Ink composition, pigment dispersion liquid, ink set, printed matter, inkjet recording device, recording method, and method for producing printed matter

Abstract

The present invention provides an active energy ray-curable ink composition which has high storage stability and discharge stability even if the active energy ray-curable ink composition contains a polymerizable compound.　Disclosed is an active energy ray-curable ink composition which is discharged by an inkjet method and contains a polymerizable compound. An aqueous suspension of the ink composition has a pH of 6.0 to 8.0 inclusive as measured by the following test method.　Test method: An aqueous suspension of an ink composition is prepared by mixing the ink composition and water so that the content of the ink composition is 10% by mass, and the pH of the aqueous suspension is measured.

Description

Ink composition, pigment dispersion, ink set, printed matter, inkjet recording device, recording method, and method for producing printed matter

[0001] The present invention relates to an ink composition, a pigment dispersion, an ink set, a printed matter, an inkjet recording apparatus, a recording method, and a method for producing a printed matter.

[0002] In recent years, the demand for small-lot, diversified printed materials has increased, and inkjet printing, an on-demand printing method, has been attracting attention as an alternative to conventional offset printing. Inkjet printing is simpler than conventional offset printing and offers advantages such as reduced waste, economic efficiency, and energy savings.

[0003] On the other hand, inkjet printing methods require inks to have good storage stability and minimal change in viscosity, which can lead to poor ejection from the inkjet head.

[0004] Conventionally, in aqueous inkjet inks, the pH has been adjusted to maintain the dispersion stability of pigments and resins (Prior Documents 1 to 5), and a pH adjuster has been added to suppress corrosion of electrodes, nozzle plates, and head nozzle members (Prior Documents 6 to 9).

[0005] JP 2000-26779 JP 10-46090 JP 2007-92071 JP 2008-297483 JP 2012-82293 JP 2009-132845 JP 2007-246841 JP 2005-23099 JP 2003-261805

[0006] Inkjet printing methods include active energy ray-curable ink compositions that are cured by polymerizing a polymerizable compound with ultraviolet rays, electron beams, or other active energy rays. Active energy ray-curable ink compositions dry quickly, and therefore can prevent ink bleeding even when printed on substrates that do not absorb ink or absorb very little ink, such as plastic, glass, and coated paper.

[0007] On the other hand, when an active energy ray-curable ink composition is not used or is stored, the viscosity of the ink composition increases even when the ink composition is not irradiated with active energy rays, and inkjet ejection may become impossible, and the reason for this has been unknown.

[0008] An object of the present invention is to provide an actinic energy ray-curable ink composition that contains a polymerizable compound and has high storage stability and ejection stability.

[0009] As a result of intensive research into solving the above problems, the inventors discovered that the above problems can be solved by controlling the components contained in the ink composition and their contents so that the pH of the aqueous suspension obtained from the ink composition falls within a specific range, and thus completed the present invention.

[0010] (1) An actinic ray-curable ink composition to be ejected by an inkjet method, the ink composition containing a polymerizable compound, and having a pH of 6.0 to 8.0 inclusive in an aqueous suspension thereof as measured by the following test method: The ink composition is mixed with water so that the content of the ink composition is 10% by mass, to prepare an aqueous suspension of the ink composition, and the pH of the aqueous suspension is measured.

[0011] (2) The ink composition according to (1), which contains a coloring material.

[0012] (3) The ink composition according to (1), which does not contain a coloring material.

[0013] (4) A pigment dispersion used in an actinic ray-curable ink composition ejected by an inkjet method, the pigment dispersion containing a pigment, a polymerizable compound, and a pigment dispersant, the pH of an aqueous suspension of which is 6.0 to 8.0 as measured by the following test method: The pigment dispersion and water are mixed so that the content of the pigment dispersion is 10% by mass to prepare an aqueous suspension of the pigment dispersion, and the pH of the aqueous suspension is measured.

[0014] (5) An actinic ray-curable ink composition that is ejected by an inkjet method, the ink composition comprising the pigment dispersion liquid according to (4) and a polymerization initiator.

[0015] (6) The ink composition according to any one of (1) to (3) and (5), wherein the water content is 5.0% by mass or less based on the total amount of the ink composition.

[0016] (7) An ink set comprising the ink composition according to any one of (1) to (3), (5) and (6).

[0017] (8) A printed matter on which the ink composition according to any one of (1) to (3), (5) and (6) is printed.

[0018] (9) An ink jet recording apparatus comprising a storage mechanism filled with the ink composition according to any one of (1) to (3), (5) and (6).

[0019] (10) A recording method, comprising ejecting the ink composition according to any one of (1) to (3), (5) and (6) by an inkjet method.

[0020] (11) A method for producing a printed matter, comprising ejecting the ink composition according to any one of (1) to (3), (5) and (6) by an inkjet method.

[0021] According to the present invention, it is possible to provide an actinic ray-curable ink composition that has excellent storage stability and ejection stability.

[0022] Specific embodiments of the present invention will be described in detail below, but the present invention is not limited to the following embodiments and can be implemented with appropriate modifications within the scope of the object of the present invention.

[0023] 1. Actinic Energy Ray-Curable Ink Composition The actinic energy ray-curable ink composition according to this embodiment contains a polymerizable compound, and is characterized in that the pH of an aqueous suspension thereof is 6.0 or more and 8.0 or less, as measured by the following test method.

[0024] Test method: An aqueous suspension of the ink composition is prepared by mixing the ink composition with water so that the content of the ink composition is 10% by mass, and the pH of the aqueous suspension is measured.

[0025]

[0006] After being applied to a substrate, an actinic ray-curable ink composition increases in viscosity due to polymerization of the polymerizable compound, and is fixed to the substrate. However, when an actinic ray-curable ink composition containing a polymerizable compound is unused or stored, even without being irradiated with actinic rays, the polymerization reaction of the polymerizable compound may progress, causing an increase in viscosity of the ink composition, the formation of a gel, or making it impossible to eject the ink onto the substrate.

[0026] The details of the cause are unknown, and the only way to deal with this is to add a polymerization inhibitor, which is generally insufficient to prevent it. On the other hand, if the amount of polymerization initiator added is reduced or the amount of polymerization inhibitor added is increased in order to suppress the polymerization reaction, the polymerization reaction may not proceed easily even when irradiated with active energy rays, resulting in poor curability and poor coating film properties.

[0027] The present inventors conducted extensive research to solve the above-mentioned problems and found that an ink composition with excellent storage stability and ejection stability can be obtained by controlling the components and their contents so that the pH (also known as hydrogen ion exponent, hydrogen ion concentration exponent, or hydrogen exponent) of an aqueous suspension obtained from an ink composition or pigment dispersion falls within a specific range. A dark reaction of a polymerizable compound may proceed even in the absence of actinic energy ray irradiation energy, leading to an increase in the viscosity of the ink, gelation, or the formation of aggregates. This can lead to an increase in the viscosity of the ink composition, gelation of the ink composition, or the formation of aggregates. The present inventors' research has revealed that the progression of such a dark reaction of a polymerizable compound is due to the pH of the aqueous suspension obtained from the ink composition. Although actinic energy ray-curable ink compositions do not originally contain water, the discovery that the pH of the suspension water affects their stability is a novel aspect of the present invention.

[0028] Therefore, by preparing an ink composition in which the components and their contents are controlled so that the pH of the aqueous suspension obtained from the ink composition falls within a specific range, it is possible to obtain an ink composition that has excellent storage stability and ejection stability. For convenience, in this specification, the pH of the aqueous suspension having a mass fraction of 10% obtained from the ink composition may be simply referred to as the "pH of the ink composition."

[0029] That is, in the actinic energy ray-curable ink composition according to this embodiment, the pH of the ink composition is set in the neutral range (a pH range of 6.0 to 8.0). This allows for an ink composition with excellent storage stability and ejection stability. If the pH of the ink composition is in the acidic range (a pH range of less than 6.0) or the basic range (a pH range of more than 8.0), the reactivity of the polymerizable compound in the ink composition may increase, and a polymerization reaction may proceed even without irradiation with actinic energy rays, resulting in an increase in the viscosity of the ink composition or the formation of a gel. Furthermore, if the ink composition becomes too acidic or too basic, the dispersibility of the colorant and the like may deteriorate, resulting in the formation of a gel or sediment, or an increase in the viscosity of the ink composition.

[0030] The pH of the ink composition is measured by a room temperature extraction method similar to the method for measuring the pH of pigments in accordance with "Japanese Industrial Standard JIS K5101-17-1:2004 Pigment Test Methods - Part 17: pH Value - Section 2: Room Temperature Extraction Method." That is, a 10% mass % water suspension of the ink composition (or pigment dispersion) to be tested is prepared using water in a container such as a glass container equipped with a stopper. The container is then stoppered and vigorously shaken for 1 minute. After allowing to stand for 5 minutes, the stopper is removed and the pH of the suspension is measured.

[0031] For example, using a pH measuring device conforming to "Japanese Industrial Standards JIS K5101-17-1:2004 Test Methods for Pigments - Part 17: pH Value - Section 2: Room Temperature Extraction Method," water, and a 50 ml glass bottle with a lid, 3.0 g of a sample for which the pH is to be measured (additives such as colorant, dispersant, polymerization initiator, polymerizable compound, surfactant, etc.) and 27.0 g of water at 25°C are placed in the glass bottle, the bottle is capped, and the mixture is vigorously shaken for 1 minute, and then left to stand for 5 minutes to prepare an aqueous suspension. Thereafter, the cap is removed, and the pH of the suspension is measured.

[0032] The following methods can be used to control the components and their contents so that the pH of the ink composition falls within a specific range. Specifically, among the components (polymerizable compound, colorant, dispersant, binder resin, surfactant, etc.), candidate components for inclusion in the ink composition (or pigment dispersion) are measured using a room temperature extraction method similar to the pigment pH measurement method in accordance with Japanese Industrial Standard JIS K5101-17-1:2004. The components and their contents are then determined so that the predicted pH of the ink composition (or pigment dispersion) estimated from the pH of the components falls within a predetermined range, and an ink composition is produced. If the pH of an aqueous suspension obtained from the ink composition does not fall within the desired pH range, the pH of the aqueous suspension obtained from the ink composition can be controlled to fall within the specific range by, for example, adding a pH adjuster to the composition or adjusting the content of an acidic or basic component so that the pH of the resulting aqueous suspension falls within the desired pH range.

[0033] The pH of the actinic energy ray-curable ink composition according to this embodiment may be from 6.0 to 8.0, preferably from 6.2 to 6.4. The pH of the ink composition is preferably from 7.8 to 7.6, more preferably from 7.6 to 7.2. The pH of the ink composition is preferably from 6.2 to 7.8, more preferably from 6.4 to 7.6.

[0034] The actinic ray-curable ink composition according to this embodiment may be a colored ink containing a coloring material. In this specification, the term "coloring material" includes dyes and pigments, and is used as a concept that also includes, for example, dyes or pigments contained in colored inks that form images of yellow, magenta, cyan, black, red, orange, violet, blue, green, and intermediate or pale colors thereof, white dyes or white pigments contained in white inks, and glitter coloring materials contained in metallic inks.

[0035] The color ink may be a color ink that forms an image in yellow, magenta, cyan, black, red, orange, violet, blue, green, or an intermediate or pale color thereof. The color ink may also be a white ink containing a white coloring material, or a metallic ink containing a glitter coloring material.

[0036] Furthermore, when the actinic energy ray-curable ink composition according to this embodiment contains a coloring material, the ink composition may contain a dispersant that disperses at least a part of the coloring material in the ink composition.

