JP6733697B2 - Photocurable ink composition for inkjet recording, inkjet recording method - Google Patents

Description

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

Conventionally, various methods have been used as a recording method for forming an image on a recording medium such as paper based on an image data signal. Among them, the inkjet method is an inexpensive apparatus and ejects the ink only to the required image portion to form an image directly on the recording medium, so that the ink can be used efficiently and the running cost is low. Further, the ink jet method is excellent as a recording method because of low noise.

In recent years, in an inkjet recording method, a photocurable ink composition that cures when irradiated with light has been used as an ink composition that can impart good water resistance, solvent resistance, scratch resistance, and the like. ..

For example, in Patent Document 1 and Patent Document 2, 2-(vinyloxyethoxy)ethyl (meth)acrylate, at least one of 2-(hydroxyethoxy)ethyl vinyl ether and diethylene glycol divinyl ether, and diethylene glycol di(meth). An ink composition and a reactive diluent composition containing an acrylate and a photopolymerization initiator are disclosed (Table 1 of [0114] and [0139] of Patent Document 1, Examples of Patent Document 2, Examples of Table 2). 1 and Table 4).

For example, in Patent Document 3, 69.82 parts by weight of propoxylated neopentyl glycol diacrylate, 10.0 parts by weight of a bifunctional vinyl ether monomer (compound having only vinyl ether group as a substituent), radical photoinitiator , And 3.60 parts by weight of a dispersible pigment, and an inkjet ink having a viscosity of 22 mPas at 25° C. is disclosed (Patent Document 3, [0021], [0022]).

For example, in Patent Document 4, 2-(2-vinyloxyethoxy)ethyl acrylate alone or 2-(2-vinyloxyethoxy)ethyl acrylate and isobornyl acrylate used together therewith, and a radical polymerization initiator. An ink liquid comprising a cationic polymerization initiator, a pigment, a dispersant, and a surfactant is disclosed (Patent Document 4, [0204] to [0207]).

For example, in Patent Document 5, 25.8 wt% of hexanediol diacrylate, 4.6 wt% of an amine addition compound of tripropylene glycol diacrylate, and 2.3 wt% of 2-(2-ethoxyethoxy)ethyl. Acrylate, 2.5 wt% alkoxylated phenoxyethyl acrylate, 3.7 wt% 2-benzyl-2-(dimethylamino)-4′-morpholinobutyrophenone, 3.2 wt% 2-hydroxy-2-methyl Propiophenone, a mixture of 2.8 wt% trimethylbenzophenone and methylbenzophenone, 0.5 wt% isopropylthioxanthone, 27.8 wt% cyan pigment dispersion, and 17.6 wt% 2-(2- A radiation-curable inkjet ink containing vinyloxyethoxy)ethyl acrylate has been disclosed (Patent Document 5, [0208], [0209]).

Japanese Patent No. 3461501 Japanese Patent No. 3544658 JP, 2009-62541, A JP, 2008-179136, A Japanese Patent Publication No. 2008-507598

However, the compositions and inks disclosed in Patent Documents 1 to 5 all have room for improvement in terms of curability. Therefore, one of the objects of the present invention is to provide a photocurable ink composition for ink jet recording having excellent curability.

The present inventors have diligently studied to solve the above problems. First, the reason why the compositions and inks disclosed in each patent document have room for improvement in terms of curability was examined. Both the composition and the ink contain 2-(vinyloxyethoxy)ethyl (meth)acrylate as a polymerizable compound. This 2-(vinyloxyethoxy)ethyl (meth)acrylate has a function of improving curability, but the ink using only 2-(vinyloxyethoxy)ethyl (meth)acrylate as the polymerizable compound is It was found that the curability cannot be said to be sufficient. In other words, it was found that an ink using another compound as the polymerizable compound in addition to the 2-(vinyloxyethoxy)ethyl (meth)acrylate may have excellent curability.
Therefore, the present inventors have examined such another kind of compound. First, the ink composition and the reactive diluent composition disclosed in Patent Document 1 and Patent Document 2 each contain a compound having only a vinyl ether group and a compound having only a (meth)acrylate group. Characteristically, it was found that these compositions are inferior in curability.

Further, as the compound disclosed in Patent Document 3, a bifunctional vinyl ether monomer (a compound having only a vinyl ether group as a substituent) can be mentioned. However, a compound having only a vinyl ether group as a substituent reduces the curing rate. Therefore, it has been found that the above-mentioned bifunctional vinyl ether monomer is not suitable as the above-mentioned compound of another type.

Moreover, isobornyl acrylate is mentioned as said another kind of compound disclosed by patent document 4. However, isobornyl acrylate also slows down the cure rate. Therefore, it was found that the above-mentioned isobornyl acrylate is not suitable as the above-mentioned compound of another kind.

Further, as the above-mentioned other type of compound disclosed in Patent Document 5, an alkoxylated phenoxyethyl acrylate can be mentioned. However, since alkoxylated phenoxyethyl acrylate has properties of relatively high viscosity and relatively poor solubility, it can be said that the curing rate of the radiation-curable inkjet ink containing the alkoxylated phenoxyethyl acrylate is sufficiently high. Absent. Therefore, it has been found that the above-mentioned alkoxylated phenoxyethyl acrylate is not suitable as the above-mentioned another type of compound.

Based on the above findings, as a result of further intensive studies by the present inventors, a polymerizable compound containing vinyl ether group-containing (meth)acrylic acid esters having a predetermined structure and phenoxyethyl (meth)acrylate, and photopolymerization The inventors have found that the above problems can be solved by a photocurable ink composition for inkjet recording containing an initiator, and completed the present invention.

That is, the present invention is as follows.
[1]
A photocurable inkjet recording ink composition comprising a polymerizable compound and a photopolymerization initiator, wherein the polymerizable compound is represented by the following general formula (I):
_{^{CH 2 = CR 1 -COOR 2 -O}} -CH = CH-R 3 ··· (I)
(In the formula, 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. It is a base.)
A photocurable ink composition for inkjet recording, which comprises a vinyl ether group-containing (meth)acrylic acid ester represented by: phenoxyethyl (meth)acrylate, and a coloring material.

[2]
The photocurable inkjet recording ink composition according to [1], wherein the content of the phenoxyethyl (meth)acrylate is 9 to 60% by mass based on the total mass of the ink composition.

[3]
The photocurable ink composition for ink jet recording according to [1] or [2], wherein the photopolymerization initiator contains an acylphosphine oxide compound in an amount of 7% by mass or more based on the total mass of the ink composition.

