JP4963805B2 - Ink composition, image forming method using the same, and printed matter - Google Patents

Description

  The present invention relates to an ink composition suitably used for inkjet recording, an image forming method, and a printed matter using the same. More specifically, an ink composition suitable for ink jet recording capable of forming a high-quality image by being excellent in colorant dispersibility, excellent color developability, cured by irradiation with active energy rays, and using the same The present invention relates to an image forming method and a printed matter using the same.

  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. Among these, the ink jet method can be implemented with an inexpensive apparatus, and the ink can be efficiently used because the ink is ejected only on the required image portion to directly form the image on the recording medium. Running cost is low. Furthermore, there is little noise and it is excellent as an image recording method.

According to the inkjet system, printing is possible not only on plain paper but also on non-water-absorbing recording media such as plastic sheets and metal plates. However, high speed and high image quality are important issues for printing. The time required for drying and curing the droplets after printing has a property of greatly affecting the sharpness of the image.
As one of the ink jet methods, there is a recording method using an ink for ink jet recording that can be cured by irradiation with active energy rays. According to this method, a sharp image can be formed by irradiating active energy rays immediately after printing and curing ink droplets.
Such a curable ink composition is required to have high pigment dispersibility and stability over time in order to form a high-definition image having excellent color developability. In order to impart a clear color tone and high coloring power to the ink composition, it is essential to make the pigment finer. In particular, in the ink used for inkjet recording, since the ejected ink droplets greatly affect the sharpness of the image, the amount of ejected droplets is small, and the thickness of the ink cured film formed from the ink is small. It is essential to use finer particles. As described above, when the pigment particles are further miniaturized in order to obtain a high coloring power, it becomes difficult to disperse the fine particles, and aggregates are easily generated. Moreover, the problem that the viscosity of a composition rises by addition of a dispersing agent also arises. The occurrence of pigment aggregates and the increase in viscosity of the ink composition both have an adverse effect on ink ejection properties, and are not preferred for use in ink compositions.

Further, when the ink composition is used for ink jet recording, the ink composition is stored in a cartridge, heated when ejected, and cooled during non-ejection and storage, and thus undergoes repeated heating-cooling temperature changes. This change in temperature also has an adverse effect on the pigment dispersibility, and the dispersibility of the pigment decreases with time, resulting in problems such as increased viscosity and aggregation.
Accordingly, there is a need for an ink composition that has sufficient fluidity, stably disperses a finely divided pigment, and is excellent in the temporal stability of pigment dispersion. Various proposals have been made on dispersants for obtaining stable pigment dispersions.

In order to improve the affinity with the pigment, it is a base as a dispersant for an ink composition using a pigment derivative as a dispersant (for example, see Patent Documents 1 and 2) and specific pigments such as phthalocyanine and quinacridone series. Dispersing agents such as an ink composition using a polymer having a functional group (see, for example, Patent Document 3), poly (ethyleneimine) -poly (12-hydroxystearic acid) graft polymer, and a specific agent that dissolves the dispersing agent An ink composition containing a monomer and not using an organic solvent (for example, see Patent Document 4) has been proposed.
Although these ink compositions certainly have improved pigment dispersion stability than the conventional ones due to the function of the dispersant, the pigments used are not sufficiently refined, and further fine pigment particles There was still room for improvement in the dispersibility improvement effect. Furthermore, there is a problem that the dispersion stability is still insufficient when the temperature change is repeated for a long period of time.
JP 2003-119414 A JP 2004-18656 A JP 2003-321628 A JP 2004-131589 A

The object of the present invention, which was made in consideration of the above problems, is excellent in the dispersibility and stability of fine colorants, particularly pigments, and can form high-quality images having clear color tone and high coloring power. Another object of the present invention is to provide an ink composition suitable for inkjet recording that can be cured by irradiation with active energy rays, and an image forming method using the ink composition.
Another object of the present invention is to provide a printed matter obtained by using an ink composition that can be cured by irradiation with active energy rays and has a clear color tone and high coloring power.

As a result of intensive studies, the present inventors have achieved excellent colorant dispersibility by using a specific heterocyclic compound as a colorant dispersant, and after long-term storage or repeated temperature changes. However, the inventors have found that an ink composition excellent in colorant dispersion stability in which a decrease in dispersion stability is effectively suppressed can be obtained, and the present invention has been completed.
That is, the present invention is as follows.

<1> including at least (a) a radical polymerizable monomer, (b) a pigment , (c) a compound represented by the following general formula (1), and (d) a photoradical initiator. An ink composition.

[In formula (1), R represents an alkyl group, an acyl group, a carbamoyl group, an alkoxycarbonyl group, an aryl group, a sulfonyl group, or a sulfamoyl group. X is A alkylene group, -O -, - S -, - NR 1 -, or -C (= O) - is any one selected from, R ¹ represents a hydrogen atom or an alkyl group. Ring A and ring B each independently represent a ring, and at least one of them is an aromatic ring. ]

<2> The ink composition according to <1>, wherein the content of the compound represented by the general formula (1) with respect to the ink composition is 2 to 80% by mass.
<3> The ink composition according to <1> or <2>, wherein the radical polymerizable monomer is (meth) acrylates or (meth) acrylamides.
< 4 > The ink composition according to any one of <1> to <3>, wherein the compound represented by the general formula (1) has a number average molecular weight of 300 or more .
<5> the (a) above <1> to ink composition according to any one of <4>, wherein the Rukoto that having a radical polymerizable monomer is 4 or more functional (meth) acrylates.

< 6 > The ink composition according to any one of <1> to < 5 >, wherein the ink composition is for inkjet.
< 7 > A step of printing the ink composition according to any one of <1> to < 6 > on a recording medium, and a step of irradiating the printed ink composition with an active energy ray to cure the ink composition An image forming method comprising:
< 8 > A printed material obtained by curing the ink composition according to any one of <1> to < 6 >.

< 9 > The printed material according to the above < 8 >, wherein the ink composition is printed on a recording medium with an ink jet printer, and then the ink composition is cured by irradiation with an active energy ray.

The ink composition of the present invention can be used for normal printing to form sharp images with excellent color developability and obtain high-quality printed materials, and is also suitable for the production of resists, color filters, and optical disks. It is also useful as an optical modeling material.
Further, by applying the image forming method of the present invention, a high-quality image can be directly formed on a non-absorbent recording medium based on digital data. Therefore, the ink composition of the present invention has a large area. It is also suitably used for the production of printed materials.

According to the present invention, the dispersibility of the fine colorant and its stability are excellent, a high-quality image having a clear color tone and high coloring power can be formed, and it can be cured by irradiation with active energy rays. An ink composition suitable for ink jet recording and an image forming method using the ink composition can be provided.
In addition, the printed matter of the present invention can be cured by irradiation with active energy rays, and has an effect that a high-quality image obtained using an ink composition having a clear color tone and high coloring power is formed. Play.

The ink composition of the present invention contains (a) a radical polymerizable monomer, (b) a pigment , (c) a compound represented by the following general formula (1), and (d) a photoradical initiator. It is characterized by.

The ink composition of the present invention, by the function of (a) a radical polymerizable monomer, you cured by applying some energy, contains (d) is a photoradical initiator composition which is cured by irradiation of an active energy ray It is a thing. Here, the active energy ray is not particularly limited as long as it can impart energy capable of generating a starting species in the ink composition by irradiation, and is widely used in α rays, γ rays, X rays, ultraviolet rays. Including visible light, electron beam, and the like, ultraviolet rays and electron beams are preferable from the viewpoint of curing sensitivity and device availability, and ultraviolet rays are particularly preferable. Therefore, the ink composition of the present invention is preferably an ink composition that can be cured by irradiating ultraviolet rays as radiation.
Hereinafter, each component used in the ink composition of the present invention will be described in order.

[(C) Compound represented by general formula (1)]
First, (c) a compound represented by the general formula (1) (hereinafter referred to as (c) a specific heterocyclic compound as appropriate), which is a characteristic component in the present invention, will be described.

In formula (1), R represents an alkyl group, an acyl group, a carbamoyl group, an alkoxycarbonyl group, an aryl group, a sulfonyl group, or a sulfamoyl group. X is A alkylene group, -O -, - S -, - NR 1 -, or -C (= O) - is any one selected from, R ¹ represents a hydrogen atom or an alkyl group. Ring A and ring B each independently represent a ring, and at least one of them is an aromatic ring.

In the formula (1), R represents an alkyl group, an acyl group, a carbamoyl group, an alkoxycarbonyl group, an aryl group, a sulfonyl group, or a sulfamoyl group.
The alkyl group preferably has 2 to 32 carbon atoms, more preferably 4 to 20 carbon atoms, and particularly preferably 8 to 18 carbon atoms.
The alkyl group may have a substituent, and examples of the substituent include an aryl group, an alkoxy group, a phenoxy group, a hydroxy group, a sulfo group, a carboxy group, an oxycarbonyl group, a carbamoyl group, and an amino group. .
Examples of the alkyl group include ethyl, n-butyl, i-butyl, t-butyl, n-hexyl, cyclohexyl, n-octyl, 2-ethylhexyl, n-decyl, and n-dodecyl. Group, n-octadecyl group, 2-hydroxyethyl group, 6-hydroxyhexyl group, 8-hydroxyoctyl group, 7,8-dihydroxyoctyl group, 11,12-dihydroxydodecyl group, 2-methoxyethyl group, 2-butoxy Ethyl group, 6-butoxyhexyl group, 8-butoxyoctyl group, 3-carboxypropyl group, 4-carboxybutyl group, 8-carboxyoctyl group, 3-sulfopropyl group, 4-sulfobutyl group, 2- (N, N -Dimethylamino) ethyl group, 3- (N, N-dimethylamino) propyl group, 6- (N, N-dimethylamino) he Preferred examples include syl group, 8- (N, N-methylamino) octyl group, 8- (N, N-diethylamino) octyl group, n-octyl group, 2-ethylhexyl group, n-decyl group, n- Dodecyl group, n-octadecyl group, 8-hydroxyoctyl group, 7,8-dihydroxyoctyl group, 11,12-dihydroxydodecyl group, 6- (N, N-dimethylamino) hexyl group, 8- (N, N- A dimethylamino) octyl group and an 8- (N, N-diethylamino) octyl group are particularly preferred.

