JP2018065911A - Energy ray-curable inkjet ink composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a solvent-free energy ray-curable inkjet ink having a low viscosity, it is conceivable to increase the ratio of a monofunctional monomer having a generally low viscosity as one of the means. However, if the ratio of the monofunctional monomer is increased, there is a concern that the reactivity will be low and the curability will be low when the ink is cured. Further, if the stretchability and curability of the ink layer are insufficient, when Roll to Roll or the like is used in the recording process, there arises a problem that the non-recording media are cracked during winding or the non-recording media are sticky to each other. SOLUTION: The energy ray-curable inkjet ink composition containing substantially no solvent includes a monofunctional monomer, a first polyfunctional monomer having an acrylic equivalent of more than 150, and a second polyfunctional monomer having an acrylic equivalent of 150 or less. To have and. [Selection diagram] None

Description

  The present invention relates to an inkjet ink composition, and more particularly to an energy ray curable inkjet ink composition.

  The ink jet recording method is a method in which liquid ink is ejected from ink head nozzles and recorded on a recording medium. One of the inks used in the ink jet recording method is an energy ray curable ink jet ink. In this method, after the ink is ejected, the polymerizable compound in the ink is cross-linked by irradiation with energy rays (for example, ultraviolet rays), whereby the energy ray curable inkjet ink is cured to form an ink layer. Energy ray curable ink-jet inks are roughly classified into a solvent system containing an organic solvent and water and a solvent-free system substantially free of an organic solvent.

  The energy ray curable inkjet ink usually needs to have a viscosity that can be discharged from an ink head nozzle. Furthermore, in order to obtain a high-definition printed matter, it is required to reduce the droplet size of the ink to be discharged and to have a lower viscosity so that the ink can be stably discharged. As an example for obtaining an energy ray curable ink jet ink having a low viscosity, Patent Document 1 discloses that “the polymerizable compound has an acrylic equivalent of 300 or less and one ethylenic double bond in one molecule. Comprising only a monofunctional monomer and a polyfunctional monomer having an acrylic equivalent of 150 or less and having two or more ethylenic double bonds in one molecule, wherein the photopolymerization initiator is an α-aminoalkyl An energy beam curable ink composition containing a phenone compound and a thioxanthone compound is described.

JP 2009-275175 A

  As described above, Patent Document 1 discloses an energy ray curable ink composition having a low viscosity. However, the energy ray curable ink composition has a lower viscosity (viscosity is about 10 mPa · s (25 ° C.) or less). The composition of the inkjet ink is not disclosed.

  In order to obtain a solvent-free energy ray curable inkjet ink having a lower viscosity, it is generally considered to increase the ratio of the monofunctional monomer having a lower viscosity. However, when the ratio of the monofunctional monomer is increased, the reactivity is lowered when the ink is cured, and the curability is lowered. In order to prevent the curability from becoming low, an energy ray curable ink jet ink composition as described in Patent Document 1 is conceivable. However, when a polyfunctional monomer is used, the curability increases, but the ink viscosity is also high. It can be considered.

  Also, in the recording process to a non-recording medium, for recording to a non-recording medium that requires winding to roll to roll, after recording to the non-recording medium, a crack is not generated at the time of winding. Also, in order to prevent stickiness between non-recording media, the stretchability and curability of the ink layer of the non-recording media are required. In patent document 1, the said point is not considered.

  An object of the present invention is to provide an energy beam curable inkjet ink having a low viscosity and excellent curability and stretchability in the energy beam curable inkjet ink.

  According to an example of the present invention, an inkjet ink composition includes a polymerizable compound and a photopolymerization initiator, and the polymerizable compound has a monofunctional monomer, an acrylic equivalent greater than 150, and ethylene in one molecule. And a first polyfunctional monomer having two or more ionic double bonds and an acrylic equivalent of 150 or less and a second polyfunctional monomer having two or more ethylenic double bonds in one molecule. .

  ADVANTAGE OF THE INVENTION According to this invention, in an energy-beam curable inkjet ink composition, it can provide the energy-beam curable inkjet ink composition which is low viscosity and excellent in sclerosis | hardenability and extendability.

  Hereinafter, this embodiment will be described.

  The energy beam curable inkjet ink (hereinafter also referred to as ink) of the present embodiment includes at least a monofunctional monomer and a polyfunctional monomer that are polymerizable compounds, and a photopolymerization initiator. In addition, a coloring agent, an additive, etc. are included.

  A polymerizable compound is a compound that undergoes a polymerization reaction upon irradiation with energy rays (such as ultraviolet rays and electron beams) and cures. Among the polymerizable compounds, the monofunctional monomer has one ethylenic double bond in one molecule, and the polyfunctional monomer has two or more ethylenic double bonds in one molecule.

  Further, the energy beam curable ink of the present embodiment is a solvent-free system and does not substantially contain a solvent. Here, it is not necessary to contain a diluting solvent as being substantially free of a solvent. However, for example, the diluting solvent may be inevitably mixed into the ink when using industrial products, and is contained in the total mass of the ink. It means that the content of the solvent is 3% by mass or less. The solvent means various known solvents such as ether, ketone, aromatic, xylene, and the like.

  Since the energy beam curable ink is solvent-free, there is no residual volatile solvent in the ink layer, which is preferable from the viewpoint of free of volatile organic compounds.

