Photocurable ink composition for inkjet printing

Abstract

The present invention addresses the problem of improving the adhesion between a printed layer and a base material to be printed in a photocurable ink-jet printing ink composition containing a pigment and a pigment dispersant, while improving the dispersion stability of the pigment in the ink composition, and improving the storage stability. As a solution, provided is a photocurable ink composition for inkjet printing, which is characterized by containing a pigment, a pigment dispersant, a photopolymerization initiator, and a photopolymerizable compound: the photopolymerizable compound containing a hydrophilic monofunctional monomer and a phosphate ester (meth) acrylate; the phosphoric acid ester (meth) acrylate is contained in an amount of 0.2-4.0 mass% relative to the entire ink composition; the mass ratio of the hydrophilic monofunctional monomer to the phosphate (methyl) acrylate is 15 to 300; the pigment dispersant is contained in an amount of 38-90 parts by mass per 100 parts by mass of the pigment.

Description

Technical Field

[0001] The present invention relates to a photocurable ink composition for inkjet printing. Background Art

[0002] Photocurable inkjet printing ink compositions are used for printing on a variety of substrates. Inkjet printing is advantageous for small-batch production because it does not require platemaking. Furthermore, photocurable (typically UV-curable) ink compositions can reduce the amount of organic solvents, offering environmental advantages by reducing VOC emissions.

[0003] Printing with a photocurable inkjet ink composition involves ejecting ink droplets onto a substrate and curing each droplet by irradiating it with light, thereby forming a printed layer consisting of a cured film on the substrate. However, depending on the substrate material and the composition of the ink composition, sufficient adhesion between the printed layer consisting of the cured film and the substrate surface may not be achieved.

[0004] In contrast, methods have been proposed for improving the adhesion between a printed layer using a photocurable inkjet printing ink composition and the printed substrate surface by adding a polymerizable compound or a polymerizable phosphate ester compound containing a phosphate group to the ink composition (Patent Documents 1 and 2). Patent Document 1 proposes a method for adding a polymerizable compound containing a phosphate group to an active energy ray-curable inkjet ink composition containing a polymerizable compound and a dye as a colorant. Furthermore, Patent Document 2 proposes using an acylphosphine oxide-based initiator as a photopolymerization initiator in an inkjet ink composition containing a polymerizable monomer containing a polymerizable phosphate ester compound and a photopolymerization initiator.

[0005] Patent Literature Patent Document 1: Japanese Patent Application Laid-Open No. 2006-328227 Patent Document 2: Japanese Patent Application Laid-Open No. 2012-162615 Summary of the Invention As mentioned above, it has been proposed that the adhesion between the printed layer (i.e., the cured coating film) and the printed substrate surface can be improved by adding a polymerizable compound or polymerizable phosphate ester compound containing a phosphate group to a photocurable inkjet ink composition. However, it has been discovered that when a pigment serving as a colorant and a pigment dispersant for dispersing the pigment are added to a photocurable inkjet ink composition, the dispersion stability of the pigment decreases, and storage stability also decreases.

[0006] Therefore, the present invention aims to improve the adhesion between the printed layer and the printed substrate in a photocurable inkjet printing ink composition containing a pigment and a pigment dispersant, while also improving the dispersion stability of the pigment in the ink composition and the storage stability.

[0007] The present invention relates to the following photocurable ink composition for inkjet printing.

[0008] [1] A photocurable inkjet printing ink composition, characterized in that it is a photocurable inkjet printing ink composition containing a pigment, a pigment dispersant, a photopolymerization initiator, and a photopolymerizable compound, wherein the photopolymerizable compound contains a hydrophilic monofunctional monomer and a phosphate (meth)acrylate, wherein the phosphate (meth)acrylate is contained in an amount of 0.2 to 4.0% by mass relative to the total mass of the ink composition, the mass ratio of the hydrophilic monofunctional monomer to the phosphate (meth)acrylate is 15 to 300, and the pigment dispersant is contained in an amount of 38 to 90 parts by mass relative to 100 parts by mass of the pigment.

[0009] Furthermore, the present invention relates to the photocurable inkjet printing ink composition described below as a preferred embodiment.

[0010] [2] The photocurable inkjet printing ink composition according to [1] above, wherein the hydrophilic monofunctional monomer contains at least one of an N-2-substituted (meth)acrylamide and a hydroxyl group-containing monomer.

[0011] [3] The photocurable inkjet printing ink composition according to [1] or [2] above, wherein the pigment dispersant contains a basic group-containing pigment dispersant.

[0012] [4] The photocurable ink composition for inkjet printing according to any one of [1] to [3] above, characterized in that the pigment dispersant contains a pigment dispersant having an amine value of less than 40 mgKOH / g and a pigment dispersant having an amine value of 40 mgKOH / g or more.

[0013] [5] The photocurable ink composition for inkjet printing according to any one of [1] to [4] above, wherein the photopolymerizable compound further contains an amine-modified oligomer.

[0014] [6] The photocurable ink composition for inkjet printing according to any one of [1] to [5] above, wherein the photopolymerizable compound further contains a polyfunctional monomer other than the phosphate (meth)acrylate.

[0015] [7] The photocurable ink composition for inkjet printing according to any one of [1] to [6] above, wherein the phosphate (meth)acrylate has three (meth)acrylate groups.

[0016] The photocurable inkjet printing ink composition of the present invention can be printed on a substrate by inkjet printing to form a colored printed layer with high adhesion. Furthermore, the ink composition has high storage stability, making it easier to handle during printing. DETAILED DESCRIPTION

[0017] [A. Composition of Photocurable Inkjet Printing Ink Composition] The photocurable ink composition for inkjet printing of the present invention (hereinafter sometimes 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 components. 3) The photopolymerizable compound may contain a combination of a hydrophilic monofunctional monomer and a phosphate (meth)acrylate, and may further contain any other photopolymerizable compound.

[0018] [A-1. About pigments] The ink composition contains a pigment. Pigments are components added to impart coloring power or covering power to the ink composition, and examples include color pigments, white pigments, and metal powders. Examples of such pigments include, without limitation, the organic and / or inorganic pigments conventionally used in ink compositions, such as those listed below.