Moreover, as an acyl group, C2-C32 is preferable, 4-20 is more preferable, 8-18 is especially preferable.
The acyl group may have a substituent, and examples of the substituent include an aryl group, an alkoxy group, a phenoxy group, a hydroxy group, a sulfo group, a carboxy group, an oxycarbonyl group, and a carbamoyl group.
Acyl groups include acetyl, propanoyl, butanoyl, hydroxybutanoyl, hexanoyl, octanoyl, 2-ethylhexanoyl, decanoyl, dodecanoyl, octadecanoyl, 1,1-dimethylpropanoyl Groups and the like.

  The carbamoyl group preferably has 2 to 32 carbon atoms, more preferably 4 to 20 carbon atoms, and particularly preferably 8 to 18 carbon atoms. Specific examples of the carbamoyl group include, for example, methylcarbamoyl group, ethylcarbamoyl group, n-propylcarbamoyl group, isopropylcarbamoyl group, n-butylcarbamoyl group, n-butylcarbamoyl group, s-butylcarbamoyl group, i-buty Examples include a rucarbamoyl group, a t-butylcarbamoyl group, an n-amylcarbamoyl group, an isoamylcarbamoyl group, a phenylcarbamoyl group, an n-octylcarbamoyl group, a 2-ethylhexylcarbamoyl group, and a cyclohexylcarbamoyl group.

  The alkoxycarbonyl group preferably has 2 to 32 carbon atoms, more preferably 3 to 20 carbon atoms, and particularly preferably 4 to 18 carbon atoms. Specific examples of the alkoxycarbonyl group include methoxycarbonyl group, ethoxycarbonyl group, propyloxycarbonyl group, butoxycarbonyl group, hexyloxycarbonyl group, 2-ethylhexyloxycarbonyl group, octyloxycarbonyl group, decyloxycarbonyl group, ethoxybutoxy Examples include carbonyl group, phenoxyethoxycarbonyl group, and benzyloxycarbonyl group, and methoxycarbonyl group, ethoxycarbonyl group, propyloxycarbonyl group, butoxycarbonyl group, hexyloxylcarbonyl group, 2-ethylhexyloxycarbonyl group, octyl are particularly preferable. Examples include an oxycarbonyl group, a decyloxycarbonyl group, and a benzyloxycarbonyl group.

  The aryl group preferably has 6 to 32 carbon atoms, more preferably 6 to 20 carbon atoms, and particularly preferably 6 to 18 carbon atoms. Specific examples of the aryl group include a phenyl group, a naphthyl group, a 2-methoxyphenyl group, a 2-decyloxyphenyl group, a 4-methoxyphenyl group, a 2-octyloxynaphthyl group, a dimethylaminophenyl group, and 2-dodecylthiophenyl. Group, 4- (4-methylphenylthioxy) phenyl group, 2-methoxy-4-dodecylthiooxyphenyl group, 2-phenoxyethoxyphenyl group, 2-dodecyloxyphenyl group, 2-octadecyloxyphenyl group, 2, 5-dibenzyloxyphenyl group, 2,5-dicyclohexylmethyloxyphenyl group, 2-methoxy-4- (2-ethylhexanoylamino) phenyl group, 2-butoxy-4-benzyloxycarbonylaminophenyl group, 2-octyloxy-4-butyloxycarbonylaminophen Le group.

  The sulfamoyl group preferably has 1 to 32 carbon atoms, more preferably 2 to 20 carbon atoms, and particularly preferably 4 to 18 carbon atoms. Specific examples of the sulfamoyl group include, for example, methylsulfamoyl group, ethylsulfamoyl group, n-propylsulfamoyl group, isopropylsulfamoyl group, n-butylsulfamoyl group, n-butylsulfa Moyl group, s-butylsulfamoyl group, i-butylsulfamoyl group, t-butylsulfamoyl group, n-amylsulfamoyl group, isoamylsulfamoyl group, phenylsulfamoyl group, n-octyl A sulfamoyl group, a 2-ethylhexylsulfamoyl group, a cyclohexylsulfamoyl group and the like can be mentioned.

  The sulfonyl group preferably has 1 to 32 carbon atoms, more preferably 2 to 20 carbon atoms, and particularly preferably 4 to 18 carbon atoms. Specific examples of the sulfonyl group include methylsulfonyl, ethylsulfonyl, propylsulfonyl, butylsulfonyl, octylsulfonyl, decylsulfonyl, dodecylsulfonyl and the like.

  The sulfamoyl group preferably has 1 to 32 carbon atoms, more preferably 2 to 20 carbon atoms, and particularly preferably 4 to 18 carbon atoms. Specific examples of the sulfamoyl group include N-ethylsulfamoyl group, N- (3-dodecyloxypropyl) sulfamoyl group, N, N-dimethylsulfamoyl group, N-acetylsulfamoyl group, N-benzoylsulfur group. Examples include a famoyl group and an N- (N′-phenylcarbamoyl) sulfamoyl group.

In the general formula (1), the alkyl group, acyl group, carbamoyl group, alkoxycarbonyl group, aryl group, sulfonyl group, or sulfamoyl group represented by R may have a specific repeating unit. The number average molecular weight is preferable. Examples of the repeating unit include polyether (eg, polyethylene glycol, polypropylene glycol, etc.), polyester (eg, polycaprolactone, etc.), polyamide (eg, polycaprolactam, etc.) and the like.
In the general formula (1), R is preferably an alkyl group or an acyl group.

In the general formula (1), X A alkylene group (e.g., methylene group, ethylene group, propylene group, trimethylene group, tetramethylene group), - O -, - S -, - NR 1 - or -C, Any one selected from (═O) —, and R ¹ is a hydrogen atom or an alkyl group (for example, a methyl group, an ethyl group, an n-propyl group, an i-propyl group, an n-butyl group, a t-butyl group). Group, n-hexyl group, n-octyl group, 2-ethylhexyl group, n-octadecyl group, etc.). Among these, X is preferably a single bond, a methylene group, —O— or —C (═O) —, and particularly preferably —C (═O) —.

  Ring A and ring B each independently represent a ring, and at least one of them is an aromatic ring. At least one of ring A and ring B represents an aromatic ring. As the aromatic ring, benzene ring, naphthalene ring, indene ring, azulene ring, fluorene ring, anthracene ring, pyridine ring, pyrazine ring, pyrimidine ring, pyrrole ring, imidazole ring, indole ring, quinoline ring, acridine ring, phenothiazine ring, Examples include phenoxazine ring, acridone ring, anthraquinone ring, benzene ring, naphthalene ring, anthracene ring, pyridine ring, phenoxazine ring, acridine ring, phenothiazine ring, phenoxazine ring, acridone ring, anthraquinone ring, benzene ring More preferred are a pyridine ring, a phenothiazine ring, a phenoxazine ring, an acridone ring and an anthraquinone ring, and particularly preferred are a benzene ring, an acridone ring and an anthraquinone ring. The ring that can be formed is preferably a 3- to 8-membered ring, more preferably a 4- to 6-membered ring, particularly preferably a 6-membered ring, which may be a monocyclic ring or a condensed ring, and may be a saturated ring or an unsaturated ring. Both A and ring B are preferably aromatic rings.

The molecular weight of the (c) specific heterocyclic compound in the present invention is preferably 300 or more, more preferably 300 to 100,000, still more preferably 400 to 50,000, and particularly preferably 500 to 10,000 as the number average molecular weight.
Specific examples of the specific heterocyclic compound (c) in the present invention can be listed below. Note that the present invention is not limited to this.

In the present invention, the (c) specific heterocyclic compound may be a commercially available compound or a compound produced by a known production method. For example, it can be obtained by the following method.
It can be synthesized by using a heterocyclic compound having NH and known N-alkylation, N-acylation, N-sulfonylation, or the like. Furthermore, it can be synthesized by anionic ring-opening polymerization in the presence of a heterocyclic compound having NH and a base.

  The (c) specific heterocyclic compound in the present invention is particularly preferably used as a dispersant (particularly for a colorant), and a heterocyclic residue having a high affinity with the colorant due to van-der-waals interaction. By having this, the adsorptivity with the colorant is good, so that a stable dispersion can be obtained. Moreover, dispersion stabilization is possible by the steric repulsion effect which the substituent on a nitrogen atom brings.

In the ink composition of the present invention, only one type of (c) specific heterocyclic compound may be added, or two or more types may be used in combination. The content of the specific heterocyclic compound (c) in the ink composition is preferably 1 to 100% by mass, more preferably 2 to 80% by mass, and 5 to 50% by mass with respect to the added amount of the colorant. Is more preferable. Adding 1 to 100% by mass of the content of the specific heterocyclic compound (c) with respect to the addition amount of the colorant improves the dispersibility of the fine colorant and its stability, resulting in a clear color tone and high It is preferable because coloring power is remarkably improved.
In the ink composition of the present invention, a known dispersant (particularly for pigments) can be used in combination with (c) the specific heterocyclic compound as long as the effect is not impaired. As this addition amount, it is preferable that it is 50 mass% or less of (c) specific heterocyclic compound.