<1. Polymerizable compound>
<1-1. Monofunctional monomer>
Specific examples of the monofunctional monomer include amyl (meth) acrylate, isoamyl (meth) acrylate, octyl (meth) acrylate, isooctyl (meth) acrylate, decyl (meth) acrylate, isodecyl (meth) acrylate, and lauryl (meth). ) Acrylate, isomyristyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, tridecyl (meth) acrylate, 2-ethylhexyl-diglycol (meth) acrylate, 2- (meth) acryloyloxyethyl hexahydrophthalic acid, neo Pentyl glycol (meth) acrylic acid benzoate, butoxyethyl (meth) acrylate, ethoxy-diethylene glycol (meth) acrylate, methoxy-triethylene glycol (meth) acrylate Methoxy-polyethylene glycol (meth) acrylate, methoxydipropylene glycol (meth) acrylate, phenoxyethyl (meth) acrylate, phenoxy-polyethylene glycol (meth) acrylate, 3,5,5-trimethylcyclohexyl acrylate 2- (2-ethoxyethoxy) Ethyl acrylate) nonylphenol ethylene oxide adduct (meth) acrylate, tetrahydrofurfuryl (meth) acrylate, isobornyl (meth) acrylate, 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 2-hydroxybutyl ( (Meth) acrylate, 2-hydroxy-3-phenoxypropyl (meth) acrylate, 2- (meth) acryloyloxyethyl-succinic acid, 2 (Meth) acryloyloxyethyl - phthalic acid, 2- (meth) acryloyloxyethyl-2-hydroxyethyl - phthalic acid, 1,4-cyclohexanedimethanol monoacrylate, and the like ethoxylated nonylphenyl acrylate. These may be used alone or in combination. The monomer may be substituted with a functional group such as phosphorus or fluorine.

  Among these, tetrahydrofurfuryl (meth) acrylate, 3,5,5-trimethylcyclohexyl acrylate, 2- (2-ethoxyethoxyethyl acrylate), and 2-ethylhexyl (meth) acrylate are more preferable because of their low viscosity. . Furthermore, it is particularly preferable to use 2-hydroxy-3-phenoxypropyl (meth) acrylate in combination. By using 2-hydroxy-3-phenoxypropyl (meth) acrylate containing a functional group such as a hydroxyl group in combination, adhesion to a non-recording medium (base material) can be imparted while maintaining low viscosity.

  As described above, two or more types of monofunctional monomers can be used in combination. One type uses a monofunctional monomer having a viscosity of 10 mPa · s or less (25 ° C.), and the other type has a viscosity of 80 mPa · s or more. A monofunctional monomer of (25 ° C.) can be used. As a result, the energy ray curable ink can have a low viscosity, and the adhesion to the non-recording medium can be improved.

  Specific examples of the monofunctional monomer having a viscosity of 10 mPa · s or less (25 ° C.) include tetrahydrofurfuryl (meth) acrylate, 3,5,5-trimethylcyclohexyl acrylate, 2- (2-ethoxyethoxyethyl acrylate), 2 -Ethylhexyl (meth) acrylate. Specific examples of the monofunctional monomer having a viscosity of 80 mPa · s or more (25 ° C.) include 2-hydroxy-3-phenoxypropyl (meth) acrylate, 1,4-cyclohexanedimethanol monoacrylate, and ethoxylated nonylphenyl acrylate. Can be mentioned. Even when a monofunctional monomer having a viscosity of 80 mPa · s or more (25 ° C.) is used, by using a monofunctional monomer having a viscosity of 10 mPa · s or less (25 ° C.), ink non-recording can be achieved while keeping the viscosity of the ink low. Adhesion to the medium can be improved.

  Furthermore, the monofunctional monomer preferably has a functional group, and specific examples include a hydroxyl group, a carboxyl group, and a phosphate group. By having these functional groups, adhesion to a non-recording medium can be improved. Among these, a hydroxyl group is particularly preferable and adhesion can be further improved.

  Moreover, it is preferable that the glass transition temperature of a monofunctional monomer is -70 degreeC or more and 30 degrees C or less. Thereby, the coating film can be imparted with an appropriate hardness and stretchability of the ink layer (ink coating film).

<1-2. Multifunctional monomer>
The polyfunctional monomer has a first polyfunctional monomer having an acrylic equivalent greater than 150 and two or more ethylenic double bonds in one molecule, an acrylic equivalent of 150 or less, and an ethylenic in one molecule. A second polyfunctional monomer having two or more double bonds; The polymerizable compound contains at least one first polyfunctional monomer and at least one second polyfunctional monomer.

  By using the first polyfunctional monomer and the second polyfunctional monomer as the polyfunctional monomer, both the stretchability and hardness (coating film strength) of the ink layer can be achieved. Further, by using a polyfunctional monomer, the curability of the ink layer can be improved.

  The acrylic equivalent is calculated by (acryl equivalent) = (molecular weight of monomer / number of functional groups of monomer).

<1-2-1. First polyfunctional monomer>
Specific examples of the first polyfunctional monomer having an acrylic equivalent larger than 150 and having two ethylenic double bonds in one molecule include polyethylene glycol (200) diacrylate, tetraethylene glycol diacrylate, Examples include polyethylene glycol (400) diacrylate, ethoxylated (3) bisphenol A diacrylate, tricyclodecane dimethanol diacrylate, propoxylated (2) neopentyl glycol diacrylate, and the like. These may be used alone or in combination.

