JP6269748B2 - Photocurable ink composition for ink jet recording and ink jet recording method using the same - Google Patents

Description

  The present invention relates to a photocurable ink composition for ink jet recording and an ink jet recording method using the same.

  Conventionally, color images formed by an ink jet method or the like have excellent reproducibility of high-quality color images, optical properties such as hue, transparency, coloring power, weather resistance, heat resistance, Durability such as solvent resistance is required. It is also required to be safe. Therefore, as a coloring material used in a composition for forming a color image, a pigment is often preferable to a dye from the viewpoint of durability.

  Color index (hereinafter abbreviated as “CI”) pigment yellow (hereinafter also referred to as “PY”) 74, 128 as a pigment for yellow among the basic colors (yellow, magenta, cyan) of colors. Etc. are widely used. However, these yellow pigments have room for improvement because they are inferior in the weather resistance of yellow.

  Therefore, many compositions for forming a yellow image, particularly inks, having sufficient properties as described above have been proposed.

  For example, Patent Document 1 discloses a Pigment Yellow 155 dispersion, an alicyclic epoxy compound, an epoxy compound, an oxetane compound, a cationic polymerizable compound represented as exemplary compound 1-H, and a surfactant. Ink composition comprising a photoacid generator and an anthracene derivative, and a dispersion of Pigment Yellow 213, an alicyclic epoxy compound, an epoxy compound, an oxetane compound, and an exemplary compound 1-G An ink composition comprising a cationically polymerizable compound, a surfactant, a photoacid generator, and an anthracene derivative is disclosed (Ink Nos. Y-6 and Y-7 in Table 2 of Patent Document 1). ).

  For example, Patent Document 2 includes (1) C.I. I. Pigment yellow 213, (2) C.I. I. Pigment yellow 213 and C.I. I. Pigment yellow 110, or (3) C.I. I. Pigment yellow 213 and C.I. I. Disclosed is an oil-based ink composition for ink jet recording comprising any one of Pigment Yellow 139 pigment dispersion, diethylene glycol diethyl ether, tetraethylene glycol dimethyl ether, γ-butyrolactone, and an acrylic resin as a binder resin. (Examples 1 to 3 of [0042] to [0045] of Patent Document 2).

  For example, Patent Document 3 discloses C.I. I. Disclosed is a yellow curable ink containing 3% by weight PY150, 60.35% by weight 2- (vinyloxyethoxy) ethyl acrylate (VEEA), and 2.5% by weight polymerization initiator. (Patent Document 3, [0405] to [0409]).

  For example, Patent Document 4 discloses 74.8% by weight of 2- (vinyloxyethoxy) ethyl acrylate, 10% by weight of a hyperbranched polymer, 8% by weight of a polymerization initiator, and a dispersion 7 of Pigment Yellow-155. A photocurable ink composition comprising 2 wt% is disclosed (Example 4 in Table 1 of Patent Document 4).

JP 2010-260281 A JP 2009-1691 A Special table 2011-500932 gazette JP 2009-57548 A

  However, since the ink composition disclosed in Patent Document 1 is difficult to cure (350 to 420 nm) using a light emitting diode (LED) having a long wavelength at the time of UV curing with a photoacid generator, it is difficult to cure. There arises a problem that the viscosity is inferior, the viscosity is increased, and the storage stability may be inferior. The oil-based ink composition for ink-jet recording disclosed in Patent Document 2 requires oiling after printing due to the fact that it is an oil-based ink, and as a result, a component that volatilizes is generated, resulting in oil-based ink (solvent ink). There arises a problem that a specific VOC (volatile organic compound) is generated and the viscosity is increased. The yellow curable ink disclosed in Patent Document 3 is C.I. I. Since PY150 is a pigment containing nickel, there is room for improvement in safety, and there is also room for improvement in the weather resistance (water resistance) during rainfall of recorded matter obtained using the ink. The photocurable ink composition disclosed in Patent Document 4 has room for improvement in storage stability.

  Accordingly, an object of the present invention is to provide a photo-curable ink composition for ink jet recording which ensures safety and is excellent in all of curability, storage stability, and weather resistance.

  The present inventors have intensively studied to solve the above problems. As a result, vinyl ether group-containing (meth) acrylic acid esters having a predetermined structure as a polymerizable compound and C.I. I. The present invention was completed by finding that the above problems can be solved by a photocurable ink composition for inkjet recording (hereinafter, also simply referred to as “ink composition”) containing CI Pigment Yellow 155 and a photopolymerization initiator. .

  That is, the present invention is as follows.

[1]
A photocurable ink composition for inkjet recording, comprising a colorant, a polymerizable compound, and a photopolymerization initiator, wherein the colorant comprises C.I. I. Pigment Yellow 155 at least, and the polymerizable compound is 10 to 67% by mass of the following general formula (I) with respect to the total mass of the ink composition:
_{^{CH 2 = CR 1 -COOR 2 -O}} -CH = CH-R 3 ··· (I)
Wherein R ¹ is a hydrogen atom or a methyl group, R ² is a divalent organic residue having 2 to 20 carbon atoms, and R ³ is a hydrogen atom or a monovalent organic residue having 1 to 11 carbon atoms. Group.)
A photocurable ink composition for inkjet recording, comprising at least a vinyl ether group-containing (meth) acrylic acid ester represented by:

[2]
The photocurable inkjet recording ink composition according to [1], wherein the polymerizable compound further contains a monofunctional (meth) acrylate other than the vinyl ether group-containing (meth) acrylic acid esters.

[3]
The monofunctional (meth) acrylate is a photocurable inkjet recording ink composition according to [2], wherein the monofunctional (meth) acrylate has at least one of an aromatic ring skeleton and an alicyclic skeleton.

[4]
The monofunctional (meth) acrylate is an ink composition for photocurable inkjet recording according to [2] or [3], which has an aromatic ring skeleton.

[5]
Content of the said vinyl ether group containing (meth) acrylic acid ester is 10-40 mass% with respect to the total mass of this ink composition, The photocurable type in any one of [1]-[4] Ink composition for inkjet recording.

[6]
Content of the said monofunctional (meth) acrylate is 10-60 mass% with respect to the total mass of this ink composition, The photocurable inkjet recording ink in any one of [2]-[5] Composition.

[7]
The photocurable inkjet recording ink composition according to any one of [2] to [6], wherein the monofunctional (meth) acrylate is at least one of phenoxyethyl (meth) acrylate and benzyl (meth) acrylate. object.

[8]
C. above. I. The content of Pigment Yellow 155 is 0.1 to 3% by mass with respect to the total mass of the ink composition, and the photocurable ink composition for ink jet recording according to any one of [1] to [7] .

[9]
The photopolymerization initiator according to any one of [1] to [8], wherein the photopolymerization initiator contains at least an acylphosphine oxide compound.

[10]
[1] to [9] A photocurable inkjet recording ink composition according to any one of [1] to [9], which is ejected onto a recording medium, and the photocurable inkjet recording ink composition ejected in the ejecting process. A curing step of irradiating the product with ultraviolet rays having a peak wavelength in the range of 350 to 420 nm to cure the photocurable ink composition for inkjet recording.