[(B) Colorant]
The ink composition of the present invention contains a colorant as an essential component.
The colorant is excellent in color developability by using the ink composition of the present invention by being uniformly and stably dispersed in the ink composition by the function of the specific heterocyclic compound (c). A sharp image can be formed. Among the colorants, a pigment is preferable from the viewpoint of color developability. The colorant preferably has a fine particle size.
There is no restriction | limiting in particular in the coloring agent which can be used here, According to a use, a well-known various pigment and dye can be selected suitably, and can be used. In particular, by using a pigment as a colorant, an image obtained from the ink composition of the present invention has excellent weather resistance.

The pigment that is preferably used as the colorant is described below, but is not particularly limited to the pigment.
The pigment is not particularly limited, and all commercially available organic pigments and inorganic pigments, and those obtained by dyeing resin particles with a dye can be used. Furthermore, commercially available pigment dispersions and surface-treated pigments, for example, pigments dispersed in an insoluble resin or the like as a dispersion medium, or those obtained by grafting a resin on the pigment surface, etc., impair the effects of the present invention. It can be used as long as it is not.
Examples of these pigments include, for example, “Pigment Dictionary” (2000), edited by Seijiro Ito. Herbst, K.M. Hunger “Industrial Organic Pigments”, JP 2002-12607 A, JP 2002-188025 A, JP 2003-26978 A, and JP 2003-342503 A3.

  Specific examples of organic pigments and inorganic pigments that can be used in the present invention include C.I. I. Pigment Yellow 1 (Fast Yellow G etc.), C.I. I. A monoazo pigment such as C.I. Pigment Yellow 74; I. Pigment Yellow 12 (disaji yellow AAA, etc.), C.I. I. Disazo pigments such as C.I. Pigment Yellow 17; I. Non-benzidine type azo pigments such as CI Pigment Yellow 180; I. Azo lake pigments such as C.I. Pigment Yellow 100 (eg Tartrazine Yellow Lake); I. Condensed azo pigments such as CI Pigment Yellow 95 (Condensed Azo Yellow GR, etc.); I. Acidic dye lake pigments such as C.I. Pigment Yellow 115 (such as quinoline yellow lake); I. Basic dye lake pigments such as CI Pigment Yellow 18 (Thioflavin Lake, etc.), anthraquinone pigments such as Flavantron Yellow (Y-24), isoindolinone pigments such as Isoindolinone Yellow 3RLT (Y-110), and quinophthalone yellow Quinophthalone pigments such as (Y-138), isoindoline pigments such as isoindoline yellow (Y-139), C.I. I. Nitroso pigments such as C.I. Pigment Yellow 153 (nickel nitroso yellow, etc.); I. And metal complex salt azomethine pigments such as CI Pigment Yellow 117 (copper azomethine yellow, etc.).

  C. As a thing which exhibits red or magenta color, C.I. I. Monoazo pigments such as CI Pigment Red 3 (Toluidine Red, etc.); I. Disazo pigments such as C.I. Pigment Red 38 (Pyrazolone Red B, etc.); I. Pigment Red 53: 1 (Lake Red C, etc.) and C.I. I. Azo lake pigments such as C.I. Pigment Red 57: 1 (Brilliant Carmine 6B); I. Condensed azo pigments such as C.I. Pigment Red 144 (condensed azo red BR, etc.); I. Acidic dye lake pigments such as C.I. Pigment Red 174 (Phloxine B Lake, etc.); I. Basic dye lake pigments such as C.I. Pigment Red 81 (Rhodamine 6G 'lake, etc.); I. Anthraquinone pigments such as C.I. Pigment Red 177 (eg, dianthraquinonyl red); I. Thioindigo pigments such as C.I. Pigment Red 88 (Thioindigo Bordeaux, etc.); I. Perinone pigments such as C.I. Pigment Red 194 (perinone red, etc.); I. Perylene pigments such as C.I. Pigment Red 149 (perylene scarlet, etc.); I. Pigment violet 19 (unsubstituted quinacridone), C.I. I. Quinacridone pigments such as CI Pigment Red 122 (quinacridone magenta, etc.); I. Isoindolinone pigments such as CI Pigment Red 180 (isoindolinone red 2BLT, etc.); I. And alizarin lake pigments such as CI Pigment Red 83 (Mada Lake, etc.).

  As a pigment exhibiting blue or cyan, C.I. I. Disazo pigments such as C.I. Pigment Blue 25 (Dianisidine Blue, etc.); I. Phthalocyanine pigments such as C.I. Pigment Blue 15 (phthalocyanine blue, etc.); I. Acidic dye lake pigments such as C.I. Pigment Blue 24 (Peacock Blue Lake, etc.); I. Basic dye lake pigments such as C.I. Pigment Blue 1 (Viclotia Pure Blue BO Lake, etc.); I. Anthraquinone pigments such as C.I. Pigment Blue 60 (Indantron Blue, etc.); I. And alkali blue pigments such as CI Pigment Blue 18 (Alkali Blue V-5: 1).

As a pigment exhibiting green, C.I. I. Pigment green 7 (phthalocyanine green), C.I. I. Phthalocyanine pigments such as C.I. Pigment Green 36 (phthalocyanine green); I. And azo metal complex pigments such as CI Pigment Green 8 (Nitroso Green).
As a pigment exhibiting an orange color, C.I. I. An isoindoline pigment such as C.I. Pigment Orange 66 (isoindoline orange); I. And anthraquinone pigments such as CI Pigment Orange 51 (dichloropyrantron orange).

Examples of the black pigment include carbon black, titanium black, and aniline black.
Specific examples of the white pigment include basic lead carbonate (2PbCO ₃ Pb (OH) ₂ , so-called silver white), zinc oxide (ZnO, so-called zinc white), titanium oxide (TiO ₂ , so-called titanium white), Strontium titanate (SrTiO ₃ , so-called titanium strontium white) or the like can be used.

  Here, titanium oxide has a smaller specific gravity than other white pigments, a large refractive index, and is chemically and physically stable, so that it has a large hiding power and coloring power as a pigment. Excellent durability against other environments. Therefore, it is preferable to use titanium oxide as the white pigment. Of course, other white pigments (may be other than the listed white pigments) may be used in combination as necessary.

For dispersion of the pigment, for example, a dispersion device such as a ball mill, a sand mill, an attritor, a roll mill, a jet mill, a homogenizer, a paint shaker, a kneader, an agitator, a Henschel mixer, a colloid mill, an ultrasonic homogenizer, a pearl mill, or a wet jet mill is used. Can do.
When dispersing the pigment, it is particularly effective to add the specific heterocyclic compound (c).
Moreover, when adding a pigment, it is also possible to use a synergist according to various pigments as a dispersion aid if necessary. The dispersion aid is preferably added in an amount of 1 to 50 parts by mass with respect to 100 parts by mass of the pigment.

As a dispersion medium for various components such as a colorant in the ink composition, a solvent may be added, and a solvent-free low molecular weight component (a) a radical polymerizable monomer described later is used as a dispersion medium. Also good. Among these, the ink composition of the present invention is preferably a radiation curable ink. From this viewpoint, the ink composition is preferably solvent-free in order to be cured after being applied onto the recording medium. This is because if the solvent remains in the cured ink image, the solvent resistance is deteriorated or a VOC (Volatile Organic Compound) problem of the remaining solvent occurs. From this point of view, the following (a) radical polymerizable monomer is used as the dispersion medium, and in particular, the radical polymerizable monomer having the lowest viscosity is selected from the viewpoint of improving dispersibility and handling of the ink composition. To preferred.

The average particle diameter of the colorant used here is preferably about 0.01 to 0.4 μm and more preferably in the range of 0.02 to 0.2 μm because the finer the color, the better. (B) Selection of colorant, dispersant, dispersion medium, dispersion conditions, and filtration conditions are set so that the maximum particle size is 3 μm, preferably 1 μm. By controlling the particle size, clogging of the head nozzle can be suppressed, and ink storage stability, ink transparency, and curing sensitivity can be maintained. In the present invention, since the (c) specific heterocyclic compound having excellent dispersibility and stability is used, a uniform and stable dispersion can be obtained even when a fine particle colorant is used.
The particle size of the colorant in the ink composition can be measured by a known measurement method. Specifically, it can be measured by a centrifugal sedimentation light transmission method, an X-ray transmission method, a laser diffraction / scattering method, and a dynamic light scattering method. In the present invention, a value obtained by measurement using a laser diffraction / scattering method is employed.
The colorant is preferably added in an amount of 1 to 20% by mass in terms of solid content in the ink composition, and more preferably 2 to 10% by mass.

Described Ingredients of the ink composition of the present invention.
[(A) Radical polymerizable monomer ]
The ink composition of the present invention, Ru curable ink composition der containing (a) a radical polymerizable monomer. (A) used in the present invention the radical polymerizable monomer, occurred a polymerization reaction by the application of some type of energy is not particularly limited as long as it is a compound that cures, can be used regardless of the type of monomer over, in particular , (d) to occur polymerization reaction by an initiating species generated from a photoradical initiator, various known polymerizable monomers known as La radical polymerizable monomer is preferred. Cationic polymerizable monomers can also be used.
One or a plurality of radical polymerizable monomers can be used for the purpose of adjusting the reaction rate, ink physical properties, cured film physical properties, and the like. Further, the radical polymerizable monomer may be a monofunctional compound or a polyfunctional compound.

Cationically polymerizable monomers which can be Te present invention smell are use as heavy polymerizable compound, for example, epoxy compounds, JP-2001-31892, the 2001-40068 JP, same 2001-55507 JP, the 2001 -310938, 2001-310937, 2001-220526, etc., epoxy compounds, vinyl ether compounds, oxetane compounds, and the like.