  Specific examples of the polyfunctional monomer having three or more ethylenic double bonds in one molecule include ethoxylated (20) trimethylolpropane triacrylate, propoxylated (3) trimethylolpropane triacrylate, and the like. . These may be used alone or in combination.

  Among the polyfunctional monomers, tricyclodecane dimethanol diacrylate, polyethylene glycol (400) diacrylate, and propoxylated (2) neopentyl glycol diacrylate are preferable. By using these polyfunctional monomers, the ink can be kept at low viscosity and the coating strength of the ink layer can be increased.

  Moreover, it is preferable that the glass transition temperature of a 1st polyfunctional monomer is -25 degreeC or more and 180 degrees C or less.

<1-2-2. Second polyfunctional monomer>
Specific examples of the second polyfunctional monomer having an acrylic equivalent of 150 or less and two ethylenic double bonds in one molecule include 1,3-butylene glycol di (meth) acrylate, 1,4- Butylene glycol di (meth) acrylate, diethylene glycol di (meth) acrylate, 1,6-hexanediol di (meth) acrylate, neopentyl glycol di (meth) acrylate, triethylene glycol di (meth) acrylate, tripropylene glycol diacrylate , Cyclohexanedimethanol di (meth) acrylate, dipropylene glycol di (meth) acrylate, and the like. These may be used alone or in combination.

  Specific examples of the polyfunctional monomer having 3 or more ethylenic double bonds in one molecule include trimethylolpropane tri (meth) acrylate, pentaerythritol tri (meth) acrylate, and tris (2-hydroxyethyl) isocyanate. Examples thereof include nurate tri (meth) acrylate, glyceryl tri (meth) acrylate, and ethylene oxide-modified, propylene oxide-modified, caprolactone-modified products thereof. These may be used alone or in combination.

  Among the polyfunctional monomers, 1,6-hexanediol di (meth) acrylate, 1,4-butanediol diacrylate, and trimethylolpropane tri (meth) acrylate are preferable. By using these polyfunctional monomers, the ink can be kept at a low viscosity and the curability of the ink layer can be improved.

  Moreover, it is preferable that the glass transition temperature of a 2nd polyfunctional monomer is 43 to 100 degreeC. Thereby, the coating film strength of the ink layer can be increased.

  Among the first polyfunctional monomer and the second polyfunctional monomer, a combination of tricyclodecane dimethanol diacrylate and 1,6-hexanediol di (meth) acrylate is preferable. Thereby, the viscosity of the ink can be lowered, and the coating film strength of the ink layer can be increased.

<1-3. About content of each polymerizable compound>
70 mass% or more and 90 mass% or less are preferable with respect to the whole ink composition, and, as for content of the polymeric compound in an ink composition, 78 mass% or more and 88 mass% or less are more preferable. If it is the range of content of the said polymeric compound, the ink which has high sclerosis | hardenability and adhesiveness can be obtained, maintaining a low viscosity.

  In addition, the content of the monofunctional monomer is preferably 50% by mass or more and 80% by mass, and more preferably 55% by mass or more and 75% by mass or less with respect to the entire ink composition. When the content of the monofunctional monomer is 50% by mass or more, a low-viscosity ink composition can be obtained. On the other hand, when the content of the monofunctional monomer is 80% by mass or less, a highly reactive polyfunctional monomer can be contained correspondingly, and curability and adhesion can be improved.

  When the content of the monofunctional monomer is less than 50% by mass, the polyfunctional monomer is increased, so that the ink cannot be kept at a low viscosity.

  The content of the first polyfunctional monomer is preferably 0.5% by mass or more and 10% by mass or less, and more preferably 1% by mass or more and 8% by mass or less with respect to the entire ink composition. By setting the first polyfunctional monomer to the above-described content, the strength of the ink coating film (coating film strength) can be imparted.

  The content of the second polyfunctional monomer is preferably 5% by mass or more and 35% by mass or less, and more preferably 6% by mass or more and 30% by mass or less with respect to the entire ink composition. By setting the second polyfunctional monomer to the above-described content, an improvement in the curing speed of the ink layer can be imparted.

  In the prior art, it has been shown that when the polyfunctional monomer has an acrylic equivalent higher than 150, even if a polyfunctional monomer having an acrylic equivalent of 300 or less is used in combination, the curability and adhesion are reduced by low energy irradiation. . On the other hand, in the present embodiment, even when a polyfunctional monomer having an acrylic equivalent greater than 150 is used, a combination of a monofunctional monomer and a polyfunctional monomer having an acrylic equivalent of 150 or less provides low viscosity and low viscosity. It is possible to obtain an energy ray curable ink that is excellent in curability and stretchability even by energy irradiation.

  Moreover, by setting the content of the polymerizable compound (monofunctional monomer, first multifunctional monomer, second multifunctional monomer) in the above range, the viscosity is low, and the curability and stretchability are excellent. An energy beam curable ink is provided.

  In the polymerizable compound of the present embodiment, the ratio of the content of the monofunctional monomer with respect to the entire ink composition is 50% by mass or more, and thus a polyfunctional compound having three or more ethylenic double bonds in one molecule as described above. Even if a functional monomer is contained, an ink composition having a low viscosity can be obtained.