[4]
The photopolymerization ink composition according to [1] or [2], wherein the photopolymerization initiator contains an acylphosphine oxide compound in an amount of 7 to 15% by mass based on the total mass of the ink composition. ..

[5]
The photopolymerization ink composition according to [1] or [2], wherein the photopolymerization initiator contains an acylphosphine oxide compound in an amount of 10 to 15% by mass based on the total mass of the ink composition. ..

[6]
The photocurable ink jet recording ink composition according to any one of [1] to [5], wherein the vinyl ether group-containing (meth)acrylic acid ester is 2-(vinyloxyethoxy)ethyl (meth)acrylate. Stuff.

[7]
The photocurable type according to any one of [1] to [6], wherein the content of the vinyl ether group-containing (meth)acrylic acid ester is 10 to 60 mass% with respect to the total mass of the ink composition. An ink composition for inkjet recording.

[8]
The photocurable inkjet recording according to any one of [1] to [7], which is cured by being irradiated with ultraviolet rays having an emission peak wavelength in the range of 350 to 420 nm with an irradiation energy of 300 mJ/cm ² or less. Ink composition.

[9]
An ejection step of ejecting the photocurable inkjet recording ink composition according to any one of [1] to [8] onto a recording medium, and a photocurable inkjet recording ink composition ejected in the ejection step. And a curing step of curing the photocurable inkjet recording ink composition by irradiating the composition with ultraviolet light.

Hereinafter, modes for carrying out the present invention will be described in detail. The present invention is not limited to the following embodiments and can be variously modified and implemented within the scope of the gist.

In the present specification, “curing” means that when the ink containing a polymerizable compound is irradiated with radiation, the polymerizable compound is polymerized to solidify the ink. "Curable" refers to the property of curing in response to light. The "adhesion" means the property that the coating film does not easily peel off from the substrate. The “rubbing resistance” refers to a property that the cured product is unlikely to peel off from the recording medium when the cured product is scratched.

In the present specification, “(meth)acrylate” means at least one of acrylate and corresponding methacrylate, and “(meth)acrylic” means at least one of acrylic and corresponding methacrylic.

In the present specification, the “recorded material” refers to a material in which ink is recorded on a recording medium to form a cured material. The cured product in the present specification means a cured substance including a cured film or coating film of ink.

[Photocurable ink composition for inkjet recording]
The photocurable inkjet recording ink composition according to one embodiment of the present invention (hereinafter, also simply referred to as “ink composition”) contains a polymerizable compound 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)
(In the formula, 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. It is a base.)
The vinyl ether group-containing (meth)acrylic acid ester represented by, phenoxyethyl (meth)acrylate, and a coloring material are included.
Hereinafter, additives (components) contained in the ink composition of the present embodiment or that may be contained therein will be described.

[Polymerizable compound]
The polymerizable compound contained in the ink composition of the present embodiment can be polymerized at the time of irradiation with ultraviolet rays by the action of the photopolymerization initiator described later, and can cure the printed ink.

(Vinyl ether group-containing (meth)acrylic acid esters)
The vinyl ether group-containing (meth)acrylic acid esters, which are essential polymerizable compounds in the present embodiment, are represented by the above general formula (I).

When the ink composition contains the vinyl ether group-containing (meth)acrylic acid ester in combination with the phenoxyethyl (meth)acrylate described below, the ink can have a low viscosity, and the curability and abrasion resistance can be improved. The adhesiveness, the adhesiveness, and the solubility of the photopolymerization initiator can be excellent. Here, the reason why the solubility of the photopolymerization initiator is excellent is that the compatibility between the polymerizable compound and the additive such as the photopolymerization initiator is good.
Furthermore, rather than using a compound having a vinyl ether group and a compound having a (meth)acrylic acid ester group (a type of radically polymerizable group) separately, the vinyl ether group and the (meth)acrylic acid ester group in one molecule It is preferable to use the compound having both of them in order to further improve the curability of the ink.

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

In the above general formula (I), the monovalent organic residue having 1 to 11 carbon atoms represented by R ³ may be linear, branched or cyclic substituted having 1 to 10 carbon atoms. A good alkyl group and an optionally substituted aromatic group having 6 to 11 carbon atoms are preferable. Among these, an alkyl group having 1 to 2 carbon atoms such as a methyl group or an ethyl group, and an aromatic group having 6 to 8 carbon atoms such as a phenyl group and a benzyl group are preferably used.

When each of the above organic residues is a group which may be substituted, the substituent is divided into a group containing a carbon atom and a group containing no 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 containing no 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, 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-methacrylate 2-vinyloxypropyl, 2-vinyloxybutyl (meth)acrylate, 4-vinyloxycyclohexyl (meth)acrylate, 6-vinyloxyhexyl (meth)acrylate, 4-vinyloxymethylcyclohexylmethyl (meth)acrylate, 3-vinyloxymethylcyclohexylmethyl (meth)acrylate, 2-vinyloxymethylcyclohexylmethyl (meth)acrylate, p-vinyloxymethylphenylmethyl (meth)acrylate, m-vinyloxymethylphenyl (meth)acrylate Methyl, o-vinyloxymethylphenylmethyl (meth)acrylate, 2-(vinyloxyethoxy)ethyl (meth)acrylate, 2-(vinyloxyisopropoxy)ethyl (meth)acrylate, (meth)acrylic acid 2 -(Vinyloxyethoxy)propyl, 2-(vinyloxyethoxy)isopropyl (meth)acrylate, 2-(vinyloxyisopropoxy)propyl (meth)acrylate, 2-(vinyloxyisopropoxy) (meth)acrylate Isopropyl, 2-(vinyloxyethoxyethoxy)ethyl (meth)acrylate, 2-(vinyloxyethoxyisopropoxy)ethyl (meth)acrylate, 2-(vinyloxyisopropoxyethoxy)ethyl (meth)acrylate, 2-(vinyloxyisopropoxyisopropoxy)ethyl (meth)acrylate, 2-(vinyloxyethoxyethoxy)propyl (meth)acrylate, 2-(vinyloxyethoxyisopropoxy)propyl (meth)acrylate, (meth) 2-(vinyloxyisopropoxyethoxy)propyl acrylate, 2-(vinyloxyisopropoxyisopropoxy)propyl (meth)acrylate, 2-(vinylo)methacrylate Xyethoxyethoxy)isopropyl, (meth)acrylic acid 2-(vinyloxyethoxyisopropoxy)isopropyl, (meth)acrylic acid 2-(vinyloxyisopropoxyethoxy)isopropyl, (meth)acrylic acid 2-(vinyloxyisopropoxy) Isopropoxy)isopropyl, 2-(vinyloxyethoxyethoxyethoxyethoxy)ethyl (meth)acrylate, 2-(vinyloxyethoxyethoxyethoxyethoxy)ethyl (meth)acrylate, 2-(isopropenoxyethoxy)methacrylate ) Ethyl, 2-(isopropenoxyethoxyethoxy)ethoxy (meth)acrylate, 2-(isopropenoxyethoxyethoxyethoxy)ethyl (meth)acrylate, 2-(isopropenoxyethoxyethoxyethoxy) (meth)acrylate Examples include ethoxy)ethyl, polyethylene glycol monovinyl ether (meth)acrylate, and polypropylene glycol monovinyl ether (meth)acrylate.