Examples of the epoxy compound include aromatic epoxides and alicyclic epoxides.
Examples of monofunctional epoxy compounds that can be used in the present invention include, for example, phenyl glycidyl ether, p-tert-butylphenyl glycidyl ether, butyl glycidyl ether, 2-ethylhexyl glycidyl ether, allyl glycidyl ether, 1,2-butylene oxide, 1,3-butadiene monooxide, 1,2-epoxydodecane, epichlorohydrin, 1,2-epoxydecane, styrene oxide, cyclohexene oxide, 3-methacryloyloxymethylcyclohexene oxide, 3-acryloyloxymethylcyclohexene oxide, 3 -Vinylcyclohexene oxide etc. are mentioned.

Examples of polyfunctional epoxy compounds include, for example, bisphenol A diglycidyl ether, bisphenol F diglycidyl ether, bisphenol S diglycidyl ether, brominated bisphenol A diglycidyl ether, brominated bisphenol F diglycidyl ether, and brominated bisphenol. S diglycidyl ether, epoxy novolac resin, hydrogenated bisphenol A diglycidyl ether, hydrogenated bisphenol F diglycidyl ether, hydrogenated bisphenol S diglycidyl ether, 3,4-epoxycyclohexylmethyl-3 ′, 4′-epoxycyclohexanecarboxy 2- (3,4-epoxycyclohexyl-5,5-spiro-3,4-epoxy) cyclohexane-meta-dioxane, bis (3,4-epoxycyclo) Xylmethyl) adipate, vinylcyclohexene oxide, 4-vinylepoxycyclohexane, bis (3,4-epoxy-6-methylcyclohexylmethyl) adipate, 3,4-epoxy-6-methylcyclohexyl-3 ′, 4′-epoxy-6 '-Methylcyclohexanecarboxylate, methylenebis (3,4-epoxycyclohexane), dicyclopentadiene diepoxide, ethylene glycol di (3,4-epoxycyclohexylmethyl) ether, ethylenebis (3,4-epoxycyclohexanecarboxylate) , Epoxyhexahydrophthalate dioctyl, epoxyhexahydrophthalate di-2-ethylhexyl, 1,4-butanediol diglycidyl ether, 1,6-hexanediol diglycidyl ether Glycerin triglycidyl ether, trimethylolpropane triglycidyl ether, polyethylene glycol diglycidyl ether, polypropylene glycol diglycidyl ethers, 1,1,3-tetradecadiene dioxide, limonene dioxide, 1,2,7,8- Examples include diepoxyoctane and 1,2,5,6-diepoxycyclooctane.
Among these epoxy compounds, aromatic epoxides and alicyclic epoxides are preferable from the viewpoint of excellent curing speed, and alicyclic epoxides are particularly preferable.

  Examples of monofunctional vinyl ethers that can be used in the present invention include, for example, methyl vinyl ether, ethyl vinyl ether, propyl vinyl ether, n-butyl vinyl ether, t-butyl vinyl ether, 2-ethylhexyl vinyl ether, n-nonyl vinyl ether, lauryl vinyl ether, cyclohexyl vinyl ether, Cyclohexylmethyl vinyl ether, 4-methylcyclohexyl methyl vinyl ether, benzyl vinyl ether, dicyclopentenyl vinyl ether, 2-dicyclopentenoxyethyl vinyl ether, methoxyethyl vinyl ether, ethoxyethyl vinyl ether, butoxyethyl vinyl ether, methoxyethoxyethyl vinyl ether, ethoxyethoxyethyl vinyl ether Methoxypolyethylene Coal vinyl ether, tetrahydrofurfuryl vinyl ether, 2-hydroxyethyl vinyl ether, 2-hydroxypropyl vinyl ether, 4-hydroxybutyl vinyl ether, 4-hydroxymethylcyclohexyl methyl vinyl ether, diethylene glycol monovinyl ether, polyethylene glycol vinyl ether, chloroethyl vinyl ether, chlorobutyl vinyl ether, Examples include chloroethoxyethyl vinyl ether, phenylethyl vinyl ether, phenoxypolyethylene glycol vinyl ether, and the like.

Examples of the polyfunctional vinyl ether include, for example, ethylene glycol divinyl ether, diethylene glycol divinyl ether, polyethylene glycol divinyl ether, propylene glycol divinyl ether, butylene glycol divinyl ether, hexanediol divinyl ether, bisphenol A alkylene oxide divinyl ether, and bisphenol F. Divinyl ethers such as alkylene oxide divinyl ether; trimethylolethane trivinyl ether, trimethylolpropane trivinyl ether, ditrimethylolpropane tetravinyl ether, glycerin trivinyl ether, pentaerythritol tetravinyl ether, dipentaerythritol pentavinyl ether, dipentaerythritol Hexavinyl ether, ethylene oxide-added trimethylolpropane trivinyl ether, propylene oxide-added trimethylolpropane trivinyl ether, ethylene oxide-added ditrimethylolpropane tetravinyl ether, propylene oxide-added ditrimethylolpropane tetravinyl ether, ethylene oxide-added pentaerythritol tetravinyl ether, propylene oxide addition Examples thereof include polyfunctional vinyl ethers such as pentaerythritol tetravinyl ether, ethylene oxide-added dipentaerythritol hexavinyl ether, and propylene oxide-added dipentaerythritol hexavinyl ether.
As the vinyl ether compound, a di- or trivinyl ether compound is preferable from the viewpoints of curability, adhesion to a recording medium, surface hardness of the formed image, and the like, and a divinyl ether compound is particularly preferable.

The oxetane compound in the present invention refers to a compound having an oxetane ring, and a known oxetane compound is arbitrarily selected as described in JP-A Nos. 2001-220526, 2001-310937, and 2003-341217. Can be used.
The compound having an oxetane ring that can be used in the ink composition of the present invention is preferably a compound having 1 to 4 oxetane rings in the structure. By using such a compound, it becomes easy to maintain the viscosity of the ink composition in a good handling property range, and it is possible to obtain high adhesion of the cured ink to the recording medium. .

  Examples of the monofunctional oxetane used in the present invention include, for example, 3-ethyl-3-hydroxymethyloxetane, 3- (meth) allyloxymethyl-3-ethyloxetane, (3-ethyl-3-oxetanylmethoxy) methyl Benzene, 4-fluoro- [1- (3-ethyl-3-oxetanylmethoxy) methyl] benzene, 4-methoxy- [1- (3-ethyl-3-oxetanylmethoxy) methyl] benzene, [1- (3- Ethyl-3-oxetanylmethoxy) ethyl] phenyl ether, isobutoxymethyl (3-ethyl-3-oxetanylmethyl) ether, isobornyloxyethyl (3-ethyl-3-oxetanylmethyl) ether, isobornyl (3-ethyl- 3-Oxetanylmethyl) ether, 2-ethylhexyl (3-ethyl) 3-oxetanylmethyl) ether, ethyldiethylene glycol (3-ethyl-3-oxetanylmethyl) ether, dicyclopentadiene (3-ethyl-3-oxetanylmethyl) ether, dicyclopentenyloxyethyl (3-ethyl-3-oxetanylmethyl) ) Ether, dicyclopentenyl (3-ethyl-3-oxetanylmethyl) ether, tetrahydrofurfuryl (3-ethyl-3-oxetanylmethyl) ether, tetrabromophenyl (3-ethyl-3-oxetanylmethyl) ether, 2- Tetrabromophenoxyethyl (3-ethyl-3-oxetanylmethyl) ether, tribromophenyl (3-ethyl-3-oxetanylmethyl) ether, 2-tribromophenoxyethyl (3-ethyl-3-oxetanyl) Til) ether, 2-hydroxyethyl (3-ethyl-3-oxetanylmethyl) ether, 2-hydroxypropyl (3-ethyl-3-oxetanylmethyl) ether, butoxyethyl (3-ethyl-3-oxetanylmethyl) ether, Examples include pentachlorophenyl (3-ethyl-3-oxetanylmethyl) ether, pentabromophenyl (3-ethyl-3-oxetanylmethyl) ether, bornyl (3-ethyl-3-oxetanylmethyl) ether, and the like.

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

The compound having such an oxetane ring is described in detail in JP-A-2003-341217, paragraph numbers [0021] to [0084], and the compounds described herein can be suitably used in the present invention. .
Among the oxetane compounds used in the present invention, it is particularly preferable to use a compound having 1 to 2 oxetane rings from the viewpoint of viscosity and adhesiveness of the ink composition.

In the ink composition of the present invention, these cationically polymerizable monomers may be used alone or in combination of two or more, but from the viewpoint of effectively suppressing shrinkage during ink curing. Is preferably used in combination with at least one oxetane compound and at least one compound selected from an epoxy compound and a vinyl ether compound.

In the present invention, that use various types of known radically polymerizable monomers that cause a polymerization reaction by an initiating species generated from a photoradical initiator (a) as a radical polymerizable monomer.
Examples of the radical polymerizable monomer include (meth) acrylates, (meth) acrylamides, aromatic vinyls and the like. In the present specification, when referring to both or one of “acrylate” and “methacrylate”, when referring to both “(meth) acrylate” and “acryl” and / or “methacryl”, “(meth) acryl” And may be described respectively.