[0037] The actinic ray-curable ink composition according to this embodiment may also be a clear ink that does not contain a colorant. Specifically, it may be a primer ink for forming a primer layer on the surface of a substrate or the like, an overcoat ink for forming an overcoat layer on the surface of a recorded material, a matte ink composition that removes the gloss of a recorded material (substrate), an ink composition for imparting gloss or texture, or an ink containing an ultraviolet absorber, a light stabilizer, or the like for forming a weather-resistant layer.

[0038] The water content in the actinic ray-curable ink composition according to this embodiment is preferably 5.0% by mass or less, more preferably 3.0% by mass or less, and even more preferably 1.0% by mass or less, of the total amount of the ink composition. The "water" referred to here is not intentionally added, but is contained as a result of the raw materials or processes.

[0039] Hereinafter, each component contained in the actinic energy ray-curable ink composition according to this embodiment will be described.

[0040] [Polymerizable Compound] The active energy ray-curable ink composition according to this embodiment contains a polymerizable compound. The polymerizable compound is a compound (polymerizable monomer) that has one or more ethylenically unsaturated double bonds and that polymerizes to form a cured product when irradiated with active energy rays. Examples of active energy rays include electromagnetic waves such as far ultraviolet rays, ultraviolet rays, near ultraviolet rays, visible light, infrared rays, X-rays, and gamma rays, as well as electron beams, proton beams, and neutron beams. This polymerizable compound is mainly liquid and has the function of polymerizing to form a cured product, as well as the function of serving as a dispersion medium or solvent for the ink composition.

[0041] The polymerizable compound may be a monofunctional polymerizable compound having one ethylenically unsaturated double bond in the compound, or a polyfunctional polymerizable compound having two or more ethylenically unsaturated double bonds in the compound.

[0042] The polymerizable compound may also be a polymerizable compound having a relatively large molecular weight, such as an oligomer.

[0043] Examples of the monofunctional polymerizable compound include tetrahydrofurfuryl (meth)acrylate, cyclic trimethylolpropane formal (meth)acrylate, (2-methyl-2-ethyl-1,3-dioxolan-4-yl) (meth)acrylate, (2-methyl-2-isobutyl-1,3-dioxolan-4-yl) (meth)acrylate, (cyclohexanespiro-2-(1,3-dioxolan-4-yl)) (meth)acrylate, and alkylcycloalkyl acrylates such as 4-t-butylcyclohexyl (meth)acrylate and n-butylcyclohexyl (meth)acrylate. (meth)acrylate, benzyl (meth)acrylate, phenoxyethyl (meth)acrylate, isobornyl (meth)acrylate, dicyclopentanyl (meth)acrylate, dicyclopentenyl (meth)acrylate, dicyclopentenyloxyethyl (meth)acrylate, γ-butyrolactone (meth)acrylate, cresol (meth)acrylate, 2-acryloyloxyethyl phthalate, 2-acryloyloxyethyl-2-hydroxyethyl phthalate, 2-acryloyloxyethyl hexahydrophthalate, 2-acryloyloxypropyl Pyrphthalate, paracumylphenoxyethylene glycol (meth)acrylate, nonylphenoxypolyethylene glycol (meth)acrylate, 1-adamantyl (meth)acrylate, cyclohexyl (meth)acrylate, cyclooctyl (meth)acrylate, hydroxycyclohexyl (meth)acrylate, 3-3-5-trimethylcyclohexyl (meth)acrylate, 2-hydroxy-3-phenoxypropyl (meth), N-vinylpyrrole acrylate, acryloylmorpholine, N-vinylcaprolactam, imide (meth)acrylate acrylate, isooctyl (meth)acrylate, tridecyl (meth)acrylate, lauryl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, stearyl (meth)acrylate, isodecyl (meth)acrylate, caprolactone (meth)acrylate, methoxypolyethylene glycol (meth)acrylate, methoxypolypropylene glycol (meth)acrylate, 2-methoxyethyl (meth)acrylate, ethyl carbitol (meth)acrylate, 2-ethylhexyl (meth)acrylate, vinylcyclohexane,tert-butyl-4-ethynylcyclohexane, cycloheptyl (meth)acrylate, cyclopentyl (meth)acrylate, cyclobutyl (meth)acrylate, phenyl (meth)acrylate, styrene, N-vinylpyrrolidone, N-vinyloxazolidone, 2-vinyl-2-oxazoline N-vinylpyridine, N-vinylimidazole, 2-isopropenyl-2-oxazoline, methyl (meth)acrylate, butyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, butyl (meth)acrylate, te rt-Butylcyclohexyl (meth)acrylate, octyl (meth)acrylate, trifluoroethyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 3-hydroxyethyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, methyl α-(hydroxymethyl) (meth)acrylate, ethyl α-(hydroxymethyl) (meth)acrylate, n-butyl α-(hydroxymethyl) (meth)acrylate, dimethylaminoethyl (meth)acrylate, diethyl Aminoethyl (meth)acrylate, N-vinyl succinimide, N-vinyl methyl carbamate, N,N-methyl vinyl acetamide, (meth)acryloyloxyethyl trimethyl ammonium chloride, (meth)acrylonitrile, N,N-dimethyl (meth)acrylamide, N,N-diethyl (meth)acrylamide, N-ethyl-N-methyl-(meth)acrylamide, N,N-diisopropyl (meth)acrylamide, N,N-dipropyl (meth)acrylamide, N,N-dibutyl (meth)acrylamide, N-ethyl-N-butyl -acrylamide, N-isopropyl(meth)acrylamide, N-propyl(meth)acrylamide, N-butyl(meth)acrylamide, N-hexyl(meth)acrylamide, N-octyl(meth)acrylamide, N-2-ethylhexyl(meth)acrylamide, N-(2-hydroxyethyl)(meth)acrylamide, N-[3-(dimethylamino)propyl](meth)acrylamide, diacetone(meth)acrylamide, N-tert-butyl(meth)acrylamide, N-(dibutylaminomethyl)(meth)acrylamide, andThese acrylates may be modified with various modifications such as alkoxy and caprolactone. Other examples include acid group-containing monomers such as 2-((meth)acryloyloxy)ethyl phosphate, 2-(meth)acryloyloxyethyl succinate, 2-(meth)acryloyloxyethyl-2-hydroxyethyl-phthalate, and 2-(meth)acryloyloxyethylhexahydrophthalate. For example, the pH of the ink composition or pigment dispersion can be adjusted by using a basic monomer containing a basic functional group such as an amine or amide, and an acidic monomer. These polymerizable compounds may be used alone, or multiple polymerizable compounds may be used in combination. The term "(meth)acrylate" refers to both "acrylate" and "methacrylate."

[0044] Examples of the polyfunctional polymerizable compound include ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, dipropylene glycol di(meth)acrylate, tripropylene glycol di(meth)acrylate, long-chain aliphatic di(meth)acrylate, 1,4-butanediol di(meth)acrylate, 1,5-pentanediol di(meth)acrylate, 3-methyl-1,5-pentanediol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, and 1,6-hexanediol di(meth)acrylate. Ethylene oxide modified (EO modified) (2), 1,6-hexanediol di(meth)acrylate ethylene oxide modified (EO modified) (3), 1,6-hexanediol di(meth)acrylate ethylene oxide modified (EO modified) (5), 1,6-hexanediol di(meth)acrylate propylene oxide modified (PO modified) (2), 1,6-hexanediol di(meth)acrylate propylene oxide modified (PO modified) (3), 1,9-nonanediol di(meth)acrylate, neopentyl glycol di(meth)acrylate ethylene oxide-modified (EO-modified) neopentyl glycol di(meth)acrylate (2), ethylene oxide-modified (EO-modified) neopentyl glycol di(meth)acrylate (3), propylene oxide-modified (PO-modified) neopentyl glycol di(meth)acrylate (2), propylene oxide-modified (PO-modified) neopentyl glycol di(meth)acrylate (8), propylene oxide-modified (PO-modified) neopentyl glycol di(meth)acrylate (16), neopentyl glycol hydroxypivalate Di(meth)acrylate, caprolactone-modified neopentyl glycol hydroxypivalate di(meth)acrylate (2), caprolactone-modified neopentyl glycol hydroxypivalate di(meth)acrylate (4), polyalkylene glycol diacrylate, ethylene oxide-modified (EO-modified) polyalkylene glycol diacrylate (4), ethylene oxide-modified (EO-modified) polyalkylene glycol diacrylate (9), ethylene oxide-modified (EO-modified) polyalkylene glycol diacrylate (14),Ethylene oxide-modified (EO-modified) polyalkylene glycol diacrylate (23), ethylene oxide-modified (EO-modified) polyalkylene glycol diacrylate (46), propylene oxide-modified (PO-modified) polyalkylene glycol diacrylate (3), propylene oxide-modified (PO-modified) polyalkylene glycol diacrylate (7), propylene oxide-modified (PO-modified) polyalkylene glycol diacrylate (12), ethylene oxide and propylene oxide-modified polyalkylene glycol diacrylate ethylene oxide-modified (PO-modified (12) & EO-modified (6)), ethylene oxide and propylene oxide-modified polyalkylene glycol diacrylate (PO-modified (6) & EO-modified (12)), ethylene oxide and propylene oxide-modified polyalkylene glycol diacrylate (PO-modified (4) & EO-modified (12)), ethylene oxide and propylene oxide-modified polyalkylene glycol diacrylate (PO-modified (4) & EO-modified (17)), ethylene oxide and propylene oxide-modified polyalkylene glycol diacrylate Propylene oxide modified (PO modified (13) & EO modified (5)), butylene oxide modified polyalkylene glycol diacrylate (BO modified) (3.5), butylene oxide modified polyalkylene glycol diacrylate (BO modified) (9), butylene oxide modified polyalkylene glycol diacrylate (BO modified) (14), stearic acid modified pentaerythritol di(meth)acrylate, propylene glycol di(meth)acrylate, glycerol di(meth)acrylate, triethylene glycol di(meth)acrylate acrylate, 2-(2-vinyloxyethoxy)ethyl acrylate, tetraethylene glycol di(meth)acrylate, tetramethylene glycol di(meth)acrylate, butylene glycol di(meth)acrylate, propoxylated neopentyl glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, polypropylene di(meth)acrylate, triglycerol di(meth)acrylate, neopentyl glycol modified trimethylolpropane di(meth)acrylate, allylated cyclohexyl di(meth)acrylate,Methoxylated cyclohexyl di(meth)acrylate, acrylated isocyanurate, bis(acryloxyneopentyl glycol) adipate, bisphenol A di(meth)acrylate, ethylene oxide modified (EO modified) bisphenol A di(meth)acrylate (2), ethylene oxide modified (EO modified) bisphenol A di(meth)acrylate (3), ethylene oxide modified (EO modified) bisphenol A di(meth)acrylate (4), ethylene oxide modified (EO modified) bisphenol A di(meth)acrylate Modified) (10), ethylene oxide modified bisphenol A di(meth)acrylate (EO modified) (20), ethylene oxide modified bisphenol A di(meth)acrylate (EO modified) (30), propylene oxide modified bisphenol A di(meth)acrylate (PO modified) (3), ethylene oxide and propylene oxide modified bisphenol A di(meth)acrylate (PO modified (6) & EO modified (3)), tetrabromobisphenol A di(meth)acrylate, bisphenol S di(meth)acrylate, butyl Diol di(meth)acrylate, phthalic acid di(meth)acrylate, phosphoric acid di(meth)acrylate, zinc di(meth)acrylate, pentaerythritol tetra(meth)acrylate, ethylene oxide-modified (EO-modified) pentaerythritol tetra(meth)acrylate (4), ethylene oxide-modified (EO-modified) pentaerythritol tetra(meth)acrylate (35), propylene oxide-modified (PO-modified) pentaerythritol tetra(meth)acrylate (4), pentaerythritol tetra(meth)acrylate Propylene oxide-modified (PO-modified) dipentaerythritol tetra(meth)acrylate (10), ditrimethylolpropane tetra(meth)acrylate, dipentaerythritol penta(meth)acrylate, dipentaerythritol hexa(meth)acrylate, ethylene oxide-modified (EO-modified) dipentaerythritol hexa(meth)acrylate (6), ethylene oxide-modified (EO-modified) dipentaerythritol hexa(meth)acrylate (12), ethylene oxide-modified (EO-modified) dipentaerythritol hexa(meth)acrylate (18),Ethylene oxide-modified (EO-modified) dipentaerythritol hexa(meth)acrylate (24), ethylene oxide-modified (EO-modified) dipentaerythritol hexa(meth)acrylate (48), propylene oxide-modified (PO-modified) dipentaerythritol hexa(meth)acrylate (6), caprolactone-modified dipentaerythritol hexa(meth)acrylate (2), caprolactone-modified dipentaerythritol hexa(meth)acrylate (3), dipentaerythritol hexa(meth)acrylate Caprolactone-modified dipentaerythritol hexa(meth)acrylate (6), caprolactone-modified dipentaerythritol hexa(meth)acrylate (12), trimethylolpropane tri(meth)acrylate, ethylene oxide-modified trimethylolpropane tri(meth)acrylate (3), ethylene oxide-modified trimethylolpropane tri(meth)acrylate (6), ethylene oxide-modified trimethylolpropane tri(meth)acrylate (9), ethylene oxide-modified trimethylolpropane tri(meth)acrylate Oxide-modified (EO-modified) (15), ethylene oxide-modified trimethylolpropane tri(meth)acrylate (EO-modified) (20), ethylene oxide-modified trimethylolpropane tri(meth)acrylate (EO-modified) (30), propylene oxide-modified trimethylolpropane tri(meth)acrylate (PO-modified) (3), propylene oxide-modified trimethylolpropane tri(meth)acrylate (PO-modified) (6), pentaerythritol tri(meth)acrylate, glycerin tri(meth)acrylate ethylene oxide-modified (EO-modified) glycerin tri(meth)acrylate (3), ethylene oxide-modified (EO-modified) glycerin tri(meth)acrylate (6), ethylene oxide-modified (EO-modified) glycerin tri(meth)acrylate (9), ethylene oxide-modified (EO-modified) glycerin tri(meth)acrylate (20), propylene oxide-modified (PO-modified) glycerin tri(meth)acrylate (3), propylene oxide-modified (PO-modified) glycerin tri(meth)acrylate (5.5),Examples include propylene oxide-modified (PO-modified) glycerin tri(meth)acrylate (6), propylene oxide-modified (PO-modified) glycerin tri(meth)acrylate (9), dimethyloltricyclodecane diacrylate, and (meth)acrylates of these with different numbers of modifications, different types of modifications, or different structures.

