Ink composition for photo-curable inkjet ink printing

Abstract

To provide an ink composition for photo-curable inkjet printing containing a pigment and a pigment dispersant in which the adhesiveness between the printing layer and a substrate to be printed is high, the dispersion stability of a pigment in the ink composition is high and the storage stability is improved and further to provide an ink composition for photo-curable inkjet printing containing a pigment and a pigment dispersant in which the adhesiveness between the printing layer and a substrate to be printed is high, the printing layer has high water resistance, the dispersion stability of a pigment in the ink composition is high and the storage stability is improved.SOLUTION: There is provided an ink composition for photo-curable inkjet printing which contains a pigment, a pigment dispersant, a photopolymerization initiator and a photopolymerizable compound, wherein the photopolymerizable compound contains a hydrophilic monofunctional monomer and a phosphate ester (meth)acrylate and contains 0.1 to 4.3 mass% of the phosphate ester (meth)acrylate based on the whole ink composition and the ink composition comprises 38 to 100 pts.mass of the pigment dispersant based on 100 pts.mass of the pigment.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a photocurable ink composition for ink-jet printing. [Background technology]

[0002] Photocurable inkjet printing ink compositions are used for printing on various substrates. Inkjet printing is advantageous for small-lot production because it does not require a plate, and photocurable (typically ultraviolet curable) ink compositions can reduce the organic solvent content, which is an advantage in terms of environmental friendliness, as it can reduce VOC emissions.

[0003] In printing with a photocurable ink composition for inkjet printing, ink droplets are deposited on a substrate to be printed, and each droplet is irradiated with light to cure, forming a printed layer made of a cured coating on the substrate to be printed. Depending on the material of the substrate to be printed and the composition of the ink composition, etc., sufficient adhesion between the printed layer made of the cured coating and the surface of the substrate to be printed may not be obtained.

[0004] In response to this, it has been proposed to incorporate a polymerizable compound containing a phosphoric acid group or a polymerizable phosphate ester compound into the ink composition as a means for enhancing adhesion between a printed layer formed by a photocurable ink composition for inkjet printing and the surface of a substrate to be printed (Patent Documents 1 and 2). Patent Document 1 proposes incorporating a polymerizable compound containing a phosphoric acid group into an active energy ray-curable inkjet ink composition containing a polymerizable compound and a dye as a colorant. Patent Document 2 also proposes using an acylphosphinic acid oxide initiator as the photopolymerization initiator in an inkjet ink composition containing a polymerizable monomer containing a polymerizable phosphate ester compound and a photopolymerization initiator. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2006-328227 A [Patent Document 2] JP 2012-162615 A Summary of the Invention [Problem to be solved by the invention]

[0006] As described above, it has been proposed to increase the adhesion between the print layer (i.e., the cured coating film) and the surface of the substrate to be printed by blending a photopolymerizable compound containing a phosphoric acid group or a photopolymerizable phosphoric acid ester compound into a photocurable ink composition for inkjet printing. However, it has been found that blending a colorant and a pigment dispersant for dispersing the pigment into a photocurable ink composition for inkjet printing and blending a photopolymerizable compound containing a phosphoric acid group or a photopolymerizable phosphoric acid ester compound into the photocurable ink composition for inkjet printing reduces the dispersion stability of the pigment and reduces the storage stability.

[0007] A first problem to be solved by the present invention is to provide a photocurable ink composition for inkjet printing that contains a pigment and a pigment dispersant, and that has high adhesion between the printed layer and a substrate to be printed, high dispersion stability of the pigment in the ink composition, and improved storage stability. A second problem to be solved by the present invention is to provide a photocurable ink composition for inkjet printing that contains a pigment and a pigment dispersant, and that has high adhesion between the printed layer and a substrate to be printed, high water resistance of the printed layer, high dispersion stability of the pigment in the ink composition, and improved storage stability. [Means for solving the problem]

[0008] The present invention relates to the following photocurable ink composition for ink-jet printing.

[0009] [Item 1] A photocurable ink composition for inkjet printing, comprising a pigment, a pigment dispersant, a photopolymerization initiator, and a photopolymerizable compound, wherein the photopolymerizable compound comprises a hydrophilic monofunctional monomer and a phosphate ester (meth)acrylate, the phosphate ester (meth)acrylate is contained in an amount of 0.1 to 4.3 mass % relative to the entire ink composition, and the pigment dispersant is contained in an amount of 38 to 100 mass parts relative to 100 mass parts of the pigment. [Item 2] The photocurable ink composition for ink-jet printing according to item 1, wherein the pigment contains carbon black, and the mass ratio of the hydrophilic monofunctional monomer to the phosphate ester (meth)acrylate is 5 to 400. [Item 3] The photocurable ink composition for ink-jet printing according to item 1 or 2, wherein the photopolymerizable compound further contains an amine-modified oligomer. [Item 4] The photocurable ink composition for inkjet printing according to any one of Items 1 to 3, wherein a mass ratio of the hydrophilic monofunctional monomer to the phosphate ester (meth)acrylate is 5 to 400. [Item 5] The photocurable ink composition for inkjet printing according to any one of Items 1 to 4, wherein the amine-modified oligomer is contained in an amount of 0.1 to 20% by mass based on the total mass of the ink composition. [Section 6] 6. The photocurable ink composition for ink-jet printing according to any one of items 1 to 5, wherein the hydrophilic monofunctional monomer contains at least one of N-2 substituted (meth)acrylamide and a hydroxyl group-containing monofunctional monomer. [Section 7] Item 7. The photocurable ink composition for ink-jet printing according to any one of items 1 to 6, wherein the pigment dispersant contains a basic group-containing pigment dispersant. [Section 8] Item 8. The photocurable ink composition for inkjet printing according to any one of items 1 to 7, wherein the pigment dispersant contains a pigment dispersant with an amine value of less than 40 mgKOH / g and a pigment dispersant with an amine value of 40 mgKOH / g or more. [Section 9] Item 9. The photocurable ink composition for ink-jet printing according to any one of items 1 to 8, wherein the photopolymerizable compound further contains a polyfunctional monomer other than the phosphate ester (meth)acrylate. [Section 10] 10. The photocurable ink composition for ink-jet printing according to any one of items 1 to 9, wherein the phosphate ester (meth)acrylate contains a phosphate ester (meth)acrylate having three (meth)acrylate groups. Effect of the Invention

[0010] The photocurable ink composition for inkjet printing of the present invention provides an ink composition for inkjet printing that has high adhesion between the printed layer and the substrate to be printed, high dispersion stability of the pigment in the ink composition, and improved storage stability.

[0043] In addition, the photocurable ink composition for inkjet printing of the present invention provides an ink composition for inkjet printing which has high adhesion between the printed layer and the substrate to be printed, high water resistance of the printed layer, high dispersion stability of the pigment in the ink composition, and improved storage stability. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] [A. Composition of photocurable inkjet printing ink composition] The photocurable ink composition for inkjet printing of the present invention (hereinafter, simply referred to as "ink composition") contains 1) a pigment, 2) a pigment dispersant, 3) a photopolymerizable compound, 4) a photopolymerization initiator, and 5) any other component; 3) the photopolymerizable compound contains a combination of a hydrophilic monofunctional monomer and a phosphoric acid ester (meth)acrylate, and may further contain any other photopolymerizable compound. The ink composition of the present invention may contain carbon black as a pigment. The ink composition of the present invention may also contain an amine-modified oligomer as a photopolymerizable compound.

[0012] [A-1. Pigments] The ink composition contains a pigment. The pigment is a component added to the ink composition to impart coloring power, hiding power, etc., and examples of the pigment include color pigments, white pigments, metal powders, etc. Examples of such pigments include, without particular limitation, the following organic and / or inorganic pigments that have been conventionally used in ink compositions.

[0013] Examples of pigments include organic pigments such as dye lake pigments, azo pigments, benzimidazolone pigments, phthalocyanine pigments, quinacridone pigments, anthraquinone pigments, dioxazine pigments, indigo pigments, thioindigo pigments, perylene pigments, perinone pigments, diketopyrrolopyrrole pigments, isoindolinone pigments, nitro pigments, nitroso pigments, flavanthrone pigments, quinophthalone pigments, pyranthrone pigments, and indanthrone pigments, as well as various inorganic pigments.