[0019] Examples of pigments include dye lake pigments, azo pigments, benzimidazolone pigments, phthalocyanine pigments, quinacridone pigments, anthraquinone pigments, dioxazines, indigo pigments, thioindigo pigments, perylene pigments, peronone pigments, dione pyrrolopyrrole pigments, isoindolinone pigments, nitro pigments, nitroso pigments, xanthrone pigments, quinophthalone pigments, pyranthrone pigments, and indanthrone pigments, as well as various inorganic pigments.

[0020] 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, alkaline blue, and Pigment Blue 15:4; colored pigments such as titanium oxide (Pigment White 6, etc.), red iron oxide, antimony red, cadmium yellow, cobalt blue, Prussian blue, ultramarine, black iron oxide, chromium oxide green, carbon black (Pigment Black 7, etc.), and graphite (including achromatic colored pigments such as white and black); and metal powders such as aluminum paste and bronze powder.

[0021] The content of the pigment in the ink composition varies depending on the type of pigment and the desired degree of coloration, and is not particularly limited. It can be, for example, approximately 2.0 to 30.0% by mass relative to the total mass of the ink composition. Furthermore, when preparing a colored ink composition, pigments or dyes of other colors may be used in combination as complementary colors, or ink compositions of other colors may be added.

[0022] [A-2. About pigment dispersants] The ink composition contains a pigment dispersant for dispersing the pigment. The pigment dispersant is preferably a polymeric pigment dispersant, and more preferably a pigment dispersant containing a basic group. Examples of pigment dispersants containing a basic group include polymeric pigment dispersants such as polyester pigment dispersants containing a basic group, acrylic pigment dispersants containing a basic group, polyurethane pigment dispersants containing a basic group, and carbodiimide pigment dispersants containing a basic group, as well as anionic surfactants.

[0023] Polymer pigment dispersants are not particularly limited and may be linear polymers having a pigment-affinity moiety composed of a basic group at at least one or both ends of the main chain, via a block or graft structure. Polymer pigment dispersants may contain 2 to 3,000 basic groups per molecule and have a number average molecular weight of 1,000 to 1,000,000.

[0024] The amine value of the pigment dispersant is preferably 10 mgKOH / g or higher, more preferably 20 mgKOH / g or higher; on the other hand, it is preferably 100 mgKOH / g or lower, more preferably 80 mgKOH / g or lower, and even more preferably 70 mgKOH / g or lower. The amine value represents the total amount of free alkali and alkali, expressed as mg of potassium hydroxide per equivalent amount of hydrochloric acid required to neutralize 1 g of the sample.

[0025] Ink compositions may preferably contain two or more pigment dispersants with different amine values. Specifically, combining a pigment dispersant with an amine value less than a certain value with a pigment dispersant with an amine value greater than a certain value can improve the dispersion stability of the pigment in the ink composition. Preferably, a pigment dispersant with an amine value less than 40 mgKOH / g and a pigment dispersant with an amine value of 40 mgKOH / g or greater are combined.

[0026] Specific forms of the pigment dispersant, preferably a pigment dispersant containing a basic group, include the following forms (1) to (17).

[0027] (1) a reaction product of an amino group and / or an imino group of a polyamine compound (e.g., a poly(lower alkyleneamine) such as polyallylamine, polyvinylamine, or polyethyleneimine) and at least one selected from polyesters, polyamides, and polyesteramides having a free carboxyl group (see Japanese Patent Application Laid-Open No. 2001-59906); (2) Reaction products of low molecular weight amino compounds such as poly(lower)alkylene imine and methyliminopropylene diamine with polyesters having free carboxyl groups (see Japanese Patent Application Laid-Open No. 54-37082 and Japanese Patent Application Laid-Open No. 01-311177); (3) A reaction product obtained by sequentially reacting an isocyanate group of a polyisocyanate compound with an alcohol such as methoxypolyethylene glycol or a polyester having one hydroxyl group such as polycaprolactone, a compound having two to three isocyanate-reactive functional groups, and an aliphatic or heterocyclic hydrocarbon compound having an isocyanate-reactive functional group and a tertiary amino group (see Japanese Patent Application Laid-Open No. 02-612); (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 formed by adding polyether chains to low molecular weight amino compounds; (6) A reaction product formed by reacting a compound having an isocyanate group with a compound having an amino group (see Japanese Patent Application Laid-Open No. 04-210220); (7) A reaction product formed 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 Japanese Patent Application Laid-Open No. 09-87537); (8) A reaction product of a polycarbonate compound having a functional group reactive with an amino group at one end and a polyamine compound (see Japanese Patent Application Laid-Open No. 09-194585); (9) Copolymers of at least one methacrylate or acrylate selected from methyl methacrylate, ethyl methacrylate, propyl methacrylate, butyl methacrylate, stearyl methacrylate, benzyl methacrylate, methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, octadecyl acrylate, benzyl acrylate, etc., with at least one basic group-containing polymerizable monomer such as acrylamide, methacrylamide, N-hydroxymethylamide, vinylimidazole, vinylpyridine, a monomer having an amino group and a polycaprolactone skeleton, and at least one other polymerizable monomer such as styrene, a styrene derivative, or other polymerizable monomers (see Japanese Patent Application Laid-Open No. 01-164429); (10) Carbodiimide pigment dispersants containing basic groups (see International Publication No. WO2004 / 000950); (11) A block copolymer composed 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 Japanese Patent Application Laid-Open No. 2005-55814); (12) Pigment dispersants obtained by Michael addition reaction of polyallylamine and polycarbonate compounds (see Japanese Patent Application Laid-Open No. 09-194585); (13) Carbodiimide compounds each having at least one polybutadiene chain and a basic nitrogen-containing group (see Japanese Patent Application Laid-Open No. 2006-257243); (14) Carbodiimide compounds each having at least one side chain having an amide group and a basic nitrogen-containing group in the molecule (see Japanese Patent Application Laid-Open No. 2006-176657); (15) A polyurethane compound having a structural unit comprising an ethylene oxide chain and a propylene oxide chain and having an amino group quaternized by a quaternizing agent (see Japanese Patent Application Laid-Open No. 2009-175613); (16) A compound obtained by reacting an isocyanate group of an isocyanate compound having an isocyanurate ring in its molecule with an active hydrogen group of a compound having a carbazole ring and / or an azobenzene skeleton in its molecule, wherein the number of carbazole rings and azobenzene skeletons in the molecule is 15 to 85% relative to 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 Japanese Patent Application Laid-Open No. 2010-107965); (17) Graft copolymers formed by introducing polyether or polyester side chains into amino-containing acrylic acid ester polymers.