Among these, when used in combination with phenoxyethyl (meth)acrylate described below, the ink can have a lower viscosity, has a high flash point, and is more excellent in curability of the ink, and therefore (meth)acrylic acid 2-( Vinyloxyethoxy)ethyl, that is, at least one of 2-(vinyloxyethoxy)ethyl acrylate and 2-(vinyloxyethoxy)ethyl methacrylate is preferable, and 2-(vinyloxyethoxy)ethyl acrylate is more preferable. .. In particular, 2-(vinyloxyethoxy)ethyl acrylate and 2-(vinyloxyethoxy)ethyl methacrylate each have a simple structure and a small molecular weight, so that the viscosity of the ink can be further 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. Note that 2-(vinyloxyethoxy)ethyl acrylate is superior in curability to 2-(vinyloxyethoxy)ethyl methacrylate.

The vinyl ether group-containing (meth)acrylic acid esters may be used alone or in combination of two or more.

The content of the vinyl ether group-containing (meth)acrylic acid ester is preferably 10 to 60% by mass with respect to the total mass (100% by mass) of the ink composition in order to further improve curability. In order to further improve the abrasion resistance and the adhesiveness in addition to the curability, the content is more preferably 10 to 30% by mass, further preferably 20 to 30% by mass. On the other hand, when the ink composition is particularly excellent in curability, it is more preferably 20 to 60% by mass, and further preferably 30 to 60% by mass.

The method for producing the vinyl ether group-containing (meth)acrylic acid ester is not limited to the following, but is a method for esterifying (meth)acrylic acid and a hydroxyl group-containing vinyl ether (production method B), (meth)acrylic acid halide. With a hydroxyl group-containing vinyl ether (Production Method C), with a (meth)acrylic acid anhydride with a hydroxyl group-containing vinyl ether (Production Method D), with a (meth)acrylic acid ester and a hydroxyl group-containing vinyl ether Exchange method (Production method E), Method of esterifying (meth)acrylic acid with halogen-containing vinyl ether (Production method F), Method of esterifying alkali (earth) metal salt of (meth)acrylic acid with halogen-containing vinyl ether (Production method G), a method of vinyl-exchange a hydroxyl group-containing (meth)acrylic acid ester with vinyl carboxylate (production method H), and a method of ether-exchange a hydroxyl group-containing (meth)acrylic acid ester with an alkyl vinyl ether (production method I). Can be mentioned.

Among these, the manufacturing method E is preferable because the desired effect of the present embodiment can be further exerted.

(Phenoxyethyl (meth)acrylate)
The ink composition of the present embodiment contains phenoxyethyl (meth)acrylate as a polymerizable compound. When the ink composition contains phenoxyethyl (meth)acrylate in addition to the vinyl ether group-containing (meth)acrylic acid ester as a polymerizable compound, the ink can have a low viscosity and is curable. , The abrasion resistance, the adhesiveness, and the solubility of the photopolymerization initiator can be excellent.

The content of phenoxyethyl (meth)acrylate is preferably 9 to 60% by mass and 10 to 50% by mass in order to further improve the curability with respect to the total mass (100% by mass) of the ink composition. %, more preferably 10 to 40% by mass. When the content is at least the above lower limit value (particularly 10% by mass), the solubility of the photopolymerization initiator will be further excellent in addition to the curability. On the other hand, when the content is less than or equal to the above upper limit value (particularly 50% by mass), the adhesiveness becomes further excellent in addition to the curability.

(Monofunctional (meth)acrylate)
The ink composition of the present embodiment may further include a monofunctional (meth)acrylate (excluding phenoxyethyl (meth)acrylate) as a polymerizable compound. The monofunctional (meth)acrylate is not limited to the following, and examples thereof include isoamyl (meth)acrylate, stearyl (meth)acrylate, lauryl (meth)acrylate, octyl (meth)acrylate, decyl (meth)acrylate, 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, 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, benzyl (meth)acrylate, ethoxylated nonylphenyl (meth)acrylate, alkoxylated nonylphenyl (meth)acrylate, and p-cumylphenol EO-modified (meth)acrylate. ..

The monofunctional (meth)acrylates may be used alone or in combination of two or more.

The monofunctional (meth)acrylate is preferably contained in the ink composition within a range that does not impair the desired effects of the present embodiment. The content of the monofunctional (meth)acrylate is preferably 50% by mass or less based on the total mass (100% by mass) of the ink composition.

(Polyfunctional (meth)acrylate)
The ink composition of this embodiment may further contain a polyfunctional (meth)acrylate as a polymerizable compound. Among the polyfunctional (meth)acrylates, the bifunctional (meth)acrylates (excluding the above-mentioned predetermined vinyl ether group-containing (meth)acrylic acid esters) are not limited to the following, but include, for example, triethylene glycol. Di(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, dimethylol tricyclodecane di (Meth)acrylate, EO (ethylene oxide) adduct of bisphenol A di(meth)acrylate, PO (propylene oxide) adduct of bisphenol A di(meth)acrylate, hydroxypivalic acid neopentyl glycol di(meth)acrylate, and Examples include polytetramethylene glycol di(meth)acrylate. Among these, at least one of dipropylene glycol diacrylate and tripropylene glycol diacrylate is preferable because the curability is fast and the viscosity of the ink can be easily reduced.

Of the polyfunctional (meth)acrylates, the tri- or higher functional (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.

The polyfunctional (meth)acrylate may be used alone or in combination of two or more.

The polyfunctional (meth)acrylate may be contained in the ink composition within a range that does not impair the desired effects in the present embodiment. The content of the polyfunctional (meth)acrylate is preferably 40% by mass or less based on the total mass (100% by mass) of the ink composition.
When the content of the polyfunctional (meth)acrylate is within the above range, it is possible to prevent the viscosity of the ink from increasing and to secure good flexibility of the recorded matter.

(Polymerizable compounds other than the above)
In addition to the above 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 compound"). 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, and Included are saturated polyethers, unsaturated polyamides, and unsaturated urethanes. Examples of the above-mentioned oligomer include oligomers formed from the above-mentioned monomers.