[0014] Among these pigments, preferred examples include yellow pigments such as disazo yellow (pigment yellow 12, pigment yellow 13, pigment yellow 14, pigment yellow 17, pigment yellow 1), Hansa yellow, pigment yellow 150, and pigment yellow 155; magenta pigments such as brilliant carmine 6B, lake red C, watching red, quinacridone, pigment red 122, and pigment red 254; cyan pigments such as phthalocyanine blue, phthalocyanine green, alkali blue, and pigment blue 15:4; colored pigments such as titanium oxide (pigment white 6, etc.), zinc oxide, red iron oxide, antimony red, cadmium yellow, cobalt blue, iron blue, ultramarine blue, iron black, chromium oxide green, carbon black (pigment black 7, etc.), and graphite (including achromatic coloring pigments such as white and black), and metal powders such as aluminum paste and bronze powder.

[0015] The content of the pigment in the ink composition varies depending on the type of pigment and the desired degree of coloring, and is not particularly limited, but may be, for example, about 2.0 to 30.0 mass % based on the total amount of the ink composition. When preparing a colored ink composition, a pigment or dye of a different color may be used in combination as a complementary color, or an ink composition of a different color may be added. In the present invention, when the pigment contains carbon black, the content of carbon black in the pigment is not particularly limited and can be set arbitrarily in the range of more than 0 mass% to 100 mass% based on the total mass of the pigment, for example, 30 mass% or more, preferably 50 mass% or more, more preferably 80 mass% or more, and even more preferably 100 mass%.

[0016] [A-2. Pigment dispersants] The ink composition contains one or more pigment dispersants for dispersing the pigment. The pigment dispersant is preferably a polymer-based pigment dispersant, and is preferably a basic group-containing pigment dispersant. Examples of the basic group-containing pigment dispersant include polymer-based pigment dispersants such as a basic group-containing polyester-based pigment dispersant, a basic group-containing acrylic-based pigment dispersant, a basic group-containing urethane-based pigment dispersant, and a basic group-containing carbodiimide-based pigment dispersant, as well as an anionic surfactant.

[0017] The polymeric pigment dispersant is not particularly limited, but may be a linear polymer having a pigment affinity moiety consisting of a basic group at least at the end of the main chain (at one end or both ends) by a block or graft structure. The polymeric pigment dispersant may contain 2 to 3,000 basic groups in one molecule and may have a number average molecular weight of 1,000 to 1,000,000.

[0018] The amine value of the pigment dispersant is preferably 10 mgKOH / g or more, more preferably 20 mgKOH / g or more; on the other hand, it is preferably 100 mgKOH / g or less, more preferably 80 mgKOH / g or less, and even more preferably 70 mgKOH / g or less. The amine value indicates the total amount of free base and base, and is expressed as the number of milligrams of potassium hydroxide equivalent to the amount of hydrochloric acid required to neutralize 1 g of sample.

[0019] It may be preferable that the ink composition contains two or more pigment dispersants with different amine values. In other words, by combining a pigment dispersant having an amine value less than a certain value with a pigment dispersant having an amine value equal to or greater than a certain value, the dispersion stability of the pigment in the ink composition can be improved. It is preferable to combine a pigment dispersant having an amine value less than 40 mgKOH / g with a pigment dispersant having an amine value of 40 mgKOH / g or more.

[0020] Specific embodiments of the pigment dispersant, preferably the basic group-containing pigment dispersant, include the following embodiments (1) to (17).

[0021] (1) A reaction product of an amino group and / or an imino group of a polyamine compound (e.g., a poly(lower alkylene amine) such as polyallylamine, polyvinylamine, or polyethylene polyimine) with at least one member selected from the group consisting of polyesters, polyamides, and polyesteramides having a free carboxyl group (see JP 2001-59906 A); (2) Reaction products of low molecular weight amino compounds such as poly(lower) alkyleneimines and methyliminobispropylamine with polyesters having free carboxyl groups (see JP-A-54-37082 and JP-A-1-311177); (3) A reaction product obtained by sequentially reacting an isocyanate group of a polyisocyanate compound with an alcohol such as methoxypolyethylene glycol, a polyester having one hydroxyl group such as caprolactone polyester, a compound having two or three isocyanate group-reactive functional groups, and an aliphatic or heterocyclic hydrocarbon compound having an isocyanate group-reactive functional group and a tertiary amino group (see JP-A-2-612); (4) A compound obtained by reacting a polymer of an acrylate having an alcoholic hydroxyl group with a polyisocyanate compound and a hydrocarbon compound having an amino group; (5) Reaction products obtained by adding polyether chains to low molecular weight amino compounds; (6) A reaction product obtained by reacting a compound having an isocyanate group with a compound having an amino group (see JP-A-4-210220); (7) A reaction product obtained by reacting a polyepoxy compound with a linear polymer having a free carboxyl group and an organic amine compound having one secondary amino group (see JP-A-9-87537); (8) Reaction products of polycarbonate compounds having a functional group capable of reacting with an amino group at one end with polyamine compounds (see JP-A-9-194585); (9) Copolymers of at least one selected from methacrylic acid esters or acrylic acid esters, such as methyl methacrylate, ethyl methacrylate, propyl methacrylate, butyl methacrylate, stearyl methacrylate, benzyl methacrylate, methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, stearyl acrylate, and benzyl acrylate, at least one basic group-containing polymerizable monomer, such as acrylamide, methacrylamide, N-methylolamide, vinylimidazole, vinylpyridine, and a monomer having an amino group and a polycaprolactone skeleton, and at least one styrene, styrene derivative, and other polymerizable monomer (see JP-A-1-164429); (10) Basic group-containing carbodiimide pigment dispersants (see WO 2004 / 000950); (11) A block copolymer consisting of a block having a basic group such as a tertiary amino group or a quaternary ammonium salt group and a block having no functional group (see JP 2005-55814 A); (12) A pigment dispersant obtained by subjecting a polyallylamine to a Michael addition reaction with a polycarbonate compound (see JP-A-9-194585); (13) Carbodiimide compounds having at least one polybutadiene chain and at least one basic nitrogen-containing group (see JP 2006-257243 A); (14) A carbodiimide compound having at least one amide group-containing side chain and at least one basic nitrogen-containing group in the molecule (see JP 2006-176657 A); (15) Polyurethane compounds having structural units having ethylene oxide chains and propylene oxide chains and having amino groups quaternized with a quaternizing agent (see JP 2009-175613 A); (16) A compound obtained by reacting an isocyanate group of an isocyanate compound having an isocyanurate ring in the molecule with an active hydrogen group of a compound having an active hydrogen group in the molecule and having a carbazole ring and / or an azobenzene skeleton, wherein the number of carbazole rings and azobenzene skeletons in the molecule of the compound is 15 to 85% of the total number of isocyanate groups derived from the isocyanate compound having an isocyanurate ring and urethane bonds and urea bonds generated by the reaction of the isocyanate groups with the active hydrogen groups (see JP 2010-107965 A); (17) Graft copolymers in which polyether or polyester side chains are introduced into acrylate polymers having amino groups.

[0022] Pigment dispersants are also available on the market. Examples of commercially available pigment dispersants include the SOLSPERSE series from Lubrizol, the Disperbyk series and BYKJET series from BYK-Chemie, the EFKA series from BASF, and the AJISPER series from Ajinomoto Fine-Techno.

[0023] Examples of the SOLSPERSE series include SOLSPERSE11200, SOLSPERSE13240, SOLSPERSE13650, SOLSPERSE13940, SOLSPERSE16000, SOLSPERSE17000, SOLSPERSE18000, SOLSPERSE20000, SOLSPERSE24000, SOLSPERSE24000SC, SOLSPERSE24000GR, SOLSPERSE2600, SOLSPERSE28000, SOLSPERSE31845, These include SOLSPERSE32000, SOLSPERSE32500, SOLSPERSE32550, SOLSPERSE32600, SOLSPERSE33000, SOLSPERSE34750, SOLSPERSE35100, SOLSPERSE35200, SOLSPERSE37500, SOLSPERSE38500, SOLSPERSE39000, SOLSPERSE56000, SOLSPERSE71000, SOLSPERSE73000, SOLSPERSE74000, etc.