[0028] Pigment dispersants are also commercially available. 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.

[0029] Examples of the SOLSPERSE series include: SOLSPERSE11200, SOLSPERSE13240, SOLSPERSE13650, SOLSPERSE13940, SOLSPERSE16000, SOLSPERSE17000, SOLSPERSE18000, SOLSPERSE20000, SOLSPERSE24000, SOLSPERSE24000SC, SOLSPERSE24000GR, SOLSPERSE2600, SOLSPERSE28000, SOLSPERSE31845, SOLSPERSE32000, SOLSPERSE32500, SOLSPERSE32550, SOLSPERSE32600, SOLSPERSE33000, SOLSPERSE34750, SOLSPERSE35100, SOLSPERSE35200, SOLSPERSE37500, SOLSPERSE38500, SOLSPERSE39000, SOLSPERSE56000, SOLSPERSE71000, SOLSPERSE73000, SOLSPERSE74000, etc.

[0030] 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-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.

[0031] 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, etc.

[0032] 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, etc.

[0033] Examples of the AJISPER series include: AJISPER PB-711, AJISPER PB-821, AJISPER PB-822, etc.

[0034] Among these, examples of pigment dispersants having an amine value of 40 mgKOH / g or more include: SOLSPERSE 24000 (41.6 mgKOH / g), SOLSPERSE 33000 (43 mgKOH / g), SOLSPERSE 71000 (75 mgKOH / g), SOLSPERSE 73000 (80 mgKOH / g), SOLSPERSE 74000 (81 mgKOH / g), Disperbyk-108 (71 mgKOH / g), Disperbyk-180 (94 mgKOH / g), Disperbyk-2008 (66 mgKOH / g), Disperbyk-2155 (48 mgKOH / g), EFKA 4300 (57 mgKOH / g), EFKA 4401 (48 to 52 mgKOH / g), EFKA PX4701 (40 mgKOH / g), EFKA PX4703 (56mgKOH / g), etc.

[0035] In addition, examples of pigment dispersants having an amine value of less than 40 mgKOH / g include SOLSPERSE 32000 (31.2 mgKOH / g), SOLSPERSE 39000 (26 mgKOH / g), SOLSPERSE 56000 (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), AJISPERPB-821 (11.2 mgKOH / g), AJISPERPB-822 (18.2 mgKOH / g), and the like.

[0036] When combining 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 greater: the pigment dispersant with an amine value of less than 40 mgKOH / g preferably has an amine value of 10 mgKOH / g or greater, more preferably 20 mgKOH / g or greater; the pigment dispersant with an amine value of 40 mgKOH / g or greater preferably has an amine value of 100 mgKOH / g or less, more preferably 80 mgKOH / g or less, and even more preferably 70 mgKOH / g or less. Furthermore, 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 greater may be 1 mgKOH / g or greater.

[0037] The content of the pigment dispersant in the ink composition can be adjusted to ensure that the pigment is dispersible. For example, the content of the pigment dispersant per 100 parts by mass of the pigment is 38 parts by mass or more, preferably 40 parts by mass or more, and more preferably 50 parts by mass or more; and 90 parts by mass or less, and preferably 80 parts by mass or less. The content of the pigment dispersant relative to the total ink composition is preferably 0.5% by mass or more, and more preferably 0.8% by mass or more; and preferably 4% by mass or less, and more preferably 3% by mass or less. Furthermore, when combining a pigment dispersant (α) having an amine value of less than 40 mgKOH / g and a pigment dispersant (β) having an amine value of 40 mgKOH / g or more, the mass ratio of α to β is not particularly limited, but is preferably within the range of α:β = 10:1 to 10:15.

[0038] [About A-3. Photopolymerizable Compound] The ink composition contains a photopolymerizable compound. Here, the photopolymerizable compound comprises a combination of a hydrophilic monofunctional monomer and a phosphate (meth)acrylate, and may also contain other optional photopolymerizable compounds. Other optional photopolymerizable compounds may preferably include oligomers (particularly amine-modified oligomers) and polyfunctional monomers (excluding phosphate (meth)acrylates). The total proportion of the photopolymerizable compounds relative to the total ink composition is preferably 80% by mass or greater, and more preferably 85% by mass or greater.

[0039] [A-3a. Hydrophilic monofunctional monomer] The hydrophilic monofunctional monomer is a monofunctional monomer having one ethylenically unsaturated group, and is a monofunctional monomer having a hydrophilic group such as a hydroxyl group, an amide group, a carboxyl group (or its salt), a sulfonic acid group (or its salt), a phosphoric acid group (or its salt), an ether group (such as a glycol group), or an amino group. The hydrophilic monofunctional monomer is preferably a monofunctional monomer having a hydroxyl group and / or an amide group.

[0040] Examples of monofunctional monomers having a hydroxyl group 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; and 2-hydroxyethyl vinyl ether (HEVE), 4-hydroxybutyl vinyl ether (HBVE), and 4-hydroxybutyl acrylate glycidyl ether (HBAGA).

[0041] The monofunctional monomer having an amide group is preferably (meth)acrylamide, more preferably (meth)acrylamide in which the two hydrogen atoms on the nitrogen of the amide group (-C(=O)NH2) are replaced by other substituents (N-2-substituted (meth)acrylamide), and particularly preferably N-2-substituted (meth)acrylamide. Examples of N-2-substituted (meth)acrylamides include (meth)acryloylmorpholine, N,N-dimethyl (meth)acrylamide, diethyl (meth)acrylamide; N-hydroxyalkyl (C1-5) (meth)acrylamides such as bis(2-hydroxyethyl) (meth)acrylamide, bis(3-hydroxypropyl) (meth)acrylamide, and bis(4-hydroxybutyl) (meth)acrylamide; and 1-3 molar adducts of these N-hydroxyalkyl (C1-5) (meth)acrylamides with ethylene oxide or propylene oxide.

[0042] In addition, the monofunctional monomer having an amide group may be 1) (meth) acrylamide, or 2) N-methyl (meth) acrylamide, N-methoxymethyl (meth) acrylamide, N-butoxymethyl (meth) acrylamide, etc., in which one hydrogen on the nitrogen of the amide group (-C (=O) NH2) is replaced by other substituents; 3) N-vinyl pyrrolidone (NVP), N-vinyl formamide, etc.

[0043] These hydrophilic monofunctional monomers may be used alone or in combination of two or more. A combination of a monofunctional monomer having an amide group (particularly N-2-substituted (meth)acrylamide) and a monofunctional monomer having a hydroxyl group is particularly preferred.