[0045] The pH of an aqueous suspension of a polymerizable compound at a mass fraction of 10% is not particularly limited. It can be adjusted by using multiple polymerizable compounds in combination, or by combining them with colorants, dispersants, polymerization initiators, additives, etc. It is also possible to adjust the pH by adding an acidic or basic component after formulating the ink. However, to make it easier to adjust the pH of the ink to 6.0 or more and 8.0 or less, the pH of an aqueous suspension of a polymerizable compound at a mass fraction of 10% (hereinafter sometimes simply referred to as the pH of the polymerizable compound) is preferably 5.0 or more, more preferably 6.0 or more, and even more preferably 6.2 or more. Among these polymerizable compounds, the pH is preferably 9.0 or less, more preferably 8.0 or less, and even more preferably 7.8 or less. Among these polymerizable compounds, the pH is preferably 5.0 or more and 9.0 or less, more preferably 6.0 or more and 8.0 or less, and even more preferably 6.2 or more and 7.8 or less. The pH of the polymerizable compound can be measured using a method similar to the room temperature extraction method described above.

[0046] The actinic energy ray-curable ink composition according to this embodiment preferably contains a monofunctional polymerizable compound and a bifunctional or higher polyfunctional polymerizable compound (polyfunctional monomer) as the polymerizable compound. When the ink composition contains a monofunctional polymerizable compound and a polyfunctional polymerizable compound, there are no particular restrictions on the content of the bifunctional polymerizable compound. However, the content of the trifunctional or higher polyfunctional polymerizable compound is preferably 50% by mass or less, and more preferably 40% by mass or less, of the total amount of the ink composition. When the ink composition contains a tetrafunctional or higher polyfunctional polymerizable compound (polyfunctional monomer), the content thereof is preferably 30% by mass or less, more preferably 25% by mass or less, and even more preferably 20% by mass or less, of the total amount of the ink composition. If the content of the trifunctional or higher polyfunctional polymerizable compound (polyfunctional monomer) is too high, curing shrinkage, in which the volume shrinks upon curing, may occur. This curing shrinkage may make the ink coating film (cured film) more likely to peel from the substrate or may make the printed material more likely to crack or warp. When the content of the tetra- or higher functional polyfunctional polymerizable compound (polyfunctional monomer) is within the above range, peeling of the cured film due to cure shrinkage can be more effectively suppressed, and as a result, it becomes possible to form a cured film with higher adhesion to the substrate.

[0047] It is also preferable that the polymerizable compound contains a polymerizable oligomer. A polymerizable oligomer generally refers to a polymer in which a relatively small number of monomers are bonded, and an example of a polymerizable oligomer is a compound in which several to several tens of structural unit molecules are polymerized and which has a weight average molecular weight of 10,000 or less. By containing a predetermined amount of polymerizable oligomer, it becomes possible to adjust the curability and viscosity of the ink composition.

[0048] Examples of polymerizable oligomers include urethane acrylate, epoxy acrylate, polyester acrylate, polymeric acrylate (acrylic acrylate), and the like, and these can be obtained from Rahn AG, Sartomer, Daicel Corporation, Taisei Fine Co., Ltd., Mitsubishi Chemical Corporation, Dai-ichi Kogyo Seiyaku Co., Ltd., Kyoeisha Chemical Co., Ltd., Shin-Nakamura Chemical Co., Ltd., and the like.

[0049] When a polymerizable oligomer is contained, the content of the polymerizable oligomer is preferably 1.0% by mass or more, more preferably 1.3% by mass or more, and even more preferably 1.5% by mass or more, of the total amount of the ink composition. The content of the polymerizable oligomer is preferably 20.0% by mass or less, more preferably 17.0% by mass or less, and even more preferably 15.0% by mass or less, of the total amount of the ink composition. The content of the polymerizable oligomer is preferably 1.0% by mass or more and 20.0% by mass or less, more preferably 1.3% by mass or more and 17.0% by mass or less, and even more preferably 1.5% by mass or more and 15.0% by mass or less, of the total amount of the ink composition.

[0050] These polymerizable compounds may be solid or liquid at room temperature. Among these, it is preferable that the polymerizable compound contained in the ink composition according to this embodiment is liquid at least at room temperature. When the polymerizable compound is liquid at room temperature, this liquid polymerizable compound can serve as a solvent (dispersion medium) that dissolves or disperses each component contained in the ink composition.

[0051] The content of the polymerizable compound is not particularly limited, but is preferably 40% by mass or more, more preferably 50% by mass or more, and even more preferably 60% by mass or more, of the total amount of the ink composition. Having a polymerizable compound content of 40% by mass or more of the total amount of the ink composition can improve the curability of the cured film of the glitter layer formed upon irradiation with active energy rays. The content of the polymerizable compound is preferably 90% by mass or less of the total amount of the ink composition, more preferably 87% by mass or less, and even more preferably 85% by mass or less. Having a polymerizable compound content of 90% by mass or less of the total amount of the ink composition can relatively increase the content of colorants, etc., thereby imparting desired properties to the ink composition and the resulting printed matter. The content of the polymerizable compound is preferably 40% by mass or more and 90% by mass or less, more preferably 50% by mass or more and 87% by mass or less, and even more preferably 60% by mass or more and 85% by mass or less, of the total amount of the ink composition.

[0052] [Polymerization initiator] The active energy ray-curable ink composition according to this embodiment may contain a polymerization initiator as needed. The polymerization initiator promotes the polymerization reaction of the polymerizable compound in the ink composition when irradiated with active energy rays. Note that the ink composition according to this embodiment does not necessarily require a polymerization initiator; for example, when an electron beam is used as the active energy ray, a polymerization initiator may not be used.

[0053] Specific examples of the polymerization initiator include bisacylphosphine oxides such as bis-(2,6-dichlorobenzoyl)phenylphosphine oxide, bis-(2,6-dichlorobenzoyl)-2,5-dimethylphenylphosphine oxide, bis-(2,6-dichlorobenzoyl)-4-propylphenylphosphine oxide, bis-(2,6-dichlorobenzoyl)-1-naphthylphosphine oxide, bis-(2,6-dimethoxybenzoyl)phenylphosphine oxide, bis-(2,6-dimethoxybenzoyl)-2,4,4-trimethylpentylphosphine oxide, bis-(2,6-dimethoxybenzoyl)-2,5-dimethylphenylphosphine oxide, and bis-(2,4,6-trimethylbenzoyl)-phenylphosphine oxide; 2,6-dimethoxybenzoyldiphenylphosphine oxide; acylphosphine oxide polymerization initiators such as 2-methyl-1-[4-(methylthio)phenyl]-2-morpholinopropan-1-one, 2-benzyl-2-dimethylamino- Examples of the polymerization initiator include aminoacetophenone-based polymerization initiators such as 1-(4-morpholinophenyl)-butan-1-one and 2-(dimethylamino)-2-(4-methylbenzyl)-1-(4-morpholinophenyl)butan-1-one, and thioxanthone-based polymerization initiators such as 2-methylthioxanthone, 2-ethylthioxanthone, 2-chlorothioxanthone, 2,4-dimethylthioxanthone, 2,4-diethylthioxanthone, and 2-isopropylthioxanthone.

[0054] The pH of an aqueous suspension containing a polymerization initiator at a mass fraction of 10% is not particularly limited. It can be adjusted by using multiple polymerization initiators in combination, or by combining them with colorants, dispersants, polymerizable compounds, additives, etc. It is also possible to adjust the pH by adding an acidic or basic component after formulating the ink. However, to make it easier to adjust the pH of the ink to 6.0 to 8.0, the pH of an aqueous suspension containing a polymerization initiator at a mass fraction of 10% (hereinafter sometimes simply referred to as the pH of the polymerization initiator) is preferably 5.0 or higher, more preferably 6.0 or higher, and even more preferably 6.2 or higher. Among these polymerization initiators, the pH is preferably 9.0 or lower, more preferably 8.0 or lower, and even more preferably 7.8 or lower. Among these polymerization initiators, the pH is preferably 5.0 or higher but 9.0 or lower, more preferably 6.0 or higher but 8.0 or lower, and even more preferably 6.2 or higher but 7.8 or lower. The pH of the polymerization initiator can be measured using a method similar to the room temperature extraction method described above.

[0055] Furthermore, although diphenyl-2,4,6-trimethylbenzoylphosphine oxide, 2-methyl-1-[4-(methylthio)phenyl]-2-morpholinopropan-1-one, 2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)-butan-1-one, and 2-(dimethylamino)-2-(4-methylbenzyl)-1-(4-morpholinophenyl)butan-1-one can more effectively promote the polymerization reaction of polymerizable compounds, they are candidates for inclusion as substances of very high concern in Annex XIV of the REACH Regulation enacted by the European Union. For this reason, it is preferable to contain a polymerization initiator other than these polymerization initiators.