The other polymerizable compounds may be used alone or in combination of two or more.

Other polymerizable compounds may be included in the ink composition as long as the desired effects of the present embodiment are not impaired. The content of the other polymerizable compound is preferably 10% by mass or less based on 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 for curing the ink existing on the surface of the recording medium by photopolymerization by irradiation of ultraviolet rays to form a print. By using ultraviolet rays (UV) among 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 light) and initiates the polymerization of the above-mentioned polymerizable compound, but a photoradical polymerization initiator or a photocationic polymerization initiator is used. It can be used, and it is preferable to use a photoradical polymerization initiator.

Examples of the above-mentioned radical photopolymerization initiator include aromatic ketones, acylphosphine oxide compounds, aromatic onium salt compounds, organic peroxides, thio compounds (thioxanthone compounds, thiophenyl group-containing compounds, etc.), and hexaarylbi compounds. Examples thereof include an imidazole compound, a ketoxime ester compound, a borate compound, an azinium compound, a metallocene compound, an active ester compound, a compound having a carbon-halogen bond, and an alkylamine compound.

Among these, it is particularly preferable to use at least one of an acylphosphine oxide compound and a thioxanthone compound, and it is more preferable to use an acylphosphine oxide compound, because the curability of the ink can be further improved. It is more preferable to use an acylphosphine oxide compound and a thioxanthone compound in combination.

Specific examples of the photoradical 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, benzoinpropyl ether, benzoinethyl ether, benzyldimethylketal, 1-(4-isopropylphenyl )-2-Hydroxy-2-methylpropan-1-one, 2-hydroxy-2-methyl-1-phenylpropan-1-one, thioxanthone, diethylthioxanthone, 2-isopropylthioxanthone, 2-chlorothioxanthone, 2-methyl -1-[4-(methylthio)phenyl]-2-morpholino-propan-1-one, bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide, 2,4,6-trimethylbenzoyl-diphenyl- Examples include phosphine oxide, 2,4-diethylthioxanthone, and bis-(2,6-dimethoxybenzoyl)-2,4,4-trimethylpentylphosphine oxide.

Examples of commercially available photoradical 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-morpholinopropan-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-cyclopentadiene-1-yl) -Bis(2,6-difluoro-3-(1H-pyrrol-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 (mixture of oxyphenylacetic acid, 2-[2-oxo-2-phenylacetoxyethoxy]ethyl ester and oxyphenylacetic acid, 2-(2-hydroxyethoxy)ethyl ester) (above, trade name manufactured by BASF), KAYACURE DETX-S (2,4-diethylthioxanthone) (trade name of Nippon Kayaku Co., Ltd.), Speedcure TPO (2,4,6-trimethylbenzoyl-diphenyl-phosphine oxide), Speedcure DETX (2,4-diethylthioxanthen-9-one) (above, trade name by Lambson), Lucirin TPO, LR8893, LR8970 ( As described above, BASF product name), Yubecryl P36 (UCB product name) and the like can be mentioned.

The photopolymerization initiators may be used alone or in combination of two or more.

The content of the photopolymerization initiator can improve the ultraviolet curing rate and make the curability excellent, and to avoid undissolved photopolymerization initiator or coloring derived from the photopolymerization initiator, It is preferably 8 to 20% by mass based on the total mass (100% by mass) of the ink composition.

In particular, when the photopolymerization initiator contains an acylphosphine oxide compound, its content is preferably 7% by mass or more, and 7 to 15% by mass based on the total mass (100% by mass) of the ink composition. %, more preferably 10 to 15% by mass, particularly preferably 10 to 14% by mass. When the content is at least the above lower limit value (particularly 10% by mass), the curability is further excellent. More specifically, the curability is further excellent because a sufficient curing rate can be obtained particularly when curing with an LED (preferable emission peak wavelength: 350 nm to 420 nm). On the other hand, when the content is not more than the upper limit value (particularly 14% by mass), the solubility of the photopolymerization initiator is further excellent.

When the content of the acylphosphine oxide compound is within the above range, the acylphosphine oxide compound is preferably 4% by mass or more, and more preferably 100% by mass with respect to the total mass (100% by mass) of the ink composition. Preferably contains 6% by mass or more of a bisacylphosphine oxide compound. When the bisacylphosphine oxide compound is contained in the above lower limit value (particularly 6% by mass) or more, the curability is further improved. Furthermore, the upper limit of the content of the bisacylphosphine oxide compound is preferably 10% by mass or less with respect to the total mass (100% by mass) of the ink composition because the solubility of the initiator is further excellent. It is more preferably 8% by mass or less.

When the content of the acylphosphine oxide compound is in the above range, the acylphosphine oxide compound is preferably 53% by mass or more based on the total mass (100% by mass) of the acylphosphine oxide compound, More preferably, it contains 55% by mass or more of a bisacylphosphine oxide compound. When the bisacylphosphine oxide compound is contained in the above lower limit value (particularly 55% by mass) or more, the curability is further improved. Furthermore, the upper limit of the content of the bisacylphosphine oxide compound is 90% by mass or less with respect to the total mass (100% by mass) of the acylphosphine oxide compound because the solubility of the initiator is further excellent. It is preferably 80% by mass or less.

Examples of the bisacylphosphine oxide compound include, but are not limited to, bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide and bis-(2,6-dimethoxybenzoyl)-2,4. 4-trimethylpentylphosphine oxide can be mentioned. On the other hand, examples of the acylphosphine oxide compound other than the bisacylphosphine oxide compound include, but are not limited to, monoacylphosphine oxide compounds. The monoacylphosphine oxide compound includes, but is not limited to, for example, 2,4,6-trimethylbenzoyl-diphenyl-phosphine oxide.

When the content of phenoxyethyl (meth)acrylate is within the above-mentioned preferable range, the solubility of the acylphosphine oxide compound is further improved, so that the content of the acylphosphine oxide compound is set within the above-mentioned preferable range. can do. Thus, there is a correlation between the content of phenoxyethyl (meth)acrylate and the content of the acylphosphine oxide compound.

When the photopolymerization initiator contains a thioxanthone compound, its content is preferably 1 to 5 mass% with respect to the total mass (100 mass%) of the ink composition.

[Coloring material]
The ink composition of the present embodiment further contains a coloring material. At least one of a pigment and a dye can be used as the coloring material. Pigments are preferred because of their excellent light resistance.

(Pigment)
In this embodiment, the light resistance of the ink composition can be improved by using a pigment as the coloring material. As the pigment, both an inorganic pigment and an organic pigment can be used.