[0044] The content of the hydrophilic monofunctional monomer in the ink composition should preferably be set to maintain pigment dispersion stability. As described below, phosphate (meth)acrylate is a component that can reduce pigment dispersion stability. However, in the ink composition of the present invention, the hydrophilic monofunctional monomer prevents the reduction in pigment dispersion stability caused by phosphate (meth)acrylate. Therefore, it is preferable to appropriately set the relative content of the hydrophilic monofunctional monomer to the phosphate (meth)acrylate (details are described in the section [A-3b.] below).

[0045] The content of the hydrophilic monofunctional monomer in the ink composition is preferably in the range of 15.0 to 75.0% by mass relative to the total ink composition. This facilitates adjustment of the physical properties of the ink composition (such as viscosity and surface tension) to an appropriate range. Furthermore, the content of the hydrophilic monofunctional monomer is preferably in the range of 20.0 to 80.0% by mass relative to the total photopolymerizable compound.

[0046] [A-3b. Phosphate (meth)acrylate] The ink composition contains a phosphate (meth)acrylate as a photopolymerizable compound. A phosphate (meth)acrylate is a compound having both a phosphate group and a (meth)acryloyl group in its molecule. Specifically, a phosphate (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 formula. In the following formula, the substituents R(1a), R(2a), R(2b), R(3a), R(3b), and R(3c) are each independently a "functional group containing a (meth)acryloyl group." A (meth)acryloyl group refers to a methacryloyl group or an acryloyl group.

[0047] [Chemistry 1]

[0048] In the above formula, the substituents R(1a), R(2a), R(2b), R(3a), R(3b), and R(3c) each independently (they may be functional groups of the same or different structures) represent a "functional group containing a (meth)acryloyl group." Examples of the functional group containing a (meth)acryloyl group include those represented by the following formula. In the following formula, R represents a hydrogen atom or a methyl group, R1 represents an alkylene group (preferably an alkylene group having 1 to 4 carbon atoms), and R2 represents an alkylene group (preferably an alkylene group having 1 to 10 carbon atoms).

[0049] [Chemistry 2]

[0050] Preferred examples of the "functional group containing a (meth)acryloyl group" in the phosphate (meth)acrylate include: ((meth)acryloyloxy)alkyl; examples of the ((meth)acryloyloxy)alkyl include: (2-(meth)acryloyloxy)ethyl, (3-(meth)acryloyloxy)propyl, etc.

[0051] More specific examples of the phosphate (meth)acrylate include the following.

[0052] [Chemistry 3]

[0053] [Chemistry 4]

[0054] [Chemistry 5]

[0055] (l, m, n each independently represent 1 or 2) In phosphate (meth)acrylates, at least one of the three -OH groups of phosphoric acid (P(=O)(OH)3) can remain as a -OH group, or a "(meth)acryloyl-containing functional group" can be introduced into all three -OH groups (no -OH groups of phosphoric acid remain). Phosphate (meth)acrylates with "(meth)acryloyl-containing functional groups" introduced into all three -OH groups offer the advantage of low viscosity, making it easier to adjust the physical properties of the ink composition. Furthermore, when combined with a hydrophilic monofunctional monomer, the substrate adhesion of the cured coating film of the ink composition can be significantly improved.

[0056] The content of the phosphate (meth)acrylate in the ink composition is 0.2% by mass or greater, preferably 0.5% by mass or greater, and 4.0% by mass or less, preferably 3.0% by mass or less, relative to the total ink composition. By keeping the phosphate (meth)acrylate content in the ink composition above a certain level, the substrate adhesion of the cured coating film of the ink composition can be improved. Furthermore, by keeping the phosphate (meth)acrylate content below a certain level, the storage stability of the ink composition, specifically the dispersion stability of the pigment, can be improved.

[0057] Phosphate (meth)acrylates can reduce pigment dispersion stability, more specifically, can reduce the functionality of pigment dispersants. Therefore, when phosphate (meth)acrylates are added, maintaining pigment dispersion stability in the ink composition can be difficult. In contrast, the ink composition of the present invention, by adding a certain amount of hydrophilic monofunctional monomer, can achieve high pigment dispersion stability even when phosphate (meth)acrylates are added.

[0058] Therefore, in order to maintain the pigment dispersion stability of the ink composition, the ratio of the phosphate (meth)acrylate to the hydrophilic monofunctional monomer is preferably determined. Specifically, the content of the hydrophilic monofunctional monomer relative to the phosphate (meth)acrylate should be 15 times or more, preferably 20 times or more, and more preferably 30 times or more; and 300 times or less, preferably 100 times or less, and more preferably 70 times or less, by mass.

[0059] The mechanism by which the addition of a hydrophilic monofunctional monomer maintains pigment dispersion stability is not particularly limited. A presumed mechanism is that, because phosphate (meth)acrylate is a relatively polar component, it aggregates locally near the equally polar pigment dispersion (and the surrounding dispersant). This interaction disrupts the pigment dispersion, potentially causing a decrease in the stability of the ink composition. The addition of a hydrophilic monofunctional monomer reduces local aggregation of phosphate (meth)acrylate, moderating the interaction between phosphate (meth)acrylate and the pigment dispersion, thereby suppressing the decrease in pigment dispersion.

[0060] [A-3c. Oligomer (amine-modified oligomer)] The ink composition may contain an oligomer as a photopolymerizable compound. An oligomer refers to a component within the molecule that has been polymerized to a higher molecular weight through the polymerization of ethylenically unsaturated bonds. Oligomers are relatively high molecular weight components before polymerization, thus imparting appropriate viscosity or elasticity to the ink composition. Furthermore, due to their relatively high polarity, oligomers may impart adhesion to non-absorbent media to the cured ink composition. Among oligomers, amine-modified oligomers are sometimes preferred in the ink composition of the present invention because they can enhance the photocurability of the ink composition.

[0061] An amine-modified oligomer is an oligomer having one or more amino groups and one or more photopolymerizable functional groups within the molecule, preferably an oligomer having two or more photopolymerizable functional groups (a multifunctional amine-modified oligomer). The photopolymerizable functional group is preferably a (meth)acryloyl group; a preferred amine-modified oligomer is an amine-modified (meth)acrylate oligomer having one or more amino groups and two or more (meth)acryloyl groups within the molecule.