[0056] Examples of polymerization initiators that are not candidates for inclusion as substances of very high concern in Annex XIV of the REACH Regulation enacted by the European Union include polymerization initiators containing phosphine oxide derivatives containing two or more alkylbenzene structures in the molecule, polymerization initiators containing alkoxyphosphine oxide derivatives, and fluorenyl amino ketone polymerization initiators. Examples include Omnirad 819 (manufactured by IGM Resins B.V.), A-TPO-N (manufactured by Gyroid Materials), SpeedCure TPO-L (manufactured by Sartomer), SpeedCure XKm (manufactured by Sartomer), NPI-20400 (manufactured by TRONLY), SPEEDCURE BMS (manufactured by Sartomer), and Omnirad ITX (manufactured by IGM Resins).

[0057] As a polymerization initiator that is not a candidate for listing as a substance of very high concern, for example, one having the following structure can be preferably used.

[0058]

[0059] In formula (2), R ４ is an alkyl group having 1 to 10 carbon atoms which may be branched, and R ５ is an alkyl group having 1 to 10 carbon atoms which may be branched.

[0060] In formula (3), R ６ is an alkyl group having 1 to 10 carbon atoms which may be branched.

[0061] In formula (4), R ７ is an alkyl group having 1 to 10 carbon atoms which may be branched.

[0062] In formula (5), R ８ is an alkyl group having 1 to 10 carbon atoms which may be branched, and R ９ is an alkyl group having 1 to 10 carbon atoms which may be branched.

[0063] In formula (6), R １０is an alkyl group having 1 to 10 carbon atoms which may be branched.

[0064] In formula (7), R １１ is an alkyl group having 1 to 10 carbon atoms which may be branched, and R １２ is an alkyl group having 1 to 10 carbon atoms which may be branched.

[0065] When the actinic energy ray-curable ink composition according to this embodiment contains a polymerization initiator, the content of the polymerization initiator is not particularly limited, but is preferably 1.0% by mass or more, more preferably 1.5% by mass or more, and even more preferably 2.0% by mass or more, of the total amount of the ink composition. The content of the polymerization initiator is preferably 15.0% by mass or less, more preferably 12.0% by mass or less, and even more preferably 10.0% by mass or less, of the total amount of the ink composition. The content of the polymerization initiator is preferably 1.0% by mass or more and 15.0% by mass or less, more preferably 1.5% by mass or more and 12.0% by mass or less, and even more preferably 2.0% by mass or more and 10.0% by mass or less, of the total amount of the ink composition.

[0066] [Polymerization Inhibitor] The ink composition according to this embodiment may contain a polymerization inhibitor as needed. The polymerization inhibitor is not particularly limited, and examples of polymerization inhibitors that can be used include diphenylpicrylhydrazide, tri-p-nitrophenylmethyl, p-benzoquinone, p-tert-butylcatechol, picric acid, copper chloride, methylhydroquinone, methoquinone, tert-butylhydroquinone, phenothiazines, and nitrosamines.

[0067] The pH of an aqueous suspension containing a polymerization inhibitor at a mass fraction of 10% is not particularly limited. It can be adjusted by using multiple polymerizable compounds in combination, or by combining the polymerization inhibitor with colorants, dispersants, polymerizable compounds, additives, etc. It is also possible to adjust the pH by adding an acidic or basic component after formulating the ink. However, to make it easier to adjust the pH of the ink to 6.0 to 8.0, the pH of an aqueous suspension containing a polymerization inhibitor at a mass fraction of 10% (hereinafter sometimes simply referred to as the pH of the polymerization initiator) is preferably 5.0 or higher, more preferably 6.0 or higher, and even more preferably 6.2 or higher. Among these polymerization inhibitors, the pH is preferably 9.0 or lower, more preferably 8.0 or lower, and even more preferably 7.8 or lower. Among these polymerization inhibitors, the pH is preferably 5.0 or higher but 9.0 or lower, more preferably 6.0 or higher but 8.0 or lower, and even more preferably 6.2 or higher but 7.8 or lower. The pH of the polymerization inhibitor can be measured using a method similar to the room temperature extraction method described above.

[0068] [Colorant] The actinic energy ray-curable ink composition according to this embodiment may contain a colorant as needed. When the actinic energy ray-curable ink composition according to this embodiment contains a colorant, the colorant is not particularly limited and may be a dye-based or pigment-based colorant. However, it is preferable to use a pigment (pigment-based colorant) from the viewpoint of providing good resistance to water resistance, light resistance, and the like of the recorded matter. The pigment that can be used in the actinic energy ray-curable ink composition according to this embodiment is not particularly limited and examples thereof include organic pigments and inorganic pigments that are used in conventional ink compositions. These may be used alone or in combination of two or more types. The ink composition according to this embodiment does not necessarily contain a colorant. Furthermore, a pigment or dye may be incorporated into the resin.

[0069] When a pigment is used in the actinic energy ray-curable ink composition according to this embodiment, the dispersion stability of the pigment can be improved by using a dispersant, a dispersion aid (pigment derivative), and a surfactant, which will be described later.

[0070] Specific examples of organic pigments include insoluble azo pigments, soluble azo pigments, dye derivatives, phthalocyanine organic pigments, quinacridone organic pigments, perylene organic pigments, perinone organic pigments, azomethine organic pigments, anthraquinone organic pigments (anthrone organic pigments), xanthene organic pigments, diketopyrrolopyrrole organic pigments, dioxazine organic pigments, nickel azo pigments, isoindolinone organic pigments, pyranthrone organic pigments, thioindigo organic pigments, condensed azo organic pigments, benzimidazolone organic pigments, quinophthalone organic pigments, isoindoline organic pigments, quinacridone solid solution pigments, and organic solid solution pigments such as perylene solid solution pigments. Other pigments include lake pigments and carbon black.

[0071] Examples of organic pigments by Color Index (C.I.) number include C.I. Pigment Yellow 1, 2, 3, 12, 13, 14, 16, 17, 20, 24, 73, 74, 75, 83, 93, 95, 97, 98, 109, 110, 114, 117, 120, 125, 128, 129, 130, 137, 138, 139, 147, 148, 150, 151, 153, 154, 155, 166, 168, 180, 185, 213, 214, C.I. C.I. Pigment Red 5, 7, 9, 12, 48, 49, 52, 53, 57:1, 97, 112, 122, 123, 146, 149, 150, 168, 177, 180, 184, 192, 202, 206, 208, 209, 215, 216, 217, 220, 223, 224, 226, 227, 228, 238, 240, 254, 255, 269, 291, C.I. Pigment Orange 16, 36, 43, 51, 55, 59, 61, 64, 71, 73, C.I. Pigment Violet 19, 23, 29, 30, 37, 40, 50, C.I. Examples of suitable pigments include C.I. Pigment Blue 15, 15:1, 15:3, 15:4, 15:6, 16, 22, 60, and 64, C.I. Pigment Green 7, 36, 58, 59, 62, and 63, C.I. Pigment Brown 23, 25, and 26, and C.I. Pigment Black 7.

[0072] Specific examples of dyes that can be used in the actinic ray-curable ink composition according to this embodiment include azo dyes, benzoquinone dyes, naphthoquinone dyes, anthraquinone dyes, cyanine dyes, squarylium dyes, croconium dyes, merocyanine dyes, stilbene dyes, diarylmethane dyes, triarylmethane dyes, fluoran dyes, spiropyran dyes, phthalocyanine dyes, indigo dyes such as indigoid, fulgide dyes, nickel complex dyes, and azulene dyes.

[0073] Specific examples of inorganic pigments that can be used in the actinic ray-curable ink composition according to this embodiment include titanium oxide, barium sulfate, calcium carbonate, zinc oxide, barium carbonate, silica, talc, clay, synthetic mica, alumina, zinc oxide, lead sulfate, yellow lead, zinc yellow, red iron oxide (red iron (III) oxide), ultramarine, Prussian blue, chromium oxide green, cobalt green, umber, titanium black, aluminum, titanium, indium, nickel, chromium, gold, silver, copper, synthetic iron black, iron oxide, mica, fish scale foil, bismuth oxychloride, inorganic solid solution pigments, etc. In addition to the above pigments, examples of materials that have optical properties or functionality other than those for decorative purposes include conductive pigments, insulating pigments, pigments that absorb light of specific wavelengths, and pigments that emit or reflect light of specific wavelengths.

[0074] The pH of a colorant (pigment) can be measured by the room temperature extraction method in accordance with Japanese Industrial Standard JIS K5101-17-1:2004. Colorants may be modified or surface-treated with acidic or basic compounds to improve their wettability or dispersibility in a dispersion medium (see, for example, JP 2001-011341, JP 2002-121411, JP 2005-523985, and Japanese Patent No. 6892947). When a colorant (pigment) is surface-treated in this way, its pH changes, and even if the color index name is the same, the pH varies depending on the manufacturer and product specifications, and the indicated pH value also varies.

[0075] The pH of an aqueous suspension of a colorant (pigment) at a mass fraction of 10% is not particularly limited. It can be adjusted by using multiple colorants (pigments) in combination, or by combining them with dispersants, polymerizable compounds, polymerization initiators, additives, etc. It is also possible to adjust the pH by adding an acidic or basic component after formulating the ink. However, to make it easier to adjust the pH of the ink to 6.0 or higher and 8.0 or lower, the pH of an aqueous suspension of a colorant (pigment) at a mass fraction of 10% (hereinafter simply referred to as the pH of the colorant) is preferably 3.0 or higher, more preferably 4.0 or higher, and even more preferably 5.0 or higher. Among these colorants, the pH is preferably 9.0 or lower, more preferably 8.0 or lower, and even more preferably 7.8 or lower. Among these colorants, the pH is preferably 3.0 or higher and 9.0 or lower, more preferably 4.0 or higher and 8.0 or lower, and even more preferably 5.0 or higher and 7.8 or lower. The pH of the colorant can be measured using a method similar to the room temperature extraction method described above.

[0076] In the actinic energy ray-curable ink composition according to this embodiment, the average particle diameter of the pigment that can be contained is not particularly limited as long as it can produce the desired color. While this varies depending on the type of pigment used, in order to obtain good pigment dispersibility and dispersion stability and sufficient coloring power, the average particle diameter is preferably 5 nm or more, more preferably 20 nm or more, and even more preferably 30 nm or more. Having an average particle diameter equal to or greater than the above lower limit can improve the lightfastness of the ink composition. From the viewpoints of dispersion stability in the ink composition and inkjet ejection properties, the average particle diameter is preferably 1000 nm or less, more preferably 800 nm or less, even more preferably 500 nm or less, and even more preferably 350 nm. The average particle diameter of the pigment is preferably 5 nm or more and 1000 nm or less, more preferably 20 nm or more and 800 nm or less, and even more preferably 30 nm or more and 500 nm or less.

[0077] In this embodiment, the volume-average particle diameter of the pigment is the volume-based cumulative 50% particle diameter (D50) measured under conditions of 25°C using a particle size distribution measuring device (such as a particle size analyzer NANOTRACWAVE manufactured by Microtrackbell Corporation, an FPIA-3000S manufactured by Sysmex Corporation, or an FPAR-1000 manufactured by Otsuka Electronics Co., Ltd.). In this specification, the term "volume-based cumulative 50% particle diameter (D50)" refers to the particle diameter at which the cumulative volume calculated from the smallest diameter side is 50%. The "volume-based cumulative 50% particle diameter (D50)" may also be referred to as the "volume-average particle diameter," "average particle diameter," or "median diameter."

[0078] In the actinic ray-curable ink composition according to this embodiment, the pigment content is not particularly limited as long as the desired image can be formed, and can be adjusted as appropriate. Specifically, although this varies depending on the type of pigment, it is preferably in the range of 0.05% by mass or more, more preferably 0.08% by mass or more, and even more preferably 0.1% by mass or more, relative to the total amount of the ink composition. It is preferably in the range of 20% by mass or less, more preferably 15% by mass or less, and even more preferably 10% by mass or less, relative to the total amount of the ink composition. The pigment content is preferably in the range of 0.05% by mass or more to 20% by mass or less, more preferably 0.08% by mass or more to 15% by mass or less, and even more preferably 0.1% by mass or more to 10% by mass or less, relative to the total amount of the ink composition. By having the pigment content in the range of 0.05% by mass or more or 20% by mass or less, an excellent balance between pigment dispersion stability and coloring power can be achieved.