[0024] Examples of the Disperbyk series include Disperbyk-101, Disperbyk-108, Disperbyk-109, Disperbyk-112, Disperbyk-116, Disperbyk-130, Disperbyk-140, Disperbyk-142, Disperbyk-145, Disperbyk-161, Disperbyk-162, Disperbyk-163, Disperbyk-164, Disperbyk-166, Disperbyk-167, Disperbyk-169, Disperbyk-200, Disperbyk-201, Disperbyk-202, Disperbyk-203, Disperbyk-204, Disperbyk-205, Disperbyk-206, Disperbyk-207, Disperbyk-208, Disperbyk-209, Disperbyk-300, Disperbyk-311, Disperbyk-312, Disperbyk-313, Disperbyk-314, Disperbyk-315, Disperbyk-316, Disperbyk-317, Disperbyk-318, Disperbyk-320, Disperbyk-325, Disperbyk-326, Disperbyk-327, Disperbyk-328, Disperbyk-329, Disperbyk-400, Disperbyk-410, Disperbyk-420, Disperbyk-421, Disperbyk-422, Disperbyk-423, Disperbyk-424, Disperbyk-425, Disperbyk-426, Disperbyk-427, Disperbyk-428, Disperbyk-429, Disperbyk-430, Disperbyk-431, Disperbyk-43 These include rbyk-167, Disperbyk-168, Disperbyk-180, Disperbyk-182, Disperbyk-183, Disperbyk-185, Disperbyk-184, Disperbyk-2000, Disperbyk-2001, Disperbyk-2008, Disperbyk-2020, Disperbyk-2050, Disperbyk-2070, Disperbyk-2150, Disperbyk-2155 etc.

[0025] Examples of the BYKJET series include BYKJET-9131, BYKJET-9132, BYKJET-9133, BYKJET-9142, BYKJET-9150, BYKJET-9151, BYKJET-9152, BYKJET-9170, BYKJET-9171, BYKJET-9175, BYKJET-9177, and the like.

[0026] Examples of the EFKA series include EFKA4008, EFKA4046, EFKA4047, EFKA4015, EFKA4020, EFKA4050, EFKA4055, EFKA4060, EFKA4080, EFKA4300, EFKA4330, EFKA4400, EFKA4401, EFKA4402, EFKA4403, EFKA4500, EFKA4510, EFKA4530, EFKA4800, EFKA PX4701, EFKA PX4703, and the like.

[0027] Examples of the AJISPER series include AJISPER PB-711, AJISPER PB-821, AJISPER PB-822, and the like.

[0028] Among these, examples of pigment dispersants with an amine value of 40 mgKOH / g or more include SOLSPERSE24000 (41.6 mgKOH / g), SOLSPERSE33000 (43 mgKOH / g), SOLSPERSE71000 (75 mgKOH / g), SOLSPERSE73000 (80 mgKOH / g), SOLSPERSE74000 (81 mgKOH / g), Disperbyk-108 (71 mgKOH / g), Disperbyk-180 (94 mgKOH / g), Disperbyk-2008 (66 mgKOH / g), Disperbyk-2155 (48 mgKOH / g), EFKA4300 (57 mgKOH / g), EFKA4401 (48 to 52 mgKOH / g), EFKA PX4701 (40 mgKOH / g), EFKA Contains PX4703 (56 mg KOH / g) etc.

[0029] Examples of pigment dispersants having an amine value of less than 40 mgKOH / g include SOLSPERSE32000 (31.2 mgKOH / g), SOLSPERSE39000 (26 mgKOH / g), SOLSPERSE56000 (39 mgKOH / g), Disperbyk-163 (10 mgKOH / g), Disperbyk-168 (11 mgKOH / g), Disperbyk-2050 (31 mgKOH / g), BYKJET-9151 (17 mgKOH / g), BYKJET-9152 (27 mgKOH / g), AJISPER PB-821 (11.2 mgKOH / g), AJISPER PB-822 (18.2 mgKOH / g), and the like.

[0030] When combining a pigment dispersant with an amine value of less than 40 mgKOH / g with a pigment dispersant with an amine value of 40 mgKOH / g or more: the pigment dispersant with an amine value of less than 40 mgKOH / g preferably has an amine value of 10 mgKOH / g or more, more preferably has an amine value of 20 mgKOH / g or more; the pigment dispersant with an amine value of 40 mgKOH / g or more preferably has an amine value of 100 mgKOH / g or less, more preferably has an amine value of 80 mgKOH / g or less, and even more preferably has an amine value of 70 mgKOH / g or less. In addition, the "difference" in amine value between the pigment dispersant with an amine value of less than 40 mgKOH / g and the pigment dispersant with an amine value of 40 mgKOH / g or more may be 1 mgKOH / g or more.

[0031] The content of the pigment dispersant in the ink composition is 38 to 100 parts by mass relative to 100 parts by mass of the pigment. The content of the pigment dispersant relative to 100 parts by mass of the pigment is 38 parts by mass or more, preferably 40 parts by mass or more, more preferably 50 parts by mass or more; and 100 parts by mass or less, preferably 90 parts by mass or less, more preferably 80 parts by mass or less. The content of the pigment dispersant relative to the entire ink composition is, for example, 0.5% by mass or more, preferably 0.8% by mass or more; for example, 4% by mass or less, preferably 3% by mass or less. In addition, when a pigment dispersant (α) having an amine value of less than 40 mgKOH / g is combined with a pigment dispersant (β) having an amine value of 40 mgKOH / g or more, the content mass ratio of α and β is not particularly limited, but is preferably in the range of α:β=10:1 to 10:15.

[0032] [A-3. Photopolymerizable compound] The ink composition contains a photopolymerizable compound, and the photopolymerizable compound contains a combination of a hydrophilic monofunctional monomer and a phosphoric acid ester (meth)acrylate, and may contain any other photopolymerizable compound. As the other optional photopolymerizable compound, it may be preferable to contain an oligomer (particularly, an amine-modified oligomer) or a polyfunctional monomer (excluding phosphoric acid ester (meth)acrylate). The total content of the photopolymerizable compounds is, for example, 70% by mass or more, preferably 80% by mass or more, and more preferably 85% by mass or more, based on the entire ink composition.

[0033] [A-3a. Hydrophilic monofunctional monomer] The hydrophilic monofunctional monomer is a monofunctional monomer having one ethylenically unsaturated group and a hydrophilic group such as a hydroxyl group, an amide group, a carboxyl group (or a salt thereof), a sulfonic acid group (or a salt thereof), a phosphoric acid group (or a salt thereof), an ether group (such as a glycol group), an amino group, etc. The hydrophilic monofunctional monomer is preferably a monofunctional monomer containing a hydroxyl group and / or an amide group.

[0034] Examples of hydroxyl group-containing monofunctional monomers include hydroxyalkyl (meth)acrylates such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 3-hydroxybutyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, and cyclohexanedimethanol mono(meth)acrylate; 2-hydroxyethyl vinyl ether (HEVE), 4-hydroxybutyl vinyl ether (HBVE), and 4-hydroxybutyl acrylate glycidyl ether (HBAGA).

[0035] The amide group-containing monofunctional monomer is preferably (meth)acrylamide, more preferably (meth)acrylamide in which two hydrogen atoms on the nitrogen of the amide group (-C(=O)NH2) are replaced with other substituents (N-2 substituted (meth)acrylamide), and particularly preferably N-2 substituted acrylamide. Examples of N-2 substituted (meth)acrylamides include N-alkylol (C1-5) (meth)acrylamides such as (meth)acryloylmorpholine, N,N-dimethyl (meth)acrylamide, diethyl (meth)acrylamide; di(2-hydroxyethyl) (meth)acrylamide, di(3-hydroxypropyl) (meth)acrylamide, di(4-hydroxybutyl) (meth)acrylamide, and 1-3 mole adducts of these N-alkylol (C1-5) (meth)acrylamides with ethylene oxide or propylene oxide.

[0036] The amide group-containing monofunctional monomer may be 1) (meth)acrylamide, 2) N-methyl(meth)acrylamide, N-methoxymethyl(meth)acrylamide, N-butoxymethyl(meth)acrylamide, etc., in which one hydrogen atom on the nitrogen of the amide group (-C(=O)NH2) is replaced with another substituent, or 3) N-vinylpyrrolidone (NVP), N-vinylformamide, etc.

[0037] These hydrophilic monofunctional monomers may be used alone or in combination of two or more. In particular, it is preferable to use a combination of an amide group-containing monofunctional monomer (particularly, an N-2 substituted (meth)acrylamide) and a monofunctional monomer having a hydroxyl group.

[0038] The content of the hydrophilic monofunctional monomer in the ink composition is preferably set so that the dispersion stability of the pigment can be maintained. As described later, the phosphate ester (meth)acrylate is a component that can have the effect of reducing the pigment dispersion stability, and the hydrophilic monofunctional monomer in the ink composition of the present invention can have the effect of preventing the reduction in the pigment dispersion stability caused by the phosphate ester (meth)acrylate. Therefore, it is preferable to appropriately set the relative content with the phosphate ester (meth)acrylate. The content ratio of the hydrophilic monofunctional monomer to the phosphate ester (meth)acrylate can be as described in the section [A-3b.] below.