[11]
The inkjet recording method according to [10], wherein the curing step is to cure the photocurable inkjet recording ink composition with an irradiation energy of ultraviolet rays of 600 mJ / cm ² or less.

[12]
The ink-jet recording method according to [10] or [11], wherein the curing step cures the photocurable ink-jet recording ink composition with a peak irradiation intensity of ultraviolet rays of 800 mW / cm ² or more.

  Hereinafter, embodiments for carrying out the present invention will be described in detail. In addition, this invention is not restrict | limited to the following embodiment, A various deformation | transformation can be implemented within the range of the summary.

In this specification, “curing” means that when an ink composition containing a polymerizable compound is irradiated with radiation, the polymerizable compound is polymerized and the ink composition is solidified. “Curable” refers to the property of curing in response to light.
In this specification, “storage stability” refers to the property that the viscosity before and after storage is not easily changed when the ink composition is stored at 60 ° C. for 1 week. “Weather resistance” refers to a property that, when a printed matter on which an image is formed is posted outdoors, the image has excellent storage stability, that is, the image is not easily faded or discolored. “Ejection stability” refers to the property of ejecting droplets of a stable ink composition from a nozzle without clogging the nozzle.

In this specification, “(meth) acrylate” means at least one of acrylate and its corresponding methacrylate, and “(meth) acryl” means at least one of acryl and its corresponding methacryl.
In this specification, “recorded material” refers to a material in which ink is recorded on a recording medium to form a cured product. In addition, the hardened | cured material in this specification means the hardened | cured substance containing the cured film and coating film of an ink.

[Photocurable ink composition for inkjet recording]
The photocurable ink composition for inkjet recording according to one embodiment of the present invention includes a polymerizable compound, a color material, and a photopolymerization initiator. The polymerizable compound has the following general formula (I):
_{^{CH 2 = CR 1 -COOR 2 -O}} -CH = CH-R 3 ··· (I)
Wherein R ¹ is a hydrogen atom or a methyl group, R ² is a divalent organic residue having 2 to 20 carbon atoms, and R ³ is a hydrogen atom or a monovalent organic residue having 1 to 11 carbon atoms. Group.)
The vinyl ether group containing (meth) acrylic acid ester represented by these is contained at least.
The color material is C.I. I. Pigment Yellow 155 is contained at least.
Hereinafter, additives (components) that are or can be included in the ink composition of the present embodiment will be described.

[Color material]
The ink composition of the present embodiment has C.I. I. Pigment Yellow 155 is contained at least.

C. I. Pigment Yellow 155 is classified as a condensed azo pigment and has a chemical name of 2,2 ′-[1,4-phenylene-bis [imino (1-acetyl-2-oxoethane-2,1-diyl) azo]] bis ( Dimethyl terephthalate) and the molecular formula is C ₃₄ H ₃₂ N ₆ O ₁₂ . Thus, C.I. I. Pigment Yellow 155 does not contain nickel and is excellent in safety. The ink composition is C.I. I. By including Pigment Yellow 155, safety can be ensured and weather resistance is excellent.

  C. above. I. The content of Pigment Yellow 155 is preferably 0.1 to 6% by mass and more preferably 0.1 to 3% by mass with respect to the total mass (100% by mass) of the ink composition. When the content is 0.1% by mass or more, C.I. I. Since the effect of adding Pigment Yellow 155 is recognized, it is preferable. Further, when the content is 6% by mass or less, the storage stability is further improved, and when the content is 3% by mass or less, the storage stability is further improved.

  The ink composition may include other color materials, and examples of the other color materials include at least one of a pigment and a dye.

(Pigment)
In this embodiment, the light resistance of the ink composition can be improved by using a pigment as the color material. Of these, yellow pigments (excluding CI PY 155) are not limited to the following, but include, for example, C.I. I. Pigment Yellow (PY) 1, 2, 3, 4, 5, 6, 7, 10, 11, 12, 13, 14, 16, 17, 24, 34, 35, 37, 53, 55, 65, 73, 74 75, 81, 83, 93, 94, 95, 97, 98, 99, 108, 109, 110, 113, 114, 117, 120, 124, 128, 129, 133, 138, 139, 147, 151, 153 , 154, 167, 172, 180, 213.

  The said yellow pigment may be used individually by 1 type, and may use 2 or more types together.

(dye)
In the present embodiment, a dye can be used as the color material. Of these, examples of yellow dyes include, but are not limited to, C.I. I. Acid Yellow 17, 23, 42, 44, 79, 142, C.I. I. Direct yellow 1,12,24,33,50,55,58,86,132,142,144,173 can be mentioned.

  The said yellow dye may be used individually by 1 type, and may use 2 or more types together.

  1-6 mass% is preferable with respect to the total mass (100 mass%) of an ink composition, and, as for the total content of a coloring material, 1-3 mass% is more preferable. When the total content is not less than the above lower limit value, the color can be sufficiently developed. When the total content is less than or equal to the above upper limit, it is possible to effectively prevent the coating from being inhibited from being cured by the light absorption of the colorant itself.

[Dispersant]
The ink composition of the present embodiment may contain a dispersant in order to improve pigment dispersibility. Although it does not specifically limit as the said dispersing agent, For example, the dispersing agent currently used for preparing pigment dispersion liquids, such as a polymer dispersing agent, is mentioned. Specific examples include polyoxyalkylene polyalkylene polyamines, vinyl polymers and copolymers, acrylic polymers and copolymers, polyesters, polyamides, polyimides, polyurethanes, amino polymers, silicon-containing polymers, sulfur-containing polymers, fluorine-containing polymers, and epoxies. The thing which has 1 or more types of resin as a main component is mentioned. Examples of commercially available polymer dispersants include Ajinomoto Fine Techno Co., Ltd., Ajisper series (trade name), Solspers series available from Avecia Co. (Solsperse 32000, 36000, etc. [trade name]), BYK Chemie, etc. Disparvic series (trade name) made by the company and Disparon series (trade name) made by Enomoto Kasei.
A dispersing agent may be used individually by 1 type, and may be used in combination of 2 or more type. The content of the dispersant is not particularly limited, and a preferable amount may be added as appropriate.

(Polymerizable compound)
The polymerizable compound contained in the ink composition of the present embodiment can be polymerized at the time of ultraviolet irradiation by the action of a photopolymerization initiator described later, and the printed ink can be cured.

(Vinyl ether group-containing (meth) acrylic acid esters)
The ink composition of the present embodiment contains at least vinyl ether group-containing (meth) acrylic acid esters represented by the above general formula (I) as a polymerizable compound.
When the ink composition contains the vinyl ether group-containing (meth) acrylic acid esters, the ink curability can be improved, and the viscosity of the ink can be lowered. In addition, it is better to use a compound having both a vinyl ether group and a (meth) acryl group in one molecule than to use a compound having a vinyl ether group and a compound having a (meth) acryl group separately. It is preferable for improving curability.