[0079] Furthermore, the actinic energy ray-curable ink composition according to this embodiment is not particularly limited in the color to be recorded (printed), and may be selected and combined according to the purpose. Colors include inks of various colors such as yellow, magenta, cyan, black, red, orange, violet, blue, and green, as well as light magenta, light cyan, light black, white, clear, and glitter inks. In this case, colorants of the same color may be selected in an ink set containing the actinic energy ray-curable ink composition according to this embodiment.

[0080] [Dispersant] A dispersant may be used in the actinic energy ray-curable ink composition according to this embodiment, if necessary. Any dispersant used in ink compositions can be used as the dispersant. It is preferable to use a polymer dispersant as the dispersant. Such dispersants have a main chain made of a polyester, polyacrylic, polyurethane, polyamine, polycaprolactone, or the like, and have polar groups such as amino groups, carboxyl groups, sulfone groups, or hydroxyl groups as side chains. Examples of polyacrylic dispersants include Disperbyk-2000, 2001, 2008, 2009, 2010, 2020, 2020N, ​​2022, 2025, 2050, 2070, 2095, 2150, 2151, 2155, 2163, 2164, BYKJET-9130, 9131, 9132, 9133, 9151, 9152 (manufactured by BYK), EfkaPX4310, PX4320, PX4330, PA4401, 4402, PA4403, 4570, 7411, 7477, PX4700, PX4701, PX4703 (manufactured by BASF), and TREPLUS D-1200, D-1410, D-1420, MD-1000 (manufactured by Otsuka Chemical Co., Ltd.), FLOWRENE DOPA-15BHFS, 17HF, 22, G-700, 900, NC-500, GW-1500 (manufactured by Kyoeisha Chemical Co., Ltd.), and the like can be used. Examples of polycaprolactone-based dispersants include Ajisper PB821, PB822, and PB881 (manufactured by Ajinomoto Fine-Techno Co., Ltd.), Hinoact KF-1000, T-6000, T-7000, T-8000, T-8000E, and T-9050 (manufactured by Kawaken Fine Chemicals Co., Ltd.), Solsperse 20000, 24000, 32000, 32500, 32550, 32600, 33000, 33500, 34000, 35200, 36000, 37500, 39000, 71000, 76400, 76500, 86000, 88000, J180, and J200 (manufactured by Lubrizol Corporation), and TEGO Dispers 652, 655, 685, 688, 690 (manufactured by EVONIK Co., Ltd.) and the like are used.Preferred dispersants include PB881, BYKJET-9130, 9131, 9132, 9133, 9151, 9152, Efka PX4310, PX4320, PX4330, PX4700, PX4701, PX4703, Solsperse 20000, 24000, 32000, 33000, 33500, 34000, 35200, 39000, 71000, 76500, 86000, 88000, J180, J200, and TEGO Dispers 655, 685, 688, and 690. These can be used alone or in combination.

[0081] The pH of an aqueous suspension containing a dispersant at a mass fraction of 10% is not particularly limited. It can be adjusted by using multiple dispersants in combination, or by combining them with colorants, polymerizable compounds, polymerization initiators, additives, etc. It is also possible to adjust the pH by adding an acidic or basic component after formulating the ink. However, to make it easier to adjust the pH of the ink to 6.0 or higher and 8.0 or lower, the pH of an aqueous suspension containing a dispersant at a mass fraction of 10% (hereinafter sometimes simply referred to as the pH of the dispersant) is preferably 4.0 or higher, more preferably 5.0 or higher, and even more preferably 6.0 or higher. Among these dispersants, the pH is preferably 12.0 or lower, more preferably 11.0 or lower, and even more preferably 10.0 or lower. Among these dispersants, the pH is preferably 4.0 or higher and 12.0 or lower, more preferably 5.0 or higher and 11.0 or lower, and even more preferably 6.0 or higher and 10.0 or lower. The pH of the dispersant can be measured using a method similar to the room temperature extraction method described above.

[0082] The content of the dispersant is not particularly limited, but it is preferable to adjust it according to the content of the coloring material contained in the ink composition.

[0083] The lower limit of the content of the dispersant is not particularly limited. When the colorant is an organic colorant, the upper limit of the content of the dispersant is preferably 80 parts by mass or less, more preferably 75 parts by mass or less, even more preferably 50 parts by mass or less, and even more preferably 35 parts by mass or less, relative to 100 parts by mass of the colorant.

[0084] When the colorant is an inorganic colorant, the upper limit of the content of the dispersant is preferably 50 parts by mass or less, more preferably 30 parts by mass or less, and even more preferably 20 parts by mass or less, relative to 100 parts by mass of the colorant.

[0085] In the actinic energy ray-curable ink composition according to this embodiment, it is preferable to adjust the content of the dispersant so that the content of the colorant is greater than the content of the dispersant (i.e., so that the content of the dispersant is less than the content of the colorant). This makes it possible to effectively disperse the colorant in the ink composition, thereby improving the storage stability and ejection stability of the ink composition.

[0086] [Dispersion Aid] The actinic energy ray-curable ink composition according to this embodiment may contain a dispersion aid as needed. The dispersion aid adsorbs to the surface of the colorant (pigment), and the functional group enhances the affinity with the polymerizable compound and dispersant in the ink composition, thereby improving dispersion stability. As the dispersion aid, known pigment derivatives having a functional group such as an acidic group, a basic group, or a neutral group in the organic pigment residue can be used.

[0087] The pH of an aqueous suspension containing a dispersion aid at a mass fraction of 10% is not particularly limited. It can be adjusted by combining it with a colorant, dispersant, polymerizable compound, polymerization initiator, additive, etc. It is also possible to adjust the pH by adding an acidic or basic component after ink preparation. However, to make it easier to adjust the pH of the ink to 6.0 or higher and 8.0 or lower, the pH of an aqueous suspension containing a dispersion aid at a mass fraction of 10% (hereinafter referred to simply as the pH of the dispersion aid) is preferably 4.0 or higher, more preferably 5.0 or higher, and even more preferably 5.5 or higher. Among these dispersion aids, the pH is preferably 11.0 or lower, more preferably 10.0 or lower, and even more preferably 9.5 or lower. Among these dispersion aids, the pH is preferably 4.0 or higher and 8.0 or lower, more preferably 5.0 or higher and 7.7 or lower, and even more preferably 5.5 or higher and 9.5 or lower. The pH of the dispersion aid can be measured using a method similar to the room temperature extraction method described above.

[0088] [Surfactant] The ink composition according to this embodiment may contain a surfactant as needed. The surfactant is not particularly limited, but specific examples include dimethylpolysiloxane-containing surfactants manufactured by BYK Corporation such as "BYK-306," "BYK-307," "BYK-331," "BYK-333," "BYK-354," "BYK-361N," "BYK-371," "BYK-377," "BYK-378," "BYK-399," "BYK-3455," "BYK-UV3500," "BYK-UV3505," "BYK-UV3510," "BYK-UV3535," "BYK-UV3570," "BYK-UV3575," and "BYK-UV3576"; and EVONIK Corporation's "TEGO Flow425," "TEGO Glide100," "TEGO Glide110," and "TEGO Glide130", "TEGO Glide432", "TEGO Glide435", "TEGO Glide440", "TEGO Glide450", "TEGO GlideZG400", "TEGO Twin4000", "TEGO "Twin4200", "TEGO Wet270", "TEGO Rad2010", "TEGO Rad2010", "TEGO Rad2100", "TEGO Rad2200N", "TEGO Rad2250", "TEGO Rad2300", "TEGO Rad2500", "TEGO Rad2700; "Polyflow KL-401," "Polyflow KL-402," "Polyflow KL-403," and "Polyflow KL-404" manufactured by Kyoeisha Chemical Co., Ltd.; acrylic polymer-based products include "Polyflow No. 75," "Polyflow No. 77," "Polyflow No. 90," "Polyflow No. 95," and "Polyflow No. 99C" manufactured by Kyoeisha Chemical Co., Ltd.; and "TEGO Wet500" manufactured by EVONIK.

[0089] The pH of an aqueous suspension containing a surfactant at a mass fraction of 10% is not particularly limited. It can be adjusted by combining it with a colorant, dispersant, polymerizable compound, polymerization initiator, additives, etc. It is also possible to adjust the pH by adding an acidic or basic component after formulating the ink. However, in order to maintain the pigment dispersion state and improve the stability of the ink composition, the pH of an aqueous suspension containing a surfactant at a mass fraction of 10% (hereinafter simply referred to as the pH of the surfactant) is preferably 4.0 or higher, more preferably 4.5 or higher, and even more preferably 5.0 or higher. Among these surfactants, the pH is preferably 12.0 or lower, more preferably 11.5 or lower, and even more preferably 11.0 or lower. Among these surfactants, the pH is preferably 4.0 or higher and 12.0 or lower, more preferably 4.5 or higher and 11.5 or lower, and even more preferably 5.0 or higher and 11.0 or lower. The pH of the surfactant can be measured using a method similar to the room temperature extraction method described above.

[0090] The content of the surfactant is preferably 0.1% by mass or more, more preferably 0.2% by mass or more, and even more preferably 0.3% by mass or more, based on the total amount of the ink composition. The content of the surfactant is preferably 5.0% by mass or less, more preferably 4.5% by mass or less, and even more preferably 4.0% by mass or less, based on the total amount of the ink composition. By setting the content to 0.1% by mass or more or 5.0% by mass or less, the ink composition has favorable wettability with respect to thermoplastic resin substrates and the like, and the active energy ray-curable ink composition can be wetted and spread without causing repelling when recording (forming an image) on the substrate, resulting in a particularly preferred ink composition. The content of the surfactant is preferably 0.1% by mass or more and 5.0% by mass or less, more preferably 0.2% by mass or more and 4.5% by mass or less, and even more preferably 0.3% by mass or more and 4.0% by mass or less, based on the total amount of the ink composition.

[0091] [Binder Resin] The active energy ray-curable ink composition according to this embodiment may contain a binder resin, if necessary. The term "binder resin" as used herein refers to a non-polymerizable resin that is different from monomers, oligomers, and additives. The binder resin is not particularly limited, but examples include acrylic resins, polystyrene resins, polyester resins, polyethylene terephthalate resins, vinyl chloride resins, vinyl acetate resins, vinyl chloride-vinyl acetate copolymer resins, polyethylene resins, polyurethane resins, rosin-modified resins, phenolic resins, xylene resins, terpene resins, polyamide resins, vinyltoluene-α-methylstyrene copolymers, ethylene-vinyl acetate copolymers, cellulose resins, silicone resins, acrylamide resins, epoxy resins, diallyl phthalate resins, allyl resins, and copolymer resins or mixtures thereof. Among these, binder resins containing at least one of vinyl chloride-vinyl acetate copolymer resins, polyethylene terephthalate resins, diallyl phthalate resins, acrylic resins, allyl resins, and cellulose resins are preferred. The molecular weight of the binder resin is preferably 10,000 or more, and more preferably 15,000 or more. The molecular weight of the binder resin is preferably 500,000 or less, and more preferably 300,000 or less. When the molecular weight is within this range, the storage stability, ejection properties, and coating film properties of the ink composition can be improved.