As the inorganic pigment, carbon black (CI pigment black 7) such as furnace black, lamp black, acetylene black and channel black, iron oxide and titanium oxide can be used.

Examples of organic pigments include azo pigments such as insoluble azo pigments, condensed azo pigments, azo lakes, chelate azo pigments, phthalocyanine pigments, perylene and perinone pigments, anthraquinone pigments, quinacridone pigments, dioxane pigments, thioindigo pigments, isoindolinone pigments, and quinophthalone pigments. Polycyclic pigments, dye chelates (for example, basic dye chelates, acid dye chelates, etc.), dye lakes (basic dye lakes, acid dye lakes), nitro pigments, nitroso pigments, aniline black, daylight Examples include fluorescent pigments.

More specifically, as carbon black used as a black ink, No. 2300, No. 900, MCF88, No. 33, No. 40, No. 45, No. 52, MA7, MA8, MA100, No. 52. 2200B etc. (above, trade name manufactured by Mitsubishi Chemical Corporation), Raven 5750, Raven 5250, Raven 5000, Raven 3500, Raven 1255, Raven 700 etc. (above, trade name manufactured by Columbia Carbon Co.). , Regal 1 400R, Regal 1 330R, Regal 1 660R, Mogul L, Monarch 700, Monarch 800, Monarch 880, Monarch 900, Monarch 1000, Monarch 1100, Monarch 1300, Monarch 1400, Monarch 1400 CA. Name), Color Black FW1, Color Black FW2, Color Black FW2V, Color Black FW18, Color Black FW200, Color B1ack ri Puri Spl, Color Black SFW, Color Black FW2, Color Black FW2, Color Black FW2, Color Black FW200 , Special Black 5, Special Black 4A, Special Black 4 and the like (these are trade names manufactured by Degussa).

Examples of pigments used in white ink include C.I. I. Pigment White 6, 18, 21.

Examples of pigments used in yellow ink include C.I. I. Pigment Yellow 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.

Examples of pigments used in magenta ink include C.I. I. Pigment Red 1,2,3,4,5,6,7,8,9,10,11,12,14,15,16,17,18,19,21,22,23,30,31,32, 37, 38, 40, 41, 42, 48 (Ca), 48 (Mn), 57 (Ca), 57:1, 88, 112, 114, 122, 123, 144, 146, 149, 150, 166, 168 , 170, 171, 175, 176, 177, 178, 179, 184, 185, 187, 202, 209, 219, 224, 245, or C.I. I. Pigment Violet 19, 23, 32, 33, 36, 38, 43, 50.

Pigments used for cyan ink include C.I. I. Pigment Blue 1, 2, 3, 15, 15:1, 15:2, 15:3, 15:34, 15:4, 16, 18, 22, 25, 60, 65, 66, or C.I. I. Butt Blue 4,60 can be mentioned.

Examples of pigments other than magenta, cyan, and yellow include C.I. I. Pigment Green 7, 10, or C.I. I. Pigment Brown 3, 5, 25, 26, or C.I. I. Pigment Orange 1, 2, 5, 7, 13, 14, 15, 16, 24, 34, 36, 38, 40, 43, 63.

The above pigments may be used alone or in combination of two or more.

(dye)
In this embodiment, a dye can be used as the coloring material. The dye is not particularly limited, and an acid dye, a direct dye, a reactive dye, and a basic dye can be used. Examples of the dye include C.I. I. Acid Yellow 17, 23, 42, 44, 79, 142, C.I. I. Acid Red 52, 80, 82, 249, 254, 289, C.I. I. Acid Blue 9,45,249, C.I. I. Acid Black 1, 2, 24, 94, C.I. I. Food Black 1, 2, C.I. I. Direct Yellow 1, 12, 24, 33, 50, 55, 58, 86, 132, 142, 144, 173, C.I. I. Direct Red 1,4,9,80,81,225,227, C.I. I. Direct Blue 1, 2, 15, 71, 86, 87, 98, 165, 199, 202, C.I. I. Dilectd Black 19, 38, 51, 71, 154, 168, 171, 195, C.I. I. Reactive Red 14, 32, 55, 79, 249, C.I. I. Reactive Black 3, 4, 35 can be mentioned.

The above dyes may be used alone or in combination of two or more.

The content of the coloring material is 1 to 20 relative to the total mass (100% by mass) of the ink composition, since it has good coloring properties and can reduce the inhibition of curing of the coating film due to light absorption of the coloring material itself. Mass% is preferred. The photocurable ink composition containing a color material has poorer curability and inferior adhesiveness and scratch resistance of the recorded matter as compared with the ink composition containing no color material. The composition can be an ink composition that is excellent in curability, adhesion, and abrasion resistance and can be used for recording an image.

[Dispersant]
When the ink composition of the present embodiment contains a pigment, it may further contain a dispersant in order to improve the pigment dispersibility. The dispersant is not particularly limited, and examples thereof include a dispersant that is commonly used for preparing a pigment dispersion liquid such as a polymer dispersant. Specific examples thereof 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. Examples of the resin include those containing one or more main components. As commercial products of polymer dispersants, Ajinomoto Fine Techno Co., Ltd., Azisper series (trade name), Solspers series (Solsperse 32000, 36000, etc. available from Avecia Co.) (above, trade name)) , Dispersion series (trade name) manufactured by BYK Chemie, and Disparon series (trade name) manufactured by Kusumoto Kasei.

The dispersants may be used alone or in combination of two or more. The content of the dispersant is not particularly limited, and a suitable amount may be added.

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

The polymerization inhibitor is not particularly limited, and examples thereof include a phenolic polymerization inhibitor. Examples of the phenolic polymerization inhibitor include, but are not limited to, 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-t-butylphenol).

Examples of commercially available phenolic polymerization inhibitors include p-methoxyphenol (trade name of 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-t-butylphenol)), BHT Swanox (Seiko Chemical Co., Ltd. trade name, 2,6-di-t) -Butyl-4-methylphenol).

The polymerization inhibitors may be used alone or in combination of two or more. The content of the polymerization inhibitor is not particularly limited, and a suitable amount may be added as appropriate.

[Slip agent]
The ink composition of the present embodiment may further contain a slip agent (surfactant). The slip agent is not particularly limited, but for example, as the silicone-based surfactant, polyester-modified silicone or polyether-modified silicone can be used, and particularly polyether-modified polydimethylsiloxane or polyester-modified polydimethylsiloxane can be used. preferable. Examples of commercially available slip agents include BYK-347, BYK-348, BYK-UV3500, 3510, 3530, and 3570 (all manufactured by BYK).
The slip agent may be used alone or in combination of two or more. The content of the slip agent is not particularly limited, and a suitable amount may be added as appropriate.