In the above general formula (I), the divalent organic residue having 2 to 20 carbon atoms represented by R ² is a linear, branched or cyclic substituted having 2 to 20 carbon atoms. May be an alkylene group, an optionally substituted alkylene group having an oxygen atom by an ether bond and / or an ester bond in the structure, and an optionally substituted divalent alkylene group having 6 to 11 carbon atoms. Aromatic groups are preferred. Among these, C2-C6 alkylene groups such as ethylene group, n-propylene group, isopropylene group, and butylene group, oxyethylene group, oxy n-propylene group, oxyisopropylene group, and oxybutylene group An alkylene group having 2 to 9 carbon atoms having an oxygen atom due to an ether bond in the structure is preferably used.

In the general formula (I), the monovalent organic residue having 1 to 11 carbon atoms represented by R ³ is a linear, branched or cyclic substituted group having 1 to 10 carbon atoms. Suitable alkyl groups and optionally substituted aromatic groups having 6 to 11 carbon atoms are preferred. Among these, C6-C2 aromatic groups, such as a C1-C2 alkyl group which is a methyl group or an ethyl group, a phenyl group, and a benzyl group, are used suitably.

  When each of the organic residues is an optionally substituted group, the substituent is divided into a group containing a carbon atom and a group not containing a carbon atom. First, when the substituent is a group containing a carbon atom, the carbon atom is counted in the carbon number of the organic residue. Examples of the group containing a carbon atom include, but are not limited to, a carboxyl group and an alkoxy group. Next, examples of the group not containing a carbon atom include, but are not limited to, a hydroxyl group and a halo group.

  Examples of the vinyl ether group-containing (meth) acrylic acid esters include, but are not limited to, for example, 2-vinyloxyethyl (meth) acrylate, 3-vinyloxypropyl (meth) acrylate, and 1-methyl (meth) acrylate. 2-vinyloxyethyl, 2-vinyloxypropyl (meth) acrylate, 4-vinyloxybutyl (meth) acrylate, 1-methyl-3-vinyloxypropyl (meth) acrylate, 1-vinyloxymethyl (meth) acrylate Propyl, 2-methyl-3-vinyloxypropyl (meth) acrylate, 1,1-dimethyl-2-vinyloxyethyl (meth) acrylate, 3-vinyloxybutyl (meth) acrylate, 1-methyl- (meth) acrylate 2-vinyloxypropyl, 2-vinyloxybutyl (meth) acrylate, (meth) a 4-vinyloxycyclohexyl silylate, 6-vinyloxyhexyl (meth) acrylate, 4-vinyloxymethylcyclohexylmethyl (meth) acrylate, 3-vinyloxymethylcyclohexylmethyl (meth) acrylate, (meth) acrylic acid 2-vinyloxymethylcyclohexylmethyl, p-vinyloxymethylphenylmethyl (meth) acrylate, m-vinyloxymethylphenylmethyl (meth) acrylate, o-vinyloxymethylphenylmethyl (meth) acrylate, (meth) 2- (vinyloxyethoxy) ethyl acrylate, 2- (vinyloxyisopropoxy) ethyl (meth) acrylate, 2- (vinyloxyethoxy) propyl (meth) acrylate, 2- (vinyloxy) (meth) acrylate Ethoxy) isopropyl, (meth) acrylic acid 2- Vinyloxyisopropoxy) propyl, 2- (vinyloxyisopropoxy) isopropyl (meth) acrylate, 2- (vinyloxyethoxyethoxy) ethyl (meth) acrylate, 2- (vinyloxyethoxyisopropoxy) (meth) acrylate ) Ethyl, 2- (vinyloxyisopropoxyethoxy) ethyl (meth) acrylate, 2- (vinyloxyisopropoxyisopropoxy) ethyl (meth) acrylate, 2- (vinyloxyethoxyethoxy) propyl (meth) acrylate 2- (vinyloxyethoxyisopropoxy) propyl (meth) acrylate, 2- (vinyloxyisopropoxyethoxy) propyl (meth) acrylate, 2- (vinyloxyisopropoxyisopropoxy) propyl (meth) acrylate, (Meth) acrylic acid 2- (vinylo) Xylethoxyethoxy) isopropyl, (meth) acrylic acid 2- (vinyloxyethoxyisopropoxy) isopropyl, (meth) acrylic acid 2- (vinyloxyisopropoxyethoxy) isopropyl, (meth) acrylic acid 2- (vinyloxyisopropoxy) Isopropoxy) isopropyl, (meth) acrylic acid 2- (vinyloxyethoxyethoxyethoxyethoxy) ethyl, (meth) acrylic acid 2- (vinyloxyethoxyethoxyethoxyethoxy) ethyl, (meth) acrylic acid 2- (isopropenoxyethoxy) ) Ethyl, (meth) acrylic acid 2- (isopropenoxyethoxyethoxyethoxy) ethyl, (meth) acrylic acid 2- (isopropenoxyethoxyethoxyethoxy) ethyl, (meth) acrylic acid 2- (isopropenoxyethoxyethoxyethoxy) D ) Ethyl, and (meth) Polyethylene glycol monovinyl ether acrylate, and (meth) acrylic acid polypropylene glycol monovinyl ether.

  Among these, since the viscosity of the ink can be further reduced, the flash point is high, and the curability of the ink is excellent, 2- (vinyloxyethoxy) ethyl (meth) acrylate, that is, 2- (vinyloxy) acrylate At least one of ethoxy) ethyl and 2- (vinyloxyethoxy) ethyl methacrylate is preferable, and 2- (vinyloxyethoxy) ethyl acrylate is more preferable. In particular, since 2- (vinyloxyethoxy) ethyl acrylate and 2- (vinyloxyethoxy) ethyl methacrylate have a simple structure and a small molecular weight, the viscosity of the ink can be significantly reduced. Examples of 2- (vinyloxyethoxy) ethyl (meth) acrylate include 2- (2-vinyloxyethoxy) ethyl (meth) acrylate and 2- (1-vinyloxyethoxy) ethyl (meth) acrylate. Examples of 2- (vinyloxyethoxy) ethyl acrylate include 2- (2-vinyloxyethoxy) ethyl acrylate and 2- (1-vinyloxyethoxy) ethyl acrylate. Incidentally, 2- (vinyloxyethoxy) ethyl acrylate is superior in terms of curability compared to 2- (vinyloxyethoxy) ethyl methacrylate.

  A vinyl ether group containing (meth) acrylic acid ester may be used individually by 1 type, and may be used in combination of 2 or more type.

  Content of the said vinyl ether group containing (meth) acrylic acid ester is 10-67 mass% with respect to the total mass (100 mass%) of an ink composition. When the content is 10% by mass or more, the viscosity of the ink can be reduced and the curability of the ink can be improved. On the other hand, when the content is 67% by mass or less, the storage stability of the ink can be improved. Further, the content is preferably 10 to 65% by mass because the viscosity of the ink can be further reduced and the curability and storage stability of the ink can be further improved. More preferably, it is 50 mass%, It is further more preferable that it is 10-40 mass%, It is especially preferable that it is 10-30 mass%. On the other hand, when importance is placed on lowering the viscosity and curability of the ink composition, it is preferably 30 to 67% by mass, more preferably 40 to 67% by mass, and 50 to 67% by mass. More preferably.