[0092] The pH of an aqueous suspension containing a binder resin at a mass fraction of 10% is not particularly limited. It can be adjusted by combining it with a colorant, dispersant, polymerizable compound, polymerization initiator, additives, etc. It is also possible to adjust the pH by adding an acidic or basic component after formulating the ink. However, to maintain the pigment dispersion state and improve the stability of the ink composition, the pH of an aqueous suspension containing a binder resin at a mass fraction of 10% (hereinafter simply referred to as the pH of the binder resin) is preferably 5.0 or higher, more preferably 5.5 or higher, and even more preferably 6.0 or higher. Among these binder resins, the pH is preferably 9.0 or lower, more preferably 8.5 or lower, and even more preferably 8.0 or lower. Among these binder resins, the pH is preferably 5.0 or higher but 9.0 or lower, more preferably 5.5 or higher but 8.5 or lower, and even more preferably 6.0 or higher but 8.0 or lower. The pH of the binder resin can be measured using a method similar to the room temperature extraction method described above.

[0093] When the actinic energy ray-curable ink composition according to this embodiment contains a binder resin, the content of the binder resin is not particularly limited, but is preferably 0.05% by mass or more, more preferably 0.08% by mass or more, even more preferably 0.1% by mass or more, and even more preferably 0.3% by mass or more, of the total amount of the ink composition. The content of the binder resin is preferably 20.0% by mass or less, more preferably 15.0% by mass or less, even more preferably 10.0% by mass or less, and even more preferably 5.0% by mass or less, of the total amount of the ink composition. The content of the binder resin is preferably 0.05% by mass or more and 20.0% by mass or less, more preferably 0.08% by mass or more and 15.0% by mass or less, and even more preferably 0.1% by mass or more and 10.0% by mass or less, of the total amount of the ink composition.

[0094] [Other Additives] The ink composition according to this embodiment may contain various other additives, such as an acidic compound, a basic compound, an organic solvent, a plasticizer, a light stabilizer, a wax, an ultraviolet absorber, an antioxidant, an alignment agent, an antibacterial agent, and an antiviral agent.

[0095]

[0033] The ink composition according to this embodiment may contain a volatile organic solvent, but if the polymerizable compound contained therein is liquid at room temperature, the polymerizable compound serves as a solvent (dispersion medium) that dissolves or disperses the contained components, and therefore the ink composition need not contain a volatile organic solvent. When the polymerizable compound contained therein is liquid at room temperature, the content of the volatile organic solvent is preferably 20.0% by mass or less, more preferably 10.0% by mass or less, even more preferably 5.0% by mass or less, and even more preferably 1.0% by mass or less, of the total amount of the ink composition. When the polymerizable compound contained therein is liquid at room temperature and the content of the volatile organic solvent is 20.0% by mass or less of the total amount of the ink composition, deposition of the contained components and an increase in viscosity due to evaporation of the ink composition in the inkjet nozzle can be suppressed, thereby further improving the inkjet ejection properties.

[0096] The ink composition according to this embodiment may also contain a pH adjuster to adjust the pH of a 10% by mass aqueous suspension to 6.0 or more and 8.0 or less. Specifically, the ink composition may contain, as an acidic compound, a compound containing an acidic functional group such as carboxylic acid, sulfonic acid, nitric acid, or phosphoric acid, and as a basic compound, a compound containing a basic functional group such as an amino group or an amide group. The ink composition may also contain various acids and their salts, salts such as hydroxides, ammonia, amino alcohols, amines, etc.

[0097] (Viscosity and Surface Tension of Ink Composition) From the viewpoint of inkjet ejection performance and ejection stability, the viscosity of the ink composition according to this embodiment at the ejection temperature (for example, 40°C) is preferably 30 mPa·s or less, more preferably 25 mPa·s or less, and even more preferably 22 mPa·s or less. Furthermore, the viscosity of the ink composition according to this embodiment at the ejection temperature (for example, 40°C) is preferably 3 mPa·s or more, more preferably 5 mPa·s or more, and even more preferably 8 mPa·s or more, although it is preferable to adjust the viscosity appropriately in accordance with the inkjet head to be used. The viscosity can be measured using a vibration viscometer, a rheometer, a falling ball viscometer, or the like.

[0098] Furthermore, from the viewpoints of inkjet ejection performance, ejection stability, and leveling ability on a substrate, the surface tension of the ink composition according to this embodiment is preferably 20 mN / m or more, more preferably 23 mN / m or more, and even more preferably 25 mN / m or more at 25° C. Furthermore, the surface tension of the ink composition according to this embodiment is preferably 40 mN / m or less, more preferably 37 mN / m or less, and even more preferably 35 mN / m or less.

[0099] The method for producing the actinic energy ray-curable ink composition of one embodiment of the present invention is not particularly limited, and a conventionally known method can be used. For example, a polymerizable compound, a colorant, and optionally a dispersant are mixed and dispersed using a disperser, and then a polymerization initiator, and optionally a polymerization inhibitor, a leveling agent, and the like are added and stirred uniformly to obtain a mixture, which is then filtered through a filter to obtain an ink composition.

[0100] 2. Pigment Dispersion The pigment dispersion according to this embodiment is a pigment dispersion used in the actinic energy ray-curable ink composition ejected by the inkjet method described above. Specifically, the pigment dispersion according to this embodiment is a pigment dispersion used in the production of an ink composition, and can produce an ink composition by adding other components (for example, a polymerization initiator) that are contained in the ink composition, such as a polymerization initiator.

[0101] The pigment dispersion according to the present embodiment contains a pigment, a polymerizable compound, and a pigment dispersant, and is characterized in that the pH of the aqueous suspension thereof, as measured by the following test method, is 6.0 or more and 8.0 or less.

[0102] Test method: A water suspension of the pigment dispersion is prepared by mixing the pigment dispersion with water so that the content of the pigment dispersion is 10% by mass, and the pH of the water suspension is measured.

[0103] By preparing a pigment dispersion in which the components and their contents are controlled so that the pH of the aqueous suspension obtained from the pigment dispersion falls within a specific range, it is possible to obtain a pigment dispersion with excellent storage stability. For convenience, in this specification, the pH of the aqueous suspension having a mass fraction of 10% obtained from the pigment dispersion may be simply referred to as the "pH of the pigment dispersion."

[0104] The pH of the pigment dispersion may be from 6.0 to 8.0, preferably from 6.3 to 6.5, more preferably from 6.5 to 6.7, more preferably from 7.5 to 7.7, and more preferably from 6.3 to 7.7, more preferably from 6.5 to 7.5.

[0105] The pH of the pigment dispersion is measured by the same room temperature extraction method as the method for measuring the pH of pigments in accordance with Japanese Industrial Standard JIS K5101-17-1: 2004. Specifically, it can be measured by the same method as the pH of the ink composition described above.

[0106] The method for controlling the components and their contents so that the pH of the pigment dispersion liquid falls within a specific range can be the same as the method for controlling the components and their contents so that the pH of the ink composition falls within a specific range described above.

[0107] Furthermore, by producing an actinic ray-curable ink composition by adding other components contained in the ink composition, such as a polymerization initiator, using a pigment dispersion liquid whose pH is controlled in the range of 6.0 to 8.0, it becomes easy to produce an actinic ray-curable ink composition whose pH is controlled in the range of 6.0 to 8.0.

[0108] The pigment, polymerizable compound, and pigment dispersant contained in the pigment dispersion liquid according to this embodiment may be the same as the pigment, polymerizable compound, and pigment dispersant contained in the actinic energy ray-curable ink composition ejected by the inkjet method described above.

[0109] 3. Ink Set The actinic energy ray-curable ink composition may be a colored ink, or a clear ink, primer ink, or overcoat ink that does not contain a colorant. The ink set according to this embodiment may be an ink set that combines these ink compositions.

[0110] The ink set according to this embodiment may be any ink set as long as at least one ink composition contained in the ink set has a pH of 6.0 or more and 8.0 or less.

[0111] Alternatively, the ink set may be a combination of colored ink compositions containing a coloring material, and may be, for example, an ink set that combines a plurality of ink compositions selected from colored ink compositions of yellow, magenta, cyan, black, red, orange, violet, blue, green, and intermediate or pale colors thereof; a white ink composition containing a white coloring material; or a metallic ink containing a glittering coloring material.

[0112] 4. Recording Method The recording method according to this embodiment is a recording method in which the ink composition having a pH of 6.0 or more and 8.0 or less is applied onto a substrate by an inkjet method.

[0113] The recording method according to this embodiment may also include a step of ink-jetting the ink composition onto the surface of a surface-treated resin substrate.

[0114] The method may further include an irradiation step of irradiating the ink composition applied to the surface of the substrate with active energy rays. This irradiation forms a cured product of the ink composition on the surface of the substrate. Examples of active energy rays include electromagnetic waves such as far ultraviolet rays, ultraviolet rays, near ultraviolet rays, visible light, infrared rays, X-rays, and gamma rays, as well as active energy rays such as electron beams, proton beams, and neutron beams. Among these, active energy rays having a peak wavelength of 365 nm or more and 395 nm or less are preferred.

[0115] The light source for irradiating the active energy rays is not particularly limited, and examples thereof include a high-pressure mercury lamp, a metal halide lamp, a low-pressure mercury lamp, an ultra-high-pressure mercury lamp, an ultraviolet laser, sunlight, an LED lamp, etc. From the viewpoints of energy saving and high flexibility in designing the printing apparatus, it is more preferable to use an LED lamp as the light source.

[0116] To obtain a surface-treated resin substrate, the method may include a pretreatment step of previously subjecting the surface of the substrate to a surface treatment to obtain a surface-treated substrate.

[0117] Examples of the surface treatment method include corona treatment, flame treatment, plasma treatment, ultraviolet irradiation treatment, silane coupling treatment, etc. Two or more of these surface treatments may be combined.

[0118] The substrate to be pretreated may be either a non-absorbent substrate or an absorbent substrate, as described below.

[0119] The ink jet ejection method for the ink composition of the present invention may be any of a piezoelectric method, an electrostatic method, etc. The ink jet method may be a serial head method or a line head method, and is not particularly limited.

[0120] Alternatively, the coating may be applied to the substrate by a method other than inkjet, such as a spray or a dispenser.

[0121] 5. Method for producing a printed matter The above-described recording method can also be defined as a method for producing a printed matter in which the ink composition is applied to a substrate by an inkjet method. In addition, a printed matter can also be produced by applying the ink composition to a substrate by a method other than an inkjet method, for example, by a spray or a dispenser.

[0122] 6. Printed Material The printed material according to the present embodiment is a printed material in which the ink composition according to the above-described embodiment is printed on the surface of a substrate. Specifically, the printed material obtained using the ink composition according to the above-described embodiment includes a substrate (recording medium) and a cured film of the ink composition laminated on the surface of this substrate (recording medium). This cured film contains a cured product of the polymerizable compound contained in the ink composition according to the above-described embodiment.

[0123] [Substrate (Recording Medium)] The substrate (recording medium) included in the recording material according to this embodiment is not particularly limited, and may be a non-absorbent substrate such as a resin substrate, metal plate, or glass, an absorbent substrate such as paper or fabric, or a substrate with a surface coating such as a substrate having a receiving layer, and various substrates can be used.

[0124] Examples of non-absorbent substrates include resin substrates such as polyester resins, polyethylene terephthalate resins, polyethylene naphthalate resins, polypropylene synthetic paper, polyolefin resins (polypropylene resins, polyethylene resins, etc.), acrylic resins, polystyrene resins, polycarbonate resins, ABS resins, vinyl chloride resins, polyimide resins, metals, metal foil-coated paper, glass, synthetic rubber, natural rubber, etc. Among these, resin substrates containing at least one selected from the group consisting of polypropylene resins, polycarbonate resins, polystyrene resins, polyethylene resins, ABS resins, vinyl chloride resins, polyethylene terephthalate resins, and acrylic resins are preferred.

[0125] In particular, an ink composition containing a polymerizable compound having a pH of 6.0 or more and 8.0 or less can form a cured film that has high adhesion even to polyvinyl chloride resin or acrylic resin substrates, and therefore it is particularly preferable that the substrate (recording medium) is a polyethylene terephthalate resin, polyvinyl chloride resin, or acrylic resin substrate.