[0062] The amine-modified (meth)acrylate oligomer can be synthesized by polymerizing a desired monomer, and may be a commercially available product. Examples of commercially available products include: GENOMER 5161, GENOMER 5275 (RAHN); CN371, CN371NS, CN373, CN383, CN384, CN386, CN501, CN503, CN550, CN551 (Sartomer); EBECRYL 80, EBECRYL 81, EBECRYL 83, EBECRYL 7100, EBECRYL 84, EBECRYLP 115 (Daicel Allnex); LAROMER PO 83F, LAROMER PO 84F, Laromer LR 8946, Laromer LR 8956, Laromer LR 8996, Laromer LR 8894 (BASF); AgiSyn 001, AgiSyn 002, AgiSyn 003, AgiSyn 008 (DSM CoatingResin Company); Photomer4771, Photomer4775, Photomer4967, Photomer5096, Photomer5662, Photomer5930 (Cognis Company); DoublecureEPD , DoublecureOPD, Doublecure115, Doublecure225, Doublecure645, PolyQ222, PolyQ226, PolyQ224, PolyQ101 (DoubleBond Chemicals Company); etc.

[0063] The viscosity of the amine-modified oligomer is not limited, but it is particularly preferred that the viscosity at 25° C. is 2000 mPa·s or less in order to keep the viscosity of the entire photocurable inkjet printing ink composition within an appropriate range.

[0064] The content of the amine-modified oligomer in the photocurable inkjet printing ink composition is preferably 0.1% by mass or more, more preferably 0.3% by mass or more, relative to the total mass of the ink composition; on the other hand, it is preferably 2.0% by mass or less, more preferably 1.0% by mass or less.

[0065] [A-3d. Multifunctional monomers (excluding phosphate (meth)acrylates and oligomers)] The ink composition may contain a polyfunctional monomer as a photopolymerizable compound. Examples of the polyfunctional monomer (a monomer having two or more ethylenically unsaturated bonds) include the following polyfunctional (meth)acrylate compounds and vinyl ether group-containing (meth)acrylate compounds.

[0066] The polyfunctional (meth)acrylate compound may be a bifunctional di(meth)acrylate compound, a trifunctional tri(meth)acrylate compound, or a polyfunctional (meth)acrylate compound of more than one type.

[0067] Examples of di(meth)acrylate compounds 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, butanediol di(meth)acrylate, pentanediol di(meth)acrylate, neopentyl glycol di(meth)acrylate, hydroxypivaloyl hydroxypivalate di(meth)acrylate, hydroxypivaloyl hydroxypivalate di(meth)acrylate, and hydroxypivaloyl hydroxypivalate di(meth)acrylate. Valeryl hydroxypivalate dicaprolactone 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, 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-pentanediol di(meth)acrylate, 3-Methyl-1,5-pentanediol di(meth)acrylate, 2-Methyl-2-propyl-1,3-propanediol di(meth)acrylate, 2,4-Dimethoxy-2,4-pentanediol di(meth)acrylate, Methyl-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, dimethyloloctane 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, tricyclodecane dimethylol di(meth)acrylate, tricyclodecane dimethylol dicaprolactone di(meth)acrylate, cyclohexanedimethanol di(meth)acrylate, dicyclopentyl 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, 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 dicaprolactone di(meth)acrylate, bisphenol F tetraethylene oxide adduct dicaprolactone di(meth)acrylate, etc., di(meth)acrylates of polyols such as glycerol, pentaerythritol, diglycerol, ditrimethylolpropane and dipentaerythritol, etc.

[0068] Examples of tri(meth)acrylate compounds include glycerol tri(meth)acrylate, trimethylolpropane tri(meth)acrylate, trimethylolpropane tricaprolactone 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, 6EO-modified, 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).

[0069] Examples of tetrafunctional or higher-functional (meth)acrylate compounds include tetrafunctional or higher-functional monomers such as trimethylolpropane tetra(meth)acrylate, pentaerythritol tetra(meth)acrylate, pentaerythritol tetracaprolactone tetra(meth)acrylate, diglycerol tetra(meth)acrylate, ditrimethylolpropane tetra(meth)acrylate, ditrimethylolpropane tetracaprolactone tetra(meth)acrylate, ditrimethylolethane tetra(meth)acrylate, ditrimethylolbutane tetra(meth)acrylate, 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 polyoxyalkylene hepta(meth)acrylate.

[0070] Examples of the (meth)acrylate compounds containing a vinyl ether group 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-vinyloxyethyl (meth)acrylate, propyl (meth)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-vinyloxymethylcyclohexyl (meth)acrylate Hexyl methyl ester, 3-vinyloxymethylcyclohexylmethyl (meth)acrylate, 2-vinyloxymethylcyclohexylmethyl (meth)acrylate, p-vinyloxymethylphenyl methyl (meth)acrylate, m-vinyloxymethylphenyl methyl (meth)acrylate, o-vinyloxymethylphenyl methyl (meth)acrylate, 2-(vinyloxyethoxy)ethyl (meth)acrylate, 2-(vinyloxyisopropoxy)ethyl (meth)acrylate, 2-(vinyloxyethoxy)propyl (meth)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-(vinyloxyisopropoxyethoxy)ethyl (meth)acrylate, 2-(vinyloxyisopropoxyisopropoxy)ethyl (meth)acrylate, etc.

[0071] The content of the polyfunctional monomer in the photocurable inkjet ink composition is preferably 10% by mass or more, more preferably 20% by mass or more, relative to the total ink composition; and preferably 70% by mass or less, more preferably 60% by mass or less. Furthermore, the content of the polyfunctional monomer in the photocurable inkjet ink composition is preferably 15% by mass or more, more preferably 25% by mass or more, relative to the total photopolymerizable compound; and preferably 80% by mass or less, more preferably 70% by mass or less.

[0072] [A-4. Regarding photopolymerization initiator] The ink composition of the present invention contains a photopolymerization initiator. Examples of photopolymerization initiators include: Benzoin ether photopolymerization initiators, acetophenone photopolymerization initiators, α-ketone photopolymerization initiators, aromatic sulfonyl chloride photopolymerization initiators, photoactive oxime photopolymerization initiators, benzoin photopolymerization initiators, benzyl photopolymerization initiators, benzophenone photopolymerization initiators, ketal photopolymerization initiators, triazine photopolymerization initiators, acylphosphine oxide photopolymerization initiators, etc. Among these, triazine photopolymerization initiators and acylphosphine oxide photopolymerization initiators are preferred from the perspective of good light curability. These photopolymerization initiators can be used alone or in combination of two or more. For example, two acylphosphine oxide photopolymerization initiators can also be used in combination.