The method for producing the vinyl ether group-containing (meth) acrylic acid esters is not limited to the following, but is a method of esterifying (meth) acrylic acid and a hydroxyl group-containing vinyl ether (Production Method B), (meth) acrylic acid halide. And esterification of (meth) acrylic anhydride and hydroxyl group-containing vinyl ether (production method D), esterification of (meth) acrylic acid ester and hydroxyl group-containing vinyl ether Method of exchange (Production method E), Method of esterifying (meth) acrylic acid and halogen-containing vinyl ether (Method of production F), Method of esterifying alkali (earth) metal salt of (meth) acrylic acid and halogen-containing vinyl ether (Production G), hydroxyl group-containing (meth) acrylic acid ester and carboxylic acid vinyl ester How to vinyl exchange and Le (Procedure H), hydroxyl group-containing (meth) How to ether exchange and acrylic acid ester and an alkyl vinyl ether (Process I).
Among these, since the desired effect can be further exhibited in this embodiment, the production method E is preferable.

(Monofunctional (meth) acrylate)
In the ink composition of the present embodiment, a monofunctional (meth) acrylate (however, the vinyl ether group-containing (meth) acrylic acid ester represented by the general formula (I) is excluded as a polymerizable compound. The same applies hereinafter. ) Is further preferably contained. In this case, the storage stability of the ink can be further improved, and the solubility of the photopolymerization initiator can be improved.

  Examples of the monofunctional (meth) acrylate include, but are not limited to, isoamyl (meth) acrylate, stearyl (meth) acrylate, lauryl (meth) acrylate, octyl (meth) acrylate, decyl (meth) acrylate, and isomyristyl. (Meth) acrylate, isostearyl (meth) acrylate, 2-ethylhexyl-diglycol (meth) acrylate, 2-hydroxybutyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate, butoxyethyl (meth) acrylate, ethoxydiethylene glycol (Meth) acrylate, methoxydiethylene glycol (meth) acrylate, methoxypolyethylene glycol (meth) acrylate, methoxypropylene glycol (meth) acrylate , Phenoxyethyl (meth) acrylate, tetrahydrofurfuryl (meth) acrylate, isobornyl (meth) acrylate, 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 2-hydroxy-3-phenoxypropyl (meth) ) Acrylate, lactone-modified flexible (meth) acrylate, t-butylcyclohexyl (meth) acrylate, dicyclopentanyl (meth) acrylate, dicyclopentenyloxyethyl (meth) acrylate, and benzyl (meth) acrylate. .

  Among these, at least one of phenoxyethyl (meth) acrylate and benzyl (meth) acrylate is preferable and at least one of phenoxyethyl acrylate and benzyl acrylate is preferable because the viscosity can be reduced and the curability is excellent. Is more preferable.

  The monofunctional (meth) acrylate preferably has at least one of an aromatic ring skeleton and an alicyclic skeleton in its structure, and more preferably has an aromatic ring skeleton. In this case, the solubility of the photopolymerization initiator can be further improved. The alicyclic skeleton can be further divided into a saturated alicyclic skeleton and an unsaturated alicyclic skeleton.

  Examples of the monofunctional (meth) acrylate having an aromatic ring skeleton include phenoxyethyl (meth) acrylate, benzyl (meth) acrylate, and 2-hydroxy-3-phenoxypropyl (meth) acrylate, among which phenoxyethyl (meta) ) Acrylate and benzyl (meth) acrylate are preferred, phenoxyethyl acrylate is more preferred, and phenoxyethyl acrylate and benzyl acrylate are more preferred.

  Examples of the monofunctional (meth) acrylate having a saturated alicyclic skeleton include isobornyl (meth) acrylate, t-butylcyclohexyl (meth) acrylate, and dicyclopentanyl (meth) acrylate. ) Acrylate is preferred, and isobornyl acrylate is more preferred.

Examples of the monofunctional (meth) acrylate having an unsaturated alicyclic skeleton include dicyclopentenyloxyethyl (meth) acrylate. Among these, monofunctional (meth) acrylates having an aromatic ring skeleton in the structure are particularly preferable in terms of curability, initiator solubility, and the like.
A monofunctional (meth) acrylate may be used individually by 1 type, and may be used in combination of 2 or more type.

  The content of the monofunctional (meth) acrylate is preferably 10 to 60% by mass, more preferably 10 to 50% by mass, and still more preferably 15 to 40% by mass with respect to the total mass (100% by mass) of the ink composition. . In particular, when the monofunctional (meth) acrylate includes a monofunctional (meth) acrylate having an aromatic ring skeleton in the structure, the content is 5% by mass with respect to the total mass (100% by mass) of the ink composition. The above is preferable, 10% by mass or more is more preferable, 15% by mass or more is further preferable, and 15 to 40% by mass is even more preferable. When the content is within the above range, the viscosity can be further reduced, and the solubility of the photopolymerization initiator and the curability of the ink can be further improved.

(Multifunctional (meth) acrylate)
The ink composition of this embodiment may further contain polyfunctional (meth) acrylate as a polymerizable compound.

  Among the polyfunctional (meth) acrylates, bifunctional (meth) acrylates (excluding the above-mentioned predetermined vinyl ether group-containing (meth) acrylic acid esters) are not limited to the following. (Meth) acrylate, tetraethylene glycol di (meth) acrylate, polyethylene glycol di (meth) acrylate, dipropylene glycol di (meth) acrylate, tripropylene glycol di (meth) acrylate, polypropylene glycol di (meth) acrylate, 1, 4-butanediol di (meth) acrylate, 1,6-hexanediol di (meth) acrylate, 1,9-nonanediol di (meth) acrylate, neopentyl glycol di (meth) acrylate, dimethyloltricyclo Candi (meth) acrylate, EO (ethylene oxide) adduct di (meth) acrylate of bisphenol A, PO (propylene oxide) adduct di (meth) acrylate of bisphenol A, neopentyl glycol di (meth) acrylate hydroxypivalate, And polytetramethylene glycol di (meth) acrylate. Among these, at least one of dipropylene glycol diacrylate and tripropylene glycol diacrylate is preferable because both viscosity reduction and excellent curability can be achieved.

  Among polyfunctional (meth) acrylates, trifunctional or higher (meth) acrylates are not limited to the following, but include, for example, trimethylolpropane tri (meth) acrylate, EO-modified trimethylolpropane tri (meth) acrylate, pentaerythritol. Tri (meth) acrylate, pentaerythritol tetra (meth) acrylate, dipentaerythritol hexa (meth) acrylate, ditrimethylolpropane tetra (meth) acrylate, glycerin propoxytri (meth) acrylate, cowprolactone modified trimethylolpropane tri (meth) ) Acrylate, pentaerythritol ethoxytetra (meth) acrylate, and caprolactam-modified dipentaerythritol hexa (meth) acrylate.

  A polyfunctional (meth) acrylate may be used individually by 1 type, and may be used in combination of 2 or more type.

  The content of the polyfunctional (meth) acrylate is preferably 2 to 30% by mass, and more preferably 5 to 20% by mass in order to lower the viscosity of the ink and further improve the curability.