[0039] The content of the hydrophilic monofunctional monomer in the ink composition can be, for example, 10% by mass or more, preferably 12% by mass or more, more preferably 15% by mass or more, and can be, for example, 80% by mass or less, preferably 75% by mass or less, and more preferably 65% ​​by mass or less, based on the entire ink composition. By setting the content of the hydrophilic monomer in such a range, it becomes easier to adjust the physical properties (viscosity, surface tension, etc.) of the ink composition to an appropriate range. In addition, the content of the hydrophilic monofunctional monomer in the entire photopolymerizable compound can be, for example, 15% by mass or more, preferably 20% by mass or more, and can be, for example, 85% by mass or less, preferably 80% by mass or less.

[0040] [A-3b. Phosphate ester (meth)acrylate] The ink composition contains one or more types of phosphate ester (meth)acrylate, which is a photopolymerizable compound. The phosphate ester (meth)acrylate is a compound having both a phosphate ester group and a (meth)acryloyl group in the molecule. That is, the phosphate ester (meth)acrylate is a compound in which a "functional group containing a (meth)acryloyl group" is introduced into one, two or three of the three -OH groups of phosphoric acid (P(=O)(OH)3), and can be represented by the following formulas (1X) to (3X). The "(meth)acryloyl group" means a methacryloyl group or an acryloyl group. [ka]

[0041] The substituents R(1a), R(2a), R(2b), R(3a), R(3b) and R(3c) in the formulae (1X) to (3X) each independently represent a "functional group containing a (meth)acryloyl group", which may be the same or different from each other. The "functional group containing a (meth)acryloyl group" includes, for example, groups represented by the following formulae (G1) to (G3). In the formulae (G1) to (G3), R 10 represents a hydrogen atom or a methyl group, A 1 ~A 4 each independently represents an alkylene group having 1 to 20 carbon atoms, and n1 to n3 each independently represent an integer of 1 to 100. [ka]

[0042] A preferred example of the "functional group containing a (meth)acryloyl group" in the phosphate ester (meth)acrylate is R 10 is a hydrogen atom or a methyl group, and A 1 is a phosphate ester (meth)acrylate of an alkylene group having 2 to 6 carbon atoms, and in formula (G2), R 10 is a hydrogen atom or a methyl group, and A 2 is an alkylene group having 2 to 6 carbon atoms, and A 3is a phosphate ester (meth)acrylate of an alkylene group having 6 to 12 carbon atoms, and in formula (G3), R 10 is a hydrogen atom or a methyl group, and A 4 is a phosphoric acid ester (meth)acrylate of an alkylene group having 2 to 12 carbon atoms.

[0043] Further specific examples of phosphate ester (meth)acrylates include the following: [ka] (In formulas (1A) to (1F), R 11 is a hydrogen atom or a methyl group, and A 11 and A 12 are each independently an alkylene group having 1 to 20 carbon atoms, and X1 to X3 are each independently an integer of 1 to 100. In the present invention, the compound represented by formula (1A) is R 11 is a hydrogen atom or a methyl group, and A 11 is an alkylene group having 2 to 6 carbon atoms, and X1 is an integer of 1 to 10. In the present invention, the compound represented by formula (1B) is R 11 is a hydrogen atom or a methyl group, and X2 is an integer of 1 to 10. In the present invention, the compound represented by formula (1C) is R 11 is a hydrogen atom or a methyl group, and A 12 is an alkylene group having 2 to 6 carbon atoms, and X3 is an integer of 1 to 10.

[0044] [ka] (In formulas (2A) to (2F), R 11 and R 12 are each independently a hydrogen atom or a methyl group; A 13 ~A 16are each independently an alkylene group having 1 to 20 carbon atoms, and X4 to X9 are each independently an integer of 1 to 100. In the present invention, the compound represented by formula (2A) is R 11 is a hydrogen atom or a methyl group, and R 12 is a hydrogen atom or a methyl group, and A 13 is an alkylene group having 2 to 6 carbon atoms, and A 14 is an alkylene group having 2 to 6 carbon atoms, X4 is an integer of 1 to 10, and X5 is an integer of 1 to 10. In the present invention, the compound represented by formula (2B) is R 11 is a hydrogen atom or a methyl group, and R 12 is a hydrogen atom or a methyl group, X6 is an integer of 1 to 10, and X7 is an integer of 1 to 10. In the present invention, the compound represented by formula (2C) is R 11 is a hydrogen atom or a methyl group, and R 12 is a hydrogen atom or a methyl group, and A 15 is an alkylene group having 2 to 6 carbon atoms, and A 16 is an alkylene group having 2 to 6 carbon atoms, X8 is an integer of 1 to 10, and X9 is an integer of 1 to 10.

[0045] [ka] (In formula (3A), R 11 ~R 13 are each independently a hydrogen atom or a methyl group; A 17 ~A 19 each independently represents an alkylene group having 1 to 20 carbon atoms, and X10 to X12 each independently represent an integer of 1 to 100.

[0046] In the phosphoric acid ester (meth)acrylate, at least one of the three -OH groups of the phosphoric acid (P(=O)(OH)3) may remain as an -OH group, or a "functional group containing a (meth)acryloyl group" may be introduced to all three -OH groups (no -OH groups of the phosphoric acid remain). The phosphoric acid ester (meth)acrylate in which a "functional group containing a (meth)acryloyl group" is introduced to all three -OH groups has the advantage of being easy to adjust the physical properties of the ink composition due to its low viscosity, and when combined with a hydrophilic monofunctional monomer, the adhesion of the cured coating film of the ink composition to the substrate can be sufficiently increased.

[0047] The content of the phosphoric acid ester (meth)acrylate in the ink composition is 0.1% by mass or more, preferably 0.2% by mass or more, more preferably 0.5% by mass or more, and 4.3% by mass or less, preferably 4% by mass or less, more preferably 3% by mass or less, based on the total amount of the ink composition. By making the content of the phosphoric acid ester (meth)acrylate in the ink composition equal to or more than a certain amount, the adhesion of the cured coating film of the ink composition to the substrate is improved. On the other hand, by making the content of the phosphoric acid ester (meth)acrylate equal to or less than a certain amount, the storage stability of the ink composition, that is, the dispersion stability of the pigment, can be improved.

[0048] Phosphate ester (meth)acrylate may have the effect of reducing the dispersion stability of the pigment, more specifically, the effect of reducing the function of the pigment dispersant. Therefore, when a phosphate ester (meth)acrylate is blended, it may be difficult to maintain the pigment dispersion stability of the ink composition. In contrast, the ink composition of the present invention is an ink composition with high pigment dispersion stability even when a phosphate ester (meth)acrylate is blended by blending a certain amount or more of a hydrophilic monofunctional monomer.

[0049] Therefore, it is preferable to set the content ratio of the phosphate ester (meth)acrylate and the hydrophilic monofunctional monomer so that the pigment dispersion stability of the ink composition can be maintained. Specifically, the mass ratio of the hydrophilic monofunctional monomer to the phosphate ester (meth)acrylate is 5 or more, preferably 7 or more, more preferably 8 or more; and 400 or less, preferably 300 or less, more preferably 200 or less, and even more preferably 100 or less. In the present invention, when the water resistance of the cured coating film of the ink composition is not important, the mass ratio of the hydrophilic monofunctional monomer to the phosphate ester (meth)acrylate can be 5 to 400, and when the water resistance of the cured coating film of the ink composition is required, it is preferable that the mass ratio of the hydrophilic monofunctional monomer to the phosphate ester (meth)acrylate is 5 to 300.

[0050] The mechanism of maintaining pigment dispersion stability by blending hydrophilic monofunctional monomer is not particularly limited. As a presumed mechanism, since phosphoric acid ester (meth)acrylate is a relatively highly polar component, it is localized near a pigment dispersant (dispersant surrounding it) that is also highly polar, and the dispersion of the pigment is destroyed by mutual interaction, which may lead to a decrease in the stability of the ink composition; however, by adding a hydrophilic monofunctional monomer, the localization of the phosphoric acid ester (meth)acrylate is reduced, and the interaction between the phosphoric acid ester (meth)acrylate and the pigment dispersant is alleviated, which can be considered to suppress the decrease in the dispersion of the pigment.