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

[Characteristics of photocurable ink jet recording ink composition]
The viscosity of the above ink composition at 25° C. is preferably less than 35 mPa·s, and 25 mPa·s or less, in order to improve the ejection stability of the ink and further improve the curability of the ink. More preferable.

The ink composition is preferably one that is cured by irradiation with ultraviolet rays having an emission peak wavelength in the range of 350 to 420 nm. If the ink composition of the present embodiment is curable at an emission peak wavelength within the above range, it is possible to cure at low energy and high speed due to the composition of the ink composition. In particular, curability with low energy leads to the use of a light emitting diode (LED), which has been attracting attention in recent years from the viewpoint of the environment, as an ultraviolet ray irradiation source, and is therefore preferable. That is, the ink composition of the present embodiment has excellent curability by LEDs.

Further, an ink composition which is cured by irradiation energy of ultraviolet rays of 300 mJ/cm ² or less is preferable, and an ink composition which is cured by irradiation energy of ultraviolet rays of 200 mJ/cm ² or less is more preferable. An image can be formed at low cost by using such an ink composition. The irradiation energy is calculated by multiplying the irradiation time by the irradiation intensity.

As described above, according to the present embodiment, light having excellent curability, low viscosity, and excellent adhesiveness and abrasion resistance of an image (cured product) and solubility of a photopolymerization initiator is also used. A curable ink jet recording ink composition can be provided.

[Recording medium]
The ink composition of the present embodiment is ejected onto a recording medium by an inkjet recording method described later to obtain a recorded matter. Examples of this recording medium include an absorptive or non-absorptive recording medium. The inkjet recording method of the embodiment described later is widely applied to recording media having various absorption performances, from non-absorbent recording media in which water-based ink is difficult to penetrate to absorbent recording media in which water-based ink is easily penetrated. Applicable. However, when the above ink composition is applied to a non-absorptive recording medium, it may be necessary to provide a drying step after irradiating with ultraviolet rays to cure.

The absorptive recording medium is not particularly limited, but for example, plain paper such as electrophotographic paper having high permeability of water-based ink, inkjet paper (ink absorbing layer composed of silica particles or alumina particles, or polyvinyl alcohol). (PVA), polyvinylpyrrolidone (PVP) or other ink-jet paper provided with an ink absorption layer composed of a hydrophilic polymer), water-based ink has relatively low penetrability, general art paper used for offset printing, coat Examples include paper and cast paper.

The non-absorbent recording medium is not particularly limited, and examples thereof include films, sheets, and plates of plastics such as polyvinyl chloride (PVC), polyethylene, polypropylene, polyethylene terephthalate (PET), iron, silver, copper, Examples thereof include plates of metals such as aluminum, metal plates produced by vapor deposition of these various metals, films made of plastic, plates of alloys such as stainless steel and brass.

[Inkjet recording method]
One embodiment of the present invention relates to an inkjet recording method. The photocurable inkjet recording ink composition of the above embodiment can be suitably used in the inkjet recording method of the present embodiment. The inkjet recording method includes an ejection step of ejecting the ink composition onto a recording medium, and a curing step of irradiating the ink composition ejected in the ejection step with ultraviolet rays to cure the ink composition. ,including. In this way, the ink composition cured on the recording medium forms an image, that is, a coating film (cured film) of the ink. Another embodiment of the present invention is the photocurable ink jet recording ink composition according to the above-described embodiment of the present invention, which is used in the ink jet recording method according to one embodiment of the present invention. Here, the photocurable ink jet recording ink composition according to the embodiment of the present invention used in the ink jet recording method according to the embodiment of the present invention performs recording by the ink jet recording method according to the embodiment of the present invention. The photocurable ink composition for inkjet recording, which is an embodiment of the present invention, is sold for a recording apparatus.

[Discharging process]
In the discharging step, the ink composition is discharged onto the recording medium, and the ink composition adheres to the recording medium. The viscosity of the ink composition at the time of ejection is preferably 3 to 20 mPa·s. If the viscosity of the ink composition is as described above when the temperature of the ink composition is room temperature or when the ink composition is not heated, the temperature of the ink composition is room temperature or the ink composition is not heated. May be discharged. At that time, the temperature of the ink during ejection is preferably 20 to 30°C. On the other hand, the ink composition may be heated to a predetermined temperature to be ejected with a preferable viscosity. In this way, good ejection stability is achieved.

The photocurable ink composition for ink jet recording of the present embodiment has a higher viscosity than a normal water-based ink composition, and thus the viscosity changes greatly due to temperature changes during ejection. Such fluctuations in the viscosity of the ink have a great influence on the change in the droplet size and the change in the droplet ejection speed, which can lead to deterioration in image quality. 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 attached 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 of ultraviolet rays to generate a starting species such as a radical, an acid, and a base, and the polymerization reaction of the polymerizable compound depends on the function of the starting species. This is because it is promoted. Alternatively, it is because the polymerization reaction of the polymerizable compound is started by the irradiation of ultraviolet rays. At this time, when the 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 decomposes by contact with the photopolymerization initiator. Can be accelerated and a more sensitive curing reaction can be achieved.

A mercury lamp, a gas/solid laser, etc. are mainly used as an ultraviolet ray source, and a mercury lamp and a metal halide lamp are widely known as a light source used for curing a photocurable ink jet recording ink composition. There is. On the other hand, from the viewpoint of environmental protection, there is a strong demand for mercury-free materials at present, and the replacement with a GaN-based semiconductor ultraviolet light-emitting device is industrially and environmentally very useful. Further, the ultraviolet light emitting diode (UV-LED) and the ultraviolet laser diode (UV-LD) have small size, long life, high efficiency, and low cost, and are expected as a light source for photocurable inkjet. Among these, UV-LED is preferable.

Here, since it is easy to increase the output of the LED, a UV-LED having a peak emission wavelength in the range of 350 to 420 nm is preferably used, and photocurable ink jet recording capable of being cured with irradiation energy of preferably 300 mJ/cm ² or less. It is preferable to use the ink composition for inkjet in an inkjet recording method. In this case, low cost printing and high printing speed can be realized. Such an ink composition is obtained by containing at least one of a photopolymerization initiator that decomposes by irradiation with ultraviolet rays in the above wavelength range and a polymerizable compound that initiates polymerization by irradiation with ultraviolet rays in the above wavelength range.
As for the irradiation intensity of the LED, it is preferable to perform curing using a UV-LED having a peak intensity of 800 mW/cm ² or more, and it is more preferable that the peak intensity is 800 to 2000 mW/cm ² . In this case, the curability of the ink composition can be further improved, and the appearance of the recorded matter can be improved.