(Polymerizable compounds other than the above)
In addition to the above-mentioned vinyl ether group-containing (meth) acrylic acid esters, monofunctional (meth) acrylates, and polyfunctional (meth) acrylates, various conventionally known monofunctional and polyfunctional monomers and oligomers are also used. It is possible (hereinafter referred to as “other polymerizable compounds”). Examples of the monomer include unsaturated carboxylic acids such as itaconic acid, crotonic acid, isocrotonic acid and maleic acid, salts or esters thereof, urethanes, amides and anhydrides thereof, acrylonitrile, styrene, various unsaturated polyesters, unsaturated monomers. Examples include saturated polyethers, unsaturated polyamides, and unsaturated urethanes. Moreover, as said oligomer, the oligomer formed from said monomer is mentioned, for example.
Another polymeric compound may be used individually by 1 type, and may be used in combination of 2 or more type. The content of the other polymerizable compound is generally 20% by mass or less with respect to the total mass (100% by mass) of the ink composition.

(Photopolymerization initiator)
The photopolymerization initiator contained in the ink composition of the present embodiment is used to form a print by curing the ink present on the surface of the recording medium by photopolymerization by ultraviolet irradiation. By using ultraviolet rays (UV) among the radiation, the safety is excellent and the cost of the light source lamp can be suppressed. There is no limitation as long as it generates active species such as radicals and cations by the energy of light (ultraviolet rays) and initiates the polymerization of the polymerizable compound. However, a photo radical polymerization initiator or a photo cationic polymerization initiator may be used. Among them, it is preferable to use a radical photopolymerization initiator.

  Examples of the photo radical polymerization initiator include aromatic ketones, acyl phosphine oxide compounds, aromatic onium salt compounds, organic peroxides, thio compounds (thioxanthone compounds, thiophenyl group-containing compounds, etc.), hexaarylbiphenyls, and the like. Examples include imidazole compounds, ketoxime ester compounds, borate compounds, azinium compounds, metallocene compounds, active ester compounds, compounds having a carbon halogen bond, and alkylamine compounds.

  Among these, it is preferable to use at least an acyl phosphine oxide compound because the curability of the ink can be further improved. It is also preferable to use a thioxanthone compound in addition to the acylphosphine oxide compound.

  Specific examples of the photo radical polymerization initiator include acetophenone, acetophenone benzyl ketal, 1-hydroxycyclohexyl phenyl ketone, 2,2-dimethoxy-2-phenylacetophenone, xanthone, fluorenone, benzaldehyde, fluorene, anthraquinone, triphenylamine. , Carbazole, 3-methylacetophenone, 4-chlorobenzophenone, 4,4′-dimethoxybenzophenone, 4,4′-diaminobenzophenone, Michler's ketone, benzoin propyl ether, benzoin ethyl ether, benzyldimethyl ketal, 1- (4-isopropylphenyl) ) -2-Hydroxy-2-methylpropan-1-one, 2-hydroxy-2-methyl-1-phenylpropan-1-one, thioxanthone, diethyl Oxanthone, 2-isopropylthioxanthone, 2-chlorothioxanthone, 2-methyl-1- [4- (methylthio) phenyl] -2-morpholino-propan-1-one, bis (2,4,6-trimethylbenzoyl) -phenyl Phosphine oxide, 2,4,6-trimethylbenzoyl-diphenyl-phosphine oxide, 2,4-diethylthioxanthone, and bis- (2,6-dimethoxybenzoyl) -2,4,4-trimethylpentylphosphine oxide Can be mentioned.

  Examples of commercially available photo radical polymerization initiators include IRGACURE 651 (2,2-dimethoxy-1,2-diphenylethane-1-one), IRGACURE 184 (1-hydroxy-cyclohexyl-phenyl-ketone), DAROCUR 1173. (2-hydroxy-2-methyl-1-phenyl-propan-1-one), IRGACURE 2959 (1- [4- (2-hydroxyethoxy) -phenyl] -2-hydroxy-2-methyl-1-propane- 1-one), IRGACURE 127 (2-hydroxy-1- {4- [4- (2-hydroxy-2-methyl-propionyl) -benzyl] phenyl} -2-methyl-propan-1-one}, IRGACURE 907 (2-Methyl-1- (4-methylthiophenyl) -2-morphol Linopropan-1-one), IRGACURE 369 (2-benzyl-2-dimethylamino-1- (4-morpholinophenyl) -butanone-1), IRGACURE 379 (2- (dimethylamino) -2-[(4- Methylphenyl) methyl] -1- [4- (4-morpholinyl) phenyl] -1-butanone), DAROCUR TPO (2,4,6-trimethylbenzoyl-diphenyl-phosphine oxide), IRGACURE 819 (bis (2, 4,6-trimethylbenzoyl) -phenylphosphine oxide), IRGACURE 784 (bis (η5-2,4-cyclopentadien-1-yl) -bis (2,6-difluoro-3- (1H-pyrrole-1-) Yl) -phenyl) titanium), IRGACURE OXE 01 (1.2-octanedione, 1- [4- (phenylthio)-, 2- (O-benzoyloxime)]), IRGACURE OXE 02 (ethanone, 1- [9-ethyl-6- (2-methylbenzoyl) -9H-carbazol-3-yl]-, 1- (O-acetyloxime)), IRGACURE 754 (oxyphenylacetic acid, 2- [2-oxo-2-phenylacetoxyethoxy] ethyl ester and oxyphenylacetic acid, 2- (Mixture of (2-hydroxyethoxy) ethyl ester) (above, manufactured by BASF), KAYACURE DETX-S (2,4-diethylthioxanthone) (manufactured by Nippon Kayaku Co., Ltd.), Lucirin TPO LR8883, LR8970 (manufactured by BASF), Ubekrill P36 (UCB), and the like.

  A photoinitiator may be used individually by 1 type and may be used in combination of 2 or more type.

  The content of the photopolymerization initiator can improve the ultraviolet curing rate and have excellent curability, and in order to avoid undissolved photopolymerization initiator and coloring derived from the photopolymerization initiator, It is preferably 3 to 20% by mass relative to the total mass (100% by mass) of the ink composition.

[Slip agent]
The ink composition of the present embodiment may further include a slip agent (surfactant). The slip agent is not particularly limited. For example, polyester-modified silicone or polyether-modified silicone can be used as a silicone-based surfactant, and polyether-modified polydimethylsiloxane or polyester-modified polydimethylsiloxane is particularly used. preferable. Specific examples include BYK-347, BYK-348, BYK-UV3500, 3510, 3530, and 3570 (above, manufactured by BYK).

  A slip agent may be used individually by 1 type, and may be used in combination of 2 or more type. The content of the slip agent is not particularly limited, and a preferable amount may be added as appropriate.

(Polymerization inhibitor)
The ink composition of this embodiment may further contain a polymerization inhibitor. When the ink composition contains a polymerization inhibitor, the polymerization reaction of the polymerizable compound before curing can be prevented.