  Moreover, the ratio of the single-capable monomer in the polymerizable compound is preferably 60% or more and 95% or less, and more preferably 62% or more and 91% or less with respect to the entire polymerizable compound.

  The ratio of the first polyfunctional monomer in the polymerizable compound is preferably 1% or more and 10% or less with respect to the entire polymerizable compound. Furthermore, the ratio of the second polyfunctional monomer in the polymerizable compound is preferably 5% or more and 35% or less.

  The ratio of the monofunctional monomer to the polyfunctional monomer in the polymerizable compound is preferably 1 to 10 in terms of the mass ratio (monofunctional monomer / polyfunctional monomer) between the content of the monofunctional monomer and the content of the polyfunctional monomer.

  The ratio of the first polyfunctional monomer having an acrylic equivalent greater than 150 and the second polyfunctional monomer having an acrylic equivalent of 150 or less in the polyfunctional monomer is determined by the content of the first polyfunctional monomer and the second polyfunctional monomer. 2-15 are preferable by mass ratio (2nd polyfunctional monomer / 1st polyfunctional monomer) with content of a monomer.

  As described above, as the polymerizable compound, a monofunctional monomer, a first polyfunctional monomer having an acrylic equivalent greater than 150, and a second polyfunctional monomer having an acrylic equivalent of 150 or less substantially contain a solvent. It is possible to provide an energy beam curable inkjet ink having a low viscosity and excellent curability and stretchability.

<2. Photopolymerization initiator>
As a photopolymerization initiator, at least one of an alkylphenone compound and a thioxanthone compound is contained. Thereby, the polymerization of the ink composition can be started by energy irradiation.

  Examples of the alkylphenone compounds include α-aminoalkylphenone compounds and benzylmethyl ketal compounds. Specifically, 2-methyl-1 [4- (methylthio) phenyl] -2-morpholinopropan-1-one, 2-Benzyl-2-dimethylamino-1- (4-morpholinophenyl) butanone-1,2-methyl-1- [4- (methoxythio) -phenyl] -2-morpholinopropan-2-one, 2,2- Examples include dimethoxy-1,2-diphenylethane-1-one. These may be used alone or in combination. Examples of commercially available alkylphenone compounds include Irgacure 369, Irgacure 907, and Irgacure 651 manufactured by Ciba.

  Specific examples of the thioxanthone compound include thioxanthone, 2-methylthioxanthone, 2-ethylthioxanthone, 2-isopropylthioxanthone, 4-isopropylthioxanthone, 2-chlorothioxanthone, 2,4-dimethylthioxanthone, 2,4-diethyl. Examples include thioxanthone, 2,4-dichlorothioxanthone, and 1-chloro-4-propoxythioxanthone. These may be used alone or in combination. Examples of commercially available thioxanthone compounds include KAYACURE DETX-S manufactured by Nippon Kayaku Co., and Chivacure ITX manufactured by Double Bond Chemical.

  The content of the photopolymerization initiator in the ink composition is preferably 8% by mass or more and 15% by mass or less with respect to the entire composition.

  In addition to the above, the ink composition includes acylphosphine oxide compounds, arylalkyl ketones, oxime ketones, acylphosphine oxides, acylphosphonates, S-phenyl thiobenzoate, titanocene, aromatic ketones, benzyl, quinone derivatives, ketocoumarins A conventionally known photopolymerization initiator such as may be further contained.

  Specific examples of these photopolymerization initiators include 2,4,6-trimethylbenzoyl-diphenyl-phosphine oxide, bis (2,4,6-trimethylbenzoyl) -phenylphosphine oxide, and 1-hydroxy. -Cyclohexyl-phenyl-ketone 1,2-octanedione- [4- (phenylthio) -2- (o-benzoyloxime)], bis (2,6-dimethoxybenzoyl) -2,4,4-trimethyl-pentylphosphine Examples thereof include oxide and 2,4,6-trimethylbenzoyl-phosphine oxide.

<3. Colorant>
Conventionally known various dyes may be used as the colorant, but it is preferable to use either or both of an inorganic pigment and an organic pigment from the viewpoint of weather resistance.

  Specific examples of inorganic pigments include titanium oxide, zinc oxide, zinc oxide, tripone, iron oxide, aluminum oxide, silicon dioxide, kaolinite, montmorillonite, talc, barium sulfate, calcium carbonate, silica, alumina, cadmium red, Bengara, molybdenum red, chrome vermilion, molybdate orange, yellow lead, chrome yellow, cadmium yellow, yellow iron oxide, titanium yellow, chromium oxide, pyridian, cobalt green, titanium cobalt green, cobalt chrome green, ultramarine blue, ultramarine blue , Bitumen, cobalt blue, cerulean blue, manganese violet, cobalt violet, mica and the like.

  Specific examples of organic pigments include azo, azomethine, polyazo, phthalocyanine, quinacridone, anthraquinone, indigo, thioindigo, quinophthalone, benzimidazolone, and isoindoline organic pigments. Can be mentioned. Carbon black made of acidic, neutral or basic carbon may be used. Furthermore, a hollow particle of a crosslinked acrylic resin or the like may be used as the organic pigment.