[0051] [A-3c. Oligomer (amine-modified oligomer)] The ink composition may contain one or more oligomers, which are photopolymerizable compounds. An oligomer is a component that polymerizes an ethylenically unsaturated bond in a molecule to obtain a high molecular weight. Since an oligomer is a relatively high molecular weight component before polymerization, it can impart appropriate viscosity and elasticity to the ink composition. In addition, an oligomer has a relatively high polarity, and may impart adhesion and adhesion to a non-absorbing medium to the ink composition after curing. Among oligomers, an amine-modified oligomer can increase the photocurability of the ink composition, so that the ink composition of the present invention may preferably contain an amine-modified oligomer.

[0052] The amine-modified oligomer is an oligomer having one or more photopolymerizable functional groups together with one or more amino groups in the molecule, and is preferably an oligomer having two or more photopolymerizable functional groups (polyfunctional amine-modified oligomer). Here, the photopolymerizable functional group is preferably a (meth)acryloyl group; the preferred amine-modified oligomer is an amine-modified (meth)acrylate oligomer having one or more amino groups together with two or more (meth)acryloyl groups in the molecule.

[0053] The amine-modified (meth)acrylate oligomer may be obtained by synthesis through polymerization of desired monomers, or may be a commercially available product. Examples of commercially available products include GENOMER5161, GENOMER5275 (RAHN); CN371, CN371NS, CN373, CN383, CN384, CN386, CN501, CN503, CN550, CN551 (Sartomer); EBECRYL80, EBECRYL81, EBECRYL83, EBECRYL7100, EBECRYL84, EBECRYLP115 (Daicel-Allnex); LAROMER PO 83F, LAROMER PO 84F, Laromer LR8946, Laromer LR8956, Laromer LR8996, Laromer LR8894 (BASF); AgiSyn001, AgiSyn002, Agisyn003, Agisyn008 (DSM Coating Resin); Photomer 4771, Photomer 4775, Photomer 4967, Photomer 5006, Photomer 5096, Photomer 5662, Photomer 5930 (Cognis); Doublecure EPD, Doublecure OPD, Doublecure 115, Doublecure 225, Doublecure 645, PolyQ222, PolyQ226, PolyQ224, PolyQ101 (DoubleBond Chemicals); and the like.

[0054] The viscosity of the amine-modified oligomer is not limited, but a viscosity of 2,000 mPa·s or less at 25° C. is particularly preferred in order to bring the viscosity of the entire photocurable ink jet printing ink composition into an appropriate range.

[0055] The content of the amine-modified oligomer contained in the photocurable ink composition for inkjet printing is not particularly limited, and is, for example, 0.1% by mass or more, preferably 0.3% by mass or more, based on the total ink composition; and, for example, 20% by mass or less, preferably 18% by mass or less, more preferably 15% by mass or less.

[0056] [A-3d. Polyfunctional monomers (excluding phosphate ester (meth)acrylates and oligomers)] The ink composition may contain one or more types of polyfunctional monomers that are photopolymerizable compounds. Examples of polyfunctional monomers (monomers having two or more ethylenically unsaturated bonds) that can be used include the following polyfunctional (meth)acrylate compounds and vinyl ether group-containing (meth)acrylate compounds.

[0057] The polyfunctional (meth)acrylate compound may be a difunctional di(meth)acrylate compound, a trifunctional tri(meth)acrylate compound, or a higher functional (meth)acrylate compound.

[0058] Examples of the di(meth)acrylate compound include ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, propylene glycol di(meth)acrylate, dipropylene glycol di(meth)acrylate, tripropylene glycol di(meth)acrylate, polypropylene glycol di(meth)acrylate, butylene glycol di(meth)acrylate, pentyl glycol di(meth)acrylate, neopentyl glycol di(meth)acrylate, Tyl glycol di(meth)acrylate, hydroxypivalyl hydroxypivalate di(meth)acrylate, hydroxypivalyl hydroxypivalate dicaprolactonate di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, 1,2-hexanediol di(meth)acrylate, 1,5-hexanediol di(meth)acrylate, 2,5-hexanediol di(meth)acrylate, 1,7-heptanediol di(meth)acrylate, 1,8-octanediol di(meth)acrylate, 1,2-octanediol di(meth)acrylate meth)acrylate, 1,9-nonanediol di(meth)acrylate, 1,10-decanediol di(meth)acrylate, 1,2-decanediol di(meth)acrylate, 1,12-dodecanediol di(meth)acrylate, 1,2-dodecanediol di(meth)acrylate, 1,14-tetradecanediol di(meth)acrylate, 1,2-tetradecanediol di(meth)acrylate, 1,16-hexadecanediol di(meth)acrylate, 1,2-hexadecanediol di(meth)acrylate, 2-methyl-2,4-pentadecane hexanediol di(meth)acrylate, 3-methyl-1,5-pentanediol di(meth)acrylate, 2-methyl-2-propyl-1,3-propanediol di(meth)acrylate, 2,4-dimethyl-2,4-pentanediol di(meth)acrylate, 2,2-diethyl-1,3-propanediol di(meth)acrylate, 2,2,4-trimethyl-1,3-pentanediol di(meth)acrylate, dimethylol octane di(meth)acrylate, 2-ethyl-1,3-hexanediol di(meth)acrylate, 2,5-dimethyl-2,5-Hexanediol di(meth)acrylate, 2-methyl-1,8-octanediol di(meth)acrylate, 2-butyl-2-ethyl-1,3-propanediol di(meth)acrylate, 2,4-diethyl-1,5-pentanediol di(meth)acrylate, tricyclodecanedimethylol di(meth)acrylate, tricyclodecanedimethylol dicaprolactonate di(meth)acrylate, cyclohexanedimethanol di(meth)acrylate, dicyclopentanyl di(meth)acrylate, bisphenol A tetraethylene oxide adduct di(meth)acrylate, bisphenol F tetraethylene oxide adduct di(meth)acrylate, bisphenol S tetraethylene oxide adduct di(meth)acrylate Ethylene oxide adduct di(meth)acrylate, hydrogenated bisphenol A tetraethylene oxide adduct di(meth)acrylate, hydrogenated bisphenol F tetraethylene oxide adduct di(meth)acrylate, hydrogenated bisphenol A di(meth)acrylate, hydrogenated bisphenol F di(meth)acrylate, bisphenol A tetraethylene oxide adduct dicaprolactonate di(meth)acrylate, bisphenol F tetraethylene oxide adduct dicaprolactonate di(meth)acrylate, etc., di(meth)acrylates of polyhydric alcohols such as glycerin, pentaerythritol, diglycerin, ditrimethylolpropane, and dipentaerythritol, etc. are included.

[0059] Examples of tri(meth)acrylate compounds include glycerin tri(meth)acrylate, trimethylolpropane tri(meth)acrylate, trimethylolpropane tricaprolactonate tri(meth)acrylate, trimethylolethane tri(meth)acrylate, trimethylolhexane tri(meth)acrylate, trimethyloloctane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, and the like; and 3EO (ethylene oxide) modified products, 6EO modified products, and 9EO modified products thereof (3EO modified trimethylolpropane tri(meth)acrylate, 3EO modified trimethylolethane tri(meth)acrylate, 3EO modified trimethylolhexane tri(meth)acrylate, and the like).

[0060] Examples of tetrafunctional or higher (meth)acrylate compounds include trimethylolpropane tetra(meth)acrylate, pentaerythritol tetra(meth)acrylate, pentaerythritol tetracaprolactonate tetra(meth)acrylate, diglycerin tetra(meth)acrylate, ditrimethylolpropane tetra(meth)acrylate, ditrimethylolpropane tetracaprolactonate tetra(meth)acrylate, ditrimethylolethane tetra(meth)acrylate, and ditrimethylolbutane tetra(meth)acrylate. and tetra- or higher functional monomers such as ditrimethylolhexane tetra(meth)acrylate, ditrimethyloloctane tetra(meth)acrylate, dipentaerythritol penta(meth)acrylate, dipentaerythritol hexa(meth)acrylate, tripentaerythritol hexa(meth)acrylate, tripentaerythritol hepta(meth)acrylate, tripentaerythritol octa(meth)acrylate, and tripentaerythritol polyalkylene oxide hepta(meth)acrylate.