[0073] Specific examples of the photopolymerization initiator 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-morpholinopropane-1-one, 4-benzoyl-4'-methyldiphenyl sulfide, 1-chloro-4-propoxythioxanthone, isopropylthioxanthone, 2-hydroxy-2-methyl-1 -phenylpropane-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-propane-1-one, 2,2-dimethyl-2-hydroxyacetophenone, 2,2-dimethoxy-2-phenylacetophenone, 2,4,6-trimethylbenzyl-diphenylphosphine oxide, 2-benzyl-2-dimethylamino-1-(morpholinophenyl)-butane-1-one, etc.

[0074] The amount of the photopolymerization initiator in the ink composition can be set according to the desired curing speed of the photocurable resin composition. As a standard, it is preferably 1% by mass or more, more preferably 3% by mass or more; and is preferably 10% by mass or less, more preferably 8% by mass or less.

[0075] [A-5. Regarding optional other components] The ink composition of the present invention may contain other optional components. Examples of other optional components include sensitizers, polymerization inhibitors, and leveling agents.

[0076] [A-5a. Sensitizer] The ink composition may contain a sensitizer to improve curability. The sensitizers may be used alone or in combination of two or more.

[0077] Examples of sensitizers 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-diethylthioxanthene-9-one, 2-isopropylthioxanthone, and 4-isopropylthioxanthone. Commercially available products of these sensitizers include anthracene-based sensitizers with the trade names "DBA" and "DEA" (Kawasaki Chemicals Co., Ltd.), and thioxanthone-based sensitizers with the trade names "DETX" and "ITX" (Lambson Corporation).

[0078] When a sensitizer is included in the ink composition, to prevent excessive addition, the sensitizer content is preferably 5.0 parts by mass or less, and more preferably 4.0 parts by mass or less, per 100 parts by mass of the total photopolymerizable compound (including phosphate (meth)acrylate, hydrophilic monofunctional monomer, amine-modified oligomer, and other polymerizable compounds). Furthermore, the combined content of the photopolymerization initiator and sensitizer is preferably 2.0 to 15.0 parts by mass per 100 parts by mass of the total photopolymerizable compound.

[0079] [A-5b. Polymerization inhibitor] The ink composition may contain a polymerization inhibitor, which can prevent the ink composition from undergoing polymerization during storage and suppress the thickening of the ink composition.

[0080] Examples of the polymerization inhibitor include phenolic compounds (including quinone compounds) such as butylated hydroxytoluene, tocopheryl acetate, nitrosamine compounds, benzotriazole, hindered amines, and the like. Among them, quinone compounds and nitrosamine compounds are more preferably exemplified.

[0081] The content of the polymerization inhibitor in the photocurable inkjet printing ink composition is appropriately set depending on the type of polymerization inhibitor. In the case of a quinone compound, the content is about 0.1 to 1.0 parts by mass based on 100 parts by mass of the total photopolymerizable component.

[0082] [A-5c. Surfactant (leveling agent)] The ink composition may contain a surfactant as a leveling agent, depending on the configuration of the print head of the inkjet printer used for printing. Known surfactants may be included without particular limitation, and examples of surfactants include nonionic surfactants, cationic surfactants, anionic surfactants, and betaine surfactants. Specific examples of surfactants include organosilicon-based surfactants such as polyether-modified silicone oils, polyester-modified polydimethylsiloxanes, and polyester-modified methylalkylpolysiloxanes, fluorine-based surfactants, and acetylene-based surfactants. These surfactants may be used alone or in combination of two or more.

[0083] Examples of the silicone surfactant 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).

[0084] Examples of the fluorine-based surfactant include F-410, F-444, and F-553 (from DIC Corporation), and FS-65, FS-34, FS-35, FS-31, and FS-30 (from Du Pont Corporation).

[0085] Examples of the acetylene surfactant include DYNOL 607, DYNOL 609, OLFINE E1004, OLFINE E1010, OLFINE E1020, OLFINE PD-001, OLFINE PD-002W, OLFINE PD-004, OLFINE PD-005, OLFINE EXP.4001, OLFINE EXP.4200, OLFINE EXP.4123, and OLFINE EXP.4300 (Nissin Chemical Industry Co., Ltd.), SURFYNOL104E, SURFYNOL104H, SURFYNOL104A, SURFYNOL104BC, SURFYNOL104DPM, SURFYNOL104PA, SURFYNOL104PG-50, SURFYNOL420, SURFYNOL440, SURFYNOL465 (EVONIK), etc.

[0086] From the perspective of reducing the surface tension of the ink composition and improving the ejection stability from the inkjet head, the content ratio of the surfactant in the ink composition is preferably 0.005% by mass or more, more preferably 0.01% by mass or more, relative to the ink composition. From the perspective of suppressing foam in the ink composition generated during the preparation process and improving the ejection stability, the content ratio of the surfactant in the ink composition is preferably 1.5% by mass or less, more preferably 1.0% by mass or less.

[0087] When a surfactant is included as a leveling agent, the content of the surfactant is preferably adjusted so that the surface tension of the ink composition at 25° C. is 20.0 to 36.0 mN / m, and more preferably 0.1 to 1.5% by mass in the photocurable inkjet printing ink composition.

[0088] [B. Physical Properties and Applications of Ink Composition] The photocurable ink composition for inkjet printing of the present invention can be printed using an inkjet device and only needs to have sufficient photocurability and adhesion to the substrate to be printed.

[0089] [B-1. Viscosity] The viscosity of the ink composition at 25°C is preferably 5.0 mPa·s or higher, more preferably 10.0 mPa·s or higher, and even more preferably 15.0 mPa·s or higher; and preferably 100.0 mPa·s or lower, 60.0 mPa·s or lower, more preferably 46.0 mPa·s or lower, and even more preferably 25.0 mPa·s or lower. The viscosity of the ink composition can be adjusted primarily by the composition of the photopolymerizable compound or photopolymerization initiator, and can also be adjusted by adding viscosity modifiers as needed. The viscosity described in this specification is measured using an E-type viscometer (RE100L, manufactured by Toki Sangyo Co., Ltd.) at 25°C and 10 rpm. A viscosity of less than 5.0 mPa·s or exceeding 100.0 mPa·s may reduce the ejection stability of inkjet printing.