  Although it does not restrict | limit especially as a polymerization inhibitor, For example, a phenol type polymerization inhibitor is mentioned. Examples of the phenol-based polymerization inhibitor include, but are not limited to, for example, p-methoxyphenol, cresol, t-butylcatechol, di-t-butylparacresol, hydroquinone monomethyl ether, α-naphthol, 3,5-di- t-butyl-4-hydroxytoluene, 2,6-di-t-butyl-4-methylphenol, 2,2'-methylene-bis (4-methyl-6-t-butylphenol), 2,2'-methylene -Bis (4-ethyl-6-butylphenol) and 4,4'-thio-bis (3-methyl-6-tert-butylphenol).

  Examples of commercially available phenolic polymerization inhibitors include p-methoxyphenol (trade name, p-methoxyphenol, manufactured by Tokyo Chemical Industry Co., Ltd.), non-flex MBP (Seiko Chemical Co., Ltd. ( Seiko Chemical Co., Ltd., trade name, 2,2′-methylene-bis (4-methyl-6-tert-butylphenol)), BHT Swanox (trade name, 2,6-di-t, manufactured by Seiko Chemical Co., Ltd.) -Butyl-4-methylphenol).

  A polymerization inhibitor may be used individually by 1 type, and may be used in combination of 2 or more type. The content of the polymerization inhibitor is not particularly limited, and a preferable amount may be added as appropriate.

[Other additives]
The ink composition of the present embodiment may include additives (components) other than the additives listed above. Such components are not particularly limited, and may include, for example, conventionally known polymerization accelerators, penetration enhancers, wetting agents (humectants), and other additives. Examples of the other additives include conventionally known fixing agents, antifungal agents, preservatives, antioxidants, ultraviolet absorbers, chelating agents, pH adjusting agents, and thickeners.

[Characteristics of Photocurable Inkjet Recording Ink Composition]
The ink composition is preferably cured by irradiation with ultraviolet rays having an emission peak wavelength in the range of 350 to 420 nm. When the ink composition of the present embodiment can be cured at the emission peak wavelength within the above range, it can be cured at a low energy and at a high speed due to the composition of the ink composition. In particular, it is preferable to be able to cure with low energy because a light emitting diode (LED) which has been attracting attention in recent years from the environmental viewpoint can be used as an ultraviolet irradiation source. That is, the ink composition of this embodiment is excellent in curability by the LED.

Also preferably, the ink composition is cured by irradiation energy of 600 mJ / cm ² or less of ultraviolet light, more preferably an ink composition that cures by irradiation energy of 500 mJ / cm ² or less of ultraviolet irradiation of 200 mJ / cm ² or less of ultraviolet More preferred are ink compositions that cure with energy. The irradiation energy is preferably 50 mJ / cm ² or more, and more preferably 100 mJ / cm ² or more. By using such an ink composition as described above, an image can be formed at low cost. The irradiation energy is calculated by multiplying the irradiation time by the irradiation intensity.

  Thus, according to the present embodiment, safety is ensured due to the nickel-free composition, and the curability, storage stability, and weather resistance, as well as the low viscosity and the solubility of the photopolymerization initiator. A photocurable ink composition for ink jet recording, which is excellent in any case, can be provided.

[Recording medium]
The ink composition of the present embodiment can be recorded by being ejected onto a recording medium by an inkjet recording method described later. Examples of the recording medium include an absorptive or non-absorbable recording medium. The ink jet recording method of the embodiment described below is widely used for recording media having various absorption performances from non-absorbing recording media in which water-based ink penetration is difficult to absorbent recording media in which water-based ink penetration is easy. Applicable. However, when the above ink composition is applied to a non-absorbable recording medium, it may be necessary to provide a drying step after being cured by irradiation with ultraviolet rays.

The absorbent recording medium is not particularly limited. For example, plain paper such as electrophotographic paper having high water-based ink permeability, ink jet paper (an ink absorbing layer composed of silica particles or alumina particles, or polyvinyl alcohol). Art paper and coats used for general offset printing with relatively low permeability of water-based ink from (PVA) and inkjet pyrrole (PVP) and other ink-absorbing layers composed of hydrophilic polymers such as polyvinylpyrrolidone (PVP). Examples thereof include paper and cast paper.
The non-absorbable recording medium is not particularly limited. For example, films, sheets and plates of plastics such as polyvinyl chloride (PVC), polyethylene, polypropylene, polyethylene terephthalate (PET), iron, silver, copper, Examples thereof include a metal plate such as aluminum, a metal plate produced by vapor deposition of these various metals, a plastic film, a plate made of an alloy such as stainless steel or brass.

[Inkjet recording method]
One embodiment of the present invention relates to an inkjet recording method. The photocurable ink composition for ink jet recording of the above embodiment can be suitably used for the ink jet recording method of the present embodiment. The ink jet recording method includes: a discharge step of discharging the ink composition onto a recording medium; and irradiating the ink composition discharged in the discharge step with ultraviolet light having a peak wavelength in a range of 350 to 420 nm. And a curing step for curing the ink composition. In this way, an image, that is, an ink coating film (cured film) is formed by the ink composition cured on the recording medium. Another embodiment of the present invention relates to the photocurable ink jet recording ink composition of the present embodiment used in the ink jet recording method of the present embodiment described above. Here, the photocurable ink composition for ink-jet recording used in the ink-jet recording method of the present embodiment is sold for a recording apparatus that performs recording using the ink-jet recording method of the present embodiment. This means the photocurable ink composition for inkjet recording of the present embodiment.

[Discharge process]
In the ejection step, the ink composition is ejected onto the recording medium, and the ink composition adheres to the recording medium. The viscosity of the ink composition during ejection is preferably less than 30 mPa · s, more preferably 25 mPa · s or less, and even more preferably 5 to 20 mPa · s. If the viscosity of the ink composition is as described above with the temperature of the ink composition at room temperature or without heating the ink composition, the temperature of the ink composition is at room temperature or without heating the ink composition. Can be discharged. In that case, it is preferable that the temperature of the ink at the time of discharge is 20-30 degreeC. On the other hand, the ink composition may be discharged to a preferable viscosity by heating to a predetermined temperature. In this way, good discharge stability is realized.
Since the photocurable ink composition of the present embodiment has a higher viscosity than a normal aqueous ink composition, the viscosity fluctuation due to temperature fluctuation during ejection is large. Such a variation in the viscosity of the ink has a great influence on the change in the droplet size and the change in the droplet ejection speed, and can cause image quality degradation. Therefore, it is preferable to keep the temperature of the ink during ejection as constant as possible.

[Curing process]
Next, in the curing step, the ink composition ejected and adhered onto the recording medium is cured by irradiation with light (ultraviolet rays). This is because the photopolymerization initiator contained in the ink composition is decomposed by irradiation with ultraviolet rays to generate starting species such as radicals, acids, and bases, and the polymerization reaction of the polymerizable compound depends on the function of the starting species. It is to be promoted. Or it is because the polymerization reaction of a polymeric compound starts by irradiation of an ultraviolet-ray. At this time, if a sensitizing dye is present together with the photopolymerization initiator in the ink composition, the sensitizing dye in the system absorbs ultraviolet rays to be in an excited state and contacts the photopolymerization initiator to decompose the photopolymerization initiator. And a more sensitive curing reaction can be achieved.