Examples of (meth) acrylates used in the present invention include the following.
Specific examples of monofunctional (meth) acrylates include hexyl group (meth) acrylate, 2-ethylhexyl (meth) acrylate, tert-octyl (meth) acrylate, isoamyl (meth) acrylate, decyl (meth) acrylate, isodecyl ( (Meth) acrylate, stearyl (meth) acrylate, isostearyl (meth) acrylate, cyclohexyl (meth) acrylate, 4-n-butylcyclohexyl (meth) acrylate, bornyl (meth) acrylate, isobornyl (meth) acrylate, benzyl (meth) Acrylate, 2-ethylhexylglycol (meth) acrylate, butoxyethyl (meth) acrylate, 2-chloroethyl (meth) acrylate, 4-bromobutyl (meth) acrylate, cyano Chill (meth) acrylate, benzyl (meth) acrylate, butoxymethyl (meth) acrylate, 3-methoxybutyl (meth) acrylate, alkoxymethyl (meth) acrylate, alkoxyethyl (meth) acrylate, 2- (2-methoxyethoxy) ethyl (Meth) acrylate, 2- (2-butoxyethoxy) ethyl (meth) acrylate, 2,2,2-tetrafluoroethyl (meth) acrylate, 1H, 1H, 2H, 2H perfluorodecyl (meth) acrylate, 4- Butylphenyl (meth) acrylate, phenyl (meth) acrylate, 2,4,5-tetramethylphenyl (meth) acrylate, 4-chlorophenyl (meth) acrylate, phenoxymethyl (meth) acrylate, phenoxyethyl (meth) acrylate Relate, glycidyl (meth) acrylate, glycidyloxybutyl (meth) acrylate, glycidyloxyethyl (meth) acrylate, glycidyloxypropyl (meth) acrylate, tetrahydrofurfuryl (meth) acrylate, hydroxyalkyl (meth) acrylate, 2-hydroxyethyl (meth) acrylate, 3-hydroxypropyl (meth) acrylate,

2-hydroxypropyl (meth) acrylate, 2-hydroxybutyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate, 3-hydroxypropyl (meth) acrylate, dimethylaminoethyl (meth) acrylate, diethylaminoethyl (meth) acrylate , Dimethylaminopropyl (meth) acrylate, diethylaminopropyl (meth) acrylate, trimethoxysilylpropyl (meth) acrylate, trimethylsilylpropyl (meth) acrylate, polyethylene oxide monomethyl ether (meth) acrylate, oligoethylene oxide monomethyl ether (meth) acrylate, Polyethylene oxide (meth) acrylate, oligoethylene oxide (meth) acrylate, oligoethyleneoxy Monoalkyl ether (meth) acrylate, polyethylene oxide monoalkyl ether (meth) acrylate, dipropylene glycol (meth) acrylate, polypropylene oxide monoalkyl ether (meth) acrylate, oligopropylene oxide monoalkyl ether (meth) acrylate, 2-methacrylate Leuoxytyl succinic acid, 2-methacryloyloxyhexahydrophthalic acid, 2-methacryloyloxyethyl-2-hydroxypropyl phthalate, butoxydiethylene glycol (meth) acrylate, trifluoroethyl (meth) acrylate, perfluorooctylethyl (meta ) Acrylate, 2-hydroxy-3-phenoxypropyl (meth) acrylate, EO-modified phenol (meth) acrylate, EO-modified Resole (meth) acrylate, EO-modified nonylphenol (meth) acrylate, PO-modified nonylphenol (meth) acrylate, EO-modified 2-ethylhexyl (meth) acrylate.

  Specific examples of the bifunctional (meth) acrylates include 1,6-hexanediol di (meth) acrylate, 1,10-decanediol di (meth) acrylate, neopentyl glycol di (meth) acrylate, 2,4- Dimethyl-1,5-pentanediol di (meth) acrylate, butylethylpropanediol (meth) acrylate, ethoxylated cyclohexanemethanol di (meth) acrylate, polyethylene glycol di (meth) acrylate, oligoethylene glycol di (meth) acrylate , Ethylene glycol di (meth) acrylate, 2-ethyl-2-butyl-butanediol di (meth) acrylate, hydroxypivalic acid neopentyl glycol di (meth) acrylate, EO-modified bisphenol A di (meth) acrylate Bisphenol F polyethoxydi (meth) acrylate, polypropylene glycol di (meth) acrylate, oligopropylene glycol di (meth) acrylate, 1,4-butanediol di (meth) acrylate, 2-ethyl-2-butylpropanediol di (Meth) acrylate, 1,9-nonane di (meth) acrylate, propoxylated ethoxylated bisphenol A di (meth) acrylate, tricyclodecane di (meth) acrylate and the like.

Specific examples of trifunctional (meth) acrylates include trimethylolpropane tri (meth) acrylate, trimethylolethane tri (meth) acrylate, trimethylolpropane alkylene oxide modified tri (meth) acrylate, pentaerythritol tri (meth) Acrylate, dipentaerythritol tri (meth) acrylate, trimethylolpropane tri ((meth) acryloyloxypropyl) ether, isocyanuric acid alkylene oxide modified tri (meth) acrylate, dipentaerythritol tri (meth) acrylate propionate, tri (( (Meth) acryloyloxyethyl) isocyanurate, hydroxypivalaldehyde-modified dimethylolpropane tri (meth) acrylate, sorbitol tri (meth) a Relate, propoxylated trimethylolpropane tri (meth) acrylate, and ethoxylated glycerin triacrylate.
Specific examples of tetrafunctional (meth) acrylates include pentaerythritol tetra (meth) acrylate, sorbitol tetra (meth) acrylate, ditrimethylolpropane tetra (meth) acrylate, dipentaerythritol tetra (meth) acrylate propionate, ethoxylation Examples include pentaerythritol tetra (meth) acrylate.
Specific examples of pentafunctional (meth) acrylates include sorbitol penta (meth) acrylate and dipentaerythritol penta (meth) acrylate.
Specific examples of hexafunctional (meth) acrylates include dipentaerythritol hexa (meth) acrylate, sorbitol hexa (meth) acrylate, phosphazene alkylene oxide modified hexa (meth) acrylate, captolactone modified dipentaerythritol hexa (meth) An acrylate etc. can be mentioned.

  Examples of (meth) acrylamides used in the present invention include (meth) acrylamide, N-methyl (meth) acrylamide, N-ethyl (meth) acrylamide, N-propyl (meth) acrylamide, Nn-butyl ( (Meth) acrylamide, Nt-butyl (meth) acrylamide, N-butoxymethyl (meth) acrylamide, N-isopropyl (meth) acrylamide, N-methylol (meth) acrylamide, N, N-dimethyl (meth) acrylamide, N , N-diethyl (meth) acrylamide, (meth) acryloylmorpholine.

  Specific examples of aromatic vinyls used in the present invention include styrene, methyl styrene, dimethyl styrene, trimethyl styrene, ethyl styrene, isopropyl styrene, chloromethyl styrene, methoxy styrene, acetoxy styrene, chloro styrene, dichloro styrene, bromo. Styrene, vinyl benzoic acid methyl ester, 3-methylstyrene, 4-methylstyrene, 3-ethylstyrene, 4-ethylstyrene, 3-propylstyrene, 4-propylstyrene, 3-butylstyrene, 4-butylstyrene, 3- Hexyl styrene, 4-hexyl styrene, 3-octyl styrene, 4-octyl styrene, 3- (2-ethylhexyl) styrene, 4- (2-ethylhexyl) styrene, allyl styrene, isopropenyl styrene, butenyls Ren, octenyl styrene, 4-t-butoxycarbonyl styrene, 4-methoxystyrene, and a 4-t-butoxystyrene.

  Furthermore, as the radical polymerizable monomer in the present invention, vinyl esters [vinyl acetate, vinyl propionate, vinyl versatate, etc.], allyl esters [eg, allyl acetate], halogen-containing monomers [vinylidene chloride, vinyl chloride, etc.], Vinyl ether [methyl vinyl ether, butyl vinyl ether, hexyl vinyl ether, methoxy vinyl ether, 2-ethylhexyl vinyl ether, methoxyethyl vinyl ether, cyclohexyl vinyl ether, chloroethyl vinyl ether, etc.], vinyl cyanide [(meth) acrylonitrile, etc.], olefins [ethylene, propylene, etc. ] Etc. are mentioned.

Among these, as the radical polymerizable monomer in the present invention, (meth) acrylates and (meth) acrylamides are preferable from the viewpoint of curing speed, and tetrafunctional or higher (meth) acrylates are particularly preferable from the viewpoint of curing speed. . Further, from the viewpoint of the viscosity of the ink composition, it is preferable to use the above polyfunctional (meth) acrylates in combination with monofunctional or bifunctional (meth) acrylates and (meth) acrylamides.
The content of the (a) radical polymerizable monomer in the ink composition is suitably 50 to 95% by mass, preferably 60 to 92% by mass, more preferably 70 to 90% by mass, based on the total solid content of the composition. Range.

[(D) Photoradical initiator]
The ink composition of the invention contains a light the radical Le opening initiator as a polymerization initiator.
Photoradical initiator in the present invention the action of light, or, through interaction with an electronic excited state of the sensitizing dye, cause chemical changes, Ru compound der for generating the radical Le.
Photoradical initiators, actinic rays to be irradiated, for example, ultraviolet rays of 400 to 200 nm, far ultraviolet rays, g-line, h-line, i-line, KrF excimer laser light, ArF excimer laser light, electron beams, X-rays, molecular beam Or what has a sensitivity to an ion beam etc. can be selected suitably, and can be used.

Specific Polymerization initiators can be used without limitation known to those skilled in the art, specifically, for example, Bruce M. Monroe et al., Chemical Review, 93, 435 (1993). R. S. By Davidson, Journal of Photochemistry and biologic A: Chemistry, 73.81 (1993). J. P. Faussier “Photoinitiated Polymerization—Theory and Applications”: Rapra Review vol. 9, Report, Rapra Technology (1998). M. Tsunooka et al. , Prog. Polym. Sci. , 21, 1 (1996). Many are described. There are many chemical amplification type photoresists and compounds used for photocationic polymerization described in (Organic Electronics Materials Research Group, “Organic Materials for Imaging”, Bunshin Publishing (1993), pages 187-192). Has been. Further, F.I. D. Saeva, Topics in Current Chemistry, 156, 59 (1990). G. G. Maslak, Topics in Current Chemistry, 168, 1 (1993). H., et al. B. Shuster et al, JACS, 112, 6329 (1990). I. D. F. Eaton et al, JACS, 102, 3298 (1980). A group of compounds that undergo oxidative or reductive bond cleavage through interaction with the electronically excited state of a sensitizing dye as described in the above.