[0061] Examples of vinyl ether group-containing (meth)acrylate compounds include 2-vinyloxyethyl (meth)acrylate, 3-vinyloxypropyl (meth)acrylate, 1-methyl-2-vinyloxyethyl (meth)acrylate, 2-vinyloxypropyl (meth)acrylate, 4-vinyloxybutyl (meth)acrylate, 1-methyl-3-vinyloxypropyl (meth)acrylate, 1-vinyloxymethylpropyl (meth)acrylate, 2-methyl-3-vinyloxypropyl (meth)acrylate, acrylate-3-methyl-3-vinyloxypropyl, (meth)acrylate-1,1-dimethyl-2-vinyloxyethyl, (meth)acrylate-3-vinyloxybutyl, (meth)acrylate-1-methyl-2-vinyloxypropyl, (meth)acrylate-2-vinyloxybutyl, (meth)acrylate-4-vinyloxycyclohexyl, (meth)acrylate-5-vinyloxypentyl, (meth)acrylate-6-vinyloxyhexyl, (meth)acrylate-4-vinyloxymethylcyclohexylmethyl, (meth)acrylate 3-vinyloxymethylcyclohexylmethyl (meth)acrylate, 2-vinyloxymethylcyclohexylmethyl (meth)acrylate, p-vinyloxymethylphenylmethyl (meth)acrylate, m-vinyloxymethylphenylmethyl (meth)acrylate, o-vinyloxymethylphenylmethyl (meth)acrylate, 2-(vinyloxyethoxy)ethyl (meth)acrylate, 2-(vinyloxyisopropoxy)ethyl (meth)acrylate, 2-(vinyloxyethoxy)propyl (meth)acrylate, acrylate-2-(vinyloxyethoxy)isopropyl, (meth)acrylate-2-(vinyloxyisopropoxy)propyl, (meth)acrylate-2-(vinyloxyisopropoxy)isopropyl, (meth)acrylate-2-(vinyloxyethoxyethoxy)ethyl, (meth)acrylate-2-(vinyloxyethoxyisopropoxy)ethyl, (meth)acrylate-2-(vinyloxyisopropoxyethoxy)ethyl, (meth)acrylate-2-(vinyloxyisopropoxyisopropoxy)ethyl, and (meth)acrylate-2-(vinyloxyisopropoxyisopropoxy)ethyl.

[0062] The content of the polyfunctional monomer in the photocurable ink composition for inkjet printing is preferably 10% by mass or more, more preferably 20% by mass or more, based on the total amount of the ink composition; and preferably 70% by mass or less, more preferably 60% by mass or less. The content of the polyfunctional monomer in the photocurable ink composition for inkjet printing is preferably 15% by mass or more, more preferably 25% by mass or more, based on the total amount of the photopolymerizable compounds; and preferably 80% by mass or less, more preferably 70% by mass or less.

[0063] [A-4. Photopolymerization initiator] The ink composition of the present invention contains a photopolymerization initiator. Examples of the photopolymerization initiator include benzoin ether-based photopolymerization initiators, acetophenone-based photopolymerization initiators, α-ketol-based photopolymerization initiators, aromatic sulfonyl chloride-based photopolymerization initiators, photoactive oxime-based photopolymerization initiators, benzoin-based photopolymerization initiators, benzyl-based photopolymerization initiators, benzophenone-based photopolymerization initiators, ketal-based photopolymerization initiators, triazine-based photopolymerization initiators, and acylphosphine oxide-based photopolymerization initiators. Among these, triazine-based photopolymerization initiators and acylphosphine oxide-based photopolymerization initiators are preferred from the viewpoint of good photocurability. These photopolymerization initiators can be used alone or in combination of two or more kinds, and for example, two kinds of acylphosphine oxide-based photopolymerization initiators may be combined.

[0064] Specific examples of photopolymerization initiators include bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide, diphenyl (2,4,6-trimethylbenzoyl)phosphine oxide, ethoxy(2,4,6-trimethylbenzoyl)phenylphosphine oxide, benzophenone, diethylthioxanthone, 2-methyl-1-(4-methylthio)phenyl-2-morpholinopropan-1-one, 4-benzoyl-4'-methyldiphenyl sulfide, 1-chloro-4-propoxythioxanthone, isopropylthioxanthone, 2-hydroxy-2-methyl-1-phenylpropan-1-one, 1-hydroxycyclohexyl Phenyl ketone, bis-2,6-dimethoxybenzoyl-2,4,4-trimethylpentylphosphine oxide, 1-[4-(2-hydroxyethoxy)-phenyl]-2-hydroxy-2-methyl-1-propan-1-one, 2,2-dimethyl-2-hydroxyacetophenone, 2,2-dimethoxy-2-phenylacetophenone, 2,4,6-trimethylbenzyl-diphenylphosphine oxide, 2-benzyl-2-dimethylamino-1-(morpholinophenyl)-butan-1-one, and the like.

[0065] The content of the photopolymerization initiator in the ink composition may be set according to the desired curing speed of the photocurable resin composition, but as a guideline, it is preferably 1 mass % or more, and more preferably 3 mass % or more, relative to the entire ink composition; and it is preferably 10 mass % or less, and more preferably 8 mass % or less.

[0066] [A-5. Optional Other Ingredients] The ink composition of the present invention may contain one or more other optional components. Examples of the other optional components include a sensitizer, a polymerization inhibitor, a leveling agent, a surface tension adjuster, a non-reactive resin, an ultraviolet absorber, an antioxidant, and the like.

[0067] [A-5a. Sensitizers] The ink composition may contain a sensitizer in order to improve photocurability. The sensitizers may be used alone or in combination of two or more kinds.

[0068] Examples of the sensitizer include anthracene-based sensitizers such as 9,10-dibutoxyanthracene, 9,10-diethoxyanthracene, 9,10-dipropoxyanthracene, and 9,10-bis(2-ethylhexyloxy)anthracene; and thioxanthone-based sensitizers such as 2,4-diethylthioxanthone, 2,4-diethylthioxanthen-9-one, 2-isopropylthioxanthone, and 4-isopropylthioxanthone. Commercially available sensitizers include anthracene-based sensitizers under the product names "DBA" and "DEA" (Kawasaki Chemical Industries, Ltd.), and thioxanthone-based sensitizers under the product names "DETX" and "ITX" (Lambson).

[0069] When a sensitizer is contained in the ink composition, from the viewpoint of preventing excessive addition, the content of the sensitizer is preferably 5 parts by mass or less, and more preferably 4 parts by mass or less, when the total amount of the photopolymerizable compounds (including phosphate ester (meth)acrylate, hydrophilic monofunctional monomer, amine-modified oligomer, and other polymerizable compounds) is 100 parts by mass. In addition, when the total amount of the photopolymerizable compounds is 100 parts by mass, the total content of the photopolymerization initiator and the sensitizer is preferably 2 to 15 parts by mass.

[0070] [A-5b. Polymerization inhibitors] The ink composition may contain a polymerization inhibitor. The polymerization inhibitor can prevent a polymerization reaction from occurring during storage of the ink composition, and can suppress an increase in viscosity of the ink composition.

[0071] Examples of the polymerization inhibitor include phenolic compounds (including quinone compounds) such as butylhydroxytoluene, tocopherol acetate, nitrosamine compounds, benzotriazole, hindered amines, and the like; among these, quinone compounds and nitrosamine compounds are more preferred.

[0072] The content of the polymerization inhibitor in the photocurable ink composition for inkjet printing is appropriately set depending on the type of polymerization inhibitor, but in the case of a quinone compound, it is about 0.1 to 1.0 part by mass when the total amount of the photopolymerizable components is 100 parts by mass.

[0073] [A-5c. Surfactants (leveling agents)] The ink composition may contain a surfactant as a leveling agent depending on the form of the printer head of the inkjet printing device used for printing. Any known surfactant may be contained without particular limitation, and examples of the surfactant include nonionic surfactants, cationic surfactants, anionic surfactants, betaine surfactants, etc. Specific examples of the surfactant include silicone surfactants such as polyether-modified silicone oil, polyester-modified polydimethylsiloxane, and polyester-modified methylalkylpolysiloxane, fluorine-based surfactants, and acetylene-based surfactants. The surfactants may be used alone or in combination of two or more.

[0074] Examples of silicone surfactants include BYK-307, BYK-315N, BYK-331, BYK-333, BYK-347, BYK-348, BYK-349, BYK-345, BYK-377, BYK-378, BYK-3455, and BYK-UV3500 (BYK-Chemie).

[0075] Examples of fluorine-based surfactants include F-410, F-444, F-553 (DIC), FS-65, FS-34, FS-35, FS-31, and FS-30 (DuPont).