  Mercury lamps and gas / solid lasers are mainly used as ultraviolet sources, and mercury lamps and metal halide lamps are widely known as light sources used for curing photocurable ink compositions for inkjet recording. Yes. On the other hand, there is a strong demand for mercury-free from the viewpoint of environmental protection, and replacement with a GaN-based semiconductor ultraviolet light-emitting device is very useful industrially and environmentally. Furthermore, ultraviolet light-emitting diodes (UV-LEDs) and ultraviolet laser diodes (UV-LDs) are small, have a long life, have high efficiency, and are low in cost, and are expected as light sources for photo-curable ink jets. Among these, UV-LED is preferable.

Here, since the likely increase the output of the LED, the emission peak wavelength preferably using UV-LED in the range of 350 to 420 nm, preferably 600 mJ / cm ² or less, more preferably 500 mJ / cm ² or less, more preferably Is preferably used for the ink jet recording method using a photocurable ink composition for ink jet recording that can be cured with an irradiation energy of 200 mJ / cm ² or less. In this case, low cost printing and high printing speed can be realized. Such an ink composition can be obtained by including at least one of a photopolymerization initiator that decomposes upon irradiation with ultraviolet rays in the wavelength range and a polymerizable compound that starts polymerization upon irradiation with ultraviolet rays in the wavelength range.
Further, the peak irradiation intensity of the LED is preferably 800 mW / cm ² or more, and more preferably 800 to 2000 mW / cm ² . By setting it to 800 mW / cm ² or more, the curability of the ink composition can be improved and the appearance of the printed matter can be improved.

  As described above, according to the present embodiment, the viscosity can be reduced, the safety can be ensured due to the nickel-free composition, and the curability, storage stability, weather resistance, and photopolymerization initiator can be secured. An ink jet recording method using a photocurable ink composition for ink jet recording excellent in both of the solubility of the ink can be provided.

  Hereinafter, the embodiments of the present invention will be described more specifically by way of examples. However, the embodiments are not limited to these examples.

[Use ingredients]
The components used in the following examples and comparative examples are as follows.

[Pigment]
Novoperm Yellow 4G01 (trade name, CI Pigment Yellow 155 manufactured by Clariant, abbreviated as “PY-155” below)
Yellow HG-AF LP901 (trade name manufactured by Clariant, CI Pigment Yellow 180, hereinafter abbreviated as “PY-180”)

[Dispersant]
Solsperse 32000 (trade name manufactured by LUBRIZOL, abbreviated as “SOL32000” below)

[Vinyl ether group-containing (meth) acrylic acid esters]
VEEA (2- (2-vinyloxyethoxy) ethyl acrylate, trade name of Nippon Shokubai Co., Ltd., hereinafter abbreviated as “VEEA”)
In the following tables, vinyl ether group-containing (meth) acrylic acid esters are abbreviated as “acrylic / vinyl-containing monomers”.

[Monofunctional (meth) acrylate]
Biscoat # 192 (phenoxyethyl acrylate, trade name of OSAKA ORGANIC CHEMICAL INDUSTRY LTD., Hereinafter abbreviated as “PEA”)
FA-BZA (benzyl acrylate, trade name of Hitachi Chemical Co., LTD., Hereinafter abbreviated as “BZA”)
IBXA (Isobornyl acrylate, trade name of Osaka Organic Chemical Co., Ltd., hereinafter abbreviated as “IBXA”)

[Multifunctional (meth) acrylate]
NK ester APG-100 (trade name, dipropylene glycol diacrylate, manufactured by SHIN-NAKAMURA CHEMICAL CO., LTD., Hereinafter abbreviated as “DPGDA”)
NK ester APG-200 (trade name, tripropylene glycol diacrylate, manufactured by Shin-Nakamura Chemical Co., Ltd., abbreviated as “TPGDA” below)

(Polymerization inhibitor)
P-methoxyphenol (trade name, p-methoxyphenol, manufactured by Tokyo Chemical Industry Co., Ltd., abbreviated as “MEHQ” below)

[Slip agent]
BYK-UV3500 (trade name of BYK, silicone-based surface conditioner, hereinafter abbreviated as “UV-3500”)

[Photopolymerization initiator (radical)]
IRGACURE 819 (trade name, manufactured by BASF, solid content: 100%, hereinafter abbreviated as “819”)
DAROCUR TPO (trade name, manufactured by BASF, solid content: 100%, hereinafter abbreviated as “TPO”)
KAYACURE DETX-S (trade name, manufactured by Nippon Kayaku Co., Ltd., solid content: 100%, hereinafter abbreviated as “DETX”)

[Examples 1 to 15 and Comparative Examples 1 to 4]
First, a pigment dispersion (hereinafter also referred to as “dispersion”) was prepared. In Table 1 and Table 2 below, the components described in the columns of the pigment, the dispersant, and the dispersion-derived monomer are added and mixed so as to have the composition (unit: mass%) described in Table 1 and Table 2. A dispersion was prepared.
Next, each dispersion liquid prepared above was stirred with a high-speed water-cooled stirrer to prepare a yellow photocurable ink composition for inkjet recording.

[Evaluation item]
About the photocurable ink composition for inkjet recording prepared in each Example and each comparative example, the viscosity, sclerosis | hardenability, storage stability, the solubility of a photoinitiator, and the weather resistance were evaluated with the following method.

(1. Viscosity)
The viscosity of the ink composition of each example and each comparative example was measured using a DVM-E type rotational viscometer (manufactured by TOKYO KEIKI INC) under the conditions of a temperature of 25 ° C. and a rotational speed of 10 rpm. .
The evaluation criteria are as follows. The evaluation results are shown in Tables 3 and 4 below.
A: 25 mPa · s or less.
B: More than 25 mPa · s and less than 30 mPa · s.
C: 30 mPa · s or more.

(2. Storage stability)
The ink compositions of Examples and Comparative Examples whose viscosity was measured in the above section “1. Viscosity” were sealed in an ink pack, put into a 60 ° C. constant temperature bath for 7 days, and stored. Thereafter, the viscosity of each ink composition whose temperature was lowered to room temperature (25 ° C.) was measured by the same method as in “1. Viscosity” above. The storage stability was evaluated based on the viscosity increase ratio before and after storage (ratio of the viscosity of the ink composition after storage to the viscosity of the ink composition before storage).
The evaluation criteria are as follows. The evaluation results are shown in Tables 3 and 4 below.
A: Less than 5%.
B: 5% or more and less than 15%.
C: 15% or more and less than 20%.
D: 20% or more.