[0090] [B-2. Surface tension] The surface tension of the ink composition at 25°C is preferably 20.0 to 36.0 mN / m. The surface tension of the ink composition can be adjusted by adding a surfactant (leveling agent) as needed. Surface tension can be measured at 25°C using a dynamic wettability tester (e.g., WET-6000, manufactured by Lesca).

[0091] [B-3. Printing method] The ink composition of the present invention can be used for printing using an inkjet printer. The type of inkjet printer that can be used is not particularly limited and may employ either a line head printer (single-path printer) or a serial head printer (multi-path printer). Furthermore, a continuous inkjet printer may be used. In this case, a conductive additive may be added to adjust the conductivity of the ink composition.

[0092] The ink composition is supplied to the print head of an inkjet printer, and the ink composition is ejected from the print head onto a substrate to be printed. The ink composition is ejected from the print head onto the substrate (printing an image) so that the coating film has a thickness of 1 to 60 μm, for example.

[0093] The ink composition sprayed onto the substrate is cured by exposure to ultraviolet light, electron beams, or visible light emitted by a light-emitting diode (LED), various lamps, or electrodes. For environmental reasons, a light-emitting diode (LED) that emits ultraviolet light with a peak wavelength of 350 to 420 nm is preferred as the light source.

[0094] [B-4. Printed substrate] The substrate to be printed is not particularly limited, as long as it is a substrate suitable for conventional photocurable inkjet ink compositions. Examples of such substrates include plastic, paper, capsules, gelatin, metal foil, glass, wood, and cloth. The photocurable inkjet ink composition of the present invention can effectively reduce the migration of the photopolymerization initiator, regardless of the substrate material used for printing. Examples of the plastic constituting the substrate include polyester polymers (e.g., polyethylene terephthalate (PET), polyethylene naphthalate, etc.), cellulose polymers (e.g., cellulose diacetate, cellulose triacetate (TAC), etc.), polycarbonate polymers, polyacrylic polymers (e.g., polymethyl methacrylate, etc.), vinyl chloride polymers, polyolefin polymers (e.g., polyethylene, polypropylene, polyolefin polymers having a cyclic or norbornene structure, ethylene-propylene copolymer polymers, etc.), polyamide polymers (e.g., nylon, aromatic polyamide polymers, etc.), polystyrene polymers (e.g., polystyrene, acrylonitrile-styrene copolymer polymers, etc.), polyimide polymers, polysulfone polymers, polyethersulfone polymers, polyetherketone polymers, polyphenylene sulfide polymers, polyvinyl alcohol polymers, polyvinylidene chloride polymers, polyvinyl butyral polymers, polyarylate polymers, polyoxymethylene polymers, polyepoxy polymers, and mixtures thereof.

[0095] Example The present invention will be described in more detail below with reference to the Examples. However, the scope of the present invention should not be construed as being limited by the Examples. The values (percentages) of the composition formulas of the components in Tables 1 and 2 are in mass %.

[0096] The materials used in the preparation of the ink composition are shown below.

[0097] 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 Pigment dispersants Solsperse 56000: Amine value 39 mgKOH / g (LUBRIZOL) Solsperse 39000: Amine value 26 mgKOH / g (LUBRIZOL) EFKA PX4701: Amine value 40 mgKOH / g (BASF) EFKA PX4703: Amine value 56 mgKOH / g (BASF) <Phosphate (meth)acrylate> SR9050: 2-(Methacryloyloxy)ethyl phosphate, monofunctional methacrylate (Sartomer) SR9051: Tris[2-(methacryloyloxy)ethyl]phosphate, trifunctional methacrylate (Sartomer) SR9053: Tris[2-(acryloyloxy)ethyl] phosphate, trifunctional acrylate (Sartomer) <Hydrophilic monofunctional monomer> N,N-dimethylacrylamide Acryloylmorpholine 4-Hydroxybutyl acrylate <Amine-modified oligomer> CN371: Amine-modified acrylate oligomer, amine value 136 mgKOH / g, functional group number 2 (Sartomer) <Other multifunctional monomers> Pentaerythritol triacrylate 1,6-Hexanediol diacrylate Dipropylene glycol diacrylate <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) <Leveling agent> BYK-UV3500: Silicone surface conditioner (BYK Chemie) The ink compositions of each example and comparative example were prepared according to the formulations shown in Tables 1 and 2. Specifically, a pigment, a pigment dispersant, and a portion of a hydrophilic monofunctional monomer were mixed and stirred to obtain a pigment dispersion. To the resulting pigment dispersion, the remaining portion of the hydrophilic monofunctional monomer, a phosphate (meth)acrylate, an amine-modified oligomer, other multifunctional monomers, a photopolymerization initiator, a sensitizer, a polymerization inhibitor, and a leveling agent were added and stirred to obtain the ink composition.

[0098] The ink compositions obtained in each of the Examples and Comparative Examples were evaluated with respect to the following items. The evaluation results are shown in Tables 1 and 2.

[0099] Storage stability Each ink composition obtained in each Example and Comparative Example was placed in a sealed glass bottle and allowed to stand at 25°C and 60°C for 3 weeks. The viscosity was then measured using an E-type viscometer (25°C, 10 rpm). The viscosity increase (%) was calculated using the following formula and evaluated according to the following evaluation criteria.

[0100] ((Viscosity value after standing at 60°C for 3 weeks / Viscosity value after standing at 25°C for 3 weeks) × 100) -100 (Evaluation Criteria) ○: Thickening rate is less than 10%.

[0101] △: The thickening rate is 10% or more and less than 20%.

[0102] ×: The thickening rate is 20% or more.

[0103] <Adhesion> Using a commercially available inkjet printer, each ink composition obtained in each Example and Comparative Example was applied to the surfaces of PVC (product name: PVC80, manufactured by Lintec) and coated paper (product name: OK top coat, manufactured by Oji Paper Co., Ltd.), and then irradiated with ultraviolet light to form a cured coating film. The resulting coating film was cross-cut with a cutter, and transparent tape (product name: Cellotape (registered trademark), manufactured by Nichiban Co., Ltd.) was attached to the cut portion. The tape was then removed, and the adhesion of the cured coating film was evaluated by peeling according to the following evaluation criteria.

[0104] (Evaluation Criteria) ○: The peeling rate of the cured coating film was 0%.