  Preferred photopolymerization initiators include (a) aromatic ketones, (b) aromatic onium salt compounds, (c) organic peroxides, (d) hexaarylbiimidazole compounds, (e) ketoxime ester compounds, f) borate compounds, (g) azinium compounds, (h) metallocene compounds, (i) active ester compounds, (j) compounds having a carbon halogen bond, and the like.

  (A) As a preferable example of aromatic ketones, “RADIATION CURING IN POLYMER SCIENCE AND TECHNOLOGY” P. FOUASSIER J.M. F. Examples include compounds having a benzophenone skeleton or a thioxanthone skeleton described in RABEK (1993), p77-117. More preferable examples of (a) aromatic ketones include α-thiobenzophenone compounds described in JP-B-47-6416, benzoin ether compounds described in JP-B-47-3981, and JP-B-47-22326. Α-substituted benzoin compounds, benzoin derivatives described in JP-B-47-23664, aroylphosphonic acid esters described in JP-A-57-30704, dialkoxybenzophenones described in JP-B-60-26483, Benzoin ethers described in JP-A-60-26403, JP-A-62-81345, JP-B-1-34242, US Pat. No. 4,318,791, and α-aminobenzophenones described in European Patent 0284561A1, P-di (dimethyla) described in JP-A-2-211452 Nobenzoyl) benzene, thio-substituted aromatic ketone described in JP-A-61-194062, acylphosphine sulfide described in JP-B-2-9597, acylphosphine described in JP-B-2-9596, JP-B-63- Examples thereof include thioxanthones described in Japanese Patent No. 61950, and coumarins described in Japanese Patent Publication No. 59-42864.

  (B) Aromatic onium salts include Group V, VI and VII elements of the Periodic Table, specifically N, P, As, Sb, Bi, O, S, Se, Te, or I fragrances Group onium salts are included. For example, iodonium salts described in European Patent No. 104143, US Pat. No. 4,837,124, Japanese Patent Laid-Open No. 2-150848, Japanese Patent Laid-Open No. 2-96514, European Patent Nos. 370693, 233567, and 297443 are disclosed. , 294442, 279210, and 422570, U.S. Pat. Nos. 3,902,144, 4,933,377, 4,760013, 4,734,444, and 2,833,827, sulfonium salts and diazonium salts (Such as benzenediazonium which may have a substituent), diazonium salt resins (formaldehyde resin of diazodiphenylamine, etc.), N-alkoxypyridinium salts, etc. (for example, US Pat. No. 4,743,528, JP 63-1383 No. 5, JP-A-63-142345, JP-A-63-142346, and JP-B-46-42363, specifically 1-methoxy-4-phenylpyridinium tetrafluoro And the compounds described in JP-B Nos. 52-147277, 52-14278, and 52-14279 are preferably used. Generates radicals and acids as active species.

  (C) “Organic peroxide” includes almost all organic compounds having one or more oxygen-oxygen bonds in the molecule. Examples thereof include 3,3 ′, 4,4′-tetra- (T-butylperoxycarbonyl) benzophenone, 3,3 ′, 4,4′-tetra- (t-amylperoxycarbonyl) benzophenone, 3,3′4,4′-tetra- (t-hexylperoxycarbonyl) ) Benzophenone, 3,3 ′, 4,4′-tetra- (t-octylperoxycarbonyl) benzophenone, 3,3 ′, 4,4′-tetra- (cumylperoxycarbonyl) benzophenone, 3,3 ′, Peroxyesters such as 4,4′-tetra- (p-isopropylcumylperoxycarbonyl) benzophenone and di-t-butyldiperoxyisophthalate are preferred. Arbitrariness.

  (D) Examples of hexaarylbiimidazoles include lophine dimers described in JP-B Nos. 45-37377 and 44-86516, such as 2,2′-bis (o-chlorophenyl) -4,4 ′, 5. , 5′-tetraphenylbiimidazole, 2,2′-bis (o-bromophenyl) -4,4 ′, 5,5′-tetraphenylbiimidazole, 2,2′-bis (o, p-dichlorophenyl) -4,4 ', 5,5'-tetraphenylbiimidazole, 2,2'-bis (o-chlorophenyl) -4,4', 5,5'-tetra (m-methoxyphenyl) biimidazole, 2, 2′-bis (o, o′-dichlorophenyl) -4,4 ′, 5,5′-tetraphenylbiimidazole, 2,2′-bis (o-nitrophenyl) -4,4 ′, 5,5 ′ -Tet Phenylbiimidazole, 2,2′-bis (o-methylphenyl) -4,4 ′, 5,5′-tetraphenylbiimidazole, 2,2′-bis (o-trifluorophenyl) -4,4 ′ , 5,5′-tetraphenylbiimidazole and the like.

  (E) As ketoxime esters, 3-benzoyloxyiminobutan-2-one, 3-acetoxyiminobutan-2-one, 3-propionyloxyiminobutan-2-one, 2-acetoxyiminopentane-3-one 2-acetoxyimino-1-phenylpropan-1-one, 2-benzoyloxyimino-1-phenylpropan-1-one, 3-p-toluenesulfonyloxyiminobutan-2-one, 2-ethoxycarbonyloxy Examples include imino-1-phenylpropan-1-one.

Examples of the (f) borate salt which is another example of the photopolymerization initiator in the present invention include U.S. Pat. Nos. 3,567,453 and 4,343,891, European Patents 109,772 and 109,773. The compounds described in No. are listed.
Examples of (g) azinium salt compounds which are other examples of photopolymerization initiators include JP-A Nos. 63-138345, 63-142345, 63-142346, and 63-63. No. 143537 and Japanese Examined Patent Publication No. 46-42363.

Examples of (h) metallocene compounds which are other examples of photopolymerization initiators include JP 59-152396, JP 61-151197, JP 63-41484, and JP 2-249. And titanocene compounds described in JP-A-2-4705 and iron-arene complexes described in JP-A-1-304453 and JP-A-1-152109.
Specific examples of the titanocene compound include di-cyclopentadienyl-Ti-di-chloride, di-cyclopentadienyl-Ti-bis-phenyl, and di-cyclopentadienyl-Ti-bis-2,3. 4,5,6-pentafluorophen-1-yl, di-cyclopentadienyl-Ti-bis-2,3,5,6-tetrafluorophen-1-yl, di-cyclopentadienyl-Ti- Bis-2,4,6-trifluorophen-1-yl, di-cyclopentadienyl-Ti-2,6-difluorophen-1-yl, di-cyclopentadienyl-Ti-bis-2,4 -Difluorophen-1-yl, di-methylcyclopentadienyl-Ti-bis-2,3,4,5,6-pentafluorophen-1-yl, di-methylcyclopentadienyl-Ti- -2,3,5,6-tetrafluorophen-1-yl, di-methylcyclopentadienyl-Ti-bis-2,4-difluorophen-1-yl, bis (cyclopentadienyl) -bis (2,6-difluoro-3- (pyridin-1-yl) phenyl) titanium, bis (cyclopentadienyl) bis [2,6-difluoro-3- (methylsulfonamido) phenyl] titanium, bis (cyclopenta And dienyl) bis [2,6-difluoro-3- (N-butylbialoyl-amino) phenyl] titanium.

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

  (J) Preferred examples of the compound having a carbon halogen bond include those described in Wakabayashi et al., Bull. Chem. Soc. Examples include compounds described in Japan, 42, 2924 (1969), compounds described in British Patent 1388492, compounds described in JP-A-53-133428, compounds described in German Patent 3333724, and the like. .

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

  Preferable specific examples of the compounds represented by the above (a) to (j) include those shown below.

(D) A radical photoinitiator can be used individually by 1 type or in combination of 2 or more types.
The content of the (d) photo radical initiator in the ink composition is preferably 0.1 to 20% by mass, more preferably 0.5 to 10% by mass, and still more preferably in terms of the total solid content of the ink composition. Is 1-7 mass%.

[Sensitizing dye]
In the present invention, a sensitizing dye may be added for the purpose of improving the sensitivity of the photo radical initiator. Examples of preferred sensitizing dyes include those belonging to the following compounds and having an absorption wavelength in the 350 nm to 450 nm region.
Polynuclear aromatics (eg, pyrene, perylene, triphenylene), xanthenes (eg, fluorescein, eosin, erythrosine, rhodamine B, rose bengal), cyanines (eg, thiacarbocyanine, oxacarbocyanine), merocyanines ( For example, merocyanine, carbomerocyanine), thiazines (for example, thionine, methylene blue, toluidine blue), acridines (for example, acridine orange, chloroflavin, acriflavine), anthraquinones (for example, anthraquinone), squalium (for example, squalium) ), Coumarins (eg 7-diethylamino-4-methylcoumarin).

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

In formula (IX), A ¹ represents a sulfur atom or NR ⁵⁰ , R ⁵⁰ represents an alkyl group or an aryl group, and L ² forms a basic nucleus of the dye together with the adjacent A ¹ and the adjacent carbon atom. R ⁵¹ and R ⁵² each independently represent a hydrogen atom or a monovalent nonmetallic atomic group, and R ⁵¹ and R ⁵² may be bonded to each other to form an acidic nucleus of the dye. Good. W represents an oxygen atom or a sulfur atom.
In formula (X), Ar ¹ and Ar ² each independently represent an aryl group and are linked via a bond with —L ³ —. Here, L ³ represents —O— or —S—. W is synonymous with that shown in the general formula (IX).
In the formula (XI), A ² represents a sulfur atom or NR ⁵⁹ , L ⁴ represents a nonmetallic atomic group that forms a basic nucleus of the dye together with the adjacent A ² and carbon atom, R ⁵³ , R ⁵⁴ , R ⁵⁵ , R ⁵⁶ , R ⁵⁷ and R ⁵⁸ each independently represents a monovalent nonmetallic atomic group, and R ⁵⁹ represents an alkyl group or an aryl group.