[0076] Examples of the acetylene surfactant include Dynol 607, Dynol 609, Olfin E1004, Olfin E1010, Olfin E1020, Olfin PD-001, Olfin PD-002W, Olfin PD-004, Olfin PD-005, Olfin EXP.4001, Olfin EXP.4200, Olfin EXP.4123, Olfin EXP.4300 (Nissin Chemical Industry Co., Ltd.), Surfynol 104E, Surfynol 104H, Surfynol 104A, Surfynol 104BC, Surfynol 104DPM, Surfynol 104PA, Surfynol 104PG-50, Surfynol 420, Surfynol 440, and Surfynol 465 (EVONIK).

[0077] The content of the surfactant in the ink composition is preferably 0.005% by mass or more, and more preferably 0.01% by mass or more, based on the total mass of the ink composition, from the viewpoints of reducing the surface tension of the ink composition and improving the ejection stability from an inkjet head, and is preferably 1.5% by mass or less, and more preferably 1% by mass or less, from the viewpoints of suppressing bubbles that are generated in the ink composition during blending and improving the ejection stability.

[0078] When a surfactant is contained as a leveling agent, the content of the surfactant is preferably adjusted so that the ink composition has a surface tension of 20 to 36 mN / m at 25° C., and more preferably 0.1 to 1.5 mass % in the photocurable ink composition for ink jet printing.

[0079] [B. Properties and Uses of Ink Composition] The photocurable ink composition for ink-jet printing of the present invention only needs to be printable by an ink-jet device, and have sufficient photocurability and adhesion to a substrate to be printed.

[0080] [B-1. Viscosity] The viscosity of the ink composition at 25°C is preferably 5 mPa·s or more, more preferably 10 mPa·s or more, and even more preferably 15 mPa·s or more; and preferably 100 mPa·s or less, more preferably 60 mPa·s or less, even more preferably 46 mPa·s or less, and even more preferably 25 mPa·s or less. The viscosity of the ink composition can be adjusted mainly by the composition of the photopolymerizable compound and the photopolymerization initiator, and may also be adjusted by blending a viscosity modifier or the like as necessary. The viscosity described in this specification is a viscosity measured using an E-type viscometer (RE100L type viscometer, manufactured by Toki Sangyo Co., Ltd.) under conditions of 25°C and 10 rpm. If the viscosity is less than 5 mPa·s or exceeds 100 mPa·s, the ejection stability by inkjet printing may decrease.

[0081] [B-2.Surface tension] The surface tension of the ink composition at 25°C is preferably 20 to 36 mN / m. The surface tension of the ink composition can be adjusted by adding a surfactant (leveling agent) as necessary. The surface tension can be measured at a temperature of 25°C using a dynamic wettability tester (for example, product name: WET-6000, manufactured by Rhesca Corporation).

[0082] [B-3. Printing method] The ink composition of the present invention can be used for printing with an inkjet printer. The type of inkjet printer that can be used is not particularly limited, and may be a line head type (single pass type) or a serial head type (multi-pass type). A continuous type inkjet printer may also be used, and in this case, a conductivity imparting agent can be further added to adjust the electrical conductivity of the ink composition.

[0083] The ink composition is supplied to a printer head of an inkjet printing device, and the ink composition is ejected from the printer head onto a substrate to be printed. The ink composition is ejected from the printer head onto the substrate (printing of an image) so that the coating film has a thickness of, for example, 1 to 60 μm.

[0084] The ink composition that has landed on the substrate is cured by exposure to ultraviolet light, electron beams, or visible light irradiated from a light-emitting diode (LED), various lamps, or electrodes. From an environmental perspective, it is preferable to use a light-emitting diode (LED) that generates ultraviolet light with an emission peak wavelength in the range of 350 to 420 nm as the light source.

[0085] [B-4. Printing base material] The substrate to be printed is not particularly limited as long as it is a substrate to which a conventionally known photocurable inkjet printing ink composition can be applied. Examples of substrates include plastic, paper, capsules, gel, metal foil, glass, wood, cloth, etc. The photocurable inkjet printing ink composition of the present invention can exhibit the effect of preventing migration of the photopolymerization initiator, regardless of the substrate to be printed, of any material. Examples of the plastic constituting the substrate include at least one selected from the group consisting of polyester-based polymers (e.g., polyethylene terephthalate (PET), polyethylene naphthalate, etc.), cellulose-based polymers (e.g., diacetyl cellulose, triacetyl cellulose (TAC), etc.), polycarbonate-based polymers, polyacrylic-based polymers (e.g., polymethyl methacrylate, etc.), vinyl chloride-based polymers, polyolefin-based polymers (e.g., polyethylene, polypropylene, polyolefin polymers having a cyclic or norbornene structure, ethylene-propylene copolymers, etc.), polyamide-based polymers (e.g., nylon, aromatic polyamide polymers, etc.), polystyrene-based polymers (e.g., polystyrene, acrylonitrile-styrene copolymers, etc.), polyimide-based polymers, polysulfone-based polymers, polyethersulfone-based polymers, polyetherketone-based polymers, polyphenylsulfide-based polymers, polyvinyl alcohol-based polymers, polyvinylidene chloride-based polymers, polyvinyl butyral-based polymers, polyarylate-based polymers, polyoxymethylene-based polymers, and polyepoxy-based polymers, as well as blends of these polymers. EXAMPLES

[0086] The present invention will be described in more detail below with reference to examples, but the description of the examples should not be construed as limiting the scope of the present invention. The numerical values ​​(percentages) of the composition formulations of each component in Tables 1 and 2 are mass%.

[0087] The materials used in preparing the ink compositions are listed below. <Pigments> Pigment Yellow 155: Yellow pigment Pigment Red 122: Red pigment Pigment Red 254: Red pigment Pigment Blue 15:4: Blue pigment Pigment Black 7: Black pigment (carbon black)

[0088] <Pigment dispersant> Solsperse 56000: Amine value 39mgKOH / g (Lubrizol) Solsperse 39000: Amine value 26mgKOH / g (Lubrizol) EFKA PX4701: Amine value 40mgKOH / g (BASF) EFKA PX4703: Amine value 56mgKOH / g (BASF)

[0089] <Phosphate ester (meth)acrylate> SR9050: 2-(methacryloyloxy)ethyl phosphate, monofunctional methacrylate (Sartomer) SR9051: Tris[2-(methacryloyloxy)ethyl]phosphate, trifunctional methacrylate (Sartomer Corporation) SR9053: Tris[2-(acryloyloxy)ethyl]phosphate, trifunctional acrylate (Sartomer)

[0090] <Hydrophilic monofunctional monomer> N,N-Dimethylacrylamide Acryloylmorpholine 4-Hydroxybutyl acrylate <Amine-modified oligomer> CN371: Amine-modified acrylate oligomer, amine value 136 mg KOH / g, functionality 2 (Sartomer) Photomer 5006: Amine-modified (meth)acrylate oligomer, amine value 200 mg KOH / g, functionality 1 (IGM Resins) EBECRYL 80: Amine-modified (meth)acrylate oligomer, functional group number 4 (Daicel-Allnex Corporation) <Other polyfunctional monomers> Pentaerythritol triacrylate 1,6-Hexanediol diacrylate Dipropylene glycol diacrylate

[0091] <Photopolymerization initiator> TPO: Diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide TPO-L: Ethoxy(2,4,6-trimethylbenzoyl)phenylphosphine oxide Omnirad 819: Bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide <Sensitizer> DETX: 2,4-diethylthioxanthone <Polymerization inhibitor> UV-22: Quinone polymerization inhibitor (BASF)

[0092] <Leveling agent> BYK-UV3500: Silicone surface conditioner (BYK-Chemie)

[0093] Ink compositions of each of the Examples and Comparative Examples were prepared according to the composition formulations in Tables 1 and 2. Specifically, a pigment dispersion was obtained by mixing and stirring a pigment, a pigment dispersant, and a portion of the hydrophilic monofunctional monomer. The remaining portion of the hydrophilic monofunctional monomer, a phosphoric acid ester (meth)acrylate, an amine-modified oligomer, other polyfunctional monomers, a photopolymerization initiator, a sensitizer, a polymerization inhibitor, and a leveling agent were added to the obtained pigment dispersion, and the mixture was stirred and mixed to obtain an ink composition.