  Specific examples of the pigment having a cyan color include C.I. I. Pigment blue 1, C.I. I. Pigment blue 2, C.I. I. Pigment blue 3, C.I. I. Pigment blue 15: 3, C.I. I. Pigment blue 15: 4, C.I. I. Pigment blue 16, C.I. I. Pigment blue 22, C.I. I. And CI Pigment Blue 60. Among these, from the viewpoint of weather resistance and coloring power, C.I. I. Pigment blue 15: 3, C.I. I. Either or both of Pigment Blue 15: 4 are preferred.

  Specific examples of pigments having a magenta color include C.I. I. Pigment red 5, C.I. I. Pigment red 7, C.I. I. Pigment red 12, C.I. I. Pigment red 48 (Ca), C.I. I. Pigment red 48 (Mn), C.I. I. Pigment red 57 (Ca), C.I. I. Pigment red 57: 1, C.I. I. Pigment red 112, C.I. I. Pigment red 122, C.I. I. Pigment red 123, C.I. I. Pigment red 168, C.I. I. Pigment red 184, C.I. I. Pigment red 202, C.I. I. Pigment red 209, C.I. I. Pigment red 254, C.I. I. Pigment violet 19 and the like. Among these, from the viewpoint of weather resistance and coloring power, C.I. I. Pigment red 122, C.I. I. Pigment red 202, C.I. I. Pigment red 209, C.I. I. Pigment red 254, and C.I. I. At least one selected from the group consisting of CI Pigment Violet 19 is preferred.

Specific examples of the pigment having a yellow color include C.I. I. Pigment yellow 1, C.I. I. Pigment yellow 2, C.I. I. Pigment yellow 3, C.I. I. Pigment yellow 12, C.I. I. Pigment yellow 13, C.I. I. Pigment yellow 14C, C.I. I. Pigment yellow 16, C.I. I. Pigment yellow 17, C.I. I. Pigment yellow 73, C.I. I. Pigment yellow 74, C.I. I. Pigment yellow 75, C.I. I. Pigment yellow 83, C.I. I. Pigment yellow 93, C.I. I. Pigment yellow 95, C.I. I. Pigment yellow 97, C.I. I. Pigment yellow 98, C.I. I. Pigment yellow 109, C.I. I. Pigment yellow 110, C.I. I. Pigment yellow 114, C.I. I. Pigment yellow 120, C.I. I. Pigment yellow 128, C.I. I. Pigment yellow 129, C.I. I. Pigment yellow 130, C.I. I. Pigment yellow 138, C.I. I. Pigment yellow 139, C.I. I. Pigment yellow 147, C.I. I. Pigment yellow 150, C.I. I. Pigment yellow 151, C.I. I. Pigment yellow 154, C.I. I. Pigment yellow 155, C.I. I. Pigment yellow 180, C.I. I. Pigment yellow 185, C.I. I. Pigment yellow 213, C.I. I. And CI Pigment Yellow 214. Among these, from the viewpoint of weather resistance, C.I. I. Pigment yellow 74, C.I. I. Pigment yellow 83, C.I. I. Pigment yellow 109, C.I. I. Pigment yellow 110, C.I. I. Pigment yellow 120, C.I. I. Pigment yellow 128, C.I. I. Pigment yellow 138, C.I. I. Pigment yellow 139, C.I. I. Pigment yellow 150, C.I. I. Pigment yellow 151, C.I. I. Pigment yellow 154, C.I. I. Pigment yellow 155, C.I. I. Pigment yellow 213, and C.I. I. At least one selected from the group consisting of CI Pigment Yellow 214 is preferred.

  Specific examples of pigments having a black color include HCF, MCF, RCF, LFF, and SCF manufactured by Mitsubishi Chemical Corporation; Monarch and Legal manufactured by Cabot; Color Black, Special Black, and Printex manufactured by Degussa Huls ; Toka Black manufactured by Tokai Carbon Co .; Raven manufactured by Columbia Co .; Among these, HCF # 2650, HCF # 2600, HCF # 2350, HCF # 2300, MCF # 1000, MCF # 980, MCF # 970, MCF # 960, MCF88, LFFMA7, MA8, MA11, MA77 manufactured by Mitsubishi Chemical Corporation MA100 and Degussa Huls, Printex 95, Printex 85, Printex 75, Printex 55, Printex 45, and at least one selected from the group consisting of Printex 45 are preferable.

  Specific examples of the pigment having white color include Pigment White 6, 18, and 21, and basic lead carbonate (2PbCO3Pb (OH) 2, so-called silver white), zinc oxide (ZnO, so-called zinc white). ), Titanium oxide (TiO2, so-called titanium white), strontium titanate (SrTiO3, so-called titanium strontium white), and the like. Among these, titanium oxide has a smaller specific gravity than other white pigments, a large refractive index, and is chemically and physically stable, so that it has high hiding power and coloring power as a pigment. Excellent durability against alkalis and other environments. Therefore, it is more preferable to use titanium oxide as the white pigment.

  The content of the colorant in the ink composition is preferably 1 to 10% by mass, and more preferably 1 to 9% by weight with respect to the entire ink composition.

  When a pigment is used as the coloring material, a pigment derivative or a pigment dispersant may be further used in order to improve the dispersibility of the pigment.

  Specific examples of the pigment derivative include a pigment derivative having a dialkylaminoalkyl group and a pigment derivative having a dialkylaminoalkylsulfonic acid amide group.