[0126] Examples of absorbent substrates include woody paper, medium-quality paper, fine paper, synthetic paper, cotton, synthetic fiber fabrics, silk, hemp, woven fabrics, nonwoven fabrics, and leather.

[0127] Examples of surface-coated substrates include coated paper, art paper, cast paper, lightweight coated paper, and lightly coated paper.

[0128] [Cured Film of Ink Composition] The cured film of the ink composition is formed by polymerization of a polymerizable compound contained in the ink composition. For example, when a colorant is contained in the ink composition, it becomes a decorative layer or an underlayer for forming a desired image. In this specification, the shape of the "cured film" is not limited to, for example, a flat plate or a layer, and may have irregularities, may have holes formed in part, or may have a cured film formed on part of the surface, for example. For convenience, the cured film of the ink composition that is absorbed into an absorbent substrate and essentially becomes part of the substrate is also referred to as the cured film of the ink composition.

[0129] When the ink composition is used as an overcoat ink, it becomes an overcoat layer formed on the surface of a recorded material. In this case, the ink composition that forms the recording layer of the recorded material may be the ink composition of the present invention, or may be an ink composition different from the ink composition of the present invention.

[0130] The thickness of the cured product of the ink composition (for example, a recording layer or an overcoat layer) is not particularly limited, but is preferably 1 μm or more, more preferably 3 μm or more, and even more preferably 5 μm or more. The thickness of the cured product of the ink composition (for example, a recording layer or an overcoat layer) is preferably 1000 μm or less, more preferably 500 μm or less, and even more preferably 100 μm or less. The thickness of the cured product of the ink composition is preferably 1 μm or more and 1000 μm or less, more preferably 3 μm or more and 500 μm or less, and even more preferably 5 μm or more and 100 μm or less. The cured product of the ink composition can be imparted with desired functions. The thickness of the cured product is the average value of thicknesses measured at multiple arbitrary locations on the surface of the cured product.

[0131] 7. Inkjet Recording Apparatus The inkjet recording apparatus according to this embodiment is an inkjet recording apparatus equipped with a storage mechanism filled with the ink composition having a pH of 6.0 or more and 8.0 or less.

[0132] The inkjet recording apparatus according to the present embodiment may be an inkjet recording apparatus of a multi-pass type (also referred to as a serial head type) in which an inkjet head reciprocates to eject the ink composition, or may be an inkjet recording apparatus of a single-pass type (also referred to as a line head type) in which an inkjet head does not move and ejects the ink composition onto a recording medium (substrate).

[0133] The storage mechanism installed in the inkjet recording apparatus according to this embodiment is not particularly limited, and examples thereof include containers such as ink bottles, pouches, bag-in-boxes, and drums. These containers may also be housed in cartridges or the like. The material of the storage container is not particularly limited, and may be a conventionally known resin, or a material that contains a metal material in part (for example, an aluminum pouch with an aluminum vapor deposition layer).

[0134] The ejection method of each ejection section may be any of a piezoelectric method, a thermal method, an electrostatic method, and the like.

[0135] The inkjet recording apparatus according to this embodiment may include a light source that irradiates actinic energy rays. The light source that irradiates actinic energy rays is not particularly limited, and examples thereof include a high-pressure mercury lamp, a metal halide lamp, a low-pressure mercury lamp, an ultra-high-pressure mercury lamp, an ultraviolet laser, sunlight, and an LED lamp. From the viewpoints of energy saving and a high degree of freedom in designing the printing apparatus, it is more preferable to use an LED lamp as the light source.

[0136] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these descriptions in any way.

[0137] 1-1. Pigment dispersions were produced in experimental examples and comparative examples. Specifically, the pigment dispersions of the examples and comparative examples were prepared so that the colorant (pigment millbase), dispersant, polymerizable compound, additive, and polymerization inhibitor were mixed in the proportions shown in the table below. The units in the table are % by mass. The pH of a 10% by mass aqueous suspension of each component was measured in advance using a room temperature extraction method similar to the method for measuring the pH of pigments in accordance with Japanese Industrial Standard JIS K5101-17-1:2004.

[0138] 1-2. Evaluation of Pigment Dispersion Liquid (Storage Stability) The storage stability of the pigment dispersion liquids of the Examples and Comparative Examples was evaluated. Specifically, the pigment dispersion liquids of the Examples and Comparative Examples were sealed in light-shielding glass bottles and stored at a temperature of 60°C for 7 days, and the pigment dispersion liquid after storage was visually inspected for the occurrence of precipitates or aggregates. Furthermore, the viscosity of the pigment dispersion liquid before and after storage was measured, and the rate of viscosity change was evaluated. [Evaluation Criteria] A: No precipitates or aggregates were generated, and the rate of viscosity change was less than 10%. B: No precipitates or aggregates were generated, and the rate of viscosity change was 10% or more but less than 20%. C: The generation of precipitates or aggregates was confirmed, or the rate of viscosity change was 20% or more. A and B are within the usable range.

[0139]

[0140]

[0141] In Tables 1 and 2, "P-1" refers to CARBON BLACK MA-8 manufactured by Mitsubishi Chemical Corporation, which is a carbon black (pigment). The pH of a 10% by mass aqueous suspension was 3.2.

[0142] In Tables 1 and 2, "P-2" refers to HP RED 2574 manufactured by Shanghai Honor Industrial Co. Ltd., which is C.I. Pigment Red 122 (pigment). The pH of a 10% by mass aqueous suspension was 6.8.

[0143] In Tables 1 and 2, "P-3" refers to FASTOGEN (registered trademark) SUPER MAGENTA JM04 manufactured by DIC, which is C.I. Pigment Red 122 / 19 (pigment). The pH of a 10% by mass aqueous suspension was 7.6.

[0144] In Tables 1 and 2, "P-4" refers to LIONOL (registered trademark) BLUE FG-7400-G manufactured by Toyocolor Co., Ltd., which is C.I. Pigment Blue 15:4 (pigment). The pH of a 10% by mass aqueous suspension was 7.4.

[0145] In Tables 1 and 2, "P-5" refers to FASTOGEN (registered trademark) BLUE 5452-SK manufactured by DIC, which is C.I. Pigment Blue 15:4 (pigment). The pH of a 10% by mass aqueous suspension was 4.6.

[0146] In Tables 1 and 2, "D-1" refers to BYKJET (registered trademark) 9151 manufactured by BYK. The pH of the aqueous suspension at a mass fraction of 10% was 7.0.

[0147] In Tables 1 and 2, "D-2" refers to TEGO (registered trademark) Disprse 685 manufactured by EVONIK. The pH of the aqueous suspension with a mass fraction of 10% was 8.0.

[0148] In Tables 1 and 2, "D-3" refers to Solsperse (registered trademark) 20000 manufactured by Lubrizol. The pH of the 10% mass fraction aqueous suspension was 11.2.

[0149] In Tables 1 and 2, "PHEA" refers to phenoxyethyl acrylate (polymerizable compound). The pH of a 10% by mass aqueous suspension was 7.0.

[0150] In Tables 1 and 2, "HXDA" refers to 1,6-hexanediol diacrylate (polymerizable compound). The pH of a 10% by mass aqueous suspension was 5.0.

[0151] In Tables 1 and 2, "TPGDA" refers to tripropylene glycol diacrylate (polymerizable compound). The pH of a 10% by mass aqueous suspension was 7.0.

[0152] In Tables 1 and 2, "IBXA" stands for isobornyl acrylate (polymerizable compound). The pH of a 10% by mass aqueous suspension was 7.0.

[0153] In Tables 1 and 2, "MPDA" refers to 3-methyl-1,5-pentanediol diacrylate (polymerizable compound). The pH of a 10% by mass aqueous suspension was 6.0.

[0154] In Tables 1 and 2, "DPGDA" refers to dipropylene glycol diacrylate (a polymerizable compound). The pH of a 10% by mass aqueous suspension was 5.0.

[0155] In Tables 1 and 2, "A-3" refers to phenylphosphonic acid (an acidic pH adjuster). The pH of a 10% by mass aqueous suspension was 1.6.

[0156] In Tables 1 and 2, "A-2" denotes triethanolamine (a basic pH adjuster). The pH of a 10% mass fraction aqueous suspension was 10.6.

[0157] In Tables 1 and 2, "S-1" denotes phenothiazine (polymerization inhibitor). The pH of the aqueous suspension with a mass fraction of 10% was 6.2.

[0158] 2-1. Ink compositions (clear ink compositions) of experimental examples and comparative examples were manufactured. Specifically, pigment dispersions of the examples and comparative examples were prepared so that the polymerizable compound, polymerization initiator, and additives were mixed in the proportions shown in the table below. The units in the table are % by mass. The ink compositions of the examples and comparative examples were prepared by adding the above ingredients. The pH of a 10% by mass aqueous suspension of each component was measured in advance using a room temperature extraction method similar to the method for measuring the pH of pigments in accordance with Japanese Industrial Standard JIS K5101-17-1:2004.

[0159] 2-2. Evaluation of Ink Compositions (Storage Stability) The storage stability of the ink compositions of the Examples and Comparative Examples was evaluated. Specifically, the ink compositions of the Examples and Comparative Examples were sealed in light-shielding glass bottles and stored at a temperature of 60°C for 7 days, and the ink compositions after storage were visually inspected for the occurrence of precipitates or aggregates. Furthermore, the viscosity of the ink compositions before and after storage was measured, and the rate of viscosity change was evaluated. [Evaluation Criteria] A: No precipitates or aggregates were generated, and the rate of viscosity change was less than 10%. B: No precipitates or aggregates were generated, and the rate of viscosity change was 10% or more but less than 20%. C: The occurrence of precipitates or aggregates was confirmed, or the rate of viscosity change was 20% or more. A and B are within the usable range.

[0160] (Ejection Performance) The ejection performance (inkjet ejection performance) of the ink compositions of the Examples and Comparative Examples was evaluated. Specifically, the ink compositions of the Examples and Comparative Examples were inkjet ejected from an inkjet head for 10 minutes using a JetXpert droplet observation device manufactured by ImageXpert, and the incidence of non-ejection, bending, and scattering of the inkjet head was evaluated. [Evaluation Criteria] A: The incidence of ejection defects is less than 3%. B: The incidence of ejection defects is 3% or more but less than 10%. C: The incidence of ejection defects is 10% or more. A and B are within the usable range.

[0161] (Curability) The curability of the ink compositions of the examples and comparative examples was evaluated. Specifically, the ink compositions of the examples and comparative examples were ejected onto the surface of a PET film (Cosmoshine A4300, manufactured by Toyobo Co., Ltd.) using an inkjet recording device, a "Material Printer DMP-2850" manufactured by Fujifilm Corporation, and the ink compositions were then irradiated with an LED lamp having a wavelength of 385 nm at a peak irradiance of 250 mW / cm. ２ , cumulative light intensity 650 mJ / cm ２ The ink composition was irradiated with active energy rays of 1000 kJ / cm² to form a cured product of the ink composition on the surface of the PET film, and the curability of the cured product was evaluated based on the following evaluation criteria. [Evaluation criteria] A: No ink adhered to the surface when rubbed with a cotton swab. B: There was some stickiness, but no ink adhered to the surface when rubbed with a cotton swab. C: The ink adhered to the surface when rubbed with a cotton swab. A and B are within the usable range.

[0162]

[0163] In Table 3, "VEEA" stands for 2-(vinyloxyethoxy)ethyl acrylate. The pH of a 10% by mass aqueous suspension was 5.0.

[0164] In Table 3, "IBXA" stands for isobornyl acrylate (polymerizable compound). The pH of a 10% by mass aqueous suspension was 7.0.