(3. Solubility of photopolymerization initiator)
Ink compositions without pigments and dispersants were not added to the ink compositions of the examples and comparative examples, and the ink compositions without pigments were similarly prepared using only the other components and stirred sufficiently. Thereafter, whether or not the photopolymerization initiator remained undissolved was visually evaluated. For samples in which the photopolymerization initiator was not dissolved, the ink composition was placed in a thermostatic bath at 0 ° C., taken out after 24 hours and returned to room temperature, and then the photopolymerization initiator was deposited in the ink composition. This was visually observed again.
The evaluation criteria are as follows. The evaluation results are shown in Tables 3 and 4 below. In Tables 3 and 4, this item was abbreviated as “initiator solubility”.
A: After stirring at room temperature and after storage at 0 ° C., no undissolved residue or precipitation of the photopolymerization initiator was observed.
B: Although there was no undissolved residue of the photopolymerization initiator after stirring at room temperature, precipitation of the photopolymerization initiator was observed after storage at 0 ° C.
C: The undissolved residue of the photopolymerization initiator was observed after stirring at room temperature.

(4. Curability)
Using an ink jet recording apparatus provided with a piezo ink jet nozzle, each nozzle row was filled with the ink composition of each example and each comparative example. A solid pattern image (printed material) having a thickness of 10 μm on a PVC sheet (Frontlite Glossy 120 g [trade name], manufactured by Cooley) at room temperature and normal pressure while adjusting the ink discharge amount. A recording resolution of 720 × 720 dpi) was printed. At this time, the dischargeability of each ink composition was good. At the same time, UV light having a peak irradiation intensity of 1 W / cm ² (1000 mW / cm ² ) and a peak wavelength of 395 nm is emitted from a UV-LED in an ultraviolet irradiation device mounted on the side of the carriage by 200 mJ per pass. The solid pattern image was cured by adding the number of passes until tack-free under irradiation conditions of / cm ² . As described above, a recorded matter in which a solid pattern image was printed on a PVC sheet was produced.

Note that the “solid pattern image” is an image in which dots are recorded for all of the pixels that are the minimum recording unit area defined by the recording resolution. The “number of passes” means the number of times the head moves relative to the recorded matter and the coating film is irradiated with ultraviolet rays from the ultraviolet irradiation device mounted on the head. The irradiation energy [mJ / cm ² ] was obtained from the product of the irradiation intensity [mW / cm ² ] on the irradiated surface irradiated from the light source and the irradiation duration [s]. The irradiation intensity was measured using an ultraviolet intensity meter UM-10 and a light receiving unit UM-400 (both manufactured by KONICA MINOLTA SENSING, INC.).

  Whether or not it can be said to be tack-free was determined under the following conditions. That is, it is determined whether ink adheres to the swab or whether the ink cured product on the recording medium is scratched. The ink does not adhere to the cotton swab and the ink cured product on the recording medium The case where no scratches were made was considered tack-free. The cotton swab used here was a Johnson swab manufactured by Johnson & Johnson (registered trademark). The number of rubbing was 10 reciprocations and the rubbing strength was 100 g load.

The curability was evaluated according to the following criteria by the number of passes until tack-free. The evaluation results are shown in Tables 3 and 4 below.
A: 1 pass.
B: 2 to 3 passes.
C: 4 passes or more.

(5. Weather resistance)
The recorded material prepared in the above section “4. Curability” is put into a xenon fade meter SX75 (manufactured by Suga Test Instruments Co., Ltd.), and the integrated value of irradiation energy is 100 MJ / m. Light was irradiated until ² . The OD value before charging and the OD value after charging were measured, and the residual ratio of OD value represented by the following formula was calculated.
OD value residual ratio = OD value after charging / OD value before charging Evaluation criteria are as follows. The evaluation results are shown in Tables 3 and 4 below.
A: The residual ratio of OD value is 80% or more.
B: The residual ratio of OD value is 60% or more and less than 80%.
C: OD value residual ratio is less than 60%.

From the above results, vinyl ether group-containing (meth) acrylic acid esters represented by the above general formula (I), C.I. I. The ink composition containing CI Pigment Yellow 155 and a photopolymerization initiator (each example) is more curable, storage stable, and weather resistant than the other ink compositions (each comparative example). Was found to be excellent in both low viscosity and solubility of the photopolymerization initiator. As a further confirmation, using a filter for the UV-LED used in the above-described curability test, the peak irradiation intensity was set to 500 mW / cm ² , the carriage moving speed was slowed down and the irradiation time irradiated in one pass was lengthened. When the curable test of the ink composition of Example 1 was performed under the same conditions as the above-described curing test except that the irradiation energy per pass was set to 200 mJ / cm ² , the result was B rank. Wrinkles were observed on the surface of the solid pattern.

Claims (9)

A photocurable ink jet recording ink composition comprising a colorant, a polymerizable compound, and a photopolymerization initiator,
The color material is C.I. I. Pigment Yellow 155 at least, and
The polymerizable compound is 10 to 67% by mass of the following general formula (I) with respect to the total mass of the ink composition:
_{^{CH 2 = CR 1 -COOR 2 -O}} -CH = CH-R 3 ··· (I)
Wherein R ¹ is a hydrogen atom or a methyl group, R ² is a divalent organic residue having 2 to 20 carbon atoms, and R ³ is a hydrogen atom or a monovalent organic residue having 1 to 11 carbon atoms. Group.)
A vinyl ether group-containing (meth) acrylic acid ester represented by:
Containing a monofunctional (meth) acrylate other than the vinyl ether group-containing (meth) acrylic acid esters,
The monofunctional (meth) acrylate has an aromatic ring skeleton,
The content of the monofunctional (meth) acrylate is 5% by mass or more based on the total mass of the ink composition,
C. above. I. A photocurable ink jet recording ink composition, wherein the content of Pigment Yellow 155 is 0.1 to 6% by mass relative to the total mass of the ink composition.   2. The photocurable ink composition for ink jet recording according to claim 1, wherein the content of the vinyl ether group-containing (meth) acrylic acid ester is 10 to 40% by mass with respect to the total mass of the ink composition. The content of the monofunctional (meth) acrylate is 10 to 60% by weight based on the total weight of the ink composition, photocurable ink composition for ink jet recording according to claim 1 or 2. The photocurable inkjet recording ink composition according to any one of claims 1 to 3 , wherein the monofunctional (meth) acrylate is at least one of phenoxyethyl (meth) acrylate and benzyl (meth) acrylate. object. C. above. I. The content of CI Pigment Yellow 155 is a 0.1 to 3% by weight based on the total weight of the ink composition, photocurable ink jet recording ink composition according to any one of claims 1-4 . The photocurable ink composition for ink jet recording according to any one of claims 1 to 5 , wherein the photopolymerization initiator contains at least an acylphosphine oxide compound. A discharge step of discharging the photocurable ink jet recording ink composition according to any one of claims 1 to 6 onto a recording medium;
A curing step of curing the photocurable ink jet recording ink composition by irradiating the photocurable ink jet recording ink composition ejected in the ejection step with ultraviolet light having a peak wavelength in a range of 350 to 420 nm. And an inkjet recording method. The ink jet recording method according to claim 7 , wherein the curing step cures the photocurable ink composition for ink jet recording with an irradiation energy of ultraviolet rays of 600 mJ / cm ² or less. The inkjet recording method according to claim 7 or 8 , wherein the curing step cures the photocurable inkjet recording ink composition with a peak irradiation intensity of ultraviolet rays of 800 mW / cm ² or more.