  Specific examples of the pigment dispersant include ionic or nonionic surfactants and anionic, cationic or nonionic polymer compounds. Among these, a polymer compound containing a cationic group or an anionic group is preferable from the viewpoint of dispersion stability. Examples of commercially available pigment dispersants include SOLSPERS manufactured by Lubrizol, DISPERBYK manufactured by BYK Chemie, EFKA manufactured by Fuka Additives, and the like.

  The content of the pigment derivative and the pigment dispersant in the ink composition is preferably 0.05 to 5% by mass with respect to the entire ink composition.

<4. Additives>
<4-1. Surface conditioner>
As the surface conditioner, a silicone compound having a polydimethylsiloxane structure can be contained. If the silicone compound is used as a surface conditioner together with the polymerizable compound, the liquid physical properties such as the surface tension of the ink can be adjusted to a range suitable for the ink jet recording system.

  Specific examples of the silicone compound include BYK-UV3500, BYK-UV3510, BYK-UV3570, manufactured by Big Chemie, Tego-Rad2100, Tego-Rad2200N, Tego-Rad2250, Tego-Rad2300, Tego- manufactured by Degussa. Rad 2500, Tego-Rad 2600, Tego-Rad 2700, UCR-L72 and UCR-L93 manufactured by Kyoeisha Chemical Co., Ltd. are preferable. Since these contain a polydimethylsiloxane structure having an ethylenic double bond in the molecule, the adhesion can be further improved.

  The content of the silicone compound in the ink composition is preferably 0.005% by mass or more and 1% by mass or less based on the entire ink composition.

<4-2. Anti-gelling agent>
It is preferable to further contain a hindered amine compound having a 2,2,6,6-tetramethylpiperidinyl group as an anti-gelling agent. If the hindered amine compound is used as a gelation inhibitor together with a highly reactive polymerizable compound and a photopolymerization initiator, an ink having excellent storage stability can be obtained without reducing the reactivity of the ink. . Specific examples of the anti-gelling agent include bis (1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl) sebacate, 2,2,6,6-tetramethylpiperidi. Nooxy, decanedioic acid bis (2,2,6,6-tetramethyl-1- (octyloxy) -4-piperidinyl) ester and the like. These may be used alone or in combination. Examples of the anti-gelling agent available on the market include IRGASTAB UV-10 and TINUVIN 123 manufactured by Ciba, HYDROXY-TEMPO manufactured by Evonik Degussa Japan.

  The content of the anti-gelling agent in the ink composition is preferably 0.1% by mass or more and 4% by mass or less with respect to the entire ink composition. When the content of the anti-gelling agent is less than 0.1% by mass, radicals generated during storage cannot be sufficiently captured, and storage stability tends to decrease. On the other hand, when the content of the anti-gelling agent is more than 4% by mass, the effect of scavenging radicals is saturated and the polymerization reaction during energy beam irradiation tends to be inhibited.

  As a gelling inhibitor, other hindered amine compounds, phenolic antioxidants, phosphorus antioxidants, hydroquinone monoalkyl ethers, and the like may be further contained. Specific examples of such an antigelling agent include hydroquinone monomethyl ether, hydroquinone, t-butylcatechol, pyrogallol, TINUVIN 111 FDL, TINUVIN 144, TINUVIN 292, TINUVIN XP40, TINUVIN XP60, and TINUVIN 400 manufactured by Ciba. Etc.

<4-3. Other additives>
If necessary, the ink composition of the present embodiment further includes a surfactant, a leveling agent, an antifoaming agent, an antioxidant, a pH adjusting agent, a charge imparting agent, a bactericidal agent, an antiseptic, a deodorizing agent, and a charge adjusting agent. Well-known general additives such as wetting agents, anti-skinning agents, and perfumes may be added as optional components.

<5. About adjustment method>
As a method for preparing the ink, conventionally known methods can be used. However, when a pigment is used as the colorant, the following preparation method is preferable.

  First, a mixed liquid is prepared by premixing a colorant, a part of the polymerizable compound, and, if necessary, a pigment dispersant, and this mixed liquid is dispersed by a disperser to prepare a primary dispersion. Specific examples of the disperser include a disperser; a container drive medium mill such as a ball mill, a centrifugal mill, and a planetary ball mill; a high-speed rotating mill such as a sand mill; and a medium agitation mill such as a stirring tank mill.

  Next, the remaining polymerizable compound, a photopolymerization initiator, a surface conditioner, and other additives such as an anti-gelling agent as necessary are added to the primary dispersion and uniformly mixed using a stirrer. Mix. Specific examples of the stirrer include a three-one motor, a magnetic stirrer, a dispaper, and a homogenizer. Further, the ink composition may be mixed using a mixer such as a line mixer. Furthermore, the ink composition may be mixed using a disperser such as a bead mill or a high-pressure jet mill for the purpose of further reducing the particles in the ink composition.

  When a pigment is used as the colorant, the dispersion average particle diameter of the pigment particles in the ink composition is preferably 20 to 250 nm, and more preferably 50 to 230 nm.

  According to the present embodiment, the monofunctional monomer, the first polyfunctional monomer having an acrylic equivalent greater than 150 and having two or more ethylenic double bonds in one molecule, the acrylic equivalent is 150 or less, and Since the polymerizable compound is composed of the second polyfunctional monomer having two or more ethylenic double bonds in one molecule, an ink composition having a low viscosity of 6 to 8 mPa · s is prepared at 25 ° C. be able to.