[0165] In Table 3, "DEAA" stands for diethylacrylamide. The pH of the aqueous suspension at a mass fraction of 10% was 6.0.

[0166] In Table 3, "HXDA" stands for 1,6-hexanediol diacrylate (polymerizable compound). The pH of a 10% by mass aqueous suspension was 5.0.

[0167] In Table 3, "TPGDA" stands for tripropylene glycol diacrylate (polymerizable compound). The pH of a 10% by mass aqueous suspension was 7.0.

[0168] In Table 3, "DPHA" stands for dipentaerythritol hexaacrylate (polymerizable compound). The pH of a 10% by mass aqueous suspension was 7.0.

[0169] In Table 3, "PETA" refers to pentaerythritol triacrylate (polymerizable compound). The pH of a 10% by mass aqueous suspension was 7.0.

[0170] In Table 3, "MPDA" stands for 3-methyl-1,5-pentanediol diacrylate (polymerizable compound). The pH of a 10% by mass aqueous suspension was 6.0.

[0171] In Table 3, "DPGDA" stands for dipropylene glycol diacrylate (polymerizable compound). The pH of a 10% by mass aqueous suspension was 5.0.

[0172] In Table 3, "O-1" refers to an oligomer: aliphatic urethane acrylate CN996 manufactured by Sartomer Corp. The pH of a 10% by mass aqueous suspension was 5.0.

[0173] In Table 3, "TPO-L" refers to SpeedCure (registered trademark) TPO-L (polymerization initiator represented by formula (3)) manufactured by Sartomer Corp. The pH of an aqueous suspension containing 10% by mass was 3.7.

[0174] In Table 3, "819" refers to Omnirad (registered trademark) 819 (polymerization initiator represented by formula (1)) manufactured by IGM Resins B.V. The pH of an aqueous suspension with a mass fraction of 10% was 7.3.

[0175] In Table 3, "DETX" refers to SpeedCure (registered trademark) DETX (a polymerization initiator represented by formula (7)) manufactured by Sartomer Corp. The pH of an aqueous suspension containing DETX at a mass fraction of 10% was 8.0.

[0176] In Table 3, "TMO" refers to PhiCure (registered trademark) TMO (polymerization initiator represented by formula (2)) manufactured by Gyroid Materials, Inc. The pH of an aqueous suspension with a mass fraction of 10% was 7.8.

[0177] In Table 3, "A-1" is a silicon-based nonionic additive, a polyether-modified polysiloxane having a weight-average molecular weight of 1000. The pH of an aqueous suspension with a mass fraction of 10% was 7.0.

[0178] In Table 3, "A-2" is triethanolamine (a basic pH adjuster). The pH of a 10% mass fraction aqueous suspension was 10.6.

[0179] In Table 3, "A-3" is phenylphosphonic acid (an acidic pH adjuster). The pH of a 10% by mass aqueous suspension was 1.6.

[0180] 3-1. Production of Ink Compositions (Colored Ink Compositions) Ink compositions (colored ink compositions) of experimental examples and comparative examples were produced. Specifically, 20 parts by mass of the pigment dispersion shown in Table 1 above, a polymerizable compound, a polymerization initiator, and additives were mixed in the proportions shown in the table below to prepare the ink compositions of the examples and comparative examples. Note that the pH of a 10% by mass aqueous suspension of each component was measured in advance using a room temperature extraction method similar to the method for measuring the pH of pigments in accordance with Japanese Industrial Standard JIS K5101-17-1:2004.

[0181] 3-2. Evaluation of Ink Compositions (Storage Stability) The storage stability of the ink compositions of the Examples and Comparative Examples was evaluated. Specifically, the ink compositions of the Examples and Comparative Examples were sealed in light-shielding glass bottles and stored at a temperature of 60°C for 7 days, and the ink compositions after storage were visually inspected for the occurrence of precipitates or aggregates. Furthermore, the viscosity of the ink compositions before and after storage was measured, and the rate of viscosity change was evaluated. [Evaluation Criteria] A: No precipitates or aggregates were generated, and the rate of viscosity change was less than 5%. B: No precipitates or aggregates were generated, and the rate of viscosity change was 5% or more but less than 10%. C: The occurrence of precipitates or aggregates was confirmed, or the rate of viscosity change was 10% or more. A and B are within the usable range.

[0182] (Ejection Performance) The ejection performance (inkjet ejection performance) of the ink compositions of the Examples and Comparative Examples was evaluated. Specifically, the ink compositions of the Examples and Comparative Examples were inkjet ejected from an inkjet head for 10 minutes using a droplet observation device JetXpert manufactured by ImageXpert, and the incidence of ejection defects such as non-ejection, bending, and scattering from the inkjet head was evaluated. [Evaluation Criteria] A: The incidence of ejection defects is less than 3%. B: The incidence of ejection defects is 3% or more but less than 10%. C: The incidence of ejection defects is 10% or more. A and B are within the usable range.

[0183] (Curability) The curability of the ink compositions of the examples and comparative examples was evaluated. Specifically, the ink compositions of the examples and comparative examples were ejected onto the surface of a PET film (Cosmoshine A4300, manufactured by Toyobo Co., Ltd.) using an inkjet recording device, a "Material Printer DMP-2850" manufactured by Fujifilm Corporation, and the ink compositions were then irradiated with an LED lamp having a wavelength of 385 nm at a peak irradiance of 250 mW / cm. ２ , cumulative light intensity 650 mJ / cm ２ The ink composition was irradiated with active energy rays of 1000 kJ / cm² to form a cured product of the ink composition on the surface of the PET film, and the curability of the cured product was evaluated based on the following evaluation criteria. [Evaluation criteria] A: No ink adhered to the surface when rubbed with a cotton swab. B: There was some stickiness, but no ink adhered to the surface when rubbed with a cotton swab. C: The ink adhered to the surface when rubbed with a cotton swab. A and B are within the usable range.

[0184]

[0185]

[0186] In Tables 4 and 5, "VEEA" stands for 2-(vinyloxyethoxy)ethyl acrylate. The pH of a 10% by mass aqueous suspension was 5.0.

[0187] In Tables 4 and 5, "IBXA" stands for isobornyl acrylate (polymerizable compound). The pH of a 10% by mass aqueous suspension was 7.0.

[0188] In Tables 4 and 5, "DEAA" stands for diethylacrylamide. The pH of the 10% by mass aqueous suspension was 6.0.

[0189] In Tables 4 and 5, "HXDA" refers to 1,6-hexanediol diacrylate (polymerizable compound). The pH of a 10% by mass aqueous suspension was 5.0.

[0190] In Tables 4 and 5, "4HBA" stands for 4-hydroxybutyl acrylate. The pH of a 10% by mass aqueous suspension was 5.0.

[0191] In Tables 4 and 5, "TPGDA" refers to tripropylene glycol diacrylate (polymerizable compound). The pH of a 10% by mass aqueous suspension was 7.0.

[0192] In Tables 4 and 5, "DPHA" refers to dipentaerythritol hexaacrylate (a polymerizable compound). The pH of a 10% by mass aqueous suspension was 7.0.

[0193] In Tables 4 and 5, "PETA" refers to pentaerythritol triacrylate (polymerizable compound). The pH of a 10% by mass aqueous suspension was 7.0.

[0194] In Tables 4 and 5, "MPDA" refers to 3-methyl-1,5-pentanediol diacrylate (polymerizable compound). The pH of a 10% by mass aqueous suspension was 6.0.

[0195] In Tables 4 and 5, "DPGDA" refers to dipropylene glycol diacrylate (polymerizable compound). The pH of a 10% by mass aqueous suspension was 5.0.

[0196] In Tables 4 and 5, "O-1" refers to an oligomer: aliphatic urethane acrylate CN996 manufactured by Sartomer Corp. The pH of a 10% by mass aqueous suspension was 5.0.

[0197] In Tables 4 and 5, "TPO-L" refers to SpeedCure (registered trademark) TPO-L (polymerization initiator represented by formula (3)) manufactured by Sartomer Corp. The pH of an aqueous suspension containing 10% by mass was 3.7.

[0198] In Tables 4 and 5, "819" refers to Omnirad (registered trademark) 819 (polymerization initiator represented by formula (1)) manufactured by IGM Resins B.V. The pH of an aqueous suspension with a mass fraction of 10% was 7.3.

[0199] In Tables 4 and 5, "DETX" refers to SpeedCure (registered trademark) DETX (a polymerization initiator represented by formula (7)) manufactured by Sartomer Corp. The pH of a 10% mass fraction aqueous suspension was 8.0.

[0200] In Tables 4 and 5, "TMO" refers to PhiCure (registered trademark) TMO (polymerization initiator represented by formula (2)) manufactured by Gyroid Materials, Inc. The pH of the aqueous suspension with a mass fraction of 10% was 7.8.

[0201] In Tables 4 and 5, "NPI" refers to NPI-20400 (registered trademark) manufactured by TRONLY (a polymerization initiator represented by formula (5)). The pH of a 10% by mass aqueous suspension was 7.2.

[0202] In Tables 4 and 5, "BMS" refers to Lunacure (registered trademark) BMS (a polymerization initiator represented by formula (6)) manufactured by DKSH GmbH. The pH of the aqueous suspension containing the compound at a mass fraction of 10% was 8.0.

[0203] In Tables 4 and 5, "A-1" is a silicon-based nonionic additive, a polyether-modified polysiloxane having a weight-average molecular weight of 1000. The pH of an aqueous suspension with a mass fraction of 10% was 7.0.

[0204] In Tables 4 and 5, "A-2" denotes triethanolamine (a basic pH adjuster). The pH of a 10% mass fraction aqueous suspension was 10.6.

[0205] In Tables 4 and 5, "A-3" denotes phenylphosphonic acid (an acidic pH adjuster). The pH of a 10% by mass aqueous suspension was 1.6.

[0206] As can be seen from the above results, a pigment dispersion liquid or ink composition in which the components and their contents are controlled so that the pH falls within a specific range has excellent storage stability and ejection stability.

Claims

1. An actinic ray-curable ink composition to be ejected by an inkjet method, the ink composition containing a polymerizable compound, the pH of an aqueous suspension of which is 6.0 or more and 8.0 or less as measured by the following test method: Test method: The ink composition is mixed with water so that the content of the ink composition is 10% by mass, to prepare an aqueous suspension of the ink composition, and the pH of the aqueous suspension is measured.

2. The ink composition according to claim 1, which contains a colorant.

3. The ink composition according to claim 1, which does not contain a colorant.

4. A pigment dispersion liquid used in an actinic ray-curable ink composition ejected by an inkjet method, the pigment dispersion liquid containing a pigment, a polymerizable compound, and a pigment dispersant, the pH of the aqueous suspension of which is measured by the following test method being 6.0 or more and 8.0 or less: Test method: The pigment dispersion liquid is mixed with water so that the content of the pigment dispersion liquid is 10% by mass to prepare an aqueous suspension of the pigment dispersion liquid, and the pH of the aqueous suspension is measured.

5. An actinic ray curable ink composition to be ejected by an inkjet method, comprising the pigment dispersion liquid according to claim 4 and a polymerization initiator.

6. The ink composition according to any one of claims 1 to 3 and 5, wherein the water content is 5.0 mass % or less of the total amount of the ink composition.

7. An ink set comprising the ink composition according to any one of claims 1 to 3, 5 and 6.

8. A printed matter, in which the ink composition according to any one of claims 1 to 3, 5 and 6 is printed on the surface of a substrate.

9. An ink jet recording device equipped with a storage mechanism filled with the ink composition according to any one of claims 1 to 3, 5 and 6.

10. A recording method comprising ejecting the ink composition according to any one of claims 1 to 3, 5 and 6 by an ink jet method.

11. A method for producing a printed matter, comprising ejecting the ink composition according to any one of claims 1 to 3, 5 and 6 by an inkjet method.

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