[0105] Δ: The peeling rate of the cured coating film exceeds 0% and is less than 20%.

[0106] ×: The peeling rate of the cured coating film is 20% or more.

[0107] Water resistance Each ink composition obtained in each Example and Comparative Example was applied to PVC (product name: PVC80, manufactured by Lintec) using a commercially available inkjet printer and irradiated with ultraviolet light to form a cured coating film. The resulting coating film was visually observed for peeling when rubbed 10 times with a bleached cloth containing water at a load of 200 g using a Gakushin-type fastness tester (manufactured by Daiei Kagaku Seiki Mfg. Co., Ltd.) using a water-retaining bleached cloth at a load of 200 g. Water resistance was evaluated according to the following evaluation criteria.

[0108] (Evaluation Criteria) ○: There is no peeling or scratching of the coating film.

[0109] △: There is no peeling of the coating film, but there are scratches on the surface.

[0110] ×: Clear peeling of the coating film was observed.

[0111] [Table 1]

[0112] [Table 2]

[0113] As shown in Comparative Example 1 in Table 2, ink compositions that do not contain a phosphate (meth)acrylate exhibit insufficient adhesion of the cured coating film to the printed substrate. In contrast, as shown in the Examples in Tables 1 and 2, ink compositions that contain a phosphate (meth)acrylate exhibit sufficient adhesion.

[0114] As shown in Comparative Example 2 in Table 2, when the total content of the hydrophilic monofunctional monomers was 12 times the mass of the phosphate (meth)acrylate, the ink composition exhibited insufficient storage stability. Furthermore, as shown in Comparative Example 5 in Table 2, when the total content of the hydrophilic monofunctional monomers was 317 times the mass of the phosphate (meth)acrylate, the resulting cured coating film exhibited insufficient water resistance. In contrast, as shown in the Examples in Tables 1 and 2, when the total content of the hydrophilic monofunctional monomers was 17 to 282 times the mass of the phosphate (meth)acrylate, the ink composition exhibited improved storage stability and the cured coating film exhibited sufficient water resistance.

[0115] As shown in Comparative Example 3 in Table 2, when the phosphate (meth)acrylate content was 4.5% by mass relative to the total ink composition, the storage stability of the ink composition was insufficient. In contrast, as shown in the Examples in Tables 1 and 2, when the phosphate (meth)acrylate content was within the range of 0.2% to 4.0% by mass relative to the total ink composition, the storage stability of the ink composition was improved. The results of Comparative Examples 2 and 3 and the Examples in Table 2 indicate that phosphate (meth)acrylate tends to reduce the storage stability of the ink composition, but by adding a certain amount or more of a hydrophilic monofunctional monomer, this reduction in storage stability can be suppressed.

[0116] As shown in Comparative Example 4 in Table 2, when the content of the pigment dispersant was 35 parts by mass per 100 parts by mass of the pigment, the storage stability of the ink composition was insufficient. In contrast, as shown in the Examples in Tables 1 and 2, when the content of the pigment dispersant was 38 to 85 parts by mass per 100 parts by mass of the pigment, the storage stability of the ink composition was improved.

[0117] Examples 1 to 6 demonstrate that when the phosphate (meth)acrylate content is within the range of 0.2% to 4.0% by mass relative to the ink composition, adhesion of the cured coating film can be achieved while maintaining the pigment dispersion stability of the ink composition. Furthermore, Examples 5 and 6 demonstrate that the desired effects can be achieved when the content ratio (mass ratio) of the hydrophilic monofunctional monomer relative to the phosphate (meth)acrylate is within the range of 17% to 282% by mass.

[0118] As can be seen from Examples 2, 7, and 8, regardless of the type of phosphate (meth)acrylate and whether the number of (meth)acrylates is one (monovalent) or three (trivalent), the ink composition can be improved in terms of adhesion, and the hydrophilic monofunctional monomer can maintain pigment dispersion stability.

[0119] From the comparison between Example 1 and Example 9, it is clear that the desired effect can be obtained even when the photopolymerization initiator is changed from TPO to TPO-L.

[0120] As shown in Examples 10 and 11, while ink compositions containing only one pigment dispersant can maintain storage stability, their stability tends to be lower when compared to the results of ink compositions such as Examples 1 to 9 and Example 12, which contain a combination of two pigment dispersants with different amine values. Thus, combining pigment dispersants with different amine values can improve the storage stability of ink compositions.

[0121] From the comparison between Examples 1 to 12 and Examples 13 to 15, it can be seen that the desired effect can be obtained regardless of the type of pigment.

[0122] Industrial applicability The photocurable ink composition for inkjet printing of the present invention forms a cured coating film (printed layer) with high adhesion to any substrate, regardless of the type of substrate being printed. Furthermore, its high storage stability (including pigment dispersion stability) facilitates handling during the printing process. Therefore, the present invention can improve the properties of various inkjet ink compositions.

Claims

1. A photocurable inkjet printing ink composition, characterized in that: The present invention is a photocurable inkjet printing ink composition containing a pigment, a pigment dispersant, a photopolymerization initiator and a photopolymerizable compound. The photopolymerizable compound contains a hydrophilic monofunctional monomer and a phosphate (meth)acrylate, The phosphate (meth)acrylate is contained in an amount of 0.2 to 4.0% by mass relative to the total mass of the ink composition. The mass ratio of the hydrophilic monofunctional monomer to the phosphate (meth)acrylate is 15 to 300, The pigment dispersant is contained in an amount of 38 to 90 parts by mass based on 100 parts by mass of the pigment.

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

3. The photocurable ink composition for inkjet printing according to claim 1 or 2, wherein: The pigment dispersant contains a pigment dispersant containing a basic group.

4. The photocurable ink composition for inkjet printing according to claim 1 or 2, wherein: The pigment dispersant includes a pigment dispersant having an amine value of less than 40 mgKOH / g and a pigment dispersant having an amine value of 40 mgKOH / g or more.

5. The photocurable ink composition for inkjet printing according to claim 1 or 2, wherein: The photopolymerizable compound further contains an amine-modified oligomer.

6. The photocurable ink composition for inkjet printing according to claim 1 or 2, wherein: The photopolymerizable compound further contains a polyfunctional monomer other than the phosphate (meth)acrylate.

7. The photocurable ink composition for inkjet printing according to claim 1 or 2, wherein: The phosphate (meth)acrylate has three (meth)acrylate groups.

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