  In addition, the ink composition of the present embodiment does not need to be diluted with a diluting solvent, has a low viscosity even without heating, and has good pigment dispersibility when the colorant is a pigment, and is preserved. It has good dispersion stability without causing problems such as an increase in viscosity during use or use, and precipitation of pigments. For this reason, in the ink jet recording system, stable ejection can be obtained at room temperature without heating the ink.

<6. Others>
The ink jet recording method is not particularly limited, but is a charge control method that discharges ink using electrostatic attraction, a drop-on-demand method (pressure pulse method) that uses the vibration pressure of a piezoelectric element, Examples include an acoustic ink jet recording method that uses a radiation pressure that irradiates ink by changing a signal into an acoustic beam, and a thermal ink jet recording method that uses ink to form bubbles by heating the ink. The inkjet recording method includes a method of ejecting a large number of low-density inks called photo inks in a minute volume, a method of improving image quality using a plurality of inks having substantially the same hue and different concentrations, and colorless and transparent. A method using ink is included.

  In the present embodiment, examples of the irradiation means include ultraviolet irradiation means such as a mercury lamp and a metal halide lamp. In the case of the ink composition of the present embodiment, low energy of 200 mJ / cm 2 or less can be used as the cumulative amount of ultraviolet light. The energy rays are preferably irradiated to the ink composition after 1 to 1,000 ms elapses after the ink composition is discharged onto the recording medium. If the elapsed time is less than 1 ms, the distance between the head and the light source is too short, and the head may be irradiated with energy rays, leading to an unexpected situation. On the other hand, if the elapsed time exceeds 1,000 ms, the image quality tends to deteriorate due to ink bleeding when multiple colors are used.

  Hereinafter, although it demonstrates more concretely based on an Example, it is not limited to these Examples. In the following, “part” means “part by mass”.

  The components of the ink composition used in each example and comparative example are shown in Table 1 below.

[Preparation of ink composition]
Examples (actual) 1 to 9 and comparative examples (ratio) 1 to 6 were adjusted according to the blending amounts of the ink compositions shown in Table 2. The display in Table 2 corresponds to the description in Table 1.

  In a 100 cc plastic bottle, weigh out the colorant, pigment dispersant, and monofunctional monomer in the amounts shown in Table 2, add 100 parts of zirconia beads to this, and use paint conditioner (Toyo Seiki Co., Ltd.) for 2 hours. Dispersion gave a primary dispersion. Next, the remaining components were added to the obtained primary dispersion in the amounts shown in Table 2, and the mixture was stirred for 30 minutes with a magnetic stirrer. After stirring, the mixture was suction filtered using a glass filter (manufactured by Kiriyama Seisakusho) to prepare an ink composition. In Comparative Examples 4 and 5, in the same manner as above except that primary dispersion was prepared using tricyclodecane dimethanol diacrylate and 1,6 hexanediol diacrylate, respectively, instead of the monofunctional monomer. Thus, an ink composition was prepared.

[Evaluation]
Viscosity was measured for each ink composition of Examples and Comparative Examples prepared as described above.

Furthermore, the following adhesion, coating film strength, stretchability, and curability were evaluated for the ink layer (printing film) recorded on the non-recording medium using the ink compositions of Examples and Comparative Examples. The following evaluation results of the examples and comparative examples shown in Table 2 are shown in Table 3.
〔viscosity〕
Using an R100 viscometer (manufactured by Toki Sangyo Co., Ltd.), the viscosity was measured under the conditions of 25 ° C. and cone rotation speed of 20 rpm.
[Curing property]
The ink composition was printed on a non-recording medium of a film made of polyethylene terephthalate (PET) to form a printed film having a thickness of 2 μm. This printing film was cured by irradiating with ultraviolet rays so that the total irradiation light quantity was 200 mJ / cm 2 using a metal halide lamp as an irradiation means.

  The printed film thus cured was touched with a finger and nail, and the presence or absence of ink adhesion to the finger and nail was visually examined and evaluated according to the following criteria.

○: Ink does not adhere to fingers and nails, and the surface of the printed film is not damaged even when rubbed with nails. ×: Ink adheres to fingers [adhesion]
An ink composition was printed on a non-recording medium of each film made of polyvinyl chloride (PVC) to form a printed film having a thickness of 2 μm. This printing film was cured by irradiating with ultraviolet rays so that the total irradiation light quantity was 200 mJ / cm 2 using a metal halide lamp as an irradiation means.

  The cross-cut test (1 mm square, 100 pieces) for confirming the peeled state with the cello tape (registered trademark) was performed on the printed film thus cured according to JIS-K-5400. The number of peels in 100 pieces was examined and evaluated according to the following criteria.

◯: The number of peels in the cross cut test is 10 or less ×: The number of peels in the cross cut test is 21 or more [coating film strength]
The ink composition was printed on a non-recording medium of an acrylic plate to form a printing film having a thickness of 2 μm. This printing film was cured by irradiating with ultraviolet rays so that the total irradiation light quantity was 200 mJ / cm 2 using a metal halide lamp as an irradiation means.

  The pencil hardness of the printed film thus cured was measured and evaluated according to the following criteria. In addition, based on the measuring method of pencil hardness prescribed | regulated to Japanese Industrial Standard (JIS) K5400, it measured using the surface property tester "HEIDON-14DR" by a Shinto scientific company.