As described above, according to the present embodiment, photocuring that is excellent in curability, has a low viscosity, and is excellent in adhesion and abrasion resistance of an image (cured product) and solubility of a photopolymerization initiator. It is possible to provide a suitable inkjet recording method using the inkjet recording ink composition.

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

[Used ingredients]
The components used in the following Examples and Comparative Examples are as follows.

[Pigment]
IRGALITE BLUE GLVO (cyan pigment (CI Pigment Blue 15:4), trade name of BASF, abbreviated as "BLUE GLVO" below)

[Dispersant]
Solsperse 32000 (trade name 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., abbreviated as "VEEA" below.)
In the table, vinyl ether group-containing (meth)acrylic acid esters are described as “acrylic/vinyl-containing monomer”.

[Monofunctional (meth)acrylate]
-Biscoat #192 (phenoxyethyl acrylate, trade name of OSAKA ORGANIC CHEMICAL INDUSTRY LTD., abbreviated as "PEA" below)
IBXA (isobornyl acrylate, trade name of Osaka Organic Chemical Company, abbreviated as "IBXA" below)

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

[Photopolymerization initiator]
-IRGACURE 819 (trade name by BASF, solid content 100%, abbreviated as "819" below).
-Speedcure TPO (trade name by Lambson, solid content 100%, abbreviated as "TPO" below)
-Speedcure DETX (trade name by Lambson, solid content 100%, abbreviated as "DETX" below).

[Polymerization inhibitor]
-P-Methoxyphenol (trade name of Tokyo Chemical Industry Co., Ltd., p-methoxyphenol, abbreviated as "MEHQ" below).

[Slip agent]
BYK-UV3500 (trade name of BYK, abbreviated as "UV3500" below)

[Examples 1 to 16 and Comparative Examples 1 to 6]
[Preparation of pigment dispersion]
Prior to the preparation of the ink composition, a pigment dispersion liquid was prepared. The pigment, the dispersant, and the polymerizable compound described in the "Dispersion liquid-derived monomer" column in Tables 1 and 2 below are mixed so as to have the composition (unit: mass%) described in Tables 1 and 2 below. Stir with a stirrer for 1 hour. The mixed liquid after stirring was dispersed by a bead mill to obtain a pigment dispersion liquid. The dispersion conditions were such that zirconia beads having a diameter of 0.65 mm were filled at a filling rate of 70%, the peripheral speed was 9 m/s, and the dispersion time was 2 to 4 hours.

[Preparation of ink composition]
The components shown in Tables 1 and 2 below are added and mixed so as to have the composition (unit: mass%) shown in Tables 1 and 2 (in Tables 1 and 2, the pigment, the dispersant, and the “dispersion”). The polymerizable compound described in the section of "Liquid-derived monomer" was added as the above pigment dispersion liquid.), and a cyan photocurable ink jet recording ink composition was prepared by stirring this with a high-speed water-cooled stirrer. did.

[Evaluation item]
With respect to the photocurable ink compositions for inkjet recording prepared in Examples and Comparative Examples, the viscosity, the solubility of the photopolymerization initiator, the curability, the adhesion, and the abrasion resistance were evaluated by the following methods.

(1. viscosity)
The viscosities of the ink compositions of Examples and Comparative Examples were measured using a DVM-E type rotational viscometer (manufactured by TOKYO KEIKI INC) at a temperature of 25° C. and a rotation 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 35 mPa·s,
C: 35 mPa·s or more.

(2. Solubility of photopolymerization initiator)
An ink composition without a pigment was prepared in the same manner as in each of the above Examples and Comparative Examples using components other than the pigment and the pigment dispersant, and sufficiently stirred to prepare each ink composition. Then, it was visually observed whether the photopolymerization initiator remained undissolved. Then, the ink composition having no undissolved photopolymerization initiator was placed in a constant temperature bath at 0° C., taken out 24 hours later, and returned to room temperature, and then whether or not the photopolymerization initiator was precipitated was visually observed again. I observed.
The evaluation criteria are as follows. The evaluation results are shown in Tables 3 and 4 below. The evaluation name in Tables 3 and 4 is abbreviated as "initiator solubility".
A: No undissolved residue or precipitation of the photopolymerization initiator was observed both after stirring at room temperature and after storage at 0°C.
B: The photopolymerization initiator did not remain undissolved after stirring at room temperature, but precipitation of the photopolymerization initiator was observed after storage at 0°C.
C: Undissolved photopolymerization initiator was observed after stirring at room temperature.

(3. curability)
An ink jet recording apparatus equipped with a piezo type ink jet nozzle was used to fill each nozzle array with the ink composition of each of the examples and comparative examples. A solid pattern image (printed matter) having a film thickness of 10 μm is formed on a PVC sheet (Frontlite Grossy 120 g [trade name], manufactured by Cooley Co.) 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 ejectability of each ink composition was good. At the same time, from the UV-LED in the ultraviolet irradiation device mounted on the side of the carriage, the ultraviolet light having the irradiation intensity of 1 W/cm ² and the peak wavelength of 395 nm was irradiated under the condition of 100 mJ/cm ² per pass. , The number of passes was added until it became tack free, and the solid pattern image was cured. As described above, a recorded matter in which a solid pattern image was printed on the PVC sheet was produced.
The “solid pattern image” is an image in which dots are recorded on all the pixels that are the minimum recording unit area defined by the recording resolution. Further, the "pass number" means the number of times that the head moves with respect to the recorded matter and ultraviolet rays are irradiated toward the coating film from the ultraviolet irradiation device mounted on the head. The irradiation energy [mJ/cm ² ] was obtained by measuring the irradiation intensity [mW/cm ² ] on the surface to be irradiated by the light source, and calculating the product of this 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.).
Here, the curability of the coating film was evaluated using the irradiation energy when tack-free as an index. Here, whether or not it can be said to be tack-free was judged under the following conditions. That is, it is judged whether or not the ink adheres to the swab, or whether or not the ink cured product on the recording medium is scratched, the ink does not adhere to the swab, and the ink cured product on the recording medium The case where no scratches were attached was made tack-free. The cotton swab used at that time was a Johnson swab manufactured by Johnson & Johnson. The number of times of rubbing was 10 reciprocations, and the rubbing strength was 100 g load.
The evaluation criteria are as follows. The evaluation results are shown in Tables 3 and 4 below.
A: 200 mJ/cm ² or less,
B: more than 200 mJ/cm ^{2 and} 300 mJ/cm ² or less,
C: more than 300 mJ/cm ² .