In formula (XII), A ³ and A ⁴ each independently represent —S— or —NR ⁶² — or —NR ⁶³ —, wherein R ⁶² and R ⁶³ each independently represent a substituted or unsubstituted alkyl group, substituted or Represents an unsubstituted aryl group, and L ⁵ and L ⁶ each independently represent a nonmetallic atomic group that forms a basic nucleus of a dye in combination with adjacent A ³ , A ^4, and adjacent carbon atoms; R ⁶⁰ and R ⁶¹ are each independently a hydrogen atom or a monovalent nonmetallic atomic group, or can be bonded to each other to form an aliphatic or aromatic ring.
In formula (XIII), R ⁶⁶ represents an aromatic ring or a hetero ring which may have a substituent, and A ⁵ represents an oxygen atom, a sulfur atom or —NR ⁶⁷ —. R ⁶⁴ , R ⁶⁵ and R ⁶⁷ each independently represent a hydrogen atom or a monovalent nonmetallic atomic group, and R ⁶⁷ and R ⁶⁴ , and R ⁶⁵ and R ⁶⁷ each represent an aliphatic or aromatic ring. Can be combined to form.

  Preferred specific examples of the compounds represented by the general formulas (IX) to (XIII) include the exemplified compounds (A-1) to (A-20) shown below.

[Co-sensitizer]
Further, the ink composition of the present invention may contain a known compound having a function of further improving sensitivity or suppressing polymerization inhibition by oxygen as a co-sensitizer.
Examples of such cosensitizers include amines such as M.I. R. Sander et al., “Journal of Polymer Society”, Vol. 10, 3173 (1972), Japanese Patent Publication No. 44-20189, Japanese Patent Publication No. 51-82102, Japanese Patent Publication No. 52-134692, Japanese Patent Publication No. 59-138205. No. 60-84305, JP-A 62-18537, JP-A 64-33104, Research Disclosure 33825, and the like. Specific examples include triethanolamine. P-dimethylaminobenzoic acid ethyl ester, p-formyldimethylaniline, p-methylthiodimethylaniline and the like.

Other examples include thiols and sulfides, for example, thiol compounds described in JP-A-53-702, JP-B-55-500806, JP-A-5-142772, and JP-A-56-75643. Examples thereof include disulfide compounds, and specific examples include 2-mercaptobenzothiazole, 2-mercaptobenzoxazole, 2-mercaptobenzimidazole, 2-mercapto-4 (3H) -quinazoline, β-mercaptonaphthalene and the like.
Other examples include amino acid compounds (eg, N-phenylglycine), organometallic compounds described in Japanese Patent Publication No. 48-42965 (eg, tributyltin acetate), and hydrogen described in Japanese Patent Publication No. 55-34414. Donors, sulfur compounds described in JP-A-6-308727 (eg, trithiane), phosphorus compounds described in JP-A-6-250387 (diethylphosphite, etc.), Si-- described in JP-A-8-65779 H, Ge-H compound, etc. are mentioned.

The ink composition of the present invention includes the essential components (b) and (c), the components (a) and (d) which are preferable optional components, and sensitizing dyes and co-intensifiers used together with these components. In addition to the sensitizer, various additives can be used in combination depending on the purpose. For example, an ultraviolet absorber can be used from the viewpoint of improving the weather resistance of the obtained image and preventing discoloration. In addition, an antioxidant can be added to improve the stability of the ink composition.
The ink composition of the present invention further includes various organic and metal complex anti-fading agents, and conductive materials such as potassium thiocyanate, lithium nitrate, ammonium thiocyanate, dimethylamine hydrochloride for the purpose of controlling ejection properties. In order to improve the adhesion to the volatile salts and the recording medium, a trace amount of organic solvent can be added.

Various polymer compounds can be added to the ink composition in order to adjust film properties. High molecular compounds include acrylic polymers, polyvinyl butyral resins, polyurethane resins, polyamide resins, polyester resins, epoxy resins, phenol resins, polycarbonate resins, polyvinyl butyral resins, polyvinyl formal resins, shellacs, vinyl resins, acrylic resins. Rubber resins, waxes and other natural resins can be used. Two or more of these may be used in combination.
In addition, nonionic surfactants, cationic surfactants, organic fluoro compounds, and the like can be added to adjust liquid properties. In addition, for example, leveling additives, matting agents, In order to improve the adhesion to the recording medium such as waxes for adjusting film physical properties, polyolefin, PET, etc., a tackifier that does not inhibit the polymerization can be contained.

The ink composition of the present invention preferably has an ink viscosity of 30 mPa · s or less, more preferably 5 to 20 mPa · s at the temperature at the time of ejection in consideration of ejection properties, so that it falls within the above range. It is preferable to adjust the composition ratio as appropriate. The temperature at the time of injection is generally 25 to 90 ° C, preferably 25 to 80 ° C, and particularly preferably 40 to 80 ° C.
The ink viscosity at 25 to 30 ° C. is 200 mPa · s or less, preferably 7 to 100 mPa · s. By setting the viscosity at room temperature high, even when a porous recording medium is used, ink penetration into the recording medium can be prevented, uncured monomer can be reduced, and odor can be reduced. Dot bleeding at the time of landing can be suppressed, and as a result, the image quality is improved. When the ink viscosity at 25 to 30 ° C. is larger than 200 mPa · s, a problem occurs in the delivery of the ink liquid.

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

The ink composition of the present invention thus adjusted is suitably used as an ink for inkjet recording. That is, it is used in an image forming method in which an image is recorded on an ink jet recording medium by ejecting the ink composition of the present invention, and thereafter, the recorded image is cured by irradiation with active energy rays.
In the printed matter obtained by the ink composition of the present invention, the image portion is cured by irradiation with active energy rays such as ultraviolet rays, and the strength of the image portion is excellent. It can be used for various purposes such as forming an ink receiving layer (image portion).
The irradiation dose of active energy is preferably ²⁰ to 2000 mJ / cm ² .

[Inkjet recording method and inkjet recording apparatus]
Next, an ink jet recording method and an ink jet recording apparatus that can be suitably employed in the image forming method of the present invention will be described below.

  In the ink jet recording method, it is preferable that the ink composition is heated to 40 to 80 ° C. to lower the viscosity of the ink composition to 30 mPa · s or less, and then ejected. By using this method, high ejection stability is achieved. Can be realized. In general, an active energy ray-curable ink composition generally has a higher viscosity than an aqueous ink, and thus has a large viscosity fluctuation range due to temperature fluctuations during printing. This viscosity variation of the ink composition directly affects the droplet size and droplet ejection speed as it is, which causes image quality deterioration. Therefore, it is necessary to keep the ink composition temperature as constant as possible during printing. is there. The control range of the ink composition temperature is preferably set temperature ± 5 ° C., more preferably set temperature ± 2 ° C., and further preferably set temperature ± 1 ° C.

  One feature of the ink jet recording apparatus is that it includes a means for stabilizing the temperature of the ink composition, and the portion to be kept at a constant temperature is a piping system from an ink tank (an intermediate tank if there is an intermediate tank) to the nozzle ejection surface. All of the members are targeted.

  The temperature control method is not particularly limited, but for example, it is preferable to provide a plurality of temperature sensors in each piping portion and perform heating control according to the ink composition flow rate and the environmental temperature. 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.

By adding a photopolymerization initiator as the (d) polymerization initiator to the ink composition of the present invention, an active energy ray-curable ink composition is obtained.
The irradiation conditions of active energy rays in such an ink composition will be described. A basic irradiation method is disclosed in JP-A-60-132767. Specifically, a light source is provided on both sides of the head unit, and the head and the light source are scanned by a shuttle method. Irradiation is performed after a certain period of time after ink landing. Further, the curing is completed by another light source that is not driven. In WO99 / 54415, as an irradiation method, a method using an optical fiber or a method in which a collimated light source is applied to a mirror surface provided on the side surface of the head unit to irradiate the recording unit with UV light is disclosed. In the present invention, these irradiation methods can be used.

  In the present invention, the ink composition is heated to a constant temperature, and the time from landing to irradiation is desirably 0.01 to 0.5 seconds, preferably 0.01 to 0.3 seconds, and more preferably Preferably, the active energy ray is irradiated after 0.01 to 0.15 seconds. Thus, by controlling the time from landing to irradiation to an extremely short time, it is possible to prevent the landing ink from bleeding before being cured. Also, since the ink composition can be exposed to a porous recording medium before it penetrates deeper than the light source reaches, unreacted monomer remains, and as a result, odor can be reduced. Can do. By using the inkjet recording method described above and the ink composition of the present invention in combination, a great synergistic effect is brought about. In particular, when an ink composition having an ink viscosity of 200 mPa · s or less at 25 ° C. is used, a great effect can be obtained. By adopting such a recording method, 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. When inks with low lightness are stacked, it is difficult for the irradiation rays to reach the lower ink, and inhibition of curing sensitivity, increase of residual monomers, generation of odor, and deterioration of adhesion tend to occur. Irradiation can be performed by injecting all colors and exposing them together, but exposure for each color is preferable from the viewpoint of curing acceleration.

There is no restriction | limiting in particular as an inkjet recording device used for this invention, A commercially available inkjet recording device can be used. That is, in the present invention, recording can be performed on a recording medium using a commercially available inkjet recording apparatus.
According to the preferable ejection conditions, the ink composition of the present invention repeats heating and cooling, but even when stored under such temperature conditions due to the function of the (c) specific heterocyclic compound. Further, the colorant dispersibility is suppressed from being lowered, and excellent color developability can be obtained over a long period of time. Further, there is an advantage that a drop in dischargeability due to aggregation of the colorant is also suppressed.