○: Pencil hardness 4H or more
X: Pencil hardness less than 4H [stretchability]
The ink composition was printed on the non-recording medium of the stretching test medium to form a print film. This printing film was cured by irradiating with ultraviolet rays so that the total irradiation light quantity was 200 mJ / cm 2 using a metal halide lamp as an irradiation means.

  The printed film thus obtained was cut into a 10 mm × 70 mm strip and used as a test piece. The positions of 10 mm on both sides of the test piece were fixed to the sample stage, and evaluated using a tensile tester: AUTOGRAGH AGS-H 100N manufactured by SIMADZU, at a pulling speed of 50 mm / min. When the printed part of the test piece was cracked, the tension was stopped, the elongation was determined, and evaluated according to the following criteria.

○: Elongation rate 160% or more ×: Elongation rate less than 160%

As shown in Table 3 above, a monofunctional monomer as a polymerizable compound, a first polyfunctional monomer having an acrylic equivalent greater than 150 and having two or more ethylenic double bonds in one molecule, and 150 A second polyfunctional monomer having the following acrylic equivalent and having two or more ethylenic double bonds in one molecule; and at least one of an alkylphenone compound and a thioxanthone compound as a photopolymerization initiator; The ink composition of the example containing a silicone compound having a polydimethylsiloxane structure as a surface conditioner has a viscosity of 6 mPa · s or more and 8 mPa · s or less at 25 ° C., and the viscosity becomes low. .

  As shown in Examples 1 to 9 in Table 2 and Table 3, according to this embodiment, the energy ray curable inkjet ink composition substantially free of a solvent has a low viscosity, and is curable. It is possible to provide an energy ray curable inkjet ink composition excellent in stretchability. For this reason, the ink composition of an Example is excellent in discharge stability, and can provide a high-definition printed matter.

  In addition, an energy ray curable ink substantially free of a solvent may contain an oligomer as a polymerizable compound. In this case, however, the viscosity of the ink becomes high and the ejection stability becomes insufficient. In addition to inferior continuous ejection properties, curability and adhesion are also insufficient.

  It can be seen that the ink composition containing only the monofunctional monomer as the polymerizable compound has poor coating strength because there is no polyfunctional monomer component, and poor adhesion and curability because there are few crosslinking components (Comparative Example 1).

  The ink composition containing a monofunctional monomer and a first polyfunctional monomer having an acrylic equivalent greater than 150 as the polymerizable compound has an inferior coating film strength because the polyfunctional monomer component of the crosslinking component is extremely reduced, resulting in a high tensile strength. It can be seen that the stretchability and adhesion are inferior because the coating strength sufficient to withstand is lost. (Comparative Example 2)

  It can be seen that the ink composition containing the monofunctional monomer and the second polyfunctional monomer having an acrylic equivalent of 150 or less as the polymerizable compound has poor coating strength because the polyfunctional monomer component of the crosslinking component is reduced. (Comparative Example 3)

  The ink composition containing only the first polyfunctional monomer having an acrylic equivalent greater than 150 as the polymerizable compound and the ink composition containing only the second polyfunctional monomer having an acrylic equivalent of 150 or less are diluted / adherent components. Since the monofunctional monomer component is no longer present, the viscosity is high and the adhesion is poor. It can be seen that since only the polyfunctional monomer is used, the coating film becomes hard and the stretchability is poor. (Comparative Examples 4 and 5)

  Even if the ink composition contains a monofunctional monomer, a first polyfunctional monomer having an acrylic equivalent of 150 or more and a second polyfunctional monomer having an acrylic equivalent of 150 or less as a polymerizable compound, the content of the monofunctional monomer is an ink composition. When the content is 45% by mass or less based on the whole product, the monofunctional monomer component that is a diluting / adhering component is eliminated, so that the viscosity is increased, the adhesion is inferior, and the polyfunctional monomer ratio of the crosslinking component is increased. It turns out that it becomes hard and a drawability is inferior. (Comparative Example 6)

Claims (6)

An inkjet ink composition comprising a polymerizable compound and a photopolymerization initiator,
The polymerizable compound is
A monofunctional monomer;
A first polyfunctional monomer having an acrylic equivalent greater than 150 and having two or more ethylenic double bonds in one molecule;
An inkjet ink composition having an acrylic equivalent of 150 or less and a second polyfunctional monomer having two or more ethylenic double bonds in one molecule. In claim 1,
The content of the monofunctional monomer is 50 to 80% by mass, the content of the first polyfunctional monomer is 1 to 10% by mass, and the content of the second polyfunctional monomer is based on the entire inkjet ink composition. An inkjet ink composition having an amount of 5 to 35% by mass. In claim 1,
The polymerizable initiator is an inkjet ink composition containing at least one of an alkylphenone compound and a thioxanthone compound. In claim 1,
The monofunctional monomer has a glass transition temperature of −70 ° C. or higher and 29 ° C. or lower,
The glass transition temperature of the first polyfunctional monomer is -25 ° C or higher and 180 ° C or lower,
The inkjet ink composition whose glass transition temperature of said 2nd polyfunctional monomer is 43 degreeC or more and 100 degrees C or less. In claim 1,
The inkjet ink composition is an inkjet ink composition containing a surface conditioner and a colorant. In claim 1,
The inkjet ink composition is an inkjet ink composition having a viscosity of 6.5 to 8.0 mPa · s at 25 ° C.