(4. Adhesion)
In the above “3. Curability” test, a recorded matter was used which was cured by being irradiated with ultraviolet rays until it became tack-free. According to JIS K-5600-5-6 (ISO2409) (Paint General Test Method-Part 5: Mechanical Properties of Coating Film-Section 6: Adhesion (Cross Cut Method)), the coating surface of the recorded material Then, cross-cut was performed, and the adhesion was evaluated based on the following ranks A to E from the results of the peeling test using the cellophane tape. Here, the cross-cut method will be described.
As a cutting tool, a single-blade cutting tool (generally commercially available cutter) and a guide for cutting at equal intervals using the single-blading cutting tool were prepared.
First, the blade of a cutting tool was applied so as to be perpendicular to the coating film, and six cuts were made in the recorded material. After making these 6 cuts, the direction was changed by 90°, and 6 more cuts were made so as to be orthogonal to the cuts already made.
Next, take out the transparent adhesive tape (width 25 ± 1 mm) to a length of about 75 mm, attach the tape to the grid-cut portion formed on the coating film, and put your finger on it so that the coating film can be seen through. I rubbed the tape with. Then, within 5 minutes after the adhesion, the film was reliably separated at an angle close to 60° in 0.5 to 1.0 seconds.
The evaluation criteria are as follows. The value of each rank is a value obtained by calculating the peel rate, and rounded to the first decimal place. The evaluation results are shown in Tables 3 and 4 below.
A: peeling rate 0 to 5%,
B: peeling rate 6 to 15%,
C: peeling rate 16-35%,
D: peeling rate 36 to 65%,
E: Stripping rate 66 to 100%.

(5. abrasion resistance)
In accordance with JIS K5701 (ISO 11628) (regarding the method for testing inks, color-developed samples, and printed matter used for lithographic printing), the Gakushin-type friction fastness tester (TESTER SANGYO CO., LTD.)) was used to evaluate the abrasion resistance. The evaluation method was carried out by placing a gold cloth on the surface of the recorded matter obtained in the above “3. Curing” test, rubbing it with a load of 500 g, and visually observing peeling of the cured surface of the recorded matter after rubbing. Compared.
The evaluation criteria are as follows. The evaluation results are shown in Tables 3 and 4 below.
A: There was no stain on the gold width, and there was no peeling or scratch on the recording surface.
B: The gold width was dirty and the recording surface was not peeled or scratched.
C: The width of the gold was dirty, and some peeling and scratches on the recording surface were seen in a linear shape.
D: The width of the gold was stained, and peeling and scratches on the recording surface were observed on the surface.

From the above results, photocuring containing a polymerizable compound containing a vinyl ether group-containing (meth)acrylic acid ester represented by the general formula (I) and phenoxyethyl (meth)acrylate, and a photopolymerization initiator Type ink jet recording ink compositions (each example) have excellent curability, lower viscosity, and solubility of the photopolymerization initiator as compared with the other ink compositions (each comparative example). It was also found that the adhesiveness and the abrasion resistance were excellent. Further, Comparative Examples 5 and 6 are ink compositions obtained by removing the coloring material and the dispersant from the ink compositions of Comparative Examples 2 and 4, respectively, but the curability is good, and Comparative Examples 2 and 4 respectively. Although the adhesion and abrasion resistance were improved by comparison, it was an ink composition containing no coloring material and could not be used for recording an image. Further, although not shown in the table, the irradiation energy per one pass was made the same as that of the above example by setting the irradiation intensity of the UV-LED to 500 mW/cm ² and lengthening the irradiation time per one pass. When the curability was evaluated under the same conditions as in Example 1 except for the above, the curability evaluation was B, and wrinkles were observed on the surface of the solid pattern.

Claims (11)

A photocurable ink composition for ink jet recording, comprising a polymerizable compound, a photopolymerization initiator, and a pigment as a coloring material,
The polymerizable compound has the following general formula (I):
_{^{CH 2 = CR 1 -COOR 2 -O}} -CH = CH-R 3 ··· (I)
(In the formula, 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. It is a base.)
A vinyl ether group-containing (meth)acrylic acid ester represented by, phenoxyethyl (meth)acrylate, and a polyfunctional (meth)acrylate,
The content of the vinyl ether group-containing (meth)acrylic acid ester is 10 to 30 mass% with respect to the total mass of the ink composition,
The content of the phenoxyethyl (meth)acrylate is 9% by mass or more and 40 % by mass or less based on the total mass of the ink composition,
The photocurable inkjet recording ink composition, wherein the content of the polyfunctional (meth)acrylate is 40% by mass or less based on the total mass of the ink composition. The photocurable ink composition for ink jet recording according to claim 1, wherein the photopolymerization initiator contains 7% by mass or more of an acylphosphine oxide compound with respect to the total mass of the ink composition. The photocurable ink composition for inkjet recording according to claim 1, wherein the photopolymerization initiator contains 4% by mass or more of a bisacylphosphine oxide compound with respect to the total mass of the ink composition. The photocurable ink jet recording according to claim 1, wherein the photopolymerization initiator contains 53% by mass or more of a bisacylphosphine oxide compound with respect to the total mass of the acylphosphine oxide compound. Ink composition. The photocurable ink jet recording ink composition according to any one of claims 1 to 4, wherein the vinyl ether group-containing (meth)acrylic acid ester is 2-(vinyloxyethoxy)ethyl (meth)acrylate. Stuff. Ultraviolet emission peak wavelength is in the range of 350~420nm is cured by being irradiated with 300 mJ / cm ² or less in the irradiation energy, light curable ink jet recording according to any one of claims 1 to 5 Ink composition. The polyfunctional (meth) acrylate containing at based on the total weight of the ink composition 10.0 wt% or more, the light-curable ink composition for inkjet recording according to any one of claims 1-6. The polyfunctional (meth) containing bifunctional (meth) acrylate as photocurable ink composition for ink jet recording according to any one of claims 1-7. The photocurable ink jet recording ink composition according to claim 8 , wherein the bifunctional (meth)acrylate contains at least one of dipropylene glycol diacrylate and tripropylene glycol diacrylate. The photocurable ink jet recording ink composition according to claim 8 or 9 , wherein the content of the bifunctional (meth)acrylate is 10% by mass or more based on the total mass of the ink composition. A discharging step of discharging the photocurable ink composition for inkjet recording according to any one of claims 1 to 10 onto a recording medium,
A curing step of irradiating the photocurable ink jet recording ink composition ejected in the ejection step with ultraviolet rays to cure the photocurable ink jet recording ink composition.