[Recording medium]
The recording medium to which the ink composition of the present invention can be applied is not particularly limited, and various non-absorbing resin materials used for ordinary non-coated paper, coated paper, and so on, so-called soft packaging, or the like. A resin film formed into a film can be used, and examples of the various plastic films include PET film, OPS film, OPP film, ONy film, PVC film, PE film, and TAC film. In addition, examples of the plastic that can be used as a recording medium material include polycarbonate, acrylic resin, ABS, polyacetal, PVA, and rubbers. Metals and glasses can also be used as the recording medium.

  The printed matter of the present invention can be obtained by printing the ink composition of the present invention on a recording medium using an ink jet printer, and then preferably irradiating the cured ink composition with an active energy ray and curing. . The printed matter of the present invention has a high-quality image with excellent color development and sharpness because the ink used for image formation contains fine colorant particles uniformly and stably dispersed, and the weather resistance of the image Because of its excellent properties, it can be applied to a wide range of fields.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples, but the present invention is not limited to the embodiments in these examples. Unless otherwise indicated, parts and% represent parts by mass and% by mass.

[Synthesis Example 1]
[(C) Synthesis of specific heterocyclic compound]
(Synthesis of Exemplified Compound H-13)
9.95 parts of 9 (10H) -acridone and 1.12 parts of potassium t-butoxy are dissolved in 20 parts of dimethyl sulfoxide and heated to 100 ° C. To this is added dropwise 6.8 parts of butoxytetraethylene glycol glycidyl ether, and the mixture is further heated and stirred at 100 ° C. for 4 hours. The reaction solution was extracted with ethyl acetate, washed with water, and concentrated and dried to obtain 6.2 parts of oily exemplified compound H-13. The number average molecular weight was 501.

[Synthesis Example 2]
(Synthesis of Exemplified Compound H-15)
Except for changing 6.8 parts of butoxytetraethylene glycol glycidyl ether of Synthesis Example 1 to 13.0 parts of butyl glycidyl ether, 14.2 parts of an oily substance of Exemplified Compound H-15 was obtained in the same manner as Synthesis Example 1. . The number average molecular weight was 1500.

[Synthesis Example 3]
(Synthesis of Exemplified Compound H-21)
In the same manner as in Synthesis Example 1 except that 1.95 parts of 9 (10H) -acridone in Synthesis Example 1 was changed to 1.70 parts of dimethylquinacridone (PR122), 1.7 parts of a colored solid of Example Compound H-21 were added. Obtained. The number average molecular weight was 2800.

[Example 1]
(C) A specific heterocyclic compound shown below is dissolved in (a) a radical polymerizable monomer , and (b) is put into a motor mill M50 (manufactured by Eiger) together with a pigment, and zirconia beads having a diameter of 0.65 mm are used. Dispersion was carried out at a speed of 9 m / s for 6 hours to obtain an active energy ray-curable ink stock solution. Next, (d) a polymerization initiator was added to the ink stock solution and mixed gently, and then pressure filtered with a membrane filter to obtain the active energy ray-curable inkjet ink of Example 1.

(B) Pigment [quinacridone pigment PR122] 5.0 parts (c) Specific heterocyclic compound [Exemplary compound H-13] 1.5 parts (a) Radical polymerizable monomer [hexanediol diacrylate]
(HDDA: manufactured by Daicel UCB Corporation) 60.0 parts (a) radical polymerizable monomer [captolactone-modified dipentaerythritol hexaacrylate]
(DPCA-60: Nippon Kayaku Co., Ltd.) 27.5 parts (d) Polymerization initiator [acylphosphine oxide compound (Lucirin TPO-L: manufactured by BASF) 5.0 parts

[Examples 2-3]
Except that (c) the specific heterocyclic compound H-13 used in Example 1 was changed to H-15 and H-21 obtained in Synthesis Examples 2-3, respectively, the same procedure as in Example 1 was carried out. A few active energy ray-curable inkjet inks were obtained.

[Comparative Example 1]
Except that (c) the specific heterocyclic compound H-13 used in Example 1 was used, a commercially available pigment dispersant “SORPERSE 24000GR” (manufactured by Nihon Librizol Co., Ltd.) was used. Thus, the active energy ray-curable inkjet ink of Comparative Example 1 was obtained.

[Comparative Example 2]
Except for using (C) specific heterocyclic compound H-13 used in Example 1 and using “SORPERSE 32000” (manufactured by Nihon Librizol Co., Ltd.), a commercially available pigment dispersant, everything is the same as Example 1. Thus, an active energy ray-curable inkjet ink of Comparative Example 2 was obtained.

[Ratio Comparative Examples 3-4]
In Comparative Examples 1-2 to obtain (a) a radical polymerizable monomer and (d) except for changing the polymerization initiator in the following, all in the same way the ratio inkjet ink Comparative Examples 3-4.

(A) Cationic polymerizable monomer : Oxetane compound (OXT-221: manufactured by Toagosei Co., Ltd.) 70.0 parts (a) Cationic polymerizable monomer : Epoxy compound (Celoxide 3000: manufactured by Daicel Chemical Industries, Ltd.) 17.5 Part (d) Polymerization initiator: Triphenylsulfonium salt (UVI-6992, manufactured by Dow Chemical Company) 5.0 parts

[Evaluation of ink composition]
The obtained inkjet ink was evaluated according to the following method. The results are shown in Table 1.

(1. Stability)
Each inkjet ink was evaluated by visual observation and viscosity change after storage at 25 ° C. for 1 month and after storage at 70 ° C. for 24 hours.
◎ is a level where there is no problem, ○ is a level where there is no problem in ejection performance, △ is a level where the ejection performance is lowered and becomes a problem in practice, and X is a level where ejection performance is impossible and a problem in practice.
◎: Precipitation does not occur, viscosity does not increase ○: Precipitation does not occur, viscosity increases slightly Δ: Precipitation does not occur, but viscosity increases ×: Precipitation occurs

(2. Average particle size)
About each inkjet ink, the volume reference average particle diameter D50 was measured and evaluated using the light-scattering diffraction type particle size distribution measuring apparatus (LA910, Horiba, Ltd. make). A is a level where there is no problem, B is a level where there is no problem in practice, and C is a level where there is a problem in practice.
A: D50 is less than 100 nm B: D50 is 100 nm or more, less than 200 nm C: D50 is 200 nm or more

(3. Curability)
The obtained ink composition was printed on art paper with an ink jet printer (printing density 300 dpi, droplet ejection frequency 4 kHz, nozzle number 64), and then an energy of 100 mJ / cm ^{2 with} a Deep UV lamp (US-7, SP-7). The sample was exposed under the following conditions to obtain a print sample. The cured film was touched with a finger, and the presence or absence of stickiness was evaluated according to the following criteria. A is a problem-free level, B is a practically problematic level, and C is a practically problematic level.
A: No stickiness B: Slightly sticky C: Extremely sticky

(4. Heat cycle property)
The obtained ink composition was subjected to a temperature increase / decrease cycle of 25 ° C. to 60 ° C. 10 times, then printed with the ink jet printer, observed for the absence of nozzles, and evaluated according to the following criteria. ○ is a level where there is no problem, Δ is a level where there is a problem in practical use, and × is a level where there is a problem in practical use.
○: High quality image formed with no missing nozzles Δ: Some satellites were observed and image defects were observed x: Nozzle missing occurred and image defects were significant

From Table 1, the ink composition of the present invention can be cured with high sensitivity to radiation irradiation, can form a high-quality image without stickiness, and is subjected to long-term storage and repeated temperature changes. In the case of storage at 1, the viscosity did not increase due to a decrease in the dispersibility of the pigment, and both the dispersibility and the dispersion stability of the pigment were good.
On the other hand, in the comparative example using a commercially available polymer dispersant, the initial pigment dispersibility is good, but in particular, storage under a high temperature condition and heat cycle property due to repeated heating are inferior, which causes a practical problem. It was a level.

Claims (9)

An ink composition comprising at least (a) a radical polymerizable monomer, (b) a pigment , (c) a compound represented by the following general formula (1), and (d) a photoradical initiator . .

[In formula (1), R represents an alkyl group, an acyl group, a carbamoyl group, an alkoxycarbonyl group, an aryl group, a sulfonyl group, or a sulfamoyl group. X is A alkylene group, -O -, - S -, - NR 1 -, or -C (= O) - is any one selected from, R ¹ represents a hydrogen atom or an alkyl group. Ring A and ring B each independently represent a ring, and at least one of them is an aromatic ring. ] 2. The ink composition according to claim 1, wherein the content of the compound represented by (c) the general formula (1) with respect to the ink composition is 2 to 80% by mass. The ink composition according to claim 1 or 2, wherein the radical polymerizable monomer is (meth) acrylates or (meth) acrylamides. The ink composition according to any one of claims 1 to 3, wherein the number average molecular weight of the compound represented by the general formula (1) is 300 or more. The ink composition according to claim 1, wherein the (a) radical polymerizable monomer has a tetrafunctional or higher functional (meth) acrylate. The ink composition according to any one of claims 1 to 5, characterized in that is used for inkjet. It includes a step of printing the ink composition according to any one of claims 1 to 6 on a recording medium, and a step of irradiating the printed ink composition with an active energy ray to cure the ink composition. Image forming method. A printed matter obtained by curing the ink composition according to any one of claims 1 to 6 . The printed matter according to claim 8 , wherein the ink composition is printed on the recording medium with an ink jet printer, and then the active energy ray is irradiated to cure the ink composition.