty Chemicals (iv) pigment)
・ Genorad 16 (Rahn Stabilizer) 0.05 part ・ Rapi-Cure DVE-3 8.0 parts (ISP Europe (iii) vinyl ether)
2,4-diethylthioxanthone (comparative sensitizing dye: the following structure) 8.0 parts (described as “DETX” in Tables 1 and 2 below)
Darocur TPO 8.5 parts (Ciba Specialty Chemicals (ii) photoinitiator)
Irgacure 907 4.0 parts (Ciba Specialty Chemicals (ii) photopolymerization initiator)
・ Byk 307 (defoamer manufactured by BYK Chemie) 0.05 parts

<Evaluation of ink>
The produced white ink composition is printed on a sheet made of polyvinyl chloride, and passed through the light of an ultraviolet light emitting diode (UV-LED) at the predetermined speed, and irradiation is performed by adjusting to a prescribed exposure amount. went. The printed matter with this ink was evaluated in the same manner as in Example 1. The results are shown in Table 2 below.
(Comparative Example 3)
The following components were stirred with a high-speed water-cooled stirrer to obtain a white UV inkjet ink.
(White ink composition-C3)
Light acrylate LA 16.4 parts [acrylic acid lauryl ester: (iii) monofunctional acrylate]
Actilane 421 (Akcros acrylate monomer) 23.0 parts [propoxylated neopentyl glycol diacrylate: (iii) bifunctional acrylate]
・ Photomer 2017 (UV diluent manufactured by EChem) 15.0 parts ・ Solsperse 36000 (dispersing agent manufactured by Noveon) 2.0 parts ・ 15.0 parts of MICROLITH WHITE RA-A (manufactured by Ciba Specialty Chemicals (iv) pigment)
・ Genorad 16 (Rahn Stabilizer) 0.05 part ・ Rapi-Cure DVE-3 8.0 parts (ISP Europe (iii) vinyl ether)
6-chlorothiochromanone (comparative sensitizing dye: the following structure) 8.0 parts Darocur TPO 8.5 parts (Ciba Specialty Chemicals (ii) photoinitiator)
Irgacure 907 4.0 parts (Ciba Specialty Chemicals (ii) photopolymerization initiator)
・ Byk 307 (defoamer manufactured by BYK Chemie) 0.05 parts

<Evaluation of ink>
The produced white ink composition is printed on a sheet made of polyvinyl chloride, and passed through the light of an ultraviolet light emitting diode (UV-LED) at the predetermined speed, and irradiation is performed by adjusting to a prescribed exposure amount. went. The printed matter with this ink was evaluated in the same manner as in Example 1. The results are shown in Table 2 below.

As is apparent from Tables 1 and 2, all of the ink compositions of Examples 2 to 1 and 10 to 20 of the present invention were cured with high sensitivity. Of these, the combination of a sensitizing dye containing a sulfur atom (sensitizing dyes represented by Examples 2 to 8 and 10 to 16) and Irgacure 907 which is an α-aminoketone as a polymerization initiator is particularly high. It was sensitivity. Further , the white ink composition of Reference Example 1 was not good in color reproducibility due to yellow coloring derived from the sensitizing dye I-1, whereas the white ink compositions of Examples 2 to 8 had high sensitivity and A white ink with good color reproducibility was given.
On the other hand, the ink composition containing the sensitizing dye that does not contain a polymerizable group in Comparative Examples 2 and 3 has higher sensitivity than Comparative Example 1 to which no sensitizing dye is added, but until the surface stickiness is completely eliminated. Required 1000 mJ and high energy.

Claims (7)

(I) a sensitizing dye represented by the following Symbol one general formula (II) having a polymerizable group as a substituent, (ii) a polymerization initiator, and (iii) a polymerizable compound having an ethylenically unsaturated bond, the An ink composition comprising the ink composition.

In one general formula (II), X is O, S, or represents NR ^b. n ₂ represents 0 or 1.
R ^b , R ¹¹ , R ¹² , R ¹³ , R ¹⁴ , R ¹⁵ , R ¹⁶ , R ¹⁷ , and R ¹⁸ each independently represent a hydrogen atom or a monovalent substituent, and at least one of them Contains a polymerizable unsaturated double bond.
Two of R ¹¹ , R ¹² , R ¹³ , and R ¹⁴ may be linked to each other to form a ring. 2. The ink composition according to claim 1, wherein (ii) the polymerization initiator is selected from the group consisting of α-aminoketones and acylphosphine oxides. The ink composition according to claim 1 or 2, wherein the polymerization initiator (ii) is an acylphosphine oxide. The ink composition according to any one of claims 1 to 3, further comprising (iv) a colorant.   The ink composition according to claim 4, wherein the colorant (iv) is a white pigment. The ink composition according to any one of claims 1 to 5 , wherein the ink composition is for inkjet recording. (A) a step of discharging the ink composition according to any one of claims 1 to 6 onto a recording medium; and (b) irradiating the discharged ink composition with actinic radiation, And a step of curing the ink composition.