[0094] The ink compositions obtained in the respective Examples and Comparative Examples were evaluated for the following items, and the evaluation results are shown in Tables 1 and 2. <Storage stability> Each ink composition obtained in each Example and Comparative Example was placed in two glass bottles and sealed, and left to stand for three weeks in an environment of 25°C or 60°C, respectively, and then the viscosity was measured using an E-type viscometer (25°C, 10 rpm). The viscosity increase rate (%) was calculated using the following formula and evaluated according to the following evaluation criteria. In the present invention, A and B are pass, and C is fail. Viscosity increase rate = ((Viscosity value after leaving at 60℃ for 3 weeks / Viscosity value after leaving at 25℃ for 3 weeks) × 100) - 100 (Evaluation Criteria) A: The thickening rate was less than 10%. B: The thickening rate was 10% or more and less than 20%. C: The thickening rate was 20% or more.

[0095] <Adhesion> Each ink composition obtained in each Example and Comparative Example was applied to the surface of PVC (vinyl chloride sheet, product name: PVC80, manufactured by Lintec Corporation) and coated paper (product name: OK Topcoat, manufactured by Oji Paper Co., Ltd.) using a commercially available inkjet printer, and cured coating films were obtained by irradiating with ultraviolet light. The resulting coating films were cross-cut with a cutter knife, and cellophane tape (product name: Cellotape (registered trademark), manufactured by Nichiban Co., Ltd.) was applied to the cut areas, and the peeling condition of the cured coating film was observed by peeling it off, and adhesion was evaluated according to the following evaluation criteria. In the present invention, A and B are pass, and C is fail. (Evaluation Criteria) A: The peeling rate of the cured coating film was 0%. B: The peeling rate of the cured coating film was more than 0% and less than 20%. C: The peeling rate of the cured coating film was 20% or more.

[0096] <Water resistance> Each ink composition obtained in each Example and Comparative Example was applied to PVC (vinyl chloride sheet, product name: PVC80, manufactured by Lintec Corporation) using a commercially available inkjet printer, and cured coating films were obtained by irradiating with ultraviolet light. The coating films obtained were rubbed 10 times with a water-soaked bleached cloth at a load of 200 g using a Gakushin type fastness tester (manufactured by Daiei Scientific Instruments Co., Ltd.), and the degree of removal of the coating film was visually observed, and water resistance was evaluated according to the following evaluation criteria. (Evaluation Criteria) A: There was no paint removal or damage. B: The paint film was not removed, but there were scratches on the surface. C: The coating film was clearly peeled off.

[0097] [Table 1]

[0098] [Table 2]

[0099] [Table 3]

[0100] As shown in Comparative Example 1 in Table 3, the ink composition not containing a phosphate ester (meth)acrylate did not provide sufficient adhesion of the cured coating film to the substrate to be printed. In contrast, as shown in each of the Examples in Tables 1 to 3, the ink composition containing a phosphate ester (meth)acrylate provided excellent adhesion of the cured coating film to the substrate to be printed.

[0101] As shown in each of the examples in Tables 1 to 3, the storage stability of the ink composition is improved when the mass ratio of the hydrophilic monofunctional monomer to the phosphate ester (meth)acrylate is in the range of 5 to 400. Furthermore, as shown in Examples 1 to 20, when the mass ratio of the hydrophilic monofunctional monomer to the phosphate ester (meth)acrylate is in the range of 5 to 300, the storage stability of the ink composition is improved and furthermore, a cured coating film having excellent water resistance is obtained. In particular, as shown in each of the Examples in Tables 1 to 3, when a pigment containing carbon black is used and / or when a photopolymerizable compound containing an amine-modified oligomer is used, it is advantageous to set the mass ratio of the hydrophilic monofunctional monomer to the phosphate ester (meth)acrylate in the range of 5 to 400.

[0102] As shown in Comparative Example 2 in Table 3, when the content of the phosphoric acid ester (meth)acrylate in the entire ink composition exceeds 4.3 mass%, the storage stability of the ink composition is insufficient. In contrast, as shown in each of the Examples in Tables 1 to 3, when the content of the phosphoric acid ester (meth)acrylate in the entire ink composition is in the range of 0.1 to 4.3 mass%, the storage stability of the ink composition is improved. From the results of each of the Examples in Tables 1 to 3 and Comparative Examples 1 and 2 in Table 3, it can be seen that although the phosphoric acid ester (meth)acrylate tends to reduce the storage stability of the ink composition, it is possible to suppress the reduction in storage stability by blending a certain amount or more of a hydrophilic monofunctional monomer.

[0103] As shown in Comparative Example 3 in Table 3, when the content of the pigment dispersant relative to 100 parts by mass of the pigment is less than 38 parts by mass, the storage stability of the ink composition is insufficient. In contrast, as shown in each of the Examples in Tables 1 to 3, when the content of the pigment dispersant is 38 to 100 parts by mass relative to 100 parts by mass of the pigment, the storage stability of the ink composition is improved.

[0104] As can be seen from Example 2, Example 7, and Example 8, etc., the phosphate ester (meth)acrylate can impart an adhesion improving effect to the ink composition regardless of the type, whether it is a phosphate ester (meth)acrylate having one (meth)acrylate group or a phosphate ester (meth)acrylate having three (meth)acrylate groups, and the hydrophilic monofunctional monomer can maintain the pigment dispersion stability.

[0105] As can be seen from a comparison between Example 1 and Example 9, the desired effects can be obtained even when the photopolymerization initiator is changed from TPO to TPO-L.

[0106] As can be seen from Examples 10 and 11, the storage stability of the ink composition containing one type of pigment dispersant can be ensured, but the storage stability tends to decrease when compared with the results of the ink compositions of Examples 1 to 9 and Examples 12 to 21, which contain a combination of two types of pigment dispersants with different amine values. In this way, the storage stability of the ink composition can be improved by combining pigment dispersants with different amine values.

[0107] As can be seen from a comparison of Examples 1 to 12 and 21 with Examples 13, 14, and 15 to 20, it is understood that the desired effects can be obtained regardless of the type of pigment. [Industrial Applicability]

[0108] According to the photocurable ink composition for inkjet printing of the present invention, it is possible to form a cured coating film (printed layer) that has high adhesion to the substrate to be printed, regardless of the type of substrate to be printed, and further, since it has high storage stability (including pigment dispersion stability), it is easy to handle in printing. Therefore, according to the present invention, it is possible to improve the properties of various inkjet printing ink compositions.

Claims

1. A photocurable ink composition for ink-jet printing, comprising a pigment, a pigment dispersant, a photopolymerization initiator, and a photopolymerizable compound, the photopolymerizable compound contains a hydrophilic monofunctional monomer and a phosphoric acid ester (meth)acrylate, The ink composition contains the phosphate ester (meth)acrylate in an amount of 0.1 to 4.3% by mass based on the total mass of the ink composition, The pigment dispersant is contained in an amount of 38 to 100 parts by mass relative to 100 parts by mass of the pigment. A photocurable ink composition for ink-jet printing.

2. the pigment comprises carbon black; and a mass ratio of the hydrophilic monofunctional monomer to the phosphate ester (meth)acrylate is 5 to 400; The photocurable ink composition for ink-jet printing according to claim 1 .

3. The photopolymerizable compound further contains an amine-modified oligomer. The photocurable ink composition for ink-jet printing according to claim 1 or 2.

4. a mass ratio of the hydrophilic monofunctional monomer to the phosphate ester (meth)acrylate is 5 to 400; The photocurable ink composition for ink-jet printing according to claim 3 .

5. The ink composition contains the amine-modified oligomer in an amount of 0.1 to 20% by mass based on the total mass of the ink composition. The photocurable ink composition for ink-jet printing according to claim 4.

6. The hydrophilic monofunctional monomer contains at least one of N-2 substituted (meth)acrylamide and a hydroxyl group-containing monofunctional monomer. The photocurable ink composition for ink-jet printing according to claim 1 or 2.

7. The pigment dispersant contains a basic group-containing pigment dispersant. The photocurable ink composition for ink-jet printing according to claim 1 or 2.

8. The pigment dispersant contains a pigment dispersant with an amine value of less than 40 mgKOH / g and a pigment dispersant with an amine value of 40 mgKOH / g or more. The photocurable ink composition for ink-jet printing according to claim 1 or 2.

9. The photopolymerizable compound further contains a polyfunctional monomer other than the phosphate ester (meth)acrylate. The photocurable ink composition for ink-jet printing according to claim 1 or 2.

10. The phosphoric acid ester (meth)acrylate contains a phosphoric acid ester (meth)acrylate having three (meth)acrylate groups. The photocurable ink composition for ink-jet printing according to claim 1 or 2.

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